Dual-injector V6 Petrol Engine

The new GS 450h employs a 3,456 cm3, 60 degree V6 petrol engine, which adopts the Otto cycle for performance orientation. It develops a maximum power of 296 DIN hp/218 kW and 368 Nm/271 lb.ft of torque.

For optimum weight saving, the engine block, cylinder heads, head covers, oil pan, pistons and bearings for both connecting rods and crankshaft are produced in aluminium, and connecting rods are forged in high-tensile steel. Thanks to advanced casting techniques, the aluminium block and cast-iron liners are produced as a single unit, reducing the spacing between cylinder bores to just 11.5 mm. Moreover, the engine's integration within the Lexus Hybrid Drive system obviates the need for either a starter motor, alternator or serpentine belt, the V6 being started by the electric generator.

The world's first automotive application of two injectors per cylinder, D-4S (Direct injection 4-stroke petrol Superior version) is the latest evolution of Lexus' stoichiometric, 4-stroke, direct injection technology. With one injector installed in the combustion chamber and a second mounted in the intake port, it combines the strengths of both direct and port injection, realising optimum engine efficiency and improving torque by 7% across the rev range, whilst minimising fuel consumption and emissions.

The system's port injectors employ 12 holes to inject fuel at a maximum pressure of 4 bar, whilst the in-cylinder injectors feature twin, 0.52 x 0.13 mm rectangular slits producing a double fan injection pattern to effect the most homogenous possible air/fuel mix. In-cylinder injection is performed at a maximum pressure of 130 bar, a reference value for petrol engines.

Under cold start conditions, D-4S employs port injection during intake and direct injection - partially around the spark plug - during compression. This produces an air/fuel mixture of 15-16:1, the richer mixture raising the combustion temperature and contributing to a quicker warm up of the two thin-wall catalysts, whilst the hybrid system's electronic management maintains the engine at a speed that minimises emissions - something not possible on a conventional engine.

At idle, the engine runs on direct injection alone. When the engine is running under a low to medium load at lower speeds, both direct and port injection systems are used during the intake stroke. This creates an homogenous, 12-15:1 stoichiometric air/fuel ratio to stabilize combustion, improve fuel efficiency and reduce emissions.

When the engine is running under heavy loads, the direct injection system alone is employed. This achieves an intake cooling effect by injecting fuel directly into the combustion chamber, which improves the efficiency of each charge. Once again, a 12-15:1 stoichiometric air/fuel ratio is effected during the intake stroke.

By reducing pre-ignition tendencies, D-4S also allows for a higher engine compression ratio of 11.8:1, improving engine efficiency.

Dual VVT-i provides the new V6 with continuously variable valve timing to both intake and exhaust camshafts, varying between 60 and 35 degrees respectively and improving performance, fuel consumption and emissions. The system has been specifically adapted to suit the characteristics of the Lexus Hybrid Drive system, with intake timing retarded, and the valves opening before and closing later than usual.

The 3.5 litre V6 exhaust system incorporates a twin-wall, stainless steel manifold to reduce noise, improve heat resistance and accelerate catalyst warm-up. Pressure control valves in both main mufflers close to reduce noise at low speed, opening as speeds rise to reduce backpressure and enhance engine performance.


Electric Motor

In order to satisfy the GS 450h performance targets, a compact, high output motor works as an electric supercharger, assisting the engine in achieving a flexible output delivery. The Lexus Hybrid Drive system employs a three phase, permanent magnet AC synchronous type motor, operating on a 650-Volt current processed by the Power Control Unit.

In order to accommodate the motor within the ultra compact hybrid transmission casing, the stator's wiring benefits from a smaller diameter and a double star wiring method, which resulted in a significant reduction in the unit's diameter. Nevertheless, the motor is the most powerful ever installed in a standard production passenger car - 20% more powerful than that fitted to the RX 400h - generating 200 DIN hp/147 kW, and 275 Nm/203 lb.ft of torque.

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