Traction Control/Active Skid Control System (TCL/ASC)
GENERAL DESCRIPTIONTraction Control/Active Skid Control System (TCL/ASC) is available for AWD models as optional equipment.
^ The Traction Control/Active Skid Control System is a combination system of active skid control system and traction control system. The active skid control system avoids a dangerous vehicle attitude by limiting the engine output and braking a set of wheels (front left and right rear, or right front and left rear) according to driving conditions. The traction control system prevents wheel spinning at vehicle start.
^ Fail-safe function ensures safety is maintained
^ Diagnostic function provides improved serviceability
^ To shorten the lines and enhance data transmission reliability, communication with other ECU is performed over a CAN (Controller Area Network).
CONSTRUCTION DIAGRAM
CONSTRUCTION DIAGRAM (PART 1):
CONSTRUCTION DIAGRAM (PART 2):
SYSTEM CHECK SOUND
When starting the engine, a thudding sound can sometimes be heard coming from the engine compartment.
This is a normal sound during the TCL/ASC self-check.
TCL/ASC OPERATION SOUNDS AND SENSATIONS
During normal operation, the TCL/ASC makes several sounds that may seem unusual at first:
^ A whining sound is caused by the TCL/ASC hydraulic unit motor.
^ When pressure is applied to the brake pedal, the pulsation of the pedal causes a scraping sound.
^ When the brakes are applied firmly, the TCL/ASC operates, rapidly applying and releasing the brakes many times per second. This repeated application and release of braking forces can cause the suspension to make a thumping sound and the tires to squeak.
SENSOR
G AND YAW RATE SENSOR
This sensor is mounted under the center console, and detects lateral acceleration, longitudinal acceleration and steering angular velocity of the vehicle.
STEERING WHEEL SENSOR
^ This sensor is mounted behind the column switch, and detects the steering wheel position.
^ The steering wheel sensor has a self-diagnosis function and a memory function. If the diagnosis function finds a trouble, it sends a DTC code to the TCL/ASC-ECU. Then the ECU will illuminate the TCL/ASC indicator light.
NOTE: For the details of the DTC codes, refer to the Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions
TRACTION CONTROL OFF SWITCH
This switch is mounted on the left side of the instrument panel, and turns on and off the system.
TRACTION CONTROL OFF SWITCH POSITION AND THEIR RESPECTIVE CONTROL
TRACTION CONTROL OFF SWITCH POSITION AND THEIR RESPECTIVE CONTROL:
NOTE:
^ The Traction control will activate when the system has not been disabled by the traction control OFF switch, and the vehicle speed has reached 6 - 14 km/h (4 - 9 mph).
^ The traction control will deactivate when the front wheel speed (both wheels) have decreased to 2 - 6 km/h (1 - 4 mph) for one second or more (four seconds or more if the system is controlling the engine output).
^ The Active skid control will be activated when the vehicle speed exceeds 20 km/h (12 mph).
^ The Active skid control will deactivate when the vehicle speed has decreased to 15 km/h (9 mph) or lower.
ACTUATOR
HYDRAULIC UNIT
The hydraulic unit includes a cut valve, suction valve and pressure switch for the active skid control additionally, compared with the conventional hydraulic unit for the ABS control.
TRACTION CONTROL/ACTIVE SKID CONTROL SYSTEM OPERATION INDICATOR LIGHT AND TRACTION CONTROL SYSTEM OFF INDICATOR LIGHT
The Traction control/Active skid control system operation indicator light and Traction control system OFF indicator light illuminate or flash under the conditions below to inform the driver.
TRACTION CONTROL/ACTIVE SKID CONTROL SYSTEM INDICATOR LIGHT
^ When the active skid control is active, the light flashes.
^ When the traction control is active, the light flashes.
^ When sensors related to traction control and active skid control are not initialized, the light flashes at a frequency of once per second.
^ When there is a failure in the traction control/active skid control system, the light illuminates.
TRACTION CONTROL SYSTEM OFF INDICATOR LIGHT
^ When the traction control is inactive, the light illuminates.
^ When the traction control/active skid control system is defective, the light flashes at a frequency of once per second.
TRACTION CONTROL/ACTIVE SKID CONTROL SYSTEM OPERATION INDICATOR LIGHT, TRACTION CONTROL SYSTEM OFF INDICATOR LIGHT AND THEIR OPERATION PATTERN
TRACTION CONTROL/ACTIVE SKID CONTROL SYSTEM OPERATION INDICATOR LIGHT, TRACTION CONTROL SYSTEM OFF INDICATOR LIGHT AND THEIR OPERATION PATTERN:
TCL/ASC-ECU
The ECU incorporates the ABS-ECU, active skid control-ECU, and traction control-ECU. The integral design allows joint operation of the TCL/ASC-ECU with the ABS and coordinated control of the driving force and braking force.
SYSTEM CONFIGURATION
The Traction Control and Active Skid Control (TCL/ASC) System is a system that adds a yaw rate sensor, a steering wheel sensor and master cylinder pressure sensor (incorporated in hydraulic unit) to the ABS system.
OVERVIEW OF CONTROL
The TCL/ASC-ECU detects vehicle movement based on information from various sensors and calculates a model of ideal vehicle movement. After comparing actual and ideal movements, it acts to bring the actual vehicle movement closer to the ideal model by controlling specific wheel brake force and governing engine output. It restrains under-steering and over-steering through a corrective yaw moment.
EXAMPLE OF ACTIVE SKID CONTROL OPERATION
The Active Skid Control manages the vehicle attitude by creating a yaw moment from altering the balance between the cornering force and each wheel's braking mechanism.
For example, on a slippery surface, if the vehicle tends to be under-steered contrary to the driver's intention, a yaw moment (a rotational moment) is created to restrain the under-steering by increasing the rear-inside braking force. On the other hand, when the vehicle tends to be over-steered, a yaw moment (a restorative moment) is created to restrain the over-steering by increasing the front-outside braking force. Furthermore, when it is determined that the vehicle is over-speeding, safe and stable cornering is enabled by deceleration from restricting engine output.
EXAMPLE OF THE EFFECT OF CONTROL
EXAMPLE OF THE EFFECT OF CONTROL:
JOINT CONTROL
The Active Skid Control transmits data necessary for control of the ABS and the Traction Control, performing joint control.
EXAMPLE OF OPERATION OF TRACTION CONTROL
The Traction Control prevents drive force loss during slipping of the drive wheels by automatically applying the brakes and sending engine torque reduction signal to the PCM when the drive wheels slip or when driving on partly low-friction surfaces.
FAIL-SAFE AND DIAGNOSTIC FUNCTIONS
The TCL/ASC-ECU regularly monitors input and output signals. If an error is detected in the system, the ECU sends a fail signal and the TCL/ASC indicator light is illuminated or blinks. Various controls are processed depending on the cause of malfunction as shown below. When the ABS system fails, the TCL/ASC system is also suspended. However, when the TCL/ASC system fails, no other systems are suspended. The appropriate indicator lights are illuminated/flashed.
The TCL/ASC-ECU includes the following functions to make system inspection easier.
^ Diagnostic trouble code
^ Displays Data list
^ Actuator test
All of the above operations can be carried out using scan tool MB991958.
ACTIVE SKID CONTROL SYSTEM OPERATION
The TCL/ASC-ECU receives information from the PCM, the steering sensor, the G and yaw-rate sensor and the wheel speed sensor. If the ECU determines that the vehicle is tending to oversteer or understeer, it sends signals to the active skid control system valves and the ABS solenoid valves to increase the fluid pressure to the wheels.
The system closes the cut valve to shut the fluid channel to the suction valve, and activates the pump motor. The brake fluid, which is pumped through the hydraulic unit reservoir, will be supplied to the front left wheel during oversteering or the rear right wheel during understeering when the vehicle is at right turn. Furthermore, the system also controls the engine if the accelerator pedal is depressed excessively.
DURING NORMAL BRAKING
DURING NORMAL BRAKING:
The brake fluid flows from the master cylinder to the cut valve and the inlet valve to supply fluid pressure to the relevant wheels.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE ABS FLUID PRESSURE IS DECREASING
WHEN THE ABS FLUID PRESSURE IS DECREASING:
The system closes the inlet solenoid valve to shut the fluid channel from the master cylinder, and opens the outlet solenoid valve to return the brake fluid from the wheel cylinders to the buffer chamber. This causes the wheel cylinder fluid pressure to decrease. Then the system activates the pump motor to return the brake fluid from the buffer chamber to the hydraulic unit reservoir.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE ABS FLUID PRESSURE IS HOLDING
WHEN THE ABS FLUID PRESSURE IS HOLDING:
The system closes the inlet solenoid valve and the outlet solenoid valve to hold the brake fluid pressure in the wheel cylinders.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE ABS FLUID PRESSURE IS INCREASING
WHEN THE ABS FLUID PRESSURE IS INCREASING:
The system opens the inlet solenoid valve and closes the outlet solenoid valve to increase the brake fluid pressure in the wheel cylinders.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE TRACTION CONTROL SYSTEM IS INCREASING FLUID PRESSURE (OR THE ACTIVE SKID CONTROL IS INCREASING FLUID PRESSURE WHEN THE BRAKE PEDAL IS NOT DEPRESSED)
WHEN THE TRACTION CONTROL SYSTEM IS INCREASING FLUID PRESSURE (OR THE ACTIVE SKID CONTROL IS INCREASING FLUID PRESSURE WHEN THE BRAKE PEDAL IS NOT DEPRESSED):
The system closes the cut valve to shut the fluid channel from the master cylinder. The brake fluid, which is pumped from the hydraulic unit reservoir, is supplied to the wheel cylinders.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE TRACTION CONTROL SYSTEM IS HOLDING FLUID PRESSURE (OR THE ACTIVE SKID CONTROL IS HOLDING FLUID PRESSURE WHEN THE BRAKE PEDAL IS NOT DEPRESSED)
WHEN THE TRACTION CONTROL SYSTEM IS HOLDING FLUID PRESSURE (OR THE ACTIVE SKID CONTROL IS HOLDING FLUID PRESSURE WHEN THE BRAKE PEDAL IS NOT DEPRESSED):
The system closes the inlet and outlet valves to hold the fluid pressure in the wheel cylinders. The brake fluid, which is pumped from the hydraulic unit reservoir, is supplied to the inlet valve. At this time, excessive fluid is returned through the relief valve to the hydraulic unit reservoir.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE TRACTION CONTROL SYSTEM IS DECREASING FLUID PRESSURE (OR THE ACTIVE SKID CONTROL IS DECREASING FLUID PRESSURE WHEN THE BRAKE PEDAL IS NOT DEPRESSED)
WHEN THE TRACTION CONTROL SYSTEM IS DECREASING FLUID PRESSURE (OR THE ACTIVE SKID CONTROL IS DECREASING FLUID PRESSURE WHEN THE BRAKE PEDAL IS NOT DEPRESSED):
The system closes the inlet valve and opens the outlet valve. This causes the brake fluid in the wheel cylinders to return through the buffer chamber to the hydraulic unit reservoir.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
WHEN THE ACTIVE SKID CONTROL IS INCREASING THE FLUID PRESSURE WHILE THE BRAKE PEDAL IS DEPRESSED
WHEN THE ACTIVE SKID CONTROL IS INCREASING THE FLUID PRESSURE WHILE THE BRAKE PEDAL IS DEPRESSED:
The system closes the cut valve to shut the fluid channel from the master cylinder to the wheel cylinders, and opens the suction valve to open the fluid channel from the master cylinder to the hydraulic unit reservoir. The brake fluid, which is pumped from the master cylinder to the hydraulic unit reservoir, is supplied to the wheel cylinders.
NOTE: At this time, the hydraulic unit reservoir can not operate due to the fluid pressure from the master cylinder.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
NOTE: *:When the ASC is operating while the brake pedal is depressed, the suction valve turns on and off according to the brake fluid amount supplied to the buffer chamber.
WHEN THE ACTIVE SKID CONTROL IS HOLDING THE FLUID PRESSURE WHILE THE BRAKE PEDAL IS DEPRESSED
WHEN THE ACTIVE SKID CONTROL IS HOLDING THE FLUID PRESSURE WHILE THE BRAKE PEDAL IS DEPRESSED:
The system closes the inlet and outlet solenoids to hold the fluid pressure to the wheel cylinders. The brake fluid, which is pumped through the hydraulic unit reservoir, may exceed a predetermined pressure.
In that case, the excessive fluid is returned through the relief valve to the hydraulic unit reservoir.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
NOTE: *: When the ASC is operating while the brake pedal is depressed, the suction valve turns on and off according to the brake fluid amount supplied to the buffer chamber.
WHEN THE ACTIVE SKID CONTROL IS DECREASING THE FLUID PRESSURE WHILE THE BRAKE PEDAL IS DEPRESSED
WHEN THE ACTIVE SKID CONTROL IS DECREASING THE FLUID PRESSURE WHILE THE BRAKE PEDAL IS DEPRESSED:
The system closes the inlet solenoid and opens the outlet solenoid. This causes the brake fluid in the wheel cylinders to return to the buffer chamber, and decreases the fluid pressure in the wheel cylinders. If the returned brake fluid pressure exceeds a predetermined pressure, excessive brake fluid is returned to the master cylinder.
STATUS OF THE OPERATION VALVE
STATUS OF THE OPERATION VALVE:
NOTE: *: When the ASC is operating while the brake pedal is depressed, the suction valve turns on and off according to the brake fluid amount supplied to the buffer chamber.
TRACTION CONTROL SYSTEM OPERATION
The TCL/ASC-ECU receives information from the PCM, the G and yaw-rate sensor, and the wheel speed sensor. If the ECU determines that a road wheel is spinning, it will control the fluid pressure to the spinning wheel to apply torque to the other road wheels. The operations of the ABS solenoid valves and the active skid control system valves are the same as for the active skid control system. Furthermore, the system also controls the engine if the accelerator pedal is depressed excessively.