Yahoo Autos Sumantics: AMG's New Plug-In-Hybrid Math Explained
From the March/April 2024 issue of Car and Driver.
Mercedes-AMG's newest generation of supersedan relies on a hybrid driveline optimized for track performance. It has one electric motor paired with a two-speed transmission that drives the rear differential's ring gear (there are two other motors in the powertrain: a starter-generator and one on the turbocharger) and a 469-hp 2.0-liter inline-four with a specific output of 235.6 horsepower per liter bolted to a nine-speed automatic (featuring AMG's multiplate clutch in lieu of a torque converter). Combined output is seriously high: 671 horsepower and 752 pound-feet of torque. (Read our review of the AMG C63 S E Performance.)
Normally, mixing motors and engines wouldn't cause our feeble minds too much trouble. But in this case, Mercedes says that the combined torque of the system is greater than the sum of the engine's peak torque (402 pound-feet) and the motor's (236 pound-feet). Typically, a hybrid's combined output (power or torque) is less than the sum of the parts. Engine and motor torque and power curves are shaped quite differently, so the respective peaks usually don't align when attempting to maximize efficiency while maintaining drivability. Performance-oriented hybrids often sacrifice some efficiency and instead are designed so that their peaks align to maximize acceleration. But 752 pound-feet had us scratching our heads. Shouldn't it be 638? It's as if we're in a class, and the professor asks, "What weighs more, 1000 horsepower or 1000 kilowatts?" And somehow the answer is "Secretariat."
We're told we need to think of the whole powertrain (driveline plus engine and motor) as one thing. And because the C63 S E Performance has an engine at one end of the driveline and a motor at the other, the motor's torque must be multiplied and reduced by the two- and nine-speed autos, respectively, to get combined torque at the crank. The key phrase is "at the crank." When torque is measured at that spot, the motor's output is influenced by the gearing. So ponder that before you send us a letter saying we can't add.
The rear-mounted 196-pound 4.8-kWh battery covers the electric drive unit and offers 94 horsepower continuously or 201 horses for up to 10 seconds.
The powertrain's maximum 752 pound-feet is only available once the nine-speed gearbox is in third gear. The system limits torque to 546 pound-feet in first and 664 in second.
The motor's two-speed transmission can shift from first (12.72:1) to second gear (5.30:1) at up to 84 mph.
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