US2174086A - Electromagnetic switch mounting - Google Patents

Description

2 Sheets-Sheet 1 mm .P

Q mu v :F N hw Q Sept. 1939- E. L. HOFFMANN ELECTROMAGNETIC SWITCH MOUNTING Filed Dec. 50, 1936 p 26, 1939- E. L. HOFFMANN 2,174,086

ELECTROMAGNET IC SWITCH MOUNTING Filed Dec. 30, 1936 2 Sheets-Sheet 2 INSULATION &2- 44 l a 9 I66 .ZZMEQ 561.15 fioFFAm/v/v.

Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE ELECTROMAGNETIC SWITCH MOUNTING Application December 30, 1936, Serial No. 118,209

5 Claims.

This invention relates to an automatic frequency selector, and more particularly to an automatic switching mechanism which is adapted to selectively connect a plurality of frequency changing elements in desired position in a high frequency apparatus. The invention is particularly suitable for use in conjunction with a radio broadcast receiving set.

In high frequency apparatus which is adapted to operate at a number of different frequencies, such for example, as radio receiving set, the change from one frequency setting to another is generally accomplished through the use of a number of variable condensers. Although the usual radio receiving set is arranged for adjustment to a very large number of different frequency settings, in practice it has been found that the equipment is usually operated at one of a relatively few frequency settings. That is to say, the programs which are provided by four or five local stations are generally suflicient to satisfy the average listener. Although the manipulation of the control knobs of a radio receiving set is relatively simple, it nevertheless has been found to be a considerable nuisance on many occasions. This is particularly true where the radio receiving equipment is mounted in an automobile where the person operating the radio receiving equipment must direct a greater part of his attention to the driving of the machine.

It is an object of the present invention to provide a novel automatic frequency selector which will enable the operator of high frequency apparatus to change from one frequency setting to another with a minimum of effort and attention.

Another object of this invention is to provide an automatic frequency selector which is economical to manufacture, which is eflicient in operation, and which is rugged and reliable in use.

A further object of this invention is to provide a novel automatic frequency selector wherein one of a predetermined number of frequency settings may be obtained by depressing one of a corresponding number of push button switches.

A still further object of this invention is to provide a novel automatic selector switch construction having a frame construction made from a single stamping.

Another and further object of this invention is to provide a novel automatic selector switch mechanism having a novel arrangement of elements.

Another and still further object of this invention is to provide a pawl and ratchet drive mechanism which permits movement of the pawl prior to the time when the pawl engages the ratchet to do work thereupon.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention 5 itself, however, both as to its organization and manner of construction, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying lo drawings, in which:

Figure 1 is a diagrammatic view of one embodiment of my invention wherein a plurality of relatively fixed condensers, such as trimmer condensers, are adapted to be selectively shunted across the three units of a gang condenser;

Figure 2 is a front elevational view partly in cross section illustrating the automatic selector switch mechanism;

Figure 3 is a side elevational view partly in cross section of the automatic selector switch mechanism shown in Figure 2; and

Figures 4 and 5 illustrate how the armature mechanism is mounted on its support.

Referring now to Figure 1 of the drawings, the arrangement illustrated therein includes a three unit gang condenser [0 having rotor plates I I, I2, and I3, and stators I4, I5, and I6. Although only one rotor plate and two stator plates have been illustrated for each condenser, it is of course to be understood that any number of rotor plates and stator plates may be employed, the number being reduced here merely for the purpose of simplicity of illustration. Three groups of trimmer condensers I'I, I8, and I9 are associated with gang condenser I0. Trimmer condenser group I1 includes five trimmer condensers 20, 2|, 22, 23, and 24, each of which has one side thereof connected to a common lead 25, which connects this group of condensers to stator I4. Trimmer con- 40 denser group I8 includes five trimmer condensers 26, 21, 28, 29, and 30, each of which has one side thereof connected to a common lead 3| which connects this group to stator I5. Trimmer condenser group I9 includes five trimmer condensers 32, 33, 34, 35 and 36, each of which has one side thereof connected to a common lead 31 which connects this group to stator I6. The opposite sides of the condensers of groups I'I, I8, and I9 are adapted to be selectively connected to rotors II, I2, and I3 through lead wires 38, 39, and 40 respectively by a selector switch mechanism presently to be described.

The rotary selector switch by which a condenser is selected from each of condenser groups 5 il, l 9, and l9 and connected across the associated units of gang condenser l9 will now be described. A plurality of multiple contact rotary switches 4 l, 42, and 49 are mounted with their respective movable contact elements 44, 45, and 49 on a common shaft 4i. As will be observed from an inspection of the drawings, movable contact elements 44, 45, and 49 have different configurations for a reason which will presently appear. Rotary switch 4i is provided with twelve annularly disposed, substantially equally spaced stationary contacts 49, 49, 59, 5E, 52, 53, 54, 95, 56, 51, 58, and 59. Movable contact element 44 of switch ll is divided into two portions 90 and 6! which are electrically insulated from each other. Portion 99 includes a substantially semi-circular conducting strip 92 and a projecting conducting tongue 93. Portion Si is similarly provided with a substantially semi-circular strip 94 and a conducting tongue 95. Stationary contacts 49 to 59 inclusive are so disposed that they will engage one of the projecting conducting tongues when that tongue passes beneath it but will not engage at any time circular portions 62 and 94.

Two additional stationary contacts 69 and 61 disposed diametrically opposite each other are arranged to engage one or the other of circular conducting strips 92 and 64 at all times, It will thus be apparent that stationary contact 95 may be electrically connected to one of stationary con tacts 49, 49, 59, 9!, 52, or 59, depending upon the position of projecting conducting tongues 99 and 65, while stationary contact 97 may be connected to one of the stationary contacts 54, 55, 56, 51, 99, and 59.

As will be seen from the drawings, stationary contacts 49 to 59 inclusive are electrically connected to trimmer condensers 29 to 24 inclusive, while stationary contacts 54 to 59 inclusive are electrically connected to trimmer condensers 26 to 39 inclusive. Stationary contact 69 is electrically connected through conductor 38 to rotor ll of gang condenser it, while stationary contact is electrically connected through conductor 39 to rotor l2 of gang condenser l9.

Movable contact element 45 of switch 42 is similar in shape to movable contact element 44 of switch 4i, with the exception that it is not severed into two complementary halves. Movable contact element 45 includes a completely circular conducting portion 99 and two projecting conducting tongues 69 and 79. Six stationary contact elements ll, l2, l9, l4, l5, and '06 are substantially equally spaced about movable contact element 45 throughout an angle of substantially 180". These stationary contacts are disposed in relation to movable contact element 45 so that they will at no time engage circular conducting portion but will engage either tongue 69 or tongue 719 as it passes therebeneath. An additional stationary contact W is arranged to engage circular conducting portion 99 at all times. Stationary contacts 12 to 76 inclusive are electrically connected to trimmer condensers 32 to 99 inclusive, while stationary contact i1 is electrically connected through conductor 49 to rotor E9 of gang condenser ill, in a manner similar to that described in connection with rotary switch 4i. As one or the other or" conducting tongues 99 or 79 engage one of the stationary contacts H to l9 inclusive that contact is electrically connected to stationary contact l! and hence to rotor l3.

Movable contact element 46 of switch 43 includes a circular conducting strip 79 which is provid'ed with two diametrically opposed cut-out portions 19 and 89. Six stationary contacts 8i,

82, 83, 84, 85, and 86 are disposed about circular contact element 45 throughout an angle of substantially 180. In contradistinction to the arrangement of rotary switches 4| and 42, stationary contacts 8! to 89 inclusive are arranged to electrically engage circular conducting strip 18 at all times, except when one of the two cut-out portions 79 and 99 fall therebeneath. An additional stationary contact element 8'! which extends further into the rotary switch 43 is arranged to engage circular conducting strip 18 at all times irrespective of the position of cut-out portions 19 and 80.

Switch 43 is the switch by which the angular position of shaft 41 is controlled. Insofar as the explanation of Figure l is concerned, it is to be understood that shaft 47, upon which movable contact elements 44-, 45, and 49 are secured, will be rotated by means of a pawl and ratchet drive (the ratchet not being shown in Figure 1 for purposes of simplicity of illustration). The pawl and ratchet drive, or, as it is sometimes called, the stepping mechanism, includes a solenoid 88, a solenoid armature 89 which is mounted for angular movement in close proximity to the upper end of solenoid 89, a pawl 99 connected to the free end of armature 99, and a ratchet (not shown in Figure 1) which is mounted on shaft 41 and arranged to be engaged and driven by pawl 99. The lower end of solenoid 88 is electrically connected to stationary contact 8'! of switch 43. The upper end of solenoid 88 is electrically connected to a leaf spring contact element 9| secured to the upper part of armature 89 which is adapted to engage a stationary contact 92 when armature 89 is in its uppermost position and to be disengaged therefrom when armature 89 is in its lowermost position. As will now be explained, solenoid 88 is adapted to be energized from a suitable source of electric energy 93 through switch 43 and contacts 9| and 92.

Electrically connected to the lower end of energy source 93 are six parallel connected push button switches 94, 95, 96, 91, 98, and 99. The opposite sides of push button switches 94 to 99 inclusive are electrically connected to stationary contacts 8| to 86 inclusive of rotary switch 43. It will thus be apparent that if one of push button switches 94 to 99 inclusive is depressed and its cooperating stationary contact on rotary switch 43 is in engagement with circular conducting strip 18, solenoid 88 will be energized and armature 89 will be moved downwardly. Downward movement of armature 89 causes contact 9| to break from contact 92, and solenoid 88 is deenergized. Biasing spring I90 connected to armature 89 causes the return of armature 89 to its uppermost position, and contact 9| again engages contact 92, whereupon if the push button switch is still depressed and its cooperating stationary contact on switch 43 is still in engage ment with circular conducting strip "i8, solenoid 88 is again energized, thereby causing armature 99 to be again depressed. Each time armature 99 is moved downwardly, pawl 99 effects engagement with its cooperating ratchet wheel (not shown in Figure 1), thereby causing rotation of shaft 41. Assuming for the moment that push button switch 9'! is the switch which is depressed, it will be readily understood that solenoid 88 will continue to effect rotation of shaft 4'! until cut-out portion 19 falls opposite stationary contact 84. At this time the rotational movement of shaft 47 will cease, irrespective of whether contact 91 is held down or not, since the electrical energization circuit to solenoid 88 is effectively broken in switch 43.

It is to be remembered. that as shaft 41 rotates movable con-tact elements 44 and 45 of switches 4| and 42 are also being rotated. Thus, when cut-out portion 18 of switch 43 moves into position opposite stationary contact 84, conducting tongue 10 of switch 42 has moved into engagement with stationary contact 14, conducting tongue 05 has moved into engagement with stationary contact 51, and conducting tongue 63 has moved into engagement with stationary contact 5|. Engagement of conducting tongue 10 with stationary contact 14 causes trimmer condenser 34 to be connected across the rear unit of gang condenser I0, while engagement of tongue '65 with stationary contact 51 causes trimmer condenser 28 to be connected across the middle unit of gang condenser I0, and engagement of tongue 63 with stationary contact 5| causes trimmer condenser 22 to be connected across the front unit of gang condenser I0. It will thus be readily understood that when push button 94 is depressed and held closed until the pawl and ratchet drive mechanism has ceased to operate, trimmer condensers 20, 26, and 32 will be connected across the front, middle, and rearward units respectively of gang condenser I0. Similarly, depression of push button 05 effects rotational movement of rotary switches M and 42 until trimmer condensers 2|, 21, and 33 are connected to gang condenser |0. Push button switch 91 connects trimmer condensers 22, 28, and 34 to gang condenser I0; push button switch 98 connects trimmer condensers 23, 29, and 35 to gang condenser I0; and push button switch 99 connects trimmer eondensers 24, 30', and 36 to gang condenser I0.

It is to be noted that push button switch 94 is associated with stationary contacts 48, 54, and 1| of switches 4| and 42, which contacts are not electrically connected to any special equipment. Preferably, contacts 48, 54, and 1| are left open circuited so that when it is desired to remove the effect of the automatic frequency selecting equipment from the high frequency apparatus, it is simply necessary to depress push button switch 94 which moves conducting tongues of switches 4| and 42 into engagement with stationary contacts 48, 54, and 1|.

Referring now to Figures 2 and 3 of the drawings, the specific structure of one form of stepping mechanism embodying the principles of the present invention will be described. The frame of the automatic selector switching mechanism is made from a one-piece stamping Idt and includes an upright partition I02, an integral solenoid base portion I03 which extends substantially perpendicular from the lower edge of partition I02, and an integral solenoid end wall and armature support I04 which extends substantially perpendicular from partition I02, as shown in Figure 2 of the drawings. The solenoid 08 of the selector switching mechanism is mounted in an upright position on base I03 in close proximity to end wall I04. Solenoid 88 is provided with the usual iron core I05 for the purpose of greatly increasing the effective magnetizing force of the solenoid.

A solenoid armature 89 is mounted for limited angular movement above the upper end of solenoid 88. Armature 89 may be pivotally secured to end wall I04 in any suitable manner, it being remembered that only a very limited angular movement is necessary to effect desired operation of the armature. One simple method of securing armature 89 to end wall I04 which has been found extremely satisfactory in practice is to slot the upper edge of end wall I04, into which slot I06 a cut-out neck portion I01 is disposed (see Fig- The upper projections I08 and ures 4 and 5).

Hi9 which define slot I06 may be peened over the neck portion I01 of armature 89 after the armature 89 is disposed within slot I06 to prevent subsequent removal thereof.

The outer end of armature 89 is turned upwardly as at IIO to permit securement thereon of drive pawl 90. Drive pawl 90' may be secured to end portion ||0 of armature 89 in any suitable manner, such as by means of a bolt II I.

Armature 89 also includes an integral downwardly extending portion ||2 which terminates a forwardly extending portion II3. Armature biasing spring I00 connects the lower end N3 of downwardly extending portion M2 to a tab i 24 which is bent forwardly from the upper edge of partition I02 and is thereby integral therewith. It will thus readily be seen that by providing this downwardly extending portion II2 on armature 03, a much more compact structure is obtained, since tab N4 of partition I02 may be disposed much closer to armature 89 than would otherwise be the case.

Armature 89 carries on its upper surface a leaf spring contact 9| which is secured to armature 89 through insulating blocks H5 and H6. Leaf spring contact 9| is arranged to engage an adjustable stationary contact 92 when armature is in its uppermost position; that is to say, when solenoid 88 is not exerting any downward force on armature 89.

A ratchet wheel II1, which is adapted to be engaged by pawl 90, is secured on shaft 41. Shaft i? is freely mounted in a bearing collar IIO carried in partition I02 of frame IOI. It will thus be apparent that as pawl moves downwardly into engagement with one of the teeth of ratchet wheel H1, shaft 41 is rotated through a small angle, depending of course upon the range of movement of the end of pawl 90' after it engages a tooth on ratchet wheel II1.

The stationary contacts of switches 4|, 42, and 43 are mounted ontwo insulating blocks I I9 and E20, which are secured to partition I02 of frame Itil by a support arm I2| which extends through partition I02. Ring blocks II9 and I20 may be conveniently secured to support arm |2| by means of a long bolt I22 which extends through support arm. |2| and a cooperating nut 23. Upon close inspection of Figure 3 of the drawings, it

will be observed that stationary contacts 48 to 5d inclusive of switch 4| are disposed. on the outer side of insulating block H9. Only two of the stationary contacts 52 and 58 of switch 4| have been shown in Figure 3 for purposes of simplicity of illustration, but it will of course be understood that twelve stationary contacts substantially equally spaced are secured to insulating block H9 as is indicated in Figure l of the drawings. Although not illustrated in Figure 3, it will also be understood that the two elongate stationary contacts 66 and 61 are arranged on insulating block I I9 in such a manner that they engage the conducting rings 62 and 64.

The short stationary contacts II to it inclusive of switch 42 and the elongate stationary contact 11 are mounted on the inner side of insulating block I20. Although only the elongate stationary contact 11 is shown in Figure 3, it will of course be understood that the short stationary contacts H to 16 inclusive are disposed about insulating block I20 in the manner indicated in Figure l of the drawings.

The stationary contacts 8! to 86 of switch 43 and elongate stationary contact 81 of switch 43 are similarly disposed on the outer face of insulating block lit (see Figures 3 and 4). The general configuration of the stationary contacts of all three rotary switches 4!, 42, and 43 will be understood from an inspection of Figure 2 of the drawings, it being understood that the stationary contacts of each rotary switch are similar in configuration.

The movable contact elements 44, 45, and 46 of rotary switches 4!, l2, and 33 are secured to two insulating blocks 52% and 125 which are secured to shaft 4?. As will be seen from an inspection of Figure 3 of the drawings, insulating blocks i2 1 and liii are disposed within circular apertures in insulating blocks H9 and i251, the apertures being sufficient in size to permit free rotation of blocks i2 2 and H25 therein.

In order to prevent movement of ratchet i H in the wrong direction, a stop pawl I26 is provided to engage the opposite side of ratchet wheel ill from that of pawl 96. Stop pawl I26 may be conveniently secured by means of a bolt I2! to a tab 528 which is bent substantially perpendicular to partition Hi2 and is integral therewith.

Now one of the important features of the present invention is the manner in which the drive pawl 96 engages ratchet wheel Ill. Referring to Figure 2 of the drawings, it will be noted that when armature 89 is in its uppermost position, the lower free end of drive pawl is disposed part way between two adjacent tooth spaces. It will thus be observed that as drive pawl $5] begins to move downwardly it does not engage a tooth on ratchet wheel ll'l until it has moved a fractional part of the tooth pitch. As drive pawl 9E1 continues to move downwardly, the lower end thereof engages a tooth on ratchet wheel ill and advances it to the position indicated in the dotted line. This arrangement of drive pawl 8E3 with respect to the ratchet wheel 5 ll permits the armature 89 to get into motion before it has to do work upon the ratchet wheel Hl. This arrangement permits the use of a much smaller solenoid for actuating the armature 89 than would otherwise be necessary if the drive pawl 90 had to immediately start to do work upon the ratchet wheel lii when the solenoid is energized.

The operation of my automatic frequency selector will now be described. Assuming for the moment that the five diiferent frequencies at which the high frequency apparatus is most used are f1, f2, f3, f4, and f5, the gang condenser H3 is adjusted so that the rotors ll, l2 and I3 are in their uppermost position, that is, outside of the stator plates id, !5 and i5. Trimmer condensers 2t, 25 and 32 are then adjusted so that the high frequency apparatus operates at frequency f1; trimmer condensers 2i, 2? and 33 are adjusted so that the high frequency apparatus operates at frequency f2; trimmer condensers 22, 23 and 3 5 are adjusted for frequency is; trimmer condensers 23, 29 and 35 are adjusted for frequency f4, and trimmer condensers 24, 3E) and 36 are adjusted for frequency is.

Assuming now that it is desired to operate the high frequency apparatus at frequency is. The push button switch 91 is depressed, thereby causing energization of the solenoid 88 which in turn causes vibratory movement of the armature 89, thereby effecting rotation of the shaft 47. The

push button switch Si! is held depressed until the vibration of armature 85 ceases, this event occurring when the cut-out portion it comes into position opposite the stationary contacts 84% of the rotary switch 43. At this time, the conducting tongue 70 of the rotary switch 62 is in engagement with the stationary contacts i l, thereby connecting the trimmer condenser '34 into operative position in the circuit of the high frequency apparatus. The conductor tongue 65 is likewise moved into position in engagement with the stationary contact 5?, thereby placing the trimmer condenser 28 into operative position in the circuit of the high frequency apparatus. Conducting tongue 53 similarly moves into engagement with the stationary contacts 55, thereby connecting the trimmer condenser 22 to the high frequency apparatus. The frequency of the high frequency apparatus has now been changed from its original value to frequency is.

Assuming now that it is desired to change the frequency setting from f3 to ii. The push button switch is depressed and held down until the vibratory action of the armature 69 has ceased. At this time, the cut-out portion 8% of the switch 43 will be opposite the stationary contact the conducting tongue 58 of the switch 1-2 will be in engagement with the stationary contact l2; the conducting tongue 63 of the switch 45 will be in engagement with the stationary contact 55; and the conducting tongue 65 will be in engagement with the stationary contact M. This arrangement of the rotary switches ll, 52 and 13 causes trimmer condensers 2d, 2 3 and to be connected in operative positions to the gang condenser l9.

Assume that it is now desired to operate the high frequency apparatus by means of the gang condenser It. The push button switch 94 is depressed and held in closed position untii the vibratory action of the armature 89 has ceased. At this time, the movable contact elements 45 and 56 of the switches ll, '52 and 63 will be in the position shown in Figure l of the drawings. Since the conducting tongues 63', and iii are in engagement with stationary contacts and H, which are open circuited, it is obvious that all of the trimmer condensers have been removed from operative circuit engagement with the gang condenser Id. The gang condenser iii may now be operated in the usual manner.

From the above description, it will be apparent that I have provided an extraordinarily simple, compact auxiliary automatic frequency selector, which may readily be connected to any high frequency apparatus. By providing adjustable trimmer condensers, any five frequencies which are desired by the user of the high frequency apparatus may be set up on the automatic frequency selector unit. It will also be understood that, because of the supreme simplicity of the construction, the automatic frequency selector is economical to manufacture.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto, since many modifications may be made, and I therefore contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. In an automatic selector switching mechanism of the type having a solenoid, an armature adapted to be actuated by said solenoid, a biasing spring for said armature, a pawl secured to an outer end of said armature, and a ratchet wheel adapted to be moved by said pawl, a frame therefor made from a single stamping having an upright partition adapted to carry said ratchet wheel, an integral base portion extending substantially perpendicular to said partition and adapted to support said solenoid, an integral solenoid end wall and armature support extending substantially perpendicular to said partition, the lower end of which is disposed in close prox imity to one edge of said base portion, and an integral upper tab extending substantially perpendicular to said partition adapted to have said biasing spring secured thereto.

2. In an automatic selector switching mecha nism of the type having a solenoid, an armature adapted to be actuated by said solenoid, a biasing spring for said armature, a pawl secured to the outer end of said armature, and a ratchet wheel adapted to be moved by said pawl, a frame therefor made from a single stamping comprising an upright partition adapted to carry said ratchet wheel, an integral base portion extending substantially perpendicular to said partition and adapted to support said solenoid, an integral solenoid end wall and an armature support extending substantially perpendicular to said partition, the lower end of which is disposed in close proximity to one edge of said base portion, an integral upper tab extending substantially perpendicular to said partition adapted to have said biasing spring secured thereto, and a second integral tab extending substantially perpendicular to said partition in close proximity to another edge of said base portion, said second tab being adapted to carry a stop pawl for said ratchet wheel.

3. A rotary switch operating mechanism comprising a side plate, a flange along one edge of said plate, a second flange along an adjacent edge of said plate and forming a corner with said first flange, a solenoid in said corner having a core parallel to said plate and said first flange, a shaft bearing carried by said side plate beside said solenoid and perpendicular to said side plate, a shaft in said bearing, a ratchet wheel on the shaft, an armature pivotally mounted on said first flange and extending across the end of said core away from said second flange, said flanges and core and armature forming a magnetic circuit, and a pawl operatively connected to said armature and placed to rotate said wheel upon reciprocation of said armature.

4. A rotary switch operating mechanism comprising a side plate, a flange along one edge of said plate, a second flange along an adjacent edge of said plate and forming a corner with said first flange, a solenoid in said corner having a core parallel to said plate and said first flange, a shaft bearing carried by said side plate beside said solenoid and perpendicular to said side plate, a shaft in said bearing, a ratchet wheel on the shaft, an armature pivotally mounted on said first flange and extending across one end of said core, said flanges and core and armature forming a magnetic circuit, a pawl carried by the armature and engaging said ratchet wheel, a lug extending perpendicular to said plate close to said armature on the opposite side thereof from said solenoid and said ratchet wheel, an arm on said armature extending away from said lug alongside of said solenoid and said ratchet wheehand a spring connecting said arm and said lug to resiliently urge said armature away from said solenoid.

5. An electrically operated rotary switch comprising a side plate, a flange along one edge of said plate, a second flange along an adjacent edge of said plate, said flanges forming a corner, a solenoid in said corner having a core perpendicular to said second flange and parallel to said side plate and said first flange, an elongated shaft bearing carried by said side plate beside said solenoid and perpendicular to said side plate, a shaft in said bearing, a ratchet wheel on the shaft adjacent said bearing, rotary switching mechanism on the shaft and spaced from said ratchet Wheel, an armature pivotally mounted on said first flange and extending across the end of said core, said flanges and core and armature forming a magnetic circuit, a pawl carried by the armature and engaging the ratchet wheel, a lug extending perpendicular to said side plate close to said armature on the opposite side thereof from said solenoid and said ratchet Wheel, an arm on said armature extending away from said lug alongside of said solenoid and between said ratchet wheel and said switching mechanism, and a spring connecting said arm and said lug to resiliently urge said armature away from said solenoid.

ELMER LESLIE HOFFMANN.

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