Abstract:
Several embodiments of variable valve lift mechanisms employing rocker arms that cooperate with high and low speed cam lobes and which are selectively coupled or uncoupled so as to operate the valve dependent upon either the low speed cam lobe configuration or the high speed cam lobe configuration. The construction is such that there are no bending loads placed on the valve stems and the actuating mechanism is relatively light and can be carried at least in part independently of the rocker arms so as to reduce the reciprocating masses and improve engine performance.

Description:
BACKGROUND OF INVENTION 
     This invention relates to a high-low speed range switching type valve mechanism for an internal combustion engine and more particularly to an improved and simplified arrangement for selectively varying the lift of a valve in response to engine conditions. 
     In order to further improve the performance of internal combustion engines in response to varying load and operating conditions, various devices have been provided for changing the effective lift of the engine valves. By changing the lift, the performance can be more closely tailored to the optimum for these various running and operating conditions. However, most of the mechanisms that have been proposed for this operation have a number of disadvantages due primarily to their complexity. 
     For example, one type of mechanism that has been proposed employs a pair of rocker arms each of which is associated with a given valve and each of which cooperates with a respective cam lobe having a different lift characteristic. Generally, one of these rocker arms directly operates the valve and the other rocker arm is selectively coupled to that one rocker arm or uncoupled from it to determine which cam lobe will control the valve lift characteristics. 
     Examples of this type of structure are shown in U.S. Pat. No. 4790274, issued Dec. 13, 1988 and now reissued as RE33411, Oct. 30, 1990; U.S. Pat. No. 4844023, issued Jul. 4, 1989 and U.S. Pat. No. 4869214, issued Sep. 26, 1989. As shown in these patents, each rocker arm is pivotally supported at one end by the engine body and has its other end engaged with the valve stem either directly or through the remaining rocker arm via a coupling mechanism. The cam lobes engage the respective rocker arms between their ends. 
     One disadvantage with this type of construction is that because the rocker is engaged between its ends, there is an amplified force exerted on the valve, which has a bending component. This requires the valve stem to be of greater strength and greater diameter. As a result, the valves are heavier. Accordingly the inertia of the engine reciprocating components increases and engine performance is deteriorated. 
     Another disadvantage with this type of mechanism is that the coupling mechanism between the rocker arms and its actuating device are all carried by one or both of the rocker arms. This further increases the reciprocating mass of the rocker arm resulting in deteriorated engine performance. 
     It is, therefore, a principal object of this invention to provide an improved variable valve lift timing mechanism wherein the engagement of the cam lobe with the rocker arm and valve is aligned so as to eliminate bending stresses. 
     Another object of this invention is to provide a variable valve lift mechanism of this type wherein not all of the components of the coupling arrangement between the rocker arms are carried by the rocker arms, thus reducing the weight of the rocker arms. 
     SUMMARY OF INVENTION 
     A first feature of the invention is adapted to be embodied in a valve operating mechanism for operating a flow controlling poppet valve of an internal combustion engine. The poppet valve has a stem portion supported for reciprocation about a valve axis in the engine for control of the flow through a port thereof by a head portion of the valve. The valve operating mechanism is comprised of a camshaft supported for rotation about a camshaft axis that is intersected by the valve axis. The camshaft has at least two cam lobes of different lift characteristics juxtaposed to the valve. A pair of rocker arms are journalled for pivotal movement about an axis offset from the camshaft axis. The rocker arms each have a follower portion engaged with a respective one of said cam lobes. One of the rocker arms has an actuating portion associated with the valve stem. An interlocking coupling selectively couples the rocker arms for simultaneous movement or permits only the one rocker arm to transmit movement to the associated valve. 
     Another feature of the invention is also adapted to be embodied in a valve operating mechanism for operating a flow controlling poppet valve of an internal combustion engine. In accordance with this other feature, the poppet valve has a stem portion supported for reciprocation about a valve axis in the engine for control of the flow through a port thereof by the head portion of the valve. The valve operating mechanism comprises a camshaft supported for rotation about a camshaft axis. The camshaft has at least two cam lobes of different lift characteristics associated with the valve. A pair of rocker arms are journalled for pivotal movement about an axis offset from the camshaft axis. The rocker arms each have a follower portion engaged with a respective one of the cam lobes. One of the rocker arms has an actuating portion associated with the valve stem. A coupling element is carried by one of the rocker arms and is engageable with the other of the rocker arms for selectively coupling the rocker arms for simultaneous movement or permitting only the one rocker arm to transmit movement to the associated valve. An actuating element is supported independently of the rocker arms for moving the coupling element. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a cross sectional view of an internal combustion engine constructed in accordance with a first embodiment of the invention taken through a plane of reciprocation containing the reciprocal axes of a pair of poppet valves and the axis of rotation of the actuating camshaft. 
     FIG. 2 is a cross sectional view taken along a plane perpendicular to the plane of FIG.  1  and through the rocker arm which directly actuates the engine valve. 
     FIG. 3 is a top plane view of the structure shown in FIGS. 1 and 2 with portions broken away so as to show how the hydraulic fluid is applied to the valve lift coupling mechanism. 
     FIG. 4 is a cross sectional view, in part similar to FIG. 1, and shows a second embodiment of the invention. 
     FIG. 5 is a cross sectional view, in part similar to FIGS. 1 and 4, and shows a still third embodiment of the invention. 
     FIG. 6 is a top plane view, in part similar to FIG. 3, but shows the construction in accordance with the third embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring first to the embodiment of FIGS. 1 through 3, a valve operating mechanism constructed in accordance with this embodiment is identified generally by the reference numeral  11 . In the illustrated embodiment, the valve actuating mechanism  11  is shown as associated with a pair of intake valves  12  each of which serves the same engine combustion chamber through a Siamese intake passage  13  (FIG.  2 ). This Siamese intake passage  13  has a pair of branch portions each of which terminates at an intake valve seat  14  formed in a cylinder head  15  of an associated internal combustion engine, indicated generally by the reference numeral  16 . 
     The cylinder head  15  is affixed in sealing relationship to an associated cylinder block  17  having one or more cylinder bores  18  and which pistons (not shown) reciprocate. The pistons are coupled to a crankshaft through a suitable driving mechanism for driving the crankshaft. Since this part of the engine is conventional, it is not illustrated. The cylinder head  15  is formed with one or more recesses  19  each of which cooperates with a respective cylinder bore  18 . 
     The intake valves  12  are comprised of stem portions  21  that are slidably supported in valve guides  22  pressed, cast or otherwise formed in the cylinder head  15 . The intake valves  12  have head portions  23  which cooperate with the valve seats  14  to control the flow into the combustion chamber recess  19  through the intake passages  13 . The intake valves  12  each reciprocate about a respective valve axis VA defined by the stem portions  21  and the cooperating valve guides  22 . 
     At their upper ends, the intake valve stems  21  carry keeper retainer assemblies  24  of any known type. The keeper retainer assemblies  24  retain one end of coil compression springs  25  that urge the valves  12  to their closed position. The other ends of the valve springs  25  act against machined surfaces of the cylinder head  15 . 
     It has been noted that two intake valves  12  are provided for each cylinder of the engine. These valves  12  have their axes VA disposed as equal distances between a line or plane of symmetry LS. The description of structure of the valve actuating mechanism which will follow is based upon the understanding that the valve actuating mechanism  11  is symmetrically disposed around this plane LS. 
     The valve actuating mechanism  11  is comprised of an intake camshaft, indicated generally by the reference numeral  26  and which comprises a main shaft portion  27  that is journalled in any suitable manner for rotation about a camshaft axis CSA in the cylinder head  15 . The camshaft  26  has a low speed cam lobe  28  and a high speed cam lobe  29  each associated with a respective one of the intake valves  12  and disposed on opposite sides of their valve axes VA. In FIGS. 1 and 3, the left hand side of the plane of symmetry LS shows the high lift cam operation while the right hand side shows the low lift valve operation. 
     The cam lobe  28  is designed for providing optimum performance under low and mid range engine running speeds and conditions and thus, provides a lower lift and, if desired, a shorter duration than the high speed cam lobe  29 . The low and high speed cam lobes  28  and  29  cooperate with low and high speed rocker arms, indicated generally by the reference numerals  31  and  32 , respectively. These rockers arms  31  and  32  have mating surfaces along a line MS which is disposed in coaxial relationship with the respective valve axis VA and midway between the cam lobes  28  and  29 . 
     A coupling mechanism, indicated generally by the reference numeral  33  determines which of the cam lobes  28  and  29  control the lift of the valves  12 . 
     In accordance with this embodiment, the low speed rocker arm  31  and high speed rocker arm  32  are both supported on a common rocker arm shaft  34  that is suitably journalled within the cylinder head  15 . This rocker arm shaft defines a pivot axis  35 , which is common for each of the rocker arms  31  and  32 . 
     The coupling mechanism  33  includes a coupling element  36  which is slidably received in a bore  37  formed in the low speed rocker arm  31 . This bore  37  is in line with a complimentary cylindrical surface  38  of the high speed rocker arm  32  when the valves are closed as shown on both sides of FIGS. 1 and 3. The coupling element  36  is normally biased by means of a coil spring  39  to a disengaged position shown in the right hand side of FIG.  1  and the bottom side of FIG. 3 so that it will only engage the low speed rocker arm  31 . 
     It will be seen that the low speed rocker arm  31  has a portion that is engaged with an adjusting shim  41  positioned in the keeper retainer assembly  24  for transmitting motion to the respective intake valve  12 . 
     When the coupling element  36  is in the position shown at the right side of FIG. 1, the high speed rocker arm  32  can continue to pivot about the pivot axis  35  during rotation of the cam shaft  26  but as shown by the phantom line view on the right of FIG. 1, this pivotal movement will not effect any operation of the valve  12 . 
     However, the rocker arms  31  and  32  are both urged toward their engaged positions with the cam lobes  28  and  29  by hairpin or mouse trap type springs  43  (FIG. 2) so that there will not be any noise generated by this idling pivotal movement of the high speed rocker arms  32 . 
     The coupling mechanism  33  further includes an actuator mechanism, indicated generally by the reference numeral  44  which is comprised of a cylinder bore  45  formed in a portion  46  of the cylinder head  15  disposed on the plane of symmetry LS. A hydraulic feed port  47  permits selective pressurization of the bore  45  so as to effect reciprocation of pistons  48  that are slidably supported in the bore  45 . Each piston  48  has a bearing arrangement with the respective coupling element  36  and is slidably relatively thereto. This fixes the axial position of the coupling element  36  while permitting its pivotal movement around the rocker arm axis  35 . 
     When the bore  45  is pressurized, the actuating pistons  48  will move outwardly as shown on the left hand side of FIG.  1  and cause the coupling element  36  to be engaged by the surface  38  of the high speed rocker arm  32 . Hence, the coupling element  36  will be operated by this rocker arm  32  and will transmit its operation to the low speed rocker arms  31  so that the valves  12  will be opened in accordance with the lift of the high speed cam lobes  29 . 
     By relieving the hydraulic pressure, the coupling elements  36  are moved back to their disengaged positions by the springs  39 . 
     Hence, with this construction the actuating arrangement for the coupling mechanism  33  is not carried by the rocker arms  31  and  32  and their resulting structure is lighter in weight. Also, since the camshaft axis CSA is aligned with the valve axis VA and the follower surface of the respective rocker arms  31  and  32 , there will be very direct operation without any bending loads being applied to the valve stems  21 . As a result, the valve stems  21  can be made lighter in weight and this will permit higher engine speeds and engine outputs since inertia is substantially reduced and valve flow is not as likely. 
     It should be noted that although FIGS. 1 through 3 appear to show the operation of the two coupling mechanism  33  independently of each other, these figures merely show two different positions, one on the right and one on the left. That is, when the cylinder bore  45  is pressurized, both actuating pistons  48  will be urged outwardly to move the coupling elements  36  to the position shown on the left hand side of FIG.  1 . When the pressure is released, both coupling elements  36  will be moved to the position shown on the right hand side of this figure. 
     FIG. 4 shows another embodiment of this invention, which is the same as the invention previously described except as will hereinafter be noted. For that reason, components which are the same have been identified by the same reference numerals and will not be described again, except insofar as is necessary to understand the construction and operation of this embodiment. 
     With this embodiment, rather than the low speed rocker arm  31  having a portion that engages the valve shim, the coupling element  36  itself engages the valve shim, which is indicated by the reference numeral  51  in this figure and has a slightly different configuration than the previous embodiment. This permits the use of an even lighter weight rocker arm assembly since all of the actuating loads are transferred from the high and low speed cam lobes  29  and  28 , respectively to the valve stems  21  by the coupling elements  36 . This offers a further performance improvement. 
     As has been previously noted, both valves of each cylinder are actuated by either the low speed cam lobes or the high speed cam lobes respectively. FIGS. 5 and 6 shows another embodiment of the invention wherein the valves cam be operated independently of each other so that one can be operated by a high speed cam lobe and the other by the low speed cam lobe. Also, this embodiment eliminates the cylinder head portion  46  with its bore  47  for supporting the actuating pistons  48 . However, in this embodiment, actuating plungers, indicated generally by the reference numeral  101  are slidably supported in bores  102  formed in the low speed rocker arms  31 . 
     In describing this embodiment, when elements have substantially the same construction or the same construction as previously described, they are identified by the same reference numerals. In this embodiment, each plunger  101  has a piston portion  103  that is slidably supported in the rocker arm bore  102 . These plunger piston portions  103  are normally urged by coil compression springs  104  that act against retainers  105  formed on the ends of piston rod portions  106  integrally formed with the actuating plunger piston portions  103 . These springs  104  normally urge the coupling mechanisms, indicated by the reference numerals  107 , to their disengaged positions as shown on the right hand side of FIG.  5 . 
     The bores  102  can be selectively pressurized through feed passages  108  to urge them to their engaged position as shown on the left hand side of FIG. 1 where they are engaged by the arcuate sections  38  of the high speed rocker arms  32  so as to provide a coupling so that the high speed cam lobes  29  will control the lifts of the valves  12 . However, it should be apparent that each rocker arm coupling element  107  may be operated independently of the other. 
     Thus, from the foregoing description it should be readily apparent that the described embodiments permit the use of rocker arm variable valve lift mechanisms without having the rocker arms exert bending loads on the valves and also wherein the weight of the individual rocker arms can be reduced since the actuating mechanism need not all be carried by the rocker arms. Of course, the foregoing description is that of preferred embodiments 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.