STILL want your SUV, but don't like diesel power or high petrol bills?
Lexus has the answer, with what it claims is the world's most efficient luxury SUV, the hybrid RX450H.
- IN A WORD
- Make: Lexus
- Model: 450H
- Price: from $89,900
- Road test: JOHN PARRY
This petrol-electric, high-riding, five-seater is as frugal as some small cars and more efficient than rival diesel SUVs.
It sips along at 6.4 litres/100km on the combined cycle - 1.7 litres/100km less than its predecessor, the RX400H, and 4.4 litres/100km less than its stablemate, the petrol-only RX350.
At a saving of about $5 for every 100km travelled, an RX450H owner would need to travel at least 140,000km to get back the minimum $7000 premium over the RX350.
But the "cheap to run but not cheap to buy" anomaly misses the point.
For owners, it is all about being seen to be green.
For Toyota, the RX450H remains a showcase of technology that is proving popular with hybrid buyers. Sales of the 450H are up by 11 per cent this year, unlike sales of hybrid cars, which are down 22 per cent.
With four motors, one petrol and three electric, to synchronise, the RX450H is a mix of electronics and mind-boggling computer power.
Yet the only visible difference from the RX350 are the "Hybrid" badges on the tail and flanks.
Interior space is also the same, although weight is up by at least 140kg, to a minimum 1975kg.
However, despite the weight penalty, the 450H is a fraction quicker than the 350. The key to this efficiency is the marriage of its 3.5-litre V6 engine to three electric motors.
The petrol engine produces 183kW at 6000rpm and 317Nm at 4800rpm, or 18 per cent more power and 10 per cent more torque than the 3.3-litre engine in the RX400H, but 20kW and 30Nm less than the same engine in the RX350.
Upgrades to the engine include water-cooled exhaust gas recirculation, exhaust heat recovery and a switch to Atkinson Cycle operation.
An Atkinson Cycle engine has a higher compression ratio than a conventional Otto Cycle engine. It keeps the exhaust valves closed until the end of the expansion stroke, which produces more torque.
The V6 engine links to an electric generator, a 123kW electric front motor and a continuously variable transmission.
Power goes to the front axle either mechanically, electrically or through a mix of both. A 50kW electric motor powers the rear wheels during take-off and acceleration.
The front generator also starts the petrol engine and energy-saving regenerative braking is fitted to all wheels.
Power steering and airconditioning are electrically powered and the brakes are electro-hydraulic.
Driving the 450H remains as quirky as other hybrids.
The first thing you notice is the lack of starter-motor noise.
Push the start-stop button and the dash lights up and signals "Ready".
Flick the gear selector into drive, press the accelerator and off you go, the petrol engine kicking in only when needed and shutting itself down when coasting or stationary. There is no noise on idle and just a slight shudder when the petrol engine kicks in. A low whine when slowing indicates regenerative braking.
Power application is silky smooth and linear. Acceleration is strong even on light throttle, such is the high torque at low revs nature of electric motors. Full throttle starts to 100km/h, using all three motors, take just 7.9 seconds.
Despite myriad micro-second decisions going on internally, there is no need for the driver to intervene.
All the swapping and sharing is done automatically. A central display screen shows the state of play, through an energy monitor that tracks the flow between the petrol and electric motors and the wheels.
There is also a consumption screen, which shows energy storage and petrol consumed.
There are three models: the Prestige, from $89,900; the Sport, from $96,900; and the Sports Luxury, from $107,900.
Standard equipment on the 450H includes 10 airbags, the latest stability control and several active and passive safety features.
