Method for controlling an axial piston pump and drive unit with such an axial piston pump and hydrostatic traction drive with such a drive unit

Abstract

In a drive unit which has an axial piston pump and an electronic control unit, the axial piston pump is pivoted with a method in which pressure-reducing valves which act in opposition to one another are suddenly energized. Since in this respect no orifices are provided in the adjustment device, a so-called initiation jump of the excited current gives rise to a sudden reduction in the assigned actuating pressure or the actuating pressure difference formed therefrom. Then, a zero crossover jump of the excited current or of the excited currents is carried out in order to overcome the centering spring and therefore ensure a continuous zero crossover of the axial piston pump. Furthermore, a hydrostatic traction drive includes such a drive unit.

Claims

1. A method for reversing a pivotable axial piston pump that includes an adjustment device, which has a double-acting actuating cylinder with (i) two actuating chambers acting in opposition to one another and (ii) two centering springs acting in opposition to one another, wherein a respective actuating pressure is applied to each of the two actuating chambers via one respective pressure-reducing valve, which is controlled by a respective current, the method comprising: detecting a pivoting angle of the axial piston pump; determining a time of a zero crossover of the pivoting angle; and suddenly changing at least one of the respective actuating pressures at approximately the time of the zero crossover by at least one zero crossover jump of the respective current associated with the at least one of the respective actuating pressures.

2. The method according to claim 1, wherein the at least one zero crossover jump of the respective current occurs in accordance with a rate of change of the pivoting angle shortly before the zero crossover.

3. The method according to claim 1, further comprising: calculating an actuating pressure difference as a first actuating pressure in a first actuating chamber of the two actuating chambers minus a second actuating pressure in a second actuating chamber of the two actuating chambers, wherein the actuating pressure difference is suddenly raised or suddenly lowered approximately at the time of the zero crossover in accordance with a reversing direction of the axial piston pump.

4. The method according to claim 3, wherein the sudden raising or lowering of the actuating pressure difference occurs by a sum of the equivalents of the two centering springs.

5. The method according to claim 1, wherein the detecting of the pivoting angle includes measuring the pivoting angle with a pivoting angle sensor.

6. The method according to claim 1, wherein the detecting of the pivoting angle includes calculating the pivoting angle based on a volume flow balance from a consumer volume flow, a leak, a rotational speed of the axial piston pump, and a displacement volume per revolution of the axial piston pump.

7. The method according to claim 1, wherein the determining of the zero crossover includes empirically parameterizing the zero crossover based on a velocity of a mobile working machine.

8. The method according to claim 1, further comprising: executing an initiation jump of at least one of the respective currents if a pivoting back of the pivoting angle or a deceleration of a mobile working machine is to begin or begins.

9. The method according to claim 8, further comprising: reducing a first current of the respective currents, at least temporarily, along a first ramp between the initiation jump and the zero crossover jump; and/or increasing a second current of the respective currents, at least temporarily, along a second ramp.

10. The method according to claim 9, further comprising: scaling at least one of (i) the initiation jump, (ii) at least one of the first and second ramps, and (iii) a pressure cut-off level of the axial piston pump using a parameter that is a function of a velocity of the mobile working machine.

11. The method according to claim 1, wherein a pressure cut-off of the axial piston pump occurs by parameterizable limitation of the respective currents.

12. The method according to claim 1, further comprising: protecting an internal combustion engine of a mobile working machine against an excessive rotational speed by throttling deceleration based on a characteristic curve or mathematical function which is comparable to the characteristic curve.

13. The method according to claim 12, wherein parameters of the mathematical function are adjusted jointly and coupled to one another in accordance with a desired behavior of the mobile working machine via a parameterizing interface.

14. A drive unit for a traction drive, the drive unit comprising: a pivotable axial piston pump having an adjustment device that includes: a double-acting actuating cylinder comprising: two actuating chambers which act in opposition to one another; and two centering springs which act in opposition to one another; and one pressure-reducing valve associated with each of the two actuating chambers and configured to supply the respective actuating chamber with actuating pressure medium; and an electronic control unit configured to: detect a pivoting angle of the axial piston pump; determine a time of a zero crossover of the pivoting angle; and suddenly change a respective actuating pressure in at least one of the respective actuating chambers at approximately the time of the zero crossover based on a zero crossover jump of an assigned current of the associated pressure-reducing valve.

15. A hydrostatic traction drive for a mobile working machine comprising: a drive unit comprising: a pivotable axial piston pump having an adjustment device that includes: a double-acting actuating cylinder comprising: two actuating chambers which act in opposition to one another; and two centering springs which act in opposition to one another; and one pressure-reducing valve associated with each of the two actuating chambers and configured to supply the respective actuating chamber with actuating pressure medium; and an electronic control unit configured to: detect a pivoting angle of the axial piston pump; determine a time of a zero crossover of the pivoting angle; and suddenly change a respective actuating pressure in at least one of the respective actuating chambers at approximately the time of the zero crossover based on a zero crossover jump of an assigned current of the associated pressure-reducing valve; and at least one hydraulic motor that is fluidically connected to the axial piston pump in a closed circuit.

16. The hydrostatic traction drive according to claim 15, wherein: the electronic control unit is further configured to calculate or define an actuating pressure difference as a first actuating pressure in a first actuating chamber of the two actuating chambers minus a second actuating pressure in a second actuating chamber of the two actuating chambers, and the actuating pressure difference is suddenly raised or suddenly lowered at approximately the time of the zero crossover in accordance with a type of change of a direction of travel of the mobile working machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of a driving unit according to the disclosure with which the method according to the disclosure is carried out is illustrated in the figures, of which:

(2) FIG. 1 shows a circuit diagram of the exemplary embodiment of the drive unit according to the disclosure,

(3) FIG. 2 shows a simplified circuit diagram of the drive unit from FIG. 1,

(4) FIG. 3 shows a profile of the pivoting angle of the axial piston pump during the reversing process with actuating pressure profiles and current profiles,

(5) FIG. 4 shows how the axial piston pump is controlled in the reversing process against the background of its characteristic diagram,

(6) FIG. 5 shows how the zero crossover jump of the current depends on the pivoting angle,

(7) FIG. 6 shows the sudden reduction in the actuating pressure difference at two different pivoting angles in two diagrams,

(8) FIG. 7 shows protection of an internal combustion engine against an excessive rotational speed, and

(9) FIG. 8 shows adjustment of the desired reversing behavior.

(10) FIG. 1 shows a circuit diagram of the exemplary embodiments of the drive unit according to the disclosure. FIG. 2 shows a circuit diagram only of the components of the drive unit from FIG. 1 which are relevant for the disclosed method.

(11) A pivotable axial piston pump has a housing 1 on which two working connections A, B are arranged and to each of which a working line of a closed circuit is connected. A traction drive is therefore formed for a mobile working machine (not shown).

(12) The axial piston pump has a drive unit 2 which is embodied with a swash plate 3, the pivoting angle .sub.pmp of which can be adjusted by means of an adjustment device 5. A double-acting actuating cylinder 6, which has a first actuating chamber 8.sub.A and a second actuating chamber 8.sub.B acting in opposition thereto, is used for this.

(13) In each actuating chamber 8.sub.A, 8.sub.B a centering spring 9.sub.A, 9.sub.B is arranged which forces the piston in the direction of the central position. A respective stop (not shown) prevents the centering spring 9.sub.A, 9.sub.B also being active beyond the central position.

(14) A first actuating pressure p.sub.stA acts in the direction of increasing the pivoting angle .sub.pmp of the axial piston pump in the first actuating chamber 8.sub.A and in the direction of increasing its swept volume Vol.sub.pmp in a first delivery direction. This is counteracted by a second actuating pressure p.sub.stB in the second actuating chamber 8.sub.B in the direction of reducing the pivoting angle .sub.pmp and therefore in the direction of reducing the swept volume Vol.sub.pmp in the first delivery direction.

(15) Because of the pivotability of the axial piston pump, the first actuating pressure p.sub.stB acts in the direction of increasing the pivoting angle .sub.pmp of the axial piston pump and therefore in the direction of increasing its swept volume Vol.sub.pmp in an opposing delivery direction.

(16) An actuating pressure difference p.sub.st=p.sub.stAp.sub.stB is defined, wherein according to the definition this actuating pressure difference p.sub.st always acts in the direction of increasing the pivoting angle .sub.pmp or the swept volume Vol.sub.pmp in the first delivery direction.

(17) By means of a drive shaft 10 of the axial piston pump, the drive unit 2 thereof is driven, and beyond that also a feed pump 14 with a rotational speed n.sub.pmp.

(18) The drive shaft 10 of the axial piston pump is driven by an internal combustion engine (not shown) which is preferably a diesel engine and whose crankshaft rotates at a rotational speed n.sub.Eng.

(19) The axial piston pump supplies, via its working connections A, B, one or more traction motors (not shown) of the mobile working machine in a closed circuit. In the forward travel, the first working pressure p.sub.A acts in the direction of reducing the pivoting angle .sub.pmp.

(20) The two actuating pressures p.sub.stA, p.sub.stB are controlled by means of two pressure-reducing valves 18.sub.A, 18.sub.B which are supplied on the input side by the feed pump 14 via a feed pressure line 22. The pressure-reducing valves 18.sub.A, 18.sub.B have respective solenoids a, b, to which excited currents I.sub.A I.sub.B are applied by an electronic control unit 16 via a respective electrical line 20.sub.A, 20.sub.B. The two pressure-reducing valves 18.sub.A, 18.sub.B are configured in such a way that the respective actuating pressure p.sub.stA, p.sub.stB is proportional to the respective strength of the current I.sub.A, I.sub.B.

(21) For the described exemplary embodiment, the first delivery direction of the axial piston pump is linked to the first pressure-reducing valve 18.sub.A and to forward delivery of the working pressure medium and to reverse travel of a mobile working machine which has a corresponding hydrostatic traction drive with hydrostatic traction motors. Correspondingly, the opposite or second delivery direction of the axial piston pump is linked to a second pressure-reducing valve 18.sub.B with reverse delivery of the working pressure medium and with reverse travel of the mobile working machine.

(22) In the following explanation of the method according to the disclosure it will firstly be assumed that there is forward delivery of the working pressure medium through the working connection A and therefore forward travel of the mobile working machine. As a result of the reversing, reverse delivery of the working pressure medium then occurs correspondingly through the working connection B or reverse travel of the mobile working machine occurs.

(23) FIG. 3 shows the pivoting angle .sub.pmp of the axial piston pump during the reversing process with the profiles of the actuating pressures p.sub.stA, p.sub.stB and the currents I.sub.A, I.sub.B.

(24) 1. The reversing is initiated. The first current I.sub.A for the forward travel drops suddenly with an initiation jump 26 in order to initiate the deceleration. At the same time, the second current I.sub.B for the reverse travel is switched on in order to pre-activate the second pressure-reducing valve 18.sub.B.

(25) 2. In the deceleration, the difference between the currents for the forward travel I.sub.A and for the reverse travel I.sub.B needs to therefore change continuously. Therefore, the current for the reverse travel I.sub.B begins to rise with a ramp as soon as the actuating pressure p.sub.stA for the forward travel reaches zero.

(26) 3. As long as the deceleration still persists, the actuating pressure p.sub.stB for the reverse travel is limited to a pressure cut-off level 27. This ensures that the deceleration does not lead to brake load pressures higher than the permissible working pressure p.sub.A, p.sub.B on the axial piston pump. In this context, the pressure cut-off of the axial piston pump takes place by means of parameterizable limitation of the second current I.sub.B during the deceleration so that the second actuating pressure p.sub.stB does not rise further.

(27) 4. If the pivoting angle .sub.pmp is returned to zero, the now relevant centering spring 9.sub.A is compensated by means of an equivalent sudden rise in the actuating pressure p.sub.stB. The latter is reached by means of a so-called zero crossover jump 24 of the second current I.sub.B. The first current I.sub.A is switched off.

(28) 5. Then, the mobile working machine passes through a further rise in the current for the reverse travel I.sub.B into the reverse-directed acceleration.

(29) FIG. 4 shows a characteristic diagram of the axial piston pump and how this is controlled, for example, by this characteristic diagram in the reversing process. Beginning at a maximum pivoting angle .sub.pmp and 200 bar working pressure p.sub.A or p.sub.B the actuating pressure difference p.sub.st is suddenly reduced (from e.g. 19 bar to 11 bar) in order to initiate the reversing. Then, the actuating pressure difference p.sub.st is reduced further by means of the ramp until the axial piston pump is pivoted back and makes the zero crossover.

(30) FIG. 5 then shows that the time of the zero crossover jump 24 of the current I.sub.A, I.sub.B has to be dependent on a rate of change 28 of the pivoting angle .sub.pmp so that it always gives rise directly to a defined actuating pressure p.sub.st and therefore a defined actuating pressure difference p.sub.st (in this case 0 bar). In the signal flow diagram shown in FIG. 5 it is shown that the trigger for the zero crossover is also shifted, apart from the pivoting angle .sub.pmp, from its rate of change 28 and from the response dynamics of the actuating pressure p.sub.stA, p.sub.stB with respect to the current I.sub.A, I.sub.B, that is to say of the pressure-reducing valve 18.sub.A, 18.sub.B. In this context, a high rate of change 28 of the pivoting angle .sub.pmp gives rise to further shifting forward of the trigger.

(31) FIG. 6 shows in the left-hand diagram the sudden reduction in the actuating pressure difference p.sub.st for initiating the reversing function at two different exemplary current pivoting angles .sub.pmp. Correspondingly, the level of the initiation jump 26 of the current I.sub.A also depends on the current pivoting angle .sub.pmp.

(32) In one application of the method according to the disclosure in the abovementioned traction drive which is driven by an internal combustion engine, a functional extension can serve to protect the internal combustion engine against an excessive rotational speed in the deceleration state of the traction drive.

(33) For this purpose, according to the illustrations in FIGS. 6 and 7, on the one hand the reduction of the actuating pressures p.sub.stA, p.sub.stB is limited as pilot control in dependence on the pivoting angle .sub.pmp, and also the initiation jump 26 and the reduction ramp are influenced in accordance with the pump rotational speed n.sub.pmp.

(34) FIG. 7 shows a diagram of protection against an excessive rotational speed for the internal combustion engine if the latter can no longer support the desired deceleration. In this context, the following rotational speed values n.sub.Eng of the internal combustion engine are plotted in an ascending sequence: lower idling rotational speed n.sub.Englowidle/maximum working rotational speed n.sub.Enghighidle/pre-warning rotational speed n.sub.Engmaxdrgctrlstrt/maximum drag rotational speed n.sub.Engmaxdrg.

(35) The scaling factor for the ramps is not increased further starting from the point when the maximum working rotational speed n.sub.Enghighidle is reached. If the internal combustion engine reaches the pre-warning rotational speed n.sub.Engmaxdrgctrlstrt, the scaling factor is reduced further. Therefore, if the internal combustion engine risks rotating at an excessive speed, the deceleration is throttled gradually so that the operator does not perceive any surprising decrease in the deceleration.

(36) FIG. 8 shows, as an extension of the method, adjustment of the desired reversing behavior, e.g. in the three stages gentle, moderate and aggressive.

(37) There are two options for adjusting the reversing for the axial piston pump in a suitable way: Option 1: response behavior, deceleration and acceleration are independently adjustable, in this context the dependence on the rotational speed n.sub.Eng of the internal combustion engine, that is to say on the position of the accelerator pedal, is not adjustable. Option 2: dynamics of the response behavior, deceleration and acceleration are permanently linked to one another. The dynamics are set as a function of the rotational speed n.sub.Eng of the internal combustion engine. Accelerator-pedal-dependent behavior can therefore be adjusted and a parameter is required less.

(38) With both options it is possible to adapt the behavior of the axial piston pump by means of percentage values without knowledge of the physics and sequencing of the reversing. These percentage values for the intensity of the reversing or the response behavior in turn scale the physical variables/parameters of the reversing algorithm.

(39) In the case of option 2 the dynamics of the reversing process are set in a manufacturer-specific fashion on the mobile working machine by the person performing the start. As is apparent from FIG. 3, the number of parameters which are to be set is high and the dependencies are complex. A minimum value for a very gentle behavior as well as a maximum value for a very aggressive behavior are preferably stored permanently in the controller for the initiation jump 26, the deceleration ramp in the left-hand early deceleration region in FIG. 3 and the acceleration ramp in the right-hand later acceleration region in FIG. 3. All three parameters can be adjusted coupled in their defined value range between gentle and aggressive by means of a single reversing dynamic parameter, which has, for example, a value range from 0 to 100%.

(40) In a further preferred embodiment, the reversing dynamics are not only a value but also a function, for example a form of a characteristic curve, of a guide variable, such as for example the position of the accelerator pedal or rotational speed n.sub.Eng of the internal combustion engine.

(41) FIG. 8 shows, in an exemplary embodiment, the table for the translation of the reversing dynamic parameter in steps 0-50-100% into values for the control function. In this example, the dynamic is additionally a function of the guide variable of the rotational speed n.sub.Eng of the internal combustion engine, wherein low rotational speed signifies a value close to the lower idling rotational speed and high rotational speed signifies a value near to the upper idling rotational speed of the all-rotational-speed regulator.

(42) The person performing the start can simply optimize the driving behavior on the basis of the stored values using the single reversing dynamic parameter.

(43) Extending the reversing algorithm constitutes electronically limiting the working pressure p.sub.A, p.sub.B in the deceleration phase. For this purpose, the actuating pressure difference p.sub.st is limited in accordance with the pump characteristic according to the algorithm.

(44) A drive unit which has an axial piston pump and an electronic control unit 16 is disclosed. The axial piston pump is pivoted with a method in which pressure-reducing valves 18.sub.A, 18.sub.B which act in opposition to one another are suddenly energized. Since in this respect no orifices are provided in the adjustment device 5, a so-called initiation jump 26 of the excited current I.sub.A gives rise to a sudden reduction in the assigned actuating pressure p.sub.stA or the actuating pressure difference p.sub.st formed therefrom. Then, a zero crossover jump 24 of at least the excited current I.sub.B is carried out in order to overcome the centering spring 9.sub.A and therefore ensure a continuous zero crossover of the axial piston pump.

LIST OF REFERENCE SYMBOLS

(45) 1 Housing 2 Drive unit 3 Swash plate 5 Adjustment device 6 Actuating cylinder 8.sub.A first actuating chamber 8.sub.B second actuating chamber 9.sub.A first centering spring 9.sub.B second centering spring 10 Drive shaft 14 Feed pump 16 electronic control unit 18.sub.A first pressure-reducing valve 18.sub.B second pressure-reducing valve 20.sub.A first electrical line 20.sub.B first electrical line 22 Feed pressure line 24 Zero crossover jump 26 Initiation jump 27 Pressure cut-off level 28 Rate of change .sub.pmp Pivoting angle of the axial piston pump A first working connection B second working connection I.sub.A first current I.sub.B second current n.sub.Eng rotational speed of the internal combustion engine n.sub.Englowidle lower idling rotational speed of the internal combustion engine n.sub.Enghighidle maximum working rotational speed of the internal combustion engine n.sub.Engmaxdrgctrlstrt pre-warning rotational speed of the internal combustion engine n.sub.Engmaxdrg maximum drag rotational speed of the internal combustion engine n.sub.pmp rotational speed of the axial piston pump p.sub.stA first actuating pressure p.sub.stB second actuating pressure p.sub.A first working pressure p.sub.B second working pressure p.sub.st actuating pressure difference T Tank Vg.sub.pmp Displacement volume of the axial piston pump