Vvti, vvtl and vtec

VVT-i, or Variable Valve Timing with intelligence, is a car with variable valve timing technology developed by Toyota, similar to the performance of the BMW VANOS. The Toyota VVT-i system replaces the Toyota VVT offered starting in December 24, 1991 on the 5-valve 4A-GE engine. The VVT ??system is a 2-stage hydraulically controlled camshaft adjustment system. The Toyota engines CEO is reported to have said, "VVT is the heart of every modern Toyota!"
VVT-i, introduced in 1996, varies the timing of the intake valves by adjusting the relationship between the camshaft (belt, scissor-gear or chain) and intake camshaft. Engine oil pressure is applied to a drive to adjust the camshaft position. Adjustments in the overlap time between the intake valve closing and opening the result in an improved efficiency of the engine exhaust. Variants of the system, including VVTL-i, Dual VVT-i VVT-iE Triple and Valvematic, have followed.


VVTL-i (Variable Valve Timing and Lift intelligent system) is a light version that can alter valve lift (and expensive) as well as valve timing. In the case of the 16 valve 2ZZ-GE engine has two camshafts, one operating intake valves and one operating exhaust valves. Each camshaft has two lobes per cylinder, a low rpm lobe and one high speed, high lift, long duration lobe. Each cylinder has two intake and two exhaust valves. Each set of two valves are controlled by a rocker arm, operated by the camshaft. Each rocker arm has a slipper follower mounted to the rocker arm with a spring, allowing the slipper follower to move up and down the high lob without the tumbler. When the engine is running below 6000-7000 rpm (depending on year, car, ECU and installed), the low lobe is operating the rocker arm and thus the valves. When the engine is running above the lift engagement point, the ECU activates an oil pressure switch to a sliding pin under the slipper follower on each rocker shaft. This effect shifts to the high lobe causing high lift and longer duration.
The system was first used in 1999 Toyota Celica SS-II with 2ZZ-GE. Toyota has now ceased production of its VVTL-i engines for most markets, because the engine meet Euro IV specifications for emissions. As a result, this engine is no longer available on some Toyota models, including the Corolla T-Sport (Europe), Corolla Sportivo (Australia), Celica, Corolla XRS, Toyota Matrix XRS, and the Pontiac Vibe GT, all had The 2ZZ-GE engine installed. The Lotus Elise, the 2ZZ-GE and 1zz-FE engine, while the new Exige provides the engine with a supercharger.


VTEC (Variable Valve Timing and Lift Electronic Control) is a valvetrain system developed by the volumetric efficiency of a Honda four-stroke internal combustion engine to improve. This system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R & D engineer Ikuo Kajitani, and was the first system of its kind. Different types of variable valve timing and lift control systems are also made by other manufacturers (MIVEC, Mitsubishi, Subaru AVCS, VVTL-i Toyota, Porsche VarioCam Plus, the VVC Rover Group, VVEL Nissan, etc.).
VTEC was initially designed for the ability of an engine to increase it to 100 hp / liter or more while maintaining functionality for use in mass production vehicles. A later variation of the system only to improve fuel efficiency, or a higher power capacity. In practice, a fully variable valve timing engine is difficult to design and implement.
In addition, Japan has a tax on engine size, where the Japanese car manufacturers to higher-performing engines with lower displacement. In cars like the Toyota Supra and Nissan 300ZX, this was achieved with a turbocharger. In the case of the Mazda RX-7 and RX-8, a rotary engine used. VTEC serves as yet another method for very high specific power (power / unit displacement) of smaller displacement engines to lead.
The VTEC system is a simple method whereby the engine with multiple camshaft profiles optimized for low and high speed operations. Instead of one cam lobe actuating each valve, there are two: one optimized for low RPM stability & fuel efficiency, the other is designed for high-RPM power to maximize. Switching between the two cams is controlled by the ECU which takes account of engine oil pressure, engine temperature, vehicle speed, engine speed and throttle position taking. Using these inputs, the ECU is programmed to switch from low lift to high lift cams when the conditions mean that engine will be improved. On the switching a solenoid is actuated which allows oil pressure from a valve of a locking pin that the high speed cam follower that binds the high RPM operation. From this point on the poppet valve opens and closes according to the high-lift profile, which opens the valve further and for a long time. The switch-over point is variable between a minimum and maximum point, and is determined by engine load. The switch back from high to low rpm cams is set to occur at a lower speed than the up-switch (hysteresis) to a situation where the engine is asked to operate continuously at or around preventing the switch-over point.
The opposite approach to variable timing is to produce a camshaft which is better suited for high speed operation. This approach means that the vehicle is very poorly at low revs and better at high rpm (where most cars spend much of their time). VTEC is the result of an attempt to marry a high speed low RPM stability.


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