To further improve efficiency and performance, Toyota explored more advanced valvetrain designs. and developed the new Toyota Variable Valve Timing and Lift system, 'VALVEMATIC' - a continuously variable valve timing (duration and phase) and lift system. This system was applied to the valvetrain of a new 2.0L L4 engine (3ZRFAE) for the Japanese market. The system can be classified into three mechanisms according to their function: the actuator which drives the control shaft which changes valve lift, the variable valve lift mechanism, and the cam phaser which controls intake and exhaust valve timing. The system has rocker arms, which allow continuously variable timing and lift, situated between a conventional roller-rocker arm and the camshaft, an electromotor actuator to drive it and a phase mechanism for intake and exhaust camshafts (Dual VVT-i). The rocking center of the rocker arm is stationary, and the axial linear motion of a helical spline changes the initial phase of the rocker arm which varies the timing and lift. The linear motion mechanism uses an original planetary roller screw and is driven by a brushless motor with a built-in electric control unit. Since the rocking center and the linear motion helical spline center coincide, a compact cylinder head design was possible, and the cylinder head is a common design with a conventional engine. Since the ECU controls intake valve duration and timing, a fuel economy gain of maximum 10 % (depending on driving condition) is obtained by reducing light to medium load pumping losses. Also intake efficiency was maximized throughout the speed range, resulting in a power gain of 10%. Further, HC emissions were reduced due to increased air speed at low valve lift.
The new Toyota variable valve timing and lift system
Die neue Toyota Ventilsteuerung für variable Steuerzeiten und Hub
2007
16 Seiten, 18 Bilder, 3 Quellen
Aufsatz (Konferenz)
Englisch
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