Steering-by-wire system, motor vehicle, and method for determining absolute steering angle

Abstract

The invention relates to a steering-by-wire system for a motor vehicle, the steering-by-wire system having a steering wheel angle detection device (10), a feedback actuator (7) and a wheel actuator (9). The wheel actuator (9) has a wheel actuator control device (91), which is communicatively connected to the feedback actuator control device (71) and is designed to control the feedback actuator (71). An absolute steering angle is calculated based on sensor values of at least two first rotation angle sensors (3a, 3b) on a second gear (2) of a steering wheel angle detection device (10) and sensor values of at least two second rotation angle sensors (6a, 6b) on a motor shaft (5) of a feedback actuator (7). The invention further relates to a motor vehicle and to a method for determining an absolute steering angle.

Description

Technical Field

[0001] The invention relates to a steer-by-wire system for a motor vehicle, a motor vehicle, and a method for determining an absolute steering angle in a steer-by-wire system for a motor vehicle. Background Art

[0002] In a steer-by-wire system, the steered wheel and the steering wheel are not coupled mechanically but electrically. The steered wheel is controlled by a steering signal. The corresponding steering wheel position is detected by a steering angle sensor. The corresponding steering signal causes the steering controller to change the position of the steered wheel. In order to produce a realistic steering feel even in the absence of a mechanical connection between the steering wheel and the steered wheel, a steer-by-wire system can have a feedback actuator that generates an appropriate resistance in the steering movement.

[0003] The correct functioning of a steer-by-wire system requires the determination of an absolute steering angle. The absolute steering angle is understood to be the angle of the steering wheel or the steering shaft connected thereto over a number of revolutions. Compared to the relative steering angle, which lies in the range of ±360°, the absolute steering angle therefore has a larger range of values, for example up to ±720°.

[0004] Furthermore, for applications in the field of (partially) autonomous driving, a so-called “true power-on” function of the steering angle sensor is often required, which has the effect that the absolute steering angle can be detected already when the system is started, without having to first perform a steering movement for this purpose.

[0005] Due to the safety-critical nature of steer-by-wire systems, it is necessary to be able to reliably and accurately determine the absolute steering angle. The requirements for the system in this regard are specified by the ASIL classification. The ASIL classification (Automotive Safety Integrity Level) is a model specified in ISO 26262 for classifying the risks posed by system components of a vehicle. Typically, the components associated with the vehicle's steering system are classified at the highest level (ASIL-D).

[0006] In the prior art, solutions are known that measure the angles of a plurality of mutually connected rotatable objects in order to determine the absolute steering angle. For example, a device is known from DE 195 06 938 A1, in which the object whose absolute rotation angle is to be determined interacts with two gears. The rotation angles of the two gears can be measured by two corresponding rotation angle sensors. From the rotation angles thus determined and the gear ratio of the two gears, the absolute rotation angle of the object can be determined unambiguously.

[0007] However, in order to realize a device as described above for measuring the absolute steering angle in a steer-by-wire system in accordance with the requirements set out in ASIL-D, additional measures are required. Therefore, it has been concluded from the requirements according to ASIL-B that each rotation angle acquired is not acquired by a single sensor, but by two corresponding sensors, the sensor values ​​of the two sensors being compensated for each other. Therefore, four rotation angle sensors are required, whose signals must be transmitted to the corresponding control devices. This increases the complexity of the interface on the control device and the occupancy rate of the communication paths in the vehicle. Summary of the invention

[0008] The object of the present invention is to provide an improved steer-by-wire system which is designed to determine the absolute steering angle when the system is activated. The object of the present invention is also to provide a corresponding motor vehicle and a method for determining the absolute steering angle.

[0009] Here, the absolute steering angle is understood to be the angle of the steering wheel or the steering shaft connected thereto after a number of rotations. Therefore, compared with the relative steering angle in the range of ±360°, the absolute steering angle has a larger value range, for example up to ±720°.

[0010] Determining the (absolute) steering angle when the system is started can be understood as the "real start" function already mentioned. Here, the (absolute) steering angle can already be detected when the system is started, without having to first perform a steering movement.

[0011] According to the invention, the object with respect to the steer-by-wire system is achieved by the subject matter of claim 1. The object with respect to the motor vehicle or the method is achieved by the subject matter of claims 7 and 8 .

[0012] The object is achieved in particular by a steer-by-wire system for a motor vehicle having a steering wheel angle detection device, a feedback actuator and a wheel actuator.

[0013] Here, the steering wheel angle detection device has:

[0014] - a first gear wheel, which is directly connected to the steering wheel of the motor vehicle;

[0015] - a second gear wheel meshing with the first gear wheel; and

[0016] At least two first rotational angle sensors, which are designed to detect the rotational angle of the second gear wheel.

[0017] In the context of the present invention, “directly connected” is understood to mean that the corresponding objects are coupled to one another in such a way that one rotation of one object corresponds exactly to one rotation of the other object.

[0018] Feedback actuators have:

[0019] a servo motor having a motor shaft and a magnet fixed to the motor shaft, wherein the motor shaft is directly connected to the first gear;

[0020] at least two second rotation angle sensors, which are designed to detect the rotation angle of the motor shaft by means of magnets; and

[0021] A feedback actuator control device is designed to receive sensor signals from at least two second rotation angle sensors.

[0022] The wheel actuator has a wheel actuator control device which is communicatively connected to the feedback actuator control device and is designed to calculate the absolute steering angle based on the sensor values ​​of at least two first rotational angle sensors and the sensor values ​​of at least two second rotational angle sensors. Alternatively or additionally, the feedback actuator control device is further designed to calculate the absolute steering angle.

[0023] The advantage of the steer-by-wire system according to the invention is that in the steering wheel angle detection device, a pair of rotation angle sensors does not need to be arranged on the first gear, so that the absolute steering angle can be determined from the rotation angle of the first gear and the rotation angle of the second gear. Instead, at least two second rotation angle sensors of the feedback actuator are used to determine the rotation angle of the motor shaft, which is driven by the servomotor of the feedback actuator. In this case, the motor shaft is directly connected to the first gear, which in turn is directly connected to the steering wheel. Therefore, one rotation of the steering wheel corresponds exactly to one rotation of the motor shaft of the servomotor in the feedback actuator. The wheel actuator control device is designed here to determine the absolute steering angle based on the following rotation angles: the rotation angle of the second gear of the steering wheel angle detection device, which is determined by the at least two first rotation angle sensors; and the rotation angle of the motor shaft of the feedback actuator, which is determined by the at least two second rotation angle sensors.

[0024] By using a rotational angle sensor or a rotor position sensor of the feedback actuator to determine the absolute rotational angle, an additional sensor in the area of ​​the steering wheel angle detection device can be omitted.

[0025] By using redundant sensors to detect the rotation angle (at least two rotation angle sensors in each case), the steer-by-wire system according to the invention can meet the requirements according to ASIL-B. If the wheel actuator control device is configured accordingly, the steer-by-wire system can meet the requirements according to ASIL-D.

[0026] Preferred embodiments of the steer-by-wire system are specified in the respective dependent claims.

[0027] Advantageously, the feedback actuator control device is communicatively connected to the wheel actuator control device, wherein these control devices can each transmit received sensor information to the other control device.

[0028] Preferably, the feedback actuator control device is designed to calculate the absolute steering angle, in particular according to the Vernier principle (or Vernier principle). In this case, the absolute rotation angle is determined based on the following variables:

[0029] - the rotation angle obtained on the second gear;

[0030] - the acquired rotation angle of the motor shaft on the servo motor (corresponding to the rotation angle of the first gear); and

[0031] - A (fixed) transmission ratio between the first gear and the second gear.

[0032] In this way, the absolute steering angle can be calculated with high accuracy. In addition, a "true start" function is ensured, that is, the absolute steering angle can be calculated when the system is started, without the need for a steering movement to set the sensor.

[0033] Preferably, the feedback actuator control device and / or the wheel actuator control device can have at least two preferably identical control device units. Preferably, the two control device units are powered independently of one another. In this way, the respective control device can have two redundant units, which are functionally identical. In this case, for example, the first unit can be connected to the first of the at least two rotation angle sensors, and the second unit can be connected to the second of the at least two rotation angle sensors. This design increases the fault resistance of the control device and allows compliance with ASIL requirements.

[0034] Preferably, at least two first rotation angle sensors are communicatively connected to the wheel actuator control device via a SENT bus. SENT (Single Edge Nibble Transmission) is a digital serial interface. The SENT bus provides a simple possibility for transmitting sensor data with high precision between the sensor and the control device.

[0035] Preferably, the feedback actuator control device is communicatively connected to the wheel actuator control device via a CAN bus. The CAN bus (Controller Area Network) is a widely used bus system for communication of control devices in a vehicle. This has the advantage that the communication of the control devices of the steer-by-wire system can be implemented using standard solutions.

[0036] In particular, the object is also achieved by a motor vehicle having a steer-by-wire system as described above.

[0037] Furthermore, the object is achieved in particular by a method for determining an absolute steering angle in a steer-by-wire system as described above. The method comprises the following steps:

[0038] - obtaining a first rotation angle of the second gear;

[0039] - Obtain a second rotation angle of the motor shaft;

[0040] - calculating the absolute steering angle based on the first rotation angle and the second rotation angle.

[0041] Therefore, a method is proposed in particular for determining the absolute steering angle in a steer-by-wire system for a motor vehicle.

[0042] The steer-by-wire system includes a steering wheel angle detection device, a feedback actuator and a wheel actuator.

[0043] Wherein, the steering wheel angle detection device comprises:

[0044] - a first gear wheel, which is directly connected to the steering wheel of the motor vehicle;

[0045] - a second gear wheel meshing with the first gear wheel; and

[0046] at least two first rotational angle sensors, which are designed to detect the rotational angle of the second gear wheel,

[0047] Among them, the feedback actuator has:

[0048] a servo motor having a motor shaft and a magnet fixed to the motor shaft, wherein the motor shaft is directly connected to the first gear;

[0049] at least two second rotation angle sensors, which are designed to detect the rotation angle of the motor shaft by means of magnets; and

[0050] a feedback actuator control device which is designed to receive sensor signals of at least two second rotation angle sensors,

[0051] The wheel actuator has a wheel actuator control device which is communicatively connected to the feedback actuator control device.

[0052] And wherein the method comprises the following steps:

[0053] - obtaining a first rotation angle of the second gear;

[0054] - Obtain a second rotation angle of the motor shaft;

[0055] - calculating the absolute steering angle based on the first rotation angle and the second rotation angle.

[0056] In this case, the absolute steering angle is determined in particular by means of a wheel actuator control device. Alternatively or additionally, the absolute steering angle can advantageously be determined by means of a feedback actuator control device.

[0057] The advantages mentioned in connection with the steer-by-wire system also apply in a corresponding manner to the motor vehicle and the method according to the invention. The features described in this context are also disclosed in connection with the motor vehicle and the method, and vice versa. In particular, the method is suitable for carrying out the calculation of the absolute steering angle in the steer-by-wire system. Conversely, the steer-by-wire system is designed to carry out the corresponding method steps.

[0058] Preferred embodiments of the method are given in the respective dependent claims.

[0059] Preferably, the absolute steering angle is calculated according to the Vernier principle (or Vernier principle). This offers the advantage of calculating the absolute steering angle with high precision. Furthermore, the calculation method does not presuppose a reference steering movement, so that a "true opening" function can be achieved.

[0060] Preferably, calculating the absolute steering angle comprises adding a center position offset value and / or a horizontal steering wheel offset value. In this way, additional parameters of the steering system can be taken into account, further improving the calculation accuracy of the absolute steering angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be explained in further detail below with reference to the accompanying schematic drawings by means of an exemplary embodiment.

[0062] It shows:

[0063] Figure 1 A schematic diagram showing a steer-by-wire system according to the present invention according to one embodiment;

[0064] Figure 2 A schematic diagram showing a steer-by-wire system according to the invention in a greater degree of detail according to one embodiment; and

[0065] Figure 3 A schematic diagram showing a communication connection in a steer-by-wire system according to the present invention according to one embodiment. DETAILED DESCRIPTION

[0066] Figure 1 Some components of a steer-by-wire system according to the invention are shown according to one embodiment. These components of the steering system are described insofar as they are necessary for understanding.

[0067] The steer-by-wire system includes a steering wheel 11 , which is connected to a steering wheel angle detection device 10 and a feedback actuator 7 via a steering shaft.

[0068] Furthermore, the steer-by-wire system has a wheel actuator 9 with a control device which is communicatively connected to the control device of the feedback actuator 7 and which is also designed to receive sensor values ​​of a steering wheel angle detection device 10 .

[0069] The control device of the wheel actuator 9 is designed to calculate the absolute steering angle set by the driver at the steering wheel 11 and to drive the steering rack 17 accordingly in order to steer the vehicle.

[0070] The present invention is not limited to steering wheels, but can be generally applied to steering mechanisms, that is, it can also be applied to other steering devices, such as handlebars. Similarly, in addition to the above-mentioned steering wheel, a steering mechanism is usually included. The present invention is also not limited to human-machine interfaces, but also includes steering systems that can realize autonomous driving.

[0071] Figure 2 Some components of a steer-by-wire system according to the invention are shown in greater detail according to one exemplary embodiment, in particular the steering wheel angle detection device 10 , the feedback actuator 7 and the wheel actuator 9 .

[0072] Therefore, the steering wheel angle detection device 10 has a first gear 1, which is directly connected to the steering wheel 11, for example, via a steering shaft. In this way, one rotation of the steering wheel 11 corresponds exactly to one rotation of the first gear 1. In addition, the steering wheel angle detection device 10 has a second gear 2, which meshes with the first gear 1 and has a smaller number of teeth than the first gear 1. Therefore, the first gear 1 and the second gear 2 form a transmission with a fixed transmission ratio. Two rotation angle sensors 3a, 3b are arranged on the second gear 2, and the two rotation angle sensors measure the position or rotation angle of the second gear 2. The rotation angle sensors 3a, 3b can work based on magnets, for example.

[0073] The feedback actuator 7 has a servomotor having a motor shaft 5 directly connected to the first gear 1. Therefore, one rotation of the first gear 1 (or the steering wheel 11) corresponds precisely to one rotation of the motor shaft 5. With the aid of a magnet (not shown) fixed to the motor shaft 5, a rotor position sensor or a rotation angle sensor 6a, 6b can detect the rotation angle of the motor shaft 5. The feedback actuator-control device 71 receives the sensor values ​​of the rotation angle sensors 6a, 6b.

[0074] The wheel actuator 9 has a wheel actuator control device 91, which is connected to the first rotation angle sensors 3a, 3b of the steering wheel angle detection device 10 via the SENT bus 4, and is also connected to the feedback actuator control device 71 via the CAN bus 8. In this way, the wheel actuator control device 91 can receive the sensor values ​​of the rotation angle sensors 3a, 3b and 6a, 6b, and calculate the absolute steering angle based on these sensor values ​​and the fixed transmission ratio of the gears 1, 2. Advantageously, the feedback actuator control device can receive the sensor values ​​of the rotation angle sensors 3a, 3b and 6a, 6b in a corresponding manner, and calculate the absolute steering angle based on these sensor values ​​and the fixed transmission ratio of the gears 1, 2.

[0075] Figure 3 A schematic diagram of a communication connection in a steer-by-wire system according to the invention is shown according to one embodiment. In the embodiment shown, redundant units, communication connections and power supply units are provided for the control devices involved.

[0076] Specifically, the feedback actuator-control device is formed by two redundant units 71a, 71b. The feedback actuator-control device unit 71a is powered by the power supply unit 20a and receives the sensor value of the first rotation angle sensor 6a. The feedback actuator-control device unit 71b is powered by the power supply unit 20b independent of the power supply unit 20a and receives the sensor value of the first rotation angle sensor 6b.

[0077] The wheel actuator-control device is formed by two redundant units 91a, 91b. The wheel actuator-control device unit 91a is powered by the power supply unit 20a and is connected to the feedback actuator-control device unit 71a via the CAN bus 8a in order to receive the sensor value of the first rotation angle sensor 6a. The wheel actuator-control device unit 91b is powered by the power supply unit 20b and is connected to the feedback actuator-control device unit 71b via the CAN bus 8b in order to receive the sensor value of the first rotation angle sensor 6b.

[0078] Through redundant design of control units, sensors and communication paths as well as independent power supplies, steer-by-wire systems offer increased fault protection, especially in applications according to ASIL-B.

[0079] Or the requirements of ASIL-D.

[0080] Description of Reference Numerals

[0081] 1 First gear

[0082] 2 Second gear

[0083] 3a, 3b first rotation angle sensor

[0084] 4SENT bus

[0085] 5 motor shaft

[0086] 6a, 6b Second rotation angle sensor

[0087] 7 Feedback Actuator

[0088] 8 CAN bus

[0089] 9 Wheel actuator

[0090] 10 Steering wheel angle detection device

[0091] 11 Steering wheel

[0092] 12 Rack

[0093] 20a, 20b power supply

[0094] 71 Feedback actuator-control device

[0095] 71a, 71b Feedback actuator-control device unit

[0096] 91 Wheel actuator-control device

[0097] 91a, 91b Wheel actuator-control device unit

Claims

1. A steer-by-wire system for a motor vehicle, in, The steer-by-wire system comprises a steering wheel angle detection device (10), a feedback actuator (7) and a wheel actuator (9). Wherein, the steering wheel angle detection device (10) comprises: - a first gear wheel (1) which is directly connected to the steering wheel (11) of the motor vehicle; - a second gear wheel (2) meshing with the first gear wheel (1); and at least two first rotation angle sensors (3a, 3b) which are designed to detect the rotation angle of the second gear wheel (2), Wherein, the feedback actuator (7) has: - a servomotor having a motor shaft (5) and a magnet fixed to the motor shaft, wherein the motor shaft (5) is directly connected to the first gear (1); - at least two second rotation angle sensors (6a, 6b) which are designed to detect the rotation angle of the motor shaft (5) by means of magnets; and a feedback actuator control device (71) which is designed to receive sensor signals of at least two second rotation angle sensors (6a, 6b), The wheel actuator (9) has a wheel actuator control device (91), which is communicatively connected to a feedback actuator control device (71) and is configured to calculate an absolute steering angle based on sensor values ​​of at least two first rotation angle sensors (3a, 3b) and sensor values ​​of at least two second rotation angle sensors (6a, 6b).

2. The steer-by-wire system according to claim 1, characterized in that: The feedback actuator control device (71) is designed to calculate an absolute steering angle.

3. The steer-by-wire system according to claim 2, characterized in that: The feedback actuator control device (71) is designed to calculate the absolute steering angle according to the Vernier principle.

4. A steer-by-wire system according to any one of the preceding claims, characterised in that The feedback actuator control device (71) and / or the wheel actuator control device (91) has at least two preferably identical control device units which are preferably independently powered.

5. A steer-by-wire system according to any one of the preceding claims, characterised in that At least two first rotation angle sensors (3a, 3b) are communicatively connected to a wheel actuator control unit (91) via a SENT bus (4).

6. A steer-by-wire system according to any one of the preceding claims, characterised in that The feedback actuator control device (71) is communicatively connected to the wheel actuator control device (91) via a CAN bus (8).

7. A motor vehicle having a steer-by-wire system according to any one of claims 1 to 6.

8. A method for determining the absolute steering angle in a steer-by-wire system for a motor vehicle, in, The steer-by-wire system comprises a steering wheel angle detection device (10), a feedback actuator (7) and a wheel actuator (9). Wherein, the steering wheel angle detection device (10) comprises: - a first gear wheel (1) which is directly connected to the steering wheel (11) of the motor vehicle; - a second gear wheel (2) meshing with the first gear wheel (1); and at least two first rotation angle sensors (3a, 3b) which are designed to detect the rotation angle of the second gear wheel (2), Wherein, the feedback actuator (7) has: - a servomotor having a motor shaft (5) and a magnet fixed to the motor shaft, wherein the motor shaft (5) is directly connected to the first gear (1); - at least two second rotation angle sensors (6a, 6b) which are designed to detect the rotation angle of the motor shaft (5) by means of magnets; and a feedback actuator control device (71) which is designed to receive sensor signals of at least two second rotation angle sensors (6a, 6b), The wheel actuator (9) has a wheel actuator control device (91) which is communicatively connected to the feedback actuator control device (71), characterized in that: The method comprises the following steps: - obtaining a first rotation angle of the second gear (2); - obtaining a second rotation angle of the motor shaft (5); - calculating the absolute steering angle based on the first rotation angle and the second rotation angle.

9. The method according to claim 8, characterized in that The absolute steering angle is calculated according to the Vernier principle.

10. The method according to claim 8 or 9, wherein: The calculation of the absolute steering angle includes adding the center position offset value and / or the horizontal steering wheel offset value.

Images