FR3011305A1 - AXIS OF PISTON - Google Patents

Abstract

The device has an anti-seizing coating limited to an angular sector corresponding at least to a friction zone subjected to a contact pressure in a preferred direction.

Description

The invention relates to the technical field of tribological contacts and more generally any system where a pin is mounted tight is biased in a preferred direction inducing a biasing of said axis along a partial angular sector. The invention advantageously relates to a piston pin.

In this type of contact, it appeared important to subject the piston pin to a coating of the DLC type in order to prevent galling of the piston pin facing antagonists generally bronze and / or aluminum. The application of an anti-seizing coating has become necessary following the increasing increase in contact pressures between the various components of the system given the desire to increase power, reduce consumption ... This increase in Contact pressure results from the reduction of the dimensions of the parts in order to reduce the mass and the lost energy resulting from the inertia.

The piston pin can be mounted floating to reduce wear and push the limit to seizure in the pin / connecting rod contact. However, with the increase in the load, the risk of seizure that may appear is unacceptable. It is also observed that the mounting of a floating shaft requires the use of a ring, usually bronze, in the connecting rod. A solution of this type emerges for example from the teaching of DE 102009026726. This results in additional cost following the supply, shrinking and in situ machining of the ring. There is also an obligation to size the connecting rod with an upper ring of larger diameter imposing an over-height piston and an overweight rod. This results in a limitation of the compactness of the engine and the additional costs of all of said engine block. Considering these disadvantages, most of the presently used industrial tools are configured for designs where the piston pin is tightly mounted in the connecting rod and free in said piston. In this type of assembly, in order to reduce wear and to push back the limit to seizing in the pin / connecting rod contact, the entire axis receives, as mentioned, a DLC-type coating. The advantage of applying this type of coating is therefore to prevent galling of the piston pin against the opposing components most often made of bronze or aluminum. Solutions of this type emerge for example from the teaching of documents WO 2009/144076 or DE 102011102209. This technical solution to prevent seizure is not entirely satisfactory since the application of the DLC-type coating is carried out on the entire diameter of the axis which significantly increases costs. The object of the invention is to remedy these disadvantages in a simple, safe, effective and rational manner.

The problem to be solved by the invention is, in the case of an axle mounted tight and biased in a preferred direction, inducing a biasing of the axis along a partial angular sector, which is particularly the case for an axis piston, to allow the engine to increase the loading load of the mobile hitch, eliminate any risk of seizure using a coating of the DLC type under special conditions to significantly reduce the costs of implementation. To solve such a problem, the piston pin has a DLC-type anti-cladding coating limited to an angular sector corresponding to at least one friction zone subjected to a contact pressure in a preferred direction.

It therefore follows from these characteristics that the anti-seizing coating is applied solely to the stressed angular sector, in order to reduce the surface to be treated and, consequently, to reduce the implementation costs.

Partially coating the axis is not obvious to a person skilled in the art who, on the contrary, is dissuaded from using such a technique that requires precise angular positioning of the axis during its assembly so that the rubbing zone corresponds to the coated zone.

It is also observed that the fact of partially coating the axis makes it possible to consider the use of an anti-seizing coating of greater thickness compared to what is practiced according to the prior art increasing, therefore , the life of the axis.

According to other features, the anti-seizing coating is DLC. The coated angular sector is between 15 ° (-7.5 ° to + 7.5 °) and 220 ° (-110 ° to + 110 °). The thickness of the coating is uniform to ± 20% on the rubbing zone. The thickness of the coating is between 1 and 10 μm.

To solve the problem of applying the anti-seizing coating of the DLC type on only part of the axis, the invention also relates to a method for applying this coating. According to one embodiment, one: circularly positions the axes on a support, in at least one row and in a tangent position, blocks in rotation the axes relative to the support, has the support equipped with the axes in a vacuum chamber, drives in rotation the support equipped with the axes, realizes the anti-seizing coating which is deposited selectively on the axes according to an angular sector defined by the positioning in tangency of said axes.

In another embodiment, one: circularly positions the axes on a support in at least one row and in the tangent or quasi-tangent position, has between each axis a protection element capable of delimiting, for each of the axes, a sector angular, blocks the axes in rotation relative to the support, arranges the support equipped with the axes in a vacuum chamber, rotates the support equipped with the axes, produces the anti-seizing coating which is deposited selectively on the angular sector delimited by the reported protection element.

The invention is described below in more detail with reference to the figures of the accompanying drawings, in which: FIG. 1 shows the application of the invention to a piston pin. Fig. 2 is a schematic cross-sectional view showing the piston pin mounted tightly in the connecting rod, the axis being partially coated with the anti-seizing coating of the DLC type according to the features of the invention. Fig. 3 is a perspective view of an exemplary mounting of the shafts on a support mounted in a PVD enclosure in order to subject the shafts to an anti-seizure treatment with application of a DLC layer according to a limited angular sector. FIG. 4 is a partial view in cross-section and on a larger scale corresponding to FIG.

Figs. 5 and 6 are, in the same way as FIGS. 3 and 4, views showing another embodiment for the application of the DLC coating in a limited angular sector is illustrated in Figure 1 a piston shaft (1) (2) tightly mounted in a rod (3). At the moment of the explosion, the axis (1) is biased in a preferential direction (F) inducing a biasing of said axis along a partial angular sector.

According to the characteristics on which the invention is based, a DLC type anti-seizing coating (4) is applied on the axis (1) according to a limited angular sector (S) corresponding at least to the friction zone subjected to pressure. contact in the preferred direction (F). Without departing from the scope of the invention other anti-seizing coatings that the DLC can be used such as CrN, or TiAIN. FIGS. 3 and 4 and FIGS. 5 and 6 show two solutions for applying a coating of the DLC type to only a part of the circumference of the axes (1). The axes (1) are positioned circularly at the periphery of a support (5) in at least one row. The axes (1) are immobilized in rotation and arranged in a tangent position. In the embodiment illustrated in FIGS. 3 and 4, the axes (1) are arranged around a central core (6) which prevents the rotation of said axes in order to block them in rotation, as indicated. Still in this embodiment, in order to process a large number of axes, the latter are stacked on each other using the internal bore of said axes which cooperates with guide rods (7).

After cleaning the pins (1), they are put in place as indicated according to the assembly as defined above which is then, in a perfectly known manner, loaded into a vacuum deposition chamber (not shown). During the operation of pumping, the vacuum deposition chamber and the 5 axes (1) are degassed by radiative heating at a set temperature respecting the axis of the return temperature. When the vacuum reaches a value of 2.10-5 mbar, argon is introduced into the chamber to reach a pressure of the order of 10 -3 mbar. The stripping parameters are adapted to allow the removal of an oxide layer naturally present from the axes (1), including in the confined areas at the junction of the axes (1) resulting from their positioning. in a tangent way. The parameters are adapted to reduce the voltage on the axes while increasing the current, in order to reduce the cathode sheath. After pickling, chromium nitride deposition is carried out by a magnetron sputtering method. At the end of PVD deposition, an amorphous carbon type deposit is deposited by PECVD process. This amorphous carbon layer a-C: H is preceded by a transition layer containing, for example, α-C: H-Si type silicon. This application of the DLC coating is well known to a person skilled in the art and is given as a non-limiting indication. The invention does not lie in the application as such of the DLC, but in the process of coating only a part of the circumference of the axes, of this DLC coating. In this configuration, tests have shown that a coating over a total angular sector of 200 ° (-100 ° to + 100 °) is obtained. This coating is adherent over a sector ranging from -85 ° to + 80 ° is a total angular sector of 155 °. The thickness of the DLC coating is uniform at ± 20% over a sector ranging from -70 ° to + 65 °, ie an angular sector of 135 °. (Note: The coating is considered functional on this angular sector.) On the opposite sector ranging from + 100 ° to -100 °, there is a complete absence of DLC coating. In the embodiment illustrated in FIGS. 5 and 6, the stop of the coated zone 5 is not induced by the contact with the adjacent axis, but by an attached protection element (8) able to delimit, for each of the axes , an angular sector. In this embodiment, the axes (1), as indicated previously in the case of the embodiment illustrated in FIGS. 3 and 4, are locked in rotation and are positioned tangentially or, in this case, substantially tangent, given the establishment of the protective element (8) between two adjacent axes (1). Tests were carried out with steel pins (1) with a diameter of 20 mm and 28 mm. These axes followed the same procedure as previously indicated for the application as such of the DLC coating (cleaning, evacuation, degassing). , stripping, deposit). In this configuration, an adherent coating is obtained over the entire coated angular sector (S) of approximately -50.degree. To + 50.degree., For the 20 mm diameter axis and from -62.5.degree. To +62.degree. 5 °, for the diameter axis 28 mm The thickness of the DLC coating is uniform at ± 20% over this same angular sector (S). For the axis of 20 mm and the opposite sector from + 50 ° to -50 ° there is a total absence of coating. It is the same with regard to the axis of diameter 28 mm on the opposite sector ranging from +62.5 ° to -62.5 ° In this form of configuration, the use of a protective insert ( 8) to define and limit the area to be coated with DLC, allows to have an adherent coating, of uniform thickness, over the entire angular sector concerned by the DLC coating and delimited by said protective element (8). A judicious positioning of this protection element (8) makes it possible to obtain an adherent coating having a satisfactory morphology over an angular sector of up to 220 ° (from -110 ° to + 110 °).

Comparative tests have been carried out in the case of the application of the DLC coating over the entire periphery of the axis according to the prior art and only a part of said periphery, according to the characteristics of the invention. .

These tests were carried out on an axis of diameter 16 mm and length 45 mm In the case of a coating DLC 360 ° (prior art), it is necessary to use a so-called triple rotation configuration. In this case, it is possible to process 4356 axes per charge in a TSD850 machine marketed by the company HEF-Durferrit. When the axes are processed, according to the characteristics of the invention, that is to say application of DLC coating on a limited angular sector and in the configuration illustrated in Figures 3 and 4, a so-called double rotation configuration is sufficient. In this case, it is possible to process 5544 axes per load in the same type of TSD 850 machine. As a result, a machine filling gain of the order of 25% is obtained. According to the invention, because of the transition from the triple rotation configuration to the double rotation configuration, a gain on the DLC coating cycle times is also obtained. In the context of a DLC coating with a thickness of 3 μm according to the prior art (360 ° coating), the cycle time in triple rotation configuration is 15.5 hours in a TSD 850 machine. according to the invention (limited angular sector coating) the cycle time in double rotation configuration, still in a TSD 850 machine, is 11.2 hours, a time saving of the order of 35%.

In addition to these advantages, it appears that the fact of applying the DLC coating on a partial angular sector of the axis makes it possible to increase the thickness of the coating while remaining economically interesting. This increase in thickness makes it possible to increase the life of the axis, and particularly interesting in the case of very busy applications. The thickness of the DLC coating can thus be between 1 and 10 μm.