1. Field of the Invention
The present invention relates to a hydraulic cylinder unit used as an actuator, and more particularly, to a simplified structural hydraulic cylinder providing simple maintenance and commonly used parts.
2. Description of the Related Art
The prior art shows a hydraulic cylinder unit 51 of a type, as shown in FIG. 4, in which oil is pumped from one end side of a cylinder to two oil chambers defined in the cylinder by a piston.
The hydraulic cylinder unit 51 comprises a cylinder body 52 including an outer cylinder 53, an inner cylinder 54, a lower cap 55 and an upper cap 56; and a piston 57 which is slidable in the inner cylinder 54. Oil is pumped from the side of the lower cap 55 to an upper chamber a and a lower chamber b (the piston 57 is at the maximum compression position, and b is indicated by a line) defined in the inner cylinder 54 by the piston 57.
That is, the lower cap 55 is provided with an upper chamber port 55a and a lower chamber port 55b. The upper chamber port 55a is communicated with an oil passage c formed between the outer and inner cylinders 53 and 54 through a first communication passage R.sub.1, and the oil passage c is in communication with the upper chamber a through a communication passage Q of the upper cap 56.
The lower chamber port 55b is in communication with the lower chamber b through a second communication passage R.sub.2.
In such a hydraulic cylinder unit 51, in order to move the piston 57 upward, a hydraulic oil is supplied from the lower chamber port 55b to increase the hydraulic pressure in the lower chamber b, and oil in the upper chamber a is discharged from the upper chamber port 55a, and in order to move the piston 57 downward on the contrary, hydraulic oil is supplied from the upper chamber port a, and oil in the lower chamber b is discharged from the lower chamber port 55b.
However, in this conventional structure, since the number of constituent parts of the cylinder body 52 is high, it takes much time to assemble the device. Further, since the upper chamber port 55a, the lower chamber port 55b, the first communication passage R.sub.1 and the second communication passage R.sub.2 are all integrally formed in the lower cap 55, there are problems due to complications in processing of the passages, the number of processing steps is high, the maintenance operation requires excessive time and labor, the cost is increased, and the lower cap is prone to be large in size.
Further, since a joint is threaded into the port portion, the port portion may be damaged if it is repeatedly attached and detached many times. In such a case, it is necessary to exchange the entire lower cap.
Furthermore, if it is necessary to vary a diameter of the inner cylinder, and to reduce a diameter of the piston, the entire inner cylinder must be integrally exchanged, and it is difficult to commonly use the parts.