US 2771780 A
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MAIL- r Nov. 27, 1956 THEODORE JEAN-BAPTISTE LAFITTE ,78
STARTING DEVICES FOR COMBUSTION ENGINES Filed Aug. 13, 1954- Z Sheets-Sheet 1 INVENTOR. 571%: M -29 aZZsZCafi% A TTORNE Y Nov. 27, 1956 THEODORE JEAN-BAPTISTE LAFlTTE ,7
STARTING DEVICES FOR COMBUSTION ENGINES Filed Aug. 13, 1954 2 Sheets-Sheet 2 BY/wX A T RNEY nite States Patent STARTING DEVICES FOR COMBUSTION ENGINES Theodore Jean-Baptiste Lafitte, Paris, France, assignor to Bendix Aviation Corporation, Elmira, N. Y.
Application August 13, 1954, Serial No. 449,566
Claims priority, application France August 26, 1953 6 Claims. (Cl. 74-7) The present invention is concerned with improvements to starting devices used for starting of explosion or combustion engines, devices in which a pinion yieldingly connected to an electric motor is thrown into mesh by a longitudinal displacement on a screw of suitable pitch with a toothed wheel connected to the engine to be started.
It has for objects:
(a) The provision of a device of the type in question, of minimum length, comprising a small number of sturdy parts, in order to reduce dangerous overhang, bending and torsion which may be the determining causes in deterioration and even rupture of the components of the device.
(b) To eliminate excessive frictions varying with the state of the surfaces in contact, whereby the spring can keep its full effect and enabl it to play efficiently its function which consists in providing the elasticity necessary to the protection of the device components.
(c) To reduce the number of teeth on the pinion in order to increase the reduction ratio and thus enable, all factors remaining equal, the use of a smaller electric motor.
(d) To suppress the extension of the electric motor shaft on which are usually mounted the starting members in question.
(e) To reduce the number of superpositions of members.
(f) To decrease substantially the weight of the unit formed by the device in question and the electric motor.
(g) To assure the support, driving and positioning of the device on the electric motor shaft, preferably by means of a conventional key.
In order to achieve these objects, as well as others which will be described hereinafter, reference will be made to the following description which refers to the annexed drawings which show, as non-limitative examples, two main embodiments of the device according to the invention.
The Figures 1, 2 and 3 show longitudinal sections of a first embodiment of the device in three characteristic positions of its operation, and
Figure 4 shows a second embodiment of the device, similar to the first one, and having similar manner of operation.
Figures 1, 2 and 3 show, secured to the end of the shaft 1 of the electric motor (not represented), by a conventional key 2 which serves for its drive and its positioning, the sleeve 3 on which a screw 4 anchors and presses by means of any eye 5, the spring 6 which is besides anchored and tightened on a nut 7 by a screw 8 which extends through its other eye 9. The nut 7 is provided with a thread 10 of a fast pitch, adapted to screw, in operation, on a corresponding thread provided on shaft 11, at the end of which is mounted a stop nut 12, and which shaft is provided at its other end with a recess 14 perpendicular to its axis. In this recess 14 is located a ball 15 loaded by a spring 16. On shaft 11 are cut the pinion 17 and the fast pitch screw 18, which is separated from the pinion 17 by a cylindrical bearing portion 19 which has a diameter equal to the base of the thread of the screw 18 and has a suitable length superior to th width of nut 7. A ring 20 of suflicient weight is connected to the pinion 17. A hearing 21 formed with a groove 22 pressed either in the starter casing 23 or in a bearing provided in the engine to be started, guides the shaft 11 and enables its rotation as well as the sliding movement thereof. The stop nut 12 can slide and rotate, with little friction, in the bore 24 of the sleeve 3 which carries a shoulder 25 against which the stop nut 12 is adapted to take support; the bearing 26 of said stop ring has a diameter smaller than the bore 27 of the shoulder 25 and a length slightly greater than the thickness of the said shoulder 25. The toothed wheel 28 united with the engine to b started in located at a suitable distance from the pinion 17. The distance D which separates the axes of the screws 4 and 8 is somewhat larger than the distance between the axes of the eyes 5 and 9 of the spring 6 in the free state. This enables the spring 6 to exert a slight pull on the nut 7 and to assure its engagement with the screw 18. The ball 15 is pushed by its spring 16 into the groove 22. A suitable space J separates th nut 7 from the sleeve 3.
Figure 1 shows the device in normal position.
The operation takes place as follows:
It is assumed that the electric motor, and consequently its shaft 1, turns clockwise, when looked upon from the side of the pinion 17; the threads 10 and 18 have in this case a right-hand pitch.
When the circuit is closed, the electric motor rotates and suddenly drives its shaft 1 and, by the key 2, the sleeve 3, the spring 6 and, by the latter, the nut 7 which pulled by the said spring 6 engages its thread 10 on the screw 18 on the shaft 11, the inertia of which increased by that of the ring 20 and assisted by the friction of the ball 15 in the groove 22 of the bearing 21, are sufficient to enable the said screw 18 to engage itself in the nut 7 with the result of disengaging the ball from the groove 22 and causing the shaft 11 and its pinion 17 to move towards the toothed wheel 28 with which it comes into contact and meshes yieldingly, owing to the longitudinal elasticity of the spring 6. The movement goes on and the shaft 11 slides in the bearing 21 while the teeth of the pinion 17 slide on the teeth of the toothed wheel 28 until the stop nut 12 comes into contact with the shoulder 25 of the sleeve 3 as indicated on Figure 2. The electric motor continuing its rotation, the nut 7 screws itself on the screw 18 and compresses the spring 6 thus reducing the space I until the said nut 7 comes into contact with the bearing 26 of the stop nut 12. The bearing 26 being by construction made longer than the thickness of shoulder 25 projects by quantity 1, to which the space I which originally separated the nut 7 from the sleeve 3 is thus reduced. The stop nut 12 and the shoulder 25 are arranged in such a manner that the compression of the spring 6 compacts the spring convolutions, leaving preferably therebtween a very slight clearance. In this position, as shown in Figure 3, the shaft 11 which carries the pinion 17 and the screw 18 rotates as a unit with the nut 7, which nut forms with the sleeve 3 a cylinder only interrupted on a short length l which can be reduced to a few tenths of millimeter if necessary. The electric motor then drives yieldingly by means of the spring 6 the shaft 11 and its pinion 17 which causes the rotation of the toothed wheel 28 and consequently that of the engine to be started. During this operation, the spring 6 winds itself more or less round the sleeve 3 and the nut 7, in accordance with the resistance opposed by the toothed wheel 23. This winding will be limited by the cylinder formed by the sleeve 3 and the nut 7 on which the convolutions of the spring 6 will come into contact if the resistance is sufficiently high, as shown in Figure 3.
The engine having been started, the toothed wheel 28 drives the pinion 17, the fast rotation of which causes the screw 18 to screw itself into the nut 7, with the effect of disengaging the pinion 17 from the toothed wheel 28, of releasing the compression of the spring 6, of bringing back the shaft 11 and stop member 12 against the end of the shaft 1 of the electric motor, of bringing the nut 7 back on the smooth cylindrical portion 19 and of engaging the ball 15 in the groove 22 as indicated in Figure 1 which is the normal position. The device is thus ready for a new start. The rebounding of the pinion 17 towards the toothed wheel 28 is prevented by the spring 6 which exerts a suitable pull on the nut 7 and by means of the latter on the screw 15 of the shaft 11, and by the effect of the ball 15 which is pressed by the spring 16 into the groove 28, and which offers a supplemental resistance to the longitudinal displacement of the shaft 11. This resistance is increased during the rotation of the shaft 11 owing to the centrifugal eifect which is exerted on the ball 15.
While enabling the complex operation described above, the device, according to the invention, is exceptionally short; the length of the active part thereof is nearly equal to the sum of the lengths of the spring 6, eyes included, and of the teeth of the pinion 17, increased by 15 to 20%. The bendings and torsions are thus limited to a minimum.
Frictions other than those of the operation are reduced to the slight one of the stop nut 12 against the stop shoulder which takes place under the small pressure resulting from the longitudinal compression of the spring 6. This friction has no ill eflect on the operation ofthe spring 6 which can thus efficiently play its part of ayielding shock absorber of the starting torque.
The protection against all permanent deformation of the spring 6 is realized by the approachment of its convolutions and of the nut 7 towards the sleeve 3, which provide, when thus brought together, a cylinder of suitable surface and diameter on which the said spring 6 can wind itself in case of an abnormal pull on the eyes thereof.
The possibility of cutting the pinion 17 on the shaft 11 allows the forming of a pinion with 6 or 7 teeth of modules 3 for instance, while keeping dimensions suitable for a good resistance of the components.
The construction, according to the invention, suppresses the usual extension of the electric motor shaft hitherto provided, and replaces it by the shaft 11 which is one of the components of the device.
The device consists of four main parts and avoids their superposition; its weight is reduced to the minimum, and owing to the important reduction ratio provided, it allows the use of a lighter electric motor, so that the unit formed by the device and the said electric motor secures,-all factors remaining equal, a considerable decrease of the total weight.
The drive and the positioning of the sleeve 3 are advantageously realized by a conventional key 2 which, owing to its oblique surface connects it rigidly and without play with the end of the shaft 1 of the electric motor.
The device according to the invention is besides characterized by the use of three stops, two of which are essential; they have a separate function each and come into play successively:
.(a) In the normal position shown in Figure 1, the stop nut 12 (or the end of shaft 11) is kept against the end of shaftl by the nut 7 which is pulled by the spring 6, the length of which between the axes of the eyes, in free state is smaller than the distance between the screws 4and 8 that hold it. This enables the holdingof-the device in abutting relation at its position of rest.
(b) In a first stage of the operation, shown in Figure 2, the stop nut 12 comes into contact with the shoulder 25 of the sleeve 3, which enables from this moment the longitudinal compression of the spring 6.
(c) In a second stage of the operation, the nut 7 screws itself on the screw 18 compressing the spring 6 until the said nut 7 is brought to abut the stop nut 12, which drivably connects it to the shaft 11.
These three stops may possibly beadjusted by means of suitable washers to give each member the most favorable position for the best operation. 7
In the second embodiment shown in Figure 4, a shaft 30 centered in sleeve 31 is arranged coaxially with the shaft 1 of the electric'motor and forms an extension of the latter. The sleeve 31 on which is secured the spring 32 by the screw 33 is connected with shaft 1 by a conventional key 34. On the other hand, the spring 32 is fixed by a nut 35 to nut 36 into which a bolt 37 has been forcibly fitted and, if necessary welded. On shaft 30, may revolve and slide with slight friction the hollow shaft 38 on which are cut the screw 39 and the pinion 40 separated by a cylindrical bearing of a length greater than the width of the nut 36 and of a diameter equal to the diameter of the base of the thread of the screw 39. On the threaded end of the hollow shaft 38 is screwed a stop nut 41 which leaves betweena flange 42 and the inner face 43 of sleeve 31 sufficient space for a spring 44. On the shaft 30, in the vicinity of the starter casing projection, is tightened and centered a ferrule 45 bored on a length which allows the location of a spring 47 when it is compressed under the pressure of the hollow shaft 38. The ferrule rotates in a ring 46 mounted in the startercasingprojection or in a suitable hearing. A washer 48 of suitable weight is crimped on the pinion 40.
This, like the preceding embodiment, includes three characteristic abutments:
1. The first one formed by the inner face 43 of the sleeve 31 on which the hollow shaft 38 can take support to ensure the normal position.
2. The second one formed by the ferrule 45 against which the hollow shaft 38 abuts after the compression of the spring 47 is similar to shoulder 25 of the sleeve 3 in the first embodiment; it is when the abutment is realized that the longitudinal compression of the spring 32 begins.
3. The third one is realized between the stop nut 41 and the nut 36, which drivingly connects the nut 36 with the hollow shaft 38.
The stops and the lengths of thedevice are'determined in such a way that, particularly, the length A should exceed the length B by a quantity 1 or alike, which will separate after the compression of spring 32, the sleeve 31 from the nut 36 after the coming into contact of the latter with stop nut 41.
The operation of this embodiment is identical to that of the device described above.
The shaft 30 may eventually be replaced by an extension of shaft 1 of the electric motor according to the construction in general use.
By eliminating the stop nuts, such as 12'or 41, it is possible to obtain either the contact of the'nuts such as 7 or 36 with the sleeves such as 3 or 31, or the complete longitudinal compression of the springs 6 or 32.
It should be understood that the invention is not limited to the embodiments previously described, given as examples, but that it comprises all similar devices, including the whole or a part of the devices in question, particularly those comprising three stops operating successively and of which two major ones, used in combination, enable, the one, the compression of the shock absorbing spring and the establishment of a practically continuous out permanent deformation; and the other one, the connection of the fast pitch nut with the member comprising the corresponding screw.
1. In an engine starter drive a motor shaft, a hollow sleeve fixedly mounted thereon, a driven shaft having a threaded portion and a toothed portion; a nut engageable with said threaded portion of the driven shaft to move said toothed portion into and out of mesh with a member of the engine to be started, a yielding means connecting the sleeve and nut, an abutment member on the driven shaft within the sleeve, and a cooperating shoulder in the sleeve positively limiting the meshing movement of the driven shaft and thereby causing said nut to move to compress said yielding means; said abutment member being also formed and arranged to engage said nut and thereby limit the compression of the yielding means.
2. In an engine starter drive a motor shaft, a hollow sleeve fixedly mounted thereon, a driven shaft having a threaded portion and a toothed portion; a nut engageable with said threaded portion of the driven shaft, yielding means connecting the sleeve and nut, an abutment on the driven shaft within the sleeve and a cooperating abutment in the sleeve positively limiting the longitudinal movement of the driven shaft; in which the driven shaft is formed with a smooth portion intermediate the threaded portion and the toothed portion having the same diameter as the bottom of the threads, and serving as a bearing for the nut in idle position.
3. A starter drive as set forth in claim 2 in which said yielding means is in the form of a coiled spring, and the motor shaft and driven shaft are provided with cooperating abutments so defining the idle position of the screw shaft that when the nut is located on the smooth portion of the screw shaft, the spring is under tension to draw the nut on to the threaded portion of the screw shaft when the motor shaft is actuated.
4. A starter drive as set forth in claim 2 in which said yielding means is in the form of a coiled spring, and the sleeve and nut are formed with cylindrical external surfaces of substantially equal diameter and when brought into contact by the screw-jack action of the screw shaft and nut form a substantially continuous smooth cylinder within said spring supporting the spring and limiting its constriction under torsional load.
5. In an engine starter drive a motor shaft, a hollow sleeve fixedly mounted thereon, a driven shaft having a threaded portion and a toothed portion; a nut engageable with said threaded portion of the driven shaft, yielding means connecting the sleeve and nut, an abutment on the driven shaft within the sleeve and a cooperating abutment in the sleeve positively limiting the longitudinal movement of the driven shaft; including further a bearing for the outer end of the screw shaft having an internal annular groove, and a yielding detent in the screw shaft positioned to seat in said groove when the screw shaft is in idle position.
6. In an engine starter drive a motor shaft, a hollow sleeve fixedly mounted thereon, a driven shaft having a threaded portion and a toothed portion, a nut engageable with the threaded portion of the driven shaft to move said toothed portion into and out of mesh with a member of the engine to be started, yielding means including a compression and torsion spring connecting the sleeve and nut, an abutment member fixedly mounted on the driven shaft slidably journalled in the sleeve, said sleeve having an internal shoulder engageable by said abutment member to define the meshed position of the driven shaft, said abutment member having a portion of reduced diameter adapted to extend beyond the end of the sleeve and engage said nut to hold it spaced from the sleeve.
References Cited in the file of this patent UNITED STATES PATENTS 1,597,330 Ringwald Aug. 24, 1926 1,634,515 Ringwald July 5, 1927 1,897,916 Sekella Feb. 14, 1933 2,084,813 Lansing June 22, 1937 2,565,170 Digby Aug. 21, 1951