In fact, the ‘400’ part of the badge is intended to hint that the RX feels more like it’s powered by a 4.0-litre V8 instead of its 3.3-litre V6. A fair presumption, given that this car can crack 0-62mph in 7.0sec and hit the ton in under 17sec.
To fully understand how the RX400h works you really need a combined degree in engineering and computer science. For starters, there’s not one but three high-efficiency motor/generators, plus a barrage of inverters, converters, controllers and switches. Add a 288-volt nickel-metal hydride battery pack plus a continously variable transmission (CVT) and you have a considerable quantity of technology packed under the RX400h’s skin.
Under the bonnet is a 3.3-litre V6 similar to the one that powers the US-spec RX330, but with its output reduced by around 10 per cent to 208bhp to better suit hybrid characteristics.The first of three electric motors is a small, integrated electric motor/generator that’s used to fire up the V6, which automatically cuts off when the RX comes to a stop, and regulate the CVT’s ratios and charge up the batteries.
Then there’s a primary traction electric motor that can send a supplementary 165bhp to the front wheels, which helps give the car its strong mid-range thrust.
There’s also a 68bhp motor that powers the rear wheels, adding the all-wheel-drive element to the Lexus. And all three motors act as battery-topping generators during regenerative braking and coasting.But the really clever part is Toyota’s Hybrid Synergy Drive technology that orchestrates all this seamless to-ing and fro-ing of power from the V6 and the electric motors to the different wheels.
You don’t fire up the V6 to move off. The key goes in the ignition, you give it a twist and a light on the dash tells you you’re ready to move off. Pull the gear selector down to ‘Drive’, squeeze the throttle and you ease away under eerily-silent electric power.
This is the ‘milk float’ mode. In stop-start traffic, this is what will move you along and boost your economy average. Squeeze the throttle harder and an animated graphic on the dash tells you the big V6 has joined the party. Not that you’d know. There’s no additional noise, no buzzy vibration. Just more power.
Stomp hard on the throttle and the CVT lets the engine spin to its torque peak; it delivers a throaty but muted roar. And without the usual shift-jerk points of a regular automatic, the power delivery feels super-smooth and refined. The Lexus simply gathers speed, squeezing you back into your seat.
Lift off the throttle, and again the instrument panel graphic tells you that electricity is being generated and is topping up the battery. Same when you touch the brakes. And when you come to a complete stop, everything goes silent as the motor cuts off.
Apart from having to get used to the unnerving feeling of an engine dying on you every time you come to a halt, driving the hybrid Lexus is essentially similar to driving the regular RX330. Similar but slightly different in that the electric steering feels rather lifeless, and the feel of the electrically controlled brakes is corrupted by their need to generate electricity for the batteries.
And whereas the RX330 feels light, nimble and agile for a 4x4, the 400h feels a bit of a lump from the extra 100kg it has to tote around. Somehow it manages to feel a lot heavier than its 1984kg.But it’s a measure of the technology’s brilliance that the 400h is not only 0.9sec quicker to 60mph than the 330, but government fuel figures show it to be a 33 per cent more economical.
Not that you should take that 34.8mpg combined average as gospel just yet. A lot of the Lexus’ high economy depends on how hard you drive it. Keep your right foot hard down to enjoy that V6 and electric motor combo, or drive a lot of motorway miles at high speed, and you might be lucky to average 22mpg.
But keep the speed down, the throttle light, and make a lot of stop-start commutes, and you might be looking at 38mpg. Only a full Autocar test will provide the answer.
To some buyers, the only other negative might be the look of the RX400h. Apart from some minor exterior changes, such as a revised front grille and unique 18-inch wheels, this new Lexus 4x4 doesn’t shout too loudly about its environmentally friendly persona.
But that’s unlikely to worry Lexus. When the RX400h goes on sale in the UK in May, chances are it will become the new must-have 4x4 for the morning school run. High economy coupled with power and performance, plus the opportunity to irritate Red Ken? Priceless.