“This new drive system provides the best combination of size, cost, efficiency, and smoothness for a rear-drive vehicle,” said Owen Thunes, Nissan North America’s Senior Project Engineer for Electric, Hybrid & Fuel Cell Vehicles.
In a presentation at the recent SAE Hybrid Vehicle Technology Symposium in San Diego, Thunes provided some details of his company’s upcoming 1M2C—the new one-motor, two-clutch hybrid-electric architecture set to debut next year in the 2012 Infiniti M35 Hybrid.
The new M35 is the first hybrid vehicle for Nissan’s upscale brand. It will launch approximately one year after the conventionally powered 2011 M sedan series, which includes a high-performance diesel V6 for the European market.
According to Thunes, the 1M2C drive system will provide the C/D-segment, gasoline-V6-powered M35 sedan with the fuel economy of a C-segment car with a much smaller-displacement engine.
“Our fuel efficiency target is that of a 1.8-L-class vehicle,” he explained. The current Nissan Fuga, on which the new M35 is based, has a curb weight of 3900 lb (1780 kg).
While the 1M2C system is aimed initially at rear-drive vehicle applications with numerically low final-drive ratios, it is designed to adapt well to front-drive applications with smaller engine sizes. This will enable Nissan to expand its production scale, Thunes noted.
Nissan developed the 1M2C entirely in-house, Thunes said. It is based on the automaker’s current seven-speed planetary automatic but replaces the torque converter with the pair of clutches and electric motor.
The first (dry) clutch resides directly behind the 3.5-L VQ-series V6, which is set up to run on the Atkinson cycle to optimize efficiency with the hybrid drive. In line behind the first clutch is a 50-kW (67-hp) interior permanent-magnet e-motor which handles traction and regeneration duties. A wet clutch is fitted on the back end behind the e-motor and provides some “slip” to help start the engine, among other duties.
In slow-speed urban driving cycles, the combustion engine shuts off and the front clutch disengages, allowing the e-motor to propel the vehicle with zero emissions. Thunes said the M35 Hybrid will be capable of EV-only operation under “light” acceleration up to approximately 100 km/h (62 mph). When hard acceleration is called for, both clutches engage and the e-motor and combustion engine work in blended mode.
In steady-state cruise mode at high road velocities, the e-motor shuts down, both clutches are engaged, and the V6 provides the propulsion. The e-motor also serves as a generator during deceleration. In the fourth (regeneration) mode, the combustion engine shuts off, the front clutch disengages, and power generated by rear-wheel braking is sent via the rear clutch and electric motor to the 345v lithium-ion battery pack.
Implementation of the system requires an integrated control system to simultaneously regulate battery, inverter, motor, clutches, engine, and transmission. Developing a high-speed control system for switching from charge to discharge modes with a single motor was key, said Thunes.
He admitted that managing the battery state-of-charge with just one e-motor is difficult—“but the rapid regeneration capability of the lithium-ion helps make up for it,” he said.
The battery pack contains 96 Li-ion cells which Nissan manufactures in its Automotive Energy Supply Corp. joint-venture with NEC Corp. The cells are a “laminated” design that improves thermal performance and enables the modules to be thin and compact. The pack’s thermal stability also is enhanced by the use of manganese spinel cathodes. The cells are similar in construction to those used in Nissan’s 2011 Leaf EV.
The M35 Hybrid also will share some power electronics with the Leaf, Thunes told the SAE audience. For Nissan, the program is a major leap forward from the Altima Hybrid program, which relied on some Toyota proprietary hybrid technology.
Fleet testing has commenced in the U.S., Europe, and Japan, with the U.S. test program being centered in the San Francisco area, Thunes said.