Patent Publication Number: US-8118002-B2

Title: Continuously variable valve lift system including valve deactivation capability on one of two dual intake valves

Description:
TECHNICAL FIELD 
     The present invention relates to variable valve lift systems for internal combustion engines; more particularly, to a system for continuously variable lift of dual intake valves; and most particularly, to such a system wherein the valvetrain of one of the dual intake valves is further equipped with means for lost motion valve deactivation. 
     BACKGROUND OF THE INVENTION 
     Continuously variable valve lift systems are known in the engine arts. See, for example, the system disclosed in US Patent Application Publication No. 2007/0125329, published Jun. 7, 2007 and incorporated herein by reference. Such a system incorporates a crank mechanism for selective continuous variation of the contact point of a special rocker subassembly (RS) with the engine camshaft to vary the angular rotational motion of the RS. The RS is positioned between the engine camshaft and the valvetrain&#39;s roller finger follower (RFF). The RS includes a secondary cam surface followed by the RFF. Varying the contact point of the RS on the camshaft has the effect of varying the lift and the opening and closing timing of the associated engine combustion valve. For a cylinder having dual intake or dual exhaust valves, the RS comprises a wide secondary cam surface that is followed identically by the RFF for each valve. 
     Variable valve activation/deactivation (WA) systems are also known in the engine arts. See, for example, U.S. Pat. No. 6,321,704 that discloses a deactivating hydraulic lash adjuster (DHLA), and U.S. Pat. No. 7,093,572 that discloses a deactivating roller finger follower (DRRF), both of which are incorporated herein by reference. Each of these prevents the rotary motion of the camshaft lobe from being translated into reciprocal motion of the associated valve stem by absorbing the equivalent motion within itself (“lost motion”). Thus the valve is “deactivated” and prevented from opening on schedule. 
     For gasoline engines, compromises inherent with fixed valve lift and event timing of a conventional valve train have prompted engine designers to consider Continuously Variable Valve Lift (CVVL) systems for more flexible air flow control optimized for each engine load and speed condition. In recent years, some relatively basic forms of CVVL have been introduced into production engines. Greater performance and drivability expectations of customers, more stringent emission regulations set by government legislators, and the mutual desire for higher fuel economy are increasingly at odds. As a solution, some vehicle manufacturing companies are considering large-scale application of higher function CVVL mechanisms in their next generation vehicles, mainly to improve fuel economy, by reducing pumping loss, and cold start combustion stability, with increased cylinder air flow tumble motion. However, the CVVL engine has two critical engineering challenges for turbulence (swirl or tumble) enhancement and cylinder by cylinder valve lift variation, which requires combustion chamber masking for tumble enhancement and costly select fit of output rocker cam or roller finger followers for CVVL. 
     When applying a prior art CVVL system, current engine combustion strategies allow the intake valve to open from zero to full lift, as described above. However, the use of variable lift mechanisms has been limited on dual intake valves to the same lift on both valves of each cylinder, which cannot provide any in-cylinder air flow turbulence enhancement. 
     What is needed in the art is a CVVL system wherein in-cylinder turbulence is enhanced during variable-lift operation of an internal combustion engine, and especially under low lift flow conditions. 
     It is a principal object of the present invention to provide increased in-cylinder turbulence during variable-lift operation of an internal combustion engine. 
     SUMMARY OF THE INVENTION 
     Briefly described, in a dual intake valve system for an internal combustion engine, a CVVL system is provided for both intake valves for one or more engine cylinders. In each cylinder, one of the intake valvetrains includes a valve deactivation device such as a DHLA or a DRFF, and the other intake valvetrain includes a non-deactivating HLA and RFF. To improve in-cylinder air flow turbulence (mainly swirl) under low valve lift, one of the intake valves is deactivated by an external actuator system, resulting in intake air or air/fuel mixture through only one valve, which generates strong swirl by unbalanced flow because the open valve is off-axis of the cylinder. 
     In a presently preferred embodiment, a CVVL engine including a valve deactivation device provides the same amount air flow for the same engine load as a non-CVVL engine by providing higher valve lift (approximately 2 times the lift of a prior art CVVL-only maximum valve lift). The higher valve lift also reduces the impact of valve lift variation by component tolerance stack-up on engine performance to provide an expanded CVVL operating zone, and especially to extend the low lift limit zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is an isometric view of a first embodiment of a CVVL system and valvetrains in accordance with the present invention; 
         FIG. 2  is an isometric view of a second embodiment of a CVVL system and valvetrains in accordance with the present invention; 
         FIG. 3  is a schematic drawing of first and second valves in a dual intake-valve engine having CVVL capability; 
         FIGS. 4   a  and  4   b  respectively are schematic lift curves for the corresponding valves shown in  FIG. 3 , showing a nominal maximum lift of 1×; 
         FIG. 5  is a schematic drawing of first and second valves in a dual intake-valve engine having CVVL and valve deactivation capability in accordance with the present invention; and 
         FIGS. 6   a  and  6   b  respectively are schematic lift curves for the corresponding valves shown in  FIG. 5 , showing a nominal maximum lift of 2× for the valve without deactivation capability and full closure of the other valve when deactivated. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention includes a CVVL system combined with a valve deactivation device. In each cylinder, one of the intake valvetrains is installed with a valve deactivation device whereas the other intake valvetrain is installed with a non-deactivating regular HLA and roller finger follower. To improve in-cylinder air flow turbulence (mainly swirl) under low valve lift conditions, one of the intake valves is deactivated by an external actuator system to provide air or fuel/air mixture entirely through the other valve, which generates strong swirl by unbalanced air flow. The CVVL engine combined with a valve deactivation device provides the same amount of air flow with higher valve lift for the same engine load. For conventional CVVL operation, the valve deactivation device is not operative and thus transmits the full lift generated by the output rocker cam to its associated valvetrain. For swirl enhancement purposes under low lift conditions, the valvetrain with the valve deactivation device is deactivated to keep the valve closed through lost motion within the valve deactivation device. 
     Referring to  FIG. 1 , a first CVVL system  10  in accordance with the present invention is shown for providing variable valve lift to first and second valvetrains  100   a , 100   b  which include first and second dual intake valves  102   a , 102   b  in an internal combustion engine  200 . Engine  200  may be either compression ignited or spark ignited. Valvetrains  100   a , 100   b  are both actuated by a standard engine camshaft  300 . 
     CVVL system  10  may take the form of a prior art system for variable valvetrain actuation, substantially as disclosed in US Patent Application Publication No. 2007/0125329 A1. Alternatively, a CVVL system  10  may take the form shown in  FIG. 1 , which is structurally similar and functionally identical to the previously disclosed system. 
     A rocker subassembly (RS)  12  is disposed between camshaft  300  and first and second rocker arms, shown herein as roller finger followers (RFFs)  14   a , 14   b  of valvetrains  100   a , 100   b . RS  12  is pivotable on or about RS shaft  16  and includes a roller  17  for engaging a lobe  302  of camshaft  300  and further includes first and second cam plates  18   a , 18   b  having output cam profiles that themselves engage the respective rollers  20   a , 20   b  of RFFs  14   a , 14   b.    
     A RS-positioning crank subassembly (CS)  22  includes a crankshaft  24  supportive of first and second crank arms  26   a , 26   b  rotatably disposed on non-rotatable circular throws  28   a , 28   b  eccentrically mounted on crankshaft  24 . Each of arms  26   a , 26   b  includes a nose  30  (only nose  30   b  visible in  FIG. 1 ) for supporting a positioning shaft  32  pivotably attached to RS  12 . Rotation of crankshaft  24  causes arms  26   a , 26   b  and positioning shaft  32  to be similarly rotated, causing RS  12  to be counter-rotated about shaft  16 . This action alters the meeting angle at which roller  17  makes contact with cam lobe  302 , which changes the degree of lift to be imparted by RS  12  to RFFs  14   a , 14   b.    
     As camshaft  300  rotates counter-clockwise, the opening flank of cam lobe  302  pushes rocker roller  18  away, causing RS  12  to rotate in a counter-clockwise direction. As RS  12  rotates, it turns about the axis of shaft  16 . Continued counter-clockwise rotation of RS  12  advances the output cam profiles ground into cam plates  18   a , 18   b . The further that RS  12  is rotated counter-clockwise about shaft  16 , the greater the lift imparted through RFFs  14   a , 14   b  to valvetrains  100   a , 100   b . However, the total lift is governed by the action of CS  22  as described above. 
     Each RFF pivots on the ball shaped tip of a hydraulic valve lash adjuster (HLA)  34   a , 34   b  conventionally disposed in engine  200 . HLA  34   a  is a conventional non-deactivating HLA. However, in accordance with the present invention, HLA  34   b  is a deactivating HLA in accordance with the prior art, permitting complete activation or deactivation of valvetrain  100   b  as may be desired. 
     Referring to  FIG. 2 , the arrangement of a second embodiment  10 ′ of a CVVL system in accordance with the present invention is identical in all respects to that just recited for first embodiment  10  except for the following: 
     a) both HLA  34   a  and  34   b ′ are conventional non-deactivating HLAs; and 
     b) RFF  14   b ′ is a deactivating roller finger follower (DRFF) in accordance with the prior art. 
     It will be seen that the deactivation of valvetrain  100   b  can be carried out to equal effect by either embodiment  10  or embodiment  10 ′, or any other method of valve deactivation such as, by way of example, a deactivating hydraulic lash adjuster. 
     Referring to  FIGS. 3 through 4   b , in a prior art CVVL system when applied to dual intake valves  102   a , 102   b  in a head for an engine  200 , the lifts  104   a , 104   b  of the valves are typically identical, as are the areas  106   a , 106   b  under the lift curve. The maximum obtainable lift with a prior art CVVL system is shown arbitrarily as x for each valve. Under conditions of low flow rate of air or air/fuel mixture through the valves, the valve lift is relatively small. Thus air flow into the engine is relatively low in volume and velocity, and is symmetrically balanced between the two valves, resulting in low mixing swirl within the cylinder. Because the resulting mixture homogenization within the cylinder is less than desirable, engine performance is also less than ideal over at least a portion of the range of engine operating conditions. 
     Referring to  FIGS. 5 through 6   b , in a CVVL and deactivation system in accordance with the present invention when applied to dual intake valves  102   a , 102   b  in a head for an engine  200 , the lifts  304   a , 304   b  of the valves are non-identical, as are the areas  306   a , 306   b  under the lift curves. Under conditions of low flow rate of air or air/fuel mixture through the valves, the operating valve lift of the non-deactivating valve  102   a  is greater than the corresponding operating lift shown in  FIG. 3 , being preferably twice as great (2×). The greater lift is readily provided by adjusting the grinding profile of cam plates  18   a , 18   b  ( FIGS. 1 and 2 ). (Further, the profiles of the two cam plates may differ if desired.) Thus air flow into the engine can be entirely though a single off-center valve, resulting in desirably greater mixing swirl within the cylinder, for the same amount of air flow into the cylinder, under low air flow conditions. 
     Because the activation or deactivation of second valvetrain  100   b  is independently controlled from the action of CS  22  ( FIGS. 1 and 2 ), at full throttle both valves can be activated and opened 2× if so desired. All intermediate flows are possible by combining variable lift of first and second valves  102   a , 102   b  with activation/deactivation of second valve  102   b . Thus, the range of flows and corresponding lifts is greater than those of a prior art CVVL system without valve deactivation on one of the dual valves, providing improved engine combustion at a wide variety of engine operating conditions. 
     In this manner, air flow turbulence such as swirl can be introduced into the cylinder for improved combustion. For example, at a time when it is desirous to introduce a swirl to the mixture charge entering the combustion chamber, only one of the two intake valves may be opened, as shown in  FIGS. 5 ,  6   a  and  6   b , permitting the same amount of charge to enter the chamber but the charge entering from only one side of the chamber to introduce the swirl. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.