I did a little digging online and was surprised I didn't quickly come across a good description of the Workhorse 7.1 or at least an animation of a crankshaftless, sinusoidal cam engine in action. I believe the basic theory, though, is that instead of converting the linear motion of a piston into rotational motion through a crankshaft, this engine would use a "floating" piston that "rests" on top of a large cam shaft (not to be confused with the cam shafts that are used to open and close the cylinder valves). The shape of the cam is calculated to maximize efficiency and power redirection from the up and down motion of the piston into rotational power to the wheels. If anyone's got any info or links, I'd love to see it.
In any case, AVEC is expecting the Workhorse 7.1 to get 40 percent better mileage and a 50-80 percent reduction in pollutants when compared to an equivalent traditional engine.
[Source: Axial Vector Engine Corporation]