Speed Control Linkage Means For Winding Bobbins

Abstract

A bobbin winding means in textile machinery having a driven spindle for the bobbin and a roller means in contact with the peripheral surface of the bobbin in a closed drive position thereof, the drive means for said bobbin including a friction gear for variation of the speed of revolution of the bobbin in response to increasing diameter of the bobbin by means of a speed control linkage means adapted to actuate a lever adjusting means on the friction gear in response to relative displacement between the bobbin spindle and the roller means, this linkage means having yielding elements which move as a single-acting unit during normal drive of the bobbin but which can be pressured or adjusted into an open position freeing the bobbin from contact with the roller means when the bobbin drive is stopped.

Description

This invention generally relates to textile machinery such as spinning, spooling or twisting machines equipped with a speed variation gear means in the drive of a thread or yarn winding position, such gear means being adjustable over a linkage or lever system connected to elements of the winding position which move out or swing out in response to the increase of the winding diameter, e.g., the growing diameter of a wound bobbin.

In the winding of threads, yarns and the like which are supplied to the bobbin of a winding position at a constant rate of speed, the depositing speed of the thread on the winding surface of the bobbin must also remain constant during the entire winding process. In order to achieve this, as is well known, the turning speed of the bobbin being wound is caused to decrease as the winding diameter increases.

In order to control this bobbin rate of revolution, it is thus a known practice to drive the bobbin on its winding circumference by means of a drive roller frictionally engaging the bobbin and turning at a constant rate, whereby the bobbin turning rate is continuously automatically adjusted in correspondence to the constant peripheral velocity applied thereto. For a number of practical reasons, this type of peripheral drive of the bobbin is not desirable, especially where the wound threads may be easily damaged.

In the case of a winding bobbin driven only at its spindle or axis, however, this constant speed control of the peripheral surface of the bobbin is not possible. In these cases, the shifting movement of the bobbin axis or, in the case of a bobbin arranged in fixed position, of a feeler roller lying against the winding surface, is employed in order to adjust the bobbin drive motor directly over a lever rod system or other suitable linkage means. When interposing a speed varying gear means, this linkage means can be used to adjust the gear in the sense of causing a speed reduction as the bobbin diameter increases.

These gear means are generally constructed as infinitely variable friction gears, this being a relatively simple and reliable mechanical means of directly controlling the speed of the winding bobbins. With the machine at a standstill, however, such a friction gear because of its extreme friction cannot be directly adjusted. As a consequence of this freezing or fixation of the gear, the pivotal movement or displacement of the bobbin spindle (or else the feeler roller) with reference to its counterpart which is on a fixed axis at the winding position is not possible, for example, for the purpose of changing a bobbin or retying a broken thread. The usual locked gear-adjusting linkage means under these circumstances thus prevents easy removal or access to the bobbin. This pivotal movement or displacement is possible as between the bobbin spindle and a contacting roller only if previously the friction gear has been mechanically disassembled from the adjusting linkage or else the adjusting linkage itself has been separated mechanically from the displaced or pivoted element of the winding position. Such a servicing of the machine is, however, overly complicated and time-consuming.

One object of the present invention to remedy the disadvantages of the known winding devices in textile machines and to make possible an easy and rapid servicing of the machine. Another object of the invention consists in making possible the described pivoting or displacing movement of the particular element of the winding position which is gradually shifted by the increasing bobbin diameter, not only during winding but also with the gear at a standstill and without dismantling or removing the adjusting linkage means.

These and other objects and advantages of the invention will become more apparent upon consideration of the following detailed specification.

It has now been found, in accordance with the invention, that the desired access and servicing of the winding position in the textile machine can be achieved in those instances wherein the winding means of a textile machine includes spindle means for rotational winding of a thread onto a bottin and roller means arranged to contact the outer peripheral surface of the bobbin during winding thereof, these spindle and roller means being mounted for displacement relative to each other in response to increasing bobbin diameter, and drive means for rotation of the bobbin on the spindle means by operation through an infinitely variable friction gear having a speed adjusting lever thereon which is movable only during the driven rotation of the gear, by providing the improvement which comprises a speed control linkage means connected to the speed adjusting lever for movement thereof in response to variations in the displacement between the spindle and roller means, this linkage means including yielding coupling means or connecting elements operating as a single-acting linkage unit during the driven rotation of the bobbin but yielding under an applied pressure which moves the bobbin away from its contacting roller means while the drive means is stopped with the adjustable lever in a fixed position.

The infinitely variable friction gear used in the combination of the invention may be of any conventional type, for example the friction disc type of variable gear as disclosed in U.S. Pat. No. 2,093,820 or the friction roller type of variable gear as disclosed in U.S. Pat. No. 2,469,653.

The yielding coupling means in the gear adjusting linkage, e.g., a system of linking rods or arms, can consist essentially of a slip coupling or a so-called slipper or release clutch, whose slipping, shifting or rotary movement either along a rod or the like or else about an axis or pivot point is preferably limited in one or both directions by a stop member which may be adjustable. In the lifting off or displacement of the winding bobbin or of the feeler roller, its carrier arm is moved or swung into any desired override position, in which operation the slip coupling yields correspondingly. The resetting of the carrier arm must then take place up to the stop member of the slip coupling, so that the winding bobbin or feeler roller carrier arm passes back into its original starting position, i.e., at any point in the overall winding operation.

A further desirable feature of the invention is one in which the starting position is automatically reoccupied after the deflection or shifting of the carrier arm to its override position in order to service the bobbin. This is accomplished, in accordance with the invention by providing as the yielding coupling means in the gear adjusting linkage means, a fulcrumed or two-armed coupling pivoting on a fixed pivot point, in which both lever arms are arranged to pivot with respect to one another and are preferably braced or tensioned against one another by means of an adjustable stop and spring means. The bobbin carrying arm or the carrying arm of the feeler roller can in this manner be manually deflected or urged from its normal contact or engaging position of the bobbin and roller means by overriding the spring tensioning force, so that an easy bobbin change or knotting operation is possible. The carrier arm, after removing the deflecting force, then returns back into its starting position under the influence of the spring force. The pivot axis or pin connecting the two lever arm of the spring-urged lever system with one another can simultaneously act as the fixed pivot axis or pin of the lever system as such, i.e., as the pivot means for relative movement of both coupling lever arms and also for the coupling member as a single-acting linkage unit. It is, however, equally suitable to construct the two axes or pins separately and to articulate or pivot one of the two lever arms on the other.

The connection between the yielding coupling of the linkage means with the adjustable member of the friction gear can also be established over a separate coupling rod. In this case, the slip coupling is then preferably arranged on the coupling rod or else the self-yielding (spring-tensioned) lever system is articulated or pivoted on the separate coupling rod.

The slip coupling or yielding connecting elements of the gear-adjusting linkage means can also be located at the pivot point or axis of the carrying arm for the bobbin spindle or the feeler roller, so that this carrying arm is yieldingly connected with a rocking lever which engages at its other end into the guide slot of a cammed rocker arm or plate which also has a predetermined cam surface or rail portion adapted to guide the adjusting member of the friction gear. With the preferred use of the resilient or spring-tensioned two arm lever connection pivoted about a fixed pivot point, one of the two lever arms can be equipped with a cammed rocker arm which guides the adjusting member of the friction gear.

The cammed rocker arm can be constructed as a contoured single-rail cam surface and also as a two-rail slot. In the case of single-rail construction of the cam, the yielding deflection or lateral movement of the bobbin or feeler roller carrying arm takes place in opposition or in contrast to the fixed position of the rocker arm brought to a standstill by the blocked or frozen gear-adjusting member. There is then no check rail or bar in the way of a return of the bobbin or feeler roller carrying arm. It is possible, therefore, without difficulty to automatically return the individual elements up to the contact of the bobbin and feeler roller at their original position before deflection or displacement from each other. The restoration of the gear adjusting member into its original position must be accomplished in this instance by a spring or similar elastic means, so that the gear adjusting member enters into or remains in contact with the guide rail of the cammed rocker arm as soon as the machine is switched on again.

In the case of the two-rail or slotted construction of the cammed rocker arm, the adjusting lever member of the friction gear is always guided on both sides and can therefore be adjusted only by the movement of the rocking lever and permits, on its part, a shifting of the cammed rocker arm only when the gear is turning. Consequently, after removing a full or partly wound bobbin and inserting a new spool or tube on a machine at a standstill, there does not immediately arise any contact between the fresh bobbin spool and the feeler roller. As soon as the machine begins to run, however, the counterweight of the bobbin carrying arm or else a pull spring or the like on the adjusting lever member of the friction gear is utilized to urge the bobbin carrier arm into the fresh winding position. This same pull spring acts oppositely to the release or override direction of the deflected carrier arm so that it can also act to draw the carrier arm back to any intermediate position of winding when used in cooperation with a suitable stop member.

The guide rail or slot of the cammed rocker arm in running contact with the gear adjusting lever can be constructed over its entire length in such a way that from the start of winding onward there is provided a predetermined reduction of the bobbin turning rate, i.e., its speed of revolution. However, in order to facilitate the start of the winding of the thread on the bobbin, for example in order to reach a desired winding speed or draw-off speed from the feed bobbin or to generate firm thread lays on the winding spool as a stable basis for the building up of the rest of the wound bobbin, it is also expedient in some instances to avoid changing the winding speed up to a certain spool diameter, to change it only very slightly and then only later to begin the gradual controlling down of the bobbin turning rate. This is achieved according to the invention by providing the guide rail or slot of the cammed rocker arm designed to receive the gear adjusting member with an initial guide zone corresponding to the winding commencement such that the guide rail has at this point a radius of curvature identical with the turning radius of the cammed rocker arm measured from its pivot point, or else this guide rail lies tangentially or secantially to this swinging arc or circular segment. In traveling through this initial guide zone, a small portion of the resulting winding can be formed with a winding speed which increases in dependence on the growth of the winding diameter. Thus, the invention also permits to at least some degree a variable programming of the winding speed by the cam arrangement.

These and similar equivalent embodiments of the invention are illustrated in greater detail by the examples given in the accompanying drawing wherein:

FIG. 1 is a partly schematic side elevational view of a winding unit in which the speed control linkage means has a linear slip coupling assembly between a pivoted carrier arm for the bobbin and an adjusting lever on the friction gear of the drive means;

FIG. 2 is a partly schematic side elevational view of a similar winding unit in which a rotational slip coupling assembly is provided in the speed control linkage means;

FIG. 3 is a partly schematic side elevational view of still another embodiment of the winding unit in which the yielding coupling means for the speed control linkage is provided by two levers braced against each other in a toggle lever arrangement;

FIG. 3a is an enlarged partial perspective view of the toggle lever provided with an adjustable stop means along one lever arm thereof;

FIG. 4 is a modified embodiment of the winding unit shown in FIG. 3 wherein one of the tensioned coupling lever arms of the toggle lever arrangement is equipped with a cammed plate to provide a guide slot for the gear speed adjusting lever;

FIG. 4a is an enlarged partial perspective view of the toggle lever and stop member used in the embodiment of FIG. 4;

FIG. 5 is a partial side elevational view of the bobbin and its carrier arm pivoted away from a supporting roller for exchanging or servicing the bobbin, two suitable blocking or temporary holding means for this open position being illustrated; and

FIG. 6 is a fragmentary side view of a cammed rocker arm or guide rail member, illustrating the manner in which the speed control can be mechanically programmed.

Similar parts in each of the various embodiments have been designated by similar reference numerals even though there may be slight variations in the design or placement of such parts.

Referring generally to FIGs. 1 to 4, there is represented a single winding position of a typical textile spinning, spooling or twisting machine, i.e., there usually being a very large number of winding units arranged side by side along a supporting frame. The winding drive takes place in all cases from the motor 1 or a chain, belt or cord 2 leading from any drive shaft onto the infinitely variable friction gear 3 and then further in a conventional manner over belt 4, deflection rollers 5 and belt 6 onto the bobbin holder or spindle 7, the wound package 8 of thread or yarn being taken up on the bobbin tube 9 which can be slipped over the holder or spindle 7.

The bobbin holder 7 is supported by a carrying arm 10 borne to pivot on the fixed pivot pin 11, and this arm 10 is weighted in such a way that the empty bobbin tube 9 or the resulting winding or bobbin 8 always tends to lean against the supporting roller 12 having its axis of rotation in a fixed position. The thread or yarn 13 runs from a thread guide and any suitable feed roll or other supply means (not illustrated) onto this roller 12 before it is deposited on the winding surface of the tube 9 or bobbin 8.

Between the carrying arm 10 and the adjustable member or speed control setting lever 14 of the gear 3, there is arranged the linkage means as a gear shifting system equipped according to the invention with a yielding coupling means or connecting elements in a pretensioned or frictionally engaged closed operating position. Different yielding couplers or slip clutch arrangements are illustrated in the drawings, and still other variations are obviously also suitable.

According to FIG. 1, the coupling means consists of the rocking lever 15 rigidly fastened to the carrying arm 10 in combination with the coupling rod 16 pivotally connected on the adjusting lever 14 and provided with stop 17 at the opposite end. A slip coupling is accomplished in the simplest case by means of sleeve 18 and spring 19 as means sliding on the rod 16 against a certain predetermined resistance, this sleeve 18 being joined at 20 with the other end of the rocking lever 15.

A pull spring 21 engaging on the control or adjusting lever 14 loads or urges this control lever of the friction gear 3 in the sense of causing a clockwise movement for speed increase. Also, when the gear 3 is engaged during the drive of the winding unit, this spring 21 with the stop member 17 alway ensures that a contact engagement of the bobbin winding 8 or of the tube 9 on the supporting roller 12 is achieved and the speed control is maintained. The clamping effect of the slip coupling elements 16, 18 and 19, i.e., as exerted by the spring clamp in sleeve 18, is chosen so as to be greater than the pull or displacing influence of the spring 21 on the coupling rod 16. During the winding, this prevents the occurrence of a false speed or turning rate by inadvertent coupling slippage.

For the changing of bobbins or for tying of a broken thread, it is now possible with the apparatus illustrated in FIG. 1, despite the immovable or fixed adjusting lever 14 with the motor at a standstill, for the bobbin carrying arm 10 to be pivoted off from the supporting roller 12 through the yielding or override movement of the slip coupling. Moreover, this easily manipulated pivotal release of the bobbin from its associated roller does not require a mechanical separation or disassembly of the speed control linkage or the gear portion of the drive means. After completion of the bobbin change or knotting operation, the swinging arm 10 is pushed back or falls back under its own weight until the sleeve 18 of the slip coupling again touches the stop member 17. A freshly slipped on empty bobbin tube or spool 9 does not at first apply itself to the supporting roller 12, since the blocked or frozen adjusting lever 14 prevents any further swinging back of the carrying arm 10. With starting of the motor 1 and the belt drive 2, however, this blocking of the gear control or adjusting lever 14 is discontinued, so that the carrying arm can then turn under the influence of its weight and/or the pull of spring 14 clockwise up to engagement of the fresh tube 9 against the supporting roller 12.

FIG. 2 illustrates, in place of the slip coupling of FIG. 1, a twist or rotational slip coupling 22, which acts on the fixed axis 11 between the carrying arm 10 and the rocking lever 15'. This rotational or torsional slip coupling is formed in a conventional manner by axial elastic bracing of annular friction surfaces, i.e., where oppositely disposed annular members are frictionally engaged about the pivot axis 11. The construction of such rotational slip couplings as such is well known and therefore does not require a separate detailed description.

The rocking lever 15' engages at its other end into a groove or slot-type guide track 23 of a cam lever 25 which rocks or pivots around the fixed position of the pivot pin at 24. The guide slot 26 of this cam lever 25 shifts the lever 14 of the friction gear 3 against the action of the pull spring 21' during increase of the winding diameter which results in a reduction of the bobbin or spindle turning rate. The manner in which this device functions corresponds substantially to that described for FIG. 1 except that the direction of speed control of the lever 14 is reversed. Again, after completion of a bobbin change or thread retying operation, the carrying arm 10 must be turned back until it lies against the stop 27 located on the arm 10 and limiting the movement of the rocking lever 15'.

In FIGS. 3 and 4 the yielding coupling means is formed, in contrast to the slip couplings of FIGS. 1 and 2, is formed as a flexible toggle lever, i.e. a two-armed lever which is resiliently moved into an open position increasing the angle between the arms. Also in FIGS. 3 and 4 as in FIG. 1, the rocking lever 15 is fastened rigidly to the pivoted bobbin carrying arm 10 turning or pivoting about the fixed axis 11. On a fixed axis or pivot 28, there are pivotally or turnably connected the levers 29 and 30. A tensioned pull spring 31 connected at either end to these two levers 29 and 30 urges the lever 29 constantly against the stop 32 seated on the upper edge of lever 30 (see especially FIGS. 3a and 4a). Lever 29 has at its other end a slot or groove 33, into which the rocking lever 15 is slidingly engaged. Lever 30 is then connected at its other end, according to FIG. 3, over the coupling rod 16' or, according to FIG. 4, over the cammed rocker arm 34 onto the adjusting lever 14 of the friction gear 3.

The pull spring 21 or 21' engages as shown in both FIGS. 3 and 4 on the adjusting lever 14 in the sense of directing a faster turning rate and a swinging of the carrying arm 10 toward the supporting roller 12 when the winding drive is in operation. Spring 31 or 31' is sufficiently strongly tensioned that the levers 29 and 30 or 30' cannot leave their normal stop position resulting from the stop member 32 or 32' under the forces conducted from spring 21 or 21' into the linking rod assembly. Thus, it is essential for the pulling force of spring 31 or 31' to be substantially greater than the spring force of the corresponding control lever spring 21 or 21'. At the same time, these are not exceptionally large spring forces so that one can manually override the pull force exerted by spring 31 or 31' in order to retract or swing out the carrier arm 11 and its spool 9 or bobbin 8 on the spindle means 7. Absent this overriding movement, on the other hand, the spring 31 or 31' does cooperate with stop member 32 or 32' to provide a single-acting two-arm linkage unit.

Through this type of yielding connection or resilient coupling there is always assured for the entire course of the winding process a substantially faultless guiding of the speed control lever 14, while at a standstill or non-driven condition of the friction gear 3, the bobbin carrying arm 10 can still be moved against the pull of the spring 31 or 31' away from the supporting roller 12 without being hampered or disturbed by the blocked control lever 14.

The stop member of the yielding coupling means or connecting elements in the linkage assembly is preferably constructed and arranged in an adjustable manner as indicated in the embodiments of FIGS. 1, 3 and 3a. For example, as shown in FIG. 1, the knurled stop nut 17 can be adjustably threaded on the linking rod 16 so as to place it at different positions from the free end of this linking rod opposite its connection to control lever 14. This naturally permits a considerable variation in the initial setting of the speed control means including lever 14. As shown in the two-arm lever arrangement of the coupling means in FIGS. 3 and 3a, the stop member 32 is adapted to slide along the upper edge of the lever arm 30 behind the pivot pin 28, and this stop 32 can be removably tightened at any position thereon by means of the lock screw 36 or any similar locking or clamping means.

As indicated in FIG. 4a, the stop member 32' can also be in a fixed position on the lever arm 30', but in this instance, other means for adjusting the initial speed control setting of the friction gear 3 should preferably be provided. For example, as indicated in FIG. 4, the slotted cam plate 34 can be attached by a pair of slot and bolt means 37 which permit an adjustment of the guide slot 26 to different initial settings of control lever 14. This also permits an easy interchange of different cam plates 34 so as to provide some differences in the dimensions and resulting winding program established by the guide slot 26.

In FIG. 5, the bobbin 8 with the spindle and spool elements 7 and 9 carried by arm 10 are illustrated after being swung about pivot 11 up to an almost vertical position at a substantial distance away from roller 12 so as to replace the bobbin or tie the broken thread 13. In order to carry out such operations without manually holding the winding means and carrier 10 in this open position, it is preferable to insert a retractable blocking member 38 of any suitable design and arrangement and/or to provide a handle member 39 which serves to pull the bobbin 8 and arm 10 away from roller 12, e.g., by a pin 40 insertable in a corresponding hole or depression in the carrying arm 10. Individual holding or catch members 41, which may also be an elongated bar or rail along the machine or part of a portable workbench or the like, can be positioned to lock the handle member 39 in place until it is lifted or removed to release the bobbin back into its normal winding position. Other temporary locking or holding means are also quite suitable, provided that once they are released, the spring 31 or 31' will pull the bobbin carrying arm 10 back into its original starting or intermediate winding position.

In the construction of the pivoted axis or bearing pin of the two levers 29 and 30, one can also readily visualize a construction in which only the lever 30 is borne on the fixed axis or pin 28 while lever 29 is pivoted or hinged on the lever 30. A reversal of this arrangement, namely lever 29 pivoted on axis 28 and lever 30 pivoted on lever 29 is at least feasible in the case of a device equipped with the coupling rod 16' according to FIG. 3.

FIG. 6 shows, in a fragmentary view, the course of curvature of a cammed rocker arm 34' along its guide edge or rail 35. This rail at its indicated end 35 is first directed uniformly at the winding commencement so as to exhibit a radius of curvature R which is about identical to the swinging radius of this initial zone of the guide edge about the fixed axis or pivot point P (corresponding to axis 24 in FIG. 2 or axis 28 in FIG. 4). At the start of the winding process then, in spite of the first slight increase of the bobbin diameter and corresponding displacement of the cammed rocker arm 34', there does not immediately occur any change of the turning rate of the bobbin or its spindle, so that the thread in this initial winding stage is wound with a slightly increasing volocity of the bobbin. When the desired winding speed is subsequently attained or the requisite base thread layers have been properly distributed on the tube at the end of this first winding stage, the lever 14 then moves out of the influence free guide range 35 of radius R on the rocker arm 34' into its active control or deflecting zone 35', which then brings about the desired reduction of the bobbin turning rate with increasing bobbin diameter.

During normal operation of the winding means, the speed control linkage assembly of the invention can operate as a single-acting programmed unit which is entirely responsive to changes in the bobbin diameter. When the winding operation is stopped for servicing, however, the yielding coupling means or coacting resilient elements of this linkage assembly permit a rapid manual disengagement of the bobbin from its associated contact roller, and after the pressure exerted to cause this disengagement has been released, the bobbin can be automatically returned to its last normal operating position without restarting the winding. Moreover, even when replacing a fully wound bobbin with any empty spool or tube, this freshly loaded spindle of the winding means can be automatically returned to the normal winding position simply by starting the winding drive motor and friction gear transmission.

All of these advantages are achieved with maximum flexibility of design and arrangement of individual parts or elements, and the apparatus of the invention is of particular value in being easily adapted to existing winding operations for textile machinery, especially where a large number of winding units are required in spinning, spooling and twisting machines.

Claims

The invention is hereby claimed as follows:

1. In combination with the winding means of a textile machine including spindle means for rotational winding of a thread onto a bobbin and roller means arranged to contact the outer peripheral surface of the bobbin during winding thereof, said spindle and roller means being mounted for displacement relative to each other in response to increasing bobbin diameter, and drive means for rotation of said bobbin on said spindle means by operation through an infinitely variable friction gear having a speed adjusting lever thereon which is movable only during the driven rotation of the gear, the improvement comprising a speed control linkage means connected to said speed adjusting lever for movement thereof in response to variations in the displacement between said spindle and roller means, said linkage means including yielding coupling means operating as a single-acting linkage unit during the driven rotation of the bobbin but yielding under an applied pressure moving said bobbin and said contacting roller means away from each other while said drive means is stopped with said adjustable lever in a fixed position.

2. The combination as claimed in claim 1 wherein said yielding coupling means is formed by a slip coupling of two surfaces in frictional engagement with each other and limited in the amount of slip by a stop member.

3. The combination as claimed in claim 2 wherein said stop member is adjustable to provide a predetermined variation in the dimensions and position of the slip coupling members in the linkage means.

4. The combination as claimed in claim 1 wherein said yielding coupling means includes a pair of lever arms pivoted with respect to each other and spring tensioned to pivot apart until restrained by a stop member connected to one of the lever arms.

5. The combination as claimed in claim 4 wherein said stop member is adjustably connected to said one of the lever arms.

6. The combination as claimed in claim 4 wherein said yielding coupling means as a single acting linkage unit is essentially in the form of a rocker mounted to pivot on a fixed axis which simultaneously provides the pivot axis of said pair of spring tensioned lever arms.

7. The combination as claimed in claim 2 wherein the slip coupling is arranged on a connecting rod which in turn is pivoted on a speed adjusting control lever of the friction gear.

8. The combination as claimed in claim 4 wherein the pivoted and spring tensioned lever arms of the yielding coupling means are pivotally connected near one end of a connecting rod which has its opposite end pivotally connected onto a speed adjusting control lever of the friction gear.

9. The combination as claimed in claim 2 wherein the slip coupling is arranged at the pivot point of the carrying arm of the bobbin or its associated roller means, said slip coupling connecting said carrying arm with a rocking lever which is engaged at its other end into guide means of a cammed rocker arm pivoted on a fixed axis and provided with a cammed surface adapted to guide the speed adjusting control lever of the friction gear.

10. The combination as claimed in claim 4 wherein one of the two lever arms pivoted on a fixed axis is attached to a cammed rocker arm having a guide means adapted to guide an adjustable speed control lever of the friction gear.

11. The combination as claimed in claim 9 wherein the initial starting zone of the cammed rocker arm guide means has a radius of curvature approximately equal to the swinging radius of the rocker arm measured from its fixed pivot point.

12. The combination as claimed in claim 10 wherein the initial starting zone of the cammed rocker arm guide means has a radius of curvature approximately equal to the swinging radius of the rocker arm measured from its fixed pivot point.