GB2141657A - Improvements in hydraulically operated hammers - Google Patents

Abstract

An hydraulically operated hammer of the kind comprising a housing 10 formed with a cylinder in which a double-acting piston 11 is reciprocable, a tool 12 projecting from the housing 10 and located so as to be impacted by the piston 11 at the end of the operating stroke thereof, and a spool valve 14 reciprocable within a valve chamber in the housing and adapted to control the flow of hydraulic fluid to and from the cylinder to control the reciprocation of the piston. The valve spool 14 extends longitudinally with respect to the cylinder 11 at one end thereof and is formed with a central longitudinal bore 34 which, in one limiting position of the spool valve, places one end of the piston 11 in communication with a hydraulic fluid pressure line 39, whereby hydraulic fluid under pressure is passed to the piston 11 through the spool valve 14 and an injector tube 13, to effect the operating stroke of the piston 11. <IMAGE>

Description

SPECIFICATION Improvements in hydraulically operated hammers The invention relates to hydraulically operated hammers and particularly, but not exclusively, to handheld road breaking hammers of hydraulic operation. The invention may equally be applied to larger machines typically mounted on excavators for the breaking of rock, demolition work etc. Furthermore, in a miniatureised form the invention may be applied to small 'pick' type machines typically used in mining and demolition industries.

The invention relates to hydraulically operated hammers of the kind comprising a housing formed with a cylinder in which a doubleacting piston is reciprocable, a tool projecting from the housing and located so as to be impacted by the piston at the end of the operating stroke thereof, and a spool valve reciprocable within a valve chamber in the housing and controlling the flow of hydraulic fluid to and from the cylinder to effect reciprocation of the piston.

The invention sets out to provide improvements to hydraulically operated hammers of this kind which may result in a generally simplified construction of the mechanism and the ability to create a more streamlined flow of hydraulic fluid to and from the piston, as well as other advantages.

According to the invention, an hydraulically operated hammer of the kind referred to is characterised in that the valve spool extends longitudinally with respect to the cylinder, and.

is located at one end thereof, and is formed with a central longitudinal bore which, in one end position of the spool valve, places one end of the piston in communication with an hydraulic fluid pressure line, whereby hydrau lic fluid under pressure is passed to the piston through the bore in the spool valve, to effect the operating stroke of the piston.

The central bore in the valve spool may communicate with an injector tube which projects longitudinally of the cylinder from one end thereof, and extends into a closed-ended bore in the piston.

The piston may comprise two portions of different diameters having an annular shoulder at the junction between the two portions, the wall of the cylinder being formed with an inlet in communication with said hydraulic fluid pressure line whereby said annular shoulder is subjected to fluid pressure to effect the return stroke of the piston when the aforesaid one end of the piston is not com ected to the pressure line by the spool valve.

There may be provided in the housing a transfer duct connecting an outlet from the cylinder to one end of the chamber containing the valve spool, said outlet being passed by the annular shoulder of the piston, so that it is placed in communication with said inlet in the cylinder, as the piston reaches the end of its return stroke, whereby said end of the spool valve chamber is placed into communication with the fluid pressure line, thereby effecting axial movement of the valve spool.

Said longitudinal bore in the valve spool may communicate with said fluid pressure line via an hydraulic accumulator.

Preferably, movement of the piston during the operating stroke thereof, after it has impacted on the tool, is opposed by a dashpot arrangement. Such arrangement may be provided by the larger diameter portion of the piston entering a portion of the cylinder beyond said inlet.

The following is a detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which Figures 1 to 5 are diagrammatic longitudinal sections through a hammer according to the invention and showing respectively different stages in the operation thereof.

As with other known types of hydraulic breaker mechanisms the hammer consists of a main housing 10 in which an impacting piston 11 oscillates to strike a chisel or other tool 1 2. Hydraulic fluid is injected into the piston via an injector tube 1 3 whilst the routing of the hydraulic fluid to and from the piston is controlled by anoscillating spool valve 14. In hand-held versions of this sytem an "On-off" control valve (not shown) would be fitted to regulate the operation of the unit.

By varying the sizes of components within the housing 10, but without altering the housing, it is possible to provide mechanisms to operate on differing rates of flow. Differing working pressures may also be achieved by the setting of an adjustable restrictor 1 5.

Whilst other types of hydraulic breaker or impacting mechanism have similar features to the above they generally operate with the spool valve disposed transversely across the machine, which creates turbulent flow within the system, or with a valve disposed directly around the top of the piston 11. The latter has the disadvantage of restricting the length of stroke that may be achieved from the piston. This affects the efficiency of the work that the apparatus can do. In apparatus according to the invention the valve 1 4 is disposed in line with the piston but separate from it, as shown in the drawings. By this means and through the unique design of the valve mechanism itself an improved flow of hydraulic fluid is achieved to and from the piston since the routing of the fluid is simplified when compared to other methods.

Valve 14 is of simple tubular stepped form having a parallel bore but with three outside diameters. The variation in outside diameters provides annular surfaces at the change of diameter at which hydraulic fluid can be brought to bear under pressure to cause movement of the valve within its housing. The upper and lower ends of the spool valve are so disposed as to open and close ports for the feeding of high pressure oil to the piston via the injector tube 1 3 and low pressure oil from the piston in a similar manner.

The operational sequence of the apparatus is as follows: Figure 1 illustrates the mechanism at rest under a condition where no fluid is moving through the circuits. It will be noted that the piston 11 is illustrated at rest at the bottom of its operating or working stroke and that the valve spool 14 is similarly at its lowermost point. An hydraulic accumulator 1 6 is provided in the upper part of the housing, and in the position of Figure 1 the accumulator is uncharged with hydraulic fluid and the diaphragm 1 7 of the accumulator extends downwards to close the entry port 38 into the accumulator chamber.A small quantity of hydraulic fluid is shown lying above the crown of the piston, as indicated at 1 8. This would occur due to a small volume of oil being discharged from a transfer duct 1 9 during the operational sequence, and also any internal leakages of fluid (due to running clearances) would also accumulate at this point.

Figure 2 illustrates the commencement of operation of the cycle where fluid has commenced to flow under pressure into entry port 39. The fluid begins to charge the accumulator 1 6. Simultaneously, pressure is applied to a chamber 20 of the spool valve 14 where it acts on the valve spool causing it to rise in its housing and seal a passage 21 that would otherwise cause fluid to pass into the piston injector tube 13. This action also opens a discharge port 22 to provide a route for the fluid to pass from the injector tube 1 3 to an outlet 23. High pressure fluid is conducted through a passage 24 into the lower part of the cylinder 25 where it reacts against the annular shoulder 26 between the two different diameter portions of the piston 11.This forces the piston 11 upwards, discharging the low pressure fluid lying in the injector tube 1 3 and piston bore through the discharge port 22 and outlet 23. Simultaneously any fluid that was lying above the crown of the piston is discharged to join the low pressure discharge flow via a check valve 27. The pressure generated within the system during the piston rise is directly related to the work required to raise the piston. In turn, this may be controlled by varying a restrictor 28 in the outlet 23. By reducing the effective orifice in the outlet 23 the restrictor 28 will cause the pressure to rise in the discharge line and thus increase the energy required to raise the piston. This in turn will cause the accumulator 1 6 to be charged more fully with hydraulic fluid during this part of the cycle.

Figure 3 shows that as the piston 11 continues to rise the annular chamber 29 formed in the lower part of the cylinder (between the piston 11 and the cylinder wall) will, through the rise of the piston, place the transfer duct 1 9 in communication with the high pressure fluid in the cylinder. High pressure fluid can now flow through the transfer duct to the upper chamber 30 of the valve housing. Here it will act against the upper annular shoulder 31 on the valve spool. This annulus is greater in area than that on which the high pressure fluid acted to raise the spool and this now causes an imbalance in the valve and the valve spool will start to descend.In descending the valve spool closes the discharge passage 32 from the injector tube 1 3 and opens the high pressure feed port 33 which then communicates with the injector tube 1 3 via a central longitudinal bore 34 in the valve spool.

Figure 4 shows the piston descending under the action of the high pressure fluid delivered through the injector tube 1 3. As the piston descends it seals off the transfer duct thus maintaining the pressure in the duct and holding the valve spool in its lower position.

As the piston 11 descends there will be a natural drop in pressure of the incoming fluid from the power source. As this occurs the fluid under pressure in the accumulator chamber 1 6 will also discharge downwards into the injector tube 1 3 to supplement the incoming flow of fluid.

The piston continues its downwards descent until the point where it impacts the tool 12, as shown in Figure 5. just before the piston impacts against the tool the crown 35 of the piston will clear the transfer duct port 36 and release the pressure in the transfer duct. During the time taken for the valve 14 to react to the change in forces created, the piston 11 impacts on the tool 1 2 and applies to the tool kinetic energy only as the fluid pressure is now cut off from the injector tube 1 3. (As the valve 14 commences to rise as previously described and illustrated in Figure 2).

It should be noted that as to tool 1 2 is able to slide vertically in its housing to provide movement needed for cutting the material on which the machine is working, the piston 11 must have the capability of moving downwards further than illustrated in the drawings.

If there were no restriction to this movement the piston would have a self destroying effect on the mechanism. Therefore a 'dashpot' is arranged at 37 to absorb piston energy on its overrun. (In a similar way to that generally used in similar mechanisms).

The arrangement according to the invention provides a generally simplified method of constructing hydraulic hammer mechanisms. It also provides the ability to create a more streamlined flow of hydraulic fluid to and from the piston; the ability, by altering the disposition of signal and high pressure feeds to and from the piston, to produce mechanisms of short or long piston stroke, (without in any way affecting the design or manufacture 0 the valve unit 14); and the ability to increase or decrease the worKing pressure of the sys- tem (and thus its output energy) by means ot a variable restrictor disposed in the discharge line from the mechanism.

Claims (9)

1. An hydraulically operated hammer of the kind comprising a housing formed with a cylinder in which a double-acting piston is reciprocable, a tool projecting from the housing and located so as to be impacted by the piston at the end of the operating stroke thereof, and a spool valve reciprocable within a valve chamber in the housing and controlling the flow of hydraulic fluid to and from the cylinder to effect reciprocation of the piston; characterised in that the valve spool extends longitudinally with respect to the cylinder, and is located at one end thereof, and is formed with a central longitudinal bore which, in one end position of the spool valve, places one end of the piston in communication with an hydraulic fluid pressure line, whereby hydraulic fluid under pressure is passed to the piston through the bore in the spool valve, to effect the operating stroke of the piston.

2. An hydraulically operated hammer according to claim 1, wherein the central bore in the valve spool communicates with an injector tube which projects longitudinally of the cylinder from one end thereof, and extends into a closed-ended bore in the piston.

3. A hydraulically operated hammer according to claim 1 or claim 2, wherein the piston comprises two portions of different diameters having an annular shoulder at the junction between the two portions, the wall of the cylinder being formed with an inlet in communication with said hydraulic fluid pressure line whereby said a nular shoulder is subjected to fluid pressure to effect the return stroke of the piston when the aforesaid one end of the piston is not connected to the pressure line by the spool valve.

4. An hydraulically operated hammer according to claim 3, wherein there is provided in the housing a transfer duct connecting an outlet from the cylinder to one end of the chamber containing the valve spool, said outlet being passed by the annular shoulder of the piston, so that it is placed in communication with said inlet in the cylinder, as the piston reaches the end of its return stroke, whereby said end of the spool valve chamber is placed into communication with the fluid pressure line, thereby effecting axial movement of the valve spool.

5. An hydraulically operated hammer according to any of claims 1 to 4, wherein said longitudinal bore in the valve spool communicates with said fluid line via an hydraulic accumulator.

6. An hydraulicaiiy operated hammer according to any of claims 1 to 5, wherein movement of the piston during the operating stroke thereof, after it hs impacted on the tool, is opposed by a dashpot arrangement.

7. A hydraulically operated hammer accord ing to claim 3 and claim 6, wherein sail dashpot arrangement is provided by the iarger diameter portion of the piston entering a portion of the cylinder beyond said inlet.

8. An hydraulically operated hammer according to any of the preceding claims, wherein hydraulic fluid displaced from the cylinder during the return stroke of the piston passes through a discharge passage, and wherein a variable restrictor is located in the discharge passage.

9. An hydraulically operated hammer substantially as hereinbefore described with reference to the accompanying drawings.