Antilock Brakes / Traction Control Systems: Description and Operation
GENERAL DESCRIPTION
Traction Control/Active Stability Control System (TCL/ASC) is available for all model as standard equipment.
- The TCL/ASC is a combination system of active stability control system (ASC) and traction control system (TCL). The ASC avoids a dangerous vehicle attitude by limiting the engine output and braking a set of wheels (front-left and right-rear, or front-right and rear-left) according to driving conditions. The TCL 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 CAN (Controller Area Network).
CONSTRUCTION DIAGRAM
SYSTEM CONFIGURATION DIAGRAM
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 floor console, and detects lateral acceleration, longitudinal acceleration and yaw angular velocity of the vehicle.
STEERING WHEEL SENSOR
- This sensor is mounted behind the column switch, and detects the steering wheel angle.
- 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.
NOTE:
For the details of the DTC codes, refer to Active Stability Control System (ASC) .
ASC OFF SWITCH
This switch is mounted on the left side of the instrument panel, and turns on and off the system.
ASC OFF SWITCH OPERATION AND THEIR RESPECTIVE CONTROLS
NOTE:
The ASC returns to the active state automatically when the ignition switch is turned to the ON position.
ACTUATOR
HYDRAULIC UNIT
The hydraulic unit includes a cut valve, suction valve and pressure switch for the ASC control additionally, compared with the conventional hydraulic unit for the ABS control.
TCL/ASC INDICATOR AND ASC OFF INDICATOR
The TCL/ASC indicator and ASC OFF indicator illuminate or flash under the conditions below to inform the driver.
TCL/ASC INDICATOR
- When the ASC is active, the indicator flashes. (4Hz)
- When the TCL is active, the indicator flashes. (4Hz)
- When sensors related to TCL/ASC are not initialized, the indicator flashes (2Hz).
- When there is a failure in the TCL/ASC, the indicator illuminates.
ASC OFF INDICATOR
- When the ASC-OFF switch is pressed for 3 seconds or more.
- When the ASC is defective, the indicator illuminates.
- When steering wheel sensor related to ASC is not initialized, the indicator flashes (2Hz).
- When the brake pad temperature is high, the ASC OFF indicator flashes at a rate of 2 Hz.
TCL/ASC INDICATOR, ASC OFF INDICATOR AND THEIR OPERATION PATTERN
TCL/ASC-ECU
The ECU incorporates the ABS-ECU, ASC-ECU, and TCL-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 TCL/ASC is a system that adds a yaw rate sensor, a lateral G 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 ASC OPERATION
The ASC 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
INTEGRATED CONTROL
The ASC transmits data necessary for control of the ABS and the TCL, performing integrated control.
EXAMPLE OF OPERATION OF TCL
The TCL prevents drive force loss during slipping of the drive wheels by automatically applying the brakes and sending engine torque reduction signal to the ECM [M/T] or PCM [A/T] 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 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.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.