| 摘要 |
PROBLEM TO BE SOLVED: To dispense with enlargement of displacement and an increase in the number of broken type jacks so as to reduce cost by bending a shield body by the expansion of a plurality of broken type jacks that connect a front hull to a rear hull. SOLUTION: Variable displacement hydraulic pumps 5A, 5B output operating oil discharge signals to pump inclined rotation control devices 6A, 6B at the same discharge as the pressure receiving area ratio of broken type jacks 3J1 -J4. Corresponding change-over valves 7A, 7B of the broken type jacks 3 in the symmetrical positions of a shield center axis are opened/closed by operation signals from lateral and vertical bending operation parts 12P, 12Q. In this case, the other corresponding change-over valve 7B is put in an opening/closing position in the opening/closing position of one corresponding change-over valve 7A of the jack 3. The respective expanding-contracting strokes of the jacks 3J1 , J2 therefore become equal to those of the jacks 3J3 , J4. A shield body is thereby bent with an axis, orthogonal to the shield center axis, as a bending rotation center axis, so that the cost of the jacks 3 can be reduced. |
