Hydraulic cylinder

A hydraulic cylinder comprising a piston rod, a piston connected to an end of said piston rod, and a cylinder body having therein a rod-side chamber and a bottom-side chamber divided by said piston, wherein said piston is fixed directly to said piston rod by a bolt inserted through a bolt through-hole formed in said piston and secured into a threaded hole provided in said piston rod while a rod-side end surface of said piston is disposed at least partially in face-to-face contact with an end surface of said piston rod,

• wherein a bottom-side cushioning device includes a cushion plunger protruding from a bottom-side end surface of said piston so as to be able to enter a cushion hole connected to a bottom-side hydraulic fluid port of said cylinder body when said piston rod is moved to contract, and
• wherein:
• said cushion plunger includes an enlarged base end portion located between the end surface of said piston rod and the rod-side end surface of said piston, and a shaft portion passing through said piston and protruding from the bottom-side end surface of said piston;
• said cushion plunger is retained with said enlarged base end portion while being allowed to radially move or tilt simultaneously when said piston is fixed to said piston rod by said bolt, said arrangement of the cushion plunger to allow the radial movement or tilting providing a centering function to bring said cushion plunger into an axial alignment align with said cushion hole when said cushion plunger enters said cushion hole.

A hydraulic cylinder for hydraulic construction machines comprising a piston rod, a piston connected to an end of said piston rod, and a cylinder body having therein a rod-side chamber and a bottom-side chamber divided by said piston and alternately supplied with a hydraulic fluid to extend and retract said piston rod, wherein said piston is fixed directly to said piston rod by a plurality of bolts inserted through bolt through-holes formed in said piston and secured into a plurality of threaded holes provided in said piston rod to open at an end surface of said piston rod within a cross-section thereof while a rod-side end surface of said piston is disposed at least partially in face-to-face contact with said end surface of said piston rod,

• wherein a bottom-side cushioning device is provided which comprises a cushion plunger protruding from a bottom-side end surface of said piston, a cushion hole which said cushion plunger is able to enter when said piston rod is moved to contract, and unidirectional flow means associated with said cushion plunger for preventing a hydraulic fluid from flowing from said bottom-side chamber into said hydraulic fluid port when said cushion plunger enters said cushion hole while allowing a hydraulic fluid to flow from said hydraulic fluid port into said bottom-side chamber when said cushion plunger is withdrawn from said cushion hole, and
• wherein said unidirectional flow means includes a first passage formed to open at an end of said cushion plunger and extend axially therein, a second passage for enabling said first passage to communicate with said bottom-side chamber, and check valve means disposed between said first passage and said second passage arranged between said first passage and second passage.