With Mark II ABS System
DESCRIPTIONTraction Control System (TCS) prevents wheel spin when the car is accelerating on a slippery surface.
The TCS system for manual transmissions consists of two subsystems, Anti-Lock Braking System (ABS) and Electronic Throttle System (ETS).
The TCS system utilizes many of the components in the ABS system. The major difference is the addition of the Electronic Throttle System. Refer to TRACTION CONTROL for ETS information.
The Manual transmission TCS has the capability to apply the front brakes independently during low speed wheel spin and also the ability to close the throttle butterfly to reduce wheel spin at any speed.
OPERATION
This system uses the speed of the rear wheels as a reference speed against the speed of each front wheel. If the speed of a front wheel exceeds that of the reference speed from the rear wheels, the condition is known as wheel spin. The magnitude of the spin together with the speed of the car determine how the system operates.
To enable the car to achieve maximum traction, a certain amount of wheel spin, which varies depending on the speed of the car, is allowed.
Low Speed Operating Mode
The front wheel having the poorer grip (lower friction) starts to spin first.
When wheel spin has reached a speed of just under 10 mph, TCS control is initiated and the TC/ABS system applies the brake for that wheel. As brake is applied to the wheel, additional torque is transferred to the other wheel, which still is maintaining good traction. If the road surface is very slippery, the other wheel may also start to spin, if it does, once it is spinning at a speed of about 4 mph, the amount of throttle is reduced electronically, inhibiting further wheel spin.
So the system is able to provide the optimum combination of traction and steering precision with the same traction or mobility as that provided by a conventional limited-slip differential.
The upper limit for the amount of wheel spin allowed before the TCS takes over is gradually reduced up to a speed of about 12 mph, after which it remains constant regardless of how much throttle is used, although the upper limit for braking will then be increased.
High Speed Operating Mode (Over 25 MPH)
Once the car reaches a speed of about 25 mph, the system switches mode and initiates throttle control when the first wheel starts spinning. Traction control by application of the brake will be initiated for the other wheel if the amount of wheel spin is great enough.
Up to a speed of about 37 mph, wheel spin of up to just under 2 mph is allowed, after which an increase of about 5 percent relative to the increased speed of the car will be allowed.
So at speed of 87 mph, for instance, wheel spin of approximately 4.4 mph will be allowed before electronic control of the throttle is initiated.
System Interaction
Conventional operation of the ABS system is the same as before, but an additional valve block (TC block) for the anti-spin function has been added onto the hydraulic unit.
The TC block, together with the main valve, wheel sensors, and inlet and outlet valves are the main components of the TC/ABS system. The system is equipped with indicator/warning lights for monitoring and checking of the system. These warning lights indicate when the system is operating and provide a warning if a fault should occur.
The wheel sensors send wheel speed information to the ABS ECU. Using the average speed of the rear wheels as a reference value, the ECU continuously monitors the amount of wheel spin in the front wheels (speed above reference value for rear wheels).
When the system detects a tendency for wheel spin, and the TCS calls for braking of the front wheel concerned, pressure is directed from the accumulator through the TC block and main valve to the front wheel circuits. The inlet and outlet valves then control the TCS initiated braking.