WO2011055400A1

WO2011055400A1 - Bidirectional coupling member with helical spring and friction trigger motion transmission mechanism

Info

Publication number: WO2011055400A1
Application number: PCT/IT2010/000439
Authority: WO
Inventors: Gabriele Rebecchi
Original assignee: Cge Services & Trading Srl
Priority date: 2009-11-04
Filing date: 2010-11-02
Publication date: 2011-05-12
Also published as: ITCR20090043A1; IT1396522B1

Abstract

The invention relates to the sector of coupling members for selective bidirectional transmission of a rotational motion from a driving shaft (2) to a driven shaft (4), and relates to a member in which the primary motion transmission mechanism is produced through a cylindrical helical spring (5), arranged astride the two shafts, wherein friction engagement means, which can be selectively activated or deactivated with external control means, determine driving of the two ends of said spring which, winding around said shafts, cause them to rotate in unison. The member is characterized in that it also comprises secondary means (20, 23) for transmitting motion from the driven shaft to the driving shaft, arranged between said driving and driven shafts, arranged for being automatically actuated when a torque C_bis generated, directed from the driven shaft to the driving shaft.

Description

BIDIRECTIONAL COUPLING MEMBER WITH HELICAL SPRING AND FRICTION TRIGGER MOTION TRANSMISSION MECHANISM

* * * * *

The invention relates to the sector of coupling or clutch members for selective bidirectional transmission of a rotational motion from a driving shaft to a driven shaft and vice versa, particularly suitable for use on moving work machines and vehicles in general.

More in detail, the invention relates to a coupling member wherein the primary motion transmission mechanism is produced through a substantially cylindrical helical extension spring, arranged astride the two shafts, wherein friction engagement means, which can be selectively activated or deactivated with external control means, determine driving of the two ends of said spring which, winding around said shafts, cause them to rotate in unison.

A device of this type for use in photocopying machines is known from patent US 4,440,280. A device of this kind presents limits and drawbacks that make it unsuitable for use on vehicles and work machines that require to transfer high powers, forces and driving torques between two shafts and which work in movement, travelling over ground that may even be very rough.

Patent application No. CR2009A000031 by the same inventor describes a coupling member particularly suitable for use on moving work machines and vehicles in general, which makes use of machines safe for operators, does not cause undesirable actuation of the driven shaft, does not produce frictions, is reliable, of simple construction and does not require particular maintenance operations.

This coupling member comprises: - a first drum associated with a driving shaft;

- a second drum associated with a driven shaft;

wherein said first and second drum have the same outer diameter and said driving and driven shafts are coaxial in the direction of a main axis; - a transmission helical spring arranged around the two drums, having a first and a second end;

- a first sleeve arranged around said spring;

- a second sleeve rotatingly associated with the first sleeve;

- a flange associated with said first drum;

- a control lever acting on said second sleeve for moving said first and second sleeve toward said flange which is arranged for acting as shoulder for said first and second sleeve;

wherein the first end of the helical spring is fixed to the first sleeve and the second end is fixed to the second drum and said first sleeve is slidingly associated with said driven shaft, in such a manner that there is no rotation of the spring and of the sleeves when there is no rotation between the two shafts.

The coupling member also comprises a return spring arranged between said second drum and said first sleeve, arranged for generating a force having the same direction as the axis of said driving and driven shafts, with a direction which opposes the movement of said first and second sleeve toward said flange, in such a manner as to prevent any accidental actuation of the coupling, if it is of the normally open type.

Notwithstanding the numerous advantages of the invention described in the aforesaid patent application, for some applications there remain some drawbacks or aspects that have not been dealt with and solved.

The main limit is that the coupling member can transmit the whole driving torque only in one direction, i.e. only from the driving shaft to the driven shaft, in practice according to the direction of winding of the driving helical spring. Usually, this limit is not serious if the member is used on agricultural work machinery such as rotary tiller or powered cultivators with irreversible worm final drive. In fact, the "engine brake" effect is hardly ever produced in these machines, i.e. the phenomenon according to which the driving torque acting on the coupling is not transferred from the engine to the transmission, but from this latter to the motor. If, vice versa, the coupling is used on wheeled transport vehicles or on powered cultivators without irreversible worm final drive, on slopes and with heavy loads it may be these latter that have to transmit torque to the main motor, but as the coupling member of the aforesaid patent application is unable to operate in two directions, there can be no transmission of torque opposite to the motor and the operator is necessarily obliged also to use the brakes of the vehicle to decelerate.

The invention intends to overcome these limits, by producing a coupling member particularly suitable for use on moving work machines and vehicles in general; which makes reverse transfer of torque, i.e. from the driven shaft to the driving shaft, possible; which makes use of machines safe for operators; which does not cause undesirable actuation of the driven shaft, which does not produce friction; which is reliable, of simple construction and does not require particular maintenance operations.

These aims are achieved with a bidirectional coupling member with helical spring and friction trigger motion transmission mechanism, comprising primary means for transmitting motion from a driving shaft to a driven shaft, wherein said primary means comprise:

- a first drum associated with a driving shaft; - a second drum associated with a driven shaft;

wherein said first and second drum have the same outer diameter and said driving and driven shafts are coaxial in the direction of a main axis;

- a main transmission helical spring, arranged around said first and second drum, having a first and a second end,

wherein said main helical spring is wound in such direction as to be able to w ind around said shafts when it has to transmit a torque directed from the driving shaft to the driven shaft;

- a first sleeve arranged around said spring;

- a second sleeve rotatingly associated with the first sleeve;

- a flange associated with said first drum;

wherein the first end of the main helical spring is fixed to the first sleeve and the second end is fixed to the second drum and said first sleeve is slidingly associated with said driven shaft, characterized in that said member comprises secondary motion transmission means for transmitting motion from the driven shaft to the driving shaft, arranged between said driving and driven shafts, arranged for automatically actuating when a torque is generated, directed from the driven shaft to the driving shaft.

According to a first aspect of the invention, said secondary means for transmitting motion from the driven shaft to the driving shaft comprise a secondary helical spring, arranged astride a third drum associated with said driving shaft and a fourth drum associated with said driven shaft, wherein said third and fourth drum have the same diameter, said spring has an inner diameter slightly smaller than that of said third and fourth drum and is wound in a direction opposite to that of the main helical transmission spring.

Preferably, the diameter of said third and fourth drum is smaller than that of said first and second drum.

According to a further aspect of the invention, said secondary means for transmitting motion from the driven shaft to the driving shaft comprise a unidirectional ratchet gear.

According to a preferred embodiment, said unidirectional ratchet gear comprises a freewheel bearing.

According to an even more preferred embodiment of the invention, the secondary helical spring comprises a first end fixed to the third drum and a second end fixed to a third sleeve rotatingly associated with the fourth drum and said first sleeve comprises a ring pad coaxial to said fourth drum, wherein the movement of said first sleeve determined by the control lever that acts on said second sleeve causes a same movement of said ring pad that as a consequence rests on said third sleeve.

According to a further aspect of the invention, said third sleeve comprises a pad of a material with a high friction coefficient arranged for cooperating with said ring pad.

According to another aspect, the connection means between said first sleeve and said ring pad comprise a plurality of adjusting screw pins arranged for allowing adjustment of the distance between said ring pad and said third sleeve.

The invention has numerous advantages:

- as the main helical transmission spring is able to transmit only torques directed from the driving shaft to the driven shaft, due to the secondary means for transmitting torques directed from the driven shaft to the driving shaft, the coupling can operate in two directions, allowing the machine to which it is fitted to make use of the "engine brake" to absorb these torques opposite to the main driving torques; due to the fact that the secondary transmission means are activated automatically when a torque is generated, directed from the driven shaft to the driving shaft, the user does not have to perform any action to control them;

due to the fact that said secondary transmission means are exclusively of mechanical type, no auxiliary electric control systems are required;

due to the fact that, in a preferred embodiment of the invention, said secondary transmission means can be selectively deactivated by the operator by acting on the control lever, the transmission of torque from the driven shaft to the driving shaft can be interrupted or temporarily suspended, for example to prevent the engine from cutting out or to allow change of the gear;

due to the two distinct mechanisms that transmit the driving torque and the braking torque, it is possible to calibrate, in relation to the constructional characteristics, the two torques, making them different from one another, with considerable benefits from all aspects, for example to develop a braking torque greater than the driving torque, etc.;

due to the independence of the two transmission mechanisms of the driving and of the braking torque, it would also be possible to delegate transmission of the main motion from the driving shaft to the driven shaft, to the secondary spring and vice versa. The advantages of the invention will be more apparent below, in the description of preferred embodiments, provided by way of non-limiting example, and with the aid of accompanying drawings wherein:

Figs. 1 and 2 represent, in section according to a longitudinal plane, a bidirectional coupling member with helical spring and friction trigger motion transmission mechanism according to the invention shown respectively in open and closed conditions of the main transmission, but always in conditions to transmit torque from the driven shaft to the driving shaft;

Fig. 3 represents, in section according to a longitudinal plane, a variant of the invention wherein the driving and driven shafts are connected by a freewheel bearing;

Fig. 4 represents, in partial cross section, an internal detail of the freewheel bearing of Fig. 3;

Fig. 5 represents, in partial section according to a longitudinal plane, a more complex variant of the bidirectional coupling member, shown in conditions with no transmission of motion between the two shafts.

All the figures illustrate a variant of the bidirectional coupling member of the normally closed type.

With particular reference to Figs. 1-2, there is shown a bidirectional coupling member with helical spring and friction trigger motion transmission mechanism, respectively in open and closed conditions of the primary transmission system, comprising a first drum 1 associated with a driving shaft 2 and a second drum 3 associated with a driven shaft 4, wherein said first and said second drum have the same outer diameter and said driving and driven shafts are coaxial, i.e. are arranged along a same axis X. The bidirectional coupling member comprises a primary transmission mechanism of a driving torque C_m between the driving shaft 2 and the driven shaft 4, wherein said primary transmission mechanism comprises a helical spring 5 arranged around the two drums 1 and 3, a first sleeve 6 arranged around said spring 5, slidingly associated with said driven shaft 4, a second sleeve 7 rotatingly associated with the first sleeve 6, a flange 8 associated w ith said first drum 1, a control lever 9 acting on said second sleeve 7 to move said first and second sleeve toward said flange 8, in opposition with a resisting elastic force generated by a return spring 18. The helical spring 5 is produced with wire with substantially square section and comprises a first end 10 fixed to said first sleeve 6 and a second end 11 fixed to said second drum 3.

The main spring 5 is wound in a manner concordant with the direction of rotation of the driving shaft and can therefore be closed winding around the drums 1 and 3 when the torque C_m must pass from the driving shaft 2 to the driven shaft 4. Vice versa, the spring 5 is released, expanding its diameter and moving away from the drums 1 and 3, when a braking torque

C_b must pass from the driven shaft 4 to the driving shaft 2.

The first sleeve 6 is rotatingly associated with the first drum 1 as a result of a ball bearing 12 interposed therebetween. Said ball bearing 12 can be omitted in the case in which there is no contact between the first sleeve 6 and the first drum 1.

The second sleeve 7 is rotatingly associated with the first sleeve 6 as a result of a ball bearing 13 interposed therebetween.

The flange 8 comprises a shoulder plane 14, to which there can be applied a pad 15 made of material with a high coefficient of friction, such as rubber, arranged for cooperating through sliding with a corresponding contact plane 16, which faces it, belonging to the first sleeve 6. The planes 14 and 16, with the axis X, form an angle of around 90°, as shown, or of different amplitude.

Alternatively, the pad 15 can be applied to the contact plane 16.

The control lever 9 is rotatingly associated with a fixed pin 17 and is thrust by elastic means 38, in such a manner as to be able to transmit a force on the second sleeve 7 directed along the axis X and with direction such as to cause the sleeves 6 and 7 to move toward the flange 8, so as to make the coupling member normally closed. Actuator means 37, opposite to the force exerted by the spring 38, on which the operator can act at his discretion, allow opening of the coupling itself.

Between the second drum 3 and the first sleeve 6 there is interposed a return spring 18, arranged for generating said resisting elastic force which opposes the movement of said first and second sleeve toward said flange 8.

Between the first drum 1 and the second drum 3 there is interposed a bearing 19, arranged for allowing centring of the components along the main axis X and for allowing mutual rotation without sliding friction between the two members when the transmission is open.

The bidirectional coupling member firther comprises a secondary transmission mechanism of a braking torque C_b between the driven shaft 4 and the driving shaft 2, wherein said secondary transmission mechanism comprises, with reference to Figs. 1 and 2, a secondary helical spring 20, a third drum 21 associated with said driving shaft and a fourth drum 22 associated with said driven shaft 4, wherein said drums 21 and 22 have the same diameter, which is smaller than that of the drums 2 and 3, and are coaxial thereto. The secondary helical spring 20 is arranged astride said drums 21 and 22, has an inner diameter slightly smaller than that of said drums and is therefore always closed thereon, but not clamped. Said spring is wound in the opposite direction to that of the main spring 5.

With reference to Figs. 3 and 4, there is shown an even simpler embodiment of the bidirectional transmission member, wherein the secondary transmission mechanism comprises unidirectional ratchet gear type mechanical means arranged between the driving shaft and the driven shaft.

In the example shown, said unidirectional ratchet gear type mechanical means comprise a freewheel bearing 23, in place of the ball bearing 19 arranged between the first drum 1 of the driving shaft 2 and the second drum 3 of the driven shaft 4, provided with pawls 24 integral with the driven shaft 4 arranged for cooperating, when the torque C_b passes from the driven shaft 4 to the driving shaft 2, with the teeth of a toothed wheel 25 associated with said driving shaft 2.

In particular, the toothed wheel 25 is fixed to an extension 26 of the first drum 1 by means of a key 27 and the pawls 24 are pivoted on a ring 28, in turn fixed inside the second drum 3 by means of a key 29.

With reference to Fig. 5, there is shown a more complex embodiment of the bidirectional transmission member, which allows interruption of the passage of torque between the driven shaft and the driving shaft.

This variant comprises, besides the components already illustrated describing Figs. 1 and 2, a third sleeve 30 rotatingly associated with the fourth drum 22 and a ring pad 31 fixed to the first sleeve 6 and slidingly associated with the fourth drum 22.

The secondary spring 20 comprises a first end 32 steadily associated with the third drum 21 and a second end 33 steadily associated with the third sleeve 30.

The third sleeve 30 comprises a pad 34 made of material with a high coefficient of friction, facing said ring pad 31 and arranged for cooperating therewith to be driven in rotation.

Alternatively, the pad 34 can be associated with the ring pad 31 .

The ring pad 31 is associated with the first sleeve 6 through a plurality of screw pins 35, which slide freely in corresponding holes 36 arranged on the drum 3.

These screw pins 35 also allow adjustment of the distance S between said ring pad 31 and said pad 34, so that it is the same as the distance S between the surfaces that must come into contact with the pad 15 and with the plane 16.

Correct adjustment of the distance S allows simultaneous contact between the pad 15 and the contact plane 16 and between the ring pad 31 and the pad 34 to be achieved with a single movement of the second sleeve 7 through the control lever 9.

In the case of bidirectional coupling member with helical spring and friction trigger motion transmission mechanism, of the normally closed type, such as the one illustrated, besides comprising all the components already described above and with the same functions, there is also provided a mechanism comprising a closing spring 38 acting constantly on the control lever 9, with a force greater than the sum of the force exerted by the return spring 18 and the minimum force required to cause engagement of the coupling member itself, so as to hold the flange 8 and the first sleeve 6 constantly in mutual contact, ensuring constant engagement of the transmission member itself. The operator can act with external means 37, for example of the pedal type, so as to transmit on the lever 9 a tractive force which, opposing the force generated by the closing spring 38, can cause separation between the flange 8 and the first sleeve 6, and consequent disengagement of the transmission member.

Also in this embodiment of the invention the external force to be applied to disengage the transmission member can be very small and in practice independent from the force transmitted between the two shafts.

Operation of the coupling member is as follows.

Reference shall firstly be made to the variants illustrated in Figs. 1 and 2.

In the case of normally open coupling and transmission of torque C_m from the driving shaft 2 to the driven shaft 4, when the engine is started, the drum 1 , connected to the driving shaft 2, starts to rotate together with the flange 8, while the drum 3, the driven shaft 4, the spring 5, the first sleeve 6, the second sleeve 7 and the components connected therewith do not rotate. The helical spring 20, arranged on the drums 21 and 22, slides thereon, but without being wound around them, as a result of the preselected direction of winding of the coils.

When with the control lever 9 a suitable force is exerted on the second sleeve 7, parallel to the direction of the rotation axis X, i.e. such as to overcome the resistance represented by the elastic force developed by the return spring 18, an axial movement of the first sleeve 6 is produced until the contact plane 16 is touching the pad 15 which may be associated with the shoulder plane 14 of the flange 8.

As the flange 8 rotates constantly together with the driving shaft 2, it tends to drive in rotation the first sleeve 6 due to the friction force that is generated between the pad 15 and the thrust plane 16. Rotation of the first sleeve 6 causes rotation of the first end 10 of the helical spring 5, which consequently closes compressing between its coils the two drums of equal outer diameter 1 and 3, the direction of winding of the spring 5 being concordant with the direction of rotation of the driving shaft 2.

This closing makes the driving shaft 2 and the driven shaft 4 integral and obliges them to rotate with the same speed, in a transient time that depends on the load acting on the driven shaft 4 and on the geometrical characteristics and the materials of the spring 5, of the drums 1 and 3, of the pad 15, of the thrust surface 16, etc..

After the transient, the spring 20 will also rotate in unison with the two shafts 2 and 4, no longer sliding on the drums 21 and 22.

The freewheel bearing 23 of the variant shown in Figs. 3 and 4 behaves in the same manner. In the initial transient, the pawls 24 will jump on the teeth of the toothed wheel 25, and then rotate in unison therewith.

When the control lever 9 no longer exerts any thrust force on the second sleeve 7, the thrust surface 16 detaches from the pad 15, also due to the elastic return force generated by the return spring 18, the helical spring 5 tends to expand again and therefore to make rotation of the driving shaft 2 once again independent from the driven shaft 4, which will quickly stop rotating only when there is no longer any braking torque C_b, i.e. when the secondary spring 20 can once again release the drums 21 and 22.

The characteristic of the coupling member lies in the fact that the tangential force T₀ required to close the spring 20 around the two drums 21 and 22, i.e. necessary to cause engagement of the secondary transmission mechanism, is very low and the friction between the spring 20 and the drum 22 is sufficient to generate it.

The force T₀ to be exerted at the first end of the spring 20, which is equal to the engagement force, is expressed by the formula:

where:

T₀ is the engagement force;

T_M is the maximum force acting on the central coil of the spring 20; f is the coefficient of friction between the internal surface of the spring 20 and the external surface of the drum 22 (if both are made of iron, equal to around 0.2);

n is the number of coils counted from the central coil.

Observing the formula it is evident that the more coils there are separating the central coil of the spring 20 from its periphery, the smaller the force required to actuate the secondary transmission mechanism of the coupling will be, as the value of the forces acting on the single coils decreases from the centre toward the periphery with exponential law, and this force T₀ can be greatly below the force T_M that determines the value of the torque C_b to be transmitted.

In the case of normally closed coupling, such as the one illustrated in Figs. 1-5, the member acts as any clutch of a mechanical transmission between rotating shafts, in which the driven shaft always rotates in unison with the driving shaft.

If the two shafts must be disconnected, for example to stop the vehicle, or to change gear, or to cut off the power to the working tools, it is sufficient to exert on the control lever 9, through external actuator means 37, a force adequate to overcome the opposed elastic forces of the elastic means 38, so as^' to cause detachment of the first sleeve 6 from the flange 8 and consequent disengagement of the coupling member.

In the case of open or closed clutch and transmission of a braking torque C_b from the driven shaft 4 to the driving shaft 2, in the initial transient the driven shaft 4 tends to rotate with a greater speed than that of the driving shaft 2. This circumstance causes the occurrence of afriction force ₀ on the end of the secondary pring 20 associated with the drum 22 which determines clamping of the spring itself on the drums 22 and 23 allowing, at the end of the transient, rotation of the shafts 4 and 2 in unison and transfer of the torque C_b therebetween. Due to opposite winding of the spring 20 with respect to the main spring 5, the same transient that allows the spring 20 to close around the drums 21 and 22 allows the spring 5 to open, releasing the members belonging to the primary transmission mechanism.

Likewise, in the embodiment illustrated in Figs. 3 and 4, during the initial transient for transferring the braking torque C_b, the freewheel bearing 23 immediately drives due to the pawls 24 that couple the teeth of the toothed wheel 25, allowing immediate transfer of the torque.

With reference to the embodiment illustrated in Fig. 5, operation is as follows.

When the driving shaft is started, operation is the same as that described for the other embodiments of the invention.

In the case of normally open transmission, not shown, when the operator acts on the control lever 9 to determine closing of the clutch, besides movement of the transmission members connected to the main spring 5, this also causes contact between the ring pad 31 and the pad 34 associated with the third sleeve 30, preparing the secondary spring 20 to act, if a braking torque Cb is to be transferred between the driven shaft 4 and the driving shaft 2.

In particular, as a result of the connections between the ends 32 and 33 of the secondary spring 20 with the third drum 21 and the third sleeve 30, this spring rotates in unison with the same speed as the driving shaft.

To summarize, rotation of the driving shaft 2 also drives in rotation the secondary spring 20, which in turn drives in rotation the third sleeve 30.

When the ring pad 31 , which is initially stopped, comes into contact with the friction pad 34 that rotates like the driving shaft 2, the secondary spring 20 is engaged and remains adhering, but only adhering, to the third drum 21 of the driving shaft 2 and to the fourth drum 22 of the driven shaft 4.

This takes place simultaneously to clamping on the first drum 1 and on the second drum 3 of the main spring 5, which therefore causes transmission of motion and rotation at the same speed of the driving shaft 2 and of the driven shaft 4, but also of the whole assembly associated with the secondary spring 20.

While it is the engine that transmits torque to the driven shaft, the main spring 5 works and the secondary spring 20 does not transmit any torque, but when the direction of the torque is reversed, i.e. passes from the driven shaft to the driving shaft, then the secondary spring clamps on the third and on the fourth drum, causing transmission of a torque C_b from the driven shaft to the driving shaft (engine brake).

If the control lever 9 stops acting on the second sleeve 7, everything is interrupted and the two springs 5 and 20 are once again released from the respective drums, no longer transmitting torque in any direction.

Similar considerations, mutatis mutandis, are valid in the case of normally closed coupling and transmission, just as in the case illustrated in Fig. 5.

As is apparent to those skilled in the art, the invention has been described with reference by way of example to moving work machines and vehicles, but can be used in all those applications in which it is necessary to have an easily actuated normally open or normally closed coupling member, always achieving the advantages described above.

Naturally, the constructional details and the embodiments can be widely varied with respect to those described and illustrated, without however departing from the scope of the present invention, as described, illustrated and claimed.

Claims

1. Bidirectional coupling member with helical spring and friction trigger motion transmission mechanism, comprising primary motion transmission means from a driving shaft to a driven shaft, wherein said primary means comprise:

- a first drum (1) associated with a driving shaft (2);

- a second drum (3) associated with a driven shaft (4);

wherein said first and said second drum (1 , 3) have the same outer diameter and said driving (2) and driven (4) shafts are coaxial in the direction of a main axis (X);

- a main transmission helical spring (5) arranged around said first and second drum (1 , 3), having a first and a second end (10, 1 1 ), wherein said main helical spring (5) is wound in such direction as to be able to wind around said shafts when it has to transmit a torque C_m directed from the driving shaft (2) to the driven shaft (4);

- a first sleeve (6) arranged around said spring (5);

- a second sleeve (7) rotatingly associated with the first sleeve (6);

- a flange (8) associated with said first drum (1 );

- a control lever (9) acting on said second sleeve (7) for moving said first and second sleeve (6, 7) toward said flange (8) which is arranged for acting as shoulder for said first and second sleeve (6, wherein the first end (10) of the main helical spring (5) is fixed to the first sleeve (6) and the second end (1 1) is fixed to the second drum (3) and said first sleeve (6) is slidingly associated with said driven shaft (4), characterized in that said member comprises secondary motion transmission means (20, 23) for transmitting motion from the driven shaft (4) to the driving shaft (2), arranged between said driving (2) and driven (4) shafts, arranged for automatically actuating when a torque Cb is generated, directed from the driven shaft (4) to the driving shaft (2).

2. Coupling member according to claim 1 , characterized in that said secondary means for transmitting the motion from the driven shaft (4) to the driving shaft (2) comprise a secondary helical spring (20), arranged astride a third drum (21) associated with said driving shaft (2) and a fourth drum (22) associated with said driven shaft (4), wherein said third and fourth drum (21 , 22) have the same diameter, said spring (20) has an inner diameter slightly smaller than that of said third and fourth drum and is wound in a direction opposite to that of the main helical transmission spring (5).

3. Coupling member according to claim 2, characterized in that the diameter of said third and fourth drum (21 , 22) is smaller than that of said first and second drum (1 , 3).

4. Coupling member according to claim 1 , characterized in that said secondary means for transmitting motion from the driven shaft (4) to the driving shaft (2) comprise a unidirectional ratchet gear.

5. Coupling member according to claim 4, characterized in that said unidirectional ratchet gear comprises a freewheel bearing (23).

6. Coupling member according to claim 5, characterized in that said freewheel bearing (23) comprises pawls (24) associated with the driven shaft (4) and a toothed wheel (25) associated to the driving shaft (2).

7. Coupling member according to claim 2, characterized in that the secondary helical spring (20) comprises a first end (32) fixed to the third drum (21 ) and a second end (33) fixed to a third sleeve (30) rotatingly associated with the fourth drum (22) and said first sleeve (6) comprises a ring pad (31) coaxial to said fourth drum (22), wherein the movement of said first sleeve (6) determined by the control lever (9) that acts on said second sleeve (7) causes a same movement of said ring pad (31) that as a consequence rests on said third sleeve (30).

8. Coupling member according to claim 7, characterized in that said third sleeve (30) comprises a pad (34) of a material with a high friction coefficient, arranged for cooperating with said ring pad (31).

9. Coupling member according to claim 7, characterized in that the connection between said first sleeve (6) and said ring pad (31 ) comprises a plurality of screw pins (35) acting as adjustment means arranged for allowing the adjustment of the distance between said ring pad (31) and said third sleeve (30).

10. Machine characterized in that it comprises a bidirectional coupling member according to at least one of the previous claims.