Hydrostatic Traction Drive and Method for Controlling the Hydrostatic Traction Drive

Abstract

A hydrostatic traction drive includes a first hydraulic machine that is coupled to a drive unit. The first hydraulic machine is hydraulically arranged in a hydraulic circuit with a second hydraulic machine. The second hydraulic machine has a drive shaft that is connected in a rotationally fixed fashion to a lockable differential. The traction drive has a control unit that is configured so as to control at least one measure for traction control as a function of a rotational speed of the second hydraulic machine. The at least one measure includes one or more of a measure for detecting a loss of traction and a measure for overcoming the loss of traction. A method for controlling the traction drive includes eliminating a loss of traction of the traction drive with use of the control unit as a function of the rotational speed of the second hydraulic machine.

Claims

1. A hydrostatic traction drive, comprising: a first hydraulic machine that is driven by a drive unit; a second hydraulic machine hydraulically connected to the first hydraulic machine, the second hydraulic machine having a drive that is connected to at least one differential of the traction drive in order to drive wheels or the like; and a control unit configured to control at least one measure for traction control, the measure controlled as a function of a rotational speed of the second hydraulic machine.

2. The hydrostatic traction drive according to claim 1, wherein the differential is of lockable configuration, and the measure is a lock of the differential.

3. The hydrostatic traction drive according to claim 1, wherein the measure is to adapt a torque of the second hydraulic machine.

4. The hydrostatic traction drive according to claim 1, wherein one or more of the second hydraulic machine and the first hydraulic machine is configured with an adjustable expulsion volume, and wherein the measure is to adapt the expulsion volume of the one or more of the second hydraulic machine and the first hydraulic machine.

5. The hydrostatic traction drive according to claim 1, wherein the control unit is configured so as to control the measure as a function of a change in the rotational speed of the second hydraulic machine.

6. The hydrostatic traction drive according to claim 1, wherein the control unit is configured so as to differentiate the rotational speed of the second hydraulic machine as a function of time.

7. The hydrostatic traction drive according to claim 5, wherein a limiting value of the change in the rotational speed or of a gradient of the rotational speed is stored in the control unit, and wherein the control unit is configured so as to determine upward transgression of the limiting value and the measure is configured to be controlled as a function thereof.

8. A method for controlling a measure for traction control of a hydrostatic traction drive, the traction drive including a first hydraulic machine that is driven by a drive unit, a second hydraulic machine hydraulically connected to the first hydraulic machine, the second hydraulic machine having a drive that is connected to at least one differential of the traction drive in order to drive wheels or the like, and a control unit, the method comprising: controlling the measure as a function of a rotational speed of the second hydraulic machine, the measure configured to be controlled by the control unit.

9. The method according to claim 8, wherein the measure includes one or more of locking the differential and adapting the torque of the second hydraulic machine.

10. The method according to claim 8, wherein controlling the measure as a function of a rotational speed of the second hydraulic machine takes place as a function of a change in the rotational speed over time.

11. The method according to claim 10, wherein the control unit is configured to determine the change of the rotational speed over time by a differentiation of the rotational speed.

12. The method according to claim 10, wherein the control unit is configured to determine an upward transgression of a limiting value of the change in the rotational speed over time, and wherein one or more of the differential is locked and the torque of the second hydraulic machine is adapted as a function of the upward transgression.

13. The hydrostatic traction drive according to claim 1, wherein the hydrostatic traction drive is configured for a mobile machine.

14. The hydrostatic traction drive according to claim 3, wherein the measure is to reduce the torque of the second hydraulic machine.

15. The hydrostatic traction drive according to claim 4, wherein the measure is to reduce the expulsion volume of the one or more of the second hydraulic machine and the first hydraulic machine.

16. The method according to claim 11, wherein the control unit is configured to determine the change of the rotational speed over time by determining a gradient of the rotational speed over time.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0040] In the text which follows, an exemplary embodiment of a hydrostatic traction drive of a wheel loader is explained in more detail with reference to a figure.

[0041] This single FIGURE shows a circuit diagram of an exemplary embodiment of a hydrostatic traction drive.

DETAILED DESCRIPTION

[0042] The FIGURE shows a hydrostatic traction drive 1 of a wheel loader which has a drive unit 3 which is connected to a drive shaft 2. The drive unit 3 is embodied as a diesel engine and drives, with a preferably constant rotational speed via the drive shaft 2, a first hydraulic machine 4 which is configured with an adjustable expulsion volume. The first hydraulic machine 4 forms, together with a second hydraulic machine 10, a hydrostatic transmission 5. The hydraulic machines 4, 10 are connected hydraulically here via working lines 6 and 8, with the result that a closed hydraulic circuit is formed. The second hydraulic machine 10 is also configured with an adjustable expulsion volume. The two hydraulic machines 4, 10 are each configured as axial piston machines with a swash plate design. The transmission ratio of the hydrostatic transmission 5 is determined here by the expulsion volumes of the hydraulic machines 4, 10.

[0043] In particular, a control unit 12 is provided for detecting and for controlling the adjustment of a respective expulsion volume or swept volume of the hydraulic machines 4, 10. Said control unit 12 is connected via three signal lines 14, 16, 18 to proportional magnets 20, 22, 24 of the hydraulic machines 4, 10. In this context, an adjustment device (not illustrated) of the respective hydraulic machines 4, 10 can be activated by the proportional magnets 20, 22, 24 in order to adjust the expulsion volumes thereof electromagnetically.

[0044] A changeover valve 26, by means of which a higher of the two pressures of the working lines 6, 8 can be selected, is connected between the working lines 6, 8. A pressure-detection unit 28 is connected to an outlet of the changeover valve 26. This signal of said pressure-detection unit 28 is transferred to the control unit 12 via a signal line 30. In the traction drive shown in the illustration according to FIG. 1, load pressure or high pressure is present in the working line 6, whereas the working line 8 conducts low pressure. Accordingly, in the shown driving state of the pressure-detection unit 28 the pressure of the working line 6 is detected and signaled to the control unit 12.

[0045] The second hydraulic machine 10 is connected via a drive shaft 32 to a mechanical distributor differential 34. The latter is mechanically connected via, in each case, a shaft 36, in particular a cardan shaft as well as, in each case, an axle differential 38, to shafts 40 of a front axle 42 and a rear axle 44 with two drive wheels 46 in each case.

[0046] A rotational speed sensor 48, by means of which a rotational speed of the second hydraulic machine 10 can be detected, is connected to the control unit 12 via a signal line 50 for transmitting signals. In said control unit 12, the method for detecting traction and for traction control, already described generally above, is stored for implementation. A description of the method follows.

[0047] In order to evaluate the signal of the rotational speed sensor 48, a time gradient of the rotational speed of the second hydraulic machine 10, which corresponds to an angular acceleration of the second hydraulic machine 10, is determined by means of the control unit 12. Subsequently, the control unit 12 is used to carry out a comparison of the gradient with a limiting value, that is to say with a maximum permissible increase in the rotational speed over time or a maximum permissible, in particular positive, gradient of the rotational speed over time.

[0048] The limiting value is stored here in a parameterized form in the control unit 12 and corresponds to a maximum possible angular acceleration of the second hydraulic machine 10 when traction of the wheels 46 is present, wherein the maximum possible angular acceleration at least the measure corresponds to the maximum possible vehicle acceleration.

[0049] If upward transgression of the limiting value is determined by means of the control unit 12, it is accordingly possible to conclude therefrom with a high level of probability that a loss of traction of at least one of the wheels 46 is a reason for this excessive angular acceleration.

[0050] By means of the control unit 12, at least two measures—alternative to one another or complementary to one another—can subsequently be initiated by means of the control unit 12 in order to recover the traction.

[0051] On the one hand, this is a reduction in the torque of the second hydraulic machine 10. This can take place, for example, by means of the reduction of a pivoting angle of the second hydraulic machine 10 by means of the corresponding actuation of the proportional magnet 20. In order to subsequently prevent a resulting acceleration of the second hydraulic machine 10—the volume flow of the first hydraulic machine 4 initially remains the same—the expulsion volume of the first hydraulic machine 4 is additionally also adapted and reduced by means of the control unit 12, approximately simultaneously in the exemplary embodiment shown.

[0052] A second measure of the control unit 12 for recovering the traction of a drive wheel 46 is to connect axle-differential lock into the axle differential 38 and/or connect an interaxle-differential lock into the distributor differential 34. By connecting the axle-differential lock the shafts 40 of the respective axle 42, 44 can be connected to one another in a rotationally fixed fashion, and by connecting the interaxle-differential lock the shafts 36 can be respectively connected to one another in a rotationally fixed fashion.

[0053] If locking is carried out by means of an interaxle-differential lock using the distributor differential 34, the shafts 36 are connected to one another in a rotationally fixed fashion. This solution is preferred if both drive wheels 46 of a front axle 42 or a rear axle 44 are affected by the loss of traction.

[0054] According to the method, the two measures for preventing the loss of traction can be carried out simultaneously or in a chronologically independent sequence. For example, when the loss of traction is detected by means of the control unit 12 the latter can switch on the axle-differential locks. In the event of the traction not being covered again by means of this first measure, for example the torque of the second hydraulic machine 10 can be reduced. It is also possible for these two measures to be carried out simultaneously. It is also possible the control unit 12 is configured in such a way that it firstly carries out the measures to reduce the torque of the second hydraulic machine 10, and only after this first measure carries out the second measure, after which the axle differentials 38 and/or the distributor differential 34 are/is locked by means of an axle-differential lock or interaxle-differential lock.

[0055] A hydrostatic traction drive having a first hydraulic machine which is coupled to a drive unit is disclosed, wherein the first hydraulic machine is arranged hydraulically in a hydraulic circuit with a second hydraulic machine. A drive shaft of the second hydraulic machine is connected here in a rotationally fixed fashion to an, in particular, lockable differential. The traction drive has a control unit which is configured in such a way that it can be used to control at least one measure for traction control, in particular a measure for detecting a loss of traction and/or for eliminating the loss of traction, as a function of a rotational speed of the second hydraulic machine.

[0056] Furthermore, a method is disclosed for controlling the traction drive with which a traction loss of the traction drive can be eliminated by means of the control unit as a function of the rotational speed of the second hydraulic machine.

LIST OF REFERENCE NUMBERS

[0057] 1 hydrostatic traction drive [0058] 2 drive shaft [0059] 3 drive unit [0060] 4 first hydraulic machine [0061] 5 hydrostatic transmission [0062] 6 working line [0063] 8 working line [0064] 10 second hydraulic machine [0065] 12 control unit [0066] 14 signal line [0067] 16 signal line [0068] 18 signal line [0069] 20 proportional magnet [0070] 22 proportional magnet [0071] 24 proportional magnet [0072] 26 changeover valve [0073] 28 pressure-detection unit [0074] 30 signal line [0075] 32 drive shaft [0076] 34 distributor differential [0077] 36 shaft [0078] 38 axle differential [0079] 40 shaft [0080] 42 front axle [0081] 44 rear axle [0082] 46 drive wheels [0083] 48 rotational speed sensor [0084] 50 signal line