Antilock Brakes / Traction Control Systems: Description and Operation
System DescriptionABS Modulator-Control Unit Inputs and Outputs for 47P Connector
ABS/TCS Modulator-Control Unit Inputs And Outputs For 47P Connector:
ABS/TCS Modulator-Control Unit Inputs And Outputs For 47P Connector:
ABS Features
When the brake pedal is pressed while driving, the wheels can lock before the vehicle comes to a stop. In such an event, the maneuverability of the vehicle is reduced if the front wheels are locked, and the stability of the vehicle is reduced if the rear wheels are locked, creating an extremely unstable condition. The ABS precisely controls the slip rate of the wheels to ensure maximum grip force from the tires, and it thereby ensures maneuverability and stability of the vehicle.
The ABS calculates the slip rate of the wheels based on the vehicle speed and the wheel speed, then it controls the brake fluid pressure to attain the target slip rate.
TCS Features
The TCS provides low speed traction. When a drive wheel loses traction on a slippery road surface and starts to spin, the ABS/TCS control unit sends a brake signal to the modulator unit, which applies brake pressure to slow the spinning wheel. At that time, the ABS/TCS control unit sends an engine retard signal to the PCM to prevent damage to the transmission.
ABS Main Control
The ABS/TCS control unit detects the wheel speed based on the wheel sensor signals it receives, then calculates the vehicle speed based on the detected wheel speed. The control unit detects the vehicle speed during deceleration based on the rate of deceleration.
The ABS/TCS control unit calculates the slip rate of each wheel, and it transmits the control signal to the modulator unit solenoid valve when the slip rate is high.
The pressure reduction control has three modes: pressure reducing, pressure retaining, and pressure intensifying.
TCS Main Control
The ABS/TCS control unit controls the TCS based on signal inputs from the accelerator pedal position sensor, engine speed, shifter position, and the wheel sensors. In addition, the ABS/TCS control unit sends an engine retard request signal to the PCM if necessary. The pressure intensifying control has three modes: pressure intensifying, pressure retaining, and pressure reducing.
Self-Diagnosis
^ The ABS/TCS control unit is equipped with a main CPU and a monitor IC. They check each other for problems.
^ The CPUs also check the circuit of the system.
^ When a problem is detected by self-diagnosis. The ABS/TCS control unit turns on the appropriate indicator(s).
On-board Diagnosis Function
The ABS and TCS can be diagnosed with the Honda PGM Tester or HDS.
The ALB Checker cannot be used with this system. For air bleeding, and checking wheel sensor signals, use the Honda PGM Tester or HDS. See the tester user's manuals for specific operating instructions.
Modulator Unit
The modulator unit consists of the inlet solenoid valve, outlet solenoid valve, TCS Normally Open (NO) solenoid valve, TCS normally closed (NC) solenoid valve, reservoir, pump, pump motor, and the damping chamber. The modulator controls the caliper fluid pressure directly. It is a circulating-type modulator because the brake fluid circulates through the caliper, the reservoir, and the master cylinder. The hydraulic control has three modes: pressure intensifying, pressure retaining, and pressure reducing. The hydraulic circuit is an independent four channel type, one channel for each wheel.
ABS Control
Pressure intensifying mode
TCS NO valve open, TCS NC valve closed, inlet valve open, outlet valve closed.
Master cylinder fluid is pumped out to the caliper.
Pump Motor
When starting the pressure reducing mode, the pump motor is ON. When stopping ABS operation, the pump motor is OFF.
The reservoir fluid is pumped out by the pump through the damping chamber to the master cylinder.
Pressure retaining mode
TCS NO valve open, TCS NC valve closed, inlet valve closed, outlet valve closed.
Pressure reducing mode
TCS NO valve open, TCS NC valve closed, inlet valve closed, outlet valve open.
TCS Control
Pressure intensifying mode
TCS NO valve closed, TCS NC valve open, inlet valve open, outlet valve closed, pump motor ON.
The reservoir and master cylinder fluid is pumped out by the pump, through the damping chamber to the front caliper.
Pressure retaining mode
TCS NO valve open, TCS NC valve open, inlet valve closed, outlet valve closed, pump motor ON.
Front caliper fluid is retained by the inlet valve and outlet valve.
Pressure reducing mode
TCS NO valve closed, TCS NC valve open, front inlet valve closed, front outlet valve open, pump motor ON.
Caliper fluid flows through the outlet valve to the reservoir.
Wheel Sensor
The wheel sensors are the magnetic contactless type. The wheel sensors detect changing of magnetic polarity on the magnetic encoder. The ABS/TCS control unit calculates the wheel speed based on signals received from the wheel sensor.
When the wheel speed drops sharply below the vehicle speed, the outlet valve opens momentarily to reduce the caliper fluid pressure. The pump motor starts at this time. As the wheel speed is restored, the inlet valve opens momentarily to increase the caliper fluid pressure.
When the front wheel speed rises sharply above the vehicle speed, the TCS NC valve opens, the TCS NO valve closes, and the pump motor starts to intensify the front caliper fluid pressure. When the wheel speed drops, the front inlet valve closes momentarily to retain the front caliper fluid pressure. When the wheel speed drops further, the front outlet valve opens momentarily to reduce the front caliper fluid pressure.
Circuit Diagram
Circuit Diagram - ABS/TCS Components:
Circuit Diagram - ABS/TCS Components:
Circuit Diagram - ABS/TCS Components:
