Vehicle Stability Control System (for Hydraulic Brake Booster)

BRAKE CONTROL: VEHICLE STABILITY CONTROL SYSTEM (for Hydraulic Brake Booster):

SYSTEM DIAGRAM













SYSTEM DESCRIPTION

1. SYSTEM DESCRIPTION
HINT:
- The skid control ECU forms a single unit with the hydraulic brake booster.
- The yaw rate sensor and deceleration sensor are combined in a single unit. This unit communicates with the skid control ECU through CAN communication.

(a) ABS with EBD and BA and TRAC and VSC operation
(1) The skid control ECU determines the wheel slipping conditions by receiving signals from each speed sensor, the yaw rate and deceleration sensor, and the steering angle sensor. The ECU controls the engine output torque using electronic throttle control, and the wheel brake pressure using the master cylinder solenoid, according to these signals.
(2) 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 TRAC is operating, and the operation being performed is displayed.
2. ACTIVE SAFETY
(a) 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 the wheel lock condition by receiving vehicle speed signals from each speed sensor, and sends control signals to the pump motor and solenoid valve. The pump motor and solenoid valve prevent the wheels from locking by controlling the oil pressure of each wheel cylinder.
The ABS warning light comes on when the ABS system malfunctions.
(b) EBD (Electronic Brake force Distribution)
The EBD control utilizes ABS, realizing proper brake force distribution between the front and rear wheels in accordance with the driving conditions.
In addition, when braking while cornering, it also controls the brake forces of the right and left wheels, helping to control the vehicle behavior.




(1) Operation description
The skid control ECU receives the speed signals from each speed sensor to detect the slip condition of the wheels and sends the control signal to the solenoid.
The solenoid valve controls the oil pressure of the rear wheel cylinder and divides the control power appropriately between the front and rear wheels and the right and left wheels.
Both of the ABS and the brake warning lights come on when the EBD system malfunctions.
(c) BA (Brake Assist)
The primary purpose of the brake assist system is to provide an auxiliary brake force to assist drivers 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 oil pressure signal from the master cylinder pressure sensor to determine whether brake assist is necessary or not. If brake assist is necessary, the skid control ECU sends control signals to the pump motor and solenoid. The pump and the solenoid valve then control the pressure applied to each wheel cylinder.
The ABS warning light comes on when the BA system malfunctions.
(d) Changing of TRAC, AUTO LSD and VSC operation permission/disablement with the VSC OFF switch




(1) Changing modes:





With the VSC OFF switch, the vehicle can be changed to normal mode, TRAC OFF mode (AUTO LSD control) and VSC OFF mode.

Vehicles in H2 (2WD) Mode





HINT:
- o: Illuminated
- -: Not illuminated
- o*: 50 km/h (31 mph) or more is not illuminated





Vehicles in H4L (High speed 4WD) Mode





HINT:
- o: Illuminated
- -: Not illuminated

Vehicles in L4L (Low speed 4WD) Mode





(2) Drive modes and functions





HINT:
- o: Operates
- -: Does not operate
- o*: Speed limitation (System returns to normal mode when vehicle speed exceeds a certain value).
- When the vehicle is in L4L mode with the rear differential locked, VSC is disabled.

(e) VSC (Vehicle Stability Control)
The VSC system helps prevent the vehicle from slipping sideways as a result of strong front wheel skid or strong rear wheel skid during cornering.




(1) Operation description
The skid control ECU determines the vehicle condition by receiving signals from the speed sensors, yaw rate and deceleration sensor, and steering angle sensor. The skid control ECU controls the engine torque through the ECM via CAN communication, and the oil pressure through the pump and solenoid valve.
The SLIP indicator light blinks and the skid control buzzer sounds when the system is operating. The SLIP indicator light come on when the VSC system malfunctions.
3. DRIVING PERFORMANCE
(a) TRAC (Traction Control)
The TRAC system helps prevent the drive wheels from slipping if the driver presses down on the accelerator pedal excessively when starting off or accelerating on a slippery surface.
HINT: The TRAC system operates when H2 (2WD) mode is selected.




(1) Operation description
The skid control ECU detects the vehicle's slip condition by receiving signals from the speed sensors and ECM via CAN communication. The skid control ECU controls the engine torque through the ECM via CAN communication, and the oil pressure through the pump and solenoid valve.
The SLIP indicator light blinks when the system is operating. The SLIP indicator light come on when the TRAC system malfunctions.
When the vehicle is in normal mode and the VSC OFF switch is pressed for a short amount of time, AUTO-LSD operation becomes possible. During TRAC OFF mode (AUTO LSD control), the combination meter's AUTO LSD indicator light and VSC OFF indicator light* illuminate, and TRAC operation is disabled.
*: At 50 km/h (31 mph) or more the system returns to normal, so the light is not illuminated
(b) A-TRAC (Active Traction Control)
During rugged off-road driving, this function controls the brake fluid pressure that is applied to slipping wheels, and distributes the drive force that would have been lost through the slippage to the remaining wheels in order to achieve a LSD (Limited Slip Differential) effect. As a result, the vehicle's off-road drivability and ability to free itself from ruts have been increased.
HINT: The A-TRAC system operates when L4L (Low speed 4WD) mode is selected.




(1) Operation description
When the vehicle is in L4L (Low speed 4WD) mode, if the A-TRAC switch is pressed , the A-TRAC indicator light comes on. When the system is operating, the SLIP indicator light blinks.
HINT: If the A-TRAC system operates constantly for a long time, the temperature of the actuator in the hydraulic brake booster may increase excessively. In such cases, the skid control buzzer sounds intermittently, the A-TRAC indicator light blinks, and the A-TRAC system is temporarily deactivated. After a while, the A-TRAC indicator light comes on and the A-TRAC system is reactivated. The vehicle can be driven normally while the A-TRAC system is deactivated.

(c) AUTO-LSD (Auto Limited Slip Differential)
When the vehicle is in H2 (2WD) mode, the AUTO LSD will operate with the VSC OFF switch on (TRAC OFF mode (AUTO LSD control)) and the accelerator pedal depressed.
the AUTO LSD will operate with the VSC OFF switch on (TRAC OFF mode (AUTO LSD control)) and the accelerator pedal depressed. The AUTO LSD system is used to apply brake pressure and limit differential slippage, thus transmitting drive torque to the other drive wheel to ensure traction when starting under the following conditions:
- One of the drive wheels spins, for example, when one drive wheel is driven off of the pavement.
- One of the drive wheels slips on snow/ice when starting on a slope.
HINT: The AUTO LSD system operates when H2 (2WD) mode is selected.




(1) Operation description
The AUTO LSD indicator light and VSC OFF indicator light* come on when the system is operating.
The SLIP indicator light comes on to indicate a malfunction in the AUTO LSD system.
Auto LSD operation becomes possible in TRAC OFF mode (AUTO LSD control). TRAC OFF mode (AUTO LSD control) begins when the vehicle is in normal mode and the VSC OFF switch is pressed for a short amount of time. During TRAC OFF mode (AUTO LSD control), the combination meter's AUTO LSD indicator light and VSC OFF indicator light illuminate, and TRAC operation is disabled.
When the vehicle speed increases to more than 50 km/h (31 mph), the vehicle automatically returns to normal mode. As long as the vehicle speed is 50 km/h (31 mph) or less, the vehicle remains in TRAC OFF mode (AUTO LSD control).
*: At 50 km/h (31 mph) or more the system returns to normal, so the light is not illuminated
(d) Downhill Assist Control
When the downhill assist control switch is pressed with the transfer in low (L4L) range and without the accelerator and brake pedals in operation, the downhill assist control activates 4-wheel hydraulic pressure control, in order to maintain a constant low vehicle speed without causing the wheels to become locked. Thus, the vehicle can descend steep hills in a stable manner.
HINT: Depressing the accelerator and brake pedals cancels control of the downhill assist control system.
Begins operating when driving down slopes at a speed of 25 km/h (16 mph) or less with the engine brake applied.




(1) Operation description
The SLIP indicator light blinks and the downhill assist control indicator light and stop light come on when the system is operating.
The SLIP indicator light comes on and the downhill assist control indicator light blinks when the downhill assist control system malfunctions.
(e) Hill-start Assist Control
When the vehicle starts off on a steep hill, hill-start assist control detects the backward descent of the vehicle and effects 4-wheel hydraulic pressure control to reduce the speed of the vehicle.
For a Maximum of 5 seconds after the control starts, fluid pressure is gradually released and the control is complete.
HINT: Depressing the brake pedal cancels control of the hill-start assist control system.
Does not operate when the shift lever in P or N , or when the vehicle is running/rolling back up a slope with the shift lever in R.




(1) Operation description
The SLIP indicator light blinks, the stop light comes on, and the skid control buzzer sounds when the system is operating.
The SLIP indicator light comes on when the hill-start assist control system malfunctions.
4. FUNCTION OF COMPONENTS