Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2002-08-02
2003-11-18
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C303S122000, C180S197000
Reexamination Certificate
active
06650989
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to anti-lock brake systems and more particularly relates to anti-lock brake systems used in combination with all wheel drive systems
BACKGROUND OF THE INVENTION
A method of this type and a circuit arrangement of this general type are disclosed in DE 35 21 960 A1.
To control the wheel slip during a braking operation with an anti-lock, i.e., slip-controlled braking system, it is principally necessary to measure the speed and speed variations of the controlled wheels and to compare these values with an appropriate reference quantity. This reference quantity must show the varying braking pressure requirements (e.g. by means of an electronic regulation and control circuit) to prevent locking of the wheels and thereby maintain driving stability and steerability without increasing the stopping distance. In prior-art slip-controlled braked systems, the so-called vehicle reference speed is used as a reference quantity, in the ideal case reproducing the vehicle speed in consideration of the optimal wheel slip.
It is difficult during a braking operation to determine the actual vehicle speed and the vehicle reference speed from the rotational behavior of the individual wheels, because slip occurs on each wheel and because the road conditions, the instantaneous load on the individual wheels, variations due to cornering, etc., are included in the measurements. To minimize these difficulties, it has already been known in the art to establish the vehicle reference speed by means of an additional wheel that runs freely during the braking operation, or is temporarily not braked. Such measures have not proven expedient for different reasons.
In practice, the vehicle reference speed is commonly fixed by logically combining the rotational behavior of the individual wheels. In state-of-the-art circuits, this reference quantity will follow the instantaneously fastest or second fastest wheel, depending on the situation, while in addition a limitation to the deceleration or acceleration of the vehicle that is maximally possible for physical reasons is effected in the various situations.
In vehicles with only one driven axle, spinning of the driven wheels due to the engine's moment of inertia, with the engine running and the clutch engaged on a slippery roadway, or as a consequence of too high a drive force can be recognized relatively easily in most situations by a comparison with the rotational behavior of the non-driven wheels. In vehicles with all-wheel drive, to which the present invention is related, additional difficulties are encountered by the coupling of the wheels by way of the drive train. This is because on roadways with a low coefficient of friction, when the differences in the road torques at the individual wheels become smaller than the coupling torques of the wheels with respect to each other, a slowly increasing positive slip may develop synchronously on all wheels which cannot be distinguished from an acceleration of the vehicle on roads with a high coefficient of friction only from the measurement of the wheel rotational behavior and logical combining of the individual wheel information. In this case, the vehicle reference speed may rise far beyond the vehicle speed. If a braking operation was now initiated, the electronic unit would detect a great difference between the wheels, which in reality run stably with the vehicle, and the—excessive—vehicle reference speed and, consequently, would start a control operation, i.e., an operation to maintain the pressure constant, or even a pressure reduction. Spinning of all four wheels, thus, leads to a too high vehicle reference speed, with the result that even if the wheels run stably again subsequently, the braking pressure will be decreased too much as long as until the reference quantity has dropped to the vehicle speed again.
A wrong reference speed can have adverse effects also outside a braking operation; it may e.g. cause an unwanted valve actuation.
Therefore, it has been disclosed in DE 35 21 960 A1 mentioned hereinabove to recognize the spinning tendency by way of the rise of the vehicle reference speed, to change over to a second control concept when the spinning tendency is detected and predetermined start conditions are reached, and to maintain the second control concept until defined exit conditions are reached.
The prior art method is so designed that when great positive vehicle reference speed gradients prevail, a change-over to the second control concept is carried out wherein the instantaneous wheel slip stays out of account and only the wheel acceleration or wheel deceleration becomes decisive for the braking pressure control. The vehicle reference speed gradient of traction slip control systems may be very low in vehicles with all-wheel drive due to TSC control, but still range above the maximum that is allowed by the coefficient of friction.
BRIEF SUMMARY OF THE INVENTION
In view of the above, an object of the present invention is to overcome the described shortcomings of prior art circuit arrangements and to develop a method for controlling an anti-lock braking system which permits detecting spinning of the wheels under all conditions, even in an all-wheel drive, and preventing an undesirable braking pressure decrease due to such a situation.
It has been found that this object can be achieved by a generic method in that the detection, or starting, or maintaining of the modified control concept is evaluated in accordance with a TCS signal.
When establishing the criteria for the change-over into the second control concept as known so far, it has been a problem in some situations with all-wheel driven vehicles with traction slip control systems in the event that all wheels undergo traction slip control, to determine the minimum value of the rise of the vehicle reference speed and/or to maintain this minimum value during the predetermined minimum period which is necessary to reach the predetermined start conditions. For example, the controller, more precisely the logical operation, cannot determine the minimum value or maintain it over the minimum period because spinning of the wheels at a very low, homogeneous coefficient of friction induces an intervention of the traction slip control, with the result of an engine intervention so that the acceleration of the wheels and, thus, the rise of the vehicle reference speed is limited. In contrast thereto, the method of the present invention permits undoubtedly detecting the spinning tendency of the wheels in every situation—even during a traction slip control operation, and even in the event of a braking operation induced after this situation, the control will be activated or the braking pressure kept constant or reduced only if the respective wheel becomes indeed unstable and tends to lock. Full braking capacity of the vehicle with the inclusion of the anti-lock control that ensures steerability and driving stability will thus be maintained even after traction slip control operations. While maintaining the method described hereinabove, the method of the present invention considers in all situations the entry into TCS control in the form of a TCS signal or a TCS quantity, and in each of the phases of detecting, starting, and/or maintaining the second control concept, the TCS signal is taken into account alternatively or in addition to the known conditions until predetermined exit conditions prevail.
In a favorable embodiment of the method of the present invention, the control is determined by the modified control concept, if a braking pressure control operation takes place in this phase starting from the TCS control, until at least one vehicle wheel on the rear axle or front axle shows a stable rotational behavior for a predetermined minimum duration. If, however, no braking pressure control is executed in this phase, the modified control concept will be maintained until all wheels lie in a speed range and an acceleration range for a long duration. When all wheels (calibrated wheel speeds or non-calibrated wheel speed
Burkhard Dieter
Gronau Ralph
Continental Teves AG & Co. oHG
Rader & Fishman & Grauer, PLLC
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