Abstract:
A switch assembly for triggering the release of a door latch that provides improved tactile feedback to a user when actuated is disclosed. The switch assembly provides a tactile response to the user that indicates proper actuation by the force feedback that is provided to the user as the button is displaced during actuation. The switch assembly includes an elastomeric button and a base supporting the button. An electrically conductive static contact is supported by the base. An electrically conductive moveable contact, also supported by the base, is operatively disposed between the button and the static contact. A film is disposed over the moveable contact and fixed to the edge of the base, sealing both contacts from the atmosphere. The film thereby effectively divides the interior of the switch assembly into an open first chamber located between the film and the button, and a closed second chamber located between the film and the base.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to door mechanisms for automobile and other vehicle applications and, more particularly, to a switch assembly for an electro-mechanical door latch mechanism.  
       BACKGROUND OF THE INVENTION  
       [0002]     Traditionally, mechanical devices have been used to latch and unlatch closures such as doors, trunks, hoods, lift gates and hatches and the like in automobiles and other vehicles. It is known, however, to utilize an electro- mechanical door latch mechanism for such applications for a variety of reasons including ease of operation, lower cost and weight, improved styling opportunities, and reduced complexity. For example, a user actuated switch can be employed to trigger the release of a mechanical latch. In this regard, an electrical switch is operable to provide an input to a controller for operating the mechanical latch when the switch is actuated. In addition, modern styling and ergonomic requirements may dictate the physical configuration of the switch. For example, the switch may need to comprise an aesthetically pleasing user actuation component (e.g., a low profile button) that is of adequate size and shape so as to be easily operated by a user under a wide variety of operating conditions in a wide variety of environments.  
         [0003]     Known switch technology for such applications generally incorporates a button having a first electrically conductive material comprising protrusions having the shape of “pills” or spring-like “fingers” that are insert molded or otherwise attached to the underside of the button. A second electrically conductive material comprising a set of contacts is located opposite the button on a base portion of the switch assembly. The second electrically conductive material may typically be in the form of a plate, tracks or a printed circuit board, for example. The first electrically conductive material completes a circuit in the switch when the switch is actuated by depressing the button. For example, when the button is depressed, the first conductive material bridges the contacts of the second electrically conductive material thereby closing an electric circuit.  
         [0004]     In one such known switch assembly configuration, the switch assembly is also sealed from the atmosphere. During its manufacture, a fixed volume air is captured in the space between the button and the base portion of the switch assembly. As such, when the ambient temperature of the switch assembly changes, so too does the volume of the air trapped within the switch assembly. Under hotter ambient temperature conditions the volume of air within the switch assembly expands; under colder ambient temperature conditions, the volume of air within the switch assembly contracts.  
         [0005]     In such a design, changes in the switch assembly&#39;s operating environment, such as extreme changes in ambient temperature, for example, can impact the perceived operation of the switch to a user. For example, the switch assembly may not reliably provide satisfactory and perceptible tactile feedback to the user signifying actuation of the switch. In such a case, depression of the button may instead provide an unsatisfactory continuous resistance to the user causing the user to be unsure whether the switch has been properly actuated.  
         [0006]     Consequently, it is desirable to provide a switch assembly having a reliable and cost-effective actuation mechanism that also provides satisfactory tactile feedback to a user for signifying proper actuation of the switch.  
       SUMMARY OF THE INVENTION  
       [0007]     A switch assembly for triggering the release of a door latch that provides improved tactile feedback to a user when actuated is disclosed. In operation, the switch assembly closes a circuit that is monitored by a controller. Upon switch actuation, the controller operates a motor or solenoid, for example, to disengage a mechanical latch.  
         [0008]     The switch assembly includes an elastomeric button and a base supporting the button. An electrically conductive static contact is supported by the base. An electrically conductive moveable contact, also supported by the base, is operatively disposed between the button and the static contact. A film is disposed over the moveable contact and fixed to the edge of the base, sealing both contacts from the atmosphere. The film thereby effectively divides the interior of the switch assembly into an open first chamber located between the film and the button, and a closed second chamber located between the film and the base.  
         [0009]     Depression of the button deforms the button, the film and the moveable contact and brings the moveable contact into engagement with the static contact. Upon release of the button, the button, the film and the moveable contact return to their undeformed configurations, and the moveable contact disengages the static contact.  
         [0010]     The switch assembly provides a tactile response to the user that indicates proper actuation. The tactile response is accomplished by the force feedback that is provided to the user as the button is displaced during actuation. In this regard, the button is depressed through a first range of travel that requires a first increasing amount of force, followed by a second range of travel that requires a decreasing amount of force, and concluding with a third range of travel that requires a second increasing amount of force.  
         [0011]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.  
         [0013]      FIG. 1  is a side elevational view of an automobile showing a schematic representation of an electro-mechanical door latch mechanism in accordance with a preferred embodiment of the invention;  
         [0014]      FIG. 2  is a perspective view of a switch assembly in accordance with a first preferred embodiment for use in the electro-mechanical door latch mechanism shown in  FIG. 1 ;  
         [0015]      FIG. 3  is an exploded perspective view of the switch assembly shown in  FIG. 2 ;  
         [0016]      FIG. 4  is an enlarged, partial perspective view of the switch assembly of the invention with a button portion removed and showing an electrical connector connected to a movable contact and a static contact;  
         [0017]      FIG. 5  is a cross-sectional side view of the switch assembly of  FIG. 2  along the line  5 - 5 ;  
         [0018]      FIG. 6  is a cross-sectional side view of the switch assembly of  FIG. 2  as shown in  FIG. 5 , wherein the button has been partially depressed;  
         [0019]      FIG. 7  is a cross sectional side view of the switch assembly of  FIG. 2  as shown in  FIG. 6 , wherein the button has been further depressed beyond that shown in  FIG. 6  to a position resulting in engagement between the moveable contact and the static contact; and  
         [0020]      FIG. 8  is a graph illustrating a force/displacement curve of the switch assembly of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]      FIG. 1  shows an automobile  14  including a door  10  that is movable between an opened and a closed position. The door  10  is secured in the closed position by an electro-mechanical door latch mechanism  15 . The electro-mechanical door latch mechanism  15  may comprise a user-actuated switch assembly  22 , a controller  20  (e.g., a computer), a solenoid  18  (or, alternatively, an electric motor), and a mechanical latch  16  (which may or may not be integral to the solenoid  18 ).  
         [0022]     In order to open the door  10 , the latch mechanism  15  securing the door  10  must first be released. Release of the latch mechanism  15  is triggered by a user&#39;s manual actuation of the switch assembly  22 . The switch assembly  22  provides a low-current electrical connection when actuated. The controller  20  monitors the switch assembly  22  for a change in state. When the controller  20  receives an input signal from the switch assembly  22 , the controller  20  operates the solenoid  18  to disengage the mechanical latch  16 , enabling the door  10  to be opened.  
         [0023]     Although it is illustrated in  FIG. 1  in the context of an automobile door, it should be appreciated that the latch mechanism  15  may be utilized for securing hoods, trunks, lift gates, sliding doors, hatches, or the like, on automobiles and other vehicles.  
         [0024]     With reference to  FIGS. 2 and 3 , a switch assembly  22  according to a preferred embodiment of the invention is shown. The switch assembly  22  generally includes a button member  30 , a film  32 , a moveable contact  34 , a static contact  38 , a base member  40  and an electrical connector  42 .  
         [0025]     The button member  30  and the base member  40  are cooperable to form the outer shell of the switch assembly  22 . The button member  30  is sized to fit around an outer perimeter  44  of the base member  40  in an assembled position. An aperture  46  is located in the base member  40  to provide access for the electrical connector  42 . The aperture  46  is then sealed. In an assembled configuration, a pair of leads  48  from an end of the electrical connector  42  are electrically connected to the moveable contact  34  and the static contact  38 , respectively.  
         [0026]     The button member  30  is preferably of a unitary construction and is made from a flexible, elastomeric material. The wall thickness of the button member  30  may vary (as shown in the cross-sectional view of  FIG. 5 ) to achieve the desired physical characteristics and operating features for the button member  30 , as will become apparent from the discussion below.  
         [0027]     The button member  30  generally includes a central actuation portion  50  and a peripheral flange portion  52 . Located intermediate the actuation portion  50  and the flange portion  52  is a peripheral wall portion  60 . The actuation portion  50  has an exterior surface or face  54 , and an interior surface  56  (see  FIG. 5 ). The actuation portion  50  generally has a material thickness that is greater than that of the wall portion  60 . Consequently, the actuation portion  50  can be, relatively, stiffer than the wall portion  60 .  
         [0028]     Assembly of the button member  30  to the base member  40  is accomplished by the peripheral flange portion  52  of the button member  30 . The peripheral flange portion  52  fits snugly around the outer perimeter  44  of the base member  40  and secures the button member  30  to the base member  40 .  
         [0029]     The wall portion  60  extends outwardly at an angle from the actuation portion  50  to the flange portion  52 . The angle illustrated in the drawings is approximately 45 degrees from the plane defined by the exterior surface  54  actuation portion  50 . It is appreciated that the wall  60  may define other angle(s) while maintaining the functionality of its construction, as is further described herein.  
         [0030]     Referring to the cross-sectional side view of  FIG. 5 , the base member  40  has a generally tiered configuration, comprising a plurality of ledges at different vertical levels, as viewed. A first, outer ledge  72  provides a surface for supporting the film  32 . A second, intermediate ledge  74  is located inward and below of the outer ledge  72  and supports the moveable contact  34  in its position located between the film  32  and the static contact  38 . An interior surface  64  ( FIGS. 3-4 ) of the base member  40  supports the static contact  38  beneath both the film  32  and the moveable contact  34 . The base member  40  may be made from a relatively rigid, lightweight material, such as plastic.  
         [0031]     Illustrated in  FIG. 3 , a plurality of column-like projections or posts  66  are shown to project upward from an interior surface  64  of the base member  40 . The projections  66  on the base member  40  are adapted to locate and secure the static contact  38  to the base member  40  by means of complementary apertures  70  in the static contact  38 . It is appreciated that the static contact  38  may be alternatively located and secured to the base member  40  by any other suitable means. Although shown in the FIGS. as being generally cylindrical, it should be understood that the projections  66  and corresponding apertures  70  may take any desired geometric shape, such as square, rectangular, triangular, polygonal and the like.  
         [0032]     The moveable contact  34  is shown to generally comprise a thin, ribbon-like electrically conductive material. As such, the moveable contact  34  can be made from and/or plated with a suitable electrically conductive material like the precious metals gold and silver. The ribbon preferably defines a pattern (for example, a serpentine pattern, as shown) to promote engagement with the static contact  38  upon depression of any part of the actuation portion  50  of the button member  30 . That is, no matter where on the button member  30  the user presses, a portion of the moveable contact  34  will be able to come into engagement with the static contact  38 .  
         [0033]     The moveable contact  34  also preferably possesses spring-like characteristics, enabling it to deflect or deform when forced into engagement with the static contact  38  by depression of the button member  30  and then return to an undeflected or undeformed configuration when the depression force is removed. As shown in  FIG. 5 , the moveable contact  34  is arched or bowed away from the static contact  38  and toward the film layer  32  such that it is biased against the depression force put on the button member  30  during actuation of the switch assembly  22 .  
         [0034]     The film  32  encloses the moveable contact  34  and static contact  38  within a space between the film  32  and the base member  40 . The film  32  is adhered or otherwise sealingly fixed about its perimeter to the base member  40  at the outer ledge  72 . For example, the film  32  can be laminated about its perimeter with an adhesive material  75  on a portion of an undersurface  78  (shown in  FIG. 3 ). The adhesive material  75  is then sandwiched between the film  32  and the ledge  72  of the base member  40  to create an air-tight seal between the film  32  and the base member  40 .  
         [0035]     As already mentioned, the passage  46  in the base member  40  is also sealed during assembly. For example, a sealing agent such as epoxy  79  can be deposited at the passage  46  in the base member  40  and around the electrical connector  42  to form an air-tight seal (see  FIG. 4 ).  
         [0036]     The film  32  is thin, flexible and is capable of deflecting or deforming under a load, but retaining its original configuration when the load is removed. A polyester film such as, but not limited to, Mylar® manufactured by the Dupont Corporation, is a suitable material for the film.  
         [0037]     The seal provided between the film  32  and the base member  40  interface, as well as the seal provided at the passage  46  creates a small-volume, air-tight chamber  80  (see  FIG. 5 ). The air-tight chamber  80  closes the moveable contact  34  and the static contact  38  from the atmosphere. The volume of air sealed in the air-tight chamber  80  is minimal and design parameters for the moveable contact  34  may be altered or modified to accommodate changing requirements without affecting performance of the switch assembly  22 . Moreover, extreme changes in the ambient environment of the switch assembly  22 , such as extreme temperature changes have negligible, if any, affect on the operation of the switch assembly  22  because of the very small volume of air in the air tight chamber  80 .  
         [0038]     As already discussed, once assembled, the peripheral flange portion  52  of the button member  30  is wrapped around the outer perimeter  44  of the base member  40 . The elastomeric properties of the button member  30  promote a gripping action between the button member  30  at the interface with the base member  40 . However, air can pass between the peripheral flange portion  52  and the outer perimeter  44  during depression and release of the button member  30 . A vented chamber  84  (see  FIG. 5 ) is therefore created, comprising the space enclosed between the button member  30  and the film  32  of the switch assembly  22 , that is not sealed from the atmosphere. Consequently, the switch assembly  22  includes two chambers—an air-tight chamber  80  and a vented chamber  84 .  
         [0039]     The elastomeric properties of the button member  30  together with the two chamber configuration (vented and sealed) of the switch assembly  22  cooperate to provide desirable tactile feedback to a user during operation of the switch assembly  22 . With reference to  FIGS. 5-7  and  FIG. 8 , the operation of the switching assembly  22  will be described.  
         [0040]      FIG. 5  illustrates the switch assembly  22  in an open, non-actuated position.  FIG. 6  shows the button member  30  of the switch assembly  22  partially deformed and depressed to an intermediate position just touching the film  32 . Displacement of the button member  30  from the open, non-actuated position ( FIG. 5 ) to the intermediate position ( FIG. 6 ) forces air contained in the vented chamber  84  to escape from the chamber  84  at the interface between the peripheral flange portion  52  and the outer perimeter  44 .  
         [0041]     Further depression of the button member  30  causes continued movement of the button member  30  from the intermediate position ( FIG. 6 ) to the actuated position ( FIG. 7 ). Displacement of the button member  30  to the actuated position ( FIG. 7 ) causes the film  32  and moveable contact  34  to deflect toward the static contact  38  until the moveable contact  34  engages static contact  38  thereby completing the circuit.  
         [0042]     The movement of the button member  30  from the intermediate position ( FIG. 6 ) to the actuated position ( FIG. 7 ) causes the volume of air in the air-tight chamber  80  to be at least partially compressed and or redistributed beneath the film  32 . A gap  100  ( FIG. 4 ) is provided at a peripheral boundary between the static contact  38  and the base member  40  to accommodate a portion of air volume in the air-tight chamber  80  to ensure the adhesive seal  75  at the interface between the film  32  and the base member  40  is not compromised.  
         [0043]     The graph illustrated in  FIG. 8  plots the actuation force required to depress the button member  30  versus travel of the button member  30  during operation of the switch assembly  22 . Point D, represents the point of initiation of switch actuation by the user ( FIG. 5 ). At D 1 , the button member  30  has not moved, and an actuation force is required to initiate movement of the button member  30 . At point D 2  the button member&#39;s  30  resistance to travel begins to decrease, such as when the wall portion  60  collapses or buckles. The force required by the user also begins to decrease. Point D 3  represents a point in the continued travel of the button member  30 , just before the button member  30  first contacts the film  34 , where the button member&#39;s  30  material properties and design configuration cause the actuation force to begin to increase, such as when the wall portion  60  becomes taught as a result of continued depression of the button member  30 . Point C represents the point at which the button member  30  just makes first contact with the film  32  ( FIG. 6 ). Point D 4  represents engagement between the moveable contact  34  and the static contact  38  and the button member  30  is precluded from further travel ( FIG. 7 ).  
         [0044]     As shown, the graph depicts three distinct areas of force progression during actuation of the switch assembly  22 . More specifically, the graph defines a first increasing force range  88  (from point D 1  to D 2 ), an intermediate decreasing force range  90  (from point D 2  to D 3 ), and a final increasing force range  92  (from point D 3 to D 4 ).  
         [0045]     In addition, in moving from its initial position ( FIG. 5 ) to its intermediate position ( FIG. 6 ) the button member  30  collapses the vented chamber  84  until it just contacts the film  32 . This button travel, which is from point D, to point C, defines a vented range identified at reference  94  in  FIG. 8 . The material properties and design configuration of the button member  30 , together with the escape of air from the vented chamber  84 , substantially oppose the actuation force during the vented range  94 .  
         [0046]     Displacement of the button member  30  from point C to point D 4  defines a sealed range identified at reference  98  in  FIG. 8 . It is presently contemplated that travel in the sealed range  98  will take place entirely within the final increasing range  92 . In the sealed range  98 , in addition to the material properties and design configuration of the button member  30 , the spring-like properties of the film  32  and moveable contact  34 , and the compression of the air in the air-tight chamber  80 , also oppose the actuation force.  
         [0047]     As represented in  FIG. 8 , about three-fourths of the total travel of the button member  30  occurs during the vented range  94 . Consequently, only about one-fourth of the total travel of the button member  30  occurs during the air-tight range  98 , through depression of the moveable contact  34  into engagement with the static contact  38 . Total travel of the button member  30  through said first, second and third range of travel can collectively defines about 1.5 mm.  
         [0048]     When the moveable contact  34  engages the static contact  38 , the switch assembly  22  closes electrically. When the button member  30  is released (i.e., the actuation force is removed), the button member&#39;s  30  design configuration and material properties cause it to return back to its undeflected/undeformed, non- actuated configuration ( FIG. 5 ). Likewise, the spring-like characteristics of the film  32  and the moveable contact  34 , cause the film  32  and the moveable contact  34  to return their undeflected/undeformed positions breaking engagement between the moveable contact  34  and the static contact  38  and opening the switch.  
         [0049]     The configuration of the switch assembly  22  of the present invention provides desirable tactile feedback to the user. The switch assembly  22  of the invention causes the user to experience a variable sequence of force to accomplish actuation of the switch. During depression of the button member  30 , the user experiences an initial increase of force (range  88 ) followed by an appreciable decrease in force (range  90 ), and finally an increase in force (range  92 ). Progression of the button member  30  through this sequence provides appreciable feedback to the that a successful actuation has been completed.  
         [0050]     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modification will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.