Method for the production of a connecting rod for an internal combustion engine

Abstract

A method for producing a connecting rod for an internal combustion engine, having a small connecting rod eye for holding a piston pin and having a large connecting rod eye for holding a crank pin, wherein at least one connecting rod eye has at least one geometric deviation from a cylindrical inner contour. It is provided according to the invention that the at least one connecting rod eye is formed by creating a bore with a cylindrical inner contour, and coating the bore with a coating comprising a resin with solid lubricant particles embedded therein. The coating forms the at least one geometric deviation from the cylindrical inner contour of the at least one connecting rod eye.

Claims

1. A method for the production of a connecting rod for an internal combustion engine, having a small connecting rod eye for accommodating a piston pin, and a large connecting rod eye for accommodating a crank journal, wherein at least one of the connecting rod eyes has at least one geometric deviation from a cylindrical inside contour, the method comprising the following steps: producing a bore having a cylindrical inside contour, and subsequently applying a coating agent comprising a resin with solid lubricant particles embedded in it to an inside surface of the bore, with a coating tool, so that the resulting coating forms the at least one geometric deviation from the cylindrical inside contour of the at least one connecting rod eye, wherein the at least one geometric deviation is formed by a stress relief pocket, an ovality or a shaped bore; and subsequently working at least one oil collection chamber into the resulting coating on the inside contour of the at least one connecting rod eye, the oil collection chamber being in the form of a channel extending in a direction of a longitudinal axis of the connecting rod eye across an entire width of the connecting rod eye, wherein the channel has two pockets extending circumferentially in opposite directions from each other and being offset from each other along the channel.

2. The method according to claim 1, wherein the at least one geometric deviation is configured by varying the amount of the coating agent given off by the coating tool and/or by varying an advance of the coating tool.

3. The method according to claim 1, wherein the coating agent is applied to the inside surface of the bore with a surface roughness of Ra (average roughness value) ≦0.8 μm.

4. The method according to claim 1, wherein the coating agent is applied by rotation atomization from a rotating nozzle introduced into the bore.

5. The method according to claim 4, wherein the rotation atomization is carried out at a rotation speed of the nozzle of 14,000 to 18,000 rotations per minute.

6. The method according to claim 1, wherein the inside surface of the bore is pre-heated before and/or during application of the coating agent, up to a temperature of 50° C. to 80° C.

7. The method according to claim 1, wherein a thermally curing coating agent is used in the step of applying, and further comprising the step of subjecting the coating to heat treatment immediately after the step of applying.

8. The method according to claim 7, wherein the heat treatment takes place at a temperature of about 200° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

(2) In the drawings, wherein similar reference characters denote similar elements throughout the several views:

(3) FIG. 1 is a front view of an embodiment of a connecting rod according to the invention;

(4) FIG. 2 is a section along the line II-II in FIG. 1;

(5) FIG. 3 is a schematic representation of a coating tool and

(6) FIG. 4 is a section showing an alternative embodiment of the invention with the oil collection chamber in the form of a channel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(7) FIGS. 1 and 2 show an exemplary embodiment of a connecting rod 10 according to the invention. The connecting rod 10 consists, in known manner, of steel, for example. The connecting rod 10 has a connecting rod shaft 11, a small connecting rod eye 20, and a large connecting rod eye 30. The small connecting rod eye 20 accommodates the piston pin of a piston (not shown), while the large connecting rod eye 30 accommodates a crank journal of a crankshaft (not shown).

(8) In the exemplary embodiment, the connecting rod eyes 20, 30 are shaped bores having a defined inside contour 21, 31 that deviates from the cylinder shape, as it is disclosed, for example, in WO 96/07841 A1. This configuration serves to relieve stress on the mechanical system of piston pin, connecting rod 10, and crank journal, during operation, in order to avoid the risk of cracks around the connecting rod eyes 20, 30. Other configurations of a connecting rod eyes that serve the same purpose are, for example, bores provided with ovality (heightwise and/or crosswise) or with stress relief pockets (not shown). These configurations are already known for pin bores.

(9) In the exemplary embodiment, the two connecting rod eyes 20, 30 are configured, according to the invention, in such a manner that they are composed of a cylindrical bore 22 and 32, respectively, and a coating 23 and 33, respectively. In this connection, the surface contour of the coating 23 or 33 is structured in such a manner that the desired inside contour 21 and 31, respectively, of the connecting rod eye 20 and 30, respectively, which deviates from the cylinder shape, is obtained. In comparable manner, ovality or a stress relief pocket can also be formed by the surface structure of the coating 23 or 33 (not shown). The coating 23 or 33 essentially consists of a resin with solid lubricant particles embedded in it, and is thus a self-lubricating coating.

(10) In the exemplary embodiment, the coating 23 or 33 is furthermore provided with oil collection chambers in the form of a channel 24 or 34 that extends in the direction of the longitudinal axis L of the connecting rod eye 20 or 30, in each instance, from which channel pockets 25 and 35, respectively, extend radially. These oil collection chambers serve to further improve the lubrication of the bearing of piston pin or crank journal, respectively, in each instance. Of course, they can be configured for any desired application, in any desired shape and size, and can be disposed relative to one another in any desired form. For example, FIG. 4 shows the oil collection chamber in the form of a channel 34a which runs radially relative to the direction of the axis L and surrounds axis L at least in part.

(11) To produce a connecting rod eye 20, 30, first the cylindrical bore 22 or 32 is made in the connecting rod shaft 11, and mechanically finished in known manner. The surface roughness Ra (average roughness value) can correspond to the one indicated in DE 41 11 368 A1, whereby in general, the Ra values amount to 0.63 μm or less for bore diameters of less than 30 mm, and Ra values of 0.8 μm or less are achieved for bore diameters between 30 mm and 60 mm. In the exemplary embodiment, the bore diameter is selected, before coating, in such a manner that the piston pin or the crank journal, respectively, has a diametral play of 10 μm to 40 μm in the finished connecting rod eye 20 or 30, respectively. The cylindrical bore 22 or 32 should be cleaned in such a manner that chips, other particles, machining oils and the like are completely removed. The inside surface of the cylindrical bore 22 or 32 can also be phosphatized.

(12) If additional oil collection chambers, for example in the form of channels 24, 34 or pockets 25, 35, are supposed to be provided, corresponding cover templates are affixed in the cylindrical bore 22 or 32 before coating takes place, in known manner. The cover templates prevent coating of the covered regions of the cylindrical bore 22 or 32. As an alternative, the finished coating 23 or 33 can subsequently be worked, and can be provided with oil collection chambers in this way.

(13) The coating agent selected in the exemplary embodiment is formed from a thermally curable resin with solid lubricant particles of one or more of the materials graphite, molybdenum sulfide, tungsten disulfide, hexagonal boron nitride, and PTFE embedded in it. In the exemplary embodiment, the resin is a very temperature-resistant polyamide imide, and the solid lubricant is a mixture of molybdenum sulfide and graphite particles having a particle size of 1 μm to 3 μm. In the exemplary embodiment, the amount of the solid lubricant is selected in such a manner that the finished coating contains about 50 to 60 wt.-% solid lubricant particles. The viscosity of the coating agent is adjusted in such a manner that droplet formation is prevented in the case of sufficient application.

(14) A device 40 for rotation atomization serves to apply the coating to the inside surface of the cylindrical bore 22 or 32, in the exemplary embodiment. The device 40 has a base body 41 that is connected with a nozzle body 42. The nozzle body 42 is mounted to rotate on the base body, by means of a bearing 43. The nozzle body 42 has a nozzle 44 having an exit opening 45. The base body 41 possesses feed channels 46, 47, in each instance, which are intended for the liquid coating material and for compressed air, and end in a mixing chamber 48 for mixing and metering. An exit channel 49 extends from the mixing chamber 48, through the nozzle body 42, and opens into the exit opening 45. A baffle plate 51 is disposed perpendicular to the exit opening 45, so that a ring-shaped gap 52 having a width of 0.5 mm in the exemplary embodiment is formed between the baffle plate 51 and the nozzle body 42. The coating agent/air mixture exits through the gap 52, in the form of a spray jet 53, radially and at a distance from the nozzle body 42.

(15) The nozzle body 42 is put into rotation by means of a drive 54, and rotates in the speed of rotation range from 14,000 to 18,000 rotations per minute in the exemplary embodiment. The coating agent/air mixture that exits from the exit opening 45 is accelerated by the centripetal forces that occur at the exit opening 45, in such a manner that it exits radially as a disk-shaped spray jet 53. Since the spray jet 53 is configured narrow in the direction of the longitudinal axis L, the inside surface of the cylindrical bore 22 or 32 that is to be coated can be sharply delimited, in the direction of the longitudinal axis L, by means of simple feed control of the coating agent/air mixture. In the exemplary embodiment, nozzles 44 having a diameter in the range between 5 and 25 mm and having depths up to 50 mm are available, so that it is possible to coat cylindrical bores 22, 32 for connecting rods of all engine types with the device 40. The diameter of the nozzle 44 is generally selected in such a manner that it approximately corresponds to half the diameter of the cylindrical bore 22 or 32.

(16) A centrifuge device S-520 from Sprimag in Kirchheim is also suitable for carrying out the coating method.

(17) In the exemplary embodiment, application of the coating agent/air mixture takes place onto the inside surface of the cylindrical bore 22 and/or 32, which has been pre-heated to 50° C. to 80° C. The nozzle 44 is introduced centrally into the cylindrical bore 22 or 32, from the outside to the inside. To configure the geometric deviation from the cylindrical inside contour, for example of the shaped bore shown in FIG. 2, the advance of the nozzle 44 is varied in a range of 10 to 20 mm/s, for example. In addition or as an alternative, the amount of the coating agent/air mixture exiting from the exit opening 45 of the nozzle 44 can be varied. For this purpose, it is practical that the device 40 works with computer control. When the nozzle 44 has reached the end of the cylindrical bore 22 or 32, the device 40 is turned off and retracted.

(18) If cover templates are provided in the cylindrical bore 22 or 32 to produce oil collection chambers, the feed of the coating agent/air mixture is shut off when such a template is reached, so that residues of the spray jet are sprayed onto the cover template. When the end of the cover template has been reached, the feed of the coating agent/air mixture is achieved again.

(19) When the coating agent has been applied, it is thermally hardened, in that the connecting rod, i.e. the connecting rod component that has the coated connecting rod eyes 20 and/or 30, is placed in an oven and held at a temperature of 200° C. between 10 and 20 minutes there, in the exemplary embodiment.

(20) The finished coating 23 or 33 is approximately 5 μm to 20 μm thick at its thinnest point, and the diametral pin play of the piston pin or crank journal amounts to about 10 μm to 20 μm. This close play is particularly advantageous for avoiding noise development. The coating 23 or 33 furthermore guarantees that despite the close play, no seizing occurs.

(21) Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.