Abstract:
A method of verifying a default state of a control parameter in an automobile engine includes checking engine controller performance with the control parameter in both a default state and an alternate state. The results of the tests are then compared to verify which state is the appropriate state for the particular engine being tested. A third engine controller performance check can be made to ensure that the controller and engine perform in a repeatable manner prior to setting the state of the control parameter.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This invention claims the benefit of U.S. Provisional Ser. No. 61/552,484, filed Oct. 28, 2011 
    
    
     FIELD 
     The present disclosure relates to a method of verifying and setting control parameters in automobile engines and more particularly to a method of verifying the suitability of a default state of a control parameter for a particular engine to improve valve timing and emissions performance. 
     BACKGROUND 
     Modern automobile engines are generally controlled by a computerized system known as an Engine Control Unit (ECU). To configure the ECU, a single engine or small sample of engines are extensively tested on a dynamometer to establish default control settings for that model of engine. These default values are then applied to the ECUs that are incorporated into the thousands or even millions of subsequently manufactured engines of that model. Among other functions, the default values determine how the ECU will model air flow through the engine. 
     Many modern vehicles include a system that provides variable valve timing. While different systems exist, each type of system has the ability to alter the opening and closing of intake valves, exhaust valves, or both, to modify the air flow characteristics of the engine. This control over engine air flow allows the engines to run more efficiently and produce fewer emissions by maintaining a predetermined combustion level. In some circumstances the predetermined combustion level may represent optimal combustion conditions but this is not required. The ECU controls the variable valve timing system; therefore, the accuracy of the air flow modeling performed by the ECU is critical to the effective operation of the variable valve timing system. 
     During the initial dynamometer testing, a specific control parameter known as the mechanical-electrical confidence bit is set in the ECU. The mechanical-electrical confidence bit is assigned one of two possible logical states and represents a fundamental assumption that underlies the air flow modeling performed by the ECU. The first state assumes that the electrical system is perfect, thus all errors are coming from the mechanical system. The second state assumes that the mechanical system is perfect, thus all errors are coming from the electrical system. The ECU models the engine air flow differently depending upon the state of the mechanical-electrical confidence bit and the underlying assumption that the state implies. 
     Currently, the mechanical-electrical confidence bit is set as a result of the initial dynamometer tests. Such tests are used to determine a default state of the mechanical-electrical confidence bit, which is then applied to all subsequently manufactured engines. In some instances, however, this default state is not the appropriate mechanical-electrical confidence bit state for a particular subsequently manufactured engine. Unfortunately, the default state is used even though an alternate state would provide more accurate air flow modeling and improved performance. An alternate state is a state which is different from the default state. In the example of the mechanical-electrical confidence bit, the mechanical-electrical confidence bit has two values and thus the alternate state is different of the default state. Thus, it is desirable to test the appropriateness of the default state of the mechanical-electrical confidence bit for each engine manufactured and to change the mechanical-electrical confidence bit state when doing so would provide improved performance over the default state. 
     SUMMARY 
     In one form, the present disclosure provides a method of setting a control parameter in an automobile engine. The method includes inputting into an engine control unit a first set of data from a sensor while the control parameter is set to a default state and calculating a first value, based on the first set of data, indicative of a first level of correction required by the engine control unit to maintain a predetermined combustion level. Then the control parameter is changed from the default state to an alternate state and a second set of data is input in order to calculate a second value, based on the second set of data, indicative of a second level of correction required by the engine control unit to maintain the predetermined combustion level. Finally the first value and the second value are compared and the control parameter is set to either the default state or the alternate state based on the result of the comparison. 
     In another form, the present disclosure provides a method of setting a control parameter in an automobile engine. The method includes inputting into an engine control unit a first set of data from a sensor while the control parameter is set to a default state and calculating a first value, based on the first set of data, indicative of a first level of correction required by the engine control unit to maintain a predetermined combustion level. Then the control parameter is changed from the default state to an alternate state and a second set of data is input in order to calculate a second value, based on the second set of data, indicative of a second level of correction required by the engine control unit to maintain the predetermined combustion level. Next the control parameter is returned to the default state and third set of data is input and a third value calculated. This third value is then compared to the first value to ensure the engine and ECU behave in a repeatable manner. If the first and third values are not within an allowable variation of one another an error is reported. If the first and third values are sufficiently similar the first value and second value are compared and the control parameter state is set based on the result of the comparison. 
     In yet another form, the present disclosure provides an automobile engine that includes a plurality of cylinders, an exhaust manifold connected to the plurality of cylinders, at least one oxygen sensor located in the exhaust manifold, a variable valve timing system for controlling airflow through the engine, and an engine control unit. The ECU is configured to receive data from the at least one O 2  sensor to control the variable valve timing system to maintain a predetermined combustion level. The ECU is further configured to carry out a method of setting a control parameter. The method includes inputting into an engine control unit a first set of data from a sensor while the control parameter is set to a default state and calculating a first value, based on the first set of data, indicative of a first level of correction required by the engine control unit to maintain the predetermined combustion level. Then the control parameter is changed from the default state to an alternate state and a second set of data is input in order to calculate a second value, based on the second set of data, indicative of a second level of correction required by the engine control unit to maintain the predetermined combustion level. Finally the first value and the second value are compared and the control parameter is set to either the default state or the alternate state based on the result of the comparison. 
     In a further form, the present disclosure provides an automobile engine that includes a plurality of cylinders, an exhaust manifold connected to the plurality of cylinders, at least one oxygen sensor located in the exhaust manifold, a variable valve timing system for controlling airflow through the engine, and an engine control unit. The ECU is configured to receive data from the at least one O 2  sensor to control the variable valve timing system to maintain a predetermined combustion level. The ECU is further configured to carry out a method of setting a control parameter. The method includes inputting into an engine control unit a first set of data from a sensor while the control parameter is set to a default state and calculating a first value, based on the first set of data, indicative of a first level of correction required by the engine control unit to maintain the predetermined combustion level. Then the control parameter is changed from the default state to an alternate state and a second set of data is input in order to calculate a second value, based on the second set of data, indicative of a second level of correction required by the engine control unit to maintain the predetermined combustion level. Next the control parameter is returned to the default state and third set of data is input and a third value calculated. This third value is then compared to the first value to ensure the engine and ECU behave in a repeatable manner. If the first and third values are not within an allowable variation of one another an error is reported. If the first and third values are sufficiently similar the first value and second value are compared and the control parameter state is set based on the result of the comparison. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, drawings and claims provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature, intended for purposes of illustration only, and are not intended to limit the scope of the invention, its application, or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an overhead view of a portion of an engine including intake and exhaust cam phasers and an exhaust manifold with an oxygen sensor; 
         FIG. 2  illustrates a front view of a portion of an engine showing various engine components and sensors; 
         FIG. 3  is a flowchart illustrating a method in accordance with the present disclosure; and 
         FIG. 4  is a flowchart illustrating another method in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have realized that it is possible to test the appropriateness of the default state of a control parameter for each engine manufactured, even when installed in a completed vehicle, and to change the state of a control parameter if necessary. One example of a control parameter is the mechanical-electrical confidence bit which is discussed herein. Although the process is discussed in relation to the mechanical-electrical confidence bit, it is not limited thereto and can be applied to many different control parameters. Such a process is desirable as it ensures that the ECU in every vehicle manufactured will have the appropriate mechanical-electrical confidence bit state. The ECU having the appropriate mechanical-electrical confidence bit state results in more accurate air flow modeling by the ECU, which in turn improves control response time and engine performance while decreasing emissions. 
       FIG. 1  illustrates a portion of an automobile engine  2  including a variable valve timing system. The engine  2  includes a bank  10  of cylinders. The bank  10  of cylinders is shown with three cylinders as part of a six cylinder engine, but can include any number of cylinders. The engine  2  further includes an exhaust manifold  12 , which allows exhaust gas to exit the cylinders for treatment by an exhaust system (not shown). An oxygen (O 2 ) sensor  14  is included within the exhaust manifold  12 . The sensor  14  indicates the presence or lack of oxygen in the gas exhausted by the engine. The sensor&#39;s  14  indication tells whether the engine is running rich (i.e., too little air for the amount of fuel) or lean (i.e., too much air for the amount of fuel). The sensor produces a voltage signal (VS), which is supplied to the ECU  20  ( FIG. 2 ). It should be appreciated that different types of O 2  sensors  14  can be used. 
     The engine portion illustrated in  FIG. 1  also illustrates an intake cam phaser  18  and an exhaust cam phaser  16 . Each cam phaser  16 ,  18  allows the ECU to modify the rotational position of the respective cam shaft relative to the crank shaft, allowing the opening and closing of the intake and exhaust valves to be varied, which changes the air flow characteristics of the engine  2 . One function of the ECU  20  ( FIG. 2 ) is to act as a feedback controller, utilizing a proportional-integral-derivative (PID) method, to provide a predetermined combustion level. Using data from the sensor  14 , along with data from the intake cam sensor  22  ( FIG. 2 ), exhaust cam sensor  24  ( FIG. 2 ), and crank shaft position sensor  26  ( FIG. 2 ) the ECU can manipulate the phasers  16 ,  18  to change the engine&#39;s air flow characteristics. In addition to the variable valve timing system the ECU controls other systems (not shown) to provide a predetermined combustion level. While both intake and exhaust cam phasers  16 ,  18  are shown, the method disclosed herein does not require both and is applicable to engines with a variety of variable valve timing systems. 
       FIG. 2  illustrates a front view of a portion of the engine  2 . A timing drive chain/belt  32  wraps around a crank shaft pulley  30 , an intake cam shaft  36 , and an exhaust cam shaft  34 . A tensioner  36  controls the tension on the timing drive chain/belt  32 . An intake cam sensor  22 , exhaust cam sensor  24 , and crank shaft position sensor  26  are electrically connected to and provide information to the ECU  20 . The sensors  22 ,  24  and  26  are typically Hall Effect sensors, but other sensors such as magnetic, magneto resistive, optical, or inductive sensors can be utilized. 
     The ECU  20  is a microprocessor-based controller, which is configured to control numerous engine functions. These functions include, but are not limited to, variable valve timing, fuel injection, ignition timing, and idle speed. The ECU  20  controls these functions by gathering data from various sensors placed throughout the engine and vehicle, performing calculations based on processes that are programmed into the ECU, and sending the appropriate control signals to the various engine systems. The advantages described herein are realized by programming the ECU to perform a process of setting a control parameter (e.g., mechanical-electrical confidence bit) as discussed relative to  FIGS. 3 and 4  below. 
     The methods disclosed herein are carried out by computer instructions (i.e., firmware or software) stored within an ECU programmed to perform the disclosed series of operations. These programmed ECUs are incorporated into a vehicle during the manufacturing process. In one embodiment the ECU is configured to carry out the method automatically at a predefined time. The predefined time can be when the engine is started for the first time during the vehicle manufacturing process, after the vehicle has traveled a specific number of miles, after the engine has run for a specific number of cycles, or after the engine has run for a specific amount of time. In an alternate embodiment, the ECU is configured to carry out the method when instructed to do so by an operator. 
       FIG. 3  is a flowchart illustrating a method  100  of setting a control parameter in accordance with the disclosed embodiments. In the illustrated example the control parameter is the mechanical-electrical confidence bit described above. At step  105 , the ECU  20  takes a first reading of data from the O 2  sensor  14 , and calculates a first value, known as an O 2  factor. This first reading and calculation are performed with the mechanical-electrical confidence bit set to the default state that was determined from previous dynamometer testing of a representative engine or small sample set of engines. During step  105 , the ECU gathers data from the O 2  sensor  14  for a predefined number of engine cycles known as a sampling period. During the sampling period, the ECU  20  continues to function as a PID controller to provide a predetermined combustion level, as discussed previously. The O 2  factor is indicative of the level of correction required by the ECU to provide the predetermined combustion level. The larger the O 2  factor, the larger the correction required by the ECU to maintain the predetermined combustion level. 
     At step  110 , the state of the mechanical-electrical confidence bit is changed from the default state to an alternate state in order to gather data for comparison. At step  120 , a second reading of data from the O 2  sensor  14  is taken and a second value is calculated. Just like step  105 , the ECU  20  gathers data from the O 2  sensor  14  for a second predefined number of engine cycles and then calculates a second value for the O 2  factor. This second value for the O 2  factor is indicative of the level of correction required by the ECU to provide the predetermined combustion level with the mechanical-electrical confidence bit in the alternate state. By changing the state of the mechanical-electrical confidence bit, the process  100  is able to measure performance of the controller under both possible states of the mechanical-electrical confidence bit to determine the best setting. 
     At step  130 , the state of the mechanical-electrical confidence bit is returned to the original default state. At step  140 , a third reading is taken and a third value of the O 2  factor is calculated. Step  140  is substantially similar to step  105  and therefore should produce similar results. At step  150 , the third value is compared to the first value. If the two values are not the same, within a predefined allowable variation, the process  100  continues at step  170  where a “failure to repeat” condition is reported and the process  100  is ended. This error indicates that something caused the ECU  20  or the engine  2  to function differently although the same state of the mechanical-electrical confidence bit was used. When the third value is not generally the same as the first value, the integrity of the test is in doubt and it is not possible to determine which state of the mechanical-electrical confidence bit is more appropriate for the specific engine without further testing. When the “failure to repeat” condition occurs, the method  100  may be restarted or the engine can be flagged for further testing to be completed at another time. 
     If the third value is within the predefined allowable variation of the first value (step  150 ) the method  100  continues at step  160 , where the first value is compared to the second value. This comparison is used to determine which state of the mechanical-electrical confidence bit required less correction by the ECU to maintain the predetermined combustion level. It is also possible to compare the second value to the third value or to mathematically combine the first and third values and compare the mathematical combination to the second value, if desired. The specific value compared is not important so long as the values compared are associated with different states of the mechanical-electrical confidence bit. 
     If the first value is greater than the second value (step  160 ), the process  100  continues at step  180  where the mechanical-electrical confidence bit is set to the alternate state and the process  100  is ended. In this instance, the alternate state of the mechanical-electrical confidence bit represents a better assumption relative to the particular engine being tested and setting the mechanical-electrical confidence bit to the alternate state will allow the ECU  20  to maintain the predetermined combustion level with minimal effort. 
     If the first value is less than or equal to the second value (step  160 ), the process  100  continues at step  190  where the mechanical-electrical confidence bit is left in the default state and the process  100  is ended. In this instance, the engine under test is behaving similarly to the sample engine that was tested on the dynamometer and the default state of the mechanical-electrical confidence bit is the appropriate state for this particular engine. 
     It is important to minimize the level of correction required by the ECU as doing so results in more responsive control of engine functions. Another way of thinking about the level of correction is to consider how much the ECU must do to create a predetermined combustion level in the engine. The ECU having the appropriate mechanical-electrical confidence bit state results in more accurate air flow modeling by the ECU, which in turn improves response time and engine performance while decreasing emissions. If the appropriate mechanical-electrical confidence bit state is not set, the ECU will take longer to bring the engine to the predetermined combustion level. Increased levels of ECU correction may even render the ECU incapable of reaching the predetermined combustion level when engine conditions are changing rapidly (i.e., during shifting, acceleration, deceleration, etc.). Additionally, increased ECU operation can cause increased movement of various control elements, resulting in unnecessary wear and shorter component life. 
       FIG. 4  shows another method  200  in accordance with a different embodiment. The method is substantially the same as that shown in  FIG. 3  except that the repeatability test (i.e. steps  130 ,  140 ,  150 , and  170 ) are removed. 
     At step  205 , the ECU  20  takes a first reading of data from the O 2  sensor  14 , and calculates a first value of the O 2  factor. This first reading and calculation are performed with the mechanical-electrical confidence bit set to the default state that was determined from previous dynamometer testing of a representative engine or small sample set of engines. 
     At step  210 , the state of the mechanical-electrical confidence bit is changed from the default state to an alternate state in order to gather data for comparison. At step  220 , a second reading of data from the O 2  sensor  14  is taken and a second value is calculated. Just like step  205 , the ECU  20  gathers data from the O 2  sensor  14  for a second predefined number of engine cycles and then calculates a second value for the O 2  factor. This second value for the O 2  factor is indicative of the level of correction required by the ECU to provide the predetermined combustion level with the mechanical-electrical confidence bit in the alternate state. By changing the state of the mechanical-electrical confidence bit, the process  200  is able to measure performance of the controller under both possible states of the mechanical-electrical confidence bit to verify the best setting. 
     At step  260  the first value is compared to the second value. This comparison is used to determine which state of the mechanical-electrical confidence bit required less operation by the ECU to maintain the predetermined combustion level. 
     If the first value is greater than the second value (step  260 ), the process  200  continues at step  280  where the mechanical-electrical confidence bit is left in the alternate state (from step  220 ) and the process is ended. In this instance, the alternate state of the mechanical-electrical confidence bit represents a better assumption relative to the particular engine being tested and setting the mechanical-electrical confidence bit to the alternate state will allow the ECU  20  to maintain the predetermined combustion level with minimal correction. 
     If the first value is less than or equal to the second value (step  260 ), the process  200  continues at step  290  where the mechanical-electrical confidence bit is reset to the default state and the process  200  is ended. In this instance, the engine under test is behaving similarly to the sample engine that was tested on the dynamometer and the default state of the mechanical-electrical confidence bit is the appropriate state for this particular engine. 
     The methods  100 ,  200  can be performed at anytime, but it is anticipated that they would be performed when an engine is started for the first time as part of testing a newly manufactured vehicle, prior to being shipped to a dealership or sold to an end user. The methods  100 ,  200 , however, are not limited to this particular schedule and may be performed at other times deemed appropriate. For instance, the best results may be achieved by performing the disclosed methods after a vehicle has traveled a predetermined number of miles or after an engine has run for a predetermined amount of time. It is also possible to configure the ECU to perform the method at any time when instructed to do so by an operator, such as a service technician.