GB2045348A - Compressed-gas-operated Reciprocatng-piston Devices - Google Patents
Compressed-gas-operated Reciprocatng-piston Devices Download PDFInfo
- Publication number
- GB2045348A GB2045348A GB8006433A GB8006433A GB2045348A GB 2045348 A GB2045348 A GB 2045348A GB 8006433 A GB8006433 A GB 8006433A GB 8006433 A GB8006433 A GB 8006433A GB 2045348 A GB2045348 A GB 2045348A
- Authority
- GB
- United Kingdom
- Prior art keywords
- muffler
- sleeve
- cylinder
- reciprocating
- ribs
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25D—PERCUSSIVE TOOLS
- B25D17/00—Details of, or accessories for, portable power-driven percussive tools
- B25D17/11—Arrangements of noise-damping means
- B25D17/12—Arrangements of noise-damping means of exhaust silencers
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/001—Gas flow channels or gas chambers being at least partly formed in the structural parts of the engine or machine
Abstract
A compressed-gas-operated reciprocating-piston device, e.g. a concrete breaker, rock drill or chipping hammer, has a cylinder comprising a rigid inner metal tube (40) in which the piston (12) reciprocates and a moulded outer sleeve (41) of rubber or plastics material, e.g. polyurethane, which surrounds the tube over the majority of its length and is bonded thereto. The sleeve has three integral moulded longitudinal ribs (43) in which are moulded longitudinal passages (32) for transmission of compressed air to the cylinder interior. An outer tubular muffler (50) of rubber or plastics material surrounds the cylinder and defines a sound-reducing path for exhaust gas from the cylinder to the atmosphere. The exhaust gas is discharged via ports (34) into spaces such as (87) defined between pairs of adjacent ribs (43) of the sleeve within the muffler, these spaces forming part of an expansion chamber in the muffler. This expansion chamber communicates with the atmosphere through exhaust ports (52). The combination of ribbed sleeve and muffler provides improved sound- damping and exhaust silencing for the device. <IMAGE>
Description
SPECIFICATION
Compressed-Gas-Operated Reciprocating
Piston Devices
This invention relates to compressed-gasoperated devices of the reciprocating-piston type, and is concerned with the construction of the cylinder components of such devices, and the formation of the passageways for exhausting used gas from their cylinders to atmosphere. The invention is particularly aithough not exclusively applicable to percussive tools such as pneumatically-operated concrete breakers, rock drilis, chipping hammers and the like.
In such devices a piston is caused to reciprocate in a cylinder and to do useful work during or at the end of its forward working stroke, for example by impacting against an anvil or the shank of a tool bit. In order to achieve reciprocation of the piston, compressed air or other pressure fluid medium has to be directed alternatively to opposite ends of the cylinder so as to move the piston. This operating fluid is usually conducted through longitudinal passages formed in the wall of the cylinder. The usual method of construction of these cylinders has been by casting or forging out of high quality case-hardenable steel or cast iron, and subsequently machining the main cylinder bore and the fluid transfer passage(s). This method of construction results in a component which is both heavy and expensive.
One object of the present invention is to provide a compressed-gas-operated reciprocating-piston device with an improved construction of cylinder component, which is used in conjunction with a surrounding tubular muffler and provides an improved sound-attenuating effect on the gas exhaust gas discharged from the device in operation, as well as on the general operating noise.
According to the present invention, a compressed-gas-operated reciprocating-piston device has a composite cylinder component comprising a rigid inner metal cylinder tube in which the piston reciprocates in use, and an outer sleeve moulded of rubber or synthetic plastics material and surrounding and bonded to the metal cylinder tube, the sleeve overlying the entire outer circumferential surface of the major part of the length of the tube, and the sleeve being formed on its outer surface with a plurality of longitudinally-extending outwardly-projecting integrally-moulded ribs spaced apart around the circumference of the sleeve, the device further including an outer tubular muffler made of rubber or synthetic plastics material which surrouds the ribbed sleeve and defines within the muffler a chamber, referred to as the first muffler chamber, which communicates with an exhaust opening leading out of the muffler into the ambient atmosphere, the cylinder component being formed with at least one gas discharge port in its wall which opens into the first muffler chamber between two adjacent ribs of the sleeve, and in which a longitudinally-extending elongate moulded passage is formed in the interior of at least one of the ribs, said passage constituting a transfer passage for supplying compressed gas to one end portion of the interior of the cylinder tube.
Preferably the said passage leads compressed gas from a distribution valve at the upstream end of the passage into one end portion of the interior of the cylinder tube via an inlet at the downstream end of the passage.
In one construction, the moulded sleeve of the cylinder component has three of the said integrally moulded ribs and has at least two of the said gas discharge ports opening into the first muffler chamber respectively between two different pairs of adjacent ribs.
Each of the three ribs may be formed with one of the said transfer passages for the supply of compressed gas to the cylinder.
However, at least one of these passages formed in the ribs may communicate at one end with the interior of the cylinder at one end, and be permanently closed at its other end, that passage acting as a pneumatic buffer for the air trapped in the cylinder at the end of the piston stroke.
The preferred material of the moulded sleeve, and also of the surrounding muffler, is polyurethane. Polyurethane is already used widely in the construction of muffler cylinders for pneumatic tools, and has properties making it eminently suitable for the purpose of the present invention, notably its soft, yielding moulded surfaces which afford good sound-absorbing and sound-damping properties, reducing internal sound reflections. To ensure intimate bonding of the polyurethane moulding material with the inner metal tube, the external surface of the latter should be treated with a suitable bonding agent.
Convenientiy the sleeve may be a moulding which was made by being moulded directly around the cylinder tube using the latter as a moulding core.
The crests of the longitudinal ribs on the moulded sleeve may act as radial locating means for at least a part of the muffler.
In one arrangement of the invention the first muffler chamber may communicate directly with the ambient atmosphere via the exhaust opening.
In another arrangement, however, the first muffler chamber communicates with the muffler exhaust opening via restriction leading into a second chamber within the muffler, the second muffler chamber communicating with the muffler exhaust opening.
The second muffler chamber may include as a part of its volume a space defined between the muffler and the sleeve and bounded by a further pair of adjacent ribs of the sleeve, between which further pair of ribs no discharge port opens from the interior of the cylinder, and in which case the general direction of exhaust gas flow in the said space is opposite to that in the first muffler chamber.
In one such arrangement, the muffler wall may
include a longitudinally-extending portion of
increased depth which protrudes laterally inwardly
into the second muffler chamber and is formed
with an internal longitudinally-extending passage
which opens at one end into the said space
bounded by said further pair of ribs and leads at
its other and downstream end to the muffler
exhaust opening, the general direction of exhaust
gas flow along the second muffler chamber being
opposite to that along the said passage.
For a good sound attenuating effect on the
exhaust of the device, it is preferred that the ratio
of the internal volume of the working end of the
cylinder with the piston in its limiting position at
the end of a working stroke (swept volume plus
clearance volume) to the volumes of the first and
second muffler chambers is in the range between 1:5:3 and
1:8:5
and the ratio of the total area of flow cross
section of the said gas discharge port(s) from the
cylinder component to that of the restriction
between the first and second muffler chambers
and to that of the outlet from the second muffler
chamber to atmosphere is in the range between 1:5:3 and
1:8:5
For example, the said ratio of volumes may be
approximately 1 : 7 : 3.6, and the said ratio of
flow cross-sectional area may be approximately 1 8 : 4.
The invention may be carried into practice in
various ways, but two specific embodiments will
now be described by way of example only and
with reference to the accompanying drawings, in which: Figure 1 is a section taken through the
longitudinal axis of a percussive tool;
Figure 2 is a cross-section on the line Il-Il of
Figure 1;
Figure 3 is a side view in part-section on the
line Ill-Ill in Figure 2;
Figure 4 is a plan view of a mould for casting
the composite cylinder of the tool of Figures 1 to
3;
Figure 5 is a combined longitudinal section on
the lines VA, VB and VC in Figure 4;;
Figure 6 is a sectional view similar to Figure 1
of the central part only of a modified percussive
tool embodying the invention, showing the
composite cylinder, the surrounding muffler and
the gas chambers within the muffler interior; and
Figures 7, 8 and 9 are respectively cross
sections on the lines VIl-VIl, VIll-VIll and IX
IX in Figure 6.
The percussive tool shown in Figures 1 to 3
comprises a composite cylinder 10 in whose bore 11 a hammer piston 12 reciprocates. At its lower -end the cylinder 10 carries a fitting 13 with a liner sleeve 14 which slidably receives the shank 1 5 of a tool bit 16, and the hammer piston 12 has a stem 1 7 which impacts against the shank 15 of the tool bit at the end of each working stroke of the piston.
A spring-loaded latch 1 8 retains the tool shank 1 5 in the sleeve 14. A sleeve 19 at one end of the cylinder 10, that which is normally lower in use, seals around the piston stem 1 7 and traps air in the cylinder to cushion the piston 12 at the end of its working stroke. At the other end of the cylinder 10, which is normally uppermost in use, is a handle fitting 20 with handles 21, an air inlet connection 22 into which is fitted an inlet stem 23 to which is connected a pressure hose (not shown) connected to a supply of compressed air, and a pivoted operating trigger 24 which when depressed advances a plunger rod 25 to lift the ball 26 of an inlet valve 27 off its seating 28, the inlet valve 27 controlling the admission of compressed air into a chamber 29 in the handle fitting 20.A pressure-responsive distribution valve assembly 30 of conventional plate type controls the admission of compressed air from the chamber 29 alternately to opposite ends of the cylinder bore 11 to cause the reciprocating motion of the hammer piston 12 in the cylinder 10, the air being transmitted to the lower end of the cylinder via longitudinal passages 32 and radial passages 33 in the wall of the cylinder for returning the piston after each working stroke. A number of discharge ports 34, in this case three, in the wall of the composite cylinder 10 are controlled by the piston 12 and releases the compressed air from the upper and lower ends of the cylinder towards the end of the working and return strokes respectively of the piston.The air is discharged through the or each discharge port 34 into an expansion chamber in the interior of an external tubular muffler 50 having final exhaust ports 52 in its wall, as will be described below. An oil reservoir 35 in the handle fitting 20 releases lubricating oil through a bleed orifice 36 into the stream of pressure air in one of the passages 32 for lubricating the piston/cylinder bearing surfaces.
The cylinder 10 is of composite construction, and comprises an inner steel tube 40 of circular section with a synthetic plastics outer sleeve 41 bonded to its outer surface. In this embodiment the outer sleeve 41 is moulded from polyurethane polymer, and the air transfer passages 32 are formed in the thickness of the moulded sleeve 41 itself. As indicated in Figure 2 there are three of the passages 32 respectively formed as moulded cavities in protruding integral longitudinal rib portions 43 of the sleeve 41. The polyurethane sleeve 41 extends over the majority of the length of the steel tube 40, between the handle fitting 20 and the lower fitting 1 3.
In order to provide a high degree of exhaust air muffling, an outer plastics muffler 50 is mounted around the cylinder 10. The muffler could be formed as a unitary moulding integral with the plastics sleeve 41, but in this embodiment a separate two-part tubular cover of muffler 50 surrounds the cylinder 10 and the fitting 13, the lower part of the muffler 50 defining an annular space 51 around the fitting 13 beyond the ends of the ribs 43, the final exhaust ports 52 leading from the space 51 into the ambient atmosphere.As shown, the or each radial exhaust port 34 (three ports 34 are shown in Figures 1-3) leads through the composite cylinder wall into a segmental region 83, 84 or 87 between two adjacent ribs 43, communicating with the annular space 51 and forming therewith an expansion chamber in the muffler 50 by which the pressure of the exhaust air discharge through the port 34 will be reduced, and its pulsations damped, before it is discharged through the final exhaust ports 52.
The two-part muffler 50 is also made of polyurethane plastics material with an annular spigot joint 49 between its two portions. The upper part of the muffler 50 is located by the upper end portions of the three ribs 43, as shown in Figures 1 and 2, and by a flanged ring 53 trapped between the end of the moulded sleeve 41 and the handle fitting 20 whilst the lower part of the muffler 50 locates around the lower fitting 13. A pair of longitudinal tie rods 54 (Figures 2 and 3) extend within the muffler 50 and are anchored at their ends respectively in the fittings 20 and 13, and can be tensioned by means of nuts 55 screwed onto their screwthreaded lower ends.
The composite cylinder 10 of the tool shown in
Figures 1 to 3 is manufactured as follows. Firstly, the cylinder liner tube 40 is manufactured by conventional fabrication techniques as a rigid steel tube of circular or other regular crosssection, having inside dimensions of correct size to accept the piston 12, and outside dimensions which need not be critically sized. The exterior of the steel tube is treated with a suitable bonding agent and the tube is then placed in a mould whose cavity has the desired outer shape of the sleeve 41 and which contains a series of rods or cores positioned where the compressed air transfer passages are required to be.The plastics moulding material, in this case polyurethane, is then introduced into the mould cavity through a suitable pouring opening, until it surrounds the steel tube and the rods or cores and fills the mould cavity, and is then allowed to cure. After curing the composite cylinder is removed from the mould and the rods or cores are withdrawn, leaving the completed composite cylinder assembly available for immediate assembly into the tool.
Figures 4 and 5 show a suitable mould for use in casting the composite cylinder 10 of the tool of
Figures 1 to 3. The mould is in two main parts, namely an open-ended tubular mould portion 60 and a locating plate 61 which closes and seals the lower end of the mould portion 60 and serves to support the steel liner tube 40, three cores 62 for the air passages 32 and two cores 63 for the apertures to receive the tie rods 54. The tubular mould portion may be made of any suitable rigid material, for example glass-fibre-reinforced plastics materials for experimental use or short production runs, or steel or aluminium for extended production. The locating plate 61 is made of steel, and is bolted to the flange 64 of the tubular mould portion 60 by three fastening bolts 65.Bushes 66 for locating the three air passage cores 62 are welded to the lower face of the locating plate 61, and are formed with steps 67 for supporting and axially locating the lower end of the steel liner tube 40 (which slides in a central aperture 68 in the plate 61 and in the open upper end 69 of the mould portion 60), and with steps 70 for supporting and axially locating the cores 63 for the tie-rod apertures. A set of core pins 71 is provided (in this case two only are shown) inserted in radial bosses 72 formed in the wall of the tubular portion 60, for moulding the exhaust ports 34. The core pins 71 extend into drilled apertures in the wall of the liner tube 40.
The passages 33 connecting the interior of the liner cylinder to the three air passages 32 are formed in a different way. A temporary plug of cured polyurethane or other soft material is inserted into each of three previously-drilled holes 73 in the liner tube 40, so as to prevent the escape of liquid moulding material into the liner tube during the moulding operation. After the cure of the main mass of plastic in the mould, the temporary plugs and the portions of the plastic wall of the moulding attached thereto are drilled through from the inner bore of the cylinder by means of an angle-head drill. This operation forms the passages 33 which connect the bore of the liner tube 40 to the three air passages 32.
The interior of the tubular portion 60 corresponds in shape to the exterior of the composite cylinder 10, providing the three rib
portions 43. At its upper end the tubular portion
60 defines a runner passage 75 and two risers
76.
The procedure for moulding is as follows. The outer surface of the steel liner tube 40 is first treated with a bonding agent. Where the moulding material for the sleeve 41 is to be polyurethane, the bonding agent is preferably that marketed under the Registered Trade Mark
THIXON by The Whittaker Corporation, Dayton
Chemical Products Division, of West Alexandra,
Ohio 45381, United State of America, this material ensuring intimate and adequate bonding of the plastics moulding material to the steel tube.
The inner surfaces of the mould portion 60 and those surface of the cores pins 62, 63, 71 and of the locating plate 61 which will come into contact with the moulding material are treated with a release agent, for example a silicone-based material or the film sold under the Registered
Trade Mark TEFLON TFE of the DuPont Company.
The liner tube 40 and core pins are then inserted in position in the mould, and casting can take place.
A preferred grade of plastics moulding material is the polyurethane rubber sold under the
Registered Trade Mark ADIPRENE L-1 00 and
available from the DuPont Company, Elastomer
Chemicals Department, Wilmington, Delaware
19898, U.S.A., who also supply the release agent
TEFLON TFE film. ADIPRENE L-1 00 when mixed
with a curing agent such as MOCA (Registered
trade mark of the DuPont Company and also
available from them) yields vulcanizates in the
hardness range 88 to 92 (durometer A).The liquid
polyurethane monomer ADIPRENE L--l 00 is
mixed with any disired colouring pigment and
with the MOCA, in accordance with the
instructions issued by the manufacturers, and
when thus prepared it is poured into the mould
cavity via the runner passage 75 and allowed to
fill the cavity completely until excess material
issues from the riser passages 76. Curing takes
place partly in the mould which is placed in an
oven at 1000C for about 1 hour, after which the
moulding on the liner tube 40 is removed from
the mould on the cure is completed at 1000C for
a minimum of a further 3 hours in the oven.
Excess runner and riser plugs are trimmed off
after the cure has been completed.
Polyurethane is a preferred material for use in
making the plastics sleeve 41 and two-part muffler
50, being already used widely in the construction
of muffler cylinders for compressed-air percussion
tools. Polyurethane has the desirable properties
that are required of a tool cylinder, in that it is
easily pourable, resists damage, is suitable for use
over a wide range of temperature and readily
bonds to steel, and is a soft, resilient material
with good sound-absorbing properties.
However other plastics materials or rubber may
also be suitable for the manufacture of the
plastics sleeve 41. For example glass-fibre
reinforced resin may be used in some cases. The
method of construction of the composite cylinder
1 0 may then differ from that described above, in
that a manual lay-up method would probably be
more appropiate than pour moulding, the inner
steel tube and the rods or cores for the transfer
passages being held in place in a jig and the glass
mat and resin being applied manually and shaped
externally in a mould, in the usual way.
The design of the cylinder component of the
percussion tool shown in Figures 1 to 3 is
comparatively simple and requires only three air
transfer passages 32 to supply the return air to
the lower end of the cylinder 10 for effecting the
return stroke of the piston.
Instead of the separate two-part muffler 50
shown in Figures 1 to 3, the muffler cylinder and
the outer sleeve of the composite tool cylinder 10
may be constructed as a single integral moulding
of the polyurethane or other plastics materials, e.g.
by moulding in a single operation in a mould
having the necessary cores to shape all the
passages and the muffler chamber.
It has been found that the composite cylinder
and muffler arrangement constructed as
described above with reference to Figures 1 to 3
has the advantage of improved noise suppression
when the tool is in use. Because of the intimate ~bonding between the plastic sleeve and the inner steel tube, the characteristic "ring" of the cylinder when struck is almost entirely eliminated.
Furthermore, the transfer passages for the compressed air are completely bounded by the plastics material of the ribs in which they are moulded, giving a degree of resilience to the passage walls which provide in itself a soundabsorbing effect, whilst the interior of the muffler into which the used air discharged from the cylinder first passes is bounded mainly by plastics material which, having a softer surface than steel or cast iron, is better able to supress the noiseproducing pulsations in the exhaust air. The three ribs 43 which protrude into the expansion chamber within the muffler have the effect of increasing the surface area of that chamber for a given volume thereby increasing the sound absorbing effect. The characteristics of polyurethane are found to be particularly beneficial in these respects.The use of the expansion chamber into which the exhaust air is initially released from the cylinder interior, also helps to attenuate the sound energy of the exhaust air before its final discharge into the atmosphere.
Figures 6 to 9 show a second embodiment of the invention, in which the internal spaces defined within the muffler are so shaped and connected as to provide a double-expansion-chamber silencing system, through which the used air discharged from the cylinder passes to the final exhaust opening to atmosphere. In Figure 6 only the central portion of the percussive tool are shown, the upper part with the handle, air inlet, and distributor valve, and the lower end with the tool-retaining latch, being omitted but being similar to the corresponding parts shown in
Figures 1 to 3. Parts of the embodiment of
Figures 6 to 9 which correspond to parts shown in
Figures 1 to 3 are given the same reference numerals but qualified by the letter 'A'.
In the embodiment of Figures 6 to 9 the steel liner tube 40A is enclosed within a moulded polyurethane sleeve 41A bonded to its outer surface as in Figures 1 to 3. The sleeve 41 A is made by a moulding process similar to that described above for the sleeve 41, using a suitably modified mould, and using the moulding materials previously indicated. The three integral longitudinal ribs 43A contain the three moulded transfer passages 32A by which compressed air from the distributor valve is admitted into the cylinder on the lower side of the piston 12, as before. In this case however the crests of the three ribs 43A are in locating engagement with the inner surface of the moulded polyurethane muffler 50A over the whole of the lengths of the ribs, lying in shaliow recesses 80A formed in elongate inwardly-projecting thickened portions 81A of the walls of the two parts of the muffler 50A, instead of being in locating engagement with the upper part only of the muffler but spaced slightly from the lower part of the muffler along their lower portions as shown in Figures 1 and 2.
The three ribs 43A thus define with the body of the sleeve 41 A and with the inner surface of the muffler longitudinally-extending spaces 83A, 84A and 87A. Each of two of these spaces 83A and 84A has one of the radial discharge ports 34A opening into it between two ribs 43A, and is otherwise entirely closed except at the lower end where the ribs 43A terminate. Below the ribs 43A these two passages 83A, 84A open into a space 85A within the muffler 50, on one side of the rods 54A and fitting 13A. The cross-section of the space 85A, is shown in Figure 8. The spaces 83A, 84A and 85A communicate with one another at the lower ends of the ribs 43A, and together form a first expansion chamber having no direct access to the atmosphere.From the space 85A the discharge air leaves the first expansion chamber and passes through a restriction 86A into a second expansion chamber on the other side of the tie rods 54A. The restriction occurs on the line R-R in Figure 8 and is created by the rods 54A themselves, which define restricted areas 86A on either side of each rod 54A between itself, the fitting 1 3A and the wall of the muffler 50A. Exhaust air at the reduced pressure in the first expansion chamber passes through the restriction 86A suffering a further pressure drop on entry into the second expansion chamber on the other side of the rods 54A.The second expansion chamber is formed by a space 88A defined between the fitting and the muffler wall, together with the third space 87A defined between the sleeve 41 A, two adjacent ribs 43A of the sleeve, and the muffler wall 50, spaces 87A and 88A communicating with one another directly at the ends of the ribs 43A. The cross-section of space 88A is shown in Figure 8, and that of space 87A in Figures 7 and 9. It will be seen that the wall of the muffler 50A is formed with a longitudinallyextending portion 90A of increased depth which protrudes inwardly into the spaces 88A and 87A and in whose interior a final exhaust duct 91A is moulded. The inlet 92A to the final exhaust duct 91 A is formed at the upper end of the wall portion 90A and communicates with the space 87A, and the downstream end of the duct 90A leads directly to the final exhaust duct 52A.There is no discharge port 34A leading from the cylinder 40A into the space 87A.
Thus the used working gas discharged'from the interior of the cylinder tube 40A through the two discharge ports 34A enters the first expansion chamber formed by the spaces 83A, 84A and 85A and suffers a first pressure drop. The exhaust gas travels to the right in Figure 6 into the space 85A and thence passes through the restriction 86A into the space 88A undergoing a further pressure drop as it enters the second expansion chamber. The exhaust gas travels along the second chamber to the left in Figure 6 from space 88A into space 87A, leaving the second expansion chamber through the inlet 92A and passing along the duct 91 A to be finally discharged to atmosphere through the outlet 52A.
A drain hole 93A is provided at the lower end of the space 88A to allow moisture and oil to drain out.
The muffler thus provides a two-stage expansion system for the exhaust gases before they are released into the atmosphere, the two expansion chambers being connected in series via the restriction 86A. With this arrangement the pressure and velocity of the exhaust gases are progressively reduced in the succeeding expansion chambers and the energy of their pulsations is dissipated partly by the two-stage expansion and partly by the sound absorption effect of the polyurethane sleeve 41 A and muffler 50A, whose comparatively soft, resilient surfaces provide the majority of the wall surfaces of the expansion chambers.Moreover the provision of the three ribs 43A which protrude into the spaces 83A, 84A and 87A has the effect of substantially increasing the surface area of soft, resilient material bounding the expansion chambers, in proportion to their volumes, thereby correspondingly increasing the sound absorption characteristic. The comparatively soft, resilient surfaces damp internal sound reflections, and reduce the characteristic "ring" of the metal liner tube 40A and fitting 1 3A due to impact vibration.
Whilst in the embodiment of Figures 6 to 9 the metal tie rods 54A are utilised to form the restriction between the two muffler expansion chambers, it will be understood that it is also possible to form this restriction in some other way, e.g. by moulded formations on the inner surface of the muffler wall which protrudes inwardly towards the fitting 13A, the tie rods 54A being located elsewhere.
The values of the successive pressure drops which the exhaust gas undergoes as it travels to the final exhaust outlet 52A, depends in part upon the volumetric proportions of the working interior spaces in the cylinder in either side of the piston to the two expansion chambers. If the cylinder working volumes (swept volume plus clearance volume, at each end of the cylinder) are designated as C, and the volume of the first and second expansion chambers as El and E2, a rough and ready rule for achieving good soundattenuating results in practice is that the ratio
C : El : E2 should be in the range between
1 : 5: 3 and 1 : 8 : 5. In one example constructed in accordance with Figures 6 to 9 the values were
C=2.1 x105 mm3 E1 =1.43x 1 o6 mm3
E2=7.7x 105 mm3 giving a ratio of
1 : 7 : i.e. within the range indicated above.
The minimum cross-sectional gas flow areas of the ports or passages which interconnect these three volumes, and their relative proportions, are also important for securing good noise reduction.
The applicants have found that the proportions of the total area of flow cross-section of the gas
discharge ports 34A to that of the restriction 86A
and that of the final exhaust duct 91 A should
preferably lie in the range between 1 : 5 :3 and
1 : 8 : 5. In the measured example referred to in the
preceding paragraph, the total flow area of ports
34A was 1 60 mm2, that of the restriction 86A at
minimum flow section was 1240 mm2, and that
of the duct 91A at minimum flow section was
640 mm2. This gave a ratio of approximately '1 8 : 4, i.e. within the range indicated.
The use of the moulded plastics sleeve 41 or 41A as the outer part of the composite cylinder
component reduces the resonant vibrations of the
steel tube 40 or 40A caused by repeated impact,
as already mentioned, as well as facilitating the
economical construction of the cylinder
component. The composite cylinder component
40 or 40A can be made by the method described
more quickly and economically than in all-metal
component made by casting or forging and
subsequent machining, and will usually be lighter
in weight. While the internal dimension of the
metal tube 40 or 40A must be accurately
controlled to receive the piston, the outer surface
of the tube need not be finished to a critical size.
Moreover, the bore of the metal liner tube 40 or
40A need not be of circular section as described
and illustrated, but could be of ovai or other
suitable section for use with a piston of
corresponding shape. Whilst the bore of the metal
liner tube will usually be of uniform cross-section
along its length this is not essential, since a
stepped bore could be used in conjunction with a
piston having two or more portions of different
diameters/sections which respectively slide in
different sections of the stepped bore.
As previously mentioned, the outer muffler 50
or 50A may be moulded integrally with the
moulded ribbed sleeve 41 or 41 A. It is however
also possible, in the case of a two-part muffler as
described, for one part only the muffler, e.g. the
upper part to be moulded integrally with the
sleeve, the lower part of the muffler being
separate and separately-fitted. Again, a one-piece
muffler could be used in place of the two-piece
construction shown, and could either be moulded
integrally with the sleeve or be separate and fitted
around the sleeve.
Variations are also possible in the arrangement
of compressed-air transfer passages in the ribs of
the sleeve. As described and illustrated each rib
43 or 43A has a transfer passage 32 or 32A
moulded in it and communicating with the
distribution valve at its other end. It is also
possible for one or more of these cavities
moulded in the ribs (but not all) to be permanently
closed at the upper end whilst still
communicating through a radial passage with the
cylinder at its other end, so as to serve as a
pneumatic cushion connected to the lower
working space in the cylinder below the piston. All
these variations are within the broad scope of the -present invention.
Claims (19)
1. A compressed-gas-operated reciprocatingpiston device, which includes a composite cylinder component comprising a rigid inner metal cylinder tube in which the piston reciprocates in use and an outer sleeve moulded of rubber or synthetic plastics material and surrounding and bonded to the metal cylinder tube, the sleeve overlying the entire outer circumferential surface of the major part of the length of the tube, and the sleeve being formed on its outer surface with a plurality of longitudinally-extending outwardlyprojecting integrally-moulded ribs spaced apart around the circumference of the sleeve, the device further including an outer tubular muffler made of rubber or synthetic plastics material which surrounds the ribbed sleeve and defines within the muffler chamber, referred to as the first muffler chamber, which communicates with an exhaust opening leading out of the muffler into the ambient atmosphere, the cylinder component being formed with at least one gas discharge port in its wall which opens into the first muffler chamber between two adjacent ribs of the sleeve, muffler and in which a longitudinally-extending elongate moulded passage is formed in the interior of at least one of the ribs, said passage constituting a transfer passage for supplying compressed gas to one end portion of the interior of the cylinder tube.
2. A reciprocating-piston device as claimed in
Claim 1, in which the moulded sleeve of the cylinder component has three of the said integrally-moulded ribs and has two of the said gas discharge ports opening into the first muffler chamber between two different pairs of adjacent ribs.
3. A reciprocating-piston device as claimed in
Claim 1 or Claim 2, in which the said passage leads from a compressed gas distribution valve at the upstream end of the passage into one end portion of the interior of the cylinder tube via an inlet at the downstream end of the transfer passage.
4. A reciprocating-piston device as claimed in
Claim 3 or Claim 4, in which at least one further longitudinally-extending elongate passage is formed as a moulded cavity within the thickness of another of the ribs, said passage communicating at one end with the interior of the cylinder and being permanently closed at its other end.
5. A reciprocating-piston device as claimed in
Claim 2, in which each of the three ribs is formed with one of the said transfer passages.
6. A reciprocating-piston device as claimed in any one of Claims 1 to 5, in which the moulded sleeve is made of polyurethane.
7. A reciprocating-piston device as claimed in any one of Claims 1 to 6, in which the sleeve is a moulding which was made by being moulded directly around the cylinder tube using the latter as a moulding core.
8. A reciprocating-piston device as claimed in any one of Claims 1 to 7, in which the muffler is made of polyurethane.
9. A reciprocating-piston device as claimed in any one of Claims 1 to 8, which is a pneumatic percussive tool.
1 0. A reciprocating-piston device as claimed in any one of Claims 1 to 9, in which the crests of the ribs act as radial locating means for at least a part of the muffler.
11. A reciprocating-piston device as claimed in
Claim 11, in which the crests of the ribs lie in radially-locating engagement with the internal surface of the muffler along the whole of their lengths.
12. A reciprocating-piston device as claimed in any one of Claims 1 to 11, in which the first muffler chamber communicates directly with the ambient atmosphere via the muffler exhaust opening.
1 3. A reciprocating-piston device as claimed in any one of Claims 1 to 11, in which the first muffler chamber communicates with the muffler exhaust opening via a restriction leading into a second muffler chamber within the muffler, and via the second muffler chamber which communicates with the muffler exhaust opening.
14. A reciprocating-piston device as claimed in
Claim 13, in which the second muffler chamber includes as a part of its volume a space defined between the muffler and the sleeve and bounded by a further pair of adjacent ribs of the sleeve, between which further pair of ribs no discharge port opens from the interior of the cylinder, and in which the general direction of exhaust gas flow in the said space is opposite to that in the first muffler chamber.
1 5. A reciprocating-piston device as claimed in
Claim 14, in which the muffler wall includes a longitudinally-extending portion of increased depth which protrudes laterally inwardly into the second muffler chamber and is formed with an internal longitudinally-extending passage which opens at one end into the said space bounded by said further pair of ribs and leads at its other and downstream end to the muffler exhaust opening, the general direction of exhaust gas flow along the second muffler chamber being opposite to that along the said passage.
1 6. A reciprocating-piston device as claimed in any one of Claims 13 to 15, in which the ratio of the internal volume of the working end of the cylinder with the piston in its limiting position at the end of a working stroke (swept volume plus clearance volume) to the volumes of the first and second muffler chambers is in the range between
1:5:3
and
1:8:5 and the ratio of the total area of flow crosssection of the said gas discharge port(s) from the cylinder component to that of the restriction between the first and second muffler chambers and to that of the outlet from the second muffler chamber to atmosphere is in the range between
1:5:3
and
1:8:5
1 7. A reciprocating-piston device as claimed in
Claim 16, in which the said ratio of volumes is approximately
1 : 7 :
3.6 and in which the said ratio of flow cross-sectional areas is approximately 1 : 8 : 4
1 8. A pneumatic percussive tool substantially as specifically described herein with reference to
Figures 1 to 3 of the accompanying drawings.
19. A pneumatic percussive tool substantially as specifically described herein with reference to
Figures 6 to 9 of the accompanying drawings.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8006433A GB2045348B (en) | 1979-02-28 | 1980-02-26 | Compressed-gasoperated reciprocating piston devices |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB7907037 | 1979-02-28 | ||
GB8006433A GB2045348B (en) | 1979-02-28 | 1980-02-26 | Compressed-gasoperated reciprocating piston devices |
Publications (2)
Publication Number | Publication Date |
---|---|
GB2045348A true GB2045348A (en) | 1980-10-29 |
GB2045348B GB2045348B (en) | 1983-01-26 |
Family
ID=26270720
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB8006433A Expired GB2045348B (en) | 1979-02-28 | 1980-02-26 | Compressed-gasoperated reciprocating piston devices |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2045348B (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0564217A1 (en) * | 1992-03-30 | 1993-10-06 | Makita Corporation | Power driven hammer drill |
-
1980
- 1980-02-26 GB GB8006433A patent/GB2045348B/en not_active Expired
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0564217A1 (en) * | 1992-03-30 | 1993-10-06 | Makita Corporation | Power driven hammer drill |
Also Published As
Publication number | Publication date |
---|---|
GB2045348B (en) | 1983-01-26 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19930226 |