A startup called Sigma Powertrain believes purpose-built multi-speed gearboxes can boost efficiency, reduce battery size and improve gradeability for heavy-duty battery-electric trucks.
For years, the prevailing wisdom in battery-electric vehicles has been simple: Electric motors produce instant torque, so transmissions are unnecessary.
John Kimes, CEO of startup company called Sigma Powertrain thinks differently. Kimes believes that logic breaks down quickly once vehicle weight and vocational demands start climbing.
“Once you get into very high gross vehicle weights, transmissions stop being a luxury and become a requirement,” Kimes said.
That’s why Sigma Powertrain is developing multi-speed electric transmissions specifically for commercial, vocational and off-highway vehicles.
Kimes said the company’s technology allows electric trucks to use smaller motors, improve efficiency by 10-15%, increase gradeability and potentially reduce battery-pack size.
That matters, he explained, because most battery-electric trucks today still rely on oversized motors paired with single-speed reduction gearboxes.
According to Sigma, those systems force motors to operate far outside their peak efficiency range for much of the duty cycle.
The result, Kimes argues, is wasted energy and larger, heavier, more expensive battery packs.
Why Commercial EVs Are Different
Kimes said the single-speed approach works reasonably well in passenger vehicles because the compromises are manageable.
Commercial trucks are another story.
“Take an electric garbage truck that needs to climb a 30% grade to dump at a site and still run highway speeds,” he explained. “If you try to do that with a single-speed setup, the motor becomes enormous.”
Sigma’s approach uses multi-speed transmissions to keep the electric motor operating closer to its optimal efficiency range across varying speeds and loads.
In one customer application cited by Kimes, a 1,200-kW motor was replaced with an 800-kW motor paired with a Sigma transmission while still improving acceleration, gradeability and overall efficiency.
The company currently offers three transmission families:
- MID-Series for Class 1-7 trucks
- EMAX for Class 6-8 vocational applications
- Terramax for large mining, drilling and off-highway equipment
The largest Terramax configuration scales up to 2.6 megawatts for 400-ton mining trucks.
A Different Kind of Transmission
Kimes’ background spans nearly four decades in powertrain engineering, primarily at Ford and General Motors. Much of Sigma’s technology stems from work he began years ago while developing transmission components at Ford.
Traditional automatic transmissions, he said, are poorly suited for EVs because of their hydraulic systems, torque converters and friction clutches, all of which create parasitic energy losses.
Battery-electric trucks simply cannot afford those inefficiencies.
“Battery energy density is terrible compared to diesel fuel,” Kimes said. “Every watt matters.”
Sigma’s solution replaces traditional friction clutches with what the company calls electronically actuated “e-clutches.” These are steel-on-steel mechanical clutches that require power only during engagement or disengagement.
There are no hydraulic systems, no clutch packs and no friction materials to wear out.
“It’s all hard steel on hard steel,” Kimes said. “The transmissions will go a million miles. We don’t have wear components.”
The transmissions also enable features like mechanical hill hold without draining battery power.
According to Kimes, a truck equipped with Sigma’s system can remain stationary indefinitely on a steep grade without consuming energy because the clutches mechanically lock into place.
Smaller, Lighter and More Efficient
One of the more surprising claims from Sigma is that the transmissions add relatively little weight compared to single-speed setups.
“Most of the mass already exists in any gearbox, Kimes said. “That includes shafts, gears, housings. We’re primarily adding clutches.”
The company’s MID-Series transmission for medium-duty trucks weighs roughly 55 to 75 kilograms, according to Kimes.
Sigma also says the transmissions allow OEMs and upfitters to downsize electric motors substantially while still improving performance.
That could become increasingly important as fleets continue struggling with the tradeoffs between range, payload capacity and battery costs.
Looking Beyond Pure Battery-Electric
While Sigma is focused heavily on battery-electric commercial vehicles today, Kimes also believes hybrid systems may eventually play a larger role in long-haul trucking.
He described future concepts that combine downsized diesel engines, multiple electric motors and Sigma’s transmission technology into highly efficient hybrid powertrains capable of all-electric urban operation and diesel-powered highway cruising.
“A properly designed hybrid system could deliver 30% fuel savings while fitting into the same space as an existing transmission,” he said.
For now, though, Sigma’s immediate focus remains commercial EVs where high torque demands and challenging duty cycles expose the limitations of single-speed drivetrains.
And after years of the industry assuming electric vehicles would eliminate transmissions altogether, Kimes believes the market may be circling back toward a more familiar solution — just executed in a very different way.
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