Drive mechanism for driving displacement members disposed in tandem

A drive mechanism for driving first and second displacement members disposed in tandem, the mechanism comprising:

• first and second driven sprockets respectively secured to the first and second displacement members;
• a hydraulic motor comprising a motor casing, a reaction member integral with the motor casing, and a cylinder block which is mounted so that the reaction member and the cylinder block rotate relative to each other about an axis of rotation, the cylinder block comprising a plurality of sets of cylinders and of pistons suitable for being fed with fluid under pressure;
• first and second driving sprockets which are mounted to be rotated by the hydraulic motor;
• and
• first and second chains disposed in a chain case the first chain engaging the first driven sprocket and the first driving sprocket, while the second chain engages the second driven sprocket and the second driving sprocket;
• wherein the hydraulic motor is a low-speed high-torque motor, whose cylinders are disposed radially about the axis of rotation, whose reaction member is an undulating cam comprising a plurality of lobes, and whose cylinder block is fixed while the reaction member and the motor casing are mounted to rotate about the axis of rotation, wherein the driving sprockets equip the motor casing, and wherein the motor is substantially contained in the chain case.