Abstract:
A method for adjusting fuel injection, the method comprising during an engine start from a non-warmed-up condition, identifying a fuel quality of fuel supplied to the engine during said start based on a performance of said start, and after said start is completed and during a transient fueling condition, adjusting a fuel injection amount based on said identified fuel quality from said start.

Description:
BACKGROUND AND SUMMARY 
   Engines utilize various types of fuel injection adjustments to provide improved engine performance. One example fuel injection compensation methods increases or decreases fuel injection to account for fuel adhered to walls of the intake manifold, intake valves, and/or intake ports. Such phenomena may be referred to as wall wetting dynamics, or transient fuel dynamics. To compensate for such dynamics, the amount of fuel injected is varied to compensate for the fuel stored in the intake manifold and intake ports based on various models and estimates taking into account engine operating conditions. In this way, more accurate air/fuel ratio control may be achieved in of the combusted air/fuel mixture. 
   One example of fuel injection control is described in U.S. Pat. No. 5,492,101. In this example, a transient fuel compensation is described that uses an atomized fuel behavioral model, intake passage fuel behavioral model, and a combustion fuel behavioral model to adjust fuel injection and control actual air/fuel ratio in the combustion chamber. Specifically, the approach utilizes a fuel property value (NF) in the intake passage behavioral model. 
   The inventors herein have recognized several issues with the above approach. First, there may be numerous fuel properties that may be included in the model, some of which may have an influence of increasing fuel injection compensation while others have an influence of decreasing fuel injection compensation. Second, the inventors herein have also recognized that the determination of fuel properties may require additional sensors, thus increasing costs. 
   In one embodiment, the above issues may be addressed by utilizing fuel volatility to adjust transient fuel injection, where the fuel volatility is determined during previous engine start-up operation. For example, Applicants have recognized that fuel volatility and/or quality can have an impact on air-fuel control during transient fueling conditions by affecting the amount of fuel stored in the intake manifold and ports, the rate of storage, and/or the rate of release. Further, by determining fuel volatility during a start, it is possible to determine an indication of fuel volatility by monitoring engine run-up speed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a vehicle illustrating various powertrain components; and 
       FIGS. 2–4  are high level flowchart of routines for controlling the engine and fuel injection. 
   

   DETAILED DESCRIPTION 
   Internal combustion engine  10  comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , 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  13 . 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  16  is coupled to exhaust manifold  48  of engine  10  upstream of catalytic converter  20 . 
   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). 
   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. 
   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 turbine speed (Wt) from turbine speed sensor  119 , where turbine speed measures the speed of the transmission input shaft, 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. 
   Continuing with  FIG. 1 , 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 . 
   In an alternative embodiment, where an electronically controlled throttle is not used, an air bypass valve (not shown) can be installed to allow a controlled amount of air to bypass throttle plate  62 . In this alternative embodiment, the air bypass valve (not shown) receives a control signal (not shown) from controller  12 . 
   As will be appreciated by one of ordinary skill in the art, the specific routines described below in the flowcharts may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the disclosure, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular control strategy being used. Further, these Figures graphically represent code to be programmed into the computer readable storage medium in controller  12 . 
   Referring now to  FIG. 2 , a routine is described showing when a fuel volatility/ or fuel quality determination may be performed. In  210 , the routine first determines whether an engine start is present. For example, an engine start may be determined via the engagement of an engine starter motor, monitoring whether engine speed is greater than a minimum engine speed, a driver key position or various others. When answer to  210  is yes, the routine continues to  212 . In  212 , the routine determines whether the time since the engine start is greater than a threshold value. The time since the engine start may be determined in various ways such as, the amount of time after the engine has reached a minimum speed such as 250 rpm. When the answer to  212  is no, the routine continues to  214 . In  214 , the routine determines whether a driver tip-in has occurred and whether the engine idle speed is stabilized. A driver tip-in can be determined in various ways such as, based on whether the driver accelerator pedal position is greater than a threshold value. Further, stable engine idle speed may be determined by comparing the measured engine idle speed to the desired engine idle speed and determine whether it has remained within a given threshold for a given number of engine cycles. If the answer to  214  is no, the routine continues to  216 . In  216  the routine determines whether close loop air/fuel ratio control is enabled. For example, the routine may determine whether exhaust gas oxygen sensors have reached a desired operating temperature, in which case fuel injection is adjusted based on feedback from the exhaust gas oxygen sensors. If the answer to  216  is no, the routine continues to  218 . In  218 , the routine determines whether the engine temperature, such as the engine coolant temperature (ECT) is within a specified operating window. If the answer to  218  is yes, the routine continues to  220  to perform the routine of  FIG. 3 . 
   Alternatively, in each of the above cases, the routine continues to the end. 
   Turning now to the control strategy depicted in  FIG. 3 , a routine for determining a parameter indicative of fuel volatility is described. Alternatively, various other determinations may be made, such as based on a fuel quality sensor, such as fuel density, viscosity, or combinations thereof. In general, the routine of  FIG. 3  uses a proportional and derivative speed feedback control to compensate for variations in fuel volatility during an engine start, where the deviation between an expected and actual engine run-up speed profile is used as an indication of the fuel volatility. 
   Continuing with  FIG. 3 , the first step is to calculate the expected engine speed run-up profile. In this example, the expected speed is determined as a minimum of two parameters at  312 . The first parameter  308  is determined at  310  as a function of engine coolant temperature (ECT), which is represented by the average ECT during the engine start and time out of engine cranking. The time out of engine cranking, or time since start can be, for example, a timer starting after engine speed reaches a minimum threshold, such as approximately 250 RPM. The second variable is a desired idle RPM value, which may be determined by an idle speed control routine (not shown). 
   Next, the expected engine speed is compared with the actual engine speed at the summing junction of  314 . The result of this comparison and an approximate derivative of measured engine speed (e.g., the filtered slope of the speed curve) from  326  are fed to  316 . An example filter that may be used to approximate the derivative is a simple first order filter. In  316 , the input values are used to calculate a fractional value (from 0 to 1), where 1 is the maximum output and 0 is the minimum output. The output is then fed to  318  and  320  and filtered depending on the direction of the change. If the output is increasing, no filtering is used ( 318 ); however, if the output is decreasing, a simple first order low-pass filter may be used ( 320 ). The output of  318 / 320  is a parameter indicative of a fuel quality, such as the amount of hesitation type fuel present during the start. 
   This parameter may then be used to adjust engine operation, such as to adjust a fuel injection amount and/or spark timing via  322  and  324 , respectively. For example, this parameter indicative of fuel quality may be used to adjust the desired air-fuel ratio and spark timing. In one example, the parameter is used to adjust the desired air-fuel ratio by increasing the richness of the air-fuel ratio as the parameter increases, where various levels of gain may be used depending on operating conditions. The spark timing may be adjusted by blending spark timing between a base timing (for starting with a minimum fuel quality level) and a maximum limit on spark timing after which torque is reduced. 
   In this way, the potentially lean combustion caused by degraded fuel quality may be compensated by richening the fuel injection and advancing spark timing (from its retarded value during an engine start to provide rapid catalyst heating). 
   Referring now to  FIG. 4 , a routine is described for utilizing the parameter indicative of fuel quality or fuel volatility in adjusting a transient fuel adjustment. First, in  410 , the routine identifies the peak, or maximum, fuel volatility parameter output from blocks  318 – 320  of  FIG. 3  during the most recent engine start. Alternatively, rather than using the most recent engine start value the routine may average a plurality of previous engine start fuel volatility parameters to identify the peak fuel volatility indication in  410 . Next, in  412 , the routine determines whether the peak value of  410  is below a minimum noise threshold. If so, the routine continues to  414 , and no compensation to the transient fuel adjustment values are made, and the routine continues to the end. 
   Alternatively, when the answer to  412  is no, the routine continues to  416 . In  416 , the routine determines whether the peak value from  410  is above a saturation threshold value. If so the routine continues to  418  to clip the fuel volatility parameter to a maximum saturation value. From either  418 , or when the answer to  416  is no, the routine continues to  420 . In  420 , the routine determines various adjustments to transient fuel parameters at different engine coolant temperatures, for example. For example, the routine may adjust a ratio of injected fuel that is stored in the intake manifold for a given coolant temperature based on the detected peak fuel volatility indication. Alternatively, or in addition, the routine may also adjust the ratio of fuel evaporating from puddles in the intake manifold or intake ports that is inducted into a cylinder during the induction stroke based on the peak volatility parameter. Still further, other adjustments to gains and/or time constant of the transient fuel compensation algorithms can be made based on the peak detected fuel volatility indication from  FIG. 3 . 
   Continuing with  FIG. 4 , in  422 , the routine performs the transient fuel calculation and fuel injection adjustment based on engine operating parameters. 
   In this way, it is possible to adjust transient fuel injection adjustment to account for variations in fuel quality where the fuel quality may be identified during an engine start. 
   In one embodiment, the captured volatility information may be used even during the engine start, although the final maximum value over the entire start is not yet identified. In other words, the routine may use the maximum value up to the current conditions during a start to adjust transient fuelling operation. Alternatively, the routine may wait to identify the maximum value before enabling adjustment of transient fuelling operation after the engine start. 
   It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above approaches can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. 
   The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
   The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.