METHOD FOR DETERMINING THE WEAR OF A VEHICLE'S STEERING SYSTEM

Description

[0001] The invention relates to a method for determining the wear of a steering system of a vehicle, wherein the steering system has a rack, wherein the steering system has a wheel actuator in the form of an electric motor, wherein the wheel actuator is arranged parallel to the rack, wherein a rack displacement force is generated by the wheel actuator by means of a toothed belt and wherein the steering system has at least one mechanical stop for the rack.

[0002] In addition, the invention relates to a steering system for a vehicle, having at least one rack, at least one wheel actuator, at least one toothed belt and at least one mechanical stop, wherein the wheel actuator is arranged parallel to the rack, wherein a rack displacement force can be generated by the wheel actuator by means of the toothed belt and wherein the rack can be displaced to the at least one mechanical stop by the rack displacement force.

[0003] Furthermore, the invention relates to a vehicle with a steering system.

[0004] Future steer-by-wire steering systems will not require a steering intermediate shaft, as the mechanical connection to the steering wheel is eliminated. In principle, it makes sense to design the wheel actuator based on current technical concepts familiar from electromechanical steering systems. One possible design is therefore to arrange the electric motor parallel to the rack (axis). The motor torque is then converted into a rack displacement force via a toothed belt drive and a ball screw drive. A key requirement for a wheel actuator is the reliable determination of the current rack position, or a steering wheel or wheel steering angle corresponding to this rack position, calculated using a (possibly variable) gear ratio factor.

[0005] This signal is required for precise and reliable position control of the rack and thus for the vehicle's guidance. A common procedure according to the current state of the art involves determining an initial reference position using a precise reference signal sensor, from which further calculations are made using the more finely resolved signal from the rotor position sensor assigned to the electric motor.

[0006] The rotor position sensor cannot be used as a standalone sensor, as it is typically designed as a single-turn sensor and always sets its zero point at the current position upon system startup. However, a calculation algorithm that uses the value provided by the reference sensor and counts the revolutions of the electric motor allows for precise and reliable determination of the steering angle or rack position over the entire steering stroke. However, the possibility of a timing belt skipping cannot be ruled out with these systems.

[0007] US 2019 / 0315390 A1, for example, also shows a vehicle steering system with a rack shaft and a conversion mechanism that converts the rotation of a rotating shaft of the motor into a reciprocating motion of the rack shaft. The conversion mechanism includes a drive pulley that rotates with the rotating shaft, a driven pulley rotatable about an axis of the rack shaft, and a toothed belt that extends around the drive pulley and the driven pulley, and converts the rotation of the rotating shaft into a reciprocating motion. As the drive pulley rotates, the rack shaft is transmitted to the driven pulley via the toothed belt. The vehicle steering system further includes a determination circuit that determines tooth skipping, which is a change in the engagement position between the drive pulley and the toothed belt.The timing belt skipping is detected but not prevented.

[0008] Even with today's steering systems with a parallel-axis wheel actuator, the problem arises that the possibility of the timing belt skipping cannot be completely ruled out. This can occur even when the system is switched off. Since this cannot be accounted for in the calculation algorithm, an error occurs in the calculated value, which in extreme cases can be safety-relevant. Storing the last value alone is therefore not sufficient; the stored value must be compared with the reference signal at regular intervals. Furthermore, this situation results in certain requirements regarding the accuracy of the reference signal generator; for example, it must be possible to measure multiple reference positions.

[0009] A steer-by-wire wheel actuator with a parallel-axis design essentially faces the same problem. The cost-intensive sensor technology described above can be used. However, this requires either a rack position sensor as a reference signal source or even a pinion on the rack to enable rotational measurement.

[0010] The invention is based on the object of specifying a method for determining the wear of a modern steering system as well as a steering system and a vehicle with a steering system, in which the determination of the wear of the steering system can be carried out effectively and less cost-intensively than by the methods known from the prior art.

[0011] This object is achieved in the present invention firstly by the features of patent claim 1 in that a motor torque is applied by the wheel actuator, by means of which the rack is moved to the mechanical stop, that a motor angle of the wheel actuator is determined, that after reaching the mechanical stop the motor torque is further increased, that the change in the motor angle of the wheel actuator is determined, that as a function of the motor angle and the motor torque a characteristic value is determined as a measure of the wear of the toothed belt.

[0012] The inventive solution exploits the fact that belt skipping becomes more likely if it has been damaged, for example, by aging, fluid penetration, such as water, or wear. Such belt damage does not occur suddenly, but is associated with a gradual change in the belt's mechanical properties. The aim of the inventive solution is therefore to detect damage to the timing belt at an early stage in order to then take measures that ensure that belt skipping practically never occurs during operation. The failure probabilities derived from the applicable standards for safety-relevant products are decisive for the design.

[0013] The subject of the invention is therefore a method for detecting toothed belt wear, where the steering system can be a steer-by-wire steering system. This method makes it possible to use a single rotor position sensor in the system for position / angle determination. An additional reference value sensor, as is common in the prior art, is eliminated. Due to the sensor properties, an initialization process is still required. The mechanical end stops, whose positions are known, are used for this purpose.

[0014] When executing the procedure, the rack is first moved to the mechanical stop. This position can be detected based on the increase in motor torque at a (virtually) constant motor angle position. A further increase in motor torque leads to an increase in the measured motor angle. This is due to the elasticity of the timing belt, since the rack cannot be moved any further at the mechanical stop. A characteristic value, such as belt elasticity, is then determined from the combination of motor torque and motor angle position and / or other variables.

[0015] Further parameters can be determined through certain patterns in the engine torque, for example vibrations and / or pulse-shaped excitations.

[0016] Further preferred embodiments of the invention emerge from the remaining features mentioned in the subclaims.

[0017] In a first embodiment of the method according to the invention, the characteristic value is compared with predefined characteristic values. The predefined characteristic values ​​can, for example, be characteristic values ​​for which it is known that wear on the timing belt has not yet occurred. It is also conceivable that the characteristic value is compared with predefined characteristic values ​​for which wear on the timing belt has already occurred.

[0018] Alternatively or additionally, a further embodiment of the method according to the invention may provide for the characteristic value to be compared with characteristic values ​​from previous test cycles. This allows short- and long-term changes in the belt properties to be detected.

[0019] In a further advantageous embodiment of the invention, a signal is generated when the characteristic value exceeds or falls below a predetermined limit. If the belt properties exceed or fall below certain limits, a system response is initiated. This could, for example, be a message in the vehicle's instrument cluster. The message could inform the driver that the steering system needs to be checked at the workshop.

[0020] In order to provide further options, a further preferred embodiment of the method according to the invention provides for the characteristic value to be stored in a vehicle memory. A system entry that is not visible to the driver of the vehicle but can be read out by a workshop is particularly advantageous as an initial reaction. This means that the steering can be checked more closely or replaced if the vehicle needs to be taken to the workshop for another reason. If this has not been done within a certain period of time following the initial notification, a notification that is visible to the driver can be issued as a result. Replacing the steering system at an early stage thus prevents unnoticed belt damage from occurring. A belt break is ruled out with sufficient probability.

[0021] In a further embodiment of the method according to the invention, the steering system is provided with a second mechanical stop at which the wear is determined. By repeatedly measuring at a second reference point, the plausibility of the measurement can be checked and the accuracy increased.

[0022] To standardize the measurement, a further embodiment of the invention provides for the wear determination to be performed when the vehicle is stationary. The measurement could also be performed automatically, for example, when the vehicle is stationary and there are no drivers or passengers in the vehicle.

[0023] To further enable measurement comparability, a further embodiment of the method according to the invention provides for wear to be determined as a function of the time of day and / or the vehicle environment and / or the outside temperature and / or the steering system temperature. In addition, the time elapsed since the last test procedure can also be taken into account. It is conceivable that the measurement is performed at a fixed time, for example, at night.

[0024] Sensors such as cameras or microphones can be used to detect the vehicle's surroundings. It may be relevant whether the vehicle is very close to a curb. In this case, it would make sense not to perform a test, or only to perform a test on the mechanical stop facing away from the curb. The sensors can also be used to check whether there are people in the immediate vicinity of the vehicle. When taking the outside temperature into account, a measurement could, for example, be performed within a specific temperature window to achieve comparable test results. Based on the aforementioned data, a decision can also be made as to whether the right or left mechanical stop is used.

[0025] The above-mentioned object is also achieved by an above-mentioned steering system for a vehicle, having at least one rack, at least one wheel actuator, at least one toothed belt and at least one mechanical stop, wherein the wheel actuator is arranged parallel to the rack, wherein a rack displacement force can be generated by the wheel actuator by means of the toothed belt and wherein the rack can be displaced to the at least one mechanical stop by the rack displacement force.

[0026] It is intended that the steering system be designed to carry out a method according to the invention. The above statements regarding the method according to the invention also apply accordingly to the device according to the invention.

[0027] In addition, the above-mentioned object is achieved by a vehicle according to the characterizing part of patent claim 10, wherein the vehicle comprises a device according to the invention.

[0028] The above statements regarding the device according to the invention also apply accordingly to the vehicle according to the invention.

[0029] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show: Figure 1 is a schematic representation of a steer-by-wire steering system, Figure 2 is a schematic representation of a steering system with a wheel actuator in a center position and Figure 3 is a schematic representation of a steering system with a wheel actuator in an end stop position.

[0030] Figure 1shows a steering system 10 for use in a motor vehicle. The steering system has a rack 12. A wheel actuator 14 is arranged parallel to the rack. The wheel actuator 14 generates a rack displacement force by means of a toothed belt 16 (not shown here), allowing the rack 12 to be moved between two mechanical stops 18. The steering system 10 receives a steering command from a sensor or the steering wheel 20 of the vehicle.

[0031] The steering commands are transmitted exclusively electrically to the wheel actuator 14 via a control unit 22. The wheel actuator 14 then executes these steering commands. Consequently, in the steering system shown here, there is no mechanical connection between the steering wheel 20 and the steered wheels 24. Such a steering system 10 is also known as a steer-by-wire system. A ball screw drive converts the movement of the rack 12 into a steering movement of the wheels 24.

[0032] A key requirement for the wheel actuator 14 is the reliable determination of the current position of the rack 12 or a steering wheel or wheel steering angle corresponding to this position, calculated using a gear ratio. This signal is required for precise and reliable position control of the rack 12 and thus the guidance of the vehicle. However, in the steering system 10, it is possible for the toothed belt 16, which is connected to the wheel actuator 14 and the rack 12, to skip.

[0033] In the Figures 2 and 3A schematic representation of a method for determining the wear condition of the timing belt 16 is shown. If the condition of the timing belt 16 is known, the likelihood of the timing belt 16 skipping can also be determined. Ideally, the timing belt 16 or the steering system 10 is replaced before the timing belt 16 can even skip.

[0034] In the process, the rack 12 is first moved from a central position, as in Figure 2 shown, moved to the mechanical stop 18, as shown in Figure 3This position can be detected based on the increase in motor torque of the wheel actuator 14 at a (virtually) constant motor angle position. The wheel actuator 14 includes an angle sensor 26, which can be used to determine the motor angle of the wheel actuator 14. The motor torque of the wheel actuator 14 is then further increased. The now additionally measured increase in the motor angle is due to the elasticity of the toothed belt 16, since the rack 12 cannot be moved any further at the mechanical stop 18. A characteristic value, for example, a belt elasticity, is calculated from the combination of values.

[0035] The wheel actuator 14 is arranged in a housing 28, which is protectively positioned around the wheel actuator 14, the toothed belt 16, and the part of the rack 12 where the wheel actuator 14 is currently located. The housing 28 encloses the rack 12 and is slidably mounted on the rack 12.

[0036] Using specific patterns in the engine torque, such as vibrations and / or pulse-like excitations, additional parameters can be determined. These parameters are stored and then compared with predefined values. In addition, the parameters are compared with those from previous test cycles. This allows short- and long-term changes in the belt properties to be detected.

[0037] If the belt properties exceed or fall below certain limit parameters, a system reaction is initiated. This could, for example, be a message in the instrument cluster that the steering needs to be checked in the workshop. The first reaction is a system entry that is not visible to the driver, but which the workshop can read so that the steering can be checked more closely or replaced if a visit to the workshop for another reason. If this has not been done within a certain period of time after the first warning, a warning that is visible to the driver is only given. By replacing the steering early, unnoticed belt damage is prevented. Belt jump is ruled out with sufficient probability. The test can also be repeated at the second mechanical stop 18 in order to determine further parameters.

[0038] Additionally, the steering angle can be initialized. A reference position must be used for the angle sensor 26 of the wheel actuator 13 to calculate the steering angle or the position of the rack 16 from there. For this purpose, the rack 12 is moved to one of the mechanical end stops 18, the exact position of which is known from the mechanical design, as shown in Figure 3 This value can then be used as a reference. If necessary, this value can be checked by approaching the other end stop 18.

[0039] This procedure is made possible by the wheel actuator 14. By determining the wear of the toothed belt 16, regular calibration with an additional reference signal is no longer necessary. The reference provided via initialization from the end stops is sufficiently accurate to meet the required safety level, together with a rotor position signal. Thus, the system can operate without a separate, internal or external, cost-intensive sensor. List of reference symbols

[0040] 10Steering system 12Rack 14Wheel actuator 16Timing belt 18Mechanical stop 20Steering wheel 22Control unit 24Wheels 26Angle sensor 28Housing

Claims

1. Method for determining the wear of a steering system (10) of a vehicle, the steering system (10) having a steering rack (12), the steering system (10) having a wheel actuator (14) in the form of an electric motor, the wheel actuator (14) being arranged in parallel with the steering rack (12), a steering rack displacement force being generated by the wheel actuator (14) by means of a toothed belt (16), and the steering system (10) having at least one mechanical stop (18) for the steering rack (12), characterized in that a motor torque is applied by the wheel actuator (14), by means of which motor torque the steering rack (12) is moved to the mechanical stop (18), in that a motor angle of the wheel actuator (14) is determined, in that after reaching the mechanical stop (18) the motor torque is further increased, in that the change in the motor angle of the wheel actuator (14) is determined, and in that, depending on the motor angle and the motor torque, a parameter is determined as a measure of the wear of the toothed belt (16).

2. Method according to claim 1, characterized in that the parameter is compared with predefined parameters.

3. Method according to either claim 1 or claim 2, characterized in that the parameter is compared with parameters from previous test cycles.

4. Method according to any of claims 1 to 3, characterized in that a signal is given when the parameter exceeds or falls below a predetermined threshold value.

5. Method according to any of claims 1 to 4, characterized in that the parameter is stored in a memory of the vehicle.

6. Method according to any of claims 1 to 5, characterized in that the steering system (10) has a second mechanical stop (18) at which the wear is determined.

7. Method according to any of claims 1 to 6, characterized in that the wear is determined when the vehicle is stationary.

8. Method according to any of claims 1 to 7, characterized in that the wear is determined depending on the time of day and / or the vehicle environment and / or the outside temperature and / or the steering system temperature.

9. Steering system (10) for a vehicle, comprising at least one steering rack (12), comprising at least one wheel actuator (14), comprising at least one toothed belt (16) and comprising at least one mechanical stop (18), the wheel actuator (14) being arranged in parallel with the steering rack (12), a steering rack displacement force being able to be generated by the wheel actuator (14) by means of the toothed belt (16) and the steering rack (12) being able to be displaced to the at least one mechanical stop (18) by the steering rack displacement force, characterized in that the steering system (10) is designed to carry out a method according to any of claims 1 to 8.

10. Vehicle having a steering system (10) according to claim 9.