Cylinder / piston assembly with eccentric piston rod

Abstract

In a cylinder / piston assembly consisting of a hydraulic cylinder and a longitudinally movable piston, sealed inside the hydraulic cylinder and bearing a piston rod on at least one side, the hydraulic cylinder has a cylinder tube with a circular cross-section closed at both ends by an end piece, and the piston rod extends along an axis eccentric to the cylinder tube, with a cylindrical element fixed to both end pieces and extending via the piston along a second axis eccentric to the cylinder tube and parallel to the first axis.

Description

[0001] Cylinder / piston assembly with a hydraulic cylinder and a longitudinally displaceable piston sealed within the hydraulic cylinder, which carries a piston rod at least on one side, wherein the hydraulic cylinder has a cylinder tube with a circular cross-section, which is closed at both ends by an end piece, and the piston rod runs along an axis eccentric with respect to the cylinder tube.

[0002] A differential cylinder with an eccentric piston rod is known, for example, from CN 1053954 A. The eccentric arrangement of the piston rod is intended to prevent rotation. However, when an external torque is applied, lateral forces act on the piston rod's bearings on the guide pieces, which can lead to wear of the seals and leaks.

[0003] A cylinder / piston assembly according to the preamble of claim 1 is known from US 4,719,847 A.

[0004] One object of the invention is to provide a cylinder / piston assembly with improved anti-rotation protection.

[0005] Furthermore, with hydraulic cylinders there is often a desire for a displacement measuring system that can determine the position of the piston.

[0006] Internal displacement measuring systems, located within a centrally located, hollow piston rod, are well-known on the market. The space required for this design necessitates a larger diameter for both the piston rod and the cylinder, which in turn results in higher forces within the system. Furthermore, with a centrally located piston rod and displacement measuring system, any rotation of the piston rod would transmit the maximum torque into the inner tube containing the measuring system. External displacement measuring systems, on the other hand, are mechanically complex, sensitive to environmental influences, and their accuracy is dependent on external forces, as any bending of the piston rod can introduce errors into the measurement.

[0007] The problem is solved by the features of claim 1. Advantageous embodiments can be found in the dependent claims.

[0008] In a cylinder / piston assembly of the type mentioned above, a cylindrical element is provided, anchored at both ends and extending through the piston along a second axis that is eccentric to the cylinder tube and parallel to the first axis. This cylindrical element is designed as a tube. By anchoring the cylindrical element at the ends and by providing a sliding, displacement-tight bearing for the cylindrical element in a corresponding bore of the piston, torque support for the piston against the hydraulic cylinder is achieved.

[0009] According to the invention, the arrangement with a tubular cylindrical element offers the possibility of integrating an internal displacement measuring device, the accuracy of which is also independent of external forces. The displacement measuring device can preferably be designed as a magnetostrictive or Hall sensor-based displacement measuring system, although the invention is not limited to this.

[0010] Particularly when the cylindrical element is tubular, it can serve additional purposes, either alternatively or cumulatively. For example, the cylindrical element can be designed as a pipe leading to a hydraulic connection at one of its two ends and featuring an opening for hydraulic fluid within the hydraulic cylinder at the opposite end. This allows the hydraulic connections of the cylinder / piston assembly to be located on the same end without external lines, which can be advantageous in installation situations with limited space.

[0011] In a preferred embodiment, the cylinder / piston assembly is designed as a synchronous cylinder in which the piston rod extends on both sides of the piston and in which the two end pieces are designed as guide pieces against which the piston rod is sealed.

[0012] In principle, pistons and piston rods can be formed as a single piece or rigidly connected. However, a further advantage arises when the piston rod is rotatably mounted on the piston, as in this case no torque is transmitted from the piston rod to the piston. This results in a more even force distribution and application between the piston and cylinder.

[0013] Advantageously, at least one of the end pieces can be connected to the cylinder tube via a flange connection, for example in the form of a locking ring engaging a collar. This takes into account the fact that, due to the cylindrical element anchored in both end pieces, the end pieces cannot be rotated independently of each other or against each other.

[0014] The other end piece, however, can be screwed onto or into the cylinder tube in the conventional manner via a threaded connection. During assembly, the screwed-on or screwed-in end piece can be mounted first, then the piston and the cylindrical element inserted, and finally the open end of the cylinder tube closed with the end piece attached via a flange connection.

[0015] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the figures. These show: Figure 1 shows a first, non-inventive example of a cylinder / piston assembly designed as a synchronous cylinder with an eccentric piston rod and a rod running parallel to the piston rod as a torque support; Figure 2 shows a second, non-inventive example of a cylinder / piston assembly with an eccentric piston rod and a hydraulic oil pipeline running parallel to the piston rod; Figure 3 shows a third, inventive embodiment of a cylinder / piston assembly with an eccentric piston rod and a displacement measuring system arranged in a tube running parallel to the piston rod; Figure 4 shows a fourth embodiment of a cylinder / piston assembly with an eccentric piston rod, in which a tube running parallel to the piston rod serves both as an oil line and for receiving a displacement measuring system; Figure 5 shows a non-inventive example corresponding to the one shown in Figure 1shown with an additionally rotatable piston rod mounted in the piston, Figure 6 is a non-inventive example corresponding to the one in Figure 2 shown with an additionally rotatable piston rod mounted in the piston, Figure 7 is an embodiment corresponding to the one in Figure 3 shown with an additionally rotatable piston rod mounted in the piston and Figure 8 an embodiment corresponding to the one in Figure 4 shown with an additionally rotatable piston rod mounted in the piston.

[0016] The in Figure 1The cylinder / piston assembly 1 shown, which is not according to the invention, comprises a hydraulic cylinder 2 with a cylinder tube 3, which is closed at both ends by an end piece 4, 5. Inside the hydraulic cylinder 2 is a longitudinally movable piston 6, which is mounted in a sealing and sliding manner against the inner cylinder wall by means of corresponding piston seals (not shown) of a known design. A piston rod 7 extends on both sides of the piston 6, so that the cylinder / piston assembly 1 acts as a synchronous cylinder. Accordingly, the two end pieces 4, 5 are designed as guide pieces and each has a through-bore 8, 9 for the piston rod 7, which is provided with a rod seal (not shown) of a known design.

[0017] The essential point here is that the piston rod 7 and the two through bores 8, 9 for the piston rod 7 in the guide pieces 4, 5 are arranged along an axis 14 that is eccentric with respect to the cylinder tube 3 or its central axis.

[0018] By arranging the piston rod 7 offset within the existing circular cross-section of the cylinder tube 3, a second bore 10 can be provided in the piston 6 in the region of eccentricity, which is closed with a cylindrical element 11. In the first embodiment, the cylindrical element is a rod 11 that extends through the piston 6 along a second axis 15 that is eccentric with respect to the cylinder tube 3 and parallel to the first axis 14. The rod 11 is inserted into blind bores 12, 13 arranged along the second axis 15 on the inner surfaces of the guide pieces 4, 5 and is thus rotationally fixed against rotation of the piston 6 in the cylinder tube 3. The rod 11 is sealed in the corresponding bore 10 in the piston 6 with a conventional rod seal (not shown), so that the piston 6 is slidable longitudinally along the rod 11.The rod 11 thus serves as an anti-rotation device and torque support for the piston 6.

[0019] The two cylinder chambers separated by the piston 6 can be supplied with hydraulic oil via lateral bores 17, 18 in the cylinder tube 3, which serve as hydraulic connections P1, P2 and for this purpose may be provided with a threaded connection (not shown) to move the piston 6 within the cylinder tube.

[0020] A further improvement regarding the force transmission via the piston rod 7 is achieved by mounting the piston rod 7 rigidly relative to the piston 6 in the displacement direction but freely rotatable in the rotation direction via a rotary bearing 16. This is shown in Figure 5The rotatable bearing of the piston rod relative to the piston 6 improves the decoupling of a torque introduced from the outside via the piston rod 7 to the components of the hydraulic cylinder 2, such as cylinder tube 3, piston 6, guide bands and piston seal.

[0021] In Figure 2Instead of a rod, a cylindrical element, a tube 11', is inserted into the hydraulic cylinder 2, running along the axis 15 through the bore 10 in the piston 6. The tube 11' also provides torque support but can additionally serve as an oil line for hydraulic oil to the left cylinder chamber, which is closed off by the guide piece 5. For this purpose, the bore 12' in the guide piece 4 is designed as a through-hole instead of a blind hole, with its outwardly facing opening 19 serving as a hydraulic connection P1 and, for this purpose, may be provided with a threaded connection (not shown). In the area just before the tube 11' ends in the blind hole 13 of the guide piece 5, a transverse bore 20 is provided in the tube 11', through which hydraulic oil can flow via the connection P1 and the tube 11' to and from the cylinder chamber on the left in the drawing. The second hydraulic connection P2 of the hydraulic cylinder 2 is as shown in Figure 1formed by a lateral bore 18 in the cylinder wall.

[0022] A further development in which the piston rod 7 is rotatably mounted relative to the piston 6 via a rotary bearing 16 is described in Figure 6 shown as an example.

[0023] At the in Figure 3In the illustrated embodiment of the invention, the pipe 11' does not serve as an oil line, but instead houses a displacement measuring device 21. The displacement measuring device 21 is a magnetostrictive displacement sensor that determines the position of a permanent magnet 22 arranged around the bore 10 in the piston 6. Such magnetostrictive displacement sensors are known per se. A sensor rod 23 is designed as a soft magnetic waveguide. A short current pulse is passed through an inner wire in the sensor rod 23, generating a circular magnetic field that is focused within the waveguide due to its soft magnetic properties. At the position of the permanent magnet 22, which serves as the position sensor, a magnetic field is present whose field lines run perpendicular to the pulse magnetic field and are also focused within the waveguide.In the region of the waveguide where the two magnetic fields overlap, an elastic deformation occurs due to magnetostriction, generating a mechanical wave which can then be converted into an electrical signal by a signal converter. The distance to the position sensor can be determined from the propagation time of the response signal, i.e., the time between sending the current pulse and receiving the magnetostrictive echo.

[0024] In addition to a magnetostrictive measuring system, other measuring methods can also be used within the scope of the invention. For example, an arrangement of Hall sensors can be used to detect a magnetic position sensor arranged on the piston. Acoustic or optical displacement measuring methods can also be used, for example, by dragging a position sensor inside the tube 11' using a permanent magnet arranged on the piston, at which a signal can be reflected and measured as a response signal.

[0025] The eccentric arrangement of a displacement measuring system in the support tube 11', which is separate from the piston rod 7, means that the piston rod and thus also the cylinder tube can be designed with a smaller diameter while maintaining the same force requirements.

[0026] A further development of the embodiment according to the invention, in which the piston rod 7 is again rotatably mounted relative to the piston 6 via a rotary bearing 16, is described in Figure 7 shown as an example.

[0027] In the Figure 4 In the fourth embodiment shown, the pipe 11' serves both as an oil line to the remote cylinder chamber and as a means of receiving a displacement measuring system 21. Since the opening of the bore 12 is occupied by the displacement measuring system 21 and its signal transducer, the hydraulic connection P1 to the pipe 11' is formed by a radially extending bore 19' in the guide piece 4, with which the pipe 11' is laterally drilled.

[0028] A further development of the fourth embodiment, in which the piston rod 7 is again rotatably mounted relative to the piston 6 via a rotary bearing 16, is described in Figure 8 shown as an example.

Claims

1. A cylinder / piston assembly comprising a hydraulic cylinder (2) having a piston (6) which is sealingly mounted and longitudinally movable within the hydraulic cylinder (2) and which, at least on one side, bears a piston rod (7), wherein the hydraulic cylinder (2) has a cylinder barrel (3) of circular cross section which is closed on both sides by in each case one end piece (4, 5), and the piston rod (7) extends along a first axis (14) that is eccentric with respect to the cylinder barrel (3), and having a cylindrical element (11, 11') which is anchored on the two end pieces (4, 5) and which extends through the piston (6) along a second axis (15) which is eccentric with respect to the cylinder barrel (3) and parallel to the first axis (14), wherein the cylindrical element (11') is tubular and characterized in that a position measuring apparatus (21) is arranged within the cylindrical element (11').

2. The cylinder / piston assembly according to claim 1, which is designed as a synchronous cylinder, wherein the piston rod (7) extends on both sides of the piston (6), and the two end pieces (4, 5) are designed as guide pieces, at each of which the piston rod (7) is sealed.

3. The cylinder / piston assembly according to any of the preceding claims, wherein the piston rod (7) is mounted rotatably on the piston by means of a rotary bearing (16).

4. The cylinder / piston assembly according to any of the preceding claims, wherein the cylindrical element (11, 11') serves as a torque support for the piston (6) with respect to the hydraulic cylinder (2).

5. The cylinder / piston assembly according to any of the preceding claims, wherein the cylindrical element (11') is designed as a pipeline which, at one of the two end pieces (4), leads to a hydraulic connection (19, 19', P1) and, within the hydraulic cylinder (2) in the region of the opposite end piece (5), has an opening (20) for hydraulic medium.

6. The cylinder / piston assembly according to any of the preceding claims, wherein the position measuring apparatus (21) is designed as a magnetostrictive position measuring system or a position measuring system based on Hall sensors.

7. The cylinder / piston assembly according to any of the preceding claims, wherein at least one of the end pieces (4, 5) is connected to the cylinder barrel (3) by a flange connection.

8. The cylinder / piston assembly according to claim 7, wherein the other end piece (4, 5) is screwed onto or into the cylinder barrel (2) by a threaded connection.