Power Steering Nana Shinde
-
Upload
nanasaheb-shinde -
Category
Documents
-
view
224 -
download
0
Transcript of Power Steering Nana Shinde
-
8/4/2019 Power Steering Nana Shinde
1/36
Presentation
OnSteering System
Nanasaheb S Shinde
-
8/4/2019 Power Steering Nana Shinde
2/36
How Car Steering Works?
-
8/4/2019 Power Steering Nana Shinde
3/36
Turning the Car
For a car to turn smoothly, each wheel must follow a different circle. Since the inside wheel
is following a circle with a smaller radius, it is actually making a tighter turn than the outside
wheel.
Ifwe draw a line perpendicular to each wheel, the lines will intersect at the center point of
the turn. The geometry of the steering linkage makes the inside wheel turn more than the
outside wheel.
-
8/4/2019 Power Steering Nana Shinde
4/36
While turning, the inside wheel turn more than the outside wheel
Turning the Car
-
8/4/2019 Power Steering Nana Shinde
5/36
Steering Ratio
One purpose of the steering mechanism is to provide mechanical advantage.
In a machine or mechanical device, it is the ratioof the output force to the input forceapplied to it.
This means that a relatively small applied force can produce a much greater force at the
other end of the device.
The higher the steering ratio, the easier it is to steer the vehicle.
However, higher the steering ratio, the more the steering wheel has to be turned to
achieve steering.
With a 30: 1 steering ratio, the steering wheel must turn 30 degrees to pivot the frontwheels 1 degree.
Variable Steering Ratio
"Variable steering ratio" means that the ratio is larger at one position than another.
Therefore the wheels are turned faster at certain positions than at others.
At the centeror straight-ahead position, the steering gear ratio is high, giving more
steering control.
However, as the wheels are turned, the ratio decreases so that the steering action is
much more rapid. This design is very helpful for parking and maneuvering the vehicle.
-
8/4/2019 Power Steering Nana Shinde
6/36
Function of Steering System
Control of front wheel (sometimes rearwheel) direction.
T
ransmit road feel (slight steeringw
heel pu
ll cau
sed by the ro
ad su
rface)to the drivers hand.
Maintain correct amount of effort needed to turn the wheels.
Absorb most of the shock going to the steering wheel as the tire hits holes
and bumps in the road.
Allow for suspension action
-
8/4/2019 Power Steering Nana Shinde
7/36
Classification of Steering Systems
Manual steering system relies on the driver to provide steering force
Power steering system uses hydraulic or electric power to help the driver applysteering force
Manual Steering Systems
-
8/4/2019 Power Steering Nana Shinde
8/36
Manual Steering System
There are several different types of manual steering systems, which are asfollows:
Worm and sector
Worm and rotter
Cam and lever
Worm and nut Rack and pinion
-
8/4/2019 Power Steering Nana Shinde
9/36
Worm and sector type steering system
Worm and roller type steering system
Cam and lever type steering systemWorm and nut type steering system
-
8/4/2019 Power Steering Nana Shinde
10/36
Manual and Power Steering Systems Have Common
Components.
Input components:
Steering wheel
Steering column
Steering shaft
-
8/4/2019 Power Steering Nana Shinde
11/36
Steering Wheel used by the driver to rotate a
steering shaft that passes through the steering
column.
Steering Shaft transfers turning motion from
the steering wheel to the steering gearbox.
Steering Column supports the steering column
and steering shaft.
Linkage Steering System (Worm Gear) Parts
-
8/4/2019 Power Steering Nana Shinde
12/36
Linkage Steering System (Worm Gear) Parts
Steering Gearbox
changes turning motion
into a straight-line motion to the left or right.
Steering gear box ratios range from 15:1 to
24:1 (with 15:1, the worm gear turns 15 timesto turn the selector shaft once).
Steering linkage
connects the steering
gearbox to the steering knuckles and wheels.
-
8/4/2019 Power Steering Nana Shinde
13/36
Steering Components Pitman arm-Connects the linkage to the steering gear.
Idler arm-Supports the centre link to the frame.
Centre link, drag link, or steering link-Controls sideways linkage movement. Tie-rods-Connect linkage to the steering knuckles.
Linkage Steering
-
8/4/2019 Power Steering Nana Shinde
14/36
Rack-and-Pinion Steering
-
8/4/2019 Power Steering Nana Shinde
15/36
Rack and Pinion
The rack-and-pini
on steering gear has bec
ome increasingly p
opu
laron smallerpassengervehicles. It is simpler, more direct acting, and may be straight
mechanical or power-assisted.
In the rack-and-pinion steering system the end of the steering gear shaft contains
a pinion gear, which meshes with a long rack.
As the steering wheel is rotated, the pinion gearon the end of the steering shaft
rotates. The pinion gear moves the rack from one side to the other. This action
pushes or pulls on the tie rods, forcing the steering knuckles orwheel spindles to
pivot on their ball joints. This turns the wheels toone side or the other so the
vehicle can be steered.
The rack-and-pinion gearset does two things:
It converts the rotational motion of the steering wheel into the linear motion
needed to turn the wheels.
It provides a gear reduction, making it easier to turn the wheels. For light cars
11:1, and for heavy trucks 18:1.
-
8/4/2019 Power Steering Nana Shinde
16/36
POWER STEERING SYSTEM
-
8/4/2019 Power Steering Nana Shinde
17/36
The need achieve the greatest possible road safety under:
Increasing traffic density
High axle loads
Poor road conditions.
Led to the development of Power Steering.
Need for Power Steering
Modes of Actuation
Hydraulic systems
Electric systems
-
8/4/2019 Power Steering Nana Shinde
18/36
Hydraulic Power Steering
Power steering systems normally use an engine-driven pump and hydraulic system to assist
steering action.Pressure from the oil pump is used tooperate a piston and cylinder assembly.
When the control valve routes oil pressure intoone end of the piston, the piston slides in its
cylinders.
Piston movement can then be used to help move the steering system components and front
wheels of the vehicles.
-
8/4/2019 Power Steering Nana Shinde
19/36
Pump
The hydraulic power for the steering is provided by a rotary-vane pump.
This pump is driven by the car's engine via a belt and pulley.
It contains a set of retractable vanes that spin inside an oval chamber. As the vanes spin, theypull hydraulic fluid from the return line at low pressure and force it into the outlet at high pressure.
The amount of flow provided by the pump depends on the car's engine speed.
The pump contains a pressure-reliefvalve to make sure that the pressure does not get too high.
The pump must be designed to provide adequate flowwhen the engine is idling. So, the pump
moves much more fluid than necessary when the engine is running at faster speeds.
-
8/4/2019 Power Steering Nana Shinde
20/36
Rotary Valve
The device that senses the force on the steering wheel is called the rotary valve.
The key to the rotary valve is a torsion bar.
The top of the bar is connected to the steering wheel, and the bottom of the bar is connected
to the pinion orworm gear (which turns the wheels), so the amount of torque in the torsion bar
is equal to the amount of torque the driver is using to turn the wheels.The bottom of the torsion bar connects to the outer part of the spool-valve assembly.
As the bar twists, it rotates the inside of the spool valve relative to the outside.
The inner part of the spool valve is also connected to the steering shaft, the amount of
rotation between the inner and outer parts of the spool valve depends on how much torque the
driver applies to the steering wheel.
-
8/4/2019 Power Steering Nana Shinde
21/36
When the steering wheel is not being turned, both hydraulic lines provide the same amount
of pressure to the steering gear. But if the spool valve is turned one way or the other, ports
open up to provide high-pressure fluid to the appropriate line.
Working of the Rotary Valve
-
8/4/2019 Power Steering Nana Shinde
22/36
Rack-and-Pinion Power Steering System
In the rack-and-pinion power-steering system, the rack has a slightly different design.Part of the rack contains a cylinderwith a piston in the middle. The piston is connected to the
rack.
There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid to
one side of the piston forces the piston to move, which in turn moves the rack, providing the
power assist.
-
8/4/2019 Power Steering Nana Shinde
23/36
Power Steering Leakage
A common problem with power steering systems is fluid leakage. With pressure over 1,000
psi, leaks can develop easily around fittings, in hoses, at the gearbox seals, or at the rack-and-
pinion assembly.
In Steering gear box, leakage occurs from:-
1.Upper Pinion seal.2.Rack bush side seal.
3.Pinion side seal.
-
8/4/2019 Power Steering Nana Shinde
24/36
Advantages
Preventing the wheels from transferring the load to the steering column Reducing the drivers fatigue
Low input torque and continuous steering function
Oil output directly proportional to the steering speed
Disadvantages
Design is compications and increased in cost.
Fluid leakage.
-
8/4/2019 Power Steering Nana Shinde
25/36
Electronic Power Steering
(EPS)
-
8/4/2019 Power Steering Nana Shinde
26/36
Electronic Power Steering
-
8/4/2019 Power Steering Nana Shinde
27/36
Electronic Power Steering (EPS) is an advanced power steering system. It eliminates the need
for a power Steering pump, hoses, hydraulic fluids, and a drive belt and pulley on the engine.
As a result, electric power steering is more energy efficient.
Electronic Power Steering (EPS)
-
8/4/2019 Power Steering Nana Shinde
28/36
Control block diagram for EPS system
-
8/4/2019 Power Steering Nana Shinde
29/36
Working
-
8/4/2019 Power Steering Nana Shinde
30/36
A "steering sensor" is located on the input shaft.
The steering sensor is actually two sensors: a "torque sensor" that converts steering
torque input and its direction intovoltage signals, and a "rotation sensor" that
converts the rotation speed and direction intovoltage signals.
There is an "interface" circuit that converts the signals from the torque sensor and
rotation sensor into signals that are sent to a microprocessor.
Inputs from the steering sensor are digested by a microprocessor control unit that
also monitors input from the vehicle's speed sensor. The sensor inputs are then compared to determine how much power assist is
required according to a preprogrammed "force map" in the control unit's memory.
The control unit then sends out the appropriate command to the "powerunit"which
then supplies the electric motorwith current.
The motor pushes the rack to the right or left depending on which way the voltage
flows (reversing the current reverses the direction the motor spins). Increasing thecurrent to the motor increases the amount of power assist.
Working
-
8/4/2019 Power Steering Nana Shinde
31/36
Classifications of EPS -
EPS can mainly classified in to 3 kinds depending up on the position of the motor:
Column assist type.
Pinion assist type.
Rack assist type.
-
8/4/2019 Power Steering Nana Shinde
32/36
Column-Assist Type:
The power assist unit, controller and the torque sensor are attached to the steering column.
This system is compact and easy to mount on vehicle.
An integrated pivot/mount and integrated controlleroption increase mounting flexibility.
Shafts offer long-term durability performance at much higher torsion loading.
-
8/4/2019 Power Steering Nana Shinde
33/36
Pinion-Assist Type:
The power assist unit is attached to steering gears pinion shaft.
The power assist unit is outside the vehicles passenger compartment, allowing assist torque
to be increased greatly without raising interior noise.
Combined with a variable ratio steering gear, this system can suffice with a compact motor
and offer superior handling characteristics.
-
8/4/2019 Power Steering Nana Shinde
34/36
Rack-Assist Type:
The power assist unit is attached to the steering gear rack.The power assist unit can be located freely on the rack, allowing great flexibility in layout
design.
The power assist units high reduction gear ratio enables very low inertia and superior driving
feel.
Electric power steering rack assist is a scalable system, suitable for midsize cars to full-size
trucks.
-
8/4/2019 Power Steering Nana Shinde
35/36
Advantages of EPS overHydraulic Power
Steering:
Reduced driver fatigue.
Enhances dependability and safety.
Compact, modular design and flexible tuning capability.
Helps improve fuel economy by reducing the pressure the pump has towork against during
straight-ahead highway speed driving.
Accommodates most vehicle platforms.
Reduced steering system operating temperature.
Lower noise under all driving conditions.
EPS has got upper hand compared toHydraulic power steering because:
-
8/4/2019 Power Steering Nana Shinde
36/36
Thank You