Abstract: A hydraulic cylinder in which a recess (21) is formed in a piston rod (3) side end surface (20) of a piston (4) so that the recess (21) serves as an axial fitting portion, and an end of the piston rod (3) is fitted into the recess (21) of the piston (4) to ensure the coaxial relationship between the piston rod (3) and the piston (4). Axial threaded holes (24) are formed in an end surface (23) of the piston rod (3) and axial bolt through-holes (25) are formed in the piston (4). The end surface (20) of the piston (4) is disposed in face-to-face contact with the end surface (23) of the piston rod (3), and under the condition bolts (22) are inserted through the bolt through-holes (25) and screwed into the threaded holes (24) to fix the piston (4) to the piston rod (3). Accordingly, the strength of a piston connecting portion can be improved with a simple structure without use of any special high-strength material for the piston rod and without any special heat treatment.

Abstract: A hydraulic-motor drive circuit system includes an auxiliary hydraulic source connected to one end of an auxiliary line, a low-pressure selector connected to the other end of the auxiliary line and a pair of main lines for causing the other end of the auxiliary line to communicate with one of the main lines on the low pressure side during rotation of a hydraulic motor for driving an inertia load, and a switching control arranged in the auxiliary line for supplying the hydraulic fluid from the auxiliary hydraulic source to the other end of the auxiliary line when the directional control valve is in a neutral position, cutting off the hydraulic fluid from the auxiliary hydraulic source to the other end of the auxiliary line when the directional control valve is in an operative position.

Abstract: A hydraulic drive traveling system has a pressure compensated low control valve connected between a hydraulic pump and a variable displacement type hydraulic motor for controlling a flow rate of the hydraulic fluid supplied to the motor. The flow rate is controlled in accordance with the delivery pressure of the pump and demanded traveling speed of the motor. When the delivery pressure of the pump is at a high level, the motor is shifted to a first capacity. When the delivery pressure of the pump is low, the motor is shifted to either the second capacity or the first capacity depending upon the demanded traveling speed.