This invention relates to a compression limiter fastener assembly that includes a threaded fastener element and a compression limiter
Often two assembly members are fastened together with a fastener element. For example, fastener elements have long been used to assemble parts of an automotive engine and other components together. A non-threaded hole is in the first assembly member and a threaded hole is machined in a second assembly member. For example, an intake manifold or oil pan may be the first assembly member and an engine block with threaded holes may be the second assembly member.
A threaded fastener with a head passes through the non-threaded hole and threadedly engages the threaded hole. The head on a washer engages the first assembly member about the non-threaded hole to retain the first and second assembly members together. While engines of the past had engine blocks of iron-based metals, typical engine blocks today have major portions made from aluminum which is substantially lighter than iron but on the other hand is also softer than iron and more prone to scratching. Furthermore, todays engines often use high compressions during the engine cycle, so it is critical that there is no leakage of air or combustion products from the cylinder and other critical components of the engine. Sealing surfaces of the engine need to be scratch free and the sealing gaskets cannot be over compressed due to over tightening, otherwise leakage may occur which would undesirably lower the end compression ratio of the engine. These aspects of todays engine place additional requirements that a fastener must address.
Furthermore, other assembly members or parts installed to the engine, for example oil pan covers and intake manifolds are more commonly made from reinforced plastic material. The use of plastic material provides a manufacturing tolerance stack up due to the inherent characteristic of the injection or other molding techniques used to make the plastic part. The thermal cooling and molding processes are not as precise as the machining of an aluminum engine block and as such certain misalignment of the holes used to install the assembly members together may occur. By today's standards, typically acceptable misalignment of a hole in a plastic part may be up to 2 mm relative to a corresponding hole in an engine block. One can spend great time and effort in eliminating these manufacturing tolerances in large and expensive members, but it is more expeditious to have a less expensive fastener assembly built to accommodate the manufacturing tolerances in the larger parts that may result in potential partial misalignment in the holes in the large parts.
Furthermore, due to the nature of certain assembly members made from plastic material, a compression limiter must be used with the fastener element to prevent excessive tightening force from otherwise cracking or otherwise exerting a compression set into the plastic material which can compromise the sealing gasket effectiveness between the two assembly members. These compression limiters must be made from material that can withstand the severe thermocycles that occur in a nearby engine block. Presently, known commercially available elastomers cannot durably survive the thermocycle issues presented by a nearby engine block. Most compression limiters in this environment are thereby made from metal material.
Furthermore, a preload range of any sealing member between the two assembly members need to be between a yielding point at the high end of the range and a separation point at the low end of the range. A spring member, commonly being a spring washer, may be used to keep the desirable preload range between the high and low points and also compensate for slackening of the plastic and other materials of the two assembled members when fastened together. The spring member can take into account the settlement of the material, particularly any elastomeric and plastic material.
In addition, many fasteners are assembled by machines or robots. The present state of art in robotics desires that the drive head is in an axially predetermined position to allow the robot to easily engage and then tighten the drive head to fasten the fasten assembly in place. This predetermined position makes it important to position the threaded fastener element relative to the compression limiter before installation of the compression limiter in the hole of the first assembly member. The compression limiters have often taken the form of a sleeve which also protects the threads on the fastener element from damage during shipment and handling.
What is a desired is a compression limiter fastener assembly that can be expeditiously made and provide for high thermal cycles, compensate for manufacturing tolerances in the assembly parts, limit compression on any plastic assembly member and any interposed gasket or sealing member, and reduce the risk of a point of a threaded fastener from scratching critical surfaces on an assembly member during installation. What is also desired is a fastener element that can be axially preset in position in a compression limiter that protects the threads and be captive in the compression limiter even when exposed to normal shipping and handling until installation.
In accordance with one embodiment of the invention, a compression limiter fastener assembly for assembling a first assembly member to second assembly member has a fastener element with a drive head and a shank extending from the drive head having a non-threaded body portion proximate to the drive head and a distal threaded portion positioned at a distal portion of the shank opposite from the drive head. The drive head is constructed to be engageable to a drive tool for actuating fastening of the fastener assembly. A sleeve element has a tubular section with a bore therethrough sized to surround the threaded portion and the non-threaded body portion of the shank with clearance about the shank to allow the shank to be laterally movable in the bore. Preferably the bore is circular in cross-section and the lateral clearance allows 360° of movement. The sleeve element has at least one radially inwardly extending tab engaging the shank such that the threaded section is axially retained within the confines of the bore within the axial extent of the sleeve element for protection until installation of the fastener element to the first and second assembly member.
The sleeve is constructed to fit within a hole of the first assembly member. The sleeve is axially dimensioned to fully extend through the hole in the first assembly member to function as a compression limiter for the first assembly member. The at least one tab is disengageable from the shank upon sufficient axial force during installation to allow the threaded section to move through the bore and engage a threaded hole in the second assembly member. This disengagement may be caused by the tabs being flexible. Alternatively, the tabs may threadably engage the shank and the shank can rotate to axially move into place.
A load distribution element is located between the drive head and the first assembly member to distribute compressive loads from the drive head to the first assembly member. In one embodiment, the load distribution element is a spring member element seated under a bearing surface of the drive head. In another embodiment, the load distribution element is a collar integrally formed with the sleeve and extending radially outwardly at one end of the sleeve element to be interposed between the bearing surface of the drive head and the first assembly member. The sleeve member and at least one tab is made from a metal wherein the tabs are integrally formed with the sleeve from a punch operation which may include a cold upset. In one embodiment, the at least one tab is a plurality of tabs that are equally circumferentially spaced about the sleeve.
Preferably, the shank has a groove circumferentially extending about the shank that is axially positioned between the drive head and the threaded portion for receiving the at least one tab to retain the portion of the shank axially set relative to the sleeve until installation. Alternately, the at least one tab engages one of the threaded section or the groove in the shank for retaining the axial position of the shank relative to the sleeve wherein the point of the threaded fastener is retained within the axial confines of the sleeve until installation.
Reference now is made to the accompanying drawings in which:
Referring now to
The fastener 14 has a drive head 22, shank 24 that includes a non-threaded body 26 and a distal threaded portion 28 as more clearly shown in
As shown in
As shown in
It should also be noted that an optional sealing gasket or other settable seal 54 may be interposed between the first and second assembly members. The thickness of seal 54 is exaggerated in the
In this position shown in
Referring now to
The collar 16 is interposed between the bearing surface 60 of the head 22 and the exposed surface 41 of first assembly member 40 and helps spread the compressive force about the first assembly member to help prevent excessive setting forces from being exerted onto assembly member 40 near and about the aperture 42. The length of the main portion 18 of the sleeve 12 applies a hard stop to the compressive forces and also prevents excessive compressive forces from deforming the first assembly member 40 and also from excessively deforming the optional gasket 54 between the first and second assembly members.
Referring now to
The end of sleeve 112 has tabs 20 to engage the threaded portion 28 or groove 30 in the same fashion as the first embodiment.
When the compression limiter fastener assembly 110 is installed as shown in
The compressive limiters 10, 110 are able to compensate for variations in thickness of the first assembly member 40. It is also preferable that the sleeves 12 and 112 and the threaded fastener can be manufactured via cold forming to accommodate different hole sizes as demanded by various manufacturers. Furthermore, by having the fastener member 14 preset and captive in the sleeve as above described protects the threads against damage, prevents the point from scratching or damaging other parts, and presets the axial position of the drive head.
Variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.