|Under the skin of the Biopower Hybrid.|
At the Stockholm Motor Show, GM’s Saab brand premiered its promised 9-3 hybrid concept car that can run on 100% ethanol (E100) with combined cycle fuel consumption of about 30 mpg US. The car is also the world’s first hybrid soft-top.
It also represents a different approach to a hybrid drive than taken in GM’s current three announced production hybrid systems: the two-mode hybrid in full-size SUVs, the mild hybrid in the Saturn VUE and the micro-hybrid in the Silverado and Sierra.
Combining a 260 hp (191 kW) 2.0-litre turbo BioPower engine and two electric motors totalling 53 kW, the BioPower Hybrid Concept can briefly generate torque values three times greater than its gasoline-only equivalent.
The new modular hybrid system features a maintenance-free, 300-volt Li-ion battery pack designed to last the lifetime of the vehicle, a 38kW rear-mounted electric motor, a 15 kW integrated starter/generator (ISG) and all-wheel-drive with electric power transmission to the rear wheels.
The all-aluminum 2.0-liter BioPower engine is modified to run on pure E100 ethanol fuel, giving zero fossil CO2 exhaust emissions, and operates in tandem with the electrical power system. This system offers fuel-saving stop/start functionality, torque boosting electric power assistance on demand, an electric-only “Zero Mode” for city driving and regenerative braking.
Saab expects the BioPower Hybrid Concept prototype car to achieve 0 to 100 kph (0 to 62 mph) acceleration in just 6.9 seconds, a substantial improvement against 8.8 seconds for the equivalent gasoline model. Acceleration from 80 to 120 kph (50 to 75 mph) is in 5.5 seconds.
Hybrids are certainly interesting for Saab in the future and this project allows us to evaluate and explore the potential of hybrid technology in combination with our existing and already-proven BioPower technology. Although the exact hybrid application shown in this concept does not currently figure in our production plans, the project has been extremely valuable in helping us further our expertise. It shows how we could develop the sporty performance associated with Saab while using only renewable resources and saving energy overall.—Jan Åke Jonsson, Saab Automobile’s Managing Director
The Saab BioPower Hybrid Concept is the first project to be announced under a joint investment program between General Motors R&D (Research and Development) and the Swedish Government. This has seen the establishment of a research and development office in Trollhättan, Sweden, focusing on vehicle safety, engine emissions and advanced manufacturing in collaboration with Swedish universities, research laboratories and suppliers.
Engine. The Saab BioPower Hybrid Concept engine is an enhancement of the current all-aluminum, 16-valve 2.0-liter turbo engine in the Saab 9-3 range. In the hybrid, the engine develops 260 hp and 375 Nm maximum torque, 24% and 25% more respectively than on gasoline.
The Saab BioPower Hybrid Concept retains a flex-fuel capability and features a Spark Ignited Direct Injection (SIDI) system for optimum combustion with E100; ensuring the same cold starting performance as a normal gasoline engine. Variable inlet and exhaust cam phasing is used for optimum breathing and more durable valves and valve seats are fitted, together with ethanol-compatible materials for the fuel system.
ISG. The compact 42-Volt ISG, built into the flywheel between the engine and transmission, provides the stop/start functionality, and also functions as a 15 kW engine power booster, working with the 38 kW motor on the rear axle. Auxiliary functions, such as the water pump, air conditioning and power steering systems, are now removed from the engine’s belt drive and electrically powered instead, further reducing fuel consumption.
Transmission. The five-speed automatic transmission, with Saab Sentronic sequential selection, includes an all-wheel-drive capability by the simultaneous addition of electrically powered drive to the rear wheels.
Hybrid booster. The Biopower Hybrid uses a parallel hybrid system configuration. Apart from converters to manage AC/DC and 12,42 and 300-volt interfaces, the system consists of just three core components: two electric motors and a battery bank.
A 42-cell, 300-volt lithium-ion battery bank provides energy storage. An electronic control unit monitors and governs its performance, and manages the current flow. This power pack is seated under the floor of the trunk, without taking up any stowage space, as demonstrated in the Stockholm show car.
|The rear-wheel electric motor assembly|
The battery powers a compact 38 kW electric motor located between the rear wheels which powers a transmission differential and drive shafts. At low speeds, this Rear Drive Unit (RDU) is able to briefly generate 666 Nm of additional torque.
In reverse operation, the motor acts as a generator to provide regenerative braking. It also performs the same function whenever the driver lifts off the throttle, harnessing the energy in the rotating drive shafts. This is achieved without any perceptible change in the rate of deceleration.
The second electric motor is the integrated starter generator (ISG) located within the flywheel between the engine and main transmission. On demand, it contributes 15 kW of additional power and 120 Nm of extra torque to the output of the engine through the front wheels.
Operating Modes. Under transient driving conditions, both electric motors are activated to augment the power of the engine, increasing standing start acceleration and in-gear performance for safe overtaking. This briefly raises total power by as much as 28%.
At take off, the Saab BioPower Hybrid Concept also exploits the instant torque generation of its electric motors, smoothly adding strong, accelerative power during the engine’s pick-up, from tick-over to about 1,500 rpm. It is during this phase that the available pulling power, or torque, is more than tripled.
An estimated fuel of saving of 5-7% is provided by the automatic engine stop/start function. Whenever the vehicle is stationary, the engine is immediately shut-off to save fuel. As soon as the brake is released, it is automatically started again by the powerful ISG. The operation is carried out seamlessly and requires no input from the driver.
In congested driving conditions, the Saab BioPower Hybrid Concept uses an all-electric Zero Mode (Zero fuel consumption, Zero emissions)—which can be selected by the driver via a button in the central console.
At speeds below 50 kph (31 mph), Zero Mode will shut off the engine and again switch the car over to electric power only through 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.
Whenever the engine is shut down, all auxiliary functions, such as the power steering, air conditioning and lighting, remain unaffected because they are now permanently electrically-powered through the battery. The removal of unnecessary loadings on the engine further contributes to fuel economy and in mixed driving the estimated range of Saab 9-3 BioPower Hybrid Concept test vehicles, with a standard 62 liter tank, is a competitive 800 kms—7.75 liters/100km, or 30 mpg (on ethanol).