Dual contact bimetallic thermostat

A dual contact thermostat includes a bimetallic strip that partially controls two sets of contact points. An adjustable temperature actuator engages the contact points whereby the activation temperature of each set of points when the points are first closed is determined by the bimetallic strip in combination with the adjustable temperature actuator.

FIELD OF THE INVENTION

The present invention relates to a thermostatic control arrangement having a dual contact thermostat arrangement.

BACKGROUND OF THE INVENTION

It is know, particularly in electrical heaters, to have a system provided with two electrical heating elements and a thermostatic control for each of the heating elements. Many of these heating systems include a switch arrangement for switching between a first heating element for producing a reduced level of heat and a second heating element or combination of heating elements for producing a higher level of heat. Typically, a rocker type switch is used to switch from the low heat output to the high heat output. For example, this type of arrangement is used in a 1500 watt heater having a 1000 watt output setting and a 1500 watt output setting.

In our prior patents U.S. Pat. Nos. 6,624,397 and 6,940,051 a heating element arrangement is shown where a fan motor is associated with the heating element and the speed of the fan motor automatically adjusts to operate at a low speed under low heat output conditions and to operate at a higher speed under high heat output conditions.

In an earlier portable 1500 watt heater, two separate thermostats are mechanically connected by a gear train such that a single control knob is used to control each of the two separate thermostats. In this way the thermostats are moved in synchronization with each other and are designed to be activated at slightly different temperatures. With this arrangement, a first set of contact points make an electrical connection at a first temperature and activate a low output heating element. If this heating element is sufficient to bring the room temperature up to a particular level then this first thermostat will cut out. If the temperature continues to drop in the area being heated the second thermostat will be activated providing power to an additional heating element. With this arrangement, a user adjusts a single control knob and the two thermostats are maintained in synchronization due to the mechanical gearing of the rotary temperature actuators of each thermostat. Each thermostat is separate and distinct. This portable heater also uses the variable fan speed disclosed in U.S. Pat. Nos. 6,624,397 and 6,940,051.

Therefore this prior art heater allows operation at a lower heat output initially and automatic operation at a higher output if the temperature continues to fall. A problem with this arrangement is the time required to set up and calibrate the two thermostats. An intermediary gear can be provided between gears of each temperature actuator to allow synchronization adjustment between the thermostats. Each individual thermostat is typically calibrated when it is manufactured however the gear train accommodates synchronization between the two thermostats.

For example one of these thermostats may make contact if the room temperature is 4° F. below a particular set temperature level whereas the second thermostat is activated when the temperature drops below 8° F. from the set temperature level.

The present invention seeks to provide an improved thermostat which is cost effective to manufacture and allows convenient calibration and adjustment.

SUMMARY OF THE INVENTION

An adjustable thermostat according to the present invention comprises a bimetallic actuator, a first set of contact points and a second set of contact points, and a temperature setting actuator. The bimetallic strip engages and controls the position of a first side of each of the first and second set of points whereby the first side of the contact points move with movement of the bimetallic strip. The temperature setting actuator engages and determines the position of a second side of each of the contact points such that the second side of the contact points move in response to movement of the temperature setting actuator. With this arrangement each of the contact points open and close as a function of the bimetallic strip and the temperature setting of the temperature setting actuator.

According to an aspect of the invention the temperature setting actuator is rotary and includes a cam surface for displacing said temperature setting actuator whereby rotation of said temperature setting actuator causes the second side of the contact points to be displaced altering the temperatures at which the contact points open and close.

In a further aspect of the invention, the temperature setting actuator includes at least one adjusting member whereby a relative position of the second side of contact points to each other as controlled by the temperature actuator is adjustable.

In an aspect of the invention, the first contact points close at a first temperature and the second contact points close at a second temperature.

In yet a further aspect of the invention, the first temperature and the second temperature are within 10° F. of each other. These temperatures are within the heater and generally correspond to about a 5° F. variation in room temperature.

The adjustable thermostat according to a different aspect of the invention includes an adjustment arrangement used to control a temperature differential such that the first set of points close at a first temperature and the second set of points close at a second temperature determined by the temperature differential and the position of the temperature setting actuator.

In a preferred aspect of the invention, the adjustable thermostat includes a first adjustment arrangement used to temperature calibrate the first set of points relative to temperature sensed by the bimetallic strip, and a second adjustment arrangement used to temperature calibrate the second set of points relative to temperature sensed by the bimetallic strip.

In an aspect of the invention, each of the first and second sides of said contact points include a cantilevered leaf spring supported by a common support arrangement at one end of the leaf springs.

In an aspect of the invention, the bimetallic strip at a free end thereof includes a non conducting standoff member having spaced first and second engagement surfaces determining the relative position of the first side of said contact points as controlled by said bimetallic strip. Preferably the first and second engagement surfaces of the non conducting standoff member have a fixed relationship.

In yet a further aspect of the invention, the leaf springs of the first side of said contact points have a spring bias to maintain contact with the bimetallic strip and move in sympathy with movement of said bimetallic strip.

In an aspect of the invention, the leaf springs of the second side of the contact points are spring biased against the temperature actuator.

According to an aspect of the invention the leaf springs of the first side of the contact points are of a greater length than the leaf springs of the second side of said contact points.

According to a further aspect of the invention the bimetallic strip engages the leaf springs of the first side of the contact points at a position beyond the leaf springs of the second side of the contact points.

In a further aspect of the invention the first adjustment arrangement includes a two sided cam having a first cam surface that moves relative to a base plate to position a second cam surface of the two sided cam at a fixed calibration distance from the base plate. The second cam surface cooperates with the temperature actuator to displace the temperature actuator relative to the base plate to adjust desired opening and closing temperatures of the contact points. Preferably the two sided cam is held in a fixed position relative to the base plate after calibration of the thermostat.

According to an aspect of the invention, the second adjustment arrangement includes an adjustment member that is displaceable along a shaft of the temperature actuator to determine an end portion of the temperature actuator in engagement with the leaf spring of the second side of the contact points.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The temperature control unit2shown inFIGS. 1,2and3includes an on/off switch4for turning an electrical device, such as an electrical heater, on or off. The dual contact thermostat6includes a temperature control knob8received within the face plate10. The face plate includes a temperature range from a low temperature indicated at14to a high temperature indicated at16. The control knob8includes a position indicator9to allow the user to position the control knob at a desired temperature setting.

The dual contact thermostat6includes a bimetallic actuator20that controls the position of a first leaf spring30(and associated contact element40) and the position of a second leaf spring32(and associated contact element50). The leaf springs30and32form a first side of the contact points39and49. The leaf springs30and32are spring biased against the plastic two-stage offset member22having a projecting end24that determines the position of the leaf spring30, and an intermediate shoulder26that determines the position of leaf spring32. Further details of this structure are shown inFIG. 15. With this arrangement, the first side of the contact points39and49include lower contact elements40and50and the position thereof is controlled by the bimetallic actuator20. The second side of the contact points39and49include upper contact elements42and52controlled by the position of the temperature control actuator72as will be subsequently described.

The bimetallic strip actuator20, the first leaf spring30, the second leaf spring32and the shorter leaf springs34and36are all supported in an offset manner by the post support70provided to one side of the base plate80.

The leaf spring34includes the upper contact element42of the first contact points39and leaf spring36includes the upper contact element52of the second contact points49. Each of these leaf springs are in engagement with the temperature control actuator generally shown as72and are spring biased against the temperature control actuator. In this way a second side of the contact points is controlled by the position of the temperature actuator.

The temperature control actuator72includes a first adjustment mechanism for controlling the position of leaf spring34and a second adjustment mechanism for controlling the position of leaf spring36. The temperature control actuator72when rotated causes the coordinated displacement of the leaf springs34and36and the displacement of the upper contact elements42and52. In this way, with adjustment of the temperature actuator72, each of the contact points39and49are adjusted in synchronization with each other. The first and second adjustment mechanisms allow calibration of the contact points relative to the temperature actuator72such that the contact points respond at the appropriate temperature.

FIG. 2shows part of the temperature actuator72where a slide rod76is inserted within the hollow cavity78with the position of the slide rod determined by the position of the adjustment screw74. The adjustment screw74is inserted into the cavity78and engages the stem of the temperature actuator72. The slide rod76bottoms out on the adjustment member74and therefore the adjustment member74determines the extent that the slide rod78projects from the shaft of the temperature actuator72. The projecting end57of the slide rod engages leaf spring36.

Turning to the exploded assembly view ofFIG. 3, the various metal and plastic components of the dual contact thermostat6are shown. The molded base plate80includes a base post82at one side of the base plate and an integral cam84to the other side of the base plate. The base plate80includes a cylindrical opening85that receives the spool component79. The spool component79includes a cylindrical port83that rotatably receives the temperature actuator shaft71.

The moulded base plate80also includes a cavity87for receiving the nut89. The base post82includes a projecting square post91with a cylindrical cavity93passing through the square post91and the base post82. A number of electrical members and insulating members are inserted on the square post91and the square post determines and maintains the angular position of at least some of these components on the square post.

A first electrical connector101slides on the plastic square post91and is supported by the top of the moulded base post82. These are non-conducting members. The leaf spring30is then inserted on the post and the leaf spring provides the electrical connection to the contact element. The leaf spring includes a square port31for engaging the square post91and includes a cylindrical pass-through port33for allowing the leaf spring engaging shoulder94to pass therethrough in a clear manner. The position of the leaf spring30is effectively determined by the bimetallic actuator20. The leaf spring shoulder94engages the leaf spring32. The slide rod76is allowed to pass through the port35in the leaf spring34and through the port37in the leaf spring32to engage and determine the position of leaf spring36due to engagement with the end57of the slide rod76.

The centers of the two leaf springs are connected to the common electrical terminal110but the leaf springs34and32are separated by the conducting washer-type element112. Other electrical connecting arrangements can be used. An insulating washer114separates the electrical connector element116and leaf spring36. Therefore the electrical connecting element116feeds the leaf spring36. Leaf spring36is Isolated by the insulating washer118from the bimetallic actuator20. The bolt member21with the washer23engages the bimetallic actuator20and passes through the base post and various members to engage the nut89.

With this arrangement the various elements of the dual contact thermostat are stacked and maintained in alignment above the molded base plate80. The rotary temperature actuator72includes a fixed moulded cam75that is in engagement with the cam77on the spool component79. The spool component79is received in the base plate80such that one side of the cam77engages the stationary cam84of the base plate. An adjustment lug81on the spool member79allows a user to rotate the spool member79relative to the fixed cam84. Rotation of the spool member allows the temperature actuator shaft72to be displaced along its axis. This adjustment is used to partially calibrate the thermostat. The spool after calibration is held in a fixed position relative to the stationary cam84. Rotation of the temperature actuator shaft72causes axial displacement of the shaft due to engagement of cam77and cam75.

Further details of the cooperation of the components are shown inFIG. 4. The spool member79is inserted in the port121and the cam77engages the fixed cam84of the base plate80. The temperature control actuator72has the shaft71thereof inserted through the port85of the spool member79. During initial calibration of the dual contact thermostat the spool member79can be rotated on the fixed cam84to a desired position. Once proper calibration has been made these two cam members may be fixed in position, for example using an adhesive, and will remain fixed during subsequent use of the thermostat by a user.

At this point the cam77of the spool member has been moved to a desired position that allows calibration of the thermostat with respect to leaf spring34and contact element42. As the cam77has now been fixed relative to the base plate80and the integral cam75of the temperature actuator72is engagement with this cam, the position of the leaf spring shoulder94is now determined. This leaf spring shoulder94effectively determines the position of the leaf spring34.

The position of the slide rod76is determined by the adjustment screw74accessible at the end of the shaft of the temperature actuator72. This adjustment is shown inFIGS. 6 and 7where the adjustment screw is moved and the slide rod76inFIG. 7is displaced outwardly at a distance131. An Allen key can be used for determining the position of the adjustment screw74. The slide rod76effectively determines the position of the leaf spring36. Therefore the temperature actuator72controls the position of the leaf springs34and36and thereby determines the position of the second contact elements of each of the contact points39and49. With this arrangement the bimetallic actuator20controls the position of the leaf springs30and32and the contact elements42and52of the contact points39and49.

FIGS. 14 and 15show two adjustments that are used in the calibration of the dual contact thermostat after assembly of the thermostat. The cam77of the spool member79is rotated relative to the fixed cam84of the base plate80. This is typically done with the lug150of the temperature actuator72in a calibration position. As the base plate80and the cam77of the spool member79are all moulded components, it is necessary to adjust the actuator to achieve the desired position of the leaf springs34and36. The leaf springs are biased against the shoulder94or the slide rod76and thus any axial displacement of the temperature actuator causes the leaf springs to move therewith. Thus rotation of the cam77allows the user to adjust the unit as indicated by the adjustment dimension155.

InFIG. 15it can be seen that the set screw74effectively controls the position of the slide rod76and thereby controls the position of the leaf spring36. This in turn controls the position of the contact element52of the second set of points49. An adjustment amount177can be controlled by movement of the adjustment nut74using the Allen key175.

With this temperature control arrangement, the first set of points39can be calibrated by movement of the cam77of the spool member79against the fixed cam84. Eventually the cam77is used with the cam75of the temperature actuator72to vary the position of both set of points. During the initial calibration, cam77is moved relative to the stationary cam84to a set position of the first set of points39.

The second set of points are calibrated using the adjustment nut74which in turn moves the leaf spring36. Once calibration has been accomplished the spool member79is fixed to the base plate80. For example a small amount of an adhesive can fix these components. Due to calibration, the particular position of the stop shoulder81of the spool member79is not initially known. This stop shoulder engages with the stop lug150of the temperature actuator72and effectively determines the two end positions, namely the low and high temperature settings. As this position is not initially known, the shaft includes a number of securing ridges that receive the temperature control knob8. In this way the temperature control knob8can be positioned in the low position to align with the low temperature indicator on the faceplate. When the control knob is moved to the high position, the stop lug150will engage the stop shoulder81.

As each of the sets of points includes an independent adjustment arrangement for calibration, the resulting temperature differential can be varied. For heater applications, an approximate 5° F. temperature differential between initiation of the first heating element and initiation of both heating elements works satisfactorily. Other temperature differentials are easily achieved by varying the calibration steps.

With the dual contact thermostat as described herein, it is desirable that the first set of contact point close when the temperature sensed by the bimetallic strip is below the particular temperature setting identified by the control knob8and the face plate. This will actuate the first heating element of the heater, and heat will be added to the room. If sufficient heat is added to the room the bimetallic temperature actuator will sense a temperature rise and cause the contact points to open. Therefore, for many applications the thermostat will actuate a first set of contact points used to actuate a first heating element and this heating element may be sufficient to maintain the room at a desired temperature or increase the temperature until operation of the heater can be temporarily discontinued.

In some cases it may be necessary to add additional heat to warm the room. For example if a first heating element is actuated and the temperature in the room continues to drop, the second set of contact points will close and actuate a second heating element. With this additional heat, the temperature in the room may eventually increase to a point where the second set of points now open. The first set of points will still be in contact and will continue to add heat to the room at the reduced rate. If the temperature in the room continues to rise then the second set of points will open and heating will temporarily discontinue. If on the other hand the temperature in the room starts to drop the bimetallic strip will respond to this reduced temperature and the second element will again be activated. The dual contact thermostat accommodates two-stage heating using a single temperature actuator shaft and single bimetallic strip. The various leaf springs are stacked one above the other with a first set of points being partially controlled by the bimetallic actuator and the second set of points partially controlled by the bimetallic actuator. The stacking of the components and the adjustment of the thermostat for calibration are simply accomplished and the synchronization of contact points to activate in a desired temperature related manner is realized using the single temperature actuator.

The dual contact thermostat has particular application for dual electrical heating elements. The thermostat can also be used for other heating or cooling applications where different temperature setting or activation points are desired. This arrangement provides a simplified and cost effective structure. In addition, calibration of the two electrical contact points is easily realized.

The electric circuit200shown inFIG. 19has an electrical plug201for connection to an appropriate power supply. An on/off switch202is provided that includes a pilot light204. This provides a visual indication to the user that the portable heater is plugged in to a power source and if the pilot light is on the switch202has been placed in the on condition. Power is provided to the variable dual-contact thermostat206having a first set of contact points208and a second set of contact points210. When contact points208are closed, power is provided to the electrical heating element212and power is also provided to the associated green pilot light214.

Assuming that the contact points210are in an open position, the current passing through the first electrical heating element212, which in this case is a 1000 watt element, is passed to the thermal unit220and the thermal fuse222to the fan motor224. This electrical heating circuit is preferably used in association with a plastic-type housing and the fan motor222causes an airflow to pass through the portable heater and across the heating element212to discharge heat from the unit. The thermal limit switch220, under normal operations, will remain closed. If for some reason the heat within the portable heater rises above a particular temperature, this thermal switch will disconnect. Once the temperature cools the thermal limit switch will then close and the unit can again operate. This is in contrast to the thermal fuse that is a further safety feature that basically disconnects the circuit and requires replacement if it is activated.

With this arrangement if only the first heating element212is on, this element controls the amount of current being provided to the motor and hence the speed of the fan motor.

The dual contact thermostat206is designed such that if the temperature continues to drop the second set of contact points210will close. This effectively brings on the second electrical heating element216which in this case is a 500 watt heating element. This heating element has an associated red pilot light218. With the circuit the heating elements are placed in parallel and as such the current provided to the fan motor224increases. This produces a higher speed of the fan motor and an increase in the airflow passing through the portable heater. This is desirable to increase the transfer of heat from the portable heater to the air stream under the maximum output conditions while also allowing the airflow to automatically be reduced when only the lower power heat element i.e. the 1000 watt element is in use.

It has been found that the comfort level to the user is associated with the temperature of the air and the rate of the airflow through the heater. By reducing the airflow when only the 1000 watt element is in use, the temperature of the airflow increases. This provides a desirable comfort condition for the user. Many other heating circuits maintain a constant airflow regardless of the output setting of the heater. This results in the temperature of the emitted air being lower although the actual amount of energy being added to the room is essentially the same. The higher speed cooler airflow is not as comfortable and is not as desirable. To a certain extent, such a high speed lower temperature airflow can almost be considered to be drafty to the user.

For many applications it has been found that the 1000 watt element is more than sufficient to maintain a room at a desired temperature. The green light indicates that the user is using the heater at a lower output and as such is saving some energy. In contrast, if both the green and the red pilot lights are on, the user has either set the thermostat at a very high level requiring both sets of contact points to close, and as such the portable heater is being used at a high power setting. Once the room has come up to temperature the heater may be capable of maintaining this temperature by operating at the lower power setting. In addition, the two light indicators encourage the user to reduce the thermostat setting such that only a single green light is on. The fact that the fan speed automatically adjusts and is lowered at the lower power setting reduces the user's previous perception that the heat being added to the room was not sufficient. For many applications users will operate the device at the lower setting and effectively save a significant portion if not approximately ⅓ of the power that would be used at maximum setting.

The circuit ofFIG. 19automatically adjusts between the lower 1000 watt output and the higher 1500 watt output and appropriately varies the fan motor speed as a function of the power output of the heater.

In the electrical circuit200aofFIG. 20only a single stage thermostat207is used and there is only a single set of contact points208. An additional high output switch211is associated with the 500 watt heating element216. In this case, the user manually selects whether he will operate with only the 1000 watt output or will operate with a 1500 watt output. If switch211is placed in an open condition, the circuit is operated under the 1000 watt output and when power is provided to the 1000 watt element212the green pilot light214will be on. When the user has closed the switch211and the contact points208are closed, both of the heating elements212and216will be on. Both the green pilot light214and the red pilot light218will be on. In this way, visual feedback is provided to the user indicating that the device is operating at a maximum power output if both pilot lights are on or operating at a lower power output if only the green pilot light is on. It has been found that this particular arrangement of providing a color indication (green pilot light) corresponding to a power efficiency mode i.e. a lower power setting of the portable heater is often sufficient to encourage a user to operate the heater in the more efficient manner. In other circumstances the user may recognize that the higher output is indeed required and can manually switch the device to the higher power output when required. The fact that the green and the red pilot light indicators are both on in the maximum power output provides a reminder to the user to return the portable heater to the lower power setting if appropriate.

With both of the circuits ofFIGS. 19 and 20, the user is provided with a visual indication of a more desirable lower power output operating condition of the heater as well as a visual indication when the heater is operating at maximum output. In the case of the automatic circuit ofFIG. 19, the user may be able to reduce the setting to operate the device with only the green pilot indicator on if he notes that the heater is often in the higher output mode. In the circuit ofFIG. 20the user is provided with a reminder to manually return the heater to the lower power setting whenever possible. In both cases, when the device is operating at the lower power setting the fan speed is automatically reduced whereby the air temperature exiting the heater is warmer. This desirable feature is a result of the fan motor speed automatically reducing at the lower power output.

It has been found that this type of visual feedback of power output and operation of the device in a lower output mode in combination with maintaining an appropriate temperature of the air leaving the heater encourages the user to operate in the more efficient mode. In other devices the air temperature leaving the heater is too low and in direct contrast to the temperature of the airflow leaving the heater under maximum conditions. Under these circumstances the user is less likely to operate under the lower power setting mode.

Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.