VTEC (Honda)
Variable Valve Timing and Lift Electronic Controlled ( VTEC ) is Honda innovation showing different mechanisms. The main difference is movement of intake valve. In the 16 valve engine, there are two intake valve and two exhaust valve in each cylinder.
VTEC is applied only on the intake valve . At this valve controlling engine efficiency is more influential . The assumption, on exhaust process does not need variable valve because the current exhaust engine work will be more lightly.
At VTEC engine, both intake valves do not always move together. For example, at low speed there is only one valve is open. Opening was relatively small because the characters are punched camshaft valve is suitable for low speed. This condition is considered fit for the machine.
As the engine rpm increased, the need for air supply is also increasing. Immediately handled second valve. Larger opening for second camshaft has character higher degree. First valve had come open wider. This is due to the pins that connect the rocker arm and push it . Automatically the pin locking two rocker arms. The second rocker arm moved by camshaft high duration, so the second valve movement follow the first valve.
In addition there is also i-VTEC (intelligent VTEC ) which features forward or rewind the ignition. Of course improve the machine.
VVT-i (Toyota)
VVT-i ( Variable Valve Timing With Intelligence ) is the engine technology that control magnitude and duration ( timing ) open and close intake valve accordance to engine speed.
- Increase engine power
- Fuel-efficient
- Environmental friendly / clean emissions
At Toyota engine, this system was applied to intake valve. The opening valve timing can be varied over a range 60 degrees . For example, at the start, a cold engine and stationary engine without load, timing rewind 30 degrees. This method will eliminate the overlap. This events in and out valves open simultaneously at the end of the disposal step for the intake valve will open after the exhaust valve close fully.
Closing exhaust valve, no fuel is wasted when sucked into the combustion chamber . Fuel consumption is so efficient and more environmentally friendly engines. When there on load , the timing will be forward 30 degrees. Degree of overlapping will increase. This is to push exhaust gas and mixture incoming fuel and air. In addition, the compression time also increased because the intake valve closing faster. The effect, volumetric efficiency will better.
There is timing gear to control VVT-i on intake camshaft. The timing gear consists of housing, on the inside there is room to move the vane ( propeller ). The propeller is connected to the camshaft. Inside it there are two oil lines to each oil room in the house VVT-i controller. From the oil line, vane will set the valve opening time
When timing on forward position, oil filling into the space behind each blade vane. So that the vane will move forward and timing forward 30 degrees. Oil pressure supplied by the camshaft timing oil and controlled by the engine ECU. Conversely, for the conditions retard (backwards), the space in front of vane is filled oil and the timing will retreat timing. Meanwhile, if required in standard conditions, there was pin that will lock the vane position still there in the middle.
Actually there are more sophisticated system, called VVTL-i ( Variable Valve Timing Lift -Intelligent ). In addition to playing a valve opening time, distinguished too high .
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