Thermostat

A thermostat has a switch, a temperature sensor, a lever, a spring, and a control plate. The sensor generates a force to operate switch in response to the ambient temperature. The lever having an arm turns with the force from the sensor to open/close contacts of the switch. The first end of the spring is hooked to the lever to bias a force to the lever in the direction opposite to the force from the sensor. The control plate is hooked to the second end of the spring and is disposed on the lever, allowing a force for turning the lever to increase or to decrease due to turning of the control plate. The control plate turns the arm to perform the forced switch-off operation.

FIELD OF THE INVENTION

The present invention relates to a thermostat having a forced switch-off mechanism.

BACKGROUND ART

In cold regions, a refrigerator is sometimes cut off electric functions completely to be used as a cabinet or a pantry for food storage. Additionally, because of installation location or the like of a refrigerator, user in some cases may want to switch off the power supply without taking trouble to disconnect the plug from the outlet. A thermostat having a forced switch-off mechanism matches both of above needs. Such a thermostat is disclosed for instance in Japanese Utility Model Unexamined Publication No. S54-45980. Next, a conventional thermostat is described with reference to drawings.

FIG. 4shows a sectional view of a conventional thermostat andFIG. 5shows a plan view of a cam body of the conventional thermostat. Sensor1converts temperature changes in a control section into pressure changes. L-shaped operation member (operation member)2makes contact with sensor1and can turn around supporting axis13. An end of spring3is hooked near an end of vertical member2B of operation member2and the other end of spring3is fixed to screw4that is screwed in housing12. An end of rod5is fixed to vertical member2B of operation member2and the other end of rod5is fixed to contact plate6. Contact plate6is provided with moving contact7on its free end and is fixed to a terminal in the other end. Moving contact7connects to or disconnects from stationary contact8. Cam10has curved surface14on circular cam body9internally. Finger grip shaft11protrudes out of housing12. In the configuration described above, curved surface14of cam10makes contact with the distal end of vertical member2B of operation member2, allowing operation member2to slide along curved surface14.

Next, operations of the thermostat having aforesaid configuration are described. Upon an increase in temperature of the control section, sensor1extends to move operation member2pivotally counterclockwise around supporting axis13. When temperature of the control section exceeds a set-temperature, operation member2presses rod5leftward in the drawing against an elastic force of spring3(corresponding to the set-temperature) set by screw4. Rod5presses contact plate6to connect moving contact7to stationary contact8, causing a circuit for power supply to be closed.

On the other hand, upon a decrease in temperature of the control section, sensor1contracts to move operation member2pivotally clockwise around supporting axis13with the elastic force of spring3. Then the pressure on contact plate6affected by rod5decreases gradually to reverse contact plate6at a predetermined temperature, causing moving contact7to disconnect from stationary contact8thereby causing the circuit for power supply to be opened. Thus, the thermostat can keep the temperature of the control section in a predetermined range.

Next, an operation forcing to open contacts independently of the temperature of the control section is described. Cam body9is moved pivotally in the direction indicated by arrow B to make a contact of curved surface14with the distal end of vertical member2B of operation member2causing vertical member2B to slide along curved surface14. Then curved surface14moves operation member2pivotally clockwise around supporting axis13. This releases the pressure affected by rod5to contact plate6to disconnect moving contact7from stationary contact8. Closed contacts can be thus forced to open.

In the conventional configuration, rotating finger grip shaft11can force the thermostat to be switched off. At the time, the distal end of operation member2is forced to slide along curved surface14of cam body9. However, a frictional force between the distal end of operation member2and curved surface14, a surface condition of curved surface14and the like would likely to increase torque forces to rotate finger grip shaft11. Moreover, the distal end of operation member2is applied pressures in two directions: leftward and frontward in the drawing. As a result, supporting axis13of operation member2is applied pressures in the similar directions, causing a position of supporting axis13to deflect from the position before the forced switch-off operation. This has risks to change the elastic force magnitude of spring3causing the set temperature to change.

SUMMARY OF THE INVENTION

A thermostat in the present invention has a switch, a temperature sensor, a lever, a spring, and a control plate. The sensor generates a force to operate the switch in response to an ambient temperature. The lever provided with an arm turns by the force from the sensor to open/close contacts of the switch. The first end of spring is hooked to the lever to apply a biasing force to the lever in the direction opposite to the force from the sensor. The control plate hooks the second end of the spring and is disposed with the lever to increase or to decrease a force needed to move the lever pivotally. The control plate allows the arm to turn causing a forced switch off operation. As the force to affect the arm is determined with a pressure in the direction from the control plate only in this configuration, a torque force to rotate the finger grip shaft can be stable because it would not be influenced by surface conditions or precisions of parts.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1Aillustrates a partial perspective sectional view of a thermostat in an exemplary embodiment of the present invention,FIG. 1Billustrates an exploded perspective view showing an essential part of the thermostat,FIG. 2illustrates a plan view showing a forced switch-off position of a cam of the thermostat, andFIG. 3illustrates a plan view showing a normal position of the cam of the thermostat.

As shown inFIGS. 1A,1B,2and3, temperature sensor22is mounted on housing21. Sensor22is provided with bellows22A to which capillary tube23is connected. Capillary tube23includes a gas that expand or contract in response to an ambient temperature. Bellows22A converts volume changes of the gas into a force to operate a switch. Generally Z shaped lever24is disposed pivotably around supporting point24A. First vertical member24B of lever24makes contact with free end22B of bellows22A to receive the force from sensor22. Horizontal member24D is disposed perpendicular to first vertical member24B. Second vertical member24C is disposed on horizontal member24D on a side identical to arm30and is hooked with an end of spring25for temperature setting.

Spacer29is disposed on horizontal member24D on a side opposite to second vertical member24C. Spacer29allows switch28to be on/off, in which stationary contact26makes contact with moving contact27and come free from the same. L-shaped arm30is disposed on an end of horizontal member24D. Arm30has ridge30A facing second vertical member24C of lever24.

The other end of spring25is screwed to control plate32via screw31. Control plate32is disposed pivotably around bottom supporting point32A on housing21, and the top end of control plate32is appressed to cam plate34having finger grip shaft33for operation temperature setting. Additionally, control plate32is disposed in a manner that control plate32makes contact with an end of arm30only when cam plate34turns at a predetermined angle for forced switch-off operation.

Next, the operation of the thermostat having aforesaid configuration is described. Upon an increase in temperature of sensor22, bellows22A extends to move lever24pivotally counterclockwise around supporting point24A provided at the end of vertical member24B. When a temperature of sensor22exceeds a set-temperature, lever24turns counterclockwise against the elastic force of spring3(corresponding to the set-temperature) set by screw31. Then spacer29allows switch28to connect stationary contact26and moving contact27to switch the power supply on.

Contrarily, upon a decrease in temperature of sensor22, bellows22A contracts to move lever24pivotally clockwise around supporting point24A due to the elastic force of spring25. At that time, the pressure affected on switch28by spacer29decreases gradually, causing moving contact7to disconnect from stationary contact8to switch the power supply off.

Next, the operation forced to open contacts independently of the temperature of sensor22is described. At the forced switch-off operation, control plate32turns in the direction indicated by arrow A against an elastic force of spring3as shown inFIGS. 1A and 2by the turn of cam plate34. At the time, the end of control plate32as well as arm30disposed on lever24turns in the direction indicated by arrow A to move lever24pivotally clockwise. This reduces the pressure from spacer29causing stationary contact26and moving contact27to be separated, and the power supply to be switched off. That is, at the forced switch-off operation, arm30receives a force in a direction from control plate32only. Therefore, torque to rotate finger grip shaft33can hardly be influenced by the parts precisions and the surface conditions of arm30, control plate32and cam plate34. Additionally, when control plate32moves arm30pivotally for the forced switch-off operation, no force in the bending direction will be applied on the axis of turning, resulting in elimination of the deflection of supporting point24A, which may be caused by the turning.

As described above, the thermostat disclosed in the embodiment includes switch28, sensor22, lever24having arm30, spring25and control plate32. Sensor22has bellows22A and capillary tube23. Bellows22A converts expansive or contractive volume changes of a gas therein in response to an ambient temperature to a force for operating switch28. The force from sensor22moves lever24pivotally around the supporting point24A to make stationary contact26contact with moving contact27of switch28and make stationary contact26release moving contact27. That is, sensor22can generate a force to operate switch28in response to the ambient temperature. Other devices such as bimetals or the like may replace sensor22. The first end of spring25is hooked to lever24to bias a force on lever24in the direction opposite to the force from sensor22. Control plate32is hooked to the second end of spring25and is disposed on lever24to turn around the supporting point32A allowing the force needed for turning of lever24to increase or to decrease. Finger grip shaft33has cam plate34to move control plate32pivotally. Arm30turns together with control plate32to open switch28, when cam plate34moves control plate32pivotally at more than a predetermined angle. Additionally, though cam plate34enables easier control of the pivotal movement of control plate32, other way such as for instance a latch, provided on housing21, that engages with control plate32to control pivotal movement positions of control plate32may also be acceptable.

In the thermostat with such a configuration, the force to affect arm30at the forced switch-off operation is determined with a pressure in only one direction from control plate32that is in contact with arm30.

The torque, therefore, to rotate finger grip shaft33is stable because it would not be influenced by dimensional precisions and surface conditions of the parts to achieve a reliable forced switch-off operation. Pivotal movement axes of control plate32and lever24are placed in parallel with each other. This configuration provides the pivotal movement axis of lever24with no bending force when control plate32presses lever24to turn it. This can eliminate the deflection of supporting point24A of lever24, resulting in a stable set temperature, as the elastic force of spring25cannot be changed easily. Moreover, raised ridge30A is provided on arm30on the side facing control plate32such that control plate32makes contact with ridge30A. This can determine the contacting position of control plate32to ridge30A so that the ratio of displacements of control plate32by pivotal movements to displacements of arm30has a constant value. Consequently, switch28is opened at a predetermined position enabling to allow the forced switch-off operation at a constant angle of cam plate34. The configuration can provide the thermostat with a high reliability, as arm30itself is stronger than a plane structure to improve bearing strength for the forced switch-off operation.

As described above, the thermostat according to the present invention has a high reliability, as the torque to rotate the finger grip shaft is not influenced by the surface conditions and dimensional precisions of parts used. Such a thermostat is suitable for equipment that needs a thermostat with a forced switch-off function for use in cold regions.