JPS5934061B2 - Rotation speed detection device for brushless motors - Google Patents

Description

[Detailed description of the invention] The present invention relates to a rotation speed detection device for a brushless transmission.

Conventional devices of this type include, firstly, generator windings are wound concentrically with each field winding to which power is applied via a switch element, and secondly, the field windings are de-energized. Sometimes, there are those that utilize the reverse induced voltage generated in the field winding due to the rotation of a permanent magnet rotor, and thirdly, there are those that attach a frequency generator to the rotating shaft of a brushless motor.

However, in the first and second types, they are affected by temperature such as ambient temperature and heat generation of the field winding, so they are not used as speed signals.
Therefore, it is not possible to always obtain a stable signal, which has the disadvantage of contributing to rotational unevenness and rotational speed drift.

Particularly, in the first type, since the generator winding is wound around the stator core together with the field winding, the number of windings of the field winding is limited and the torque is reduced.

Moreover, the third method has the disadvantage that the structure is complicated and expensive.

The present invention was invented in view of the above points, and aims to obtain a stable rotational speed signal at low cost.The present invention will be described below with reference to the drawings.

First, the electric circuit of the brushless motor will be explained based on FIG. 1. Each field winding L (subscripts a and b in the figure) will be explained below.

C indicates a different phase.

same as below. ) are each connected to the DC power supply terminal P via a switch transistor T1, a control transistor T2 is connected to the base of each transistor T1, and each control transistor T2 is connected to the DC power supply terminal P via a common transistor T3. to form a differential amplification circuit.

Further, the output coil t of the oscillator O is applied with a DC bias from the DC bias circuit C, and is connected to a series circuit of a resistor R3 and a position detection coil t2, and the intermediate node of the series circuit is connected to the base of the control transistor T2. ing.

The position detection coil 4 has a saturable magnetic core, and its impedance value changes depending on the proximity of the magnetic pole portions of the rotor permanent magnets, that is, the position of the rotor, so that the conduction of the corresponding control transistor T2 is controlled.

Therefore, each field winding is sequentially switched and energized, so that a rotating magnetic field is generated and the rotor rotates in tandem.

Next, t3 is a detection coil for detecting rotational speed, which is wound around a saturable magnetic core in the same way as position detection coil 4, and resistor R
It is connected between both ends of the output coil l-1 via 2.

The frequency output of the detection coil t3 is applied to the conversion circuit AC via the diode D and converted into a voltage.

The output of the conversion circuit AC is compared with the reference voltage of the reference voltage circuit BC by the comparison circuit CC, and when the rotor reaches a predetermined speed or higher, the common transistor T3 is cut off to perform constant speed control.

Next, as shown in FIG. 2, the field winding is wound around the stator core 1, and the core is fixed to the outer periphery of a resin sleeve 3 attached to the stator case 2, and is inserted into the central hole 4 of the sleeve. A bearing 5 is fitted, and a shaft 7 of a rotor 6 is supported by the bearing.

The rotor 6 is composed of an annular permanent magnet 8 and a magnetic bottomed cylindrical rotor case 9 that covers the magnet. magnetic pole 10;
Lower end magnetic poles 11 are alternately magnetized with different polarities in the circumferential direction on the lower end surface.
and an outer circumference magnetic pole 12 magnetized at the lower end of the outer circumference.

The inner circumferential magnetic pole portion 10 opposes the magnetic pole of the stator core 1, and generates rotational torque by electromagnetic force with the rotating magnetic field generated by the field winding.

Further, the lower end magnetic pole 11 opposes the three position detection coils 4 provided in the stator case 2, and serves as a position detection magnet.

On the other hand, a comb-like tooth piece 14 is formed by drilling a large number of slits 13 at the opening edge of the rotor case 2, and a part of the outer circumferential magnetic pole 12 is covered with this tooth piece 14, and the outer circumferential magnetic pole 12
The remainder of the detection coil t3 is exposed through the slit 13, and the detection coil t3 is attached to the stator case 2 through the slit 13 so as to oppose the outer magnetic pole 12.

As shown in FIG. 3, the outer magnetic poles 12 are alternately magnetized to different polarities in the circumferential direction.

This magnetization may be formed by magnetizing the inner circumferential magnetic pole 10 in the radial direction without performing any special magnetization.

The teeth 14 of the rotor case 9 are positioned on the outer surface of the boundary between adjacent magnetic poles on the outer periphery of the outer magnetic pole 12 .

That is, the outer magnetic poles 12 are alternately magnetized with different polarities in the circumferential direction, and the magnetic flux density distribution of each magnetic pole is generally approximately trapezoidal, and N
Since the boundary between the pole and the south pole is a region where the magnetic flux density distribution is reversed between positive and negative, the magnetic flux density at this boundary is small.

Therefore, by covering the boundary portion where the magnetic flux density is low with the tooth piece 14, only the magnetic pole region where the absolute value of the magnetic flux density is large is exposed in the slit 13 between the tooth pieces 14, 14.

In this case, the detection coil t3 has the fifth output coil from the output coil t1.
When the high frequency signal e shown in the figure is applied and the slit 13 approaches the detection coil t8 due to the rotation of the first rotor 6, the saturable magnetic core 15 around which the detection coil t3 is wound is magnetically saturated due to the magnetic flux from the outer magnetic pole 12. Therefore, its magnetic permeability becomes small, the inductance of the detection coil t3 becomes small, and the detection voltage e1 of the detection coil t3 becomes small.

On the other hand, when the tooth piece 14 approaches the detection coil t3, the voltage e2 across the detection coil t3 increases.

Therefore, the voltage across the detection coil t3 changes in magnitude, and the change is proportional to the rotational speed.

Next, FIG. 4 shows a different embodiment of the outer circumference magnetic pole 12, in which a permanent magnet 8 is magnetized at the lower end of the outer circumference in the direction of the axis 7 and formed in an annular shape.

In this case, the upper pole (N pole) of the outer magnetic poles 12 is covered with the rotor case 9, and the lower pole (S pole) has a slit 13.
and tooth piece 14 are located.

Therefore, at the lower end of the outer circumference of the rotor case 9, magnetic pole parts exposed from the slit 13 and non-magnetic pole parts covered by the teeth 14 are alternately formed, and as in the case of FIG. 3, the detection coil t3 The voltage across both ends is as shown in FIG.

As described above, according to the present invention, a large number of slits are formed in the opening edge of the magnetic bottomed cylindrical rotor case that covers the annular permanent magnet, and the outer circumferential magnetic pole of the magnet is connected to the comb-toothed pieces formed between the slits. The outer magnetic poles are exposed at equal intervals through the slits, and the magnetic sensing elements for rotational speed detection are mounted on the stator side through the slits so as to oppose the outer magnetic poles. There is no need for wires, there is no heat influence from the field windings, rotational unevenness and drift in rotational speed can be reduced, and the magnetic sensing element can also be used as a position detection sensing element, making it easy to use. Therefore, it is possible to provide an inexpensive rotational speed detection device.

In the case where the outer magnetic poles are magnetized with different polarities alternately in the outer circumferential direction, the tooth pieces are positioned on the boundary surface between adjacent magnetic poles, so that the impedance change or voltage change of the rotational speed detection magnetic sensing element is reduced. It becomes binary, the change can be made large, and rotational speed detection becomes easy.

Furthermore, when the outer circumferential magnetic poles are magnetized vertically in the rotor axial direction, it is not necessary to determine the positions of the teeth, making it easier to attach the rotor case to the permanent magnets.

[BRIEF DESCRIPTION OF THE DRAWINGS] The drawings show a rotational speed detection device according to the present invention, FIG. 1 is an electric circuit diagram of a brushless motor, FIG. 2 is an assembled sectional side view of the motor, and FIG.
3 and 4 are perspective views of permanent magnets having different outer circumferential magnetic poles, and FIG. 5 is a diagram of voltage waveforms across the magnetic sensing element. 8... Permanent magnet, 9... Rotor case, 12...
Outer magnetic pole, 13... slit, t3... magnetic sensing element,
14...Tooth piece.

Claims (1)

[Scope of Claims] 1. A large number of slits are formed in the opening edge of a magnetic bottomed cylindrical rotor case that covers an annular permanent magnet, exposing a portion of the outer magnetic poles of the magnet at equal intervals, and A rotational speed detection device for a brushless motor, comprising a magnetic sensing element for rotational speed detection that opposes the outer circumferential magnetic pole and is attached to a stator side. 2. The outer circumferential magnetic pole portion of the magnet is formed of magnetic poles magnetized with different polarities alternately in the outer circumferential direction, and the teeth between the slits of the rotor case are positioned on the outer surface of the boundary between the adjacent magnetic pole portions. A rotational speed detection device for a brushless electric motor according to claim 1. 3. The rotational speed detection device for a brushless motor according to claim 1, wherein the outer circumferential magnetic pole of the magnet is formed of magnetic poles magnetized vertically.