Note: Descriptions are shown in the official language in which they were submitted.
CA 02343047 2009-06-08
Page 1
HYDRAULIC IMPACT MACHINE ACTUATOR
FIELD OF THE INVENTION
This invention relates to a hydraulically operable actuator for an impact
machine
such as a rock drill or the like which includes a reciprocal sleeve which
surrounds
a piston in the machine body for controlling reciprocation of the piston and
to a
method of starting the actuator.
BACKGROUND TO THE INVENTION
Hydraulic reciprocating machines such as rock drills and the like typically
include
a piston that moves sealingly within two or more hydraulic chambers. The
piston
typically has stepped diameters which define differential piston areas on
which
the hydraulic fluid acts. Typically, in use, one or more of the piston drive
chambers of the machine is constantly supplied with hydraulic fluid at supply
pressure. At least one other chamber, the "control" or return chamber is
alternatively supplied with hydraulic fluid at or approximately at supply
pressure,
and then isolated from supply pressure and allowed to exhaust to a low
pressure
to cause reciprocation of the piston between the hydraulic chambers. The fluid
access to the controlled chamber/s is typically regulated by valve/s which in
conjunction with the differential areas of the piston results in the
reciprocating
motion of the piston.
CA 02343047 2009-06-08
Page 2
Various valve arrangements and means for operating the valve/s are known in
the art. Spool valves have in the past been utilised extensively in hydraulic
actuators, however the use of poppet valves in such machinery is a more recent
innovation (see US patent No. 4,450,920). The valve/s may either be operated
by mechanical means or by hydraulic interactions.
Drills utilising hydraulic interaction for moving the valving device/s of
their
actuators such as those disclosed in the specifications of US patent Nos.
5,626,068 and 5,826,482 are often difficult to start reliably.
Both of the above drills are typically water powered and include a rock drill
body,
a piston which is reciprocal in the body, a piston drive chamber in the body,
a
reciprocal poppet valve type sleeve which surrounds and extends over a length
of the piston including a stepped portion of the piston to define, on the
inside of
the sleeve around a step in the piston a piston return chamber. One end of the
sleeve defines with a fixed seat in the valve body an exhaust valve from the
piston return chamber which opens and closes an exhaust port from the body
with the other end of the sleeve together with a fixed seat in the body
defining an
inlet valve directly or indirectly from the drive chamber into the return
chamber
which is open when the exhaust valve is closed and vice versa. The drills are
typically started by applying water at supply pressure to the drive chamber
and
then the return chamber. The drills function well during operation due to the
fact
that appropriate piston speeds generate the necessary hydraulic interaction
between the piston and sleeve for smooth cyclic operation of the sleeve and
CA 02343047 2009-06-08
Page 3
piston. On starting, however, during the initial piston starting stroke the
sleeve
may not be optimally positioned in the machine for reliable starting and so
may
cause a disruption of hydraulic conditions which are required for continuation
of
the piston cyclic operation. This situation is aggravated if the drill is
under thrust
and the piston impacts the drill steel prematurely on its starting drive
stroke to
limit its return stroke sufficiently to stall the drill actuator.
SUMMARY OF THE INVENTION
An actuator for a hydraulically operable impact machine according to the
invention includes a machine body, a piston drive chamber in the body, a
stepped piston which is reciprocal in the body and drive chamber, a sleeve
which
surrounds a step in the piston to define, on the inside of the sleeve, between
the
sleeve and a portion of the piston, a piston return chamber with a forward end
of
the sleeve and a seat in the body defining an exhaust valve which opens to the
outside of the body with the rear end of the sleeve and a seat in the body
defining an inlet valve for feeding hydraulic fluid under pressure from the
drive
chamber into the return chamber, and a seal bearing, in which the piston is
reciprocable, between the drive and return chambers characterised in that the
actuator includes a pusher which is reciprocally located in the body for
movement
between a first position in which its rear end is engaged with the sleeve to
close
the return chamber inlet valve and open the exhaust valve and a second
position
in which it is held clear of the valve sleeve by fluid pressure in the drive
chamber
CA 02343047 2009-06-08
= Page 4
and means biasing the pusher to its first position of operation when the
machine
drive chamber is vented to atmosphere.
Conveniently the pusher is a cylindrical body which surrounds the exhaust
valve
end of the sleeve with a portion of its length from its forward end slidably
located
in a circular groove in an end wall of the machine body with the biasing means
being a spring which acts on a formation at the rear end of the pusher body to
bias the pusher to its first position of operation.
The pusher groove may have a blind end in the machine body end wall and the
machine body includes a passage which extends between the blind end of the
pusher groove and the outside of the machine body. The formation on the
pusher body may be an outwardly directed flange on the rear end of the pusher
body and the spring is a coil spring which surrounds the pusher body to bear
on
the machine body adjacent the pusher groove and the formation.
The piston preferably includes a fluid passage which extends over a portion of
the length of the piston with its one end open to hydraulic fluid in the drive
chamber during reciprocation of the piston and its other end open, across the
piston seal bearing, into the return chamber only during the final portion of
the
piston drive stroke and the initial portion of its return stroke. The piston
fluid
passage may be a flute in the surface of the piston.
An actuator for a hydraulically operable impact machine according to the
invention includes a machine body, a piston drive chamber in the body, a
CA 02343047 2009-06-08
Page 5
stepped piston which is reciprocal in the body and drive chamber, a sleeve
which
surrounds a step in the piston to define, on the inside of the sleeve, between
the
sleeve and a portion of the piston, a piston return chamber with a forward end
of
the sleeve and a seat in the body defining an exhaust valve which opens to the
outside of the body with the rear end of the sleeve and a seat in the body
defining an inlet valve for feeding hydraulic fluid under pressure from the
drive
chamber into the return chamber, and a seal bearing, in which the piston is
reciprocable, between the drive and return chambers characterised in that the
machine includes a fluid passage in the piston which extends over a portion of
the length of the piston with its one end open to hydraulic fluid in the drive
chamber during reciprocation of the piston and its other end open, across the
piston seal bearing, into the return chamber only during the final portion of
the
piston drive stroke and the initial portion of its return stroke. Conveniently
the
piston fluid passage is a flute in the surface of the piston.
A method of starting a hydraulically operable impact machine actuator such as
that described above which includes a machine body, a piston drive chamber in
the body, a stepped piston which is reciprocal in the body and drive chamber,
a
sleeve which surrounds a step in the piston to define, on the inside of the
sleeve,
between the sleeve and a portion of the piston, a piston return chamber with a
forward end of the sleeve and a seat in the body defining an exhaust valve
which
opens to the outside of the body with the rear end of the sleeve and a seat in
the
body defining an inlet valve for feeding hydraulic fluid under pressure from
the
CA 02343047 2009-06-08
Page 6
drive chamber into the return chamber, and a seal bearing, in which the piston
is
reciprocable, between the drive and return chambers according to the invention
includes the steps of :
venting the drive and return chambers to atmosphere,
applying force to the sleeve to close the return chamber inlet valve to
isolate the
drive and return chambers from each other and to open the return chamber
exhaust valve,
charging the drive chamber with hydraulic fluid at supply pressure to cause
the
piston to be moved in its drive stroke direction towards the open return
chamber
exhaust valve,
charging the return chamber with hydraulic fluid prior to the opening of the
inlet
valve at supply pressure when a formation on the piston reaches an exhaust
flow
restriction formation on the inner surface of the sleeve, and
decelerating the piston and reversing its direction of motion into its return
stroke
direction at a rate of acceleration which is adequate for starting of the
cyclic
action of the actuator.
Preferably the method includes the step of charging the return chamber with
hydraulic fluid at supply pressure prior to the opening of the return chamber
inlet
valve through a fluid passage in the piston which is open at one end to the
drive
CA 02343047 2009-06-08
Page 7
chamber and open at its other end to the return chamber across the piston seal
bearing.
BRIEF DESCRIPTION OF THE DRAWING
An embodiment of the invention is now described by way of example only with
reference to the drawing which is a diagrammatic sectioned side elevation of
the
actuator of the invention including the actuator start arrangement.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The drill actuator of the invention is, in this embodiment of the invention,
basically
the water powered actuator disclosed in the specification of US patent No.
5,826,482 and is shown in the drawing to include a housing 10, a piston 12 and
a
control sleeve 14.
The actuator housing includes a composite piston drive chamber which is
composed of two drive chamber sections 18 and 20 which are separated from
each other by a divider wall 22 which includes fluid passages 19 which
hydraulically connect the two drive chamber sections. A water inlet 24 is open
into the drive chamber section 20 and is controlled by an inlet valve 25. The
forward end wall of the drive chamber section 18 is recessed to provide a bore
23 from which a plurality of circumferentially spaced exhaust ports 27 are
open to
atmosphere on the outside of the housing. The housing additionally includes
four
seal bearings 26, 28, 30 and 31 which support the piston 12 and in which the
CA 02343047 2009-06-08
Page 8
piston is sealingly reciprocal. A further seal bearing 34 is located in the
bore 23
and sealingly supports the sleeve 14 for reciprocal movement.
The piston 12 is downwardly stepped on either side of a central zone 36 to
provide a hydraulically exposed piston drive area 38 in the drive chamber
section
20 and a piston return area which is a combination of a portion of the piston
area
40 and a further stepped area 44. The piston further includes an outwardly
stepped portion 42. The net return area of the piston is larger than the
piston
drive area.
The control sleeve 14 is in the form of a stepped sleeve with its forward
smaller
diameter portion located in the bore 23 for reciprocatory movement on the seal
bearing 34. The step in the sleeve 14 extends beyond the inner surface of the
small diameter portion of the sleeve to provide an inner flow restriction rib
46 in
the sleeve cavity. The inner surface of the rib is just larger in diameter
than the
diameter of the piston portion between the piston steps 42 and 44. (The term
"just" in this specification is to be taken to mean a separation distance
between
components which is typically less than 0,15mm). The central zone of the inner
surface of the large diameter portion of the sleeve is recessed as shown in
the
drawing to provide fluid flow restrictor surfaces 48 and 50 in the sleeve
cavity.
The diameters of the surfaces 48 and 50 are just greater than the outer
diameter
of the piston step 42. The step in the sleeve 14 wall provides, on the outside
of
the sleeve, a hydraulically exposed sleeve return area 52 which is, during
operation of the actuator, exposed to fluid under pressure in the drive
chamber
CA 02343047 2009-06-08
Page 9
section 18 and on the inside of the sleeve a sleeve drive area 54. The net
return
area of the sleeve is the diametrical difference between the restrictor
surface 50
and the outer diameter of the reduced diameter portion of the sleeve. The
annular surface at the front end of the sleeve seats on a valve seat 56 on the
transverse end wall portion of the bore 23 with the seat and the forward end
surface of the sleeve defining between them an exhaust valve for the actuator.
The space between the inner surface of the larger diameter portion of the
sleeve
14 and the outer surface of the piston defines a piston return chamber 58. The
rear annular end surface of the sleeve defines with a seat 59 on the partition
wall
22 an inlet valve to the return chamber 58.
The piston 12 includes grooves or flutes 62 which are circumferentially spaced
about the central zone 36 of the piston and extend, in this embodiment of the
invention, from the drive area 38 step in the piston to the forward position
on the
piston shown in the drawing beneath the seal bearings 28 and 30 to bring the
drive chamber section 20 into communication with the return chamber at the
extremity of the piston drive stroke as is explained below.
The start arrangement of the invention includes of a cylindrical pusher 60,
and a
vent valve 64.
The pusher 60 is slidable in an annular groove 66 in the inner forward surface
of
the drive chamber section 18. The blind end of the groove 66 is open through
an
air vent passage 68 to at least one of the exhaust ports 27 as shown in the
CA 02343047 2009-06-08
Page 10
drawing. The depth of the groove 66 is greater than the distance between the
right hand end of the pusher 60 and its seat 69 on the sleeve 14, as shown in
the
drawing, to ensure that the pusher does not become dislocated from its
position
in the actuator, in use. The forward end of the pusher 60 has an outwardly
directed flange against which one end of a biasing spring 70 bears with the
other
end of the spring bearing up against the end wall of the drive chamber section
18
to bias the pusher to the right in the drawing.
In use, to start the drill, the drive chamber inlet valve 25 is, in the
absence of
water leakage from the housing, closed and the vent valve 64 opened to drop
all
water pressure in the actuator housing to ambient pressure. With no water
under
pressure in the drill the pusher biasing spring 70 biases the pusher 60 to the
right
in the drawing up against the sleeve 14 seat 69 and moves the sleeve with it
to
the right until its end surface abuts the seat 59 to close the inlet valve to
the
return chamber and to open the exhaust valve. The vent valve 64 is now closed
and the inlet valve 25 opened to flood the drive chamber sections 18 and 20
with
water at supply pressure. As the rear end of the pusher 60 is vented to
atmosphere the pressure acting on the pusher in the drive chamber forces the
pusher, against the bias of its spring 70, back to its parked position as
shown in
the drawing clear of the sleeve 14 where it remains during operation of the
actuator. The pressure water in the drive chamber section 18 now acts on the
return area 52 of the sleeve to hydraulically lock the sleeve onto its return
chamber inlet seat 59. The water supply pressure acting on the drive area 38
of
CA 02343047 2009-06-08
Page 11
the piston in the drive chamber section 20 has, in the meantime, commenced
driving the piston to the left in the drawing and in so doing to cause the
return or
reset area 40 on the piston to force water in the return chamber from the
chamber through the open return chamber exhaust valve and exhaust ports 27.
When the piston has reached the position shown in the drawing at which the
stepped return area 44 of the piston has reached the sleeve rib 46 flow
restriction
area and the forward ends of the flutes 62 in the piston are clear of the
forward
end of the seal bearing 28, water at supply pressure from the drive chamber
section 20 is forced through the flutes 62 beneath the seal bearings 28 and 30
to
flood the return chamber 58. The resultant water pressure in the return
chamber
acting on the sleeve drive surface 54 breaks the hydraulic lock across the
return
chamber inlet valve to open the valve and move the forward end surface of the
sleeve 14 onto its seat 56 to close the exhaust valve. Water pressure in the
return chamber 58 acting on the piston return area 40 overcomes the drive
force
of the supply water pressure acting on the drive area 38 of the piston. As the
net
return areas of the piston are greater than its net drive areas the piston
forward
motion is braked and the piston is driven on its return stroke to the right in
the
drawing. The acceleration of the piston to the right is such that by the time
the
stepped portion 42 of the piston reaches the flow restrictor surface 50 of the
sleeve the piston will have achieved an adequate speed for the stepped portion
42 of the piston hydraulically to interact with the flow restricting sleeve
portion 50
to drop the fluid pressure in the return chamber 58, to break the hydraulic
lock on
CA 02343047 2009-06-08
Page 12
the exhaust valve seat 56 and to force the sleeve to the right in the drawing
until
the rear edge of the sleeve seats on the inlet seat 59 on the divider wall 22.
In
this position the return chamber 58 is vented to atmosphere through the now
open exhaust ports 27, the grooves 62 are again sealed from the return chamber
by the seal bearing 28, and the water pressure acting on the sleeve return
area
52 hydraulically locks the sleeve onto its inlet seat 59 to prevent fluid flow
from
the drive chamber section 18 into the return chamber 58. The fluid pressure
acting on the piston drive area 38 in the drive chamber section 20 stops and
reverses the direction of piston travel into its drive stroke as described
above for
the commencement of the next cycle of operation of the actuator.
The flutes 62 ensure that during a start stroke there is a sufficient fluid in
the
return chamber 58 for fluid pressure build up to break the lock on the valve
inlet
seat 59. This is particularly important if the actuator is stared while
thrusting on
the drill steel 74 when the effective stroke of the piston to the left is
limited. The
positioning of the forward ends of the piston flutes 62 ensure that for a
large
portion of the piston stroke, i.e. to the right of the position shown in the
drawing,
the flutes are closed to the return chamber 58 by the seal bearing 28.
As the piston commences its drive stroke, during normal cyclic operation after
starting, the rapid acceleration of the piston to the left in the drawing
again
causes the piston return areas 40 and 44 to expel hydraulic fluid in the
return
chamber 58 from open exhaust ports 27 until the outward step 44 on the piston
again reaches the restriction surface on the rib 46 in the sleeve 14 to
restrict
CA 02343047 2009-06-08
Page 13
exhaust fluid flow from the machine and to cause, a fluid pressure build-up in
the
return chamber 58 the fluid flow through the flutes 62 being unimportant. The
pressure build-up in the return chamber breaks the hydraulic lock between the
sleeve and its inlet seat 59 and the net fluid force now acting on the sleeve
drives
the sleeve onto its exhaust seat 56 as described above. The piston is now
decelerated by fluid force acting on its return areas 40 and 44 until the free
end
72 of the piston strikes the drill steel 74 or until the hydraulic cushion
formed
between the inner sleeve diameter 48 and the stepped portion 42 of the piston
rapidly decelerates the piston in preparation for its next return stroke.
Although the actuator described above is mentioned as being water driven this
is
not to be taken as a limitation of the claimed invention as the actuator could
equally well be driven by hydraulic oils, oil and water emulsions and the
like.
Additionally the flutes 62 in the piston need not necessarily be rearwardly as
long
as they are for the return chamber to be permanently open into the drive
chamber, as it is only necessary to open the return chamber to the drive
chamber
through them only when the piston is in the final portion of its drive stroke
and the
return chamber inlet valve is still closed.
Additionally, the above description of the invention is illustrative and
explanatory
thereof and various changes in the apparatus and starting method may occur to
those skilled in the art. It is intended that all such variations within the
scope and
spirit of the appended claims be embraced thereby.
