Method for determining and/or controlling a position of an electric motor

Abstract

The invention relates to a method for determining and/or controlling a position of an electric motor, in particular in a clutch actuation system of a motor vehicle, wherein the position of a rotor of the electric motor is picked up by a sensor system situated on a stator of the electric motor outside an axis of rotation of the electric motor, and the position signal picked up by the sensor system is analyzed by an analysis unit. In a method in which the rotor position is detected with a high level of certainty, the position signal is transmitted to the analysis unit depending on a transmission distance between the sensor system and the analysis unit by means of an SPI protocol signal for short transmission distances, and/or by means of a PWM signal for longer transmission distances.

Claims

1. A method of determining and controlling a position of an electric motor in a clutch actuation system of a motor vehicle, comprising: arranging a stator of the electric motor outside an axis of rotation of the electric motor; detecting the position of a rotor of the electric motor by a sensor system; transferring a position signal from the sensor system to an analysis unit; and, analyzing the position signal from the sensor system by the analysis unit, wherein when the transmission distance between the sensor system and the analysis unit is a first transmission distance, the position signal is transmitted by a serial peripheral interface protocol signal, or when the transmission distance between the sensor system and the analysis unit is a second transmission distance, the position signal is transmitted by a pulse width modulation signal; and utilizing the sensor system to commutate the electric motor based upon the position signal, wherein the commutation occurs in response to utilizing serial peripheral interface protocol signal or the pulse width modulation signal, wherein the pulse width modulation signal includes information about an absolute position of a pole pair of the rotor of the electric motor and the serial peripheral interface protocol signal includes information regarding the absolute position of the rotor.

2. The method of claim 1, wherein the absolute position of the pole pair of the rotor of the electric motor is transmitted by the sensor system via the serial peripheral interface protocol signal or the pulse width modulation signal to the analysis unit when the electric motor is started, whereupon the electric motor is then supplied with current via a commutation derived by the analysis unit from an incremental position of the rotor of the electric motor.

3. The method of claim 2, wherein a pulse to no-pulse ratio of the pulse width modulation signal is analyzed to transmit the absolute position of a pole pair of the rotor of the electric motor.

4. The method of claim 2, wherein a comparison is carried out between an incremental position of the rotor calculated by the analysis unit and the absolute position of the pole pair.

5. The method of claim 4, wherein the comparison is carried out cyclically.

6. The method of claim 1, wherein a small-diameter magnetic transmitter ring fastened to the rotor of the electric motor which has only one pole pair is used to determine the position of the rotor.

7. The method of claim 6, wherein the magnetic transmitter ring having a larger diameter and a plurality of pole pairs, fastened to the rotor of the electric motor, is used to determine the position of the rotor, wherein the number of pole pairs of the magnetic transmitter ring is equal to the number of pole pairs of the rotor.

8. A clutch actuation system, comprising: an electric motor having a rotor and a stator, the stator arranged outside an axis of rotation; a sensor system configured to detect a position of the rotor of the electric motor; and an analysis unit configured to analyze a position signal from the sensor system, wherein the sensor system is configured to transmit the position signal to the analysis unit via a peripheral interface protocol in response to a transmission distance between the sensor system and the analysis unit being a first transmission distance, and to transmit the position signal via a pulse width modulation signal in response to the transmission distance between the sensor system and the analysis unit being a second transmission distance.

9. The clutch actuation system of claim 8, wherein the analysis unit is configured to commutate the electric motor based upon the position signal in response to utilizing serial peripheral interface protocol signal that includes information regarding the absolute position of the rotor, or in response to utilizing the pulse width modulation signal that includes information about an absolute position of a pole pair of the rotor.

10. The clutch actuation system of claim 8, wherein an absolute position of a pole pair of the rotor is transmitted by the sensor system via the serial peripheral interface protocol signal or the pulse width modulation signal to the analysis unit when the electric motor is started, whereupon the analysis unit is configured to supply current to the electric motor based on an incremental position of the rotor.

11. The clutch actuation system of claim 10, wherein the analysis unit is configured to analyze a pulse to no-pulse ratio of the pulse width modulation signal to transmit the absolute position of the pole pair of the rotor.

12. The clutch actuation system of claim 10, wherein the analysis unit is configured to carry out a comparison between the incremental position of the rotor and the absolute position of the pole pair.

13. The clutch actuation system of claim 12, wherein the comparison is carried out cyclically.

14. The clutch actuation system of claim 8, further comprising a small-diameter magnetic transmitter ring fastened to the rotor including one pole pair, wherein the small-diameter magnetic transmitter ring is configured to determine the position of the rotor.

15. The clutch actuation system of claim 14, further comprising a larger-diameter magnetic transmitter ring having a plurality of pole pairs, wherein the larger-diameter magnetic transmitter ring is fastened to the rotor of the electric motor and is configured to determine the position of the rotor, wherein a number of pole pairs of the magnetic transmitter ring is equal to a number of pole pairs of the rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments are disclosed, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts, in which:

(2) FIG. 1 is a schematic view of a clutch actuation system of the present invention;

(3) FIG. 2 is a schematic view of transmission of an output signal from the sensor system to an analysis unit;

(4) FIG. 3 is a perspective view of a magnetic transmitter ring;

(5) FIG. 4 is a first embodiment of a magnetic transmitter ring having a first ring diameter; and,

(6) FIG. 5 a second embodiment of a magnetic transmitter ring having a second ring diameter.

DETAILED DESCRIPTION

(7) At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects.

(8) Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It, is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure.

(9) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure.

(10) FIG. 1 depicts in simplified form clutch actuating system 1 for an automated clutch. Clutch actuating system 1 is assigned to friction clutch 2 in a drivetrain of a motor vehicle, and includes master cylinder 3, which is connected to slave cylinder 5 via hydraulic line 4, also referred to as a pressure line. Movable axially in slave cylinder 5 is slave piston 6, which actuates friction clutch 2, by means of actuating organ 7 and with bearing 8 interposed. Master cylinder 3 is connected to equalizing container 9 through connecting aperture 9A. Master piston 10 is movable in master cylinder 3. Piston rod 11, which is movable linearly in the longitudinal direction together with master piston 10, extends from master piston 10. Piston rod 11 of master cylinder 3 is coupled by means of threaded spindle 12 with positioner 13 operated by an electric motor. The electric-motor-operated positioner 13 includes electric motor 14 designed as a commutated DC motor and analysis unit 15. Threaded spindle 12 converts a rotary motion of electric motor 14 to a longitudinal motion of piston rod 11 or of master cylinder piston 10. Friction clutch 2 is actuated automatically by electric motor 14, threaded spindle 12, master cylinder 3 and slave cylinder 5.

(11) Integrated onto or into electric-motor-operated positioner 13 is sensor system 16, as depicted in FIG. 2. Sensor system 16 is spatially separated from analysis unit 15. Thus sensor system 16 can be situated, for example, in a transmission bell, while analysis unit 15 is positioned outside of the transmission bell. Situated inside sensor system 16 is signal conditioning circuit 17, which has SPI interface 18 and/or PWM interface 19. In addition, signal conditioning circuit 17 includes incremental interface 20.

(12) FIG. 3 shows rotor 22 of electric motor 14, which is designed as a hollow shaft. Rotor 22 of commutated electric motor 14 (not shown in further detail) has, on a side facing toward sensor system 16, which is positioned on the stator (not shown in further detail), magnetic transmitter ring 23, which includes a specified number of N, S magnetic poles. Rotor magnets 24 are fastened within rotor 23, rotor magnets 24 having the same number of N, S pole pairs as magnetic transmitter ring 23. An N, S pole pair is made up here of two N, S magnetic poles, whose directions of magnetization run in opposite directions. Such an off-axis system operates with very high resolution and precision, and is able to permit rapid and reliable data transmission through the use of a standard sensor system.

(13) When turning on electric motor 14, first the absolute position of rotor 22 of electric motor 14 is determined. The absolute position sensed in a N, S pole pair is transmitted via PWM interface 19 or SPI interface 18. The selection between SRI interface 18 and PWM interface 19 is made depending on the distance between sensor system 16 and analysis unit 15. The SPI protocol signal is always used to transmit the absolute position of rotor 22 if only short transmission distances have to be surmounted between sensor system 16 and analysis unit 15. But if the distance between sensor system 16 and analysis unit 15 is greater, the absolute position is transmitted by means of the digital PWM signal. Such a PWM signal has the advantage of not being susceptible to interference acting on the output signal of sensor system 16 along the transmission path. Advantageously, the absolute position is ascertained by analysis unit 15 from the pulse to no-pulse ratio of the PWM signal.

(14) If the absolute position in the electrical period is known, the electrification and actuation of electric motor 14 begins. From this moment on, the rotor position is transmitted with incremental information, which is issued via incremental interface 20 of sensor system 16. Within analysis unit 15, the position of rotor 22 of electric motor 14 is calculated from the incremental information, based on the absolute position of a pole pair. In the present example, a fast incremental sensor, for example a giant magnetoresistance (GMR) sensor, is used in sensor system 16 to ascertain the position of rotor 22. The output signal of incremental interface 20 of sensor system 16 is preferably transmitted via an A/B signal track. Signal tracks A, B are electrically phase-shifted by 90 relative to each other, which corresponds to half a pulse. The use of these two signal tracks has the advantage that interference in the signal transmission path is avoided, or should interference occur, a plausibility check of the output signal from sensor system 16 is possible. Furthermore, the direction of motion of rotor 22 can be detected simply in this way. The incremental position of rotor 22 transmitted via the A/B track is likewise read in analysis unit 15 directly into the inputs of microprocessor 21, which is positioned in analysis unit 15, and which counts the flanks of the output signal of each signal track A, B. Every interrupt triggers a block commutation, where the number of interrupts depends on the number of pulses delivered by sensor system 16 per commutation step.

(15) So as to increase confidence in the calculated position information, and to detect any transmission and/or computing errors, a comparison of the incremental position of rotor 22 calculated in analysis unit 15 to the absolute position of electric motor 14 in the pole pair, as ascertained at the beginning of operation of electric motor 14, is performed cyclically.

(16) It is significant for the proposed method that the output signal A issued from sensor system 16 is always unambiguous within one electrical period. Two methods for realizing this are proposed. FIG. 4 shows magnetic transmitter ring 23 with a small ring diameter. Such a magnetic transmitter ring 23 is also known as a diametric-magnetic tray, and has only one pole pair consisting of one south pole S and one north pole N (FIG. 4a). The GMR sensor contained in sensor system 16 delivers via this pole pair a signal which is electrically unambiguous through 360. This is particularly recognizable in the signal course of the output signal A issued by the sensor system, which has a sufficiently noticeable gradient which can be readily analyzed. But if the diameter of magnetic transmitter ring 23 is enlarged, the use of only one pole pair results in a course of the output signal A of sensor system 16 which has a flattened signal course, which cannot be analyzed with sufficient precision by analysis unit 15 (FIG. 4b).

(17) If, as depicted in FIG. 5, the diameter of magnetic transmitter ring 23 is enlarged, and if a variety of pole pairs are distributed alternately around magnetic transmitter ring 23, this guarantees that the output signal A from sensor system 16 also remains clearly within one electrical period of 360 with such a multi-pole sensor, if magnetic transmitter ring 23 has exactly as many pole pairs as rotor 22.

(18) In view of the explanations given, an off-axis sensor system is presented which has short signal transit times, in order to use position information for commutating electric motor 14. At the same time, the output signal A from sensor system 16 is electrically unambiguous through 360. Through the use of a PWM signal to determine the absolute position, in particular the analysis of the pulse to no-pulse ratio of this PWM signal, a precise determination of the absolute position of electrical motor 14 at its start is possible. At the same time, interference-proof transmission between sensor system 16 and analysis unit 15 free of external interference signals is realized. Furthermore, plausibility checking of the calculated incremental position against the absolute position in a pole pair is possible at any time. Thus, an off-axis electric motor is presented which is simple to construct, and whose rotor position is detected with a high level of certainty.

(19) It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

LIST OF REFERENCE NUMBERS

(20) 1 clutch actuating system 2 friction clutch 3 master cylinder 4 hydraulic line 5 slave cylinder 6 slave piston 7 actuating organ 8 clutch release bearing 9 equalizing container 9A aperture 10 master piston 11 piston rod 12 threaded spindle 13 positioner 14 electric motor 15 analysis unit 16 sensor system 17 signal conditioning circuit 18 SPI interface 19 PWM interface 20 incremental interface 21 microprocessor 22 rotor 23 magnetic transmitter ring 24 rotor magnet N north pole S south pole A output signal