The invention relates to a sealing ring made of plastic, having a separating through-cut, and also a step-shaped overlap which is provided in the separating region and in which the mutually overlapping ring ends lie against each other in a sliding surface. The said sealing rings made of plastic are used, for example, for the sealing of a shaft or spindle shoulder from a bore in, for example, automatic transmissions, servo units for power-assisted steering, brake boosters, retarders and the like and have a particularly influential effect on the quality of the performance which these components can achieve- In the case of a known sealing ring made of plastic of the said type, the step-shaped separating region is provided with two radially running sliding regions lying against each other. These sliding regions form the sealing surface in the installed state. One problem is that particularly close production tolerances have to be maintained in the production of the sealing rings, making production very cost-intensive. If the diameter of the known sealing ring is too small, leakages occur in operation, since the separating cut is not closed. If, on the other hand, the diameter is too large, overlapping in the separating region occurs in operation, likewise causing a radial leakage.

Therefore, it is in fact necessary to produce sealing rings in the form of a semi-finished product, after production of the semi-finished product, by for example sintering and/or pressing, to work them further in an additional machining production step, for example to grind them, until the dimensions of the final sealing ring are achieved within the tolerance, the dimensions continually having to be measured.

The invention is therefore based on the object of further developing the known sealing rings in such a way that they can be produced more easily and therefore at lower cost. According to the invention, this object is achieved by the sliding plane of the sealing ring being offset by an angle with respect to the perpendicular to the plane taken through the neutral axis. The sliding surface produced by the step cut consequently forms an area of the lateral surface of a truncated cone.

The configuration of the step cut according to the invention achieves the effect that the seal can be produced in wider tolerances and nevertheless can be used in operation directly after production, by for example sintering and/or pressing, without an additional production step.

It is even possible to produce the seal by low-cost injection moulding, without an additional production step, which is not possible with the known sealing rings.

A further advantage is that the configuration of the step cut according to the invention achieves the effect that a tightness is ensured in the cut region even if the ambient medium enclosing the sealing ring, for example oil, is not at the usual operating temperature.

Yet another advantage is that the sealing ring according to the invention can be made from plastics which cannot be used for the production of the known sealing ring, because the plastics are not suitable or not very suitable for the production of mouldings which are dimensionally very accurate. Incidentally, such plastics may have very favourable other properties or be inexpensive. Although US 615902 discloses a sealing ring with a separating cut like the sealing ring according

to the invention, the sealing ring is not produced from plastic, and it is also not disclosed by US 615902 that the sealing ring can be produced from plastic in the advantageous way. Furthermore, in the very long period of time in which the sealing ring from US 615902 was known, no-one had the idea of producing the sealing ring from plastic, without subsequent working.

The sealing ring according to the invention may be provided with a rectangular, square, round or other suitable cross-section.In the separating region the cross-sections of the mutually overlapping ring ends at both sides of the sliding surface are congruent taken along the separating region, as they are separated by the sliding surface. In the case of a sealing ring of rectangular or square cross-section, the sliding surface can run under an angle with respect to the diagonal and preferably runs parallel to the diagonal of the sealing ring cross-section. In the case of this embodiment, the sliding surface is laterally offset parallel to the diagonal of the sealing ring cross-section, so that the sealing ring cross-section is divided by the cut into a triangle and a pentagon with two additional edges. Preferably, this distance from the diagonal is about 20%. The two edges bear against the bore or the shoulder such that they have the effect of achieving a sealing of the sliding surface in a wide tolerance range of the sealing ring, even in the event that the ambient medium is not at its normal operating temperature. At the same time, the enlarged edges have the effect of reducing the risk of material abrasion by the ambient medium flowing around, caused by cavitations.

The sliding surface preferably forms a single plane, so in the cross-section of the ring in the separating region the intersecting line of the cross

section and the sliding surface is a straight line.

However it is also possible that the sliding surface is otherwise formed, the intersecting line not being a straight line, but being bended or even running stepwise. In this case the plane section running between the two intersecting lines of the sliding surface and the outside surfaces of the ring body forms an area of the lateral surface of a truncated cone.

In its particularly suitable embodiment, the sealing ring is installed in such a way that the sliding surface is arranged offset to the side away from the pressure.

In an even further improved embodiment in the separating region the sealing ring comprises two sliding surfaces, the sliding surfaces being positioned in an angle with respect to one another.

An advantage of such a sealing ring is that no matter how the ring is installed always one of the two sliding surfaces is arranged offset to the side away from the pressure.

Preferably the ring comprising the two sliding surfaces is having a rectangular or square cross-section, the sliding surfaces both have an intersecting line with one outside surface of the ring body, the outside surface being parallel to the plane taken through the neutral axis and one sliding surface is having an intersecting line with one outside surface of the ring body perpendicular to the plane taken, through the neutral axis and the other sliding surface is having an intersecting line with the other outerside surface of the ring body the outside surface being perpendicular to the plane taken through the neutral axis.

In the production of the sealing rings from plastic, plastics which are well suited for sliding applications are preferably used. Apart from the good

sliding friction values, these plastics have a high wear resistance and temperature resistance.

In an advantageous embodiment, the plastic polytetrafluoroethylene (PTFE) is used for production. This plastic may be modified with synthetic mica to improve the pressure resistance and abrasion resistance and to reduce the thermal expansion. PTFE has the properties of extreme chemical resistance and low friction values. The mica does not attack the materials sliding on each other.

In a further embodiment of the invention, a poly(amide-imide) which has a high strength and can be used in the temperature range from -190°C to 260°C, is used as the plastic. In addition, PTFE and graphite additives can improve the sliding/abrasion behaviour. The extremely low coefficient of thermal expansion has the result that there is virtually no longer any difference from metallic materials.

For producing the sealing rings, there can likewise be used the plastic polyetherether ketone, which has unique serviceability and high flexural fatigue strength. In addition, polyetherether ketones have long-term heat resistance at 250°C, have good chemical resistance and can be used even in hot water, steam and under a high vacuum.

Yet further examples of suitable plastics are polyphenylene sulphide (PPS) and polyaryl ether ketone (PAEK).

The sealing ring according to the invention may also be designed in its separating region as a hook-lock ring.

The sealing ring is preferably produced by injection moulding, without any additional machining production step. It is preferred to locate the sprue on the inside diameter of the ring. The injection-moulding process is known to a person skilled in the art.

The invention is illustrated by way of example in the drawing and is described in detail below with reference to the drawing, in which: Fig. 1 shows a plan view of the sealing ring according to the invention.

Fig. 2 shows a section along the line II-II from

Fig. 1, Fig. 3 shows a section along the line III-III from

Fig. 1 and Fig. 4 shows an installation example of the sealing ring according to the invention in the detail of an automatic transmission. Fig. 5a, show crosssections of the sealing ring 5b, 5c according to the invention in the separating region having different kinds of sliding surfaces. Fig. 6a, show cross-sections of sealing rings 6b, 6c according to the invention in teh separating region having two sliding surfaces being positioned in an angle with respect to one other.

According to the drawing, the sealing ring 1 comprises an annular element 2 having a radial slit 3. The ends 4, 5 of the sealing ring lying opposite each other are configured as sliding surfaces 6, 7.

As revealed in particular by Fig. 2, the sliding surface in the preferred embodiment of the invention is offset parallel to the diagonal of the sealing ring cross-section at a distance from the latter. In this way there are produced two additional edges 8 and 9 at the sliding surface 6.

As Fig. 4 reveals, these two edges 8 and 9 form with the housing bore 10 and the shaft shoulder 12 of a shaft 11 additional sealing surfaces which seal the step-shaped overlap against leakages by means of the oil pressure 13 at every point in time and in a

O 96/21116 PCI7NL96/00005

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wide tolerance range of the sealing ring. This is also the case if the ambient medium is not at its predetermined operating temperature and, under certain circumstances, the expansion of the sealing ring material is inadequate or excessive.

In order to ensure this tightness, care must be taken that the sealing ring is always installed such that the sliding surface of the sealing ring is arranged offset to the side away from the pressure. Apart from the exemplary application represented in

Fig. 4, the sealing ring according to the invention can also be used in other areas in which shafts/spindles have to be sealed with respect to housing bores, such as for example if the shaft/spindle is provided with a groove in which the sealing ring is arranged.

Fig. 5a shows the cross-section in the separating region of a sealing ring according to the invention having a sliding surface (represented by intersecting line 3) running stepwise. The sliding surface is separating two mutually overlapping ring ends 1 and 2.

The intersecting lines of the sliding surface (3) and the outside surfaces of the ring body run through the points 4 and 5, the line connecting the two points being part of the area of the lateral surface of a truncated cone.

Fig. 5b shows a cross-section of a sealing ring according to the invention the sliding surface being bended. In Fig. 5c the sliding surface is running stepwise in a single step.

In Fig. 6a the intersecting lines of the sliding surfaces 1 and 2 run through points 6 and 7 of one outside surface (represented by 3, the outside surface being perpendicular to the plane of the figure) of the ring body, parallel to the plane taken through the neutral axis and further run through points 8 and 9

of the outside surfaces 4 and 5 both being perpendicular to the plane taken through the neutral axis.