Regarding the structure and casting process of aluminum cyl.blocks, there are numerous types and combinations of such types. Selection of a suitable combination appears to be a source of headaches for all manufacturers concerned. At this time, we would like to introduce the design concepts at Nissan related to this factor.
Nissan has been using aluminum cyl.blocks in the MA series engine for MICRA since 1982. They were developed for application with the super-light engines for the liter car. Now, we have made, new aluminum cyl.blocks for compact and luxury class passenger cars based on the knowledge gained from our latest research and improvements on the MA engines.
VH45 (V8) and SR18,20 (L4) aluminum cyl.blocks were introduced into the market mounted in INFINITI Q45 and G20(PRIMERA) passenger cars since 1989. They have been made lighter by 30kg and 9 kg, respectively, in comparison with the cast iron cyl.blocks of their respective forerunner engines, Y44 and CA18,20 engines, to improve total vehicle performance, for example, acceleration, braking, fuel economy and handling(Fig.1).
With the VH and SR engines, attention was devoted not merely to reduce weight, but to assure functional reliability and to improve NVH characteristics.
A closed top deck design, produced by LPDC with sand cores, was adopted for excellent cyl.head gasket sealability and NVH characteristics, instead of the general open deck design by HPDC. A cast iron cyl.liner was adopted for reliable durability and low cost. The material used is JIS AC2A, familiar for cyl.heads in NISSAN. In order to reduce aluminum growth, it is heat treated in an original process before machining. T6 heat treatment was not adopted to avoid unhomogeneous structure. Because the cyl.block is a very big and complex casting product, it is difficult to heat treat homogeneously. In order to assure the thread strength and to avoid shrinkage voids, deep holes, for example, counter bore of cyl.head bolt boss, oil gallery and oil drain, are casted by sand cores or core pins.
The drawings and main specifications of the VH45 and SR20 cyl.blocks are shown in Fig.2,3 and Table.1
Full scale production of VH45 and SR18,20 engines was begun in 1989, and they are being turned out at the rate of 3,000 units and 30,000 units, respectively, per month.
