As is known, there exists anti-locking brake and drive traction regulation systems for use on motor vehicles equipped with air brake systems. With anti-locking brake systems, the goal is to prevent locking of the braked wheels, enhancing the ability to maintain control of the vehicle during braking situations. To achieve this goal, braking forces are reduced when an impending lock-up is sensed and increased when the impending lock-up ceases to exist. With drive traction regulation systems, the goal is to prevent the drive wheels from slipping during acceleration of the vehicle. To achieve this goal, braking forces can be applied to the slipping wheels, thereby increasing torque to the non-slipping wheels.
A drive traction regulation system can employ other strategies as well, such as reducing motor torque by controlling combustion, or by upshifting if an automatic transmission is involved. Due to similarities in the hardware required to implement them, anti-lock and drive traction regulation systems often co-exist on vehicles.
Referring now to FIG. 1, there is illustrated a block diagram of an existing combination anti-lock braking/drive traction regulation system shown generally by the reference numeral 20. The combination system 20 includes an electronic control module 22, multiple wheel speed sensors 24, multiple anti-lock brake valves 36, multiple double-check valves 28 and multiple high flow traction control valves 26.
During the traction control event, the vehicle is accelerating and as such, there is torque applied to the rear wheels 30. When the electronic control module 22 senses a slipping rear wheel based upon data from the wheel speed sensors 24, it energizes the traction control valve 26 on the slipping wheel only. This causes the pressure from reservoirs 32 to be applied via line 34 to the appropriate double-check valve 28, on through the anti-lock valve 36 and to the brake chamber 38. Applying the brakes to the slipping wheel causes the torque (which normally takes the path of least resistance) to be transferred to the non-slipping wheel, thus providing enhanced traction capability. The anti-lock valve 36 will then be used to control the pressure on the slipping wheel such that the optimal traction condition can be maintained. A similar system which employs multiple valves and multiple double-check valves is described in U.S. Pat. No. 4,819,995, issued to Lohmann et al.
Referring now to FIG. 2, there is illustrated a block diagram for another existing combination anti-lock/traction control system, shown generally by reference numeral 50. As shown, the combination system 50 includes an electronic control unit 52, multiple wheel speed sensors 54, a single high flow traction control valve 56, multiple anti-lock brake valves 58 and multiple double-check valves 60.
During the traction control event, the vehicle is accelerating and as such, there is torque applied to the rear wheels 62. When the electronic control module 52 senses a slipping wheel based upon data from the wheel speed sensors 54, it energizes the traction control valve 56 and energizes the ABS valve 58 associated with the non-slipping wheel. Energizing the traction control valve 56 results in air flow from the reservoir 64 to the double-check valves 60, thus causing them to seal off air to lines 66. This prevents the air from being exhausted out through the relay valve 68. This air then continues on to the ABS valves 58. The ABS valve 58 associated with the non-slipping wheel is energized and as such, it does not allow air to flow to the associated brake chamber 70. The ABS valve 58 associated with the slipping wheel will allow air to pressurize the associated brake chamber 70 and as such, the torque will be transferred to the non-slipping wheel. The anti-lock valve 58 will then be used to control the pressure on the slipping wheel such that the optimal traction condition can be maintained.
The design of both traction control systems 20 and 50 is such that they require the traction control valves to supply air from the high pressure system reservoir directly to the brake chambers. The fact that the brake chambers are of an appreciable volume and that the traction control system must react reasonably quickly, requires these valves and the associated double check valves to be of a design level that provides a high flow capability. This makes these valves large and complex and as such, more costly. The braking forces required for traction control are also only a fraction of those required for full braking. Therefore, applying the full system pressure to the brake chambers, as is done in both systems 20 and 50, makes the control of these systems more difficult.
It is, therefore, desirable to provide a traction control system with less components and that these components be of a less complex and less costly design level. Also, it is desirable to utilize a control pressure that is at a lower level than full system pressure.