PURELY ELECTRIC DRIVE SYSTEM WITH TWO MOTORS

Description

[0001] The invention relates to a purely electric drive system, in particular for a motor vehicle, according to the type defined in more detail in the preamble of claim 1.

[0002] In addition to hybridized drive systems, which use both an internal combustion engine and electric motors to power a vehicle, purely electric drive systems are also becoming increasingly important. These can include a drive system for a purely electrically driven axle with a gear ratio that can be shifted via a transmission, in particular with multiple gear stages. As prior art, the present application is based on DE 10 2008 002 380 A1. This shows some of the features of the preamble of the applicable claim, but unlike the present invention, it is based on a hybrid system and not on a purely electric drive system. The design provides for a group transmission with a main group and a range group, which has a planetary gear set.Two electric motors are provided, each driving its own input shaft of the main group, while an internal combustion engine can drive the output shaft of the main group via a switchable clutch. This output shaft of the main group is connected to the sun gear of the planetary gear set of the range group, whose planet carrier represents the output of the hybrid drive system. Furthermore, AT520555A4 discloses a drive system with two electric motors and a transmission in countershaft design. Finally, DE 10 2008 002 380 A1 discloses a hybrid transmission with two electric motors, a main transmission group, and a transmission range group in planetary design.

[0003] From EP 2 450 215 A1 a hybrid transmission is known, for example for a motor vehicle, comprising two transmission input shafts which are arranged axially parallel to one another, and a transmission output shaft arranged axially parallel between the two transmission input shafts, which form a countershaft transmission, in which one of the two transmission input shafts is assigned to an internal combustion engine and the other transmission input shaft is assigned to an electric machine, and in which gearwheels are arranged in at least two gear set planes to form gears, wherein gearwheels designed as loose gears can be connected in a rotationally fixed manner to the associated shafts via switching devices.In order for the hybrid transmission to have a high level of functionality and performance and to be compact in terms of this performance and to be comparatively inexpensive in terms of design and cost, at least one planetary gear is arranged on the transmission output shaft, which can be coupled to the transmission input shafts and which can be optionally locked together, operated in a freely rotating manner, or switched in such a way that, in operative connection with the countershaft transmission, fixed speed ratios are produced for two components of the planetary gear.

[0004] From WO 2021 / 073748 A1, a drive train for a vehicle is known, comprising a first electric machine, a second electric machine, and a transmission arranged to transmit torque from the electric machines to a drive axle. The transmission comprises: first and second input shafts arranged to be driven by the first and second electric machines, respectively; a common output shaft; a first primary gear set comprising: first and second input gears, via which the torque from the first and second input shafts, respectively, is transmittable to the output shaft; a second primary gear set comprising: third and fourth input gears, via which the torque from the first and second input shafts, respectively, is transmittable to the output shaft; means for isolating each individual electric machine from one another and from the output shaft.The transmission comprises an intermediate shaft drivable by the first and / or second input gear, and an auxiliary gear set with two gear ratios arranged between the intermediate shaft and the common output shaft, wherein at least the first and second input gears are arranged to drive the output shaft via the intermediate shaft and the auxiliary gear set.

[0005] CN 104948716 A describes a longitudinally arranged dual-motor manual transmission. The transmission uses two motors as power inputs. The sensible arrangement of a fixed-shaft gearbox and a shift sleeve ensures that there are no interruptions in power during gear shifting. Meanwhile, the motors actively adjust the speed difference during gear shifting so that the motors operate within the correct operating range and can meet special requirements. Special requirements include, for example, the frequent starting and parking of city buses. Here, the power of one motor and the power of the other motor are each fed into the transmission via input shafts, with the transmission being coupled to the power of one motor and the power of the other motor.

[0006] The object of the invention is to create a purely electric drive system with the features in the preamble of claim 1, which enables comfortable and long-lasting operation.

[0007] According to the invention, this object is achieved by a purely electric drive system having the features in claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments emerge from the dependent claims.

[0008] The purely electric drive system according to the invention, similar to the hybrid drive system in the prior art mentioned at the outset, uses two electric motors which drive an output shaft of the group transmission via a group transmission with a main transmission and a range group comprising a planetary gear set. This is then used to drive, for example, one or more driven axles of a vehicle, in particular a commercial vehicle. According to the invention, exactly two idler gears are provided coaxially to the first input shaft of the main group, as well as coaxially to the second input shaft of the main group. This creates a total of four discretely shiftable gears via the two electric motors and, if required, corresponding virtual intermediate gears, without the need for corresponding expenditure on additional idler gears, as would be the case, for example, with a hybrid drive system.

[0009] By using exactly two idler gears on each of the two input shafts and, correspondingly, exactly two fixed gears to connect the output shaft of the main group to its input shafts, whereby one of the idler gears of the input shafts meshes with the first fixed gear of the output shaft and the two other idler gears of the respective input shaft mesh with the second fixed gear of the output shaft, a design is created that enables shifting under load within the respective range group position. This is possible with simple claw shift elements, as provided in a particularly advantageous development of the electric drive system according to the invention.In contrast to complex and wear-sensitive friction shift elements, shifting can now be carried out simply, comfortably and in a wear-optimized manner by appropriately shifting the idler gears on the respective input shaft under load and with synchronization by means of the electric machine.

[0010] A further advantage is achieved by positioning the electric motors on the two different input shafts, allowing for virtual intermediate gears, which particularly improves starting performance. This is especially true for heavy vehicles, which is why the preferred, but not exclusive, application is in commercial vehicles.

[0011] A further advantage resulting from the use of the two electric machines is that in partial load operation, which, for example, accounts for around 70% of the total driving share in long-distance commercial vehicle transport, one of the two electric machines can be shut down, which has an overall impact on the service life and efficiency of these units.

[0012] Furthermore, according to the invention, a third fixed gear is arranged coaxially with the output shaft of the main group. This third fixed gear permanently meshes with a fourth fixed gear, which in turn is connected in a rotationally fixed manner to the first element of the planetary gear set. Such a connection of the planetary gear set, and thus the range group of the group transmission, allows for an efficient and compact design.

[0013] Furthermore, according to the invention, a gear wheel connected in a rotationally fixed manner to the output shaft meshes with the differential wheel, which in turn is connected in a rotationally fixed manner to a differential cage of the differential gear.

[0014] Furthermore, according to the invention, an axis of rotation of the first input shaft, an axis of rotation of the second input shaft, an axis of rotation of a sun shaft of the planetary gear set and an axis of rotation of the differential gear are all arranged parallel to one another.

[0015] A rotationally fixed connection in the sense of the invention is understood to mean a connection between rotating elements arranged coaxially to one another, which connects these elements to one another in such a way that they rotate at the same angular velocity.

[0016] As already indicated above, the idler gears are correspondingly switchably connected to their respective input shafts, wherein according to a very advantageous embodiment of the invention, a first and a second switching element for the first and second idler gears and the third and fourth idler gears are provided in the region of each of the input shafts, wherein the respective first switching element is designed to connect the first or third idler gear to its respective input shaft, and wherein the respective second switching element is designed to connect the second or fourth idler gear to its respective input shaft. In total, four switching elements are provided in the region of the input shafts, one for each of the idler gears. These are designed in such a way that they optionally connect the idler gear to its input shaft or not, so that the idler gear rotates freely relative to the input shaft.This is sufficient to achieve a total of four gears, whereby these gears can be powershifted within the same position of the range group, and whereby the drive can be provided either by one, the other or both electric motors.

[0017] According to a further, highly advantageous embodiment of this concept, the first and second shifting elements of the respective input shaft are combined to form a double shifting element with a neutral position and an actuator. This use of a double shifting element for the first and second shifting elements of the respective input shaft ultimately reduces the total required number of elements to two double shifting elements, one for each input shaft. Each of these double shifting elements can be controlled via just one actuator, thus also reducing the effort required for the actuators. This overall reduces the complexity of the design and saves space, installation space, and components.

[0018] Within the range group, according to a very advantageous development of the electric drive system according to the invention, a brake switching element is provided for locking the third element of the planetary gear set. This allows the gear ratio of the range group to be changed. Another very advantageous embodiment further provides that, alternatively or in particular additionally, a locking switching element is provided for locking the first and third elements of the planetary gear set.

[0019] According to an extremely advantageous further development, in which the locking switching element and the brake switching element are both present, these can also be combined to form a double switching element with an actuator, so that here too the effort is reduced accordingly, comparable to that above with regard to each of the input shafts.

[0020] As already mentioned above, the rotors of the two electric machines can be coupled or coupleable to the respective input shaft of the main group. According to an extremely advantageous development of the electric drive system according to the invention, the rotor of the first electric machine is connected in a rotationally fixed manner to the first input shaft, and a rotor of the second electric machine is connected in a rotationally fixed manner to the second input shaft. This eliminates the need for an additional shifting or clutch element between the rotors of the respective electric machines and the input shafts, since the input shafts are already switchably connected to the idler gears, and when the respective shifting elements of the idler gears are in the neutral position, they ultimately remain decoupled from the output shaft of the main group of the group transmission, making the additional clutch elements unnecessary, thus saving costs, installation space, and weight.

[0021] Within the range group, according to an exceptionally advantageous development of the electric drive system according to the invention, it can be provided that a sun gear of the planetary gear set is designed as the first element, a planet carrier as the second element, and a ring gear as the third element of the planetary gear set. In this case, the range group is connected to the input shaft via a connection to the sun gear, the output via the planet carrier, while the ring gear, according to the advantageous embodiment described above, can be braked via the brake switching element and / or directly connected to the sun gear via the interlocking switching element in a rotationally fixed manner.

[0022] The first and second shifting elements on the respective input shaft can, as already mentioned above, be designed as positive-locking shifting elements, in particular as claw shifting elements. These have the great advantage of being largely wear-free. Due to the special configuration of the group transmission according to the invention, they can also be shifted under load, whereby any resulting power loss can be fully or at least partially compensated for by boosting with the other electric motor. This motor can therefore take over synchronization to enable highly comfortable shifting despite the positive-locking shifting elements.

[0023] Further advantageous embodiments of the electric drive system according to the invention also emerge from the exemplary embodiment which is described in more detail below with reference to the figures.

[0024] Showing: Fig. 1 shows a schematic gear set diagram of a possible design of an electric drive system according to the invention; and Fig. 2 shows a shift table describing the position of the shift elements in four gears.

[0025] In the presentation of the Fig. 1 an electric drive system, designated overall by 1, can be seen. This has a first electric machine 2 and a second electric machine 3. A rotor of the first electric machine 2 is rotationally fixed to a first input shaft 4 and a rotor of the second electric machine 3 is rotationally fixed to a second input shaft 5. The input shafts 4, 5 are part of a main group 6 of a group transmission 7. An output shaft 8 of the main group 6 of the group transmission 7 is coupled to a range group 9, which has a planetary gear set 10. Here, the output shaft 8 of the main group 6 is connected to a sun shaft 11 of the planetary gear 10 of the range group 9. An output shaft 13 of the group transmission 7 is driven via a planet carrier 12. The output shaft 13 meshes via a gear 14 with a differential gear 15, which in turn is rotationally fixed to a differential cage of a differential gear 16.Finally, two driven wheels 17 of an electrically driven axle of a vehicle, in particular a commercial vehicle, are driven via the differential gear 16. The differential gear 16 is considered to be part of general technical knowledge, so it need not be discussed further here. It is illustrated here as an example of a differential gear 16 with a switchable differential lock.

[0026] The output shaft 14, which is arranged coaxially to the sun shaft 11, is preferably designed as a hollow shaft and arranged surrounding the sun shaft 11, which is designed as a solid shaft.

[0027] With regard to a torque flow from the electric machines 2, 3 to the wheels 17, the electric machines 2, 3, the main group 6, the range group 9, the differential gear 15 and the wheels 17 are arranged one after the other in the order mentioned.

[0028] A first idler gear 18 and a second idler gear 19 are arranged on the first input shaft 4 of the main group 6. A third idler gear 20 and a fourth idler gear 21 are arranged on the second input shaft 5. In addition, first shifting elements S1 and S1', respectively, and second shifting elements S2 and S2', respectively, are arranged on the respective input shafts 4, 5 in such a way that they can each connect the idler gears 18, 19 and 20, 21, respectively, arranged coaxially to the respective input shafts 4, 5, in a rotationally fixed manner to the respective input shafts 4, 5. Preferably, the shifting elements S1 / S2 and S1' / S2' are designed as double shifting elements with a neutral position, as shown here. They are controlled by a single actuator for each double shifting element S1 / S2.

[0029] The first idler gear 18 and the third idler gear 20 of the respective input shaft 4, 5 mesh with a first fixed gear 22 on the output shaft. The second idler gear 19 and the fourth idler gear 21 mesh with a second fixed gear 23 on the output shaft 8. The input shafts 4, 5 and the output shaft 8 are connected to each other exclusively via these two fixed gears 22, 23. Unlike in the gear set diagram shown here, they are typically not arranged in one plane. Therefore, a third fixed gear 24 can be placed axially between the two fixed gears 22, 23, which meshes with a fourth fixed gear 25 on the sun gear shaft 11 of the planetary gear set 10 and thus drives a sun gear 26 of the planetary gear set 10 when the output shaft 8 of the main group 6 of the group transmission 7 is driven. The fourth fixed gear 25 is permanently connected in a rotationally fixed manner to the sun gear 26 of the planetary gear set 10.The planetary gear set 10, used as range group 9, is thus driven by the output shaft 8 of the main group 6 via the third gear 24 and the fourth gear 25. In the gear set diagram, the fact that the third fixed gear 24 permanently meshes with the fourth fixed gear 25 is indicated by a dashed line.

[0030] The gear 14 is advantageously arranged axially between the fourth fixed gear 25 and the planetary gear set 10.

[0031] Advantageously, the fourth fixed gear 25 and either the first switching element S1, S1' or the second switching element S2, S2' are arranged axially overlapping one another, so that overall a very compact arrangement is obtained.

[0032] The term "axial" refers to an axial direction, and the axial direction means the direction of a rotational axis of the output shaft 8 or the rotational axis of the first input shaft 4 or the rotational axes of other shafts arranged parallel thereto.

[0033] Planet gears 27 on the planet carrier 12 of the planetary gear set 10 mesh accordingly with the sun gear 26 and a ring gear 28 as the third element of the planetary gear set 10. The drive is therefore via the sun gear 26 as the first element, and the output is via the planet gears 27 or their planet carrier 12, which represents the second element of the planetary gear set. If necessary, the ring gear 28 can be braked using a brake switching element S3. The ring gear 28 is then connected in a rotationally fixed manner, for example, to the housing of the group transmission 7 and therefore does not rotate. This results in a first gear ratio of the range group 9. Using a blocking switching element S4, which in turn can be combined with the brake switching element S3 as a double switching element, it is also possible to connect or block the sun gear 26 as the first element of the planetary gear set 10 with the ring gear 28.This results in a different gear ratio between the sun shaft 11, which acts as the input shaft into the range group, and the planet gear carrier 12, which is connected to the output shaft 13.

[0034] The planetary gear set 10 is advantageously arranged axially overlapping the first electric machine 2 and also axially overlapping the second electric machine 3.

[0035] The term "axially overlapping" refers to two axially overlapping components where at least a portion of one component and at least a portion of the other component are located in the same axial region. The same axial region is defined by the same axial coordinate.

[0036] Advantageously, the output shaft 8, the sun shaft 11, and a rotational axis of the differential gear 15 are arranged substantially in a common plane. Advantageously, the two input shafts 4, 5 are arranged in a further plane, wherein the further plane is arranged substantially perpendicular to the common plane.

[0037] In the presentation of the Fig. 2The four individually shiftable gears are now shown in principle using a shift matrix. The first column shows the respective gear, the second column the position of the first shift element S1 or the first shift element S1' on the respective input shaft 4, 5. The second column shows the second shift element S2 or the second shift element S2', the third column the state of the third shift element, i.e. the brake shift element S3, and the fourth column the state of the interlock shift element S4. In first gear, the shift element S1 and / or the shift element S1' is engaged, so the first idler gear 18 or the third idler gear 20 are connected to the respective input shaft 4 or 5, depending on which of the two electrical machines 2, 3 is driving the motor, although both can also be driving the motor if necessary.At the same time, the brake switching element S3 is connected, so that the ring gear 28 is braked in a rotationally fixed manner, for example, to the housing of the group transmission 7. Without this switching position changing within the range group 9, it is now possible to change from first to second gear by releasing the switching element S1 or S1' and engaging the switching element S2 or S2', even under load, whereby this switching process can be synchronized by the electric motors 2, 3 if necessary. It is therefore very convenient to switch between gears 1, 2 or 3, 4 and to make the two related gears 1, 2 or 3, 4 powershiftable within the respective position of the range group 9. For this, and this is a decisive advantage over the prior art, no friction switching element is required, but rather the switching elements S1 and S2 orS1' and S2' can be designed as positive-locking shift elements, particularly as dog-type shift elements. This shift pattern is repeated for third and fourth gears, whereby, unlike gears 1 and 2, range group 9 is now shifted such that the locking shift element S4 is active and the brake shift element S3 is released accordingly.

[0038] By positioning the two electric motors 2, 3 on different input shafts 4, 5 and thus ultimately on different gears, virtual intermediate gears can also be enabled by driving both electric motors 2, 3 differently on the output shaft 8. The intermediate gears achieved in this way can particularly improve the starting performance of heavy vehicles, such as commercial vehicles. During regular operation, which very often is partial load operation, the operation of one of the two electric motors 2, 3 is then sufficient, so that the other electric motor 2, 3 and the parts of the main group 6 of the group transmission 7 connected to it do not need to be used, thus reducing wear, increasing efficiency and extending the service life of the structure.

Claims

1. A purely electric drive system (1) comprising a first electric machine (2), a second electric machine (3), a differential transmission (16), a driven wheel (17) and a group transmission (7) comprising a main group (6) and a range group (9), wherein the range group (9) includes a planetary set (10), wherein a first input shaft (4) of the main group (6) is coupled or coupleable with the first electric machine (2) such that torques from the first electric machine (2) can be introduced into the group transmission (7) via the first input shaft (4), wherein a second input shaft (5) of the main group (6) is coupled or coupleable with the second electric machine (3) such that torques from the second electric machine (3) can be introduced into the group transmission (7) via the second input shaft (5), wherein an output shaft (8) of the main group (6) is permanently coupled with a first element (26) of the planetary set (10) for transmitting torque, and wherein a second element (12) of the planetary set is permanently coupled with a driven shaft (13) of the group transmission (7) for transmitting torque, wherein, with respect to a torque flow from the electric machines (2, 3) to the wheel (17), the first electric machine (2), the main group (6), the range group (9), a differential wheel (15) and the wheel (17) are sequentially disposed in the stated order, characterised in that exactly two idler wheels (18, 19), namely a first idler wheel (18) and a second idler wheel (19), are disposed coaxially to the first input shaft (4), wherein exactly two further idler wheels (20, 21), namely a third idler wheel (20) and a fourth idle wheel (21), are disposed coaxially to the second input shaft (5), wherein the two input shafts (4, 5) are coupled or coupleable with the output shaft (8) via exactly two fixed wheels (22, 23) disposed coaxially to the output shaft (8), wherein a first fixed wheel (22) of the fixed wheels (22, 23) is in permanent intermeshing engagement with the first and the third idler wheel (18, 20), and wherein a second fixed wheel (23) of the fixed wheels (22, 23) is in permanent intermeshing engagement with the second idler wheel (19) and the fourth idler wheel (21), wherein a third fixed wheel (24) is disposed coaxially to the output shaft (8) and permanently intermeshed with a fourth fixed wheel (25), which is in turn non-rotatably connected to the first element (26) of the planetary set (10), wherein a gear wheel (14) non-rotatably connected to the driven shaft (13) is intermeshed with the differential wheel (15), which is in turn non-rotatably connected to a differential cage of the differential transmission (16), wherein an axis of rotation of the first input shaft (4), an axis of rotation of the second input shaft (5), an axis of rotation of a sun shaft (11) of the planetary set (10), and an axis of rotation of the differential wheel (15) are all disposed in parallel and axially offset from one another.

2. The purely electric drive system (1) according to claim 1, characterised in that a first and a second switching element (S1, S1'; S2, S2') for each of the first and the second idler wheel (18, 19), and each of the third and the fourth idler wheel (20, 21), respectively is provided in the region of each of the input shafts (4, 5), wherein the respective first switching element (S1, S1') is arranged to connect the first idler wheel (18) and the second idler wheel (20) to their respective input shaft (4, 5), and wherein the respective second switching element (S2, S2') is arranged to connect the second idler wheel (19) and the fourth idler wheel (21) to their respective input shafts (4, 5).

3. The purely electric drive system (1) according to claim 2, characterised in that the first and the second switching element (S1, ST; S2, S2') of the respective input shaft (4, 5) are combined into a dual switching element having a neutral position and an actuator.

4. The purely electric drive system according to claim 2 or claim 3, characterised in that the fourth fixed wheel (25) is disposed axially overlapping the first switching element (S1, ST) or the second switching element (S2, S2').

5. The purely electric drive system (1) according to one of claims 1 to 4, characterised in that a braking switching element (S3) for locking the third element (28) of the planetary set (10) is provided.

6. The purely electric drive system (1) according to one of claims 1 to 5, characterised in that an interlocking switching element (S4) for interlocking the first and the third element (26, 28) of the planetary set (10) is provided.

7. The purely electric drive system (1) according to claims 5 and 6, characterised in that the braking switching element (S3) and the interlocking switching element (S4) are combined into a dual switching element having an actuator.

8. The purely electric drive system (1) according to one of the preceding claims, characterised in that a rotor of the first electric machine (2) is non-rotatably connected to the first input shaft (4), and a rotor of the second electric machine (3) is non-rotatably connected to the second input shaft (5).

9. The purely electric drive system (1) according to one of the preceding claims, characterised in that a sun (26) as a first element, a planet carrier (12) as a second element, and a ring wheel (28) as a third element are formed in the planetary set (10).

10. The purely electric drive system (1) according to one of claims 2 to 9, characterised in that the switching elements (S1, S1'; S2, S2') associated with the respective input shafts (4, 5) are each designed as positive-fit switching elements, in particular as pawl switching elements.

11. The purely electric drive system (1) according to one of the preceding claims, characterised in that the planetary set (10) is disposed axially overlapping the first electric machine (2) and axially overlapping the second electric machine (3).

12. The purely electric drive system (1) according to one of the preceding claims, characterised in that the driven shaft (13) is formed as a hollow shaft and is disposed coaxially with and surrounding the sun shaft (11).