Abstract:
Variable valve control method and apparatus for an internal combustion engine provided with a variable valve mechanism that varies an operating characteristic of an intake valve, for controlling a gas amount passing back through the intake valve by variably controlling the operating characteristic. A storage section stores previously a correlation between a value equivalent to an opening area of the intake valve and a valve passing gas amount, corresponding to predetermined effective cylinder capacity. A conversion section converts that value equivalent into the valve passing gas amount by referring to the correlation. A correction section corrects the value equivalent based on a ratio between the converted valve passing gas amount and a requested valve passing gas amount. A calculating section calculates requested effective cylinder capacity (by which the requested valve passing gas amount can be obtained based on the value equivalent to the opening area) based on the valve passing gas amount obtained by referring to the correlation based on the corrected value equivalent to the opening area, and the requested valve passing gas amount. A control section controls the variable valve mechanism according to the requested effective cylinder capacity calculated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. Ser. No. 10/716,532, filed Nov. 20, 2003, now U.S. Pat. No. 7,013,211 which is incorporated herein by reference. 

   BACKGROUND 
   The present invention relates to a variable valve control apparatus and a variable valve control method for an internal combustion engine, and in particular to a technology for controlling an amount of working medium by variably controlling an operating characteristic of an intake valve. 
   Heretofore, there has been known an apparatus in which a target torque is set based on an accelerator opening and an engine rotation speed, and an operating characteristic of an intake valve is varied so that a target intake air amount equivalent to the target torque can be obtained (refer to Japanese Unexamined Patent Publication No. 6-272580). 
   Further, there has also been known a variable valve event and lift mechanism that successively varies valve lifts of engine valves together with operating angles of the engine valves (refer to Japanese Unexamined Patent Publication No. 2001-012262). 
   Here, since there is a constant correlation between an opening area of the intake valve and a total amount of working medium in a cylinder, it is possible to estimate the total amount of working medium in the cylinder based on the opening area of the intake valve. 
   Note, the total amount of working medium in the cylinder is the sum of a fresh air amount and a residual gas amount in the cylinder. 
   Further, the residual gas amount in the cylinder includes a spit-back gas amount to an intake side at the valve overlap time, a spit-back gas amount to the intake side at the intake valve closing time, and further a residual gas amount which has not been discharged via an exhaust valve to remain in the cylinder. 
   In a region where the opening area of the intake valve is large, a gas temperature in the cylinder rises with an increase of residual gas, and volume efficiency is lowered with the rise of gas temperature. 
   Accordingly, in the region where the opening area of the intake valve is large, the total amount of working medium in the cylinder is changed to decrease relative to an increase of opening area. 
   Therefore, in the region where the opening area of the intake valve is large, two opening areas exist corresponding to the total amount of inner-cylinder working medium. 
   Here, if it is regarded that the total amount of inner-cylinder working medium is not changed relative to the increase of opening area, it is possible to determine the number of opening areas corresponding to the total amount of inner-cylinder working medium to 1. 
   However, there is caused a problem of the occurrence of control error, if it is regarded that the total amount of inner-cylinder working medium is not changed relative to the increase of opening area. 
   Further, a correlation between the opening area of the intake valve and an intake valve passing gas amount exists for each effective cylinder capacity that is changed depending on closing timing of the intake valve. 
   Accordingly, in a system which controls an intake air amount using a variable valve mechanism that successively varies a valve lift and a valve operating angle, it is required to prepare a table indicating the correlation between the opening area ad the valve passing gas amount for each effective cylinder capacity (closing timing of the intake valve). 
   However, if the table indicating the opening area and the valve passing gas amount is prepared for each effective cylinder capacity, large storage capacity is required and also a large number of processes is required for matching each table. 
   SUMMARY 
   It is therefore an object of the present invention to enable a high accurate control of a gas amount passing through an intake valve, based on a correlation between an opening area of the intake valve and the valve passing gas amount. 
   A further object of the present invention is to enable the control of the valve passing gas amount without the necessity of a large storage capacity and also with a small number of matching processes. 
   In order to accomplish the above-mentioned objects, the present invention is constituted so that a fresh air amount flown into a cylinder of an engine and a gas amount spit back to an intake side from the inside of the cylinder when the intake valve is opened are calculated, and a gas amount passing through the intake valve is calculated based on the fresh air amount and an amount of predetermined times the spit-back gas amount of the time when the intake valve is opened, to control a variable valve mechanism based on the intake valve passing gas amount. 
   Moreover, according to the present invention, a correlation between a value equivalent to an opening area of the intake valve and the valve passing gas amount is stored previously, the value equivalent to the opening area of the intake valve is converted into the valve passing gas amount by referring to the correlation, the value equivalent to the opening area is corrected based on a ratio between the valve passing gas amount obtained by the conversion and a requested valve passing gas amount, and requested effective cylinder capacity by which the requested valve passing gas amount can be obtained at the value equivalent to the opening area, is calculated based on the valve passing gas amount obtained by referring to the correlation based on the corrected value equivalent to the opening area and the requested valve passing gas amount, to control the variable valve mechanism according to the requested effective cylinder capacity. 
   The other objects and features of the invention will become understood from the following description with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a system structure of an internal combustion engine in an embodiment. 
       FIG. 2  is a cross section view showing a variable valve event and lift mechanism (A—A cross section of  FIG. 3 ). 
       FIG. 3  is a side elevation view of the variable valve event and lift mechanism. 
       FIG. 4  is a top plan view of the variable valve event and lift mechanism. 
       FIG. 5  is a perspective view showing an eccentric cam for use in the variable valve event and lift mechanism. 
       FIGS. 6(A) and 6(B)  are cross sectional views showing an operation of the variable valve event and lift mechanism at a low lift condition (B—B cross section view of  FIG. 3 ). 
       FIGS. 7(A) and 7(B)  are cross sectional views showing an operation of the variable valve event and lift mechanism at a high lift condition (B—B cross section view of  FIG. 3 ). 
       FIG. 8  is a valve lift characteristic diagram corresponding to a base end face and a cam surface of a swing cam in the variable valve event and lift mechanism. 
       FIG. 9  is a characteristic diagram showing valve timing and a valve lift of the variable valve event and lift mechanism. 
       FIG. 10  is a perspective view showing a rotational driving mechanism of a control shaft in the variable valve event and lift mechanism. 
       FIG. 11  is a longitudinal cross section view of a variable valve timing mechanism in the embodiment. 
       FIG. 12  is a block diagram showing the calculation of requested closing timing of an intake valve in the embodiment. 
       FIG. 13  is a block diagram showing the calculation of a requested valve passing gas amount in the embodiment. 
       FIG. 14  is a block diagram showing the calculation of a spit-back gas amount in the closing timing of the intake valve in the embodiment. 
       FIG. 15  is a graph showing, at each closing timing, a correlation between an opening area of the intake valve and the valve passing gas amount in the embodiment. 
       FIG. 16  is a block diagram showing the calculation of requested opening timing of the intake valve in the embodiment. 
       FIG. 17  is a block diagram showing the calculation of a target operating characteristic of the intake valve in the embodiment. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a diagram of a system structure of an internal combustion engine for vehicle comprising a variable valve mechanism according to the present invention. 
   In  FIG. 1 , in an intake passage  102  of an internal combustion engine  101 , an electronically controlled throttle  104  is disposed for driving a throttle valve  103   b  to open and close by a throttle motor  103   a.    
   Air is sucked into a combustion chamber  106  via electronically controlled throttle  104  and an intake valve  105 . 
   A combusted exhaust gas is discharged from combustion chamber  106  via an exhaust valve  107 . 
   Then, the combusted exhaust gas is purified by an exhaust purification catalyst  108  and thereafter, emitted into the atmosphere via a muffler  109 . 
   Exhaust valve  107  is driven by a cam  11  axially supported by an exhaust side camshaft  110 , to open and close at fixed valve lift amount, valve operating angle and valve opening/closing timing. 
   A valve lift and a valve operating angle of intake valve  105  are varied successively by a variable valve event and lift mechanism (to be referred to as VEL hereunder)  112 . 
   On an end portion of an intake side camshaft  113 , there is disposed a variable valve timing mechanism (to be referred to as VTC hereunder)  114  that varies successively a center phase of the operating angle of intake valve  105  by changing a rotation phase of intake side camshaft  113  relative to a crankshaft. 
   A control unit  115  incorporating therein a microcomputer, receives various detection signals from an accelerator opening sensor APS  116 , an air flow meter  117  detecting an intake air amount (mass flow amount) Qa, a crank angle sensor  118  taking out a rotation signal Ne from the crankshaft, a cam sensor  119  detecting a rotation position of intake side camshaft  113 , a throttle sensor  120  detecting an opening TVO of throttle valve  103   b , and the like. 
   Then, control unit  115  adjusts an amount of working medium of engine  101  by the control of an operating characteristic of intake valve  105  by VEL  112  and VTC  114 . 
   Further, control unit  115  controls an opening of throttle valve  103   b  so that a fixed negative pressure (for example, −50 mmHg) is generated for canister purging and blow-by gas processing. 
   Here, the structure of VEL  112  will be described. 
   VEL  112 , as shown in  FIG. 2  to  FIG. 4 , includes a pair of intake valves  105 ,  105 , a hollow camshaft  13  rotatably supported by a cam bearing  14  of a cylinder head  11 , two eccentric cams  15 ,  15  being rotation cams, axially supported by camshaft  13 , a control shaft  16  rotatably supported by cam bearing  14  and arranged at an upper position of camshaft  13 , a pair of rocker arms  18 ,  18  swingingly supported by control shaft  16  through a control cam  17 , and a pair of swing cams  20 ,  20  disposed independently from each other to upper end portions of intake valves  105 ,  105  through valve lifters  19 ,  19 , respectively. 
   Eccentric cams  15 ,  15  are connected with rocker arms  18 ,  18  by link arms  25 ,  25 , respectively, and rocker arms  18 , 18  are connected with swing cams  20 ,  20  by link members  26 ,  26 . 
   Each eccentric cam  15 , as shown in  FIG. 5 , is formed in a substantially ring shape and includes a cam body  15   a  of small diameter, a flange portion  15   b  integrally formed on an outer surface of cam body  15   a . A camshaft insertion hole  15   c  is formed through the interior of eccentric cam  15  in an axial direction, and also a center axis X of cam body  15   a  is biased from a center axis Y of camshaft  13  by a predetermined amount. 
   Eccentric cams  15 ,  15  are pressed and fixed to camshaft  13  via camshaft insertion holes  15   c  at outsides of valve lifters  19 ,  19 , respectively, so as not to interfere with valve lifters  19 ,  19 . Also, outer peripheral surfaces of cam body  15   a  are formed in the same cam profile. 
   Each rocker arm  18 , as shown in  FIG. 4 , is bent and formed in a substantially crank shape, and a central base portion  18   a  thereof is rotatably supported by control cam  17 . 
   A pin hole  18   d  is formed through one end portion  18   b  which is formed to protrude from an outer end portion of base portion  18   a . A pin  21  to be connected with a tip portion of link arm  25  is pressed into pin hole  18   d . A pin hole  18   e  is formed through the other end portion  18   c  which is formed to protrude from an inner end portion of base portion  18   a . A pin  28  to be connected with one end portion  26   a  (to be described later) of each link member  26  is pressed into pin hole  18   e.    
   Control cam  17  is formed in a cylindrical shape and fixed to a periphery of control shaft  16 . As shown in  FIG. 2 , a center axis P 1  position of control cam  17  is biased from a center axis P 2  position of control shaft  16  by α, thereby creating spacing  17   a.    
   Swing cam  20  is formed in a substantially lateral U-shape as shown in  FIG. 2 ,  FIG. 6  and  FIG. 7 , and a supporting hole  22   a  is formed through a substantially ring-shaped base end portion  22 . Camshaft  13  is inserted into supporting hole  22   a  to be rotatably supported. Also, a pin hole  23   a  is formed through an end portion  23  positioned at the other end portion  18   c  of rocker arm  18 . 
   A base circular surface  24   a  of base end portion  22  side and a cam surface  24   b  extending in an arc shape from base circular surface  24   a  to an edge of end portion  23 , are formed on a bottom surface of swing cam  20 . Base circular surface  24   a  and cam surface  24   b  are in contact with a predetermined position of an upper surface of each valve lifter  19  corresponding to a swing position of swing cam  20 . 
   Namely, according to a valve lift characteristic shown in  FIG. 8 , as shown in  FIG. 2 , a predetermined angle range θ 1  of base circular surface  24   a  is a base circle interval and a range of from base circle interval θ 1  of cam surface  24   b  to a predetermined angle range θ2 is a so-called ramp interval, and a range of from ramp interval θ 2  of cam surface  24   b  to a predetermined angle range θ 3  is a lift interval. 
   Link arm  25  includes a ring-shaped base portion  25   a  and a protrusion end  25   b  protrudingly formed on a predetermined position of an outer surface of base portion  25   a . A fitting hole  25   c  to be rotatably fitted with the outer surface of cam body  15   a  of eccentric cam  15  is formed on a central position of base portion  25   a . Also, a pin hole  25   d  into which pin  21  is rotatably inserted is formed through protrusion end  25   b.    
   Link arm  25  and eccentric cam  15  consist a swing-drive member. 
   Link member  26  is formed in a linear shape of predetermined length and pin insertion holes  26   c ,  26   d  are formed through both circular end portions  26   a ,  26   b . End portions of pins  28 ,  29  pressed into pin hole  18   d  of the other end portion  18   c  of rocker arm  18  and pin hole  23   a  of end portion  23  of swing cam  20 , respectively, are rotatably inserted into pin insertion holes  26   c ,  26   d.    
   Snap rings  30 ,  31 ,  32  restricting axial transfer of link arm  25  and link member  26  are disposed on respective end portions of pins  21 ,  28 ,  29 . 
   Control shaft  16  is driven to rotate within a predetermined angle range by an actuator  201 , such as a DC servo motor, disposed on one end portion thereof, as shown in  FIG. 10 . By varying an angle of control shaft  16  by actuator  201 , the valve lift amount and valve operating angle of each of intake valves  105 ,  105  are successively varied (refer to  FIG. 9 ). 
   Namely, in  FIG. 10 , the rotation of actuator (for example, DC servo motor)  201  is transmitted to a threaded shaft  203  via a transmission member  202 , to change the axial position of a nut  204  through which shaft  203  is inserted. 
   Control shaft  16  is rotated by a pair of stays  205   a ,  205   b , each mounted on the tip end of control shaft  16  and one end thereof fixed to nut  204 . 
   In this embodiment, as shown in the figure, the valve lift amount is decreased as the position of nut  204  approaches transmission member  202 , while the valve lift amount is increased as the position of nut  204  gets away from transmission member  202 . 
   Further, a potentiometer type angle sensor  206  detecting the angle of control shaft  16  is disposed on the tip end of control shaft  16 . Control unit  115  feedback controls actuator  201  so that an actual angle detected by angle sensor  206  coincides with a target angle. 
   Next, the structure of VTC  113  will be described based on  FIG. 11 . 
   Note, VTC  114  is not limited to the one in  FIG. 11 , and may be of the constitution to successively vary a rotation phase of a camshaft relative to a crankshaft. 
   VTC  114  in this embodiment is a vane type variable valve timing mechanism, and comprises: a cam sprocket  51  (timing sprocket) which is rotatably driven by a crankshaft  120  via a timing chain; a rotation member  53  secured to an end portion of intake side camshaft  113  and rotatably housed inside cam sprocket  51 ; a hydraulic circuit  54  that relatively rotates rotation member  53  with respect to cam sprocket  51 ; and a lock mechanism  60  that selectively locks a relative rotation position between cam sprocket  51  and rotation member  53  at predetermined positions. 
   Cam sprocket  51  comprises: a rotation portion (not shown in the figure) having on an outer periphery thereof, teeth for engaging with timing chain (or timing belt); a housing  56  located forward of the rotation portion, for rotatably housing rotation member  53 ; and a front cover and a rear cover (not shown in the figure) for closing the front and rear openings of housing  56 . 
   Housing  56  presents a cylindrical shape formed with both front and rear ends open and with four partition portions  63  protrudingly provided at positions on the inner peripheral face at 90° in the circumferential direction, four partition portions  63  presenting a trapezoidal shape in transverse section and being respectively provided along the axial direction of housing  56 . 
   Rotation member  53  is secured to the front end portion of intake side camshaft  113  and comprises an annular base portion  77  having four vanes  78   a ,  78   b ,  78   c , and  78   d  provided on an outer peripheral face of base portion  77  at 90° in the circumferential direction. 
   First through fourth vanes  78   a  to  78   d  present respective cross-sections of approximate trapezoidal shapes. The vanes are disposed in recess portions between each partition portion  63  so as to form spaces in the recess portions to the front and rear in the rotation direction. Advance angle side hydraulic chambers  82  and retarded angle side hydraulic chambers  83  are thus formed. 
   Lock mechanism  60  has a construction such that a lock pin  84  is inserted into an engagement hole (not shown in the figure) at a rotation position (in the reference operating condition) on the maximum retarded angle side of rotation member  53 . 
   Hydraulic circuit  54  has a dual system oil pressure passage, namely a first oil pressure passage  91  for supplying and discharging oil pressure with respect to advance angle side hydraulic chambers  82 , and a second oil pressure passage  92  for supplying and discharging oil pressure with respect to retarded angle side hydraulic chambers  83 . To these two oil pressure passages  91  and  92  are connected a supply passage  93  and drain passages  94   a  and  94   b , respectively, via an electromagnetic switching valve  95  for switching the passages. 
   An engine driven oil pump  97  for pumping oil in an oil pan  96  is provided in supply passage  93 , and the downstream ends of drain passages  94   a  and  94   b  are communicated with oil pan  96 . 
   First oil pressure passage  91  is formed substantially radially in a base  77  of rotation member  53 , and connected to four branching paths  91   d  communicating with each advance angle side hydraulic chamber  82 . Second oil pressure passage  92  is connected to four oil galleries  92   d  opening to each retarded angle side hydraulic chamber  83 . 
   With electromagnetic switching valve  95 , an internal spool valve is arranged so as to control relatively the switching between respective oil pressure passages  91  and  92 , and supply passage  93  and drain passages  94   a  and  94   b.    
   Control unit  115  controls the power supply quantity for an electromagnetic actuator  99  that drives electromagnetic switching valve  95 , based on a duty control signal superimposed with a dither signal. 
   For example, when a control signal of duty ratio 0% (OFF signal) is output to electromagnetic actuator  99 , the hydraulic fluid pumped from oil pump  97  is supplied to retarded angle side hydraulic chambers  83  via second oil pressure passage  92 , and the hydraulic fluid in advance angle side hydraulic chambers  82  is discharged into oil pan  96  from first drain passage  94   a  via first oil pressure passage  91 . 
   Consequently, an inner pressure of retarded angle side hydraulic chambers  83  becomes a high pressure while an inner pressure of advance angle side hydraulic chambers  82  becomes a low pressure, and rotation member  53  is rotated to the most retarded angle side by means of vanes  78   a  to  78   d . The result of this is that a valve opening period (opening timing and closing timing) is delayed. 
   On the other hand, when a control signal of duty ratio 100% (ON signal) is output to electromagnetic actuator  99 , the hydraulic fluid is supplied to inside of advance angle side hydraulic chambers  82  via first oil pressure passage  91 , and the hydraulic fluid in retarded angle side hydraulic chambers  83  is discharged to oil pan  96  via second oil pressure passage  92 , and second drain passage  94   b , so that retarded angle side hydraulic chambers  83  become a low pressure. 
   Therefore, rotation member  53  is rotated to the full to the advance angle side by means of vanes  78   a  to  78   d . Due to this, the opening period (opening timing and closing timing) of intake valve  105  is advanced. 
   Note, variable valve timing mechanism  114  is not limited to the above vane type mechanism, and may be of the constitution as disclosed in Japanese Unexamined Patent Publication Nos. 2001-041013 and 2001-164951 in which a rotation phase of a camshaft relative to a crankshaft is changed by friction braking of an electromagnetic clutch (electromagnetic brake), or of the constitution as disclosed in Japanese Unexamined Patent Publication No. 9-195840 in which a helical gear is operated by a hydraulic pressure. 
   Next, there will be described controls of VEL  112  and VTC  114 , by control unit  115 , referring to block diagrams. 
   The block diagram of  FIG. 12  shows the calculation of requested closing timing of intake valve  105 . 
   In  FIG. 12 , a requested engine torque calculated based on the accelerator opening and the like is converted into a requested volume flow ratio TQH 0 ST (requested fresh air amount) in b 101 . 
   In b 102 , a requested valve passing gas amount in intake valve  105  is calculated based on the requested volume flow ratio TQH 0 ST, an upstream pressure of intake valve  105  and a requested residual gas rate. 
   The calculation of requested valve passing gas amount in b 102  is executed as shown in the block diagram of  FIG. 13 . 
   In  FIG. 13 , in b 501 , a target residual gas rate is calculated based on the requested volume flow ratio TQH 0 ST and the engine rotation speed Ne. 
   In b 502 , target residual gas mass is calculated based on the target residual gas rate and the requested volume flow ratio TQH 0 ST. 
   In b 503 , the target residual gas mass is divided into a residual gas amount that has not been discharged at the closing time of exhaust valve  107 , to remain in the cylinder just as it is, and a spit-back gas amount spit-back to an intake pipe side at the valve overlap time (at the opening time of intake valve). 
   In b 504 , the spit-back gas amount at the valve overlap time is doubled. 
   In b 505 , the amount of two times the spit-back gas amount at the valve overlap time and the spit-back gas amount at the closing time of intake valve  105  to be calculated in b 506  are added together. 
   It is supposed that the gas spit-back to the intake pipe side at the valve overlap time is again flown into the cylinder. As a result, the gas passes through intake valve  105  twice and therefore, is doubled. 
   However, the spit-back gas is not necessarily doubled, and what multiplication is performed on the spit-back gas should be appropriately set according to the actual behavior of spit-back gas at the valve overlap time. 
   In b 507 , the sum of the doubled amount of the spit-back gas amount at the valve overlap time to be calculated as mass and the spit-back gas amount at the closing time of intake valve  105 , is converted into a volume flow ratio. 
   Then, in b 508 , the volume flow ratio obtained in b 507  and the requested volume flow ratio TQH 0 ST are added together, and a result of the addition is finally output as the requested valve passing gas amount. 
   That is, the requested valve passing gas amount is calculated based on a fresh air amount, the doubled amount of the spit-back gas amount at the valve overlap time (the spit-back gas amount at the opening time of intake valve) and the spit-back gas amount at the closing time of intake valve. 
   The spit-back gas amount at the closing time of intake valve is calculated as shown in the block diagram of  FIG. 14 . 
   In  FIG. 14 , in b 601 , an opening area AIVC of intake valve  105  correlating to the spit-back gas amount is obtained based on target closing timing of intake valve  105  and a target angle TGVEL of control shaft  16  in VEL  112 . 
   In b 602 , the opening area AIVC obtained in b 601  is converted into a basic spit-back gas amount WIVC 0  at the closing time of intake valve. 
   On the other hand, in b 603 , a correction value KPMPE based on an intake pressure Pm is calculated, and in b 604 , a correction value KHOSNE based on the engine rotation speed Ne is calculated. 
   Then in b 605 , the correction value KPMPE is multiplied on the basic spit-back gas amount WIVC 0 , and in b 606 , a result of multiplication in b 605  is further multiplied by the correction value KHOSNE. A result of multiplication in b 606  is output as a final spit-back gas amount at the closing time of intake valve. 
   The requested valve passing gas amount calculated in the above manner tends to be increased in all of the regions relative to an increase of opening area of intake valve  105 , as shown in  FIG. 15 . 
   Accordingly, based on the correlation between the valve passing gas amount and the opening area, a request of opening area for obtaining the requested valve passing gas amount is primarily determined. 
   Then, the opening area for obtaining the requested valve passing gas amount is obtained based on an actual correlation between the valve passing gas amount and the opening area, thereby enabling of a high accurate control of valve operating characteristic. 
   Here, the description shall be returned to the block diagram of  FIG. 12  to be continued. 
   In b 103 , an angle INPVEL of control shaft  16  in VEL  112  is set for calculating the target opening timing and target closing timing of intake valve. 
   The angle INPVEL is sequentially updated so as to calculate the target opening timing and target closing timing for each valve lift amount within a control range. 
   The angle INPVEL is converted into an opening area TVELAA of intake valve  105  in b 104 . 
   In b 105 , the opening area TVELAA is divided by the engine rotation number (rpm) at the time. 
   In b 106 , a result of division in b 105  is further divided by a piston displacement VOL# of engine  101 , so that the opening area TVELAA is converted into a state amount AADNV. 
   The state amount AADNV is converted into a reference valve passing gas amount of intake valve  105  in b 107 . 
   A correlation between the state amount AADNV and the valve passing gas amount exists for each effective cylinder capacity. Here, a table is prepared for a correlation of the time when the effective cylinder capacity is 100%. 
   Note, when the closing timing of intake valve is made a bottom dead center, the effective cylinder capacity is 100%. 
   Then, the above conversion table is referred to, so that the state amount AADNV is converted into the reference valve passing gas amount. 
   In b 108 , the reference valve passing gas amount is divided by the requested valve passing gas amount comprising the fresh air amount, the doubled amount of the spit-back gas amount at the valve overlap time and the spit-back gas amount at the closing timing of intake valve. 
   In b 109 , a calculation result in b 108  is multiplied on the state amount AADNV. 
   That is, an output from b 109  has the following value.
 
Output AADNV′  from  b 109= AADNV ×(reference valve passing gas amount/requested valve passing gas amount)
 
   In b 110 , by referring to the conversion table same as that referred to in b 107 , the valve passing gas amount corresponding to the state amount AADNV′ corrected in b 109  is obtained. 
   In b 111 , the requested valve passing gas amount is divided by the valve passing gas amount obtained in b 110 , to obtain a requested cylinder capacity ratio.
 
Requested cylinder capacity ratio=Requested valve passing gas amount/valve passing gas amount corresponding to  AADNV′ 
 
   In b 112 , the requested cylinder capacity ratio is converted into the requested closing timing of intake valve  105  according to the engine rotation speed Ne at the time. 
   The requested closing timing of intake valve  105  is set such that intake valve  105  is closed before the bottom dead center as the requested cylinder capacity ratio becomes smaller. 
   The correlation between the state amount AADNV and the valve passing gas amount exists for each effective cylinder capacity. As shown in  FIG. 15 , the characteristic lines of the state amount AADNV and the valve passing gas amount are in a relation similar to each other. 
   Here, the referring to the correlation of the time when the effective cylinder capacity=100% based on the state amount AADNV′ corrected based on the reference valve passing gas amount/requested valve passing gas amount equals to the referring to the correlation obtained by similarly enlarging the correlation in the effective cylinder capacity by which the requested valve passing gas amount can be obtained based on the state amount AADNV. 
   Then, the requested valve passing gas amount is divided by the valve passing gas amount obtained by referring to the correlation of the time when the effective cylinder capacity=100% based on the state amount AADNV′, resulting in that the effective cylinder capacity for obtaining the requested valve passing gas amount is obtained based on the angle INPVEL at the time. 
   If the constitution is such that the effective cylinder capacity for obtaining the requested valve passing gas amount is obtained based on the angle INPVEL at the time, as described above, since it is only necessary to store the correlation between the state amount AADNV of the time when the effective cylinder capacity=100% and the valve passing gas amount, it is possible to reduce the storage capacity and the matching processes. 
   On the other hand, the requested opening timing of intake valve  105  is set as shown in the block diagram of  FIG. 16 . 
   In b 201 , the target residual gas rate is set based on the requested volume flow ratio TQH 0 ST and the engine rotation speed Ne. 
   In b 202 , the target residual gas mass is calculated based on the target residual gas rate and the requested volume flow ratio TQH 0 ST. 
   In b 203 , the target residual gas mass is divided into a portion to remain as it is in the cylinder at closing timing of exhaust valve  107  and a portion to be spit back at the valve overlap time. 
   In b 204 , the requested opening timing of intake valve  105  is calculated based on the spit-back portion at the valve overlap time, the engine rotation speed Ne and the intake pressure. 
   The block diagram of  FIG. 17  shows the calculation of a control target angle TGVEL of control shaft  16  in VEL  112  based on the requested closing timing and requested opening timing of intake valve  105  and also the calculation of an advance control target by VTC  114 . 
   In b 301 , a requested operating angle REQEVENT is calculated based on the requested closing timing and requested opening timing of intake valve  105 . 
   In b 302 , the angle INPVEL is converted into an operating angle CALEVENT of intake valve  105 . 
   Then, in b 303 , the control target angle TGVEL is calculated based on the above described REQEVENT and CALEVENT. 
   Specifically, a deviation between REQEVENT and CALEVENT is calculated to be stored for each angle INPVEL, to select a combination of the angle INPVEL at which an absolute value of the deviation becomes smallest, the requested closing timing and the requested opening timing. 
   Then, the angle INPVEL at which the absolute value of the deviation becomes smallest is set to the control target angle TGVEL, and the requested closing timing and the requested opening timing calculated corresponding to the angle INPVEL at which the absolute value of the deviation becomes smallest are set as final target opening/closing timing, to be output together with the control target angle TGVEL to b 304 . 
   In b 304 , an advance target of valve timing for achieving the target opening/closing timing at the control target angle TGVEL, that is, a control target TGVTC of VTC  114 , is set. 
   Then, VTC  114  is controlled based on the control target TGVTC, and the center phase of the operating angle of intake valve  105 , which is determined based on the control target angle TGVEL, is controlled to be advanced or retarded in accordance with the control target TGVTC. 
   Thus, intake valve  105  is driven at the opening area and the opening/closing timing, at which the requested valve passing gas amount and the requested residual gas rate can be obtained. 
   The entire contents of Japanese Patent Application Nos. 2002-350276 and 2002-350277, filed Dec. 2, 2002, respectively, priorities of which are claimed, are incorporated herein by reference. 
   While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. 
   Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.