Hydraulic circuit supply system

Abstract

The invention relates to an system for supplying a hydraulic circuit with hydraulic fluid. The system includes a working reservoir and an auxiliary reservoir connected to the working reservoir by a hydraulic line. An air pump has an inlet connected to a suction line that opens into a liquid-free portion of the auxiliary reservoir so that a negative pressure can be built up in the auxiliary reservoir relative to the atmospheric ambient pressure. The air pump inlet is also connected to a control line, which comprises a control opening which is covered by the hydraulic fluid in the working reservoir, at least before the air pump is started up.

Claims

1. A supply system for supplying a hydraulic circuit with hydraulic fluid, comprising: a working reservoir for holding hydraulic fluid for operating the hydraulic circuit; an auxiliary reservoir, connected to the working reservoir via a hydraulic line, the auxiliary reservoir providing interim storage of hydraulic fluid removed from the working reservoir; an air pump, the air pump having an inlet connected to a suction line issuing into a fluid-free area of the auxiliary reservoir, so that relative to atmospheric ambient pressure, a negative pressure can be built up in the auxiliary reservoir, and the air pump inlet also being connected to a control line having a control opening which is covered by the hydraulic fluid in the working reservoir, at least before the air pump goes into operation; and a float valve is arranged in the suction line.

2. The supply system of claim 1, wherein: the hydraulic line runs between a lower portion of the working reservoir and a lower portion of the auxiliary reservoir.

3. The supply system of claim 1, wherein: the suction line is directly connected to the control line.

4. The supply system of claim 1, wherein: the control opening comprises a throttle.

5. The supply system of claim 1, wherein: the float valve includes a float which actuates a ball valve to produce a pressure equalization connection between the low-pressure side of the air pump and the working reservoir.

6. The supply system of claim 1, wherein: a throttle communicates the control line into a fluid-free area of the working reservoir.

7. The supply system of claim 1, wherein: a pressure limitation valve is connected to the control line between a throttle and the air pump, to equalization pressure between the low-pressure side of the air pump and the working reservoir.

8. The supply system of claim 1, wherein: a pressure limitation valve is connected to the inlet of the air pump.

9. The supply system of claim 1, wherein: a pressure limitation valve and the float valve are connected to the inlet of the air pump.

10. The supply system of claim 1, wherein: a throttle is arranged in the control line.

11. The supply system of claim 1, wherein: the control opening is formed in a terminal portion of the control line projecting into the working reservoir.

12. The supply system of claim 11, wherein: several control openings are formed in the terminal portion of the control line projecting into the working reservoir, wherein the control openings are arranged one above another.

13. The supply system of claim 1, wherein: the control line is surrounded in the area of the control opening by a shielding element.

14. The supply system of claim 13, wherein: the shielding element is a cylindrical shielding tube and a fluid-permiable grating is mounted in a lower end of the cylindrical shielding tube.

15. The supply system of claim 13, wherein: the shielding element is a cylindrical shielding tube and the cylindrical shielding tube and the control line cooperate to form an upwardly opening annular gap, the gap communicating the control opening with hydraulic fluid in the working reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a first embodiment of a hydraulic supply system according to the invention;

(2) FIG. 2 is a schematic diagram of a second embodiment of a hydraulic supply system according to the invention;

(3) FIG. 3 is a schematic diagram of a third embodiment of a hydraulic supply system according to the invention; and

(4) FIG. 4 is a schematic diagram of a fourth embodiment of a hydraulic supply system according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) Referring to FIG. 1, a supply system 10 supplies hydraulic fluid to an hydraulic, circuit of an agricultural utility vehicle (not shown). The agricultural utility vehicle may be, for example, a tractor, a harvester, a forage chopper or a spraying machine.

(6) The system 10 is preferably located in the engine compartment or the area of the transmission assembly of the agricultural utility vehicle. The system 10 includes a working reservoir 12 for holding the hydraulic fluid provided for operating the hydraulic circuit and an auxiliary reservoir 16. The auxiliary reservoir 16 is connected to the working reservoir 12 via a hydraulic line 14, for interim-storing or buffering hydraulic fluid removed from the working reservoir 12.

(7) The working reservoir 12 is constructed, for example, as a differential casing for a differential gear unit comprised by the agricultural utility vehicle The hydraulic fluid in the differential casing simultaneously constitutes a sump for lubricating the differential gear unit. The hydraulic fluid is a conventional hydraulic or transmission fluid.

(8) In order to allow a free flow of hydraulic fluid back and forth between the two reservoirs 12 and 16, the hydraulic line 14 runs between a lower area of the working reservoir 12 and a lower area of the auxiliary reservoir 16. The auxiliary reservoir 16 is elevated with respect to the working reservoir 12, and the hydraulic line 14 is connected to an underside of the auxiliary reservoir 16 so that the auxiliary reservoir 16 can be completely emptied into the working reservoir 12.

(9) The hydraulic fluid is supplied by a charge oil pump 18 via an interpolated oil filter 20 to an internal combustion engine 22 of the vehicle, as well as to additional power transmitting components for the purpose of lubrication. A controllable high-pressure pump 24 downstream of the oil filter 20 supplies hydraulically operated vehicle unit 26 such as a steering and braking system or an implement that can be attached to the agriculture utility vehicle and has hydraulic actuating cylinders or the like. Hydraulic fluid that is no longer needed or is in surplus is conducted back to the working reservoir 12 via lines, not shown.

(10) An air pump 28 has a low-pressure or inlet side which is connected to a suction line 32 issuing into a fluid-free area 30 of the auxiliary reservoir 16 and which is connected to a control line 34 having several identical control openings 36a constructed as throttles as well as a control opening 38b formed by a downwardly open end of the control line 34. This creates a negative pressure relative to the ambient atmospheric pressure in the auxiliary reservoir 16. The control openings 36a and 36b are completely covered by the hydraulic fluid in the working reservoir 12, at least before start-up of the air pump 28, before build-up of the negative pressure in the auxiliary reservoir 16. This situation is indicated by the fluid level labeled a) in FIG. 1.

(11) If the air pump 28 is started up, then hydraulic fluid flows tram the working reservoir 12 against the force of gravity into the auxiliary reservoir 16 via hydraulic line 14 due to the negative pressure built up in the auxiliary reservoir 16. In the process, the fluid level in the working reservoir 12 decreases, so that the control openings 36a and then the control op opening 36b are successively exposed and the negative pressure built up in the suction line 32 falls due to the air drawn in via the control line 34 from the environment to a value that is dependent on the flow resistance of the exposed control openings 36a and 38b and leads to the regulation or control of an equilibrium position of the fluid level in the working reservoir 12. This situation is illustrated by the fluid level labeled b) in FIG. 1.

(12) The control openings 36a and 36b are arranged one above another in a terminal area 38 of the control line 34 projecting into the working reservoir 12. The control openings 36a are constructed in the control line 34 as circular or slit-shaped inlets, the latter being oriented in the longitudinal direction of the control line 34. The control opening 36b formed by the open end of the control line 34 typically has the diameter on the order of 25 mm.

(13) It may be noted at this point that the representation of several control openings 36a and 36b has only an exemplary character. Alternately, it is also conceivable to provide only a single control opening 36b in the form of a downwardly open end of the control line 34.

(14) The air pump 28 is a vacuum pump of conventional construction driven by the internal combustion engine 22 of the vehicle. It creates a negative pressure on the order of typically 50 mbar in the auxiliary reservoir 16.

(15) According to an advantageous refinement of the invented system 10, the control line 34 is surrounded in the area of the control openings 36a and 36b by a shielding element 40. The shielding element 40 is a cylindrical shielding tube 42 that is closed off at its lower end by means of a fluid-permeable grating 44. The cylindrical shielding tube 42 is dimensioned so that, together with the control line 34, it forms an annular gap 46 open towards the top, via which the control openings 36a and 36b can communicate with the hydraulic fluid located in the working reservoir 12.

(16) In case the working reservoir 12 is overfilled with hydraulic fluid, there is a possibility that the fluid level in the working reservoir 12 may not decrease sufficiently after start-up of the air pump 28 to expose the control openings 36a and the control opening 36b in particular, due to the limited capacity of the auxiliary reservoir 16. In order to prevent an undesired penetration of hydraulic fluid into the suction line 32 or the control line 34, and thus ultimately into the air pump 28, a throttle or restriction 48, 50 arranged in the suction line 32 and control line 34, respectively, increases the negative pressure built up by the air pump 28 sufficiently when fluid enters, that a pressure limitation valve 52 connected between the throttle 50 and the air pump 28 becomes transmissive when a predetermined negative pressure is exceeded and creates a pressure equalization connection between the low-pressure side of the air pump 28 and the working reservoir 12. The pressure limitation valve 52 is arranged for this purpose directly in a fluid-free area of the working reservoir 12. The pressure limitation valve 52 is a conventional spring-loaded one-way valve.

(17) Referring now to FIG. 2, a second exemplary embodiment of the system differs from the first exemplary embodiment of FIG. 1 in the sense that only a single throttle 54 is provided in place of the two throttles 48 and 50. The pressure limitation valve 52 is arranged in this case outside the working reservoir 12 and connected to it via a pressure equalization line 56.

(18) At low operating temperatures and with the consequent increased viscosity of the hydraulic fluid, it is possible that after start-up of the air pump 28, the hydraulic fluid in the control line 34 cannot flow off in the direction of the working reservoir 12 and the fluid level in the working reservoir 12 consequently cannot assume a stable equilibrium position. This can ultimately lead to overfilling of the auxiliary reservoir 16 and therefore the penetration of hydraulic fluid via the suction line 32 into the connected air pump 28. Therefore a throttle 60 issuing into a fluid-free area of the working reservoir 12 is optionally provided in the control line 34 and, in connection with the pressure limitation valve 52 (comparable to the throttle 54), prevents an excessive negative pressure from being built up in the suction line 32 when the air pump 28 starts up at low operating temperatures with a consequently increased viscosity of the hydraulic fluid. The flow resistance of the throttle 60 is dimensioned such that a sufficient negative pressure can be built up in the suction line 32 connected to the control line 34, and therefore in the auxiliary reservoir 16, at normal operating temperatures.

(19) Referring now to FIG. 3, a third exemplary embodiment of the system differs from the second embodiment of FIG. 2 in that a check valve 58 is provided in place of the throttle 54 and is arranged such that it is closed in case of penetrating hydraulic fluid. The check valve 58 has, in particular, a movingly arranged valve ball that is pressed by invading hydraulic fluid against the valve seat so that an undesired flow of hydraulic fluid is suppressed.

(20) In contrast to the two previous exemplary embodiments, the suction line 32 does not open directly into the control line 34. Instead there is only an indirect connection between the suction line 32 and the control line 34. For this purpose, the control line 32 likewise opens directly into the fluid-free area 30 of the auxiliary reservoir 16. An additional protection from an undesired penetration of hydraulic fluid drawn in from the working reservoir 12 via the control line 34 into the air pump 28 connected to the suction line 32 is provided, since the two lines 32 and 34 communicate only indirectly with one another in this case. For example, the suction line 32 and the control line 34 are connected at the upper side of the auxiliary reservoir 16.

(21) Referring now to FIG. 4, a fourth embodiment of the system differs from the third embodiment of FIG. 3 in the sense that, in place of the check valve 58, a float valve 62 is provided, whose float is pressed against a valve seat by penetration of hydraulic fluid to such an extent that the connection to the auxiliary reservoir 16 via the suction line 32 is interrupted and at the same time a pressure equalization connection is created between the low-pressure side of the air pump 28 and the working reservoir 12 by actuation of a ball valve 64 connected to the float, bypassing the pressure limitation valve 52.

(22) While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. It will be noted that alternative embodiments of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims.