Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-04-18
2003-08-05
Nguyen, Tan Q. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S072000, C701S094000
Reexamination Certificate
active
06604036
ABSTRACT:
BACKGROUND OF THE INVENTION
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).
Using a mathematical model of the tire and a mathematical model of the vehicle, and based on measurements supplied by sensors recording the actions of the driver of the vehicle (steering wheel angle, brake pedal depress, accelerator pedal depress) by speed sensors for the wheels, and on measurements of the lateral acceleration and yaw velocity, an ESP system constantly calculates the forces at the center of the wheels and estimates the grip potential of the road surface as a function of the lateral acceleration. Furthermore, the ESP system evaluates the handling of the vehicle, compares it to the handling desired by the driver, and corrects this handling if it establishes that the vehicle is not moving along a stable trajectory.
However, the use of tire models can introduce a certain number of approximations into the overall model. Furthermore, the fact that a control system is based on the displacements of the vehicle necessarily leads to a response a posteriori, which can be effective only after a delay depending on the inertia of the vehicle. It can be seen from this that an ESP system, since its variables include, inter alia, measurements of the lateral acceleration and the yaw velocity of the vehicle, first of all has to measure the displacement of the vehicle before deciding whether the displacement is within the bounds of stability or not, and can only then act on the operating means of the vehicle.
The system will detect a displacement of the vehicle not in accordance with the command given by the driver, the more slowly the greater the inertia of the vehicle, and the necessary correction will be all the more difficult the greater the inertia. At the present time the operating means are basically the vehicle's brakes, controlled in this case wheel by wheel and outside the voluntary action of the driver, and the engine force, which can be reduced automatically by regulating the engine.
Furthermore, the detection of yaw movements requires the use of costly sensors. Also, existing systems have to estimate the grip of the wheels on the road surface in order to select the actuating parameters. This estimation deviates to a greater or lesser degree to the actual conditions.
SUMMARY OF THE INVENTION
The object of the present invention is to obviate the aforementioned disadvantages and, more particularly, to exclude completely the inertia of a vehicle in order to be able to act on the appropriate operating means so as to maintain the vehicle in a stable trajectory in accordance with the driver's commands, by regulating the operating means in such a way that the actual forces acting at the center of each wheel correspond to the desired forces.
The invention provides a method for controlling the stability of a vehicle that has the advantage that it can be carried out without having to measure the yaw angle of the vehicle. The invention relates to a vehicle comprising a body and at least one front axle and one rear axle. A preferred but not limiting field of application of the invention is the case where each axle involves at least two suspension devices, each comprising one wheel, the said suspension devices being mounted on both sides of the mid-plane of symmetry of the vehicle, for example in the case of 4-wheeled touring vehicles. Each suspension device comprises a wheel, generally equipped with a tire or, which is the same in the context of the present invention, a non-pneumatic outer casing in contact with the ground. The vehicle is provided with operating means to act on the forces transmitted to the ground by each of the wheels, such as brakes, means for steering the wheels, optionally operating in a selective manner wheel by wheel, and distribution of the loads carried by each of the wheels.
According to a first embodiment of the invention, the method comprises the following steps:
measuring in real time the lateral forces “Y” acting at the center of each of the front and rear wheels;
calculating for each of the wheels the desired lateral forces “Y
desired
” on the basis of commands from the driver of the vehicle;
comparing the desired lateral forces with the measured lateral forces in order to obtain an error signal with respect to the desired lateral forces, and
if the forces acting on one of the axles do not correspond to the desired lateral forces, acting on the operating means so as to minimize the error signal.
The commands of the driver of the vehicle are intended to maintain the vehicle on a straight line trajectory regardless of the ambient disturbances (for example sidewind gusts), or are intended to cause the vehicle to execute a lateral displacement (change of lane for overtaking on a motorway) or to turn. Regardless of the operating means of the vehicle actuated by the driver (conventional steering wheel, operating lever as illustrated for example in patent application EP 0 832 807), the driver's aim in fact is to impose certain lateral forces or certain variations of lateral forces. The invention accordingly involves measuring in real time the effective forces, comparing them with commands by the driver translated into lateral forces or variations in lateral forces, and as a result controlling appropriate operating means available on the vehicle.
According to a second embodiment of the invention, involving processing the driver's commands differently (the reasons for which will be discussed in more detail hereinafter), the method comprises the following steps:
measuring in real time the lateral forces “Y” acting at the center of each of the front and rear wheels, and calculating in real time the effective yaw moment exerted by the wheels on the vehicle;
measuring in real time a signal at the device for controlling the steering and calculating the desired yaw moment “M
desired
”;
comparing the effective and desired yaw moments in order to obtain an error signal with respect to the desired yaw moment; and
if the effective yaw moment is greater than the desired yaw moment, acting on the operating means so as to minimize the error signal.
Accordingly, if the lateral force of the front axle saturates, the vehicle will understeer since the lateral force (forces) of the front axle are less than the forces desired by the driver. An automatic action, for example of the type already known per se in conventional ESP systems (other types of actions will be discussed hereinafter) enables a resultant force to be exerted on the vehicle chassis in accordance with the driver's wishes and thus enables understeering to be avoided.
If on the other hand it is the lateral force of the rear axle that saturates, then the vehicle will oversteer since the lateral forces of the rear axle are less than the forces desired by the driver. The said automatic action enables a resultant force to be exerted on the vehicle chassis in accordance with the driver's wishes and thus enables oversteering to be avoided.
The above description relates to what is conventionally called a steady state (or established state). When c
Michelin & Recherche et Technique S.A.
Nguyen Tan Q.
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