Patent ID: 7464549

Claim:
A variable gear hydraulic drive system comprising: (a) an input drive system comprising: (i) a first cam element having a first lobed profile moved by a power source; (ii) a first set of pistons comprising hydraulic fluid and cam-followers which are disposed to act against said first cam element so that the movement of the first lobed profile against the cam-followers applies pressure to the hydraulic fluid; and (b) an output drive system comprising: (i) a second cam element having a second lobed profile; (ii) a second set of pistons comprising cam-followers disposed to act against said second cam element, wherein said second set of pistons comprise hydraulic fluid and each piston of said second set of pistons is connected to at least one of said first set of pistons with a hydraulic fluid line so that pressure applied to the hydraulic fluid is applied to the cam-followers of said second set of pistons, and wherein said cam-followers of said second set of pistons are disposed relative to the lobed profile of said second cam element to move said second cam element according to the lobed profile of said second cam element and applied pressure; and (c) at least one further cam element, interchangeable with one of said first and second cam elements, wherein said at least one further cam element comprises a different lobed profile to the interchanged cam element; wherein said input drive cam profile and said output drive cam profile are formed as shaft and cylinder coaxial to one another.