Press Release
Direct petrol injection for IS250
IS250 has Lexus stoichiometric direct petrol injection system to optimise performance, increase fuel efficiency and reduce emissions.
The direct injection system controls fuel injection timing and volume, air/fuel ratio and throttle valve position.
Fuel is injected directly into the combustion chamber at high pressure, improving combustion efficiency and reducing pumping losses.
Direct injection enhances the intake air cooling effect in the cylinder, increasing charging efficiency and resistance to engine knock.
The ability to resist engine knock (detonation) allows for a high compression ratio, improving power and torque across the engine revolution range.
Direct petrol injection boosts power and torque, compared to a multi-port injection engine.
The direct injection-equipped Lexus engine has compact, high-pressure single-orifice slit-nozzle injectors to maximise fuel atomisation.
The injector atomises fuel into a fine mist and expands it to form a large, fan-shaped pattern in the combustion chamber.
This occurs as the downstroke of the piston draws in a large volume of air. The cooling effect of the fuel (taking advantage of the latent heat of vaporisation) increases the intake air volume and improves charging efficiency.
The lower temperature of the compressed charge allows the engine designers to employ a high compression ratio for increased power while reducing the chance of detonation.
Moreover, the intake air forms a vertical swirl current (tumble current) to promote improved fuel-air mixing, and, therefore, improve performance and reduce emissions.
The injector has a special coating on its nozzle to resist carbon deposits. The area where the injector body meets the cylinder head has an insulator and the injector shaft has two Teflon seals. This helps resist cylinder pressure, improve sealing performance and reduce vibration.
The Lexus direct injection system utilises a high compression ratio of 12.0:1 in IS250 to boost performance.
At light engine loading, the stratified charge system creates an area of rich mixture near the spark plug, so it ignites easily.
The mixture becomes leaner in the combustion chamber extremities.
At high engine loading, the combustion mixture is more uniform.
Injection timing varies according to driving conditions, with the system programmed to inject at the optimal point in the intake stroke to achieve a homogenous air/fuel mixture.
However, the fuel is injected at the end of the compression stroke when the engine is cold. This raises engine temperature, accelerating engine and catalyst warm-up which improves exhaust purification.
Stratified charge combustion technology has existed within the Lexus domain for a decade.
Lexus V6 has raft of new technology
IS250’s Quad Cam V6 engine combines the Lexus technologies of direct petrol injection and intelligent variable valve timing (VVT-i) for inlet and exhaust.
It also has roller rockers, high-tumble inlet ports, swirl-control valves in the inlet ports, an electronic Acoustic Control Induction System (ACIS) and a die-cast aluminium cylinder block.
Lexus designed the 60-degree V6 for a combination of high performance, fuel efficiency, package efficiency, reliability and serviceability, coupled with light weight, low noise, vibration and harshness (NVH) and low emissions.
The Lexus 4GR-FSE engine has an oversquare bore and stroke relationship of 83.0mm x 77.0mm for a swept capacity of 2500cc.
Compression ratio is 12.0:1 (the highest in the Lexus range) for increased power and economy across the engine revolution range.
The combination of direct petrol injection and dual VVT-i boosts performance and economy, while minimising emissions.
The 4GR-FSE engine has high-tumble inlet ports to increase turbulence in the combustion chamber, improving combustion.
Cut-outs in the wall of the intake port – opposite the valve guide – help promote a swirl pattern inside the cylinder.
The flow pattern is down the cylinder walls and up in the centre towards the centrally mounted spark plug.
The “slanted squish” combustion chamber shape is based on a narrow included valve angle.
Lexus engineers have adopted roller rockers (with maintenance-free valve clearance adjusters) to create the narrow included valve angle while providing sufficient spacing between the camshafts for the primary camshaft drive sprockets.
The compact combustion chamber shape offers a low surface-to-volume ratio, reducing cooling losses and increasing fuel efficiency.
The 4GR-FSE engine also has swirl control valves in the inlet ports to improve fuel atomisation at low engine speeds and low engine temperatures, improving fuel efficiency.
The swirl control valve – a butterfly valve in one of each pair of inlet ports – closes at low engine temperatures and low engine revolutions to increase turbulence in the cylinder.
The new Lexus V6 has electronic control for the ACIS – based on information on engine revolutions and throttle position.
ACIS varies the effective length of the inlet runners to make maximum use of the inlet pulsation effect for increased breathing efficiency.
It creates a long manifold effect to boost torque in the low to medium engine speed ranges and a short manifold effect to boost power at high rpm.
The stainless-steel exhaust manifold has a dual-pipe (air gap) structure and a built-in three-way catalyst to boost catalyst temperature and reduce HC emissions from cold start.
This design accelerates the warm-up of the catalyst immediately after start-up, which in turn reduces exhaust emissions.
Lexus has maximised reliability and serviceability by adopting cast hypereutectic aluminium alloy pistons, chain camshaft drive, maintenance-free valve clearance adjusters, a replaceable element oil filter, direct ignition, electronic engine control, an oil-level sensor and an air/fuel ratio sensor.
Hypereutectic aluminium alloy pistons allow for tighter skirt clearances than a forged piston to avoid cold-start piston slap.
In addition to strength, the hypereutectic piston improves resistance to scuffs and seizure, and generally runs cooler.
The 4GR-FSE’s weight-saving features include its thin-wall cast-aluminium inlet manifold, die-cast aluminium cylinder block and simplified cylinder head structure, with two-piece heads that divide at the cam journals.
The engine has a service weight of 180kg, compared to 213kg for the superseded IS300 engine.
Dual VVT-I Engine for IS250
IS250 has a dual variable valve timing engine, for improved performance and fuel efficiency, and lower emissions.
The Lexus dual VVT-i system provides optimum inlet and exhaust valve timing across the range of engine operating conditions.
The IS250 Quad Cam V6 engine offers the benefit of improved torque at low revolutions.
It also makes better use of the expansion ratio in the cylinder and better use of exhaust pulsation to improve engine breathing at high revolutions.
These goals are mutually exclusive in conventional engines.
The Lexus dual VVT-i system boosts torque from idle to 3000rpm engine speed range and in the high engine speed range.
The dual VVT-i system in the 2.5-litre 4GR-FSE engine can independently vary inlet timing over a range of 40 degrees (relative to crankshaft angle) and independently vary exhaust timing over a range of 35 degrees.
It optimises the valve overlap period according to engine and driving conditions, to make full use of exhaust pulsation and increase cylinder filling at high rpm.
The system can vary the range of valve overlap from minus three degrees (when the exhaust camshaft timing is fully advanced and the inlet camshaft timing is fully retarded) to plus 72 degrees.
The inlet camshafts have 244 degrees of duration and the exhaust camshafts have 240 degrees of duration.
Lexus’ dual VVT-i has four main operating scenarios:
Low engine temperature, engine start, idling or light load: inlet camshaft on full retard, 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.
Medium load range:: inlet timing is advanced 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, thereby 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.
The 4GR-FSE engine’s ECU controls camshaft advance and retard, via an oil control valve mounted on the cylinder head and vane-type actuators on the ends of the four camshafts.
New six-speed manual transmission for IS250
Lexus’ new IS250 and IS250 Sports models have the choice of new close-ratio six-speed manual or six-speed sequential automatic transmissions. IS200 was one of the first cars in its class at its Australian launch in 1999 with a six-speed transmission. IS250’s new Lexus RA62 manual transmission combines compact construction and high-quality shift feel.
It has triple-cone synchromesh on first, second and third gears to improve shift quality and gearbox durability.
A remote-controlled shift mechanism reduces gear knob vibration.
The shift mechanism includes four shift forks and a sliding-shaft-type shift shaft.
The RA62 transmission uses an output reduction system in the gear train rather than an input shaft reduction system, to reduce transmission size, weight and shift effort.
Safety features include a clutch-start system (the engine will not start unless the clutch pedal is depressed) and a release collar on the shift lever to prevent accidental engagement of reverse gear.
The RA62 transmission has ratios of first, 3.791; second, 2.275; third, 1.524; fourth, 1.185; fifth, 1.000; sixth, 0.786 and reverse, 3.466.
It is matched to a 3.583:1 final drive ratio.
IS250 manual has 261 square centimetres of clutch facing area, for optimum reliability.
The clutch pedal has a turnover mechanism to reduce pedal effort.
