GB2246093A - Power impact tools - Google Patents

Abstract

A power impact tool, such as a drill, hammer, pick or breaker, has a piston engine in which the piston (34) is intermittently forced upwards by burning gas in the combustion chamber (58), and which is returned in the downward direction under the action of a compression coil spring (35) so as to strike an anvil (40) towards the end of the downward stroke. Fuel, such as propane or butane, is supplied from a gas bottle (20) which is mounted on the tool. <IMAGE>

Description

POWER IMPACT TOOLS This invention relates to power drills, hammers, picks and breakers, and similar power impact tools.

Such tools are conventionally operated by compressed air, an electric motor or by a conventional petrol engine. The compressed-air or pneumatic tool suffers from the disadvantage that a compressor is required, to which the tool is connected, and therefore the tool must either be used near the compressor or a long length of air line is required.

Also compressors are expensive, noisy and transportation is a problem.

The electrically-powered tool suffers from the disadvantage that a source of electricity is required, either the mains or a generator, and if mains electricity is used an isolating transformer is required for outdoor work.

Also, electrically-powered tools are usually of low power compared with pneumatic tools. Petrol-engine powered tools have an advantage that a separate power supply is not required. However, they tend to be heavy.

Also, petrol engines are normally used for low-speed applications such as in compactors and rammers. Furthermore, the transportation and storage of supplies of petrol can be hazardous.

According to one aspect of the present invention, there is provided a power impact tool comprising a cylinder and cooperating piston. Fuel is introduced into the cylinder to one side of the piston and is ignited to urge the piston intermittently in one direction in the cylinder. A spring is arranged to urge the piston in the opposite direction in the cylinder, so that the piston reciprocates in the cylinder. The piston is arranged to provide impacts to the tool upon such reciprocation. It is anticipated that such a tool will be lighter than a comparable tool driven by a conventional petrol engine, because the tool according to this aspect of the invention does not need a heavy flywheel and a strong connecting rod connecting the piston to the flywheel, but rather uses the spring to return the piston.

According to another aspect of the invention, there is provided a power impact tool having a piston engine arranged to provide impacts to the tool, the engine being adapted to operate on liquefied gas fuel, and the tool having means for attaching a container of such fuel thereto. It will be appreciated that bottled gas can be stored and transported more safely and conveniently than petrol.

The above-mentioned two aspects of the present invention may be embodied in the same tool, as will be apparent from the following detailed description, given by way of example, of a specific embodiment of the invention, reference being made to the accompanying drawings, in which: Figure 1 is a schematic elevational view of a power tool; and Figure 2 is a partially sectioned view of the tool as seen in the direction II in Figure 1.

Referring to Figure 1 of the drawings, the tool 10 has a cylinder 12 from the lower end of which a shank 14 projects downwardly and to which a pick bit 16 is attached. A pair of handles 18 are attached to the upper end of the cylinder. A pair of butane or propane gas bottles 20 are attached to the top of the cylinder by straps or other suitable means and each feeds through a conventional connector 22 and pipe to a change-over valve 24. The change-over valve can connect the pipe from either gas bottle 20 or from a connector 26 (to which a larger external gas bottle can be connected by a suitable hose) to an outlet pipe which supplies fuel from the selected source to an adjustable regulator valve 28 which is mounted on one of the handles and which can be adjusted by a lever 30.

From the valve 28, fuel is supplied to a carburettor 32.

Referring to Figure 2, a piston 34 is mounted inside the cylinder and is shown in its uppermost position in the drawing. The piston 34 is urged downwardly by a strong compression coil spring 35 which extends between the top of the piston and the top wall 36 of the cylinder. The shank 14 extends through the bottom wall 38 of the cylinder, and an anvil 40 is attached to the upper end of the shank 14. The shank can move vertically to an extent limited by a collar 42 on the shank and is shown in the drawing in its uppermost position. It is urged to this position by a light compression coil spring 44 acting between the anvil 40 and the bottom wall 38 of the cylinder.

The cylinder 12 has an inlet port 46 supplied by the carburettor 32, a transfer port 48, an exhaust port 50 connecting to an exhaust pipe 52 or silencer, and a sparking plug 54, all arranged so that the piston can operate on a two-stroke cycle. Thus, starting with the piston 34 at its lower-most position, the transfer and exhaust ports 48, 50 are closed, and the inlet port 46 is open, through which a fresh charge of air and gas has been supplied by the carburettor 32 to a supply chamber 56 above the piston 34. As the piston 34 moves up under the action of the burning charge in the combustion chamber 58 below the piston, the inlet port 46 closes and the fresh charge in the supply chamber 56 is compressed. The exhaust port 50 then opens, to release the burned charge to the exhaust pipe 52.The transfer port 48 then opens, and the partly-compressed fresh charge transfers from the supply chamber 56 to the combustion chamber 58. The spring 35 has now become compressed and starts to force the piston down. Thus, the transfer port 48 and then the exhaust port 50 are closed, and the charge in the combustion chamber 58 begins to be compressed. Also, the inlet port 46 opens so that a fresh charge can be sucked into the supply chamber. The piston 34 is arrested in its downward movement by striking the anvil 40, and thus an impact is provided to the shank 14 and pick 16. At this stage, a spark is produced by the sparking plug 54 to ignite the compressed charge in the combustion chamber, and thus the piston 34 is forced upwardly, and the above process is repeated.

Accordingly, a succession of impacts is provided as the piston reciprocates up under the action of the burning charge and down under the action of the spring 35.

As shown in Figure 2, the piston 34 is connected to a rod 60 which passes through the upper wall 36 of the cylinder. This rod 60 is provided for starting and for ignition triggering. A starting lever 62 is pivotally mounted to the upper end of the cylinder 12 and is shown in its nonoperative position in the drawing. A releasable clip or the like may be provided to hold the lever 62 in this position. At the upper end of the rod 60, there is a small sideways projecting lug 64 having an inclined upper surface and a square lower surface (see Figure 1). When the tool is to be started, the rod 60 will project out of the cylinder only to a small extent.

In order to start the tool, the lower end of the lever 62 is raised manually, and accordingly the upper end of the lever is lowered, and is forced past the lug 64. The lower end of the lever 62 can then be forced down, to raise the piston 34 against the action of the spring 35, and as the lever 62 reaches the end of its travel, the upper end of the lever 62 comes clear of the lug 64, so that the piston 34 is released downwardly. It will be appreciated that this action may need to be repeated a number of times before the tool starts.

The ignition system comprises a high-tension piezo-electric element 66 mounted on the upper end of the cylinder and having an actuator element which faces the rod 60. A cam element 68 is mounted on the upper end of the rod 60 and engages the actuator element when the piston 34 is at or near its lowermost position. This causes a high voltage pulse to be produced which is fed to the sparking plug 54 by a suitable HT cable.

It will be appreciated that many modifications, developments and refinements may be made to the tool described above.

Claims (8)

1. A power impact tool comprising a cylinder and a cooperating piston, means to introduce fuel into the cylinder to one side of the piston and to ignite the fuel to urge the piston intermittently in one direction in the cylinder, a spring arranged to urge the piston in the opposite direction in the cylinder, so that the piston reciprocates in the cylinder, and the piston being arranged to provide impacts to the tool upon such reciprocation.

2. . A tool as claimed in claim 1, wherein an anvil is provided at one end of the cylinder, the anvil being connected to a tool shank which passes through the end of the cylinder, and the anvil being impacted by the piston during reciprocation of the piston.

3. A tool as claimed in claim 2, wherein the spring is a compression spring which acts between the piston and the other end of the cylinder.

4. A tool as claimed in any preceding claim, wherein the tool is arranged to operate on liquefied gas fuel.

5. A tool as claimed in claim 4, further comprising means for attaching a container of liquefied fuel to the tool.

6. A power impact tool having a piston engine arranged to provide impacts to the tool, the engine being adapted to operate on liquefied gas fuel, and the tool having means for attaching a container of such fuel thereto.

7. A tool as claimed in claim 5 or 6, further comprising a connector for connecting to an external supply of fuel.

8. A power impact tool substantially as described with reference to the drawings.