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In a little over a year, the new Lexus LC500 and LC500h flagship coupes go on sale. We got a quick look at the 500h hybrid ahead of its auto-show debut in Geneva. The hybrid won’t be in showrooms for quite a while, but when it does arrive, the one thing you are sure to never hear a salesman say about the hybrid is, “this transmission is like a semi truck’s.” No one wants to hear that their potential new Lexus luxury coupe has anything in common with a Peterbilt. In reality though, they sort of do. Lexus’s new hybrid transmission, dubbed Multi Stage, is essentially two transmissions bolted up to one another: a Toyota hybrid CVT and an Aisin four-speed automatic, which is just like the dog-tooth manual and range selector found in a tractor-trailer’s 18-speed manual.
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Before we dive in the shallow end of Multi Stage, lets have a quick primer on Toyota Hybrid Synergy Drive (HSD). Debuting in Toyota’s home market in the 1997 Prius as the Toyota Hybrid System, HSD’s concept is complex but the design is rather simple. HSD consists of an internal-combustion engine (ICE), two motor-generators (MG1 and MG2), and a planetary gear set (in some cases, multiple planetaries). MG1’s role is that of a generator and it also sets the reduction (gear ratio) by changing its speed, and acts as a starter for the ICE. MG2 is the traction motor, battery-limited to 60 horses in the LC500h, and is the primary harvester of regenerative-braking energy. These components are fundamentally the same in all HSD applications and have evolved, broadening the HSD’s capabilities in the last 19 years. While most Toyota and Lexus hybrids have transverse powertrains, only two cars, the Lexus GS450h and LS600hL, utilize a longitudinal setup.
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Back to the LC500h: The CVT half of Multi Stage is an evolution of the longitudinal hybrid transmission found in those Lexus sedans. The big difference in Multi Stage from the older tranmission is the additional four-speed planetary gearbox attached at the CVT’s output. In the current GS and LS, MG2 gets a two-speed reduction, but in the Multi Stage the ICE drives MG1 and/or MG2 directly, but both MG2 and the ICE get the additional reduction of the four-speed auto. This keeps MG1 from hitting its redline, the cutoff for electric-only driving, and allows for EV driving as fast as 87 mph (up from 40 mph in the GS and LS).
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Also, Multi Stage expands the hybrid operating range, increasing the LC500h’s ability to accelerate at high rpm in a lower gears and cruise at higher speeds turning lower rpms in higher (read: overdrive) gears. Keeping MG1 revs down also limits the electrical losses, a boon to efficiency. And along with improved power electronics, the electrical improvements over the previous-generation transmission realize the biggest gain in efficiency. Howerver, according to Lexus the biggest gains aren’t measured on a dyno or with a tail-pipe sniffer, they are found from behind the wheel.
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Multi Stage claims to improve the relationship between car and hybrid. Multi Stage is still a continuously variable transmission and there is potential for a dramatic disconnect between engine rpm and throttle inputs, the so-called “rubber-band” effect that is a relationship killer. LC chief engineer Koji Sato says their goal is to eliminate this disconnected feeling. In normal driving modes he admits the trans will perform much like a conventional CVT because it is more efficient to keep the engine in optimal operating conditions (load and rpm). In the new “M” mode, Multi Stage will mimic a 10-speed automatic, creating discrete ratios through a combination of HSD and planetary reductions. If you’re so inclined, you can shift with paddles located behind the steering wheel.
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If Multi Stage sounds somewhat familiar, that’s because it is. General Motors, Daimler-Chrysler, and BMW partook in an automotive ménage a trois resulting in the hybrid transmission called Two-Mode. It was more-or-less a stillborn piece of technology utilizing a similar power-split CVT and planetary arrangement. Two-Mode made it into a few Tahoes and Escalades before the project was shelved. Two-Mode could provide electric-only driving up to 32 mph and, at a certain speed, the transmission functioned as a planetary automatic. Multi Stage, from what we’ve seen, is similar in the component set, but far more capable in its execution. And more complex, too.
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- 2016 Toyota Prius Frist Drive Review
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- Instrumented Test: 2013 Lexus LS600hL
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- 2017 Lexus LC500 Coupe Dissected: Design, Powertrain, Chassis, and More
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The internal combustion engine in the LC500h is a new version of the 3.5-liter V-6 that Toyota calls 2GR-FSX. It runs the more efficient Atkinson cycle exclusively and makes 295 horsepower at 6600 rpm. With MG2 sucking juice from a compact, air-cooled lithium-ion battery, the LC500h produces a maximum of 354 horsepower and Lexus says the LC500h will hit 60 mph in less than five seconds. We will test those paddles, this transmission, and everything else on these new coupes when we get behind the wheel in about a year.
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from Car and Driver Blog http://blog.caranddriver.com/two-trans-enter-one-trans-leaves-details-of-the-new-lexus-multi-stage-hybrid/
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