Patent Publication Number: US-2004055568-A1

Title: Method and system for minimizing torque intervention of an electronic throttle controlled engine

Description:
TECHNICAL FIELD  
       [0001] This invention relates to electronic throttle controlled engines and more particularly to systems and method for intervening in such throttle control in the event of an apparent fault in estimates of engine operating parameters used to control such throttle.  
       BACKGROUND AND SUMMARY OF INVENTION  
       [0002] As is known in the art, a torque monitor function is used for engines equipped with electronic throttle control. This function achieves a high level of safety by checking the desired engine torque, (i.e., driver demanded torque from, for example, a sensing of driver accelerator pedal position) with two independent measures of torque, for example, a throttle based (e.g., throttle position) estimate and an air-meter (i.e., Mass Air Flow, MAF) based method. If the air-meter based method calculates a torque that exceeds the driver demanded torque, the torque monitor function will intervene by one of several methods including shutting off fuel to cylinders.  
       [0003] The inventors have recognized that if a real failure has occurred, say due to a stuck open throttle, then this intervention is appropriate. However, if the intervention was due to other factors, like an air-meter which reads too high due to dirt, or a whole host of other reasons, then the intervention is obnoxious to the driver, and shutting off fuel to cylinders is probably not an appropriate control reaction to measurement errors. In such case, intervention should be prevented.  
       [0004] The general philosophy of intervention prevention is that if the vehicle behavior can be modified in a subtle manner not likely to be noticed by the driver in order to prevent monitor intervention (e.g., shutting off fuel to cylinders), then such modification is a more preferable choice. Even if the driver notices the control changes as a result of intervention modification by vehicle behavior modification in such a subtle manner, such intervention modification may still be a better control choice than an intervention which shuts off fuel to cylinders. So in the end intervention should be limited to real failures, as opposed to momentary misalignment of various calculations due to a number of inconsequential factors.  
       [0005] One known torque monitoring algorithm compares torque demand (i.e., driver-demanded torque computed primarily from acceleration pedal position), with two independent torque estimates (e.g., one estimated from throttle position and one estimated from mass airflow (MAF) to the intake manifold). If the maximum of the two actual torque estimates exceeds the driver-demanded torque, the monitoring algorithm logic intervenes in engine torque production (e.g., shuts off fuel to cylinders) and lights a service (wrench) light.  
       [0006] In accordance with the invention, in order to prevent, or minimize, unnecessary intervention, an adjustment is made to the driver-demanded torque. For example, driver-demanded torque-is reduced by a factor based on the ratio of the two actual torque estimates thereby minimizing the cases where the monitor will intervene by, for example, shutting off fuel to cylinders.  
       [0007] In one embodiment, a method is provided for controlling intervention of an internal combustion engine having an electronically controlled throttle. The method includes comparing at least two independent estimates of torque with a commanded torque demand on the engine. If the maximum of the two independent estimates of torque exceeds the commanded torque demand, torque demand on the engine is potentially intervened. If the load as estimated from an airmeter is greater than the load estimated from the throttle, then the demand is reduced to prevent said potential intervention.  
       [0008] In one embodiment, if such comparison indicates the maximum of the two torque estimates exceeds the torque demand, potentially intervening in engine torque production, and, in order to prevent, or minimize, unnecessary engine torque production intervention, reducing a torque demand signal to the throttle by a factor, such factor being a function of airflow meter demand divided by throttle demand.  
       [0009] In accordance with another feature of the invention, a method for controlling intervention of an internal combustion engine is provided. The engine includes an electronically controlled throttle disposed in the airflow to an intake manifold of the engine and an airflow meter disposed in such airflow to the intake manifold of the engine. The engine has a torque demand input to the engine through an operator pedal. The torque demand increases as such pedal position increases and decreases as such pedal position decreases, such torque demand producing a signal fed to the electronically controlled throttle. The method includes comparing, measured throttle load with measured airflow load. If the measured airflow load is greater than the measured throttle load, calculating a factor tr_intprv_ml, where tr_intprv_ml is equal to F1′+(1−F1′) P, where: F1′ is a function of measured throttle load divided by measured airflow load and P=0 if pedal position is relatively low, 1 if pedal position exceed a predetermined relatively high pedal position, or a proportional intermediate value between 0 and 1 if the pedal position is between the relatively low and relatively high pedal positions and applying such calculated factor to the signal fed to the electronically controlled throttle. If the measured airflow load is less than the measured throttle load having the factor tr_intprv_ml equal to a value of 1.  
       [0010] With such method, if the air-meter reads higher than the throttle based estimate of air and torque, then the method simply closes the throttle until the air-meter is satisfied. It is judged that most drivers will not notice that they are getting slightly less torque at a given pedal position, and even if they notice will prefer this control action to an intervention. Further, if the driver still wishes higher torque than produced by the driver-demanded torque which has been reduced by the applied factor, the driver will merely demand more torque by increase accelerator pedal position. More particularly, at high pedal angles (i.e., the driver depresses the accelerator pedal to, or near, its maximum thereby demanding maximum torque), the method disables intervention completely. That is, if the driver is demanding close to maximum torque, then it doesn&#39;t make sense to monitor power greater than demand; the driver wants all the torque available. This override of intervention prevention is achieved in a smooth and continuous manner with the logic by blending the effect out over a range of pedal angle. The same blending is done to disable the monitor itself, using the same ramp versus pedal. However, if the throttle is stuck this method will not be able to prevent the intervention, which is appropriate.  
       [0011] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0012]FIG. 1 is a block diagram of a vehicle illustrating various components related to the present invention;  
     [0013]FIG. 2 is a block diagram of an engine system in accordance with the invention; and  
     [0014]FIG. 3 is a flow diagram of a process used by the engine system of FIG. 2 in accordance with the invention. 
    
    
     [0015] Like reference symbols in the various drawings indicate like elements.  
     DETAILED DESCRIPTION  
     [0016] Referring to FIG. 1, internal combustion engine  10 , further described herein with particular reference to FIG. 2, is shown coupled to torque converter  11  via crankshaft  13 . Torque converter  11  is also coupled to transmission  15  via turbine shaft  17 . Torque converter  11  has a bypass clutch (not shown) which can be engaged, disengaged, or partially engaged. When the clutch is either disengaged or partially engaged, the torque converter is said to be in an unlocked state. Turbine shaft  17  is also known as transmission input shaft. Transmission  15  comprises an electronically controlled transmission with a plurality of selectable discrete gear ratios. Transmission  15  also comprises various other gears, such as, for example, a final drive ratio (not shown).  
     [0017] Transmission  15  is also coupled to tire  19  via axle  21 . Tire  19  interfaces the vehicle (not shown) to the road  23 .  
     [0018] Internal combustion engine  10  comprising a plurality of cylinders, one cylinder of which is shown in FIG. 2, is controlled by electronic engine controller  12 . Engine  10  includes combustion chamber  30  and cylinder walls  32  with piston  36  positioned therein and connected to crankshaft  1   3 . Combustion chamber  30  communicates with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Exhaust gas oxygen sensor  1   6  is coupled to exhaust manifold  48  of engine  10  upstream of catalytic converter  20 .  
     [0019] Intake manifold  44  communicates with throttle body  64  via throttle plate  66 . Throttle plate  66  is controlled by electric motor  67 , which receives a signal from ETC driver  69 . ETC driver  69  receives control signal (DC) from controller  12 . Intake manifold  44  is also shown having fuel injector  68  coupled thereto for delivering fuel in proportion to the pulse width of signal (fpw) from controller  12 . Fuel is delivered to fuel injector  68  by a conventional fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown).  
     [0020] Engine  10  further includes conventional distributorless ignition system  88  to provide ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . In the embodiment described herein, controller  12  is a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , electronic memory chip  106 , which is an electronically programmable memory in this particular example, random access memory  108 , and a conventional data bus.  
     [0021] Controller  12  receives various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: measurements of inducted mass air flow (MAF) from mass air flow sensor  110  coupled to throttle body  64 ; engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling jacket  114 ; a measurement of throttle position (TP) from throttle position sensor  117  coupled to throttle plate  66 ; a measurement of transmission shaft torque, or engine shaft torque from torque sensor  121 , a measurement of turbine speed (Wt) from turbine speed sensor  119 , where turbine speed measures the speed of shaft  17 , and a profile ignition pickup signal (PIP) from Hall effect sensor  118  coupled to crankshaft  13  indicating an engine speed (N). Alternatively, turbine speed may be determined from vehicle speed and gear ratio.  
     [0022] Continuing with FIG. 2, accelerator pedal  130  is shown communicating with the driver&#39;s foot  132 . Accelerator pedal position (PP) is measured by pedal position sensor  134  and sent to controller  12 .  
     [0023] The CPU  102  is programmed to execute a torque monitoring algorithm and compares torque demand (i.e., driver-demanded torque computed primarily from acceleration pedal position), with two independent torque estimates (e.g., one estimated from throttle position and one estimated from mass airflow (MAF) to the intake manifold). If the maximum of the two actual torque estimates exceeds the driver-demanded torque, the monitoring algorithm logic intervenes in engine torque production (e.g., shuts off fuel to cylinders) and lights a service (wrench) light. In order to prevent, or minimize, unnecessary intervention, an adjustment is made to the driver-demanded torque. For example, driver-demanded torque is reduced by a factor based on the lower of the two actual torque estimates thereby minimizing the cases where the monitor will intervene by, for example, shutting off fuel to cylinders.  
     [0024] More particularly, if the air-meter reads higher than the throttle based estimate of air and torque, then the method simply closes the throttle until the air-meter is satisfied. It is judged that most drivers will not notice that they are getting slightly less torque at a given throttle, and even if they notice will prefer this control action to an intervention. Further, if the driver still wishes higher torque then produced by the driver-demanded torque which has been reduced by the applied factor, the driver will merely demand more torque by increase accelerator pedal position. More particularly, at high pedal angles (i.e., the driver depresses the accelerator pedal to, or near, its maximum thereby demanding maximum torque), the method disables intervention completely. That is, if the driver is demanding close to maximum torque, then it doesn&#39;t make sense to monitor power greater than demand; the driver wants all the torque available. This override of intervention prevention is achieved in a smooth and continuous manner with the logic by blending the effect out over a range of pedal angle. The same blending is done to disable the monitor itself, using the same ramp versus pedal. However, if the throttle is stuck this method will not be able to prevent the intervention, which is appropriate.  
     [0025] The process compares measured throttle load with measured airflow load. If the measured throttle load is greater than the measured airflow load, calculating a factor tr_intprv_ml, where tr_intprv_ml is equal to F1′+(1−F1′) P, where: F1′ is a function of measured airflow load divided by measured throttle load and P=0 if pedal position is relatively low, 1 if pedal position exceeds a predetermined relatively high pedal position, or a proportional intermediate value between 0 and 1 if the pedal position is between the relatively low and relatively high pedal positions and applying such calculated factor to the signal fed to the electronically controlled throttle. On the other hand, if the measured throttle load is less than the measured airflow load having the factor tr_intprv_ml equal to a value of 1.  
     [0026] Referring now to FIG. 3, the flow diagram of the process is shown in more detail.  
     [0027] As noted above, the process calculates a variable factor, tr_intprn_ml, which is applied later to driver demand torque. When this variable is less than 1.0 the driver demand will be lowered to satisfy the ETC monitor so cylinders will not be disabled.  
     [0028] In Step  100 , if the load as measured in response to signals from the MAF meter is less than the load as measured from the sensed throttle position (i.e., IF (load_from_airmeter&lt;load_from_throttle ), a term. Base_mul=1 (Step  102 ). In such condition, the MAF will not indicate actual power is greater than demanded power so that no adjustment to driver demand required.  
     [0029] If, on the other hand in Step  100  it is determined that the load as measured in response to signals from the MAF meter is greater than the load as measured from the sensed throttle position, in Step  104 , the term Base_mul=the load_from_airmeter divided by load_from_throttle.  
     [0030] The process now clips the base_mul value to a calibratable minimum. This allows the impact of intervention prevention on driveability to be controlled.  
     [0031] More particularly, in Step  106 , base_mul&lt;BASE_MUL_MIN, base_mul=BASE_MUL_MIN, Step  108 , having typical values from 0.9 to 0.85.  
     [0032] Otherwise, in Step  110 , the base_mul is filtered to prevent rapid changes and to minimize negative impact on driveability. (It is noted that in Step  106 , if base_mul&lt;BASE_MUL_MIN, base_mul=BASE_MUL_MIN, these values of BASE_MUL_MIN are also filtered in Step  110 ).  
     [0033] The filtering in Step  110 , uses a calibratable value, BASE_MUL_FK, to selectively weight new values relative to old values of base_mul. This is known in the art as a filter constant. Alternately, a time constant could be used.  
     [0034] Here, the filtering used is:  
     base —   mul   —   filt =base —   mul *BASE —   MUL   —   FK +base —   mul   —   filt* ( 1−BASE —   MUL   —   FK )  
     [0035] The process now calculates the adjustment to the above ratio based on pedal position. Note, at high pedal there is no such thing as power greater than demand, so the above ratio, Base_mul, is blended toward 1, indicating no adjustment, and the monitor is disabled.  
     [0036] Thus, in Step  112 , if the current accelerator pedal position is greater than a second calibratible pedal point, POS 2 , (i.e., IF (pedal_position&gt;PEDAL_POS 2 ), a pedal multiplier factor pedal_mul is set equal to 1 (Step  114 ), i.e., pedal_mul=1.0 and no adjustment is made to driver demand at thus relatively high accelerator pedal position POS 2 .  
     [0037] On the other hand, if the current accelerator pedal position is less than the second calibratible pedal point, POS 2  in Step  112 , and if the current pedal_position is less than or equal to a small pedal position, POS 1 , (Step  114 ) the pedal_factor is made 0 (Step  116 ). That is, if the current pedal less than or equal to first calibratible pedal point POS 1 , pedal_mul=0.  
     [0038] On the other hand, if the current accelerator pedal position is less than the second calibratible pedal point, POS 2  in Step  112 , and if the current pedal_position is greater than the small pedal position, POS 1 , (Step  114 ) the pedal_factor is made equal to (pedal_position-PEDAL_POS 1 ) divided by (PEDAL_POS 2 -PEDAL_POS 1 ), in Step  118 . That is, pedal_factor is linearly varied between 0 and 1 as the pedal travels between PEDAL_POS 1  and PEDAL_POS 2 . Next, in Step  120 , a factor tr_intprv_ml is calculated in accordance with:  
       Tr   —   intprv   —   ml =base —   mul   —   filt +(1−base —   mul   —   filt )* pedal —   mul    
     [0039] Or, as noted above, tr_intprv_ml is equal to F1′+(1−F1′) P, where: F1′ is a function of measured throttle load divided by measured airflow load and P=0 if pedal position is relatively low, 1 if pedal position exceed a predetermined relatively high pedal position, or a proportional intermediate value between 0 and 1 if the pedal position is between the relatively low and relatively high pedal positions and applying such calculated factor to the signal fed to the electronically controlled throttle. If the measured airflow load is less than the measured throttle load having the factor tr_intprv_ml equal to a value of 1.  
     [0040] Next, in Step  122 , a driver demanded brake engine torque is calculated from position and engine speed. More particularly,  
     Desired_brake_engine_tq=DRIVER_DEMAND_TORQUE_LOOKUP_TABLE (pedal_position, engine_speed)  
     [0041] where: DRIVER_DEMAND_TORQUE_LOOKUP_TABLE is a function of pedal_position and engine_speed, the data in such table being determined a priori during product development.  
     [0042] Friction is added to form an indicated torque, the torque equivalent of the torque on top of the piston in Step  124 . That is,  
     Desired_indicated_engine —   tq =desired_brake_engine —   tq +friction —   tq    
     [0043] where:  
     [0044] friction tq is described in U.S. Pat. No., 5,241,855, the entire subject matter thereof being incorporated herein by reference.  
     [0045] The process next (Step  126 ) applies the intervention prevention multiplier tr_intprv_ml to the calculation of airflow required to achieve a driver demand. If the airmeter is reading high, adjust the driver demand down so the monitor does not trip. More particularly, adjusted_desired_indicated_engine_tq=Desired_indicated_engine_tq*tr_intprv_ml  
     [0046] This desired indicated torque is converted to a desired airflow and then a desired throttle using methods known in the art.  
     [0047] A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.