US2413045A - Engine starting mechanism - Google Patents

Description

Dec. 24, 1946.

H. D. HOEKSTRA ENGINE STARTING MECHANISM 3 Sheets-Sheet l Filed Feb. i9, 1941 ltmnuf Ic. 24, 1946. H. D. HOEKSTRA 2,413,045

ENGINE STARTING MECHANISM Filed Feb. 19, 1941 5 Sheets-Sheet 2 32 '52gr== A Y:

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H. D. HOEKSTRA NGINE STARTING MECHAN I SM Filed Feb. 19, 1941 3 Sheets-Sheet 3 Haro/Zd DHoe/rS/rcf,

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Patented Dec. 24, 1946 UNITED STATES PATENT V OFFICE l 2,413,045l 4 v f ENGINE STARTING MECHANISM Harold D. Hoekstra, Rockville, Md.

Application February 19, 1941, Serial No. 379,705 1 claim. (o1. 18s- 39) My invention relates in general to engine starting mechanisms and in particular-to a starter of the spring motor type adapted for use in cranking internal combustion engines of the airplane type.

An object of my invention is to provide a start er of this type which will be light weight, simple, and inexpensive, being particularly adapted for use with low and medium powered aircraft.

Another object is to provide a starter of this type in which a varying amount of energy may be stored (at a rapid or slow rate) and which energy may be expended as' desired by the oper- It is also the object of this invention to provide a starter which canot be wound to anexcessive degree either by the operator, or by an engine back-nre.

Still another object of my invention is to provide a novel release and clutching means -which will insure ready release and positive clutching action and which will be free-running with no rubbing action when disengaged.

A further object of this invention is 'to provide means whereby the eiiicient and desireable comi .i

pression type spring with its rectilinear motion may be utilized to secure rotary motion.

Another object of this invention is to provide safety means to harmlessly dissipate the stored energy in the starter in the event of clutch failure or inadvertent release.

Other objects of the invention will be manifest from the following description of the preferred form of the invention, taken in connection with the accompanying drawings, wherein Fig. 1 is a side elevational view of an airplane engine starter constructed in accordance with the present invention, illustrating its application to an engine, the latter being fragmentarily shown;

Fig. 2 is a longitudinal sectional View of the my starter showing in detail portions v`of Athe wind-up mechanism;

Fig. 6 is a sectional view taken on line -S of Fig. looking in the direction of the arrows, showing the motor casing engaging spring in `,side elevation;

`nism, generally designated I8. The engine start- Fig. 7 is a fragmentary sectional view of the starter, showing to advantage the clutch with the rollers omitted;

Fig. 8 is a sectional view taken on the line 8-8 of Fig. 7, looking in the direction of the arrows,

showing the clutch with rollers mounted in clutch cage.

end elevation,

Fig. 12 is a fragmentary detail sectional view taken. on the une |2-a 2 of Fig. 11, poking in -the direction of the arrows, showing to advantage the modified form of roller, the latter being shown in side elevation, and

Fig. 13 is an elevational view of a tooth fragment of the worm showing a conventional form 0I" thread superimposed thereon, in dotted lines, pressure and pitch lines being also illustrated thereon.

In order to villustrate the application of my invention I have shown in Fig. 1 a fragment of an airplane engine I5 and its crankshaft IS, a pilots seat I1, and an engine starting mechaclude a shaft 22 which extends axially through said shell and housing and has formed on the engine end an inner race 23 of a roller clutch.

vOn the shaft 22 a coarse pitch multiple thread 24 is provided and mating therewith a large diameter iianged nut 25. Formed on twosides of nut 25 are grooves 26 which mate with splines ,2l formed in the shell 20 to prevent rotation of nut 25 while allowing translational movement thereof along the longitudinal axis of the housing. Compression springs 28 and 29, coaxial with shaft 22, react against the housing 2| and nut 25 and serve to store energy when nut 25 is displaced towards the engine end of starter mechanism, Bearing 3B carries the thrust load from shaft 22 into housing 2|. Fixedly attached to shaft 22 is worm wheel 3| which reacts with a worm 32 attached to shaft 33 as shown to advantage in Fig. 3. Shaft 33 is carried by a bearing 34 formed in a drum housing 35. Worm 32 and shaft 33 are rotatable, in one direction only, by the drum 3S of a drum housing 35 through a conventionalratchet and pawl mechanism 31 and 38 respectively. The pawls are engaged, for 1a manifest purpose, by springs 39 as shown to advantage in Fig. 5. Worm 32 and shaft 33 are rotated in a direction to cause rotation of worm wheel 3| in the wind direction as shown by the arrow in Fig. 3 by means of cable 40 passing around drum 36. Cable 40 is trained around pulley 4| and passes into the cabin orcockpit ofthe airplane and is there attached to handle 42. The handle 42 is positioned adjacent the seat |1 for convenient; accessibility to the pilot for winding the motor of the starter mechanism, as shown in Fig. 1. The return rotation of drum 36 is accomplished by means of a torsion' spring 43, the two ends of which are anchored in housing 35 and drum 36 respectively. The worm and housing assembly is rotatably mounted on bolt 43' which is anchored in boss 44 formed on shell 29, to permit disengaging worm 32 from worm wheel 3|.

A basically -conventional roller type overrunning clutch, such as shown in Figs. 2, '1, and 8, is mounted in the engine end of the starter mechanism. The clutch comprises an outer race 45 which is attached to engine I5, inner race 23, and rollers 45. A novel arrangement is provided to prevent the rollers contacting the outer race 45 during the over-running or disengaged period. This consists of roller cage 41 with spring members 48, pin 49, slots 50 vand 5| of the inner race 23 and cage 41 respectively, clutch rod 52, button 53, and spring 54. The rollers are kept free of the outer race 45, except when starting. The axial movement of clutch rod 52 is transformed into rotary motion by means of pin 49 and slot 59 in the inner race 23. Then by means of pin 49 and slot 5| in cage 41, the roller cage is rotated thus bringing the rollers out of engagement with outer race 45.

Another type of over-running clutch which has been found to work very satisfactorily is shown in Figs. 10, l1 and 12 wherein conical rollers 46 are employed and react between the inner race 23 and the conical outer race 45. This type of over-running clutch permits direct axial movement of clutch rod 52 to engage or disengage.

The operation of the starting mechanism is as follows: Tostore energy or to wind-up the starter motor, the pilot or operator pulls handle 42 and cable 49 rotates drum 36 and the worm 32 -Which in turn rotates worm Wheel 3| in the direction of the wind-up arrow shown in Fig. 3.. Rotation of the worm wheel 3| turns the threaded shaft 22 and nut 25 is moved in a direction to compress springs Y28 and 29. Storage of energy in the springs can be stopped at any point desired and it "is impossible-to compress springs 28 and 29 to an excessive degree through manual energy storage or through back-fire since the nut 25 travels oif thethreads of shaft 22 when a predetermined compression value is reached, 'as' shown at 55 in Fig. 2. The ends of the threads on shaft 22 and in nut 25 may beA rounded, as at 55 in-Fig. 2, to avoid a dead center position, when vthe starter is fully wound, thus'insuring positive,

quick release for starting.

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Starting is accomplished by depressing the starting pedal 51 in Fig. 1`Which operates cable 58 and pulls down lever 59. Lever 59 is rotatably attached to bolt 43' by means of boss 44. Formed vin lever 59, is slot 60 which mates with pin 6| anchored in housing 35. Spring 62 tends to rotate the lever 59 in a direction opposite to that produced by tension in cable 58 and acts to prevent unintentional release of the starting mechanism. Clutch engaging spring 63 is attached to lever 59 and through a portion of the travel of lever 59 bears upon button 53 depressing the same. As the button 53 is depressed, it operates to advance the clutch rod 52 and places the clutch in an operative position and at the same time lever 59, by means of pin 6|' and slot 60, disen- `gages the worm 32 from the worm wheel 3| thereby allowing the springs to utilize the stored energy and rotate the engine to be started.

In the event that the starter springs have been partially or fully compressed and the lever 59 is operated while the engine is running or if there is clutch slippage, the stored energy in springs 28 and 29 cannot be utilized in the usual manner and must be dissipated in some other manner to avoid damage to the starter. This is accomplished by means of a seal 64 attached to the flange of nut 25 thus forming an air buffer cylinder in shell 29, as shown to advantage in Fig. 2. A metering valve 65 is provided in shell 20, consisting of an orifice setscrew 66 to permit adjustment of the airflow therethrough and consequently to allow adjustment to the proper degree of buillng to prevent injury to the starting mechanism.

Preferably, as shown in Fig. 13, the threads of the worm 32 and Worm wheel 3| have the meshing faces thereof rounded so that the pitch line is substantially as indicated at X while the pressure angle lines are as indicated at Y. This embodiment'of the invention taken with the preferred location of bolt 43 in close proximity to the extension of the pressure angle line Y, whilst being a substantial distance from pressure angle .line Z, permits reversibility in the wind direction, to prevent damage from reverse engine rotation due, for-example, to back-nre during contact of worm Wheel 3| and Worm 32 because of sudden release of pedal 51 immediately after starting. It will be readily seen that the tendency of worm wheel 3| to rotate in the start direction shown on Figure 3 Will, due to the shape of the meshing teeth on both worm wheel 3| and worm 32,'eXert a force substantially along the line Y of Figure 13. Since by specification bolt 43 is in close proximity to line Y extended, there is no appreciable tendency for the worm and drum assembly and the housing 35 in which they are mounted to pivot about bolt 43. Hence the teeth will remain in mesh and the system may be considered irreversible. However, rotation of Worm wheel 3| in the wind direction applies force to the worm 32 along a line normal to the mating teeth faces subjected to the force and hence displacing the Worm 32 out of contact with worm wheel 3| by pivoting of housing 35 and its assembled components about bolt 43. Hence, in this direction the system is reversible. As is well known to those versed in the art, spring 54, though it will tend to disengage the Vclutch upon release of pedal 51, will not normally have suincient force to overcome clutch friction and hence the above described worm reversibility is necessary.

It is to be understood that various changes may said Worm wheel and located in close proximity to the projection of a line passing through the pitch circle of the said worm Wheel normal to the teeth faces having the lesser pressure angle and at the point of Worm and Worm Wheel contact so as to permit relative translation between said Worm and worm Wheel substantially parallel to one pair of mating tooth faces and at an appreciable angle to the adjacent pair of mating tooth 10 faces.

HAROLD D. HOEKSTRA.

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