Electrical drive systems for automobiles

Abstract

The present invention relates to an electric drive system (1) for a motor vehicle, comprising a first electric machine (3) having a first rotor (6), a differential transmission (9) having a differential input shaft (14) and a first differential output shaft (15) and a second differential output shaft (16), the two differential output shafts (15, 16) being arranged coaxially with the first rotor (6), a first side shaft (17) non-rotatably connected to the first differential output shaft (15), and a second side shaft (18) non-rotatably connected or connectable to the second differential output shaft (16). The electric drive system according to the invention comprises a second electric machine (4) having a second rotor (8) arranged coaxially with the first rotor (6), a first shift member (SE1) by means of which the first rotor (6) can be non-rotatably connected to a first side shaft (17), and a second shift member (SE2) by means of which the second rotor (8) can be non-rotatably connected to a second side shaft (18), and the first rotor (6) is or can be non-rotatably connected to a differential input shaft (14).

Description

[Technical field]

[0001] The invention relates to an electric drive system for a motor vehicle with an electric machine and a differential transmission and gear stages as defined in the preamble of claim 1. [Background technology]

[0002] DE 10 200 033 337 A1 describes such an electric drive, which comprises an electric machine driving, via a three-shaft planetary differential, two differential output shafts or side shafts which drive the wheels of the driven vehicle. The rotors of the electric machine and the planetary differential are here arranged coaxially with the side shafts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] DE 102007021359 Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide an improved electric drive system, as defined in the preamble of claim 1, which allows for a compact construction in the axial direction and at the same time can be switched very flexibly and can operate very efficiently.

[0005] According to the invention, this problem is solved by an electric drive system with the features of claim 1, and here in particular with the features of the characterizing part of claim 1. Advantageous embodiments and developments emerge from the dependent claims which are dependent on claim 1.

[0006] The electric drive system for a motor vehicle according to the invention comprises, as in the prior art arrangements mentioned at the beginning, a first electric machine with a first rotor and a differential transmission with a differential input shaft and a first and a second differential output shaft, the differential output shaft being arranged coaxially with the first rotor. The electric drive system further comprises a first side shaft non-rotatably connected to the first differential output shaft and a second side shaft non-rotatably connected or connectable to the second differential output shaft.

[0007] A non-rotatable connection in the context of the present invention is understood to mean a connection between two rotatably supported parts which are arranged coaxially with respect to one another and which are connected to one another by means of a non-rotatable connection in such a way that the two parts rotate with the same angular velocity.

[0008] According to the invention, there is further provided a second electric machine having a second rotor arranged coaxially with the first rotor, the first rotor being non-rotatably connected or connectable to a differential input shaft, a first shift member enabling the non-rotatably coupling of the first rotor to the first side shaft, and a second shift member providing a non-rotatable coupling of the second rotor to the second side shaft.

[0009] This inventive configuration of the electric drive system allows a very compact yet very flexible configuration in which the side shafts and thus the wheels of the vehicle connected via the side shafts can be selectively driven directly and independently of each other by one of the two electric machines via the first and second shift members. Furthermore, the inventive configuration of the electric drive system allows both side shafts to be driven exclusively via the first electric machine via the rotor of the first electric machine, which is non-rotatably connected or connectable to the differential input shaft. This results in a very efficient configuration in which it is possible to selectively switch between a differential mode with electric machines or a single-wheel drive with torque vectoring. In the normal differential mode, the second electric machine can be decoupled from the differential and does not have to be towed together, thereby realizing an increase in efficiency.

[0010] Here, the differential transmission itself can be designed in almost any manner. A typical design is, for example, a differential transmission in the form of a bevel gear transmission with a differential cage. In order to achieve a correspondingly compact design, particularly in the axial direction of the rotation shaft of the electric machine, the shift elements or at least one of the two shift elements can be designed to overlap in the axial direction with the differential cage, i.e. to lie at least partially in a common plane perpendicular to the axial direction, which contains both at least one shift element and at least a part of the differential cage. Correspondingly, this design must of course lie in another radial plane, so that the elements do not interfere with each other.

[0011] However, according to a very preferred development of the electric drive system according to the invention, it is expedient that the differential gear is designed as a three-shaft planetary differential. Such a three-shaft planetary differential with a sun gear, an annular gear and a planet carrier or alternatively with a first sun gear, a second sun gear and a planet carrier can be used as the differential gear. In this case, the differential input shaft can be connected in a rotationally fixed manner to a first shaft of the three-shaft planetary differential, for example an annular gear. In this case, the first differential output shaft can be connected in a rotationally fixed manner to a second shaft of the three-shaft planetary differential, for example a planet carrier. In this case, the second differential output shaft can also be connected in a rotationally fixed manner to a third shaft of the three-shaft planetary differential, for example a sun gear. Such an arrangement with a planetary differential allows, for example in the above-mentioned preferred interconnection, a very compact construction in the axial direction, so that, overall, a more compact drive system is realized than with a bevel gear differential.

[0012] Particularly preferably, the differential gearing has exactly one sun gear, exactly one planet carrier and exactly one ring gear.

[0013] In another very advantageous embodiment of the electric drive system according to the invention, a third shift member is further provided, via which the first rotor can be coupled non-rotatably to the differential input shaft, i.e. via such a third shift member the connection between the first electric machine and the differential gearing is switchable, so that, in particular in the case of single-wheel drive via one of the electric machines, it is not necessary to pull the differential gearing together, which makes the construction very energy-efficient.

[0014] Here, as viewed in the axial direction, the first electric machine, the first shift member, the differential transmission, the second shift member and the second electric machine can be arranged one after the other in the order described, which makes the construction approximately symmetrical and very compact in the axial direction, particularly when a planetary differential is used as the differential transmission, but also when a planetary differential is used as the differential transmission.

[0015] As an alternative to the switchable connection of the first rotor to the differential transmission, a highly preferred development of the electric drive system according to the invention provides that the first rotor is permanently connected to the differential input shaft and that a fifth shift member is provided, via which the second differential output shaft can be connected to the second side shaft in a fixed manner. This connection is thus moved to the area of ​​the second differential output shaft or the second side shaft and to the area of ​​the connection of the second electric machine. This construction therefore allows a very efficient construction for operation with the first electric machine, and a simplified construction for the drive control, since here only a shifting process with the fifth shift member is required for the differential mode via the first electric machine, by permanently connecting the first rotor of the first electric machine to the differential input shaft. If this is not the case, the structure can be switched so that the second electric machine is completely decoupled or, in the case of single-wheel drive, simply and efficiently coupled, while the first electric machine is permanently coupled to the other side shaft, in this case via a differential transmission.

[0016] Furthermore, when switching the individual shift members independently of one another, it is possible to correspondingly use both operation with a differential lock using one electric machine, here the first electric machine, and also operation with a differential lock using two electric machines.

[0017] According to a very advantageous development of the electric drive system according to the invention, it is particularly efficient in terms of drive control if the first, second and fifth shift members are coupled in such a way that they can be operated via a single actuator. Such an operation via a single actuator is much more efficient than operating each shift member via its own actuator. On the one hand, only one actuator is required, and on the other hand, the omission of a separate actuator not only saves constructional space and weight, but also eliminates wiring that must be routed to the individual actuators and that must always be designed in a correspondingly complex manner in the constructional space provided in a small transmission. A single actuator for operating three coupled shift members is therefore a significant advantage.

[0018] The connection of the three shift members can be made in particular such that in a first position of the actuator, the first and second shift members are closed, while the fifth shift member is open. In a second position of the actuator, the first and second shift members are opened, while the fifth shift member is closed. With this structure, it is possible to efficiently switch between a mode using the first electric machine and a single-wheel drive via the actuator.

[0019] According to a very advantageous development of this second embodiment variant with a permanently non-rotatably connected differential input shaft and a first rotor, in accordance with a further very advantageous configuration, the first electric machine, the differential transmission, the first shift member and the second electric machine are arranged one after the other in the stated order, as viewed in the axial direction. This can be realized with a correspondingly compact size and allows a very short axial construction of the electric drive system, especially when a planetary differential is used. In this case, according to an advantageous embodiment, the first rotor, the second rotor, the differential transmission and the two side shafts are all arranged coaxially with respect to one another. [Brief description of the drawings]

[0020] [Figure 1] 1 shows a first possible configuration of an electric drive system according to the invention; [Diagram 2] 3 shows a second possible configuration of the electric drive system according to the invention. [Diagram 3] 3 shows a shift table for illustrating possible states of the electric drive system shown in FIG. 2; [Figure 4] 3 shows an alternative configuration of the electric drive system according to FIG. 2; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 1 shows an electric drive system 1, which is used to drive a motor vehicle, not shown here. The drive output to the wheels of the motor vehicle is symbolically represented by an arrow with the reference number 2, which thus essentially represents the driven wheels 2 of the motor vehicle 1. The electric drive system 1 comprises a first electric machine 3 as well as a second electric machine 4. A first stator 5 of the first electric machine 3 is connected to a housing of the electric drive system 1 in a rotationally fixed manner.

[0022] The first rotor 6 of the first electric machine 3 is arranged coaxially with the second rotor 8 of the second electric machine 4. The second electric machine 4 has a second stator 7, which is likewise connected in a rotationally fixed manner to the housing of the electric drive system 1. The two electric machines 3, 4 are therefore arranged coaxially about a common axis of rotation, which is here formed by the lower border of what is shown in the figure. Only the upper half of the rotationally symmetrical construction is therefore shown in the figure. The common axis of rotation of the rotors 6, 8 of the electric machines 3, 4 here defines the axial direction a of the electric drive system 1.

[0023] Between the two electric machines 3, 4, as viewed in the axial direction a, there is a differential transmission 9. The differential transmission 9 is advantageously arranged coaxially with the common axis of rotation of the rotors 6, 8. The differential transmission 9 can be configured as a bevel gear transmission, for example with a differential cage. However, in order to be able to realize the construction along the axial direction a as compact as possible, the differential transmission 9 is realized here as a planetary differential. This planetary differential comprises a sun gear 11, an internal gear 12 as well as a double planetary carrier 13. Here, a differential input shaft 14 is connected to the internal gear 12. The double planetary carrier 13 is itself connected in a non-rotatable manner to a first differential output shaft 15, while the sun gear 11 is connected to a second differential output shaft 16. The first differential output shaft 15 is itself connected in a non-rotatable manner to a side shaft 17, which establishes a connection with the driven wheels 2, for example directly or possibly also via further gear stages not shown here. The same applies to the side shaft 18 which establishes the connection between the driven wheels shown on the right hand side of FIG.

[0024] Axial-adjacent to the differential transmission 9, or here its double planetary carrier 13, on the side facing the first electric machine 3, there is a first shift member SE1, and axially adjacent to this first shift member SE1, a third shift member SE3. Via the first shift member SE1, the first rotor 6 can be connected non-rotatably to a side shaft 17 and to a first differential output shaft 15. In this case, the first electric machine 3 directly drives the driven wheels 2, shown here on the left. Alternatively to this, via the aforementioned shift member SE3, the first rotor 6 can be connected to a differential input shaft 14 and thus to an internal gear 12 of the differential transmission 9, so that the two side shafts 17, 18 are driven via the differential transmission 9.

[0025] Between the differential transmission 9 and the second electric machine 4, substantially mirror-symmetrically in the axial direction a with respect to the differential transmission 9, as viewed from the differential transmission 9, there is a second shift member SE2 and a fourth shift member SE4 axially adjacent to the second shift member SE2. The second shift member SE2, like the first shift member SE1 for the first electric machine 3, realizes the connection of the second electric machine 4 or its rotor 8 to the right-hand side shaft 18 or the second differential output shaft 16, so that the driven wheels 2, shown on the right side of FIG. 1, can be driven exclusively via the second electric machine 4. Alternatively, when the fourth shift member SE4 is engaged, instead of or in addition to being driven by the first electric machine 3, the differential input shaft 14 can also be driven via the second electric machine 4, so that the two side shafts 17, 18 are driven correspondingly via the differential output shafts 15, 16 and by means of the differential transmission 9.

[0026] This construction allows a great deal of flexibility, as it is possible to drive either via one or the other of the two electric machines 3, 4 as single-wheel drive in torque vectoring mode, for example via a differential transmission 9 by one of the electric machines 3, 4, or, in particular for boost mode, via both electric machines 3, 4. Furthermore, the two electric machines 3, 4 can also be decoupled, so that in cases where they are not needed, there is no need to tow them together, which makes the electric drive system 1 according to the invention very energy efficient.

[0027] An alternative construction of the electric drive system 1 can be seen from the diagram in FIG. 2. Here, in the axial direction a, all shift elements are located between a differential gear 9 in the form of an epicyclic differential, which is configured similarly to the one shown in FIG. 1, and the second electric machine 4. In this case, the first rotor 6 of the first electric machine 3 is permanently connected in a non-rotatable manner to the differential input shaft 14. The first differential output shaft 15 and the left side shaft 17, which is connected in a non-rotatable manner to this first differential output shaft 15, are again connected in a non-rotatable manner to the double planet carrier 13, as was the case in the embodiment according to FIG. 1. The first electric machine 3 and the differential gear 9, which is arranged directly adjacent to this first electric machine 3 in the axial direction a, are followed in the axial direction a by a first shift element SE1.

[0028] The first shift member SE1 is configured here as a lock shift member and can connect the double planet carrier 13 to the second differential transmission output shaft 16 and thus to the sun gear 11 of the differential transmission 9. In this locked state, in which the double planet carrier 13 and the sun gear 11 rotate together, the first electric machine 3 is connected non-rotatably to the first differential output shaft 15 and thus to the left side shaft 17.

[0029] The first shift member SE1 is here generally formed as a locking shift member. In the configuration of Fig. 2, the differential transmission 9 can also be formed, for example, as a bevel gear differential, in which case the first shift member SE1 is formed in such a way that it can lock the differential transmission and thereby achieve the same effect as described above for the locking of the planetary differential.

[0030] Advantageously, in the torque flow between the left side shaft 17 or the right side shaft 18 and the wheels 2, a gear stage 20, 21, i.e. a first gear stage 20 and a second gear stage 21, respectively, are arranged. Advantageously, these gear stages 20, 21 can likewise be used in the corresponding places of the structure of FIG. 1. The advantageous features and configurations of the gear stages 20, 21 listed below are also applicable to the structure of FIG. 1. Advantageously, the gear stages 20, 21 are configured as simple planetary gear trains, with a sun gear of each of the simple planetary gear trains being connected in a rotation-tight manner to the respective side shaft 17, 18, a ring gear of each of the simple planetary gear trains being connected in a rotation-tight manner to the housing, and a planet carrier of each of the simple planetary gear trains being connected in a rotation-tight manner to a respective wheel.

[0031] Between the gear stages 20, 21 and the wheels there are wheel-side axles, not shown in detail, so that the gear stages 20, 21 are preferably arranged directly adjacent to the two electric machines 3, 4 and not, for example, in the vicinity of the wheels 2. It is particularly advantageous for the gear stages and the differential gear 9 to be arranged in a common housing.

[0032] Adjacent to this first shift member SE1 in the axial direction a is a fifth shift member SE5, which can either connect the second differential output shaft 16 to the right side shaft 18 in a rotationally fixed manner or, as shown in the exemplary embodiment shown, can also decouple the two members from each other. The two shift members SE1 and SE5 are also followed, also viewed in the axial direction a, by a second shift member SE2, which is also designed to connect the second electric machine 4 or the second rotor 8 to the right side shaft 18. This second shift member SE2 can also be realized as an open freewheel, which opens accordingly when the fifth shift member SE5 is engaged, i.e. when the second differential output shaft 16 and the right side shaft 18 are connected, and thus decouples the second electric machine 4. When the fifth shift member SE5 is open, the drive of the right side shaft 18 is achieved via the second electric machine 4 and the second shift member SE2 configured as a freewheel.

[0033] This construction allows for a large number of different positions in the compactly constructed construction in the axial direction a, which are correspondingly visualized in the shift table shown in Fig. 3. The shift members SE1, SE2 and SE5 as shown in Fig. 2 are closed if a cross is shown in the shift table and are open if the corresponding fields in the shift table are blank.

[0034] In the structure of FIG. 2, advantageously viewed in the axial direction a, the first gear stage 20, the first electric machine 3, the differential transmission 9, the first shift member SE1, the second electric machine 4 and the second gear stage 21 are arranged one after the other in the order described.

[0035] In contrast, advantageously, in the structure of FIG. 1, as viewed in the axial direction a, the first gear stage 20 (not shown in FIG. 1), the first electric machine 3, the first shift member SE1, the differential transmission 9, the second shift member SE2, the second electric machine 4 and the second gear stage 21 (also not shown in FIG. 1) are arranged successively in the order described.

[0036] In the embodiment of Fig. 2, the two electric machines 3, 4 are configured as axial machines, which allows for a particularly compact construction in the axial direction and also represents an overall highly efficient electric drive system 1. The configuration of the electric machines 3, 4 as axial machines is also realised with the same advantages in the configurations of Figs. 1 and 4.

[0037] The first state is an efficiency mode with only one electric machine, here the first electric machine 3. In this case, the fifth shift member SE5 is closed, so that the second differential output shaft 16 is connected to the right side shaft 18, while the other two shift members SE1 and SE2 are open. The first electric machine 3 drives both the first differential output shaft 15 and the second differential output shaft 16 via the differential transmission 9, while the second electric machine 4 is decoupled by the open second shift member SE2. This achieves an efficiency mode in which the first electric machine 3 is driven while the second electric machine 4 remains stopped.

[0038] By closing the two shift members SE1, SE2 and simultaneously opening the fifth shift member SE5, the planetary gear used as the differential gear 9 is locked, so that the first rotor 6 is non-rotatably connected to the left side shaft 17, while the right side shaft 18 is non-rotatably connected directly to the second rotor 8 of the second electric machine 4 via the second shift member SE2. This results in a single-wheel drive in torque vectoring mode, in which each driven wheel 2 can be driven via one of the electric machines 3 or 4, respectively. In this single-wheel drive, there is no connection between the left side shaft 17 and the right side shaft 18.

[0039] Alternatively, in the embodiment of the electric drive system 1 according to FIG. 2, the differential lock mode can be realized either with one or with both of the electric machines 3, 4. In the differential lock mode with one electric machine, here the first electric machine 3, the first shift member SE1 is closed, since on the one hand it is necessary to lock the planetary differential used as the differential transmission 9. The fifth shift member SE5 connects the second differential output shaft to the right side shaft 18, while the second shift member SE2 is open, whereby the second electric machine 4 is correspondingly decoupled. In this case, the first electric machine 3 drives both driven wheels 2 in the differential lock mode.

[0040] By additionally closing the second shift member SE2, a second electric machine 4 can also be added, so that a differential lock mode with both electric machines is also achieved, with a correspondingly higher power output.

[0041] With the alternative configuration according to FIG. 2, a further operating mode, i.e. torque vectoring via the differential transmission 9, is realized. In this further operating mode, the fifth shift member SE5 and the second shift member SE2 are closed, while the first shift member SE1 is open. In this case, the second rotor 8 is connected in a rotationally fixed manner to the right side shaft 18 and also to the second differential output shaft 16. Thus, via the second rotor 8, a part of the second torque of the second electric machine 4 is introduced to the right side shaft 18, and another part of the second torque of the second electric machine 4 is introduced to the differential transmission 9. At the same time, in this operating mode, the first electric machine 3 supplies a first torque to the differential transmission 9. In this operating mode, it is possible to determine how much torque finally reaches the two side shafts 17, 18 via the magnitude of the torques supplied, i.e. the magnitude of the first and second torques. In this case, the two torque amounts may be different.

[0042] In this operating mode, it is necessary to control the three shift members SE1, SE2 and SE5 independently of one another. This requires corresponding costs in terms of actuator members and wiring to the actuators for the individual shift members SE1, SE2 and SE5. Now, in order to reduce costs and nevertheless ensure the two most important states, namely the efficiency mode with electric machine and the single-wheel drive, the three shift members SE1, SE2 and SE5 can also be coupled and controlled via a single actuator 10. This actuator 10 is shown in FIG. 4, which otherwise corresponds to FIG. 2. This actuator 10 realizes a very simple and efficient control. This can be realized in particular in such a way that either the first shift member SE1 or the second shift member SE2 is open, while the fifth shift member SE5 is correspondingly closed, so that the efficiency mode with an electric machine, here the first electric machine 3, is used, as shown in FIG. 3. This shift position of the actuator 10 for the efficiency mode is referred to here as the second position. In that other shift position, referred to here as the first position, the actuator 10 can switch the three shift members SE1, SE2, SE5 accordingly, so that the first shift member SE1 and the second shift member SE2 are accordingly closed and the fifth shift member SE5 remains open. As is also evident from the shift table in Fig. 3, there is a switch for single-wheel drive, where in torque vectoring mode each of the driven wheels 5 can be driven independently of one another via a respective electric machine 3, 4.

[0043] This efficient combination of the three shift members SE1, SE2 and SE5 via one actuator 10 results in the corresponding omission of the other possibility of a differential lock mode, which in this case is likewise available in the torque vectoring mode on the software side, so that the omission of the mechanical differential lock mode is not a practical limitation.

Claims

1. An electric drive system (1) for a motor vehicle, comprising: a first electric machine (3) having a first rotor (6); A differential transmission (9) having a differential input shaft (14) and a first differential output shaft (15) and a second differential output shaft (16), the two differential output shafts (15, 16) being arranged coaxially with the first rotor (6); An electric drive system (1) having a first side shaft (17) non-rotatably connected to the first differential output shaft (15) and a second side shaft (18) non-rotatably connectable to the second differential output shaft (16), a second electric machine (4) having a second rotor (8) arranged coaxially with the first rotor (6) connected to the differential input shaft (14) so ​​as not to rotate relative to the first rotor (6); a first shift member (SE1) formed as a lock shift member; a second shift member (SE2) by means of which the second rotor (8) can be non-rotatably connected to the second side shaft (18); The differential transmission (9) is formed as a planetary differential, the differential input shaft (14) is connected to an internal gear (12) so as to be non-rotatable relative to the gear, the first differential output shaft (15) is connected to a double planetary carrier (13) so as to be non-rotatable relative to the gear, and the second differential output shaft (16) can be connected to a sun gear (11) so as to be non-rotatable relative to the gear, the first rotor (6) is permanently connected to the differential input shaft (14) so ​​as not to rotate relative to the first rotor (6); and a fifth shift member (SE5) is provided, through which the second differential output shaft (16) can be connected to the second side shaft (18) so as not to rotate relative to the first rotor (6); 1. An electric drive system (1), characterized in that the first shift member (SE1) is capable of connecting the double planetary carrier (13) to the second differential output shaft (16).

2. 2. The electric drive system (1) according to claim 1, characterized in that the first shift member (SE1), the second shift member (SE2) and the fifth shift member (SE5) are connected such that the first shift member (SE1), the second shift member (SE2) and the fifth shift member (SE5) are operable via a single actuator (10).

3. 3. The electric drive system (1) according to claim 2, characterized in that in a first position of the actuator (10), the first shift member (SE1) and the second shift member (SE2) are closed and the fifth shift member (SE5) is open, and in a second position of the actuator (10), the first shift member (SE1) and the second shift member (SE2) are open and the fifth shift member (SE5) is closed.

4. 4. The electric drive system (1) according to claim 1, 2 or 3, characterized in that, as viewed in the axial direction (a), the first electric machine (3), the differential transmission (9), the first shift member (SE1) and the second electric machine (4) are arranged in this order.

5. 4. An electric drive system (1) according to claim 1, characterized in that the first rotor (6), the second rotor (8), the differential transmission (9) and the two side shafts (17, 18) are arranged together coaxially with respect to one another.

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