To improve durability of a liquid-tightness holding part by supplying to the liquid-tightness holding part a lubricant different from a hydraulic fluid for driving an hydraulic driving device.
In the hydraulic driving device, seal parts 97b, (97a) for supporting a first and second piston rods 20b, (20a) are provided to the inside peripheral surfaces of a first and second cover members 96, (94) in a cylinder mechanism 22. A lubricant 130 is supplied to a first oil holding member 140a mounted in mounting grooves 120b, (120a) in the seal parts 97b, (97a) through the medium of a supply passage 132 and an oil supply port 134. While the lubricant 130 having a different property from the hydraulic fluid for driving a piston in the cylinder mechanism 22 is held in first oil holding member 140a, the lubricant 130 is supplied to a clearance 148 formed between the first and second cover members 96, (94) and the first and second piston rods 20a, 20b so as to form an oil film.
SAITO AKIO
NAGAI KOTARO
Toshiyuki Miyadera
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