VEHICLE DRIVE TRAIN AND METHOD FOR OPERATING A DRIVE TRAIN

Abstract

A vehicle drive-train with a drive engine, a drive output and a transmission device connected in the power flow between the drive engine and the drive output. The transmission device has at least two transmission units whose transmission ratios can be varied continuously, at least in some ranges, and which are arranged in power-trains running parallel with one another between the drive engine and the drive output. The power-trains can each be functionally connected with a respective axle of the drive output. At least one shifting element is provided by which the power-trains can be functionally connected in the area between the transmission units and the drivable axles. In addition, a method for operating the vehicle drive-train is described, in which the shifting element is actuated as a function of torque to be transmitted via the transmission device between the drive engine and the drive output.

Claims

1-12. (canceled)

13. A vehicle drive-train (1) comprising. a drive engine (2), a drive output (3), a transmission device (4) being connected in a power flow between the drive engine (2) and the drive output (3), the transmission device (4) comprising at least two transmission units (7, 8) whose transmission ratios are continuously variable, at least in some ranges, and which are arranged in power-trains (9, 10) running parallel with one another between the drive engine (2) and the drive output (3), the power-trains (9, 10) each being functionally connectable with a respective vehicle axle (5, 6) of the drive output (3), and at least one shifting element (16) being provided by which the power-trains (9, 10) can be functionally connected with one another in an area between the two transmission units (7, 8) and the drivable vehicle axles (5, 6).

14. The vehicle drive-train according to claim 13, wherein the shifting element (16) is an interlocking shifting element.

15. The vehicle drive-train according to claim 13, wherein the shifting element (16) is a frictional shifting element which has a transmission capacity that is continuously variable.

16. The vehicle drive-train according to claim 13, wherein a force flow between the drive engine (2) and the drive output (3), at least in an area of one of the power-trains (9, 10), is interruptable by at least one shifting element.

17. The vehicle drive-train according to claim 13, wherein the transmission ratio in an area of the transmission units (7, 8) is individually adjustable.

18. The vehicle drive-train according to claim 13, wherein an output shaft (11) of the drive engine (2) is functionally connectable with transmission input shafts (12, 13) of the transmission units (7, 8), and transmission output shafts (14, 15) of the transmission units (7, 8) are, in each case, coupled with at least one of the drivable vehicle axles (5, 6) and connectable by the shifting element (16) to a respective transmission output shaft (14 or 15) of the other transmission unit (7 or 8).

19. A method of operating a vehicle drive-train (1) having a drive engine (2), a drive output (3) and a transmission device (4) connected in the power flow between the drive engine (2) and the drive output (3), the transmission device (4) comprises at least two transmission units (7, 8) whose transmission ratios are continuously variable at least in some ranges, and which are arranged in power-trains (9, 10) running parallel with one another between the drive engine (2) and the drive output (3), and the power-trains (9, 10) are each functionally connectable with a respective vehicle axle (5, 6) of the drive output (3), at least one shifting element (16) is provided, by which the power-trains (9, 10) are functionally connectable with one another in an area between the two transmission units (7, 8) and the drivable vehicle axles (5, 6), the method comprising: actuating the shifting element (16) as a function of torque which is to be transmitted between the drive engine (2) and the drive output (3) by way of the transmission device (4).

20. The method according to claim 19, further comprising changing the shifting element (16) to an engaged operating condition, if a predefined threshold value of the torque to be transmitted by way of the transmission device (4) between the drive engine (2) and the drive output (3) is exceeded.

21. The method according to claim 19, further comprising interrupting the force flow between the drive engine (2) and the drive output (3) in the area of one of the power-trains (9, 10), if the torque currently to be transmitted by way of the transmission device (4) between the drive engine (2) and the drive output (3) is below a threshold value.

22. The method according to claim 19, further comprising controllably regulating slipping in an area of wheels of the drivable vehicle axles (5, 6) by varying the transmission ratio in an area of the transmission units (6, 7) with the shifting element (16) either disengaged or operating with slip.

23. The method according to claim 19, further comprising, in an area of one of the transmission units (7), which is in a form of a continuously variable power branched transmission with a variator designed as a hydrostat, carrying out a transmission ratio and high-pressure regulation by virtue of an adjustment strategy that takes a current driver's wish into account.

24. The method according to claim 23, further comprising, in an area of the further transmission unit (8), which is also in a form of a continuously variable power branched transmission with a variator designed as a hydrostat, carrying out a transmission ratio regulation whereas the high-pressure regulation in the area of the variator of the further transmission unit (8) is operated as a function of the high-pressure regulation in the area of the other transmission unit (7).

25. A vehicle drive-train (1) comprising: a drive engine (2), a drive output (3), a transmission device (4) being connected in a flow of power between the drive engine (2) and the drive output (3), the transmission device (4) including at least two transmission units (7, 8) having transmission ratios that are continuously variable at least in some ranges, and which are arranged in power-trains (9, 10) running parallel with one another between the drive engine (2) and the drive output (3), the power-trains (9, 10) being functionally connectable with a respective drivable vehicle axle (5, 6) of the drive output (3), and at least one shifting element (16) being engagable to functionally connect the two power-trains (9, 10) in an area between the two transmission units (7, 8) and the drivable vehicle axles (5, 6).

Description

BRIEF DESCRIPTION OF THE DRAWING

[0030] The sole FIGURE shows a very schematic representation of a vehicle drive-train with a drive engine, a drive output and with a transmission device provided in the power flow between the drive engine and the drive output.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The FIGURE shows a vehicle drive-train 1 with a drive engine 2, a drive output 3 and a transmission device 4 connected between the drive engine 2 and the drive output 3. In the present case the drive engine is in the form of an internal combustion engine, preferably a diesel engine. Furthermore it is also possible for the drive engine 2 to comprise a combination of an internal combustion engine and an electric machine, or even a plurality of internal combustion engines and/or electric machines, in order to be able to produce a required traction force in the area of the drive output 3. In addition it is also possible for the drive engine 2 to consist of one or more electric machines.

[0032] In turn, the drive output 3 comprises two drivable vehicle axles 5, 6, such that in this case the vehicle axle 5 is the front axle of the vehicle and the axle 6 is the rear axle of the vehicle made with the drive-train 1, which vehicle can for example be a working machine such as a wheel loader or the like.

[0033] In the present case the transmission device 4 is made with two transmission units 7, 8, which are essentially structurally the same, each being a continuously variable power branched transmission with a variator in the form of a hydrostat. The transmission ratios of the transmission units 7, 8 can be varied continuously, at least in some ranges. In addition, the two transmission units 7, 8 are arranged in power-trains 9, 10 that run parallel with one another between the drive engine 2 and the drive output 3. The power-train 9 is in functional connection with the vehicle axle 5, whereas the power-train 10 is coupled to the vehicle axle 6.

[0034] An output shaft 11 of the drive engine 2 is functionally connected to transmission input shafts 12, 13. In the area of the transmission output shafts 14, 15, the transmission units 7, 8 are coupled to the drivable vehicle axles 5 and 6 respectively. In addition, the transmission output shafts 14, 15 of the transmission units 7, 8 can be brought into functional connection with one another by means of a shifting element 16 arranged between the transmission output shafts 14, 15, which shifting element 16 is in the present case in the form of a friction clutch and can also be operated with slip, should there be a corresponding need. The shifting element 16 can be controlled electronically and is therefore designed to be shifted fully automatically. Moreover, due to the arrangement of the shifting element 16, when the shifting element 16 is in its closed operating condition in each case only half of the total drive output torque is transmitted, namely the torque passing by way of one of the respective transmission units 7, 8.

[0035] Thus, the arrangement of the shifting element 16 described above makes it possible to design the shifting element 16 in a space-saving manner. This space-saving design of the shifting element 16 also has the advantage that in the open operating condition of the shifting element 16 only small drag torque losses are produced, since in the area of the shifting element 16 only small rotational speed differences occur throughout the operating range of the vehicle drive-train 1.

[0036] The above-described configuration of the vehicle drive-train 1 makes it possible in an inexpensive way to equip vehicles having powerful drive engines with standard transmissions which have a comparatively lower power, whereby the manufacturing costs of powerful vehicles can be limited to a desired extent.

[0037] Furthermore, the above-described configuration of the vehicle drive-train 1 when the shifting element 16 is open makes it possible to divide the torque to be passed via the transmission device 4 and the power to be transmitted, by virtue of the parallel connection, between the two transmission units 7 and 8. Then, the power transmitted via the transmission unit 7 can be made available in the area of the vehicle axle 5, whereas the power transmitted via the transmission unit 8 is provided in the area of the vehicle axle 6. During such an operating condition of the vehicle drive-train 1, in a simple manner internal stresses that occur with a conventional, solid connection between the vehicle axles 5 and 6 are avoided. This has fuel consumption advantages and reduces tire wear in the area of the vehicle axles 5 and 6.

[0038] In addition, by virtue of the individual regulation of the transmission ratio in the area of the transmission units 7 and 8, the slip in the area of the vehicle axles 5 and 6 can be regulated, which for example is very advantageous for agricultural tractors.

[0039] Until the maximum transmissible power or the maximum drive torque that can be transmitted by the transmission unit 7 or the transmission unit 8 is reached, it is also possible to disconnect the transmission unit 7 or the transmission unit 8 for example by opening a range clutch of the transmission unit 7 or of the transmission unit 8. This is advantageous, since in the decoupled operating condition of the transmission unit 7 or the transmission unit 8 no power loss occurs in the area of the hydrostatic variator.

[0040] In this context range clutches are shifting elements by means of which fixed gearwheel pairs in the area of the transmission units 7 and 8 can be connected or disconnected and by means of which fixed transmission ratios can be obtained. By virtue of the combination of the respective hydrostats provided and the fixed transmission ratios that can be engaged in each case, defined transmission ratio ranges of the transmission units can be obtained, within which the overall transmission ratio of the transmission units 7 and 8 can be varied continuously by adjusting the hydrostats.

[0041] Furthermore, it is also possible to disconnect the transmission unit 7 or the transmission unit 8 by correspondingly decoupling them from the drive engine 2, this being done for example by opening so-termed driving direction clutches by means of which the rotational direction in the area of the drive output 3 can be changed for forward driving or driving in reverse.

[0042] During operating condition variations in which, in the area of the drive output 3, more power or a higher drive torque has to be provided than can be passed through the transmission unit 7 or the transmission unit 8 alone, the previously disconnected transmission unit 7 or 8 is reconnected again and correspondingly transmits power or an appropriate drive torque onward in the direction toward the vehicle axle 5 or 6. The power transmitted by the additionally connected transmission unit 7 or 8 can be adjusted in a variable ratio to the drive output torque transmitted by the previously already connected transmission unit 7 or transmission unit 8.

[0043] If the drive torque provided by the drive engine 2 is transmitted simultaneously toward the drive output 3 by both of the transmission units 7 and 8, then the transmission ratio set in the area of the transmission units 7 and 8 and also their initial rotational speeds have to be set almost equal to one another. In this operating condition of the vehicle drive-train 1, in which the shifting element 16 is fully open or at least operated with slip, the vehicle axles 5 and 6 of the drive output 3 are interconnected by way of the wheels of the vehicle axles 5 and 6 and the ground being driven over. If inequalities occur, for example during a range change in the area of one of the transmission units 7 or 8, then torque peaks are damped by virtue of the elasticity of the tires of the vehicle axles 6 and 5 or compensated for to some extent by a corresponding tire slip.

[0044] For example, if a wheel loader is made with the vehicle drive-train 1, it is now possible that during a filling process of a scoop of the wheel loader the total drive torque provided by the drive engine has to be applied as a drive torque in the area of the front axle 5. During such an operating condition of the vehicle drive-train 1, the fixed mechanical connection between the front axle 5 and the rear axle 6 is still in place. For this, however, the shifting element 16 which can be in the form of a claw-type shifting element or a powershift clutch, is closed or at least its transmission capacity is increased to an extent such that the torque provided by the drive engine 2 is delivered in large measure to the front axle 5. The fixed connection between the transmission units 7 and 8 that can be produced by means of the shifting element 16 is in each case formed only for as long as necessary.

[0045] To avoid internal stress conditions in the area of the vehicle drive-train 1, it is provided that when the shifting element 16 is fully closed, the transmission unit 7, which in the present case is a so-termed master transmission, is operated using an adjustment strategy known in itself, by virtue of which a transmission ratio and high-pressure regulation is carried out with reference to a nominal value determined in accordance with a driver's wish or a predetermined limitation related to the transmission ratio and high pressure. The transmission unit 8, which is called the slave transmission in what follows, is operated with an adjustment strategy different from this, wherein the specification of the transmission ratio takes place as in the master transmission 7. The high-pressure regulation of the slave transmission 8, however, is operated with a nominal value specification determined on the basis of the high pressure in the master transmission 7. This means that the nominal value for the high-pressure regulation of the slave transmission 8 is not specified externally, but is determined with reference to the measured value determined in the area of the master transmission 7. In that way a 50:50 power division between the two transmission units 7 and 8 can be produced.

[0046] For example, if a slightly lower transmission ratio is set in the area of the master transmission 7 than in the area of the slave transmission 8, then in the area of the master transmission 7 a higher output rotational speed will be produced than in the area of the slave transmission 8. During such an operating condition of the vehicle drive-train 1, the slave transmission 8 brakes and increases the load in the area of the master transmission 7. However, since the high-pressure regulation in the area of the slave transmission 8 takes place at the same high pressure as in the area of the master transmission 8, the transmission ratio of the slave transmission 8 is reduced until in the area of the slave transmission 8 the same high pressure is set as in the area of the master transmission 7.

[0047] If a slightly higher transmission ratio is set in the area of the master transmission 7 than in the area of the slave transmission 8, the master transmission 7 brakes and increases the load in the area of the slave transmission 8. Due to the high-pressure regulation provided in the area of the slave transmission 8, which causes the high pressure in the area of the slave transmission 8 to change to the value of the high pressure in the area of the master transmission 7, the transmission ratio of the slave transmission 8 increases until in the area of the slave transmission 8 a high pressure is produced which corresponds to the high pressure in the area of the master transmission 7.

[0048] Depending on the application case at the time it is up to the discretion of a person with knowledge of the field to provide between the drive engine and the drive output of the vehicle drive-train more than two power-trains running parallel with one another, such that each power-train is made with at least one transmission unit. Furthermore, it is also possible in the area of the power-trains to provide in turn a parallel power branch with so-termed sub-power-trains, such that again each such train must be made with a transmission unit.

INDEXES

[0049] 1 Vehicle drive-train [0050] 2 Drive engine [0051] 3 Drive output [0052] 4 Transmission device [0053] 5 Vehicle axle, front axle [0054] 6 Vehicle axle, rear axle [0055] 7 Transmission unit [0056] 8 Transmission unit [0057] 9 Power-train [0058] 10 Power-train [0059] 11 Output shaft [0060] 12 Transmission input shaft [0061] 13 Transmission input shaft [0062] 14 Transmission output shaft [0063] 15 Transmission output shaft [0064] 16 Shifting element