With the introduction of the 1994 model 3 Series (E36), BMW is pleased to announce a new Automatic Stability Control with Traction Control System (ASC+T) known as ASC+T (Teves).
This system is available as optional equipment on all M50 engine equipped 1994 3 Series vehicles. The Teves ASC+T system is a further development of the Teves ABS Mark IV system. The Automatic Stability Control Plus Traction (ASC+T) system is incorporated into the Teves ABS Mark IV system with the addition of only a few additional components.The technician is encouraged to review the following Technical Reference bulletins in order to review the concepts of wheel slip, lateral locating forces, braking coefficients, and features and limitations of previous ABS, ACS, and ASC+T systems:
34 04 83 (2035) Antilock Braking System
12 01 89 (2095) Automatic Stability Control
34 01 90 (2105) Automatic Stability Control with Traction Control System
The function of the Teves ASC+T system is similar to ASC systems installed in other BMW models, namely the control of wheel slip by providing traction control (while driving off and at slow speeds) and stability control (while driving at cruising speeds and while cornering). By controlling wheel slip, frictional contact is maximized between the tires and the road surfaces under a variety of driving conditions.
The Teves ABS/ASC+T is a four channel, front/rear split system. Each rear brake caliper has its own hydraulic line from the hydraulic unit. The ASC+T control determines the degree of slip based on the signals from the wheel speed sensors. The control module averages the speeds of the two front wheels to determine vehicle speed. The speeds of the front and rear wheels on each side are monitored to determine the degree of slip. The programming of the control module will then activate ASC+T regulation using one of the following principles, based on various combinations of vehicle speed and traction conditions:
Select High - Traction: Select Low - Stability
1. Rear Brake Control 1. Throttle Control
2. Throttle Control 2. Ignition Control
3. Ignition Control 3. Rear Brake Control
During ASC+T regulation the ASC Control Module has the ability to pulse the rear brakes individually or together. This depends on the degree of control required to restore traction as determined by the control module. During ABS regulation the Control Module will pulse the rear brakes together as with previous anti-lock systems. In addition to the traction control, the ASC+T Control Module interfaces with the DME control module. This will further reduce the engine's output torque. The total scope of engine control is the same as other ASC systems and includes:
· Engine Intake Air Regulation
· Ignition Timing Retard
· Ignition/Injection Fade Out
On vehicles equipped with automatic transmissions, the ASC+T system interfaces with the EGS control module. This will delay or inhibit shifts during ASC regulation to prevent instability.
The Teves system uses one control module to house all of the electronics for ABS/ ASC+T and ADS regulation. The control module (1) is mounted behind the glove box in the passenger compart-ment.
The hydraulic unit is mounted under the brake booster. It contains the components as listed in the following illustration.
ADS II Motor
The ADS II motor is located just above the hydraulic unit mounted to the left front shock tower. I is connected to the throttle valve through a bowden cable.
THROTTLE VALVE WITH DUAL FEEDBACK POTENTIOMETER
The throttle valve is operated via cable from the accelerator pedal as in the past. An additional tension spring allows the ADS motor to close the throttle valve regardless of how far the accelerator is being pressed.
Dual Feedback Potentiometer
The throttle potentiometer is a dual potentiometer. One potentiometer is the throttle position input signal to the DME as in the past. The second potentiometer is the actual throttle valve position input to the ASC+T control module during ASC regulation.
HYDRAULIC SYSTEM OVERVIEW
ASC+T Hydraulic Operation
The inclusion of the ASC+T function to the Teves Mark IV ABS system is done quite simply by modifying the existing ABS components and utilizing them to achieve stability control. One such
modification of the system is the addition of a separator valve to the hydraulic unit. The separate valve isolates the brake master cylinder from the hydraulic unit when in ASC+T regulation.
HYDRAULIC OPERATION - TRACTION CONTROL PHASE