The fixed relationships of the elliptic cam ring are replaced by 4 curved surface (cupped) movable pistons located at the 4 sealing areas, at 12,3,6, and 9 o'clock like the face of a clock. The curvature of each piston rides on a 'hydrodynamic oil bearing' similar to hydroplaning tires in the wet and this virtually eliminates metal-to-metal contact and friction. The first Hydristor achieved almost 95% efficiency overall and the present designs are in the 97+% range. If the 4 pistons are positioned equidistant from the center of rotation, no oil is expressed or accepted by any of the kidney ports. This is called 'neutral'. For a clockwise rotation, if 3 and 9 pistons are moved inward with 6 and 12 moving outward, all moving an equal amount, then a device displacement in proportion to the piston movement is created. If the 6 and 12 pistons were moved in with 3 and 9 moving equally out, then all the oil flows reverse. Since the piston positions are infinitely variable, any possible displacement between zero and + or - maximum displacement can be created. If two such Hydristor units are packaged face-to-face with the 4 port kidney plate between them, an infinitely variable transmission is formed. This transmission can select any ratio in the forward direction and in the reverse direction without the need for any gears.
