MHI Achieves Low-cost Mass Production of Hollow-head Engine Valves,
Leveraging Proprietary Integrated Forging Technology
-- Enabling Higher Fuel Efficiency and Lower CO2 Emissions --

With MHI's hollow-head valve production technology (patents pending in Japan and abroad), the hollow is formed during the forging process; no equipment is required other than the forging press. The elimination of conventional boring by drill or electric spark machining enables low-cost mass production. MHI developed this machining method jointly with Yoshimura Company of Nagoya, based on MHI technology for producing hollow valves for aircraft engines. Hyoji Yoshimura, president of the company, is a former MHI employee.

As MHI's production method performs consecutive forming of the hollow-head valve from cylindrical metal material mainly during cold-forging, a significant reduction in processing time is achieved. To realize maximum benefit from hollow valves, the company analyzed various factors - shape of the hollow, valve strength, generated stress, etc. - and studied how to form shapes that conventional machines have been unable to form.

Because hollow valves can add to cooling efficiency through improved thermal conductivity by encapsulating sodium (natrium) in the hollow, the heat resistance of exhaust valves can also be increased, enabling accommodation of the higher exhaust temperatures associated with high-efficiency engine combustion. Coupled with reduced friction loss due to weight reduction, hollow valves can boost fuel efficiency substantially, thereby contributing to reduced CO2 emissions.

MHI's Machine Tool Division has already established a production structure capable of producing 25,000 hollow-head valves per month. It has also started shipments of samples mainly to automobile manufacturers, and launched development of customized products reflecting the diversified needs of users and the results of their evaluation testing.

As a measure to combat global warming, CO2 emission controls, especially for automobiles, are becoming more stringent. In response, automobile manufacturers around the world are fiercely competing to develop more fuel-efficient cars and electric vehicles. In parallel with these initiatives, stepped-up efforts are being made to reduce auto engine weight further, lower friction loss and enhance combustion efficiency.

MHI views hollow-head valves as a differentiated product that can contribute largely to enhancement of automobile engine efficiency. Going forward the company will aggressively conduct marketing activities of the new valves by offering a lineup of metals - ranging from heat-resistant steel to nickel alloy - for not only the automobile industry but other potential users as well.