Abstract: A hydraulic drive to, for example, a wheeled excavator comprises two motors (4, 6) connectable to the input side of a gearbox (8) whereby each motor (4, 6) can apply a driving force to a load connected to the output side of the gearbox (8), one motor (6) being selectively disconnectable from the load independently of the other motor (4) by means of a clutch (10). A control system for effecting said disconnection comprises a hydraulic pump (20) drive n by the gearbox (8) to be rotated at a speed proportional to that of the other motor (4), pressure-sensing means (24) for detecting the pressure of fluid displaced by the pump (20), and control means (28) for achieving selective actuation of the clutch (10) such that, when the sensing means (24) detect a pressure associated with a predetermined speed of the other motor (4) at which the drive from the one motor (6) becomes redundant, the control means (28) operate to disconnect the one motor from the gearbox (8).

Abstract: The present invention relates to an apparatus for controlling the running speed of a hydraulic motor. A hydraulic motor employable for a construction machine such as a power shovel or the like as a driving power source is constructed such that its rotational speed can be changed to assume either a high speed (low torque) or a low speed (high torque) so as to cope with differences in the running state of the construction machine. The apparatus of the subject invention assures that the running state of the construction machine is determined by not only the running load of a hydraulic motor but also its rotational speed, whereby the construction machine can run smoothly at all times.