5A4-2 ABS/ASR
ABS/ASR System
Description of Function and Operation
Description of ABS/ASR
ABS (Anti-lock Brake System) and ASR (Anti-Slip Reg-
ulator) are the system to prevent the wheels from lock-
ing and wheel spin, and to assure stability and steering
ability of the vehicle.
When a malfunction occurs in the system, fail-safe de-
activate the ABS and ASR, and the warning lamp comes
on. Also, the self-diagnosis function is equipped to im-
prove serviceability.
Contents of ABS Control
The ABS controls the brake fluid pressure in the way
that the electronic hydraulic control unit (EHCU) hold/
decrease/increase the brake fluid pressure during brake
operation, based on the signal transmitted from the
wheel speed sensor.
The EHCU calculate the wheel speed, the wheel accel-
eration speed, and the vehicle speed based on the sig-
nal transmitted from the wheel speed sensor. When
brake is applied while the vehicle is running, the wheel
speed abruptly goes down, and the difference from the
vehicle speed becomes more than specified; the EHCU
judges that the wheel turns toward being locked, and it
performs holding of the brake fluid pressure.
When the vehicle speed further goes down, the system
judges that the wheel is about to be locked, and it per-
forms decreasing of the brake fluid pressure. Conse-
quently, when the system judges that wheel lock is
avoided, it performs holding and increasing of the brake
fluid pressure repeatedly.