Method and steering system for steering a vehicle

Abstract

A method for steering a vehicle that comprises a steering system with a steering wheel and a front axle as well as a rear axle with wheels, wherein it is provided that a direction of the vehicle is adjusted manually by a driver of the vehicle by adjustment of a steering wheel angle of the steering wheel, as a result of which, for the wheels of at least one of the axles, a steering angle is adjusted, which is obtained from the steering wheel angle plus a superposition angle, wherein, through an automatically adjustable steering ratio for the wheels of at least one of the axles, a ratio of the steering wheel angle to the steering angle for the wheels is set, wherein the vehicle travels into a curve on a circular path with a radius at a speed with a first value, wherein a steering wheel angle is adjusted by the driver.

Claims

1. A method for steering a vehicle that comprises a steering system with a steering wheel and a front axle as well as a rear axle with wheels, the method comprising: adjusting a direction of the vehicle is manually by a driver of the vehicle by adjustment of a steering wheel angle of the steering wheel, as a result of which, for the wheels of at least one of the axles, a steering angle is adjusted, which is obtained from the steering wheel angle plus a superposition angle; setting a ratio of the steering wheel angle to the steering angle for the wheels through an automatically adjustable steering ratio for wheels of at least one of the axles, wherein the vehicle travels at a speed with a first value into a curve on a circular path with a radius; adjusting a superposition angle that is a function of the first value of the speed automatically by a steering system, taking into consideration a characteristic curve for a relation between the superposition angle and the speed; and changing the steering ratio automatically by the steering system as a function of the speed, while the radius of the circular path is kept constant.

2. The method according to claim 1, further comprising: adjusting the superposition angle automatically while the steering wheel angle is held constant.

3. The method according to claim 1, further comprising: altering the steering ratio when the steering wheel angle is altered by the driver, while the radius of the circular path remains constant.

4. The method according to claim 1, further comprising: altering the superposition angle for the wheels of the at least one axle in accordance with a change in the steering ratio.

5. The method according to claim 1, further comprising: reducing the speed from the first value to a second value.

6. The method according to claim 1, further comprising: changing at least one of a steering ratio for the wheels of the front axle and a steering ratio for the wheels of the rear axle depending on a change in the steering wheel angle.

7. The method according to claim 1, further comprising: changing the steering ratio in proportion to a change in the speed.

8. A steering system for steering a vehicle comprising: a steering wheel; a front axle; and a rear axle with wheels, wherein a direction of the vehicle can be adjusted manually by a driver of the vehicle by adjusting a steering wheel angle of the steering wheel, the steering system is configured to adjust a steering angle for the wheels of at least one of the axles depending on the adjusted steering wheel angle, said steering angle being obtained from the steering wheel angle plus a superposition angle, adjust a steering ratio automatically for the wheels of at least one of the axles to set a ratio of the steering wheel angle to the steering angle for the wheels, wherein, when the vehicle travels into a curve on a circular path with a radius at a speed with a first value and a steering wheel angle is adjusted by the driver, taking into consideration a characteristic curve for a relation between the superposition angle and the speed, adjust a superposition angle that is a function of the first value of the speed automatically, and change the steering ratio as a function of the speed automatically, while keeping the radius of the circular path constant.

9. A steering system according to claim 8, further comprising: at least one actuator, which is associated with at least one axle and is configured to automatically adjust the steering angle for the wheels of the at least one axle, taking into consideration the manually adjustable steering wheel angle and the automatically adjustable steering ratio.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is illustrated schematically on the basis of embodiments in the drawing and will be described schematically and in detail with reference to the drawing.

(2) FIG. 1 shows, in schematic illustration, a vehicle, which has an embodiment of the steering system according to the invention, when an embodiment of the method according to the invention is carried out.

DETAILED DESCRIPTION

(3) The vehicle 2 shown schematically in FIG. 1 comprises a front axle 4 with front wheels 6 and a rear axle 8 with rear wheels 10. The embodiment of the steering system 12 has a steering wheel 14, a front actuator 18 for adjusting a steering angle as a parameter of the wheels 6 of the front axle 4, a rear actuator 20 for adjusting a steering angle as a parameter of the wheels 10 of the rear axle 4, and a control device 16.

(4) A direction of the vehicle 2 is influenced by a driver of the vehicle 2 by controlling the steering wheel 14, with a steering wheel angle of the steering wheel 14 being adjusted—for example, altered—as a parameter of the vehicle 2. Starting from the respectively currently adjusted steering wheel angle of the steering wheel 14, the actuators 18, 20 are controlled by the control device 16, as a result of which, in turn, the axles 4, 8 and wheels 6, 10 arranged on them are steered. In this case, a front steering angle is adjusted for the wheels 6 of the front axle 4 through a front steering ratio that is adjusted by the control device 16 and a rear steering angle is adjusted for the wheels 10 of the rear axle 8 through a rear steering ratio that is adjusted by the control device 16. In this case, through the particular steering ratio that is automatically adjusted and can be changed by the control device 16, a provided ratio of the steering wheel angle to the steering angle of the particular axle 4, 8 is fixed or defined. If the vehicle 2 travels into and/or through a curve 22, the vehicle 2 moves on a circular path, which has a radius or can be defined by the radius. In this case, the steering angle is obtained from the steering wheel angle plus a superposition angle, which, taking into consideration a characteristic curve, is a function of the speed of the vehicle and the radius of the circular path that the vehicle describes in the curve 22.

(5) In the embodiment of the method for steering a vehicle 2, it is provided that, during travel along a curve, a direction of the vehicle 2 is changed by the curve 22, with the steering wheel angle and at least one steering angle that results based on a particular steering ratio and a superposition angle for the wheels 6, 10 of the at least one axle 4, 8 differing from 0° or being greater than or less than 0° and/or being altered. Furthermore, in this case, a particular steering angle is automatically adapted to the speed on the basis of the adaptation to the changed speed.

(6) If, during travel along a curve with a change in direction of the vehicle 2, the speed of the vehicle 2 is further changed, the steering ratio is also automatically changed, taking into consideration a functional dependence of the steering ratio on the speed, and is usually reduced during braking of the vehicle 2 and increased during acceleration of the vehicle 2, but with the superposition angle being dynamically adapted in such a way that the steering effort stays constant. On account thereof, the steering angle is increased during braking and is automatically reduced during acceleration, without it being necessary for the driver to turn inward or outward.

(7) Here, in a first case, the steering ratio is kept constant, wherein the steering ratio is changed only when the steering wheel angle is changed. In a second case, the steering ratio is automatically altered and the steering wheel angle is held constant.