Differential transmission for motor vehicles with integrated oil pump

Abstract

A motor vehicle transmission unit (7) comprising a differential (6) with a ring gear (2) having a shaft (A1) and having teeth (21), and a differential housing (1), the teeth being circumscribed within a peripheral toothed cylinder (C2) passing through the crest of the teeth, with a radial gap (ER) left free between the peripheral toothed cylinder and the differential housing, said radial gap having a minimum dimension at a pump reference angle (12), characterized in that a convergence zone (11) is arranged below the reference angle, according to which the radial gap decreases in the direction of the pump reference angle, and a divergence zone (13) is arranged above the reference angle, according to which the radial gap increases with distance from the pump reference angle. Abstract figure: Fig. 2

Description

Title of the invention: Differential transmission for motor vehicles 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 through the rotation of the differential input wheel, also called the ring gear in this document.

[0002] Such a transmission unit can, for example, be used in an electric vehicle or a hybrid vehicle, without excluding its use in a conventional internal combustion engine vehicle.

[0003] 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.

[0004] It should be specified here that the oil pump function is ensured when the differential ring gear rotates in a direction corresponding to the vehicle's forward movement. It should be noted that reverse vehicle sequences are generally very short and performed at low speeds, the lubrication requirement being therefore much lower than in forward driving situations. Certain forward driving situations, such as uphill driving and / or trailer towing, are the most critical with regard to lubrication requirements. It should also be noted that lubrication also performs a thermal function and cools the transmission components, particularly the hottest areas, e.g., the bearings and the contact areas between gear teeth.

[0005] According to known solutions, the radial gap between the teeth and the housing has a constant dimension at the location of the integrated pump. To meet the lubrication specifications, the geometric configuration of the teeth relative to the housing is such that it also generates hydraulic drag, particularly related to the oil viscosity, including during level cruising phases, which are statistically the most frequent phases of the vehicle's life cycle.

[0006] 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, particularly for critical phases of the point of from the perspective of lubrication and, secondarily, cooling.

[0007] To this end, a transmission unit for a motor vehicle is proposed, comprising at least one differential with a ring gear having an axis and being provided with radially external teeth, the transmission unit comprising a differential housing, the teeth being circumscribed in a peripheral toothed cylinder passing through the crest of the teeth of the teeth, with a radial gap left free between the peripheral toothed cylinder and the differential housing, said radial gap having a minimum dimension at the location of a pump reference angle, said 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 (

[31] , according to which the radial interval decreases in the direction of the pump reference angle, and a divergence zone is provided arranged above the reference angle and having a second angular range (

[32] , according to which the radial interval increases as it moves away from the pump reference angle.

[0008] Put another way, the pump core is formed by a strait zone which acts as a pump when the ring rotates in a direction corresponding to the direction of advance 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 rotational 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 reservoir 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, on the first angular range, the convergence zone has a convergence angle between 20° and 40°, preferably close to 30°. According to one embodiment, the first angular range is between aO-pl and aO, a0-[31 being lower than aO. The angle [31 can be chosen for example in the vicinity of 15°.

[0014] It is noted that the convergence zone allows for oil compression under the combined effect of the rotation of the differential ring gear and the reduction of the radial gap from approximately 10 mm to 3 mm. The inventors have found that a convergence angle (01) of approximately 30° proves to be optimal, 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 (R[32) is between aO and a0+ (32. The angle [32 can be chosen for example in the vicinity of 15°. The inventors have found that such a divergence angle proves to be beneficial to 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 housing is nominally 3 mm, or 3 mm ± 1.5 mm with standard dimensional tolerances. This remains within standard manufacturing tolerances. Thus, thermal expansion and other dimensional variations, as well as any potential wear clearances, are taken into account.

[0018] Preferably, the minimum dimension ER may be minimal over a point zone, 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 efficiency.

[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 a steady speed of 500 rpm or higher, this reservoir chute stores up to 50% of the total amount of oil present in the transmission unit casing.

[0022] 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 is also higher, which allows gravity flow from this reservoir chute.

[0023] According to one embodiment, the reservoir trough includes flow ports and, where applicable, oil supply channels above one or more points to be lubricated. This optimizes the lubricating oil flow paths and minimizes the total quantity of oil required for proper lubrication.

[0024] According to one embodiment, a stop element is provided on the inner wall of the housing to deflect the oil flow towards the inside of the filler neck to the reservoir. This promotes good filling of the filler neck to the reservoir from the oil that runs down the housing wall following its projection from the pump.

[0025] According to one embodiment, the crown gear teeth are in flat engagement with the driving pinion of the intermediate gear, the driving pinion rotating on an axis (A1) parallel to the axis of the differential (A2). According to one embodiment, the teeth are helical, which allows for minimal operating noise.

[0026] According to one embodiment, the oil level at rest (Z0) is located approximately halfway between the axis of the ring gear and the lowest point of the ring gear teeth. In other words, the oil level at rest is at half the radius RI of the ring gear. Consequently, the oil at rest partially bathes the seals of the bearings that guide the ring gear and the differential housing in rotation.

[0027] In one embodiment, RI is defined as the radius of the peripheral cylinder (Cl) of the gear teeth, and a low point (29) of the ring gear teeth is defined. The operating oil level (ZF) is located at a height of at most 25% of the radius RI relative to the low point (29) of the ring gear teeth. In one embodiment, the operating oil level (ZF) may be between 10% and 25% of the radius RI.

[0028] This is a significantly lower level than the oil level at rest. During operation, under steady-state conditions, the decrease in the oil level at the bottom of the crankcase reduces splashing and the hydraulic drag caused by the splashing of the ring gear in the oil present at the bottom of the crankcase.

[0029] 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 lowest 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. It should be noted here that the pump automatically re-primes in the event of loss of prime if the oil level in operation drops too low or if a tilt of the vehicle results in the convergence zone or the pump no longer being properly supplied.

[0031] The present invention also relates to an electric or hybrid vehicle, comprising at least one transmission unit as described above.

[0032] The invention will be further detailed by describing non-li- embodiments

[0033]

[0034]

[0035]

[0036]

[0037] figuratives, and based on the attached figures illustrating variants of the invention, in which: - [Fig.1] schematically illustrates a cross-sectional view of a transmission unit in which the present invention is implemented; - [Fig.2] schematically illustrates in more detail the area of ​​the oil pump integrated; - [Fig.3] schematically illustrates a cross-sectional view in a horizontal plane passing through the axis of the crown, along the section line III-III visible in [Fig.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 housing, 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 differential crown gear teeth. In the various figures, the same references designate identical or similar elements. For the sake of clarity, some elements are not necessarily shown to scale, particularly intervals. With reference to the figures, we now describe a transmission unit 7, or simply a 'transmission'. Such a transmission unit 7 can typically be used in an electric or hybrid vehicle. Its use in a conventional internal combustion engine vehicle is also possible. The transmission unit can be installed in either the front or rear axle of the vehicle. It can be installed in either a steering or non-steering axle. In the illustrated example, an electric motor provides torque which enters the transmission unit, to be distributed to the two wheels of the axle. As is known, 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 are two wheel shafts, one connected to the left wheel and the other to the right wheel of the vehicle (not shown). Only a portion of one of the wheel shafts is shown in [Fig. 4] at reference 26. The transmission unit 7 includes at least one differential 6. The differential 6 comprises a ring gear 2 and a housing 22, which will be discussed later. The ring gear forms the input wheel of the differential. Note here that the ring gear's engagement is parallel; it is not a bevel gear. The ring gear 2 has teeth 21. In In the illustrated example, the teeth are oblique; they are not parallel to the axis.

[0038] The ring 2 is driven by an intermediate gear 4. As seen in [Fig.6], this intermediate gear 4 comprises a first pinion 41 of large diameter and a second pinion 42 of small diameter integral with the first pinion 41. The second pinion is permanently engaged with the teeth 21 of the ring 2 of the differential.

[0039] The rotor RM of the electric motor rotates around the axis AO. 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.

[0040] The crown 2 rotates about an axis labeled A2. The intermediate gear 4 rotates about an axis labeled Al. The axes Al and A2 are parallel. It is also noted that the axis A0 is parallel to the axes Al and A2.

[0041] The radially external toothing 21 is circumscribed in a first peripheral cylinder denoted Cl of toothing (see [Fig.7]) passing through the vertices 21a of the teeth of the toothing. The first peripheral cylinder Cl has a radius RI. The peripheral cylinder Cl has a height W2 corresponding to the thickness of the toothing.

[0042] 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-R2.

[0043] The transmission unit comprises a differential housing 1.

[0044] The housing 1 houses the differential. In addition, in the example illustrated, the housing 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 [Fig.6]) on which the crown and the pinions are mounted as known per se, therefore not described in detail here.

[0045] The crankcase 1 contains a certain quantity of lubricating oil. In the illustrated example, this quantity of oil is between 500 ml and 1 liter.

[0046] Turning to Figures 3 and 6, we now discuss the geometric configuration of the area of ​​the casing which, together with the crown gear teeth, forms the integrated oil pump.

[0047] The pump core area 12 is centered around a pump reference angle a0. The reference angle defines a reference direction Dref.

[0048] The reference direction Dref is defined around the axis A2 with respect to a horizontal reference direction denoted aH.

[0049] In the illustrated example, 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 terrain slope is unfavorable.

[0050] The direction aH corresponds substantially to a local horizontal direction when the transmission unit is in a motor vehicle and this motor vehicle is parked on horizontal local ground.

[0051] 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.

[0052] Similarly, dynamic effects can be taken into account such as significant braking or acceleration situations which momentarily move the oil at the bottom of the sump to one side or the other relative to the pump area.

[0053] Depending on the geometric constraints and the functional specifications, the pump reference angle a0 can be adjusted downwards to ensure proper operation of the pump. In order to minimize hydraulic drag, the pump reference angle a0 is chosen to be as high as possible given the constraints otherwise present.

[0054] The oil pump is formed by the meeting of a convergence zone, the aforementioned pump core zone and a divergence zone.

[0055] 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.

[0056] 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 angle of pump reference a0, i.e., towards zone 12 of pump core.

[0058] The first angular range, denoted Rpl, extends between a0-pl and aO, a0-[31 being lower than a0. The angle pl can be chosen, for example, in the vicinity of 15°.

[0059] The divergence zone 13 is arranged above the reference angle a0.

[0060] In the divergence zone 13, the radial interval increases as it moves away from the pump reference angle.

[0061] The second angular range noted Rp2 extends between a0 and a0+p2. The angle [32 can be chosen for example in the vicinity of 15°.

[0062] Lower 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.

[0063] The toothing 21 has a width W2. The crown 2 comprises 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 much as W20. The differential input wheel can be manufactured in several pieces or entirely in a single piece.

[0064] The input wheel of the differential is integrally connected to a differential body 22 which carries planetary pinions 24 beveled in a known manner. Output beveled pinions 23 mesh with the planetary pinions 24 in a known manner. The output beveled pinions 23 each drive a wheel shaft 26.

[0065] At the level of the pump core 12, the minimum dimension ERm of the radial gap is chosen at 3 mm nominal.

[0066] 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.

[0067] Furthermore, the gear teeth are framed on their sides by flanks 17, 18 of the housing 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 achieving optimal performance. The left and right flanks are separated by a distance W8 visible in [Fig. 3]. The axial clearance E1 separates the rim of the gear teeth 21 from the right flank 18. The axial clearance E2 separates the rim of the gear teeth 21 from the left flank 17.

[0068] In the example illustrated, the transmission unit 7 further comprises a reservoir chute 3.

[0069] 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 a0.

[0070] This reservoir chute 3 receives the oil flow projected by the pump, acts as a buffer reservoir, and distributes oil through orifices by gravity. From a certain rotational speed of the ring gear, the oil flow projected by the pump progresses along the inner wall of the housing; this is therefore an upward wall flow, which is illustrated in [Fig. 1] by the 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.

[0072] In addition, an overflow function may be provided which allows more oil to be poured from the reservoir spout in order to prevent the oil level at the bottom of the crankcase from falling too low, if the conditions prevailing at the pump are particularly favorable.

[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 recessed area suitable for retaining oil, at least temporarily, for example in the shape of a basin or bowl.

[0074] Along the axial direction, the chute is wider than the ring. As can be seen in [Fig.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 ring plus the axial dimension W4 of the first pinion 41 of the intermediate gear.

[0075] During operation, under steady-state conditions, the reservoir chute contains a significant quantity of lubricating oil. In one embodiment, the chute reservoir contains up to 40% to 50% of the total oil volume included in the crankcase 1. The filling level Z3 of the reservoir filler neck is visible in figures 1 and 4.

[0076] The 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 in the bottom of the crankcase at the location where the crown splashes directly into the oil.

[0077] The oil level at rest in the bottom of the casing is established 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 teeth of the crown.

[0078] 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 zone, then progressively in the interior volume of the reservoir chute, as well as a film present elsewhere in the lubricated parts of the components of the transmission unit.

[0079] Under optimal operating conditions, the oil level in ZF operation is at a height of no more than 25% of the radius RI relative to the lowest point 29 of the ring gear teeth. According to a preferred embodiment, the oil level in ZF operation can be between 10% and 25% of the radius RI. A sufficiently low oil level in ZF operation significantly reduces hydraulic drag losses due to the rotation of the bottom of the ring gear in the oil.

[0080] It is noted that the time required to reach the established operating speed for the pump from zero speed is only one to two seconds. In practice, filling the reservoir chute to its cruising speed level Z3 takes less than one minute. Consequently, the oil level at the bottom of the crankcase rises from level Z0 to level ZF in less than one minute, and the desired reduced hydraulic drag conditions are very quickly achieved.

[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.

[0082] Optionally, a wall flow arrester system is provided to direct the oil flow circulating against the inner wall of the housing 1 into the reservoir trough. For this purpose, as illustrated in [Fig. 1], the inner wall of the housing is equipped with a groove 45 into which a tongue 35 of the reservoir trough fits. The wall flow that rises from the slope along the path denoted P2 is stopped by the tongue 35 and deflected into the reservoir trough.

[0083] It should be noted that when the rotational speed of the crown is low, the oil is projected not towards the reservoir chute but towards the intermediate gear 4 as illustrated by the path marked PI in [Fig. 1]. On the other hand, beyond a certain speed, for example 400 revolutions per minute, the reservoir chute is supplied by the flow along path P2.

[0084] Turning to [Fig.5], it can be seen that the pump core zone 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 [Fig.5], the convergence zone is represented to the left of the central zone and the divergence zone is represented to the right of the central zone.

[0086] According to one embodiment, the convergence zone has a convergence angle 01 close to 30°. More generally, it can be predicted that the convergence zone has a convergence angle 01 between 20° and 40°. Depending on the type of transmission unit, the nature of the oil selected, and the geometric properties of the gear teeth, the convergence angle 01 can be chosen at an optimal value between 20° and 40°.

[0087] According to one embodiment, the divergence zone has a convergence angle 02 close to 10°. More generally, it can be predicted that the divergence zone has a divergence angle 02 between 5° and 15°. Depending on the type of transmission unit, the nature of the oil selected, and the geometric properties of the gear teeth, the divergence angle 01 can be chosen at an optimal value between 5° and 15°.

[0088] The first angular range Rpl of convergence is between a0-pl and a0, a0-[31 being lower than a0. According to one embodiment, the angle pl can be chosen for example in the vicinity of 15°.

[0089] 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] Regarding certain dimensions mentioned above, W2 can be chosen in a range from 15 mm to 30 mm. W4 can also be chosen in a range from 15 mm to 30 mm, which gives W3 in a range from 30 mm to 60 mm.

[0091] W8 = W2 + El + E2, with for example the axial clearances El and E2 in an interval going from 1 mm to 4 mm.

[0092] RI can be chosen in a range from 40 mm to 60 mm.

[0093] 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 (Cl) 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 (R[31),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 (R[32), 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, wherein, 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, wherein 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. A 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 several points to lubricate.

8. A transmission unit according to any one of claims 1 to 7, wherein a resting oil level (Z0) is approximately midway between the axis (A2) of the crown and a low point (29) of the crown teeth.

9. Transmission unit according to any one of claims 1 to 8, in which RI is defined as the radius of the peripheral cylinder (Cl) 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 RI 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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