Method and shaft position determination device for determining the rotational position of a shaft

Abstract

Method for determining a rotational position of a shaft, wherein the shaft (14) comprises magnetic pole pairs (22, 25) along its circumferential direction of rotation, characterized in that the method comprises: - Detecting magnetic field direction information (31) of a magnetic field generated by the pole pairs (22, 25), - Acquiring magnetic field strength information (32) of the magnetic field generated by the pole pairs (22, 25), - Determining the rotational position of the shaft (14) by evaluating the magnetic field direction information (31) and the magnetic field strength information (32), - Determining magnetic field direction change information as a function of several successively recorded magnetic field direction information (31), - Determining magnetic field strength change information as a function of several successively recorded magnetic field strength measurements (32), - Determining the rotational position of the shaft (14) as a function of the magnetic field direction information (31) when the magnetic field strength change information is below a predetermined first threshold value, and - Determining the rotational position of the shaft (14) as a function of the magnetic field strength information (32) when the magnetic field direction change information is below a predetermined second threshold value.

Description

[0001] The present invention relates to a method for determining a rotational position of a shaft and a corresponding shaft position determining device that uses the method. The present invention further relates to a motor having a shaft and a shaft position determining device for determining a rotational position of the shaft, as well as a steering aid for a vehicle having a motor and a shaft position determining device.

[0002] When commutation is performed on an electric motor, the motor position is often used to optimally control the motor. Various methods are known for detecting the motor position, i.e., for determining the current rotation angle of a motor shaft. For example, in electric steering systems in a motor vehicle, such as a passenger car or a truck, coordinate converters called resolvers can be used, or sensors based on magnetoresistive sensors, for example, at the motor shaft end.

[0003] For example, DE 19 818 799 A1 relates to a device for measuring angles with at least one magnetoresistive sensor unit and a magnetic scale. The device has at least two magnetically coded rings mounted on a rotatable axis and rigidly connected to this axis as the magnetic scale. The sensor unit has two magnetoresistive sensors, which are operated in the saturated state, and a Hall sensor is additionally provided.

[0004] DE 10 2004 050 586 A1 relates to a device for contactless detection of the angle of rotation of a rotatable element, comprising at least one magnetoresistive sensor element that emits at least one magnetoresistive sensor signal, and a first sensor element operating according to the Hall principle that emits a first Hall sensor signal. At least one further sensor element operating according to the Hall principle emits at least one further Hall sensor signal, so that angles of rotation of more than 360° can be detected.

[0005] DE 10 2010 040 584 A1 relates to a method for interference field compensation by means of a signal processing unit for determining the angle of rotation and / or speed of a rotor shaft of an electric motor in a power steering system of a motor vehicle.

[0006] The signal processing unit is connected to at least one stationary sensor element. The sensor element detects the magnetic field of a sensor magnet rotating with the rotor shaft to provide a raw sensor signal for the signal processing unit. To do this, the effect of a magnetic interference field on the raw sensor signal is first determined in order to generate a compensation signal. This preferably occurs before the power steering system is put into operation. Later, during operation, the respective raw sensor signal is then subjected to the generated compensation signal. This signal is then fed to the signal processing unit as a sensor signal, cleansed of the interference field, for determining the angle of rotation.

[0007] WO 2011 / 069904A2 relates to a device, in particular a circuit, that generates a compensation signal by factoring two sinusoidal signals. This exploits the fact that sinusoidal drive currents are already available in an electric power steering system, and the addition of phase-shifted sinusoidal signals with the same frequency again results in a sinusoidal signal with this frequency. A sensor arrangement is used to control a motor of the power steering system. This sensor arrangement can, for example, comprise magnetoresistive sensors and / or Hall sensors, which detect the rotor position of the electric motor and transmit it as a sensor signal to the electrical circuit.

[0008] DE 10 2007 000 945 A1 relates to a superposition actuator for a vehicle steering system with a superposition gear and a rotation angle sensor for measuring the rotation angle of one of the shafts of the superposition gear or of an electrically commutated servomotor. The rotation angle sensor is formed by a sensor bearing or by an at least two-pole magnetic wheel, which is scanned by at least two holding elements arranged offset from one another, or by a resolver, and the rotation angle sensor is penetrated by one of the shafts of the superposition gear.

[0009] DE 10 2008 021 591 A1 relates to an electromechanical steering system comprising a steering rod with a toothed section, an input shaft with a steering pinion, and a hollow-shaft motor. The hollow-shaft motor is arranged coaxially around the input shaft. A drive torque from the hollow-shaft motor is transmitted to the input shaft or the steering pinion via a reduction gear. A motor position sensor is located between the hollow shaft and a housing cover, providing position feedback on the motor's rotation angle.

[0010] US 2009 / 0 267 594 A1 describes position sensors and position sensor arrangements for contactless position detection using redundant magnetically sensitive sensor elements.

[0011] DE 10 2012 202 404 A1 describes a rotation angle sensor for detecting an absolute angle of rotation during single or multiple revolutions with respect to a rotation axis.

[0012] DE 198 18 799 A1 describes a method and a device for measuring angles of rotation of a rotation axis with a magnetic scale and a sensor unit assigned to the scale.

[0013] In electric steering systems or power steering systems with an electric drive, where the motor is arranged concentrically to the rack or steering column, the use of a magnetoresistive sensor at the shaft end is often not possible if the motor has a hollow shaft, for example. In this case, a ring magnet with an associated magnetoresistive sensor can be used. However, with this type of sensor, no more than one or half a mechanical revolution of the motor can generally be detected. In addition, the magnetoresistive sensor often has only a low angular resolution in the areas between two poles. Since, depending on the motor design, only the electrical revolution must be detected for motor commutation, the magnetic ring can, for example, be adapted to the number of pole pairs of the motor.For example, if the motor has five pole pairs, a corresponding ring magnet for position detection can also have five pole pairs, making it possible to determine the electrical rotation. However, it can be problematic if the magnetic field lines close to the magnetic ring only show a small angular change in the area of ​​the transition between two poles (north pole and south pole). Since further away from the magnetoresistive sensor the angular change is greater, the sensor must be arranged at a corresponding distance from the ring. However, the further the sensor is from the magnetic ring, the higher the field strength of the magnetic ring must be so that the field strength can still be detected by the sensor. This can increase the cost of the magnetic ring. Therefore, a compromise must be found between clear motor position detection, pole length and sensor-magnet air gap as well as cost and required installation space.Since the ring diameter of the magnetic ring cannot be chosen as small as desired when using a hollow shaft and, on the other hand, the air gap between the sensor and the magnetic ring should be kept as small as possible for cost reasons, a high degree of accuracy in determining the motor position can be difficult to achieve.

[0014] The object of the present invention is therefore to improve the accuracy of motor position determination, in particular in the previously described configuration of a magnetic ring on a hollow shaft.

[0015] According to the present invention, this object is achieved by a method for determining a rotational position of a shaft according to claim 1, a shaft position determining device for determining a rotational position of a shaft according to claim 7, a motor according to claim 9, a steering aid for a vehicle according to claim 11, and a vehicle according to claim 12. The dependent claims define preferred and advantageous embodiments of the invention.

[0016] According to the present invention, a method for determining a rotational position of a shaft is provided. The shaft has magnetic pole pairs along its circumferential rotational direction. In the method, magnetic field direction information of a magnetic field generated by the pole pairs and magnetic field strength information of the magnetic field generated by the pole pairs are acquired. The rotational position of the shaft is determined by evaluating the magnetic field direction information and the magnetic field strength information.

[0017] If you observe the magnetic field generated by pairs of magnetic poles attached to a shaft, such as a hollow shaft, in the form of a magnetic ring, you will see that both the magnetic angle, i.e. the direction of the magnetic field, and the magnetic flux, i.e. the magnetic field strength, change. Relative to a point that is fixed in relation to the rotation of the shaft, there are rotation angle ranges of the shaft in which the magnetic angle changes very sharply, and rotation angle ranges in which the magnetic flux changes very sharply. These rotation angle ranges are different, i.e. in angular ranges in which the magnetic angle changes very sharply, the magnetic flux changes only slightly and conversely there are ranges in which the magnetic angle changes only slightly but the magnetic flux changes very sharply.By evaluating both the magnetic field direction information and the magnetic field strength information to determine the rotational position of the shaft, a very precise change in the rotational angle of the shaft can be recorded for each rotational position of the shaft.

[0018] According to the invention, the magnetic field direction change information is determined as a function of several magnetic field direction information items acquired one after the other.

[0019] In addition, magnetic field strength change information is determined as a function of several pieces of magnetic field strength information acquired one after the other. The rotational position of the shaft is then determined as a function of which of the pieces of change information has a suitably large value. The rotational position of the shaft is determined as a function of the magnetic field direction information if the magnetic field strength change information is below a predetermined first threshold value. The rotational position of the shaft is determined as a function of the magnetic field strength information if the magnetic field direction change information is below a predetermined second threshold value. In other words, the rotational position of the shaft is determined as a function of the magnetic field strength information if the magnetic field direction information is unsuitable for determining the rotational position due to insufficient angular changes in this rotational position of the shaft.Conversely, the rotational position of the shaft is determined depending on the magnetic field direction information if the magnetic field strength change information is so small in this rotational range of the shaft that no accurate determination of the rotational position of the shaft can be made based on the magnetic field strength information.

[0020] According to a further embodiment, the magnetic field direction information is acquired at a first location fixed to the shaft, and the magnetic field strength information is acquired at a second location fixed to the shaft. The first location and the second location are arranged at an angle relative to the shaft such that the angle between the first location and the second location corresponds to an integer multiple of a corresponding angle of the magnetic pole pairs on the shaft. Expressed geometrically, an angle between a ray from a point on a longitudinal axis of the shaft through the first location and a ray from the point through the second location is thus an integer multiple of a corresponding angle between a ray from the point through a start of one of the magnetic pole pairs and a ray from the point through an end of the magnetic pole pair.The integer multiple can in particular also mean that the first position is equal to the second position, i.e. that the magnetic field direction information and the magnetic field strength information are detected at the same position. The magnetic field direction information can be detected, for example, by means of a magnetoresistive sensor or by means of a Hall sensor. The magnetic field strength information can be detected, for example, by means of a magnetoresistive sensor or by means of a Hall sensor. Preferably, the magnetic field direction information is detected by means of a magnetoresistive sensor and the magnetic field strength information is detected by means of a Hall sensor. Depending on the available installation space and the sensors, it can be advantageous to arrange the two sensors at the same position. Alternatively, it can be advantageous if the two sensors are arranged at different positions.An angle between the two sensors relative to the shaft corresponds to an integer multiple of the angle spanned by a magnetic pole pair on the shaft.

[0021] The magnetic field direction information and the magnetic field strength information can be acquired outside the outer circumference of the shaft, on a shaft end face, or within the inner circumference of the shaft. Thus, the method can be used for both solid and hollow shafts. Furthermore, the method can also be used for shafts installed in such a way that measurement at the end faces of the shaft is not possible. The magnetic pole pairs are preferably arranged equidistantly along the circumferential direction of rotation of the shaft. This results in equal angles for each spanned magnetic pole pair.

[0022] According to the present invention, a shaft position determining device for determining a rotational position of a shaft is further provided. The shaft position determining device comprises a plurality of magnetic pole pairs arranged on the shaft along a circumferential rotational direction of the shaft. The shaft position determining device further comprises a first sensor, a second sensor, and a processing unit. The first sensor detects magnetic field direction information of a magnetic field generated by the pole pairs. The second sensor detects magnetic field strength information of the magnetic field generated by the pole pairs. The processing unit, which is coupled to the first sensor and the second sensor, is capable of determining the rotational position of the shaft by evaluating the magnetic field direction information and the magnetic field strength information.

[0023] The shaft position determination device can, in particular, have exactly one first sensor and exactly one second sensor. Additional sensors for shaft position determination are not required. This allows the shaft position determination device to be implemented cost-effectively. According to the invention, the shaft position determination device is designed to carry out the method described above and therefore also includes the advantages described above.

[0024] According to the present invention, a motor, in particular an electric motor with electrical or electronic motor commutation, is further provided. The motor comprises a shaft driven by the motor and a shaft position determination device for determining the rotational position of the shaft, as previously described. With the aid of the shaft position determination device, a cost-effective position determination of the motor shaft is possible, for example, to support electronic commutation or to determine the motor position and motor speed.

[0025] According to the present invention, a steering aid for a vehicle is further provided, which comprises the above-described motor. Since the shaft position determining device of the motor operates by means of magnetic pole pairs, which are arranged on the shaft, for example, as a magnetic ring, the motor can comprise a hollow shaft, thereby creating a compact steering aid for the vehicle.

[0026] Finally, according to the present invention, a vehicle with the steering assistance described above is provided.

[0027] The present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 shows a vehicle according to an embodiment of the present invention. Fig. 2 shows a cross-sectional view of a hollow shaft of a motor according to an embodiment of the present invention. Fig. 3 shows magnetic field signals detected in a method according to an embodiment of the present invention.

[0028] Fig. 1 shows a vehicle 10 with an electric steering system 11. The electric steering system 11 can, for example, comprise a power-assisted steering system by means of an electric motor 12. However, the electric steering system 11 can also comprise an electric steering system, a so-called steer-by-wire steering system. The electric motor 12 is arranged concentrically to the steering column 18 and therefore has a hollow shaft 14. The steering column 18 or hollow shaft 14 is coupled to a steering gear 13 for controlling the steered wheels of the vehicle 10. On the hollow shaft 14, as will be described below with reference to Fig. 2, magnetic pole pairs in the form of a magnetic ring are attached to detect the current rotational position of the hollow shaft 14. To sense the rotational position of the hollow shaft 14, a sensor 15 for detecting a magnetic field direction and a sensor 16 for detecting a magnetic field strength are arranged adjacent to the hollow shaft 14. The sensors 15, 16 can comprise, for example, magnetoresistive sensors and / or Hall sensors. Preferably, the sensor 15 is a magnetoresistive sensor and the sensor 16 is a Hall sensor. The sensors 15, 16 are coupled to a processing unit 17. The processing unit 17 determines the current rotational position of the hollow shaft 14 and controls the electric motor 12 depending on the rotational position of the shaft 14 thus determined.

[0029] Fig. 2 shows a cross-sectional view of the hollow shaft 14. Magnetic pole pairs 22 and 25 are arranged circumferentially on the hollow shaft 14. Each magnetic pole pair 22, 25 consists of a north pole 21, 24 and a south pole 20, 23. Thus, north poles and south poles alternate along the circumferential direction of the hollow shaft 14. The magnetic pole pair 22 comprises the south pole 20 and the north pole 21 and the magnetic pole pair 25 comprises the south pole 23 and the north pole 24. The hollow shaft 14 rotates about its longitudinal axis 28. A magnetic pole pair, for example the one shown in Fig. The magnetic pole pair 22 shown in Figure 2 extends along the circumference of the hollow shaft 14 over a predetermined angular range 26. The magnetic pole pairs are preferably arranged equidistantly along the circumferential direction of the hollow shaft 14, whereby the angle 26 is the same for all magnetic pole pairs. For example, if five angle pairs are arranged along the circumferential direction of the hollow shaft 14, the angle 26 is 72° in each case. The sensors 15, 16 are also arranged at an angle 27 to one another with respect to the rotational axis 28 of the hollow shaft 14, which angle is an integer multiple of the angle 26. In the Fig. In the embodiment shown in Figure 2, angle 27 corresponds to angle 26. However, in the aforementioned example, in which angle 26 is 72°, angle 27 could also have other values, for example, 144°. Furthermore, angle 27 can also have the value 0°, so that sensors 15 and 16 are arranged at the same location.

[0030] Fig.3 shows sensor values ​​31 and 32, which are output by the sensors 15, 16 while the pole pairs 22 and 25 move past the sensors 15, 16 in a direction of movement 30. Reference numeral 31 indicates magnetic field direction information, which is output by the sensor 15, for example a magnetoresistive sensor, as a function of the angle of the magnetic field lines to the sensor 15. Reference numeral 32 indicates magnetic field strength information, which is output by the magnetic field sensor 16, for example a Hall sensor, as a function of the magnetic flux from the magnetic field sensor 16. In a region 33, when the sensor 15 is located in the region of the transition between the north pole and south pole of a pole pair, the magnetic angle of the field lines at the sensor 15 changes only slightly, so that the magnetic field direction information 31 hardly changes in this region 33.As a result, precise sensing of a rotational movement of the hollow shaft 14 in the region 33 based on the magnetic field direction information 31 can only be determined imprecisely. In the region 33, however, the magnetic field strength information 32, i.e. the magnetic flux, changes considerably, so that in this region 33 a change in the rotational position of the hollow shaft 14 can be determined very precisely based on the magnetic field strength information 32. Conversely, in a region 34, i.e. in a central region of one of the poles 20, 21, 23 or 24, the change in the magnetic field strength information 32 when the position of the hollow shaft 14 changes is only very slight. In the region 34, however, the magnetic field direction information 31 changes considerably even with small changes in the angle of rotation, so that precise detection of the rotational position of the hollow shaft 14 in the region 34 is possible using the sensor 15.

[0031] In summary, using only one magnetic field angle sensor and one magnetic field strength sensor in conjunction with a magnetic ring, the rotational position of a shaft can be determined with high accuracy for any rotation angle. The present invention was previously described with reference to the hollow shaft 14. However, the present invention is not limited to use in conjunction with a hollow shaft, but can also be used in conjunction with, for example, a solid shaft. Furthermore, the sensors 15, 16 can be arranged not only externally along a circumference of the shaft 14, but also inside a hollow shaft or on an end face of a shaft.

Claims

[1] Method for determining a rotational position of a shaft, wherein the shaft (14) comprises magnetic pole pairs (22, 25) along its circumferential direction of rotation, characterized by that the procedure includes: - detecting magnetic field direction information (31) of a magnetic field generated by the pole pairs (22, 25), - detecting magnetic field strength information (32) of the magnetic field generated by the pole pairs (22, 25), - determining the rotational position of the shaft (14) by evaluating the magnetic field direction information (31) and the magnetic field strength information (32), - determining a magnetic field direction change information as a function of several magnetic field direction information items (31) acquired one after the other, - determining a magnetic field strength change information as a function of several magnetic field strength information items (32) acquired one after the other, - determining the rotational position of the shaft (14) as a function of the magnetic field direction information (31) when the magnetic field strength change information is below a predetermined first threshold value, and - Determining the rotational position of the shaft (14) as a function of the magnetic field strength information (32) when the magnetic field direction change information is below a predetermined second threshold value. [2] Method according to claim 1, characterized byin that the magnetic field direction information (31) is detected at a first location fixed to the shaft (14) and the magnetic field strength information (32) is detected at a second location fixed to the shaft (14), wherein an angle (27) between a ray from a point on a longitudinal axis (28) of the shaft (14) through the first location and a ray from the point through the second location is an integer multiple of an angle (26) between a ray from the point through a start of one of the magnetic pole pairs (22) and a ray from the point through an end of the magnetic pole pair (22). [3] Method according to one of the preceding claims, characterized by that the magnetic field direction information (31) and the magnetic field strength information (32) - outside an outer circumference of the shaft (14), - on one end face of the shaft (14), or - within an inner circumference of the shaft (14), wherein the shaft (14) is a hollow shaft. [4] Method according to one of the preceding claims, characterized by that the magnetic field direction information (31) is detected by means of a magnetoresistive sensor (15) or by means of a Hall sensor (15). [5] Method according to one of the preceding claims, characterized by that the magnetic field strength information (32) is detected by means of a magnetoresistive sensor (16) or by means of a Hall sensor (16). [6] Method according to one of the preceding claims, characterized by that the magnetic pole pairs (22, 25) are arranged equidistantly along the circumferential direction of rotation of the shaft (14). [7] Shaft position determining device for determining a rotational position of a shaft, characterized by that the shaft position determination device is designed to carry out the method according to one of claims 1-6 and comprises the following: - a plurality of magnetic pole pairs (22, 25) arranged on the shaft (14) along a circumferential direction of rotation of the shaft (14), - a first sensor (15) for detecting magnetic field direction information (31) of a magnetic field generated by the pole pairs (22, 25), - a second sensor (16) for detecting magnetic field strength information (32) of the magnetic field generated by the pole pairs (22, 25), and - a processing unit (17) which is designed to determine the rotational position of the shaft (14) by evaluating the magnetic field direction information (31) and the magnetic field strength information (32). [8] Shaft position determining device according to claim 7, characterized by that the shaft position determining device comprises exactly one first sensor (15) and exactly one second sensor (16). [9] Engine, comprising: - a shaft (14) which can be driven by the motor (12), and - a shaft position determining device for determining a rotational position of the shaft (14) according to one of claims 7-8. [10] Engine according to claim 9, characterized by that the motor (12) is an electric motor. [11] Steering aid for a vehicle, characterized by that the steering aid (11) comprises a motor (12) according to claim 9 or 10. [12] Vehicle with a steering aid (11) according to claim 11.

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