Antilock Brakes / Traction Control Systems: Description and Operation

BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: VEHICLE STABILITY CONTROL SYSTEM:














*1: Models with pre-collision system
*2: Models with dynamic radar cruise control system


BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: VEHICLE STABILITY CONTROL SYSTEM: 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 electronic power steering. However, VDIM integrates these systems to improve "driving, turning and stopping" the motion performance of the vehicle in other words.
(c) In conventional vehicles, control starts at the vehicle's limit. 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) VDIM uses 2 control modes (SPORT/NORMAL) linked to the sport mode total control switch (pattern select switch) to optimize VSC according to the road surface conditions and driver's ability. When the sport mode total control switch (pattern select switch) is in the SNOW position, VDIM operates in normal control mode.





(e) The VDIM manages all functions, such as the ABS with EBD, BA, the TRAC, and the VSC. It is operated by the VSC system, which regulates a brake fluid pressure. The steering cooperative control function is also available. The VDIM is able to perform comprehensive management.
(f) Conventional brake control systems begin to control either the braking or motive force in order to stabilize the vehicle 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 and steering systems in accordance with changes in vehicle balance before the vehicle becomes unstable. As a result, smooth vehicle control is achieved.
(g) Conventional brake control systems manage all related functions, such as the ABS with EBD, 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. FUNCTION DESCRIPTION
HINT: The yaw rate and acceleration sensor is made up of 2 individual sensors that are combined in a single unit. One of the sensors is the yaw rate sensor and the other is the acceleration sensor. This unit communicates with the skid control ECU via CAN communication.

(a) Regarding enabling and disabling TRAC and VSC operation through the VSC OFF switch.
Changing modes: Through the VSC OFF switch, the vehicle can be changed to normal mode, TRAC off mode and VSC off mode.
(1) Normal mode: When the vehicle is in TRAC off mode or VSC off mode, and the VSC OFF switch is pressed for a short amount of time, the vehicle changes to normal mode. During normal mode, TRAC and VSC operation is possible. After the engine switch is turned on (IG), the vehicle is in normal mode.
(2) TRAC off mode: When the vehicle is in normal mode and the VSC OFF switch is pressed for a short amount of time, the vehicle changes to TRAC off mode. During TRAC off mode, the combination meter's slip indicator light illuminates, and TRAC operation is disabled. During TRAC off mode, if the vehicle speed increases to 50 km/h (31 mph) or more, the vehicle automatically returns to normal mode.
(3) VSC OFF mode: When the vehicle is stopped and the VSC OFF switch is pressed for 3 seconds or more, the vehicle changes to VSC off mode. During VSC off mode, the combination meter's slip indicator and VSC OFF indicator lights illuminate. Also, VSC and TRAC operation are disabled. During VSC off mode, even if the vehicle speed increases, the vehicle does not return to normal mode.
(b) ABS (Anti-lock Brake System)
The ABS helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.





(1) Operation description
The skid control ECU detects wheel lock by receiving vehicle speed signals from each speed sensor, and sends control signals to the solenoid valves. The solenoid valves avoid wheel lock by controlling the brake fluid pressure of each wheel cylinder.
The ABS warning light comes on when the ABS system is malfunctioning.
(c) EBD (Electronic Brake force Distribution)
The EBD control utilizes the ABS, to properly distribute brake force between the front and rear wheels in accordance with driving conditions.
When braking while cornering, it also controls the brake force distribution between 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 wheel lock. The skid control 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 force distribution 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.
(d) BA (Brake Assist)
The primary purpose of the brake assist system is to provide auxiliary brake force to assist a driver who cannot generate a large enough brake force during emergency braking, thus helping to maximize the vehicle's brake performance.





(1) Operation description
The skid control ECU receives the speed signal from each speed sensor and the fluid pressure signal from the master cylinder pressure sensor to determine whether brake assist is necessary. If brake assist is necessary, the skid control ECU sends control signals to the pump motor and solenoid valves. The pump and the solenoid valves then control the pressure applied to each wheel cylinder.
The ABS warning light comes on to indicate a malfunction in the BA system.
(e) TRAC (Traction Control)
The TRAC system helps prevent the drive wheels from slipping when the driver presses down on the accelerator pedal excessively when starting off or accelerating on a slippery surface.





(1) Operation description
The skid control ECU detects the vehicle's slip condition by receiving signals from each speed sensor and ECM via CAN communication. The skid control ECU sends via CAN communication to the ECM in order to control engine torque. The skid control ECU controls brake hydraulic pressure using the pump and solenoid valves.
The slip indicator light blinks when the system is operating. When there is a malfunction in the TRAC system, both the slip indicator and master caution indicator lights will come on and the DTC will be displayed on the multi-information display.
The VSC OFF switch stops TRAC operation.
HINT: When the VSC OFF switch is pressed, the vehicle changes to TRAC off mode, and TRAC operation is disabled. During TRAC off mode, if the VSC OFF switch is pressed again or the vehicle speed increases to 50 km/h (31 mph), TRAC operation becomes possible. During TRAC off mode, the slip indicator light illuminates.

(f) 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 condition by receiving signals from the speed sensor, yaw rate and acceleration sensor and steering angle sensor. The skid control ECU sends via CAN communication to the ECM in order to control engine torque. The skid control ECU controls brake hydraulic pressure using the pump and solenoid valves.
The slip indicator light blinks and the skid control buzzer sounds when the system is operating. When there is a malfunction in the VSC system, both slip indicator and master caution indicator lights will come on and the DTC will be displayed on the multi-information display.
The VSC OFF switch stops VSC operation.
HINT: When the VSC OFF switch is pressed for 3 seconds or more with the vehicle stopped, the VSC system changes to VSC off mode. If the VSC OFF switch is pressed again with the system in VSC off mode, the TRAC and VSC systems can be operated. When the system is in VSC off mode, the slip indicator light and VSC OFF indicator light illuminate.

3. STEERING COOPERATION CONTROL
(a) The VDIM effects coordinated control consisting of the VSC system and electronic power steering system. By integrating these preventive safety functions, the VDIM ensures excellent driving stability and maneuverability of the vehicle.
(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 electronic power steering provides steering torque assist control or active steering wheel angle control to facilitate the driver's steering control.
4. LSD CONTROL
(a) Sometimes the wheels will spin when accelerating in a turn because the vehicle weight moves to the outside of the turn and it is difficult to transfer drive force to the inside.
(b) The VSC system detects wheelspin while turning, and applies the brake to the drive wheel on the inside of the turn to restrict wheelspin. This transfers drive force to the wheel on the outside of the turn, so that the driver's intended acceleration is obtained.
HINT: The LSD function will continue to operate even after TRAC, VSC, or both functions are disabled using the VSC OFF switch.
However, the LSD function may be restricted if the brake system temperature of either drive wheel is high.

5. HILL-START ASSIST CONTROL
(a) The hill-start assist control detects rearward motion of the vehicle. It automatically increases the brake hydraulic pressure to the four wheels in order to reduce the rearward speed of the vehicle.
(b) The vehicle tends to slide backward when the driver moves his or her foot from the brake pedal to the accelerator pedal trying to start on a steep or slippery uphill. This function is effective in this kind of difficult starting situation.
(c) After a maximum of 5 seconds, hydraulic pressure is gradually released and control will be completed.
6. DYNAMIC RADAR CRUISE CONTROL (with Dynamic Radar Cruise Control)
(a) This system is designed to maintain an appropriate distance to the vehicle ahead, proportional to the vehicle speed. The distance to the vehicle ahead is measured based on signals sent from the millimeter wave radar sensor. To maintain an appropriate distance, this system controls the engine output and also applies the brakes if the distance to the vehicle ahead is too short.
7. PRE-COLLISION CONTROL (with Pre-collision Control)
(a) The pre-collision system predicts frontal collisions with other vehicles or objects. By pretensioning the seat belts prior to a collision, and performing brake control and brake assist control, it lessens the collision impact.
(b) The millimeter wave radar sensor recognizes if there is a vehicle or object on the road ahead, and the distance control ECU makes a judgement on whether a collision is unavoidable based on the position, speed, and course of the object.
(c) The distance control ECU sends this information via CAN communication to the seat belt control ECU, suspension control ECU and skid control ECU, in order to operate each component of the pre-collision system.
8. ABS with EBD, BA, TRAC and VSC OPERATION
(a) The skid control ECU calculates vehicle stability based on signals from the speed sensor, yaw rate and acceleration sensor, and steering angle sensor. In addition, it evaluates the results to determine whether any control actions (control of the engine output torque using the electronic throttle control or brake pressure using the brake actuator assembly) should be implemented.
(b) The slip indicator blinks and the skid control buzzer sounds to inform the driver that the VSC system is operating. The slip indicator also blinks when traction control is operating, and the operation being performed is displayed.
9. FAIL SAFE
(a) When a failure occurs in the ABS with BA, TRAC and VSC systems, the ABS warning light, slip indicator, master caution indicator lights come on, and a DTC will be displayed on the multi-information display and ABS with BA, TRAC and VSC operations are prohibited. In addition to this, when there is a malfunction that disables EBD operation, the brake warning light also comes on and 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.
10. INITIAL CHECK
(a) When the vehicle speed first reaches approximately 6 km/h (4 mph) or more after the engine switch is turned on (IG), each solenoid valve and motor of the brake actuator are sequentially activated to perform an electrical check. During this initial check, the operating sound of each solenoid valve and motor can be heard from the engine compartment, but this is not a malfunction.
11. INSPECTION MODE
(a) VSC operation can be disabled by operating the Techstream Service Precautions.
12. FUNCTION OF COMPONENTS