JP2000228890A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor capable of reducing the cost of a drive circuit and reducing switching noise. SOLUTION: A five-phase brushless motor is energized at a four-phase armature coil by switching MOSFETs 36-45 using a parallel path. The current passing through the MOSFETs 36-45 becomes one half that of the conventional three- phase full-wave driven system, so that the respective MOSFETs 36-45 can use an inexpensive element having lower current capacity. When exciting phases are switched, one of two exciting phases is turned off at one exciting path of the parallel paths, and one non-exciting phase is turned on. As a result, the change in the total current of the motor become low in switching exciting phases, so as to reduce the switching noise. When required rotation speed is low, the motor torque is reduced to cause the rotational speed of the motor to be reduced by energizing only two-phase armature coil (two-phase energization). As a result, the rotational speed of the motor can be made variable without conducting PWM control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor for rotating a magnet rotor by sequentially switching energization to armature coils of each phase by a switching element.

[0002]

2. Description of the Related Art A conventional brushless motor is, for example, shown in FIG.
There are many brushless motors of the three-phase full-wave drive type as shown in FIG. In this three-phase full-wave drive system, six MOSFETs 2 to 7 are sequentially switched according to the rotational position of a magnet rotor (not shown), and a three-phase armature coil U8 of a U-phase, a V-phase, and a W-phase. , V8, W8 are sequentially switched,
The magnet rotor is driven to rotate by energizing the two-phase armature coils among the three phases. That is,
According to the rotational position of the magnet rotor, the current-carrying phase is switched between three combinations of U-phase and V-phase, V-phase and W-phase, and W-phase and U-phase.

[0003]

In the above-described brushless motor of the three-phase full-wave drive system, since a current flows from a power supply (+ B) to a two-phase armature coil in a serial path, the total current flowing through the motor (hereinafter referred to as "motor") All current))
It flows to FET2-7. Therefore, MOSFETs 2 to 7
Requires an expensive element having a large current capacity to withstand the entire motor current, and cannot meet the demand for cost reduction. In addition, since the two-phase armature coil is energized in a series path, immediately after switching of the energized phase, the back electromotive force generated when energizing the armature coil of the phase that has not been energized before is started. After the current instantaneously becomes 0, the current starts to flow through the two-phase armature coil. For this reason, the change in the total motor current during the energized phase switching becomes large, which causes the switching noise to increase.

[0004] The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to provide a brushless motor capable of realizing cost reduction of switching elements and reduction of switching noise. is there.

[0005]

According to a first aspect of the present invention, there is provided a brushless motor comprising a plurality of armature coils of four or more phases, and a plurality of phase armatures energized by drive control means. A switching element is connected so that current flows through the coil in a parallel path, and when the energized phase is switched by the drive control means according to the rotational position of the magnet rotor, the energized phase is overlapped before and after the switching. Control the switching operation of.

In other words, if currents are passed in parallel through the two current paths through the armature coils of a plurality of phases, the current flowing through each switching element becomes smaller than before, and the current capacity of the switching element can be reduced accordingly. And cost reduction. Moreover, if the energized phases are switched so as to overlap before and after the energized phase is switched, only the energized phase of one energized path is switched at the time of energized phase switching, and the other energized path in parallel with this is switched. , The energized phase is not switched and the coil current does not change. For this reason,
The change of the motor total current at the time of the energized phase switching becomes smaller than that of the conventional three-phase full-wave drive system, and the switching noise can be reduced. Further, since there is no moment when the current becomes 0, the torque ripple can be reduced.

As described in Japanese Patent Application Laid-Open No. 9-42096, the control of the motor rotation speed is performed by controlling the on / off duty ratio of the switching element by a PWM method and controlling the motor current to control the rotation speed. It is proposed to do. However, the PWM control has a problem that high-frequency switching noise is generated because the switching elements are switched at a high speed. For example, when applied to a drive motor of a fuel pump of a vehicle, the high-frequency switching noise due to the PWM control causes a problem. There is a possibility that noise may be included in the voice of the vehicle or other electronic components mounted on the vehicle may malfunction.

Therefore, it is preferable to switch the switching timing of the switching element so as to change the number of energized phases according to the required motor output. That is, when the number of energized phases is changed according to the required motor output, the coil resistance of the path through which the current flows changes, the coil current changes, and the motor torque changes. As a result, the motor speed can be varied without performing PWM control, and the occurrence of high-frequency switching noise can be prevented, and the problem of high-frequency switching noise can be solved.

Further, when the motor is started or overloaded, a large coil current flows and a large current also flows through the switching element, so that the load on the switching element increases. In consideration of such circumstances, it is preferable that the switching timing of the switching element be switched so as to increase the coil resistance value of the path through which the current flows at the time of starting the motor and / or at the time of overload. .
With this configuration, at the time of starting the motor and / or at the time of overload, the coil current is limited by the increase in the coil resistance value, and the current flowing through the switching element is limited. Therefore, even if a switching element having a small current capacity is used, the current flowing through the switching element at the time of starting the motor or overload can be suppressed to the rated capacity or less, and the switching element can be protected.

It is preferable that the switching operation of the switching element is controlled so that the number of energized phases is an even number. As described above, if the number of energized phases is set to an even number, the number of coils in one energized path and the number of coils in the other energized path of the parallel path can be made equal to each other. The value and the coil current can be the same, and the brushless motor can be rotated with good balance.

In this case, it is preferable that the number of phases of the armature coil is an odd number of five or more. With this configuration, when the number of non-energized phases is set to one and the number of energized phases is maximized, the number of energized phases can be set to an even number. Can be done.

Further, for example, a brushless motor of a four-phase or more full-wave drive system requires eight or more switching elements. Therefore, all the switching elements are incorporated in one IC chip. It is good to adopt a configuration. In this case, the number of parts can be significantly reduced, the assemblability can be improved, and the cost can be further reduced.

Incidentally, the brushless motor generates a rotational torque by an interaction between a magnetic field generated by energizing the armature coil and a magnetic field of the magnet of the magnet rotor. In order to generate this rotational torque efficiently, it is necessary to make the boundary between the N pole and the S pole of the magnet rotor face the armature coil of the energized phase.

Therefore, the number of poles P (the number of magnets) of the magnet rotor and the number of poles M of the stator are defined as claim 7.
The relationship between (the number of salient poles) and the number of motor phases x may be set as follows. ｛(X−1) / x｝ M ≦ P ≦ ｛(x + 1) / x｝ M (where P is an even number and x is an integer of 4 or more)

With this arrangement, even when the x-phase brushless motor is energized at the same time for each (x-1) phase, the N pole of the magnet rotor and the S pole are applied to all energized armature coils.
The boundary portion between the poles can be opposed, and the torque can be efficiently generated and the motor efficiency can be improved, and the torque ripple can be reduced.

Further, the number of poles M of the stator may be set to an even multiple of the number of motor phases x, and the number of poles P of the magnet rotor may be set to 4 × m (where m is a natural number). With this configuration, since the magnetic force generated between the armature coil of the energized phase and the magnet of the magnet rotor facing the armature is symmetrical with respect to the rotation axis, the magnetic force acting on the magnet rotor is The force component acting in the radial direction of the magnet rotor can be canceled. Thereby, the load applied to the bearing of the rotary shaft can be reduced, the durability can be improved, and the run-out of the rotary shaft can be prevented.

The brushless motor according to the present invention described above can be used as a drive motor for various devices. For example, if the brushless motor is used as a drive motor for a fuel pump of a vehicle, the drive circuit of the drive circuit can be reduced. The cost can reduce the cost of the fuel pump, reduce switching noise, and prevent radio noise and malfunction of onboard electronic components due to switching noise.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which the present invention is applied to a fuel pump of a vehicle will be described below with reference to FIGS. The fuel pump 11 is configured by incorporating a pump unit 13 and a brushless motor 14 in a cylindrical housing 12. Explaining the configuration of the pump section 13, a pump chamber is composed of a pump casing 15 and a pump cover 16 fixed to one end of the cylindrical housing 12 by press fitting, caulking, or the like, and an impeller 17 is housed in the pump chamber. . The impeller 17 is fitted on a rotating shaft 24 of the brushless motor 14.

On the other hand, the brushless motor 14
This is a brushless motor of a phase full-wave drive system, and is configured as follows. A cylindrical stator 19 is fitted and fixed in the cylindrical housing 12.
As shown in FIG. 1, for example, ten salient poles 20 are formed. Two armature coils A21 to E21 of five phases A to E are mounted on the salient poles 20 in the order of A phase, B phase, C phase, D phase, and E phase. Two coils are arranged at positions symmetrical with respect to the rotation axis 24 (positions opposite by 180 °), and two coils of each phase are connected in series (see FIG. 3).

The 10-pole stator 1 constructed as described above
A magnet rotor 23 is arranged on the inner peripheral side of the magnet 9. The magnet rotor 23 includes a rotor core 25 fitted to a rotating shaft 24 and, for example, eight field magnets 26 fixed to the outer periphery of the rotor core 25 by bonding or the like. However, as shown in FIG. 2, N poles and S poles are arranged alternately. Thus, an eight-pole magnet rotor 23 is configured.

The number of poles P of the magnet rotor 23 described above.
(8 poles), the number of poles M (10 poles) of the stator 19, and the number of motor phases x (5 phases) are set so as to satisfy the following equations (1) to (3). ｛(X−1) / x｝ M ≦ P ≦ ｛(x + 1) / x｝ M (1) M = 2 × nx (where n is a natural number) (2) P = 4 × m ( However, m is a natural number.

The above equation (1) indicates that the boundary between the N pole and the S pole of the magnet rotor 23 is applied to all the armature coils to be energized even when the (x-1) phases are energized at the same time in the x-phase brushless motor. This is a necessary condition for facing the parts.
In the expressions (2) and (3), the magnetic force generated between the energized phase armature coil and the magnet 26 of the magnet rotor 23 opposed thereto is made symmetrical with respect to the rotation axis 24 (even Force).

As shown in FIG. 1, the magnet rotor 23
One end of the rotating shaft 24 is rotatably supported by a bearing cylinder 28 at the center of the pump casing 15 via a bearing 27, and a bearing 29 supporting the other end of the rotating shaft 24 is fixed in the cylindrical housing 12. The bearing holder 30 is assembled. A drive control circuit 31 (drive control means) of a five-phase full-wave drive system is assembled to the bearing holder 30. When the motor is driven, the drive control circuit 31 sequentially switches energization to the armature coils 21 of each phase. . The opening on the drive control circuit 31 side of the cylindrical housing 12 has a discharge port 3
A housing cover 33 having a housing 2 is fitted.

The pump unit 1 is driven by the brushless motor 14.
When the impeller 17 is driven to rotate, fuel in a fuel tank (not shown) is sucked into a pump chamber from a suction port (not shown) of the pump cover 16 and a discharge port (not shown) of the pump casing 15. ) Is discharged into the cylindrical housing 12. The fuel flows through a gap between the stator 19 and the magnet rotor 23, is discharged from a discharge port 32 of the housing cover 33 into a fuel pipe (not shown), and is sent to a fuel injection valve (not shown).

As shown in FIG. 4, the armature coil A of each phase
21 to E21 are Y-connected. Further, the drive control circuit 31 controls the control unit 35 to which a control signal is input from an engine control circuit (not shown), and energizes the armature coils A21 to E21 of each phase based on the output of the control unit 35. And a driving circuit 46 for switching.
Reference numeral 6 is configured by incorporating ten MOSFETs 36 to 45 into one IC chip. These 10 MOs
The SFETs 36 to 45 are connected in pairs in the form of a bridge between the battery voltage (+ B) side and the ground side in pairs, and the intermediate connection points of the two MOSFETs in each pair are connected in Y-phase to A-E. It is connected to one end of the phase coils A21 to E21.

The drive control circuit 31 sets the operation mode of the brushless motor 14 to four when the required fuel amount of the engine is large.
The mode is switched to the phase energization mode, and when the required engine fuel amount is small, the mode is switched to the two-phase energization mode.

In the 4-phase energizing mode, the brushless motor 1
4 is driven. At this time, the drive control circuit 31 detects the rotational position of the magnet rotor 23 by an induced voltage induced in the non-energized phase coil, and based on the detected signal,
As shown in FIG. 5, the MOSFETs 36 to 45 are sequentially switched to energize the four-phase armature coils in a parallel path. For example, as shown in FIG. 2A, when the rotational position of the magnet rotor 23 is at a position where the A-phase, B-phase, C-phase, and D-phase armature coils A21, B21, C21, and D21 are energized, Only the MOSFETs 36, 38, 42, and 44 are turned on (FIG. 5), and the power supply (+ B) is supplied to the power supply path from the A-phase coil A21 to the D-phase coil D21 and the power supply path from the C-phase coil C21 to the B-phase coil B21. )).

If the four-phase armature coil is divided into two current-carrying paths for each two-phase and current is supplied in parallel as described above, a half of the current of the motor flows through the armature coil of each current-carrying path. At the same time, half of the total motor current flows through each of the MOSFETs 36 to 45.

Thereafter, when the rotational position of the magnet rotor 23 reaches the position shown in FIG.
Turns off the MOSFET 44 and turns on the MOSFET 45 while keeping the three MOSFETs 36, 38 and 42 in the on state (FIG. 5), and switches the current supply to the E-phase coil E21 instead of the D-phase coil D21. . Thereby, the A-phase coil A21 to the E-phase coil E
The current flows in parallel through the power supply path to the power supply 21 and the power supply path from the C-phase coil C21 to the B-phase coil B21.

In this way, one of the two current-carrying phases is turned off in one current-carrying path of the parallel path according to the rotational position of the magnet rotor 23,
By switching one non-energized phase up to that time, the energized phases are sequentially switched one by one.

The drive control circuit 31 switches the operation mode of the brushless motor 14 to the two-phase conduction mode when the required engine fuel amount is small. In this two-phase energizing mode, only two-phase armature coils among the five phases are energized,
The brushless motor 14 is driven. For example, when the rotation position of the magnet rotor 23 is at the position shown in FIG. 2A, only the two MOSFETs 36 and 44 are turned on,
Power is supplied to only the A-phase coil A21 and the D-phase coil D21 in a series path.

In the two-phase energizing mode, the coil resistance of the energizing path of the brushless motor 14 as a whole is about twice as large as that in the four-phase energizing mode. As a result, the motor torque is reduced to about 1/2, and the motor speed characteristic as shown in FIG. 6 is obtained. As a result, when the mode is switched from the four-phase energizing mode to the two-phase energizing mode, the motor speed decreases and the discharge amount of the fuel pump 11 decreases.

Further, the drive control circuit 31 sets the operation mode of the brushless motor 14 to two when the motor is started and when the motor is overloaded.
By switching to the phase energizing mode, the coil resistance value of the energizing path of the entire motor is increased. As a result, the coil current at the time of starting the motor or at the time of overload is appropriately suppressed by the coil resistance value, thereby preventing a large current from flowing through the MOSFETs 36 to 45.

In addition to the above-described four-phase energizing mode and two-phase energizing mode, a three-phase energizing mode for energizing a three-phase armature coil is set, and the operation mode of the brushless motor 14 is switched between three stages. You may do it.

In the conventional brushless motor of the three-phase full-wave drive system shown in FIG. 7, a current flows from a power source (+ B) to a two-phase armature coil in a serial path. Therefore, an expensive MOSFET having a large current capacity is required.

On the other hand, in the five-phase brushless motor 14 of the present embodiment, when the four-phase current is supplied, the current flows in parallel through the two current paths through the four-phase armature coil.
The current flowing through the ETs 36 to 45 is の of that of the conventional three-phase full-wave drive system, and accordingly, the MOSFETs 36 to 45 can use inexpensive devices having a small current capacity.

In the present embodiment, if the current capacity of each of the ten MOSFETs 36 to 45 constituting the drive circuit 46 is K, the drive circuit 46 as a whole needs a current capacity of K × 10. On the other hand, in the conventional three-phase full-wave drive system shown in FIG. 7, the motor full current (twice the current in this embodiment) flows through the six MOSFETs 2 to 7 constituting the drive circuit 1, so that each MOSFET 2
To 7 times the current capacity of this embodiment (K × 2)
The driving circuit 1 as a whole has K × 2 ×
6 = K × 12 current capacity is required. Therefore, in the present embodiment, the current capacity of the entire driving circuit 46 can be made smaller than that of the conventional three-phase full-wave driving method. Even when the entire driving circuit 46 is integrated into one chip, the present embodiment is more suitable. It is advantageous.

Further, in the conventional three-phase full-wave drive system, since the two-phase armature coil is energized in a series path, immediately after the energized phase is switched, the two-phase armature coil is energized to the phase that has not been energized. Due to the back electromotive force generated when energization starts,
After the current instantaneously becomes 0, the current starts to flow through the two-phase armature coil. For this reason, the change in the total motor current during the energized phase switching becomes large, and the switching noise becomes large. Further, since there is a moment when the current becomes 0, the torque ripple increases.

On the other hand, in the present embodiment, the power is supplied from the power supply (+ B) to the two power supply paths in parallel during the four-phase power supply. One of the two current-carrying phases can be switched off and the other non-current-carrying phase can be turned on. For this reason, only the energized phase of one energized path is switched at the time of energized phase switching, and the energized phase of the other energized path parallel to this is not switched, and the coil current does not change. As a result, the change in the total motor current at the time of the energized phase switching becomes almost half of that in the conventional three-phase full-wave drive system, and the switching noise can be reduced. In this case, since there is no moment when the current becomes 0, the torque ripple can be reduced.

Further, since the number of energized phases is changed to change the number of rotations of the motor, the discharge amount of the fuel pump 11 can be variably controlled without performing PWM control. Therefore, the generation of high-frequency switching noise due to the PWM control can be prevented, and the switching noise can be greatly reduced in combination with the above-described effect of reducing the switching noise at the time of energization switching. Malfunction can be prevented.

Further, in the present embodiment, since the ten MOSFETs 36 to 45 constituting the drive circuit 46 are incorporated in one IC chip, the number of parts can be greatly reduced, and the demand for improved assemblability and lower cost is required. Can also be satisfied. It goes without saying that the drive circuit 46 and the control unit 46 may be incorporated in one IC chip.

In the present embodiment, the number of poles P of the magnet rotor 23, the number of poles M of the stator 19, and the number of motor phases x
Is defined as {(x−1) / x｝ M ≦ P ≦ ｛(x + 1) / x｝ M
Therefore, even when the x-phase brushless motor is energized at the same time for (x-1) phases at a time, the N of the magnet rotor 23 is applied to all the armature coils to be energized.
The boundary between the pole and the S pole can be opposed to each other, so that the rotational torque can be efficiently generated, the motor efficiency can be improved, and the torque ripple can be reduced.

Further, the number of poles M of the stator 19 is set to an even multiple of the number of motor phases x, and the number of poles P
Is set to 4 × m (where m is a natural number), so that the armature coil of the energized phase and the magnet rotor 23 opposed thereto
Can be made symmetrical with respect to the rotation axis, and the magnetic force acting on the magnet rotor 23 can be a couple. This allows
Since the force component acting in the radial direction of the magnet rotor 23 can be canceled, the load applied to the bearing 27 of the rotary shaft 24 can be reduced, the durability can be improved, and the rotation of the rotary shaft 24 can be prevented. Smooth rotation can be realized.

The same effect can be obtained even if the number of poles P of the magnet rotor 23 and the number of poles M of the stator 19 are appropriately changed as long as the above-mentioned expressions (1) to (3) are satisfied. .

In the present embodiment, the number of phases of the armature coil is set to five. However, the number of phases may be set to four, six or more, and preferably an odd number of five or more. If five or more odd phases are used, the number of energized phases can be made even when the number of energized phases is maximized by setting one non-energized phase to one phase. The number of coils and the number of coils in the other energizing path can be the same, respectively.
The coil resistance value and the coil current of the two current paths can be made the same, and the brushless motor can be rotated with good balance.

Further, as the switching element of the drive circuit 46, another switching element may be used instead of the MOSFET. Further, the driving method is not limited to the full-wave driving method, but may be a half-wave driving method. The connection of the armature coils A21 to E21 of each phase is not limited to the Y connection.

In addition, the present invention relates to the magnet rotor 23
May be detected by a position detection element such as a Hall element, and the energized phase may be switched based on the detection signal. The scope of the present invention is the fuel pump 1
The present invention is not limited to one drive motor, and can be used as drive motors for various devices.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a fuel pump showing one embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views taken along line AA of FIG. 1 at different rotational positions of a magnet rotor.

FIG. 3 is a diagram illustrating a method of winding armature coils of each phase.

FIG. 4 is a circuit diagram showing an electrical configuration of the brushless motor.

FIG. 5 is a diagram showing a switching pattern of each MOSFET in a four-phase conduction mode.

FIG. 6 is a diagram showing torque-rotation speed characteristics of a brushless motor.

FIG. 7 is a circuit diagram showing an electrical configuration of a conventional three-phase full-wave drive type brushless motor.

[Explanation of symbols]

11 fuel pump, 13 pump section, 14 brushless motor, 19 stator, 23 magnet rotor, 2
6 magnet, 31 drive control circuit (drive control means), 35 control unit, 36 to 45 MOSFET, 46
... Drive circuits, A21, B21, C21, D21, E21
... armature coils.

Claims (9)

[Claims] 1. A brushless motor in which a stator having armature coils of each phase mounted thereon is opposed to a magnet rotor, and energization of the armature coils of each phase is sequentially switched to thereby rotate the magnet rotor. A switching element is connected so that a current flows in a parallel path to the armature coils of a plurality of phases to be energized, and when the energized phase is switched according to the rotational position of the magnet rotor, the switching is performed. A brushless motor, comprising: a drive control unit for controlling a switching operation of the switching element so that current-carrying phases overlap before and after. 2. The brushless motor according to claim 1, wherein the drive control unit switches the switching timing of the switching element so as to change the number of energized phases according to a required motor output. 3. The drive control unit switches the switching timing of the switching element so as to increase a coil resistance value of a current flowing path at the time of starting the motor and / or at the time of overload. Or the brushless motor according to 2. 4. The brushless motor according to claim 1, wherein the drive control means controls the switching operation of the switching element so that the number of energized phases is an even number. 5. The brushless motor according to claim 1, wherein the number of phases of the armature coil is an odd number of five or more phases. 6. All the switching elements are one IC
The brushless motor according to any one of claims 1 to 5, wherein the brushless motor is incorporated in a chip. 7. The relationship among the number of poles P of the magnet rotor, the number of poles M of the stator, and the number of motor phases x is as follows: ｛(x−1) / x｝ M ≦ P ≦ ｛(x + 1) / x｝ M 7. The brushless motor according to claim 1, wherein P is an even number and x is an integer of 4 or more. 8. The number M of poles of the stator is set to an even multiple of the number x of motor phases, and the number P of poles of the magnet rotor is four.
The brushless motor according to any one of claims 1 to 7, wherein the brushless motor is set to xm (where m is a natural number). 9. The brushless motor according to claim 1, wherein the brushless motor is used as a drive motor for a fuel pump of a vehicle.