Saab Biopower Hybrid Concept
Saab's 9-3 BioPower Hybrid Concept can generate torque values three times greater than its petrol-only equivalent, according to Saab -- and the car makes its world premiere today at the Stockholm Motor Show. We mentioned the car briefly in an earlier story -- see link below.
Packing a 260bhp 2.0-litre turbo BioPower engine and 53kW electric motors, the BioPower Hybrid Concept brings improved performance and fuel economy, and an extended driving range, according to the Swedish carmaker. Torque is 277lb-ft, 25 per cent more than the equivalent petrol engine.
Saab's modular hybrid system features a maintenance-free, 300V battery bank designed to last the lifetime of the vehicle, a 38kW rear-mounted electric motor, a 15kW integrated starter generator and all-wheel-drive with electric power transmission to the rear wheels. According to Saab, the entire system has been packaged without sacrificing cabin accommodation or trunk space, as demonstrated by its unveiling in the Saab 9-3 Convertible.
The all-aluminium 2.0-litre BioPower engine is modified to run on pure E100 bioethanol fuel, giving zero CO2 exhaust emissions at the point of use, and operates in tandem with the electrical power system. This offers fuel-saving stop/start functionality, torque boosting electric power assistance on demand, an electric-only 'Zero Mode' for city driving and regenerative braking. One would hope the zero mode works for long enough to find the next bioethanol filling station.
The car's expected to achieve zero to 62mph acceleration in 6.9 seconds, a substantial improvement against 8.8 seconds for the equivalent petrol model, and a 50 to 75 mph acceleration on kick-down in 5.5 seconds.
According to Saab, the Saab 9-5 2.0t BioPower, which uses E85 (85 per cent bioethanol/15 per cent petrol) fuel is selling well in Sweden, where E85 is increasingly distributed.
BioPower propulsion
The concept uses an evolution of the current all-aluminium, 16-valve 2.0-litre turbo engine in the Saab 9-3 range. Its engine incorporates an integrated starter generator (ISG) and also charges the battery bank mounted under the boot floor.
The 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 petrol engine. Variable inlet and exhaust cam phasing is used for optimum breathing and more durable valves and valve seats are fitted, together with bioethanol-compatible materials for the fuel system.
The compact 42-volt ISG, built into the flywheel between the engine and transmission, is the power behind the concept's fuel-saving, stop/start functionality. It serves a multi-functional role as a starter motor, alternator and 15kW engine power booster, while also helping to iron out residual crankshaft vibrations.
For this application, fuel saving is improved by running auxiliary functions, such as the water pump, air conditioning and power steering systems, not from the engine's belt drive but powering them electrically instead, through the hybrid system.
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
A parallel hybrid system has been adopted, where the control strategy is based on efficient 'energy management' – recovering, storing and feeding back energy that is otherwise lost in a vehicle powered only by an internal combustion engine. In concert with parent company GM, Saab's engineering team has developed stop/start engine functionality, electric rear-wheel drive systems and regenerative braking. 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.
Electric energy storage is provided by a 42-cell, 300-volt lithium-ion battery bank, designed to be entirely maintenance-free throughout the lifetime of the vehicle. Its performance is carefully monitored and governed by an electronic control unit, through which electric current from the engine is fed.
This power pack is accommodated under the floor of the trunk, without taking up any stowage space, as demonstrated in the Stockholm show car.
The battery supplies 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 491lb-ft of additional torque.
In reverse operation, the motor acts as a generator to provide 'regenerative braking'. It automatically recovers kinetic energy otherwise lost during braking and converts this into additional battery charging. 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 86lb-ft of extra torque to the output of the engine through the front wheels.
Driving benefits
Engine and motors are controlled by electronics with the aim of providing a seamless hand-over between power sources. 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 per cent but, said Saab, without raising fuel consumption.
At take-off, the car uses the instant torque of the electric motor from tick-over to about 1,500 rpm. It is during this phase that the available pulling power, or torque, is more than tripled, said Saab.
An estimated fuel saving of five to seven per cent is provided by the automatic engine stop/start function. When the vehicle is stationary, the engine is immediately killed. When the brake is released, it is restarted by the ISG, all without driver input.
In congested driving conditions, Saab claimed zero fuel consumption -- which sounds perilously close to claiming a source of free energy -- and zero emissions. This is selected via a button in the central console. At speeds below 50 km/h, this 'zero mode' will shut off the engine and 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 kilometres. The batteries also power ancillaries and lights. The engine is re-engaged when the battery runs down or the throttle opening requires acceleration beyond the 30mph operating limit.
And in low grip road conditions, rear-wheel drive kicks in so when, for example, the electronic traction control system is activated at the front wheels, the car is balanced by the application of rear drive.
Driver instrumentation for the Saab BioPower Hybrid Concept is as discreet as the installation of its hybrid engineering. In the main instrument cluster, icons are illuminated to indicate when the car is running on engine and/or electric power. An additional gauge is also fitted to show the power status of the battery bank. Under electric power, the needle will steadily fall and then rise again when the engine provides charging. The turbo boost gauge is calibrated by tree icons, a reminder of the car's renewable energy source.
Next steps
Saab's concept is the first project to be announced under a joint investment programme between General Motors R&D and the Swedish Government. It's the first step towards the implementation of a three-tiered, advanced propulsion technology strategy. The ultimate goal, according to Saab, is the introduction of hydrogen fuel cell powered vehicles that emit only water and remove the vehicle from the environmental debate.
All we have to do then is figure out how to make hydrogen without burning fossil fuels.