HYDRAULIC PERCUSSIVE MACHINES

MACHINES DE PERCUSSION A COMMANDE HYDRAULIQUE

English Abstract

A B S T R A C T
In a hydraulic percussive rock drilling machine of the differential
piston area type, in which hydraulic fluid is constantly supplied to
a return stroke chamber and fluid alternately supplied to and
exhausted from a working stroke chamber, the dashpots for damping
overtravel are provided in the working stroke chamber.

Claims

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THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1.
A hydraulic percussive machine comprises a cylinder, a piston arranged
to reciprocate in the cylinder to perform a power stroke and a return
stroke, an inlet for fluid at high pressure, a front space in the
cylinder connected to the inlet, a back space in the cylinder, the
piston being formed with piston areas working in the front and back
spaces with the piston area in the back space being larger than that
working in the front space, a valve, and timing grooves on the piston
and ports in the cylinder, the valve and the timing grooves co-operating
to connect the back space alternatively to the inlet and to tank, is
provided with a piston having a cushioning flange operating in the
back space and adapted to enter an annular dashpot cavity on overtravel
of the piston in the forward stroke direction.
2.
The machine claimed in claim 1 in which at the back end of the back
space there is a further annular dashpot cavity to receive the
cushioning flange on overtravel of the piston on the return stroke.

Description

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Background of the InYention
This invention relates to hydraulic percussive machines oF the kind which
are suitable for use as rock drilling machines or pavement breakers.
In order to prevent stalling during overtravel of the reciprocating
piston it has already been proposed. to provide the piston of such a machine
with a cllshioning flange wh;ch moves into a space acting as a dashpot. In
this regard see SA patents Nos. 74/5601 and 76/1650 In both of these
proposals the dashpot is in a front or return chamber. In the former of
these proposals return of the flange from the dashpot relies on the fact
that the flange also provides the piston area for the return stroke of
~,~ 10 the piston. In ~he second of these proposals return is facilitated by
connecting the space in which the flange works to tank. It has been found
that the timing grooves and lands required for this lead to leakage
probiems.
~ummary oF the Invent;on
Accordiny to the invention a hydraulic percussive machine comprises a
cylinder, a piston arranged to reciprocate in the cyl-inder, to perform
a power stroke and a return stroke, an inlet for -fluid at high pressure,
a front space in the cylinder connected to the inlet, a back space in the
cylinder, the piston being for~ed with piston areas working in the front
and back spaces with the piston area in the back space being larger than
2CI that working in the fron-t space, a YalYe, and ti~ing yrooves on the pistonand ports in the cylinder, the valve and the -ti~ning grooves co-operatin~
to connect the back space alternati~ely to the inlet and to tank~ is
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proYided with a piston hayin~ a cushi~ning flan~e operatin~ in the back
space and adapted to enter an annular dashpot cavity on overtraYel of the
piston in the forward stroke direction. Since the dashpot leads from a
space which is alternately pressurised and depressurised, there is no
need for special timing grooYes to ensure return of the cushioning flange
from the dashpot.
The invention also provides that at the back end of the back space there
be a further annular dashpot cavity to receive the cushioning ~lange on
overtravel'of the pi$ton on the return stroke. Such overtraYel is very
rare in normal operation of this kind of machine.
Description of the Drawlng
It is a section through a hydraulic recip,rocating machine with the ~alve and
hydraulic connections shown schematically.
Description of a Preferred Embodiment
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In the ;llustrated embodiment a piston 20 having sections marked from 1 to
6 moves in a cylinder ~ to strike a tool 7. The chucking arrangement for
lS the tool 7 has not been shown.
.
At its back end the cylinder is formed with a space 10 and at its forward
end with a space 21~ A pump 22 supplies hydraulic fluid under pressure to
an inlet line 23 which is permanently connected to the space 21 and
intermittently so to the space 10 via a flow path 25 and through a shuttle
valve 11 of known construction. When the valve 11 does not connect the
space 10 to the path 25 and the line 23, it connects it to tank through an
outlet line 24. Accumulators 12 and 13 are connected to the paths 25 and
24 respectively to smooth fluid flow and provide make-up for transient
demands.
~5 The diameter 5 of the piston is larger than the diameter 6. The eonstant
h;gh pressure ;n the chamber 21 acts on the differential ~iston area and tends
to force the piston to the 'left. In the chamber ln the net piston area is
the area represented by the differences between the dia~7eters 3 and 1 and
is larger than the area preserlted to the chamber 21. Thus, ~hen the
chamber 10 is connected to hi~h pressure~ the piston will moJe to the right.
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The chamber 10 is so connected via the shuttle Yalve 11 and the path
25 leading from the chamber 21, When ~he valve 11 exhausts the chamber
lo to tank, the piston moves to the left. Movement of the valve 11 thus
causes the piston to reciprocate.
The valve 11 has two faces 26 and 2~ exposed to the driving fluid. lhe
area of the face 28 .s about twice that of the face 26. The latter is
constantly exposed to the fluid under pressure ;n the chamber 21 via
the path 25 so that the shuttle valve 11 is biased to the right. When the
piston moves to its backward position (left in the drawing) high pressure
fluid ;n the chamber 21 is also connected to the face 28 throuyh a chamber
34 and a path 32. This causes the valve 11 to move to the left and high
pressure fluid is connected to the chamber 10 to drive the piston to the
position shown in the drawing. At that position, the chamber 34 is
connected via a chamber 36, and outlet path 38 and the path 24 to tank,
thus causing tl~e valve 11 to move to the right again and to cut off
the connection to the chamber 10 while connecting the latter to the
outlet path 24 .
.
The section of the piston marked 2 is the cushioning flange. If the
tool 7 is absent the piston can overtravel to the right and then the
section 2 enters an annular dashpot cavity 9. As soon as the valve 11
changes over, the space 10 is connected to tank and the section 2 easily
moves back out of the dashpot 9.
The section 2 can have as large oras small a diameter as may be
necessary without affecting the diameters of any o~ the other piston
sections.
.
A further dashpot cavity 14 leads off the space 10. In the rare event
of overtravel on the upstroke, the section 2 enters that cavity.
It will be seen that in relation to the prior art the overall length of
the machine is shortened and that construction of the machine may be
greatly simplified.
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