The Route extended range electric powertrains incorporate a range-extending genset designed to recharge the high-power battery pack (currently from A123 Systems) and Wrightspeed’s own geared traction drive (GTD) ( earlier post ). Wrightspeed, founded by Ian Wright, one of the original co-founders of Tesla Motors, has used a 65 kW Capstone microturbine in earlier Route powertrains. The 65 kW Capstone unit weighs 300 lbs (136.1 kg), for a power-to-weight ratio of 478 W/kg; by comparison, Wrightspeed’s new Fulcrum microturbine offers a power-to-weight ratio of 750 W/kg. With Fulcrum, on which the company has been working for about 3 years, Wrightspeed now owns 100% of the Intellectual Property of its powertrain products.

Wrightspeed Inc., a developer of range-extended electric vehicle powertrains for medium- and heavy-duty vehicles ( earlier post ), has unveiled the Fulcrum, a new proprietary turbine generator for use in its Route family of electric powertrains (Route for Class 3-6, Route HD for Class 7-8). The new 80 kW Fulcrum is a radial inflow, axial turbine, intercooled and recuperated. Fulcrum is a single shaft machine, the generator runs at turbine speed (~100,000 rpm). Weighing in at 250 lbs (113.4 kg), the Fulcrum is approximately 1/10 th the weight of its piston generator counterparts and it is designed to have a 10,000-hour lifetime.



Rendering of the 80 kW Fulcrum microturbine generator. The recuperator and combustor are at left; the generator with integrated power electronics at right. The two tubes lead to and from the intercooler, which is not shown in this rendering. Click to enlarge.

A two-stage compression process and novel recuperation design make the Fulcrum 30% more efficient than existing turbine generators, while tripling usable power, Wrightspeed says. Its multi-fuel capabilities allow it to burn diesel, CNG, LNG, landfill gases, biodiesel, kerosene, propane, heating oil, and others. In addition, the Fulcrum will make for a smooth, comfortable ride for drivers and a quiet, clean experience for neighborhoods because of its ultra-low vibration.

While piston generators rely on catalytic converters to reduce their emissions by 10x to meet ever-increasing California Air Resources Board standards, the Fulcrum turbine generator is so much cleaner, that it meets emissions standards without adding to its weight and complexity.

Noise, said Wright, is mostly intake and is high frequency, much smaller than than from a jet engine; the recuperator also acts as a buffer. There is no vibration, he added. Spinning at 100,000 rpm, it has to be very precisely balanced, or it would come apart.







Top: Tandem drive truck with Route powertrain using Fulcrum turbine. The turbine unit is just behind the cab, sitting atop the high-power battery pack. The intercooler (yellow) is shown, but not connected to the turbine. Bottom: Close-up of turbine. Click to enlarge.

Microturbines operate on the Brayton Cycle. Atmospheric air is compressed and heated (usually by introducing and burning fuel); these hot gases then drive an expansion turbine that drives both the inlet compressor and a drive shaft. Other than the size difference, microturbines differ from larger gas turbines in that they typically have lower compression ratios and operate at lower combustion temperatures.

To increase efficiency, microturbines can recover a portion of the exhaust heat in a heat exchanger (recuperator) to increase the energy of the gases entering the expansion turbine—thereby boosting efficiency. “Without a recuperator,” said Wright, “efficiency is just horrible.”

The use of microturbines in autos has been explored for a long time, with a number of manufacturers actively exploring the potential shortly after World War II: these included Rover in the UK; Fiat’s Turbina, introduced in 1954; a Chrysler Plymouth prototype turbine car also introduced in 1954; GM with its Firebird prototypes, also introduced in the early 1950s; and the limited production run Chrysler Turbine Cars, introduced from 1962-1964.

The Japanese began a 100 kW automotive ceramic gas turbine (CGT) project in 1990 and concluded it in 1997. The US Department of Energy (DOE) in the 2000s ran a cooperatively funded, multi-path technology development program called the advanced microturbine system (AMTS).

None lasted, although interest in the approach—now especially for hybrid vehicles—is still strong, with one of the most recent OEM examples being the Jaguar C-X75 gas micro-turbine extended range electric vehicle concept in 2010. Jaguar was using a turbine from Bladon Jets. (Earlier post.)

There have been a number of problems with automotive applications of turbines, Wright noted, among them fuel economy and efficiency, and cost.

While turbines have seen great success in aviation, a fundamental challenge with the use of a turbine as the main traction engine in an on-road vehicle is that turbines are not efficient at low-load points; they are only efficient at full power, noted Wright. In other words, fuel economy is a significant problem. However, he added, the advent of the range-extended EV architecture alters the operational requirements significantly; instead of coping with varying load, the turbine can operate at its most efficient point—similar to the high efficiency large-scale turbines used in power generation—to produce power for the battery pack, which in turn powers the electric motors.

The automotive industry is in the midst of a fundamental disruption, with electric vehicles merely symbolizing the beginning of the movement. The Fulcrum, together with our range-extended EV architecture, is perfectly suited for achieving maximum efficiency in extremely high-power stop-and-go applications, such as garbage trucks. For many of the same reasons that aviation changed from piston engines to turbines decades ago, we believe turbines will begin to replace piston engines in range-extended electric vehicle applications.

It doesn’t matter what the driver is doing, you operate the turbine only at its most efficient point. It’s only 250 lbs, incredibly clean and also multi-fuel. It has all those advantages. —Ian Wright

Further, Fulcrum’s design with its intercooler, recuperator and pressure ratio enables a higher efficiency than usually seen in this class of turbine, Wright said.

A further disadvantage for turbines in automotive applications has been cost. Wrightspeed addressed that by deliberately designing Fulcrum for low cost manufacturing, leveraging turbocharger technology with great economies of scale at this point.

Wrightspeed emphasizes the use of high-power batteries rather than high-energy batteries in its powertrain.

One of the things that enables the story is that the batteries have become extremely reliable and long life, even when at high power. We use the smallest pack we can. In general, we save fuel in three separate ways: first is with a grid charge; second is regenerative braking—we run very high power regen, much, much higher than anyone and we pretty much avoid the use of friction brakes; and third is running the engine at the sweet spot. —Ian Wright

None of those three approaches work very well in long-haul trucking in which the big rigs with optimized engines and gearing are cruising for long stretches at an optimal, constant speed. On the other hand, a big rig in an urban environment is just horrible at fuel efficiency, Wright said. As a result, the Route extended range electric powertrain is ideally suited for urban environments. FedEx, which is already running a couple of trucks using the Route powertrain, has ordered 25 more.

Resources