NZ507999A - Control circuit for solenoid valve - Google Patents

Abstract

A circuit for controlling a valve 10 includes a solenoid 14 having a coil 56 and a permanent magnet 90. A pair of switching circuits is connected to the first and second ends of the coil. When the first switching circuit is activated, current passes through the coil in one direction to move the permanent magnet in a first axial direction. When the second switching circuit is activated, current passes through the coil in a second direction to move the permanent magnet in a second axial direction.

Description

50 79 g 9 NEW ZEALAND PATENTS ACT, 1953 No Divided out of NZ 505535 Date: Dated 3 July 2000 COMPLETE SPECIFICATION CONTROL CIRCUIT FOR SOLENOID VALVE ASSEMBLY We, MAC VALVES, INC. a corporation of the state of Michigan, of 30569 Beck Road, P O Box 111, Wixom, Michigan 48393, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) INTELLECTUAL PROPERTY OFFICE OF N.Z - 7 flCiV 2000 RECEIVED BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates, generally, to solenoid actuated valves and, more specifically, to control circuits for operating same. 2. Description of the Related Art Solenoids are well known electromechanical devices used to convert electrical energy into mechanical energy and particularly into short stroke mechanical motion. As such, solenoids have long been employed to actuate valves in response to an electrical signal. For example, it is known in the related art to employ a solenoid to bias a valve 10 member in one direction against the biasing force of a return spring. When power to the solenoid is interrupted, the return spring biases the valve member back to its first position.

In certain applications, valve members must be positively maintained in different predetermined positions to control the flow of fluids, such as air, through the valve One 15 embodiment employed in the related art to achieve this results eliminates the return spring employed to bias the valve member to a specific location and replaces it with a second solenoid The second solenoid is powered to positively move the valve member to a predetermined position and maintain it there until the second solenoid is de-energized and the first solenoid is energized to move the valve member back to the other 20 position. However, this approach suffers from the disadvantage that double solenoid operated valves increase the size, weight, cost and complexity of the valve. Further, in la the case of poppet-type valves, at least one coil must be powered at all times to ensure that the valve member is properly seated in the predetermined position. An unexpected, inadvertent or even planned shut down of power to the solenoid results in a loss of control of the valve. Additionally, in applications where the efficiency of the solenoid 5 is of concern, such as where there is a limited source of electrical power, solenoids which must be continually powered to hold a valve member in a specific position or double solenoid actuated valves are generally unacceptable.

To decrease the power dissipated by the solenoid, and particularly in applications where the solenoid is to be retained in the actuated position for significant time periods, 10 latching mechanisms are employed in the related art to hold the mechanical output of the solenoid in one position or the other without continuous power required to the solenoid. To this end, conventional self-latching solenoids known in the related art typically employ a movable pole piece and a fixed permanent magnet which are subject to an electromagnetic flux to bias a valve member. Usually, current flowing through the coil 15 in one direction causes the pole piece to move away from the permanent magnet and to be attracted to another stationary element in the solenoid thereby actuating the valve member. Power to the coil is then interrupted but the latent magnetic force acting on the movable pole piece causes it to remain magnetically attracted to the stationary portion of the solenoid or "latched" in its last position.

Control circuits are used to reverse the direction of current through the solenoid coil thereby reversing the direction of electromagnetic flux. Reversing the direction of current through the coil reverses the "polarity" of the movable pole piece, driving it in the opposite direction toward the permanent magnet where it again becomes "latched" 2 after the power to the solenoid has been interrupted. The return spnng is then typically free to bias the valve member m the opposite direction In this way, the valve member may be moved to, and maintained in, any predetermined position by actuation of the solenoid after a relatively short pulse of electrical current through the solenoid coil.

While the self-latching solenoid actuated valves known m the related art have generally worked well for their intended purposes, there continues to be a need for smaller, faster acting self-latching solenoid actuated valves having low power consumption. This is especially true for small pneumatic valves used, for example, to control small air cylinders. In addition, there continues to be a need for control circuits 10 which result in lower power consumption than those circuits known m the related art.

SUMMARY OF THE INVENTION The present invention overcomes these deficiencies m the related art in a circuit for controlling a valve assembly This circuit is necessary m applications where 15 electrical isolation of the two control signal supply lines is required to prevent damage of control circuits caused by a reverse polarity feedback signal or other transient signal. The circuit includes a solenoid having a coil. The coil has a first end and a second end. The circuit also includes a first switching circuit electrically connected to the first and second ends of the coil to allow current to pass therethrough in a first direction to move 20 a permanent magnet against a pushpin m a first axial direction. The circuit further includes a second switching circuit electrically connected to the first and second ends of the coil to allow a current to pass therethrough in a second direction to move the permanent magnet away from the pushpm m a second axial direction Further, when 3 either switching circuit is allowing current to flow through the coil, it electrically isolates one negative control source from the other.

In addition, the use of a pair of switching circuits electrically connected to the coil results in a relatively low voltage drop across the circuit when compared with 5 conventional circuits known in the related art.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when 10 considered in connection with the accompanying drawings, wherein: Figure 1 is a perspective view of a self-latching solenoid valve assembly; Figure 2 is a cross-sectional side view of a self-latching solenoid valve assembly showing the permanent magnet latched to the pole piece, Figure 3 is a cross-sectional side view of a self-latching solenoid valve assembly 15 showing the permanent magnet adjacent to the latch; and Figure 4 illustrates the electrical control circuit of the present invention employed to reverse the direction of the current through the coil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A self-latching solenoid valve assembly is generally indicated at 10 in Figures 1 through 3 where like numerals are used to describe like structure. The solenoid valve assembly 10 includes a valve body 12 and a solenoid assembly 14 mounted to the valve body 12 The valve body 12 includes a pressurized air supply inlet port 16 for 4 communicating with a source of pressurized air and at least one cylinder port 18, 20. A valve member 22 is supported in the valve body 12 so as to be movable between predetermined positions to selectively direct pressurized air from the inlet port 16 to at least one of the cylinder ports 18, 20.

More specifically, the valve body 12 is rectangular in shape and includes a valve bore 24 extending axially through the valve body 12 which provides fluid communication between the air supply inlet passage 16, a pair of cylinder passages 18, 20 and a pair of exhaust ports 26, 27 As shown in the drawings, the valve member is a poppet valve 22 which is supported within the valve bore 24 for reciprocal movement 10 therein to control the flow of fluid through the valve body 12. The poppet valve member 22 is preferably an aluminum insert over molded and bonded with rubber m specific areas of the valve member 22 and ground to specific dimensions to form valve elements 30, 32, 34 The valve elements 30, 32, 34 engage adjacent valve seats 36, 38, 40, 41 presented m the valve bore 24 for sealing various flow passages as the valve member 22 15 is reciprocated between positions within the valve bore 24 A cup shaped retainer 42 is threadably disposed at one end of the valve bore 24. A threaded insert 44 is located in the bore 24 opposite the retainer 42. A biasing member 46, such as a coiled return spring, is positioned between the retainer 42 and one end of the poppet valve member 22. The return spring 46 applies a constant biasing force 20 against the poppet valve member 22 and to the left as viewed in Figure 2. On the other hand, the poppet valve member 22 is actuated in the opposite direction, or to the right as viewed in Figure 2, under the influence of the solenoid assembly 14 as will be descnbed in greater detail below. As described above and shown m the drawings, the valve assembly employs a four way valve. However, those having ordinary skill in the art will appreciate that the present invention as described and claimed herein may also be employed with two way, three way or any other type of solenoid actuated valve.

The solenoid assembly 14 includes a housing, generally indicated at 48. The 5 housing 48 includes a pole plate 50 abutting the valve body 12, a cap 52 disposed opposite the pole plate 50 and a solenoid can or frame 54 extending therebetween. The frame 54 supports a coil 56 including a conductive wire 58 conventionally wrapped around a bobbin 60. The conductive wire 58 is connected to a source of electrical current through leads, generally indicated at 62. The leads 62 are supported in the cap 52 and 10 include lead pins 64, electrical contacts 66 and lead wires 68. The lead wires 68 are operatively connected to the source of electrical current. The direction of the current through the coil 56 and thus the direction of the electromagnetic force generated thereby is controlled by a control circuit, generally indicated at 70 m Figure 4 as will be described m greater detail below. A top plate 55 is mounted adjacent to the bobbin 60 and between 15 a portion of the frame 54 and the cap 52.

The pole plate 50 includes an opening 72 extending therethrough. The solenoid assembly 14 further includes a ferromagnetic pole piece 74 having a stepped portion 78 with a smaller cross-sectional area than the rest of the pole piece 74. The stepped portion 78 is received in the opening 72 of the pole plate 50 for mechanically fixing the pole 20 piece 74 to the pole plate 50. A thin piece of non-magnetic stainless steel 80 caps the pole piece 74 opposite the pole plate 50 A centrally located passage 82 extends through the pole piece 74. A pushpin 84 is movably supported m the passage 82. 6 The cap 52 of the solenoid housing 48 includes a threaded bore 86. A ferromagnetic latch 88 is threadably mounted to the solenoid housing 48 in the bore 86 but spaced from the pole piece 74. The latch 88 is made of iron but may be made of any ferromagnetic material. A permanent magnet 90 is disposed between the latch 88 and 5 the pole piece 74 A bushing 92 guides the magnet 90 within the bobbin 60. The permanent magnet 90 is movable toward the pole piece 74 under the influence of an electromagnetic flux generated by a pulse of current flowing through the coil 56 in one direction. This flux drives the permanent magnet 90 against the pushpin 84 to move the valve member 22 to one predetermined position. Furthermore, the permanent magnet 90 10 is movable away from the pole piece 74 and toward the latch 88 under the influence of an oppositely directed electromagnetic flux generated by a pulse of current flowing through the coil 56 in the opposite direction. When this occurs, the biasing member 46 moves the valve member 22 to another predetermined position, for example to the left as shown in Figure 3 To this end, the pushpin 84 presents an enlarged head 94 which is disposed adjacent one end of the poppet valve member 22 for contacting it when the permanent magnet 90 contacts the pushpin 84. In addition, the enlarged head 94 of the pushpin 84 limits the movement of the pushpin 84 within the passage 82 of the pole piece 74 under the influence of the biasing member 46 through the valve member 22 when the 20 permanent magnet 94 has moved toward the latch 88. The limited movement of the pushpin 84 presents a gap 96 between the permanent magnet 90 and the pole piece 74 as shown in Figure 3 7 As illustrated in Figure 2, a space 102 is defined between the latch 88 and the permanent magnet 90 when the permanent magnet is moved toward the pole piece 74. Furthermore, the position of the latch 88 toward and away from the permanent magnet 90 may be adjusted by adjusting the position of the threaded latch 88 within the threaded 5 bore 86 in the cap 52. Accordingly, the size of the space 102 between the latch 88 and the permanent magnet 90 when the permanent magnet has moved toward the pole piece 74 may be adjusted. In this way, the attractive force between the latch 88 and the permanent magnet 90 may be modulated.

The permanent magnet 90 may be of any suitable type but preferably is a rare 10 earth neodymium-iron-boron magnet. The permanent magnet 90 defines north and south poles at opposite ends thereof as indicated in the figures. However, it will be appreciated by those having ordinary skill in the art that the poles may be reversed. A protective cap 98 is bonded to the north pole and a protective cap 100 is bonded to the south pole. These caps 98, 100 protect the permanent magnet 90 as it is cycled toward the pole piece 15 74 and the latch 88.

Referring to Figure 4, a circuit, generally indicated at 70, is shown for controlling the self-latching solenoid valve assembly 10 The circuit 70 includes a solenoid 14 having a coil 56 and a permanent magnet 90 The electrical leads 62 of the coil 56 extend out of a first end 150 and a second end 152 of the solenoid 14. Current travels 20 through the coil 56 through the lead 62 at either end 150, 152 The direction of the current as it passes through the ends 150,152 determines whether the permanent magnet 90 will be biased m a first axial direction or a second axial direction opposite that of the first axial direction. 8 Connected to the first end 150 of the solenoid 14 is a first switching circuit 154 and a second switching circuit 156. The first switching circuit 154 allows current to flow through the solenoid 14 in one direction and the second switching circuit 156 allows current to flow through the solenoid 14 in a second direction opposite in direction to that 5 of the first direction.

The first switching circuit 154 includes a first transistor 158 and a second transistor 160 In the embodiment shown in Figure 4, the first transistor 158 is a pnp bipolar junction transistor. The second transistor 160 is a MOSFET. The reasons for using two different types of transistors is to reduce the overall voltage drop across the 10 transistors 158, 160 as well as to reduce the bias requirements. A base 162 of the first transistor 160 is connected to a gate 164 of the second transistor 160 through a resistor 166. The gate 164 of the second transistor 160 is also connected to a drain 168 of the second transistor 160 through a resistor 170. The drain 168 and resistor 170 are also connected to a negative input control source 172. The negative input control source 172 15 provides the input required to determine whether the self-latching valve assembly 10 is to be forced in the direction provided in the first switching circuit 154. A collector 174 of the first transistor 178 is connected to the first end 150 of the solenoid 14 and a source of 176 of the second transistor 160 is connected to the second end 152 of the solenoid 14. An emitter 178 of the first transistor 158 is connected to the power supply, 24 volts in 20 this embodiment.

The second switching circuit 156 mirrors the first switching circuit in that it includes a third transistor 180 and a fourth transistor 182. The differences are that the third transistor 180 is a bipolar junction transistor with its collector 184 electrically 9 connected to the second end 152 of the solenoid 14 and the fourth transistor 182 is a MOSFET with its source 186 electrically connected to the first end 150 of the solenoid 14. A resistor 188 is connected between the gate 190 of the fourth transistor 182 and the base 192 of the third transistor 180. Another resistor 194 is connected between the gate 5 190, the resistor 188, and the drain 196 of the fourth transistor 182. The resistor 194 and the drain 196 are also connected to a negative input control source 198 providing input to switch the self-latching valve assembly 10 in the opposite direction as that from the negative input 172. Power is received by the solenoid 14 through the emitter 200 of the third transistor 180 which is connected directly to the power supply.

A red LED 202 and a green LED 204 are connected to the first end 150 and the second end 152 of the solenoid 14. These LEDs 202, 204 are connected in opposite directions such that when the solenoid 14 is activated m one direction, the red LED 202 will emit light and when the solenoid 14 is activated in the opposite direction, the green LED 204 will emit light. This allows an operator to view the assembly 10 and know in 15 which mode the self-latching valve assembly 10 should be operating.

OPERATION In operation, current is driven through the coil 56 in one direction which generates an electromagnetic flux The electromagnetic flux polarizes the pole piece 74 attracting the permanent magnet 90. The movable permanent magnet 90 is thus driven 20 toward the pole piece 74 across the gap 96 and engages the pushpin 84, as shown in Figure 2 This drives the pushpin 84 to the right moving the poppet valve 22 also to the right and against the biasing force of the coil spring 46.

Power to the coil 56 is then interrupted. However, the permanent magnet 90 remains in its position shown at Figure 2 and "latched" to the pole piece 74 due to the residual attractive forces that remain even in the absence of an electromagnetic flux. In this disposition, valve element 30 cooperatively seals with valve seat 36 and valve 5 element 32 cooperatively seals with valve seat 40. Conversely, the valve element 32 is open with respect to the valve seat 38 and the valve element 34 is open with respect to the valve seat 41.

With the valve member 22 shifted to the right as described above and shown in Figure 2, pressurized air flowing into the valve body 12 via the inlet port 16 passes the 10 valve element 32 and valve seat 38, flows through the valve bore 24 and out the cylinder passage 18 At the same time, air is exhausted from the cylinder passage 20 past the valve element 34 and valve seat 41 and out the valve body 12 via the exhaust port 27. The exhaust port 26 is sealed by the valve element 30 and the valve seat 36.

The valve member 22 remains in this disposition until current is again driven 15 through the coil 56 in an opposite direction. This produces an electromagnetic flux in a direction opposite to the first flux described above. The oppositely directed magnetic flux changes the polarity of the pole piece 74 which acts to repel the permanent magnet 90 Thus, the permanent magnet 90 moves away from the pole piece 74 and toward the latch 88 thereby closing the space 102 therebetween. The coil spring 46 biases the valve 20 member 22 to the left as shown in Figure 3. The pushpin 84 is also shifted to the left under the influence of this biasing force acting through the valve member 22. Current to the coil 56 is then interrupted. However, the permanent magnet 90 remains in the « 11 position shown in Figure 3 and is "latched" to the latch 88 due to the residual attractive forces that remain even in the absence of an electromagnetic flux.

In this disposition, the valve element 32 cooperatively seals with the valve seat 38 and valve element 34 cooperatively seals with valve seat 41. Conversely, the valve 5 element 32 is now open with respect to the valve seat 40 and the valve element 30 is open with respect to the valve seat 36 With the valve member 22 shifted to the left as described above and shown in Figure 3, pressurized air flowing into the valve body 12 via the inlet port 16 passes the valve element 32 and valve seat 40, flows through the valve bore 24 and then out the 10 cylinder passage 20. At the same time, air is exhausted from the cylinder passage 18, past the valve element 30 and valve seat 36 and then out the valve body 12 via the exhaust port 26. The exhaust port 27 is sealed by the valve element 34 and the valve seat 41 The valve member 22 remains in this disposition until current is again driven through the coil 56 in an opposite direction. The valve member 22 is then shifted back 15 to the right as shown in Figure 2 and descnbed above.

The present invention is directed toward a pair of switching circuits that are employed to control the direction of current to the coil and to electrically isolate one negative control input source from the other negative control input source. This effectively prevents damage to the control circuits caused by a reverse polarity feedback 20 signal or other transient signal. Switching circuits of the present invention provide a relatively low voltage drop across the circuit when compared with conventional circuits known in the related art. Accordingly, the self-latching solenoid valve assembly of the 12 present invention facilitates reduced cost and size in a fast-acting valve assembly having self-latching capabilities.

The invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Many modifications and variations of the invention are possible in light of the above teachings Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described. 13

Claims (5)

WHAT WE CLAIM IS:

1 A circuit for controlling a valve comprising: a solenoid having a coil and a permanent magnet, said coil having a first end and a second end; a first switching circuit electrically connected to said first and second ends of said coil to allow a current to pass therethrough in a first direction to move said permanent magnet in a first axial direction; and a second switching circuit electrically connected to said first and second ends of said coil to allow a current to pass therethrough in a second direction to move said permanent magnet in a second axial direction.

2. A circuit as set forth in claim 1 wherein said first switching circuit includes a first transistor connected to said first end and a second transistor connected to said second end.

3. A circuit as set forth in claim 2 wherein said second switching circuit includes a third transistor connected to said first end and a fourth transistor connected to said second end

4. A circuit as set forth in claim 3 wherein said first and third transistors are bipolar junction transistors and said second and fourth transistors are MOSFETs. 14

5. A circuit for controlling a valve substantially as hereinbefore described with reference to the accompanying drawings. By tha authorised agents A. J. PARK 15