- crankshaft with cold-rolled fillets with induction hardening
- cylinder liner and piston rings coated with wear-resistant ceramic
These breakthroughs have been well-proven through the accelerated fatigue testing of individual components and other fundamental testing and analysis as well as through the longterm endurance tests of the prototype 6ADD30V.
e) easy maintenance
External piping and flange connections are greatly reduced by using drilled holes and air starters which require no piping along the engine. It makes the maintenance job easier.
Fig. 4 Breakthroughs Against Increased Power Rate
3. Design Features
The principal breakthroughs shown in Fig. 4 are described below.
3.1 Engine Frame
The engine frame composed of cylinder and crankcase parts is the key to weight-reduction since it comprises a third of the total weight. Instead of conventional cast iron or nodular cast iron, the engine frame is the welded integral of steel modules which ensures high rigidity to withstand high cylinder pressure and high inertia force as keeping the weight low. The engine frame is devided into several steel modules with simple shape in which cast steel is extensively used, and the whole is welded into an integral structure, as shown in Fig.5. This module construction is advantageous for mass-production, keeping common modules in stock.
The cylinder liner of free standing type makes it possible to reduce the weight of a cylinder part, since a gas force is transmitted to a crankcase part through a cylinder liner made of high-strength steel which can be used owing to the wear-resistant ceramic described later.
The module profile and the welded sections are well-designed through 3-D FEM analysis and the experiment with a test model under various loading conditions, taking both casting and welding qualities into consideration. The durability was confirmed through the accelerated hydraulic fatigue test of the 2-cylinder model of the actual size. The stress measurement made with the prototype 6ADD30V shows that the max. alternative stress is as low as 25MPa.
3.2 Crankshaft
The crankshaft is a RR-forged integral. Journals and crankpins are induction-hardened and thereafter all the fillets are subjected to cold-rolling which compensates for residual tensile stress caused on the fillets by induction-hardening. The cold-rolled fillets ensure higher fatigue strength. The measured max. alternative stress is 190MPa on the prototype 6ADD30V, while the measured fatigue stress is approximately 800MPa on the cold-rolled crankthrow of the actual size[1]. The main bearing is a tri-metal type of leaded copper overlaid without nickel plating to be seizure-proof after the overlay is completely worn. The min. oil film thickness is more than 10μm.
The crankpin bearing is a tri-metal type of leaded tin bronze with the same overlay as the main bearing. Unsymmetrical oil grooves are provided to minimize the cavitation erosion as well as to increase the loading capacity.
