Patent Publication Number: US-2017363224-A1

Title: Proportional Valve, Electric Shower Incorporating the Proportional Valve and Tap Incorporating Same

Description:
This invention relates to a proportional valve which may be incorporated in an electric shower. 
     There are many known valves for controlling the flow of a fluid through a system. A proportional valve allows the flow rate to be varied throughout a range by varying the signal applied to a solenoid forming part of the proportional valve. 
     Proportional valves are known in which an input port is in fluid communication with a control chamber through small holes provided in a diaphragm. The diaphragm carries a diaphragm plate that, when positioned in a main orifice between the input port and an output port, blocks the flow path between the input port and the output port except for a pilot orifice through the diaphragm plate. The solenoid has an armature that, in the absence of a signal being applied to the field winding of the solenoid, is biased by a spring to pass through the control chamber and abut the diaphragm plate so as to move the diaphragm plate into the main orifice and to block the pilot orifice. The fluid pressure in the control chamber assists in holding the diaphragm plate in the main orifice, so that no fluid flows from the inlet port to the outlet port when no signal is applied to the field winding of the solenoid. 
     When a signal is applied to the field winding to move the armature away from the diaphragm plate against the spring force, fluid is able to pass through the pilot orifice creating a pressure differential that allows the diaphragm plate to lift out of the main orifice so that fluid is permitted to flow between the inlet port and the outlet port through the main orifice. In particular, the diaphragm plate lifts out of the main orifice until the diaphragm plate abuts once again the end of the armature. The position of the end of the armature is determined by the signal applied to the field winding of the solenoid, and accordingly the gap available for fluid to flow through to the main orifice is determined by the signal applied to the field winding of the solenoid. 
     For an electric shower, proportional valves are desired that achieve average flows from 0.5 litres per minute to 12 litres per minute across 0.5-5 bar dynamic water pressure. A problem with known proportional valves is that under mains water pressure, at low flow rates there is an initial, transient surge of water when the valve is first opened, before a steady state flow rate is achieved. Previous attempts to address this problem have concentrated on the forces applied on the armature by the field winding of the solenoid and the spring. 
     After much investigation, the present inventors have determined that the diaphragm plate and/or main orifice can be shaped in such a way as to inhibit transient fluid flow peaks. For example, by reducing the size of the pilot orifice, the rate of increase in the pressure differential between the inlet port and control chamber sides of the diaphragm can be reduced, thereby slowing the lifting of the diaphragm plate out of the main orifice. Further, the part of the diaphragm plate that sits in the main orifice can be shaped so that the gap through to the main orifice increases approximately linearly with movement of the diaphragm plate. 
    
    
     
       By way of example, embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: 
         FIG. 1  shows a perspective view of a proportional valve according to the invention; 
         FIG. 2  shows a cross-section through the valve illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged detail of the spring assembly of the valve illustrated in  FIG. 1 ; 
         FIG. 4 a    shows a cross-section through a diaphragm plate forming part of the valve illustrated in  FIG. 1 ; 
         FIGS. 4 b  and 4 c    respectively show side and top views of the diaphragm plate; 
         FIGS. 5 a  to 5 e    show the diaphragm plate at five different positions relative to the main orifice; 
         FIG. 6  illustrates an electronically-controlled shower system having hot and cold inlets, in which the flow rate through each inlet is controlled by the valve of  FIG. 1 ; 
         FIG. 7  shows an electronically-controlled shower system having a cold inlet feeding into a heater, in which the flow rate through the cold inlet is controlled by the valve of  FIG. 1 ; 
         FIG. 8  is an enlarged detail of part of the diaphragm plate of the valve of  FIG. 1 ; 
         FIG. 9  is a plot of flow area against displacement of the diaphragm plate; 
         FIG. 10  is a table of measurements of flow area against displacement of the diaphragm plate; and 
         FIG. 11  is a plot of biassing force generated by the spring assembly of the valve illustrated in  FIG. 1 . 
     
    
    
     As shown in  FIG. 1 , in an embodiment of the invention a proportional valve  1  has an inlet port  3  and an outlet port  5 . The valve  1  includes a solenoid  7  having electrical contacts  9   a  and  9   b . In this embodiment, the solenoid  7  is a 24V DC 8 W solenoid. As will be discussed in more detail hereafter, the flow of liquid through the inlet port  3  of the proportional valve  1  to the outlet port  5  is controlled by an electrical signal applied to the solenoid  7  via the electrical contacts  9   a ,  9   b.    
     As shown in  FIG. 2 , the proportional valve  1  has a housing  11  which defines the inlet port  3  and the outlet port  5 , as well as defining a main orifice  20  between the inlet port  3  and the outlet port  5 . The housing  11  also defines a cylindrical guide tube  22 , generally aligned with the main orifice  20 , along which an armature  15  of the solenoid  7  can move along the cylindrical axis. A spring chamber  23  is provided at the end of the guide tube  22  distal to the main orifice  20 , and a control chamber  24  is formed at the end of the guide tube proximate the main orifice. As shown in  FIG. 2 , in this embodiment the housing  11  is formed of two members: the first member  11   a  defining the inlet port  3 , the outlet port  5  and the main orifice  20 ; the second member  11   b  defining the spring chamber  23 , guide tube  22  and control chamber  24 . Threading provided on an internal surface of the first housing member  11   a  and an external surface of the second housing member  11   b  enable the second housing member to be screw-fitted into the first housing member. In this embodiment, the housing  11  is made from moulded plastics, in particular glass-filled nylon. 
     A spring assembly  13  is provided in the spring chamber  23  and applies a biasing force to one end of the armature  15  urging it towards the main orifice  20 . As shown in  FIG. 2 , a field winding  17  of the solenoid  7  is provided around the guide tube  22  housing the armature  15 . The armature  15  is made of a ferrous material so that a magnetic field generated by a current flowing through the field winding  17  exerts a force on the armature along the cylindrical axis. 
     In this embodiment, the armature  15  is made of magnetic stainless steel, apart from a rubber boot  25  provided at the end of the armature  15  adjacent the main orifice  20 . In this embodiment, an aperture for receiving the guide tube  22  is formed through the field winding  17  having a diameter of 8.8-8.9 mm, which is a standard sizing for such a solenoid  7 . The thickness of the housing portion forming the guide tube  22  is 0.75 mm, significantly less than for previous proportional valves, which allows for a larger diameter of 7 mm for the armature  15  (compared to 6 mm that is conventionally used). In this way, a stronger force can be applied to the armature  15  by current flowing in the field winding  17  than in comparison with the same current flowing in conventional proportional valves. Further, the use of magnetic stainless steel provides a comparatively low inertia system, which also assists in the controllability of the position of the armature  15  within the guide tube  22 . 
     A small gap is provided between the armature  15  and the guide tube  22  so that the spring chamber  23  is in fluid communication with the control chamber  24 . This has the advantage that any air trapped in the spring chamber  23  can dissipate through the valve  1 , and therefore no bleed arrangement need be provided. Those skilled in the art will appreciate that this is particularly advantageous when the valve has been in use, where a gas build-up in the spring chamber  23  would otherwise require bleeding and recalibration of the valve, such recalibration in many circumstances being unfeasible. 
     A flexible diaphragm  19  is mounted in the housing  11  between the first housing member  11   a  and the second housing member  11   b , so that the inlet port  3 , outlet port  5  and main orifice  20  are on one side of the diaphragm  19  and the control chamber  24  and armature  15  are on the other side of the diaphragm  19 . Several small holes are provided in the diaphragm  19  to allow liquid to move from the inlet port  3  into the control chamber  24 . The diaphragm  19  carries a rigid diaphragm plate  21 . As will be described hereafter, the positional relationship between the diaphragm plate  21  and the main orifice  20 , which is controlled by the current flowing in the field winding  17 , determines the flow rate through the valve  1 . 
     A pilot orifice  31  is formed through the centre of the diaphragm plate  21 , and is generally aligned with the cylindrical axis of the guide tube  22  which guides the movement of the armature  15 . As such, in the absence of current in the field winding  17 , the spring assembly  13  urges the armature  15  against the diaphragm plate  21 , both inserting the diaphragm plate  21  into the main orifice  20  and blocking the pilot orifice  31  with the rubber boot  25 . In this way, fluid flow between the inlet port  3  and the outlet port  5  is blocked. Further, fluid in the control chamber  24  applies pressure on the diaphragm  19  and diaphragm plate  21  that assists in holding the diaphragm plate  21  in the main orifice  20 . 
     When a current flows in the field winding  17  in a direction that exerts a force on the armature  15  counter to the force of the spring assembly  13 , the armature  15  lifts away from the diaphragm plate  21 , thereby opening the pilot orifice  31 . Subsequent movement of liquid through the pilot orifice  31  generates a pressure differential between the inlet port  3  and the control chamber  24 , resulting in the diaphragm  19  lifting the diaphragm plate  21  out of the main orifice  20  to a position where the diaphragm plate  21  again abuts the armature  15 . In this way, liquid is allowed to flow through the main orifice  20 . 
     In conventional proportional valves, when the diaphragm plate  21  first lifts from its seat within the main orifice  20 , a sudden flow of liquid through the main orifice applies an impulsive force to drive the diaphragm plate  21  into the armature  15 , causing the diaphragm plate  21  and armature  15  to move further against the biassing force of the spring assembly  13 . This additional movement of the diaphragm plate  21  leads to a temporary surge in the flow rate through the valve until equilibrium is established between the magnetic force and the spring force on the armature  15 . Previous attempts to address this problem have concentrated on the solenoid design. The present invention arises from the realisation that by careful design of the diaphragm plate  21  and the way that the diaphragm plate  21  sits in the main orifice  20 , the sudden inflow of liquid through the main orifice as the diaphragm plate  21  lifts can be ameliorated. In particular, in previous proportional valves, the flow of liquid through the main orifice  20  typically increased exponentially with movement of the diaphragm plate  21  along the axis of movement of the armature. In contrast, for a valve according to an embodiment of the invention, the flow of liquid through the main orifice  20  can increase generally linearly with movement of the diaphragm plate  21  along the axis of movement of the armature  15 . 
     The diaphragm plate  21  will now be described in more detail with reference to  FIGS. 4 a  to 4 c   . As shown in  FIG. 4 a   , the cross-section of the diaphragm plate  21  has three portions: an inverted frusto-conical portion  33 , a neck portion  35  and a top portion  37 . The pilot orifice  31  has a narrow diameter portion  31   a  within the top portion  37  and a wider diameter portion  31   b  through the neck portion  35  and the top portion  37 . In this embodiment, the diameter of the narrow portion  31   a  of the pilot orifice is 0.75 mm, which is significantly less than that of pilot orifices for conventional proportional valves. This means that the rate of increase of the pressure differential when the pilot orifice  31  is first opened is less than for conventional proportional valves, which helps reduce the speed of movement of the diaphragm plate  21  and accordingly the rate of increase in the liquid flow through the main orifice. To prevent blocking of the pilot orifice  31  by particulates, an inlet filter (not shown) having a mesh size of 0.2 mm is used. The diameter of the wider portion  31   b  of the pilot orifice is 1.5 mm. This offset in diameter between the narrow portion  31   a  and the wider portion  31   b  of the pilot orifice  31  assists in the moulding process for the diaphragm plate  21 . 
     The diaphragm  19  is fitted around the neck portion  35  of the diaphragm plate  21 , with the frustoconical section  33  on the main orifice side of the diaphragm and the top portion  37  on the control chamber side of the diaphragm  19 . The main part of the conical surface of the frusto-conical section  33  is sloped at an angle α of 39°, in contrast to previous diaphragm plates which typically slope away at a much larger angle apart from a number of radial guide fins. The depth of the frusto-conical section is 3.25 mm, significantly shorter than previous diaphragm plates. As seen in  FIGS. 4 b   , a series of ribs  38  are evenly spaced about the conical surface of the frusto-conical section  33 , in this case eight. Each rib  38  has the same, substantially constant, depth. As well as reducing the possibility of the diaphragm plate  21  sticking in the main orifice, these ribs  38  further restrict the flow path for liquid to flow through the main orifice at low flow rates. 
     The precise shape and configuration of the frusto-conical portion  33  of the diaphragm plate  21  and of the ribs  38  is seen in greater detail in  FIG. 8 . At its root adjacent to the diaphragm  19 , the diaphragm plate  21  presents a plain cylindrical surface, indicated by the letter A in  FIG. 8 , extending parallel to the axis of the main orifice  20 . From there, the surface of the diaphragm plate  21  extends away at an angle to produce its characteristic frusto-conical form. The ribs  38  start at the junction of these two surfaces and initially extend parallel to the axis of the main orifice  20 , flush with the plain cylindrical surface of the diaphragm plate  21 , indicated in  FIG. 8  by the letter B. After a short distance, the ribs  38  turn and follow a path parallel to the frusto-conical surface of the diaphragm plate, but spaced from it, indicated in  FIG. 8  by the letter C. 
     It will be understood that this particular configuration of the ribs  38  will effect a variable rate of change of the annular space between the diaphragm plate  21  and the main orifice  20  as the diaphragm plate is drawn out of it. This is deliberate and advantageous, because it can be designed to more closely mimic the ideal configuration which would bring about a linear rate of change of the annular gap. The gap between the diaphragm plate  21  and the main orifice  20  varies in proportion to the square of the diameter, which implies that the ideal shape for the diaphragm plate would in fact be a parabolic curve, rather than frusto-conical. 
       FIGS. 5 a  to 5 e    show the position of the diaphragm plate  21  as it moves from the reset position, in which the main orifice  20  is closed, to a position in which the diaphragm plate is at the other end of its range of movement and the main orifice is fully open. Table 1 below gives details of the main orifice  20  cross-section and extent of openness of the main orifice for the five positions of the diaphragm plate  21  shown in  FIGS. 5 a  to 5 e   . It can be seen from the values given in Table 1 below that the cross-sectional area varies approximately linearly with the position of the diaphragm plate  21 . This is significantly different from conventional proportional valves, in which the cross-sectional area increases exponentially with movement of the diaphragm plate. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Variation of main orifice flow parameters with position of diaphragm plate 
               
            
           
           
               
               
               
               
            
               
                   
                 Orifice 
                   
                   
               
               
                 Diaphragm Position 
                 Cross-Sectional 
                 Proportion of being 
                   
               
               
                 (% of top position) 
                 Area (mm 2 ) 
                 fully open 
                 Difference 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 0 
                 0 
                 0 
                 — 
               
               
                 25 
                 6.19 
                 33.0% 
                 33.0% 
               
               
                 50 
                 10.25 
                 54.6% 
                 21.6% 
               
               
                 75 
                 14.61 
                 77.8% 
                 23.2% 
               
               
                 100 
                 18.77 
                  100% 
                 22.2% 
               
               
                   
               
            
           
         
       
     
     As discussed above, the diaphragm plate  21  in this embodiment differs from those of conventional proportional valves in two main ways. Firstly, the pilot orifice  31  is narrower, which slows down the rate of increase in the pressure differential. Secondly, the portion of the diaphragm plate  21  that sits in the main orifice  20  is shaped so that the cross-sectional area available for fluid flow increases substantially linearly with movement of the diaphragm plate  21  out of the main orifice. These differences contribute to providing a significant improvement in the controllability of the flow rate through the valve in comparison with conventional valves, in particular by inhibiting transient liquid flow peaks through the output port  5  in response to initial unblocking of the main orifice  20 . 
     A plot of the rate of change of the annular gap between the diaphragm plate  21  and the main orifice  20 , ie the flow area for passage of water, in the earlier stages of opening is seen in  FIG. 9 . The initial part of the plot represents the phase of withdrawal of the diaphragm plate  21  indicated by the letter A in  FIG. 8 . The remainder of the plot represents the phases of withdrawal indicated by the letters B and C in  FIG. 8 , and it can be seen how this varies in a substantially linear manner. Measurements taken for an embodiment of the valve with this configuration are shown in  FIG. 10 . 
     The proportional valve of this embodiment was designed for use in an electronically controlled shower system with signal voltage proportional to the target flow, thereby providing control of hot and or cold water flows. As such, the invention encompasses an electric shower including such proportional valves. 
     As shown in  FIG. 6 , in one embodiment the electronically-controlled shower hot water and cold water are mixed, with the flow rates of the hot and cold water being controlled by a proportional valve as described above. In particular, cold water flows from a cold water inlet to a first proportional valve  101   a  via a first temperature sensor  103   a . The output of the first valve  101   a  flows to a mixing chamber  105  via a first flow meter  107   a . Similarly, hot water flows from a hot water inlet to a second proportional valve  101   b  via a second temperature sensor  103   b . The output of the second valve  101   b  flows to the mixing chamber  105  via a second flow meter  107   b . The first and second temperature sensors  103   a ,  10     3 b  and the first and second flow meters  107   a ,  107   b  are connected to a microcontroller  109 . A user control  111 , via which the user of the shower indicates desired temperature and flow rate, is also connected to the microcontroller  109 . An algorithm within the microcontroller  109  calculates, based on the user-desired temperature and flow rate and the respective temperatures of the cold water and the hot water, required flow rates through the valves  101   a ,  101   b  and send control signals to the solenoids of the valves  101   a ,  101   b  to achieve those flow rates, as measured by the flow meters  107   a ,  107   b . Optionally, the output of the mixing chamber  105  can be fed to the shower head (not shown) via a third temperature sensor  103   c  to verify that the temperature of the water supplied to the shower head matches the user-desired temperature. 
     As shown in  FIG. 7 , in another embodiment the electronically-controlled shower heats cold water to a desired temperature, with the flow rate of the cold water being controlled by a proportional valve as described above. In particular, cold water flows from a cold water inlet to a proportional valve  121  via a first temperature sensor  123   a . The output of the valve  121  is directed to a heater  125  via a flow meter  127 . The first temperature sensor  123   a  and the flow meter  127  are connected to a microcontroller  129 . A user control  131 , via which the user of the shower indicates a desired temperature and flow rate, is also connected to the microcontroller  129 . An algorithm within the microcontroller  129  calculates, based on the user-desired temperature and the temperature of the cold water and the user-desired flow rate, a required flow rate through the valve  121  and a required heating power by the heater  125 . The microcontroller then sends a heater control signal to the heater to activate one or more heating elements to achieve the desired heating power, and a control signal to the valve  121  to achieve the desired flow rate, as measured by the flow meter  127 . The temperature of the water output by the heater is measured using a second temperature sensor  123   b , as the microcontroller  129  can only provide coarse control of the heater  125 . To provide fine temperature control, the microcontroller  129  varies the control signal to the valve  121  to achieve the desired temperature. 
     A feature of the proportional valve described above is that in addition to providing proportional flow control over 0.5-5 bar dynamic pressure, a simple on/off operation can take place as low as 0.2 bar static pressure. This means that it is not necessary to incoroporate separate on/off valves in the electronicaly-controlled showers in addition to the proportional valves. 
     Modifications and Further Embodiments 
     As discussed with reference to  FIGS. 6 and 7  above, a proportional valve as described above can be incorporated within an electronically-controlled shower to control the flow and temperature of water supplied to a shower head. Alternatively, the proportional valve can be incorporated into a tap or faucet. For a mixer tap, an arrangement analogous to that of  FIG. 6  or that of  FIG. 7  could be used. In alternative embodiments, a hot tap or a cold tap may include a single proportional valve as described above. 
     In the specific embodiment described above, the pilot orifice  31  has a portion with a diameter of 0.7 5mm, which was found to be generally optimal. Improvements can, however, be achieved with pilot orifices having a diameter of less than 0.8 mm. Generally, the mesh size of the inlet filter should be less than 250 μm. 
     While the cone angle of the frusto-conical section  33  of the diaphragm  19  in the embodiment described above is 39°, improvements can also be obtained with cone angles generally in the region of 30° to 45°. 
     In conventional proportional valves, the biassing force for the armature is typically provided by a single constant-rate spring. In a further improvement on conventional design, the armature  15  here is arranged to be biassed by means of a spring assembly  13  consisting of two springs  51 ,  52 , rather than by a single spring. As seen in  FIG. 3 , the spring assembly  13  is arranged within the spring chamber  23 , as with the single spring of a conventional valve. The two springs  51 ,  52  are of different lengths and spring rates. They are also formed of different diameter coils, so that one is able to fit conveniently within the other (in this case, the longer spring  51  fitting inside the shorter one  52 ). Both springs  51 ,  52  have linear spring rates, with the longer one  51  having a lower spring rate than the shorter one  52 , which is stiffer. The longer spring  51  is installed in the spring chamber  23  so as to exert pre-compression on the armature  15 . This is to ensure that the armature  15  will seat against the diaphragm plate  21  in the de-energised condition of the valve in any orientation, ie whether the valve  1  sits in a horizontal, vertical or otherwise inverted plane. The seating of the armature  15  on the diaphragm plate  21  is necessary to ensure that the pilot orifice  31  will remain closed off when the valve is de-energised. In this de-energised condition of the valve  1 , the shorter spring  52  exerts no biassing force on the armature  15 . 
       FIG. 11  shows in plot X how the biassing force applied by the spring assembly  13  varies with the position of the armature  15 , as compared with plot Y for a conventional spring arrangement. As will be seen, the biassing force acting on the armature  15  is generally at a lower spring rate than in a conventional valve. 
     With the spring assembly  13 , when the solenoid  7  is energised, the initial movement of the armature  15  will be resisted mostly by the softer spring  51 . This corresponds to the initial movement of the diaphragm plate  21  out of the main orifice  20  from its reset (ie closed) position. It may also apply to small movements of the diaphragm plate  21  during lower flow rates through the valve. It has been found that the use of a softer than usual spring resistance reduces the tendency for the diaphragm plate  21  to oscillate, thus helping to regularise its movement. Further opening movement of the diaphragm plate  21 , when there are higher flow rates through the valve, is mostly controlled by the biassing action of the stiffer spring  52 . The application of two spring rates has been found to help break up resonance and enhance flow stability compared with conventional single spring arrangements. Also, by reducing resonance in the system, wear on the rubber boot  25  attached to the tip of the armature  15  caused by abrasion against the diaphragm plate  21  is reduced, improving life expectancy. 
     It will be appreciated that the configuration and characteristics of the two springs  51 ,  52  in the spring assembly  13  can be tailored to provide a wide variety of different biassing actions. It will also be appreciated that the spring assembly  13  could take other forms, for example by incorporating more than two springs, or possibly by consisting of a single spring with a non-linear spring rate.