Electrically operable axle drive train

Abstract

The invention relates to an electrically operable axle drive train for a motor vehicle, comprising an electric machine which is drivingly connected to a wet-running gearing assembly located in a gearing housing which comprises a sump (30) which is located at the bottom in relation to a line of action of gravity (29) and in which hydraulic fluid accumulates during operation of the axle drive train, which fluid is suctioned out of the sump (30) via a suction opening (31). The aim of the invention is to functionally improve the electrically operable axle drive train, in particular in terms of its cooling and / or lubrication. This aim is achieved in that a guide structure (32) is provided upstream of the suction opening (31) in the sump (30), by means of which guide structure the distance the hydraulic fluid has to cover in the sump (30) to reach the suction opening (31) is significantly increased.

Description

[0001] Electrically operated axle drive train

[0002] The invention relates to an electrically operable axle drive train for a motor vehicle, comprising an electric machine which is drivingly connected to a wet-running transmission arrangement which is arranged in a transmission housing which comprises a sump arranged at the bottom with respect to a line of action of the earth's gravity, in which sump a hydraulic fluid collects during operation of the axle drive train and is sucked out of the sump via a suction opening.

[0003] Electric motors are increasingly being used to power motor vehicles, creating alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday suitability of electric drives and also to provide users with the same level of driving comfort they are accustomed to.

[0004] A detailed description of an electric drive can be found in an article in the magazine ATZ 113th year, 05 / 2011, pages 360-365 by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold with the title: Highly integrated and flexible electric drive unit for electric vehicles, which arguably represents the closest state of the art. This article describes a drive unit for one axle of a vehicle which comprises an electric motor which is arranged concentrically and coaxially to a bevel gear differential, with a switchable 2-speed planetary gear set being arranged in the power train between the electric motor and bevel gear differential, which is also positioned coaxially to the electric motor or the bevel gear differential or spur gear differential. The drive unit is very compact and, thanks to the switchable 2-speed planetary gear set, allows a good compromise between climbing ability, acceleration and energy consumption.Such drive units are also referred to as electric axles or electrically operated drive trains. DE 10 2010 048 837 A1 discloses such a drive device with at least one electric motor and at least one planetary differential drivable by a rotor of the electric motor, wherein the planetary differential has at least one planet carrier operatively connected to a rotor of the electric motor, first planetary gears and second planetary gears rotatably mounted on the planet carrier, and a first sun gear and a second sun gear, each of which is operatively connected to an output shaft of the planetary differential. The first planet gears mesh with the first sun gear, and each of the second planet gears meshes with the second sun gear and with one of the first planet gears. Furthermore, the sun gears are arranged coaxially with a rotational axis of the rotor.

[0005] To ensure the operation and longevity of such vehicle transmissions, appropriate oiling or lubrication of the gears and bearings within a planetary gear set is necessary. There are various current approaches to achieving this, including oil baffles and / or oil holes designed to create a defined oil path for the lubricating oil. In a passively lubricated transmission, which runs in an oil bath, the oil is distributed throughout the transmission by the rotating components, such as the planetary gear stage, gears, etc. Depending on the oil level, the components are partially covered with oil. The oil is then passed on to the bearings and / or gearing (tooth mesh) via oil baffles and / or oil holes. Depending on the operating point (low speeds, uphill / downhill driving, cornering, etc.), the oil flow may be increased.), oil level in the gearbox, arrangement and / or design of the gearbox components, a sufficient oil supply to bearings and gears cannot be guaranteed.

[0006] For example, dynamic driving situations such as acceleration, braking, or cornering can cause oil in a reservoir of the axle drive train to be excited and transported via an overflow into the transmission area for suction, which can lead to unwanted splashing losses in the planetary gear. German patent application DE 10 2015 221 901 A1 discloses a pumping device for pumping oil from an oil sump to a consumer of an internal combustion engine or a transmission of a motor vehicle, with an oil pump driven by a mechanical direct drive and a switchable electric drive.wherein the oil pump has a rotor and a rotor part enclosing the rotor, two relatively movable components for pumping the oil, and the mechanical direct drive is connected to a first of the relatively movable components and the switchable electric drive is connected to a second of the relatively movable components, wherein a housing has a shell section open on one side with a large internal cross-section for introducing the components of the oil pump, and wherein the housing has a housing base or housing cover with a constriction section with a comparatively small internal cross-section, and wherein a seal for separating the pressure side of the oil pump from a suction side is arranged on the constriction section.

[0007] The object of the invention is to functionally improve an electrically operated axle drive train according to the preamble of patent claim 1, in particular with regard to its cooling and / or lubrication.

[0008] The object is achieved in an electrically operated axle drive train for a motor vehicle, with an electric machine that is drivingly connected to a wet-running transmission arrangement that is arranged in a transmission housing that includes a sump that is arranged at the bottom with respect to a line of action of the earth's gravity, in which sump a hydraulic fluid collects during operation of the axle drive train and is sucked out of the sump via a suction opening, in that a guide structure is provided in the sump upstream of the suction opening, with the aid of which guide structure a path of the hydraulic fluid in the sump to the suction opening is significantly extended. The hydraulic fluid serves in the transmission housing to cool and / or lubricate transmission components. The hydraulic fluid can be hydraulic oil. However, it could also be water.The hydraulic fluid sucked out of the sump can advantageously be cooled in a suitable circuit, for example with the help of a heat exchanger. A pump in the circuit is used, for example, to suck out the hydraulic fluid. During operation of the axle drive train, it has been found that the hydraulic fluid in the sump foams in an undesirable manner. This foaming, also known as oil foaming, can lead to a wet space in the transmission housing being flooded with hydraulic fluid to such an extent that the required cooling and / or lubricating function is no longer ensured or no longer sufficiently ensured. In addition, the foaming leads to a reduction in the heat capacity of the hydraulic fluid. A higher oil level in the wet space of the transmission housing can also lead to splashing losses. Furthermore, hydraulic fluid can escape in an undesirable manner, for example through a vent opening.The stressed guide structure and the resulting extension of the oil path allow the oil to flow slowly and as desired from an area with dynamically moving transmission components. The guide structure advantageously includes additional ribs and / or openings to slow the flow of the hydraulic fluid. The resulting stabilization of the hydraulic fluid prevents unwanted foaming. The guide structure can be used to create a labyrinth for the hydraulic fluid on its way to the suction opening, particularly in combination with a separating device, e.g., a solid seal.

[0009] A preferred embodiment of the electrically operated axle drive train is characterized in that the guide structure has an upper guide rib with respect to the line of action of the earth's gravity, which shields the sump upwards like a roof, but without completely closing the sump at the top, whereby a radial passage opening towards the sump remains free. The term radial refers to an axis of rotation or an axis of a ring gear of the transmission arrangement. Radial means perpendicular to the axis of rotation. Analogous means axial in the direction of or parallel to the axis of rotation. The radial passage opening is advantageously arranged offset from the suction opening. In this way, the upper guide rib can be used to significantly extend the path of the fluid to the suction opening, which is designed, for example, as a suction bore, in a simple manner.A further preferred embodiment of the electrically operable axle drive train is characterized in that the transmission housing comprises an engine-side housing shell and a transmission-side housing shell, with a sealing device arranged between the two housing shells, which seals a wet space. A ring gear belonging to a planetary gear or epicyclic gear system is formed in the transmission-side housing shell. The sealing device seals the wet space and the sump from the environment. The sealing device, which is known per se, prevents any undesired escape of hydraulic fluid from the wet space and the sump.

[0010] A further preferred embodiment of the electrically operable axle drive train is characterized in that a separating device is arranged between the two housing shells, which divides the sump into two cavities at a parting plane between the housing shells such that the hydraulic fluid in the sump is deflected three-dimensionally in a labyrinthine manner on its way to the suction opening. This ensures, using simple means, alternating flow of hydraulic fluid through a transmission-side and an engine-side cavity on its way to the suction opening.

[0011] A further preferred embodiment of the electrically operable axle drive train is characterized in that the separating device comprises at least one axial passage opening, which is arranged in the sump below the radial passage opening relative to the line of action of the earth's gravity. This enables the desired passage of hydraulic fluid in the axial direction in a simple manner. The flow through or around the guide structure can be adjusted or adapted using simple design and manufacturing techniques by adjusting the size and / or number of multiple passage openings.

[0012] A further preferred embodiment of the electrically operable axle drive train is characterized in that the separating device comprises at least one axial passage opening, which is arranged in the sump in at least partial overlap with the suction opening in the sump. This provides, among other things, the advantage that the suction opening can be limited or enclosed by means of the guide structure to ensure the desired calming of the hydraulic fluid in the sump upstream of the suction opening.

[0013] A further preferred embodiment of the electrically operable axle drive train is characterized in that the upper rib extends as an extension of a circular-arc-shaped sealing track provided on a ring gear integrated into the transmission-side housing shell. This simplifies the manufacture of the transmission-side housing shell with the upper rib.

[0014] A further preferred embodiment of the electrically operable axle drive train is characterized in that the guide structure has a lower guide rib relative to the line of action of the earth's gravity, which defines a settling volume for the hydraulic fluid in the sump. This allows the outflow of the hydraulic fluid to be further effectively slowed. The settling volume is advantageously less than half the sump volume in the transmission housing.

[0015] A further preferred embodiment of the electrically operable axle drive train is characterized in that the upper guide rib is at least one-third longer than the lower guide rib in a circumferential direction. This has proven advantageous, particularly in combination with the previously described offset arrangement of the radial passage opening relative to the suction opening.

[0016] The invention further relates to a transmission housing, in particular a transmission-side or engine-side housing shell, a sealing device, and / or a separating device for an electric axle drive train described above. The separating device is advantageously combined with the sealing device described above. The aforementioned parts are available separately.

[0017] The electric machine is intended in particular for use within an electrically operated drive train of a motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and in particular greater than 100 km / h can be achieved. The electric motor particularly preferably has an output greater than 30 kW, preferably greater than 50 kW, and in particular greater than 70 kW. It is further preferred that the electric machine provides speeds greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, and most particularly preferably greater than 12,500 rpm.

[0018] The transmission arrangement of the electric axle drive train can be coupled, in particular, to the electric motor, which is designed to generate a drive torque for the motor vehicle. The drive torque is particularly preferably a main drive torque, so that the motor vehicle is driven exclusively by the drive torque.

[0019] The transmission can further preferably be configured as a planetary gear or comprise a planetary gear. The planetary gear can preferably have a sun gear and a plurality of planetary gears meshing with the sun gear and rotatably mounted in a planetary gear carrier, which rotate around the sun gear, as well as a ring gear arranged coaxially to the sun gear, in which the planetary gears roll.

[0020] The transmission arrangement may include a differential gear. A differential gear may, in particular, be a planetary gear with one input and two outputs. It typically serves the function of driving two wheels of a motor vehicle so that they can rotate at different speeds in curves but with the same propulsive force.

[0021] According to a further preferred development of the invention, the differential gear can also be designed as a spur gear differential gear. Alternatively, according to a likewise advantageous embodiment of the invention, the differential gear can be designed as a bevel gear differential gear. The planetary gear according to the invention is preferably configured for use in a gear arrangement of an axle drive train. In addition to the planetary gear according to the invention, the gear arrangement can also comprise other gears, as described above.

[0022] The sun gear is preferably rotatably mounted via at least one rolling bearing. Such rolling bearings can be used, in particular, to enable rotational movements with the lowest possible friction losses. Rolling bearings can be used, in particular, for the fixation and / or support of axles and shafts. Depending on their design, they absorb radial and / or axial forces while simultaneously enabling the rotation of the shaft or the components mounted on an axle.

[0023] According to an advantageous embodiment of the invention, the first housing shell can be formed from a cast metal. The technical advantage is that a cast metal housing shell has high strength and rigidity and is therefore well suited to absorbing the high loads in the planetary gear. The high rigidity of the housing can improve the accuracy of the gear, allowing higher performance to be achieved with smaller dimensions. Furthermore, the cast metal offers good heat dissipation, which is beneficial for a longer service life of the gear.

[0024] Further advantages, features, and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawings. They show:

[0025] Figure 1 shows a motor vehicle with an electric axle drive train in a schematic block diagram;

[0026] Figure 2 shows a planetary gear with a stepped planet in a schematic sketch;

[0027] Figure 3 shows a planetary gear in an axial sectional view; Figure 4 shows a housing shell of the gear housing in a perspective view;

[0028] Figure 5 shows an enlarged section of Figure 4 with a sump equipped with an additional guide structure for extending the path of the lubricating medium to a suction opening in a plan view of a motor-side housing shell;

[0029] Figure 6 is an analogous plan view of a gearbox-side housing shell;

[0030] Figure 7 is a similar representation to Figure 6 with arrows to illustrate the path of the lubricating medium through the sump to the suction opening; and the

[0031] Figures 8 and 9 show two alternative designs of the guide structure in the sump.

[0032] Figure 1 shows an electrically operable axle drive train 1 in a motor vehicle 2, comprising an electric machine 3 and a transmission assembly 4 coupled to the electric machine 3, which forms a structural unit with the electric machine 3. The transmission assembly 4 comprises a wet-running planetary gear 5 with an internally toothed ring gear 6, as also sketched in Figure 2.

[0033] The planetary gear 5 has a sun gear 24 and a plurality of planet gears 22 which mesh with the sun gear 24 and are rotatably mounted in a planet gear carrier 23 and which rotate around the sun gear 24, as well as the ring gear 6 which is arranged coaxially to the sun gear 24 and in which the planet gears 22 roll.

[0034] As can be seen from Figure 3, the ring gear 6 is accommodated in a two-part gear housing 7 with a first housing shell 8 and a second housing shell 9, which are designed such that for the assembly of the planetary gear 5 the ring gear 6 can be inserted into the first housing shell 8 or the second housing shell 9 from the axial direction, which can be clearly seen from the combination of Figure 3 and Figure 4.

[0035] For this purpose, the first housing shell 8, formed from a cast metal, has an annular groove 10 with a radially inner, axially extending surface 11 and a radially outer, axially extending surface 12, wherein the ring gear 6 axially bears against the radially inner surface 12 of the groove 10 and the outer surface 12 has at least one inflow opening 13 for a hydraulic fluid 14 in the upper half of the groove 10 in the direction of gravity and at least one outflow opening 15 for the hydraulic fluid 14 in the lower half of the groove 10 in the direction of gravity. The second housing shell 9 bears against the radially outer surface 12 of the groove 10, so that a cylindrical ring-like channel is defined by the groove 10, the ring gear 6 and the second housing shell 9. The first housing shell 8 and the second housing shell 9 have a contact surface 21 extending essentially in a radial plane 20.

[0036] The annular groove 10 is formed integrally, in particular monolithically, with the first housing shell 8. As shown in Figure 4, a high sump 16 for storing the hydraulic fluid 14 is arranged in the transmission housing 7. In its upper region in the direction of gravity, said high sump 16 has an overflow opening 17 which is hydraulically connected to the inlet opening 13. In dynamic driving situations, such as during acceleration, braking, or cornering, it can happen that hydraulic fluid 14 located in the high sump 16 of the axle drive train 1 is conveyed into the transmission area via the overflow opening 17.In order to prevent unwanted splashing losses in the planetary gear 5, the hydraulic fluid 14 is not directed uncontrollably into the gear interior, but is guided in a controlled manner via the groove 10 onto a hydraulic path that runs circumferentially past the planetary gear 5, preventing the interior of the ring gear 6 and thus also of the planetary gear 5 from being subjected to this "overflowing" hydraulic fluid 14. This can be clearly seen from the dashed arrows in Figure 4, which outline the hydraulic path in question. The radially inner circumferential surface 11 has at least one drain opening 18 for the hydraulic fluid 14 in the lower half of the groove 10 in the direction of gravity, so that the hydraulic fluid 14 can flow downwards from the interior of the gear under the influence of gravity. The groove 10 opens in its lower half in the direction of gravity into a suction reservoir 19, from which the hydraulic fluid 14 can be pumped back into the high sump 16.

[0037] In Figures 5 and 6, the earth's gravity is indicated by an arrow 29. The lower end regions of the transmission housing shells 8 and 9 define a sump 30 in the transmission housing. The sump 30 comprises a motor-side cavity 43 and a transmission-side cavity 44. Figure 5 shows that the motor-side cavity 43 in the sump 30 is equipped with a guide structure 32.

[0038] The guide structure 32 comprises an upper guide rib 38 and a lower guide rib 48. The upper guide rib 38 extends as an extension of a sealing web 37, which is formed on the inside of the motor-side housing shell 8, visible in Figure 5. The sealing web 37 essentially has the shape of a circular arc and, with the interposition of a sealing device, comes into sealing contact with the gearbox-side housing shell 9 in the assembled state of the gearbox housing.

[0039] Figure 6 shows a sealing track 40 shown with the sealing device.

[0040] The sealing device with the sealing track 40 serves to seal a wet chamber 41 in the transmission housing. The wet chamber 41 contains hydraulic fluid that collects in the sump 30 during operation of the axle drive train and is extracted from there via a suction opening 31. The suction opening 31 is located, as can be seen in Figure 5, at the lower right end of the sump 30. The suction opening 31 is also enclosed by a circle 28 to clarify the position of the suction opening 31.

[0041] In Figure 5 it can be seen that the upper guide rib 38, which is also referred to as the upper rib 38 for short, extends from right to left in the direction of a sealing web 50 as an extension of the sealing web 37, so far that a radial passage opening 39 in Figure 5 remains free from top to bottom from the wet space 41 into the sump 30. The lower guide rib 48, on the other hand, starts from a sealing web 52 and extends to a sealing web 51. This ensures that the lower guide rib 48 delimits a calming volume 49 for the hydraulic fluid in the area of ​​the suction opening 31.

[0042] In Figure 6, the guide structure 32 is only indicated by dashed lines. The guide structure 32 can be designed in this or a similar way. The radial passage opening 39 is missing in the dashed representation of the guide structure 32. The radial passage opening 39 can also be represented by slots or openings in the upper guide rib. Figure 6 shows that a separating device 42 is arranged in the sump between the two housing shells.

[0043] The separating device 42 is advantageously connected in one piece with the sealing device. Accordingly, the separating device 42 is designed, for example, as a solid seal. Circles in Figure 6 indicate axial passages 45, 46, and 47 in the separating device 42. The axial passage 45 allows hydraulic fluid to pass into the cavity 44. The axial passage 47 allows hydraulic fluid to pass to the suction opening. The axial passages 45 to 47, which are only indicated, can vary in size, shape, and number.

[0044] In Figure 7, an arrow 33 indicates how hydraulic fluid flows from the wet chamber 41 from above into the sump 30. A dashed arrow 34 indicates how the hydraulic fluid is deflected in a labyrinth-like manner in the sump 30 before it passes through the axial passage opening 47 to the suction opening.

[0045] In Figure 7, circles indicate air bubbles 35, which are advantageously scraped off in a plane-like manner on the indicated lower guide rib 48. Furthermore, an ellipse in Figure 7 indicates that a differently shaped axial passage opening can also be arranged between the two circular axial passage openings 45 and 47.

[0046] Figures 8 and 9 show how the guide structure 32 can be realized in the sump with the help of additional components 55, 56. The components 55, 56 are formed, for example, from a plastic material and inserted into the motor-side housing shell 8 to represent the guide structure 32. However, for large-scale production, the guide structure 32 shown in Figure 5, which is preferably made of cast metal, is more cost-effective.

[0047] List of reference symbols axle drive train motor vehicle electric machine gear arrangement planetary gear ring gear gear housing housing shell housing shell groove outer surface outer surface inlet opening hydraulic fluid / lubricant outlet opening high sump overflow opening outlet opening intake reservoir radial plane 1 contact surface planetary gear planet carrier sun gear 8 circle 9 earth's gravity 0 sump 1 suction opening 2 guide structure arrow dashed arrow circles axial passage opening sealing web upper guide rib radial passage opening sealing track wet room separating device cavity cavity axial passage opening axial passage opening axial passage opening lower guide rib settling volume sealing web sealing web sealing web component component

Claims

Patent claims 1. Electrically operable axle drive train (1) for a motor vehicle (2), comprising an electric machine (3) which is drivingly connected to a wet-running transmission arrangement (4) which is arranged in a transmission housing (7) which comprises a sump (30) arranged at the bottom with respect to a line of action of a gravitational force (29), in which sump a hydraulic fluid (14) collects during operation of the axle drive train (1), which is sucked out of the sump (30) via a suction opening (31), characterized in that upstream of the suction opening (31) in the sump (30) a guide structure (32) is provided, with the aid of which guide structure a path of the hydraulic fluid (14) in the sump (30) to the suction opening (31) is significantly lengthened.

2. Electrically operable axle drive train according to claim 1, characterized in that the guide structure (32) has an upper guide rib (38) with respect to the line of action of the earth's gravity (29), which shields the sump (30) upwards like a roof, but without completely closing the sump (30) at the top, wherein a radial passage opening (39) remains free in the direction of the sump.

3. Electrically operable axle drive train according to claim 2, characterized in that the transmission housing (7) comprises an engine-side and a transmission-side housing shell (8, 9), wherein a sealing device is arranged between the two housing shells (8, 9) which seals off a wet space (41).

4. Electrically operable axle drive train according to claim 3, characterized in that a separating device (42) is arranged between the two housing shells (8, 9), which divides the sump (30) in a parting plane between the housing shells (8.9) into two cavities (43, 44) such that the hydraulic fluid (14) in the sump (30) is deflected three-dimensionally in a labyrinthine manner on the way to the suction opening (31).

5. Electrically operable axle drive train according to claim 4, characterized in that the separating device (42) comprises at least one axial passage opening (36, 45, 46) which is arranged in the sump (30) below the radial passage opening (36, 35, 46) with respect to the line of action of the earth's gravity (29).

6. Electrically operable axle drive train according to claim 4 or 5, characterized in that the separating device (42) comprises at least one axial passage opening (47) which is arranged in the sump (30) in at least partial overlap with the suction opening (31) in the sump (30).

7. Electrically operable axle drive train according to one of claims 2 to 6, characterized in that the upper rib (38) extends in extension of a circular arc-shaped sealing track (40) which is provided on a ring gear (6) integrated into the transmission-side housing shell (9).

8. Electrically operated axle drive train according to one of claims 2 to 7, characterized in that the guide structure (32) has a lower guide rib (48) with respect to the line of action of the earth's gravity (29), which delimits a calming volume (49) in the sump (30) in front of the suction opening (31) for the hydraulic fluid (14).

9. Electrically operable axle drive train according to one of claims 2 to 7, characterized in that the upper guide rib (48) is at least one third longer than the lower guide rib (38) in a circumferential direction.

10. Gearbox housing (7), in particular gearbox-side or engine-side housing shell (8,9), sealing device and / or separating device (42) for an electric axle drive train (1) according to one of the preceding claims.

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