Power plants – Pressure fluid source and motor – Having a signal – indicator or inspection means
Reexamination Certificate
2002-11-06
2004-10-05
Lazo, Thomas E. (Department: 3745)
Power plants
Pressure fluid source and motor
Having a signal, indicator or inspection means
C060S420000, C060S484000, C060S486000, C340S463000, C340S626000
Reexamination Certificate
active
06799424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic circuit for supplying pressure oil to a plurality of actuators, etc., and more particularly to a hydraulic circuit for use in construction machines such as a crawler vehicle provided with a plurality of actuators, including a hydraulic excavator.
2. Description of the Related Art
Known hydraulic circuits for use in construction machines such as a crawler vehicle are disclosed in, e.g., Japanese Unexamined Patent Application Publication Nos. 4-118428 and 57-184136. Those disclosed hydraulic circuits are used in construction machines provided with a pair of right and left hydraulic travel actuators (crawler travel devices) and hydraulic work actuators (such as a bucket, a boom, an arm, and a swivel), and include directional control (selecting) valves for controlling a direction of connection between a hydraulic pump or tank and each actuator and a flow rate of pressure oil therebetween in order to operate the actuator.
In each of the hydraulic circuits disclosed in Japanese Unexamined Patent Application Publication Nos. 4-118428 and 57-184136, pressure oil is supplied from three first to third hydraulic pumps, and each of these hydraulic pumps is connected to three hydraulic circuits including respectively directional control valves for the right and left hydraulic travel actuators (hereinafter referred to as “right and left travel directional control valves”) and a directional control valve for the swivel actuator (hereinafter referred to as a “swivel directional control valve”). More specifically, the first and second hydraulic pumps are connected to hydraulic circuits (hereinafter referred to as “first and second circuits”) each including the right or left travel directional control valve and the directional control valves for the other work actuators (hereinafter referred to as “other work directional control valves”), while the third hydraulic pump is connected to a hydraulic circuit (hereinafter referred to as a “third circuit”) including the swivel directional control valve, etc. Such an arrangement ensures independency of the swivel operation from the operation of the other actuators.
Then, any of those hydraulic circuits includes a selector valve (combined operation control valve, hereinafter referred to as a “merging valve”) for changing over the third pump, which is connected to the third circuit, to be connectable with the first or second circuit as well. Upon shift of the merging valve, the pressure oil from the third pump can also be supplied to the first or second circuit so that when the travel actuator and the other work actuator(s) both connected to the first or second circuit are operated at the same time, the pressure oil is supplied at a sufficient flow rate to the other work actuator(s).
In the hydraulic circuit disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 4-118428, the merging valve is connected to a hydraulic line led out of the side upstream of the swivel directional control valve (swivel control valve), thus enabling the pressure oil to be supplied to the first or second circuit through the associated hydraulic lines. With such an arrangement, the pressure oil from the third pump can be supplied to the other work actuators in the first or second circuit upon the shift of the merging valve. In the merging mode, however, there is a fear that the pressure oil is supplied at a larger flow rate to one of the other work actuators in the first and second circuits, which is subjected to a lower load, and the pressure oil supplied to the swivel directional control valve, etc. in the third circuit (including a directional control valve connected to a blade cylinder in the above-cited Japanese Unexamined Patent Application Publication No. 4-118428) is reduced. This may deteriorate the operability of the actuators connected to those directional control valves.
Also, in the hydraulic circuit disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 57-184136, the merging valve is connected to the third circuit downstream of the swivel directional control valve, thus enabling the pressure oil to be supplied to the other work actuators in the first or second circuit (first directional control valve group in the above-cited Japanese Unexamined Patent Application Publication No. 57-184136). With such an arrangement, when the swivel directional control valve in the third circuit is shifted to such an extent that an unloading line is closed, the pressure oil is no longer supplied to the merging valve. In such a case, therefore, the pressure oil from the third pump cannot be supplied to the other work actuators in the first or second circuit.
SUMMARY OF THE INVENTION
In view of the state of the art mentioned above, it is an object of the present invention to provide a hydraulic circuit, which can efficiently distribute pressure oil supplied from a third pump connected to a third circuit to a first and/or second circuit as well, and can improve the operability of actuators.
To achieve the above object, the present invention provides a hydraulic circuit for driving actuators by pressure oil supplied from a first pump, a second pump and a third pump and returned to a tank, the hydraulic circuit comprising a first circuit including a directional control valve supplied with the pressure oil from the first pump, the directional control valve in the first circuit controlling connection between the first pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a second circuit including a directional control valve supplied with the pressure oil from the second pump, the directional control valve in the second circuit controlling connection between the second pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a third circuit including a directional control valve supplied with the pressure oil from the third pump, the directional control valve in the third circuit controlling connection between the third pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a first merging line disposed to be capable of supplying the pressure oil sent from the third pump under a pressurized state to the directional control valve in the first circuit; a second merging line disposed to be capable of supplying the pressure oil sent from the third pump under a pressurized state to the directional control valve in the second circuit; and a merging valve for selectively communicating or cutting off the first merging line and the second merging line with or from the third pump, the merging valve having a first shift position at which the third pump is connected to the second merging line, and a second shift position at which the third pump is connected to the first merging line and the second merging line, the merging valve being continuously shifted between the first shift position and the second shift position depending on a state of the first circuit or the second circuit.
In the hydraulic circuit constructed as set forth above, preferably, when the directional control valve in the first circuit is not operated, the merging valve is shifted to the first shift position, and when the directional control valve in the first circuit is operated, the merging valve is shifted toward the second shift position depending on a state of operation of the directional control valve in the first circuit.
Alternatively, in the hydraulic circuit constructed as set forth above, the merging valve may be continuously shifted between the first shift position and the second shift position depending on a flow rate of the pressure oil required by the directional control valve in the first circuit or the second circuit so that the pressure oil from the third pump is distributed and sent to the first circuit or the second circuit under a pressurized state.
With the above features, when the directional control valve in the first c
Ioku Kensuke
Segawa Hitoshi
Lazo Thomas E.
Nabco Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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