by Jack Rosebro
|The RX 450h. Click to enlarge.|
Lexus premiered two second-generation mid-sized luxury sport-utility vehicle at the Los Angeles Auto Shows: the 2010 RX 350, and the 2010 RX 450h hybrid. The vehicles replace the current RX 350 and RX 400h SUVs, respectively.
The RX 350 and RX 450h are both slightly longer and wider then their predecessors. The RX 350 is powered by a 275 hp (205 kW) 3.5L V6, mated to a six-speed automatic transaxle, while total system output of the RX 450h is 27% higher than its predecessor at 295 hp (220 kW). Both vehicles use undertrays to help achieve a coefficient of drag (Cd) of 0.32.
The RX 450h features an enhanced Lexus Hybrid Drive system with a 3.5-liter V6 gas engine that runs on an Atkinson cycle.
The new inverter used in the RX 450h employs a power transistor cooling structure that was first used in the Lexus LS 600hL sedan. The new structure enables the design of a smaller inverter (earlier post) without compromising the operating temperature of the inverter assembly.
The RX 450h also utilizes an exhaust heat recovery system, that consists of a thermostatically operated butterfly valve behind the catalytic converter which restricts the exhaust stream during warmup, and diverts much of the exhaust heat to a heat exchanger.
Heat from the heat exchanger warms up engine coolant, which then transfers heat to intake manifold coolant passages as well as the cabin heater circuit, enabling the internal combustion engine to turn off earlier, more often, and for longer periods of time, while maintaining low emissions at startup. The result is an improvement in both fuel economy and emissions.
The exhaust heat recovery system used in the RX 450h is simpler and less expensive to construct than the coolant heat storage system (CHSS) uses on Toyota’s current Prius, which employs a stainless-steel 3-liter coolant heat storage tank, two electric coolant pumps, and a motorized coolant valve assembly to carry out similar functions.
The RX 450h also employs a cooled exhaust-gas recirculation system that reduces engine pumping losses, which also helps to improve economy.
The RX 450h is SULEV-rated, and will be available in both front-wheel-drive and all-wheel-drive, with the AWD version employing a rear-mounted motor-generator.
Lexus did not release fuel economy ratings, but said that the RX 450h was expected to achieve a higher fuel economy rating than most of today’s conventionally powered mid-size sedans. Representatives said that the RX 350 is due in showrooms by February 2009, with the RX 450h scheduled to follow several months later.
The third generation RX 350 will be powered by an improved 275-horsepower, 3.5-liter V6 engine mated to an electrically controlled, sequential-shift six-speed transaxle. The all-wheel-drive version will feature an Active Torque Control AWD system that optimizes torque depending on driving conditions, resulting in improved efficiency and performance.