Wheel drive assembly for a hydrostatic traction drive and hydrostatic traction drive

Abstract

In a hydraulic motor and a hydrostatic traction drive with such a hydraulic motor, the regulating of the displacement of the hydraulic motor is done via a pilot-operated pressure regulator. The feedforward controller calculates an estimated motor displacement and relays this to the pressure regulator.

Claims

1. A wheel drive assembly for a hydrostatic traction drive comprising: a hydraulic motor comprising an electrical adjusting unit configured to adjust a motor displacement of the hydraulic motor to achieve a continuous relation between a motor drive current and the motor displacement; and an electronic control unit comprising: a pressure regulator configured to regulate the motor displacement in dependence on an actual pressure supplied to the hydraulic motor and a setpoint pressure of the hydraulic motor; and a feedforward controller associated with the pressure regulator and configured to preset a preset motor displacement, wherein the preset motor displacement is a calculated motor displacement calculated based on a model via the feedforward controller based on the setpoint pressure, a motor rotational speed, a pump rotational speed, and one of a pump delivery volume and a pump swivel angle.

2. The wheel drive assembly according to claim 1, wherein the pressure regulator is nonlinear.

3. The wheel drive assembly according to claim 1, wherein at least one of the pressure regulator and the feedforward controller have, as an input variable, a rotational speed limit for the hydraulic motor.

4. A hydrostatic traction drive comprising: a wheel drive assembly comprising: a hydraulic motor comprising an electrical adjusting unit configured to adjust a motor displacement of the hydraulic motor to achieve a continuous relation between a motor drive current and the motor displacement; and an electronic control unit comprising: a pressure regulator configured to regulate the motor displacement in dependence on an actual pressure and a setpoint pressure; and a feedforward controller associated with the pressure regulator and configured to preset a preset motor displacement; and an axial piston pump comprising an adjusting unit configured to adjust a pump delivery volume of the axial piston pump, wherein the preset motor displacement is a calculated motor displacement calculated based on a model via the feedforward controller based on the setpoint pressure, a motor rotational speed, a pump rotational speed, and one of the pump delivery volume and a pump swivel angle.

5. The hydrostatic traction drive according to claim 4, wherein the pump swivel angle is a calculated pump swivel angle, which is calculated on the basis of a model with the aid of a volume flow balance.

6. The hydrostatic traction drive according to claim 4, wherein the pump swivel angle is a calculated pump swivel angle, which is calculated on the basis of a model in dependence on a leakage under actual pressure, on the motor rotational speed, and on the pump rotational speed and on the motor drive current.

7. The hydrostatic traction drive according to claim 6, wherein the leakage under actual pressure is a calculated leakage under actual pressure, which is calculated on the basis of a model in dependence on the actual pressure.

8. The hydrostatic traction drive according to claim 4, wherein the setpoint pressure is determined based on a model in dependence on at least one of: the pump rotational speed, the motor rotational speed, a control element to relay a driver's wish, a forward-neutral-reverse unit, an inching pedal, and a limit load regulator.

9. The hydrostatic traction drive according to claim 4, wherein at least one of the pressure regulator and the feedforward controller has, as an input variable, a rotational speed limit of the axial piston pump.

10. The hydrostatic traction drive according to claim 4, wherein the adjusting unit of the axial piston pump comprises an actuating cylinder having a first actuating pressure chamber in which a first actuating pressure is set via a first pressure reducing valve, the first actuating pressure being dependent on a preselected first current strength at a first magnet of the first pressure reducing valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the traction drive according to the disclosure is represented in the figures, in which:

(2) FIG. 1 shows a circuit diagram of the traction drive according to the disclosure in accordance with the exemplary embodiment,

(3) FIG. 2 shows a diagram for the exemplary embodiment of FIG. 1,

(4) FIG. 3 shows a further diagram for the exemplary embodiment of FIG. 1,

(5) FIG. 4 shows a diagram with logic blocks and signal flows of the exemplary embodiment of FIG. 1, and

(6) FIG. 5 shows a diagram with multiple parameters plotted against time during launching of the traction drive according to the exemplary embodiment of FIG. 1.

DETAILED DESCRIPTION

(7) FIG. 1 shows a circuit diagram of the exemplary embodiment of the traction drive according to the disclosure. Only the components relevant to the disclosure are described. The traction drive has an axial piston pump 1, on whose housing two working ports A, B are formed. Via the working ports A, B and via working lines of a closed circuit, a hydraulic motor 3 is fluidically connected to the axial piston pump 1. A wheel (not shown) is coupled in a rotationally fixed manner to an output shaft of the hydraulic motor 3. In this way, a traction drive is formed for a mobile working machine (not shown in more detail).

(8) The axial piston pump 1 is designed with a swash plate 2, whose pump swivel angle α.sub.Pmp can be set via an adjusting unit 4a. For this, a dual-action actuating cylinder 6 is used, having a first actuating pressure chamber 8.sub.1 and, acting in opposition to this, a second actuating pressure chamber 8.sub.2.

(9) A first control pressure p.sub.st1 acts in the first actuating pressure chamber 8.sub.1 in the direction of an increase in the swivel angle α.sub.Pmp and thus in the direction of an increase in the pump delivery volume Vg.sub.Pmp. Acting in opposition to this is a second actuating pressure p.sub.st2 in the second actuating pressure chamber 8.sub.2 in the direction of a decrease in the swivel angle α.sub.Pmp and thus in the direction of a decrease in the pump delivery volume Vg.sub.Pmp. In this way, an actuating pressure difference can be defined Δp.sub.st=p.sub.st1−p.sub.st2, which by definition always acts in the direction of an increase in the pump swivel angle α.sub.Pmp or in the pump delivery volume Vg.sub.Pmp.

(10) A drive shaft 10 of the axial piston pump 1 drives its power unit 12 and furthermore also a feed pump 14. The drive shaft 10 is driven by a diesel engine (not shown), whose crankshaft rotates with a rotational speed n.sub.Eng. Therefore, the drive shaft 10 rotates with the same or with a proportionally altered pump rotational speed n.sub.Pmp.

(11) The pump rotational speed n.sub.Pmp acts together with the actuating pressure difference Δp.sub.st in the direction of an increase in the pump swivel angle α.sub.Pmp. More precisely, an increase in the pump rotational speed n.sub.Pmp acts in this manner.

(12) When the axial piston pump 1 shown is supplying the hydraulic motor 3 by its working ports A, B, let it be assumed that working port B is the high-pressure port during forward travel of the mobile working machine. Accordingly, the working line connected to the working port B is denoted as high pressure HD, while the other working line is denoted as low pressure ND. The high pressure HD acts in the direction of a decrease in the pump swivel angle α.sub.Pmp. These mentioned effects of the actuating pressure difference Δp.sub.st, the pump rotational speed n.sub.Pmp and the high pressure HD are measured. Their aforementioned effects on the pump swivel angle α.sub.Pmp are saved in an electronic control unit 16 of the wheel drive assembly according to the disclosure as formulas and/or as characteristic maps or characteristic curves. In this way, operating points of the axial piston machine 1 can be actuated without therefore requiring feedback in the sense of a feedback control circuit.

(13) The two actuating pressures p.sub.st1, p.sub.st2 are controlled by two pressure reducing valves 18.sub.1, 18.sub.2. These have a respective electromagnet a, b, which are connected via a respective electrical line 20.sub.1, 20.sub.2 to the electronic control unit 16. The two pressure reducing valves 18.sub.1, 18.sub.2 are designed such that the respective actuating pressure p.sub.st1, p.sub.st2 is proportional to the respective current strength i.sub.Pmp Fwd, i.sub.Pmp Rvs.

(14) The two pressure reducing valves 18.sub.1, 18.sub.2 are supplied at their inlet side from the feed pump 14 via a feed pressure line 22.

(15) Via an electrical line 25, a control element 26 is connected to the control unit 16 in order to relay the driver's wish, the control element 26 being preferably designed as an accelerator pedal.

(16) As a secondary machine, the aforementioned hydraulic motor 3 is connected to the two working lines HD, ND of the connected circuit. A motor displacement Vg.sub.Mot is adjustable via an electrical adjusting unit 4b. This is connected via an electrical line 24 to the control unit 16 and is controlled and regulated in the manner of the disclosure described below.

(17) FIGS. 2 and 3 respectively show a schematic diagram in regard to the control of the traction drive as per FIG. 1. In both diagrams, the motor rotational speed n.sub.Mot and, as examples, several rotational speeds n.sub.Eng of the internal combustion engine are plotted along the X-axis. In FIG. 2, the setpoint pressure HD.sub.soll is plotted on the Y-axis. It can be seen herein that the setpoint pressure HD.sub.soll is increased by increasing rotational speed n.sub.Eng of the internal combustion engine. In FIG. 3, the output torque of the hydraulic motor is plotted on the Y-axis.

(18) In both diagrams it is shown schematically that, during a starting and an increase in the velocity of the mobile working machine, corresponding to the motor rotational speed n.sub.Mot, at first a region of a pump controller and then a region of a motor controller is provided. More precisely, at first the adjusting unit 4a is used to increase the pump swivel angle α.sub.Pmp and then the adjusting unit 4b is used to decrease the motor displacement Vg.sub.Mot. If the hydraulic motor 3 is also an axial piston machine, this occurs through reducing the swivel angle of the hydraulic motor 3.

(19) FIG. 2 shows in an exemplary manner the setpoint pressure behavior in dependence on the current rotational speed n.sub.Eng of the internal combustion engine and the influence of an inching pedal. As per FIG. 2, by presetting the setpoint pressure characteristic it is possible to define the power of the traction drive. As per FIG. 3, it is possible to define the characteristic of the output torque of the hydraulic motor. The preconditions for this are that the pump swivel angle α.sub.Pmp and the rotational speed n.sub.Eng of the internal combustion engine are constant, as shown by FIG. 2.

(20) FIG. 4 shows logic blocks and signal flows of the control and regulation of the hydraulic motor 3 according to the disclosure. In logic block 31 there is a calculation of the setpoint pressure HD.sub.soll in dependence on the pump rotational speed n.sub.Pmp or the rotational speed n.sub.Eng of the internal combustion engine and in dependence on the motor rotational speed n.sub.Mot and in dependence on the accelerator pedal 26 and in dependence on a FNR and in dependence on the inching pedal and in dependence on a limit load regulator.

(21) First of all, the setpoint pressure HD.sub.soll is preset as a function of the rotational speed n.sub.Eng of the internal combustion engine. The precise dependency on the rotational speed n.sub.Eng is parametrized with a characteristic curve when placing the traction drive of the disclosure in operation, such that the power of the internal combustion engine is utilized meaningfully in operation. The technical details of the internal combustion engine and the kind of usage of the mobile working machine play a role here.

(22) Furthermore, the inching pedal has an influence on the setpoint pressure HD.sub.soll. Depending on the position of the inching pedal, an “inch factor” between 0% and 100% is determined with a characteristic curve, which acts in multiplicative manner on the setpoint pressure HD.sub.soll and can therefore reduce it if the driver desires. In addition, there is a “limit load regulator factor” between 0% and 100%, which reduces the setpoint pressure HD.sub.soll when the internal combustion engine is overloaded.

(23) The driving direction lever acts as follows on the setpoint pressure HD.sub.soll: when the desired driving direction is set at “neutral”, then the setpoint pressure HD.sub.soll is set at 0 bar, because the driver then wishes a standstill.

(24) The setpoint pressure HD.sub.soll may furthermore also be dependent on the motor rotational speed n.sub.Mot, and on the position of the control element 26, which is preferably an accelerator pedal.

(25) This setpoint pressure HD.sub.soll serves as an input variable for a logic block 33, in which a model-based determination of the leakage at setpoint pressure HD.sub.soll occurs, and for a feedforward controller 35, in which a model-based determination of the motor displacement Vg.sub.Mot occurs, and for a nonlinear pressure regulator 36, which ultimately outputs the motor displacement Vg.sub.Mot to be set.

(26) Further input variables for the feedforward controller 35 are the calculated leakage at setpoint pressure HD.sub.soll of the logic block 33 and the pump rotational speed n.sub.Pmp and the motor rotational speed n.sub.Mot, which are detected by respective rotational speed sensors (not shown). From these values, the feedforward controller 35 calculates a motor displacement Vg.sub.Mot. Use is made herein of the fact that the leakage is a linear function of the pressure.

(27) The model-based regulator 36 is based on the following volume flow balance:
delivery volume flow Q.sub.Pmp of the hydraulic pump=displacement flow Vg.sub.Mot of the hydraulic motor+leakage at setpoint pressure HD.sub.soll

(28) This equation is solved for the displacement flow Vg.sub.Mot, which is then a function of the pump rotational speed n.sub.Pmp (measured by sensor) the motor rotational speed n.sub.Mot (measured by sensor) the pump swivel angle α.sub.Pmp (estimated with model) the leakage at setpoint pressure HD.sub.soll (estimated with model).

(29) The motor displacement flow Vg.sub.Mot is then computed with these values, wherein the pump rotational speed n.sub.Pmp and the pump swivel angle α.sub.Pmp are smoothed out with signal filters in order to suppress oscillations of the system.

(30) The motor displacement Vg.sub.Mot calculated by the feedforward controller 35 serves as an approximate value or starting value for the nonlinear pressure regulator 36. The pressure regulator 36 also has as a further input variable the measured actual pressure HD.sub.ist.

(31) The actual pressure HD.sub.ist also serves as an input variable for a logic block 32 in which a model-based determination of the leakage at actual pressure HD.sub.ist is done. This value and furthermore the pump rotational speed n.sub.Pmp and the motor rotational speed n.sub.Mot and the motor drive current i.sub.Pmp Fwd or i.sub.Pmp Rvs serve as input variables for a logic block 34. In this block, a model-based determination of the pump swivel angle α.sub.Pmp is done, which serves as a further input variable for the feedforward controller 35.

(32) Finally, an overspeeding protection means 37a and a velocity limiting means 37b are optionally also provided, whose limit values are taken into account by the feedforward controller 35 and by the pressure regulator 36.

(33) FIG. 5 shows various values and parameters of the traction drive according to the disclosure as per the preceding figures. More precisely, the behavior of the pressure regulator 36 is shown during a slow acceleration process of the traction drive or the mobile working machine. The driver sets a power request via the control element, which is preferably the accelerator pedal, which request is converted into a setpoint pressure HD.sub.soll (dot and dash line). The model-based regulator 35 adapts the motor displacement Vg.sub.Mot so that the actual pressure HD.sub.ist is adjusted.

(34) A hydraulic motor and a hydrostatic traction drive therewith are disclosed, wherein the regulating of the displacement of the hydraulic motor is done via a pilot-operated pressure regulator. The feedforward controller calculates an estimated motor displacement and relays this to the pressure regulator.