GB1599127A - Powered percussive hand tools - Google Patents

Description

(54) POWERED PERCUSSIVE HAND TOOLS (71) We, DOBSON PARK INDUSTRIES LIMITED, a British Company, of Dobson Park House, Colwick Industrial Estate, Colwick, Nottingham NG4 2BX, 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 invention relates to powered percussive hand tools, particularly of the type commonly called "road drills" and hitherto normally pneumatically operated.

Prior pneumatically operated hand-held percussive or impact tools are noisy and of variable efficiency. Thev frequentlv produce hissing noises due to exhausting of compres- sed air to atmosphere and/or to wear of both moving parts and seals, especially the latter.

The inherent compressibility of the working pressure fluid enhances noise as it is moved through the tool and exhausted to atmosphere. Wholly, hydraulically operated hand-held percussive tools may not be entirely satisfactory if only in view of the incompressibility of working pressure fluid and the consequent transmlsslon of shocks to the operator or the provision of expensive shock absorption means.

It is an object of this invention to provide a tool that is at least in the above respects better suited to hand-held operation.

According to the present invention there is provided a powered percussive hand tool having a hand grip arrangement spaced from a tool bit reception end of the tool, a reciprocable drive piston movable in one direction by a relatively incompressible working fluid to compress a compressible fluid trapped in a chamber, and in the opposite direction by reaction of the compressible fluid following release of the working fluid, further comprising means arranged to respond to a predetermined pressure of the compressible fluid to initiate said release of the working fluid.

Tools operating in this general way have been previously proposed by us, see our Patent No. 1 356 022, and have been successful in relatively large mining or rock breaking machines for mining or quarrying.

It has been found that adaptation of such a mode of operation to hand-held tools can provide a high energy chisel blow of the order of 170 Joules or more with an all-up tool weight of about 30 kilograms, which we have found to be a general improvement on previous wholly pneumatic tools, or wholly hydraulic tool designs we have considered.

In developing particular embodiments of the invention, we have generally used a main hydraulic fluid control valve operated by a pilot valve responsive, at least for initiating a drive stroke, directly to pressure in the trapped volume of compressible fluid.

There is clearly a requirement for both flow and return lines for the hydraulic fluid, usually from a dedicated independent mobile power supply, and this is most conveniently achieved using a coaxial double hose.

Another desirable feature is to provide for hydraulic pulse absorption, partly to protect the operator and partly to protect the hosing, and we have found that a particularly satisfactory provision is an accumulator or attenuator on the pressure feed side, but, on the return side, and thus cutting down on overall weight and bulk, relying on compliance in a "soft" return hose which may be the outer of coaxial hosing for which the inner is reinforced, typically by wire.

A handle for the tool, usually but not necessarily a double handle making an overall T-shape, preferably has adjacent thereto or incorporated therein a "deadman" facility so that the tool will not operate unless that facility is positively operated from a self-return position. A suitable facility comprises a push-button or lever operated by-pass valve normally intercoupling hydraulic flow and return but movable, say against a spring bias, to cut-off such by-pass via the valve.

One convenient way to preset operating blow frequency makes use of a delay means whereby the drive stroke is initiated on attainment of a predetermined trapped gas volume pressure but the retraction stroke is delayed therefrom by a prescribed delay, which may be adjustable from a minimum upwards, say to cope with lower power supplies, but not necessarily readily adjustable without a special tool, especially where dedicated special purpose supplies are the norm.

In the main, tools of the order of 30 kilograms in weight are usually operated with their working bit or chisel downwardly directed and chisel or other retention is, herein, preferably of a readily releasable type, say a spring clip or latch that may well require no tools at all for release or at least no more than a levering action.

The gas charge used for the trapped volume is normally pressurised to a desired level at full extension of the drive piston, i.e.

at maximum drive stroke, and is preferably of an inert gas, such as nitrogen, that is relatively resistant to adiabatic heating, at least compared to air. Carbon dioxide may also be suitable. However, cylinders of such gases are not commonly available on construction, demolition or road-working sites and it is preferred to provide for the use of charging capsules, usually of one-charge capacity. Such charging capsules may be of a rupturable type with a gas inlet valve adapted for rupturing purposes.

A particularly effective arrangement arises where main hydraulic control and gas pressure response valves are of spool types with their spool axes at right angles to the axis of the drive piston, thereby minimising interaction or interference by tool blows.

One embodiment of the invention will now be particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic layout of a typical tool and its control valving; Figure 2 is one view of a particular handheld impactor tool; Figure 3 is a view at right angles to that of Figure 1 and partly broken away.

Figure 4 shows details of a main hydraulic control valve of Figure 1; and Figure 5 shows details of a pilot valve of Figure 1.

In the drawings, a hand-held impactor tool 10 has a casing in three parts 11, 12, 13 secured together by tie bolts 14. Rear or upper casing part 11 is hollow and defines a chamber 15 for a trapped volume of gas introduced via a valve 16 at any convenient position and resembling, in action, the general type used for pneumatic tyres of motor vehicles but with the valve element 17 thereof adapted to rupture a charging cap sule and further fitted with a seal 18 for such a capsule. Front or lower casing part 13 is essentially tubular with a hexagonal section forward bore part 20 to hold end 21 of a chisel 22 and provide integral bearing surfaces for sliding thereof, and a circular section rearward bore part 23 into which hammer part 24 of a drive piston 25 extends and is accommodated.Mid-casing part 12 is also tubular but with a constant diameter bore 26 housing forward and rearward, usually removable, bearings 27, 28 for the drive piston 25 proper, and a central insert 29 defining an annular chamber 30 for hydraulic fluid via aperture 31 and passage 32 to and from a main control valve.

Both of the bearings 27, 28 provide stops 35, 36 for a flange 37 of the piston 25 to limit the total stroke thereof. Forward bearing 27 is stepped to provide stop 35 at a shoulder and the enlarged part corresponds in bore to the diameter of flange 37 so as to give a slowing or snubbing action to the piston by entrapment therein of hydraulic fluid. In practice, the piston 25 is unlikely ever to reach the position shown except when unconnected to hydraulic fluid and will normally rebound at least under the weight of the tool resting on the chisel so that hydraulic fluid under pressure will be able to drive its retraction stroke due to the reduced diameter of piston part 24. Otherwise, "priming" is by way of banging the tool chisel on the ground to give the hydraulic working fluid driving access to the flange.

Both of the bearings 27, 28 are drained to the hydraulic fluid return by bores 42, 43, respectively, between their stops 35, 36 and seals 44, 45 to the piston, the rear bearing being spring or piston loaded to withstand substantial pressure, typically of the order of 2000 psi, and the forward bearing 27 has an additional wiper 49.

A valve block 50 is secured in a recess 51 of the central casing part 12 and houses both a main hydraulic control valve 52, a gas pressure responsive pilot valve 53 therefor, and a button or plunger operated safety by-pass valve 54. The valve block 50 also has a coaxial hose connection 55 for hydraulic fluid, its inner element 56 serving for pressure fluid supply from an inner hose 57 reinforced with wire 58 and its outer element 59 serving for pressure fluid return via a relatively soft outer hose 60. An accumulator or attenuator 61 is secured to or made integral with the block 50 resting in a recess 62 of the rear casing part 11 and serving to absorb or reduce the effects of pulsing in the pressure fluid supply.

The rear casing part 11 also has sideways extending handles 63, 64 with, in one (63) of them, a pivotally mounted and a preferably spring-loaded lever 65 having an angled extension 66 to actuate the by-pass valve 54 to cut off direct communication between pressure fluid supply and return only when that handle is firmly gripped by the operator.

The pulse attenuator or accumulator 61 is indicated diagrammatically in Figure 1 as being of a trapped gas and diaphragm type with hydraulic fluid communication 67 to the hydraulic supply branched at 68 to the by-pass valve 54 for communication via holes 69 in valve sleeve 70 with branch 71 to the pressure fluid return. The sleeve 70 is biassed by spring 72 to the position shown and will cut-off the flow to return connection only when moved against its bias by the lever 65.

The main control valve 52 has a spool 73 operated by end pilot pistons 74, 75 via bores 76, 77 from the pilot valve 53 which also has a spool 78 and pressure fluid flow and return coupling bores 79 and 80 to corresponding chambers of the main valve 52, the return bore 80 being branched to spaced pilot valve cylinder positions. The pilot valve spool 78 is spring biassed at 81 to the position shown and drivable therefrom by gas pressure over bore 82 from a gas res- sure delay valve 83. The gas pressure delay valve 83 offers two possible communications from the chamber 15 to bore 82, one via an adjustable needle valve element 84 and the other via a spring biassed one-way overload valve element 85.Thus, the oneway valve element 85 will open at a predetermined gas pressure in the chamber 15, operating the pilot valve to initiate the impact stroke, then close when the pressure drops. The needle valve element 84 will then determine the rate of decay of pilot spool operating pressure in bore 82, and hence the interval between the impact stroke and the subsequent retraction stroke.

As best seen in Figure 4, the main control valve spool 73 has two spaced and circumferentially grooved lands 86, 87 capable, as shown, of just spanning two spaced medial annuli 88, 89 formed in a cylinder bore 90.

The spool 73 is slidable between extreme positions defined by end faces of plugs 91, 92 sealed at 93, 94 relative to the spool work space and at 95, 96 beyond wells 97, 98 communicating via bores 99, 100 with the pilot pistons 74, 75 which are also circumferentially grooved for sealing purposes and are slidable with a close-fit in blind bores 101, 102 of the plugs 91, 92. In the left-most position of the valve spool 73, the annuli 88, 89 are in communication, annulus 88 being connected to the hydraulic supply with a direct straight bore 67 to the accumulator 61 and to the pilot valve supply bore 79, and annulus 89 being connected to the tool drive piston retraction chamber 30 over bore 32.As the valve spool 73 moves to the right, it will first block hydraulic fluid supply annulus 88 and then open communication between the annulus 89 and a further annulus 103 connected to the hydraulic fluid return to allow the drive stroke of the tool piston 25.

Figure 5 shows details of the pilot valve 53. Its spool 78 has three spaced main diameter reductions 104, 105, 106 between end lands 107, 108 and two lesser diameter reductions 109, 110 between flanges 111, 112 and 113, 114 terminating the main diameter reductions. The end lands 107 and 108 have U-type and O-ring type seals 115, 116 respectively, the latter relative to a gas receiving chamber 117 formed by and through one or more apertures 118 in a right-most spool end stop insert 119. At its other end the spool 78 is acted on by a centrally hollowed bearing plate 120 loaded by the spring 81 accurately located within a spring housing sleeve 121 and shimmed appropriately at 122 to achieve desired operation.Main spool bore 125 is crossbored at 126, 127, for communication to the main valve pilot operating bores 76, 77, at positions flanking the pressure fluid inlet bore 79 and between pressure fluid return branches 128, 129 of bore 80. The spool end lands 107, 108 are just capable of spanning the hydraulic fluid return branch bores 128, 129, but, in the right-most spool position shown, there is communication between cross-bore 126 and return branch bore 128 and between cross-bore 127 and supply bore 79. In moving left, the spool 78 first closes communication between cross-bore 127 and supply bore 79, then shuts crossbore 126 off from return branch bore 128.

Communications between cross-bore 127 and return branch bore 129, and between cross-bore 126 and supply bore 79, are established in that order during leftwards movement of the spool, and it may be advantageous for there to be momentary communication between supply bore 79 and return branch-bore 128 to aid draining of bore 125.

It is preferred in many cases to provide a means of indicating charge in the compressible fluid chamber, at least as to whether it is up to minimum specified, say by the use of an indicator button held in once operated until pressure drops below a preset minimum, determined for example by spring strength or rate of a latch biassed by the spring against gas pressure tending to hold the latch in. Such an arrangement readily permits of provision for the spring bias to be adjustable, say by way of screw thread adjustment of a spring seat.

WHAT WE CLAIM IS: 1. A powered percussive hand tool having a hand grip arrangement spaced from a tool bit reception end of the tool, a reciprocable drive piston movable in a retraction stroke in one direction by a relatively incompressible working fluid to compress a compressible fluid trapped in a chamber, and in an impact stroke in the opposite direction by reaction of the compressible fluid following release of the working fluid,

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

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. being of a trapped gas and diaphragm type with hydraulic fluid communication 67 to the hydraulic supply branched at 68 to the by-pass valve 54 for communication via holes 69 in valve sleeve 70 with branch 71 to the pressure fluid return. The sleeve 70 is biassed by spring 72 to the position shown and will cut-off the flow to return connection only when moved against its bias by the lever 65. The main control valve 52 has a spool 73 operated by end pilot pistons 74, 75 via bores 76, 77 from the pilot valve 53 which also has a spool 78 and pressure fluid flow and return coupling bores 79 and 80 to corresponding chambers of the main valve 52, the return bore 80 being branched to spaced pilot valve cylinder positions. The pilot valve spool 78 is spring biassed at 81 to the position shown and drivable therefrom by gas pressure over bore 82 from a gas res- sure delay valve 83. The gas pressure delay valve 83 offers two possible communications from the chamber 15 to bore 82, one via an adjustable needle valve element 84 and the other via a spring biassed one-way overload valve element 85.Thus, the oneway valve element 85 will open at a predetermined gas pressure in the chamber 15, operating the pilot valve to initiate the impact stroke, then close when the pressure drops. The needle valve element 84 will then determine the rate of decay of pilot spool operating pressure in bore 82, and hence the interval between the impact stroke and the subsequent retraction stroke. As best seen in Figure 4, the main control valve spool 73 has two spaced and circumferentially grooved lands 86, 87 capable, as shown, of just spanning two spaced medial annuli 88, 89 formed in a cylinder bore 90. The spool 73 is slidable between extreme positions defined by end faces of plugs 91, 92 sealed at 93, 94 relative to the spool work space and at 95, 96 beyond wells 97, 98 communicating via bores 99, 100 with the pilot pistons 74, 75 which are also circumferentially grooved for sealing purposes and are slidable with a close-fit in blind bores 101, 102 of the plugs 91, 92. In the left-most position of the valve spool 73, the annuli 88, 89 are in communication, annulus 88 being connected to the hydraulic supply with a direct straight bore 67 to the accumulator 61 and to the pilot valve supply bore 79, and annulus 89 being connected to the tool drive piston retraction chamber 30 over bore 32.As the valve spool 73 moves to the right, it will first block hydraulic fluid supply annulus 88 and then open communication between the annulus 89 and a further annulus 103 connected to the hydraulic fluid return to allow the drive stroke of the tool piston 25. Figure 5 shows details of the pilot valve 53. Its spool 78 has three spaced main diameter reductions 104, 105, 106 between end lands 107, 108 and two lesser diameter reductions 109, 110 between flanges 111, 112 and 113, 114 terminating the main diameter reductions. The end lands 107 and 108 have U-type and O-ring type seals 115, 116 respectively, the latter relative to a gas receiving chamber 117 formed by and through one or more apertures 118 in a right-most spool end stop insert 119. At its other end the spool 78 is acted on by a centrally hollowed bearing plate 120 loaded by the spring 81 accurately located within a spring housing sleeve 121 and shimmed appropriately at 122 to achieve desired operation.Main spool bore 125 is crossbored at 126, 127, for communication to the main valve pilot operating bores 76, 77, at positions flanking the pressure fluid inlet bore 79 and between pressure fluid return branches 128, 129 of bore 80. The spool end lands 107, 108 are just capable of spanning the hydraulic fluid return branch bores 128, 129, but, in the right-most spool position shown, there is communication between cross-bore 126 and return branch bore 128 and between cross-bore 127 and supply bore 79. In moving left, the spool 78 first closes communication between cross-bore 127 and supply bore 79, then shuts crossbore 126 off from return branch bore 128. Communications between cross-bore 127 and return branch bore 129, and between cross-bore 126 and supply bore 79, are established in that order during leftwards movement of the spool, and it may be advantageous for there to be momentary communication between supply bore 79 and return branch-bore 128 to aid draining of bore 125. It is preferred in many cases to provide a means of indicating charge in the compressible fluid chamber, at least as to whether it is up to minimum specified, say by the use of an indicator button held in once operated until pressure drops below a preset minimum, determined for example by spring strength or rate of a latch biassed by the spring against gas pressure tending to hold the latch in. Such an arrangement readily permits of provision for the spring bias to be adjustable, say by way of screw thread adjustment of a spring seat. WHAT WE CLAIM IS:

1. A powered percussive hand tool having a hand grip arrangement spaced from a tool bit reception end of the tool, a reciprocable drive piston movable in a retraction stroke in one direction by a relatively incompressible working fluid to compress a compressible fluid trapped in a chamber, and in an impact stroke in the opposite direction by reaction of the compressible fluid following release of the working fluid,

further comprising means arranged to respond to a predetermined pressure of the compressible fluid to initiate said release of the working fluid.

2. A tool according to claim 1, further including means for setting a delay between the impact stroke and the next retraction stroke.

3. A tool according to claim 2, wherein a main control valve for said working fluid is controlled by a pilot valve, and the means responsive to said predetermined pressure has a pilot valve actuator element opened by said predetermined pressure and a presettable delay element between said pilot valve and the chamber for the compressible fluid.

4. A tool according to any preceding claim wherein said hand grip arrangement is a double-handle, one handle to each side of a tool body housing, in line with said tool bit reception end, said drive piston with associated control valve gear, and said chamber for said compressible fluid, said doublehandle flanking said chamber.

5. A tool according to any preceding claim, further comprising hydraulic fluid pulse absorption means.

6. A tool according to claim 5, wherein said pulse absorption means comprises, for working fluid supply, a pressure fluid side accumulator or attenuator.

7. A tool according to claim 6, wherein said accumulator or attenuator is directly connected to a main working fluid valve at its pressure fluid supply input porting.

8. A tool according to claim 6 or claim 7, wherein pulse absorption for working fluid return is provided for by relative flexibility of a hose therefor.

9. A tool according to any preceding claim, wherein working fluid supply is via a coupling for a coaxial double hose.

10. A tool according to claim 9 with claim 8, wherein the hose for working fluid return is an outer hose of a coaxial double hose having a reinforced inner pressure supply hose.

11. A tool according to any preceding claim, wherein said hand-grip arrangement incorporates means for actuating a safety valve from a position interconnecting working fluid flow and return.

12. A tool according to claim 11, wherein said safety valve is operative against a spring bias predetermining that working fluid flow is connected to working fluid return.

13. A tool according to any preceding claim normally actuated with its tool bit reception end downwards, and further comprising latching means for retention and ready release of said tool bit.

14. A tool according to any preceding claim, further comprising a means of charge ing said member for the compressible medium and having automatic means for releasing compressible medium from a pressurised capsule.

15. A tool according to any preceding claim, wherein a or said main valve for incompressible working fluid and/or a or said pilot valve for actuating said main valve is or are of spool type with the spool or spools thereof disposed along an axis or axes at right angles to the drive piston axis.

16. A powered percussive hand tool substantially as herein described with reference to and as shown in the accompanying drawings.