WO2010108596A1

WO2010108596A1 - System for sealing a piston guided in a cylinder bore

Info

Publication number: WO2010108596A1
Application number: PCT/EP2010/001513
Authority: WO
Inventors: Bernhard Evermann
Original assignee: Robert Bosch Gmbh
Priority date: 2009-03-26
Filing date: 2010-03-11
Publication date: 2010-09-30
Also published as: DE102009014996A1

Abstract

The invention relates to a system for sealing a piston (2) guided in a cylinder bore, having a piston (2) and a piston ring (9). The piston ring (9) is inserted in a recess (15) made in an outer circumference of the piston (2) for axially retaining the ring. The piston ring (9) comprises a closed, annular locking segment (11, 12). In the region of the outer circumference thereof, a sealing segment (13) extends in the axial direction.

Description

System for sealing a piston guided in a cylinder bore

The invention relates to a system for sealing a guided in a cylinder bore piston.

In many machines, hydrostatic piston machines are used to actuate movable elements. However, hydrostatic drives are also frequently used in traction drives, since such infinitely variable transmissions are easy to implement. The pressures occurring are significant. Even small leakage gaps therefore lead to large efficiency losses.

It is therefore known to improve the efficiency, the pistons, which are longitudinally displaceable, for example, in a hydrostatic axial piston machine in cylinder bores of a cylinder drum to seal by means of piston rings. A correspondingly formed piston is known from DE 10 2004 061 863 A1. To mount the piston rings, the slotted piston rings are slightly widened in order to use them in a groove of the piston can. The piston rings are slightly resilient and attach to the wall of the cylinder bore after insertion into the cylinder bore. Depends on the

Manufacturing accuracy, the temperature and pressure conditions occurring while the slot of the piston ring is more or less wide open. In order to minimize the leakage due to the high pressures that occur through the slot, a second piston ring is generally provided, as is the case in DE 10 2004 061 863 A1. Its slot is usually offset from the position of the slot of the other piston ring. Therefore, there is a kind of labyrinth seal, which, however, brings a considerable manufacturing effort. A disadvantage is the one that two independently formed grooves must be arranged on the outer circumference of the piston. In addition, two piston rings are provided, which usually also have different profiles to improve the effectiveness. The

Use of identical parts is thus hardly possible. With increasing shrinkage in the cylinder wall, there is also during operation to a widening of the slot, so that the resulting leakage path always increases.

It is therefore the object of the invention to provide an improved over the known arrangement with a plurality of slotted piston rings system in which the loss of efficiency due to leakage is reduced.

The object is achieved by the system according to the invention with the features of claim 1.

According to the invention, the system for sealing a piston guided in a cylinder bore comprises a piston and a piston ring. The piston ring is used for axial locking in a recess introduced on the outer circumference of the piston. According to the invention, the piston ring has a closed ring-shaped

Arretierungsabschnitt, wherein on the outer circumference, a extending in the axial direction sealing portion is arranged. Such a design decouples the function of locking the piston ring on the piston from its sealing function. This allows the

Sealing section closed, so unsliced to be executed. Due to the pressure difference on both sides of the seal, the sealing section experiences a force which acts on it in the direction of the cylinder wall. This leads to an elastic widening of the piston ring in the region of the sealing section extending in the axial direction. From it is decoupled one Arretierungsabschnitt formed on the piston ring. This ensures a secure attachment of the piston ring to the piston. Because of in the cylinder room ^! prevailing pressure of the sealing portion elastically deformed and so applies to seal the cylinder chamber to the cylinder wall, a slit of the piston ring is not required. The piston ring is therefore closed overall annular.

The subclaims characterize advantageous developments of the system according to the invention.

In particular, a wall thickness of the sealing portion extending in the axial direction is smaller than a radial extent of the locking portion. This has the consequence that the locking portion for secure fixation can relatively far into a groove which is arranged on the outer circumference of the piston, engage and at the same time extending axially extending sealing portion can be sufficiently thin, so that an elastic deformation is possible. In contrast to conventional piston sealing rings, in which the locking portion and the sealing portion are each formed by the entire cross section of the piston ring, is thus a decoupling of the functionality of

Arretierungsabschnitts of the sealing effect possible.

In this case, preferably with respect to an axis of symmetry of the piston and thus also of the piston ring outwardly directed sealing surface is curved at the sealing portion in the axial direction. This results in a slightly convex outer contour, so that this sealing surface bears regardless of their respective elastic deformation state each tangent to the cylinder wall. Such a curved design reduces wear that might otherwise result from deformation. Furthermore, each becomes the narrowest point lie between the piston ring and the cylinder wall in the region of the sealing portion, that the pressure difference can generate a direction in the direction of the cylinder wall force directed to the sealing portion.

The piston ring preferably has a substantially U-shaped profile. By such a U-shaped profile ensures that not only for the arranged at the outer peripheral edge sealing portion has a sufficient axial length is available to take advantage of the pressure ratios can, but that on the side facing away from the inner side, by the second Leg of the U-shaped profile is formed, a height is available, which allows a recording in a recess of the piston. Excessive narrow grooves on the outer circumference of the piston are thus avoided and the production costs can be kept as low.

It is particularly preferred if the inner leg of the U-shaped profile seen in the radial direction has a smaller extent in the axial direction than the outer leg forming the sealing portion. This ensures that even with an arrangement of the piston ring near the piston surface of the piston, the recess can be introduced as a groove in the piston, that in the axial direction of the outer leg can be arranged close to the piston surface, but on the other hand, the groove in the Piston can be introduced so that a secure fixation of the piston ring is possible. In particular, it is also preferred that the inner leg has at its free end a smaller distance from the axis of symmetry than at its end connected to the outer leg. This can be used, in particular, to form a snap connection between the piston and the piston ring, whose open side of the U-shaped profile points to the side leading the higher pressure. During touchdown on the piston, the inner leg deforms by a widening in the radial direction outwards until the piston ring is completely arranged in the groove. Due to the conical arrangement of the inner leg thus a secure locking of the piston ring is achieved.

Preferably, the piston is formed so that such a snap device is formed together with the piston ring. In particular, it is provided for this purpose that the locking portion is inserted into a groove of the piston, wherein the radial extent of the piston is smaller on the side of the groove, in which the sealing portion is directed, than on the other side. The piston ring is thus arranged on the piston, that the inner sides of the U-shaped geometry is substantially directly connected to the piston space to be sealed. This ensures at the same time that the pressure acting on the inside on the sealing portion extending in the axial direction is equal to the pressure in the cylinder bore. A pressure drop over a small gap, which is already generated by the piston itself, is thus avoided, thus ensuring the function of elastic expansion.

A preferred embodiment is shown in the drawing and will be explained in more detail in the following description. Show it:

Fig. 1 is an overview of a piston arranged in a cylinder bore, - and

Fig. 2 is an enlarged view in detail II to illustrate the details.

The operation of hydrostatic piston engines is well known, so that here on the structure does not have to be discussed in detail. Fig. 1 shows only a detail to illustrate the sealing portion of the piston in a cylinder bore. The system for sealing comprises a piston 2, which is guided longitudinally displaceably in a cylinder bore 3. To avoid loss of efficiency, a seal between the piston and the cylinder bore must be provided. The cylinder bore 3 is introduced, for example, into a cylinder drum 4 in the case of a hydrostatic axial piston machine. The cylindrical space formed in FIG. 1 to the right of the piston 2 is temporarily connected via an opening 5 in a known manner to a high-pressure or low-pressure connection of the axial piston machine. The piston 2 has a ball head 6 for attachment to a sliding block. At its end facing away from a piston surface 7 is formed, which limits the cylinder space. The piston 2 is rotationally symmetrical to an axis of symmetry 8. At the end of the piston 2 facing the piston surface 7, a sealing arrangement is provided, which will be explained in detail below with reference to FIG.

The enlarged view of FIG. 2 again shows the piston 2, which is sealingly guided relative to a cylinder wall 3. The piston ring 9 is designed substantially as a closed ring and has a well-recognizable in Fig. 2 U-shaped profile. On the piston ring 9, a locking portion 10 is formed, which locks the piston ring 9 in a recess 15 of the piston 2. The recess 15 is introduced as Außenumfangsnut in a peripheral surface 14 of the piston 2. The depth of the recess 15 of the piston peripheral surface 14 is chosen so that between the locking portion 10 and the bottom of the groove 15 formed as a recess remains a distance. This distance allows a displacement of the piston ring 9 relative to the piston 2 and thus allows, for example, compensation for temperature fluctuations. The locking portion 10 is formed in the illustrated embodiment of a U-shaped piston ring 9 by an inner leg 11 and a connecting portion 12. The connecting portion 12 extends substantially in relation to the symmetry axis 8 in the radial direction and connects the inner leg 11 with an outer leg, which forms a sealing portion 13. At the sealing portion 13, a sealing surface 13 'is formed, which is formed by the cylindrical wall 3 towards outwardly oriented outer peripheral surface of the piston ring 9.

The wall thickness t of the sealing portion 13 is selected so that an elastic deformation is possible at an occurring inside pressure p, which acts on the inner wall of the sealing portion 13. To the elastic deformation occurs, as the pressure prevailing in the cylinder space high pressure only acts on the sealing portion 13 of its sealing surface 13 ^■ up to the point P. In contrast, in FIG. 2, to the left of point P, the low pressure acts. Thus, there is an imbalance of forces at the sealing portion 13, which acts on the sealing portion 13 in the direction of the wall of the cylinder bore 3 out. In the axial direction of the outer leg 13 is curved, so that there is a spherical outer contour and the piston ring forms a sealing line at the point P along the circumference.

The two legs 11 and 13 of the U-shaped piston ring 9 are of different lengths. While the inner leg 11 has an extension in the axial direction with a first height h _x , the axial extent of the second leg and sealing portion 13 is formed with a height h ₂ , which is larger. By shortening the facing to the inside of the piston ring 9 toward the first leg, a groove 15 in the direction be dimensioned strong enough on the piston surface 7 to be limited section 16, so that there a snap connection can be formed. The section 16 is designed so that the surface on the outer circumference, starting from the piston surface 7 radially expands slightly. As a result, an insertion bevel 17 is formed, which enables easier assembly of the piston ring 9. The piston ring 9 in turn is shaped so that the inner leg 11 on its side facing the piston surface 7 side, so the free end of the inner leg 11 a smaller distance dj. from the axis of symmetry has as the distance d ₂ , at the connected to the connecting portion 12 end of the inner leg 11. In this case, preferably corresponds to the distance d ₂ , at the connected to the connecting portion 12

End approximately the distance of the transition from the piston surface 7 in the insertion bevel 17 from the axis of symmetry eighth

The transitions' between the inner leg 11 and the connecting portion 12 and the connecting portion 12 to the sealing portion 13 are rounded. In particular, by the rounding between the inner leg 11 and the connecting portion 12 thus easy mounting on the piston 2 is possible. When placing the piston ring 9 in FIG. 2 from the right side, a radial force is exerted on the inner leg 11 by the insertion bevel 17. As a result, the inner leg 11 expands elastically until the connecting portion 12 abuts the limiting wall of the recess 15. The width of the groove is introduced according to the height h _{λ of} the inner leg 11. The inner leg 11 is due to the deformation under tension and snaps behind the portion 16 of the piston 2. Thus, the piston ring 9 is securely locked in the recess 15. The invention is not limited to the illustrated embodiment. In particular, it is not necessary for the function of the invention that the two legs 11 and 13 are approximately the same height. Thus, the inner leg 11 could also be made considerably shorter. In an extreme case, it may correspond to the thickness of the connecting portion 12, in which case a snap connection between the piston 2 and the piston ring 9 can no longer be formed. It is crucial, however, that the sealing portion 13 in the axial

Direction extends so that its the symmetry axis 8 facing inner wall is acted upon by the higher pressure and a portion of its sealing surface 13 is acted upon by the lower pressure. This force difference leads to the formation of the expanding force, which ultimately leads to a sealing contact of the sealing surface 13 'on the wall of the cylinder bore 13.

Claims

claims

A system for sealing a piston (2) in a cylinder bore with a piston (2) and a piston ring (9) which is inserted for axial locking in a recess (15) inserted in an outer periphery of the piston (2) , characterized in that the piston ring (9) has a closed annular locking portion (11, 12), wherein in the region of the outer periphery of a extending in the axial direction sealing portion (13) is arranged.

2. System according to claim 1, characterized in that a wall thickness (t) of the extending in the axial direction of the sealing portion (13) is smaller than a radial extent of the locking portion (11, 12).

3. System according to claim 1 or 2, characterized in that with respect to an axis of symmetry (8) radially outwardly directed sealing surface (13 ') on the sealing portion (13) is curved in the axial direction, so that a cylinder bore wall, against the the sealing surface (13) seals tangentially against the sealing section.

4. System according to one of claims 1 to 3, characterized in that the piston ring (9) has a substantially U-shaped profile.

5. System according to claim 4, characterized in that an inner leg (11) of the U-shaped profile has a smaller extension (hj.) In the axial direction, which is smaller than the extension (h ₂ ) of the sealing portion forming outer leg (13) in the axial direction.

6. System according to claim 4 or 5, characterized in that the inner leg (11) at its free end a smaller distance (di) from the axis of symmetry

(8) than at its with the outer leg

(13) connected end.

7. System according to one of claims 1 to 5, characterized in that for fixing the piston ring (9) on the piston (2) is formed a snap connection.

8. System according to one of claims 1 to 6, characterized in that the locking portion (11, 12) in a groove (15) of the piston (2) is inserted, wherein the radial extent of the piston (2) on one of the piston surface ( 7) facing side of the groove (15) is smaller than on the other side.