|
(11) | EP 1 598 561 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||
| (54) | Hydraulic control apparatus |
| (57) A driving loss of a pump is avoided to reduce a load of an engine driving the pump.
At least a first circuit group and a second circuit group, each including switching
valves 11 to 19 to switch supply of operating oil to actuators, an auxiliary switching
valve 16 disposed in the first circuit group to switch supply of the operating oil
to an auxiliary actuator, and at least two pumps supplying the operating oil to each
of the first circuit group and the second circuit group are provided. A convergence
flow passage 40 to converge the operating oil from the second circuit group to the
first circuit group, a drain flow passage 43 branched from the convergence flow passage
40 to release the operating oil to a side of a reservoir, and a control valve 42 interposed
in the branched portion are provided, wherein the control valve 42 is operated to
be switched in accordance with a difference in pressures between the first circuit
group and the second circuit group, and introduces the operating oil of the first
circuit group to the drain flow passage 43 when supply pressure of the first circuit
group is higher than supply pressure of the second circuit group. |