Abstract:
An electromagnetically actuated proportional flow control is provided, with an integral differential pressure regulator, that delivers constant fluid flow independent of input fluid supply pressure and output fluid back pressure in a force balanced spool and sleeve configuration. The force on the spool is controlled by a mechanical device and an electromagnetic device. The force on the spool from the electromagnetic device is variable according to changes in the fluid pressures, the applicable environment and the mechanical components of the system in order to create a the desired force balance on the spool. This arrangement may be used to create proportional fluid control for a single fluid, as for example in a fuel system, or multiple fluids, as for example in a beverage dispensing system.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
         [0001]    The present invention relates to fluid flow control systems having differential pressure regulators and, more particularly, to beverage dispensing systems wherein a plurality of fluids are mixed in a given proportion, such as carbonated beverages.  
           [0002]    There are a number of fluid flow systems in which it is desirable to control the fluid flow rate over a range of conditions both internal and external to the systems. In such systems it can be advantageous to throttle the flow of fluid proportionally to changing input signals. Such systems can employ a single fluid or be used to precisely ratio the flow of multiple fluids. One example of the latter type of system is in “post mix” beverage dispensing, where multiple fluids are stored separately and then mixed together at the point of dispensing to create the beverage.  
           [0003]    In general, such beverage dispensing systems employ valves to meter the amount of carbonated water and syrup at prescribed fluid flows and ratios to produce a desired end product mix. Previously, these arrangements have included solenoid actuated valve ports and “spool and sleeve” differential pressure fluid flow regulators. These regulators have been mechanically adjusted and pre-set for a specific flow rate. In some cases, the regulators have been field adjustable, but are not part of a dynamic closed loop control system. Instead, they are part of a closed loop fluid flow control that is calibrated to a desired fluid flow rate, mechanically set and operate independent of external input.  
           [0004]    One alternative approach has been to create a valve arrangement to control the fluid flow. This approach can be divided into two groups. The first is to use an on-off valve and to pulse the valve on and off as a function of on time in order to obtain the integrated total flow desired. The second is to use a proportional solenoid and stepper motor in order to obtain a variable total flow. This approach has required the use of a flow sensor in order to establish the desired metered fluid flow rate.  
           [0005]    Another alternative approach has been to meter fluid flow by positive displacement of a piston. The actuation of the piston through repetitive strokes establishes the total desired fluid flow. Various means to actuate the piston have been accomplished using additional flow control solenoids or by actuating the piston with the supply pressure from the controlled fluid.  
           [0006]    In such designs, the intent of the beverage dispenser is to control the amount of syrup and the amount of water in a dispensed serving such that the total flow rate and the ratio of the constituents of the flow are controlled to a level of desired accuracy. The uncontrolled variables that affect the desired level of accuracy are often the input supply pressure of the fluids, the temperatures of the fluids over time and the available flow capacity of the upstream delivery lines and manifolds (heat exchangers). These uncontrolled variables are often what lead to a less than desired degree of performance and quality that are measured typically by the accuracy of the syrup-to-water ratio. For example, the consumer at a busy restaurant may notice a difference in beverage taste from a beverage obtained immediately before and immediately after lunch.  
           [0007]    The field adjustability of prior systems allows for some degree of compensation for these shortcomings and environmental variations, but does not provide for closed loop control that would result from a dynamic control to continuously compensate for the changing supply and environmental conditions. Pulsed flow occurs in positive displacement types of fluid control technology, but has resulted in a beverage presentation that is undesirable, and can result in an incomplete mixture of the dispensed fluids. Pulsed on-off flow can also be achieved in solenoid actuated flow control designs, but also can result in undesirable beverage presentation and incomplete mixture of the fluids. For example, such prior systems can result in audible or mechanical oscillations at the point of dispensing. Also, prior stepper motor designs cannot actuate or change flow settings due to the magnitude of the transient displacement require from some off to on settings, as, for example, when the dispenser is momentarily actuated in an attempt to “top-off” a beverage serving. Similarly, prior systems that utilize a volumetric displacement method cannot always control small volumes of fluid flow to a desired ratio of fluid dispensed due to an incremental pulse of fluid (the smallest resolvable flow increment).  
           [0008]    Accordingly, it is an object of the present invention to provide an improved valve arrangement, and more particularly, a valve arrangement which:  
           [0009]    1. Provides proportional fluid flow control,  
           [0010]    2. Integrates flow regulation and proportional electromagnetic actuation,  
           [0011]    3. Provides an output fluid flow rate that is independent of inlet pressure and outlet pressure within the limits of a usable supply pressure, output pressure and delivery flow,  
           [0012]    4. Dispenses mixed component beverages at a desired component ratio independent of environmental changes and system component changes,  
           [0013]    5. Includes a differential pressure regulator having a dynamic, closed loop control to compensate for changing conditions.  
           [0014]    6. Is compact and of simplified construction, with common components for various different fluids,  
           [0015]    7. Is relatively inexpensive to manufacture and to service and maintain during operation, and  
           [0016]    8. Is reliable in operation over long periods of use.  
           [0017]    These and other advantages are obtained by the use of an electromagnetically actuated proportional flow control, with an integral differential pressure regulator, that delivers constant fluid flow independent of input fluid supply pressure and output fluid back pressure in a force balanced spool and sleeve configuration. The force on the spool is controlled by a mechanical device and an electromagnetic device. The force on the spool from the electromagnetic device is variable according to changes in the fluid pressures, the applicable environment and the mechanical components of the system in order to create a the desired force balance on the spool. This arrangement may be used to create proportional fluid control for a single fluid, as for example in a fuel system, or multiple fluids, as for example in a beverage dispensing system.  
           [0018]    Other objects, advantages and novel features of the present invention will readily become apparent to those skilled in the pertinent art from the following drawings and detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 shows in schematic form a beverage dispensing system incorporating the present invention.  
         [0020]    [0020]FIG. 2 shows a cross sectional view of the valve arrangement of FIG. 1.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    The present invention provides a force balanced, differential pressure regulator that can be used in a number of different applications. For purposes of illustration, one such application is in post mix dispensing of beverages.  
         [0022]    [0022]FIG. 1 shows a beverage dispensing system  10  according to the teachings of the present invention. System  10  includes at least two supplies  12  of fluid to be mixed together at an output point  14 . Supplies  12  can be located substantially remote from output point  14  and are connected thereto by fluid lines  16 . A valve arrangement  18  is mounted within at least one of fluid lines  16  to meter the volume of the fluid passing through that line. Valve arrangement  18  is preferably mounted close to outlet point  14 . A control circuit  20  is connected to valve arrangement  18  and includes a digital driver  22  of conventional construction. Control circuit  20  receives input signals from various sensors  24  connected to the fluid lines as desired, both upstream and downstream of valve arrangement  18 .  
         [0023]    The circuit of digital driver  22 , creates, for example PWM signals (pulse width modulated signals) in a conventional manner. One such suitable driver would be a Digital Valve Driver Model DVD, P/N BD-102-100PP, available from Hydro Electronic Devices, Inc. of Hartford, Wis. Similarly, a variety of conventional sensor devices to monitor fluid flow rate, temperature and pressure can be employed as sensors  24 . Also, a standard hydraulic actuator valve circuit, such as an Electronic Interface Control Model EC0003, available from Brand Hydraulics, Inc. of Omaha, Nebr., can be employed as control circuit  20  to create the force balance and dither action on valve arrangement  18  as described further below.  
         [0024]    Valve arrangement  18  includes, for example, a PWM solenoid valve designed to provide a uniform, continuous flow of dispensed fluid. When used in conjunction with one or more similar units, the combined total flow with appropriate ratios of dispensed fluid can be achieve and controlled. In general, valve arrangement  18  integrates flow regulation and proportional electromagnetic actuation together to affect an electrically variable proportional fluid flow. The output flow is independent of inlet fluid pressure and outlet fluid pressure, or backpressure, within the limits of the usable fluid supply pressure, outlet pressure and delivery flow. Integral differential pressure regulation changes with electrical signal input, and that differential pressure occurs across a fixed internal restriction or orifice.  
         [0025]    As shown in FIG. 2, valve arrangement  18  includes a sleeve  30  with a spool  32  slidably mounted therein as a fluid flow regulator. Sleeve  30  is connected between fluid supply inlet conduit  34 , having fluid passageway  36  therein, and fluid outlet port or dispenser housing  38 . By way of orientation, a conventional dispenser shut off valve (not illustrated), such as a solenoid valve, to terminate flow upon completion of dispensing can be mounted to housing  38  downstream of valve arrangement  18 . Spool  32  includes a fluid passageway  40  therethrough from a restrictor orifice  42  leading to conduit  34 . The spool and sleeve serve as a pressure regulator to control the differential pressure across orifice  42  between conduit  34  and passageway  40 . In applications such as beverage dispensing, the controlled fluids are considered to be substantially incompressible. Thus, the amount of fluid passing through orifice  42  is proportional to the differential pressure across the orifice.  
         [0026]    Spring  44  is mounted to apply a balancing force to one side of spool  32 , opposing the force created by the fluid flow on spool  32  (the differential pressure times the exposed area of the end face  46  of spool  32 ). As will be generally understood by those skilled in the art, increased flow through orifice  42  is proportionate to the differential pressure (input pressure from conduit  34  at passageway  36  minus output pressure in passageway  40 ) as related by Bernoulli&#39;s equation. When the force of excess pressure across spool  32 , as applied to end face  46 , causes the spool to move to the right (downstream in this orientation), the spool will begin to close off vent holes  48  in sleeve  30 . These vent holes permit passage of the fluid from passageway  40  downstream to outlet port  39 . As spool  32  starts to close vent holes  48 , the fluid flow through the vent holes is reduced. This creates inherent pressure feedback that reduces the differential pressure across orifice  42 . Therefore, this portion of valve arrangement  18  serves as a differential pressure regulator, controlling the fluid flow at a fixed level in relation to the initial load of spring  44 . Accordingly, the inlet fluid pressure or the outlet downstream pressure can vary over any normal operating range consistent with the design intent of a particular application and the relationship between the inlet pressure, the spool passageway pressure, the resultant differential pressure, the orifice and the spring load remains unchanged. Thus, the fluid fiow rate can remain constant.  
         [0027]    Valve arrangement  18  includes, however, several additional features to allow for electrical input that affects the rate of fluid flow therethrough. Wire coil  50  is mounted about sleeve  30 . Washer  52  is mounted about sleeve  30  downstream of coil  50 . Bracket  54  is mounted about sleeve  30  to contain coil  50  and washer  52 . Washer  52  and bracket  54  are, for example, selected to be made from magnetic metal alloys so as to complete a magnetic circuit. Spool  32  is preferably formed from a material of magnetic quality, such as 430 Stainless Steel. Sleeve  30  is preferably formed from a non-magnetic material such as ceramic. Thus, when electric current is applied to coil  50 , an electromagnetic field can be imparted on spool  32 . The force from this field is generated between end face  46  and bracket  54  such that increasing the current to coil  50  will increase the force on the spool in the direction urged by spring  44 . Therefore, the force balance on spool  32  between the differential fluid pressure force and the spring load, and the fluid flow therethrough, can be regulated according to the coil current as well.  
         [0028]    Further, the current applied to coil  50  is controlled via the digital driver circuit with a pulsed electrical signal. A common description of such pulsed electrical signals is called pulse width modulation (PWM). A signal suitable for valve arrangement  18  in the present example is operated at a frequency of approximately 40 Hertz, although other frequencies can be used in other embodiments of the present invention as suited for particular fluids and applications. In the present example, the PWM signal is established such that the magnitude of the signal will impart a dither action on spool  32 . Previously, dither actions have been known to be used in hydraulic actuators merely to move the position of an element. In the present application, however, this dither action is being used to create a proportional force balance. In the present application, by means of conventional control techniques, the magnitude of the dither and the frequency of the signal to the coil can be adjusted to effectively eliminate any significant inherent friction or “stiction” between spool  32  and sleeve  30 . As the pulse width is modulated from 0% to 100% on-time, the average total integrated energy applied to the coils increases. Therefore, the percentage on-time of the PWM signal will be proportionate to the fluid flow through orifice  42 .  
         [0029]    Conventional controls can be applied to modulate the PWM signal to coil  50  according to signals from sensors  24  to control circuit  20 . In this manner, a closed loop control can be created to maintain the desired fluid flow rate regardless of changes in inlet fluid pressure (as for example when syrup containers start to run low on fluid) or temperature changes (as for example when the dispenser has been operational for long periods of time without refreshing the fluid coolant, typically ice) or fluid viscosity and density changes, etc.  
         [0030]    Summarizing then, the present invention provides a differential flow regulator function utilizing a force balanced spool and sleeve design with the total force exerted on the spool being the sum of the spring and the electromagnetic force created by the coil. The input electrical signal to the coils is directly proportional to the force on the spool. The total force on the spool is directly proportional to the differential pressure through the orifice, which is in turn proportional to the throughtput fluid flow rate. The dither action applied to the spool eliminates any significant drag, friction or inherent non-repeatability in function, as for example can be created by long term fatigue, deterioration or contamination of the spring force. Thus, also, replacement springs are not needed to change the set point to obtain low, medium or high dispensing rates in given applications. Flow is continuous with the present invention, without significant discontinuity or interruption and without obvious audible or mechanical oscillation. Compensation of force to maintain the desired fluid flow rates is faster than with prior designs since the electromagnetic force changes are imparted nearly instantaneously. Transient displacements to top-off applications are readily accommodated.  
         [0031]    Although the present invention has been described above in detail with respect to preferred embodiments, the same is by way of illustration and example only and not by way if limitation. For example, various magnetic circuits can be employed to impart force to spool  32 . Washers at either end of coil  50  can be used. Sleeve  30  need not have a stepped down end portion  51 . Another form of mechanical or hydraulic force can be applied to spool  32  instead of or supplemental to spring  44 . Further, the present invention can be applied to various other applications besides beverage dispensing. Accordingly, the spirit and scope of the present invention are limited only by the terms of the following claims.