Powertrain of an internal combustion engine with piston and connecting rod

A powertrain for an internal combustion engine having a connecting rod with a piston supported at one end which is adapted for easy assembly and disassembly without expensive tools. The piston is supported on the connecting rod by a universal joint defined by a spherical surface of an integral connecting rod end and an end plate of the piston having a correspondingly configured spherical recess. The connecting rod end is formed with flat surfaces on opposed sides for engagement by releasable securement members which maintain the piston in proper seated position on the connecting rod during normal usage, but which are releasable to permit removal of the piston upon rotation of the connecting rod 90° about its longitudinal axis.

FIELD OF THE INVENTION

The present invention relates generally to powertrains for internal combustion engines, and more particularly, to an improved connecting rod and piston arrangement for use in such engines.

BACKGROUND OF THE INVENTION

The connecting rod of internal combustion engines typically consist of a connecting-rod shank and two end bearings, which link the piston and the corresponding crank pin of a crankshaft to a powertrain. One end performs oscillating motions, the other moves with the crank pin in the crank circle, so that a so-called “violin-shaped connecting rod,” i.e., a violin-shaped motion curve of the connecting rod, is created.

From DE 35 05 964 C1, a powertrain with a connecting rod is known, which comprises, in a typical way, an end bearing in the form of a connecting-rod head, i.e., the upper connecting-rod eye, a connecting-rod shank, and an opposite end bearing in the form of the connecting-rod bearing, i.e., the lower connecting-rod eye. Such an arrangement represents a connecting-rod element between the straight part of a crank drive, thus to the piston, and the crankshaft. The connecting-rod head can be complete or in parts. The bearing cover of the divided connecting-rod bearing, thus of the lower connecting-rod eye, is connected to the connecting-rod foot by at least two fitted strain screws. The connecting-rod bearing is formed by the connecting-rod foot and connecting-rod cover, in which bearing shells expand into a complete bearing sleeve. In addition, such connecting-rod bearing receives the crank pin and associated impact-like stresses when the pressure changes, which produce high bearing loads. Because the connecting rod must be guided partially through the engine cylinder when the piston is assembled, at least for a strong crank pin the lower connecting-rod eye or the connecting-rod shank generally had to be divided.

The piston operates under great mechanical and thermal loads. At the same time it must perform several tasks, such as the conversion of pressure energy into mechanical work, sealing of the cylinder chamber from the crankcase, and straight guidance of the upper end of the connecting rod in so-called trunk piston engines. The bearing of the piston on the connecting-rod head has included a piston bolt in the connecting-rod eye, which transferred the forces evenly between piston and connecting rod. Previously, the position of the piston bolt had been determined by two factors. To prevent tipping motions of the piston, its center of gravity should lie on the axis of the bolt. On the other hand, the piston bolt must be fixed in the center of the shaft of the piston so that the normal force is transferred uniformly to the cylinder wall. Because both demands cannot be satisfied simultaneously, the piston bolt previously had been installed slightly above the center of the shaft.

Large pistons of a known type have been made of two or more parts. Thus, the piston base, e.g., made from steel or case iron, is screwed together with the shaft, e.g., made from special cast iron or an aluminum alloy.

From DE 100 46 214 C1, a powertrain is further known, for which a connecting rod is used in the form of a marine head with a one-part connecting-rod shank (which means savings in terms of weight and cost, compared with a connecting-rod shank divided for assembly reasons), which features a special configuration of connecting-rod bearing for receiving the crank pin, and thus enables a compact construction. For this reason, a smaller overall engine height also is possible and the drawing of the piston through the engine cylinder is eased considerably.

Now there is also the need to optimize the bearing of the piston on the connecting-rod head, which had been effected previously by means of a piston bolt, which transfers the forces between the piston and the connecting rod and the connecting-rod eye. In particular, there is the need to form this piston/connecting-rod connection more compactly and to make the piston assembly even simpler.

OBJECTS AND SUMMARY OF THE INVENTION

Starting with the foregoing background, it is an object of the present invention to provide a powertrain with an improved bearing for the piston on a connecting-rod head.

Another object is to provide a powertrain as characterized above in which piston assembly and disassembly is possible without expensive tools.

A further object is to provide a powertrain of the above kind which is lighter in weight and which can be more economically produced.

In carrying out the invention, the powertrain has a ball bearing/universal ball joint which permits elimination of a piston bolt typically required of the prior art, which substantially reduces oscillating mass. Instead, release of the bearing can be effected by turning the piston about its axis before permitting the piston to be drawn from the engine block without the connecting rod. Hence, division of the connecting rod shank also can be eliminated without necessity for realizing the specially configured connecting rod bearing according to DE 100 46 214 C1. Hence further weight reduction and cost savings can be obtained, as well as lower dynamic operating forces.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now more particularly to the drawings, there is shown an illustrative powertrain in accordance with the invention which includes a connecting-rod1having a unitary or undivided connecting-rod head2extending at one end of a connecting-rod shank4having a piston3supported thereon and a connecting-rod foot5, as depicted inFIGS. 4 and 5, at the other end of the shank4for connection to the crankshaft of a power driven engine. The connecting-rod foot5in this case has a connecting-rod cover7fixed to the foot5by means of tension screws6ato form a lower crankshaft receiving connecting-rod eye8. The connecting-rod eye8in this instance has two bearing shells10a,10bwhich expand into a complete bearing sleeve that surrounds the crank shaft and retains a crank pin in rotatable sliding contact. For lubricating the connecting-rod head2and for also cooling the piston, the connecting-rod shank4has an axial oil bore hole9drilled lengthwise through the shank for communication with a lubrication distribution system22that opens at the connecting-rod head2.

The bearing support of the piston3on a connecting-rod head2includes a universal ball joint part11which has a spherical bearing surface12on its outer periphery. Opposite the outer connecting-rod head bearing surface12is a correspondingly spherical bearing seat formed in a end plate13which axially retains the universal ball joint part11while permitting relative pivotal movement about a universal ball joint center relative to the end plate. As depicted inFIG. 2, the bearing surface defined by the outer spherical periphery12of the universal ball joint part11extends on both sides of a universal ball joint center plane14that extends through the points of the universal ball joint part at its greatest diameter. In the preferred embodiment, the connecting-rod head2is configured as the spherical universal ball joint part11and the end plate13forms base or end15of the piston, which is configured with the spherical bearing seat reverse the configuration of the ball joint part11. The piston in this case, as depicted inFIG. 2, has a two part construction consisting of a top part or piston base15and a bottom part or piston shaft20. Alternatively a piston could be formed in three parts in a known manner, consisting of a piston cap, piston shroud, and piston bottom part. Piston base15and piston shaft20in this case are connected to each other by appropriate fastening screws21.

In the illustrated embodiment, as depicted inFIG. 1, the bottom part20of the piston3has an interior adapted for receiving the connector rod head2adjacent the bearing seat defined by the end plate13. The connecting-rod head2and the piston define at least two recesses17,18on diametrically opposed sides of the connecting-rod head2.

In carrying out the invention, rotational securement element23a,23bare respectively disposed within the recesses17a,17bon opposed sides of the connecting-rod head2, as depicted inFIG. 6, and are fixed within the piston bottom part20by screws24. The spherical universal ball joint11, defined by the spherical connecting-rod head2, is formed with a pair of flattened wall sections16a,16bwhich are retained by the rotational securement elements23a,23bto prevent relative rotation of the piston and connecting-rod head about a long axis of the connecting-rod. The rotational securement members23a,23btherefore each can be fixed within the piston by means of the screws24when in assembled position occupying the recesses17a,17bon opposite sides of the connecting-rod head2, or they can be released to permit removal of the piston as will become apparent. To ensure reliable permanent lubrication of the ball bearing/universal ball joint11,13a lubricating reservoir is provided in front of the spherical surface18of the end plate13which can be appropriately sealed on the engine side.

Thus, consistent with an important feature of the invention, a ball bearing/universal ball joint11,13is provided that has a bearing body11formed with a spherical outer surface12immersed in a lubricating means and held against an annular or partially spherical surface at its axially end in the pot-like recess of the end plate13and the separation of the connecting-rod1from the piston3can be effected simply by removal of the rotational securement elements23a,23bfor allowing rotation of the piston3relative to the connecting-rod by 90°, which permits positioning of the spherical surfaces of the connecting-rod head into the recesses17a,17band the flattened wall sections16a,16bof the connecting-rod head opposite the spherical surfaces of the end plate so that separation of the positive lock of the ball bearing/universal ball joint11,13is effected and the piston can be easily removed from the connecting-rod head2.

The configuration of the ball bearing/universal ball joint11,13according to the invention further improves the direct gas-force transmission to the connecting-rod shank4. The previously used piston bolt deployed in such connecting rod arrangements can be eliminated. Hence, the oscillating mass of the connecting rod is reduced significantly, as much as 20%, and frictional resistance also becomes smaller overall.

It will also be appreciated that division of the connecting rod shank into multiple components is no longer necessary, because drawing of the piston3through the engine cylinder can now take place in a simple way when the connecting rod is completely detached. Further savings are achieved by reason of reduced weight and cost. The piston disassembly also can be performed without expensive or hydraulic tools. Thus a small overall piston height further can be achieved.