Abstract:
A poppet valve operating system for an internal combustion engine features variable valve lift and camshaft phasing. A planetary phaser uses control inputs which are shared with a variable lift mechanism. The phaser adjustment and the variable lift mechanism are controlled by a single positioning motor.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a system for operating poppet-type cylinder valves of reciprocating internal combustion engine, so as to selectively control the duration and phasing of the valve opening events.  
       BACKGROUND  
       [0002]     Variable valve duration control devices have been the subject of much invention during the past few decades. U.S. Pat. No. 5,373,818 discloses but one example of such inventive activity. The &#39;818 patent describes a variable duration valve operating system having at least one embodiment which is useful with bucket tappets. U.S. Pat. No. 6,932,035, which is assigned to the assignee of the present invention, and which is hereby incorporated by reference in its entirety in this specification, discloses a cylinder valve operating system which permits adjustment of valve lift, particularly with roller finger follower systems. The system of the &#39;035 patent does not, however, provide for camshaft phasing.  
         [0003]     The present system may be used with such systems as axially shiftable camshafts and other valve lift control devices to control both valve lift and valve or camshaft timing.  
       SUMMARY  
       [0004]     A poppet valve operating system for an internal combustion engine includes a poppet valve, a camshaft, a variable valve lift control system driven by the camshaft. The variable valve lift control system has an angular control input. The present system further includes a camshaft phaser driving the camshaft and having an angular control input, and a controller for providing angular position control for the variable valve lift control system and for the camshaft phaser.  
         [0005]     According to another aspect of the present invention, the system&#39;s controller includes a single motor operatively connected with an angular control shaft incorporated within the variable valve lift control system, with said controller further including a servo system extending between the valve lift control system and the angular control input of the camshaft phaser. Either a hydraulic motor, or an electric motor, such as a stepper motor, could be used with the present valve control system. In a preferred embodiment, the servo system may include a flexible position transmitting system.  
         [0006]     One type of servo system suitable for practicing the present invention includes a drive sprocket mounted to the angular control shaft of the variable valve lift control system, a driven sprocket mounted to that portion of the camshaft phaser which functions as an angular control input, and a chain extending between the drive and driven sprockets. As an alternative, the servo system may include a gear train having at least a drive gear attached to the angular control shaft and a driven gear attached to the angular control input of the camshaft phaser.  
         [0007]     According to yet another aspect of the present invention, a phaser suitable for use with this invention includes a planetary drive having a sun gear driven by the engine&#39;s crankshaft, and a number of planet gears driven by the sun gear. The planet gears are mounted rotatably upon a carrier having an angular position which is determinative of the camshaft&#39;s timing. A ring gear driven by the planet gears is rotatably locked to the camshaft. With this configuration, the carrier is coupled to the valve lift control system by the servo mechanism.  
         [0008]     According to yet another aspect of the present invention, a method for controlling the valve lift and timing of a poppet valve for an internal combustion engine includes the steps of: providing a variable valve lift control system driven by a camshaft and having an angular input control shaft; providing a planetary camshaft phaser for driving said camshaft and having an angular input control carrier; and providing a single-motor controller for controlling the angular positions of said angular input control shaft and said angular input control carrier.  
         [0009]     The present valve operating system offers the advantages attendant the ability to control of both valve lift and timing, but with lower cost, less complexity, and less package volume than known systems, because of the need for only a single actuator motor.  
         [0010]     Other advantages, as well as objects and features of the present invention, will become apparent to the reader of this specification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic representation of a poppet valve operating system according to the present invention.  
         [0012]      FIG. 2  is a partially schematic representation of a planetary phaser shown in  FIG. 1 , taken along the line  2 - 2  of  FIG. 1 .  
         [0013]      FIG. 3  is shows a family of valve lift and timing curves typical of those achievable by a system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     As shown in  FIG. 1 , the present cylinder valve operating system,  10 , is intended for use with poppet valves  14 , which are mounted within cylinder head  18  of an engine. Valves  14  are returned to their closed positions by means of valve springs  16 . Each of valves  14  is actuated by means of a finger follower,  20 , which has a first end in contact with valve  14  and a second end in contact with lash adjuster  28 , which is mounted to cylinder head  18 . Finger follower  20  has a roller,  24 , which contacts intermediate rocker  30 .  
         [0015]     Intermediate rocker  30  is biased into contact with drive cam  40  by means of compression spring  62 . Alternatively, a torsion spring (not shown) could be used for this purpose. Intermediate rocker  30  rotatably actuates finger follower  20  as drive cam  40 , which is mounted upon camshaft  44 , and driven either by a crankshaft or other rotating member of the engine (not shown), pushes upon rocker roller  32 , thereby moving intermediate rocker  30  translationally. Camshaft  44  and intermediate rocker  30  are mounted so that the motion imparted by camshaft  44  and drive cam  40  to intermediate rocker  30  is purely translational. This translational movement is controllably transformed into rotational movement of intermediate rocker  30  by control roller  48 , which is mounted upon support shaft  50 . In essence, intermediate rocker  30  pivots about an instantaneous contact point existing between control surface  34  and the outer diametral surface of control shaft  58 . Support shaft  50  is carried within control slot  54  formed in cylinder head  18   c.  Alternatively, support shaft  50  may be carried within a slotted member rigidly attached to cylinder head  18 .  
         [0016]     Control slot  54  permits translational movement of support shaft  50 . This translational movement is produced by control cam  56  which is mounted upon control shaft  58 . As control shaft  58  is rotated by control motor  70 , control cam  56  displaces control shaft  50  within slot  54 , so as to move control roller  48  to a new operating position. In general, when control roller  48  is moved closer to camshaft  44 , valve lift will be increased because control roller  48  will be operating on rocker ramp  34 , which is a control surface formed in intermediate rocker  30 .  
         [0017]     Engine control unit  74 , which may be selected from commonly employed engine controllers known to those skilled in the art and suggested by this disclosure, operates control motor  70 , which, as described above, is coupled to control shaft  58 . Control unit  74  receives inputs from the vehicle&#39;s driver, in the form of a torque demand, as well as inputs from a variety of sensors known to those skilled in the art and suggested by this disclosure.  
         [0018]     Mounted at the opposite end of shaft  58  from control motor  70 , drive sprocket  78  receives the same motion inputs as control shaft  58 . Drive sprocket  78  is connected by means of drive chain  80  to driven sprocket  86  of phaser  72 . Crankshaft  76  powers phaser  72  and ultimately, camshaft  44 , by means of a chain or belt  77 . In essence, motor  70  provides angular position control for control shaft  58  and for phaser  72 , which has an angular input control carrier.  
         [0019]      FIG. 2  is a partially schematic representation of the construction of phaser  72 . Camshaft  44  is shown as being attached to ring gear housing  91 , which is driven by planet gears  94 . Planet gears  94  are pivotally attached to angular input control carrier  102 , which also carries sprocket  86 , a driven sprocket. Thus, sprockets  78  and  86 , and drive chain  82  form a servo mechanism, in this case, a flexible drive, for positioning carrier  102  according to the input position of the variable lift mechanism. Phaser  72  also includes ring gear  90 , which is driven by planet gears  94  and sungear  98 . Driven sprocket  92 , which occupies a common shaft with sun gear  98 , is connected with crankshaft  76  by means of chain or belt  77 . Thus, sprocket  92  drives sun gear  98 . In one configuration, the various gear ratios are set so that camshaft  44  will rotate at one-half the rotational speed of crankshaft  76 . This will produce the valve timing commonly associated with a four-stroke cycle internal combustion engine.  
         [0020]     When engine control unit  74  sets the position of control shaft  58  by means of control motor  70 , sprockets  78  and  86  and chain or belt  80  set the position of carrier  102 . The rotational position of carrier  102  determines the valve timing, or in another words, the camshaft phasing. Note that carrier  102  is intended to operate in a stationary position; carrier  102  does not rotate with the balance of phaser  72 .  
         [0021]      FIG. 3  illustrates a plot of variable valve lift and camshaft phasing. Because of the phasing relationship produced by phaser  72  in combination with sprockets  78  and  86  and drive chain  82 , it is possible to produce the series of curves shown in  FIG. 3 . Curve  110  it would be useful for operating an engine at full load. Curves  112  and  114  would be more useful at part load; more specifically, curve  114  would be more useful at idle. If the ability to control cam phase did not exist, each of the curves would be centered about a common point instead of being shifted on the timing, or phase angle, axis. It is anticipated that control motor  70  will position angular input control shaft  58  and said angular input control carrier  102  in one of a plurality of predetermined positions, with at least some of the positions corresponding to the various curves of  FIG. 3 .  
         [0022]     Because control motor  70  operates not only the variable lift function of the present system, but also the camshaft timing function the need for a second motor and an attendant support system is obviated. This reduces the cost, weight, complexity, and package volume of the present system, as compared with other systems requiring two actuators.  
         [0023]     Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.