STEER-BY-WIRE STEERING SYSTEM AND METHOD FOR OPERATING A STEER-BY-WIRE STEERING SYSTEM

Abstract

A steer-by-wire steering system (10) for a vehicle comprises a steering wheel actuator (12) for moving and detecting movements of a steering wheel (16) of the vehicle, wherein the steering wheel actuator (12) has a steering wheel electric motor (20) and is connected to the steering wheel (16) of the vehicle. Furthermore, the steer-by-wire steering system (10) has an axle actuator (14) for moving and detecting movements of wheels of an axle of the vehicle, wherein the axle actuator (14) comprises an axle electric motor (32) and an axle control unit (30) and is connected to the axle of the vehicle. In addition, the steer-by-wire steering system (10) comprises an equivalent circuit (36), which is designed to measure a current (U, V, W) induced by the steering wheel electric motor (20) and to provide the axle control unit (30) with at least one measurement value depending on the induced current (U, V, W) for controlling the axle electric motor (32).

A method for operating such a steer-by-wire steering system (10) is also specified.

Claims

1. A steer-by-wire steering system for a vehicle with a steering wheel actuator (12) for moving and detecting movements of a steering wheel (16) of the vehicle, which has a steering wheel electric motor (20) connected to the steering wheel (16) of the vehicle, an axle actuator (14) for moving and detecting movements of wheels of an axle of the vehicle, which comprises an axle electric motor (32) and an axle control unit (30) and which is connected to the axle of the vehicle, and an equivalent circuit (36), which is designed to measure a current (U, V, W) induced by the steering wheel electric motor (20) and to provide the axle control unit (30) with at least one measurement value depending on the induced current (U, V, W) for controlling the axle electric motor (32).

2. The steer-by-wire steering system as claimed in claim 1, wherein the equivalent circuit (36) has at least one current sensor (26) which is assigned to a phase of the steering wheel electric motor (20), in particular wherein the equivalent circuit (36) has as many current sensors (26) as the steering wheel electric motor (20) has phases.

3. The steer-by-wire steering system as claimed in claim 1, wherein as many measurement values are provided as the steering wheel electric motor (20) has phases.

4. The steer-by-wire steering system as claimed in claim 1, wherein the equivalent circuit (36) has a logic circuit, in particular wherein the equivalent circuit (36) is a purely logic circuit.

5. The steer-by-wire steering system as claimed in claim 1, wherein the axle control unit (30) is set up to record the measurement value and to control the axle electric motor (32) on the basis of the measurement value, in particular wherein the axle control unit (30) is set up to determine the position of the steering wheel and/or a relative steering angle (φ) on the basis of the at least one measurement value.

6. The steer-by-wire steering system as claimed in claim 1, wherein the equivalent circuit (36) has at least one branch that has a comparator (38a, 38b, 38c) and a switching element (40a, 40b, 40c), in particular a transistor, wherein the comparator (38a, 38b, 38c) is connected to at least one current sensor (26) and is designed to actuate the switching element (40a, 40b, 40c) when the current (U, V, W) measured by the current sensor (26) exceeds a predetermined threshold value (S).

7. The steer-by-wire steering system as claimed in claim 1, wherein the equivalent circuit (36), in particular the at least one branch, has a capacitor (42a, 42b, 42c), the voltage of which represents the measurement value.

8. The steer-by-wire steering system as claimed in claim 6, wherein the equivalent circuit (36) has a voltage source (43) which is connected to the capacitor (42a, 42b, 42c) via the switching element (40a, 40b, 40c) when the switching element (40a, 40b, 40c) is actuated.

9. The steer-by-wire steering system as claimed in claim 6, wherein the equivalent circuit (36), in particular the switching element (40a, 40b, 40c), is set up to discharge the capacitor (42a, 42b, 42c) if the current (U, V, W) measured by the current sensor (26) is below a predetermined threshold value (S).

10. The steer-by-wire steering system as claimed in claim 6, wherein the equivalent circuit (36) has several branches, in particular a branch for each phase of the steering wheel electric motor (20), wherein each branch contains a logic block (44a, 44b, 44c) connected to the comparator (38a, 38b, 38c) of the branch and the comparators (38a, 38b, 38c) of another branch, wherein the logic block (44a, 44b, 44c) is set up to discharge the capacitor (42a, 42b, 42c) when the measured current (U, V, W) of the at least one other branch exceeds the threshold value (S).

11. The steer-by-wire steering system as claimed in claim 1, wherein the steering wheel actuator (12) has a steering wheel control unit (18) which is connected to the axle control unit (30) for data exchange.

12. A method for operating a steer-by-wire steering system (10), which has a steering wheel actuator (12) with a steering wheel electric motor (20) and a steering wheel control unit (18), an axle actuator (14) with an axle electric motor (32) and an axle control unit (30) and an equivalent circuit (36), wherein the method includes the following steps: Checking whether there is a malfunction of the steering wheel control unit (18), in particular by the axle control unit (30); Measuring the current (U, V, W) induced by the steering wheel electric motor (20) by the equivalent circuit (36) and providing a measurement value depending on the induced current (U, V, W); Obtaining at least one measurement value from the equivalent circuit (36) by the axle control unit (30); and Controlling the steering movement of the axle by the axle control unit (30) by means of the axle electric motor (32) depending on the at least one measurement value obtained if there is a malfunction.

13. The method as claimed in claim 12, wherein a measurement value is provided for each phase of the steering wheel electric motor (20).

14. The method as claimed in claim 12, wherein each phase is assigned a capacitor (42a, 42b, 42c), wherein the capacitor (42a, 42b, 42c) is charged, in particular linearly charged, when the current (U, V, W) of the phase exceeds a predetermined threshold value (S).

15. The method as claimed in claim 12, wherein the at least one measurement value is a voltage, in particular the voltage of the corresponding capacitor (42a, 42b, 42c).

16. The method as claimed in claim 12, wherein the axle control unit (30) determines the position of the steering wheel and/or a relative steering angle φ using the at least one measurement value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Further advantages and properties of the invention result from the following description and the drawings. In the figures:

[0053] FIG. 1 shows a schematic representation of a steer-by-wire steering system according to the invention,

[0054] FIG. 2 shows an equivalent circuit of the steer-by-wire steering system from FIG. 1,

[0055] FIG. 3 shows diagrams of the variation of several current signals and the measurement values produced from these current signals by means of the equivalent circuit from FIG. 2, and

[0056] FIG. 4 shows a schematic flow diagram of the method according to the invention.

DESCRIPTION

[0057] In FIG. 1, a steer-by-wire steering system 10 according to the invention is shown, with a steering wheel actuator 12 and an axle actuator 14.

[0058] The steering wheel actuator 12 is coupled to a steering wheel 16 of a (not shown) vehicle and comprises a steering wheel control unit 18 and a steering wheel electric motor 20.

[0059] The steering wheel 16 is also monitored by an angle sensor 22 and a torque sensor 24, by means of which a steering angle φ and a torque M applied to the steering wheel 16 can be determined. The angle sensor 22 and the torque sensor 24 are connected to the steering wheel control unit 18, which can process the information received from the sensors 22, 24.

[0060] In addition, the control unit 18 is connected to the steering wheel electric motor 20. The steering wheel electric motor 20 can also perform a steering movement of the steering wheel 16.

[0061] The steering wheel electric motor 20 also has multiple current sensors 26, which are in particular Hall sensors. The current sensors 26 are designed to measure the current of each phase of the steering wheel EM 20.

[0062] The axle actuator 14 acts on one axle of the vehicle, in the embodiment shown on the rack 28 of the front axle of the vehicle, and comprises an axle control unit 30 and an axle electric motor 32.

[0063] The position of the axle or the rack 28 can be monitored by means of a position sensor 34, which is connected to the axle control unit 30.

[0064] During the normal operation of the steer-by-wire steering system, the steering movement of the driver is detected by means of the angle sensor 22 and the torque sensor 24, is processed by the steering wheel control unit 18 and corresponding data are transmitted to the axle control unit 30. The axle control unit 30 controls the axle electric motor 32 based on the transmitted data, whereby a movement of the axle or the rack 28 is generated and thus a steering movement of the vehicle is performed.

[0065] In the case of a partial or complete failure of the steering wheel actuator 12, the method according to the invention for operating the steer-by-wire steering system 10 is used.

[0066] For this purpose, an equivalent circuit 36 is used, which is arranged in the steering wheel control unit 18 in the embodiment shown. In principle, however, the equivalent circuit 36 could also represent a separate component of the steer-by-wire steering system or could be formed in the axle actuator 14.

[0067] A malfunction of the steering wheel control unit 18 is determined in particular by the axle control unit 30 (step S1 in FIG. 4), for example by the fact that the axle control unit 30 is no longer receiving information of the angle sensor 22 and/or the torque sensor 24.

[0068] In this case, the electric motor 20 acts as a generator during a steering movement of the steering wheel 16, wherein the current sensors 26 can forward the induced current to the equivalent circuit 36 as an input signal.

[0069] Alternatively, the current sensors 26 can also be part of the equivalent circuit 36 instead of being part of the steering wheel electric motor 20. In this case, the equivalent circuit 36 is arranged so dose to the steering wheel electric motor 20 that nevertheless a current is induced in the current sensors 26 by the movement of the steering wheel electric motor 20.

[0070] The equivalent circuit 36 is shown in detail in FIG. 2. In the embodiment shown here the equivalent circuit 36 has three branches, wherein each branch processes a current signal U, V, W. Basically, the equivalent circuit has in particular as many branches as the steering wheel electric motor 20 has phases.

[0071] The equivalent circuit 36 is purely a logic circuit, so no microcontroller and no software is necessary to operate the equivalent circuit 36. Thus, the equivalent circuit 36 can be operated even in the event of a failure of the steering wheel control unit 18. Accordingly, the current signals U, V, W are evaluated at least qualitatively.

[0072] The equivalent circuit 36 has three comparators 38a, 38b and 38c as well as three switching elements 40a, 40b and 40c, each assigned to a comparator 38a, 38b and 38c. In the embodiment shown here, the switching elements 40a, 40b, 40c are transistors.

[0073] The respective switching elements 40a, 40b and 40c are actuated when it is determined by means of the respective comparators 38a, 38b and 38c that the corresponding current signal U, V, W exceeds a predetermined threshold Value S.

[0074] In the embodiment shown, the threshold value S is 25% of the maximum amplitude of the current signal U, V, W, for example. The maximum value can be determined by the components used, the selected geometry of the components of the steer-by-wire steering system 10 or by means of a measurement.

[0075] The equivalent circuit 36 also has three capacitors 42a, 42b and 42c, the voltages of which represent the measurement values provided by the equivalent circuit 36.

[0076] The capacitors 42a, 42b and 42c are charged by means of a voltage source 43, wherein the voltage source 43 is connected to the capacitors 42a, 42b 42c via the respective switching element 40a, 40b, 40c. The voltage source 43 charges each of the capacitors 42a, 42b and 42c which belong to the branches of the equivalent circuit 36, the switching element 40a, 40b and 40c of which is currently actuated.

[0077] Accordingly, the respective capacitor 42a, 42b and 42c is charged only if the current signal U, V, W belonging to the respective branch exceeds the threshold value S.

[0078] In addition, the equivalent circuit 36 has logic blocks 44a, 44b and 44c, each connected to all comparators 38a, 38b and 38c. In addition, the logic blocks 44a, 44b and 44c are connected to the respective capacitors 42a, 42b and 42c.

[0079] The logic blocks 44a, 44b and 44c are used to discharge the associated capacitors 42a, 42b and 42c to a predetermined voltage value, in particular to completely discharge them, when the current signal of one of the other branches of the equivalent circuit 36 exceeds the threshold value S. This eliminates the need to evaluate the negative half waves of the current signals U, V, W.

[0080] FIG. 3 illustrates the relationship between the current signals U, V, W and the capacitor charge. In the upper diagram, the three current signals U, V, W are shown against time. In addition, the threshold value S is shown.

[0081] As can be seen, the current signals U, V, W each describe a phase of the three-phase alternating current, which is detected by the current sensors 26 during a steering movement of the steering wheel 16.

[0082] In the lower diagram in FIG. 3, the voltages of the capacitors 42a, 42b and 42c assigned to the respective current signals U, V, W are shown against time.

[0083] As can be seen, the capacitors 42a, 42b and 42c are charged linearly over a period of time, which is determined by the fact that the corresponding current signal U, V, W is above the threshold value S. This region is shown as an example of the current signal V in FIG. 3.

[0084] As soon as the current signal U, V, W drops below the threshold value 5, the corresponding capacitor 42a, 42b and 42c will discharge, as shown in FIG. 3.

[0085] In the variant shown in FIG. 3, two of the capacitors 42a, 42b and 42c can be charged simultaneously over a limited period of time. Via the logic blocks 44a, 44b arid 44c, however, it is also possible, as previously described, that the capacitor, for example, the capacitor 42b, which was previously in the charging process, is immediately discharged as soon as another of the capacitors starts to charge, for example the capacitor 42c.

[0086] Ultimately, the current induced by the steering wheel electric motor 20 is measured by the equivalent circuit 36 and the voltages of the capacitors 42a, 42b and 42c are provided as measurement values depending on the induced current (step S2 in FIG. 4).

[0087] The axle control unit 30 can then receive the measurement values provided by the equivalent circuit 36 (step S3 in FIG. 4).

[0088] The axle control unit 30 can determine the position of the steering wheel 16 and/or the relative steering angle φ based on the provided measurement values. The corresponding conversion formula and value table are stored in the axle control unit 30.

[0089] The axle control unit 30 then controls the steering movement of the axle or rack 28 by means of the axle electric motor 32 depending on the obtained measurement values (step S4 in FIG. 4).

[0090] Thus, even in the event of a malfunction of the steer-by-wire steering system 10, a movement of the steering wheel is converted into a steering movement.