Title

Connecting rod for an internal combustion engine with adjustable compression ratio Background

Internal combustion engines with adjustable compression ratio are commonly known from the prior art.

By way of example, prior art documents DE 10 2012 020 999 A1 , DE 10 2013 014 090 A1 and DE 10 2005 055 199 A1 disclose internal combustion engines with a cylinder piston and a crank shaft coupled with each other by means of a connecting rod having an adjustable effective length e.g. in order to increase fuel efficiency of the internal combustion engines under varying loads.

The connecting rod comprises a crank pin bearing eye for connecting the connecting rod to the crank shaft on the one hand and a connecting rod bearing eye for connecting the connecting rod to a cylinder piston on the other hand. In order to adjust the effective length of the connecting rod, the connecting rod comprises an eccentrical element adjustment device for adjusting the effective length of the connecting rod. For this purpose, the eccentrical element adjustment device comprises an eccentrical element including a bore hole for receiving a piston pin, an eccentrical element lever non-rotatably connected to the eccentrical element and two eccentrical element rods engaging the eccentrical element lever. The eccentrical element rods are operatively connected to hydraulic cavities in the body of the connecting rod in order to generate a force onto the eccentrical element rods generated by hydraulic pressure. The eccentrical element lever is thereby actuated by the eccentrical element rods.

The hydraulic cavities are loadable with hydraulic oil through hydraulic oil conduits from the crank pin bearing eye. The crank pin bearing eye and the crank shaft pin both have a cylindrical shape. During operation of the internal combustion engine, there is an inherent oil flow in the axial direction of the crank pin bearing eye. The axial flow leads to a reduction of oil pressure in the hydraulic cavities of the connecting rod. Thereby, the fuel efficiency of the internal combustion engine is restricted. Summary of the invention

It is therefore an object of the present invention to provide an internal combustion engine machine with an adjustable compression ratio which is less prone to oil pressure reduction in the hydraulic cavities.

The object of the present invention is achieved by a connecting rod for an internal combustion engine with an adjustable compression ratio comprising a crank pin bearing eye for connecting the connecting rod to a crank shaft of the internal combustion engine, a connecting rod bearing eye for connecting said connecting rod to a cylinder piston of said internal combustion engine and an eccentrical element adjustment device for adjusting the distance between said crank pin bearing eye and said connecting rod bearing eye, wherein said eccentrical element adjustment device comprises an eccentrical element including said connecting rod bearing eye, an eccentrical element lever and eccentrical element rods engaging the eccentrical element lever, wherein said eccentrical element rods are actuated with a force generated by hydraulic pressure in hydraulic cavities, wherein the crank pin bearing eye comprises a first bearing surface designed to contact a second load bearing surface of said crank shaft in a load-bearing area that bears the forces acting between the crank pin bearing eye and the crank shaft when the internal combustion engine is operated, wherein the first bearing surface of the crank pin bearing eye has a convex profile.

The object of the present invention is further achieved by an internal combustion engine with an adjustable compression ratio comprising a crank shaft and at least one connecting rod comprising a crank pin bearing eye for connecting the connecting rod to the crank shaft, a connecting rod bearing eye for connecting said connecting rod to a cylinder piston of said internal combustion engine and an eccentrical element adjustment device for adjusting an effective connecting rod length, wherein said eccentrical element adjustment device comprises an eccentrical element including a bore hole for receiving a piston pin, an eccentrical element lever and eccentrical element rods engaging the eccentrical element lever, wherein said eccentrical element rods are actuated with a force generated by hydraulic pressure in hydraulic cavities, wherein a first bearing surface of the crank pin bearing eye and a second bearing surface of the crank shaft and are in close contact to one another in a load-bearing area that bears the forces acting between the crank pin bearing eye and the crank shaft when the internal combustion engine is operated, wherein the second bearing surface of the crank shaft in its load-bearing area features a concavely curved profile in the longitudinal shaft section and that the bearing surface of the crank pin bearing eye features a convex profile being in close contact with the concave profile of the crank shaft.

According to the present invention, it is thereby advantageously possible to increase inflow to the oil chambers from the crank pin bearing eye. During operation of the internal combustion machine the crank pin bearing eye and the crank pin of the crank shaft are subject to tensile forces and compression forces that elastically deform the crank pin bearing eye as well as the crank pin. Alternately, small gaps are opening and closing between the bearing surfaces of the crank pin bearing eye and the crank pin which result in a sucking effect that pumps hydraulic oil inside the gap between the respective bearing surfaces. Thus, the convex profile of the crank pin bearing eye and the concave profile of the crank pin of the crank shaft create an oil pocket at the bearing surface. Compared to the state of the art connecting rods for variable compression internal combustion engines with cylindrical profiles of the crank pin bearing eye and the crank shaft pin the amount of oil available for transport into the hydraulic cavities and the pressure of the oil is increased. Thereby, the eccentrical element adjustment device may be properly operated to influence the effective length of the connecting rod. Adjustment of the compression ratio is not compromised. Thus, it is possible to more reliably control the fuel efficiency and reduce C0 ₂ emissions of the internal combustion engine.

According to the present invention, it is thereby advantageously possible to reduce outflow of hydraulic oil from the crank pin bearing eye by changing the profile configuration, i.e. convergence and / or divergence levels between connecting rod and crankshaft surfaces. Furthermore, the curved profiles of the bearing surfaces allow an effective lubrication of the bearing surfaces because operating displacements and / or elastic deformations of the crank drive result in an oil pump effect between the cooperating convex and concave bearing surfaces. The concave curvature of the second bearing surface of the crank shaft is also advantageous for oil lubrication between the second bearing surface of the crankshaft and the adjoining first bearing surface of the crank pin bearing eye. When the crank drive is operated the crankshaft works under tensile and compression strength due to the inertia and gas load effects. Under tensile and compression forces the crank pin and the crank pin bearing eye mounted thereon are deformed elastically such that small gaps of a few micrometers are opened and closed in the load-bearing area. When the throw of the connecting rod is under tensile load oil that drips from the piston after the jet oil flow has cooled and lubricated the piston pin region is captured in a first region of the crank pin which is facing towards the small end of the connecting rod. A second region of the crank pin located opposite of the first region and therefore facing away from the small end of the connecting rod works as a guiding for the connecting rod and also to pump the captured oil to the center of the crank pin. When the throw is under compression the first region works as a guide for the connecting rod and also to pump oil to the center of the crank pin.

The first bearing surface of the crank pin bearing eye may have a convex profile in the longitudinal crank shaft section. In other words, the convex profile of the first bearing surface may be a curve arranged in a plane, wherein the plane includes the longitudinal axis of the connecting rod and the plane is perpendicular to an opening area of the crank pin bearing eye.

It is preferred that the clearance between the first bearing surface of the crank pin bearing eye and the second bearing surface of the crank shaft varies in a direction parallel to a longitudinal crank shaft axis. In other words, the curvature of the first bearing surface of the crank pin bearing eye and the curvature of the second bearing surface of the crank shaft do not match. The bearing surfaces are either converging or diverging in longitudinal shaft section thereby adjusting axial oil outflow.

According to the present invention, it is preferred that a hydraulic oil conduit extends from one of said hydraulic cavities to an aperture in the first bearing surface of the crank pin bearing eye. Oil may be supplied to the hydraulic oil conduit from the crank pin bearing eye through the aperture. Thus the oil pocket created at the bearing surfaces may supply a hydraulic cavity with oil via the hydraulic oil conduit.

According to the present invention, it is preferred that the aperture is arranged close to, in particular on, a vertex of the convex profile of the first bearing surface. The oil pocket created at the first bearing surface has its maximum close to, in particular at, the vertex of the convex profile. By having the aperture arranged in that region of the first bearing surface of the crank pin bearing eye the oil supply to the hydraulic oil conduit is further improved. The aperture may either be arranged on a shank portion of the connecting rod or on a cap portion of the connecting rod, wherein the cap portion is connected to the shank portion, e.g. by means of a screw.

According to another preferred embodiment of the present invention, the first bearing surface features a curved profile that is symmetrical to the longitudinal axis of the connecting rod extending between the center of the crank pin bearing eye and the center of the connecting rod bearing eye.

These and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accom- panying drawings, which illustrate, by way of example, the principles of the invention. The description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

Brief description of the drawings illustrates schematically a connecting rod for an internal combustion engine with an adjustable compression ratio according to an exemplary embodiment of the present invention.

Figure 2 illustrates schematically part of a crank shaft and part of a connecting rod for an internal combustion engine with an adjustable compression ratio according to another exemplary embodiment of the present invention in a sectional view onto a plane including the crank shaft axis.

Figure 3 illustrates schematically part of a crank shaft and part of a connecting rod for an internal combustion engine with an adjustable compression ratio according to yet another exemplary embodiment of the present invention in a sectional view onto a plane including the crank shaft axis.

Detailed description

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Where an indefinite or definite article is used when referring to a singular noun, e.g. "a", "an", "the", this includes a plural of that noun unless something else is specifically stated.

Furthermore, the terms first, second, third and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

In figure 1 , an exemplary connecting rod for an internal combustion engine having an adjustable compression ratio is shown.

The connecting rod 1 is provided for connecting a crank shaft (not shown) of the internal combustion engine with a cylinder piston (not shown) of the internal combustion engine. For this approach, the connecting rod 1 comprises a crank pin bearing eye 2 for connecting the connecting rod 1 to the crank shaft and a connecting rod bearing eye 3 for connecting the connecting rod 1 to the cylinder piston. The connecting rod 1 has a shank portion 14 and a cap portion 15 which are connected by connection elements 16, e.g. screws.

The internal combustion engine has an adjustment mechanism to adjust the compression ratio inside the cylinder. This is achieved by adjusting the effective length l _eff of the connecting rod 1 . In order to adjust the effective length l _eff of the connecting rod 1 , the connecting rod 1 comprises an eccentrical element adjustment device 4 for adjusting the distance l _eff between the center of the crank pin bearing eye 2 and the center of a bore hole 7 of the eccentrical element 5 which is suited for receiving a piston rod.

The eccentrical element adjustment device 4 comprises the eccentrical element 5 with the bore hole 7. The eccentrical element 5 is non-rotatably connected to an eccentrical element lever 6. The eccentrical element lever 6 comprises a through bore in which the eccentrical element 5 is mounted. The bore hole 7 is located outside the rotational center of the eccentri- cal element 5, so that rotating the eccentrical element 5 varies the distance between the center of the bore hole 7 and the center of the crank pin bearing eye 2. The eccentrical element lever 6 is torque-proof and non-rotatably connected to the eccentrical element 5, so that a rotation the eccentrical element 5 can be initiated by rotating the eccentrical element lever 6. For this purpose, the eccentrical element lever 6 comprises two fixation points provided on opposite sides of the eccentrical element lever 6. In each fixation point one end of an eccentrical element rod 8 is mounted by means of a bolt. The other end of the eccentrical element rod 8 is linked to a supporting piston that is operatively connected to a hydraulic cavity 9 provided in the body of the connecting rod 1 . The hydraulic cavity 9 is filled with oil in order to generate a force onto the eccentrical element rods 8 generated by hydraulic pressure. The function of the hydraulic system and the eccentrical element rods 8 rotating the eccentrical element lever 6 is explained e.g. in prior art document DE 10 2013 014 090 A1 .

The torque-proof and non-rotatably connection between the eccentrical element 5 and the eccentrical element lever 6 is realized by a form-fit connection: The outer circumferential surface of the eccentrical element 5 is provided with a plurality of teeth extending outwardly from the eccentrical element 5 and engaging a corresponding teeth and groove structure at the inner border of the through bore 7 in the eccentrical element lever 6. Alternatively, a welded connection between the eccentrical element 5 and the eccentrical element lever 6 may be applied.

In figure 2, a crank shaft 20 and a connecting rod 1 of an internal combustion engine with an adjustable compression ratio is illustrated in a sectional view onto a plane including the crank shaft axis C.

The crank pin bearing eye 2 comprises a first bearing surface 10 designed to contact a second load bearing surface 21 of said crank shaft 20 in a load-bearing area that bears the forces acting between the crank pin bearing eye 2 and the crank shaft 20 when the internal combustion engine is operated, wherein the first bearing surface 10 of the crank pin bearing eye 2 has a convex profile. The first bearing surface 10 of the crank pin bearing eye 2 and a second bearing surface 12 of the crank shaft 20 are in close contact to one another in a load- bearing area that bears the forces acting between the crank pin bearing eye 2 and the crank shaft 20 when the internal combustion engine is operated, wherein the second bearing surface 12 of the crank shaft 20 in its load-bearing area features a concavely curved profile in the longitudinal shaft section and that the bearing surface 10 of the crank pin bearing eye 2 features a convex profile being in close contact with the concave profile of the crank shaft 20. Thereby, necessary oil pressure can be maintained in the hydraulic cavities 9 so as to be able to control the effective length of the connecting rod 1 in order to allow for fuel efficient operation of the internal combustion engine.

As depicted in figure 2, a hydraulic oil conduit 1 1 extends from one of the hydraulic cavities (not shown) to an aperture 12 in the first bearing surface 10 of the crank pin bearing eye 2. The hydraulic oil conduit 1 1 is arranged in a shank portion 14 of the connecting rod 1. The aperture 12 is arranged close to, in particular on, a vertex V of the convex profile of the first bearing surface 10. The convex profile of the first bearing surface is a curved profile that is symmetrical to the longitudinal axis L of the connecting rod 1 extending between the center of the crank pin bearing eye 2 and the center of the connecting rod bearing eye 3.

The convex curvature of the first bearing surface 10 is also advantageous for oil lubrication between the first bearing surface 10 of the connecting rod 1 and the second bearing surface 21 of the crank shaft 20. During operation of the internal combustion engine the crank shaft 20 works under tensile and compression forces due to the inertia and gas load effects. Under the tensile and compression forces the crank pins of the crank shaft 20 and the crank pin bearing eye 2 mounted thereon are deformed elastically such that small gaps of few micrometers are opened and closed in the edge region of the convex profile of the crank pin bearing eye 2. Those gaps restrict axial oil flow and lead the oil in the direction of the vertex V of the convex profile, thus, towards the aperture 12 of the hydraulic oil conduit 1 1 . Thus an oil pump effect is achieved which increases the oil flow into the hydraulic cavities 9.

In figure 3, a crank shaft 20 and another embodiment of a connecting rod 1 of an internal combustion engine with an adjustable compression ratio is illustrated in a sectional view onto a plane including the crank shaft axis C.

In contrast to the embodiment depicted in figure 2, a hydraulic oil conduit 1 1 is arranged in a cap portion 15 of the connecting rod 1 . The oil conduit 1 1 connects to an oil cavity (not shown). The cap portion 15 is connected to the shank portion 14 of the connecting rod 1 by screws 16. The hydraulic oil conduit 1 1 ends in an aperture 12 in the first bearing surface 10 of the crank pin bearing eye 2. Thus, the aperture 12 is arranged in the cap portion 14 of the connecting rod 1. The aperture 12 is arranged close to, in particular on, a vertex V of the convex profile of the first bearing surface 10. The convex profile of the first bearing surface is a curved profile that is symmetrical to the longitudinal axis L of the connecting rod 1 extending between the center of the crank pin bearing eye 2 and the center of the connecting rod bearing eye 3. Similar to the embodiment depicted in figure 2, an oil pump effect is achieved that increases the oil flow into the hydraulic cavities 9 via the conduit 1 1 .

According to yet another embodiment not depicted in the figures, the connecting rod 1 features oil conduits 1 1 in both the shank portion 14 and the cap portion 15. Apertures at the crank pin bearing eye 2 may be arranged both in the shank portion 14 and the cap portion 15.

Reference signs

1 connecting rod

2 crank pin bearing eye

3 connecting rod bearing eye

4 eccentrical element adjustment device

5 eccentrical element

6 eccentrical element lever

8 eccentrical element rod

9 hydraulic cavity

10 bearing surface

1 1 hydraulic oil conduit

12 aperture

13 supporting piston

14 shank portion

15 cap portion

16 connection element

20 crank shaft

21 bearing surface

C longitudinal crank shaft axis le _ff effective length

L longitudinal axis

V vertex