Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2001-09-10
2003-06-24
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
C180S244000, C180S248000, C180S197000, C303S139000
Reexamination Certificate
active
06584398
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and device for implementing a differential lock function for a vehicle.
BACKGROUND INFORMATION
The production or implementation of a differential lock function, especially the implementation of an interaxle lock function, by actively decelerating wheels having a drive slip that is too high, is known from the related art. In known methods heretofore, an interaxle lock function is usually produced or implemented by using so-called individual control systems. In this context, the individual wheel control system simultaneously assumes the locking function in the transverse direction, and in the longitudinal direction.
German Published Patent Application No. 34 21 776 describes a vehicle having all-wheel drive. In this vehicle, not only are the wheels of one axle connected to the drive shaft, but also the drive shafts are connected to the driving motor via a differential gear. The object of German Published Patent Application No. 34 21 776 is to provide an electronic alternative for the differential locks. The electronic differential locking is implemented by supplying braking pressure to the individual wheel brakes in response to the occurrence of drive slip. That is, one or more wheels are decelerated when this wheel or these wheels undergoes or undergo wheelslip in comparison to the other wheels. When the last wheel slips as well, then the engine torque is reduced. In other words, all of the wheels are adjusted to an optimum drive slip, and therefore allow good lateral grip.
With regard to the implementation of the differential lock function, one can only deduce the supply of braking pressure from German Published Patent Application No. 34 21 776. The use or provision of a specific requirement regarding the level of the braking pressure to be supplied cannot be gathered from this document. Consequently, one can also not infer from it that, within the framework of implementing the differential lock, a braking moment is set in accordance with a preselected setpoint value. Therefore, the actions carried out in this manner do not ensure that the speeds of the driven vehicle axles approach each other in a desired manner.
Therefore, the object of the present invention consists in improving existing methods and devices for implementing a differential lock function.
SUMMARY OF THE INVENTION
The method of the present invention is a method for implementing a differential lock function for a vehicle. In response to incipient slippage of at least one driven wheel the method of the present invention implements the function of a differential lock, using actions carried out independently of the driver, on at least one arrangement for controlling the wheel torque. The implemented differential lock function should preferably be a differential lock acting between the front axle and the rear axle of the vehicle. At least one setpoint value for a wheel torque to be set is selected for carrying out the actions executed independently of the driver.
The vehicle is advantageously a vehicle having all-wheel drive. Therefore, the differential lock function is an interaxle lock acting between the front axle and the rear axle of the vehicle. However, this should not represent a limitation. The present invention's method for implementing an interaxle lock function, which is represented for an all-wheel drive vehicle in the exemplary embodiment, can also be appropriately modified for use in a vehicle having a single driven axle, in order to implement an axle differential locking function. However, this use shall not be discussed in any more detail within the framework of the present application.
The selection of the at least one setpoint value—there are two driven axles in a vehicle having all-wheel drive, which is why two setpoint values are selected—allows the speeds of the driven vehicle axles to approach each other. This measure assures optimum traction for the vehicle.
The arrangement for controlling the wheel torque is advantageously a brake actuator, which is assigned to a wheel of the vehicle, and is a part of a braking system that can generate braking torques at individual vehicle wheels, independently of the driver. On the other hand, the braking system can be a hydraulic, electrohydraulic, pneumatic, electropneumatic, or electromechanical braking system. A controllable mechanical locking device or a controllable clutch can be used as an alternative to the brake actuator.
Such a controllable mechanical locking device or controllable mechanical clutch could be used to bypass an open, center differential, or to directly couple the second drive axle to the main drive axle, as would be possible in the case of a front-wheel drive vehicle having a coupleable rear-wheel drive. In this case, the coupling torque to be transmitted, which results from the equation |MBrSymLSVA−MBrSymLSHA|, would be used as a setpoint value. This setpoint value is input via a torque interface to the secondary controller, as a setpoint value for the coupling torque.
If the arrangement for controlling the wheel torque is a brake actuator, then a setpoint value for a wheel-brake torque is advantageously selected as a setpoint value. In the case of a vehicle, which has all-wheel drive, and consequently has two driven axles, a setpoint value is selected for each of the two axles.
A setpoint value for the Cardanic speed of an axle is ascertained as a function of first wheel speed variables that describe the free-rolling wheel speeds, and as a function of a setpoint value for the drive slip. An actual value for the Cardanic speed of the same axle is ascertained as a function of second wheel speed variables, which describe the wheel speeds ascertained with the aid of wheel speed sensors. A deviation variable is determined as a function of this setpoint value and this actual value. Using a controlling arrangement, in particular a PI controller, this deviation variable is converted into the setpoint value for a wheel torque to be set.
The setpoint value for the Cardanic speed is selected in such a manner, that the differential lock function is activated as a function of time, prior to controlling the engine torque. To this end, the setpoint value for the Cardanic speed is especially ascertained as a function of a speed variable, which describes the vehicle speed. This procedure is based on the following: Measures are initially taken in the starting range, in order to improve the traction by locking action. As long as this potential is not exhausted, the engine torque is only reduced slightly. The drive torque is only reduced sharply, when all four wheels have too much drive slip, or the vehicle becomes unstable. This is accomplished by interventions in the engine-torque control.
Effects in the second wheel speed variables, which originate from reciprocal oscillations of the wheel speeds at the respective axle, are considered in the determination of the deviation variable.
It is advantageous, when the controlling arrangement has a proportional component and an integral component. The integration gain for the integration component is ascertained as a function of the value of the differentiated deviation variable. The integral component is reduced quickly, when at least one wheelslip variable for the respective axle exceeds a predetermined value. The wheelslip is monitored for the following reason: Because of the active build-up of braking pressure at the drive wheel, it can never be ruled out that this wheel is being overly decelerated. This results in brake slip at the overly decelerated wheel, which is to be immediately eliminated by reducing the pressure.
In the case of all-wheel drive vehicles, optimum traction can only be achieved when all of the driving wheels are rotating at speeds that are as uniform as possible. In particular, no differential speed, or as small a differential speed as possible, should occur between front axle (VA) and rear axle (HA), in order that the engine torque can be optimally transmitted through the wheels, to the grou
Cuchlinski Jr. William A.
Hernandez Olga
Kenyon & Kenyon
Robert & Bosch GmbH
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