Nippon Piston Ring Co., Ltd.

Nittan Valve Co., Ltd.

Kouji Kunitake

Kenichi Sato

Hiroshi Oshige

Satoshi Ikemi

Kiyoshi Suwa

Ryouichi Yoshino

In an assembly of a hollow poppet valve and a valve seat insert, the hollow poppet valve's head is integrally formed with a stem end, a hollow part is formed from the head to a stem, and coolant is filled into the hollow part along with an inert gas. The valve seat insert is formed of iron base sintered alloy and obtained by integrating two layers of a supporting material side layer and a valve contact face side layer. The hollow poppet valve is formed of a material having thermal conductivity of 5-45 (W/m&#xb7;K) at 20-1000&#xb0; C. The valve seat insert includes the supporting material side layer having thermal conductivity of 23-50 (W/m&#xb7;K) at 20-300&#xb0; C. and a valve contact face side layer having thermal conductivity of 10-22 (W/m&#xb7;K) at 20-300&#xb0; C. This enables a valve temperature decrease throughout an engine's entire RPM range compared with the prior art.

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Kanagawa, Japan

Kouji Kunitake