For Chief Engineer Koji Sato, the greatest engineering achievement on the 2018 Lexus LC is the coupe’s sharp and refined driving dynamics.
To help achieve that crisp performance, engineers focused on finding the ideal inertia specifications, including a low center of gravity that’s close to the driver’s H-point. They designed the LC’s body structure with the highest torsional stiffness of any Lexus and they developed a new suspension design.
“We had to be creative with the suspension architecture so the suspension tower height would be kept low while still being able to house large 21-in wheels," Sato explained. "We also focused on the design and suspension pick up points to not only lower the height but also to enhance the rigidity.
"So we applied a multi-link suspension," he said. “It took six months to find the best geometry of the suspension arms.” Veteran Toyota engineer Sato and Lexus product experts spoke with Automotive Engineering during a February media preview of the all-new LC 500 and the hybrid LC 500h on the Big Island of Hawai'i.
Lightweight materials mix
Both versions of the visually captivating LC coupe debut Toyota's GA-L (Global Architecture-Luxury) front engine/rear drive platform for high-performance/luxury models, for global markets.The car's design is exceedingly close to the LF-LC concept shown at the 2012 Detroit auto show. But what’s unseen is equally intriguing. The coupe’s underbody went through extensive CFD simulation and wind tunnel testing for downforce and diffuser design evaluations.
“We needed to create suitable airflow in correlation to the air pressure being produced from the upper body towards the rear of the vehicle,” Sato explained. “The underbody is obviously covered to have optimum airflow. We also have created an air duct in the front part of the rear wheel to reduce turbulent air flowing through the door side panels as well as the wheel housing.”
The 113-in (2870 mm)-wheelbase LC rides on run-flat tires supplied by Bridgestone, Dunlop and Michelin. Eliminating the need for a spare tire provided trunk space for the auxiliary battery and weight savings. LC’s 4280-lb/1935-kg curb weight (4435-lb/2012-kg for hybrid version) derives from a mix of lightweight materials.
Front fenders, hood, and side door panels are aluminum. The die-cast aluminum front suspension towers were joined to steel via self-piercing rivets, a Lexus first. Carbon fiber reinforced plastic (CFRP) is used in the inner door panels and trunk lid. And a CFRP roof is available with the performance package, which also adds an active rear spoiler. The platform extensively uses ultra high tensile strength steel.
Aisin 10-speed, new Hybrid system
The normally aspired Toyota 5.0-L gasoline V8 delivers a rated 471 hp (351 kW) at 7100 rpm and 398 lb·ft (539 N·m) at 4800 rpm. This engine is based off that used in the Lexus RC F sports coupe and the GS F sedan. “The intake/exhaust valve design and layout as well as the exhaust pipe configuration is newly developed for the LC,” noted Sato, and the ECU is remapped. A sound generator fine-tunes the V8’s intake noise that is piped to the cabin.
The V8 mates to Aisin's new Direct Shift 10-speed planetary automatic with a full range lock-up control torque converter. “By having 10 gear sets to work with, it allowed for a quiet and comfortable drive at higher cruising speed, while still being able to enjoy a wide range of gearshifts through acceleration and deceleration,” Sato explained.
The transmission’s AI-SHIFT control, a Lexus first application, selects the optimum gear based on vehicle speed, accelerator use and via an estimation of the driver’s preferences/intentions. LC is the first in its segment with a 10-speed automatic, with 8- and 9-speed units predominating.
LC 500h debuts Lexus’ first Multi Stage Hybrid System. Unlike a conventional full hybrid powertrain in which engine output is amplified by an electric motor’s reduction gear, the multi-stage system amplifies the electric motor via the automatic transmission.
The multi-stage shift device changes the output in four stages: first/second/third simulated gears to match the first mechanical gear; fourth/fifth/sixth virtual gears to match the second mechanical gear; seventh/eighth/ninth simulated gears to match the third mechanical gear; and an overdrive virtual gear ratio to match the fourth mechanical gear.
According to Bill Kwong, a Lexus College technical expert, “The multi-stage aspect is akin to a transfer case or an automatic differential.” The LC hybrid driver can opt for manual gear selection using the steering-wheel-mounted magnesium alloy paddle shifters that provide a Lexus hybrid-first ‘manual-hold’ feature.
LC 500h uses a 3.5-L gasoline V6, similar to the current RX 450h crossover vehicle. It's rated at 295 hp (219 kW) at 6600 rpm and 256 lb·ft (347 N·m) at 4900 rpm. The "dual injection" system uses both direct and port injectors, with variable valve timing with intelligence wide (VVT-iW) on the intake and VVT-i on the exhaust.
“The previous hybrid system could only go into Atkinson cycle,” Kwong said. “But now with both Atkinson cycle and auto-cycle, it’s possible to have wide, broad cam-phasing.” This new hybrid system essentially responds to driver inputs without a lag between rpm and vehicle speed.
There are two permanent magnet synchronous motors on the LC hybrid. The primary generator (Motor Generator 1/MG1) handles engine start and controls engine speed. Motor Generator 2 (MG2) drives the rear wheels and handles regenerative braking. Positioned between the rear seats and the luggage compartment are 84 lithium-ion cells producing 310.8 V. This Li-ion battery pack, a first for a Lexus vehicle, is 20% smaller than the NiMh pack in the Lexus LS.
The LC 500 and 500h will be sold globally with U.S. sales beginning in spring 2017.
“We’re forecasting that the sales split will be 90% for the LC 500 and 10% for the LC 500h,” said Brian Bolain, Lexus’ General Manager Product & Consumer Marketing. MSRP for LC 500 is $92,000 and $96,510 for the LC 500h.Continue reading »