US2653489A

US2653489A - Automatic torque transformer

Info

Publication number: US2653489A
Application number: US102992A
Authority: US
Inventors: Jean F G M L Charpentier
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-07-12
Filing date: 1949-07-05
Publication date: 1953-09-29
Anticipated expiration: 1970-09-29

Description

Sept. 29, 1953 J. F. G. M. L. CHARPENTIER AUTOMATIC -ToRQuE TRANSFORMER 3 Shees-Sheet l Filed July 5, 1949 {lll/11111111,

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ATTORNEYS Sept. 29, 1953 J. F. G. M. L. CHARPENTIER 2,653,489

AUTOMATIC TORQUE TRANsFoRMER Filed July 5, 1949 3 Sheets-Sheet 2 "www ATTORNEYS Sept. 29, 1953 J. F. G. M. CHARPENTIER 2,653,489

v AUTOMATIC TORQUE TRANSFORMER Filed July 5, 1949 5 Sheets-Sheet 3 wwf/M6567 ATTORN EY Patented Sept. 29, 1953 V UNITED STATES PATENT OFFICE nn'roMArio. rfiimwsronmnn -Jean F. G. M. L. Charpentier, St. Cloud, France t Glaiins..-

This invention relates to torque transiorrning. gears and more especially` to. a gear unit gamble. of. transforming torque automatically between a motor or other drivingelement and adriven elementv .in this Sense that it automatically rnaintains stability of the equilibrium oi operation when the opposed turning moments (torques) vary in respect oi their relative intensities- For the. purpose. of, achieving this, the. new device according to the invention utilizes. only the variations. of intensity of the intrinsic forces which are developed on its. organs by thev infill..- enoe of the movement.

The variations.. are:

1.- The variations of the. intensity of. the. driving torque.:

.2. The variations of. the .intensity oi the driven torque;

3.- 'Ihe variations of the in.tenein-I of the cen.- trfugal torce;

.i. The variations. ofthe intensity of. the inertia. forces;

5. The. variations of. the. intensity of friction..

These. variations are utilized both directions for enabling the. device connecting the driving and driver groups, viewed from a, state of equino.- riurn. of operation, to fulll the iollowi-ns revers-` ible function;

1. The intensity ci the driven. torque rises..

.In this oase. the function of the. new device consists therein.' to.. automatically lend to the driving eier-nentv narallelly to. the. rise of intensity oiV the drivenV torque,l one. or. plurality of aune porting points and adding their actions.. thereby to enable it to multiply the, intensity of its torque 1.

as many times as required by the driven torque to become equilibrated. y

2. 'I'he intensity of' the driven torque drops.

In this case the funation of the device reversesV itself so as to automatically. and4 parallelly. to, the

drop of this intensity withdraw' the supportingl systems which multipliedvthe intensity of the driving torque until it became overabundant.

In the device acgsordingI to the invention the identically to itself. or in definite. ratio or mul-l tiniieation..

The device comprisesV niunber or. eiernen.ts union is. equal to. the. number of the .factors of multiplication, the product of vwhich imparts to 2 the nal transformed driving torque that intensity which corresponds to the maximum intensity attainable by the driven torque.

ln the drawings aflxed to this specication and forming part thereof` several embodiments of this invention are illustrated diagrammatically by way of example.

It should however be understood that in these examples every torque transforming gear unit comprises parts well known as such and other parts which are specific of this invention, and that these specific parts mayas well form part of other assemblies without thereby leaving the orbit of this invention.

In the drawings:

Fig. l is an elevationalview from the-direction of the arrows l--I of Fig. 2, with parts broken away and parts shown `in section of a transforming gear unit embodying my invention; the posivtion of the members assures transmission of the driving torque at a multiplication greater than 1 and smaller than 2.

Fig. 2 is a ver-tical cross sectional yView along the line 2-2 of Fig. 1'.

Fig. 3 is a View of a portion of the unit shown in Figs. 1 and 2 with the spring in elongated positionl asin high speed or direct drive.

Fig, 4 san elevationalv view partly in section ofl a portion of a modified form of transforming gear yunit showing' a rigid anchor for the brake means instead of the springl or resilientr anchor shown in Fig'. l.

Fig; 5 is an elevational View with parts broken away from andlpar-ts partly in section of a portion of a modied form of' a ini-arisforming-v gear unit wherein the torque controllable clutch actuating-meanssuch asthe parts shown in section is controllable by centrifugal torce. The spring is shown in elongatedv positionas atrest or at very small'drivenrtorque.

Fig. 6 is a sectional viewon the line tsl-. of Fig. 5.

Fig. 7 is a view similarto that of Fig. 5 of the portion shown in Fig. 5' with the spring of the .'tordueoontrollable clutch actuating means in compressed. position but with. the, driving and driven shaftsloclsed.'together as when the drivenv torque is, relatively low and the. rotational speed is h ilgh- Fig-.81S an elevationalview with parts, broken away of a. torque transforming gear unit. equipped with pedal operative clutching means. y

Fig... 9 is aview partly in section of. a nortionof 11u56 'Gllellaiorming, gear unit with. the pedalat- 55- tached at .another position..

Referring to the drawings, the torque transforming gear unit comprises a train of hypoepicycloidal gears in combination with the specinc members forming part of this invention. In this combination the driving torque is transmitted to the device located inside the casing it by means of the driving shaft I which carries along the drum 2 of cylindrical circumference 3 which carries the internal gear ring 4i. This gear ring li meshes With a number of pinions 20 mounted on axles 2i Which are secured to a disc 22 which is keyed on the driven shaft 23 that extends through the casing l0. The system of gears hereabove described is the hypo-cycloidal part of the train.

The pinions 20 are in mesh as planet gears with a sun gear 30. This system constitutes the epicycloidal part of the train.

The sun gear 3@ is mounted on the hub 3l of a disc 32 carrying the cylindrical drum 40.

rEhe hub 3i, the sun gear 30 and the drum il@ can freely rotate around the driven shaft 23. The drum d@ of the sun gear Sli embraces with a clearance the driving drum 3. A second drum E@ embraces this drum completely and isfree to turn about it. The internal driving gear 4, the hub 3! of the sun gear S, the driven shaft 23 and the drums du and 5@ are arranged coaxially` The two drums l and 50 are coupled on tne one hand by means of a clutch band 6i) and on the other by a spring l0. The band E@ is wound in a spiral around the cylindrical outer surface of the driving drum 3, its ends di, 5i are fixed to arms d2, 52 mounted on the drums ll and 5t, respectively. The ends fil, 5l of the band are crossed as shown in Figs. 2 and 3 so that the tension of the spring f, which is being compressed between the arms M and 5I of the drums, tightly pulls the band 59 around the drum 3 of the driving ring 4.

The cylindrical surface of the drum 5S is spirally embraced by a band 80, both ends d and itt of which are xed to the casing. The end SG may either be xed to the casing rigidly, as shown in Figure 4, or by means of a spring 92 as shown in Fig. l, While the other end Iii@ may either be free or attached to the casing by a spring mi. The operation of this device is analyzed beginning with the starting phase when the driven torque Cr has an intensity always greater than that of the driving torque. As mentioned above, Figs. 2 and 3 represent thedevice as viewed from the side of the driven shaft 23 and the direction of rotation of the driving shaft if defined by that of the tangential driving force im is in this case the positive trigonometric direction.

The driving torque Cm which is transmitted to the torque transforming gear thru the annulus 4 with the radius pitch R3, exerts on the teeth of each of the n planet gears a fraction im of the tangential driving force Tm The planetary gears 20 carry along their support such as the disc 22 (Fig. 2), to whose shaft is applied the resistance torque Cr which exerts on each of the 1L axes 2l of the planetary gears 2G a resistance R to being carried along. (Cf=n.R.R2) where R2' is the radius of the circle passing thru al1 of the axes of said planetary gears.

For the carrying along of their axis 2l in the direction of movement impressed on them bythe ring ii, the p-inions 20 take support from the sun along the drum xed to it. The drum lil then exerts on the spring 10 a tension Where R1 and R4 are respectively the pitch radius of the sun gear and the radius of the circle to Which the center line of spring is tangent wherein R4 is the effective radius of the drum, which acts on the spring it, While R1 is the pitch radius of the sun gear 30.

The spring 10 transmits the tension T to the drum 5t which also tends to turn in a direction counter to that of the driving member. At that point the band 80 enters into action, which is a brake whose Winding is so arranged that its braking effect is abolished by unvvinding, when the drum Sii tends to rotate in the same sense as the driving shaft. However, in order that this braking effect become automatically and instantaneously active and block the drum cil, when it tends to rotate in a sense counter to that of the driving shaft, which corresponds exactly to the case here in question, the spring f, being subjected to the compression force T, simultaneously creates an effect proportional to the intensity of the force t, which effect enables the points @i and iii, at which the ends of the band di? (the clutch band) are attached, to approach .each other. This approach of the two points 4i, 5i results in a relief of the clutch band te. Being thus relieved, the clutch band also relieves the drum 4Q (which is the drum of reaction) and the drum 50 (which is the supporting drum) of all effort, by the driving drum 3, to carry them and, together With them, the sun gear 30 along which is integral with the tWo drums. Under these conditions the internal driving gear which is ,f moving at an angular speed wm corresponding to the driving torque Cm, carries along the planet gears 2B, which act on the immobile sun gear Si) With the effect of carrying along the disc 22;, on which they are mounted, and the driven shaft 23 xed to it, at the speed under the condition that (0.5 X wm) wrdm Where wr is the rotational speed of the driven shaft and wm is the speed of the driving shaft transmitting to the shaft 23 a transformed driving torque This first explanation presents the torque transforming gear, which operates as a multiplier of the driving torque, an operation which occurs inthe same way as that of a classical train of gears of the same composition.

3 illustrates the operation of the torque transforming gear, when the intensity of the driven torque Cr has been reduced until it has become equal to-thatfof the: intensity of' the driving torque Cm.

Starting from` thev case of lllig.` 1,. when the intensity of the driven .torque drops, thev spring. l (Fig. 3') expands, reducingv its effect andino-ving asunderthe attaching points M and-` 'it of theA clutch band 60, whereby this band. is forced to approachY the driving drum 3.1 which it embraces, when the. equality of the intensities of the driving and driven torques is. established. The springV 'm thenA attains its elongation, to which corresponds the tension, to, which is designed to assure to the clutch band 60 the winding pressure required to obtain.. the relative blocking of the elements of'the train of gears: The blocking, by abolishing the relative speedsof all the members which constitute the Atorque transforming gear unit, determines thecarrying along. of the driven shaft 23 at the angular speed om of the driving shaft I.

Obviously the device can operate only if the initial tension tu of the spring, which is necessary for effecting the blocking of the train of gears when the intensities of the opposing torques are equal in absolute values, is lower than the tension produced by the reaction. drum Ml. The intensity of the driven torque then becomes greater than the driving torque. rPhis condition is necessary in order that the band Gil can. relieve the drum 4 from its tension. By' utilizing a-spiral clutch band 50 and b-y using a larger or lesser number of turns in the spiral one may obtain any desired clutching force between the band S0. and the drum I4) and still have a spring which has thedesired tension, to, to be compressed at the desired torque so. that the drum il!) have release for rotation at a speed different from the rotation speed of the driven shaft.

With the tension to therelative blocking of the train of gears can be obtained in theV following manner:

The of the spring extends tangentially to the device. Consequently the effect of itstension tn on each: of its two points' of xation is affected by a sign as follows:

On point 4i there acts the tension -l-t'n, On point 5l the tension -td Since the system is carried along by the drum 4 in the positive sense, the relative tension -f-to which acts on the point 4l of the band 60., exerts on the opposed point 5l and on the-drum 50 a positive traction effect T which as. function of a gure arzt-.11. of the encircling windings, has the intensity: T=tnef-a- This positive traction -I-T which assuresy the carrying along of the entire reaction system (pinion 30, drums l0 and 58) by the driving ring 4, for the coupling traction T. I

The coupling traction T is determined in the folowing manner:

The transformer device is considered as functioning as a multiplier of the driving `torque Cnt/r being `the multiplication factor ofthe driving torque Cin, such as C,-=C, in the present case, where'the ring 4 is the driving element,

supposing that the device has a stable function, satisfying the condition,

slmpcisimg; further that the intensity ofthe receptive torque -Cr drops. until Cnr becomes equalas absolute vaineV to the driving 'torque Cm, then the driven shaft 2i3' opposesv to the driving shaft l a; torque: of an intensity Cm equal to own; (fs-Cr). However, owing to the` equation of the planet gears 20, the opposing torque correspending to, -Ce and effectivelyy opposed to. the driving torque Cm on its* shaft l, is a torque:

QQ Cm The driving torque Cm thusv is relieved of a fraction of; the driven torque, whoseV intensity, equalv to Mlm, is: expressed as follows Consequently the term in reversal of the multiplying factor of the driving. torque Cm, is the demultiplying factor gof the angular speed of the driven shaft with 0.5.. l, which results in. ACm=Cm(l-).

Since the driving torque is Cm=2t.R3, thev coupling traction is expressed as The second explanation furnished hereabove presents the mechanism of passage of the initial operation from the torque transforming gear as a multiplier of the driving torque (and, in consequence thereof, a demultiplying factor of the angular speed of the driven shaft 23) to the operation in direct connection with identical torques and angular speeds on the driving and driven shafts.

It has thus been established that the equipment comprisingl theV band Gil, the reaction drum 40 xed to the sun gear 3d, the spring 'l and the supporting drum 50, fulfills the purpose of utilizing the difference of intensity which may arise between the driving torque and the driven torque, when this latter becomes equal to the former, for restoring the equilibrium of the intensities of these torques` by the application ofv a complementin'g or "compensating supercharge ACm to the driving torque Cm. This supercharge is the clutching traction obtained simply by suppressing automatically therein the action of the multiplying work ofthe planet gear 2li.

The automatically operative equipment described above constitutes the compensating system ofthe transformer device according tov the invention.

The mechanisms of passage from the condition of the torque multiplier to that of a coupler in direct connection which was defined hereabove is obviously reversible. It was in fact described in the beginning of the rst explanation. If from the moment when operation in direct connection sets in, the driven torque rises, the driving shaft is braked, the reaction on the sun gear rises also and movement of the equipment slows down until complete standstill is reached, while the compensating spring lll, which was compressed from the beginning of the brake action by themain force of the equipment to which it is secured, releases the ends of the band E0, allowing them to approach each other, whereby the compensating systeml of the driving drum 4 is declutched and operation by multiplication of .torquesrendered possible again, so that then the working conditions described in the rst explanation are reestablished.

In the foregoing exposition of the gear unit forming the operation of the auto-torque transformer it was assumed implicitly that the driving element operated with a constant opening of the intake port of the motor.

In this case the initial tension of the compensating spring l@ (Figs. l, 2 and 3) can easily be determined by the condition that the rate of relief of the operation as multiplier be slightly higher than that corresponding to the highest value of the driving torque. This satisfactory condition allows avoiding the risk, for the driving element, of being carried along at the highest speed of the zone of stable operation by the braking of the driven torque.

In reality, however, there exists an infinite number of openings for the fuel intake of a motor between the end positions of opening and closure. To this innite number corresponds an infinite number of curves of torque producing the torque diagram of the driving element. Consequently there corresponds to each of these curves a point analogous to the one above defined which lies near a rate slightly superior to that of maximum value, from which on the release of the operation of the auto-torque transforming gear must be eected. This is the condition which must be fuliilled in order that the auto-to .lue transforming gear be enabled to constitute an integral solution of the problem here in view. This condition requires that there be as many tensions to as there are curves. rlhe condition is fufilled if there is imposed to the compensating spring iii a rule of tension depending from the rate of operation, to becoming a function of the variable n.

This condition is suiiicient, for the other values here in view are functions of n.

The material performance permitting to obtain this result consists in the utilization of the action of the centrifugal force acting on a mass which communicates to the compensating spring a tension which this spring transmits to the clutch band in following the function imposed to it, viz.

an expression in which FC is the centrifugal force acting on the m when it rotates at a speed o around the general axis of the device situated at a distance R from center of gravity, while A is a function or w which permits of transforming the centrifugal parabola into an appropriate curve within the range of speeds utilized.

In Figs. l to 7, is illustrated an application of the principle here set out. The compensating spring l@ is mounted on a cylindrical support ii, on which it is free to slide. One end of the support is engaged in a bore H2 provided inside a joint l2, in which the support il is free to slide. The joint 'i2 is fitted in a notch S73 formed in the disc 32 which renders the reaction pinion (illintegral with its drum dii. rEhe joint 'l2 is free to turn in its notch, in which it held transversely by means of flanges i3 (Fig. Ll). rIhe support 'li is formed at its free end with a fork le carrying' a roller 'l5 which is free to turn about an axle ne spring is engaged between the joint 'i2 and the fori; 55, being held between them and tending to force them asunder. The roller 'it is applied against cam face 'il on the drum the proiile of this cam being designated as A. It is engaged in an opening oi the disc 32 and thereby held within its plane, as are also all the other members d here described, and able to oscillate within this opening.

Fig. 5 shows this device in its condition of rest. The repulsive force which maintains, by the distance between the drums d!! and Eil, the tension acting on the brake band 5G, is the initial tension ti of the compensating spring lil. In order to facilitate the adiustment of the transformer, the connection 5l of the band 69 with the drum 5! is provided with means (not shown) for regulating the tension, which is accessible from without the casing I0. This regulating means might also be mounted on the connection lll or drum ed.

The mobile equipment comprising the support H and its fork 14, the spring "EB, the roller and its axle le, its washer and cotter (not shown) has a mass m calculated and situated at its center of gravity g, spaced by the radius R from the general axis of rotation. In the case where the driving drum of the driven shafts are in direct connection, under the iniluence oi the speed oi rotation this equipment is thrown outwardly by centrifugal force as shown in Figure 5, and turns about the axis of the joint 'l2 which forms the center of articulation, while thel roller climbs on the face of the cam il', compressing the spring 'i0 in order that the tension to at each one of its positions assume the intensity imposed by the corresponding spe-ed of rotation.

Fig. 6 illustrates this device in the extreme position corresponding to the highest rotation speed, the spring 7B being fully compressed.

The following points are to be noted with respect to the structural embodiment here described.

The exterior brake B5 on the drum t@ is connected to the casing it by its ends 9@ and ist (Figs. 2 and 3). The end Si? may be connected to the casing by elastic means such as the .spring S2 (Fig. 2), the end lil by the spring H92. The end 9B is iixed to a small piston Si with a spring 92 exerting on the piston a constant tension equal and opposed to the tension of the maxin. torque before it is transmitted by the torque transforming gear. This tension is impressed on the piston by a nut 93. rlhe other end (itil) is ixed to a piston lili which is acted upon by the very low tension of a small spring M32 which merely serves the purpose of avoiding loosening of the band 83. rhe piston lili does not contact the nut 63 on the cylinder idd.

If, with the several members arranged as de scribed, a supercharge or extra heavy load is imn posed on the brake band Si?, ior instance in the sense of a declutching by the instantaneous application of the maximum torque, the negative traction of the brake @il which is carried along by the drum 5i?, imposes on the spring force which permits the brake and its support negative rotation which induces the opposite end of the band. to apply its piston i9! against nut lii of the cylinder whereby the band is unwound from the cylindrical surface of the drum 5D to the extent of allowing it to dampen by negative rotation without outward effect pulse received, the period of ti....ic consumed thereby being equal to the oscillation period of the spring 92.

As illustrated in Figs. 8 and 9 provision is made for controlling the supercompression of the spring e2 or i512 by actuation of a pedal and for utilizing this device in the place of the classical declutching device, to which it is superior insofar as it does not force mechanical pieces in motion to weight on each other.

Figs. 9 and 10 illustrate two settings permitting to let loose'brake band 80 by operating upon one of its ends. The setting by Fig. 9 ,is in relation with the instance of a free end of brake band 80. A pedal actuating a groove I2| pushes a pin |22 which -distends the brake band. A spring |23 draws thepedal hack yina neutralpcsition.

Setting refered -to in Fig. lconcerns the exention of a thrust upon the ties of -brake band die.

Same setting may be employed for the opposite tie 90, but spring 82 is quite stiffer than spring |02.

As mentioned above, the piston |0| does not contact the threaded cylinder cap |03. The gap between them communicates with the space at the bottom of the casing by way of a conduit |05 situated in the plane of rotation of the disc 32 of drum 40 and opening in a negative sense.

While the gear unit constituting the torque transformer operates in direct connection with the driving and driven shafts, the

drums

40 and 50 rotate at the general speed of the system. The brake 80 then does not play any role and it is advisable to separate it from the cylindrical surface of drum 50. The cil in the casing is projected under pressure by the circumferential acceleration imparted to it by the

drums

60 and 50 toward the conduit 05 and acts on the small piston |0| which in rising in its cylinder |04 (Fig. 3) unwinds the brake band 80 and thereby lifts it from the drum surface.

When the torque transforming gear unit goes through an ascending phase, the drum 50 is braked, the oil pressure which is a function of a2, drops rapidly and the brake band 80 has returned to its position to become operative before the drum 50 is arrested. The drum may be provided with vanes to build up the oil pressure required in the cylinder |04.

While the torque transforming gear unit comprises amongst its specic members a free-wheel device, it does not possess a free-Wheel action itself.

Propulsion by the kinetic energy of the vehicle` in which the transformer may be mounted, converts the planet-wheel carrier into a driving element which will act in two ways:

1. The motor is slowed down, starting from the operation in direct connection, i. e. at high speed. The compensator is then subjected to the locking action of the transformed centrifugal force Fc|- the locking continues and the vehicle is braked by the motor in the unitary sense.

2. The motor is slowed down, starting from the multiplying` of the torque, and the braking effect is then produced in corresponding multip-lication.

The application of the principle of the direct torque transforming gear unit according to this application also comprises the provision of a torque 'de-multiplying and speed multiplying element which can be mounted in series with other torque transforming gears. In that case the driving torque is led into the element by the planet wheel carrier, the reaction sun gear is fixed and the internal gear ring receives and conveys to the outside the transformed torque and speed.

The device here described presents many dif ferent possibilities of use of its different elements. For instance- 1. The coupling drum which '-in the example described is constituted by thedriving drum, 1may be a drum integral Vwith the planet-gear carrier. This means onemere member, 'however the angular speed is weaker and the start more progressive.

2. 1The planet-gear carrier may comp-rise the clutch `men'rber `and fits 'compensator and can engage either the driving'or the reacting drum.

3. Ihetrains ,of gears may be formed with helicoidal teeth `and the variation of the axial thrust of the planet gears or of the reactor may be utilized together with an appropriate compensator for causing the coupling of the element selected.

I wish it to be understood that I do not desire to be limited to the details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. In a mechanical automatic torque transformer of the kind described in combination, a stationary casing, a driving shaft and a driven shaft arranged coaxially in, and exten-ding outwardly through the walls of said casing, a first drum fixed to said driving shaft, an internal gear ring fixed to said first drum, a gear carrier disc fixed to said driven shaft, planet gears rotatably mounted on said gear carrier disc and meshing with said internal gear ring, a sun gear freely rotatable only in the driving sense, mounted on said driven shaft in mesh with said planet gears, a second drum integral with sai'd sun gear surrounding said rst drum, and a third drum mounted on said second drum for angular displacement relative to same, elastic means arranged between said second and third drums for controlling their relative angular displace-ment and rotation in common, an automatic braking means attached to said stationary casing for braking said third drum in a sense counter to the revolution of said driving shaft, and an automatic clutching means capable of coupling said internal gear ring with said second drum, said clutching being controlled by a relative angular displacement of said second and third drums.

2. The device of claim 1 in which the automatic braking is constituted by a brake band aixed by one of its ends to the stationary casing and spirally wound about said third drum, the sense of such Winding counter-acting the driving sense.

3. The device of claim 2 in which the tie of one of the ends of said brake band on the stationary casing comprises a dea'dening spring.

4. The device of claim 2 in which the second end of same said brake band may be actuated outwardly, from the stationary casing, in order to loosen said brake band and to procure declutching action between the motor and the automatic torque transformer.

5. The device of claim l wherein said automatic clutch is constituted by a clutch band spirally wound about said rst drum, one end portion of said clutch band being attached to said second ldrum and the other end being attached to said third drum.

6. The device of claim 1 wherein said'elastic means between said second and third drums is a spring whose reaction is tangentially exerted on said second and third drums and is transmitted 11 by these drums to the far ends of the clutch band to brake the first driving drum.

7. The device of claim 1 in which the tension of the spring forming the elactic means inserted between second and third ldrums is a function of rotational speed and comprises a cylindrical joint formed with a bore and capable of turning in a cylindrical notch formed in the rst drum, a piston movable in said bore, the said spring ten'ding to push said piston away from said joint and a cam face on said second drum being in contact with said piston and tending to increase said spring action.

JEAN F. G. M. L. CHARPENTIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Henriod Apr. 6, 1909 Levedahl Feb. 8, 1916 Christie Nov. 4, 1930 Cotterman June 14, 1938 Fleischel Nov. 17, 1938 Taylor June 3, 1941 Snow July 8, 1941