METHOD FOR PRODUCING A UNIT CONSISTING OF ECCENTRIC ROD AND PISTON OF A CONNECTING ROD OF AN INTERNAL COMBUSTION ENGINE

Abstract

A method is provided for producing an assembly of an eccentric rod (15, 16) and a piston (20, 21) of a connecting rod of an internal combustion engine having an adjustable compression ratio. The method includes providing an eccentric rod (15, 16) having a first end (36, 37) for attachment to an eccentric lever of an eccentric adjusting device of the connecting rod and a second end (38, 39) for attachment to a piston (20, 21) that can be guided in a hydraulic chamber of the connecting rod. The method then includes arranging the second end (38, 39) of the eccentric rod (15, 16) in the piston (20, 21); introducing an injection-molding tool (47) into the piston (20, 21); and injection-molding a circumferentially closed retaining ring (43) between the piston (20, 21), the second end (38, 39) of the eccentric rod (15, 16) and the injection-molding tool (47).

Claims

1. A method for producing an assembly that includes an eccentric rod and a piston of a connecting rod of an internal combustion engine that has an adjustable compression ratio, the method comprising: providing the eccentric rod having a first end for attachment to an eccentric lever of an eccentric adjusting device of the connecting rod and a second end for attachment to a piston that is configured to be guided in a hydraulic chamber of the connecting rod; providing the piston which, in the mounted state of the connecting rod, is guided in the hydraulic chamber of the connecting rod; arranging the second end of the eccentric rod in the piston; introducing an injection-molding tool into the piston; injection-molding a circumferentially closed retaining ring between the piston, the second end of the eccentric rod and the injection-molding tool; and removing the injection-molding tool.

2. The method of claim 1, wherein the second end of the eccentric rod is a ball head and the piston has a ball shell segment, the step of arranging the second end of the eccentric rod in the piston comprises inserting the ball head at the second end of the eccentric rod partially into the ball shell segment in the piston, the step of introducing the injection-molding tool into the piston comprises placing the injection-molding tool on a portion of the ball head that projects out of the ball shell segment, and wherein the step of injection-molding the circumferentially closed retaining ring comprises forming the circumferentially closed retaining ring between the piston, the portion of the ball head that projects out of the ball shell segment of the piston, and the injection-molding tool.

3. The method of claim 2, wherein the step of placing the injection-molding tool on a portion of the ball head that projects out of the ball shell segment comprises placing the injection-molding tool on the portion of the ball head that projects out of the ball shell segment of the piston so that the ball head is pressed against the ball shell segment; the method further comprising displacing at least one of the ball head and the injection-molding tool in a defined manner relative to the piston to set a defined gap between the ball head and ball shell segment; and forming the circumferentially closed retaining ring by injection-molding between the piston, the portion of the ball head that projects out of the ball shell segment of the piston, and the injection-molding tool.

4. The method as claimed in claim 3, wherein the defined gap between a portion of the ball head that projects into the ball shell segment of the piston and the ball shell segment is set so that no injection-molding material enters this gap during injection-molding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 shows a connecting rod of an internal combustion engine known from the prior art having an adjustable compression ratio.

[0019] FIG. 2 shows a detail of a first connecting rod according to the invention.

[0020] FIG. 3 shows the detail of FIG. 2 during the production thereof.

DETAILED DESCRIPTION

[0021] An internal combustion engine with an adjustable compression ratio has at least one, preferably a plurality of, cylinder(s). Each cylinder has a piston that is coupled to a crankshaft of the internal combustion engine by a connecting rod 10.

[0022] Each connecting rod 10 has a small end bearing eye 12 at one end and a big end bearing eye 11 at an opposite end. The respective connecting rod 10 acts by way of its big end bearing eye 11 on a crankshaft bearing pin of the crankshaft in such a way that a connecting rod bearing shell is positioned between the crankshaft bearing pin and the big end bearing eye, with a lubricating oil film being able to build up between the connecting rod bearing shell and the crankshaft bearing pin.

[0023] An internal combustion engine with an adjustable compression ratio has, in the region of each connecting rod 10, an eccentric adjusting device 13 for adjusting the effective connecting rod length of the respective connecting rod 10.

[0024] The eccentric adjusting device 13 has an eccentric, an eccentric lever 14 and eccentric rods 15, 16 that can be displaced to adjust the compression ratio in dependence on a hydraulic pressure that prevails in hydraulic chambers interacting with the eccentric rods. The hydraulic chambers interacting with the eccentric rods 15, 16 can be supplied with hydraulic oil starting from the big end bearing eye 11 of the respective connecting rod.

[0025] The adjustment of the eccentric adjusting device 13 is initiated by the action of inertia forces and load forces of the internal combustion engine.

[0026] The eccentric rods 15, 16 act by first ends 36, 37 on the eccentric lever 14. Eccentric rods 15, 16 are fastened by opposite second ends 38, 39 to the respective piston 20, 21 that is guided in a respective hydraulic chamber 22, 23 of the connecting rod 10.

[0027] FIG. 2 shows a detail of an eccentric rod 15, 16 in the region of a second end 38, 39 of the respective eccentric rod 15, 16, with the respective eccentric rods 15, 16 being designed as a ball head in the region of these second ends 38, 39.

[0028] This second end 38, 39 of the respective eccentric rod 15, 16 that is designed as a ball head projects by a first portion 40 into a corresponding ball shell segment 41 of the respective piston 20, 21 and projects by a portion 42 out of this ball shell segment 41.

[0029] The second end 38, 39 of the respective eccentric rod 15, 16 is secured in the respective piston 20, 21 via a circumferentially closed retaining ring 43 that forms a type of ball shell segment 44 against which there bears the portion 42 of the ball head that projects out of the ball shell segment 41 of the respective piston 20, 21. As already stated, this retaining ring 43 is closed in the circumferential direction and has a central aperture 45 through which the eccentric rod 15, 16 extends. As shown in FIG. 2, the circumferentially closed retaining ring 43 engages behind an undercut 46 in the respective piston 20, 21, with the result that the second end 38, 39 of the respective eccentric rod 15, 16 is captively guided in the respective piston 20, 21 via the respective closed retaining ring 43.

[0030] The invention therefore relates to a method for simply and reliably producing such an assembly of an eccentric rod 15, 16 and a piston 20, 21 acting on the second end 38, 39 of the eccentric rod 15, 16, together with a closed retaining ring 43.

[0031] For this purpose, there is first provided the respective eccentric rod 15 with first and second ends 36, 37 and the eccentric rod 16 with first and second ends 38, 39. The respective first ends 36, 37 of the eccentric rod 15, 16 attach to the eccentric lever 14, and the respective second ends 38, 39 attach to the respective piston 20, 21.

[0032] The pistons 20, 21, in the mounted state of the connecting rods, are guided in hydraulic chambers 22, 23 thereof.

[0033] In addition to the respective eccentric rod 15, 16, the respective piston 20, 21s also is provided.

[0034] The second end 38, 39 of each of the eccentric rods 15, 16 is a ball head arranged in the respective piston 20, 21 so that the ball head of the eccentric rod 15, 16 has a portion 40 that projects into a ball shell segment 41 of the respective piston 20, 21. A portion 42 of the ball head that adjoins the portion 40 of the ball head that projects into the ball shell segment 41 projects out of the ball shell segment 41 of the respective piston 20, 21.

[0035] Subsequent to arranging the respective second end 38, 39 of the eccentric rod 15, 16 in the respective piston 20, 21, an injection-molding tool 47 (see FIG. 3) is introduced partially into the respective piston 20, 21, with a portion 47a of the injection-molding tool 47 that projects into the piston 20, 21 pressing against the portion 42 of the ball head that projects out of the ball shell segment 41 of the second end 38, 39 of the eccentric rod 15, 16.

[0036] After arranging the injection-molding tool 47 with the portion 47a in the piston 20, 21, the circumferentially closed retaining ring 43 is formed by injection-molding with the aid of the injection-molding tool 47.

[0037] The injection-molding tool 47 then is removed from the piston 20, 21.

[0038] During injection-molding, the circumferentially closed retaining ring 43 is formed between the portion 42 that projects out of the ball shell segment 41 of the piston 20, 21 of the respective second end 38, 39 of the eccentric rod 15, 16 and the piston 20, 21 and the injection-molding tool 47. A clearance between the portion 47a of the injection-molding tool 47 that projects into the piston 20, 21, the piston 20, 21 and the portion 42 of the second end 38, 39 of the eccentric rod 15, 16 that is designed as a ball head, is filled with injection-molding material to form the circumferentially closed retaining ring 43 with engagement behind the undercut 46 of the piston 20, 21. The circumferentially closed retaining ring 43 then is accommodated captively in the piston 20, 21 and thus also captively retains the piston 20, 21 on the second end 38, 39 of the eccentric rod 15, 16.

[0039] The portion 47a of the injection-molding tool 47 is placed on the portion 42, that projects out of the ball shell segment 41 of the piston 20, 21, of the second end 38, 39 of the respective eccentric rod 15, 16 that is designed as a ball head in such a way that the ball head at the second end 38, 39 of the eccentric rod 15, 16 presses by way of the portion 40 against the ball shell segment 41 of the piston 20, 21. The ball head at the second end 38, 39 of the eccentric rod 15, 16 together with the portion 47a of the injection-molding tool 47 then are displaced relative to the piston 20, 21 in a defined manner to set a defined gap 48 between the ball head at the second end 38, 39 of the eccentric rod 15, 16 and the ball shell segment 41 of the piston 20, 21. This gap 48 is set and dimensioned so that no injection-molding material enters the gap 48 during injection-molding. After setting this defined gap 48, the circumferentially closed retaining ring 43 is formed by injection-molding, namely by filling the cavity between the portion 47a of the injection-molding tool 47, the piston 20, 21 and the portion 42 of the ball head with injection-molding material, with the gap 48 not being filled by injection-molding material. As a result, after injection-molding the circumferentially closed retaining ring 43, the gap 48 ensures a good articulated attachment of the second end 38, 39 of the eccentric rod 15, 16 to the respective piston 20, 21.

[0040] A thermoplastic such as polyether ether ketone preferably is used as injection-molding material.