JPS6215034B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Prior U.S. Pat. These control circuits are connected to a triax connected in series with the starting winding and to the gate of this triax,
It includes a timing circuit to turn it on and provide input to the starting winding for a predetermined period of time measured from the start of input to the motor. This timing circuit is heated to a transition temperature for a stated period of time and shuts off the triax when heated above this transition temperature.
Includes PTC resistor.

Although this type of circuit performs satisfactorily, it has many drawbacks. These circuits contain a large number of components, making them expensive, increasing the chance of failure, and difficult to package compactly. Furthermore,
The time required for the PTC resistance to transition from a low resistance state to a high resistance state is relatively long, and this transition occurs over many cycles of the AC power supply. Because triaxes are usually not completely symmetrical devices, they often produce half-wave operation during the transition time.
This is equivalent to introducing a DC component into the power supply line, and a motor with such a control circuit will generate noise during the transition period.

A general object of the invention is to provide an improved control circuit that does not suffer from the above-mentioned drawbacks.

The control circuit according to the present invention is a starting winding cutoff circuit for an AC motor in which a starting winding is connected in parallel with a main winding connected to an AC power supply line. A two-way electronic switch is connected in series with the starting winding. Connect a thermal switch to activate the electronic switch. The thermal switch includes a U-shaped self-heating bimetallic conductive member formed by a central portion and two legs that move during self-heating.

The thermal switch further includes a switch contact operated by the electrically conductive member to control operation of the electronic switch. One of the contacts is connected to the central portion of the conductive member and the other contact is connected to the gate of the electronic switch. An auxiliary coil is inductively connected to both windings by being substantially centrally located between the central axis of the main winding and the starting winding. A voltage is continuously induced in the auxiliary coil by the main winding, and a voltage is induced in the auxiliary coil by the starting winding only when the electronic switch is turned on by the thermal switch. The auxiliary coil is connected to one of the legs of the conductive member to supply current to the conductive member for heating the conductive member with an induced current. Connect the other leg to one of the power supply lines. The one of the contacts is connected to the other of the power supply line.

These and other objects and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

The drawing is a schematic diagram of a control circuit according to the invention.

The drawing diagrammatically shows an AC motor of the split-phase induction type with a main winding 101 and a starting winding 102 .
Both windings 101 and 102 are wound around a stator (not shown) of a motor and are displaced from each other by 90 electrical degrees. As is well known in the art, in order to obtain the starting torque of an electric motor, the main winding 102 is connected to the starting winding 102.
By providing a reactance different from 1, a displacement in time or phase is generated between both windings.
One side of each winding 101, 102 is a power supply line 104
The other side of the main winding 101 is connected to the power supply line 10
Connect to 3. Both wires 103, 104 connect to an AC power source, such as a 60 cycle single phase AC power source.

The main winding 101 is directly connected to both power supply lines 103, 104, while the starting winding 102 can be connected to both power supply lines by means of a control circuit. This control circuit allows energization of the starting winding 102 for a short time or period during the initial energization of the motor. This time period may be, for example, one-half second long. As described below, starting winding 102 may also be re-energized if the motor stalls. The control circuit includes a selectively closeable two-way electronic switch, generally known as a triax, designated by the reference numeral 107. Triax 107 has a first main (power) terminal 108 , a second main (power) terminal 109 and a gate 111 . As is well known in the art, the triax 107 provides a low resistance path between the main terminals 108 and 109 when a potential is present between the main terminals 108 and 109 and a trigger signal is present on the gate 111 during each AC half cycle. exhibits. Otherwise, triac 107 presents a very high resistance or open circuit to current between main terminals 108, 109. The main terminal 108 is the starting winding 1
02, and the other main terminal 109 is connected to the resistor 112.
It is connected to the power supply line 103 via. It is therefore clear that the starting winding 102 and the triax 107 are connected in series, and that they are connected to the main winding 101.
It is connected in parallel to power supply lines 103 and 104, and when the triax 107 is closed or triggered, the starting winding 102 is energized.

The control circuit also includes a time delay circuit 106 as a thermosensitive switch for triggering the triac 107 into conduction. Time delay circuit 106
The self-heating conductive bimetallic heat-sensitive member 113 included in this example is generally U-shaped.
The member 113 is comprised of two layers of metal, which metal layers have different coefficients of thermal expansion, as is well known. The lower ends of the legs 113a and 113b of the member 113 are fixed or held fixedly, and the movable contact 116 is fixed to the cross portion of the member 113. Fixed contact 117
is located adjacent to member 113 and contacts 116,1
17 are normally closed. However, when the member 113 is heated, it curves, and the movable contact 116 is connected to the fixed contact 1.
17 and disengage from it.

Contact 117 is called a fixed contact in this book, but
It may have some degree of flexibility. Contact 117
can be fixed to a bendable bimetallic member, and when the bimetallic member is heated, contact 117 becomes contact 1.
Move in the same direction as 16. This configuration compensates for changes in ambient temperature that can affect the operation of the circuit.

Fixed contact 117 is electrically connected to gate 111 of triac 107. A resistor 119 is connected between contact 117 and gate 111. Contact 117 is also connected to wire 104 between winding 102 and triax 107 via resistor 118 . The leg portion 113b of the member 113 is the resistor 112
electrically connect with. The other leg 113a is electrically connected to a current source, which in this embodiment consists of an auxiliary coil 114. The coil 114 has a leg portion 113a.
and the power line 103, and as can be seen, when a voltage is induced in the coil 114, current flows through the loop that includes the coil 114, both legs of the bimetallic member 113, and the line 103, and as shown in the coil 114.
Return to The coil 114 has an angular displacement from the main winding 101 and is mounted on the stator of the motor so that it is electrically located between both windings 101,102.

To describe the operation of this circuit, the power lines 103, 10
4 is connected to an AC power source, the current flows through the main winding 101.
flows. Initially, member 113 is cold and contacts 116, 117 are in electrical engagement. During a particular half cycle of the supply voltage, substantially the entire line potential appears across the main terminals 108, 109 of the triac 107 as the supply voltage begins to increase above zero. Due to the potential between the main terminals, a current flows from the main terminal 108 through the internal triac resistor between this terminal 108 and the gate 111, and the resistor 119,
It flows through contacts 116, 117 and member 113 to power line 103. As the supply voltage increases during the AC half cycle, terminal 108 and gate 1
The current between terminals 11 and 11 increases, and the potential between terminals 108 and 109 also increases. If the gate current is, for example, 20~
When it reaches 30 milliamps, the triax 107
is triggered on and the total starting winding current is in winding 10
2 and triax 107. This occurs very early in the half-cycle, and current continues to flow until the end of the AC half-cycle, when the triac 1
07 is cut at the next zero intersection. Of course, the above sequence of events occurs again in the next AC half-cycle until contacts 116 and 117 open, interrupting the current path through gate 111. This gate current is
13, but not enough to significantly heat member 113. Once triac 107 is triggered, the current flowing through gate 111 is limited by the short circuit formed by the conducting triac. The only voltage appearing on gate 111 is the triac forward voltage drop, which is of course extremely low. Therefore, no gate resistance is required as is normally required in conventional circuits. Deleterious current surges in the gate circuit are prevented by the inductance of the starting winding 102.

The current flowing through the motor windings also induces a voltage in coil 114. This induced voltage causes current to flow through the coil 114 and the leg portions 113a and 11 of the member 113.
Flows through 3b.

This current causes resistance or self-heating of the two metal layers of member 113, and after some time, member 1
13 becomes sufficiently heated and curves, opening the normally closed contacts 116, 117. The length of this time mainly depends on the dimensions and mass of the member 113, the type of metal, the number of turns of the coil 114, and the size and mass of the member 113.
It is determined by the amount of heat lost from 3. This length is selected to correspond to the time normally required for the motor to reach cutout speed when driving the motor's design load. For example, an electric motor designed to drive a groundwater pump will reach cutout speed in about 0.5 seconds.

As already mentioned, contacts 116, 117 open at the end of a preselected time. After that, coil 11
The voltage induced in 4 and the resulting current flowing in bimetallic member 113 causes member 113 to
The contact is kept open by keeping it heated. During operation of the electric motor, the rotor has coil 11
4, the induced current is sufficient to keep member 113 heated and contacts 116, 117 open.

When contacts 116, 117 open, the only current flowing through them is the residual current flowing through the gate 111 circuit after the triax has been triggered, which is extremely small. Therefore, contacts 116, 117 can be made very small and durable for long-term use.

This circuit has many advantages. Since the bimetallic member 113 carries only a small portion of the starting winding current, it can be made very small. This small size provides little thermal inertia, so member 113 heats up quickly and cools relatively quickly when the motor stalls, triggering triax 107 and re-energizing the starting winding. . As an example, the leg member 113
The overall length of members a, 113b may be about one-quarter inch, and the overall width of member 113 in the other direction may be about one-eighth of an inch.

Another advantage derived from the small dimensions of the bimetallic part 113 is that very little current is required to heat it. Coil 114 may need only one or a few turns around a few teeth of the stator to heat member 113 and contact points 116,1.
After 17 opens, provide sufficient current to keep it heated. A heat sink or other circuit component may be provided adjacent member 113 to prevent damage to member 113 due to overheating after contacts 116, 117 open. Such heat sinks and components, however, will not have a significant effect on operation during initial excitation. This is because the member 113 heats up rapidly and does not lose a large amount of heat.

A further advantage of this circuit is that at the moment of initial energization of the motor, all of the supply voltage is applied to contacts 116, 117.
, so there are no problems due to insufficient electrical contact. Nevertheless,
No problems arise due to current accumulation in the gate 111 circuit. This is because the rapid excitation of triac 107 limits the current, thereby preventing damage to contacts 116 and 117.

As already mentioned, the auxiliary coil 114 is wound on the stator so that it is electrically intermediate between the motor windings 101 and 102. Winding 114 is located on the stator at a point so that the current flowing through the two legs of member 113 has a phase displacement angle as close as possible to 90 degrees from the phase angle of the starting winding current flowing through the legs. do. Coil 114 may be positioned such that its current leads or lags the starting winding current by 90 degrees.

During a particular AC half cycle, the starting winding current flows from the starting winding 102 through the resistor 118;
Furthermore, the line 103 passes through both legs 113a and 113b.
flows to The current generated by the coil 114 flows from the coil 114 to the leg 113a, the leg 113b, and the wire 1.
03 and returns to the coil 114. If the starting winding current and auxiliary coil current have the same phase, then
The auxiliary coil current adds to the starting winding current flowing in one of the legs of member 113 and subtracts from the starting winding current in the other leg, so that different amounts of current flow in both legs 113a, 113b. become. However, because the auxiliary coil 114 is located on the stator at a point where the current flowing through the member 113 due to the coil 114 is displaced 90 degrees from the starting winding, the current flowing through the bimetallic member 113, the total current, and the heating effect are different. The same is true for the leg portions 113a and 113b.

While triax 107 is conducting, the starting winding current flows through triac 107 and resistor 112.
and a branch path including resistor 118 and bimetal member 113 . The proportion of starting winding current flowing through these two branches can then be adjusted by suitably choosing the relative resistances of both branches, thus obtaining the desired amount of current through member 113 and the rate of opening of the contacts. . This is resistance 11
2,118 is suitably achieved. The two resistors 112, 118 can be part of internal motor winding resistances and/or external resistors.

[Brief explanation of the drawing]

The accompanying drawing is a schematic diagram of a control circuit according to the invention. 101...Main winding, 102...Start winding, 10
3,104...Power supply line, 106...Control circuit, 107...Triack, 108,109...
...Main terminal, 111...Gate, 112...Resistance,
113...Bimetal member, 113a, 113b
... Legs, 116 ... Movable contacts, 117 ... Fixed contacts, 118, 119 ... Resistors.

Claims (1)

[Scope of Claims] 1. A starting winding cutoff circuit for an AC motor in which a starting winding 102 is connected in parallel with a main winding 101 connected to AC power supply lines 103, 104, and in series with the starting winding. Connect the two-way electronic switch 107,
In a configuration in which a heat-sensitive switch 106 is connected to operate the electronic switch 107, and the heat-sensitive switch includes a U-shaped self-heating bimetal conductive member 113 formed by a central part and two legs that move during self-heating. , switch contacts 116, 117 operated by the conductive member 113 to control operation of the electronic switch are further included in the thermal switch, one of the contacts being connected to the central portion of the conductive member and the other contact being connected to the central portion of the conductive member. is connected to the gate 111 of the electronic switch, and the auxiliary coil 114 is inductively connected to both windings by providing it substantially in the middle between the central axis of the main winding and the central axis of the starting winding. A voltage is continuously induced in the auxiliary coil by the main winding, and only when the electronic switch is turned on by the heat-sensitive switch, a voltage is induced in the auxiliary coil by the starting winding, inducing the conductive member. the auxiliary coil is connected to one of the legs of the electrically conductive member to supply current to the electrically conductive member for heating with an electric current, the other leg is connected to one of the power supply lines, and the contact point A circuit characterized in that the one of the two is connected to the other of the power supply line. 2. In claim 1, the bimetal conductive member 113 is further connected to receive the current flowing through the starting winding 102, so that the conductive member is connected to both the auxiliary coil 114 and the starting winding. A circuit characterized in that it responds to a current from. 3. In claim 1, the switch contact connected to the central portion of the bimetal conductive member 113 is a movable contact 116, and the switch contact connected to the gate 111 of the electronic switch 107 is a fixed contact 117. wherein the bimetallic conductive member heats and bends in response to a heating current flowing therethrough, and bending the bimetallic conductive member causes movement of the movable contact 116. 4. The circuit according to claim 3, wherein the fixed contact 117 and the movable contact 116 are normally closed when the bimetal conductive member 113 is at a low temperature. 5. In claim 3, the auxiliary coil 114 further includes a connection from the starting winding 102 to the bimetal conductive member 113, and the connection includes a resistor 118 and the contacts 116, 117. circuit. 6. In claim 1, the auxiliary coil 114 is arranged on the motor so that the current flowing through the bimetallic conductive member 113 due to the auxiliary coil is caused by the current in the bimetallic conductive member caused by the current from the starting winding 102. A circuit characterized in that it is wound at a position more substantially offset by 90 degrees. 7. In claim 5, a second resistor 119 is connected in series with the electronic switch 107, and the two resistors 118, 119 are sized to produce a predetermined amount of heating current in the bimetallic conductive member 113. A circuit characterized by balancing.