Patent Publication Number: US-2004055575-A1

Title: System and method for common rail pressure control

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a system and method for controlling fluid pressure within a common rail fluid distribution device of a multi-cylinder internal combustion engine.  
       [0003] 2. Background Art  
       [0004] Common rail fluid distribution systems are used in various types of internal combustion engines, such as diesel engines, for example. An accumulator or rail is used to distribute a fluid to multiple sites around the engine, each typically associated with an engine cylinder. The fluid may be used to control the operation of engine components, such as the hydraulic oil used to control actuation of injectors in a HEUI (hydraulically actuated electronic unit injector) system. A common rail may also be used to deliver fuel to injectors or nozzles associated with each cylinder of the engine.  
       [0005] Whether used to distribute hydraulic fluid, fuel, or another liquid, the timing and quantity of the liquid delivered to its destinations is dependent upon the pressure within the common rail. As such, a number of strategies have been developed to control or govern the rail pressure. Conventional control theory may be applied to control the rail pressure using feedback control including proportional (P), integral (I), and/or derivative (D) control often in combination with feed forward (FF) control. The behavior of the control system is determined largely based on the gains applied to the various terms (P,I,D, and/or FF) used by the pressure controller or governor. The gains may be fixed scalar values that are determined during calibration of the engine control system, such as disclosed in U.S. Pat. No. 6,016,791 to Thomas et al. Alternatively, variable gains have been used to adjust the control system behavior based on one or more current operating conditions or parameters. For example, one prior art strategy varies control parameters or gains based on rail pressure error (the difference between desired and measured rail pressure) and engine speed. While this approach may provide more desirable control characteristics for some applications, it requires additional resources for calibration and testing, and may not provide optimal accuracy for control, particularly under transient operating conditions.  
       [0006] The present inventors have recognized the shortcomings of the prior art approaches and have developed a system and method for controlling pressure for common rail systems that is believed to provide more accurate and continuous control.  
       DISCLOSURE OF THE INVENTION  
       [0007] The present invention provides a system and method for controlling pressure within a common rail fluid distribution system of an internal combustion engine having a pump for supplying pressurized fluid to a common rail. A pressure controller monitors pressure within the common rail and controls the pump to reduce the error between a desired rail pressure and an actual rail pressure as measured by a pressure sensor. The pressure controller implements a combined feedback/feed forward control strategy with variable gains. In one embodiment, the feedback control loop includes proportional, integral, and derivative terms with variable gains determined based on pumped fluid quantity and engine speed, with the pumped fluid quantity preferably corresponding to pumped fuel. In an alternative embodiment, the proportional, integral, and derivative gains are determined based on injected fuel quantity and engine speed. Another embodiment determines the proportional, integral, and derivative gains based on pumped output, i.e. the product of pumped fluid quantity and engine speed. The present invention also preferably includes a variable gain feed forward control with gains based on pumped fuel quantity and engine speed, or alternatively based on pumped output.  
       [0008] The present invention also includes computer readable storage media having stored instructions executable by a computer to control rail pressure of a common rail fluid distribution system in an internal combustion engine.  
       [0009] The present invention provides a number of advantages. For example, determining PID and feed forward controller gains according to the present invention provides more accurate control of the rail pressure over the entire engine operating range as compared to prior art approaches. This may lead to improved performance, emissions, and driveability of vehicles employing this strategy. Use of injected fuel quantity and engine speed based gains may be able to reduce the effort required for engine calibration. PID and feed forward control based on pumped output provides more continuous gain tables that result in improved rail pressure stability and ease of calibration. In addition, gains based on pumped output reduce the memory required for the controller by requiring less calibration tables.  
       [0010] Various other advantages and features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a schematic/block diagram illustrating operation of a system or method for controlling pressure within a common rail fluid distribution system of an internal combustion engine according to one embodiment of the present invention;  
     [0012]FIG. 2 is a block diagram illustrating a common rail fuel system with a pressure control strategy according to one embodiment of the present invention;  
     [0013]FIG. 3 is a block diagram illustrating alternative embodiments for a rail pressure governor having gains based on injected fuel per cycle or pumped fuel per cycle according to the present invention;  
     [0014]FIG. 4 is a block diagram illustrating another alternative embodiment for a rail pressure governor having gains based on pump output according to the present invention; and  
     [0015]FIG. 5 is a flow chart illustrating operation of a system or method for controlling pressure in a common rail fluid distribution system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
     [0016]FIG. 1 provides a schematic/block diagram illustrating operation of a system or method for controlling pressure within a common rail fluid distribution system of an internal combustion engine according to one embodiment of the present invention. System  10  includes a multi-cylinder compression ignition internal combustion engine, such as a diesel engine  12 , which may be installed in a vehicle  14  depending upon the particular application. In one embodiment, vehicle  14  includes a tractor/semi-trailer  16 . Diesel engine  12  is installed in tractor/semi-trailer  16  and interfaces with various sensors and actuators located on engine  12  and tractor/semi-trailer  16  via engine and vehicle wiring harnesses. In other applications, engine  12  may be used to operate industrial and construction equipment, or in stationary applications for driving generators, compressors, and/or pumps and the like.  
     [0017] An electronic engine control module (ECM)  20  receives signals generated by engine sensors  22  and vehicle sensors  24  and processes the signals to control engine and/or vehicle actuators such as high pressure pump (FIG. 2) and/or fuel injectors  26 , for example. ECM  20  preferably includes computer-readable storage media, indicated generally by reference numeral  28  for storing data representing instructions executable by a computer to control engine  12 . Computer-readable storage media  28  may also include calibration information in addition to working variables, parameters, and the like. In one embodiment, computer-readable storage media  28  include a random access memory (RAM)  30  in addition to various non-volatile memory such as read-only memory (ROM)  32 , and non-volatile memory (NVRAM)  34 . Computer-readable storage media  28  communicate with a microprocessor  38  and input/output (I/O) circuitry  36  via a standard control/address bus. As will be appreciated by one of ordinary skill in the art, computer-readable storage media  28  may include various types of physical devices for temporary and/or persistent storage of data which includes solid state, magnetic, optical, and/or combination devices. For example, computer readable storage media  28  may be implemented using one or more physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash memory, and the like. Depending upon the particular application, computer-readable storage media  28  may also include floppy disks, CD ROM, DVD, and the like.  
     [0018] In a typical application, ECM  20  processes inputs from engine sensors  22 , and vehicle sensors/switches  24  by executing instructions stored in computer-readable storage media  28  to generate appropriate output signals for control of engine  12  via corresponding actuators. In one embodiment of the present invention, engine sensors  22  include a timing reference sensor (TRS)  40  which provides an indication of the crankshaft position and may be used to determine engine speed, preferably in revolutions per minute (rpm). An oil pressure sensor (OPS)  42  and oil temperature sensor (OTS)  44  are used to monitor the pressure and temperature of the engine oil, respectively. Oil temperature may be used to determine a desired rail pressure set point as described in greater detail below.  
     [0019] An air temperature sensor (ATS)  46  is used to provide an indication of the current intake or ambient air temperature. A turbo boost sensor (TBS)  48  is used to provide an indication of the boost pressure of a turbocharger which is preferably a variable geometry or variable nozzle turbocharger. As known by those of ordinary skill in the art, TBS  48  may also be used to provide an indication of the intake manifold pressure. Coolant temperature sensor (CTS)  50  is used to provide an indication of the coolant temperature. Depending upon the particular engine configuration and application, various additional sensors may be included. For example, engines which utilize exhaust gas recirculation (EGR) preferably include an EGR temperature sensor (ETS)  51  and an EGR flow sensor (EFS)  53 .  
     [0020] Common rail fluid distribution systems may include one or more pressure sensors to detect the pressure within the common rail and provide a corresponding signal to the pressure controller within the ECM  20 . As previously described, common rail systems may be used to distribute hydraulic oil or fluid, such as used in some HEUI systems, or to distribute fuel. A common rail fuel system preferably includes a corresponding fuel pressure sensor (CFPS)  52 . Similarly, an intercooler coolant pressure sensor (ICPS)  54  and temperature sensor (ICTS)  56  may be provided to sense the pressure and temperature of the intercooler coolant. Engine  12  also preferably includes a fuel temperature sensor (FTS)  58  and a synchronous reference sensor (SRS)  60 . SRS  60  provides an indication of a specific cylinder in the firing order for engine  12 . This sensor may be used to coordinate or synchronize control of a multiple-engine configuration such as used in some stationary generator applications.  
     [0021] Engine  12  may also include an oil level sensor (OLS)  62  to provide various engine protection features related to a low oil level. A fuel restriction sensor (FRS)  64  may be used to monitor a fuel filter and provide a warning for preventative maintenance purposes. A fuel pressure sensor (FPS)  68  provides an indication of fuel pressure to warn of impending power loss and engine fueling. Similarly, a crankcase pressure sensor (CPS)  66  provides an indication of crankcase pressure which may be used for various engine protection features by detecting a sudden increase in crankcase pressure indicative of an engine malfunction.  
     [0022] System  10  preferably includes various vehicle sensors/switches  24  to monitor vehicle operating parameters and driver input used in controlling vehicle  14  and engine  12 . For example, vehicle sensors/switches  24  may include a vehicle speed sensor (VSS) which provides an indication of the current vehicle speed. A coolant level sensor (CLS)  72  monitors the level of engine coolant in a vehicle radiator. Switches used to select an engine operating mode or otherwise control operation of engine  12  or vehicle  14  may include an engine braking selection switch  74  which preferably provides for low, medium, high, and off selections, cruise control switches  76 ,  78 , and  80 , a diagnostic switch  82 , and various optional, digital, and/or analog switches  84 , such as a high idle switch, for example. ECM  20  also receives signals associated with an accelerator or foot pedal  86 , a clutch  88 , and a brake  90 . ECM  20  may also monitor position of a key switch or ignition switch  92  and a system voltage provided by a vehicle battery  94  to determine current operating conditions and control engine  12  and/or vehicle  14 .  
     [0023] ECM  20  may communicate with various vehicle output devices such as status indicators/lights  96 , analog displays  98 , digital displays  100 , and various analog/digital gauges  102 . In one embodiment of the present invention, ECM  20  utilizes an industry standard data link  104  to broadcast various status and/or control messages which may include engine speed, accelerator pedal position, vehicle speed, and the like. Preferably, data link  104  conforms to SAE J1939 and SAE J1587 to provide various service, diagnostic, and control information to other engine systems, subsystems, and connected devices such as display  100 . Preferably, ECM  20  includes control logic to determine current engine and ambient operating conditions to select corresponding gains for a PID and/or feed forward pressure controller to control the pressure within one or more common rail fluid distribution systems. As described in greater detail below, ECM  20  preferably determines at least a current operating mode, oil temperature and engine speed to determine a desired rail pressure. In addition, ECM  20  uses engine speed and injected fuel per cycle or pumped fuel per cycle, or uses pump output to determine appropriate PID and feed forward gains.  
     [0024] A service tool  106  may be periodically connected via data link  104  to program selected parameters stored in ECM  20  and/or receive diagnostic information from ECM  20 . Likewise, a computer  108  may be connected with the appropriate software and hardware via data link  104  to transfer information to ECM  20  and receive various information relative to operation of engine  12 , and/or vehicle  14 . Similarly, transceiver  110  and antenna  112  may be used to wirelessly send and/or receive program, diagnostic, or other information.  
     [0025]FIG. 2 is a block diagram illustrating the components and fluid flow in a representative common rail fluid distribution system utilizing a pressure control strategy according to one embodiment of the present invention. Common rail fluid distribution system  200 , in this embodiment, is used to deliver fuel from a fuel tank  202 . Low-pressure gear pump  206  draws fuel from fuel tank  202  via a primary fuel filter  204  and pumps the fuel through a secondary filter  208  into a high-pressure pump  210 . A fuel metering valve or proportional valve  212  is electronically controlled by ECM  20  via wiring harness  214  to direct fuel into a high-pressure plunger cavity of high-pressure pump  210 . The remaining fuel is spilled as represented by  218  to junction block  222  where it is combined with injector spill fuel and returned to fuel tank  202 . Metering valve  212  is preferably an integral component of high-pressure pump  210  to reduce losses. However, implementations using a discrete metering valve or multiple metering valves may be appropriate for certain applications and are within the scope of the present invention. As used throughout this description, control of high-pressure pump  210  is used interchangeably with control of metering valve  212 . In actual operation, high-pressure pump  210  may be turned on or off separately from control or modulation of metering valve  212 .  
     [0026] In one preferred embodiment, a rail pressure governor or controller implemented within the ECM  20  uses variable gains to control the amount of current sent to metering valve  212  as explained in greater detail below. In general, the rail pressure governor controls metering valve  212  based upon a desired rail pressure and measured rail pressure (determined by pressure sensor  52  and communicated to ECM  20  via wiring harness  214 ) with control system parameters or gains determined according to current engine operating conditions. In various embodiments, PID controller gains of the rail pressure governor are determined based on pumped or injected fuel quantity and engine speed, or pump output per unit time. A feed forward controller provides open-loop control with its gain based on pumped fuel quantity and engine speed or alternatively pump output per unit time. It should be noted that pump speed could be used in place of engine speed and that engine load could be used in place of injected or pumped fuel quantity. In addition, injected fuel quantity could be used in place of pumped fuel quantity for the feed forward controller of the rail pressure governor. The rail pressure governor or controller attempts to reduce the pressure error or deviation between the desired and actual rail pressure to maintain the fuel pressure in high-pressure rail  216  by modulating metering valve  212  to control the amount of fuel supplied by high-pressure pump  210 .  
     [0027] Common rail  216  is used to deliver fuel to a plurality of engine locations. In this embodiment, the plurality of engine locations correspond to injectors  26 , each associated with an engine cylinder (not specifically illustrated). Injectors  26  are actuated by ECM  20  via wiring harness  214  to control the quantity and timing of injected fuel  224  for each cylinder. As known by those of ordinary skill in the art, the quantity and timing of fuel injected into the combustion chamber of each cylinder is also a function of the pressure within common rail  216 . As such, continuous and accurate control of the pressure within common rail  216  is beneficial to improve emissions, efficiency, and drivability. A regulator valve  220  regulates the upstream pressure of injector spilled fuel which is then combined with pump spilled fuel at junction block  222  before being returned to fuel tank  202 .  
     [0028]FIG. 3 is a block diagram illustrating alternative embodiments for a rail pressure governor having gains based on injected fuel per cycle or pumped fuel per cycle according to the present invention. Rail pressure governor  300  determines a desired rail pressure based on a current engine operating conditions or modes as represented by block  302 . The desired rail pressure or rail pressure setpoint is preferably determined as described in commonly owned and copending U.S. Patent application Ser. No. 10/___,___ (Docket No. 98-1-138/DDC0406PUS) titled “Injection Control For A Common Rail Fuel System”, the disclosure of which is hereby incorporated by reference in its entirety. However, the present invention is independent of the particular method used to determine the desired rail pressure as represented by block  302 . A measured or inferred rail pressure is determined as represented by block  304  and is used to determine a rail pressure error or deviation at block  306 .  
     [0029] A software calibration switch or flag represented by reference  308  determines whether an injected fuel per cycle  310  or pumped fuel per cycle  312  calculation is used by the PID controller. Pumped fuel per cycle or pumped output (illustrated in FIG. 4) is preferably used by the feed forward controller in determining an open loop setpoint. Engine speed  314  is used to access a corresponding look-up table to determine an estimate of the total spilled fuel at block  316 . The spilled fuel quantity may be represented by a control quantity of the injectors and a leaked quantity of the injectors as described in greater detail in commonly owned and copending U.S. Patent application Ser. No. 10/___,___ (Docket No. 01-1-167/DDC0483PUS) titled “Engine Control For A Common Rail Fuel System Using Fuel Spill Determination”, the disclosure of which is hereby incorporated by reference in its entirety. The injected fuel per cycle  310  and estimated spilled fuel  316  is used to determine the pumped fuel per cycle  312  as represented by block  318 . In this embodiment, the pumped fuel per cycle  312  is used in combination with the engine speed  314  to determine the feed forward open loop setpoint term  320  which is combined with the PID controller terms  322  as represented by block  340  to determine a pulse width modulated (PWM) control signal for the high-pressure pump or metering valve. Similarly, variable gains represented by block  326 ,  332 , and  338  may be determined based on engine speed  314  and pumped fuel per cycle  312  or injected fuel per cycle  310  depending upon the value of calibration switch  308 . Variable proportional gain  326  (preferably accessed from a two-dimensional look-up table) is used in combination with a programmable high-pressure pump proportional gain  328  (preferably a scalar) and pressure error  306  to determine a proportional term for the PID controller at block  324 . Likewise, variable integral gain  332  (preferably provided by a two-dimensional look-up table) is used in combination with programmable high-pressure pump integral gain  334  (preferably a scalar) and rail pressure error  306  to determine the integral term of the PID controller as represented by block  330 . Variable derivative gain  338  (preferably provided by a two-dimensional look-up table) is used in combination with a programmable high-pressure pump derivative gain  340  (preferably a scalar) and rail pressure error  306  to determine a derivative term of the PID controller at block  336 . The gains are preferably stored in memory and accessed based on the current engine operating conditions, i.e. engine speed and pumped fuel per cycle or injected fuel per cycle. Depending upon the particular application, one or more equations may be used to in place of corresponding values stored in memory with the applicable gains periodically calculated using current engine operating conditions.  
     [0030]FIG. 4 is a block diagram illustrating another alternative embodiment for a rail pressure governor having gains based on pump output per unit time according to the present invention. The present inventors have recognized that high-pressure pump utilization and pump output per unit time could be expressed as a function of metering valve current. As such, the two-dimensional tables used to specify the variable gains of the PID and feed forward controllers may be reduced to a single column. This may reduce the calibration and testing effort required and ultimately provide improved accuracy and continuity for the rail pressure governor.  
     [0031] Rail pressure governor  400  determines a desired rail pressure  402  in a similar fashion as described above with reference to FIG. 3. Desired rail pressure  402  is combined with a measured rail pressure  404  to determine a pressure error at block  406 . The pump output per unit time is determined as represented by block  410  based on engine speed  412  and pumped fuel per cycle  414 , which in turn is based upon injected fuel per cycle  416  and spilled fuel per cycle  418 . A feed forward open loop set point  420  may then be a programmable scalar value rather than a single column of values based on the pump output  410 . PID controller  422  then calculates a proportional term at block  424  using a variable proportional gain  426  (preferably a single column) based on pump output  410 , a high-pressure pump proportional gain  428  (preferably a programmable constant or scalar) and pressure error  406 . Similarly, PID controller  422  determines an integral term at block  430  based on high-pressure pump integral gain  432  (preferably a programmable constant or scalar), variable integral gain  434  determined based on pump output  410 , and pressure error  406 . Likewise, PID controller  422  determines a derivative term at block  440  based on high-pressure pump derivative gain  444  (preferably a programmable constant or scalar), variable derivative gain  442  based on pump output  410 , and pressure error  406 . The various control terms are combined at block  446  to determine an appropriate control signal for the high-pressure pump or metering valve as represented by block  450 .  
     [0032] A block diagram illustrating operation of one embodiment for a system or method for controlling rail pressure in a common rail fluid distribution system according to the present invention is shown in FIG. 5. As will be appreciated by one of ordinary skill in the art, the block diagram of FIG. 5 represents control logic which may be implemented or effected in hardware, software, or a combination of hardware and software. The various functions are preferably effected by a programmed microprocessor, such as included in the DDEC controller manufactured by Detroit Diesel Corporation, Detroit, Mich. Of course, control of the engine/vehicle and/or associated components may include one or more functions implemented by dedicated electric, electronic, or integrated circuits or controllers. As will also be appreciated by those of skill in the art, the control logic may be implemented using any of a number of known programming and processing techniques or strategies and is not limited to the order or sequence illustrated in FIG. 5. For example, interrupt or event driven processing is typically employed in real-time control applications, such as control of an engine or vehicle rather than a purely sequential strategy as illustrated. Likewise, parallel processing, multi-tasking, or multi-threaded systems and methods may be used to accomplish the objectives, features, and advantages of the present invention. The invention is independent of the particular programming language, operating system, processor, or circuitry used to develop and/or implement the control logic illustrated. Likewise, depending upon the particular programming language and processing strategy, various functions may be performed in the sequence illustrated, at substantially the same time, or in a different sequence while accomplishing the features and advantages of the present invention. The illustrated functions may be modified, or in some cases omitted, without departing from the spirit or scope of the present invention.  
     [0033] In various embodiments of the present invention, the control logic illustrated is implemented primarily in software and is stored in computer readable storage media within the ECM. As one of ordinary skill in the art will appreciate, various control parameters, instructions, and calibration information stored within the ECM may be selectively modified by the vehicle owner/operator while other information is restricted to authorized service or factory personnel. The computer readable storage media may also be used to store engine/vehicle operating information and diagnostic information. Although not explicitly illustrated, various steps or functions may be repeatedly performed depending on the type of processing employed.  
     [0034] In the representative embodiment of the present invention illustrated in FIG. 5, block  500  represents determination of the current engine speed. As described above, depending upon the particular application, pump speed could be used in place of engine speed without departing from the invention. A desired rail pressure is determined as represented by block  510 . A measured rail pressure is determined as represented by block  520 . One or more control parameters are then determined based on the engine speed and a fluid quantity as represented by block  530 . Feed forward controller parameters  532  may be based upon pumped fuel per cycle  536  (or alternatively engine load) or pump output per unit time  538 . Similarly, PID controller parameters  534  may be based upon pumped fuel per cycle  536 , pump output per unit time  538 , or injected fuel per cycle  540 . Any particular application may include one or more of the methods described above with selection based upon a calibration flag or switch, a hardwired switch, an engine mode or operating conditions, or the like.  
     [0035] The control parameters determined as represented by block  530  may be used in combination with other scaling factors or gains to control the high-pressure pump to reduce rail pressure deviation (the difference between desired rail pressure  510  and measured rail pressure  520 ) as represented by block  550 . Control of the high-pressure pump is preferably performed using a proportional metering valve as represented by block  552 .  
     [0036] As described above, the present invention provides various systems and methods for more accurately controlling pressure in a common rail fluid distribution system having variable gains. The invention may be used to improve performance and emissions for common rail systems and may lead to improved driveability in vehicle applications. Some embodiments may reduce necessary calibration effort and controller memory requirements while also improving control accuracy relative to prior art approaches.