GB2034166A

GB2034166A - Hydraulic control device

Info

Publication number: GB2034166A
Application number: GB7938338A
Authority: GB
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1978-11-16
Filing date: 1979-11-06
Publication date: 1980-06-04
Also published as: DE2849704A1; FR2441750B1; FR2441750A1; GB2034166B; DE2849704C2

Abstract

The invention presents a hydraulic control device, more particularly for use in an agricultural machine having a hydraulic installation, comprising a spool valve for supplying pressure medium to a double-acting lift cylinder (12), the valve spool (2) being switchable into a plurality of selectable positions; namely Release (F), Lower (S), Neutral (N) and Lift (H), a spring (4) to return the valve spool to one selectable position at the end of a hydraulic operation, a cam form (35, 36, 37, 38) at one end of the valve spool (2), a non-return valve (21) in one feed line (17) to the lift cylinder (12), and a guide (25) connected to the non- return valve (21) and engaged by the cam form (35, 36, 37, 38), so arranged that in all but one selectable position the non-return valve (21) is held open. <IMAGE>

Description

SPECIFICATION Hydraulic control device This invention relates to a hydraulic control device, more particularly for use in an agricultural machine having a hydraulic installation, comprising a spool valve for supplying pressure medium to a double-acting lift cylinder, the valve spool being switchable into a plurality of selectable positions, namely Release (F), Lower (S), Neutral (N) and Lift (H), and a spring to return the valve spool to one selectable position at the end of a hydraulic operation.

Modern tractors are generally provided with a plurality of attachments and lifting devices for hydraulic accessories which require a corresponding number of hydraulic control devices for their operation. In addition, many attachments and self-propelled agricultural units are provided with hydraulic equipment requiring hydraulic control gear. The problem which then arises is that, for example, control devices with only one connection sealed with respect to the cylinder and one floating position are unsuitable for use with a double-acting cylinder because the second cylinder connection is absent. On the other hand, in control devices for double-acting cylinders, as are essential for operating front-end power lift devices, the cylinder connection sealed by a valve is absent.The manufacturers of various types of control devices must, however, not only meet the high cost of manufacture but also face further drawbacks such as, for example, greater difficulty in obtaining spare parts and the provision of a stock requiring much outlay.

The invention aims to create a control device of the kind outlined above which avoids the drawbacks referred to and which, using simple means, is suitable for hyraulic systems with double-acting and single-acting lift cylinders, and with at least one cylinder connection being sealed by a valve.

The invention achieves this aim by providing a hydraulic control device, more particularly for use in an agricultural machine having a hydraulic installation, comprising a spool valve for supplying pressure medium to a double-acting lift cylinder, the valve spool being switchable into a plurality of selectable positions, namely Release (F), Lower (S), Neutral (N) and Lift (H), a spring to return the valve spool to one selectable position at the end of a hydraulic operation, a cam form at one end of the valve spool, a non-return valve in one feed line to the lift cylinder, and a guide connected to the non-return valve and engaged by the cam form, so arranged that in all but one selectable position the non-return valve is held open.

A control device having these features can be produced relatively simply and is equally suitable for hydraulic appliances with single-acting or double-acting lift cylinders. The non-return valve prevents a falling off in the load on the load side due to leakage at the valve spool even with double-acting cylinders.

In a further development of the invention, the valve spool is arranged to be axially centered by the spring in the selected position N. The guide is inactive with respect to the valve spool in this position and the non-return valve is closed.

In another advantageous further embodiment of the invention, the guide and the non-return valve are arranged in series and have a common load-applying spring. It is here advantageous if the guide and the non-return valve are an integral unit.

To facilitate maintenance and repair work it is beneficialjor the unit comprising the guide and the non-return valve to be so designed and disposed in the control device housing as to be accessible from the outside.

In order to return the valve spool automatically after it has initiated a lift cylinder lifting operation, in the selected position H, the guide, in accordance with the invention, is connected to the pressure medium pump via the valve spool and a second non-return valve fitted immediately ahead of the valve spool is connected to the pump.

Erroneous hydraulic switching of the guide is prevented by the second non-return valve being arranged to be shut off from the pressure medium pump in the selected positions N and F.

To make a sensitive actuation of the spool available despite appropriate spring loading of the guide, it is advantageous to arrange a further annular valve body on the lift valve body in axially displaceable manner. This further valve body has an internal seat for the valve body seated in it and an external conical structure forming a second non-return valve with a corresponding seat in the housing, which closes in the same sense. Further, a weaker spring engages in the annular valve body to act against the stronger spring of the inner valve body. Finally, the spring-loaded side of the annular valve body is arranged on the pump side and the other side of the valve body is arranged to be on the cylinder side.It is especially advantageous if the movement of the spring acting against the spring applying a load to the inner valve body or the guide when the cylinder is relieved of pressure is limited to a value less than the total valve spool disengagement travel of the guide.

Two examples of hydraulic control devices in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional view through one form of hydraulic control device according to the invention with a combination of guide and non-return valve; and Figures 2 to 4 are sectional views through a second form of hydraulic control device showing the guide and non-return valve in three selected positions.

The control device illustrated in Figure 1 has a controlling sliding valve spool 2 which by means of a hand lever 3 can be moved to the left into the position H "Lift" and to the right into the Position S "Lower" and the position F "Release" from the selected position N "Neutral" shown. Five annular spaces 5, 6, 7, 8 and 9 are provided in the housing 1 of the control device. Two of these spaces, 6 and 8, are connected to a pressure medium pump (not shown), while the annular space 7 is connected to a pressure medium reservoir (also not shown). A line 10 connects the annular space 9 to one end 11 of a double-acting lift cylinder 12.

From the annular space 5 a duct 14 leads to one side of a non-return valve 1 5 inside the housing 1.

A duct 1 6 on the other side of the non-return valve 1 5 and a line 17 lead to the other end 18 of the lift cylinder. The spool 2 has two annular grooves 1 9 and 20 which, in the Neutral position shown, connect the annular spaces 6, 7 and 8 to one another. The spring 4 is arranged and adjusted such that in each case it returns the valve spool 2 to Neutral when it is released.

The non-return valve 1 5 comprises a conical valve body 21 whose seat is arranged in the housing 1 between the two ducts 14 and 1 6. A spring 22 acting on the valve body 21 in the sense of effecting closure is supported by an abutment in a detachable housing lid 23. A guide 25 is rigidly joined to the non-return valve 1 5 by connecting member 26. The guide 25 comprises a cylindrical body 28 and a co-axial cylindrical body 29 of larger diameter guided in the housing 1, and these bodies are separated from one another by an annular groove 27. The annular groove 27 communicates with an annular space 30 connected to a second non-return valve 31.An axial bore 32 through the guide 25 and the nonreturn valve 1 5 connects its space 33 on the spring side behind the valve body 21 to a space 34 which, in turn, communicates with the return flow. In addition, the bore 32 communicates with the annular space 30 via a restriction 32a. Four notches or the like 35,36, 37 and 38 for the selectable positions F, S, N and H are provided on the spool 2 for the guide 25 to engage in. The notch 37 for the Neutral position shown is of such a nature that in the end-position shown the guide 25 does not touch the spool 2 when the nonreturn valve is closed. A line 30 connects the second non-return valve for the hydraulic actuation of the guide 25 to the annular space 30 and a line 40 connects it to the duct 14.

In the Neutral position shown, the line 10 leading to the said one end of the lift cylinder 1 2 is shut off from the return flow by the valve spool 2, while the line 1 7 connected to the load pressure end 18 of the cylinder 12 is shut off in leakagefree manner by the non-return valve 1 5 closed in this position by the force of the spring 22 and the action of the pressure medium. The advantage which results is that a load acting on the piston of the lift cylinder remains in its given position. The pressure medium conveyed into the annular spaces 6 and 8 of the control device by the pressure medium pump in-the Neutral position immediately returns to the reservoir through the annular space 7.

In the selected Neutral position of the valve spool 2, this member shuts off the duct 14 from the return flow so that, for example, pressure built up in the return flow region by a directional valve does not affect the second non-return valve 31 or the guide 25.

When the valve spool 2 is moved to the left in the drawing into the selection position H by the hand lever 3, the annular spaces 6 and 8 are, on the one hand, shut off from the annular space 7 and, on the other hand, the annular space 6 is connected to the duct 14. At the same time the line 10 is connected to the return flow via space 34. Moving the spool 2 to the left moves the guide 25 axially towards the spring 22 and the valve body 21 of the non-return valve 15 is opened, thus causing pressure medium to pass through the line 1 7 to the said other end 1 8 of the lift cylinder 1 2. Consequently, the lift cylinder piston is raised and displaces pressure medium from the end 11 through the line 10 and the space 34 into the reservoir. The guide 25 is positioned in the catch 38 in the selected position H.As soon as a predetermined pressure has been reached in the pressure-side line system behind the spool 2 and, hence, also at the second non-return valve 31, the second non-return valve 31 opens, and the guide 25 is moved towards the spring 22 when acted upon in the region of the annular groove 27. Thus, the guide 25 is disengaged from the catch 38 and releases the spool 2, causing it to be returned to Neutral by its spring 4. Appropriate tuning of the second non-return valve 31 means that the hydraulic action of the guide 25 is always brief.

The guide therefore returns to the starting position determined by the force of the spring 22 after each actuation, thus also closing the non-return valve 1 5.

When the valve spool 2 is moved to the right in the drawing from Neutral, it reaches selectable positon S when catch 36 engages guide 25. In this selectable position the sliding valve spool connects, on the one hand, duct 14 to the return flow and, on the other hand, annular space 8 to annular space 9. Pressure medium can now pass to the end 11 of the lift cylinder 12 from the pressure medium pump through the named annular spaces and the following-on line 10. In order to reach the required pressure in annular space 8, annular spaces 6 and 8 are shut offfrom the return flow side annular space 7 in the selectable position S. During movement of the valve spool 2 from N to S the guide 25 moves axially towards spring 22 and also opens valve 1 5.

Pressure medium displaced from the end 1 8 of the lift cylinder 12 can then reach the space 34 connected to the return flow via the line 1 7 and the ducts 1 6, 14.

When the valve spool 2 is moved even further to the right in the drawing from the seiectable position S, the guide 25 ultimately engages in the catch 35 to reach the selectable position F. The connection between the two annular spaces 6 and 7 is then blocked, while the other annular space 8 communicating with the pressure medium pump is connected to the annular space 7 leading to the reservoir. Also, in the selectable position F the non-return valve 1 5 is open due to the action of the spool 2 on the guide 25, thus connecting the end 1 8 of the lift cylinder 12 to the reservoir line 17, ducts 14, 16 ancl space 34. In the same way the end 11 of the lift cylinder 12 communicates with the reservoir via lines 10 and 14, so that the piston of the lift cylinder 12 is free to move in either direction.

Figures 2 to 4 show a structurally different embodiment comprising a guide 41 and a double valve 42. The structural unit 41,42 is so constructed that it can straight-forwardly take the place of the structural unit 15,25 of Figure 1.

Equivalent parts have therefore been given the same reference numerals as are used in Figure 1.

The shape of the guide 41 substantially matches that of Figure 1, while the double valve 43 has an inner valve body 43 and an annular valve body 44 surrounding and displaceable over the inner body.

A conical sealing surface 45 having its seat 46 in the annular valve body 44 is provided for the inner valve body 43. In the same way the valve body 44 has an external conical sealing surface 47 having its seat 48 in the housing 1. The valve body 44 is sealingly urged against the valve body 43 by a spring 49 supported in the housing 1. An end member 50 constructed integrally with the inner valve body 43 is supported on a spring 52 via a spring plate. The spring 52 is seated in a valve cover 53 which is releasably connected to the housing 1 in a manner not illustrated, and is sealed with respect to the outside atmosphere. It is made stronger than the spring 49.

When the valve spool 2 is moved from the selectable position N shown in Figure 2 to the right as in Figure 3, for example, the axial displacement of the guide 41 and of the valve 41 initially lifts the valve body 43 from its seat 46, thus giving equal pressure on both sides of the valve body 43. This is the case, for example, in the position of the guide 41 and the valve 42 shown in Figure 3. When the pressure is equalized at the valve 42, the spring 49 engaging the valve body 44 in the sense of effecting closure acts counter to the spring 52 effecting closure at the valve body 43 and imposing a load on the guide 41. This reduces the total spring force acting on the guide 41 ,so that the valve spo.ol 2 is sensitively actuable to move from the selectable position N ;nto the adjacent selectable position. Following a movement of the guide 41 corresponding to the ) radial position of the valve spool 2 shown in Figure 4, the back of the valve body 44 makes contact with a stationary surface 54 serving as an abutment. As a result, the action of the spring 49 opposing the spring 52 is eliminated so that, when j the guide 41 is moved axially beyond the position shown in Figure 4, only the stronger spring acts. In this way a reliable locking engagement in the selectable positions is ensured, despite a sensitive operation of the valve spool 2.

Claims

1. A hydraulic control device, more particularly for use in an agricultural machine having a hydraulic installation, comprising a spool valve for supplying pressure medium to a double-acting lifting cylinder, the valve spool being switchable into a plurality of selectable positions, namely Release (F), Lower (S), Neutral (N) and Lift (H), a spring to return the valve spool to one selectable position at the end of a hydraulic operation a cam form at one end of the valve spool, a non-return valve in one feed line to the lift cylinder, and a guide connected to the non-return valve and engaged by the cam form, so arranged that in all but one selectable position the non-return valve is held open.

2. A device according to claim 1, in which, in the selectable position N, the spring moves the valve spool into its central axis position, the guide is inactive with respect to the valve spool, and the non-return valve is closed.

3. A device according to claim 1 or claim 2, in which the guide and the non-return valve are arranged in series and have a common loadapplying spring.

4. A device according to any preceding claim, in which the guide and the non-return valve are formed as an integral unit.

5. A device according to claim 4, in which the integral unit comprising the guide and the nonreturn valve is so disposed in the control device housing as to be accessible from the outside.

6. A device according to any preceding claim, in which, in the selectable position H, the guide is in hydraulic actuation communication with the pressure medium pump via the valve spool and a second non-return valve connected immediately upsteam of the guide.

7. A device according to any preceding claim, in which the second non-return valve for the guide is shut off from the pressure medium pump in the selected positions N and F.

8. A device according to any preceding claim, in which an annular valve body is arranged on the valve body of the non-return valve to be axially displaceable, internally has a seat for the inner valve body and externally by means of a conical structure with a corresponding seat in the housing forms a second non-return valve which closes in the same sense, in which a spring engages the annular valve body with less force against the load-imposing spring of the inner valve body or the guide, and in which the spring-loaded side of the annular valve body is arranged on the pump side and the other side of the valve body is arranged on the lift cylinder side.

9. A device according to any preceding claim, in which the movement of the.spring acting counter to the load-imposing spring of the inner valve body or the guide when the cylinder is relieved of pressure is limited to a value less than the total travel of the guide effecting disengagement of the valve spool.

1 0. A hydraulic control device, more particularly for use in an agricultural machine having a hydraulic installation, constructed and arranged substantially as herein described, with reference to and as illustrated in the accompanying drawings.