TCS Control unit
Acceleration Control:
The TCS control unit gets signals from the wheel sensors about the rotational speed of each wheel. Traction control
is activated when the rotational speed of the driving wheels differs from the rotational speed of the driven wheels (i.e.,
vehicle speed).
Handling Control:
Based on signals about driving wheel and driven wheel rotational speeds, the control unit calculates the car’s “yaw”
rate (i.e., the turn rate of the car’s body). Based on signals from the steering angle sensor, the control unit also calculates
the yaw rate expected by the driver. If the difference between actual and expected yaw rates is substantial—that is,
if the direction of the car’s body will exceed the driver’s expected line—the control unit signals the throttle actuator,
which closes the throttle valve, thus reducing engine power and maintaining the expected line.
Rough Road Control:
Based on signals from the wheel sensors, the control unit detects a rough road based on frequency of wheel rotational
vibration. The control unit then signals the throttle actuator to relax engine power, thus improving acceleration efficiency.
Grip Control:
Based on signals about wheel speed and yaw rate, the control unit determines the efficiency of the grip of the tires on
the road and signals the throttle actuator to relax engine power if necessary, thus improving grip.
Construction and Function
DRIVE WHEELS
Right wheel Left wheel
WHEEL SENSORS
Driving Wheel
Speed
Average speed
of left and
right wheels
Vehicle speed
Advance acceleration
Tire grip control
Acceleration
control
Target slip
ratio
Engine control block
ENGINE CONTROL
MODULE (ECM)
Throttle actuator (step motor)
Throttle valve control
Handling control
Rough road
detection
Rough road
control
Reference yaw rate
Lateral
acceleration
TCS CONTROL UNIT
STEERING ANGLE SENSOR
DRIVEN WHEELS
Right wheel Left wheel
Actual
yaw rate
Rotational
vibration
Speed difference in the
left and right wheels
Fail-Safe Function:
If the control unit detects an abnormality, it shuts the
traction control system off and causes the TCS in-
dicator light to come on. However if the abnormality is
detected while the TCS is activated, the control unit
first establishes the appropriate wheel spin velocity,
then shuts the system down, thus preventing excessive
wheel spin.
Self-Diagnosis Function:
If the control unit detects an abnormality, it records a
Diagnostic Trouble Code (DTC) which can be used to
diagnose the problem. The DTC is shown at the TCS in-
dicator light when the Service Check connector ter-
minals are connected with a jumper wire.
Steering Angle Detection
Steering angle is detected by the steering angle sensor,
located on the steering column. The sensor uses two
magneto-resistor (MR) elements to determine steering
angle and direction of rotation. When the driver turns
the steering wheel, a magnet in the steering shaft
generates waves in the “MR” elements. These waves
are amplified and converted into signals which the con-
trol unit can interpret as angle and direction of turn.
Vehicle Speed Detection
Wheel rotation speed is detected by the wheel sensors,
located at each wheel. The signals are sent to the con-
trol unit, which compares each wheel’s speed and de-
termines whether traction control is required.
MR ELEMENT
WHEEL SENSOR
GEAR PULSER
MR
ELEMENT
INDICATOR LIGHT
System Description
Engine Output Control
When the TCS is activated, the control unit signals the throttle actuator, located next to the throttle valve. The throttle
actuator is linked to the throttle valve through a series of reduction gears. Although the accelerator pedal position is
still within the driver’s control, the throttle valve is automatically relaxed to achieve optimum traction.
Construction and Function
LOST MOTION SPRING
(INSIDE RETURN SPRING)
THROTTLE VALVE
RETURN SPRINGS
DURING NORMAL DRIVING:
LOST
MOTION
SPRING
THROTTLE
LEVER
THROTTLE
RETURN SPRING
THROTTLE DRUM
THROTTLE
VALVE
THROTTLE ACTUATOR
(STEP MOTOR)
Movement of parts
while accelalator pedal open.
Movement of parts while
TCS is actuated.
DURING TCS ACTUATION:
THROTTLE ACTUATOR
(STEP MOTOR)
THROTTLE POSITION SENSOR
THROTTLE VALVE
THROTTLE DRUM
ACCELERATOR PEDAL
ANGLE SENSOR
TCS THROTTLE
LEVER