Electric drive system for a motor vehicle

Abstract

Electric drive system (1) for a motor vehicle comprising a housing (2), an electric machine (3) comprising a rotor (5) non-rotatably connected to a rotor shaft (6), a planetary gear (7) and an axle drive (13), wherein the planetary gear (7) comprises exactly one sun gear (8) and exactly one planet carrier (9), and wherein the rotor shaft (6) is non-rotatably connected to the sun gear (8), wherein the planet carrier (9) carries a set of first planet gears (10) and a set of second planet gears (11), wherein the first planet gears (10) have a larger diameter than the second planet gears (11), wherein one of the first planet gears (10) and one of the second planet gears (11) are non-rotatably connected to each other, and wherein the sun gear (8) is in mesh with the first planet gears (10), wherein exactly one ring gear (12) is provided which is non-rotatably coupled to the housing (2).and which meshes with the second planet gears (11), characterized in that a coupling element (28) acting in a positive-locking manner in at least one direction of rotation is provided between the planet carrier (9) and an input shaft (15) of the axle drive (13), by means of which the planet carrier (9) is coupled or can be coupled to the input shaft (15) in such a way that a rotationally fixed connection between the planet carrier (9) and the input shaft (15) can be established at least in one forward direction of rotation of the rotor (5), wherein a first radial bearing (22) is provided, by means of which the planet carrier (9) is radially supported relative to the housing (2), wherein a planet carrier-side bearing half of the first radial bearing (22) is arranged radially outside a housing-side second bearing half,wherein the planet carrier (9) is supported radially outside via the first radial bearing (22) on a radially inwardly arranged and axially projecting collar of a housing intermediate wall, wherein a second radial bearing (29) is provided by means of which the planet carrier (9) is supported radially relative to the axle drive (13), wherein a first planet carrier-side bearing half of the second radial bearing (22) is arranged radially outside a second axle drive-side bearing half, wherein the second bearing half of the second radial bearing (29) is supported in particular on the input shaft (15) of the axle drive (13).

Description

The invention relates to an electric drive system for a motor vehicle comprising a housing, an electric machine, a planetary gear and an axle gear of the type defined in more detail in the preamble of claim 1. A generic electric drive system for a vehicle is essentially known from DE 10 2013 225 519 A1. This patent describes a system comprising an electric machine, a planetary gear set, and an axle drive, wherein the planetary gear set has a planet carrier with two rotationally fixed planet gears for each planet. These mesh with two different ring gears, which can be braked against a housing of the electric drive system by means of braking elements. This allows for two different gear ratios between the electric machine on the one hand and the axle drive on the other. The disadvantage of the described two-speed system lies particularly in the switching and braking elements for the two planetary gears. These must be designed as multi-plate shift elements, which leads to increased losses during open-circuit operation, i.e., when the vehicle is coasting. Ultimately, this results in a higher power requirement for the vehicle itself and thus reduces its range. A very similar design is also shown in US 2012 / 0 149 520 A1. In this design, the mechanism also switches between two different ring gears, whereby a claw switching element can be provided for switching between the ring gears. Other electric drive systems are known from US 9 033 839 B2, EP 1 142 743 B1, US 10 024 430 B2, DE 10 2020 109 112 A1 and the generic DE 10 2020 200 137 B3. The object of the present invention is to provide an improved electric drive system which in particular avoids or at least reduces the aforementioned disadvantages. According to the invention, this problem is solved by an electric drive system with the features in claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments are described in the dependent claims. The electric drive system according to the invention comprises, similar to the drive system in the prior art mentioned above, an electric machine whose rotor shaft is connected, on the one hand, in a rotationally fixed manner to the rotor of the electric machine, and on the other hand in a rotationally fixed manner to exactly one sun gear of the planetary gear. This assumes that the planet carrier carries a set of first planet gears and a set of second planet gears, the first planet gears having a larger diameter than the second planet gears, and each set of first planet gears and second planet gears being rotationally fixed to one another. The sun gear can be meshed with the first planet gears. Furthermore, a ring gear, which is fixed to the housing, is connected to the second set of planetary gears. The different diameters of the planetary gears allow for a very efficient and space-saving high gear ratio between the electric motor and the input shaft of the axle drive. "Rotationally fixed" within the meaning of the present invention means that the elements or components coupled to one another in such a way that they rotate at the same angular velocity. For this purpose, the elements or components connected in this way in a rotationally fixed manner must necessarily be arranged coaxially with one another. According to the invention, a coupling element is provided that acts in a positive-locking manner in at least one direction of rotation and is arranged between the planet carrier and an input shaft of the axle drive. The planet carrier is coupled to the input shaft via this coupling element, or can be coupled to the input shaft via this coupling element, such that a rotationally fixed connection between the planet carrier and the input shaft can be established in at least one forward direction of rotation of the rotor. For traction operation, i.e., when the vehicle is to be driven by the electric machine in its motor mode, power can be transmitted via this coupling element to the input shaft of the axle drive and thus ultimately to the wheels of the vehicle driven by the axle drive. Furthermore, according to the invention, a first radial bearing is provided by means of which the planet carrier is radially supported relative to the housing, wherein a planet carrier-side bearing half of the first radial bearing is arranged radially outside a housing-side second bearing half. The planet carrier is thus supported via the first radial bearing from the radial outside on a radially further inwardly arranged and axially projecting collar of a housing intermediate wall. Furthermore, according to the invention, a second radial bearing is provided by means of which the planet carrier is radially supported relative to the axle drive, wherein the first bearing half of the second radial bearing, on the planet carrier side, is arranged radially outside a second bearing half on the axle drive side. The support is thus provided by a planet carrier that rests externally on the axle drive. The second bearing half of the second radial bearing can preferably rest on the input shaft of the axle drive. In the previously mentioned configuration as a bevel gear differential, this bearing half of the second radial bearing would then rest accordingly on the differential cage. The term "forward rotation" refers to one of two possible directions of rotation of the rotor. Specifically, "forward rotation" refers to a direction of rotation of the rotor intended for forward operation of the vehicle. "Traction operation" refers to an operation of the electric machine in which a drive torque generated by the electric machine is transmitted from the electric machine to the axle drive for the purpose of propelling the vehicle. According to a particularly advantageous further development, the coupling element can have a first freewheel. This first freewheel is located between the planet carrier and an input shaft of the axle drive, by means of which the planet carrier is coupled to the input shaft in such a way that rotation of the planet carrier relative to the input shaft in a forward direction of rotation of the electric machine's rotor is blocked. Thus, only traction torques of the electric machine can be transmitted via the first freewheel between the ring gear and the housing. During deceleration, automatic disengagement occurs, and upon a change from deceleration to traction, automatic re-engagement takes place. The design is exceptionally simple and efficient, and without the need for any actuators, it enables the electric motor to transmit torque to the axle gearbox in the forward direction of rotation. In the reverse direction, i.e., when the power flows from the axle gearbox towards the electric motor, the motor does not need to be dragged along. Instead, it is automatically decoupled along with the entire planetary gearbox via the first freewheel, allowing coasting without additional power losses in the electric drive system. This increases the overall performance and efficiency of the electric drive system. As a result, a vehicle equipped with such an electric drive system as its primary or auxiliary drive has a greater range. Due to the decoupling during deceleration via the first freewheel, reverse travel and recuperation are inherently impossible. According to a particularly advantageous further development of this embodiment of the electric drive system according to the invention, the coupling element can therefore be provided with a second freewheel, which is arranged between the planet carrier and the input shaft. This second freewheel couples the planet carrier to the input shaft of the axle drive in such a way that rotation of the planet carrier relative to the input shaft opposite to the forward rotation of the rotor is blocked. This second freewheel thus operates during deceleration and not during traction. During traction operation of the electric motor, it therefore acts on the axle drive via the first freewheel, which opens during deceleration.At the same time, a connection is established via the second freewheel, which opens automatically during train operation, during push operation, so that both reversing and recuperation are possible. To maintain the aforementioned advantage of lossless or low-loss sailing, the second freewheel is designed to be switchable. In the context of the invention, "switchable" means that the freewheel can be turned on and off. When engaged, it functions like a non-switchable freewheel, blocking rotation in one direction and allowing free rotation in the opposite direction. When disengaged, the blockage is released, the freewheel is deactivated, and the connection can rotate freely in both directions. By disengaging the second freewheel, the blockage it creates during coasting is released, thus enabling lossless sailing with an electric drive system during coasting.If recuperation is required or a reverse drive is necessary, such operation can be enabled simply and efficiently by switching the second freewheel so that its blocking function is switched on again. As an alternative to such a design with one or two freewheels, one of which is switchable, the clutch element can also be provided with a dog clutch element with at least two switching positions. In a first switching position, this dog clutch element allows the planet carrier and the input shaft of the axle drive to be connected in a rotationally fixed manner, thus enabling a rotationally fixed connection for both traction and deceleration. This allows for forward and reverse travel, as well as energy recuperation during braking of the vehicle, with the electric motor then operating as a generator. In the second switching position of this dog clutch element, the input shaft of the axle drive and the planet carrier are then disengaged, allowing coasting without the electric motor and planetary gear having to be dragged along.This enables exceptionally energy-efficient sailing and, through the use of the claw switching element, allows for simple and efficient switching, which does not cause any losses in the open state of the claw switching element, as would be the case with lamellar switching elements, for example. A further very advantageous embodiment of this variant of the drive system according to the invention with the claw switching element further provides that the claw switching element has a third switching position in which the input shaft of the axle drive can be connected to the housing in a rotationally fixed manner. This position would then represent a parking lock position in which the input shaft of the axle drive is connected to the housing of the electric drive system in a rotationally fixed manner, so that the axle drive and the wheels of the vehicle cannot rotate. Alternatively, the electric drive system according to the invention can also provide a parking lock wheel and a switching element via which the input shaft of the axle drive can be connected to the housing in a rotationally fixed manner in order to implement a parking lock state. This variant with the parking lock wheel could be implemented both with the design of the clutch element with one or two freewheels and with the design of the clutch element with a claw switching element. According to a further highly advantageous embodiment of the electric drive system according to the invention, the second planet gears can be arranged to overlap axially with the axle drive. Such an axially overlapping arrangement with the axle drive, so that the second planet gears lie at least partially within the same area in the axial direction of the electric drive system, enables a very compact design in the axial direction. For the purposes of this invention, the axial direction shall always be understood as the axial direction along or parallel to the main axis of rotation of the electric drive system, here parallel to the axis of rotation of the rotor shaft. The radial direction, as described herein, is perpendicular to this axial direction. Another exceptionally advantageous design of the electric drive system involves the axle drive having a bevel gear differential with a differential cage. This differential cage, which can also be referred to as the differential housing, forms the differential input shaft. Particularly with this axle drive design, a significant space saving can be achieved through axial overlap with the second planet gears, i.e., the smaller diameter planet gears on the planet carrier. According to a particularly advantageous embodiment of the electric drive system of the invention, the rotor shaft can be supported by combination bearings. For this purpose, a first combination bearing and a second combination bearing are provided, each configured to provide axial and radial support for the rotor shaft relative to the housing. In both the first and second combination bearings, the respective rotor shaft-side bearing half is arranged radially within the respective housing-side bearing half. The rotor shaft is thus supported against parts of the housing, such as radially extending intermediate walls of the housing, which lie radially outside the rotor shaft. The electric machine can preferably be implemented as an axial flux machine. Further advantageous embodiments of the electric drive system also result from the exemplary embodiments, which are described in more detail below with reference to the figure. Figure 1 shows a first possible embodiment of an electric drive device according to the invention; and Figure 2 shows a second possible embodiment of an electric drive device according to the invention. Figure 1 schematically depicts an electric drive system 1 for a motor vehicle (not shown). The electric drive system 1 comprises a housing 2 and an electric machine 3 with a stator 4 fixed against rotation relative to the housing 2 and a rotor 5 rotatable relative to the stator 4, which in turn is fixed against rotation to a rotor shaft 6. The electric drive system 1 also comprises a planetary gear set 7 with a sun gear 8, which is non-rotatably connected to the rotor shaft 6, and a planet carrier 9, which carries a set of first planet gears 10 and a set of second planet gears 11. The first planet gears 10 have a larger diameter than the second planet gears 11. The adjacent first and second planet gears 10 and 11 are each non-rotatably coupled to each other. The second planet gears 11, with a smaller diameter than the first planet gears 10, mesh with a ring gear 12 of the planetary gear set 7. This ring gear 12 is non-rotatably mounted relative to the housing 2. In addition, the electric drive system 1 includes an axle drive 13, which is designed here as a bevel gear differential. An output shaft 14 of the axle drive 13 forms the output, indicated by the arrows, in particular to the wheels of the vehicle. The differential cage 15 forms the input shaft 15 of the axle drive 13 and is coupled, or can be coupled, to the planet carrier 9 in a manner described in more detail later. The differential cage 15 can also be fixed against rotation relative to the housing 2 by means of a parking lock gear 16 and a corresponding switching element 17, in order to implement a parking lock for the vehicle. The assembly shown here with the single ring gear 12 of the planetary gear 7 ultimately represents a single-gear system for driving or at least partially driving the motor vehicle via the electric drive system 1. Between the differential cage 15, which serves as the input shaft 15 of the axle drive 13, and the planet carrier 9, a coupling element 28 is arranged, which acts in a positive-locking manner in at least one direction of rotation and is outlined here by a dashed line. In the configuration shown in Fig. 1 of the electric drive system 1, this coupling element 28 comprises a first freewheel 18 and a second switchable freewheel 19. The first freewheel 18 transmits only traction torque from the electric motor 3 to the output shaft 14, while in overrun mode, the first freewheel 18 automatically rotates freely, thus decoupling the electric motor 3 and the planetary gear 7 from the axle drive 13. This allows overrun mode without dragging the electric motor 3 and the planetary gear 7, enabling efficient and low-loss operation of the electric drive unit 1 during so-called coasting, i.e., when the vehicle is coasting without power. When switching back from overrun to traction, the first freewheel 18 engages automatically, and the torque from the electric motor 3 can again be transmitted to the output shaft 14. The first freewheel 18 alone would not allow for recuperation, nor would it be possible to reverse the vehicle using the electric motor 3, as this would require power transmission between the output 14 and the electric motor 3 in the opposite direction, i.e., the direction of thrust. To enable this, a second freewheel 19 is provided. This freewheel 19 is designed to transmit torque during deceleration but not during acceleration. It thus complements the first freewheel 18, making recuperation and reverse driving possible. The second freewheel 19 is switchable. By switching this second freewheel 19, as shown in the illustration in Fig.As indicated by the arrow 1, the locking function can be switched on or off, so that the second freewheel 19 either operates in the described manner as a locking freewheel 19 in thrust or can be switched to a freewheel 19 that is free in both thrust and traction, so that depending on the switching position of this second freewheel 19 either recuperation or reverse driving is possible, while with the locking function switched off, sailing without dragging the electric machine 3 is made possible. The combination of the two freewheels 18, 19, of which the second freewheel 19 is switchable, thus enables a permanent connection in one direction and a switchable connection in the other direction of rotation or force. The two freewheels 18, 19 can preferably be combined as an integrated coupling element 28, which is arranged, in particular in the radial direction R, outside the differential cage 15 but axially overlapping it. The assembly is preferably easily accessible from the outside of the housing 2, in particular to allow simple and efficient actuation of the switching actuator of the second freewheel 19, for example by means of a hydraulic line, an electrical signal line, and / or the like. Overall, the assembly can be realized in an exceptionally compact manner. Not only can the coupling element 28 with the two freewheels 18, 19 be designed to overlap the axle drive 13 or its differential cage 15 in the axial direction A of the output shaft 14 or the rotor shaft 6, but also, in particular, the set of the second planet gears 11 and preferably the ring gear 12. All of this results in a very compact assembly, especially in the axial direction A. The electric machine 3, which can be designed in particular as an axial flux machine, can be supported on the housing 2 with respect to its rotor shaft 6 by a first combination bearing 20 and a second combination bearing 21, wherein the rotor shaft 6 is arranged radially inside and the housing is arranged radially outside the two combination bearings 20, 21. The combination bearings can transmit both axial and radial forces, and are thus a combination of axial and radial bearings. In particular, they can be angular contact ball bearings, four-point contact ball bearings, or the like. The planet carrier 9 of the planetary gear 7 can then also be supported on the housing 2 via a first radial bearing 22, wherein the housing 2 is arranged radially inside and the planet carrier 9 radially outside this first radial bearing 22. The radial bearing 22 can be designed, in particular, as a cylindrical roller bearing or a deep groove ball bearing, as is generally known and customary. The planets 10, 11 are mounted on the planet carrier via a further radial bearing 23 in a manner known per se. Further relevant bearing points in the assembly of the electric drive system 1 are located in the area of ​​the output shaft 14, where, in the illustration of Fig. 1 on the left, a radial bearing 26 is arranged and, in the illustration of Fig. 1 on the right, a combination bearing 27, which can transmit axial and radial forces, is arranged. In these, the radially inner output shaft 14 is supported on the radially outer housing 2. Figure 2 shows an alternative embodiment of the electric drive system 1. The same components are designated with the same reference numerals and will not be explained again below. Their construction is comparable to that discussed in the previous embodiment. The difference lies in the fact that the clutch element 28 has a claw switching element 24 instead of the two freewheels 18, 19. This claw switching element 24 can be switched into different positions, particularly from outside the housing 2, via an actuator 25, which is indicated here only by a line. In the embodiment shown in Figure 2, there are three discrete switching positions. The middle switching position shown in Figure 2 is a neutral position, in which the claw switching element 24 is connected only to the differential cage 15 as the input shaft 15 of the axle drive 13.This means it can rotate freely, which is typically referred to as the neutral position or colloquially as "idle". If the claw-type switching element 24 is now shifted to the left in the illustration of Fig. 2, it connects the planet carrier 9 to the differential cage 15 as the input shaft 15 of the axle drive 13. This creates a rotationally fixed connection between the input shaft 15 of the axle drive 13 and the planet carrier 9. This rotationally fixed connection acts in both the tensile and compressive directions, so that when the rotationally fixed connection is engaged, forces are transmitted in both directions via the claw-type switching element 24. In this switching position, it is therefore possible to drive the output shaft 14 and, via the output shaft 14, to drive the electric machine, which then acts as a generator to recover energy when the vehicle is decelerating.In addition to this so-called recuperation, it is also possible to drive the vehicle in reverse by rotating the electric machine in the opposite direction and thus, as it were, delivering force to the output shaft 14 in the direction of thrust. To enable energy-efficient coasting of the vehicle, the claw switching element 23 is simply switched back to its neutral position, as shown in Fig. 2, via the actuator 25. This allows for low-loss coasting without dragging the electric motor 3 and the planetary gear 7. As already mentioned, the claw switching element 24 in Fig. 2 has a third switching position. In this third switching position, the claw switching element 24 in Fig. 2 is moved to the right by the actuator 25. It then connects the input shaft 15 of the axle drive 13 to the housing 2 of the electric drive system 1 in a rotationally fixed manner. This enables a parking lock function because the input shaft 15 is now held rotationally fixed relative to the drive and thus the output shaft 14 cannot rotate. Of course, it would also be conceivable to implement the claw switching element 24 with only two switching positions instead of three: in the illustration of Fig. 2, the neutral position and the left position for connecting the planet carrier 9 to the input shaft 15. To still be able to implement a parking lock, the parking lock wheel 16 with its switching element 17 could be integrated into the structure of Fig. 2 analogously to the illustration in Fig. 1. Conversely, this would also be conceivable, in order to use the intermediate element extending in the axial direction A instead of the parking lock wheel with its radial extension R. This intermediate element could then be held rotationally fixed against the housing by the switching element 17. In addition to the bearings already described, a second radial bearing 29 can be seen in Fig. 2. This radial bearing 29 is located between the planet carrier 9 and the differential cage 15, forming the input shaft 15 of the axle drive 13. Its bearing half on the planet carrier side is radially outward, and its bearing half on the axle drive side is radially inward. The planet carrier 9 is thus supported externally on the differential cage 15 by this second radial bearing 29. This second radial bearing 29 would, of course, also be possible in the configuration shown in Fig. 1, although it is not shown there for the sake of simplicity. Furthermore, with regard to the actuator 25, the axially overlapping and radially outside the differential cage 15 arrangement is of course also advantageous here, so that it is relatively easy to access from outside the housing 2, as has already been described above for an actuator of the second switchable freewheel 19.

Claims

Electric drive system (1) for a motor vehicle comprising a housing (2), an electric machine (3) comprising a rotor (5) non-rotatably connected to a rotor shaft (6), a planetary gear (7) and an axle drive (13), wherein the planetary gear (7) comprises exactly one sun gear (8) and exactly one planet carrier (9), and wherein the rotor shaft (6) is non-rotatably connected to the sun gear (8), wherein the planet carrier (9) carries a set of first planet gears (10) and a set of second planet gears (11), wherein the first planet gears (10) have a larger diameter than the second planet gears (11), wherein one of the first planet gears (10) and one of the second planet gears (11) are non-rotatably connected to each other, and wherein the sun gear (8) is in mesh with the first planet gears (10), wherein exactly one ring gear (12) is provided which is non-rotatably coupled to the housing (2).and which meshes with the second planet gears (11), characterized in that a coupling element (28) acting in a positive-locking manner in at least one direction of rotation is provided between the planet carrier (9) and an input shaft (15) of the axle drive (13), by means of which the planet carrier (9) is coupled or can be coupled to the input shaft (15) in such a way that a rotationally fixed connection between the planet carrier (9) and the input shaft (15) can be established at least in one forward direction of rotation of the rotor (5), wherein a first radial bearing (22) is provided, by means of which the planet carrier (9) is radially supported relative to the housing (2), wherein a planet carrier-side bearing half of the first radial bearing (22) is arranged radially outside a housing-side second bearing half,wherein the planet carrier (9) is supported radially outside via the first radial bearing (22) on a radially inwardly arranged and axially projecting collar of a housing intermediate wall, wherein a second radial bearing (29) is provided by means of which the planet carrier (9) is supported radially relative to the axle drive (13), wherein a first planet carrier-side bearing half of the second radial bearing (22) is arranged radially outside a second axle drive-side bearing half, wherein the second bearing half of the second radial bearing (29) is supported in particular on the input shaft (15) of the axle drive (13). Electric drive system (1) according to claim 1, characterized in that the coupling element (28) has a first freewheel (18) between the planet carrier (9) and the input shaft (15) of the axle drive (13), by means of which the planet carrier (9) is coupled to the input shaft (15) in such a way that a rotation of the planet carrier (9) relative to the input shaft (15) in a forward direction of rotation of the rotor (5) is blocked. Electric drive system (1) according to claim 2, characterized in that the coupling element (28) has a second freewheel (19) between the planet carrier (9) and the input shaft (15), which is switchable, and by means of which the planet carrier (9) is coupled to the input shaft (15) in such a way that a rotation of the planet carrier (9) relative to the input shaft (15) against the forward direction of rotation of the rotor (5) is blocked in the switched-on state. Electric drive system (1) according to claim 1, characterized in that the coupling element (28) has a claw switching element (24) with at least two switching positions, by means of which the planet carrier (9) and the input shaft (15) of the axle drive (13) can be connected in a rotationally fixed manner in a first switching position, and by means of which the planet carrier (9) and the input shaft (15) of the axle drive (13) are disconnected from each other in a second switching position. Electric drive system (1) according to claim 4, characterized in that the claw switching element (24) has a third switching position in which the input shaft (15) can be connected to the housing (2) in a rotationally fixed manner. Electric drive system (1) according to one of claims 1 to 4, characterized in that the input shaft (15) of the axle drive (13) can be connected to the housing (2) in a rotationally fixed manner via a parking lock wheel (16) and a switching element (17). Electric drive system (1) according to one of the preceding claims, characterized in that a first combination bearing (20) and a second combination bearing (21) are provided, each of which is arranged to provide axial and radial support for the rotor shaft (6) against the housing (2), wherein in both the first combination bearing (20) and the second combination bearing (21) the respective rotor shaft-side bearing half is arranged radially within the respective housing-side bearing half. Electric drive system (1) according to one of the preceding claims, characterized in that the electric machine (3) is designed as an axial flux machine.

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