US3504557A - Thermal motor - Google Patents

Description

April 7, 1970 Q woo ET AL 3,504,557

THERMAL MOTOR 2 Sheets-Sheet 2 Filed Jan. 8, 1969 INVENTORS. Lee 0. Woods, .DO ala L/vaa Attorney.

United States Patent O US. Cl. 74-128 8 Claims ABSTRACT OF THE DISCLOSURE A thermal motor includes a bimetallic drive mounted for sequential deflection in opposite directions and a rotatably mounted ratchet wheel. A pawl is connected to the bimetallic drive and mounted for sliding movement in axially opposite directions in response to deflection of the bimetallic drive in its opposite directons. The pawl includes a bifurcated section spanning the ratchet wheel and a spring dog which engages the ratchet wheel and rotates it a predetermined incremental amount in a first direction as the pawl moves in one direction. The dog exerts some force on the ratchet wheel tending to rotate it in a second direction as the pawl moves in its other direction. A restraining spring allows free rotation of the ratchet wheel in its first direction while restraining rotation of the ratchet wheel in the opposite direction. One form of the restraining spring includes a pair of spaced arm sections joined by a transverse section. The distal end of one arm section and its junction with the transverse section engage a pair of spaced spart seats while the junction of the transverse section with the other arm section abuts a support surface. The distal end of the other arm section resiliently urges an idler wheel into engagement with the ratchet wheel. In another form, the spring is a helically wound member mounted on the axial post for the ratchet wheel and engaging the ratchet wheel to be loosened or tightened about the post dependent on the direction the ratchet wheel is moved.

BACKGROUND OF THE INVENTION This invention relates to thermal motors and, more particularly, to an improved indexing arrangement for such motors.

Thermal motors are well-known and commonly incorporate a bimetallic element and accompanying heater and switch. The heater, when energized, heats the bimetallic element, causing it to flex in one direction. This opens the switch and deenergizes the heater. The bimetal then cools and flexes in the other direction. This closes the switch and re-energizes the heater. Thus the bimetallic element deflects or flexes sequentially in opposite directions. An indexing mechanism is provided to advance a timing device, such as a ratchet wheel, an incremental amount for each cycle of the bimetallic element. The indexing mechanism normally includes restraining means to prevent backward rotation of the ratchet wheel.

Prior art indexing mechanisms have often been less than what might be desired. Most restraining means have been some type of spring or resilient mechanism to allow movement in one direction while preventing movement in the other. Such restraining means have often been sensitive to the physical orientation of the motor, functioning properly only if the motor is mounted in a particular orientation.

Often the indexing mechanism has been very complicated in order to assure accuracy in the incremental advance of the ratchet wheel.

In some applications of thermal motors it is desirable to strongly restrain reverse movements of the ratchet wheel yet allow some movement of this type without breaking the mechanism. Most prior art restraining mechanisms would be broken if the ratchet wheel were forcibly rotated in the reverse direction.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an improved thermal motor.

It is another object of the present invention to provide a thermal motor having an improved indexing mechanism.

It is yet another object of this invention to provide a thermal motor having greater consistency in the incremental advancement of the timing device with variations in the amount of deflection of the drive element.

It is still another object of this invention to provide a thermal motor having an indexing mechanism which is insensitive to the physical orientation of the motor.

It is a further object of this invention to provide a thermal motor with an indexing mechanism which strongly restrains the timing device against reverse movement without being broken by such movement.

It is still a further object of this invention to provide a thermal motor with an improved indexing mechanism including a simple, low cost and yet highly effective re straining means.

In carrying out the invention, in one form thereof there is provided a thermal motor comprising a bimetallic drive means mounted for deflection sequentially in opposite directions and a rotatably mounted ratchet Wheel. An elongated movable prawl is mounted at one end for sliding movement and is connected at the other end to the drive means so that the pawl moves axially in opposite directions in response to deflection of the drive means in its opposite directions. The pawl includes a bifurcated section spanning the ratchet wheel. A spring dog extends across a portion of the bifurcated section for engagement with the ratchet wheel to rotate the ratchet wheel a predetermined incremental amount in a first direction as the pawl moves in one direction, the dog exerting some force on the ratchet wheel tending to rotate it in a second direction as the pawl moves in its other direction. Resilient restraining means engages the ratchet wheel to freely allow rotation of the ratchet wheel in its first direction while strongly restraining the ratchet wheel from rotation in its second direction.

BRIEF DESCRIPTION OF THE DRAWINGS The subject which we regard as our invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a refrigerator defrost control, with the cover removed, including a thermal motor incorporating one form of the present invention;

FIG. 2 is a cross-sectional view taken generally along the line 22 of FIG. 1, but with the cover in place;

FIG. 3 is a fragmentary perspective view of a portion of the device of FIG. 1 showing certain details of the indexing mechanism;

FIG. 4 is a plan view of the pawl used in the indexing mechanism;

FIG. 5 is a perspective view of the restraining mechanism used in the device of FIG. 1;

FIG. 6 is a fragmentary view, partly in cross-section, taken along the line 66 of FIG. 1;

FIG. 7 is a fragmentary view, in perspective, showing certain features of the heater switch used in the defrost control of FIG. 1;

FIG. 8 is a fragmentary front view, similar to the upper left-hand corner of FIG. 1, but showing another form of restraining mechanism suitable for use in the present invention; and

FIG. 9 is a fragmentary view taken generally along the line 99 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, particularly to FIGS. 1 and 2, there is shown a refrigerator defrost control, generally indicated at 15, which incorporates an improved thermal motor, generally indicated at 16, in accordance with one embodiment of this invention. An enclosing case 17, preferably molded from a suitable plastic insulating material, is provided and has top and bottom walls 18 and 19, side walls 20 and 22, a back wall 23, and a removable cover 24. Back wall 23 is formed with a threaded boss 23a which receives a screw or bolt 24a to releasably secure the cover 24 on the case 17. Of course, for more permanent assemblies a rivet can be used in place of the screw, or other suitable means of joining the housing can be used. Bottom wall 19 has an opening 25 formed therein which receives a terminal board 26. Thermal motor 16, and a defrost switch and cam assembly 27 are positioned within the enclosing case 17.

The thermal motor has a bimetallic drive means mounted for deflection sequentially in opposite directions. This bimetallic drive means includes a bimetallic drive element 28 having opposite ends 29 and 30. The end 29 has a longitudinally extending slot formed therein, which receives a restraining and adjusting screw 30a in sliding relationship thereto. The screw 30 is threadedly mounted in a plate 31 which, in turn, is retained in slots formed in molded bosses 32 and 33 respectively formed in top wall 18 and side wall 20. An opening 34, formed in side wall 20, provides access to the slotted end 35 of the adjusting screw 30a. After proper adjustment of the screw, the opening 34 may be closed by any suitable means such, as a snap-in cap (not shown). The sliding engagement between thte end 29 of the bimetallic drive member 28 and the screw 30a restrains the bimetallic element 28 from movement in directions transverse to its direction of elongation, while accommodating longitudinal movement of end 29 in the direction of elongation of the element 28 in response to flexing of the elementdue to heating and cooling thereof.

End 30 of bimetallic element 28 is pivotally mounted on back wall 23 by a mounting assembly 36. The mounting assembly 36 comprises a pair of spaced or stacked lever members, one of which is shown at 37. The levers are pivotally mounted intermediate their ends by means of a pivot post 38 which extends into and is secured to a boss 39 formed on back wall 23. Each of the levers has spaced distal ends 40 and 41. The end 40 of each of the lever members is rigidly secured to the bimetallic drive element 28 adjacent its end 30. A conventional electrically energized resistance heater 42 is positioned about the bimetallic element 28 intermediate its ends 29, 30 and is separated therefrom by a sheet 43 of insulative material. This places the heater 42 in heat transfer relationship to the bimetallic drive element 28, with sheet 43 serving to delay heat transfer to the drive element. One lead 44 of the heater is connected to plug-in terminal 45, mounted in the terminal board 26.

A timing element, in the form of a toothed ratchet wheel 46, having a pinion 47 attached thereto, is rotatably mounted on a shaft 48, which extend into and is secured to a boss 49 formed on back wall 23. An indexing mechanism is provided for incrementally advancing ratchet wheel 46 and includes a pawl 49. As best seen in FIGS. 3 and 4, the pawl is formed as an elongated strip of relatively thin sheet metal having opposite end 50 and 51. End 50 of the pawl is supported by guide members 52 and 53 for g nera y l ngitudinal sliding movem n between a first position, shown in solid line in FIG. 3, and a second position, shown in dotted line in FIG. 3. The guide members 52 and 53 are formed as molded bosses extending outwardly from the side wall 22 and back wall 23' of the casing 17 and define a slot 54 therebetween which slidably receives the end 50 of the pawl 49. The pawl 49 extends generally tangentially of the ratchet wheel 46 and includes a bifurcated section forming a slot 55 into which the toothed edge of the ratched wheel extends. The sides forming the slot 55 have complementary positioned, inwardly bowed portions 56 and 57 which fit closely adjacent the sides of the ratchet wheel 46 to assure proper positioning between the pawl 49 and the ratchet wheel 46. A leaf spring dog 58 is secured at one end 59 to the end 50 of pawl 49 and extends partially across the slot 55, with its other or distal end 60 adapted to drivingly engage a tooth of the ratchet wheel 46 in response to movement of the pawl 58 from its first position to its second position, a shown by the arrow 61 in FIG. 1. The dog thus rotates the ratchet wheel 46 an incremental amount in the direction shown by arrow 62 each time the pawl moves from its first to its second position.

The pawl 49 is moved between its first and second positions by an elongated ambient compensating bimetal element 63 having opposite ends 64 and 65. The end 41 of each of the lever members 37 is rigidly connected to the compensating bimetal 63 adjacent its end 65. The compensating bimetal 63, extends in spaced, generally parallel relationship with the bimetallic drive element 28 when both bimetals are at the same temperature and screw 30a is in a neutral position not bending the bimetallic drive element 28. In other words the lever members 37 pivotally mount the bimetallic drive element 28 and the compensating bimetal element 63 in generally coaxial juxtaposition in the direction of their elongation.

Referring additionally to FIG. 6, end 64 of the compensating bimetal 63 has a pair of legs 66 and 67, defining a slot 68 therebetween. The legs 66 and 67 have notches 69 and 70, respectively, formed therein and the legs 66 and 67 extend through an opening 71 formed in end 51 of pawl 46, with notches 69 and 70 resiliently engaging the side edges of the opening 71.

A heater switch assembly 72 is provided and comprises a stationary contact 73 secured to a terminal 74 mounted on back wall 23 by some suitable means such as rivet 75. Terminal 74 is connected by lead 76 to plug-in terminal 77, mounted in terminal board 26. A movable contact 78 of switch assembly 72 is carried by end 79 of an overcenter switch blade assembly 80. As best seen in FIG. 7, switch blade assembly 80 comprises spaced, parallel side elements 82 and 83, respectively, joining its opposite ends 79 and 84; side elements 82 and 83 having undulations formed therein, as shown. Center elements 85 and 86 extend inwardly from the ends 79 and 84 and have their inner ends 87 and 88 spaced apart as shown. Ends 87 and 88 are seated in grooves 89 and 90. respectively, of a support and terminal member 92, which is mounted on the back wall 23 by some suitable means. The other end of resistance heater 42 is connected by a lead 94 to an extension portion 92a of the support and terminal member 92.

Opposite the arms 82, 83 and 86 the end 84 is formed into a section 95 of decreasing width which terminates in a tab 96. The tab 96 is received in a grommet 97. which is slidably positioned in an opening 98 in the pawl 49. The grommet 97 has a central opening 99 through which the tab 96 extends and the opening 99 is wider than the tab 96. The tab may be bent relative to the section 95 to adjust the positioning of the switch blade assembly 80 relative to the pawl 49. The grommet 97 acts as a mechanical energy absorber and electrical insulator between the switch assembly and the pawl. For instance, when the pawl 49 is in its first position, the tab 96 engages the g ommet 97 at the left-hand edge of the open ing 99 (as seen in FIG. 3) and causes the grommet to be positioned at the left-hand edge of opening 98. As the pawl moves from its first to its second position, it moves the grommet 97 and tab 96 to the right together until the switch mechanism reaches its over-center position, at which time it snaps to the right. This snap action of the switch mechanism 80 causes the tab 96 to move through the opening 99 and engage the grommet 97 at the righthand edge of the opening 99. Then it forces the grommet across the opening 98 and into engagement with the pawl at the other edge of the opening 98. This lost motion arrangement between the pawl, the grommet and the tab, together with a certain resiliency of the material of both the tab and the grommet, serves as a mechanical energy absorber. For instance the switch mechanism 80 normally would be constructed from a suitable spring steel and the grommet 97 normally be constructed of a material such as nylon.

When the pawl 49 is moved from its second to its first position, the switch mechanism 80 executes a similar over-center snap action in the opposite direction. When the switch mechanism has snapped over-center to the right (as shown in FIG. 1) the contacts 73 and 78 are opened; and when the switch mechanism has snapped over-center to the left, the contacts 73 and 78 are closed. A stop 100, such as a molded boss formed on back wall 23, is disposed to engage the end 79 of the switch blade assembly 80 and limit the movement of the movable contact 78 in the open position of the contacts.

Ratchet wheel 46 drives a contact-actuating cam 102 through a gear train generally indicated at 103. Gear train 103 comprises the pinion 47, which is formed on ratchet wheel 46 to mesh with a drive gear 104. Gear 104- has a pinion 105 connected thereto and i rotatably mounted on a shaft 106. Shaft 106 extends into and is secured to a boss 107 formed on the back wall 23. Pinion 105 meshes with and drives a gear 108, having cam 102 connected thereto. Cam 102 and gear 108 are rotatably mounted on a shaft 109 which extends into and is connected to a boss 110 formed on the back wall 23. Cam 102 has a high portion 112 which, in the counterclockwise direction as seen in FIG. 1, gradually merges with a low portion 113. Also portions 112 and 113 are joined by a wall 114' which extends generally radially of the axis of shaft 109 but is slightly undercut.

Three elongated switch blades 115, 116 and 117 are provided and have their ends 118, 119 and 120, respectively, secured to plug-in terminals 121, 77 and 122, mounted on terminal board 26. Contacts 123, 124 and 125 are mounted adjacent the free ends of switch blade element 115, 116 and 117, respectively. Blade elements 115 and 117 are connected together and spaced apart by an insulating spacer 126 which extends through a spot 127 in the middle switch blade element 116. The spacer provides a minimum distance between contacts 123 and 125 which is large enough to prevent contact 124 from simultaneously engaging both of them. The spacer also provides a maximum distance between the contacts 123 and 125 so that contact 124 will be in firm engagement with each at the proper time.

As shown in FIG. 1, blade element 116 is biased so that, in all positions of cam 102 other than that shown in FIG. 1, contacts 123 and 124 are closed, while contacts 12 and 125 are open. However, during a few degrees of rotation of cam 102, as shown in FIG. 1, end 129 of switch blade element 116 will be engaged by the high portion 112 of cam 102 while end 140 of switch blade 115 is engaged by the low portion 113. This results in opening contacts 123 and 124 and closing contacts 124 and 125. The slightly undercut configuration of wall 114 assures that blade ends 129 and 130 will fall off a high portion 112 cleanly to give a snap action in closing and opening the pairs of contacts 123-124 and 124125.

Conventionally, with the defrost control shown, the terminals 45 and 77 would be connected to a suitable source of electrical energy while the terminals 121 and 122 would be connected to one side of the source through a conventional compressor and control and through a defrost heater respectively. Most of the time, that is when contacts 123 and 124 are closed, the compressor would be energized through its normal control to provide cooling. During the short period of time when contacts 124 and are closed the compressor circuit would be deenergized and the defrost heater circuit would be energized.

It will be noted that the bimetal heater 42 and heater switch assembly 72 are always connected between the two sides of the power source. Thus electrical energy is cyclically provided ot the heater 42, depending upon whether the contacts 73 and 78 are opened or closed. When the contacts 73 and 78 are closed, heater 42 heats the bimetal drive element 28 causing it to bend and to slide longitudinally over the adjusting screws 30a. This causes the end 30 to rotate the mounting assembly 36 so that the ambient compensating element 63 moves the pawl 49 from its first position (solid lines in FIG. 3) to its second position (dotted lines in FIG. 3). This movement of the pawl opens the contacts 73 and 78 to deenergize heater 42. Bimetal drive element 28 then cools and causes a reverse rotation about the mounting assembly 36 and movement of the pawl back to its first or solid line position. This recloses the contacts 73 and 78. Each time the pawl 49 moves to its second position the dog 58 advances the ratchet wheel 46 a predetermined incremental amount.

This movement is transmitted through the gear train 103 to advance the cam 102. The cam 102 may also be advanced -by means of a manual setting knob 131 which extends outwardly from the cam 102 through an opening 132 in the cover 24. A ring shaped dust seal 133 may be provided to close the opening 132 and prevent foreign matter from entering the motor.

As an important aspect of this invention, there is provided a resilient restraining means for freely allowing the forward incremental movement of the ratchet wheel 46 while strongly restraining movement of the ratchet wheel in the reverse direction. One form of this restraining means, as seen particularly in FIGS. 1, 3 and 5, includes a leaf spring element 158 having a pair of spaced, generally parallel arm sections 159 and 160 joined by a transverse section 161. Although the leaf spring element, by way of illustration, is shown as including cutout portions 162a and 1621) it may be constructed of solid spring material.

The junction between arm section 159 and transverse section 161 is formed as bends 163 while the junction between transverse section 161 and arm section 160 is formed as an elongated bend 164. A detent roller 165 is mounted on an axle 166 which, in turn, is attached to the arm 160 so that the roller 165 is free to rotate within an opening 167 adjacent the distal end 168 of the arm section 160.

Referring now particularly to FIGS. 1 and 3, the boss 53 includes a first portion 170, extending into the casing 17 perpendicular to the side wall 22 and a section 171 extending perpendicularly from a section 170 towards the top wall 18. The juncture of these sections 170 and 171 form a right angle seat 172. An embossment 173 is formed filling the corner between side wall 22 and top wall 18 and the junction between the embossment 173 and the side wall 22 forms a corner or seat 174. The seats 172 and 174 are in a facing relationship, they are offset from each other, and they are spaced apart a distance slightly less than the length of the arm 159. The leaf spring element 158 is positioned in housing 17 with the distal end or edge 175 of arm section 159 seated in or engaging the seat 172, andwith the junction between arm section 159 and transverse section 161, or bends 163, seated in or engagingthe seat 174. Since the distance between these two seats is less than the length of the arm section 159, the arm section 159 will be slightly bent as seen in FIG. 1. The elongated bend 164, or junction between transverse section 161 and arm section 160 engages or abuts against the Supporting surface formed by the inner side of top wall 18. Thus the leaf spring element 158 is firmly mounted within the housing 17 and retains its position regardless of the physical orientation of the control during use. The arm section 160 extends generally downwardly so that the detent roller 165 will engage the toothed edge of the ratchet wheel 46 with the roller normally resting between adjacent pairs of the teeth 175. The spring element 158 is formed so that the arm section 160 will resiliently force the detent roller 165 against the ratchet wheel '46. Also as an important aspect of this form of the invention, the long axis of arm section 160 extends at an acute angle relative to the ratchet wheel in the direction of its reverse rotation, that is in the direction opposite the arrow 62.

With this mechanism, movement of the pawl 49 from its first to its second position will cause one of the teeth 175 to push the detent wheel 165 upwardly against the force of the spring arm 160 so that the arm 160 and detent Wheel assume the dot and dashed line position of FIG. 1. Then, after the tooth has gone by the edge of the wheel 165, the arm and wheel return to their solid line position. Since the leaf spring element 158 is a thin flexible member, it provides very little resistance to this movement; and the ratchet wheel may be freely rotated incremental amounts in its first direction, as shown by arrow 62. As the pawl 49 returns from its second to its first position, the end 60 of dog 58 will drag across the top of the next tooth 175, tending to rotate the ratchet wheel in the reverse direction. When this occurs, the tooth just to the right of the detent roller 165 will exert a force upwardly and to the left on the detent roller. This places a compressive force on the arm section 160 and must cause the arm section 160 to bow upwardly in order to allow this reverse motion. Thus leaf spring element 158 exerts a strong force restraining the ratchet wheel from such a reverse movement. This force is sufficient to prevent the movement of pawl 49 from its second to its first position causing this reverse incremental movement of the ratchet wheel 46.

Also, it will be noted that the pawl 49 might not move exactly the same distance to the right each cycle. The detent roller will compensate for any reasonable deviation in the stroke of the pawl 49. The roller 65 substantially fills the space between each adjacent pair of teeth 175. Thus, each time a tooth is forced under the roller, the ratchet wheel 46 will assume a position which is advanced substantially the same incremental distance each time. The detent roller will serve to provide this exact positioning for any length of movement of the pawl between that just sufficient to bring the first tooth beyond the axis of the roller to that just short of bringing the next tooth beyond the axis of the roller.

It will be understood that the leaf spring element 158 may be constructed such that a very firm force exerted on the knob 131 tending to rotate the cam 102 in its reverse direction will bring a tooth 175 against the roller 165 with sufficient force to move the ratchet wheel 46 in its reverse direction. However, this requires substantially more effort on the part of the user than is required to manually rotate the cam 102 in its forward direction, with the attendant forward rotation of the ratchet wheel 46. This will serve as a Warning to the user that such rotation is not desired yet will not result in a broken mechanism, as was often the case in prior art devices.

Referring now to FIGS. 8 and 9 there is shown another form of resilient restraining means for use in the thermal motor. In the embodiment of these figures the ratchet wheel 46 and pinion 47 are mounted on a shaft 180 which extends a substantial distance beyond the surface of the rachet wheel 46. A wound spring 181 is mounted about the shaft 180 and includes a tab 182 which extends through a. suitable opening 183 provided in the ratchet Wheel 46.

A retaining clip 184 is provided for holding the spring 181 on the shaft 180. The helix of the spring 181 is such that movement of the ratchet wheel 46 in the direction of arrow 62 causes the spring 181 to tend to unwind from around the shaft 180 so that the spring readily slips about the shaft and the ratchet wheel 46 is free to rotate. A force exerted on the tab 182 in the direction resulting from an attempt to rotate the ratchet wheel 46 in the direction opposite the arrow 62 will cause the spring 181 to be wound tightly about the shaft 180 so as to firmly seize upon the shaft and prevent rotation of the ratchet wheel 46.

While this form of resilient restraining means does not regulate the incremental advance of ratchet wheel 46 with varying strokes of the pawl 49, it is extremely quiet, as there is no reciprocal movement similar to the movement of the leaf spring arm section between its solid and dotted line positions. In some applications, such as refrigerator defrost control, this may be very desirable as the installation of the thermal motor is one which tends to amplify any noise of the motor. Thus what are normally very slight noises may become somewhat objectionable.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A thermal motor comprising:

(a) bimetallic drive means mounted for deflection sequentially in opposite directions;

(b) a rotatably mounted ratchet wheel;

(c) an elongated movable pawl mounted at one end for sliding movement and connected at the other end to said drive means so that said pawl moves axially in opposite directions in response to deflection of of said drive means in its opposite directions;

(d) said pawl including a bifurcated section spanning said ratchet wheel and a spring dog extending across a portion of said bifurcated section for engagement with said ratchet wheel to rotate said ratchet wheel a predetermined incremental amount in a first direction as said pawl moves in one direction, said dog exerting some force on said ratchet wheel tending to rotate it in a second direction as said pawl moves in its other direction; and

(e) resilient restraining means engaging said ratchet wheel to freely allow rotation of said ratchet wheel in said first direction while strongly restraining said ratchet wheel from rotation in said second direction.

2. The invention as set forth in claim 1 wherein said restraining means engages the toothed edge of said ratchet wheel and includes a resilient arm extending from said ratchet wheel at an acute angle with respect to said ratchet wheel in said second direction so that rotation of said ratchet wheel in said second direction will exert a compressive force on said resilient arm.

3. The invention as set forth in claim 1 wherein said ratchet wheel is mounted for free rotation about a shaft and a wound spring is mounted about said shaft and engages said ratchet wheel; said spring being wound in a direction such that the force exerted on said spring when said ratchet wheel rotates in said first direction tends to loosen said spring and the force exerted on said spring when said ratchet wheel rotates in said second direction tends to tighten said spring.

4. A thermal motor comprising:

(a) bimetallic drive means mounted for deflection s6- quentially in opposite directions;

(b) a rotatably mounted ratchet wheel;

(c) pawl means interconnecting said bimetallic drive means and said ratchet wheel to rotate said ratchet wheel a predetermined incremental amount in a first direction in response to deflection of said bimetallic drive means in one direction;

(d) resilient restraining means including a pair of spaced arm sections and a transverse section joining corresponding ends of said arm sections;

(e) mounting means including a pair of facing, olfset,

spaced apart seats and a support surface spaced from said seats; and

(f) said restraining means being positioned with the distal end of one arm section engaging one seat, the juction of said one arm section and said transverse section engaging said other seat, and the junction of the other arm section and said transverse section engaging said support surface so that said other arm section engages said ratchet wheel to freely allow rotation of said ratchet wheel in said first direction while strongly restraining said ratchet wheel from rotation in the reverse direction of rotation.

5. The invention as set forth in claim 4 wherein said second arm section extends from said ratchet wheel at an acute angle with respect to said ratchet wheel in said reverse direction of rotation so that rotation of said ratchet wheel in said reverse direction will exert a compressive force on said resilient arm.

6. The invention as set forth in claim 5 wherein said restraining means includes a detent wheel mounted for free rotation adjacent the distal end of said second arm section, said seocnd arm resiliently urging said detent wheel into engagement with the toothed edge of said ratchet wheel.

7. The invention as set forth in claim 4 wherein the distance between said seats is less than the length of said first arm section so that said restraining means is firmly held in its proper relationship to said ratchet wheel.

8. A thermal motor comprising:

(a) bimetallic drive means mounted for deflection sequentially in opposite directions;

(b) a stationary shaft;

(c) a timing means rotatably mounted on said shaft;

((1) pawl means interconnecting said bimetallic drive means and said timing means to rotate said timing means a predetermined incremental amount in a first direction in response to deflection of said bimetallic drive means in one direction; and

(e) a helically wound spring mounted about said shaft and firmly engaging said ratchet wheel, the helix of said spring being such that a force exerted upon said spring in said first direction of rotation of said timing means causes said spring to loosen for permitting free rotation of said timing means while a force exerted upon said spring in the reverse direction of rotation of said timing means causes said spring to tighten for firmly holding said timing means from rotation.

References Cited UNITED STATES PATENTS 2,093,835 9/1937 Grooms 62154 2,530,961 11/1950 Hansen 74142 3,399,541 9/1968 Thorner 62-234 2,970,454 2/1961 Everard et al.

3,113,438 12/1963 Hubacker et al.

WESLEY S. RATLIFF, JR., Primary Examiner US. Cl. X.R, 62-155

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