WO2014206873A1

WO2014206873A1 - Hydraulic cylinder having a piston rod

Info

Publication number: WO2014206873A1
Application number: PCT/EP2014/063003
Authority: WO
Inventors: Oliver GERHARD
Original assignee: Robert Bosch Gmbh
Priority date: 2013-06-26
Filing date: 2014-06-20
Publication date: 2014-12-31
Also published as: DE102013212224A1; EP3014129B1; EP3014129A1

Abstract

A hydraulic cylinder having a piston rod is disclosed, said piston rod being surrounded by an annular pressure chamber and being guided in a through-aperture in the hydraulic cylinder. A split bushing forms a split seal with the piston rod over a particular axial length and in a precise fit with the piston rod. A first circular-cylindrical annular gap is formed on the outer circumference of the split bushing, with the result that the split bushing is inserted into the hydraulic cylinder with radial play. The annular gap is fluidically connected to the pressure chamber. A seal is arranged on the outer circumference of the split bushing and is at an axial distance from a first end side, facing the pressure chamber, of the split bushing. As a result, the working pressure of the pressure chamber can apply counter-pressures that are directed radially inwards to the split bushing, over a section of the outer circumference that extends from the pressure chamber to the seal, said counter-pressures counteracting the forces that are directed radially outwards and arise in the split seal. Thus, the split bushing is relieved of mechanical loads.

Description

Hydraulic cylinder with piston rod

description

The invention relates to the guidance and support of a piston rod in a hydraulic cylinder and the sealing of a piston rod surrounding the annular pressure chamber of the hydraulic cylinder.

Hydraulic cylinders with a tubular cylinder housing in which a piston is moved, on which at least one side a piston rod is fastened, with a cylinder base and with a cylinder head, through which the piston rod passes outward, are known from the prior art. It is - viewed radially - between the cylinder housing and the piston rod and - viewed axially - between the piston and the end face an annular pressure chamber arranged.

During operation of the hydraulic cylinder, the piston and the piston rod move in translation, wherein the piston rod must be guided and stored in the cylinder head of the cylinder, in particular when transverse forces act on the piston rod. In addition, a seal is required between the piston rod and the cylinder head to seal the pressure chamber under working pressure against the environment. In the document EP 1 1 10 017 B1 such a hydraulic cylinder is shown with a cylinder head, wherein the cylinder head is penetrated by the piston rod. To seal the annular pressure chamber designated as a dimensionally stable sealing ring gap bushing, which forms a gap seal with the piston rod, game used in a special guide bushing. The gap bushing has a certain axial extent and a precisely manufactured fit with the piston rod to fulfill the sealing function. To seal the gap between the split sleeve and the guide bush, which results from the game, a further seal is provided, which is inserted into an end face of the split sleeve and rests against a radial step of the guide bush. As the pressure in the annular pressure chamber increases, there is an increasing radial load on the gap sleeve to the outside. In order to avoid a corresponding widening of the gap bushing and thus an enlargement of the precisely manufactured fit, the gap bushing must be very dimensionally stable. This can only be achieved by materials with a high modulus of elasticity or by a large radial extent or thickness of the gap bushing.

In contrast, the invention is based on the object to provide a hydraulic cylinder with piston rod, the annular pressure chamber is sealed with a split sleeve, the device complexity is minimized. It is intended to create a sealing system that brings only a slight and pressure-independent friction between the piston rod and the leading and supporting components with it.

This object is achieved by a hydraulic cylinder having the features of patent claim 1.

The claimed hydraulic cylinder has a piston rod which is surrounded by an annular pressure chamber and which is guided in a through-passage of the hydraulic cylinder. A split sleeve forms a gap seal with the piston rod through a precise fit with the piston rod over a certain axial length. As a result, the functions storage of the piston rod and pressure reduction of the chamber pressure in the gap seal structurally separated. The gap bushing is inserted with radial play into the hydraulic cylinder, in particular into the cylinder housing, so that a first circular-cylindrical annular gap is formed on the outer circumference of the gap bushing, which fluidly connects to the pressure chamber. According to the invention, a seal is arranged on the outer circumference of the gap bushing, which has an axial distance to a first end face of the gap bushing facing the pressure chamber. As a result, the working pressure of the pressure chamber at a extending from the pressure chamber to the seal extending portion of the outer circumference radially inwardly generate opposing forces on the split sleeve, which generated in the gap seal between the piston rod and the split sleeve by the local pressure on the split sleeve and radially Counteract outward forces. Thus, the gap bushing is mechanically relieved and can be performed relatively easily. Preferably, the split sleeve is circular cylindrical. Preferably, the seal is inserted into an outer circumferential groove of the gap bushing. Further advantageous embodiments of the invention are described in the dependent claims. In a particularly preferred embodiment, the axial distance of the seal from the end face is selected such that the gap bush is pressure-compensated in the radial direction. Then in the sum no radial forces on the gap bush, so that mechanically optimally relieved. The position of the seal is chosen depending on various parameters of the gap bushing, for example, depending on the width, thickness and modulus of elasticity.

Preferably, a second annular gap is formed between the piston rod and the through-hole whose radial dimension is smaller than the radial dimension of the first annular gap. As a result, the piston rod is accommodated with play in the through-hole. It may have by transverse forces corresponding deviations from the concentric position and be supported on the through hole. It remains on the outer circumference of the gap sleeve always a remainder of the first annular gap, which is connected to the pressure chamber, so that radially no contact between the gap bushing and the part can occur, in which the gap bushing is used. Usually, the split sleeve is inserted into the cylinder housing. In particular, the pressure force compensation of the gap bushing is always maintained at an axial distance of the seal from the end face.

In particular, the gasket can accommodate different width annular gaps if it has an outer seal (e.g., piston seal) and an inner O-ring. The latter is compressed in its cross section and thus biases the sealing ring outwards against the hydraulic cylinder. This results in the seal a "task sharing" between the sealing function and the elastic application of force radially outward.

If the hydraulic cylinder has a cylinder head which is fastened to an, for example, tubular cylinder housing of the hydraulic cylinder and in which the passage recess for the piston rod is formed, it is particularly preferred if the gap bushing bears against the cylinder head with a second end face. The second end face may be ground or provided with a coating, for example made of plastic, around the To keep friction between the split sleeve and the cylinder head low and to ensure a slight radial displacement of the split sleeve.

In this case, the gap bushing can be accommodated in a device-like manner simply between the cylinder head and a radial projection or a radial step on the inside of the cylinder housing.

The first end of the gap bushing may limit the annular pressure chamber. A working port of the pressure chamber should open adjacent to the radial projection or the radial step in the pressure chamber, so that the piston can approach the projection or the stage maximum and the working range of the hydraulic cylinder according to the invention is maximized. As an alternative to the direct mounting of the piston rod in the passage recess of the cylinder head, a separate sliding bearing for the piston rod may be provided in the through-hole.

In the following an embodiment of a hydraulic cylinder according to the invention with piston rod is described in detail with reference to FIGS.

Show it

Figure 1 shows a detail of the embodiment in a longitudinal section and

FIG. 2 shows a section of FIG. 1.

1 shows a section of a tubular cylinder housing 1 of the hydraulic cylinder according to the invention. The front side of the cylinder housing 1, a cylinder head 2 is fixed, the radial collar 4 protrudes into the cylinder housing 1 such that the two parts 1 and 2 are centered.

Inside the cylinder housing 1, an annular pressure chamber 6 is provided, which - viewed radially - is limited by the cylinder housing 1 and a piston rod 8, while - viewed axially - is limited by a split sleeve 10 and a piston (not shown). When loading the pressure chamber 6 via a working port 12th with pressure medium, the piston moves (in Figure 1) to the right, taking with it the attached piston rod 8 with. The piston rod retracts. Seen from the cylinder head 2, beyond the piston, there is a second pressure chamber (not shown). When this pressure medium is supplied, the piston rod extends.

The piston rod 8 penetrates a through-passage 14 of the cylinder head 2, wherein between the piston rod 8 and the through-hole 14 some play is provided. Thus, the piston rod 8 can move within narrow limits in an eccentric position relative to a longitudinal axis 16 of the hydraulic cylinder. Since the cylinder head 2 is made of a material with good sliding properties, for example of a nodular cast iron, the guide and a bearing 18 of the piston rod are formed directly in the through-hole 14. In the bearing 18, a spiral groove is introduced over the circumference of the through hole, which opens into a visible from Figure 1, but unspecified leakage connection to the cylinder head 2. Due to the leakage oil flowing through the spiral groove, the bearing is rinsed and thereby also cooled. With respect to the pressure chamber 6 outside, a pressure-relieved seal pack is further provided on the cylinder head 2, which is inserted into the cylinder head 2 and rests against the piston rod 8. More specifically, it is a rod seal 20 which bears against the piston rod 8 and which is tensioned via an O-ring in the direction of the piston rod 8. Furthermore, a voltage applied to the piston rod 8 scraper 22 is inserted into the cylinder head 2.

Even if the piston rod 8 assumes a somewhat eccentric position with respect to the longitudinal axis 16, the rod seal 20 and the wiper 22 remain in contact therewith. When the piston rod 8 assumes a somewhat eccentric position relative to the longitudinal axis 16, the gap bushing 10 is carried along by the piston rod 8. This is made possible because the radial play on an outer circumference 26 of the split bushing 10 is greater than the radial play of the piston rod 8 in the through-hole 14. FIG. 2 shows an enlarged detail of FIG. 1. The split bush 10 forms a snug fit with the piston rod 8 a gap seal 24. On the inner circumference a plurality of circumferential and axially spaced grooves are introduced in the gap bushing 10 over its entire length to ensure pressure equalization over the inner circumference. At the outer periphery 26 of the gap bushing 10 remains even at maximum positional deviation of Piston rod 8 from the longitudinal axis 16 always a certain distance from the cylinder housing 1 of the hydraulic cylinder. Since the gap bushing 10 is also accommodated with some axial play between the radial collar 4 of the cylinder head 2 and a radial step 28 of the cylinder housing 1, a gap 30 also remains between a first end face 38 of the split bush 10 and the step 28. Thus, during operation of the invention Hydraulic cylinder always under working pressure p standing pressure fluid from the pressure chamber 6 via the gap 30 in the annular gap on the outer circumference 26 of the split sleeve 10 a. This effect is limited in its axial extent by a piston seal 32, which is inserted together with an O-ring 34 in a groove on the outer circumference 26 of the split sleeve 10. The O-ring 34 biases the piston seal 32 radially outward against the cylinder housing 1 of the hydraulic cylinder according to the invention. In this case, their elasticities are designed such that the piston seal 32 remains in contact with the cylinder housing 1 even when the piston rod 8 is maximally eccentric or tilted with respect to the longitudinal axis 16 (see FIG. Thus, on the outer circumference 26 of the gap bushing 10, the working pressure p on the axial gap 36 always act on the split sleeve 10, while the working pressure p on the gap seal 24 also acts on the inner circumference of the split sleeve, but from the first end face 38 over the entire length of the split sleeve 10 decreasing to a second end 40. This results in the inner circumference of the gap bushing 10 in the ideal case linearly decreasing reduced working pressures p1.

According to the invention the seal of the split sleeve 10, which consists of the piston seal 32 and the O-ring 34, disposed on the outer circumference 26 of the split sleeve 10 at the point at which acting on the outer circumference 26 working pressure p with the working on the inner circumference working pressures p1 in compensate for their resulting forces. This point is marked with the axial distance 36, which refers to the first end face 38 of the gap bushing 10, which faces the annular channel 6.

In a linear course of the reduced pressure p1 on the inner circumference of the split bushing 10, the axial distance 36 may correspond, for example, to half the length of the split bush 10.

Notwithstanding the embodiment shown, a sliding bearing can be used in the through-hole 14 or a coating can be applied, for example, of plastic in order to guide the piston rod 8 with particularly low friction. Disclosed is a hydraulic cylinder with a piston rod which is surrounded by an annular pressure chamber, and which is guided in a through-passage of the hydraulic cylinder. A split sleeve forms a gap seal with the piston rod over a certain axial length and a precise fit with the piston rod. On the outer circumference of the gap bush, a first circular-cylindrical annular gap is formed, whereby the gap bushing is inserted with radial clearance in the hydraulic cylinder. The annular gap is fluidically connected to the pressure chamber. On the outer circumference of the gap bushing, a seal is arranged and has an axial distance to a pressure chamber facing the first end face of the gap bushing. As a result, the working pressure of the pressure chamber can apply radially inwardly directed opposing forces to the gap bush via a portion of the outer circumference extending from the pressure chamber to the seal, which counteract the radially outward forces arising in the gap seal. Thus, the gap bushing is mechanically relieved.

Claims

claims

1 . Hydraulic cylinder with a piston rod (8), which is surrounded by an annular pressure chamber (6) and which is guided in a passage recess (14), and with a gap bushing (10) which has a gap seal (24) with the piston rod (8). forms, and on its outer periphery (26) has radial clearance, whereby a first annular gap is formed, which is fluidically connected to the pressure chamber (6), wherein on the gap bushing (10) a seal is attached, characterized in that the seal on Outside circumference (26) of the gap bushing (10) is arranged and an axial distance (36) to one of the pressure chamber (6) facing the first end face (38) of the gap bushing (10).

2. Hydraulic cylinder according to claim 1, characterized in that the axial distance (36) is selected such that the gap bushing (10) is pressure-compensated in the radial direction.

3. Hydraulic cylinder according to claim 1 or 2, characterized in that between the piston rod (8) and the through-passage (14), a second annular gap is formed, whose radial dimension is smaller than the radial dimension of the first annular gap.

4. Hydraulic cylinder according to one of the preceding claims, characterized in that the seal has an outer sealing ring (32) and an inner O-ring (34).

5. Hydraulic cylinder according to one of the preceding claims with a cylinder head (2) which is fixed to a cylinder housing (1) of the hydraulic cylinder, and in which the through-hole (14) is formed, characterized in that the gap bushing (10) a second end face (40) against the cylinder head (2).

6. Hydraulic cylinder according to claim 5, characterized in that the gap bushing (10) is received between the cylinder head (2) and a radial step (28) or a radial projection of the inside of the hydraulic cylinder.

7. Hydraulic cylinder according to one of the preceding claims, characterized in that the first end face (38) of the gap bushing (10) delimits the pressure chamber (6).

8. Hydraulic cylinder according to claim 6 or 7 with a working connection (12) of

Pressure chamber (6) characterized in that the working port (12) adjacent to the step (28) or to the projection in the pressure chamber (6) opens.

9. hydraulic cylinder according to one of the preceding claims characterized in that in the through-hole (14) a sliding bearing (18) or a coating for guiding the piston rod (8) is provided.