Patent Publication Number: US-6707358-B1

Title: High current bistable relay with arc suppression

Description:
FIELD OF THE INVENTION 
     This invention relates broadly to electromechanical control devices and, more particularly, pertains to a compact, high current, low resistance, bistable relay particularly useful in handling the electrical requirements of a growing number of automotive accessories expected to be operated at voltages exceeding the current standard 24 volts dc. 
     BACKGROUND OF THE INVENTION 
     As explained in U.S. Pat. No. 6,084,488 issued to Macbeth et al., Jul. 4, 2000, electromechanical relays of the type with which this invention is concerned include one or more pairs of movable contacts that can be selectively brought into engagement to complete an electrical circuit called “contact make”, or moved apart, called “contact break”, to open the circuit. During either make or break when the contacts are at some very small separation (&lt;1×10 −6  m), an arc is formed. A variety of techniques have been employed in the past to minimize the amount of arcing, and/or compensate for the arcing, to provide a relay that continues to operate effectively. 
     When an arc occurs, it is common for material to be transferred from one relay contact to another, and in many cases, an actual weld, albeit a small one, is formed between the contacts. In normally open contacts, for example, if a weld is formed between contacts when the contacts are closed, the weld may tend to hold the contacts closed when operating forces are removed, and this may prevent the relay from opening as desired. Typically, electromechanical relays include a solenoid for physically bringing the contacts together, and rely on a spring to force the contacts open when the solenoid is deenergized. 
     It is common to arrange relay contacts so that they engage and/or separate with a combination of relative movements, including opening and closing movements generally perpendicular to the surfaces of the contacts, and wiping movements generally transverse to the surface. The relative wiping movement of the contacts reduces the tendency for arcing to create strong welds during closure and adds a torsional force to help break welds on demand to open, therefore making the relay more reliable. In addition, and equally important for reliability and high performance in systems requiring a very low resistance device, a properly designed contact wipe will remove the thin but high resistance tarnish film which occurs on Nobel metals. 
     In the aforementioned &#39;488 patent, a compact high current relay is provided having first and second fixed contacts connected in circuit relationship with the apparatus to be controlled. An elongated bus bar has first and second movable contacts at opposite ends thereof, the bus bar characterized by a stiffness such that upon application of a first predetermined force to the bus bar between the contacts, the bus bar flexes and the movable contacts both tilt and wipe with respect to the first and second fixed contacts. A solenoid is connected to the bus bar between the first and second contacts for exerting a force on the bus bar greater than the predetermined force. 
     While the Macbeth et al. patent is generally satisfactory for relays with a flexible bus bar design, it remains desirable to provide a differently styled relay having unique structure to suppress arcing, to allow wiping of the contacts as the contacts are closed, and to apply a strong torsional force to the contacts on opening. Minimization of both the total resistance across the device and the power required to hold the device in either the contact open or the contact closed state are also desired. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide an arc suppressing high current relay with enhanced DC interruption capability at voltages exceeding those of typical relays. 
     It is also an object of the present invention to provide an insulator receiving structure for the fixed contacts of the relay that will enable cooling of the arc. 
     It is an additional object of the present invention to provide a means to move the arc towards the insulator in order to enhance cooling. 
     It is an additional object of the present invention to provide an improved movable contact assembly which will effectively wipe the fixed contacts of the relay in a manner that prevents tarnish build up between the contacts and also minimize the chance of hard welds. 
     It is an additional object of the present invention to provide an improved movable contact assembly that will provide a torsional component of force and increase the weld break capability of the device on contact break. 
     It is an additional object of the current invention to provide a device which can remain fixed in either the open or closed position after being commanded there by the coil and the power to the coil is subsequently removed. 
     In one aspect of the invention, there is provided a relay subject to arcing when contacts make or break, and susceptible to welding and erosion due to arcing. The relay includes a solenoid having a plunger movable into and out of the solenoid. The solenoid is comprised of two sets of windings such that power may be applied to the solenoid to create a field with the north pole towards the contacts in the one instance and with the south pole directed towards the contacts in the other. A permanent magnet with a field which could be oriented either such that its north pole faces towards the contacts or that its south pole faces the contacts, is included in the magnetic circuit with the plunger part of its magnetic path. Upon application of power to the solenoid that provides a supplemental field to the magnet, the plunger will move into the solenoid and latch. Upon subsequently removing the power to the solenoid the device will remain in the latched position. Upon application of power to the solenoid creating a field opposing the permanent magnet, the plunger will unlatch and move forward out of the solenoid. Upon subsequent removal of power to the solenoid the solenoid will remain in its forward position. A pair of fixed contacts is provided along with a movable bridge assembly having a pair of movable contacts adapted to engage and disengage the fixed contacts upon unlatch and latch of the plunger. The bridge assembly is connected via a ball joint arrangement to the solenoid plunger, the ball joint arrangement enabling the movable contact to move laterally with respect to the stationary contact causing contact wipe to occur and thin film tarnish to be removed from the contacts on closing. Additionally, the ball joint arrangement provides a torsional force to break welds on opening. An insulator surrounds the movable contacts for cooling the arc between the movable and fixed contacts. The solenoid is supported in a generally rectangular frame having an end plate. The fixed contacts are carried on outwardly and downwardly angled legs of a pair of generally L-shaped brackets. The relay has a housing for supporting the solenoid in its frame, the insulator, the movable bridge assembly and the L-shaped brackets. The contacts and contact bus are oriented relative to the field of the permanent magnet and opening solenoid such that a current through the opening contacts will experience a force due to that field. The contacts and contact bus are also oriented such that a current through them will also experience a force due to their “self field.” The force experienced by the current due to the permanent magnet and the solenoid will supplement the force due to the self field for current flowing in one direction and partially supplement it and partially oppose it for current flowing in the opposite direction. The force of the self-field on the current is towards the insulator regardless of the direction of the current flow. The plunger has a cylindrical portion and a spherical portion. The spherical portion is received within a swivel cap attached to the movable bridge assembly to define a swivel arrangement for the movable contacts on the bridge assembly. The insulator is preferably constructed of LEXAN polycarbonate. The relay housing has one cavity for holding the solenoid in its frame, and another cavity for holding the insulator, the movable bridge assembly and the angled legs of the L-shaped brackets. The insulator is formed with pockets for receiving lowermost ends of the angled legs of the L-shaped brackets. The L-shaped brackets include horizontal legs integrally connected to the outwardly and downwardly angled legs. The outwardly and downwardly angled legs are disposed at an angle of about 95 degrees relative to the horizontal legs. A coil spring has one end disposed against the end plate and a second end disposed against a rearward end of the bridge assembly. 
     In another aspect of the invention, a relay has a pair of fixed contacts, a pair of movable contacts adapted to be engaged and disengaged with the fixed contacts, and a solenoid having a plunger movable into and out of the solenoid, the plunger having an outer end operably connected to the movable contacts. The invention is improved by a motion translating and preferably a ball joint arrangement interconnecting the plunger and the movable contacts to enable wiping of the contacts on make to remove thin film tarnish and to provide torsional force to aid in the breaking of welds on opening. The invention is further improved by an insulator surrounding the movable contacts for cooling the arcing. The ball joint arrangement provides for swivel movement of the movable contacts. The ball joint arrangement includes a spherical portion formed on one end of the plunger, a cylindrical swivel cap liner for receiving the spherical portion of the plunger, and a cylindrical swivel cap for receiving the liner, the swivel cap being attached to the movable contacts. The insulator includes a top wall overlying the movable contacts. The fixed contacts are carried on outwardly and downwardly angled legs that are received in a pair of pockets formed in the insulator. The insulator is constructed of a gas expelling material. The contacts and contact bus are oriented relative to the field of the permanent magnet and opening solenoid such that a current through the opening contacts will experience a force due to that field. The contacts and contact bus are also oriented such that a current through them will also experience a force due to their “self field.” The force experienced by the current due to the permanent magnet and the solenoid will supplement the force due to the self field for current flowing in one direction and partially supplement it and partially oppose it for current flowing in the opposite direction. The force of the self-field on the current is towards the insulator regardless of the direction of the current flow. 
     In yet another aspect of the invention, a relay includes a solenoid having a plunger movable into and out of the solenoid. The solenoid is comprised of two sets of windings such that power may be applied to the solenoid to create a field with the north pole towards the contacts in the one instance and with the south pole directed towards the contacts in the other. A permanent magnet with a field which could be oriented either such that its north pole faces towards the contacts or that its south pole faces the contacts, is included in the magnetic circuit with the plunger part of its magnetic path. Upon application of power to the solenoid that provides a supplemental field to the magnet, the plunger will move into the solenoid and latch. Upon subsequently removing the power to the solenoid the device will remain in the latched position. Upon application of power to the solenoid creating a field opposing the permanent magnet, the plunger will unlatch and move forward out of the solenoid. Upon subsequent removal of power to the solenoid the solenoid will remain in its forward position. A frame is provided for holding the solenoid. A pair of generally L-shaped brackets has horizontal legs integrally formed with outwardly and downwardly angled legs carrying a pair of fixed contacts. A movable bridge assembly is provided with a pair of movable contacts adapted to engage and disengage the fixed contacts upon respective unlatch and latch of the plunger. The bridge assembly is connected via a ball joint arrangement to the solenoid plunger. The ball joint arrangement enables wiping of the contacts and removal of thin film tarnish on make and also provides a torsional force to aid in breaking of welds on opening. A coil spring surrounds the ball joint arrangement and has one end disposed against the frame and another end disposed against the bridge assembly. An insulator surrounds the movable contacts for cooling the arc. The contacts and contact bus are oriented relative to the field of the permanent magnet and opening solenoid such that a current through the opening contacts will experience a force due to that field. The contacts and contact bus are also oriented such that a current through them will also experience a force due to their “self field.” The force experienced by the current due to the permanent magnet and the solenoid will supplement the force due to the self field for current flowing in one direction and partially supplement it and partially oppose it for current flowing in the opposite direction. The force of the self field on the current is towards the insulator regardless of the direction of the current flow. 
    
    
     Various other objects, features and advantages of the invention will be made apparent from the following description taken together with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is a perspective view of a high voltage relay embodying the present invention with its cover removed; 
     FIG. 2 is an exploded, perspective view of the components of the high voltage relay of FIG. 1; 
     FIG. 3 is an enlarged, sectional view taken on line  3 — 3  of FIG. 1; 
     FIG. 4 is an enlarged, partial sectional view taken on line  4 — 4  of FIG. 3; 
     FIG. 5 is a partial view of FIG. 3 showing the fixed contacts and the movable contacts of the relay in a normally open position; 
     FIG. 6 is a view like FIG. 5 showing a wiping of the contacts as the movable contacts continue to move to their closed position. 
     FIG. 7 is a view like FIG. 6 showing the closing of the movable contacts upon the fixed contacts; 
     FIG. 8 is a view like FIG. 7 showing a beginning of the reopening of the movable and fixed contacts; 
     FIG. 9 is a view like FIG. 8 showing the contacts at the position just prior to break and initiation of the arc from the last touch position; and 
     FIG. 10 is a simplified diagram depicting one desirable magnetic field orientation and current orientation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, FIGS. 1 through 3 illustrate a high voltage relay  10  such as may be used in the electrical system of a vehicle. Relay  10  includes a generally rectangular housing  12  having a first cavity  14  (FIG. 2) for receiving an insulator  16  having a pair of side walls  18 ,  20  integrally connected to a base  22 . A rearward end in base  22  is formed with an upstanding pillar  24  having a threaded aperture  26  extending throughout its height. A pair of pockets  28 , one on each side of the pillar  24 , is also provided in the base  22  of the insulator  16 . As one feature of the invention, the insulator  16  is formed of a clear material made of LEXAN polycarbonate which has been found to improve the performance of the relay  10  as will be further described below. While LEXAN polycarbonate is used in the preferred embodiment, it should be understood that other suitable materials may also be chosen that provide similar off gassing properties. The pockets  28  in insulator  16  disposed in the first cavity  14  receive the lowermost ends of a pair of generally L-shaped brackets  30  having horizontal legs  32 , and outwardly and downwardly bent legs  34  which carry a pair of fixed contacts  36 . Horizontal legs  32  are each formed with a pair of apertures  38  which are aligned with a pair of threaded holes  40  on a rear deck  42  of the housing  12 . Suitable fasteners  44  are provided which are passed through the aligned apertures  38  and secured into the holes  40  to fasten the L-shaped brackets  30  to the housing  12  with their lowermost ends protruding into the pockets  28  in the insulator  16 . 
     As can be seen best in FIG. 3, the legs  34  carrying the fixed contacts  36  are bent an angle of about 95 degrees relative to the horizontal legs  32  to facilitate particular engagement with a movable contact structure to be described. A generally T-shaped top wall  46  has a through hole  48  which is registerable with the aperture  26  in the pillar  24  so that it can be attached between the top of the side walls  18 ,  20  of the insulator  16  by a fastener  50 . A generally rectangular cover  52  has a pair of holes  54  alignable with a pair of apertures  56  on the deck  42  of the housing  12 . A pair of fasteners (one being shown at  58 ) is passed through the holes  54  and threaded into the apertures  56  to secure the cover  52  over the insulator  16  and a major portion of the L-shaped bracket horizontal legs  32 . 
     The relay housing  12  also has a second cavity  60  for accommodating a solenoid arrangement including a generally U-shaped frame  62 , which receives a solenoid  64 . The solenoid  64  has a bobbin  66  with a through passage  68 , a coil (not shown) wrapped around the bobbin  66 , and a protective covering  70  surrounding the coil. A set of electrical wires  72  adapted to be connected to a source of electrical power extends from the coil. The solenoid  64  also includes a backstop  74  having a cylindrical portion  76  which is inserted into one end of the bobbin passage  68  and a solenoid holding magnet  78  which is attached to a circular top  80  of the backstop  74 . The other end of the bobbin passage  68  receives a cylindrical portion  82  of a plunger  84  known to be moved in and out of the solenoid  64  as power to the coil is applied in a sense that produce fields that respectively aid and oppose the field of the magnet. Plunger  84  has the cylindrical portion  82  integrally connected with a spherical portion  86 . With the cylindrical portion  82  lodged in the other end of the bobbin passage  68 , the spherical portion  86  protrudes through an opening  88  in an end plate  90  which is secured to the side plates  92  of the frame  62  as seen in FIG.  4 . The spherical portion  86  of plunger  84  is swivel mounted in a TEFLON resin liner  94  which fits into a swivel cap  96 . The cap  96  has a projection  98  that is secured to a generally U-shaped contact bridge assembly  100  having a pair of movable contacts  102 . A coil spring  104  surrounds the spherical portion  86  of plunger  84 , the liner  94  and the swivel cap  96 . The spring  104  has one end  106  which is disposed against the end plate  90  and another end  108  which is placed against a rear wall of the bridge assembly  100 . 
     During assembly, the solenoid  64  along with the backstop  74 , magnet  78  and the cylindrical portion  82  of the plunger  84  is held within the frame  62  with end plate  90  connected thereto and defines a solenoid arrangement which is disposed in the second cavity  60  of the relay housing  12 . With the solenoid arrangement in the relay housing  12 , the spherical portion  86  of the plunger  84 , the cap  96  and its liner  94  project beyond the end plate  90  of frame  62 , and the contact bridge assembly  100  is disposed within the insulator  16  in the first cavity  14  spaced apart from the fixed contacts  36  on the L-shaped brackets  30 . Furthermore, the contact bridge assembly  100  has a central channel  110  which normally is spaced from the pillar  24  of insulator  16  when the contacts  36 ,  102  are in an open position as shown in FIGS. 3 and 4. As a second feature of the invention, the engagement of the spherical portion  86  of plunger  84  with the swivel cap  96  and its liner  94  defines a ball joint arrangement which permits the contact bridge assembly  100  and its movable contacts  102  to swivel in a manner which will enable a wiping action of the fixed contacts  36  as will be further appreciated hereafter. 
     The relay  10  is shown in its assembled condition with cover  52  removed as shown in FIGS. 1 and 3. 
     The relay  10  is brought to its open position (FIG. 5) with a momentary energization of the solenoid coil in a sense that produces a field that adds to the field of the permanent magnet  78 . Once in its full open position the plunger  84  is held latched to the stop  80  by the force of the permanent magnet  78  alone, the power to the coil is removed, and the movable contacts  102  are spaced from the fixed contacts  36  and are disposed in a generally vertical attitude facilitated by the spring  104  acting against the back of the bridge assembly  100 . To move to its operating or closed position (FIG.  7 ), the solenoid  64  is unlatched with a momentary energization of the solenoid coil in a sense that produces a field which opposes the field of the permanent magnet  78  and causes the plunger  84  to move out of the solenoid  64  as shown by the arrow A. As the plunger  84  moves from the solenoid  64 , the ball joint arrangement permits the movable contacts  102  to drop (arrow A, FIG. 6) so that they eventually engage the downwardly angled plane of the fixed contacts  36  at an angle perpendicular thereto (FIG.  7 ). When it is desired to break the electrical connection, the solenoid  64  is energized momentarily in a sense that adds to the field of the permanent magnet  78  so that spring  104  will be compressed and the plunger  84  pulled in a reverse direction into the solenoid  64  as shown by the arrow B in FIG.  8 . As the force is applied to the plunger, a torsional force will be applied to any weld which may have occurred between the contacts. As the plunger  84  continues to retract in the direction of arrow C, FIG. 9, the movable contacts  102  move upwardly and away in the direction of arrow D from the fixed contacts  36  due to the ball joint arrangement in a manner which causes final contact touch to occur at the edge of the contact close to the insulator. It should be appreciated that the angle of the fixed contacts  36  contributes to the effectiveness of the wiping action as well as to causing the arc to initiate in its optimum location for cooling (FIG.  10 ). Continued movement of the plunger  84  returns the movable contacts  102  to the open position as shown in FIG.  5 . 
     In order to deal with the arcing which occurs when the movable contacts  102  and the fixed contacts  36  are moved towards or away from each other, the relay  10  relies upon the LEXAN polycarbonate insulator  16  which acts to expel gas caused by the arcing, the gas having a tendency to cool the arc. At the time the contacts are opening and the arc is initiated, a component of the magnetic field produced by the combined contributions of the permanent magnet and the actuation of the coil, passes through the plunger and extends past it through the current loop as shown in FIG.  10 . The orientation of the field and current is such that a force is created on the current in the direction of the insulator  16  and its corresponding surfaces  18 ,  20 ,  22 , for cooling. A further outward force, proportional to the current and due to the self field of the current in the current loop (FIG. 10) acts on the current until its extinction. 
     It should be appreciated that the present invention provides a high current relay which markedly lengthens the surface lifetime of its contacts by using a particular fabricated insulator to cool the arc, magnetic fields which support movement of the arc towards the insulator, and a ball joint supported movable contact assembly combined with an angled fixed contact structure to enable an effective wiping of the fixed contacts and optimum initial location of the arc. 
     While the invention has been described with reference to a preferred embodiment, those skilled in the art will appreciate that certain substitutions, and omissions may be made without departing from the spirit thereof. For example, although the preceding description discloses the magnetic fields facing in one particular direction, it should be understood that the fields may face in either direction. Accordingly, the foregoing description is meant to be exemplary only, and should not be deemed limitative on the scope of the invention set forth with the following claims.