This invention relates to a solenoid valve, and, more particularly, to a new and improved time delayed solenoid valve that can be contained within a single housing or package.
A solenoid valve is utilized in oil burner systems to supply fuel oil to the burner at the appropriate times. In most oil burner systems, the introduction of the fuel oil to the burner and thereby the ignition of the burner is delayed a short period of time, such as three to seven seconds, after closing of a thermostat or the like. The short time delay allows the draft fan to establish a stable air pattern at a high enough velocity to establish good fuel mixing when the burner is actually ignited.
Various time delay devices have been used to delay ignition of the oil burner. At one time, a resistance wire was wound about bimetallic blades on which were mounted switch contacts. After a short time, the heat generated from the resistance wire would cause the blades to move together closing the switch contacts. In addition, the same type of switches were mounted in a glass enclosure similar to a vacuum tube.
Thereafter, vacuum tube rectifiers having an indirectly heated cathode were utilized for establishing the delayed operation of the solenoid valve. The delay time was determined by the time required for heating the cathode in the tube. Subsequently, a thermistor was mounted in series with the solenoid coil and the delay time was determined by the resistance change of the thermistor as it was self-heated by the current being supplied to the coil.
Unfortunately, these various arrangements were all dependent on some type of thermal mechanism and had very little or no compensation for thermal changes, especially as the ambient temperatures decreased. When such devices were installed in an unheated area where the ambient temperature might be as low as 40° F, the delay time established by these devices tended to increase and many times increased to such an extend that the delay time was longer than the safety lock out time required by the burner system. In these instances, such thermal devices became completely unusable.
In order to overcome the inherent difficulties in these temperature sensitive devices, one type of solid state control circuit was developed and made commercial. This type of control circuit was packaged in a separate housing from the solenoid coil itself and connected to the solenoid coil by appropriate conductors or leads. In this type of control circuit line potential is coupled to a normally nonconductive silicon controlled rectifier (SCR) through a thermostat or switch and a full wave rectifier. When the SCR is placed in a conductive state due to the supplying of its gate electrode with a positive potential, the SCR supplies an operating potential through a choke to a solenoid coil located in a separate package or housing. In order to delay the rendering of the SCR conductive for a short period of time after the closure of the switch, the positive potential supplied to the gate electrode is delayed by a delaying circuit including a neon light and an integrating capacitor. Once rendered conductive, the SCR is maintained conductive by discharging the choke into the gate electrode of the SCR so as to maintain a positive potential on the gate electrode.
Unfortunately, since such a device requires the utilization of a full wave rectifier and a choke, the resulting high operating temperatures of the solenoid coil and the control circuit causes excessive temperatures so that the delay circuit and the solenoid coil cannot be placed in a single package. Moreover, this type of device tended to have radically different delay times if the line voltage varied.
Accordingly, objects of the present invention are to provide a new and improved solenoid valve for utilization with an oil burner system; to provide a time delay solenoid valve that can be placed in a single package or housing; to provide a new and improved time delay circuit for a solenoid valve for an oil burner system; to provide a new and improved time delay circuit for an oil burner valve such that the valve can be operated on half wave rectified current; and to provide a new and improved time delay circuit for a solenoid coil that is not appreciably affected by line voltage discrepancies.
In accordance with these and many other objects, an embodiment of the present invention comprises a time delay control circuit for a solenoid valve used with an oil burner system. The control circuit operates on normal line voltage and includes a half wave rectifier that supplies a regulated time delay circuit with a DC potential. After a predetermined time delay, the time delay circuit renders a silicon controlled rectifier conductive so that the rectified current is also supplied through the silicon controlled rectifier to a solenoid coil resulting in the opening of the solenoid valve. The silicon controlled rectifier is maintained conductive by means of a latching circuit including the coil and a rectifier. In the preferred embodiment, the control circuit is mounted within the same housing or package in which the coil of the solenoid valve is located.
Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:
FIG. 1 is a schematic diagram of one embodiment of a time delay control circuit for a solenoid actuated valve for an oil burner or the like;
FIG. 2 is another embodiment of the time delay control circuit of FIG. 1;
FIG. 3 is a perspective view of a solenoid valve package made in accordance with the present invention;
FIG. 4 is a top view partially cut away of the solenoid valve package of FIG. 3;
FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4; and
FIG. 6 is an exploded view of the solenoid valve package of FIG. 3.
Referring now more specifically to FIG. 1 of the drawings, there is illustrated a control circuit for a solenoid valve, which control circuit is indicated generally as 10 and which embodies the present invention. Upon closing of a switch 12, either manually or automatically by means of a thermostat or the like, a source of AC potential 14 is coupled to the control circuit 10. Under normal circumstances, the source 14 is a power distribution line or the like having a line voltage of 60 cycles, single phase, 120 volts. After a predetermined period of time, the control circuit 10 supplies an energizing current to a solenoid coil 16 resulting in the opening of a valve 18 so that fuel oil or the like is allowed to pass through the valve 18 to a burner system (not shown). The period of time after the closure of the switch 12 before the coil 16 is energized allows a draft fan in the burner system to establish appropriate air patterns in the burner for good fuel mixing of the fuel oil before the burner is actually ignited due to the supplying of oil through the open valve 18.
More specifically, with the closing of the switch 12, AC input power or line potential from the power source 14 is supplied to a pair of input terminals 20 and 22 of the control circuit 10, the input terminal 22 being coupled directly to a ground terminal 24. The line potential received at the input terminal 20 is coupled to an anode electrode 26 of a normally nonconductive silicon controlled rectifier 28 through a diode 30. The diode 30 acts as a half wave rectifier so that the line potential is converted into a DC potential and is supplied to the anode electrode 26 of the silicon controlled rectifier 28. Coupled between the anode electrode 26 and the input terminal 22 is a capacitor 32 which filters the rectified potential being supplied by the diode 30 and assists in filtering out any line transients that might adversely affect the operation of the control circuit 10.
The rectified potential supplied by the diode 30 is also coupled to a timing or delay circuit 34 including resistors 36, 37 and 38, an integrating capacitor 40, a neon light 42, and a Zener diode 44. When the rectified potential is supplied to the timing circuit 34 and in particular to the capacitor 40 through the resistors 37 and 38, the capacitor 40 begins to charge. Once the capacitor 40 charges to a potential beyond the breakdown potential of the neon light 42, the neon light 42 fires allowing a positive potential to be supplied to a gate electrode 46 of the silicon controlled rectifier 28. Upon application of the positive potential to the gate electrode 46, the silicon controlled rectifier 38 is actuated or becomes conductive and remains conductive as long as the anode electrode 26 receives a relatively positive potential with respect to the potential at a cathode electrode 48 of the silicon controlled rectifier 28. The capacitor 32 ensures that the anode electrode 26 is receiving a relatively positive potential when the positive potential is supplied to the gate electrode 46 through the neon light 42.
Since the stability of the silicon controlled rectifier 28 increases in proportion with decreasing gate resistance, a resistor 50 is coupled between the gate electrode 46 and the cathode electrode 48 and is selected to provide a minimum amount of gate resistance commensurate with the timing circuit 34. In addition, a capacitor 52 is also coupled in parallel with the resistor 50 between the gate electrode 46 and the cathode electrode 48 to assist the capacitor 32 in preventing undesired actuation of the silicon controlled rectifier 28 due to line transients or other voltage changes.
Upon rendering of the silicon controlled rectifier 28 conductive, the half wave rectified current from the diode 30 is allowed to pass through the conductive path between the anode electrode 26 and the cathode electrode 48 of the silicon controlled rectifier 28 so that a DC half wave rectified energizing current is supplied to the solenoid coil 16. With the coil 16 energized, the valve 18 opens and fuel oil or the like can be supplied to the burner system. Accordingly, the control circuit 10 only allows fuel oil to be supplied through the valve 18 after a short time delay has occurred subsequent to the closing of the switch 12.
This time delay is determined by the timing circuit 34, and, in particular, the amount of time to charge the capacitor 40 to a value in excess of the breakdown voltage of the neon light 42. By appropriately adjusting the RC value of the timing circuit 34 and particularly the value of the resistors 36, 37 and 38 and the capacitor 40 and by selecting the appropriate neon light 42, the time delay produced by the timing circuit 34 can readily be selected. However, this time delay would change significantly with changes in the line potential received from the power source 14 if it were not for the Zener diode 44 that is coupled across or in parallel with the series circuit of the resistor 38 and the capacitor 40. With the Zener diode 44 so connected, the Zener diode 44 regulates the potential supplied to the capacitor 40 through the resistor 38 and enables the timing circuit 34 to provide a time delay that does not change significantly with changes in the potential received from the power source 14.
Once the silicon controlled rectifier 28 is rendered conductive, the capacitor 40 tends to discharge through the neon light 42 and the gate electrode 46 until the neon light 42 can no longer be maintained ignited. Then the capacitor 40 continues to slowly discharge through the resistors 37 and 38 because the RC time constant provided by the timing circuit 34 is relatively high.
As long as the silicon controlled rectifier 28 remains conductive, energizing potential is supplied to the coil 16 and the valve 18 remains open. In order to maintain the silicon controlled rectifier 28 conductive during the entire time period in which the switch 12 is closed, the anode electrode 26 must be supplied with a relatively positive potential as compared to the potential at the cathode electrode 48. Seemingly, the capacitor 32 would ensure that such a positive potential is continuously being supplied to the anode electrode 26. However, the value of the capacitor 32 cannot be made sufficiently large to maintain such a positive potential at the anode electrode 26 because the capacitor 32 must be small enough to filter the output of the diode 30.
Accordingly, a diode 54 is coupled between the coil 16 and the anode electrode 26. The latching circuit including the inductance of the coil 16 and the diode 54 provides for the latching of the silicon controlled rectifier 28 in its conductive state until the switch 12 is opened. Once the switch 12 is opened, the silicon controlled rectifier 28 returns to its nonconductive state and the valve 18 closes.
Advantageously, additional valves like the valve 18 can be controlled by the control circuit 10. This is accomplished by coupling additional coils between the cathode electrode 48 of the silicon controlled rectifier 28 and the ground terminal 24.
Referring now to FIG. 2, an alternate embodiment of the control circuit 10, control circuit 56, is disclosed. The control circuit 56 operates in essentially the same manner as the control circuit 10 shown in FIG. 1 and the components in the control circuit 56 have been designated by the same reference numerals by which corresponding components in the control circuit 10 have been designated. The only additional component is the diode 58 coupled in parallel with the resistor 38.
As heretofore indicated, after the neon light 42 fires and a positive potential is supplied to the gate electrode 46, the capacitor 40 first discharges through the neon light 42 and the gate electrode 46 and then through the resistors 37 and 38. However, in some circumstances the rate of discharge of the capacitor 40 is too slow if the control circuit 10 is utilized during a time when the switch 12 is being opened and closed at a fairly rapid rate. In the event that the capacitor 40 does not completely discharge between such closures of the switch 12, the time delay provided by the time delay circuit 34 is of a shorter duration then desired and the silicon controlled rectifier 28 is rendered conductive too quickly. Accordingly, by coupling the diode 58 in parallel with the resistor 38, the effective RC time constant for the discharge of the capacitor 40 is lowered and the capacitor 40 is allowed to discharge at a greater rate. In this manner, the capacitor 40 should be fully discharged before the switch 12 is again closed and the timing circuit 34 provides the appropriate time delay for the control circuit 56 even during repeated rapid opening and closing of the switch 12.
Referring now to FIGS. 3-6, therein is disclosed a time delayed solenoid valve package 60 which utilizes either the control circuit 10 shown in FIG. 1 or the control circuit 56 shown in FIG. 2. The package 60 includes a hollow, generally rectangular shaped housing 62 and a valve 63 (schematically shown in FIGS. 1 and 2 and designated as 18). The housing 62 has a conduit 64 inserted through one of its side walls 66, through which conduit 64 extends leads or conductors 68, 70 and 72 into the housing 62. Two of the leads 68 and 70 are coupled to the input terminals 20 and 22, respectively, of the control circuit 10 or 56 so as to provide AC line potential to the control circuit 10 or 56. The third lead 72 is coupled to the cathode electrode 48 so that if additional solenoid valves are to be controlled by the control circuit 10 or 56, they merely have to be coupled to the lead 72. In the event no additional valves like the valve 63 are to be controlled by the control circuit 10 or 56, the lead 72 is not used.
Within the housing 62 is mounted a printed circuit board 74 on which the components of the control circuit 10 or 56 are mounted. A solenoid coil 75, which is schematically shown in FIGS. 1 and 2 and referred to as 16, is also located within the housing 62 and is coupled by appropriate leads to the cathode electrode 48 and the ground terminal 24 of the control circuit 10 or 56 located on the printed circuit board 74. The coil 75 is inserted into the housing 62 through a generally circular opening 76 in the bottom wall 77 of the housing 62. The coil 74 consists of a plurality of turns of wire 78 on a generally cylindrical base 80 having a bore 82 extending through the center thereof. When the coil 75 is positioned within the housing 62, a stem portion 84 of the fuel valve 63 is inserted through the bore 82, a washer 86, a hole 88 in the top wall 90 of the housing 62, and a washer 92. The stem portion 84 is locked in position by a C-ring 94 that fits into a groove 96 in the upper end of the stem portion 84. By so locking the stem portion 84, a cap 98 on the valve 63 maintains the coil 75 properly positioned within the housing 62 and encloses the hole 76.
When the coil 75 is energized by the control circuit 10 or 56 after a desired time delay, the valve 63 is opened so that fuel oil or the like is allowed to flow through the opened valve 63. Advantageously, by utilizing the control circuit 10 or 56 on the printed circuit board 74 enables the placing of both the circuit board 74 and the solenoid coil 75 in a single package 60 having the small housing 62. One factor in enabling the mounting of the coil 75 in the housing 62 along with the control circuit 10 or 56 is that the control circuit 10 or 56 utilizes half wave rectified current for energizing the coil 75. If AC current is used in such a valve assembly, the temperature rise is quite significant and the circuit board 74 cannot be placed in the same package or housing as the coil 75. In addition, by utilizing the control circuit 10 or 56 on the printed circuit board 74, larger components used in previously designed control circuits are eliminated so that the printed circuit board 74 can be easily mounted within the housing 62.
While the present invention has been described in connection with the details of a single illustrative embodiment thereof, it should be understood that these details are not intended to be limitative of the invention except insofar as set forth in the accompanying claims.