Key assembly for vehicle ignition locks

A method of decreasing resonant frequency shifting of an electrical circuit mounted on a vehicle key includes providing a frame in an opening in the head portion of a vehicle key and locating the transponder in the frame. The frame comprises substantially rigid non-metallic material, and the frame includes a support structure for supporting the transponder while decreasing forces produced on the transponder by thermal expansion and contraction of the head portion of the key, thereby decreasing shift in the resonance of the electrical circuit of the transponder. The frame, the transponder and the head portion of the key are overmolded providing an outer covering that encloses and protects the transponder.

BACKGROUND OF THE INVENTION

The present invention relates to an automobile security system, and more particularly, to a key assembly for use in a vehicle ignition and lock unit.

Various types of security systems used in conjunction with the ignition circuit of a vehicle are known in the art. Many of these systems include anti-theft and/or anti-tampering mechanisms which are incorporated to deter the unauthorized use of vehicles. An electronic vehicle ignition lock is a component of some of these systems which can increase vehicle security and even lower insurance rates in some countries.

An electronic interlock system uses a coded activation signal which enables a vehicle operator to run a vehicle. Coded activation signals are generally read electronically within an ignition lock and subsequently sent to an electronic control module. The electronic control module controls engine operation and enables the vehicle to run only if the correct activation signal is received. Therefore, an electronic interlock system prevents a vehicle from running even if the ignition lock is bypassed or pulled. This system makes vehicle theft more difficult and time consuming.

The ignition keys employed for use with electronic interlock systems traditionally contain mechanical and/or electronic interlock codes. One such system incorporates a resistor pellet in the ignition key. The resistor pellet provides a resistor of a resistance such that when the ignition key is inserted into and rotated within a vehicle's ignition cylinder unit, an electrical current is applied through the resistor. A decoding circuit determines if the resistance of the resistor pellet in the ignition key is within a predetermined resistance “window.” If the resistance provided by the resistor pellet in the ignition key is within the predetermined resistance range, the vehicle will run. To the contrary, if the resistance falls outside of the predetermined resistance window, the vehicle will not run. Examples of these interlock systems and associated keys are illustrated in U.S. Pat. Nos. 4,250,482, 5,083,362 and 5,156,032.

In another electronic interlock system, radio frequency identification (RFID) is used in the enabling or disabling of engine operation. An RFID interlock system consists of a reader which sends a signal to an antenna associated with a transponder that is mounted in a key. The transponder includes a transponder circuit, which can comprise an integrated circuit or discrete components, and a resonant circuit formed by a capacitor and an inductor or coil. The signal energizes the transponder, and the transponder responsively transmits a unique identification code back to the reader which decodes the identification code. If the signal transmitted by the transponder represents a valid identification code, the reader transmits this information to the vehicle's electronic control module thereby enabling engine operation. However, if the signal is not a valid identification code, the reader causes the electronic control module to prevent engine operation. Typically, the antenna associated with the transponder produces a relatively high energy electromagnetic field which is coupled to the coil of the transponder and converted to a DC voltage which is used to power the electronic circuits of the transponder. The transponder transmits its unique identification code in the form of a low energy radio frequency signal that is received and decoded by the reader as described above.

Precisely because RFID electronic interlock systems are such effective security devices, it is critical that these systems work dependably in all the conditions a vehicle might encounter. The result of an RFID system failure is that a vehicle owner, or other person properly in possession of the keys for a given vehicle, is stranded and unable to bypass the interlock system to operate the vehicle. Electronic interlock systems are industry specified. Industry test configurations and requirements reflect conditions and circumstances which RFID interlock systems might actually encounter and, therefore, are a fairly reliable indicator of the dependability of the security systems.

Older RFID systems used transponder chips that are packaged in glass vials, often containing silicone, in an effort to protect the electronic components contained within the vials. Developments in the electronic industry have resulted in transponders that are overmolded with plastic and such transponders have gained wide acceptance in RFID interlock systems for vehicles. Recently, the inventors have discovered that harsh operating conditions affect the performance of RFID interlock systems in which the transponders are packaged in plastic material. However, RFID systems employing such transponders molded in key heads meet industry requirements, only when used with relatively expensive receivers.

One of the most popular configurations of transponders currently available is produced by Texas Instruments, Inc., as Texas Instruments, Inc. part number RI-TRP-W9WK. Another popular transponder configuration is that manufactured by Motorola, as Motorola part no. 05504-001. Both transponders include an overmold of a plastic material with electronic components located substantially within the overmold.

SUMMARY OF THE INVENTION

The inventors have found a problem involving a shift in inductance of the coil and the capacitance of the capacitor of the resonant circuit of the transponder which affects the operation of RFID security systems which occurs when the transponders are used in conjunction with prior key assembly designs. A shift in the inductance and capacitance of the transponder's resonant circuit changes the resonant frequency of the transponder which can result in failure of the transponder to receive the interrogation signal being transmitted, or in the weakening of the strength of the signal sent to the receiver so that the receiver cannot detect signals transmitted by the transponder. The end result is that the vehicle engine cannot be started and/or run using the ignition or otherwise. The shift is believed to result from mechanical and/or thermal effects which produce forces upon the transponder, ultimately shifting the resonant frequency of the transponder. The greatest shift in resonant frequency, occurs in cold temperatures. For the Motorola and Texas Instruments, Inc. transponders, resonant frequency shift can be up to about 7 KHz, depending upon material in which the transponder is molded.

Decreasing, with the ultimate goal of completely eliminating, the amount of resonant frequency shift associated with the transponder eradicates the problem described herein above concerning RFID ignition lock systems. Testing has demonstrated that shifting in the resonance of the transponder is reduced when there is minimum contact between the transponder and any substantially rigid material that supports the transponder in the key assembly. Testing also has demonstrated that reducing the mass of the substantially rigid material that is located adjacent to the transponder in the key assembly reduces the shift. These favorable results are believed to be attributable to minimizing external forces applied to the transponder by limiting the force transmitting ability of the substantially rigid material structure adjacent to the transponder.

In accordance with the invention, both mechanical and thermal considerations are incorporated into improving the key assembly design to make RFID systems more dependable. Mechanical considerations are addressed in the structural design of the key assembly, and thermal considerations are addressed through the careful selection of construction materials and structural design, so that a delicate balance is achieved in the improved key design provided by the invention.

Achieving a balance between the mechanical and thermal considerations is critical because of their interrelated nature. Constructing the key head of a relatively hard material alleviates mechanical problems concerning key head deformation or failure from shear or torsional forces. However, the nature of harder plastic material is such that it tends to cause higher forces to be applied to the transponder under temperature excursions. Correspondingly, using a relatively soft plastic material to construct the key head tends to abate thermally-related problems because such material is less likely to produce high forces on adjacent components than does a harder material. However, the softer material is more prone to mechanical deformation by externally applied forces. This softer material can also adversely impact the structural integrity of the key head. The present invention attains a delicate equilibrium between minimization of the adverse effects of thermal expansion and contraction and mechanical stability.

The operating characteristics of transponders can be changed by forces caused by thermal expansion and contraction, and by impact force and compressive force occurring during manufacturing of the key assembly, especially during the molding processes. Two procedures have been found by the inventors to alleviate damage due to impact force applied to the transponder during the molding process. These procedures include the use of a specially gated, two-step molding process for producing the key assembly and the use of a novel frame and mounting structure for supporting the transponder.

The present invention addresses a number of concerns that affect the operation of the transponder. One concern is breakage or other damage to the transponder due to mechanical forces applied to the transponder during the molding processes. Another concern is damage that can result due to the heat that is applied to the transponder during the molding process. A further concern is damage that can be caused by the shrinking or contracting of the undermold and/or overmold material during cooling of the key assembly following the molding operation. Yet another concern is changes in operating conditions, including but not limited to changes in temperature, in the daily operation of a key assembly that includes a transponder.

More specifically, the inventors have invented a method for molding the key assembly for vehicle ignition locks equipped with RFID systems that substantially eliminates the problem of resonant frequency shift. In accordance with highly preferred embodiments of the present invention, the transponder is first surrounded by an undermold using injection molding techniques. The undermold comprises a relatively hard plastic material which surrounds and protects the transponder from certain outside forces along its weakest axes and holds the transponder in the proper location within the key. Voids can be formed in the undermold during the first stage of the process. Then, the key assembly is overmolded, providing an outer covering that encloses and protects the transponder. During overmolding of the key assembly, the voids formed in the undermold provide a space for the overmold material to fill, which further secures the top and bottom center portions of the overmold, thereby increasing the integrity of the overmold and ensuring that the overmold of the key assembly will not separate and disfigure the key.

Further in accordance with the invention, the injection molding process is conducted so as to minimize impact forces applied to the transponder during the molding process. Preferably, the undermold material is injected, in liquid form, through a gate that directs the material against a corner of the transponder causing the material to be split into two portions. Consequently, the liquid material that forms the undermold encircles the transponder as the material is being injected producing substantially even hydrostatic pressures. Encircling the transponder with the liquid material (which will eventually harden to form the undermold of the key assembly), substantially prevents the application of impact forces directly to the planar surfaces of the transponder, with an attendant reduction in the potential for damage to the transponder which could cause the device to fail.

In accordance with a feature of the invention, during the injection molding process, strategically located voids are formed in the undermold. These voids, which can be extremely small, eliminate pressure differentials which can otherwise develop between the adjacent portions of the mold. Eliminating the potential for a pressure differential prevents the transponder from shifting or cracking within the key assembly during overmolding.

Another benefit of molding the key assembly in two stages, namely first undermolding and subsequently overmolding, is that while the plastic is cooling following the injection molding process, overall heat and compressive force imposed on the transponder are substantially reduced. While the harder plastic material undergoes a greater degree of compression during cooling, the impact on the transponder is minimized because less material is used in forming the undermold.

Moreover, the component tending to cause a shift in the resonance of transponders for key assemblies used in RFID systems is substantially eliminated using the overmolding process provided by the invention. The softer plastic material which is used to form the overmold portion of the key head tends to abate thermal problems because the overmold material is less inclined to exert pressure and distort the transponder to the degree that harder material would. However, softer material is more prone to mechanical deformation by shear or torsional forces.

A further benefit of the present invention is the use of an injection molding device which supports and contains the transponder within the key assembly along its weakest axis to prevent cracking, fracturing, and other adverse effects, any of which can contribute to failure. The mold plates forming the molds that are used in molding the undermold and the overmold of the key assembly further serve to reduce, even prevent thermal excursion during manufacture of the key assembly because the mold plates function as heat sinks. The mold plates absorb auxiliary heat and thermal energy so that the affects of the heat upon the transponder in both the undermold and overmold processes are substantially reduced. Preferably, the mold plates comprise a relatively massive material with good heat transfer characteristics.

The improved process for manufacturing RFID systems incorporating known transponders, such as those produced by Texas Instruments, Inc. and Motorola, minimizes the impact and compressive force applied along the weak axis (or axes in the case of the Motorola device) of the transponder and, thus, reduces the chance that the transponder will fail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and more particularly toFIG. 1, a vehicle ignition lock incorporating an RFID electronic interlock is indicated generally at1. The major components of the RFID interlock preferably comprise a transponder2, shown mounted on a key, an antenna3, and a reader (not shown). The reader is typically contained within an RFID ignition module (not shown) which also preferably contains logic circuits and a control circuit. The antenna3can be formed by a wire coil, for example, and preferably is located in the ignition lock1. The transponder2is mounted on a key which together with the transponder2form a key assembly4. The reader of the RFID electronic interlock can be similar to the RFID interlock that is disclosed in U.S. Pat. No. 5,433,096, which is assigned to the assignee of this patent application.

The function of the major components of the RFID system is known in the art and, accordingly, will not be described in detail. Briefly, the transponder2is adapted to respond to a radio frequency signal transmitted by the reader and transmit a unique identification code back to the reader. The radio frequency signal transmitted by the reader is coupled to the transponder via the antenna3. The transponder also produces an electromagnetic field for radiating radio frequency signals generated by the transponder back to the reader via antenna3. The reader converts the radio frequency signal from the transponder2to a digital signal for processing by the logic circuits. The logic circuits verify that the identification code is valid for the vehicle. When a valid identification code is detected, the reader generates an enable signal for a vehicle engine control module (not shown) which controls engine operation including, for example, fuel injection and ignition spark generation. If, on the other hand, the identification signal is determined to be invalid, the logic circuits control the engine control module so that engine operation is not enabled. The vehicle battery (not shown) provides power for the automobile security system.

Considering the transponder2in more detail, the transponder2is mounted in the head5of the key4and in one embodiment, includes an approximately 3.8×22 millimeter glass encapsulated, encrypted transponder, such as those available from Texas Instruments under Model No. RI-TRP-BRHP. Referring also toFIG. 52, in its simplest form, the transponder2includes electronic circuits2aand a coil2b. Preferably, the transponder2includes a capacitor2cthat is connected in parallel with the coil2b. In one preferred embodiment, the electronic circuits2aof the transponder are fabricated as an integrated circuit. However, the electronic circuits of the transponder circuits can be formed as discrete components. The transponder2can be anything that is capable of receiving and sending signals. Also, in some applications, the transponder can function as a transmitter that is energized to transmit an identification signal or the like in response to application of an RF signal to the transponder, as for example, in result of insertion and/or rotation of the key assembly into the ignition lock.

Referring again toFIG. 1, in one preferred embodiment, the reader is energized in response to inserting the key assembly4into the ignition lock1and turning the key to the start position, causing battery voltage to be applied. When battery voltage is applied, the RFID ignition module is energized and causes the reader to send out a 134.2 KHz pulse. By way of example, the pulse can last approximately 50 milliseconds. The pulse is applied to the antenna3and coupled to the coil of the transponder circuit. In the transponder, the pulse is converted to a DC voltage by a rectifier circuit (not shown). The DC voltage is regulated down, stored on a small capacitor2dand used to supply the electrical circuits of the transponder2. When the pulse terminates, the transponder transmits an identification code. Typically, the identification code is a unique factory programmed 64 bit code. The transponder transmits the identification code in the form of frequency shift keying. The antenna3receives the modulated identification code sent by the electrical circuit and the identification code is decoded by the reader which translates the frequency signal to a digital identification code and sends the digital identification code to the logic circuit. Only after the digital signal is verified as the valid identification code will engine operation be enabled. An invalid identification code will prevent engine operation. Once all data have been sent, the storage capacitor on the transponder containing electrical circuit discharges and the electrical circuit resets for the next read cycle. The total read cycle lasts approximately 120 milliseconds. While in one preferred embodiment the information transmitted by the transponder is a multi-digit identification code, encryption (challenge response) methods can be used and the signal verification process can include multiple handshakes, for example.

The ignition lock1preferably includes a hollow cylindrical sleeve6fixed within a housing7. The housing7can comprise a steering column of a vehicle, although those of ordinary skill in the art will recognize that numerous acceptable mounting locations are available. The sleeve6includes a cylindrical outer surface8and a cylindrical inner surface9to receive an elongated rotatable cylinder10. As shown inFIG. 1, the rearward end of the cylinder10is to the left while the forward end of cylinder10is to the right inFIG. 1adjacent to a wall11of the steering column housing. The cylinder10includes a cylindrical outer surface12which rotationally interfaces with the inner surface9of the sleeve6. The key assembly4rotates the cylinder10from an off position to a start position when the cylinder10is rotated in a clockwise direction from the position shown in FIG.1. Once rotated into the start position, upon release of the key, the cylinder10is rotated back in a counterclockwise direction from the start position to a run position in the conventional manner.

The cylinder10can include a plurality of axially spaced tumblers (not shown) which engage with the notches in the key assembly4and cooperate conventionally with a side bar13. Although the ignition lock1is illustrated as including a side bar13, alternative embodiments of the present invention may incorporate non-side bar locks. For example, locks which use only tumblers to engage the cylinder10and the sleeve6.

As shown inFIG. 1, the antenna3is integrally molded within an annular module14. The antenna3is preferably located at the forward end of the sleeve6and the cylinder10. Locating the antenna3as illustrated inFIG. 1limits the effects of the metallic composition of the sleeve6and the cylinder10from interfering with the electromagnetic field radiating from the antenna3. The antenna3is preferably wrapped about the sleeve6and the cylinder10to form an annular coil with a central opening coaxial with the longitudinal axis of the ignition lock1. The annular module14preferably forms an annular ring with an inner diameter dimensioned to mechanically fit with the outer surface8of the sleeve6. Thus, the annular module14slides over the forward end of the sleeve6and is received and fixedly mounted on the sleeve6in a convenient manner. For example, as evident to those of ordinary skill in the art, the annular module14may be staked or snapped in place to ensure that the annular module is integrally mounted on the sleeve6. It is pointed out that instead of the single antenna3illustrated inFIG. 1, the RFID interlock system alternately can include an exciter coil and a receiving coil similar to the two-coil antenna that is commercially available from Hughes Identification Devices under Model No. HS51051 hand held reader.

Referring now toFIGS. 2-4, there is illustrated a first embodiment for mounting the transponder2in the key head5of the key assembly4. As shown, the key assembly4includes an elongated shank15having a toe end16and a heel end17. The key head5preferably is integrally coupled to the heel end17of the shank15with pins18formed while the key head5is molded. As best shown inFIG. 3, the transponder2is mounted in a bore19formed in the key head5. The bore is dimensioned to receive the transponder and a plug20is adapted to close off the bore19. The bore19includes a blind end adapted to engage the transponder and an open end which opens to one end of the key head5. As best shown inFIG. 3, the blind end of the bore19is spaced from the heel end17of the shank15and the longitudinal axis of the bore19is preferably aligned with the elongated shank15. As shown, the bore19opens to the rear end of the key head5. Alternatively, the open end of the bore19may open to any surface of the key head5including a top surface21, a bottom surface22, a rear surface23, or opposite sides24,25. Preferably, the plug20and the key head5comprise the same plastic material, for example, Polypropylene Himont 7523. The bore19can further comprise a cushioning material such as a silicone compound supplied after the transponder has been inserted.

FIGS. 5-7illustrate a second embodiment of the key assembly of the present invention wherein the key assembly26includes the shank27having the toe end28and the heel end29, and the key head30constructed of a plastic material integrally molded on the heel end29in the same manner as illustrated and described in FIG.3. In this alternative embodiment, however, the transponder2is mounted within an opening comprising a substantially T-shaped recess31formed in one side32of the key head30. The recess31is dimensioned to substantially correspond with the dimensions of the transponder2. Additionally, a cushioning material, such as a silicone compound, may be supplied in the recess31at the time the transponder is installed. The recess31preferably has a closed bottom end33and an open top end34which opens to the side32of the key head30.FIG. 6illustrates the plug35which is preferably an adhesive-backed panel member which covers the transponder2and is received within the open top end34so that the side32is relatively smooth for the key assembly26. One of ordinary skill in the art will recognize that, although the recess31is illustrated as opening toward the side32of the key head30, the recess31can open to any surface of the key head30including the top surface36, the bottom surface37, the rear surface or the other side surface39in addition to the side32. The plug35can be any desired configuration, but incorporates a “medallion” or logo of the vehicle manufacturer in preferred embodiments of the present invention.

Yet a third embodiment of the present invention is illustrated in FIG.8. The key assembly ofFIG. 8is substantially similar to the key assembly ofFIGS. 5-7, however, the opening which receives the transponder2extends completely through the key head40from one side41to the opposite side42. As best shown inFIG. 8, the opening formed in the key head40includes a central section43for receiving the transponder2and a pair of opposite outer sections44,45opening to opposite sides41,42, respectively, of the key head40. A cushioning material such as a silicone compound may also be supplied in the central section43when the transponder2is installed. In this embodiment, the plugs46,47for the openings extending through the key head40comprises a pair of adhesive-backed plugs46,47received by the outer sections44,45for covering the openings in the key head40such that the transponder2is positioned between the plugs46,47. The plugs46,47of preferred embodiments of the present invention include medallions or logos which can be seen from opposite sides41,42of the key head40.

A fourth embodiment of the present invention is illustrated in FIG.9. In this embodiment, the key head48, is formed in two parts—specifically, a base member49and a cover member50. As best shown inFIG. 9, the base member49is coupled to the heel end51of the key shank52with pins53. The transponder2is received by the recess54formed in the base member49dimensioned in accordance with the dimensions of the transponder2. Again, a cushioning material such as a silicone compound may also be supplied in the recess54of the transponder. In this embodiment of the present invention, the cover member50serves to plug the recess54itself. Accordingly, the cover member50attaches to the base member49with a snap lock assembly comprising fingers55projecting from the base member49and passageways56formed in the cover member50to receive the fingers55. Thus, the cover member50assembles on the base member49merely by aligning the fingers55in the passageways56and forcing the base member49and the cover member50together to position the transponder2there between in the recess54. Alternatively, the cover member50can be sonic welded to the base member49or adhesively coupled to the base member49.

FIGS. 10 and 11, illustrate a fifth embodiment of the key assembly of the present invention. While this embodiment is similar to the embodiment ofFIG. 9, the base member57and the cover member58of the key head59are interconnected with a living hinge60along the bottom edges of the base member57and the cover member58. As illustrated, the base member57is integrally attached to the heel end61of the key shank62via pins63. The heel end61preferably comprises a substantially U-shaped frame member with opposing legs66. The transponder2mounts within the recess64formed in the base member57which, like embodiments described herein above, is dimensioned to receive the transponder2. A cushioning material, such as a silicone compound, can also be supplied in the recess64when the transponder2is installed. The transponder2is preferably oriented along a longitudinal axis disposed in alignment with the key shank62, and accordingly, the corresponding recess65is formed in the cover member58so that the transponder is properly aligned with the key shank62. Similar to the embodiment depicted inFIG. 9, the base member57and the cover member58couple with a snap lock assembly comprising fingers67projecting from the base member57and received within the passageways—formed in the cover member58. This construction permits the cover member58to pivot toward the base member57until the fingers67are received within the passageways68and the pins63are received within blind holes68aso that the transponder2is positioned between the base member57and the cover member58. This is best shown in FIG.11. The cover member58may alternatively be sonic welded to the base member57or the base member57and cover member58can be attached adhesively.

Referring now toFIGS. 12 and 13, a sixth embodiment of the key assembly of the present invention is illustrated. As shown, the key shank69includes a toe end70and a heel end71. The heel end71includes an open rectangular-shaped frame member forming a loop consisting of legs72-75which encircle a carrier76for the transponder2. The carrier76includes a flat base77, a component receiving recess78formed in the base77and a means for attaching the base77to the heel end71. As best shown inFIG. 13, the recess78is elongated and dimensioned to substantially match the dimensions of the transponder2so that the transponder is oriented along a longitudinal axis disposed in alignment with the longitudinal axis of the key shank69. Also shown best inFIG. 13, the base77of the carrier76is attached to the heel end71of the key shank69by pins79at one end of the carrier76which are received within the leg72and a pair of pins80at the opposite end of the carrier76which are received within another leg74. The pins79,80are received within corresponding openings formed in the legs72and74to temporarily mount the carrier76and the transponder2to the heel end71of the key shank69. Thereafter, the key head81is integrally molded over the heel end71, the legs72-75, and the carrier76, securing the transponder2to the key.

A seventh embodiment of the present invention is illustrated inFIGS. 14-15. In this embodiment, the key shank82includes a substantially U-shaped heel end83comprising a pair of opposing and spaced-apart legs84,85. The mounting arrangement for the transponder2comprises the carrier86with a hollow cylindrical base87dimensioned to receive the transponder2, and four wing members88,89,90,91extending from base the87to attach the base87carrying the transponder2to the legs84,85of the heel end83of the key shank82. As best shown inFIG. 15, each wing member88,89,90,91is preferably integral with the base87at one end and includes a pin92at its outermost end to be coupled with the legs84,85of the substantially U-shaped frame member of the heel end83. Thus, the carrier86is mounted on the legs84,85of the substantially U-shaped frame member with pins92inserted into corresponding openings in the legs84,85to initially attach the carrier86and the transponder2in place. Thereafter, the key head93is preferably integrally molded over the carrier86, the heel end83, and the legs84,85to affix the transponder2in a position oriented along a longitudinal axis aligned with the longitudinal axis of the key shank82.

FIGS. 16-17depict an eighth alternative embodiment of the present invention. In this embodiment, the key shank94includes the substantially U-shaped heel end95with the pair of opposite spaced-apart legs96,97as described herein above. In this embodiment, the mounting arrangement for the transponder2again comprises the carrier98. The carrier98comprises a hollow cylindrical base99dimensioned to receive the transponder2and two wing members100,101extending from the base99which attach the base99carrying the transponder2to the legs96,97of the heel end95of the key shank94. As shown best inFIG. 16, each wing member100,101is integral at one end with the base99and includes cylindrical sleeves102,103which slidably receive the legs96,97of the substantially U-shaped frame member. The key head104is preferably integrally molded over the heel end95, the carrier98and the legs96,97to affix the transponder2in position oriented along a longitudinal axis in alignment with the longitudinal axis of the key shank94.

Referring now toFIGS. 18-20, a ninth embodiment of the key assembly of the present invention is illustrated. In this embodiment, the key shank105includes the heel end106formed as a substantially U-shaped frame member having the pair of opposing spaced-apart legs107,108as described herein above. The ends of the legs107,108preferably include bases109,110to mount the carrier111. The carrier111comprises a substantially flat base112, the recess113, the pair of leg receiving recesses114,115formed in the base112and disposed on opposite sides of the component receiving recess113for receiving the legs107,108as well as the bases109,110. The carrier111further includes the cover member116which cooperates with the base member112to enclose recesses113,114,115and to mount the transponder2therein. Since the transponder2is oriented along the longitudinal axis aligned with the longitudinal axis of the elongated key shank105, the cover member116includes recesses117,118,119corresponding to the recesses113,114,115, as best shown in FIG.20. The base member112and the cover member116are preferably pivotally connected together by means of a hinge120extending along their bottom sides. For the purpose of attaching the base member112and cover the member116together to position the transponder2between them, the base member112includes a pair of projecting pins121, and the cover member116includes a pair of corresponding passageways122which, as shown best inFIG. 20, provide a snap-lock assembly for interconnecting the members112,116. Thereafter, the key head123is preferably integrally molded over the carrier111and the legs107,108and the heel end106of the key shank105to fixedly secure the transponder2in its desired location with respect to the key shank105.

FIGS. 21-22illustrate a tenth embodiment of the key assembly of the present invention. In this alternative embodiment of the prevent invention, the key shank125includes the heel end126which is integrally attached to a carrier or undermold127for the transponder2by pins128preferably formed while the undermold127is formed. In other words, the undermold127is integrally molded around the transponder2and is preferably simultaneously attached to the heel end126. Thereafter, the key shank125and the undermold127, with the transponder2therein, are molded within an overmold129composed of a plastic material so that the undermold127and the overmold129form the key head130. The material for the overmold in one alternative embodiment of the present invention129is the same material used for the undermold127, although those of ordinary skill in the art will recognize that the undermold127and the overmold129do not have to be the same material.

Referring now toFIGS. 23-29, an eleventh embodiment of the key assembly for the present invention is illustrated. In this alternative embodiment, the key shank140comprises the heel end141which is integrally attached, by molding, to the undermold142containing the transponder2. In this embodiment, the undermold142is preferably integrally molded around the heel end141of the key, and during the molding process simultaneously forms a cage for slidably receiving the transponder2. This embodiment is best shown in FIG.24. Thereafter, an overmold is formed to encase the key140and the undermold142with the transponder2within the cage as best illustrated in FIG.27. The plastic material for the overmold, as well as the undermold142, can be the same or different, but preferably the undermold142comprises a relatively hard plastic material and the overmold comprises a softer material. More specifically, the undermold material can be a high flow polypropylene having a melt index on the order of about 16-24, or a hydrocarbon resin material. The overmold material can be a soft polyvinylchloride (PVC) having a melt index on the order of about 60 to 80, or a thermoplastic rubber, such as that commercially available under the trade name Santoprene, for example.

The cage illustrated inFIG. 24for the transponder2is simultaneously formed with the undermold142and includes a longitudinal opening for receiving the transponder2formed by a plurality of spaced bars143each having an outer surface preferably flush with the outer surface of the undermold142and an inner arcuate surface144which conforms to the cylindrical circumference of the transponder2(best shown in FIG.26). A plurality of openings145are formed opposite the arcuate surfaces144of each bar143in order to accommodate the male components of the mold and to receive the softer overmold material during the overmolding process as described below. As best shown inFIGS. 24,25,28and29, the two bars143adjacent each end of the undermold142preferably include a thin flexible membrane integrally formed therewith for engaging the transponder2and flexibly supporting the transponder2within the undermold142. The membranes146preferably hold the transponder2in a position spaced inwardly from the arcuate surfaces to enable the softer overmold material to flow between the outer surface of the transponder2and the arcuate surfaces to provide cushioning for the transponder2. A resilient stop147is formed at the end of the undermold142to engage the end of the transponder2and preferably to ensure that the transponder2is properly located within the cage formed by the undermold142, as best shown in FIG.29.

Referring now toFIGS. 27 and 28, the overmold is illustrated as comprising an outer shell148and a generally cylindrical layer149which surrounds the transponder2. The outer shell148and the cylindrical layer149thus preferably provide a cushioning layer of material for the transponder2which prevents the transponder2from shattering or breaking in the event the key assembly of the present invention is accidentally dropped.

Referring now toFIGS. 30-38, a twelfth embodiment of the key assembly of the present invention is illustrated. In this alternative embodiment, the key shank150includes the heel end151formed as a substantially circular frame member having a central opening152for receiving the transponder153therein. In this alternative embodiment, the transponder153is substantially rectangular in shape in contrast to its being cylindrical in shape for previous embodiments. As best shown inFIGS. 31-36, the undermold154is formed around the transponder153and simultaneously attached to the substantially circular heel end151of the key shank150. To accomplish this, the key shank150is positioned within a mold plate155such that the transponder153is within the central opening152, best shown inFIGS. 31 and 32. The transponder153preferably is held in position in this central opening by four pins156which prevent the transponder153from moving forwardly, rearwardly, upwardly or downwardly. In order to prevent the transponder153from moving laterally, a plurality of raised bosses157can be employed. After a second mold plate158is closed to encompass the key shank150and the transponder153substantially, as shown inFIG. 33, plastic is injected into the mold to form the undermold154, as shown best in vertical section in FIG.34and in longitudinal section in FIG.36. Thereafter, the key shank150, the heel end151, the transponder153and the undermold154are preferably inserted into a second mold, as shown inFIG. 37, preferably having cavities159,160formed in corresponding plates161,162. Plastic material is then injected into the mold cavities159,160to form the overmold163which surrounds the transponder153.

Referring now toFIGS. 39-44, a thirteenth embodiment of the key assembly of the present invention is illustrated. In this embodiment, the key shank164includes a shortened heel end165further comprising a pair of oppositely extending legs166,167. Each leg166,167includes a corresponding opening168,169formed therein. In this alternative embodiment of the present invention, the transponder170is substantially rectangular in shape and includes a pair of opposite, arcuate-shaped notches171formed on the upper and lower edges of this transponder170. As best shown inFIGS. 41 and 42, the edges of the transponder170are slightly tapered from one side to the other. Transponder170is attached to the heel end165of the key shank164by a carrier172, formed substantially as shown inFIG. 42, and forms half of the key head. To form the carrier172, the transponder170and the key shank are substantially positioned between a pair of mold plates173,174and mold plate173has a cavity175formed therein in the shape of one half of the desired configuration for the carrier172of the key head. After the plastic material is injected, the transponder170is attached to the key heel end165and simultaneously substantially one half of the grip portion of the key assembly is formed. The transponder170is preferably connected to the carrier172by molding the plastic material over the tapered edges of the transponder170. The connection between the key shank164and the carrier172is enhanced because plastic material flows into the openings168,169formed in the legs166,167of the heel end165. Thereafter, the other half of the grip portion of the key head is formed by placing the carrier172, the transponder170and the key shank164into a mold containing plates176,177as shown in FIG.43. After molten plastic is injected and cooled, the completed key assembly produced is as illustrated in FIG.44.

Referring now toFIGS. 45-51, a fourteenth embodiment of the key assembly of the present invention is shown. In this embodiment, the key shank178includes a shortened heel end179having opposite legs180,181with respective openings182,183formed through the legs180,181of the shank similar to the key assembly previously described and illustrated in FIG.40. The transponder184has a configuration identical to that described, with respect to the transponder170and is preferably integrally attached to this heel end179by an undermold185. The undermold185is preferably integrally molded around the transponder184which is held in position by pins196,197and is simultaneously attached to heel end179using a plastic material which preferably fills the openings182,183in a manner similar to that previously described with respect toFIGS. 39-44. In this alternative embodiment of the present invention, however, the undermold185merely functions to interconnect the transponder184with the heel end179.

This is accomplished by placing the head portion of the key178and the transponder184within the mold plates186,187and injecting molten plastic material to fill cavities188,189to form the undermold185, substantially as shown in FIG.49. When forming the undermold185, a tab195is preferably simultaneously formed along the edge of the undermold185that is opposite the key shank178. Thereafter, the head of the key178, the transponder184, and the undermold185are placed into a second mold including mold plates190and191. The mold plates190and191have respective mold cavities192and193conforming to the desired shape for the grip portion of the key assembly. Then, the mold is closed and plastic material is injected into the mold cavities192and193, forming the overmold around the heel end179, the transponder184, and the undermold185to form the grip portion194for the key assembly, as illustrated in FIG.51. The tab195functions to prevent the undermold185from flexing or moving with respect to the key shank178while the mold cavities192and193are being filled. Preferably, the tab195is broken off after formation of the key assembly is completed.

Background of the Problem

The inventors have discovered that a problem which affects the operation of RFID security systems involves a shift in resonant frequency of the transponder2(FIG.52). Such a shift in the resonant frequency ultimately results in failure of the transponder to receive radio frequency signals being transmitted by the reader, or in the signals being transmitted to the receiver by the transponder being of weakened strength, resulting in the inability of the receiver circuit of the reader to detect the signals transmitted by the transponder. In either case, the security interlock system will prevent the vehicle engine from being enabled using the ignition key or otherwise. The shift in resonance is believed to result from mechanical effects which produce large and/or unevenly distributed mechanical forces on the transponder. These forces can affect the performance of the transponder by shifting the inductance of the coil2bor capacitance of the capacitor2cof the resonant circuit of the transponder2(FIG.52).

These undesirable mechanical forces can be produced during use of the key assembly and/or as the result of ambient conditions. Moreover, these mechanical forces can result from conventional manufacturing techniques used to produce the key assembly. The most problematic forces are those produced by severe temperatures and/or by temperature changes which thermodynamically affect the mechanical structure of the transponder of the key assembly or the mechanical structure of the key assembly. Decreasing, with the ultimate goal of completely eliminating, the amount of resonance shift associated with the transponder can eliminate reliability problems described herein above concerning RFID ignition lock systems.

In known RFID ignition key assemblies, the head portion of the key assembly and the transponder mounted therein are enclosed within a relatively hard or rigid plastic material, typically polypropylene, that also secures the transponder to the key. The inventors have discovered that minimizing the amount of contact between the transponder and the rigid material used to secure the transponder to the key can reduce shift in resonance. Moreover, the inventors have found that reducing the bulk or mass of the rigid plastic material that is located adjacent to the transponder in the key assembly can also reduce the shift in resonance.

The problem involving a shift in resonance of the transponder's resonant circuit identified herein above has both mechanical and thermal considerations. While both mechanical and thermal considerations are incorporated in the present invention to decrease or substantially eliminate such shift in resonance to make the RFID system more dependable, these aspects of the problem have conflicting solutions. Thus, mechanical considerations are addressed primarily in the structural design of the key assembly, including the shape of the key used in the key assembly and the configuration of the undermold. Thermal considerations are addressed through careful selection of materials, structure and manufacturing processes so that adverse effects on the transponder of thermal expansion and contraction are minimized. As will be shown, preferred embodiments of the transponder mounting arrangement according to the invention balance structural support for the transponder with considerations that minimize degradation to radio frequency signal transmission.

As is indicated above, the present invention addresses a number of concerns that affect operation of the transponder. One concern is breakage or other degradation of the transponder due to mechanical forces that are applied to the transponder during the molding processes. Another concern is degradation of the transponder that could result due to the heat that is applied to the transponder during the molding process. A further concern is degradation that can be caused by shrinking or contracting of the undermold and/or overmold material during cooling of the key assembly following the molding operation.

Briefly,FIG. 53illustrates another alternative embodiment of a key assembly200provided by the invention. In accordance with the invention, a transponder202is mounted to a key, such as the key221shown inFIG. 55A, using a two-stage process in which first an undermold201is formed and then an overmold199is formed. The undermold201frames and supports the transponder202within the head portion222of the key221. The undermold201maintains the transponder substantially immobile within the key. In addition, the undermold201forms a base onto which the overmold199is subsequently molded. The overmold199, which is shown partially broken away inFIG. 53, covers or encloses the transponder202, the undermold201and the head portion222of the key. In addition, as will be described, portions of the overmold material, indicated by the reference numeral199a, fill voids that are created in the undermold201between the head portion222of the key and the transponder202during the process of forming the undermold. This two-step molding process ensures proper filling of surface blemishes caused by gating, locating or other initial molding and mounting considerations. In this embodiment, preferably the undermold201comprises a relatively hard plastic material, such as a high flow polypropylene, and the overmold199comprises a softer material, such as PVC, or a thermoplastic rubber such as that commercially available under the trade name Santoprene.

The transponder mounting arrangement according to the invention provides a compromise between: a) factors related to providing a mechanically sound package; and b) factors related to minimizing thermodynamic effects and to the effects of mechanical forces applied to the key assembly, particularly the transponder and its associated mounting structure. To these ends, the relatively hard plastic undermold material201is used to secure the transponder to the key. However, as will be described, a point contact approach is used to minimize the amount of contact between the relatively hard undermold material and the transponder. In addition, the bulk or mass of the undermold material is minimized at points for those portions of the undermold material that are disposed adjacent to and/or in contact with the transponder. This is accomplished, for example, by configuring the undermold material as relatively thin strips that extend along the periphery of the transponder, and/or by providing voids or recesses along the periphery of the transponder. Filling such voids or the gaps between the thin strips with the relatively soft material that forms the overmold portion of the key assembly (as will be shown) can reduce degradation of the RFID signal.

In accordance with another aspect of the invention, mechanical forces that are applied to the key assembly during use of the key assembly, as well as under certain other conditions, are redistributed in such a way as to minimize the affect of such forces on the performance of the transponder. The redistribution of mechanical forces is provided by the transponder mounting arrangement of the undermold portion of the key assembly as will be described in detail. This is a particularly important aspect of the invention with respect to ensuring the integrity of the transponder. Thus, in accordance with the invention, the undermold is configured to minimize the application of mechanical forces where the transponder is weakest. This reduces the likelihood of deterioration of or damage to the transponder and consequential shift in the resonance of the transponder.

Transponder Configurations

To better understand the mechanics of the problem, it is helpful to have a basic knowledge of the fundamental types of transponders that are used in the industry. Most commercially available transponders have generally flat, elongated or rectangular packages which do not provide a completely rigid structure, and as such, are capable of being flexed to some extent. In many applications, the transponder components are mounted on a printed circuit board or other relatively rigid support and the transponder is contained within an enclosure which affords a degree of protection against deformation of the transponder in use, e.g., glass vials. This is generally not the case, however, for the transponders that are used in key assemblies for RFID systems and the like, and in which forces applied to the key are coupled or translated to the transponder through its enclosure, i.e., overmolded plastic case. Such forces can result in temporary or permanent deformation of the transponder, which can affect the performance of the electronic circuits of the transponder. The susceptibility of the overmolded plastic cased transponder to these forces is dependent upon several factors, including the physical layout of the electronic circuits of the transponder, the nature of the mechanical mounting of the transponder to the key, and the direction of the forces applied to the transponder.

Referring toFIG. 52, typically, the transponder circuit2ais located at one side of the package and the coil2bis located at the opposite side of the package. The region of the package that is held rigid due to mounting can affect the performance of the transponder when undesirable stress forces are applied to the package for any reason. The transponder is most vulnerable to impact forces that are applied where the transponder is weakest. For example, breakage or other damage to the transponder can occur due to mechanical forces that are applied to the transponder during the molding processes. Moreover, damage to the transponder can result due to temperature excursions during manufacture of the key assembly. For example, because the plastic material must be injected in liquid form during the molding operation, the heat applied to the transponder during the molding process can damage to the transponder. In addition, damage to the transponder can be caused by shrinking or contracting of the undermold material during cooling of the key assembly following the molding operation. Moreover, temperature excursions can result in to a change in operating characteristics of the transponder. Finally, post-molding temperature excursions can cause shrinkage or expanding of the molded material(s), producing mechanical forces on the transponder.

Referring toFIG. 54A, there is illustrated an enlarged isometric view of a transponder202that has one of the transponder configurations that are commonly used for RFID applications. Transponders having this configuration are commercially available from Motorola, Inc., as part no. 05504-001. The transponder202is generally rectangular in shape and is overmolded with a plastic material. By way of example, transponder202typically is approximately ¾ inch along its long or “y” axis, indicated by reference numeral204inFIG. 54A, and approximately ½ inch along its short or “x” axis, indicated by reference numeral206. The transponder202is approximately ⅛ inch thick along its “z” axis208. The transponder202has a compact rectangular side profile, with the side surfaces207being relatively long and relatively thin. This configuration makes the transponder susceptible to deformation along both the x axis and the y axis because the x axis and the y axis are the weakest axes for transponders having the configuration of the transponder202depicted in FIG.54A.

As will be readily apparent to those of ordinary skill in that art, because of the length and relative thinness of the transponder202along its x and y axes, the application of forces along either of those axes due to a bending moment caused by a force directed along the weak axis, will subject the transponder to potentially damaging forces. Such forces can deform the transponder to such an extent as to impair the operational state of the transponder, and possibly even fracture the transponder. Therefore, in accordance with the invention, the undermold that is provided for securing transponders that are configured substantially as the transponder202depicted inFIG. 54A, is designed to minimize, and preferably eliminate to the extent possible, the application of forces near opposing edges of the transponder both along the y axis and along the x axis.

Referring toFIG. 54B, there is shown an enlarged isometric view of a transponder210that has another popular configuration that is commonly used for RFID applications. Examples of transponders having this configuration are produced by Texas Instruments, Inc., and are commercially available as Texas Instruments, Inc. part no. RI-TRP-W9WK, which is a read/write transponder, and Texas Instruments, Inc. part no. RI-TRP-B9WK, which is an encrypted transponder. The transponder210, which is commonly referred to as a “wedge” transponder, is generally trapezoidal in shape. The transponder210is approximately ½ inch in length along one side211which extends along the “y” axis, indicated by reference numeral212in FIG.54B. The transponder210is approximately ¼ inch in width along one end213, extending along its short or “x” axis, indicated by reference numeral214, and tapers along side216to approximately 3/16 inch in width at the opposite end215, which also extends along the x axis214. The transponder210is approximately ⅛ inch thick along its “z” axis218. Transponders that have the configuration of transponder210are most susceptible to deterioration and damage as the result of mechanical forces directed along the y axis which is represented by reference numeral212in FIG.54B. The Texas Instruments, Inc. type transponder has advantages and disadvantages that are similar to those for the Motorola, Inc. style transponder illustrated in FIG.54A. Therefore, the undermold or support structure for holding transponders configured substantially as the transponder210depicted inFIG. 54B, is designed to minimize, and preferably eliminate to the extent possible, the application of forces along the y axis thereof.

Key Shapes

A further consideration is that the configuration of the transponder that is used dictates to some extent the configuration of the key that is used for a given key assembly. The configuration of the key can provide structural stability for the entire key assembly. The selection of the configuration of the key which provides the basic support structure for the key assembly requires a tradeoff. On the one hand, a key having a large amount of metal provides a more rigid structure that better withstands the torsional forces that are applied to the key assembly in use, and during thermal expansion and contraction, and results in a smaller portion of the force being translated through the key to the transponder mounted thereon. On the other hand, a larger amount of metal results in a higher susceptibility to detuning the transponder and interference with the signal by the metal key material.

In preferred embodiments of the present invention, the head and the blade of the key preferably are made of a substantially rigid metal as is the convention in the automotive industry. Brass is the most common metal used to construct vehicle ignition keys because of its manufacturability, cost and compatibility with the tumblers of the lock.

One preferred embodiment of the key221is shown inFIGS. 55A and 55B. The key221includes a head portion222and a blade or shank portion223. The shank portion223of the key is milled at224to match the keyway and can include bits in the conventional manner to engage tumblers in the ignition lock. As is shown inFIG. 55B, the thickness of the rigid metal portions of the head portion222and the shank portion223of the key221are substantially uniform except, of course, at locations at which the milling224has been preformed to accommodate the keyway of the ignition lock for a particular vehicle with which the key is used.

The head portion222of the key221is generally oval in shape and contains an opening225that is located substantially in the center of the head portion222. The opening225in the head portion222has a generally D-shaped configuration and extends axially from the head portion222to the shank portion223of the key221, with the curved side226of the opening225being located proximal to the blade of the key and the opposing straight side227of the opening being located distal of the blade. The opening225is large enough to allow a transponder, such as transponder202(FIG.54A), to be placed within the opening225spaced from the metal portion of the key221. One preferred placement of a transponder202within the head portion222of the key221is shown inFIGS. 53 and 56C, for example.

Referring also toFIG. 56C, in a highly preferred embodiment of the invention, the opening225(FIG. 55A) in the head portion222of the key221is large enough to provide at least 5 mm of clearance on each side of the transponder coil. As is known, metal interferes with the transmission of radio frequency signals under some circumstances, and the gap provided between the sides of the transponder202and the metal of the key221reduces the extent to which the metal material of the key interferes with transmission of radio frequency signals by circuits of the transponder and the reception of radio frequency signals by the circuits of the transponder. The gaps between the sides of the transponder and the key are filled in part with undermold material201, and in part by overmold material portions199a, as is shown inFIG. 56C, for example.

Referring toFIGS. 55A and 56A, in preferred embodiments of the present invention. a slot228is provided in the head portion225of the key on the side of the head opposite the shank portion of the key. The slot228permits the key assembly to be placed on a key ring or key chain and stored with the vehicle operator in a conventional manner. Preferably, the slot228is relatively small as compared to the opening225provided in the head portion of the key.

The D-shape configuration of the opening225in the head portion222of the key221is preferable because this configuration permits numerous configurations for the undermold of the present invention as will be discussed below. Additionally, the D-shaped configuration of the head of the key provides a more rigid key assembly because the underlying metal portion defines the support structure. The key assembly is configured as a closed loop that extends around the entire finger grip portion of the key and completely encircles the transponder202mounted on the key as is shown in FIG.56C. Thus, this key configuration better absorbs torsional and bending forces applied to the key assembly in use.

While in one preferred embodiment shown inFIG. 55A, the opening in the head portion of the key221has a generally D-shaped configuration that is particularly suitable for mounting the transponder202, the opening in the head of the key can be configured to accommodate any number of different configurations of transponders, such as the transponder210shown inFIG. 54B, for example. Thus, in accordance with a further embodiment shown inFIG. 55C, the key231includes a head portion232that is substantially solid, but which is shaped to define an open portion or notch233, i.e., providing a part of the head of the key in which there is no metal. The shank portion223includes a milling224in the manner of key221shown in FIG.55A. The thickness of the rigid metal portions of the head portion232and the shank portion223of the key231are substantially uniform except, of course, at locations at which the milling224has been preformed. The open portion233of the metal head portion of the key comprises approximately a quarter segment, i.e., about 90° or less, of the generally oval peripheral edge of the key head portion. In this embodiment, the head portion232of the shape of the head portion of the key resembles a question mark (“?”). The mounting area for the transponder, such as transponder210shown inFIG. 54B, is defined by the relatively small open portion233(90° or less) of the head portion of the key231. One example of a key assembly400including such a transponder210is shown inFIGS. 61A-61E. Because most of the head portion232of the key231is solid, except for the region233, the key provides a degree of resistance against shear and torsional forces. Consequently, this key head configuration, like that for the key221ofFIG. 55A, reduces susceptibility to force problems because of the relatively solid head configuration which increases structural strength and reduces the forces transmitted and imposed upon the transponder. Further openings234are preferably provided through the head portion232to facilitate interconnection of the two halves of the overmold during fabrication of the key assembly400including the key231as will be described.

Referring toFIG. 55D, in an alternative embodiment of the key241, the head portion242comprises two arcuate arms243that extend away from the shank portion223of the key. The arcuate arms243provide increased structural strength for the key assembly and reduce the transmission of forces to the transponder as compared to key assemblies employing the generally T-shaped key shown inFIG. 45, for example. In accordance with yet another embodiment of a key246, which is shown inFIG. 55E, the head portion248of the key is substantially Y-shaped and includes two arms249that extend beyond the base of the shank portion223of the key in the manner of arms243of key241(FIG.55D). A key ring opening or slot can be formed in the overmold of the key assembly of the present invention as will be discussed herein below.

It is pointed out that keys having various configurations for the key head portions have been illustrated for the purpose of showing the latitude in support structures, i.e., keys, that can be used in producing the key assembly in accordance with the invention. It will be apparent to those of ordinary skill in the art that a number of other alternative support structures, such as those shown inFIGS. 1-51, can be used in the key assembly of the present invention. Moreover, any of the alternative key configurations discussed above can be modified to further include the slot for placing the key assembly of the present invention on a key ring or other comparable storage device.

Force Distribution

Referring again toFIG. 53, the following description provides additional structural and functional detail of the undermold of a key assembly, such as the undermold201for the key assembly200. Additional detail is provided regarding the manner in which the undermold is configured to offset mechanical considerations that contribute to shift in the resonance of a transponder, such as a transponder202having a physical layout shown inFIG. 54A, for example. Although the following description refers to the transponder202, the description also applies to transponders having other configurations, such as the transponder210shown inFIG. 54Bof the key assembly400shown inFIGS. 65A-65B, for example, or undermold structures used in these embodiments.

As has been stated above, preferred embodiments of the mounting arrangement according to the present invention balance structural support for the transponder with considerations that minimize interference with radio frequency signal transmission. To this end, the mounting arrangement for key assembly200, which includes an undermold201and an overmold199, provides a compromise between providing a mechanically sound package and minimization of adverse thermal effects. This compromise takes into account the effects of external mechanical forces applied to the key assembly, and in particular to the transponder202and its associated mounting structure, e.g., the undermold201provided by the invention.

The force and redistribution provided by the undermold201of the key assembly200is a particularly important aspect of the invention with respect to ensuring the integrity of the transponder202. The undermold201is formed of a material that is suitable for rigidly attaching the transponder to the key and consequently comprises a material that is harder than the material of the overmold199for this preferred embodiment. In accordance with one aspect of the invention, the undermold201contacts the transponder202along surfaces of the transponder such that forces applied along the weaker axis, or axes of the transponder are distributed so as to minimize the magnitude of the force applied at any point along a weak axis of the transponder.

The overmold199, which encloses the transponder202, the undermold201and the head portion222of the key221, is preferably formed of a material that is softer than the material of the undermold201to reduce external forces applied to the transponder by the substantially rigid undermold material. Preferably, the undermold and the overmold are formed using a two-step injection molding process as will be described.

Embodiments with Support Structure

Referring toFIGS. 56A-56E, which illustrate further views of the embodiment of the key assembly200shown inFIG. 53, the key assembly200includes the transponder202of FIG.54A and the key221ofFIG. 55A, and accordingly, corresponding elements have been given the same reference numerals as inFIGS. 54A and 55A. The undermold201frames and supports the transponder202within the head portion222of the key221. The undermold201is formed of a relatively hard plastic material, such as a high flow polypropylene as described above, and rigidly attaches the transponder202to the key, maintaining the transponder substantially immobile within the key. The overmold199is formed of a material such as a soft PVC or a thermoplastic rubber, such as that commercially available under the trade name Santoprene, for example, or other similar material that is softer than the material of the undermold.

More specifically,FIGS. 57A-57Eillustrate the key assembly200prior to the formation of the overmold and inFIGS. 57A-57E, this key “sub-assembly” has been given the reference numeral200′. The undermold201, which couples the transponder to the head of the key, comprises a frame or support structure252and a mounting structure254. In this embodiment, the undermold201is designed such that the surface area of the relatively “hard” plastic material that forms the frame structure252that physically contacts the transponder202is minimized. In addition, the mass of “hard” plastic material that forms the mounting structure254generally is spaced from the transponder and the portion of the “hard” material that is located in the proximity of the transponder is kept as small as possible.

To these ends, the frame structure252, by which the transponder202is held in position relative to the head portion of the key, comprises a plurality of tabs261-264and271-274, shown inFIGS. 57D and 57E, for example. The design configuration of the tabs261-264and271-274of the undermold and their locations around the periphery of the transponder are dictated by the configuration of the transponder as well as the shape of the key. For the embodiment illustrated inFIGS. 56A-56G, the tabs are located at the corners of the generally rectangular transponder. In this embodiment, the frame structure252includes a first series of the tabs261-264located at the corners of the planar surface260of the transponder202and a second series of the tabs271-274located at the corners of the opposing planar surface276of the transponder. As is discussed above, the weak axes for the transponder202extend along both the x axis and the y axis. Because both the x and y axes are weak axes for this transponder configuration, the frame structure is configured to minimize the effect on the transponder of any forces directed along both the y axis and the x axis.

Each of the tabs provides substantially point contact with the transponder202for the undermold material. The tabs261-264and271-274are preferably produced as an integral portion of the undermold. Moreover, in accordance with the invention, the relatively massive sections of the “hard” plastic material, specifically those sections which form the mounting structure254of the undermold, are spaced apart from the transponder. Keeping the majority of the “hard” plastic material of the undermold spaced from the transponder reduces the likelihood that the mechanical expansion and contraction of the “hard” plastic material surrounding the transponder will affect the transponder and, consequently, the likelihood that the integrity or operability of the electrical circuits and/or the coil associated with the circuits of the transponder202will be degraded.

The frame structure252of the undermold retains the transponder202on the key221while decreasing shift in the resonance of the transponder202. The frame structure252supports the transponder202such that mechanical forces imposed upon the transponder202are minimized and properly distributed, whether such forces result from forces applied to the exterior of the key assembly or are produced by thermal expansion or contraction of the overmold or undermold. This reduces the likelihood of deterioration of the transponder which could otherwise affect the performance of the transponder, as for example, by producing a shift in the inductance of the coil of the transponder. The preferable placement of the tabs of the frame structure252relative to the transponder varies depending on the configuration of the transponder and the configuration of the head of the key.

In some preferred embodiments of the invention that include key assembly200, the undermold201does not completely cover the transponder202. Rather, as shown inFIG. 57C, the frame structure of the undermold201, represented by tabs261,262and271,272, for example, overlies and/or contacts only very small portions of the opposing planar surfaces260and276of the transponder202. Moreover, the mounting portion254of the undermold201, as represented inFIG. 57Bby portions254a,254b,254cand254d, is disposed along the peripheral edge portions of the transponder, in contact therewith or spaced apart from the transponder as will be shown. Stated in another way, with respect to the rigid undermold material201, a point contact method is used for securing the transponder to the key and a minimal amount of the undermold material is located in contact with or adjacent to the transponder of the key assembly. The frame structure securely holds the transponder, but can only apply a minimal amount of force to the transponder. As a result, undesirable externally applied forces which are applied to the key are strategically and deliberately directed to reduce their effect on the transponder. In some preferred embodiments, the mounting structure254also defines at least a portion of the outer surface of the key assembly that is gripped by a user of the key assembly. Moreover, the use of the hard overmold enables truncation of the metal portion of the key, as for key179(FIG.40).

Thus, the undermolding process secures the transponder202to the key221. The overmolding process encloses or encapsulates the transponder and also defines the primary finger gripping surface for a user of the key assembly as shown inFIGS. 56F and 56G. In addition, the overmolding step covers cavities or marks left by transponder positioners in the mold and flaws, such as blemishes, pinholes, and the like in the undermold. The use of the two-stage process minimizes the amount of contact between the transponder202and the relatively hard undermold material that supports the transponder during the second stage of the process. The first stage of the two-stage process includes forming the undermold201for framing and supporting the transponder within the head of the key. The second stage of the process includes overmolding the transponder and the undermold201with the overmold material199. As shown inFIGS. 56C and 56D, the overmold199covers the transponder202, the undermold201and the head portion of the key. Portions of the overmold material, indicated by the reference numeral199a, fill the voids that are created in the undermold material201during the process of forming the undermold.

Consequently, this reduces the effects of expansion and contraction of the plastic components surrounding the transponder. Thermal expansion and contraction of the plastic components surrounding the transponder have been found to be a significant factor in causing deterioration of transponders, resulting in a shift in inductance of the transponder coil and/or a shift in the capacitance of the capacitor, in turn causing a shift in resonant frequency for the transponder circuit. The inventors have determined that the use of point contact methods for supporting the transponder on the key helps preserve the integrity and operational state of the transponder in the event of thermal expansion and contraction of the plastic of the undermold201and the overmold199. The invention preserves the transponder's integrity, regardless of whether the expansion or contraction is initiated by molding thermal excursion or by environmental thermal excursion. Molding thermal excursion generally produces expansion and contraction of a plastic material during injection molding operations. Environmental thermal excursion occurs as the result of environmental conditions during use of the key assembly.

FIGS. 58A and 58Bshow a simplified representation of the transponder202and the frame structure252of the undermold which are shown enlarged to illustrate the relationship between the frame structure252and the transponder202. InFIG. 58A, each of the rectangular solids represents a portion of the frame structure252and these portions of the frame structure are formed integrally with the mounting structure254as is shown inFIGS. 57A,57D and57E, for example. The tabs have relatively thin planar surfaces that extend coincident to the surface of the transponder lying along the y axis as defined in FIG.54B. The thickness “t” of the tabs preferably is less than about 0.050 inch. Moreover, in one preferred embodiment, the tabs are constructed such that for each pair of tabs, such as tab pair261and271, one of the tabs261engages the planar surface260of the transponder and the other tab271of the pair engages the opposing planar surface276of the transponder as can be seen by comparingFIGS. 57D and 57E. Consequently, the tabs provide support on the plane of the surface260and on the plane of the surface276of the transponder. Also, the tabs261,262,263and264, as well as complementary tabs271,272,273and274, are preferably located at corners of the transponder. This tab placement is often preferable because it evenly distributes, over a wide area of the transponder, any force which is transmitted to or imposed upon the transponder along either the x axis, along the y axis, or along both axes.

Alternatively, the tabs can be placed differently if sensitive components such as coils are located at the corners of the transponder. For example, the frame structure252can include tabs265-268which are rotated about 45° from the orientation for the tabs261-264ofFIG. 58A, as is shown in FIG.58C. Each of the tabs265-268has an associated tab, such as tabs269and270for tabs265and267, respectively, which define tab pairs which engage the opposing planar surfaces of the transponder in the manner described above with reference to FIG.58A.

Referring toFIGS. 57C,57D and57E, the tabs261-264and271-274are preferably formed in pairs by the injection molding process. Molding the tabs coincident to one another on the opposing planar side surfaces260and276of the transponder202helps maintain an even force distribution on the transponder. In addition, maintaining the relatively thin cross-section of the tabs and lessens the degree of expansion and contraction that the tabs undergo both during fabrication of the key assembly and in use of the key. The cross-section of the tabs of the undermold is preferably in the range of approximately 0.020-0.050 inch. In this range, the tabs are small enough to minimize forces and other mechanical effects on the transponder due to expansion or contraction of the undermold material as the result of molding thermal excursion or environmental thermal excursion in use of the key assembly.

Referring again toFIGS. 57A-57E, in accordance with a further aspect of the invention, spaces or voids253are provided in the mounting structure254of the undermold201. In this preferred embodiment, the voids253are formed in portions254a-254cof the undermold between three sides of the transponder202and the bulk portion of the undermold material as shown inFIG. 57B, for example. The voids253are formed during the injection molding process, and are produced by inserts provided in the mold tools as will be described. One function of the voids253is to allow expansion and contraction of the undermold and/or the overmold during the molding process.

The two-stage process, including producing an undermold and subsequent producing of an overmold, permits the voids to be located strategically in the undermold, which in one preferred embodiment illustrated inFIGS. 57A-57E, for example, forms voids253in the undermold material between the forward end of the transponder and the front edge of the heel end of the key221and between the sides of the transponder and the side portions of the heel end of the key221. These voids253, which can be extremely small, serve to eliminate the potential for pressure differentials which might otherwise develop and result in breakage of the transponder during the overmolding process. When the key subassembly200′ (FIG. 57A) is overmolded, these voids253provide space for portions of the overmold plastic to fill. These voids253form regions into which the liquid plastic material can flow during the overmolding process, binding the two sides of the overmold together ensuring that the overmold portion of the key assembly does not expand following removal of the key assembly from the mold, which could result in disfiguring of the key assembly200. In addition, this functions to secure together the center of the front and back sides of the overmold, thereby increasing the integrity of the overmold.

Further Embodiments of the Undermold

While for the embodiment shown inFIGS. 57A-57E, the tabs261-264are flat elements which are generally rectangular in shape, the tabs can also take other shapes. For example, with reference toFIG. 59A, which is a view similar toFIG. 58A, in accordance with a further embodiment, the frame structure252which physically contacts the transponder202comprises a plurality of generally cylindrically shaped portions of the frame structure, which define four tabs, such as tabs281-284, which contact the planar surface260of the transponder, and four tabs, two of which285and286are shown inFIG. 59A, which engage the planar surface276of the transponder202. Each tab is located at a corner of the transponder in the manner of the embodiment of FIG.57A. Each of the cylindrically shaped portions of the frame structure is molded over the corner of the transponder, forming a recessed portion290as shown in FIG.59B. Moreover, the tabs can have a teardrop shape to prevent warping of the tabs. For such configuration, the tab is oriented with its narrow tip or end extending into overlying engagement with a planar surface of the transponder.

Referring now toFIG. 59C, in accordance with a further preferred embodiment, the undermold support structure252, which physically contacts the transponder202, comprises a plurality of tabs301-304which are generally rectangular in cross section and located to overlie the planar surface260of the transponder at adjacent corners305-308of the transponder in a manner similar to that for the embodiment of FIG.57. However, each tab is offset from the edge and overlies a portion of the end, in the manner shown for tabs302and304. In addition, tabs301and303are located on opposite sides of the transponder, and the tabs302and304are located at opposite ends of the transponder. Four mating tabs, such as tabs311,313and314shown inFIG. 59C, are provided to engage the planar surface276of the transponder. As is shown inFIG. 59D, each rectangular portion of the frame structure252has a recess315that is generally rectangular in cross section and which is dimensioned to receive one of the corners of the transponder.

The tabs of the embodiment of the undermold shown inFIG. 59Aalso can be located offset relative to the corners to extend along sides near the corners in the manner of tabs321-324and tabs331,333and334as shown in FIG.59E. For such embodiment, the section of frame structure has a cutout portion in the form of a chord326as shown in FIG.59F.

Referring toFIG. 60A, in accordance with a yet another embodiment of a key assembly, the support structure252of the undermold comprises a plurality of generally rectangular or cylindrical sections or portions of the frame structure, defining tabs341-344located at or near each corner of the transponder in the manner of the embodiments ofFIGS. 57A-57G,58A,58C,59A,59C and59E, for example. In this embodiment, the portions of the frame structure252that define the tabs341-344, for example, are interconnected by thin bands or strips346of the undermold material that extends around the periphery of the transponder202. Preferably, the bands or strips346of undermold material201are spaced apart from the transponder202, defining voids347between the transponder202and the undermold material. The bands346, in turn, are connected to the main portion, or mounting structure of the undermold material348which is overmolded onto the key heel portion. Although in one preferred embodiment illustrated inFIG. 60A, the bands346are spaced apart forming the voids347, because of the relatively thin profile of the bands346of undermold material, these portions346of the undermold material can contact the transponder202along one or more of the edges349of the transponder.

As has been described, an important function of the tabs of the frame structure252of the undermold in accordance with the present invention is to minimize localized forces applied to the transponder at any location of the transponder202during the overmolding process. By using a number of tabs, forces on the transponder are distributed over a number of points on the transponder with the result that less force has to be carried by each tab at each of those points. For example, if tabs are located at all four corners of the transponder in the manner for the embodiments that are illustrated inFIGS. 57A-57E,58A,58C,59A,59C and59E, each tab is required to transmit less force to those locations on the transponder than if only three tabs were located on only three corners of the transponder. Moreover, if tabs are placed at all four corners, or at three corners of the transponder, each tab is required to transmit less force to those locations on the transponder than if only two tabs were provided at only two corners of the transponder. On the other hand, it is also desirable that there be as little contact as possible between the transponder and the undermold material once the overmold has been formed. Thus, the number of tabs is selected to provide a balance between these concerns.

Those of ordinary skill in the art will be aware of alternative methods and the details in configuration and in location for constructing the tabs. Thus, for example, as an alternative to locating the tabs of the undermold at all four of the corners of the transponder, the tabs can be located at diametrically opposed corners, or at three of the corners, for example. Also, as shown inFIG. 60B, the tabs350can be located substantially at the middle of the side edges352of the transponder. Voids354can be formed in the undermold material between the sides of the transponder and the key. Locating the tabs350at the middle of the side edges352of the transponder better distributes compressive and/or torsional forces imposed on the transponder and the points of application of the forces to the transponder are located closer together. The relative locations of the tabs350can affect the amount of deformation of the transponder, particularly if the force distribution should at some time become unstable or unevenly distributed. Therefore, it is preferable to maintain the points at which the forces are applied to the transponder through the tabs of the undermold as close together as possible. In addition, locating the tabs350at the mid point of the side edges352of the transponder minimizes the possibility that the transponder will be deformed due to the increased leverage that results when the spacing between tabs is greater, as when the tabs are located at the corners of the transponder.

In another embodiment illustrated inFIG. 60C, the support structure comprises a single tab370that is located at one end372of the transponder and which extends between the two corners374of the transponder at that end for connecting one end of the transponder to the mounting structure. A thin band376of undermold material connects the opposite end378of the transponder to the mounting structure380.

With reference toFIG. 60D, in accordance with yet another embodiment, the support structure382of the undermold comprises a band384of the undermold material that extends around the periphery of the transponder and contacts the transponder on all four sides. In this alternative embodiment of the present invention, the transponder is secured within the undermold of the present invention with a thin (0.020 inch) layer of molding which preferably encircles the periphery of the transponder entirely and extends from the top to the bottom the transponder. Voids386are provided along three sides388of the transponder, but the band384is connected to the main portion or mounting structure390of the undermold at the fourth side of the transponder392. However, a void394is provided in the bulk material in the proximity of the fourth side of the transponder to provide room for expansion and contraction of the undermold material. In this embodiment, the frame structure portion382is coupled to the mounting portion390of the undermold using one of the techniques described herein above.

Alternative methods and configurations for affixing the tabs to the mounting structure include molding rectangular, cylindrical, or alternatively shaped posts at the locations of the tabs during the injection molding process. Such a method of securing the tabs facilitates an integral and one-step construction of the undermold being efficient both economically and from a time perspective. Moreover, relatively small and short pins can be inserted into the undermold mold to hold the transponder in place during the first stage of the injection molding process. Thereafter, the pins can be removed, leaving holes to be filled by the overmolding process. While in accordance with some preferred embodiments of the present invention as described above, the tabs are produced during the injection molding process as an integral portion of the undermold, the tabs can be produced as a separate structure which can also be molded in addition to the undermold.

A further embodiment of the key assembly400, shown inFIGS. 61A-61E, includes the transponder210of FIG.54B and the key231of FIG.55C. In this embodiment, the transponder210is mounted in the notch233provided at one side of the key. As in the previous embodiments, the undermold201is formed of a relatively hard plastic material, such as a high flow polypropylene, and rigidly couples the transponder210to the key231, maintaining the transponder substantially immobile within the key. The overmold199is formed of a material such as a soft PVC, a thermoplastic rubber, such as that commercially available under the trade name Santoprene, for example, or other similar material that is softer than the material of the undermold.

More specifically, referring also toFIGS. 62A-62F, which illustrate the key assembly400prior to the formation of the overmold and in which the key subassembly has been given the reference numeral400′, in this embodiment, the frame structure410includes tabs411and412preferably located near diametrically opposed corners414and415of the planar surface416of the transponder210(FIG.62F), and tabs421and422located near diametrically opposed corners424and425of the planar surface426of the transponder (FIG.62E). The tabs411,412,421and422are generally semicircular in cross section and define finger-like projections extending from the undermold material in overlying relationship with the transponder on opposite sides thereof. In addition, the undermold includes a mounting structure413formed by undermold material that couples the frame structure to a portion to the heel end of the key231.

The design configuration of the tabs411-412and421-422of the undermold410in this embodiment and their locations along the sides of the transponder210are dictated by the configuration of the transponder as well as the shape of the key221of the key assembly400. As is discussed above, the weak axis for the transponder210extends along the y axis as shown in FIG.54B. Because the y axis is the weak axis for this transponder configuration, the frame structure410is configured to minimize the affect on the transponder of any forces directed along the y axis. As is discussed above, because the transponder is relatively thin along its x axis214(FIG.54B), applying an undue amount of strain at either end of the transponder, along the y axis212will subject the transponder to forces capable of deforming the transponder.

The tabs411-412and421-422have relatively thin planar surfaces that extend coincident to the surface of the transponder lying along the y axis as defined in FIG.54B. The tabs are preferably less than 0.050 inch in thickness. Preferably, the tabs are constructed such that for each pair of tabs, such as tab pair411and421, one of the tabs411is located to engage the planar surface416of the transponder and the other tab421of the pair is located to extend along and engage the opposing planar surface426of the transponder as can be seen by comparingFIGS. 62E and 62F. Consequently, the tabs provide support in the planes of the opposing planar surfaces of the transponder. The tabs411and412, which are positioned to engage the planar surface416, are located adjacent opposite corners of the transponder and the tabs421and422, which are positioned to engage the opposing planar surface426, also are located adjacent corresponding corners of the transponder, each underlying the respective tab411and412of the pair. This tab configuration is preferable because it provides for a more even distribution, over a wide area of the transponder210, of any force which is translated to or transferred to the transponder along the y axis.

The tabs411-412and421-422are formed in pairs by the injection molding process. Molding the tabs coincident to one another on the opposing planar surfaces of the transponder210assists in maintaining an even force distribution on the transponder. In addition, the formation of the tabs of the undermold is controlled to maintain the tabs relatively thin in cross-section to lessen the degree of expansion and contraction that the tabs undergo both during fabrication of the key assembly and in use of the key. The tabs of the undermold are small enough in cross-section, typically 0.020 inch, to minimize forces and other mechanical effects on the transponder due to expansion or contraction of the undermold material as the result of environmental thermal excursion.

In accordance with a further aspect of the invention, spaces or voids440are provided between the mounting structure413of the undermold and the transponder for permitting the undermold and/or the over mold to expand and/or contract with changes in ambient conditions. For example, as shown inFIG. 62C, voids440are formed in portions of the undermold between the sides of the transponder and the bulk portion413of the undermold material. These voids440are formed during the injection molding process, and are produced by a plurality of locators provided in the mold tools as will be described. The locators locate the transponder within the mold during the undermolding process and prevent movement of the transponder210during the undermolding process.

A further embodiment of the key assembly401, shown inFIGS. 61F-61G, includes the transponder210ofFIG. 54B and akey231a. As in the previous embodiments, the undermold201is formed of a relatively hard plastic material, such as a high flow polypropylene, and rigidly couples the transponder210to the key231a, maintaining the transponder substantially immobile within the key. The overmold199is formed of a material such as a soft PVC, a thermoplastic rubber, such as that commercially available under the trade name Santoprene, for example, or other similar material that is softer than the material of the undermold.

As shown inFIG. 61G, elongated strips of overmold material199b, fill voids formed in portions of the undermold along the periphery of the transponder and the bulk portion of the undermold material. These voids are formed during the injection molding process, and are produced by a plurality of locators provided in the mold tools as has been described. Also, the holes234provided through the metal portion of the key are filled with overmold material as the result of the overmolding process. Preferably, a layer of the undermold material201is allowed to be formed on the inner circumference of the holes to enhance the ability of undermold material to be connected to the key in the regions of these holes. The overmold material covers the heel portion of the key231aas well as the undermold material and the transponder210that is coupled to the heel portion of the key by the undermold material. As shown inFIG. 61F, a relatively thin portion199cof overmold material is formed at the center of the head of the key. This portion of the overmold material interconnects the portions of the overmold on one side of the key with the overmold material on the opposite side of the key.

Alternative Embodiments for Tabs

Referring toFIG. 63A, there is shown a simplified representation of the transponder210and the frame structure of the undermold in accordance with a further embodiment, and which are shown enlarged to illustrate the relationship between the frame structure252and the transponder210of FIG.54B. InFIG. 63A, each of the generally trapezoidally-shaped solids represents a portion of the frame structure252. The frame structure includes four frame structure portions identified by reference numbers252a-252d. Each of the frame structure portions252a-252d, such as portion252ashown inFIG. 63B, includes a lower arm291and an upper arm292interconnected by upright portion295. The frame structure portion252ais configured to conform to the shape of the transponder210at its side216which has a tapered edge surface293along its side216. Thus, the upper arm292of frame structure portion252ahas a tapering lower surface294that conforms to the tapered edge surface293. The other three frame structure portions252b-252dcan have generally parallel upper and lower arms which engage upper and lower surfaces of the transponder as shown inFIG. 63Ato conform to the shape of edges213,211and215of the transponder. Frame structure portions252band252dare located at opposite ends213and215of the transponder. Frame structure portion252cis located at side211of the transponder near the corner thereof. Each frame structure portions defines a pair of tabs that engage opposing planar surfaces of the transponder. For example, frame structure portion252bincludes tabs296and297, and frame structure portion252aincludes tabs298and299. The frame structure portions252a-252dare formed integrally with the mounting structure254in the manner of tabs411and412as shown inFIG. 62A, for example.

The transponder210can be mounted in the key231using any of the arrangements illustrated for the transponder202. For example, as shown inFIGS. 31-35, the transponder210can be mounted in the open head portion of the key221(FIG. 53) with the undermold filling all or a part of the opening and the overmold being molded around the head portion covering the transponder, the undermold material and the metal portion of the head. Tabs extend into engagement with the transponder. The top and bottom surfaces are not covered by or engaged by the undermold material except for the tabs at the thin end of the transponder. In addition, in these embodiments, voids are formed in the undermold material by locators in the mold. The voids created during the undermold are filled with overmold material to hold the center portions of the overmold together. Moreover, molding a portion of the overmold material through the key ring opening228, as is shown inFIG. 57D, for example, assists in securing together the front and back sides of the overmold.

Further Embodiments

In accordance with other embodiments for the key assembly, both the undermold and the overmold comprise a relatively hard material. In these embodiments, contact between the relatively “hard” undermold material and the transponder is minimized by using a compressible material as an interface between the hard material and the transponder during the undermold and/or overmold process.

For example, in one embodiment of a key assembly452illustrated inFIGS. 64A and 64B, a thin membrane288is wrapped or molded around the transponder prior to forming the undermold. The membrane288can be of a compressible material and can be approximately 0.020 inch in thickness. The transponder202can be held in place in the mold by pins while the hard undermold material is introduced into the mold, the hard material being in contact with the membrane, but out of contact with the transponder.

In another embodiment, cork, or some other compressible material can be mixed into the undermold material prior to molding the undermold material around the transponder. The undermold material secures the transponder in place on the key, with the impregnated compressible material that forms the undermold capable of absorbing mechanical forces.

Referring toFIGS. 64C and 64D, in yet another embodiment for a key assembly456, the frame structure that maintains the transponder in place during formation of the undermold comprises a plurality of thin strips289(FIG. 64C) of a hard material or other material that shrinks during over molding, leaving voids. The strips extend over and under the transponder and are molded integrally with the body of the hard undermold material that fills the spaces between the transponder and the metal portion of the head. The strips289can be arranged in a variety of shapes or patterns, but preferably define a porous-like structure at the upper and lower surfaces of the transponder. The material is selected such that some of the strips, such as strips289a, shrink and become thinner or break completely as shown for strips289bin FIG.64D. Because the undermold material is needed only during the overmolding process to keep the transponder from moving within the mold, it is desirable that it decrease in size following the overmolding process and leave voids. However, the porous material can withstand the overmold process without disentegrating or losing its properties that enable the porous-like structure to protect the transponder from impact forces. During the overmolding process, the porous-like structure substantially prevents the overmold material from penetrating the well in which the transponder is located. This structure, along with selection of the mold configuration and the undermold material, serve to keep hard overmold material structures of significant size out of contact with the transponder during overmolding. Consequently, the voids in the porous-like structure minimize transfer of mechanical forces to the transponder.

Referring toFIGS. 64E-64G, in a further embodiment of the key assembly458, the portion of the undermold which corresponds to the frame structure252ais formed as a rigid, box-like support structure459which has a bottom or base459a, four sides459b-459e, and is open at the top. In this embodiment, the transponder202is inserted into the support structure after the undermold, i.e. support structure459, has been formed.

The support structure459includes a plurality of ribs460-464which support and cushion the transponder202, represented by the dashed lines inFIG. 64G, on the bottom and sides thereof during the overmolding process. The ribs460and461-464are formed on the base459aand sides459b-459e, respectively, of the support structure. As shown inFIGS. 64E and 64F, the ribs460extend in a parallel spaced relation along the length of the base459a. The ribs461and463extend upwardly in a parallel spaced relation from the base to the upper edge of the sides459band459d. The ribs462and464extend upwardly in a parallel spaced relation from the base to the upper edge of the sides459cand459e. Ribs462and464can converge with the ends of ribs460on the base459a. In one embodiment, shown inFIGS. 64E-64F, the support structure includes four ribs460, with four vertically extending ribs462and464at each end thereof. In addition, four ribs461and463extend vertically at the both of the sides of the support structure, such that four ribs engage the lower surface of the transponder and four ribs engage each side surface of the transponder. The lower surface of the transponder rests on the support ribs460and the ribs461-464engage the sides of the transponder, with the transponder being held in place by an interference fit. However, fewer or more ribs can be provided at any of these transponder surfaces. Although the box-like structure is generally rigid, the ribs are sufficiently thin as to enable the ribs to deform or crush somewhat during the overmold process and when stress is applied during environmental conditions while maintaining a cushion between the transponder and the relatively hard overmold material. Moreover, a compressible material, such as compressible membranes288, cork288(FIG. 64B) or other forms of compressible material, can be used in combination with or to replace the support structure459, the compressible material being located below and/or along the sides of the transponder that is located within the frame459. Compressible material can also be placed above the box-like structure to close it off at its upper end.

Thus, this embodiment of the key assembly458is formed using a process in which the box-like support structure is formed first and connected to the key. The portion of the undermold that defines the support structure459can include portions that couple to the head of the key in the manner described above for the key200, as shown in FIG.57D. Then, the transponder is inserted into the support structure459. The sub-assembly of the key, the support structure and the transponder is then overmolded.

In this process, a relatively hard undermold material is formed for supporting the transponder, with a compressible material being used to interface the undermold material and the transponder. A hard overmold material is used to enclose the formation of the undermold and the compressible/shrinkable material. Alternatively, the compressible material can be embodied as a sheath in which the transponder is placed. The sheath can be formed of a compressible material, such as ribbed material, for spacing the transponder from the inner surface of the sheath and can be extruded if desired. In this embodiment, the ribs of the sheath can deform or crush somewhat during the overmold process maintaining a cushion between the transponder and the overmold material.

Referring toFIGS. 65A and 65B, in a further embodiment, a key assembly470is formed with both soft undermold material471and a soft overmold material (not shown). The key assembly470includes a transponder153mounted on a key having a key shank150and a heel end151with central opening152which are similar to those for the key assembly illustrated inFIG. 32, for example.

In the embodiment ofFIG. 65A, the transponder153is supported during the undermolding process. One way of doing this is to use an insert molding process with the transponder153being held by retractable pins156(FIG. 65B) during forming of the undermold471.FIG. 65Billustrates the key assembly in a mold tool prior to forming of the undermold. When the undermold has been formed, the pins156are retracted and the transponder153is held by the undermold material471during the overmold process. In this embodiment, retraction of the pins forms voids472in the undermold material as shown in FIG.65A. These voids472are filled with the overmold material (not shown) during the overmold process, to interconnect the center portions of the undermold material.

A similar process can be used in forming a key assembly having a hard undermold material and soft overmold material, which is a variation on the key assembly shown inFIGS. 56A-56G, for example.

In another embodiment, the amount of relatively hard undermold material is maximized while maintaining a minimum of contact between the transponder and the undermold material. With reference toFIGS. 65C-65E, in this embodiment of a key assembly450, a portion of the undermold material is used to form paired tabs (similar to the tabs261-264and tabs271-274shown inFIGS. 57D and 57E) in such a way as to minimize the points of contact between the relatively hard undermold material252and the transponder202. However, in key assembly450, the balance of the undermold material covers substantially all of the key portions located away from the transponder with the tabs261-264(and271-274) being connected to the bulk portion of the undermold material. In key assembly450, the overmold material199is used to fill the regions above, below and around the frame and surfaces of the transponder, such that the center portion of the head of key, in which the transponder is located, is defined by the relatively soft over mold material199. Thus, in this embodiment, the majority of the key221is covered with the relatively hard undermold material252and only the portion of the key in which the transponder is located is covered with the relatively soft overmold material199. This arrangement provides increased strength for the key assembly because the undermold252forms most of the outer coating of the key assembly450. In an alternative embodiment of the key assembly450in which the undermold is maximized, the undermold material252can be formed to include a box-like recess (with or without compressible ribs), which can be similar to the box-like structure459(FIG.64F), and which is open to the top. The recess is sized to receive the transponder and after the transponder has been positioned in the recess, the open upper end of the recess, and the transponder, can be covered with overmold material, which can be similar to, or softer than the undermold material.

An alternate method for supporting the transponder202on a key221during the overmolding process is illustrated inFIGS. 65F-65G. In this embodiment, the undermold480which supports the transponder202on the key is a relatively thin membrane-like member which extends within the opening225in the head222of the key and is fixed to the key along the peripheral edge226of the opening. In one embodiment, the membrane-like member480conforms substantially to the shape of the opening and has its peripheral edge portion482fixed to the key along the peripheral edge226of the opening. Alternatively, the membrane-like member can be generally rectangular in shape and can be fixed to the key at opposite ends of the opening in the head of the key.

In one preferred embodiment, the transponder202is partially enclosed within the membrane-like member as shown inFIG. 65F, but the transponder202can be completely enclosed as well. The membrane-like member480is of a material that is sufficiently rigid to support the transponder, but which allows the center portion of the membrane-like member480to flex slightly within the opening of the key.

Process

As is indicated above, the present invention addresses a number of concerns that affect operation of the transponder. One concern is breakage or other degradation of the transponder due to mechanical forces that are applied to the transponder during the molding processes. As is discussed above, these problems are addressed by minimizing contact between the transponder and the relatively hard material that forms part of the molded key head, and including molding the key assembly in two stages.

Another concern is degradation of the transponder that could result due to the heat that is applied to the transponder during the molding process. To address this problem, the mold plates of the mold used in producing the undermold, as well as the mold plates of the mold used in producing the overmold, comprise a relatively massive material with good heat transfer characteristics.

A further concern is degradation that can be caused by shrinking or contracting of the undermold and/or overmold material during cooling of the key assembly following the molding operation. A further benefit gained in molding the key assembly in two stages, using a relatively hard undermold material and a relatively soft overmold material, is a substantial reduction in the amount of compressive force imposed on the transponder while the plastic undermold material is cooling following the injection molding process. Although the relatively hard undermold material can exert higher compression forces during cooling because of its greater hardness, the impact on the transponder is minimized because a lesser amount of the relatively hard material is used in forming the undermold.

In general, the process for making the key assemblies described above is similar although some of the process steps can vary as a function of the shape of the key, the transponder used and the configuration of the molded portion of the key head. Accordingly, the process will be described with reference to producing the key assembly200(FIGS.56A-56G).

Referring toFIGS. 66A-66E, the following is a description of one process for producing the key assembly200(FIG. 56A) in accordance with one embodiment of the present invention. First, the key221is positioned in a recess637of one of the mold plates641of a mold640(FIG.66A). Then, the transponder202is positioned in the mold plate641, located in the open portion225of the heel end222of the key as shown in FIG.66B. The mold plate641includes a mold surface643that defines the configuration for a portion of the undermold. The mold includes a plurality of locators645which hold the transponder in position in the mold to prevent the transponder from moving in the mold during the injection of the first plastic material into the mold. After the transponder is placed in the opening in the head of the key, a second mold plate642is closed on the first mold plate641to encompass the key and the transponder as shown inFIGS. 66C and 66D. As shown inFIG. 66A, the mold plate642includes a mold surface644that is generally a mirror image of the mold surface of mold plate641and defines the remaining position of the undermold. Mold surface644can include openings645afor receiving distal ends of the locators645of mold plate641.

In the next step of the process, a first plastic material, such as a high flow polypropylene, is injected into the first mold640through an inlet646of the mold640to form the undermold201that surrounds a portion of the transponder202and the heel end222of the key221with the first plastic material and which integrally couples the transponder to the heel end of the key. The presence of the locators645in the mold640causes voids253to be formed in the undermold material201as shown in FIG.57D and inFIG. 66E, for example.

The voids253also serve to alleviate the affects of molding thermal excursion that can occur during the manufacturing process, such that, should molding thermal excursion affect some part of the key assembly during the manufacturing process, the voids allow for expansion to minimize compressive forces on the transponder. The undermold process of the present invention permits the voids253to be located strategically between the front and back of the head portion the key assembly. These voids also serve to eliminate the potential for a pressure differential which might otherwise develop in the mold during the overmold process. Eliminating the potential for a pressure differential permits the transponder from being moved within the key assembly during the overmold process. Subsequently, when the key assembly is overmolded, these holes provide a space for the overmold plastic to fill, thus securing the centers of the front and back sides of the overmold thereby increasing the integrity of the overmold and ensuring that the overmold of the key assembly does not expand to disfigure the key assembly.

As has been indicated, an important consideration is the prevention of damage to the electrical circuit by both impact forces and compressive forces while the key assembly is manufactured, especially during the molding processes. The injection molding process is conducted in a manner as to minimize the affect of impact forces applied to the transponder during the molding process. To this end, in accordance with a preferred method used during the injection molding process for forming the undermold, the liquid plastic material that forms the undermold201is directed around the transponder so that it does not apply an undistributed force to the transponder. Preferably, the undermold material is injected through a gate647, mounted on one of the two mold plates641and642. The gate647can be conventional, but is configured such that the liquid plastic material being introduced into the mold640is directed substantially against a corner of the transponder202as shown inFIG. 66B. Aright angle plate650, which extends the thickness of the transponder at the corner thereof, protects the transponder while the undermold material is being injected into the mold. The right angle plate650also forms a void at the corner which subsequently will be filled with overmold material during the overmold process. Consequently, the material is split into two flow portions as indicated by the arrows648and649. The material is not directed to the upper and lower planar surfaces of the transponder, but rather flows along the sides of the transponder. In addition, the material flow is laminar rather than turbulent, further reducing the likelihood of impact forces being directed onto the planar surfaces of the transponder. The gate647forces the liquid plastic, which will eventually harden to form the undermold, to move in a substantially circular pattern around the transponder. Causing the liquid plastic material to encircle the transponder as the material is being injected into the mold, results in substantially even hydrostatic pressures which prevents the application of direct impact forces on the weak axes of the transponder which could result in breakage of the transponder.

Referring toFIG. 66E, after the first material has been injected into the mold and allowed to cool, the heel end of the key, and the undermold and the transponder which now are integrally coupled to the heel end of the key, are removed as a unit from the first mold640and positioned in a mold plate651of a second mold652which together with a second mold plate653define mold cavities654and655of the second mold652which forms the overmold material to the shape of the key head as shown inFIG. 56F and 56G, for example. After the second mold plate653of the mold652is closed on the first mold plate651, a second plastic material, in liquid form is injected into the mold cavities654and655of the mold652to produce the overmold as an outer shell over the transponder202, the heel end222of the key221, and the first plastic material that forms the undermold201. The undermold material201also forms a base for molding the overmold material199and as such, aids in securing the overmold material199to the key221. In addition, the overmold fills the voids253, interconnecting the center portions of the overmold. In some embodiments, such as the embodiments illustrated in FIGS.53and61A-61E, for example, the second plastic material is a material such as thermoplastic rubber or similar material, which is softer than the material that forms the undermold. However, in other embodiments, such as the embodiments illustrated inFIGS. 64D-64J, for example, the second plastic material can be of the same material that forms the undermold or a material other than thermoplastic rubber or similar material.

Mold Heat Transfer Characteristics

The mold plates641and642of the mold640that is used in producing the undermold201, as well as the mold plates651and653of the mold652that is used in producing the overmold199, comprise a relatively massive material with good heat transfer characteristics. The mold plates of the molds640and652minimize thermal excursion by allowing the molds to function as heat sinks, absorbing auxiliary heat and thermal energy so that the effects of the heat on the transponder and on both the undermold and overmold are substantially reduced.

The mold tooling absorbs a relatively large portion of heat which would otherwise cause excessive thermal excursion when liquid plastic material at a temperature sufficiently high as to liquefy the material, is injected into the mold in the regions surrounding the transponder and associated metal portions of the key. Thus, temperature changes, which occur while the liquid plastic is being injected into the mold and as the liquid plastic subsequently hardens during both the undermolding process and the overmolding process, could effectively deteriorate or damage the transponder, without the heat sink characteristic of the molds. In addition, the multiple stage process decreases the amount of material being introduced in each stage of the process, thereby lessening the heat impacting the transponder in each process stage and in the overall process.

Process for Key Assembly400

Referring toFIGS. 67A-67E, the process for producing the key assembly400(FIG. 61A) of the present invention is similar to that described above. The key231is positioned in one of the mold plates661of a mold660. The transponder210positioned in the mold plate661is located in the cut out portion233of the heel end of the key. The mold plate661includes a mold surface664which defines the configuration of the undermold. The mold plate661includes a plurality of locators665which hold the transponder210in position in the mold660to prevent the transponder from moving in the mold during the injection of the first plastic material into the mold. The locators665can be provided as inserts in the mold660. After the transponder is placed in the cut out portion233in the heel end of the key, a second mold plate662of the mold660is closed on the first mold plate661to encompass the heel end of the key and the transponder. The second mold plate662includes a mold surface667that defines the configuration for the balance of the undermold.

In the next step of the process, a first plastic material is injected into the first mold660to form the undermold or carrier that surrounds a portion of the transponder and the heel end of the key with the first plastic material and which integrally couples the transponder to the heel end of the key. In addition, the locators665form the voids640in the undermold material.

Preferably, the undermold material is injected through a gate647in the manner described above with reference to FIG.66B. The gate647is conventional and is configured such that the liquid plastic material being introduced into the mold is directed against a corner of the transponder210, having disposed thereat a plate650(FIG. 66B) to cause the undermold material to be split into two flow portions. The undermold material is not directed to the upper and lower planar surfaces of the transponder210, but rather flows along the edges of the transponder. In addition, the material flow is laminar rather than turbulent, further reducing the likelihood of impact forces being directed onto the planar surfaces of the transponder.

Referring toFIG. 67E, then after a sufficient cooling time, the assembly of the heel end of the key, with the transponder integrally coupled to the heel end of the key by the undermold, is removed from the first mold660and positioned in a mold plate671of a second mold670, which includes a second mold plate672. The mold670has mold cavities674and675formed in respective mold plates671and672of the mold. After the mold plate672of the mold670is closed on the mold plate671, a second plastic material is injected into the mold cavities of the mold670to mold the overmold199. The overmolding process surrounds the transponder210with the overmold material. The holes234provided through the heel end of the key231are filled with a portion of the overmold material during the overmold process for interconnecting the centers of the overmold.

Key assemblies incorporating the undermold configurations shown inFIGS. 59C-59Fcan be produced in a manner similar to that described above with reference to the molding apparatus illustrated inFIGS. 66A-66E.

SUMMARY

In summary, the thermal component tending to cause a shift in the resonance of a transponder used in a key assembly for an RFID system is substantially eliminated using the combined undermolding/overmolding process. Thermal expansion and contraction are preferable minimized by carefully designing the undermold and the overmold of the key assembly of the present invention so that the materials have an insignificant reaction to temperature changes and so that the design allows space for these state changes to occur without having to encroach on the space reserved for the transponder.

The softer plastic overmold material which is used to construct the key head tends to abate thermal problems because the overmold material is less inclined to exert pressure and contort the transponder to the degree that harder material does. However, the softer overmold material is more prone to mechanical deformation by shear and torsional forces.

Moreover, the combined undermold/overmold structure along with the frame structure and mounting structure provided by the invention, alleviate the mechanical component tending to cause a shift resonance of transponders of key assemblies that are used in RFID systems.

While the benefits of the undermolding and overmolding process and method of manufacturing the key assembly of the present invention have been described herein above, the details and benefits of the design of the key assembly itself also have preferable characteristics. The key is assembled so that the potential for resonant frequency shift due to a change in inductance of the coil and capacitance of the capacitor of the transponder's resonant circuit is decreased. Resonant frequency shift can result from severe temperature changes, a damaged transponder, or proximity to metal or other conductive components located too near the coil of the transponder of the present invention.