Friends, I had a chance to examine (and ride in) the diesel electric hybrid class-7 truck that Solectria is showing across the country.
See http://www.solectria.com/news/super7.html
It was at Crane Carrier's plant Aug 11. It's really a neat set-up. It consists of a smaller diesel engine, automatic clutch, 2 AC induction motors in-line in the drive shaft, auto-shifting transmission, then continues the drive line to rear axle. It uses ultracapacitors instead of batteries - enough energy (0.5 kWhr) for about 1/5 mile EV. Neat control system. Starts moving EV then starts the diesel for cruising. It has strong regeneration. They expect to obtain a 35% increase in fuel economy over the original diesel truck.
The truck performance is designed to save fuel by running the engine at its most efficient speed while charging the capacitors and then using the capacitors and motors to deliver the high torque for starting. When the truck is first started (by the electric motors), it revs the engine to charge the caps (gearbox in neutral). Then the engine shuts down. Releasing the brake and stepping on the accelerator causes the motors to drive the truck. During this time, the clutch is disengaged so that the motors turn the driveshaft ahead of the gearbox. The gears are upshifted automatically as needed during acceleration. All you hear is the whine of the gearbox. It gets up to at least 4th gear before the engine starts. When the engine is needed, it is automatically started by clutching into the driveshaft.
The driver can ignore all of this and just use the accelerator pedal as usual. The pedal has the same action as that in the Force -- the upper half of the travel controls regeneration and the lower half controls motoring. During EV mode, the terminal voltage of the capacitor bank starts at 340V and declines to 140V as energy is withdrawn. Their inverters can operate over that range of input voltage. The declining voltage is not a problem when accelerating the truck because the motors need less field as their speed increases. This is rather similar to field-weakening a DC motor to get higher speed at the expense of torque.
The truck is a prototype, and they plan to reduce weight and repackage it. They intend to sell it as a kit for truck makers such as Crane Carrier to install. I imagine that the final design will lay the electronics between the frame rails. The prototype has the electronics in the foreward end of the payload bay behind a plexiglas window. They say that the total capacitance in the ultracapacitors is 952,000 Farads. But I think that must be the parallel value. Ultracaps have a low voltage rating (2 to 3 volts, as I recall), so they must be series-connected to handle the 340 volts that the truck uses. So in series, it's nowhere near that number of Farads. One big advantage of ultracapacitors is that they have a virtually unlimited lifetime.
China has asked Solectria to work on a small HEV car with concept much like the ParaDyne-Proxima. Solectria is also designing a pure-EV truck for UPS so the truck can be driven inside closed warehouses. This will use the same batteries (Sonnenschein) that I have in my Force. They say that Sonnenschein batteries are the best lead-acids that they have found. They hope to get the time to design and build their own charger, which will eliminate the current problem they have with flaky chargers.
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