Centrifugal switching device of single-phase induction motor

A centrifugal switching device of a single-phase induction motor includes a centrifuge and pressure switches. The centrifuge includes a centrifugal sleeve, a centrifugal base, shaft coupling blocks, and a spring. The spring is directly fitted on the centrifugal base. Under a centrifugal force generated by the rotation of the motor, shaft coupling blocks I and II slide axially against an axial force of the spring, thus forcing an axial end surface of the centrifugal sleeve to be separated from contacts of the pressure switches, such that a starting winding of a stator ferrite-core coil of the single-phase induction motor is disconnected and a heater is turned on. The shaft coupling blocks I and II adopt a design with round transition, central sliding contact, and smooth rotation, thereby achieving a simple structure, convenient mounting, and safety usage.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application claims the priority of the Chinese patent application No. 200710191471.5 filed on Dec. 19, 2007, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a centrifugal switching device of a single-phase induction motor.

2. Related Art

Since single-phase induction motor has a simple but firm structure, and a single-phase power supply can be easily found, the single-phase induction motor serving as a driving motor for electrical appliances is widely applied in family, office, industry, and agriculture. However, the motor cannot activate automatically. Therefore, in order to generate a starting torque, besides an operating winding, a starting winding having a phase difference with the operating winding should be further provided. When the rotating speed of a rotator reaches 70%-80% of the synchronous speed, a centrifugal switching device is activated to disconnect the starting winding.

The centrifugal switch has an operating winding and a starting winding. The starting winding has a large resistance, and a start switch is serially-connected. When the rotating speed reaches 75%-80% of the synchronous speed, the centrifugal switch is turned off to disconnect the starting winding from the power supply. The operating winding has a small resistance and a large reactance, and the starting winding has a large resistance and a small reactance. Under different impedance ratios of the two-phase winding, the two-phase current has different phases, and thus a rotating magnetic field is generated to activate the motor with a required starting torque.

Hereinafter, the conventional centrifugal switching device of a single-phase induction motor is illustrated with the accompanying drawings.

Referring toFIGS. 1 and 2, the centrifugal switch driving device of a single-phase induction motor includes a sleeve20, a slider30, a centrifugal switch60, a pair of governor weights40, and a pair of springs50. The sleeve20is rotatably integrated with a spindle10of the single-phase induction motor. The slider30is rotatably integrated with the sleeve20and formed with a collar32of an expanded diameter, and the collar32, when sliding in an axial direction of the spindle10with respect to the sleeve20, contacts a movable control rod62of a centrifugal switch60, so as to turn on/off the centrifugal switch60. The centrifugal switch60forms an open circuit from a secondary coil to a primary coil enwinding the stator of the single-phase induction motor due to the operation of the slider30. The pair of governor weights40is joined to the slider30and capable of moving with respect to the same, and rotate under a centrifugal force generated by the rotation of the spindle10, so as to force the slider30to move in the axial direction with respect to the sleeve20. The pair of springs50has one end joined to the governor weights40respectively, and provides an elastic force in a direction of drawing the governor weights40closer.

The centrifugal switch60includes a housing61with a certain internal space, a movable control rod62, a spring63, a first leaf spring switch control rod65, a second leaf spring switch control rod67, a secondary coil terminal68, a heater power terminal69a, and a heater power terminal69b. The movable control rod62is constituted by a hinge axis62ahinged to the housing61and serving as a reference, a collar contact portion62bformed on an opening portion of the housing61and exposed for contacting the above collar32, and a contact driving portion62cprotruding toward the internal side of the housing61. The spring63is used for elastically supporting the contact driving portion62cof the movable control rod62. The first leaf spring switch control rod65, mounted adjacent to the contact driving portion62c, has one side fixed to a primary coil terminal64, and protrudes out a certain length in order to gain elasticity. The second leaf spring switch control rod67, mounted adjacent to the contact driving portion62c, has one side fixed to a heater power terminal66, and protrudes out a certain length to gain elasticity. The secondary coil terminal68and the heater power terminal69aare correspondingly mounted at two sides of the other distal end of the first leaf spring switch control rod65, and are controlled by the first leaf spring switch control rod65to turn on/off. The heater power terminal69bis mounted adjacent to the other distal end of the second leaf spring switch control rod67, and is controlled by the second leaf spring switch control rod67to turn on/off.

Moreover, in order to turn on/off the first leaf spring switch control rod65and the second leaf spring switch control rod67, a pressure should be exerted. Therefore, at an distal end of the above contact driving portion62c, a pressing protrusion62dprotruding a certain height is respectively formed at a position adjacent to the first leaf spring switch control rod65and the second leaf spring switch control rod67.

Based on the above structure, the conventional centrifugal switch driving device of a single-phase induction motor operates in the following manner.

When the spindle10stops, under the elastic force of the spring50, the governor weights40are set at an original position close to the spindle10, and the slider30is disposed at a position far from a guide device. At this time, as shown inFIG. 2, the collar contact portion62bof the movable control rod62remains in a pressed state via the collar62. Moreover, as the pressing protrusions62dformed at the distal end of the contact driving portion62crespectively exert a pressure on the first leaf spring switch control rod65and the second leaf spring switch control rod67, the distal ends of the two control rods are respectively connected to the secondary coil terminal68, such that the primary coil terminal64is connected to the secondary coil terminal68. Thereby, a power is supplied to the primary coil and the secondary coil, and the spindle10starts rotating.

Once the rotating speed of the spindle10reaches 70%-80% of the synchronous speed, the centrifugal force exerted on the governor weights40is larger than the pulling force of the spring50. Thus, one side of each governor weight40moves outward along with the guide device, and meanwhile the other side movable with respect to the slider30moves toward the guide device. In this manner, the slider30moves in the axial direction of the spindle10toward the guide device.

At this time, the collar32originally exerting a pressure on the collar contact portion62bof the movable control rod62is removed, so as to release the collar contact portion62bfrom the pressed state. Moreover, under the elastic force of the spring63for elastically supporting the contact driving portion62c, the movable control rod62, as shown inFIG. 2, rotates counterclockwise.

Along with the rotation of the movable control rod62, the pressing protrusions62dformed at the distal end of the contact driving portion62calso release the pressure exerted on the first leaf spring switch control rod65and the second leaf spring switch control rod67respectively. Therefore, the first leaf spring switch control rod65and the second leaf spring switch control rod67moves toward the movable control rod62under the elastic forces of their own. At this time, the distal end at the other side of the first leaf spring switch control rod65assumes a turn-off state relative to the secondary coil terminal68and assumes a turn-on state relative to the heater connecting terminal69a, and the second leaf spring switch control rod67turns from a turn-off state to a turned-on state relative to the heater connecting terminal69b. That is, when turning into an open-circuit state, the primary coil and the secondary coil assume a closed-circuit state relative to the heater connecting terminal69a, and thus the spindle10continues to rotate only by the power provided for the primary coil.

In view of the above, in the conventional centrifugal switch of a single-phase induction motor, when the motor rotates and reaches a certain rotating speed, the governor weights used for balancing the weight stretch in the radial direction under the centrifugal force, and thus the movable collar slides along the spindle. Due to the movement of the movable collar, the movable control rod of the centrifugal switch is driven to operate the switches in the housing, and as the governor weights stretching in the radial direction under the centrifugal force are pulled by the springs during the operation, once the motor stops, the governor weights will restore to their original positions under the elastic restoring force of the springs. In the above processes, the following problems may occur. As the movable control rod62always operates at one side of the circle, the slider30may be easily seized during the actuation, and in the long run, the spring may rupture or the governor weights may generate noises. Further, the structure of the movable control rod62is complicated and constituted by a plurality of different parts, so during the assembling of the whole movable portion, additional processes are needed, thus prolonging the assembling time and reducing the productivity.

Meanwhile, the conventional product also has a problem that, electric sparks may easily occur due to a long switching time during the operation of the first leaf spring switch control rod and the second leaf spring switch control rod in the switching structure, and a large transient current will be generated to damage the motor and even cause fire.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a centrifugal switch driving device of a single-phase induction motor, which may effectively overcome the defects in the conventional art. The centrifugal switching device of a single-phase induction motor provided by the present invention includes a centrifugal sleeve, a centrifugal base, a first shaft coupling block (also referred to as a shaft coupling block I), a second shaft coupling block (also referred to as a shaft coupling block II), a spring, and pressure switches. The present invention is characterized in that: the first and second shaft coupling blocks are designed to be coupled through a straight pin, and have a smooth rotation without making any noise; the first and second shaft coupling blocks are designed to slide axially to prevent the centrifugal switch from being easily damaged; the spring is directly fitted on an outer cylindrical surface of the centrifugal base, the centrifugal sleeve moves axially under a uniform force exerted by the spring; and an axial end surface of the centrifugal sleeve transiently releases contacts of the pressure switches.

The technical solutions adopted by the present invention for solving the technical problem are as follows.

1. The conventional centrifuge has the following defects: a centrifugal hammer and the centrifugal sleeve contact in a linear way, the centrifugal hammer is usually made of metal, and the centrifugal sleeve is usually made of plastic. Thereby, after a long time of operation, the centrifugal sleeve will be abraded and separated from the centrifugal hammer, and thus the stated functions cannot be achieved. However, in the present invention, the centrifugal switch of a motor employs the first and second shaft coupling blocks with round transition, central sliding contact, and smooth rotation without making any noise, thereby solving the defects in the above conventional structure.
2. The spring (12) in the conventional centrifugal switch operates in the radial direction of the spindle (10), such that the centrifugal sleeve (16) suffers a non-uniform force. However, the spring (12) in the present invention is directly fitted on the centrifugal base (17), and operates in the axial direction of the spindle (10), thus having a simple and practical structure.
3. The centrifugal hammer of the conventional centrifuge has to be mounted passing through a slide bar and engaged with the spring, so the fabrication and assembling processes are difficult. On the contrary, the spring in the present invention is directly fitted on the centrifugal base, and the shaft couplers1and2are mounted through a pin, which is rather simple and convenient.
4. The axial end surface of the centrifugal sleeve (16) transiently releases the contacts (112) of the winding pressure switch (22) and the heater pressure switch (25), and the pressure switches suffer a uniform force.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be further illustrated below with the accompanying drawings.

Referring toFIGS. 3 and 4, a single-phase induction motor includes a centrifugal switch (60), a winding pressure switch (22), a heater pressure switch (25), and a spindle (10). Under the centrifugal force generated by rotation, the centrifugal sleeve (16) rotating together with the spindle of the motor makes the first shaft coupling block (13) and the second shaft coupling block (14) slide in an axial direction of the spindle, so as to be separated from the winding pressure switch (22) to disconnect the starting winding enwinding the single-phase induction motor, and to be separated from the heater pressure switch (25) to turn on the heater. When the rotating speed is lowered, the centrifugal sleeve (16) is restored by the force of a spring. The spring (12) in the conventional centrifugal switch operates in the radial direction of the spindle (10), such that the centrifugal sleeve (16) suffers a non-uniform force. However, the spring in the present invention is directly fitted on the centrifugal base (17), and operates in the axial direction of the spindle (10), so the centrifugal sleeve (16) suffers a uniform force, and has a simple and practical structure.

The first shaft coupling block (13) and the second shaft coupling block (14) are connected through a straight pin (15), the first shaft coupling block (13) is connected to the centrifugal base (17), and the second shaft coupling block (14) is connected to the centrifugal sleeve (16). The spindle (10) is interference fit into an inner hole of the centrifugal base (17). The fast rotation of the spindle (10) propels the centrifugal sleeve (16) and the centrifugal base (17) to rotate at a high speed. Thus, when the rotating speed reaches 70%-80% of the synchronous speed of the motor, the centrifugal sleeve (16) moves in the axial direction under the effect of the centrifugal force, such that the axial end surface of the centrifugal sleeve (16) is separated from the two winding pressure switches (22), so as to disconnect the starting winding.

FIG. 5shows parts of the centrifugal sleeve (16). A pin hole (161) is connected to a pin hole (141) of the second shaft coupling block (14), and a guide block (162) matches a guide slot (173) in the centrifugal base (17), such that the centrifugal sleeve (16) moves in an axial direction.

FIG. 6shows parts of the centrifugal base. The spring (12) is directly fitted on an outer cylindrical surface of the centrifugal base (17). When the rotating speed is lowered, the centrifugal sleeve (16) is restored by the force of the spring (12). The spring (12) in the conventional centrifugal switch operates in the radial direction of the spindle (10), such that the centrifugal sleeve (16) suffers a non-uniform force. However, the spring in the present invention is directly fitted on the centrifugal base (17), and operates in the axial direction of the spindle (10), thus achieving a simple and practical structure.

FIG. 7shows a pressure switch, in which the winding pressure switch (22) and the heater pressure switch (25) each have a contact (112) and a rivet hole (113), and the rivet holes (113) are directly riveted to the end covers.

FIG. 8is a schematic view of a normal-off pressure switch. When the pressure switch is in the normal-off state, a normal-off contact is in a normal-off state under the effect of a spring sheet1and a spring sheet2.

FIG. 9is a schematic view of a normal-on pressure switch. When an operation button moves upward under an external mechanical force, the normal-off contact quickly moves downward under the effect of the spring sheets1and2, and a contact at the right end of a moveable spring turns to contact a normal-on contact, so as to realize the circuit switching. When the external force is removed, the contact will switch transiently under the restoring force of the spring.

The pressure switch is a device having a small displacement and doing transient action. Under a small force and after a certain displacement, the contact of the pressure switch acts quickly to accomplish the circuit switching. When an external mechanical force is exerted on the operation button, the operation button quickly moves downward to stretch the spring via a hook. When the spring is stretched to a certain extent, the moveable spring quickly moves downward, and the contact at the right end of the moveable spring turns to contact the normal-on contact below, so as to realize the circuit switching. When the external force is removed, the contact will switch transiently under the restoring force of the spring.

Referring toFIGS. 10 and 11, the pin hole (141) of the second shaft coupling block (14) is connected to the pin hole (161) of the centrifugal sleeve (16), the first shaft coupling block (13) and the second shaft coupling block (14) are integrated with a straight pin hole (131) and a straight pin hole (142) through the straight pin (15), and a guide pole (132) matches a slot hole (171) in the centrifugal base (17), thereby achieving a smooth connection without making any noise.