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Clean energy vehicle Technology & Transportation
PREPARED By: SAILESH ADHIKARI 063/33/BIE THAPATHALI CAMPUS
Regenerative braking SYSTEMRegenerative braking is used on hybrid gas/electric automobiles to recoup some of the energylost during stopping. This energy is saved in a storage battery and used later to power the motorwhenever the car is in electric mode.
Understanding how regenerative braking works may require a brief look at the system itreplaces. Conventional braking systems use friction to counteract the forward momentum of amoving car. As the brake pads rub against the wheels (or a disc connected to the axle),excessive heat energy is also created. This heat energy dissipates into the air, wasting up to30% of the car's generated power. Over time, this cycle of friction and wasted heat energyreduces the car's fuel efficiency. More energy from the engine is required to replace the energylost by braking.Hybrid gas/electric automobiles now use a completely different method of braking at slowerspeeds. While hybrid cars still use conventional brake pads at highway speeds, electric motorshelp the car brake during stop-and-go driving. As the driver applies the brakes through aconventional pedal, the electric motors reverse direction. The torque created by this reversalcounteracts the forward momentum and eventually stops the car.
But regenerative braking does more than simply stop the car. Electric motors and electricgenerators (such as a car's alternator) are essentially two sides of the same technology. Bothuse magnetic fields and coiled wires, but in different configurations. Regenerative brakingsystems take advantage of this duality. Whenever the electric motor of a hybrid car begins toreverse direction, it becomes an electric generator or dynamo. This generated electricity is fedinto a chemical storage battery and used later to power the car at city speeds.Regenerative braking takes energy normally wasted during braking and turns it into usableenergy. It is not, however, a perpetual motion machine. Energy is still lost through friction withthe road surface and other drains on the system. The energy collected during braking does notrestore all the energy lost during driving. It does improve energy efficiency and assist the mainalternator.
Regenerative braking in Hybrid electric vehicleHybrid vehicles make use of an internal combustion engine and an electric motor.How is a hybrid vehicle different from a fully electric vehicle? Well, hybrid electric vehicles useboth an electric motor and an internal combustion engine to provide a best-of-both-worldsdriving experience. They combine the driving range of an internal combustion engine with thefuel efficiency and emissions-free characteristics of an electric motor. If a hybrid is to havemaximum fuel efficiency and produce as few carbon emissions as possible, it's important thatthe battery remain charged as long as possible. If a hybrid vehicle battery were to lose itscharge, the internal combustion engine would be entirely responsible for powering the vehicle.
At that point, the vehicle is no longer acting as a hybrid but rather just another car burning fossilfuels.
Automotive engineers have come up with a number of tricks to wring the maximum efficiencyout of hybrids, like aerodynamic streamlining of the bodies and use of lightweight materials, butarguably, one the most important is regenerative braking. In a hybrid setup, however, thesetypes of brakes can provide power only to the electric motor part of the drivetrain via thevehicle's battery. The internal combustionengine gains no advantage from these kinds of brakes.In part, these efficiencies are necessary due to the extreme difficulty in finding a place torecharge a hybrid. This makes longer trips difficult without relying on the hybrid's internalcombustion engine, which actually cancels out some of the advantage of owning a hybrid.Up next, we'll learn about a new take on this idea of regenerative braking.
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Clean energy vehicle Technology & Transportation
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FUEL INJECTION SYSTEMFuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the
primary fuel delivery system used in gasoline automotive engines, having almost completely replaced
carburetors in the late 1980s.A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle. Most
fuel injection systems are for gasoline or diesel applications. With the advent of electronic fuel injection
(EFI), the diesel and gasoline hardware has become similar. EFI's programmable firmware has permitted
common hardware to be used with different fuels. Carburetors were the predominant method used to
meter fuel on gasoline engines before the widespread use of fuel injection. A variety of injection
systems have existed since the earliest usage of the internal combustion engine.
The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by
forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on low pressure
created by intake air rushing through it to add the fuel to the airstream.
The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from a pump or a
pressure container farther back in the fuel supply.
The functional objectives for fuel injection systems can vary. All share the central task of supplying
fuel to the combustion process, but it is a design decision how a particular system will be
optimized. There are several competing objectives such as:
y power output
y fuel efficiency
y emissions performance
y ability to accommodate alternative fuels
y reliability
y driveability and smooth operationy initial cost
y maintenance cost
y diagnostic capability
y range of environmental operation
Certain combinations of these goals are conflicting, and it is impractical for a single engine control
system to fully optimize all criteria simultaneously. In practice, automotive engineers strive to best
satisfy a customer's needs competitively. The modern digital electronic fuel injection system is far
more capable at optimizing these competing objectives consistently than a carburetor.
Carburetors have the potential to atomize fuel better (see Pogue and Allen Caggiano patents).
Engine operation
Operational benefits to the driver of a fuel-injected car include smoother and more dependable engine
response during quick throttle transitions, easier and more dependable engine starting, better operation
at extremely high or low ambient temperatures, increased maintenance intervals, and increased fuel
efficiency.On a more basic level, fuel injection does away with the choke which on carburetor-equipped
vehicles must be operated when starting the engine from cold and then adjusted as the engine warms
up.
An engine's air/fuel ratio must be precisely controlled under all operating conditions to achieve the
desired engine performance, emissions, driveability, and fuel economy. Modern electronic fuel-injection
systems meter fuel very accurately, and use closed loop fuel-injection quantity-control based on a
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variety of feedback signals from an oxygen sensor, a mass airflow (MAF) or manifold absolute pressure
(MAP) sensor, a throttle position (TPS), and at least one sensor on the crankshaft and/or camshaft(s) to
monitor the engine's rotational position. Fuel injection systems can react rapidly to changing inputs such
as sudden throttle movements, and control the amount of fuel injected to match the engine's dynamic
needs across a wide range of operating conditions such as engine load, ambient air temperature, engine
temperature, fuel octane level, and atmospheric pressure.
A multipoint fuel injection system generally delivers a more accurate and equal mass of fuel to each
cylinder than can a carburetor, thus improving the cylinder-to-cylinder distribution. Exhaust emissions
are cleaner because the more precise and accurate fuel metering reduces the concentration of toxic
combustion byproducts leaving the engine, and because exhaust cleanup devices such as the catalytic
converter can be optimized to operate more efficiently since the exhaust is of consistent and predictable
composition.
Fuel injection generally increases engine fuel efficiency. With the improved cylinder-to-cylinder fuel
distribution, less fuel is needed for the same power output. When cylinder-to-cylinder distribution is less
than ideal, as is always the case to some degree with a carburetor or throttle body fuel injection, some
cylinders receive excess fuel as a side effect of ensuring that all cylinders receive sufficientfuel. Poweroutput is asymmetrical with respect to air/fuel ratio; burning extra fuel in the rich cylinders does not
reduce power nearly as quickly as burning too little fuel in the lean cylinders. However, rich-runningcylinders are undesirable from the standpoint of exhaust emissions, fuel efficiency, engine wear, and
engine oil contamination. Deviations from perfect air/fuel distribution, however subtle, affect the
emissions, by not letting the combustion events be at the chemically ideal (stoichiometric) air/fuel ratio.
Grosser distribution problems eventually begin to reduce efficiency, and the grossest distribution issues
finally affect power. Increasingly poorer air/fuel distribution affects emissions, efficiency, and power, in
that order. By optimizing the homogeneity of cylinder-to-cylinder mixture distribution, all the cylinders
approach their maximum power potential and the engine's overall power output improves.
A fuel-injected engine often produces more power than an equivalent carbureted engine. Fuel injection
alone does not necessarily increase an engine's maximum potential output. Increased airflow is needed
to burn more fuel, which in turn releases more energy and produces more power. The combustion
process converts the fuel's chemical energy into heat energy, whether the fuel is supplied by fuelinjectors or a carburetor. However, airflow is often improved with fuel injection, the components of
which allow more design freedom to improve the air's path into the engine. In contrast, a carburetor's
mounting options are limited because it is larger, it must be carefully oriented with respect to gravity,
and it must be equidistant from each of the engine's cylinders to the maximum practicable degree.
These design constraints generally compromise airflow into the engine. Furthermore, a carburetor relies
on a restrictive venturi to create a local air pressure difference, which forces the fuel into the air stream.
The flow loss caused by the venturi, however, is small compared to other flow losses in the induction
system. In a well-designed carburetor induction system, the venturi is not a significant airflow
restriction.
Fuel is saved while the car is coasting because the car's movement is helping to keep the engine
rotating, so less fuel is used for this purpose. Control units on modern cars react to this and reduce or
stop fuel flow to the engine reducing wear on the brakes.
History and development
Herbert Akroyd Stuart developed the first system laid out on modern lines (with a highly-accurate 'jerk
pump' to meter out fuel oil at high pressure to an injector. This system was used on the hot bulb engine
and was adapted and improved by Robert Bosch for use on diesel engines - Rudolf Diesel's original
system employed a cumbersome[citation needed] 'air-blast' system using highly compressedair.[clarification needed]
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The first use of direct gasoline injection was on the Hesselman engine invented by Swedish engineer
Jonas Hesselman in 1925.[1][2] Hesselman engines use the ultra lean burn principle; fuel is injected
toward the end of the compression stroke, then ignited with a spark plug. They are often started on
gasoline and then switched to diesel or kerosene.[citation needed] Fuel injection was in widespreadcommercial use in diesel engines by the mid-1920s. Because of its greater immunity to wildly changing
g-forces on the engine, the concept was adapted for use in gasoline-powered aircraft during World War
II, and direct injection was employed in some notable designs like the Daimler-Benz DB 603, the BMW
801, the Shvetsov ASh-82FN (M-82FN) and later versions of the Wright R-3350 used in the B-29
Superfortress.
Alfa Romeo tested one of the very first electric injection systems (Caproni-Fuscaldo) in Alfa Romeo
6C2500 with "Ala spessa" body in 1940 Mille Miglia. The engine had six electrically operated injectors
and were fed by a semi-high pressure circulating fuel pump system.[3]
One of the first commercial gasoline injection systems was a mechanical system developed by Bosch and
introduced in 1955 on the Mercedes-Benz 300SL. This was basically a high pressure diesel direct-
injection pump with an intake throttle valve set up. (Diesels only change amount of fuel injected to vary
output; there is no throttle.) This system used a normal gasoline fuel pump, to provide fuel to a
mechanically driven injection pump, which had separate plungers per injector to deliver a very high
injection pressure directly into the combustion chamber. When combined with Desmo valves in racingthe 300 SL was capable of over 100 horsepower per liter, still better than what's commonly possible
today without a turbo.
Another mechanical system, also by Bosch, (CIS) but injecting the fuel into the port above the intake
valve was later used by Porsche from 1969 until 1973 for the 911 production range in the USA and until
1975 on the Carrera RS 2.7 and RS 3.0 street models in Europe. Porsche continued using it on its racing
cars into the late seventies and early eighties. Porsche racing variants such as the 911 RSR 2.7 & 3.0,
904/6, 906, 907, 908, 910, 917 (in its regular normally aspirated or 5.5 Liter/1500 HP Turbocharged
form), and 935 all used Bosch or Kugelfischer built variants of injection. The Kugelfischer system was
also used by the BMW 2000/2002 Tii and some versions of the Peugeot 404/504 and Lancia Flavia. Lucas
also offered a mechanical system which was used by some Maserati, Aston Martin and Triumph models
between ca. 1963 and 1973. The first factory electronic fuel injection, a true multi-point system, withdual 2-bbl. throttles, was optional on 1958 Chrysler products, both Hemi and wedge engines. It wasjointly engineered by Chrysler and Bendix.
A system similar to the Bosch inline mechanical pump was built by SPICA for Alfa Romeo, used on the
Alfa Romeo Montreal and on US market 1750 and 2000 models from 1969 until 1981. This was
specifically designed to meet the US emission requirements, and allowed Alfa to meet these
requirements with no loss in performance and a reduction in fuel consumption.
Chevrolet introduced a mechanical fuel injection option, made by General Motors' Rochester Products
division, for its 283 V8 engine in 1957. This system directed the inducted engine air across a "spoon
shaped" plunger that moved in proportion to the air volume. The plunger connected to the fuel
metering system which mechanically dispensed fuel to the cylinders via distribution tubes. This system
was not a "pulse" or intermittent injection, but rather a constant flow system, metering fuel to all
cylinders simultaneously from a central "spider" of injection lines. The fuel meter adjusted the amount
of flow according to engine speed and load, and included a fuel reservoir, which was similar to a
carburetor's float chamber. With its own high-pressure fuel pump driven by a cable from the distributor
to the fuel meter, the system supplied the necessary pressure for injection. This was "port" injection,
however, in which the injectors are located in the intake manifold, very near the intake valve. (Direct
fuel injection is a fairly recent innovation for automobile engines. As recent as 1954 in aforementioned
Mercedes-Benz 300SL or the Gutbrod in 1953) The highest performance version of the fuel injected
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engine was rated at 283 bhp (211 kW) from 283 cu in (4.6 L). This made it among the early production
engines in history to exceed 1 hp/in (45.5 kW/L), after Chrysler's Hemi engine and a number of others.
During the 1960s, other mechanical injection systems such as Hilborn were occasionally used on
modified American V8 engines in various racing applications such as drag racing, oval racing, and road
racing.[citation needed] These racing-derived systems were not suitable for everyday street use, havingno provisions for low speed metering or even starting (fuel had to be squirted into the injector tubes
while cranking the engine in order to start it). However they were a favorite in the aforementioned
competition trials in which essentially wide-open throttle operation was prevalent.
The first commercial electronic fuel injection (EFI) system was Electrojector, developed by the Bendix
Corporation and was to be offered by American Motors (AMC) in 1957.[4] A special muscle car model,
the Rambler Rebel, showcased AMC's new 327 cu in (5.4 L) engine. The Electrojector was an option and
rated at 288 bhp (214.8 kW). The RebelOwners Manual described the design and operation of the new
system.[5] Initial press information about the Bendix system in December 1956 was followed in March
1957 by a price bulletin that pegged the option at US$395, but due to supplier difficulties, fuel-injected
Rebels would only be available after June 15.[6] This was to have been the first production EFI engine,
but Electrojector's teething problems meant only pre-production cars were so equipped and none were
made available to the public.[7] The EFI system in the Rambler was a far more-advanced setup than the
mechanical types then appearing on the market and the engines ran fine in warm weather, but sufferedhard starting in cooler temperatures.[6]
Chrysler offered Electrojector on the 1958 Chrysler 300D, Dodge D500, Plymouth Fury and DeSoto
Adventurer, arguably the first series-production cars equipped with an EFI system. The early electronic
components were not equal to the rigors of underhood service, however, and were too slow to keep up
with the demands of "on the fly" engine control. Most of the 35 vehicles originally so equipped were
field-retrofitted with 4-barrel carburetors. The Electrojector patents were subsequently sold to Bosch.
Bosch developed an electronic fuel injection system, called D-Jetronic (D for Druck, German for"pressure"), which was first used on the VW 1600TL in 1967. This was a speed/density system, using
engine speed and intake manifold air density to calculate "air mass" flow rate and thus fuel
requirements. The system used all analog, discrete electronics, and an electro-mechanical pressure
sensor. The sensor was susceptible to vibration and dirt.[citation needed] This system was adopted byVW, Mercedes-Benz, Porsche, Citron, Saab, and Volvo. Lucas licensed the system for production withJaguar.
Bosch superseded the D-Jetronic system with the K-Jetronic and L-Jetronic systems for 1974, though
some cars (such as the Volvo 164) continued using D-Jetronic for the following several years. The
Cadillac Seville was introduced in 1977 with an EFI system made by Bendix and modelled very closely on
Bosch's D-Jetronic. L-Jetronic first appeared on the 1974 Porsche 914, and uses a mechanical airflow
meter (L for Luft, German for "air") that produces a signal that is proportional to "air volume". Thisapproach required additional sensors to measure the barometer and temperature, to ultimately
calculate "air mass". L-Jetronic was widely adopted on European cars of that period, and a few Japanese
models a short time later.
In 1982, Bosch introduced a sensor that directly measures the air mass flow into the engine, on their L-
Jetronic system. Bosch called this LH-Jetronic (L for Luftmasse and H for Hitzdraht, German for "airmass" and "hot wire", respectively). The mass air sensor utilizes a heated platinum wire placed in the
incoming air flow. The rate of the wire's cooling is proportional to the air mass flowing across the wire.
Since the hot wire sensor directly measures air mass, the need for additional temperature and pressure
sensors is eliminated. The LH-Jetronic system was also the first fully digital EFI system, which is now the
standard approach.[citation needed] The advent of the digital microprocessor permitted the integrationof all powertrain sub-systems into a single control module.
Supersession of carburetors
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The ultimate combustion goal is to match each molecule of fuel with a corresponding number of
molecules of oxygen so that neither has any molecules remaining after combustion in the engine and
catalytic converter. Such a balanced condition is known as stoichiometry. Extensive carburetor
modifications and complexities were needed to approach stoichiometric engine operation in order to
comply with increasingly-strict exhaust emission regulations of the 1970s and 1980s. This increase in
complexity gradually eroded and then reversed the simplicity, cost, and packaging advantages
carburetors had traditionally offered over fuel injection systems.
There are three primary types of toxic emissions from an internal combustion engine: Carbon Monoxide
(CO), unburnt hydrocarbons (HC), and oxides of nitrogen (NOx). CO and HC result from incomplete
combustion of fuel due to insufficient oxygen in the combustion chamber. NOx, in contrast, results from
excessive oxygen in the combustion chamber. The opposite causes of these pollutants makes it difficult
to control all three simultaneously.Once the permissible emission levels dropped below a certain point,
catalytic treatment of these three main pollutants became necessary. This required a particularly large
increase in fuel metering accuracy and precision, for simultaneous catalysis of all three pollutants
requires that the fuel/air mixture be held within a very narrow range of stoichiometry. The open loop
fuel injection systems had already improved cylinder-to-cylinder fuel distribution and engine operation
over a wide temperature range, but did not offer sufficient fuel/air mixture control to enable effective
exhaust catalysis. Closed loop fuel injection systems improved the air/fuel mixture control with anexhaust gas oxygen sensor. The O2 sensor is mounted in the exhaust system upstream of the catalytic
converter, and enables the engine management computer to determine and adjust the air/fuel ratio
precisely and quickly.
Fuel injection was phased in through the latter '70s and '80s at an accelerating rate, with the US, French
and German markets leading and the UK and Commonwealth markets lagging somewhat, and since the
early 1990s, almost all gasoline passenger cars sold in first world markets like the United States, Canada,
Europe, Japan, and Australia have come equipped with electronic fuel injection (EFI). Many motorcycles
still utilize carbureted engines, though all current high-performance designs have switched to EFI.
Fuel injection systems have evolved significantly since the mid 1980s. Current systems provide an
accurate, reliable and cost-effective method of metering fuel and providing maximum engine efficiency
with clean exhaust emissions, which is why EFI systems have replaced carburetors in the marketplace.EFI is becoming more reliable and less expensive through widespread usage. At the same time,
carburetors are becoming less available, and more expensive. Even marine applications are adopting EFI
as reliability improves. Virtually all internal combustion engines, including motorcycles, off-road
vehicles, and outdoor power equipment, may eventually use some form of fuel injection.
The carburetor remains in use in developing countries where vehicle emissions are unregulated and
diagnostic and repair infrastructure is sparse. Fuel injection is gradually replacing carburetors in these
nations too as they adopt emission regulations conceptually similar to those in force in Europe, Japan,
Australia and North America.
The process of determining the necessary amount of fuel, and its delivery into the engine, are known as
fuel metering. Early injection systems used mechanical methods to meter fuel (non electronic, or
mechanical fuel injection). Modern systems are nearly all electronic, and use an electronic solenoid (the
injector) to inject the fuel. An electronic engine control unit calculates the mass of fuel to inject.
Modern fuel injection schemes follow much the same setup. There is a mass airflow sensor or manifold
absolute pressure sensor at the intake, typically mounted either in the air tube feeding from the air filter
box to the throttle body, or mounted directly to the throttle body itself. The mass airflow sensor does
exactly what its name implies; it senses the mass of the air that flows past it, giving the computer an
accurate idea of how much air is entering the engine. The next component in line is the Throttle Body.
The throttle body has a throttle position sensor mounted onto it, typically on the butterfly valve of the
throttle body. The throttle position sensor (TPS) reports to the computer the position of the throttle
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butterfly valve, which the ECM uses to calculate the load upon the engine. The fuel system consists of a
fuel pump (typically mounted in-tank), a fuel pressure regulator, fuel lines (composed of either high
strength plastic, metal, or reinforced rubber), a fuel rail that the injectors connect to, and the fuel
injector(s). There is a coolant temperature sensor that reports the engine temperature to the ECM,
which the engine uses to calculate the proper fuel ratio required. In sequential fuel injection systems
there is a camshaft position sensor, which the ECM uses to determine which fuel injector to fire. The last
component is the oxygen sensor. After the vehicle has warmed up, it uses the signal from the oxygen
sensor to perform fine tuning of the fuel trim.
The fuel injector acts as the fuel-dispensing nozzle. It injects liquid fuel directly into the engine's air
stream. In almost all cases this requires an external pump. The pump and injector are only two of
several components in a complete fuel injection system.
In contrast to an EFI system, a carburetor directs the induction air through a venturi, which generates a
minute difference in air pressure. The minute air pressure differences both emulsify (premix fuel with
air) the fuel, and then acts as the force to push the mixture from the carburetor nozzle into the
induction air stream. As more air enters the engine, a greater pressure difference is generated, and
more fuel is metered into the engine. A carburetor is a self-contained fuel metering system, and is cost
competitive when compared to a complete EFI system.
An EFI system requires several peripheral components in addition to the injector(s), in order to duplicateall the functions of a carburetor. A point worth noting during times of fuel metering repair is that early
EFI systems are prone to diagnostic ambiguity. A single carburetor replacement can accomplish what
might require numerous repair attempts to identify which one of the several EFI system components is
malfunctioning. Newer EFI systems since the advent ofOBD II diagnostic systems, can be very easy to
diagnose due to the increased ability to monitor the realtime data streams from the individual sensors.
This gives the diagnosing technician realtime feedback as to the cause of the drivability concern, and can
dramatically shorten the number of diagnostic steps required to ascertain the cause of failure,
something which isn't as simple to do with a carburetor. On the other hand, EFI systems require little
regular maintenance; a carburetor typically requires seasonal and/or altitude adjustments.
Typical EFI components
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Animated cut through diagram of a typical fuel injector.
y Injectors
y Fuel Pump
y Fuel Pressure Regulator
y ECM - Engine Control Module; includes a digital computer and circuitry to communicate with
sensors and control outputs.y Wiring Harness
y Various Sensors (Some of the sensors required are listed here.)
y Crank/Cam Position: Hall effect sensor
y Airflow: MAF sensor, sometimes this is inferred with a MAP sensor
y Exhaust Gas Oxygen:Oxygen sensor, EGO sensor, UEGO sensor
Functional description
Central to an EFI system is a computer called the Engine Control Unit (ECU), which monitors
engine operating parameters via various sensors. The ECU interprets these parameters in order to
calculate the appropriate amount of fuel to be injected, among other tasks, and controls engine
operation by manipulating fuel and/or air flow as well as other variables. The optimum amount of
injected fuel depends on conditions such as engine and ambient temperatures, engine speed andworkload, and exhaust gas composition.
The electronic fuel injector is normally closed, and opens to inject pressurized fuel as long as
electricity is applied to the injector's solenoid coil. The duration of this operation, called the pulse
width, is proportional to the amount of fuel desired. The electric pulse may be applied in closely-
controlled sequence with the valve events on each individual cylinder (in a sequential fuel
injection system), or in groups of less than the total number of injectors (in a batch fire system).
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Since the nature of fuel injection dispenses fuel in discrete amounts, and since the nature of the 4-
stroke-cycle engine has discrete induction (air-intake) events, the ECU calculates fuel in discrete
amounts. In a sequential system, the injected fuel mass is tailored for each individual induction
event. Every induction event, of every cylinder, of the entire engine, is a separate fuel mass
calculation, and each injector receives a unique pulse width based on that cylinder's fuel
requirements.
It is necessary to know the mass of air the engine "breathes" during each induction event. This is
proportional to the intake manifold's air pressure/temperature, which is proportional to throttle
position. The amount of air inducted in each intake event is known as "air-charge", and this can be
determined using several methods. (See MAF sensor, and MAP sensor.)
The three elemental ingredients for combustion are fuel, air and ignition. However, complete
combustion can only occur if the air and fuel is present in the exact stoichiometric ratio, which
allows all the carbon and hydrogen from the fuel to combine with all the oxygen in the air, with no
undesirable polluting leftovers.Oxygen sensors monitor the amount of oxygen in the exhaust, and
the ECU uses this information to adjust the air-to-fuel ratio in real-time.
To achieve stoichiometry, the air mass flow into the engine is measured and multiplied by the
stoichiometric air/fuel ratio 14.64:1 (by weight) for gasoline. The required fuel mass that must be
injected into the engine is then translated to the required pulse width for the fuel injector. Thestoichiometric ratio changes as a function of the fuel; diesel, gasoline, ethanol, methanol,
propane, methane (natural gas), or hydrogen.
Deviations from stoichiometry are required during non-standard operating conditions such as
heavy load, or cold operation, in which case, the mixture ratio can range from 10:1 to 18:1 (for
gasoline). In early fuel injection systems this was accomplished with a thermotime switch.
Pulse width is inversely related to pressure difference across the injector inlet and outlet. For
example, if the fuel line pressure increases (injector inlet), or the manifold pressure decreases
(injector outlet), a smaller pulse width will admit the same fuel. Fuel injectors are available in
various sizes and spray characteristics as well. Compensation for these and many other factors are
programmed into the ECU's software.
Throttle body injectionThrottle-body injection (called TBI by General Motors and Central Fuel Injection (CFI) by Ford) or single-
point injection was introduced in the 1940s in large aircraft engines, (then called the pressure
carburetor) and in the 1980s in the automotive world. The TBI system injects fuel at the throttle body
(the same location where a carburetor introduced fuel). The induction mixture passes through the
intake runners like a carburetor system, and is thus labelled a "wet manifold system". The justification
for the TBI/CFI phase was low cost. Many of the carburetor's supporting components could be reused
such as the air cleaner, intake manifold, and fuel line routing. This postponed the redesign and tooling
costs of these components. Most of these components were later redesigned for the next phase of fuel
injection's evolution, which is individual port injection, commonly known as MPFI or "multi-point fuel
injection". TBI was used extensively on American-made passenger cars and light trucks in the 1980 to
1995 timeframe and some transition-engined European cars throughout the early and mid 1990s.
Continuous injection
Bosch's K-Jetronic (K for kontinuierlich, German for "continuous"- a.k.a. CIS- Continuous InjectionSystem) was introduced in 1974. In this system, fuel sprays constantly from the injectors, rather than
being pulsed in time with the engine's intake strokes. Gasoline is pumped from the fuel tank to a large
control valve called afuel distributor, which separates the single fuel supply pipe from the tank intosmaller pipes, one for each injector. The fuel distributor is mounted atop a control vane through which
all intake air must pass, and the system works by varying fuel volume supplied to the injectors based on
the angle of the air vane, which in turn is determined by the volume flowrate of air past the vane, and
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by the control pressure. The control pressure is regulated with a mechanical device called the control
pressure regulator (CPR) or the warm-up regulator (WUR). Depending on the model, the CPR may be
used to compensate for altitude, full load, and/or a cold engine. On cars equipped with an oxygen
sensor, the fuel mixture is adjusted by a device called the frequency valve. The injectors are simple
spring-loaded check valves with nozzles; once fuel system pressure becomes high enough to overcome
the counterspring, the injectors begin spraying. K-Jetronic was used for many years between 1974 and
the mid 1990s by BMW, Lamborghini, Ferrari, Mercedes-Benz, Volkswagen, Ford, Porsche, Audi, Saab,
DeLorean, and Volvo. There was also a variant of the system called KE-Jetronic with electronic instead of
mechanical control of the control pressure.
In piston aircraft engines, continuous-flow fuel injection is the most common type. In contrast to
automotive fuel injection systems, aircraft continuous flow fuel injection is all mechanical, requiring no
electricity to operate. Two common types exist: the Bendix RSA system, and the TCM system. The
Bendix system is a direct descendant of the pressure carburetor. However, instead of having a discharge
valve in the barrel, it uses aflow dividermounted on top of the engine, which controls the dischargerate and evenly distributes the fuel to stainless steel injection lines which go to the intake ports of each
cylinder. The TCM system is even more simple. It has no venturi, no pressure chambers, no diaphragms,
and no discharge valve. The control unit is fed by a constant-pressure fuel pump. The control unit simply
uses a butterfly valve for the air which is linked by a mechanical linkage to a rotary valve for the fuel.Inside the control unit is another restriction which is used to control the fuel mixture. The pressure drop
across the restrictions in the control unit controls the amount of fuel flowing, so that fuel flow is directly
proportional to the pressure at the flow divider. In fact, most aircraft using the TCM fuel injection
system feature a fuel flow gauge which is actually a pressure gauge that has been calibrated in gallonsper hourorpounds per hourof fuel.Central port injection (CPI)
General Motors implemented a system called "central port injection" (CPI) or "central port fuel
injection" (CPFI). It uses tubes with poppet valves from a central injector to spray fuel at each intake
port rather than the central throttle-body[citation needed]. The 2 variants were CPFI from 1992 to 1995,and CSFI from 1996 and on[citation needed]. CPFI is a batch-fire system, in which fuel is injected to all
ports simultaneously. The 1996 and later CSFI system sprays fuel sequentially.[8]Multi-point fuel injection
Multi-point fuel injection injects fuel into the intake port just upstream of the cylinder's intake valve,
rather than at a central point within an intake manifold, referred to as SPFI, or single point fuel injection.
MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's
intake stroke, batched, in which fuel is injected to the cylinders in groups, without precise
synchronization to any particular cylinder's intake stroke, or Simultaneous, in which fuel is injected at
the same time to all the cylinders.
All modern EFI systems utilize sequential MPFI. Some Toyotas and other Japanese cars from the 1970s
to the early 1990s used an application of Bosch's multipoint L-Jetronic system manufactured under
license by DENSO.
Many diesel engines feature direct injection (DI). The injection nozzle is placed inside the combustion
chamber and the piston incorporates a depression (often toroidal) where initial combustion takes place.
Direct injection diesel engines are generally more efficient and cleaner than indirect injection engines.
Some recent gasoline engines utilize direct injection as well. This is the next step in evolution from multi-
port fuel injection and offers another magnitude of emission control by eliminating the "wet" portion of
the induction system. By virtue of better dispersion and homogeneity of the directly injected fuel, the
cylinder and piston are cooled, thereby permitting higher compression ratios and more aggressive
ignition timing, with resultant enhanced output. More precise management of the fuel injection event
also enables better control of emissions. Finally, the homogeneity of the fuel mixture allows for leaner
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air/fuel ratios, which together with more precise ignition timing can improve fuel economy. Along with
this, the engine can operate with stratified mixtures and hence avoid throttling losses at low and part
load. Some direct-injection systems incorporate piezo electronic injectors. With their extremely fast
response time, multiple injection events can occur during each power stroke of the engine.
The first use of direct gasoline injection was on the Hesselman engine invented by Swedish engineer
Jonas Hesselman in 1925.[9][10]
DFI costs more than indirect injection systems; the injectors are exposed to more heat and pressure, so
more costly materials and higher-precision electronic management systems are required.
Maintenance hazards
Fuel injection introduces potential hazards in engine maintenance due to the high fuel pressures used.
Residual pressure can remain in the fuel lines long after an injection-equipped engine has been shut
down. This residual pressure must be relieved, and if it is done so by external bleed-off, the fuel must be
safely contained. If a high-pressure diesel fuel injector is removed from its seat and operated in open air,
there is a risk to the operator of injury by hypodermic jet-injection, even with only 100 psi pressure.
[11]. The first known such injury occurred in 1937 during a diesel engine maintenance operation[12].
PRESSURE SENSO
RA pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression of the force
required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure
sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the
purposes of this article, such a signal is electrical.
Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure
sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level,
and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters,
pressure senders, pressure indicators and piezometers, manometers, among other names.
Pressure sensors can vary drastically in technology, design, performance, application suitability and cost.
A conservative estimate would be that there may be over 50 technologies and at least 300 companies
making pressure sensors worldwide.
There is also a category of pressure sensors that are designed to measure in a dynamic mode for
capturing very high speed changes in pressure. Example applications for this type of sensor would be in
the measuring of combustion pressure in an engine cylinder or in a gas turbine. These sensors are
commonly manufactured out of piezoelectric materials such as quartz.
Some pressure sensors, such as those found in some traffic enforcement cameras, function in a binary
(on/off) manner, i.e., when pressure is applied to a pressure sensor, the sensor acts to complete or
break an electrical circuit. These types of sensors are also known as a pressure switch.
Types of pressure measurements
silicon piezoresistive pressure sensors
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Pressure sensors can be classified in term of pressure ranges they measure, temperature ranges of
operation, and most importantly the type of pressure they measure. In terms of pressure type,
pressure sensors can be divided into five categories:
y Absolute pressure sensor
This sensor measures the pressure relative to perfect vacuum pressure (0 PSI or no pressure).
Atmospheric pressure, is 101.325 kPa (14.7 PSI) at sea level with reference to vacuum.
y Gauge pressure sensor
This sensor is used in different applications because it can be calibrated to measure the pressure
relative to a given atmospheric pressure at a given location. A tire pressure gauge is an example of
gauge pressure indication. When the tire pressure gauge reads 0 PSI, there is really 14.7 PSI
(atmospheric pressure) in the tire.
y Vacuum pressure sensor
This sensor is used to measure pressure less than the atmospheric pressure at a given location.
This has the potential to cause some confusion as industry may refer to a vacuum sensor as one
which is referenced to either atmospheric pressure (ie measure Negative gauge pressure) or
relative to absolute vacuum.
y Differential pressure sensor
This sensor measures the difference between two or more pressures introduced as inputs to thesensing unit, for example, measuring the pressure drop across an oil filter. Differential pressure is
also used to measure flow or level in pressurized vessels.
y Sealed pressure sensor
This sensor is the same as the gauge pressure sensor except that it is previously calibrated by
manufacturers to measure pressure relative to sea level pressure (14.7 PSI).
Pressure Sensing Technology
There are two basic categories of analog pressure sensors.
Force Collector Types These types of eletronic pressure sensors generally utilize a force collector
(such a diaphragm, piston, bourdon tube, or bellows) to measure strain (or deflection) due to
applied force (pressure) over an area.
y
Piezoresistive Strain GageUses the piezoresistive effect of bonded or formed strain gages to detect strain due to applied
pressure. Common technology types are Silicon (Monocrystalline), Polysilicon Thin Film, Bonded
Metal Foil, Thick Film, and Sputtered Thin Film. Generally, the strain gages are connected to form
a Wheatstone bridge circuit to maximize the output of the sensor. This is the most commonly
employed sensing technology for general purpose pressure measurement. Generally, these
technologies are suited to measure absolute, gauge, vacuum, and differential pressures.
y Capacitive
Uses a diaghragm and pressure cavity to create a variable capacitor to detect strain due to applied
pressure. Common technologies utilize metal, ceramic, and silicon diaphragms. Generally, these
technologies are most applied to low pressures (Absolute, Differential and Gauge)
y Electromagnetic
Measures the displacement of a diaphragm by means of changes in inductance (reluctance), LVDT,
Hall Effect, or by eddy current principal.
y Piezoelectric
Uses the piezoelectric effect in certain materials such as quartz to measure the strain upon the
sensing mechanism due to pressure. This technology is commonly employed for the measurement
of highly dynamic pressures.
y Optical
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Uses the physical change of an optical fiber to detect strain due applied pressure. A common
example of this type utilizes Fiber Bragg Gratings. This technology is employed in challenging
applications where the measurement may be highly remote, under high temperature, or may
benefit from the technologies inherent immunity to eletromagnetic interference.
y Potentiometric
Uses the motion of a wiper along a resistive mechanism to detect the strain caused by applied
pressure.
ther Types
These types of eletronic pressure sensors utilize other properties (such as density) to infer
pressure of a gas, or liquid.
y Resonant
Uses the changes in resonant frequency in a sensing mechanism to measure stress, or changes in
gas density, caused by applied pressure. This technology may be used in conjunction with a force
collector, such as those in the category above. Alternatively, resonant technology may be
employed by expose the resonating element iteself to the media, whereby the resonant frequency
is dependent upon the density of the media. Sensors have been made out of vibrating wire,
vibrating cylinders, quartz, and silicon MEMS. Generally, this technology is considered to provide
very stable readings over time.y Thermal
Uses the changes in thermal conductivity of a gas due to density changes to measure pressure. A
common example of this type is the Pirani gage.
y Ionization
Measures the flow of charged gas particles (ions) which varies due to density changes to measure
pressure. Common examples are the Hot and Cold Cathode gages.
y Others
There are numerous other ways to derive pressure from it's density (speed of sound, mass, index
of refraction) among others.
ApplicationsThere are many applications for pressure sensors:
y Pressure sensing
This is the direct use of pressure sensors to measure pressure. This is useful in weather
instrumentation, aircraft, cars, and any other machinery that has pressure functionality
implemented.
y Altitude sensing
This is useful in aircraft, rockets, satellites, weather balloons, and many other applications. All
these applications make use of the relationship between changes in pressure relative to the
altitude. This relationship is governed by the following equation:
This equation is calibrated for an altimeter, up to 36,090 feet (11,000 m). Outside that range, an
error will be introduced which can be calculated differently for each different pressure sensor.
These error calculations will factor in the error introduced by the change in temperature as we go
up.
Barometric pressure sensors can have an altitude resolution of less than 1 meter, which is
significantly better than GPS systems (about 20 meters altitude resolution). In navigation
applications altimeters are used to distinguish between stacked road levels for car navigation and
floor levels in buildings for pedestrian navigation.
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y Flow sensing
This is the use of pressure sensors in conjunction with the venturi effect to measure flow.
Differential pressure is measured between two segments of a venturi tube that have a different
aperture. The pressure difference between the two segments is directly proportional to the flow
rate through the venturi tube. A low pressure sensor is almost always required as the pressure
difference is relatively small.
y Level / Depth sensing
A pressure sensor may also be used to calculate the level of a fluid. This technique is commonly
employed to measure the depth of a submerged body (such as a diver or submarine), or level of
contents in a tank (such as in a water tower). For most practical purposes, fluid level is directly
proportional to pressure. In the case of fresh water where the contents are under atmospheric
pressure, 1psi = 27.7 inH20 / 1Pa = 9.81 mmH20. The basic equation for such a measurement is
P =p * g * hWhere P = Pressure, p = Density of the Fluid, g = Standard Gravity, h = Height of fluid column
above pressure sensor
y Leak Testing
A pressure sensor may be used to sense the decay of pressure due to a system leak. This is
commonly done by either comparison to a known leak using differential pressure, or by means ofutilizing the pressure sensor to measure pressure change over time.
TRAFFIC SIGNS USED
SIGNSTraffic signs tell you about traffic rules, special hazards, where you are, how toget where you are going and where services are available.The shape and color of traffic signs give clues to the type of information they
provide:REGULATION SIGNS usually are white rectangles with black lettering orsymbols, but some are different shapes, and some may use red letters orsymbols.WARNING SIGNS usually are yellow and diamond-shaped, with blacklettering or symbols.DESTINATION SIGNS are green with white letters and symbols.SERVICE SIGNS are blue with white letters and symbols.Know the signs shown below and what they mean. You will be asked aboutthem on your written test.Here are descriptions of the most common traffic signs and what they
mean:STOP SignCOLOR: Red, with white letters.
MEANING: Come to a full stop, yield the right-of-way to vehicles andpedestrians in or approaching the intersection. Go when it is safe. You must
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come to a stop before the stop line, if there is one. If not, you must stopbefore entering the crosswalk. (See "Stop and Crosswalk Lines" under the"Pavement Markings" section of this chapter.) If there is no stop line orcrosswalk, you must stop before entering the intersection, at the point nearestthe intersection that gives you a view of traffic on the intersecting roadway.YIELD SignCOLOR: Red and white, with red letters.
MEANING: Slow down as you approach the intersection. Prepare to stop andyield the right-of-way to vehicles and pedestrians in or approaching theintersection. You must come to a full stop at a YIELD sign if traffic conditionsrequire it. When you approach a YIELD sign, check carefully for traffic, and beprepared to stop.REGULATION SignsCOLOR: White, with black and/or red letters or symbols.
MEANING: These signs give information about rules for traffic direction, laneuse, turning, speed, parking, and other special requirements.Some regulation signs have a red circle with a slash over a symbol indicatingthat an action, such as a right turn, is not allowed, or that certain vehicles arerestricted from the road. Rectangular white signs with black or red letters orsymbols are clues to be alert for special rules.WARNING Signs
COLOR: Yellow, with black letters or symbols.MEANING: You are approaching an especially hazardous location or a placewhere there is a special rule, as shown in the sample signs. Sometimes awarning sign is combined with a rectangular yellow and black "recommendedspeed" sign. This means reduced speed is advised in that area.RAILROAD CROSSING WARNING Sign
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COLOR: Yellow with black letters "RR" and "X" symbol.MEANING: There is a railroad crossing ahead. Use caution, and be preparedto stop. If you are following a bus or truck toward a railroad crossing, becareful. Most buses and some trucks must stop at railroad crossings. (See"Railroad Crossing Signals" later in this chapter.)WORK AREA Signs
COLOR: Orange, with black letters or symbols.MEANING: People are working on or near the roadway, and traffic may becontrolled by a flag person. A work area speed limit as low as 25 MPH (40km/h) may be posted. Even if no speed limit is posted, you must drive at areduced speed through the work zone, and you must always obey flagpersons. These illustrations show some of the signals a flag person will use.Know and obey them.
STOP PROCEED SLOW
DESTINATION Signs
COLOR: Green, with white lettering.MEANING: Show direction and distance to various locations.ROUTE SignsCOLOR: Varied.
MEANING: Indicate interstate, U.S., state or county routes. The shape tells
you what type of route you are on. The sample signs, left to right, are forstate, U.S., and interstate routes. When planning a trip, use a highway map todecide which routes to take. During the trip, watch for destination signs so youwill not get lost, or have to turn or stop suddenly.SERVICE Signs
COLOR: Blue, with white letters or symbols.
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MEANING: Show the location of services, such as rest areas, gas stations,hospitals and campgrounds.TRAFFIC SIGNALS
Traffic LightsTraffic lights are usually red, yellow and green from top to bottom, or left toright. At some intersections, there are single red, yellow or green lights. Sometraffic lights are steady, others flash. Some are circular, and some are arrows.State law requires that if the traffic lights or controls are out of service ormalfunctioning when you approach an intersection, you must come to a stopas you would for a stop sign. You must then proceed according to the rules ofright of way, unless you are directed to proceed by a traffic officer.Here is what various traffic lights mean:STEADY RED: Stop. Do not go until the light is green. If a green arrow isshown with the red light, you may go only in the direction of the arrow andonly if the way is clear.You may make a right turn at a steady red light after coming to a full stop andyielding the right-of-way to oncoming traffic and pedestrians. You may make aleft turn at a steady red light when turning from a one-way road into anotherone-way road after coming to a full stop and yielding the right-of-way tooncoming traffic and pedestrians.You may not make a turn at a red light if there is a NO TURN ON RED signposted, or another sign, signal or pavement marking prohibits the turn. Also,turning on a red light is not allowed in New York City unless a sign is posted
permitting it.The driver of a school bus carrying pupils may not turn right on any red light.
FLASHING RED: Means the same as a STOP sign: Stop, yield the right-of-way, and go when it is safe.RED ARROW: Do not go in the direction of the arrow until the red arrow lightgoes out and a green light or arrow light goes on. A right or left turn on red isnot permitted at a red arrow.
STEADY
Y
ELLOW: The light is changing from green to red. Be ready to stopfor the red light.FLASHING YELLOW: Drive with caution.
YELLOW ARROW: The protection of a green arrow is ending. If you intend toturn in the direction of the arrow, be prepared to stop.STEADY GREEN: Go, but yield the right-of-way to other traffic at theintersection as required by law (see Chapter 5).
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GREEN ARROW: You may go in the direction of the arrow, but you must yieldthe right-of-way to other traffic at the intersection as required by law (seeChapter 5.)Lane Use Control LightsSpecial overhead lights are sometimes used to indicate which lanes of ahighway may be used at certain times:STEADY RED "X": Do not drive in this lane.STEADYYELLOW "X": Move out of this lane.FLASHING YELLOW "X": This lane may only be used for a left turn.GREEN ARROW: You may use this lane.Railroad Crossing Signals
Flashing red lights, lowered crossing gates and/or a ringing bell at a railroadcrossing mean that you must stop, at least 15 feet (5 m) from the tracks. Donot cross the tracks until the lights and bell have stopped and the crossinggates are all the way up. Do not drive around or under a gate that is beinglowered or raised.Look and listen for trains before crossing any railroad tracks. If an approachingtrain is near enough or going fast enough to be a danger, you may not cross
the tracks, even if there are no signals or the signals are not working.You may not cross any railroad tracks unless there is room for your vehicle onthe other side. If other traffic prevents you from crossing all the way, wait, andcross only when there is room.School buses with or without passengers, other buses while carryingpassengers, and vehicles carrying explosives or flammable cargo must stop atall railroad crossings. Keep this in mind if you are following one of these
SOME TRAFFIC SYMBOLES
RIGHT LANEENDS MERGELEFT
YIELD MERGING TRAFFICENTERING FROMRIGHT
STOP
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RAILROADCROSSING
TRAFFICSIGNALAHEAD
SCHOOL CROSSING KEEP RIGHT OFDIVIDER
SLIPPERY WHENWET
NO LEFT TURN DIVIDED HIGHWAYENDS
ONE WAY TRAFFIC DONOT ENTER
TWO WAYTRAFFIC
HILL AHEAD NO U-TURN HOSPITAL EMERGENCYSERVICES TO THERIGHT
PARKING IN HILLS
Parking Uphill:- Turn your signal on and pull to the curb onto the gutter line or about 6-8 inches from thecurb- Place the vehicle's gear lever in neutral- Turn the wheels away from the curb one full turn- Release brake pressure and roll back until the front tire touches the curb- Place the vehicle's gear lever in parkPulling away from Uphill parking:- Place the vehicle's gear lever in drive- Signal in the direction your pulling away from the curb- Check your blind spot over your shoulder in the direction your pulling away from the curb- Release brake pressure and straighten your vehicle's wheels while gradually acceleratingParking Downhill:- Turn your signal on and pull to the curb onto the gutter line or about 6-8 inches from thecurb- Place the vehicle's gear lever in neutral
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- Turn the wheels towards the curb one full turn- Release brake pressure and roll forward until the front tire touches the curb- Place the vehicle's gear lever in parkPulling away from Downhill parking:- Place the vehicle's gear lever in reverse- Release brake pressure and if necessary tap the gas pedal to back 6-8 inches off the curb
- Straighten the vehicle's front wheels- Place the vehicle's gear lever in drive- Signal in the direction your pulling away from the curb- Check your blind spot over your shoulder in the direction your pulling away from the curb- Turn the steering wheel 1/4 turn in the direction your pulling away from the curb- Release brake pressure and straighten your vehicle's wheels while gradually accelerating
Inserted from
ELECTRIC MOTOR USED IN HYBRID VECHILES
Eectric motors
An electric motor is a device using electrical energy to produce mechanical energy, nearly always by the
interaction of magnetic fields and current-carrying conductors. The reverse process, that of using
mechanical energy to produce electrical energy, is accomplished by a generator or dynamo. Traction
motors used on vehicles often perform both tasks.
As a convention, a powerplant operating on electricity is called electric motor. The word electric enginerefers to a railroad electric locomotive.
Electric motors are found in a myriad of applications such as industrial fans, blowers and pumps,machine tools, household appliances, power tools, and computer disk drives, among many other
applications. Electric motors may be operated by direct current from a battery in a portable device or
motor vehicle, or from alternating current from a central electrical distribution grid. The smallest motors
may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and
characteristics provide convenient mechanical power for industrial uses. The very largest electric motors
are used for propulsion of large ships, and for such purposes as pipeline compressors, with ratings in the
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thousands of kilowatts. Electric motors may be classified by the source of electric power, by their
internal construction, and by application.
The physical principle of production of mechanical force by the interaction of an electric current and a
magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed
throughout the 19th century, but commercial exploitation of electric motors on a large scale required
efficient electrical generators and electrical distribution networks.
The principle
The principle of conversion of electrical energy into mechanical energy by electromagnetic means was
demonstrated by the British scientist Michael Faraday in 1821 and consisted of a free-hanging wire
dipping into a pool of mercury. A permanent magnet was placed in the middle of the pool of mercury.
When a current was passed through the wire, the wire rotated around the magnet, showing that the
current gave rise to a circular magnetic field around the wire[2]. This motor is often demonstrated in
school physics classes, but brine (salt water) is sometimes used in place of the toxic mercury. This is the
simplest form of a class of electric motors called homopolar motors. A later refinement is the Barlow's
Wheel. These were demonstration devices, unsuited to practical applications due to limited power.
Type Advantages Disadvantages
AC Induction
(Shaded Pole)
Least expensive
Long life
high power
Rotation slips from frequency
Low starting torque
AC Induction
(split-phase capacitor)
High power
high starting torque
Rotation slips from frequency
AC Synchronous Rotation in-sync with freq
long-life (alternator)
More expensive
Stepper DC Precision positioning
High holding torque
Requires a controller
Brushless DC electric motor Long lifespan
low maintenanceHigh efficiency
High initial cost
Requires a controller
Brushed DC electric motor Low initial cost
Simple speed control (Dynamo)
High maintenance (brushes)
Low lifespan
[9]
Servo motor
Main article: Servo motor
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A servomechanism, or servo is an automatic device that uses error-sensing feedback to correct the
performance of a mechanism. The term correctly applies only to systems where the feedback or
error-correction signals help control mechanical position or other parameters. For example, an
automotive power window control is not a servomechanism, as there is no automatic feedback
which controls positionthe operator does this by observation. By contrast the car's cruise
control uses closed loop feedback, which classifies it as a servomechanism.
Synchronous electric motor
Main article: Synchronous motor
A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing
magnets at the same rate as the alternating current and resulting magnetic field which drives it.
Another way of saying this is that it has zero slip under usual operating conditions. Contrast this
with an induction motor, which must slip in order to produce torque. Synchronous motor is like an
induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to
conduct current to rotor. The rotor poles connect to each other and move at the same speed
hence the name synchronous motor.
Induction motor
Main article: Induction motor
An induction motor (IM) is a type of asynchronous AC motor where power is supplied to therotating device by means of electromagnetic induction. Another commonly used name is squirrel
cage motor because the rotor bars with short circuit rings resemble a squirrel cage (hamster
wheel). An electric motor converts electrical power to mechanical power in its rotor (rotating
part). There are several ways to supply power to the rotor. In a DC motor this power is supplied to
the armature directly from a DC source, while in an induction motor this power is induced in the
rotating device. An induction motor is sometimes called a rotating transformer because the stator
(stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is
the secondary side. Induction motors are widely used, especially polyphase induction motors,
which are frequently used in industrial drives.
Electrostatic motor (capacitor motor)
Main article: Electrostatic motorAn electrostatic motor or capacitor motor is a type of electric motor based on the attraction and
repulsion of electric charge. Usually, electrostatic motors are the dual of conventional coil-based
motors. They typically require a high voltage power supply, although very small motors employ
lower voltages. Conventional electric motors instead employ magnetic attraction and repulsion,
and require high current at low voltages. In the 1750s, the first electrostatic motors were
developed by Benjamin Franklin and Andrew Gordon. Today the electrostatic motor finds frequent
use in micro-mechanical (MEMS) systems where their drive voltages are below 100 volts, and
where moving charged plates are far easier to fabricate than coils and iron cores. Also, the
molecular machinery which runs living cells is often based on linear and rotary electrostatic
motors.
DC Motors
A DC motor is designed to run on DC electric power. Two examples of pure DC designs are Michael
Faraday's homopolar motor (which is uncommon), and the ball bearing motor, which is (so far) a
novelty. By far the most common DC motor types are the brushed and brushless types, which use
internal and external commutation respectively to create an oscillating AC current from the DC
sourceso they are not purely DC machines in a strict sense.
Brushed DC motors
Main article: Brushed DC electric motor
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The classic DC motor design generates an oscillating current in a wound rotor, or armature, with a
split ring commutator, and either a wound or permanent magnet stator. A rotor consists of one or
more coils of wire wound around a core on a shaft; an electrical power source is connected to the
rotor coil through the commutator and its brushes, causing current to flow in it, producing
electromagnetism. The commutator causes the current in the coils to be switched as the rotor
turns, keeping the magnetic poles of the rotor from ever fully aligning with the magnetic poles of
the stator field, so that the rotor never stops (like a compass needle does) but rather keeps
rotating indefinitely (as long as power is applied and is sufficient for the motor to overcome the
shaft torque load and internal losses due to friction, etc.)
Many of the limitations of the classic commutator DC motor are due to the need for brushes to
press against the commutator. This creates friction. At higher speeds, brushes have increasing
difficulty in maintaining contact. Brushes may bounce off the irregularities in the commutator
surface, creating sparks. (Sparks are also created inevitably by the brushes making and breaking
circuits through the rotor coils as the brushes cross the insulating gaps between commutator
sections. Depending on the commutator design, this may include the brushes shorting together
adjacent sectionsand hence coil endsmomentarily while crossing the gaps. Furthermore, the
inductance of the rotor coils causes the voltage across each to rise when its circuit is opened,
increasing the sparking of the brushes.) This sparking limits the maximum speed of the machine,as too-rapid sparking will overheat, erode, or even melt the commutator. The current density per
unit area of the brushes, in combination with their resistivity, limits the output of the motor. The
making and breaking of electric contact also causes electrical noise, and the sparks additionally
cause RFI. Brushes eventually wear out and require replacement, and the commutator itself is
subject to wear and maintenance (on larger motors) or replacement (on small motors). The
commutator assembly on a large machine is a costly element, requiring precision assembly of
many parts. On small motors, the commutator is usually permanently integrated into the rotor, so
replacing it usually requires replacing the whole rotor.
Large brushes are desired for a larger brush contact area to maximize motor output, but small
brushes are desired for low mass to maximize the speed at which the motor can run without the
brushes excessively bouncing and sparking (comparable to the problem of "valve float" in internalcombustion engines). (Small brushes are also desirable for lower cost.) Stiffer brush springs can
also be used to make brushes of a given mass work at a higher speed, but at the cost of greater
friction losses (lower efficiency) and accelerated brush and commutator wear. Therefore, DC
motor brush design entails a trade-off between output power, speed, and efficiency/wear.
A: shunt
B: serieC: compound
There are four types of DC motor:
1. DC series motor
2. DC shunt motor
3. DC compound motor - there are also two types:
1. cumulative compound
2. differentially compounded
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4. Permanent Magnet DC Motor
Brushless DC motors
Main article: Brushless DC electric motor
Some of the problems of the brushed DC motor are eliminated in the brushless design. In this
motor, the mechanical "rotating switch" or commutator/brushgear assembly is replaced by an
external electronic switch synchronised to the rotor's position. Brushless motors are typically 85-
90% efficient or more (higher efficiency for a brushless electric motor of up to 96.5% were
reported by researchers at the Tokai University in Japan in 2009[10]), whereas DC motors with
brushgear are typically 75-80% efficient.
Midway between ordinary DC motors and stepper motors lies the realm of the brushless DC
motor. Built in a fashion very similar to stepper motors, these often use a permanent magnet
external rotor, three phases of driving coils, one or more Hall effect sensors to sense the position
of the rotor, and the associated drive electronics. The coils are activated, one phase after the
other, by the drive electronics as cued by the signals from either Hall effect sensors or from the
back EMF of the undriven coils. In effect, they act as three-phase synchronous motors containing
their own variable-frequency drive electronics. A specialized class of brushless DC motor
controllers utilize EMF feedback through the main phase connections instead of Hall effect sensors
to determine position and velocity. These motors are used extensively in electric radio-controlledvehicles. When configured with the magnets on the outside, these are referred to by modelists as
outrunner motors.
Brushless DC motors are commonly used where precise speed control is necessary, as in computer
disk drives or in video cassette recorders, the spindles within CD, CD-ROM (etc.) drives, and
mechanisms within office products such as fans, laser printers and photocopiers. They have
several advantages over conventional motors:
y Compared to AC fans using shaded-pole motors, they are very efficient, running much cooler than
the equivalent AC motors. This cool operation leads to much-improved life of the fan's bearings.
y Without a commutator to wear out, the life of a DC brushless motor can be significantly longer
compared to a DC motor using brushes and a commutator. Commutation also tends to cause a
great deal of electrical and RF noise; without a commutator or brushes, a brushless motor may beused in electrically sensitive devices like audio equipment or computers.
y The same Hall effect sensors that provide the commutation can also provide a convenient
tachometer signal for closed-loop control (servo-controlled) applications. In fans, the tachometer
signal can be used to derive a "fan OK" signal.
y The motor can be easily synchronized to an internal or external clock, leading to precise speed
control.
y Brushless motors have no chance of sparking, unlike brushed motors, making them better suited
to environments with volatile chemicals and fuels. Also, sparking generates ozone which can
accumulate in poorly ventilated buildings risking harm to occupants' health.
y Brushless motors are usually used in small equipment such as computers and are generally used
to get rid of unwanted heat.
y They are also very quiet motors which is an advantage if being used in equipment that is affected
by vibrations.
Modern DC brushless motors range in power from a fraction of a watt to many kilowatts. Larger
brushless motors up to about 100 kW rating are used in electric vehicles. They also find significant
use in high-performance electric model aircraft.
Coreless or ironless DC motors
Nothing in the design of any of the motors described above requires that the iron (steel) portions
of the rotor actually rotate; torque is exerted only on the windings of the electromagnets. Taking
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advantage of this fact is the coreless or ironless DC motor, a specialized form of a brush or
brushless DC motor. Optimized for rapid acceleration, these motors have a rotor that is
constructed without any iron core. The rotor can take the form of a winding-filled cylinder, or a
self-supporting structure comprising only the magnet wire and the bonding material. The rotor
can fit inside the stator magnets; a magnetically-soft stationary cylinder inside the rotor provides a
return path for the stator magnetic flux. A second arrangement has the rotor winding basket
surrounding the stator magnets. In that design, the rotor fits inside a magnetically-soft cylinder
that can serve as the housing for the motor, and likewise provides a return path for the flux. A
third design has the windings shaped as a disc (originally formed on a printed wiring board)
running between arrays of high-flux magnets facing the rotor and arranged in a circle.
The windings are typically stabilized by being impregnated with electrical epoxy potting systems.
These are filled epoxies that have moderate mixed viscosity and a long gel time. They are
highlighted by low shrinkage and low exotherm, and are typically UL 1446 recognized as a potting
compound for use up to 180C (Class H) (UL File No. E 210549).
Because the rotor is much lighter in weight (mass) than a conventional rotor formed from copper
windings on steel laminations, the rotor can accelerate much more rapidly, often achieving a
mechanical time constant under 1 ms. This is especially true if the windings use aluminum rather
than the heavier copper. But because there is no metal mass in the rotor to act as a heat sink,even small coreless motors must often be cooled by forced air.
Another advantage of ironless DC motors is that there is no cogging (vibration caused by
attraction between the iron and the magnets) and parasitic eddy currents cannot form in the iron.
This can greatly improve efficiency, but variable-speed controllers must use a significantly higher
switching rate (>150kHz) or direct current because of the decreased electromagnetic induction.
These motors were commonly used to drive the capstan(s) of magnetic tape drives and are still
widely used in high-performance servo-controlled systems, like radio-controlled vehicles/aircraft,
humanoid robotic systems, industrial automation, medical devices, etc.
Related limited-travel actuators have no core and a bonded coil placed between the poles of high-
flux thin permanent magnets. These are the fast head positioners for rigid-disk ("hard disk")
drives.Universal motors
A variant of the wound field DC motor is the universal motor. The name derives from the fact that
it may use AC or DC supply current, although in practice they are nearly always used with AC
supplies. The principle is that in a wound field DC motor the current in both the field and the
armature (and hence the resultant magnetic fields) will alternate (reverse polarity) at the same
time, and hence the mechanical force generated is always in the same direction. In practice, the
motor must be specially designed to cope with the AC (impedance must be taken into account, as
must the pulsating force), and the resultant motor is generally less efficient than an equivalent
pure DC motor.
Operating at normal power line frequencies, the maximum output of universal motors is limited
and motors exceeding one kilowatt (about 1.3 horsepower) are rare. But universal motors also
form the basis of the traditional railway traction motor in electric railways. In this application, to
keep their electrical efficiency high, they were operated from very low frequency AC supplies, with
25 and 16.7 hertz (Hz) operation being common. Because they are universal motors, locomotives
using this design were also commonly capable of operating from a third rail powered by DC.
The advantage of the universal motor is that AC supplies may be used on motors which have the
typical characteristics of DC motors, specifically high starting torque and very compact design if
high running speeds are used. The negative aspect is the maintenance and short life problems
caused by the commutator. As a result such motors are usually used in AC devices such as food
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mixers and power tools which are used only intermittently. Continuous speed control of a
universal motor running on AC is easily obtained by use of a thyristor circuit, while stepped speed
control can be accomplished using multiple taps on the field coil. Household blenders that
advertise many speeds frequently combine a field coil with several taps and a diode that can be
inserted in series with the motor (causing the motor to run on half-wave rectified AC).
Universal motors generally run at high speeds, making them useful for appliances such as
blenders, vacuum cleaners, and hair dryers where high RPM operation is desirable. They are also
commonly used in portable power tools, such as drills, circular and jig saws, where the motor's
characteristics work well. Many vacuum cleaner and weed trimmer motors exceed 10,000 RPM,
while Dremel and other similar miniature grinders will often exceed 30,000 RPM.
Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the
unit is operated with no significant load. On larger motors, sudden loss of load is to be avoided,
and the possibility of such an occurrence is incorporated into the motor's protection and control
schemes. In smaller applications, a fan blade attached to the shaft often acts as an artificial load to
limit the motor speed to a safe value, as well as a means to circulate cooling airflow over the
armature and field windings.
With the very low cost of semiconductor rectifiers, some applications that would have previously
used a universal motor now use a pure DC motor, sometimes with a permanent magnet field.AC motors
Main article: AC motor
In 1882, Nikola Tesla invented the rotating magnetic field, and pioneered the use of a rotary field
of force to operate machines. He exploited the principle to design a unique two-phase induction
motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris
published his research in a paper to the Royal Academy of Sciences in Turin.
Tesla had suggested that the commutators from a machine could be removed and the device
could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin
to building a perpetual motion machine.[11] Tesla would later attain U.S. Patent 0,416,194,
Electric Motor(December 1889), which resembles the motor seen in many of Tesla's photos. This
classic alternating current electro-magnetic motor was an induction motor.MichailOsipovich Dolivo-Dobrovolsky later invented a three-phase "cage-rotor" in 1890. This type
of motor is now used for the vast majority of commercial applications.
Components
A typical AC motor consists of two parts:
y An outside stationary stator having coils supplied with AC current to produce a rotating magnetic
field, and;
y An inside rotor attached to the output shaft that is given a torque by the rotating field.
Torque motors
A torque motor (also known as a limited torque motor) is a specialized form of induction motor
which is capable of operating indefinitely while stalled, that is, with the rotor blocked from
turning, without incurring damage. In this mode of operation, the motor will apply a steady torque
to the load (hence the name).
A common application of a torque motor would be the supply- and take-up reel motors in a tape
drive. In this application, driven from a low voltage, the characteristics of these motors allow a
relatively-constant light tension to be applied to the tape whether or not the capstan is feeding
tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the
torque motors can also achieve fast-forward and rewind operation without requiring any
additional mechanics such as gears or clutches. In the computer gaming world, torque motors are
used in force feedback steering wheels.
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Another common application is the control of the throttle of an internal combustion engine in
conjunction with an electronic governor. In this usage, the motor works against a return spring to
move the throttle in accordance with the output of the governor. The latter monitors engine
speed by counting electrical pulses from the ignition system or from a magnetic pickup [12] and,
depending on the speed, makes small adjustments to the amount of current applied to the mot