Differential transmission for a motor vehicle with an integrated oil pump

Abstract

The invention relates to a transmission unit (7) for a motor vehicle, comprising a differential (6) with a ring gear (2) having an axis (A1) and being provided with teeth (21), and a differential case (1), the teeth being circumscribed in a peripheral tooth cylinder (C2) passing through the top of the teeth, with a radial interval (ER) left free between the peripheral tooth cylinder and the differential case, the radial interval having a minimum dimension at the location of a pump reference angle (12), characterised in that it is provided with a convergence area (11) arranged below the reference angle, according to which the radial interval decreases in the direction of the pump reference angle, and a divergence area (13) arranged above the reference angle, according to which the radial interval increases as it moves away from the pump reference angle.

Description

DESCRIPTION TITLE OF THE INVENTION: Differential transmission for a motor vehicle with integrated oil pump

[0001] The present invention relates to a differential transmission unit for a motor vehicle, in which the oil pump function is obtained by rotating the differential input wheel, also called the crown wheel in this document. [0 Such a transmission unit can be used, for example, in an electric vehicle or a hybrid vehicle, without excluding its use in a vehicle with a conventional thermal engine. [0 It is known to form the oil pump function of a transmission unit using the crown wheel of the differential which has a substantial diameter with at least part of its teeth arranged opposite the transmission casing which contains the differential. By providing a radial gap of a fairly small dimension at this location between the teeth and the casing, the rotation of the input wheel or crown wheel projects transmission oil towards the other components of the transmission unit in order to lubricate them. Thus the oil pump is integrated and there is no specific separate part for the transmission oil pump function. It should be noted here that the oil pump function is ensured when the differential crown rotates in a direction corresponding to a forward movement of the vehicle. It should be noted that the sequences of the vehicle in reverse gear are generally very short and carried out at low speed, the need for lubrication being then much lower than in forward movement situations. Certain forward movement situations, uphill and / or in trailer towing configuration are the most critical in terms of the need for lubrication. It should also be noted that lubrication also provides a thermal function and cools the transmission components, particularly the hottest areas, e.g. bearings and contact areas between teeth. According to known solutions, the radial gap between the teeth and the casing has a constant dimension at the location of the integrated pump. To meet the requirements of the lubrication specifications, the geometric configuration of the teeth with respect to the casing is such that it also causes hydraulic drag, particularly linked to the viscosity of the oil, including for flat cruising phases which are statistically the most frequent phases of the vehicle's life cycle. The inventors sought to improve the situation, in particular to reduce hydraulic drag in order to improve the overall performance of the vehicle, while ensuring the lubrication performance required, in particular for critical phases from the point of view of lubrication and, incidentally, cooling. For this purpose, a transmission unit for a motor vehicle is proposed, comprising at least one differential with a crown wheel having an axis and being provided with radially external teeth, the transmission unit comprising a differential housing, the teeth being circumscribed in a peripheral tooth cylinder passing through the top of the teeth of the tooth, with a radial gap left free between the peripheral tooth cylinder and the differential housing, said radial gap having a minimum dimension at the location of a pump reference angle, said angle reference angle being defined around the axis with respect to a horizontal reference direction, characterized in that a convergence zone is provided arranged below the reference angle and having a first angular range (pi), according to which the radial interval decreases in the direction of the pump reference angle, and a divergence zone arranged above the reference angle and having a second angular range (p2), according to which the radial interval increases away from the pump reference angle. Expressed differently, the pump core is formed by a strait zone which plays the role of a pump when the crown rotates in a direction corresponding to the direction of travel of the vehicle.

[0009] Thanks to these arrangements, the hydraulic drag of the oil pump function is reduced. The inventors observed a reduction in hydraulic drag of up to 30% compared to the reference case with a constant radial gap in the pump area.

[0010] This results in improved energy efficiency without sacrificing lubrication performance.

[0011] From a certain rotation speed, the oil is projected far enough to lubricate all the components of the transmission unit that require it. We will see later that a buffer tank can be used.

[0012] The pump reference angle is denoted a0, said reference angle is defined as an angular position around the axis A2 relative to a horizontal reference direction denoted aH. The pump reference angle a0 is between 30° and 45°. The pump reference angle a0 is oriented downwards from the horizontal direction. It is determined so that the oil at rest is sufficiently high relative to the pump core, i.e. in the immediate vicinity of the pump core. Thus the pump can be primed reliably even if the slope of the terrain is unfavorable.

[0013] According to one embodiment, over the first angular range, the convergence zone has a convergence angle of between 20° and 40°, preferably close to 30°. According to one embodiment, the first angular range is between a0-pi and a0, a0-pi being lower than a0. The angle [31 can be chosen for example in the vicinity of 15°. It is noted that the convergence zone allows compression of the oil under the combined effect of the rotation of the crown of the differential and the reduction of the radial interval from approximately 10 mm to 3 mm. The inventors have noted that the convergence angle (01) of the order of 30° turns out to be an optimum, from the point of view of the compromise between efficiency and reduction of hydraulic drag.

[0015] According to one embodiment, over the second angular range, the divergence zone has a divergence angle of between 5° and 15°, preferably close to 10°. According to one embodiment, the second angular range (Rp2) is between a0 and a0+p2. The angle [32 can be chosen, for example, to be in the vicinity of 15°. The inventors have found that such a divergence angle proves to be beneficial for the projection of the oil into the open air and along the upper inner wall of the casing.

[0016] According to one embodiment, the minimum dimension of the radial interval is between 1.5 mm and 4.5 mm, preferably close to 3 millimeters.

[0017] In other words, the clearance between the crown and the casing is nominally 3 mm, or 3 mm +- 1.5 mm with the usual dimensional tolerances. We remain within your standard manufacturing tolerances. This takes into account thermal expansion and other dimensional variations and possible wear and tear. Preferably, the minimum dimension ER may be minimal over a point area, but it is not excluded that the minimum dimension prevails over an angular range of a few degrees forming the pump core.

[0019] According to one embodiment, the teeth are framed on their sides by sides of the casing with an axial clearance on each side of between 1.5 mm and 3.5 mm. This lateral framing contributes to the efficiency of the pump function and to the establishment of optimal performance.

[0020] According to one embodiment, the transmission unit may further comprise a reservoir chute arranged in a position above the axis. This reservoir chute receives the flow of oil projected by the pump, acts as a buffer tank and distributes oil through orifices by gravity effect.

[0021] When operating at steady state with a speed greater than or equal to 500 rpm, this reservoir chute stores up to 50% of the total quantity of oil present in the transmission unit housing. This reservoir chute is spatially arranged opposite the pump area inside the transmission unit housing, it is a place where there is more space available and it is higher which allows gravity flow from into this reservoir chute.

[0023] According to one embodiment, the reservoir chute comprises flow orifices, and where appropriate oil supply conduits above one or more points to be lubricated. This optimizes the lubricating oil paths and minimizes the total quantity of oil required for good lubrication. According to one embodiment, a stop element is provided on the inner wall of the casing to deflect the flow of oil towards the inside of the reservoir chute. This promotes good filling of the reservoir chute from the oil which trickles up against the wall of the casing following projection from the pump. According to one embodiment, the crown gear toothing is in flat engagement with the driving pinion of the intermediate gear, the driving pinion rotating on an axis (A1) parallel to the differential axis (A2). According to one embodiment, the toothing is oblique, which allows for minimal operating noise.

[0026] According to one embodiment, the oil level at rest (Z0) is approximately halfway between the crown gear axis and the lowest point of the crown gear teeth. In other words, the oil level at rest is at the height of half the crown gear radius R1. As a result, the oil at rest partially bathes the seals of the bearings that guide the crown gear and the differential body in rotation. According to one embodiment, R1 is defined as the radius of the peripheral cylinder (C1) of teeth and a low point (29) of the teeth of the crown is defined, and an operating oil level (ZF) is at a height of at most 25% of the radius R1 relative to the low point (29) of the teeth of the crown. According to one embodiment, the operating oil level (ZF) may be between 10% and 25% of the radius R1. This is significantly lower than the oil level at rest. In steady-state operation, lowering the oil level at the bottom of the crankcase reduces splashing and reduces hydraulic drag. caused by the crown splashing in the oil at the bottom of the crankcase. According to one embodiment, the operating oil level (ZF) is at most three times the height of the teeth (i.e. R1 -R2, depth of the teeth) relative to the low point of the crown teeth.

[0030] This level is much lower than the oil level at rest, and allows for a drastic reduction in hydraulic drag. Note here that the pump automatically re-primes in the event of loss of prime if the operating oil level drops too low or if a tilt of the vehicle causes the convergence zone or the pump to no longer be properly supplied.

[0031] The present invention also relates to an electric or hybrid vehicle, comprising at least one transmission unit as described previously. The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig.1] schematically illustrates a sectional view of a transmission unit in which the present invention is implemented; - [Fig.2] schematically illustrates in more detail the area of ​​the integrated oil pump; - [Fig.3] schematically illustrates a sectional view in a horizontal plane passing through the axis of the crown, according to the section line lll-lll visible in figure 2; - [Fig.4] schematically illustrates a front view of the transmission unit, the casing not being shown; - [Fig.5] shows a diagram showing the evolution of the gap left free between the peripheral teeth of the crown and the radial inner wall of the casing, as a function of the angular position; - [Fig.6] illustrates the torque kinematic chain from the engine to the heart of the differential; - [Fig.7] illustrates a simplified geometric construction at the level of the teeth of the differential crown.

[0033] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the presentation, certain elements are not necessarily represented to scale, in particular the intervals. With reference to the figures, a transmission unit 7 or simply called 'transmission' is now described. Such a transmission unit 7 can typically be used in an electric vehicle or a hybrid vehicle. It is not excluded to use it in a vehicle with a conventional thermal engine. The transmission unit can be installed in a front axle or a rear axle of a vehicle. The transmission unit can be installed in a steering or non-steering axle. In the example shown, an electric motor provides torque which enters the transmission unit, to be distributed to the two wheels of the axle. As known per se, this transmission unit is driven by an input shaft here formed by the output shaft of the electric motor. At the output of the transmission unit 7, there are two wheel shafts, one connected to the left wheel and the other connected to the right wheel of the vehicle (not shown). Only a part of one of the wheel shafts is shown in Figure 4 at reference 26

[0037] The transmission unit 7 comprises at least one differential 6. The differential 6 comprises a crown 2 and a body 22 which will be discussed later. The crown forms the input wheel of the differential. It is noted here that the attack of the crown is parallel, it is not a bevel gear. The crown 2 is provided with a toothing 21. In the example illustrated, the toothing is oblique, it is not parallel to the axis. [0 The crown 2 is driven by an intermediate gear 4. As seen in Figure 6, this intermediate gear 4 comprises a first pinion 41 of large diameter and a second pinion 42 of small diameter secured to the first pinion 41. The second pinion is permanently engaged with the teeth 21 of the crown 2 of the differential.

[0039] The rotor RM of the electric motor rotates around the axis A0. The rotor RM of the electric motor is rotationally fixed to a primary pinion 71. Said primary pinion 71 is permanently engaged with the first pinion 41 of the intermediate gear 4. Crown 2 rotates around an axis marked A2. Intermediate gear 4 rotates around an axis marked A1. Axes A1 and A2 are parallel. We also note that axis A0 is parallel to axes A1 and A2. The radially external toothing 21 is circumscribed in a first peripheral cylinder denoted C1 of toothing (see figure 7) passing through the vertices 21a of the teeth of the toothing. The first peripheral cylinder C1 has a radius R1. The peripheral cylinder C1 has a height W2 corresponding to the thickness of the toothing. A second peripheral cylinder C2 is also defined which passes through the bottom 21b of the spaces between teeth. The second peripheral cylinder C2 has a radius R2. Expressed differently, the height of the teeth is equal to R1- The transmission unit includes a differential housing 1. The casing 1 houses the differential. In addition, in the example illustrated, the casing 1 houses the intermediate gear 4 and the primary pinion 71. The casing 1 is provided with bearings receiving the bearings 81, 82, 83, 84 and 86 (see Figure 6) on which the crown and pinions are mounted as known per se, therefore not described in detail here. Crankcase 1 contains a certain amount of lubricating oil. In the example shown, this amount of oil is between 500 ml and 1 liter. Turning to Figures 3 and 6, we now discuss the geometric configuration of the area of ​​the crankcase which, together with the crown gear teeth, forms the integrated oil pump. The pump core area 12 is centered around a pump reference angle a0. The reference angle defines a reference direction Dref. The reference direction Dref is defined around the axis A2 relative to a horizontal reference direction noted aH. In the example shown, the pump reference angle a0 is between 30° and 45°, downwards relative to aH. It is determined so that the oil at rest is sufficiently high relative to the pump core, i.e. in the immediate vicinity of the pump core. Thus the pump can be reliably primed even if the slope of the terrain is unfavorable. The direction aH corresponds substantially to a local horizontal direction when the transmission unit is located in a motor vehicle and this motor vehicle is parked on horizontal local ground. The direction aH may be different from the local horizontal if the vehicle is parked on a slope, for example in an uphill or downhill lane. Similarly, dynamic effects can be taken into account, such as heavy braking or acceleration situations that momentarily move the oil in the sump to one side or the other relative to the pump area.

[0053] Depending on geometric constraints and functional specifications, the pump reference angle a0 can be adjusted downwards to ensure proper pump operation. In order to minimize hydraulic drag, the pump reference angle a0 is chosen to be as high as possible given the constraints otherwise present. The oil pump is formed by the union of a convergence zone, the aforementioned pump core zone and a divergence zone. At the location of the pump core 12, a radial gap ER of minimum dimension ERm is provided. The radial gap denoted ER is the gap left free between the peripheral cylinder C1 and the inner wall 15 of the opposite differential casing. The convergence zone 11 is arranged below the reference angle a0.

[0057] In the convergence zone 11, the radial interval decreases in the direction of the pump reference angle a0, i.e. , in the direction of the pump core zone 12. The first angular range noted Rpi extends between aO-pi and a0, aO-pi being lower than a0. The angle pi can be chosen for example in the vicinity of The divergence zone 13 is arranged above the reference angle a0. In the divergence zone 13, the radial interval increases away from the pump reference angle. The second angular range denoted Rp2 extends between a0 and a0+p2. The angle p2 can be chosen for example in the vicinity of 15°. Further down towards the bottom of the casing 10, the radial interval between the peripheral circle C1 and the inner wall of the casing is of the order of 10 mm. The toothing 21 has a width W2. The crown 2 includes a web 20 of thickness W20 smaller than the width W2 of the toothing. For example, W2 can be chosen to be at least twice as large as W20. The differential input wheel can be manufactured in several pieces or entirely in one piece. The differential input wheel is integrally connected to a differential body 22 which carries planetary gears 24 bevel gears in a known manner. Output bevel gears 23 mesh with the planetary gears 24 in a known manner. The output bevel gears 23 each drive a wheel shaft 26. At the level of the pump core 12, the minimum dimension ERm of the radial gap is chosen at 3 mm nominal. In practice, the minimum dimension ERm is between 1.5 mm and 4.5 mm, i.e. 3 mm +- 1.5 mm with dimensional tolerances. Furthermore, the teeth are framed on their sides by sides 17, 18 of the casing with an axial clearance on each side of between 1.5 mm and 3.5 mm. This lateral framing contributes to the efficiency of the pump function and to the establishment of optimal efficiency. The left and right sides are separated by a distance W8 visible in figure 3. The axial clearance E1 separates the rim of the toothing 21 of the right flank 18. The axial clearance E2 separates the rim from the toothing 21 of the left flank 17. In the illustrated example, the transmission unit 7 further comprises a reservoir chute 3. The reservoir chute 3 is arranged in a position above the axis, in an area from the axis A2 diametrically opposite to that of the direction aO. This reservoir chute 3 receives the flow of oil projected by the pump, acts as a buffer tank and distributes oil through orifices by gravity effect. From a certain rotation speed of the crown, the flow of oil projected by the pump progresses along the inner wall of the casing, it is therefore an upward parietal flow, which is illustrated in figure 1 by path P2.

[0071] The reservoir chute 3 comprises flow orifices, 33, 34 and where appropriate supply conduits 38 for the oil above one or more points to be lubricated. The section of the orifices is such that for an established regime with a crown rotation greater than or equal to 500 revolutions per minute, the filling flow rate is at least equal to the flow rate through the orifices. In addition, an overflow function can be provided which allows more oil to be poured from the reservoir filler neck so as not to let the oil level at the bottom of the crankcase drop too low, if the conditions prevailing at the pump are particularly favourable.

[0073] The reservoir chute 3 is made of plastic by molding. This allows complex shapes to be obtained from a single piece. The reservoir chute 3 includes at least one hollow area capable of retaining oil, at least temporarily, for example in the shape of a bowl or a trough. In the axial direction, the chute is wider than the crown. As seen in Figure 4, the dimension of the chute along the axial direction is marked W3, it is greater than the sum of the axial dimension W2 of the crown plus the axial dimension W4 of the first pinion 41 of the intermediate gear.

[0075] In operation, in steady state, the reservoir chute contains a significant quantity of lubricating oil. In an exemplary embodiment, the reservoir chute contains up to 40% to 50% of the total oil volume included in the casing 1. The filling level Z3 of the reservoir chute is visible in Figures 1 and 4.

[0076] Reservoir chute 3 acts as a buffer tank. Thanks to this function, a significant quantity of oil is stored in this tank and no longer in the bottom of the crankcase. This results in a significant drop in the oil level at the bottom of the crankcase where the crown splashes directly into the oil.

[0077] The oil level at rest in the bottom of the crankcase is at the level marked Z0. According to an exemplary embodiment, the level Z0 is approximately halfway between the axis A2 of the crown and a low point 29 of the crown teeth. As soon as a sufficient rotation speed of the crown is present, the oil level drops due to the presence of oil on the one hand in the pump area, then gradually in the internal volume of the reservoir chute, as well as a film present elsewhere in the lubricated parts of the components of the transmission unit. Under optimal operating conditions, the oil level in ZF operation is at a height of at most 25% of the radius R1 relative to the low point 29 of the crown teeth. According to a preferred embodiment, the oil level in ZF operation may be between 10% and 25% of the radius R1. A sufficiently low oil level in ZF operation makes it possible to very significantly limit losses by hydraulic drag due to the rotation of the bottom of the crown in the oil. It is noted that the time required to reach the established speed for the pump starting from zero speed is only one to two seconds. In practice, filling the reservoir filler neck to its cruising speed level Z3 requires less than a minute. As a result, the oil level at the bottom of the sump goes from level Z0 to level ZF in less than a minute, and the desired reduced hydraulic drag conditions are obtained very quickly.

[0081] According to a particular example, the oil level in ZF operation is at most three times the height of the teeth (i.e. R1-R2, depth of the teeth) relative to the low point 29 of the toothing 21 of the crown. Optionally, a wall flow stop system is provided to direct the flow of oil circulating against the inner wall of the casing 1 inside the reservoir chute. For this purpose, as illustrated in Figure 1, the inner wall of the casing is equipped with a groove 45 in which a tongue 35 of the reservoir chute is housed. The wall flow which rises from the slope along the path noted P2 is stopped by the tongue 35 and deflected towards the inside of the reservoir chute.

[0083] It should be noted that when the rotation speed of the crown is modest, the oil is projected not in the direction of the reservoir chute but in the direction of the intermediate gear 4 as illustrated by the path noted P1 in figure 1. On the other hand, beyond a certain speed, for example 400 revolutions per minute, the reservoir chute is supplied by the flow according to the path [0 Turning to Figure 5, it can be seen that the pump core area 12 which has the minimum radial interval ERm can extend over a range RaO of a few degrees, for example 2° to 4°. The pump body can also be a point strait with a range RaO of less than 1°.

[0085] In Figure 5, the convergence zone is shown to the left of the central zone and the divergence zone is shown to the right of the central zone. According to one embodiment, the convergence zone has a convergence angle 01 close to 30°. More generally, it can be provided that the convergence zone has a convergence angle 01 of between 20° and 40°. Depending on the type of transmission unit, the nature of the oil selected and the geometric properties of the teeth, the convergence angle 01 can be chosen at an optimal value between 20° and 40°. According to one embodiment, the divergence zone has a convergence angle 02 close to 10°. More generally, it can be provided that the divergence zone has a divergence angle 02 of between 5° and 15°. Depending on the type of transmission unit, the nature of the oil selected and the geometric properties of the teeth, the divergence angle 01 can be chosen at an optimal value between 5° and 15°.

[0088] The first angular range Rpi of convergence is between aO-pi and aO, aO-pi being lower than aO. According to one embodiment, the angle pi can be chosen for example in the vicinity of 15°. The second angular range Rp2 of divergence is between a0 and a0+p2. According to one embodiment, the angle p2 can be chosen for example in the vicinity of 15°.

[0090] For some of the above dimensions, W2 can be chosen in the range from 15 mm to 30 mm. Alternatively, W4 can be chosen in the range from 15 mm to 30 mm, which gives W3 in the range from 30 mm to 60 mm. W8 = W2 + E1 + E2, with for example the axial clearances E1 and E2 in a range from 1 mm to 4 mm. R1 can be chosen in the range from 40 mm to 60 mm. It should be noted that the proposed solution is compatible with a differential lock function option. The differential lock can be an accessory of the differential, or even arranged remotely from the differential.

Claims

CLAIMS 1. Transmission unit (7) for a motor vehicle, comprising at least one differential (6) with a crown wheel (2) having an axis (A2) and being provided with a toothing (21), the transmission unit comprising a differential housing (1), the toothing being circumscribed in a peripheral toothing cylinder (C1) passing through the top of the teeth of the toothing, with a radial gap (ER) left free between the peripheral toothing cylinder and the differential housing, said radial gap having a minimum dimension at the location of a pump reference angle (12), said reference angle being defined around the axis with respect to a horizontal reference direction, characterized in that a convergence zone (11) is provided arranged below the reference angle and having a first angular range (Rpi),according to which the radial interval decreases in the direction of the pump reference angle and a divergence zone (13) arranged above the reference angle and having a second angular range (Rp2), according to which the radial interval increases away from the pump reference angle., 2. Transmission unit according to claim 1, in which, over the first angular range, the convergence zone has a convergence angle (01) of between 20° and 40°, preferably close to 30°.

3. Transmission unit according to claim 1, in which, over the second angular range, the divergence zone has a divergence angle (02) of between 5° and 15°, preferably close to 10°.

4. Transmission unit according to any one of claims 1 to 3, in which the minimum dimension (ERm) of the radial gap is between 1.5 mm and 4.5 mm, preferably close to 3 millimeters.

5. Transmission unit according to any one of claims 1 to 4, characterized in that the teeth are framed on their sides by sides (17, 18) of the casing with an axial clearance on each side of between 1.5 mm and 3.5 mm.

6. Transmission unit according to any one of claims 1 to 5, further comprising a reservoir chute (3) arranged in a position above the axis (A2).

7. Transmission unit according to claim 6, in which the reservoir chute (3) comprises flow openings (33, 34) and, where appropriate, supply conduits (38) for the oil above one or more points to be lubricated.

8. Transmission unit according to any one of claims 1 to 7, in which an oil level at rest (Z0) is located approximately halfway between the axis (A2) of the crown and a low point (29) of the teeth of the crown.

9. Transmission unit according to any one of claims 1 to 8, in which R1 is defined as the radius of the peripheral cylinder (C1) of teeth and a low point (29) of the teeth of the crown is defined, and in which an oil level in ZF operation is at a height of at most 25% of the radius R1 relative to the low point (29) of the teeth of the crown.

10. Electric or hybrid vehicle, comprising at least one transmission unit according to any one of claims 1 to 9.

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