Method for inspecting a steering system

Abstract

A method for inspecting a steering system having an electric motor for steering assistance, wherein the steering system is controlled by an excitation signal, the controller providing the steering system with a variable, and the current required by the electric motor is measured and analyzed in order to detect the presence of a mechanical fault in the steering system.

Description

[0001] Description

[0002] title

[0003] The invention relates to a method for checking a steering system and an arrangement for carrying out the method.

[0004] State of the art

[0005] Steering systems are devices used to influence the direction of travel of vehicles. Actuated steering systems typically feature an electric motor designed to amplify the steering torque applied by the driver with additional torque, thus assisting the driver. This electric motor, also known as a servo motor, typically interacts with the steering mechanism of the steering system.

[0006] Currently, only a very small proportion of the mechanical abnormalities that can occur during operation of a vehicle or steering system are detected automatically. The majority of the abnormalities must therefore be discovered by the driver themselves. However, with the increasing trend towards automated and / or autonomous driving, this type of manual error detection is becoming less and less possible. In addition, vehicles with steer-by-wire steering systems are known, which do not require a direct mechanical connection between a steering wheel and the steered vehicle wheels. Due to the mechanical decoupling, mechanical abnormalities that can occur, for example, in a steering gear are not directly fed back to the steering wheel, which also makes manual detection more difficult. Many steering assemblies and steering systems are sent from the field for analysis to diagnostic centers. There, the steering systems can be examined.If the examination results in "no treble found," this means that no defect was found. However, the examinations at these diagnostic centers are generally complex and therefore expensive.

[0007] The document DE 10 2022 200 268 A1 describes a method for operating a steering system of a vehicle, wherein the steering system has a steering mechanism and at least one electric motor that interacts with the steering mechanism and serves to assist the steering. In the method, the stiffness of at least one steering assembly of the steering mechanism and / or play in the steering mechanism is determined. For this purpose, the steering mechanism is brought into a defined test position and / or blocked in the test position, and the electric motor is controlled with an excitation signal. The stiffness and / or play in the steering mechanism is then determined by monitoring a motor torque and a rotor position angle of the electric motor while the electric motor is controlled with the excitation signal, and evaluating a change in the motor torque as a function of the rotor position angle.

[0008] Disclosure of the invention

[0009] Against this background, a method having the features of claim 1 and an arrangement according to claim 10 are presented. Embodiments emerge from the dependent claims and from the description.

[0010] The presented method is used to test a steering system, which is usually designed as a rack and pinion steering system. This steering system typically includes an electric motor for steering assistance, which interacts with a steering mechanism of the steering system. In this context, testing means that it is to be examined whether there is an impairment of functionality and thus a fault in the steering system. In the method, the steering system is controlled with an excitation signal by an arrangement, e.g. a control unit, specifying a value to the steering system. The current required by the electric motor is then measured and evaluated. This evaluation makes it possible to detect the presence of a mechanical fault in the steering system. This means that it is fundamentally possible to detect whether there is a mechanical fault and, if necessary, it may also be possible to determine what type of fault is present.

[0011] The steering system can be controlled with an excitation signal that specifies a changing variable, such as a changing steering angle. A current curve is then typically recorded against the changing variable.

[0012] Furthermore, it can be controlled with a changing excitation signal.

[0013] In one embodiment, the excitation signal specifies an angular velocity. The excitation signal is typically constant if the angular velocity is constant. However, a constant angular velocity means a changing angle of rotation of the steering system. In this case, the current curve is plotted against the changing angle of rotation for evaluation. The changing angle of rotation or the angular velocity can then be considered as the specified variable.

[0014] The procedure can also take into account the current temperature in the steering system during the evaluation, as this also has an influence on the behavior of the steering system.

[0015] This procedure makes it possible to reduce the number of tests that were unnecessary if the result was "no problem found." This is particularly the case with mechanical problems. For E / E errors, however, there are already clear error codes that the system determines itself during operation. There has not been such a procedure for mechanical errors to date. If there is a mechanical complaint, e.g. a noise, the mechanic can put the steering system into self-test mode in the workshop. To do this, the vehicle is raised on a hoist so that the front wheels can rotate freely. If necessary, this can also be accomplished without a hoist. The mechanic then starts the self-test via the diagnostic system.

[0016] This makes it possible to examine a steering system for mechanical faults without the need for additional effort from sensors and other components.

[0017] The presented arrangement serves to carry out the method and for this purpose comprises an evaluation unit, e.g., a processing unit. The arrangement can be implemented in hardware and / or software. The arrangement is, for example, at least partially integrated into a vehicle control unit or can be designed as such a control unit. The arrangement specifies the variable using the excitation signal, measures the resulting motor current, and evaluates it. These steps can be performed in a central arrangement or in a distributed arrangement.

[0018] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0019] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0020] Short description of the drawings

[0021] Figure 1 shows a schematic, highly simplified representation of a vehicle with a steering system.

[0022] Figure 2 shows a current profile graph to illustrate one embodiment of the presented method. Figure 3 shows another current profile graph to illustrate one embodiment of the presented method.

[0023] Embodiments of the invention

[0024] The invention is illustrated schematically in the drawings using embodiments and is described in detail below with reference to the drawings.

[0025] Figures 1a and 1b show a simplified representation of a vehicle 12, embodied by way of example as a motor vehicle, with a plurality of vehicle wheels 34, 36 and with a steering system 10. The vehicle 12 is suitable for automated and / or autonomous driving. The steering system 10 has an operative connection with the vehicle wheels 34, 36 and is provided for influencing a direction of travel of the vehicle 12. Furthermore, the steering system 10 is embodied purely by way of example as an electrically assisted steering system and has electrical auxiliary power assistance in the form of a power steering system. Alternatively, however, a steering system can also be embodied as a known steer-by-wire steering system.

[0026] The steering system 10 comprises a steering mechanism 14 known per se and a steering actuator system 40 which interacts with the steering mechanism 14 and is known per se.

[0027] The steering mechanism 14 comprises a steering handle 42, in the present case designed as a steering wheel, for applying a manual torque, as well as a plurality of steering assemblies 18, 20, 22 operatively connected to the steering handle 42. In the present case, the steering mechanism 14 comprises a first steering assembly 18 designed as a servo train, a second steering assembly 20 designed as a sensor train, and a third steering assembly 22 designed as a vehicle axle and / or part of a vehicle axle. The first steering assembly 18 corresponds to a steering gear, designed as a rack and pinion steering gear, for example, and comprises at least one steering actuating element 28, in the present case designed in particular as a rack. The first steering assembly 18 is provided for converting a steering command at the steering handle 42 into a steering movement of the vehicle wheels 34, 36, designed in particular as front wheels.The second steering assembly 20 in this case corresponds to a steering shaft and serves to connect, in particular mechanically, the steering handle 42 to the first steering assembly 18. The third steering assembly 22 can comprise at least a portion of the tie rods assigned to the vehicle wheels 34, 36 and / or a portion of the rims of the vehicle wheels 34, 36. Alternatively, a steering handle could also be designed as a steering lever and / or steering ball or the like. Furthermore, it is conceivable to dispense with a steering shaft and / or a steering handle, such as in a steer-by-wire steering system.

[0028] The steering actuator system 40 comprises an electric motor 16 and has an operative connection with the first steering assembly 18, in particular the steering actuator 28. The steering actuator system 40 is intended to provide a steering torque by means of the electric motor 16. In the present case, the steering actuator system 40 is intended at least to provide a steering torque in the form of an assist torque and to transmit it to the steering actuator 28.

[0029] Furthermore, the vehicle 12 has a control unit 54. The control unit 54 is designed as a steering control unit and is therefore part of the steering system 10. The control unit 54 has an electrical connection to the steering actuator system 40, in particular the electric motor 16. The control unit 54 is provided to control the operation of the steering system 10. In the present case, the control unit 54 is provided at least to control the electric motor 16. Alternatively, a control unit could also be different from a steering control unit and, for example, be designed directly as a central vehicle control unit.

[0030] The control unit 54 comprises a computing unit 38. The computing unit 38 comprises at least one processor (not shown), for example in the form of a microprocessor, and at least one operating memory (not shown). Furthermore, the computing unit 38 comprises at least one operating program stored in the operating memory. This computing unit 38 can serve as an evaluation unit for the presented arrangement.

[0031] Furthermore, the control unit 54 comprises a steering controller 26, known per se, for controlling the electric motor 16. The steering controller 26 has an electrical connection to the computing unit 38. Furthermore, the steering controller 26 is electrically connected to the electric motor 16. In the present case, the steering controller 26 is provided, at least during driving operation of the vehicle 12, for controlling a position of the steering actuator 28 and thus, in particular, a direction of travel of the vehicle 12.

[0032] In this case, the control unit 54 is an embodiment of the arrangement presented and is also designed to measure and evaluate the motor current of the electric motor 16.

[0033] It should be noted that steering noises are primarily caused by play. During the test, the control unit 54 sets a constant angular speed to the electric motor 16 of the steering system 10 and measures the required current. For example, a voltage can be specified, which then generates the rotational speed. The rotational speed can then be determined via a position sensor that may already be installed in the motor. If there is play in the steering system 10, the required current is significantly lower than in the case where the electric motor 16 must move the steering rack.

[0034] Figure 2 shows, in a graph 100, on whose abscissa 102 the angle of rotation is plotted and on whose ordinate 104 the current in [A] is plotted, a first curve 110 representing a motor current curve in a steering system with play, and a second curve 112 representing a motor current curve in a steering system without play. In a region 120 with small angles of rotation, it is clearly visible that in this region 120 the current curve 110 with play is significantly lower than the current curve 112 without play. This difference is significant for the presence of play. If such a difference is detected, it can be concluded that there is play in the steering system. An arrow 130 indicates the value of the angle of rotation at which the play is overcome and the current is constant. With regard to the Hakeln test program, the arrangement, e.g. the control unit, thus specifies a constant angular speed for the steering system motor and measures the required current.If there is a hitch in the steering system, the required current is significantly higher than in other areas.

[0035] Figure 3 shows, in a graph 150, with the angle of rotation plotted on the abscissa 152 and the current in [A] plotted on the ordinate 154, a first curve 160 representing the motor current profile for a steering system with jerking, and a second curve 162 representing the motor current profile for a steering system without jerking. In a region 170 at medium angles of rotation, it is clearly evident that the current profile 160 with jerking is significantly higher than the current profile 162 without jerking. This difference is significant for the presence of jerking. If such a jerk is detected, it can be concluded that jerking is present in the steering system.

Claims

Claims 1 . Method for testing a steering system (10) having an electric motor (16) for steering assistance, wherein the steering system (10) is controlled by an excitation signal in which the control unit specifies a variable to the steering system, and the current required by the electric motor (16) is measured and evaluated in order to detect the presence of a mechanical fault in the steering system (10).

2. Method according to claim 1, in which the steering system (10) is controlled by an excitation signal which specifies a changing variable and a course of the current over the changing variable is recorded.

3. Method according to claim 1 or 2, in which control is carried out with a changing excitation signal.

4. Method according to one of claims 1 to 3, in which an angular velocity of rotation is specified with the excitation signal.

5. Method according to claim 4, wherein a constant rotational angular velocity is specified with the excitation signal.

6. Method according to one of claims 1 to 5, which is used in a rack and pinion steering system.

7. Method according to one of claims 1 to 6, wherein, if a reduced current is detected in a region, a play in the steering system (10) is detected.

8. The method according to any one of claims 1 to 6, wherein, if an increased current is detected in a region, a jerk in the steering system (10) is detected.

9. The method according to any one of claims 1 to 8, wherein a current Temperature is taken into account.

10. Arrangement for testing a steering system (10) comprising an electric motor (16) for steering assistance, the arrangement having an evaluation unit configured to carry out a method according to one of claims 1 to 8.

11. Arrangement according to claim 9, which is associated with a control unit (54) for controlling the electric motor (16).

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