Hydraulic control system for hydraulically operated road grader

Claim 1

In combination with an earthworking machine having a pair of double acting cylinders each having a base end and a rod end providable with fluid under pressure for operating an earth working blade, and a separate control valve for each of said cylinders, each control valve having a pair of lines comprising selectively actuable first and second lines for operating the one of said double acting cylinders associated therewith, the improvement comprising a selector valve in fluid communication with the first and second lines of one of said control valves and to the cylinder associated therewith, said selector valve provided with means movable to a first position wherein said first and second lines are in fluid communication with the corresponding cylinder, and a second position wherein said first and second lines from said one control valve will be in fluid communication with separate outlet ports of said selector valve, a first flow integrator valve having a pair of first inlet ports and a first outlet port, said first outlet port being in fluid communication with one of said outlet ports of said selector valve, and said first inlet ports each being in fluid communication with the base end of a different one of said cylinders from the cylinder in fluid communication with the other of said first inlet ports, and a second flow integrator valve having a pair of second inlet ports and a second outlet port, and said second outlet port being in fluid communication with the other of said outlet ports of said selector valve and said second inlet ports being in fluid communication with the rod end of a different one of said cylinders from the cylinder in fluid communication with the other of said second inlet ports, said flow integrator valves each permitting parallel fluid flow in a direction from their respective outlet ports to their respective inlet ports, but preventing substantially dissimilar fluid flow from each of the respective inlet ports to their respective outlet port whereby said flow integrator valves meter the exhaust flows from both of said double acting cylinders to insure equal exhaust flows, and permit parallel operation of said cylinders with substantially equal movement thereof.