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The Lexus GS 450h Hybrid System

Gs450h1_1
System configuration of the GS 450h. Click to enlarge.

At last week’s SAE Hybrid Vehicle Technologies Symposium 2007, Akihiro Yamanaka from Toyota provided some details on the hybrid drivetrain for the Lexus GS 450h—the first FR (front-engine, rear-wheel drive) passenger car hybrid on the market.

As it has introduced more hybrid models, Toyota continues to develop enhancements to the original Hybrid Synergy Drive II, which is the core of the second-generation Prius, relevant to various vehicle applications.

The company’s first foray into hybrid systems for vehicles that require more power—such as SUVs—was the system applied in the Rx 400h and Highlander Hybrid SUV. This system adds a conventional planetary gearset as a motor speed reduction gear at the rear of the transmission to increase torque.

By increasing system torque with the reduction gear, Toyota was able to reduce the size of the transmission’s two electric motors, and properly match the hybrid system with a larger engine.

L110
Schematic of the GS 450h transmission. Click to enlarge.

The hybrid system in the GS 450h takes a step further, and uses a two-stage motor speed reduction device. Specifically developed for rear-wheel drive systems, the Toyota Hybrid System II with Two-Stage Motor Speed Reduction Device utilizes the motor’s high-efficiency region over a wider range of gear ratios than before. The hybrid system in the GS 450h supports both high output and high vehicle speed.

Evolution of Toyota Hybrid System
Year 2000 2003 2005 2006 2007
System Toyota Hybrid System (THS) Hybrid Synergy Drive (THS II) Lexus Hybrid Drive
w/ motor reduction gear
Lexus Hybrid Drive FR
two-stage motor reduction
Lexus Hybrid Drive AWD
Vehicle Prius Prius Rx 400h GS 450h LS 600h
Drive FF (front-engine, front-wheel drive) FF 4WD FR AWD
Engine L4 1.5L
53 kW
L4 1.5L
57 kW
V6 3.3L
155 kW
V6 3.5L
218 kW
V8 5.0L
Motor 33 kW 50 kW 123 kW 147 kW
System 82 kW 200 kW 254 kW More than 300 kW
Gs450h3_2
High and low gear operation.

To engage the low gear range, Toyota opens the conventional planetary gearset’s brake 1 and locks brake 2, resulting in a reduction gear ratio of 3.900. For high gear, brake 1 is locked and brake two is open, with a reduction gear ratio of 1.900. (The Rx 400h uses a fixed reduction ratio of 2.478.) The result is that the motor in the 450h acts as a single high-torque and high-speed motor. Motor size can then be reduced enough to fit the transmission in the GS450h floorpan tunnel.

The GS 450h uses a DC boost converter (288 Vdc to 650 V max) to support increased motor speed.

In addition to motor improvements, the GS 450h uses a new compact and high power control unit, commonly referred to as an inverter assembly, that is downsized through an improved cooling system. The new inverter assembly, which is similar to the inverter assembly used in the Camry hybrid, is about the same size as an auxiliary battery, and is located at the passenger side rear of the engine bay. The auxiliary 12V battery is moved to the luggage compartment.

Gs450h4
Acceleration vs. CO2. Click to enlarge.

Combined with the dual injection (direct and port) 3.5-liter engine, the GS 450h is able to achieve lower carbon dioxide emissions than the 3-liter class diesel engine group, while delivering the acceleration that is an important attribute for this vehicle segment.

The GS 450h uses hydraulic brakes in the front and rear, and regenerative braking on the rear axle only. As front brake energy is unrecoverable, the GS 450h distributes braking force to the rear wheels as much as possible.

The dual injection (direct and port) 3.5-liter engine of the GS 450h produces lower carbon dioxide emissions than the 3-liter class diesel engine group, yet is capable of 0-60 mph acceleration in 5.2 seconds.

Interestingly, a recently published SAE paper on the GS450h transmission compares its form factor to that of the automatic transmission used in the current Toyota Tacoma.

Comments

mahonj

It is a pity they do not build something in the 60-120KW region, or redo the 82 KW of the prius, and concentrate on smaller cars for economy instead of putting all the effort into trophy cars.
It would be interesting to see what they could do with a hybrid MPV.

Patrick

They have a hybrid MPV...in Japan.

Ash

They should put this in a Yaris ^_^

Andrey

Amazing how hybrid system’s designs converge. GM (+BMW and DC) two mode hybrid transmission adds another planetary gear after power split module and claims even higher efficiency and four fixed pure mechanical gearing ratios.

DCE

Rolling out new or improved technology in an automakers "trophy cars" is a normal way for the automakers to get real-world feedback. It enables them to introduce the tech. without a potential disaster of a large, high sales platform having problems. Think GM over the years with introducing new tech in the Corvette and Caddys first.

The most important statement of the entire article is in the last sentence. Can you say "hybrid Tacoma".

Dan

Patrick

Hmmm, put it in a Yaris????...a Yaris with a 3.5L V-6, electric motors and RWD: Fast in a straightline, but I feel sorry for you when you try to go through a turn or have to stop ( I don't think you'd fit rubber much wider than 215 in those wheel wells).

Travis Rassat

Dan latched on to the same thing I did - I think the idea of a hybrid Tacoma is exciting. My wife and I love our Toyota Camry Hybrid, but it's sure hard to haul any lumber in it!

I'm definitely no expert in any of this, but here's my take on it - When considering the purpose of this car, we need to consider Lexus's target market. It's not me, that's for sure. I can't afford this car. It just isn't practical for me to spend $50,000+ on a car. But, there are people who can, or think they can. Some of these people are addicted to big, fast, luxurious cars as a form of status. Plus, if you can afford the car, you must be able to afford to get 10 mpg too, huh? Part of that status is built on the perceptions of the traditional car enthusiast - status is gained by owning a fast, high performance car, a luxurious car, or the all-important performance-luxury car.

Lexus is using hybrid technology to improve make the GS Hybrid the fastest GS and the hybrid stuff is the newest gadgetry. It's performance-luxury++! I talk with people on a daily basis who just don't get hybrid technology - they see it as a bunch of "treehugging hippie crap" and a fad. They just don't get it. Most people are too damn short-sighted to make an effort to do something good for the Earth unless there's something in it for them. For people to adopt clean technology, it needs to be either standard or give them a perceived gain (i.e. performance). Plenty of people will spend extra money for the "SS" or "GT" performance option. Lexus has made the hybrid their GT. I like that idea a lot. If a hybrid car is considered the top of the line, it's going to reshape the public image of the technology, and people will want it. People will buy it and it will continue to evolve.

I also think that concentrating on designing and building something that can withstand the stress of the additional weight and torture inflicted by larger or higher performance vehicles with greater horsepower requirements will scale down to more reliable smaller vehicles. I think it's a worthwhile effort, and frankly I'm afraid it might be the only way hybrids are going to catch on with the mainstream.

That's just my opinion.

Patrick

If they do produce some type of hybrid Tacoma I hope they include a 110VAC outlet.

Roger Pham

For all the appearance of increase complexity in this design vs. that of the Prius, all Toyota added to the HSD of the Prius is a 2-speed planetary transmission gear set linking the motor/engine output to the wheel.

The reason is simple: The Prius is not intended for high performance, so high acceleration torque at the wheel is not a high priority in comparison to lower purchasing cost. Whereas, this latest Lexus Hybrid drive is intended for high-acceleration which requires a low gear for low-speed acceleration and a high gear for high cruise efficiency, while at the same time, able to reduce the size of the electric motor. Apparently, gears are cheaper than permanent magnets and copper winding!

I don't think that this is anything like the GM dual-mode hybrid transmission.

Apex Alex

TWO points:

1. i fully agree with Roger on the desirability of a WIDE RANGE of gearing options. the wider the range, the more "have your cake and eat it too" returns. i believe the 8-speed offered in the new Lexus LS is as much to exploit this, as it is just one-upping the competition.

2. if a Hybrid Tacoma is in the pipeline, i believe it may well create a whole new market in efficient pickups. i have owned 4-cyl japanese pickups since 1986, which have returned up to 35 mpg. further, despite its "compact" status, my '94 toy is still rated at a FULL 3/4 load capacity. 1610 pounds to be exact!

the ONLY disadvantage it suffers vis-a-vis full sizers, is lack of a torquey V8 (90% compensated for by GEARING) and a large box (MAIN advantage: only in hauling more low density cargo. most loads exceed 1500 lbs FAR sooner than the VOLUME of even a compact's box.)

the recent trend to upsize compact p/us seemed to me a step BACKWARD. i have not had ANY incentive to trade my '94 toy p/u for a current Tacoma. (initially, the new style was uglier; newer models look better, but are also still LESS efficient.) i don't believe there is ANY new p/u today that is capable of 30 mpg, much less 35.

a new hybrid tacoma could CHANGE that!

(and for those for whom size does matter, a Hybrid Tundra would really put toyota up front, across the board.)

Apex Alex


clarification: full 3/4 TON

richard schumacher

GM's hybrid also uses two clutches. Icky, icky, icky.

Schmeltz

Travis:
I agree with you on what you are saying about hybrids. People just can't seem to except the technology yet in widespread numbers. Many justify their hybrid hesitance on the technology being more expensive, and therefore can't see a return on their investment for 5 or more years. Yet, in the same stroke, they will opt for the power moonroof, navigation system, all leather seats, special chrome wheels, etc., etc. How many years does it take for those things to return their investment? My primary hesitation is durability and reliability of a hybrid drivetrain. Will a hybrid car provide reliable transportation for 10 years, or even 5 years? We hope so, but the technology hasn't been on American roads long enough to know for sure. Nobody has a 10 year old Prius to ask. Another problem I can see is the lack of maintenance/repair experience of shade tree mechanics with hybrids. You are stuck with your dealership if anything needs work or repairs. Most other service shops aren't quite as knowledgable...yet. I am happy to see more and more hybrids being sold every year, though. This is a growing process, and is nice to see this new industry beginning to mature.

As far as a potential hybrid Tacoma, I say "Bring it on!". I would like to see a hybrid option for all vehicles, just like you choose a V-6, or V-8.

Nick

"Will a hybrid car provide reliable transportation for 10 years, or even 5 years? "

Consumer Reports says Prius owners report very high reliability so far.

Wells

I'm thinking no Japanese full-size truck will succeed in the USA. I was watching my favorite TV show, "King of the Hill", the other day, and the latest Toyota Truck commercial aired. I was shocked! Hank Hill would never buy an import truck.

I remember the episode where Hank's old truck wore out. He and his wife Peggy were watching some chick flick she made him take her to see at the movies, where he realized suddenly the sad truth between being bored. Peggy asked him if he was getting emotional about the movie, but Hank was weepy about his truck's last days. The episode ended with the truck committing suicide by stalling on a railroad, so that Hank could go on with his life. I think the truck's name was Betsy, and the new truck Betsy II. :-)

Travis Rassat

Schmeltz,

That's a great point about maintenance - that makes a lot of sense and I didn't really think about that.

Going back to the Lexus target market, I think you and I differ from their clientele in the sense that we want to make our cars last - I hope to get 10 years or more out of our Camry Hybrid. I'm also do all my own maintenance. The type of person who can afford a Lexus may be the type of person who buys a new car every year or two years. They probably won't be so concerned about the reliability. They might drop it off at the dealer for maintenance and not even pay attention to what was done. This hands-off, disposable car attitude is great for the dealerships, but sad for the smaller businesses, environment, and the consumers. Unfortunately, I think it's the consumer's fault.

Anyway, I don't know where I'm going with this, other than to say that you make some great points there that got me thinking... Good stuff! I really enjoy reading the articles and posts on this site - some of it is way over my head, but it all gets me thinking.

Travis

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