US2755642A

US2755642A - Engine starters

Info

Publication number: US2755642A
Application number: US426062A
Authority: US
Inventors: Gilbert Samuel
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1954-04-28
Filing date: 1954-04-28
Publication date: 1956-07-24
Anticipated expiration: 1973-07-24

Description

July 24, 1956 s. GILBERT ENGINE STARTERS Original Filed May 19, 1949 INVENTOR. SAMUEL G/LBERT HTTORA/Er tate Patent 01 2,755,642 Patented July 24, 1956 ENGINE STARTERS Samuel Gilbert, Qedar Grove, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. 1., a corporation of Delaware Continuation of application Serial No. 94,091, filed May 19, 1949. This application April 28, 1954, Serial No. 426,062

3 Claims. (Cl. 64-30) The present application is a continuation of U. S. application Serial No. 94,091 filed May 19, 1949, and relates to engine starters and more particularly to direct cranking engine starters.

In starters of the type having a rotatable barrel internally connected through an interleaved friction disc pack to a spline nut, it is necessary to have the spline nut centered accurately within the barrel in order to ob tain smooth operation of the clutch. In order to keep the spline nut centered it has been customary, as shown in Lansing U. S. Patent No. 2,064,670, granted December 15, 1936, to use a solid guide bushing aflixed to the spline nut and having a relatively small clearance between the barrel and the bushing. This arrangement, however, has proven unsatisfactory for certain applications due to the wide range in temperature to which the starter is subjected. Thus, if the bushing is fitted with a proper clearance at normal temperatures, the clearance becomes entirely too large for operation at sub-zero temperatures and too small at high temperatures due to the thermal coefficient of expansion of the bushing. This change in clearance in either direction adversely affects the operation of the disc pack by causing uneven pressure thereon due to the misalignment of the spline nut.

One object of the present invention is to provide simple means whereby the objections of the above described centering arrangement may be avoided.

Another object of the present invention is to provide a novel arrangement in a starter of the above mentioned type whereby the spline nut is kept in alignment with the driving barrel irrespective of temperature changes.

Another object of the present invention is to provide means whereby a slight modification of a conventional spline nut guide bushing will substantially prevent changes of the outside diameter thereof with changes in temperature.

Still another object of the present invention is to provide simple means for preventing a cylindrical member from changing its outside diameter with changes in temperature.

The above and other objects and features of the invention will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawing wherein one embodiment of the invention is illustrated by way of example.

In the drawings:

Figure 1 is a view partly in section and partly in ele vation of a starter embodying the present improvement.

Figure 2 is a view taken along line 2-2 of Figure 1.

The starter shown in Figure l is of a type well known in the art and comprises a jaw actuating mechanism generally indicated at it? adapted to extend starter jaw 12 into engagement with engine jaw 14 and driven from a motor output pinion 16 through planetary gearing 18 and enclosed by housing 29. As is well known, rotation of barrel 22 of jaw actuating mechanism is transmitted to axially stationary spline nut 24 through a torque limiting disc pack 26. The long lead internal threads of the spline nut mesh with corresponding threads of screw 28 which is connected to starter jaw 12 by axial splines 30 for rotation therewith.

Starter jaw 12 and screw 28 are restricted against rotation by friction exerted against the starter jaw 12 by a friction ring 36 and oil seal 38 which is sufficient to prevent the screw from rotation with the spline nut. Rotation of spline nut 24 moves screw 28 to the left as viewed in the drawing until shoulder 32 of the screw 23; abuts corresponding shoulder 34 of the spline nut 24 and hence forces starter jaw 12 into driving engagement with the engine jaw 14. Upon the shoulder 32 abutting the shoulder 34, the friction exerted against the starter jaw 12 is overcome and it rotates with the screw 28 to crank the engine.

The planetary gearing 18 as shown comprises the motor output pinion 16 functioning as the sun gear, a stationary orbit gear .6 shown as being integral with starter housing 2% and one or more planet gears 42 mounted on end wall 44 of the barrel 22.

Starter housing 20 is provided with a flange 46 for mounting on an engine mount indicated at 43 with bolts 4% as shown.

In starters of this type a spline nut guide bushing 50 is provided in order to maintain the spline nut 24 in a centered position relative to the barrel 22. This guide bushing Eli also serves as a pressure plate for the disc pack 26 as shown and is placed between outwardly extending flange 52 of spline nut 24 and the disc pack 26. Recesses are formed in the spline bushing on the face abutting the flange 52 of the spline nut 24 in order to provide grease pockets to insure proper lubrication.

The discs of disc pack 26 are forced into the frictional engagement with each other by a plurality of circumferentially spaced springs 60 compressed between flange 52 and an adjustable nut 62 threaded into the barrel and set so that the disc pack 26 will slip at a predetermined torque thereby permitting relative motion between the spline nut 24 and the barrel 22 should the engine abnormally resist cranking or if the engine should backfire.

Heretofore clearance 64 between the guide bushing 50 and the barrel 22 had to be made sufficiently large to prevent the guide bushing from binding with the barrel 22 at the highest temperature to which the guide bushing 50 might be exposed during normal operation of the starter. During extremely cold weather, however, the guide bushing 58 will contract and the outside diameter thereof decrease to such an extent as to make it ineffective to center the spline nut 2 properly within the barrel 22. The resulting misalignment between the spline nut 24 and barrel 2% will cause erratic clutch values.

In the solution of the problem here involved, it should be recognized that the annular length of the bushing is relatively much greater than the width of the sleeve of the bushing so that changes in effective temperature will cause relatively greater change in the annular length of the bushing than the relatively minor change in the width of the sleeve of the bushing. In a bushing of the solid type such change in the annular length of the bushing will in'tu-rn cause greater change in the outer diameter of the bushing than does the relatively negligible change in the width of the sleeve of the bushing due to such change in the temperature aifecting the bushing.

The bushing 50, as shown in Figure 1, is located adjacent the clutch pack 26 of the starter and is in what is commonly referred to as a hot spot and is subject to the high temperatures resulting upon slippage or friction at the clutch pack 25. Such high temperatures at the hot spot to which the bushing 50 is subject causes a relatively great increase in the annular length of the bushing 50 and in the case of a solid bushing a corresponding increase in the outer diameter of the bushing tending to cause the bushing to seize or bind with the barrel 22, unless the clearance 64 be made excessively large with the attendant difliculties, as heretofore explained. In order to avoid these difliculties, there is provided the arrangement of the split bushing 50, as herein explained.

According to the present invention the objectionable changes in the outside diameter of the spline guide bushing 50 with variations of temperature are made negligible by cutting a relatively narrow slit 66 through the bushing 50 as indicated in Figure 2. The width of the slit 66 is determined by the temperature coefficient of expansion of the bushing 50. By selecting the width of the slit 66 so that it is almost closed at the highest temperature to which the bushing 50 may be exposed and having the split bushing 50 so formed that under cold operating conditions, the bushing 50, when unconfined, has an inner circumferential surface normally of smaller diameter than the periphery of flange 52 so that under cold or extremely low temperatures the bushing 50 when positioned on the flange 52, as shown in Figure 1, makes a tight fit on the flange 52 of spline nut 24 and under high temperatures bushing 50 may expand causing the diameter of the inner circumferential surface thereof to tend to approach substantially the same diameter as that of the periphery of flange 52 and under which high temperature conditions slit 66 is almost closed, so that, as shown in Figure l, the clearance 64 may be accurately preset to a predetermined desirable value which clearance will not be substantially affected by variation in temperature.

The split bushing 50, as shown in Figure 1, bears upon and is internally confined by the flange 52 of the spline nut 24 so that upon an increase in temperature the annular length of the split bushing 50 expands, but instead of forcing the peripheral edge of the bushing 50 outward, as in the case of a solid bushing, the ends of the split bushing 50 expand annularly about the flange 52 while upon a decrease in the temperature aifecting the split bushing 50, the free ends thereof contract annularly increasing the width of the slit 66.

Thus such expansion and contraction of the split bushing in a lengthwise or annular sense (as distinguished from the relatively minor change in the width of the sleeve portion of the bushing 50) will not cause a substantial change in the overall diameter of the split bushing 50, as in the case of a solid bushing, since the slit 66 in the split bushing 50 permits such change in the annular length of the bushing 50 without a substantial change in the outer diameter or peripheral edge of the split bushing 50.

The ends of the split bushing 50 being unconfined in the slit 66 may therefore expand freely around the flange 52 without causing a corresponding expansion in the outer diameter of the bushing 50 as would be characteristic with a bushing of the solid type due to the circumferential expansion thereof.

The arrangement of the split bushing 50 thus permits a greater expansion of the annular length of the bushing 59 without substantial change in the outer diameter of the bushing 50 and thus permits closer fits than would a bushing of the solid type, such as shown in the Lansing U. S. Patent No. 2,064,670, made of a like material.

It is thus seen that the bushing will provide proper centering for the spline nut 24 relative to the barrel 22 at all times because the width of the slit 66 will increase or decrease with changes in temperature and the over-all diameter of the bushing 50 will remain substantially cons stant, or in other words the slit 66 acts as means for pro viding annular expansion and contraction of the bushing to prevent radial expansion and contraction thereof.

Although only one embodiment of the invention has been illustrated and described, various changes in the form and relative arrangements of the parts may be made to suit requirements.

What is claimed is:

1. In a starter having a driving barrel member, an annular member within said barrel member, and means for driving said annular member from said barrel member; the improvement comprising means for centering said annular member within said barrel member including an annular split bushing surrounding said annular member and bearing upon a portion of said annular member, said bushing being of a size so as to provide clearance between said bushing and said barrel, said split bushing being normally subject to annular expansion and contraction with changes of temperature and under extreme low temperatures having an inner circumferential surface normally of smaller diameter than the periphery of said annular member so as to make a tight fit on the annular member under the last mentioned low temperatures, said split bushing expanding with increase in temperature so as to cause the inner circumferential surface thereof to approach under maximum permissible temperatures substantially the same diameter as that of the periphery of said annular member, said split bushing having free ends defining a radial slit in said bushing, said slit permitting free movement of said ends relative one to the other upon the annular expansion and contraction of said bushing upon changes in temperature, and thereby substantially lessen radial expansion and contraction of said bushing due to said changes in temperature, and said radial slit being so proportioned as to be substantially closed when subjected to the high end of the temperature range.

2. In a starter having a driving barrel member, an annular driven member within said barrel member and means for drivingly connecting said barrel member with said driven member; the improvement comprising annular centering means for said driven member mounted thereon and rotatable therewith, said centering means having a running clearance between the circumference thereof and said barrel member, said centering means being a ring-like member mounted on said driven member and normally subjected to annular expansion and contraction due to temperature changes, said ring-like member having a slit therethrough, said ring-like member under extreme low temperatures having an inner circumferential surface normally of smaller diameter than the periphery of said annular driven member so as to make a tight fit on the annular driven member under the last-mentioned low temperatures, said ring-like member expanding with increase in temperature so as to cause the inner circumferential surface thereof to approach under maximum permissible temperatures substantially the same diameter as that of the periphery of said annular driven member, the slit through said ring-like member permitting the annular contracting and expansion of the ring-like member upon changes in temperature so as to substantially prevent upon said annular expansion a corresponding radial expansion of said ring-like member and seizure of the ring-like member with the barrel member, the width of said slit being determined by the coetficient of expansion of said ring-like member to provide a minimum opening for all temperatures.

3. In a starter having a rotatable barrel, a rotatable spline nut adapted to extend a jaw member into engagement with an engine jaw member of an engine to be started, a torque limiting disc pack providing driving connection between said barrel and said spline nut, and an outwardly extending annular flange member on said spline nut; the improvement comprising an annular ring member rotatable with said spline nut and forming the pressure plate for said disc pack, said ring member interposed between said flange member and said disc pack and being of such a size as to have a close running clearance with said barrel, said ring member having a radial slit therethrough and free ends movable relative one 5 to the other, said ring member under extreme low temperatures having an inner circumferential surface normally of smaller diameter than the periphery of said annular flange member so as to make a tight fit on the annular flange member under the last mentioned low temperatures, said ring member expanding with increase in temperature so as to cause the inner circumferential surface to approach under maximum permissable temperature substantially the same diameter as that of the periphery of said annular flange member, the free ends of said ring member being movable upon annular expansion of said ring member with increase in temperature due to friction at said disc pack so as to lessen radial expansion of the ring member to prevent seizure of the ring member in the barrel, said slit being proportional to the temperature coeflicient of expansion of said ring member.

References Cited in the file of this patent UNITED STATES PATENTS 2,064,670 Lansing Dec. 15, 1936