Transmission system

Abstract

Transmission system (1) for a vehicle, comprising: − a speed reducer (10) comprising a planetary gear train (3), the planetary gear train (3) comprising a sun gear (4); − a hollow shaft (1102); − a drive shaft (2) housed inside the hollow shaft (1102) and comprising a first rotational connection (200) with the hollow shaft (1102) and a second rotational connection (201) with the sun gear (4), the second rotational connection (201) being arranged in cantilevered fashion axially opposite the first connection (200) so as to allow radial displacement of the sun gear (4); an elastic device (8) being arranged between the hollow shaft (1102) and the drive shaft (2).

Description

[0001] Description

[0002] Title of the invention: Transmission system Technical field

[0003] [1] The present invention relates to the field of powertrains for motor vehicles, particularly for hybrid or electric vehicles. More specifically, the invention relates to a powertrain connected to a wheel via a speed reducer using a planetary gear set linked to the rotor part of the motor.

[0004] Technological background

[0005] [2] Document FR2727655A1 describes a powertrain in which a speed reducer transmits the torque delivered by a motor to the wheels of a vehicle via a planetary gear train and a differential arranged coaxially with the motor. Such a coaxial arrangement improves radial compactness, particularly compared to speed reducers using parallel gear trains.

[0006] [3] As is known, a planetary gear train inherently exhibits a statically indeterminate structure when misalignment of its components occurs, for example, due to manufacturing defects or misalignment of said components. This static indeterminacy can then cause wear, breakage, or jamming of the meshing of these components. To resolve this problem, document FR2727655A1 proposes a powertrain architecture in which the planetary gear of the planetary gear train is driven in rotation by the engine via a flexible shaft capable of transverse deflection, thereby absorbing the misalignment of the planetary gear train components.

[0007] [4] However, such shaft deflection has the disadvantage of generating significant vibrations that propagate within the speed reducer, causing impacts between gear teeth and undesirable noise. Summary

[0008] [5] In what follows, ordinal numeral adjectives are used to differentiate features. They do not define the position of a feature. Therefore, for example, a third feature of a product does not mean that the product has a first and / or a second feature.

[0009] [6] An idea underlying the invention is a transmission system that makes it possible to solve one or more technical problems of the prior art, for example the aforementioned problems.

[0010] [7] The invention relates to a vehicle transmission system comprising:

[0011] - a speed reducer comprising a planetary gear train, the planetary gear train comprising a planetary pinion;

[0012] - a hollow shaft rotating around an axis of rotation;

[0013] - a drive shaft housed wholly or partly radially inside the hollow shaft, the drive shaft having a first rotational link with the hollow shaft and a second rotational link with the planetary pinion, the second rotational link being arranged in axial cantilever opposite the first link in order to allow radial movement of the planetary pinion;

[0014] an elastic device being disposed between the hollow shaft and the drive shaft.

[0015] [8] The use of such an elastic device allows free radial movement of the planetary gear while damping radial accelerations related to the flexibility of the drive shaft. Shocks, particularly between the teeth of the planetary gear train components, are thus reduced, and therefore mechanical damage and noise produced by these shocks are significantly attenuated.

[0016] [9] For the purposes of this application:

[0017] - "axial" means "parallel to the axis of rotation";

[0018] - "radial" means "along an axis belonging to a plane orthogonal to the axis of rotation and intersecting this axis of rotation"; - "circumferential" means "around the axis of rotation";

[0019] - "rotationally linked" means "assembled so that they do not rotate relative to each other." In other words, it is a rotationally fixed joint, possibly with very little play such as spline play;

[0020] - two parts are said to be "fixed" when they are permanently immobilized relative to each other, this immobilization being able to result from the fixing of the first part on the second part directly or through one or more intermediate parts.

[0021]

[0010] According to an additional feature of the invention, the elastic device is housed in a recess arranged radially in the hollow shaft and / or in the drive shaft.

[0022]

[0011] Such a recess allows the positioning and retention of the elastic device.

[0023]

[0012] According to one aspect of the invention, the recess is an annular groove extending circumferentially.

[0024]

[0013] According to another aspect of the invention, a plurality of circumferentially distributed recesses are arranged radially in the hollow shaft and / or in the drive shaft, the plurality of recesses being configured to receive several portions of the same elastic device or several distinct elastic devices.

[0025]

[0014] According to a further feature of the invention, the elastic device is composed in whole or in part of a damping material such as elastomer, felt or plastic.

[0026]

[0015] According to a further feature of the invention, the elastic device is formed by a washer having radially oriented undulations or radially oriented blades.

[0016] These last two features make it possible to determine the shape and / or material suitable for obtaining the desired elastic, viscoelastic and damping properties for the elastic device.

[0027]

[0017] According to one aspect of the invention, the elastic device is in the form of an elastomer O-ring.

[0028]

[0018] According to another aspect of the invention, the elastic device is in the form of an annular felt ring.

[0029]

[0019] According to another aspect of the invention, the elastic device is in the form of a metal washer, in particular made of steel, which has undergone a surface hardening treatment.

[0030]

[0020] According to another aspect of the invention, the elastic device is in the form of a washer formed of radial undulations succeeding each other circumferentially.

[0031]

[0021] According to another aspect of the invention, the elastic device is in the form of a support washer provided with a plurality of radially curved lugs inserted axially into a plurality of recesses provided in the hollow shaft and / or in the drive shaft.

[0032]

[0022] According to another aspect of the invention, the elastic device is in the form of a plurality of helical springs inserted radially into a plurality of recesses, in particular cylindrical holes, provided in the hollow shaft and / or in the drive shaft.

[0033]

[0023] According to a further feature of the invention, the elastic device is configured to exert friction against the hollow shaft and / or against the drive shaft during the radial movement of the planetary gear.

[0034]

[0024] Thus, the friction generated causes energy dissipation allowing additional damping of the radial displacement of the planetary gear.

[0035]

[0025] According to an additional feature of the invention, the elastic device is mounted radially tightly between the hollow shaft and the drive shaft.

[0036]

[0026] Thanks to this latter feature, radial play is completely eliminated between the elastic device and the hollow shaft on the one hand, and between the elastic device and the drive shaft on the other. The elastic device therefore performs its damping function even for small values ​​of radial displacement of the drive shaft.

[0037]

[0027] According to an additional feature of the invention, the radial clamping preload of the elastic device is between 100 N and 2500 N, in particular between 100 N and 1500 N.

[0038]

[0028] According to a further feature of the invention, the drive shaft and the hollow shaft are assembled together with the elastic device by axial fitting, the axial fitting force being between 50 N and 250 N, in particular between 50 and 150 N.

[0039]

[0029] Thus, the clamping preload is maintained at a level that does not make press-fit assembly difficult, but is high enough to achieve the objective of the invention. Higher preload values ​​are conceivable, particularly for truck and heavy-duty vehicle transmissions.

[0040]

[0030] According to an additional feature of the invention, the elastic device generates a resisting friction torque during a relative rotation of the hollow shaft with respect to the drive shaft, said friction torque being between 1 and 10 Nm, in particular between 1 and 3 Nm.

[0041]

[0031] This last characteristic allows, in the case where the first rotating link is a splined link having circumferential play in its meshing, to ensure the damping of tangential shocks and vibrations occurring between said splines when the vehicle's transmission line operates in said circumferential play at very low torque levels.

[0042]

[0032] According to a further feature of the invention, the elastic device, the hollow shaft and the drive shaft are further configured so that part of the torque generated by the motor passes through the elastic device.

[0043]

[0033] According to an additional feature of the invention:

[0044] - the drive shaft also includes external teeth;

[0045] - the hollow shaft further comprises an internal toothing spaced radially from the external toothing and conforming to the shape of said external toothing; and the elastic device is inserted radially and circumferentially between the external toothing and the internal toothing.

[0046]

[0034] These last two characteristics allow, on the one hand, both circumferential and radial damping of the drive shaft, and on the other hand, improved mechanical strength of the drive shaft and the hollow shaft by passing part of the torque through an additional rotational link between said shafts.

[0047]

[0035] According to an additional feature of the invention:

[0048] - the hollow shaft is supported by a fixed frame, in particular a casing, via a first bearing and a second bearing, the first bearing being positioned axially further from the planetary pinion than the second bearing; and - the first rotating link is positioned axially further from the planetary pinion than the second bearing, in particular the first rotating link is positioned axially further from the planetary pinion than the first bearing.

[0049]

[0036] This relative positioning of the first and second links with respect to the bearings of the hollow shaft advantageously leads to a powertrain structure where the flexing length of the drive shaft is increased, thus making it easy to give it the desired flexibility.

[0050]

[0037] According to a further feature of the invention, the first rotating link and the second rotating link are respectively positioned on a first end and a second end axially opposite to the drive shaft.

[0051]

[0038] According to a further feature of the invention, the first bearing and / or the second bearing are needle bearings or ball bearings or roller bearings or plain bearings.

[0052]

[0039] According to a further feature of the invention, the elastic device is positioned axially between the planetary gear and the first rotating link, in particular the elastic device is positioned axially between the planetary gear and the second bearing.

[0040] Thus, the elastic device is positioned at the point where its damping effect is most effective, namely close to the planetary gear and the maximum radial displacement of the drive shaft.

[0053]

[0041] According to a further feature of the invention, the drive shaft has a bending length measured axially between the first rotating link and the second rotating link and an outside diameter, the ratio between the bending length and the outside diameter being between three and seven, in particular between four and six.

[0054]

[0042] Thanks to this last characteristic, it is possible to give the drive shaft the dimensions adapted to obtain the desired flexibility while ensuring sufficient mechanical resistance for the transmission of torque.

[0055]

[0043] By measured bending length, we mean here the minimum measurable axial length between the first rotating joint and the second rotating joint, excluding any portion of the first rotating joint and any portion of the second rotating joint.

[0056]

[0044] By outside diameter, we mean here the average outside diameter of the entire measured flexing length.

[0057]

[0045] According to an additional feature of the invention, the radial displacement of the planetary gear is between plus or minus 0.2 mm and plus or minus 0.6 mm.

[0058]

[0046] This radial displacement range makes it possible to compensate for misalignment or manufacturing tolerances of the planetary gear train components. Thanks to the flexibility of the drive shaft achieved by the invention, it is possible to reach this radial displacement value while ensuring the mechanical strength of the drive shaft.

[0059]

[0047] According to a further feature of the invention, the drive shaft is made from a plurality of cylindrical portions fixed together end to end.

[0060]

[0048] According to one aspect of the invention, the first rotational link is a splined link.

[0049] This splined link has the advantage of ensuring the transmission of torque while allowing, thanks to its small internal backlash between teeth, a possibility of a small angle of the drive shaft relative to the axis of rotation, and thus providing an additional free radial displacement of the planetary pinion positioned axially opposite the drive shaft.

[0061]

[0050] According to another aspect of the invention, the first rotational link is a welded link or a press-fit link.

[0062]

[0051] According to one aspect of the invention, the second rotating link is a monobloc link, the planetary pinion and the drive shaft being made together from the same material.

[0063]

[0052] According to another aspect of the invention, the second rotational link is a splined link or a welded link or a press-fit link.

[0064]

[0053] According to an additional feature of the invention:

[0065] - the transmission system includes a transmission casing;

[0066] - the planetary train further comprises a fixed outer toothed ring, at least one planetary pinion meshing with the planetary pinion and the outer toothed ring, and a planet carrier on which at least one planetary pinion is pivotally mounted;

[0067] - the speed reducer further includes a differential, the differential having a housing fixed to the planet carrier, the differential being configured to drive two wheel half-shafts in rotation; and

[0068] - the drive shaft is hollow and radially surrounds one of the two wheel half-shafts.

[0069]

[0054] The overall architecture thus defined makes it possible to improve the radial and axial compactness of the transmission system according to the invention, while having a speed reducer with a significant reduction ratio.

[0070]

[0055] The invention further relates to a powertrain comprising:

[0071] - a transmission system as described above;

[0072] - a motor configured to rotate the hollow shaft;

[0073] - an engine casing housing the engine.

[0056] According to an additional feature of the invention, the engine is an electric motor.

[0074]

[0057] According to a further feature of the invention, the motor is an axial flux electric motor.

[0075]

[0058] The invention is advantageously associated with an axial flux motor because the hollow shaft is structurally shorter, and therefore less flexible, for this type of motor than for radial flux motors.

[0076] Brief description of the figures

[0077]

[0059] Figure 1 is a broken cross-sectional view of an embodiment of a powertrain comprising the transmission system according to the invention.

[0078]

[0060] Figure 2 is an enlarged view of Figure 1.

[0079]

[0061] Figure 3 is an isometric view of a drive shaft of a transmission system according to the invention.

[0080]

[0062] Figure 4 is an isometric view of a first embodiment of the elastic device of a transmission system according to the invention.

[0081]

[0063] Figure 5 is an isometric view of a second embodiment of the elastic device of a transmission system according to the invention.

[0082]

[0064] Figure 6 is an isometric view of a third embodiment of the elastic device of a transmission system according to the invention.

[0083]

[0065] Figure 7 is a cross-sectional view in a plane perpendicular to the axis of rotation of a fourth embodiment of the elastic device of a transmission system according to the invention.

[0084] Description of the implementation methods

[0085]

[0066] In all the figures, identical elements or elements performing the same function are identified by the same reference numerals. The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference numeral relates to the same embodiment or that the features apply only to a single embodiment. Simple features from different embodiments can also be combined or interchanged to provide other embodiments.

[0086]

[0067] Figure 1 illustrates a powertrain 1 comprising a transmission system according to an embodiment of the invention. The powertrain 1 includes a motor 11 and a speed reducer 10 for rotating two half-shafts 13 and 14 of a vehicle axle.

[0087]

[0068] Such a powertrain 1 is for example intended for a hybrid vehicle.

[0088] Thus, powertrain 1, for example, is capable of transmitting torque from motor 11, motor 11 being an electric motor, to a rear or front axle of the vehicle, while another powertrain coupled to another motor, such as an internal combustion engine, generates torque and transmits it between this other motor and the half-shafts of the wheel axle of the vehicle's other axle. The vehicle can also be fully electric and have one or more powered axles.

[0089]

[0069] The motor 11 can be an electric motor comprising a stator 1100, a rotor 1101 and a hollow shaft 1102. The hollow shaft 1102 is rotationally linked to the rotor 1101 and rotates about an axis of rotation X. The motor 11 can be housed in a motor housing 12.

[0090]

[0070] The speed reducer 10 is intended to establish a speed ratio between the motor 11 and the wheel half-shafts 13 and 14 of the vehicle. Thus, the speed reducer 10 enables the vehicle to achieve good speed and torque performance by limiting losses, while allowing the motor 11 to operate within a favorable speed and torque range.

[0091]

[0071] For this purpose, the speed reducer 10 includes a transmission housing 100 in which are housed a drive shaft 2 having an axis of rotation X, a planetary gear train 3 and a differential 9. The drive shaft 2, the planetary gear train 3 and the differential 9 can be coaxial with the axis of rotation X.

[0092]

[0072] In the embodiment of Figure 1, the motor 11 is coaxial with the drive shaft 2 and is configured to rotate the drive shaft 2. The drive shaft 2 may be hollow. A half-shaft of the wheel 13 is coaxial with the drive shaft 2 and may pass axially inside the hollow drive shaft 2.

[0093]

[0073] As illustrated in Figure 2, the planetary gear train, also commonly referred to as an "epicyclic gear train," may comprise a planetary gear 4, an external ring gear 5, a plurality of planetary gears 6 meshing with the planetary gear 4 and the external ring gear 5, and a planetary carrier 7 having shafts 701 on which the plurality of planetary gears 6 are pivotally mounted. The external ring gear 5 may be fixed to the transmission housing 100, for example by shrink fitting.The satellite gears 6 can be double satellite gears, each comprising a large satellite gear 601 and a small satellite gear 602 having a diameter smaller than that of the large satellite gear 601, the large satellite gear 601 and the small satellite gear 602 being rotationally linked and arranged axially side by side, the large satellite gear 601 being meshed with the planetary gear 4 and the small satellite gear 602 being meshed with the outer ring gear 5. This planetary gear train configuration is known to be called a "type 2 planetary gear train".

[0094]

[0074] As illustrated in Figure 2, the differential 9 may include a housing 900 containing a set of gears 901 configured to distribute the torque supplied by the motor 11 to the wheel half-shafts 13 and 14, allowing them to rotate at different speeds. The planet carrier 7 may be formed from the same material as the differential housing 900, for example, obtained by a casting process. The differential housing 900 and / or the planet carrier 7 may be supported and guided in rotation on the transmission housing 100 via ball bearings [not shown].

[0095]

[0075] As illustrated by Figure 1, the drive shaft 2 is housed radially inside the hollow shaft 1102, the drive shaft 2 having a first rotational link 200 with the hollow shaft 1102 and a second rotational link 201 with the planetary pinion 4, the second rotational link 201 being arranged in axial cantilever opposite the first link 200 in order to allow radial movement of the planetary pinion 4.

[0096]

[0076] In this embodiment, the first rotating joint 200 is a splined joint. The male part of the splines 200 is formed on the drive shaft 2 and cooperates with the female part of the splines 200 formed on the hollow shaft 1102. The second rotating joint 201 is here a monobloc joint, the planetary gear 4 and the drive shaft 2 being formed from a single piece of material.

[0097]

[0077] The hollow shaft 1102 can be supported by the motor housing 12 via a first bearing 15, here a ball bearing, and a second bearing 16, here a roller bearing. The first bearing 15 can be positioned axially further from the planetary gear 4 than the second bearing 16. The first rotating link 200 can be positioned axially further from the planetary gear 4 than the second bearing 16. The first rotating link 200 is also positioned axially further from the planetary gear 4 than the first bearing 15.

[0098]

[0078] As can be seen in Figure 3, the drive shaft 2 has a bending length L measured axially between the first rotating link 200 and the second rotating link 201 and an outside diameter D, the ratio between the bending length L and the outside diameter D being between three and seven, in particular between four and six.

[0099]

[0079] An elastic device 8 is disposed between the hollow shaft 1102 and the drive shaft 2 so as to dampen the radial displacement of the planetary gear 4. As can be seen in Figure 2, the elastic device 8 can be housed in a recess, here an annular groove 1103, formed radially in the hollow shaft 1102. The elastic device 8 can be radially press-fitted between the hollow shaft 1102 and the drive shaft 2. Thus, the clearance provided in the annular groove 1103 can be less in the radial direction than the radial dimension of the elastic device 8 in its free state. The elastic device 8 can be positioned axially between the planetary gear 4 and the second bearing 16.

[0080] As illustrated in Figure 4, the elastic device 8 can be in the form of an annular piece made of damping material, such as here an elastomer O-ring configured to fit into the annular groove 1103.

[0100]

[0081] As illustrated in Figure 5, the elastic device 8 can be in the form of an elastic washer having radially oriented undulations 801 arranged circumferentially. This washer can, for example, be a steel washer press-fitted into the annular groove 1103. This washer can exert friction against the hollow shaft 1102 and against the drive shaft 2 during the radial movement of the planetary gear 4.

[0101]

[0082] As illustrated in Figure 6, the elastic device 8 can be in the form of a support washer 802 provided with a plurality of radially curved tabs 803 configured to fit axially into a plurality of recesses (not shown) formed in the hollow shaft 1102 and / or in the drive shaft 2. The support washer 802 can be configured to axially abut one end of the hollow shaft 1102. The tabs 803 can be press-fitted and exert friction against the hollow shaft 1102 and the drive shaft 2 during the radial movement of the planetary gear 4.

[0102]

[0083] As illustrated in Figure 7, the elastic device 8 can be inserted radially and circumferentially between an external tooth 202 of the drive shaft 2 and an internal tooth 1104 of the hollow shaft 1102. The internal tooth 1104 can be spaced radially from the external tooth and can conform to the shape of the external tooth 1104. Thus, the elastic device 8 can dampen displacements, shocks, or vibrations in both the radial and circumferential directions. The elastic device 8 can be made of a material having elastic properties, such as a plastic or elastomer, and fixed to the hollow shaft 1102 or the drive shaft 2 by press-fitting or overmolding.

[0103]

[0084] It is emphasized that all features, as they are apparent to a person skilled in the art from the present description, drawings and attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, can be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances make such combinations impossible or meaningless.

[0104]

[0085] The use of the verb "comporter", "comprendre" and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0105]

[0086] In the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Demands 1. Vehicle transmission system comprising: - a speed reducer (10) comprising a planetary gear train (3), the planetary gear train (3) comprising a planetary pinion (4); - a hollow shaft (1102) rotating around an axis of rotation (X); - a drive shaft (2) housed wholly or partly radially inside the hollow shaft (1102), the drive shaft (2) having a first rotational link (200) with the hollow shaft (1102) and a second rotational link (201) with the planetary pinion (4), the second rotational link (201) being arranged in axial cantilever opposite the first link (200) in order to allow radial movement of the planetary pinion (4); characterized in that an elastic device (8) is disposed between the hollow shaft (1102) and the drive shaft (2).

2. Transmission system according to claim 1, wherein the elastic device (8) is housed in a recess (1103), in particular an annular groove, arranged radially in the hollow shaft (1102) and / or in the drive shaft [2].

3. Transmission system according to any one of the preceding claims, wherein the elastic device (8) is composed in whole or in part of a damping material such as elastomer, felt or plastic.

4. Transmission system according to any one of the preceding claims, wherein the elastic device (8) is formed by a washer having radially oriented undulations (801) or radially oriented blades (803).

5. A transmission system according to any one of the preceding claims, wherein: - the hollow shaft (1102) is supported by a fixed frame, in particular a housing (12), via a first bearing (15) and a second bearing (16), the first bearing (15) being positioned axially further from the planetary pinion (4) than the second bearing (16); and- the first rotating link (200) is positioned axially further from the planetary pinion (4) than the second bearing (16), in particular the first rotating link (200) is positioned axially further from the planetary pinion than the first bearing (15).

6. Transmission system according to claim 5, in which the elastic device (8) is positioned axially between the planetary pinion (4) and the first rotating link (200), in particular the elastic device (8) is positioned axially between the planetary pinion (4) and the second bearing (16).

7. Transmission system according to any one of the preceding claims, wherein the drive shaft (2) has a bending length (L) measured axially between the first rotating link (200) and the second rotating link (201) and an outside diameter (D), the ratio between the bending length (L) and the outside diameter (D) being between three and seven, in particular between four and six.

8. A transmission system according to any one of the preceding claims, wherein the first rotating link (200) is a splined link.

9. A transmission system according to any one of the preceding claims, wherein: - the transmission system includes a transmission housing (100); - the planetary train (3) further includes an external toothed ring (5) fixed to the transmission housing (100), at least one planetary pinion (6) meshing with the planetary pinion (4) and the external toothed ring (5), and a planet carrier (7) on which at least one planetary pinion (6) is pivotally mounted; - the speed reducer (10) further comprises a differential (9), the differential (9) having a housing (900) fixed to the planet carrier (7), the differential (9) being configured to drive two wheel half-shafts (13,14) in rotation; and - the drive shaft (2) is hollow and radially surrounds one of the two wheel half-shafts (13,14).

10. Transmission system according to any one of the preceding claims, wherein the elastic device (8) is configured to exert friction against the hollow shaft (1102) and / or against the drive shaft (2) during the radial movement of the planetary pinion (4).

11. Transmission system according to any one of the preceding claims, wherein the elastic device (8) is mounted radially clamped between the hollow shaft (1102) and the drive shaft (2).

12. Transmission system according to claim 11, wherein the radial clamping preload of the elastic device (8) is between 100 N and 2500 N, in particular between 100 N and 1500 N.

13. Transmission system according to any one of claims 11 or 12, wherein the elastic device (8) generates a resisting friction torque during a relative rotation of the hollow shaft (1102) with respect to the drive shaft (2), said friction torque being between 1 and 10 Nm, in particular between 1 and 3 Nm.

14. Transmission system according to any one of claims 1 to 13, wherein: - the drive shaft (2) further comprises external teeth (202); - the hollow shaft (1102) further comprises internal teeth (1104) spaced radially from the external teeth (202) and conforming to the shape of said external teeth (202); and - the elastic device (8) is inserted radially and circumferentially between the external dentition (202) and the internal dentition (1104).

15. Powertrain (11) comprising: - a transmission system according to any one of the preceding claims; - a motor (11) configured to drive the hollow shaft (1102) in rotation; And an engine casing (12) housing the engine (11).

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