Abstract:
A control for oil flow in a hydraulic system wherein a standard open closed type solenoid valve is modified so that the rate of flow through the valve relates to the electrical power supplied to the valve solenoid coil.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a variable flow solenoid for the pilot control of an hydraulic valve. 
     2. Description of Related Art 
     In hydraulic control systems, it may be required to vary the flow of oil controlling the speed of a mechanical element, for example the speed of a hydraulic elevator. This can be done by employing known solenoid type proportional valves which respond to the signals given by a computer, this having received measurements of the actual speed of the elevator, comparing this speed with the value of a pre-determined target speed and calculating the required adjustment of electrical power to the proportional valve solenoid effecting oil flow to achieve the required correction of elevator speed. 
     Proportional valves are more complex in their design than standard open-closed type solenoid valves and far more expensive. Both of these types are shown in the drawings (see description of FIG.  1  and FIG. 2 in Brief Description of the Drawings). 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to employ the major parts of low cost standard open closed type solenoid valves with inexpensive modifications such that the rate of oil flow through the solenoid valve is relative to the electrical power supply to the solenoid coil, as with a proportional valve. 
     A further object of the invention is to reduce manufacturing and stocking costs of two essential types of flow metering valves by providing the options of having the flow path of the solenoid either “open” or “closed” in their position of rest when no electrical power is applied, employing identical parts in the solenoid assembly, with one minor exception. 
     A further object of the invention is to achieve interchangeability between a standard open-close two position type solenoid and a variable flow solenoid without the requirement of additional installation space or any other modification to the main hydraulic valve manifold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a prior art standard type proportional valve, the relative complexity of which may be obvious. 
     FIG. 2 shows a prior art standard open-close type solenoid valve unsuitable for variable flow control. 
     FIG. 3 a  illustrates the variable flow solenoid valve of the present invention, of the “open when de-energized” type. 
     FIG. 3 b  illustrates the variable flow solenoid valve of the present invention, of the “closed when de-energized” type. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The coil housing  11  and electrical coil  12  are standard to the industry. The solenoid casing  13  consists of a non-magnet tube  14  welded together with a magnetisable soft steel anchor  15  at the upper end and a threaded flange  16  at the lower end. A soft steel core  17  fitting loosely within the tube assembly, carries a firmly attached flow metering needle  18  with an axial center bore  19  and a radial orifice  20  or  21  connecting a higher pressure source passage  30  with a lower pressure source passage  31 . The radial orifice may be situated either at the upper end of the flow metering needle where it is “open” to flow in relation to the upper metering lip  23  as in (FIG. 3 a ) when the coil is de-energized or it may be at the lower end of the flow metering needle where it is “closed” to flow in relation to the lower metering lip  24  as in (FIG. 3 b ) when the coil is de-energized. 
     The flow metering needle fits closely but freely moveable in the needle guide  22  which is clamped into a recess in the main valve manifold  1  by the solenoid casing. Between metering lips  23  and  24  of the needle guide is a cavity  25  from which leads a radial bore  26  connecting the cavity to a lower pressure source through passage  31 . 
     The direction of oil flow through the solenoid can be from passage  30  to passage  31  as described or in the reverse direction, depending to which passages the higher and lower pressure sources are attached. 
     In rest position, the core  17  is pressed downwards against the needle guide  22  by the metering spring  27  creating a gap between the core and the anchor. 
     A trimming screw ( 28 ) is threaded into anchor ( 15 ) and is adjustable to increase or reduce the compression of spring ( 27 ), and thus the force exerted by the spring ( 27 ) against needle ( 18 ). Screw ( 28 ) has a socket ( 29 ) to receive a suitable adjusting tool, which can rotate the screw to provide the adjustment. 
     FIG. 3 a  illustrates the solenoid arrangement with the needle radial orifice  20  below the “upper” metering lip  23  of the guide assembly and therefore “open” to flow through spring pressure when the coil is de-energized. 
     Increasing the electrical power applied to the coil moves the coil with needle towards the anchor against the force of the spring, proportionally “reducing” the size of the opening of the orifice  20  relative to the metering lip  23  thereby “decreasing” the rate of flow of pilot oil from a higher to a lower pressure source. 
     FIG. 3 b  illustrates the alternative solenoid arrangement with the needle radial orifice  21  below the “lower” metering lip  24  of the guide assembly and therefore “closed” to flow through spring pressure when the coil is de-energized. 
     Increasing the electrical power applied to the coil moves the core with needle towards the anchor against the resistance of the spring proportionally “increasing” the size of the opening of the orifice  21  relative to the metering lip  24  thereby “increasing” the rate of flow of pilot oil from the higher to the lower pressure source.