US2469792A - Engine starter gearing - Google Patents

Description

May 10, 1949. .1. E. BUXTON ETAL 2,469,792

ENGINE STARTER GEARING Filed May 27, 1947 INVENTORS James 6.

Patented May 10, 1949 ENGINE ISTARTERGEARING ilames E; Buxton; Frank T; Gl'ifistian, and Rene E. DemurmilElmira; N. Ys assignorsto' Bendix Aviation iflonponatiomra corporation of Delaware Application May 27, 1947;"Srial No; 7501726 :3 Claims. (01; 34-47) 1 The present invention relates toengine starter gearing and more particularly to a star ter drive of the type in 'wh'ich ap'inion is automatically traversed into and out of mesh with a' 'ear of an'engine tobe started.

Engine starter drives as now commercially manufactured are generally oi -the socalled barrel type in which a smooth-bored-dr ive pinion is slidably journalled on the motor shaft ior 'longitudinal movement intoand out of mesh with-an engine gear, and is 'actu-atedbya control nut threaded-on a *motor driven-screw :shaitfithespinion "being I connected to the control nut by a. hollow barrel member.

In order to secure reliable traversingaction-of thenut 'under all conditions or congealed lubricant -etc., it is necessary that the inertia of the nut, barrel and pinion as respects rotation be large relatively to the inertia of these parts in respect to "longitudinal movement. "This result may readily-be secured by increasing the-diameter of thebarrel while-preferably reducing "its "wall thickness, but when this practice is iollowed too far; undesired re'enga'gements of the pinion with the *eng'ine'gear after demes'hare encoun- 9 tered. These undesired reeng'agements are caused by the iact that the operator doesznot ordinarily'open the starting switch at the instant the engine fires and demeshes the'pinion. The

starting motor therefore accelerates due *to' 'the release of the cranking load thereon and consequenltly traverses the control -nut, barreland=pinion back toward the-engine fly wheel "until the pinion strikes the side of the rapidly rotating engine gear;causingunnecessary wear and noise.

It is an object of the present invention to provide a novel engine starter drive having adequate rotational inertia to secure traversal under adverse circumstances, but having means for preventingtraversal of the :pinion ba'c'k towardthe Eig; 2 is -a-section taken substantially entire -Riel- 3 is a detail in perspective, partly-broken away and 'in' section, of the barrel and pinion assembly; and

"Fig. 4 is a view similar to Fig. 2 0f a modified .iorm of the invention.

Filn Fig. -1 oi the drawing, there is illustrated "answer sha'it i whioh maybe the extended-"arma- *ture s'haiftoi astarting motor notillustrated the outer end -oi which is .supported invan outboard bearing 2 preferably attached to the iramemiithe startingmotor. A pinion 371s s'lidably iournalled on the power shaft for longitudinal "movement "into and out or mesh "with a gear 4 of the engine to be started. I Lat-hollow sleeve i5 is fixed on the power shaft l asbymeans-lof a qiin6 and'is*yield ably "c'onnect'ed by means oi -adrive :spring" '1 to a screw-shafts which is :slidably tjournallied: :on a reduced portion 9 of saidsleeve, the screw shaft being retained on the sleeve by a stop Ii.

A .control nut "l 2 is threaded .on the screw shaft band is rigidly connected as indicated at: .i 3 to a=cyllndrical-barrel M which is rigidly attached to themiiiion-fi asrsh'own at 1:5. I

T-he threads of the-screw shaft :8 terminate ad jacen t-the idle position of the controlnut -l2-1eaving a smooth portion I6 on'whichthe control nut is "free to rotate when the pinion zandbarrel assenibl yioverrun the screwsshait, and alight-compr ession anti-drift .spring .1 .1 bearing on the conitrolrnut tZ and stop nut :ltl: urges the stop nut to'wardidle' position. Means :for causing the eontro'l nut to enter upon the threads :of the :screw shaft-so as to be traversed to the vi'ightiupon acceleration ioi' the 'screw shait :is provided in the form of a re-entry spring ?I 8 flocatedzin the inner end o'f the barrel M and bearingagainsta thimble E9 whichznormally crests against the stop nut 11. Means for limiting the :expansion of the :reentry 'sp'ring l iiflis lprovided in the form rof a lock zring 2 seated-Tina grooveiin theiinterior-oi the barrel in pos'it'ionto en'gage the l eripheralilange- 22 of thelthimble. 119 5 0 as to maintain the re-entr-y spring under initial compression.

.:.-In:.order to increasethe rotational inertia of the pinion and barrel assembly, a hollow cylindrical inertia member 23 of considerably greater diameter than the barrel is rigidly mounted on the exterior thereof. This inertia member is also utilized to prevent undesired traversal of the pinion and barrel assembly toward the engine gear when the parts are rotating. This function is accomplished by mounting the inertia member 55 eccentrically with respect to the barrel so that rotation thereof around the axis of the barrel causes a radial thrust to be applied to the control nut I2 thereby developing a frictional gripping effect of the control nut on the threads of the screw shaft.

As best shown in Figs. 2 and 3, the rigid attachment of inertia member 23 to the barrel I4 is preferably brought about by forming depressions or dimples 24 in the inertia member at substantially diametrical positions in relation to the barrel and arranged to closely engage the barrel, while the intermediate portion of the inertia member 23 is fixed to the barrel by welding or brazing as indicated at 25 so as to form a rigid permanent connection.

In the operation of this drive, starting with the parts in the positions illustrated in Fig. l, rotation of the power shaft l in the direction of the arrow is transmitted to the screw shaft 8,lcausing the control nut 2 to be traversed to the right along the screw shaft until the pinion 3 is fully meshed with the engine gear 4, at which time the control nut l2 engages the stop nut l I whereupon the pinion 3 is constrained to rotate with the screw shaft to crank the engine. During this traversal, the inertia member 23 by virtue of its large diameter and comparatively thin wall, greatly increases the rotational inertia of the pinion and barrel assembly relative to its inertia as respects longitudinal movement so as to insure traversal of the pinion into mesh under the most adverse conditions.

When the engine fires, the acceleration of the engine gear 4 is transmitted to the pinion 3, causing the pinion and barrel assembly to overrun the screw shaft 8 whereby the control nut 12 is threaded back along the screw shaft until it runs off the ends of the threads thereon. Since the pinion 3 is thus demeshed from the engine gear 4, the pinion and barrel assembly quickly decelerates to the speed of the screw shaft, whereupon the re-entry spring it becomes effective to reengage the control nut l2 with the ends of the threads on the screw shaft 8. It will be understood that this demeshing action normally takes place in a fraction of a second so that the screw shaft and motor shaft are still rotating substantially at cranking speed.

If, under these circumstances the operator fails to open the starting switch so as to deenergize the starting motor, the power shaft l and screw shaft 8 will be rapidly accelerated by the release of the cranking load therefrom, and this acceleration will tend to traverse the control nut and the pinion and barrel assembly toward the engine gear. At this time, however, the pinion and barrel assembly including the inertia member 23 are in rotation, and the eccentricity of the inertia member 23 causes it to press the control nut l2 against the threads of the screw shaft on the side to which the eccentric inertia member is attached. The eccentricity of the inertia member is so related to the rotational moment of inertia of the pinion and barrel assembly and the accelerational characteristics of the starting motor that adequate lateral pressure is brought to bear Fig. 4 illustrates a modification of the inven- I tion in which the eccentric weighting of the barrel member is obtained by forming the eccentric cylindrical member integral with the barrel itself. As there shown, the interior cylindrical surface 26 of the barrel I4 is coaxial with the screw shaft 8 as in the first embodiment of the invention, but the exterior cylindrical surface 21 of the barrel is abaxial thereto so as to weight the barrel eccentrically.

Rotation of the barrel will cause centrifugal force to apply radial pressure from the barrel to the nut to increase the friction of the nut on the screw shaft, and thereby oppose relative rotation therebetween the same as in the first embodiment of the invention.

Although but two embodiments of the invention have been shown and described in detail, it will be understood that other embodiments are possible and that changes may be made in the proportions and arrangement of the parts without departing from the spirit of the invention as defined in the claims appended hereto.

What is claimed is:

1. In an engine starter drive, a power shaft, a pinion slidably journalled thereon for movement into and out of mesh with a gear of an engine to be started, a screw shaft, means connecting the screw shaft to rotate with the motor shaft, a control nut threaded on the screw shaft, a barrel member connecting the control nut and pinion, a hollow cylindrical inertia member, and means for connecting the inertia member to rotate with the barrel member while maintaining the inertia member eccentric thereto.

2. An engine starter drive as set forth in claim 1 in which said inertia member is in the form of a cylinder having an internal diameter substantially greater than the outside diameter of the barrel, and rigidly fixed thereto on one side.

3. An engine starter drive as set forth in claim 1 in which said inertia member is in the form of a cylinder having an internal diameter substantially greater than the outside diameter of the barrel, and rigidly fixed thereto on one side, said cylinder having inwardly protruding means for engaging the exterior of the barrel at points circumferentially spaced from its attachment thereto so as to prevent lateral movement of the cylinder on the barrel.

JAMES E. BUXTON. FRANK T. CHRISTIAN. RENE E. DEMURE.

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

UNITED STATES PATENTS Number Name Date 1,820,442 Cooper Aug. 25, 1931 2,117,999 Whitney May 17, 1938

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