GB2076891A - Combustion-powered fastener- driving tool - Google Patents

Abstract

Propane at a relatively low pressure and oxygen at a higher pressure are fed successively to combustion chamber 31 by way of duct 21, in which is closing valve 25, and duct 22 respectively, under the control of slide valve 13 which is coupled, by lateral arm 12 with an axially displaceable fastener guide tube 11 protruding at the muzzle of the tool and aligned with shaft 4 of piston 3. Upon pressing-in of the tube 11 when the tool is pressed against fastener-receiving material, recess 46 registers with nose 42a of trigger 42 to allow the latter to be actuated to supply ignition current to plug 37 and initiate combustion of the propane/oxygen mixture, thereby to drive the piston 3 and a fastener 48 previously loaded into the tube 11. <IMAGE>

Description

SPECIFICATION Combustion-powered fastener-driving tool This invention relates to a combustion-powered fastener-driving tool comprising a guide cylinder, a working piston which is driven by the combustion pressure of a gas mixture, a combustion chamber which adjoins the guide cylinder contrary to the driving direction of the working piston, an ignition device, associated with the combustion chamber, for the gas mixture, a control slide valve which provides for successive flowing-in of two mixture components into the combustion chamber and which is provided with feed pipes for the mixture components which are under different pressures, and a check valve in an intake channel between the control slide valve and the combustion chamber.

In a known combustion-powered fastener-driving tool, which serves, for example for driving nails into receiving materals, a gas mixture, consisting of propane and air, is used to drive the working piston.

The gas mixture, kept ready under a charging pressure in a combustion chamber, is ignited by electrical ignition or by means of a glow plug. The combustion pressure which builds up opens a mains valve which seals the combustion chamber against the cylinder chamber, whereupon the combustion pressure acts upon a rear end surface of the working piston and the latter is accelerated forwardly in the guide cylinder, to effect a driving-in operation, towards the receiving material.

The gas mixture arises as a result of separate consecutive admission of the two mixture components at different pressures into the combustion chamber, which is accomplished by a controal slide valve. In order to prevent any flooding back of the gas mixture which is present in the combustion chamber, more especially upon the occurrence of the high combustion pressure, into the intake channel between the control slide valve and the combustion chamber, a check valve is provided.

The propane, which is at a lower pressure in eomparison with the air, passes into a storage chamber prior to admission into the combustion chamber. The effect of this storage chamber is, inter alia, to ensure that part of the gas mixture which has built upon forming the mixture and which remains in the intake channel after closing of the check valve, and the pressure of which corresponds to that of the air, does not flow into the propane feed pipe upon the subsequent change-over of the control slide valve. This would lead, on the one hand, to adulteration of the propane that is to be supplied for the mixture formation and to a change in the pressure in the propane feed pipe and thus to control difficulites.

A considerable disadvantage of the known tool is its limited power delivery. The limits arise more especially from the degree of filling (or the volumet- ric efficiency, or degree of admission) of the combustion chamber, since only a small amount of propane is fed to such chamber, because the propane is kept ready underfeed-pipe pressure in the storage chamber and subsequently the amount of propane, limited by the storage chamber, flows through only to the extent of the pressure balance into the connected combustion chamber.

A further disadvantage of this known tool is the complicated mode of construction, a large number of control lines and also a storage chamber having to be present, which, from experience, leads to increased susceptibility of the tool to breakdown.

Furthermore, the handling thereof is complicated, for example the actuating of the control slide valve being effected manually and separately from triggering of the ignition procedure, which is also effected manually.

The problem underlying the invention is to provide a combustion-powered fastener-driving tooi which is distinguished by high power output and by constructional, functional and handling simplicity.

In accordance with the invention, this problem is solved in that the feed pipe for the mixture component having the lower pressure has a closing valve which is closed upon the flowing into the combustion chamber of the component having higher pressure.

The tool of the invention is distinguished by high output capacity. The reason for this lies basically in the fact that both mixture components pass into the combustion chamber, without passing through a storage chamber which would reduce the pressure of the one mixture component, at the source pressure prevailing in the feed pipes. To achieve high performance, use is preferably made, as the components of the mixture, of propane, and oxygen at a pressure which is higher than that of the propane. As with the known tools, first of all the propane is introduced into the combustion chamber and then the second component at a higher pressure, namely the oxygen, is introduced for forming the mixture.

Further decisive advantages may be derived from the tool of the invention in that it can be of simpler construction, have fewer and shorter control lines and involve a simpler operating cycle than the known tools.

A structurally simple and operationally reliable design for the closing valve is achieved if the valve body thereof has spring means loading it contrary to the inflow direction of the low pressure mixture component. This spring means advantageously is a compression spring, since such springs are distinguished by low fatigue failure.

To increase the closing pressure and thus the closing reliability of the closing valve it is of advantage to provide a feed channel between the closing valve and the feed pipe of the higher pressure mixture component. Such an arrangement provides for the effect of the compression spring on the valve body to supplemented by the force of the higher pressure mixture component.

Furthermore, the actuation of the tool can be significantly simplified, in accordance with a further proposal of the invention, by an actuating mechanism for the control slide valve. Such actuating mechanism is advantageousiy comprising part of a press-in safety mechanism including a component which in the rest position of the tool projects beyond the muzzle of the tool and which, when the tool is pressed against receiving material, is pressed in wards of the tool. Mechanical coupling of this mechanism with the control slide valve can be accomplished in a simple way so that upon the pressing of the tool against the receiving material, the valve automatically closes the described control path.

For simplifying the operation of the tool, it preferably has a release mechanism, for its ignition device, which is also coupled with the control slide valve to move simultaneousiy therewith. In this way, the additional safety feature can be achieved, that actuation of the ignition device, and thus the ignition of the gas mixture, is possible only when the control slide valve is in the appropriate operational position.

In order to achieve significant structural simplification of the tool, retaining means are preferably provided to keep the working piston frictionally in the ignition position whilst the charging pressure of the gas mixture is building up. In this way, the need to provide other structurally complicated measures for preventing premature forward propulsion of the working piston by the charging pressure of the gas mixture can be avoided. In the case of the known tool referred to in the introduction hereof, the main valve is provided to fulfil this function, and this, without doubt, entails problems of control and wear.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a part-sectional side elevation illustrating a preferred embodiment of the fastener-driving tool of the invention, the section being taken along the line I - I of Figure 4; Figure 2 is an enlarged sectional side elevation illustrating a control unitofthetool with a control slide valve thereof in a partially-actuated position; Figure 3 is a view similar to Figure 2 but showing the control slide valve in its fully actuated position; Figure 4 is a cross-section taken on the line IV - IV of Figure 1 , showing the checkvalve in the closed condition and; Figure 5is a cross-section taken on the line V - V of Figure 2, showing the check valve in the open position.

The illustrated embodiment of the combustion- powered fastener-driving tool conforming to the invention comprises a housing which is designated as a whole by the reference numeral 1 and which provides, frontally, a guide cylinder 2 in which a working piston, designated as a whole by the numeral 3, is mounted so as to be displaceable. The piston 3 comprises a frontal shaft 4 and a head 5 of larger diameter than the shaft. Towards the front, screwed into the guide cylinder 2 is a sleeve 6 against which abut the front faces of retaining jaws 7 which are disposed so as to be radially movable. The jaws 7 engage into a cross-sectional narrowing or groove 4a on the shaft 4, a clamping ring 8 around the jaws 7 applies thereto the necessary pressure for the engagement thereof into the groove 4a.At their rear faces, the retaining jaws 7 and the clamping ring 8 abut gainst and are supported by a locking washer 9.

The sleeve 6 furthermore serves for the displaceable reception of a tubular fastener guide 11 which, upon forward displacement of the working piston 3, is penetrated by the shaft 4. Connected to the rear end of the guide 11 is a lateral arm 12 which in turn is coupled with a control slide valve which is designated as a whole by the numeral 13. The assembly consisting of the fastener guide 11,the lateral arm 12 and the control slide valve 13 is pressed by a helical spring 14 towards the forward position illustratedin Figure 1, in which the fastener guide 11 projects beyond the front end face of the housing 1.Axial connection of the lateral arm 12 to the control slide valve 13 is provided, on the one hand, by a supporting shoulder 15 and, on the other hand, by a screw 16 whose head abuts a disc 17 and which engages in the control slide valve 13. The control slide valve 13 is mounted so as to be displaceable with part thereof sliding directly in the housing 1 and a rear portion thereof sliding in a control bush 18 and a guide bush 19.

A feed pipe 21 for propane and a feed pipe 22 for oxygen, which pipes are connected to a source remote from the tool as indicated by a connection flange 23, lead up through a handle 24 on the tool to the control slide valve 13. Disposed in the propane feed pipe 21 is a closing valve which is designated as a whole by the numeral 25 and comprises a valve body 26 which is held in its closing position by spring means 27, in the form of a compression spring, against an elastic sealing ring 28.

In accordance with a control procedure performed by the control slide valve 13, the propane, and the oxygen, which is at a higher pressure as compared with the propane, pass consecutively, by way of an intake channel 29 in the beginning of which is indicated in Figure 1, into a combustion chamber 31 which is disposed rearwardly of the guide cylinder 2.

As can be seen more particularly in Figure 4, associated with the intake channel 29 is a check valve which is designated as a whole by the numeral 32 and valve body 33 of which is in turn loaded into its closing position by a compression spring 34.

Serving as an abutment for the compression spring 34 and for guiding the valve body 33 is an annular body 35 which, in the release position of the valve body 33, allows the passage of the mixture components, by way of an annular gap 41, into the combustion chamber 31 (see Figure 5). The upper end of the intake channel 29 is sealed by a plug 36.

Ignition of the gas mixture which has flowed into the combustion chamber 31 is effected by means of an ignition plug which is designated as a whole by the numeral 37 and has a centre electrode 38 to which an ignition impulse is supplied by way of a connection lug 39 from a source of currentwhich is not shown. The ignition plug 37 is surrounded, at its front portion, by an annular gap 41 which opens to the combustion chamber 31, and seals by its rear portion in the housing 1.

Opening into the annular gap 41, and arranged asymmetrically, is the intake channel 29, as can be seen from Figure 4. The tangential introduction of the mixture components into the annular gap 41 which results therefrom, upon each filling operation, leads to an effective cleaning of the ignition plug by the mixture components flowing in, and also en sures a good intermixture of the components.

Initiation of the ignition procedure is effected by means of a trigger 42 which, when pressed so as to overcome the force of a restoring spring 43, swings about a pivot axis 44 and, in so doing, actuates an electrical switch 45 which is shown only diagrammatically. The trigger 42 can be brought into the triggering position only when the gas mixture has been formed in the combustion chamber 31. For this purpose, the slide valve 13 has had previously to be shifted, contrary to the force of the spring 14, into its rear end position, which is achieved by pressing the setting tool against receiving material and thereby ensuring pressing-in of the fastener guide 11. In the said end position of the control slide 13, a recess 46 lies in register with nose 42a of the trigger 42, so that engagement of the nose 42a into the recess 46 permits the trigger 42 to be actuated.After the ignition procedure has been initiated, the control slide valve 13, is driven by the cylinder spring 14, runs forwardly into the rest position there-of, during which the recess 46, having an inclined flank 46a, brings the nose 42a, and thus the trigger 42, back into its initial position.

The tool is connected by way of the connection flange 23 to external sources of the mixture components of propane and oxygen. The propane is thus supplied by way of the feed pipe 21 to the closing valve 25. Since the pressure in the small-volume control chamber situated after the closing valve is less than the propane pressure in the feed pipe 21, the valve body 26 is raised off the sealing ring 28 so that it leads to pressure balance between the said control chamber and the feed pipe 21. The valve body 26 is then brought by the spring means 27 back into the closed position. Meanwhile, also the feed pipe 22, which is filled with oxygen, is shut off by the control slide valve 13 which is in the rest position.

The access of the mixture components to the control slide valve 13 is effected byway of annular channels 47 and passage bores 18a in the control bush 18 into which the outlets of the feed pipes 21 and 22 open.

A fastener 48 having previously been inserted into the fastener guide 11, the tool is pressed, by its muzzle, against receiving material (not shown) with the result that the guide 11, and with it the transverse arm 12 and the control slide valve 13, shift rearward ly against the force of the spring 14. During this displacement, during which the pin guide 11 and the transverse arm 12 fulfill the function of an actuating mechanism for the control slide valve 13, the gas mixture is formed in the combustion chamber 31. To explain this mixture formation, the control sequence which occurs upon the pressing of the tool against the fastener-receiving material will now be described.

Whilst in the rest position (Figure 1) of the setting tool, both mixture components present in the feed pipes 21, 22 are prevented by the control slide valve 13 from flowing further, as shown in Figure 2, upon displacement into an intermediate position the control slide valve 13 establishes a connection between the feed pipe 21 containing propane and the intake channel 29. Since only atmospheric pressure prevails in the combustion chamber 31, the pressure of the propane opens the closing valve 25 and the check valve 32, as shown by Figure 5, and it thus leads to a flooding of the propane into the combustion chamber 31. This filling of the combustion chamber 31 is effected within a fraction of a second, the propane flowing by way of the bores and passages which are brought into registration by the control slide valve 13 and the control bush 18.Ring seals are present around the valve 13 and the bus 18 to seal these components appropriately. There is, however, no fundamental functional significance in these rings, so that they are not described in detail.

After the propane in the combustion chamber 31 has reached the same pressure as prevails in the feed pipe 21, the two valves 32 and 25 close by reason of the spring force thereof.

Of functional importance is, furthermore, the fact that the working piston 3, during the charging procedure of the gas mixture, remains in the rear initial position shown in Figure 1 and is not, for instance, shifted forwardly by the charging pressure of the gas mixture. Provided this purpose are frictional retaining means in the form of the retaining jaws 7 by the clamping ring 8 resiliently against the cross-sectional narrowing or groove.

Upon the tool being fully pressed against the receiving material, the control slide valve 13 occupies the end position shown in Figure 3. At this stage, the oxygen feed pipe 22 opens into a connecting channel 49 of the control slide valve 13, which establishes a passage of the oxygen to the intake opening 29. Since the oxygen pressure is considerably higher than that of the propane previously introduced into the combustion chamber 31, the oxygen rushes into the combustion chamber 31. For this purpose, it opens the check valve 32. In this way, there is formed, in the combustion chamber 31, a gas mixture having a charging pressure which is determined by the pressure of the oxygen. The spring-loaded check valve 32 now automatically closes once more.

The control slide valve 13, which is in the rear end position, now stands with the recess 46 over the nose 42a, so that the trigger 42 can be actuated and the ignition plug 37 then receives the current impulse necessary for ignition. The combustion pressure which now builds up in the combustion chamber 31, and which exceeds the charging pressure by a multiple, exceeds by far the forces of the retaining means 7, 8 previously restraining the working piston 3, so that the jaws 7 the working piston 3 for acceleration by the combustion pressure in the forward direction.

After the fastener-driving operation has been effected, and the tool has been lifted away from the receiving material, the control slide valve 13 is brought by the spring 14 back into its front initial positon. Meanwhile, the closing valve 25 remains held closed by the spring means 27, to ensure that residual oxygen at high pressure present in the connecting channel 49 and in the intake channel 29 cannot penetrate into the propane feed pipe 21 which is at a pressure which lower in comparison therewith. To supplement the closing function, there is provided, in addition, a feed channel 51 (Figure 3) by way of which the high pressure of the oxygen present in the connection channel 49 additionally acts in the closing direction on the valve body 26 (Figure 1). Then, it is only necessary for the working piston 3 to be brought back into its initial positon for the tool to be ready for re-use.

In order to prevent unchecked afterflow or outflow of the mixture components by way of the intake opening 29 and the combustion chamber 31 and openings which are not shown into the atmosphere, directly after the fastener-driving operation, when the pressure in the combustion chamber 31 and in the cylinder chamber has dropped, the actuating mechanism for the control slide valve 13 is advantageously so designed that such control slide valve 13 returns immediately afterthe mixture formation into the rest position shown in Figure 1.

Of course, it is also possible to use, instead of propane and oxygen, other mixture components.

Claims (7)

1. A combustion-powered fastener-driving tool comprising a guide cylinder, a working piston which is located in the guide cylinder and which is driven by the combustion pressure of a gas mixture, a combustion chamber which adjoins the guide cylinder contrary to the driving direction of the working piston, an ignition device, associated with the combustion chamber, for the gas mixture, a control slide valve which provides for successive flowing-in of two mixture components into the combustion chamber and which is provided with feed pipes for the mixture components which are under different pressures, and a check valve in an intake channel between the control slide valve and the combustion chamber, characterised in that the feed pipe for the mixture component having the lower pressure has a closing valve which is closed when the component having higher pressure flows into the combustion chamber.

2. A tool as claimed in claim 1, characterised in that the closing valve includes spring means which urges a body of the valve contrary to the inflow direction of the low pressure mixture component.

3. Atool as claimed in claim 1 or 2, characterised in that a feed channel is provided between the closing valve and the higher-pressure mixture component.

4. Atool as claimed in clam 1,2 or 3 characterised by an actuating mechanism which serves to actuate the control slide valve upon pressing of the tool against fastener-receiving material.

5. Atool as claimed in any preceding claim characterised by a triggering mechanism for the igniting device.

6. Atool as claimed in any preceding claim characterised by frictional retaining means which keeps the working piston in the ignition position whilst the charging pressure of the gas mixture is building up.

7. A combustion-powered fastener-driving tool substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.