CA1148063A - Hydraulically operated impact motor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An hydraulically operated impact motor, for example a jack hammer, has a hammer piston (12) with a single land (18). The hammer piston surfaces (19, 20) of the land (18) form two cylinder chambers (21, 22) together with the cylinder of the piston. The rear cylinder chamber (21) is constantly pres-surized by the pump pressure and the front cylinder chamber (22) is periodically pressurized and drained by means of a valve (28). The valve (28) is controlled by two control passages (32, 41) that have ports (33, 34 and 47-50 respectively)into the cylinder and conveys the control pressure to valve shifting piston surfaces (30, 39). The larger one (39) of the valve shifting piston surfaces (30, 39) is the end surface of a plunger (36) and an intermediate chamber (35) is formed between the plunger (36) and the valve spool (28). The intermediate chamber (35) is constantly pressurized through a passage (54). Internal leak passages (52, 55) in the valve spool makes the valve spool stable in its two positions.

Description

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 . : ~

~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 .
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: - 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_ .
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~ ' ~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.

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.' ~ ' . -': ' ~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.

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 reciprocably mounted in said cylinder and arranged to im-pact upon an anvil means said hammer piston defining with said cylinder first and second pressure chambers, said first and second pressure chambers being in selec-tive communication with said first and second port means;
a single piston land on said hammer piston;
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 use;
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 alter-natively to said source of high-pressure hydraulic motive fluid and to a motive fluid outlet;
said 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 first 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 away 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 for moving said second piston means away from said valving element when said second piston means is 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 selectively block said first and second port means in response to its axial position in the cylinder.

2. The impact motor of claim 1 wherein said one direction is the direction of delivering impact to said anvil means by said hammer piston.

3. The impact motor of claim 1 wherein said third piston means has a piston area that is smaller than the piston area of said first piston means.

4. The impact motor of claim 1 or 3 wherein said first piston means has a piston area that is smaller than the piston area of said second piston means.

5. The impact motor of claim 1 wherein said single piston land is arranged to alternatively open said first port means to said first and second pressure chambers and to block said first port means with an interval there-between, and said single piston land is further arranged to alternatively open said second port means to said second pressure chamber and to block said second port means.

6. The impact motor of claim 3 wherein said first port means includes an opening leading into said first pressure chamber and an opening leading into said second pressure chamber; and said second port means is located within axial limits defined by said two openings and extends axially a distance that is substantially smaller than the distance between said openings.

7. The impact motor of claim 6 wherein the distance between said first and second piston surfaces of said single land is larger than the distance between said openings of said first port means.

8. The impact motor of claim 6 wherein said first port means comprises two separate ports in said cylinder at an axial distance from each other; and said second port means comprises a plurality of ports that are selectively con-nectable to said second control passage.

9. The impact motor of claim 1 wherein said first port means comprises two separate ports in said cylinder at an axial distance from each other.

10. The impact motor of claim 9 wherein said second port means comprises a plurality of ports that are selectively connectable to said second control passage.

11. The impact motor of claim 1 wherein said means for constantly pressurizing said first pressure chamber and said means for constantly pres-surizing said third piston means are coupled to said source of high pressure motive fluid.

12. The impact motor of claims 1, 5 or 3 further comprising a source of low pressure hydraulic fluid; and a one-way valve coupling said low pressure source to said second pressure chamber for permitting flow of low pressure hydraulic fluid only in the direction towards said second pressure chamber.

13. The impact motor of claims 1, 5 or 3 further comprising a source of low pressure hydraulic fluid; and a one-way valve coupling said low pressure source to said second pressure chamber for permitting flow of low pressure hydraulic fluid only in the direction towards said second pressure chamber, and wherein said source of low pressure hydraulic fluid comprises an exhaust line from said valve, said exhaust line being coupled to a chamber defined between said valving element and said valve cylinder.