Abstract:
A battery bypass assembly for bypassing for bypassing a first battery cell electrically connected to a second battery cell. The battery bypass assembly has a first bypass contact and a second bypass contact. A voltage sensing mechanism is electrically connected between the first battery contact and the second battery contact for sensing a predetermined voltage loss. An expansive material within the housing expands upon the voltage sensing mechanism sensing a predetermined voltage loss. A plunger mechanism is moveable from a first position to a second position with a maintaining mechanism maintaining the plunger mechanism in the first position and moveable to allow the plunger mechanism to move into the second position. An actuating mechanism contacts the expansive material and the maintaining mechanism for moving the maintaining means upon expansion of the expansive material wherein the plunger mechanism, upon reaching the second position, bypasses the first battery cell.

Description:
The present application is a continuation-in-part of pending provisional patent application Ser. No. 60/177,312, filed on Jan. 21, 2000, entitled “Battery Bypass Assembly”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a battery bypass assembly and, more particularly, it relates to a battery bypass assembly for a spacecraft battery supply system which removes a failing battery cell from the battery supply system without causing power loss within the battery supply system. 
     2. Description of the Prior Art 
     Today, spacecraft in high-earth orbit, such as satellites and the like, are becoming more and more important in supplying technological advances to feed an increasing government, business, and consumer appetite. In order to provide an uninterrupted power supply to the spacecraft, the spacecraft has a battery supply system. The conventional spacecraft battery supply system is typically constructed from a plurality of battery cells arranged in series or parallel arrays, according to the required voltage and current output of the battery supply system. While most of the equipment within the spacecraft can properly operate at voltages of twenty-two (22 V) volts, twenty-four (24 V) volts, or twenty-six (26 V) volts, the desired total voltage to power the spacecraft is twenty-eight (28 V) volts in the event that one or more of the battery cells becomes inoperable. 
     In most spacecraft, the plurality of battery cells are either nickel cadmium (NiCd), nickel-metal hydride (NiMH) batteries having an approximate voltage of between 1.2 volts and 1.5 volts or lithium ion battery cells having an approximate voltage of between 2.0 volts and 2.5 volts. While nickel-metal hydride batteries are typically used in spacecraft today, lithium ion batteries are rapidly becoming the power source of choice for future space applications. The lithium ion batteries exhibit high energy and power both per unit volume and per unit weight in comparison with other rechargeable type batteries. 
     The design of the battery supply system of a spacecraft presents special challenges not typically found in sub-orbit applications. The spacecraft battery supply system must continue to operate in an acceptable manner for years while physically inaccessible to maintenance and repair because the spacecraft is in high-earth orbit. When one of the battery cells starts going bad or otherwise loses power, the failing or failed battery cell ceases pumping voltage. As the battery cell continues to decline, the battery cell actually becomes a resistor to the entire battery supply system pulling power from the battery supply system and creating excessive heat. Loss of power and excessive heat can interfere with the operation of the spacecraft and could, potentially, cause the battery cell to explode. 
     In the past, a battery bypass has been used for each battery cell to bypass any battery cell which loses power to remove the battery cell from the battery supply system. Otherwise, as mentioned above, if one of the battery cells were to fail to an open circuit condition, the battery would be rendered inoperable in the open-circuit state. The battery bypass permits the failed battery cell to be bypassed, so that the battery supply system continues to functions although at a slightly diminished performance level. Therefore, it is common practice to overdesign the spacecraft battery supply systems according to the statistical probabilities of failure of one or more of the battery cells in the battery supply system, so that, through the use of the battery bypass, the battery supply system can continue to function in an acceptable manner. 
     Previous battery cell management devices for the battery supply system typically used diodes or a relay device to short out failed cells. Unfortunately, these conventional battery bypass systems were unreliable, heavy, and generated excessive heat which could damage the entire spacecraft and its functions. Furthermore, conventional battery bypass systems can suffer damage during launch thereby jeopardizing the entire functionality of the spacecraft upon battery supply system failure. 
     Accordingly, there exists a need for a battery bypass assembly which can remove individual battery cells from the battery supply system. Additionally, a need exists for a battery bypass assembly which is lightweight and reliable for high-earth orbit applications. Furthermore, there exists a need for a battery bypass assembly which safely maintains a battery supply system in an operating condition with all types of rechargeable battery cells. 
     SUMMARY 
     The present invention is a battery bypass assembly for bypassing a first battery cell electrically connected to a second battery cell. Each battery cell has a first battery contact and a second battery contact. The battery bypass assembly comprises a housing having a first bypass contact and a second bypass contact. Voltage sensing means is mounted within the housing and is electrically connected between the first battery contact and the second battery contact for sensing a predetermined voltage loss in the battery cell. An expansive material within the housing expands upon the voltage sensing means sensing a predetermined voltage loss in the battery cell. A plunger mechanism is slidably mounted within the housing and is moveable from a first position to a second position. Maintaining means maintains the plunger mechanism in the first position and is moveable to allow the plunger mechanism to move into the second position. Actuating means contacts the expansive material and the maintaining means for moving the maintaining means upon expansion of the expansive material wherein the plunger mechanism, upon reaching the second position, bypasses the first battery cell. The present invention additionally includes a battery bypass mechanism for bypassing a battery cell. The battery cell has a first battery contact and a second battery contact. The battery bypass mechanism comprises a first bypass contact electrically connected to the first battery contact and a second bypass contact electrically connected to the second battery contact. Contact means are selectively movable to close the circuit between the first battery bypass contact and the second battery contact. Expansive actuating means actuate movement of the contact means to close the circuit and bypass the battery cell upon occurrence of a predetermined event. 
     The present invention further includes a method for bypassing a battery cell with a battery bypass assembly. The battery bypass assembly has a first bypass contact electrically connected to a first battery contact and a second bypass contact electrically connected to the second battery contact. The method comprises selectively moving a conductive bar between the first battery bypass contact and the second battery contact from a first position to a second position to close the circuit, providing a plunger rod within an expansive material, expanding the expansive material upon the occurrence of a predetermined event, substantially ejecting the plunger rod from the paraffin material, moving the conductive bar to the second position, and closing the circuit and bypassing the battery cell. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational side view illustrating the battery bypass assembly, constructed in accordance with the present invention, with the battery bypass assembly being connected to a first battery cell and a second battery cell; 
     FIG. 2 is a perspective view of the battery bypass assembly, constructed in accordance with the present invention: 
     FIG. 3 is a side elevational view of the battery bypass assembly of FIG. 1, constructed in accordance with the present invention; 
     FIG. 4 is a side sectional view of the battery bypass assembly of FIG. 1, constructed in accordance with the present invention; 
     FIG. 5 is an exploded perspective view of an actuator assembly of the battery bypass assembly of FIG. 1, constructed in accordance with the present invention; 
     FIG. 6 is a perspective view of a plunger mechanism of the battery bypass assembly of FIG. 1, constructed in accordance with the present invention; 
     FIG. 7 is a perspective view of a flexure contact of the battery bypass assembly of FIG. 1, constructed in accordance with the present invention; 
     FIG. 8 is an elevational side view illustrating another embodiment of the battery bypass assembly, constructed in accordance with the present invention, with the battery bypass assembly being connected to a first battery cell; 
     FIG. 9 is a perspective view the battery bypass assembly of FIG. 8, constructed in accordance with the present invention; 
     FIG. 10 is another perspective view of the battery bypass assembly of FIG. 8, constructed in accordance with the present invention with the cover being removed; 
     FIG. 11 is an exploded perspective view of the battery bypass assembly of FIG. 8, constructed in accordance with the present invention; 
     FIG. 12 is an exploded perspective view of a latch subassembly of the battery bypass assembly of FIG. 8, constructed in accordance with the present invention; 
     FIG. 13 is an exploded perspective view of an actuator assembly of the battery bypass assembly of FIG. 8, constructed in accordance with the present invention; 
     FIG. 14 is an exploded perspective view of an actuator diode assembly of the battery bypass assembly of FIG. 8, constructed in accordance with the present invention; and 
     FIG. 15 is an exploded perspective view of a fuse assembly of the battery bypass assembly of FIG. 8, constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in FIG. 1, the present invention is a battery bypass assembly, indicated generally at  10 , for use with a plurality of battery cells  12 , such as a first battery cell  12   a  and a second battery cell  12   b  arranged in series or parallel arrays depending on the application and the desires of the user. Each battery cell  12  has a first battery cell contact  14  and a second battery cell contact  16  with the first battery cell contact  14  and the second battery cell contact  16  being electrically connected to an adjacent battery cell (not shown). 
     As described herein, the battery bypass assembly  10  is especially suited for use in a spacecraft (not shown) for flying in a high-earth orbit. The spacecraft can include any type of spacecraft including, but not limited to, satellites and space vehicles. It should be noted, however, that the battery bypass assembly  10  of the present invention can be used with battery cells  12  for powering various applications on a spacecraft or other structure or system. 
     Still referring to FIG. 1, the battery bypass assembly  10  of the present invention includes a main body  18  having a first bypass contact  20 , a second bypass contact  22 , and a third bypass contact  24 . The first bypass contact  20  is electrically connected to the second battery cell contact  14  of the battery cell  12   a , the second bypass contact  22  is electrically connected to the first battery cell contact  14  of the battery cell  12   b , and the third bypass contact  24  is electrically connected to the second battery cell contact  16  of the first battery cell contact  14 . 
     While the battery bypass assembly  10  has been described and illustrated as having a first bypass contact  20 , a second bypass contact  22 , and a third bypass contact  24 , it is within the scope of the present invention to have a battery bypass assembly  10  having more than three bypass contacts, i.e., four bypass contacts, five bypass contacts, six bypass contacts, etc. 
     Referring now to FIGS. 2 and 3, the battery bypass assembly  10  additionally includes a housing body  26  . The housing body  26  is preferably constructed from a non-conductive plastic material formed through injection molding or vacuum molding although forming the housing body  26  from other materials through other processes is within the scope of the present invention. 
     As illustrated in FIGS. 4 and 5, the battery bypass assembly  10  further includes an expansive material assembly  28  mounted within the housing body  26 . The expansive material actuator assembly  28  includes an actuator diode assembly  30  having an actuator housing  32 . The actuator housing  32  includes a plurality of sidewalls  34  and a threaded opening  36 . A first diode  38  and a second diode  40  are mounted to opposite sidewalls  34  of the actuator housing  32 . In a preferred embodiment, the first diode  38  and the second diode  40  are Schotky diodes having a threshold rating of approximately 0.7 volts although using other types of diodes  38 ,  40  having other threshold ratings are within the scope of the present invention. 
     A first diode contact  42  electrically connected to the first battery contact  14  is mounted to the first diode  38  and a second diode contact  44  electrically connected to the second battery contact  16  is mounted to the second diode  40 . The expansive material actuator assembly  28  additionally includes an actuator output shaft  46  with at least a portion of the actuator output shaft  46  being received within the threaded opening  36  of the actuator housing  32 . A substantially annular resilient O-ring  48  is positioned about the actuator output shaft  46  to releasably secure the actuator output shaft  46  within the threaded opening  36  and creating a void area  50  within the actuator housing  32  threaded opening. A washer  52  is slidably positioned over the actuator output shaft  46  nearingly adjacent the O-ring  48  to assist in guiding the actuator output shaft  46  and providing proper seal clearances, as will be described in further detail below. A threaded actuator plug  54  is slidably mounted over the actuator output shaft  46  and threadably received within the threaded opening  36 . 
     A paraffin or other expansive material  56  is positioned within the void area  50  surrounding at least a portion of the actuator output shaft  46 . The paraffin or other expansive material  56  is designed to expand upon melting thereby forcing the actuator output shaft  46  from the actuator housing  32  through the threaded opening  36 . In a preferred embodiment the paraffin or other expansive material  56  expands by at least approximately fourteen (14%) percent although using a paraffin or other expansive material  56  having an expansion greater than approximately fourteen (14%) percent and less than approximately fourteen (14%) percent is within the scope of the present invention. Actual operation of the battery bypass assembly  10 , including the expansive material actuator assembly  28  will be described in further detail below. 
     At present the battery bypass assembly  10  of the present invention includes a first embodiment as illustrated in FIGS. 1-7 and a second embodiment as illustrated in FIGS. 8-15. The battery bypass assembly  10  of the first embodiment includes a detent slide  58 , as illustrated in FIG. 4, having a first slide surface  60  and a second slide surface  62  with the detent slide  58  slidably mounted within the housing body  26 . The detent slide  58  has an aperture  64  for receiving at least a portion of the actuator output shaft  46 . An actuator spring  66  biases the detent slide  58  in a general direction toward the expansive material actuator assembly  28  thereby maintaining the actuator output shaft  46  within the actuator housing  32  and inhibiting accidental release of the actuator output shaft  46  therefrom during vibrational events such as spacecraft testing and lift-off. 
     A substantially cylindrical detent housing  68 , as also illustrated in FIG. 4, is positioned adjacent the detent slide  58  for allowing the detent slide  58  to freely slide thereon. The detent housing  68  has at least one housing aperture  70  for receiving a substantially spherical ball member  72 . In a first position, the ball member  72  is positioned within the housing aperture  70  between the first slide surface  60  of the detent slide  58  and the detent slide  58 . As the detent housing  58  moves in a general direction away from the expansive material actuator assembly  28  upon expansion of the paraffin or other expansive material  56 , the ball member  72  will move out of the housing aperture  70  of the detent housing  68  and toward the second slide surface  62  of the detent housing  68 . Actual operation of the detent housing  68  and detent slide  58  will be described in further detail below. 
     As illustrated in FIG. 4, the battery bypass assembly  10  of the present invention includes a plunger rod  74  at least partially receivable within the detent housing  68 . The plunger rod  74  has an annular groove  76  aligned with the housing aperture  70  for receiving the ball member  72  therein. An activation spring  78  biases the plunger rod  74  with the ball member  72  maintaining the first and initial position of the plunger rod  74  relative to the detent housing  68 . The activation spring  78  preferably has approximately ten (10 lbs.) pounds of force although other sizes of springs are within the scope of the present invention. 
     As illustrated in FIGS. 4 and 6, the battery bypass assembly  10  of the present invention includes a slidable plunger mechanism  79  contactable by the plunger rod  74  upon release of the plunger rod  74  from the first position. The plunger mechanism  79  includes a first plunger contact  80 , a second plunger contact  82 , and a third contact plunger  84  for contacting the respective bypass contacts  20 ,  22 , and  24 . As illustrated in FIG. 7, each bypass contact  20 ,  22 , and  24  is preferably a flexure contact  86  with multiple contacts  88 . The flexure contact  86  provides increased current capacity because current through each flexure contact  86  is split between the multiple contacts  88  thereby providing better current conduction and more consistent electrical loading between the flexible contact  88  interfaces. Preferably, each flexure contact  86  includes eight (8) flexible contacts  88  machined from a single piece of copper although constructing each flexure contact  86  from other conductive materials and/or several pieces is within the scope of the present invention. 
     When in the first position, the first plunger contact  80  of the plunger mechanism  79  contacts the first bypass contact  20  and the second plunger contact  82  contacts the second bypass contact  22  with the flexure contacts  86  of each bypass contact  20 ,  22  squeezing down on the plunger mechanism  79  thereby closing the circuit between the first bypass contact  20  and the second bypass contact  22 . As the detent slide  58  is moved by action of the expansive material actuator assembly  28 , thereby releasing the ball member  72 , the plunger rod  74  is released and, under the bias of the activation spring  78 , contacts the plunger mechanism  79  and moves the plunger mechanism  79  to a second position. In the second position, the first plunger contact  80  no longer contacts the first bypass contact  20 , the second plunger contact  82  continues to contact the second bypass contact  22 , and the third plunger contact  84  moves into contact with the third bypass contact  24  to electrically connect the plunger mechanism  79  to the second bypass contact  22  and the third bypass contact  24  thereby opening the circuit between the first bypass contact  20  and the second bypass contact  22  and closing the circuit between the second bypass contact  22  and the third bypass contact  24 . The flexure contact  86  self-centers and guides the plunger mechanism  79  while sliding within the housing body  26  from the first position to the second position such that additional mechanisms for guiding the plunger mechanism  79  are not required. 
     The plunger mechanism  79  further includes a stop  90  formed between the second plunger contact  82  and the third plunger contact  84 . As the plunger mechanism  79  moves from the first position to the second position, the stop  90  of the plunger mechanism  79  contacts a shoulder  92  formed in the housing body  26 . The contact between the stop  90  and the shoulder  92  inhibits further movement of the plunger mechanism  79  relative to the housing body  26  to insure the closing of the circuit between the second bypass contact  22  and the third bypass contact  24 . 
     Furthermore, as illustrated in FIG. 4, the battery bypass assembly  10  of the present invention includes a stabilizing spring  94  between the plunger mechanism  79  and the housing body  26  adjacent the first plunger contact  80 . The stabilizing spring  94  maintains the position of the plunger mechanism  79  during vibrational events while in the first position. Preferably the stabilizing spring  79  has a one (1 lb.) pound force although other sizes of springs are within the scope of the present invention. 
     The operation of the first embodiment of the battery bypass assembly  10  of the present invention will now be described. During operation of the battery bypass assembly  10 , the first diode  38  and the second diode  40  of the expansive material actuator assembly  28  sense current through the battery cell  12 . When voltage in the battery cell  12  has dropped to a predetermined voltage, such as when the battery cell  12  is failing or has failed, a back EMF in the circuit through the battery cell  12  causes current to flow through the first diode  38  and the second diode  40 . As current flows through the first diode  38  and the second diode  40 , the first diode  38  and the second diode  40  begin to heat up and the paraffin or other expansive material  56  within the void area  50  of the actuator housing  32  begins to melt and expand. As the paraffin or other expansive material  56  expands, the paraffin or other expansive material  56  forces the actuator output shaft  46  from within the actuator housing  32  and through the threaded opening  36 . The movement of the actuator output shaft  46  overcomes the bias of the actuator spring  66  causing the detent slide  58  to move in a general direction away from the expansive material actuator assembly  28 . 
     As the detent slide  58  moves away from the expansive material actuator assembly  28 , the second slide surface  62  of the detent slide  58  moves over the detent housing  68 . The activation spring  78  forces the ball member  72  from the annular groove  76  of the plunger rod  74 . The removal of the ball member  72  from the annular groove  76  allows the activation spring  76  to bias the plunger rod  74  into contact with the plunger mechanism  79  to move the plunger mechanism  79  into the second position, as described above. The plunger mechanism  79  continues to move until the stop  90  of the plunger mechanism  79  contacts the shoulder  92  formed in the housing body  26 . 
     The second embodiment of the battery bypass assembly  110  of the present invention is illustrated in FIGS. 8-15. As illustrated in FIGS. 8-11 the battery bypass assembly  110  has the main body  118  with a first bypass contact  120  electrically connected to the first battery contact  114  and a second bypass contact  122  electrically connected to the second battery contact  116 . A test contact  124  is provided between the first bypass contact  120  and the second bypass contact  122 . As illustrated in FIG. 15, a fuse assembly  196  is provided between the first bypass contact  120  and the test contact  124 . 
     The battery bypass assembly  110  includes the expansive material actuator assembly  128 , as illustrated in FIG.  13 . The plunger mechanism  179  varies from the above-described plunger mechanism  79  in that the plunger mechanism  179  includes a plunger aperture  181  for receiving a plunger pin  183  resting upon a latch plate  185 , and an annular slot  187  for connecting to a conductive contact bridge  189 . The contact bridge  189  closes the circuit between the first bypass contact  120  and the second bypass contact  122  when the plunger mechanism  179  moves from the first position to the second position, as will be described in further detail below. 
     As in the first embodiment, the plunger mechanism  179  is biased toward the second position by the activation spring  178  with the interaction of the plunger pin  183  against the latch plate  185  maintaining the plunger mechanism  179  in the first position. The latch plate  185  has a rod-receiving slot  191  formed therein for receiving the plunger rod pin  183  upon activation of the expansive material actuator assembly  128  and allowing the plunger mechanism  179  to move into the second position. A latch plate spring  193  biases the latch plate  185  to maintain the latch plate  185  in the first position. 
     The operation of the second embodiment of the battery bypass assembly  110  of the present invention will now be described. During operation of the battery bypass assembly  110  similar to the first embodiment of the battery bypass assembly  10 , the first diode  138  and the second diode  140  of the expansive material actuator assembly  128  sense current through the battery cell  112 . When voltage in the battery cell  112  has dropped to a predetermined voltage, such as when the battery cell  112  is failing or has failed, a back EMF in the circuit through the battery cell  112  causes current to flow through the first diode  138  and the second diode  140 . As current flows through the first diode  138  and the second diode  140 , the first diode  138  and the second diode  140  begin to heat up and the paraffin or other expansive material  156  within the void area  150  begins to melt and expand. As the paraffin or other expansive material  156  expands, the paraffin or other expansive material  156  forces the actuator output shaft  146  from within the void area  150  and through the threaded opening  136 . The actuator output shaft  146  pushes against the latch plate  185  overcoming the bias of the latch plate spring  193  causing the latch plate  185  to move thereby allowing the plunger rod pin  183  to fall through the rod-receiving slot  191  in the latch plate  185 . 
     As the latch plate  185  moves under the force of the actuator output shaft  146 , the plunger mechanism  179  moves into the second position with the contact bridge  189  moving, under the bias of the activation spring  176 , into contact with the test contact  124  and the second bypass  122  contact thereby closing the circuit through the battery bypass assembly  110  of the first battery contact  14  and the second battery  16  contact through the fuse assembly. 
     The battery bypass assembly  10 ,  110  of the present invention is perfectly suited for spacecraft and other environments. The battery bypass assembly  10  of the first embodiment is a perfectly suited for lithium ion battery cells in that it is a “make before break” bypass. The battery bypass assembly  10  maintains a continuous circuit with no interruption of current flow. The battery bypass assembly  110  of the second embodiment is a direct shorting device bypass which simply closes the new circuit which is perfectly suited for all other types of battery cells. Furthermore, in the second embodiment, the battery bypass assembly  110  includes a safety device, i.e., the fuse assembly  196  in case the battery bypass assembly  110  was to inadvertently close the circuit of a fully charged or “good” battery cell  112 . 
     The foregoing exemplary descriptions and the illustrative preferred embodiments of the present invention have been explained in the drawings and described in detail, with varying modifications and alternative embodiments being taught. While the invention has been so shown, described and illustrated, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention, and that the scope of the present invention is to be limited only to the claims except as precluded by the prior art. Moreover, the invention as disclosed herein, may be suitably practiced in the absence of the specific elements which are disclosed herein.