Internal lubrication transmission mechanism and associated electric propulsion assembly

Abstract

The invention relates to an internal lubrication transmission mechanism (M) comprising: - a casing (40a, 40b) comprising a base (42) and a circumferential rim (43) defining an internal volume suitable for accommodating a lubricating fluid; - at least one transmission shaft (10, 20, 30) comprising a toothed pinion (11, 21, 22, 31) rotatable relative to the casing about an axis of rotation (X1, X2, X3); - a guide bearing (100a, 200a, 300a) comprising rolling elements, supporting the transmission shaft relative to the casing, wherein the guide bearing is inserted into a cylindrical cavity (41) formed in the bottom of the casing, and wherein a thermal insulation device (70) at least partially axially and / or radially covers the non-toothed portions of the transmission shaft.

Description

DESCRIPTION TITLE: INTERNALLY LUBRICATED TRANSMISSION MECHANISM AND ASSOCIATED ELECTRIC PROPULSION ASSEMBLY TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the lubrication of components arranged inside a transmission mechanism, and in particular a speed reduction mechanism. More specifically, the invention concerns the rise in temperature of the lubricating fluid within the speed reduction mechanism between the start-up of the motorized vehicle and the achievement of a stabilized temperature, the time required to achieve this stabilized temperature being reduced. The motorized vehicle may be an electrically powered vehicle, a thermally powered vehicle or even a hybrid vehicle. STATE OF THE PRIOR ART

[0002] To lubricate the components of a transmission mechanism, and in particular the rotating guide bearings and gears of such a mechanism, it is known to arrange the rotating mobile components of the mechanism inside a casing containing oil, but without the mobile components, for example a transmission shaft supporting pinions, being completely immersed in the oil. It is then the movement of the transmission mechanism which, by splashing, stirs the oil and projects it throughout the entire interior volume of the casing, to ensure the desired lubrication of the entire mechanism, including the non-immersed parts.

[0003] When the electric or hybrid vehicle is started, the transmission mechanism, all of its components and the lubricating fluid contained in the mechanism housing are at room temperature. The guide bearings supporting the rotating moving components, for example ball bearings, are lubricated and are generally crossed by the flow of lubricating fluid. As they rotate, the guide bearings heat up and the dissipated calories are evacuated by the lubricating fluid which also rises in temperature. However, after being evacuated from the guide bearing, the fluid is projected into the casing and in particular on rotating parts that are still at room temperature. Contact with rotating parts delays the rise in temperature of the lubricating fluid. The thermal inertia of the rotating parts constituting the speed reduction mechanism therefore slows down the rise in temperature of the lubricating fluid, for example lubricating oil.

[0004] For example, the thermal inertia of a speed reduction mechanism as illustrated for example in document JP2011214658 A2 is very high, so that it takes several tens of minutes for the temperature of the lubricating oil to reach stable conditions. This means that for short usage cycles of the electric or hybrid vehicle, the oil temperature may never be stabilized and potentially remain in conditions below the optimal usage conditions. During this transient phase, the internal timing of the guide bearings will not be respected due to the erratic temperature rise of the various internal components of the transmission mechanism during this transient phase. This transient temperature rise phase must be as short as possible to quickly obtain the correct axial timing of the guide bearings and thus improve their reliability. STATEMENT OF THE INVENTION

[0005] The invention aims to remedy the drawbacks of the state of the art and to propose a transmission mechanism having reduced internal thermal inertia.

[0006] To do this, according to a first aspect of the invention, a transmission mechanism with internal lubrication is proposed, comprising: - a casing comprising a base and a circumferential rim delimiting an internal volume capable of receiving a lubricating fluid; - at least one transmission shaft comprising a pinion with teeth, said transmission shaft being movable in rotation relative to the casing around an axis of rotation of the transmission shaft; - a guide bearing supporting the transmission shaft relative to the casing which comprises rolling elements, the guide bearing being inserted into a cylindrical housing arranged in the base of the casing, in which a thermal insulation device at least partially axially and / or radially covers the tooth-free parts of the transmission shaft, the thermal insulation device being located outside the cylindrical housing and interposed axially between the guide bearing and the pinion of the transmission shaft in the internal volume of the casing, the thermal conductivity of the thermal insulation device being lower than the thermal conductivity of the transmission shaft.

[0007] The thermal conductivity of the thermal insulation device is at least two times lower than the thermal conductivity of the drive shaft, for example three times lower than the thermal conductivity of the drive shaft.

[0008] The unit of measurement for thermal conductivity is Watts per meter-kelvin (W / m K). The higher the thermal conductivity, the more heat-conducting the material is; the lower the thermal conductivity, the more insulating the material is.

[0009] The thermal insulation device allows the rotating moving components to be thermally insulated from the lubricating fluid temporarily, long enough to allow the lubricating fluid to reach its optimum operating temperature. This solution therefore aims to reduce the thermal inertia of the transmission mechanism without increasing the overall volume of the transmission mechanism.

[0010] Preferably, the transmission shaft may comprise rough machined surfaces and machined surfaces in contact with the guide bearing and / or splined surfaces in contact with a pinion, the rough machined surfaces being partly covered by the thermal insulation device. This solution aims to reduce the thermal inertia of the transmission shaft without increasing the overall volume of the transmission mechanism.

[0011] The transmission shaft may include one or more gears, which may be integral in rotation with the transmission shaft or rotate freely around the transmission shaft.

[0012] The pinion comprises a toothing offset radially relative to the axis of rotation of the transmission shaft and pinion flanks forming the junction between the central part of the transmission shaft and the toothing, the thermal insulation device being able to cover the flanks of the pinion.

[0013] Advantageously, the thermal insulation device can cover the rolling elements of the guide bearing without axial and / or radial contact, the thermal insulation device is a plate which comprises a lubricating fluid discharge slot located in the lower part of said plate relative to the axis of rotation when the transmission mechanism is in a reference operational position.

[0014] According to a variant of the invention, the thermal insulation device may be a plate fixed to the casing, the transmission shaft rotating inside the thermal insulation device.

[0015] Advantageously, the thermal insulation device may be a plate having a partially cylindrical shape of revolution, for example a sheath shape, extending axially along the axis of rotation of the transmission shaft and which surrounds a cylindrical portion of the transmission shaft.

[0016] Preferably, the thermal insulation device may be a plate having a partial disc shape which radially surrounds a flat side face of the pinion of the transmission shaft.

[0017] Advantageously, the thermal insulation device may be a plate which alternately combines the cylindrical shape of revolution, for example a sheath shape, and the disc shape so as to partially surround the transmission shaft.

[0018] Preferably, the plate-shaped thermal insulation device may comprise a central bore into which the drive shaft is inserted.

[0019] For example, the plate may include fixing lugs that rest on the casing.

[0020] For example, the plate can be fixed using fixing screws resting on the fixing lugs.

[0021] For example, the mounting brackets can be snapped onto the housing.

[0022] For example, the thermal insulation device can be an injected plastic plate

[0023] According to a variant of the invention, the thermal insulation device can be rotationally fixed to the transmission shaft.

[0024] Preferably, the thermal insulation device may be a surface coating applied to the rough machined surfaces of the drive shaft.

[0025] According to a variant of the invention, the transmission mechanism may comprise, housed in the casing, a first transmission shaft guided in rotation about a first axis of rotation by a first guide bearing and integral in rotation with at least one drive pinion, a second transmission shaft guided in rotation about a second axis of rotation by a second guide bearing and integral in rotation with at least one intermediate pinion, and a third transmission shaft guided in rotation about a third axis of rotation by a third guide bearing and integral in rotation with at least one driven pinion, the thermal insulation device at least partially axially and / or radially covers the tooth-free parts of at least two transmission shafts chosen from the first, second and third transmission shafts.

[0026] Preferably, the thermal insulation device can be crossed by at least two transmission shafts chosen from the first, the second and the third transmission shaft.

[0027] For example, the first drive shaft, the second drive shaft, and the third drive shaft are parallel to each other.

[0028] Advantageously, the third transmission shaft may be a differential body obtained by casting, comprising machined surfaces in contact with the third guide bearing, in contact with satellite gears arranged inside the differential body or even in contact with a toothed crown acting as a receiving pinion, the thermal insulation device axially and / or radially covering all or part of the rough machined surfaces.

[0029] Advantageously, the thermal insulation device can cover more than 50% of the rough machining surfaces of the third transmission shaft, for example more than 70% of the rough machining surfaces of the third transmission shaft.

[0030] Preferably, the transmission mechanism may comprise one or more gears establishing a fixed speed ratio between the drive pinion and the driven pinion, this speed ratio being greater than one.

[0031] Advantageously, the transmission mechanism may include several thermal insulation devices.

[0032] According to another aspect of the invention, it relates to an electric propulsion assembly comprising an electric motor and a transmission mechanism incorporating all or part of the characteristics mentioned above, the first transmission shaft constituting an output shaft of the electric motor or being integral in rotation with a drive shaft of the electric motor.

[0033] Advantageously, a stator of the electric motor can be fixed to the housing.

[0034] Preferably, the casing may be composed of a main casing supporting the electrical machine and a closing casing bearing on the main casing, the main casing supporting a first thermal insulation device and the closing casing supporting a second thermal insulation device.

[0035] This solution therefore aims to reduce the internal thermal inertia of the transmission mechanism without increasing the overall volume of the electric propulsion assembly.

[0036] The invention is more particularly applicable to a reduction transmission mechanism, and in particular to a speed reducer with a fixed ratio or with two reduction ratios, to a reducer with parallel shafts or even to a speed reducer of the coaxial type comprising an epicyclic train, in which the axis of rotation of the electric motor is concentric with the output shaft of the epicyclic train. BRIEF DESCRIPTION OF THE FIGURES

[0037] Other characteristics and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures. [Fig. 1] Figure 1 illustrates a section of the transmission mechanism according to a first embodiment of the invention. [Fig. 2] Figure 2 illustrates a detailed view of the transmission mechanism of Figure 1. [Fig. 3] Figure 3 illustrates another detailed view of the transmission mechanism of Figure 1. [Fig. 4] Figure 4 illustrates a view of the transmission mechanism along a substantially vertical section plane, the transmission mechanism being in the reference operational position. [Fig. 5] Figure 5 illustrates a partial view of the transmission mechanism according to a second embodiment of the invention. [Fig. 6] Figure 6 illustrates a partial view of the transmission mechanism according to a third embodiment of the invention.

[0038] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION OF EMBODIMENTS

[0039] Figures 1 to 4 illustrate an electric propulsion assembly 1, comprising an electric machine 60 and a transmission mechanism M according to a first embodiment of the invention. The transmission mechanism M is in this example a speed reduction mechanism transmitting the torque from the electric machine 60 to the wheels of the electric or hybrid vehicle.

[0040] The electrical machine 60 may be, for example, an induction electric motor, comprising a rotor 62 and a stator 61, electrically powered with three-phase alternating current by storage batteries via a current converter (not shown in FIG. 1).

[0041] The electric machine 60 is held on a casing 40a, 40b. The casing is generally composed of a main casing 40a supporting the electric machine 60 and a closing casing 40b bearing on the main casing 40a, at a joint plane 48, to seal a cavity delimited by the main casing 40a and the closing casing 40b. Each of the casings 40a, 40b comprises a base 42 and a circumferential rim 43 delimiting an internal volume capable of receiving a lubricating fluid.

[0042] The electric machine 60 rotates a first transmission shaft 10 which penetrates the main casing 40a. The first transmission shaft 10 constitutes an input shaft of the transmission mechanism M, which also comprises a second transmission shaft 20, and a third transmission shaft 30 which constitutes an output shaft of the transmission mechanism M.

[0043] The second transmission shaft 20 which constitutes an intermediate shaft of the transmission mechanism M is parallel to the input shaft 10 and the output shaft 30 of the transmission mechanism M. At the output of the speed reducer, the third transmission shaft 30 is a differential which is used to transmit and distribute a torque coming from the electric machine 60, not illustrated, to two wheel shafts 2, 3 of an axle of a motor vehicle

[0044] As illustrated in Figure 1, the input shaft 10 is aligned with the motor shaft 63 of the electrical machine 60 relative to the casing 40a, 40b, and carries at least one toothed wheel, here called motor pinion 11, linked in rotation to the transmission shaft. The input shaft 10 is guided by two guide bearings 100a, 100b in rotation so as to rotate about a first axis of rotation XI relative to the casing 40a, 40b.

[0045] The guide bearing 100a which supports the first transmission shaft relative to the casing comprises in particular rolling elements 103, in this case rolling balls. The guide bearing 100a is inserted into a cylindrical housing 41 arranged in the base 42 of the closing casing 40b.

[0046] To lubricate the various components of the transmission mechanism M, the casing 40a, 40b contains lubricating oil. The guide bearings and the pinions of the transmission shafts are partially immersed in the oil. It is then the movement of the transmission mechanism which, by splashing, stirs the oil and projects it throughout the entire interior volume of the casing, to ensure the desired lubrication of the entire mechanism, including the non-immersed parts.

[0047] The output shaft 30 carries in joint rotation at least one driven pinion 31. The output shaft 30 further comprises a fixed connection in rotation with a planet carrier of a differential 32, or constitutes the planet carrier of the differential 32. The differential 32 can be open or limited slip, depending on the desired properties. The output shaft 30 is guided by two guide bearings 300a, 300b in rotation so as to rotate around a third axis of rotation X3 relative to the casing 40a, 40b.

[0048] Like the input shaft 10 and the output shaft 30, the intermediate shaft 20 is guided by several guide bearings 200a, 200b in rotation around a second axis of rotation X2, and carries two intermediate pinions 21, 22 in joint rotation, the first intermediate pinion 21 forming a first speed reduction gear with the motor pinion 11 of the input shaft 10, and the second intermediate pinion 22 forming a second speed reduction gear with the receiving pinion 31 of the output shaft 30.

[0049] The first, second and third rotation axes XI, X2, X3 are parallel to each other. The first rotation axis XI and the third rotation axis X3 are located in a reference plane P of the transmission mechanism M. As illustrated in Figure 4, the second rotation axis X2 is located outside the reference plane P.

[0050] The driving pinion 11 has a diameter and a number of teeth smaller than the diameter and the number of teeth of the intermediate pinion 21 of the intermediate shaft 20 forming the first speed reduction gear. Similarly, the second intermediate pinion 22 of the intermediate shaft 20 forming the second speed reduction gear has a diameter and a number of teeth smaller than the diameter and the number of teeth of the receiving pinion 31 of the output shaft 30. The transmission mechanism M is therefore reducing and without changing ratio.

[0051] For the remainder of the description, a reference operational position of the transmission mechanism M is defined as the three-dimensional orientation in which the transmission mechanism M is installed in a vehicle horizontally. In this reference operational position, the second axis of rotation X2 is located above the reference plane P. In the remainder of this description, unless otherwise stated, the invention will be described in a reference operational position.

[0052] The objective of the invention is to reduce the internal thermal inertia of the transmission mechanism. For this purpose, the transmission mechanism M comprises a first thermal insulation device 70a which at least partially axially covers tooth-free parts of the first transmission shaft 10, at least partially axially and radially covers tooth-free parts of the second transmission shaft 20.

[0053] The first thermal insulation device 70a is a plate having a partially cylindrical shape of revolution, for example a sheath shape, extending axially along the axis of rotation XI and which surrounds a portion cylindrical 10a of the first transmission shaft 10. The plate 70a is fixed directly to the main casing 40a using fixing screws 75. Thus, the first transmission shaft rotates inside the thermal insulation device.

[0054] The first thermal insulation device 70a is in particular interposed axially between the guide bearing 100b and the pinion 11 of the first transmission shaft 10 in the internal volume of the main casing 40a. The first transmission shaft 10 is made of steel, like the guide bearing 100b, and the first thermal insulation device 70a is made of plastic, for example polyamide.

[0055] The thermal conductivity K2 of the first transmission shaft 10 is about 50 W / m K while the thermal conductivity Kl of the first thermal insulation device 70a is about 1 W / m K.

[0056] Since the thermal conductivity Kl of the first thermal insulation device 70a is lower than the thermal conductivity K2 of the first transmission shaft 10, the lubricating fluid projected into the casing and in particular onto the rotating part is not cooled when the electric or hybrid vehicle is started. The gain is effective when the thermal conductivity Kl of the thermal insulation device is at least twice lower than the thermal conductivity K2 of the transmission shaft.

[0057] Thanks to its thermal conductivity Kl of about 16 W / m K, stainless steel could be used for the manufacture of the first 70a thermal insulation device.

[0058] As illustrated in Figures 1 and 3, the transmission mechanism M comprises a second thermal insulation device 70b which at least partially axially and radially covers tooth-free parts of the third transmission shaft 30.

[0059] The second thermal insulation device 70b is a plate which alternately combines the cylindrical shape of revolution, for example a sheath shape, and the disc shape so as to partially surround the third transmission shaft 30. The plate 70b comprises a central bore 73 in which the transmission shaft is inserted. The plate 70b axially and radially covers a portion of the rough machined surfaces 32b of the differential 32.

[0060] The plate 70b comprises fixing lugs 74 bearing on the casing 40b. For example, the thermal insulation device 70b is a plate made of injected plastic and the fixing lugs 74 are snapped onto the casing. The plate 70b comprises stiffening ribs 76 which connect the sheath shape and the disc shape.

[0061] As illustrated in Figure 3, a disc portion of the plate 70b is interposed axially between the driven gear 31 and the first intermediate gear 21.

[0062] As illustrated in Figures 1 and 4, the transmission mechanism M comprises a third thermal insulation device 70c which at least partially axially and radially covers tooth-free portions of the first transmission shaft 10 and the second transmission shaft 20.

[0063] The third thermal insulation device 70c is located outside the cylindrical housing 41 and interposed axially between the guide bearing 100a and the pinion 11 of the first transmission shaft 10 in the internal volume of the closing casing 40b.

[0064] In this embodiment of the invention, the third thermal insulation device 70c partially covers the closing casing 40b, in an insertion zone 50 of the guide bearing 100a formed on the casing. The insertion zone 50 of the guide bearing comprises a first substantially annular rim 51 which surrounds the cylindrical housing 41 and the guide bearing 100a. The third thermal insulation device 70c is axially supported on the casing 40a, at least in the insertion zone 50 of the guide bearing. In this case, the third thermal insulation device 70c covers the closing casing 40b with contact.

[0065] The third thermal insulation device 70c is arranged on the front of the guide bearing, i.e. facing the drive pinion of the transmission shaft, which also prevents the introduction of lubricating fluid projections, such as oil, into the guide bearing. This controls the flow of lubricating fluid through the guide bearing.

[0066] In Figure 4 the transmission mechanism M is illustrated in a partial and simplified front view showing the first transmission shaft 10 guided in rotation by means of the guide bearing 100a, and in the reference operational position.

[0067] In operation, the closing casing 40b is filled with lubricating oil up to a prescribed limit which corresponds to an oil level plane at rest, this oil level plane at rest being horizontal when the transmission mechanism is in the reference operational position.

[0068] A portion of the reference plane P of the transmission mechanism M, delimited by the input shaft 10 and the output shaft 30, is located above the oil level plane at rest.

[0069] An oil collecting tank 80 is arranged between the first transmission shaft 10 and the third transmission shaft 30. The oil collecting tank 80 retains a portion of the oil sprayed by the elements of the transmission mechanism which splash in the oil. The oil collecting tank 80 has at least one upper opening 82, located above the oil level plane at rest as well as outlet orifices 81 located below the upper opening 82. It is thus possible to precisely bring a flow of lubricating oil into an upper region of the closing casing 40b.

[0070] The oil collecting tank 80 makes it possible to provide a dynamic oil level depending on the rotational speed of the input shaft 10, and more precisely, to reduce the oil level in the bottom of the casing 40a, 40b when the speed increases, by retaining a portion of the oil sprayed by the elements of the transmission mechanism which splash in the oil.

[0071] At rest, that is to say when stopped, the oil collecting tank 80 located above the oil level plane at rest is empty, and the oil level corresponds to oil level plane at rest. The maximum oil level varies only slightly when the transmission mechanism M is operating at very low speed. This is explained by low-speed rotation of the driven pinion 31, the driven pinion 31 being the largest toothed wheel of the transmission mechanism M and therefore the wheel most capable of projecting the oil through the casing 40a, 40b.

[0072] The higher the rotation of the transmission shafts, the more oil will be projected through the casing 40a, 40b by the rotation of the pinions. When the oil is projected into the casing, it falls back onto a mechanical part such as a pinion or a bearing; and / or into the bottom of the casing where the oil rests; and / or into the oil collecting tank 80 shown in Figure 4.

[0073] The oil collected by the oil collecting tank 80 is then partly directed into a groove 45 formed in the closing casing 40a in order to be conveyed into the guide bearing 100a as illustrated by arrows in FIG. 3. The groove 45 opens into the upper part of the cylindrical housing 41 of the guide bearing 100a.

[0074] To control the flow of lubricating fluid passing through the guide bearing 100a, the transmission mechanism M uses the third thermal insulation device 70c axially covering without contact the rolling elements of the guide bearing 100a. The third thermal insulation device 70c is a plate having a partial disc shape which radially surrounds a flat side face of the pinion 11 of the first transmission shaft 10 and a flat side face of the first intermediate pinion 21 of the second transmission shaft 20.

[0075] The guide bearing 100a is interposed axially between the bottom of the cylindrical housing 41 and the plate 70c. The plate 70c at least partially covers the groove 45 and comprises a lubricating fluid discharge passage 72 located in the lower part of said plate relative to the first axis. of rotation XI when the transmission mechanism is in the reference operational position.

[0076] A flow of lubricating oil is therefore conveyed towards the guide bearing 100a to a space available between the bottom of the cylindrical housing 41 and the rear face of the guide bearing 100a. By gravity, the lubricating fluid descends along the groove 45, then enters the cavity formed by the cylindrical housing of the closing casing 40b before exiting through a notch formed in the casing and through the lubricating fluid discharge passage 72 provided on the plate 70c. The lubricating fluid discharge passage 72 is a slot located in the lower part of said protective plate relative to the axis of rotation when the transmission mechanism M is in the reference operational position.

[0077] The guide bearing 100a comprises a rotating inner ring, an outer ring that is not rotating relative to the closing casing 40b, and the rolling elements 103 arranged between the two rings. The third thermal insulation device 70c covers the space available between the non-rotating outer ring and the rotating inner ring of the guide bearing.

[0078] In this example, the lubricating fluid discharge passage 72 is a slot passing right through the thickness of the protective plate. The slot 72 is elongated, more particularly oblong. The slot 72 opens opposite the space available between the outer ring and the inner ring of the guide bearing. The lubricating fluid discharge slot 72 is oriented downwards relative to the first axis of rotation XI when the transmission mechanism M is in the reference operational position. The geometry and size of the slot 72 makes it possible to adjust the lubricating fluid discharge flow rate within the guide bearing.

[0079] We will now describe with reference to Figure 5, a second embodiment of the invention, which differs from the first embodiment by a different geometry of the thermal insulation device 70 which partially covers the third transmission shaft 30. The third transmission shaft 30 is a body of differential 32 obtained by casting, comprising machined surfaces 32a in contact with the third guide bearing 300a, 300b, in contact with satellite gears 35 arranged inside the body of the differential or in contact with a toothed crown acting as a receiving pinion 31, the thermal insulation device axially and radially covering a large part of the rough machined surfaces 32b.

[0080] In this second embodiment, the thermal insulation device 70 is constituted by two plates 70d, 70e connected to each other which surround the differential 32. In the present case, the thermal insulation device is integral in rotation with the transmission shaft.

[0081] The first plate 70d has a partial cylindrical shape of revolution, for example a sheath shape, extending axially along the third axis of rotation X3 and which surrounds a cylindrical portion 30a of the third transmission shaft 30. The plate 70d comprises a central bore 73 in which the third transmission shaft is inserted. The plate 70b axially and radially covers the rough machining surfaces 32b of the differential 32. The plate 70d also comprises fixing lugs 74 snapped onto the differential 32.

[0082] The second plate 70e is partially disc-shaped which radially surrounds a portion of the differential 32. The second plate 70e is fixed to the differential by means of the assembly screws 39 of the driven pinion 31 on the differential 32. The plate 70e also comprises stiffening ribs 76.

[0083] Given the complex shapes of the two plates 70d, 70e, these can be made of injected plastic. The thermal conductivity Kl of the thermal insulation device is at least three times lower than the thermal conductivity K2 of the drive shaft. For example, the thermal conductivity of the drive shaft made of steel is 50 W / m K. In comparison, the thermal conductivity of the plate made of plastic is of the order of 0.1 W / m K. Given the difference in thermal conductivity, the lubricating fluid projected into the casing and in particular onto the rotating part is not cooled when the electric or hybrid vehicle is started.

[0084] We will now describe with reference to Figure 6, a third embodiment of the invention, which differs from the first embodiment by a different implementation of the thermal insulation device 70 which is here a surface coating applied to the rough machined surfaces 32b of the third transmission shaft 30.

[0085] The third transmission shaft 30 is a differential body 32 obtained by casting, comprising machined surfaces 32a in contact with the third guide bearing 300a, 300b, in contact with satellite gears 35 arranged inside the differential body or in contact with a toothed crown acting as a receiving pinion 31, the thermal insulation device axially and radially covering all of the rough machined surfaces 32b.

[0086] The surface coating is applied directly to the rough casting of the differential housing 32 and to the rough forging of the driven pinion body 31. During the machining operations, the surface coating is removed from all of the machined surfaces 32a but remains present on all of the rough machining surfaces 32b. The machined surfaces 32a are, for example, the bearing surfaces of the guide bearings, the splines, the teeth, the drill holes, the bearing surfaces of the planet gears 35 or the bearing surfaces of the driven pinion 31.

[0087] The surface coating is, for example, a water-based reactive prepolymer paint. This coating can be applied, for example, by electrostatic powder coating.

[0088] Alternatively, the surface coating can be Teflon-based or a ceramic coating.

[0089] The advantage of the surface coating is that it can be avoided by the complexity of the shapes of the drive shaft and in this case the shapes of the differential housing 32. The thermal conductivity Kl of the surface coating is at least three times lower than the thermal conductivity K2 of the drive shaft. For example, the thermal conductivity of the drive shaft made of steel is 50 W / m K. In comparison, the thermal conductivity of the surface coating is less than 2 W / m K. Given the difference in thermal conductivity, the lubricating fluid projected into the casing and in particular onto the rotating part is not cooled when the thermal, electric or hybrid vehicle is started.

[0090] Alternatively, the surface coating can be applied after machining.

[0091] Naturally, the examples shown in the figures and discussed above are given for illustrative purposes only and are not limiting. It is explicitly provided that the different embodiments illustrated can be combined with each other to propose others.

[0092] According to a variant not illustrated, the transmission mechanism M is of the coaxial type comprising an epicyclic train.

[0093] The transmission mechanism M described above is a reduction mechanism with a constant speed ratio to an intermediate shaft, but the invention is also intended to be applied to mechanisms with several intermediate shafts, or without an intermediate shaft, to mechanisms with several speed ratios, and / or to mechanisms whose ratio of the input speed to the output speed is less than 1.

[0094] The transmission mechanism M described above is a speed reducer mechanism with internal splash lubrication, but the invention is also intended to be applied to a speed reducer mechanism with internal pressure lubrication in which the oil is directed via pipes or hoses to the main points of the reducer to be lubricated. The oil then falls by gravity into the bottom of the casing. In this other example, a mechanical or electrical pump is used to bring the pressurized fluid into the pipes or hoses.

Claims

CLAIMS 1. Transmission mechanism (M) with internal lubrication comprising: - a casing (40a, 40b) comprising a base (42) and a circumferential rim (43) delimiting an internal volume capable of receiving a lubricating fluid; - at least one transmission shaft (10, 20, 30) comprising a pinion with teeth, said transmission shaft being movable in rotation relative to the casing around an axis of rotation (XI, X2, X3) of the transmission shaft; - a guide bearing (100a, 100b, 200a, 200b, 300a, 300b) supporting the transmission shaft relative to the casing which comprises rolling elements (103, 203, 303), the guide bearing being inserted into a cylindrical housing (41) arranged in the base (42) of the casing, characterized in that a thermal insulation device (70, 70a, 70b, 70c, 70d, 70e) at least partially axially and / or radially covers the tooth-free parts of the transmission shaft, the thermal insulation device (70, 70a, 70b, 70c, 70d, 70e) being located outside the cylindrical housing and interposed axially between the guide bearing and the pinion of the transmission shaft in the internal volume of the casing, the thermal conductivity (Kl) of the thermal insulation device being lower than the thermal conductivity (K2) of the transmission shaft.

2. Transmission mechanism (M) according to the preceding claim, characterized in that the thermal conductivity (Kl) of the thermal insulation device (70, 70a, 70b, 70c, 70d, 70e) is at least twice lower than the thermal conductivity (K2) of the transmission shaft, for example three times lower than the thermal conductivity of the transmission shaft.

3. Transmission mechanism (M) according to one of the preceding claims, characterized in that the transmission shaft (10, 20, 30) comprises rough machined surfaces (32b) and machined surfaces (32a) in contact with the guide bearing and / or splined surfaces in contact with a pinion, the surfaces raw machining being partly covered by the thermal insulation device (70, 70a, 70b, 70c, 70d, 70e).

4. Transmission mechanism (M) according to one of the preceding claims, characterized in that the thermal insulation device (70, 70a) is a plate having a partially cylindrical shape of revolution, for example a sheath shape, extending axially along the axis of rotation (XI, X2, X3) of the transmission shaft and which surrounds a cylindrical portion (10a, 20a, 30a) of the transmission shaft (10, 20, 30).

5. Transmission mechanism (M) according to one of claims 1 to 3, characterized in that the thermal insulation device (70, 70c) is a plate having a partial disc shape which radially surrounds a flat lateral face of the pinion of the transmission shaft (10, 20, 30).

6. Transmission mechanism (M) according to the combination of claims 4 and 5, characterized in that the thermal insulation device (70, 70b) is a plate which alternately combines the cylindrical shape of revolution and the disc shape so as to partially surround the transmission shaft (10, 20, 30).

7. Transmission mechanism (M) according to one of the preceding claims, characterized in that the plate-shaped thermal insulation device (70, 70a, 70b, 70c) comprises a central bore (73) into which the transmission shaft (10, 20, 30) is inserted.

8. Transmission mechanism (M) according to one of the preceding claims, characterized in that the thermal insulation device (70, 70a, 70b, 70c) is a plate fixed to the casing (40a, 40b), the transmission shaft rotating inside the thermal insulation device.

9. Transmission mechanism (M) according to one of claims 1 to 4, characterized in that the thermal insulation device (70, 70d, 70e) is rotationally integral with the transmission shaft (10, 20, 30).

10. Transmission mechanism (M) according to claim 1 to 3, characterized in that the thermal insulation device (70) is a surface coating applied to the rough machined surfaces (32b) of the transmission shaft (10, 20, 30). 11 . Transmission mechanism (M) according to one of the preceding claims, further comprising, housed in the casing (40a, 40b), a first transmission shaft (10) guided in rotation about a first axis of rotation (X1) by a first guide bearing (100a, 100b) and rotationally fixed to at least one drive pinion (11), a second transmission shaft (20) guided in rotation about a second axis of rotation (X2) by a second guide bearing (200a, 200b) and rotationally fixed to at least one intermediate pinion (21, 22), and a third transmission shaft (30) guided in rotation about a third axis of rotation (X3) by a third guide bearing (300a, 300b) and rotationally fixed to at least one driven pinion (31), the thermal insulation device (70, 70a, 70c) at least partially covers axially and / or radially the tooth-free parts of at least two transmission shafts chosen from the first,the second and third transmission shafts (10, 20, 30)., 12. Transmission mechanism (M) according to the preceding claim, in which the thermal insulation device (70, 70a, 70c) is crossed by at least two transmission shafts chosen from among the first, the second and the third transmission shaft (10, 20, 30).

13. Transmission mechanism (M) according to claim 11, characterized in that the third transmission shaft (30) is a differential body obtained by casting, comprising machined surfaces (32a) in contact with the third guide bearing, in contact with satellite gears (35) arranged inside the differential body or in contact with a toothed crown (31) acting as a receiving pinion, the thermal insulation device (70) axially and / or radially covering all or part of the rough machined surfaces (32b).

14. Transmission mechanism (M) according to one of claims 1 to 8, characterized in that the thermal insulation device (70, 70a, 70b, 70c) covers axially and / or radially without contact the rolling elements (103, 203, 303) of the guide bearing, the thermal insulation device is a plate which comprises a slot (72) for discharging lubricating fluid located in the lower part of said plate relative to the axis of rotation when the transmission mechanism (M) is in a reference operational position.

15. Electric propulsion assembly (1) comprising an electric motor (60) and a transmission mechanism (M) according to one of the preceding claims, the first transmission shaft (10) constituting an output shaft of the electric motor (60) or being rotationally integral with a drive shaft (63) of the electric motor.

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