Abstract:
A method for detecting improper operation of a charge motion control device (CMC) based on exhaust temperature is disclosed. It has been found that when the charge motion control device is switched between two positions, the exhaust temperature changes by as much as 100 degrees C. The expected exhaust temperature, based on commanded charge motion control device position and current engine operating condition, and the measured exhaust temperature are compared to determine whether the charge motion control device has failed to attain the desired position.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The invention relates to internal combustion engines and more particularly to methods and systems for diagnosing proper operability of air or air-fuel mixture, referred to herein as charge, motion control (CMC) devices used in such engines. Still more particularly, the invention relates to cam profile switching mechanisms and swirl control valves used in such engines to provide such charge motion. 
     2. Background Information 
     As is known in the art, charge motion control devices (CMCs) are used to provide greater combustion stability over a wider range of operation in internal combustion engines. One such charge motion device is a cam profile (CPS) switching mechanism. For example, cam profile switching is a mechanism by which the cam operating an intake valve of the engine is changed from following a first cam to following a second cam, such change occurring in about one engine revolution. This switching action results in the generation of charge motion in the cylinder. 
     As is also known in the art, at marginal combustion conditions, e.g., with lean air/fuel mixtures in the cylinder or air/fuel mixture diluted with a large fraction of exhaust gases in the cylinder, it is desirable to have a high air/fuel motion turbulence level to aid in the ignition produced flame propagating through the cylinder. At more robust combustion conditions, such as those that occur at high torque demand, high turbulence causes harsh, noisy combustion in the cylinder due to the flame propagating too fast thereby causing an excessive rate of pressure rise in the cylinder. With a CPS device, the cam can be switched to provide the appropriate charge motion in the cylinder, thereby conforming to the engine operating condition. 
     The inventors of the present invention have recognized the desirability of confirming that the charge motion control device is operating as expected. Since CPS affects primarily charge delivery, it is natural to attempt to determine CPS integrity based on a charge model. However, the inventors of the present invention have discovered that engineering data show little or no sensitivity in charge data to CPS position at part load. 
     SUMMARY OF INVENTION 
     The inventors of the present invention have observed that when CPS position is changed from one cam to the other, at a constant engine operating condition, engine exhaust temperature changes by 50 to 100 degrees Celsius, depending on engine operating condition. The inventors have discovered that a determination can be made as to whether a charge motion (CMC) device is operating properly by comparing actual exhaust temperature with exhaust temperature expected from operating the engine with the CMC device in a predetermined one of at least two different charge motion generating positions. 
     The exhaust temperature difference that is noticed when the CMC device is in the other of the positions than is expected is due to the fact that when the electronic control unit commands a first position, the electronic controller also commands spark timing, fuel injection, exhaust gas recirculation quantity, and other parameters assuming that the CMC device has, indeed, assumed the commanded position. If the CMC device is inoperable and is in the other position than that commanded, but the electronic control unit commands the other engine parameters for the appropriate positioning of the CMC device, then the values of the engine parameters are inappropriate for the actual CMC device position, thus, yielding the rather substantial difference in exhaust temperature from that expected, i.e., a 50-100 degree Celsius differential. 
     The inventors have also discovered that if the CMC device has been found to operating improperly, information about the improper operation can also be assessed. By comparing both measured exhaust temperatures and expected temperatures with the CMC commanded to be in a first one of the positions and then with the CMC commanded to be in the other position, such an assessment can be made. 
     The inventors disclose a method for detecting a proper operability in a charge motion control device in an internal combustion engine, the charge motion control device being capable of assuming one of at least two positions. The method includes commanding the charge motion control device to assume one of the two positions. The method determines a measured exhaust temperature, Tm 1 . The method also determines a first expected exhaust temperature, Ts 1 , based on a present engine operating condition and the position commanded to the charge motion control device. The method provides detection of improper operability in response to the measured temperature and said first expected exhaust temperature. Further, a second expected exhaust temperature, Ts 2 , based on a present engine operating condition and the charge motion control device being in the other of the two positions is determined. The improper operability is detected based also on the second expected exhaust temperature. Additionally, the charge motion control device is commanded to assume such other position. A second measured exhaust temperature, Tm 2 , is measured in response to commanding the charge motion control device to be in the other position. The improper operability detection is further based on Tm 2 . 
     The inventors also disclose a system for detecting an improper operating charge motion control device disposed in an internal combustion engine. The charge motion control device is capable of assuming a first position and a second position. The system includes a temperature sensor disposed in an engine exhaust and an electronic control unit operably coupled to the charge motion control device, the engine, and the temperature sensor. The electronic control unit commands the charge motion control device to assume the first position. The electronic control unit determines a first expected exhaust temperature, Ts 1 , based on a present engine operating condition and the charge motion control device being in the first position. The electronic control unit detects the improper operation based on the first expected exhaust temperature and a measured temperature, Tm 1 , determined from the temperature sensor. The electronic control unit determines a second expected exhaust temperature, Ts 2 , based on the present engine operating condition and the charge motion control device being in the second position and bases the improper operation detection further on Ts 2 . 
     The present invention provides a robust method for detecting improper operation of a charge motion control device based on a signal from a temperature sensor in the engine exhaust. 
     Another advantage of the present invention is that it provides differentiation between a dislocated and a stuck charge motion control device. A stuck device is one that is stuck in an unknown position, i.e., could be in the first position, the second position or any position in between. A dislocated device is one that is in the second position when it is commanded to the first position or vice versa. 
     Another advantage of the invention is that the method provides several levels of error checking provided to prevent a false indication that an error has occurred. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     These and other advantages will be more fully understood by reading an example of an embodiment in which the invention is used to advantage, referred to herein as the Detailed Description, with reference to the drawings wherein: 
     FIG. 1 is a schematic of an internal combustion engine having charge motion control devices; 
     FIG. 2 is a drawing of a poppet valve actuated by a rocker arm and acted on by a camshaft having two cam profiles, i.e., cam profile switching used in the engine of FIG. 1; and 
     FIG. 3 is a flowchart illustrating a method according to the present invention and used with the engine of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, an internal combustion engine  10  is shown. Engine  10  is supplied air through intake manifold  14  with throttle valve  12  to control airflow to engine  10 . Typically, engines are equipped an exhaust gas recirculation (EGR) system (not shown) which has an EGR duct leading from the engine&#39;s exhaust system to the intake system. Gases flow though the duct due to pressure in the intake being less than that in the exhaust. Flow through the EGR system is controlled by an EGR valve (not shown). 
     A fuel injector  20  supplies fuel into cylinder  22  of engine  10 , such an arrangement is commonly called direct injection. Alternatively, fuel injector  20  is placed in an intake manifold  14  and supplies fuel into the intake manifold; such a system is commonly referred to as port fuel injection. 
     Manifold  14  has an air motion (i.e., charge motion) control plate  18  in each of the runners leading to cylinders  22 . When charge motion control plate  18  is partially closed, turbulence is induced into the airflow as it passes the restriction. An alternative not shown in FIG. 1 is an engine having two intake valves per cylinder  22  with two runners to supply air to the two intake valves. A swirl control plate is placed in one of the two runners. At low speed, low torque engine operating conditions, the swirl control throttle is closed causing the bulk of the airflow to travel through the open runner. This approximately doubles the airflow rate through the open runner, thereby roughly doubling the turbulence level. Additionally, because the flow enters cylinder  22  through one intake valve, thus, asymmetrically a swirling flow is induced into the in-cylinder air/fuel mixture. Both a charge motion control plate  18  and a swirl control plate can be used as two-position devices and fully variable devices. In either case, these devices produce charge motion in the engine cylinders. 
     Here, in this example, a two-position application of these fully variable devices will be described. Furthermore, the present invention can be used to diagnose problems with fully variable devices by conducting the diagnostic procedure for example at two positions, preferably, the two extreme positions of the fully variable device. 
     Continuing to refer to FIG. 1, exhaust from cylinders  22  is exhausted through exhaust manifold  24 . An exhaust component sensor  26  is disposed in the exhaust gas stream. In one embodiment, exhaust component sensor  26  is an exhaust gas oxygen sensor, from which an air-fuel ratio of the exhaust gases can be determined. Exhaust gas aftertreatment device  32  is disposed in the intake duct. Exhaust temperature sensor  28  is shown in FIG. 1 to be located downstream of exhaust gas aftertreatment device  32 . Alternatively, it can be located anywhere in the exhaust duct or exhaust manifold  24 . 
     Continuing to refer to FIG. 1, electronic control unit (ECU)  40  is provided to control engine  10 . ECU  40  has a microprocessor  46 , called a central processing unit (CPU), in communication with memory management unit (MMU)  48 . MMU  48  controls the movement of data among the various computer readable storage media and communicates data to and from CPU  46 . The computer readable storage media preferably include volatile and nonvolatile storage in read-only memory (ROM)  50 , random-access memory (RAM)  54 , and keep-alive memory (KAM)  52 , for example. KAM  52  may be used to store various operating variables while CPU  46  is powered down. The computer-readable storage media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, some of which represent executable instructions, used by CPU  46  in controlling the engine or vehicle into which the engine is mounted. The computer-readable storage media may also include floppy disks, CD-ROMs, hard disks, and the like. CPU  46  communicates with various sensors and actuators via an input/output (I/O) interface  44 . Examples of items that are actuated under control by CPU  46 , through I/O interface  44 , are swirl control valve position, position of camshaft (cam profile position), fuel injection timing, fuel injection rate, fuel injection duration, throttle valve position, spark plug timing (in the event that engine  10  is a spark-ignition engine), and others. Sensors  42  communicating input through I/O interface  44  may be indicating piston position, engine rotational speed, vehicle speed, coolant temperature, intake manifold pressure, accelerator pedal position, throttle valve position, air temperature, exhaust temperature, exhaust stoichiometry, exhaust component concentration, and air flow. Exhaust component sensor  26  is preferably an exhaust gas oxygen sensor. Some ECU  40  architectures do not contain MMU  48 . If no MMU  48  is employed, CPU  46  manages data and connects directly to ROM  50 , RAM  54 , and KAM  52 . Of course, the present invention could utilize more than one CPU  46  to provide engine control and ECU  40  may contain multiple ROM  50 , RAM  54 , and KAM  52  coupled to MMU  48  or CPU  46  depending upon the particular application. 
     Referring now to FIG. 2, a camshaft having cam profile switching (CPS) for use in the engine of FIG. 1 is shown. Camshaft  62  rotates around its axis at half crankshaft speed. Typically, camshaft  62  is coupled to a pulley (not shown) which is driven by a belt or a chain (also not shown) from the engine&#39;s crankshaft (not shown). When camshaft  62  rotates, camshaft lobe  66  (or  64 , depending on the lateral position of camshaft  62  along its axis) pushes down on rocker arm  58 . Rocker arm  58  is pivots around its axis. The lobe pushing on rocker arm  58  causes it to push down on poppet valve  60 . In FIG. 2, valve  60  is in the closed position, by virtue of its valve spring holding it upward in the closed position. When valve  60  is depressed by engagement with either lobe  64  or lobe  66 , valve  60  is forced downward away from the valve seat thereby allowing gases to flow past valve  60 . As noted above, camshaft  62  has two cam lobes,  64  and  66 . Cam lobe  66  is a more aggressive cam lobe which causes valve  60  to open farther and remain open for a longer duration. The type of valve event associated with cam lobe  66  is more appropriate for high speed, high torque engine operation when a maximum amount of airflow into the engine is desired. The less aggressive cam lobe  64  is appropriate for low speed, low torque engine operation when a shorter lift induces turbulence into the incoming air, which aids the ensuing combustion event. There is a mechanism (not shown), which laterally displaces camshaft  62  along its axis of rotation. In one axial (i.e., transverse) position, cam lobe  64  rides on rocker arm  58 . In the other axial (i.e., transverse) position, cam lobe  66  rides on rocker arm  58 . If the switching mechanism between these two transverse positions were to become stuck in the position with cam lobe  66  actuating valve  60 , the engine would operate roughly at low speed, low torque operation. If the switching mechanism were to become stuck with cam lobe  64  actuating valve  60 , engine peak power would be reduced somewhat and the combustion event would be harsh, i.e., high rate of pressure rise. 
     Referring again to FIG. 2, a variable valve timing (VVT) mechanism is similar to what is shown in FIG. 2, except the camshaft has only one lobe for actuating valve  60 . That is, camshaft does not move axially. Instead, in VVT systems, the phasing of the camshaft  62  is shifted with respect to crankshaft rotation by rotating camshaft  62  about its axis, i.e., with respect to the engine&#39;s crankshaft (not shown). By changing the phasing of camshaft  62 , the timing of the valve events are shifted temporally. The profile, including the open duration and the lift, remain fixed with such a system. Some VVT mechanisms are continuously variable devices capable of selecting any crank angle offset between two limits (maximum advance and maximum retard). Other VVT mechanisms are two-position devices allowing only an advanced position and a retarded position to be accessed. The present invention applies to both types of VVT devices. With the continuously variable device, however, the diagnostic is, in this example, performed at two distinct positions, within the allowable range, that have a significant enough phase shift to provide a detectable difference in exhaust temperature. 
     Two types of charge motion control (CMC) devices have been described herein which alter valve timing and/or lift and as such are charge motion control devices. The present invention applies to any kind of CMC device which can alter the valve event, e.g., electronic valve actuation, electrohydraulic valve actuation, variable valve lift, as examples. 
     A flowchart according to the present invention is shown in FIG.  3 . The algorithm is stored as computer executable code in a storage medium, here, for example, in ROM  50  (FIG.  1 ). The process performed by execution of the stored code begins in step  80 . In step  82 , the charge motion control (CMC) device is commanded to assume a desired position. In some situations, step  82  is completed prior to entering the algorithm at step  80 . The desired position is determined in another computer executed routine based on one or more of engine speed, engine coolant temperature, driver demanded torque, ambient temperature and pressure or other engine parameters. In step  84 , the exhaust temperature is measured, Tm 1 . In step  86 , an expected exhaust temperatures are computed for the CMC device being in one of the two commandable positions, here position Ts 1 , and for the CMC device being in the “other” of the two commandable positions, here position Ts 2 . These are computed in an engine model based on current engine parameters or found in a lookup table stored in ROM  50 . 
     In step  88 , it is determined whether |Tm 1 −Ts 1 | is greater than |Ts 1 −Ts 2 |/2. The vertical bars around the quantity Tm 1 −Ts 2  signify absolute value. That nomenclature is used herein and in the Figures. If a negative result from step  88 , the CMC device is determined to be operating properly and the diagnostic routine of FIG. 3 is exited at step  90 . 
     If a positive result in step  88 , additional tests are made to determine the cause of the improper operation of the CMC device. First control passes to steps  94  and  96  in which the CMC device is commanded to assume the “other” of the two commandable positions, i.e., not the desired position, and the resulting exhaust temperature, Tm 2 , is measured. Control passes to step  98  in which |Tm 2 −Tm 1 | is compared to a threshold temperature, T thresh . If the absolute value of the difference is found to be less than T thresh , a stuck CMC device is determined, step  100 . A stuck CMC device indicates that the device is stuck in the first position, the second position, or in between the two positions. If it is stuck in one of the first or second positions, it may be ascertained which position it is in. 
     If, on the other hand, it is found to be greater, control passes to step  102  in which it is determined if |Tm 1 −Ts 2 | is less than |Ts 1 −Ts 2 |/2; if |Tm 2 −Ts 1 | is less than |Ts 1 −Ts 2 |/2; and if |Tm 2 −Ts 2 | is greater than |Ts 1 −Ts 2 |/2. If all three are true, it indicates a dislocated CMC device, step  104 . If one or more of the tests are found to be false, CMC device is not dislocated and control passes to step  90  where the routine exits. A dislocated CMC device is one in which when commanded to a first position, the device is in the second position, or vice versa. 
     In another embodiment, a CMC device improper operation is based on the difference of a measured temperature, Tm, and an expected temperature, Ts, being greater than a threshold temperature. The threshold is selected large enough so that the possibility of a false detection is limited. In one example, the threshold temperature is 20 degrees Celsius. Alternatively, the threshold temperature is based on the engine operating condition. 
     In another embodiment, the CMC device is commanded to move between the two positions and a temperature measurement is taken at each position, Tm 1  and Tm 2 . If the difference between the two temperatures is less than a predetermined temperature difference, improper operation of the CMC device is determined. The predetermined temperature difference, which is the expected change in temperature by moving the CMC device between its two positions, is 20 degrees Celsius. As stated above, a typical change in temperature caused by moving from one position to the other is typically more than 50 degrees Celsius. To ensure that false detections do not occur, the predetermined temperature difference is selected to be large enough to signify a difference in the presence of sensor noise, etc. but significantly less than that minimum difference. 
     While several modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize alternative designs and embodiments for practicing the invention. The above-described embodiments are intended to be illustrative of the invention, which may be modified within the scope of the following claims.