Two-speed screwdriver with gear change via acceleration control

Description

1. Domaine de l'invention

[0001] The field of the invention is that of the design and manufacture of portable tools intended to be used to carry out screwing / unscrewing operations.

[0002] More specifically, the invention relates to a screwing / unscrewing device offering several screwing / unscrewing speeds. This device is more particularly intended for continuous tightening screwdrivers whose torque exceeds 150 Nm (high torque screwdrivers). 2. Art antérieur

[0003] Screwdriving devices are commonly used in various industrial sectors to carry out screwdriving and / or unscrewing operations on assemblies.

[0004] A screwing operation generally comprises two successive phases, namely: a pre-tightening phase during which the element to be tightened is driven at a rapid speed until a certain pre-tightening torque level is reached, then a slower tightening phase until a target tightening torque and / or target tightening angle are reached.

[0005] Electric motor-driven screwdriving devices are typically associated with control means and include a tightening torque and / or tightening angle sensor.

[0006] These control means make it possible to program screwing strategies, i.e. the parameters of the pre-screwing and tightening phases, in particular the rotation speeds of the motor in the pre-screwing and tightening phases, as well as the target torque and / or angle value at the end of tightening. Thus, during the performance of a screwing operation, the control means control the motor to drive the element to be tightened at the pre-screwing speed during the pre-screwing phase and then at the tightening speed during the tightening phase until the target torque and / or angle are reached.

[0007] Continuous tightening screwdrivers, i.e. screwdrivers that apply an uninterrupted and increasing torque to the screw during tightening, incorporate a transmission between the motor and the output device driving the screw. This transmission generally consists of one or more epicyclic gear sets. These epicyclic gear sets provide sufficient tightening torque on the output shaft. This torque is the result of multiplying the engine torque by the transmission reduction ratio and its efficiency.

[0008] To be able to achieve high tightening torques, for example greater than 150 Nm, screwdriver manufacturers are therefore required to have a high reduction ratio by having several epicyclic gear trains in the transmission. This has the disadvantage that the rotation frequency of the screwdriver output shaft becomes relatively low, resulting in a long screwing time, which penalizes productivity.

[0009] Thus, manufacturers of high-torque screwdrivers have come up with a device integrated into the transmission to short-circuit one of the epicyclic gear trains during pre-screwing. The reduction ratio implemented during pre-screwing therefore becomes lower than in the torque increase during tightening, with the benefit of a high rotation frequency during pre-screwing and a high torque during the torque increase during tightening. This epicyclic gear train, which can be short-circuited or disengaged, is called an additional gear train.

[0010] The pre-screwing and tightening speeds applied during the pre-screwing and tightening phases therefore require the implementation of an additional engageable-disengageable gear train which makes it possible to define different reduction ratios between the rotor and the output member depending on whether it is activated or not. Thus, the additional gear train is not activated during the pre-tightening phase so that the pre-screwing speed is fast. Conversely, the additional train is activated during the tightening phase so that the tightening speed is slower and the tightening torque achievable by the screwing device is higher.

[0011] The additional gear train is automatically mechanically engaged at the end of the pre-tightening phase. For this purpose, in state-of-the-art solutions, the transmission incorporates an elastic element which allows, when the tightening torque reaches, during the pre-tightening phase, a predetermined torque threshold for gear change, to automatically activate the additional gear train.

[0012] This type of mechanism is advantageous in that it allows for simple and efficient automatic screw speed changes. However, this type of technology can still be improved.

[0013] Indeed, the predetermined tightening torque threshold for gear change from which the additional gear is automatically activated cannot be configured since it depends on the sizing of the elastic element integrated into the transmission. Consequently, this type of technology does not allow for the provision of versatile screwdrivers adaptable to different screwdriving operations requiring a gear change after reaching a pre-tightening threshold of different values.

[0014] A screwing device according to the preamble of claim 1 is known from document EP2679346A1. 3. Objectifs de l'invention

[0015] The invention aims in particular to provide an effective solution to at least some of these different problems.

[0016] In particular, according to at least one embodiment, an objective of the invention is to provide a two-speed screwing / unscrewing device which is versatile in terms of speed change.

[0017] In particular, the invention aims, according to at least one embodiment, to provide such a two-speed screwing / unscrewing device which makes it possible to switch from one speed to the other independently of the tightening torque value reached.

[0018] Another objective of the invention is, according to at least one embodiment, to provide a two-speed mechanism which is simple in design and versatile.

[0019] In particular, one objective of the invention is to provide, in at least one embodiment, a two-speed mechanism that can be easily integrated into various screwing / unscrewing devices. 4. Présentation de l'invention

[0020] For this, the invention proposes a screwing device comprising: a casing; a motor provided with a rotor; an output member capable of rotating a drive element of an element to be screwed; a transmission connecting said rotor to said output member, said transmission comprising at least one additional gear train capable of being engaged / disengaged; means for controlling said motor; said device comprising means for engaging said additional gear train, said engaging means being able to take at least: an engaged state in which said additional gear train is engaged, and a disengaged state in which said additional gear train is not engaged, the reduction ratio of said transmission between said rotor and said output member being different depending on whether or not said additional gear train is engaged, said reduction ratio being higher when said additional gear train is engaged.

[0021] According to the invention, said control means of said motor are configured to generate a predetermined acceleration or deceleration of said rotor, said predetermined acceleration or deceleration acting on said engagement means to make them pass from one of their states to the other.

[0022] Thus, according to this aspect, the invention is based on an original approach according to which the engagement from one speed to another is done, independently of the value of the tightening torque reached, as a function of the acceleration-deceleration of the motor.

[0023] The invention thus offers great versatility in the choice of the instant at which the speed change takes place since it is sufficient to play on the value of the acceleration / deceleration of the motor, this being possible by simply acting on the control of the motor. The speed change is therefore, according to the invention, completely independent of the tightening torque delivered by the device.

[0024] According to a possible characteristic, said engagement means comprise a selection member movable in rotation relative to said rotor between at least two engagement / disengagement positions of said additional gear train, said predetermined acceleration or deceleration acting on said selection member to make it pass from one to the other of its positions.

[0025] According to a possible characteristic, a device according to the invention comprises means for rotationally connecting said selection member with said rotor, said rotational connection means ensuring, when said selection member occupies one of its positions, a rotational connection of said selection member with said rotor as long as said motor delivers an acceleration-deceleration lower than a predetermined speed change acceleration-deceleration threshold, the delivery by said motor of an acceleration / deceleration greater than said predetermined speed change acceleration-deceleration threshold inducing the rotation of said selection member from one to the other of its positions.

[0026] According to a possible characteristic, said rotational connection means comprise at least one locking element integral in rotation with said rotor and capable of being housed alternately in two housings of complementary shape provided in said selection member, said locking element being movable along an axis orthogonal to the axis of said rotor, against the effect of elastic return means, between at least: a rotationally connected position in which said locking element is housed in one or other of said housings so that said rotor and said selection member are rotationally connected, and a release position in which said locking element is not housed in either of said housings so that said rotor and said selection member are not rotationally connected.

[0027] According to a possible characteristic: said rotational connection means are capable of transmitting a predetermined limit torque CI beyond which said rotor and said selection member are no longer linked in rotation and can no longer transmit torque, said selection member has an inertia Jos along its axis of rotation; the value of said acceleration-deceleration of speed change being equal to the quotient of said limit torque CI by said inertia Jos.

[0028] According to a possible characteristic, said epicyclic gear train comprises a sun gear integral in rotation with said rotor, a planet carrier integral in rotation with said output member, and an internal toothed ring gear meshing with planet gears carried by said planet carrier, said ring gear being: movable in rotation relative to said casing in said state of disengagement of said additional gear train, and locked in rotation relative to said casing in said state of engagement of said additional gear train.

[0029] According to a possible characteristic, a device according to the invention comprises a first pair of one-way clutches comprising said casing and said inner ring.

[0030] According to a possible characteristic, a device according to the invention comprises a second pair of one-way clutches comprising said rotor and a rotational drive ring, said second pair of one-way clutches engaging said rotor with said rotating drive ring when said engagement means occupy said disengagement state of said additional gear train and said rotor rotates in the screwing direction, said first pair of one-way clutches leaving said inner ring gear free to rotate, said second pair of one-way clutches not engaging said rotor with said driving ring when said engagement means occupy said engagement state of said additional gear train and said rotor rotates in the screwing direction, said first pair of one-way clutches locking said inner ring gear in rotation.

[0031] According to a possible characteristic: said second pair of one-way clutches does not engage said rotor with said drive ring when said engagement means occupy said disengagement state of said additional gear train and said rotor rotates in the unscrewing direction, said first pair of one-way clutches locking said inner ring gear in rotation, said second one-way clutch does not engage said rotor with said drive ring when said said engagement means occupy said engagement state of said additional gear train and said rotor rotates in the unscrewing direction, said first pair of one-way clutches leaving said inner ring gear free to rotate.

[0032] According to a possible characteristic, a device according to the invention comprises at least one rotation locking member, integral in rotation with said rotor, and movable between: a rotational locking position, taken when said engagement means occupy said disengagement state of said additional gear train, in which it cooperates with a locking housing provided in said drive ring such that said ring and said rotor are linked in rotation, and a rotational unlocking position, taken when said engagement means occupy said selection state of said additional gear train, in which it does not cooperate with said locking housing provided in said drive ring such that said ring and said rotor are not linked in rotation.

[0033] According to a possible characteristic: when said rotation locking member occupies said rotation locking position and said rotor rotates in the screwing direction, said first one-way clutch leaves said inner ring gear free to rotate, when said rotation locking member occupies said rotation unlocking position and said rotor rotates in the screwing direction, said first one-way clutch blocks said inner ring gear in rotation. According to a possible characteristic: when said rotation locking member occupies said rotation locking position and said rotor rotates in the unscrewing direction, said first one-way clutch leaves said inner ring gear free to rotate, when said rotation locking member occupies said rotation unlocking position and said rotor rotates in the unscrewing direction, said first one-way clutch blocks said inner ring gear in rotation. 5. Description des figures

[0034] Other characteristics and advantages of the invention will appear on reading the following description of particular embodiments, given as a simple illustrative and non-limiting example, and the appended drawings among which: [ Fig 1 ] there figure 1 illustrates a longitudinal sectional view of a device according to the invention according to a first embodiment; [ Fig 2 ] there figure 2 illustrates a section along the BB axis of the figure 1 when the selection means are in a first position of selection-deselection of the additional gear train; [ Fig 3 ] there figure 3 illustrates a section along the CC axis of the figure 1 when the selection means are in a first position of selection-deselection of the additional gear train; [ Fig 4 ] there figure 4 illustrates a section along the DD axis of the figure 1 when the selection means are in a first position of selection-deselection of the additional gear train; [ Fig 5 ] there figure 5 illustrates a section along the EE axis of the figure 1 when the selection means are in a first position of selection-deselection of the additional gear train; [ Fig 6 ] there figure 6 illustrates a section along the BB axis of the figure 1 when the selection means are in a second selection-deselection position of the additional gear train; [ Fig 7 ] there figure 7 illustrates a section along the CC axis of the figure 1 when the selection means are in a second selection-deselection position of the additional gear train; [ Fig 8 ] there figure 8 illustrates a section along the DD axis of the figure 1 when the selection means are in a second selection-deselection position of the additional gear train; [ Fig 9 ] there figure 9 illustrates a section along the EE axis of the figure 1 when the selection means are in a second selection-deselection position of the additional gear train; [ Fig 10 ] there figure 10 illustrates a perspective view of a selection member of a device according to the invention according to a first embodiment; [ Fig 11 ] there figure 11 illustrates a perspective view of a drive shaft of a device according to the invention according to a first embodiment; [ Fig 12 ] there figure 12 illustrates a perspective view of a rotation drive ring of a device according to the invention according to a first embodiment; [ Fig 13 ] there figure 13 illustrates a perspective view of a crown of a device according to the invention according to a first embodiment; [ Fig 14 ] there figure 14 illustrates a perspective view of pebbles; [ Fig 15 ] there figure 15 illustrates a longitudinal sectional view of a device according to the invention according to a second embodiment when the selection means are in their position for deselection of the additional gear train; [ Fig 16 ] there figure 16 illustrates a section along the BB axis of the figure 15 ; [ Fig 17 ] there figure 17 illustrates a section along the CC axis of the figure 15 ; [ Fig 18 ] there figure 18 illustrates a section along the DD axis of the figure 15 ; [ Fig 19 ] there figure 19 illustrates a section along the EE axis of the figure 15 ; [ Fig 20 ] there figure 20 illustrates a section along the FF axis of the figure 15 ; [ Fig 21 ] there figure 15 illustrates a longitudinal sectional view of a device according to the invention according to a second embodiment when the selection means are in their position for selecting the additional gear train; [ Fig 22 ] there figure 22 illustrates a section along the BB axis of the figure 21 ; [ Fig 23 ] there figure 23 illustrates a section along the CC axis of the figure 21 ; [ Fig 24 ] there figure 24 illustrates a section along the DD axis of the figure 21 ; [ Fig 25 ] there figure 25 illustrates a section along the EE axis of the figure 21 ; [ Fig 26 ] there figure 26 illustrates a section along the FF axis of the figure 21 ; [ Fig 27 ] there figure 27 illustrates a perspective view of a locking member according to the second embodiment; [ Fig 28 ] there figure 10 illustrates a perspective view of a crown of a device according to the invention according to a first embodiment; [ Fig 29 ] there figure 29 illustrates a perspective view of a drive shaft of a device according to the invention according to a first embodiment; [ Fig 30 ] there figure 30 illustrates a perspective view of a rotating selection member of a device according to the invention according to a first embodiment; [ Fig 31 ] there figure 31 illustrates a perspective view of a drive ring of a device according to the invention according to a second embodiment; [ Fig 32 ] there figure 32 illustrates a method of controlling a device according to the invention. 6. Description de modes de réalisation particuliers 6.1. Premier mode de réalisation 6.1.1. Architecture

[0035] We present, in relation to the figures 1 à 14 , an example of a first embodiment of a screwing / unscrewing device according to the invention.

[0036] As shown, such a screwing / unscrewing device conventionally comprises a casing 10. This is a pistol-grip type casing in which the axis of the handle 11 forms an angle with the axis of the output member 12. Alternatively, it could be a casing in which the axis of the handle coincides with the axis of the output member.

[0037] The casing 10 houses an electric motor 13 comprising a stator 130 and a rotor 131 provided with a motor shaft 132.

[0038] The device comprises an output member 12 placed at the end of the casing 10. This output member 12 is capable of rotating a drive element of an element to be screwed, in particular a screw socket or other.

[0039] The device comprises a transmission T connecting the shaft 132 of the rotor 131 to the output member 12 so as to drive the latter in rotation.

[0040] The transmission T comprises a two-speed mechanism 14 which comprises two transmission chains having different transmission ratios. For this purpose, the transmission T comprises an additional gear train capable of being engaged / disengaged. As will be described in more detail later, this additional train here comprises an epicyclic train which can be deactivated by making its inner ring gear free to rotate or activated by locking its ring gear in rotation.

[0041] The two-speed mechanism 14 comprises means for engaging the additional gear train, these means being able to take at least: an engagement state in which the additional gear train is engaged, and a disengagement state in which the additional gear train is disengaged.

[0042] The reduction ratio of the transmission between the rotor and the output member is different depending on whether the additional gear train is engaged or not, the reduction ratio being higher when the additional gear train is engaged. In this way, for a given rotation frequency of the rotor, the rotation frequency of the output member is higher when the additional gear train is not activated and slower when it is activated so that the tightening torque capable of being delivered by the device is higher when the additional gear train is activated.

[0043] The engagement means comprise a selection member 15 movable between at least a first and a second selection / deselection positions of the additional gear train.

[0044] In this embodiment, the direction of rotation of the rotor has an impact on the engagement of the additional gear train. Indeed: when the rotor rotates in the screwing direction and the selection member is in a first of its positions, the additional gear train is deactivated: the device allows pre-tightening at high speed; when the rotor rotates in the unscrewing direction and the selection member is in a first of its positions, the additional gear train is activated: the device allows unscrewing at slow speed; when the rotor rotates in the screwing direction and the selection member is in a second of its positions, the additional gear train is activated: the device allows tightening at slow speed and higher torque; when the rotor rotates in the unscrewing direction and the selection member is in a second of its positions, the additional gear train is deactivated: the device allows unscrewing at high speed.

[0045] This two-speed mechanism comprises a drive shaft 16 linked in rotation with the shaft 132 of the rotor 131. These two components could, in a variant, constitute a single part.

[0046] The selection member 15 is crossed by an internal longitudinal bore 150 housing the drive shaft 16. The selection member 15 is mounted to be able to rotate around the drive shaft 16 between two extreme positions corresponding to its two selection positions.

[0047] In each of these two extreme positions, the selection member 15 is connected in rotation to the drive shaft 16 by rotational connection means. For this, the drive shaft 16 is crossed by a transverse bore 160 arranged along an axis perpendicular to its longitudinal axis. This bore 160 houses an elastic return means which comprises in this embodiment a compression spring 17. At each end of the compression spring 17 is placed a locking element. These locking elements are in this embodiment produced by bocage balls 18.

[0048] The selection member 15 comprises, at the periphery of the internal bore 150 housing the drive shaft 16, two pairs of diametrically opposed locking housings 151. The housings 151 of each pair are connected by a groove 152.

[0049] The locking balls 18 are movable along an axis orthogonal to the axis of the drive shaft 16, against the effect of the elastic return means 17, between at least: a rotational connection position in which the balls 18 are housed in two of the diametrically opposed locking housings 151 so that the drive shaft 16 and the selection member 15 are rotationally connected (cf. figures 2 And 6 ), and a release position in which the balls 18 are not housed in any of the locking housings 151, but are located in the grooves 152, so that the drive shaft 16 and the selection member 15 are not linked in rotation.

[0050] When the selection member 15 is in its first position, the locking balls 18 are housed in the first two of the opposite housings 151 (cf. figure 2 ). When the selection member 15 is in its second position, the balls 18 are located in two other of the opposite housings 151 (cf. figure 6 ).

[0051] When the balls are in their rotationally locked position, the rotational connection means are able to transmit a predetermined limit torque CI beyond which the balls pass into their release position in which the drive shaft and the selection member are no longer rotationally connected and can no longer transmit torque. This predetermined torque depends in particular on the stiffness of the spring 17, the size of the balls, the geometry of the locking housings and the grooves. This torque can be conventionally determined by calculation or empirically.

[0052] The device conventionally comprises means for measuring the tightening torque delivered by the device at the output member. These measuring means may, for example, comprise a torque sensor placed in the transmission between the rotor and the output member or a current sensor consumed by the motor.

[0053] The device conventionally comprises motor control means 19. These means make it possible to control the motor by controlling in particular its electrical power supply. They can be totally or partially located inside the casing or outside it.

[0054] The control means 19 of the motor make it possible, by acting on the acceleration / deceleration of the rotor 131 of the motor 13, to switch the engagement means from one of their states to the other, i.e. to switch the selection member 15 from one of its positions to the other relative to the drive shaft 16.

[0055] To enable the engagement means to move from one position to the other, the acceleration / deceleration generated by the motor must be greater than the quotient of the limit torque CI transmissible by the rotating connection means by the inertia Jos of the selection member along its axis of rotation. This acceleration / deceleration is called speed change acceleration / deceleration insofar as it enables the additional gear train to be engaged / disengaged and thus the reduction ratio of the transmission between the rotor and the output member to be modified.

[0056] During the performance of a screwing / unscrewing operation, the motor typically produces accelerations and variations in acceleration, particularly at start-up. It is therefore appropriate that the acceleration / deceleration which induces the switching of the engagement means from one state to the other be sufficiently discriminating, i.e. distant from and more precisely greater than the accelerations that are typically likely to occur, for example at start-up or stop-up, so as not to inadvertently cause the selection means to switch from one state to the other.

[0057] The transmission comprises an epicyclic gear train comprising a sun gear 20 rotationally secured to the drive shaft 16, a planet carrier 21 rotationally secured to the output member 12, and an internal toothed crown 22 meshing with planet gears 23 carried by the planet carrier 21. In variants, the planet carrier may be rotationally linked to the input of another epicyclic gear train or a cascade of epicyclic gear trains, the output of which will be rotationally linked to the output member.

[0058] The two-speed mechanism comprises a ring 24 for driving the crown 22 in rotation.

[0059] This rotation drive ring 24 comprises two male dogs 240 cooperating with two female dogs 220 arranged in the crown 22 so that the crown 22 and the rotation drive ring 24 are linked in rotation along the axis of the rotor 131. However, there is play between the male and female dogs to allow the one-way clutches to be released.

[0060] The rotation drive ring 24 is crossed by a longitudinal internal bore 241 housing on one side the selection member 15 and on the other side the crown 22. The peripheral wall of the drive ring 24 is crossed by two diametrically opposite slots 242 located at the level of the crown 22.

[0061] The selection member 15 is crossed at its periphery by two diametrically opposed lights 153.

[0062] The crown 22 has, at its periphery, two pairs of diametrically opposed blocking ramps 221.

[0063] The device comprises a first pair of one-way clutches and a second pair of one-way clutches. The one-way clutches of each pair are antagonistic, i.e. they operate in opposite directions.

[0064] The first pair of one-way clutches comprises the crown 22, the casing 10, and rollers 25 housed, between the crown 22 and a bore formed in the casing 10, in the slots 242 of the rotation drive ring 24 at the ramps 221 of the crown 22. The rotation drive ring 24 allows, depending on its position, to activate or not the one-way clutches of this pair.

[0065] The drive shaft 16 has, at its periphery, two pairs of diametrically opposed locking ramps 161.

[0066] The second pair of one-way clutches comprises the drive ring 24, the drive shaft 16, and rollers 25 housed, between the drive shaft 16 and the inner bore 241 of the drive ring 24, in the slots 153 of the selection member 15, at the level of the locking ramps 161 of the drive shaft 16. The selection member 15 makes it possible, depending on its position, to activate or not the one-way clutches of this pair.

[0067] The position and inclination of the ramps 161 of the drive shaft 16 as well as the position and inclination of the ramps 221 of the crown 22 are chosen such that: the second pair of one-way clutches engages the drive shaft 16 with the drive ring 24 when the engagement means occupy the disengagement state of the additional gear train and the rotor 131 rotates in the screwing direction, the first pair of one-way clutches leaving the internal toothed crown 22 free to rotate (cf. figures 3 et 4 ), the crown 22 then rotates at the same speed as the drive shaft: rapid pre-screwing; the second pair of one-way clutches does not engage the drive shaft 16 with the drive ring 24 when the engagement means occupy the engagement state of the additional gear train and the rotor 131 rotates in the screwing direction, the first pair of one-way clutches blocking the rotation of said internal toothed crown 22 (cf. figures 7 et 8 ): tightening and higher torque; the second pair of one-way clutches engages the drive shaft 16 with the drive ring 24 when the engagement means occupy the disengagement state of the additional gear train and the rotor 131 rotates in the unscrewing direction, the first pair of one-way clutches locking the internal toothed ring 22 in rotation (cf. figures 3 et 4 ), the first pair of one-way clutches leaving the inner toothed crown 22 free to rotate: rapid unscrewing, the second pair of one-way clutches does not engage the drive shaft 156 with the drive ring 24 when the engagement means occupy the engagement state of the additional gear train and the rotor 131 rotates in the unscrewing direction, (cf. figures 7 et 8 ): slow unscrewing.

[0068] In variants, one or more permanent gear trains, i.e. non-deactivatable, for example epicyclic, may be arranged between the planet carrier 21 and the output member 12.

[0069] When the additional gear train is disengaged, the reduction ratio of the transmission is equal to 1 since the drive shaft 16 and the planet carrier rotate at the same rotation frequency, or to the reduction ratio of the permanent gear train or to their product if several permanent trains are implemented.

[0070] When the additional gear train is engaged, the reduction ratio of the transmission is equal to the reduction ratio of the additional epicyclic gear train, or to its product with the reduction ratio(s) of the permanent gear train(s) if applicable. 6.1.2. Fonctionnement

[0071] A screwdriving operation is described below, comprising a pre-tightening phase at high speed followed by a tightening phase at slower speed.

[0072] Before starting a screwing / unscrewing operation, the operator in charge programs into the controller, for example using a touch screen, a keyboard, a smartphone or other, the value of the predetermined speed change torque threshold CchangementVitesse which, when reached at the output of the screwing device during a pre-screwing phase, causes a speed change and the transition to the tightening phase. The operator can also program the value of the target torque to which he wishes the assembly to be screwed to be tightened at the end of the tightening phase.

[0073] When starting the screwing device in order to carry out such a screwing / unscrewing operation, the control means control the motor in such a way that it generates, in the screwing direction, a speed change acceleration. ẇ whose value is greater than the quotient of the predetermined limit torque CI ( w ˙ > Cl Jos ), beyond which the balls pass into their release position in which the drive shaft and the selection member are no longer linked in rotation, by the inertia Jos of the selection member. In this way, the engagement means of the additional gear train are placed in their disengagement state. The control means then command the motor so as to make it rotate in the screwing direction to carry out the pre-screwing phase.

[0074] In the disengaged state of the additional gear train, the second pair of one-way clutches, taking into account the relative position of the selection member 15 with respect to the drive shaft 16, engages the drive shaft 16 with the rotating drive ring 24 when the rotor of the motor is rotated in the screwdriving direction which in this embodiment is counterclockwise when the screwdriving device is viewed from the output member towards the rear of the screwdriver.

[0075] The rotating drive ring 24 therefore rotates counterclockwise and rotates the crown wheel 22 in this direction, the second pair of one-way clutches not engaging the crown wheel 22 with the casing so that the crown wheel is free to rotate.

[0076] The crown 22 meshes with the satellites 23 as does the sun gear 20 which is rotationally fixed to the drive shaft 16. The crown 22 thus rotates at the same rotation frequency as the sun gear 20. As a result, the satellite carrier 21 rotates at the same frequency as the drive shaft 16. Thus, the output member 12 is rotated in the screwing direction at high speed.

[0077] The control means control the motor in such a way that the output member is rotated at high speed during the pre-screwing phase until the tightening torque delivered by the screwing device reaches the predetermined speed change torque threshold CchangementVitesse.

[0078] When the control means detect by means of the torque sensor that this threshold is reached, the control means brake the motor in order to generate a speed change deceleration whose value is greater than the quotient of the predetermined limit torque CI by the inertia Jos of the selection member. In this way, the selection means are moved into their state of engagement of the additional gear train.

[0079] When this deceleration is generated, the balls 18 come out of their housings 151 to circulate in the grooves 152 until they are housed in the other locking housings 151 of the selection member 15. The selection means are then in their state of engagement of the additional gear train.

[0080] The control means then drive the motor so that it reaches its nominal rotation frequency while generating an acceleration ẇ less than the gear change acceleration in order to ensure that the selection means remain in their additional gear train engagement state; in other words, the acceleration ẇ must be such that w ˙ < Cl Jos The control means then command the motor so as to make it rotate in the screwing direction to carry out the tightening phase.

[0081] In the engagement state of the additional gear train, when the rotor rotates in the screwing direction, the second pair of one-way clutches does not engage the drive shaft 16 with the rotating drive ring 24 so that the latter is rotationally immobile. The first pair of one-way clutches engages the casing 10 with the ring gear 22 so that the latter is rotationally immobilized.

[0082] The drive shaft 16 rotates the sun gear 20 in an anticlockwise direction, which meshes with the satellites 23 secured to the planet carrier 21, which rotates to rotate the output member 12 in the screwing direction at a slower speed, providing a higher available torque.

[0083] The control means thus control the motor until they detect, by means of the torque sensor, the reaching of the objective tightening torque at which it is desired to tighten the assembly being screwed.

[0084] The torque sensor can be a current measurement. It could be considered to cause the engagement / disengagement of the additional train based on a reason other than the torque measurement, for example a time measurement.

[0085] When the target torque is reached, the control means brake the motor preferentially with a deceleration lower than the speed change deceleration until the rotation frequency of the motor becomes zero. However, braking with a stronger deceleration would have no effect given that the sliding torque of the selection member 15 relative to the drive shaft 16 is significantly stronger when the balls no longer have the opportunity to pass into a groove 152.

[0086] At the same rotation frequency of the motor during the fast pre-tightening and slow tightening phases, the difference in speed of the output member is due to the fact that during the pre-tightening phase, the crown is free to rotate while it is immobile in rotation during the tightening phase. In other words, the additional gear train is disengaged during the pre-tightening phase but engaged during the tightening phase. Thus, the transmission chains stressed during these two phases have different transmission ratios.

[0087] In this embodiment, the motor rotates counterclockwise for a screwdriving operation and non-clockwise for a screwdriving operation as viewed from the output member towards the rear of the screwdriver.

[0088] If acceleration is required for the selection means to move from their additional gear train disengagement state to their additional gear train engagement state, deceleration will be required to move from their additional gear train disengagement state to their additional gear train engagement state to their additional gear train disengagement state to their additional gear train disengagement state, and vice versa.

[0089] Furthermore, driving the motor in the unscrewing direction while the engagement means of the additional gear train are placed in their disengaged state makes it possible to achieve rotational drive of the output member in the unscrewing direction at slow speed.

[0090] Driving the motor in the unscrewing direction while the engagement means of the additional gear train are placed in their engagement state makes it possible to achieve rotational drive of the output member in the unscrewing direction at high speed. 6.2. Deuxième mode de réalisation 6.2.1. Architecture

[0091] We present, in relation to the figures 15 to 31 , an example of a second embodiment of a screwing / unscrewing device according to the invention.

[0092] As shown, such a screwing / unscrewing device conventionally comprises a casing 10. This is a pistol-grip type casing in which the axis of the handle 11 forms an angle with the axis of the output member 12. Alternatively, it could be a casing in which the axis of the handle coincides with the axis of the output member.

[0093] The casing 10 houses an electric motor 13 comprising a stator 130 and a rotor 131 provided with a motor shaft 132.

[0094] The device comprises an output member 12 placed at the end of the casing 10. This output member 12 is capable of rotating a drive element of an element to be screwed, in particular a screw socket or other.

[0095] The device comprises a transmission T connecting the shaft 132 of the rotor 131 to the output member 12 so as to drive the latter in rotation.

[0096] The transmission comprises a two-speed mechanism which comprises two transmission chains having different transmission ratios. For this purpose, the transmission T comprises an additional gear train which can be engaged / disengaged. As will be described in more detail later, this additional train here comprises an epicyclic gear train which can be deactivated by making its inner ring gear free to rotate or activated by locking its ring gear in rotation.

[0097] The two-speed mechanism includes means for engaging the additional gear train, these means being able to take at least: an engagement state in which the additional gear train is engaged, and a disengagement state in which the additional gear train is disengaged,

[0098] The reduction ratio of the transmission between the rotor and the output member is different depending on whether the additional gear train is engaged or not, the reduction ratio being higher when the additional gear train is engaged. In this way, for a given rotation frequency of the rotor, the rotation frequency of the output member is higher when the additional gear train is not activated and slower when it is activated so that the tightening torque capable of being delivered by the device is higher when the additional gear train is activated.

[0099] The engagement means comprise a selection member 15 movable between at least: an additional gear train selection position, and an additional gear train de-selection position;

[0100] In this embodiment, the direction of rotation of the rotor has an impact on the engagement of the additional gear train.

[0101] This two-speed mechanism comprises a drive shaft 16 connected in rotation with the rotor shaft 132. These two components could, in a variant, constitute a single part.

[0102] The selection member 15 is crossed by an internal longitudinal bore 150 housing the drive shaft 16. The selection member 15 is mounted to be able to rotate around the drive shaft 16 between two extreme positions corresponding to its two selection positions.

[0103] In each of these two extreme positions, the selection member 15 is connected in rotation to the drive shaft 16 by rotational connection means. For this, the drive shaft 16 is crossed by a first transverse bore 160 arranged along an axis perpendicular to its longitudinal axis. This bore 160 houses an elastic return means which comprises in this embodiment a compression spring 17. At each end of the compression spring is placed a locking element. These locking elements are in this embodiment produced by bocage balls 18.

[0104] The selection member 15 comprises, at the periphery of the internal bore 150 housing the drive shaft 16, two pairs of diametrically opposed locking housings 151. The housings 151 of each pair are connected by a groove 152.

[0105] The locking balls 18 are movable along an axis orthogonal to the axis of the drive shaft 16, against the effect of the elastic return means 17, between at least: a rotational connection position in which the balls 18 are housed in two of the diametrically opposed locking housings 151 so that the drive shaft 16 and the selection member 15 are rotationally connected (cf. figures 16 And 22 ), and a release position in which the balls 18 are not housed in any of the locking housings 151, but are located in the grooves 152, so that the drive shaft 16 and the selection member 15 are not linked in rotation.

[0106] When the selection member 15 is in the deselection position of the additional gear train, the locking balls 18 are housed in the first two of the opposite housings 151 (cf. figure 16). When the selection member 15 is in the selection position of the additional gear train, the balls 18 are located in two other of the opposite housings 151 (cf. figure 22 ).

[0107] When the balls are in their rotationally locked position, the rotational connection means are able to transmit a predetermined limit torque CI beyond which the balls pass into their release position in which the drive shaft and the selection member are no longer rotationally connected and can no longer transmit torque. This predetermined torque depends in particular on the stiffness of the spring 17, the size of the balls, the geometry of the locking housings and the grooves. This torque can be conventionally determined by calculation or empirically.

[0108] The device conventionally comprises means for measuring the tightening torque delivered by the device at the output member. These measuring means may, for example, comprise a torque sensor placed in the transmission between the rotor and the output member or a current sensor consumed by the motor.

[0109] The device typically includes motor control means. These means enable the motor to be controlled, in particular by controlling its power supply.

[0110] The motor control means allow, by acting on the acceleration / deceleration of the motor rotor, to switch the engagement means from one of their states to the other, i.e. to switch the selection member from one of its positions to the other relative to the drive shaft.

[0111] To enable the engagement means to move from one position to the other, the acceleration / deceleration generated by the motor must be greater than the quotient of the limit torque CI transmissible by the rotating connection means by the inertia Jos of the selection member along its axis of rotation. This acceleration / deceleration is called speed change acceleration / deceleration insofar as it enables the additional gear train to be engaged / disengaged and thus the reduction ratio of the transmission between the rotor and the output member to be modified.

[0112] During the performance of a screwing / unscrewing operation, the motor typically produces accelerations and variations in acceleration, particularly at start-up. It is therefore appropriate that the acceleration / deceleration which induces the switching of the engagement means from one state to the other be sufficiently discriminating, i.e. distant from and more precisely greater than the accelerations typically likely to occur so as not to inadvertently cause the selection means to switch from one state to the other.

[0113] The transmission comprises an epicyclic gear train comprising a sun gear 20 rotationally secured to the drive shaft 16, a planet carrier 21 rotationally secured to the output member 12, and an internal toothed crown 22 meshing with planet gears 23 carried by the planet carrier 21.

[0114] The two-speed mechanism comprises a ring 24 for driving the crown 22 in rotation.

[0115] This rotation drive ring 24 comprises two male dogs 240 cooperating with two female dogs 220 arranged in the crown 22 so that the crown 22 and the rotation drive ring 24 are linked in rotation along the axis of the rotor. However, there is clearance between the male and female dogs to allow the one-way clutches to be released.

[0116] The rotation drive ring 24 is crossed by a longitudinal internal bore 241 housing on one side the selection member 15 and on the other side the crown 22. The peripheral wall of the drive ring 24 is crossed by two diametrically opposite slots 242 located at the level of the crown 22.

[0117] The rotation drive ring 24 has at its opposite end, i.e. on the side of the selection member, teeth 243 projecting longitudinally.

[0118] The selection member 15 comprises, at its end opposite the rotor, two diametrically opposed grooves 154. These grooves 154 extend to the outer periphery of the inner bore and their radial depth narrows from one end to the other to form ramps (or cams). The grooves 154 are symmetrical with respect to the axis of the selection member.

[0119] The device comprises at least one rotational locking member, two in this embodiment, although there could be more. Each locking member comprises an axle 26 at one end of which is formed a flat 260.

[0120] The drive shaft 16 is crossed by a second transverse hole 162 arranged parallel to the first transverse hole 160. The end 261 without flat of the locking members is housed in this second hole 162. An elastic return means, here a compression spring 27, is placed in the second hole 162 between the locking members 26. The locking members are thus linked in rotation with the drive shaft 16.

[0121] The flat 260 of each locking member 26 comes to bear against one of the ramps of the grooves 154 of the selection member 15 against which it is held in abutment by the return means. The projecting part 262 extending at the flat end 260 of each locking member 26 extends longitudinally outside the selection member 15.

[0122] When the selection member 15 moves from one to the other of its extreme positions relative to the drive shaft 16, the flat 260 of each locking member 26 slides along the corresponding ramp formed in the groove 154 in which it is located. As a result, each locking member 26 is movable between: a rotational locking position, taken when the selection member 15 occupies its deselection position of the additional gear train, in which it projects radially from the surface of the selection member 15 and cooperates with one of the locking housings 244 delimited in the drive ring 24 by two consecutive notches 243 so that said drive ring 24 and said rotor 131 are linked in rotation (cf. figures 15 , 17 And 18, and a rotational unlocking position, taken when the selection member 15 occupies the selection position of the additional gear train, in which it does not project radially outside the selection member 15 and does not cooperate with any of the locking housings 244 delimited in the drive ring 24 by two consecutive notches 243 so that the drive ring 24 and the rotor 131 are not linked in rotation (cf. figures 21 , 23 And 24 ).

[0123] The crown 22 has, at its periphery, two pairs of diametrically opposed blocking ramps 221.

[0124] The device comprises a pair of one-way clutches comprising the crown 22, the casing 10 constituting a one-way clutch, and rollers 25 are housed, between the crown 22 and the casing 10, in the slots 242 of the rotation drive ring 24 at the ramps 221 of the crown 22. The drive ring 24 allows, depending on its position, to activate one or the other of the one-way clutches of this pair or to deactivate them both, as will be described in more detail later.

[0125] The ramps 161 are arranged on the periphery of the drive shaft 16. They are grouped in pairs opposite each other with respect to a plane passing through the longitudinal axis of the drive shaft. The ramps 161 of each pair of ramps are symmetrical with respect to a plane passing through the longitudinal axis of the drive shaft 16 and perpendicular to the preceding plane. The ramps 161 of each pair are joined by a plate 1610 which extends in a plane parallel to the longitudinal axis of the drive shaft 16. Starting from this plate, they are inclined towards the longitudinal axis of the drive shaft.

[0126] The position and inclination of the ramps 221 of the crown 22 are chosen such that: when the rotation locking members 26 occupy the rotation locking position, the pair of one-way clutches leaves the internal toothed ring 22 free to rotate (cf. figures 15 to 20), when the rotation locking members occupy the rotation unlocking position and, the pair of one-way clutches locks the internal toothed crown in rotation (cf. figures 21 to 26 ).

[0127] In variants, one or more permanent gear trains, i.e. non-deactivatable, for example epicyclic, may be arranged between the planet carrier 21 and the output member 12.

[0128] When the additional gear train is disengaged, the reduction ratio of the transmission is equal to 1 since the drive shaft 16 and the planet carrier rotate at the same rotation frequency, or to the reduction ratio of the permanent gear train or to their product if several permanent trains are implemented.

[0129] When the additional gear train is engaged, the reduction ratio of the transmission is equal to the reduction ratio of the additional epicyclic gear train, or to its product with the reduction ratio(s) of the permanent gear train(s) if applicable. 6.2.2. Operation

[0130] A screwdriving operation is described below, comprising a pre-tightening phase at high speed followed by a tightening phase at slower speed.

[0131] Before starting a screwing / unscrewing operation, the operator in charge programs into the controller, for example using a touch screen, a keyboard, a smartphone or other, the value of the predetermined speed change torque threshold CchangementVitesse which, when reached at the output of the screwing device during a pre-screwing phase, causes a speed change and the transition to the tightening phase. The operator can also program the value of the target torque to which he wishes the assembly to be screwed to be tightened at the end of the tightening phase.

[0132] When starting the screwing device in order to carry out such a screwing / unscrewing operation, the control means control the motor in such a way that it generates, in the screwing direction, a speed change acceleration. ẇ whose value is greater than the quotient of the predetermined limit torque CI ( w ˙ > Cl Jos ), beyond which the balls pass into their release position in which the drive shaft and the selection member are no longer linked in rotation, by the inertia Jos of the selection member. In this way, the engagement means of the additional gear train are placed in their disengagement state. The control means then command the motor so as to make it rotate in the screwing direction to carry out the pre-screwing phase.

[0133] In the disengaged position of the additional gear train, the locking members 26, taking into account the relative position of the selection member 15 with respect to the drive shaft 16, are in the locking position so that the drive shaft 16 and the drive ring 24 are linked in rotation.

[0134] The motor is driven in the screwing direction, which here is counterclockwise when the device is viewed from the output member towards the rear of the screwdriver, and the rotation drive ring 24 rotates counterclockwise and rotates the crown 22 in this direction, the one-way clutch not engaging the crown 22 with the housing 10 so that the crown 22 is free to rotate.

[0135] The crown 22 meshes with the satellites 23 as does the sun gear 20 which is rotationally fixed to the drive shaft 16. The crown 22 thus rotates at the same rotation frequency as the sun gear 20. As a result, the satellite carrier 21 rotates at the same frequency as the drive shaft 16. Thus, the output member 12 is rotated in the screwing direction at high speed.

[0136] The control means control the motor in such a way that the output member is rotated at high speed during the pre-screwing phase until the tightening torque delivered by the screwing device reaches the predetermined speed change torque threshold CchangementVitesse.

[0137] When the control means detect by means of the torque sensor that this threshold is reached, the control means brake the motor in order to generate a speed change deceleration whose value is greater than the quotient of the predetermined limit torque CI by the inertia Jos of the selection member. In this way, the selection means are moved into their state of engagement of the additional gear train.

[0138] When this acceleration is generated, the balls 18 come out of their housings 151 to circulate in the grooves 152 until they are housed in the other locking housings 151 of the selection member 15. The latter is then in its position for selecting the additional gear train (cf. figures 21 to 26 ).

[0139] The control means then drive the motor so that it reaches its nominal rotation frequency while generating an acceleration ẇ less than the gear change acceleration in order to ensure that the selection means remain in their additional gear train engagement state; in other words, the acceleration ẇ must be such that w ˙ < Cl Jos The control means then command the motor so as to make it rotate in the screwing direction to carry out the pre-screwing phase.

[0140] In this selection position of the additional gear train, when the rotor 131 rotates in the screwing direction, the blocking (or locking) members 26 are in their unlocked position so that the drive shaft 16 is not linked in rotation with the rotating drive ring 24 so that the latter is immobile in rotation. The one-way clutch engages the casing 10 with the crown 22 so that the latter is immobilized in rotation.

[0141] The drive shaft 16 drives the sun gear 20 in clockwise rotation, which meshes with the satellites 23 secured to the planet carrier 21, which rotates to drive the output member 12 in rotation at a slower speed, providing a higher available torque.

[0142] The control means thus control the motor until they detect, by means of the torque sensor, the reaching of the objective tightening torque at which it is desired to tighten the assembly being screwed.

[0143] The torque sensor can be a current measurement. It could be considered to cause the engagement / disengagement of the additional train based on a reason other than the torque measurement, for example a time measurement.

[0144] When the target torque is reached, the control means brake the motor preferentially with a deceleration lower than the speed change deceleration until the rotation frequency of the motor becomes zero. However, braking with a stronger deceleration would have no effect given that the sliding torque of the selection member 15 relative to the drive shaft 16 is significantly stronger when the balls no longer have the opportunity to pass into a groove 152.

[0145] At the same rotation frequency of the motor during the fast pre-tightening and slow tightening phases, the difference in speed of the output member is due to the fact that during the pre-tightening phase the crown is free to rotate while it is immobile in rotation during the tightening phase. In other words, the additional gear train is disengaged during the pre-tightening phase but engaged during the tightening phase. Thus, the transmission chains stressed during these two phases have different transmission ratios.

[0146] In this embodiment, the motor rotates counterclockwise for a screwing operation and non-clockwise for a loosening operation as seen from the output member towards the rear of the screwdriver. These directions of rotation could be reversed in variants.

[0147] If acceleration is required for the selection means to move from their additional gear train disengagement state to their additional gear train engagement state, deceleration will be required to move from their additional gear train disengagement state to their additional gear train engagement state to their additional gear train disengagement state to their additional gear train disengagement state, and vice versa.

[0148] Furthermore, driving the motor in the unscrewing direction while the engagement means of the additional gear train are placed in their disengaged state makes it possible to achieve rotational drive of the output member in the unscrewing direction at high speed.

[0149] Driving the motor in the unscrewing direction while the engagement means of the additional gear train are placed in their engagement state makes it possible to achieve rotational drive of the output member in the unscrewing direction at slow speed. 6.3. Procedure

[0150] There figure 32 generally illustrates a method of controlling a device according to one or other of the embodiments described above.

[0151] Such a method comprises a step 320 of starting the screwdriver by pressing the trigger.

[0152] The method continues with a step 321 of accelerating the motor in the screwing direction with an acceleration w ˙ > Cl Jos in such a way that the selection member moves into a position such that the means for engaging the additional gear train are in their disengaged state (step 322).

[0153] The method continues with a step 323 of maintaining the rotation of the motor at a pre-screwing frequency.

[0154] When it is detected that the tightening torque delivered by the screwdriver exceeds a speed change torque threshold Cchange Speed ​​(step 324), a motor deceleration step 325 is implemented with a deceleration w ˙ < Cl Jos .

[0155] Under the effect of this deceleration, the selection member moves into a position such that the engagement means of the additional gear train are in their engagement state (step 326).

[0156] The method continues with a step 327 of accelerating the motor in the screwing direction with an acceleration w ˙ < Cl Jos .

[0157] The motor is rotated until it is detected (step 328) that the tightening torque delivered by the screwdriver reaches the predetermined target tightening torque to which it is desired to tighten the assembly being screwed.

[0158] When this threshold is reached, the engine is stopped (step 329).

Claims

1. A screwing device comprising: - a casing (10); - a motor (13) provided with a rotor (131); - an output member (12) likely to drive in rotation a drive element of an element to be screwed; - a transmission (T) connecting said rotor (13) to said output member (12), said transmission (T) comprising at least one additional gear train likely to be engaged / disengaged; - means (19) for controlling said motor (13); said device comprising means for engaging said additional gear train, said means for engaging being able to take at least: - an engagement state in which said additional train is engaged, and - a disengagement state in which said additional gear train is not engaged, the reduction ratio of said transmission between said rotor (131) and said output member (12) being different depending on whether said additional gear train is engaged or not, said reduction ratio being higher when said additional gear train is engaged, characterised in that said means (19) for controlling said motor (13) are configured to generate a predetermined acceleration or deceleration of said rotor (131), said predetermined acceleration or deceleration acting on said means for engaging to cause them to switch from one of their states to the other.

2. The device according to claim 1, wherein said means for engaging comprise a selection member (15) which is movable in rotation relative to said rotor (131) between at least two positions of engagement / disengagement of said additional gear train, said predetermined acceleration or deceleration acting on said selection member (15) to move it from one of its positions to another.

3. The device according to claim 2 comprising means for rotational connection of said selection member (15) with said rotor (31), said means for rotational connection ensuring, when said selection member (15) occupies one of its positions, a rotational connection of said selection member (15) with said rotor (131) as long as said motor (13) delivers an acceleration-deceleration less than a predetermined speed change acceleration-deceleration threshold, delivering by said motor (13) of an acceleration / deceleration which is greater than said predetermined speed change acceleration-deceleration threshold inducing rotation of said selection member (15) from one to the other of its positions.

4. The device according to claim 3, wherein said means for rotational connection comprise at least one blocking element (18) rotationally fixed to said rotor (131) and capable of being alternatively housed in two housings (151) of complementary shape formed in said selection member (15), said blocking element (18) being movable along an axis orthogonal to the axis of said rotor (131), against the effect of elastic return means (17), between at least: - a rotational connection position in which said blocking element (18) is housed in one or the other of said housings (151) such that said rotor (131) and said selection member (15) are connected in rotation, and - a release position in which said blocking element (18) is housed in none of said housings (151) so that said rotor (131) and said selection member (15) are not connected in rotation.

5. The device according to claim 4, wherein: - said means for rotational connection are capable of transmitting a predetermined limit torque Cl beyond which said rotor (131) and said selection member (15) are no longer linked in rotation and can no longer transmit torque, - said selection member (15) has an inertia Jos along the axis of rotation thereof; - the value of said speed change acceleration-deceleration being equal to the quotient of said limit torque Cl by said inertia Jos.

6. The device according to any one of claims 1 to 5, wherein said at least one additional gear train comprises a sun gear (20) rotationally fixed to said rotor (131), a planet carrier (21) rotationally fixed to said output member (12), and an inner ring gear (22) engaging with planet gears (23) carried by said planet carrier (21), said ring gear (22) being: - movable in rotation relative to said casing (10) in said disengagement state of said additional gear train, and - blocked in rotation relative to said casing (10) in said engagement state of said additional gear train.

7. The device according to claim 6 comprising a first pair of one-way clutches comprising said casing (10) and said inner ring gear (22)8. The device according to claim 7 comprising a second pair of one-way clutches comprising said rotor (131) and a rotating drive ring (24), said second pair of one-way clutches engaging said rotor (131) with said rotating drive ring (24) when said means for engaging occupy said disengagement state of said additional gear train and said rotor (131) rotates in the screwing direction, said first pair of one-way clutches leaving said inner ring gear (22) free to rotate, said second pair of one-way clutches not engaging said rotor (131) with said drive ring (24) when said means for engaging occupy said engagement state of said additional gear train and said rotor (131) rotates in the screwing direction, said first pair of one-way clutches blocking said inner ring gear (22) in rotation.

9. The device according to claim 8, wherein: said second pair of one-way clutches does not engage said rotor (131) with said drive ring (24) when said means for engaging occupy said disengagement state of said additional gear train and said rotor (131) rotates in the unscrewing direction, said first pair of one-way clutches blocking said inner ring gear (22) in rotation, said second one-way clutch does not engage said rotor (131) with said drive ring (24) when said means for engaging occupy said engagement state of said additional gear train and said rotor (131) rotates in the unscrewing direction, said first pair of one-way clutches leaving said inner ring gear (22) free to rotate.

10. The device according to claim 7 comprising at least one rotation locking member (26), rotationally fixed to said rotor (131) and movable between: - a rotation blocking position, taken when said means for engaging occupy said disengagement state of said additional gear train, in which it cooperates with a blocking housing (244) formed in said drive ring (24) such that said drive ring (24) and said rotor (131) are connected in rotation, and - a rotation unblocking position, taken when said means for engaging occupy said engagement state of said additional gear train, in which it does not cooperate with said blocking housing (244) formed in said drive ring (24) such that said drive ring (24) and said rotor (131) are not connected in rotation.

11. The device according to claim 10, wherein: - when said rotation locking member (26) occupies said rotation blocking position and said rotor (131) rotates in screwing direction, said first one-way clutch leaves said inner ring gear (22) free to rotate, - when said rotation locking member (26) occupies said rotation unblocking position and said rotor (131) rotates in screwing direction, said first one-way clutch blocks said inner ring gear (22) in rotation.

12. The device according to claim 10, wherein: - when said rotation locking member (26) occupies said rotation blocking position and said rotor (131) rotates in unscrewing direction, said first one-way clutch leaves said inner ring gear (22) free to rotate, - when said rotation locking member (26) occupies said rotation unblocking position and said rotor (131) rotates in unscrewing direction, said first one-way clutch blocks said inner ring gear (22) in rotation.