Method for controlling the stability of a vehicle based on lateral forces exerted on each wheel

#The present invention relates to systems for controlling the stability of a vehicle, commonly known as ESP(Electronic Stability Program) systems.

#In safety systems for vehicles, it is necessary to be able to assess the handling of the vehicle in real time. This is the basis of the so-called ESP systems for controlling stability. These systems currently rely on, inter alia, monitoring movements of the vehicle by installing sensors in order to measure the lateral acceleration of the vehicle and the yaw velocity of the vehicle.

#When moving under good safety conditions, that is to say when the stability of the vehicle is not compromised, the vehicle obeys the driver's commands. If the driver, essentially as a result of his actions of steering the wheel, drives the vehicle beyond the limits of safety, the vehicle will exhibit oversteering or understeering. The vehicle turns, that is to say performs a yaw movement, in excess of that desired by the driver (oversteering) or less than desired by the driver (understeering).

#The invention will be described in more detail hereinafter with the aid of the following figures, in which:

#FIG. 1 is a block diagram illustrating the invention,

#FIG. 2 shows the arrangement of a two-wheel vehicle,

#We shall start from the fact that, at a given speed, an angle at the steering wheel imposed by the driver may be interpreted as a lateral force expectation or as a yaw moment expectation on the vehicle. This is shown diagrammatically in the top part of FIG. 1. Furthermore, it has been seen that in order to implement the present invention, it is necessary to have measurements of the real lateral forces (lateral forces of the pneumatic tires or elastic tire casings used in the suspension device). This is illustrated in the left-hand section, starting from “vehicle” in FIG. 1. The diagram in FIG. 1 superimposes two methods: either the actions of the driver are interpreted as lateral forces demands (i.e. expectations), which are compared with the measured lateral forces, or the actions of the driver are interpreted as a yaw moment demand (i.e. expectations), and the lateral force measurements are converted into a measured yaw moment in order to make the required comparison.

#It will be assumed that the lateral forces of the front axle are less than the forces required by the driver. An automatic action enables a resultant of force on the vehicle chassis to be obtained in accordance with the wishes of the driver and thus enables understeering to be avoided.

#As an alternative or in addition to a braking action, an action on an additional steering means, exerted for example by means of an irreversible stepping motor mounted in the steering column, also enables the resultant of forces on the vehicle chassis to be approximated in accordance with the wishes of the driver. Another possible way of effecting the action on a steering means consists for example in sending the appropriate control commands to the controller described in U.S. Pat. No. 5,884,724.