Motors: expansible chamber type – Working member position feedback to motive fluid control – Electrical input and feedback signal means
Reexamination Certificate
1999-05-17
2001-07-10
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Electrical input and feedback signal means
C091S36300A, C137S625650
Reexamination Certificate
active
06257118
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to an apparatus for controlling the actuation of a hydraulic cylinder and, more particularly, to an apparatus for limiting the velocity of the hydraulic cylinder piston as it nears an end of stroke.
BACKGROUND ART
Hydraulic systems are particularly useful in applications requiring significant power transfer and are extremely reliable in harsh environments, for example, in construction and industrial work places. Earthmoving machines, such as excavators, backhoe loaders, and wheel type loaders are a few examples where the large power output and reliability of hydraulic systems are desirable.
Typically, a diesel or internal combustion engine powers the hydraulic system. The hydraulic system, in turn, delivers power to the machine's work implement. The hydraulic system typically includes a pump for supplying pressurized hydraulic fluid and a directional valve for controlling the flow of hydraulic fluid to a hydraulic motor which in turn delivers power to a work attachment, e.g., a bucket.
Conventionally, such earth working machines include a mechanical cushion within the hydraulic cylinders to ease the shock when the hydraulic cylinder piston strikes a stroke end of the cylinder. Typically, an operator displaces a lever device to control the velocity of the hydraulic cylinder piston. If the operator fully displaces the lever, causing the piston to strike the stroke end, the mechanical cushion cannot completely absorb the inertial force of the impact, which subjects the cushion chamber to high pressures, adversely affecting the durability of the cylinder and leading to higher structural cost. In addition, the impact causes the machine body to shake, which can lead to operator discomfort.
The present invention is directed toward overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, an apparatus controllably moves a moveable element within a hydraulic motor. A lever device establishes an operator command signal indicative of a desired velocity and direction of movement of the moveable element. A position sensor senses the position of the moveable element and produces a position signal. An electronic controller receives the operator command signal and position signal, determines the actual velocity of the moveable element, and determines a limit value in response to the actual velocity of the moveable element. Additionally, the controller compares the operator signal magnitude to the limit value and produces a flow control signal in response to the comparison. An electrohydraulic controller receives the flow control signal and responsively controls the movement of the moveable element.
REFERENCES:
patent: 5189940 (1993-03-01), Hosseini et al.
patent: 5305681 (1994-04-01), Devier et al.
patent: 5383390 (1995-01-01), Lukich
patent: 5511458 (1996-04-01), Kamada et al.
patent: 5701793 (1997-12-01), Gardner et al.
Duffy John D.
Koehler Douglas W.
Wilbur R. Carl
Caterpillar Inc.
Lazo Thomas E.
Look Edward K.
Masterson David M.
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