Patent Publication Number: US-9850872-B2

Title: System and method for adjusting on-time calibration of a fuel injector in internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/867,893, filed Aug. 20, 2013, which is incorporated by reference herein in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a system and method for determining the amount of fuel provided by a fuel injector to a combustion chamber of an internal combustion engine and adjusting an on-time calibration of the fuel injector in response to the measured amount of fuel. 
     BACKGROUND 
     A fuel injector of an internal combustion engine is affected by wear, environmental conditions, and other factors. When a fuel injector is initially tested and assembled into an internal combustion engine, a control system of the engine is provided with calibration values that provide for optimal operation of the fuel injector, such as the amount of fuel delivered for an injector on-time. As the fuel injector&#39;s performance changes with time, the original calibration values may lead to less than optimal performance for the fuel injector. 
     SUMMARY 
     Various embodiments of the disclosure relate to a method of calibrating fuel injectors. The method comprises receiving an engine shutdown value; providing a fuel injection value to initiate a fuel injection event for a fuel injector corresponding to a cylinder in response to the engine shutdown value; receiving a pressure value representing a fuel pressure over a period of time, which includes the fuel injection event; calculating an amount of fuel actually injected in response to the pressure value; producing a deviation value in response to the amount of fuel and a commanded amount of fuel; and determining a correction factor for the injector in response to the deviation value. In some embodiments, the fuel injection value is provided while sufficient pressure remains in the fuel accumulator to permit proper functioning of the fuel injector. The method may further comprise operating the fuel injector in response to the correction factor. 
     In some embodiments, the deviation value may be determined in response to a trend analysis including the amount of fuel delivered and a previous amount of fuel delivered. In yet other embodiments, the correction factor is determined in response to a statistical analysis of fuel injection events. 
     Various other embodiments relate to a control system, comprising a memory configured to store a commanded amount of fuel for a fuel injector corresponding to a cylinder and an analysis module coupled to the memory. The analysis module is configured to detect an engine shutdown value; determine a deviation value in response to the commanded amount of fuel and an amount of fuel delivered; and determine a correction factor in response to the deviation value. 
     The controls system may include a correction module coupled to the analysis module and configured to receive the correction factor; produce a modified on-time calibration for the fuel injector; and provide a calibration value representing the modified on-time calibration to a corresponding lookup table. 
     In some embodiments, a calculation module is coupled to the analysis module and configured to receive pressure information directly or indirectly from an accumulator pressure sensor; calculate an amount of fuel delivered by the fuel injector to the cylinder; and provide the amount of fuel. 
     In yet other embodiments, a fuel injection module is coupled to the calculation module and a set of fuel injectors corresponding to a set of cylinders. The fuel injection module is configured to receive sensor information, including piston position information; determine the cylinder for receiving fuel in response to the piston position information; and provide a fuel injection value to the fuel injector corresponding to the cylinder. 
     Various embodiments also relate to an engine system. The engine system includes an engine block having a set of cylinders; a fuel injection system including a fuel pump, a fuel accumulator, and a set of fuel injectors in fluid communication with the fuel accumulator, each fuel injector configured to inject fuel into a corresponding cylinder; and means for adjusting an on-time value of a fuel injector in response to a deviation between an amount of fuel and a commanded amount of fuel, wherein error in the amount of fuel caused by an operating fuel pump is mitigated. 
     Advantages and features of the embodiments of this disclosure will become more apparent from the following detailed description of exemplary embodiments when viewed in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of an internal combustion engine in accordance with some embodiments of the present disclosure. 
         FIG. 2  is a fuel injector on-time calibration module of the engine of  FIG. 1  in accordance with some embodiments of the present disclosure. 
         FIG. 3  is a process flow diagram for a fuel injector calibration process of the fuel injector calibration module of  FIG. 2  in accordance with some embodiments of the present disclosure. 
         FIG. 4  is a graph showing a fuel injector control signal and data acquired after operation of the engine of  FIG. 1  has stopped in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a portion of an internal combustion engine in accordance with an exemplary embodiment of the present disclosure is shown as a simplified schematic and generally indicated at  10 . Engine  10  includes an engine body  12 , which includes an engine block  14  and a cylinder head  16  attached to engine block  14 , a fuel system  18 , and a control system  20 . Control system  20  receives signals from sensors located on engine  10  and transmits control signals to devices located on engine  10  to control the function of those devices, such as one or more fuel injectors  30 . The fuel injectors  30  are tested and characterized prior to installation in engine  10 . When each fuel injector  30  is installed into engine  10 , the performance characteristics of each fuel injector is loaded into control system  20  as calibration values that permit control system  20  to adjust the operation of each fuel injector to optimize fuel delivery. One challenge with a fuel injector  30  is that its performance changes with time. The originally programmed calibration values, such as the relationship between an on-time and a fuel amount delivered, for each fuel injector  30  lead to less optimal performance of each fuel injector as each fuel injector ages. The system and method of the present disclosure provides the ability to dynamically re-measure the ability of each fuel injector  30  to deliver fuel under specific operating conditions, and the system and method compares the measured fuel delivery to a lookup table of injector on-times. Determining the amount of fuel delivered by a fuel injector  30  while engine  10  is operating is difficult and can lead to significant errors because a fuel rail or accumulator  40  is subject to a significant number of pressure changes during operation as fuel flows into and out from the fuel accumulator, some of which may appear to be noise. The system and method of the present disclosure eliminates these sources of pressure changes and noise by actuating a single fuel injector  30  after engine  10  stops operation, and while sufficient pressure remains in the fuel accumulator  40  to permit proper functioning of the fuel injector. The actuation of a fuel injector  30  causes a pressure drop or decrease in a fuel rail or accumulator  40  that is measured. In some embodiments, the amount of fuel may be measured or indicated, in particular, by the pressure drop of decrease. For example, the system and method uses the pressure drop information to calculate the amount of fuel delivered and to analyze the calculated amount of fuel delivered versus a commanded amount of fuel delivered and to change or “trim” an injector on-time calibration in response to deviations from the commanded amount of fuel delivery. By limiting the injection event to a period after engine  10  has stopped operation, and by using pressure drop information, this system and method are non-intrusive. 
     Engine body  12  includes a crankshaft  22 , a plurality of pistons  24 , and a plurality of connecting rods  26 . Pistons  24  are positioned for reciprocal movement in a plurality of engine cylinders  28 , with one piston positioned in each engine cylinder  28 . One connecting rod  26  connects each piston  24  to crankshaft  22 . As will be seen, the movement of pistons  24  under the action of a combustion process in engine  10  causes connecting rods  26  to move crankshaft  22 . 
     A plurality of fuel injectors  30  are positioned within cylinder head  16 . Each fuel injector  30  is fluidly connected to a combustion chamber  32 , each of which is formed by one piston  24 , cylinder head  16 , and the portion of engine cylinder  28  that extends between a respective piston  24  and cylinder head  16 . 
     Fuel system  18  provides fuel to injectors  30 , which is then injected into combustion chambers  32  by the action of fuel injectors  30 , forming one or more injection events. Fuel system  18  includes a fuel circuit  34 , a fuel tank  36 , which contains a fuel, a high-pressure fuel pump  38  positioned along fuel circuit  34  downstream from fuel tank  36 , and a fuel rail or accumulator  40  positioned along fuel circuit  34  downstream from high-pressure fuel pump  38 . While fuel rail or accumulator  40  is shown as a single unit or element, accumulator  40  may be distributed over a plurality of elements that transmit or receive high-pressure fuel, such as fuel injector(s)  30 , high-pressure fuel pump  38 , and any lines, passages, tubes, hoses, conduits, and the like that connect high-pressure fuel to the plurality of elements. Fuel system  18  may further include an inlet metering valve  44 , positioned along fuel circuit  34  upstream from high-pressure fuel pump  38 , and one or more outlet check valves  46 , positioned along fuel circuit  34  downstream from high-pressure fuel pump  38  to permit one-way fuel flow from high-pressure fuel pump  38  to fuel accumulator  40 . Though not shown, additional elements may be positioned along fuel circuit  34 . For example, inlet check valves may be positioned downstream from inlet metering valve  44  and upstream from high-pressure fuel pump  38 , or inlet check valves may be incorporated in high-pressure fuel pump  38 . Inlet metering valve  44  has the ability to vary or shut off fuel flow to high-pressure fuel pump  38 , which thus shuts off fuel flow to fuel accumulator  40 . Fuel circuit  34  connects fuel accumulator  40  to fuel injectors  30 , which receive fuel from fuel accumulator  40  and then provide controlled amounts of fuel to combustion chambers  32 . Fuel system  18  may also include a low-pressure fuel pump  48  positioned along fuel circuit  34  between fuel tank  36  and high-pressure fuel pump  38 . Low-pressure fuel pump  48  increases the fuel pressure to a first pressure level prior to fuel flowing into high-pressure fuel pump  38 . 
     Control system  20  may include a controller or control module  50  and a wire harness  52 . Many aspects of the disclosure are described in terms of sequences of actions to be performed by elements of a computer system or other hardware capable of executing programmed instructions, for example, a general purpose computer, special purpose computer, workstation, or other programmable data processing apparatus. It will be recognized that in each of the embodiments, the various actions could be performed by specialized circuits (e.g., discrete logic gates interconnected to perform a specialized function), by program instructions, such as logical blocks, program modules etc. being executed by one or more processors (e.g., one or more microprocessor, a central processing unit (CPU), and/or application specific integrated circuit), or by a combination of both. For example, embodiments can be implemented in hardware, firmware, middleware, microcode, or any combination thereof. The instructions can be program code or code segments that perform necessary tasks and can be stored in a non-transitory machine-readable medium such as a storage medium or other storage(s). A code segment may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. 
     The non-transitory machine-readable medium can additionally be considered to be embodied within any tangible form of computer readable carrier, such as solid-state memory, magnetic disk, and optical disk containing an appropriate set of computer instructions, such as program modules, and data structures that would cause a processor to carry out the techniques described herein. A computer-readable medium may include the following: an electrical connection having one or more wires, magnetic disk storage, magnetic cassettes, magnetic tape or other magnetic storage devices, a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (e.g., EPROM, EEPROM, or Flash memory), or any other tangible medium capable of storing information. 
     It should be noted that the system of the present disclosure is illustrated and discussed herein as having various modules and units which perform particular functions. It should be understood that these modules and units are merely schematically illustrated based on their function for clarity purposes, and do not necessarily represent specific embodiments. In this regard, these modules, units and other components may be implemented to substantially perform their particular functions explained herein. The various functions of the different components can be combined or segregated as modules in any manner, and can be useful separately or in combination. Input/output or I/O devices or user interfaces including but not limited to keyboards, displays, pointing devices, and the like can be coupled to the system either directly or through intervening I/O controllers. Thus, the various aspects of the disclosure may be embodied in many different forms, and all such forms are contemplated to be within the scope of the disclosure. 
     Control system  20  may also include an accumulator pressure sensor  54 , an engine temperature sensor  60 , an altitude sensor  62 , and a crank angle sensor  64 . While sensor  54  is described as being a pressure sensor, sensor  54  may be other devices that may be calibrated to provide a pressure signal that represents fuel pressure, such as a force transducer, strain gauge, or other device. Engine temperature sensor  60  may be positioned to measure a coolant temperature or may be positioned to measure a temperature of engine body  12 , including engine block  14  or cylinder head  16 . Altitude sensor  62  may be positioned at any location on engine  10  or in another location, such as a vehicle on which engine  10  is mounted, to measure the altitude at which engine  10  is operating. The crank angle sensor  64  may be a toothed wheel sensor  56 , a rotary Hall sensor  58 , or other type of device capable of measuring the rotational angle of crankshaft  22 . Control system  20  uses signals received from accumulator pressure sensor  54  and the crank angle sensor  64  to determine which combustion chamber  32  contains a piston  24  in position to receive fuel. The control system  20  analyzes the signals received from accumulator pressure sensor  54  to determine a pressure drop. 
     Control module  50  may be an electronic control unit or electronic control module (ECM) that may monitor conditions of engine  10  or an associated vehicle in which engine  10  may be located. Control module  50  may be a single processor, a distributed processor, an electronic equivalent of a processor, or any combination of the aforementioned elements, as well as computer-readable instructions, electronic storage, fixed lookup tables and the like. Control module  50  may include a digital or analog circuit. Control module  50  may connect to certain components of engine  10  by wire harness  52 , though such connection may be by other means, including a wireless system. For example, control module  50  may connect to and provide control signals to inlet metering valve  44  and to fuel injectors  30 . 
     When engine  10  is operating, combustion in combustion chambers  32  causes the movement of pistons  24 . The movement of pistons  24  causes movement of connecting rods  26 , which are drivingly connected to crankshaft  22 , and movement of connecting rods  26  causes rotary movement of crankshaft  22 . The angle of rotation of crankshaft  22  is measured by engine  10  to aid in timing of combustion events in engine  10  and for other purposes. The angle of rotation of crankshaft  22  may be measured in a plurality of locations, including a main crank pulley (not shown), an engine flywheel (not shown), an engine camshaft (not shown), or on the camshaft itself. Measurement of crankshaft  22  rotation angle may be made with toothed wheel sensor  56 , rotary Hall sensor  58 , and by other techniques. A signal representing the angle of rotation of crankshaft  22 , also called the crank angle, is transmitted from toothed wheel sensor  56 , rotary Hall sensor  58 , or other device to control system  20 . 
     Crankshaft  22  drives high-pressure fuel pump  38  and low-pressure fuel pump  48 . The action of low-pressure fuel pump  48  pulls fuel from fuel tank  36  and moves the fuel along fuel circuit  34  toward inlet metering valve  44 . From inlet metering valve  44 , fuel flows downstream along fuel circuit  34  through inlet check valves (not shown) to high-pressure fuel pump  38 . High-pressure fuel pump  38  moves the fuel downstream along fuel circuit  34  through outlet check valves  46  toward fuel rail or accumulator  40 . Inlet metering valve  44  receives control signals from control system  20  and is operable to block fuel flow to high-pressure fuel pump  38 . Inlet metering valve  44  may be a proportional valve or may be an on-off valve that is capable of being rapidly modulated between an open and a closed position to adjust the amount of fuel flowing through the valve. 
     Fuel pressure sensor  54  is connected to fuel accumulator  40  and is capable of detecting or measuring the fuel pressure in fuel accumulator  40 . Fuel pressure sensor  54  sends signals indicative of the fuel pressure in fuel accumulator  40  to control system  20 . Fuel accumulator  40  is connected to each fuel injector  30 . Control system  20  provides control signals to fuel injectors  30  that determines operating parameters for each fuel injector  30 , such as the length of time fuel injectors  30  operate and the number of fueling pulses per a firing or injection event period, which determines the amount of fuel delivered by each fuel injector  30 . 
     Referring to  FIG. 2 , a fuel injector calibration module of control system  20  is shown in accordance with an exemplary embodiment of the present disclosure and generally indicated at  100 . Fuel injector calibration module  100  includes a sensor input module  102 , a fuel injection module  104 , a calculation module  106 , an analysis module  108 , and a correction module  110 . Sensor module  102  receives an engine off or end of engine operation signal  112 , which may come from a sensor tied to operation of engine  10  or from elsewhere in control system  20 . In an exemplary embodiment, the engine off signal may be received when an ignition key (not shown) is rotated from a “RUN” position to a non-run position, such as “AUX” or “OFF.” In another exemplary embodiment, control system  20  may use a signal from the crank angle sensor  64  to determine that engine  10  has ceased operating. Control system  20  then generates and transmits the engine off signal  112  to sensor input module  102 . Sensor module  102  also receives signals from the crank angle sensor  64 , such as, but not limited to, toothed wheel sensor  56  or rotary hall sensor  58 , fuel rail or accumulator pressure sensor  54 , engine temperature sensor  60 , and altitude sensor  62 . After sensor module  102  receives engine off signal  112 , sensor module  102  transmits data received from the crank angle sensor  64 , pressure sensor  54 , engine temperature sensor  60 , and altitude sensor  62  to fuel injection module  104 . 
     Fuel injection module  104  uses the data provided by sensor input module  102  to determine which piston  24  is in a position that would normally receive fuel from an associated fuel injector  30 . Once fuel injection module  104  determines which piston is in the position to receive fuel, fuel injection module  104  transmits a single fuel injector actuation signal  114  to one fuel injector  30  to initiate a fuel injection event, which causes fuel to flow from fuel accumulator  40  through fuel injector  30  into a respective combustion chamber  32 . The flow of fuel from fuel accumulator  40  changes the pressure decay profile in fuel accumulator  40 , described further hereinbelow. Once the fuel injection event has ended, fuel injection module  104  transmits the sensor information provided by sensor input module  102  to calculation module  106 . 
     Calculation module  106  receives sensor inputs from fuel injection module  104  and receives pressure signals from accumulator pressure sensor  54 . Calculation module  106  uses the sensor inputs, particularly pressure signals from pressure sensor  54  before and after the injection event, to calculate the amount of fuel delivered by fuel injector  30 . Once the amount of fuel delivered by fuel injector  30  has been calculated, the fuel amount delivered by a specific fuel injector  30  is transmitted to analysis module  108 . 
     Analysis module  108  receives the calculated amount of fuel delivered and the particular fuel injector  30  associated with the fuel delivered. The amount of fuel delivered is compared to the amount of fuel commanded to be delivered for the specific fuel injector on-time stored in a lookup table to determine whether an associated fuel injector  30  is providing a different amount of fuel as compared to the amount of fuel commanded to be delivered. Analysis module  108  then analyzes the deviation from the lookup table values during previous injection events after the stop of engine operation to perform a trend analysis on the deviation in the amount of fuel injected, thus reducing noise in the calculation. If the analysis of the current and previously calculated fuel amounts delivered is different from the amount that should have been delivered based on the on-time recorded in the lookup table, then analysis module  108  provides the information to correction module  110 . If analysis module  108  determines that no correction is required, then the process of fuel injector calibration module  100  stops at analysis module  108  or provides information to correction module  110  indicating that no correction is to be made. 
     Correction module  110  receives a correction factor from analysis module  108  and fuel injector  30  associated with the correction factor. Correction module  110  adjusts the on-time calibration for associated fuel injector  30  and transmits a calibration signal  116  representing the modified fuel injector on-time to the lookup table, where the value will be stored for future injection events, and thus ending the process of fuel injector calibration module  100 . In some embodiments, the correction factor is zero based on information indicating that no correction is to be made. 
     Referring to  FIG. 3 , a process flow diagram for a fuel injector calibration process of fuel injector calibration module  100  in accordance with an exemplary embodiment of the present disclosure is shown and generally indicated at  150 . Fuel injector calibration process  150  is included at least partially in the modules of fuel injector calibration module  100 . Calibration process  150  begins at a process  152 , which is the receipt of the signal indicating engine  10  has ceased operation. Control is then passed to a sensor input process  154 , where signals from one or more sensors are received, such as the crankshaft angle sensor, accumulator pressure sensor  54 , engine temperature sensor  60 , and altitude sensor  62 . Control is then passed to a fuel injector selection process  156 , which uses the sensor signal inputs received from sensor input process  154  to determine which piston  24  is in position to receive injected fuel, which then determines which fuel injector  30  should be actuated. The information regarding which fuel injector  30  requires actuation is sent to a fuel injector actuation process  158 . 
     In fuel injector actuation process  158 , signals are transmitted to fuel injector  30  determined by fuel injector selection process  156  to initiate a fuel injection event. The fuel injection event begins with movement of a needle or nozzle valve element (not shown) to open one or more injector orifices to permit fuel to flow into associated combustion chamber  32 , and ends when the needle or nozzle valve element blocks fuel flow through the one or more fuel injector orifices. At the end of the injection event, control passes to a pressure sensor signal process  160 . 
     Pressure sensor signal process  160  receives signals from accumulator pressure sensor  54 , which is provided, along with pressure information received from input process  154 , to a pressure drop or decrease calculation process  162 , where a pressure drop in fuel accumulator  40  due to the fuel injector event is calculated or determined. The pressure drop information is provided to a fuel calculation process  164 , where the pressure drop is used to calculate the amount of fuel delivered by fuel injector  30 . The calculated amount of fuel delivered and the position of fuel injector  30  that delivered the fuel is provided to a comparison process  166 , where the calculated amount of fuel is compared with the amount of fuel that should have been delivered using the injector on-time stored in a lookup table to determine a deviation from a calibration value. The deviation information is provided to a statistical process  168 . 
     In statistical process  168 , the fuel deviations over a plurality of previous injection events, in combination with the current event, is analyzed to determine whether a change to an injector calibration value is desirable. For example, if the amount of fuel delivered is determined or calculated to be consistently 5% lower than the amount actually commanded, using the fuel injector on-time from the lookup table, then statistical process  168  indicates the need to make a change to a decision process  170 . If a change to a calibration value is not required, then control moves to a process  172 , which terminates or ends fuel calibration process  150 . If a change to a calibration value is required, control passes to an update or change process  174 . Change process  174  takes the information provided by statistical process  168  and updates the fuel injector on-time in the lookup table for future fuel injection events. Once the lookup table has been updated, fuel calibration process  150  ends with a termination process  176 . 
     While the processes described above discuss analyzing deviations in fuel delivery, other approaches to analyzing the fuel delivery information may be used. For example, calculated fuel delivery may be statistically analyzed over a series of fuel injection events, and the statistically analyzed fuel delivery may then be compared to the delivery expected using the on-time from the lookup table. Other approaches for statistically analyzing the fuel delivery data may be used and thus the specific analytical approach is illustrative only. 
     Referring to  FIG. 4 , graphs representing a fuel injector actuation signal corresponding to a fuel injection event and an associated pressure drop in fuel accumulator  40  are shown. The lower graph of  FIG. 4  shows the duration of a fuel injection actuation signal, which approximately correlates with the fuel injection event, beginning with a start of injection  200  and finishing with an end of injection  202 , defining a fuel injection event  204 . Fuel injection event  204  may be for a fixed length of time, for example about 160 microseconds, or for a fixed change in fuel pressure, for example about 70 Bar. The upper graph in  FIG. 4  shows the pressure signal from accumulator pressure sensor  54 , which shows a pressure decay curve  206  to be expected when high-pressure fuel pump  38  stops operating, which occurs when engine  10  stops operating at  212  (i.e. engine shutdown). During fuel injection event  204 , pressure decreases in fuel accumulator  40  due to the fuel flowing into combustion chamber  32 , which can be seen as a fuel injection pressure drop  208 , which then defines a new pressure decay curve  210 . Pressure drop  208  may be used to calculate the amount of fuel delivered by associated fuel injector  30  without the noise induced by operation of high-pressure fuel pump  38  and the shock waves induced in fuel system  18  by operation of high-pressure fuel pump  38  and the other fuel injectors  30 . 
     While various embodiments of the disclosure have been shown and described, it is understood that these embodiments are not limited thereto. The embodiments may be changed, modified and further applied by those skilled in the art. Therefore, these embodiments are not limited to the detail shown and described previously, but also include all such changes and modifications.