anti-lock braking system

Editor's Notes

• #4: Conventional braking system – Wheel lockup during braking causes skidding which in turn cause a loss of traction and vehicle control. Reduces the steering ability to change direction- The vehicle slides out of control. With Anti-lock Braking system (ABS), the driver can brake hard, take the evasive action and still be in control of the vehicle in any road condition at any speed and under any load
• #5: Anti-lock braking system (ABS) is an automobile safety system prevent the wheels of a vehicle locking as brake pedal pressure is applied - often suddenly in an emergency or short stopping distance. This enables the driver to have steering control, preventing skidding and loss of traction.
• #6: 1929 :- ABS was first developed for aircraft by the French automobile and aircraft pioneer Gabriel Voisin, as threshold braking on airplanes is nearly impossible. 1936: German company Bosch is awarded a patent an “Apparatus for preventing lock-braking of wheels in a motor vehicle”. 1936-: Bosch and Mercedes-Benz partner - R&D into ABS. 1972: WABCO partners with Mercedes-Benz developing first ABS for trucks. 1978: First production-line installation of ABS into Mercedes and BMW vehicles. 1981: 100,000 Bosch ABS installed. 1985: First ABS installed on US vehicles.
• #7: 1986: 1M Bosch ABS installed. 1987: Traction control - in conjunction with ABS – used on passenger vehicles. 1989: ABS hydraulic unit combined with standard hydraulic brake unit 1992: 10M Bosch ABS installed. 1995: Electronic Stability - in conjunction with ABS and TCS - for passenger cars. 1999: 50M Bosch ABS installed. 2000: 6 of 10 new cars on the road are ABS equipped. 2003: 100M Bosch ABS installed. Nowadays:- Almost all new cars have ABS.
• #12: When the brake pedal is depressed during driving, the wheel speed decreases and the vehicle speed does as well. The decrease in the vehicle speed, however, is not always proportional to the decrease in the wheel speed. The non-correspondence between the wheel speed and vehicle speed is called “slip” and the magnitude of the slip is expressed by the “slip ratio” which is defined as follows: Slip ratio = (Vehicle speed – Wheel speed)/Vehicle speed × 100% When the slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed. When it is 100%, the wheels are completely locking (rotating at a zero speed) while the vehicle is moving.
• #17: ABS brake system are Integrated An integrated system has the master cylinder and control valve assembly made together. Nonintegrated A nonintegrated has the master cylinder and control valve assembly made separate.
• #18: ABS Controller; the brains of the system.  ABS Controllers are a computer that reads the inputs and then controls the system to keep the wheels from locking up and skidding. ABS Speed Sensors; there are generally one on each wheel (sometimes they are located on the differential).  It detects a change in acceleration in the longitudinal direction of the vehicle and outputs it to the ABSCM as a voltage signal ABS Modulator/Valves; some system have separate valves for each wheel with a modulator to control them.  Other systems they are combined.  In either case they work with the controller and the pump to add or release pressure from the individual wheels brakes to control the braking ABS Pumps; since the ABS modulator/valves can release pressure from the individual wheels brakes there needs to be a way to restore the pressure when required.  That is what the ABS pumps job is. When the pump is cycling, the driver may experience a slight pedal vibration.  This cycling is happening many times per second and this slight vibration is natural.
• #22: Play video
• #25: During pressure increase mode of operation fluid is allowed to flow through both solenoids to the brake caliper
• #26: During Pressure Hold mode of operation both solenoids are closed and no additional fluid is allowed to flow to brake calipers.
• #27: During Pressure Vent mode the pressure increase solenoid is closed. The Vent solenoid opens allowing fluid to vent into an accumulator chamber
• #29: Four-channel, four-sensor ABS This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force. Three-channel, three-sensor ABS This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle. One-channel, one-sensor ABS This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
• #31: ESC incorporates yaw rate control into the anti-lock braking system (ABS). Yaw is a rotation around the vertical axis; i.e. spinning left or right Anti-lock brakes enable ESC to brake individual wheels Steering wheel angle sensor: determines the driver's intended rotation; i.e. where the driver wants to steer. This kind of sensor is often based on AMR-elements. Yaw rate sensor: measures the rotation rate of the car; i.e. how much the car is actually turning. The data from the yaw sensor is compared with the data from the steering wheel angle sensor to determine regulating action. Lateral acceleration sensor: often an accelerometer Wheel speed sensor: measures the wheel speed ESC uses a hydraulic modulator to assure that each wheel receives the correct brake force.
• #33: ESC intervenes only when it detects a probable loss of steering control, i.e. when the vehicle is not going where the driver is steering.[27] This may happen, for example, when skidding during emergency evasive swerves, understeer or oversteer during poorly judged turns on slippery roads, or hydroplaning. ESC may also intervene in an unwanted way during high-performance driving, because steering input may not always be directly indicative of the intended direction of travel (i.e. controlled drifting). ESC estimates the direction of the skid, and then applies the brakes to individual wheels asymmetrically in order to create torque about the vehicle's vertical axis, opposing the skid and bringing the vehicle back in line with the driver's commanded direction. Additionally, the system may reduce engine power or operate the transmission to slow the vehicle down. ESC can work on any surface, from dry pavement to frozen lakes.[28][29] It reacts to and corrects skidding much faster and more effectively than the typical human driver, often before the driver is even aware of any imminent loss of control.[30] In fact, this led to some concern that ESC could allow drivers to become overconfident in their vehicle's handling and/or their own driving skills. For this reason, ESC systems typically inform the driver when they intervene, so that the driver knows that the vehicle's handling limits have been approached. Most activate a dashboard indicator light and/or alert tone; some intentionally allow the vehicle's corrected course to deviate very slightly from the driver-commanded direction, even if it is possible to more precisely match it.[31]
• #36: When the traction control computer (often incorporated into another control unit, such as the ABS module) detects one or more driven wheels spinning significantly faster than another, it invokes the ABS electronic control unit to apply brake friction to wheels spinning with lessened traction
• #37: Generally, the main hardware for traction control and ABS are mostly the same. In many vehicles traction control is provided as an additional option to ABS. Each wheel is equipped with a sensor which senses changes in its speed due to loss of traction. The sensed speed from the individual wheels is passed on to an electronic control unit (ECU). The ECU processes the information from the wheels and initiates braking to the affected wheels via a cable connected to an automatic traction control (ATC) valve. In all vehicles, traction control is automatically started when the sensors detect loss of traction at any of the wheels.
• #39: System damage - A variety of factors can cause the system to be less effective, and can present with everything from shuddering of the vehicle to loud noises while trying to stop
• #40: Statistics show that approximately 40 % of automobile accidents are due to skidding. Skidding , vehicle instability, steer inability and long distance stopping, These problems commonly occur on vehicle with conventional brake system which can be avoided by adding devices called ABS. If there is an ABS failure, the system will revert to normal brake operation. Normally the ABS warning light will turn on and let the driver know there is a fault.