An optical sensing system is used to measure engine torque. A pair of patterns
are formed on a driveshaft between a transmission and axle differential. The patterns
are spaced apart from one another by a predetermined distance and are formed about
the circumference of the driveshaft. Lasers and photo receivers are used to scan
the patterns as the driveshaft rotates. Data from the photo receives is used to
determine the angle of twist on the driveshaft which is proportional to the engine
torque. The torque for each cylinder can be measured by generating a torque profile
for every two revolutions of the driveshaft. The torque profile is read in 120
degree increments for a six cylinder engine and in 90 degree increments for an
eight cylinder engine, for example.
