Patent Publication Number: US-6219611-B1

Title: Control method for engine having multiple control devices

Description:
FIELD OF THE INVENTION 
     The field of the invention relates to engine control, wherein the engine has multiple control devices. 
     BACKGROUND OF THE INVENTION 
     In some engines, an electronically controlled throttle is used for improved performance. In particular, the electronic throttle is used to control airflow to a desired value determined from operating conditions and an operator command. In this way, the vehicle can achieve improved drive feel and improved fuel economy. 
     In this system, the required airflow is used to determine an initial setting of the throttle. Also, a difference between required airflow and actual measured airflow is used to adjust the initial setting of the throttle. Thus, the throttle is used to control airflow and thereby engine torque. Such a system is described in U.S. Pat. No. 5,019,989. 
     It is also known to have a variable camshaft timing mechanism to adjust engine breathing and residual burnt gas fraction. In this system, camshaft timing is generally determined as a function engine speed and engine load. Position the camshaft as a function of speed and load is used to optimize steady state performance giving minimized emissions and fuel consumption. Such a system is disclosed in U.S. Pat. No. 4,856,465. 
     The inventors herein have recognized a disadvantage with the above approaches. In particular, a disadvantage with using throttle position is that the throttle cannot quickly change engine torque since the throttle controls flow entering an intake manifold. 
     Controlling flow entering the manifold cannot rapidly control cylinder charge due to manifold volume. For example, if the throttle is instantly closed, cylinder air charge does not instantly decrease to zero. The engine must pump down the air stored in the manifold, which takes a certain number of revolutions. Therefore, the cylinder air charge gradually decreases toward zero. 
     Also, the inventors herein have recognized that prior art approaches for controlling variable camshaft timing systems sacrifice dynamic performance. In other words, since the variable cam timing is scheduled versus engine speed and load to provide optimum steady state performance, transient operation is sub-optimal and many opportunities go overlooked. Further, these methods for providing variable cam timing steady state setpoint control are done without regard to manifold dynamics and cause degraded performance. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an engine control method for an engine having both an inlet control device and an outlet control device to provide optimum steady state performance as well as good dynamic response. 
     The above object is achieved and disadvantages of prior approaches overcome by a method for controlling an engine having at least one cylinder, the engine also having an intake manifold, an outlet control device for controlling flow from the intake manifold into the cylinder, and an inlet control device for controlling flow into the intake manifold, comprising: determining a desired outlet control device setpoint; and adjusting said inlet control device and said outlet control device based on said desired outlet control device setpoint without changing amount of flow into the cylinder. 
     By adjusting the inlet and outlet control device in opposite directions, it is possible to provide the desired steady state optimized performance, without suffering from degraded performance. In addition, disadvantages of the prior approaches are overcome when transitioning to the steady state conditions since the air amount is provided even when the outlet control device is being adjusted. 
     An advantage of the above aspect of the present invention is improved drive feel since changes in engine airflow are avoided even when adjusting the outlet control device to a desired value. 
     In another aspect of the present invention, the above object is achieved and disadvantages of prior approaches overcome by a method for controlling an engine having at least one cylinder, the engine also having an intake manifold, an outlet control device for controlling flow from the intake manifold into the cylinder, and an inlet control device for controlling flow into the intake manifold, comprising: determining a desired air amount entering the cylinder; determining a desired outlet control device setpoint; adjusting said inlet control device and said outlet control device in response to a respective inlet control device command and an outlet control device command; adjusting said inlet control device command and said outlet control device command to provide said desired air amount; and adjusting said inlet control device command and said outlet control device command to provide said desired outlet control device setpoint. 
     By using both the outlet control device to rapidly adjust flow into the cylinder faster than possible by using the inlet control device alone, it is possible achieve rapid airflow control. In other words, dynamic control response is greatly improved. Further, steady state optimization is still provided by gradually adjusting both the inlet and outlet control devices to provide the desired air amount as well as the steady state outlet control device setpoint. 
     An advantage of the above aspect of the invention is improved dynamic control while optimizing steady state performance. 
     Another advantage of the above aspect of the invention is improved airflow control. 
     Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The object and advantages of the invention claimed herein will be more readily understood by reading an example of an embodiment in which the invention is used to advantage with reference to the following drawings wherein: 
     FIGS. 1A and 1B are a block diagrams of an embodiment in which the invention is used to advantage; 
     FIG. 2A is a block diagram of an embodiment in which the invention is used to advantage; 
     FIGS. 2B-20 are graphs describing operation of the embodiment in FIG. 2A; 
     FIGS. 3-5,  8 - 10  are high level flowcharts which perform a portion of operation of the embodiment shown in FIGS. 1A,  1 B, and  2 A; 
     FIG. 6 is a graph showing how various factors are related to engine operation according to the present invention; 
     FIG. 7 is a graph depicting results using the present invention; 
     FIGS. 11A-11F are graphs describing operation of an embodiment of the present invention; and 
     FIGS. 12,  13 , and  14  are a block diagrams of an embodiment in which the invention is used to advantage. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Direct injection spark ignited internal combustion engine  10 , comprising a plurality of combustion chambers, is controlled by electronic engine controller  12 . Combustion chamber  30  of engine  10  is shown in FIG. 1A including combustion chamber walls  32  with piston  36  positioned therein and connected to crankshaft  40 . In this particular example piston  30  includes a recess or bowl (not shown) to help in forming stratified charges of air and fuel. Combustion chamber, or cylinder,  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valves  52   a  and  52   b  (not shown), and exhaust valves  54   a  and  54   b  (not shown). Fuel injector  66 A is shown directly coupled to combustion chamber  30  for delivering liquid fuel directly therein in proportion to the pulse width of signal fpw received from controller  12  via conventional electronic driver  68 . Fuel is delivered to fuel injector  66 A by a conventional high pressure fuel system (not shown) including a fuel tank, fuel pumps, and a fuel rail. 
     Intake manifold  44  is shown communicating with throttle body  58  via throttle plate  62 . In this particular example, throttle plate  62  is coupled to electric motor  94  so that the position of throttle plate  62  is controlled by controller  12  via electric motor  94 . This configuration is commonly referred to as electronic throttle control (ETC) which is also utilized during idle speed control. In an alternative embodiment (not shown), which is well known to those skilled in the art, a bypass air passageway is arranged in parallel with throttle plate  62  to control inducted airflow during idle speed control via a throttle control valve positioned within the air passageway. 
     Exhaust gas oxygen sensor  76  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . In this particular example, sensor  76  provides signal EGO to controller  12  which converts signal EGO into two-state signal EGOS. A high voltage state of signal EGOS indicates exhaust gases are rich of stoichiometry and a low voltage state of signal EGOS indicates exhaust gases are lean of stoichiometry. Signal EGOS is used to advantage during feedback air/fuel control in a conventional manner to maintain average air/fuel at stoichiometry during the stoichiometric homogeneous mode of operation. 
     Conventional distributorless ignition system  88  provides ignition spark to combustion chamber  30  via spark plug  92  in response to spark advance signal SA from controller  12 . 
     Controller  12  causes combustion chamber  30  to operate in either a homogeneous air/fuel mode or a stratified air/fuel mode by controlling injection timing. In the stratified mode, controller  12  activates fuel injector  66 A during the engine compression stroke so that fuel is sprayed directly into the bowl of piston  36 . Stratified air/fuel layers are thereby formed. The strata closest to the spark plug contains a stoichiometric mixture or a mixture slightly rich of stoichiometry, and subsequent strata contain progressively leaner mixtures. During the homogeneous mode, controller  12  activates fuel injector  66 A during the intake stroke so that a substantially homogeneous air/fuel mixture is formed when ignition power is supplied to spark plug  92  by ignition system  88 . Controller  12  controls the amount of fuel delivered by fuel injector  66 A so that the homogeneous air/fuel mixture in chamber  30  can be selected to be at stoichiometry, a value rich of stoichiometry, or a value lean of stoichiometry. The stratified air/fuel mixture will always be at a value lean of stoichiometry, the exact air/fuel being a function of the amount of fuel delivered to combustion chamber  30 . An additional split mode of operation wherein additional fuel is injected during the exhaust stroke while operating in the stratified mode is also possible. 
     Nitrogen oxide (NOx) absorbent or trap  72  is shown positioned downstream of catalytic converter  70 . NOx trap  72  absorbs NOx when engine  10  is operating lean of stoichiometry. The absorbed NOx is subsequently reacted with HC and catalyzed during a NOx purge cycle when controller  12  causes engine  10  to operate in either a rich homogeneous mode or a stoichiometric homogeneous mode. 
     Controller  12  is shown in FIG. 1A as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , an electronic storage medium for executable programs and calibration values shown as read only memory chip  106  in this particular example, random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: measurement of inducted mass air flow (MAF) from mass air flow sensor  100  coupled to throttle body  58 ; engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a profile ignition pickup signal (PIP) from Hall effect sensor  118  coupled to crankshaft  40 ; and throttle position TP from throttle position sensor  120 ; and absolute Manifold Pressure Signal MAP from sensor  122 . Engine speed signal RPM is generated by controller  12  from signal PIP in a conventional manner and manifold pressure signal MAP provides an indication of engine load. In a preferred aspect of the present invention, sensor  118 , which is also used as an engine speed sensor, produces a predetermined number of equally spaced pulses every revolution of the crankshaft. 
     In this particular example, temperature Tcat of catalytic converter  70  and temperature Ttrp of NOx trap  72  are inferred from engine operation as disclosed in U.S. Pat. No. 5,414,994 the specification of which is incorporated herein by reference. In an alternate embodiment, temperature Tcat is provided by temperature sensor  124  and temperature Ttrp is provided by temperature sensor  126 . 
     Continuing with FIG. 1A, camshaft  130  of engine  10  is shown communicating with rocker arms  132  and  134  for actuating intake valves  52   a ,  52   b  and exhaust valve  54   a .  54   b . Camshaft  130  is directly coupled to housing  136 . Housing  136  forms a toothed wheel having a plurality of teeth  138 . Housing  136  is hydraulically coupled to an inner shaft (not shown), which is in turn directly linked to camshaft  130  via a timing chain (not shown). Therefore, housing  136  and camshaft  130  rotate at a speed substantially equivalent to the inner camshaft. The inner camshaft rotates at a constant speed ratio to crankshaft  40 . However, by manipulation of the hydraulic coupling as will be described later herein, the relative position of camshaft  130  to crankshaft  40  can be varied by hydraulic pressures in advance chamber  142  and retard chamber  144 . By allowing high pressure hydraulic fluid to enter advance chamber  142 , the relative relationship between camshaft  130  and crankshaft  40  is advanced. Thus, intake valves  52   a ,  52   b  and exhaust valves  54   a ,  54   b  open and close at a time earlier than normal relative to crankshaft  40 . Similarly, by allowing high pressure hydraulic fluid to enter retard chamber  144 , the relative relationship between camshaft  130  and crankshaft  40  is retarded. Thus, intake valves  52   a ,  52   b  and exhaust valves  54   a ,  54   b  open and close at a time later than normal relative to crankshaft  40 . 
     Teeth  138 , being coupled to housing  136  and camshaft  130 , allow for measurement of relative cam position via cam timing sensor  150  providing signal VCT to controller  12 . Teeth  1 ,  2 ,  3 , and  4  are preferably used for measurement of cam timing and are equally spaced (for example, in a V-8 dual bank engine, spaced  90  degrees apart from one another) , while tooth  5  is preferably used for cylinder identification, as described later herein. In addition, Controller  12  sends control signals (LACT,RACT) to conventional solenoid valves (not shown) to control the flow of hydraulic fluid either into advance chamber  142 , retard chamber  144 , or neither. 
     Relative cam timing is measured using the method described in U.S. Pat. No. 5,548,995, which is incorporated herein by reference. In general terms, the time, or rotation angle between the rising edge of the PIP signal and receiving a signal from one of the plurality of teeth  138  on housing  136  gives a measure of the relative cam timing. For the particular example of a V-8 engine, with two cylinder banks and a five toothed wheel, a measure of cam timing for a particular bank is received four times per revolution, with the extra signal used for cylinder identification. 
     Referring now to FIG. 1B, a port fuel injection configuration is shown where fuel injector  66 B is coupled to intake manifold  44 , rather than directly cylinder  30 . 
     Referring now to FIG. 2A, a more general diagram shows manifold  44   a , with inlet flow, m_in, and outlet flow, m_out. Inlet flow, m_in, is governed by inlet control device  170 . Outlet flow, m_out, is governed by outlet flow device  171 . In a preferred embodiment, manifold  44   a  is an intake manifold of an engine, inlet control device  170  is a throttle, and outlet control device  171  is a variable cam timing mechanism. However, as one skilled in the art would recognize, there are many alternative embodiments of the present invention. For example, outlet control device could be a swirl control valve, a variable valve timing mechanism, a variable valve lift mechanism, or an electronically controlled intake valve used in camless engine technology. 
     Continuing with FIG. 2A, there are other variables that affect flow entering and exiting manifold  44   a . For example, pressures p1 and p2, along with inlet control device  170 , determine flow m_in. Similarly, pressures p2 and p3, along with outlet device  171  determine flow m_out. Therefore, flow storage in manifold  44   a , which dictates how fast pressure p2 can change, affects flow m_out. In an example where manifold  44   a  is an intake manifold of an engine operating at stoichiometry, flow m_out represents flow entering a cylinder and is directly proportional to engine torque. 
     FIGS. 2B-2K illustrate the effect of such interrelationships on system performance. In FIG. 2B, inlet control device  170  is rapidly changed at time t1. The resulting change in outlet flow (m out ) is shown in FIG.  2 C. The resulting change in inlet flow (m_in) is shown in FIG.  2 D. This example has outlet control device  171  fixed, and therefore represents conventional engine operation and prior art operation where throttle position is used to control outlet flow (m_out). In this example, a rapid change in inlet control device  170  does not produce an equally rapid change in exit flow m _out. 
     According to the present invention, in FIG. 2E, outlet control device  171  is rapidly changed at time t2. The resulting change in outlet flow (m_out) is shown in FIG.  2 F. The resulting change in inlet flow (m_in) is shown in FIG.  2 G. This example has inlet control device  170  fixed, and therefore represents adjustment of outlet device  170  only to control outlet flow (m_out). In this example, a rapid change in outlet control device  170  does produce an equally rapid change in exit flow m_out . However, the rapid change is not completely sustained. 
     According to the present invention, in FIG. 2H, inlet control device  170  is rapidly changed at time t3. Similarly, in FIG. 2I, outlet control device  171  is rapidly changed at time t3. The resulting change in outlet flow (m_out) is shown in FIG.  2 J. The resulting change in inlet flow (m_in) is shown in FIG.  2 K. This example varies both inlet control device  170  and outlet control device  170  concurrently. In this example, a rapid change in both inlet control device and  170  outlet control device  171  does produce an equally rapid change in exit flow m_out, where the rapid change is sustained. 
     According to the present invention, in FIG. 2L, inlet control device  170  is rapidly changed at time t4. Similarly, in FIG. 2M, outlet control device  171  is rapidly changed at time t4 to a greater extent than in FIG.  2 I. The resulting change in outlet flow (m_out) is shown in FIG.  2 N. The resulting change in inlet flow (m_in) is shown in FIG.  20 . This example varies both inlet control device  170  and outlet control device  170  concurrently. In this example, a rapid change in both inlet control device and  170  outlet control device  171  does produce an equally rapid change in exit flow m_out, where the rapid change is sustained and actually produces a certain amount of peak, or overshoot. This represents how the present invention can be used to not only rapidly produce an increase in outlet flow, but to also add an overshoot. Thus, a control system according to the present invention can therefore generate a airflow lead control. Such lead control is advantageous for engine idle speed control to counteract engine inertia, or for vehicle launch conditions, to give improved drive feel. 
     According to the present invention, by using an outlet control device it is possible to rapidly control flow exiting a manifold. Further, by controlling both an inlet and outlet control device it is possible to more accurately rapidly control flow exiting a manifold in various shapes. 
     In cases where engine  10  operates at a stoichiometric air/fuel ratio, then engine torque directly proportional to cylinder charge, which is in turn proportional to exit flow m_out and engine speed. Thus, according to the present invention, by controlling engine airflow to a desired value. 
     Engine Idle Speed Control 
     Referring now to FIG. 3, a routine is described for controlling engine speed using both throttle position and cam timing. In step  310 , an engine speed error (Nerr) is calculated based on a difference between the desired engine speed (Ndes) and an actual engine speed (Nact). Then, in step  320 , the desired change in cylinder charge is calculated from speed error using controller K 1 , where controller K 1  is represented in the Laplace domain as K 1 (s) as is known to those skilled in the art. The desired in cylinder charge (Δmcyl) is preferably calculated using a proportional controller. Therefore, in the preferred embodiment, controller K 1  represents a proportional controller. However, as those skilled in the art will recognize, various other control schemes can be used in place of proportional controller K 1 . For example, proportional integral derivative controllers, or sliding mode controllers, or any other controllers known to those skilled in the art, can be used. Next, in step  330 , an intermediate throttle position (Tpint) is calculated from speed error and controller K 3 . As described above, various controllers can be used for controller K 3 . In a preferred embodiment, controller K 3  is an integral controller. Next, in step  340 , a nominal cam timing error (VCTerr) is calculated based on a difference between a desired nominal cam timing (VCTdesnom) and an actual cam timing (VCTact). Desired nominal cam timing (VCTdesnom) can be determined based on operating conditions, for example, based on idle mode, or drive mode. Also, desired nominal cam timing (VCTdesnom) can be set as a function of desired engine torque, or any other steady state scheduling method known to those skilled in the art. Next, in step  350 , an intermediate timing (VCTint) is calculated from nominal cam timing error and controller K 2 . Controller K 2  can be any controller known to those skilled in the art. In the preferred embodiment, controller K 2  is a proportional integral controller. 
     Referring now to FIG. 4, a routine is described for calculating adjustments to cam timing and throttle position to rapidly change cylinder charge. First, in step  410 , manifold pressure (Pm) is estimated or measured using sensor  122 . In the preferred embodiment, manifold pressure (Pm) is estimated using methods known to those skilled in the art. For example, manifold pressure can be estimated using signal MAF from mass airflow sensor  100 , engine speed, and other signals known to those skilled in the art to effect manifold pressure. Next, in step  412 , the desired change in cylinder charge (Δncyl) is read from FIG.  3 . Next, in step  414 , a change in cam timing (ΔVCT) is determined to give the desired change in cylinder charge at manifold pressure (Pm) read in step  410 . Step  414  is performed using maps relating to cam timing, cylinder charge, and manifold pressure. The maps can be determined theoretically using engine models or measured using engine test data. Next, in step  416 , a change in throttle position (ΔTP) is determined to give the desired change in cylinder charge (Δncyl) at manifold pressure (Pm) determined in step  410 . Step  416  is similarly performed using characteristic maps relating parameters, throttle position, cylinder charge, and manifold pressure. The maps can be determined either using engine models or engine test data. 
     Regarding FIG. 5, the routine is described for calculating the desired cam timing and desired throttle position. First, in step  510 , a desired cylinder, desired cam timing (VCTdes) is determined based on the desired change in cam timing and intermediate cam timing. Next, in step  512 , the desired throttle position (TPdes) is determined based on intermediate throttle position and desired change in throttle position. 
     However, when a cam timing position is desired that is greater than a maximum possible cam timing, or when a minimum cam timing is less than a minimum possible cam timing, desired cam timing (VCTdes) is clipped to the maximum or minimum value. In other words adjustment of cam timing may not be able to provide the desired increase, or decrease in cylinder air charge. In this case, cam timing is clipped to the achievable limit value and throttle position is relied upon to provide control. 
     Steady State Constraints 
     As described above herein with particular reference to FIGS. 3-5, a control method for controlling engine airflow, or engine torque, and thereby engine speed was described. In addition, the method included a method for rapidly controlling cylinder charge using both an inlet and outlet control device, while also relatively slowly controlling the outlet control device to a nominal position. Both of these process are now further illustrated using both FIGS. 6 and 7. 
     Referring now to FIG. 6, a graph is shown with throttle position (TP) on the vertical axis and cam timing (VCT) on the horizontal axis. Dash dotted lines are shown for constant values of engine torque (Te), assuming stoichiometric conditions, while solid lines show constant value of manifold pressure. According to the present invention, the engine can quickly change operating points along the lines of constant pressure (thereby rapidly changing engine airflow and torque) since there are no manifold dynamics in this direction. However, the engine can change only relatively slowly along the dash dotted lines if air/fuel ratio is fixed (for example at stoichiometry). The dashed vertical line represents the nominal desired cam timing for the given operating conditions. For example, the nominal timing for idle conditions, or the nominal timing for the current desired engine torque. 
     In other words, manifold dynamics represent dynamics associated with changing manifold pressure and explain why flow entering the cylinder is not always equal to flow entering the manifold. Manifold pressure cannot instantly change due to manifold volume. As manifold volume increases, manifold dynamics become slower. Conversely, as manifold volume decreases, manifold dynamics become faster. Thus, manifold dynamics, or manifold delay, is a function of manifold volume. As described above, when moving along lines of constant pressure, manifold dynamics are essentially immaterial. Therefore, flow changes are not limited by manifold dynamics when inlet and outlet control devices are changed to affect flow in similar directions. By changing inlet and outlet control devices faster than manifold dynamics to increase along both the abscissa and ordinate of FIG. 6, cylinder flow changes faster than manifold dynamics. Stated another way, cylinder flow changes faster than it would if only the inlet control device changed infinitely fast. When inlet and outlet control devices are changed to affect flow in opposite directions, cylinder charge can be kept constant. In particular, both the inlet and outlet control devices are changed slower than manifold dynamics since manifold pressure is changed. This is particular useful when engine airflow, or engine torque, is to be kept relatively constant yet it is desired to place either the inlet control device or the outlet control device in a specified location. 
     Referring now to both FIGS. 6 and 7, an example of operation according to an aspect of the present invention is now described. First, the system is operating at point  1 . For example, the desired engine torque (Ted) is Te2, or this happens to be the engine torque to maintain a desired engine speed. Then, either the desired engine torque (Ted) changes to Te3, or a torque disturbance causes an engine speed to drop, thereby requiring an increase in engine torque to Te3 to maintain the desired engine speed. At this point (time t5), controller  12  causes both the throttle position and cam timing to change so that the engine system quickly moves to point  2 . Next, in order to maintain cam timing and the nominal cam timing, controller  12  causes both the throttle position and cam timing to move to point  3  at a rate slower than the manifold dynamics. 
     Thus, according to the present invention, throttle position and cam timing are caused to move in the following way. When it is desired to rapidly increase cylinder air charge irrespective of manifold volume: 1) throttle position moves in a way that causes an increase in throttle opening area, and 2) cam timing is adjusted in a way to increase the inducted cylinder air charge for a given manifold pressure moved. Similarly, when it is desired to rapidly decrease cylinder air charge irrespective of manifold volume: 1) throttle position moves in a way that causes a decrease in throttle opening area, and 2) cam timing is adjusted in a way to decrease the inducted cylinder air charge for a given manifold pressure. Thus, it is possible to rapidly change and maintain flow into the cylinder by this combined action. 
     However, when it is desired to maintain cylinder air charge and either increase throttle opening or cause cam timing to move so that less air charge is inducted for a given manifold pressure, or both, 1) throttle position moves in a way that causes an increase in throttle opening area, and 2) cam timing is adjusted in a way to decrease the inducted cylinder air charge for a given manifold pressure. Thus, cylinder charge can be kept constant by this opposing action. Alternatively, when it is desired to maintain cylinder air charge and either decrease throttle opening or cause cam timing to move so that more air charge is inducted for a given manifold pressure, or both, 1) throttle position moves in a way that causes a decrease in throttle opening area, and 2) cam timing is adjusted in a way to increase the inducted cylinder air charge for a given manifold pressure. Again, cylinder charge can be kept constant by this opposing action. 
     Such coordinated control is advantageous in that steady state optimization constraints on cam timing can be provided while still providing the ability to control cylinder air charge rapidly. 
     Engine Torque Control 
     Referring now to FIG. 8, a routine is described for controlling engine torque rather than engine speed as described in FIG.  3 . Engine torque control according to the present invention may be used for various reasons, including normal driving operating, traction control, and/or cruise control. In other words, FIG. 8, along with FIGS. 3-5 can be used to control engine torque, where steps  310 - 330  are replaced by FIG.  8 . Regarding FIG. 8, first, in step  810 , a desired engine torque (Ted) is determined. Those skilled in the art will recognize that desired engine torque (Ted) can be determined in various ways. For example, desired engine torque (Ted) can be determine from desired wheel torque and gear ratio, from pedal position and vehicle speed, from pedal position and engine speed, or any other method known to those skilled in the art. Then, in step  820 , desired cylinder charge (mcyld) is determined based on a function (h) of desired engine torque (Ted). Function (h) is based on a desired air/fuel ratio, such as stoichiometric conditions. 
     Continuing with FIG. 8, in step  830 , desired change in cylinder charge (Dmcyl) is determined based on the difference between desired cylinder charge (mcyld) and actual cylinder charge (mcyl). Then, in step  840 , intermediate throttle position (Tpint) is calculated from desired change in cylinder charge (Dmcyl) and controller K 3 . As described above, various controllers can be used for controller K 3 . In a preferred embodiment, controller K 3  is an integral controller. Then, in step  850 , a nominal cam timing (VCTdesnom) if determined based on function (g) and desired engine torque (Ted). Then, the routine continues to step  340  in FIG.  3 . 
     Alternative Embodiment for Cylinder Charge, Torque, and Engine Speed Control 
     An alternative embodiment is now described that can be used to control either cylinder air charge, Engine Torque at a given air/fuel ratio, or engine speed. Referring now to FIG. 9, in step  910 , a determination is made as to whether the engine is currently in an idle condition. Those skilled in the art will recognize various methods for determining idle conditions such as accelerator pedal position, engine speed, and various other factors. When the answer to step  910  is YES, the routine continues to step  912 . In step  912 , the desired cylinder charge (mcyldes) based on an engine speed error (Nerr). The desired cylinder charge is calculated using function L1, which can represent any function such as, for example, engine speed error multiplied by a constant gain, which is the preferred embodiment. Otherwise, when the answer to step  910  is NO, the routine continues to step  914 . In step  914 , the desired cylinder charge is calculated based on either a driver command or operating conditions using function (L2). Those skilled in the art will recognize various methods for calculating a desired cylinder charge from a driver command such as, for example, to provide a desired engine torque, a desired wheel torque, an engine output, or provide any other condition requested by the driver. Those skilled in the art will also recognize various operating conditions that can affect a desired cylinder charge such as, for example, engine starting conditions, cold conditions, or cranking conditions. 
     Continuing with FIG. 9, the routine continues from either step  912  or step  914  to step  916 . In step  916 , a cylinder charge error (mcylerr) is calculated based on desired cylinder charge and actual cylinder charge (mcylact). Next, in step  918 , cam timing nominal error is calculated. Next, in step  920 , intermediate cam timing is calculated from cam timing nominal error and controller H 1 . In a preferred embodiment, controller H 1  is an integral controller known to those skilled in the art. Also, in a preferred embodiment, the gains of controller H 1  are determined so that the cam timing is adjusted slower than manifold dynamics. In other words, the gains of controller H 1  are determined based on manifold volume, and engine speed. However, controller H 1  can be any controller known to those skilled in the art such as, for example, a PID controller, a PI controller, or a P controller. Next, in step  930 , intermediate throttle position is calculated from cylinder charge error and controller H 2 . In a preferred embodiment, controller H 2  is an integral controller; however, as those skilled in the art will recognize, various controllers can be used. Next, in step  940 , a difference in cam timing is calculated from cylinder charge error and controller H 3 . In a preferred embodiment, controller H 3  is a lead controller or a high pass filter type controller. Next, the routine continues to step  950 , where a difference in throttle position is calculated from the difference in cam timing using controller H 4 . In a preferred embodiment, controller H 4  is simply a constant gain. Next, the routine continues to FIG.  5 . 
     Air/Fuel Constraints in Lean Conditions 
     Referring now to FIG. 10, a routine for restricting air/fuel ratio to specific regions is described. In step  1010 , a determination is made as to whether the engine is operating in stratified conditions. When the answer to step  1010  is YES, the routine continues to step  1012 . In step  1012 , the required fuel injection amount (fi) is calculated based on driver commands or operating conditions. Again, those skilled in the art will recognize various methods for determining a fuel injection amount based on driver command or engine operating conditions. Next, the routine continues to step  1014 , where a restricted air range is calculated. The restricted air range is calculated using a maximum and minimum allowable air/fuel ratio, the fuel injection amount, and a band parameter (B). The band parameter is used to allow room for calculation inaccuracies. Next, the routine continues to step  1016 , where a determination is made as to whether actual cylinder charge is between the maximum and minimum allowable cylinder charges (mcyl1, mcyl2). When the answer to step  1016  is YES, a determination is then made in step  1018  as to whether it is possible, given the current operating conditions, to produce air charge (mcyl1). This determination can be made based on factors such as, for example, engine speed and atmospheric pressure. In particular, as atmospheric pressure increases, engine  10  is able to pump a greater maximum air amount. Therefore, in a preferred embodiment, limit mcyl1 is selected when atmospheric pressure is greater than a calibrated value, and mcyl2 is selected otherwise. In other words, in step  1018 , a determination is made as to whether the engine can physically produce upper air charge (mcyl1). When the answer to step  1018  is NO, the routine sets the desired cylinder charge (mcyldes) equal to lower air charge (mcyl2) in step  1020 . Otherwise, the desired cylinder charge is set to upper cylinder charge (mcyl1). 
     Referring now to FIG. 11, the present invention is compared to prior art approaches in controlling engine torque or keeping an air/fuel ratio outside of a restricted air/fuel ratio range. The FIGS. 11 a  through  11   f  show a comparison of the present invention as represented by solid lines, and prior approaches as represented by dashed lines. In prior approaches, as shown in FIG. 11 a , fuel injection amount increases at time T6 in response to a change in desired engine torque shown in FIG. 11 d . To maintain the air/fuel ratio at a desired point, as shown in FIG. 11 e , increased airflow is required. To provide increased airflow, prior approaches change throttle position, as shown in FIG. 11 c , at time T6. However, because of airflow dynamics due to the manifold volume, air charge does not increase fast enough, as shown in FIG. 11 f . This results in a temporary excursion in the air/fuel ratio into the restricted region as shown in FIG. 11 e . Thus, the prior approaches cannot keep the air/fuel ratio completely out of the restricted region. 
     According to the present invention, and as described in FIG. 10, at time T6, cam timing, as shown in FIG. 11 b , is also increased. This allows the air/fuel ratio, as shown in FIG. 11 e , to refrain from entering the restricted air/fuel range. This is possible since the airflow was quickly changed using both cam timing and throttle position as shown in FIG. 11 f  by the solid line. 
     Vehicle Launch Improvement 
     Vehicle driveability is improved according to the present invention by providing engine torque increases at a rate faster than available by prior art methods. Regarding FIG. 12, engine  10  is coupled to automatic transmission (AT)  1200  via torque converter (TC)  1210 . Automatic transmission (AT)  1200  is shown coupled to drive shaft  1202 , which in turn is coupled to final drive unit (FD)  1204 . Final drive unit (FD) is coupled wheel  1208  via second drive shaft  1208 . In this configuration, engine  10  can be somewhat downsized and still produce acceptable drive feel by controlling engine torque or airflow using both throttle position and cam timing as describe above herein. 
     Regarding FIG. 13, torque converter  1210  is removed. Thus, even without downsizing engine  10 , using prior approaches driveability is reduced. In other words, vehicle launch is normally assisting from torque multiplication provided by torque converter  1210 . Without torque converter  1210 , vehicle launch feel is degraded. To compensate for the lack of torque converter  1210 , engine  10  is controlled according to the present invention using both throttle position and cam timing to rapidly increase engine torque or airflow, thereby improving drive feel and allowing elimination of torque converter  1210 . 
     In a preferred embodiment, during vehicle launch at low vehicle speed and low engine speed, both inlet control device and outlet control device  170  and  171  are coordinated to rapidly control engine cylinder charge, thereby improving drive feel. Further to enable such operating, nominal cam timing (VCTdesnom) is set to a value where a large potential increase in cylinder air charge can be achieved when the transmission is in drive and vehicle speed is below a predetermine vehicle speed indicating potential for vehicle launch. 
     Turbo Lag Compensation 
     Referring now to FIG. 14, a configuration is shown where engine  10  is coupled to a compression device  1400 . In a preferred embodiment, compression device  1400  is a turbocharger. However, compression device  1400  can be any compression device such as, for example, a supercharger. Engine  10  is shown coupled to intake manifold  44   b  and exhaust manifold  48   b . Also shown is outlet control device  171  coupled between intake manifold  44   b  and engine  10 . Inlet control device  170  is also shown coupled between intake manifold  44   b  and compression device  1400 . Compression device  1400  contains compressor  1410 . 
     According to the present invention, it is now possible to compensate for delays related to turbo lag. In a preferred embodiment, during vehicle launch at low vehicle speed and low engine speed, both inlet control device and outlet control device  170  and  171  are coordinated to rapidly control engine cylinder charge, thereby compensating for the delayed pressure buildup from compression device  1400 . However, such an approach can be used throughout various driving conditions, such as, for example, during highway cruising operation. 
     While the invention has been shown and described in its preferred embodiments, it will be clear to those skilled in the arts to which it pertains that many changes and modifications may be made thereto without departing from the scope of the invention. For example, as described above herein, any device that affects flow exiting intake manifold  44  and entering cylinder  30  can be used as an outlet control device. For example, a swirl control valve, a charge motion control valve, an intake manifold runner control valve, or an electronically controlled intake valve can be used according to the present invention to rapidly change cylinder fresh charge. Further, any device that affects flow entering intake manifold  44  can be used in place of intake control device. For example, an EGR valve, a purge control valve, or an intake air bypass valve can be used in conjunction with the outlet control device so rapidly change cylinder fresh charge. 
     Also, the invention can be applied to any situation where engine cylinder charge needs to be controlled faster than manifold dynamics would normally allow. Accordingly, it is intended that the invention be limited only by the following claims.