Abstract: When an arm end exceeds a boundary line K2 and enters a slowdown area R1, a proportional solenoid pressure reducing valve 13 is operated to reduce a pilot pressure for slowing down a first boom cylinder 1A, thereby slowing down an arm end speed. When the arm end exceeds a boundary line K1 and enters a restoration area R2, a restoration gain is calculated in control gain block 200 depending on an intrusion amount by which the arm end enters the restoration area, while a feedback gain is calculated depending on an arm end speed at that time on the basis of functions 204, 205, 206, 207, 208 and 209. In accordance with these gains, a second boom 2 is automatically dumped depending on the intrusion amount of the arm end into the restoration area and the arm end speed at that time so that the arm end is moved for return to the slowdown area. As a result, such work as requiring a work front to be moved toward the operator is continuously smoothly performed and working efficiency is improved.

Abstract: To provide a burglarproof device for a hydraulic machine which has a high degree of security against burglary, ensures high safety, and can be simply installed in a location where the device is hard to find for burglars, a solenoid valve 23 of a burglarproof device 20 is installed in a pilot primary pressure line 3 between a pilot hydraulic pump 1 and a pilot valve device 4. Unless ten numeral keys 21a of a key input device 21 are depressed in the order of the password, an unlocking electronic circuit 22K does not generate an unlock signal and the solenoid valve 23 keeps the pilot primary pressure line 3 cut off. Therefore, a pilot primary pressure from the pilot hydraulic pump 1 is shut off and, even with a manual lever 4c of the pilot valve device 4 operated, no pilot secondary pressure is produced and a main control valve 6 is kept standstill. As a result, a hydraulic cylinder 8 is not operated and the hydraulic machine is unable to move.

Abstract: When an operator makes the reversing-lever operation by operating a control lever 4A in a direction x.sub.2 in the event a solenoid proportional valve 91A of a directional control valve 8A is failed to be left open, an operation position sensor 30A.sub.2 outputs a low-level signal and operation position sensors 30A.sub.1, 30B.sub.1, 30B.sub.2 output high-level signals. Therefore, an AND circuit 6b.sub.2 outputs a low-level signal and an AND circuit 6b.sub.1 outputs a high-level signal, whereupon a switch signal is output from an amplifier 6h to a solenoid switching valve 121 for shifting it to a right-hand position shown in FIG. 1 so that a pilot line 51 is kept communicated with a reservoir 97. No switch signal is output from the amplifier 6h to a solenoid switching valve 122 for holding it in a left-hand position shown in FIG. 1 so that the pilot line 52 is kept communicated with a pilot pump 96.

Abstract: A working machine such as a hydraulic excavator is provided with a working apparatus including a boom pivotally mounted on the body of the working apparatus and a boom-cylinder hydraulic system for the working apparatus. The hydraulic system includes an actuator for moving the boom up and down and a directional selecting valve. The directional selecting valve is arranged to effect selective switching of the feed of a pressurized working fluid to and the discharge of the working fluid from with respect to the rod-side and the bottom-side hydraulic chamber. The hydraulic system further includes a device for relieving the pressure of the bottom-side hydraulic chamber of the actuator. This relieving device is connected to the bottom-side hydraulic chamber of the actuator via a hydraulic circuit. When the pressure in the bottom-side hydraulic chamber changes from rise to fall, the pressure is released to a low-pressure side of the hydraulic circuit, thereby suppressing oscillation of the boom.

Abstract: In an internal combustion engine provided with a hot-wire air flowmeter and a canister for supplying fuel evaporated from a fuel tank into an intake passage, there exists a state where an excessively-rich mixture is supplied from the canister to the intake passage because of trouble of the canister and therefore engine stops. If the hot wire is heated in such a state as described above for removal of contaminations sticked onto the hot wire after an ignition switch has been turned off, there exists a problem such that rich mixture may be fired by the heated hot wire. To overcome this problem, an engine stop detecting means is additionally provided in order to inhibit the hot-wire from being heated up when the ignition switch is turned off after engine stop. That is, the hot wire is heated only when the engine is running before the ignition switch is turned off.