INTERNALLY LUBRICATED TRANSMISSION MECHANISM AND ASSOCIATED ELECTRIC PROPULSION ASSEMBLY

Abstract

An internally lubricated transmission mechanism (M) comprising: - a housing (40a, 40b) including a base (42) and a circumferential rim (43) delimiting an internal volume suitable for receiving a lubricating fluid; - at least one transmission shaft (10, 20, 30) including a pinion (11, 21, 22, 31) with teeth which is rotatable relative to the housing about an axis of rotation (X1, X2, X3); - a guide bearing (100a, 200a, 300a) supporting the transmission shaft relative to the housing which includes rolling elements, the guide bearing being inserted in a cylindrical housing (41) provided in the bottom of the housing, in which a thermal insulation device (70) covers at least partially axially and / or radially the toothless parts of the transmission shaft. (Abstract figure: 1)

Description

Title of the invention: INTERNALLY LUBRICATED TRANSMISSION MECHANISM AND ASSOCIATED ELECTRIC PROPULSION ASSEMBLY TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the lubrication of components located within a transmission mechanism, and in particular a speed reduction mechanism. More specifically, the invention focuses on the temperature rise of the lubricating fluid within the speed reduction mechanism between the start-up of the motorized vehicle and the attainment of a stabilized temperature, with the time required to reach this stabilized temperature being reduced. The motorized vehicle may be an electric vehicle, a combustion engine vehicle, or a hybrid vehicle. PREVIOUS STATE OF THE 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 place the rotating moving components of the mechanism inside a housing containing oil, but without the moving components, for example a transmission shaft supporting gears, being completely immersed in the oil. The movement of the transmission mechanism then, by splashing, mixes the oil and projects it throughout the entire internal volume of the housing, 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 its components, and the lubricating fluid contained in the mechanism's housing are at ambient temperature. The guide bearings supporting the rotating moving components, for example, ball bearings, are lubricated and are generally traversed by the flow of lubricating fluid. As they rotate, the guide bearings heat up, and the dissipated heat is carried away by the lubricating fluid, which also heats up. However, after being expelled from the guide bearing, the fluid is sprayed into the housing and, in particular, onto the rotating parts, which are still at ambient temperature. Contact with the rotating parts slows down the heating of the lubricating fluid.The thermal inertia of the rotating parts constituting the speed reduction mechanism therefore slows down the temperature rise of the lubricating fluid, for example lubricating oil.

[0004] For example, the thermal inertia of a speed reduction mechanism, as illustrated for instance in document JP2011214658 A2, is very high, such that it takes several tens of minutes for the lubricating oil temperature to reach stable conditions. This means that for short operating cycles of the electric or hybrid vehicle, the oil temperature may never stabilize and could potentially remain below optimal operating conditions. During this transitional phase, the internal alignment of the guide bearings will not be maintained due to the erratic temperature rise of the various internal components of the transmission mechanism. This temperature rise phase must be as short as possible to quickly achieve the correct axial alignment of the guide bearings and thus improve their reliability. Description of the invention

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

[0006] To this end, according to a first aspect of the invention, an internally lubricated transmission mechanism is proposed, comprising:

[0007] - a housing comprising a base and a circumferential rim delimiting a volume internal structure suitable for receiving a lubricating fluid;

[0008] - at least one transmission shaft comprising a gear with teeth, said shaft transmission being mobile in rotation relative to the casing around an axis of rotation of the transmission shaft;

[0009] - a guide bearing supporting the transmission shaft relative to the housing which includes bearing elements, the guide bearing being inserted into a cylindrical housing formed in the base of the casing,

[0010] in which a thermal insulation device covers at least partially axially and / or radially the toothless 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 housing, the thermal conductivity of the thermal insulation device being lower than the thermal conductivity of the transmission shaft.

[0011] The thermal conductivity of the thermal insulation device is at least twice as low as the thermal conductivity of the transmission shaft, for example three times lower than the thermal conductivity of the transmission shaft.

[0012] The unit of measurement for thermal conductivity is watts per meter-kelvin (W / mK). The higher the thermal conductivity, the more conductive the material is; the lower the thermal conductivity, the more insulating the material is.

[0013] The thermal insulation device allows for the temporary thermal isolation of the rotating moving components from the lubricating fluid, long enough to allow the lubricating fluid to reach its optimal operating temperature. This solution therefore aims to reduce the thermal inertia of the transmission mechanism without increasing its overall volume.

[0014] Preferably, the transmission shaft may include raw machined surfaces and machined surfaces in contact with the guide bearing and / or splined surfaces in contact with a pinion, the raw machined surfaces being partially 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.

[0015] The transmission shaft may have one or more gears, these may be fixed in rotation with the transmission shaft or rotate freely around the transmission shaft.

[0016] Advantageously, the thermal insulation device can cover without axial and / or radial contact the bearing elements of the guide bearing, the thermal insulation device is a plate which includes a lubricating fluid evacuation slot located in the lower part of said plate relative to the axis of rotation when the transmission mechanism is in a reference operating position.

[0017] According to one variant of the invention, the thermal insulation device can be a plate fixed to the casing, the transmission shaft rotating inside the thermal insulation device.

[0018] Advantageously, the thermal insulation device can be a plate having a partially sheath-like shape extending axially along the axis of rotation of the transmission shaft and surrounding a cylindrical portion of the transmission shaft.

[0019] Preferably, the thermal insulation device can be a plate having a partially disc shape which radially surrounds a flat lateral face of the transmission shaft pinion.

[0020] Advantageously, the thermal insulation device can be a plate which alternately combines the shape of a sheath and the shape of a disc so as to partially surround the transmission shaft.

[0021] Preferably, the plate-shaped thermal insulation device may include a central bore into which the transmission shaft is inserted.

[0022] For example, the plate may include fixing tabs that bear against the housing.

[0023] For example, the plate can be fixed using fixing screws bearing against the fixing tabs.

[0024] For example, the mounting tabs can be snapped onto the housing.

[0025] For example, the thermal insulation device may be a plate made of injected plastic

[0026] According to a variant of the invention, the thermal insulation device can be rotationally fixed to the transmission shaft.

[0027] Preferably, the thermal insulation device can be a surface coating applied to the raw machined surfaces of the transmission shaft.

[0028] According to a variant of the invention, the transmission mechanism may include, housed in the casing, a first transmission shaft guided in rotation around a first axis of rotation by a first guide bearing and fixed in rotation to at least one drive pinion, a second transmission shaft guided in rotation around a second axis of rotation by a second guide bearing and fixed in rotation to at least one intermediate pinion, and a third transmission shaft guided in rotation around a third axis of rotation by a third guide bearing and fixed in rotation to at least one driven pinion, the thermal insulation device covers at least partially axially and / or radially the toothless parts of at least two transmission shafts chosen from the first, second and third transmission shafts.

[0029] Preferably, the thermal insulation device can be traversed by at least two transmission shafts chosen from the first, second and third transmission shaft.

[0030] For example, the first transmission shaft, the second transmission shaft and the third transmission shaft are parallel to each other.

[0031] Advantageously, the third transmission shaft can 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 in contact with a toothed ring acting as a driven pinion, the thermal insulation device covering axially and / or radially all or part of the raw machined surfaces.

[0032] Advantageously, the thermal insulation device can cover more than 50% of the raw machining surfaces of the third transmission shaft, for example more than 70% of the raw machining surfaces of the third transmission shaft.

[0033] Preferably, the transmission mechanism may include one or more gears establishing a fixed speed ratio between the driving pinion and the driven pinion, this speed ratio being greater than one.

[0034] Advantageously, the transmission mechanism may include several thermal insulation devices.

[0035] 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 rotationally fixed to a drive shaft of the electric motor.

[0036] Advantageously, a stator of the electric motor can be fixed to the housing.

[0037] Preferably, the housing can be composed of a main housing supporting the electric machine and a closing housing bearing on the main housing, the main housing supporting a first thermal insulation device and the closing housing supporting a second thermal insulation device.

[0038] This solution therefore aims to reduce the internal thermal inertia of the transmission mechanism without increasing the overall volume of the electric propulsion system.

[0039] The invention is particularly applicable to a reduction transmission mechanism, and especially to a fixed-ratio or two-ratio speed reducer, a parallel-shaft reducer, or a coaxial-type speed reducer comprising an epicyclic gear train, in which the axis of rotation of the electric motor is concentric with the output shaft of the epicyclic gear train. BRIEF DESCRIPTION OF THE FIGURES

[0040] Other features and advantages of the invention will become apparent from the following description, with reference to the attached figures.

[0041] [Fig.1] Fig.1 illustrates a cross-section of the transmission mechanism according to a first embodiment of the invention.

[0042] [Fig.2] The [Fig.2] illustrates a detailed view of the transmission mechanism of the [Fig.1].

[0043] [Fig.3] The [Fig.3] illustrates another detailed view of the transmission mechanism of the [Fig.1].

[0044] [Fig.4] The [Fig.4] illustrates a view of the transmission mechanism along a substantially vertical cutting plane, the transmission mechanism being in the reference operational position.

[0045] [Fig.5] The [Fig.5] illustrates a partial view of the transmission mechanism according to a second embodiment of the invention.

[0046] [Fig.6] Fig.6 illustrates a partial view of the transmission mechanism according to a third embodiment of the invention.

[0047] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED description of implementation methods

[0048] 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. In this example, the transmission mechanism M is a speed reduction mechanism transmitting the torque from the electric machine 60 to the wheels of the electric or hybrid vehicle.

[0049] The electric machine 60 can be, for example, an induction electric motor, comprising a rotor 62 and a stator 61, electrically supplied with three-phase alternating current by accumulator batteries via a current converter (not shown in [Fig.1]).

[0050] The electric machine 60 is held on a housing 40a, 40b. The housing generally consists of a main housing 40a supporting the electric machine 60 and a closing housing 40b bearing against the main housing 40a, at a joint 48, to seal a cavity delimited by the main housing 40a and the closing housing 40b. Each of the housings 40a, 40b includes a base 42 and a circumferential rim 43 delimiting an internal volume suitable for receiving a lubricating fluid.

[0051] The electric machine 60 drives in rotation a first transmission shaft 10 which enters the main housing 40a. The first transmission shaft 10 constitutes an input shaft of the transmission mechanism M, which also includes a second transmission shaft 20, and a third transmission shaft 30 which constitutes an output shaft of the transmission mechanism M.

[0052] 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 used to transmit and distribute torque from the electric machine 60 (not shown) to two wheel shafts 2, 3 of an axle of a motor vehicle.

[0053] As illustrated in [Fig. 1], the input shaft 10 is aligned with the motor shaft 63 of the electric machine 60 relative to the housing 40a, 40b, and carries at least one gear, here called the motor pinion 11, which is rotationally connected 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 housing 40a, 40b.

[0054] The guide bearing 100a, which supports the first transmission shaft relative to the housing, includes, in particular, rolling elements 103, in this case, rolling balls. The guide bearing 100a is inserted into a cylindrical housing 41 formed in the base 42 of the closing housing 40b.

[0055] To lubricate the various components of the transmission mechanism M, the housing 40a, 40b contains lubricating oil. The guide bearings and the gears of the transmission shafts are partially immersed in the oil. The movement of the transmission mechanism then, by splashing, mixes the oil and projects it throughout the entire internal volume of the housing, ensuring the desired lubrication of the entire mechanism, including the non-immersed parts.

[0056] The output shaft 30 carries in joint rotation at least one driven pinion 31. The output shaft 30 also has a fixed rotational connection with a planet carrier of a differential 32, or constitutes the planet carrier of the differential 32. The differential 32 may 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 about a third axis of rotation X3 relative to the housing 40a, 40b.

[0057] 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 X 2, and carries two intermediate pinions 21, 22 in joint rotation, the first intermediate pinion 21 forming a first speed reduction gear with the driving pinion 11 of the input shaft 10, and the second intermediate pinion 22 forming a second speed reduction gear with the driven pinion 31 of the output shaft 30.

[0058] The first, second, and third axes of rotation XI, X2, X3 are parallel to each other. The first axis of rotation XI and the third axis of rotation X3 are located in a reference plane P of the transmission mechanism M. As illustrated in [Fig. 4], the second axis of rotation X2 is located outside the reference plane P.

[0059] The drive pinion 11 has a diameter and number of teeth smaller than the diameter and number of teeth of the intermediate pinion 21 of the intermediate shaft 20 forming the first speed-reducing gear. Similarly, the second intermediate pinion 22 of the intermediate shaft 20 forming the second speed-reducing gear has a diameter and number of teeth smaller than the diameter and number of teeth of the driven pinion 31 of the output shaft 30. The transmission mechanism M is therefore a reduction gear with no change in ratio.

[0060] For the remainder of this exposition, a reference operational position of the transmission mechanism M is defined as the three-dimensional orientation in in which the transmission mechanism M is installed in a horizontal vehicle. 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.

[0061] The objective of the invention is to reduce the internal thermal inertia of the transmission mechanism. To this end, the transmission mechanism M comprises a first thermal insulation device 70a which covers at least partially axially toothless portions of the first transmission shaft 10, and covers at least partially axially and radially toothless portions of the second transmission shaft 20.

[0062] The first thermal insulation device 70a is a plate having a partially sheath-like shape extending axially along the axis of rotation XI and surrounding a cylindrical portion 10a of the first transmission shaft 10. The plate 70a is fixed directly to the main housing 40a using fixing screws 75. Thus, the first transmission shaft rotates inside the thermal insulation device.

[0063] The first thermal insulation device 70a is notably interposed axially between the guide bearing 100b and the pinion 11 of the first transmission shaft 10 in the internal volume of the main housing 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.

[0064] 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.

[0065] Since the thermal conductivity Kl of the first thermal insulation device 70a is lower than the thermal conductivity K2 of the first drive shaft 10, the lubricating fluid sprayed within the housing, and particularly onto the rotating part, is not cooled during the start-up of the electric or hybrid vehicle. This benefit is realized when the thermal conductivity Kl of the thermal insulation device is at least twice as low as the thermal conductivity K2 of the drive shaft.

[0066] Thanks to its thermal conductivity Kl of about 16 W / m K, stainless steel could be used for the manufacture of the first thermal insulation device 70a.

[0067] As illustrated in figures 1 and 3, the transmission mechanism M includes a second thermal insulation device 70 b which covers at least partially axially and radially tooth-free parts of the third transmission shaft 3 0.

[0068] The second thermal insulation device 70b is a plate that alternately combines a sleeve shape and a disc shape so as to partially surround the third drive shaft 30. The plate 70b includes a central bore 73 into which the drive shaft is inserted. The plate 70b axially and radially covers a portion of the raw machined surfaces 32b of the differential 32.

[0069] The plate 70b includes mounting tabs 74 that bear against the housing 40b. For example, the thermal insulation device 70b is an injection-molded plastic plate, and the mounting tabs 74 are snapped onto the housing. The plate 70b includes stiffening ribs 76 that connect the sleeve shape and the disc shape.

[0070] As illustrated in [Fig.3], a portion of the disc of the plate 70b is interposed axially between the receiving pinion 31 and the first intermediate pinion 21.

[0071] As illustrated in Figures 1 and 4, the transmission mechanism M includes a third thermal insulation device 70c which covers at least partially axially and radially tooth-free parts of the first transmission shaft 10 and the second transmission shaft 20.

[0072] The third thermal insulation device 70 c 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 housing 40b.

[0073] In this embodiment of the invention, the third thermal insulation device 70c partially covers the closing housing 40b, within an insertion area 50 of the guide bearing 100a formed on the housing. The insertion area 50 of the guide bearing comprises a first substantially annular rim 51 that surrounds the cylindrical housing 41 and the guide bearing 100a. The third thermal insulation device 70c bears axially on the housing 40a, at least within the insertion area 50 of the guide bearing. In this configuration, the third thermal insulation device 70c covers the closing housing 40b in contact with it.

[0074] The third thermal insulation device 70c is located at the front of the guide bearing, i.e., facing the drive pinion of the transmission shaft. This also prevents the introduction of lubricating fluid, for example oil, into the guide bearing. The flow of lubricating fluid through the guide bearing is thus controlled.

[0075] Figure 4 illustrates the transmission mechanism M in a partial and simplified front view showing the first transmission shaft 10 guided in rotation via the guide bearing 100a, and in the reference operational position.

[0076] In service, the closing housing 40 b is filled with lubricating oil up to a prescribed limit which corresponds to a resting oil level plane, this resting oil level plane being horizontal when the transmission mechanism is in the reference operating position.

[0077] 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.

[0078] An oil collection reservoir 80 is provided between the first drive shaft 10 and the third drive shaft 30. The oil collection reservoir 80 retains some of the oil sprayed by the transmission mechanism components that are splashing in the oil. The oil collection reservoir 80 has at least one upper opening 82, located above the oil level plane at rest, and outlet ports 81 located below the upper opening 82. This makes it possible to precisely deliver a flow of lubricating oil to an upper area of ​​the closing housing 40b.

[0079] The oil collector reservoir 80 allows a dynamic oil level to be provided as a function of the rotational speed of the input shaft 10, and more specifically, to decrease the oil level in the bottom of the crankcase 40a, 40b when the speed increases, by retaining some of the oil sprayed by the transmission mechanism elements which bubble in the oil.

[0080] At rest, i.e., when stopped, the oil collection reservoir 80 located above the oil level plane at rest is empty, and the oil level corresponds to the oil level plane at rest. The maximum oil level varies only slightly when the transmission mechanism M operates at very low speed. This is due to the low-speed rotation of the driven pinion 31, the driven pinion 31 being the largest gear in the transmission mechanism M and therefore the gear best suited to project oil through the housing 40a, 40b.

[0081] The higher the rotation of the transmission shafts, the more oil will be projected through the casing 40a, 40b by the rotation of the gears. When the oil is projected into the casing, it falls back down • on a mechanical part such as a gear or bearing; and / or • in the bottom of the crankcase where the oil rests; and / or • in the oil collector reservoir 80 shown in [Fig.4].

[0082] The oil collected by the oil collection reservoir 80 is then partly directed into a groove 45 formed in the closing housing 40a in order to be conveyed to 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.

[0083] To control the flow of lubricating fluid through the guide bearing 100a, the transmission mechanism M uses the third thermal insulation device 70c, which axially covers the rolling elements of the guide bearing 100a without contact. The third thermal insulation device 70c is a plate partially shaped like a disc that radially surrounds a flat lateral face of the pinion 11 of the first transmission shaft 10 and a flat lateral face of the first intermediate pinion 21 of the second transmission shaft 20.

[0084] The guide bearing 100a is interposed axially between the bottom of the cylindrical housing 41 and the plate 70 c. The plate 70 c covers at least partially the groove 45 and includes a lubrication fluid evacuation 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 operating position.

[0085] A flow of lubricating oil is thus conveyed towards the guide bearing 100a to an available space 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 drain passage 72 provided on the plate 70c. The lubricating fluid drain 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 operating position.

[0086] The guide bearing 100a comprises a rotating inner ring, a non-rotating outer ring relative to the housing 40b, and the rolling elements 103 arranged between the two rings. The third thermal insulation device 70c covers the available space between the non-rotating outer ring and the rotating inner ring of the guide bearing.

[0087] In this example, the lubrication fluid drainage passage 72 is a slot extending completely through the thickness of the protective plate. The slot 72 is elongated, more specifically oblong. The slot 72 opens opposite the available space between the outer and inner rings of the guide bearing. The lubrication fluid drainage slot 72 is oriented downwards with respect to the first axis of rotation XI when the transmission mechanism M is in its reference operating position. The geometry and size of the slot 72 allow adjustment of the lubrication fluid drainage flow rate within the guide bearing.

[0088] We will now describe, with reference to [Fig. 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 shaft of transmission 30. 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 ring acting as a driven pinion 31, the thermal insulation device covering axially and radially a large part of the raw machined surfaces 32b.

[0089] In this second embodiment, the thermal insulation device 70 consists of two plates 70d, 70e connected together which surround the differential 32. In the present case, the thermal insulation device is rotationally fixed to the transmission shaft.

[0090] The first plate 70d partially has a sleeve-like shape extending axially along the third axis of rotation X3 and surrounding a cylindrical portion 30a of the third drive shaft 30. The plate 70d includes a central bore 73 into which the third drive shaft is inserted. The plate 70b axially and radially covers the raw machined surfaces 32b of the differential 32. The plate 70d also includes mounting tabs 74 that snap onto the differential 32.

[0091] The second plate 70e has a partially disc-shaped form 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 includes stiffening ribs 76.

[0092] Given the complex shapes of the two plates 70d, 70e, these can be made of injection-molded plastic. The thermal conductivity K1 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 a drive shaft made of steel is 50 W / m K. In comparison, the thermal conductivity of the plate made of plastic is on the order of 0.1 W / m K. Due to this difference in thermal conductivity, the lubricating fluid sprayed into the housing, and particularly onto the rotating part, is not cooled during the starting of the electric or hybrid vehicle.

[0093] We will now describe, with reference to [Fig.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 raw machining surfaces 32b of the third transmission shaft 30.

[0094] The third drive 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 ring acting as of receiving pinion 31, the thermal insulation device covering axially and radially all the raw machining surfaces 32b.

[0095] The surface coating is applied directly to the as-cast part of the differential housing 32 and to the as-forged part of the driven pinion body 31. During machining operations, the surface coating is removed from all machined surfaces 32a but remains present on all as-machined surfaces 32b. The machined surfaces 32a are, for example, the bearing surfaces of the guide bearings, the splines, the teeth, the drilled holes, the bearing surfaces of the planetary gears 35, or the bearing surfaces of the driven pinion 31.

[0096] The surface coating is, for example, a water-based reactive prepolymer paint. This coating can, for example, be applied by electrostatic powder coating.

[0097] Alternatively, the surface coating can be Teflon-based or a ceramic coating.

[0098] The advantage of the surface coating is that it eliminates the complexity of the drive shaft's shape and, in this case, the shape of the differential housing 32. The thermal conductivity K1 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 a steel drive shaft is 50 W / m K. In comparison, the thermal conductivity of the surface coating is less than 2 W / m K. Given this difference in thermal conductivity, the lubricating fluid sprayed into the housing, and particularly onto the rotating part, is not cooled when the internal combustion, electric, or hybrid vehicle is started.

[0099] Alternatively, the surface coating can be applied after machining.

[0100] Naturally, the examples shown in the figures and discussed above are given by way of illustration only and are not intended to be limiting. It is explicitly intended that the different embodiments illustrated may be combined to propose others.

[0101] According to an unillustrated variant, the transmission mechanism M is of coaxial type comprising an epicyclic train.

[0102] The transmission mechanism M described above is a constant speed ratio reduction mechanism with one 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 input speed to output speed is less than 1.

[0103] The transmission mechanism M described above is a speed reduction mechanism with internal splash lubrication, but the invention is also intended to be applied to a speed reduction mechanism with internal pressure lubrication In this system, the oil is directed via pipes or hoses to the main points of the gearbox requiring lubrication. The oil then falls back down by gravity to the bottom of the crankcase. In this other example, a mechanical or electric pump is used to deliver the pressurized fluid through the pipes or hoses.

Claims

1. Demands Internally lubricated transmission mechanism (M) comprising: - a housing (40a, 40b) including a base (42) and a circumferential rim (43) delimiting an internal volume suitable for receiving a lubricating fluid; - at least one transmission shaft (10, 20, 30) comprising a gear 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 housing which includes rolling elements (103, 203, 303), the guide bearing being inserted into a cylindrical housing (41) formed in the base (42) of the housing, in which a thermal insulation device (70, 70a, 70b, 70c, 70d, 70e) covers at least partially axially and / or radially the toothless portions 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 transmission shaft pinion within the internal volume of the housing, the thermal conductivity (Kl) of the device thermal insulation being lower than the thermal conductivity (K2) of the transmission shaft, characterized in that the transmission mechanism comprises, housed in the casing (40a, 40b),a first transmission shaft (10) guided in rotation about a first axis of rotation (XI) by a first guide bearing (100a, 100b) and fixed in rotation 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 fixed in rotation 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 fixed in rotation to at least one driven pinion (31), the thermal insulation device (70, 70a, 70c) covers at least partially axially and / or radially the toothless parts of at least two, drive shafts chosen from the first, second and third drive shaft (10, 20, 30).

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

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

5. Transmission mechanism (M) any one of claims 1 to 3, characterized in that the thermal insulation device (70, 70c) is a plate having a partially 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 shape of a sheath and the shape of a disc so as to partially surround the transmission shaft (10, 20, 30).

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

8. Transmission mechanism (M) according to any 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 any one of claims 1 to 4, characterized in that the thermal insulation device (70, 70d, 70e) is rotationally fixed to 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 machining surfaces (32b) of the transmission shaft (10, 20, 30).

11. Transmission mechanism (M) according to any one of the preceding claims, wherein the thermal insulation device (70, 70a, 70c) is traversed by at least two transmission shafts selected from the first, second and third transmission shaft (10, 20, 30).

12. Transmission mechanism (M) according to any one of the preceding claims, 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 ring (31) acting as a driven pinion, the thermal insulation device (70) covering axially and / or radially all or part of the raw machined surfaces (32b).

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

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

15. Electric propulsion assembly (1) according to the preceding claim, characterized in that a stator (61) of the electric motor (60) is fixed to the housing (40a, 40b).

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