Motor vehicles – With means for detecting wheel slip during vehicle...
Reexamination Certificate
2000-03-06
2002-12-17
Johnson, Brian L. (Department: 3618)
Motor vehicles
With means for detecting wheel slip during vehicle...
C701S001000
Reexamination Certificate
active
06494281
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for stabilizing a motor vehicle.
BACKGROUND INFORMATION
German Published Patent Application No. 19 02 944 describes a device for preventing vehicles from skidding. The device contains measurement instruments for determining the instantaneous vehicle condition, connected to a control unit that responds to certain limit values of the vehicle. The device also includes means that can be switched on for automatic control of at least one device for keeping the vehicle on track, triggered by the control unit on reaching a predetermined limit value for the transverse acceleration. If a maximum possible transverse acceleration for a vehicle design is detected, the program for the control unit is set at a lower value. This means that the brakes are activated regardless of the driver's reaction even below the critical threshold value, i.e., before the vehicle is oversteered, and the power regulating element of the machine is reset at a lower driving power.
German Published Patent Application No. 35 45 715 describes a device for regulating the drive of motor vehicles in the sense of maintaining stable driving conditions. This device includes a computing unit for determining a setpoint and a tolerance range for the rpm difference of the front wheels or the transverse acceleration or the yaw rate and a comparison unit, when this setpoint or tolerance range is compared with the actual value measured. The difference between the actual value and the setpoint or tolerance range serves as a control signal for the brakes of the wheels and/or for a power controlling element of the vehicle's engine.
With the devices described above, the brakes of the wheels and/or a power controlling element for the engine are driven as a function of a comparison between an actual value of a quantity describing the transverse dynamics of the vehicle and a respective limit value so that the vehicle is stabilized on the basis of the reduction in vehicle speed. The vehicle speed resulting from the interventions in the brakes and/or the engine is not preset here.
The object of the present invention is to improve upon existing devices and methods for stabilizing motor vehicles to the extent that on the basis of the vehicle speed a defined condition is established for the vehicle for the case when a quantity describing the transverse dynamics of the vehicle is greater than or equal to a characteristic value for the quantity describing the transverse dynamics of the vehicle.
SUMMARY OF THE INVENTION
The method according to the present invention for stabilizing a motor vehicle is used in particular to prevent a vehicle from rolling over about a vehicle axis oriented in the longitudinal direction of the vehicle. To do so, a quantity describing the transverse dynamics of the vehicle is determined and is compared with at least one characteristic value, in particular a threshold value, for the quantity describing the transverse dynamics of the vehicle. For the case when the quantity describing the transverse dynamics of the vehicle is greater than or equal to the characteristic value, braking measures at least are implemented on at least one wheel and/or engine measures and/or retarder measures are implemented. These braking measures and/or engine measures and/or retarder measures are advantageously implemented in such a way that the speed of the vehicle is reduced to a preselectable speed value or is kept at a preselectable speed value.
Due to the fact that the speed of the vehicle is reduced to or kept at a preselectable speed value by the braking measures and/or by the engine measures and/or by the retarder measures, a defined condition is established for the vehicle in situations that are critical from the standpoint of transverse dynamics. For example, this defined condition may correspond to turning a curve at a maximum possible curve speed. In this case, the preselectable speed value corresponds to the maximum possible curve speed.
The speed of the vehicle is referred to below as the vehicle speed. At this point, the phrase “a vehicle axis oriented in the longitudinal direction of the vehicle” should be explained. First, the vehicle axis about which there is a tendency of the vehicle to roll may be the actual longitudinal axis of the vehicle. Second, it may be a vehicle axis which is twisted by a certain angle with respect to the actual longitudinal axis of the vehicle. It does not matter here whether or not the twisted vehicle axis passes through the center of gravity of the vehicle. The case of the twisted vehicle axis should also allow an orientation of the vehicle axis at which the vehicle axis corresponds to either a diagonal axis of the vehicle or to an axis parallel to the diagonal axis.
The value of the quantity describing the transverse dynamics of the vehicle, which is allowed for the vehicle without the vehicle becoming unstable on reaching this value, is used to advantage for the characteristic value. The term unstable is understood here to refer to the onset of skidding or rolling of the vehicle.
The characteristic value is either a fixedly predetermined value or a value determined for the respective driving condition of the vehicle. The fixedly predetermined value is determined in advance by driving trials, for example, and the resulting vehicle performance, and is supported by simulations. It is assumed that at this characteristic value the vehicle performance is stable in corresponding operating states where this value is reached. Or the characteristic value is determined for the respective vehicle condition. In other words, the characteristic value is determined during driving operation of the vehicle on the basis of the quantities determined for this driving operation.
The characteristic value is advantageously determined at least as a function of a quantity describing the wheel load of at least one wheel. A quantity describing the contact force of the respective wheel is used to advantage as the quantity describing the wheel load of the minimum of one wheel. This quantity is normally available in traction control systems.
Two alternative methods are available for determining the characteristic value. First, the characteristic value is determined as a function of the wheel load of at least one inside wheel in turning a corner and the quantity describing the transverse dynamics of the vehicle. If, as mentioned previously, the contact force of the respective wheel is used as the quantity describing the wheel load, a linear relationship between the quantity describing the transverse dynamics of the vehicle and the contact force is approximated to determine the characteristic value. The characteristic value is then obtained by interpolation, i.e., the characteristic-value corresponds to the value of the quantity describing the transverse dynamics of the vehicle at which the contact force is zero.
This procedure makes use of the fact that the instability of a motor vehicle is manifested first in wheel performance in situations that are critical from the standpoint of transverse dynamics. In other words, this type of determination yields a prompt and accurate measure of the maximum allowed transverse dynamics of a vehicle in the relevant situation. In situations that are critical from the standpoint of transverse dynamics, an imminent instability is manifested first on the inside wheels of the vehicle in turning a corner, so the characteristic value is advantageously determined as a function of a quantity describing the wheel load of an inside wheel in turning a corner.
In the second alternative, a quantity describing the mass of the vehicle is determined as a function of the quantities describing the wheel loads. Then the characteristic value is read out of an engine characteristics map with the help of the quantity describing the mass of the vehicle. The individual values of the engine characteristics map can also be determined in advance by driving tests supported by simulations. Therefore, the vehicle mass is used as
Faye Ian
Leimbach Klaus-Dieter
Wetzel Gabriel
Johnson Brian L.
Kenyon & Kenyon
Klebe G. B.
Robert & Bosch GmbH
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