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Study of bonded valve-seat system (BVS)
Technical Paper
2000-05-0144
Sector:
Language:
English
Abstract
The Bonded Valve Seat System is the latest technology to realize
drastic reduction in valve temperature in SI engines characterized
by the good thermal conductivity of extremely thin valve seats
bonded directly on the aluminum cylinder head. A unique and highly
rationalized resistance bonding technique was developed to maintain
adequate bonding strength and positioning precision in a short
bonding period of around one second. Engineering data on
optimization of bonding-section geometry, valve seat material and
the surface treatment and bonding parameters were presented and
discussed regarding the mechanism. The geometry of the bonding
section of the cylinder head was optimized by FEM analysis so that
the aluminum material should deform to embed the valve seat ring
with the action of expelling the surface contamination and the
oxide film. The bonding facility was modified so that the electrode
axis should move flexibly according to distortion of the cylinder
head during bonding. A new non-destructive inspection methodology
was developed to guarantee the sound bonding status in mass
production.
The effect of bonded thin valve seats on temperature
distribution of a cylinder head assembly was studied using FEM
analysis as well as engine bench testing. Results showed that the
valve temperature in the bonded valve seat system was lower by as
much as at least 50\mDC compared to that in the conventional
press-fit-type valve seat system. Endurance testing using several
automotive engines was carried out to confirm the reliability. The
testing results revealed the engines with the system had passed the
endurance criterion. Metallurgical study of the bonded section
showed neither brittle intermetallic compounds nor destructive
faults generated at the bonding interface.
It is concluded that the bonded valve seat system is effective
in reducing the engine valve temperature and has adequate
reliability for application to high-volume engine
manufacturing.