Abstract:
An improved journaling and sensor mounting arrangement for the VVT mechanisms of a twin overhead cam engine. By utilizing a combined single bearing cap for the VVT ends of the camshafts that mounts the sensors that are associated with timing wheels on the respective camshafts, it is possible to maintain a very neat external appearance and a compact construction. Also, high accuracy can be obtained because of the positive rotation of the components. In addition, a simplified oil supply and control arrangement is also disclosed for lubricating the thrust surfaces of the camshaft bearings and other bearing surfaces as well as supplying hydraulic fluid to the VVT mechanisms.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to four-cycle internal combustion engines and more particularly to an improved variable valve timing control and journalling arrangement for the camshafts of such an engine.  
           [0002]    It has been recognized that the performance of an engine can be improved through a wide variety of engine speeds and loads by employing a variable valve timing (VVT) mechanism. In this way, the valve timing can be optimized for the particular running condition so as to provide the desired performance. Generally, the variable valve timing mechanism is interposed in the drive of the camshaft from the engine crankshaft and frequently is mounted on one end of the associated camshaft. When twin overhead camshafts are employed, it is common to have the variable valve timing mechanisms at the same end of the respective camshafts.  
           [0003]    In order to perfect the control, it is also necessary or desirable to have a sensor associated with each of the camshafts so as to sense the angular position of the respective camshaft. Various arrangements have been proposed for mounting the camshaft sensor and those methods, which have been proposed, have some disadvantages.  
           [0004]    In accordance with one method, the camshafts have a timing wheel or the like mounted at one end thereof, normally the end opposite from the variable valve timing mechanism. A sensor is fixed to the engine body adjacent this timing wheel so as to provide the signal indicative of the camshaft position.  
           [0005]    One way in which the sensor may be mounted is by supported it from the bearing cap for this end of the camshaft. This means that the camshaft is elongated beyond the bearing surface so as to accommodate the mounting of the timing wheel and associated sensor. This presents problems inasmuch as the engine is elongated by such an arrangement.  
           [0006]    Another form of sensor for camshaft angle mounts the sensor on the cam cover of the engine. However, this is a rather imprecise way of monitoring the position due to the fact that the cam cover is not always accurately positioned relative to the camshaft or the cylinder head. That is, a sealing gasket is interposed between the cam cover and the cylinder head and this can permit the cam cover and accordingly the sensor to shift relative to the camshaft.  
           [0007]    Although keying of the cam cover to the cylinder head can be employed to avoid this problem, this complicates the assembly and nevertheless, there still can be variations in the spacing between the cam cover and the cylinder head even though the axial alignment may be maintained. Also, this keying can generate some engine noise since the silencing of the effect of the gasket is eliminated.  
           [0008]    Another way of mounting the sensor is by fastening it directly to the cylinder head itself. However, such mounting may place the sensor in a juxtaposed position to the either the intake or the exhaust sides of the cylinder head. This can cause difficulties, particularly undo heating of the sensor if positioned adjacent the exhaust side as generally must be done when the angular position of the exhaust camshaft is being sensed. Also, this can present difficulties in mounting the electrical leads for conveying signals from the sensor to the control for the VVT mechanism.  
           [0009]    It is, therefore, a principal object to this invention to provide an improved camshaft sensor arrangement for a four-cycle internal combustion engine wherein the sensor is accurately mounted and does not cause elongation of the engine nor routing problems for the electrical conduits.  
           [0010]    It is a further object to this invention to provide an improved and simplified sensor mounting arrangement particularly for multiple camshaft engines wherein each camshaft has a variable valve timing mechanism associated with it.  
         SUMMARY OF INVENTION  
         [0011]    This invention is adapted to be embodied in a four-cycle internal combustion engine having an engine body with a plurality of axially spaced bearing sections. A plurality of axially spaced bearing caps are fixed to the engine body and cooperate with the bearing sections for journaling axially spaced bearing surfaces of a camshaft. A variable valve timing mechanism is associated with one end of the camshaft for driving the camshaft in an adjustable, timed fashion from an engine crankshaft. One of the journalled camshaft bearing surfaces is juxtaposed to the variable valve timing mechanism. A timing member is formed on the camshaft on the side of the one journalled camshaft bearing surface opposite to the variable valve timing mechanism. A timing sensor cooperates with the timing member for providing a signal indicative of camshaft angle. The timing sensor is carried by the bearing cap that journals the one of the journal camshaft bearing surfaces. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0012]    [0012]FIG. 1 is a top plan view showing one end of a cylinder head of an internal combustion engine constructed in accordance with an embodiment of the invention, with the cam cover removed, and with portions of the valve actuating mechanism eliminated in order to more clearly show the construction.  
         [0013]    [0013]FIG. 2 is a front elevational view of the structure shown in FIG. 1 and illustrates the cam cover in place and shows the control valve mechanism associated with the variable valve timing mechanism.  
         [0014]    [0014]FIG. 3 is a cross sectional view taken through the cylinder head and generally along the axis of one of the camshafts.  
         [0015]    [0015]FIG. 4 is a perspective view showing the bearing cap for the driven ends of the camshafts with the timing sensors mounted therein.  
         [0016]    [0016]FIG. 5 is a perspective view looking from below showing one of the timing sensors.  
         [0017]    [0017]FIG. 6 is a cross sectional view taken generally through the timing sensor and associated timing wheel formed integrally with one of the camshafts.  
         [0018]    [0018]FIG. 7 is a schematic hydraulic diagram showing the lubricating oil passages and control mechanism for the intake and exhaust valve timing mechanisms. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring now in detail to the drawings and initially primarily to FIGS. 1 through 3, a portion of an internal combustion engine constructed and operated in accordance with the invention is identified generally by the reference numeral  11 . Since the invention deals primarily with the camshaft driving and bearing arrangement for the engine  11 , only the cylinder head structure of the engine  11  is depicted. This comprises a main cylinder head member  12  to which a cam cover  13  is detachably affixed in a well known manner. A timing case, indicated generally by the reference numeral  14 , is formed at the front of the cylinder head member  12  and is closed by a timing case cover  15  at the lower end and by the cam cover  13  at the upper end. This cover  15  also encloses the un-shown front portion of the cylinder block to which the cylinder head member  12  is affixed in the manner to be described.  
         [0020]    The main cylinder head member  12  forms a plurality of combustion chambers and, in the illustrated embodiment, each combustion chamber is served by two intake valves and two exhaust valves. These valves are not illustrated in the drawings but the valves are operated by thimble tappets that are received within bores  16  formed in the cylinder head member  12 . Since this type of construction is well known in the art, it is not believed necessary to illustrate the valves and their association with the cylinder bores.  
         [0021]    However, the cylinder head member  12  is affixed to an associated cylinder block (not shown) by threaded fasteners, one of which is shown in FIG. 3, and which is identified by the reference numeral  17 . These threaded fasteners  17  are passed through four fasteners holes  18  formed at the peripheral edges of the associated cylinder head member  12  around each cylinder bore and threaded into tapped openings in the associated cylinder block to affix the cylinder head member  12  to the cylinder block in a manner that is well known in the art.  
         [0022]    Journalled in the cylinder head member  12 , in a manner to be described, is an intake camshaft  19  and an exhaust camshaft  21 . These camshafts  19  and  21  rotate about respective rotational axes CI and CE. The intake camshaft  19  has individual cam lobes  22  that are associated with the un-shown tappets in the tappet bores  16  on the intake side of the engine. In a like manner, the exhaust camshaft  21  has exhaust lobes  23  that cooperate with the tappets in the tappet bores  16  on the exhaust side of the engine. Again, this type of structure is well known in the art and, for that reason, further details of its construction are not believed to be necessary to understand the construction and operation of the invention.  
         [0023]    At axially spaced positions along its length, the intake and exhaust camshafts  19  and  21  are formed with axially spaced bearing surfaces  24  and  25 , respectively, that are journalled in bridges  26  formed in the cylinder head member  12  at spaced locations along its length. Individual bearing caps (not shown) are affixed to each of the bridges  26  by threaded fasteners that are received in tapped holes  27  formed between the respective lobes  22  and  23  associated with each cylinder.  
         [0024]    A central spark plug well  28  is formed in the cylinder head member  12  at the center of each cylinder bore and receives a spark plug for firing the charge in the combustion chambers in a manner well known in the art.  
         [0025]    In addition to the spaced bearing surfaces  24  and  25  of the intake and exhaust camshafts  19  and  21 , respectively, each camshaft has an end bearing surface  29  and  31 , respectively. These end bearing surfaces  29  and  31  are journalled in an upstanding front end wall  32  of the cylinder head member  12  which is adjacent the timing case  14 .  
         [0026]    Each camshaft  19  and  21  is formed with a pair of thrust faces  33  and  34 , respectively, that are engaged with machined surfaces formed on the cylinder head wall  32  for providing axial location for the intake and exhaust camshafts  19  and  21 .  
         [0027]    A unitary bearing cap assembly, indicated generally by the reference numeral  35 , is affixed to the cylinder head wall  32  by threaded fasteners  36  that are received in tapped holes formed therein and which pass through openings  37  (FIG. 4) formed in the respective bearing cap portions that cooperate with the respective cylinder head bearing surfaces formed by the wall  32 . These bearing portions are joined by a partially cantilevered bridging part  38  of the bearing cap member  35 . This bridging part  38  has a further opening  39  to receive a further threaded fastener that engages the cylinder head member  12  to provide rigidity for the cantilevered bridging part  38 .  
         [0028]    Continuing to refer primarily to FIGS. 1 through 3, the drive for driving the intake and exhaust camshafts  19  and  21 , which is contained within the timing case  14  will now be described. A first timing chain  41  is entrained around a suitable sprocket affixed to the crankshaft of the engine and a tensioner pulley. This chain  41  drives a first sprocket part  42  of a two sprocket assembly that is connected to the intake camshaft  19  via a first VVT mechanism  43 . This VVT mechanism will be described in more detail later.  
         [0029]    Integrally formed with the first sprocket  42  is a second sprocket  44  which, in turn, drives a further timing chain  45  that drives a sprocket  46  that is connected to the exhaust camshaft  21  by a second VVT mechanism, indicated generally by the reference numeral  47 . It will be seen that the WT mechanisms  43  and  47  are staggered relative to each other so as to provide clearance for the timing chain  41  and crankshaft driven timing sprocket  42 . This permits a very compact assembly and also accommodates the drive of the camshafts  19  and  21  at one half-crankshaft speed while maintaining a close relationship between the camshaft rotational axes CI and CE.  
         [0030]    A chain tensioner  53  is carried by the cylinder head member  12  and tensions the timing chain  45  that transfers the drive from the intake camshaft  19  to the VVT mechanism  47  for the exhaust camshaft  21 .  
         [0031]    The VVT mechanisms  43  and  47  may be of any known type and, in the illustrated embodiment, are of the sliding vane type that includes respective pairs of fluid chambers  48  and  49  (VVT  43 ) and  51  and  52  (VVT  47 ). These chambers  48  and  49  and  51  and  52  are pressurized selectively, in a manner, which will be described shortly, so as to vary the phase angle between the camshafts  19  and  21  and also between these camshafts and the crankshaft.  
         [0032]    The hydraulic control arrangement for supplying fluid to actuate the VVTs  43  and  47  as well as lubricating the camshaft bearings, will now be described by particular reference to FIGS. 2, 3 and  7  although certain of the components also appear in other figures. As seen in FIG. 2, a main oil gallery  54  is formed in the cylinder head member  12  and cooperates with a corresponding main oil gallery formed in the associated cylinder block. An enlarged bore is formed at the upper end of the oil gallery  54  and receives a replaceable filter element  55  for filtering the oil delivered to solenoid actuated, spool, intake and exhaust timing control valves  56  and  57 , respectively.  
         [0033]    The main gallery  54  is intersected by a transversely extending gallery  58  that extends across the cylinder head member  12  and which is intersected the spools of the control valves  56  and  57 . The solenoid actuated spool valve  56  selectively supplies pressure to the chambers  48  and  49  of the intake VVT mechanism  43  through passages  59  and  61 , which are formed in the cylinder head member  12 . In a like manner, the chambers  51  and  52  of the exhaust VVT mechanism  47  are selectively supplied with lubricating oil from the solenoid operated control valve  57  through passages  62  and  63 , respectively.  
         [0034]    This system also provides an arrangement for lubricating the bearings of the intake and exhaust camshafts  19  and  21 . The main gallery  58  of the cylinder head member  12  downstream of the filter  55  is intersected by a pair of further supply passages,  64  which communicate with drillings  65  and  66  (FIG. 7) formed in the intake and exhaust camshafts  19  and  21 . These drillings intersect longitudinally extending drillings  67  and  68  that are formed in the intake and exhaust camshafts  19  and  21 , respectively. The drillings  67  and  68  are intersected by radial drillings  70  formed at each of the bearing surfaces including the bearing surfaces  25  and  31  of the exhaust camshafts as shown in FIG. 3 and like drillings formed in the intake camshaft.  
         [0035]    These drillings  67  and  68  also terminate in axially extending drillings  69  and  71 , respectively, formed in the bearing cap  35  which terminate at the respective thrust faces  33  and  34  for lubricating these highly loaded surfaces. Thus, the system provides very effective hydraulic supply and lubrication control.  
         [0036]    The sensor arrangement for sensing the rotational position of the intake and exhaust camshafts  19  and  21  will now be described by primary reference to FIGS. 1 through 6. It will be seen the cantilevered bridging portion  38  of the front bearing cap  35  is provided with a pair of openings that receive and pass a sensor  75  of a sensor mounting assembly  76 . This sensor mounting assembly  76  has a somewhat egg-shaped supporting bracket  77  from which the sensor  75  depends and passes into proximity with respective timing wheels  78  and  79  associated with the intake and exhaust camshafts  19  and  21 , respectively. These timing wheels  78  and  79  have, in the illustrated embodiment, four individual teeth or lugs  81 . As these lugs they pass the respective sensor element  75  it will generate a signal. This may be done either magnetically or through a photosensitive device. The mounting bracket portions  77  are formed with further openings  82  that receive threaded fasteners that are tapped into the cantilevered portion  38  of the bearing cap  35  so as to hold them against rotation. Because these devices extend inwardly, the elongation of the assembly is avoided and a very compact assembly results.  
         [0037]    As seen in FIG. 3, the cam cover  1   3  is provided with an opening through which a portion of the mounting part  77  and sensor  75  can pass so as to provide an electrical connector  83  which transfers the signals to the control ECU for the variable valve timing mechanisms  43  and  47 . An elastic seal  84  is mounted in a groove in the cam cover  13  around its opening so as to sealingly engage the mounting part  77  of the assembly and thus, provide good sealing while maintaining a simple external electrical connection.  
         [0038]    Therefore, from the foregoing description it should be readily apparent to those skilled in the art that the device provides a very compact yet highly effective sensor and lubricating arrangement as well as varying arrangements for the twin overhead camshafts. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.