GB2368039A

GB2368039A - Chain saw tensioning device

Info

Publication number: GB2368039A
Application number: GB0118633A
Authority: GB
Inventors: Mario Possamai
Original assignee: ALPINA SpA
Current assignee: ALPINA SpA
Priority date: 2000-10-17
Filing date: 2001-07-31
Publication date: 2002-04-24
Also published as: GB0118633D0; FR2815284A3; ES1049139Y; ES1049139U; ITVE20000042A1; FR2815284B3; DE20110562U1

Abstract

A tensioning device particularly for a power chain saw comprises a housing (2) and a guide bar (18) for a chain (14), said guide bar being displaceably axially secured to one end to the housing, characterised in that it comprises elastic means (36) urged so that their reaction causes the axial displacement of the guide bar in the sense of tensioning the chain.

Description

2368039 TENSIONING DEVICE PARTICULARLY FOR POWER CHAIN SAWS This invention

relates to a tensioning device particularly for power chain saws.

Power chain saws are known consisting of a casing provided with a handgrip and housing an electric motor or internal combustion engine, to the shaft of which there is fixed a sprocket wheel engaging a chain provided with teeth and guided in its rotation by a tensioning bar.

These power chain saws have however the drawback that with use, their chain tends to lose its degree of tensioning with consequent slackening This slackening on the one hand represents a danger for the operator as the chain could escape from its seat on the bar, and on the other hand could generate vibration which is annoying to the operator and causes working difficulties.

To eliminate this drawback it has been proposed to occasionally adjust the axial position of the tensioning bar and hence adjust the chain tension, using an adjustment screw which acts on a tensioning pin engaged in a hole provided in the bar.

This device has however the drawback that the adjustment is made subjectively and hence constant tensioning is not always ensured.

An object of the invention is to eliminate this drawback by providing a tensioning device for power chain saws which enables the tensioning to be adjusted to a predefined precise load in a simple and comfortable manner.

A further object of the invention is to provide a device which enables tensioning to be effected without requiring the use of particular tools.

These and further objects which will be apparent from the ensuing description are attained according to the invention by a tensioning device particularly for a power chain saw comprising a housing a tensioning device particularly for a power chain saw comprising a housing and a guide bar for a chain, said guide bar being displaceably axially secured to one end to the housing, characterised in that it comprises elastic means urged so that their reaction causes the axial displacement of the guide bar in the sense of tensioning the chain.

A preferred embodiment of the present invention is described in detail hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section through a power chain saw of the invention shown during its tensioning; Figure 2 shows it in the same view as Figure 1 but with the bar tensioned; and Figure 3 is a side view of a modified embodiment thereof.

As can be seen from the figures, the power chain saw of the invention comprises substantially a casing 2 provided with a handgrip (not shown in the drawings) and housing an electric motor 6 or internal combustion engine, to the transmission shaft 8 of which there is rigidly fixed a sprocket wheel 10 which engages the links 12 of a chain 14 provided with blades 16 and guided along a bar 18.

The bar comprises a slotted hole 20 through which there is inserted a bolt 22 with nut 46 for fixing a casing cover 24.

The bar 18 has a hole 26 in which there engages an appendix 30 provided at the end of an elastic strip 32 having its other end rigid with a shell-shaped slider 34 internally housing a coil spring 36 and sliding within a counter-shell 38.

Rigid with the shell there is a pin 40 which is slidable along a slotted hole 42 in, the casing cover and is provided with an operating knob 44.

The power chain saw of the invention operates in the following manner.

After removing the casing cover by disengaging the nut 46 the bar is inserted into the casing 2 and the casing cover is then applied.

At this point the knob 44 is operated in the direction which causes the spring 36 to compress and the appendix 30 of the strip 32 to engage in the hole 26 provided in the bar 18 The knob 44 is then released, with the result that the bar moves axially as a consequence of the elastic reaction of the spring, with consequent tensioning of the chain retained by it The nut 46 is then strongly tightened on the bolt 22 to ensure secure gripping of the bar by the two jaws.

When the chain tends to lose its tensioning effect it is sufficient to slacken the nut engaged on the bolt 22 with a traditional spanner to enable the elastic reaction of the spring to axially return the bar to its effective tensioning configuration.

From the aforegoing it is apparent that the tensioning device for power chain saws according to the invention presents numerous advantages and in particular:

it enables constant, precise and predefined tensioning to be effected, it enables this tensioning to be effected in a simple and comfortable manner.

In the modified embodiment shown in Figure 3, a lever 50 is applied by a pin 48 to the locking nut 46 for the bolt 22.

With this embodiment, the operating tool for the locking nut is always available, and can have a sufficient arm to reduce the locking force.

Claims

1 A tensioning device particularly for a power chain saw comprising a housing and a guide bar for a chain, said guide bar being displaceably axially secured to one end to the housing, characterised in that it comprises elastic means urged so that their reaction causes the axial displacement of the guide bar in the sense of tensioning the chain.

2 A tensioning device as claimed in Claim 1, characterised in that said adjustment means consists of a compressed coil spring housed in the interior of a telescopic shell, the movable part of which interacts with the bar.

3 A device as claimed in Claim 1, characterised in that to the movable part of the shell there is applied an elastic strip having its other end provided with an appendix engageable in a hole provided in the bar.

4 A device as claimed in Claim 2, characterised in that with the shell there is rigid a pin which is slidable along a slotted hole in the housing and is provided with an operating knob.

5 A tensioning device as claimed in Claim 1, characterised in that the housing consists of a casing and a casing cover which are connected together by a bolt which also engages in a slotted hole provided in the bar.

6 A device as claimed in Claim 5, characterised in that an operating lever is applied to the locking nut for the bolt.

7 A device substantially as hereinbefore described with reference to the accompanying drawings.