Hydrostatic transmission, traction drive having the transmission, and method for controlling the transmission

Abstract

A hydrostatic transmission for a traction drive includes a first hydraulic machine that is coupled to a drive machine and that has an adjustable displacement volume and a second hydraulic machine that is fluidically connected to the first hydraulic machine and that is coupled to a drive output of the traction drive. At the first hydraulic machine, a control pressure acts in the direction of an enlargement of its displacement volume and a working pressure of the second hydraulic machine acts in the opposite direction. The hydrostatic transmission further includes a control device that varies the control pressure to influence a torque of the second hydraulic machine. The control device stores a characteristic map by which a setpoint control pressure is determined as a function of a setpoint torque and a displacement volume of the second hydraulic machine so as to regulate the torque of the second hydraulic machine.

Claims

1. A hydrostatic transmission for a traction drive, comprising: a first hydraulic machine coupled to a drive machine and having an adjustable displacement volume; a second hydraulic machine configured to be (i) fluidically connected to the first hydraulic machine and (ii) coupled to a drive output of the traction drive; and a control device by which a control pressure is configured to be adjusted in order to regulate a torque of the second hydraulic machine, wherein, at the first hydraulic machine, the control pressure acts in the direction of an enlargement of the displacement volume of the first hydraulic machine, and a working pressure of the second hydraulic machine, which is dependent on the adjustment of the control pressure, acts in the opposite direction, and wherein the control device stores a characteristic map by which a setpoint control pressure for the control pressure is configured to be determined as a function of a setpoint torque and a displacement volume of the second hydraulic machine, and of the displacement volume of the first hydraulic machine, in order to regulate the torque of the second hydraulic machine.

2. The hydrostatic transmission according to claim 1, wherein the control pressure is stored in the characteristic map as a function of the working pressure and as a function of the displacement volume of the first hydraulic machine and as a function of one or more of a rotational speed and a rotational speed range of the first hydraulic machine.

3. The hydrostatic transmission according to claim 1, wherein the control pressure is stored in the characteristic map for one or more of traction operation and braking operation of the second hydraulic machine.

4. The hydrostatic transmission according to claim 1, wherein the displacement volume of the first hydraulic machine is adjustable to both sides of a zero position and, in the characteristic map, the control pressure is stored to both sides of the zero position.

5. The hydrostatic transmission according to claim 1, further comprising: a first rotational speed detection unit configured to detect a rotational speed of the first hydraulic machine; and a second rotational speed detection unit configured to detect a rotational speed of the second hydraulic machine.

6. The hydrostatic transmission according to claim 1, wherein, by way of the control device, a volume flow of the transmission is configured to be determined as a function of a rotational speed of the second hydraulic machine and as a function of the displacement volume of the second hydraulic machine.

7. The hydrostatic transmission according to claim 6, wherein, by way of the control device, the displacement volume of the first hydraulic machine is configured to be determined as a function of the rotational speed of the first hydraulic machine and as a function of the volume flow.

8. The hydrostatic transmission according to claim 1, wherein, by way of the control device, a setpoint working pressure is configured to be determined as a function of the setpoint torque of the second hydraulic machine and as a function of the displacement volume of the second hydraulic machine.

9. The hydrostatic transmission according to claim 8, wherein, by way of the control device, the setpoint control pressure is configured to be determined from the characteristic map as a function of the setpoint working pressure and as a function of the displacement volume of the first hydraulic machine and as a function of a rotational speed of the first hydraulic machine.

10. The hydrostatic transmission according to claim 1, further comprising a pressure detection unit configured to detect the working pressure.

11. The hydrostatic transmission according to claim 1, wherein, by way of the control device, the displacement volume of the second hydraulic machine is configured to be controlled as a function of a rotational speed of the second hydraulic machine.

12. The hydrostatic transmission according to claim 11, wherein: an interval of the displacement volume of the first hydraulic machine is parameterized in the control device, the interval having a maximum displacement volume as an upper limit, and by way of the control device, in order to increase the rotational speed of the second hydraulic machine, a reduction in size of the displacement volume of the second hydraulic machine is performed within the interval, and an enlargement of the displacement volume of the first hydraulic machine is performed outside the interval.

13. A hydrostatic traction drive, comprising: a hydrostatic transmission including: a first hydraulic machine coupled to a drive machine and having an adjustable displacement volume; a second hydraulic machine configured to be (i) fluidically connected to the first hydraulic machine and (ii) coupled to a drive output of the traction drive; and a control device by which a control pressure is configured to be varied in order to regulate a torque of the second hydraulic machine, wherein, at the first hydraulic machine, the control pressure acts in the direction of an enlargement of the displacement volume of the first hydraulic machine, and a working pressure of the second hydraulic machine, which is dependent on the adjustment of the control pressure, acts in the opposite direction, and wherein the control device stores a characteristic map by which a setpoint control pressure for the control pressure is configured to be determined as a function of a setpoint torque and a displacement volume of the second hydraulic machine, and of the displacement volume of the first hydraulic machine, in order to regulate the torque of the second hydraulic machine.

14. A method for regulating a torque of a second hydraulic machine of a hydrostatic transmission, the hydrostatic transmission including a first hydraulic machine having an adjustable displacement volume and a control device by which a control pressure is configured to be varied in order to influence the torque of the second hydraulic machine, the second hydraulic machine configured to be fluidically connected to the first hydraulic machine, the method comprising: determining a setpoint control pressure as a function of a setpoint torque and as a function of a displacement volume of the second hydraulic machine by way of a characteristic map stored in the control device, including; determining a setpoint working pressure as a function of the setpoint torque of the second hydraulic machine and as a function of the displacement volume of the second hydraulic machine, and determining the setpoint control pressure from the characteristic map as a function of the setpoint working pressure and as a function of the displacement volume of the first hydraulic machine and as a function of a rotational speed of the first hydraulic machine.

15. The method according to claim 14, wherein: by way of the control device, the displacement volume of the second hydraulic machine is configured to be controlled as a function of a rotational speed of the second hydraulic machine, an interval of the displacement volume of the first hydraulic machine is parameterized in the control device, the interval having a maximum displacement volume as an upper limit, and in order to increase the rotational speed of the second hydraulic machine within the interval, the method further comprises reducing the displacement volume of the second hydraulic machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of a traction drive according to the disclosure having a hydrostatic transmission according to the disclosure, and a method for controlling the transmission, are illustrated in the drawings. The disclosure will now be discussed in more detail on the basis of the figures of said drawings.

(2) In the drawings:

(3) FIG. 1 shows a hydraulic circuit diagram of the exemplary embodiment,

(4) FIG. 2 shows a block diagram of a method according to the disclosure for regulating the drive output torque M.sub.HM in interaction with the hydraulic machines of the transmission of the traction drive as per FIG. 1, and

(5) FIG. 3 shows a characteristic map of the setpoint control pressure p.sub.Stsoll as a function of the working pressure p of the hydrostatic transmission and as a function of the displacement volume V.sub.HP of the first hydraulic machine, which is coupled to the drive machine, of the transmission.

DETAILED DESCRIPTION

(6) As per FIG. 1, a hydrostatic traction drive 1 has a hydrostatic transmission 2, a drive machine 4, a drive output 6 and a control unit 8.

(7) The hydrostatic transmission 2 has a first hydraulic machine 10 with adjustable displacement volume, said first hydraulic machine being designed as an axial piston machine of swashplate type of construction. Said first hydraulic machine is coupled by way of a drive shaft 12 to the drive machine 4. The first hydraulic machine 10 is fluidically connected in a closed hydraulic circuit to a second hydraulic machine 18 via a first and a second working line 14 and 16. The second hydraulic machine 18 is coupled by way of a drive shaft 20 to a mechanical transmission 22 of the drive output 6. The mechanical transmission 22 is coupled to two drive output axles 24 of the drive output 6.

(8) The transmission 2 has a first rotational speed detection unit 26 for detecting a rotational speed n.sub.HP of the first hydraulic machine 10 and a second rotational speed detection unit 28 for detecting a rotational speed n.sub.HM of the second hydraulic machine 18. Furthermore, the transmission 2 has a pivot angle detection unit 30 by way of which a pivot angle of the first hydraulic machine 10 can be detected.

(9) The first hydraulic machine 10 has an adjustment device 32 which can be charged with control pressure medium, wherein a control pressure acts, via the adjustment device 32, in the direction of an enlargement of the displacement volume V.sub.HP of the first hydraulic machine 10, and the working pressure p prevailing in the working lines 14 or 16 acts in the direction of a reduction in size of the displacement volume V.sub.HP of the first hydraulic machine 10. This is achieved, in the exemplary embodiment shown, by way of a twist of a control disk (not illustrated) of the first hydraulic machine 10.

(10) The second hydraulic machine 18 has an electroproportionally controlled adjustment device 34 by way of which the displacement volume V.sub.HM of the second hydraulic machine 18 can be controlled.

(11) FIG. 2 illustrates the mode of operation of the control unit 8 as per FIG. 1 in interaction with the first hydraulic machine 10 and the second hydraulic machine 18.

(12) The traction drive 1 as per FIG. 1 is regulated in torque-based fashion, making possible to realize a natural driving feel, for example in a passenger motor vehicle.

(13) Here, the position of a setpoint value transducer, for example an accelerator pedal, is for example proportional to the available torque of the drive machine 4.

(14) The action of the control unit 8 makes it possible, for example, to realize direct influencing of a traction force characteristic of the traction drive 1 in all four quadrants.

(15) Alternatively or in addition, there may be stored in the control unit 8 a characteristic which permits a greater traction force, that is to say a greater torque M.sub.HM of the second hydraulic machine 18, during forward travel than during reverse travel.

(16) Alternatively or in addition, by way of the control unit 8, a limitation of the torque M.sub.HM is implemented by the driver by way of an HMI, for example if the pavement surface is sensitive.

(17) Alternatively or in addition, by way of the control unit 8, braking is performed with a constant torque M.sub.HM or with a brake characteristic of any desired form.

(18) It is also possible by way of the control unit 8 to realize driving with a minimum required torque M.sub.HM, and immediate stoppage if a traveling resistance increases, for example in order to prevent damage when maneuvering.

(19) A parameterization of the traction drive 1 is possible on the basis of vehicle-related parameters, such that no software skills are necessary.

(20) For example, a maximum starting torque M.sub.HMmax may be stored in parameterized form in the control unit 8 for the purposes of influencing driving dynamics of the traction drive 1.

(21) It is also possible for a drag torque of the traction drive 1 during coasting to be stored in parameterized form, in order to permit maneuvering using the accelerator pedal alone, or in order to realize fuel consumption-optimized coasting operation of the traction drive.

(22) A further advantage of the traction drive 1 according to the disclosure and of the transmission 2 according to the disclosure is that the torque M.sub.HM of the second hydraulic machine 18, regulated in accordance with the setpoint torque M.sub.HMsoll, is, in the case of a known rotational speed n.sub.HM, proportional to a regulated power P.sub.HM. Thus, a power demand is known before it arises. Correspondingly, it is for example possible for a power management system of a hybrid system or power-split transmission to decide whether and how said power P.sub.HM is provided jointly by the internal combustion engine and for example by an electric machine in order to optimize fuel consumption.

(23) As per FIG. 2, the control unit 8 receives, as input variables, the demanded setpoint torque M.sub.HMsoll, the rotational speed n.sub.HP of the first hydraulic machine 10, as detected by the rotational speed detection unit 26, and the rotational speed n.sub.HM of the second hydraulic machine 18, as detected by the rotational speed detection unit 28. Said input variables are minimum prerequisites for the regulation of the torque M.sub.HM of the second hydraulic machine 18 by way of the control unit 8.

(24) The second hydraulic machine 18, which in the exemplary embodiment shown is in the form of a hydraulic motor that can be operated in 4-quadrant operation, exhibits proportional, in particular electroproportional, control of its displacement volume V.sub.HM. Accordingly, a setpoint value V.sub.HMsoll, output by the module 40 of the control unit 8, of the displacement volume V.sub.HM substantially corresponds to the actual displacement volume V.sub.HM. Since this is however not a detected but an assumed value of the displacement volume V.sub.HM of the second hydraulic machine 18, said value will hereinafter be designated V.sub.HM*.

(25) Firstly, by way of the control unit 8 and the pressure/torque calculation module 36 thereof, the relationship M.sub.HMsoll=P.sub.soll V.sub.HM* is used for determining the setpoint working pressure p.sub.soll as a function of the setpoint torque M.sub.HMsoll and the present displacement volume V.sub.HM* of the second hydraulic machine 18. Furthermore, the control unit 8 uses the relationship Q=n.sub.HM V.sub.HM* and the detected rotational speed n.sub.HP for determining the present displacement volume V.sub.HP of the first hydraulic machine 10. The determined values p.sub.soll and V.sub.HP and the detected rotational speed n.sub.HP of the first hydraulic machine 10 are input into a pressure regulation module 38 of the control unit 8. In said pressure regulation module there is stored a characteristic map of the control pressure p.sub.St as a function of the working pressure p, in this case as a function of the setpoint working pressure p.sub.soll, and as a function of a relative displacement volume v.sub.HP (v.sub.HP=V.sub.HP/V.sub.HPmax) of the first hydraulic machine 10 at a given rotational speed n.sub.HP.

(26) For example, assume that the relative displacement volume v.sub.HP is presently 0.5, that is to say the displacement volume V.sub.HP is presently at half of its maximum V.sub.HPmax. Assume also that the demanded or setpoint torque M.sub.HMsoll at the present displacement volume V.sub.HM of the second hydraulic machine 18 yields a setpoint working pressure p.sub.soll of 300 bar. As per the characteristic map in FIG. 3, the setpoint control pressure p.sub.Stsoll then emerges from the ordinate of the diagram. The setpoint control pressure p.sub.Stsoll thus determined is input as a setpoint value into the adjustment device 32 of the first hydraulic machine 10 as per FIG. 1, which has a pressure regulation valve 32a. By way of the pressure regulation valve 32a, the control pressure p.sub.St is regulated to the corresponding value, whereby this acts at the pivot cradle of the first hydraulic machine 10. In accordance with the simultaneously acting working pressure p, the pivot cradle of the first hydraulic machine 10 experiences a force imbalance, and a corresponding adjustment of its displacement volume, until force equilibrium at the pivot cradle is restored.

(27) As per FIG. 3, the set of curves from 0 to 450 bar for positive relative displacement volumes v.sub.HP of the first hydraulic machine 10 corresponds to traction operation during forward travel, the set of curves from 0 to 450 bar in the case of positive relative displacement volumes v.sub.HP corresponds to braking operation during forward travel, the set of curves from 0 to 450 bar in the case of negative relative displacement volumes v.sub.HP of the first hydraulic machine 10 corresponds to braking operation during reverse travel, and the remaining set of curves from 0 to 450 bar in the case of negative displacement volumes v.sub.HP of the first hydraulic machine 10 corresponds to traction operation during reverse travel. The curve of 0 bar in this case represents torque-free coasting operation during forward or reverse travel.

(28) To further improve the calculation of the control unit and the precision thereof, the pivot angle detection unit 30 is provided as already mentioned, which pivot angle detection unit renders the calculation of the displacement volume V.sub.HP by way of the control unit 8, if desired, superfluous.

(29) Furthermore, in FIG. 2, the working pressure p is illustrated as a detected value (this is optional) which is input as an input variable into the respective module 38 and 40. The exchange of the setpoint torque M.sub.HMsoll and of the torque M.sub.HM with the surroundings can be referred to as traction strategy interface.

(30) The exchange of the rotational speeds n.sub.HP, n.sub.HM, of the displacement volumes V.sub.HP, V.sub.HM, and of the determined setpoint control pressure p.sub.Stsoll described immediately above, with the hydraulic machines 10 and 18 can be referred to as component control interface.

(31) An exemplary embodiment of a regulation method according to the disclosure for the torque M.sub.HM of the second hydraulic machine 18 is stored, for execution, in the modules 36, 38 and 40 of the control unit 8.

LIST OF REFERENCE DESIGNATIONS

(32) 1 Hydrostatic traction drive 2 Hydrostatic transmission 4 Drive machine 6 Drive output 8 Control unit 10 First hydraulic machine 12 Drive shaft 14 Working line 16 Working line 18 Second hydraulic machine 20 Drive shaft 22 Mechanical transmission 24 Axle 26 Rotational speed detection unit 28 Rotational speed detection unit 30 Pivot angle detection unit 32 Hydrostatic adjustment device 34 Electroproportional adjustment device 36 Pressure/torque calculation 38 Pressure regulation 40 Controller of second hydraulic machine n.sub.HP Rotational speed of first hydraulic machine n.sub.HM Rotational speed of second hydraulic machine V.sub.HP Displacement volume of first hydraulic machine V.sub.HM* Displacement volume of second hydraulic machine V.sub.HMsoll Setpoint displacement volume of second hydraulic machine M.sub.HP Torque of first hydraulic machine M.sub.HMsoll Setpoint torque of second hydraulic machine M.sub.HM Torque of second hydraulic machine Q Volume flow p Working pressure p.sub.soll Setpoint working pressure p.sub.Stsoll Setpoint control pressure