US2452372A - Cam mechanism - Google Patents

Description

Oct. 26, 1948. H KN S 2,452,372

CAM MECHANISM Filed Nov. 2, 1944 Inventor: Joseph R Harkness,

His Attor'he s.

Patented Oct. 26, 1948 CAM MECHANISM Joseph R. Harkness,. Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application'November 2, 1944, Serial No. 561,568

(Cl. 7 i567) 2 Claims. 1

My inventionrelates to ignition'system circuit interrupters and particularly to such devices'as are used withzmagnetos for supplying ignition to multi-bank engines.

An objectof my invention is to provide an improved ignition system circuit interrupter.

Another object of my invention is to provide an improved ignition circuit interrupter operable by a composite laminated cam for providing the de sired circuit interruptions to a single set of breaker contacts for providing ignition to all. of the cylinders-of all of the banks of a multi-bank engine;

Further objects and advantages of my invention will become apparent and my invention will be better understood from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In the drawing Fig. 1 is a plan View of a circuit interrupter incorporating an embodiment of my invention; Fig. 2 is an enlarged end view of the composite laminated cam shown in Fig. 1 mounted on a cam shaft; Fig. 3 is a side view of the compositelaminated cam shown in Figs. 1 and 2; and Fig. 4 illustrates the end views of the two sides of cam laminations forming the compositecam shown in Figs. 1, 2, and 3.

In ignition systemsprovided with magnetos as the source of electrical power, one conventional circuit-interrupter arrangement includes a pair of circuit breakers each of which is operated to open the circuit when the current in the primary of themagneto reaches a maximum current value in one direction of current flow. This has been found to result inadefinite transfer of metal from one of the contactsof the breaker to the other contact, resulting in a building up of one contact and a wearing away of the other. This metal transfer is not the same as pitting which results from= arcing and sparking. between the contacts of the circut interrupter, and is not detrimental in the same sense as the pitting of the contacts, as; the spacing between the contacts tends to remain substantially the same until one of the contacts becomes. worn. away. However, this action is often misinterpreted by mechanics and maintenance. men with the result: that breakers hav ing'contacts of thistype are replaced when such replacement is not necessary. It is desirable, therefore, that this condition should be eliminated or minimized and, therefore, I provide an improved circuit interrupter to overcome this undesirable condition.

Ihe drawing illustrates one embodiment of my invention in which an ignition system circuit interrupter is adapted to interrupt the primary circuit of an ignition system magneto for each maximum current condition of the magneto primary winding for both directions of current flow through this winding. Furthermore, this single set of contacts is adapted to be operated by a single composite laminated cam. In multiple cylinder engines of the multi-bank type it becomes necessary to provide a very large number of lobes onthe cam for operating such a circuit breaker and it becomes increasingly difficult to manufacture a cam of this type and to maintain a reasonable small dimension for the diameter of the cam. There are a number of reasons for the impracticability of manufacturing a one-piece multiple cylinder cam of this type among which is the difficulty encountered in grinding the lobe surfaces on the cam. As is well known in the grinding art, there is a maximum efficiency for the surface speed of the grinder for manufacturing certain articles of specific materials, and if a cam is to be made with a large number of lobes the distance between adjacent lobes decreases directly with the decrease in the size of the cam, and also with the number of lobes for the cam. This results in a decreasing size of the grinding wheel for performing the grinding operation in making the lobes on the cam and requires thatthe grinding wheel be operated at a correspondingly increased speed in order to maintain the desired surface speed for manufacturing the cam. In my improved construction, the cam which is used tooperate the circuit breaker of my improved circuit interrupter is formed of multiple laminations arranged in sets, each of which is adapted to provide the desired circuit interruption for a corresponding bank of cylinders in a multi-bank engine. This type cam. could equally well be used for an engine having a very large number of cylinders even if the engine were notv of the multi-bank type. With such an arrangement itis possible to arrange the laminations of the cam such that the lobes of each set of laminations, or of each lamination if only one laminationis used per set, are fixedly displaced a predetermined angular distance or circumferentially spaced apart from. the lobes of the other sets of laminationsto operate the circuit breaker at the desired timing to provide the desired operation of the circuit breaker into circuit breaking. position for providing the required circuit interruptions toathe ignition system.

Referring to thedrawing, I have shown an em:- bodiment of my improved ignition system circuit interrupter adapted to be used With a twobank engine in which the circuit interrupter is provided with a circuit breaker including a relatively stationary contact mounted on an adjustable supporting bracket 2 and a relatively movable contact 3 mounted on an insulating operating crank i and electrically connected by conductor 5 to a terminal 6 which is insulated 3 from the stationary mounting bracket 2. The movable contact 3 is arranged to cooperate with the stationary contact I for making and breaking the electrical circuit of the ignition system by operation of the crank 4 which is pivotally supported by a pivotal mounting I. The crank 4 is provided with a crank arm 8 on which the movable contact 3 is mounted and with another crank arm 9 arranged with the end thereof formed as a cam follower biased into engagement with the surface of a multi-lobe composite cam. This cam comprises a plurality of similar cam laminations Ii) and II fixedly mounted on a cam shaft l2 and retained against relative rotation thereon by a suitable key is arranged in a keyway on the cam shaft and in complementary keyways in the cam laminations, and retained fixedly on the cam shaft by a suitable nut M which threadedly engages the end of the cam shaft 2 for clamping the cam laminations between the nut and a shoulder IS on the cam shaft. In this construction the composite laminated cam is formed of three laminations, however, any suitable number of laminations arranged in proper axial aligned sets may be used to provide the desired number of lobes to the cam. The illustrated circuit interrupter is adapted to be used with a two-bank engine, although it'might be equally applicable to an engine having the same number of cylinders arranged otherwise than as a two-bank engine. The keyway I6 is formed offset from a median between two lobes on the laminations as shown in Fig. l, and by assembling adjacent laminations on the key l3, the outer two laminations ll! of the three cam laminations are arranged with the lobes thereof in aXial alignment intermediate the lobes of the other intermediate inner cam lamination ll. With this type arrangement, the alternate laminations are arranged in axial alignment and in eifect form a single set of lobes, while the single intermediate lamination H forms another set of cam lobes. This type circuit interrupter is particularly adaptable for use with radial engines of the multi-bank type as all of the cam laminations may be made identical with the same compensation of the cam lobes for each of the laminations if the piston rods of each bank of the engine are arranged in the same order, and the desired angular displacement between adjacent sets of lobes can be provided by the proper location of the keyways in the laminations as shown in Figs. 1, 2, and 3.

In order to provide the desired circuit interruption by the circuit breaker contacts I and 3, the follower end of the crank arm 9 is made of such a width as to span and engage the laminations of both sets of cam lobes as shown in Fig. 3. By making the cam slightly longer axially than the cam follower, the proper operation of the circuit breaker is assured, and an even wear of the follower for both sets of cams will result. If another bank of cylinders were to be used with this ignition system, it would only be necessary to space the lobes of adjacent cam laminations to provide the desired circumferential spacing by 4 properly offsetting the keyway in the cam laminations, With this type arrangement it is possible to manufacture the cam laminations with a relatively large grinding wheel, thereby simplifying the method of manufacture and further assuring the desired accuracy for the spacing and compensation of the cam lobes of the cam, while retaining a relatively small cam diameter for operating a single breaker circuit interrupter.

While I have illustrated a particular embodiment of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, however, that my invention is not to be limited to the particular arrangement disclosed, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

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

1. A cam mechanism for actuating a periodically operated device comprising a rotatable cam shaft, a multi-lobe composite cam member comprising three cam laminations fixedly mounted on said cam shaft adjacent each other with the lobes of the outer cam laminations arranged in axial alignment and the lobes of the intermediate laminations circumferentially spaced from the lobes of outer laminations, a single cam follower having a member engaging and bridging all three of said cam laminations and means for biasing said cam follower into engagement with said cam member.

2. A cam mechanism for operating a periodic switch comprising a rotatable cam shaft, a multilobe composite cam comprising an odd number of similarly shaped cam laminations fixedly mounted on said shaft adjacent each other with the lobes of alternate laminations axially aligned and staggered relative to the lobes of the intermediate lamination, a pivotally mounted cam follower for actuating switching mechanism, said cam follower having a cam-engaging portion bridging all of said cam laminations whereby said cam follower is actuated during each revolution of said shaft a number of times equal to a multiple of the lobes on each lamination, the alignment of the lobes of the alternate cam 1aminations acting to prevent the application of rocking torques to said pivoted cam follower.

JOSEPH R. HARKNESS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,263,247 I-Ionold Apr. 16, 1918 1,322,319 McCutchen Nov. 18, 1919 2,025,191 Davis Dec. 24, 1935 2,303,771 Thomas Dec. 1, 1942 FOREIGN PATENTS Number Country Date 392,454 France July 18, 1908

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