10/1/2009 | 6 MINUTE READ

The Lexus HS 250h: The Relentless Pursuit Of Hybrids

No luxury builder had more hybrids in its lineup before Lexus rolled out with the HS 250h. And it is the first hybrid-only sedan in the luxury set, from any manufacturer.
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Lexus has long held a leadership position among the luxury brands as regards offering hybrid vehicles.


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Lexus has long held a leadership position among the luxury brands as regards offering hybrid vehicles. In fact, with the exception of the Cadillac Escalade Hybrid, it is still the only brand with an array of hybrids in its market space. There is the RX 400h crossover, the GS 450h sport sedan (or demurely described as a "bat-out-of-hell" vis-à-vis performance), and the LS 600h L, flagship.

Even though all of these are hybrids, and even though "hybrid" is often thought to connote "fuel efficiency," that is not the case with these vehicles (particularly not the GS 450h). By and large, the hybrid powertrains in the Lexus models are about performance, not Priusness. One way to look at these vehicles is to see them as technological tour de forces rather than as what has come to be understood as "hybrids." If there were dilithum-crystal technology for powertrains, they might be under the hoods of these cars.

As the economy has shifted and as there is a greater societal awareness of environmental issues, Lexus owners, explains Mark Templin, group vice president and general manager, Lexus Div., are interested in more fuel-efficient yet still premium transportation. And they did their homework on the potential for a car like the HS 250h, the fourth hybrid in the lineup and the world's first dedicated luxury hybrid (i.e., it isn't a variant on an existing vehicle in the lineup).

Templin: "Did you know that more than 60% of entry-luxury car buyers would have considered buying a hybrid if one had been available? We also know that 54% of hybrid owners have a household income of more than $100,000, so gener-ally hybrid owners are an affluent group. What's also interesting is that 16% of hybrid buyers from all makes already have a luxury vehicle in their household fleet."

Templin says that they're expecting to sell 25,000 HS 250s in its first full year on sale. Since the first RXh introduced in 2005, Lexus has sold some 170,000 hybrid vehicles, which puts them way ahead of all other makers in the category.

So what is it?

Chief engineer Hiro Koba says that the goal of the engineering team was "delivering the future first." This would be the result of the orchestration of three main elements: Environmental tech, driver-friendly systems, and luxurious features.

"At the foundation of the environmental technologies concept is the car's hybrid system," he says. It makes use of a 2.4-liter, DOHC inline four that produces 147 hp @ 6,000 rpm and 138 lb-ft of torque @ 4,400 rpm. The engine operates on the Atkinson cycle, which provides thermal efficiency as compared to the conventional Otto-cycle engine, which generally has a higher exhaust gas temperature, and provides a clean burn, which contributes to the California SULEV emissions certification and Tier 2 Bin 3 in other states. In addition to which, there is the electronically controlled continuously variable transmission (CVT), power control unit (PCU), and high-voltage battery. The CVT balances the motive power from the engine and the motor generator; the PCU includes an inverter that converts 224.8 volts of DC from the high-voltage battery up to 650 volts. The inverter also works to charge the battery during regenerative braking. The high-voltage battery, 244.8 volts DC, which consists of 204 cells combined into 34 modules, is located between the rear seat and trunk; it has an output of 40 hp. (Speaking of the trunk, although the car is dimensionally smaller than the GS 450h or LS 600h L* the HS has the largest trunk, thanks, in part, to the efforts made to efficiently position the hybrid functional components.) The total powertrain output is 187 hp. This provides 35 mpg city, 34 mpg highway, and 35 mpg combined.

Another consideration in the environ-mental arena is using as little energy as possible. So there is a engine exhaust heat recovery system that helps reduce warm-up time and to improve fuel economy; electric power steering is used, which provides a 3% fuel economy improvement as compared with a hydraulic system; the windshield reduces the transmission of infrared radiation into the cabin by 30%, thereby reducing the load on the air conditioning system; and LED headlamps are available, which are 30% more efficient than the standard halogen bulbs. (An interesting fact about the LED headlamps: washers are needed because there is insufficient heat generated to melt the snow that could accumulate on them.)

There is even the use of "ecological plastics" that use plant-derived polylactic acid, polyester, and polyol. Based on surface area, these materials account for 30% of the interior and luggage trim areas.

In the "driver-friendly systems" and "luxurious features" areas, this is more along the traditional Lexus lines. For example, there is a camera-based "intelligent" high beam system that automatically switches between high and low beams based on the detection of vehicles. There's SmartAccess, based on a combination of proximity sensors on each door as well as electrobiological sensors on the front door (e.g., grab the door handle, and it opens if you have the fob on your person). There's a human-machine interface system that is located in the center console and is essentially like a computer mouse in that it allows the selection of items (e.g., on the navigation screen), but which provides haptic feedback as the options are rolled over. And there is even an available heads-up display that provides information including speed, audio status, and turn-by-turn directions.

Is it a Prius? Because it is small, because the new Prius is bigger, it only seems that the HS 250h must be based on the Prius right?

Well the answer that comes from Bob Allan, Lexus College product education manager might be summed up as “sort of.” As he puts it: “It is generically the same platform as the Prius, but there are not shared suspension or body components.”

The hybrid transaxles and the motor generators are sourced from the Kokura factory that is part of the Kyushu manufacturing facility on the southern Japanese island. Like the Kyushu assembly plant, where the HS and the RX are assembled, care was taken to control the atmosphere within Kokura, even to the extent of having comparatively low ceilings to minimize the amount of air that must be managed within the building.

Consider this: Because it is a hybrid-only luxury vehicle, it represents a segment of one.

*HS 250h wheelbase, length, width, and height: 106.3 in., 184.8 in., 70.3 in., and 59.3 in. GS 450h: 112.2 in., 190 in., 71.7 in., and 56.1 in. LS 600h L: 121.7 in., 202.8 in., 73.8 in., and 58.3 in. One interesting thing to note is that the HS is actually taller than the other two vehicles.


The Chief Engineer
So, what does chief engineer Hiro Koba drive? A Toyota MR2. And a Ducati motorcycle.

Koba started at Toyota Motor Corp. in 1986, when he went to work in the Plastics Production Engineering Div. Given his background in polymers, it should be no surprise that there is the extensive use of the plant-based plastics in the HS 250h. Koba also worked in the Chassis Engineering Div.; the Product Planning Div., where he focused on European vehicles; and at the Toyota Technical Center USA in Ann Arbor, before returning to Japan in 2006 and becoming part of the Lexus Development Center team.


How to Open a Top
The IS C features 15 electric motors and sensors in 37 locations to drive and control the elements that fold the three-piece aluminum-paneled roof into the trunk in 20 seconds. In a very Toyota Product Development-like approach, there are actually overlapping processes during the mechanical sequence in order to perform without wasted time or motion.

The IS Gets a Drop-Top

“Convertibles are tricky to engineer as you can imagine, especially ones with three-part, hard-top roofs. The IS C roof was designed and engineered in-house, and we had three major goals at the start of vehicle development.
Junichi Furuyama

“We started our design as you would expect from the top down. First, we wanted to produce a
quality roof that would compliment
the exterior design of the first IS convertible.

“Second, we wanted to maintain the vehicle’s driving performance and rigidity, whether the roof was up or down.

“The third goal was the most important to me. Since the majority of convertible owners are very passionate about their cars, we had to ensure a great experience for the IS C’s driver and passengers.”—Junichi Furuyama, chief engineer, Lexus IS.


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