Hydraulically actuated piston guided in a cylinder, and hydraulic working tool

Abstract

The invention relates to a hydraulically actuated piston (9) guided in a cylinder (8), and to a hydraulic working tool (1) having a working head (2), wherein the piston (9) has an impact surface (15) which borders an impact space (16) on the piston side provided between the piston (9) and the cylinder (8), and wherein hydraulic fluid (17) can act on the impact surface (15) by increasing the impact space (16) in order to move the piston (9) in an impact direction (r), and the piston (9) forms a limiting device (25) for a through-flow of the hydraulic fluid (17). According to the invention, in order to design a hydraulic piston guided in a cylinder or a hydraulic working tool in such a way that no undue signs of wear occur even during working processes with the sudden disappearance of the counter pressure, a hydraulic chamber (19) filled with the hydraulic fluid (17) is formed in the impact direction (r) after the limiting device (25), wherein a volume of the hydraulic chamber (19) is reduced according to the increase in the impact space (16), by means of the displacement of hydraulic fluid (17) out of the hydraulic chamber (19) and into the impact space (16) via the limiting device (25).

Claims

1. An assembly comprising: a cylinder; a hydraulically actuated piston in the cylinder, the piston having an impact surface and a limiting device which limits a through-flow of hydraulic fluid through the piston; an impact space provided upstream of the limiting device between the impact surface of the piston and the cylinder, wherein hydraulic fluid can act on the impact surface to enlarge the impact space in order to move the piston in an impact direction; and a hydraulic chamber filled with the hydraulic fluid is formed in the impact direction downstream of the limiting device, the hydraulic chamber having a fill valve which is open while the piston moves opposite to the impact direction, wherein a volume of the hydraulic chamber diminishes based on the enlargement of the impact space, forcing hydraulic fluid out of the hydraulic chamber through the limiting device into the impact space.

2. The assembly of claim 1, wherein a ratio between areas of surfaces of the hydraulic chamber and the impact space in the impact direction is provided such that a higher pressure arises in the hydraulic chamber than in the impact space while the piston moves in the impact direction without any relevant counter-pressure on the piston.

3. The assembly of claim 2, wherein the piston interacts with an inner surface of the cylinder to form the impact space.

4. The assembly of claim 2, wherein the higher pressure is up to 5 times higher.

5. The assembly of claim 1, wherein the piston interacts with an inner surface of the cylinder to form the impact space.

6. An assembly comprising: a cylinder; a hydraulically actuated piston in the cylinder, the piston having an impact surface, a rear surface and a limiting device which limits a through-flow of hydraulic fluid through the piston between the rear surface and the impact surface; an impact space provided upstream of the limiting device between the impact surface of the piston and the cylinder, wherein hydraulic fluid can act on the impact surface to enlarge the impact space in order to move the piston in an impact direction; and a hydraulic chamber filled with the hydraulic fluid is formed in the impact direction downstream of the limiting device, wherein the hydraulic fluid in the hydraulic chamber acts on the rear surface of the piston, wherein a volume of the hydraulic chamber diminishes based on the enlargement of the impact space, forcing hydraulic fluid out of the hydraulic chamber through the limiting device, wherein the limiting device a provides throttling such that the hydraulic chamber is quasi-closed when a counter-pressure on the piston is eliminated, and the hydraulic fluid in the hydraulic chamber is exposed to a pressure rise of the hydraulic fluid in the hydraulic chamber caused by movement of the piston.

7. The assembly of claim 6, wherein a ratio between areas of surfaces of the hydraulic chamber and the impact space in the impact direction is provided such that a higher pressure arises in the hydraulic chamber than in the impact space while the piston moves in the impact direction without any relevant counter-pressure on the piston.

8. The assembly of claim 7, wherein the piston interacts with an inner surface of the cylinder to form the impact space.

9. The assembly of claim 7, wherein the higher pressure is up to 5 times higher.

10. The assembly of claim 6, wherein the piston interacts with an inner surface of the cylinder to form the impact space.

11. The assembly of claim 6, wherein the hydraulic chamber has a fill valve which is open while the piston moves opposite to the impact direction.

12. A hydraulic working tool comprising: a working head; a cylinder attached to the working head; a hydraulically actuated piston in the cylinder, the piston having an impact surface, a rear surface and a limiting device which limits a through-flow of hydraulic fluid through the piston between the rear surface and the impact surface; an impact space provided upstream of the limiting device between the impact surface of the piston and the cylinder, wherein hydraulic fluid can act on the impact surface to enlarge the impact space in order to move the piston in an impact direction; and a hydraulic chamber filled with the hydraulic fluid is formed in the impact direction downstream of the limiting device, wherein the hydraulic fluid in the hydraulic chamber acts on the rear surface of the piston, wherein a volume of the hydraulic chamber diminishes based on the enlargement of the impact space, forcing hydraulic fluid out of the hydraulic chamber through the limiting device, wherein the limiting device provides throttling such that the hydraulic chamber is quasi-closed when a counter-pressure on the piston is eliminated, and the hydraulic fluid in the hydraulic chamber (is exposed to a pressure rise of the hydraulic fluid in the hydraulic chamber caused by movement of the piston.

13. The hydraulic working tool of claim 12, wherein a ratio between areas of surfaces of the hydraulic chamber and the impact space in the impact direction is provided such that a higher pressure arises in the hydraulic chamber than in the impact space while the piston moves in the impact direction without any relevant counter-pressure on the piston.

14. The hydraulic working tool of claim 13, wherein the piston interacts with an inner surface of the cylinder to form the impact space.

15. The hydraulic working tool of claim 13, wherein the higher pressure is up to 5 times higher.

16. The hydraulic working tool of claim 12, wherein the piston interacts with an inner surface of the cylinder to form the impact space.

17. The hydraulic working tool of claim 12, wherein the hydraulic chamber has a fill valve which is open while the piston moves opposite to the impact direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained below based on the attached drawing, which only shows an exemplary embodiment. The drawing shows:

(2) FIG. 1 A hydraulic working tool with a hydraulically actuatable piston guided in a cylinder, in elevation;

(3) FIG. 2 A side view of the working tool;

(4) FIG. 3 The section according to line III-Ill on FIG. 1;

(5) FIG. 4 A magnified view of area IV on FIG. 3 involving a base piston position;

(6) FIG. 5 The section according to line V-V on FIG. 4;

(7) FIG. 6 A magnified view of area VI on FIG. 4;

(8) FIG. 7 An illustration corresponding to FIG. 4 while displacing the piston in the impact direction;

(9) FIG. 8 Another illustration corresponding to FIG. 4 and relating to an intermediate position during the return of the piston;

(10) FIG. 9 An illustration according to FIG. 4 with a hydraulic chamber that can be evacuated into a separate reservoir;

(11) FIG. 10 An illustration of the embodiment on FIG. 9 with the piston advanced;

(12) FIG. 11 An alternative embodiment of a leak between the piston and an inner cylinder surface.

DESCRIPTION OF THE EMBODIMENTS

(13) Depicted and described initially with reference to FIG. 1 is a hydraulic, in particular electrohydraulic working tool 1 suitable for one-handed operation for actuating a working head 2. As shown, the working head 2 can be designed as a head that can be interchangeably mounted on the working tool 1. A head non-detachably joined with the tool is likewise possible. The working head 2 is designed as a cutting head in the exemplary embodiment shown. However, working heads 2 in the form of punching or pressing heads can also be arranged on the working tool 1, for example.

(14) The working head 2 can be hooked up to the working tool 1 for hydraulic supply purposes.

(15) As also preferred, the hydraulic working tool 1 can be a base device of the kind also depicted and described in the WO 2003/084719 A2 (U.S. Pat. No. 7,412,868 B2) cited at the outset. With reference to the illustration on FIG. 3, the upper area of the working tool 1 reveals the link with the subject matter described in the mentioned WO publication, e.g., with respect to a return valve 3, a tank 4 and a pumping plunger 5. By way of further explaining the hydraulic working tool 1 preferably used here, reference is otherwise made to the mentioned WO or US publication in its entirety, also with the aim of including the purposes and features described in the WO or US publication with regard to the structural design of the working tool in the claims of the application.

(16) The working head 2 is both mechanically and hydraulically joined with the working tool 1 by way of a flange 6. To this end, the flange 6 is initially designed to be screwed with a neck 7 of the working tool 1. The neck 7 simultaneously forms a cylinder 8 for a piston 9 of the working head 2. The area within which the working tool 1 and working head 2 interact is generally designed rotationally symmetrical to an x axis.

(17) The flange 6 of the working head 2 encompasses the neck 7, and on the working head side of the neck 7 transitions into a retainer 10 with a bow-shaped design. A fixed blade 11 is arranged on this retainer 10 in the exemplary embodiment depicted.

(18) Another movable blade 12 is arranged upstream toward the fixed blade 11. The blade 12 is coupled with the piston 9, which correspondingly is also a constituent of the working head 2.

(19) The piston 9 and therefore the blade 12 can be linearly displaced in the working head 2, along the x axis in the use position.

(20) The piston 9 has a piston shaft 13 with a plate-shaped piston flange or piston head 14 facing away from the working area or connection area of the blade 12 to the piston shaft 13.

(21) The diameter of the piston head 14 is adjusted to the inner diameter of the receiving cylinder 8. The interacting surfaces of the piston 9 or piston head 14 and the cylinder 8 yield a limiting device 25.

(22) The piston shaft diameter is diminished relative to the outer diameter of the piston head 14, and hence relative to the inner diameter of the cylinder 8, for example corresponding to 0.5 to 0.7 times the piston head diameter. This correspondingly results in an annular chamber enveloping the piston shaft 13.

(23) The piston head 14 facing away from this annular chamber forms an impact surface 15 for the hydraulic fluid 17 conveyed in the impact space 16 formed between the cylinder 8 and piston 9 in front of the impact surface 15 during operation of the working tool 1.

(24) The piston 9 is loaded against an impact direction r caused by a pressure increase in the impact space 16 toward a basic position, for example as depicted on FIG. 4. A spring 18 is provided for this purpose, in particular a cylinder compression spring. The spring 18 abuts against the working head 2 at one end in the area of the retainer 10, and acts on the piston shaft 13 at the other end.

(25) The annular chamber that comes about radially between the piston shaft 13 and cylinder 8 forms a hydraulic chamber 19. The latter is bordered essentially by the piston head 14 opposite the impact direction r, and by a surface that is fixed relative to the cylinder 8 in the impact direction r. In the exemplary embodiment shown, the fixed surface is formed by a collar 20 of a sleeve 21 retained on the working head 2 that acts to seal the inner surface of the cylinder 8. The fixed surface could also be an integral part of the cylinder. The sleeve 21 can envelop the spring 18, and in the depicted position of the working head 2 connected to the working tool 1 preferably abuts the cylinder 8 on the interior side of the wall.

(26) The area of the collar 20 continuously accommodates a seal 22 radially outwardly, so as to act as a seal against the inner cylinder surface. The collar 20 also has a seal 23 radially inwardly for interacting with the cylindrical outer surface of the piston shaft 13.

(27) The hydraulic chamber 19 is thus sealed in the area of the collar 20 as viewed in the impact direction r. By contrast, preferably no or at least no completely continuous seal is provided in the direction of the piston head 14. Rather, a clearance fit is provided between the piston head 14 and inner surface of the cylinder 8, for example. This provides an intentional leak between the piston 9 and cylinder 8, and further between the hydraulic chamber 19 and impact space 16.

(28) The hydraulic chamber 19 is filled with the same hydraulic fluid 17 as the impact space 16. Proceeding from a basic piston position according to FIG. 4 or a basic working head position according to the illustrations on FIGS. 1 to 3, the preferably electrically operated pump provided in the working tool 1 is actuated to pump hydraulic fluid 17 into the impact space 16. This causes a linear displacement of the piston 9 relative to the cylinder 8 inside of the cylinder 8 in the impact direction. The movement takes place opposite the force exerted by the spring 18, which in particular serves to restore the system to the basic position.

(29) Due to the ratio between the effective surfaces of the impact space 16 (impact surface 15) and hydraulic chamber 19 (annular surface 24 of the piston head 14), a pressure elevated by comparison to the pressure in the impact space 16 arises in the hydraulic chamber 19 as the piston 9 advances as the result of pumping hydraulic fluid into the impact space 16. In any event, this hydraulic chamber pressure can measure 5 times, for example, and possibly even beyond that, of the impact space pressure, as long as no notable counter-pressure prevails.

(30) The limiting device 25 preferably provided in the area where the piston 9 or piston head 14 interacts with an inner wall of the cylinder 8 has the kind of leak that allows hydraulic fluid 17 to be forced out of the hydraulic chamber 19 into the impact space 16 (also) as a result of the given pressure difference as the piston 9 moves in the impact direction r (see arrows a on FIG. 7). Accordingly, a volumetric enlargement of the impact space 16, and hence a piston displacement in the impact direction r, is accompanied by a volumetric reduction of the hydraulic chamber 19.

(31) In a preferred embodiment, the size of the hydraulic chamber 19, in particular its axial measure in the direction of extension of the x axis, can be selected in such a way that the hydraulic chamber 19 still remains filled with a residual quantity of hydraulic fluid 17 with the piston 9 in a completely forwardly displaced position (which can also be limited by a stop).

(32) Given a sudden forward displacement of the piston 9, i.e., during a cutting process in the exemplary embodiment shown, the partial hydraulic fluid quantity in the hydraulic chamber 19 damps the movement of the piston 9. In particular toward the end of the process of extending the piston 9 or given a high acting counter-force and a correspondingly high pressure in the impact space, which is often clearly present before the extension process has ended, a pressure roughly the same as in the impact space 16 elevated by about the pressure difference caused by the limiting device arises based on the prevailing counter-force in the hydraulic chamber 19 in the depicted exemplary embodiment. If the object to be cut breaks (brittle fracture) in such a position, in which 500 bar or more, for example 600 or 700 bar, act on the piston 9, the system is suddenly relieved, whereupon the piston 9 tends to push forward in the impact direction r. This is to be avoided by the hydraulic buffer in the hydraulic chamber 19. The hydraulic means in the hydraulic chamber 19 effectively decelerates the piston 9 over a very short path and in a very short time measuring fractions of a second. A very distinct, relevant further pressure rise in the hydraulic chamber 19 here takes place over the short term. As a result, the hydraulic fluid in the hydraulic chamber 19 can also be compressed, and thus absorb force as elastically as a spring, which immediately thereafter tries to press the piston in the opposite direction.

(33) The return process of the piston 9 can be initiated automatically by the working tool 1, controlled by a valve, or alternatively in a manual operation. The return displacement is achieved by having the spring 18 act opposite the impact direction r, wherein the hydraulic fluid 17 located in the impact space 16 is forced back into the tank 4.

(34) During this return displacement, the volume of the impact space 16 diminishes. At the same time, the volume of the hydraulic chamber 19 increases.

(35) During the return displacement of the piston, hydraulic fluid 17 flows out of the impact space 16 into the hydraulic chamber 19 (see arrow b on FIG. 8). This can take place through the leak provided in the area of the limiting device 25.

(36) To this end, a return flow channel 26 with a fill valve 27 is preferably provided.

(37) As also depicted, the return flow channel 26 can be a radially directed branch channel, which empties radially outwardly in the area where the piston 9, in particular the piston head 14, and an inner surface of the cylinder 8 interact, for example in the area of the limiting device 25. The return flow channel 26 can radially inwardly empty in the area of a central cavity 28 of the piston 9, wherein the cavity 28 is part of the impact space 16.

(38) The branch channel-like return flow channel 26 empties radially outwardly in the area of the limiting device 25, for example, into a flow section 29 that opens toward the hydraulic chamber 19 and is essentially axially aligned. An area 30 expanded in relation to the return flow channel 26 is situated upstream from the flow section 29 in the direction of flow of the hydraulic fluid 17 during the return displacement of the piston 9. A valve ball 31 can be displaced therein in the direction of flow, so as to open the flow-through path for the hydraulic fluid 17 during the return displacement of the piston 9.

(39) During a piston displacement in the impact direction r and given the corresponding overpressure here present in the hydraulic chamber 19, the valve ball 31 is forced into the closed position of the return flow channel 26.

(40) FIGS. 9 and 10 show an embodiment in which the hydraulic fluid located in the hydraulic chamber is evacuated into a separate tank 4. In such a configuration, a lower pressure can be present in the hydraulic chamber until the counter-force is eliminated.

(41) The limiting device can basically be designed as described above in this embodiment as well.

(42) The separate tank 4 can be designed in a variety of ways. Strictly by way of example, the exemplary embodiment provides a bellows 32, which can expand against a return spring 33 acting on it while hydraulic fluid is being conveyed in the separate tank 4.

(43) After completion of an operation and a corresponding pressure drop in the impact space, the piston 9 travels back, wherein the return spring 33 causes the volume of hydraulic fluid previously accommodated in the separate tank 4 to again empty into the impact space, in the exemplary embodiment by way of a check valve 34.

(44) In this embodiment, a fixed partition wall 35 in the cylinder 8 provides the transition to the separate tank 4. The limiting device 25 can be formed between a radial lateral surface 36 of the partition wall 35 and the inner surface of the cylinder 8. As also evident from the magnified view on FIG. 9, it is solely provided by a leak between the allocated surfaces in the exemplary embodiment shown. Hydraulic fluid that flows through can then proceed in the direction of flow in front of a radial seal 37 and enter into a borehole 38, which provides access to the separate tank 34.

(45) As shown in the schematic diagram on FIG. 10, the limiting device can also be formed, if necessary even only, by a flattened region 39 of the piston head or partition wall specifically formed at a circumferential area. Several such flattened regions 39 can also be provided around the circumference. In this way, the limiting device can be formed at one or several specific locations over the circumference in a targeted manner.

(46) The flattened region shown on FIG. 10 is exaggeratedly large for the sake of clarity.

REFERENCE LIST

(47) 1 Working tool 2 Working head 3 Return valve 4 Tank 4 Separate tank 5 Pumping plunger 6 Flange 7 Neck 8 Cylinder 9 Piston 10 Retainer 11 Fixed blade 12 Blade 13 Piston shaft 14 Piston head 15 Impact surface 16 Impact space 17 Hydraulic fluid 18 Spring 19 Hydraulic chamber 20 Collar 21 Sleeve 22 Seal 23 Seal 24 Annular surface 25 Limiting device 26 Return flow channel 27 Fill valve 28 Cavity 29 Flow section 30 Expanded area 31 Valve ball 32 Bellows 33 Restoring spring 34 Check valve 35 Partition wall 36 Lateral surface 37 Radial seal 38 Borehole 39 Flattened region a Arrow b Arrow r Impact direction x Axis