CA2435356A1 - Self-latching solenoid valve assembly and control circuit - Google Patents

Abstract

A self-latching solenoid valve assembly including a valve body having a pressurized air supply inlet port for communicating with a source of pressurized air and at least one cylinder port. A valve member is supported in the valve body so as to be movable between predetermined positions to selectively direct pressurized air from the inlet port to at least one cylinder port. A biasing member is employed to move the valve member in one direction and a solenoid assembly is used to move the valve member in an opposite direction. The solenoid assembly includes a housing with a solenoid coil supported therein and a fixed ferromagnetic pole piece having a passage extending therethrough with a pushpin movably supported in the passage. A ferromagnetic latch is also supported by the housing and spaced from the pole piece. A permanent magnet is disposed between the latch and the pole piece. The magnet is movable toward the pole piece under the influence of an electromagnetic flux generated by a pulse of current generated through the coil in one direction thereby driving the permanent magnet against the pushpin to move the valve member to one predetermined position. In addition, the permanent magnet is also movable away from the pole piece and toward the latch under the influence of an electromagnetic flux generated by a pulse of current flowing through the coil in an opposite direction.
When this occurs, the biasing member moves the valve member to another predetermined position. A control circuit for changing the direction of the current through the coil is also disclosed.

Description

SELF-LATCHTNG SOLENOID VALVE ASSFM»LY
AND C:O1VTROL C1'H(~U1T
BAC>C~'GRO~UN1) OF THE INVENTrON
Field ofthe InyEntion The rresGnt invention relates, Sencrally, 1v solenoid actuatett valves arid, more cPrcifically, to self latchin; solenoid ac;tuatcd valves cold control circuits for operating same.

2. Description ot~dhe Xeluled Art Solenoids are well known electrornechcuucal devices used to convert electrical energy into mechanical energy and particularly into short stroke mechanical motion. hs such, solenoids have long been employed to actuate valves iii response to an electrica.!
signal. For example, it is known in the related art to employ a solenoid to bias a valve member in one direction against the biasing force or a return spring. When power to the solenoid is intemipted, the return spring biases the value 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. nne 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 cer.~,~
solenoid. T'fie second solenoid is powered to positively m«ve the valE~c~
rn.ember to a predetermined position and maintain i1 there until the second sc~lenoi~t is de-energi~d and the first solenoid is energized to rrtove the valve memhPr hack to the other position.
However, this approach suffers from the disadvantage that double solenoid operated valves t nerease the Size. weight, enst and aompl~city of the valve. Furthc.~r, t n the cast of pupp~l-type valves, at Ieast one onil must be powered at adl times to ensure that the vat vc member is properly seated in the predetermined position. An unexpected, iuaclvcrtent or even planned shrtt down aF power to the solenoid results in a loss uC control of the valve.
2S Ariditionally, in applications when: the efficiency of the solenoid is of concern, such as where there is a limited source of electrical power, solenoids which must he oontinually powered to hold a valve member in a spccifi~ position or double solenoid actuated valves are ~enerolly unacccptablc.

To decrease the power dissipated by the solenoid, and particularly in ~prlications where the solenoid is to be retained in the actuated position fir cignificant time pariods, latching mechanisms are employed in the related art to hold the rneehsnical output of the solenoid in one position or the other withnut_continuous power reduircd tv tha sulcnctid.
To this end, conventional self latchirl6 solenoids known in flit ralatcWu~:
typically employ a movable pole piece and a fixrd permanent ~ua~nef which are subject tc) an electri>magnetic flux tc~ bias a valve ~«Ctnber_ LJsually, current flowing through the coil in one direction causes the pole picc;e to move away from the permanent magnet and to be attxactcd to aclulhcr 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 circtuts 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" afthe movable pole piece, driving it in the apno~Tre direction toward the permanent magnet where it again becomas''latci,arJ'' after the power to the solenoid has been interrupted. The return spring is then typically free to bias the valve member in the opposite direction_ In this way, the valve member may be emr~vad to, and maintained in, any Isrndet~rmined position by actuation ofthc solenoid aflar a relatively short Ptrlse of electrical Current through the solenoid coil.
While the Self latching solcnoi~t aclualc;d valves tctlown in the related art have general ly workrd well famhCir intended purposes, there continues to be a head 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 which result in lower power consumption than those circuits known in the related art.
SUMNrARY t1F THE INVENTION
The present invention overcomes these deficiencies in the related art in a self-latching solenoid valve assembly including a valve body having a pressurized air cutsPly inlet port for cc~mcnunic;ating with a source of pressurized air and at least one cylinder pmt.
A valve membcris supported in the valve body so as to be movable between predetermined puaicioizs to seltrc;tivety direct pressurirxd air ti~om the inlet port to at mast one cylinder port. A biasing member is employed for moving the valve member in one ~iirPCt~on and a solenoid assembly is used to move the valve member in the nPposite direction. The solenoid assembly includes a housing with a solennid coil fiupported therein and a hxcd, ferromagnetic pole piece having apasSage extending therathrottgh with apushpumnnuvabJy supported in the passage. In addition, a ferromagnetic latch is suppurla;d by the housing and spacPrl floor the pole pieca. A permanent magnet is disposed between the latch and the pole piece. The permanent ~uaguct is movable toward the pole piece order the influence of an clcctromagnetiv flux generated by a pulse of current. flowing through the coil lo om dirCC~i~n thereby driving the permanent magnet against the pushpin to move the valve member to one predetermined position. Additionally, the permanent magnet is movable away from the pole piece and tc>ward the latch under the influence of an electromagnetic flux generated by a pulse ofcurrent flowing through the coil in an opposite direction. .When this occurs, the biasing member moves the valve member to the other predetermined position.
1 S 'fhe present invention also includes d circuit for controlling a valve assernhly This circuit is necessary in applications where electrical isolation of the two control signal supply lines is required to prevent damage of control cirr..uits caused by a reverse polarity feedback signal or other transient si ~nai. The circuit includes a solenoid having a. coil. The coil has a first end and a second c'~d. The iircuit also includes a first swiCching circuit 2U electriraily connected to the first and second ends of thG coil to allow curre~lt to pass tharethrough in a fit direction to n tows Ctrc permanent magnet against the pushpin in a first axial direction. The circuit further includes a second switching circuit eleetric;ally conncxacd to the Crm and second ends of the coil to allow a current to pass therethrough in a second direction to move ttte permanent magnet away from the pushpin in a second 25 axial direction. further, when 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 conventional circuits known in the related art.

BRIEF DI~~CR1PT10N OF THE DRAWINGS
Other advantages ofthe invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered t n connection with the accompanying drawings, wherein.
Figure 1 is a perspective view of the self=latching solenoid valve 3c~~mbly of the present invention;
Figure 2 is a cross-sectional side view of the self latching solenoid valve sssombly showing the permanent magnet latched to the pole piece.:
Figure 3 is a cross-sectional side view of a self latching solenoid vtilvc assembly of the present invention showing the permanent masnat adjuccnt to the latch;
and figure 4 illustrates the electrical control circuit employed to reverse the direction of the current through the coil.
D»:TATL»D DESCRirTrON OF THE ritEFEIRZZED EMl3c)DiMFNTfS) A self latching soicnuid valve assembly of the present invention is generally indicrxtcd at 10 in Figeu~s I through 3 where like numerals are used to describE like structure. Tltc solenoid valve assembly 1 U mclades d valve body 12 and a solenoid a~scmbly I 4 mounted to W a valve be>dy 12. The valve body 12 includes a pressurized air supply inlet port 16 for communicating with a source of pressurized air wd at least one cylinder port 18, ?U. A valve member 22 is supported in the valve body 12 so as to he movable between predetermined positions to selectively dimcL pressurized air from the inlet port 1b to at least one of the cylinder ports 18, 20.
Mare 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 1 A, 2U
and a pair of exhaust ports 26, 27. As shown in the drawings, the valve member is a poppet valve ?2 which is supported within the valve bore 24 far reciprocal movement 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 in specific arena of th~~
valve member 22 and ground to specifc dimensions to form valve alements '~fl, 32, 34. 'f'th~
valve elements 30, 32, 34 engage adjacent valve seats 3d, 35. 40, 41 r,-esented in the valve bore 24 for sealing various flow passages as the valve member 72 is reciprocated betwaen petitions 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 bcue 24 opposite the retainer 42. A
biasing member 46, such as a coiled retttm spring, is positioned between the retainer 42 and one end of the poppet valve member 22. 'fhe return spring 46 applies a. constant biasing force against the S 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 lo figure 2, under the influence ofthe solenoid assembly I4 as v~rill be described in ~:reater detail below. As described above and shown in the drawings, the valve assembly employs a four way valve. However, those having ordinary skill in ttie art ~uvill appreciate that the t 0 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 a~embly 14 includes a housing, generally indicated at 4R The housing 48 includes apole plate SU abutting the valve body 12, a cap 62 disposed nProsite the pole plate 50 and a. solenoid can or frame 54 extending therebeiween The frame 54 supports a coil 56 including a conductive wire 58 conventionally wrapped:round a bobbin 60. 'fhe conductive wire 58 is connected to a source of electricAl current through leads, generally indicated at 62. The Leads 62 are supported in the can 57 and include feed pins Cr4, electrical contacts 66 and lead wires 68. The lead wires 6R arP
roperatively connected to the soutre of electrical current. The direction of the crtrrant through the coil S6 and thus the direction of the electromagnetic force generated thereby is controlled by tZ control circuit, generally indicated at 7U in Figure 4 as will be described in greau:r detail below.
A top plate 55 is mounted adjacent to the h~hhin EU and between a portion of the fi-a.me 54 and the cap 52.
The pole plate 50 includes an opening ?2 extending thercthrough. 'fhc sulc;noi.d assembly 14 further includes a ferromagnetic pole piece 7~! having a stepped ~i~r~tivn 7$
with a srnallc;r Cross-sectinnal area than the rest vftho pole piece 74. ThC
stGppGd portion 78 is received in the opening 7~ r.~f the pole plate SO for mechanically f xing tlm pole piece 74 to the pole plate S(7. A thin piece ofnon-nv~netic stainless steel SO caps the pole piece 74 opposite the pole; Plate s0. A centrally located passage 82 extcttds through the pole 3U piece 74. A P'irshpin 84 is movably supported in the passage 82.
The car S7. of the solenoid housing 48 includes a thrcttded bore 8ti, .A
ferromagnetic latch RR is threadably mounted to the solenoid housing 4S in the bore Rti bvt sErcuc;ed from the pole piece 74. The latch 88 is made of iron but may be tiix~ic of any b ierroniagnetic material. A permanent magnet 90 is disposed between the latch 8R anrl the pole piece 74, A bushing 92 guides the magnet 90 within the bobbin bU. TMe pernnanent magr<et 90 is movable toward the pole piece 74 'under the influence of an elrctrornagnetic flux generated by a pulse of current flowing throui.;h the coil 56 in one direction. This flux > drives the permanent magnet 9U against the pushpin 84 to mc,vP the. valve member ?2 to one predeterrninedposition. Furthermore, the permanent magnet 90 is movable away from the pole piece 74 and toward the latch 88 under the iWluence of an oppositcIy dircctad electromagnetic flux generated by a puiaP of current flowing through the coil SG in the opposite direction. When this occurs, the biasing member46 moves the wdlve member 22 1 U to another predetermined position, for e~:nmplc to the Icft as shown In Figure 3.
To this end, the pushpin t34 presents lm cmia.~. ad head 94 which is disposed adjacent one. e.nd of the poppet vu,lvc; member ?? iur wnlactlng it when tile permanent magnet 90 contacts the pushpin. 84. Irr addition, the enlarged head 94 oi~ the pushpin $4 limits the movement ofthe pushpiei 84 within the passage 82 of the pole piece 74 under the iniluenee 1.5 ot'thc biasing me~r~bcr 46 through the valve member 22 when the permanent magnet 94 has moved wwaz~ci the latch 88. 'I-he limited movement of the pushpin 84 presents a gap 96 t~twoen the permanent magnet 9U and the pole piece 74 as shown in 1~ figure 3.
As illustrated in r figure 2, a space t 02 is defined between the latch 8R and the permanent magnet 90 when the permanent magnet is moved toward the pole piece 74.
2U 1-'urthermore, the position of the latch 88 toward and away from the permanent magnet 9U
may be adjusted by adjusting the position of the threaded latch 8$ within the threaded bore 86 in the cap 52. Accordingly, the six of the space 1 U2 between the latch 88 and the permanent magnet 90 when the permanent magnet has moved toward the pole piece may be adjusted. In this way, the attractive force between the latch 88 and the pennanent 25 magnet 9U may be modulated.
The permanent magnet 90 may be of any suitable type but preferably is a. rare e~erth neodymiaun-iron~boron magnei_ The permanc.'nt magnet 90 dernes north anct 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 he reversed. A
protective cap E~8 30 is bonded to the north pole and a protective cap 100 is bonded to the south pole. Thcsc caps 98, 100 protect the permanent magnet 90 as it is cycled toward the pole pierc 7~ amd the latch 88.

Referring to Figure 4, a circuit, generally indicated at 70, is shown for evntmllinQ
the self latching solenoid valve assembly 1 U. The circuit 70 includes a solenoid I 4 having a coil 56 and a permanent magnet 9U. The electrical leads 62 of the coil Sli extend out o1' a first end 1 SO and a second end 152 of the solenoid 14. t'.urrent travels through the coil S 56 through the lead 62 at either end 15h, 152. The di.reclion of the current as it passes through the ends 1 S0, 1 S2 determines whether the permanent magnet 90 will be bia..sed in a first axial direction or a second axial direction apposite that of the first axial direction.
Connected to the first end 1 SO ofthe solenoid l4 is a first switching circuit 154 and a second switching circuit 156. The first switching circuit l S4 allows current ro flow U through the solenoid 14 in one direction and the second switching circuit I
5h allows current to flow through the solenoid I4 in a second direction opposite in directic,n to that of the first direction.
2'he first switching circuit 154 includes a first transistor 1 S8 and a second transistor 160. 1n the embodiment shown in Figure 4, the firsttransistor l :5R is a pup bipolar junction IS transistor. The second transistor 160 is a MOSFET. 'the reaccns for using two different types of transistors is to reduce the overall voltage rlrnp across tha trainsistar3 1 ~8, I 6o a5 well as tct reduce the bias requirements. A base 162 of the first transistor 16Q is cannccteci to a gate 164 of the second t~cc8ztsistor 160 through .j resistor 166. The gate 164 of the second transistor 16U is also connected to a drain 168 of the second transistor 160 through ~0 a resistor I 7U. The drain 1 (i8 and resister 1 ?0 are. also eonnectad to a negative input control source 172. 'the negative input control snuree 17? provides the input rcyuired to determine whether the self latching valve assEmbly 10 is to he forocd in the dirGCtiun providod in the first switching aitruit 154. A collector 174 of the first t~~ausisl.ur 1'78 is connected to the first end 1 SO of the solenoid 1~1 ;and a source of 17f ur the second 25 tt~tlsistor I60 is ccmnected to the. second end 1 S2 of the solenoid 14.
~1u Ctnitter 17$ Of the ~~tL'st tt'anSi~r 1 SS is connected to the power supply, 24 volts iu lttis embodiment.
The cecond switching circuit 156 mirrors the first swil,c;hing circuit in that tt incior~ies a third transistor I 80 srtd a fourth transistor 182. fhe differences are that the third transistor 1 g0 is a bipolar junction transistor with ita wllactor 184 electrically cotanLeted 'itl to the second end 152 of the solc;noid 14 and the Cuurlh transistor 182 is a MC)Sl?ET with its rnurce 1 Sfi electrically connected to the first cud 1 SO of the solenoid 14. A, resistor I 88 is connected between the gate 19U of the fourth transista~ 182 and the base 1 X72 of the third tra~imur I 8U. Another resistor t 94 is connected between the date 190, tlm resistor 158, g and the drain 196 of the fourth transistor 182. The resistor 194 and the drain 196 are also cc.~rtnecied to a negative input control source 198 providing input to sW tch 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 o.f he third transistor 180 which is connected directly to the power supply.
A red LED 202 and a green LED ?04 are connected to the first end 150 and the second end 1 ~? of the solenoid 14. These L.EDs 202, 204 are conneeti:d in opposite directions such that when the solenoid 14 is aetivatc~i in one direction, the red LED 202 will emit light and when the solenoid I4 is activated in the apposite direction, the green LED 204 will emit light. This allows an operator to view the assembly 10 and know in which mode the aelf latching valve assembly 10 should be operadnp.
UPERATIUN
In operation, current is driven through the coil 56 in one direction which generates an electromagnetic flux. The electromagnetic flux polarizes the ale: piece 74 attracting the permanent magnet 90. The movable permanent magnet 9015 thus driven wward the pole piece 74 across the gap 96 and engages the pushpin R4, as shown in Figure 2. This drives the pushpin $4 to the right moving the poppet valve 7.7. also to the right and against the hiasing force of the coil spring 46.
Power to the coil Sfi is then interrupted. 1-lc~wwer, the perrnanont magnet 90 remains in its position shown at Figure 2 and ''latcheri" 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 s~~:ais with valve seat 3b ;md vrrtvc elenzcnt 32 cooperatively seals with valve seat 4(l. Conversely, the valve element 32 is uYcn with respect to the valve seat :~8 and the valve element 34 is open with rcspecl to the valve seat 41.
Vi~ith the valve member 22 shifted to the right rxs described aLuvc and shown in Figure 2, pressurized air t~nwing into the valve body 12 via the inlet purl 1 b passes tf~e valve element 37. and valve seat 38, flows through the; valve L«rC 24 and out the cylinder passage 18. At the same time. air is exhausted from the cylimdcr passage 20 past the valve element 34 and valve seat 4i and out the valve body 12 via the exhaust port l7. T'lte exhaust port 2~ is sealed by the valve element 3U and tlzc walvc seat 36.
The valve member ~~ remains in this dispc~sitiom unlit current is agaita driven through the coil 56 in r1n oPp~.Qiy~~ direction. This producea rut clcctmma~uclic: flux in a ~liccction opposite to the first flux described above_ 1'he oppositely directed magnetic flux clmcyrs the polarity of the pale pioce 74 which acts to repel the permanent magnet 90.
Thus, the permanent magnet 90 moves away from the pole piece ?4 and toward the latch 88 uuereby closing the spa~c~ 102 therebetween. 'fhe coil spring 46 biases the valve mmnher 2? to the !eft as shown in Figure 3. The pushpin 84 is also shifted to the left under tl~a influence of this biasing force acting through the valve membc;r 22.
Current to the coil 56 is then interrupted. However, the permanent magnet 9U remains in the position shown in Figure 3 dnd is "latched" to the latch 88 due tea the residual attractive forces that remain ev~c~ in the ahsence of an electromagnetic flux.
In this disposition, the valve element 32 cooperatively Seals with the valve seat 38 and valve element a4 cooperatively seals wills valve seat 41. Conversely, the valve dement 3? 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 memher 22 Shifted to the left as described above and shovm in l5 Figure 3, pressurised air Mowing into the valve body 12 via the inlet port 1.6 passes the valve element 3~? and valve seat 40, flows through the valve bore ?4 and then out the cyliuciGr passage 2U. At the same time, air is exhausted from the cylinder passage 18, past rhc vat vc; element 30 and valve seat 36 and then out the valve body 12 via the; exhaust port 2C~. The exhaust port 27 is sealed by the valve element 34 and the valve seat 41. ?he valve ?0 mctnber 22 remains in this disposition until current is again driven through the coil ~fi in an opposite direction. The valve member 22 is then shifted back to the right as shown in ribule 2 and described above.
Iu addition, a pair of switcheng circuits is employed to control the direction of cLlt'i'CIIt LU the coil and to electrically isolate one negative control input source from the 25 c~ll~Cr negative conuol input source. This effectively prev~;nts damage to the control circuits ~:ausad by a reverse polarity feeclhaek signs! or other transient signal. Switching circuit' of the present invention provide a relatively low voltage drop across the circuit wlicn cu~upered with conventional circuits known in the related art.
Accordingly, the self Iatcluy solenoid valve assembly of the present invention facilitates reduced cost and size 30 in a fast-acting v:~lvC r~sSGmbly having self latetung capabilities.
The inveutium lees bc~n described in a~n illustrative manner. It is to be understood that the tcrrninolo~y wluch has been used is intended to be in the nature of words of ~fm-ipEic~a rr~W er ttlan of limitation.

la Many rnodificati~ns and variatsons of the invzntion are possible in light of the shove taachiags. Thctefurc, within the scope ot~the appended claims, the invention t2lay be practiced other than as spcv:ifically described.

Claims (4)

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 pads 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.