Brushless Electric Machine

Abstract

The present invention relates to a brushless electric machine (1), in particular a brushless DC motor, having a housing (2), at least one rotor (4) arranged on a shaft (3) rotatably supported in the housing (2), and a stator (7) fixed to the housing, wherein the rotor (4) is provided with a contactless rotor position recognition device having a multi-pole magnetic ring (9) non-rotatably arranged on the shaft (3) and at least one magnetic field-sensitive sensor (10) attached to the housing and radially fixed to the outer circumference of the magnetic ring (9). It is proposed to make the number of pole pairs (z4) of the rotor (4) and the number of pole pairs (z9) of the magnetic ring (9) prime numbers.

Description

[Technical Field]

[0001] The present invention relates to a brushless electric machine, in particular a brushless DC motor, having a housing, at least one rotor arranged on a shaft rotatably supported in the housing, and a stator fixed to the housing, wherein the rotor is provided with a rotor position recognition device operating in a contactless manner, which includes a multi-pole magnetic ring non-rotatably arranged on the shaft and at least one magnetic field-sensitive sensor fixed to the housing and radially associated with the outer circumference of the magnetic ring. [Background technology]

[0002] Brushless electric machines are known from the prior art. It is essential for their operation to be able to accurately determine the rotor's current rotation angle or current angular position so that the stator can be controlled. Correct commutation of the electric machine is possible only with knowledge of the current angular position. For example, in permanently excited synchronous machines, it is known to attach a signal generator non-rotatably to the rotor and axially to it a sensor element that monitors the signal generator's magnetic field, thereby enabling the sensor to determine the entire 360° rotation angle of the signal generator. Since the current rotation angle is immediately known, the electric machine can be controlled immediately after system startup. Designs in which the signal generator has a multi-pole magnetic ring are also known. The advantage of this is that the magnetic ring can be arranged between the rotor and the mechanical output part of the electric machine (e.g., a drive pinion fixedly arranged on the shaft), increasing system options. However, this implies that the sensor must be fixed to the housing and arranged radially relative to the magnetic ring. Accordingly, it is no longer possible to easily and unambiguously determine the mechanical rotation angle of the rotor from the sensor signal. Summary of the Invention

[0003] The electric machine of the present invention, which has the features of claim 1, has the advantage that its preferred configuration allows for an unambiguous assignment of the sensor signal to the rotation angle or angular position of the rotor. To this end, the invention provides for the number of pole pairs of the rotor and the number of pole pairs of the magnetic ring to be relatively prime. This relatively prime number of pole pairs ensures that the rotation angle segments of the magnetic ring and, based on the detected rotation angle segments, the current rotation angle can be determined from the sensor signal in the shortest possible time, particularly using the caliper or vernier principle. The invention thus offers a favorable solution for unambiguously determining the rotation angle with only minor additional costs. Thus, although the electric machine is not immediately controllable after commissioning because it is not known in which direction the current and voltage must be adjusted for control purposes, the rotation angle position, and therefore the current and voltage settings, can be determined in a sufficiently short time and with a sufficiently small load torque.

[0004] In a preferred embodiment of the present invention, the rotor has a pole pair number of 4. As a result, this rotor corresponds to a rotor that is frequently used, and existing rotors can be utilized without any additional costs.

[0005] The magnetic ring preferably has a pole pair number of 5, which results in a relatively prime number of pole pairs. Since the magnetic ring itself is constructed with less complexity than the rotor, adapting the pole pair number to 5, or any other relatively prime number of pole pairs, is feasible at low cost, i.e. in particular the electric machine has a pole pair number of 4 in the rotor and a pole pair number of 5 in the magnetic ring.

[0006] The number of pole pairs of the magnetic ring here determines the number of rotation angle segments of the rotor position recognition device. When the system is started, the rotation angle segment in which the rotor or the magnetic ring is located is first determined, and then the current rotation angle is determined depending on the detected rotation angle segment. For this purpose, the following method is preferably implemented or can be implemented by a control device of the electric machine: After initialization of the electric machine, the mechanical angle is unambiguously determined within an angle range of 0 to 360°, allowing any corrections that may depend on the mechanical angle to be applied, thereby ensuring a good commutation of the electric machine in subsequent operation.

[0007] In a preferred development of the invention, the brushless electric machine has a control device that is specifically set up to determine the rotation angle segments depending on the signals of the sensor and to determine the rotation angle depending on the determined rotation angle segments, as already explained above. This provides the advantages already mentioned. For this purpose, the control device is advantageously electrically connected to the sensor, in particular to the sensor output of the sensor. In particular, the control device is configured to evaluate the sensor output signal in order to evaluate the magnetic field of the magnetic ring as well as its orientation and influence on the sensor. Preferably, a TMR sensor (TMR = magnetic tunnel resistance or magnetoresistance effect) is present as the sensor.

[0008] In particular, to determine the rotation angle segment, the control device first loads the stator with a first current to rotate the rotor in a first rotation direction to a first selected rotation angle segment. A monitoring device is present and is intended to monitor the rotor's rotational movement by means of this monitoring device. When the machine or rotor remains stationary at start-up, the rotor is already located in the selected first rotation angle segment. Then, based on knowledge of the rotation angle segment, the rotation angle position is determined using the rotation angle segment based on the sensor signal. However, when it is recognized that the rotor is moving or rotating, it becomes clear that the rotor was not located in the selected first rotation angle segment at its initial position. This already limits the scope of the search for the correct rotation angle segment. The control device preferably has at least one volatile or non-volatile memory, and the determined results are stored in the memory for later use. In particular, whether the rotor is rotating and, if so, in which direction (e.g., left or right) are stored.

[0009] The monitoring or control device is therefore preferably configured to monitor the rotational movement with respect to the direction of rotation. Depending on the direction of rotation detected during the first control rotational movement, the control device performs a second control of the rotor, which further limits the selection of the rotation angle segment. Knowledge of the direction of rotation makes it possible to determine whether the rotor is moving in the expected first direction of rotation or in the opposite direction of rotation. Depending on whether the rotor is moving in the expected or opposite direction of rotation, the control device then controls or loads the rotor with a second current with the aim of achieving a specific direction of rotation.

[0010] It is particularly preferred that the control device be configured so that, if the rotor is moving in the first or opposite direction of rotation to the expected direction of rotation, in a next step the stator is loaded with a second current for rotating the rotor by two rotational angle segments, preferably in the opposite direction to the first direction of rotation, and the subsequent rotational movement is monitored by the monitoring device. If the rotor is not moving, i.e., if the rotor has stopped after a settable time has elapsed, it is determined that the rotor is located in the third or fourth segment (depending on the direction of rotation at the start of the method) in the above-mentioned embodiment with a pole pair ratio of 4:5. The rotational angle segment is then known, and the rotational angle position can be unambiguously determined based on the sensor signals.

[0011] The control device is preferably configured to monitor the subsequent rotational movement with respect to the direction of rotation or to confirm the direction of rotation of the rotational movement using the monitoring device. The procedure described above is performed. In particular, the detected direction of rotation is compared with a second direction of rotation, i.e., a direction of rotation opposite to the first direction of rotation. For this purpose, the direction of rotation and the rotational movement stored in memory are read and compared with each other by the control device. For this purpose, the control device has an evaluation logic, particularly embodied in a microprocessor and / or an integrated circuit. When the rotor is moving in a direction opposite to the intended direction, the stator is loaded with a third current to rotate the rotor by one rotational angle segment in the opposite direction. The rotor must remain stationary at this time, and the current rotational angle segment can be confirmed. Depending on the direction of correction, the rotor or the magnetic ring will be positioned at the second or fourth rotational angle segment when the system is started.

[0012] Further advantages and preferred features and feature combinations will become apparent from the above description and from the claims.The present invention will now be described in more detail with reference to the drawings. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a simplified perspective view of a brushless electric machine; [Figure 2] 1 is a graph illustrating a preferred method of operation. [Figure 3] 1 is a table to further explain the method. [Figure 4] 1 is a flowchart illustrating the method. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1 shows in a simplified diagram a brushless electric machine 1 having a housing 2 in which a shaft 3 is rotatably mounted. A rotor 4 and, at its free end, a drive pinion 5 are arranged non-rotatably on the shaft 3. The shaft 3 is rotatably supported in the housing 2 by a number of bearings 6, in particular by means of antifriction bearings. The rotor 4 is further associated with a stator 7 having at least one energizable stator winding, which is arranged coaxially relative to the rotor 4.

[0015] Furthermore, a magnetic signal generator 8 in the form of a multi-pole magnetic ring 9 is arranged non-rotatably on the shaft 3 between the rotor 4 and the drive pinion 5. A sensor 10, which is designed to be sensitive to magnetic fields, is attached to the magnetic ring 9 and is fixed to the housing. The sensor 10 thus serves as a signal receiver for the signal generator 8.

[0016] The numbers of pole pairs of the rotor 4 and the magnetic ring 9 are configured to be mutually prime. In the present example, the rotor 4 has a number of pole pairs z4 = 4 and the magnetic ring 9 has a number of pole pairs z9 = 5. By means of the sensor arrangement consisting of the sensor 10 and the magnetic ring 9, the angular position of the rotor 4 is determined, in particular for system starting of the electric machine 1, by means of a control device 11 set up to carry out the method described below.

[0017] In this regard, first, Fig. 2 shows the behavior of the electric machine 1 as a function of the mechanical rotation angle φ mech The top graph shows the mechanical rotation angle φ mech2 shows the characteristic curve of the rotor 4 with four pole pairs. The graph below shows the electrical rotation angle of the rotor 4 with four pole pairs. The graph below shows the magnetic rotation angle of the magnetic ring 9 with respect to the mechanical rotation angle of 4. The bottom section of FIG. 2 shows the rotation angle segments I to V defined by the magnetic ring 9 with five pole pairs.

[0018] To determine the current rotation angle of the rotor 4 using the caliper or vernier principle, the control device 11 is configured to first determine the rotation angle segment in which the current rotation angle of the rotor 4 is located, and then determine the current rotation angle using a signal detected by a sensor depending on the determined rotation angle segment. If the load torque is sufficiently small, the rotation angle segment can be identified within a short time using the caliper or vernier principle.

[0019] Subsequently, the exact mechanical angle φ is immediately determined, including all angle corrections. For this purpose, when the system is started, the sensor device is first initialized. That is, it is determined in which rotation angle segment the magnetic ring 9 is located. This is solved by a method described below with reference to FIGS. 3 and 4, which determines the correct rotation angle segment through the position of the electric field or current.

[0020] The number of pole pairs z9=5 in this example results in five different rotational angle positions in which the rotor 4 can be magnetically locked when de-energized, resulting in five different rotational angle segments I-V in which the rotor can be located when it is stopped. A preferred method determines the correct rotational angle segment I-V. For this reason, it is preferably intended that the method be carried out only if the electric machine 1 can reach a low or no load torque condition at start-up, in order to ensure that the rotor 4 is locked.

[0021] As shown in Figure 2, based on the number of relatively prime pole pairs, an angular offset of a multiple of 18° occurs: 360° / (z4 × z9) = 18°. Then, based on the overflow of the circle, the following holds: the forward angle α4 of 3 × 18° is 4’ Similarly, the forward angle of α5 = 4 × 18° corresponds to α 5’ = -1 × 18°, i.e. the direction of rotation of the rotor 4 is important here. For a better understanding, the following forward angles apply in the following: 0°; 18°; 36°; -36°; -18°.

[0022] The method described below, implemented by the control device 11, makes it possible to switch on the current quickly, thereby ensuring particularly short initialization times, so that the electric machine 1, configured as a permanent magnet excited DC motor, remains almost motionless when switched on, and in some situations a short high current ramp is already sufficient to initialize and determine the current rotation angle of the rotor 4.

[0023] The premise is that a blocked electric machine 1 or a blocked rotor 4 can be excluded.

[0024] In this example, based on the knowledge that there are five different angular offsets of the magnetic ring 9 based on its number of pole pairs z5=5, the correct rotation angle segments I to V can be determined in an approximate manner with a maximum of two corrections.

[0025] For this purpose, after the system is initialized in step S1, first in step S2 the stator is loaded with current so that the rotor 4 is adjusted in the direction of segment I. Then in step S3 the rotor 4 is monitored for rotational movement. In substep S3a it is first checked whether this rotational movement is taking place in the preset direction of rotation, and in substep S3b it is checked whether rotational movement is taking place in the direction opposite to the predetermined direction of rotation. If this check shows that no rotational movement is taking place because no detection has been made in either the direction of rotation or the opposite direction of rotation (n), then in step S4 it is determined that the rotor 4 is already located in rotational angle segment I.

[0026] However, if the answer to query S3a is yes (j), and the rotor 4 is moving in the desired direction of rotation, then in step S5 the current angle is adjusted in the opposite direction by two segments as a first correction angle β1, thereby rotating the rotor in the opposite direction by two rotation angle segments. If the rotor 4 remains stationary, then depending on which direction of rotation was selected at the start, the rotor 4 was in the third segment III at system startup. This is checked in step S6. If the machine moves in the direction opposite to the controlled direction (j), then in step S7 the current angle is adjusted again in the opposite direction by one segment as a second correction angle β2. The rotor 4 must then stop. Depending on the direction of the correction, the magnetic ring 9 was in the second segment II at system startup. If the query in step S6 reveals that the rotor 4 is not moving (n), then in step S8 it is confirmed that the rotor was in the third segment and that no further control is required.

[0027] If the inquiry in step S3b shows that the rotor 4 has rotated in the opposite direction to the first direction of rotation (j), then in step S9 the stator 7 is energized with current so that the rotor rotates in the opposite direction by two rotational angle segments (β1 = +36°). In the following inquiry S10, it is checked again whether the rotational angle movement has been carried out in the desired direction. If this is the case (j), then in step S11 the stator 7 is again energized with current so that the rotor 4 rotates in the opposite direction to the first direction of rotation by one rotational angle segment β2 = -18°, so that it can be determined that the rotor 4 is now in the fifth rotational angle segment V.

[0028] When the inquiry in step S10 reveals that the rotor 4 is not moving, no further control is required and in step S12 it is determined that the rotor 4 is already in rotation angle segment IV.

[0029] To this end, FIG. 3 shows a table illustrating the method for this embodiment. The first column lists the segments I to V. The second column lists the advance angle α. The third column lists the speed Ω1 detected after the first switch-on of the current. This speed is determined, inter alia, by the signal of sensor 10. The fourth column lists the first correction angle β1, the fifth column lists the speed Ω2 achieved at the second switch-on of the current, and the last column lists the second correction angle β2.

[0030] The above-described method or control device 11 can be applied or used for any combination of the rotor 4 and the magnetic ring 9 with a relatively prime number of pole pairs, in which case the individual steps are adapted accordingly to obtain unambiguous information. [Explanation of symbols]

[0031] 1 Brushless Electric Machine 2. Housing 3 shafts 4 rotors 7 Stator 9 Magnetic Ring 10 Magnetic field sensitive sensor 11 Control device

Claims

1. A brushless electric machine (1) having a housing (2), at least one rotor (4) arranged on a shaft (3) rotatably supported in the housing (2), and a stator (7) fixed to the housing, the brushless electric machine (1) being provided with a rotor position recognition device operating in a contactless manner, the rotor position recognition device having a multi-pole magnetic ring (9) non-rotatably arranged on the shaft (3), and at least one magnetic field sensitive sensor (10) attached to the housing and fixed at a position radially spaced from the outer circumference of the magnetic ring (9), The number of pole pairs (z4) of the rotor (4) and the number of pole pairs (z9) of the magnetic ring (9) are relatively prime, a control device (11) for determining the positions of the rotation angle segments (I to V) of the magnetic ring (9) when the system is initialized, and for determining the rotation angle of the rotor (4) corresponding to the positions of the rotation angle segments (I to V) depending on the signal of the sensor (10); the control device (11) loads the stator (7) with a current so that the direction of rotation and the rotational movement are adjusted to the direction and movement stored in the memory of the control device when the system is initialized, and the position of the rotational angle segments (I to V) is determined by evaluating the direction of rotation and the rotational movement of the rotor (4) by a monitoring device; The brushless electric machine is characterized in that the rotation angle of the rotor (4) is determined by comparing the rotation angle of the magnetic ring (9) corresponding to the signal of the sensor (10) and the position of the determined rotation angle segments (I to V) with a characteristic curve of the rotation angle stored in the memory of the control device.

2. 2. A brushless electric machine according to claim 1, characterized in that the rotor (4) has a number of pole pairs (z4) of 4.

3. 3. A brushless electric machine according to claim 1 or 2, characterized in that the magnetic ring (9) has a number of pole pairs (z9) of 5.

4. 4. Brushless electric machine according to claim 1, characterized in that the number of pole pairs (z9) of the magnetic ring (9) determines the number of rotation angle segments of the rotor position recognition device.

5. A brushless electric machine as described in any one of claims 1 to 4, wherein the control device (11) loads the stator (7) with a first current to rotate the rotor (4) in a first rotational direction to a first rotational angle segment (I) to determine the position of the rotational angle segment (I to V) of the magnetic ring (9) when the system is initialized, and the monitoring device evaluates the rotational movement of the rotor (4).

6. 6. The brushless electric machine of claim 5, wherein the control device (11) loads the stator (7) with a second current to rotate the rotor (4) through two rotational angle segments (β1) in a rotational direction that is parallel to the first rotational direction, and the monitoring device evaluates the rotational movement of the rotor (4).

7. A brushless electric machine as described in claim 6, wherein when the monitoring device recognizes that the rotor (4) has rotated in the first rotational direction due to the second current, the control device (11) loads the stator (7) with a third current to rotate the rotor (4) in a direction opposite to the first rotational direction by one rotational angle segment (β2), and the monitoring device evaluates the rotational motion of the rotor (4).

8. A brushless electric machine as described in any one of claims 1 to 7, wherein the brushless electric machine is a brushless DC motor.

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