Abstract:
An electromechanical valve that includes a cylindrical housing having a first axially disposed chamber containing a valve body and a spool reciprocally mounted in the body for movement along the axis of the housing. A second chamber is located within the housing adjacent to the first chamber which contains a voice coil actuator having a coil holder that is coupled to the spool so that the spool moves linearly when a current is applied to the coil. Materials having a high thermal conductivity are placed in the voice coil actuator for rapidly transmitting heat energy generated in the coil to the housing so that the energy is dissipated into the surrounding ambient before it can damage the actuator.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to apparatus for rapidly dissipating the heat energy generated by a voice coil actuator that is used to control the positioning of a valve spool. 
     BACKGROUND OF THE INVENTION 
     As evidenced by U.S. Pat. No. 5,460,201 to Borcea et al. and U.S. Pat. No. 5,076,537 to Mears, Jr., linear voice coil actuators have been used for some time in association with spool type valves to control the positioning of the valve spool. The voice coil actuator generally involves a tubular wire coil located within a magnetic flux field provided by a stationary magnet. Applying an electrical current to the coil produces a directional force that is proportional to the current input producing relative motion between the magnet and the coil. Typically, the magnet is stationarily mounted and the coil is suspended in a frame within the flux field so that the frame moves linearly when a current is applied to the coil. In a spool valve application, the coil frame is coupled to valve spool and the position of the spool controlled by regulating the amount of current applied to the coil and the direction of current flow. Voice coil actuators have reliable operating characteristics, are generally hysteresis free and provide a smooth motion that makes them ideally well suited for use in controlling the operation of a spool valve. 
     Voice coil actuators, however, tend to generate a good deal of heat, particularly when the valve is cycled frequently over a relatively extended period of time. When housed in a compact package, the heat can build up rapidly to a point where the coil is damaged, thus rendering the actuator inoperative. By the same token, any electrical components located in close proximity with an overheated actuator can also become dangerously overheated. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of the current invention to improve the heat dissipating characteristics of voice coil activated spool type valves. 
     A further object of the present invention is to improve the operation of spool valves by use of a voice coil actuator. 
     Another object of the present invention is to mount a spool type valve, a voice coil actuator for positioning the valve spool and electrical control components associated with the actuator in a compact package so that the actuator coil and the electronic components are not damaged by heat generated by the coil. 
     Yet another object of the present invention is to extend the operating life of a voice coil operated spool type valve by improving the heat dissipation characteristics of the valve. 
     These and other objects of the present invention are attained by a voice coil activated spool valve that includes a housing having a first chamber that contains a valve sleeve and a valve spool mounted for reciprocal movement within the sleeve along the axis of the housing. The housing further contains a second chamber adjacent the first chamber. The second chamber contains a linear voice coil actuator having a stationary magnet and a movable coil frame that is connected to the valve spool so that the spool is positionable when a current is applied to the coil. A thermally conductive polymer is placed between the outer surfaces of the actuator assembly and adjacent surfaces of the housing so that heat energy generated by the coil is rapidly transferred to the housing and the surrounding ambient. A highly conductive ferrofluid is also placed in the flux region of the magnet so that internal heat stored in the core of the actuator is transferred rapidly to the outer surface of the actuator. Fins are placed along the outside of the housing to further aid in the dissipation of heat to the surrounding ambient. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a better understanding of these and objects of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, wherein: 
     FIG. 1 is a top view of a spool valve embodying the teachings of the present invention; 
     FIG. 2 is a bottom view of the valve illustrated in FIG. 1; 
     FIG. 3 is a section view taken along lines  3 — 3  in FIG. 1; 
     FIG. 4 is an enlarged partial view in section illustrating voice coil actuators employed in the practice of the present invention; 
     FIG. 5 is an enlarged partial view in section illustrating a further embodiment of the invention; and 
     FIG. 6 is also an enlarged partial view in section illustrating a still further embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIGS. 1-3, there is illustrated a liquid fuel splitter valve, generally referenced  10  that is contained within a cylindrical housing  12 . The valve  10  further includes a cylindrical valve body or sleeve  13  in which a spool  15  is slidably mounted for reciprocal movement along the central axis  17  of the housing. An inlet port  18  (FIG. 3) to the valve is located in the lower part of the housing and a pair of outlet ports  20  and  21  are located in the upper part of the housing. The splitter valve is of conventional design and is arranged so that an incoming fluid can be selectively routed to one of the outlet ports by selectively positioning the spool along the axis of the housing. Suitable seals  22 - 22  are provided to prevent the in process fluid from escaping from the valve region. 
     Although the present invention will be described with specific reference to splitter valve, it should become evident from the disclosure below that the present invention is not restricted to this particular valve and is applicable for use in association with various types of valves employing a spool for controlling the flow of a fluid. 
     The valve is located in a first chamber  27  within the housing which will herein be referred to as the valve chamber. A voice coil actuator generally referenced  30 , is also contained within the housing in a second chamber  32  that is adjacent the first chamber and separated therefrom by a wall  33 . The second chamber will herein be referred to as the actuator chambers. In practice, the housing is divided into two sections  35  and  36  with the first section containing the valve  10  and the second section  36  containing the voice coil actuator  30 . The sections are joined together at the wall  33  and are secured in assembly by a series of bolts  39 - 39  (See FIGS.  1  and  2 ). Dividing the housing as illustrated facilitates assembly of the components contained within the housing. 
     With further reference to FIG. 4, the voice coil actuator  30  is a conventional design and includes a cylindrical soft iron ferromagnetic core  40  that is surrounded by a tubular soft iron ferromagnetic shell  41  that surrounds the core to establish an annular air gap  81  therebetween. In practice, the core and the shell can be fabricated from the same piece of material. A permanent magnet  46  is embedded in either the shell or the core to establish a flux field within the air gap. A non-permeable end flange  52  is secured thereto using screws  44 . Threaded plugs  45  are passed through the end flange and are threaded into the back of the air gap, the purpose of which will be explained in greater detail below. A coil holder, generally referenced  50  is inserted into the air gap of the actuator. The holder includes a cylindrical body  51  about which a wire coil  53  is wound and a circular end wall  54  that is located adjacent to the wall  33  that divides the two housing chambers. Two lead wires  68  and  69  are attached to wall  52  to provide current to the coil. A specially designed groove in the housing  35  allows the wires to be connected to a controller that includes circuit boards  66  and  67 . The actuator sleeve forms a close running fit with the inner wall of the actuator chamber so that the actuator is axially aligned with the central axis of the housing. 
     The spool contains a pair of end shafts  55  and  56  that are carried in suitable linear bearings mounted within bearing blocks  57  and  58 , respectively. End shaft  55  is arranged to pass through the dividing wall  33  of the housing and is connected by any suitable coupling to the end flange  52  of the coil holder  50  so that axial movement of the coil holder will cause the valve spool to be repositionable. In assembly, the spool is held in a neutral position by means of opposed failsafe springs  59  and  60  thereby preventing fluid from passing through the valve. Repositioning of the valve spool is achieved by applying a current to the actuator coil. The direction of current flow through the coil determines the direction of movement of the coil holder while the force generated by the current flow is a function of the amount of current applied to the coil and the magnetic flux density in the air gap. 
     The end flange  52  of the actuator assembly extends radially beyond the shell and is seated in a shoulder  63  formed in actuator chamber and secured in place using any suitable means such as threaded fasteners or the like (not shown). A pair of radially disposed spaced apart circuit boards  66  and  67  are mounted within the actuator chamber  32  immediately behind the actuator assembly. The boards contain circuitry of a digital controller that is arranged to regulate the activity of the voice coil actuator and thus, the positioning of the valve stem. The controller circuitry is connected both to the coil wires  68  and  69  and to an elongated stationary contact blade  70  mounted upon a pad  71  in parallel alignment with the axis of the housing. The pad is located within a hole  72  provided in the actuator core. A moveable wiper blade  73  is secured to the end wall of the coil holder by a beam  74  and moves with the coil holder to provide accurate positioning information to the controller. The controller, in response to input commands, causes suitable current to be applied to the actuator coil so as to move the spool to a desired location. Command leads  77  to the controller as passed through an opening  78  in the rear of the housing and through terminal block  79 . 
     As illustrated in FIG. 4 ferrofluid  80 , having a high thermal conductivity, is injected into the actuator air gap through the threaded plug holes  81 . The ferrofluid is applied to the magnetized surfaces of the actuator using a syringe. The fluid fills the vacant spaces in the air gap and thus provides a path of travel over the gap such that heat generated in the core and coil region of the actuator is transferred rapidly to the outer surfaces of the housing  35  which is adjacent to and in close proximity with the inner wall of the housing. Suitable ferrofluids having high thermal conductivity are commercially available through Ferrofluidics Corp. having a place of business in Chanhassen, Minn. 
     The inside surface of the actuator end flange, as well as the outer surface of the actuator shell are coated with a polymer material  85  that also has a high thermal conductivity. The polymer fills the region between the end flange and the housing and the shell and the housing to provide a highly conductive path over which heat generated by the voice coil actuator can be transferred to the housing. Polymers having a high thermal conductivity around 1.5 W/m-K suitable for use in this application are available from the Bergquist Company that has a place of business in Nashua, N.H. The housing is preferably fabricated of a non-magnetizable material, such as aluminum or stainless steel, both of which have a relatively high thermal conductivity. The outer surface of the housing, in turn, is provided with laterally extended cooling fins  88 - 88 , particularly in and about the region overlying the voice coil actuator. The fins serve to discharge the heat energy in the housing to the surrounding ambient. To aid in the dissipation of heat from the housing, the thickness of the housing wall surrounding the actuator is reduced by forming a circular groove  90  within this region. 
     As can be seen, the present invention enhances the flow of heat away from the voice coil and rapidly discharges the energy into the surrounding ambient. As a result of this controlled rapid heat flow out of the housing, the valve and the actuator can be mounted in a side-by-side relationship within an extremely compact package, that is a package of a size such that the heat generated by the coil would ordinarily lead to early failure of the coil itself. It should also be evident from the present disclosure because of the rapid dissipation of heat energy from the housing, it is now possible to store many of the electronic control components in the package in close proximity with the voice coil actuator without the danger of the components becoming heat damaged. Accordingly, the need for long wire connections is eliminated and all problems associated therewith eliminated. 
     Turning now to FIG. 5, there is illustrated a further embodiment of the invention wherein the magnet  100  is located within the housing wall  101  between a pair of annular rings  102  and  103 . The rings are formed of the same material as the housing having a high coefficient of heat transfer so that heat generated within the actuator is transferred rapidly to a series of fins  106  mounted within an annular recess  107  formed in the outer surface  108  of the housing. As explained with reference to FIG. 4 above, the moving coil assembly  110  surrounds the pole piece  111  that generates a magnet flux field. The coil  112  further includes a head piece  114  that is connected to the valve spool by a connecting rod  115 . A position sensor  117  as described above provide accurate position related to the controller. The movable contact of the sensor is mounted upon an arm  118  that forms part of the coil frame and which passes into the coil frame and which passes into a central opening  120  in the pole piece. 
     The moveable coil, as explained above, is surrounded by transmission oil having a cooling effect on the coil as well as a relatively high heat conductivity. The oil completely fills the cavity  119  between the housing and the pole piece thus eliminating the air gap typically found in the region. Suitable oil seals are provided to maintain the oil within the air gap. Because heat from the coil is transferred directly to the housing wall surrounding the actuator, the need for heat conducting polymers and ferrofluids is also eliminated in this embodiment. As a result, heat generated by the actuator will be rapidly transferred through the necked down section of the housing and the fins into the surrounding ambient. 
     FIG. 6 is a still further embodiment of the present invention wherein the coil assembly  121 , as described above in detail with reference to FIG. 4, surrounds the core piece  122  containing magnetic coil  125 . The coil assembly is moveable within an annular cavity  126  located between the magnetic core and the housing. Here again, the cavity is filled with a ferrofluid  130 , the type noted above, however, because the actuator is now an integral part of the housing, the need for heat conducting polymer is eliminated. Fins  132  are mounted in an annular recess  135  that surrounds the actuator. The coil frame  136  is connected to the valve spool  139  by a connecting rod  140 . 
     In this embodiment of the invention, the sliding contact  141  of the position sensor  142  is mounted on the coil frame while the stationary contact  142  is connected directly to the housing. Suitable electrical lines connect the boards  145  and  146  of the controller to the coil and the position sensor. 
     While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.