WO1994020778A1

WO1994020778A1 - One-way valve for automatic or manual actuation in holders for chain-saw guidebars

Info

Publication number: WO1994020778A1
Application number: PCT/SE1994/000162
Authority: WO
Inventors: Per-Olov LÖFGREN
Original assignee: Sandvik Ab
Priority date: 1993-03-02
Filing date: 1994-02-28
Publication date: 1994-09-15
Also published as: AU6223994A; SE9300692L; SE500995C2; SE9300692D0

Abstract

Valve for hydraulic systems, especially tensioning systems for chain saw machines, connected to one input channel (18) and one output channel (19), comprising a housing, a spring-loaded lower body (11) which in normal one-way position blocks fluid flow from the output channel to the input channel and in open position allows flow in any direction, and a spring-loaded middle body (12) which in closed position blocks all fluid flow, and where the valve can be repositioned from one-way position to open position and to closed position under influence of a manually adjustable device (17) as well as automatically influenced by pressure changes in the output channel (19).

Description

ONE-WAY VALVE FOR AUTOMATIC OR MANUAL ACTUATION IN HOLDERS FOR CHAIN-SAW GUIDEBARS

Background

One-way valves where a fluid can only flow in one direction are common components in hydraulic systems, and one-way valves which can be manually changed to other functions are also known. One example is the patent SE 467 488 describing a holder for chain saw guidebars comprising a one-way valve manually changeable to both directions open or both directions closed.

In some applications is is desired to have a one-way valve which is automatically changed to open or closed function in response to certain pressure changes on the output side of the valve.

The present invention concerns a one-way valve, which can be manually changed to open or closed position, and which is automatically changed to open position by slow pressure increase on the output side, and automatically changed to closed position by rapid pressure increase on the output side.

One application of such valves is in holders for chain saw guidebars, made as separate items as described in SE 467 488 or integral with the power unit of the chain saw. Such valves can also be used in other applications such as clamping of tools or workpieces.

Description

The valve is described with reference to the drawings showing cross-sections of the valve in different positions, where figure 1 shows a normal working position as a one¬ way valve, figure 2 an automatically open position, figure 3 an automatically closed position, figure 4 a manually ope position and figure 5 a manually closed position. A valve according to the invention comprises a housing without mobile components, made as part of a larger element or as a separate unit lodged in the larger element. The housing is connected to an input channel (18) with substantially constant pressure, and to an output channel (19) leading to a mobile part, the motion of which is to be controlled by the valve. The pressure in the output channel will then depend on the motion and working conditions of that part. One example of such a part is a hydraulic cylinder for maintaining the chain tension by moving the guidebar of a chain saw in a tree harvesting machine.

In a lower room (23) in the valve housing is located a mobile lower body (11) which may be shaped as a sphere. In the one-way position shown in figure 1 it is pressed agains a sealing seat in the housing by a lower spring (24) .

If the fluid pressure in the output channel (19) is reduced because elongation of the chain has reduced the chain tension, the pressure in the lower room (23) is also reduced. The fluid pressure in the input channel (18) will then overcome the force of the lower spring (24) , force the lower body (11) from its seat and allow fluid to pass through the lower room (23) , a narrow channel (22) and the output channel (19) to the hydraulic cylinder to tension th chain. When the correct tension is reached, the pressure rises in the lower room (23) , and the lower body (11) seals again against the housing as in figure 1.

Above the lower body (11) is a mobile middle body (12) acte upon by a middle spring (15) , and a mobile upper body (16) the mobility of which can be restricted by a manually adjustable device such as an excentric arm (17) . Alternatively, the mobile upper body (16) could be substituted by a narrow extension of the middle body (12) , although that would cause some difficulty in assembly.

If the pressure in the output channel (19) increases above the pressure in the input channel (18) when a heat expanded chain cools, the pressure in an upper room (21) will also increase, and with a larger area in the upper room (21) tha at the seat of the lower body (11) , the middle body (12) will be forced down, pushing the lower body (11) away from its seat by means of an extension (14) as shown in figure 2 to allow some fluid to flow back past the lower body (11) into the input channel (18) . This allows the guidebar to move back some distance to lower the chain tension.

When the pressures in the output channel (19) and the input channel (18) are equalized, the lower spring (24) will lift the lower body, and the middle spring (15) will lift the middle body (12) to the normal one-way working position shown in figure 1.

If the pressure increase in the output channel is large and rapid, the pressure rise in the upper room (21) will be high and rapid since the connecting passage (20) is wide, while the pressure rise in the lower room (23) will be moderate and slow, since the fluid will be slowed down by the narrow channel (22) . The resulting force on the middle body (12) will be large enough to compress both the lower and middle springs (24,15) to make a taper surface (13) on the underside of the middle body (12) seal against a seat i the housing as shown in figure 3. In this automatically closed position the guidebar has only moved a very short distance and no fluid can flow back to the input channel (18) . This sequence of events can occur if the nose end of the guidebar hits a solid obstacle, or if the chain _sis stopped by foreign objects in the timber. In such cases th force might become as large as the chain will stand, but the chain will remain on the guidebar.

When the excess pressure in the output channel no longer increases, the pressure in the lower room (23) will reach the same level as in the upper room (21) , the springs (15,24) will raise the lower and middle bodies (11,12) fir to the automatically open position in figure 2, then to the one-way position of figure 1.

Open and closed positions can also be manually selected by manually adjustable device such as an excentric arm (17) . manually open position as shown in figure 4 is used to allo pushing the guidebar inward to relax the chain as a first step in removal of the chain for service.

A manually closed position as shown in figure 5 is used to lock the guidebar in a pushed-in position with relaxed chai as a following step in removal of the chain and replacement with a new chain. In this position, the sealing of the tape part (13) of the middle body (12) against the housing prevents fluid flow through the valve in any direction.

In the above description, the words upper, lower, up and down have been used with reference to the figures, and not with reference to how the valve is located or held in the machine, during assembly or in use.

Claims

1. Valve for hydraulic systems connected to one output channel (19) and one input channel (18) and comprising a spring-loaded lower body (11) which in normal one-way working position blocks fluid flow from the output channel (19) to the input channel (18) but not in the other direction, and in an open position allows fluid flow in any direction, and a middle body (12) which in a closed positio blocks all fluid flow, c h a r a c t e r i z e d by the lower body (11) being able to move to the open position and the middle body (12) being able to move to the closed position under influence of a manually adjustable device (17) as well as under influence of pressure changes in an upper room (21) connected to the output channel (19) .

2. Valve according to claim 1, c h a r a c t e r i z e d by the upper room (21) being connected to the output channe (19) through a wide channel (20), and a lower room (23) containing the lower body (11) being connected to the outpu channel (19) through a narrow channel (22) , causing rapid pressure increases in the output channel to move the lower body (11) to the open position and the middle body (12) to the closed position, and causing slow pressure increases to move only the lower body (11) to the open position.

3. Valve according to clain 1 or 2, c h a r a c t e r i z e d by the manually adjustable devic (17) being an excentric arm.

4. Valve according to claim 1 or 2, c h a r a c t e r i z e d by the lower body (11) being a sphere .

5. Valve according to claim 1 or 2, c h a r a c t e r i z e d by being part of a machine for felling timber with a chain saw, and by the pressure in the output channel (19) depending on the tension force in the saw chain.