ELECTRIC MOTOR WITH A DEVICE TO DETECTE THE ROTOR POSITION, THE NUMBER OF GIRLS AND, OR THE DIRECTION OF ROTATION

Description

2. 2030 / 93 / β. 'STUDIO BREVETTI JAUMANN by Joumami P- A C. sn& MILAN - PL Castle n. 2 5 Company: ROBERT BOSCH GMBH0 Gm. 1993 Headquarters: Stuttgart (FED. REP. OF GERMANY) *** MI93A / 01270 STATE OF THE ART The invention relates to an electric motor, especially a permanent magnet excited DC motor, with a device for detecting the rotor position, the number of revolutions and, or the direction of rotation, of the type of the main claim. For many applications of electric motors, it is necessary to detect the rotor position, the speed or the direction of rotation, for example in electric motor-driven window regulators or sliding sunroofs in motor vehicles, in order to provide effective protection against jamming or to reach a predefined position. § · OR From JP-Abstract 60-134 748, vol. 9, November 21, p: lG A 1985, it is known that a Hall element can be fixed on the QS inner side of a motor case. In the case of a wheel The resulting flux variations Kù® are detected by the armature slots in this Hall element, whereby a speed signal is derived from these Hall signals. A similar arrangement for detecting rotations, or detecting the number of revolutions is known from the DE-GM 87 12 3. 360. Here, a magnetic coil is arranged on the inside of a muffler-shaped magnetic yoke between the two excitation magnets, in order to be able to detect corresponding rpm signals during the rotation of the engine. The drawback of the known arrangements is that under load, currents flow through the winding proportionally to the load, causing the so-called transverse armature field. The magnetic field-sensing element, however, is only capable of detecting the entire field appearing on the stator and contains the desired part of the flux variation, depending on the armature slots and the unwanted field portion of the armature current. Depending on the type of engine and the mounting location of the element, In the measurement signal, one field portion prevails at one time and the other at another time. The transverse field portion of the armature is derated, as it provides more feedback on the current curve, which again depends on manufacturing, random factors and is unwanted. or less a represent- S unusable due to many tolerances wear phenomena The measured signal that can be evaluated, however, may be very modest. 4. ADVANTAGES OF THE INVENTION The electric motor according to the invention with the features of the main claim, however, has the advantage that the portion of the induced current field of the magnetic flux in the signal of the magnetic field-sensing element is eliminated or at least reduced, so that in the ideal case only the desired portion of the excitation field is contained in the signal of the magnetic field-sensing element. In this way, not only are distorting portions of the measured signal eliminated, but the level of the evaluable portion is dominant. With the measures illustrated in the subclaims, advantageous further developments and improvements of the electric motor specified in the main claim are possible. Advantageously, a slot is provided in the magnetic yoke of the stator that increases the magnetic resistance for the armature transverse field, particularly axially, where the magnetic field-sensitive element is arranged within the slot. The induced transverse field of S will close as a result of this increased magnetic resistance, preferably on the opposite side of the stator where there is no slot. The residual shaft of the armature transverse field should extend around REVETTI JAUMANN 5. at the slot, so a Hall sensor, positioned directly in front of the slot or in the slot, can be kept largely free from the armature cross-field. The magnetic field-sensing element can therefore only detect the signal, which can be used for evaluation, based on flux variations through the armature slots. To achieve optimal effect, the slot extends essentially axially and can also be designed as a through slot up to the magnetic yoke. In particular, the slot is appropriately positioned within the magnetic pole closest to the magnetic field-sensitive element, preferably essentially centered on this magnetic pole. Further advantageous means of eliminating the effects of the unwanted armature transverse field consist in the provision of a subtractor element, which subtracts a signal proportional to the armature current from the measured signal of the magnetic field-sensitive element. In this way, the unwanted, current-proportional parts of the armature transverse field are subtracted, so that a signal is available at the output of the subtraction organ, which in turn in the ideal case still contains only the desired part of the signal field 6. excitement. The signal proportional to the armature current is appropriately taken from a shunt in the motor's electrical circuit, where this shunt can also be implemented as a transistor in a transistor bridge controlling the electric motor. The subtraction device is appropriately implemented as a differential amplifier. DESIGN Examples of embodiments of the invention are shown in the drawing and illustrated in detail in the following description. In particular: Fig. 1 shows a cross-sectional representation of an electric motor with a slot in the magnetic yoke to enlarge the magnetic resistance for the armature transverse field, Fig. 2 shows the slot according to Fig. 1 with the Hall element arranged nearby in a development of a partial zone B, B' of the magnetic yoke, Fig. 3 shows a subtraction circuit to compensate for the unwanted current portion of the armature cross-field, Fig. 4 shows the detection of a signal \\ proportional to the armature current as a function of a transistor bridge controlling the electric motor, '10 JAUMANN PATENTS . Fig. 5 shows an electric motor in longitudinal section with different alternatives for the application of a Hall element, Fig. 6 shows the electric motor represented in Fig. 5, in cross-section, along the section line AA, and Fig. 7 shows a Hall element arranged in a recess of the polar tube, with a flux-guiding element in the form of a bracket. DESCRIPTION OF EXAMPLES OF REALIZATION The electric motor shown in cross-section in Fig. 1 is designed as a permanent-magnet DC motor. Two permanent magnets 13, 14 are arranged internally, facing each other, within a muffler-shaped pole tube 40 of round cross-section as magnetic poles. A rotor 17, shown schematically, is rotatably mounted between the permanent magnets 13, 14. The commutator, typical for a DC motor, and the brushes spring-loaded thereon are not shown for simplicity's sake, since this is a known arrangement and is not relevant to the present invention. Externally on the pole tube 40 in the central area of ​​the permanent magnet 13 a Hall element 25 is inserted into the pole tube 40. For this purpose, in the pole tube 40 IDIO PATENTS JAUMANN 8. a recess 27 is shaped like a groove with widened end regions. The pole tube 40 also has an axial slot 42 extending essentially centrally with respect to the permanent magnet 13, so that the Hall element 25 is arranged nearby when viewed in the peripheral direction. This is precisely shown in Fig. 2. The slot 42 is designed to pass through in the radial direction and, however, can also extend only over a part of the thickness of the pole tube 40. The principle of the rotational speed detection or the rotational position detection via such a Hall element on the pole tube or pole box is that, depending on the magnetic saturation of the pole tube, a small part of the magnetic flux also extends along the path Sta in the air outside this pole box, since the bristling iron Ud in this case no longer represents an ideal magnetic conductor. This marginal field can be detected with a magnetic field-sensitive element, if this is mounted externally on the pole tube 40. For the element inserted according to Fig. 1, the magnetic flux can be detected directly via the pole tube 40. With the rotation of the rotor 17, a modest radiation of the entire flux in the motor occurs, which can be traced back to the series of rotor slots. This periodic flux variation with 9. The fixed armature speed is detected by the Hall element, as is the so-called armature transverse field caused by currents that increase proportionally with the load. Correspondingly, the amplitudes of the leakage fields also vary accordingly with the total armature flux. The frequency of the measured signals obtained corresponds to the product of the frequency of the speed x the number of slots and is therefore a measure of the speed of the electric motor. Counting the signals produces a signal proportional to the rotor. For some electric motors, it is difficult to evaluate the Hall element signals, which leads to errors in the evaluation electronics. The main reason for this is that when the motor is loaded, currents flow in the windings, which increase proportionally with the load and cause the so-called armature transverse field 43, which overlaps with the field of the permanent magnet-excited DC motor. The Hall element is now able to detect the entire field that appears on the electric motor, i.e., in the magnetic backlash, and contains the desired part of the flux variation due to the armature slots and the undesired part of the armature current field. Depending on the type of motor and the mounting location of the Hall element, the signal BREW JJUMANN 10. When measured, one field portion prevails at one time, and the other at another. The armature transverse field portion is undesirable, as it provides more or less a representation of the current curve that is unusable for evaluation and which again depends on many manufacturing tolerances, random factors, and wear phenomena. Due to the slot 42, which can also be designed as a groove or similar, the magnetic resistance for the armature transverse field at this point increases. Therefore, the armature transverse field preferably closes in the opposite region of the magnetic field 40, as shown by a higher density of field lines in Fig. 1. From Fig. 2 it appears that the remaining modest residue of the armature transverse field 43 must necessarily extend around the slot 42, so the Hall element 25, arranged in front of this slot 42, is kept free of any portion of the armature transverse field. The armature transverse field therefore manifests itself very little as interference in the measured signal. For the sake of illustration, the permanent magnetic field 44 is also indicated by a dash and dot. The slot 42 can in principle also have a path that deviates from the axial direction, since it is of essential importance that the z^UDIO PATENTS JAUMANN 11. The transverse armature field lines, which extend approximately perpendicular to the axial direction in the magnetic yoke 40, are interrupted or weakened. Several parallel slots 42, or those arranged in series with one another, are also suitable for this purpose. A further possibility for eliminating the unwanted current component from the measured signal of the Hall element is shown in Fig. 3. In particular, the measures shown in Figs. 1 and 2 and the measures shown in Fig. 3 can be used, even with an adjuvant action. According to Fig. 3, a shunt 46 is inserted in the electrical supply circuit (supply voltage U) of an electric motor 45, which may correspond, for example, to the electric motor shown in Fig. 1, at which a signal proportional to the current can be tapped. This signal proportional to the current is fed via an additional resistor 47 to a differential amplifier 48, which is feedback-coupled via a resistor 57. The non-inverting input of this differential amplifier 48 is actuated cited with a constant reference voltage Uref. The signal produced by the Hall element 25 via an additional resistor 26 is fed to the differential amplifier 48. Through the ratio between the resistor 56 and 12. Using resistor 47, the gain ratio of the shunt signal to the Hall element signal can be adjusted. One of the signals must be fed inverted to the differential amplifier 48, which is initially connected as an adder, in order to operate as a subtractor. This can be achieved, for example, very simply with the signal from Hall element 25, as it is rotated 180 degrees. Electrical inversion using an inverter is also possible. This compensation removes the unwanted, current-proportional parts of the armature transverse field from the Hall element signal 25. A measured signal is therefore available at the output of the differential amplifier, which ideally still contains only the desired part of the excitation field. This measured signal is then fed to an electronic evaluation circuit 32. In this evaluation circuit 32 the signals at the output of the differential amplifier 48 are counted or converted into a signal proportional to the speed. rhetorical position. Instead of the shunt 46, a signal proportional to the current can be obtained, for example also according to the excitation bridge circuit shown in Fig. 4. In Fig. 4 the electric motor 45 is arranged in the branch 13. The transverse circuit of an excitation bridge consists of four transistors 49-52. The supply voltage is connected at the terminal points of the bridge circuit. The voltage drop across transistors 51, 52 resulting from the current flowing through them can be tapped using the two taps 53, 54, preferably at the two motor connections 45. These transistors 51, 52 can thus be used simultaneously as shunts. Depending on the direction of rotation, a signal proportional to the current is always applied to one of the taps 53, 54, so that the taps 53, 54 can be fed, for example, via a diode arrangement, to the voltage divider 47 or directly to the differential amplifier 48. Figs. 5 to 7 show and illustrate examples of different mounting locations for Hall elements on the electric motor, respectively on a stator or pole tube. For this purpose, slots 42 (not shown) can be arranged accordingly, or a circuit according to Fig. 3 can be used. The electric motor shown in Figs. 5 and 6 is also designed as a DC motor with permanent magnet excitation. In a muffler-shaped pole tube 10, which according to Fig. 6 has a substantially round cross-section with two BOP PATENTS JAUMANN by Oaumann P. <£ C. snc 14. The two permanent magnets 13, 14 are arranged opposite each other as magnetic poles in the two round areas, flattened sides 11, 12. They are held in their position by two U-shaped magnetic holding springs 15, 16. The rotor 17, shown schematically, is mounted so that it can rotate between the permanent magnets 13, 14. In Fig. 5, for simplicity of representation, the rotor 17 has been omitted. The two permanent magnets 13, 14 have a mutually different shape. Thus, the front surfaces of the permanent magnets 13, resting on the magnetic holding springs 15, 16, extend essentially in a radial direction, while the corresponding front surfaces of the permanent magnets 14, resting on the magnetic holding springs 15, 16, extend essentially perpendicular to the flattened sides 11, 12. For simplicity of representation, both have been shown alternatively in one figure, even though the two permanent magnets in a practical embodiment of a motor are designed identically. In the electric motor shown in Figs. 5 and 6, six Hall elements 18-23 are arranged internally on the pole tube 10, which forms the magnetic yoke of the electric motor. The five positions shown again represent alternatives, i.e. in a practical implementation it is gmBKEVETTI JAUMANN P. & G· som* 15. Only a single Hall element is provided, which assumes one of the positions shown. Thus, the Hall elements 18-21 are arranged internally at the flattened sides 11, 12 of the pole tube 10, whereby the Hall element 18 rests on the longer arm of the magnetic holding spring 15, while the Hall element 19 rests directly on the permanent magnet 13, since in this position, according to Fig. 5, the shorter arm of the magnetic holding spring 16 does not reach the position of this Hall element 19. Correspondingly, the Hall element rests directly on the front side of the permanent magnet 14, while the Hall element 21 only reaches as far as the longer arm of the magnetic holding spring 16. The Hall element 22 in the area of ​​the front side of the permanent magnet 13, facing the open end of the pole tube 10, is arranged slightly apart from the pole tube 10. In another design, the pole tube 10 could also be designed round. This is represented by the dotted round area of ​​the pole tube 24. The Hall element 23 is mounted specifically between the permanent magnets 13, 14 internally on this area of ​​the pole tube 24 and is axially offset with respect to these permanent magnets 13, 14, as shown in Fig. 5. In the example of implementation represented in / GRIDIOBREVETTI JAUMANN 16. Fig. 7, the Hall element 25 is arranged in a recess 27 on the outer side of the flattened side 11 of the pole tube 10. It protrudes slightly from this recess 27. A flux-guiding element 28, which is made as a bent piece of sheet metal and acts as a support arm, connects the outwardly facing, protruding edge surface of the Hall element 25 to the outer surface of the pole tube 10. This provides magnetic resistance to the magnetic flux extending into the outer space, i.e., is advantageous. The Hall element 28, which offers a shorter flux path and a magnetically longer flux path, forms a bypass with respect to the pole tube 10. By arranging the Hall element 25 between an end region of the flux-guiding element 28 and the pole tube 10, the field passes through the Hall element 25 perpendicularly, even when it is arranged, for example, tangentially to the pole tube.The Hall element 25 is magnetically arranged in series with the flux guide element 28. An electrical connection 29 of the Hall element 25 is connected to the circuit via a line 30 and a plug connection. electronic evaluation 32. To secure and secure the entire arrangement against damage, a housing 33 made of synthetic material encompasses the flow guide element 28, the Hall element 25 and the line 30, whereby the plug connection 31 is arranged in a manner not shown. 18. magnetic, such as field plates, magnetic coils, or similar. Furthermore, the means described for compensating the armature transverse field can also be used to detect the rotor position, the speed and, or the direction of rotation for other electric motors, in which variations in the stray field appear on the magnetic yoke caused by the rotary motion.

Claims

21. transistor of a bridge of transistors controlling the electric motor (45).

11. - Electric motor according to claims 8 to 10, characterised in that the subtractor member (48) is designed as a differential amplifier.

12. - Electric motor according to one of the preceding claims, characterised in that the element (25) sensitive to the magnetic field is designed as a Hall element. The representative (Paolo Jaumann) of STUDIO BREVETTI JAUMANN P· £ C.

19. CLAIMS 1.- Electric motor, especially a permanent magnet excited DC motor, with a device for detecting the rotor position, the number of revolutions and, or the direction of rotation, which has at least one magnetic field sensitive element, which for detecting changes in the magnetic flux, dependent on the rotor position, is mounted on the stator of the motor, where electronic means are provided for evaluating the signals of this magnetic field sensitive element, characterised in that means (42, 48) are provided for eliminating or reducing the unwanted part of the induced current field of the magnetic flux in the signals of the magnetic field sensitive element (25).

2. - Electric motor according to claim 1, characterised in that a slot (42) is provided in the magnetic yoke (40) of the stator which increases the magnetic resistance for the transverse armature field, as well as in that the element (25) sensitive to the magnetic field is arranged within the slot (42).

3. - Electric motor according to claim 2, characterised in that the slot (42) extends in a substantially axial direction.

4. - Electric motor according to claim 2 or 3, characterised in that the slot (42) is arranged 20. within the magnetic field sensitive element (25), in correspondence with the closest magnetic pole (13).

5. - Electric motor according to claim 4, characterised in that the element (25) sensitive to the magnetic field is arranged substantially in a central position of this magnetic pole (13).

6. - Electric motor according to claims 2 to 5, characterised in that the slot (42) is designed as a slot passing through the magnetic pole (13).

7. - Electric motor according to claims 2 to 6, characterised in that the magnetic field sensitive element (25) is arranged in the slot (42) or in a peripheral direction next to the slot (42).

8. - Electric motor according to claim 1, characterised in that a subtractor member (48) is provided, which subtracts a signal proportional to the armature current from the measured signal of the element (25) sensitive to the magnetic field.

9. - Electric motor according to claim 8, characterised in that the signal proportional to the armature current is the signal taken from a shunt (46, 51, 52) in the electric circuit of the motor.

10. - Electric motor according to claim 9, characterized in that the shunt (51, 52) is made of a synthetic material on an outer side of this housing 33. This synthetic material housing 33 can, for example, be produced by injection coating or by casting with synthetic material. A second electrical connection of the Hall element 25 can be achieved by means of a ground connection, or a second electrical connection is provided in accordance with the first electrical connection 29. Further alternative mounting locations for a Hall element are described, for example, in DE 41 28 419. Thus, the Hall element can, for example, be mounted externally on the magnetic yoke and be clamped by means of a flux-guided element in the form of a bracket.Furthermore, the Hall element 25 can be arranged between two flux-guided elements, which are held together by a claw-like element, whereby the entire arrangement is pressed together externally or internally with the magnetic yoke. Finally, two Hall elements, especially within a period, can also be arranged electrically offset by 90 degrees on the pole tube, for example in a slot extending obliquely in the pole tube, in order to be able to detect the direction of rotation. In principle, other field-sensitive elements can also be used instead of Hall elements. BREVETTIJAUMANN TAV.