Antilock Brakes / Traction Control Systems: Description and Operation

BRAKE CONTROL: ELECTRONICALLY CONTROLLED BRAKE SYSTEM: SYSTEM DIAGRAM

SYSTEM DIAGRAM






















BRAKE CONTROL: ELECTRONICALLY CONTROLLED BRAKE SYSTEM: SYSTEM DESCRIPTION

SYSTEM DESCRIPTION

1. VDIM (Vehicle Dynamics Integrated Management) DESCRIPTION
(a) This vehicle is equipped with VDIM. It is a concept of vehicle motion control that integrates brake control, drive force control and steering control.
(b) Conventional vehicles use a combination of independent functions such as ABS, TRAC, VSC and EPS. However, VDIM integrates these systems to improve "drive, turn and stop," the motion performance of the vehicle in other words.
(c) In conventional vehicles, control starts at the limit of the vehicle. However, VDIM exercises control before the limit is reached, creating a smooth vehicle response. This expands the limits of the vehicle, and increases driving pleasure.





(d) The VDIM manages all functions, such as the ABS with EBD, the BA, the TRAC, and the VSC. It is operated by the Electronically Controlled Brake system, which regulates a brake fluid pressure. The regenerative brake cooperative control and steering cooperative control functions are also available. Thus the VDIM is able to perform the comprehensive management.
(e) Conventional brake control systems begin to control either the braking or motive force in order to stabilize the vehicle motion when it becomes unstable due to loss of tire traction. In contrast, in order to maintain stable vehicle control, the VDIM commences controlling the brake, hybrid and steering systems in accordance with changes in balance before the vehicle becomes unstable. As a result, smooth vehicle control is achieved.
(f) Conventional brake control systems manage all related functions, such as the ABS with EBD, the BA, the TRAC and the VSC independently, according to the vehicle dynamics. In contrast, the VDIM provides smooth control by seamlessly integrating all those functions.
2. ELECTRONICALLY CONTROLLED BRAKE SYSTEM DESCRIPTION
(a) The system detects the degree of brake pedal operation with a brake pedal stroke sensor and two master cylinder pressure sensors, and calculates the optimum hydraulic brake force. The hydraulic pressure source is adjusted based on this so that the optimum hydraulic control is independently performed on all four wheels.
(b) Meanwhile, the Electronically Controlled Brake system performs control of the normal brakes, ABS, TRAC, VSC and BA in accordance with the operations of the driver.
(c) There is a hydraulic backup mechanism that applies master cylinder pressure generated by human power to the wheel cylinder when the brake control stops. In addition, as a fail safe mechanism, when the brake control is malfunctioning, the system excludes the malfunctioning sections and continues to perform brake control on the normal sections. A power backup unit (brake control power supply) is also used to ensure a stable supply of power to the system.





3. FUNCTION DESCRIPTION
HINT: The yaw rate sensor and acceleration sensor are combined in a single unit. This unit communicates with the skid control ECU via CAN communication.

(a) ABS (Anti-lock Brake System)
The ABS helps prevent the wheels from locking when the brakes are applied suddenly and firmly or applied on a slippery surface.




(1) Operation description
The skid control ECU detects wheel lock based on speed signals it receives from the wheel speed sensors. Based on this information, the skid control ECU controls the solenoid valves. The solenoid valves are used to prevent wheel lock by controlling the hydraulic pressure applied to the brakes at each wheel. The ABS warning light will come on when the system is malfunctioning.
(b) EBD (Electronic Brake force Distribution)
The EBD control utilizes ABS, performing proper brake force distribution between the front and rear wheels in accordance with driving conditions.
When braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain vehicle behavior.




(1) Operation description
The skid control ECU receives a speed signal from each wheel speed sensor, and uses these signals to detect locking of the wheels. The ECU uses this information in order to determine appropriate control of the solenoid valves.
The solenoid valves control the hydraulic pressure applied to the brake cylinder at each wheel. In this way, the solenoid valves are used to control the brake power split between the front and rear, and left and right wheels.
The BRAKE warning light will come on if there is a malfunction in the EBD system.
(c) BA (Brake Assist)
The primary purpose of the brake assist system is to provide auxiliary brake force to assist the driver who cannot generate a brake force large enough during emergency braking, thus helping to maximize the brake performance of the vehicle.




(1) Operation description
The skid control ECU receives the brake pedal stroke sensor signal and the oil pressure signal from the master cylinder pressure sensor to determine whether brake assist is necessary or not. If brake assist is deemed necessary, the skid control ECU will send control signals to the solenoid. The solenoid valve then controls the pressure applied to each wheel cylinder.
The ABS warning light comes on to indicate a malfunction in the BA system.
(d) TRAC (Traction Control)
The TRAC system helps prevent the drive wheels from slipping when the driver depresses the accelerator pedal excessively while starting off or accelerating on a slippery surface.




(1) Operation description
The skid control ECU detects wheelspin by receiving signals from each speed sensor and the HV control ECU via CAN communication. The skid control ECU controls engine torque with the HV control ECU via CAN communication and brake hydraulic pressure through the solenoid valve.
The SLIP indicator light blinks when the system is operating. When there is a malfunction in the TRAC system, the brake control warning, master caution indicator and SLIP indicator lights come on and DTC will appear on the multi information display.
(e) VSC (Vehicle Stability Control)
The VSC system helps prevent the vehicle from slipping sideways as a result of strong front or rear wheel skid during cornering.




(1) Operation description
The skid control ECU determines the vehicle operating conditions based on signals received from the wheel speed sensors, yaw rate and acceleration sensor, and steering angle sensor. The skid control ECU sends signals via CAN communication to the HV control ECU in order to control engine torque. The skid control ECU controls brake hydraulic pressure using the solenoid valves.
The SLIP indicator light will blink, and the skid control buzzer will sound when the system is operating. If a malfunction occurs in the VSC system, both the brake control warning, master caution indicator and the SLIP indicator lights will come on. In addition, the DTC will appear on the multi information display.
4. STEERING COOPERATION CONTROL
(a) The VDIM system effects coordinated control consisting of VSC and EPS (Electronic Power Steering). By integrating these preventive safety functions, the VDIM system ensures higher driving stability and maneuverability performance.
(b) If the vehicle loses stability due to a slippage, this function effects brake control by applying hydraulic pressure to the wheels. At the same time, the EPS provides steering torque assist control to facilitate the driver's steering maneuver.
5. FAIL SAFE
(a) When a failure occurs in the ABS with BA, TRAC and VSC systems, the ABS warning, brake control warning, and SLIP indicator lights come on and the DTC will be displayed on the multi information display and ABS with BA, TRAC and VSC operations will be prohibited. In addition, when there is a failure that disables the EBD operation, the BRAKE warning light also comes on and the EBD operation is prohibited.
(b) If control is prohibited due to a malfunction during operation, control will be disabled gradually. This is to avoid sudden vehicle instability.
6. INSPECTION MODE
(a) VSC operation can be disabled by operating Techstream Service Precautions.
HINT: Refer to the Techstream operator's manual for further details.

7. FUNCTION OF COMPONENTS