Automatic speed variable drive screw

Abstract

Spike driver (100) comprising: a spike driver head (3) including a tip (35) adapted to screw or unscrew a railway track fastener (101) (102), and a drive unit (1) for rotating the tip (35). The spike driver (100) includes a continuously variable transmission (7) configured to automatically adjust the rotational speed of the tip (35) in an operating mode of the spike driver (100), the continuously variable transmission (7) being, in the operating mode, connected to the drive unit (1) and the spike driver head (3). Figure to be published with the abbreviation: Fig. 2

Description

Title of the invention: Automatic speed variation screw driver Technical field of the invention

[0001] The present invention relates to a screw driver, in particular intended for railway construction sites. In particular, the screw driver is a machine designed to selectively screw or unscrew the fasteners which fix the rails to the railway sleepers. State of the prior art

[0002] In the field of railway construction sites, it is known to use a screw driver to screw or unscrew fasteners. The screw driver comprises a motor connected to a screw driving head with a rotating tip for the desired screwing or unscrewing.

[0003] For both screwing and unscrewing, the bit torque is appropriately chosen. For example, for a fastener screwing, this screwing must end with a lasting tightening over time: the bit torque must then be adapted. For example, in the context of loosening, or even tightening, one or more hard points may have to be passed, which also requires sufficient torque. At constant power of the screw driver motor, it is possible to maximize the bit torque, however this would be to the detriment of the rotation speed and therefore the productivity of the screw driver on site.

[0004] To improve the productivity of the screw driver, it is known to use a gearbox with manual gear change in the case of a screw driver with mechanical transmission or automatic in the case of a screw driver with hydraulic transmission. The gearbox then includes a slow speed to promote the torque of the tip of the screw driver head and a fast speed to promote the screwing or unscrewing speed. The hydraulic screw driver has the following disadvantages: it is expensive due to its construction, compared to the solution of a screw driver with mechanical transmission; it is complex to maintain.

[0005] When screwing the fastener, the fast speed can be used as long as the fastener is not in the tightening phase and the slow speed can be used to tighten the fastener to the correct torque at the end of screwing.

[0006] When unscrewing the fastener, the slow speed can be used to loosen the fastener and the fast speed can then be used following loosening to remove the fastener.

[0007] However, both when screwing and unscrewing the fastener, a hard point may appear, such as when the fastener seizes, so it is advisable to change speed to pass the hard point, which implies that the operating torques operation of the screw driver, for each of the slow and fast speeds, are well adapted. For this purpose, it is known to oversize the motor or to use a flywheel in the case where it is not sought to oversize the motor. The flywheel does not allow to respond to a continuous demand for torque but allows to obtain sufficient torque, linked to its inertia, to pass the hard point only at low speed.

[0008] Oversizing the engine or the presence of a flywheel is to the detriment of the weight of the screw driver, which leads to a reduction in its ergonomics of use on site.

[0009] Therefore, there is a need to improve the management of the torque of the tip of the screw head during the screwing or unscrewing of a fastener. Subject of the invention

[0010] The aim of the present invention is to selectively screw or unscrew the fasteners which make it possible to fix the rails to the railway sleepers, in particular while respecting certain productivity and ergonomic constraints.

[0011] To this end, the invention relates to a screw driver comprising: • a screw driving head comprising a tip capable of screwing or unscrewing a railway track fastener; • a drive unit, to drive the tip in rotation; the screw driver comprises a continuously variable transmission configured to automatically adapt the rotational speed of the bit in an operational mode of the screw driver, the continuously variable transmission being, in the operational mode, linked to the drive unit and the screw driver head.

[0012] Such a screw gun is advantageous in the sense that the automatic adaptability of the rotation speed of the bit makes it easier to pass a hard point, if necessary when screwing or unscrewing the fastener, and makes it possible to increase productivity on site.

[0013] The screw driver may further comprise one or more of the following features.

[0014] According to a characteristic of the screw driver, the screw driver is such that: • the screw driver includes a drive shaft and a driven shaft; • the continuously variable transmission is coupled, on the one hand, to the shaft drive and, on the other hand, to the driven shaft, the driven shaft being coupled to the end piece in the operational mode.

[0015] A continuously variable transmission has the advantage of continuously varying the gear ratio of the drive shaft, in particular of the drive unit, to the driven shaft coupled to the screw driving head (and therefore ultimately to the end piece) resulting in an automatic adaptation of the rotation speed of the bit according to the resistance that the fastener opposes to the bit during the screwing or unscrewing of the fastener, thus facilitating the passage of a hard point.

[0016] According to a characteristic of the screw driver, the continuously variable transmission comprises: • a drive pulley mounted on the drive shaft, the drive pulley comprising a first flange fixed relative to the drive shaft and a second flange movable in translation along the drive shaft; • a driven pulley mounted on the driven shaft, the driven pulley comprising a third flange fixed relative to the driven shaft and a fourth flange movable in translation along the driven shaft; • a first return member constantly urging the second flange in a direction opposite to the first flange; • a second return member constantly urging the fourth flange towards the third flange; • a belt connecting the drive pulley and the driven pulley.

[0017] The use of a continuously variable transmission according to this arrangement has the following advantages, particularly in comparison with a hydraulic transmission: limitation of the manufacturing cost of the screw driver, simplicity of maintenance of the screw driver, cleanliness of the screw driver, as well as the lightness of the screw driver. In addition, thanks to this architectural arrangement, the size of the screw driver is reduced, which facilitates its use by an operator.

[0018] According to a characteristic of the screw driver, the continuously variable transmission is configured to allow a variation in the value of its transmission ratio as a function of a variation in the engine speed of the drive unit and / or a resistive torque of the driven shaft.

[0019] This makes it possible to overcome a hard point linked to the resistive torque caused by the cooperation of the tip of the screw head with the fastener and propagating from the tip to the driven shaft. The continuously variable transmission adapts, while seeking to tend towards the conservation of the engine speed of the drive unit, to overcome this resistive torque. This remains true up to a critical point where the engine power is exceeded and the continuously variable transmission is no longer sufficient; of course, this is a case to be avoided because it does not represent normal operation. The continuously variable transmission thus aims to maintain the drive unit at its optimal operating speed in order to obtain the best performance from the drive unit and increased durability.

[0020] According to a characteristic of the screw driver, the fourth flange is mounted relative to the driven shaft according to a helical connection.

[0021] This helical connection makes it possible to pass a hard point linked to the resistant torque caused by the cooperation of the screw head tip with the fastener and propagating from the tip to the driven shaft without causing a drop in engine speed, thus allowing the drive unit to be maintained at its optimum operating speed in order to obtain the best performance from the drive unit and increased durability.

[0022] According to a characteristic of the screw driver, the continuously variable transmission comprises at least one guide ramp, fixed relative to the driven shaft, in contact with which is placed a contact member belonging to the fourth flange so as to define, with the translational mobility of the fourth flange along the driven shaft, the helical connection.

[0023] The use of the contact member and the guide ramp makes it possible to adjust the value of the transmission ratio of the continuously variable transmission by increasing or decreasing it in order to tend to eliminate the resistive torque and overcome the associated hard point when screwing or unscrewing the fastener without necessarily requiring a variation in the engine speed in the event of a torque peak which could lead to the drive unit stalling.

[0024] According to a characteristic of the screw driver, the screw driver comprises a reverser for the direction of rotation of the tip.

[0025] The inverter allows you to adapt the operation of the screw gun whether you want to screw or unscrew a fastener.

[0026] According to a characteristic of the screw driver, the screw driver comprises a transmission device comprising: • an input shaft formed by the driven shaft or coupled to the driven shaft, and • an output shaft, the output shaft being connected to the end piece to drive it rotating in operational mode, the transmission device comprising the inverter configured to selectively present: • a first operating mode in which the driven shaft is coupled to the output shaft to drive the tip in a first direction of rotation; • a second mode of operation in which the driven shaft is coupled to the output shaft to drive the bit in a second direction of rotation opposite to the first direction of rotation.

[0027] The transmission device here makes it possible to choose the direction of rotation of the tip of the screw-driving head downstream of the continuously variable transmission according to the direction of propagation of the rotational movement between the drive group and the tip. This specific positioning makes it possible to avoid jolts linked to the reversal of the direction of rotation and thus to make the operation of the screw-driving machine more fluid.

[0028] According to a characteristic of the screw driver, the screw driver comprises a box a single speed forming a reducer placed downstream of the continuously variable transmission and upstream of the screw driving head, or placed in the screw driving head.

[0029] This configuration with a single-speed gearbox makes it possible to simplify the design, reduce the cost and simplify the use, in particular improving the comfort of use, of the screw driver.

[0030] According to a characteristic of the screw driver, the screw driver comprises a gearbox comprising a first transmission ratio and a second transmission ratio, the gearbox being separate from the continuously variable transmission, the screw driver is configured to selectively engage the first ratio or the second ratio so as to influence the rotation speed of the bit.

[0031] This configuration with a gearbox comprising two transmission ratios allows the use of a lower power engine. This has advantages in terms of engine costs and energy consumption and makes it possible to lighten the screw driver (thus improving its ergonomics).

[0032] According to a characteristic of the screw driver, the transmission device comprises the first and second transmission ratios and each of the first and second operating modes of the transmission device comprises: • a first state in which the first gear is engaged between the driven shaft and the output shaft; • a second state in which the second gear is engaged between the driven shaft and the output shaft.

[0033] By combining the continuously variable transmission with a two-speed gearbox, this makes it possible to increase the diversity of choice of engines that can be used in the drive unit. It will then be possible to reduce the power of the drive unit in order to lighten the jackhammer.

[0034] According to a characteristic of the screw driver, the continuously variable transmission is configured to, in the operational mode: • adapting the rotation speed of the tip between a first rotation speed and a second rotation speed in the first operating state, for example the first rotation speed is equal to 70 rpm and the second rotation speed is equal to 250 rpm; • adapting the rotation speed of the tip between a third rotation speed and a fourth rotation speed in the second operating state, for example the third rotation speed is equal to 35 rpm and the fourth rotation speed is equal to 125 rpm;

[0035] This makes it possible to pass one or more hard points without having to change gear between the first gear and the second gear. The operator can select the first gear during screwing to implement the tightening phase or during the unscrewing to implement the loosening phase, then for the rest of the screwing or unscrewing the second gear will be sufficient and will adapt to optimize work productivity automatically.

[0036] According to a feature of the screw driver, the continuously variable transmission is directly coupled to a first shaft and a second shaft such that, in the operational mode, rotation of the first shaft drives, via the continuously variable transmission, the second shaft, the first shaft and the second shaft being offset.

[0037] This architecture has advantages with respect to the size of the screw driver and the proximity of the drive unit to the operator who can more easily interact with the drive unit if necessary.

[0038] Other advantages and characteristics may emerge from the detailed description which follows. Brief description of the drawings

[0039] The invention will be better understood upon reading the detailed description which follows, given solely by way of non-limiting example and made with reference to the appended drawings listed below.

[0040] [Fig-1] [Fig.l] schematically represents a perspective view of a tire mold maker according to a particular embodiment.

[0041] [Fig.2] [Fig.2] schematically represents the screw driver of [Fig.l] equipped of a trolley and arranged on a railway track and in particular in an operational mode of the puller.

[0042] [Fig.3] [Fig.3] represents a side view of the screw driver of [Fig.l].

[0043] [Fig.4] [Fig.4] represents a sectional view of the screw tap practiced parallel aligned with the plane of [Fig.3] so that the cutting plane passes through a driven shaft of the screw driver.

[0044] [Fig.5] [Fig.5] represents a partial view of the screw driver of [Fig.3] where the ti reforging machine includes a continuously variable transmission, said view showing in exploded form the mounting of the continuously variable transmission within the reforging machine with a belt of the continuously variable transmission removed in order to more clearly show components of the continuously variable transmission.

[0045] [Fig.6] [Fig.6] schematically represents in a side view, in a manner isolated and according to a particular embodiment a driven pulley of the continuously variable transmission mounted on the driven shaft.

[0046] [Fig.7] [Fig.7] schematically represents, according to one embodiment, a view in perspective of a movable flange of the driven pulley.

[0047] [Fig.8] [Fig.8] schematically represents, according to one embodiment, a view in perspective of a part of the continuously variable transmission, the part comprising guide ramps for the movable flange of the driven pulley.

[0048] [Fig.9] [Fig.9] represents a block diagram schematically describing an architecture in C.

[0049] [Fig. 10] [Fig. 10] represents a block diagram schematically describing a Z-shaped architecture.

[0050] [Fig. 11] [Fig. 11] represents a block diagram schematically describing an L-shaped architecture.

[0051] In these figures, the same references are used to designate the same elements. The elements represented in the different figures are not necessarily drawn to scale in order to facilitate understanding of the figures. Detailed description

[0052] In the present description, two elements are "coupled" or "linked", for example mechanically, when they are associated with each other by a connection, for example mechanical, causing the behavior of one of the two elements to affect that of the other element. This connection may be direct when the two elements considered are in contact, or indirect when the two elements considered are linked via one or more intermediate elements such as drive shafts or the like.

[0053] A screw driver 100 according to the invention, a particular embodiment of which is illustrated in FIGS. 1 to 5, comprises a screw driving head 3 comprising a tip 35, a drive group 1 for driving the tip 35 of the screw driving head 3 in rotation and a continuously variable transmission 7. The tip 35 of the screw driving head 3 is capable of screwing or unscrewing a fastener 101 of a railway track 102 in particular depending on the direction of rotation of the tip 35.

[0054] The fastener 101 may be any type of mounting element used for fixing a rail 103 of the railway track 102, such as for example a lag screw or a threaded fastener, to a sleeper 104 of the railway track 102.

[0055] The end piece 35 may be a tightening key, for example hexagonal, having a shape adapted to cooperate with a head of the fastener 101, the fastener 101 then being able to comprise a threaded body screwed into the crosspiece 104.

[0056] The drive group 1 has the role in particular of generating mechanical energy which it transmits to the outside by means of an output shaft of the drive group 1, preferably rotary. The screw driver 100 can then be configured to exploit, in an operational mode (also called operational configuration) described in more detail below, the mechanical energy from the output shaft of the drive group 1 in order to ensure the appropriate rotation of the end piece 35 of the screw driver head 3 to ensure the desired screwing or unscrewing of the fastener 101.

[0057] The continuously variable transmission 7, also known as CVT which stands for "Continuously Variable Transmission" in English, is configured to automatically adapt the rotation speed of the tip 35 in the operational mode of the screw driver 100. The continuously variable transmission 7 is, in the operational mode, linked (i.e. coupled, for example mechanically) with the drive group 1 and the screw driving head 3 (and therefore in particular the tip 35).

[0058] Thus, the screw driver 100 is configured so as to present / understand the operational mode, preferably in which the tip 35 of the screw driving head 3 is rotated by the drive group 1 and in which the continuously variable transmission 7, linked to the drive group 1 and the screw driving head 3, automatically adapts the rotation speed of the tip 35 of the screw driving head 3. In other words, in the operational mode and according to the exemplary embodiment of [Fig.l], a movement, in particular rotation, can be propagated from the drive group 1 to the tip 35 of the screw driving head 3, passing at least through the continuously variable transmission 7 which automatically adapts the rotation speed of the tip 35.

[0059] The automatic adaptation of the rotation speed of the bit 35 makes it easier to pass a hard point when screwing or unscrewing the fastener 101 and to increase productivity on a construction site. Productivity in this context is linked to an increase in the rotation speed of the bit 35 while having torques punctually adapted to the different screwing and unscrewing operations, in order to make the operation of screwing or unscrewing a corresponding fastener 101 faster.

[0060] In particular, a transmission system is defined directly coupled, on the one hand, to the drive group 1, and, on the other hand, to the screw driving head 3 or at least to a part of the screw driving head 3 in order to ensure the rotation of the end piece 35 in the operational mode of the screw driving machine 100. This transmission system makes it possible to define a propagation path of a movement, in particular rotation, from the drive group 1 to the screw driving head 3. This transmission system comprises at least the continuously variable transmission 7, preferably in direct coupling with the drive group 1. The transmission system can be seen as the whole of the component(s), for example mechanical, (therefore including the continuously variable transmission 7) by which the movement from the drive group 1 is propagated.A corresponding component can have an influence on the way in which the movement propagates, for example by slowing it down or speeding it up, by changing the direction of rotation (depending on whether the fastener 101 is to be screwed or unscrewed).

[0061] The drive group 1 may comprise a motor 18 whose motor shaft forms the output shaft of the drive group 1 or may comprise the motor 18 and a reduction mechanism (not shown) coupled, for example mechanically, to the motor shaft of the motor 18 in order to present the output shaft of the drive group 1 with a predefined reduction in rotation in the operational mode of the screw driver 100.

[0062] The motor 18 may be an electric, thermal, hydraulic or hydrogen engine.

[0063] The screw driver 100 is generally used in the following manner: the screw driver 100 is arranged on the railway track 102 to move along the latter in order to position it in a suitable manner to proceed with the screwing or unscrewing of a corresponding fastener 101. For this purpose, the screw driver 100 may comprise a rolling carriage 105 configured to roll on the railway track 102 and configured to allow a tilting of a part of the screw driver 100 comprising at least the screw driver head 3 in order to position it to allow cooperation of the end piece 35 with a corresponding fastener 101 to be screwed or unscrewed and / or to release it from the fastener 101 once this fastener 101 has been screwed. The rolling carriage 105 may comprise parts 105a, 105b each provided with wheels and positioned to roll on rails 103 of the railway track 102.The parts 105a, 105b of the carriage can be connected to each other by a crosspiece 105c of the carriage 105 on which said part of the screw driver 100 is mounted to tilt and rotate orthogonally to the tilting axis to allow fasteners 101 to be screwed or unscrewed on either side of the same rail 103.

[0064] In particular, and in order to facilitate its handling, the screw driver 100 may comprise a control station 34 comprising two guide arms each equipped with a handle 20, 21 allowing the handling of the screw driver 100 by an operator and in particular allowing the tilting mentioned above to be guided.

[0065] In particular, in the operational mode of the screw driver 100, the latter is preferably positioned so that the end piece 35 is oriented towards the ground S ([Fig.2]), in particular so as to allow its cooperation with a corresponding fastener 101.

[0066] According to one embodiment, the screw driver 100 comprises a drive shaft 2 and a driven shaft 5. In particular, the drive shaft 2 and the driven shaft 5 are rotary shafts, i.e. mounted to rotate along their extension axes within the screw driver 100. The continuously variable transmission 7, as illustrated in more detail and by way of example in FIGS. 1 to 5, is coupled, for example mechanically, on the one hand, to the drive shaft 2 (in particular by direct coupling) and, on the other hand, to the driven shaft 5 (in particular by direct coupling) in particular to ensure, in the operational mode, the automatic adaptation of the rotation speed of the end piece 35. The rotation of the drive shaft 2 can then cause, via the continuously variable transmission 7, the rotation of the driven shaft 5. Of course, in the operational mode, the driven shaft 5 is coupled, for example mechanically, to the screw-driving head 3 and more particularly to the end piece 35. This thus results in an automatic adaptation of the rotation speed of the screw-driving head 3 as a function of the resistance that the fastener 101 opposes to the end piece 35 of the screw-driving head 3 during the screwing or unscrewing of the fastener 101, which facilitates the passage of a possible hard point. In other words, in the operational mode of the screw-driving machine 100, the continuously variable transmission 7 ensures the automatic adaptation of the rotation speed of the end piece 35 of the screw-driving head 3 by continuously varying the gear ratio / transmission of the drive shaft 2 to the driven shaft 5.

[0067] The drive shaft 2 may be the output shaft of the drive group 1, and, if appropriate, may be the motor shaft. The drive shaft 2 may alternatively be coupled to the output shaft of the drive group 1 either in its extension or in an offset manner by any means suitable within the scope of the person skilled in the art.

[0068] The driven shaft 5 makes it possible to propagate the movement from the drive group 1 downstream of the continuously variable transmission 7. It is therefore part of the transmission system mentioned above.

[0069] Preferably, the continuously variable transmission 7 is arranged at the output of the drive group 1 (i.e. the continuously variable transmission 7 is directly coupled to the drive shaft 2 which preferably forms the output shaft of the drive group 1 or which extends the output shaft of the drive group 1) to have a maximum centrifugal force (and therefore a maximum speed), which makes it possible to maximize the operation of the continuously variable transmission 7.

[0070] A particular embodiment of the continuously variable transmission 7 is now described, as illustrated in Figures 1 to 5. According to this embodiment, the continuously variable transmission 7 comprises a driving pulley 8, a driven pulley 11, a first return member 14a (shown diagrammatically in [Fig. 5]), a second return member 14b ([Fig. 5]) and a belt 15 connecting the driving pulley 8 and the driven pulley 11. The driving pulley 8 is mounted on the drive shaft 2 and comprises a first flange 9 fixed relative to the drive shaft 2 and a second flange 10 movable in translation along the drive shaft 2, for example according to a sliding connection. The first return member 14a constantly urges the second flange 10 in a direction opposite to the first flange 9, thus tending to move the second flange 10 away from the first flange 9.The driven pulley 11 is mounted on the driven shaft 5 and comprises a third flange 12 fixed relative to the driven shaft 5 and a fourth flange 13 movable in translation along the driven shaft 5. The second return member 14b constantly urges the fourth flange 13 in the direction of the third flange 12, thus tending to bring the fourth flange 13 closer to the third flange 12.

[0071] Such a continuously variable transmission 7 according to this arrangement has the following advantages, in particular in comparison with a variable transmission continuous hydraulic which is a possible variant: the limitation of the manufacturing cost of the screw driver 100, the simplicity of maintenance of the screw driver 100, the cleanliness of the screw driver 100, as well as the lightness of the screw driver 100. In addition, thanks to the architectural arrangement with pulleys described above, the size of the screw driver 100 is reduced which facilitates its use by an operator.

[0072] The first return member 14a and the second return member 14b may be a compression spring or any type of return member controlled via an actuator.

[0073] In [Fig.5], the function of the first return member 14a is shown diagrammatically, the first return member 14a being able to be in reality housed in a dome 41 of the drive pulley 8.

[0074] The belt 15 may be made of a flexible material such as, for example, rubber or synthetic polymers. The role of the belt 15 is to transmit the movement of the driving pulley 8 to the driven pulley 11 by connecting them together when the drive shaft 2 rotates along its axis.

[0075] In a manner known per se for a continuously variable transmission, the continuously variable transmission 7 comprising the driven pulley 11 and the driving pulley 8 (figures 4 and 5) is in particular such that: • the driving pulley 8 comprises a groove 22 delimited by two flanks 23, 24 converging towards each other in the direction of the axis of the drive shaft 2, these two flanks 23, 24 being respectively delimited by the first flange 9 and the second flange 10; • the driving pulley 8 comprises a variable primitive diameter, orthogonal to the axis of the drive shaft 2, depending on the width of the belt 15, according to the position of the second flange 10 relative to the first flange 9; • the driven pulley 11 comprises a groove 25 delimited by two flanks 26, 27 converging towards each other in the direction of the axis of the driven shaft 5 and respectively delimited by the third flange 12 and the fourth flange 13; • the driven pulley 11 comprises a variable primitive diameter, orthogonal to the axis of the driven shaft 5, depending on the width of the belt 15, according to the position of the third flange 12 relative to the fourth flange 13.

[0076] The primitive diameter is understood as the diameter of the corresponding pulley (i.e. the driving pulley 8 or the driven pulley 11) at the bottom of the groove as a function of the width of the belt 15.

[0077] In particular, the first flange 9 is closer to the motor 18 of the drive group 1 than is the second flange 10, and the fourth flange 13 is closer to the motor 18 of the drive group 1 than is the third flange 12.

[0078] The continuously variable transmission 7 is advantageously configured to allow, in particular in the operational mode, a variation of the value of its transmission ratio as a function of a variation in the engine speed of the drive group 1 and / or a resistive torque of the driven shaft 5. Indeed, in the operational mode of the screw driver 100, both during the screwing and unscrewing of the fastener 101, a hard point, linked to the resistive torque caused by the cooperation of the end piece 35 of the screw driver head 3 with the fastener 101 and propagating from the end piece 35 to the driven shaft 5, may appear. To overcome this resistive torque (and therefore pass the hard point), it is conventional to increase the engine torque of the drive group 1. However, a large increase in torque can lead to a drop in the engine speed of the drive group 1, hence the need to maintain the power of the drive group 1 (proportional to the engine torque and the rotational speed of the drive shaft 2) at a substantially constant value: this is what the continuously variable transmission 7 allows.

[0079] The use of the continuously variable transmission 7 to reduce the rotation speed (when passing a hard point) by varying the value of its transmission ratio from the drive shaft 2 to the driven shaft 5 advantageously makes it possible to maintain the engine speed of the drive group 1. Thus, the engine 18 of the drive group 1 can be maintained at its optimal operating speed in order to obtain the best efficiency of the drive group 1 and increased durability (in particular compared to the service life of the engine 18 of the drive group 1). In other words, the continuously variable transmission 7 adapts, while seeking to tend towards the maintenance of the engine speed of the drive group 1, to overcome this resistive torque.This remains true up to a critical point where the power of drive group 1 is exceeded and the continuously variable transmission 7 is no longer sufficient; of course, this is a case to be avoided because it does not represent normal operation.

[0080] Furthermore, maintaining the engine speed makes it possible to tend to ensure constant consumption of the drive group 1, thus avoiding overconsumption of the latter, for example in fuel.

[0081] According to one embodiment, the fourth flange 13 of the driven pulley 11 is mounted relative to, and in particular on, the driven shaft 5 according to a helical connection. In other words, the fourth flange 13 and the driven shaft 5 have a combined rotational and translational movement forming a helical connection between them. This helical connection facilitates the passage of a hard point while tending to avoid a drop in the engine speed of the drive group 1 in the operational mode.

[0082] It results from what has been described above a need to implement the helical connection in a suitable manner. To this end, as can be seen in Figures 3 to 6, the continuously variable transmission 7 comprises at least one guide ramp 17, fixed relative to the driven shaft 5, in contact with which is placed a member 16 contact plate belonging to the fourth flange 13 so as to define, with the translational mobility of the fourth flange 13 along the driven shaft 5, the helical connection. The guide ramp 17, because it is fixed relative to the driven shaft 5, participates in particular in the rotational drive of the driven shaft 5.

[0083] Depending on the guide ramp 17, the permitted rotation of the fourth flange 13 around the driven shaft 5 is limited in amplitude, as is the translational amplitude of the fourth flange 13 along the driven shaft 5. These amplitudes are adapted for the application and will depend in particular on the characteristics of the continuously variable transmission 7.

[0084] The use of the contact member 16 and the guide ramp 17 makes it possible to adjust the value of the transmission ratio of the continuously variable transmission 7 by increasing or decreasing it in order to tend to eliminate the resistive torque and to pass the associated hard point during the screwing or unscrewing of the fastener 101 without necessarily requiring a variation in the engine speed of the drive group 1 in the event of a torque peak which could lead, if necessary, to the stalling of the drive group 1.

[0085] According to an exemplary embodiment as can be deduced from Figures 6, 7 and 8, the continuously variable transmission 7 comprises three guide ramps 17 each intended to cooperate by contact with a corresponding contact member 16 of the fourth flange 13 (i.e. the fourth flange comprises three contact members 16). The number of guide ramps 17 and contact members 16 can be adapted to make the design more robust (the more the number of guide ramps 17 and contact members 16 increases, the more the contact forces between the guide ramps 17 and the contact members 16 are reduced).

[0086] The or each guide ramp 17 may be formed in a part 28, also called a “cam” in the field ([Fig.8]), for example molded or machined. The part 28 is fixed to the driven shaft 5.

[0087] The or each contact member 16 may adopt the form of a finger formed on the side of a first face of the fourth flange 13 opposite a second face of the fourth flange 13 participating in delimiting the groove 25 of the driven pulley 11.

[0088] The second return member 14b may be a compression spring crossed by the driven shaft 5 and bearing, on the one hand, against the fourth flange 13 and, on the other hand, against the part 28 mentioned above.

[0089] Of course, the value of the transmission ratio of the continuously variable transmission 7 is variable depending on the input rotation speed, i.e. that of the drive shaft 2 on which the drive pulley 8 is mounted.

[0090] A preferred operating diagram of the continuously variable transmission 7 is now described on the side of the driving pulley 8 and on the side of the driven pulley 11.

[0091] According to this preferred operating diagram, seen from the side of the driving pulley 8, the driving pulley 8 is designed such that the first flange 9 on the side of the drive group 1 is fixed on the drive shaft 2 and the second flange 10 is movable in translation along the axis of rotation of the drive shaft 2, in particular according to a sliding connection. There are then three operating modes at the level of the driving pulley 8: • a first operating mode in which the continuously variable transmission 7 is at rest (i.e. it is not rotating because the drive group 1 is stopped): a spring (i.e. the first return member 14a) of the drive pulley 8 pushes on the first and second flanges 9, 10 to separate them, the belt 15 is free and there is no transmission; • a second operating mode in which the speed of the drive shaft 2 is strictly lower than the engagement speed of the continuously variable transmission 7; the rotation of the drive pulley 8 causes a centrifugal force which acts on the flyweights / cams of the drive pulley 8 (for example housed in the dome 41); the flyweights / cams press on the second flange 10 and push against the spring of the drive pulley 8; the speed being still too low, the pressing force of the flyweights / cams is not sufficient to overcome the spring of the drive pulley 8, the first and second flanges 9, 10 therefore remain separate and there is no drive of the pulley 11 driven via the belt 15; • a third operating mode in which the speed of the drive shaft 2 is strictly greater than the engagement speed of the continuously variable transmission 7, the pressing force of the cams / weights is sufficient to overcome the spring of the drive pulley 8 and the second flange 10 is therefore pushed towards the first flange 9; the belt 15 is then driven and the transmission begins (i.e.the driven pulley 11 starts rotating, thus driving the driven shaft 5); the more the rotation speed of the drive shaft 2 increases, the closer the second flange 10 gets to the first flange 9, which, thanks to the inclination of the sides 23, 24 of the groove 22 of the drive pulley 8, has the consequence of varying the primitive diameter of the drive pulley 8 and therefore the value of the transmission ratio of the continuously variable transmission 7; the more the speed of the drive shaft 2 increases, the more the primitive diameter of the drive pulley 8 increases and the more the value of the transmission ratio of the continuously variable transmission 7 decreases, which causes an acceleration of the driven shaft 5. The second mode of operation is not mandatory, but it allows the continuously variable transmission 7 to fulfill the role of a centrifugal clutch. Some continuously variable transmissions have this second mode, others do not and the drive is done directly without going through this acceleration phase where the speed of the drive shaft 2 must exceed the engagement speed of the continuously variable transmission 7.

[0092] According to this preferred operating diagram, seen from the side of the driven pulley 11, the driven pulley 11 comprises two flanks 26, 27 (delimited by the third and fourth flanges 12, 13. This time, it is the fourth flange 13, on the drive group 1 side, which is movable, in particular according to a helical connection, relative to the driven shaft 5 while the third flange 12 is fixed relative to the driven shaft 5; this inversion of the movement with respect to the first and second flanges 9, 10 makes it possible to keep the belt 15 on the same plane and constantly pressed between the third and fourth flanges 12, 13 of the driven pulley 11.The movement of the fourth flange 13 is opposite to the movement of the second flange 10, that is to say that when the first and second flanges 9, 10 move towards each other, the third and fourth flanges 12, 13 move away, and vice versa; if the movable flanges were on the same side, the belt 15 would no longer be correctly pressed when the second flange 10 of the driving pulley 8 moved away and there would no longer be any transmission. For this driven pulley 11, the third and fourth flanges 12, 13 are constantly urged towards each other under the action of a spring of the driven pulley 11 (i.e. the second return member 14b). The movement of the fourth flange 12 takes place when, under the effect of the cams / weights of the driving pulley 8, the belt 15 is stretched and pulls on the fourth flange 13 of the driven pulley 11, which results in a force on the inclined flanks 26, 27 of the driven pulley 11 and comes to fight against the spring of the driven pulley 11.There are then four operating modes at the level of the driven pulley 11: . • a first operating mode in which the continuously variable transmission 7 is at rest, as the weights of the drive pulley 8 have not overcome the force of the spring of the drive pulley 8, the belt 15 is not tensioned: the third and fourth flanges 12, 13 remain proximal, for example pressed against each other; • a second operating mode in which the speed of the drive shaft 2 is strictly lower than the engagement speed of the continuously variable transmission 7: as the weights of the drive pulley 8 have not overcome the force of the spring of the drive pulley 8, the third and fourth flanges 12, 13 remain proximal, for example pressed against each other; • a third operating mode in which the speed of shaft 2 drive is strictly greater than the engagement speed of the continuously variable transmission 7: the weights / cams of the drive pulley 8 have overcome the force of the spring of the drive pulley 8; the second flange 10 comes to rest on the belt 15 which climbs on its inclined side; the belt 15 is stretched and pulls on the sides 26, 27 of the driven pulley 11 and overcomes the force of the spring of the driven pulley 11 which sets the fourth flange 13 in motion and reduces the primitive diameter of the driven pulley 11; the more the speed of the drive shaft 2 increases, the more the primitive diameter of the driven pulley 11 decreases; therefore, the more the speed of the drive shaft 2 increases, the more the value of the transmission ratio of the continuously variable transmission 7 decreases; a fourth operating mode in which the driven pulley 11 sees / undergoes a resistive torque, the driven pulley 11 has a system allowing it to adapt to the resistive torques, for this purpose, the movement of the fourth flange 13 is indexed on the guide ramp 17 (helical ramp participating in forming the helical connection) which aims to push the fourth flange 13 towards the third flange 12 (and therefore to increase the value of the transmission ratio of the continuously variable transmission 7); the principle is that the guide ramp 17 is fixed relative to the driven shaft 5 while the fourth flange 13 is free to rotate according to a predetermined amplitude; its rotation is stopped by a pad (the contact member 16) which slides on the guide ramp 17;if the resistive torque is sufficiently low, under the effect of the tension of the belt 15 which pushes the fourth flange 13, the latter will screw along the guide ramp 17 and the primitive diameter of the driven pulley 11 will reduce and the value of the transmission ratio of the continuously variable transmission 7 decreases; if now the resistive torque increases, the guide ramp 17 will experience a brake on its rotation, while there the fourth flange 13 continues to rotate, there is therefore a relative movement which will allow the fourth flange 13 to slide along the guide ramp 17;by following the guide ramp 17, the fourth flange 13 will tend to move closer to the third flange 12 for example until it presses against the third flange 12, which will increase the original diameter of the driven pulley 11, and therefore increase the value of the transmission ratio of the continuously variable transmission 7, this increase in the value of the transmission ratio of the continuously variable transmission 7 will continue until the resistive torque on the transmission disappears, or if it does not disappear, until the drive group 1 stalls or the; belt 15 slips (case where the resistive torque is greater than the transmission torque).

[0093] The preferred operating scheme described above is not limiting in the sense that its description applies to a particular embodiment of the screw driver 100. Some continuously variable transmissions may be smaller and more compact and / or may be simpler in their operation and / or do not have the guide ramp 17 which allows a variation in the value of the transmission ratio of the continuously variable transmission 7 according to the resistive torque. These simplified systems are simply controlled by the variation in the engine speed (the engine 18 will slow down in the event of a torque peak). Moreover, some continuously variable transmissions do not allow the belt 15 to be free when the engine speed is low; these systems must be coupled with a centrifugal clutch.

[0094] A particular embodiment of a continuously variable belt transmission has been described above, and in particular controlled internally via first and second spring-type return members and flyweights / cams. Alternatively, the continuously variable transmission 7 may be chosen from: • a continuously variable belt transmission 7 with external control (using a pneumatic, electric or hydraulic actuator, for example, to replace the first and second spring-type return members and the weights / cams); • a 7-speed hydraulic continuously variable transmission, for example with a viscous coupling or a torque converter; • a mechanical continuously variable transmission 7, for example toroidal, conical, or by epicyclic gear train.

[0095] According to one embodiment, the screw driver 100 comprises a reversing switch 29 for the direction of rotation of the end piece 35 ([Fig.4]). This makes it possible to adapt the operation of the screw driver 100 to screw or unscrew the fastener 101 by choosing the direction of rotation of the end piece 35. The direction reversing switch 29 is in particular a component, for example a mechanical one, of the transmission system and is located after the continuously variable transmission 7 on the path of propagation of the movement between the drive group 1 and the end piece 35.

[0096] As illustrated in figures 1 to 5 and 9, the screw driver 100 may comprise a transmission device 4 comprising: • an input shaft formed by the driven shaft 5 or coupled to the driven shaft 5 for example in its extension, and • an output shaft 6 then forming in particular a component, for example mechanical, of the transmission system mentioned above. The output shaft 6 is connected, for example mechanically, with the end piece 35 for drive it in rotation in the operational mode. In addition, the transmission device 4 comprises the reverser 29 for the direction of rotation of the tip 35 configured to selectively present: • a first operating mode in which the driven shaft 5 is coupled, for example mechanically, to the output shaft 6 to drive the end piece 35 in a first direction F1 of rotation; • a second operating mode in which the driven shaft 5 is coupled, for example mechanically, to the output shaft 6 to drive the end piece 35 in a second direction F2 of rotation opposite to the first direction F1 of rotation.

[0097] According to one embodiment, the reverser 29 for the direction of rotation of the end piece 35 can be controlled from a selector, for example located at / formed by one of the control handles 20, 21 of the screw driver 100. The handles 20, 21 being each arranged at the end of a corresponding arm of the control station 34, one of the arms can be movable and thus forms the selector so that the position of said arm can induce the appropriate control of the direction reverser 29.

[0098] The transmission device 4 makes it possible in particular to choose the direction of rotation of the end piece 35 of the screw-driving head 3 downstream of the continuously variable transmission 7 according to the direction of propagation of the rotational movement between the drive group 1 and the screw-driving head 3. This specific positioning makes it possible to avoid jolts linked to the reversal of the direction of rotation and thus to make the operation of the screw-driving machine 100 more fluid.

[0099] According to one embodiment, the screw driver 100 may comprise a single-speed gearbox 40 forming a reducer placed downstream of the continuously variable transmission 7 and upstream of the screw driving head 3, in particular on the path of propagation of the movement ([Fig.4]), or placed in the screw driving head 3. This gearbox 40 may be integrated into the transmission device 4 between the input shaft and the output shaft 6 so that in the first and second operating modes the coupling between the input shaft and the output shaft 6 is effected at least via the direction inverter 29 and the gearbox 40. If the drive group 1 is powerful enough, the single-speed gearbox 40 may be sufficient.

[0100] In the case where the screw driver 100 comprises the single-speed gearbox 40, the continuously variable transmission 7 is preferably configured to adapt the rotation speed of the end piece 35 between a first rotation speed and a second rotation speed, for example the first rotation speed is equal to 70 rpm and the second rotation speed is equal to 250 rpm.

[0101] According to one embodiment, the screw driver 100 comprises a gearbox 30 comprising a first transmission ratio and a second transmission ratio, the gearbox 30 being separate from the variable transmission 7. continues. The screw driver 100 is then configured to selectively engage, either manually using a lever (not shown) extending from the gearbox 30 or automatically on command of an actuator (not shown) for example arranged on one of the handles 20, 21, the first gear or the second gear so as to influence the rotation speed of the end piece 35. Advantageously, by combining the continuously variable transmission 7 with a gearbox 30 with two transmission ratios, this makes it possible to increase the diversity of choice of usable motors. It will then be possible to reduce the power of the motor 18 of the drive group 1 in order to lighten the screw driver 100.

[0102] According to one embodiment, the transmission device 4 comprises the first and second transmission ratios. Each of the first and second operating modes of the transmission device 4 comprises a first state, in which the first ratio is engaged between the driven shaft 5 and the output shaft 6, and a second state, in which the second ratio is engaged between the driven shaft 5 and the output shaft 6. In other words, the gearbox 30 can be integrated into the transmission device 4 and is coupled, in the first operating mode and in the second operating mode, to the input shaft and to the output shaft 6.

[0103] It is also possible that the gearbox 30 is integrated into the reforging head.

[0104] The use of the first and second transmission ratios makes it possible to mount a lower power motor within the screw driver 100, which reduces the costs of the motorization and the energy consumption (gasoline, electricity or other) and makes the screw driver lighter.

[0105] According to one embodiment and in the operational mode of the screw driver 100, the continuously variable transmission 7 is configured to adapt the rotation speed of the bit 35 between a first rotation speed and a second rotation speed in the first operating state, for example the first rotation speed is equal to 70 rpm and the second speed is equal to 250 rpm; in the second operating state, the continuously variable transmission 7 is configured to adapt the rotation speed of the bit 35 between a third rotation speed and a fourth rotation speed, for example the third rotation speed is equal to 35 rpm and the fourth rotation speed is equal to 125 rpm. This embodiment makes it possible to pass one or more hard points without having to change gear between the first gear and the second gear.The operator can select the first gear during screwing to implement the tightening phase or during unscrewing to implement the loosening phase, then for the rest of the screwing or unscrewing the second gear will be sufficient and will adapt to optimize work productivity automatically.

[0106] By "between two speeds" associated with speed values, it is understood that the range defined between these two values ​​is understood to include the limits.

[0107] According to one embodiment, the continuously variable transmission 7 is coupled, for example mechanically, and directly to a first shaft and a second shaft so that the rotation of the first shaft drives, via the continuously variable transmission 7, the second shaft, the first shaft and the second shaft being offset. By "offset" it is understood here that the first and second shafts are not aligned with each other or coincident / coaxial. The first shaft may be, in the exemplary embodiment described in FIGS. 3 to 5, the drive shaft 2 and the second shaft may be the driven shaft 5. Thus, the drive group 1, the continuously variable transmission 7 and the transmission device 4 may be arranged in different ways which increases the range of possibilities in terms of structure of the screw driver 100. For example, in [Fig.3], the screw driver 100 is such that the drive group 1, the continuously variable transmission 7, and the driven shaft 5 in particular associated with the transmission device 4 form a C (schematically represented in [Fig.9]), in particular open in the direction of the control station 34 (not represented in [Fig.9]); this makes it possible, for example, to bring the drive group 1 closer to the operator who can more easily interact with the drive group 1, for example: . • with a launcher 31 (notably visible in figures 1, 2, 3 and 5) of the drive group 1 allowing the engine 18 of the drive group 1 to be launched; • with a tank 32 (notably visible in figures 1 to 5) of the drive group 1 to fill it with fuel if the engine 18 is a thermal engine supplied with fuel by the tank 32.

[0108] According to other embodiments, the drive group 1, the continuously variable transmission 7 and the driven shaft 5 can be mounted according to Z or L architectures. The locations of the drive group 1 and the continuously variable transmission 7 vary according to the architecture considered.

[0109] For example, for the C-shaped architecture already mentioned above, the drive group 1 can be directly above the driven shaft 5 in the operational mode and the continuously variable transmission 7 connects the driven shaft 5 to the drive group 1. This architecture makes it possible to limit the length of the screw driver 100, the size of the screw driver 100 is thus limited.

[0110] For example, for the Z-shaped architecture, as shown in [Fig. 10], the location of the drive group 1 is such that the latter forms a first end of the screw driver 100 opposite a second end of the screw driver 100 formed by the screw driver head 3. We then find, depending on the length of the screw driver 100, the drive group 1, the continuously variable transmission 7, the driven shaft 5 and the 3-point screw driving head. This architecture allows for good latitude in adjusting the center of gravity of the 100 screw driving machine.

[0111] For example, for the L-shaped architecture, as shown in [Fig. 11], the locations of the drive group 1, the continuously variable transmission 7 and the driven shaft 5 may be such that they overlap in a direction given by the height in the operational mode. This makes it possible, for example, to use a drive group 1 whose output shaft would be oriented downwards in a configuration for using the drive group 1.

[0112] According to other embodiments and according to the solution envisaged, the arrangement of elements of the screw driver 100, participating in the propagation of the rotational movement from the drive shaft 2 and up to the end piece 35, can vary in terms of the order of positioning of these elements as long as they perform their function. For example, the transmission device 4 and the continuously variable transmission 7 can have different orders of arrangement than that described above along the path of propagation of the movement.

[0113] When the motor 18 is an electric or hydraulic motor, the latter can directly reverse its direction of rotation. Therefore, the inverter 29 mentioned above is no longer necessary and is therefore not present within the screw driver 100 downstream of the motor 18 along the path of propagation of the movement. In this case, the continuously variable transmission 7 will be adapted to operate regardless of the direction of rotation of the drive shaft 2.

[0114] The screw driving head 3 may comprise an angle gear 33, notably visible in [Fig.4], making it possible to propagate the desired rotational movement to the end piece 35 then oriented towards the ground S in [Fig.2]. In fact, the screw driving head 3 may comprise an input shaft 36 coupled to the output shaft 6 of the transmission device 4, the angle gear 33 which may provide a reduction and be arranged in a casing 38, and an output shaft 37, connected to the angle gear 33 in the casing 38, at the end of which the end piece 35 is arranged. In this case, and as illustrated in [Fig.4], the transmission device 4 is at a distance from the casing 38.

[0115] According to an embodiment not shown, the transmission device 4 can be located in the casing 38 or fixed to the casing 38 (the transmission device 4 is thus integrated into the screw-driving head 3).

[0116] The embodiments described above may, where appropriate, be combined.

[0117] The present invention finds an industrial application in the field of railways, in particular by allowing an operator to accelerate the screwing or unscrewing of fastener(s) 101.

Claims

1.

2.

3. Claims Screw driver (100) including: • a screw driving head (3) comprising a tip (35) capable of screwing or unscrewing a rail track (102) fastener (101); • a drive group (1) for driving the tip (35) in rotation; characterized in that the screw driver (100) comprises a continuously variable transmission (7) configured to automatically adapt the rotation speed of the bit (35) in an operational mode of the screw driver (100), the continuously variable transmission (7) being, in the operational mode, linked to the drive group (1) and the screw driving head (3). Screw driver (100) according to claim 1, characterized in that: • the screw driver (100) comprises a drive shaft (2) and a driven shaft (5); • the continuously variable transmission (7) is coupled, on the one hand, to the drive shaft (2) and, on the other hand, to the driven shaft (5), the driven shaft (5) being coupled to the end piece (35) in the operational mode. Screw driver (100) according to claim 2, characterized in that the continuously variable transmission (7) comprises: • a drive pulley (8) mounted on the drive shaft (2), the drive pulley (8) comprising a first flange (9) fixed relative to the drive shaft (2) and a second flange (10) movable in translation along the drive shaft (2); • a driven pulley (11) mounted on the driven shaft (5), the driven pulley (11) comprising a third flange (12) fixed relative to the driven shaft (5) and a fourth flange (13) movable in translation along the driven shaft (5); • a first return member (14a) constantly urging the second flange (10) in a direction opposite to the first flange (9); • a second return organ (14b) constantly requesting the fourth flange (13) towards the third flange (12); • a belt (15) connecting the drive pulley (8) and the driven pulley (11).

4. A screw driver (100) according to any one of claims 2 to 3, characterized in that the continuously variable transmission (7) is configured to allow a variation in the value of its transmission ratio as a function of a variation in the engine speed of the drive group (1) and / or of a resistive torque of the driven shaft (5).

5. A screw driver (100) according to claim 3 or according to claim 3 and 4, characterized in that the fourth flange (13) is mounted relative to the shaft (5) driven according to a helical connection.

6. A screw driver (100) according to claim 5, characterized in that the continuously variable transmission (7) comprises at least one guide ramp (17), fixed relative to the driven shaft (5), in contact with which is placed a contact member (16) belonging to the fourth flange (13) so as to define, with the translational mobility of the fourth flange (13) along the driven shaft (5), the helical connection.

7. A screw driver (100) according to any one of claims 1 to 6, characterized in that it comprises a reverser (29) for the direction of rotation of the end piece (35).

8. A screw driver (100) according to claims 2 and 7, characterized in that the screw driver (100) comprises a transmission device (4) comprising: • an input shaft formed by the driven shaft (5) or coupled to the driven shaft (5), and • an output shaft (6), the output shaft (6) being connected to the end piece (35) to drive it in rotation in the operational mode, the transmission device (4) comprising the inverter (29) configured to selectively present: • a first operating mode in which the driven shaft (5) is coupled to the output shaft (6) to drive the end piece (35) in a first direction (F1) of rotation; • a second operating mode in which the shaft (5) driven is coupled to the output shaft (6) to drive the tip (35) in a second direction (F2) of rotation opposite to the first direction (F1) of rotation.

9. A screw driver (100) according to any one of claims 1 to 8, characterized in that the screw driver (100) comprises a single-speed gearbox (40) forming a reducer placed downstream of the continuously variable transmission (7) and upstream of the screw driver head (3), or placed in the screw driver head (3).

10. A screw driver (100) according to any one of claims 1 to 8, characterized in that the screw driver (100) comprises a gearbox (30) comprising a first transmission ratio and a second transmission ratio, the gearbox (30) being separate from the continuously variable transmission (7), and in that the screw driver (100) is configured to selectively engage the first ratio or the second ratio so as to influence the rotation speed of the tip (35).

11. A screw driver (100) according to claim 10 and claim 8, characterized in that the transmission device (4) comprises the first and second transmission ratios and in that each of the first and second operating modes of the transmission device (4) comprises: • a first state in which the first ratio is engaged between the driven shaft (5) and the output shaft (6); • a second state in which the second ratio is engaged between the driven shaft (5) and the output shaft (6).

12. A screw driver (100) according to any one of claims 1 to 11, characterized in that the continuously variable transmission (7) is directly coupled to a first shaft and a second shaft such that, in the operational mode, rotation of the first shaft drives, via the continuously variable transmission (7), the second shaft, the first shaft and the second shaft being offset.

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