JPH0474956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a direct current brushless electric motor, and more specifically, a permanent magnet rotor, a stator disposed opposite to the rotor through a gap, A direct current device configured to rotationally drive the rotor, including a position detector that detects the magnetic pole position of the rotor, and an energization control device that supplies current to the excitation winding of the stator according to the output of the position detector. This relates to brushless motors, and in particular, it attempts to control the rotor speed to any speed below the rated speed while keeping the supplied voltage unchanged.For example, it is used for relatively light-load motors such as fan motors. Applies to electric motors.

[Background of the invention]

A conventional example will be explained with reference to FIG. FIG. 1a is a sectional view of a DC brushless motor, and FIG. 1b is a diagram of its energization control circuit. In FIG. 1, 1 is a rotor shaft, 3 is a permanent magnet that is directly connected to the rotor shaft 1 via a rotating hub (not visible in the figure) and rotates integrally with the rotor shaft 1. These 1 and 3 constitute the rotor of the electric motor. The permanent magnet 3 has a cylindrical shape, and half the circumference of the cylinder is magnetized to the north pole, and the remaining half circumference is magnetized to the south pole. In addition, if this electric motor is used as a drive source for a cooling fan,
A plurality of fan blades will be planted on the outer circumferential side of the permanent magnet. 5a and 5b are pole shoes of the stator iron core, 6a and 6b are stator magnetic poles, and 7
Reference numerals a and 7b denote excitation windings wound around the respective stator magnetic poles 6a and 6b, 8 a stator yoke, and 9 a position detector for detecting the rotating magnetic pole position of the permanent magnet 3. 4 is a gap between the inner circumferential surface of the permanent magnet 3 and the outer circumferential surface of the pole shoes 5a, 5b of the stator iron core, and the position detector 9 symmetrically moves the pole shoes 5a, 5b within this gap 4. It is placed at a position slightly off the center line that bisects the area. In figure b, Q _a and Q _b are transistors that control energization of the excitation windings 7 a and 7 b, and R ₁ , R ₂ , R ₃ , and R ₄ are resistors, respectively.

In Fig. 1b is the power supply terminal, and when a predetermined DC voltage is applied here, the position detector 9
In the state shown in FIG. 1a, is opposed to the S pole of the permanent magnet 3, so the S pole is detected and the transistor Q _a
A positive voltage is applied to the base of , and a negative voltage is applied to the base of Q _b , which makes the transistor Q _a conductive and causes a current to flow through the excitation winding 7 a, and the magnetic field generated by this current causes the permanent magnet 3 to, for example, A clockwise rotational force is generated, and the rotor rotates clockwise.
When the rotor rotates half a turn, the position detector 9 detects the permanent magnet 3.
A positive voltage is applied to the base of the transistor Q _b and a negative voltage is applied to the base of the transistor Q _a , which makes Q _b conductive and causes current to flow through the excitation winding 7b.
The magnetic field generated by this current causes the permanent magnet 3 to
The same clockwise rotational force is generated and the rotor continues to rotate clockwise. The following works in the same way,
The excitation winding 7 is energized every half rotation of the rotor.
a and 7b are switched to continuously generate clockwise rotational force.

Conventionally, electric motors for driving cooling fans are
Generally, AC induction motors were used. The reason for this was that induction motors have a simple structure, can be manufactured at low cost, and have a long lifespan as there are no parts that wear out. However, induction motors have the disadvantage that they can only be used in places with AC power.On the other hand, in the process of promoting the miniaturization and wide-area spread of electronic devices that are cooled by cooling fans, There has been a demand to standardize the cooling fan to a low DC voltage, and to meet this demand, it has become necessary for the motor for driving the cooling fan to be able to operate at a low DC voltage.

In response to this request, using a normal DC motor with a commutator and brushes as a drive motor is disadvantageous because abrasion powder generated from the brushes contaminates electronic equipment and the life of the motor is shorter than that of an induction motor. Because of the disadvantages such as scratches, a DC brushless motor with a simple structure, which does not have brushes and does not require a speed generator, as illustrated in FIG. 1, is preferred.

However, when a DC brushless motor is used as a drive source for a cooling fan, it is required that the rotation noise generated by the motor be as small as possible. Therefore, if the same amount of air is generated, rotating a larger fan at a lower speed will generate less noise than rotating a smaller fan at a higher speed. There are many requests for brushless electric motors to rotate at lower rotational speeds. In order to rotate an electric motor at low speed, it is necessary to change the stator winding specifications, increase the number of turns, and reduce the wire diameter of the winding. However, increasing the number of turns increases the number of winding man-hours, If the wire diameter is made smaller, there will be more wire breaks during winding, resulting in lower yields and higher manufacturing costs. Furthermore, in order to obtain low-speed rotation, a method of lowering the voltage applied to the excitation winding using a control element such as a transistor in a conduction control circuit is often used. In the case of electric motors that are made smaller by using the switching action of transistors, the above method requires a transistor with large collector loss for voltage control, which generates a large amount of heat, requires installation space, and reduces efficiency. Inconveniences such as worsening of
Not suitable for small products. Furthermore, in order to obtain low speed rotation, a method of adding a low damping element to the winding has been conventionally used, but this method also has the same effect as adding a collector with a large collector loss as described above. It's inconvenient. Furthermore, all of the above methods have the disadvantage that the torque at startup is smaller than that of an electric motor with high-speed rotation specifications.

In addition, single-phase DC brushless motors are often adopted, which use reluctance torque generated by the size of the air gap, etc., for starting. However, in this case, the electromagnetic starting torque generated by energizing the windings Since the motor is small, there is a problem that the reverse rotation reluctance torque is not canceled out at the time of starting, and the electric motor may not be able to start.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, to provide a system that can be operated at any low speed below the rated speed and has excellent starting characteristics.
The object of the present invention is to provide a DC brushless motor with a simple structure.

[Summary of the invention]

In order to achieve the above object, the features of the present invention are as follows:
The energization control device for a DC brushless motor,
A sawtooth wave generation circuit generates a sawtooth voltage signal synchronized with the output signal of the position detector, a smoothing circuit smoothes this sawtooth wave voltage, and compares the sawtooth wave voltage and the smoothed voltage to generate a sawtooth wave voltage signal. a first comparator that produces an output when the waveform voltage is less than the smoothed voltage;
A second voltage generator that compares the smoothed voltage with a set voltage that is set to a voltage value larger than the smoothed output voltage during low-speed rotation, and generates an output when the set voltage is smaller than the smoothed voltage.
The comparator and the gate circuit which energizes the excitation winding of the stator when the output from either the first or second comparator is generated are biased. be.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. FIG. 2 is a power supply control circuit diagram, and FIG. 3 is a time chart of various signals. This embodiment is directed to an energization control device for a DC brushless motor having one position detector and two stator excitation windings as shown in FIG.

In FIG. 2, a positive output signal 10 and a negative output signal 1 of a position detector 9, such as a Hall element, are shown.
0' is one input of each AND circuit 70, 75, and these AND circuits 70, 7
The respective outputs 80, 85 of 5 are supplied to the excitation windings (7a, 7b in FIG. 1) of the stator, respectively. 20 is a sawtooth wave generation circuit that generates a sawtooth voltage signal synchronized with the output signal of the position detector 9; for example, a constant current source is connected to a series circuit of a resistor and a capacitor, and the circuit is connected to a terminal of the capacitor. output signals 10 and 1 of position detection 9.
Turns on with a pulse signal generated at the rising edge of 0'
By taking out the terminal voltage of the capacitor as the output signal 20, the signal 20 starts charging immediately after being cleared by the rising edge of the digit 10, and continues charging until it is cleared by the rising edge of the signal 10'. This results in a sawtooth wave voltage signal that continues to rise. Therefore, the peak value of this sawtooth voltage signal 20 becomes higher as the speed of the motor is lower, as shown in FIG. 30 is a smoothing circuit that smoothes this sawtooth wave voltage signal 20. A first comparator 40 compares the sawtooth voltage signal 20 and the smoothed voltage 30 from the smoothing circuit 30, and when the sawtooth voltage 20 is smaller than the smoothed voltage 30,
An output signal 40 is generated. 45 is a second comparator, which sets the set voltage 5 set by the setting device 50 to a voltage value larger than the smoothed output voltage when the motor rotates at low speed.
0 and the smoothed voltage 30, and when the set voltage 50 is smaller than the smoothed voltage 30, the output signal 45
occurs. 60 is an OR circuit, and the first comparator 4
0 output 40 and the output 45 of the second comparator 45 are received as inputs, an output signal 60 is generated, and the AND
It is sent as the other input of each of circuits 70, 75.

The energization control device having the above configuration operates as follows. First, considering the first comparator 40, the energization period to the stator excitation winding is only the period when the sawtooth wave voltage 20 is smaller than the smoothed voltage 30, and in the steady operation state of the motor, the energization period is 50%. Therefore, even if the supplied power supply voltage is constant, the effective voltage supplied to the excitation winding is approximately 1/2, and therefore the torque generated by the motor is approximately 1/2, and the generated torque and load torque of the motor are smooth. rotate at a speed that At this time, the period of the sawtooth voltage 20, which functions to adjust the generated torque, is synchronized with the output signals 10, 10' of the position detector 9, so that speed feedback is applied, and a speed generator is provided. Even though it is not a feedback control system, the operating speed is stable.

However, with only the configuration including the first comparator 40, self-starting is not possible because the sawtooth wave voltage 20 is higher than the smoothed voltage 30 when starting the motor. The second comparator 45 is provided to cope with this problem. That is, a second comparator is provided to compare the smoothed voltage 30 with a set voltage 50 set to a voltage value larger than the smoothed output voltage during constant speed rotation, and when the set voltage 50 is smaller than the smoothed voltage 30, the comparison is made. generates a device output. The gate circuit is configured to energize the stator excitation winding with the output of the position detector 9 when an output is generated from either the first comparator or the second comparator.

With this configuration, since the peak value of the sawtooth voltage 20 is high when the motor is started, the output of the smoothed voltage 30 is also higher than the set voltage 50, and therefore the second comparator 45 generates the output signal 45. However, this output signal 45 fully energizes the rotor excitation winding and starts the motor. Although the rotor is gradually accelerated, the second comparison device 5 continues to output the energization signal until the smoothed voltage 30 becomes lower than the set voltage 50, so that the current flowing through the excitation winding is fully energized. When the rotor is further accelerated and the smoothed voltage 30 becomes lower than the set voltage 50, the output signal 45 of the second comparator 45 disappears, and from then on, the output of the first comparator 40 turns on and off.
The off-energization command signal is sent to a gate circuit composed of an OR circuit and an AND circuit, and low-speed operation is performed according to the output of the first comparator 40. This first comparator 4
Adjustment of the speed during low-speed operation using an output of 0 is performed using the output voltage 20 of the sawtooth wave generation circuit 20 and the smoothing circuit 3.
0 output voltage 30 is divided by a voltage divider (not shown) and input to the first comparator 40, and the on/off ratio of the output 40 generated by the first comparator 40 is changed. This is easily possible.

As described above, according to the embodiment of the present invention, the supplied DC voltage is kept constant, and the output from the sawtooth wave generation circuit and its smoothed voltage are adjusted and compared by the first comparator. This allows the energization rate to the stator windings to be adjusted arbitrarily, and the motor to be operated at a low speed corresponding to the energization rate.Moreover, this speed is detected by a position detector and fed back negatively. Therefore, the operating speed is stable even without a separate speed generator, and furthermore,
Since the configuration includes a second comparator for startup, the stator winding is fully energized at startup, regardless of the control by the first comparator output.
It has the advantage that it can be stably started with the maximum starting torque and that control automatically shifts to control using the first comparator output when a predetermined speed is reached.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to arbitrarily and automatically adjust the energization rate to the stator windings while the supply voltage remains unchanged, thereby allowing operation at a speed lower than the rated speed. It is possible to perform this operation stably and to reduce the generated noise.Furthermore, since it is fully energized at startup, the startup is stable, and furthermore, the transition from the above-mentioned full energization operation to operation based on the energization rate is possible. Since the configuration is automatic, it is possible to provide a DC brushless motor with a simple structure and good operability.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the prior art, in which a is a sectional view, b is an energization control circuit diagram, FIG. 2 is an energization control circuit diagram showing an embodiment of the present invention, and FIG. 3 is a diagram of various signals in FIG. 2. It is a time chart. Explanation of symbols, 1... Rotor shaft, 3... Permanent magnet, 4... Air gap, 5a, 5b... Pole shoe,
6a, 6b... Stator magnetic poles, 7a, 7b... Excitation windings, 8... Stator yoke, 9... Position detector,
20... Sawtooth wave generation circuit, 30... Smoothing circuit,
40...first comparator, 45...second comparator,
50...Setting voltage setting device, 60...OR circuit, 7
0,75...AND circuit.

Claims (1)

[Claims] 1 A permanent magnet rotor, a stator installed opposite to the rotor through an air gap, a position detector for detecting the magnetic pole position of the rotor, and a current according to the output of the position detector fixed as above. In a direct current brushless motor that drives the rotor and includes an energization control device that energizes an excitation winding wound around the rotor, a sawtooth motor generates a sawtooth voltage signal synchronized with the output signal of a position detector. a wave generating circuit, a smoothing circuit that smoothes the sawtooth voltage, and a first comparator that compares the sawtooth voltage and the smoothed voltage and generates an output when the sawtooth voltage is smaller than the smoothed voltage. , a second comparator that compares the smoothed voltage with a set voltage set to a voltage value larger than the smoothed output voltage during low speed rotation and generates an output when the set voltage is smaller than the smoothed voltage; A direct current brushless motor, characterized in that it is an energization control device comprising a gate circuit that energizes a stator excitation winding with the output of the position detector when an output is generated from one of the comparators.