EP0879473A1

EP0879473A1 - Voltage sensitive energy regulator using parallel control

Info

Publication number: EP0879473A1
Application number: EP97948433A
Authority: EP
Inventors: Brent A. Honsberger; Matthew J. Kindler; Robert L. Weber
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1996-11-25
Filing date: 1997-11-25
Publication date: 1998-11-25
Also published as: WO1998024104A1; AU5450698A

Abstract

The invention is an infinite switch (100) for controlling heat output of a heater element by controlling a time duration that the heater element receives current. The switch has a bi-metal strip (106) and a strip heater (105). The bi-metal strip (106) exerts a force by bending in the direction of the low expansion metal. The force of the bending is proportional to a duration of activation of the strip heater (105). The switch (100) has a set of cycling contacts for making and breaking current flow through the strip heater (105) and the heat element. The switch (100) also has a cycling arm (112) for adjusting the time duration that the cycling contacts (115, 116) are opened and closed. The switch (100) also has a pivot arm (110) that contacts the cycling arm (112) on one side, and contacts the bi-metal strip (106) on the other side. The force from the bi-metal strip (106) rotates the pivot arm (110) about a pivot point (143) until the pivot arm (110) engages the cycling arm (112). The cycling arm (112) prevents any further rotation, and thus, the force from the bi-metal strip (106) laterally shifts the pivot arm (110) to engage a snap spring (109) which opens the cycling contacts (115, 116).

Description

VOLTAGE SENSITIVE ENERGY REGULATOR USING PARALLEL CONTROL

BACKGROUND OF THE INVENTION

Technical Field

This invention relates to energy regulators, also known as "infinite switches, which control the power output of heater elements and, more particularly, through an electric range top heater element.

Background Art

FIGURE 7 depicts an example of a prior art parallel type infinite control 700, which is also known as a voltage sensitive switch. The control switch 700 comprises a plastic base 701 with five terminals on the outside of the switch (not shown) and a single shaft 702 on the opposite side of the control. The terminals LI 703 and L2 704 are for connecting the incoming load, typically 240 volts AC, with the required current being between 5 and 13 amps depending on the electric range element wattage. The terminals HI 705 and H2 706 connect the switch to the electric range heater element. The P terminal 707 is the pilot terminal, which is used to connect the switch to a device such as an indicator light to signify the presence of power to the control switch and range top heater element. The control 700 is mounted from behind the panel with the shaft 702 protruding through the panel. The fastening screws are turned in through the panel and into the switch. The shaft has a range manufacturer specified profile and mates with the manufacturer supplied knob. The shaft is rotated to provide variable power settings from off to full-on. The shaft may have a push- then-turn motion for safety reasons.

The control switch 700 has two sets of contacts designed to break both incoming lines, a manual set 708,709 and a cycling set 710,711. The cycling contact side has a set of contacts 710,711 that are cycled by the action of a bimetal strip 712 and a heating element 713. The heating element 713 of the parallel control switch is a very fine diameter nichrome wire that is wound around two mica paper insulators and then painted with a silicone rubber adhesive. The ends of this fine wire are welded to jumper wires of a nichrome ribbon wire. This heater assembly 713 is slipped over the main bi-metal assembly 712. The main bi-metal assembly 712 has a main bi-metal blade and an ambient compression blade 714 welded to a pivot pin 715. The bi-metal assembly 712,714 with the heater 713 is placed inside a steel armature 717 that is crimped around the pivot pin 715. The bi-metal/armature assembly is inserted into the case and the heater ribbon ends are welded to the HI 705 and H2 706 terminals placing the heater 713 on electrical parallel to the load or stove burner. This makes the control 700 sensitive to changes in voltage.

The L2 terminal 704 has a magnet 716 held behind it and one of the cycling contacts 711 on its face. Mated to this contact is a second contact 710 welded onto a cycling blade with an H2 terminal 706 welded to it. As the shaft 702 is turned from the off position, the cycling contacts close 710,711 and the strip heater 713 generates heat. As the bi-metal 712 heats up, it bends and generates a force against the armature 717 opposite to the magnetic force of the magnet 716. When the bi-metal force overcomes the magnetic force, the contacts 710,711 open, breaking the current flow. The bi-metal 712 cools down, thus closing the contacts. Rotation of the shaft 702 rotates the cam 718 and the cam follower 719 rides against the cam 718. Thus, by changing the amount of cam follower 719 displacement, the amount of heat required to deform the main bi-metal 712 and open the contacts 710,711 is changed, thereby affecting the amount of percent on time. As the bi-metal is heating, the ranger top burner element is also heating and thus longer on time yields and a proportionally hotter range element.

The manual contacts 708,709 has terminal LI 703 formed into, or connected to, a spring that rides on the cam 718. This spring biases to open the set of manual contacts 708,709. Turning the cam out of the off position overcomes this bias to close the contacts 708,709. The contacts are closed in all positions except off. The HI terminal 705 is connected to the second of the manual contact pair 709 such that the electrical circuit from LI 703 to HI 705 is continuous in all positions except off.

To counteract any movement of the main bi-metal strip 712 due to ambient air temperature changes, the compensating bi-metal strip 714 flexes in the opposite direction and applies force to the base of the bi-metal assembly. This counteracts the movement of the main bi-metal and the net result is zero movement. The problem with this arrangement is that the use of the compensating strip 714 adds complexity to the assembly process, and adds to the cost of the switch to have the additional part.

The control switch uses a calibration screw 720 to set the calibration point for the bi-metal assembly. However, the use of this screw 720 also tends to deflect or distort the metal member 719, thus requiring the release of turning torque to check calibration. The control switch calibrates in such a way that the linear movement of the calibration screw produces a large movement of the cycling contact. This yields a control switch that is very sensitive to small movements of the calibration screw. The problem with this arrangement is that overtime, the screw will loosen, and a small change in the position of the screw will throw the switch out of calibration.

In addition, the control switch 700 relies on the geometry of the LI spring 703 to define the shaft angle where the manual contacts 708,709 close. Thus, if the spring 703 should become damaged or bent, this would affect how the manual contacts 708,709 operate.

The control switch 700 also lacks a terminal spacing that allows for economical off-the-shelf terminal blocks to be used. The terminal blocks would help prevent miswiring and improve the reliability of the control to wiring interface.

DISCLOSURE OF THE INVENTION

The inventive switch is a parallel type control switch. The terminals are oriented such that LI and L2 terminals and the HI and H2 terminals are adjacent to each other and spaced for off the shelf connection blocks. The switch operates two different sets of contacts. The first set or manual contact side has the LI terminal formed to spring the set of contacts open. This terminal rides against the cam which is rotated by a shaft. The cam overrides the spring bias of the terminal and closes the set of contacts connecting the LI and HI terminals. The LI terminal also closes a set of contacts for a P terminal. The P terminal is spring loaded against a boss in the case which allows for the distance between the LI contact and the P contact to be controlled precisely. The second set of contacts or the cycling contacts are opened by a valverti type snap spring mechanism. This snap spring mechanism pivots on the H2 terminal and the cycling contacts are biased closed. The snap mechanism is acted upon by the main bi-metal assembly to open the contacts, and thus, cycle the control based upon the heat setting of the cam. The main bi-metal assembly has a main bi-metal strip and a heater. A hinge spring holds a ceramic heater in place against the main bi-metal strip. The heater may be a silkscreen printed resistance layer on a ceramic substrate. The heater spring is biased against the H2 terminal and thus makes electrical contact for current to flow from the H2 terminal to the heater. The switch includes a calibration bar which is set to permit the range of movement of the bi-metal strip.

The user input is through a cam turned by a shaft. This cam provides a force on one side of the cam that in turn moves a pivot arm. The pivot arm has a seesaw motion with one end being driven by the bi-metal assembly and the other end by the manual input through the cam arm with the pivot point riding on H2 terminal to push against the snap spring to open the contacts. The cam arm rides on the cam and transmits the cam rise to the pivot arm without transmitting the rotational torque of the cam.

The snap spring mechanism shortens the arc time duration for breaking or making the circuit. This eliminates problems of contact wear associated with slow moving contacts.

The cam arm pivots on the switch base such that only the radial force is transmitted to the pivot arm. The force to turn the cam may be transmitted to the metal members that ride on their surfaces, and these forces flex the members and change the cycling action of the controls by introducing variations into the control cycling process.

The inventive switch uses a calibration bar instead of a calibration screw.

Screw type calibration is very sensitive to the calibration screw movement. As the calibration bar is held by the switch base and not a flexible member, the calibration procedure is less sensitive to outside forces and will not change due to screw torque and side-loads.

The ceramic heater does not require a burn-in. Thus, assembly time is greatly reduced. It is advantageous to have a switch without a permanent shaft. This simplifies the assembly and provides additional features to the end user, such as a flat cleaning surface.

It is a further feature of this invention to use a spring retaining washer that holds the push-to-turn spring in a compressed state. Thus, during assembly, the cover does not need to align several parts and compress the spring.

It is a still further feature of this invention to form the pivot arm from bi-metal material to serve as the compensating bi-metal strip in addition to its other pivoting function.

It is a still further feature of the invention to include a twist to lock feature in the switch cover that uses two sets of locking tabs to secure the switch to a customer panel.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention which form the subject of the claims of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRffiF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGURE 1 depicts the layout of the inventive switch;

FIGURE 2A depicts the switch of FIGURE 1 in an off position;

FIGURE 2B depicts the switch of FIGURE 1 in a full-on or high position; FIGURE 3 is perspective view of the switch of FIGURE 1; FIGURE 4 depicts an exploded view of the switch of FIGURE 1 with the cover, the shaft, the push-to-turn spring and washer, and the cam;

FIGURES 5A-5B depict the operation of the push-to-turn spring and washer of the switch of FIGURE 1;

FIGURE 6 depicts the terminal layout of the switch of FIGURE 1; and FIGURE 7 depicts a prior art parallel switch.

BEST MODES FOR CARRYING OUT THE INVENTION

FIGURES 1, 3, and 6 depict different views of the inventive parallel infinite switch 100. The switch has power lines in LI and L2 and two power lines out HI and H2 to the range top heater element and has two sets of electrical contacts to break each circuit. This means that the parallel relationship between the ceramic heater 105 and the range top heater.

Power comes in to the switch through LI terminal assembly 114. The terminal assembly 114, includes blade terminal portion 122, detent 123, silver contact 124 and a terminal end portion 125. L2 terminal 111, includes a blade terminal portion 126 and a contact 115. The HI heater terminal 108 includes a silver contact 128.

The switch further includes a pilot terminal 107, which has a contact area 129 for contacting the terminal end portion 125 of the LI terminal 114. The pilot terminal is constructed so as to be pre-loaded against the plastic case boss 127. The pilot terminal has a quick connect terminal portion 130. The terminal enters the back of the case of the switch and is secured by the boss. Boss 127 also secures the contact 128 of the HI heater terminal 108. The pilot terminal may be a single layer of material.

The calibration bar 102 is inserted from behind the switch case in a slot and includes finger members 131. These members capture one end 132 of the main bi-metal strip 106.

The bi-metal sub-assembly 134 also includes a hinge spring 104 and a printed strip heater 105. The heater comprises a ceramic base with a conducting path along the entirety of its length. Preferably, the conducting path comprises two terminal pads and a conductive path silk screened onto the ceramic surface.

The hinge spring 104 has a first tab portion 135 and a second tab portion 136. The first tab portion 135 secures the heater 105 in an operative relation to the main bi-metal strip 106. The second tab portion 136 connects to the bimetal with the hole in the bi-metal lining up on the dimple in the hinge spring. The bi-metal subassembly 134 pivots about a plastic boss 137. The free end 138 of the bi-metal strip 106 contacts the pivot arm 110 and transmits force from the bi-metal subassembly 134 to the pivot arm 110. Heater spring 117 electrically connects the bi-metal assembly 134 to the

HI terminal 108. The heater spring biases the heater toward the bi-metal strip and away from the center of the case. H2 subassembly 139 comprises three main parts; the heater H2 terminal 103, the pivot arm 110, and the snap spring 109. The hinge spring 104 has a tab portion 152 that is biased against the H2 terminal 103, thus, electrically connecting the HI terminal 108 and the H2 terminal 103 through the ceramic heater 105. The one end of the snap spring

109 is connected to H2 terminal 103 at point 140. The other end of the snap spring 109 has contact 116. The contacts 115/116 form the cycling contacts.

The snap spring 109 opens and closes the cycling contacts. The snap spring includes a middle blade portion 167 and two outer spring tabs 168, 169. Each of the two spring tabs 168, 169 is fitted into a corresponding groove 170 (only one is shown) in the H2 terminal 103 and retained in a compressed state. The compressed state is biased to maintain the cycling contacts closed. The middle blade 167 has a portion 143 for contacting the pivot arm 110. The force from the bi-metal assembly 134 is transferred through the pivot arm 110 to the snap spring at the portion 143, as the force increases to a point that overcomes the compressed state of the spring, the spring snaps open, very quickly opening the contacts 115/116. As the force decreases, the spring snaps back because of the bias, and thus quickly closes the contacts 115/116. This type of spring is called a valverti-type snap spring.

The pivot arm 110 has a portion 141 that is in contact with cam arm 112. Another portion 145 of pivot arm 110 is in contact with an end portion 138 of the bi-metal strip 106. The pivot arm 110 also has two slots 171, 172 that define the fulcrum of the pivot arm. The slots 171, 172 fit onto flanges 173, 174 of the H2 terminal 103. The pivot arm rotates about the fulcrum as either the force from the bi-metal strip 106 changes or the force from the cam arm 112 changes. Depending upon the applied force from the cam arm 112, which is determined from the heat setting of the cam 113, an appropriate amount of force from the bi-metal strip 106 will cause the pivot arm 110 to rotate about its fulcrum and engage the snap spring 109 at point 143 causing the contacts 115/116 to open.

Cam arm 112 freely rotates in a cavity 146 in the housing 101. Cam arm 112 has a mid portion 147 that is in contact with pivot arm 110 at point 141. Cam arm 112 also has an end portion 148 in contact with cam surface 154 of cam 113. The cam arm 112 is held in place by flange 133 of the L2 terminal 111.

Cam 113, as shown in FIGURES 1 and 4, includes a central receiving cavity 150, leg washer receiving cavities 151, and an upper cam surface 153 and a lower cam surface 154. Upper cam surface 153 is essentially circular except for notches 149, 155. Detent 123 of the LI terminal 114 contacts the upper cam surface 153. The detent fits into notch 155 when the switch is in an off position. When the switch is rotated out of the off position, the detent rises out of the notch 155 and closes the manual contact set 124/128 and the pilot light contacts 125/129. The detent fits into notch 149 when the switch is in the high or full-on position, which aids in maintaining the switch in the high position, but does not open the manual contact set 124/128 or the pilot contacts 125/129.

Detent 148 of cam arm 112 contacts the lower cam surface 154. In the off position, as shown in FIGURE 2A, the detent 148 contacts a plateau portion 157 of the lower cam surface 154. Thus, in the off position, all of the contact sets 125/129, 124/128, and 115/116, are open and no current flows through LI or L2 into the range heating element. As the cam surface is rotated clockwise by approximately 45 degrees to a position corresponding to a low heat setting, the control switch 100 will be operating with a three to ten percent on time. In other words, the cycling contacts will be closed for three to ten percent of any given time period. Furthermore, from all positions from approximately 45 degrees to approximately 325 degrees, the manual contacts 124/128 and the pilot contacts 125/129 are closed. As the shaft 118 is rotated clockwise, the detent 123 of LI terminal 114 rides up from the notch 155 on to the circular portion of the upper cam surface 153. This brings the contact 125 of the LI terminal 114 into contact with the contact portion of the pilot terminal 107. This turns on the indicator light on the stove. As detent 123 continues to ride the circular portion of the upper cam surface, contact 124 is brought into contact with contact 128.

Simultaneously, detent 148 of the cam arm 112 is moving off the plateau portion 157 of the lower cam surface 154 and via contact point 147 of cam arm 112, reduces the force being applied to the pivot arm 110 at the junction of 147 and 141, thus allowing the rotation of the pivot arm, and causes the pivot arm to shift laterally toward the center of the cam 113, disengage the snap spring 109, allowing the cycling contacts 115/116 to close. When the cycling contacts 115/116 close, two electrically parallel current path result.

The first path is through the range top heating element. LI terminal 114 is in electrical contact with HI heater terminal 108 via manual contacts 124/128. The HI terminal 108 is connected to the range top heating element. Current then passes through the range top heating element to H2 terminal 103 and into the snap spring 109. The snap spring is connected to L2 line terminal 111 via cycling contacts 115/116. In the second current path, current passes through the ceramic heater element 105. Current flows from LI terminal 114 via the manual contacts 124/128 and into the HI heater terminal 108. The terminal 108 is electrically connected to the heater spring 117. The heater spring maintains a mechanical bias against the ceramic heater element 105 and thus passes current through the heater element 105 to the hinged spring 104. Current then passes along the spring 104 which is electrically connected to the H2 terminal and then to the snap spring 109. Current then passes from the snap spring 109 through the contacts 115/116 to the line terminal L2 111.

The cycling operation of the cycling contacts begins sometime after detents 123 and 148 have moved on to their respective cam surfaces from their off positions. The higher the heat setting, the longer the amount of time until the cycling operation begins and the longer the amount of time between cycling times. Current flows from LI terminal 114 through the heater spring 117 and into the ceramic heater 105. Heat is generated as the current flows through the ceramic heater. This heat is passed to the main bi-metal strip 106. The bimetal strip begins to bend toward the side of the low expansion metal. In this switch, the low expansion side is toward the outer casing and away from the center of the case. The main bi-metal strip has end portion 132 ensnared by fingers 131 of the calibration bar 102. The position of the calibration bar 102 sets is used to set an upper and/or lower limit on the movement of the bi-metal strip 106. Once the set point is determined, the calibration bar 102 is held in place by friction from the slot in the back of the switch case 101. Alternatively, the calibration bar 102 may be secured in the slot by a sufficient amount of glue or other affixent, for example glyptal.

As bi-metal strip 106 bends, the heater spring 117 flexes to maintain an electrical contact with the ceramic heater 105. The force from the bending of main bi-metal strip 106 is transmitted to the pivot arm 110. Thus, as the main bi-metal strip 106 bends, the end portion 145 of the pivot arm 110 rotatably moves toward the outer case. The other end portion 141 of the pivot arm rotatably moves toward the center of the case until firmly engaging cam arm 112. At this point, the rotation of the pivot arm stops, and the pivot arm then slides laterally on flange 173 of the H2 terminal and engages the snap spring 109 at point 143. As the force from the bi-metal strip increases, the force will overcome the compressed state of the snap spring causing the spring to snap open, thus opening the contacts 115/116.

The movement of pivot arm 110 is regulated by the lower cam surface 154 of the cam 113 via cam arm 112. As cam arm 112 moves further from the center of the cam, the pivot arm rotates less before engaging the cam arm, thus, the bi-metal strip 106 has to bend less and exert less force to open the contacts 115/116. As cam arm 112 moves closer to the center of the cam, the pivot arm rotates more before engaging the cam arm, thus, bi-metal strip 106 has to further bend and exert more force to open the contacts 115/116. When the detent 148 of cam arm 112 reaches the valley 166 of the lower cam surface, as shown in FIGURE 2B, no amount of bending of the bi-metal strip 106 will open up the contacts 115/116. This is the high or full-on setting of the control.

After the contacts 115/116 have opened, current flow through the heater 105 is stopped. Thus, the heater stops generating heat, allowing bi-metal strip 106 to begin to cool. As the bi-metal strip begins to cool, it starts to bend in the opposite way, back to a straight position. This reduces the force exerted by the portion 138 on the pivot arm 110. This force is reduced to a point that can no longer resist the bias of snap spring 109, and the spring snaps closed, thus closing the contacts. After the contacts 115/116 are closed, the current flows through heater 105 again and the cycle starts over.

As previously stated, it is essential that the switch have a compensating bi-metal strip that flexes in the opposite direction to the main bi-metal strip. The prior art shown in FIGURE 7, uses a separate compensating bi-metal strip 714. An alternative to the prior art method is to have the main bi-metal strip actually comprise two bi-metal strips welded together, with one of the strips serving as the compensating strip. However, this method is also unsatisfactory, because the weld is a weak point in the assembly, and over time, the weld may give way. Also using the welded assembly increases manufacturing complexity. In the inventive switch 100, the compensating bi-metal strip is the pivot arm 110.

Another feature of the inventive switch is the terminal layout as shown in FIGURE 6. The HI terminal 108 and the P terminal 130 are located on opposite sides of the case and are arranged so that the terminal blades are parallel to each other. The LI 122 and L2 126 terminals are arranged on the same side of the case as the P terminal, are parallel and in line with each other and orthogonal to the P and HI terminals. The H2 terminal 103 is on the same side of the case as the HI, but is orthogonal to the terminal HI. This arrangement simplifies the production process and helps prevent mis-wiring of the control, which could result in the burnout of control. This terminal geometry also allows the range manufacturer to attach a pair of burner element lead wires and a pair of incoming power wires with off the shelf terminal blocks. This shortens assembly time by attaching two wires at a time instead of one. Another feature of the inventive switch is the twist to lock feature.

The switch has a cover design, as shown in FIGURE 4, that includes two sets of locking tabs. The first set of tabs 156 will pass through holes punched into a customer panel (not shown). Turning the switch 100 will cause the tabs 156 to apply a pinching force on the customer panel that will tightly fasten the switch 100 to the panel. Further turning of the switch 100 will cause the second set of tabs 158 to enter the punched holes in the panel and lock into place. This locking will prevent the switch 100 from being turned any further. This feature secures the switch to the panel such that no additional mounting hardware such as screws are required.

Another feature of the control 100 is a washer 159, which holds a spring 164 in a compressed state into the washer 159 as it is loaded. Thus, during assembly, the cover 144 of the switch is not needed to simultaneously align several parts and compress the spring 164. FIGURES 4, 5A and 5B show washer 159 with shaft hole 160 and spring retaining legs 161 and alignment leg 162. The legs 161 fit into the corresponding cavities 151 of the cam. The spring 164 is slipped into the washer 159 and held in a compressed state by legs 161. During assembly of the control switch 100, this washer/spring assembly is slipped into the cam 113. This greatly eases assembly of the control switch as the compressive force of the spring 164 is not acting on any other elements. This washer prevents the parts of the switch from spontaneously disassociating from one another. Therefore, the cover 144 of the switch 100 does not have to be precisely placed upon the unit and compress the spring 164, at the same time. FIGURES 5A-5B show the cooperation between the shaft 118, the cover

144, the washer 159 and the spring 164 to form a push to turn feature. As shown in FIGURE 5A, the cover tab 165 is in a locked position in the cavity 163 of the washer 159. FIGURE 5B shows the shaft 118 pushed in and rotated 90 degrees. The push to turn tab 165 rides on top of the washer until it lines up with cavity 163 where it locks back into place.

Another feature of the invention is that the control does not use a permanent shaft. The shaft and knob can easily be removed, which would allow the consumer to have a flat surface which is easy to clean. The shaft 118 has a key 119 that will only allow the shaft 118 to be removed when the key is lined up with a slot 120, and this will only occur when the switch is in an off position. Thus, the shaft 118 is removable only in the off position. This safety feature prevents the shaft from being removed while the switch is in an on position. The knob (not shown) can be integrally attached or connectably attached to the shaft. The shaft, of course, would have to meet the necessary dimensional limitations of the spring retaining washer 159 and the cam 113. The shaft can have adaptive segments 121, which can be broken off to allow for different type of knobs to be used with the shaft 118. The absence of a shaft simplifies the manufacturing process and greatly reduces the cost of transportation of finished parts as they will pack better without the shaft.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A switch for controlling heat output of a heater element by controlling a time duration that the heater element receives current comprising: a bi-metal assembly having a bi-metal strip and a strip heater, wherein the bi-metal strip exerts a force by bending in a predetermined direction, the force is proportional to a duration of activation of the strip heater; a set of cycling contacts for making and breaking current flow through the strip heater and the heat element; a cycling arm for adjusting a duration that the cycling contacts are opened and closed; a pivot arm with a fulcrum, operably connected to the cycling arm on one side of the fulcrum, and operably connected to the bi-metal assembly on the other side of the fulcrum; and wherein the force from the bi-metal strip rotates the pivot arm about the fulcrum until the pivot arm engages the cycling arm, whereby the force moves the pivot arm to open the cycling contacts.

2. A switch according to claim 1, wherein the set of cycling contacts make and break current flow through the strip heater and the heat element by making and breaking current flow between a L2 terminal and a H2 terminal, the switch further comprising: a set of manual contacts that make and break current flow through the strip heater and the heat element by making and breaking current flow between a LI terminal and a HI terminal, with one of the manual contacts being electrically connected to the HI terminal; a cam with a first cam surface and a second cam surface, each surface having a respective profile; a manual arm that engages the first cam surface, is connected to the LI terminal and to the other manual contact, and opens and closes the manual contacts based upon the profile of the first surface; and wherein the cycling arm engages the second cam surface, and changes location relative to the pivot arm based upon the profile of the second surface.

3. A switch according to claim 2, wherein when the cycling arm changes location to a position closer to the pivot arm: the rotation of the pivot arm is lessened, the movement of the pivot arm is advanced, the opening of the cycling contacts is advanced, and duration that the heater element receives current is shortened.

4. A switch according to claim 2, wherein when the cycling arm changes location to a position further from the pivot arm: the rotation of the pivot arm is increased, the movement of the pivot arm is retarded, the opening of the cycling contacts is retarded, and duration that the heater element receives current is lengthened.

5. A switch according to claim 2, further comprising: a set of pilot contacts that are opened and closed by the manual arm, approximately concurrent with the manual contacts; and whereby when the pilot contacts are closed, an indicator light is activated signifying that the manual contacts are closed.

6. A switch according to claim 5, wherein one of the pilot contacts is connected to the manual arm, and the other pilot contact is connected to a pilot terminal, the pilot terminal includes: a pilot blade that is spring loaded against a boss of the switch.

7. A switch according to claim 1, further comprising: a calibration bar for setting an operating limit of the bi-metal assembly, the bar retaining an end of the bi-metal strip; wherein the bar is secured in a slot of the switch.

8. A switch according to claim 1, wherein: the main bi-metal is approximately L-shaped; the bi-metal assembly is supported at the corner by a boss, being operably connected to the pivot arm such that the force from the bi-metal strip is transmitted around the corner.

9. A switch according to claim 8, further comprising: a compensating bi-metal element that offsets any force from the bi-metal assembly from changes in an ambient air temperature.

10. A switch according to claim 9, wherein: the pivot arm is the compensating bi-metal element.

11. A switch according to claim 1, wherein: the heater element and the strip heater arranged electrically parallel to each other.

12. A switch according to claim 2, wherein: the heater element and the strip heater arranged electrically parallel to each other between the HI and H2 terminals.

13. A switch according to claim 2, wherein: the LI and L2 terminals are electrically connected to an external power source.

14. A switch according to claim 2, further comprising: a snap spring that is operably connected to the pivot arm, and opens and closes the cycling contacts when the pivot arm is moved.

15. A switch according to claim 14, wherein: the snap spring is connected to the H2 terminal and includes a middle blade portion and two outer spring tabs; each of the two spring tabs is fitted into a respective groove in the H2 terminal and retained in a compressed state, whereby the compressed state is biased to maintain the cycling contacts closed; the middle blade is connected to one of the cycling contacts and the L2 terminal is connected to the other cycling contact; and the middle blade has a contact portion that is acted on by the pivot arm when the pivot arm is moved.

16. A switch according to claim 15, wherein: the snap spring is a valverti-type snap spring.

17. A switch according to claim 2, wherein the pivot arm further comprises: a slot that defines the fulcrum of the pivot arm, this slot is received onto a portion of the H2 terminal.

18. A switch according to claim 2, further comprising: a removable shaft that is inserted into the cam, and operates to rotate the cam.

19. A switch according to claim 18, further comprising: a knob that is integral with the shaft for interfacing the switch with a user.

20. A switch according to claim 18, further comprising: a knob that is removably attached to the shaft for interfacing the switch with a user.

21. A switch according to claim 2, wherein: each of the terminals has a respective terminal blade, a portion of which protrudes from the switch for insertion into an external panel; the HI and H2 blades are located on one side of the switch; the LI and L2 blades are located on an opposite side of the switch from the one side; the HI blade is arranged perpendicular to the LI and L2 blades; and the H2 blade is arranged parallel to the LI and L2 blades.

22. A switch according to claim 6, wherein: each of the terminals has a respective terminal blade, a portion of which protrudes from the switch for insertion into an external panel; the HI and H2 blades are located on one side of the switch; the LI and L2 blades are located on an opposite side of the switch from the one side; the HI blade is arranged perpendicular to the LI and L2 blades; the H2 blade is arranged parallel with the LI and L2 blades; the P blade is located on the opposite side; and the P blade is arranged parallel with HI blade.

23. A switch according to claim 1, further comprising: a planar retaining washer having a posterior face from which two retaining legs protrude orthogonally therefrom at diametrically opposing sides of a perimeter of the washer, each of the legs is approximately J-shaped with the hook of the J-shape oriented to point toward a central axis orthogonal to the plane of the washer.

24. A switch according to claim 23, wherein the retaining washer has a tab cavity located on the perimeter of the washer between the retaining legs, the tab cavity receives a locking tab mounted on a cover of the switch, the switch further comprising: a push-to-turn spring that is mounted in the retaining washer and held in a compressed state by the retaining legs; and a shaft that is mounted through a central cavity of the washer and into the cam; wherein the washer, the locking tab, the push-to-turn spring, and the shaft cooperate to form a push-to-turn feature of the switch whereby the locking tab engages the washer in the tab cavity and prevents rotation of the shaft until the shaft is pushed inward overcoming the push-to-turn spring and disengaging the locking tab from the tab cavity.

25. A switch according to claim 1, including a cover, the cover comprising: a first set of tabs for securing the switch to an external member; wherein the first set of tabs are fitted into corresponding holes in the external member and then rotated, thereby securing the switch to the external member by clamping the external member between the cover and the first set of tabs.

26. A switch according to claim 25, wherein the cover further comprises: a second set of tabs for locking the switch to the external member; wherein the second set of tabs are aligned with the holes and prevent the first set of tabs from rotating.

27. A switch for controlling heat output of a heater element by controlling a time duration that the heater element receives current, the switch comprising: bi-metal means for exerting a force by bending in a predetermined direction when heated by a strip heater, the force is proportional to a duration of activation of the strip heater; cycling means for making and breaking current flow through the strip heater and the heat element; cycling adjusting means for setting a duration that the cycling means are opened and closed; and pivot means for receiving and rotating from the force until engaging the cycling adjusting means and then shifting laterally to open the cycling means.

28. A switch according to claim 27, further comprising: manual means for making and breaking current flow through the strip heater and the heat element; cam means for rotationally controlling the manual means and the cycling means, with a first cam surface and a second cam surface, each surface having a respective profile; manual adjusting means arm that engages the first cam surface, for opening and closing the manual means based upon the profile of the first surface; and wherein the cycling adjusting means engages the second cam surface, and changes location relative to the pivot means based upon the profile of the second surface.

29. A switch according to claim 28, wherein when the cycling adjusting means changes location to a position closer to the pivot means: the rotation of the pivot means is lessened, the lateral shifting of the pivot means is advanced, the opening of the cycling means is advanced, and duration that the heater element receives current is shortened.

30. A switch according to claim 28, wherein when the cycling adjusting means changes location to a position further from the pivot means: t h e rotation of the pivot means is increased, the lateral shifting of the pivot means is retarded, the opening of the cycling means is retarded, and duration that the heater element receives current is lengthened.

31. A switch according to claim 27, further comprising: calibration means for setting an operating limit of the bi-metal means, the calibration means retaining a portion of the bi-metal means; wherein the calibration means is secured in a slot of the switch.

32. A switch according to claim 27, wherein the bi-metal means further comprises: compensating means for applying an offsetting force to the bi-metal means, by bending opposite to the predetermined direction, to counteract a portion of the force being generated by ambient temperature.

33. A switch according to claim 27, wherein: the heater element and the strip heater arranged electrically parallel to each other.

34. A switch according to claim 27, further comprising: snap spring means that is operably connected to the pivot means for opening and closing the cycling means when the pivot means is laterally moved.

35. A switch according to claim 27, including a cover, the cover comprising: means for securing the switch to an external member.

36. A switch according to claim 35, wherein the cover further comprises: means for clamping the external member to the cover; and means for locking the switch to the external member; wherein the means for locking prevents the means for clamping from moving.