US2816638A - Constant speed drive mechanism with floating mount - Google Patents

Description

CONSTANT SPEED DRIVE MECHANISM WITH FLOATING MOUNT I Dec. 17, 1957 A. B. CAMPBELL Filed Aug. 13. 1953 CA -r-ro nu E. yf'

CA v'tkuv Campbell N United States pate-m O CONSTANT SPEED DRIVE MECHANISM WITH FLOATIN G MOUNT Arthur B. Campbell, Peru, Ill., assignor to General Time Corporation, New York, N. Y., a corporation of Delaware Application August 13, 1953, Serial N o. 373,941

3 Claims. (Cl. 192-104) The present invention relates to constant speed drive mechanisms and particularly to a device for driving a loaded gear `train or the like at constant speed from a variable speed power source.

-It is an object to provide a constant speed drive mechanism which is completely reliable in operation, which holds the speed substantially constant in spite of variations in the speed of the driving element over a wide range, and which is simple and inexpensive to construct.

kOther objects and advantages will be apparent from the specification and drawing, in which Figures l and 2 are front and side views representative of a bomb fuse employing the present invention, the side view being in partial section.

Fig. 3 is an enlarged vertical section showing the driving member and constant speed outp-ut member in engagement with one another.

Fig. 4is a view of the output member looking along the line 4--4 in Fig. 3.

Fig. 5 is a fragmentary view showing the floating mounting of the drive member.

While the invention is susceptible of various modiiications and alternative constructions, there is shown in .the drawings and will herein be described in detail the preferred embodiment. It is to be understood, however, that I do not intend to limit the invention to the form disclosed, but do intend to cover all modilications, alternative constructions and equivalents falling within the spirit and scope of the invention, as expressed in the appended claims.

While the present device has general application to mechanism requiring constant speed of rotation, the features and advantages may be best understood by describing its use in bombs to be dropped from aircraft for which it was originally developed. A bomb of conventional type -is equipped with a' fuse which may be preset to explode after a desired time interval or upon contact with the earth. For safetys sake, the bomb is prevented from premature explosion by an arming device which is usually driven by a small vane or propeller mounted at the nose of the bomb and which is turned by the air stream. After a predetermined number of revolutions of an output member controlled by the vane, the bomb automatically becomes armed and the ring devices ean then take over to fire the bomb at the desired instant. A vane-driven arming mechanism does not depend upon delicate timing devices and is therefore largely foolproof. There is, however, a drawback to conventional arming mechanisms: the arming interval may vary over rather wide limits depending upon the speed of the airplane from which the bomb is dropped. The problem is accentuated where bombs must be dropped at low altitude and where the arming period must be correspondingly shortened. Thus, when a diving run must be made from high speed jet aircraft, it can readily be seen that premature arming presents a hazard to the dropping craft as well as those following in close formation.

Turning now to the drawings, the fuse is indicated lICC generally at 10 having a nose piece 11, a barrel 12 and a cylindrical housing 13 for the timing mechanism. At the rear end of the housing 13 is a threaded connection 14 which screws into the front of the bomb, the latter being indicated by the dot-dash outline at 15.

Rotatably mounted at the front end of the fuse is a vane or propeller 20 having a pair of angled blades 21, 22, as well as a pair of diametrically extending arms 23, 24 for wiring the vane in place during transport. The vane 20 is coupled to a gear train (not shown) in the barrel 12, the gear train having an input gear 26, by coupling mechanism to be described. The gear train is in turn coupled to a suitable arming mechanism (not shown) which causes the bomb to be armed after ythe gear 26 makes a predetermined number of revolutions.

For the purpose of timing the firing interval, a timing mechanism is provided in the housing 13. While the timing mechanism is not shown in the drawing, it will be understood that the setting of .the timing mechanism may be readily varied by turning the barrel into an adjusted position relative to the housing 13, a scale 31 on the barrel cooperating with an indicator 32 on the housing. After adjustment, the barrel is lfixed in position relative to the housing by tightening a knurled thumb screw 33. It will be further understood that internal mechanism is provided for automatically varying the arming interval in accordance with the firing interval. Thus, shortening the timing interval causes the arming interval to be correspondingly shortened. The mechanism for accomplishing this is outside of the scope of the present application, and it will suice to say .that means are provided for varying the number of revolutions of the output gear 27 of the gear train which must take place before the firing mechanism is armed.

Turning to the structural details of the nose piece 11, 1t will be noted in Fig. 2 that the vane 20 is mounted on a hollow drive shaft 40, being securedthereto by a nut 41 at the forward end. A thrust bearing 42 is provided so that the drive shaft 40 may rotate freely in the nose piece, the speed depending upon the speed of the air stream.

In accordance with the present invention, a centrifugal spring-loaded drive connection is interposed between the variable speed drive shaft 40 and the input gear 26 of the gear train. The details of the centrifugal drive connection are shown in Figs. 3 and 4. It will be noted that the drive connection, indicated generally at 45, has a drive member 46 which engages an output member 47. The output member includes an output disc 48 having a set of symmetrically arranged weight members 51-54, re spectively, each of which is radially movable on the disc 48. The weight members are arcuately shaped and are biased inwardly into contact with the driving member 46 by an encircling garter spring 55. In carrying out the present invention, the driving member 46 is in the, shape of a cylindrical cup, oatinglyl mounted 'at its'v base on thev drive shaft 40, and having a narrow cylindrical rim 60. It is therefore free to move laterally relative to the drive shaft 40 so as to center itself with respect to the weight members and to balance the forces applied by such weight members. The floating mounting is obtained by providing an oversized central aperture 61 which is loosely keyed to a notched disc 62 at the end of the shaft 40. In the preferred construction, this is accomplished by tabs 63, 64 which are integrally formed in the drive member and which register with corresponding notches in the disc 62.

With regard to the details of the output disc 48, it will be seen that it is mounted on a stub shaft 65 which is mounted at the center of a closure plate 66, such closure plate being sandwiched between the nose piece 11 and the barrel 12 and held in position by suitable bolts 67. Lying adjacent the output disc 48 and journaled on the 3 stub-sha`ft=65fis-adriveipihion 68. Clearance for the drive pinion-isprovided by-for-ming a'central `boss inthe closure plate 66, a window 69 being cut into the boss to permit the pinion 68 to mesh with the input gear 26 of the gear train.

To understand the construction of the individual weight members,=reference is made to yFigs. 3 and 4. Taking the weight member 51 by way of example, it will be noted that it includes 'asector-shaped yplate 70 which is 'loosely vfastened to the 'output disc 48 by rivets 71, 72 which vare radially silidable in appropriate slots 73, 74, respectively. Arranged at the outer edge ofthe plate 70 is an arcuate weight i7'5 which, in vthe present instance, is formed of three weight elements 76-78 Alaminated together.

In accordance with one of 'the detailed features of the invention, the weight element 781extends radially outward beyond its companions to provide a groove for securely `receiving the garter Vspring 55. As a further feature of the present device, the weight element 77 extends inwardly beyond the adjacent members to present a surface 77a which engages the cylindrical rim 60cm the drive member 46. This tends to yconcentrate the frictional force along a narrow path and tends to insure that each of the weight members will have 4the same area in sliding contact with the drive member.

With the above construction in mind, it will be apparent to one skilled in the art that excessively fast rotation will cause the weight members 51-54 to be thrown outwardly against the biasing force of the garter spring 55 and out of contact with the driving member 46. Assuming that the connected gear train is frictionally loaded, any reduction in the speed of the output disc 4S will immediately cause a reduction in centrifugal force,

resulting in reengagement between the weight members I and the drive member and producing a corrective speed increase. A point of equilibrium is quickly reached at which the torque transmitted through the coupling is at some intermediate value between full on and full ott and at which the speed of the disc 48 tends neither to increase 'nor decrease.

Practical tests confirm that the output speed tends to remain substantially constant over a wide range of input or vane speed. It is believed that the constant speed characteristics of the present device are due in vsome measure to the fact that the weight members 51-54, which are permanently coupled to the gear train, have a llywheel action which tends to smooth out any minor variations in speed which may result as the device searches out the point of exact operating equilibrium. In addition,

since the weight members need only move a hairsbreadth between zero and maximum torque, there is very little speed droop and the speed is largely independent of the ordinary variations of loading torque.

Adequate reliability may be achieved using ordinary machining tolerances and employing ordinary care during i the assembling operation. Thus, the closure plate 66 which mounts the output disc 48 need not be precisely centered relative to the nose piece, any lack of precision at this point being taken up by the floating mounting of the-cup-shaped drive member 46. Furthermore, the'drive member is not required to have a perfectly cylindrical shape throughout its length inasmuch as the weight elements engage it along a narrow ribbon-like area.

As a result of using the above construction, the arming of a bomb or other projectile may be accomplished with a precision heretofore thought unobtainable in a vaneoperated arming device. One skilled in the art will, moreover, appreciate that the drive mechanism ymay be cmplo'yed wherever a relatively constant speed is required from a variable speed power source.

What I claim is:

1. A constant speed drive mechanism comprising, in combination, a drive shaft, a cylindrical drive member at the end of said drive shaft, a rotatable output member coaxially adjacent said drive member, a plurality of weight members on said output member and symmetrically distributed about said drive member, said Weight members being radially movable on said output member and having a garter spring encircling all of them for biasing them into frictional Contact with the drive member, and means for floatingly mounting said drive member on said drivc shaft so that it is free to assume a position which is precisely centered with respect to the frictional surfaces on said weight members.

2. A constant speed drive mechanism comprising, in combination, a drive shaft, a cylindrical drive member on said drive shaft, a rotatable output member coaxially adjacent said drive member, a plurality of weight members on said output member and symmetrically distributed about said drive member, said weight members being radially movable on said output element and having means for biasing them inwardly into frictional engagement with the drive member, and means for lloatingly mounting said drive member on said drive shaft so that it is free to assume a position in which balanced forces are applied thereto by said weight members.

3. A constant speed drive mechanism comprising, in combination, a drive shaftq a rotatable cup-shaped drive member, means connecting said drive member for rotation with said drive shaft while permitting the member to move laterally with respect to the shaft, and a driven member coaxially adjacent said drive shaft, said driven member comprising a plate, a plurality of weights mounted on and radilly movable with respect to said plate and surrounding the axial flange of said cup-shaped drive member, and means for biasing said weights inwardly into frictional engagement with said ange.

References Cited in the file of this patent UNITED STATES PATENTS 1,196,363 Hunter et a1 Aug. 29, 1916 1,924,322 Knight Aug. 29, 1933 2,097,128 McCormack Oct. 26, 1937 2,223,660 Horton Dec. 3, 1940 2,564,826 Yoder Aug. 21, 1951

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