Electric drive unit in reduction gear design with coaxial arrangement of electric machine and differential

Abstract

Electric drive unit (1) for a purely electric or hybrid-driven motor vehicle, comprising an electric machine (2), a differential (6) having two output shafts (3a, 3b), wherein the output shafts (3a, 3b) are arranged coaxially to a rotational axis (4) of a rotor shaft (5) of the electric machine (2), and a transmission device (8) comprising a planetary gear (7) coupling the rotor shaft (5) to the differential (6), wherein a first sun gear (10) forming an input (9) of the planetary gear (7) is connected to the rotor shaft (5) and an output (11) of the planetary gear (7) is permanently rotationally coupled to a differential input (12), characterized in that the multi-start transmission device (8) has a countershaft (13) coupling the output (11) of the planetary gear (7) to the differential input (12),wherein an input gear (14) forming the differential input (12) is arranged radially in the direction of the axis of rotation (4) within the countershaft (13) and the planetary gear set (7) has at least one double planetary gear (16) rotatably mounted on a planet carrier (15), wherein a first toothed section (17) of the at least one double planetary gear (16) engages with the first sun gear (10) and a second toothed section (18) of the at least one double planetary gear (16) engages with a second sun gear (19) coupled to the countershaft (13).

Description

[0001] The invention relates to an electric drive unit, also referred to as an electric drive axle or simply as an electric axle, for a purely electric or hybrid-powered motor vehicle, comprising an electric machine, a differential having two output shafts, wherein the output shafts are arranged coaxially to a rotational axis of a rotor shaft of the electric machine, and a transmission device comprising a planetary gear unit coupling the rotor shaft to the differential, wherein a first sun gear forming an input of the planetary gear unit is (permanently) connected to the rotor shaft and an output of the planetary gear unit is permanently and rotatably coupled to a differential input.

[0002] Electric axles of this type are already known in various designs. For example, DE 10 2017 108 005 A1 discloses a drive device for a motor vehicle, which shows a single-start drive axle. Furthermore, electric drive axles are known in principle that are designed as two-start axles and not capable of load switching, or as two-start axles and capable of load switching.

[0003] US Patent 2011 / 0218070A1 discloses an electric drive module for a motor vehicle comprising an electric motor, a two-speed module, a reduction unit, and a differential assembly. The electric motor drives the first input element via a rotor shaft. The two-speed module connects the first input element and the first output element at two different gear ratios. The reduction unit, positioned at one end of the electric motor, has a second input element and a second output element, which is driven at a reduced speed. At the other end is the two-speed module, and the reduction unit contains two gears on a countershaft that is parallel to the axis of rotation of the first input element. The differential assembly has two outputs for driving the output shafts and is driven by the second output element.

[0004] US Patent 11,273,701 B2 discloses an electric drive axle comprising two coaxial axle shafts, a differential, an electric motor with stator and rotor, and a drive shaft coupled to the rotor. A first drive gear is mounted on the drive shaft. A driven shaft with two gears meshes with this first gear. There is also a parallel countershaft with two gears. The first countershaft gear meshes with the second gear on the driven shaft. The second countershaft gear is coupled to the differential housing. Additionally, there is a third driven gear on the driven shaft, which meshes with a second driven gear on the drive shaft. A switching element allows either the first or second driven gear to be engaged for rotation with the drive shaft.

[0005] However, the disadvantage of the known multi-start designs is that they often have a relatively large radial structure and consequently occupy a relatively large installation space in the vehicle. Furthermore, these drive units are often relatively complex, equipped with many additional components, which significantly increases the manufacturing and assembly effort.

[0006] It is therefore an object of the present invention to eliminate these disadvantages known from the prior art and in particular to provide an electric drive unit which has a design that is as compact as possible, especially in the axial direction, while still ensuring multiple starts in order to drive a drive train as efficiently as possible.

[0007] This is solved according to the invention by the fact that the multi-start (preferably double-start) gear unit has a countershaft coupling the output of the planetary gear with the differential input, wherein an input wheel forming the differential input is arranged in the radial direction of the axis of rotation inside the countershaft.

[0008] This space-saving nesting of the countershaft with the differential not only provides an additional, cost-effectively designed transmission, but also a drive unit that is as small as possible.

[0009] According to the invention, for the simplest possible construction of the planetary gear system, the planetary gear system comprises at least one double planetary gear rotatably mounted on a planet carrier, wherein a first toothed section of the at least one double planetary gear meshes with the first sun gear, and a second toothed section of the at least one double planetary gear meshes with a second sun gear coupled to the countershaft. However, at least two double planetary gears are preferably provided.

[0010] Further advantageous embodiments are claimed in the dependent claims and are explained in more detail below.

[0011] It is also advantageous if the first gear section (of at least one double planetary gear) has a larger pitch circle diameter than the second gear section (of at least one double planetary gear).

[0012] If the planetary gear unit is designed without a hollow gear, its construction is further simplified.

[0013] It is also advantageous if a clutch is installed between the first sun gear and the planet carrier in such a way that the first sun gear is directly locked / connected to the planet carrier in the closed position of the clutch. This results in a shifting device that can be integrated as compactly as possible for shifting the respective gears of the transmission. Shifting always requires the simultaneous operation of the clutch and brake.

[0014] Furthermore, in this context it is advantageous if a brake is used between the planet carrier and a housing-fixed support section in such a way that the planet carrier is fixed / held in an activated state of the brake relative to the support section.

[0015] Thus, the transmission system is designed in such a way that, in the activated state of the brake and the clutch in its open position, a first gear is realized. Conversely, when the clutch is in its closed position and the brake is in its deactivated / open state, a second gear is realized.

[0016] The intermediate shaft is also preferably designed as a (double) loose gear or fixed gear.

[0017] In this respect, it is again advantageous if a first toothed area of ​​the countershaft is in tooth mesh with the second sun gear and a second toothed area of ​​the countershaft is in tooth mesh with the input gear of the differential.

[0018] The layshaft advantageously has a larger pitch circle diameter on the side of its first toothed area than on the side of its second toothed area.

[0019] In other words, according to the invention a so-called "power-shift e-axis" is implemented, which is designed in a reduction gear construction with a coaxial arrangement of the electric motor and differential.

[0020] The invention is explained in more detail below with reference to a figure.

[0021] It shows the only Fig. 1 A schematic longitudinal section view of an electric drive unit according to the invention in a preferred embodiment.

[0022] The figure is merely schematic and therefore serves solely to illustrate the invention.

[0023] The electric drive unit 1 according to the invention is equipped with Fig. Figure 1 illustrates a preferred embodiment. The electric drive unit 1 is used in its operating state as an e-axle in a motor vehicle to transmit drive power to corresponding wheels of the motor vehicle connected to output shafts 3a, 3b, preferably in a hybrid-driven motor vehicle, in support of the drive of an internal combustion engine, or, more preferably, in a purely electric-driven motor vehicle.

[0024] The electric drive unit 1 comprises an electric machine 2, the electric machine 2 having a stator 25 fixed to the housing and a rotor 26 rotatably mounted radially within the stator 25. The rotor 26 is directly and non-rotatably connected to a rotor shaft 5, which is rotatably mounted about the central axis of rotation 4. It can also be seen that the two output shafts 3a, 3b of the drive unit 1 are aligned coaxially with this rotor shaft 5 / the axis of rotation 4. The first output shaft 3a extends through the rotor shaft 5, which is implemented as a hollow shaft.

[0025] A transmission device 8 according to the invention is arranged between the rotor shaft 5 and a differential input 12 of a differential 6. The transmission device 8 forms a two-start transmission. In addition to a planetary gear 7, the transmission device 8 has a reduction stage 27. While an input 9 of the planetary gear 7 is directly connected to the rotor shaft 5, a reduction shaft 13 of the reduction stage 27 is directly and rotatably coupled to the differential input 12. A differential output is directly implemented via the output shafts 3a, 3b.

[0026] The planetary gear 7 is implemented without a hollow gear. The planetary gear 7 has two sun gears 10, 19, of which a first sun gear 10 directly forms the input 9 of the planetary gear 7 and is directly connected to the rotor shaft 5, and a second sun gear 19 forms an output 11 of the planetary gear 7 and is rotatably coupled to the countershaft 13.

[0027] Both sun gears 10, 19 are in mesh with two axially spaced tooth sections 17, 18 of one or more double planetary gears 16, which are distributed circumferentially (with respect to a circle around the axis of rotation 4) and have different pitch circle diameters. In this embodiment, the first tooth section 17, which meshes with the first sun gear 10, has a larger pitch circle diameter than the second tooth section 18, which meshes with the second sun gear 19.

[0028] A planet carrier 15, which rotatably mounts the double planetary gears 16 in the form of loose gears, can be coupled differently by two different switching devices 20, 22 for changing the two gears of the transmission device 8. A first switching device is implemented by a clutch 20 and is positioned between the first sun gear 10 and the planet carrier 15. In an open position of the clutch 20, the planet carrier 15 and the first sun gear 10 can therefore rotate relative to each other, whereas in a closed position of the clutch 20, the first sun gear 10 is locked to the planet carrier 15.

[0029] A second switching device is provided in the form of a brake 22, which is positioned between a housing-fixed support section 21 and the planet carrier 15. In an activated state of the brake 22, the planet carrier 15 is held relative to a housing 30, and in a deactivated state, its rotation is released relative to the housing 30.

[0030] The second sun gear 19 forms a double loose gear. The first tooth 28 of the second sun gear 19 engages with the second tooth section 18. A second tooth 29 of the second sun gear 19 is permanently engaged with a first tooth section 23 of the countershaft 13.

[0031] A second gear section 24 of the countershaft 13 engages with the input gear 14, which directly forms the differential input 12. The second gear section 24 has a smaller pitch circle diameter than the first gear section 23. As can be further seen, the countershaft 13 forms a loose gear, which is rotatably mounted on a corresponding bearing shaft 31. In other embodiments, the countershaft 13 is also implemented as a fixed gear.

[0032] In Fig.Figure 1 also illustrates the axial integration of the differential 6 according to the invention with respect to the axis of rotation 4 radially within the countershaft 13. The differential 6, with its input gear 14 and the corresponding planetary stages 32a, 32b, is located radially or partially radially within the countershaft 13, in particular radially within the second gear section 24. The input gear 14 and planetary stages 32a, 32b are arranged together with the second gear section 24 in a gear plane.

[0033] Furthermore, it can be seen that the planetary stages 32a, 32b and the input gear 14 are essentially (at least partially) at the same level as the countershaft 13 / the second gearing area 24 in the axial direction / along the axis of rotation 4.

[0034] In other words, in the drive unit 1 according to the invention, the planetary gear stage 7 consists of two sun gears 10, 19, a planet carrier / spacer 15, and at least two double planets 16. A ring gear is not required. The first sun gear 5 is operatively connected to the electric machine 2 and to the double planets 16 of the planetary gear stage 7. The second sun gear 19 is designed as a double loose gear and is operatively connected to the double planet 16 of the planetary gear stage 7 and to a further double loose gear 13, which is designed as a reduction gear. For space reasons, the differential 6 is arranged radially below the second double loose gear 13. The final drive is formed by means of the double loose gear 13 and the external teeth on the differential 6.

[0035] A clutch 20 and a brake 22 are proposed as switching elements. The clutch 20 is operatively connected to the first sun 10 and the planet carrier / bridge 15. The brake 22 is operatively connected to the planet carrier / bridge 15 and the housing 30. This allows the following switching states: 1st gear: The planet carrier / bridge 15 is fixed to the housing 30, with the brake 22 closed / activated and the clutch 20 open. 2nd gear: The planet carrier / bridge 15 rotates and the first sun 10 and the planet carrier / bridge 15 are locked together, with the brake 22 open / deactivated and the clutch 20 closed.

[0036] The gear ratio spread, or the step difference between 1st and 2nd gear, is achieved by means of the planetary gear set 7. One gear stage, usually 2nd gear, corresponds to the fixed ratio of the transmission structure after planetary gear set 7. Here, planetary gear stage 7 is locked with i = 1. In the illustrated embodiment, a 2nd gear ratio i fest > 5 can be easily implemented (i fest is the translation implemented between the second sun wheel 19 and the output shafts 3a, 3b).

[0037] A major advantage of the reduction gear design lies in the possibility of arranging the differential 6 in a highly integrated manner below the reduction gear double loose gear 13 with coaxial output 3a, 3b to the electric motor 2. Compared to an electric axle with a dual clutch, further advantages arise: no excessive speed of the transmission component in the 1st gear path when using 2nd gear; fewer tooth engagements with rolling elements in 2nd gear; simple design, no nesting of hollow shafts. Reference symbol list 1 drive unit 2 electric machine 3a first output wave 3b second output wave 4 axis of rotation 5 Rotor shaft 6 Differential 7 planetary gears 8 Gearbox unit 9 Input of the planetary gear 10 first sun wheel 11 Output of the planetary gear 12 Differential input 13 Countershaft 14-inch single wheel 15 planetary carriers 16 Double planetary wheel 17 First gear section of the double planetary gear 18 second gearing area of ​​the double planetary gear 19 second sun wheel 20 Clutch 21 Support section 22 Brake 23 First gear section of the countershaft 24 second gear area of ​​the countershaft 25 Stator 26 Rotor 27th gear stage 28 first gearing 29 second gearing 30 cases 31 Bearing shaft 32a first planetary stage 32b second planetary stage

Claims

[1] Electric drive unit (1) for a purely electric or hybrid-powered motor vehicle, comprising an electric machine (2), a differential (6) having two output shafts (3a, 3b), wherein the output shafts (3a, 3b) are arranged coaxially to a rotational axis (4) of a rotor shaft (5) of the electric machine (2), and a transmission device (8) comprising a planetary gear (7) coupling the rotor shaft (5) to the differential (6), wherein a first sun gear (10) forming an input (9) of the planetary gear (7) is connected to the rotor shaft (5) and an output (11) of the planetary gear (7) is permanently rotationally coupled to a differential input (12), characterized by, that the multi-start gear assembly (8) has a countershaft (13) coupling the output (11) of the planetary gear (7) with the differential input (12), wherein an input gear (14) forming the differential input (12) is arranged in the radial direction of the axis of rotation (4) inside the countershaft (13) and the planetary gear (7) has at least one double planetary gear (16) rotatably mounted on a planet carrier (15), wherein a first toothed section (17) of the at least one double planetary gear (16) engages with the first sun gear (10) and a second toothed section (18) of the at least one double planetary gear (16) engages with a second sun gear (19) coupled to the countershaft (13). [2] Drive unit (1) according to claim 1, characterized by , that the first gear section (17) has a larger pitch circle diameter than the second gear section (18). [3] Drive unit (1) according to one of claims 1 or 2, characterized by , that the planetary gear (7) is designed without a hollow gear. [4] Drive unit (1) according to one of claims 1 to 3, characterized by , that a coupling (20) is inserted between the first sun gear (10) and the planet carrier (15) in such a way that the first sun gear (10) is directly locked to the planet carrier (15) in a closed position of the coupling (20). [5] Drive unit (1) according to any one of claims 1 to 4, characterized by , that a brake (22) is installed between the planet carrier (15) and a housing-fixed support section (21) in such a way that the planet carrier (15) is fixed relative to the support section (21) in an activated state of the brake (22). [6] Drive unit (1) according to any one of claims 1 to 5, characterized by , that the countershaft (13) is designed as a loose gear or fixed gear. [7] Drive unit (1) according to any one of claims 1 to 6, characterized by , that a first toothed area (23) of the countershaft (13) is in tooth mesh with the second sun gear (19) and a second toothed area (24) of the countershaft (13) is in tooth mesh with the input gear (14). [8] Drive unit (1) according to claim 7, characterized by , that the first toothed section (23) of the layshaft (13) has a larger pitch circle diameter than its second toothed section (24).

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