US3817153A

US3817153A - Hydraulic control circuit

Info

Publication number: US3817153A
Application number: US00292696A
Authority: US
Inventors: E Zunzer
Original assignee: GL Rexroth GmbH
Current assignee: Bosch Rexroth AG
Priority date: 1971-09-29
Filing date: 1972-09-27
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: DE2148502A1; DE2148502B2

Abstract

A plurality of valve units, each including a plurality of main valves connected in series in an idling conduit connecting the outlet of a control pump with a discharge space, is used for supplying hydraulic consumer motors with pressure fluid. Each main valve has an idling position for connecting the outlet of the pump with the discharge space through the idling conduit, and two operative positions for supplying and discharging fluid from the respective consumer motor, and for closing the idling circuit. Each main valve includes hydraulic operating means for shifting the main valve between idling and operative positions. A plurality of control valves supplies fluids to and discharge fluids from the hydraulic operating means, and a pressure control unit connects the idling conduit with the control valves. the pressure control unit includes a pressure reducing valve, a pressure fluid accumulator, a check valve between the accumulator and the pressure reducing valve so that a selected pressure is maintained in the hydraulic operating means when the respective main valve is in one of the operating positions. Preferably, a pressure limiting valve is arranged downstream of the pressure reducing valve, and has a higher pressure than the same. A pressurizing valve is provided between the idling conduit and the discharge space for maintaining a pressure in the idling conduit by which the operation of the operating means is started.

Description

United States Patent [191 Zunzer HYDRAULIC CONTROL CIRCUIT [75] Inventor: Egon Zunzer, Lohr, Main, Germany [73] Assignee: G. L. Rexroth GmbH, Lohr/Main,

Germany [22] Filed: Sept. 27, 1972 [21] Appl. No.: 292,696

[30] Foreign Application Priority Data Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT A plurality of valve units, each including a plurality of [4 June 18, 1974 main valves connected in series in an idling conduit connecting the outlet of a control pump with a discharge space, is used for supplying hydraulic consumer motors with pressure fluid. Each main valve has an idling position for connecting the outlet of the pump with the discharge space through the idling conduit, and two operative positions for supplying and discharging fluid from the respective consumer motor, and for closing the idling circuit. Each main valve includes hydraulic operating means for shifting the main valve between idling and operative positions. A plurality of control valves supplies fluids to and discharge fluids from the hydraulic operating means, and a pressure control unit connects the idling conduit with the control valves. the pressure control unit includes a pressure reducing valve, a pressure fluid accumulator, a check valve between the accumulator and the pressure reducing valve so that a selected pressure is maintained in the hydraulic operating means when the respective main valve is in one of the operating positions. Preferably, a pressure limiting valve is arranged downstream of the pressure reducing valve, and has a higher pressure than the same. A pressurizing valve is provided between the idling conduit and the discharge space for maintaining a pressure in the idling conduit by which the operation of the operating means is started.

8 Claims, 3 Drawing Figures Bier/L153 PATENTEDJIII 1 8 m4 SHEET 2 BF 2 E i-a Fig.3

1 HYDRAULIC CONTROL CIRCUIT BACKGROUND OF THE INVENTION The present invention relates a hydraulic control circuit for hydraulic operation of the type in which the pressure fluid flows back to a low pressure container in the position of rest of control valves. Hydraulic control circuits of this type are advantageously used for movable hydraulic apparatus, such as dredging apparatus.

In the prior art apparatus, the pressure fluid for the control valves which control the main valves, is supplied by a gear pump which is independent of a main pump. It is also known to operate the control valves directly by pressure fluid taken from the main pump, eliminating a separate control pump. The control pressure fluid is taken from the main operating fluid between the pump for the operating fluid and a control valve by means of an adjustable throttle together with a pressure limiting valve which is adjusted to a position corresponding to the maximum control pressure. If there is no control fluid required, the control fluid is returned through the pressure limiting valve to the low pressure discharge container. When the control fluid is taken between the control valve and the low pressure container, a pressure controlled check valve with a throttle is disposed in the conduit leading to the discharge container. The flow of working fluid is throttled by the throttle to such an extent that the pressure required for the operation of the main valve, is obtained. The prior art apparatus of the type in which the control fluid for operating the main valves is influenced by the main flow of working fluid, detrimentally affects the total efficiency of the hydraulic apparatus, since part of the control pressure fluid flows back to the low pressure container without being used, while in another case the pressure level downstream of the main valve must be maintained at a high level. In addition to this loss of efficiency, the developed heat loss must be compensated by the control pressure fluid.

SUMMARY OF THE INVENTION It is an object of the invention to take control pressure fluid for control valves from the flow of working fluid through the main valve, without causing substantial loss.

This object of the invention is obtained by a circuit in which the initial control pressure for operating the main valves, andthe pressure of the working fluidflowing back to the low pressure discharge container in the initial position of the main valves, correspond to each other. Furthermore, inaccordance with the invention, the control valves by which the positions of the main valves are controlled, include a pressure reducing valve and a pressure fluid accumulator, a check valve being provided between the pressure fluid accumulator and the pressure reducingvalve. Due to the fact that the pressure of the circulating fluid, and the initial control pressure for operating the main valves correspond to each other, it is assured that the main valves can be operated starting with the initial position. The higher control pressure required after starting of the shifting of the main valves, is obtained by throttling the circulating working fluid which causes a higher pressure in the sure is sufficient to move the main valves to the desired position. The pressure-reducing valve limits the pressure of the control fluid, and the additionally provided pressure fluid accumulator assures an operation of the main valves, for example for lowering a load to the ground, even if the pump fails.

In a preferred embodiment of the invention, where the hydraulic circuit includes two or more pumps, the pressure fluid is taken from the main flow through each of the pumps, and supplied to the pressure reducing valve by a double check valve having two inlets and an outlet connected with the pressure reducing valve. This has the advantage that the control fluid is branched off the flow of the pump which has the highest pressure. It is advantageous to combine the pressure reducing valve, the check valve, and the pressure limiting valve, together with the accumulator, in a pressure control unit which is substantially a valve block formed with bores in which movable valve elements are mounted.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagramatic view schematically illustrating a hydraulic control circuit in accordance with an embodiment of the invention, serving for operating a dredging apparatus;

FIG. 2 is a sectional view taken on line Il--II in FIG. 3, and illustrating a pressure control unit in accordance with the invention; and

FIG. 3 is a sectional view taken on line III-Ill in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT A pump unit 1 includes two

hydraulic pumps

3 and 4 whose displaced volume can be adjusted by operation of a setting cylinder and piston means 5. An electric motor 6 drives the two

pumps

3 and 4.

Pumps

3 and 4 pump pressure fluid through conduits 7 and 12 to the inlets P1 and P2, respectively, of two valve units 11 and 16. The pressure conduit 7 flows through an

idling conduit

23, 24, 25, 26 through three

main valves

8, 9 and 10, when the

main valves

8, 9 and 10 are in the illustrated idling position. From the point T the fluid flows through conduit 27 and discharge conduit 27a, and through pressurizing valves 55 and a check valve 55a into the low pressure discharge container T from which

pumps

3 and 4 suck fluid. Conduit 12 is connected at the point P of valve unit 16, with pressure fluid flowing through the

idling conduit

28, 29,. 30, 31 and through the

main valves

13, 14, 15 in the illustrated idling position to the point T which is connected by conduit 32 and discharge conduit 27a with the above-described pressurizing valve means 55 and 55a.

Each of the main valves 8 to 10 and 13 to 15 has, in addition to the illustrated idling position, two operative positions for supplying and discharging pressure fluid to associated hydraulic consumer apparatus 17 to 19 and 20 to 22, the flow being reversed in the two operative positions of the respective main valve.

For example, the working conduits A8 and B8 are connected with the vehicle drive means 17 on the left side of the vehicle, and the conduits A13 and B13 are connected with the vehicle drive means 20 on the right side of the vehicle. The working conduits A9 and B9 of the main valve 9 are connected with an hydraulic cylinder and piston motor 18 which operates the arm of the dredging apparatus, and the working conduits A10 and B10 of the main valve are connected with a hydraulic cylinder and piston motor 19 which operates the scoop of the dredging apparatus.

The working conduits A14 and B14 of main valve 14 are connected with a rotary hydraulic motor 21, and the working conduits A15 and B15 of main valve 15 are connected with the hydraulic cylinder and piston motor 22 by which the boom is operated.

In the illustrated idling positions of main valves 8 to 10 and 13 to 15, the working conduits are closed except that in main valve 14, the working conduits A14 and B15 are connected in valve 14 by a throttle 14c.

The

conduit sections

23, 24, 25 and 26 are connected with each other by the main valves in the idling position, so that the fluid from

pumps

3 and 4 can flow through

idling conduits

7, 23, 24, 25, 26, 27 and 12, 28, 29, 30, 31, and 32 between the pump and the low pressure discharge conduit 27a and discharge container T. The pressurizing valves 55 maintain certain pressure in the idling conduits, and the check valve 55a prevents return flow from the tank.

A pressure conduit 70 branches off the pump conduit 7, and a pressure conduit 120 branches off the pump conduit 12.

Conduits

7a and 12a are connected to inlets of a pressure control unit 2, which is shown schematically in FIG. 1 and in detail in FIGS. 2 and 3. As best seen in FIG. 3, the two

inlets

7a and 12a cause the ball of the double check valve 33 to assume such a position that flow into the pressure control unit 2 is possible only from the one of the

conduits

7a and 12a in which the greater pressure prevails. The outlet 33a of the double check valve 33 is connected with a pressure reducing valve 34, and the fluid at reduced pressure flows through a conduit 35 and the check valve 36 to three

control valve units

37, 38, and 39, each of which contains four control valves 40 to 43, 44 to 47, and 48 to 51. Control valves 40 and 43 are connected by control conduits 40a and 43a to pressure chambers 9a and 9b of the main valve 9 so that the valve slide piston, not shown, of main valve 9 is shifted, as desired, between the illustrated idiing position, and two operative positions in which the respective hydrauilc consumer motor 18 is operated in forward or rearward direction, respectively. The control valves 41 and 42 of the control valve unit 37 are connected by control conduits 41a, 42a to the control chambers 10a, 10b of the main valve 10 cooperating with the hydraulic consumer motor 19. The control valves 44 and 45 of the control valve unit 38 are connected by control conduits 44a, 450 with the control chambers 8a, 8b of the hydraulic consumer motor 17 which drives the left drive means of the vehicle, while the control valves 46 and 47 of the same control valve unit 38 are connected by

control conduits

46a, 47a with the control chambers 13a, 13b of the main valve 13 which is associated with the hydraulic motor 20 by which the drive means on the right side of the vehicle are operated.

The control valves 48, 51 of the control valve unit 39 are connected by control conduits 48a, 51a with the control chambers 15a, 15b of the hydraulic motor 22 for operating the boom of the dredging apparatus under the control of main valve 15, and the

control valves

49 and 50 are connected by control conduits 49a, 50a with the control chambers 14a, 14b of the main valve 14 operating the rotary hydraulic apparatus 21 by which a support of a dredging apparatus is rotated.

In the illustrated idling position of the main valves 8 to 10, and 13 to 15, pressure develops in the idling conduits 7, 23 to 26, 27 and 12, 28 to 31, and 32 due to flow losses occurring in the ducts of the main valves and in the pressure conduits 7 and 12. If the flow losses are not sufficient to maintain a certain pressure in the idling conduits, the pressurizing valves 55 are provided to maintain the pressure in the idling conduits at a predetermined pressure which is still partly produced by the flow losses in the valve units 11 and 16.

The predetermined pressure produced and maintained in this manner in the idling conduit, corresponds to the control pressure required in the initial operation of the main valves out of the illustrated circulation position toward one of the two operative positions. A throttling of the flow cross section takes place which causes a further pressure increase in the respective pressure conduit 7 or 12 of the

pumps

3 or 4. This pressure increase is sufiicient for operating a respective main valve toward one or the other selected operative end position. In the operative end positions of the main valves 8 to 10, and 13 to 14, the

hydraulic motors

17, 20, 21 and 18, 19, 22 are operated by pressure fluid, resulting in an average pressure corresponding to the power load of the hydraulic consumer motors 17 to 19 and 20 to 22. The pressure reducing valve 34 in the pressure control unit 2 maintains the fluid pressure independently of the magnitude of the pressure of the fluid in the working conduits and in the consumer apparatus. When control fluid under pressure flows through the outlet conduit 35 of the pressure control unit 2, the fluid pressure accumulator 52 is charged. In the event that one of the

pumps

3 or 4 fails, the check valve 36 prevents a discharge of the fluid from pressure fluid accumulator 52 into the pressure conduits 7 and 12, so that an amount of pressure fluid is maintained in the accumulator for an emergency operation of the main valves 8 to 10 and 13 to 15.

A pressure limiting valve 53 which is arranged downstream of the pressure reducing valve 34, is set to a slightly higher pressure than the pressure reducing valve 34. Due to this arrangement, the supply of control fluid to the control valves 40 to 51 is assured, while at the same time during normal operations, a discharge of fluid is effectively prevented.

FIGS. 2 and 3 illustrate the pressure control unit 2 in detail, and it will be seen that a block 54 is provided with threaded bores 54a, 54b in which threaded plugs 12a and 12b are mounted which form the

inlet conduits

7a and 12a of the double check valve 33 whose outlet is connected with the pressure reducing valve 34, which includes a spring 34a, as best seen in FIG. 2. Downstream of the pressure reducing valve 34, the pressure limiting valve 53 includes a spring 53a acting on a pointed valve member cooperating with a valve seat 53b. A discharge conduit 530 communicates with a low pressure discharge container T.

The pressure control unit illustrated in FIG. 2 and 3 requires only connectors for the

branch conduits

12a and 7a, and for the conduit 35 which is connected with the control valves 40 to 51. The pressure fluid accumu lator 52 has a threaded portion secured in a threaded bore 52a of the block 54.

The accumulator is connected with the conduit 35 via the valve body 36 which is provided with a (not visible) blind bore. The latter communicates via bores 36a and via bores 360 of the member 36b with a space 35d, which in turn communicates with outlet 35c (FIG. 3) leading to conduit 35.

The threaded connectors permit a very quick connection of the pressure control unit 2 with the respective conduits.

Only two valve units 11 and 16 have been shown, but it is understood that a greater number could be provided. If more than two

pumps

3 and 4 are provided, the check valve means 33 have to be accordingly constructed to permit flow into the pressure control unit 2 only from the pump operating at the highest pressure.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of hydraulic control circuits differing from the types described above.

While the invention has been illustrated and described as embodied in a hydraulic control circuit, particularly for dredging apparatus, provided with a pressure control unit for reducing the pressure provided by a pump to the pressure suitable for hydraulic operation of main valves 8 to 10 and 13 to 15, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

1 claim:

1. Hydraulic control circuit, comprising a control pump having an outlet for pressure fluid; a discharge space; idling conduit means between said outlet of said pump and said discharge space; at least one valve unit including a plurality of main valve means connected in series in said idling conduit, and being respectively associated with hydraulic consumer motors, each main valve means having an idling position for connecting said outlet of said pump with said discharge space through said idling conduit, and at least one operative position for supplying fluid to, and discharging fluid from the respective consumer motor, and for closing said idling conduit, each main valve means including hydraulic operating means for shifting said main valve means between said idling and operative positions; a plurality of control valve means for supplying fluid to, and for discharging fluid from said hydraulic operating means, respectively; and a pressure control unit connecting said outlet of said pump and idling circuit with said control valve means so that in said idling position the initial pressure in said idling conduit starts said operating means, said pressure control unit including pressure reducing valve means, a pressure fluid accumulator, and a check valve between said accumulator and said pressure reducing valve means opening toward the former so that a selected pressure is maintained in said hydraulic operating means when said main valve means is in said operative position.

2. Hydraulic control circuit as claimed in claim 1 comprising pressurizing valve means between said idling conduit and said discharge space for maintaining a pressure in said idling conduit in said idling position of said control valve means. i

3. Hydraulic control circuit as claimed in claim 2 wherein said pressurizing valve means includes a check valve opening towards said discharge space.

4. Hydraulic control circuit as claimed in claim 1 wherein said pressure control unit includes a pressure limiting valve downstream of said pressure reducing valve, said pressure limiting valve being set to a higher pressure than said pressure reducing valve.

5. Hydraulic control circuit as claimed in claim 1 comprising two control pumps; two idling conduits; two valve units; and wherein said pressure control unit includes a shiftable double check valve having two inlets connected near outlets of said pumps with said idling conduits, respectively, and one outlet connected with said pressure reducing valve means.

6. Hydraulic control circuit as claimed in claim 5 wherein said pressure control unit includes a pressure limiting valve downstream of said pressure reducing valve, said pressure limiting valve being set to a higher pressure than said pressure reducing valve means; and wherein said pressure control unit includes a valve block formed with bores in which said pressure reducing valve means, said pressure limiting valve means, and said double check valve are located, and having a threaded bore into which said accumulator is threaded.

8. Hydraulic control circuit as claimed in claim 1 wherein each main valve means has two operative positions and said idling position; and wherein said consumer motors are reversed in said two operative positions.

Claims

2. Hydraulic control circuit as claimed in claim 1 comprising pressurizing valve means between said idling conduit and said discharge space for maintaining a pressure in said idling conduit in said idling position of said control valve means.

7. Hydraulic control circuit as claimed in claim 5 wherein said two control pumps include adjusting means for adjusting said control pumps to discharge fluid at different pressures at said outlets, respectively.