Coupling device for reduction gear having two gear ratios

Abstract

The invention relates to a device for coupling shafts, comprising a main shaft oriented along a main axis (A1), two idler gears (22) mounted for free rotation on the main shaft, and a coupling system (50) interposed between the two idler gears. According to the invention, the coupling system comprises:-a hub (540), which rotates together with the main shaft; -a selection slip ring (520) slidably mounted relative to the hub between a position coupled to one of the idler gears and a position coupled to the other of the idler gears; and-a locking slip ring (530) slidably mounted relative to the hub between a position coupled to one of the idler gears and a position coupled to the other of the idler gears, the locking slip ring comprising ejection means adapted to eject the locking slip ring (530) after the selection slip ring has moved from one position to the other position. The locking slip ring is automatically moved from one position to another.

Description

Technical Field

[0001] The present invention relates generally to shaft coupling systems capable of transmitting torque from one shaft to another, and more particularly to constant mesh and dual ratio reduction gear systems.

[0002] More specifically, the present invention relates to a shaft coupling device, comprising:

[0003] - a main shaft, which is oriented along the main axis,

[0004] - two idler gears mounted to rotate freely on the main shaft about the main axis, and

[0005] - A coupling system, which is interposed between the two idler pinions.

[0006] The invention also relates to a reduction gearbox comprising a shaft coupling device as described above, and to a motor vehicle equipped with such a gearbox.

[0007] It has particularly advantageous application in the transmission of torque in electric machines. Background Art

[0008] Internal combustion engines generate a torque that varies with the rotational speed of the crankshaft. Therefore, the range of use of such engines is limited. In a motor vehicle equipped with such an engine, it is then necessary to associate a gearbox with the engine.

[0009] Many gearbox systems have been developed in this field. Typically, such a gearbox comprises two shafts provided with opposing gears of different diameters meshing with each other, wherein the gears of one shaft are, for example, mounted idlingly on the shaft (i.e., freely rotating on the shaft), while the other gears are fixedly mounted on the other shaft. To change the gear ratio, these gearboxes use a coupling device designed to couple one of the idling mounted gears with the gearbox on which it is mounted, in order to balance their rotational speeds.

[0010] For this purpose, the coupling device usually comprises a sliding sleeve which is rotationally coupled to one of the gearbox shafts and is adapted to slide on this shaft so as to engage the teeth of the idler gear by means of fingers.

[0011] In an electric (or hybrid) motor vehicle, the electric motor is coupled to a reduction gearbox. Generally, such a gearbox is single-ratio. Therefore, a gearbox is usually not required. The electric motor is designed to deliver a substantially constant torque over a wide speed range. Therefore, it can be used with such a reduction gearbox in a motor vehicle. The advantages of a single-ratio reduction gearbox are that it is simple, cheap, and does not cause problems with torque interruption (when changing the gear ratio).

[0012] However, it should be noted that once the motor reaches a certain speed threshold, the torque it can deliver decreases significantly. Therefore, the power it can produce is saturated. In other words, the torque delivered by the electric motor is not infinitely constant. Therefore, it is still of interest to combine a multiple-ratio reduction gearbox with such a motor, especially in the automotive field. Typically, a two-ratio reduction gearbox makes it possible to reduce the size of the motor, or to use the motor in a rpm range where the motor consumption remains low, or to install the motor in a specific vehicle, such as a commercial vehicle capable of moving heavy loads, or a sports car capable of reaching high speeds.

[0013] The disadvantages of dual-ratio reduction gearboxes are that they are currently complex, expensive and bulky, or they are slow when shifting from one gear to another, resulting in torque interruption, which is incompatible with the automotive field. Summary of the invention

[0014] In order to make up for the above-mentioned shortcomings of the prior art, the present invention proposes a dual-speed ratio reduction gearbox, which has a simple structure and hardly causes torque interruption when changing the gear ratio.

[0015] More specifically, a shaft coupling device for a reduction gearbox is proposed, comprising: a main shaft oriented along a main axis, two idler gears mounted to freely rotate on the main shaft around the main axis, and a coupling system interposed between the two idler gears. According to the present invention, the coupling system comprises:

[0016] - a hub, which is rotationally fixed to the spindle,

[0017] - a selector shifter slidably mounted relative to the hub along the main axis between a position coupled to one of the idler gears and a position coupled to another of the idler gears,

[0018] - means for moving the selector shifter from one of the two coupled positions to the other,

[0019] a locking shifter slidably mounted relative to the hub along the main axis between a position coupled to one of the idler gears and a position coupled to another of the idler gears, and

[0020] - an ejection device adapted to automatically move the locking shifter from a position coupled with any one of the idler gears to a position coupled with the other of the idler gears after the selector shifter has been moved from a position coupled with one of the idler gears to a position coupled with the other of the idler gears.

[0021] The two shifters together allow the main shaft to be coupled to one of the idler gears.

[0022] The use of two shifters allows the first of these shifters (the selector shifter) to easily engage one of the idler gears before the other shifter completely blocks the idler gear relative to the main shaft.

[0023] The ejection device is designed so that the locking shifter is moved only when the idler gear has been engaged by the selector shifter.

[0024] Thus, thanks to the invention, the main shaft is always designed to be coupled to one of the idler gears, so that the reduction gearbox is always in one of the two speed ratios. Thus, this reduction gearbox has no stable neutral position and therefore little or no torque interruption, which makes it suitable for electric or hybrid vehicles.

[0025] Furthermore, the invention does not require the gearbox to be decoupled from the motor when changing gears, so no clutch is needed. It may be useful to use a torque limiter instead of such a clutch to give the system greater flexibility. The torque limiter can be easily adjusted because the gear changes can be designed to always be made at the same speed.

[0026] Furthermore, the gear changes are carried out without synchronisation of the differential between the main shaft and the idler gear to be coupled, which means that the gear changes can be carried out very quickly without any noticeable torque interruption for the user.

[0027] Other advantageous and non-limiting features of the coupling device according to the invention, considered individually or in any technically possible combination, are as follows:

[0028] -The selector shifter and the lock shifter have a circular shape and are nested one inside the other;

[0029] - Each idler gear has at least one claw facing the other idler gear;

[0030] - the selector and the locking shifter comprise fingers adapted to grip the dogs of the idler gear in such a way that, when the selector and the locking shifter are in the same position coupled to the idler gear, their fingers clamp each dog of the idler gear;

[0031] - Each idler gear comprises a plurality of claws evenly distributed around the main axis, the claws being greater than or equal to two;

[0032] - the selector and locking shifters have a number of fingers regularly distributed around the main axis, the same number as the number of dogs on each idler gear;

[0033] - the angular space around the main axis defined between the two dogs is strictly greater than twice the angular space around the main axis occupied by the selector shifter finger;

[0034] - the hub has on its outer surface a plurality of notches distributed around the main axis, the notches being suitable for guiding the sliding of the fingers of the selector and lock shifters;

[0035] - the ejection device is adapted to mechanically move the locking shifter after the selector shifter has been moved to a position coupled with another of the idler gears;

[0036] - each idler gear has a bevel, and the ejection means comprises at least two bevels on the locking shifter, the bevels being adapted to slide against the bevels of any one of the idler gears after the selector shifter has been moved to a position coupled to another of the idler gears;

[0037] - the locking shifter comprises indexing means adapted to block the locking shifter along the main axis (preferably relative to the hub) when the ejection means are inoperative;

[0038] - the indexing device comprises at least one protruding element, preferably a rolling element, located on one of the locking shifter and the hub, which extends in a groove having a variable depth and recessed in the other of the locking shifter and the hub when the locking shifter is moved from one coupling position to the other;

[0039] The selector shifter and the locking shifter are shaped in such a way that, for movement from one coupled position to the other, the selector shifter covers a distance which is strictly greater than the distance which the locking shifter covers for movement from one coupled position to the other, preferably twice as great.

[0040] The invention also relates to a reduction gearbox comprising a primary shaft carrying a gear wheel fixed relative thereto, and a coupling device as described above, the idler gear wheel of the coupling device meshing with the fixed gear wheel.

[0041] The present invention also relates to a motor vehicle, comprising: a motor, a differential, a drive wheel connected to the differential, and a torque limiter between the motor and the differential, the input of the torque limiter being connected to the motor; a reduction gearbox as described above, one of the prime mover shaft and the main shaft of the reduction gearbox being connected to the output of the torque limiter, and the other of the prime mover shaft and the main shaft being connected to the differential.

[0042] Of course, the various features, variations and forms of the present invention may be associated with each other in various combinations as long as they are not incompatible or mutually exclusive. DETAILED DESCRIPTION

[0043] The following description of the invention together with the attached non-limiting drawings will make clear what the invention consists of and how it is implemented.

[0044] In the attached picture:

[0045] Figure 1 is a schematic perspective view of a reduction gearbox including a shaft coupling device according to the present invention;

[0046] Figure 2 yes Figure 1 A schematic exploded perspective view of a clutch system of a coupling device;

[0047] Figure 3 yes Figure 1 A schematic exploded perspective view of one of the idler gears of the coupling device and a selector shifter;

[0048] Figure 4 Shown from different angles Figure 1 A schematic diagram of two idler gears and a clutch system of the coupling device shown;

[0049] Figure 5 is a diagram showing the first idler gear when it is clutched, viewed from a first angle Figure 1 A schematic diagram of a first idler gear, a clutch system and a clutch of a second idler gear of a coupling device;

[0050] Figure 6 is a diagram showing the speed ratio during the change of the speed ratio viewed from a second angle Figure 1 A schematic diagram of a clutch system of a coupling device and a claw of a second idler gear;

[0051] Figure 7 is similar to Figure 5 The schematic diagram of the gear shifting process shown;

[0052] Figure 8 It shows that during the speed ratio change, Figure 1 A schematic diagram of a first idler pinion of a coupling device of and a locking shifter, the first idler pinion in particular having one of its claws; and

[0053] Fig. 9 Five schematic diagrams of a clutch system are shown in cylindrical cross-section (the outermost part of the system has been cut away), showing the five consecutive states the system assumes when changing speed ratio.

[0054] In the remainder of the description, the term "coupling" will be used to denote a connection between two elements that enables torque to be transmitted from one of these elements to the other.

[0055] Figure 1 A double-speed ratio constant mesh reduction gearbox 1 is shown.

[0056] This reduction gearbox 1 is described as two-speed in the sense that it provides exactly two reduction ratios, which is perfect for use in motor vehicles. It is "constant mesh" in the sense that it always transmits torque and therefore has no stable neutral position in which the shafts are separated from each other.

[0057] The reduction gearbox 1 is preferably designed for installation in a motor vehicle, but it can also be used in other fields (robotics, aviation, etc.).

[0058] The motor vehicle equipped with the reduction gearbox comprises:

[0059] - an electric machine, hereinafter referred to as an electric motor, although it can be used as an alternator,

[0060] - wheels, usually four in number, two of which are drive wheels,

[0061] - A differential 30 interposed between the two driving wheels.

[0062] Then, the reduction gearbox 1 is placed between the motor and the differential 30 so that it can transmit the motor torque to the wheels (or vice versa).

[0063] It has a housing (not shown) that houses the various components.

[0064] like Figure 1 As shown, the reduction gearbox 1 has a two-stage shaft housed in a housing. Thus, it comprises a prime mover shaft 10 coupled to the motor shaft and a main shaft 21 coupled to the differential 30 (the reverse is also possible).

[0065] The prime mover shaft 10 may be coupled directly to the motor shaft. Preferably, however, and for reasons detailed below, a torque limiter 11 is interposed between the two shafts to facilitate speed change.

[0066] The drive shaft 10 carries two fixed gears 12, 13, ie two gears that always rotate at the same speed as the drive shaft. The two fixed gears 12, 13 have different diameters to provide different speed ratios.

[0067] The main shaft 21 extends along a main axis A1 parallel to the axis of the motive shaft 10 and is therefore engaged in bearings 29 at both ends.

[0068] The main shaft 21 carries two idler gears 22, 23 respectively meshing with the two fixed gears 12, 13. These gears are described as idler in the sense that they are mounted so as to rotate freely on this shaft about the main axis A1 and they are prevented from translating along this axis.

[0069] Figure 1It is shown that the main shaft 21 also carries a fixed gear which meshes with the gears of the differential 30 .

[0070] In order to transmit the torque from the drive shaft 10 to the main shaft 21, a clutch system 50 is provided for the idler gears 22, 23. The clutch system 50 enables one or the other idler gear to be coupled to the main shaft 21 depending on the speed ratio engaged.

[0071] The clutch system 50, more precisely the subject of the present invention, comprises Figure 2 The four main components are shown.

[0072] Thus, it comprises a hub 540 coupled to the main shaft 21 , two shifters referred to as a selection shifter 520 and a locking shifter 530 , and a selection device 510 enabling the selection shifter 520 to move.

[0073] It is envisaged that the hub 540 will be formed with the spindle 21. However, here the hub 540 is a separate component from the spindle 21. Thus, it has a central opening through which it slides onto the shaft, the edge of which has grooves or serrations that engage in corresponding protrusions provided on the spindle 21 to couple the hub 540 to the spindle 21.

[0074] The two shifters (selection shifter 520 and locking shifter 530) are then mounted relative to the hub 540 so that they can move in translation along the main axis A1, but are prevented from rotating about this axis. They thus enable one or the other of the idler gears 22, 23 to engage, thereby coupling it to the main shaft 21.

[0075] like Figure 3 and Figure 4 As clearly shown, each of these idler gears 22, 23 conventionally comprises a main disc 225, 235 having a central opening, here delimited by a crown, for mounting on the main shaft 21 and externally delimited by teeth enabling it to mesh with one of the fixed gears 12, 13. To achieve its clutching, each idler gear 22, 23 comprises at least one dog 220, 230, here a projection protruding from one face of the main disc 225, 235 (the face facing the other idler gear) and by means of which it can be driven in rotation.

[0076] Precisely three dogs 220 , 230 are provided on each idler gear 22 , 23 , the dogs being evenly spaced apart around the main axis A1 at 120° from one another.

[0077] Here, each claw 220, 230 extends over a limited angular sector of about 30° and has substantially the shape of a prism with its base located on the above-mentioned face of the main disc 225, 235. Each claw thus has four side faces and an end face facing the other idler gear.

[0078] The inner side (located on one side of the main axis A1 ) is curved around this axis, and the same applies to the outer side. The other two side surfaces (hereinafter referred to as radial surfaces) each extend at least partially in a radial plane (ie in a plane containing the main axis A1 ).

[0079] It can be seen that the main face is joined to most of the side faces by a fillet. However, it is only connected to one of the two radial faces by an inclined flat portion forming a chamfer 231, the function of which will become clear below.

[0080] Note here that the inclined surfaces 221 , 231 of the three claws 220 , 230 of each idler gear 22 , 23 are oriented in the same direction about the main axis A1 , and this direction is opposite to the direction in which the inclined surfaces of the claws of the other idler gear are oriented.

[0081] It is also noted that the ramps 221 , 231 extend over only part of the thickness of the jaws 220 , 230 .

[0082] like Figure 2 As shown, both the select shifter 520 and the lock shifter 530 have an annular shape so that they can be assembled together (the select shifter 520 is located outside the lock shifter 530).

[0083] Therefore, the locking shifter 530 includes an annular body 533 whose inner diameter is adjusted to the outer diameter of the hub 540 so that it can slide freely on the hub 540 parallel to the main axis A1.

[0084] Similarly, the selection shifter 520 includes an annular body 523 whose inner diameter is adjusted to the outer diameter of annular body 533 of the locking shifter 530 so that it can slide freely on the annular body 533 parallel to the main axis A1. It should be noted that the locking shifter 530 has a smooth rotating cylindrical outer surface.

[0085] The two shifters are blocked by 540 from rotating relative to the main shaft 21 about the main axis A1 .

[0086] For this reason, Figure 2As shown, the hub 540 has a notched "tulip" shape. Thus, although the hub 540 has a constant thickness along the main axis A1, the hub 540 has a non-cylindrical outer surface having several recesses (here identical) regularly distributed around the main axis A1. These recesses thus form notches 541 by which the two shifters are prevented from rotating.

[0087] Each notch 541 is shaped in such a way that its cross section (i.e. its cross section in a plane perpendicular to the main axis A1) is uniform along the main axis A1. The cross section is U-shaped so that each notch has a flat bottom bounded by two flat sides extending in a radial plane. Six identical notches 541 are provided here.

[0088] The locking shifter 530 accordingly has at least one finger adapted to slide in one of the notches 541. In practice, it has exactly three, evenly distributed around the main axis A1 and whose cross section is uniform and has the same shape opposite the notches 541. These fingers 531 are fixed to the inner surface of the annular body 533 of the shifter. They therefore have radial faces that slide against the radial faces of the notches 541 to prevent any rotational movement of the shifter relative to the hub 540.

[0089] In the same way, the selector 520 comprises at least one finger adapted to slide in one of the notches 541 defined by the hub 540. In practice, it has exactly three, regularly distributed around the main axis A1 and whose cross section is uniform and of the same shape opposite the notches 541. These fingers 531 extend a distance from the inner surface of the annular body 523 of the selector, which slides along the outer surface of the annular body 533 of the other selector. In practice, they are connected to this inner surface only by one of their ends. The fingers 521 have radial faces that slide against the radial faces of the notches 541 to prevent any rotational movement of the selector relative to the hub 540.

[0090] The two shifters are therefore free to slide between the idler gears 22 , 23 between two extreme positions, ie a position coupled to one idler gear and a position coupled to the other idler gear.

[0091] In the remainder of the description, the first idler gear 23 will refer to, for example, an idler gear capable of establishing a first gear ratio, and the second idler gear 22 will refer to an idler gear capable of establishing a second gear ratio.

[0092] like Figure 5 As shown, only the claw 230 of the first idler gear 23 is shown. When a speed ratio ( Figure 5When the first speed ratio is set in the first gear ratio, the two shifters (select shifter 520 and locking shifter 530) are in the coupling position.

[0093] In this position, the first ends of their fingers 521, 531 are positioned on either side of each dog 230 of the corresponding idler gear 23, so that the radial faces of the dogs are in contact with the corresponding radial faces of the shifter fingers 521, 531. The hub 540 is thus prevented from rotating relative to this idler gear 23.

[0094] It should be noted here that, since the contact faces of the fingers and the claws are radial (ie extend in planes substantially radial with respect to the main axis A1 ), torque transmission can take place without difficulty. Of course, these various faces may alternatively not be completely radial.

[0095] The first end of each finger 521 of the selector 520 (which faces the first idler gear 23) extends from the second end of the finger by a distance that is less than the distance between the end faces of the two dogs 220, 230, so that the selector cannot simultaneously engage the two idler gears 22, 23. In fact, this distance is substantially equal to the thickness of the hub 540 (along the main axis A1).

[0096] Therefore, it must be moved to change the speed ratio.

[0097] The selector shifter 520 is designed to be moved from one coupling position to another coupling position by the selector device 510. Figure 2 As clearly shown, the selection device 510 comprises a single fork which engages in a groove 528 defined by two peripheral ribs arranged to protrude from the outer surface of the selection shifter 520 .

[0098] Thus, by moving the selection device 510 along the main axis A1 , it is possible to place the finger 521 of the selection shifter 520 against the dog 220 , 230 of one or the other of the idler gearwheels 22 , 23 in order to change the speed ratio.

[0099] On the other hand, the locking shifter 530 is not controlled. Therefore, no fork is associated with it. It is designed to automatically and mechanically move from a position coupled with any one idler gear to a position coupled with another idler gear after the selection shifter 520 has moved to a position coupled with another idler gear (due to such movement).

[0100] For this reason, Figure 2As clearly shown, the end face 534 of the finger 531 of the locking shifter 530 extends in a plane that is not orthogonal to the rotation axis A1 but is inclined relative to the rotation axis A1, thereby forming a ramp having a slope that matches the slope of the ramps 221, 231 of the dog.

[0101] The end faces 534 of the fingers 531 thus extend parallel to the inclined surfaces 221 , 231 of the jaws 220 , 230 facing them.

[0102] The inclination angle of the slope relative to the plane orthogonal to the main axis A1 is preferably 5 to 45 degrees, and is 20 degrees here.

[0103] The two end faces 534 of each finger 531 extend in parallel planes.

[0104] The first end of each finger 531 of the locking shifter 530 (the side thereof facing the first idler gear 23) extends from the second end of the finger by a distance which is strictly greater than the distance between the end faces of the two claws 220, 230 (see Fig. 9 ). This distance is also less than the sum of the thickness of the claw and the thickness of the hub. In this way, the finger 531 of the locking shifter 530 is always located on the claw channel of one and / or the other idler gear.

[0105] Therefore, the overall thickness of the locking shifter 530 measured along the main axis A1 is greater than the overall thickness of the hub 540 .

[0106] At this stage we can describe how the clutch of the idler gear works. Fig. 9 Five consecutive configurations (C1-C5) adopted by the system are shown.

[0107] like Figure 5 As shown, we can start from the situation where the first idler gear 23 is initially coupled to the main shaft 21 via two gear shifters.

[0108] As already explained, in this configuration C1 (such as Fig. 9 As shown in FIG. 1 ), the dog 230 of the first idler gear 23 is clamped between the fingers 521, 531 of the two shifters. The surface of the finger against each dog is radial, so this support ensures good torque transmission.

[0109] In fact, when the first speed ratio is engaged, the locking shifter 530 transmits torque to the main shaft 21 (when the torque is positive). Therefore, the forces applied to the selection shifter remain limited, especially in the acceleration phase just before changing to the second speed ratio.

[0110] At this stage, the claws 220 of the second idler gear 22 remain free, since nothing prevents them from freely pivoting on the main shaft 21. Therefore, the idler gear 22 rotates at a different speed than the first idler gear 23, since these two idler gears mesh in fixed gears 12, 13 of different diameters. In this case, the second idler gear 22 rotates faster than the first idler gear 23.

[0111] In order to change the speed ratio, the selection device 510 selects the shifter 520 from the position in which it is coupled to the first idler gear 23 ( Figure 5 ) slides to a position connected to the second idler gear 22 ( Figure 6 and Fig. 9 Configuration C2 in FIG. 5 ). The sliding distance of the selector shifter 520 is indicated here as D1. This sliding is effortless because, as described above, the torque is transmitted by the locking shifter.

[0112] During this shifting process, the selector shifter 520 initially turns slower than the second idler gear 22. However, due to the large angular spacing between two consecutive dogs 220, the second end of its finger 521 can slide into the space left between the two dogs. The movement speed of the selector device 510 is fast enough to quickly engage the clutch.

[0113] It will be appreciated that such clutch engagement may be somewhat abrupt, as it will impose a strong deceleration on the second idler gear 22 and thus on the prime mover shaft 10. This is why a torque limiter is preferably provided between the motor and the prime mover shaft 10.

[0114] In other words, when the clutch is engaged, the second idler gear 22 decelerates the prime mover shaft 10, and the dog 220 of the second idler gear 22 abuts against the finger 521 of the selector shifter 520, the rotation speed of which is determined by the forward speed of the motor vehicle. Fig. 9 It should be noted here that the claw 220 contacts the finger 521 of the selector 520 without rebound or with very little rebound (depending on the gear mechanism). Fig. 9 As is clearly shown, the finger 531 of the locking shifter 530 is offset relative to the dog 220 of the second idler gearwheel 22 .

[0115] The deceleration of the driving shaft 10 causes the deceleration of the first idler gear 21. Due to this deceleration, Figure 7 As indicated by the middle arrow F1, the claws 230 of the first idler gear 23, no longer held by the fingers 521 of the selector shifter 520, will move angularly until their bevels 231 come into contact with the end faces 534 in the form of cooperating bevels of the fingers 531 of the locking shifter 530, as shown in FIG. Fig. 9Configuration C4 shown.

[0116] The mechanical support generates a reaction force, the axial component of which (in Figure 8 The locking shifter 530 is forced to move toward the second idler gear 22 (indicated by arrow F2 in the figure). This movement enables the finger 531 of the locking shifter 530 to abut against the corresponding radial face of the claw 220 of the second idler gear 22, which is opposite to the finger 521 of the selection shifter 520. In this position, similar to Figure 5 The position shown in Fig. 9 In the illustrated configuration C5 , the second idler gearwheel 22 is therefore prevented from rotating relative to the hub 540 .

[0117] The sliding distance of the locking shifter 530 is here equal to half the sliding distance D1 of the select shifter 520 (this is explained by the length of the fingers of the select shifter, which is shorter than the length of the fingers of the locking shifter 530 ).

[0118] At this stage, when the second speed ratio is engaged, the selector shifter 520 transmits torque to the main shaft 21 (when the torque is positive). In this way, the force applied to the locking shifter remains limited.

[0119] It should be noted at this point that locking the idler gear by means of two fingers located on either side of each dog is particularly useful in the case of torque reversal, i.e. when the torque at the wheels becomes greater than the engine torque (e.g. during regenerative braking, when the engine acts as an alternator). In this case, in fact the fingers 531 of the locking shifter 530 will be mainly stressed.

[0120] It should also be noted that the speed ratio change is asynchronous in that there is no need to synchronize the speed of one shifter with the speed of the idler gear to be clutched.

[0121] During the subsequent ratio change, the dynamics will be essentially the same as explained above, the only difference being that the prime mover shaft 10 will not be braked but accelerated and therefore the direction of the ramp will have to be reversed, as clearly shown in the figure.

[0122] It should be noted here that during the shift from first gear to second gear or vice versa, the selector shifter 520, which is always controlled by the selector device 510, starts to slide before the locking shifter 530. The latter slides when the dog of the idler gear pushes it towards the other idler gear (the gear to which the selector shifter is coupled).

[0123] It should also be noted that during such a ratio change, the torque transmitted to the main shaft 21 is reduced, or even negative, so that the forces applied to the selector shifter 520 are limited, so that the fork can easily move it from one coupled position to another.

[0124] During a speed ratio change from the first gear to the second gear or vice versa, when the selection device 510 moves the selection shifter 520, it may happen that the finger of the selection shifter 520 hits the end face of the dog of the selected idler gear.

[0125] There are several possible solutions to prevent outages.

[0126] A first solution is to control the change of the ratio at the appropriate moment, namely when the dog is angularly offset relative to the finger of the selector. This solution is not preferred because it requires suitable sensors.

[0127] The solution adopted here is Figure 1 , in which it can be seen that a resilient system 40 is provided between the electromechanical actuator of the movement selection device 510 and the device itself.

[0128] In this case, the actuator output is fixed to a U-shaped bracket 41, whose two arcuate arms straddle a selection shaft 42, which is fixed to a fork forming the selection device 510. This selection shaft 42 has a central portion of reduced cross-section, on whose horizontal plane slides 43 are mounted so that they can translate between the two arms of the bracket 41. The two slides 43 are kept at a distance from each other by springs 44. Thus, when the actuator moves the bracket 41 and the fork is blocked in place (by the claws against which the fingertips of the selector 520 rest), the springs compress so that the bracket can continue to move.

[0129] like Figure 2 As shown, to prevent such contact from occurring too frequently and for too long, the end faces of the fingers 521 of the selection finger 520 may be inclined (and not orthogonal to the main axis A1 ).

[0130] It is important to prevent the locking shifter 530 from moving in the reverse direction after a speed ratio change.

[0131] Preferably, means are provided to hold the locking shifter 530 in a fixed position when a speed ratio is engaged and no change to a new speed ratio is planned.

[0132] These are indexing means designed to keep the locking shifter 530 in a fixed position relative to the hub 540 as long as a fork does not exert a force on the selection shifter 520 along the main axis A1 to change the speed ratio.

[0133] like Figure 2 As shown, the indexing means is in the form of a ball 536 which is held in a recessed housing in the inner surface of a finger 531 of the locking shifter 530. Three balls are provided here, one each in three fingers 531.

[0134] The balls 536 are held in the housings so that they cannot escape but are pushed outwards. Elastic return means such as springs are used for this purpose.

[0135] like Figure 2 As clearly shown, these indexing means also comprise a groove 546 recessed in the outer surface of the hub 540 at the bottom of the three notches 541 , wherein the aforementioned balls 536 can pass during a change in speed ratio.

[0136] Each groove 546 has the same depth at its two ends, but the thickness decreases between these two ends. In this way, the balls are naturally kept at the ends of these grooves 546, in the position where the locking shifter is connected to one of the idler gears 22, 23.

[0137] Thus, the means for elastically returning the balls to the outside make it possible to block the locking shifter 530 relative to the hub 540 to a certain extent, but cannot prevent the shifter from sliding relative to the hub 540 during a speed ratio change.

[0138] At this stage it should be noted that there is no torque interruption during the change from the first speed ratio to the second speed ratio.Torque transfer during acceleration is initially achieved by locking the fingers of the shifter 530 so that the selector shifter 520 can be disengaged by the selector device 510 under load.

[0139] When shifting from the second speed ratio to the first speed ratio, it is necessary to reduce the torque applied by the motor, but this reduction is natural because the speed ratio is shifted when the rpm of the motor decreases.

[0140] The selected speed ratio is locked for a very short time, depending on the speed difference between the first speed and the second speed during the speed ratio change. For example, a speed difference of 3000 rpm results in a lock time of less than 0.01 seconds.

[0141] Preferably, once the speed of the main shaft exceeds a first predetermined threshold or is lower than a second predetermined threshold, the second predetermined threshold being slightly lower than the first predetermined threshold (for example, between 90% and 98% of the first threshold), the speed ratio change will be automatically controlled.

[0142] In this way, it will be possible to dimension the torque limiter so that it performs its function in an optimal manner, taking into account the speed at which it will operate.

[0143] The invention is in no way limited to the embodiments described and shown, but a person skilled in the art will know how to apply any variant in accordance with the invention.

[0144] Often, an active system (such as a controlled clutch) can be used instead of a (passive) torque limiter.

Claims

1. A shaft coupling device (20), comprising: A main shaft (21) oriented along a main axis (A1), two idler gears (22, 23) mounted to rotate freely on the main shaft (21) around the main axis (A1), and a coupling system (50) interposed between the two idler gears (22, 23), Characterized in that the connection system (50) comprises: - a hub (540) rotatably fixed to the spindle (21), a selector shifter (520) slidably mounted relative to the hub (540) along the main axis (A1) between a position coupled to one of the idler gears (22, 23) and a position coupled to the other of the idler gears (22, 23), and - means (510) for moving the selector shifter (520) from one of the two coupled positions to the other, a locking shifter (530) slidably mounted relative to the hub (540) along the main axis (A1) between a position coupled to one of the idler gears (22, 23) and a position coupled to the other of the idler gears (22, 23), and - an ejection device (534) adapted to automatically move the locking shifter (530) from a position coupled to any one of the idler gears (22, 23) to a position coupled to the other of the idler gears (22, 23) after the selection shifter (520) has been moved from a position coupled to one of the idler gears (22, 23) to a position coupled to the other of the idler gears (22, 23).

2. The coupling device (20) according to claim 1, wherein: Each idler gear (22, 23) comprises at least one claw (220, 230) facing the other idler gear (22, 23), and wherein the selector shifter (520) and the locking shifter (530) comprise fingers (521, 531) adapted to clamp the claws (220, 230) of the idler gears (22, 23) in such a manner that when the selector shifter (520) and the locking shifter (530) are in the same position coupled to the idler gears (22, 23), the fingers (521, 531) of the selector shifter (520) and the locking shifter (530) clamp each claw (220, 230) of the idler gears (22, 23) in between.

3. The coupling device (20) according to claim 2, wherein: Each idler gear (22, 23) comprises a plurality of dogs (220, 230) evenly distributed around the main axis (A1), the dogs being greater than or equal to two, and wherein the selector shifter (520) and the locking shifter (530) comprise the same number of fingers evenly distributed around the main axis (A1).

4. The coupling device (20) according to claim 3, wherein: The angular space around the main axis (A1) defined between the two claws (220, 230) is strictly greater than twice the angular space around the main axis (A1) occupied by the finger (521) of the selector shifter (520).

5. The coupling device (20) according to any one of claims 2 to 4, wherein: The hub (540) has a plurality of notches on its outer surface distributed around the main axis (A1), the notches being suitable for guiding the sliding of the fingers (521, 531) of the selection shifter (520) and the locking shifter (530).

6. The coupling device (20) according to any one of claims 1 to 5, wherein: The ejection device (534) is adapted to mechanically displace the locking shifter (530) after the selection shifter (520) has been displaced to a position coupled with the other of the idler gears (22, 23).

7. The coupling device (20) according to claims 2 and 6, wherein: Each idle gear (22, 23) has a bevel (221, 231), and the ejection device (534) includes at least two bevels (531) on the locking shifter (530), the bevels (531) being adapted to slide against the bevels (221, 231) of any one of the idle gears (22, 23) after the selection shifter (520) has moved to a position coupled with the other of the idle gears (22, 23).

8. The coupling device (20) according to any one of claims 1 to 7, wherein: The locking shifter (530) comprises an indexing device (536) adapted to block the locking shifter (530) along the main axis (A1) when the ejection device (534) is not in operation.

9. The coupling device (20) according to claim 8, wherein: The indexing device (536) includes at least one protruding element, preferably a rolling element, located on one of the locking shifter (530) and the hub (540), and when the locking shifter (530) moves from one coupled position to another position, the protruding element extends in a groove (546) having a variable depth and recessed in the other of the locking shifter (530) and the hub (540).

10. The coupling device (20) according to any one of claims 1 to 9, wherein: The selector shifter (520) and the locking shifter (530) are shaped in such a way that, in order to move from one coupled position to another, the distance covered by the selector shifter (520) is strictly greater than the distance covered by the locking shifter (530) when moving from one coupled position to another, preferably twice as great.

11. A reduction gearbox (1), comprising a driving shaft (10) carrying fixed pinions (12, 13), characterized in that: The reduction gearbox (1) further comprises a coupling device (20) according to any one of claims 1 to 10, the idler gear (22, 23) of the coupling device (20) meshing with the fixed pinion (12, 13).

12. A motor vehicle comprising a motor, a differential (30) and a drive wheel coupled to the differential (30), characterized in that: The motor vehicle further comprises: a torque limiter (11) between the motor and the differential (30), the input of the torque limiter (11) being coupled to the motor; a reduction gearbox (1) according to claim 11, one of the prime mover shaft (10) and the main shaft (21) of the reduction gearbox (1) being coupled to the output of the torque limiter (11), and the other of the prime mover shaft (10) and the main shaft (21) of the reduction gearbox being coupled to the differential (30).

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