GB2205385A

GB2205385A - Improvements in a load holding and control valve, in particular for hydraulic circuits with either open or closed centre directional control valve

Info

Publication number: GB2205385A
Application number: GB08811170A
Authority: GB
Inventors: Andrea Storci
Original assignee: Oil Control SpA
Current assignee: Oil Control SpA
Priority date: 1987-05-15
Filing date: 1988-05-11
Publication date: 1988-12-07
Anticipated expiration: 2008-05-11
Also published as: IT213216Z2; GB8811170D0; IT8728950V0; GB2205385B

Abstract

A load holding and control valve for a hydraulic actuator enables operation with either open or closed centre directional control, and comprises a coaxially - arranged check valve 19 and a pressure - operable valve 18 having therethrough a bore 32 which may be closed by one end of a coaxial needle valve 31 whose other end is also exposed to pressure. In a further embodiment (figs. 4, 5) two such assemblies are coaxially arranged to share a single needle valve. <IMAGE>

Description

AN IMPROVED LOAD HOLDING AND CONTROL VALVE SUITABLE IN PARTICULAR FOR HYDRAULIC CIRCUITS WITH OPEN OR CLOSED CENTRE DIRECTIONAL CONTROL VALVE The invention relates to improvements in a load holding and control valve, suitable in particular for hydraulic circuits with either open or closed centre directional control valve.

Such improvements concern the construction of a type of hydraulic valve used in conjuction with hydrautic actuators to hold and control descending loads.

Valves of the kind are widely adopted in hydraulic circuits to control flow exhausted from the bottom chamber of a hydraulic actuator, and are provided with first and second passages, as shown in fig 1; the first passage admits oil under pressure from the pump, and incorporates a check valve, whilst the second, the return passage, incorporates a counterbalance valve of conventional design.

A control valve of the type in question is disclosed in Italian patent no 199059, property of the same applicant; the component parts are all housed in a bore formed coaxially in the valve body, and use is made of a pilot piston to enable closed centre type operation. The body also incorporates passages to relieve backpressure, produced when the directional control valve is closed.

While conventional in embodiment, and affording a considerable improvement over valves embraced by the art prior thereto, this previous valve nonetheless exhibits certain structural complexities deriving from the fact that the backpressure relief passages are located parallel to the main bore accommodating the valve parts, and from the need to incorporate a pilot piston for closed centre operation.

Accordingly, the object of the invention is one of producing a simpler embodiment of the type of valve in question.

The improved valve affords the particular advantage of being easily convertible to the end of providing a dual version that will control the flow exhausted from both chambers of a hydraulic actuator.

The stated object is realized with an improved load holding and control valve according to the present invention, which is of the type commonly utilized in hydraulic circuits with first and second oil lines connecting the work ports of a directional control valve to the respective first and second chambers of an actuator, and comprises: a first passage through which oil flows under pressure to the first chamber of the actuator to raise the load; a second passage through which oil returns from the first chamber of the actuator as the load descends; a check valve and a counterbalance valve, connected respectively with the first passage and the second passage, the parts of which, in accordance with a type of embodiment disclosed in Italian patent no 199059, are housed coaxially in a first bore passing through the body of the valve; and an arrangement whereby the element of a counterbalance valve installed on the first oil line of the circuit is piloted to open by pressure diverted from the second oil line, and viceversa.

The improved valve according to the invention is characterized in that it comprises: a second bore passing through the counterbalance valve element, which causes a first part of the valve, connecting with the directional control valve, to communicate with a second part of the valve in receipt of pilot pressure; a needle, accommodated by and axially slidable internally of a seat coaxial with the end of the second bore that emerges into the second part of the valve, one end of which is exposed to pilot pressure, its remaining end embodied and positioned such as to insert partly into and block the mouth of the bore offered to the second part of the valve.

The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: fig 1 is a hydraulic circuit diagram illustrating the improved valve; fig 2 is a section illustrating an embodiment of the improved valve; fig 3 is the section through III-III in fig 2-; fig 4 is a hydraulic circuit diagram illustrating the dual version of the improved valve; fig 5 is a section illustrating an embodiment of the dual version of the improved valve.

The improved valve disclosed is used to hold and control the descent of a load manoeuvred by means of a hydraulic actuator 1; the actuator receives oil at high pressure from a directional control valve 2, which is a closed centre type in the case of the drawings.

In the example of fig 1, the improved valve affords a first passage 3, incorporating a check valve 4, and a second passage denoted 5. Oil is allowed to flow under pressure from the directional control valve 2 into the first passage 3 and through a first line 7 toward the first chamber la of the actuator, in order to raise the load. The second passage leads into a counterbalance valve 6, which is piloted to open by the pressure of flow directed from the pump through a second line 8 to the second chamber ib of the actuator during descent of the load; the opening movement of the valve 6, which allows a controlled return of the oil exhausted from the first chamber Ia to the directional control valve 2, is triggered by the pressure of the oil exhausting through the passage 5 immediately upstream, and offset by a bias spring 17.

It will be seen from fig 1 that the two passages 3 and 5 are installed in parallel on the first line 7 of the hydraulic circuit, and more exactly, between a branch denoted 7a connecting with the directional control valve 2, and a branch denoted 7b connecting with the actuator.

In similar fashion to the valve disclosed in Italian patent nO 199059, the body 14 of the improved valve affords a first bore 12, passing through from end to end and exhibiting sections of varying diameter.

The bore 12 has a first threaded end 15, occupied by a device 16 serving to preload the bias spring 17 in its housing; the second and opposite end 15a is also threaded, and stopped by a plug 30. The element 18 of the counterbalance valve 6 is accommodated by the bore 12, and comprises a first cylindrical section -18a, a second cylindrical section 18c of diameter smaller than that of the first, and a section 18b of frusto-conical shape interconnecting the first and second sections; the element 18 also exhibits a third cylindrical section 18d of diameter smaller than the first 18a and greater than the second 18c, which slides fluid-tight internally of the bore 12 and creates a differential frontal area exposed to the pressure of the oil exhausted from the actuator during the descent manoeuvre.

The element 19 of the check valve 4 is annular in shape, and breasted slidably with the inside of the bore 12 in a fluid-tight fit, encircling the second section 18c of the counterbalance valve element. The annular element 19 is biased by a return spring 20 toward the frusto-conical section 18b of the counter balance element 18, which thus constitutes the seat of the check valve 4. The differential frontal area referred to above does not reflect the difference between cylindrical sections 18a and 18b as might be supposed, but that between the area afforded by the seat of the annular element 19 and the area of the third cylindrical section 18d.

10 denotes a first externally accessible threaded port disposed perpendicular to the bore 12; the port merges with the bore 12 near to its first end 15, and is connected with one of the work ports of the directional control valve 2 by way of the branch of the first oil line denoted 7a. 11 denotes a second threaded port, likewise externally accessible and disposed perpendicular to the bore 12, which merges with the bore at a point coinciding with the second cylindrical section 18c of the counterbalance valve element; this second port 11 connects with the first chamber la of the actuator by way of the branch of the first oil line denoted 7b.

9 denotes a third externally accessible threaded port, incorporated into the plug 30 and teed into the second oil line 8 of the hydraulic circuit that connects the second chamber 1b of the actuator with the remaining work port of the directional control valve 2. The bore 12 is embodied with a number of axially disposed projections 25 located near to the junction with the first threaded port 10, internally of which a fourth section 27 of the counterbalance valve element 18 is accommodated slidably to an exact fit; the diameter of this fourth section 27 is greater than that of all the remaining sections of the element 18.

The improved valve also comprises a second bore 32, passing through the counterbalance valve element 18, which connects a first part of the valve associated with the directional control valve, i.e. the first port 10, and a second part of the valve, namely that exposed to pilot pressure, i.e. the butt end of the third cylindrical section 18d of the counterbalance valve element. 31 denotes a needle, accommodated by and axially slidable internally of a seat 34 coaxial with the second bore 32, one end of which is subject to pilot pressure admitted through the port 9 in the plug 30; the remaining end of the needle is embodied and positioned such as to insert partly into and block the mouth of the bore 32 that opens onto the second part of the valve. 35 denotes a stem, one end of which is rigidly and coaxially attached to the end of the counterbalance valve element occupying the first part of the valve, i.e. that connecting with the directional control valve (the left hand end as viewed in fig 2); the remaining end of the stem 35 penetrates a vented cavity 36a fashioned in a plug 36 forming part of the device 16 by which the bias spring 17 is loaded. The function of the stem 35 is to ensure a tight seal between the cavity 36a and the remainder of the valve.

The cross sectional area of the stem is calculated such that the area of the counterbalance element 18 occupying the first part of the valve and exposed to pressure from the directional control valve, i.e.

the left hand end of the element 18 directly exposed to backpressure through the first port 10, is made equal to the area of the selfsame element 18 exposed to similar pressure in the second part of the valve, i.e. the cylindrical section denoted 18d. In short, the cross sectional area of the stem 35 is equal to the difference between the area of the seat offered to the annular check element 19 and the area of the third cylindrical section 18d of the counterbalance element. Accordingly, with backpressure registering through the first port 10 as the directional control valve closes, the force on the counterbalance valve element will remain identical in both the opening and closing directions; operation of the improved valve therefore remains unaffected by such pressure.

Eliminating the plug 30, it becomes possible to combine two valves, identical in embodiment and in operation to that already described, and thus create a dual package that will control flow exhausted through both lines of the circuit; this dual version of the valve would utilize a single needle 31 having both ends embodied and positioned so that each will insert partly into and block the mouth of the second bore 32 opening onto the second part of the relative single valve.

Fig 5 illustrates an embodiment of the dual version of the valve, which is incorporated into a single body; identical components in the two single valves are denoted by a common reference number, with the addition of an apostrophe to distinguish the right hand valve from the left hand. The hydraulic circuit diagram of fig 4 illustrates how the valve of fig 5 is integrated into a circuit for which load control is required on both return lines.

The option exists of embodying the valve without the stem 35 whether in single or dual version, though at the expense of sacrificing faultless closed centre operation; nonetheless, one retains the considerable advantages of simplified construction obtained by incorporating the second bore 32 and the needle 31, esepcially in case of the dual version.

Operation of the improved valve with an open centre directional control valve remains identical in all respects to that described in aforementioned Italian patent nO 199059.

In closed centre operation, backpressure generated downstream of the valve and registering through the first port 10 would, if not released, cause the counterbalance valve element 18 to close and block the outlet; instead, pressure is diverted through the element 18 to its rear end 18d, with the result that the needle 31 shifts, opening the second bore 32 and blocking the port 9 in the plug 30 at one and the same time. Exhausted backpressure thus invests the rear end of the counterbalance valve element 18, urging it toward the open position and offsetting the inlet pressure that urges it toward the closed position; accordingly, the valve is prevented from blocking completely.

Any hazardous pressure peaks will be vented by the relief valve 36 installed on the first oil line 7.

The dual valve of fig 5 functions in precisely the same way; with an open centre directional control valve, pilot pressure generated from one line of the circuit is directed into the section of the valve connecting with the other line by way of the second bore 32 or 32' and the seat occupied by the needle.

In the case of closed centre operation, backpressure exhausting from either valve is transmitted by way of the relative second bore 32 to the rear end of the counterbalance valve element, as described with reference to figs 1 and 2, the needle 31 in this instance serving to block the second bore 32 or 32' of the other valve.

Claims

1) An improved load holding and control valve suitable in particular for hydraulic circuits with open or closed centre directional control valves (2), and of the type commonly used in hydraulic circuits with first and second oil lines (7,.8) connecting the work ports of a directional control valve to the respective first and second chambers (la, 1b) of an actuator (1), comprising:: -a first passage (3) through which oil flows under pressure to the first chamber (1a) of the actuator to raise the load; -a second passage (5) through which oil returns from the first chamber (1a) of the actuator as the load descends; -a check valve (4) and a counterbalance valve (6), connected respectively with the first passage and the second passage, the parts of which, according to a type of embodiment disclosed in Italian patent nO 199059, are housed coaxially in a first bore (12) passing through the body (14) of the valve; and -an arrangement whereby the element (18) of acounter balance valve installed on the first oil line (7) of the circuit is piloted to open by pressure diverted from the second oil line (8), and viceversa; characterized...

...in that it comprises: -a second bore (32) passing through the counter balance valve element, which causes a first part of the valve, connecting with the directional control valve, to communicate with a second part of the valve in receipt of pilot pressure; and -a needle (31), accommodated by and axially stidable internally of a seat (34) coaxial with the end of the second bore that emerges into the second part of the valve, one end of which is exposed to pilot pressure, its remaining end embodied and positioned such as to insert partly into and block the mouth of the second bore offered to the second part of the valve.

2) A valve as in claim 1, comprising a stem (35), one end of which is rigidly and coaxially attached to the end of the counterbalance valve element (18) that occupies the first part of the valve connected with the directional control valve, the remaining end insertable in a vented cavity (36a) exposed to atmospheric pressure; wherein the cross sectional area of the stem (35) is such that the area of the counterbalance valve element occupying the first part of the valve and exposed to pressure from the directional control valve, will be equal to another area of the same element exposed to similar pressure registering in the second part of the valve.

3) A valve as in claim 2, comprising a plug (36) with a vented cavity (36a) into which the unattached end of the stem inserts to a fluid-tight fit.

4) An improved load holding and control valve suitable for hydraulic circuits with either open or closed centre directional control valves, substantially as described and illustrated in the foregoing and as intended for the object stated.