Abstract:
A system and method for operating a solenoid valve is disclosed. The solenoid valve is operated by moving a first valve element ( 4 ) with respect to a second valve element ( 6, 7 ) a first distance. And then pulling the second valve element ( 6, 7 ) with the first valve element ( 4 ) a second distance where the second valve element ( 6, 7 ) moves against resistance from a seal ( 8 ) and where the movement of the second valve element ( 6, 7 ) opens a gap with respect to an orifice ( 10 ). The second element ( 6, 7 ) then moves a third distance under spring load to open an increased gap with respect to the orifice ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
     Typical direct acting solenoid valves employ an armature containing a seal which is held against an orifice by a spring. Fluid pressure acts over the orifice area either against or with the spring load, giving a tendency either to leak or prevent opening of the valve. Some solenoid valves employ “balanced” armatures where the pressure across the orifice is counteracted by pressure across a seal of the same effective diameter as the orifice. This results in a significantly reduced load across the armature, particularly at higher pressure differentials. Balanced valves may have a significant seal frictional force that the valve needs to overcome to operate. The frictional forces typically increase with increasing pressure differential between the ports of the valve and with increasing seal diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a solenoid valve in an example embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
       FIG. 1  is a sectional view of a solenoid valve in an example embodiment of the invention. Solenoid valve comprises a solenoid coil  1 , an iron circuit  2 , a fixed stem  3 , a moving armature  4 , a seat housing  6 , a seat  7 , a seal  8 , a return spring  9 , an orifice  10 , and a main spring  11 . In some embodiments of the invention the seat housing  6  and the seat  7  may be integrated into one piece. A magnetic circuit in the solenoid valve comprises the solenoid coil  1 , the iron circuit  2 , the fixed stem  3 , and the moving armature  4 . The effective magnetic force acting on the armature  4  increases with increasing coil power and/or a decrease in the size of gap  5  between the armature  4  and fixed stem  3 . The armature  4 , the seat housing  6 , the seat  6 , the seal  8  and the return spring comprise an armature/seat subassembly. Main spring  11  holds armature/seat subassembly against orifice  10 . Fluid connections are made through ports P 1  and P 2  where a port is coupled to each side of orifice  10 . 
     In operation, when the coil is not energized the seat  7  is held against the orifice  10  by main spring  11  acting through the armature  4  and seat housing  6 . The armature  4  is contained wholly within the fluid of port P 1 . Because armature  4  is completely surrounded by the fluid from port P 1  the armature does not need any sealing elements and does not have a pressure differential across any part of the armature  4 . The fluid from port P 1  is sealed from entering port P 2  in two places. The first place is between the seat holder  6  and the valve body at the location of seal  8 . The second place is between the seat  7  and the orifice  10 . In one example embodiment of the invention the seal  8  in seat housing  6  and the orifice diameters  10  are closely matched to reduce or balance the net load due to the pressure differential across seat housing  6 . In another example embodiment of the invention, the diameter of seal  8  and the orifice diameter are intentionally miss-matched to create a force between the seat housing  6  and the orifice  10  when the valve is closed. The force is due to the net difference in area under pressure between the seal  8  and the orifice  10 . The direction of the force can be changed by making the seal diameter larger than, or smaller than, the orifice diameter. The direction of the net biasing force can be used to increases the force between the seat housing  6  and the orifice  10  or decrease the force between the seat housing  6  and the orifice  10 . In one example embodiment of the invention the orifice edge radius is kept small to minimize the effective seating width which may help maintain low pressure load hysteresis. As the coil  1  is energized, the armature  4  is pulled towards the stem  3  against the combined force of the main spring  11  and the return spring  9 . In one example embodiment of the invention, the initial gap  5  is approximately 2 mm. Other initial gap sizes may be used. After traveling a short distance without any resistance due to seals, the armature contacts the seat housing  6 . In one example embodiment of the invention, the short travel distance is approximately 1 mm or half the initial gap  5 . Other short travel distances may be used and the short travel distance may be a smaller or larger fraction of the initial gap. Once the armature  4  has contacted the seat housing  6 , the armature  4  will pull the seat housing  6  along with the armature  4 . To move the seat housing  6  the armature  4  must overcome the friction between seal  8  in the seat housing  6  and the body of the valve. The armature  4  may also be required to overcome a net pressure load when initially moving the seat housing  6 . These additional forces are overcome by the increased magnetic force due to the reduced gap  5  and by the momentum of the moving armature  4 . By using the higher magnetic forces and the momentum of the moving armature to overcome the seal friction and any pressure differential, a smaller coil or lower coil power can be used for a given size solenoid valve. As seat housing  6  and seat  7  move away from orifice  10 , fluid flow between port P 1  and P 2  is enabled. As the armature  4  and seat housing  6  continue to move, armature will reduce gap  5  to zero and contact stem  3 . In this state, full flow may not yet be established as the space between the seat  7  and the orifice will be approximately 1 mm. Return spring  9  will continue to move seat housing  6  away from orifice until the top side of seat housing  6  contacts armature  4 . Once seat housing  6  contacts armature  4  the gap between seat  7  and orifice  10  will be at the maximum size. 
     The operating sequence for opening the valve starts when the coil  1  is energized. The energized coil  1  causes the armature to move a first distance before contacting one end of the seat housing  6 . Once the armature  4  has contacted the seat housing  6 , the energized coil  1  moves both the armature  4  and the seat housing  6  a second distance until the armature  4  contacts the fixed stem  3 . The return spring  9  continues to move the seat housing  6  a third distance until the seat housing  6  contacts the other end of the armature  4 . 
     To close the valve, coil  1  is de-energized and main spring  11  forces armature  4 , seat housing  6  and seat  7 , back down against orifice  10 .