Power plants – Pressure fluid source and motor – Condition responsive control of or by input to input pump...
Reexamination Certificate
2002-01-10
2004-06-15
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of or by input to input pump...
C417S044200
Reexamination Certificate
active
06748739
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hydraulic power system for supplying an operational fluid of a controlled flow rate and/or controlled pressure to a load line leading to a plurality of hydraulic actuators from a reservoir and vice versa.
BACKGROUND ART
U.S. Pat. No. 4,801,247 describes a variable displacement piston pump of the type in which its output flow and output pressure are electrically controlled by a proportional electro-hydraulic control valve. In this conventional hydraulic pump, the hydraulic pressure acting on a control piston and opposing to a spring force is controlled by the proportional electro-hydraulic control valve so as to adjust the tilt angle of a swash plate arranged inside the pump by the displacement of the control piston. In a flow control mode, the control valve is energized by an input current corresponding to the difference between a flow command signal and a flow detection signal to communicate the pressure chamber of the control piston with a pump discharge port or a tank line with an opening proportional to the input current. When the output pressure reaches a certain predetermined pressure value, the control mode is changed to a pressure control mode and the tilt angle of the swash plate is controlled in the vicinity of a cutoff position. This conventional control system relied on the tit angle of the swash plate is advantageous in that both the flow control and the pressure control are effected by the single proportional electro-hydraulic control valve thereby smoothly effecting changeover between the flow control mode and the pressure control mode. In this conventional hydraulic pump, however, the hydraulic control system for controlling the tit angle of the swash plate is complicated in construction so that the flow control characteristics in the low pressure region are deteriorated and the driving motor must always be rotated during the operation of the pump irrespective of the presence or absence of output flow thus giving rise to a problem that the pump is disadvantageous from the standpoint of energy loss.
Japanese Laid-Open Patent Application No. 10-131865 describes a hydraulic pump of the type in which its rotational speed is controlled by a servomotor to supply a hydraulic fluid of a flow rate corresponding to the rotational speed. The servomotor is controlled by an inverter in accordance with the difference between a speed command signal and a rotational speed detection signal. The pump output pressure is detected by a pressure detector and also the difference between a pressure command signal and a pressure detection signal is detected. The detected pressure difference signal is combined with a non-proportional function signal produced according to the rotational speed detection signal so that a smaller one of the resulting sum value and a flow command value is used as a speed command signal. This pump control system relied on the rotational speed is disadvantageous in that there is a limitation to the changeover stability and continuity due to the addition of a non-proportional function signal to a pressure command signal for the purpose of changeover between the flow control and pressure control modes for the rotational speed control loop of the servomotor and that this control system is inferior in response characteristic to the swash plate tilt angle control system due to the driving of the servomotor by the inverter control.
DISCLOSURE OF INVENTION
It is the primary object of the present invention to provide a hydraulic power system capable of realizing control characteristics which are more excellent than those of the previously mentioned prior art.
It is another object of the present invention to provide a hydraulic power system capable of realizing a stable and smooth changeover between control modes and higher response characteristics by the use of a hydraulic pump which is relatively simple in construction and easy in maintenance.
According to a preferred embodiment of the present invention, the foregoing objects can be accomplished by a hydraulic power system for supplying hydraulic fluid of a controlled flow rate and/or controlled pressure from a reservoir to a load line communicating with a hydraulic actuator or vice versa, said system comprising:
a reversible hydraulic pump motor having a rotary shaft and adapted to serve as a hydraulic pump for feeding the fluid at a flow rate corresponding to the rotational speed of the rotary shaft rotating in a forward direction when feeding the fluid to the load line from the reservoir and to serve as a hydraulic motor for rotating the rotary shaft in a reverse direction at a rotational speed corresponding to the flow rate of the fluid when feeding the fluid to the reservoir from the load line,
a variable-speed servomotor having a driving shaft coupled to the rotary shaft in a torque transmitting manner, the driving shaft being rotatable in either of the forward direction and the reverse direction with both a rotational speed and a rotation direction corresponding to the driving current supplied to the servomotor,
pressure detecting means for generating a first electric signal corresponding to the fluid pressure in the load line,
rotational speed detecting means for generating a second electric signal corresponding to the rotational speed of the driving shaft,
signal command means for generating a preprogrammed pressure signal and a preprogrammed flow command signal,
signal processing means for preferentially generating a speed command signal of a magnitude corresponding to the flow command signal by a limiter operation when a pressure difference signal corresponding to the difference between the pressure command signal and the first signal is higher than a predetermined limiting level and for preferentially generating a speed command signal of a magnitude corresponding to the pressure difference signal when the pressure difference signal is equal to or lower than the limiting level, and
rotational speed control means responsive to the speed command signal and the second signal for controlling the magnitude of the driving current supplied to the servomotor through a closed feedback loop of the rotational speed so that the rotational speed of the servomotor corresponds to the speed command signal.
The hydraulic power system according to the present invention is usable in applications in which a hydraulic power is supplied to a machinery including a hydraulic actuator requiring a continuous and smooth changeover between the respective modes of flow control and pressure control, e.g., an injection molding machine, hydraulic press machine, hydraulic press fitting machinery, hydraulic bending machine and the like. In these machines, an energy is inputted in the form of an electric energy which is converted to a hydraulic power by the hydraulic power system of the present invention and this hydraulic power is substantially coincident with the desired values of a flow rate and a pressure to be supplied to the actuator in the respective operating phases of the machine. Thus, by using the hydraulic power system of the present invention, there is no need to use the electro-hydraulic proportional control valve required for controlling these desired values in the conventional systems.
The hydraulic power system according to the present invention employs the reversible hydraulic pump motor which functions as a hydraulic pump during its forward rotation and which functions as a hydraulic motor during its reverse rotation. While a variable displacement type can be used for this hydraulic pump motor, preferably use is made of a fixed displacement type which is relatively simple in pump construction and easy in maintenance. The variable-speed servomotor having the driving shaft connected to the rotary shaft of the hydraulic pump motor in a torque transmitting manner is also a reversible type and preferably a magnet-field synchronous AC servomotor can be used for it.
In the hydraulic power system according to the present invention, control commands are respectively supplied in t
Hashimoto Toshio
Hattori Shiro
Hirano Kenichi
Ohba Koichi
Frishauf Holtz Goodman & Chick P.C.
Leslie Michael
Look Edward K.
Yuken Kogyo Kabushiki Kaisha
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