Abstract:
An improved compact engine construction that facilitates positioning in close quarters while still affording ease of assembly and servicing. This is accomplished by mounting the camshafts at different heights and by providing a two-piece spark plug tube in the cylinder head that facilitates removal in sections rather than all at once.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an internal combustion engine and more particularly to an improved spark plug mounting arrangement for the cylinder heads of such engine. 
     With many types of internal combustion engines and particularly those utilized for automotive application, the ignition system includes an individual coil that is associated with each spark plug of the engine. These individual coils are mounted on the upper end of the electrical terminal that connects the coil output to the spark plug. This presents a problem in servicing as may be best understood my reference to FIG. 1, which shows a typical prior art type of construction, utilized for this purpose. 
     As seen in this figure, an internal combustion engine, indicated generally by the reference numeral  21  has a cylinder head assembly, indicated generally by the reference numeral  22 . This cylinder head assembly  22  is comprised of a cylinder head  23  and a cam cover  24  that is affixed to the cylinder head  23  with a sealing gasket interposed there between (not shown). This defines a cam chamber  25  in which a valve actuating mechanism, shown partially and identified by the reference numeral  26  is positioned. 
     The cylinder head  23  has a lower surface in which combustion chamber recesses  27  are formed. The combustion chamber recesses  27  of the cylinder head defining the combustion chamber is formed with a tapped opening  28  so as to receive the threaded end of a spark plug  29  with its terminals projecting into the combustion chamber. 
     It will be seen that the upper end of the spark plug  29  extends into a tubular spark plug tube  31  which has its lower end sealingly engaged in a spark plug tube receiving pocket  32  of cylindrical configuration formed in a lower surface  33  of the cylinder head  23 . This tubular spark plug tube  31  extends upwardly and passes through an opening  34  formed in the cam cover  24  with a sealing grommet  35  being interposed there between. 
     The spark plug is fired by a coil  36  that is activated by an associated ignition system and terminal  37  that are inserted into the tubular spark plug tube  31  with the lower end of the terminal engaged with the terminal end of the spark plug  29  as shown in the cylinder to the right in FIG.  1 . 
     A problem in connection with servicing arises, however, when the placement of the engine  21  is such that one or more of the tubular spark plug tube  31  is disposed in an obstructed area. For example, FIG. 1 shows a conventional brake booster  38 , which overlies the end cylinder of the engine and accordingly blocks the removal of the coil  36  and terminal  37  for servicing of the spark plug  29 . 
     In addition to the servicing problem, this type of construction also presents difficulty in engine assembly. That is, it is necessary when building the engine or when servicing the engine to place all of the tubular spark plug tube  31  in the cylinder head  23  and then attach the cam cover  24  while guiding the sealing grommets  35  around the periphery of the upwardly projecting tubular spark plug tube  31 . The greater number of cylinders, the more difficult it is to connect and assemble them. 
     It is, therefore, a principal object to this invention to provide an improved cylinder head structure of this general type, but one in which the spark plugs can be easily accessed for servicing without encountering the problems in connection with the prior art type of construction. 
     It is a further object to this invention to provide an improved spark plug receiving tube assembly for the cylinder head of an internal combustion engine that facilitates servicing and minimizes operational and assembly costs. 
     SUMMARY OF THE INVENTION 
     This invention is adapted to be embodied in a cylinder head assembly for an internal combustion engine that comprises a cylinder head and a cam cover. The cam cover is affixed to the cylinder head so as to define a cam chamber between an upper surface of the cylinder head and the interior of the cam cover. The cylinder head is formed with at least one spark plug receiving, threaded hole leading into a combustion chamber of the cylinder head. The cylinder head forms a spark plug tube attaching hole that is greater in diameter than and surrounds the at least one spark plug receiving, threaded hole. A spark plug tube inserting hole is formed in the cam cover and is aligned with the cylinder head spark plug tube attaching hole. A lower spark plug tube is sealingly affixed at one end thereof to the cylinder head spark plug tube attaching hole. An upper spark plug tube is sealing engaged at one end thereof to the cam cover spark plug tube attaching hole and is sealingly engaged at the other end thereof to the other end of the lower spark plug tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view showing a portion of a prior art internal combustion engine and an associated component of a vehicle powered by the engine. 
     FIG. 2 is an end elevational view of an engine constructed in accordance with an embodiment of the invention and embodied in the engine compartment of an associated vehicle. 
     FIG. 3 is a top plane view of the cylinder head of the engine with the cam cover removed and operating components thereof removed. 
     FIG. 4 is a cross sectional view taken along the line  4 — 4  of FIG. 3 but showing the complete cylinder head assembly. 
     FIG. 5 is a top plane view of the cylinder head assembly. 
     FIG. 6 is a cross sectional view in part similar to FIG. 4 but closer to the end of the engine where the cam shafts are driven. 
     FIG. 7 is a cross sectional view in part similar to FIG. 4 and 6 but with the rocker arms removed. 
     FIG. 8 is a cross sectional view taken along the line  8 — 8  of FIG.  7 . 
     FIG. 9 is a top plane view of the portion of the cylinder head shown in cross section in FIG.  8 . 
     FIG. 10 is a cross sectional view taken along the line  10 — 10  of FIG.  7 . 
     FIG. 11 is a view, in part similar to FIG. 1, and shows how the removal of the coil and spark plug attaching terminal is facilitated with this invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now in details and initially primarily to FIG. 2, an engine constructed in accordance with an embodiment of the invention is identified generally by the reference numeral  51 . The engine  51  is shown positioned transversely in an engine compartment  52  of an associated motor vehicle. This engine compartment  52  is defined in part by a firewall or toe board  53  of the vehicle body. 
     The engine  51  is of the V8 type and is comprised of a cylinder block  54  having left and right banks designated by the subscripts  54 L and  54 R, respectively. These cylinder banks each are formed with four cylinder bores  55 , only one of which is shown in broken lines in FIG.  2 . Pistons  56  reciprocate in the cylinder bores  55 . 
     Connecting rods  57  connect the pistons  56  to a crankshaft  58  that is rotatably journalled in a crankcase assembly formed by a crankcase member  59  that is affixed to the lower end of the cylinder block  54  and an oil pan  61  that is affixed to and depends therefrom. The axes of the cylinder bores  55  are indicated at CL and CR, respectively, and which intersect at the rotational axis of the crankshaft  58 . 
     Left and right cylinder heads  62 L and  62 R are affixed to the cylinder banks  54 L and  54 R, respectively. These cylinder heads  62  are formed with combustion chamber recesses  63  which cooperate with the cylinder bores  55  and pistons  56  to form the combustion chambers of the engine  51 . Since the combustion chamber recesses  63  form the major portion of the combustion chamber volume at top dead center position, as times this reference numeral will be used to also designate the combustion chamber. 
     A lower surface of the cylinder head  62 , indicated at  64 , surrounds the combustion chamber recess  63  and is held in sealing engagement with the upper surface of the respective cylinder bank  54 L and  54 R. 
     Referring now additionally and primarily to FIGS. 3 and 4, the construction of each cylinder head  62  will be described in detail. On the side of the respective cylinder head  62  facing the valley between the cylinder banks, there is provided an inlet passage  65  that extends from an outer surface  66  of the cylinder head  62  to a pair of respective valve seats  67 . An induction system, indicated generally by the reference numeral  68 , is affixed in the valley between the cylinder banks. The induction system  68  includes an air inlet device (not shown) that draws atmospheric air from within the engine compartment  52  and a plenum or surge chamber served by this air inlet. Individual manifold runners  69  extend from the surge chamber of the induction system  68  to the cylinder head intake passages  65  for each bank. Poppet type intake valves  71  cooperate with the valve seats  67  and control the flow of intake air into the combustion chamber  63 . These poppet type intake valves  71  are urged to their closed positions by a suitable return spring assembly (not shown). The intake valves  71  are opened by an intake camshaft  72  via a rocker arm assembly  73  that is pivotal in the cylinder head about a rocker arm shaft  74 . The intake camshaft  72  is driven at one half crankshaft speed in a manner to be described. 
     Basically, the mounting for the intake camshaft  72  is provided by a camshaft mounting arrangement, indicated generally by the reference numeral  75  and which will be described in more detail later. This mounting arrangement includes a plurality of axially spaced intermediate bearing portions  76  that are engaged with the upper surfaces of projections  80  formed on the intake side of the cylinder head  62 . Each of the intermediate portions has an upper surface  77  formed only on the intake side thereof for a reason to be described. A bearing cap  78  is affixed to this upper surface  77  and the cylinder head  62  by threaded fasteners  79  at the intake side of the cylinder head. The opposite side of the bearing caps  78  is held in place by shorter fasteners  81  that connect the bearing cap  78  only to the intermediate bearing portion  76 . Bearing surfaces  82  formed by the intermediate bearing portion  76  and bearing cap  78  cooperate with bearing surfaces on the intake camshaft  72  for its journal support. The fasteners  79  are received in tapped holes  83  formed in the projections  80  of the cylinder head  62 . The fasteners  81  are received in threaded openings  84  formed in the intermediate bearing portion  76 . 
     Fuel is mixed with the air charge admitted by the induction system  68  to the combustion chambers  63  by means of fuel injectors  85  that are mounted in receiving openings  86  formed in the cylinder head  62 . These openings  86  communicate with the intake passage  65  through a transfer passage  87  so that fuel injected by the injectors  85  will flow smoothly with the intake air into the intake passages  65  and combustion chambers  63 . Positioned substantially on the cylinder bore axes CL and CR, are spark plugs  88 . The spark plugs  88  are received in threaded spark plug receiving openings  89  formed in the cylinder head  62  and which intersect the combustion chamber recess  63  coincident with the respective cylinder bore axes CL and CR. The spark gap  91  of the spark plugs  88  therefore, lies on the respective cylinder bores axes CL or CR to provide good flame propagation. 
     The spark plugs  88  are fired in a manner which will be described shortly to initiate combustion and the burning gases expand and drive the pistons  56  downwardly in the cylinder bores  55  so as to drive the crankshaft  58 . 
     Exhaust passages  92  are formed in the cylinder head  62  and extend from exhaust valve seats  93  formed in the combustion chamber recess  63  of the cylinder head  62  to an exit port formed in an outer surface  94  of the cylinder head  62 . This outer surface  94  is disposed on the side opposite the intake passages  65 . 
     A suitable exhaust system including an exhaust manifold, indicated generally by the reference numeral  95 , is mounted on the cylinder head surface  94  and has individual runner sections  96  that communicate with the exhaust passages  92 . A suitable exhaust system (not shown) is attached to the exhaust manifold  95  and discharges the exhaust gases to the atmosphere. 
     The flow of exhaust gases through the exhaust passages  92  is controlled by means of poppet type exhaust valves  97  that are mounted in the cylinder head  62  on the side opposite the intake valves  71 . Like the intake valves  71 , the exhaust valves  97  are urged toward their closed positions by coil spring assemblies, which are not shown. 
     An exhaust camshaft  98  is journalled in the cylinder head  62  in a manner, which will be described. This is exhaust camshaft  98  operates the exhaust valves  97  through a rocker arm assembly  99 . The rocker arms of this rocker arm assembly  99  are pivotally supported on a rocker arm shaft  100 . 
     The intermediate bearing portion  76  that support the intake camshaft  72  also support the exhaust camshaft  98 . However, in this instance, a bearing surface  101  is formed in a lower part  102  of each intermediate bearing portion  76 . This part  102  is engaged with an elevated surface  103  of the cylinder head  62 . First and second threaded fasteners  104  and  105  affix the intermediate bearing portion  76  to the cylinder head  62 . Thus, because of the fact that the exhaust camshaft  98  is mounted directly on the cylinder head surface  103  and in bearing portions  106  thereof, it can be mounted lower than the intake camshaft  72  which is mounted above the elevated surface  103 . The significance of this will be described later. 
     Like the intake camshaft  72 , the exhaust camshaft  98  is also driven at one-half crankshaft speed by a suitable timing drive. Although any known type of timing drive may be used for this purpose, it should be noted from FIG. 4, that the intake camshaft  72  has affixed to its forward end a compound sprocket assembly  107  that is comprised of a first sprocket  108  which is driven from the crankshaft by a suitable driving arrangement at one half crankshaft speed. These places the larger sprocket required for the speed reduction in the area of the valley between the cylinder banks  54 L and  54 R. A second sprocket  109  is formed in the compound sprocket  107  and drives a third sprocket  111  associated with the exhaust camshaft  98  through a further drive. By placing the larger sprocket required for the speed reduction in the area of the valley between the cylinder banks  54 L and  54 R the overall width of the engine  51  can be reduced as seen in FIG.  2 . 
     It has been previously noted that the intake and exhaust camshafts  72  and  98  are journalled between the individual cylinders of the engine by the bearing arrangements provided for by the intermediate bearing portions  76  and the bearing caps  78  cooperating with, respectively, the cylinder head elevated surface  103  and the intermediate bearing portion  76  and particularly the bearing surfaces  101  thereof. The cylinder head elevated surface  103  are formed on raised areas  112  of the cylinder head  62  which are generally aligned with the raised portions  80  on the intake side. A similar arrangement is provided at the back ends of the camshafts  72  and  98 . 
     At the front of the engine  51  and adjacent the driving sprockets  107 ,  108 ,  109  and  111 , a somewhat different bearing arrangement is employed. This bearing arrangement is shown in FIG.  6  and is comprised of a bearing cap  113  that cooperates with a bearing surface  114  formed in an intermediate bearing member  115  for journaling the front end of the exhaust camshaft  98 . The intermediate bearing member  115  also journals the adjacent end of the intake camshaft  72  along with a bearing cap  116 . Long fasteners  117  pass through the bearing caps  113  and  16  into the cylinder head  62  for securing these members together. Shorter fasteners  118  pass through only the bearing caps  113  and  116  and the intermediate bearing member  115  for completing the hold down of the bearing caps  113  and  116 . 
     The timing drive for driving the intake and exhaust camshafts  72  and  98 , respectively, including the sprockets  108 ,  109  and  111  can employ a variable valve timing mechanism. This variable valve timing mechanism is controlled by a solenoid operated pilot valve  119  that is mounted on an axis VT at the front of the engine and may be of any known type that varies the timing of one or both of the camshafts  72  and  98  relative to the crankshaft. This solenoid operated pilot valve  119  includes a valve spool  121  that cooperates with suitable passages formed in the intermediate bearing member  115  for varying the valve timing. 
     In addition, a variable valve lift mechanism is provided in either or both of the rocker arm assemblies  73  and  99  for varying the degree of lift of the valves operated by these rocker arm assemblies  73  and  99 . This variable valve lift mechanism may comprise, for example, two different rocker arms operated by different cam lobes and which are selectively coupled by a suitable coupling mechanism of any known type for their operation. A solenoid operated valve assembly, indicated generally by the reference numeral  122  is associated with the intake camshaft mounting assembly for controlling this variable lift mechanism. The valve assembly  122  includes a valve spool  123  that cooperates with suitable passages formed in the intermediate bearing member  115  for varying the valve lift. Of course, the solenoid operated pilot valves  119  and  122  may have their functions reversed. 
     In addition, the bearing cap  116  for supporting the front end of the intake camshaft also carries a phase angle sensor  124  which may be of any known type and outputs a signal to an ECU indicating the camshaft phase. This can be used for both varying the valve timing and lift as well as fuel injection and spark timing. 
     The cylinder head  62  is affixed to the associated cylinder block  54  and specifically the banks thereof by threaded fasteners. These threaded fasteners pass through holes  125  formed in the cylinder head  62  in the area of the front camshaft bearings but slightly to the rear of them and additional holes  126  that are formed in the area between the camshaft bearing portions provided by the raised cylinder head areas  112  and  80  which are aligned with each other as shown in FIG.  3 . 
     It has been previously noted that the variable valve lift rocker arm assemblies  73  and  99  are mounted on rocker arm shafts  74  and  100 , respectively. The mounting arrangement for these rocker arms shafts will now be described by particular reference to FIGS. 7 through 10. 
     Referring first to the support for the exhaust valve rocker arm assembly  99 , it will be seen that the cylinder head  62  is formed in the area of the raised area  112  with a shaft opening  127  through which the exhaust camshaft rocker arm shaft  100  passes. As may be seen in FIG. 8, the side surfaces of the intermediate raised area  112  are provided with outwardly facing shoulders  128  which form thrust surfaces for the rocker arm assembly  99  and the rocker arm shaft  100 . The front most raised portion on which the bearing cap  113  is mounted, is formed with a thrust taking outwardly facing shoulders  129 . 
     As may be seen in FIG. 9, these outwardly facing shoulders  128  and  129  may be machined by a cutting tool indicated in phantom line by the reference numeral  131  in FIG. 9 so as to machine the thrust surfaces for the appropriate type of rocker arm and shaft assembly utilized for providing the variable lift. 
     In connection with the intake rocker arm assembly  73  and specifically its rocker arm shaft  74 , this is journalled by a first bearing surface  132  formed in the cylinder head elevated surface  103  with which the lower part  102  of the intermediate bearing portion  76  is engaged. The intermediate bearing portion  76  is formed with a complimentary bearing surface  133  and this surface is bounded on one or both sides by thrust taking projections  134  formed on the bearing caps  78 . Again, by machining these surfaces it is possible to accommodate difference types of variable lift mechanisms and rocker arm assemblies. 
     The valve actuating mechanism which has been thus far described is mounted in part within the cylinder head  62  in a cam chamber formed at its upper portion. This cam chamber is closed by a cam cover, indicated generally by the reference numeral  135 . The cam cover  135  is detachably affixed to the cylinder head  62  in any suitable manner. 
     The mounting arrangement for the camshafts also provides a more compact arrangement that facilitates mounting in compact engine compartments particularly those having transverse engine placement as seen in FIG.  2 . If the camshafts  72  and  98  were positioned at the same level as shown by the phantom line view  98 A in this figure, the cylinder head and cam cover  135  would have to be quite a bit larger and the engine moved forwardly. However, with the lower mounting of the exhaust or outside camshaft as seen in this figure, the length L can be substantially reduced and the engine can be easily serviced even without moving the crankshaft axis forwardly. 
     It has been previously noted that the solenoid operated pilot valves  119  and  122  for controlling the valve timing and valve lift and the sensor  124  for controlling at least in part their operation extend upwardly from the respective supporting members i.e. the intermediate member  115 , the bearing caps  116 . These members also extend through openings in the cam cover  135  as best seen in FIGS. 5 and 6. 
     For example, the solenoid operated pilot valve  119  extends through an opening  136  formed in the cam cover  135  and is surrounded by a sealing elastic ring  137 . In a like manner, the cam phase angle sensor  124  passes through an opening  138  formed in the cam cover  135  and is sealingly engaged by an annular elastic seal  139 . Finally, the solenoid operated valve  122  extends through an opening  141  formed in the cam cover  135  and is sealed by an elastic seal  142 . Thus, each of these members  119 ,  122  and  124  may be readily serviced without having to remove the cam cover  135 . 
     The mounting and servicing for the spark plugs  88  will now be described by reference primarily to FIGS. 4,  5 ,  7 ,  10  and  11 . It has been previously noted that the spark plugs  88  have their threaded portions received in threaded openings  89  formed in the cylinder head  62 . A spark plug receiving tube assembly, indicated generally by the reference numeral  143 , extends from the area adjacent this cylinder head threaded spark plug receiving openings  89  through the cam cover  135 . 
     This spark plug receiving tube assembly  143  includes a lower tube  144  and an upper tube  145 . A two-part tube structure is employed for the reasons which will be apparent very shortly and which overcome the servicing problems attended with the prior art type of constructions as mentioned in conjunction with the description of FIG.  1 . 
     The cylinder head  62  is formed with a bored, plug tube receiving opening  146  in which the lower end of the lower spark plug tube  144  is fitted with a press type fit. This opening  146  is concentric to the axis of the spark plug  88  indicated at PA in FIG.  4 . 
     The upper spark plug receiving tube  145  is formed with a flanged lower part  147  that is sized so as to snugly engage the outer periphery  148  of the lower spark plug tube  144 . If desired, an O-ring seal may be provided in this area. 
     The upper end of the upper spark plug receiving tube portion  145  has an enlarged flange  149  which is complimentary to and received in an enlarged opening  151  formed in the cam cover  135 . Again, an O-ring seal, indicated at  152  may be provided in this area. 
     A combined coil mounting and spark plug terminal assembly, indicated generally by the reference numeral  153  is mounted on the tube assembly  143  and includes a terminal portion that is complimentary to and received on the terminal  154  of the spark plug  88 . This terminal portion, indicated by the reference numeral  155 , is mounted at the upper end of the coil and terminal assembly  153  on a plastic sealing plug  156 . A mounting flange portion  157  is formed at the upper end thereof and it has a projection  158  which sealingly engages a recess formed in the upper plug tube end flange  149 . 
     A coil assembly  159  is mounted on this flange  157  and receives input from a terminal  161  which communicates with the ECU for engine control. 
     Because of the two-piece spark plug tube arrangement  145 , the engine embodying the invention is much easier to build and assemble and hence, can have a reduced cost. Unlike the prior art construction, the cylinder head assembly can be completed with the lower plug tube  144  in position and then the cam cover  135  installed. After the cam cover  135  is installed, then the upper plug tube  145  can be installed one cylinder at a time, rather than having to line up with all of the cylinders simultaneously. This greatly facilitates assembly. Subsequently, the coil carrier and terminals  153  may be installed and the electrical connections made to the connectors  161 . 
     The servicing arrangement is also made much easier as may be seen in FIG. 11, particularly when comparing this with FIG.  1 . In this case, when there is an obstruction such as the break booster  38  above the spark plug opening  151  in the cam cover  135 , there is no problem for servicing. First, the coil and terminal assembly  153  can be removed in a unit along with the upper plug tube  145  by canting the structure. This is possible because the opening  151  in the cam cover  135  can be made large enough to clear the flanged lower part  147  as well as to provide additional clearance as seen by the gap  162  in this figure. Once this assembly is removed, there will considerable room for accessing the spark plug  88  for its removal and replacement. Obviously, reinstallation of the upper plug tube  145  is possible in the reverse mode. 
     Thus, from the foregoing description, it should be readily apparent from the described construction that is permits a very compact engine and one which is easy to assemble and service and which leads itself to confined engine compartments without significant problems in the servicing. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modification may be made without departing from the spirit and scope of the invention, as defined by the appended claims.