Four Wheel Anti-Lock Brake System (ABS) for Four-Wheel Drive Vehicles

When vehicles equipped with part-time four-wheel drive (4WD) are in the 4WD phase, the front and rear drive shafts are rigidly engaged. This rigid engagement of these drive shafts requires that the sum of front right and left wheel speeds equal the sum of the rear right and left wheel speeds. However, with vehicles equipped with standard anti-lock brake system (ABS) which control the front/rear wheels independently, the front/rear wheels rotation sums may become unequal during braking due to the ABS's independent modulation of the front/rear wheels. This causes the torque interference of the drive shafts and unanticipated torque transfer over the brake torque. Consequently, the ABS control of wheel slippage becomes difficult.

AKEBONO proposes one of the solutions to this problem using a diagonal 2 channel, 4 sensor ABS arrangement where each channel monitors diagonal front and rear wheel speeds. This arrangement provides effective modulation of all four wheels' speeds and minimizes the potential torsional vibration and torque transfer problems of part-time 4WD equipped with ABS.