Abstract:
A door handle and actuation assembly for opening a door of a vehicle includes a striker and a latch assembly. The latch assembly includes a latch biased to engage the striker to secure the vehicle door in a closed position. A first latch actuator is configured to receive an electronic signal for disengaging the latch from the striker. A second latch actuator is redundant to the first latch actuator and a power source is available for providing an electrical signal to the second latch actuator. The second latch actuator includes a shape memory alloy having a first configuration and a second configuration that different from the first configuration when subject to an electrical current. The second configuration is cooperable with the latch assembly for disengaging the latch from the striker.

Description:
PRIOR APPLICATIONS 
       [0001]    The present application claims priority to U.S. patent application Ser. No. 62/078,684, filed Nov. 12, 2014, the contents of which are included herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates toward an electronic latch actuator for a vehicle door. More specifically, the present invention relates toward a low-voltage backup assembly for actuating an electronic latch using a secondary power source. 
       BACKGROUND 
       [0003]    Mechanical devices on vehicles are being replaced with electronic devices on an ever-increasing basis. One such example is replacement of mechanically-actuated latches used for opening doors, tailgates, and trunks of motor vehicles with electronic latches. Electronic latches use power from a primary vehicle power source such as, for example, a 12-volt vehicle battery for powering an integrated servo motor. Electronic latches typically include a latch (or pawl) that locks onto a striker to securely close a vehicle door. Presently, electronic latches are actuated by servomotors that require a significant amount of electrical energy to disengage the latch from the striker. However, this arrangement is ineffective if a vehicle battery loses power. In such instances, the servomotor, not having been powered, is incapable of disengaging the latch from the striker. The result is an inability to gain access to a vehicle interior when the vehicle battery has lost power. Additionally, redundant mechanically-actuated devices are typically required to actuate an interior door latch from the vehicle interior to prevent an occupant from being trapped in the interior upon loss of power to the vehicle battery. 
         [0004]    To overcome a loss of primary battery power, super capacitors that retain an electrical charge are included providing energy to both a sensor disposed in a door handle and the servomotor used to disengage the latch from the striker to open a vehicle door. However, super capacitors are known to lose their charge at low temperatures such as, for example, negative 40° C., which is typical of northern climates. Additionally, super capacitors are known to be heavy. To provide sufficient power and low temperatures, multiple super capacitors have been employed to reach a voltage level necessary to operate the servo motors and gear train drives used in current latch assemblies. The use of a super capacitor with this design is not considered very functional. Therefore, an improved electronic latch assembly capable of operating at very low temperatures and low voltage for actuating a vehicle latch would be desirable. 
       SUMMARY 
       [0005]    A door handle and actuation assembly for opening a door of a vehicle includes a striker and latch assembly. A latch assembly includes a latch to engage the striker to secure the vehicle door in a closed position. The first latch actuator is configured to receive an electronic signal for disengaging the latch from the striker. A second latch actuator is redundant to the first latch actuator and a secondary power source is available for providing an electrical signal to the second latch actuator. The second latch actuator includes a shape memory alloy having a first configuration and a second configuration that is different from the first configuration when subject to an electrical current. The second configuration is cooperable with the latch assembly to disengage the latch from the striker. The shape memory alloy provides the ability to actuate a latch assembly with very low voltage, for example, three volts or less. This allows the ability to provide a secondary power source that is both compact and light, such as, for example, a lithium ion battery providing a secondary power for the secondary actuation assembly to open a vehicle door in the event insufficient power is provided to a servomotor from a main power source of the vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Other advantages of the present invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0007]      FIG. 1  shows an environmental view of a vehicle door actuation assembly disposed upon a vehicle; 
           [0008]      FIG. 2  shows a schematic of the assembly of the present invention for actuating a door latch of a vehicle; 
           [0009]      FIGS. 3A and 3B  shows a shape memory alloy device; 
           [0010]      FIG. 4  shows one embodiment of assembly of the present invention; and 
           [0011]      FIGS. 5A-5D  show an alternative embodiment for storing energy sufficient to actuate an electronic vehicle door latch without the use of a vehicle battery. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , a vehicle using the apparatus of the present invention is generally shown at  10 . A front vehicle door  12  includes a door handle  14  and an actuation assembly  16  used to open and close the vehicle door  12  as will be explained further herein below. For simplicity, the actuation assembly  16  is shown only on the front vehicle door  12 , but the actuation assembly may also be included on a rear vehicle door  18  and trunk or deck lid, (not shown) as desired. 
         [0013]    Referring now to  FIG. 2 , the latch actuator assembly  16  provides electronic actuation by way of a servomotor (not shown) or other electrical device. As best shown in  FIG. 4 , a latch assembly  20 , which is included in the latch actuator assembly  16  disengages a pawl or latch  22  from a striker  24  when actuated by the servo motor. The striker is securely mounted on a pillar  26  of the vehicle  10  while the latch assembly  20  is securely mounted on the vehicle door  12 , each in a known manner. 
         [0014]    Referring again to  FIG. 2 , a latch control  28  sends an electronic signal to the latch assembly actuator  16  as represented by dashed lines used throughout  FIG. 2 . The latch control  28  signals the latch assembly actuator  16  to actuate the latch assembly  20  when receiving a signaled intent to actuate the latch assembly  20 . The latch control  28  receives the signal from a variety of sources, including the exterior door handle  14 , interior door handle  30 , and a keypad  32 . It should be understood that the exterior door handle  14 , interior door handle  30  and keypad  32  are meant to be exemplary and not limiting. Other sources of a signal to the latch control  28  include, for example, a cellular phone (not shown), a remote cellular signal, a motion sensor, a proximity sensor, or any other electronic device capable of signaling the latch control  28 . In addition, the interior door handle  30  may also include a mechanical link to the latch assembly actuator  16  to provide the method of mechanically actuating the latch assembly  20  in an emergency situation. 
         [0015]    For security, a key FOB  34  optionally signals a receiver/transmitter (not shown) in the door handle  14  or other vehicle component that subsequently signals the latch control  28  authority to actuate the latch assembly  20 . The latch control  28  will not signal the latch assembly  20  to actuate the latch  22  without also sensing a presence of a key FOB  34 , or other security device to verify authorization to actuate the latch  22 . Additionally, the key FOB  34  need not be present if an intent to actuate the latch  22  is signaled from the interior door handle  30 . 
         [0016]    A power source  36  secondary to a main vehicle battery (not shown) provides electrical energy to the latch control  28  and to a shape memory alloy actuator (SMA)  38 . The secondary power source  36  is separate and independent of the primary vehicle battery and is capable of providing electric current to the latch control  28  and to the SMA actuator  38  when the main vehicle battery has lost its electrical charge. While the secondary power source  36  is contemplated to be a coin-type lithium ion battery, it can further take the form of conventional batteries, rechargeable batteries, small capacitors, or any other device capable of holding an electrical charge independent of the primary vehicle battery. It is further contemplated by the inventors that the secondary power source  36  is rechargeable when electric energy is received from the primary vehicle battery, an alternator, or in the event of an electric vehicle, when a charge is received while charging the vehicle batteries from an external source of electrical power. 
         [0017]    The SMA actuator  38  includes an SMA device  40  as best represented in  FIGS. 4A and 4B . The SMA device  40  includes a plastically-deformable alloy member  42  comprising a shape memory alloy, or equivalent disposed in a first configuration  44  generally shown in  FIG. 4A . A first connector  46  securely engages a lever  47  or equivalent force transfer element of the latch  22  (shown in  FIG. 4 ). A second connector  48  is fixedly attached in an immovable position relative to the latch  22  and first connector  46 . Further, the second connector  48  is adapted to receive electrical current from the secondary power source  36 , which is used to raise the temperature of the alloy member  42  causing plastic deformation of the alloy member  42  to a second configuration  45  as shown in  FIG. 4B .  FIG. 4B  shows a contraction of the alloy member  42  causing the first connector  46  to move in the direction of arrow  50  translating mechanical motion to the latch  22  to disengage the striker  24 . 
         [0018]    It should be understood that when no electrical current is transferred to the alloy member  42  through the second connector  48 , the alloy member  42  returns to ambient temperature causing the alloy member  42  to return to a first configuration shown at  44  from the second configuration shown at  60 . The SMA actuator  38  is capable of generating sufficient force to disengage the latch  22  from the striker  24  with a minimal amount of electrical energy. For example, three volts or less received from the secondary power source  36  is capable of providing enough heat energy to the alloy member  42  to generate enough force to disengage the latch  22  from the striker  24 . It should be further understood that alternative methods of raising the temperature of the alloy member  42  are within the scope of this invention and that the examples set forth above are merely exemplary and not limiting in nature. 
         [0019]    An alternative embodiment is shown in  FIGS. 5A-5C  where mechanical energy sufficient to disengage the latch  22  from the striker  24  is disclosed for further reducing the amount of electrical energy required to disengage the latch  22  from the striker  24 . A rotary member  52  includes a plurality of ratchet teeth  54  that engage a pawl  56 . The pawl  56  is biased to engage the ratchet teeth  54  to prevent the rotary member  52  from rotating in a clockwise direction as the ratchet member  52  is biased to do so. The bias is derived from a coil spring  58  or equivalent to rotate the rotary member  52  in the clockwise direction. A first SMA device  58  is fixedly attached to a translation arm  60  that translates counterclockwise motion to the rotary member  52  when electrical current is provided causing the first SMA device  58  to move from a first configuration  44  to a second configuration  48  as set forth above. 
         [0020]    The first SMA device  58  is electrically linked to the vehicle car battery (not shown) or other source of electrical power to continuously receive enough electrical energy to maintain the first SMA device  58  in the second configuration  50 . Therefore, when the vehicle battery loses power, the first SMA device  58  returns to the first configuration  44  enabling the rotary member  52  to rotate in a counterclockwise direction when not engaged with the pawl  56 . Alternatively, electrical current is provided to the first SMA device  58  only a sufficient amount of time to translate the first SMA device  58  from the first configuration  44  to the second configuration  48  relying on the pawl  56  to maintain the rotary member  52  in a biased disposition. In this embodiment, the first SMA device  58  provides no additional force upon the rotary member  52  once it is rotated in a counter clockwise direction an amount sufficient to fully load the rotary member. 
         [0021]    A second SMA device  62  is affixed to the pawl  56 . The second SMA device  62  receives an electrical charge from the secondary power source  36  when signaled to do so by the latch control  28  as set forth above. Upon receiving the electrical charge from the secondary power source  36 , the second SMA device contracts from the first configuration  44  to the second configuration  48  disengaging the pawl  56  from the ratchet teeth  54  of the rotary member  52  allowing the rotary member  52  to rotate in a clockwise direction thereby releasing the latch  22  from engagement with the striker  24 . In this manner, even less force is required to be generated by the second SMA device  62  because the necessary mechanical energy to actuate the latch  22  has been translated to the coil spring  55  by the first SMA device  58  when receiving adequate electrical power from the primary vehicle battery. Therefore, only enough electrical energy to disengage the pawl  56  from the rotary member  52  is required. 
         [0022]    The invention has been described in an illustrative manner, that is to be understood that the terminology that has been used is intended to be in the nature of words a description rather than that of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within this specification, the referenced numerals are merely for convenience, and are not to be in any way limiting. Therefore, the invention may be practiced otherwise and is specifically described throughout the specification.