Double-Acting Cylinder

Abstract

Disclosed and claimed is a double-acting cylinder comprising a cylinder housing, a first floating piston, a second floating piston and a central piston which is movable to three stationary positions along an actuation direction of the cylinder. A movement of the floating pistons in the cylinder bore is delimited by end stop arrangements. A movement of the central piston in the cylinder bore is delimited by the first and the second floating piston. Each floating piston comprises a first section and a second section. A circumferential length of the floating pistons is greater in the first section than in the second section. In the first sections a first seal is arranged for a sealing engagement with an inner wall of the cylinder bore. In the second sections a second seal is arranged for a sealing engagement with the inner wall of the cylinder bore or an inner wall of the central piston.

Claims

1. A double-acting cylinder (1) comprising a cylinder housing (3), a first floating piston (7), a second floating piston (9) and a central piston (11) which is movable to three stationary positions along an actuation direction (13) of the cylinder (1), wherein the cylinder housing (3) defines a cylinder bore (5) which extends along the actuation direction (13) and is delimited on opposing ends by a first and a second cylinder cap (15, 17), respectively, wherein a movement of the first floating piston (7) in the cylinder bore (5) along the actuation direction (13) of the cylinder (1) is delimited towards the second floating piston (9) by a first end stop arrangement (35, 73), wherein a movement of the second floating piston (9) in the cylinder bore (5) along the actuation direction (13) of the cylinder (1) is delimited towards the first floating piston (7) by a second end stop arrangement (37, 75), wherein a movement of the central piston (11) in the cylinder bore (5) along the actuation direction (13) of the cylinder (1) is delimited by the first and the second floating piston (7, 9), characterized in that each floating piston (7, 9) comprises a first section (47, 49) and a second section (51, 53), wherein a circumferential length of the first floating piston (7) in a plane extending perpendicular to the actuation direction (13) of the cylinder (1) is greater in the first section (47) than in the second section (51) and a circumferential length of the second floating piston (9) in a plane extending perpendicular to the actuation direction (13) of the cylinder (1) is greater in the first section (49) than in the second section (53), wherein in the first section (47, 49) of each floating piston (7, 9) a first seal (55) is arranged for a sealing engagement with an inner wall (36, 71, 77) of the cylinder bore (5) and wherein in the second section (51, 53) of each floating piston (7, 9) a second seal (57) is arranged for a sealing engagement with the inner wall (36, 71, 77) of the cylinder bore (5) or an inner wall (59) of the central piston.

2. Cylinder (1) according to claim 1, wherein the movement of the first floating piston (7) in the cylinder (1) bore (5) along the actuation direction (13) of the cylinder (1) and away from the second floating piston (9) is delimited by the first cylinder cap (15) and wherein the movement of the second floating piston (9) in the cylinder (1) bore (5) along the actuation direction (13) of the cylinder (1) and away from the first floating piston (7) is delimited by the second cylinder cap (17).

3. Cylinder (1) according to claim 2, wherein the first end stop arrangement (73) is attached to the first cylinder cap (15) and the second end stop arrangement (75) is attached to the second cylinder cap (17).

4. Cylinder (1) according to claim 3, wherein a cross section of the cylinder bore (5) in a plane extending perpendicular to the actuation direction (13) is constant between the first cylinder cap (15) and the second cylinder cap (17).

5. Cylinder (1) according to claim 3 or 4, wherein each cylinder cap (15, 17) comprises a guiding section (21, 23) which extends from the respective cylinder cap (15, 17) towards the central piston (11) and which is spaced from an inner wall (36, 71, 77) of the cylinder (1) bore (5) wherein the first end stop arrangement (73) is formed by a protrusion (73) arranged at the guiding section (21) of the first cylinder cap (15) and the second end stop (75) is formed by a protrusion (75) arranged at the guiding section (23) of the second cylinder cap (17).

6. Cylinder (1) according to claim 1 or 2, wherein the cylinder bore (5) comprises a first section (29), a second section (31) and a central section (33), wherein an inner circumferential length of the cylinder bore (5) in a plane extending perpendicular to the actuation direction (13) in the first and the second section (29, 31) is greater than a circumferential length of the cylinder bore (5) in a plane extending perpendicular to the actuation direction (13) in the central section (33), and wherein a transition from the first section (29) to the central section (33) forms the first end stop arrangement (35) and a transition from the second section (31) to the central section (33) forms the second end stop arrangement (37).

7. Cylinder (1) according to claim 6, wherein the first seal (55) of the first floating piston (7) is arranged for a sealing engagement with the inner wall (36, 71) of the cylinder bore (5) in the first section (29) and the first seal (55) of the second floating piston (9) is arranged for a sealing engagement with the inner wall (36, 71) of the cylinder bore (5) in the second section (31).

8. Cylinder (1) according any of claims 1 to 6, wherein the central piston (11) comprises a first flange (39) and a second flange (41), wherein the first flange (39) extends from the central piston (11) towards the first cylinder cap (15), is at least partially arranged between the inner wall (36, 71) of the cylinder bore (5) and the second section (51) of the first floating piston (7) and forms the inner wall (59) for sealing engagement with the second seal (57) of the first floating piston (7) and wherein the second flange (41) extends from the central piston (11) towards the second cylinder cap (17), is at least partially arranged between the inner wall (36, 71) of the cylinder bore (5) and the second section (53) of the second floating piston (9) and forms the inner wall (59) for sealing engagement with the second seal (57) of the second floating piston (9).

9. Cylinder (1) according to claim 8, wherein an outer wall (60) of the first flange (39) and an outer wall (60) of the second flange (41) form a continuous surface of the central piston (11) towards the inner wall (36, 71) of the cylinder bore (5).

10. Cylinder (1) according to any of the preceding claims, wherein the central piston (11) comprises a permanent magnet (67) and wherein a position of the permanent magnet (67) along the actuation direction (13) is detectable through the cylinder (1) housing for determining a position of the central piston (11) along the actuation direction (13).

11. Cylinder (1) according to claim 10 comprising a sensor (69) for detecting the position of the permanent magnet (67).

12. Cylinder (1) according to any of the preceding claims comprising a piston rod (25) attached to the central piston (11).

Description

[0027] In the following exemplary embodiments of the present invention will be described with reference to the drawings, wherein

[0028] FIG. 1 shows a first exemplary embodiment of a double-acting cylinder with a central piston in a first stable position,

[0029] FIG. 2 shows the exemplary embodiment of FIG. 1 with a central piston in a central stable position,

[0030] FIG. 3 shows the exemplary embodiment of FIGS. 1 and 2 with a central piston in a second stable position,

[0031] FIG. 4 shows a second exemplary embodiment of a double-acting cylinder with a central piston in a first stable position,

[0032] FIG. 5 shows the exemplary embodiment of FIG. 4 with a central piston in a central stable position,

[0033] FIG. 6 shows the exemplary embodiment of FIGS. 4 and 5 with a central piston in a second stable position,

[0034] FIG. 7 shows a third exemplary embodiment of a double-acting cylinder with a central piston in a first stable position,

[0035] FIG. 8 shows the exemplary embodiment of FIG. 7 with a central piston in a central stable position and

[0036] FIG. 9 shows the exemplary embodiment of FIGS. 7 and 8 with a central piston in a second stable position,

[0037] Throughout the Figures and the various embodiments shown therein like reference numerals will be used to indicate like elements.

[0038] With reference to FIGS. 1 to 3 a first exemplary embodiment of a double-acting cylinder 1 according to the present invention will be described in the following paragraphs. The double-acting cylinder 1 comprises a cylinder housing 3 forming a cylinder bore 5 in which a first floating piston 7, a second floating piston 9 and a central piston 11 are arranged. The cylinder housing 3 generally has that shape of a hollow cylinder and extends along an actuation direction 13. Thus, in a plane extending perpendicular to the actuation direction 13 a cross-sectional area of the cylinder bore 5 is generally circular. Other cross-sectional areas such as rectangular, square or oval are also conceivable. The cylinder bore 5, the floating pistons 7, 9 and the central piston numeral 11 are shaped such that only a translational movement along the actuation direction 13 of the pistons 7, 9, 11 relative to the cylinder housing 3 is possible.

[0039] The cylinder bore 5 is delimited at opposing ends by first and second cylinder caps 15, 17. The first cylinder cap 15 is arranged on the same side of the central piston 11 as the first floating piston 7 and the second cylinder cap 17 is arranged on the same side of the central piston 11 as the second floating piston 9. In other words, the first floating piston 7 is arranged between the first cylinder cap 15 and the central piston 11 and the second floating piston 9 is arranged between the central piston 11 and the second cylinder cap 17.

[0040] The cylinder caps 15, 17 have different functions. Amongst others, they delimit the overall movement of the floating pistons 7, 9 away from the central piston 11 and also prevent accidental spilling of working fluid out of the cylinder bore 5. To this end, seals 19 in form of O-rings are provided for sealing the cylinder caps 15, 17 to the cylinder housing 3. The cylinder caps 15, 17 further comprise guiding sections 21, 23 which extend from the respective cylinder cap 15, 17 towards the central piston 11 and which are provided for guiding a piston rod 25 attached to the central piston 11. To prevent loss of working fluid at the interface between the piston rod 25 and the guiding sections 21, 23 circumferential seals 27 in form of lip seals are provided at free ends of the guiding sections 21, 23 for sealing engagement with the piston rod 25.

[0041] The cylinder bore 5 comprises a first section 29, a second section 31 and a central section 33 arranged between the first section 29 and the second section 31. A cross-sectional area in a plane extending perpendicular to the actuation direction 13 is smaller in the central section 33 as in the first and second section 29, 31. In the exemplary embodiment shown in FIGS. 1 to 3 the cross-sectional area of the first and the second section 29, 31 is the same. However, it is also conceivable that their cross-sectional areas differ.

[0042] At the transition from the first section 29 to the central section 33 of the cylinder bore 5 a step or edge 35 is formed by an inner wall 36 of the cylinder housing 3. The step 35 serves as a first end stop arrangement 35 limiting a movement of the first floating piston 7 towards the second floating piston 9. A second end stop arrangement 37 is formed by an edge or step 37 in the inner wall 36 of the cylinder housing 3 at the corresponding transition from the second section 31 of the cylinder bore 5 to the central section 33. The second end stop arrangement 37 delimits a movement of the second floating piston 9 towards the first floating piston 7.

[0043] The central piston 11 has a double cup-shape wherein openings of the cups face away from each other and towards the cylinder caps 15, 17. In other words, the central piston 11 comprises first and second flanges 39, 41 extending from a core 43 of the central piston 11 towards the first cylinder cap 15 and second cylinder cap 17, respectively. The piston rod 25 is rigidly connected to the core 43 of the central piston 11 by means of a pin or bolt 45. Seals provided between the core 43 of the central piston 11 and the piston rod 25 make sure that no working fluid can flow past the central piston 11, i.e., from one side of the cylinder bore 5 to the other.

[0044] Both floating pistons 7, 9 comprise a first section 47, 49 and a second section 51, 53. A circumferential length of an outer surface of the first floating piston 7 in the first section 47 is greater than a circumferential length of the first floating piston 7 in the second section 51. As a cross-section of the floating piston 7 in a plane extending perpendicular to the actuation direction 13 is circular this corresponds to stating that a diameter or cross-sectional area of the first floating piston 7 in the first section 47 is greater than a diameter or cross-sectional area of first floating piston 7 in the second section 51. Likewise, a circumferential length of an outer surface of the second floating piston 9 in the second section 51 is smaller than a circumferential length of an outer surface of the second floating piston 9 in the first section 49. Both floating pistons 7, 9 are provided with first and second seals 55, 57. The first seals 55 are mounted as O-rings at the respective first sections 47, 49 and provided for sealing engagement with the inner wall 36 of the cylinder housing 3. Other O-rings are mounted as corresponding second seals 57 to the second sections 51, 53 of the floating pistons 7, 9. The second seals 57 seal the floating pistons 7, 9 towards an inner wall 59 of the central piston numeral 11 and, to be more precise, the inner wall or surface 59 of the first and second flanges 39, 41. In the embodiments shown in FIGS. 1 to 6 the flanges 39, 41 and the core 43 of the central piston 11 provide an even outer surface 60 towards the inner wall 36 of the cylinder bore 5. As the central piston 11 is guided by the floating pistons 7, 9 it has good clearance to the cylinder wall 36 of the cylinder housing 3.

[0045] Hence, the floating pistons 7, 9 form together with the first and second seals 55, 57 and the flanges 39, 41 of the central piston 11 cavities 61 which remain permanently free of working fluid that is used to operate the double-acting cylinder 1. The cavities 61 are connected to the environment of the double-acting cylinder 1 by means of venting holes or openings which are not shown in FIGS. 1 to 3. Through the venting holes air can freely flow into and out of the cavities 61 from the environment. The cavities 61 are, therefore, also referred to as vented cavities 61.

[0046] The double-acting cylinder 1 can be operated by ingesting a pressurized fluid or working fluid through control openings 63, 65 in the cylinder housing 3 into the cylinder bore 5. A first control opening 63 is provided for ingesting a hydraulic or working fluid into the part of the cylinder bore 5 in which the first floating piston 7 is arranged. For providing working fluid to the other part of the cylinder bore 5 in which the second floating piston 9 is arranged, a second control opening 65 has been drilled.

[0047] In FIG. 1 the central piston 11 is shown in a first position in which the first floating piston 7 and the central piston 11 are arranged as close as possible to the first cylinder cap 15. The second floating piston 9 also has been moved as closely as possible towards the first cylinder cap 15 and is in engagement with the second end stop arrangement 37. In order to keep the central piston numeral 11 stable in the first position as shown in FIG. 1 pressurized working fluid is ingested through the second control opening 65. The working fluid acts on the second floating piston 9 and the central piston 11.

[0048] For moving the central piston 11 along with the piston rod 25 from the first (stable) position to the central (stable) position as shown in FIG. 2, pressurized working fluid is ingested through the first control opening 63. If the pressure of the working fluid is at least the same as the pressure of the working fluid provided through the second control opening 65, the central piston 11 will move to the central position due to the larger combined effective surface area of the central piston 11 and first floating piston 7 towards the first cylinder cap 15 compared to the effective surface area of the central piston 11 towards the second cylinder cap 17. The effective surface area of a piston 7, 9, 11 is defined as the surface area of the piston 7, 9, 11 projected on a plane extending perpendicular to the actuating direction 17. Effective outer surface areas of the first and second floating piston 7, 9 face towards the first and second cylinder cap 15, 17, respectively. Effective inner surface areas are those surface areas of the first and second floating piston 7, 9 facing towards the central piston 11. An effective first surface area of the central piston 11 faces towards the first cylinder cap 15 and an effective second surface area of the central piston 11 faces towards the second cylinder cap 17.

[0049] When the central piston 11 has reached the central position, the first floating piston 7 engages with the first end stop arrangement 35 which prevents a further movement of the first floating piston 7 towards the second cylinder cap 17. Hence, the effective surface area available for the working fluid to act on is the same on either side of the central piston 11. Hence, the central position is stable. As soon as the central piston 11 only moves the slightest bit out of the central position, it engages with one of the floating pistons 7, 9. For example, if the central piston 11 moves towards the second floating piston 9 and engages with the second floating piston 9, the effective surface area pushing the central piston 11 towards the first cylinder cap 15 is the combination of the effective outer surface area of the second floating piston 9 and the effective second surface area of the central piston 11. This effective surface area is considerably larger than the effective first surface area of the central piston 11 which remains for pushing the central piston 11 towards the second cylinder cap 17. Thus, the central piston 11 is immediately pushed back to the central position.

[0050] Finally, for moving the central piston 11 from the central position to a second (stable) position as close to the second cylinder cap 17 as possible, the pressure of the working fluid ingested through the second control opening 65 has to be reduced or preferably completely taken away.

[0051] The exemplary embodiment of a double-acting cylinder 1 shown in FIGS. 1 to 3 has the advantage that due to the two-section design of the floating pistons 7, 9 the effective outer surface area is considerably larger than the effective inner surface area. Thereby, it is ensured that if a working fluid is ingested into the cylinder bore 5 through the first or the second control opening 63, 65 the resulting force acting onto the respective floating piston 7, 9 is always directed towards the central piston 11. Furthermore, as the second seals 57 engage with an inner wall 59 of the central piston 11 and not with an inner wall 36 of the cylinder housing 3, the inner wall 36 of the cylinder housing 3 does not need to be machined as carefully in the central section 33 which reduces the manufacturing cost.

[0052] In addition, the double-acting cylinder 1 comprises an arrangement for sensing a position of the central piston 11. To this end a permanent magnet 67 is arranged in the central piston 11. The cylinder housing 3 comprises a sensor 69 which can be used to sense the position of the permanent magnet 67 and, thereby, the position of the central piston 11.

[0053] A second embodiment of a double-acting cylinder 1 is shown in FIGS. 4 to 6. For the sake of brevity only differences between the first embodiment shown in FIGS. 1 to 3 and the second embodiment will be discussed here. Further, to keep the Figures simple only those reference numerals will be repeated for FIGS. 4 to 9 that are essential for understanding the differences between the different embodiments.

[0054] The double-acting cylinder 1 shown in FIGS. 4 to 6 comprises a cylinder bore 5 with a smooth inner wall 71. In other words, a diameter or cross-section of the cylinder bore 5 is a constant over the entire length of the cylinder bore 5 from the first cylinder cap 15 to the second cylinder cap 17. Hence, the end stop arrangements 73, 75 are not formed by steps in the inner wall of the cylinder housing 3 but are instead provided at a free ends of the guiding sections 21, 23 of the cylinder caps 15, 17. In the embodiment of FIGS. 4 to 6 the end stop arrangements 73, 75 are provided in the form of ring-shaped protrusions which extend radially from the guiding sections 21, 23 towards the cylinder housing 3. This embodiment has the additional advantage that the cylinder housing 3 has a smooth inner wall 71 and does not need to provide sections of different diameter and the outer wall 60 of the central piston 11 has a smooth or continuous surface towards the inner wall 71 of the cylinder housing 3. This does not only make manufacturing of the cylinder housing 3 easier, it also reduces the overall dimensions and the weight of the double-acting cylinder 1 as the thickness of the cylinder housing 3 or cylinder wall can be reduced as compared to the example shown in FIGS. 1 to 3.

[0055] Finally, a third embodiment is shown in FIGS. 7 to 9. As before, only the differences compared to the first embodiment shown in FIGS. 1 to 3 will be described.

[0056] In this embodiment the central piston 11 is not double cup-shaped but comprises only a core 43 without any flanges. Thus, the second seals 57 of the first and second floating pistons 7, 9 directly engage with an inner wall 77 of the cylinder housing 3 in the central section 33 of the cylinder bore 5. In this embodiment venting openings 79 for supplying air to the venting cavities 61 are shown.

[0057] The third embodiment shares the advantages of the first and second embodiment related to the different size of the effective inner and outer surface areas of the floating pistons.