DE102016224628A1 - Hydrostatic transmission, and method for operating a hydrostatic transmission - Google Patents

Abstract

The invention relates to a hydrostatic transmission (9), in particular for a power-split transmission (4), comprising two hydrostatic machines (22, 23) which can each be operated in pump operation and / or in engine operation and in each of which a flow rate can be varied. The hydrostatic machines (22, 23) are hydraulically connected to each other in a hydraulic circuit (26), wherein at least one pressure accumulator (28, 29) is provided, which can be connected to the hydraulic circuit (26). In order to achieve not only the representation of hybrid functions but also a low control effort in the hydrostatic transmission (9), the delivery rates of the hydrostatic machines (22, 23) are forcibly coupled only forcibly coupled together. Furthermore, the invention relates to a method for operating a hydrostatic transmission (9).

Description

The invention relates to a hydrostatic transmission, in particular for a power-split transmission, comprising two hydrostatic machines which are each operable in hydraulic pump operation and / or hydraulic motor operation and in each of which a flow rate is variable, wherein the hydrostatic machines are hydraulically connected in a hydraulic circuit, and wherein at least one pressure accumulator is provided, which is connectable to the hydraulic circuit. In addition, the invention has a power-split transmission with an aforementioned hydrostatic transmission, as well as a motor vehicle drive train to the object.

Furthermore, the invention relates to a method for operating a hydrostatic transmission in which two hydrostatic machines are hydraulically connected in a hydraulic circuit, wherein of the hydrostatic machines, one machine is operated as a hydraulic pump and the other machine as a hydraulic motor and delivery rates of the machines are variable , and wherein at least one pressure accumulator is connected in the context of at least one operating function with the hydraulic circuit.

In commercial vehicles come as a continuous motor vehicle transmission partly also power-split gearboxes for use, which usually consist of a hydrostatic transmission and a mechanical transmission. A power split is usually carried out via a summation stage which is seated either on the drive side or on the output side, which is often designed as a planetary stage. By superposition of the mechanical power branch with the hydrostatic power branch can be realized in the end a continuous transmission ratio of the transmission.

In the area of the power-split transmission, it is also known in the respective hydrostatic transmission to provide one or more pressure accumulators in which pressurized hydraulic fluid can be stored and selectively supplied to a hydraulic circuit of the hydrostatic transmission. As a result, a storage of energy and their targeted delivery is possible.

From the DE 10 2010 036 817 A1 shows a power-split transmission, which consists of a mechanical transmission and a hydrostatic transmission. The hydrostatic transmission here comprises two hydrostatic machines which can each be operated in hydraulic pump mode and also in hydraulic motor mode and in each of which a respective delivery rate can be varied. The two hydrostatic machines are in this case hydraulically connected to each other in a hydraulic circuit via intermediate pressure lines, wherein additionally at least one pressure accumulator is provided, which can also be connected via a respectively associated switching valve with the hydraulic circuit. As a result, hydraulic fluid can be selectively stored in the pressure accumulator and also removed therefrom.

Based on the above-described prior art, it is now the object of the present invention to provide a hydrostatic transmission in which hybrid functions can be represented via at least one pressure accumulator, which at the same time, however, is characterized by a low control effort.

From a device technical point of view, this object is achieved on the basis of the preamble of independent claim 1 in conjunction with its characterizing features. In contrast, a solution to this problem from a procedural point of view, starting from the preamble of the independent claim 9 in conjunction with its characterizing features. The following, dependent claims give advantageous refinements of the invention again. A power split transmission with a hydrostatic transmission according to the invention is also the subject of claim 7, while claim 8 has a motor vehicle powertrain with a power split transmission to the object.

According to the invention, a hydrostatic transmission comprises two hydrostatic machines which can each be operated in hydraulic pump operation and / or in hydraulic motor operation and in which a respective intake volume is variable.

In particular, in a so-called double-yoke design of the hydrostat, the displacement volume of both hydrostats can be changed with only one displacement device. The hydrostatic machines are hydraulically connected to each other in a hydraulic circuit, wherein in addition at least one pressure accumulator is provided, which can be connected to the hydraulic circuit.

According to the invention, the two hydrostatic machines of the hydrostatic transmission can each be operated either as a hydraulic pump or as a hydraulic motor, but preferably both as a hydraulic pump and as a hydraulic motor. In the latter case, then an operation of a hydrostatic machine as a hydraulic pump and the other hydrostatic machine as a hydraulic motor, as well as a mirrored for this purpose Operation possible. Furthermore, the flow rate of the respective hydrostatic machine can be changed by varying their respective displacement. More preferably, the hydrostatic machines are each designed as axial piston machines, in which a change in the respective flow rate by appropriate adjustment of a respective pivot angle takes place. Thus, the single axial piston machine could be designed as a bent axis machine, as a swash plate machine or as a swash plate machine.

The two hydrostatic machines are hydraulically interconnected in a hydraulic circuit, with pressure lines between the hydrostatic machines. In this case, one of the pressure lines acts as a high-pressure line and one of the pressure lines as a low-pressure line, wherein the assignment depends, inter alia, which of the hydrostatic machines is currently operated as a hydraulic pump and which of the hydrostatic machines is currently operated as a hydraulic motor.

The invention also provides a method for operating a hydrostatic transmission, in which two hydrostatic machines are hydraulically connected to one another in a hydraulic circuit. The hydrostatic machines operate one machine as a hydraulic pump and the other as a hydraulic motor, whereby the flow rates of the machines can be changed. In the context of at least one operating function, at least one pressure accumulator is also connected to the hydraulic circuit.

Within the scope of the method, therefore, one hydrostatic machine is operated as a hydraulic pump and the other hydrostatic machine as a hydraulic motor within at least one operating function via the at least one pressure accumulator from the outside additionally supplied hydraulic fluid or can be removed through the at least one pressure accumulator ,

The invention now includes the technical teaching that the delivery rates of the hydrostatic machines can be changed only forcibly coupled together. When operating the hydrostatic transmission, the flow rates of the hydrostatic machines are accordingly varied only forcibly coupled together. Thus, it is not possible in the hydrostatic transmission according to the invention to change the flow rate of a hydrostatic machine regardless of the flow rate of the other hydrostatic machine, but a change in a flow inevitably pulls a change in the other flow rate by itself.

Such a design of a hydrostatic transmission has the advantage that due to the positively coupled changes in the flow rates in both hydrostatic machines an actuator of the hydrostatic transmission can be simplified accordingly, since a common adjustment of both hydrostatic machines can be done via a common actuator. In addition, different functions of the hydrostatic transmission can be represented via the at least one pressure accumulator which can be integrated in the hydraulic circuit, by supplying additional pressurized hydraulic fluid or taking hydraulic fluid under pressure from the hydraulic circuit in suitable situations. Overall, this makes it possible to realize a hydrostatic transmission which can be controlled with little effort and in which, in addition, hybrid functions can be realized.

In the DE 10 2010 036 817 A1 is not further described how the flow rates are varied in the hydrostatic machine. Accordingly, the DE 10 2010 036 817 A1 Also, not to change the flow rates of hydrostatic machines together forcibly coupled.

According to one embodiment of the invention, the delivery rates of the hydrostatic machines are variable by changes in pivoting angles of the hydrostatic machines, wherein the hydrostatic machines are mechanically coupled to each other during pivoting. Particularly preferably, the hydrostatic machines are arranged together in two relatively pivotable housing parts, wherein the pivoting of the housing parts to each other just then pulls a pivoting of the hydrostatic machines and thus a change in their flow rates by itself. The hydrostatic machines are in this case designed in particular as axial piston machines in which a specific displacement volume is represented as a function of the respectively adjusted pivoting angle.

More preferably, the pivot angle of the two hydrostatic machines are at a constant angular offset from one another, which is in particular in the range of 43 ° to 45 °. In addition, the maximum tilt angle for hydrostatic machines is 43 ° to 45 °. As a result, one hydrostatic machine is in a position close to a pivoting angle of 0 ° when the other hydrostatic machine is pivoted to the maximum.

According to a further embodiment of the invention, the at least one pressure accumulator can be connected to the hydraulic circuit via an interposed switching valve. A joining the at least one pressure accumulator with the hydraulic circuit can therefore be made specifically via a switching valve, which is in particular electrically operated and designed as a directional control valve.

In a further development of the aforementioned design option, the at least one pressure accumulator can then be connected selectively via the switching valve either upstream or downstream of the individual hydrostatic machine. The at least one pressure accumulator can thus be connected upstream and downstream of both hydrostatic machines with the hydraulic circuit, so that just depending on the operation of the machine as a hydraulic pump or hydraulic motor always a connection with the currently acting as a high-pressure line pressure line of the hydraulic circuit is possible.

It is a further embodiment of the invention that two pressure accumulators are provided, of which a first accumulator is provided as a high pressure accumulator and a second accumulator as a low pressure accumulator. In this case, the high-pressure accumulator is connected in connection with the hydraulic circuit with the pressure line acting as a high-pressure line, while at the same time or slightly delayed designed as a low pressure accumulator accumulator is brought into communication with the low pressure line forming pressure line. The said slight delay for establishing the connection can be generated, for example, by opening a throttle to the low-pressure accumulator a moment later. This can be accomplished in combination with the aforementioned design option via a common switching valve, which produces the appropriate connections in switch positions. Alternatively to the described embodiment, but instead of a low-pressure accumulator, a tank may be provided, with which the each acting as a low-pressure line pressure line is connectable.

In a further development of the invention, an adjustable throttling point is provided between the at least one pressure accumulator and the hydraulic circuit. As a result, the amount of fluid flowing between the pressure accumulator and the hydraulic circuit can be throttled, which is preferably infinitely possible. The one controllable throttle point can be present as a separately present, controllable throttle point or be realized by appropriate design of a switching valve by the switching valve is designed for example as a proportional valve.

A hydrostatic transmission according to the invention is, in particular, part of a power-split transmission which, in addition to the hydrostatic transmission, then preferably also comprises a mechanical transmission. Both gears are provided between a transmission input and a transmission output of the power-split transmission, wherein a branching of a power is done either on the drive side or output side to the hydrostatic transmission and the mechanical transmission. The branching or the merger of the power branches is realized particularly preferably via a planetary stage in conjunction with a spur gear. The mechanical transmission is preferably designed as a stepped transmission and can be present concretely as a spur gear or as a planetary gear. There are also conceivable gear arrangements with two planetary gears, in which case each drive and driven side a planetary gear for splitting or summing the power paths is provided (so-called compound construction).

A power-split transmission described above is then furthermore preferably part of a drive train of a motor vehicle, which is in particular a commercial vehicle in the form of a construction machine, such as a wheel loader. Within the motor vehicle drive train, the power-split transmission is then connected to a drive side with an upstream drive machine, which is present in particular as an internal combustion engine. On the output side, however, a connection to one or more driven axles of the motor vehicle is made, this being done via each intermediate axle drive.

It is an advantageous embodiment of the method according to the invention that at the beginning of a start-up or boost function of the at least one high-pressure accumulator pressure accumulator downstream of the machine operating as a hydraulic pump and upstream of the machine operating as a hydraulic motor connected to the hydraulic circuit and hydraulic fluid is supplied from the pressure accumulator. In this case, the delivery rate of the machine operating as a hydraulic pump is at least initially set to a value when connecting the accumulator acting as a high-pressure accumulator, in which a receiving capacity of the machine operating as a hydraulic pump remains unchanged or virtually unchanged. In this case, the hydraulic circuit is thus supplied with energy from the outside, by removing pressurized hydraulic fluid from the pressure accumulator and fed downstream of the operated as a hydraulic pump machine. This then has the consequence that driving the machine operating as a hydraulic motor can be assisted via the hydraulic fluid supplied from the pressure accumulator or can be accomplished alone. Accordingly needs about as a hydraulic pump operated machine no or at least only a smaller flow rate for driving the working as a hydraulic motor machine are provided. Accordingly, a start from the stoppage of the motor vehicle can be completed more quickly or even while driving the motor vehicle, the prime mover are specifically supported (Boosten).

A delivery rate of the hydrostatic machine operated as a hydraulic pump is to be set in such a way that in the course of supplying hydraulic fluid from the pressure accumulator the intake capacity of the machine operated as a hydraulic pump does not increase or only insignificantly increases. Because with supply of the pressurized hydraulic fluid from the memory downstream of the hydraulic pump, this now has to work against the higher pressure, which would increase depending on the set flow the necessary drive torque of the hydraulic pump. This would then also mean that a higher drive torque for the hydraulic pump would be provided by the upstream of the transmission prime mover, which could lead to stalling derselbigen in particular in the course of the startup in extreme cases. Therefore, the delivery rate of the engine operating as the hydraulic pump is adjusted at least at the beginning of the start-up or boosting operation so that the pressure increase downstream of the hydraulic pump via the accumulator does not cause an excessive or excessive increase in the intake capacity of the hydraulic pump.

In a further development of the aforementioned embodiment, the flow rate of the machine operating as a hydraulic pump is increased in the course of the start-up or boost function, wherein parallel to a supplied via the high-pressure accumulator amount of hydraulic fluid is throttled in response to the change in the flow rate of the machine. In the course of the start-up or boost function, hydraulic fluid is therefore increasingly being conveyed via the machine operating as a hydraulic pump, which due to the forced coupling of the delivery quantities of the machines results in a reduction of the delivery rate of the machine operating as a hydraulic motor. Since the amount of fluid supplied from the accumulator throttled in parallel and thus increasingly reduced, the machine operated as a hydraulic pump increasingly takes over the drive of working as a hydraulic motor machine. It is thus transferred to increase the flow rate of the working as a hydraulic pump machine in the regular operation of the hydrostatic transmission.

According to a further embodiment possibility of the method according to the invention, in the course of a braking function, the at least one pressure accumulator acting as a high-pressure accumulator is connected downstream of the machine operating as a hydraulic pump and upstream of the machine operating as a hydraulic motor to the hydraulic circuit and hydraulic fluid is conveyed from the hydraulic circuit into the pressure accumulator. This has the advantage that over the hydrostatic transmission thus a braking torque can be generated by the machine operating as a hydraulic pump promotes hydraulic fluid in the pressure accumulator acting as a high-pressure accumulator. In this respect, an additional braking torque for decelerating the motor vehicle can be provided when using the hydrostatic transmission in a motor vehicle drive train. In particular, this is done in addition to a provided via a prime mover of the motor vehicle braking torque. By storing the pressurized hydraulic fluid in the high-pressure accumulator, the energy thus stored can subsequently be utilized by being selectively removed again from the high-pressure accumulator during a later start-up or boosting process. It is also conceivable in further developments to fill the high pressure accumulator by the prime mover.

In a further development of the aforementioned embodiment, the delivery rate of the machine operating as a hydraulic pump is set to the highest possible value, so that on the one hand generates a high braking torque and on the other hand the largest possible amount of fluid is fed into the pressure accumulator. However, the machine operating as a hydraulic pump and thus also the machine operating as a hydraulic motor should not be pivoted too far from the flow rate since otherwise a very wide pivoting of the hydrostatic machines might be necessary in the event of a change from braking operation to traction operation of the motor vehicle.

The invention is not limited to the specified combination of the features of the independent or the dependent claims. It also results in ways to combine individual features, even if they emerge from the claims, the following description of preferred embodiments of the invention or directly from the drawings. The reference of the claims to the drawings by use of reference numerals is not intended to limit the scope of the claims.

• 1 eine schematische Ansicht eines Kraftfahrzeugantriebsstranges mit einem leistungsverzweigten Getriebe entsprechend einer ersten Ausführungsform der Erfindung;
• 2 eine schematische Darstellung des Kraftfahrzeugantriebsstranges aus 1, gezeigt in einer ersten Betriebsfunktion des leistungsverzweigten Getriebes;
• 3 eine schematische Ansicht des Kraftfahrzeugantriebsstranges aus 1, gezeigt in einer zweiten Betriebsfunktion des leistungsverzweigten Getriebes; und
• 4 eine schematische Ansicht eines Kraftfahrzeugantriebsstranges mit einem leistungsverzweigten Getriebe entsprechend einer zweiten Ausgestaltungsmöglichkeit der Erfindung.

Advantageous embodiments of the invention, which are explained below, are shown in the drawings. It shows:

• 1 a schematic view of a motor vehicle drive train with a power split transmission according to a first embodiment of the invention;
• 2 a schematic representation of the motor vehicle drive train 1 shown in a first operating function of the power split transmission;
• 3 a schematic view of the motor vehicle drive train 1 shown in a second operating function of the power split transmission; and
• 4 a schematic view of a motor vehicle drive train with a power-split transmission according to a second embodiment of the invention.

1 shows a schematic view of a motor vehicle drive train 1 , wherein the associated motor vehicle is preferably a commercial vehicle and more preferably a construction machine, for example in the form of a wheel bearing. The motor vehicle powertrain 1 includes a prime mover 2 , which is designed as an internal combustion engine and the output side with a transmission input 3 a power-split transmission 4 connected is.

As in 1 can be seen, is the power-split transmission 4 at a transmission output 5 with a downstream axle drive 6 connected, the one transmission output side drive power to two drive wheels 7 and 8th divides. The power-split transmission 4 is designed according to a first embodiment of the invention and consists of a hydrostatic transmission 9 and a mechanical transmission 10 together, the latter being shown here only as a black box. A branch of the by the prime mover 2 provided drive power to the hydrostatic transmission 9 and the mechanical transmission 10 is about a planetary stage 11 completed in the area of the transmission input 3 is provided. This is the planetary stage 11 from a sun wheel 12 , a planet carrier 13 and a ring gear 14 together and is designed as a minus planet set. So leads the planet carrier 13 at least one planetary gear 15 , which rotatably on the planet carrier 13 is stored and both with the sun gear 12 , as well as the ring gear 14 is in meshing. The planet carrier 13 is non-rotatable with the drive machine 2 connected while the sun gear 12 non-rotatable with an input side of the mechanical transmission 10 communicates.

By contrast, the ring gear 14 the planetary stage 11 rotatably with a spur gear 16 a spur gear 17 connected, with the spur gear 16 with another spur gear 18 the spur gear stage 17 is in meshing. This spur gear 18 In turn, with a drive side of the hydrostatic transmission 9 connected, the output side via a downstream spur gear 19 with the transmission output 5 of the power split transmission 4 communicates. Thus, a non-rotatably meshes with the transmission output 5 and also an output side of the mechanical transmission 10 connected spur gear 20 the spur gear stage 19 with a spur gear 21 , which is non-rotatable with the output side of the hydrostatic transmission 9 is coupled.

In the mechanical transmission 10 For the purposes of the invention, it may be any type of mechanical transmission, but preferably the mechanical transmission 10 is in the form of a stepped transmission and may be embodied concretely as a spur-gear transmission or planetary-gear transmission. This defines the mechanical transmission 10 a certain number of gear ratios whose gear ratios due to the power split with each side of the hydrostatic transmission 9 shown gear ratios can be superimposed, so that a total of a continuously variable transmission of the prime mover 2 realizes applied drive movement.

As in 1 can be seen, includes the hydrostatic transmission 9 two hydrostatic machines 22 and 23 of which the hydrostatic machine 22 rotatably with the spur gear 18 and the hydrostatic machine 23 rotatably with the spur gear 21 connected is. The hydrostatic machines 22 and 23 are each designed as axial piston machines and can each be operated both as a hydraulic pump, as well as a hydraulic motor. One behind the other are the hydrostatic machines 22 and 23 over intermediate pressure lines 24 and 25 in a hydraulic circuit 26 hydraulically connected to each other, depending on which spur gear 17 or 19 into the hydrostatic transmission 9 which is a hydrostatic machine 22 or 23 is operated as a hydraulic pump and doing the other hydrostatic machine 23 or22 drives as a hydraulic motor.

At the hydrostatic machines 22 and 23 The respective flow rates can be adjusted by adjusting the swivel angle of the hydrostatic machines 22 and 23 to be changed. The flow rates of the hydrostatic machines can 22 and 23 but not be adjusted independently, but these are forcibly coupled together in their adjustment. So are the two hydrostatic machines 22 and 23 mechanically coupled during pivoting, as in 1 over the dashed line 27 is indicated. Specifically, this is in particular solved so that the two hydrostatic machines 22 and 23 together in two relative to each other pivotable housing parts are arranged, the pivot angle of the hydrostatic machines to each other during pivoting 22 and 23 change. The swivel angle of the two hydrostatic machines 22 and 23 lie at a constant angular offset from each other, which is preferably in the range of 43 ° to 45 °. So that's the one hydrostatic machine 22 respectively. 23 at a swivel angle of the other hydrostatic machine 23 respectively. 22 pivoted from 0 ° to an angle in the range of 43 ° to 45 °.

The hydrostatic transmission 9 are also two accumulators 28 and 29 assigned, of which the accumulator 28 as a low-pressure accumulator and the pressure accumulator 29 acts as a high-pressure accumulator. The two accumulators 28 and 29 can have a common, intermediate switching valve 30 with the hydraulic circuit 26 be connected, wherein the switching valve 30 this is designed as a 4/3-way valve. This is how the switching valve separates 30 in an unconfirmed basic position, the two accumulators 28 and 29 from the hydraulic circuit 26 while the switching valve 30 in a first switching position the accumulator 28 with the pressure line 24 and the accumulator 29 with the pressure line 25 connects and realized in a second switching position for this purpose a mirrored connection, ie the pressure accumulator 28 with the pressure line 25 and the accumulator 29 with the pressure line 24 combines. In addition, there are between the accumulators 28 and 29 and the hydraulic circuit 26 two adjustable throttle points 31 and 32 provided, via which the respective between the respective pressure accumulator 28 respectively. 29 and the hydraulic circuit 26 flowing amount of hydraulic fluid can be throttled continuously.

In the in 1 shown basic position of the switching valve 30 are the two accumulators 28 and 29 from the hydraulic circuit 26 decoupled so that the hydrostatic transmission 9 in a conventional manner by pure hydraulic coupling of the two hydrostatic machines 22 and 23 is operated. However, about the hydrostatic transmission 9 still specifically different operating functions are presented to the prime mover 2 to support. This will be described below with the help of the other 2 and 3 To be received:

In 2 is the motor vehicle powertrain 1 out 1 in a first operational function of the hydrostatic transmission 9 and thus also the power-split transmission 4 shown, wherein in this operating mode, a starting process of the motor vehicle is designed. Since the vehicle is at the beginning of the startup, is also the spur gear 19 and, with the gear engaged in the mechanical transmission 10 , also the sun wheel 12 , In contrast, the planet carrier runs 13 with idling speed of the prime mover 2 so that also the ring gear 14 also turns. At the beginning of the starting process, the switching valve 30 now in the in 2 shifted switching position shifted, whereby the pressure accumulator 29 with the pressure line 25 and the accumulator 28 with the pressure line 24 is connected.

As a result, pressurized hydraulic fluid from the pressure accumulator 29 in the pressure line 25 and thus upstream of the engine operated as a hydraulic motor 23 and downstream of the operated as a hydraulic pump machine 22 brought in. The hydrostatic machine 22 is set to a swivel angle in the range of 1 °, which has the consequence that the hydrostatic machine 23 almost maximum swiveled. The following is the hydrostatic machine operated as a hydraulic motor 23 over the from the accumulator 29 introduced and pressurized hydraulic fluid driven and is doing over the spur gear 19 the transmission output 5 in rotation.

As the hydrostatic machine operated as a hydraulic pump 22 now against the in the pressure line 25 prevailing pressure has to work on the intermediate spur gear 17 also the ring gear 14 braked causing the drive machine 2 support and also can transmit a drive torque. However, it is important that the hydrostatic machine 22 is set at the beginning of the starting process to a flow rate at which a power input of the hydrostatic machine 22 , So a drive torque of the working as a hydraulic pump machine 22 , remains essentially constant and it does not press the prime mover 2 comes what could otherwise cause a stalling.

In the course of the starting process, the hydrostatic machine operating as a hydraulic pump becomes 22 increasingly adjusted to a higher flow rate, which due to the forced coupling a reduction in the flow rate of working as a hydraulic motor machine 23 entails. Parallel and oriented on the pressure accumulator 29 supplied hydraulic fluid by means of the throttle point 32 increasingly throttled to gradually to normal operation without supply via the pressure accumulator 29 proceed. Finally, then the switching valve 30 moved back to its basic position.

Similarly, a boost function can be realized as an operating function, in which the prime mover 2 during the journey of the motor vehicle by connection of the pressure accumulator 29 is supported. Also in this case, the accumulator 29 to those described above Switched way, although the hydrostatic machine 22 and also the hydrostatic machine 23 due to the already prevailing driving speed of the motor vehicle are adjusted according to their flow rates accordingly different.

In contrast, in 3 the motor vehicle drive train 1 out 1 in the course of a braking operation as an operating function. In this case, the switching valve 30 moved to the other switching position, so that the pressure accumulator 28 now with the pressure line 25 of the hydrostatic transmission 9 and the accumulator 29 with the pressure line 24 connected is. As when braking the motor vehicle in its overrun a drive on the drive wheels 7 and 8th The hydrostatic machine works 23 in this case as a hydraulic pump, while the hydrostatic machine 22 is operated as a hydraulic pump.

By the integration of the pressure accumulator 29 downstream of the hydrostatic machine operating as a hydraulic pump 23 and upstream of the hydrostatic machine operated as a hydraulic motor 22 that's about the machine 23 delivered hydraulic quantity into the accumulator 29 promoted and stored there. Here is the hydrostatic machine 23 set to a high flow rate, which has due to the forced coupling of the flow rates result in that the hydrostatic machine 22 is set to a correspondingly low flow rate. In the course of braking operation, this can cause a deceleration of the motor vehicle via the drive machine 2 get supported.

Finally shows 4 a schematic representation of a motor vehicle drive train 33 with a power split transmission 34 according to a second embodiment of the invention. The motor vehicle powertrain 33 and also the power-split transmission 34 Correspond essentially to the previous variant of the 1 to 3 , in contrast, only a pressure accumulator 35 is present, which acts as a high-pressure accumulator. In contrast, one is in the variant of the 1 to 3 low-pressure accumulator to be used now through a tank 36 has been replaced, which takes over the function of the low-pressure accumulator of the previous variant. Incidentally, the embodiment corresponds to 4 the previous variant described by the 1 to 3 so that to the rest of the structure and also the functioning of the on the 1 to 3 Described reference is made.

By means of the embodiments of a hydrostatic transmission according to the invention can be realized in this hybrid functions at the same time low control effort. Also, the aforementioned embodiments require less design effort.

In addition to the embodiments described in the figures, the hydrostatic transmission or the power-split transmission can be designed as a 2- or 3-range transmission.

LIST OF REFERENCE NUMBERS

1

Motor vehicle drive train

2

prime mover

3

transmission input

4

power split transmission

5

transmission output

6

transaxles

7

drive wheel

8th

drive wheel

9

hydrostatic transmission

10

mechanical transmission

11

planetary stage

12

sun

13

planet carrier

14

ring gear

15

planet

16

spur gear

17

spur gear

18

spur gear

19

spur gear

20

spur gear

21

spur gear

22

hydrostatic machine

23

hydrostatic machine

24

pressure line

25

pressure line

26

hydraulic circuit

27

coupling

28

accumulator

29

accumulator

30

switching valve

31

restriction

32

restriction

33

Motor vehicle drive train

34

power split transmission

35

accumulator

36

tank

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010036817 A1 [0005, 0016]

Claims (13)

Hydrostatic transmission (9), in particular for a power-split transmission (4; 34), comprising two hydrostatic machines (22, 23), each operable in pump operation and / or engine operation and in each of which a flow rate is variable, the hydrostatic Machines (22, 23) in a hydraulic circuit (26) are hydraulically interconnected, and wherein at least one pressure accumulator (28, 29, 35) is provided, which is connectable to the hydraulic circuit (26), characterized in that the flow rates of the hydrostatic Machines (22, 23) are only forcibly coupled together changeable. Hydrostatic transmission (9) after Claim 1 , characterized in that the flow rates of the hydrostatic machines (22, 23) by variations of pivoting angles of the hydrostatic machines (22, 23) are variable, wherein the hydrostatic machines (22, 23) are mechanically coupled to each other during pivoting. Hydrostatic transmission (9) after Claim 1 or 2 , characterized in that the at least one pressure accumulator (28, 29; 35) can be connected to the hydraulic circuit (26) via an interposed switching valve (30). Hydrostatic transmission (9) after Claim 3 characterized in that said at least one pressure accumulator (28, 29, 35) is selectively connectable via the switching valve (30) either upstream or downstream of the single hydrostatic machine (22, 23). Hydrostatic transmission (9) according to one of the preceding claims, characterized in that two pressure accumulators (28, 29) are provided, of which a first accumulator (29) is provided as a high pressure accumulator and a second accumulator (28) as a low pressure accumulator. Hydrostatic transmission (9) according to one of the preceding claims, characterized in that a controllable throttle point (31, 32) is provided between the at least one pressure accumulator (28, 29, 35) and the hydraulic circuit (26). A power split transmission (4; 34) for a motor vehicle powertrain (1; 33), comprising a hydrostatic transmission (9), which according to one or more of Claims 1 to 6 is designed. Motor vehicle drive train (1; 33), comprising a power-split transmission (4; 34) according to Claim 7 , Method for operating a hydrostatic transmission (9), in which two hydrostatic machines (22, 23) are hydraulically connected to one another in a hydraulic circuit (26), of which hydrostatic machines (22, 23) the one machine (22; Hydraulic pump and the other machine (23; 22) is operated as a hydraulic motor and flow rates of the machines (22, 23) are variable, and wherein at least one pressure accumulator (28, 29, 35) connected in at least one operating function with the hydraulic circuit (26) is characterized in that the delivery rates of the hydrostatic machines (22, 23) are forcibly coupled together only. Method according to Claim 9 , characterized in that at the beginning of a start-up or boost function, the at least one pressure accumulator (29; 35) operating downstream of the machine (22) operating as a hydraulic pump and upstream of the machine (23) operating as a hydraulic motor are connected to the hydraulic circuit (26) and hydraulic fluid from the pressure accumulator (29, 35) is supplied, wherein the delivery rate of the machine operating as a hydraulic pump (22) is at least initially set to a value at the time when connecting the pressure accumulator (29; as a hydraulic pump operating machine (22) remains unchanged. Method according to Claim 10 , characterized in that in the course of the start-up or boost function, the flow rate of the machine operating as a hydraulic pump (22) is increased, wherein parallel to a via the high-pressure accumulator (29; 35) supplied amount of fluid in response to the change in the flow rate of the working as a hydraulic pump machine (22) is throttled. Method according to Claim 9 Characterized in that in the course of a braking operation of at least one functioning as the high-pressure accumulator pressure accumulator (29; 35) downstream of the working as a hydraulic pump engine (23) and upstream of operating as a hydraulic motor machine (22) to the hydraulic circuit (26) and hydraulic fluid from the hydraulic circuit (26) in pressure accumulator (29, 35) is conveyed. Method according to Claim 12 , characterized in that the delivery rate of the machine operating as a hydraulic pump (23) is set to the highest possible value.

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