Abstract:
A cam cover for a cylinder head of an internal combustion engine which has an aperture in the cam cover adapted to permit spark plug installation into the cylinder head and two tabs protruding vertically from the cam cover adapted to retain a boss extending from an ignition coil is disclosed. The ignition coil has a portion adapted to fit over the spark plug and an orifice through the boss. The cam cover also has a recess between the tabs with the recess extending into the cam cover which is adapted to accept a self-tapping screw in the event of a tab failure. The tabs have a varying cross-section along their length such that they allow the orifice to be slid over the tabs by them squeezing together and then snapping into place when the orifice clears the ramps on the side of the tabs.

Description:
BACKGROUND 
     1. Technical Field 
     The present development relates to retaining ignition coils or other engine accessories on covers of internal combustion engines. 
     2. Background Art 
     Spark-ignition engines typically have one spark plug/ignition coil per cylinder. The spark plug is typically threaded into the cylinder head through an aperture in the cam cover. The ignition coil is assembled over the tip of the spark plug that extends away from the combustion chamber. The ignition coil has a boss that defines an orifice through which a threaded fastener engages the cam cover to retain the coil in place. In some cases, a fastener may be inserted into a tapped hole in the cam cover. The threaded fastener and threaded plug are more costly and necessitate additional parts for each cylinder of the engine. 
     U.S. Pat. No. 6,609,508 B2 discloses a U-shaped retaining clip for attaching an ignition coil assembly to a cam cover. This design obviates the need for a threaded fastener. However, it requires a modification of existing cam covers and requires that the ignition coil engage the U-shaped retaining clip which necessitates a change in the design of the coil. Furthermore, no servicing procedure is disclosed in the event that one of the plastic elements fails, for example, during maintenance operations. 
     The above limitations and disadvantages are addressed by the present development as summarized below. 
     SUMMARY 
     A cam cover for a cylinder head of an internal combustion engine defines an aperture for installing a spark plug in the cylinder head. Two tabs extend outwardly from the cam cover at a location near the aperture. A boss extending from an ignition coil receives the two tabs to retain the ignition coil on the spark plug in a snap-fit relationship. 
     According to an embodiment of the present disclosure, a standard ignition coil from the prior art with no modifications is used. By using a standard ignition coil standardization of parts across engine and vehicle lines is facilitated. In some prior art applications, a brass insert is provided in the cam cover to mate with the threaded fastener as well as a cylindrical aluminum insert in the mounting hole in the coil. The present development obviates the need for the brass insert, the threaded fastener, and the aluminum insert per ignition coil and for each engine accessory using this embodiment. 
     A method for replacing a coil installed on a cam cover of a cylinder head is disclosed in which tabs protruding from the cam cover are squeezed together to facilitate removing the coil by sliding the orifice of the coil boss over the tabs. A replacement coil is installed by placing the orifice of the replacement coil boss over the tabs, placing the replacement coil over a spark plug mounted into the cylinder head, and pressing down on the replacement coil thereby squeezing the tabs together to allow the replacement coil to be coupled with the spark plug. 
     In the event that a tab is damaged, the replacement coil is installed by placing the orifice of the coil over the cam cover surface, pressing the coil over a spark plug mounted in the cylinder head, threading a self-tapping screw through the orifice of the coil boss, and screwing the self-tapping screw into a recess formed in the cam cover. 
     Much of the discussion above is directed to an application involving a spark plug coil secured to a cam cover. However, the present development may apply to other engine accessories. For example, it is known to have sensors and actuators mounted within a cam cover or any engine cover. An aperture is provided in the cam cover through with the wires travel to the sensor or actuator enclosed between the cam cover and cylinder head or through any cover. A non-limiting list of examples includes: a camshaft position sensor, a variable valve timing actuator, and a valve lift actuator in regards to a cam cover. In regards to other covers, a non-exhaustive list may include: temperature, pressure, humidity, Hall effect, position, and magnetic sensors as well as piezoelectric, hydraulic, and solenoid actuators. 
     The above, as well as other advantages of the present development will become apparent to those skilled in the art from the detailed description when considered in the light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a fragmentary perspective a cylinder head with a cam cover through which several coils are installed; 
         FIG. 2  is a fragmentary, plan view of the cam cover showing an installed coil; 
         FIG. 3  is a fragmentary, elevation view of the cam cover and an uninstalled coil; 
         FIG. 4  is a fragmentary, elevation view of the cam cover and an installed coil; 
         FIG. 5  is a fragmentary, elevation view of the cam cover and an installed coil showing an alternative embodiment including a service repair part; 
         FIG. 6  is a plan view of tabs according to an alternative embodiment in an unsqueezed configuration; 
         FIG. 7  is a plan view of tabs according to an alternative embodiment in a squeezed configuration; 
         FIG. 8  is a fragmentary, elevation view of a cover and an adapter, the adapter being uninstalled; 
         FIG. 9  is a plan view of the adapter showing an example drive feature; 
         FIG. 10  is a cross-sectional view of a cover and an adapter with a tool coupled to the drive feature of the adapter; 
         FIG. 11  is a fragmentary, elevation view of a cover with an installed adapter; 
         FIG. 12  is a fragmentary, elevation view of a cover with an installed adapter and a accessory coupled with tabs of the adapter; and 
         FIG. 13  is a fragmentary, elevation view of a cover and an adapter with the adapter being uninstalled. 
     
    
    
     DETAILED DESCRIPTION 
     An internal combustion engine may have one or two cylinder heads which form the upper portion on the combustion chamber for three to six cylinders depending on whether the engine is configured as an I-4, I-6, V-6, or V-8 engine. Intake and exhaust valves permit fresh air to enter the combustion chambers and exhaust to exit the combustion chambers are actuated by a valvetrain mechanism in the cylinder head. A cover encloses and seals the valvetrain from the outside. The cover is generally referred to as a valve cover with reference to either a cam-in-block or an engine with an overhead camshaft. The term “cam cover” used herein applies to what is commonly referred to as: a valve cover, a rocker arm cover, or a cam cover. 
     Referring to  FIG. 1 , a cam cover  1  is mounted on cylinder head  2  via fasteners  3 . Ignition coils  4  protrude through cam cover  1  through apertures defined in cam cover  1 . Ignition coils  4  couple with spark plugs (not visible) mounted in cylinder head  2 . Ignition coils  4  have connectors  5  provided for making electrical connection to ignition coils  4 . Ignition coils  4  also have bosses  6  extending outwardly from ignition coils  4  with retaining orifices  7  defined in bosses  6  for securing ignition coils  4  to cam cover  1 . Cam cover  1  seals a non-combustion side  8  of cylinder head  2 , keeping lubricant for the rocker arms and other moving parts within the space between cylinder head  2  and cam cover  1 . 
     Referring to  FIG. 2 , a cam cover  10  is shown with an installed coil  12  according to one embodiment of the present disclosure. Coil  12  has a connector receptacle  14  to which a wiring connector may be connected. Coil  12  has a boss  16  that defines an orifice  18 . Tabs  20  extend outwardly from cam cover  10  through orifice  18  to retain coil  12 . 
     Referring to  FIG. 3 , coil  12  is aligned with, but not installed on cam cover  10 . Cam cover  10  defines an aperture  22  through which a spark plug  24  is installed. Coil  12  fits over spark plug  24  as orifice  18  is fitted over tabs  20 . The distance between centerlines of coil  12  and orifice  18  is the same as the distance between the centerline of aperture  22  and the center of tabs  20 . 
     When properly aligned, coil  12  engages spark plug  24  as orifice  18  engages tabs  20 . When orifice  18  is first brought into contact with tabs  20 , orifice  18  slides over distal sections  25  of tabs  20 . As orifice  18  of boss  16  is lowered further, orifice  18  engages a ramp of engagement section  26  of tabs  20  and can be lowered no further without tabs  20  moving. By applying a force on boss  16 , tabs  20  bend toward each other to fit through orifice  18 . When orifice  18  of boss  16  clears engagement section  26  of tabs  20 , tabs  20  return to their original, undeformed, vertical position when orifice  18  engages body sections  27  of tabs  20 . A radially extending surface  28  holds boss  16  and coil  12  in place on cam cover  10   
     Continuing to refer to  FIG. 3 , tabs  20  are of constant cross section along the length of distal sections  25 . Proceeding further down the length, the cross section increases along engagement sections  26 , in one embodiment the cross section increases monotonically in a direction toward cam cover  10 . As shown in  FIG. 4 , engagement sections  26  appear to increase in width linearly along the length, i.e., forming a ramp. This is a non-limiting example. In one embodiment, engagement sections  26  have a feature to facilitate grabbing the tabs with a tool so that they can be squeezed together for removal of the coil or other engine accessory. In embodiments with such a grabbing feature on engagement section  26 , distal section  52  may be omitted. Engagement sections  26  may be any shape, i.e., which allows orifice  18  to be guided over tabs  20  and then snap back after orifice  18  clears engagement sections so that the coil or other accessory is secured in place. Proximate section  27  has a constant cross section with the outside dimension being about the same or slightly less than the inside dimension of orifice  18 . The length of body section  27 , indicated as L in  FIG. 3 , is at least as long as the height of boss  16 , indicated at H in  FIG. 3 , so that engagement sections  26  clear boss and snap to their original vertical shape to hold boss  16  in place. 
     In  FIG. 4 , an installed coil is shown. According to an embodiment of the present development, removal of coil  12  or spark plug  24  requires the removal of boss  16  from tabs  20 . A pliers  26  can be used to push tabs  20  together while pulling up on coil  12  for removal. When coil  12  is removed, spark plug  24  can be accessed. When removing coil  12 , tabs  20  may be damaged or broken. If the tabs are found inadequate to retain coil  12 , a service fix, as shown in  FIG. 5 , includes a self-tapping screw  30 . At least distal section  25  and engagement section  26  of tabs  20  are removed to accommodate self-tapping screw  30 . Cavity  28 , provided in cam cover  10  to accommodate self-tapping screw  30 , can be seen in  FIGS. 3 and 4 . 
     Plan views of one alternative embodiment of tabs  50  are shown in  FIGS. 6 and 7 . In  FIG. 7 , tabs  50  are in an unsqueezed state, in which a gap of X exists between the two tabs  50 . The distal section  52  has a diameter equal to or slightly less than D, the diameter of the orifice  56  with which tabs  50  engage. Tabs  50  also have engagement sections  54 , which, as shown in  FIG. 7 , have a broadest dimension from the edge of one tab to the other of W. In  FIG. 8 , the tabs are shown squeezed together. In such a configuration, a width of the outside edges of engagement sections  54  is D or less so that engagement sections  54  can be placed over an orifice of diameter D. As squeezed together, the width of the two distal sections  52  is D minus X. 
     In  FIG. 3 , coil  12  is engaged with spark plug  24  and retaining orifice  18  of boss  16  couples with tabs  20 . According to other embodiments of the disclosure, other accessories can be coupled with tabs similar to tabs  20 , but supplied at a different location on the cam cover or on any engine cover. Engine accessory may be one of: a camshaft position sensor, a variable valve timing actuator, and a valve lift actuator. In such a case, an aperture is provided for an operative end of the accessory to gain access inside the cam cover. 
     Embodiments of the present disclosure in which the tabs are integral with the cover is appropriate for situations in which the mold for the cover is being newly designed or redesigned. However, in the middle of a production run, redesigning the mold to integrate the tabs may be prohibitively expensive. Thus, according to an alternative embodiment, shown in  FIG. 8 , cover  40  having an aperture  42  to provide access for an accessory and having a cylindrical cavity is coupled with an adapter  46 . Cover  40  may be a cover of the prior art in which cylindrical cavity  44  might have been fitted with a brass insert so that a conventional bolt could be used to secure the accessory. According to the present development, adapter  46  has a connection section  48  having a diameter roughly equal to the diameter of cylindrical cavity  44 . Adapter  46  has tabs  50  which include proximate section  52 , engagement section  54 , and distal section  56 . Defined in the top of connection section  48  is a drive feature  60 . In the embodiment of  FIG. 8 , the drive feature is a flathead key. Alternatively, drive feature  48  may be keyed to permit it to mate with other known drivers, such as Allen, TORX, Phillips, etc. 
     A plan view of adapter  46  is shown in  FIG. 9  in which distal section  56  and engagement section  54  can be viewed. Connection section  48  has a groove (or key)  60  defined in an end closest to the tabs. In  FIG. 10 , adapter  46  is slid into cylindrical cavity of cover  40  and a tool  61  is inserted in groove  60 . A torque applied to tool  61  is transmitted through groove  60  to rotate adapter  46 . By rotating adapter  46  with respect to cover  40 , frictional forces causes the rubbing surfaces to heat up and melt. Upon cooling, adapter  46  is coupled with cover  40 . This process is commonly known as spin welding. The coupled adapter  26  and cover are shown in  FIG. 11 . 
     Also shown in  FIG. 11  is that proximate section  52  extends outwardly from cover  40  is length, L. Accessory  64  has height H, at least in the vicinity of retaining orifice  63 . Accessory  64  is held in place by engagement sections  54  of adapter  46  by sliding retaining orifice  63  over adapter  46 . Referring now to  FIG. 12 , accessory  64  is shown installed on cover  40 . Accessory has a sensor  65  which gains access inside of cover  40  through aperture  42  (which is not called out in  FIG. 12  since it is filled with sensor  65 ). Sensor  65  can be any known type of sensor. Alternatively, element  65  is an actuator. To seal the accessory at the aperture in cover  40 , an O-ring  66  can be provided in groove  66 . Alternatively, any other type of known sealing configuration can be provided. The snap-fit relationship of the tabs of adapter  40  with accessory  64  provides sufficient downward force to deform the O-ring or other seal. 
     Another embodiment of an adapter  68  is shown in  FIG. 13 . Connection section  70  comprises threads. Cylindrical cavity  44  of cover  40  has a diameter D. The threads on connection section have a major diameter, M, which is greater than D, and a minor diameter, m, which is less than D. Adapter  68  has tabs  72  which include: a proximate section  74 , engagement section  76 , and distal section  78 . Connection section  70  has a drive feature  80  formed in the end of connection feature closer to tabs  72 . Drive feature  80  can be any keyed arrangement such as: flat head, TORX, Allen, Phillips, etc, but shown as a flat head in  FIG. 13 . The threads on connection section  70  are self-tapping threads. By inserting adapter  68  into cylindrical cavity  44  as far as possible; placing a tool, such as tool  61  of  FIG. 10  into drive feature  80 ; and rotating adapter  68  by such a tool, the self-tapping threads engage with the surface surrounding cylindrical cavity  44 . Adapter  68  is pulled into cavity  44  until the threads are fully engaged. 
     Embodiments of the disclosure can be practiced otherwise than as specifically illustrated and described with departing from its spirit or scope. For example, while the present development has been described for mounting an ignition coil, those skilled in the art will appreciate that the present development can be used to attach various types of components within the scope of the development.