New powder metallurgy parts for variable valve timing (VVT) systems

November 12, 2010

Variable valve timing (VVT) systems are installed in modern internal combustion (IC) engines instead of the traditional camshaft. VVT’s are constructed of two subsystems, one is the mechanical valve train system which drives the intake valve and the other is the electrical actuator system which operates the mechanical valve train system to change the amount of valve lift. PM parts have been finding increasing applications in VVT systems in recent years.

As previously reported, VVT systems have done much to improve fuel efficiency and to reduce emission levels of automotive IC engines by advancing or retarding the timing of the intake or exhaust valves. Japanese researchers at Diamet Corp. (Niigata), Hitachi Automotive Systems Ltd (Kanagawa), Nissan Motors Ltd (Yokohama), and the Sibaura Institute of Technology (Tokyo) reported in a presentation (by Kinya Kawase, et al.) at PM2010 in Florence, Italy, that two new PM parts, ‘link A’ and ‘input cam’, have been developed for a Nissan VVT system with the ‘input cam’ used to convert rotating to oscillating movement with ‘link A’. The mechanical valve train system in the VVT system used at Nissan Motors Ltd is shown in Fig.1, and the location of the two new PM parts in the VVT system is shown in Fig.2.

Diamet Corp., one of Japan’s leading PM companies, is reported in the presentation to be producing the ‘link A’ PM part (Fig.3) for Nissan Motors using a sintered Fe-Mo-C material to achieve high fatigue strength after heat treatment (340 MPa), whilst the ‘input cam’ (Fig.4) is produced from a sintered Fe-Cu-C material with high copper content which also displays high fatigue strength (220 MPa). The input cam is subjected to a manganese phosphating treatment to achieve the desired low friction properties which is said to be essential for good fuel economy of the VVT system.

fig-3_1