Method for monitoring a belt drive of a steering system and steering system for a motor vehicle

Abstract

Method for monitoring a belt drive (5) of a steering system (1) for a motor vehicle, which has a toothed belt (53) drivingly circulating around two belt pulleys (51, 52), wherein one belt pulley (51) is coupled to the motor shaft of a motor (41) and one belt pulley (52) is operatively connected to a steering actuator (4), and by means of a sensor (8) of a monitoring device (8, 9) the rotation of at least one of the belt pulleys (51, 52) is detected and evaluated in a control device (9), characterized in that an angular acceleration of the belt pulley (51, 52) interacting with the sensor (8) is measured and evaluated in order to detect a deviation from a predetermined threshold value.

Description

State of the art

[0001] The invention relates to a method for monitoring a belt drive of a steering system for a motor vehicle, which comprises a toothed belt drivingly circulating around two pulleys, wherein one pulley is coupled to the motor shaft of a motor and one pulley is operatively connected to a steering actuator. The rotation of at least one of the pulleys is detected by a sensor of a monitoring device and evaluated in a control device. A steering system for implementing such a method is also the subject of the invention.

[0002] Steering systems for motor vehicles are known in which the steering angle of the steerable wheels is generated entirely or partially by an electric motor-driven steering drive. Steer-by-wire steering systems, which have no mechanical connection between the steering handle and the steerable wheels, convert manually input steering commands into electrical control signals that actuate the steering drive purely electrically. In power steering systems, the electric steering drive provides an auxiliary force that supports the manual steering input.

[0003] Steering drives are known in the prior art that have a belt drive, preferably a toothed belt drive, for transmitting torque from an electric motor, for example, from the generic document DE 10 2017 214 649 A1. This drive comprises a belt pulley connected to the motor, a belt pulley coupled to an actuator element, and a toothed belt that circulates around the belt pulleys as a traction means.

[0004] To ensure steerability, the proper functioning of the belt drive is crucial, especially in a steer-by-wire steering system. The required synchronous torque transmission from the motor to the actuator or control element can be impaired by slippage, for example, in a timing belt due to so-called tooth jumps or timing belt jumps. This occurs when a tooth of the timing belt does not mesh positively with the toothing of the belt pulley and jumps over, resulting in a missing tooth width during power transmission in the pulling direction. Such malfunctions can be triggered, for example, by wear and insufficient belt tension, and lead to further increased wear.

[0005] In the aforementioned DE 10 2017 214 649 A1, a rotation angle of the motor's rotor is detected by means of a first sensor designed as a rotor position sensor, and the rotor position measurement thus generated is compared with the measurement value of a second sensor designed as an index sensor for detecting the actual position of a steering actuator driven by the toothed belt drive, for example, the steering angle of a steering shaft interacting with steerable wheels. A tooth jump can be detected from a deviation between the measured values ​​of the two sensors. This enables monitoring of the operating status of the belt drives and ensures safe operation. A disadvantage, however, is the complex design, which always requires two sensors.

[0006] In view of the problems explained above, it is an object of the present invention to enable reliable monitoring of the belt drive with less effort. Description of the invention

[0007] This object is achieved according to the invention by the method according to claim 1 and the steering system having the features of claim 7. Advantageous further developments emerge from the subclaims.

[0008] In a method for monitoring a belt drive of a steering system for a motor vehicle, which has a toothed belt drivingly rotating around two belt pulleys, wherein one belt pulley is coupled to the motor shaft of a motor and one belt pulley is operatively connected to a steering actuator, and by means of a sensor of a monitoring device the rotation of at least one of the belt pulleys is detected and evaluated in a control device, it is provided according to the invention that an angular acceleration of the belt pulley interacting with the sensor is measured and evaluated in order to detect a deviation from a predetermined threshold value.

[0009] The detection method according to the invention is based on the fact that when a tooth jump occurs, the drive-side pulley coupled to the motor shaft briefly loses positive contact with the toothed belt and thereby spins relative to the toothed belt, which continues to rotate continuously at the current rotational speed due to the inertia of the belt drive and the associated steering actuator. This results in a pulse-like, steep increase in the rotational speed of the drive-side pulley, which corresponds to an increased angular acceleration. This is detected according to the invention. If the angular acceleration increases beyond a predetermined threshold value, which corresponds to an upper limit, this is a clear and unambiguous indicator of a tooth jump.

[0010] One advantage of the method according to the invention is that a single sensor enables reliable detection of a tooth jump or other malfunction of the timing belt drive associated with drive slip. This reduces manufacturing costs and increases operational reliability.

[0011] A further advantage is that the practical implementation of the method can, in principle, be achieved by appropriately evaluating the measured values ​​provided by a known sensor. Such an evaluation can be performed with minimal effort using specially designed algorithms in an electronic control unit connected to the sensor. This allows the monitoring system to be implemented in a simpler, more robust, and more cost-effective manner than the state of the art.

[0012] The sensor can transmit measured values ​​correlated with an angular position or angular velocity to the control device, which then generates a rotational angular acceleration value. For example, the sensor can have an incremental encoder that outputs a pulse sequence correlated with the angular velocity. The temporal sequence of the pulses indicates the angular velocity, from which the rotational angular acceleration can be derived.

[0013] Preferably, the angular acceleration is compared with a predetermined threshold value, and if the threshold value is exceeded, a warning signal is issued and / or a safety mode is activated. This can take place in an electronic evaluation unit of the control device according to an algorithm implemented therein. If a deviation of the angular acceleration above a limit value is detected, a warning signal can be issued indicating a fault in the steering system. Preferably, a safety mode can be activated automatically, in which a redundant steering mode can be activated, for example via torque vectoring or another redundant steering system, and additionally or alternatively, a controlled braking or stopping of the vehicle can be initiated. This can increase the safety level, particularly of steer-by-wire steering systems.

[0014] It is preferable to measure the angular acceleration of the belt pulley connected to the motor shaft. This is the drive-side pulley, which is usually the smaller of the two pulleys. The drive torque is transmitted via the toothed belt to the driven inertial masses of the belt drive and the actuator element via this drive pulley, so the risk of potential belt jumps is greatest there. This ensures reliable monitoring.

[0015] It is possible for the sensor to measure the angular position or angular velocity of the pulley. The control unit can be designed accordingly to determine the rotational angular acceleration from this, according to the invention.

[0016] In a steering system for a motor vehicle, comprising a belt drive which has a toothed belt drivingly rotating around two belt pulleys, wherein one belt pulley is coupled to the motor shaft of a motor and one belt pulley is operatively connected to a steering actuator, and a monitoring device is provided which has a sensor connected to a control device for detecting the rotation of at least one of the belt pulleys, it is provided according to the invention that the monitoring device is designed to detect an angular acceleration of the belt pulley interacting with the sensor.

[0017] In the steering system according to the invention, all features described above in connection with the method according to the invention can be implemented.

[0018] It is possible for the sensor to comprise a rotation sensor. This can comprise an angle sensor that outputs the current angular position as a measured value, or an angular velocity sensor that outputs the current angular velocity as a measured value. From this, the control device can generate the rotational angular acceleration values ​​according to the invention.

[0019] For this purpose, it can preferably be provided that the control device is designed to generate a rotational angular acceleration value and compares this in an evaluation unit with a predetermined threshold value. The rotational angular acceleration can be determined in the control device from the second derivative of the measured values ​​of the angular positions provided by the sensor, or from the first derivative of the measured values ​​of the angular velocity provided by the sensor. In the evaluation unit, the value of the rotational angular acceleration is compared with a predetermined threshold value, which represents a limit value. A brief deviation at which the threshold value is exceeded serves as an indicator of an irregular circular movement of the toothed belt, which occurs in the event of a tooth jump or also in the event of a tooth belt failure, for example due to the toothed belt jumping off the pulley, overstretching, or tearing.If a deviation occurs, the control device can emit a warning signal indicating a fault in the steering system and, preferably automatically, activate a safety mode in which a redundant steering mode can be activated, for example via torque vectoring or another redundant steering system, and additionally or alternatively a controlled braking or stopping of the vehicle can be initiated.

[0020] As already mentioned above in connection with the method according to the invention, it can preferably be provided that the sensor interacts with the motor shaft. In this case, one of the two pulleys is usually connected directly or indirectly to the motor shaft, so that its angular acceleration is detected.

[0021] The sensor can be designed as a magnetic (inductive) and / or capacitive and / or optical and / or electrical sensor. For example, the sensor can comprise, in a conventional manner, an incremental encoder which, according to one of the aforementioned measuring methods, outputs a pulse sequence correlated with the rotation of the pulley, which is processed by the evaluation unit. Alternatively, it can also be designed to output continuously varying measured values, for example, a voltage value correlated with the rotational speed or the like. Alternatively, it is possible to provide an electrical sensor that monitors the motor's power supply so that certain current-voltage patterns can be detected there that are clearly correlated with an increase in the angular acceleration of the motor shaft.In any case, since in principle only a single sensor is required to implement the method according to the invention, reliable monitoring can be achieved with less effort than in the prior art.

[0022] Preferably, an electric motor-driven steering drive can be provided for the belt drive. In a steer-by-wire steering system, the steering actuator (steering actuator) can comprise one or more steering drives designed according to the invention. Due to the lack of mechanical coupling of the manual steering input with the wheels to be steered, a particularly high level of operational reliability of the belt drive is required from a safety perspective. The design according to the invention enables reliable detection of malfunctions and wear with less effort than in the prior art.

[0023] It is also conceivable and possible to realize the advantages of the invention in an auxiliary drive.

[0024] An electric motor-driven steering drive can be implemented, for example, by coupling a belt pulley to the motor and connecting a belt pulley to a spindle nut of a spindle drive. The spindle drive serves to convert the rotation of the belt pulley into a linear movement of an actuator acting on steerable wheels, analogous to the rack of a known rack-and-pinion steering gear. The invention enables, in particular, a more compact and lightweight design than the prior art. Description of the drawings

[0025] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. In detail: Fig. 1 a schematic representation of a steer-by-wire steering system according to the invention, Fig. 2 a schematic representation of a steering drive according to the invention of a steering system according to Fig. 1. Embodiments of the invention

[0026] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0027] Fig. 1 schematically shows a steer-by-wire steering system 1 comprising a steering column 2. This system has a support unit 21 mountable on a vehicle body (not shown), of which a steering spindle 22 is rotatably mounted about its longitudinal axis L. At its rear, driver-side end relative to the direction of travel, a steering wheel 23 is non-rotatably mounted on the steering spindle 22 for inputting manual steering commands.

[0028] In the steering column 2, a rotation angle and torque detection sensor system (not shown in detail) is accommodated, which converts a steering command introduced into the steering spindle 22 as a rotation of the steering wheel 23 into an electrical control signal, namely a steering signal.

[0029] The control signal is transmitted via an electrical control line 3 to an electrical steering actuator 4 according to the invention.

[0030] The steering actuator 4 has a belt drive 5 which has a first belt pulley 51 and a second belt pulley 51 and a toothed belt 53 which runs around the belt pulleys 51, 52 as a traction means.

[0031] The first pulley 51 is attached to an electric motor 41, and the second pulley 52 is operatively connected to a spindle drive. This drive comprises, in a conventional manner—not explicitly shown here—a spindle nut that is axially supported and rotatably mounted in the steering actuator 4 and coupled to the pulley 52. ​​A threaded spindle engages the spindle nut and is mounted in the steering actuator for longitudinal displacement along its spindle axis A, which corresponds to the rotational axis of the pulley 52 and the spindle nut, as indicated by the double arrow.

[0032] The first pulley 51 on the drive side, connected to the motor shaft of the motor 41, is smaller than the second pulley 52, ie has a smaller diameter.

[0033] The threaded spindle is connected to steerable wheels 61 via tie rods 6 in a manner known per se.

[0034] The belt drive 5 is in Fig.2 in a schematically isolated view in the direction of the parallel axes of rotation of the pulleys 51 and 52.

[0035] A sensor 8 is connected to a control device 9 via a control line 81. It has a measuring transducer 82 that interacts with the first pulley 51.

[0036] The measuring sensor 81 of the sensor 8 can operate according to a magnetic (inductive) and / or capacitive and / or optical measuring principle and is designed to detect a rotational movement of the pulley 51, for example, as an incremental encoder that outputs an electrical pulse sequence correlated with the rotation as a measured value. The measuring sensor 81, together with the sensor 8, can also be referred to as a rotation sensor.

[0037] Alternatively or additionally, it can be provided that an electrical measuring sensor is integrated into an electrical supply line of the motor 41 (not shown here) in order to detect current and / or voltage values ​​of the power supply of the motor 41.

[0038] The control device 9 is designed to generate a rotational angular acceleration value from the measured values ​​transmitted by the sensor. This rotational angular acceleration value is continuously compared with a predetermined threshold value in an evaluation unit 91 during operation. If the threshold value is exceeded as a result of a rotational angular acceleration caused by a gear jump, a warning signal can be output, for example via a signal generator 92. Preferably, additionally or alternatively, a safety mode of the steering system 1 or the motor vehicle can be activated automatically, in which a redundant steering mode can be activated, for example via torque vectoring or another redundant steering system, and additionally or alternatively, a controlled braking or stopping of the vehicle can be initiated. List of reference symbols 1 steering system 2 steering column 21 Support unit 22 Steering spindle 23 Steering wheel 3 control line 4 Steering actuator 41 Engine 5 Belt drive 51, 52 pulley 53 Timing belt 6 Tie rod 61 wheels 8 Sensor 81 Control line 82 sensors 9 Control device 91 Evaluation unit 92 signal generators L Longitudinal axis A spindle axis U Direction of rotation

Claims

[1] Method for monitoring a belt drive (5) of a steering system (1) for a motor vehicle, which has a toothed belt (53) drivingly rotating around two belt pulleys (51, 52), wherein a belt pulley (51) is coupled to the motor shaft of a motor (41) and a belt pulley (52) is operatively connected to a steering actuator (4), and by means of a sensor (8) of a monitoring device (8, 9), the rotation of at least one of the belt pulleys (51, 52) is detected and evaluated in a control device (9), characterized by that a rotational angular acceleration of the belt pulley (51, 52) cooperating with the sensor (8) is measured and evaluated in order to detect a deviation from a predetermined threshold value. [2] Method according to claim 1, characterized by that the sensor (8) transmits measured values ​​correlated with an angular position or an angular velocity to the control device (9), which generates a rotational angular acceleration value therefrom. [3] Method according to one of the preceding claims, characterized by that the angular acceleration is compared with a specified threshold value and, if the threshold value is exceeded, a warning signal is issued and / or a safety mode is activated. [4] Method according to one of the preceding claims, characterized by that the angular acceleration of the belt pulley (51) connected to the motor shaft is measured. [5] Method according to one of the preceding claims 1 to 3, characterized by that the rotational angular acceleration of a smaller of the two pulleys (51, 52) is recorded. [6] Method according to one of the preceding claims, characterized by that the sensor (8) detects the angular position or the angular speed of the belt pulley (51, 52) as a measured value. [7] Steering system (1) for a motor vehicle, comprising a belt drive (5) which has a toothed belt (53) drivingly rotating around two belt pulleys (51, 52), wherein a belt pulley (51) is coupled to the motor shaft of a motor (41) and a belt pulley (52) is operatively connected to a steering actuator (4), and a monitoring device (8, 9) is provided which has a sensor (8) connected to a control device (9) for detecting the rotation of at least one of the belt pulleys (51, 52), characterized by that the monitoring device (8, 9) is designed to detect an angular acceleration of the belt pulley (51, 52) cooperating with the sensor (8). [8] Steering system according to claim 7, characterized by that the sensor (8) has a rotation sensor (81). [9] Steering system according to one of claims 7 or 8, characterized bythat the control device (9) is designed to form a rotational angular acceleration value and compares this with a predetermined threshold value in an evaluation unit (91). [10] Steering system according to one of claims 7 to 9, characterized by that the sensor (8) interacts with a smaller of the two pulleys (51, 52). [11] Steering system according to one of claims 7 to 10, characterized by that the sensor (8) interacts with the motor shaft. [12] Steering system according to one of claims 7 to 11, characterized by that the sensor (8) is designed as a magnetic (inductive) and / or capacitive and / or optical and / or electrical sensor. [13] Steering system according to one of claims 7 to 12, characterized by that an electric motor steering drive has the belt drive (5). [14] Steering system according to one of claims 7 to 13, characterized bythat a belt pulley (51) is coupled to the motor (41) and a belt pulley (52) is connected to a spindle nut of a spindle drive. [15] Steering system according to one of claims 7 to 14, characterized by that it is designed as a steer-by-wire steering system (1).

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