The IS F 5.0-litre Quad-Cam V8 engine has an intelligent electric controlled, continuously variable valve timing system on the intake camshafts.
The electric inlet camshaft actuation system – known as Variable Valve Timing – intelligent Electric, or VVT-iE – improves engine performance and fuel efficiency, as well as reducing emissions and engine vibration.
The IS F engine also has intelligent variable exhaust camshaft timing, with hydraulic activation.
The dual VVT-i system is designed to continually optimise intake and exhaust timing, according to engine load, temperature, revolutions and throttle position.
It offers benefits across the engine revolution range, including increased low-end torque and higher top-end performance – the latter by making optimum use of the ‘breathing’ advantages of valve overlap.
Lexus dual VVT-i also contributes to a significant reduction in exhaust emissions, such as oxides of nitrogen (NOx) and hydrocarbons (HC).
Lexus developed electrically controlled VVT-i to provide additional benefits and greater valve timing control.
Hydraulic VVT-i cannot operate below 1000rpm or when the engine is cold.
However, the VVT-iE system will operate across the full engine revolution and temperature spectrum, with a cam response speed of some 50 degrees per second in the retardation phase and 150 degrees per second in the advance phase.
The Lexus 2UR-GSE engine in IS F has a range of 40 degrees of inlet camshaft timing variation (relative to crankshaft angle) and 35 degrees of exhaust camshaft timing variation.
It can vary valve overlap (the period when both the exhaust and inlet valves are open) from a minimum minus 10 degrees to a maximum of 65 degrees.
The IS F inlet cams have 248 degrees duration and the exhaust cams have 244 degrees duration.
The Quad Cam 2UR-GSE engine has separate primary cam chains to drive the inlet camshaft in each cylinder head, and secondary chains to drive the accompanying exhaust camshaft from each inlet cam.
Lexus now offers dual VVT-i engine technology in eight models.
The new-generation dual VVT-i Lexus Quad-Cam engines meet the previously conflicting goals of:
improved torque at low revolutions, and
better use of the expansion ratio in the cylinder and exhaust pulsation to improve engine breathing at high revolutions.
The dual VVT-i system boosts torque at both low and high engine speeds.
It makes full use of exhaust pulsation to increase cylinder filling at high rpm.
The engine ECU controls camshaft advance and retard, via electric motors for the inlet camshafts. It controls exhaust camshaft timing via an oil control valve mounted on the cylinder head and vane-type actuators on the ends of the exhaust camshafts.
There are five main dual VVT-i operating scenarios.
Engine idle: inlet camshaft neutral position, exhaust camshaft on full advance. This eliminates valve overlap, thereby reducing volume of exhaust gas blowback into the cylinder and inlet ports – for stable combustion and improved fuel economy.
Low engine speed range with light to medium load: inlet timing is retarded and exhaust timing is retarded for increased overlap. This creates two parallel effects: increased internal exhaust gas recirculation rate to reduce oxides of nitrogen and re-burn hydrocarbon, and reduced pumping losses and hence improved fuel economy.
High-load range, low-to-medium engine speed: inlet timing is advanced to close the intake valve earlier, reducing the volume of intake air blowback into the inlet ports and improving volumetric efficiency.
High-load range, high engine speed: inlet timing retarded, exhaust timing advanced. Retarding the inlet timing (according to the inertial force of the inlet air) improves volumetric efficiency and hence power.
At low temperatures: Retarded intake timing and exhaust in the full advance position, to eliminate valve overlap to the intake side. Fixing the valve timing at extremely low engine temperatures – and controlling the range as the temperature rises – stabilises fast idle and improves fuel economy.