JP2004048829A - Brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brushless DC motor which can be driven with maximum rotation efficiency even in normal rotation or reverse rotation. <P>SOLUTION: In the brushless DC motor 15, a rotating shaft 56 consists of the first shaft 70 fixed to the rotor 50 and the second shaft 72 connected to the load side, and a detection magnet is fixed to the second shaft 72, and the second shaft 72 can rotate freely at a specified angle to the first shaft 70 so that the position of the detection magnet 74 may come to a position for normal rotation and a position for reverse rotation, and when the rotor 50 is rotating, the second shaft 72 is fixed in a position where it is rotated by a specified angle by the normal rotation of the first shaft, and when it is rotating reversely, the second shaft 72 is fixed in a position where it is rotated by a specified angle so that it may be in a reversal position by the reverse rotation of the first shaft 70. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for a brushless DC motor, and more particularly, to a control device for use in an electric tool such as an electric driver or an impact driver that performs forward and reverse rotation, or a turbine for a pump.
[0002]
[Prior art]
A brushless DC motor (hereinafter simply referred to as a motor) detects the rotational position of a rotor using a Hall element or a magnetic detection element such as a Hall IC incorporating the Hall element, and detects the detected rotational position of the rotor. The drive current is applied to the corresponding stator coil in accordance with the rotation to rotate.
[0003]
In the case where the brushless DC motor is of a reversible type capable of normal rotation and reversal, the following two types of mounting structures are generally used for mounting the magnetic detection element to the stator core of the brushless DC motor.
[0004]
In the first mounting structure, the magnetic detection element is mounted at a position shifted by a predetermined electrical angle with respect to the teeth of the stator core at a position where priority is given to rotation efficiency in one of forward rotation and reverse rotation.
[0005]
In the second mounting structure, the rotation efficiency is reduced in both the forward rotation and the reverse rotation, but the magnetic detection element is provided at a position corresponding to the position of the neutral point. That is, when the magnetic detecting element detects the rotational position of the rotor, the position of normal rotation (CW) and the position that can be detected at the maximum efficiency of reverse rotation (CCW) are different as shown in the hysteresis graph of FIG. In addition, as shown in FIG. 10, the magnetic detection element is mounted in a state of being shifted by α ° about the rotation axis O of the rotor.
[0006]
[Problems to be solved by the invention]
However, in either of the above two mounting structures, the brushless DC motor cannot be rotated at the maximum rotational efficiency in the forward rotation direction and the reverse rotation direction.
[0007]
In view of the above problems, the present invention provides a brushless DC motor that can be driven with maximum rotational efficiency even in forward rotation and reverse rotation.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is an inverter circuit that outputs a drive signal to a brushless DC motor, a gate drive circuit that controls the inverter circuit, an arithmetic circuit that performs PWM control on the gate drive circuit, and a rotor of the brushless DC motor. A magnetic detecting element for detecting the rotational position of the magnetic detecting element, and a position detecting circuit for switching a rotational signal indicating the rotational position from the magnetic detecting element based on a rotational direction command signal indicating a forward / reverse rotation direction and outputting the switching signal to the arithmetic circuit. A motor control device, wherein the rotor has a torque generating magnet, and the magnetic detecting element has a disc-shaped detecting magnet for detecting the rotational position of the rotor, The detection magnet is disposed separately from the magnet, and the detection magnet is disposed coaxially with the rotor, and is located at a forward rotation position and a reverse rotation position. The brushless motor is rotatable at an angle, wherein the detection magnet rotates to a forward rotation position by forward rotation of the rotation shaft, and the detection magnet rotates to a reverse rotation position by reverse rotation of the rotation shaft. It is a DC motor.
[0009]
The invention according to claim 2 is that the rotating shaft comprises a first shaft fixed to the rotor and a second shaft connected to a load side, wherein the detection magnet is fixed to the second shaft. The second axis is rotatable by the predetermined angle with respect to the first axis so that the detection magnet is at the forward rotation position or the reverse rotation position, and the second axis is rotated by the first axis in the forward direction. 2. The brushless DC motor according to claim 1, wherein the brushless DC motor is fixed at a forward rotation position after being rotated by a predetermined angle, and is fixed at a reverse rotation position after being rotated by the predetermined angle by reversing the first axis. 3. It is.
[0010]
The invention according to claim 3 is that the detection magnet is arranged rotatably by the predetermined angle with respect to the rotation shaft, and is fixed at a forward rotation position where the detection magnet is rotated by the predetermined angle by forward rotation of the rotation shaft. 2. The brushless DC motor according to claim 1, wherein the detection magnet is fixed at the reverse rotation position rotated by the predetermined angle by the reverse rotation of the rotating shaft.
[0011]
The invention according to claim 4 is the brushless DC motor according to any one of claims 1 to 3, wherein the brushless DC motor is an IPM (Interior Permanent Magnet) type brushless DC motor. .
[0012]
The invention according to claim 5 is the brushless DC motor according to any one of claims 1 to 3, wherein the brushless DC motor is a driving source of an electric tool such as an electric screwdriver or an impact driver. It is a motor.
[0013]
The invention according to claim 6 is the brushless DC motor according to any one of claims 1 to 3, wherein the brushless DC motor is used for a dual rotation pump.
[0014]
[Operation]
With the brushless DC motor of the present invention, when the rotating shaft is rotating forward, the rotation of the rotating shaft causes the position of the detection magnet to rotate to the forward rotating position. The reverse rotation causes the position of the detection magnet to rotate to the reverse rotation position, so that the motor can be driven with the highest efficiency even in the case of forward rotation and reverse rotation.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
First Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 4, FIG. 7, and FIG.
[0016]
(1) Configuration of Impact Driver 11 FIG. 7 is a side view of the impact driver 11 according to the present embodiment.
[0017]
The configuration of the impact driver 11 will be described with reference to FIG.
[0018]
The impact driver 11 includes a main body 12 having a substantially cylindrical outer shape as a body, a chuck portion 13 in which a driver tool is mounted on a distal end portion of the main body 12, and a grip portion 14 formed to be a pistol type. Have.
[0019]
At the rear of the main body 12, a brushless DC motor (hereinafter simply referred to as a motor) 15 and a striking section 16 which also functions as a gearbox and a striking mechanism are incorporated.
[0020]
The grip portion 14 is formed so that an operator can grip it with a hand, and a trigger-like trigger switch 17 is arranged at a position where a finger is located in the grip state.
[0021]
A circuit board of a control device 18 that controls the motor 15 with a predetermined rotation speed and torque by operating the trigger switch 17 is disposed below the motor 15.
[0022]
A battery 19 and a large-capacity power supply voltage smoothing capacitor 20 that is electrically connected in parallel with the battery 19 are housed inside the holding unit 14.
[0023]
(2) Structure of Motor 15 The motor 15 is an IPM (Interior Permanent Magnet) type brushless DC motor having three slots and two poles.
[0024]
The stator has three teeth projecting inward, and a coil 48 is wound around each tooth. The coil 48 wound around each tooth portion is Y-connected to form three phases including a U phase, a V phase, and a W phase. Note that the three-phase coils 48 are connected to each other at a point N in FIG.
[0025]
(2) Structure of Rotor 50 Next, the structure of the rotor 50 will be described with reference to FIGS.
[0026]
The rotor 50 is formed by laminating disk-shaped steel plates 52 to form a rotor core 54. A rotary shaft 56 penetrates in the rotor core 54 in the axial direction, and since it is an IPM type, four storage holes 60 for storing the torque generating magnets 58 are opened at equal intervals in the circumferential direction. ing. The torque generating magnet 58 has a curved plate shape, and N poles, S poles, N poles, and S poles are alternately magnetized. The torque generating magnets 58 are arranged at intervals of 90 °.
[0027]
A frame 62 made of synthetic resin is arranged on the right side of the stator core 54 in FIG. In order to position the substantially cylindrical frame 62 and the stator core 54, a protrusion 64 projects from the left surface of the frame 62, and a positioning hole 66 is formed in the stator core 54 at a position corresponding to the protrusion 64. Is open. A fan 63 is integrally formed on the right side of the frame 62 (see FIG. 4).
[0028]
On the right side of the frame 62, a bearing 68 for rotatably supporting the rotating shaft 56 is arranged.
[0029]
The rotating shaft 56 is divided into a first shaft 70 and a second shaft 72, as shown in FIG. The first shaft 70 penetrates through the rotor core 54 and is fixed to the rotor 50. On the other hand, the second shaft 72 is a rotating shaft on the load side, which is connected to the load, and penetrates the center of the disk-shaped detection magnet 74 as shown in FIG. Is fixed against The detailed structure of the rotating shaft 26 will be described later.
[0030]
N-pole and S-pole magnets are disposed on the disc-shaped detection magnet 74 at intervals of 90 °.
[0031]
On the left side of the detection magnet 74, a bearing 88 that rotatably supports the rotating shaft 56 is arranged.
[0032]
A substrate 90 to which three Hall elements H1, H2, and H3 for detecting magnetism from the detection magnet 74 are fixed is disposed in the vicinity of the detection magnet 74. Is fixed inside.
[0033]
(3) Configuration of Control Device 18 Next, the control device 18 for controlling the motor 15 will be described with reference to FIG.
[0034]
FIG. 8 is a block diagram showing the control device 18 of the motor 15.
[0035]
A drive signal is supplied from the inverter circuit 21 to the U-phase, V-phase, and W-phase coils 86 of the motor 15. Using the six switching transistors constituting the inverter circuit 21, bipolar driving is performed in which a bidirectional driving current is applied to the three-phase coil 86 of the motor 15 that is connected in a Y-connection. As a bipolar driving method, a 120 ° energized rectangular wave driving method may be used.
[0036]
The rotation signals S1, S2, and S3 from the Hall elements H1, H2, and H3 that detect the rotation position of the rotor 88 of the motor 15 are output to the position detection circuit 23.
[0037]
The inverter circuit 21 is supplied with DC power as a battery 19, and the power supply voltage smoothing capacitor 20 is connected between the inverter circuit 21 and the battery 19 in parallel with the battery 19.
[0038]
A gate drive circuit 28 for sending a gate signal to the gate terminals of the switching transistors Tr1 to Tr6 of the inverter circuit 21 is provided, and an arithmetic circuit 22 for supplying a PWM (pulse width modulation) signal to the gate drive circuit 28 is provided. I have. The arithmetic circuit 22 sends the PWM signal to the gate drive circuit 28 based on the position signal from the position detection circuit 23, the speed command signal from the speed command circuit 24, and the rotation direction command signal from the rotation direction command circuit 25. Output.
[0039]
The above-described trigger switch 17 is connected to the speed command circuit 24 that outputs the speed command signal. The speed command circuit 24 outputs the speed command signal to the arithmetic circuit 22 according to the pressing state of the trigger switch 17 by the operator. . That is, the speed command signal is output so as to rotate faster by pulling the trigger switch 17 many times.
[0040]
The main body 12 is provided with a rotation direction changeover switch 26 as shown in FIG. 7. By switching the rotation direction changeover switch 26 forward or reverse, a rotation direction command signal corresponding to the rotation direction is given. The circuit 25 outputs to the arithmetic circuit 22 and the position detection circuit 23.
[0041]
A lock protection circuit 27 is provided between the gate drive circuit 28 and the arithmetic circuit 22. In the lock protection circuit 27, the position detection circuit 23 detects that the rotation of the motor 15 is not detected by the rotation signals from the Hall elements H1, H2, and H3 even though the drive signal is output to the motor 15. Then, the circuit forcibly shuts off the signal from the arithmetic circuit 22 to the gate drive circuit 28.
[0042]
A resistor 32 for detecting a drive current output from the battery 19 is connected, and an overcurrent protection circuit 29 for detecting a drive current flowing through the resistor 32 is provided. When the drive current flowing through the resistor 32 exceeds a set value, the overcurrent protection circuit 29 determines that the current is an overcurrent and outputs a control signal to the arithmetic circuit 22 to instruct the arithmetic circuit 22 to reduce the rotation speed or the torque. . When this control signal is output, the arithmetic circuit 22 forcibly narrows the pulse width of the PWM waveform and lowers the output of the motor 15. As a result, further generation of heat of the motor 15 is suppressed, and the control device 18 can be prevented from being damaged by heat without causing a temperature rise.
[0043]
(4) Structure of Rotation Shaft 56 Next, the structure of the rotation shaft 56 will be described.
[0044]
First, a portion of the rotary shaft 56 where the first shaft 70 and the second shaft 72 engage will be described.
[0045]
A male portion 76 protrudes from the end of the first shaft 70. As shown in FIGS. 1 to 3, the male portion 76 has a pair of fan-shaped pressing portions 80, 80 protruding from both sides of a center shaft 78 protruding coaxially with the first shaft 70.
[0046]
At the end of the second shaft 72, a female portion 82 having a concave shape is formed so that the male portion 76 fits therein. A pair of pressure receiving portions 84, 84 protrude from the inner peripheral side of the female portion 82. When the central shaft 78 of the male part 76 of the first shaft engages with the female part 82, the pair of pressing parts 80 presses the pair of pressure receiving parts 84 in the circumferential direction.
[0047]
In addition, grease is applied to the engagement portion between the male portion 76 and the female portion 82 in order to make the engagement smooth.
[0048]
The most important point of this embodiment is that a gap 86 exists between the pressure receiving portion 84 and the pressing portion 80 as shown in FIG. This gap 86 is (C + C ′) ° in angle. That is, as described with reference to FIG. 10 in the section of the prior art, the position of the maximum efficiency between the forward rotation position and the reverse rotation position is shifted by an angle α ° about the neutral point O, so that the neutral point O is There is a position of maximum efficiency for reverse rotation at a position shifted by the angle C °, and a position of maximum efficiency for normal rotation at a position shifted by a position of angle C ′ ° from the position of the neutral point O. Therefore, as shown in FIG. 2, the angle of the gap 86 is kept at an angle of (C + C ′) ° so that the first shaft 70 can rotate around the second shaft 72 by this angle.
[0049]
In this manner, when the first shaft 70 rotates in the reverse rotation direction, the pressing portion 80 of the first shaft 70 rotates in the reverse rotation (CCW) direction to press the pressure receiving portion 84, as shown in FIG. Thus, the detection magnet 74 is shifted from the torque generating magnet 58 by the angle C °. Thus, in the case of reverse rotation, the Hall element can detect its position with maximum efficiency.
[0050]
In the case of rotation in the normal rotation (CW) direction, as shown in FIG. 3, the pressing portion 80 rotates in the normal rotation direction by the angle (C + C ') ° to press the pressure receiving portion 84, and The magnet 74 is rotated and fixed by an angle C ′ ° with respect to the torque generating magnet 58. Thus, the position of the rotor 50 can be detected with maximum efficiency even in the case of normal rotation.
[0051]
2 and 3, the boundary between the N pole and the S pole and the boundary between the S pole and the N pole of the torque generating magnet 58 are expressed as the boundary between the main magnetic poles.
[0052]
With the motor 15 having the above-described configuration, when the motor 15 is rotated in the reverse direction, a load is applied to the second shaft 72, and the pressing portion 80 of the first shaft 70 receives the pressure receiving portion 84 of the second shaft 72 as a reaction force. Since the detection magnet 74 rotates while maintaining the state shifted by the relative angle C °, the three Hall elements H1 to H3 can detect the position of the rotor 50 with maximum efficiency.
[0053]
Further, even in the case of rotating in the normal rotation direction, the detection magnet 74 rotates in a state shifted by the relative angle C ′ ° with respect to the torque generating magnet 58 in the same manner. The position of the child 50 can be detected.
[0054]
Even when the pressing portion 80 does not press the pressure receiving portion 84 and cannot maintain a predetermined angle due to the impact load acting on the rotating shaft 56, the load is applied as the load is light and the rotation increases at low speed. Therefore, the above state can be maintained.
[0055]
(Second embodiment)
Next, a second embodiment of the motor 15 will be described with reference to FIGS. The difference between this embodiment and the first embodiment lies in the mounting structure of the rotating shaft 56 and the detection magnet 74.
[0056]
In the present embodiment, the rotating shaft 56 is not separated like the first shaft 70 and the second shaft 72 as in the first embodiment, but is constituted by one shaft. A cylindrical bush 92 is fitted in the corresponding position. A pair of pressing portions 94 protrude from the outer peripheral surface of the bush 92.
[0057]
On the other hand, a through hole 96 through which the rotating shaft 56 and the bush 92 penetrate is opened at the center of the detection magnet 74, and a pair of pressure receiving portions 98 protrudes from the inner peripheral surface of the through hole 96.
[0058]
As shown in FIG. 2, the pressing portion 94 and the pressure receiving portion 98 have a gap 100 corresponding to the angle (C + C ′) °.
[0059]
When the rotor 50 rotates in the normal rotation (CW) direction, as in the first embodiment, the pressing portion 94 presses the pressure receiving portion 98 so that the detecting magnet 74 is moved relative to the torque generating magnet 58. It rotates in a state shifted by the angle C '°, and the rotation state can be detected with the highest efficiency.
[0060]
In the case of rotation in the reverse rotation (CCW) direction, the pressing portion 94 presses the pressure receiving portion 98 so that the detection magnet 74 rotates in a state shifted from the torque generating magnet 58 by C °. However, the position of the rotor 50 can be detected with the highest efficiency.
[0061]
(Modification 1)
In the first embodiment, the male member 76 is provided on the first shaft 70 and the pressing portion 80 is provided, and the female portion 82 is provided on the second shaft 72 and the pressure receiving portion 84 is provided. The shaft 70 may be provided with a female portion 82 and a pressure receiving portion 84, and the second shaft 72 may be provided with a male portion 76 and a pressing portion 80.
[0062]
(Modification 2)
In the above embodiment, the impact driver 11 has been described. Alternatively, the motor 15 may be used as a drive source of an electric tool such as an electric screwdriver, a cordless electric screwdriver, or a cordless impact driver. It may be used as a driving source.
[0063]
【The invention's effect】
As described above, with the brushless DC motor of the present invention, both forward and reverse rotation can be operated with high efficiency.
[Brief description of the drawings]
FIG. 1 is a partially cutaway perspective view of a rotor of a motor according to a first embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between the torque generating magnet and the detecting magnet when the motor rotates in reverse.
FIG. 3 is a diagram showing a relationship between a torque generating magnet and a detecting magnet during normal rotation.
FIG. 4 is a sectional view of a rotor of the motor of the first embodiment.
FIG. 5 is a partially cutaway perspective view of a rotor of a motor according to a second embodiment of the present invention.
FIG. 6 is a relationship diagram between a torque generating magnet and a rotating shaft.
FIG. 7 is a side view of the impact driver showing the first and second embodiments.
FIG. 8 is a block diagram of a control device for a motor of an impact driver according to the first and second embodiments.
FIG. 9 is a hysteresis graph showing the position of normal rotation (CW) and the position where the rotation can be detected at the maximum efficiency of reverse rotation (CCW) when the Hall element detects the rotational position of the rotor.
FIG. 10 is a diagram showing positions of the Hall element at the time of forward rotation and at the time of reverse rotation.
[Explanation of symbols]
11 Impact Driver 15 Motor 17 Trigger Switch 18 Controller 21 Inverter Circuit 22 Arithmetic Circuit 23 Position Detection Circuit 24 Speed Command Circuit 25 Rotation Direction Circuit 26 Rotation Direction Switch 28 Gate Drive Circuit 29 Overcurrent Protection Circuit 50 Stator 54 Stator Iron core 56 Rotating shaft 58 Torque generating magnet 70 First shaft 72 Second shaft 74 Detecting magnet 76 Male portion 78 Central shaft 80 Pressing portion 82 Female portion 84 Pressure receiving portion 86 Gap

Claims (6)

An inverter circuit that outputs a drive signal to the brushless DC motor; a gate drive circuit that controls the inverter circuit; an arithmetic circuit that performs PWM control on the gate drive circuit; and a magnetic circuit that detects a rotational position of a rotor of the brushless DC motor. A motor control device comprising: a detection element; and a position detection circuit that switches a rotation signal indicating a rotation position from the magnetic detection element based on a rotation direction command signal indicating a forward / reverse direction and outputs the switching signal to the arithmetic circuit. ,
The rotor has a torque generating magnet,
A disk-shaped detection magnet for the magnetic detection element to detect the rotational position of the rotor is disposed separately from the torque generating magnet,
The detection magnet is disposed coaxially with the rotor, and is rotatable by a predetermined angle between a forward rotation position and a reverse rotation position,
By the forward rotation of the rotating shaft, the detection magnet rotates to a forward rotation position,
A brushless DC motor, wherein the detection magnet rotates to a reverse rotation position by the reverse rotation of the rotating shaft. The rotating shaft includes a first shaft fixed to the rotor and a second shaft connected to a load side;
The detection magnet is fixed to the second shaft,
The second axis is rotatable by the predetermined angle with respect to the first axis so that the detection magnet is at a forward rotation position or a reverse rotation position.
Due to the normal rotation of the first axis, the second axis rotates by the predetermined angle and is fixed at the normal rotation position,
2. The brushless DC motor according to claim 1, wherein the second shaft is fixed at the reverse rotation position rotated by the predetermined angle by the reverse rotation of the first shaft. The detection magnet is arranged rotatably at the predetermined angle with respect to the rotation axis,
By the forward rotation of the rotation shaft, the detection magnet is fixed at the forward rotation position rotated by the predetermined angle,
The brushless DC motor according to claim 1, wherein the detection magnet is fixed at the reverse rotation position rotated by the predetermined angle by the reverse rotation of the rotation shaft. 4. The brushless DC motor according to claim 1, wherein the brushless DC motor is an IPM (Interior Permanent Magnet) type brushless DC motor. 5. The brushless DC motor according to any one of claims 1 to 3, wherein the brushless DC motor is a driving source of an electric tool such as an electric screwdriver or an impact driver. The brushless DC motor according to any one of claims 1 to 3, wherein the brushless DC motor is used for a dual rotation pump.

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