Patent Publication Number: US-6659053-B1

Title: Fully variable valve train

Description:
BACKGROUND OF THE DISCLOSURE 
     The present invention relates to valve control systems for internal combustion engine poppet valves, and more particularly, to such valve control systems which are capable of controlling the amount of the valve lift, the timing of the valve lift, and the duration of the valve event (valve lift). 
     As is well know to those skilled in the internal combustion engine art, conventional camshaft and rocker arm type valve gear trains are relatively simple and have been generally effective in commercial use. However, the conventional camshaft actuated valve gear train has typically represented a compromise in regard to engine performance. At relatively low speeds, the engine poppet valves open more than is needed (thus resulting in pumping energy losses), while at relatively higher engine speeds, the valves do not open enough to get the flow quantity of air-fuel mixture necessary to achieve optimum engine performance. 
     In addition, it is now understood that engine efficiency can be improved by varying the timing of the opening and closing of the poppet valves as a function of engine speed, and also as a function of load on the engine. One known method of varying the timing of the opening and closing of the engine poppet valves is by means of a variable cam phase change device (“variable cam phaser”. The function of such a cam phaser device is to vary the angular position of the camshaft, relative to the angular position of the crankshaft. 
     Those skilled in the valve gear train art have, for many years, been developing various systems for variable valve actuation/variable valve timing (VVA/VVT) for modifying the amount of valve lift and/or the timing of the valve lift in valve gear trains of the type driven by a camshaft. More recently, the assignee of the present invention has developed a VVT system which is able to vary both the amount of lift and the timing of the lift simultaneously in a valve gear train having a camshaft as its input, this VVT system being illustrated and described in co-pending application U.S. Ser. No. 09/841,572, filed Apr. 24, 2001 in the name of Majo Cecur for a “Rocker Arm Device For Simultaneous Control Of Valve Lift And Relative Timing In A Combustion Engine”, also assigned to the assignee of the present invention, and incorporated herein by reference. 
     Although the VVT system of the co-pending application appears to be a substantial improvement over the known prior art, and is able to adjust timing as much as is desired, the referenced system still has limitations whereby neither the valve lift nor the duration of the valve opening can ever go to zero. 
     In an effort to achieve a valve control system which is truly capable of fully variable valve train (FVVT) operation, those skilled in the art have developed various camless valve control systems in which the engine poppet valve has its opening and closing controlled directly by a valve actuator which may be electromagnetic or electro-hydraulic. Although such camless systems have certain benefits, such as infinitely variable valve lift, duration, and timing, and eliminating the frictional losses inherent in camshaft and rocker arm type valve gear train, there are still a number of disadvantages to the camless systems. By way of example only, in a typical camless system, it is necessary to provide sensors capable of sensing the position of the engine poppet valve and providing a feedback signal to control the operation of the electrical/electronic portion of the valve actuator. The sensors capable of performing the function just described are not yet commercially available, but even if they were, the requirement for such sensors would add substantially to the overall cost and complexity of the typical camless valve control system. 
     Another problem associated with the conventional camshaft and rocker arm type of valve gear trains is the need to provide “ramps” to finely control the speed of the opening and closing of the engine poppet valve. Such ramps are typically provided by grinding an appropriate shape on the cam profile of the camshaft, at both the beginning and end of the lift profile. Unfortunately, the accurate grinding of a pair of such shapes for each cam lobe adds substantially to the overall manufacturing cost of the camshaft. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a valve control system for an engine poppet valve which is capable of achieving fully variable valve train operation. 
     It is a more specific object of the present invention to provide such a valve control system in which both the valve lift and the timing of the valve lift may be controlled simultaneously, but independently of each other. 
     It is an even more specific object of the present invention to provide a valve control system of the type which achieves the above-stated objects in which the valve lift may be varied anywhere between a maximum lift and a theoretical zero lift; the duration of the lift may be varied anywhere between a maximum duration and a theoretical zero duration; and the timing of the valve opening and closing may be varied as desired to achieve optimum engine performance. 
     The above and other objects of the invention are accomplished by the provision of a valve control system for an internal combustion engine of the type including a cylinder head, an engine poppet valve, and a valve actuating camshaft defining a cam profile. The valve control system comprises a rocker arm having a first portion fixed to pivot relative to the cylinder head and a second portion operable to transmit cyclic opening and closing motion to the engine poppet valve. A cam follower assembly includes a first cam follower member in engagement with the cam profile whereby cyclic rise and fall motion is transmitted from the cam profile to the cam follower assembly in response to rotation of the camshaft. 
     The improved valve control system is characterized by a cam member disposed for to and fro movement relative to the camshaft and defining a cam surface disposed in a generally face-to-face relationship to an engagement surface defined by the rocker arm. The cam follower assembly includes a second cam follower member in operable engagement with both the engagement surface defined by the rocker arm and the cam surface defined by the cam member, and being disposed therebetween. The cam follower assembly further includes a rigid follower linkage interconnecting the first and second cam follower members, thus transmitting the cyclic rise and fall motion to the second cam follower member. An arrangement includes a link member having one end fixed relative to the cam member and the other end operably associated with an input member to vary the to and fro position of the cam member. An adjustable timing linkage has one end fixed to the first cam follower member and is operable, in response to a timing input motion, to advance or retard the point of contact of the first cam follower member on the cam profile. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a somewhat simplified, transverse cross-section illustrating an internal combustion engine cylinder head including the valve control system of the present invention. 
     FIG. 2 is a transverse view similar to FIG. 1, but with certain parts shown only fragmentarily, to illustrate further the cam assembly which comprises one aspect of the present invention. 
     FIG. 3 is an axial cross-section, taken through FIG. 2, and illustrating the cam assembly which comprises one aspect of the present invention. 
     FIG. 4 is a fragmentary, transverse cross-section, similar to FIG. 1, with the camshaft rotated to the maximum lift portion of the cam profile, and the engine poppet valve at maximum lift. 
     FIG. 5 is a fragmentary, transverse cross-section, similar to FIG. 4, but with the engine poppet valve now in a minimum lift condition. 
     FIG. 6 is a transverse view, similar to FIGS. 1,  4  and  5 , illustrating one means of varying the position of the cam assembly. 
     FIGS. 7A,  7 B, and  7 C are graphs of valve lift as a function of time, or more precisely, as a function of rotational position of the camshaft. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, which are not intended to limit the invention, FIG. 1 illustrates a valve control system, made in accordance with the present invention, for use in controlling an engine poppet valve of an internal combustion engine. It should be noted that FIG. 1 illustrates only the cylinder head and the valve gear train of the present invention, but does not include any portion of the engine cylinder block. 
     The valve control system as shown in FIG. 1 includes a cylinder head  11  defining an upper portion  13  of a combustion chamber, the rest of which would be defined by the cylinder and piston. The cylinder head  11  defines an intake passage  15  and an exhaust passage  17 . The flow of air-fuel mixture and combustion gasses respectively to and from the combustion chamber  13  is accomplished by means of a pair of engine poppet valves, including an intake valve  19  and an exhaust valve  21 , respectively. 
     Each of the engine poppet valves  19  and  21  is supported for reciprocable movement relative to the cylinder head  11  between a closed position (shown in FIG. 1) and an open position, to be illustrated and described subsequently. The upper end of each of the poppet valves includes a spring retainer  23 , against which is seated a valve return spring  25 , which biases the respective poppet valve  19  or  21  to the closed position shown in FIG.  1 . 
     In a manner well know to those skilled in the art, a camshaft  27  is fixed, relative to the cylinder head  11 , for rotation about its axis. The camshaft  27  defines a plurality of cam profiles  29  (only one of which is shown in FIG.  1 ), each cam profile  29  including a base circle portion  31  and a lift portion  33 . It will be understood by those skilled in the art that the lift portion  33  of the cam profile  29  is, in the subject embodiment, designed for the maximum amount of lift desired, and for the maximum duration of lift desired. 
     The valve control system of the present invention preferably operates in a manner to provide, selectively, either the maximum lift and duration, as determined by the configuration of the lift portion  33 , or something less than the maximum lift and duration, all the way down to a minimum lift (or duration), corresponding to what is illustrated in FIG.  6 . It will be understood by those skilled in the engine art that the minimum lift corresponds to an ideal idle speed condition. As noted previously, the valve control system of the present invention has, as one of its aspects, the capability of reducing the lift and duration to the minimum and furthermore, has the capability of varying timing of the poppet valve opening and closing, and doing so independently of the variations in the lift and duration. 
     Referring still primarily to FIG. 1, it should be noted that the valve control system of the present invention is utilized to control only the intake valve  19 , and provide the intake valve  19  with the “fully variable valve train” capability, whereas in the subject embodiment, the exhaust valve  21  is operated in a conventional “fixed” valve timing relationship relative to its respective cam profile. If the engine were, for example, an in-line 4-cylinder engine, the FVVT mechanism shown in FIGS. 1 through 3 would be present on the intake valve  19  of each of the 4 cylinders, and all four of the FVVT mechanisms would, typically, be controlled in unison. In other words, at any given point in time, each of the four FVVT mechanisms would be in exactly the same condition, or operational position. Obviously, however, the lift portions  33  of the four different cam profiles  29  would be in four different positions, relative to each other. 
     The upper end of the stem of the intake valve  19  is in engagement with a valve pad  35  formed at the reciprocable end of a rocker arm  37 . The rocker arm  37  includes an annular portion  38  (see FIG. 4) which pivots about a cylindrical support member  39 , which is fixed relative to the cylinder head  11 . Disposed on axially opposite sides (see FIG. 3) of the rocker arm  37  is a cam assembly, generally designated  41 , which preferably includes a pair of generally V-shaped end plates  43 , which are attached to each other by means of a pair of cylindrical connectors  45  and  47 . Toward the bottom portion (as viewed in the drawing figures) of the V-shaped end plates  43  there is another cylindrical support member  49  fixed relative to the cylinder head  11 , and thus providing a pivot location about which the cam assembly  41  pivots, in a manner to be described subsequently. Disposed between the pair of end plates  43  is a pair of cam members  51 , each of which has one end fixed to rotate about the cylindrical connector  45 . However, the opposite end of each of the cam members  51  can have a limited range of up and down movement relative to the cylindrical connector  47  because the cam members  51  define slightly elongated openings  53 , through which the connector  47  passes. 
     The arrangement described permits the cam assembly  41  to include a hydraulic lash compensation device  54 , shown only in FIG. 2, and by way of example only. Preferably, the lash compensation device  54  would include some sort of mechanical “lift loss” capability of the general type which is now well known to those skilled in the lash compensation art. However, it should be understood that the provision of lash compensation in the valve control system of the invention is preferred, but not essential, and therefore, the particular type of lash compensator and its specific location within the system are also not essential features of the invention. 
     In engagement with the cam profile  29  is a cam follower  55 , which is fixed to rotate relative to an upper end  56  of an adjustable timing linkage  57  (see FIG.  4 ), which will be described in greater detail subsequently. Also fixed to pivot relative to the cam follower  55  is a generally rigid follower linkage  59  which projects between the end plates  43 , and includes, at its right end in FIG. 1, a pair of second cam followers  61 , the function of which will also be described subsequently. As will be understood by those skilled in the engine art, from a reading and understanding of the remainder of this specification, the timing linkage  57  moves in a generally vertical direction, in response to an input from the engine ECU. This input may be generated using the same engine and vehicle parameters as would be used to generate the input used to control a variable cam phaser, in view of the fact that the vertical movement of the linkage  57  accomplishes the same function and purpose as rotating the camshaft relative to the crankshaft. 
     As may best be seen in FIG. 6 (but not shown in FIGS. 1,  4  and  5 , for simplicity) there is, attached to the cylindrical connector  45 , an eccentric link arrangement, generally designated  63 , including an eccentric link member  65 . The link member  65  has one end  65   a  pivotably disposed about the cylindrical connector  45  and its opposite end  65   b  associated with an eccentric actuator  67 , whereby a rotational input motion may be provided to the arrangement  63  (for example, in response to movement of the vehicle accelerator pedal). Specifically, rotational input motion to the eccentric actuator  67  results in longitudinal motion of the eccentric link member  65 , thus pivoting the cam assembly  41  about its pivot location (i.e., the cylindrical support member  49 ). 
     In accordance with the subject embodiment, and by way of example only, as the eccentric actuator  67  rotates over a range of about  600  of rotation, the cam assembly  41  is pivoted between the extreme positions shown in FIGS. 4 and 5, corresponding, respectively, to a maximum lift condition (“MAX. LIFT” in FIG. 7B) and a minimum lift condition (“MIN. LIFT” in FIG.  7 B). It may be seen in FIG. 7B, by comparing the various lift graphs, that lift duration is generally proportional to lift amplitude, and that both are directly proportional to the angle of the cam assembly  41 , as it is moved from the minimum lift condition of FIG. 5 to the maximum lift condition of FIG.  4 . 
     Referring now primarily to FIGS. 2 and 3, in conjunction with FIG. 1, the rocker arm  37  defines an upper (in the orientation of FIG. 1) engagement surface  69  which is in engagement with a roller cam follower  70 , disposed between the pair of second cam followers  61 . Similarly, the cam members  51  define, on their undersides, cam surfaces  71  which are in engagement with the second cam followers  61 . As was mentioned in the BACKGROUND OF THE DISCLOSURE, the need to grind a pair of very accurate surfaces on the cam profile, to provide the valve opening and closing “ramps” is a primary reason for the typical camshaft being very expensive. In accordance with an important benefit of the present invention, the desired valve opening and closing curve, including the “ramps”, is provided in the forming of the cam surface  71  and, because that surface is traversed twice during each valve event (opening + closing), only one accurately formed portion to define the ramps must be provided. As a result, the cam profile  29  may remain as a “net shape”, thus making the camshaft substantially less expensive. 
     Referring now primarily to FIGS. 4 and 7, the variable valve timing portion of the system will be described. A linkage member  73  is provided, having one end (right end in FIG. 4) fixed to rotate with the cylindrical support member  49 , about which the cam assembly  41  pivots. The other end of the linkage member  73  is pivotally connected by a cylindrical member  75  to the adjustable timing linkage  57 . Therefore, the support member  49  serves two functions, first, as the pivot location for the cam assembly  41  and, second, as the input to control the system timing. Those skilled in the art will understand that rotation of the support member  49 , to control valve timing, may be accomplished in any one of several ways, such as by means of a rotary solenoid, such input to the member  49  not comprising part of the invention. When variations in the desired timing are provided to the system in the form of rotation of the support member  49 , the linkage member  73  pivots about the axis of the member  49 , either raising or lowering the linkage  57 , depending upon the direction of rotation of the support member  49 . 
     With the position of the linkage member  73 , as shown in FIG. 4, comprising the “normal” timing (corresponding to the timing shown in FIG.  7 B), and assuming clockwise rotation of the camshaft  27 , rotation of the support member  49  clockwise will raise the timing linkage  57 . As a result, the lift portion  33  of the cam profile  29  will engage the cam follower  55  sooner, thus producing the “ADVANCED” timing shown in FIG.  7 A. If, on the other hand, the support member  49  were rotated in the counter-clockwise direction, the timing linkage  57  would be lowered. As a result, the lift portion  33  would engage the cam follower  55  later than “normal”, thus producing the “RETARDED” timing shown in FIG.  7 A. 
     Referring now to FIG. 7C, it should be apparent to those skilled in the art, from a careful reading and understanding of the foregoing specification, that, because the support member  49  (timing control member) and the eccentric actuator  67  can be controlled independently of each other, any desired combination of valve lift and valve timing is possible with the present invention. In other words, the valve lift can be varied anywhere between the MIN. LIFT and MAX. LIFT conditions shown in FIG. 7B, while the valve timing can be varied anywhere between the ADVANCED timing and the RETARDED timing shown in FIG.  7 A. Furthermore, unlike many prior art systems, it is possible to achieve any of the possible valve lifts in combination with any of the possible valve timings. There is no pre-determined set of possible combinations whereby certain valve lift amounts correspond to only certain valve timing conditions, or vice versa. 
     The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.