Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1995-12-04
1998-03-31
Michalsky, Gerald A.
Internal-combustion engines
Charge forming device
Fuel injection system
123 9012, 13762564, 251905, F01L 902, F16K 13043
Patent
active
057326789
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a spool valve for control of a hydraulic drive, such as a drive for a fuel pump or an exhaust valve of an internal combustion engine, in which the hydraulic drive comprises a driving piston journalled in a hydraulic cylinder which, through a flow passage, is in communication with the spool valve, the spool of which may occupy a position in which the flow passage is connected with a high-pressure source for hydraulic oil, and another position, where the flow passage is connected with a low-pressure port, and in which the spool is positionable by means of a positioning means electrically activated by a control unit, and in which the positioning means has a movable part and a sensor signalizing the actual position of the movable part to the control unit which determines intended positions for the spool and for the movable part.
A spool valve of this kind is known from WO89/03939 but there the movable part is in the axial direction positionally locked to the spool, and consequently the positioning means has to move the whole mass of the spool. The comparatively large forces required to position the spool make it necessary to design the positioning means as a hydraulic linear drive, the piston of which is axially locked to the spool. This drive is slow-acting.
For some years it has been usual for the exhaust valve of large two-stroke internal combustion engines to be activated by a hydraulic drive, the driving piston of which is driven by a camshaft. More recently it has been suggested to replace the camshaft activation of the exhaust valve and/or the fuel pump by a hydraulic drive, the driving piston of which is connected with the piston of the fuel pump or delivers oil to the driving piston of the exhaust valve or is directly connected with the spindle of the exhaust valve. A number of different spool valves are known, in which the position of the driving piston of the drive is fed back to the spool via a rod and thread connection, which is described, for example, in Swiss patents Nos. 660 637 and 668 463. It is typical for this type of spool valves that the spool itself is set by means of a rotating electric motor turning a rod inserted in a thread and being displaced by the turning in the longitudinal direction of the spool, and thus pulling the spool along in the rod movement. As a consequence of the dimension of the rotating masses in the driving motor and in the associated thread-connected rods, these spool valves are relatively slow-acting.
Furthermore a large number of spool valves are known, using solenoid valves as electrically activated positioning means. Upon activation, solenoid valves jump from an extreme position to an opposite extreme position, where there is a relatively short distance between the extreme positions, such as a few millimeters. These valves are suitable as switching valves which keep a pressure line either fully open or fully closed. In these valves, the displacement of the spool is thus determined by the time in which the solenoid valve is open, which causes such spool valves to be relatively slow-acting as well.
Spool valves are also known, in which the spool is controllingly connected with a core material positioned in a coil and being displaceable in the longitudinal direction of the spool by current being passed through the coil. The relatively large mass of the core material causes the setting times for the valve to be impossible to bring down to such low values that secondary pressure control systems are expendable.
To obtain a sufficiently accurate control of hydraulic systems requiring a very well-defined, rapid and accurate control of the pressure on the delivery side of the hydraulic drive, it is thus necessary to use secondary control systems, such as pressure relief valves on the high-pressure side of the drive. Therefore, the known hydraulic systems are often quite complicated in order to obtain a sufficiently accurate control of pressure conditions in the systems.
The object of the invention is to provide a spool valve which is quick-actin
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IBM Technical Disclosure Bulletin, A.W. Orlando, vol. 6, No. 5, Oct. 1963.
Gabriel Stefan
Hampejs Karel
Hansen Erik Rosenlund
Lindquist Henning
Man B&W Diesel A/S
Michalsky Gerald A.
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