1. Automotive Brake System

2. Brake Principle Purpose of a Brake Vehicle is accelerated
Large amount of energy still remain which is called Kinetic Energy
Tractive resistance
Friction
Energy supplied by the engine causes the vehicle speed to increase
The existence of kinetic energy can be seen when a vehicle is moving and neutral gear is selected. The car does not immediately stop; instead it travels for a considerable distance before become stationary. 2

3. CONVERT KINETIC ENERGY TO HEAT ENERGY
Brake Principle 2
In order to drastically reduce the stopping distance of a vehicle , BRAKE SYSTEM is needed to convert the energy at a faster rate.
CONVERT KINETIC ENERGY TO HEAT ENERGY 3

4. Brake Principle 3
The speed of energy conversion controls the Rate of Deceleration
Brake Force Padel
Heat
Kinetic Energy
Road force at driving wheel
Heat generation at the brake is obtained by rubbing a fixed pad or shoe against a rotating object driven by the motion of the vehicle 4

5. Brake Principle 4 The brake engineer has two challenges:
Create enough deceleration to stop the car as quickly as the driver wishes, without exceeding the drivers comfort level with regard to pedal effort or pedal travel.
2. Manage the resulting heat energy so as not to damage the brake system or the rest of the vehicle.
An interesting observation is that a typical car of this size has an engine with about KW ( HP). This means that the brakes have to deal with about TWICE THE POWER of what the engine puts out. 5

6. Brake Principle 5
Since the kinetic energy of a moving vehicle is a function of the square of the speed, the speed from which you wish to stop a vehicle is much more important than the mass of the vehicle. When selecting a brake system the performance of the powertrain must be taken into consideration. 6

7. Brake Principle 6
Weight transfer increases the load on the front wheels while the load on the rear wheels is reduced. 7

8. Brake Principle 7 When the limit is reached…….the wheel starts to skid
At that moment extra applied at brake pad is useless. No benefit is reducing the stopping distance
On icy surface …………light pressure can lock-up the brake system
Important information: adhesion between the tyre & road is the main factor that control the minimum stopping distance
Road adhesion is affected by 1. type of road surface
2. Condition of road surface
3. Design of tread & composition of
tread material and depth of tread 8

9. Brake Principle 8 Equation involve:-
The equation for kinetic energy , that is energy of motion may be given by:-
The work done in bringing the vehicle to rest is given by :-
When braking a moving vehicle to standstill, the work done by the brake must be equal to initial kinetic energy possessed by the vehicle
Where F is an average brake force 9

10. Example ANSWER : A) 40KJ. B) 2KN
A car of mass 800kg is travelling at 36km/h. Determine the following.
The kinetic energy it possesses
The average braking force to bring it to rest in 20 meters.
ANSWER : A) 40KJ. B) 2KN 10

11. Type of Brake
Generally all motors vehicle must be equipped with at least two mutually independent brake systems.
Service Brake System – primarily serve to reduce vehicle speed
Emergency brake system – Used to stop a vehicle in the event of a malfunction
Parking brake system – to prevent unintentional rolling of a stationary vehicle ( Hand Brake) 11

12. Brake System Requirement
Wheel brake must meet the following requirements
Uniform effectiveness
Smooth, graduated response
Resistance to contamination & corrosion
Extreme reliability
Durability
Resistance to wear
Ease of maintenance 12

13. General Brake System
1. Drum Brake
2. Disc Brake 13

14. Braking Mechanism When you apply the brakes,
brake fluid is forced under
pressure into the wheel
cylinder, which in turn
pushes the brake shoes
into contact with the
machined surface on the
inside of the drum.  When
the pressure is released,
return springs pull the
shoes back to their rest
position.   As the brake linings wear, the shoes must travel a greater distance to reach the drum.  When the distance reaches a certain point, a self-adjusting mechanism automatically reacts by adjusting the rest position of  the shoes so that they are closer to the drum. 14

15. Master Cylinder
To increase safety, most modern car brake systems are broken into two circuits, with two wheels on each circuit. If a fluid leak occurs in one circuit, only two of the wheels will lose their brakes and your car will still be able to stop when you press the brake pedal.
The master cylinder supplies pressure to both circuits of the car. It is a remarkable device that uses two pistons in the same cylinder in a way that makes the cylinder relatively failsafe. The combination valve warns the driver if there is a problem with the brake system, and also does a few more things to make your car safer to drive. 15

16. Master Cylinder operation
When brake pedal is pressed - primary piston closes off the primary compensating port to develop pressure in primary circuit. Fluid pressure created in front of the primary piston forces against rear of secondary piston, so that it also moves.
When secondary piston moves, it covers secondary compensating port and pressure develop in secondary circuit.
As brake pedal continues to be pressed , both piston will moved to displace fluid to their circuits and apply the brakes. 16

17. Master Cylinder operation
When pedal is released:
Recuperation – action of the piston to return to its position that creates low pressure in front of the piston so that momentarily pressure in reservoir is higher than the pressure in cylinder. Thus cause small amount of fluid to flow from reservoir to the front part of cylinder.
This keep the cylinder full of fluid ready for next brake application. 17

18. Master Cylinder Mechanism
When the first circuit leaks, the pressure between the primary and secondary cylinders is lost. This causes the primary cylinder to contact the secondary cylinder. Now the master cylinder behaves as if it has only one piston. The second circuit will function normally, but the driver will have to press the pedal further to activate it. Since only two wheels have pressure, the braking power will be severely reduced.
Loss of brake fluid will increase pedal travel and brakes will operate on two wheels only 18

19. Drum Brake 1 19

20. Drum Brake 2
Figure shows that as the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force.
The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. But, because of the wedging action, the shoes must be pulled away from the drum when the brakes are released. This is the reason for some of the springs. Other springs help hold the brake shoes in place and return the adjuster arm after it actuates. 20

21. Drum Brake 3
In the figure, you can see that as the pad wears down, more space will form between the shoe and the drum. Each time the car stops, the shoe is pulled tight against the drum. When the gap gets big enough, the adjusting lever rocks enough to advance the adjuster gear by one tooth. The adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns, lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can advance again, so it always keeps the shoes close to the drum. 21

22. Drum Brake 4 22

23. Disk Brake 1
A disc brake system consists of a brake rotor, a brake caliper and brake pads. When the brake pedal is applied, pressurized hydraulic fluid squeezes the brake pad friction material against the surface of the rotating brake disc.
The result of this contact produces friction which enables the vehicle to slow down or stop.
The disc brake is a lot like the brakes on a bicycle. Bicycle brakes have a caliper, which squeezes the brake pads against the wheel. In a disc brake, the brake pads squeeze the rotor instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down. 23

24. Disk Brake 2
Vented disc brakes have a set of vanes, between the two sides of the disc, that pumps air through the disc to provide cooling
The single-piston floating-caliper disc brake is self-centering and self-adjusting. The caliper is able to slide from side to side so it will move to the center each time the brakes are applied. Also, since there is no spring to pull the pads away from the disc, the pads always stay in light contact with the rotor (the rubber piston seal and any wobble in the rotor may actually pull the pads a small distance away from the rotor).
In cars with disc brakes on all four wheels, an emergency brake has to be actuated by a separate mechanism than the primary brakes in case of a total primary brake failure. Most cars use a cable to actuate the emergency brake. 24

25. Valves for Brake System
The valve does the job of three separate devices:
The metering valve
The pressure differential switch
The proportioning valve
Metering Valve
The metering valve section of the combination valve is required on cars that have disc brakes on the front wheels and drum brakes on the rear wheels. You know that the disc brake pad is normally in contact with the disc, while the drum brake shoes are normally pulled away from the drum. Because of this, the disc brakes are in a position to engage before the drum brakes when you push the brake pedal down.
The metering valve compensates for this, making the drum brakes engage just before the disc brakes. The metering valve does not allow any pressure to the disc brakes until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in.
Having the rear brakes engage before the front brakes provides a lot more stability during braking. Applying the rear brakes first helps keep the car in a straight line, much like the rudder helps a plane fly in straight line. 25

26. Valves for Brake System
Pressure Differential Switch The pressure differential valve is the device that alerts you if you have a leak in one of your brake circuits. The valve contains a specially shaped piston in the middle of a cylinder. Each side of the piston is exposed to the pressure in one of the two brake circuits. As long as the pressure in both circuits is the same, the piston will stay centered in its cylinder. But if one side develops a leak, the pressure will drop in that circuit, forcing the piston off-center. This closes a switch, which turns on a light in the instrument panel of the car. The wires for this switch are visible in the picture shown. 26

27. Valves for Brake System
Proportioning Valve The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi. 27

28. Vacuum Booster
Back in the day, when most cars had drum brakes, power brakes were not really necessary -- drum brakes naturally provide some of their own power assist. Since most cars today have disk brakes, at least on the front wheels, they need power brakes. Without this device, a lot of drivers would have very tired legs.
The vacuum booster is a metal canister that contains a clever valve and a diaphragm. A rod going through the center of the canister connects to the master cylinder’s piston on one side and to the pedal linkage on the other. 28

29. Vacuum Booster 2
The photo above shows the check valve, which is a one-way valve that only allows air to be sucked out of the vacuum booster. If the engine is turned off, or if a leak forms in a vacuum hose, the check valve makes sure that air does not enter the vacuum booster. This is important because the vacuum booster has to be able to provide enough boost for a driver to make several stops in the event that the engine stops running -- you certainly don't want to lose brake function if you run out of gas on the highway. 29

30. Vacuum Booster 3 30

31. ABS 1
The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. If you have been stuck on ice, you know that if your wheels are spinning you have no traction. This is because the contact patch is sliding relative to the ice. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways: You'll stop faster, and you'll be able to steer while you stop.
There are four main components to an ABS system:
Speed sensors
Pump
Valves
Controller 31

32. ABS 2
Speed Sensors The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.
Valves There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:
In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
In position three, the valve releases some of the pressure from the brake.
Pump Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.
Controller The controller is a computer in the car. It watches the speed sensors and controls the valves. 32

33. ABS 3
ABS at Work
The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second. 33

34. EBD and ESC
Electronic brakeforce distribution or EBD or EBFD is an automobile brake technology that automatically varies the amount of force applied to each of a vehicle's brakes, based on road conditions, speed, loading, etc. Always coupled with anti-lock braking systems, EBD can apply more or less braking pressure to each wheel in order to maximize stopping power whilst maintaining vehicular control.
EBD may work in conjunction with ABS and Electronic Stability Control ("ESC") or Vehicle Stability Control (VSC) to minimize yaw accelerations during turns. ESC compares steering wheel angle to vehicle turning rate using a yaw rate sensor. "Yaw" is the vehicle's rotation around its vertical center of gravity (turning left or right). If the yaw sensor detects more/less yaw than the steering wheel angle should create, the car is understeering or oversteering and ESC activates one of the front or rear brakes to rotate the car back into its intended course. For example, if a car is making a left turn and begins to understeer (the car plows forward to the outside of the turn) ESC activates the left rear brake, which will help turn the car left. The sensors are so sensitive, and the actuation is so quick that the system may correct direction before the driver reacts. ABS helps prevent wheel lock-up and EBD helps apply appropriate brake force to make ESC work effectively. 34