DE102009048807A1 - Method for controlling hydrostatic gearbox, involves connecting valve-controlled hydro machines of hydrostatic gearbox fluidically with each other over pressure pipe - Google Patents

Abstract

The method involves connecting valve-controlled hydro machines (2,3) of hydrostatic gearbox fluidically with each other over a pressure pipe (14). A pressure fluid volume flow is lowered in the pressure pipe by a valve control of the hydro machines before switching one of the hydro machines from a pump operation to engine operation or vice versa. The hydro machines are arranged in an open hydraulic circuit and are respectively connected with a tank (12). The volume flow in the pressure pipe is lowered to zero before switching.

Description

The invention relates to a method for controlling a hydrostatic transmission and a hydrostatic transmission according to the preamble of patent claim 14.

In the WO 2008/012558 and the EP 0 494 236 B1 such a hydrostatic transmission is disclosed. This has a first hydraulic machine connected to an internal combustion engine and a second hydraulic machine connected to a consumer, for example wheels of a vehicle. The two hydraulic machines are in fluid communication via two pressure lines and form a closed hydraulic circuit.

A displacement / delivery volume of the hydraulic machines is variable via a valve control, wherein cylinder-piston units of the hydraulic machines can be switched on and off and operated in a "full mode", in a "partial mode" or in the "idle mode" , Such hydraulic machines are referred to as digital displacement units (DDU).

The hydraulic machines can each be used as a hydraulic pump or motor. Thus, these may serve as a hydrostatic transmission for a vehicle, wherein in the normal driving mode of the vehicle, the first hydraulic machine used as a driven by the internal combustion engine hydraulic pump and the second hydraulic machine as a hydraulic pump driven by the hydraulic motor, which in turn drives the wheels. For example, when braking the vehicle, the second hydraulic machine can be reversed from engine operation in a pumping operation to recover braking energy and then promotes hydraulic pump, driven by the wheels of the vehicle, pressure fluid via one of the pressure lines in a hydraulic accumulator.

A disadvantage of such hydrostatic transmissions is that when reversing the hydraulic machines, for example from a pump to a motor operation, high shocks or pressure peaks in the pressure lines and in the hydraulic machines occur, for example due to a change in direction of a pressure medium flow in a pressure line.

In contrast, the invention has the object to provide a method for controlling a hydrostatic transmission, with which this can be reversed or substantially shock-free shockless. A further object of the invention is to provide a hydrostatic transmission which is of simple construction and can be reversed or repositioned without any shocks.

This object is achieved with regard to the method according to the features of patent claim 1 and with regard to the device according to the features of patent claim 14.

The invention provides a method for controlling a hydrostatic transmission. This has at least two valve-controlled hydraulic machines, which are fluidly connected to each other via a pressure line. At least one of the hydraulic machines can be switched from pumping to engine operation or vice versa. Before switching, a pressure medium flow in the pressure line is lowered by controlling valves of the hydraulic machines.

Experiments have shown that the lowering of the pressure medium flow in the pressure line allows a low-impact or bumpless switching of at least one hydraulic machine, whereby this solution avoids high loads of the system in the short term.

The hydraulic machines preferably form an open hydraulic circuit and are each connected to a tank in pressure medium connection.

In order to allow the most shock-free switching, the volume flow in the pressure line is lowered to about zero before switching.

Advantageously, the first hydraulic machine with a drive unit and the second hydraulic machine are connected via a drive shaft with wheels of a vehicle, whereby the hydraulic machines can be used for example for the recovery of braking energy.

In order to enable driving of the vehicle with the hydraulic machines, the first hydraulic machine can be used as a hydraulic pump and the second hydraulic machine as a hydraulic motor prior to switching.

An advantageous application possibility of the hydraulic machine may be that after switching the second hydraulic machine are used as a hydraulic pump and / or the first hydraulic machine as a hydraulic motor.

To reduce pressure peaks in the pressure line, a pressure relief valve is preferably arranged between this and the tank.

If the hydraulic machine, which is used as a hydraulic motor, has a higher flow rate of the pressure medium than the hydromachine used as a hydraulic pump, can for sucking pressure medium of the hydraulic motor from the tank between the pressure line and the tank an in Pressure fluid flow direction to the tank closing check valve may be arranged.

In order to enable both functions - pressure limiting and re-suction - the pressure relief valve and the check valve can be arranged parallel to each other.

So that a leading to cavitation pressure drop in the pressure line, for example, changes in the ratio of the rotational speeds of the hydraulic machines is avoided, used as a hydraulic pump hydraulic machine can - as a buffer imaginary - higher throughput of the pressure medium than the hydraulic motor used as a hydraulic motor. The excess pressure of the hydraulic pump is dissipated via the pressure relief valve to the tank. A short-term increased pressure medium requirement of the hydraulic motor thus does not lead to the pressure drop in the pressure line, but to the fact that less pressure medium flows through the pressure relief valve to the tank.

The hydraulic machine used as a hydraulic motor can have a higher throughput of the pressure medium than the hydromachine used as a hydraulic pump and vacuum the additional amount of pressure medium via the check valve. As a result, pressure peaks in the pressure line are substantially avoided, since at an increased flow rate of the pressure medium of the hydraulic pump - for example, due to a change in speed of the hydraulic pump - the hydraulic motor simply sucks less pressure fluid through the pressure relief valve.

For uniform lowering of the pressure medium flow in the pressure line, the hydraulic machines during reduction preferably a largely constant ratio of their Förden- or displacement volumes, taking into account a possible change in the speed of one or the other hydraulic machine.

The valve control for changing the volume flow in the pressure line takes place by approximately synchronous connection or disconnection of cylinder-piston units of both hydraulic machines. Thus, the delivery and the displacement volume flow can be uniformly reduced and the transmission ratio between the drive unit and the wheels are maintained.

According to the invention, a hydrostatic transmission has two hydraulic machines in an open hydraulic circuit which is in each case fluidically connected to a tank and via a pressure line. The hydraulic machines are valve-controlled. The hydrostatic transmission is simple in terms of apparatus and is suitable for the method described above, whereby shocks during the switching of the hydraulic machines are largely avoided.

To reduce pressure peaks, a pressure limiting valve is arranged between the pressure line and the tank.

For sucking up pressure medium, a check valve closing towards the tank is arranged between the pressure line and the tank.

The pressure relief valve and the check valve are advantageously arranged parallel to each other.

Other advantageous developments of the invention are the subject of further subclaims.

In the following preferred embodiments of the invention will be explained in more detail with reference to schematic drawings. Show it:

1 in a schematic representation of a hydrostatic transmission according to a first embodiment;

2 in a schematic representation of the hydrostatic transmission according to a second embodiment;

3 in a schematic representation of the hydrostatic transmission according to a third embodiment;

4 in a schematic representation of the hydrostatic transmission according to a fourth embodiment.

In 1 is a hydrostatic transmission 1 shown in a schematic representation according to a first embodiment. This has two valve-controlled hydraulic machines 2 . 4 , These are displacement machines whose delivery / displacement volume can be adjusted digitally by switching cylinder-piston units on and off (DDU). The switching on and off takes place by a specific control of the respective cylinder-piston unit associated high and low pressure valves. Such a hydraulic machine is, for example, in the above-described prior art EP 0 494 236 B1 disclosed.

The hydrostatic transmission is used, for example, in vehicles with continuously variable transmissions (Infinitely Variable Transmission / IVT) in addition to a planetary gearbox or as a hydraulic drive for a serial or parallel hybrid drive.

Via a drive shaft 6 is the hydraulic machine 2 with a drive unit 8th , in particular an internal combustion engine, mechanically connected. The hydraulic machine 2 has a tank connection T, on which one with a tank 12 connected tank line 10 connected. A working port A of the hydraulic machine 2 is with a pressure line 14 connected via these the two hydraulic machines 2 . 4 are fluidically connected by the hydraulic machine 4 also with a working port A on the pressure line 14 connected. The hydraulic machine 4 further includes a tank port T via a tank line 16 with the tank 12 is in pressure medium connection. The hydraulic machine 4 is about a shoot shaft 18 and a gearbox 20 with wheels 22 a vehicle in operative connection.

To get the vehicle over the wheels 22 will drive in the 1 left hydraulic machine 2 as a hydraulic pump and the right hydraulic machine 4 used as a hydraulic motor. The drive unit 8th then drives the hydraulic machine 2 on, causing these pressure fluid from the tank 12 in the pressure line 14 promotes and thus the hydraulic machine 4 drives. This transmits a torque via the drive shaft 18 , The gear 20 on the wheels 22 ,

To brake the wheels 22 For example, when driving downhill of the vehicle, the hydrostatic transmission 1 be used. For this is a load reversal of the hydraulic machines 2 . 4 necessary. In the 1 right hydraulic machine 4 is then used as a hydraulic pump and the left hydromachine 2 used as a hydraulic motor. This now promotes the hydraulic machine 4 Pressure medium from tank 12 , via the pressure line 14 to the hydraulic machine 2 , The hydraulic machine 2 then acts the drive unit 8th counter, whereby a so-called engine braking is possible. When reversing the load thus also the direction of the pressure medium flow in the pressure line 14 reversed. So that this reversal is possible low impact or bum-free, and thus low loads in the pressure line and the hydraulic machines 2 . 4 occur, the method explained below is used for this purpose.

In this process, before switching the hydraulic machine 2 from pump to engine operation and hydraulic machine 4 from engine to pump operation, the intake or displacement volume of the hydraulic machines 2 . 4 uniformly reduced by appropriate valve control, whereby the pressure medium flow in the pressure line 14 is also reduced. The lowering of the delivery / displacement volume of the hydraulic machines 2 . 4 is done by switching off cylinder-piston units. Here are both hydraulic machines 2 . 4 in about synchronous, for example, a full-mode in a partial mode and switched by this in an idle mode. Here it is advantageous if the transmission ratio of the speeds of the hydraulic machines 2 . 4 is substantially constant, since then an additional adjustment of the delivery / absorption volume of the hydraulic machines 2 during the lowering of the pressure medium flow in the pressure line 14 to a new gear ratio is not necessary. A change in the transmission ratio of the hydraulic machines 2 . 4 without adaptation of the delivery / displacement volume would lead to pressure peaks or a pressure drop.

Are units of both hydraulic machines 2 . 4 largely in idle mode, so is the pressure medium flow in the pressure line 14 about zero, which now when switching the hydraulic machine 2 from pumping to engine operation and from the hydromachine 4 from engine to pump operation by means of corresponding valve control of the high and low pressure valves, this is essentially bum-free. After switching, the delivery / displacement flow rate of the hydraulic machines 2 . 4 increased again. The increase in the volume flow takes place while maintaining or under an adapted transmission ratio of the rotational speeds of the hydraulic machines 2 . 4 by reactivating the units.

The state in which the volume flow in the pressure line is approximately zero is determined by measuring a pressure of the pressure medium in the pressure line 14 , or by measuring a velocity of the pressure medium flow in the pressure line 14 or by measuring the load torque on the gearbox 20 detected.

The hydrostatic transmission 1 can be used in addition to the braking of the vehicle for the recovery of braking energy (recuperation). In this case, the pressure medium flow in the pressure line 14 lowered to about zero and then the in the 2 right hydraulic machine 4 switched from a motor to a pumping operation. The hydraulic machine 4 then promotes pressure medium via the pressure line 14 in one in the 1 not shown hydraulic accumulator.

The method explained above is in all operating modes of the hydrostatic transmission 1 can be used, in which switching at least one of the hydraulic machines 2 . 4 he follows. So this can also be in a start-up or boost operation, in which the hydraulic machine 2 - Before use as a hydraulic pump - in motor operation, the drive unit 8th supported, used.

2 shows a schematic representation of the hydrostatic transmission 1 according to a second embodiment. Here is between the pressure line 14 and the tank 12 a pressure relief valve 24 arranged. This is via a pressure port P to one with the pressure line 14 connected connection cable 26 connected and via a tank connection T and a tank line 28 with the tank 12 connected. A valve spool of the pressure relief valve 24 is connected via a control line connected to the pressure port P. 30 in the opening direction with the pressure in the pressure line 14 and in the closing direction with a spring force of a spring 32 applied. The spring force of the spring 32 is adjustable, whereby the opening pressure of the pressure relief valve 24 is changeable.

Through the pressure relief valve 24 are pressure peaks in the pressure line 14 avoided, for example, in a change in the transmission ratio of the hydraulic machines 2 and 4 occur. At a pressure in the pressure line above the set opening pressure of the pressure relief valve 24 lies, opens this and the pressure line 14 becomes a tank 12 relieved.

The gear ratio of the hydraulic machines 2 . 4 is with the pressure relief valve 24 adjustable such that the hydraulic machine used, for example, when driving the vehicle as a hydraulic pump 2 a higher throughput of pressure medium than the hydraulic machine used as a hydraulic motor 4 having. An increase in pressure in the pressure line 14 is here by the pressure relief valve 24 avoided. If, for example, the transmission ratio of the hydromachines changes for a short time 2 . 4 in which the speed of the hydraulic machine 2 is reduced, this does not lead to a pressure drop in the pressure line 14 but to have less or no pressure fluid through the pressure relief valve 24 flows. Thus, with the pressure relief valve 24 in connection with a certain gear ratio of the hydraulic machines 2 . 4 a substantially constant pressure in the pressure line 14 available.

3 represents the hydrostatic transmission 1 in a schematic representation according to a third embodiment. In this case, instead of a pressure relief valve 24 out 3 a check valve 34 between the pressure line 14 and the tank 12 arranged. A valve body is a valve seat 38 assigned and is in the closing direction of the pressure in the pressure line 14 and the spring force of a spring 40 applied.

With the check valve 34 is a pressure drop in the pressure line 14 due to a change in the transmission ratio of the hydraulic machine 2 . 4 preventable. For example, decreases the speed of the hydraulic machine used as a hydraulic pump 2 , then sinks into the pressure line 14 promoted pressure medium flow. So now the hydraulic machine used as a hydraulic motor 4 can be supplied at a constant speed with a constant pressure medium flow and the pressure in the pressure line 14 does not fall, sucks these pressure medium via the pressure line 14 and the check valve 34 from the tank 12 to. About the check valve 34 is thus a reduced pressure medium flow in the pressure line 14 compensated.

The control of the hydraulic machines 2 . 4 out 3 can be done so that the hydromachine used as a hydraulic pump 2 . 4 a lower throughput of pressure medium, as the hydraulic machine used as a hydraulic motor 2 . 4 having. The additionally required pressure medium is via the check valve 34 from the tank 12 sucked. An increase in the throughput of pressure medium of the hydraulic machine used as a hydraulic pump 2 . 4 due to a speed change then does not lead to an increase in pressure in the pressure line 14 but to a reduced suction of pressure medium via the check valve 34 ,

4 shows a schematic representation of the hydrostatic transmission 1 according to a fourth embodiment. Here are the pressure relief valve 24 and the check valve 38 parallel to each other between the pressure line 14 and the tank 12 arranged. Differences between the intake and delivery flow rates of hydraulic machines 2 . 4 are thus arbitrarily compensated.

Disclosed is a method for controlling a hydrostatic transmission with at least two valve-controlled hydraulic machines. These are connected via a pressure line with each other in pressure medium connection. At least one of the hydraulic machines can be used in a pump or in an engine operation. Before switching from pumping to engine operation or vice versa, a pressure medium volume flow in the pressure line is lowered by switching off cylinder-piston units of at least one hydraulic machine by a valve control to avoid shocks.

LIST OF REFERENCE NUMBERS

1

hydrostatic transmission

2

hydromachine

4

hydromachine

6

drive shaft

8th

drive unit

10

tank line

12

tank

14

pressure line

16

tank line

18

drive shaft

20

transmission

22

wheel

24

Pressure relief valve

26

connecting cable

28

tank line

30

control line

32

feather

34

check valve

36

valve body

38

valve seat

40

valve spring

T

tank connection

A

working port

P

pressure connection

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

• WO 2008/012558 [0002]
• EP 0494236 B1 [0002, 0032]

Claims (16)

Method for controlling a hydrostatic transmission ( 1 ) with at least two valve-controlled hydraulic machines ( 2 . 4 ), which via a pressure line ( 14 ) are fluidly connected to each other, wherein prior to switching at least one of the hydraulic machines ( 2 . 4 ) from a pump to a motor operation or vice versa a pressure medium volume flow in the pressure line ( 14 ) by a valve control of the hydraulic machines ( 2 . 4 ) is lowered. Process according to claim 1, wherein the hydromachines ( 2 . 4 ) arranged in an open hydraulic circuit and each with a tank ( 12 ) are connected. Method according to claim 1 or 2, wherein the volume flow in the pressure line ( 14 ) is lowered to about zero before switching. Method according to one of the preceding claims, wherein the first hydraulic machine ( 2 ) with a drive unit ( 8th ) and the second hydraulic machine ( 4 ) via a drive shaft ( 18 ) with wheels ( 22 ) are connected to a vehicle. Method according to one of the preceding claims, wherein prior to switching the first hydraulic machine ( 2 ) as a hydraulic pump and the second hydraulic machine ( 4 ) are used as a hydraulic motor and wherein after switching the second hydraulic machine ( 4 ) as a hydraulic pump and / or the first hydraulic machine ( 2 ) are used as a hydraulic motor. Method according to one of the preceding claims, wherein between the pressure line ( 14 ) and the tank ( 12 ) a pressure relief valve ( 24 ) is arranged. Method according to one of the preceding claims, wherein between the pressure line ( 14 ) and the tank ( 12 ) in a pressure fluid flow direction to the tank ( 12 ) closing check valve ( 34 ) is arranged. Method according to claim 7, wherein the pressure relief valve ( 24 ) and the check valve ( 34 ) are arranged parallel to each other. Process according to claims 6 to 8, wherein the hydraulic machine used as a hydraulic pump ( 2 . 4 ) substantially a higher throughput of pressure medium than that as a hydraulic motor ( 2 . 4 ) used hydraulic machine ( 2 . 4 ) having. Method according to one of claims 7 to 9, wherein the hydraulic machine used as a hydraulic motor ( 2 . 4 ) substantially a higher throughput of pressure medium than that as a hydraulic pump ( 2 . 4 ) used hydraulic machine ( 2 . 4 ) having. Method according to one of the preceding claims, wherein the hydraulic machines ( 2 . 4 ) when lowering the volume flow in the pressure line ( 14 ) have a largely constant transmission ratio. Method according to one of the preceding claims, wherein the valve control for lowering the volume flow in the pressure line ( 14 ) by approximately synchronous connection or disconnection of cylinder-piston units of both hydraulic machines ( 2 . 4 ) and / or by approximately synchronous shortening of the opening times of the cylinder-piston units associated high-pressure valves. Hydrostatic transmission with two hydraulic machines ( 2 . 4 ) in an open circuit, each with a tank ( 12 ) and via a pressure line ( 14 ) are fluidly connected to each other, characterized in that the hydraulic machines ( 2 . 4 ) are valve-controlled. Hydrostatic transmission according to claim 13, wherein between the pressure line ( 14 ) and the tank ( 12 ) a pressure relief valve ( 24 ) is arranged. Hydrostatic transmission according to one of claims 13 and 14, wherein between the pressure line ( 14 ) and the tank ( 12 ) to the tank ( 12 ) closing check valve ( 34 ) is arranged. Hydrostatic transmission according to claim 15, wherein the pressure relief valve ( 24 ) and the check valve ( 34 ) are arranged parallel to each other.

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