Valves and valve actuation – Fluid actuated or retarded – Pilot or servo type motor
Reexamination Certificate
2000-06-14
2001-09-25
Fox, John (Department: 3753)
Valves and valve actuation
Fluid actuated or retarded
Pilot or servo type motor
C251S077000
Reexamination Certificate
active
06293513
ABSTRACT:
The invention relates to a servo-controlled magnetic valve having a main valve, the main closure member of which can be raised from the main valve seat, which is fixed relative to the housing, by the operating stroke of a servo piston, and having a servo valve, the servo closure member of which can be raised from the servo valve seat when, after an empty stroke, a solenoid plunger entrains a slide member that carries the servo closure member and, as a result, pressure is released to the low pressure side from a pressure chamber on the side of the servo piston that is remote from the main valve seat.
In a known magnetic valve of that type, the slide member consists of a rod that carries the servo closure member at one end and a stop at the other end and, between them, carries a second stop. Arranged between the two stops is the solenoid plunger having corresponding counter-stops. During a first section of the operating stroke of the solenoid plunger, the plunger is accelerated without load so that, after an empty stroke, it comes into contact with the slide member with considerable energy. Since, simultaneously, the magnetic force has also increased, relatively small electromagnetic systems are sufficient to actuate the magnetic valve. After the empty stroke there follows a second section of the operating stroke in which the slide member is removed from the region of the main valve seat so that the main closure member, which is provided, together with the servo valve seat, at the base of a pot-shaped servo piston, can open wide enough. This results in a relatively large operating stroke of the solenoid plunger and thus a large overall height of the magnetic valve.
The problem underlying the invention is to provide a magnetic valve that, under conditions that are otherwise the same, makes possible a relatively small overall height combined with a relatively large opening stroke of the main valve.
The problem is solved according to the invention in that the servo piston is an annular piston that surrounds an insert that carries the main valve closure member and the servo valve seat and which, during the operating stroke, entrains the slide member by means of first stops and the insert by means of second stops.
In that construction, after the solenoid plunger has executed the empty stroke, the slide member is no longer drawn outwards by the solenoid plunger, but is pushed outwards by the servo piston, the slide member carrying out a stroke relative to the solenoid plunger in the opposite direction to the empty stroke. Since the slide member does not need to project out of the free end of the solenoid plunger, the desired small overall height is possible.
During its operating stroke, the servo piston also entrains the insert that carries the main closure member, resulting in a large opening of the main valve. The entrainment of the insert, which is delayed relative to the slide member, ensures that the servo valve remains open during the opening stroke of the main closure member and thus the opening action is not interrupted. The empty stroke path of the solenoid plunger, the second stop and a step on the insert are so adapted to one another that the servo valve cannot close. Overall, a relatively large degree of valve opening can be obtained with a very low differential pressure for opening.
It is recommended that the first stops be formed by the annular end face of the servo piston and co-operate with stop faces of the slide member that project radially beyond the insert, and/or that the second stops be formed by an inner flange of the servo piston and co-operate with an outer step on the insert. Such constructions can be manufactured very easily.
In a preferred embodiment, the slide member is generally in the shape of a pot having a base plate and a pot wall, the adjacent end of the plunger piston engages inside the pot and relative movement is limited by stops on the pot and on the plunger piston to the size of the empty stroke. This results in coupling between the slide member and plunger piston that lends itself to the short overall height.
It is advantageous for the base plate to carry the servo closure member in its centre and to project outwards beyond the diameter of the pot. The projecting portion forms the desired stop faces without the diameter of the pot having to be substantially larger than the diameter of the solenoid plunger.
It is also advantageous for the pot wall to have a cut-away portion, through which the solenoid plunger can be inserted transversely to the stroke direction. In that manner, assembly can be simplified substantially.
It is advantageous for the base plate to have notches at its edge and/or holes that are located further in. In that manner, channels are produced through which fluid can, during movement of the slide member, pass without a large throttling action, so that the movement of the slide member is not hindered. This ensures that the fluid in the pressure chamber can flow out of the slide member when the valve is fully opened, which would not otherwise be able to take place because of the position of the servo piston resting against the slide member.
It is recommended that the operating stroke of the solenoid plunger be only slightly larger than the empty stroke. An extremely small overall height is thus obtained.
Preferably, in addition to a closing spring that acts upon the solenoid plunger, a relatively weak pressure spring is provided between the slide member and the solenoid plunger. That pressure spring prevents the solenoid plunger from “sticking” to the slide member and hence stops the servo valve from opening before the empty stroke has been completed.
Moreover, in addition to a closing spring that acts upon the solenoid plunger, it is advantageous for a relatively weak pressure spring that acts in the direction of the operating stroke to be provided between the housing and the servo piston. That pressure spring ensures that the servo piston starts its operating stroke as soon as the servo valve is open. In the limit, the differential pressure for opening can be reduced to zero.
The invention is described hereinafter in greater detail with reference to preferred embodiments shown in the drawings, in which:
FIG. 1
is a section through a magnetic valve according to the invention in the closed state;
FIG. 2
shows the magnetic valve of
FIG. 1
in the open state;
FIG. 3
is a perspective view of a slide member that can be used according to the invention; and
FIG. 4
is a modified construction.
REFERENCES:
patent: 2666451 (1954-01-01), Ray
Danfoss A/S
Fox John
Lee, Mann, Smith McWilliams, Sweeney and Ohlson
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