System Description
Fig. 1 Traction Control System Components:
W/MANUAL TRANSMISSION
SYSTEM DESCRIPTION
Traction Control System (TCS), Fig. 1. is used to prevent wheel spin when the car is accelerating on a slippery surface.
The TCS system for manual transmissions consists of two subsystems, the Anti-lock Braking System (ABS) and Electronic Throttle System (ETS).
TCS utilizes many of the components in the ABS system. The major addition to the system is the Electronic Throttle System.
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.
SUBSYSTEM DESCRIPTION
Electronic Throttle System (ETS)
The main purpose of the ETS system is to electronically control the position of the throttle butterfly.
The throttle housing is equipped with an actuating motor for the throttle butterfly, a vacuum unit, a throttle potentiometer and a safety cutout switch. Connected to the accelerator pedal is a pedal sensor with associated solenoid valves and a non-return valve fitted on the bulkhead. For additional safety, a parallel system using a throttle cable is provided, which will take over in the limp-home mode.
Automatic Idling Control (AIC)
The ETS eliminates the need for separate components for Automatic Idling Control (AIC) and load related control over the entire working range of the engine.
Smooth Response To Heavy-Footed Use Of Accelerator
If the driver depresses or releases the accelerator abruptly, the throttle butterfly will be operated in two steps within a period of just a few milliseconds. This allows the car responding smoothly on both acceleration and deceleration.
Integral Cruise Control Function
The ETS system incorporates a cruise control function. Since operation of the cruise control system is based on acceleration control, maximum engine performance is available under all conditions, unlike some previous systems which reverted to basic boost when cruise control was operating.
Intelligent System
The ETS is an intelligent or adaptive system, which means that it adapts itself automatically to changes in air pressure, humidity and variations due to wear in components.
The ETS also incorporates an AIC function for the warm-up phase, governed by time and coolant temperature.
The system continuously processes data from the speedometer, direct ignition system, ABS system, LH system and temperature sensor. It also monitors the position of the throttle butterfly and accelerator.
On the basis of this input data, the ECU controls the actuating motor for the throttle butterfly.
TRACTION CONTROL SYSTEM 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.