Anti-lock-braking system
An anti-lock braking system, or ABS (from the German, Antiblockiersystem) is a safety system on motor vehicles which prevents the wheels from locking while braking.
A rotating road wheel allows the driver to maintain steering control under heavy braking, by preventing a locked wheel or skid, and allowing the wheel to continue to forward roll and create lateral control, as directed by driver steering inputs. Disadvantages of the system include increased braking distances under some limited circumstances (ice, snow, gravel, soft surfaces), and the creation of a "false sense of security" among drivers who do not understand the operation, and limitations of ABS.
History
Anti-lock braking systems were first developed for aircraft in 1929, by the French automobile and aircraft pioneer, Gabriel Voisin, as threshold braking an airplane is nearly impossible. An early system was Dunlop's Maxaret system, introduced in the 1950s and still in use on some aircraft models.
A fully mechanical system saw limited automobile use in the 1960s in the Ferguson P99 racing car, the Jensen FF and the experimental all wheel drive Ford Zodiac, but saw no further use; the system proved expensive and, in automobile use, somewhat unreliable. However, a limited form of anti-lock braking, utilizing a valve which could adjust front to rear brake force distribution when a wheel locked, was fitted to the 1964 Austin 1800.
How Antilock Brake Systems Work
ABS on your vehicle you should always refer to the specific service and repair manuals for your vehicle.
The ABS is a four-wheel system that prevents wheel lock-up by automatically modulating the brake pressure during an emergency stop. By preventing the wheels from locking, it enables the driver to maintain steering control and to stop in the shortest possible distance under most conditions.
During normal braking, the ABS and non-ABS brake pedal feel will be the same. During ABS operation, a pulsation can be felt in the brake pedal, accompanied by a fall and then rise in brake, pedal height and a clicking sound.
Vehicles with ABS are equipped with a pedal-actuated, dual-brake system.
An anti-lock braking system, or ABS (from the German, Antiblockiersystem) is a safety system on motor vehicles which prevents the wheels from locking while braking.
A rotating road wheel allows the driver to maintain steering control under heavy braking, by preventing a locked wheel or skid, and allowing the wheel to continue to forward roll and create lateral control, as directed by driver steering inputs. Disadvantages of the system include increased braking distances under some limited circumstances (ice, snow, gravel, soft surfaces), and the creation of a "false sense of security" among drivers who do not understand the operation, and limitations of ABS.
History
Anti-lock braking systems were first developed for aircraft in 1929, by the French automobile and aircraft pioneer, Gabriel Voisin, as threshold braking an airplane is nearly impossible. An early system was Dunlop's Maxaret system, introduced in the 1950s and still in use on some aircraft models.
A fully mechanical system saw limited automobile use in the 1960s in the Ferguson P99 racing car, the Jensen FF and the experimental all wheel drive Ford Zodiac, but saw no further use; the system proved expensive and, in automobile use, somewhat unreliable. However, a limited form of anti-lock braking, utilizing a valve which could adjust front to rear brake force distribution when a wheel locked, was fitted to the 1964 Austin 1800.
How Antilock Brake Systems Work
ABS on your vehicle you should always refer to the specific service and repair manuals for your vehicle.
The ABS is a four-wheel system that prevents wheel lock-up by automatically modulating the brake pressure during an emergency stop. By preventing the wheels from locking, it enables the driver to maintain steering control and to stop in the shortest possible distance under most conditions.
During normal braking, the ABS and non-ABS brake pedal feel will be the same. During ABS operation, a pulsation can be felt in the brake pedal, accompanied by a fall and then rise in brake, pedal height and a clicking sound.
Vehicles with ABS are equipped with a pedal-actuated, dual-brake system.
The hydraulic system consists of the following:
· ABS hydraulic control valves and electronic control unit
· Power brake booster
· Brake master cylinder
· Necessary brake tubes and hoses
The anti-lock brake system consists of the following components:
· Hydraulic Control Unit (HCU).
· Anti-lock brake control module.
· Front anti-lock brake sensors / rear anti-lock brake sensors.
Anti-lock Brake System (ABS) operates as follows:
· When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the HCU inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the HCU, then through the outlet ports of the HCU to each wheel.
· The primary (rear) circuit of the brake master cylinder feeds the front brakes.
· The secondary (front) circuit of the brake master cylinder feeds the rear brakes.
· If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.
· The anti-lock brake control module then looks at the anti-lock brake sensor signal from the affected wheel again.
· If that wheel is still decelerating, it opens the solenoid valve for that circuit.
· Once the affected wheel comes back up to speed, the anti-lock brake control module returns the solenoid valves to their normal condition allowing fluid flow to the affected brake.
· The anti-lock brake control module monitors the electromechanical components of the system.
· Malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power-assisted braking remains.
· Loss of hydraulic fluid in the brake master cylinder will disable the anti-lock system.
· The 4-wheel anti-lock brake system is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will perform a preliminary self-check on the anti-lock electrical system indicated by a three second illumination of the yellow ABS wanting indicator.
· During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.
· Each time the vehicle is driven, as soon as vehicle speed reaches approximately 20 km/h (12 mph), the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time, a mechanical noise may be heard. This is a normal function of the self-check by the anti-lock brake control module.
· When the vehicle speed goes below 20 km/h (12 mph), the ABS turns off.
· Most malfunctions of the anti-lock brake system and traction control system, if equipped, will cause the yellow ABS warning indicator to be illuminated.
Traction control
The ABS equipment may also be used to implement traction control system (TCS, ASR) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. Manufacturers often offer this as a separately priced option even though the infrastructure is largely shared with ABS. More sophisticated versions of this can also control throttle levels and brakes simultaneously.
Mercedes-Benz was the first to offer this electronic traction control system in 1985.
· ABS hydraulic control valves and electronic control unit
· Power brake booster
· Brake master cylinder
· Necessary brake tubes and hoses
The anti-lock brake system consists of the following components:
· Hydraulic Control Unit (HCU).
· Anti-lock brake control module.
· Front anti-lock brake sensors / rear anti-lock brake sensors.
Anti-lock Brake System (ABS) operates as follows:
· When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the HCU inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the HCU, then through the outlet ports of the HCU to each wheel.
· The primary (rear) circuit of the brake master cylinder feeds the front brakes.
· The secondary (front) circuit of the brake master cylinder feeds the rear brakes.
· If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.
· The anti-lock brake control module then looks at the anti-lock brake sensor signal from the affected wheel again.
· If that wheel is still decelerating, it opens the solenoid valve for that circuit.
· Once the affected wheel comes back up to speed, the anti-lock brake control module returns the solenoid valves to their normal condition allowing fluid flow to the affected brake.
· The anti-lock brake control module monitors the electromechanical components of the system.
· Malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power-assisted braking remains.
· Loss of hydraulic fluid in the brake master cylinder will disable the anti-lock system.
· The 4-wheel anti-lock brake system is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will perform a preliminary self-check on the anti-lock electrical system indicated by a three second illumination of the yellow ABS wanting indicator.
· During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.
· Each time the vehicle is driven, as soon as vehicle speed reaches approximately 20 km/h (12 mph), the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time, a mechanical noise may be heard. This is a normal function of the self-check by the anti-lock brake control module.
· When the vehicle speed goes below 20 km/h (12 mph), the ABS turns off.
· Most malfunctions of the anti-lock brake system and traction control system, if equipped, will cause the yellow ABS warning indicator to be illuminated.
Traction control
The ABS equipment may also be used to implement traction control system (TCS, ASR) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. Manufacturers often offer this as a separately priced option even though the infrastructure is largely shared with ABS. More sophisticated versions of this can also control throttle levels and brakes simultaneously.
Mercedes-Benz was the first to offer this electronic traction control system in 1985.
