ELECTRIC DRIVE UNIT FOR A MOTOR VEHICLE

Description

[0001] The invention relates to an electric drive unit for a motor vehicle, comprising an electric drive, a multi-stage transmission downstream of the electric drive, which is arranged alone or together with the electric drive in a drive housing, the drive housing comprising a housing shell which surrounds the transmission in a ring shape with its inner side, and an end wall formed integrally with the housing shell, which is centrally provided with a transmission opening for the transmission output shaft of the transmission, wherein coolant is passed through the drive housing to cool the components of the transmission, wherein an annular chamber is formed on the outside of the end wall around the transmission opening, wherein coolant channels are formed in the drive housing which lead from the inside of the housing shell into the annular chamber.

[0002] Such an electric drive unit serves as the propulsion system for a vehicle. It is used as part of an electric drive axle for a commercial vehicle. In this type of vehicle axle, a multi-stage transmission is connected downstream of the electric drive, which is positioned close to the vehicle's center for optimal weight distribution. The transmission is located, either alone or together with the electric drive, in a drive housing. This housing consists of a substantially cylindrical casing and an end wall formed integrally with the casing. The casing of the drive housing surrounds the transmission components within it in a ring-like fashion on its inner surface, and the end wall of the drive housing features a central transmission opening through which the transmission output shaft exits the gearbox.The transmission output shaft is either also the drive shaft leading to the respective vehicle wheel, or it is non-rotatably connected to a separate drive shaft. The transmission output shaft or the drive shaft rotates within a predominantly tubular axle housing of the electric drive axle. The axle housing is rigidly attached at its transmission-side end to the front face of the drive housing and has a steering knuckle at its other end, on which the driven vehicle wheel is rotatably mounted.

[0003] To cool the transmission elements, coolant is passed through the drive housing, which serves as the transmission housing, in the form of a circuit in which the coolant flows through as many mechanically stressed areas of the transmission as possible, including the existing rolling bearings, for which purpose the coolant is circulated within the drive housing.

[0004] The circulation of the coolant within the drive housing reaches its limits in mechanically highly stressed gearboxes, as the gearboxes are often of a very compact design and there is little installation space available to accommodate the components required for further improved cooling performance in the existing housing.

[0005] US Patent 5,443,130 discloses a differential gear comprising an input element connected to an electric motor and two output elements, the motor power received by the input element being distributed to a first wheel drive element and an intermediate shaft extending through a hollow output shaft of the motor and connected to a second wheel drive element.

[0006] The invention is based on the objective of improving the cooling performance of an electric drive unit, the component of which is a drive housing with a liquid-cooled gearbox arranged therein, by utilizing precisely the design-related special features of the electric drive unit.

[0007] To solve this problem, an axle housing enclosing the gearbox output shaft is proposed for an electric drive unit of the type specified above, which is provided with a flange facing the drive housing, which is attached to the end wall and wherein a ring plate of the flange together with the end face forms the annular chamber.

[0008] According to the invention, a ring chamber is therefore part of the coolant circulation system. However, this ring chamber is not located inside the drive housing, but rather on the outside of the drive housing's end wall, surrounding the gearbox opening. To allow coolant to enter this ring chamber, coolant channels are formed in the drive housing, leading from the inside of the housing shell into the ring chamber.

[0009] The arrangement of the annular chamber on the outside of the end wall of the drive housing is advantageous because the drive housing offers little available space inside, and because the electric drive shaft inherently includes an axle housing, which is attached to the end wall where the annular chamber is located according to the invention. The axle housing is provided with a flange facing the drive housing. The flange of the axle housing is attached to the end wall, and an annular portion of the flange, together with the groove formed in the end wall, forms the annular chamber.

[0010] Due to the unique design of the electric drive axle, an annular chamber for circulating the coolant can be implemented. This chamber is partially bounded by the end wall of the drive housing and partially by an annular section on the axle housing. Therefore, the annular chamber is not formed solely by the drive housing, but rather by the design-related combination of the drive housing and the axle housing, which surrounds the transmission output shaft and is attached to its end face.

[0011] A preferred embodiment is one in which the annular chamber is partially formed, namely on the side of the drive housing, by a groove in the outside of the end wall.

[0012] The axle housing is part of the electric drive axle and is equipped at its end facing away from the flange with a steering knuckle for mounting a vehicle wheel.

[0013] According to one embodiment of the drive unit, a coolant connection nozzle is arranged on the flange, and a coolant channel leads from the coolant connection nozzle into the annular chamber, for example to fill it with fresh coolant or, in the case of active recirculating cooling, to continuously pump coolant into it.

[0014] Furthermore, a first and a second seal between the flange and the end wall are preferred. Preferably, the first seal is an annular seal arranged between the annular chamber and the central gearbox opening, and the second seal is an annular seal arranged around the annular chamber. Preferably, the annular seals are seated in annular grooves open towards the outside of the end wall, the annular grooves being formed in the end wall.

[0015] According to a further embodiment, the two seals are arranged axially offset from each other in the longitudinal direction of the gearbox output shaft, with the second seal being the seal closer to the drive side.

[0016] According to a further embodiment, additional coolant channels are formed in the drive housing, with these additional coolant channels extending from the annular chamber through the end wall to its inner surface. The coolant can therefore leave the annular chamber and flow back into the interior of the drive housing via these additional coolant channels. Preferably, these additional coolant channels are bores arranged with a diameter smaller than the diameter on which the coolant channels are arranged, relative to the central axis.

[0017] From a manufacturing perspective, it is advantageous if the axes of the other coolant channels are aligned parallel to the central axis.

[0018] With regard to favorable flow through the annular chamber, it is advantageous if the further coolant channels open at the bottom, and the coolant channels open into the side wall of the annular chamber, which is designed as a trough.

[0019] Furthermore, it is proposed that the flange of the axle housing be fastened to the end wall of the drive housing by means of a plurality of screws arranged on a common pitch circle. Preferably, the diameter of the pitch circle is larger than the largest diameter of the annular chamber, and preferably larger than the diameter of the second seal.

[0020] Preferably, the screws engage with their threads in threaded holes formed in the end wall.

[0021] For a compact design of the drive housing and the attachment of the axle housing to it, it is advantageous if the coolant channels lead into the annular chamber on such circumferential sections where no threaded blind holes are formed in the end wall.

[0022] Furthermore, it is proposed that the end wall and the flange are axially aligned to each other by means of centering surfaces formed on them and in mutual contact.

[0023] Preferably, the centering surfaces are arranged on a diameter that is smaller than the smallest diameter of the annular chamber and larger than the diameter of the first seal.

[0024] Further advantages and details of the electric drive axle for a commercial vehicle will become apparent from the following description of an exemplary embodiment shown in the drawing. Specifically, the drawing shows: Fig. 1 : in a perspective view individual parts of an electric drive axle for a commercial vehicle, namely a multi-stage gearbox in the design as a double planetary gearbox, a drive housing receiving the gearbox in a partial section, as well as an axle housing that can be attached to the front of the drive housing, whereby the aforementioned components are shown separately for the sake of clarity; Fig. 2 : a front view of the drive housing according to the one in Fig. 1 Reproduced viewing direction II; Fig. 3 : a longitudinal section through one half of the electric drive axle along a Fig. 2 offset cutting plane designated "III - III"; Fig. 4 : an enlarged section of the Fig. 3 .

[0025] Fig. 3 Figure 1 shows a partial longitudinal section, presented here as an overview, of one half of an electric drive axle for a motor vehicle. The depicted half of the drive axle serves to drive a motor rotatably mounted on a steering knuckle 1, in Fig. 3 The vehicle wheel 2, shown with a dashed line on the left edge, is shown with a dashed line. The similarly designed second half of the drive axle is located symmetrically on the other side of the wheel shown with a dashed line. Fig. 3 The registered vehicle center plane M, and carries the respective vehicle wheel on the opposite side of the vehicle. The electric drive axle is, in its entirety, a rigid axle extending from one side of the vehicle to the other.

[0026] For each side of the vehicle, and thus for the drive of the respective vehicle wheel 2, an electric drive 5, in particular an electric motor, is provided near the vehicle's central plane M. A gearbox 6, here in the form of a two-stage planetary gearbox, is connected downstream of each electric motor towards the outside of the vehicle.

[0027] The two electric drives 5 and two gearboxes 6 of the electric drive unit are located in a drive housing 4, which can be one or more parts. In the embodiment described here, the drive housing 4 consists of three parts or sections, with both electric drives 5 located in a common drive housing part and each of the two gearboxes 6 in a separate, individual drive housing part. Alternatively, the electric drive 5 and its gearbox 6 can be arranged together in a common drive housing 4 for each side of the vehicle.

[0028] The drive housing 4 is therefore also the gearbox housing of the drive unit and consists of a substantially cylindrical housing shell 11, whose inner surface 11a surrounds the gearbox elements of the gearbox 6 in a ring-like manner, and of an end wall 12 formed integrally with the housing shell 11. The end wall 12 is predominantly closed, but leaves a gearbox opening 17 in its center, through which the gearbox output shaft 18 of the gearbox 6, rotating on the central axis of rotation A, passes.

[0029] The transmission output shaft 18 can be connected, preferably via a splined connection, to a drive shaft which leads to and drives the vehicle wheel 2. Unlike the transmission output shaft 18, the drive shaft is not shown in the drawing. The drive shaft rotates in a tubular axle housing 15 of the drive unit, which extends along the central axis A. The axle housing 15 is attached to the end face of the drive housing 4.

[0030] The axle housing 15 of the drive unit is provided with the steering knuckle 1 at its outer end. The brake caliper bracket of the vehicle brake, preferably a disc brake caliper bracket, is also attached to the axle housing 15. A longitudinal control arm and, if applicable, a transverse control arm of the vehicle axle are also attached to the axle housing 15.

[0031] To fasten the axle housing 15 to the drive housing 4, the axle housing 15 is provided at its inner end with a radially widened flange 16. The flange 16 is rigidly bolted to the end wall 12 of the drive housing 4 by means of several bolts 19. The bolt heads 19 bear against the flange 16 and their threads engage in threaded blind holes 20 formed in the end wall 12.

[0032] The drive housing components, i.e., the drive housing component accommodating the electric drive 5 on the one hand and the drive housing component accommodating the gearbox 6 on the other, are also connected by means of screw connections 29, for which purpose the respective ends of these drive housing components are designed as flanges that are firmly and preferably liquid-tightly connected to each other via the screw connections 29. Whenever the drive housing 4 is referred to in general terms below, this always refers to the drive housing component in which the gearbox 6, and preferably a two-stage planetary gearbox, is located.

[0033] The drive housing not only serves as a housing, but it is also itself part of the planetary gear system, in that according to Fig. 1 The inner surface 11a of the housing shell 11 has a helical gear 17a of the first gear stage arranged around the axis of rotation A, and axially offset, a helical gear 17b of the second gear stage arranged around the axis of rotation A. The orientation or helical position of the teeth of the helical gear 17b is opposite to that of the teeth of the first helical gear 17a.

[0034] The helical gears 17a, 17b formed on the inside of the housing 11 mesh with the planet gears of the two gear stages of the planetary gear. The remaining gear elements are arranged in a gear carrier 17c rotatable on axis A, which is inserted into the drive housing 4 as a pre-assembled unit.

[0035] The gearbox 6 is of the planetary gearbox type. The planet gears and ring gears of the planetary gearbox have a tooth helical arrangement that creates a scooping action on the coolant pointing away from the end wall 12, and in the case of passive sump cooling, a scooping action on the coolant pointing towards the end wall 12.

[0036] The central part of the transmission carrier 17c is the transmission output shaft 18 rotating on the axis A, which protrudes from the centrally arranged transmission opening 17 of the drive housing 4 and extends into the axle housing 15.

[0037] In the case of active recirculating cooling, the gearbox 6 and its partially heavily loaded teeth, pinions, and bearings are cooled by means of coolant circulated by an external pump. The pump draws the fluid from the drive housing 4, passes it through an external heat exchanger, and then delivers it to a connection port 21, through which the coolant flows directly into the annular chamber 33 and thus back into the circuit. The connection port 21 is located on the flange 16 of the axle housing 15.

[0038] In the case of passive sump lubrication, however, the fluid is circulated exclusively within the drive housing 4 including the annular chamber 33, without the need for an external pump.

[0039] Regardless of the type of circulation, the coolant is preferably a gear oil, so that the fluid both lubricates the gear elements and takes care of heat dissipation.

[0040] Due to its planetary gear design, cooling and lubricating fluid is flung outwards from the planet gears against the helical gears 17a, 17b by centrifugal forces. The cooling fluid therefore collects on the inner surface 11a of the housing 11. The measures described in more detail below serve to transport the fluid accumulating on the inner surface 11a of the housing 11 back to more central areas of the gearbox 6 and to the area of ​​rolling bearings, for example, to the rolling bearings 31 of the gearbox output shaft 18.

[0041] To improve coolant transport and cooling performance, an annular chamber 33 is arranged on the outside of the end wall 12, surrounding the central axis of rotation A and the gearbox opening 17 in the form of a complete ring. Coolant can collect in this chamber for further circulation. At the same time, several coolant channels 35 are formed in the transition area between the housing shell 11 and the end wall 12 of the drive housing. These channels lead from the inside 11a of the housing shell 11 into the annular chamber 33. Therefore, fluid that has accumulated inside the housing shell 11, and especially on the helical gears 17a, 17b, first passes through the coolant channels 35 into the annular chamber 33, which thus forms a reservoir for coolant.

[0042] An annular chamber requires space that is not available in the very compact drive housing 4. Therefore, the annular chamber 33 is located on the outside of the drive housing 4, on the end face facing the vehicle wheel 2. Crucially, the annular chamber 33 is not formed solely by the drive housing 4 itself, but also partly by the axle housing 15. This is achieved by forming part of the annular chamber 33 through an annular groove formed in the outer surface of the end wall 12, and part through an annular area on the end face of the flange 16. The annular area on the end face of the flange 16, together with the groove formed in the end wall 12, thus forms the annular chamber 33, so that not only components of the transmission are involved in the coolant flow and circulation, but also other components of the drive unit, namely the flange 16 of the axle housing 15.

[0043] The circulation of the coolant and the improvement of the cooling performance are achieved in this way by taking advantage of the design-related special features of the electric drive unit, since the axle housing 15 is also part of this drive unit.

[0044] In order for the annular chamber 33 to serve as a collector, a large number of the aforementioned coolant channels 35 are provided, wherein the coolant channels 35 are preferably arranged evenly distributed over the circumference of the round drive housing 4.

[0045] The coolant collected in the annular chamber 33 flows back into the interior of the drive housing 4 via further coolant channels 41. These further coolant channels 41 are also numerous and evenly distributed around the circumference of the round drive housing 4. They extend from the annular chamber 33 through the end wall 12 and open onto the inner surface 12a of the end wall 12.

[0046] In the embodiment described here, the additional coolant channels 41 are each through-bores extending parallel to the axis of rotation A of the transmission output shaft 18. With respect to the axis of rotation A, the additional coolant channels 41 are arranged on a diameter that is smaller than the diameter on which the coolant channels 35 are arranged.

[0047] To transport the coolant medium accumulated in the area of ​​the inner surface 11a into the annular chamber 33, the coolant channels 35 run at an inclination to the central axis A of the drive unit. The opening of each coolant channel 35 into the interior of the drive housing 4 is located radially further outwards than the opening of each coolant channel 35 into the annular chamber 33.

[0048] According to Fig. 2 The coolant channels 35 on the one hand and the further coolant channels 41 on the other hand open into the trough-shaped annular chamber 33 such that the further coolant channels 41 open into the bottom 42 of the annular chamber 33, and the coolant channels 35 open into a side wall 43 of the annular chamber 33 that is arranged at an angle to the bottom 42. In the exemplary embodiment, the side wall 43 of the trough into which the coolant channels 35 open is arranged at an angle to the bottom 42 of the trough, whereas the other side wall is arranged essentially perpendicular to the bottom 42 of the trough. This design achieves a uniform coolant distribution within the annular chamber 33.

[0049] The annular chamber 33 is sealed radially inwards by a first seal 51 and radially outwards by a second seal 52, so that no liquid can escape either inwards or outwards. Preferably, both seals 51 and 52 are ring seals arranged around the central axis A. The groove for receiving the respective ring seal is formed in the end face of the end wall 12.

[0050] The end wall 12 and the flange 16 are axially aligned with each other by centering surfaces 55 formed on them and in mutual contact. The centering surfaces, in the form of a step extending in a ring shape around the central axis A, are arranged on a diameter that is smaller than the smallest diameter of the annular chamber 33. The annular centering surfaces 55 are thus located radially between the annular chamber 33 and the inner, first seal 51.

[0051] The screws 19, which fasten the flange 16 to the end wall 12 and are arranged on a uniform pitch circle, each engage with their thread in a threaded blind hole 20 which is formed in the end wall 12.

[0052] For an overall compact design, the threaded blind holes 20 and the coolant channels 35 are arranged on different circumferential sections ( Fig. 2 For example, in the circumferential direction, a screw 19 or its threaded blind hole 20 can alternate with one of the coolant channels 35. However, the configuration according to is preferred. Fig. 2 , where the number of coolant channels is 35, half the number of screws (19) or threaded blind holes (20).

[0053] According to Fig. 4The additional coolant channels 41 are oriented such that the coolant exiting them reaches the rolling bearing 31, which supports the transmission output shaft 18 in the housing 11, almost directly. This improves both the cooling and lubrication of this heavily loaded rolling bearing 31.

[0054] The radial sealing of the transmission output shaft 18 against the surrounding transmission opening 17 is achieved by means of a radial shaft seal 58 arranged between these components. Reference symbol list

[0055] 1: Steering knuckle 2: Vehicle wheel 4: Drive housing 5: Electric drive 6: Gearbox 11: Housing shell 11a: Inside of housing shell 12: End wall 12a: Inside of end wall 15: Axle housing 16: Flange 17: Gearbox opening 17a: Helical gear 17b: Helical gear 17c: Gearbox carrier 18: Gearbox output shaft 19: Screw 20: Threaded blind hole 21: Connection stub 29: Screw connection 31: Rolling bearing 33: Ring chamber 35: Coolant channel 41: Coolant channel 42: Base 43: Side wall 51: First seal, ring seal 52: Second seal, ring seal 55: Centering surfaces 58: Radial shaft seal A: Central axis, axis of rotation M: Vehicle center plane

Claims

1. Electric drive unit for a motor vehicle, comprising an electric drive (5), a multi-stage transmission (6) connected downstream of the electric drive (5) and arranged alone or together with the electric drive (5) in a drive housing (4) which is composed of a housing casing (11) which annularly surrounds the transmission (6) with its inner face (11a), and a front wall (12) which is formed in one piece with the housing casing (11) and which is centrally provided with a transmission opening (17) for the transmission output shaft (18) of the transmission (6), cooling fluid being passed through the drive housing (4) to cool the components of the transmission (6), an annular chamber (33) is arranged on the outside of the front wall (12) around the transmission opening (17), coolant channels (35) which lead from the inner face (11a) of the housing casing (11) into the annular chamber (33) being formed in the drive housing (4), characterized by an axle housing (15) enclosing the transmission output shaft (18) and provided with a flange (16) which faces the drive housing (4) and is fastened to the front wall (12), and in that an annular region of the flange (16) together with the front face (12) forms the annular chamber (33).

2. Electric drive unit according to claim 1, characterized in that the annular chamber (33) is partially formed by a groove in the outside of the front wall (12).

3. Electric drive unit according to claim 1 or 2, characterized in that the axle housing (15) is provided at its end facing away from the flange (16) with a steering knuckle (1) for supporting a vehicle wheel (2).

4. Electric drive unit according to any of the preceding claims, characterized in that a coolant connection piece is arranged on the flange (16), and in that a coolant channel leads from the coolant connection piece into the annular chamber (33).

5. Electric drive unit according to any of the preceding claims, characterized by a first and a second seal between the flange and the front wall (12), the first seal being an annular seal (51) arranged between the annular chamber (33) and the transmission opening (17), and the second seal being an annular seal (52) arranged around the annular chamber (33).

6. Electric drive unit according to claim 5, characterized in that the annular seals (51, 52) are seated in ring grooves in the front wall (12) which are open toward the outside of the front wall (12).

7. Electric drive unit according to claim 5 or 6, characterized in that the two seals (51, 52) are arranged axially offset from one another in the longitudinal direction of the transmission output shaft (18), the second seal (52) being the seal closer to the drive side.

8. Electric drive unit according to any of the preceding claims, characterized in that in the drive housing (4) further coolant channels (41) are formed, and in that the further coolant channels (41) lead from the annular chamber (33) through the front wall (12) to its inner face (12a).

9. Electric drive unit according to claim 8, characterized in that the further coolant channels (41) are bores which are arranged, with respect to the central axis (A), on a diameter which is smaller than the diameter on which the coolant channels (35) are arranged.

10. Electric drive unit according to claim 8 or 9, characterized in that that the axes of the further coolant channels (41) are aligned in parallel with the central axis (A).

11. Electric drive unit according to any of claims 8-10, characterized in that the further coolant channels (41) open onto the bottom (42), and in that the coolant channels (35) open into the side wall (43) of the annular chamber (33) designed as a groove.

12. Electric drive unit according to any of the preceding claims, characterized in that the flange (16) of the axle housing (15) is fastened to the front wall (12) by means of a plurality of screws (19) arranged on a common pitch circle.

13. Electric drive unit according to claim 12, characterized in that the diameter of the pitch circle is larger than the largest diameter of the annular chamber (33), and preferably larger than the diameter of the second seal (52).

14. Electric drive unit according to claim 12 or 13, characterized in that the screws (19) engage with their thread in threaded blind holes (20) formed in the front wall (12).

15. Electric drive unit according to claim 14, characterized in that the coolant channels (35) lead into the annular chamber (33) on the circumferential portions on which no threaded blind holes (20) are formed in the front wall (12).

16. Electric drive unit according to any of claims 12-15, characterized in that the front wall (12) and the flange (16) are axially aligned with each other by centering surfaces (55) formed on them and in mutual contact.

17. Electric drive unit according to claim 16, characterized in that the centering surfaces (55) are arranged on a diameter which is smaller than the smallest diameter of the annular chamber (33).