US3077747A

US3077747A - Defrosting system for refrigeration apparatus

Info

Publication number: US3077747A
Application number: US73618A
Authority: US
Inventors: Jr Clark E Johnson
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-12-05
Filing date: 1960-12-05
Publication date: 1963-02-19
Anticipated expiration: 1980-02-19

Description

Feb. 19, 1963 c. E. JOHNSON, JR

DEFROSTING SYSTEM FOR REFRIGERATION APPARATUSl Filed Dec. 5, l1960 ATTORNEY United States Patent Ofice dii? Patented Fels. 1li?, 1353 3,077,747 DEFRSTWG SYSTEM EUR REFRGERATIGN APPARATUS Clark E. Johnson, ltr., Minneapolis, Minn. (1h03 ist Ave. S., Hopkins, Minn.) Filed Dec. 5, 196i?, Ser. No. '73,618 9 Claims. (Cl. 62--14-) This invention relates generally to refrigeration apparatus utilizing forced air circulation, and pertains more particularly to a system for automatically defrosting the evaporator cooling coils when an objectionable amount of frost has accumulated thereon.

lt is well known that the building up of frost and ice on the cooling coils of a refrigeration unit impairs its eiiiciency. Consequently, various arrangements have been devised for ridding the evaporator of the ice that has collected.

For instance, timing arrangements have been rather extensively employed wherein at prescribed intervals `a defrosting cycle is inaugurated. However, it will become immediately apparent that such a cycle is initiated whether the coils have an objectionably thick coating of ice on them or not. On the other hand, the defrosting cycle may be put into operation long after the need therefor arises, if the rate of deposit is quite rapid. Stated somewhat differently, the air passing over the cooling coils may contain varying amounts of moisture depending upon the particular operating and load conditions. The alluded to prior art type of defrosting system maires no allowance for different rates of frost accumulation. Various thermostatic devices have also been used, but these devices are quite local in their detection. ln other words, frost layers will not necessarily be of uniform thickness, nor will the change in thickness always be the same at any given spot in the evaporator.

One object of the present invention is to provide a mechanism that will be highly effective in sensing the frost build up throughout the entire evaporator. More specifically, the invention has for an aim the incorporating into a defrosting system an air actuated switch so disposed that air forced through the evaporator will strike a pivotal vane associated with the switch. When the rate of air ilow is above a preselected magnitude, the switch can be made to operate in one manner; when below the preselected value, the switch can then be made to operate in a reverse fashion. The rate of air flow through the evaporator will vary inversely with the amount of frost that has formed on the cooling coils, for as the coating of ice becomes thicker, greater reriction occurs causing -a decrease in the rate of air flow through the evaporator.

Another object of the invention is to provide an eiiicient defrosting cycle inasmuch as the defrosting action is initiated each time the frost has reached substantially the same degree of accumulation. A constant defrosting interval is employed which is iust long enough to assure the complete de-icing of the coils without overshoot Thus, the defrosting of the cooling coils is only for the requisite period so that the cooling action can be started once again without needless delay after the ice has been removed, thereby preventing unnecessary transmission of heat into the refrigerated area.

A still further object is to provide a defrosting system for refrigerating apparatus that will be simple, inexpensive and reliable in its operation. ln this regard, it is aim of the invention to provide a system of the envisaged character that can be readily installed in conjunction with existing refrigeration equipment of various designs and which will require little or no attention there-l after.

Y et another object is to permit facile adjustment of the control mechanism for different degrees of ice accumulation in order that desired defrosting cycles can be achieved when circumstances so dictate.

Other objects willzbe in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exempliiied in the construction hereafter set forth and the scope of the application of which will be indicated in the appended claims.

In the drawing:

The single FIGURE exemplifying the invention is a schematic representation of my defrosting system in combination with refrigeration apparatus of conventional construction.

The drawing pictures a typical freezing compartment, box or cold-storage room lll having a door l2 via which commodities and the like to be kept chilled may be introduced. For the purpose of facilitating an understanding of the invention, conventional refrigeration apparatus has been illustrated in association with the room li), the apparatus appearing largely in bloclt form owing to its generally well known construction.

The illustrated refrigerating apparatus comprises a compressor lll driven by an electric motor 16 normally controlled through a starter ld. The discharge side of the compressor .i4 is connected through a conduit or line Ztl to a condenser 22 wherein the compressed refrigerant can cool before being delivered to a reservoir or receiver labeled 24. A line 26 having a thermostatic expansion valve 25 therein leads to an evaporator cornprised of one or more cooling coils 3@ (hereinafter rcferred to in the plural). A suitable drain arrangement labeled 3l underlies the evaporator 3i?. In order to simplify the drawing as much as possible the evaporator cooling coils 3i? are shown connected directly to the inlet to the compressor 2i? through a suction line 32, although in actual practice a re-evaporator would normally be employed in the hot-gas defrosting system that has been t illustrated in order to assure that only gaseous refrigerant returns to the compressor i4 from the evaporator 36. Either a pressure motor control or thermostatic motor control can be used for stopping and starting the compressor la. In this instance, a pressure type of control has been illustrated in the form of a pressure switch 33 responsive to the pressure in the suction line 32, such a switch merely closing the circuit to the motor starter 1S on rising pressure and opening on falling pressure.

It should be distinctly understood that my invention can be used with various defrosting systems other than the hot-gas type mentioned above, the use of electrical heating elements in juxtaposition with the coils 30 being but one example. As a matter of fact, it is within the broad contemplation of the invention to employ the invention in connection with Peltier effect thermoelectric cooling, should such cooling systems ultimately become more popular. However, since hot-gas defrosting systems are rather extensively used at the present, the invention will be explained in conjunction with such a defrosting system. Accordingly, a 2-way valve 34 has been shown in the line 2li, the second outlet of the valve being connected to the evaporator cooling coils Sil by a by-pass line. Valved by-pass lines of this type are old and well known, so the details thereof need not be given here other than to say that the object is to supply refrigerant that has been heated by the compressor directly to the evaporator coils Sil so that the evaporator acts temporarily as a condenser. The means for operating the 2-way valve 34 is a solenoid 3S, the control of which will later be described.

In order to circulate the air to be cooled by the coils 30 it is customary to provide a. fan 40 for blowing air through the evaporator as indicated by the arrows 42 and 44, the fan being driven by a motor 46. It is also usual in installations of the depicted type to employ a door switch 48 which is normally held closed when the door 12 is closed in order to energize the fan motor 46. My control system is designed to include both the fan`motor 46 and the door switch 48 in its circuitry, as will presently be made manifest.

With the above background information in mind, it is believed that the reader will have no trouble in understanding the role played by my dcfrosting system, The heart of the system lies in the use of an air actuated switch unit designated generally by the reference numeral 50. The switch unit is located so that it will be subjected to a portion of 4the air stream designated by the arrows 44, this being the air leaving the evaporator coils 30. In its pictured form the switch unit 50 includes a housing 52 having a vane 54 pivotally mounted thereon by reason of a pin 56. Projecting through the housing 52 so as to be engageable by the vane 54 is a plunger 58 which is biased outwardly in the direction of the free or lower end of the pivotal vane 54 by a coil spring 68. Through the agency of an adjusting screw 62 the force exerted by the spring 60 against the vane 54 can be changed. The action of the air between the evaporator coils 30 will normally be suflicient to overcome the biasing action of the spring 60 to the extent thata pair of contacts 64 will be held open to prevent the starting of a defrosting cycle. In order to prevent any of the moving parts of the switch unit 5t), including the vane 56, from freezing it is most desirable that a small electrical heating element be used, this being shown at 66. The heating element may be on the order of only 5.0l watts or so.

Describing now the control circuit of which the contacts 64 are a part, it will be first explained that a suitable source 68 of A.C. power has been illustrated. This may be a 120 volt A.-C. domestic outlet, or it may be D.C. At any rate a disconnect switch 70 has also been pictured. It will be perceived that the heating element 66 is energized as soon as the switch 70 is closed, this being by way of

conductors

72, 74.

For the purpose of timing the duration of the defrosting cycle, a timing motor 76 is employed. The motor 76, when energized, drives a shaft 78 in a clockwise direction as indicated by the arrows 80. The shaft 78 in actual practice carries a single cam, but for drafting reasons two cams 82, S4 have been illustrated. Each

cam

82, 84 is formed with an

arcuate notch

86, 88, respectively.

Actuated by the cam 82 is a first switch unit 90 having iirst and second sets of normally closed

contacts

92, 94 and first and second sets of normally open contacts 96,

98, these being of the make before break variety inasmuch as the

contacts

96 and 98 are closed before the

contacts

92 and 94 are opened. The switch unit 90 also includes a set of normally open contacts 99. Actuated by the cam 84 is a second switch unit 100 provided with a set of normally closed contacts 102 and a set of normally open contacts 104, these contacts also being of the make before break type since it is planned that the contacts 102 be re-engaged before the contacts 104 are opened. Also, forming a part of the switch unit 100 is a pair of normally closed contacts 105.

A slow pickup relay 106 having a time delay of approximately 20 seconds is preferably employed, this relay including normally open contacts 108 in series with the normally closed contacts 92 of the switch unit 90. The function of the relay 106 is to delay the operation of the timing motor 7 6, as initial energization of the timingA motor 76 is from the conductor 74, through the motor 76, through the contacts 108, through the contacts 92,` 64 8.144105, Swith 48, andsntsfs 1.022.111,19 94 t0, the ctmductor 72.

The operation will be readily comprehended from what has already been herein said taken in conjunction with the additional comments that are now to be presented. With the switch 70 closed, the heating element 66 will be immediately energized as has already been explained, At this time the fan 40 will also be placed in operation, for a conductive path will exist through the normally closed

contacts

94 and 102, and the door switch 48. The fan 40 produces a stream of air that enters the evaporator 30, this air being denoted by the arrows 42. After passing around and between the coils 30 constituting the evaporator, the air emerges from the opposite side as indicated by the arrows 44. A portion of this air 44 impinges against the vane 54. With the adjusting screw 62 properly positioned, the velocity head developed by the air striking the vane 54 will be sufficient to overcome the biasing action of the coil spring 60 for an un-iced condition of the coils 30. Consequently, during normal refrigeration of the room 10, the contacts 64 will remain open.

Whenever the door 12 is opened in order to gain entrance to the compartment or room 10, the door switch 48 will open to break the circuit to the motor 46. Hence, the fan 4t) is inoperative when the door 12 is open.

To give the fan 40 a chance to re-establish the requisite pressure needed to maintain the air switch contacts 64 open, the 4time delay relay 106 is preferably utilized. Assuming that the previously mentioned 20 second delay is used, the relay contacts 108 will not close until this selected interval of time has elapsed. Therefore, a circuit is not completed through the timing motor 76 to initiate a defrosting period during the short time that the door 12 is open for normal passage into and out of the cold-storage roorn 10.

However, when the ilow of air has been diminished by the building up of frost on the cooling coils 30 to the extent governed by the setting of the screw 62 and the resulting force applied by the spring 60 against the vane 54 via the plunger 58, the vane 54 is pivoted counterclockwise or toward the coils 30, causing the contacts 64 to close. After 20 seconds the relay 106 causes its normally open contacts 108 to close, thereby completing a circuit through the timing motor 76, the normally closed contacts 92 of the first switch unit 90, the now closed air switch contacts 64, the normally closed contacts 105 of the second switch unit 160, the door switch 48, the other normally closed contacts 102 of switch unit 100, and finally through the normally closed contacts 94 of switch unit 90.

Operation of the motor 76 causes cam 82 to rotate with the consequence that the plunger of switch unit is urged downwardly as the notch 86 rotates out of registry with the plunger, this in turn closing the contacts 96 and thus assuring continued operation ofthe motor 76. At the same time, the starter 18 is energized through contacts 99 and the solenoid 38 is energized through contacts 98. This starts the compressor 14 and simultaneously shifts the 2-way valve 34 so that flow of refrigerant is diverted from its normal path through the line 20 as indicated by the solid arrow 110 to the by-pass line 36 as denoted by the broken arrow 112. This causes the evaporator cooling coils 30 to be supplied with heated refrigerant.

yIn actual practice, as previously explained, a single cam corresponding in function to the two

cams

82, 84 would be used. This would involve the simple expedient of offsetting the switch unit 100 from the switch unit 90, each of their plungers then normally projecting into but a single arcuate notch. However, the same degree of dis placed action is herein achieved by having the notch S8 angularly displaced from the notch 86. Thus, the plunger belonging to the switch unit 100 is forced downwardly a short time, say, two minutes, after the switch unit 90 is actuated. Opening of the contacts 102 breaks the circuit through the fan motor 4 6 which prevents blowing of melted ice throughout the interior of the freezing cont` partment or room lll. Closing of the contacts 164, on the other hand, assures a conductive path for the timing motor '76 until the entire defrosting cycle has been completed which is when the notch 88 is again brought into registry with the plunger of the switch unit ldd. It might be explained that defrosting cycles can vary quite widely as to their periods. Five to iifteen minutes would be typical, even these times being influenced by the thickness of ice allowed to build up, the heat available for defrosting, and other factors. However, for a given defrosting time, the collection of frost can be limited so that the defrosting period is just adequate and not too long.

When the cam S2 has been rotated through almost one revolution, its notch Se comes into registry with the plunger of the switch unit 9G, thus opening contacts 99 and 93 and breaking the circuit to both the motor le via the starter i3 and the circuit to the solenoid 33, respectively. Consequently, the compressor la stops and the Z-way valve 3d returns by spring action (not shown) to its normal position, that is, so that refrigerant will be passed to the condenser 22 in the direction indicated by the arrowl il@ when the compressor is restarted (or immediately if provision is made for its uninterrupted compressor operation at the end of a defrosting cycle).

Although the compressor 1li is restarted, or more aptly expressed, continues to run due to the pressure switch 33, it is not desirable to have the fan il operated until Suthcient cooling has taken place to assure that any water still clinging to the evaporator coils 3@ has been refrozen. Gf course most of the melted ice has been drawn off via the drain 3l, but even the small amount remaining on the coils 3@ should not be blown about within the compartment lll. Thus, While the motor lo is energized through the pressure switch 33 when the contacts 99 on the switch unit 9b are opened, the fan motor to does not at this time become energized due to the fact that the contacts lili on the switch unit lil@ have not closed, the plunger of this unit still being depressed by the cam 8d. However, when the cam has rotated for an additional period which interval is purposely selected to give the evaporator coils Sil enough time to freeze any moisture remaining thereon, a circuit through the fan motor da is then completed from the conductor 72 through the normally closed contacts d, the now reclosed contacts 192, and the door switch i8 to the conductor 7d. ln other words, the orientation of the notches 35 and and the arcuate span of the notch Se are such that this desired interval of postponement with respect to the restarting of the fan di) is realized. The arcuate length of the notch 83, on the other hand, determines the earlier-suggested two minute time interval or delay between the depressing of the plunger belonging to the switch unit 9d and the depressing of the plunger of the switch unit Stili? during the beginning portion of the defrosting cycle.

Thus, when the notch S8 of the cam 3d aligns itself with the plungeof switch unit ltltl, as outlined immediately above, the fan motor #in starts again. Because the contacts ldd open, it follows that the timing motor K will stop, the make before break feature incorporated into the operation of the contacts ldd, lo?. makes certain that the contacts llZ are reclosed before the contacts idd are opened to de-energize the timing motor 7d. Since the ice that had previously formed on the coils lill is now gone, the air from the fan di? meets with only normal resistance from the evaporator coils themselves and the air actuated switch unit Si? is again opened because the vane S4 urges the plunger 5% to the left to open the contacts 64.

Should new frost accumulate at an accelerated rate, the derosting cycle will be repeated more quickly than if the build up rate is rather slow. Thus, the inauguration of a defrosting period is independent of time, although the defrosting period is for a deiinite time. These two important factors contribute immeasurably to the realization of a most eflicient defrosting system.

As many changes could be made in the above construction and many apparently Widely diiierent embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed:

l. in combination with a refrigerating apparatus having an evaporator and fan means for causing air to iiow through said evaporator, a defrosting system including means for removing accumulated frost from said evaporator, an air actuated switch located in the path of the air leaving said evaporator, said switch having a pair of cooperable contacts biased to closed position and having a vane for maintaining said contacts open when sufficient air is leaving said evaporator but permitting said contacts to close when insutlicient air is leaving said evaporator, cam means, a motor for rotating said cam means, means in circuit with said contacts for energizing said motor to cause rotation of said cam means after said contacts have closed, means actuated by rotation of said cam means for intiating operation of said frost removing means and subsequently terminating operation thereof, and means actuated bys said cam means for stopping said motor after said motor has operated for a predetermined period of time.

2. A defrosting system in accordance with claim l including means actuated by said cam means for stopping said fan means during the defrosting period, and means actuated by said cam means for postponing the restarting of said fan means until a predetermined time after the operation of said frost removing means has been terminated.

3. In combination with a refrigerating apparatus having an evaporator, a fan and an electric motor for operating said fan to cause air to iiow through said evaporator, a defrosting system including means for removing accumulated frost from said evaporator, an air actuated switch having a vane located in the path of the air leaving said evaporator and having a pair of co-operable contacts held open by said vane when suilcient air is leaving said evaporator and biased to closed position when insuficient air is leaving said evaporator, cam means, a timing motor for rotating said cam means, means in circuit with the contacts of said air switch for causing said timing motor to start after said air switch contacts have closed, means actuated lby rotation of said cam means for initiating operation of said frost removing means, means actuated by rotation of said cam means for subsequently terminating the operation of said defrosting means, means actuated by rotation of said cam means for stopping said fan motor during the defrosting period, and means actuated by said cam means for restarting said fan motor a predetermined time after termination of the defrosting period.

4. ln combination with a refrigerating apparatus having an evaporator and fan means for causing air to iiow through said evaporator, a defrosting system including means for removing accumulated frost from said evaporator, an air actuated switch located in the path of the air caving said evaporator, said switch having a pair of cooperable contacts biased to closed position and having a vane for maintaining said contacts open when sufficient air is leaving said evaporator but permitting said contacts to clos-e when insuilicient air is leaving said evaporator, a time delay relay having slow pick-up characteristics adapted to be energized when the contacts of said air actuated switch are closed, a motor energizable after said time delay relay has picked up `so as to prevent energization of said motor when said contacts are closed for relatively short periods of insuicient air tlow, cam means actuated by said motor, means actuated by said cam means for initiating operation of said frost removing means and subsequently terminating operation thereof, and means actuated by said cam means for stopping said motor after said motor has operated for a predetermined period of time.

5. In combination, a cold-storage room having a door leading thereinto, refrigerating apparatus including an evaporator disposed Within said room, a fan, an electric motor for operating said fan to cause air to flow within s'aid room and through said'evaporator and a door switch for stopping said fan while said door is open, a defrosting system including means for removing accumulated frost from said evaporator, an air actuated switch having a vane located in the path of the air leaving said evaporator and having a pair of co-operable contacts held open by said vane when sufiicient air is leaving said evaporator and said contacts being biased to closed position when insuflicient air is leaving said evaporator, a timing motor, cam means rotatable by said timing motor, a slow pick-up relay in circuit with said air switch contacts for causing operation of said timing motor a predetermined period of time after closure of said air switch contacts, means actuated by rotation of said cam means for initiating operation of said frost removing means, and means actuated by sufcient rotation of said cam means for subsequently terminating operation of said defrosting means.

6. A defrosting system in accordance with claim including means actuated by rotation of said cam means for stopping said fan motor a predetermined time after starting of said timing motor.

7. A defrosting system in accordance with claim 6 including means actuated by said cam means for restarting said fan motor a predetermined time after termination of the defrosting period.

8. In combination with a refrigerating apparatus having an evaporator, a fan and electric motor for operating said fan to cause air to flow through said evaporator, a defrosting system including means for removing accumulated frost from said evaporator, an air actuated switch located in path of air leaving said evaporator, said switch having contacts biased to closed position when insufficient air is leaving said evaporator and maintained open `when sufficient air is leaving said evaporator, a timing motor, cam means rotatable by said timing motor, first means responsive to said air` switch providing an energizing electrical path through said timing motor to cause rotation of said timing motor` when said air switch contacts are closed, means actuated by said cam means for continuing energization of said timing motor during a predetermined amount of rotation of said cam means, means actuated by said cam means for causing operation of said frost removing means during one portion of said predetermined amount of rotation of said cam means, and means actuated by said cam means for stopping said fan motor during a second portion of said predetermined amount of rotation of said cam means, the beginning of said second rotative portion starting before the ending of said first portion.

9. In combination, a cold-storage room having a door leading thereinto, refrigerating apparatus including an evaporator disposed within said room, a fan, an electric motor` for operating said fan to cause air to flow within said room and through said evaporator, and a door switch for stopping said fan motor when said door is open, a defrosting system including means for removing accumulated frost from said evaporator, an air actuated switch having a vane located in the path of the air leaving said evaporator and having a pair of co-operable contacts held open by said vane when sufiicient air is leaving said evaporator and said contacts being biased to closed position when insufiicient air is leaving said evaporator, a timing motor, a cam means rotatable by said timing motor, a rst switch unit actuated by initial rotation of said cam means having first and second sets of normally closed contacts and first, second and third sets of normally open contacts, a second switch unit actuated after a given amount ot rotation of said cam means having tirst and second sets of normally closed contacts and a set of normally open contacts, a slow pick-up relay having normally open contacts, circuit means connecting said fan motor to said power supply through said door switch, the first set of normally closed contacts of said second switch unit and the second set of normally closed contacts of said first switch unit, circuit means connecting said relay to a power supply through the first set of normally closed contacts of said first switch unit, said air switch contacts, the second set of normally closed contacts of said second switch unit, the door switch, the rst set of normally closed contacts of said second switch unit and the second set of normally closed contacts of said tirst switch unit to cause encrgization of said relay, circuit means connecting said timing motor to said power supply through the normally open contacts of said relay, the first set of normally closed contacts of said first switch unit, said air switch contacts, the second set of normally closed contacts of said second switch unit, the door switch, the first set of normally closed contacts of said second switch unit and the second set of normally closed contacts of said irst switch unit to cause operation of said timing motor, means in circuit with the first set of normally open contacts of said first switch unit for continuing the energization of said timing motor from said power source during actuation of said first switch unit, circuit means connecting said frost removing means to said power supply through the third set of normally open contacts of said first switch unit to cause operation of said frost removing means, circuit means connecting said timing motor to said power supply through the normally open contacts of said second switch unit and the second set of normally closed contacts of said first switch unit, and circuit means connecting said timing motor to said power supply through the second set of normally closed contacts of said first switch unit and the normally open contacts of said second switch unit, said cam means actuating said first switch unit for a period of time and later actuating said second switch unit for a period of time equal to or`shorter than the period of time the first switch unit is actuated with the actuation of the second switch unit terminating after the actuation of the first switch unit.

Crago Ian. 10, 1939 Von Arb Dec. 6, 1960

Claims

1. IN COMBINATION WITH A REFRIGERATING APPARATUS HAVING AN EVAPORATOR AND FAN MEANS FOR CAUSING AIR TO FLOW THROUGH SAID EVAPORATOR, A DEFROSTING SYSTEM INCLUDING MEANS FOR REMOVING ACCUMULATED FROST FROM SAID EVAPORATOR, AN AIR ACTUATED SWITCH LOCATED IN THE PATH OF THE AIR LEAVING SAID EVAPORATOR, SAID SWITCH HAVING A PAIR OF COOPERABLE CONTACTS BIASED TO CLOSED POSITION AND HAVING A VANE FOR MAINTAINING SAID CONTACTS OPEN WHEN SUFFICIENT AIR IS LEAVING SAID EVAPORATOR BUT PERMITTING SAID CONTACTS TO CLOSE WHEN INSUFFICIENT AIR IS LEAVING SAID EVAPORATOR, CAM MEANS, A MOTOR FOR ROTATING SAID CAM MEANS, MEANS IN CIRCUIT WITH SAID CONTACTS FOR ENERGIZING SAID MOTOR TO CAUSE ROTATION OF SAID CAM MEANS AFTER SAID CONTACTS HAVE CLOSED, MEANS ACTUATED BY ROTATION OF SAID CAM MEANS FOR INTIATING OPERATION OF SAID FROST REMOVING MEANS AND SUBSEQUENTLY TERMINATING OPERATION THEREOF, AND MEANS ACTUATED BY SAID CAM MEANS FOR STOPPING SAID MOTOR AFTER SAID MOTOR HAS OPERATED FOR A PREDETERMINED PERIOD OF TIME.