|Advanced Hybrid System. Click to enlarge.|
At the upcoming British International Motor Show, GM is unveiling a new version of the Saab BioPower Hybrid (earlier post) that incorporates an application of the two-mode hybrid transmission GM is co-developing with DaimlerChrysler and BMW Group.
The earlier version of the E100-capable flex-fuel hybrid, introduced at the Stockholm Motor Show, featured a 300-volt Li-ion battery pack, a 38kW rear-mounted electric motor (rear drive unit—RDU), a 15 kW integrated starter/generator (ISG) and all-wheel-drive with electric power transmission to the rear wheels. It was also widely believed to incorporate the capability for plug-in recharging, although GM/Saab declined to confirm that.
|The E100 Biopower Hybrid concept now features the two-mode hybrid transmission.|
The two-mode BioPower Hybrid Concept builds on this by incorporating the two-mode transmission while keeping the RDU. The new version of the concept thus combines an all-aluminum flex-fuel engine capable of generating 260 hp (191 kW) with three electric motors that can generate a total of 148 kW. As a result, the Saab BioPower Hybrid Concept provides significantly greater torque than its gasoline-only equivalent.
Although it has the potential to run on E100, the BioPower engine can use any combination of gasoline and bioethanol.
The two-mode hybrid offers torque boosting electric power assistance on demand, fuel-saving stop/start functionality, regenerative braking, seamless gear changing from the continuously variable transmission modes and an electric-only Zero Mode option for city driving.
This concept allows us to evaluate and explore the potential of hybrid technology in combination with BioPower. As part of this process, we are now developing our expertise further by introducing the two-mode hybrid technology. It shows how we can continue to express the sporty performance associated with Saab while using renewable resources and saving energy overall.—Jan Åke Jonsson, Saab Automobile Managing Director
Hybrid Transmission. The hybrid transmission combines two 55 kW electric motors and four fixed gears within a single transmission housing. Commonly described as a two-mode hybrid due to the low- and high-speed electric continuously variable transmission (ECVT) modes, the system also incorporates four fixed gear ratios for a total of six operating functions. (Earlier post.)
The two-mode hybrid’s electric motors can be used for electric-only propulsion, boosting the internal combustion engine and providing regenerative braking.
Additional fuel-saving efforts include removing auxiliary functions, such as the water pump, air conditioning and power steering systems, from the engine’s belt drive and transferring them to electric power through the hybrid system.
The two-mode hybrid transmission is similar in size to a conventional automatic transmission. Its adaptable design allows it to be scaled to the size, mass and performance needs of various engines and vehicles. GM has announced that it will apply the two-mode transmission to hybrid versions of its full-size SUVs starting in 2007.
Engine. The engine is a BioPower evolution of the current all-aluminum, 16-valve 2.0-liter turbo engine in the Saab 9-3 range. Utilizing the higher octane ratings offered by E100, it develops 260 hp (191 kW) and 375 Nm (277 lb-ft) maximum torque, an increase of 24% and 25%, respectively, compared to its gasoline-only equivalent.
A Spark Ignited Direct Injection (SIDI) system provides optimum combustion with E100, to enable the same cold-starting performance as a gasoline engine. Variable inlet and exhaust cam phasing is used for optimum air flow and more durable valves and valve seats are fitted, together with bioethanol-compatible materials for the fuel system.
RDU. The RDU features a 38 kW motor, located between the rear wheels, which powers a transmission differential and drive shafts. Under acceleration at low speeds, the RDU is able to briefly generate 665 Nm of additional torque. The motor is also configured to provide regenerative braking and energy recovery from the rotating drive shafts during deceleration.
Battery. Energy storage for all three electric motors is provided by a high-capacity 300-volt lithium-ion battery with fan cooling. This is packaged under the floor of the trunk, without eliminating storage space. Battery performance is carefully monitored and governed by a dedicated electronic control unit.
Zero Mode. The driver can select Zero Mode via a button in the central console. At speeds below 50 kph (31 mph), Zero Mode will shut off the engine and switch the car over to electric power only from the RDU. In this mode, the battery bank provides a range of between 10 and 20 kilometers (6 to 12 miles). The engine is smoothly re-engaged whenever the battery status approaches a low charge level or the electronic throttle opening requires acceleration beyond the 50 kph operating limit.