Title:
CONTROL AND REGULATOR DEVICE FOR A LOAD-INDEPENDENT REGULATED HYDRAULIC SYSTEM
United States Patent 3841096


Abstract:
A control device for the control and load-independent regulation of hydraulic consumers of hydraulically driven installations, a pressure-influencing valve with a pressure reducing piston being present, said valve being in controllable flow connection with a load pressure pilot bore, there also being present a control piston for producing a constant leakage loss, said device being suitable for maintaining even a slight pressure difference, whilst upon application for the load-independent regulation of a plurality of slide members, the pump pressure will adjust itself to the highest load pressure.



Inventors:
Koppen, Dirk Jan (The Hague, NL)
Metz, Hendrik Theodoor (Appingedam, NL)
Application Number:
05/400897
Publication Date:
10/15/1974
Filing Date:
09/26/1973
Assignee:
METZ H,NL
KOPPEN D,NL
Primary Class:
Other Classes:
60/484, 91/519, 91/529, 91/530, 91/532, 137/596.13
International Classes:
F15B11/16; F15B13/02; F15B13/04; (IPC1-7): F15B11/16
Field of Search:
60/420,431,445,452,462 91
View Patent Images:
US Patent References:
3406850Hydraulic system for excavator1968-10-22Hancox
2782598Power transmission1957-02-26Gatwood
2713772Hydraulic transmission and control for machine tool tables1955-07-26Horlocher
2102865Combined flow control and relief valve1937-12-21Vickers



Foreign References:
CH444601A
Primary Examiner:
Geoghegan, Edgar W.
Attorney, Agent or Firm:
Depaoli & O'Brien
Parent Case Data:


CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of United States application Ser. No. 267,206 of Koppen et al. filed June 28, 1972, now abandoned.
Claims:
What is claimed is

1. In a hydraulic device for the control and load-independent regulation of hydraulic consumers of a hydraulic medium, said device comprising:

2. pump pressure acting on one end of said pressure-regulating spool valve and

3. the sum of consumer pressure, propagated from said consumer ports through pilot bores, plus a regulating valve spring acting on the other end of said spool valve; and

4. The improvement of claim 1 wherein said pressure-influencing valve cartridge comprises a pressure-influencing cartridge spring and a pressure-influencing piston which, by variation of the axial displacement thereof, forms a pilot throttle orifice in said at least one pilot bore, whereby one end of said piston is under the influence of the pressure upstream of said pilot-throttle orifice and its other end is under the influence of the pressure downstream of said pilot-throttle orifice and of said cartridge spring.

5. The improvement of claim 2 which further comprises a leak piston, which interrupts first and second leak bores branching from said at least one pilot bore downstream from said pilot-throttle orifice and leading to said return channel, said leak piston forming in said leak bores a first leak throttle orifice for producing a constant leakage, whereby one end of said leak piston is in a first leak chamber and under the influence of the pressure in said at least one pilot bore and its other end is in a second leak chamber and under the influence of the pressure downstream of said first leak throttle orifice but upstream of a second leak throttle orifice formed between said second leak chamber and said second leak bore, as well as under the pressure of a leak piston spring.

6. The improvement of claim 3 which further comprises a throttle screw which adjustably interrupts said at least one pilot bore for adjustment of the throttle passage therewithin in order to adjust the pressure build-up and pressure drop time at said spring-loaded other end of said pressure-regulating spool valve.

7. A device for the control and load-independent regulation of a hydraulic medium supplied to hydraulic consumers of hydraulically driven installations, comprising:

8. a pump port, which is connected to a pump channel, for receiving said hydraulic medium from a pump in said hydraulically driven installation,

9. a return port, which is connected to a return channel, for discharging said hydraulic medium to a reservoir in said hydraulically driven installation;

10. a pressure regulating spool valve which is loaded at one end with said pump pressure and at its other end with pressure from a regulating valve spring plus secondary consumer pressure within a pilot pressure chamber, said secondary consumer pressure being fed back thereto via secondary pilot bores, and

11. a pressure limiting valve, which separates said pilot pressure chamber from a valve chamber, for selectively limiting the maximum permissible system pressure by selectively passing said hydraulic medium from said pilot pressure chamber to said valve chamber which is connected to said return channel; and

12. a control spool valve, which slideably operates within a control valve bore, for starting, stopping and reversing movement of said one consumer and for determining the size of the controlling throttle opening for said hydraulic medium,

13. first and second consumer ports which are selectively connected with said pump channel or with said return channel and with said one hydraulic consumer,

14. a primary pilot bore which provides flow connection with one of said consumer ports and transmits primary consumer pressure therefrom, and

15. a pressure-influencing valve cartridge which is connected to and interrupts said primary pilot bore and is connected to said secondary pilot bores.

16. The device of claim 5 wherein said pressure-influencing valve cartridge comprises a pressure-influencing piston and a cartridge spring which loads the end of said piston in flow contact with said secondary pilot bores.

17. The device of claim 6 wherein said pressure-influencing valve cartridge further comprises a stop means for said pressure-influencing piston which stops movement of said piston and shuts off communication between said primary pilot bore and said secondary pilot bore when said secondary consumer pressure in said secondary pilot bores plus the pressure of said cartridge spring exceeds said primary consumer pressure in said primary pilot bore, whereby said pressure-influencing valve cartridge functions as a non-return valve.

18. The device of claim 7 wherein said pressure regulating valve unit further comprises a leak piston, which is connected to said secondary pilot bores and to said return channel, for discharging said pump pressure when said spool valve is in neutral position and for producing a pressure-independent leakage loss during operation, whereby increases of said secondary consumer pressure are continuously levelled in conformity with variations of said primary consumer pressure so that said valve cartridge is responsive to decreases in said primary consumer pressure.

19. The device of claim 8 wherein said control valve unit is connected by means of said pump channel and said return channel to additional control valve units, each connected to one of said hydraulic consumers, whereby at least two of said control valve units can be displaced simultaneously because the highest consumer pressure from the heaviest loaded of said consumers maintains said valve cartridge connected to the lesser loaded of said consumers in closed position, whereby said pump pressure adjusts itself to said highest consumer pressure so that all of said consumers can be operated and controlled.

20. A control device for the control and load-independent regulation of hydraulic consumers of hydraulically driven installations, comprising:

21. two consumer ports,

22. a control spool valve through which each said consumer port can be selectively connected with a pump channel and a primary pilot bore or with a return channel,

23. a pressure-influencing valve cartridge which selectively interrupts the through-connection of said primary pilot bore with a secondary pilot bore and comprises a pressure-influencing piston which, by variation of its axial displacement forms a pilot throttle orifice in said pilot bores, whereby one end of said pressure-influencing piston is under the influence of the pressure upstream of said pilot-throttle orifice and its other end is under the influence of the pressure downstream of said pilot-throttle orifice and of a pressure-influencing cartridge spring;

24. a pressure regulating spool valve which, as a result of the action of the pump pressure on one end thereof and the action of the consumer pressure feedback, propagated from said consumer ports via said pilot bores in addition to a regulating valve spring at its other end, forms a regulating throttle orifice between said pump channel and said return channel,

25. supply and discharge means for the hydraulic medium from and towards said pressure regulating spool valve, and

26. a leak piston which interrupts leak bores branching from said pilot bores downstream of said pilot-throttle orifice and leading to said return channel, said leak piston forming a first leak throttle orifice in said leak bore for producing a constant leakage, whereby one end of said leak piston is in a first leak chamber and under the influence of the pressure in said pilot bores and its other end is in a second leak chamber and under the influence of the pressure downstream of a leak throttle passage through said leak piston but upstream of a second leak throttle orifice formed between said second leak chamber and said leak bores, as well as under the pressure of a leak piston spring.

27. The control device according to claim 10 wherein said at least one pressure influencing valve cartridge is accommodated within a cylindrical bore in said control valve unit and further comprises:

28. The control device of claim 11 wherein said at least one pressure-influencing valve cartridge additionally comprises:

29. The control device of claim 12, wherein said pressure-influencing piston is slidable in said axially disposed bore, said pressure-influencing piston comprising a shank having at each end a gland, said glands bounding a chamber in said axially disposed bore around said shank, one of said glands forming said pilot-throttle orifice, upon displacement of said pressure-influencing piston against the action of said cartridge spring, between said chamber and said second cartridge cross bore, while said chamber is in continuous flow connection via said first cartridge cross bore with said primary chamber and with said one end of said pressure-influencing piston.

30. A control device for the control and load-independent regulation of hydraulic consumers of a hydraulically driven installation, comprising:

31. two consumer ports,

32. a control spool valve through which each said consumer port can be selectively connected with a pump channel or a return channel,

33. primary pilot bores which are selectively through-connected with one of the consumer ports of each said at least one control valve unit by a main gland of the corresponding control spool valve, and

34. at least one pressure-influencing valve cartridge which interrupts the connection of said primary pilot bores with secondary pilot bores by forming a pilot-throttle orifice therein;

35. The control device of claim 14 wherein each said at least one valve cartridge comprises a combination of a cone, loaded by a cartridge spring, and a valve seat with a valve bore, whereby one end of said cone is under the influence of the pressure upstream of said pilot-throttle orifice and its other end is under the influence of the pressure downstream of said pilot-throttle orifice and of said cartridge spring.

36. The control device of claim 14 wherein each said at least one valve cartridge comprises a combination of a ball, loaded by a cartridge spring, and a valve seat with a valve bore, whereby one end of said ball is under the influence of the pressure upstream of said pilot-throttle orifice and its other end is under the influence of the pressure downstream of said pilot-throttle orifice and of said cartridge spring.

37. The control device of claim 14 wherein each said at least one valve cartridge comprises a combination of a piston, loaded by a cartridge spring, and a valve seat with a valve bore, whereby one end of said piston is under the influence of the pressure upstream of said pilot-throttle orifice and its other end is under the influence of the pressure downstream of said pilot-throttle orifice and of said cartridge spring.

38. The control device of claim 14 wherein said at least one valve cartridge comprises:

39. The control device of claim 18 wherein said resilient biasing means is a cartridge spring and said bias force is selected so that, upon increase of the sum of the pressure in said secondary pilot bores and said bias force to a pressure equal to or higher than the pressure in said primary pilot bores, the connection between the corresponding consumer port and said pressure regulating valve unit is selectively interrupted.

40. The control device of claim 19 wherein said pressure-regulating valve unit comprises a leak piston, which interrupts leak bores branching from said secondary pilot bores downstream of said pilot-throttle orifice and leading to said return channel, for producing a constant leakage loss, independent of hydraulic pressure variations.

41. The control device of claim 20 wherein said leak piston:

42. glands in said cylindrical bore which bound and seal first and second leak chambers, one at either end of said piston,

43. a leak piston spring which acts within said second leak chamber against the downstream end of said piston, and

44. a leak-throttle passage, axially disposed in said leak piston, which provides the throughflow of the hydraulic fluid between said first leak chamber, being in flow connection with said pilot bores at one end, and said second leak chamber, being in flow connection with said return channel at the spring-loaded downstream end of said leak piston.

45. The control device of claim 21 wherein said leak piston is connected to more than one said control valve unit and said pressure regulating valve unit comprises a pressure regulating spool valve, which forms a regulating throttle orifice between said pump channel and said return channel, and supply and discharge means for said hydrulic medium from and towards said pressure regulating spool valve.

46. The control device of claim 22 wherein said pressure regulating valve unit comprises:

47. The control device of claim 23 wherein:

48. The control device of claim 23 wherein for the regulation of the pump delivery in accordance with the available motor capacity for driving the pump, a pressure reducing valve is disposed in an intermediate unit mounted between the pressure regulating valve unit and said control valve unit, said pressure reducing valve acting on the combined pilot bore between said valve cartridges and said pressure regulating valve unit, and functioning as a pressure reducing valve with a slide valve mechanism whose pressure reducing piston is similar to the corresponding pressure-influencing piston of said pressure-influencing valve cartridges.

49. The control device according to claim 25 wherein said pressure reducing piston is loaded with a spring bias force which is directly controlled by the displacement of a piston acting on said force of a single-acting cylinder when the pressure of the pump overcomes the bias of the spring of said cylinder.

50. The control device according to claim 26 wherein said pressure reducing piston is loaded by the electrically controllable force of an armature of a control solenoid, the electrical signal being given by an electric potentiometer, the resistance of which is changed by the displacement of a piston of a pressure device when the pressure of the pump overcomes tension of the spring of said pressure device.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a control and regulation device for the control and the load-independent regulation of hydraulic consumers of hydraulically driven installations.

2. Description of the Prior Art

Swiss Patent No. 444,601 describes such a device having at least one control valve unit, each comprising two consumer ports and a control spool valve through which each consumer port can be selectively connected with a pump channel or a return channel, as well as a pressure regulating valve unit for maintaining a constant pressure difference between said pump channel and the consumer ports connected with said pump channel, said unit comprising a regulating spool valve which, as a result of the action of the pump pressure at one end thereof and the action of the consumer pressure propagated from said last mentioned consumer ports via pilot bores, as well as a regulating valve spring at its other end, forms a regulating throttle orifice between pump channel and return channel, while supply and discharge means are provided for the hydraulic medium towards and from said pressure regulating spool valve.

A drawback of this known device is that the pressure difference to be kept constant by the pressure regulating spool valve can only be influenced by exchange of the spring of this valve. In case a rather weak spring is chosen, there will be the risk that the pressure regulating spool valve, during the control functioning, is not moved with sufficient reliability. Another drawback is that when the pressure regulating spool valve is applied with more than one control valve unit, and there being for instance two control spool valves simultaneously in an operable position, the pump pressure adjusts itself to the lowest load pressure.

SUMMARY OF THE INVENTION

The invention aims at avoiding the above drawbacks, in a fluid control device for influencing the pressure difference between a pump channel and consumer ports connected to said pump channel, by interrupting the pilot bores, which are to be selectively throughconnected by a main gland of the corresponding control spool valves with said consumer ports, by pressure-influencing valve cartridges.

According to one embodiment of the invention, each of said pressure-influencing valve cartridges comprises a pressure-influencing piston which, by variation of the axial displacement, forms a pilot throttle orifice in said pilot bores, whereby one end of said pressure-influencing piston is under the influence of the pressure upstream of the pilot-throttle orifice and its other end is under the influence of the pressure downstream of the pilot-throttle orifice and of a pressure-influencing cartridge spring. There is furthermore present a leak piston, which interrupts leak bores branching from pilot bores downstream from the pilot-throttle orifices and leading to the return channel, said leak piston forming in said leak bores a first leak throttle orifice for producing a constant leakage, whereby one end of the leak piston is in a first leak chamber and under the influence of the pressure in the pilot bores and its other end in a second leak chamber and under the influence of the pressure downstream the leak throttle passage through said leak piston but upstream of a second leak throttle orifice formed between said second leak chamber and second leak bore, as well as under the pressure of a leak piston spring.

BRIEF DESCRIPTION OF THE DRAWINGS

In explanation of the invention, an embodiment according to the invention will be described with reference to the drawings, while a number of possible variants will be explained by way of some hydraulic diagrams.

In the drawings:

FIG. 1 is a side view of the device,

FIG. 2 is a front view thereof,

FIG. 3 is a top view thereof,

FIG. 4 is a cross-section on the line IV--IV in FIG. 1,

FIG. 5 is a cross-section on the line V--V in FIG. 3,

FIG. 5A is a cross-section of the pressure-influencing valve cartridge in FIG. 5, but on an enlarged scale,

FIG. 5B is a cross-section of a varient embodiment of a pressure-influencing valve cartridge,

FIG. 6 is a cross-section on the line VI--VI in FIG. 3,

FIG. 7 is a cross-section on the line VII--VII in FIG. 1, with omission of pressure-balance piston,

FIG. 8 is a cross-section on the line VIII--VIII in FIG. 1, with omission of pressure-balance piston,

FIG. 9 is a cross-section according to the line IX--IX in FIG. 7,

FIG. 10 is a cross-section on the line X--X in FIG. 7,

FIG. 11 ia cross-section on the line XI--XI in FIG. 7,

FIG. 12 is a cross-section on the line XII--XII in FIG. 7,

FIG. 13 is a cross-section on the line XIII--XIII in FIG. 8,

FIG. 14 is a cross-section on the line XIV--XIV in FIG. 8,

FIG. 15 is a hydraulic diagram for the control device in the embodiment with load-independent 3-way volume control, in combination with a pump with a constant piston stroke,

FIG. 16 is a hydraulic diagram for a control device with load-independent 2-way volume control for application in a circuit fed by a pressure accumulator, or by a pump with a controllable pump yield, or equipped with a constant-pressure control member;

FIG. 17 is a hydraulic diagram for a control device for the load-independent control of the output of a pump with a controllable pump yield on the volume not passed by the control device; and

FIG. 18 is a hydraulic diagram for a load-independent control device for the load-dependent reduction of the output of a pump having a controllable pump yield.

DEFINITIONS AND TERMINOLOGY

For easy understanding of the terminology used, definitions of the components, parts and bores are first given as follows: Definition FIG. Nos. Nos. Definitions ______________________________________ 1 1,3,6,7,8,9,10,11,12,13 and 14 Pressure regulating valve unit for the discharge of the pump pressure in the neutral position of the control valve unit 2, as well as for the production of a constant pressure difference required for a load-independent volume flow control. 2 1,3,4,5,6 Control valve units a, b and c for directing the hydraulic fluid to and from the consumer, and for the production of a controlling throttle opening between pump and consumer. 3 1,2,3, and 6 Retaining plate for keeping together the several components by means of tie rods, as well as for interconnecting the two return channel sections 50a and 50c to build return channel 50. 4 1 and 6 Pump port of pressure regulating valve unit 1. 5 1,6,7,8 Return port of pressure regulating valve unit 1 for discharging the return hydraulic fluid to the reservoir. 6 1 and 4 Second consumer port disposed at each control valve unit 2 and communicating with pump channel 48 or with return channel section 50c. 7 1 and 4 First consumer port disposed on each control valve unit 2 and connecting with pump channel 48 or with return channel section 50a. 8 2,3,5,6 First pressure-influencing valve cartridge screwed into a control valve unit 2 and communicating with consumer port 7. 9 2,3,5,6 Second pressure-influencing valve cartridge screwed into a control valve unit 2 and communicating with consumer port 6. 10 4 and 6 Control spool valve, present in each of the control valve units 2 serving for determining the effective direction of a consumer; responsible for starting, stopping and reversing consumer movements; also determines the size of the controlling throttle opening for the hydraulic fluid quantity per time unit to be passed to the consumer. 11 4 and 6 Control land on spool valve 10, corresponding with consumer port 7, responsible for forming the throttle orifice between pump channel 48 and consumer port 7. 12 4 and 6 Control land on spool valve 10, corresponding with consumer port 6, responsible for forming the throttle orifice between pump channel 48 and consumer port 6. 13 4 and 6 Control land on spool valve 10, corresponding with consumer port 7 and return channel 50a. 14 4 and 6 Control land on spool valve 10 corresponding with port 6 and return channel 50c. 15 4 and 6 Cylindrical control valve bore wherein spool valve 10 is slidably displacable, so that in neutral position the consumer ports 6 and 7 are shut off from pump channel 48 on the one hand and from return channel sections 50c, 50a respectively on the other; upon displacement of spool valve 10 in the first direction, pump channel 48 is connected to consumer port 6 and consumer port 7 with return channel 50a; upon displacement in the second direction pump channel 48 is connected with consumer port 7 and consumer port 6 with return channel 50c (naturally there are many variants possible here). 16 6 Pressure regulating spool valve in pressure regulating valve unit 1 for producing a constant pressure difference between the pump pressure in pump channel 48 and the consumer pressure; to this effect loaded at one end with the pump pressure, and at the other end by a spring, as well as the consumer pressure fed back via pilot bores from one of the consumer ports 6 or 7. 17 6 Cross bores in the interior of spool valve 16, serving for transmitting the pump pressure from pump port 4 via chamber 46 to the non-spring-loaded side of spool valve 16. 18 6 Cylindrical bore in valve unit 1 wherein spool valve 16 is slidably displaceable, whereby the connection, dependent of the amount of spool valve displacement, between the chamber 46 and the chamber 47 is fully interrupted or there is formed a throttle orifice therebetween. 19 6 Regulating valve spring acting on spool valve 16 and responsible for the constant pressure difference between pump pressure and the consumer pressure feedback to spool valve 16. 20 6 Pressure limiting valve serving for limiting the maximum permissible system pressure and acting on the feedback consumer pressure on pressure balance piston 16; when the pressure on this pressure limiting valve 20 exceeds the maximum set, said valve is opened and hydraulic fluid from the chamber 52 is passed to return channel 50, thus maintaining the consumer pressure feedback at a value below the maximum value set, and thus controlling also the maximum pump pressure. 21 6 Valve seat for pressure limiting valve cone 22. 22 6 Valve cone of pressure limiting valve 20; is together with valve seat 21 responsible for closing and opening the connection between chamber 52 and return channel 50. 23 6 Pressure limiting valve spring acting on pressure limiting valve cone 22; the force of said spring determines the maximum allowable system pressure. 24 6 Shoulder piece for good support of spring 23. 25 6 Screw pin acting on shoulder piece 24, serving for adjusting and thereby varying the force of spring 23. 26 6 Adjustment nut to be screwed and pinned on screw pin 25, for the adjustment of spring 23. 27 6 Lock nut for securing screw pin 25. 28 5,5A Pressure-influencing piston in pressure-influencing valve cartridge 8 or 9; responsible for producing a constant pressure drop in the consumer pressure feedback to the pressure regulating valve unit 1. 29 5,5A First gland of pressure-influencing piston 28, whereon the primary consumer pressure feedback is acting. 30 5,5A Second gland of pressure-influencing piston 28, whereon the secondary consumer pressure feedback is acting, at the same time forming the throttle opening between the primary and secondary pilot bores for the consumer pressure feedback to the valve unit 1. 31 5,5A Shank of piston 28 between glands 29 and 30. 32 5,5A Cylindrical bore in valve cartridges 8, 9 respectively, wherein piston 28 is slidably displaceable. 33 5,5A Stop collar for limiting the stroke of piston 28. 34 5,5A Pressure-influencing cartridge spring acting on piston 28, determining the constant pressure drop in the consumer pressure feedback. 35 5,5A Adjusting pin for setting the bias pressure of spring 34 to the desired pressure drop. 36 5,5A Lock nut for securing adjustment pin 35. 37 7,11 Leak piston responsible for discharging the pump pressure when the spool valves 10 are in neutral position; also producing a leakage loss during operation, which loss is independent of pressure variations; required for a good functioning of the valve cartridges 8 and 9 and for maintaining a constant pressure difference between pump pressure and consumer pressure feedback set via valve cartridges 8,9. 38 7 Leak throttle passage axially disposed in piston 37 serving for passing hydraulic fluid to the spring-loaded end of piston 37; diameter and length of said bore determines the constant leakage loss. 39 7 and 11 Gland of piston 37 for sealing chamber 79a from 79b. 40 7 and 11 Gland of piston 37, forming with cylindrical bore 41 and leak bore 80 (FIG. 7) a throttle opening. 41 7 and 11 Cylindrical bore wherein piston 37 is slidably displaceable. 42 7 and 11 Leak piston spring acting on piston 37 and responsible for the constant pressure difference determining the required leakage loss through passage 38. 43 7 and 11 Screw plugs for plugging the bore 41. 44 8 and 13 Throttle screw for adjustment of the throttle passage of the cylindrical space 70, to adjust the pressure buildup and pressure drop time at the spring-loaded end of spool valve 16. 45 7,8,12,13,14 Screw to prevent ingress of dirt. 46 6 Pump chamber around piston 16 in continuous flow connection with pump port 4. 47 6 Return chamber around piston 16 in continuous flow connection with return port 5. 48 4,5,6 Pump channel running through the entire device, in continuous flow connection via chamber 46 with pump port 4. 49 4 and 6 Chamber around each spool valve 10 of control valve units 2 intersecting pump channel 48. 50a 4,5 and 6 First return channel section corresponding with consumer ports 7 of control valve units 2. 50b 6 Third return channel section in retaining plate 3 for connecting return channel section 50a with return channel section 50c. 50c 4,5 and 6 Second return channel section, corresponding with consumer ports 6 of control valve units 2 and in continuous flow connection with return chamber 47. 51 6 Pressure chamber formed in cylindrical bore 18 of valve unit 1; pump pressure is transmitted via bores 17 into pressure chamber 51. 52 6 Pilot pressure chamber in cylindrical bore 18 of valve unit 1, formed at the spring-loaded end of spool valve 16, its other end being limited by pressure limiting valve 20. 53 6 and 12 Valve chamber above valve cone 22 in pressure limiting valve 20; in continuous flow connection with return channel 50 via circular bore 54 and auxiliary bore 55. 54 6 and 12 Circular bore connecting chamber 53 to auxiliary bore 55. 55 6 and 12 Auxiliary bore connecting bore 54 to return channel 50. 56 4 and 6 Main gland of spool valve 10; in neutral position of spool valve 10 closing the primary pilot bores 61 and 62 and interrupting the connection between chamber 49 (pump channel) with consumer ports 6 and 7. 57 4 and 6 First gland of spool valve 10; in neutral position of spool valve 10 interrupting the connection between consumer port 7 and chamber 59 (return). 58 4 and 6 Second gland of spool valve 10; in neutral position of valve 10 interrupting the connection between consumer port 6 and chamber 60 (return). 59 4 and 6 Chamber around spool valve 10 in continuous flow connection with return channel section 50a. 60 4 and 6 Chamber around spool valve 10, in continuous flow connection with return channel section 50c. 61 4,5B and 6 First primary pilot bore ending in bore 15 of control valve unit 2, upon displacement of valve 10 in downward direction (as in FIG. 4) in flow connection with consumer port 7; in neutral position and upon displacement in upward direction of valve 10 the mouth of pilot bore 61 is blocked by gland 56. 62 4 and 6 Second primary pilot bore ending in bore 15 of control valve unit 2, upon displacement of valve 10 in upward direction in flow connection with consumer port 6; in neutral position and upon displacement in downward direction of valve 10 (as FIG. 4) the mouth of pilot bore 62 is blocked by gland 56. 63 4,5 and 6 First auxiliary pilot bore at right angles to pilot bore 61, leading to valve cartridge 8. 64 4,5 and 6 Second auxiliary pilot bore at right angles to pilot bore 62, leading to valve cartridge 9. 65 5 Primary chamber around housing valve cartridge 8 (or 9), intersected by and in continuous flow connection with auxiliary pilot bore 63 (or 64). 66 5 First cartridge cross bore in valve cartridge 8 (or 9) in continuous flow connection with chamber 65, at the same time intersecting cylindrical bore 32 wherein piston 28 is slidably displaceable. 67 5 Chamber formed around the shank 31 of piston 28 and limited by glands 29 and 30 of piston 28 in cylindrical bore 32. 68 5 Second cartridge cross bore in valve cartridge 8 (or 9), being in flow connection with groove 69. 69 5 Groove around valve cartridge 8 (or 9) in continuous flow connection with pilot bore 70 as well as bore 69a. 69a 5 Auxiliary cartridge bore connecting groove 69 with bore 32 at the spring biased side of piston 28. 70 4,5,6,7,8,10,5B First secondary pilot bore connected to groove 69 (or 169) of valve cartridge 8. 71 4,5,6,7,9 Second secondary pilot bore, connected to groove 69 (or 169) of valve cartridge 9. 72a 6,7,10 Auxiliary bore, parallel to auxiliary bore 72b; in flow connection with auxiliary bore 78 to leak piston

37. 72b 6,8,10 Auxiliary bore wherein pilot bore 70 ends, parallel to auxiliary bore 72a; also in flow connection with bore 70. 73 8,13,10,11 Auxiliary bore on bore 72b; leading to the cylindrical space 74. 74 8,13 Throttle bore limited by throttle screw 44. 75 6,8,12,14 Continuation of auxiliary bore 73. 76 6,8,14 Cross bore of auxiliary bore 75 leading to pilot pressure chamber 52. 77 6,7,9 Auxiliary bore which communicates pilot bore 71 with auxiliary bore 78. 78 6,7,9,10,11,12,13,14 First leak bore, connecting bores 77 and 72a with chamber 79a at one end of leak piston 37. 79a 7 and 11 First leak chamber limited by leak piston 37 and screw plug 43; connecting leak bore 78 via passage 38 in piston 37 with chamber 79b at the spring-loaded end of piston 37. 79b 7 and 11 Second leak chamber at spring-loaded side of piston 37. 80 7,12,13,14 Second leak bore ending in the chamber 79b at the spring-loaded end of piston 37, the gland 40 of said piston forming a throttle opening between said chamber and said bore. 80a 6,7,12 Auxiliary leak bore connecting bore 80 with circular bore 54 so that via bore 54 and bore 55 there is a flow connection between bore 80 and return channel section 50a. 81 1,2,4,5,6,7 Tie rods with which the components 1, 2 and 3 are held together. 82 1,2,6 Nuts on tie rods 81. 83 1,2,3,4 Control mechanism for displacing spool valves 10 of control valve units 2. 84 1,2,3,4 Operating lever of control mechanism 83. 85 4 Toothed racks disposed on spool valves 10 of control valve units 2. 86 4 Pinions wherein the operating levers 84 are screwed; by moving lever 84 in downward direction, the valve 10 is moved in upward direction and, upon moving lever 84 upwards, the valve 10 is moved downwards. 87 1,2,4 Spring caps on control valve units 2. 88 4 Centering springs acting on valves 10 of control valve units 2; upon releasing operating lever 84, valve 10 automatically returns to the neutral position through the action of spring 88. 89 4 Spring guides, also acting as stroke limitation for the displacement to be made by control piston 10. 90 4 Auxiliary bore connecting chamber 59 (return channel 50a) with the interior of the control mechanism 83 and permitting change of the hydraulic fluid volume in control mechanism 83 as valve 10 is displaced. 91 6 Auxiliary bore connecting return channel 50c with the interior of the spring cap 87 and permitting change of hydraulic fluid volume therein as valve 10 is displaced. 128 5B Cone of valve cartridge 180. 132 5B Cylindrical bore in valve cartridge 180. 134 5B Pressure-influencing cartridge spring of valve cartridge 180. 135 5B Adjust screw for setting the bias pressure of spring 134. 165 5B Primary chamber. 168 5B Cartridge cross bore. 169 5B Groove. 180 5B Variant of pressure-influencing valve cartridge 8 or 9. 181 5B Valve seat of valve cartridge 180. 182 5B Bore in valve seat 181. ______________________________________

DESCRIPTION OF THE PREFERRED EMBODIMENT

For a better understanding of the whole complex of consumer pressure feedback and production of an arbitrarily set constant difference between pump pressure and consumer pressure, the valve cartridges 8 and 9 and the leak piston are described before the whole device is described.

A. valve cartridges 8 and 9.

FIG. 5A shows an enlargement of the cross section of a valve cartridge 8. It is clear that the construction of a valve cartridge 9 is fully identical, so that a description of a valve cartridge 8 will suffice.

As shown in FIG. 5A, a valve cartridge 8 comprises a metal housing with hexagonal faces, a screw thread and a shoulder. Such a cartridge may be screwed into the housing of the control valve units 2 (a,b,c, . . ). In the drawn embodiment, the housing of such a valve cartridge is provided with an axially disposed cylindrical bore 32. In said cylindrical bore 32 the pressure-influencing piston 28 has been slidably mounted. Piston 28 comprises a shank 31 and two glands 29 and 30. The stroke of pressure-influencing piston 28 is limited in one direction by a stop collar 33.

The cartridge is provided with a first cross bore 66, intersecting the cylindrical bore 32, and also with a similar second cross bore 68 and a groove 69 (which is more than twice as wide as the diameter of the second cartridge cross bore 68 ending in said groove). An auxiliary bore 69a is formed from said groove 69, leading at an angle to cylindrical bore 32.

The pressure-influencing piston 28 is pressed against stop collar 33 by means of the spring force of a cartridge spring 34, and forming a chamber 67 between the glands 29 and 30 in cylindrical bore 32, said chamber being in communication, via first cross bore 66, with a primary chamber 65 which is formed around cartridge 8, after screwing it into the housing of a control valve unit 2 (a,b,c, . . . ).

The chamber 67 between the glands 29 and 30 is, via first cross bore 66 and chamber 65, in continuous flow connection with the end of pressure-influence piston 28 at gland 29, while gland 30 closes off communication between the chamber 67 and cross bore 68.

The bias force of cartridge spring 34 is set by means of adjusting pin 35, which is screwably disposed in the cylindrical bore 32 and secured against loosening by vibration during operation by lock nut 36.

The valve cartridge 8 is so disposed in the housing of control valve unit 2 (a,b,c, . . ) that bore retaining the valve cartridge intersects a pilot auxiliary bore 63. Said bore 63 is in continuous flow connection with the primary pilot bore 61, which, as shown in FIG. 4, ends in cylindrical control valve bore 15 for the control spool valve 10.

When now control spool valve 10 (FIG. 4) is moved downwards, there is established a connection between first consumer port 7 and bore 61. The pressure prevailing in first consumer port 7 is transmitted via bores 61, 63 and chamber 65 to pressure-influencing piston 28 at gland 29. At the same time the consumer pressure is transmitted into chamber 67, but as the glands 29 and 30 are fully identical, the pressure prevailing in chamber 67 has no influence on the displacement of piston 28.

As soon as the consumer pressure, in chamber 67 against gland 29 at the end of piston 28, overcomes the bias force of spring 34, the piston 28 is moved against the action of spring 34, thus producing a communication between chamber 67 and cross bore 68. Consequently, there flows, via cross bore 68 and groove 69 and auxiliary bore 69a, fluid into the cylindrical bore 32 at the spring-loaded side of piston 28.

Consequently, in addition to the biasing force of spring 34 at this end of piston 28, there also prevails hydraulic pressure. The displacement of piston 28 therefore only continues until the secondary pressure acting over the cross-sectional area of the spring-loaded gland 30, together with the bias force of the spring 34, is equal to the primary pressure from the consumer port 7 acting on the gland 29 of piston 28.

Upon increasing consumer pressure, piston 28 is so far moved against the action of spring 34 until the pressure drop again has attained a value corresponding to the bias force of spring 34. Now it is clear that an increased bias force of spring 34 produces a greater (and a reduction of the bias force, a lower) pressure drop but that a once arbitrarily set pressure drop remains constant, however great the consumer pressure variations may be.

Upon decreasing primary consumer pressure the piston 28, as shown in FIG. 5A, would act as a non-return valve, for then the pressure at the gland 30 of the piston 28 would be decreased, after which, without suitable provisions, displacement of piston 28 would take place, as a result of which the communication between bore 68 and chamber 67 would be shut off. This would mean that the difference between pump pressure and consumer pressure would increase and, consequently, more hydraulic medium would pass to the consumer.

To avoid this, a leak piston 37 has been disposed in the pressure regulating valve unit 1, causing a constant leakage loss, as a result of which increases of the secondary consumer pressure at the spring-loaded end of pressure-influencing piston 28 are continuously levelled in conformity with the varying primary consumer pressure.

The fact that the valve cartridge 8 can also function as a non-return valve is of great advantage to the control device, for now two control valve units 2 can be displaced simultaneously, as the load pressure of the heaviest loaded consumer keeps the valve cartridge 8 closed against the less heavier loaded consumer in the above described manner and, consequently, only the load pressure of the heaviest loaded consumer is fed back. Upon simultaneous operation of various control valve units 2, the pump pressure will therefore adjust itself under all circumstances to the highest consumer pressure, as a result of which all consumers can be operated and controlled.

A variant 180 of the described pressure-influencing valve cartridges 8 and 9 is represented by FIG. 5B. This variant is simpler and because of that cheaper in production. However, the accuracy of adjustment is somewhat less good, but in practice good enough for a number of applications.

The pressure-influencing piston 28 has been replaced by a cone 128, which closes a bore 182 in a valve seat 181. The bore 182 is in flow connection with primary pilot bore 61 (respectively 62). The cone 128 is loaded by a spring 134 of which the spring force is adjustable by an adjust screw 135.

Whenever a spool valve 10 (FIG. 4) is moved downwards, a flow connection is established between consumer port 7 and primary pilot bore 61. The pressure prevailing in consumer port 7 is via chamber 165 and the bore 182 transmitted to the cone 128.

As soon as the primary consumer pressure on cone 128 overcomes the bias force of spring 134, the cone 128 is moved from seat 181, this producing a flow communication between chamber 165 and cross bore 168. Consequently, fluid flows via cross bore 168 around groove 169 into the secondary pilot bore 70.

Since the diameter of cone 128 is smaller than the diameter of bore 132, the pressure available in bore 70 prevails within bore 132. Consequently, in addition to the biasing force of spring 134 at the cone 128, this cone 128 is loaded with secondary consumer pressure feedback as well.

So the cone 128 is closing the bore 182 of seat 181 again at the moment that the primary consumer pressure feedback prevailing in bore 182 is equal to the sum of secondary consumer pressure feedback prevailing in bore 70 and the bias force of spring 34. The working principle in fact is that of a sequence valve.

It is clear, that also a valve cartridge of this type functions as a non-return valve as well as that here also the pressure drop between the primary pilot bore 61 and secondary pilot bore 70 is determined by the adjustable biasing force of spring 134. Furthermore, it is obvious that the cone 128 could be replaced by a ball.

B. leak Piston 37.

As shown above, the production of a leakage loss is a necessity for the correct functioning of the valve cartridges 8 and 9, it being required, however, to keep the leakage loss produced within pre-established limits and independent of pressure variations. Such a leakage loss can be caused by a leak position 37, as shown in the pressure requlating valve unit 1 shown in FIGS. 7 and 11.

As shown in FIG. 7, pressure regulating valve unit 1 is provided with a cylindrical bore 41, wherein a leak piston 37 is slidingly displacable. Piston 37 is provided with glands 39 and 40 of which gland 39 bounds and seals a first leak chamber 79a in cylindrical bore 41 and gland 40 bounds and seals a second leak chamber 79b. Both chambers 79a and 79b are in continuous flow connection with each other via a leak throttle passage 38 axially disposed in piston 37. In chamber 79b furthermore there is a spring 42 acting on piston 37. Cylindrical bore 41 is sealed at both ends by a screw plug 43.

The bore 41 is intersected in chamber 79a by a leak bore 78, which in a manner as explained hereunder is in continuous flow connection with the pilot pressure chamber 52 (FIG. 6) at the end of spool valve 16 loaded by the light control spring 19 of pressure differential valve unit 1. The same bore 78 furthermore is in continuous flow connection with groove 69 around the valve cartridges 8 and 9 (FIG. 5).

Chamber 79b of cylindrical bore 41 is furthermore in continuous flow connection with a second leak bore 80, which via auxiliary leak bore 80a (FIGS. 7,12) is in continuous flow connection with circular bore 54 of the pressure limiting valve 20. The mouth of leak bore 80 and chamber 79b, together with gland 40, form a throttle opening.

As soon as one control spool valve 10 of one of the control valve units 2 (a,b,c, . . ) is displaced, fluid will flow in the earlier described manner into groove 69 around valve cartridge 8 (or 9) and, since said groove is in connection with the bore 78, the pressure in chamber 79a will increase, as a result of which the leak piston 37 will be displaced in a direction opposite to the action of spring 42, and gland 40 will reduce the throttle opening between chamber 79b and bore 80.

At the same time fluid also passes via throttle passage 38 from chamber 79a into chamber 79b, which fluid can only pass the throttle opening formed by gland 40 with bore 41 and 80 with a pressure drop. On leak piston 37 are thereby acting two forces, viz. at gland 39 the pressure in chamber 79a and at gland 40 the pressure of spring 42, as well as the pressure prevailing downstream of the throttle point between bore 41 and bore 80. The piston consequently, will be displaced and adopt an equilibrium position, wherein both forces are in equilibrium and, consequently, the pressure drop at said throttle opening, together with the force exerted by spring 42, is equal to the pressure in chamber 79a.

The pressure difference upstream and downstream of piston 37 is determined by the spring force of spring 42 and, this being to all intents and purposes constant, also the pressure difference is constant. The volume passed through throttle passage 38 per unit of time is then determined by the difference between the pressures in chambers 79a and 79b, and by the diameter and the length of throttle passage 38 and, as all three factors are constant, also the volume passed or the leakage loss produced is constant under all circumstances.

As a result of the action of leak piston 37, a valve cartridge 8 or 9, upon decrease of the consumer pressure, will not function as a non-return valve, since the earlier consumer pressure feedback, through the action of the piston 37, decreases simultaneously with the pressure drop of the actual consumer pressure. As always, very small volumes of fluid are displaced, load pressure changes are dealt with without delay, and a leakage loss of approximately 20 cc per minute, at a spring force corresponding to 2 kg/cm2 of oil pressure on spring 42, is sufficient in practice.

When spool valves 10 of control valve units 2 (a,b,c, . . ) are in the neutral position, no further supply of fluid feedback takes place. As a result of the leakage produced in piston 37, the pressure in chamber 79a is diminished and as chamber 79a is in flow connection with pilot pressure chamber 52 at the spring-loaded end of spool valve 16 by means of bores 78, 72a, 70, 72b, 73, 74, 75, and 76, the latter is relieved at its spring-loaded end.

C. embodiment of an entire control device.

According to FIG. 1, the control device with pressure-compensated volume control is composed of a single pressure regulating valve unit 1 and three control valve units 2a, 2b and 2c. Said units are effectively bolted together by means of a retaining plate 3 and a plurality of tie rods 81 to create a single device.

The pressure regulating valve unit 1 is provided with a pump port 4 and a return port 5 which serve respectively for connecting the device to a pump for supplying hydraulic fluid and to a reservoir for discharging returning fluid from consumers connected to the device, as well as for the discharge of that part of the pump yield which is not passed for direct supply of the system. Each of the control valve units 2 (a,b,c, . . ) is provided with two consumer ports 6 and 7 serving for connecting a double-acting consumer. It is clear that if the downstream consumer need only be operated in one direction, the corresponding control valve unit 2 (a,b,c, . . ) need only be provided with one of the consumer ports 6 or 7.

The pump port 4, as shown in FIG. 6, ends in a pump chamber 46 wherein also ends a centrally disposed pump channel 48. The channel 48 traverses the entire device and intersects in each control valve unit 2 (a,b,c, . . ) a cylindrical control valve bore 15 axially disposed in the housing of each control valve unit 2 (a,b,c, . . ). A chamber 49 is disposed each time where the pump channel 48 crosses such a bore 15. The pump channel 48 is bounded and shut off by retaining plate 3.

The return port 5 ends in a return chamber 47 which again is in continuous flow connection with a return channel section 50c of a return channel 50, which also traverses the entire device. Via a return channel section 50b in the retaining plate 3, return channel section 50c is in continuous flow connection with a return channel section 50a. Channel section 50a also traverses the entire device. Both return channel sections 50a and 50c intersect, as is the case with pump channel 48, the control valve bores 15 as well. Where return channel section 50a crosses bore 15 there is disposed a chamber 59. Where the return channel section 50c crosses bore 15 there is also disposed a chamber 60.

As shown in FIGS. 4 and 6, there is disposed in bore 15 of each control valve unit 2 (a,b,c, . . ) a control spool valve 10 which is slidingly displaceable, which in the neutral position drawn in FIG. 6, closes the connection between pump channel 48 and consumer port 7 and between pump channel 48 and consumer port 6 by the main gland 56 disposed on spool valve 10.

In the same way the spool valves 10 of each control valve unit 2 (a,b,c . . ) shut off, through its gland 57, the connection, between return channel section 50aand consumer port 7, as well as through its gland 58, the connection between return channel section 590c and consumer port 6. A consumer connected to the consumer ports 6 and 7, in the neutral position, is therefore neither in flow connection with the pump nor with the reservoir. In practice it may occur that one or even both sides of a consumer in the neutral position of control valve unit 2 has to remain in flow connection with the reservoir or with the pump. It is clear that for such cases the glands 56, 57 and 58 will have a different form.

It is also shown in FIGS. 4 and 6 that in each control valve unit 2 (a,b,c, . . ) two primary pilot bores 61 and 62 end in control valve bore 15 and that the mouths of said pilot bores 61 and 62, in the neutral position as drawn, are also closed off by the main gland 56 of spool valve 10.

The displacement of spool valve 10 in bore 15 is produced by displacement of a operating lever 84, as shown in FIG. 4. Operating lever 84 is screwed into a pinion 86, whose teeth engage the teeth of the toothed rack 85 disposed on spool valve 10. Displacement of operating lever 84 in the upward direction produces a displacement of spool valve 10 in the downward direction, while displacement of operating lever 84 in the downward direction produces a displacement of spool valve 10 in the upward direction.

As shown in FIG. 4, each control valve unit 2 (a,b,c, . . ) is provided at the end opposite to operating lever 84 with a spring mechanism which ensure that spool valve 10, after releasing operating lever 84, automatically returns to its neutral position. Each spring mechanism comprises a centering spring 88 and two spring guides 89 and is enclosed in a space bounded by spring cap 87. Spring guides 89 ensure a good guiding of spring 88, as well as limiting the stroke of spool valve 10.

It will be noted that the embodiment described here allows many variations, which make no difference, however, to the function of the invention as long as spool valve 10 can be moved upwards and downwards by hand, hydraulically, mechanically or other means.

It can be easily seen from FIG. 4, that, upon displacement of spool valve 10 in upwards direction, first the mouth of pilot bore 62 comes in flow connection with consumer port 6, so that fluid from consumer port 6 passes into pilot bore 62, so that the consumer pressure (or load pressure) also prevails in pilot bore 62.

It is also clear that further movement of spool valve 10 in upwards direction then opens a connection between pump channel 48 and consumer port 6 and that, consequently, fluid flows from pump channel 48 via consumer port 6 to the consumer.

On the other hand, upon displacement of spool valve 10 in downwards direction as shown in FIG. 4, there will first be effected a flow connection between consumer port 7 and pilot bore 61 and only upon further movement of spool valve 10 in downward direction will there be produced a flow connection between pump channel 48 and consumer port 7. Of decisive importance for the entire functioning of the device is the fact that the mouths of the pilot bores 61 and 62 in valve bore 15 are shut off by gland 56 in the neutral position of spool valve 10, while upon movement of spool valve 10 in one of the operative positions, gland 56 only ceases to occlude that mouth which corresponds with the consumer port actually brought in communication with pump channel 48. It can also be seen in FIGS. 4 and 6 that upon downward movement of spool valve 10 (see FIG. 6, control valve unit 2c), gland 58 releases a connection between consumer port 6 and return channel section 50c. In that case the consumer is loaded at one side via port 7 as stated above and via port 6 relieved at the other side. In the same way upon upwards movement of spool valve 10 the consumer is loaded at one side via port 6 and relieved at the other side via port 7.

In the above manner it is therefore possible arbitrarily to cause a consumer connected to a control valve unit 2 (a,b,c, . . ) to perform a movement, to have said movement stopped and to reverse same. The volume passed to a consumer is determined by the control orifice between the pump channel 48 and the currently connected consumer port 6 or 7. For example, the control valve unit 2c of FIG. 6 is drawn in a displaced condition. Here the control orifice is formed because gland 56, upon movement in downwards direction of spool valve 10, opens an orifice between chamber 49, in flow connection with pump channel 48, and that part of valve bore 15 which is in flow connection with consumer port 7, thus realizing a connection between pump channel 48 and consumer port 7.

Gland 56 is provided with a cone 11, also called a control land. It is clear that with a continued displacement of spool valve 10, as a result of the presence of control land 11, the control orifice becomes increasingly larger. The volume of fluid passed from pump channel 48 to consumer port 7 is determined by the size of said control orifice, as well as by the difference between pressures upstream and downstream of said control orifice. By keeping said pressure difference constant, the volume passed to the consumer is therefore only dependent on the size of the control orifices and consequently, the volume is exclusively determined by the displacement of spool valve 10.

Obviously, upon displacement of spool valve 10 in upwards direction, the gland 56 with control land 12 can effectuate a similar control orifice between pump channel 48 and consumer port 6. The form of the control lands 11 and 12 determines the control orifice. When these control lands have been disposed at a small angle, the control orifice is small and therefore also the throughflow at full displacement of spool valve 10. The greater this angle, the greater the control orifice at full displacement of spool valve 10 and, consequently, also the maximum volume of fluid passed is greater. Furthermore it is clear that in addition to the form of the control lands 11 and 12 on gland 56, also the stroke of control piston 10 determines the volume passed to the consumer and that by limiting said control stroke also the maximum volume of fluid passed is limited.

FIG. 4 shows that the pilot bore 61 is intersected by an auxiliary pilot bore 63 and the pilot load pressure bore 62 by an auxiliary pilot bore 64. FIG. 5 shows that bore 63 opens into the chamber around valve cartridge 8 and that bore 64 opens into the chamber around valve cartridge 9. Upon displacement of spool valve 10 in downwards direction, bore 63 receives, via pilot bore 61, fluid at consumer pressure from consumer port 7. Upon displacement fo spool valve 10 in upwards direction, bore 64 similarly receives fluid at consumer pressure from consumer port 6.

It has already been described that the pressure-influencing piston 28 of valve cartridge 8 or 9 is adapted to effect a flow connection between the chamber 67 and annular groove 69, whereby, however, a pressure drop is produced that is determined by the bias force of spring 34. Since, as already said, bore 63 is in connection with chamber 65 of valve cartridge 8, and said chamber 65 being in communication with chamber 67 via cross bore 66, fluid will flow from consumer port 7 in annular groove 69 of cartridge 8 upon displacement of spool valve 10 in downwards direction. Upon displacement of spool valve 10 in upwards direction, fluid will therefore flow from consumer port 6 into an identical annular groove 69 of valve cartridge 9.

The annular groove 69 around valve cartridge 8 is in continuous flow connection with a secondary pilot bore 70, while the same annular groove 69 around valve cartridge 9 is in continuous flow connection with a secondary pilot bore 71. As shown in FIG. 6, both secondary pilot bores intersect all control valve units 2 (a,b,c, . . ). Within the housing of pressure regulating valve unit 1, bore 71, as indicated in FIGS. 6 and 7, opens into auxiliary bore 77 which is in continuous flow connection with first leak bore 78. The bore 70 intersects, within the housing of pressure regulating valve unit 1, bores 72a and 72b. Bore 72a is in continuous flow connection with bore 78, so that chamber 79a, at the end of leak piston 37 opposite spring 42, is in continuous flow connection with both pilot bores 70 and 71.

Auxiliary bore 72b as shown in FIGS. 8 and 10, is in continuous flow connection with bore 73. Bore 73 opens into a throttle bore 74 and continuing thereafter to bore 74. The mouths of bores 73 and 75 in bore 74 can be throttled arbitrarily to a greater or lesser degree by a throttle screw 44, so that the passing fluid is throttled accordingly.

Bore 75, as shown in FIGS. 7, 14 and 6, is in continuous flow connection via cross bore 76 with pilot pressure chamber 52 at the end of pressure regulating spool valve 16, which is loaded by spring 19.

It follows from the above that the pilot pressure chamber 52, via bores 76, 75, throttle bore 74, as well as bores 73, 72b, 70,72a and 78, is also in flow connection with chamber 79a at the end of piston 37 opposite spring 42. When spool valves 10 of all control valve units 2 (a,b,c, . . ) are in the neutral position, no consumer pressure feedback takes place, because the pilot bores 61 and 62 are occluded by glands 56 of spool valves 10.

As earlier explained, the piston 37 provides a constant flow connection from chamber 79a to return channel section 50a, which means that the pressure in chamber 79a, and therefore also in pilot pressure chamber 52, is reduced. In the position shown in FIG. 6, the communication between chambers 46 and 47, in flow connection with pump port 4 and return port 5 respectively, is closed by pressure regulating spool valve 16. Chamber 46, however, via cross bores 17, is in continuous flow connection with chamber 51 at the lower end of pressure regulating spool valve 16 opposite the spring 19.

When the pump now is started, there will be a pressure build-up in chamber 46, which pressure, via cross bores 17, is also present in chamber 51. As already explained, the pilot pressure chamber 52 in the neutral position of spool valves 10 of control valve units 2 (a,b,c, . . ) is free from pressure. On one end of spool valve 16 is thus only acting the bias force of spring 19, and on the other end in chamber 51 is acting the pump pressure. As soon as the pump pressure in chamber 51 overcomes the bias force of spring 19, the piston 16 will be moved upwards, thus opening a connection between chambers 46 and 47. The pump yield is now directly discharged to the reservoir via pump port 4, chamber 46, chamber 47 and return port 5, at a bypass pressure determined by the bias force of spring 19. In practice the bias force of spring 19 corresponds to a hydraulic pressure of approximately 6 kp/cm2.

As soon as spool valve 10 of one of the control valve units 2 (a,b,c, . . ) is displaced, for instance in a downward direction, pressure fluid from consumer port 7 will pass to pilot bore 61 in a manner as already earlier described. Subsequently, the load pressure control fluid flows via the pilot bore 63 into chamber 65 around valve cartridge 8 and thereafter via cross bore 66, chamber 67, cross bore 68, annular groove 69 and at a reduced pressure into pilot bore 70.

From pilot bore 70 the fluid flows via bores 72b, 73, 74, 75, and 76 into pilot pressure chamber 52 at the end of pressure regulating spool valve 16 containing the spring 19. So on this end of spool valve 16 is acting the consumer pressure feedback from port 7, as well as the spring force of spring 19. Thus higher loaded at this end, the spool valve 16 will be moved downwards, thus reducing the throttle orifice between the chambers 46 and 47. This means that the fluid flow passes said throttle orifice at increased pressure and the pressure in chamber 51 increases via cross bores 17. The displacement of spool valve 16 continues to such extent until the pump pressure in chamber 51 is again equal to the sum of the consumer pressure feedback in chamber 52 and the bias force of spring 19. The pump pressure has meanwhile attained a value which is higher than the consumer pressure.

A further displacement of spool valve 10 in downward direction produces a through-flow of the pump yield from pump channel 48 to consumer port 7. As already demonstrated, the fluid flow from channel 48 to consumer port 7 is determined by the control land 11 on gland 56, as well as by the difference of the pressure in pump channel 48 upstream the throttle orifice and the pressure in consumer port 7 downstream the throttle orifice. This pressure difference is determined by the spring tension of spring 19 on spool valve 16, as well as by the secondary consumer pressure feedback to the spring-loaded end of valve 16. It was already demonstrated that the secondary consumer pressure is determined by the bias force of spring 34 of valve cartridge 8 and the primary consumer pressure.

By increasing the bias of spring 34, the secondary consumer pressure fed back to spool valve 16 decreases and therefore also the pump pressure in pump channel 48 decreases. Consequently, also the difference between pump pressure upstream the controlling throttle orifice between channel 48 and consumer port 7 and the primary consumer pressure downstream said throttle orifice has become smaller, and automatically less hydraulic medium will flow to the consumer. An arithmetical example may explain this:

It is assumed that the consumer is loaded with a consumer pressure of 100 kp/cm2 ; that spring 34 of valve cartridge 8 is set at a bias corresponding with a hydraulic pressure of 1 kp/cm2 on pressure-influencing piston 28; and that spring 19 exerts a spring force corresponding to a hydraulic pressure of 6 kp/cm2. Upon displacement of spool valve 10 in downward direction, a primary consumer pressure of 100 kp/cm2 is fed back, and is reduced through valve cartridge 8 by 1 kp/cm2, being the bias force of spring 34, to a secondary consumer pressure of 99 kp/cm2. In chamber 51, below spool valve 16, is thus acting a pressure of 105 kp/cm2, viz. 6 kp/cm2 through the effect of spring 19, and the consumer pressure feedback of 99 kp/cm2. The effective difference between pump presure and consumer pressure is consequently 5 kp/cm2, and the fluid flow via the throttle orifice between pump channel 48 and consumer port 7 is determined by said pressure difference for any given displacement of spool valve 10.

Now, when the bias force of spring 34 of valve cartridge 8 is increased, for instance to a value corresponding to 4 kp/cm2 fluid pressure on pressure-influencing piston 28, the primary consumer pressure feedback is reduced by 4 kp/cm2 to a secondary consumer pressure of only 96 kp/cm2. On the spool valve 16 is then only exerted a pressure of 102 kp/cm2, and the difference between pump and consumer pressure is therefore only 2 kp/cm2. It is clear that in a similar manner it is possible for each separate consumer port 6 or 7 of each separate control unit 2 (a,b,c, . . ) to set a separate pressure difference between pump and consumer pressure by means of adjustment of screw 35 of valve cartridges 8, 9, respectively, while maintaining the full control stroke of each separate control piston 10 and without it being necessary to provide spool valves 10 with control lands 11 and 12 adapted to the required flow to the consumer ports. The device therefore allows an optimal adaption to operating conditions, even when the prevailing pressure conditions should change drastically.

Upon simultaneous displacement of two control valve units 2 (a,b,c, . . ), only the consumer pressure of the heaviest loaded consumer is fed back, for on the primary end of pressure-influencing piston 28 of valve cartridge 8 or 9, which acts on the consumer pressure of the least loaded consumer, is acting the lower consumer pressure and on the secondary end the higher consumer pressure from the heavier loaded consumer, as well as the spring pressure of spring 34. Consequently, pressure reducing piston 28 slides away from the direction of the spring 34, so that gland 30 of pressure reducing piston 28 closes the pilot pressure bore of the lower loaded consumer port.

At all times, consequently, upon simultaneous displacement of two control valve units 2 (a,b,c, . . ), only the pressure on the heaviest loaded consumer is fed back to pressure regulating valve unit 1, and the pump pressure automatically adjusts itself to this highest pressure, thus enabling the manipulation of both pressures. It can be concluded from FIG. 5 that the cost price of a valve cartridge in series production will be very low, and is less than the saving obtained through the omission of pilot bores with very costly cross bores in each control valve unit for relieving the control spool valves 10 in the operable positions, as well as through the omission of the necessity to provide the spool valves 10 with specially adapted control lands.

As already explained, the feedback, derived from the consumer port connected with the pump channel 48, is conducted to the pilot pressure chamber 52 at the end of spool valve 16 biased by the spring 19. It can be established from FiG. 8 that the throttle screw 44 can be adjusted to throttle the passage between pilot bores 73 and 75 arbitrarily to a lesser or greater extent. In other words, the passing consumer pressure feedback flow can be throttled to a lesser or greater degree and so the time for pressure build-up and pressure decrease in pilot pressure chamber 52 is adjustable. This provision, together with the fact that upon displacement of a control valve unit 2 (a, b, c, . . ) the pump pressure has already increased before the realization of the flow of the medium to the consumer to a value which is only to a small extent higher than the consumer pressure, enables very flexible and shockfree operation.

The functioning of the above-described control device with pressure-compensated volume control is also shown by means of a hydraulic diagram in FIG. 15.

DESCRIPTION OF VARIANTS OF THE PREFERRED EMBODIMENT

The above-described control device with pressure-compensated volume control regulates the passage to the consumers through a three-way volume control principle. By applying only a few changes, the control device can be made suitable for a volume control through a two-way volume control principle. Such a control device is used in a hydraulic system fed by a pump having controllable yield, said pump being provided with adjusting means to adjust the pump so that as much delivery is provided as is necessary for maintaining a set system pressure.

The same control device can also be used in a system fed by a hydraulic pressure accumulator in combination with a pump having a constant yield and an automatic pump relief valve, which ensures that, upon attaining the maximum accumulator pressure, the pump is relieved.

In the hydraulic diagram of FIG. 16 is shown a variant of the control device whereby the control valve units 2 (a,b,c, . . ) are fully identical to those of the control device already described in part C. Place and function of the pilot bore system and valve cartridges 8 and 9 remain fully unchanged, as well as for leak piston 37 and pressure limiting valve 20. The port 4 on pressure regulating valve unit 1, however, is closed by a screw plug, while port 5 previously serving for the connection to the reservoir is now connected to a pressure source 92. The passage between return channel section 50c and chamber 47 is also blocked, for instance by fitting a plug in the housing of pressure regulating valve unit 1. To permit the discharge of the fluid returned from the consumer to the reservoir, the retaining plate 3 is provided with a return port 5a which is in continuous flow connection with return channel section 50b in retaining plate 3.

The major change concerns the shaping of pressure regulating spool valve 16 of pressure differential valve unit 1. Pressed fully downwards in the operating direction of spring 19, the spool valve 16 now fully opens the passage between chambers 47 and 46, while a displacement of spool valve 16 in upward direction gradually closes said passage. Functioning and functions of said control device with pressure-compensated two-way volume control are explained by the hydraulic diagram shown in FIG. 16.

When the port 5 of pressure regulating valve unit 1, as shown in FIG. 16, is connected with pump 92, and when the latter is started, there will be a pressure build-up in chamber 47. Since initially the chambers 47 and 46 are in communication with each other, there will also be a pressure build-up in chamber 46. Chamber 46, however, is in continuous flow connection through cross bore 17 in the interior of spool valve 16, with chamber 51 at the end of spool valve 16 opposite spring 19. On the latter end is thus acting pressure from chamber 46. The spring-loaded end of piston 16, as already explained, is fully relieved when control valve units 2 (a,b,c, . . ) are in neutral position.

On spool valve 16 are thereby acting two forces, viz. at one end the spring pressure of spring 19 and on the oteer end the pressure from chamber 46. It is clear that spool valve 16 seeks an equilibrium condition wherein both forces are equal. This means that spool valve 16 closes the passage between chambers 47 and 46, and that in chamber 46, as well as in pump channel 48, a secondary pressure will prevail equal to a hydraulic pressure corresponding to the spring force exerted on spool valve 16 by spring 19.

If a control valve unit 2 (a,b,c . . ) is displaced, consumer pressure is first fed back to the end of spool valve 16 loaded by spring 19. The pressure on this end increases accordingly and causes a displacement of spool valve 16 in downward direction, thus slightly opening the throttle orifice formed by valve 16 between chambers 46 and 47. Pressure fluid therefore flows from chamber 47 into chamber 46. The pressure in chamber 46 consequently increases and also therefore in chamber 51. There will now be produced a new equilibrium condition, in which the pressure in chamber 46 is equal to the sum of the consumer pressure feedback and the spring force of spring 19, in other words an intermediate pressure will prevail in pump channel 48 which is derived from the pressure source 92, said intermediate pressure being somewhat higher than the consumer pressure.

Again the difference between the primary consumer pressure in the consumer and the intermediate pressure in pump channel 48 is determined on one hand by the spring bias of spring 19 and on the other hand by the secondary consumer pressure fed back through valve cartridges 8 and 9. Increase of the bias of spring 34 of a valve cartridge 8 or 9 causes a reduction of the consumer pressure feedback and so a reduction of the pressure difference at the throttle orifice, made by spool valve 10 between pump channel 48 and consumer port. Fully in accordance with the earlier described device, here too it is possible to limit the maximum volume to be passed to the consumers, again with maintenance of the full control stroke.

A second variant is shown by a hydraulic diagram in FIG. 17. The control device with pressure-compensated volume control, according to FIG. 17, has also the function to decrease or increase the pump delivery in accordance with the volume passed to the consumer. The hydraulic system hereby is fed by a pump 92 with controllable volume yield, said pump being provided with an adjusting cylinder 96, which through the pressure produced by the return flow derived from the control device according to the invention, effects the setting of the pump, thereby changing the pump delivery.

The only variation, relative to the above explained control device, is that the passage between return channel section 50c and chamber 47 is blocked and that there is provided an additional return port 5a, which is in continuous flow connection with return channel section 50b in retaining plate 3. The pump port 4 is thereby quite normally connected with the pump 92. However, the return line 93 leading from return port 5 is connected via a throttle valve 95 to the reservoir and to adjusting cylinder 96 of the hydraulic pump 92. A pressure relief valve 94 protects the mechanism from overpressure, and provides an alternative path to the reservoir.

The volume control between pump channel 48 and consumer ports 6 or 7 is quite identical to the control of the original device described in part C. The return fluid from the consumers is discharged via return port 5a on retaining plate 3 directly to the reservoir. The fluid not passed to the consumers is, however, discharged via return port 5. Said return oil flow in line 93 can only pass via adjustable throttle 95 to the reservoir, thus building up pressure in the return line 93 upstream throttle 95, which pressure also prevails in the adjusting cylinder 96 of hydraulic pump 92. As a result of this pressure increase, the piston 98 of cylinder 96 adjusts the setting of the pump 92, decreasing the pump delivery so as to correspond to little more than the volume passed to the consumers.

The pump delivery is therefore adapted to the useful volume passed to the consumers and by appropriate adjustment of valve cartridges 8 and 9 for each consumer port of each control valve unit 2 the pump yield corresponds to the fluid volume usefully passed to the consumers.

The advantage of such a system is that no power is unnecessarily consumed, as no partial flow is discharged against the actual load pressure. The hydraulic circuit of FIG. 17 represents a power match, where the input power and output power are in direct relationship.

A further variant is shown by a hydraulic diagram in FIG. 18. The control device is fully in accordance with the control device according to FIG. 17, with the difference that between the pressure regulating valve unit 1 and control valve unit 2a there is an additional intermediate unit 108, wherein the two pilot bores 70 and 71 are united to a single pilot bore 101. Pilot bore 101 opens in a piston bore 8a wherein a pressure reducing piston 28a is slidingly displaceable, similar to the construction of valve cartridges 8 and 9. In again similar manner said pressure reducing piston 28a forms a throttle orifice between pilot bore 101 and a pilot bore 102, the latter again opening into auxiliary bores 72a and 72b, as shown in FIGS. 6, 7 and 10.

This additional pressure reducing piston 28a, however, is not biased by a spring but by the armature of a control solenoid 100. By changing the current through the solenoid coil, the force exerted by the solenoid armature is also changed, and thereby the mechanical force on one end of pressure reducing piston 28a. By incorporation of a potentiometer in the electric circuit, through which the current through the solenoid is controllable between 0 and maximum, the mechanical force on the pressure reducing piston may also be controlled between 0 and maximum, and as this mechanical force determines the pressure difference between pump pressure and consumer pressure and thereby both the fluid volume passed to the consumer and the partial volume drained off via return port 5, the pump adjustment and, consequently, the pump delivery, have become a function of an electrical signal.

This electrical signal can in turn be made a function of the system pressure. To this effect it is possible to branch a control line 103 from the pump line, which is connected to a single-acting cylinder 104, wherein piston 105 is displaced by the pump pressure against the return action of a spring 106. The spring 106 should have a specific spring constant so that upon pressure build-up, piston 105 is correctively displaced. The linear stroke of piston 105 may thereby be transformed into a rotary motion by means of which the potentiometer 107 is adjusted.

At low pressure, piston 105 is fully in the retracted position and the resistance of potentiometer 107 is at its highest value. Upon increasing pressure, piston 105 is forced out against the action of spring 106, thus gradually decreasing the resistance of potentiometer 107, and increasing the current through solenoid 100. With increasing pump pressure there will be an increasing force of the armature of the solenoid, which causes decrease of the secondary consumer pressure feedback in pilot pressure chamber 52, as well as the pressure difference between pump and consumer and thereby the flow to the consumers, so that the volume returning from return port 5 increases. As a result the pump delivery will decrease as earlier explained and there will therefore be an adaption of the pump delivery to correspond to the volume passed to the consumers. The spring 106 in cylinder 104 should be so chosen that it is not compressed and piston 105 does not move upwards until a specific pump pressure is available. Up to this pressure the pump will provide the full delivery, in accordance with the available capacity of motor driving the pump 92. When exceeding said pressure, the piston 105 is forced out and therefore the potentiometer 107 is operated.

The solenoid 100 needs only to exert a small force, which force should correspond with the spring force of the spring 34 of valve cartridge 8 or 9 originally used.

A control device of this type is very useful for the hydraulic systems of fork lift trucks. Here the requirements are on the one hand that loads should be positioned very accurately and without shocks, which therefore requires an optimal control of all movements and which necessitates therefore the application of control devices with load-independent volume control. On the other hand it is wished that the speed with which heavy loads are lifted is automatically limited at a lower value, while light loads are to be lifted rapidly. This means in fact a load-dependent volume control with a controllable pump is to be preferred, as the purpose is optimal utilization of available motor capacity, which cannot be realized with a pump with constant yield in combination with a control device with pressure-compensated two-way or three-way volume control, as then the partial volume not used on the consumers is discharged against the prevailing load pressure.

The hydraulic system described above complies with the current requirements of manufacturers and users of fork lift trucks With increasing load pressure on one hand the pump delivery decreases to correspond with the available motor capacity, while on the other hand, under all pressure circumstances, within the limit of the available pump delivery, the volume passed to the consumers remains controllable within zero and maximum through the continued reduction of the pump delivery, always fully maintaining the complete control stroke of the control piston 10 of control valve units 2 (a,b,c, . . ).

It is possible to directly mount such a pressure measuring device or cylinder 104 in the intermediate unit 108 between pressure-influencing valve unit 1 and control valve unit 2a. By utilizing the outward stroke of piston 105 for changing the bias force of a control spring on a pressure reducing piston 28a, it is also possible to influence the pressure difference between pump pressure and consumer pressure and thereby the volume passed to the consumers.