Abstract:
Methods and apparatus are provided for ensuring that a throttle increase accompanying a change in the number of active cylinders of an internal combustion engine will not occur too long with more than a selected fraction of all the cylinders activated, so as to not startle a driver. The apparatus comprises an electronic controller that generates the throttle increase if less than all the cylinders are requested to be activated. A determination is made as to whether the number of cylinders being fueled is equal to or less than the selected fraction. A timer is started if the number of cylinders being fueled is greater than the selected fraction. The throttle increase is turned off if the amount of time measured by the timer exceeds a threshold before the number of cylinders being fueled becomes either less than or equal to the selected fraction.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to electronic throttle security, and more particularly relates to such security for internal combustion engines having electronic throttle control systems for enabling cylinder activation and deactivation.  
         BACKGROUND OF THE INVENTION  
         [0002]    Those skilled in the art of internal combustion engine design understand that control of internal combustion engines preferably includes engine cylinder activation and deactivation or displacement on demand to improve fuel economy. This engine control strategy generally involves reducing the number of active engine cylinders as a reduced amount of power is requested from the engine, and the valves of deactivated cylinders are generally configured to improve fuel efficiency. For example, the valves of the deactivated cylinders are at least substantially closed to reduce pumping losses. However, in this example, after some of the cylinders are at least substantially closed to reduce pumping losses, the remaining active cylinders are generally configured to receive a throttle increase to maintain the same level of output torque from the engine. Furthermore, when the power requirements increase a sufficient amount, the deactivated cylinders are reactivated and the throttle level is altered so that the engine continues to deliver the desired amount of power.  
           [0003]    It is desirable for the adjustments of the control strategy to occur with minimal, and preferably no awareness of the engine operator. This statement is particularly true in the case of an automobile engine operating under the control of an operator that is providing a substantially constant accelerator pedal position. In this situation, the engine throttle is preferably adjusted a predetermined amount in response to cylinder deactivation and preferably adjusted a predetermined amount in response to cylinder reactivation. While these control strategies for internal combustion engines provide the proper engine power and improve fuel efficiency, other improvements are continually sought.  
           [0004]    In view of the foregoing, it should be appreciated that there is a need to provide methods and apparatus for providing security for electronically controlled cylinder activation and deactivation. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention, brief summary of the invention, abstract, and appended claims, taken in conjunction with the accompanying drawings and this background of the invention of the invention.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In accordance with the teachings of the present invention security methods and apparatus are provided for ensuring that a throttle increase accompanying a decrease in the number of active cylinders of an internal combustion engine will be limited to a predetermined threshold period with more than a selected fraction of all the cylinders of the engine being activated. The apparatus comprises an electronic controller that generates the throttle increase if less than all the cylinders are requested to be activated. A query is made to determine if the number of cylinders being fueled is equal to or less than the selected fraction. A timer is started if the number of cylinders being fueled is greater than the selected fraction of all the cylinders. The throttle increase is turned off if the amount of time measured by the timer exceeds the predetermined threshold before the number of cylinders being fueled becomes either less than or equal to the selected fraction.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like reference numbers denote like elements, and  
         [0007]    [0007]FIG. 1 is a schematic diagram of a vehicle drive train having a security system for cylinder deactivation and reactivation;  
         [0008]    [0008]FIG. 2 is a flow chart of a software program for use with the system of FIG. 1 in accordance with an embodiment of the invention;  
         [0009]    [0009]FIG. 3 is a timing diagram indicating a normal mode of operation of the security system of FIGS. 1 and 2; and  
         [0010]    [0010]FIG. 4 is a timing diagram indicating a fault mode of operation of the security system of FIGS. 1 and 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description.  
         [0012]    Referring to FIG. 1, a vehicle drive train  10  is generally illustrated that includes an internal combustion engine  12  coupled to transmission  14 , which in turn is coupled by drive shaft  16  and differential  18  to a pair of driven wheels  20   a - 20   b . The position of a throttle  22  disposed within a manifold  21  of engine  12  is controlled to enable engine  12  to produce the desired output torque for driving wheels  20   a - 20   b . In the illustrated embodiment, throttle  22  is mechanically de-coupled from driver accelerator pedal  23  and instead is positioned by electric motor  24  under the direction of powertrain control module (PCM)  26  that also controls the operation of engine  12  and transmission  14 . PCM  26  includes electronic throttle control (ETC)  27  for operating throttle  22 . ETC  27  provides signals to motor  24 . PCM  26  is microprocessor based and includes various logic units and memories such as ROM and RAM.  
         [0013]    PCM  26  operates in response to a number of inputs. These inputs include an engine speed signal (Ne) on line  28 , a vehicle speed signal (Nv) on line  30 , an accessory loading signal (ACC) on line  34 , a Throttle Position Feedback signal (TPS) on line  36 , a Manifold Absolute Pressure (MAP) signal on line  38  and Pedal Position Sensor signal (PPS) on line  39 . These inputs are provided by conventional sensors such as illustrated shaft speed sensors  40 ,  42  and accelerator pedal position sensor  44 . In general, ETC module  27  activates motor  24  to position throttle  22  in response to the positioning of accelerator pedal  23 , but various other functions such as idle speed control, engine governor control, cruise control and torque reduction are also provided for providing the ETC function in a known manner. Additionally, PCM  26  controls conventional spark control device  50  and other fuel control device  52 , which are coupled to engine  12 .  
         [0014]    More specifically, internal combustion engine  12  utilizes the PCM/ETC functions provided by system  26  to adjust the fuel, the spark and the amount of airflow through intake manifold  21  in response to sensor monitored operator variations of accelerator pedal  23 . Operator throttle adjustment is typically accomplished using an accelerator-input mechanism, such as a foot pedal  23 , joystick, hand pedal, lever or track ball. The input mechanism is mechanically coupled to sensors in block  44  that in turn provide PPS control signals having magnitudes indicative of the accelerator position to the ETC module  27 . In response, PCM  26  generates additional electrical control signals for enabling the hardware of the vehicle engine to provide the desired operating level requested by the driver as indicated by the accelerator-input mechanism  23 . Such ETC systems provide numerous advantages such as reduced costs, improved simplicity, engine noise reduction, throttle command conditioning for emissions reduction, and/or torque based control functions.  
         [0015]    DEAC system  54  provides cylinder activation, deactivation and reactivation to improve a number of operating parameters, such as fuel economy. This is generally accomplished by shutting off or deactivating a predetermined number of the cylinders of engine  12  when the power requirements of the engine are at or below a predetermined lower power level (i.e., the power level is too low) and reactivating the cylinders when the power requirements sufficiently are at or exceed a predetermined upper power level. As can be appreciated by those of ordinary skill in the art, the predetermined power levels can be determined according to any number of techniques. Ideally, the operator of engine  12  or driver of a vehicle including engine  12  is not aware of these transitions. Engine  12  has a predetermined number of cylinders and a selected fraction of this number is operated when deactivation reaches a steady state. For instance, if engine  12  has eight cylinders, which is a well known V8 configuration, and the fraction is one half, then engine  12  could be operated on all eight cylinders when the need for power is high (i.e., the power level is at or exceeds the predetermined upper power level). In addition, the engine  12  could transition to eventually operate on only four cylinders when the need for power is sufficiently low (i.e., at or below the predetermined low level). Engine  12  could also have twelve cylinders. In this case, engine  12  could run on eight, six or four cylinders depending on the power demand requirements, for instance. In any event, the valves of any deactivated cylinders are at least partially closed and preferably completely closed.  
         [0016]    DEAC system  54  is coupled to monitor engine  12  and transmission  14  through respective lines  56  and  57  to enable DEAC  54  to provide control signals to PCM  26  through line  58 . When some of the cylinders of engine  12  are shut off, the other active cylinders of the engine are run in response to a higher opening of throttle  22  referred to herein as THROTTLE OFFSET. This action maintains substantially the same level of output torque being delivered through transmission  14  and differential  18  to wheels  20   a  and  20   b . It is desirable for the larger opening of throttle  22  to occur with minimal and preferably, no action or even awareness by the operator of the engine of the cylinder deactivation event. In addition, it is desirable for the operator to have minimal awareness of cylinder reactivations. To ensure a seamless transition, throttle  22  should be opened at a time slightly before the cylinders are in a deactivated mode. The system preferably avoids the opening of throttle  22  to provide the THROTTLE OFFSET without verification that fuel is shut off to at least some of the cylinders.  
         [0017]    Engine  12  could have any number of cylinders greater than one. For purposes of illustration, engine  12  is assumed the aforementioned V8, which is operated on four cylinders when conditions are correct for cylinder deactivation. DEAC  54  provides the THROTTLE OFFSET during the time the cylinder deactivation logic is requesting the throttle to be opened, but the THROTTLE OFFSET is allowed to continue if half or less of the fuel injectors are disabled before a predetermined threshold period (or time limit threshold) is met or exceeded.  
         [0018]    Referring to FIG. 2, a method  60  is illustrated that is preferably conducted by the PCM  26 . However, the method can be conducted by other electronic controllers, individually or in combination. The timing diagrams  62  and  64  respectively of FIG. 3 and FIG. 4 illustrate the operation of apparatus  10  of FIG. 1 and method  60  of FIG. 2 Abscissa axis  66  of FIG. 3 is the time between times T0 and T18. Time, T0 on axis  66  corresponds to BEGIN step  68  of method  60 .  
         [0019]    DEAC MODE REQUEST graph  70  of FIG. 3 is initially assumed to be requesting that all eight cylinders receive fuel as indicated by level  72 . Accordingly, eight cylinders are being fueled between times T0 and T1 as indicated by level  74  of graph  76  which indicates the NUMBER OF CYLINDERS BEING FUELED. Decision block or method step  78  of FIG. 2 determines if DEAC  54  is requesting activation of less than all the cylinders. Since the answer is NO between T0 and T1, the TIMER is RESET as indicated by block  85 . Accordingly, OFFSET FUEL ON FLAG  86  is FALSE as indicated by block  86  of FIG. 2 and level  88  of OFFSET FUEL ON FLAG waveform  90  of FIG. 3. OR block  92  of FIG. 2 responds to FALSE level  88  to ensure that the THROTTLE OFFSET is OFF per block  94  to provide level  96  of THROTTLE OFFSET waveform  98  of FIG. 3. Hence, engine  12  does not receive the THROTTLE OFFSET fuel increase between T0 and T1.  
         [0020]    Referring to FIG. 1, DEAC  54  receives input on line  57  identifying which gear is being employed in transmission  14 . Deactivation of any of the cylinders is not desirable if transmission  14  is in a predetermined lower gear or a predetermined set of lower gears (i.e., the gear or gears is too low), such as either the first or the second gear, for instance. If the gear is too low for cylinder deactivation to be desirable, then the NO decision from block  100  of FIG. 2 causes block  102  to provide a GEAR STATE ENABLE FLAG having a FALSE indication to OR block  92 . This causes the THROTTLE OFFSET request to be OFF as indicated by block  94 . Alternatively, if the gear is a gear other than the predetermined lower gear or gears, then the YES from decision block  100  causes the GEAR STATE ENABLE FLAG to be TRUE as indicated by block  104  of FIG. 2. For purposes of the following discussion herein, it is assumed that the gear level is correct for deactivation resulting in the TRUE GEAR STATE ENABLE FLAG of block  104 .  
         [0021]    At time T1 of FIG. 3, DEAC  54  requests deactivation of half of the predetermined maximum number of cylinders as indicated by level  105  of waveform  70 . The number of cylinders being fueled then transitions from eight to seven as indicated by level  106  of waveform  76  of FIG. 3. Accordingly, decision step  78  of FIG. 2 now provides a YES. As a result, the OFFSET FUEL ON FLAG is TRUE as indicated by block  108  and level  109  of waveform  90 . AND block  112  responds to the TRUE from block  108  and the TRUE from block  104  to provide the THROTTLE OFFSET ON SIGNAL of block  113  as indicated by level  114  of waveform  98  of FIG. 3. Level  114  results in an increased amount of fuel being supplied to the active cylinders.  
         [0022]    THROTTLE OFFSET ON signal  114  of block  113  of FIG. 2 initiates the decision step of block  115  which determines if the number of fueled cylinders is less than or equal to one half the number of all the cylinders, for instance. Since seven, six and five as indicated by respective levels  106 ,  116  and  117  of waveform  76  of FIG. 3 are all greater than four the answer to decision  115  is NO between times T1 and T4. Accordingly, the START TIMER signal of block  118  causes OFFSET FUEL OFF TIMER waveform  119  to ramp from reset level  120  to begin measuring time from T1 as indicated by ramp  121  of waveform  119 .  
         [0023]    At time T4, the number of cylinders being fueled equals four as indicated by level  125  of waveform  76 . Accordingly, the decision from block  115  becomes YES which RESETS the TIMER as indicated by block  126  of FIG. 2 to cause transition  128  of waveform  119  back to reset level  120 . The amount of time from T1 to T4 is less than a predetermined or selected THRESHOLD amount of time (i.e., the predetermined threshold period), T5. Hence, the answer of decision block  130  is NO which allows the OFFSET FUEL ON FLAG to continue to be TRUE as indicated by block  108 . The above sequence of events represents the “normal case” for the operation of the DEAC function. The THRESHOLD time, T5 may be calibrated or changed in response to monitored parameters.  
         [0024]    At time T6 of FIG. 3, DEAC MODE signal  70  changes to and remains at level  130  to facilitate operation in the steady state four cylinder active condition until time T10 when signal  70  moves to level  132  to indicate a request for reactivation of an additional cylinder. Since activation of all cylinders is not being requested at T10, decision block  78  provides a YES so that the OFFSET FUEL ON FLAG continues to be TRUE resulting in THROTTLE OFFSET signal  98  remaining at level  114 . Five cylinders are being fueled between T10 and T11 as indicated by level  134  of waveform  76 . Accordingly, at T10 decision block  115  provides a NO which again provides the START TIMER signal of block  118  and waveform  119  begins ramp  136 . Six, seven and eight cylinders are respectively reactivated at T11, T12 and T13 as indicated by respective levels  138 ,  140  and  142  of waveform  76 .  
         [0025]    At T14, the system returns to the reactivated eight-cylinder mode as indicated by level  143  of DEAC signal  70 . As a result, decision block  78  becomes NO which causes the TIMER to RESET to level  120  of waveform  119  per block  85 . The NO from block  78  also initiates the FALSE OFFSET FUEL ON FLAG of block  86  which causes waveform  90  to return to level  88 . Accordingly, the THROTTLE OFFSET OFF signal of block  94  causes signal the THROTTLE OFFSET  98  to return to level  96 . Such reactivation occurs is another “normal case” of operation for the DEAC function.  
         [0026]    [0026]FIG. 4 illustrates a “fault case” for the DEAC function which employs the previously mentioned security method and apparatus. Between T0 and T3, the waveforms of FIG. 4 are the same as in FIG. 3 indicating the same method as previously described for FIG. 2. However, at T3 waveform  76  representing the number of cylinders being fueled undesirably remains at six cylinders as indicated by level  116  rather than dropping to five cylinders. Accordingly, system  10  is now operating in the abnormal or fault mode. Since the NUMBER OF FUELED CYLINDERS does not become equal to or less than four, TIMER RESET  126  of FIG. 2 is not enabled by decision block  115 . Thus, OFFSET FUEL OFF TIMER waveform  119  portion  150  of FIG. 4 continues to ramp through the time THRESHOLD T5. As a result, decision block  130  provides a YES which enables the FALSE FUEL ON ENABLE FLAG of block  86  which causes signal  90  to drop to level  88  at T5. As a result, the THROTTLE OFFSET  98  returns to level  96  at T5 to remove the extra fuel being applied to the activated cylinders of engine  112 .  
         [0027]    Furthermore, referring again to FIG. 3, if only seven cylinders are reactivated during the reactivation sequence, then ramp  136  of waveform  119  would continue on to form dashed portion  152  which would cross time THRESHOLD T15. This event also would result in a YES from decision block  130  causing the OFFSET FUEL ON FLAG to become FALSE and the THROTTLE OFFSET also becoming FALSE. Hence, the extra fuel would again be terminated.  
         [0028]    The previously described embodiments of the invention therefore provide a security apparatus and method which ensure that the higher THROTTLE OFFSET fuel level  114  will not be used for a long enough time with more than a selected fraction of the predetermined maximum number of cylinders. For instance, the invention provides security to ensure that THROTTLE OFFSET  98  is not allowed to remain on at level  114  long enough with more than half of the cylinders enabled.  
         [0029]    While the exemplary embodiments have been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that these exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the spirit and scope of the invention as set forth in the appended claims.