As known to those skilled in the art, reciprocating engines with hydrodynamic bearings typically use separate steel or iron main caps to mount and support the crankshaft to the cylinder block (regardless of the cylinder block material). The main caps are independently bolted with two or four vertical bolts per main cap. Additionally, in some case, the main caps can be tied to a deep skirted cylinder block via horizontally disposed bolts, for example, two bolts per main cap. The deep-skirt can either be integral to the cylinder block or be a bolt-on ladderframe. The deep skirt attachment allows for a stiffer cylinder block structure, which in turn can lead to more load capacity, higher power output and better noise, vibration and harshness (NVH) characteristics.
Referring now to FIG. 1, there is shown an illustrative reciprocating engine having a hydrodynamic cranktrain including a crankshaft 10, a connecting rod with a connecting rod big end and a plain bearing that is disposed between a surface of the crankshaft and an opposing surface of the connecting rod big end. In such an engine, the crankshaft 10 is rotatably supported by the main plain bearing(s) or hydrodynamic bearings 12 that are secured between the cylinder block 14 and the main bearing cap(s) 16, which are secured to the block. In such an engine, the piston is movably received in a cylinder and is rotatably coupled to the crankshaft by the connecting rod.
The hydrodynamic bearing 12 typically is arranged so as to have shell halves that are fit into the cylinder block 14 and the main bearing cap. Typically, such a hydrodynamic bearing 12 is circular and of uniform thickness in the radial direction, for example, a thickness in the radial direction of approximately 2 mm.
During the installation process, the cylinder block 14 is typically inverted when the crankshaft 10 is being installed on the bearing halve(s) that are fit into the cylinder block. Thereafter, the other bearing halve(s) are located and the main bearing cap(s) 16 are installed over the crankshaft. The main bearing cap(s) 16 are then secured to the cylinder block 14 using the main cap bolts 18. The number of main cap bolts 18, are dependent upon a number of factors such as the size and configuration of the engine; however, as shown in the illustrated embodiment, at least two bolts are used to secure the main caps(s) 16 to the cylinder block 14.
For purposes of increasing the strength and rigidity or stiffness of the cylinder block 12, a ladderframe 20 is bolted to the cylinder block 14. Typically the ladderframe 20 extends from a lower surface of the cylinder block 14 and is bolted about the periphery of the ladderframe so as to form a deep skirted cylinder block. There typically is no direct structural joint between the ladderframe and the main caps.
It also should be recognized that in the illustrated embodiment, the cylinder block 14 and ladderframe 20 are made of aluminum; however the main cap(s) 16 are made of a steel or other such material. Consequently, there is differential thermal expansion between the main caps 16 and the cylinder block 14 and the ladderframe 20, which must be taken into account when designing the engine.
As indicated above, plain hydrodynamic bearings are used in conventional reciprocating engines to rotatably support the connecting rod and the crankshaft 10. In order to improve engine performance, it has been considered to replace the plain bearings with roller element or roller type bearings 22 (FIG. 2). Referring now to FIG. 2 there is shown a cross-sectional side view of a cylinder block 24 that is operably coupled to the crankshaft 10 illustrating use of such a roller type bearing using conventional techniques. As with a conventional engine, the connecting rod, more particularly the connecting rod big end 23, is rotatably supported off the crankshaft 10 by a roller bearing that is disposed between a surface of the crankshaft and an opposing surface of the connecting rod big end. Similarly, the crankshaft 10 is rotatably supported by another rolling bearing 24 between the cylinder block and main cap(s) 26.
Such a roller bearing; however, is typically thicker than a hydrodynamic bearing. For example and as shown in FIG. 2, a roller type bearing is approximately 11 mm thick, where the outer steel race is about 3.5 mm in thickness and the caged needle bearings (e.g., plastic caged needle bearings) is approximately 7.5 mm in thickness. As a result of this increased thickness as compared to the typical hydrodynamic bearing, material must be removed from the cylinder block and the bearing caps for use of the thicker rolling bearing element. Removal of such material tends to weaken the cylinder block and the main bearing caps. As there is no direct structural joint between a ladder frame and the main caps, the ladderframe cannot compensate for the loss of strength for the main caps and the cylinder block.
It thus would be desirable to provide a bedplate that connects to the cylinder block and which increases the rigidity of the cylinder block as well as functionally replacing the main caps of a conventional engine. It would be particularly desirable to provide such a bedplate that is made of similar material as the cylinder block so as to minimize the effect of thermal expansion between the bedplate and the cylinder block. It also would be particularly desirable to reduce part counts while maintaining structural requirements. It would be yet further desirable to provide such a bedplate that can be as easily installed as the lower support structures of conventional cylinder blocks and usable with rollerized cranktrains as herein described.