Following the world premiere of the V8-powered LC 500 at the North American International Auto Show (NAIAS) in January 2016, Lexus introduced its hybrid variant, the new LC 500h. (Earlier post.) The LC is a new flagship 2+2 performance coupe for Lexus’ global model range, and will go on sale in the US in Spring 2017.
The LC 500h is the first model to feature the new Multi Stage Hybrid system. (Earlier post.) Adding a multi stage shift device to the 3.5-liter V6 hybrid powertrain delivers greater torque, more usable power across a wider range of engine speeds and rhythmic, linear acceleration that gives the driver the sensation of working with a 10-speed automatic gearbox.
Lexus took a series series of detailed design and engineering measures to fine tune the performance of the 3.5-liter V6 gasoline engine featured in the LC 500h’s full hybrid powertrain, including a reduction in the diameter of the cylinder intake port to increase flow speed and efficiency. The engine makes good use of Dual VVT-i (intelligent variable valve-timing), with timing precisely gauged in line with driving conditions, helping to secure high torque at all engine speeds.
Measures to reduce friction losses and thus help enhance engine efficiency include the adoption of narrow, lightweight roller rocker arms and low-friction timing chains, while D-4S direct fuel injection helps create optimum combustion conditions, contributing to enhanced fuel efficiency.
|The Multi Stage Hybrid System for rear-wheel drive.|
The Multi Stage Hybrid System amplifies engine and motor output due to a new multi stage shift device, which changes the output in four stages in order to utilize the engine speeds across the entire speed range. The speed range has also been expanded to a maximum 6600 rpm.
|Wider speed range. Source: Toyota Motor. Click to enlarge.|
This creates a system that responds much more directly to driver inputs and achieves a higher level of dynamic performance and driving pleasure, while maintaining smoothness and efficiency.
Acceleration at start using the LC 500h’s combination of Multi Stage Hybrid System and 3.6-liter V6 exceeds the performance of the 5.0L V8. Such is the level of torque and acceleration when pulling away from a complete stop, the LC 500h is the first Lexus hybrid that can spin its rear wheels, according to Chief Engineer Koji Sato.
|Top: Vehicle speed and drivepower. Bottom: Acceleration performance. Source: Toyota Motor. Click to enlarge.|
In a conventional full hybrid vehicle, engine output is amplified by the electric motor via a reduction gear; with the new Multi Stage Hybrid System, the power from the V6 engine and the electric motor can be amplified by the automatic transmission, allowing much greater drive power to be generated when accelerating off the line.
Lexus has succeeded in increasing maximum engine rpm from 6,000 to 6,600 rpm. With the Multi Stage Hybrid System, the operating range in first, second and third gears has been increased, so that maximum rpm is reached at about 50km/h (31 mph).
|Improved electrical path efficiency. Source: Toyota Motor. Click to enlarge.|
Although the multi stage shift device changes the output in four stages, the D range has a simulated shift control pattern that replicates the feel of driving with 10 gears. As vehicle speed rises, engine speed increases with a linear, direct and continuous acceleration feel that avoids the “rubber band” effect witnessed in some continuously variable transmissions. In the 10th gear range, the CVT control allows for cruising at lower engine revs for quiet, smooth and more fuel-efficient performance.
|Smooth acceleration with 10-speed A/T simulated control. Click to enlarge.|
In another first for a Lexus hybrid, the transmission benefits from an enhanced version of the AI shift control found in conventional automatics. This enables intelligent, optimum gear selection to be made in line with driving conditions and driver inputs, for example when going up or downhill.
The system also includes an automatic Drive Mode switching control. This means it can adjust gear shifts to suit the driver’s style and behavior, without the driver having to select a different drive mode to get the kind of performance they want from the transmission.
Lithium-ion hybrid battery. The LC 500h is the first production Lexus to use a compact, lightweight, lithium-ion hybrid battery. Twenty percent smaller than the nickel-metal hydride unit featured in the Lexus LS, it fits neatly between the rear seats and the luggage compartment and has a higher power density, with its 84 cells producing 310.8 Volts.
Using lithium-ion technology has also reduced the component’s weight, helping reduce the LC 500h’s overall mass, and contributed to the effective management of the car’s inertia specifications. This supports overall fuel economy, emissions performance and the coupe’s handling balance.
It is also the first Lexus hybrid battery to feature a satellite construction design, in which the cell voltage monitoring function has been made separate from the battery ECU. This allows for efficient use of what would otherwise be empty space inside the battery pack to house the wiring harness and battery cooling blower, thus reducing the unit’s overall dimensions. The cooling blower itself has been made more powerful and thinner in size.
Adopting lithium-ion battery technology results in more compact packaging, helping to ensure that luggage space is maintained. It also assists in reducing the overall vehicle weight.