Subaru’s new B5-TPH hybrid concept made its North American debut at the 2006 North American International Auto Show. The B5-TPH concept vehicle applies the company’s Turbo Parallel Hybrid (TPH) powertrain system (earlier post) and lithium-ion battery technology in a two-seat grand touring car that offers fuel economy of 40 mpg.
Subaru’s parent—Fuji Heavy Industries (FHI)—has been developing the TPH powertrain for future mass production and will test-launch TPH-powered Legacys in the Japanese market next year.
Subaru also showcased a test version of its R1e urban electric vehicle (earlier post) equipped with next-generation long-life lithium-ion type batteries from NEC Lamilion Energy.
NEC and FHI jointly established NEC Lamilion in 2002 for the development of secondary batteries. Designed to meet the needs of city mobility, the Subaru R1e is projected to achieve an 80% recharge in about fifteen minutes. The resulting charge can supply enough power to serve most daily commuting needs in congested urban areas. (More on the R1e and the Li-ion technology in a subsequent post.)
Subaru has always been, and will continue to be, committed to safeguarding the natural environment that so many of our customers avidly enjoy. We will continue to make these technologies a priority in our product development, manufacturing and business processes.—Kunio Ishigami, chairman, president and CEO, Subaru of America
The Turbo Hybrid Powertrain. The Subaru TPH powertrain in the B5-TPH places a thin, 10-kW motor generator between a newly-developed 2.0-liter Miller cycle engine and the automatic transmission.
The engine is based on the standard Legacy 2.0-liter Boxer (horizontally opposed) engine, with modifications to the cams and engine management software to implement the Miller cycle.
A Miller-cycle engine (similar to the Atkinson cycle) leaves the intake valve open during part of the compression stroke. The late closing of the intake valve eliminates the substantial amount of energy normally required to overcome friction (as well as pumping losses) in the process of completing a normal compression stroke. The result is increased engine efficiency, at around 10%–15%, although with a loss of power.
To compensate for the power loss, the prototypic Miller engine uses a supercharger. Subaru instead applies a turbocharger to make up for the power loss in the mid-range. The additional assistance provided by the electric motor compensates for low-end power loss.
The combination of the motor-generator and the turbocharged Subaru Boxer engine creates a system that not only provides power in the mid-speed ranges when the turbocharger is active—as with conventional turbo models—but it also delivers excellent acceleration and fuel economy.
In the Subaru B5-TPH, the Miller Cycle turbo Boxer engine operates up to 30% more efficiently than a conventional gasoline engine. Overall, the engine delivers 256 hp, with 343 Nm of torque.
|Breakaway view of the TPH powertrain with the motor exposed.||Engine performance graph showing the affect of the different components.|
Subaru plans to equip the system with high-performance manganese lithium-ion batteries. FHI is also developing Li-ion capacitors, and is currently conducting performance tests on prototype cells. The Li-ion capacitor dramatically enhances energy density, while retaining the inherently superior capability of instantaneous charge/discharge and the high durability of regular capacitors.
The Li-ion capacitor’s negative electrode uses newly developed Li-ion occlusive carbon material, while its electrolyte is also made of Li-ion. Pre-doping enables occlusion of a large amount of Li-ion on the negative electrode, boosting its capacity and increasing the electrical potential difference. This in turn enables high voltage without deterioration in positive electrode performance.
FHI believes that the application of certain new materials to the positive electrode, combined with the pre-doping technique of the Li-ion capacitor, will theoretically double the estimated accumulation capacity of capacitors available in today’s market.
(More on FHI’s work with Li-ion batteries and capacitors subsequently.)
|Quick Comparison: 2007 Toyota Camry Hybrid vs. Subaru B5-TPH Concept|
| ||2007 Camry Hybrid||B5-TPH Concept|
|Gasoline engine||2.4-liter Atkinson Cycle||2.0-liter Turbocharged Miller Cycle|
|Engine Power||147 hp (110 kW)||256 hp (191 kW)|
|Engine Torque||187 Nm||343 Nm|
|Hybrid Type||Full (with all-electric mode)||Mild (power assist)|
|Motor Output||105 kW||10 kW|
|Motor Torque||270 Nm||150 Nm|
|Fuel Economy (combined)||40 mpg US||40 mpg US|
|Fuel consumption (combined)||5.9 l/100km||5.9 l/100km|