Antilock Brake System Description

TEVES MARK 20e SYSTEM DESCRIPTION
This information covers the physical and operational descriptions, and the diagnostic service procedures for the Teves Mark 20e Antilock Brake System. It is the only antilock brake system (ABS) available on this vehicle.

The purpose of the antilock brake system is to prevent wheel lockup under braking conditions on virtually any type of road surface. Antilock braking is desirable because a vehicle that is stopped without locking the wheels retains directional stability and some steering capability. This allows the driver to retain greater control of the vehicle during braking.

All vehicles equipped with ABS use Electronic Variable Brake Proportioning (EVBP) to balance front-to-rear braking when the brakes are applied in the partial braking range.

A Controller Antilock Brake (CAB) module is used to monitor wheel speeds and to modulate (control) hydraulic pressure in each brake channel when ABS is actuated. The CAB also provides a vehicle speed signal (VSS) to the powertrain control module via PCI BUS.

During a non-ABS stop, the system functions as a standard diagonally split configuration. The primary hydraulic system supplies brake fluid pressure to the right front and left rear brakes, and the secondary hydraulic system supplies the right rear and left front brakes. A conventional proportioning valve is not used. This system uses the existing ABS solenoids to replace and perform the same functions that the proportioning valves do. The CAB has a special software program that monitors the wheel speeds and when certain criteria are met the software will enable the solenoids to perform the same brake fluid management control as the proportioning valves.

During an ABS stop, the system still uses the diagonal hydraulic split; however, the brake system pressure is further split into four control channels. During ABS operation, all wheels are controlled independently and are on four separate control channels.

During an antilock stop, "wheel lock-up" does not necessarily mean that the wheel has locked, it means only that the wheel is turning slower than the vehicle speed. This is called "wheel slip" and is indicated as a percentage. 0% slip means that the wheel is rolling free and 100% slip means that the wheel is locked. The antilock system maintains an average of approximately 20% wheel slip.

It is important to remember that the antilock brake system does not shorten the vehicle stopping distance under all driving conditions, but provides improved control of the vehicle while stopping. Vehicle stopping distance is still dependent on vehicle speed, weight, tires, road surface, and other factors.