ARRANGEMENT FOR OPERATING A LOAD-CONTROLLED HYDRAULIC SYSTEM OF AN AGRICULTURAL TRACTOR

Abstract

An arrangement for operating a load-controlled hydraulic system of an agricultural tractor, includes a hydraulic pump generating a system pressure and having an actuating device to adjust a displacement volume, a hydrostatic vehicle steering system connected to the hydraulic pump and having a steering orbitrol and a first load-indicating pressure, a pressure-regulating valve connected upstream of the steering orbitrol and actuated via a pressure difference decreasing across a throttle element counter to a predetermined restoring force in accordance with the first load-indicating pressure, a second hydraulic consumer connected to the hydraulic pump and feeding a second load-indicating pressure back to a shuttle valve arrangement, which compares and transmits the respectively higher of the first and second load-indicating pressures to the actuating device to adjust the displacement volume, and a pressure-copying valve indirectly feeding back the first load-indicating pressure to the shuttle valve arrangement.

Claims

1. An arrangement for operating a load-controlled hydraulic system of an agricultural tractor, comprising: a hydraulic pump generating a system pressure and having an actuating device to adjust a displacement volume; a hydrostatic vehicle steering system connected to the hydraulic pump and having a steering orbitrol and a first load-indicating pressure; a pressure-regulating valve connected upstream of the steering orbitrol and actuated via a pressure difference decreasing across a throttle element counter to a predetermined restoring force in accordance with the first load-indicating pressure; a second hydraulic consumer connected to the hydraulic pump and feeding a second load-indicating pressure back to a shuttle valve arrangement, which compares and transmits the respectively higher of the first and second load-indicating pressures to the actuating device to adjust the displacement volume; and a pressure-copying valve indirectly feeding back the first load-indicating pressure to the shuttle valve arrangement by transmitting the system pressure reduced to a hydraulic pressure that follows the first load-indicating pressure.

2. The arrangement of claim 1, wherein the pressure-copying valve has a proportional valve with an inlet side of which the system pressure is applied and an outlet side of which the hydraulic pressure transmitted to the shuttle valve arrangement is applied, wherein the proportional valve is urged into an open position under the effect of the first load-indicating pressure counter to the hydraulic pressure applied at the outlet side.

3. The arrangement of claim 1, wherein the system pressure is a hydraulic pressure at a delivery outlet of the hydraulic pump.

4. The arrangement of claim 1, wherein the system pressure is a hydraulic pressure generated by the hydraulic pump to operate the hydrostatic vehicle steering system.

5. The arrangement of claim 1, wherein the hydraulic pressure transmitted from the pressure-regulating valve to the shuttle valve arrangement can be limited via a pressure-limiting valve that opens into a hydraulic reservoir according to a predefined maximum value.

6. The arrangement of claim 1, further comprising a pressure-limiting valve limiting the hydraulic pressure transmitted to the shuttle valve arrangement to a predefined maximum value.

7. The arrangement of claim 1, further comprising a pressure-limiting valve limiting the hydraulic pressure transmitted to the actuating device of the hydraulic pump to a predefined maximum value.

8. The arrangement of claim 7, further comprising a throttle element connected between the pressure limiting valve limiting the hydraulic pressure transmitted to the actuating device of the hydraulic pump and a hydraulic reservoir.

9. An agricultural tractor, comprising: a hydraulic pump generating a system pressure and adjustable in terms of a displacement volume; a hydrostatic vehicle steering system connected to the hydraulic pump and having a steering orbitrol and a first load-indicating pressure; a pressure-regulating valve connected upstream of the steering orbitrol and actuated via a pressure difference decreasing across a throttle element counter to a predetermined restoring force in accordance with the first load-indicating pressure; a second hydraulic consumer connected to the hydraulic pump and feeding a second load-indicating pressure back to a shuttle valve arrangement, which compares and transmits the respectively higher of the first and second load-indicating pressures to an actuating device of the hydraulic pump to adjust the displacement volume; and a pressure-copying valve indirectly feeding back the first load-indicating pressure to the shuttle valve arrangement by transmitting the system pressure reduced to a hydraulic pressure that follows the first load-indicating pressure.

10. The agricultural tractor of claim 9, wherein the pressure-copying valve has a proportional valve with an inlet side of which the system pressure is applied and an outlet side of which the hydraulic pressure transmitted to the shuttle valve arrangement is applied, wherein the proportional valve is urged into an open position under the effect of the first load-indicating pressure counter to the hydraulic pressure applied at the outlet side.

11. The agricultural tractor of claim 9, wherein the system pressure is a hydraulic pressure at a delivery outlet of the hydraulic pump.

12. The agricultural tractor of claim 9, wherein the system pressure is a hydraulic pressure generated by the hydraulic pump to operate the hydrostatic vehicle steering system.

13. The agricultural tractor of claim 9, wherein the hydraulic pressure transmitted from the pressure-regulating valve to the shuttle valve arrangement can be limited via a pressure-limiting valve that opens into a hydraulic reservoir according to a predefined maximum value.

14. The agricultural tractor of claim 9, further comprising a pressure-limiting valve limiting the hydraulic pressure transmitted to the shuttle valve arrangement to a predefined maximum value.

15. The agricultural tractor of claim 9, further comprising a pressure-limiting valve limiting the hydraulic pressure transmitted to the actuating device of the hydraulic pump to a predefined maximum value.

16. The agricultural tractor of claim 15, further comprising a throttle element connected between the pressure limiting valve limiting the hydraulic pressure transmitted to the actuating device of the hydraulic pump and a hydraulic reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The arrangement according to the disclosure will be explained in more detail below with reference to the appended drawings. In this case, corresponding reference signs relate to identical components or components that are comparable with respect to their function. In the drawings:

[0024] FIG. 1 shows a schematically illustrated first exemplary embodiment of the arrangement according to the disclosure for operating a load-controlled hydraulic system of an agricultural tractor;

[0025] FIG. 2 shows a variant of the first exemplary embodiment of the arrangement according to the disclosure depicted in FIG. 1;

[0026] FIG. 3 shows a schematically illustrated second exemplary embodiment of the arrangement according to the disclosure for operating a load-controlled hydraulic system of an agricultural tractor; and

[0027] FIG. 4 shows a variant of the second exemplary embodiment of the arrangement according to the disclosure depicted in FIG. 3.

DETAILED DESCRIPTION

[0028] The embodiments or implementations disclosed in the above drawings and the following detailed description are not intended to be exhaustive or to limit the present disclosure to these embodiments or implementations.

[0029] FIG. 1 shows a schematically illustrated first exemplary embodiment of the arrangement according to the disclosure for operating a load-controlled hydraulic system of an agricultural tractor, which is not depicted.

[0030] The arrangement 10 comprises, as part of the load-controlled hydraulic system 12, a hydraulic pump 14, which is adjustable in terms of its displacement volume, for supplying a multiplicity of hydraulic consumers 16 with pressurized hydraulic fluid. The displacement volume of the hydraulic pump 14 is adjusted in accordance with a load-indicating pressure LS_Pump transmitted to an actuating device 18 of the hydraulic pump 14. This allows a hydraulic supply corresponding to the actual power requirement for the hydraulic consumers 16.

[0031] For example, the hydraulic consumers 16 depicted in FIG. 1 include first and second (primary) hydraulic consumers 16a, 16b, which are used to carry out superordinate hydraulic functions of a hydrostatic vehicle steering system 20 and of a hydraulic braking system 22, as well as a plurality of further (secondary) hydraulic consumers 16c, 16d for carrying out subordinate hydraulic functions relating to various comfort functions and working functions of the agricultural tractor, such as, for example, of a hydraulic axle suspension or cab suspension, of a working hydraulic unit including supplying hydraulically operated working units of an additional device or mounted device that is attached to the agricultural tractor, but also of a hydraulically actuatable three-point hitch.

[0032] In this case, the first hydraulic consumer 16a or the hydrostatic vehicle steering system 20 has a steering orbitrol 24 and a first pressure-regulating valve 26, which is connected upstream of the steering orbitrol 24 and is actuated in accordance with a pressure difference that decreases across a throttle element 28 counter to a predetermined restoring force in accordance with a load requirement, represented by a first load-indicating pressure LS_P1S, of the hydrostatic vehicle steering system 20.

[0033] In this manner, a hydraulic pressure P_Pump applied at a delivery outlet 30 of the hydraulic pump 14 is reduced to a supply pressure P_P1S corresponding to the first load-indicating pressure LS_P1S, whereas a supply pressure P_P1B provided for operating the hydraulic braking system 22 is directly tapped off at the delivery outlet 30 of the hydraulic pump 14.

[0034] The first load-indicating pressure LS_P1S is fed back, together with a second load-indicating pressure LS_P1B, which represents a load requirement of the hydraulic braking system 22, and further load-indicating pressures LS_P2, LS_P3 resulting on account of associated load requirements of the further hydraulic consumers 16c, 16d, to a shuttle valve arrangement 32.

[0035] In order to ensure an adequate supply of hydraulic energy, the specification of the displacement volume of the hydraulic pump 14 is based on the respectively highest of the load-indicating pressures LS_P1S, LS_P1B, LS_P2, LS_P3 fed back by the hydraulic consumers 16. For this purpose, the shuttle valve arrangement 32 forms a shifting logic system, which consists of hydraulic shuttle valves 32a, 32b, 32c and compares the load-indicating pressures LS_P1S, LS_P1B, LS_P2, LS_P3 applied at associated load-indicating lines 34a, 34b, 34c, 34d with one another in pairs in a cascade-like manner and transfers or transmits the respectively highest pressure to the actuating device 18 of the hydraulic pump 14 via a feedback line 36.

[0036] In the present case, the actuating device 18 provided for adjusting the displacement volume of the hydraulic pump 14 is a directly pressure-actuated actuator 38. In a departure therefrom, the actuating device 18 can however also be designed as an actuator that is electrically actuated in accordance with a pressure detection using sensors. In both cases, the actuator is used to change a pump pivot angle in a targeted manner, wherein the displacement volume of the hydraulic pump 14 increases as the pump pivot angle increases.

[0037] Since one and the same hydraulic pump 14, the delivery capacity of which is, however, limited, is used for operating the hydraulic consumers 16, different supply priorities are assigned to the hydraulic consumers 16. In this case, the hydrostatic vehicle steering system 20 as well as the hydraulic braking system 22 constitute superordinate hydraulic functions with the highest supply priority. An inadequate supply that results in possible functional impairments is intended to be ruled out as far as possible in these hydraulic consumers 16a, 16b. Accordingly, a lower supply priority is assigned by means of a priority valve arrangement 40 to the further hydraulic consumers 16b, 16c in view of the fact that they are used to carry out merely subordinate hydraulic functions, with the objective of restricting the hydraulic supply thereof where necessary in favor of whichever of the two hydraulic consumers 16a, 16b has the higher supply priority.

[0038] In this case, the first and second hydraulic consumers 16a, 16b are directly connected or connectable to the delivery outlet 30 of the hydraulic pump 14, whereas the further hydraulic consumers 16c, 16d are connected or connectable to said delivery outlet via interposed second and third pressure-regulating valves 42, 44, which are part of the priority valve arrangement 40 and are used to provide associated supply pressures P_P2, P_P3. The further hydraulic consumers 16c, 16d are subdivided into first and second groups 46, 48, respectively, wherein the first group 46 can be connected to the delivery outlet 30 of the hydraulic pump 14 via the second pressure-regulating valve 42, and the second group 48 can be connected to said delivery outlet via the third pressure-regulating valve 44. The illustration of two groups 46, 48 is intended in this case to have a merely exemplary character; provision can also be made for a number of groups or pressure-regulating valves that differs therefrom.

[0039] If, in accordance with the exemplary embodiment of the arrangement 10 depicted in FIG. 1, provision is made for a plurality of pressure-regulating valves 42, 44, these are thus brought into their closed position in a predefined sequence, specifically with a successive decrease in the difference between the hydraulic pressure P_Pump applied at the delivery outlet 30 of the hydraulic pump 14 and the hydraulic pressure LS_Pump transmitted to the actuating device 18 of the hydraulic pump 14 below a first or second threshold value P_P2_min, P_P3_min (P_P2_min>P_P3_min), in order to reduce the power requirement in accordance with the delivery capacity of the hydraulic pump 14.

[0040] This allows the supply priorities of the further hydraulic consumers 16c, 16d to be further subdivided or gradated, so that the operation of specific hydraulic functions can be maintained as far as possible. Thus, in terms of the sequence of throttling the hydraulic volumetric flow passing through the two pressure-regulating valves 42, 44, provision can be made for comfort functions to be affected first of all and for any working functions, including hydraulic transmission control of a gearbox and/or power take-off transmission comprised by a drivetrain of the agricultural tractor, to be affected subsequently.

[0041] As can also be seen in FIG. 1, the first load-indicating pressure LS_P1S is fed back to the shuttle valve arrangement 32 merely indirectly via a pressure-copying valve 50, which is provided for fluidic separation, for which purpose the pressure-copying valve 50 transmits a system pressure P_Sys, which is generated by means of the hydraulic pump 14 through reduction to a hydraulic pressure LS_P1S that follows the first load-indicating pressure LS_P1S, to the shuttle valve arrangement 32.

[0042] In other words, the first load-indicating pressure LS_P1S is used merely to activate the pressure-copying valve 50 without a significant hydraulic flow occurring. There is no direct fluidic connection to the shuttle valve arrangement 32, insofar as undesired repercussions on the first load-indicating pressure LS_P1S can be reliably ruled out. In the case of the first hydraulic consumer 16a designed as a hydrostatic vehicle steering system 20, this ensures a consistent steering behavior that is independent of the shift state of the shuttle valve arrangement 32.

[0043] Load peaks occurring during operation of the hydrostatic vehicle steering system 20 result in a corresponding increase in the pressure difference that decreases across the throttle element 28 and cause an increase in the deflection of the first pressure-regulating valve 26 connected upstream of the steering orbitrol 24 in the direction of an open position, which, on account of the short control path, results in a particularly fast-reacting and thus dynamic adaptation of the hydraulic pressure P_P1S generated in order to operate the hydrostatic vehicle steering system 20. To this end, the pressure difference is predefined in the order of magnitude of from 10 to 20 bar.

[0044] The slight but continuous flow of hydraulic fluid through the throttle element 28 in the range from 1 to 5 liters per minute further ensures that a temperature gradient that is present within the hydraulic circuit of the hydrostatic vehicle steering system 20 in the case of a cold start of the agricultural tractor is rapidly overcome, and no jamming, in particular of the steering orbitrol 24, on account of thermal differences or mechanical stresses caused thereby, occurs. This is particularly relevant at low or wintry external temperatures.

[0045] According to FIG. 1, the pressure-copying valve 50 has a proportional valve 52, at the inlet side of which the system pressure P_Sys, which is generated by means of the hydraulic pump 14, is applied, and at the outlet side of which the hydraulic pressure LS_P1S transmitted to the shuttle valve arrangement 32 is applied, wherein the proportional valve 52 is urged into an open position under the effect of the first load-indicating pressure LS_P1S counter to the hydraulic pressure LS_P1S applied at the outlet side. This is carried out until a pressure equilibrium is established between the inlet and outlet of the proportional valve 52, wherein the load-indicating pressure LS_P1S transmitted from the pressure-copying valve 50 or the proportional valve 52 to the shuttle valve arrangement 32 then corresponds to the first load-indicating pressure LS_P1S, except for an offset, which is caused by a restoring force, which urges the pressure-copying valve 50 into a closed position, of a spring element 54. The offset is typically in the order of magnitude of from 1 to 4 bar.

[0046] In terms of the provision of the system pressure P_Sys, various variants are conceivable. On the one hand, according to FIG. 1, it is possible for the system pressure P_Sys to be the hydraulic pressure P_Pump applied at the delivery outlet 30 of the hydraulic pump 14. This is usually in the order of magnitude of from 200 to 250 bar. On the other hand, according to FIG. 2, it can also be the hydraulic pressure P_P1S generated by the hydraulic pump 14 in order to operate the hydrostatic vehicle steering system 20. This pressure corresponds substantially to the first load-indicating pressure LS_P1S plus the pressure difference that decreases across the throttle element 28 and is between 190 and 240 bar.

[0047] In the case of the first exemplary embodiment depicted in FIGS. 1 and 2, the hydraulic pressure LS_P1S transmitted from the first pressure-regulating valve 26 to the shuttle valve arrangement 32, and thus ultimately the hydraulic pressure P_P1S generated in order to operate the hydrostatic vehicle steering system 20, can be limited by means of a pressure-limiting valve 58 that opens into a hydraulic reservoir 56 according to a predefined maximum value P_P1S_max. The pressure-limiting valve 58 is attached to the outlet of the pressure-copying valve 50 or of the proportional valve 52 comprised by the latter. The maximum value P_P1S_max is predefined in the range from 170 to 200 bar.

[0048] In addition, the hydraulic pressure LS_Pump transmitted to the actuating device 18 of the hydraulic pump 14 can be limited by means of a pressure-regulating valve 60 to a predefined maximum value LS_Pump_max at an outlet that communicates with the actuating device 18. The maximum value LS_Pump_max is specified in such a manner that the hydraulic pressure P_Pump generated at the delivery outlet 30 of the hydraulic pump 14 does not exceed a value of 200 and 250 bar. Damage caused by overpressure to the hydraulic system or to the hydraulic consumers or peripheral components operated thereby can thus be reliably prevented. The use of the pressure-regulating valve 60 ensures that the hydraulic pressure P_Pump generated at the outlet side, and thus at the delivery outlet 30 of the hydraulic pump 14, remains constant in the sense of a stable hydraulic supply once the predefined maximum value LS_Pump_max has been reached.

[0049] A drainage connection in the direction of the hydraulic reservoir 56 is established by means of a further throttle element 62 connected to the outlet of the pressure-regulating valve 60. The further throttle element 62 allows the hydraulic pressure LS_Pump transmitted to the actuating device 18 of the hydraulic pump 14 to be relieved in the case in which, on account of a reduced load requirement that has been fed back by the hydraulic consumers 16, a corresponding reduction in the displacement volume by pivoting the hydraulic pump 14 back is necessary.

[0050] If the hydraulic losses occurring when the pressure-limiting valve 58 is being shifted in the direction of the hydraulic reservoir 56 are to be avoided, in the case of a second exemplary embodiment of the arrangement 10 according to the disclosure depicted in FIGS. 3 and 4, a further pressure-regulating valve 64, by means of which the hydraulic pressure LS_P1S transmitted to the shuttle valve arrangement 32 can be limited to a predefined maximum value LS_P1S max at an outlet that communicates with the shuttle valve arrangement 32, is thus provided instead of the pressure-limiting valve 58. The specification of the maximum value LS_P1S max is based on the abovementioned maximum value P_P1S_max and is approximately 10 to 20 bar below the latter.

[0051] FIGS. 3 and 4 differ in turn with respect to the provision of the system pressure P_Sys. In order to avoid repetitions, reference should therefore be made to the relevant description of the variants in question in conjunction with FIGS. 1 and 2.

[0052] The terminology used herein is for the purpose of describing example embodiments or implementations and is not intended to be limiting of the disclosure. As used herein, the singular forms a, an, and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the any use of the terms has, includes, comprises, or the like, in this specification, identifies the presence of stated features, integers, steps, operations, elements, and/or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0053] Those having ordinary skill in the art will recognize that terms such as above, below, upward, downward, top, bottom, etc., are used descriptively for the drawings, and do not represent limitations on the scope of the present disclosure, as defined by the appended claims. Furthermore, the teachings may be described herein in terms of functional and/or logical block components or various processing steps, which may include any number of hardware, software, and/or firmware components configured to perform the specified functions.

[0054] Terms of degree, such as generally, substantially, or approximately are understood by those having ordinary skill in the art to refer to reasonable ranges outside of a given value or orientation, for example, general tolerances or positional relationships associated with manufacturing, assembly, and use of the described embodiments or implementations.

[0055] As used herein, e.g., is utilized to non-exhaustively list examples and carries the same meaning as alternative illustrative phrases such as including, including, but not limited to, and including without limitation. Unless otherwise limited or modified, lists with elements that are separated by conjunctive terms (e.g., and) and that are also preceded by the phrase one or more of or at least one of indicate configurations or arrangements that potentially include individual elements of the list, or any combination thereof. For example, at least one of A, B, and C or one or more of A, B, and C indicates the possibilities of only A, only B, only C, or any combination of two or more of A, B, and C (e.g., A and B; B and C; A and C; or A, B, and C).

[0056] While the above describes example embodiments or implementations of the present disclosure, these descriptions should not be viewed in a restrictive or limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the appended claims.