Patent Application
20080271470
This invention generally relates to appliance timers and, in particular, to a defrost timer for a refrigerator or a freezer.
Modern appliances such as refrigerators and freezers typically include no-frost or frost free systems or mechanisms that permit the appliance to automatically and regularly defrost itself Many conventional no-frost freezers/refrigerators include four basic components, namely a defrost timer, a heater, a defrost thermostat and a fridge/freezer thermostat commonly called a “cold control”.
Every few hours, the defrost timer activates the heater to defrost the evaporator coil in the appliance and at the same time cuts power to the compressor motor. Because the heater is disposed proximate the evaporator coil of the freezer, the heater is able to melt away any ice that has accumulated there. If the defrost thermostat sensor senses that the temperature has risen above thirty-two degrees Fahrenheit (32° F.), which is approximately equivalent to zero degrees Celsius (0° C.), the heater is turned off to limit the temperature rise, during this time any ice build up is melted. After a limited defrosting time the defrost timer disconnects the defrost heater and connects the compressor motor through the cold control again. After another few hours, the defrost timer once again activates the heater and the process is repeated. As a result, the freezer remains relatively frost free during use.
There are many different cycle time combinations for defrost and non defrost (Heating/cooling) specified by fridge/freezer manufacturers to suit their particular appliance requirements.
Unfortunately, conventional mechanical defrost timers are relatively expensive and include numerous components. Also as there are many cycle time model variations required the prior art needs many different combinations of gearing components to provided the required variations. There exists, therefore, a need in the art for a simple, low-cost defrost timer for an appliance such as a refrigerator or freezer. The invention provides such a defrost timer. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
In one embodiment, a timer including a rotatable electrically non-conducting ratchet gear, an electrically conducting pawl mechanism, and an electronic drive circuit is provided. The ratchet gear has a plurality of teeth and the pawl mechanism includes a pawl. The pawl is configured to engage one of the plurality of teeth on the ratchet gear. The electronic drive circuit is electrically coupled to the pawl mechanism. The electronic drive circuit passes a current through the pawl mechanism such that the pawl advances the ratchet gear by one tooth pitch.
In another embodiment, an appliance timer including a base, a rotatable non-metal ratchet gear, a metal pawl mechanism, and an electronic drive circuit is provided. The rotatable non-metal ratchet gear is operably coupled to the base and has a plurality of teeth. The metal pawl mechanism includes a spring, a pawl, and a nickel titanium alloy wire operably coupled together and secured between first and second pins protruding from the base. The pawl is configured to engage one of the plurality of teeth on the ratchet gear. The electronic drive circuit is electrically coupled to the first and second pins and passes a current through the pawl mechanism at regular intervals. An embodiment of the electronic control circuit can vary the regular intervals at which current is passed through the pawl mechanism during a portion of the operating cycle of the timer. The current causes the wire to contract such that the pawl advances the ratchet gear by one tooth pitch.
In yet another embodiment, a method of initiating a defrost cycle in an appliance is provided. The method includes the steps of alternatively contracting and expanding an alloy wire to advance a ratchet gear and initiating the defrost cycle in the appliance when the ratchet gear has been advanced one revolution.
A benefit of embodiments of the present invention is that the timer can replace the prior defrost timers with a lower cost device. As will become more apparent from the following detailed description, another benefit is that of flexibility of setting the compressor and heater on and off times without having to use different gears. Such flexibility is also possible with fully electronic timers incorporating a relay or triac to switch the compressor/heater on and off, albeit at a substantially higher cost. As such, embodiments of the present invention provide a useful alternative to mechanical and electronic defrost timers at a lower cost than both yet providing advantages only heretofore available from an electronic defrost timer.
Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.
Referring to
The base 12, while depicted as a rectangular plate, may take a variety of forms depending on, for example, the space provided within the appliance (not shown) for the appliance timer 10. The base 12 is generally made from an electrically non-conducting (i.e., insulating) material such as, for example, a plastic. Even so, the base 12 may be made from a variety of other suitable materials.
In the illustrated embodiment, the ratchet gear 14 is a relatively flat, generally cylindrical gear. The ratchet gear 14 is generally formed from an electrically non-conducting material. In the illustrated embodiment, the ratchet gear 14 is formed from a plastic. Even so, other electrically non-conducting materials may be suitably employed to form the ratchet gear 14.
The base 12 supports the ratchet gear 14 in a manner that permits the ratchet gear to, at times, rotate relative to the base. In that regard, in the illustrated embodiment a ratchet gear drive shaft 18 passes through both a central channel 20 in the ratchet gear 14 and an aperture (not shown) in the base 12. The drive shaft 18 is secured to the ratchet gear 14 but not the base 12. Therefore, the drive shaft 18 and the ratchet gear 14 rotate together and the drive shaft rotates relative to the base 12.
As shown in
In addition to the shape of the teeth 22, a blade spring 26 is also provided to prevent rotation in an undesirable direction. The blade spring 26 is a flat, resilient member having a blade spring holder 28 and an engagement end 30 on opposing ends. The blade spring holder 28 is operably coupled to a blade spring pin 32 secured to the base 12. The engagement end 30 is configured to engage with the side wall 24 and a rear surface 34 (
A tensioning pin 36 operably coupled to the base 12 and engaged with the blade spring proximate the blade spring holder 28 biases the blade spring 32 toward the ratchet gear 14. Therefore, the engagement end 30 is generally forced to slide over the contour of the front surface 38 of the teeth 22 as the ratchet gear 14 moves. When the engagement end 30 is forcibly biased against the side wall 24 and the rear surface 34, the ratchet gear 14 is prevented from rotating in an unwanted direction. In the illustrated embodiment of
The distance between two adjacent teeth 22 on the ratchet gear 14, when measured from one tip to another, is known as a tooth pitch 40. The tooth pitch 40 of the ratchet gear 14 is generally dependant on the number of teeth 22 included on the ratchet gear 14. With more teeth 22, the tooth pitch 40 typically becomes smaller. In contrast, with less teeth 22 the tooth pitch 40 typically becomes larger.
Referring back to
Referring back to
In the illustrated embodiment, the spring 46 is a coil spring (a.k.a., a helical spring) that operates to keep the pawl mechanism in tension. The spring 46 has first and second spring ends 56, 58. As shown in
In the illustrated embodiment, the pawl 48 is formed from a folded or shaped length of round wire. To correspond to that round shape, a slot 60 formed in between the tips 62 of each set of adjacent teeth 22 on the ratchet gear 14 has a generally rounded bottom 64. Therefore, the pawl 48 will easily fit or seat within the slot 60 formed between the teeth 22 on the ratchet gear 14. In addition, the pawl 48 will also easily fit and move within the channel 44 (see
The combination of the shape of the slot 60, the shape of the pawl 48, and the tension of the spring 46 encourages the pawl to remain in contact with the ratchet gear 14 when the pawl is driving the ratchet gear, as will be more fully explained below. The combination also permits the pawl 48 to move back over the teeth 22 when the pawl is pulled in a direction back toward the first pin 52 by the spring 46.
The pawl 48 is formed from an electrically conducting material such as, for example, a hardened steel, an annealed steel, and the like. Even so, other electrically conducting materials may be suitably employed in forming the pawl 48. As shown, the pawl 48 includes first and second pawl ends 66, 68. The first pawl end 68 is operably coupled to the second spring end 58. In the illustrated embodiment, the first pawl end 66 is formed into a loop to facilitate the coupling of the pawl and the spring 46. Even so, other coupling structures, members, or mechanisms may be used to operably couple the first pawl end 66 to the second spring end 58.
As shown in
The second pawl end 68 is operably coupled to a first alloy wire end 72. In the illustrated embodiment, the second pawl end 68 is formed into a rounded hook to facilitate the coupling of the pawl 48 and the alloy wire 50. Even so, other coupling structures, members, or mechanisms may be used to operably couple the second pawl end 68 to the first alloy wire end 72.
As shown in
The alloy wire 50 is an electrically conducting wire that is, in general, formed from more than one metal (e.g., a bi-metal). In one embodiment, the alloy wire 50 is a nitinol wire. Nitinol, which is an acronym for Nickel Titanium Naval Ordnance Laboratory, is a family of intermetallic materials, which contain a nearly equal mixture of nickel (55 wt. %) and titanium. Even so, other elements can be added to adjust or “tune” the material properties of the nitinol.
In the illustrated embodiment, the alloy wire 50 is a nitinol wire manufactured by Dynalloy, Inc., of Costa Mesa, Calif., and sold under the trademark Flexinol® (hereinafter “Flexinol”). A Flexinol wire typically contracts between about 2% to about 5% of its length when an electrical current is passed through the wire or the wire is otherwise heated. After contracting, the Flexinol wire will return to its original length (or close thereto) under a sufficient biasing force (e.g., the spring 46) when cooled. Because of this characteristic, the Flexinol wire is referred to as a “shape memory” wire (SMW). Without a sufficient biasing force, the Flexinol wire will not return to its original length. The biasing force is needed to reset, or stretch, the Flexinol wire back to its original length during the low temperature phase.
Under certain conditions, the Flexinol wire will contract up to about 8% to about 10% of its length. However, for longer lifetime (greater than one million cycles and even up to tens of millions of cycles), contraction of the Flexinol wire should be restricted to between about 5% to about 6% of its length. While the length of the Flexinol wire will change during contraction and expansion, the absolute volume of the wire remains constant.
The Flexinol wire is generally available in a variety of sizes each having a variety of different characteristics. For example, for a Flexinol wire having a diameter of about 0.001 of an inch, the wire has a resistance of about 45 Ohms per inch, has about 7 grams of pull force, requires a current of about 20 milliamps (mA) for suitable contraction, contracts in about 1 second, and takes about 0.1 of a second to cool to 70° C. However, for a Flexinol wire having a diameter of about 0.02 of an inch, the wire has a resistance of about 0.16 Ohms per inch, has about 3,562 grams of pull force, requires a current of about 4,000 milliamps (mA) for suitable contraction, contracts in about 1 second, and takes about 17 seconds to cool to 70° C. Flexinol wires with diameters between 0.001 of an inch and 0.02 of an inch will have characteristics and properties within the parameters noted above.
In the illustrated embodiment of
Referring now to
As shown in
The micro switch 86 is located adjacent to the cam 84 such that the micro switch 86 and the cam 84 are operatively engaged. The micro switch 86 is supported by the base 12 through a pair of micro switch pins 98. Although two micro switch pins 98 are shown, more or few may be employed so that the base 12 will support the micro switch 86. Also, components or mechanisms other than the pins 98 are used in other embodiments to secure the micro switch 86 to the base 12. As shown, the micro switch 86 includes a plurality of terminals 100 and the cam follower 92. The terminals 100 are configured to electronically couple with, for example, a wiring harness, an electrical connector, wires or leads, and the like.
The cam follower 92 is spring-loaded or otherwise configured to project outwardly and away from the remainder of the micro switch 86. In the illustrated embodiment, the cam follower 92 has a partially rounded outer surface 102. Therefore, the cam follower 92 is suitable for sliding along the outer surface 90, the contoured surface 96, and the flat surface 94 of the cam 84.
Referring now to
Despite
As mentioned above, the third resistor 120 depicted in the electronic drive circuit 104 schematic is not a discrete resistor found in the electronic drive circuit 102. Instead, the third resistor 120 schematically represents the overall resistance of the alloy wire 50 from
Still referring to
Returning again to
A cathode 134 of the Zener diode 114 is coupled to the fourth node 132 while an anode 136 is coupled to a fifth node 138. The second resistor 116 is disposed between the fifth node 138 and a sixth node 140. An anode 142 of the SCR 112 is coupled to the fourth node 132, a gate 144 of the SCR is coupled to the sixth node 140, and a cathode 146 of the SCR is coupled to a seventh node 148. Each of the seventh node 148 and the first node 122 is coupled to one of the first and second pins 52, 54 on the base 12 (see
In operation, the capacitor 110 shown in
The current passing through the alloy wire 50, and the heat generated by the current, causes the alloy wire to contract in length. The contracted alloy wire 50 forces the pawl 48 to exert a biasing force on the rear surface 34 of one of the teeth 22 on the ratchet gear 14. The biasing force causes the ratchet gear 14 to rotate and advance by one tooth pitch 40 in the clockwise direction as oriented in
When the ratchet gear 14 is advanced by one tooth pitch 40, the drive shaft 18 translates the rotation of the ratchet gear to the gear box 82. In turn, the gear box 82 translates the rotation to the cam 84. In the orientation of
After the cam 84 has been locked in position as noted above, eventually the current experienced at the gate 144 of the SCR 112 is no longer sufficient to trigger the SCR and the SCR closes. The closed SCR 112 results in the capacitor 110 once again starting to build a charge and the current to cease passing through the alloy wire 50. The lack of current through the alloy wire 50 permits the alloy wire to cool. The lack of current also permits the spring 46 to expand the alloy wire 50 back toward or to its original length. When this occurs, the pawl 48 is biased back toward the first pin 52 and slides over the front surface 38 of one of the teeth 22.
When the alloy wire 50 has expanded to a sufficient length, the pawl 48 falls into the slot 60 immediately behind the slot in which the pawl mechanism was just located. In other words, the pawl 48 moves about one tooth pitch 40 in a linear direction back toward the first pin 52. The pawl 48 once again engages with the rear surface 34 of another of the teeth 22 and is in position to advance the ratchet gear 14 by another tooth pitch 40.
When the capacitor 110 has been sufficiently charged, the above-described cycle is repeated and the cam 84 is rotated (in a counterclockwise direction in
Eventually, the cam 84 is rotated to a position where the cam follower 92 approaches the flat surface 94 of the notch 88. When the cam follower 92 passes the flat surface 94 due to continued rotation of the cam 84, the cam follower fully springs into the notch 88 and the micro switch 86 is activated or deactivated depending on the micro switch 86 configuration. In the illustrated embodiment, because there is a single notch 88 on the cam 84, the micro switch 86 will be activated once per revolution of the cam. Even so, additional notches (not shown) may be included on the cam 84 such that the micro switch 86 is activated more than once per revolution.
The activated micro switch 86 causes, for example, the defrost mechanism or system (not shown) in the appliance to turn on. That defrost mechanism then defrosts the appliance. In other embodiments, the activated micro switch 86 will temporarily activate or deactivate some other feature or function of the appliance.
As the cam 84 continues to rotate, the cam follower 92 encounters the contoured surface 96 of the notch 88. The contoured surface 96 begins progressively forcing the cam follower 92 back into the remainder of the micro switch 86. When the cam follower 92 has been rotated such that the cam follower leaves the contoured surface 96 of the notch 88 and begins sliding upon the round and regular outer surface 90 of the cam 84, the micro switch is deactivated.
The deactivated micro switch 86 causes, for example, the defrost mechanism or system (not shown) in the appliance to turn off. That defrost mechanism then discontinues defrosting the appliance. However, the cam 84 continues to rotate by one tooth pitch 40 along with the ratchet gear 14 each time the electronic drive circuit 104 supplies a current to the alloy wire 50. Therefore, the defrost cycle in the appliance is repeated at regular, spaced apart intervals in the illustrated embodiment.
As introduced above and as illustrated in
Form the foregoing, those skilled in the art will appreciate that the appliance timer 10 described herein may be used as a simple, low-cost defrost timer for an appliance. In particular, the appliance timer 10 provide a method of slowly rotating a cam 84 to activate the micro switch 86 and initiate the defrost cycle in the appliance.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
