Brakes Training Animation, Automotive Appreciation- Part 8

Brakes Training Animation, Automotive Appreciation- Part 8


hi welcome to automotive appreciation part eight in this course we learned about braking systems disc brakes drum breaks vacuum assist system to agonal split brakes anti-lock brakes and ventilated discs when we get a car to move the next issue is how to stop it safely this is achieved with the brakes which convert kinetic energy into heat using a hydraulic braking system we start with disc brakes the discs are rotor is attached to the wheel and is surrounded by the brake caliper the brake pads are located on both sides of the disc with a hydraulic system when we apply a force to an incompressible liquid the force is transmitted throughout the fluid by adjusting the size of the Pistons we vary the available force and the distance traveled by the slave cylinder here we see the master cylinder with a reservoir for brake fluid on top when the pedal is pressed the piston moves forward and closes off the inlet from the tank the fluid is then pressurized and activates the slave cylinders when the brakes are applied the rubber seal deflects slightly when the brake is released the seal returns to its normal shape and moves the piston back slightly from the wheel if the fluid expands due to heat some can return to the reservoir if there’s a leak in the system the fluid will be chopped up from the reservoir excessive leakage would be detected by the level switch if there was a severe leak in the system we would lose all brakes but this is a single piston floating caliper self adjusting and self centering which is used in most cars cooling air is channeled over the brakes to assist with heat dissipation periodically the pads will require changing some parts have a metal wear indicator which makes a squealing noise when it contacts the disc all the cars have wires embedded in the pad when the pad wears out the rotor completes the electrical circuit and activates a warning light in the past the friction material was secured to the shoe with rivets but now a bonding adhesive is used drum brakes consist of an outer drum which the wheel is attached to and the inner brake shoes when the pedal is pressed the high-pressure fluid forces out the two Pistons in the brake cylinder pressing the shoes against the drum when this brake shoe contacts the drum there is a wedging action which helps to increase braking force but it also requires a spring to retract it when the brake pads where the adjuster is used to alter the bottom anchor position the hand brake or emergency brake is independent of the hydraulic system and usually cable operated drum brakes are more difficult to inspect service and cool under heavy braking the brakes will heat and become less effective this is called brake fade [Music] as this brakes do not have a wedging action similar to drum brakes considerable effort is required to operate them usually a car will have a braking power assist system this uses vacuum from the air intake system when the car is started there’s vacuum on both sides of the diaphragm when the pedal is pressed it first closes the valve to the vacuum side and then opens the valve to atmosphere now there’s a pressure differential across the diagram vacuum on one side atmospheric pressure on the other which assists with application of the brakes when the brake is released the valve to atmosphere is closed and the vacuum valve is opened restoring a vacuum on both sides the joules circuit breaking system there are two Pistons in the master cylinder when the brake pedal is pressed the piston moves forward pressurizing the fluid and also moves the second piston forward a similar high pressure would be exerted in both lines again assistance will be provided by the vacuum assist if we have a leak in the left-hand circuit its piston will move all the way to the left as there is no restriction the brake pedal will depress further but will eventually build pressure in the other circuit the division and the plastic storage tank ensures that we have a leak in one circuit will not lose all the fluid in the other circuit if we have a leak in the right circuit this piston will strike the other piston and build pressure in the healthy circuit as the brakes will only be applied to two wheels braking force would be compromised [Music] with diagonally split breaks two circuits are used circuit one front right and back left circuit two front left and back right if a leak occurs on one circuit the car can still be stopped with the other circuit a car has the optimum grip when the tire is in the verge of sliding on the road surface when the tire is sliding the grip is reduced dramatically to prevent the wheel from sliding an anti-lock braking system is used here we have a four channel four sensor ABS system where each wheel is controlled individually wheel speed is detected by a proximity sensor located beside a toothed wheel which sends a signal to the ECU between the master cylinder at wheel is a modulating valve imminent wheel lock can be determined by one wheel decelerating at a higher rate than the other three wheels or a wheel decelerating at a rate which is physically not possible without locking up when the ECU determines that a wheel is on the verge of locking the ECU activates the modulating valve and releases the brake pressure the modulator valve is normally in the open position and has no effect on the braking system at the top left there’s a connection to a high-pressure pump and at the top right there’s a connection back to the reservoir bottom right is the input from the master cylinder and bottom left is the outlet to the wheel when the ECU detects that a wheel is on the verge of locking it activates the ABS solenoid the solenoid moves to the left and allows through the high-pressure fluid from the pump the high-pressure fluid exerts a force in the piston and closes the valve against the spring pressure when the piston moves to the left it also allows more place for the brake fluid and reduces its pressure releasing the brakes when the solenoid is de-energized the high-pressure fluid is released back to the reservoir the spring force opens the valve and the additional rod volume also increases the fluid pressure and reapplies the brakes this cycle can happen 20 times per second and resolves in a pulsing sensation in the brake pedal ABS pulses the brakes on and off it prevents the wheels from locking the car will stop in a shorter distance and it can be steered to improve braking performance and avoid brake fade ventilated brake discs are used they consist of two disks separated by vanes or fins which allow air to circulate for cooling slots and holes also help to improve air circulation under heavy braking the weight of the car is transferred towards the front therefore the front wheels do most of the braking also when a car corners the weight would be transferred to the outside wheels when the weight is transferred to one side of the car there’s a possibility of the wheels on the other side locking EBD electronic brake-force distribution uses many of the ABS sensors to determine wheel speed and also the steering wheel position sensor to determine the intended path of the driver this data is processed by the ECU to determine if some of the wheels are lightly loaded the braking force is reduced on the lightly loaded wheels and increased on wheels which are braking most effectively in effect the EBD activates before an ABS situation arises and helps to improve stability and reduce stopping distance similar to other systems controlled by the ECU if a defect is detected in the ABS system the driver would be alerted via a warning light we hope you learned from automotive appreciation


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