Case StudiesHydraulics/ Braking Systems/ Lifting

devices

1. Fluid mechanics

Is the study of fluids such as liquids and gases and the ways in which they interact with forces applied to them. Fluids deform to take the shapes of their surroundings; the diagram below illustrates what would happen when a force is applied to a toothpaste tube with four holes in it. The force is transferred equally in every direction to all parts of the container.

Section 1

Blaise Pascal who was a French mathematician, physicist and inventor, established that “pressure applied to an enclosed liquid is transmitted undiminished to every point in the fluid and to the walls of the container.”

Pascal’s principle is applied in sealed hydraulics systems such as the operation of a four wheeled hydraulic automobile braking system. This is illustrated in the diagram below, when pressure is applied to a brake pedal this forces the piston in the master cylinder against the fluid in that cylinder and transfers equal force to all other brake shoes, thus stopping the vehicle.

There are many industries that use hydraulics such automobiles, petrol pumps, cranes, robotic and aircrafts.

Industries

The following two digital resources demonstrate how Pascal’s law and hydraulic brakes

  http://www.youtube.com/watch?v=VxLTDtaR

CZk http://www.youtube.com/watch?v=d66EiKw

ySt4&feature=related

Digital resources

Archimedes was a Greek philosopher and discovered that the level of water in a tub rose when he sat in it, he found that “a body wholly or partially submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body.”

(Writing)

2. Case studies – use of hydraulic principles in braking systems

Hydraulic brakes are commonly used in the automobile industry, they work on the principle of Pascal law, Hydraulic brakes consists of a master cylinder, four wheel cylinder and pipes carrying a brake fluid from the master cylinder to the wheel cylinder. The pressure of the brake fluid forces out the two pistons in the wheel cylinders, pistons are connected to brake shoes. The brake shoes expand out against drums due to friction between the brake linings and drum the wheels slow down.

Personal transport vehicles

Automobile hydraulic-brake system.

1) Brake pedal; 2) piston; 3) master cylinder; 4) hydraulic line; 5) brake cylinder; 6) brake piston; 7) brake band; 8) wheel; 9) return spring.

(Association, 2004)

There are many advantages of hydraulic brakes such as the equal braking action of all wheels, increased braking force, simple construction, low wear rate of brake lining and a mechanical advantage. The disadvantages are that when a leakage occurs or there is air inside the tubing’s the whole braking systems fails.

A Motorcycle hydraulic brakes work similar to car brakes, in the same way they deliver brake fluid under pressure from the master cylinder to the brakes. The difference is on a motorcycle the rider controls the front and rear brakes manually.

Motorcycle hydraulic brakes

The front brake is operated by the rider’s right hand, and the rear brakes are operated by the rider’s right foot. This requires the rider’s skill in determining the appropriate amount of pressure to both front and rear brakes. Generally brake lines are visible on motorcycles than cars, brake lines usually run along the motorcycles frame.

(Works, 2011)

Motorcycle hydraulic brakes

Buses   Hydraulic Antilock Braking systems (HABS)

operated on buses since March 1 1999, HABS help maintain control and stability of a bus in extreme braking circumstances. The unit is an electronic system with four solenoid valves and two or more electric hydraulic pumps. The four solenoids pressure valves control brake fluid pressure for each wheel and slow bus down.

Public transport vehicles

Railway air brakes is a straight air system where compressed air pushes on a piston in a cylinder, the piston is connected to a brake shoe that uses friction to slow a train down. One pressurized air cylinder can evenly distribute the force to 8 – 12 wheels. The pressurized air comes from a air compressor inside the train and sent by pipes and hoses beneath each of the carriages. The problem with railway air brakes is that any breakage or separation between hoses and pipes can cause a loss of air pressure, this affects the force applied to the brakes.

(Wikipedia, 2012)

Railway

3. Innovations

The Electronic Wedge Brake (EWB) bypasses any hydraulic system that works on a similar principle with the brakes of horse drawn carriages, where a wedge is used to bring a wheel to a stop. The EWB is simply powered by a 12-volt power system in which already exists in cars. The EWB is proven to react faster and works about a third quicker than conventional breaks, only requiring 100ms to reach full braking power compared to a hydraulic brake’s 170ms.

The design of the EWB is basically a wedge connected to a brake pad that is pressed between the rod and disc. The electric motor pushes the pad onto the disc, the use of the wedge means braking power is multiplied with minimal energy and the faster the car is going the stronger the brake force is. The cars kinetic energy is being converted into breaking energy. The EWB has a back up power source in case power supply is disrupted.

EWB

The highly sophisticated sensor technology prevents brakes from locking up and guarantees highly efficient and controlled braking.

When released, the brake disk runs freely (left). A sight amount of pressure from the wedge on the disk (right) applies the brake. Enhanced braking results because the disk’s rotation drags the wedge with it, thereby generating drag 

(Siemens, 2005)

EWB

http://paultan.org/2007/03/15/siemens-electronic-wedge-brake-ewb/

Video Wonder Wegde

Section 2 Developments in lifting devices

One of the first hydraulic lift devices were invented by William Armstrong in 1845, the crane was water powered. Armstrong used water in cylinders to create a force to lift and move loads vertically and horizontally.

Hydraulic crane

The hydraulic crane was significant in the growth and development of North East of England, the sea port imported and exported goods and the hydraulic crane enable greater efficiency, safety and a reduction in labour costs, as a result it became one of the most important cities of the time.

In 1970 hydraulic elevators were quite common generally used for low level building with 2- 5 floors, cylinders were underground. Further development introduced a Rope hydraulic elevator this allowed the elevator to travel further than the piston had to move. The impact of these elevators were that they used less energy, as a pump worked against gravity to push the elevator upwards, a greater capacity to lift more people and faster travelling time. The negative was the possibility of cylinders leaking fluid into the ground and causes damage the environment.

Elevators

Forklifts

Forklifts are design to move objects or loads up and down, the operator uses a hydraulic system to move forks. Pressure is applied to a bar with rolling chains that are located in the forklift.

 

2. An innovation of a lifting device

An incline platform lift enables disabled people access places where before were not possible due to stairs. The incline lift can be installed to straight and curved stairways, they can travel 50m, are fully automated and have load capacity of 225kg.

 

Incline platform lift

Incline platform lift

The forest timber harvester is a forestry vehicle that cuts timber to length, delimbs and transports the tree. The harvester is a diesel powered vehicle that is wheel or tracked the harvester has a hydraulic drive arm that maneuvers out to the harvester head. The harvester is operated by a single person who can fell, process and transport the trees. The impact that the harvesters has is efficiency, safety and productivity.

Forest timber harvester

Forest timber harvester

3. Hydraulic in Aeronautics industry

Aircraft hydraulics enables energy to from one place to another safely and efficiently. A hydraulic system takes engine power and converts it to hydraulic power by a hydraulic pump. This power is transported throughout the plane by tubing through the aircraft. Hydraulic power can be reconverted to mechanical power by an actuating cylinder or turbine.

The following are devices operated by hydraulic systems in an aircraft, primary control boosters, landing gear, sweep back and forth of wings, opening and closing of doors and hatchways, shock absorbing systems, dive, landing, speed, and flap brakes.

The advantages of a hydraulic system are, that it is lighter in weight, reliable, easily maintained and it can develop practically unlimited force or torque.

  (Aeronautics Learning Laboratory for

science, 2004)

Aeronautical Hydraulic Shock