There is provided a hydraulic driving device for working machine having operability handling a change in burden weight in a front working device due to a loaded burden and the like when the working machine that accumulates energy in an accumulator and recovers and regenerates the energy performs an operation of lowering the front working device. A hydraulic driving device 5 includes a main pump 101, a boom cylinder 3, a tank 20, a flow rate control valve 6, an accumulator 300, a first differential pressure control valve 201, and a second differential pressure control valve 202. The first differential pressure control valve 201 is located between the boom cylinder 3 and the accumulator 300. The first differential pressure control valve 201 performs control on discharge oil from the boom cylinder 3 such that a differential pressure between before and after the flow rate control valve 6 becomes a target differential pressure. The second differential pressure control valve 202 is located between the accumulator 300 and the tank 20. The second differential pressure control valve 202 performs control on the discharge oil such that a differential pressure between an upstream pressure and a downstream pressure of the flow rate control valve 6 and the first differential pressure control valve 201 becomes the target differential pressure. The first and the second differential pressure control valves 201 and 202 are configured such that the target differential pressure increases according to an increase in pressure of the discharge oil.

A hydraulic drive device for a cargo vehicle includes a hydraulic cylinder supplying and discharging of hydraulic oil, an operation member that operates the hydraulic cylinder, a hydraulic pump, a lowering oil path connecting the hydraulic cylinder and the hydraulic pump, an operation valve disposed in the lowering oil path, a bypass oil path that branches off from the lowering oil path, a bypass flow rate control valve disposed in the bypass oil path and that controls a bypass flow rate, and a resistance element that is disposed closer to the hydraulic cylinder than the operation valve in the lowering oil path and that increases a fluid resistance. A pilot flow path of the bypass flow rate control valve is connected to a part of the lowering oil path between the hydraulic cylinder and the resistance element.

A hydraulic drive device for a cargo vehicle includes a first hydraulic cylinder for raising and lowering, a second hydraulic cylinder for performing an operation different from the first hydraulic cylinder, a first operation member, a second operation member, a hydraulic pump, an electric motor, a lowering oil path, an operation valve, a bypass oil path that branches off from the lowering oil path, a bypass flow rate control valve in the bypass oil path, a command rotational speed setting unit that sets a command rotational speed of the electric motor, and an electric motor control unit. A command rotational speed deceleration which is a deceleration of the command rotational speed set by the command rotational speed setting unit is larger than an actual rotational speed deceleration which is a deceleration of an actual rotational speed of the electric motor by the controlling output of the electric motor control unit.

The invention relates to a discharge pressure scale (30) consisting of at least one valve housing (41) having at least three fluid connection points in the form of a functional connector (A), a return flow connector (T) and a control connector (28), wherein a valve piston (52) is guided such that it moves longitudinally against the effect of an energy accumulator (42), moving from a respective opening or regulating position, against a valve seat (94), into a closed position, wherein the control (28) and return flow connectors (T) are separated from one another, characterised in that the fluid pressure present at the control connector (28) can be guided onto a pressure-active surface (A.sub.1*) of the valve piston (52) by means of a pressure compensation device (70) in such a way that it moves into its respective opening or regulating position in a pressure-compensated manner due to the force of the energy accumulator (42).

There is provided a hydraulic driving device for working machine having operability handling a change in burden weight in a front working device due to a loaded burden and the like when the working machine that accumulates energy in an accumulator and recovers and regenerates the energy performs an operation of lowering the front working device. A hydraulic driving device 5 includes a main pump 101, a boom cylinder 3, a tank 20, a flow rate control valve 6, an accumulator 300, a first differential pressure control valve 201, and a second differential pressure control valve 202. The first differential pressure control valve 201 is located between the boom cylinder 3 and the accumulator 300. The first differential pressure control valve 201 performs control on discharge oil from the boom cylinder 3 such that a differential pressure between before and after the flow rate control valve 6 becomes a target differential pressure. The second differential pressure control valve 202 is located between the accumulator 300 and the tank 20. The second differential pressure control valve 202 performs control on the discharge oil such that a differential pressure between an upstream pressure and a downstream pressure of the flow rate control valve 6 and the first differential pressure control valve 201 becomes the target differential pressure. The first and the second differential pressure control valves 201 and 202 are configured such that the target differential pressure increases according to an increase in pressure of the discharge oil.

Open centre hydraulic distributor, comprising: a free circulation line connecting a supply line from a negative control pump to a discharge; a delivery line connecting the supply line to users; at least one directional valve that intercepts the free circulation line and the delivery line, so that it narrows a transit area of the free circulation line and opens a transit area of the delivery line, and vice versa; a slide valve arranged on the free circulation line downstream of the directional valve; a valve device that is activated when a threshold value of a pressure delta between upstream and downstream of the directional valve is reached, and maintains this pressure delta equal to the threshold value; a negative control line to pick up a pressure signal from the free circulation line downstream of the directional valve and upstream of the slide valve.

Open centre hydraulic distributor, comprising: a free circulation line connecting a supply line from a negative control pump to a discharge; a delivery line connecting the supply line to users; at least one directional valve that intercepts the free circulation line and the delivery line, so that it narrows a transit area of the free circulation line and opens a transit area of the delivery line, and vice versa; a slide valve arranged on the free circulation line downstream of the directional valve; a valve device that is activated when a threshold value of a pressure delta between upstream and downstream of the directional valve is reached, and maintains this pressure delta equal to the threshold value; a negative control line to pick up a pressure signal from the free circulation line downstream of the directional valve and upstream of the slide valve.