GB1592751A - Hydraulic impact tool - Google Patents

Description

(54) HYDRAULIC IMPACT TOOL (71) We, NIPPON PNEUMATIC MANUFACTURING CO. LTD., a Japanese company, of 11-5, 4-chome, Kami ji, Higanshinari-ku, Osaka-shi, Osaka-fu, Japan, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to an impact tool having a piston reciprocated under hydraulic and gas pressure to hit a chisel or other tool.

An impact tool is known which includes a cylinder, a liner mounted therein, a piston mounted in said liner to be reciprocated under hydraulic and gas pressure to hit a chisel, a tubular valve for controlling a hydraulic circuit slidably mounted on said liner to be pushed up hydraulically against the bias of a spring, and a gas accumulator disposed over the cylinder.

gulch an impact tool was liable to trouble due to poor bias or breakage of the spring serving to push down the tubular valve.

Also, it was complicated in construction owing to the provision of the gas accumulator.

An object of this invention is to provide an impact tool which is less liable to trouble and has a greater durability.

Another object of this invention is to provide an impact tool which is simpler in design and is more inexpensive to manufacture.

The invention consists in an impact tool comprising a cylinder, a liner mounted therein so as to form an annular space between itself and the said cylinder, a piston reciprocably mounted in said liner and having an enlarged portion substantially midway along its length, a tool holder secured to the bottom of said cylinder, to be hit by said piston upon its downward stroke, a tubular valve slidably mounted on said liner to introduce the hydraulic oil supplied to said cylinder into an annular space below said enlarged portion to push up the piston when it is in its lower position and to allow the oil in said annular space to be discharged out of the cylinder when it is in its upper position, at least one rod slidably mounted on the cylinder for pushing down said tubular valve under hydraulic pressure, a gas reservoir provided above the cylinder for containing gas so as to be compressed directly by said piston as said piston goes up, and a hydraulic circuit formed in said cylinder and said liner to push up said tubular valve under hydraulic pressure when the piston is in its lower position and to cause said rod to push down said tubular valve under hydraulic pressure when the piston is in its upper position.

The invention will now further describe, by way of example, with reference to the accompanying drawings, in which; Figure 1 is a vertical sectional view of an embodiment of the present invention; and Figure 2 is an outline view of another embodiment with no handle or valve box attached, showing a manner in which it is mounted e.g. on an excavator; and Figure 3 is a sectional view of the embodiment of Figure 2 taken along the line A-A.

Referring to Figure 1, the numeral 1 generally designates a cylinder in which a liner 2 is fixedly mounted so as to form an annular space 4 between the cylinder 1 and itself. Another liner 3 is mounted on the liner 2 at the upper end thereof. A piston 5 having an enlarged portion 6 substantially midway along its length is slidably mounted in the liner 2. A tubular valve 7 is slidably mounted on the liner 2 and is disposed in the annular space 4.

A valve box 8 is fixed to the side of the cylinder 1. It is formed with an oil inlet 9 to be connected with a hydraulic unit, an oil outlet 10 to which an oil discharge pipe is connected, an oil supply port 12 communicating with an annular space 11 formed between the liners 2 and 3, and an oil discharge port 13 communicating with the annular space 4, all of the ports being open to a through hole in the valve box 8.

A handle 15 is secured to a handle mounting member 14 secured to the top of the cylinder 1. On the handle 15 is pivoted a lever 17 used to operate a valve body 16 slidably mounted in the through hole in the valve box 8. The valve body is urged by a spring 18 toward the lever 17 so that the oil inlet 9 normally communicates with the oil outlet 10. When the lever 17 is pressed down to lower the valve body 16 against the bias of the spring 18, the oil outlet 10 is disconnected from the oil inlet 9.

The liner 2 is formed with radial ports 19, 20 and 21 from bottom to top, said ports having an annular recess at each end thereof. The liner 2 is also formed in its wall with an axial passage 22 communicating with the annular space 11, and two radial ports 23 and 24 branching outwardly from the axial passage 22. The tubular valve 7 is formed on its inner surface with an annular recess 25 connecting the radial-ports 19 and 23 to each other when it is in its lower position, and with an annular recess 26 connecting the radial ports 20 and 24 to each other when it is in its upper position.

The liner 3 is formed with a plurality of axial holes 27 extending from its lower end to the annular space 11. In each axial hole is mounted a rod 28 with its lower end bearing on the tubular valve 7. The liner 2 is shaped to have a slightly reduced outer diameter above the radial port 20 and accordingly the tubular valve 7 is formed in its inner surface with a shoulder 29 so as slidably to fit on the reduced portion of the liner 2. This arrangement is adopted to ensure that the cross sectional area of the tubular valve 7 at the shoulder 29 is larger than the total cross sectional areas of the rods 28.

A chisel holder 30 is screwed on the lower end of the cylinder 1 to hold a chisel 31.

Also, a head 32 is secured to the top of the handle mounting member 14. The head 32 and the member 14 form a gas reservoir 33 into which compressed air or nitrogen gas is supplied through a gas supply port 34 provided with a check valve.

In operation, the impact tool according to this invention is used with the chisel 31 on a workpiece. While the operating lever 17 is in its normal position, hydraulic oil flows from the oil inlet 9 into the valve box 8, but returns to the tank through the oil outlet 10.

Thus, no hydraulic pressure is applied to the cylinder 1 so that the piston 5 remains in its lower position.

When the lever 17 is pressed down to lower the valve body 16 against the spring 18 to disconnect between the oil inlet 9 and the outlet 10, hydraulic oil flows through the oil supply port 12, annular space 11, axial passage 22, radial port 23, annular recess 25, radial port 19 into a lower chamber formed between the liner 2 and the piston 5 below the enlarged portion 6, applying pressure to the latter. Pressure is also applied to the top of the rods 28.

Since an upper chamber formed between the liner 2 and the piston 5 above the enlarged portion 6 communicates with the oil discharge port 13 through the radial port 21, the piston 5 is pushed up by hydraulic pressure acting on the enlarged portion 6.

When the bottom of the enlarged portion 6 comes above the radial port 20, part of the oil flows into the port 20, acting under the shoulder 29.

Since as mentioned before the cross sectional area of the tubular valve 7 at the shoulder 29 is designed to be larger than the total cross sectional areas of the rods 28, the tubular valve 7 rises against the hydraulic pressure applied by the rods 28 so that the radial port 20 communicates with the radial port 24 through the annular recess 26. As soon as the tubular valve 7 goes up, the hydraulic oil in the lower chamber is allowed to flow through the radial port 19 and the annular space 4 into the upper chamber where the drop of the piston, which will be described below, makes some additional space for hydraulic oil.

On the other hand, since the gas in the gas reservoir 33 is compressed by the rising piston 5, the latter rapidly drops by reaction of the gas, hitting the chisel 31, as soon as the hydraulic pressure acting on the bottom of the enlarged portion 6 drops. When the enlarged portion 6 comes below the radial port 20, the upper chamber between the liner 2 and the piston connects the radial ports 20 and 21 to each other so that hydraulic pressure does not act on the shoulder 29 any more. This allows the rods 28 to press down the tubular valve 7 to its original lowermost position. Now, the cycle described above starts again.

While the lever 17 is kept pressed to lower the valve body 16, the cycle described above is repeated so that the piston 5 reciprocates, hitting the chisel 31 repeatedly. When lever 17 released, the valve body 16 rises under the bias of the spring 18 to communicate the oil inlet 9 with the oil outlet 10 so that the piston 5 stops.

It will be understood from the foregoing that the impact tool according to this invention is less liable to trouble and has a longer working life since no spring is used to urge the tubular valve 7 downwardly, Also, it is simpler in construction and less expensive to manufacture since no gas accumulator is needed.

Although this invention has been described with reference to an embodiment having a valve box 8 and a handle 15 mounted on the impact tool itself, these control units may be mounted e.g. on an excavating machine such as a backhoe or a power shovel and be connected with the impact tool through flexible hoses for supplying and discharging hydraulic oil. In such a case, the impact tool without a handle or a valve box may be mounted on the tip of the arms of such an excavator.

Figures 2 and 3 show such an arrangement in which the cylinder 1 is formed with a projecting portion 35 at which the impact tool is clamped by two bolts 36 between two mounting plates 37 secured to arms 38 extending from an excavator.

While a preferred embodiments have been described, various changes or variations can be made without departing from the scope of this invention as defined in the appended claims.

WHAT WE CLAIM IS: 1. An impact tool comprising a cylinder, a liner mounted therein so as to form an annular space between itself and the said cylinder, a piston reciprocably mounted in said liner and having an enlarged portion substantially midway along its length, a tool holder secured to the bottom of said cylinder, to be hit by said piston upon its downward stroke, a tubular valve slidably mounted on said liner to introduce the hydraulic oil supplied to said cylinder into an annular space below said enlarged portion to push up the piston when it is in its lower position and to allow the oil in said annular space to be discharged out of the cylinder when it is in its upper position, at least one rod slidably mounted on the cylinder for pushing down said tubular valve under hydraulic pressure, a gas reservoir provided above the cylinder for containing gas so as to be compressed directly by said piston as said piston goes up, and a hydraulic circuit formed in said cylinder and said liner to push up said tubular valve under hydraulic pressure when the piston is in its lower position and to cause said rod to push down said tubular valve under hydraulic pressure when the piston is in its upper position.

2. An impact tool as claimed in claim 1 further comprising a second liner mounted on said liner at the upper end thereof and formed with at least one axial hole in which said rod is slidably mounted.

3. An impact tool structured and adapted to operate substantially as hereinbefore described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. Although this invention has been described with reference to an embodiment having a valve box 8 and a handle 15 mounted on the impact tool itself, these control units may be mounted e.g. on an excavating machine such as a backhoe or a power shovel and be connected with the impact tool through flexible hoses for supplying and discharging hydraulic oil. In such a case, the impact tool without a handle or a valve box may be mounted on the tip of the arms of such an excavator. Figures 2 and 3 show such an arrangement in which the cylinder 1 is formed with a projecting portion 35 at which the impact tool is clamped by two bolts 36 between two mounting plates 37 secured to arms 38 extending from an excavator. While a preferred embodiments have been described, various changes or variations can be made without departing from the scope of this invention as defined in the appended claims. WHAT WE CLAIM IS:

1. An impact tool comprising a cylinder, a liner mounted therein so as to form an annular space between itself and the said cylinder, a piston reciprocably mounted in said liner and having an enlarged portion substantially midway along its length, a tool holder secured to the bottom of said cylinder, to be hit by said piston upon its downward stroke, a tubular valve slidably mounted on said liner to introduce the hydraulic oil supplied to said cylinder into an annular space below said enlarged portion to push up the piston when it is in its lower position and to allow the oil in said annular space to be discharged out of the cylinder when it is in its upper position, at least one rod slidably mounted on the cylinder for pushing down said tubular valve under hydraulic pressure, a gas reservoir provided above the cylinder for containing gas so as to be compressed directly by said piston as said piston goes up, and a hydraulic circuit formed in said cylinder and said liner to push up said tubular valve under hydraulic pressure when the piston is in its lower position and to cause said rod to push down said tubular valve under hydraulic pressure when the piston is in its upper position.

2. An impact tool as claimed in claim 1 further comprising a second liner mounted on said liner at the upper end thereof and formed with at least one axial hole in which said rod is slidably mounted.

3. An impact tool structured and adapted to operate substantially as hereinbefore described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.