Pumps – Condition responsive control of drive transmission or pump... – Having condition responsive pumped fluid control
Patent
1997-06-05
1999-09-07
Thorpe, Timothy S.
Pumps
Condition responsive control of drive transmission or pump...
Having condition responsive pumped fluid control
4172221, 60450, 60452, F04B 4900, F16D 3102
Patent
active
059476958
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a control device for controlling a variable displacement hydraulic pump, which is driven by an engine.
BACKGROUND ART
The conventional control device for a variable displacement hydraulic pump includes a variable displacement hydraulic pump 2 (hereinafter, referred to a hydraulic pump 2) driven by an engine 1, and a pilot pump 3 (for example, refer to Japanese Patent Application Publication No. 5-53948). The hydraulic pump 2 has a swash plate angle, which is controlled by a servo piston 4, and is connected to a servo valve 5 for controlling the operation pressure of the servo piston 4. The servo valve 5 is controlled by a neutral control valve 6 (hereinafter referred to as a NC valve 6), a cut-off valve 7 (hereinafter referred to as a CO valve 7), and a variable torque control valve 8 (hereinafter, referred to as a torque control valve 8), which are connected in series.
A conduit 12a, branching from a discharge conduit 12 of the hydraulic pump 2, connects an actuating portion 7e of the CO valve 7 and an actuating portion 8d of the torque control valve 8 via branch conduits 12d and 12c, respectively. A conduit 13a branching from a discharge conduit 13 of the pilot pump 3 connects to a conduit 13b. An engine speed sensor 1a for detecting the engine speed of the engine 1 is connected to a control device 10 via an electric circuit 9. The control device 10 is connected to an operating portion 8c of the torque control valve 8 via an electric circuit 11.
A direction switching valve 16, connected to the discharge conduit 12, is connected to a hydraulic cylinder 20 via conduits 21a and 21b, and is connected to a jet sensor (a pressure detecting portion) 17 via a conduit 18. The jet sensor 17 is connected to a drain conduit 19. The discharge conduit 13 is connected to a pressure controller 14, which is equipped with an operating lever 15. The pressure controller 14 is connected to opposite actuating portions of the direction switching valve 16 via conduits 14a and 14b. 12b is a relief valve.
Now, the operation will be explained. The value of the pressure, detected at the jet sensor 17, is inputted via conduit 23 into the operating portion 6d at one end of the NC valve 6, and the value of the pressure, detected at the drain conduit 19 at the downstream side of the jet sensor 17, is inputted via conduit 22 into an operating portion 6c at the other end. The NC valve 6 is switched by the pressure difference of sites before and after the jet sensor 17. The NC valve 6 is moved to its position 6b when the direction switching valve 16 is moved to either of its end operating positions. By placing the direction switching valve 16 at the center valve position as illustrated in the drawing, the entire discharge of the hydraulic pump 2 is drained through the jet sensor 17 and the drain conduit 19 into the sump tank. Therefore, the pressure difference before and after the jet sensor 17 is greater and the NC valve 6 is at its position 6a in the drawing.
At this time, the engine speed signal, from the engine speed sensor 1a, is inputted into the control device 10, and in response to the engine speed signal, a command signal of the control device 10 is inputted into an actuating portion 8c of the torque control valve 8. The discharge pressure of the hydraulic pump 2 is also inputted into the actuating portion 8d of the torque control valve 8. When the discharge pressure of the hydraulic pump 2 is low, relative to the command signal of the engine speed, the torque control valve 8 is at its position 8a as illustrated in the drawing. When the CO valve 7 is at its position 7a and the NC valve 6 is at its position 6a, the pilot pressure from the conduit 13b is inputted into the actuating portion of the servo valve 5, therefore the servo valve 5 is switched to its position 5a. As a result, the servo piston 4 moves toward the left in the direction of an arrow Y, since the oil at the bottom side is drained and the oil from the conduit 13a flows into the head side, and the discharge of the
REFERENCES:
patent: 3635020 (1972-01-01), Mahlmann
patent: 4523430 (1985-06-01), Masuda
patent: 5279122 (1994-01-01), Shirai et al.
patent: 5784883 (1998-07-01), Ohkura et al.
Kimoto Kenzo
Nagaoka Kou
Komatsu Ltd.
Thorpe Timothy S.
Tyler Cheryl J.
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