US3638423A

US3638423A - Pneumatic tool

Info

Publication number: US3638423A
Application number: US30833A
Authority: US
Inventors: Willem Jan Van Heijst
Original assignee: IHC Holland NV
Current assignee: IHC Holland NV
Priority date: 1969-04-24
Filing date: 1970-04-22
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01
Also published as: FR2046372A5; DE2021038A1; BE749419A; DE2021038C3; JPS4930189B1; NL140448B; NL6906350A; DE2021038B2

Abstract

A reciprocatory pneumatic tool has a positive displacement pump for introducing a constant volume of liquid into the tool side of the piston upon each return stroke, and a valve operated in timed sequence with the pump for exhausting liquid upon each return stroke. The air on the opposite side of the piston is confined and of constant quantity, so that when the tool encounters high resistance, the tool will not advance as far on the working stroke and liquid will tend to accumulate on the tool side of the piston and the air will be more greatly compressed to deliver a more powerful working stroke. Conversely, when the tool encounters less resistance, the tool advances farther on the working stroke and more liquid is pumped out than is pumped into the cylinder, so that the compressed air is expanded and delivers a less powerful stroke. The force of impact is thus automatically adjusted in accordance with the resistance encountered. In a modification, liquid can be pumped through the piston one way in the direction of the air, and an outlet port normally covered by the piston can be exposed when the piston moves too far in either direction.

Description

United States Van Heijst atent [4 Feb. I, 1972 2,867,086 1/1959 Haley ..60/51 FOREIGN PATENTS OR APPLICATIONS 729,941 5/1955 Great Britain ..60/52 HF Primary Examiner-Edgar W. Geoghegan Attorney-Young & Thompson [5 7] ABSTRACT A reciprocatory pneumatic tool has a positive displacement pump for introducing a constant volume of liquid into the tool side of the piston upon each return stroke, and a valve operated in timed sequence with the pump for exhausting liquid upon each return stroke. The air on the opposite side of the piston is confined and of constant quantity, so that when the tool encounters high resistance, the tool will not advance as far on the working stroke and liquid will tend to accumulate on the tool side of the piston and the air will be more greatly compressed to deliver a more powerful working stroke. Conversely, when the tool encounters less resistance, the tool advances farther on the working stroke and more liquid is pumped out than is pumped into the cylinder, so that the compressed air is expanded and delivers a less powerful stroke. The force of impact is thus automatically adjusted in accordance with the resistance encountered. In a modification, liquid can be pumped through the piston one way in the direction of the air, and an outlet port normally covered by the piston can be exposed when the piston moves too far in either direction.

3 Claims, 2 Drawing Figures PATENTED FEB 1 I972 INVENTOR BY rcJXA-W ATTORNEYS PNEUMATIC TOOL This invention relates to pneumatic tools of the type comprising a cylinder with a piston which acts on the pneumatic tool and performs its operating stroke under the influence of the pressure of a gaseous medium.

Pneumatic tools of this type are generally known for various applications. The operation of these pneumatic tools is generally based on a constant supply of gaseous medium under pressure, by which the piston is driven in the direction of stroke, while the medium is allowed to escape at the end of said stroke. In this arrangement there may be various types of devices (such as a spring in the most simple designs) by which the piston is returned to its staring position where it acts on a valve which supplies another quantity of medium under pressure. In this instance the adjustment of the force of impact is often determined by the pressure head which is permissible in the cylinder. Pressure-controlling valves are provided in tools that are manually operated, these vales allowing a larger or smaller quantity of pressure mediumto pass, which quantity depends on the pressure exerted by the operator.

In the case of tools that are operated by remote control, i.e., not manually, however, the problem of pressure control is more difficult.

Accordingly, it is an object of the present invention to provide a pneumatic tool in which the force of impact is automatically adjusted to the resistance met by the pneumatic tool.

It is also an object of the invention to provide a pneumatic cutter of the type utilized in the vicinity of the suction nozzle of a suction dredger in order to be able to break up areas of fering strong resistance, such as areas with a rocky bottom.

Finally, it is an object of the present invention to provide a pneumatic tool which will be relatively simple and inexpensive to manufacture, easy to operate, maintain and repair, and rugged and durable in use.

These and other objects are achieved according to the invention in that the cylinder at that side of the piston that is turned away from the side on which the gaseous medium acts is connected to a hydraulic system by which a given volume of liquid is periodically supplied to that side of the piston that is turned toward the pneumatic tool, which volume is smaller than the optimum displaceable volume of the piston, while each time after the liquid is supplied an orifice is given access to, so that the supplied liquid can flow away. With this arrangement a pneumatic tool is provided, the force of impact of which is still initiated by the pressure of a compressed, gaseous medium. The piston making the stroke is each time withdrawn over a distance that corresponds with the quantity of liquid which is forced into the cylinder, for instance by a plunger pump during its delivery stroke. If only little resistance is met by the pneumatic tool, for instance the pneumatic cutter, the piston will also be displaced over quite a great distance in the cylinder and in the direction of stroke by the gaseous medium. The supplied, constant quantity of liquid which is forced into the cylinder at each delivery stroke of the plunger pump in order to return the striking piston will in this instance bring this piston to a position in which the gaseous medium will be compressed to a lesser extent than if the pneumatic cutter had met stronger resistance and would therefore have been displaced to a less forward position. If the pneumatic cutter has met little resistance, its next stroke will be less forceful, clue to the gaseous medium having been compressed to a lesser extent, than if the cutter had met strong resistance, because in that case the gaseous medium would have been compressed to a higher pressure. It is thus possible to obtain an automatic adjustment of the force of impact to the resistance met by the cutter without any manipulations having to be performed by the operator.

Further according to the invention, the pneumatic tool may be designed in such a way that there is liquid on either side of the piston of the cylinder, while the side that has to supply the operating pressure is connected to a pressure accumulator and said piston is provided with a longitudinal duct with a check valve, which check valve opens towards the accumulator, and the cylinder is furthermore provided with an outlet port which is controlled by the piston and occupies such a position in the cylinder that the range of stroke of the piston is bounded by it in both directions. By this arrangement a compact design of the tool is ensured, while the automatic adjustment of the force of impact to the resistance met by the tool is preserved. The gaseous medium in the accumulator will increase in pressure because liquid will be pumped toward the accumulator via the duct with check valve when the resistance increases. Owing to its greater range of stroke, the piston will give access to the outlet port when the resistance decreases, so that the liquid can escape and the pressure in the accumulator will decrease. A too high pressure inside the accumulator cannot be built up either, because in that case the other side of the piston will give access to the outlet port.

Still further according to the invention, the longitudinal duct may be provided with a throttling device. This may serve to prevent the adjustment from being made too soon.

Other objects, features and advantages of the present invention will become apparent from a consideration of the following description, taken in connection with the accompanying drawing, in which:

FIG. 1 is a somewhat diagrammatic view of a first embodiment of pneumatic tool according to the present invention; and

FIG. 2 is a view similar to FIG. 1 but showing a different embodiment of pneumatic tool.

Referring now to the drawing in greater detail, and first to the embodiment of FIG. 1, there is shown a pneumatic cutter l which is rigidly attached to a piston 2 in the cylinder 3, which cylinder is filled with a liquid in the form of hydraulic fluid to the left of the piston 2 and with a gaseous medium under pressure to the right in space 4. A one-cylinder plunger pump 5 with a driving shaft 6 acts on driving means, not shown in the drawing, while said plunger pump is connected to the space 8, on the left of the piston 2, by means of a pressure pipe 7. A branch pipe 9 with a valve 10 empties into reservoir 11.

On the shaft 6 of the plunger pump there is a cam disc 12 which controls the valve 10 via rod 13. Cam disc 12 is so positioned and shaped that at the end of the delivery stroke of the plunger pump 5, valve 10 is displaced to take up a position in which the pipe 9 is opened between space 8 and reservoir 11.

With each delivery stroke of the plunger pump 5, a predetermined quantity of liquid will be passed into the space 8 via pipe 7, and this causes the piston 2 with the pneumatic cutter l to be displaced to the right and the gaseous medium to be compressed in the space 4. The extent to which the gaseous medium is compressed will be determined by the starting position of the piston 2, while the starting position in its turn will be determined by the resistance met by the cutter 1. At the end of each delivery stroke or pump 5, the cutter 1 having thus been displaced to the right as seen in the drawing, the valve 10 will give access to the connection of the space 8 with the reservoir 11, and this enables the liquid to flow out of the cylinder 3 and the gaseous medium to initiate an operating stroke of the cutter.

In the embodiment shown in FIG. 2, identical parts have been indicated by the same reference numerals as in FIG. 1. This embodiment differs from that of FIG. 1, however, in that the cylinder 14 is connected to an accumulator 15 via pipe 16, so that there is liquid on either side of the piston 17. In the piston there is a longitudinal duct 18 with a check valve 19 and a throttling device 20. The cylinder is furthermore provided with an outlet port which is designed as an annular duct 21, which outlet port is connected to the reservoir 11 by a pipe 22.

Owing to the presence of the connecting rod 23, during each delivery stroke of the plunger pump there will be a somewhat higher pressure in the space 24 than in the space 25. Because of this, a small quantity of liquid can flow -to the space 25 via the longitudinal duct 18 and increase the pressure in the accumulator. An increase in pressure will lengthen the stroke of the piston, while the range of the stroke is limited by the annular duct 21, for as soon as this duct is exposed by the piston, liquid will escape and the pressure in the accumulator will decrease. The access to the outlet port provided by duct 21 will also prevent the piston from being displaced too far to the right. Because of this, the range of stroke of the cutter is limited, while an automatic adjustment to the resistance met by the cutter 1 has been preserved. This makes it possible for the design to be compact, while this arrangement offers the additional advantage that the piston can be guided in a more efficient way.

In view of the foregoing disclosure, therefore, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

What is claimed is:

1. in a pneumatic tool comprising a cylinder, and a piston in the cylinder that acts on a pneumatic tool to effect a working stroke under the influence of a gaseous medium which is on the side of the piston opposite the tool; the improvement comprising means for repeatedly supplying to the cylinder on the same side of the piston as the tool a constant volume of liquid between working strokes, and means to exhaust from the cylinder at least some of said liquid between periods of supply of said liquid thereby to permit the volume of said liquid in said cylinder to vary as the resistance met by said tool, a portion of said liquid being disposed on said opposite side of said piston, said gaseous medium being confined in an accumulator in which is also disposed a portion of said liquid, said piston having a duct therethrough communicating between opposite sides of said piston, said cylinder having an outlet port for said liquid, the rangetof possible movement of said piston being such as to permit exposure of said outlet port by said piston on either side of said piston.

2. Apparatus as claimed in claim I, and a one-way check valve in said duct to permit flow ofliquid toward said accumulator but to prevent flow of liquid away from said accumulator.

3. Apparatus as claimed in claim 1, and throttling means in said duct.

Claims

1. In a pneumatic tool comprising a cylinder, and a piston in the cylinder that acts on a pneumatic tool to effect a working stroke under the influence of a gaseous medium which is on the side of the piston opposite the tool; the improvement comprising means for repeatedly supplying to the cylinder on the same side of the piston as the tool a constant volume of liquid between working strokes, and means to exhaust from the cylinder at least some of said liquid between periods of supply of said liquid thereby to permit the volume of said liquid in said cylinder to vary as the resistance met by said tool, a portion of said liquid being disposed on said opposite side of said piston, said gaseous medium being confined in an accumulator in which is also disposed a portion of said liquid, said piston having a duct therethrough communicating between opposite sides of said piston, said cylinder having an outlet port for said liquid, the range of possible movement of said piston being such as to permit exposure of said outlet port by said piston on either side of said piston.

2. Apparatus as claimed in claim 1, and a one-way check valve in said duct to permit flow of liquid toward said accumulator but to prevent flow of liquid away from said accumulator.

3. Apparatus as claimed in claim 1, and throttling means in said duct.