I’ve always wanted to get a big monster truck. Huge tires, sits really high off the road, good visibility, don’t have to worry about road obstructions like pot holes, goes in the snow, even take it off-road. The problem is that these big monster trucks don’t get very good gas mileage.
Well now Oshkosh Truck Corporation (OSK) has designed a truck using Diesel Electric Hybrid technology that increases fuel efficiency 20% over the truck it replaces. The HEMTT A3 truck is being built for the military, which is pretty demanding about reliability and performance.
Oshkosh says the truck is production ready. The truck has a 400 HP Cummins ISL Diesel Engine with a 305 KW electric generator. The generator charges a 1.5 MJ ultra-capacitor. The capacitor feeds power directly to electric motors mounted on the wheels. The vehicle can work off-road, climb a 60% grade, and achieve 65 mph on secondary roads. The truck weights 3000 pounds less than its conventional predecessor, but still can carry a 13 ton load.
The capacitor is the heart of the drive system. It stores the equivalent of 0.42 Kwh of electricity, equivalent to 0.035 gallons of gasoline (4.5 ounces). You can’t get very far on that amount of power so the vehicle does not work as a home plug-in. The capacitor does buffer the power from the engine allowing the engine to always run at an efficient speed. The capacitor provides for bursts of power when the vehicle accelerates and can capture the power from regenerative braking. That is what gives the vehicle its improved fuel economy.
The real point to discussing this vehicle is that this drive train technology could also be used on more conventional vehicles like cars or utility trucks. A capacitor in a car could allow for a smaller, lighter engine to be used. It would be optimized to run at peak efficiency. You can eliminate heavy parts like the transmission. More of the car becomes solid-state electronics which are very reliable. The capacitor also recovers the energy from braking. The number of cycles on the capacitor should be almost unlimited so it won't degrade over time like a battery.
Assuming a 20% increase in efficiency, a 30 mpg car becomes a 36 mpg car. If every car on the road today used this technology, we would save about 1.9 million barrels of oil each day, along with a reduction in greenhouse gas emissions. You also could add a battery to this design to create a plug-in vehicle. The battery would not need the capacity to power the entire car (making it cheaper). It would only re-charge the capacitor; sort of like how a battery on a camera charges a capacitor that powers the flash. You might never need to run the engine just traveling around town.
The vehicle design here is basically a solid-state version of a Toyota (TM) Prius. The Prius design uses a battery and electric motor to provide a mechanical assist to the power from the gasoline engine. The power assist is added to the mechanical drive train. The HEMTT A3 has a diesel engine that drives a generator that powers electric motors on the wheels. The capacitor provides an electrical assist to increase the power to the wheels for short periods of time. Both systems can recapture energy from braking. By allowing the engine to run at a more constant speed and recapturing energy both systems improve fuel economy. The Ford (F) Escape Hybrid uses this same type of system.
The Chevy (GM) Volt also is a similar system to the HEMTT, except that it uses a battery to provide power. The Chevy Volt has a gasoline engine that is only used to charge the battery in the car. The size of the battery in the Chevy Volt allows the car to be charged externally and operate for a considerable distance without any power from the engine. The size of the battery is sufficient to provide the current necessary for acceleration.
Diesel electric locomotive engines have been around for decades. The advantage here is the tremendous torque produced by the electric motors, which is very efficient in getting a very heavy train moving. It eliminates the need for shifting through numerous gears and a huge clutch.
Ultra capacitors have a lot of potential for creating hybrid cars. Capacitors are generally light in weight. They are solid state devices that can charge and discharge very fast, which can supply a lot of power when you need it. They are very efficient at storing electric energy. The constraints are that they can only store a fraction of the power stored in a battery and they can be expensive. I believe that high power capacitor technology will continue to improve and capacitors could be an important enabling technology to improve gas mileage and help solve our energy problems.
Disclosure: I have no stock position in any of the companies mentioned.