Anti-Lock Braking Mode

ABS-VI has been designed to improve the controllability and steerability of a vehicle during braking that would cause one or more wheels to lock up. ABS-VI accomplishes this objective by controlling the hydraulic pressure applied to each wheel brake. Anti-lock braking occurs only when the brakelight switch is closed and the EBCM determines one or more wheels is about to lose traction during braking. The EBCM will then control the hydraulic modulator to change the brake pressures several times each second to keep the wheel(s) from locking and provide the driver with maximum vehicle controllability. The result is greatly improved braking, enabling the driver to more easily maintain steerability and to bring the vehicle to a controlled stop. ABS-VI provides effective braking and directional control over a wide range of road surfaces and driving conditions.

If any wheel(s) begins to approach lock-up, the EBCM will control the 3 motors and 2 solenoids, appropriately, to control brake pressure to the affected wheel(s). During front wheel ABS operation, the solenoids are turned ON to isolate brake pressure path to the wheel. The EBCM then provides controlled current to the motors to regulate the speed and amount of movement. As the motors move backward, the piston follows the nut downward, allowing the check valve to seat. The brake pressure to the wheel is now a function of the controlled volume within the piston chamber.

To reduce brake pressure, the motor drives the nut further downward. To reapply or increase brake pressure, the motor drives the nut and piston upward. If ABS was entered during low brake pressure (such as on ice) and dry pavement is then encountered during reapply, the piston is driven all the way to the top. This results in the unseating of the check valve, and a return to base brakes until sufficient brake pressure exists to cause the wheel to approach lock-up again. At this point, the ABS cycle would start again. This process can occur in less than one second if the driver is pressing firmly on the brake pedal.

Total brake pressure during ABS is limited to the brake pressure present when ABS was entered. Also, any time wheel brake pressure exceeds the brake pressure at the master cylinder (caused by reduced force on the brake pedal), the check valve unseats and a small volume of brake fluid is returned to the master cylinder. When ABS is no longer required, the pistons are returned to home position. The solenoids on the front channels are simultaneously opened to again provide a redundant brake fluid path.

The rear channel operates in a similar manner except no solenoid is used. Both rear brake pressures are controlled by the same motor and both rear brake pressures are controlled together. If either rear wheel begins to lock-up, brake pressure to both rear wheels is reduced to maximize vehicle stability.