Motor vehicle drive train and method of operating a drive train

Abstract

A drive train for a motor vehicle, having a drive unit which comprises a prime mover, a multi-step transmission and a power-splitting device which distributes the driving power between a first and a second drive shaft of a driven axle. The transmission comprises a transmission input and a first sub-transmission and a second sub-transmission. The prime mover is directly connected to the transmission input, wherein each of the two drive shafts is assigned a first and a second friction clutch. The first friction clutches connect the respective drive shaft to the first sub-transmission. The second friction clutches connect the respective drive shaft to the second sub-transmission. The first friction clutches and the second friction clutches form the power-splitting device.

Claims

1. A drive train for a motor vehicle, having a drive unit which comprises a prime mover, a multi-step transmission which comprises a transmission input and a first sub-transmission and a second sub-transmission, and having a power-splitting device which distributes the driving power between a first and a second drive shaft of a driven axle, wherein the prime mover is directly connected to the transmission input, wherein each of the two drive shafts is assigned a first and a second friction clutch, wherein the first friction clutches connect the respective drive shaft to the first sub-transmission and wherein the second friction clutches connect the respective drive shaft to the second sub-transmission, such that the first friction clutches and the second friction clutches form the power-splitting device.

2. The drive train as claimed in claim 1, wherein the prime mover comprises an internal combustion engine.

3. The drive train as claimed in claim 1, wherein the first sub-transmission comprises a first intermediate shaft, wherein gear ratios of the first sub-transmission are formed by wheel sets, which connect a transmission input shaft to the first intermediate shaft.

4. The drive train as claimed in claim 3, wherein the second sub-transmission comprises a second intermediate shaft, wherein gear ratios of the second sub-transmission are formed by wheel sets, which connect the transmission input shaft to the second intermediate shaft.

5. The drive train as claimed in claim 1, wherein the first friction clutches are arranged coaxially to a shaft of the first sub-transmission.

6. The drive train as claimed in claim 1, wherein the second friction clutches are arranged coaxially to a shaft of the second sub-transmission.

7. The drive train as claimed in claim 1, wherein the drive unit comprises an electric motor for supplying driving power, which can be connected to at least one of the sub-transmissions by means of a shifting clutch arrangement.

8. The drive train as claimed in claim 1, wherein the prime mover comprises an electric motor.

9. The drive train as claimed in claim 8, wherein the first sub-transmission comprises a single first gear ratio and/or wherein the second sub-transmission comprises a single second gear ratio.

10. The drive train as claimed in claim 9, wherein the multi-step transmission comprises a single transmission input shaft, on which two fixed wheels for the first gear ratio are fixed, which the two fixed wheel engage with loose wheels, which loose wheels can be shifted by means of the first friction clutches in the power flow, and on which the single transmission input shaft having two further fixed wheels for the second gear ratio are fixed, said further fixed wheels engaging with loose wheels, which can be shifted by means of the second friction clutches in the power flow, in order to distribute the driving power between the two drive shafts.

11. The drive train according to claim 8, wherein the drive unit comprises an internal combustion engine connected to the transmission input by means of a shifting clutch arrangement.

12. The drive train as claimed in claim 1, wherein the transmission input comprises a single transmission input shaft.

13. The drive train as claimed in claim 1, wherein both sub-transmissions comprise a starting gear ratio with the same transmission ratio, such that starting can take place by means of the two first and by means of the two second friction clutches.

14. The drive train as claimed in claim 1, wherein the first and second friction clutch of at least one of the first and the second drive shaft are arranged coaxially to the first and/or the second drive shaft.

15. The drive train as claimed in claim 1, wherein at least one of the first and the second friction clutches are configured as starting clutches.

16. The drive train as claimed in claim 1, wherein one of the two sub-transmissions comprises odd-numbered gear ratios and the other of the two sub-transmissions comprises even-numbered gear ratios.

17. The drive train as claimed in claim 1, wherein the first and the second drive shaft are connected to one another via a mechanical differential, the differential cage of which is connected to a longitudinal shaft, which is connected to a second driven axle.

18. The drive train as claimed in claim 1, wherein output members of the first and second friction clutches are connected via a transmission step to the drive shafts.

19. The drive train as claimed in one of the claim 1, wherein at least one of the first and the second friction clutches are identical in design.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Exemplary embodiments of the invention are represented in the drawing and explained in greater detail in the following description. In the figures:

(2) FIG. 1 shows a schematic representation of an embodiment of a drive train according to the invention;

(3) FIG. 2 shows a schematic sectional view through a further embodiment of a drive train according to the invention;

(4) FIG. 3 shows a schematic sectional view through a further embodiment of a drive train according to the invention;

(5) FIG. 3a shows an optional addition for the drive trains in FIG. 2 or 3;

(6) FIG. 4 shows a longitudinal sectional view through a further embodiment of a drive train according to the invention, in which four-wheel drive functionality is realized in addition;

(7) FIG. 5 shows a schematic sectional view through a further embodiment of a drive train according to the invention, in which four-wheel drive functionality is achieved;

(8) FIG. 6 shows a schematic sectional view through a further embodiment of a drive train according to the invention, in which a prime mover is formed by an electric motor; and

(9) FIG. 7 shows a modified embodiment of the drive train in FIG. 6, wherein an internal combustion engine can be connected up in addition to perform a range extender function.

DETAILED DESCRIPTION OF THE INVENTION

(10) A first embodiment of a drive train according to the invention is represented in schematic form in FIG. 1 and generally labeled as 10.

(11) The drive train 10 is used to drive a schematically depicted motor vehicle 11 and comprises a prime mover in the form of an internal combustion engine 12. The internal combustion engine 12 is connected straight to a single transmission input shaft 14 of a multi-step transmission 16. The multi-step transmission 16 comprises a first sub-transmission 18 and a second sub-transmission 20. The first sub-transmission 18 preferably contains odd-numbered gear ratios. The second sub-transmission 20 preferably contains even-numbered gear ratios. A reverse gear ratio may be arranged on the first or on the second sub-transmission 18, 20.

(12) The drive train 10 further contains a driven axle 22, having a first drive shaft 24, R, which is connected to a first driven wheel 28R, and having a second drive shaft 26, L, which is connected to a second driven wheel 28L.

(13) A clutch arrangement 30 is arranged between the drive shafts 24, 26 and the multi-step transmission 16, said clutch arrangement acting as a power-splitting mechanism, in order to distribute driving power supplied via the multi-step transmission 16 to the first and second drive shaft 24, 26.

(14) The clutch arrangement 30 contains a first friction clutch 32, the input member of which is connected to an output 35 of the first sub-transmission 18. In addition, the clutch arrangement 30 comprises a further first friction clutch 34, the input member of which is connected to the output 35 of the first sub-transmission 18. The clutch arrangement 30 further exhibits a second friction clutch 36, the input member of which is connected to an output 39 of the second sub-transmission 20, and also a further second friction clutch 38, the input member of which is connected to the output 39 of the second sub-transmission 20.

(15) The output members of the first friction clutch 32 assigned to the first sub-transmission 18 and also those of the second friction clutch 36 assigned to the second sub-transmission 20 are rigidly connected to the first drive shaft 24. In a corresponding manner, an output member of the further first friction clutch 34 and an output member of the further second friction clutch 38 are rigidly connected to the second drive shaft 26.

(16) Driving power generated by the prime mover 12 can then be transmitted using any ratio of the first sub-transmission 18 to the left or right driven wheel 28L, 28R. Parallel to this or independently thereof, the driving power may be supplied by the prime mover 12 via the second sub-transmission 20 to the left or right driven wheel 28L, 28R.

(17) The four friction clutches 32, 34, 36, 38 which form the clutch arrangement 30 can be activated independently of one another.

(18) During normal driving, a gear ratio is set up in one of the two sub-transmissions (for example, sub-transmission 18) and the friction clutches (in this case 32, 34) assigned to the first sub-transmission are engaged in order to distribute the driving power between the two driven wheels 28L, 28R. When cornering, the friction clutch assigned to the inside wheel can, for example, be activated with a smaller torque in this case, in order to achieve a dual-clutch differential function and/or torque vectoring.

(19) In order to carry out a gear change, the two first friction clutches 32, 34 are disengaged and the two second friction clutches 36, 38 are engaged in a manner overlapping therewith, wherein in the second sub-transmission 20 a target gear ratio is preselected. In this way, a gear change can take place from a source gear ratio of the first sub-transmission 18 to a target gear ratio of the second sub-transmission 20 without any loss of tractive force. In a corresponding manner, a gear change can be made from the second sub-transmission 20 to the first sub-transmission 18.

(20) It is possible, moreover, for the inside wheel to be driven using a low ratio and the outside wheel to be driven using a higher ratio during cornering, so that the outside wheel turns more quickly. In other words, the inside wheel may, for example, be driven via the first sub-transmission 18 and the first friction clutch 32, and the outside wheel may be driven, for example, via the second sub-transmission 20 (using a higher gear ratio than in the first sub-transmission) and the second friction clutch 38 (in this case the other first friction clutch 34 and the other second friction clutch 36 are open).

(21) All friction clutches may be disengaged or engaged or they may be set at a given torque, for which they are activated in the slipping state.

(22) In the following FIGS. 2 to 5, further embodiments of drive trains are illustrated, which correspond to the drive train 10 in FIG. 1 in terms of design and function. The same elements are therefore labeled using the same reference numbers. The principle differences are explained below.

(23) In the case of the drive train 10 in FIG. 2, the multi-step transmission 16 comprises a first intermediate shaft 40 for the first sub-transmission 18 and a second intermediate shaft 42 for the second sub-transmission 20. The first sub-transmission 18 comprises gear ratios 1, 3, 5, which are formed by wheel sets, which connect the transmission input shaft 14 and the first intermediate shaft 40 to one another. The second sub-transmission 20 comprises gear ratios 2, 4, 6, which are formed by wheel sets, which connect the transmission input shaft 14 and the second intermediate shaft 42 to one another.

(24) It is clear that in order to shift the wheel sets in a manner known per se, shifting clutches are provided, which may be configured as synchronous self-shifting clutches, for example, and are preferably arranged on the intermediate shafts 40, 42 (in this case, the wheels arranged on the intermediate shafts are designed as loose wheels and the wheels arranged on the transmission input shaft 14 are designed as fixed wheels).

(25) The wheel sets of the first sub-transmission 18 are jointly referred to as 44. The wheel sets of the second sub-transmission 20 are jointly referred to as 46.

(26) The first intermediate shaft 40 is connected to a dual-clutch package 30. To be more precise, the first intermediate shaft 40 is connected to input members of the two first friction clutches 32, 34, which are arranged coaxially to the first intermediate shaft 40. In a corresponding way, the second two friction clutches 36, 38 are arranged coaxially to the second intermediate shaft 42 and input members of these second two friction clutches 36, 38 are connected to the second intermediate shaft 42.

(27) Output members of the two first friction clutches 32, 34 are connected via a first transmission ratio 50a to the left or right drive shaft L, R. In a corresponding way, output members of the two second friction clutches 36, 38 are connected via a second transmission ratio 50b to the left or right drive shaft L, R.

(28) Gear ratio 1 is provided as the starting gear ratio. In order to reduce the load of the first friction clutches 32, 34, an additional wheel set is provided in the second sub-transmission 20, namely in the form of an additional wheel set 48, which sets up the same ratio as gear ratio 1 in the first sub-transmission 18.

(29) In this embodiment, starting can take place by activating all four clutches 32, 34, 36, 38, so that the load for the individual clutch is significantly reduced.

(30) The drive train 10 shown in FIG. 3 generally corresponds to the drive train in FIG. 2 in terms of design and function. The principle differences are explained below.

(31) While the clutch arrangement 30 in the drive train 10 in FIG. 2 is arranged on the side of the transmission 16 facing away from the prime mover 12, the clutch arrangement 30 in FIG. 3 is arranged in the region of the input side of the transmission 16.

(32) It can further be recognized that the additional wheel set 48 comprises a separate fixed wheel 52 in the embodiment in FIG. 3. While in the case of the embodiment in FIG. 2 only one single fixed wheel is provided on the transmission input shaft 14 for the gear ratio 1, said single fixed wheel being engaged with a loose wheel of the first sub-transmission 18 and with the additional loose wheel 48 in the second sub-transmission 20, in the embodiment in FIG. 3 a separate fixed wheel 52 is provided for the additional wheel set 48. Different axle distances can thereby be balanced, in order to set up the same transmission for the starting gear ratio 1 on the intermediate shafts 40, 42.

(33) In addition, FIG. 3a shows that the drive trains can be combined with an electric motor 54, in order to set up hybrid functionality. In this case, the electric motor 54 may be generally connected to the transmission input shaft 14. As shown, however, the electric motor 54 is preferably connectable via a shifting clutch arrangement 56 to the first intermediate shaft 40 or alternatively to the second intermediate shaft 42. In addition, a transmission ratio 58 is set up between the electric motor 54 and the first intermediate shaft 40 and a further transmission ratio 60 is set up between the electric motor 54 and the second intermediate shaft 42.

(34) The electric motor 40 may also be used to form a torque support during gear changes in low gear ratios.

(35) In this way, the load for the friction clutches can be further reduced.

(36) The arrangement shown in FIG. 3a can be combined both with the drive train 10 in FIG. 2 and also with the drive train 10 in FIG. 3 and likewise with the drive train 10 in FIG. 4.

(37) The drive train 10 in FIG. 4 generally corresponds to the drive train 10 in FIG. 2 in terms of its design and function. However, the first friction clutches 32, 34, which are assigned to the first sub-transmission 18, are connected to the first intermediate shaft 40 at axially opposite ends of the transmission 16. The second two friction clutches 36, 38 are connected in a corresponding manner to the second intermediate shaft 42 at axially opposite ends of the transmission 16. In this embodiment, the first friction clutch 32 and the second friction clutch 36, which are assigned to the right drive shaft R, form a clutch package. The first friction clutch 34 and the second friction clutch 38 form a second clutch package axially spaced therefrom, said clutch package being assigned to the second drive shaft L.

(38) The drive shafts L, R are generally rotatable independently of one another in the embodiments described above.

(39) However, a variant is shown in FIG. 4, in which the drive shafts L, R are connected to one another via a mechanical differential 65, in order to form an axle drive 64 for a further driven axle (not depicted). To be more precise, the drive shafts 24, 26 are connected to side wheels of the differential 65, whereas the differential cage 66 is connected to a longitudinal shaft 68, which is connected to the second driven axle. The mechanical differential is therefore operated in reverse like a traditional mechanical differential.

(40) A further drive train 10.sup.IV is shown in FIG. 5, which corresponds to the drive train 10 in FIG. 3. In this case, four-wheel functionality is set up in addition, in that the left and right drive shafts L, R are connected to one another via a differential 65, the differential cage 66 whereof being connected to a longitudinal shaft 68, so that the same functionality results as in the embodiment in FIG. 4.

(41) Further embodiments of drive trains according to the invention are shown in FIGS. 6 and 7. These generally correspond to the drive train 10 in FIG. 1 in terms of design and functionality. However, instead of an internal combustion engine, an electric motor 70 is provided as the prime mover.

(42) The electric motor 70 is connected to a single transmission input shaft 14, namely directly, without the interposition of a clutch.

(43) On the transmission input shaft 14 two fixed wheels are appointed for a first gear ratio 1, as well as two fixed wheels for a gear ratio 2. In the present case, the drive train 10.sup.V in FIG. 6 is designed as the drive train for an electric vehicle, wherein the multi-step transmission only comprises two gear ratios.

(44) In order to achieve the functionality described above, the wheel sets for the gear ratios are doubled in this case, wherein the four friction clutches 32, 34, 36, 38 are all arranged coaxially to the drive shafts L, R. The loose wheels engaged with the fixed wheels for the gear ratios 1 and 2 in this case are likewise rotatably mounted on the left or right drive shaft L, R.

(45) In the present case, the friction clutches are also used as shifting clutches for engaging and disengaging the gear ratios.

(46) A modification of the embodiment shown in FIG. 6, namely in the form of a drive train 10.sup.VI, is shown in FIG. 7.

(47) In this embodiment, the four friction clutches 32, 34, 36, 38, which are arranged coaxially to the loose wheels, said loose wheels being engaged with the fixed wheels for the gear ratios 1 and 2, are arranged coaxially to one another, but on an axis 71 which runs parallel to the drive shafts L, R. More precisely, the first friction clutch 32 and the second friction clutch 36 are arranged on a first intermediate shaft 80, which is connected to the right drive shaft 24, R via a first transmission ratio 50a. In a corresponding manner, the further first friction clutch 34 and the further second friction clutch 38 are arranged on a second intermediate shaft 82, which is connected to the left drive shaft 26, L via a further transmission ratio 50b.

(48) In this embodiment, the friction clutches may each be smaller in size, since they are exposed to smaller torques. As in FIG. 6, the second gear ratio is shifted using the separating clutches 38 and 36 and the first gear ratio using the separating clutches 32 and 34.

(49) In the embodiments in FIGS. 6 and 7, the drive trains 10.sup.V, 10.sup.VI are generally designed for electric vehicles. In both cases, the drive trains may, however, also be designed as range extender drive trains. In this case, an internal combustion engine 72 may be provided, which can be connected to the transmission input shaft 14 via a shifting clutch arrangement 74. In the present case, an engine shaft 75 of the internal combustion engine 72 is connected to a generator 78, and the engine shaft 75 may be connected via the shifting clutch arrangement 74 and, where appropriate, a transmission ratio 76 to the transmission input shaft 14. An optionally provided generator which can be connected to the internal combustion engine 72 is shown with 78. During normal driving, a battery of the drive train, which is not shown, is charged up by running the internal combustion engine 72 so that the generator 78 produces electrical power. The electrical power may be taken by the electric motor 70 to drive the motor vehicle. In addition, it is possible to drive the vehicle simply by means of the internal combustion engine 72, for which purpose the shifting clutch arrangement 74 is engaged. In this case, however, the electrical motor 70 and the generator 78 must be carried along, insofar as no separating clutches are provided. When the friction clutches 32, 34, 36, 38 are disengaged, the internal combustion engine 72 may be started by means of the electric motor 70, for which purpose the shifting clutch arrangement 74 is likewise engaged.