Steering system with front-axle steering and rear-axle steering, method for controlling such a steering system and motor vehicle

Abstract

Steering system for a motor vehicle (1), comprising a front-axle steering system (3) with a steering assistance device (11), a steering assistance control unit (13) for controlling the steering assistance device (11), and a rear-axle steering system (15) with two steering actuators (19), one steering actuator (19) being assigned to each rear wheel of the motor vehicle (1), the steering assistance control unit (13) of the front-axle steering system (3) being used to control the two steering actuators (19) of the rear-axle steering system (15), the two steering actuators (19) of the rear-axle steering system (15) being connected to the steering assistance control unit (13) of the front-axle steering system (3) via a bus system (23), each of the steering actuators (19) being assigned its own power electronics unit (21) which is connected to the steering assistance control unit (13) of the front-axle steering system (3).

Description

[0001] The invention relates to a steering system with front axle steering and rear axle steering, a method for controlling such a steering system and a motor vehicle.

[0002] In such steering systems with front-axle and rear-axle steering, the steering angle on the rear axle is set in the same direction as the steering angle on the front axle if greater vehicle stability and better straight-line stability are desired. In contrast, the steering angle on the rear axle is set in the opposite direction to the steering angle on the front axle if the vehicle's maneuverability is to be improved by increasing the overall steering angle.

[0003] DE 10 2012 015 988 A1 discloses a steering system with front-axle steering and rear-axle steering, as well as a method for controlling such a steering system. A first control unit is provided for controlling the front-axle steering, and a second control unit is provided for controlling the rear-axle steering. The first control unit for the front-axle steering and the second control unit for the rear-axle steering can be connected to each other via a bus system.

[0004] From DE 11 2010 005 485 T5 a vehicle with a tire steering angle varying device is known.

[0005] From DE 11 2013 006 873 T5 a vehicle with a front wheel steering device and a rear wheel steering device is known.

[0006] From DE 10 2013 220 921 A1 a steering angle device for a vehicle is known.

[0007] From DE 40 06 150 A1 a front and rear wheel steering device for a vehicle is known.

[0008] The invention is based on the object of providing a steering system for a motor vehicle with front-axle steering and rear-axle steering that has a simple and cost-effective design while enabling particularly safe operation. For the same purpose, a method for controlling a steering system is to be provided.

[0009] The object is achieved according to the invention by a steering system having the features of claim 1, by a method having the features of claim 3 and by a motor vehicle having the features of claim 4.

[0010] A steering system for a motor vehicle according to the invention comprises a front-axle steering system with a power steering device, a power steering control unit for controlling the power steering device of the front-axle steering system, and a rear-axle steering system with two steering actuators. The power steering control unit of the front-axle steering system also serves to control the two steering actuators of the rear-axle steering system.

[0011] The steering system according to the invention has the advantage that the electronic architecture of the power steering control unit is used to control the steering actuators of the rear-axle steering system, thus eliminating the need for a separate control unit for the steering actuator(s) of the rear-axle steering system. This also reduces the required installation space and the complexity and cost of the electrical components and connections.

[0012] The electronic control of the rear-axle steering actuators can therefore be easily integrated as an additional option into the power steering control unit for controlling the front-axle steering system. This has the advantage that identical power steering control units can be used in different vehicles, regardless of whether the vehicle in question is equipped with an optional rear-axle steering system or only has front-axle steering. This can also be referred to as steering system scalability.

[0013] The safety concept of the front-axle steering system can also be applied in the same way to the steering actuators of the rear-axle steering system. This increases the operational reliability of the entire steering system and, in the event of a possible defect, easily ensures emergency operation and thus the availability of the steering system.

[0014] The same advantages arise in the motor vehicle according to the invention and in the method according to the invention for controlling a corresponding steering system according to claim 3, in which the two steering actuators of the rear axle steering are controlled by the steering aid control unit of the front axle steering.

[0015] Advantageous further developments of the invention are specified in the subclaims.

[0016] According to the invention, two steering actuators for the rear-axle steering are provided on the rear axle of the motor vehicle, with one steering actuator being assigned to each rear wheel of the motor vehicle. For a simple design and safe operation of the steering system according to the invention, it is advantageous if the steering control unit for the front-axle steering serves, according to the invention, to control both steering actuators of the rear-axle steering.

[0017] It is also advantageous for a simple construction of the steering system according to the invention and a simple steering assistance on the front axle steering as well as a simple control of the steering actuators if the front axle steering and the rear axle steering are designed as electromechanical steering systems, ie the front axle steering is electromechanically assisted and the rear axle steering is electromechanically actuated.

[0018] In order to connect the two steering actuators of the rear axle steering to the steering aid control unit of the front axle steering as simply as possible for its control, it is advantageous to establish this connection via a bus system according to the invention.

[0019] For the power supply of the steering actuators located near the rear axle, it is advantageous if, according to the invention, the steering actuators are assigned their own power electronics, which are connected to the steering assist control unit of the front-axle steering. The power supply and power electronics of the steering actuators on the rear axle can also be integrated directly into the actuators or implemented by an external, combined-function control unit, e.g., a central driver assistance control unit with power electronics.

[0020] An embodiment of a steering system according to the invention for a motor vehicle is shown in the figure in a simplified representation.

[0021] The figure shows a highly simplified schematic view of a motor vehicle 1 with an electromechanical front-axle steering system 3. The front-axle steering system 3 is used to steer two front wheels 9 of the motor vehicle 1. The driver's steering input is transmitted to the front-axle steering system 3 via a steering wheel 5 and a steering column 7. In order to make it easier for the driver to apply the steering force or torque required to steer the motor vehicle 1, a steering assist device 11 and a steering assist control unit 13 are provided for controlling and regulating the steering assist device 11. The steering assist device 11 has, for example, an electric motor (not shown), which applies additional force or torque to the front-axle steering system and thus assists the driver.To measure the manual steering torque applied by the driver, a torque measuring device (not shown) is arranged in the area of the steering column 7, which is connected to the steering assistance control unit 13. This manual steering torque determines the amount of steering assistance or steering support applied by the steering assistance device 11.

[0022] The motor vehicle 1 also has a rear-axle steering system 15. In steering systems with front-axle steering and rear-axle steering, the steering angle on the rear axle can be set in the same direction as the steering angle on the front axle to achieve greater vehicle stability and better straight-line stability. In contrast, the steering angle on the rear axle is set in the opposite direction to the steering angle on the front axle if the vehicle's maneuverability is to be improved by increasing the overall steering angle. Thus, there is an interaction between the front-axle steering system 3 and the rear-axle steering system 15.

[0023] In the illustrated embodiment, each rear wheel 17 of the motor vehicle 1 is assigned a separate steering actuator 19 with its own power electronics 21. However, it is also possible for the rear-axle steering system 15 to have only a single, common steering actuator 19 with its own corresponding power electronics 21 for the joint steering of the two rear wheels 17. Furthermore, only one position sensor is required for each steering actuator 19 in order to be able to determine the respective position of the steering actuator 19 during operation of the motor vehicle 1.

[0024] According to the invention, the power steering control unit 13 serves not only to control and regulate the power steering device 11, but also to control the two steering actuators 19 of the rear-axle steering system 15. For this purpose, the power steering control unit 13 and, for example, the two power electronics units 21 of the two steering actuators 19 are connected to one another via a bus system 23 shown in simplified form. This can be, for example, a LIN bus or a CAN bus.

[0025] The invention is not limited to the embodiments described above. It may be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art. List of reference symbols 1 motor vehicle 3 front axle steering 5 Steering wheel 7 Steering column 9 Front wheel 11 Steering aid device 13 Power steering control unit 15 Rear-axle steering 17 Rear wheel 19 Steering actuator 21 Power electronics 23 Bus system

Claims

[1] Steering system for a motor vehicle (1) comprising a front axle steering system (3) with a steering aid device (11), a steering aid control unit (13) for controlling the steering aid device (11) and a rear axle steering system (15) with two steering actuators (19), one steering actuator (19) being assigned to each rear wheel of the motor vehicle (1), the steering aid control unit (13) of the front axle steering system (3) being used to control the two steering actuators (19) of the rear axle steering system (15), the two steering actuators (19) of the rear axle steering system (15) being connected to the steering aid control unit (13) of the front axle steering system (3) via a bus system (23), each of the steering actuators (19) being assigned its own power electronics unit (21) which is connected to the steering aid control unit (13) of the front axle steering system (3). [2] Steering system according to claim 1, characterized by that the front axle steering (3) and / or the rear axle steering (15) is an electromechanical steering system. [3] Method for controlling a steering system of a motor vehicle (1) with a front axle steering system (3), comprising a steering aid device (11), a steering aid control unit (13) and a rear axle steering system (15) with two steering actuators (19), wherein one steering actuator (19) is assigned to each rear wheel of the motor vehicle (1), wherein the two steering actuators (19) of the rear axle steering system (15) are controlled by the steering aid control unit (13) of the front axle steering system (3), wherein the two steering actuators (19) of the rear axle steering system (15) are controlled by the steering aid control unit (13) via a bus system (23). [4] Motor vehicle with a steering system according to one of claims 1 to 2.

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