Method for determining a set steering angle of steered wheels of a vehicle
The invention relates to a method for determining a set steering angle β o of steered wheels of a vehicle comprising a tractor and a trailer that is articulated with regard to the tractor. This method makes it possible to produce a set value that can be used for various purposes. This set value can thus be used for controlling an actuator acting upon the steering angle or for being communicated in order to inform the driver. According to the invention, during reversing maneuvers: based on a target point C via which the driver would like the path of the vehicle to pass, an angle set value ? c between the axes of the trailer and of the tractor is determined according to said target point C and to the dimensions of the vehicle, and; the set steering angle β of the steered wheels is determined according to a servo-system causing the measured angle ? between the axis of the trailer and the tractor to tend toward said angle set value ? c .
1. A method of determining a steering setpoint angle (β 0 ) for the steered wheels of a vehicle ( 1 ) comprising a tractor ( 2 ) and a trailer ( 8 ) that is articulated with respect to the tractor ( 2 ) during backing-up maneuvers, wherein:
a setpoint angle value (θ C ) is determined for the angle between the axes of the trailer ( 33 ) and of the tractor ( 38 ) using a target point (C) through which the path of the vehicle is to pass and as a function of said target point (C);
the steering angle setpoint value (β 0 ) for the steered wheels is determined as the result of feedback control that causes the measured angle (θ) between the axis of the trailer and of the tractor to tend toward said angle setpoint value (θ C ); and
the value of the setpoint angle (θ C ) between the axes of the trailer ( 33 ) and of the tractor ( 38 ) is determined as a function of the geometry of the vehicle, said geometry comprising a dimension that is taken in the lengthwise direction of the vehicle.
2. The method as recited in claim 1 , wherein the selected target point (C) lies at a predetermined distance (x C ) from the rear of the trailer.
3. The method as recited in claim 1 , wherein the steering angle setpoint value (β 0 ) for the steered wheels includes a component (β 1 ) which is a function of the radius of curvature of the path of the point (B) at which the trailer ( 8 ) is articulated to the tractor ( 2 ).
4. The method as recited in claim 1 , wherein the radius of curvature is calculated with respect to a point of rotation (R) situated on the line ( 34 ) of the rear axle of the vehicle and equidistant from the target point (C) and from the middle (A) of said rear axle.
5. The method as recited in claim 1 , wherein the steering angle setpoint value (β 0 ) for the steered wheels includes a component (β 2 ) that is a function of the difference between the measured angle (θ) between the axes of the tractor ( 38 ) and of the trailer ( 33 ), and said setpoint angle (θ c ).
6. The method as recited in claim 5 , wherein the component (β 2 ) is the result of a proportional, integral, derivative processing of the difference between the measured angle (θ) between the axes of the tractor ( 38 ) and of the trailer ( 33 ) and said setpoint angle (θ C ).
7. The method as recited in claim 1 , wherein the steering angle setpoint value (β 0 ) for the steered wheels includes a component (β 3 ) taken into account when the angle (θ) between the axes of the tractor and of the trailer crosses a predetermined threshold (θ 0 ) and which is intended to reduce said angle (θ).
8. The method as recited in claim 1 , wherein the dimension that is taken in the lengthwise direction of the vehicle is the distance from a point (B) where the trailer is articulated with respect to the tractor to a point (A) that is aligned, as seen from above, with a rear axle of the trailer.
9. The method as recited in claim 1 , wherein the trailer has a plurality of rear axles and the dimension that is taken in the lengthwise direction of the vehicle is the distance from a point (B) where the trailer is articulated with respect to the tractor to a point (A) that is located midway between the rear axles of the trailer.
10. The method as recited in claim 1 , wherein the setpoint angle value (θ C ) between the axes of the trailer ( 33 ) and the tractor ( 38 ) is calculated so that the thrust exerted by the tractor is along a first line ( 37 ) which is perpendicular to a second line ( 36 ) that connects a center of rotation (R) to a first point (B) where the trailer is articulated with respect to the tractor, with the center of rotation (R) being situated at equal distances from the target point (C) and a second point (A) that is aligned, as seen from above, with a fixed rear axle of the vehicle or, when the vehicle has multiple fixed rear axles, that is situated midway between the rear axles, the distance from the center of rotation (R) to the second point (A) being taken perpendicular to the longitudinal axis ( 33 ) of the trailer.