MHI "Hollow-Head" Engine Valves Adopted in Nissan GT-R Sports Car
-- High Cooling Efficiency Contributes to Enhanced Fuel Efficiency --
Tokyo, August 2, 2012 - Mitsubishi Heavy Industries, Ltd. (MHI) has commenced shipments of "hollow-head" engine valves - engine valves*1 hollow through to the head - to Nissan Motor Co., Ltd. for adoption in the 2012 model of the automaker's luxury GT-R sports car. Nissan chose MHI's hollow-head engine valves not only in recognition of their weight reduction but also their potential to improve fuel efficiency significantly as a result of their high cooling efficiency and ability to prevent engine knocking*2. Going forward, MHI plans to pursue orders not only from the auto industry but broadly, leveraging its proprietary forging technology enabling lower production costs than other hollow valves.
Hollow-head engine valves are manufactured from cylindrical metal material using a forging press to create a hollow extending throughout both the valve stem and head. The absence of welding joints in the head results in outstanding strength, while the elimination of conventional boring by drill or electric spark machining results in shorter machining operations, enabling lower cost and short delivery schedules. MHI's proprietary forging technology is based on the company's unique production knowhow in hollow valves for aircraft engines accumulated over many years.
In hollow-head engine valves, metallic sodium is encapsulated in the hollow. This feature increases the valves' thermal conductivity and enhances their cooling efficiency, and also enables a near 15% reduction in weight compared to solid valves*3. As the valve temperature can be kept to 600°C during engine drive, which is 100-200°C lower than with solid valves, excessive rises in temperature can be prevented even when the compression ratio of the air/fuel mixture is increased to improve fuel efficiency. This enables prevention of engine knocking, a contributing factor to power erosion. The elimination of expensive heat-resistant materials also enables cost reductions.
The 2012 model of the Nissan GT-R, launched in November 2011, features 12 of MHI's hollow-head engine valves per vehicle. Compared to the 2011 model, maximum engine power has been increased by 14 kilowatts (kW), demonstrating how hollow-head valves contribute to more powerful engines.
In today's broad quest to prevent global warming, automakers in Japan, the U.S. and Europe are actively developing and launching vehicles that emit less carbon dioxide (CO2) throughout their lifecycles. They are also focusing on the development of compact turbocharged engines and high-efficiency engines for use in hybrid vehicles, etc., demonstrating strong interest in technologies and knowhow for raising fuel efficiency to optimal levels.
MHI sees its hollow-head engine valves as a differentiated product that can contribute substantially to higher efficiency in all types of engines, automotive included. Going forward the company aims to develop a wide array of products responding closely to customer needs and to boost its proposal-based marketing stance in a quest to attract expanded orders.
1.Engine valves are mounted in the cylinder heads of 4-stroke (air intake, compression, combustion, exhaust) engines. During the air intake phase,
they take fuel mixed with air into the combustion chamber, and during the exhaust phase they open to allow combusted gas to discharge.
Engine valves are required to offer heat resistance high enough to withstand combusted gas temperatures up to 1,000°Cithout deformation
or abrasion. Light weight is also of importance in order to keep pace with developments in high-speed engines.
2.Engine knocking refers to metallic noise or vibration in a piston engine. Causes vary. In cases of spark knocking, when incompletely mixed air in
the cylinders of a gasoline engine is compressed and the temperature and pressure exceed their limits, spontaneous ignition results, causing
reductions in power and combustion efficiency. Hollow-head engine valves are effective in preventing such occurrences.
3.Solid valves have no hollow at all. "Hollow-stem valves" are hollow only through the stem, whereas "hollow-head valves" are hollow from the stem
through the head.
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