The Technology of TOYOTA Engine

~The Technology of TOYOTA Engine

VVT-I

How VVT-I will help ?

The VVT-I achieves "high output power". "low fuel consumption", and "clean exhaust gases" by using the operting condition of "Idling","normal driving", and "uphill or passing acceleration" as VVT-I controls examples. Car Operating Condition Normal Engine Operation VVT-I Operation VVT-I Advantage Idling: During idling, the engine does not need to generate power to runthe vehicle. Then, the performance that is demanded of the engine during idling is to operate in a stable manner with minimal vibration and low fuel consumption. Because of valve overlap the exhusts gases get into the intake port and mix with the air-fuel mixture. When the air-fuel mixture is contaminated in this manner, it does not produce reliable combustion and results in an unstable engine rpm. VVT-I delays the timing at which the intake valve opens to eliminate the valve overlap, thus preventing the exhaust gases from flowing back into the intake port 1.Stable combustion, which result into less vibration. 2.Better fuel economy. Normal Driving: During normal driving, when the accelerator pedals depressed somwhat with a certain amount of force fuel economy and clean exhaust gases are demanded of the engine. During normal driving, when the throttle valve is not opened too widely, a vacuum is created in the intake port. Similar to when the throttle valve is large, this vacuum causes the exhaust gases to flow back into the intake. VVT-I utilize the backflow of the backflow of the exhaust gases into the intake port to an advantage by: 1. By reducing the engine power loss. 2.By utilizing the unburnt fuel contained in the exhaust gases and also by lowering the combustion temperature. 1.Increased fuel economy 2.Cleaner exhaust gases High Speed or Sudden Acceleration : During sudden acceleration, a large amount of torque is demanded of the engine. During Sudden acceleration, when the piston turns around at ists lowest position, the pressure in the cylinder and the pressure in the intake port soon reach their equilibrium . Therefore, unless the intake valvel is closed before the piston comes up, the air-fuel mixture gets pushed back and thus reducing the efficiency. During the acceleration pedal continues to be depressed, the engine rpm increases, resulting in alonger intake lag. Using sensors to monitor the engine rpm, the VVT-I gradually delays the timing to close the valve so that the maximum amount of air-fuel mixture can be drawn-in according to the increase in the engine speed. Maximize the potentinal of engine which result in: 1.Maximum power. 2.Optimum fuel consumption. 3.Cleaner exhaust gases.