Transmission unit with wet clutch

Abstract

A transmission unit for a saddle vehicle including a gearbox and an oil-bath clutch configured to separate the gearbox from the drive shaft of the saddle vehicle, the gearbox including: - a primary shaft operatively connected to the drive shaft and a secondary shaft operatively connected to a driving wheel of the vehicle, - toothed wheels mounted on these shafts, - at least one engagement sleeve configured to rotate integrally with the secondary shaft and to slide axially on it, the sleeve having front teeth suitable to couple with respective engagement seats provided in a first toothed wheel mounted loosely on the secondary shaft, so that, when the front teeth are engaged in the engagement seats, the first toothed wheel is suitable to rotate integrally with the secondary shaft; the transmission unit also comprises a deceleration ring arranged between the sleeve and the first toothed wheel and having a side of interaction with the sleeve and a side of sliding against said first toothed wheel.

Description

TRANSMISSION UNIT WITH WET CLUTCHDescriptionTechnical Field

[0001] The present invention relates to the field of mechanical transmission systems for vehicles, and more particularly it relates to a transmission unit with gearbox and oil -bath clutch.

[0002] The invention also relates to a saddle vehicle using this transmission unit.State of the Art

[0003] As is known, modern motorcycles are equipped with transmission units with a multi-speed gearbox of the front-dog type, combined with a clutch.

[0004] The transmission unit comprises, at the input, a clutch to which a drive shaft coming from the engine is connected, for example derived from the shaft directly exiting the engine by means of one or more transmission joints. The gearbox is operatively connected to the clutch. The clutch separates the gearbox from the drive shaft.

[0005] In the gearbox casing there are two or more shafts that carry the toothed wheels of the gearbox (the gears). In practice, there is a power input axis coming from the engine, associated with a shaft called "primary shaft", and an output axis associated with a shaft called "secondary shaft", which delivers power, by means of a transmission, to one or more wheels of the vehicle. Obviously, the input and output rotational speeds are different depending on the selected gear ratio.

[0006] In order to change the gear ratio, the gearbox comprises engagement forks, provided with guide pins, which interact with the toothed wheels of the gearbox by means of sleeves sliding on the rotation shafts on which the toothed wheels are mounted. The forks are mounted on a rotating rod, or drum, provided with grooves in which the guide pins of the forks slide. By rotating the rod, for example by means of a ratchet device connected to the gearshift lever available to the driver, a fork is moved along the rod depending on the shape of the grooves (it is in practice a guidedcoupling), thus moving the sleeve on the shaft. The sleeve can slide axially on the shaft and is however constrained to rotate integrally therewith. A toothed wheel (or two toothed wheels) may be present on a sleeve, which can therefore translate with the sleeve on the respective shaft and rotate integrally therewith. Other toothed wheels of the transmission are fixed to the respective shaft on which they are mounted (generally those at the gearbox input or output), whereas others are free to rotate about the shaft without being able to translate thereon. Each sleeve is provided with a system for engagement in the axial direction with the wheels that are free to rotate on the shafts, so that, when the sleeve is engaged with a free wheel, this wheel is prevented from rotating freely and is forced to rotate integrally with the shaft. Depending on the various engagement combinations, the various gear ratios are thus obtained.

[0007] In a typical configuration, the clutch transmits, through the primary shaft, a torque to the toothed wheel of the first speed present on the secondary shaft, which, if coupled to an engagement sleeve, can rotate integrally with the secondary shaft and therefore transmit motion to the driving wheel of the vehicle.

[0008] A typical problem of these transmission systems arises when, with the vehicle at a standstill and the gearbox in neutral, with the engine running, it is necessary to engage the first speed. When the gearbox is in neutral, the clutch is engaged and transmits power from the drive shaft to the primary shaft, while the engagement sleeve present on the secondary shaft and relating to the first speed is in a neutral position (the sleeve is not engaged with the first wheel relating to the first gear, which therefore idles on the secondary shaft as a result of the rotation of the primary shaft). The secondary shaft is therefore not rotating and thus the vehicle is stationary.

[0009] When the clutch is disengaged, that is, when the driver pulls the clutch lever, due to the viscosity of the oil bath within the clutch casing, the internal discs of the clutch tend to continue rotating, keeping in rotation the gear train directly connected to the clutch and directed towards the secondary shaft. Consequently, the toothed wheel of the first speed (mounted idle) on the secondary shaft also continues to rotate. In this situation, the engagement of the sleeve with the wheel of the first speed (that is, making that wheel integral with the secondary shaft) causes the transmission of kinetic energy from that wheel to the secondary shaft and therefore to the driving wheel of the vehicle, which tends to undergo a small annoying forward movement. In substance,there is a sudden transmission of kinetic energy accumulated by the oil-bath clutch to the driving wheel of the vehicle.

[0010] An object of the present invention is to solve the problems connected with the engagement of the first speed in a saddle vehicle which is stationary with the engine running.

[0011] In connection with this object, a further important object of the present invention is to provide a transmission unit with gearbox and oil-bath clutch, for saddle vehicles, which makes it possible to reduce the transmission of energy between the clutch and the driving wheel during the engagement of the first speed.

[0012] Another important obj ect of the present invention is to provide a transmission unit with gearbox and oil-bath clutch for saddle vehicles, which is reliable in operation.

[0013] A further important object of the present invention is to provide a transmission unit with gearbox and oil-bath clutch for saddle vehicles, which can be easily applicable even on already existing vehicles.

[0014] These and other objects, which will become clearer hereinafter, are achieved with a transmission unit for a saddle vehicle comprising a gearbox and an oil-bath clutch configured to separate the gearbox from a drive shaft of a saddle vehicle, the gearbox comprising:- a primary shaft operatively connected to the drive shaft,- a secondary shaft operatively connected to a driving wheel of the vehicle,- toothed wheels mounted on the primary shaft and on the secondary shaft, respectively,- at least one engagement sleeve configured to rotate integrally with the secondary shaft and to slide axially thereon, the sleeve having front teeth adapted to be coupled with respective engagement seats provided in a first toothed wheel mounted loosely on the secondary shaft, so that, when the front teeth are engaged in the engagement seats, the first toothed wheel is adapted to rotate integrally with the secondary shaft;characteristically, the gearbox comprises a deceleration ring, arranged between the sleeve and the first toothed wheel and configured to realize a synchronization by means of a frictional interaction between the sleeve and the first toothed wheel.

[0015] The deceleration ring makes it possible to slow down the first wheel which is idling on the secondary shaft, so that when the sleeve is engaged with the first wheel, the kinetic energy of the wheel coming from the gear train upstream of the wheel is dissipated instead of being transferred to the secondary shaft and thus to the driving wheel of the vehicle.

[0016] Preferably, the deceleration ring includes an interaction side for interacting with the sleeve and a sliding side for sliding against the first toothed wheel, wherein, during the axial engagement stroke of the sleeve for coupling to the first wheel,- in a first part of the axial engagement stroke, when the sleeve and the first toothed wheel are not yet coupled together, the sleeve is configured to push the deceleration ring against the first toothed wheel so that, with the first toothed wheel rotating, the deceleration ring reduces the rotation of the first toothed wheel by friction,- in a second part of the axial engagement stroke, following the first part of the axial engagement stroke, the front teeth of the sleeve are adapted to enter into the engagement seats, thereby rotationally coupling the first toothed wheel, the sleeve and the deceleration ring.

[0017] Advantageously, the gearbox is of the front-dog type.

[0018] The gearbox may be, for example, of the sequential or desmodromic type.

[0019] The gearbox may comprise a neutral condition, in which the gearbox does not transmit motion between the primary and secondary shafts; when the gearbox is in the neutral condition, the sleeve has, on the secondary shaft, at least one neutral position in which it is not coupled to any toothed wheel; during the axial engagement stroke, the sleeve moves from a neutral position to the position of coupling to the first wheel.

[0020] In the preferred embodiment, the gearbox is of the two-shaft type, that is, only the primary shaft and the secondary shaft.

[0021] Preferably the side of interaction of the deceleration ring with the sleeve is a coupling side, preferably of toothed type, with the sleeve.

[0022] Preferably, the first toothed wheel is the toothed wheel of largest diameter present on the secondary shaft, that is, it corresponds to the toothed wheel on the secondary shaft relating to the first speed of the gearbox.

[0023] Preferably, on thee sleeve, a second toothed wheel is integrated, configured to mesh with a toothed wheel provided on another shaft, preferably on the primary shaft; preferably, the second toothed wheel has a diameter intermediate between the maximum and minimum diameters of the toothed wheels mounted on the secondary shaft. In the preferred case, the gearbox has six speeds, and the second toothed wheel is the toothed wheel corresponding to the fifth speed.

[0024] If a second toothed wheel is integrated on the sleeve, preferably the deceleration ring has an annular crown and engagement teeth facing inwardly, i.e., extending radially from the ring crown toward the central axis of the ring, configured to mesh with the teeth of the second wheel integrated on the sleeve, wherein the teeth of the second toothed wheel are outer teeth, i.e., extending radially in a direction opposite to the axis of rotation of the secondary shaft.

[0025] Preferably, each of the engagement teeth of the deceleration ring has a front face facing the teeth of the second wheel integrated on the sleeve; this front face has a chamfered or approximately pointed shape toward the second wheel, so that, preferably, on the front face of each engagement tooth, respective approximately inclined side portions are provided, converging toward one another in the direction of the second wheel, so as to facilitate the entry of the teeth of the second wheel integrated on the sleeve between the engagement teeth of the deceleration ring.

[0026] Preferably, during the first part of the axial engagement stroke, the teeth of the second toothed wheel are adapted to push on the engagement teeth of the ring and at least partially to slide rotationally on these engagement teeth; in practice, during the pushing of the second wheel against the ring, the pushing takes place between the teeth of the one and of the other, and, by virtue of the different relative rotational speed between the decelerating ring and the sleeve, in addition to pushing there is also rotational sliding, so that, at a certain point of the first stroke, the teeth of the secondwheel are facing the space between the teeth of the deceleration ring, and a further axial movement of the sleeve causes the engagement, i.e. the meshing, of the teeth of the second toothed wheel between the engagement teeth of the deceleration ring.

[0027] According to preferred embodiments, the first toothed wheel includes a first surface of contact with the deceleration ring, wherein the first contact surface is conical, and wherein the deceleration ring has a sliding surface configured to contact the first surface, which has a complementary conical shape.

[0028] According to preferred embodiments, the first toothed wheel comprises an annular cavity, in which the deceleration ring is arranged coaxially and which is open axially toward the sleeve; preferably the annular cavity is defined at least partially between the outer toothing of the first toothed wheel and the hub of the first wheel. In practice, the deceleration ring is preferably entirely contained within the cavity, so that, in a plan view, the ring is always inside the contour of the first toothed wheel.

[0029] Preferably, the annular cavity has an annular element preventing the deceleration ring from exiting the annular cavity in the axial direction; preferably, the annular element is blocked on the first toothed wheel; preferably, the annular element is an elastic ring inserted into an annular groove cut in the first wheel, or the annular element is a toroidal body welded, glued, or press-fitted by interference on the periphery of the annular cavity.

[0030] According to preferred embodiments, the clutch, adapted to couple / to release the drive shaft of the vehicle to / from the primary shaft, is arranged coaxially to the drive shaft, or is arranged coaxially to the primary shaft.

[0031] According to another aspect, the invention relates to a saddle vehicle including a drive engine having a power output axle, and a transmission unit from the drive shaft to at least one wheel of the vehicle, wherein, between the drive shaft and the wheel of the vehicle, there is operatively arranged a transmission unit of one or more of the configurations provided above.of the

[0032] The invention will be better understood from the following description and the attached drawings, which illustrate an exemplary non-limiting embodiment of the invention. More particularly, in the drawing:Fig. 1 is a partial, schematic, axonometric view of a transmission unit for a saddle vehicle according to the invention, in which many toothed wheels of the gearbox are omitted and in which the aforementioned deceleration ring and the engagement sleeve of the first speed on the secondary shaft, according to the invention, are shown moved away from their operative position;Fig. 2 is a schematic axial section of the gearbox of a transmission unit according to the invention;Fig. 3 shows a schematic axonometric view of the secondary shaft of the transmission unit according to the previous figures, in which many toothed wheels of the gearbox are omitted and in which the deceleration ring and the engagement sleeve of the first speed are shown moved away from their operative position;Fig. 4 is a schematic axonometric view of a deceleration ring according to the invention, for a transmission unit as in the preceding figures;Fig. 5 shows a schematic axial section of a portion of the gearbox of the transmission unit of the preceding figures, in which the sleeve on the secondary shaft is in the neutral position and starts the engagement stroke toward the first toothed wheel in order to engage the first speed of the gearbox;Fig. 6 shows an enlargement of the same view of Fig. 5, in which the sleeve is moved further toward the first toothed wheel and starts the contact with the deceleration ring;Fig. 7 shows the same view as Figs. 5 and 6, in which the sleeve is moved further toward the first toothed wheel, and pushes the deceleration ring;Fig. 8 shows the same view as Fig. 5, in which the front teeth of the sleeve are inserted in their respective seats provided in the first toothed wheel;Fig. 9 shows a schematic axonometric view of the secondary shaft of the transmission unit according to the preceding figures, in which the teeth of the second toothed wheel integrated on the sleeve are facing the space between the engagement teeth of the deceleration ring;Fig. 10 shows a diagram of the interaction between the teeth of the second toothed wheel integrated on the sleeve and the engagement teeth of the deceleration ring (and also of the front teeth of the sleeve with their respective seats on the first toothed wheel to be engaged) in three successive different instants a), b) and c);Fig. 11 shows a saddle vehicle using a transmission unit according to the preceding figures;Fig. 12 shows a schematic view of a transmission unit variant with respect to the previous one, in which the clutch is associated with the primary shaft.Detailed description of embodiments

[0033] With reference to the figures mentioned above, a saddle vehicle using a transmission unit according to the invention is indicated as a whole with the letter V.

[0034] The vehicle V (Fig. 11) comprises an engine M, for example of the internalcombustion type. The transmission unit according to the invention is indicated as a whole with the reference number 10.

[0035] A power drive shaft B, or drive shaft B, which may also comprise a transmission joint G for changing the direction of the power axle at the engine output, is associated with the engine M. The drive shaft B is operatively connected to the transmission unit 10 (Fig. 1).

[0036] The transmission unit 10 comprises an oil-bath multi-disc clutch 11, for example of known type, which separates the drive shaft B from a gearbox 12. With reference to the example of Fig. 1, the clutch 11 is coaxial with the last portion of the drive shaft B. In a known manner, the clutch 11 has two operative sides, so that, when it is engaged, the two sides are connected and the clutch 11 transmits motion, whereas, when it is disengaged, the two sides are disconnected and the clutch 11 does not transmit motion.

[0037] One operative side of the clutch 11 is fixed to the drive shaft B, whereas the other operative side of the clutch is fixed to a first toothed gear wheel 13, which is coaxial with the drive shaft B (which passes through the toothed gear wheel 13).

[0038] In this example, the gearbox 12 is sequential or desmodromic and it is of the front-dog type.

[0039] In this example there are two shafts, parallel to each other, carrying toothed wheels or toothed gear wheels, which, in various combinations, provide the various speeds. In the specific example, the gearbox 12 is a two-shaft, for example six-speed, gearbox. In Fig. 1 a transmission unit 10 is shown, in which the gearbox 12 shows only those toothed wheels or toothed gear wheels that are useful for describing the invention, the others not being shown (but being visible in Fig. 2).

[0040] In particular, there is a primary shaft 14 and a secondary shaft 15, parallel to each other (and, in this example, parallel to the axis of the first toothed gear wheel 13).

[0041] The primary shaft 14 is operatively connected to the drive shaft B by means of the clutch 11. The secondary shaft 15 is operatively connected, in a known manner not shown here, to the driving wheel R of the vehicle.

[0042] More specifically, in this example a second toothed gear wheel 16 is provided on the primary shaft 14, configured to rotate always integrally with the primary shaft 14, which is meshed with the first toothed gear wheel 13.

[0043] A third toothed gear wheel 17, configured to rotate always integrally with the primary shaft 14, is also provided on the primary shaft 14.

[0044] A first toothed wheel 18 is mounted idle on the secondary shaft 15; this wheel is idling, i.e. it rotates freely on the secondary shaft 15 when it is not coupled to an engagement sleeve 20, as explained below.

[0045] This first toothed wheel 18 is constantly meshed with the third toothed gear wheel 17.

[0046] The first toothed wheel 18 is the toothed wheel of largest diameter present on the secondary shaft 15 and corresponds to the toothed wheel on the secondary shaftrelating to the first speed of the gearbox, i.e. the first speed to be engaged starting from the neutral position of the gearbox.

[0047] When the clutch is engaged and the engine of the vehicle is running, the engine transmits to the drive shaft B a torque, which is in turn transmitted to the gearbox 12 by means of the clutch 11. The clutch 11 rotates the first toothed gear wheel 13, which rotates the primary shaft 14 by means of the second toothed gear wheel 16. The rotation of the primary shaft 14 rotates the third toothed gear wheel 17, which in turn rotates the first toothed wheel 18 on the secondary shaft 15.

[0048] In should be noted that, equivalently, the clutch 11 may be arranged coaxially to the primary shaft 14, as schematically shown in Fig. 12. In this case, one operative side of the clutch is fixed to the second toothed gear wheel 16, while the other operative side of the clutch is fixed to the primary shaft (the second toothed gear wheel 16 is idling on the primary shaft, which passes through the second gear wheel). The first toothed gear wheel 13 is fixed integrally to the motor shaft B. When the engine is running, the drive shaft B rotates the first toothed gear wheel 13, which rotates the second toothed gear wheel 16. If the clutch is engaged, i.e. is adapted to transmit torque, the rotation of the second toothed gear wheel 16 is transmitted to the primary shaft 14, which rotates the first toothed wheel 18 through the third toothed gear wheel 17. If the clutch 11 is not engaged, the drive shaft B, through the first toothed gear wheel 13, rotates the second toothed gear wheel 16, which rotates coaxially to the primary shaft 14, which however remains stationary (the clutch does not transmit motion thereto).

[0049] The interaction of the primary shaft 14 with the secondary shaft 15 remains the same in the two cases of positioning of the clutch described above.

[0050] As regards the secondary shaft 15, as mentioned, the first toothed wheel 18 is mounted thereon idling, i.e. idle. The first wheel 18 is constantly meshed with the third toothed gear wheel 17 integral with the primary shaft 14.

[0051] Axially adjacent to the first toothed wheel 18 there is a first engagement sleeve 20, which, in a known manner, is slidably meshed on radial grooves 21 defined on the secondary shaft 15. The first sleeve 20 therefore rotates integrally with the secondary shaft 15 and can slide axially along it.

[0052] The first sleeve 20 has first front teeth 22, facing the first toothed wheel 18 and configured to be coupled, by means of an axial movement, with engagement seats 23 defined in the first toothed wheel 18. In practice, the first sleeve 20 is moved along the secondary shaft 15 from a position distal from the first toothed wheel 18, where the front teeth 22 are not inserted in the seats 23 and therefore the first toothed wheel 18 can rotate freely on the secondary shaft 15, to an engaged position, where the front teeth 22 of the first sleeve 20 are inserted in the engagement seats 23, so that the first toothed wheel 18 is forced to rotate integrally with the first sleeve 20 and the secondary shaft 15.

[0053] A second toothed wheel 25 is integrated on the first sleeve 20 and is configured to mesh with a third toothed wheel 26 provided on the primary shaft 14 (Fig. 2). For example, the second toothed wheel 25 has a diameter intermediate between the maximum and minimum diameters of the toothed wheels mounted on the secondary shaft and, in the specific case, corresponds to the toothed wheel of the fifth speed.

[0054] On the side of the first sleeve 20 opposite to the side from which the first front teeth 22 project, there are second front teeth 27 (see Fig. 3) facing a fourth toothed wheel 28, that is arranged free to rotate on the secondary shaft 15, and are configured to be coupled, by means of an axial movement, with respective engagement seats defined in the toothed wheel 28.

[0055] The first sleeve 20 also has an annular cavity 29 for the insertion of the end of a fork rod, not shown in the figures, associated with a gear selection device, also not shown in the figures, both for example of known type (the movement of the sleeve is obtained through the movement of the rod).

[0056] In this example, a second engagement sleeve 30, similar to the first sleeve 20, is also arranged on the secondary shaft 15, and has, on its respective sides, front teeth for respective fifth and sixth toothed wheels 31 and 32 mounted idling on the secondary shaft 15. A seventh toothed wheel 33 is integrated on the second sleeve 30.

[0057] The gearbox 11 further comprises, in this example, on the primary shaft 14, in addition to the second and third toothed gear wheels 16 and 17 coupled respectively to the first toothed gear wheel 13 and the first toothed wheel 18, an eighth toothedwheel 34 mounted idling on the shaft 14, as well as a third engagement sleeve 36 arranged between this eighth toothed wheel and the third toothed wheel 26, similar to the first and second sleeves, on which a tenth and an eleventh toothed wheels 37 and 38 are integrated. The third sleeve 36 has on opposite sides respective front teeth for coupling with the eighth and the third toothed wheels 34 and 26. Lastly, there is a fourth toothed gear wheel 39, mounted integrally with the primary shaft, meshed with the sixth toothed wheel 31 of the secondary shaft 15.

[0058] In a known manner, the position of the engagement sleeves relative to the respective toothed wheels determines the transmission ratio between the drive shaft and the gearbox output to the driving wheel of the vehicle.

[0059] With reference again to the first toothed wheel 18, a deceleration ring 40 is associated therewith, arranged between the first engagement sleeve 20 and the first toothed wheel 18.

[0060] The deceleration ring 40 performs a synchronization by effect of a frictional interaction between the engagement sleeve 20 and the first toothed wheel 18. In other words, the deceleration ring 40 provides a frictional contact between the engagement sleeve 20 and the first toothed wheel 18, by effect of the axial stroke performed by the engagement sleeve 20 toward the first toothed wheel 18. The contact between the parts produces a synchronization between the engagement sleeve 20 (static) and the first toothed wheel 18, which instead rotates (by inertial effect of the oil present in the clutch) and is thus slowed down, in order to obtain a first-speed engagement without jerks forward of the motorcycle.

[0061] More specifically, the first toothed wheel 18 includes an annular cavity 41 (Fig. 3) in which the deceleration ring 40 is arranged coaxially and which is open axially toward the first sleeve 20.

[0062] The annular cavity 41 is provided between the crown on which an external toothing 18A is defined and a hub 18B of the first toothed wheel 18. Advantageously, the deceleration ring is entirely contained within the annular cavity 41, so that, in a view along the axis of rotation, the ring 40 is always inside the contour of the first toothed wheel 18.

[0063] The annular cavity 41 advantageously comprises an annular element 42 preventing the deceleration ring 40 from exiting the annular cavity 41 in the axial direction. For example, the annular element 42 is an elastic ring inserted in an annular groove 43 (Fig. 5) formed in the crown on which the first teeth 18A of the external toothing of the first toothed wheel 18 are defined. In other embodiments, the annular element 42 may be a toroidal body welded, glued, or press-fitted by interference, on the periphery of the annular cavity 41.

[0064] The deceleration ring 40 has a first side 45 of interaction with the first sleeve 20 and a second side 46 of sliding against the first toothed wheel 18. Advantageously, the inside of the annular cavity 41 of the first toothed wheel 18 defines a first surface 47 of contact with the second sliding side 46 of the deceleration ring, and this first contact surface 47 is conical, with the convergence of the conicity oriented in the direction opposite to the position of the first sleeve 20.

[0065] The second sliding side 46 of the deceleration ring has a second surface 48 of sliding against the first toothed wheel 18, configured to come into contact with the first contact surface 47 of the first toothed wheel 18, likewise having a conical shape complementary to the first contact surface 47.

[0066] The conical shapes of the first contact surface 47 of the first toothed wheel 18 and of the second sliding surface 48 of the deceleration ring 40 are dimensionally complementary, so that the maximum and minimum diameters of the two surfaces 47 and 48 are essentially equal, with a slight clearance between the two surfaces to prevent the deceleration ring from jamming in the annular cavity 41.

[0067] In order to promote friction between the two surfaces 47 and 48, while reducing the risk of jamming of the deceleration ring 40, grooves 49, preferably circumferential, for example coaxial with the axis of the ring 40 (Fig. 4), are preferably provided on the second sliding surface 48 of the deceleration ring 40. Transverse millings 50, which interrupt the circular continuity of the grooves 49, may be optionally provided.

[0068] The deceleration ring 40 has an annular crown 51 and engagement teeth 52 facing internally, i.e. extending radially from the crown 51 toward the central axis of the deceleration ring 40. These engagement teeth 52 are configured to mesh with thesecond teeth 53 of the second toothed wheel 25 integrated on the first sleeve 20 (the teeth of the second toothed wheel, like those of all other toothed wheels of the gearbox described above, are external teeth, i.e. extending radially in the direction opposite to the axis of rotation of the secondary or primary shaft). The first interaction side 45 of the deceleration ring 40 is basically a coupling side for coupling with the first sleeve 20, as will be described in greater detailed below.

[0069] Each engagement tooth 52 of the deceleration ring 40 has a front face facing the teeth 53 of the second toothed wheel 25 integrated on the second sleeve 20. This front face comprises two approximately inclined side portions 55A and 55B (Fig. 4), converging toward each other in the direction of the second wheel 25, in practice defining a chamfered or approximately pointed shape toward the second toothed wheel 25; this configuration allows the facilitated entry of the teeth 53 of the second toothed wheel 25 between the engagement teeth 52 of the deceleration ring 40 (Fig. 9).

[0070] In this example, the side portions 55A and 55B project by an amount "s" (Fig. 6) also in the axial direction with respect to the annular crown 51 of the deceleration ring 40 (i.e. they project with respect to the side 51 A of the toothed crown 51 facing the second sleeve), which further facilitates the entry of the teeth 53 of the second toothed wheel 25 into the meshing space between the engagement teeth 52 of the deceleration ring 40.

[0071] As mentioned, the gearbox has a neutral condition, in which the gearbox does not transmit motion between the primary shaft 14 and the secondary shafts 15. When the gearbox is in the neutral condition, the first sleeve 20 has, on the secondary shaft 15, a neutral position in which it is not coupled to any toothed wheel.

[0072] In order to move from the gearbox in neutral to the first-speed engaged, the first sleeve 20 performs an axial engagement stroke, from the neutral position (for example as in Fig. 5), where it is not coupled to any toothed wheel, to the position of coupling with the first toothed wheel 18 (as in Fig. 8 and Fig. 10c), where the front teeth 22 of the first sleeve 20 are inserted in the respective seats 23 of the first toothed wheel 18.

[0073] In a first part of the axial engagement stroke, when the first sleeve 20 and the first toothed wheel 18 are not yet coupled together, the first sleeve 20 is configured (asin Figs. 6, 7, 10a, 10b) to push the deceleration ring 40 against the first toothed wheel 18 so that, with the first toothed wheel 18 rotating, the deceleration ring 40 reduces the rotation of the first toothed wheel 18 by friction.

[0074] More specifically, during the first part of the axial engagement stroke, the teeth 53 of the second toothed wheel 25 are adapted to push on the engagement teeth 52 of the deceleration ring 40 and at least partially to slide rotationally on these engagement teeth 52.

[0075] In practice, in the phase of engagement of the first speed, at the beginning for example the gearbox is in neutral with the clutch engaged (i.e. it transmits power from the drive shaft to the primary shaft) and the first engagement sleeve 20 is in a neutral position. The secondary shaft 15 is therefore not rotating and thus the vehicle is stationary. In order to engage the first speed, the clutch is disengaged (i.e. the drive shaft is disconnected from the primary shaft) and the first toothed wheel 18 remains rotating by virtue of the rotation of the primary shaft 14 due to the drag of the oil in the discs of the clutch, as indicated in the preamble of the present description. The movement of the first sleeve 20 from the neutral position toward the first toothed wheel 18 brings the second toothed wheel 25 into contact with the engagement teeth 52 of the deceleration ring 40 (as in Fig. 5 and Fig. 10a). More particularly, the second toothed wheel 25 comes into contact, with the front faces 53 A of its second teeth 53, against the engagement teeth 52 of the deceleration ring 40. For example, the front faces 53A of its second teeth 53 may also have substantially inclined side portions, converging toward each other in the direction of the first toothed wheel 18, in practice defining a chamfered or approximately pointed shape toward the first toothed wheel, in order to facilitate the entry between the engagement teeth 52 of the deceleration ring 40.

[0076] There is therefore a pushing of the second sleeve 20 (with the second toothed wheel 25 integrated thereon) against the deceleration ring 40, which is pushed against the conical sliding surface 47 of the first toothed wheel 18, with consequent frictional deceleration of the first toothed wheel. There is a different relative axial angular speed between the first wheel, deceleration ring and the second toothed wheel.

[0077] In this phase, as schematically shown in Fig. 10, by virtue of the different angular speed that is established, the second teeth 53 of the second toothed wheel 25 of the first sleeve 20, in addition to pushing, start to slide rotationally on the engagement teeth 52 of the deceleration ring 40, so that there is an angular offset between the teeth 53 of the second toothed wheel 25 and the engagement teeth. In practice, the second teeth 53 of the second toothed wheel 25 pass for example from sliding on the vertices of the front faces of the engagement teeth 52 of the ring 40 (Fig. 10a and Fig. 6 ), to the inclined portions of the faces 55A and 55B (Fig. 10b and Fig. 7), continuing to push the deceleration ring 40 against the first toothed wheel 18, until the second teeth 53 of the second toothed wheel 25 are angularly aligned with the space between the engagement teeth 52 of the deceleration ring 40. A continuation of the stroke of movement of the first sleeve 20 (and thus of the second toothed wheel 25) causes the entry, i.e. the meshing, of the second teeth 53 of the second toothed wheel 25 between the engagement teeth 52 of the deceleration ring 40 (Fig. 10c and Fig. 8). At this point, the deceleration ring 40 is forced to rotate with the second toothed wheel 25, and the second sleeve can continue its axial stroke (the engagement teeth 52 of the deceleration ring no longer offer resistance). A continuation of the stroke of movement of the first sleeve 20 brings the front teeth 22 of the sleeve to enter the seats 23 in the first toothed wheel 18, so that the latter becomes rotationally integral with the secondary shaft 15. When the clutch is engaged again, the drive shaft transmits motion to the primary shaft and then to the secondary shaft, so that torque is transmitted from the engine to the driven wheel of the vehicle.

[0078] The fact that, during the engagement of the first speed, there is a reduction (up to possible complete cancellation) of the rotational speed of the first toothed wheel 18 (rotation due to the "tail" of torque transmission from thee drive shaft due to the viscosity of the oil in the clutch) by effect of the friction of the deceleration ring pushed by the first sleeve, leads to a reduction or cancellation of the transmission of kinetic energy between the first toothed wheel and the secondary shaft 15, thereby eliminating the problem of the small movement of the vehicle at the moment of engagement by the driver of the first speed with the vehicle at a standstill.

[0079] It is understood that what is illustrated purely represents possible nonlimiting embodiments of the invention, which may vary in forms and arrangements without departing from the scope of the concept on which the invention is based. Anyreference numerals in the appended claims are provided for the sole purpose of facilitating the reading thereof in the light of the description above and the accompanying drawings and do not in any way limit the scope of protection.

Claims

Claims1. A transmission unit for a saddle vehicle including a gearbox and an oil-bath clutch (11) configured to separate the gearbox from the drive shaft (B) of the saddle vehicle, the gearbox including:- a primary shaft (14) operatively connected to the drive shaft (B),- a secondary shaft (15) operatively connected to a driving wheel of the vehicle,- toothed wheels mounted on the primary shaft (14) and the secondary shaft (15), respectively,- at least one engagement sleeve (20) configured to rotate integrally with the secondary shaft (15) and to slide axially on it, the sleeve (20) having front teeth configured to couple with respective engagement seats provided in a first toothed wheel (18) mounted loosely on the secondary shaft (15), so that, when the front teeth are engaged in the engagement seats, the first toothed wheel (18) rotates integrally with the secondary shaft (15); characterized by including a deceleration ring (40), arranged between the sleeve (20) and the first toothed wheel (18) and configured to realize synchronization by means of frictional interaction between the sleeve (20) and the first toothed wheel (18).

2. The transmission unit of claim 1, wherein the deceleration ring (40) includes an interaction side for interacting with the sleeve (20) and a sliding side for sliding against the first toothed wheel (18), wherein, during the axial stroke of the sleeve (20) for coupling to the first toothed wheel (18),- in a first part of the axial stroke, when the sleeve (20) and the first toothed wheel (18) are not yet coupled together, the sleeve (20) is configured to push the deceleration ring (40) against the first toothed wheel (18) so that, with the first toothed wheel (18) rotating, the deceleration ring (40) reduces the rotation of the first toothed wheel (18) by friction,- in a second part of the axial stroke, following the first part of the axial stroke, the front teeth of the sleeve (20) enter their respective engagement seats, rotationally coupling the first toothed wheel (18), the sleeve (20) and the deceleration ring.

3. The transmission unit of claim 1, wherein the first toothed wheel (18) corresponds to the toothed wheel on the secondary shaft (15) corresponding to the first gear of the gearbox.

4. The transmission unit of one or more of the preceding claims, wherein on the sleeve (20) there is integrated a second toothed wheel (25), configured to engage with a toothed wheel on the primary shaft (14); preferably the second toothed wheel (25) has a diameter intermediate between the maximum and minimum diameters of the toothed wheels mounted on the secondary shaft (15); preferably the gearbox provides six gears, and the second toothed wheel (25) is the toothed wheel corresponding to the fifth gear.

5. The transmission unit of claim 4, wherein the deceleration ring (40) has engagement teeth (52) facing inwardly, i.e., extending radially from the ring crown toward the central axis of the ring, configured to mesh with the teeth of the second wheel (25) integrated on the sleeve (20), and wherein the teeth of the second toothed wheel (25) are outer teeth, i.e., extending radially in a direction opposite to the axis of rotation of the secondary shaft (15).

6. The transmission unit of claim 5, wherein each engagement tooth (52) of the deceleration ring (40) has a front face facing the teeth of the second wheel integrated on the sleeve (20), which has a pointed shape toward the second wheel, so that on the front face of each engagement tooth there are provided respective side portions (55 A, 55B) inclined towards each other in the direction of the second wheel, so as to make easier for the teeth of the second wheel integrated on the sleeve (20) to enter between the engagement teeth of the deceleration ring (40).

7. The transmission unit of any one of claims 4 to 6, wherein, during the first part of the axial stroke, the teeth (53) of the second toothed wheel (25) are suitable to push the engagement teeth (52) of the decelerator ring (40) and at least partially to slide rotationally on the engagement teeth, so that, at some point in the first stroke, the teeth (53) of the second toothed wheel (25) face the space between the teeth (52) ofthe deceleration ring (40), and a further axial movement of the sleeve (20) causes the teeth of the second toothed wheel (25) to be inserted between, i.e., to engage with, the engagement teeth of the deceleration ring (40).

8. The transmission unit of one or more of the preceding claims, wherein the first toothed wheel (18) includes a first surface (47) of contact with the deceleration ring (40), the first contact surface being conical, and wherein the deceleration ring (40) has a sliding surface (48) configured to contact the first surface (47), which has a complementary conical shape.

9. The transmission unit of one or more of the preceding claims, wherein the first toothed wheel (18) includes an annular cavity (41) in which the deceleration ring(40) is coaxially arranged and which is open axially toward the sleeve (20); preferably the annular cavity (41) is defined at least partially between the outer toothing (18 A) of the first wheel and the hub (18B) of the first wheel.

10. The transmission unit of claim 9, wherein the annular cavity (41) has an annular element (42) preventing the deceleration ring (40) from exiting the annular cavity (41) in the axial direction; preferably the annular element (42) is blocked on the first wheel (18); preferably the annular element (42) is an elastic ring inserted into an annular groove (43) cut in the first wheel, or the annular element (42) is a toroidal body welded, glued, or press-fitted by interference on the periphery of the annular cavity(41).

11. The transmission unit of one or more of the preceding claims, wherein the oilbath clutch (11) is suitable to couple / to release the drive shaft (B) of the vehicle to / from the primary shaft (14), and is arranged coaxially to the drive shaft (B), or is arranged coaxially to the primary shaft (14).

12. A saddle vehicle including a drive engine having a power output axle, and a transmission unit from the drive shaft (B) to at least one wheel of the vehicle, wherein between the drive shaft (B) and the wheel of the vehicle there is operatively arranged the transmission unit of one or more of the preceding claims.

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