|Volvo’s heavy hybrids.|
The Volvo Group has unveiled a prototype hybrid system for heavy-duty vehicles (buses and trucks) which promises fuel savings of up to 35%, depending upon usage. The company is targeting series production of the hybrid vehicles by 2009.
Designated I-SAM (Integrated Starter, Alternator, Motor), the parallel hybrid system comprises a combined starter motor, drive motor and alternator fit between the clutch and the I-Shift automatic transmission. Effpower bi-polar lead-acid batteries are recharged by the diesel engine and via regenerative braking.
I think hybrid technology is an important step in the long-term vision of becoming oil independent, and with that have sustainable transport in society. We can see hybrids taking off a big part of fuel consumption. Hybrids also lend themselves well for the incoming use of biofuels or alternative fuels to diesel.
I think we see now quite the enhanced interest in reducing fuel consumption. Obviously that is driven by fiscal availability of oil, it is driven by political availability of oil, and it is perhaps above all driven by climate change issues.—Leif Johansson, President and CEO of Volvo
|Volvo’s I-SAM system.|
The Powertrain Management Unit (PMU) contains the key logics on gear shifting strategies and power split between diesel engine and electric motor. The high power and torque output from the permanent magnet motor enables the downsizing of the diesel engine.
The electric traction motor provides all-electric acceleration from stop as well as power assist to the diesel engine, as well as stop-start and idle-stop functionality. Auxiliary functions such as the servo pump and AC compressor are driven electrically in the hybrid truck instead of by the diesel engine.
The battery system for the hybrid uses bi-polar lead acid technology from Effpower, a Swedish company in which Volvo has a 45.8% interest.
|Monopolar versus bi-polar.|
Many lead-acid batteries today are monopolar—a configuration in which a large number of plates can be stacked in every cell, increasing the capacity of the battery, with cells serially coupled to increase voltage.
Since the current in a monopolar battery is introduced in one post in the upper end of the battery and leaving via another post adjacent to the first one, high currents will be unevenly distributed over the electrodes with maximum current flowing close to the posts.The bipolar lead-acid battery uses a stack of serially coupled bipolar electrodes. Each such electrode, except the ones at the ends, has one side of a conducting partitioning wall covered with porous lead, which is the negative side of the bipolar electrode, and the other side (the positive), covered with porous lead dioxide.
Because current can pass only through the end electrodes, it flows perpendicular to all electrode surfaces, efficiently utilizing all active materials with a minimum of internal resistance.
Effpower designed its bi-polar batteries specifically for use in hybrid electric vehicles. The system are characterized by:
800 W/kg discharge—about double that of advanced lead-acid batteries, and approaching the low-end of NiMH systems, but at a much lower cost
A cost of about US$10/kW in high volume, compared to $8/kW for conventional lead acid systems and about $50/kW for NiMH
Very high cycling ability: more than 500,000 shallow cycles
Bi-polar lead-acid technology has been under investigation for more than a decade by different researchers and companies. The European Union had funded a specific research project on the subject: Bipolar Lead Acid Power Source For Hybrid Vehicles (BILAPS).