Patent Publication Number: US-7912621-B2

Title: Dual throttle position sensor diagnostic system with reduced stalling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/977,533, filed on Oct. 4, 2007. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to engine control systems, and more particularly to diagnostic systems and methods for engine control systems with two or more throttle position sensors. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Referring now to  FIG. 1 , a functional block diagram of an engine system  100  is shown. Air is drawn through a throttle valve  102  into an intake manifold  104 . An air fuel mixture is created by injecting fuel from a fuel injector  106  into the intake manifold  104 . The air fuel mixture is drawn through an intake valve  108  into a representative cylinder  110 . An ignition coil  112  activates a spark plug  114  to ignite the air/fuel mixture within the cylinder  110 . After ignition, an exhaust valve  116  allows the cylinder  110  to vent the products of combustion to an exhaust system  118 . 
     A control module  120  receives signals from first and second throttle position sensors (TPS&#39;s)  122  and  124 . The control module  120  outputs a control signal to an electronic throttle control (ETC) motor  126 , which actuates the throttle valve  102 . The control module  120  controls the fuel injector  106  and the ignition coil  112 . The control module  120  monitors inputs, such as a position of a gas pedal (not shown), determines a desired throttle position, and instructs the ETC motor  126  to actuate the throttle valve  102  to the desired throttle position. 
     In general, the engine control module activates the ETC motor to position the throttle according to a desired throttle area determined in response to accelerator pedal position and various other control functions, such as idle speed control, engine governor control, cruise control, and traction control. Some engine control systems set indicated throttle to a higher one of the first and second TPS&#39;s during an out of correlation (OOC) error and/or fault. The OOC error occurs when a difference between the two TPS sensors is greater than a predetermined threshold. 
     An out of range (OOR) error may also occur. The TPS sensors may be set to provide a voltage output between first and second voltages. For example, a first TPS may provide a voltage between 0.5 V and 4.5 V corresponding to closed throttle and wide open throttle (WOT). The second TPS may provide a voltage between 4.5 V and 0.5 V corresponding to closed throttle and wide open throttle (WOT). Outputs of the first and second TPS may be input to a lookup table (LUT), which converts the voltages from both the first and second TPS to a percentage of throttle. The OOR error may occur for one of the sensors when the voltage is greater than 4.5 V or less than 0.5 V. 
     Typically, the OOC error occurs before the OOR error. When the higher of the two TPS is selected during the OOC error, the closed-loop control system may try to close the throttle and the engine may stall. 
     Also, when a TPS OOC fault is set due to the TPS sensors shorted together, engine shutdown may occur because indicated throttle was set higher than the throttle return fault diagnostic expected. When the throttle OOC fault occurs because one of the sensors is shifted high (which is most likely case), the system will use the high throttle position for the remainder of the ignition cycle. The engine stalls in most cases since the control system will drive the throttle into the stop. 
     SUMMARY 
     A system comprises an out of correlation (OOC) detection module that detects an OOC error between a first throttle position sensor (TPS) and a second TPS. An out of range (OOR) detection module detects first and second OOR errors for the first and second TPS, respectively. An OOC counter sets an OOC error when an OOC count is greater than or equal to a first OOC value. An OOR counter sets first and second OOR errors when first and second OOR counts, respectively, are greater than or equal to a second OOR value that is less than the first OOC value. A control module increments the OOC count when the OOC error occurs, the first OOR count when the first OOR error occurs, and the second OOR count when the second OOR error occurs. The control module sets at least one of the first and second OOR counts equal to the OOC count when the at least one of the first and second OOR errors occur after the OOC error. 
     A method comprises detecting an OOC error between a first throttle position sensor (TPS) and a second TPS; detecting first and second OOR errors for the first and second TPS, respectively; setting an OOC error when an OOC count is greater than or equal to a first OOC value; setting first and second OOR errors when first and second OOR counts, respectively, are greater than or equal to a second OOR value that is less than the first OOC value; incrementing the OOC count, the first OOR count, and the second OOR count when the OOC error, the first OOR error and the second OOR error, respectively, occur; and setting at least one of the first and second OOR counts equal to the OOC count when the at least one of the first and second OOR errors occur after the OOC error. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram of an engine control system according to the prior art; 
         FIG. 2A  is a functional block diagram of an engine control system according to the present disclosure; 
         FIG. 2B  is a functional block diagram of the control module or ETC module according to the present disclosure; and 
         FIG. 3  is a flowchart illustrating steps of a method for controlling indicated throttle during OOC and/or OOR errors and/or faults. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring now to  FIG. 2A , a functional block diagram of an exemplary engine system  200  according to the present disclosure is shown. For purposes of clarity, reference numerals from  FIG. 1  are used to identify similar components. 
     The control module  202  receives throttle position signals from the first and second throttle position sensors (TPS&#39;s)  122  and  124 . The control module  202  receives a mass air flow (MAF) signal from a MAF sensor  208  and a manifold absolute pressure (MAP) signal from a MAP sensor  210 . The control module  202  receives an engine speed signal in revolutions per minute (RPM) from an RPM sensor  212 , which is in communication with a crankshaft (not shown). The control module  202  may also receive other signals (not shown). 
     The control module  202  communicates control signals to the fuel injector  106 , the ignition coil  112 , and the electronic throttle control (ETC) motor  126 . Based upon inputs such as an accelerator pedal position, the control module  202  instructs the ETC motor  126  to open and close the throttle valve  102 . The control module  202  determines the position of the throttle valve  102  based upon signals from the TPS&#39;s  122  and  124 . 
     If the TPS&#39;s  122  or  124  have OOC and/or OOR errors and/or faults, the control module  202  may take corrective action with respect to indicated throttle position. The throttle valve  102  may include return springs that, in the absence of power to the ETC motor  126 , will return the throttle valve  102  to a learned default position. For example only, the learned default position may be a throttle position in the 20-30% throttle range. This will allow the vehicle to operate in a “limp home” mode. 
     The ETC motor may set the throttle based on a difference between indicated throttle (indicated by TPS 1  or TPS 2  when no errors are present or set by the control module to default or desired throttle in some circumstances) and a desired throttle generated by the control module. 
     Referring now to  FIG. 2B , the control module  202  may include a TPS diagnostic module  230 , an airflow prediction module  240  and an airflow diagnostic module  242 . The airflow prediction module  240  predicts airflow based on engine operating conditions. The airflow diagnostic module  242  compares the airflow prediction with measured airflow and selectively generates a fault when the difference is greater than calibrated thresholds. During some circumstances, the TPS diagnostic module will disable the airflow diagnostic module  242  to prevent detection of airflow errors as will be described further below. 
     The TPS diagnostic module  230  further includes an OOC counter  254 , an OOR counter  258 , an OOC error detection module  262 , an OOR error detection module  266 , a percentage (%) throttle normalization module  270  and an indicated throttle LUT  274 . The OOC error detection module  262  compares the first and second % throttle signals from the percentage throttle normalization module  270 . If the two values differ by more than a predetermined amount, an OOC error occurs. If the error persists for a first predetermined number of cycles (first OOC value) as determined by the OOC counter  254 , an OOC fault occurs. One error and/or fault is generated for both TPS 1  and TPS 2  when the OOC error and/or fault occurs. As can be appreciated, the raw TPS 1  and TPS 2  data can also be compared to determine whether an OOC error occurred. 
     The OOR error detection module  266  compares both the TPS 1  and TPS 2  signals to upper and lower limits. For example, the TPS 1  and TPS 2  ranges may be between 0.5V and 4.5V. If either sensor is greater than the upper limit or less than the lower limit, an OOR error occurs for the respective TPS. If the error persists for a second number of cycles (or second OOR value) as determined by the OOR counter  258 , an OOR fault occurs for the TPS. The indicated throttle LUT  274  sets indicated throttle based on the OOC error and/or fault and the OOR errors and/or faults as will be described below. 
     Referring now to  FIG. 3 , steps for operating the TPS diagnostic system are shown at  300 . Control begins with step  304 . In step  306 , the OOC and OOR counters are set to zero. In step  308 , control determines whether an OOC error has occurred. If step  308  is true, control determines whether an OOC counter is equal to zero in step  310 . If step  310  is true, control accesses the LUT and determines indicated throttle in step  312  based on the OOC and OOR errors and/or faults. In this case, there is an OOC error and no OOR error and control sets indicated throttle equal to desired throttle to prevent stalling. In step  314 , control disables the airflow diagnostic to prevent airflow errors from being triggered as a result of the OOC error. 
     Control continues from steps  310  (if false) and step  314  with step  316  and increments the OOC counter. In step  320 , control determines whether any of the TPS have an OOR error. If step  320  is false, control determines whether the OOC counter is equal to the first OOC value TH 1  in step  324 . If step  324  is false, control returns to step  308 . If step  328  is true, control sets the OOC fault in step  328 , enables the airflow diagnostic system in step  330  and looks up indicated throttle as a function of the OOC and OOR errors and/or faults in step  332 . Control continues from step  332  with step  308 . 
     If step  320  is false, control continues with step  336 . In step  340 , control determines whether the OOR counter for one of the TPS sensors such as TPS 1  is equal to zero. If step  340  is false, control determines whether the OOR counter for the TPS 1  is not equal to zero. If step  342  is true, control increments the OOR counter in step  344  and continues with step  350 . If step  340  is true, control sets the OOR counter equal to the OOC counter in step  346  and continues with step  350 . 
     In step  350 , control determines whether the OOR counter is equal to the second OOR value TH 2 . If step  350  is true, control sets the OOR fault for TPS 1  in step  354 . In step  356 , control enables the airflow diagnostic system. Control continues from step  350  (if false) and step  356  with step  358 . In step  358 , control determines whether there is another TPS (such as TPS 2 ). If true, control returns to step  340 . Otherwise control continues with step  332 . 
     During OOC and OOR errors and not OOC and OOR faults, the airflow diagnostic may be disabled to prevent false diagnosis of airflow errors according to the present disclosure. The airflow errors may occur in conventional systems when the higher one of the TPS sensors is selected during OOC errors. When the higher one of the two TPS sensors is selected in conventional systems, the closed loop system may attempt to close throttle due to differences between indicated throttle and desired throttle. In addition, an airflow error may occur in the conventional system due to differences between predicted and measured airflow. 
     Since the OOC error typically preceded an OOR error, it was difficult to detect an OOR error. In the present disclosure, the OOR counter is set equal to the OOC counter when the OOR error occurs. In addition, the first OOC value set in the OOC counter is set less than the second OOR value in the OOR counter. Therefore, when an OOR error occurs, the OOR counter will detect the OOR fault before the OOC fault is detected. That way, the OOR faults can be diagnosed independently from the OOC faults. 
     Table I set forth below shows indicated throttle as a function of OOR and/or OOC errors and/or faults: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 TPS OOC error 
                 TPS OOC error 
                   
               
               
                   
                 False 
                 True 
                 TPS OOC Fault 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 OOR_1 error or 
                 TPS1 
                 Desired 
                 Default 
               
               
                 fault = False; and 
               
               
                 OOR_2 error or 
               
               
                 fault = False. 
               
               
                 OOR_1 error or 
                 TPS1 
                 Desired 
                 Default 
               
               
                 fault = False; and 
               
               
                 OOR_2 error or 
               
               
                 fault = True. 
               
               
                 OOR_1 error or 
                 TPS2 
                 Desired 
                 Default 
               
               
                 fault = True; and 
               
               
                 OOR_2 error or 
               
               
                 fault = False. 
               
               
                 OOR_1 fault = 
                 Default 
                 Default 
                 Default 
               
               
                 True; and 
               
               
                 OOR_2 fault = 
               
               
                 True. 
               
               
                 OOR_1 error or 
                 Desired 
                 Desired 
                 Default 
               
               
                 fault = True; and 
               
               
                 OOR_2 error or 
               
               
                 fault = True. 
               
               
                   
               
            
           
         
       
     
     The diagnostic system according to the present disclosure avoids unnecessary engine stalling during single sensor OOR failure conditions. The present disclosure also prevents the control module from driving the throttle closed during OOC fault conditions by disabling the airflow diagnostic system under selected conditions. The present disclosure also improves diagnosis by reporting a correct problem code for OOC and OOR faults. This is performed in part by setting the OOR count equal to the OOC count when the OOR error occurs and by using an OOR count value that is less than the OOC count value. Therefore, when the OOC error occurs first as a result of the OOR error, the OOR error will be correctly diagnosed.