Note: Descriptions are shown in the official language in which they were submitted.
1~8{~63
This is a Division of our co~pending Canadian Patent Application
No. 337,956 filed October 18th 19790
This invention relates to a hydraulically operated impact motor com-
~rising a hammer piston which is reci~rocably mounted in a cylinder to define
therewith a first cylinder chamber and a second cylinder chamber, said hammer
piston having a first piston surface in said first cylinder chamber to effect
the working strokes of the hammer piston and a second piston surface in said
second c~linder chamber to effect the return strokes of the hammer piston, and
a hammer piston controlled valve coupled to connect said second cylinder chamber
alternativel~ to an inlet of high pressure hydraulic fluid and to an outlet,
said valve comprising: An axiall~ movable valving element, a first piston means
for forcing said valving element lnto a first position when subject to pressure,
a first control passage leading between a first port means into said cylinder
and said first piston means, a second piston means for forcing said valving
element into a second position when subject to pressure, and a second control
passage leading between a second port means into said cylinder and said second
piston meansO
Such an impact motor is described in Uni~ed States patent 3 741 072.
The piston of the impact motor shown therein has two annular lands and a perma-
nentl~ drained chamber is formed between the lands so that the valve control pas-
sages are periodicall~ drainedO There is internal leakage across the lands and
leakage across the lands of the valveO
It is advantageous to have a single land on the piston and such
hydraulic impact motors are known in the prior art.
A valve and a valve control system of the kind shown in United States
patent 3 741 072 does not function reliably when the piston has a single land.
.,
-
: '
11~8~63
In the prior art hydraulic impact motors with a single land are known but their
valve functions are usually not satisfactory.
The present invention provides hydraulically operated impact motor
comprising: a source of high-pressure hydraulic motive fluid; a cylinder having
first and second port means leading into said cylinder; a hammer piston recipro-
cably mounted in said cylinder and arranged to impact upon an anvil means, said
hammer piston defining with said c~linder first and second pressure chambers,
said first and second pressure chambers being in selective communication with
said first and second port means; a single piston land on said hammer piston;
10 a first piston surface on said land and located in said first pressure chamber
to effect a stroke of said hammer piston in one direction; means coupled to
said first pressure chamber for constantly pressurizing said first pressure
chamber in us~e; a second piston surface on said land and located in said second
pressure chamber to effect a stroke of said hammer piston in the other direction;
a valve coupled to connect at least said second pressure chamber alternatively
to said source of high-pressure hydraulic motive fluid and to a motive fluid
outlet; ~aid valve comprising: means defining a valve cylinder; a valving element
axially movable in said valve cylinder; a first piston means on said valving
element for forcing said valving element into a first position when subject
to pressure; a first control passage leading between said irst piston means and
said first port means which leads into said cylinder; a second piston means for
forcing said valving element into a second position when subject to pressure,
said second piston means being movable awa~ from said valving element; a second
control passage leading between said second port means which leads into said
cylinder and said second piston means; a third piston means fo~ mo~ing said
second piston means away from said valving element when said second piston means
--2--
. : ~
~148063
i$ relieved of pressure; means coupled to said third piston means for constantly
subjecting said third piston means to pressure; said piston land being arranged
to selectivel~ block said first and second port means in respon~ to its axial
position in the cylinder.
The invention will be des:cribed in more detail with reference to
the accompan~ing dra~ings which show an embodiment of the in~ention.
Figure 1 is a schematic longitudinal section through a hydraulic
impact motor in a form of a jack hammer, the front~portlon of the impact motor
being cut awa~.
Figure 2 shows in a longitudinal section the front position of the
jack hammer sho~n in Figure lo
Figure 3 is a section taken along line 3-3 in Figure 1.
Figures 4-6 are longitudinal sections corresponding to Figure 1 but
showing some details of the impact motor in other relative positions.
The impact motor shown in the figures comprises a housing 11 that
forms a c~linder in which a hammer piston 12 is slidable ~Figure l~o A tool in
the form of a chisel 13 is insertable into the front end of the housing and
it is prevented from falling out b~ means of a chisel holder 14 (Figure 2). The
chisel takes support rearwardly with a shoulder 16 against an annular support
piston 17 that is axially slidable in the housing and forced forwardly towards
its illustrated position in the housing b~ the pump pressure that is transmitted
through a conduit 15 to an annular piston surface 19 on the support piston 17.
The support piston 17 is forced forwardl~ b~ a force that is greater than the
feed force that is norma~l~ transmitted to the houslng during operat~on so that
the support piston will define the impact position of the chisel as sho~n ln
Pigures 1 and 2. The jack hammer can be hand~held jack hammer in ~hich the feed
.
:, - ~ :
' ' ~ , ' ' ' ''' ''''~'':
: - i
1148~)63
force is manuall~ applied or it can be mounted or example on a back~hoe. The
impact motor can also be used in a rock drill.
The hammer pis,ton 12 has a head in the form of an annular land 18
~ith two annular piston surfaces 19, 20. The rear piston surface 19 makes a
movable wall to a rear pressure chamber 21 that is formed in the cylinder ll
~the housing) and the front piston surface 20 a movable ~all of a front pressure
chamber 22 that is formed in the cylinder.
The front piston surface 20 is larger than the rear one.
The impact motor has a maln inlet 23 and a main outlet 24 for the hyd-
raulic fluid e.g. hydraulic oil, and when the main inlet 23 is pressurized, the
rear pressure chamber 21 is permanently pressurized through a conduit 25, 26.
A gas pressure accumulator 27 is connected to the rear pressure chamber 21. A
valve in the form of a spool 28 is arranged to alternativel~ pressurize and
exhaust the front pres;sure chamber 22 via a connection conduit 29.
The valve 28 has a cylindrical end face 30 located in a cylindrical
control chamber 310 A conduit 32 leads bet~een the control chamber 31 and
the main cylinder and this conduit is branched so that it has two ports 33, 34
to the cylinder. The other end of the valve 28 has a cylindrical bore 35 that
forms a control chamber into which a control piston 36 protrudes. The bore 35
and the control piston 36 have end faces 37, 38 that are smaller than the end
face 30 at the other end of the valve. The control piston 36 has its other and
larger end face 39 located in a control chamber 40 that, by means o a control
conduit 41, is connected to an annular chamber 42 of a device 43 for adjusting
the stroke length. The end face 39 of the control piston is larger than the end
face 30 of the valve. The device 43 comprises an annular bush 44 that is fixed
to the hous~ing. Inside the bush there is a manually turnable cock 45. This
-
1~48~63
cock 45 has a passage 46 that selectively connects the annular chamber 4Z
and thereb~ the control chamber 40 to anyone of four ports 47-50 into the cylinder
bore. ln the figures, the port 47 is coupled to the control passage 41. All
the ports 47.50 are positioned axiall~ ~ithin limits defined by the opening
edges of the ports 33 and 34, and the distance bet~een the piston surfaces 19,
20 of~the land 18 of the piston is larger than the distance between the opening
edges of the ports 33 and 34O The ports 33 and 34 need not be two separate
ports but ma~ be a single slot-formed port that extends all the way between the
ports 33 and 34.
A restricted passage 52 leads hetween the control chamber 40 and an
intermediate chamber 51 which is always connected to exhaust through a larger
passage 53. The bore or control chamber 35 is alwa~s connected to inlet via a
passage 54 whereas the control chamber 31 at the other end of the valve is
: always connected to the connection conduit 29 b~ means of a restricted passage
55. An intermediate chamber 58 is alwa~s connected to exhaust through a passage
59O Between the main inlet 23 and an annular inlet chamber 56 of the valve
there is a variable restriction 57.
An accumulator 60 has an accumulator chamber 61 that is continuously
connected to the connection conduit 29 via a conduit 62 that contains a one-way
valve 63 that permits flow only in the direction from the accumulator chamber
to connection conduit, that is, onl~ in the direction from the accumulator
chamber 61 to the fron~t pressure chamber 22. The accumulator chamber 61 is
also continuousl~ connected to the main outlet 24 through a passage 64. A
piston 65 forms a movable wall of the accumulator chamber 61. The piston 65 is
preloaded b~ the pressure in the rear pressure chamber 21 transmitted through
a conduit 67 to act on the end face 68 of a piston rod of the piston 65. Thus,
' , , ' ,
8~63
the piston rod is itsel a pistonO An inter~ediate chamber 69 in the accumulator
is connected to an end chamber 70 in ~he c~linder at the rear of the h = er
piston 12 b~ means of a conduit 71. ~he intermediate chamber 69 and the end
chamber 70 are filled with air of atmospherlc pressure or with air or other
gas of slightl~ higher pressure. The~ are provided ~ith non-illustrated drain
canduits for leading away hydraulic oil that leaks into the cham~er.
In the figures, the valve 28 and the accumulators 27, 60 are shown
outside of the housing 11 although the~ are in fact located in the housing 11
and the conduits shown in the figures are conveniently channels in the housing.
The dra~ings are schematic and it should be noted that the hammer piston 12, the
valve 28 and the accumulators 27, 60 are not drawn to the same scale. This
fact ~ill however not be harmful to the understanding of the operation.
The operation of the impact motor ~ill no~ be described. Assume that
the hammer piston 12 during operation just impacts on the anvil surface 72 of
the chisel as shown in Figure 1 and that the valve 28 has just changed over to
its position shown in Figure 1 in ~hich it pressuri~es the front pressure cha~ber
22 via the connection conduit 29.
The valve 28 is in its illustrated position because of the pressure
in the conduit chamber 31 and the control piston 36 is in its illustrated
2~ position because the control passage 41 is shut off ~the port 47 is blocked
b~ the land 18 of the hammer piston)~ Oil that leaks into the control chamber
4Q is drained off through the passage 52. ~uring a portion of its return move-
ment, the hammer piston 12 will cover both ports 33, 34 of the control passage
32 as s;hown in Pigure 4 but during thls period the pressure in the control
chamber 31 is maintained b~ the leak passage 55 in the valve. It ~ill not affect
the valve that the port 34 is opened to pressure chamber 22 during the return
11~8~63
stroke since pre~sure chamber 22 is then under pre$sure. When the hammer
piston 12 reaches its position shown in ~igure S and opens the port 47, the
control conduit 41 and the control chamber 40 are pressurized from the front
pressure cha~er 22 so that the control piston 36 shifts the valve 28 into the
position of Figure 5. (The piston surface 3~ is, larger than the piston surface
30). The front pressure chamber 22 is now connected to the outlet 24 and the
control piston 36 ~ill therefore return to its previous position as shown in
Figure 6 ~hereas; the valve 28 remains in its position of Figure 5 because of
the press,ure in the control chamber 35. The pressure chamber 3n is relieved
of press,ure since the port 34 is open to the front pressure chamber 22 which
is now connected to the outlet 24.
The hammer piston ~ill no~ retard and turn because of the continuous
pressure in the rear press,ure chamber 21 and during the work-stroke shown in
Pigure 6 the land 18 of the hammer pi$ton will again cover the port 34, but
the valve 28 will remain stabl~ in its position because oil that leaks into the
control chamber 31 is conveyed through the passage 55 without increasing the
pres,sure in the control chamber 31. If oil leaks into the control passage 41
~hen the port 47 is blocked it is drained off continuously through the passage
52.
Just prior to impact the land 18 o the hammer pi~ton opens the port
33 to the rear pressure chamber 21 so that the control chamber 31 is pres:surized
and the valve 28 changes over to its position sho~n in Figure 1 in ~hich it
pressurizes the front pressure chamber 22.
During the work-stroke of the hammer piston, hydraulic oil is forced
out from the front pressure chamber 22 and into the main outlet 24. Because of
the large flow-, some of the oil is accumulated in the accumulator chamber 61 at
_7_
.
'-,~
~ '
~1~8063
a some~hat increased pressure.
~ hen the hammer piston impacts on the chisel, a shock ~ave is induced
in the chisel and it propagates forwardl~ through the chisel. If the end
of the chisel does not protrude full~ into the material being worked because
the material is too hard, part of the shock wave ~ill re1ect at the chisel
end and move hack up~ardl~ through the chisel and reach the hammer piston so
that the hammer piston hounces back from the chisel. Because of this rebound,
the hammer piston can have such a big instantaneous acceleration that the valve
28 cannot supply enough oil to the front pressure chamber 22. The pressure in
the front pressure chamber 22 can therefore instantaneousl~ be low. If the
pres;sure in the pressure chamber 22 becomes lower than the pressure in the
accumulating chamber 61 of the accumulator 60, oll ~ill be forced through the
passage 62 and the one-wa~ valve 63 into the front pressure chamber 22~ At
least part of the rebound energ~ of the hammer piston will then be returned to
the high pressure accumulator 270 The ad~ustable re$triction 57 can therefore
be used to restrict the s;uppl~ to the valve 28 without affecting the impact
energy per blo~0 Thus, by red~cing the inflo~ to the valve by means of the
restriction 57, the impact rate is reduced and the total output is also reduced,
but the impact energy per blow remains substantially constant. The impact
motor can therefore be connected to low output pumps and still operate with full
energ~ impacts. The impact rate ~ith full~ open restriction 57 is basically
determined b~ the difference area 20 minus area 19 which is the effective area
for effecting the return strokesO For a jack hammer this effective area can
suitabl~ be about 10 % of area 19 which makes the return strokes slo~. For a
rock drill, this effective area can instead be about 50 % of area 19, so that a
suitahle higher impact rate is achieved.
.
.'
~ ' . -
': '
~48(~63
A one_wa~ valve can ~e ln$erted into the conduit 26 to permit flow
onl~ in the direction towards the rear pressure cham~er 21. Such a one-wa~ valve
makes the accumulator 27 ~ork as a spring a~ove the pump pres;sure, and the
characteris-tic cur~e of the accumulator ~ that is, the curve defining the pressure
as a function of the accumulated volume - can ~e chosen more steep than when
the accumulator must work at the pump pres:sure all the time.
: . . :
,
' , ,.
: .
