US2446808A - Engine starter gearing - Google Patents

Description

Augu 10, 1948. BUXTON 2,446,808

ENGINE STARTER GEARING Filed May 20, 1946 2 Sheets-Sheet 1 IN V EN TOR.

WITNESS; by James mm. in; ,g

TTORNE Y 1948. J. E. BUXTON 2,446,808

ENGINE STARTER GEARING Filed May 20. 1946 2 Sheets-Sheet 2 46 49Tfi;\, 1:; 4F46Q5- 44} Ly 5 58 V INVENTOR. WITNESS! BY j TORNE Y Patented Aug. 10, 1948 ENGINE STARTER GEARING James E. Buxton, Elmira, N. Y., assignor to Bendix Aviation Corpor Delaware ation, a corporation of Application May 20, 1946, Serial No. 671,062

6 Claims.

The present invention relates to engine starter gearing and more particularly to a starter drive incorporating a friction clutch which is arranged to slip when a predetermined overload is applied thereto. This invention constitutes an improvement over the structure shown in applicant's prior Patent No. 2,319,441 which issued on May 18, 1943 to the assignee of the present application.

In those starter drives which employ a yielding element in the form of a member of elastically deformable material which is placed under compression by the operation of the drive, there is a tendency for the drive to stick when it is subjected to an overload such as ma occur when the starter is energized at a time that the engine flywheel is rotating backward. Moreover, if the backward rotation of the flywheel is rapid, the shock of engagement of the drive may be destructive in spite of the cushioning effect of the elastically deformable material.

It is an object of the present invention to provide a novel engine starter drive having means for limiting the maximum torque transmitted therethrough.

It is another object to provide such a device 2 incorporating a self-tightening friction clutch, and means for limiting the compression of the clutch so as to limit its torque capacity.

It is another object to provide a novel engine starter driVe which is arranged to automatically disconnect and allow the starting pinion to overrun freely when the engine starts, with yielding means for holding the pinion in idle position, and yielding means for insuring traversal of the pinion into operative position when the starter is actuated, both said yielding means being so arranged as to avoid interference therebetween.

Further objects and advantages Will be apparent from the following description taken in connection with the accompanying drawing in which Fig. 1 is a side elevation partly broken away and in section of a preferred embodiment of the "invention, the parts being shown in overrunning position;

Fig. 2 is a similar view showing the parts in cranking position;

Fig. 3 is a detail in perspective of the clutch ring which transmits torque from the yielding member to the drive pinion.

Fig. 4 is a view similar to Fig. 1, of a second embodiment of the invention; and

Fig. 5 is a view similar to Fig. 4, showing the parts in cranking position.

In Fig. 1 of the drawing there is illustrated a power shaft I having a smooth reduced extension 2 providing a shoulder 3 against which a thrust ring 4 is normally seated. A hollow shaft 5 which is threaded for a portion of its length as indicated at 6, is fixedly mounted on the free end of the power shaft I by suitable means such as a cross pin I.

A drive pinion 8 is slidably journalled on the smooth portion 2 of the power shaft I for movement into and out of engagement with a member such as a gear 9 of the engine to be started, the operative position of the pinion being determined by its abutment with the thrust ring 4. The pinion has a flange II fixed thereto in any suitable manner as indicated at I2.

Means for actuating the pinion 8 from the screw shaft 5 is provided comprising a nut I3 on the screw shaft having a flange I4 forming a seat for a cylindrical block I5 of elastically deformable material such as rubber. A driving clutch member I6 is arranged to engage the end of the rubber block I5 so as to be rotated thereby. If deemed desirable the clutch member may be connected thereto by suitable means such as knurling as indicated in Fig. 3 so as to positively prevent relative rotation. A thimble I I provided with a radial flange I8 forming a driven clutch element is fixed to the flange I I of the pinion as by welding or brazing as indicated at I9. Said thimble has a longitudinally extending skirt 2| which fits slidably over the exterior of the control nut l3. A barrel member 22 is arranged to enclose the yielding member I5 and is attached to the flanges I8 and II of thimble I1 and inion 8 respectively as shown at 23. The barrel 22 bears on the flange M of the control nut and has a shoulder 24 arranged to engage said flange and thereby hold the yielding member I5 normally under a slight compression.

Compression of the yielding member I5 forces th driving clutch member I6 into frictional engagement with the driven clutch flange I8 so as to transmit cranking torque to the drive pinion 8. Means for limiting the torque so transmitted to a predetermined maximum is provided in the form of a cylindrical stop member 25 interposed between the flange I I of the pinion and the control nut I3 which arrests the longitudinal movement of the nut I3 after the space 26 therebetween has been taken up by compression of the member I5. Thrust washers 30 are preferably interposedbetween the nut I3 and stop member 25 to facilitate relative rotation. These washers may, if desired,

be of some self-lubricating material such as an oil-impregnated alloy.

The nut l3, when returned to its idle position runs off the ends of the threads 6 of the screw shaft as shown in Fig. 1, so that it may rotate freely on the smooth portion 21 of the screw shaft. Means for urging the nut into initial enagement with the threads 6 is provided comprising a thimble 28 slidably mounted on the end of the shaft and retained thereon by means of a lock ring 29. A second thimble 3| is also slidably mounted on the end of the shaft 5, an'da reentry spring 32 is seated onsaid thimbles and causes the thimble 3| to exert yieldi'rig pressure on flange M of the control nut. The longitudinal movement of thible 3| is limited by a sholll der 33 on the shaft 5 which accordingly senses the normal demeshed clearance between the pinion and the engine gear 9.

Means normally holding the pinion 8 in idle pos'itioii against the th'imbleai is provided comprising an anti-drift spring 34 seated at one end on the thimb'le 3| and at its other end bearing against an in-turn'e'd flange 35 on an extension 38 or the barrel member 22. It will be noted that fs'iiieethe anti-drift spring :4 beer on the thimble 3'! which also serves as a seat for th reentry spring 32, the pressure of the anti drift sprin assist the flange 35 (if the barrel is not transmitted to reentr sprihgaz but simply urges the stage '14 r the central nutagai'nst Said thi'mble. Each of t ese two springs therefore performs its specialized flih'c'tioh without opposition or interereuee by the other and may therefore be designed independently for optimum performance.

-In the operation of the diivje, starting with the parts iii the ositio s illustrated in Fig. 1, rotation er the power shaft I n the direction or the arrow a by the start n meter, not illustrated, causes the control niit l3. to thread itself to the right along the sheet: shaft s'u t l the pinidn a engages the hrust this 4. Further meve e'h of the contrdl nut is yieldably resisted by the rubber block l5, the eeihe'rejssiefh er which threes the drivihg luteh nie 'nher l6 inte ehga'sernht with the driven clutieh membe'ifl fl 'iintil su'fiifci'ent tor ue is built up to. cause the pinion 8 to rotate the engine la W ien the engine starts, acceleration of the ping ieii i3 is transm tted back to the control "nut |3 which eeeeigiihgi' threads itself back along the screw shaft 5th idle position with the assistari' e of the 'an'thdrift spring 34. Just before 'nut '13 runs or: the ends of the threads 6, the flange l l thereof encounters the thimb'le fil thereby hempr'essing the r-entry spring 32 which accordingly urges the nut 'int'o initial engagement with threads 6 after its momentum has been dissipated.

If the starter should inadvertently be energized at a time that the engine gear 9 is rotating backward, a collisionbetweer'l the forwardly rotating parts or thestarter and the ba'ckw'ardly rotatin Barts of the engine occurs which may be so violent that the yielding member I5 is inadequate to prevent damage to the drive. In the present structiire, such damage is prevented by limiting the torque capacity of the clutch l6, 18 by the cylindrical spacing member 25 which allows the member I5 to exert no more than a pre-determined maximum pressure on the clutch elements. Any loads which exceed the safe maximum ,for the drive, therefore, merely cause theclutch l6, l8 to slip and dissipate the kinetic energy of the rotati paits In Figs. 4 and 5 there is illustrated an embodi- 4 ment of the invention in which the screw shaft is formed of two parts clutched together in order to allow the pinion and its associated parts to overrun the starting motor, and in which the anti-drift spring also serves to secure initial engagement of said clutch.

As there shown, a motor shaft 4| which may be the extended armature shaft of a motor not illustrated, is supported at its outer end in an outboard bearing 42 preferably provided by an extension oi the motor frame. A pinion 43 is slidab'ly mtiiinted on the motor shaft for movement into and out of engagement with an engine gear 4 Means for actuating the pinion is provided comprising a'screw 'shaf t 45 slidably joul'nalled on the motor shaft and having clutch teeth 40 etiehtea to eheeee similar clutch teeth 41 on a driving head 48 which is anchored to the shaft by a cross pin 49.

A control nut 5|having a radial flange 52 forms a seat for one endof an annular block 53 of elastically deformable material such as rubber, the opposite end of which bears against a driving clutch member in the form of a friction ring 54. A, driven clutch member in the form of a thiinbl e 55 is slidably mounted in telescopic rel'a'tien with the nut 52 ahd is rigidly clamped at its outer end against a radial flange member 56 which is fixed to the pinion 4,3 in any suitable manner as, indi 'ca'ted at 57. The thirhhle 55 nd flange'js are mounted in the eiid of a barrel member 58, and are lamp'ed tog'ether by spinning over of the end of the barrel {as showhat 59. The thimbl'e and flange are preferablywelded or brazed together as indicated. a p

Barrel 58 surrounds the r bber block 53 and has an internalshoiild'er to iefrmihg ah abutmeht ier' the flanges: or the control n'l'it, which is so lo: cated as to maintain the 'r'ubbe'r, block '53 unset initial compression; The barrel 58 ,estehasreei wardly beyond the driving liad 48 and has aii inwardly dire'cted f ange 6| adapted tde'rig'fa'ge the 'd'riviiig heafd and thereby limit longitudinal movement of the pinioh so as "to define its ineshe'd position. 4 V

Means for noriii ally'mainteining the "pinion and barrel in idlepos'i'tlon are provided in the foriii of an anti-drift spring 62 hearing at one end against the flange s1 er the barrel and at its other end seated 'on a heh'getl ring t3 which surround the driving head '48 so as 'to fretain the pin 3'9 therein ahdfse'ats against a shoulder 64 on said driving head, The backward movement of the pinion is preferably limited by engagement of the control hut 5| with the ends of the threads on the screw shaft '45.

In 'order to liiilit the tr'a'rismission 'cj'f torque te the pini'dr'l by liniitifrig the eehihres'sieh of the friction cliitch member's '55, positive spacing ineahs ete previiied for limiting the ee'mpressien of the riibb'er bloek5'3. As here shown this means is in the form of a thrust ring 65 interposd between the flange 56 of the pinion and the adjacent end of the'control hut 52.

It is desirable to reduce as far as practicablethe transmission of torque from control nu't 5| to the pinion flange 56 directly through the thrust ring 55 since the torque so transmitted is added to that transmitted through the friction clutch 5d, 55 and to that extent reduces the effectiveness of the control of the load by said friction 'cl'utch. The small diameter of the thrust ring 65 reduces torque transmitted therethrough to a 'm i'r'l'oi value, and this is preferab still flirtherre'diiced by the interposition of thrust rings 66, B! which may be of anti-friction material or even formed as a ball thrust bearing if 50 desired.

In the operation of this embodiment of the invention, starting with the parts in the positions illustrated in Fig. 4, energization of the motor causes rotation of the motor shaft 4| in the direction of the arrow 1 whereby the control nut 5| is moved to the right, traversing the pinion 43 and its associated parts until the flange 61 of the barrel engages the head 48 as shown in Fig. 5. Further rotation of the motor shaft causes the nut 5i to compress the rubber block 53 and transmit torque thereby through the friction clutch 54, 55 to the pinion to cause the pinion to rotate the engine gear.

Should the drive be actuated while the engine gear is rotating backwardly, collision of the forwardly rotating motor-actuated parts with the backwardly rotating engine gear causes the control nut 5! to move forward further, compressing the clutch 54, 55 until the nut engages the thrust ring 65. Thereupon the clutch members slip and so limit the stresses placed upon the parts of the drive to a safe value.

When the engine starts, the acceleration of the pinion 43 causes the nut 5| to be rotated faster than the screw shaft whereby the parts are returned to idle position, the excess speed of the barrel and associated parts causing the screw shaft to overrun the drive head 48 as permitted by the dental clutch 46, 41. These clutch teeth are preferably of the saw-tooth type as shown in order to facilitate the over-running action. When the parts come to rest the dental clutch 46, 41 is held in initial engagement by the anti-drift spring 62.

Although certain embodiments of the invention have been shown and described in detail, it will be understood that other embodiments are possible and various changes may be made in the design and arrangement of the parts without departing from the spirit of the invention as defined in 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, means actuated by rotation of the power shaft for moving the pinion into mesh with the engine gear including a control member having an inclined connection with the power shaft a driven friction clutch member fixed to the pinion, a driving clutch member cooperating therewith, and means including an elastic pressure and torque transmitting member conmeeting the control member to the driving clutch member for pressing the clutch members together and transmitting torque to the driving clutch member, and an anti-friction thrust bearing between the control member and pinion for limiting the pressure applied to the clutch members to thereby cause the clutch to slip when the drive is subjected to a predetermined overload.

2. An engine starter drive as set forth in claim 1 including further means for preventing slippage between the elastic member and the driving clutch member.

3. 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, an abutment on the shaft defining the meshed position of the pinion, a driven clutch member fixed to the pinion, a flanged con trol nut having a threaded connection with the shaft, a barrel member surrounding the control nut and driven clutch member, a driving clutch member loosely mounted in the barrel, an elastic pressure and torque transmitting member between the control nut and driving clutch member, and an annular anti-friction thrust bearing between the control nut and the driven clutch member for limiting the pressure of the elastic member on the driving clutch member.

4. 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 hollow shaft threaded for a portion of its length, means connecting the hollow shaft to the power shaft for rotation therewith, a control nut on the hollow shaft having a yielding driving connection with the pinion, a barrel rigidly connected to the pinion and enclosing the nut and driving connection, an anti-drift spring connected between the hollow shaft and barrel urging the barrel and its associated parts toward idle position where the nut is on the unthreaded portion of the hollow shaft, a re-entry spring connected to the hollow shaft operative to move the control nut toward meshed position, and means for so limiting the expansion of said re-entry spring as to allow it to move the control nut into initial engagement with the threads of the hollow shaft.

5. An engine starter drive as set forth in claim 4 in which said hollow shaft has a thimble anchored thereon forming a seat for one end of the re-entry spring, and a second thimble slidably mounted on the hollow shaft having seats for both the anti-drift and re-entry springs, and formed to abut the control nut when in idle position.

6. In an engine starter drive a power shaft, a

- pinion movable thereon into and out of mesh with a gear of an engine to be started, means for actuating the pinion including a screw shaft connected to rotate with the power shaft, a control nut on the screw shaft, and means connecting the nut to the pinion said nut being arranged to run off the threads of the screw shaft when the nut is returned to idle position; yielding reentry means for urging the nut into initial engagement with the threads of the screw shaft, and yielding anti-drift means for urging the control nut into engagement with the re-entry means.

JAMES E. BUXTON.

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

UNITED STATES PATENTS Number Name Date 2,221,083 Fitzgerald Nov. 12, 1940 2,319,441 Buxton May 18, 1943 2,325,007 Douglas July 20, 1943

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