DE102008036657B4 - Piston ring with adaptive coating and manufacturing method thereof - Google Patents

Abstract

A piston ring for an internal combustion engine, comprising at least one tread, characterized by a tread coating of a copper-based alloy, said alloy comprising 0.1 to 4 percent by weight beryllium and 0.1 to 0.8 percent titanium by weight.

Description

The present invention relates to piston rings of internal combustion engines, with an adaptive coating which serves both as a run-in and wear protection layer, and to methods for their preparation.

Piston rings are provided with anti-wear layers on the running surface of the cylinder wall in order to ensure functional performance in all operating conditions of the motors and to ensure a long service life of the motors. Different demands are placed on the tread coating over the runtime.

During the start-up phase of a new motor, the coating should be able to adapt the surface topography microscopically and macroscopically to the circumstances of the counterparty, without damaging it or causing consequential damage. After completion of the break-in phase properties such as high wear resistance and fire safety with low wear of the counterparty as well as low friction values are required. This means that different functionalities will be required as the runtime increases.

In practice, these requirements are met by in addition to the wear protection layers applied run-in layers, which may be formed both as homogeneous layers or as gradient layers with continuous changes in properties over the layer height. Wear protection and enema layers can be applied in different processes, which can additionally increase the production costs. A further disadvantage is that in the case of any necessary post-processing of the tread, the already applied inflow layer is partially removed again and thus is no longer available for the running-in process.

DE 10 2004 043 914 A1 discloses a sliding bearing component with an applied layer of a bearing metal and a method for applying the layer.

DE 676628 A relates to an alloy of copper with additions of beryllium and chromium.

DE 1254869 B discloses a use of thermosetting copper-titanium alloy as a material.

DE 3329034 A1 relates to a liquid-sealed shaft seal with a rotating sealing ring, which consists of a hardened copper beryllium.

The object of the invention is therefore to eliminate the abovementioned disadvantages and to provide a piston ring with a coating which can be applied as a homogeneous coating and serves both as an enema and as a wear protection layer. Furthermore, a method for producing the piston ring is to be provided.

According to a first aspect of the present invention, there is provided a piston ring for an internal combustion engine, comprising at least one tread, characterized by a tread coating of a copper-based alloy having an additive of Ti and Be.

This piston ring has an adaptive coating. This adaptive behavior means that the coating originally has a comparatively low hardness. In this state, it acts as an inlet layer, for example in a piston ring in an internal combustion engine during the running-in phase of the new engine. Smaller bumps between piston ring and cylinder are compensated by adjusting the inlet layer, d. H. the inlet layer adapts to the structure of the cylinder wall without damaging it. A good seal between the piston ring and the cylinder wall is thus ensured.

As the engine continues to operate, precipitation solidification of the coating occurs under the action of the high temperatures. This increases in hardness, so that it acts as a wear protection layer after completion of the inlet process. Due to the adaptive adaptability of the coating according to the invention, this transition from inlet properties to anti-wear properties is temperature-dependent. The motor load and associated temperature of the coating thus controls the transition from an enema layer to a wear protection layer. Higher engine load also results in a faster transition to forming a wear resistant layer, which then retains its properties for the life of the engine.

According to one embodiment, the alloy comprises 0.1 to 4 weight percent beryllium and 0.1 to 0.8 weight percent titanium, preferably 1 to 3 weight percent beryllium and 0.2 to 0.6 weight percent titanium, most preferably ca. 2 weight percent beryllium and about 0.4 weight percent titanium.

According to a second aspect of the present invention, there is provided a method of manufacturing a piston ring for an internal combustion engine, comprising depositing one Alloy based on copper, which has an additive of Ti and Be.

In one embodiment, the deposition comprises a thermal spray process. The thermal spraying process can be high velocity oxy fuel (HVOF) or plasma spraying.

According to one embodiment, the alloy comprises 0.1 to 4 weight percent beryllium and 0.1 to 0.8 weight percent titanium, preferably 1 to 3 weight percent beryllium and 0.2 to 0.6 weight percent titanium, most preferably ca. 2 weight percent beryllium and about 0.4 weight percent titanium.

The invention makes it possible for the coating to be applied homogeneously, as a result of which a faster and more cost-effective production of, for example, piston rings becomes possible. A coating with separate wear protection and enema layers, which would be tedious and expensive, can thus be avoided. Also, an inventive piston ring can be easily reworked, without causing a separate inlet layer is removed, which would then no longer be available for the inlet process.

Since a piston ring according to the invention has only a homogeneous coating which has the properties of an inlet layer in the original state, the running properties are not lost even if the post-processing is necessary, provided that a sufficient residual thickness is maintained. The anti-wear properties are only obtained by the coating in the engine.

Compared to conventional piston rings is a further advantage of piston rings according to the invention that the coating is substantially homogeneous even after running in their hardness. In the case of conventional piston rings, however, in some areas, residues of the running-in layer as well as exposed areas of the wear-resistant layer are usually present, which inevitably differ in hardness. While areas with remaining run-in layer are relatively softer, areas with exposed wear protection layer are relatively harder.

In the present invention, since the hardness is adaptive to the entire coating, there will be a substantially homogeneous hardness of the coating even after shrinking. The wear protection is thereby increased because not as in the conventional piston ring areas with lower hardness remain.

It has also been found that in the piston rings according to the invention compressive stresses occur in the layer which provide additional resistance against the formation and propagation of cracks.

There are alloy systems that are initially in thermodynamic imbalance after production at room temperature. If, for example, energy is supplied in the form of heat, separate phases are precipitated, which can lead to hardening of the material and possibly to an increase in wear resistance. According to the invention it is proposed to apply such alloys by suitable methods as a tread coating on piston rings or other motorized sliding elements. The coating thus produced fulfills the function of a soft inlet layer in the non-pretreated state.

Due to the heat generated during operation of the engine in the combustion chamber and the resulting heating of the components at the same time begins the precipitation hardening of the coating. Since this is temperature dependent, the curing of the coating will proceed faster with increasing motor load, i. H. the load condition of the motor itself controls the transition from an inlet layer to a wear resistant layer, which then retains its anti-wear properties during the life of the engine.

With regard to an improvement in mechanical properties, iron, aluminum, copper and other metal base systems have a variety of elements that can alter the properties of the base material through precipitation strengthening along with cold or hot aging. Among others, alloys based on aluminum with additions of Cu, Co, Mg, Si, Mn or Zn are known for their ability to increase strength and hardness during hot aging. Also alloys based on copper with additives of Ti, Co, Cr, Zr or Be meet these requirements.

Embodiment:

A tread coating on a piston ring was performed by depositing a CuBeTi alloy containing about 2 wt% beryllium and 0.4 wt% titanium by a thermal spray process. The hardness of the layer after coating was about 310 HVO.3. In this state, the coating behaves as a running-in layer. On the other hand, a sample which had been removed from the off-engine wear test (0.5 h at 300 ° C.) had a hardness of approximately 400 HVO.3. In this state, the coating behaves as a wear protection layer.

As an additional advantage, examinations with precipitation-hardened copper-based alloys proved that inherent compressive stresses were present in the layer, which offered additional resistance to possible cracking and crack propagation.

Claims (8)

A piston ring for an internal combustion engine, comprising at least one tread, characterized by a tread coating of a copper-based alloy, said alloy comprising 0.1 to 4 percent by weight beryllium and 0.1 to 0.8 percent titanium by weight. A piston ring according to claim 1, wherein said alloy comprises 1 to 3 weight percent beryllium and 0.2 to 0.6 weight percent titanium. The piston ring of claim 1, wherein the alloy comprises 2 weight percent beryllium and 0.4 weight percent titanium. A method of making a piston ring for an internal combustion engine, comprising depositing a copper-based alloy by a thermal spraying method on the tread of the piston ring to form a tread coating, said alloy comprising 0.1 to 4 percent by weight beryllium and 0.1 to 0.8 weight percent titanium. The method of claim 4, wherein the alloy comprises 1 to 3 weight percent beryllium and 0.2 to 0.6 weight percent titanium. The method of claim 4, wherein the alloy comprises 2 weight percent beryllium and 0.4 weight percent titanium. The method of claim 4, wherein the thermal spraying process comprises high velocity flame spraying or plasma spraying. Method according to one of claims 4 to 7, wherein the coating is applied homogeneously.