WO2008051146A1

WO2008051146A1 - Hydraulic impact device

Info

Publication number: WO2008051146A1
Application number: PCT/SE2007/000932
Authority: WO
Inventors: Stig Roland Henriksson
Original assignee: Atlas Copco Construction Tools Ab
Priority date: 2006-10-25
Filing date: 2007-10-24
Publication date: 2008-05-02
Also published as: EP2076364A4; EP2076364A1; SE0602237L; SE530617C2

Abstract

In a hydraulic impact device an impact piston (12) is reciprocated in a cylinder bore (10) and has a central drive portion (20) energised in an activation section (16) of the cylinder bore (10), and a forward end portion (23) and a rear end portion (25) of the impact piston (12) form clearance seals (24,26) visavi the cylinder bore (10), and at the ends of the cylinder bore (10) there are provided low pressure chambers (34,35) which together with a communication passage (36) form a low pressure circuit which is continuously connected to the tank (28). The low pressure chambers (34,35) at the ends of the cylinder bore (10) enables the impact piston (12) to be sealed off by clearance seals only, whereby piston leakage is prevented without the use of seal rings.

Description

Hydraulic: impart, device.

The invention relates to a hydraulic impact device of the type comprising an impact piston reciprocally driven in a cylinder bore and intended to deliver repeated impact energy to a working implement, wherein the impact piston is provided with a central drive portion to be pressurized via a distribution valve for reciprocating the piston in the cylinder, and an anvil arranged to transfer impact energy from the impact piston to the working implement .

Impact devices of this type normally suffer from a couple of problems such as leakage and/or mechanical wear of piston seals, i.e. impact devices have been provided either with seal elements with a moderate contact force and a risk for leakage or very tight seal elements with friction losses, heavy mechanical wear and heat development as a result. Heat generated by such tight seal elements could be of such a magnitude that the surface hardening of the piston disappears and the mechanical wear of the piston increases drastically.

Other problems with today's impact devices are due to the direct mechanical contact between the impact piston and the anvil at delivery of impact energy. Two different problems are identified, namely very noisy blows as the impact piston hits the anvil, and a noisy rattling of the working implement relative to the housing of the impact device since there is no continuously acting contact force between the anvil and the working implement.

Still another problem with prior art hydraulic impact devices resides in the fact that the impact piston has to be formed of a corrosion resistant material or to be provided with a corrosion resistant surface layer, because the ends of the piston are exposed to atmospheric air including moisture etc. which means that the piston ends are prone to get rusty. This will have a detrimental effect on the surfaces being in contact with the piston seal elements, and the service life of the piston seals will be substantially reduced.

The invention aims to create a hydraulic impact device by which the above described problems are avoided. This is accomplished by an improved impact device wherein the impact piston operates without any mechanical seal elements, which means that there are no friction losses, no limited service life due to worn down seal elements, and no heat generation in the impact piston. By the invention there is also accomplished an impact device wherein the impact piston is sealed off from the atmospheric air and thereby protected against rust attacks, which means that a cheaper material may be used in the impact piston.

Further characteristics and advantages will appear from the following specification and claims.

A preferred embodiment of the invention is described below with reference to the accompanying drawings.

In the drawings

Fig. 1 A shows a hydraulic impact device according to one embodiment of the invention and illustrates the impact piston in its rear end position.

Fig. 1 B shows the impact device in Fig. 1 A but illustrates the impact piston in its forward impact delivering position.

Fig. 2 A shows an impact device according to an alternative embodiment of the invention and illustrates the impact piston in its rear end position.

Fig. 2 B shows the impact device in Fig. 2 A but illustrates the impact piston in its forward impact delivering position. Fig. 3 shows an impact device according to a slightly different embodiment of the invention and illustrates the impact piston in its rear end position.

Fig. 4 shows an impact device according to still another embodiment of the invention and illustrates the impact piston in its rear end position.

The impact device shown in Figs. 1 A and IB comprises a housing with a cylinder bore 10, an impact piston 12 reciprocally guide in the cylinder bore 10, and an anvil 13 also guided in the cylinder bore 10 and arranged to transfer impact energy from the impact piston 12 to a working implement 14 inserted in the forward end of the cylinder bore 10. The cylinder bore 10 has a central larger diameter activation section 16, a rear guide section 17, and a forward guide section 18, and the impact piston 12 has a central drive portion 20 sealingly guided in said activation section 16 of the cylinder bore 10, thereby forming a working stroke drive chamber 21 and a return stroke drive chamber 22 on opposite sides of the impact piston drive portion 20. The impact piston 12 further comprises a forward end portion 23 guidingly supported in said forward guide section 18 and forming a clearance seal 24 therewith, and a rear end portion 25 guidingly supported in said rear guide section 17 and forming a clearance seal 26 therewith.

The return stroke drive chamber 22 is continuously connected to a pressure fluid source 27, whereas the working stroke drive chamber 21 is alternatingly connected to the pressure fluid source 27 and to a tank 28 by means of a distribution valve 30 so as to reciprocate the piston 12 in the cylinder bore 10. The working stroke drive chamber 21 is connected to the tank 28 during return strokes via a passage 31 and the valve 30. At the rear end of the cylinder bore 10 there is provided a rear low pressure chamber 34 continuously communicating with the rear end of the piston 12, and at the forward end of the cylinder bore 10 there is provided a forward low pressure chamber 35, The latter is penetrated by the forward end section 23 of the impact piston 12 during the working strokes. The forward and rear low pressure chambers 34 and 35 are continuously connected to each other via a communication passage 36 and to the tank 28 and form together with the communication passage 36 a low pressure circuit which is supplied with pressure fluid from the return stroke drive chamber 22 via a feed passage 38 as the piston 12 occupies its rear end position, as illustrated in Fig. 1 A. Due to a certain flow resistance in a drain passage 39 to the tank 28 there will always remain a certain pressure in the low pressure circuit 34, 35, 36 which results in a maintained pressure in the forward low pressure chamber 35, and a forward directed force on the anvil 13 is thereby maintained during operation of the impact piston 12. This force will keep the anvil 13 in continuous contact with the working implement 14 and no metallic striking sound will be generated.

In a common way a pressure accumulator 41 is connected to the pressure fluid supply line to reduce pressure transients in the drive system, and another pressure accumulator 42 is connect to the low pressure circuit to smoothen out the pressure therein.

During the impact strokes the forward end the impact piston 12 passes through the forward low pressure chamber 35, and when passed the chamber 35 the piston 12 resumes a clearance seal engagement with the cylinder bore 10. Thereby, a high pressure fluid cushion 44 is enclosed between its forward end and the anvil 13 for transferring the kinetic energy of the piston 12 to the anvil 13 and the working implement 14. Due to an annular groove 46 in the forward guide section 18 the low pressure circuit is still connected to the tank 28.

In order to protect the device from damage in case of idle blows, i.e. working strokes performed with no working implement attached, the annular groove 46 acts as a damping chamber as it is connected to the tank 28 via a flow restriction 47. This will dampen the piston 12 and preventing it from hitting the anvil 13 with metallic contact .

At working strokes the working stroke drive chamber 21 is supplied with pressure fluid from the pressure fluid source 27 via the distribution valve 30, as illustrated in Fig. 1 A, whereas the return stroke drive chamber 22 is continuously pressurized. Due to the fact that the annular piston surface at the rear end of the central drive portion 20 is larger than that at the forward end thereof, the force acting on the rear surface will dominate during the working strokes, despite the same fluid pressure acting on the oppositely facing surface.

An impact stroke is started with the impact piston 12 is in its rear end position where the pressure in the return stroke drive chamber 22 is conducted to the rear low pressure chamber 34 to pressurize the low pressure circuit, including the communication passage 36 and the forward low pressure chamber 35. Then, the piston 12 accelerates forwards towards the anvil 13, and when having passed through the forward low pressure chamber 35 a high pressure cushion 44 is enclosed between the piston 12 and the anvil 13 to transfer the kinetic energy of the piston 12 to the anvil 13 and the working implement 14. The minor leakage that occurs from the high pressure cushion 44 via the clearance seal 24 will be collected in the low pressure chamber 35 and in the damping groove 46 and returned to the tank 28. As the forward end position of the piston 12 is reached, see Fig. 1 B, the rear low pressure chamber 34 has been expanded and momentarily received some fluid from the forward low pressure chamber 35 as the latter has decreased. Since the distribution valve 30 has now stopped directing pressure fluid to the working stroke drive chamber 21 the full pressure in the return stroke drive chamber 22 will drive the piston 12 in the opposite direction.

So, as the drive pressure is discontinued in the working stroke drive chamber 21 the piston 12 will return to its rear end position, and while doing so the volume of the rear low pressure chamber 34 decreases at the same time as the forward low pressure chamber 35 expands. This means that fluid is pumped not only to the forward low pressure chamber 35 via passage 36 but also to the tank 28. Due to the fact, as described above, that there is always a certain remaining pressure in the low pressure circuit due to inevitable flow restrictions in the tank passage 39 a bias force is continuously upheld on the anvil 13.

The anvil 13 is provided with an annular flange 48 which is received in an enlarged portion 49 of the bore 10, and an enclosed air volume will dampen forward movement of the anvil 13 at occurring idle blows, i.e. when no working implement is attached.

In the embodiment illustrated in Figs. 2 A and B the impact device is identical to the one described above except for the low pressure circuit communication passage 50 which is located inside the impact piston 12. In order to have the passage 50 communicate with the forward low pressure chamber 35 the piston 12 is provided with an annular groove 51 adjacent its forward end. The rest of the design and the operation order is the same as for the above described embodiment .

The impact device illustrated in Fig. 3 is identical with the above described devices except for the arrangement of a high pressure damping volume 55 at a forward facing end surface 56 of the anvil 53. The damping volume 55 is continuously connected to the pressure fluid source 27 via a passage 57. This arrangement will ensure a safe damping and protection of the device in case of idle blows, as described above .

An alternative damping means is illustrated in Fig. 4 wherein the anvil 63 has been provided with a larger annular flange 60 with a forward facing end surface 66, and the damping chamber 61 is continuously connected via a passage 64 to the low pressure circuit and the tank 28. The inevitable flow restrictions in the drain passages to the tank 28 will provide a sufficient damping effect.

The embodiments of the invention are not limited to the above described examples but can be freely varied within the scope of the claims .

Claims

Cl aims .

1. Hydraulic impact mechanism for delivering repeated impact energy to a working implement

(14), comprising a housing with a cylinder bore (10) and an impact piston (12) reciprocally driven in the cylinder bore

(10) , the cylinder bore (10) has a central activation section (16) , a rear guide section (17) , and a forward guide section (18), and the impact piston (12) has a central drive portion (20) sealingly guided in said central activation section (16), a forward end portion (23) sealingly guided in said forward guide section (18) , and a rear end portion (25) sealingly guided in said rear guide section (17) , a distribution valve (30) for directing pressure fluid to the activation section (16) to reciprocate the impact piston (12) , and an anvil (13) arranged to transfer kinetic energy from the impact piston

(12) to the working implement (14) , c h a r a c t e r i z e d in that said forward end portion

(23) forms a clearance seal (24) with said forward guide section (18) , and said rear end portion (25) forms a clearance seal with said rear guide section (17) , a rear fluid chamber (34) is provided to be entered by the rear end portion (25) of the impact piston (12) during return strokes, and a forward fluid chamber (35) is provided to be penetrated by the forward end portion (23) of the impact piston (12) during working strokes, said forward and rear fluid chambers (35,34) are continuously connected to each other via a communication passage (36;50), wherein said forward fluid chamber (35) , said rear fluid chamber (34) and said communication passage (36,50) form a low pressure circuit which is continuously connected to tank (28) .

2. Impact device according to claim 1, wherein a fluid volume is enclosed by the forward end portion (23) of the impact piston (12) when passing through said forward fluid chamber (35) , said fluid volume forms an impact energy transferring fluid cushion (44) between the impact piston (12) and the anvil (13) during working strokes of the impact piston (12) .

3. Impact mechanism according to claim 1 or 2, wherein the central activation section (16) comprises a working stroke drive chamber (21) and a return stroke drive chamber (22), and said low pressure circuit is connected to the working stroke drive chamber (21) during return strokes of the impact piston (12) .

4. Impact mechanism according to anyone of claims 1-3, wherein said communication passage (50) extends axially through the impact piston (12) .

5. Impact mechanism according to anyone of claims 1-4, wherein said low pressure circuit includes a pressure accumulator (42).