Fluid-pressure and analogous brake systems – Speed-controlled – And traction control
Reexamination Certificate
2001-08-30
2003-12-16
Graham, Matthew C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
And traction control
C303S166000, C303S189000, C303S191000, C701S070000
Reexamination Certificate
active
06663196
ABSTRACT:
The present invention relates to a device and a method for controlling wheel slip for a motor vehicle according to the preamble of Patent claim
1
and the preamble of Patent claim
6
, respectively.
Devices for controlling wheel slip are known in various designs. For example, such a device for controlling wheel slip can be an antilock braking system, also known as a brake-slip controller. With these means, the brake slip is controlled in a known manner by a reduction in braking pressure independently of the driver, such that the wheels braked by the driver are prevented from locking (antilock controller function, brake-slip controller function; ABS). The device for controlling wheel slip can also be designed as a traction controller, with which the drive slip of the driven wheels is controlled at least by a braking-pressure buildup carried out independently of the driver, such that the driven wheels are prevented from spinning, for example, during a standing start (traction controller function; TCS). It is furthermore conceivable that the device for controlling wheel slip is designed as a vehicle dynamics control {electronic stability program) or yaw-rate control (ESP) as is known, for example, from the publication “
FDR—Die Fahrdynamikregelung von Bosch
” (ESP—The Electronic Stability Program of Bosch) appearing in the Automobiltechnische Zeitschrift (ATZ) 96, 1994, issue 11, on pages 674 through 689.
The following explanations relate essentially to a device for controlling wheel slip, with which at least the brake slip is controllable. However, this is not intended to represent any restriction; the subject matter of the present invention can be utilized in all the devices for controlling wheel slip indicated above. A traction control system is usually combined with a brake-slip control. A vehicle dynamics control is composed first of all of a higher-level yaw-rate controller, and secondly of a brake-slip controller and a traction controller, both of which are subordinate to the yaw-rate controller. As further explained in the following, with a view to the subject matter of the present invention, the anti-lock control system, i.e. the brake-slip control on the one hand, and the traction control system or the vehicle dynamics control on the other hand differ first and foremost in the manner as to how the wheels are brought into high slippage or to locking in response to a detected skidding.
If a vehicle, which is not equipped with a device for controlling wheel slip by which at least the brake slip is controllable, goes into a skid when braking with locked wheels, then generally the moving direction of the motor-vehicle center of gravity existing prior to the skid is retained, since locked wheels are unable to transmit any lateral forces. In the same way, such a vehicle behaves so that the wheels lock when, unbraked, it goes into a skid because of exceeding vehicle-dynamic limits and the driver actuates the brakes during the skidding process.
A device for controlling wheel slip, with which at least the brake slip is controllable, prevents the triggering of a skidding process during braking as long as vehicle-dynamic limits (e.g. excessive curve speed) are not exceeded. However, if braking is carried out during a skidding process, or if a skidding process is triggered during a controlled braking, the wheels continue to be able to transmit lateral guiding forces because of the brake-slip control with which locking of the wheels is intended to be avoided. As long as the yaw velocity and the float angle of the vehicle are not too great, the driver, depending on his/her skill, is still able to hold the vehicle on the desired course. If the yaw velocity and float angle, respectively, exceed certain limits, then even the experienced driver may no longer be able to keep the skid under control.
In addition, because of the kinematics of a skidding process, with increasing float angle, the tires of a motor vehicle experience a decrease in the effective circumferential (longitudinal) force. The resulting reduction in pressure causes an increase in the lateral guiding forces at the front axle, whereby, depending on the adjusted steering angle, an uncontrollable change in the travel direction can result which further intensifies the skid.
The German Patent 42 19 750.3 describes an anti-lock control system for a motor vehicle that normally varies the braking pressure at the vehicle wheels depending on the motion behavior of the vehicle wheels (wheel deceleration, wheel acceleration and/or wheel slip), and upon detection of a vehicle skid, brings at least a part of the wheels into high slippage, preferably locks them, by a buildup of braking pressure, a prerequisite for the skid detection being that at least one rear wheel lies in a predefined deceleration band and pressure was reduced at it over a predefined time, a judgment of skidding being made when the two named conditions are present simultaneously and for a predefined time.
From PCT/EP89/00961, it is known to strongly brake (bring into high slippage) or to lock the front wheels in response to an unequivocal ascertainment of such a problematic driving situation, whereby the vehicle is able to re-orient itself in the direction of travel. An additional assistance can be provided by influencing the braking force at the rear wheels. To detect skidding, in this document, the sum of the differences of pressure reduction time minus pressure buildup time is determined at at least one front wheel and one rear wheel, the ascertained time being set in relationship with the total control time, and a judgment of skidding being made when this relationship exceeds a predefined value. This method is regarded as relatively costly, since the ascertainment of the relationship ties up computer capacity to a not inconsiderable extent.
In response to a detected vehicle skid, the front wheels are strongly braked. In this context, the braking of the front wheels should be so strong that they are able to transmit almost no lateral force. In the ideal case, the front wheels lock, i.e. because of the braking intervention at the front wheels, no lateral guidance exists at them any longer. Usually such braking interventions are not carried out at the rear wheels, that is to say, the rear wheels are not strongly braked. In the normal case, only braking interventions of the anti-lock braking system, i.e. the brake-slip control, are carried out at the rear wheels, that is, the wheels of the rear axle are in a stable state; they are able to transmit lateral forces. The result is that the rear axle of the vehicle forms a pole about which the vehicle can rotate. If one thinks of the time sequence with which the individual steps proceed, then it is comprehensible that the vehicle can orient itself again in the direction of travel. First of all, a vehicle skid is detected. This detection is carried out in such a timely manner that the vehicle still does not exhibit all too large an angle of rotation about its vertical axis relative to its original travel direction or orientation which existed prior to the start of the skid. That is to say, the vehicle still has not rotated all too much compared to its original travel direction. As soon as the skid is detected, the front wheels are strongly braked, which means no lateral guidance is present any longer at the front wheels. Since the rear wheels still exhibit the lateral forces which existed before the skid began, and therefore permit a lateral guidance, the vehicle is rotated about its rear axle back into the direction of travel.
If, in addition to the wheels of the front axle, the wheels of the rear axle are also brought into high slippage, i.e. locked, then the vehicle is no longer able to re-orient itself into its original direction of travel, that is, the rotation of the vehicle about its vertical axis is reduced or limited. In this case, the movement of the vehicle is led back to an essentially purely translatory movement. The movement of the vehicle in this case follows the movement of its center of gravity. As
Graham Matthew C.
Kenyon & Kenyon
Robert & Bosch GmbH
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