The initial proof-of-concept features a 1,599cc inline three-cylinder engine. To keep it notably compact, it’s a cam-in-block pushrod design. To keep it simple, it features a monoblock casting with no separate cylinder head and uses just two valves per cylinder with no variable timing or lift. To minimize friction, there are no journal bearings—the crank, camshaft, and connecting rods all ride on roller bearings, and the crank is offset 12 millimeters from the cylinder-bore centers to reduce piston side loading. There’s also no accessory drive; all auxiliaries including the water pump operate electrically on demand. Each end of the crankshaft connects to the planet carrier of an epicyclic gearset. The sun gear on each side attaches to a motor functioning primarily as a generator, and the outer ring gear connects to a primary traction motor geared to the wheel. As with Toyota Hybrid Synergy Drive, the car can be driven with the engine on or off (making it suitable for HEV or PHEV/range-extender duty), and with two planetary arrangements, there’s no need for a differential (offsetting some of the cost of the two planetary and reduction-drive gear sets). Note that a common lubricant is shared with the engine and the planetary gear sets. An upgrade to axial-flux traction motors is also envisioned, which would further shrink the DHE powertrain’s overall width.