The 100% electric transmission boosting EV and hybrid range
Eliminating hydraulic drag in favor of independent smart clutches, Sigma Powertrain’s multi-gear electric transmission optimizes electric and hybrid motor torque under severe commercial payloads.
While single-speed direct-drive setups perform adequately in passenger electric vehicles, commercial applications face severe efficiency losses under heavy payloads and steep gradients. Oversizing electric motors to improve launch performance becomes economically and operationally impractical as vehicle gross weight increases into Classes 5 through 8. To solve this torque band limitation, electric transmission manufacturer Sigma Powertrain has developed a fully electric, multi-gear transmission platform.
For commercial fleet managers and powertrain integrators, the architecture addresses thermal management and power draw bottlenecks. Unlike alternative EV transmissions utilizing fluid hydraulics, Sigma’s Emax transmission is 100% electric. Removing hydraulic pumps eliminates parasitic drag and heat generation, driving an overall powertrain efficiency gain of up to 15 percent.
Hydraulic-Free Modular Architecture
By eliminating internal hydraulic channels, engineers accommodated 30 percent larger gear sets within a compact casing. The manufacturer utilizes a scalable modular design sharing common gear components across vehicle segments: the Mid-Series covers Class 1–6 light- and medium-duty trucks, while the Emax targets Class 6–8 severe-service platforms.
The core innovation centers on proprietary electronic smart clutches. Operating independently without continuous power draw, these clutches engage only during gear shifts via integrated speed sensors. This mechanical independence enables bi-directional locking, delivering a hill-hold capability that secures fully loaded Class 8 vehicles without engaging service brakes or drawing battery power from the traction motor.
Hybrid Applications for Long-Haul Freight
Beyond pure battery-electric architectures, the technology integrates into serial or parallel hybrid systems. In a Class 8 long-haul diesel-hybrid configuration, a four-inch-wide transmission unit paired with dual electric motors enables active power splitting.
The system supplies supplemental battery torque during vehicle launch or hill climbs, keeping the internal combustion engine within its narrow peak-efficiency operating island. Sigma CEO John Kimes states that this power-split configuration can improve long-haul fuel economy by up to 30 percent while simultaneously powering hotel-load auxiliary power units (APUs) during driver rest periods. Currently available for fleet upfit applications, the transmission platform offers a bridge for operators seeking to reduce diesel consumption while scaling zero-emission vehicle adoption.
