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A newly developed AR series 4-cylinder engine has achieved high fuel efficiency through the following: adopting roller rocker arms for the valvetrain system and a variable output oil pump to reduce the friction losses, optimizing the combustion chamber and its cooling system for high compression ratio, and adopting VVT-i (Variable Valve Timing-intelligent) for both intake and exhaust camshafts to enhance thermal efficiency of the engine. Engine torque has been enhanced across the entire range of engine speeds while high performance at low engine speed is achieved by adopting a variable induction intake manifold system (ACIS-III). Output power has been enhanced by making the intake and exhaust systems highly efficient. A hinge type tumble control valves were developed to improve emissions at low temperature by improving combustion when the engine is cold in order to comply with the U.S. Cold-NMHC.

A direct injection spark ignition (DISI) gasoline engine with a new stratified charge combustion concept has been launched on the Japanese domestic market. This new concept consists of two components. First, a thin fan-shaped spray from a slit nozzle enables wide spray dispersion, moderate spray penetration and a fine atomization. Second, a shell-shaped piston cavity allows better mixture formation, however avoiding distinct charge motions (such as tumble or swirl). Simple intake port geometry increases the full load performance. The combustion concept, at the same time allows stratified charge to be used at higher load and at higher engine speeds and improves the homogeneous charge combustion. A new 3L in-line 6 gasoline engine with this combustion concept showed 20% better fuel economy than a 3L port fuel injection (PFI) engine (λ=1 feed back system) under the Japanese 10-15 mode.