Lexus Changes Tack on Transmissions
Last month, we looked at the trend for manufacturers of hybrid vehicles to begin offering stepped automatic transmissions in place of the CVTs that are widely perceived as unresponsive, spoiling the fun of driving. Now comes news that the strongest advocate of CVT efficiency, Toyota, is beginning to acknowledge the importance of driveline responsiveness in the fun-to-drive equation, which translates directly into customer appeal. Lexus, Toyota’s premium brand, will introduce its first stepped transmission system with the hybrid version of its latest and most prestigious model, the LC 500 luxury coupé.
The regular V8 version of the svelte LC coupé already started on a challengingly high note. Announced at the 2106 Detroit auto show as a 2017 model, its four-cam V8 gives 467 hp, channelled to the rear wheels through a brand-new 10-speed planetary automatic from Aisin, the first such device on the market. That’s the kind of innovation expected from Lexus, but the specification for the hybrid version marked a departure in an entirely unanticipated direction.
Lexus LC 500 luxury coupé: Regular V8 has 10-speed auto, hybrid will have 10 gears, too.
Revealed in public at the Geneva show in March following a technical presentation some weeks beforehand, the LC 500h hybrid has taken the dramatic step of abandoning Toyota-Lexus’s signature policy of CVT is best, adding a four-speed stepped automatic into the mix. This will, in the company’s own words, “create a hybrid with a more sporting and engaging driving experience, with a closer alignment between engine speed and throttle inputs, while at the same time achieving the best balance of power and fuel consumption.”
Labelled the Multi Stage Hybrid System, the new driveline places a four-speed automatic transmission at the output of the familiar Hybrid Synergy Drive’s CVT. The variable ratios generated by the electronic CVT’s complex balance of generator, motors and planetaries are thus multiplied by the AT’s ratio changes before being fed along the propeller shaft and to the rear axle. This allows the AT to multiply the torque being delivered through the CVT so that the CVT itself does not need to cover such a wide ratio span for a given range of road speeds, helping allow the V6 gasoline engine to run at lower cruising rpm for improved NVH and lower fuel consumption.
But those are not the main points of the new driveline. Its central purpose is to restore the feeling of a direct relationship between throttle application and engine response, and between engine sound and road speed – that sporty driver’s feel that is so lacking in CVT vehicles and most hybrids. Central to that feeling are the sensation of stepped gear changes, the change in engine note, and the quick response to the throttle. That is why Lexus has built in no fewer than ten ratio steps into the combined transmission, some of them genuine mechanical shifts and some “virtual” shifts achieved through the CVT.
Though full assessment of the new driveline and its operating logic will have to wait until a test drive of a production LC 500h in 2017, it appears from engineers’ comments and the company’s published material that in two of the four drive modes – Normal and Eco – the transmission skips the two lower ratios of the automatic, letting the CVT do the work after the electric launch has taken place. It is not clear what role (if any) the “manual” gearshift paddles play in these modes, but an important benefit of the additional AT’s ratio multiplication is that the electric-only maximum speed is raised from 100 km/h to 140. This means the LC can cruise at over 80 mph with its 295 hp combustion engine switched off.
Hybrid version of LC 500 places the lithium-ion battery at the rear for optimum weight distribution, and closure panels are made of aluminium to help keep overall mass at the same level as the regular model
Switching the mode selector into Sport or Sport Plus brings in a very different drive logic. Now the CVT steps between its six pre-set “virtual” ratios; these interleave with the four mechanical ratio steps in the AT to generate a set of ten overall ratios. Lexus engineers at the presentation said that as a driver or passenger it was almost impossible to tell the difference between virtual and actual gearshifts, and also stated proudly that the LC 500h was the first Lexus hybrid that was able to spin up its rear tires on dry tarmac.
Additionally, Lexus engineers say the complete Multi Stage Hybrid System is no heavier than a dual clutch transmission of comparable torque and with hybrid componentry built in.
The LC 500h is built on the Toyota-Lexus group’s new GA-L architecture for luxury cars with inline engines and rear- or four-wheel drive. The new Multi Stage Hybrid System can thus be expected to appear – or be offered – in upcoming generations of Lexus models with rear-wheel drive, such as the GS and LS sedans.
Although the additional four-speed AT is built into the structure of the transmission casing, the system as it is presently configured is much too long to fit into a transverse application. However, competition from major hybrid players such as BMW and Hyundai-Kia is intensifying and, as we saw last month, these companies also understand the importance of driving enjoyment. With Toyota’s huge global resources and its eagerness to listen to customers, it should not be long before the lessons learned with Lexus find their way into smaller – and more responsive – models such as the Prius and the growing family of hybrid derivatives of other medium car lines.
|Lexus: LC 500 V8 versus LC 500h|
|LC 500||LC 500h|
|Engine type||V8 gasoline||V6 gasoline, Atkinson cycle|
|Max power||467 hp||295 hp|
|Hybrid system||—||59 hp e-motor, lithium-ion battery|
|Transmission||Aisin 10-speed planetary||Lexus eCVT plus 4-speed AT|
|Total system output||467 hp||354 hp|
|Acceleration 0-100 km/h||4.5 sec||Sub 5.0 (target)|
SOURCE: DRIVELINE NEWS