Single-phase AC 4-pole synchronous motor

Abstract

This invention provides a single-phase AC 4-pole synchronous motor that suppresses the generation of reverse rotation torque during startup, enabling stable synchronous pulling, and has enhanced waterproof performance to withstand harsh operating environments with long periods of continuous operation. [Solution] The stator core 6a has teeth 6c with different shapes on both sides of the radial center line so asymmetrically with respect to the center line of the teeth 6c, and the circumferential development angle θ of the tip of the teeth 6c is set to 65° in central angle, and the effective magnetization angle by trapezoidal wave magnetization of each magnetic pole of the rotor magnet 5d, which is positioned opposite the tip of the teeth 6c, is set to 62°±5°.

Description

Technical Field

[0001] The present disclosure relates to a single-phase AC 4-pole synchronous motor.

Background Art

[0002] A small-sized synchronous motor with high efficiency and reliability that can surely shift from starting operation to synchronous operation has been developed. This synchronous motor performs starting operation by subjecting an alternating current supplied from an AC power source to full-wave rectification through a rectifier bridge circuit by switching control of the alternating current. At this time, the current waveform is converged to one side by regulating, by switching, the energization range corresponding to the positive or negative side of the rectified current. When the rotational speed of the magnet rotor reaches near the synchronous rotational speed with respect to the power source frequency, an operation switching switch is switched to shift to synchronous operation (see Patent Document 1; Japanese Patent No. 4030571).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the starting operation circuit of the synchronous motor described above, since the DC resistance value of the motor coil at the time of starting is small and a large current flows, it is necessary to use expensive electronic components with a large rated capacity. In addition, a large surge voltage is generated when switching the direction of the energization current flowing through the motor coil as the rotor rotates, and there is a risk of damaging the electronic components. Even if a surge absorption element such as a varistor is provided between the rectifier bridge circuit and the switching circuit in the starting operation circuit, there is a problem that the surge voltage cannot be completely absorbed.

[0005] Furthermore, during startup, the rotational phase of the rotor poles is converged to the phase of the power supply voltage waveform by restricting the flow of either the positive or negative side of the full-wave rectified sinusoidal current (Figure 8B) supplied from the single-phase AC power supply (Figure 8A) using chopper operation. Alternatively, it is possible to smooth the motor current flowing through the motor coil and use electronic components with lower rated capacity. For example, Figure 8C shows the rotational startup waveform obtained by smoothing the full-wave rectified waveform with a filter circuit. With the rotational startup waveform shown in Figure 8C, the power supply frequency information is lost due to smoothing, making it impossible to time the synchronous pull-in.

[0006] Figure 9A shows the Hall element detection signal (square waveform) and power supply voltage waveform (sine waveform) during synchronous operation at rated load, and their phases are almost identical. However, during startup, the phase of the motor current lags behind the rotation phase of the rotor poles. The main reason for this is that, as shown in Figure 9B, even when the rotor pole position switches, the direction of the motor current flowing through the motor coil does not switch simultaneously with the power supply voltage waveform due to the influence of the motor coil's inductance. As a result, a reverse rotation torque is generated in the rotor during startup. This reverse rotation torque has almost no effect at low rotor speeds, but it becomes significant as the rotation speed increases and the energization switching time becomes shorter, potentially preventing the rotation speed from reaching above the synchronous speed.

[0007] In single-phase AC 4-pole synchronous motors, there are currently no disclosed or suggested technical concepts that focus on the relationship between the magnetization waveform of the rotor magnetic poles and the expansion angle of the teeth tip of the stator core in order to suppress the reverse rotation torque generated in the rotor during startup. Furthermore, since single-phase AC 4-pole synchronous motors are expected to operate for long periods of time as a power source for refrigerators, vegetable processing plants, chicken coops, pig barns, etc., it was also necessary to improve motor efficiency and enhance the waterproof performance of the motor to withstand harsh operating environments.

[0008] The purpose of this disclosure is to solve the above-mentioned problems and provide a single-phase AC 4-pole synchronous motor that can suppress the generation of reverse rotation torque during startup and perform stable synchronous pulling, and has improved motor efficiency and enhanced waterproof performance to withstand harsh operating environments for long periods of continuous operation. [Means for solving the problem]

[0009] This disclosure has the following configuration in order to achieve the above objectives. The rotor comprises a cylindrical rotor yoke mounted on an output shaft rotatably supported through a stator core, with an annular rotor magnet having four alternating N and S poles magnetized on the inner surface of the rotor yoke, and a stator having a stator core with teeth protruding radially from the center of the annular core at 90° phase differences, and motor coils wound on the teeth facing each other radially around the output shaft with different winding directions, and the operation changeover switch activates the starting switching means according to the detection signal of the detection sensor while the AC power supply is connected to the starting operation circuit. A single-phase AC 4-pole synchronous motor that starts up by switching control and switches to a synchronous operation circuit when the rotor speed reaches a predetermined speed near the synchronous speed, wherein the stator core has teeth with different shapes on both sides of the radial center line so asymmetrical with respect to the center line of the teeth, and the circumferential development angle θ of the tip of the teeth is set to 65° in central angle, and the effective magnetization angle by trapezoidal wave magnetization of each magnetic pole of the rotor magnet which is arranged opposite to the tip of the teeth is set to 62°±5°.

[0010] Thus, in a single-phase AC 4-pole synchronous motor, the stator core is configured such that the circumferential expansion angle θ of the tip of each tooth is set to 65° in terms of the central angle, and the rotor magnet is configured such that the effective magnetization angle due to trapezoidal wave magnetization of each magnetic pole is set to 62°±5°. This causes the back electromotive force waveform generated when the rotor magnetic poles switch to follow a sine wave curve, improving motor efficiency and enabling stable synchronous pulling. Furthermore, because the shape of the tip of each tooth differs on both sides of the radial centerline so that each tooth is magnetically asymmetrical with respect to the centerline, rotational dead spots are eliminated during startup.

[0011] The output shaft is rotatably supported by a pair of bearings concentrically mounted to the housing body and the lower housing, and preferably, at least a first resin sheet material and a second resin sheet material are mounted overlapping in the axial direction between the housing body and the lid, and a sealing material is installed between the first resin sheet material and the lid. As a result, at least a first resin sheet material and a second resin sheet material are overlapped in the axial direction between the housing body and the lid, and a sealing material is installed between the first resin sheet material and the lid, so that moisture intrusion around the output shaft is suppressed and waterproof performance that can withstand harsh operating environments can be maintained.

[0012] Preferably, the radial dimension of the first resin sheet material is larger than that of the second resin sheet material, and when these are superimposed on the housing body with the same outer diameter, the excess portion on the inner diameter side of the first resin sheet material flexes along the output shaft, thereby filling the gap formed between the first resin sheet material and the second resin sheet material around the output shaft with lubricating oil. Thus, when lubricating oil is filled into the gap formed between the first resin sheet material and the second resin sheet material around the output shaft, the rotational movement of the output shaft becomes smoother, and stable rotational movement can be maintained without leakage of lubricating oil even after long-term use.

[0013] The first and second resin sheet materials are preferably resin sheet materials in which a fluororesin is added to a PPS (polyphenylene sulfide) resin material. Thus, when fluororesin is added to the PPS (polyphenylene sulfide) resin material, the first and second resin sheet materials have high resistance to sliding and abrasion, and can withstand harsh operating environments such as prolonged use. [Effects of the Invention]

[0014] This invention provides a single-phase four-pole synchronous motor that suppresses reverse rotation torque generation during startup, enabling stable synchronous pulling, and also offers improved motor efficiency and enhanced waterproof performance to withstand harsh operating environments. [Brief explanation of the drawing]

[0015] [Figure 1] This is an explanatory diagram of the starting operation circuit and the synchronous operation circuit of a single-phase AC 4-pole synchronous motor. [Figure 2] These are the sensor output waveform diagram, the output signal waveform diagram of the output terminal, and the motor drive voltage waveform diagram. [Figure 3] This is an explanatory diagram showing the phase relationship between the sensor output waveform and the motor current waveform during synchronous retraction. [Figure 4] Figure 4A is a plan view of a single-phase AC 4-pole synchronous motor, and Figure 4B is a cross-sectional view in the direction of arrow XX in Figure 4A. [Figure 5] This is an enlarged cross-sectional view of section C in Figure 4B. [Figure 6] Figures 4A and 4B show exploded perspective views of a single-phase AC 4-pole synchronous motor. [Figure 7] Figure 7A is a plan view of the stator core, Figure 7B is a right side view of Figure 7A, and Figure 7C is an explanatory diagram showing the magnetization waveform due to trapezoidal wave magnetization of the rotor magnet. [Figure 8] Figure 8A shows the single-phase AC power supply waveform, Figure 8B shows the full-wave rectified waveform of Figure 8A, and Figure 8C is an explanatory diagram showing the energized waveform of the motor coil of a single-phase AC 4-pole synchronous motor. [Figure 9] Figure 9A is the sensor waveform diagram, and Figure 9B is the power supply voltage waveform diagram. [Figure 10] Figure 10A is an explanatory diagram of the sensor output waveform in startup operation, Figure 10B is a power supply voltage waveform diagram, Figure 10C is an explanatory diagram of the motor drive voltage waveform, Figure 10D is the sensor output waveform diagram during synchronous operation, and Figure 10E is a power supply voltage waveform diagram. [Figure 11] Figure 11 is a reverse electromotive force waveform diagram during startup operation. [Figure 12] Figure 12A is an explanatory diagram comparing and displaying the maximum values of the output efficiencies of an AC single-phase 4-pole synchronous motor, an AC 4-pole induction motor, and a DC 4-pole brushless motor of the 8W class output, and Figure 12B is a graph comparing the output efficiencies at the maximum output among these motors.

Best Mode for Carrying Out the Invention

[0016] Hereinafter, the best mode for implementing the invention will be described in detail based on the accompanying drawings. First, as an example, an embodiment of a single-phase AC 4-pole synchronous motor with a motor output of generally 10W or less will be shown. Figure 4A is a plan view of the single-phase AC 4-pole synchronous motor M, and Figure 4B shows a cross-sectional view taken along the X-X direction of Figure 4A.

[0017] In Figure 4B, the single-phase AC 4-pole synchronous motor M has a rotor 5 and a stator 6 housed in a motor case 4 composed of an upper lid 1, a housing body 2, and a lower housing 3. The configuration of the rotor 5 will be described. A cup-shaped rotor yoke 5b is assembled to an output shaft 5a that is rotatably supported through a stator core 6a. A cylindrical portion 5c is provided on the hub of the rotor yoke 5b and is press-fitted and fixed to the output shaft 5a. The output shaft 5a is rotatably supported by bearings 7a, 7b provided on the housing body 2 and the lower housing 3.

[0018] An annular rotor magnet 5d magnetized with N poles and S poles alternately in 4 poles is mounted on the inner peripheral surface of the rotor yoke 5b. The rotor magnet 5d can be an isotropic magnet such as a ferrite magnet, alnico magnet, or neodymium magnet, or an anisotropic rubber magnet. Each magnetic pole of the rotor magnet 5d is magnetized using a trapezoidal wave magnetization method as shown in Figure 7C. The effective magnetization angle (the range in which the magnetic flux density is constant) of each magnetic pole is set to 62°±5°.

[0019] Next, the configuration of the stator 6 will be described. In Figures 7A and 7B, the stator core 6a is a laminated core formed by stacking pieces of electromagnetic steel sheets that have been punched out. In Figure 7A, the stator core 6a has teeth 6c projecting radially from the annular core center 6b at a 90° phase difference. The core center 6b is provided with a through hole 6b1 through which the output shaft 5a is inserted. The stator core 6a has teeth 6c with different shapes on both sides of the radial center line of the teeth 6c so as to be magnetically asymmetric with respect to the center line of the teeth 6c. Specifically, stepped portions 6c1 are formed on the outer circumferential surface of the teeth 6c, which is the magnetic flux acting surface. This eliminates the rotational dead center when the motor stops. In addition, the circumferential expansion angle θ of the tip of the teeth 6c is set to 65° at the central angle. This expansion angle θ is calculated by 360°-100° / n (where n is the number of poles).

[0020] Thus, when the circumferential expansion angle θ of the tip of each tooth section 6c is set to 65° in terms of the central angle, and the effective magnetization angle of each magnetic pole of the rotor magnet 5d due to trapezoidal wave magnetization is set to 62°±5°, the back electromotive force waveform during startup will draw a sine wave curve, improving motor efficiency and enabling stable synchronous pulling.

[0021] In Figure 4B, a bobbin 6d is assembled to each tooth portion 6c, and a motor coil 6e is wound around each bobbin 6d. Specifically, motor coils 6e are wound in different directions on tooth portions 6c that are radially opposite each other with respect to the output shaft 5a. Lead wires drawn from the motor coils 6e are connected to a wiring board 3a provided on the lower housing 3. The stator core 6a is assembled by screwing fixing screws 6f through each tooth portion 6c and into screw holes in boss portions 3b provided on the lower housing 3. As shown in Figure 6, a sensor board 3c is assembled to the lower housing 3, and the magnetic pole position and rotational speed of the rotor 2 are detected by a Hall element 3d provided on the sensor board 3c opposite the inner circumference side of the rotor magnet 5d. Power supply wires 3e that supply power to the sensor board 3c and wiring board 3a are bundled by a holder 3f and wired to the outside of the motor case 4 (see Figure 4A).

[0022] Furthermore, since the single-phase AC 4-pole synchronous motor M is expected to be used as a power source for refrigerators, vegetable processing plants, chicken coops, pig barns, etc., it requires waterproof performance that can withstand harsh operating environments with long periods of continuous operation. The waterproof structure of the bearing section of the output shaft 5a will be described below. As mentioned above, in Figure 4B, the output shaft 5a is rotatably supported by a pair of bearings 7a and 7b that are assembled concentrically to the housing body 2 and the lower housing 3.

[0023] Figure 5 is an enlarged cross-sectional view of section C in Figure 4B. Between the top cover 1 (outer cover) and the housing body 2, at least a first resin sheet material 8a and a second resin sheet material 8b are mounted overlapping in the axial direction. The first resin sheet material 8a and the second resin sheet material 8b are annular resin sheet materials with a central hole through which the output shaft 5a is inserted (see Figure 6). An O-ring 9 (sealing material) is interposed between the first resin sheet material 8a and the top cover 1. A wave washer 10 is interposed between the bearing 7a (outer ring side) and the housing body 2, and preload is applied to the bearing 7a along the axial direction.

[0024] Furthermore, in Figure 5, a gap 11 is formed between the first resin sheet material 8a and the second resin sheet material 8b around the output shaft 5a. Specifically, the radial dimension of the first resin sheet material 8a is larger than that of the second resin sheet material 8b, and these are superimposed with their outer diameters aligned. As a result, the excess portion on the inner diameter side of the first resin sheet material 8a flexes along the output shaft 5a, forming a gap 11 between it and the second resin sheet material 8b. This gap 11 is filled with grease 12 (lubricating oil).

[0025] As a result, at least the first resin sheet material 8a and the second resin sheet material 8b are overlapped axially between the top cover 1 and the housing body 2, and the first resin sheet material 8a is assembled with an O-ring 9 between it and the top cover 1, thereby enhancing waterproof performance that can withstand harsh operating environments for extended periods. Furthermore, if grease 12 is filled into the gap 11 formed between the first resin sheet material 8a and the second resin sheet material 8b around the output shaft 5a, the rotational movement of the output shaft 5a becomes smoother, and stable rotational movement can be maintained without lubrication oil leakage even after long-term use.

[0026] For the first resin sheet material 8a and the second resin sheet material 8b, a resin sheet material in which fluororesin is added to a PPS (polyphenylene sulfide) resin material is preferably used. Thus, the first and second resin sheet materials 8a and 8b, when fluororesin is added to PPS (polyphenylene sulfide) resin material, have high sliding resistance and abrasion resistance, and can withstand harsh operating environments such as prolonged use.

[0027] Figure 6 is an exploded perspective view of a single-phase 4-pole synchronous motor M. The stator 6 is assembled by screwing the stator core 6a into the threaded holes of the boss portion 3b provided in the lower housing 3 using fixing screws 6f that pass through each tooth portion 6c. The rotor 5 has an annular rotor magnet 5d mounted on the inner surface of a cup-shaped rotor yoke 5b, and one end of the output shaft 5a passes through the through hole 6b1 of the stator core 6a and is rotatably supported by the bearing 7b of the lower housing 3, while the other end of the output shaft 5a is rotatably supported by the housing body 2 via the bearing 7a and wave washer 10. The housing body 2 is assembled by overlapping a second resin sheet material 8b and a first resin sheet material 8a concentrically with the output shaft 5a, interposing an O-ring 9, and overlapping the top cover 1, which is then assembled to the housing body 2 with set screws 1a.

[0028] Next, an example of a drive circuit for the single-phase 4-pole synchronous motor described above will be explained with reference to Figure 1. The starting operation circuit 20 is a circuit that starts the single-phase 4-pole synchronous motor as a DC brushless motor. That is, the AC current supplied from the AC power supply 21 is rectified by a rectifier bridge circuit (diode bridge circuit) 22, and a smoothed DC current is generated by a filter circuit (capacitor C in this embodiment) 23. Then, the direction of the motor current is switched according to the rotation angle of the rotor magnet 5d by starting transistors Q1 to Q6, which are an example of a starting switching means, and the motor coil 6e is energized to start the motor. The filter circuit 23 may be a capacitor C, or a capacitor C and a choke coil connected in series.

[0029] On the other hand, the synchronous operation circuit 24 is a circuit that energizes the motor coil 6e connected to the AC power supply 21 to operate the 4-pole synchronous motor as an AC synchronous motor in a synchronous manner. The starting operation circuit 20 and the synchronous operation circuit 24 are switched by operation changeover switches SW1 and SW2, which are provided between the motor coil 6e connected to the AC power supply 21. The operation changeover switches SW1 and SW2 are switched by electromagnetic drive through a relay driver 25, which is an example of a switching means, to switch contacts P1 and P2. In starting operation, the operation changeover switches SW1 and SW2 are open from contacts P1 and P2, and in synchronous operation, they are connected to contacts P1 and P2. At this time, the output from the drive control unit 26 to the starting transistors Q1 to Q6 of the starting operation circuit 20 is turned OFF, and it becomes open to the motor coil 6e.

[0030] An example of a control means is the drive control unit (microcomputer) 26, which controls the operation of the starting operation circuit 21, the synchronous operation circuit 24, and the relay driver 25. Power frequency information from the AC power supply 21 is input to the input terminal IN1 of the drive control unit 26. In addition, information such as the rotor magnetic pole position and rotor rotation speed detected by the Hall element 3c is input to the input terminal IN2. Furthermore, transistor Q1 is turned ON / OFF from the output terminal OUT1, transistor Q2 is turned ON / OFF from the output terminal OUT2, and a switching signal is output to the relay driver 25 from the output terminal OUT3.

[0031] The drive control unit 26 turns off the operation changeover switches SW1 and SW2, and with the AC power supply 21 and the starting operation circuit 20 connected, it switches and controls the starting transistors Q1 to Q6 according to the detection signal of the Hall element 3d to perform a starting operation. Furthermore, when the rotor rotation speed reaches a predetermined rotation speed near the synchronous rotation speed, the drive control unit 26 performs a starting operation while suppressing the range of motor current so that the motor current waveform, which lags in phase with the output waveform of the Hall element 3d, switches its direction of current in a predetermined energizing range at least before the zero-crossing point (switching point) of the sensor output waveform. Then, while switching and controlling the starting transistors Q1 to Q6 to maintain the rotor rotation speed near the predetermined rotation speed, when the phase difference between the rotation phase of the rotor magnetic pole and the power supply voltage waveform reaches within a predetermined electrical angle, the relay driver 25 is activated to turn on the operation changeover switches SW1 and SW2, connect to the motor coil 6e, and transition to synchronous operation.

[0032] Here, we will explain an example of the startup operation. In Figure 1, when describing the energized circuit for a rotor 1 rotation angle in the range of 0° to 90°, an output signal is output from output terminal OUT1, turning on the startup transistor Q1, and startup transistors Q3 and Q5, which are connected in series with transistor Q1, also turn on. At this time, a DC current (square wave current) flows through the motor coil 6e in the direction indicated by the solid arrow α.

[0033] Next, regarding the power supply circuit for rotor 1 with a rotation angle in the range of 90° to 180°, an output signal is output from output terminal OUT2, turning on the starting transistor Q2, and also turning on the starting transistors Q4 and Q6 which are connected in series with transistor Q2. At this time, a DC current (square wave current) flows through the motor coil 6e in the direction indicated by the dashed arrow β. Note that output signals are output alternately from output terminals OUT1 and OUT2, and they are never output simultaneously.

[0034] Figure 2 shows the output waveform of the Hall element 3d (sensor output waveform), the output waveforms from the output terminals OUT1 and OUT2 of the drive control unit (microcomputer) 26, and the motor drive voltage waveform. The first half of Figure 2 is the waveform diagram during initial startup operation, and the second half is the waveform diagram of the startup operation state at synchronous rotation speed × (0.7~0.8). While the rotor 1 rotates once, the sensor output outputs an output signal (square wave) alternately in 90° increments corresponding to the N and S poles, and the output terminals OUT1 and OUT2 output an energizing signal alternately in accordance with the sensor output. The motor current is output in synchronization with the sensor output.

[0035] When the rotational speed of rotor 1 reaches a predetermined rotational speed near the synchronous rotational speed, the motor current waveform lags behind the output waveform of the detection sensor (Hall element 3c) shown in the upper part of Figure 3, as shown in the middle part, due to the influence of braking current caused by the inductance of the motor coil 6e. The middle part of Figure 3 shows the conventional motor current waveform, and the lower part shows the motor current waveform of this embodiment. At this time, the shaded area X of the conventional current waveform indicates the range of motor current flow that causes the generation of reverse torque. Because this range of current flowing in reverse exists, the rotational speed of rotor 1 may not reach the synchronous rotational speed. Therefore, as shown in the lower part of Figure 3, the motor current waveform is started while suppressing the range of motor current flow so that the direction of current switching occurs at least at the zero-crossing point (switching point) of the sensor output waveform.

[0036] Specifically, when the rotational speed of the rotor 1 increases to 70% to 80% of the synchronous rotational speed, the drive control unit 26 suppresses the energization range controlled by the output signals from output terminals OUT1 and OUT2 in Figure 2 and continues the startup operation. In Figure 2, if the energization range of the normal motor current according to the sensor output is T0 and the suppressed energization range is T1, then the energization is suppressed to a range of T1 ≈ T0 × 0.7 to 0.8.

[0037] The drive control unit 26 then controls the switching of the starting transistors Q1 to Q6 to maintain the rotor speed at a predetermined speed near the synchronous speed. When the phase difference between the rotation phase of the rotor magnetic poles and the power supply voltage waveform reaches within a predetermined electrical angle, it outputs an output signal from the output terminal OUT3 to the relay driver 25, connecting SW1 and SW2 to contacts P1 and P2 to switch to synchronous operation. At this time, in Figure 1, the AC current indicated by the dashed-dotted arrow γ supplied from the AC power supply flows through the circuit in which the AC power supply 21 and the motor coil 6e are connected in series. During synchronous engagement, the drive control unit 26 can maintain the rotational speed of the rotor 1 at a predetermined speed near the synchronous rotational speed (for example, a speed within approximately 3% of the synchronous rotational speed) by, for example, switching the starting transistors Q1 to Q6, and then switch to the synchronous operation circuit 24 by turning on the operation changeover switches SW1 and SW2 to transition to synchronous operation, thereby enabling a smooth transition.

[0038] Figures 10ABC show the sensor output waveform, power supply voltage waveform, and motor drive voltage waveform during startup, while Figures 10D and E show the sensor output waveform and power supply voltage waveform during synchronous operation. When the rotor speed reaches +3% of the synchronous speed and the phase difference between the rotor magnetic pole rotation phase (Figure 10A) and the power supply voltage waveform (Figure 10B) reaches within, for example, ±25% in electrical angle, the operation changeover switches SW1 and SW2 are switched to synchronous operation, transitioning to the synchronous operation shown in Figures 10D and E. If the DC brushless motor continues to rotate at, for example, +3% of the synchronous speed, a point will appear where the phase difference between the rotor magnetic pole rotation phase and the power supply voltage waveform matches within a predetermined range, as shown in Figures 10A and B. Note that the sensor output waveform and motor drive voltage waveform during synchronous operation are almost the same as those in Figures 10D and E.

[0039] Figure 11 shows an example of a back electromotive force waveform during startup. When the back electromotive force waveform follows a sine curve, the generation of reverse rotation torque is suppressed, improving the motor's power factor and thus the power efficiency. Figure 12A is an explanatory diagram comparing the maximum efficiencies of a single-phase AC 4-pole synchronous motor, an AC 4-pole induction motor, and a DC 4-pole brushless motor in the 8W output class. It was found that while the maximum efficiency of the AC 4-pole induction motor and the DC 4-pole brushless motor is around 50%, the maximum efficiency of the single-phase AC 4-pole synchronous motor is around 85%.

[0040] Figure 12B is a graph comparing the torque and output efficiency of the aforementioned 8W class motors. According to this, while the output efficiency of AC 4-pole induction motors and DC 4-pole brushless motors drops to about 50% of their maximum efficiency when operated at maximum output (e.g., 8W), the output efficiency of a single-phase AC 4-pole synchronous motor remains at its maximum efficiency of about 85% when operated at maximum output (e.g., 8W). Therefore, it can be seen that single-phase AC 4-pole synchronous motors offer tremendous energy-saving benefits when operated continuously for long periods at maximum output (e.g., 8W).

[0041] As explained above, when the circumferential expansion angle θ of the tip of the teeth portion 6c of the stator core 6a is set to a central angle of 65°, and the effective magnetization angle due to the trapezoidal wave of each magnetic pole of the rotor magnet 5c is set to 62°±5°, the back electromotive force waveform generated when the rotor magnetic poles switch will draw a sine wave curve, improving motor efficiency and enabling stable synchronous pulling. Furthermore, since at least the first resin sheet material 8a and the second resin sheet material 8b are overlapped axially between the housing body 2 and the top cover 1, and the first resin sheet material 8a is assembled with an O-ring 9 between it and the top cover 1, the waterproof performance of the motor can be enhanced to withstand harsh operating environments.

[0042] The above example illustrates a single-phase AC 4-pole synchronous motor, but the configuration and drive control of the starting operation circuit 20 described above can also be applied to other synchronous motors such as 4-pole, 6-pole, and 8-pole motors. [Explanation of Symbols]

[0043] M Single-phase AC 4-pole synchronous motor 1 Top cover 1a Set screw 2 Housing body 3 Lower housing 3a Wiring board 3b Boss part 3c Sensor board 3d Hall element 3e Power supply line 3f Holder 4 Motor case 5 Rotor 5a Output shaft 5b Rotor yoke 5c Cylindrical part 5d Rotor magnet 6 Stator 6a Stator core 6b Core center 6b1 Through hole 6c Teeth part 6c1 Stepped part 6d Bobbin 6e Motor coil 6f Fixing screw 7a,7b Bearing 8a First resin sheet material 8b Second resin sheet material 9 O-ring 10 Wave washer 11 Gap part 12 Grease 20 Startup operation circuit 21 AC power supply 22 Rectifier bridge circuit 23 Filter circuit Q1~Q6 Startup transistor 24 Synchronous operation circuit SW1, SW2 Operation changeover switch 25 Relay driver 26 Drive control unit

Claims

1. A single-phase AC 4-pole synchronous motor is provided, comprising: a rotor on which a cylindrical rotor yoke is mounted on an output shaft rotatably supported through a stator core, and an annular rotor magnet with four poles of alternating N and S poles magnetized on the inner circumferential surface of the rotor yoke; and a stator having a stator core with teeth portions projecting radially from the center of the annular core at 90° different phases, and motor coils wound on the teeth portions facing each other radially around the output shaft with different winding directions; and a single-phase AC 4-pole synchronous motor which starts up by switching a starting switching means according to a detection signal from a detection sensor while the AC power supply is connected to the starting operation circuit, and switches to the synchronous operation circuit for synchronous operation when the rotor rotation speed reaches a predetermined rotation speed near the synchronous rotation speed. A single-phase AC four-pole synchronous motor characterized in that the stator core has teeth with different shapes on both sides of the radial centerline of the teeth so asymmetrically with respect to the centerline of the teeth, the circumferential expansion angle θ of the tip of the teeth is set to 65° in central angle, and the effective magnetization angle of each magnetic pole of the rotor magnet, which is positioned opposite the tip of the teeth, is set to 62° ± 5° due to trapezoidal wave magnetization.

2. The single-phase AC 4-pole synchronous motor according to claim 1, wherein the output shaft is rotatably supported by a pair of bearings concentrically assembled to the housing body and the lower housing, and at least an annular first resin sheet material and an annular second resin sheet material are mounted in the axial direction between the housing body and the lid, and a sealing material is assembled between the first resin sheet material and the lid.

3. The single-phase AC 4-pole synchronous motor according to claim 2, wherein the radial dimension of the first resin sheet material is larger than that of the second resin sheet material, and these are superimposed on the housing body with the same outer diameter, causing the excess portion on the inner diameter side of the first resin sheet material to flex along the output shaft, and lubricating oil is filled into the gap formed between the first resin sheet material and the second resin sheet material around the output shaft.

4. The single-phase AC 4-pole synchronous motor according to claim 2 or claim 3, wherein the first resin sheet material and the second resin sheet material are resin sheet materials in which fluororesin is added to a PPS (polyphenylene sulfide) resin material.

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