Hydraulic drive for the feed rollers of a head of a complete timber harvester

A hydraulic drive for feed rollers of a head of a complete timber harvester, comprising:

• a radial piston motor unit including
• a first radial piston motor having a first and second hydraulic port, and
• a second radial piston motor having a third and fourth hydraulic port;
• a first shaft operably connected to the radial piston motor unit;
• a hydraulic motor unit;
• a second shaft operably connected to the hydraulic motor unit;
• and
• a speed selector valve configured as a 5/2-way valve with a valve spool preloaded into a first position by a first spring and configured to be moved into a second position by a control pressure of a first control pressure port, wherein:
• in the second position of the valve spool, the speed selector valve places the hydraulic drive in a first operational state by placing the third and fourth hydraulic ports in fluid communication with each other such that hydraulic fluid circulates into the second radial piston motor through the third port and out of the second radial piston motor through the fourth port without the circulating hydraulic fluid causing the first shaft to rotate, and wherein the circulating hydraulic fluid is in fluid communication with a control pressure line or the first control pressure port in the first operational state;
• in the first position of the valve spool of the speed selector valve places the hydraulic drive in a second operational state by placing the third and fourth hydraulic ports in fluid communication with first and second main ports of the hydraulic drive;
• the control pressure line or the first control pressure port is connected via a control pressure branch line to a control pressure space of the speed selector valve, the control pressure space acting counter to the first spring, and configured to be connected via a further control pressure branch line to a second control pressure port of the speed selector valve;
• and
• in the second position of the valve spool, the second control pressure port is connected to the third and fourth hydraulic ports.