Steering system for motor vehicles

Abstract

Steering system (100) for a motor vehicle, comprising: a steering column module (101) for detecting a steering request from a user; a steering gear (120); a servo motor (121) connected to the steering gear; and a signal line (130) for transmitting the steering request from the steering column module to the steering gear, wherein the steering system (100) is configured to execute the transmitted steering request in a steer-by-wire mode by means of the servo motor (121) and the steering gear (120), wherein the steering system (100) can still be switched to a mechanical control mode in which the motor vehicle can be mechanically steered, wherein in this case the servo motor (121) can be passively switched, wherein the steering system (100) comprises a steering linkage (110) with a safety coupling (111) which is configured to be closed in mechanical control mode and to mechanically connect the steering column module (101) to the steering gear (120), wherein the safety coupling (111) comprises an input shaft connected to the steering column module (101) and an output shaft connected to the steering gear (120), characterized in that the steering system (100) comprises a mechanical sensor (112) which is configured to detect that the mechanical control mode is active, wherein the mechanical sensor (112) is a torque sensor (113) between and steering gear (120) which is configured to measure the torsion between safety clutch (111) clutch output shaft and steering gear (120).

Description

[0001] The invention relates to a steering system for a motor vehicle, comprising: a steering column module for detecting a steering request from a user; a steering gear; a servo motor connected to the steering gear; and a signal line for transmitting the steering request from the steering column module to the steering gear, wherein the steering system is configured to execute the transmitted steering request in a steer-by-wire mode by means of the servo motor and the steering gear, wherein it is further possible to activate a mechanical control mode of the steering system in which the motor vehicle is mechanically steerable, in which case the servo motor is passively switchable.

[0002] Such a steering system is known from US Patent 11,066,096 B2. This patent describes a control method for vehicle steering in which steering wheel vibrations are suppressed when a clutch is engaged during rotation, in order to prevent discomfort to the driver. This method involves the transition from a steer-by-wire mode, in which a steering clutch, mechanically connecting the steering wheel and the left and right front wheels, is disengaged, to an EPS control mode, in which the steering clutch is engaged and an assist torque, corresponding to a detected torque from a torque sensor, is transmitted to the left and right front wheels. The assist torque is limited to a value corresponding to the detected torque from the torque sensor at the moment the steering clutch is engaged, until a prescribed time has elapsed.Furthermore, the prior art reveals a steer-by-wire system to which the methods and device for control are applied. With regard to a mechanical system, the steer-by-wire system consists of a steering wheel, a steering force actuator, a steering clutch, a rotary actuator, and left and right front wheels (steerable wheels). A steering force control module receives as inputs a detected torque from the torque sensor, a steering angle detected by a steering angle sensor, and a rotation angle detected by a rotation angle sensor. The torque sensor is located on the lower steering shaft and detects the transmitted torque (axial torque) at the steering shaft.

[0003] As is known to those skilled in the art, the torque sensor comprises a torsion bar with lower torsional stiffness than the steering shaft, and the torque sensor detects the torque in a steering direction acting on the steering shaft due to a twisting of the torsion bar.

[0004] A steering system, particularly for motor vehicles, is known from EP 1 461 236 B1. It comprises a steering wheel connected to a steering wheel actuator. The steering wheel actuator is a differential drive with at least one servo motor for driving at least one gear stage connected to a rack. A hydraulic device is provided to provide hydraulic assistance to the rack movement. This device includes a steering valve that can be actuated by the differential drive. The steering wheel can also be connected to the steering valve by closing a brakeable clutch. The steering wheel actuator is arranged on or in a steering linkage directly behind the steering handle, which is designed as the steering wheel. A clutch is used on the steering linkage on the side of the steering wheel actuator facing away from the steering wheel. The clutch is designed as a clutch-brake combination for disconnecting the steering linkage.In this system, the clutch side is braked against a housing. When the clutch is engaged, the steering handle is directly connected to a steering valve of a hydraulic system or a steering torque sensor. To drive in steer-by-wire mode, the steering linkage can be advantageously disconnected by the clutch when the vehicle's ignition is started, with the clutch side opposite the steering wheel being braked against the housing. The servo motor, which is more powerful than conventional superimposed gears, takes over the steering process. The servo motor is controlled or regulated by the steering wheel actuator via a control unit, which is not shown. The steering torque generated by the steering wheel actuator for the driver can be freely programmable. It is advantageous if the clutch is engaged in an emergency steering function.In the event of a failure of the superimposed gearbox or a failure of the hydraulics, the steering system can continue to operate by closing the clutch, as with a classic rack and pinion hydraulic steering system.

[0005] From the generic DE 198 41 913 A1, an electrochemical steering actuator, in particular for steer-by-wire applications in motor vehicles, is known, comprising an electronic control unit that generates at least steering signals for an electric actuator motor that acts on a steered link of a wheel steering system, characterized in that a switchable clutch is provided which, in the event of a fault in the steering system, in response to a signal generated by the control unit, positively connects the steering wheel to the steered link.

[0006] The invention is based on the objective of enabling an emergency steering function, particularly when it is designed with a clutch acting as a safety circuit which closes in the event of a fault.

[0007] This problem is solved by the features of claim 1.

[0008] This use of a torque sensor to detect the clutch status is advantageous compared to the conventional method of measuring current through the clutch, as it indicates clutch engagement even when the electrical connection to the clutch is interrupted. Advantageously, the torque sensor can be mounted directly on the steering gear. A further advantage is that the clutch's safety circuit can be implemented independently of the steering gear's switching mechanism, ensuring that the clutch engages reliably in the event of a fault and that the steering gear is safely switched to passive mode if the clutch engages, even without an electrical connection between the clutch and the steering gear. In this way, the present invention increases the safety of the steering system by preventing the servo motor from interfering with the mechanical steering when the clutch engages.

[0009] The problem is also solved by the features of method claim 6.

[0010] Furthermore, the problem is solved by the non-volatile storage medium according to claim 10 and the vehicle according to claim 11, each implementing the corresponding method or device.

[0011] Advantageous embodiments are defined by the dependent claims.

[0012] The steering system is advantageously designed to automatically activate the mechanical control mode in case of a fault.

[0013] According to the invention, the steering system comprises a steering linkage with a clutch which is configured to be closed in mechanical control mode and to mechanically connect the steering column module to the steering gear, wherein the clutch comprises an input shaft connected to the steering column module and an output shaft connected to the steering gear.

[0014] The clutch is advantageously designed to open in steer-by-wire mode.

[0015] According to the invention, the mechanical sensor is designed as a torque sensor between the clutch and the steering gear, which is configured to measure the torsion between the clutch output shaft and the steering gear.

[0016] Advantageously, the torque sensor includes a torsion bar that has a lower torsional moment than the clutch output shaft.

[0017] Advantageously, the torque sensor incorporates strain gauges arranged in an azimuthal direction or obliquely in an azimuthal-longitudinal direction. Alternatively, the torque sensor can be an inductive torque sensor.

[0018] The torque sensor is advantageously located between the clutch and the clutch output shaft, or alternatively between the clutch output shaft and the steering gear.

[0019] The steering system is advantageously configured to passively switch the servo motor when the torque sensor measures torque.

[0020] Advantageously, the steering column module includes a rotation angle sensor to detect the steering request.

[0021] The steering request is advantageously transmitted in digital form.

[0022] The signal line is advantageously a bus connection.

[0023] Furthermore, switching the steering system to the mechanical control mode is advantageous, as it includes receiving an error signal and, based on the error signal, automatically activating the mechanical control mode.

[0024] According to the invention, activating the mechanical control mode includes closing a clutch between the steering column module and the steering gear.

[0025] According to the invention, the method for controlling the vehicle further comprises, based on the detection of a torque between the clutch output shaft and the steering gear, the passive switching of the servo motor.

[0026] Advantageously, the detection, using a mechanical sensor, that the mechanical control mode has been activated includes the measurement of a torque between an output shaft of the clutch connected to the steering gear and the steering gear.

[0027] The transmission of the steering request is advantageously carried out using a bus connection.

[0028] An exemplary embodiment is explained in more detail below with reference to the drawings. They show Fig. 1 a schematic representation of the steering system according to the invention, and Fig. 2 a flowchart of the control method according to the invention.

[0029] Fig. Figure 1 shows the steering system 100 according to one embodiment of the invention. The steering system includes a steering column module 101 with a steering wheel 102, which in a mechanical control mode is mechanically connected via a steering linkage 110 to a steering gear 120 for controlling the steerable wheels, e.g., the front wheels 140, 141, 142. This steering linkage 110 can be separated into two steering linkage parts 110a, 110b via a safety coupling 111.

[0030] As an alternative to this mechanical control mode, the steering system 100 also has a steer-by-wire mode in which the safety clutch 111 is open and control is effected via a servomotor 121 connected to the steering gear 120. For this purpose, the steering column module 101 is connected to the servomotor 121 via a signal line 130, preferably a bus connection 131. The steering column module 101 is configured to receive a steering input from the steering wheel 102, convert it into an electronic, preferably digital, signal, and transmit it to the signal line 130 or bus connection 131. The servomotor 121 is further configured to receive the steering input from the signal line 130 or bus connection 131 and to act on the steering gear 120 to execute the transmitted steering input.

[0031] The steering column module 101 contains a steering angle sensor 103 for detecting the steering request.

[0032] In purely mechanical control mode, the servomotor 121 is switched passively to ensure trouble-free mechanical control.

[0033] The safety clutch 111 is a clutch that closes in the event of a fault. Therefore, it is possible that the safety clutch 111 could close unexpectedly, thus activating the mechanical control mode.

[0034] To detect whether the mechanical control mode has been activated, or whether the safety clutch 111 has closed, the system 100 includes a mechanical sensor 112, specifically a torque sensor 113, located between the safety clutch 111 and the steering gear 120. This sensor is configured to measure torque between the steering gear 120 and the steering column module 101, or between the steering gear 120 and the safety clutch 111. Such torque occurs when the steering wheel 102 is turned with the servo motor 121 switched on and the safety clutch 111 is closed, i.e., when the steer-by-wire mode is still active with the mechanical connection closed. In this case, the mechanical sensor 112 is configured to send a signal to the servo motor 121 to switch it to passive mode, thus terminating the steer-by-wire mode and enabling purely mechanical control.

[0035] Various embodiments are known to those skilled in the art for both the steering angle sensor 103 and the mechanical sensor 112 or torque sensor 113. For example, the torque sensor 113 can be designed as a torsion bar, which has a lower torsional moment than the steering system, and the torsion bar can be provided with diagonal strain gauges or have a strain-dependent refractive index. Likewise, the steering angle sensor 103 can be designed, for example, as a slip ring or as a Hall sensor.

[0036] Fig. Figure 2 shows a flow chart of a method 200 according to an embodiment of the present invention in a steering system 100 according to Fig. 1.

[0037] In particular, the procedure 200 includes a switching cycle 210 of the steering system 100 in steer-by-wire mode, consisting of steps 211 to 214. In the first step 211, a steering request from the driver is detected. For this purpose, the steering angle sensor 103 detects a rotational movement of the steering wheel 102 and generates a steering request signal. In the subsequent step 212, the steering request signal is transmitted to the servo motor 121 via the signal line 130 or bus connection 131. In the following step 213, the servo motor 121 executes a steering movement at the steering gear 120, depending on the received steering request signal, which results in a steering movement of the steerable wheels 141, 142.

[0038] In a verification step 214, which is activated at predetermined time intervals, it is checked whether the mechanical sensor 112 or torque sensor 113 has detected a torque between the safety clutch 111 and the steering gear 120 that signals the engagement of the safety clutch 111. If no torque is detected, the procedure continues in the first step 211. If a torque is detected in verification step 214, this means that the safety clutch 111 has engaged, and the procedure continues in the following step 215, in which the servo motor 121 is switched to passive mode, and then to the following step 216, in which further control of the vehicle takes place in a purely mechanical control mode without support from the servo motor 121.

[0039] Parallel to the switching cycle of the steering system in steer-by-wire mode 210, the procedure 200 can include the following steps 220, performed by the safety clutch 111: In the first step 221, the safety clutch 111 is open. In the following step 222, it is checked whether the safety clutch 111 has received a fault signal. If not, the procedure continues to the first step 221. If the safety clutch 111 has received a fault signal, or is de-energized or without control, the clutch closes in the following step 223, so that the mechanical control mode is active by means of the closed steering linkage 110 224. As explained above, the closing of the safety clutch 111 during a steering movement leads to the detection of a torque in the mechanical sensor 112.Torque sensor 113 in check step 214, the passive switching of the steering gear in the following step 215 and thus to the use of the steering system in purely mechanical control mode without support of the servo motor, in the further following step 216, leads to.

[0040] The decoupling of the safety coupling 111 from the other ensures that the safety coupling 111 can be safely closed in the event of a fault. Reference symbol list 100 steering system 101 Steering column module 102 Steering wheel 103 Steering angle sensor 110 Steering system 110a first steering train part 110b second steering train part 111 Safety coupling 112 mechanical sensor 113 Torque sensor 120 steering gear 121 Servomotor 130 Signal line 131 bus connection 140 steerable wheels 141 left front wheel 142 right front wheel 200 procedures 210 steering system switching cycles in steer-by-wire mode 211 Recording the steering request 212 Transmitting the steering request 213 Executing the steering request 214 Detect that mechanical mode has been activated 215 Passive switching of the servo motor 216 controls in purely mechanical control mode 220 switching cycles of the safety clutch in steer-by-wire mode 221 Clutch open 222 Detecting an error signal 223 Closing the clutch 224 Activation of the mechanical control mode

Claims

[1] Steering system (100) for a motor vehicle, comprising: a steering column module (101) for detecting a steering request from a user; a steering gear (120); a servo motor (121) connected to the steering gear; and a signal line (130) for transmitting the steering request from the steering column module to the steering gear, wherein the steering system (100) is configured to execute the transmitted steering request in a steer-by-wire mode by means of the servo motor (121) and the steering gear (120), wherein the steering system (100) can still be switched to a mechanical control mode in which the motor vehicle can be mechanically steered, wherein in this case the servo motor (121) can be passively switched, wherein the steering system (100) comprises a steering linkage (110) with a safety coupling (111) which is configured to be closed in mechanical control mode and to mechanically connect the steering column module (101) to the steering gear (120), wherein the safety coupling (111) comprises an input shaft connected to the steering column module (101) and an output shaft connected to the steering gear (120), characterized by , that the steering system (100) includes a mechanical sensor (112) which is configured to detect that the mechanical control mode is active, wherein the mechanical sensor (112) is a torque sensor (113) between and steering gear (120) which is configured to measure the torsion between safety clutch (111) clutch output shaft and steering gear (120). [2] Steering system (100) according to claim 1, characterized by , that the steering system (100) is set up to automatically activate (224) the mechanical control mode in case of a fault. [3] Steering system (100) according to claim 1, characterized by , that the safety clutch (111) is configured to open in steer-by-wire mode. [4] Steering system (100) according to any one of claims 1 to 3, characterized by , that the steering system (100) is configured to passively switch the servo motor (121) when the torque sensor (113) measures a torque. [5] Steering system (100) according to any one of claims 1 to 4, characterized by , that the signal line (130) includes a bus connection (131). [6] Method (200) for steering a vehicle using a steering system (100), comprising: Detection (211) of a steering request at a steering column module (101) of the steering system (100); Transmitting (212) the steering request by means of a signal line (130) to a steering gear (120) of the steering system (100); Execution (213) of the transmitted steering request in a steer-by-wire mode using a servomotor (121) connected to the steering gear (120); Activating (224) a mechanical control mode of the steering system (100) to steer the vehicle mechanically; Detect (214), with the aid of a mechanical sensor (112), that the mechanical control mode (224) has been activated; and based on the detection (214) that the mechanical control mode has been activated (224), passive switching (215) of the servo motor (121), wherein activating (224) the mechanical control mode includes closing (223) a safety clutch (111) between steering column module (101) and steering gear (120), characterized by, that the detection, with the aid of a mechanical sensor (112), that the mechanical control mode has been activated (224), includes the measurement of a torque between an output shaft of the safety clutch (111) connected to the steering gear (120) and the steering gear (120). [7] Method (200) according to claim 6, characterized by , that activating (224) the mechanical control mode includes: Detection (222) of an error signal and; based on the fault signal: automatic activation (224) of the mechanical control mode. [8] Method (200) according to claim 6, characterized by , that the method (200) further comprises: Based on the detection (214) of a torque between clutch output shaft and steering gear (120), passive switching (215) of the servo motor (121) and control of the steering system in a purely mechanical control mode (216). [9] Method (200) according to any one of claims 6 to 8, characterized by, that the transmission of the steering request is carried out using a bus connection (131). [10] Non-volatile storage medium comprising instructions which, when executed by one or more processors, implement a method (200) according to any one of claims 6 to 9. [11] Vehicle with steering system (100) according to any one of claims 1 to 5.

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