Pressing the brake pedal while driving may lock the wheels before the vehicle comes to a halt. If the front wheels are blocked, the vehicle's maneuverability is reduced, if the rear wheels are blocked, the vehicle's stability is reduced. In both cases, a dangerous situation is created. The ABS system precisely controls the degree of wheel slip and ensures maximum tire grip on the road surface, thus helping to maintain the vehicle's agility and stability.
The ABS system calculates the wheel slip ratio based on vehicle speed and wheel speed, and then distributes brake fluid pressure to achieve the specified amount of slip.
ABS control unit
The ABS control unit determines the wheel speed based on the signals received from the wheel sensors, then calculates the vehicle speed based on the wheel speed. The control unit determines the vehicle speed during deceleration based on the intensity of the deceleration.
The ABS control unit calculates the degree of slip of each wheel and, if it is high, sends a control signal to the modulator solenoid valve.
The pressure regulator operates in three modes: pressure reduction, pressure holding and pressure increase.
Self-diagnosis function
The ABS control unit has a main central processing unit (CPU) and a sub-CPU that check each other when a fault occurs. The CPUs check the system circuit.
When a malfunction is detected by the central processor, the ABS control unit turns on the ABS and / or brake system indicator and stops the system.
Self-diagnosis can be divided into the following four categories:
- 1. Primary diagnosis
- 2. Without ABS control
- 3. With ABS control
- 4. When an alarm is given
OBD function
The ABS system can be diagnosed using the Honda PGM Tester. The ALB Checker cannot be used with this system. Use the Honda PGM Tester when bleeding and checking the wheel sensor signals. See the Honda PGM tester owner's manual for specific instructions.
ABS modulator
The ABS modulator consists of an inlet solenoid valve, an outlet solenoid valve, a reservoir, a pump motor and a damping chamber. The modulator directly reduces fluid pressure in the caliper. This is a circulation type modulator, because. brake fluid circulates through the caliper, reservoir and master cylinder.
The hydraulic regulator operates in three modes: pressure increase, pressure hold and pressure decrease.
The hydraulic circuit is an independent four-channel type, one channel for each wheel.
- Pressure boost mode: Inlet valve open, outlet valve closed. The fluid from the master cylinder is pumped to the caliper.
- Pressure holding mode: 1g Inlet valve closed, outlet valve closed. Fluid is held in the caliper by an inlet and outlet valve.
- Pressure reduction mode: Inlet valve closed, outlet valve open. Fluid from the caliper flows through the outlet valve into the reservoir.
- Motor operating mode: When entering the pressure reduction mode, the pump motor is running.
When the ABS system stops working, the pump motor does not work.
The fluid from the reservoir is pumped through the shock absorber chamber into the master cylinder.
Wheel sensor
Wheel sensors - magnetic, non-contact type. When the gear wheel rotates close to the magnetic coil of the wheel sensor, an alternating current is generated. The frequency of the alternating current varies depending on the speed of the wheel. The ABS control unit detects the frequency signal from the wheel sensor and thus determines the wheel speed (drawing on the right).
When the wheel speed suddenly drops below vehicle speed, the exhaust valve instantly opens and reduces fluid pressure in the caliper. At this point, the pump motor starts. When the wheel speed is restored, the intake valve instantly opens and increases fluid pressure in the caliper.
Electronic brake force distribution (EBD)
The ABS control unit regulates the distribution of the braking force between the front and rear wheels accordingly, depending on the load, by changing the carrying capacity or deceleration and applying the braking force when braking.
The ABS control unit calculates the required brake force distribution between the front and rear wheels from the difference in the speed of the front and rear wheels and sends a control signal to the modulator unit. The modulator unit adjusts the brake force on the rear wheels accordingly (scheme).
EBD regulator
When braking beyond a certain value, the inlet valve closes and holds the brake fluid pressure when the rear wheel speed drops below the front wheel speed. As the rear wheel speed drops further, the exhaust valve instantly opens and reduces brake fluid pressure. When the wheel speed is restored, the intake valve instantly opens and increases the pressure of the brake fluid (diagram).
During these operations, the pump motor is not running.