Patent Publication Number: US-6988029-B1

Title: Transient speed- and transient load-based compensation of fuel injection control pressure

Description:
FIELD OF THE INVENTION 
   This invention relates generally to internal combustion engines for propelling motor vehicles, and particularly to fueling strategies for such engines. More specifically it relates to a strategy for modifying fuel injection control pressure during certain engine speed and engine load transients in order to improve engine performance by reducing, and ideally eliminating, any tendency of the engine to stumble and/or generate extra exhaust smoke during such speed transients. 
   BACKGROUND OF THE INVENTION 
   Certain diesel engines have fuel injection systems that utilize hydraulic fluid (oil) under pressure to force fuel into engine combustion chambers. The hydraulic fluid is supplied to a respective fuel injector at each engine cylinder. When a valve mechanism of a fuel injector is operated by an electric signal from an engine control system to inject fuel into the respective cylinder, the hydraulic fluid is allowed to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber. 
   A fuel injection control strategy may include a strategy for controlling the pressure of the hydraulic fluid that is supplied to the fuel injectors. The pressure may vary depending on the values of certain input data utilized in the control strategy. One type of hydraulic system for controlling the pressure comprises a regulator valve that is controlled by the engine control system&#39;s execution of the pressure control strategy. If a fuel injector comprises an intensifier piston that forces the ejection of fuel from the injector, the pressure applied to the fuel will be some multiple of the hydraulic pressure applied by the hydraulic system to the fuel injector. 
   The pressure control strategy may utilize closed-loop control that seeks to secure correspondence of actual pressure to a desired control pressure. However, to enhance performance, the control strategy may include a feed-forward component that improves response to changing inputs that influence control pressure. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an injection pressure control strategy that can further improve response to changing inputs that influence control pressure. In particular, the inventive strategy relates to the inclusion of one or more maps, based on engine speed, that provide a respective data component for algebraic summing with a calculated data value for desired control pressure to compensate that calculated data value for engine acceleration and deceleration. The calculated data value that is being modified by the invention is based in large part, although not necessarily exclusively, on steady state engine operation where parameters such as speed are substantially constant. 
   The present invention can attenuate, and ideally eliminate, undesired effects on tailpipe emissions and/or drivability of a motor vehicle being propelled by the engine when the engine accelerates or decelerates. One map utilizes engine speed and rate of change of engine speed as inputs. Another map utilizes engine speed and rate of change of engine fueling, and therefore load, as inputs. 
   Accordingly, one generic aspect of the present invention relates to an internal combustion engine comprising a fueling system that uses hydraulic fluid to force fuel into engine combustion chambers via fuel injectors and an engine control system for controlling various aspects of engine operation including fueling of the engine combustion chambers by the fuel injectors and the pressure of the hydraulic fluid that forces fuel into the combustion chambers via the fuel injectors. 
   The control system comprises a steady state strategy for processing certain data to develop a data value for desired steady state hydraulic fluid pressure based on steady state engine operation and a transient strategy for developing transient data values to account for certain transients in engine operation by processing engine speed data and data representing rate of change in at least one of engine speed and engine fueling to develop a data value for a transient component. 
   The control system modifies the data value for desired steady state hydraulic fluid pressure based on steady state engine operation by the data value for the transient component to develop a data value for a transient-modified desired hydraulic fluid pressure, compares the transient-modified desired hydraulic fluid pressure with a data value for actual hydraulic fluid pressure to develop a data value for an error signal, and processes the data value for the error signal through a closed-loop strategy to develop a data value for pressure control that controls the hydraulic fluid pressure. 
   Another generic aspect relates to the control system just described. 
   Still another generic aspect relates to the method for hydraulic pressure control performed by the control system. 
   The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a general schematic diagram of a presently preferred embodiment of pressure control strategy according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Engine fuel injectors are under the control of an engine control system that comprises one or more processors that process various data to develop data for controlling various aspects of engine operation including controlling pressure of hydraulic fluid supplied to the fuel injectors and the timing of operation of valve mechanisms in the fuel injectors. The engine comprises a hydraulic system that pressurizes the hydraulic fluid and controls the hydraulic fluid pressure. When a valve mechanism of a fuel injector is operated by an electric signal from the engine control system to inject fuel into the respective cylinder, the hydraulic fluid is enabled to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber. 
   An example of a pressure control strategy  10  that includes principles of the inventive strategy is disclosed in  FIG. 1 . The pressure control strategy is part of a comprehensive engine control strategy implemented by algorithms that are repeatedly executed by a processor, or processors, of the engine control system. 
   The strategy controls hydraulic fluid pressure by control of an electric operated regulator valve that regulates the pressure of fluid being pumped by an engine-driven hydraulic pump. That valve and related components, such as a driver that drives a solenoid of the valve, are represented by an IPR regulator  12 . 
   Closed-loop control of the valve is accomplished by an error signal ICP — ERR whose data value is calculated by subtracting the data value for actual injection control pressure ICP from the data value for desired injection control pressure ICP — DES —   2  via an algebraic summing function  14 . The data value for ICP is provided by a pressure sensor. 
   The data value for ICP — ERR is evaluated against maximum and minimum limits ICP — ERR — LMX and ICP — ERR — LMN by an evaluation function  16  to assure that it is within predefined limits, and if it is not to then limit it value to the data value of the appropriate one of the two limits. 
   Because the particular closed-loop strategy shown here employs both proportional and integral control components, the data value for ICP — ERR that results from evaluation function  16  is multiplied by a proportional gain factor ICP — KP for the proportional control component using a multiplication function  18  and by an integral gain factor ICP — KI for the integral control component using another multiplication function  20 . Each of the two factors is a function of engine temperature EOT and engine speed N, and so a respective map  22 ,  24  that uses engine temperature EOT and engine speed N as inputs provides the corresponding factor based on those two parameters. 
   The product of ICP — KP and ICP — ERR is designated ICP — P — DTY and forms one input to a summing function  26  and the integral of the product of ICP — KI and ICP — ERR, as integrated by an integral function  28 , is designated ICP — I — DTY and forms another input to summing function  26 . Two other data inputs to summing function  26  are provided by a parameter designated ICP — FF — DTY and a parameter designated ICP — FF — OFST. 
   ICP — FF — DTY represents a feed-forward control component that provides some degree of open loop control that renders the strategy more response to certain changing conditions. The data value for ICP — FF — DTY is calculated by an appropriate algorithm that is based on those conditions. The data value for ICP — FF — OFST is a function of engine temperature and actual injection control pressure and serves to compensate for the influence of those parameters on physical characteristics of the hydraulic fluid. A map  30  that uses engine temperature EOT and actual injection control pressure ICP as inputs provides a data value for ICP — FF — OFST based on those inputs. 
   The data value for the sum provided by summing function  26  controls ICP regulator  12  so that the regulator valve provides actual injection control pressure corresponding to the desired injection control pressure ICP — DES —   2 . 
   Data values for desired injection control pressure ICP — DES —   2  are provided by a summing function  32  that sums a data value for a parameter ICP — DES —   1 , a data value for a parameter ICP — FF — TS, and data value for a parameter ICP — FF — TL. The latter two parameters ICP — FF — TS and ICP — FF — TL relate to improvements provided by incorporation of principles of the present invention in the control of injection control pressure. Both parameters ICP — FF — TS and ICP — FF — TL are based on engine speed N, and each parameter may be considered a sub-component of the transient strategy. The data value for ICP — DES —   1  is the result of processing certain data according to a steady state strategy that determines an appropriate steady state value for injection control pressure based in large part, although not necessarily exclusively, on constant engine speed and fueling. Because the inventive strategy is invoked during transient operation, the calculated data value for ICP — DES —   1  may change as execution of the steady state iterates during transients. 
   A data value for ICP — FF — TS is obtained from a map  34  that contains multiple data values for ICP — FF — TS, each of which is correlated with both a data value for engine speed N falling within a particular range of engine speeds and a data value for rate of change in engine speed ND (i.e., engine acceleration/deceleration) falling within a particular range of engine acceleration/deceleration. In other words, for various combinations of engine speed and acceleration/deceleration, there is a corresponding data value for ICP — FF — TS. 
   A data value for ICP — FF — TL is obtained from a map  36  that contains multiple data values for ICP — FF — TL, each of which is correlated with both a data value for engine speed N falling within a particular range of engine speeds and a data value for rate of change in engine fueling MFDESD (which may also be considered to approximate rate of change in engine load) falling within a particular range of fueling rate change. In other words, for various combinations of engine speed and rate of fueling change, there is a corresponding data value for ICP — FF — TL. 
   As engine speed N changes, map  34  provides a data value for ICP — FF — TS that is correlated with speed and the rate at which the engine is accelerating or decelerating. That data value is algebraically summed with the data value for ICP — DES —   1 . 
   As engine speed N changes, map  36  provides a data value for ICP — FF — TL that is correlated with speed and the rate at which the engine fueling is changing. That data value is also algebraically summed with the data value for ICP — DES —   1 . 
   The result of the summation of ICP — FF — TS and ICP — FFTL with ICP — DES —   1  creates a data value for ICP — DES —   2 . 
   Data values for the respective maps  34 ,  36  are determined empirically by testing in a vehicle, by engineering calculations, and/or a combination of both. When the engine is running at a steady speed, both maps will typically provide data values of zero, thereby not modifying the steady state calculated value ICP — DES —   1 . As the engine accelerates or decelerates, the calculated steady state value ICP — DES —   1  will be modified by the summation of a data vale from one or both maps  34 ,  36  with that steady state value. It should be understood that the steady state value ICP — DES —   1  does not necessarily remain constant during a speed change because the data value for ICP — DES —   1  is being updated at the rate at which the pressure control strategy iterates. 
   The inventive strategy is effective to counteract incipient engine stumbling and extra smoke generation by accounting for unique operating conditions that occur during speed transients and tend to cause stumbling and extra exhaust smoke. The invention is especially useful in diesel engines. 
   While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.