The goal is to increase the air entering the cylinder and thus burning more gasoline. The requirement of varying the different parameters is to allow more fuel to burn at high rpm, to give the good torque at high rpm and also to let more fuel to enter the cylinder during cold start.
Variable Valve events-
• Valve timing- Change the timing of valve opening and closing
• Valve duration- Increasing the valve open time for exhaust valve in order to allow maximum exhaust gases to leave the cylinder thus more fresh mixture can adjust in cylinder
• Valve lift-Increasing the extend of valve lift in order to increase the volume flowrate into the cylinder
• Valve duration- Increasing the valve open time for exhaust valve in order to allow maximum exhaust gases to leave the cylinder thus more fresh mixture can adjust in cylinder
• Valve lift-Increasing the extend of valve lift in order to increase the volume flowrate into the cylinder
NAME OF THIS TECHNOLOGY BY DIFFERENT AUTOMOBILE COMPANIES
VTVT (Hyundai)
VVT-i (Toyota)
i-VTEC (Honda)
VCT (Ford)
VVL (Nissan)
Vario Cam (Porsche)
Valuelift (Audi)
VVT-i (Toyota)
i-VTEC (Honda)
VCT (Ford)
VVL (Nissan)
Vario Cam (Porsche)
Valuelift (Audi)
Working
There are various versions of this technology,
two of them are explained as following
two of them are explained as following
Phaser Rotor Valve Timing
As we know the camshaft is driven by crankshaft usually by the chain drive. In this technology the camshaft sprocket has been modified by phaser and rotor assembly. The ring sprocket is mount on the phaser and locked with phaser. The rotor is connected to the camshaft, the rotor and phaser (i.e. sprocket and camshaft) can move 35-45 degree independent of each other. The motion of rotor is controlled by hydraulic actuator on signal given by ECU ( after receiving the information from MAP,Throttle position sensor, exhaust sensor etc). During the normal operation of engine there is no relative motion of phaser and rotor. At high rpm there is relative motion between the rotor and phaser in order to enhance the intake and exhaust timing (in case of dual VTVT).
Camshaft Profile Shift
In this version of technology the engines have an extra intake cam with its own rocker, which follows this cam. The profile on this cam keeps the intake valve open longer than the other cam profile. At low engine speeds, this rocker is not connected to any valves. At high engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves.
