Note: Descriptions are shown in the official language in which they were submitted.
WO 95/23049 '.' ~' S~ ~ ~ r ik pCT/SE95100208
2i82980~
1
VALVE ARRANGEMENT IN CQMPRESSED AIR DRIVEN MOTORS
The present invention relates to a valve arrangement in
compressed-air operated impact motors comprising a machine
housing having a cylinder and a bore connecting therewith,
a valve housing mounted in the bore and supporting a flat
valve which is movable in the valve housing between a front
valve seat and a rear valve seat, wherein the rear valve seat
is connected to the end of the cylinder that is located
distal from the bore through channels provided in the machine
housing, and the front valve seat is open towards the
cylinder at a location adjacent the bore, wherein compressed
air is delivered to the space between the valve seats through
a delivery channel which opens laterally into the bore, and
wherein a hammer piston is sealingly guided for reciprocating
movement in the cylinder in response to movement of the flat
valve and the hammer piston, said movement being governed by
the alternating effect of compressed air on both sides of the
hammer piston and the subsequent release of air through air-
ventilation openings in a centre part of the cylinder.
As illustrated in UK Patent Application GB 2 018 904 for
instance, valve arrangements of this kind are normally
comprised of metal components which need to be precision made
and to fit accurately with one another in their assembled
state, i.e. are dependent on time-consuming and expensive
machining processes. Another drawback is that in the case of
hand-carried machines, the metal components cause the
machines to be relatively heavy and troublesome to the user
and also tend to cause rust problems after the machine has
been used for a long period of time. Furthermore, convention-
al valve housing components have a form which do not enable
the components to be readily exchanged constructively in
practice for components that are lighter in weight and that
are made of a corrosion-resistant material. The conventional
valve housing parts may also include small components, which
also makes such an exchange difficult to achieve in practice.
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The object of the present invention is to provide
valve arrangements or assemblies of the aforesaid kind with
which the aforementioned drawbacks with regard to weight,
cost and durability are eliminated, and therewith give the
valve housing a form which will enable the housing to be
manufactured conveniently from plastic material, such as to
enable the housing to be assembled and fitted immediately
without needing to machine the housing components to precise
finishes, therewith lowering the cost of the valve housing.
Another object is to construct the valve housing so that the
airflow to the valve seats in the housing interior can be
calibrated appropriately in a manner to optimize the
reciprocating movement of the impact breaker. These objects
are achieved with an inventive valve arrangement having the
characteristic features set forth in the following Claims.
A broad aspect of the invention provides a
compressed-air operated impact motor comprising: a machine
housing having a cylinder and a bore connecting therewith; a
valve housing mounted in the bore and supporting a flat
valve which is movable in the valve housing between a front
valve seat and a rear valve seat; wherein the rear valve
seat is connected to the end of the cylinder that is located
distal from the bore through channels provided in the
machine housing, and the front valve seat is open towards
the cylinder at a location adjacent the bore; wherein
compressed air is delivered to the space between the valve
seats through a delivery channel which opens laterally into
the bore; and wherein a hammer piston is sealingly guided
for reciprocating movement in the cylinder in response to
movement of the flat valve and the hammer piston, said
movement being governed by the alternating effect of
compressed air on both sides of the hammer piston and the
subsequent release of air through air-ventilation openings
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2a
in a center part of the cylinder; the valve housing having
the form of a plastic bowl which is outwardly flanged at the
bowl mouth and at the bowl bottom and in which the flat
valve is movable between the bowl bottom, which forms the
one valve seat, and a bowl cover member for the bowl mouth
which forms the other valve seat, wherein the lie against
the wall of the bore and define therebetween a groove which
connects with the delivery channel and which functions to
deliver compressed air to the flat valve inside the bowl
through the medium of side openings provided in the bowl
wall between the flanges on both sides of an undivided bowl
wall portion that encircles the region of the length of the
working stroke of the flat valve; wherein the bowl cover
member is made of a plastic material and forms a detachable
bowl closure for the bowl mouth, attached to the valve
housing with the aid of a stop ring.
The present invention will now be described in
more detail with reference to the accompanying drawings, in
which Fig. 1 is a partially fragmented longitudinal section
view of an impact breaker, which in the illustrated
embodiment is a pneumatic pick, fitted with an inventive
valve arrangement; Fig. 2 is a sectional view seen along the
line 2-2 in Fig. 1; Figs. 3A-3D are cross-sectional views
which illustrate the four components that form the valve
arrangement in Fig. 1, these components being shown in a
slightly enlarged and exploded presentation, wherein Fig. 3A
shows the valve housing, Fig. 3B the flat valve, Fig. 3C the
cover member, and Fig. 3D the stop ring; Fig. 4 shows the
stop ring of Fig. 3D from above; Fig. 5 is a sectional view
of the valve housing seen along the line 5-5 in Fig. 3A; and
Fig. 6 is a sectional view corresponding to the centre part
of the section shown in Fig. 2 and illustrates the valve
housing with a modified cover member.
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The pneumatic pick 10 shown in Fig. 1 comprises a
machine housing 11 which includes a back piece 12 provided
with a handle part 18, and front piece 13, these components
being
W 0 95f23049
PCT/SE95/DD208
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3
held together in the intermediate machine housing 11 in line
with one another along the central axis 15 of a cylinder 20
mounted in'the machine housing 11. The cylinder 20 is
extended rearwardly via an annular shoulder 21 in an enlarged
bore 23', and forwardly in a front bore 25. The bore 25
accommodates an intermediate part 17 which projects sealingly
into the cylinder 20 and has an annular end surface 24 which
faces towards the cylinder. The intermediate member 17 serves
as a rear guide bushing or sleeve for guiding movement of
an
intermediate block 14 which transmits impact forces to the
tool 16. The tool 16 is guided for limited axial movement
in
the front piece 13 and the journal bearing and locking means
used to this end are of a conventional design. A detailed
description in this regard is found, for instance, in Patent
Specification SE 9400685-5 and need not therefore be dealt
with in further detail in this document. The machine housing
11 is provided rearwardly with two side walls 27 which
project rearwardly beyond the back piece 12, over the central
part of the handle part 18. The handle part 18 is fixed to
the machine housing 11 between the side walls 27, by means
of a wedge 26 which is passed through a transverse bore 19
in the centre of the handle part 18 and pressed into coaxial
bores 29 at the side walls 27. The handle part 18 supports
rearwardly against a cover member 31, suitably made of a
plastic material (polyurethane) and pushed laterally into
opposed grooves or slots 30 at the side walls 27.
The handle part 18 supports inwardly of the cover member 31
a laterally extending pivotal lever arm 33. As the lever arm
33 is swung towards or away from the handle part 18, an
intermediate pin 34 projecting into the housing 11 is
activated so as respectively to open or close a governor
valve 35, said valve being biased in a valve closing direc-
tion by means of a valve spring 36. The valve 35 functions
to open or close a connection between a compressed-air inlet
38 and a delivery channel 39 provided in the housing 11 and
opening laterally into the bore 23 at a location adjacent the
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4
shoulder 21.
The impact motor illustrated in Fig. 1 also includes a
distribution-valve housing 40 which rests against the
shoulder 21 in the bore 23 and forms the cylinder head of the
cylinder 20. The back piece 12 has the form of a plug which
is made of a plastic material (polyurethane) or, when
necessary, of metal and which is inserted sealingly in the
bore 23 from the rear and functions to hold the distributor-
l0 valve housing 40 axially in abutment with the annular
shoulder 21 in the bore 23, through the medium of a peripher-
al sealing ring 41. The back piece 12 includes two mutually
opposing recessed or cupped shoulders 43, as shown at 42,
Figs. 1 and 2 and 6, which are directed rearwardly on both
sides of the handle part 18 and support against the wedge 26,
such as to lock the back piece 12 axially in the bore 23
between the valve housing 40 and the wedge 26. The back piece
12 further includes a transverse passageway or channel 45
which is open centrally towards the valve housing 40 and
which connects with a passageway or channel 44 which opens
into the cylinder 20 at a location distanced from the bottom
24.
A hammer piston 22 is sealingly guided for reciprocating
movement in the cylinder 20 and in the illustrated case
functions to impart an impact force to the tool 16 via the
intermediate block 14, Fig. 1. Alternatively, the front part
of the pneumatic pick 10 can be modified so that the hammer
piston will strike directly on the tool 16. When the hammer
3o piston 22 approaches the end of its stroke, that side of the
piston which is under pressure is ventilated through a
respective air-ventilating opening 60 or 61 provided in the
cylinder 20, said air being ventilated to the surroundings
of the machine housing 11.
The valve housing 40 (Fig. 3A) is injection-moulded from a
plastic material, preferably from acetal plastic (Delri.n*) aad
*Trade-mark
WO 95!230.19 218 2 9 8 0 i ~' fyPC~YftEQSI00208
has the form of an outwardly flanged or lipped bowl 46 which
is symmetrically rotational in relation to a centre axis 37
and includes a circumferentially extending groove 54 defined
between an upperflange 47 and a lower flange 48. A similarly
_ 5 plastic (acetal plastic) flat valve 50 (Fig. 3B) can be
inserted in the bowl 46 inwardly of the groove 54 and moves
axially between a forward valve seat 51, which forms the
bottom of the bowl 46 and which when assembled in the machine
housing 11 is open towards the cylinder 20, and a rearward
valve seat 52 which is open towards the transverse channel
45 in the back piece 12. The symmetry axis 37 of the valve
housing 40 passes through the centre of the valve seat 51 in
the bottom of the bowl 46. The rear valve seat 52, which is
also made of acetal plastic, forms a bowl cover member 53
(Fig. 3C) and can be fixed in a slightly lowered position
within the opening or mouth of the bowl 46 and essentially
flush with the upper flange 47, with the aid of a stop ring
55 (Figs. 4 and 3D) inserted in a locking groove 56.
Calibrated side openings 57, 58 for delivering compressed
air
to respective sides of the flat valve 50 are provided in
the
bowl 46 between the flanges 47, 48. The side openings 57,
58
are uniformly distributed peripherally and are, for instance,
four in number for each valve seat 51, 52. The side openings
58 leading to the front valve seat 51 are calibrated experi-
mentally to a greater degree than the side openings 58 such
as to achieve a greater impact force of determined value
during a working stroke. That part of the bowl wall which
extends between the side openings 57, 58 is imperforate and
surrounds the region travelled by the valve 50 between the
valve seats 51, 52, ie the working stroke of the valve, so
that compressed air-injected into the valve housing 40 will
not impinge on the flat valve 50. The length of stroke of
the
valve is limited by annular walls 59 extending around the
valve seats 51, 52, with the side openings 57, 58 lying on
the same level as the walls.
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PCTlSE95100208
6
If desired, the valve 40 may alternatively be fitted in the
bore 23 with the cover member and the valve seat 52 facing
towards the cylinder 20. Fig. 6 illustrates a modified ,
embodiment in which the rear valve seat 52 is, by way of
example, constructed as a part of the actual back-piece plug ,
12', as a cover member alternative. ~hl the case of this
alternative, the back piece 12 includes~'an outwardly project-
ing cover member 53 having the foxin-~of a nose around the
4~~,
orifice of the transverse channel 45.. The rear valve seat 52
and its wall 59 are included in the nose or cover member 53
of the back piece 12. With regard to the back piece 12, the
handle part 18 can be formed integrally with the back-piece
plug 12', suitably from polyurethane plastic, if desired.
When the pneumatic pick 10 is handled by the operator and
pressed against a working surface with the aid of the handle
part 18, the components of the impact motor will be in the
positions shown in Fig. 1. When activating the pressure arm
33, compressed air is delivered from the mains-connected
outlet 38 to the inlet valve 35 and the delivery channel 39
and hence to the bore 23 and the valve housing 40. It is
assumed that the flat valve 40 covers the front valve seat
51 and that compressed air is passed to the cylinder bottom
24 through the rear valve seat 52, the transverse channel 45
in the back piece 12, and the channel 44, so as to move the
hammer piston 22 away from the tool 16, and the cylinder 20
is ventilated beneath the hammer piston 22 via the ventilat-
ing openings 61 as the piston approaches the end of its
return stroke in the cylinder 20. As a result of the drop in
pressure caused by ventilating the cylinder, in combination
with the increase in pressure in front of the returning
hammer piston 22, the flat valve 50 is thrown over against
the rear valve seat 52. Compressed air now enters above the
hammer piston 22, causing the piston to turn, and drives the
piston into hammer contact with the tool 16, the hammer
piston now being in the position shown in Fig. 1. Ventilation
of air from the cylinder 20 above the hammer piston 22,
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through the ventilating opening 60, in combination with the
increase in pressure beneath the hammer piston 22 throws the
. flat valve 50 back onto the forward valve seat 51 and the
hammer piston 22 therewith continues to move reciprocatingly
with repetition o~'the aforedescribed cycle.
The possibility of injection-moulding the valve housing 40
from a plastic material is able to provide a durable and
inexpensive advantageous construction which permits the
distribution valve to be assembled and fitted without
requiring the valve to be accurately machined. There is also
obtained a repetitive uniform quality with small deviations
in tolerances. The mould is constructed so that it can be
separated sideways to enable the mould to be parted when the
flanges 47, 48 have been moulded, and comprises four parts
which can be exchanged to enable side openings 57, 57 of
mutually different sizes to be moulded in accordance with the
size of the impact tool and. the mechanical effect for which
the distribution valve is intended.
