System and method for determining the height of the center of gravity of a vehicle

[0002] The present invention relates to a system for determining the height of the center of gravity of a vehicle having an arrangement configured to determine the difference between wheel contact forces and an arrangement configured to determine a transverse acceleration. Furthermore, the present invention relates to a method for determining the height of the center of gravity of a vehicle, which includes the steps of determining a difference between wheel contact forces and determining a transverse acceleration.

[0003] In extreme circumstances, vehicles, in particular motor vehicles, can roll over. In particular, this is true if the center of gravity of the vehicle is relatively high. In such instances, taking a curve at an excessive speed may be enough to cause the vehicle to roll over. However, even in the case of vehicles having a center of gravity so low that they do not roll over during smooth travel along a single curve, when performing dynamic maneuvers, such as taking switchback curves, a build-up process may result in a roll-over. In all cases, the higher the vehicle's center of gravity, the greater the tendency to roll over, it being important that the center of gravity may shift significantly due to the loading of the vehicle, e.g., if additional loads are placed on the roof. The position of a vehicle's center of gravity may be measured, and, based on the results of these measurements, the vehicle dynamics control system should be subjected to influence, ultimately in order to prevent rolling over. Moreover, a system of this kind, which is based on measuring the lateral forces involved in the taking of a curve in a defined manner, among other things does not keep the vehicle from rolling over in the case of dynamic maneuvers such as taking switchback curves.

[0004] The present invention relates to a system that includes an arrangement configured to determine comparison values which compare the change in the difference between wheel contact forces with the change in the transverse acceleration and an arrangement configured to evaluate a roll model which determines the height of the center of gravity using the comparison values. In this manner, it is possible to influence driving behavior not only in the case of static driving behavior, such as that which arises when a vehicle takes a curve in a defined manner, but also to influence driving behavior under extreme conditions, such as that which arises in switchback curves. A roll model, which modulates or models the vehicle's roll motion, may determine the height of the center of gravity from a comparison of the change in the wheel contact force difference with the change in the transverse acceleration. Thus, it is possible to determine whether countermeasures to prevent an imminent roll-over may be taken.

[0005] The device configured to determine the difference between wheel contact forces may measure wheel contact forces on the left side of the vehicle and on the right side of the vehicle using sensors and may calculate a difference between the wheel contact forces that are measured. This arrangement may be particularly useful, as in many vehicles sensors for measuring wheel contact forces are present, e.g., in vehicles equipped with ABS systems (anti-lock brake systems) or TCS systems (traction control systems).

[0006] However, it may also be useful that the arrangement configured to determine the difference between wheel contact forces includes sensors configured to perform direct measurement. Sensors of this type may be arranged, for example, on the motor vehicle's stabilizer. As the difference is measured directly, there is no need to calculate the difference using absolute values.

[0007] The arrangement configured to determine transverse acceleration may include an arrangement configured to measure the transverse acceleration. These yield reliable values so that the height of the center of gravity may be determined precisely.

[0008] However, it may also be useful for the arrangement configured to determine a transverse acceleration to include an arrangement configured to estimate the transverse acceleration. By using estimate algorithms, the expenditure associated with measuring components on the vehicle may be reduced, and thus also the number of vehicle components may be reduced. As estimate algorithms are used in TCS systems (traction control systems), using them constitutes a sensible measure.

[0009] It may be especially useful for the arrangement configured to evaluate a roll model to be configured to determine a moment of inertia about a critical axis, it being possible to determine the height of the center of gravity from the moment of inertia. As the moment of inertia is a characteristic value in conjunction with the rotation movement that is present in the case of a roll-over, it may be particularly suitable for performing follow-up determination of the height of the center of gravity.

[0010] An arrangement configured to modify a transverse acceleration threshold based on the height of the center of gravity may be provided. Thus, the transverse acceleration threshold above which engine output is reduced or the vehicle is braked may be reduced if the height of the center of gravity is increasing.

[0011] The present invention also relates to a method in which comparison values are determined, the change in the difference between wheel contact forces being compared with the change in the transverse acceleration, and in which with the help of a roll model the height of the center of gravity may be determined from the comparison values. In this manner, it is possible to influence driving behavior not only in the case of static driving behavior, which occurs, for example, when the vehicle takes a curve in a defined manner, but also under extreme conditions, which are, for example, present when the vehicle takes switchback curves. A roll model which modulates or models the roll movement may determine the height of the center of gravity from a comparison of the change in the wheel contact force difference with the change in the transverse acceleration. Thus, it is possible to determine whether countermeasures to prevent an imminent roll-over may be taken.

[0012] The difference between wheel contact forces may be determined, wheel contact forces on the left side of the vehicle and on the right side of the vehicle being measured by sensors, and the difference between the measured wheel contact forces may be determined. This arrangement may be particularly useful, as in many vehicles sensors for measuring wheel contact forces are present, e.g., in vehicles equipped with ABS systems (anti-lock brake systems) or TCS systems (traction control systems).

[0013] However, the difference between wheel contact forces may be determined via direct measurement using sensors. Sensors of this type may be arranged, for example, on the motor vehicle's stabilizer. As the difference is measured directly, there is no need to calculate the difference using absolute values.

[0014] The transverse acceleration may be measured. This arrangement yields reliable values so that the height of the center of gravity may be determined precisely.

[0015] Moreover, the transverse acceleration may be estimated. By using estimate algorithms, the expenditure associated with measuring components on the vehicle may be reduced, and thus also the number of vehicle components may be reduced. As estimate algorithms are used in TCS systems (traction control systems), using them constitutes an especially sensible measure.

[0016] A moment of inertia about a critical axis may be determined, and the height of the center of gravity may be determined from the moment of inertia. As the moment of inertia is a characteristic value in conjunction with the rotation movement that is present in the case of a roll-over, it may be particularly suitable for performing a follow-up determination of the height of the center of gravity.

[0017] A transverse acceleration threshold may be modified based on the height of the center of gravity. Thus, the transverse acceleration threshold above which the engine output is reduced or the vehicle is braked may be reduced if the height of the center of gravity is increasing.

[0018] The present invention is based on the unanticipated discovery that rolling-over of the vehicle may be prevented even in the case of dynamic driving maneuvers, such as in switchback curves. This result is achieved by using a roll model, which provides a model of the vehicle's roll movement so that dynamic driving maneuvers that differ dramatically from the taking of a curve in a defined manner may also be subjected to control.

[0019] FIG. 1 is a schematic view of a system according to the present invention.

[0020] FIG. 1 is a schematic view of a system according to the present invention. Wheel 100 represents the wheels of a motor vehicle. A wheel contact force is measured at this wheel. Furthermore, wheel contact forces at the other wheels are measured. These measured values are input into an arrangement 10 configured to determine a difference between wheel contact forces, via which subsequently the difference between the wheel contact forces on the left side of the vehicle and on the right side of the vehicle is calculated. Furthermore, an arrangement 12 is configured to calculate a transverse acceleration, for example, measured values which are measured at a suitable point on the vehicle being sent to arrangement 12. The values for the difference between the wheel contact forces and the transverse accelerations that have been determined are sent to an arrangement 14 configured to determine comparison values, which compares, for example, the increase in the wheel contact forces difference with the increase in the transverse acceleration. In accordance with arrangement 16, the height of the center of gravity is determined from these comparison values in conjunction with a roll model. This height of the center of gravity is sent to an arrangement 18 configured to modify a transverse acceleration threshold. Arrangement 18 may, for example, if the height of the center of gravity is increasing, cause braking of the vehicle in the manner illustrated, or if the height of the center of gravity is increasing the engine output may be reduced.

[0021] The above description of the example embodiments according to the present invention is for illustrative purpose only and is not intended to limit the scope of the present invention. Various changes and modifications are possible within the scope of the present invention.