Liftgate reinforcement arrangements

A liftgate structure having a structural inner panel with an outside surface and an inner surface having a lower perimeter surface area extending across substantially the entire width of the structural inner panel. The structural inner panel includes a wiper motor housing recess formed on the inner surface. A plurality of brackets are connected to the outside surface of the structural inner panel, where each of the brackets has at least one friendly hole. The liftgate structure further includes a tether having 2 ends each having at least one over molded retainer for connecting the tether to a wiper motor housing positioned within the wiper motor housing recess of the structural inner panel. Additionally the tether is positioned through each of the at least one friendly holes of the plurality of brackets.

FIELD OF THE INVENTION

The present invention relates to a tether component and method of manufacturing the tether component, which is implemented in a liftgate for an automobile.

BACKGROUND OF THE INVENTION

One of the current trends in the automobile industry is to lower vehicle weight to help achieve better fuel economy, thus helping to meet fuel economy standards and to offset the higher fuel prices. Another trend is that there is a broader range of vehicle models, which in turn reduces the volume of vehicles produced on a per model basis. Liftgates are traditionally made from stamped steel panels that are heavy and have a high tooling cost and are susceptible to corrosion. Sheet Molding Compound (SMC) is an alternative to steel for the inner and outer panels of the liftgate. Using SMC has several manufacturing concerns related to the material and process. Steel and SMC liftgates have a mass penalty over thermoplastics. There are also styling restrictions with traditional sheet metal and SMC components.

In certain applications where liftgates are made from composite materials, tethers made from steel are used to strengthen the liftgate. The use of steel tethers can be difficult to attach and increase the assembly complicity. It is therefore desirable to design liftgates that have tether systems that are easier to assemble, require less attachment points and still provide the desired level of strength to the liftgate.

It is therefore desirable to develop and provide a new tether that has a stronger attachment clip that is over molded to the fibers of the tether in such a way that the integrity and strength of the individual fibers is preserved. It is further a desirable to provide a tether system that is flexible and is connected to the liftgate panel through apertures thereby reducing the number of physical anchor points used. It is also desirable to provide a tether system that allows the installed tether to have slack at each aperture that allows for the tether to avoid damage to the tether upon impact.

SUMMARY OF THE INVENTION

The present invention is directed to a liftgate structure for an automobile that is preferably formed from composite material. The liftgate structure includes a structural inner panel with an outside surface and an inner surface having a lower perimeter surface area extending across substantially the entire wide of the structural inner panel. The lower perimeter surface area in some applications is where additional structures such as door latches, window actuators and window wiper motors are mounted. As described herein the structural inner panel includes a wiper motor housing recess formed on the inner surface.

The structural inner panel also includes a plurality of brackets connected on the outside surface used for providing additional mounting and strengthening structure to the structural inner panel. Also the plurality of brackets each include at least one friendly hole used for loosely interweaving a tether to each of the plurality of brackets.

The tether has two ends each having at least one over molded retainer for connecting the tether to a wiper motor housing that is connected to the wiper motor housing recess. The tether is positioned through each of the friendly holes of each of the plurality of brackets in a manner that there is slack in each length of tether extending between adjacent friendly holes. In the event of an accident, the structural inner panel can break into pieces and the slack helps to catch and hold fragments of structural inner panel located between the plurality of brackets. The slack also reduces the tension between the plurality of brackets that would be present if the tether did not have slack, which in some applications can cause smaller pieces to break from the structural inner panel since the tether would be tensioned between the plurality of brackets and apply unnecessary force brought on by the tether being taught rather than slacked.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIGS.1-7there is shown a liftgate structure having a structural inner panel10with an outside surface12and an inner surface14. The structural inner panel is covered by an outer panel or outer panels (not shown) that have an exterior show surface. The liftgate structure, and the structural inner panel10are made of composite material, however it is within the scope of this invention for different materials to be used such as aluminum, manufactured diecast, metal, etc. The structural inner panel10has a lower perimeter surface area16extending across substantially the entire width of the structural inner panel10. The structural inner panel10also includes a wiper motor housing recess18formed on the inner surface14. Also included is a plurality of brackets including a left side bracket20, a center lower bracket22and a right side bracket24. It is within the scope of this invention for a greater or fewer number of brackets to be implemented depending on the particular application. The plurality of brackets are connected to the outside surface12of the structural inner panel10. Each of the plurality of brackets also include one or more friendly holes26, which are apertures through the respective brackets that allow for a tether28to pass through. As shown inFIGS.4-7the friendly holes26each have a curled edge30that creates a smooth edge to prevent any snagging of the tether28material.

The tether28includes two ends each having at least one over molded retainer32for connecting the tether28to a wiper motor housing34in the wiper motor housing recess18. The tether28is positioned through each of the friendly holes26of each of the plurality brackets20,22,24. While the present embodiment of the invention depicts the tether28as being routed through various bracket members, it is within the scope of this invention for the friendly holes26, to be formed with the structural inner panel10, thereby eliminating the need for different brackets20,22,24. Additionally the placement of the brackets20,22,24are located in predetermined tether reinforcement zones A, B, C inFIG.1, which are areas on the structural inner panel10that are determined to be structurally stronger areas of the liftgate than the portions of the inner panel not located in the tether reinforcement zones A, B, C. The tether reinforcement zones A, B, C are best for placement of connections for the tether28. The structural reinforcement zones A, B, C allow for the tether28to span areas of the composite liftgates that are structurally weaker and will benefit from having the tether28passing across the weaker area to be connected to the tether reinforcement zones A, B, C of the liftgate. The location of the tether reinforcement zones can vary depending upon the design of the liftgate. Factors such as shape, material thickness, material makeup and the dimensions of the liftgate can have an effect on the location of the tether reinforcement zone. Routing the tether28between each tether reinforcement zones A, B, C causes the tether28to cross weaker areas of the liftgate to create a type of safety net that will hold the structural inner panel together in the event of breaking of the structural inner panel in the weaker areas between the tether reinforcement zones A, B, C.

When assembled the tether28has a significant amount of slack through each of the friendly holes26to allow the tether28to flex and move in the event of a crash that breaks the structural inner panel10into several pieces. The slack of the tether28allows for additional force absorption. The amount of slack is at least 1.5 cm between each tether reinforcement zones A, B, C. For example, the portion of tether28length extending from reinforcement zones A to B, B to C and C to A each have greater than or equal to 1.5 cm of slack in each respective length.

The tether28is made of a tether material that has elongated fiber strands (shown inFIG.9) extending along the length of the tether in a parallel orientation. The elongated fiber strands107are held together by cross strands105(shown inFIG.9), but the elongated fiber strands107are able to slide apart, which is helpful during the method of forming the over molded retainer32as discussed below. The elongated fiber strands107used can be any type of suitable fiber material, and include but are not limited to glass fibers, carbon fibers, metal strands and aramid fibers. It is also within the scope of this invention for the tether28to have a bright color, such as white, yellow or any other lighter color that will allow for easier visual inspection of the assembled liftgate structure.

As shown in the drawings generally and with particular reference toFIG.14the tether28has two over molded retainers32,35at each end of the tether28, which are also spaced apart creating a length of tether107,107′ (shown inFIG.9andFIG.2) at opposite ends of the tether28. When connected to the structural inner panel12the length of tether107,107′ of each end will overlap in the region of the motor housing34thereby providing additional strength in the region of the motor housing34so that if the motor housing34were to break away from the structural inner panel12in the event if an accident it will be held by one or both ends of the tether28. Both of the over molded retainers have an aperture40formed through the respective over molded retainers32,35. The aperture40serves the purpose of receiving a fastener41that is used to connect the tether28to the structural inner panel10and the wiper motor housing34. This allows the tether28used to also prevent the wiper motor housing34from detaching and flying away from the liftgate structure in the event of an accident. Two of the over molded retainers32are configured to be received in snap hooks42formed on the other of the over molded retainers35. The snap hooks42are optional, but serve the purpose of aligning the aperture40in each of the over molded retainers32,35, which are aligned and receive a fastener41for connection of the tether28. During assembly one end of the tether28remains in the wiper motor housing recess18, while the other and of the tether28is passed through each of the friendly holes26and then enters back into the wiper motor housing recess18where the over molded retainers32,35on the second end of the tether28are aligned with the over molded retainers32,35of the first end of the tether28. Thus both ends of the tether28are fastened together to the wiper motor housing34and to the structural inner panel10in the wiper motor housing recess18. While the present embodiment of the invention describes the tether as being connected to the wiper motor housing34, it is within the scope of this invention to be connected to other components and not necessarily the wiper motor housing. For example the tether28can be connected to the structural inner panel10itself, any or the brackets20,22,24or the ends of the tether28can be connected together and left loose, without being fastened to any of the components of the assembly.

One of the problems encountered regarding the placement of retainers on fibrous tethers is that often retainers are pinched or crimped onto the tether28. This causes breakage of the fibers, which weakens the strength of the tether28. The method, according to the present invention increases the strength of the retainer32,35and tether28by overmolding the retainer32,35onto the tether28using injection molding techniques. Using this process the fibers are encapsulated with a molten resin, thereby maintaining their integrity and not breaking the fibers, which results in a stronger tether. Referring now toFIGS.8and9a method of overmolding a retainer onto the tether will now be discussed.FIG.8shows upper half101, which is the upper half shown inFIG.9, of an injection molding machine100, which has a mold cavity102for receiving molten resin.FIG.9shows both the upper half101and lower half103of the injection molding machine100. It is within the scope of the invention for the upper half101and the lower half103to be reversed depending on a particular application. The lower half103also has a mold cavity102′ that aligns with mold cavity102of upper half101. The mold cavity102′ has a pin tool104extending from the surface of the mold cavity102′.FIG.9also shows tether material106placed across the mold cavity102′ with the pin tool104sliding through the fibers of the tether material106. The pin tool104is shaped to push the fibers aside without breaking the fibers. The pin tool104is configured to create the aperture in the over molded retainer, which is used to receive the fastener when attaching the finished tether to the liftgate.

Referring toFIGS.8and9the method includes the steps of providing an injection molding machine100having at least two mold pieces101,103that form the mold cavity102,102′ when the mold pieces are positioned in a mold closed position. Injection molding machine is operable to move the mold pieces between a mold open position and the mold closed position. The method also includes a step of providing an injection head, which is not shown, connected to the mold cavity for delivering molten resin to the mold cavity. There is also tether material that is formed into a tether, which has an elongated body made of fiber strands, where the body has two ends where the retainers are over molded near. Where the retainers are over molded onto the tether material will depend upon a particular application; however they are generally near each of the two ends sense as described above the two ends of the tether overlap during connection of the tether to the structural inner panel10. Provided in the mold cavity102, as discussed above are pin tools that extend from the surface of the mold cavity.

During the molding method a step of moving the mold pieces to the mold open position allows access to the mold cavity. Then during a step of loading the at least one of the two ends of the tether are loaded into the mold cavity by pushing the elongated body of the tether onto at least one of the plurality of pin tools. It is within the scope of this invention for multiple pin tools to be positioned within the mold cavity, or they may be positioned within separate mold cavities, which are part of the same injection molding machine. During the step of loading the tether each one of the plurality pin tool slide past the fiber strands so that the pin tool extends completely through the elongated body of the tether. Next the step of moving the mold pieces to the mold close position takes place, followed by injecting molten resin into the mold cavity and allowing the molten resin to cure and encapsulate portions of the fiber strands. During the step the over molded retainers are formed onto the tether and the plurality of pin tools cause the formation of a through hole through each of the over molded retainers. Finally the injection molding machine is opened and the completed tether with over molded retainers is removed.

Referring now toFIG.10an alternate embodiment of a tether128is shown being connected between the structural inner panel10and a structure130. The structure130can be any type of bracket as shown in the previous figures, wiper motor housing or any type of component of the liftgate. In the present embodiment of the invention the tether128extends underneath the structure130and is bonded to the structural inner panel10and structure130using an adhesive132. In the event that the tether128encounters a force strong enough to break the bond of the adhesive132, the tether128has an over molded stop134formed on the tether128using the methods above. Over molded stop134is designed to come into contact with the structure130to prevent the tether128from sliding away from the structure130if the load exceeds adhesive strength.

Referring now toFIG.11another alternate embodiment is shown. In this alternate embodiment there is a tether136pinched between the structural inner panel10and a structure138that has an aperture140and shoulder142for receiving an over molded stop144that has a neck146and a shoulder148. The neck146is configured to slide through the aperture140and the shoulder148is configured to contact the shoulder142of the structure138. In this embodiment of the invention the over molded stop144is aligned and held in place using the neck146extending through the aperture140, while the shoulder148of the over molded stop144press against the shoulder142of the structure138to prevent the tether136from sliding away from the structure138. Connection between the structure138and the structural inner panel10can be accomplished using different techniques including fasteners, adhesives, etc. The structure138can be any type of bracket as shown in the previous figures, or wiper motor housing or any type of component of the liftgate.

FIG.12shows an alternate embodiment of the invention where the structural inner panel10has three separate tethers228,230,232. Tethers228,230have a different width than tether232, and extend between a center bracket234and side brackets236,238. Tether232extends between side brackets236,238and has a more narrow width. Each tether228,230,232is connected at each end to a bracket using a fastener extending through an over molded retainer. However it is within the scope of this invention for each end of the tether228,230,232to be adhesively bonded and pinched behind the respective brackets. The difference between tethers228,230and the tether232is the width, which results in the tethers having different strengths. This embodiment of the invention allows for different types of tethers to be used in a particular application, thereby providing different degrees of strength at different locations on the structural inner panel10.

FIG.13shows another alternate embodiment of the invention. In this particular embodiment of the invention the structural panel10is reinforced with a single tether328. The single tether328is connected to the structural inner panel10at brackets330,332,334. The single tether328is connected to the structural inner panel10by pinching the tether328behind each of the brackets330,332,334; which are connected to the structural inner panel10using fastener adhesives or other attachment mechanisms. Additionally, as shown the tether328is also bonded to the structural inner panel10using an adhesive336in the area behind each of the brackets330,332,334.