The new Sanderson mechanism avoids this limitation with a rocker arm solution, which reportedly can be applied to any design currently using a crankshaft, bent axis, swash plate, or a wobble plate. Explains Sanderson, "The principle of the mechanism is similar to a 90° rocker arm used in overhead-valve engines: a rotating crank displaces a push rod, which applies force and motion to one end of a rocker arm. This causes the rocker arm to pivot, thereby transmitting the force and motion at its opposite end to a valve stem."
Sanderson continues, "The 90° rocker arm can be connected to ground with a simple cross universal joint to give the rocker arm an additional degree of motion. The U-joint allows one end of the rocker arm to track the circular movement of the output crank with a suitable journal bearing, while the other end of the rocker arm is simultaneously constrained to follow a straight-line path and to reciprocate.
"If you imagine such a rocker arm mounted on a conventional U-joint, with one arm straight out, this arm can trace any path on the surface of a sphere within a solid angle of at least 30°. As this action takes place, because the U-joint cannot rotate, the other arm can only nod back and forth in a single plane. The motion of this arm is affected only by a single component of the motion of the first arm. Therefore, if the first arm is moving in a circle, then the motion of the second arm is a simple sine wave."
Additional benefits
Other substantial benefits exist, points out Sanderson. "The rocker arm works equally well in both directions. At mid-stroke, a push of 100 lb from the piston side can result in a 100-lb push in the circumferential direction along the path of the output crank. Virtually all the push of the piston converts directly to output torque. There is no need for side force on the cylinder walls to support either of these forces. Indeed, the side force of a Sanderson mechanism is normally zero, which eliminates a major source of friction in a crank mechanism."
The rocker arm works just as well in the reverse direction, says Sanderson. "Circumferential force of 100 lb converts to 100 lb of force to drive a piston. Again, the losses of a rocker arm and of piston-cylinder friction are minute. Total frictional load is negligible compared to the frictional losses of crankshafts, swash plates, wobble plates, and bent-shaft mechanisms."
According to Sanderson, SED now has hydraulic motors and pumps that exhibit efficiencies in the mid-nineties. This creates immediate applications in fields where the convenience of hydraulics has been outweighed by the need for energy conservation, such as windmills or automobile drive trains.
He offers that electric generators could be removed from the top of wind power generators and replaced by a hydraulic pump at the top for a lighter weight, smaller, and less expensive tower construction. Hydraulic motors on the ground could drive the generator with high efficiency and variable speed, if necessary.
Variable displacement