Technologue

Does torque still matter? Not as much as before, SAE says.

- Frank Markus

You’ve probably noticed how, for years now, our spec panels describing hybrid vehicles endeavor to list the peak output (power and torque) of the engine and each motor that helps propel the vehicle, along with a peak combined output. The numbers seldom add up, because of the vastly different power delivery characteristics of combustion and electric machines. Establishing those peak combined figures can be so tricky that the Society of Automotive Engineers convened a working group of industry pros to publish a nonbinding best-practices report, dubbed SAE J2908, describing four ways to determine peak combined … power. Did they leave the job half finished?

First a brief refresher on torque and horsepower. Torque is the twisting force that quantifies the work a powertrain can do (in lb-ft or newton-meters). Power describes the rate at which it does this work (in horsepower or kilowatts). The two are mathematically linked, with horsepower equaling torque multiplied by rpm and divided by a constant (5,252 imperial; 9.55 metric). A dynamometer can directly measure both, strain gauges on output shafts can directly measure torque, and an electric machine’s power can be calculated with reasonable accuracy by measuring electric current flow.