Expansible chamber devices – With inspection window in expansible chamber wall portion – With lock
Patent
1987-12-29
1989-07-11
Garrett, Robert E.
Expansible chamber devices
With inspection window in expansible chamber wall portion
With lock
324207, 324208, 91DIG4, F01B 2526, F01B 3112
Patent
active
048460486
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic cylinder with a piston slidable in the inner of the cylinder and with magnetic position indication comprising at least one magnetically sensitive component mounted in the cylinder wall.
BACKGROUND ART
It is known to sense the position of a hydraulic piston by means of a magnetic sensor. In the known devices, the permanent magnet is usually mounted in the slidable piston and an inductive sensor is placed at the location in the cylinder wall where a position indication is desired. The known sensors are, however, less reliable in hard frost.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a hydraulic cylinder with a reliable, exact, and yet inexpensive position indication which can use a magnetic sensor of the Hall-element type in order to preserve the reliability at low temperatures, as it must be considered that hydraulic cylinders on working machines such as bulldozers and tractors sometimes must work in hard frost.
According to the invention, the cylinder is characterised in that the magnetically sensitive component is embedded in a magnetically essentially non-conducting material and forms part of a first closed magnetic circuit comprising at least one permanent magnet, and that the slidable piston in a predetermined position forms a second closed magnetically better conducting circuit including said permanent magnet(s), but excluding the magnetically sensitive component. When the piston is placed in the position in which an indication is wanted, the steel material of the piston forms part of the second closed magnetic circuit and almost all the magnetic flux passes through the piston. In this situation the first closed circuit with the sensor in the magnetically bad conducting material carries only little flux. The magnetically sensitive component is thereby brought into a first, non-magnetised condition when the piston opposes the position indicator. When the piston is placed elsewhere in the cylinder, the entire magnetic flux will tend to follow the first magnetic circuit so that a magnetic south pole is formed on one side of the magnetically sensitive component and a magnetic north pole on the other side. As a result the component is placed in a magnetic field and is brought into another, magnetised condition which can be registered in electric circuits connected to the sensor circuit.
BRIEF DESCRIPTION OF THE DRAWING
The invention is explained more detailed in the following with reference to the accompanying drawing, in which
FIG. 1 shows a hydraulic cylinder with several position determination devices according to the invention,
FIG. 2 is an example of the structure of a position determination device according to the invention,
FIG. 3 shows the structure of FIG. 2 with an indication of the magnetic circuit when the piston is displaced from the position determination device, and
FIG. 4 shows same structure as FIG. 2 and the magnetic circuit when the piston opposes the position determination device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1 shows a hydraulic cylinder with several position determination devices according to the invention. These are preferably placed in the bottom members of the cylinder, but may also be placed in the side wall.
FIG. 2 is a sectional view through a cylinder wall 11 which is preferably the end wall of a cylinder. The pressure of a hydraulic liquid such as oil 13 reciprocates the piston 12. A cylindric bore is provided in the cylinder wall, the position determination device being placed in a tight fit in said bore. It must be emphasized that this type of hydraulic cylinders must be able to handle considerable pressures. The position determination device comprises a magnetic material 14 which at one end forms a circular plate filling the cross section of the bore, said material abutting via a central stem 14a an electronic sensor circuit 15 surrounded by non-magnetic material 20, e.g. an epoxy resin. A magnetic post 16 abuts the opposite side of
REFERENCES:
patent: 3453937 (1969-07-01), Haberman
patent: 4229696 (1980-10-01), Gustafson
patent: 4316145 (1982-02-01), Tann
patent: 4401966 (1983-08-01), Ohmura et al.
patent: 4419646 (1983-12-01), Hermle
patent: 4517514 (1985-05-01), Howell
patent: 4617451 (1986-10-01), Gibson et al.
patent: 4618823 (1986-10-01), Dahlheimer et al.
patent: 4652820 (1987-03-01), Maresca
patent: 4726282 (1988-02-01), La Bair
patent: 4736674 (1988-04-01), Stoll
Product Sheet, Micro Switch, Micro Switch Corp., Freeport, Ill.
Christensen Finn D.
Hvilsted Niels
Pedersen Kaj
Denion Thomas
Garrett Robert E.
Hvilsted Niels
Pedersen Kaj
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