BRUSHLESS ELECTRICAL MACHINE

Abstract

A brushless electrical machine, in particular, a brushless d.c. motor, having a housing, at least one rotor, which is positioned on a shaft rotationally mounted in the housing, and a stator attached to the housing; the rotor being assigned a rotor position detection device, which operates contactlessly and includes a multipole magnetic ring positioned on the shaft in a rotatably fixed manner and at least one sensor, which is sensitive to magnetic fields and is attached to the housing radially with respect to the outer circumference of the magnetic ring. The number of pole pairs of the rotor and the number of pole pairs of the magnetic ring are coprime.

Claims

1-10. (canceled)

11. A brushless electrical machine, comprising: a housing; at least one rotor, which is positioned on a shaft rotationally mounted in the housing; a stator attached to the housing; and a rotor position detection device, the rotor being assigned the rotor position detection device, the rotor position detection device being configured to operate contactlessly and includes a multipole magnetic ring positioned on the shaft in a rotatably fixed manner, and at least one sensor, which is sensitive to magnetic fields and is attached to the housing radially with respect to an outer circumference of the magnetic ring; wherein a number of pole pairs of the rotor and a number of pole pairs of the magnetic ring are coprime.

12. The brushless electrical machine as recited in claim 11, wherein the brushless electrical machine is a brushless d.c. motor.

13. The brushless electrical machine as recited in claim 11, wherein the number of pole pairs of the rotor is 4.

14. The brushless electrical machine as recited in claim 11, wherein the number of pole pairs of the magnetic ring is 5.

15. The brushless electrical machine as recited in claim 11, wherein the number of pole pairs of the magnetic ring determines a number of angular segments of the rotor position detection device.

16. The brushless electrical machine as recited in claim 11, further comprising: a control unit configured to ascertain an angular segment of the magnetic ring as a function of a signal of the sensor, and to determine an angle of rotation as a function of the ascertained angular segment.

17. The brushless electrical machine as recited in claim 16, further comprising a monitoring device, wherein to ascertain the angular segment, the control unit is configured to induce a first current in the stator to turn the rotor in a first direction of rotation, into a first angular segment, and wherein the monitoring device is configured to monitor the rotor for an angular motion.

18. The brushless electrical machine as recited in claim 17, wherein the monitoring device is configured to monitor the angular motion for a direction of rotation.

19. The brushless electrical machine as recited in claim 17, wherein the control unit is configured to induce a second current in the stator to turn the rotor two angular segments in a direction of rotation opposite to the first direction of rotation, and the monitoring device is configured to monitor the rotor for the angular motion.

20. The brushless electrical machine as recited in claim 19, wherein the monitoring device is configured to monitor the angular motion for a direction of rotation.

21. The brushless electrical machine as recited in claim 20, wherein the control unit is configured to induce a third current in the stator, to turn the rotor one angular segment in the first direction of rotation, when the monitoring device has detected that the rotor turned in the first direction of rotation, due to the second current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows a simplified perspective view of a brushless electrical machine, in accordance with an example embodiment of the present invention.

[0014] FIG. 2 shows a graph for explaining an advantageous operating method, in accordance with an example embodiment of the present invention.

[0015] FIG. 3 shows a table for clarifying the method in accordance with an example embodiment of the present invention.

[0016] FIG. 4 shows a flow chart for explaining the method, in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0017] FIG. 1 shows a simplified view of a brushless electrical machine 1 that includes a housing 2, in which a shaft 3 is rotationally mounted. A rotor 4 and, at a free end, a driving pinion 5, are mounted on shaft 3 in a rotatably fixed manner. Shaft 3 is rotationally mounted in housing 2, using a plurality of bearings 6, in particular, rolling element bearings. Rotor 4 is also assigned a stator 7 having at least one stator winding capable of being supplied with current; stator 7 being positioned coaxially to rotor 4.

[0018] In addition, a magnetic signal generator 8 in the form of a multipole magnetic ring 9 is mounted on shaft 3, between rotor 4 and driving pinion 5, in a rotatably fixed manner. A sensor 10, which is attached to the housing and is designed to be sensitive to magnetic fields, is assigned to magnetic ring 9. Thus, sensor 10 is used as a signal receiver of signal generator 8.

[0019] The number of pole pairs of rotor 4 and of magnetic ring 9 are designed to be coprime. According to the present exemplary embodiment, the number of pole pairs of rotor 4 is z.sub.4=4, and the number of pole pairs of magnetic ring 9 is z.sub.9=5. Using the sensor device made up of sensor 10 and magnetic ring 9, the angular position of rotor 4, in particular, at the start of the system of electrical machine 1, is determined with the aid of control unit 11, which is adapted to carry out the method described in the following.

[0020] To this end, in several graphs, FIG. 2 initially shows the behavior of electrical machine 1 over mechanical angle of rotation φ.sub.mech. In this context, the uppermost graph shows the characteristic curve of mechanical angle of rotation φ.sub.mech. The graph underneath it shows the electrical angle of rotation of the rotor 4 having 4 pole pairs. The underlying graph shows the magnetic angle of rotation of magnetic ring 9 versus mechanical angle of rotation 4. The lowest portion of FIG. 2 shows the angular segments I through V defined by magnetic ring 9, due to its pole-pair number of 5.

[0021] With the aid of the Nonius or Vernier Principle for determining the current angle of rotation of rotor 4, control unit 11 is configured to initially determine the angular segment, in which the current angle of rotation of rotor 4 lies, and, with the aid of the signal acquired by the sensor, to determine the current angle of rotation as a function of the determined angular segment. At a sufficiently low load torque, the angular segment may be identified within a short period of time with the aid of the Nonius or Vernier principle.

[0022] Subsequently, the exact mechanical angle φ, including all angle corrections, is certain. To that end, when the system is started, the sensor device is first initialized. That is, the angular segment, in which magnetic ring 9 is situated, is ascertained. This is achieved with the aid of the method, which is described in the following with reference to FIGS. 3 and 4 and determines the correct angular segment by adjusting an electric field or current.

[0023] Due to the number z.sub.9=5 of pole pairs, there are presently five different angular positions, in which rotor 4 may magnetically lock into place in the de-energized state, which means that when the rotor is at a dead stop, there are five different angular segments I through V, in which it may be located. The correct angular segment I through V is ascertained with the aid of the advantageous method. For this, it is preferably intended that the method only be carried out, if, upon start-up, electrical machine 1 may reach a low-torque or torque-free state, in order that the locking into place of rotor 4 is reliably ensured.

[0024] As FIG. 2 shows, based on the coprime pole pairing, angular offsets of multiples of 18° result: 360°/(z.sub.4×z.sub.9)=18°. In this context, on the basis of the overtravel of a circle, the following is valid: A trailing angle α.sub.4 of 3×18° also corresponds to a trailing angle α.sub.4′=−2×18°. Similarly, a trailing angle α.sub.5=4×18° corresponds to a trailing angle of α.sub.5′=−1×18°; thus, it depends on the direction of rotation of rotor 4. For improved understanding, the following trailing angles are used below: 0°; 18°; 36°; −36°; −18°.

[0025] The method, which is described in the following and is executed by control unit 11, allows the current to be switched on rapidly, so that a particularly short initialization time is ensured; electrical machine 1, which takes the form of a permanent-magnet d.c. motor, remaining almost motionless upon being switched on, and it being possible for a brief ramp-up of the current to already suffice for the initialization and determination of the current angle of rotation of rotor 4. It is assumed that a jammed electrical machine 1 and/or a jammed rotor 4 may be ruled out.

[0026] With the knowledge that there are presently five different angular offsets of magnetic ring 9 due to its number of pole pairs z.sub.5=5, in the approximation method, the correct angular segment I through V may be ascertained with the aid of a maximum of two corrections.

[0027] To that end, after initialization of the system in step S1, in step S2, the stator is initially acted upon by a current in such a manner, that rotor 4 is adjusted in the direction of segment I. In this instance, in a step S3, rotor 4 is monitored for an angular motion. In a substep S3a, it is initially checked if the angular motion occurs in the predetermined direction, and in a substep S3b, it is checked if an angular motion occurs in a direction opposite to the predefined direction of rotation. If the inquiry reveals that no angular motion has taken place, since one in neither the direction of rotation, nor contrary to the direction of rotation, has been detected (n), then, in step S4, it is determined that rotor 4 is already in angular segment I.

[0028] However, if rotor 4 turns in the desired direction of rotation when inquiry S3a is answered in the positive (y), then, in step S5, the phase angle is adjusted by two segments in the opposite direction as a first correction angle β.sub.1, so that the rotor is turned two angular segments in the opposite direction. If rotor 4 stops, then, when the system was started, rotor 4 was in third segment III, depending on which direction of rotation was selected at the beginning. This is checked in step S6. If the machine moves in the direction opposite to the selected direction (y), then, in step S7, the phase angle is adjusted once more by one segment in the opposite direction, in the form of second correction angle β.sub.2. Rotor 4 must stop, now. When the system was started, magnetic ring 9 was in the second segment II, depending on the direction of the correction. If the inquiry in step S6 reveals that rotor 4 did not move (n), then, in a step S8, it is determined that the rotor was in the third segment, and further activation is not necessary.

[0029] If the inquiry in step S3b reveals that rotor 4 turned in the direction opposite to the first direction of rotation (y), then, in a step S9, stator 7 is acted upon by a current in such a manner, that the rotor is turned two angular segments (β.sub.1=+36°) in the opposite direction. In the following inquiry S10, it is checked once more if the angular movement occurred in the desired direction. If this is the case (y), then, in step S11, stator 7 is again acted upon by a current in such a manner, that rotor 4 turns by one angular segment β.sub.2=−18° in a direction opposite to the first direction of rotation, which means that it may be established, that rotor 4 is now in fifth angular segment V.

[0030] If the inquiry in step S10 reveals that rotor 4 is not moving, then no further activation is necessary, and in step S12, it is determined that rotor 4 was already in angular segment IV.

[0031] In addition, FIG. 3 shows the method for the present exemplary embodiment in a table. Segments I through V are listed in the first column. Trailing angle α is given in the second column. Speed Ω.sub.1, which is measured after the first instance of switching on the current, is in the third column. The speed is calculated, in particular, with the aid of the signal of sensor 10. First correction angle β.sub.1 is listed in the fourth column, speed Ω.sub.2, which is attained when the current is switched on a second time, is given in the fifth column, and second correction angle β.sub.2 is listed in the last column.

[0032] The above-described method and control unit 11 may be applied and used, respectively, in all coprime combinations of the numbers of pole pairs of rotor 4 and of magnetic ring 9; the individual steps then being adapted appropriately, in order to obtain unequivocal results.