WHY NOT SERIAL OR PARALLEL HYBRID?
THE PROBLEM
Excessive cost and weight remain the two nemeses of progress for these hybrid Class 8b Freight Trucks
In electric drive mode:
Just like full-time battery-electric trucks, serial and parallel hybrids must generate very high motor torque at zero RPM startups, especially when launching uphill under full load. This demands a massive surge of electrical current—not just once, but repeatedly in stop-and-go traffic on grades.
Adding tare weight or increasing purchase price is a consistent killer of any trucking idea.
THE TOLL OF SURGE CURRENT
How to cook your truck’s electric drive—or spend more and weigh more to then burn up profits.
To survive electric-only launches on steep hills, these systems require:
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Oversized batteries to keep C-rate < 2.0 peak, < 0.5 average
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Heavy inverters, cooling systems, and cables
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High-cost capacitors to buffer inrush current
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Ruggedized controls to prevent burnout​
That’s a whole lot of weight and cost—for basic performance and the goal of protecting battery longevity.
CLASS 8b IS NOT A CAR
The need is to go beyond ‘mild hybrid’ or ‘hybrid assist’ for freight trucks.
Serial and parallel hybrids worked for cars and buses—but freight is different:
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Electric motors must upsized with higher peak torque from inrush current
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Batteries and electric systems must tolerate frequent full-load launches
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Cooling systems are expanded to higher load capacity for motors, inverters and batteries
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Freight trucks operate with over 8× the weight-to-power ratio of light-duty vehicles
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Every added pound of tare weight cuts into payload and range
After more than two decades of trying, these 2 hybrid systems still haven’t scaled for Class 8b freight trucks.
SURGE CURRENT: DIRECT DRIVE VS. HYDROSTATIC IVT DRIVE
The graph below shows a current draw comparison for achieving the same torque—with 80% less stress. IVT is clearly EM’s best friend!
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Direct Drive: Surges over 1000 amps at 0 mph start—severely stressing the EV motor, battery, inverter, controls, and cables
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Hydrostatic IVT Drive: Keeps current draw smooth and low—under 200 amps during zero-speed launch
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Diesel engines produce no torque at zero RPM, while electric motors can deliver peak torque from a standstill—but only for a few seconds, due to extreme inrush current. In contrast, a Hydrostatic IVT Drive can sustain full torque at zero RPM all day long.
IVT (Infinitely Variable Transmission) allows continuous motor spin at zero truck speed and infinite ratio control—eliminating inrush current without sacrificing torque.
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(9% grade, 25-ton load, 600 volts, 250kW motor)
ZERO-EMISSION ZONES ARE EXPANDING
Clean city air. Never idle again—and deliver zero tailpipe emissions in every city.
In Europe and now starting in the U.S., local governments are enforcing zero emission sectors and ZEDZ (Zero-Emission Delivery Zones). Fleets now need:
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Electric-only capability in cities
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Fuel-powered range for cross-country travel
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Low system weight to preserve payload
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Break-even within two years for all zero-tailpipe investments from efficiency gains
A hybrid that can’t meet all of this—won’t be the solution.
THE FREIGHT HYBRID DILEMMA
More cost than diesel, more weight than BEV—and no real advantage.
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Serial hybrids: Engine + generator + batteries + motors = overload
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Parallel hybrids: Double drivetrain complexity = double headaches
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Neither delivers a balanced solution for cost, weight, or performance
The real opportunity? Replace the truck’s transmission with an IVT paired to a smaller engine and just enough battery and electric motor—with no need for a big surge current.
Results are less cost and less weight with a Hydrostatic IVT.
BATTERY ELECTRIC TRUCKS ADVANTAGE WITH A HYDROSTATIC TRANSMISSION
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Eliminates inrush surge current, which is extremely taxing during startup.
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Easier to build or retrofit a truck: replace the engine with a single electric motor and the transmission with the HST
→ retaining existing axles (no need for dual e-axles).
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No inrush current enables a lighter, simpler system by eliminating the need for oversized: motors, inverters, capacitors, cables, cooling system, and control systems.
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Allows the use of a smaller, high-RPM electric motor with the same kW output—since surge current and peak torque are no longer limiting factors or design constraints.
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Removes high-voltage components and electronics from bouncing around as unsprung mass on the axles
→ Especially important in rugged applications like concrete mixers, where durability counts.
Surge Current is the Achilles’ Heel for Electric Drives. The Hydrostatic Transmission is a better way to EV in heavy trucks.
