JP5644564B2 - Fuel pumping system, fuel pumping control device and computer program - Google Patents

Description

  The present invention relates to a technique for injecting fuel under pressure, and more particularly to a technique preferable for injecting fuel used for combustion of an internal combustion engine.

  As a fuel injection system for an internal combustion engine, a common rail (pressure accumulator) type fuel injection system is known. This fuel injection system includes a pressure pump that pumps fuel to a common rail. In recent years, common use of a common pressure pump has been attempted for various internal combustion engines, that is, internal combustion engines having different numbers of cylinders (for example, a 4-cylinder engine, a 5-cylinder engine, a 6-cylinder engine, and the like). For this common use, the combustion cycle of the internal combustion engine (injection cycle of the injector of each cylinder) and the fuel pumping cycle of the fuel from the pumping pump need to be asynchronous so that the fuel pumping to the common rail is not necessarily synchronized. ing. However, in general, the desynchronization of fuel pumping and injector injection has caused a variation in the actual injection amount of the injector, resulting in a difference in the inter-cylinder injection amount. The change in the actual injection amount of the injector is caused by a change in the injection amount of the injector when an overlap occurs between the fuel feeding period to the common rail and the injection period of the injector. In order to solve such a problem, a technique has been proposed in which a correction amount is calculated from a fuel pumping amount during an injection period, and a command injection amount of an injector is corrected (Patent Document 1). This correction amount is calculated from the amount of fuel pumped to the common rail during the injector injection period and the calculated amount and the common rail pressure.

  On the other hand, conventionally, the pumping amount (discharge amount from the pumping pump to the common rail) is based on the volume change of the internal pressure chamber by utilizing the positive displacement pump that pumps fuel to the common rail. Calculation based on this has been formed as common technical knowledge of those skilled in the art at the time of filing. The positive displacement pump is a pump that discharges liquid by changing the volume of a pressure chamber by a reciprocating motion or a rotational motion.

JP 2005-127164 A

  However, the present inventor newly discovered that leakage at the time of discharge pumping is becoming a non-negligible amount in the pumping pump as the discharge pressure of the pumping pump is increased.

  The present invention was created to solve the above-described conventional problems, and an object of the present invention is to provide a technique for improving the calculation accuracy of the amount of fuel pumped to the common rail.

  Hereinafter, effective means for solving the above-described problems will be described while showing effects and the like as necessary.

In the first invention, a pressure accumulating portion for accumulating fuel, a cylinder in which a pressure chamber is formed, and a pressurizing movement that is a movement in a pressurizing direction in the cylinder are performed. A plunger that pumps fuel to the pressure accumulating unit by causing a volume change in the pressure chamber; and a control unit that controls a pumping amount of fuel to the pressure accumulating unit, and the control unit includes an inner circumference of the cylinder. The amount of fuel leakage from the gap between the surface (forming a pressure chamber) and the outer peripheral surface of the plunger is estimated, and the pressure according to the estimated amount of leakage and the stroke of the plunger during the pressurizing movement And a volume change amount in the room, and a pumping amount calculation unit that calculates the pumping amount using the volume change amount.

  According to the above invention, the amount of fuel leakage from the gap between the inner peripheral surface of the cylinder forming the pressure chamber and the outer peripheral surface of the plunger is estimated, and the pumping amount is calculated using the estimated value. Therefore, it is possible to suppress an error in the amount of pumping due to the amount of fuel leakage from the gap. Thereby, the calculation accuracy of the fuel pumping amount to the common rail can be improved. According to the experiments of the present inventors, it has been found that leakage from the gap between the inner peripheral surface of the cylinder and the outer peripheral surface of the plunger increases nonlinearly (rapidly) as the discharge pressure to the common rail increases. It was done. Therefore, it can be seen that the present invention is a technology that is becoming increasingly important in increasing the pressure of the common rail.

According to a second aspect of the present invention, the pumping amount calculation unit calculates a resistance value with respect to the flow of fuel flowing through the gap based on the stroke, and estimates the leakage amount using the resistance value. .

  According to the above invention, in the calculation of leakage from the gap between the inner peripheral surface of the cylinder and the outer peripheral surface of the plunger, the resistance value of the flow path resistance against the fuel flow can be calculated based on the stroke. The amount of leakage can be estimated easily and accurately.

In a third aspect of the invention, the pumping amount calculation unit calculates a pumping speed to the pressure accumulating unit based on a difference between a plunger chamber pressure that is a pressure in the pressure chamber at the time of pressurization and a pressure of the pressure accumulating unit. It is characterized by that.

  According to the above invention, the pumping speed to the high pressure passage can be calculated based on the difference between the plunger chamber pressure and the pressure in the pressure accumulating portion. This method is different from the conventional method in which the pumping amount is calculated according to the volume change of the pressure chamber of the positive displacement pump based on the assumption of the positive displacement pump, and the pressure change is calculated from the volume change in the pressure chamber. The pumping amount can be calculated based on the change. This eliminates the need for the assumption of a conventional positive displacement pump, and eliminates the error caused by the assumption of the positive displacement pump, which decreases in fidelity as the pressure increases. Can be realized.

According to a fourth aspect of the present invention, the pumping amount calculation unit regards the fuel as a predetermined compressive fluid, and uses the bulk elastic modulus of the predetermined compressive fluid during the pressurization caused by the pressurization movement. The amount of increase in the plunger chamber pressure, which is the pressure in the pressure chamber, is calculated, and the predetermined compressive fluid is previously determined based on at least one of elastic deformation of at least one of the cylinder and the plunger and volume elastic deformation of the fuel. It has a determined bulk modulus.

  According to the above invention, the fuel is treated as a predetermined compressive fluid having a predetermined bulk elastic modulus based on at least one of the elastic deformation of at least one of the cylinder and the plunger and the bulk elastic deformation of the fuel. Therefore, it is possible to easily realize calculation in consideration of expansion of the pressure chamber 53 and the like due to elastic deformation.

  The present invention can be embodied not only in a fuel pumping system but also in the form of a fuel pumping control device, a computer program that embodies the control method and control function, a program medium that stores the program, or a program product. .

1 is an overall configuration diagram showing a configuration of a common rail fuel injection system 10 according to the present embodiment. The graph showing the experimental result of the relationship between the pressure of a common rail and the discharge amount of a high-pressure pump. The figure which shows the calculation formula for calculating the discharge amount of the high pressure pump. The flowchart which shows the processing content for calculating the discharge amount of the high pressure pump. Explanatory drawing which shows a mode that the injection quantity increases resulting from the overlap of the injection period of an injector, and the pumping period (discharge period) to a common rail. Explanatory drawing which shows the content of the injection correction of this embodiment compared with a comparative example. The flowchart which shows the processing content for performing injection amount correction | amendment. The block diagram which shows the content of the main processes of this process. The figure which shows the calculation formula used for injection amount correction | amendment. The chart which shows the mode of the pressure drop of the fuel inside a common rail in the injection at the time of non-overlap and overlap.

  Hereinafter, an embodiment applied to a diesel engine equipped with a common rail fuel injection system 10 according to the present invention will be described with reference to the drawings.

(Details of discharge amount calculation process)
FIG. 1 is an overall configuration diagram showing a configuration of a common rail fuel injection system 10 according to the present embodiment. The common rail fuel injection system 10 is a system for injecting fuel into each cylinder of a four-cylinder diesel engine 80 (hereinafter referred to as an engine) having a four-cycle (stroke) (not shown). The common rail fuel injection system 10 includes four injectors 71 to 74, a common rail 60 that is a pressure accumulator, a high pressure pump 50 that pressure-feeds fuel to the common rail 60, and a feed pump 30 that supplies fuel to the high-pressure pump 50. , A supply control valve (SCV) 40 for controlling the amount of fuel supplied from the feed pump 30 to the high-pressure pump 50, a fuel tank 20, and an electronic control unit (hereinafter referred to as ECU) 70 for electronically controlling them. .

  The common rail 60 is also called a pressure accumulating unit. The electronic control unit 70 is also called a control device or a control unit, and also functions as the above-described pumping amount calculation unit.

  The common rail 60 is a pressure accumulation container for accumulating high-pressure fuel and supplying it to the injectors 71 to 74. High-pressure fuel discharged from the high-pressure pump 50 is supplied to the common rail 60 through the high-pressure supply pipe 16. The high pressure supply pipe 16 is equipped with a check valve 15 for preventing a back flow to the high pressure pump 50. The common rail 60 includes a rail pressure sensor 61 that measures the pressure of high-pressure fuel accumulated in the common rail 60. The output value Pout of the rail pressure sensor 61 is input to the ECU 70. The ECU 70 can estimate the fluctuation amount of the total amount of the high-pressure fuel accumulated in the common rail 60 based on the rail pressure Pout. Details of this estimation will be described later.

  The ECU 70 determines the injection timing and the injection amount according to the engine speed Ne and the accelerator amount, and executes an injection command to the four injectors 71 to 74. The injectors 71 to 74 are electromagnetic fuel injection valves for injecting the high-pressure fuel supplied from the common rail 60 into each cylinder of the four-cylinder diesel engine 80. As for the injection amount, a correction process is executed when the injection timing and the pumping timing from the high-pressure pump 50 to the common rail 60 overlap. The contents of the correction process will be described later. The injectors 71 to 74 are also called injection units.

  A fuel supply pipe 11 and a return flow path 17 for supplying fuel to the feed pump 30 are connected to the fuel tank 20. The return flow path 17 is a flow path for returning the fuel leaked from the high-pressure pump 50 to the fuel tank 20. A return flow path 18 for recirculating the leaked fuel of the common rail 60 and a return flow path 19 for recirculating the leaked fuel of the injectors 71 to 74 are directly or indirectly connected to the return flow path 17. ing.

  The feed pump 30 supplies fuel to the high-pressure pump 50 via the supply control valve 40 and the fuel supply pipes 12 and 13. The fuel supply pipe 13 is equipped with a check valve 14 for preventing a backflow to the supply control valve 40. The supply control valve 40 is a valve for adjusting (throttle adjustment) the amount of fuel supplied to the high-pressure pump 50. The supply amount is adjusted by a command from the ECU 70.

  The high-pressure pump 50 includes a cylinder wall surface 54 that is a cylindrical inner wall, a plunger 51 that is slidably stored on the cylinder wall surface 54, and a cam 52 that is driven to cause the plunger 51 to reciprocate. The plunger 51 has a planar end surface 56 that forms the pressure chamber 53 together with the cylinder wall surface 54, and an outer peripheral surface 55 having the shape of a cylindrical outer peripheral surface. The outer peripheral surface 55 is set to an outer diameter so as to have a clearance of a minute clearance amount Cr of micron order with the cylinder wall surface 54. Lubricity between the outer peripheral surface 55 and the cylinder wall surface 54 is realized by a part of the fuel leaking from the pressure chamber 53 to the internal return flow path 58.

  The operation content of the high-pressure pump 50 is as follows. The cam 52 rotates at an angular velocity ω by a driving force from a crankshaft (not shown) of the engine 80. In FIG. 1, the high-pressure pump 50 is in a state where the plunger 51 has moved from the bottom dead center in the direction of narrowing the pressure chamber 53 by the stroke X1. The bottom dead center is set at a position where the end surface 56 of the plunger 51 is inserted from the end surface 57 of the cylinder wall surface 54 by a distance L. The sliding surface between the outer peripheral surface 55 and the cylinder wall surface 54 is formed by a length X2 in the axial direction. The length X2 is an addition amount of the distance L from the end surface 57 to the end surface 56 at the bottom dead center position and the stroke X1 of the plunger 51.

  The high pressure pump 50 sucks fuel into the pressure chamber 53 as follows. The intake of the fuel is performed by the plunger 51 driven by the cam 52 moving downward (in the direction of expanding the pressure chamber 53) in accordance with the amount of fuel supplied from the supply control valve 40. The high pressure pump 50 pumps fuel to the common rail 60 as follows. The fuel is pumped by the plunger 51 driven by the cam 52 moving upward (pressurizing the pressure chamber 53) and pressurizing. Such movement is also called pressure movement.

  Since the high-pressure pump 50 is a so-called positive displacement pump having a plunger, conventionally, the fuel is regarded as an incompressible fluid, and the discharge amount Q1 to the common rail 60 is measured based on the fluctuation amount of the pressure chamber 53. However, the present inventor has found that the leak amount Q2 from the gap of the clearance amount Cr between the outer peripheral surface 55 and the cylinder wall surface 54 increases rapidly as the common rail 60 increases in pressure, and the leak amount. A technique has been devised to accurately measure the discharge amount Q1 regardless of the increase in Q2.

  FIG. 2 is a graph showing the experimental results of the relationship between the pressure of the common rail and the discharge amount (pressure feed amount) of the high-pressure pump. The horizontal axis shows the maximum pressure at the time of the experiment of the rail pressure Pout which is the pressure of the common rail as “1” as a comparison. The vertical axis shows the maximum discharge amount during the experiment of the discharge amount of the high-pressure pump at a predetermined stroke as “1” as a comparison.

  A line C1 represents a result measured by a conventional method that does not consider the leak amount Q2. A line C2 represents a result measured by a method of an embodiment described later in consideration of the leak amount Q2. A line C3 is an actual measurement value. As can be seen from the figure, in the conventional method, the error rapidly increases with the increase in the pressure of the common rail, whereas the method of the embodiment can accurately measure the discharge amount regardless of the increase in the pressure. I understand that.

  FIG. 3 is a diagram showing a calculation formula for calculating the discharge amount of the high-pressure pump 50. The calculation formulas F1 to F4 are essentially different from the conventional method based on the change in the capacity of the pressure chamber 53, and are characterized in that they are calculated based on the pressure. The calculation formula F1 is a calculation formula for calculating the flow rate by regarding the check valve 15 as an orifice. The calculation formula F1 calculates the instantaneous discharge amount (flow rate or flow velocity) ΔQ1 using the differential pressure between the plunger chamber pressure Proom which is the pressure of the pressure chamber 53 and the rail pressure Pout which is the internal pressure of the common rail 60.

  The pressure downstream of the check valve 15 is substituted by the rail pressure Pout, assuming that the pressure drop in the high pressure supply pipe 16 is negligible compared to the pressure drop in the check valve 15. The rail pressure Pout is a value that can be measured by the rail pressure sensor 61. The flow coefficient Cq is an experimental value and is used as a known fixed value. The discharge valve opening area A is the orifice area (known) of the check valve 15. The fuel density ρ is a known fixed value. However, the plunger chamber pressure Proom is calculated by integrating (or integrating) the instantaneous change amount (change rate) ΔProom of the plunger chamber pressure.

  The instantaneous change amount ΔProom of the plunger chamber pressure can be calculated using calculation formulas F2 and F3. The calculation formula F2 is based on the same concept as the state equation of an ideal gas (compressible fluid). That is, the instantaneous change amount ΔProom of the plunger chamber pressure is calculated by dividing the fuel pressurization amount ΔQroom by the pressure chamber volume V which is the internal volume of the pressure chamber 53 and multiplying by the volume elastic coefficient κ. The pressure chamber volume V is an amount calculated based on the plunger stroke X1. The fuel pressurization amount ΔQroom is a virtual flow rate (flow velocity) that appears when the fuel corresponding to the decrease in the pressure chamber volume V flows.

  As the bulk modulus κ, the bulk modulus (known) of the fuel can be used. However, not only the bulk elastic coefficient of the fuel but also the expansion of the pressure chamber 53 due to the deformation of the cylinder wall surface 54 or the elastic deformation of at least one of the plungers 51 may be regarded as a part of the bulk elastic deformation of the fuel. That is, the expansion due to the elastic deformation of the pressure chamber 53 may be regarded as the compression of the fuel to determine the bulk elastic coefficient κ, and a predetermined fluid having the bulk elastic coefficient κ may be used instead of the fuel. By doing so, it is possible to easily realize calculation in consideration of expansion of the pressure chamber 53 due to elastic deformation. Elastic deformation can be determined by calculations, experiments, or the like using the finite element method.

  The calculation formula F3 is a calculation formula for calculating the fuel pressurization amount (flow velocity) ΔQroom. In the fuel pressurization amount ΔQroom, a decrease in the pressure chamber volume V is calculated as a product of the time differential value of the plunger stroke X1 and the pressure chamber area S1, and it is considered that fuel corresponding to the decrease has flowed in. On the other hand, when the pressure chamber volume V is decreased, a leak from the clearance Cr between the outer peripheral surface 55 and the cylinder wall surface 54 also occurs. Therefore, the leak amount (rate) ΔQ2 is subtracted from the above-described virtual flow rate. ing.

  The leak amount ΔQ2 can be calculated using the calculation formula F4. The calculation formula F4 is a calculation formula assuming a crevice flow of a cylinder (a laminar viscous flow). Since π × d (plunger diameter) is the outer peripheral length of the plunger 51, it is a known fixed value. The clearance amount Cr is a known fixed value between the outer peripheral surface 55 and the cylinder wall surface 54. Since μ is a viscosity coefficient of fuel, it is a known fixed value. X2 is the length (gap length) of the clearance gap Cr in the axial direction, and can be obtained by adding the distance L (see FIG. 1) to the plunger stroke X1. The clearance amount Cr may be handled as an amount that increases according to the plunger chamber pressure Proom.

  In the calculation formula F4, the reciprocal of the coefficient of the plunger chamber pressure Proom can also be grasped as the resistance value of the channel resistance. That is, since the gap between the cylinders can be grasped as a flow path and considered as the flow path resistance, the flow path resistance can also be handled as a function of the plunger stroke X1 as a value proportional to the flow path length X2.

  Since the cylindrical gap (clearance amount Cr) between the outer peripheral surface 55 and the cylinder wall surface 54 is a very narrow gap on the order of microns, the fluid flow therein is generally a laminar flow. This is because the Reynolds number Re available for turbulent flow discrimination is extremely small. As for the Reynolds number Re, it is known that the flow changes to turbulent flow as the value increases, but the characteristic length L is a gap in the calculation formula (= characteristic length L × characteristic speed v / dynamic viscosity coefficient ν). This is because the thickness is extremely small. However, in the case of turbulent flow, a well-known calculation formula for turbulent flow can be used, which is common in that the leak amount ΔQ is inversely proportional to the gap length X2.

  FIG. 4 is a flowchart showing the processing contents for calculating the discharge amount of the high-pressure pump 50. This calculation process is executed by the ECU 70 using a dedicated tool (for example, an AME-Sim model) or a numerical integration method (or an integration method). In the present embodiment, for the sake of easy understanding, the most simplified integration method will be described as an example. This integration method includes an iterative calculation process executed, for example, every 10 microseconds.

  In step S1, the ECU 70 inputs an initial value. The initial values are the initial pressure Proom0 of the pressure chamber 53 at the start of pressurization and the plunger stroke X1 of the plunger 51. Since the initial pressure Proom0 is at the start of pressurization, the gauge pressure becomes zero. The plunger stroke X <b> 1 is determined based on the amount of fuel sucked into the high-pressure pump 50 that is metered by the supply control valve 40.

  In step S2, ECU 70 calculates plunger pressure increase amount ΔProom using calculation formulas F2 to F4. The ECU 70 first calculates the fuel pressurization amount ΔQroom using the calculation formula F3. The integrated amount ΔX1 of the plunger stroke X1 is calculated as the plunger stroke X1 that advances in 10 microseconds based on the angular velocity ω of the cam 52 and the cam profile of the cam 52. On the other hand, since the initial pressure Proom0 is zero gauge pressure, the leak amount ΔQ2 is zero. Finally, the ECU 70 calculates the plunger pressure increase amount ΔProom using the calculated fuel pressurization amount ΔQroom.

  In step S3, the ECU 70 determines the plunger chamber pressure Proom by adding the plunger pressure increase amount ΔProom to the initial pressure Proom0 (gauge pressure zero). In addition, when calculating the plunger pressure increase amount ΔProom, the discharge amount to the common rail 60 is not taken into consideration as can be seen from the calculation formula F3. The reason will be described later.

  In step S4, the ECU 70 compares the plunger chamber pressure Proom and the rail pressure Pout. When the plunger chamber pressure Proom is equal to or lower than the rail pressure Pout, the ECU 70 proceeds to step S8 and skips steps S5 to S7. On the other hand, when the plunger chamber pressure Proom is larger than the rail pressure Pout, the ECU 70 advances the process to step S5. As described above, the measured value of the rail pressure sensor 61 (see FIG. 1) can be used as the rail pressure Pout.

  In step S5, the ECU 70 calculates an instantaneous fuel discharge amount ΔQ1 from the high-pressure pump 50 to the common rail 60. The calculation of the discharge amount is performed using the calculation formula F1. The instantaneous discharge amount ΔQ1 is the amount of fuel discharged to the common rail 60 in 10 microseconds.

  In step S6, the ECU 70 calculates a plunger pressure drop amount ΔProom. The plunger pressure drop amount ΔProom is a fluctuation amount of the plunger chamber pressure Proom that drops due to the discharge of the instantaneous discharge amount ΔQ1. The plunger pressure drop amount ΔProom can be calculated by substituting the instantaneous discharge amount ΔQ1 instead of the fuel pressurization amount ΔQroom using the calculation formula F2.

  In step S7, the ECU 70 determines the plunger chamber pressure Proom by subtracting the plunger pressure drop amount ΔProom from the plunger chamber pressure Proom (the determined value in step S3). Thus, in this calculation process, the plunger chamber pressure Proom increases due to the plunger 51 rising, the fuel discharge of the instantaneous discharge amount ΔQ1 to the common rail 60, and the plunger chamber pressure Proom decrease due to fuel discharge (pressure feeding). The behavior is modeled.

  However, in reality, the increase in the plunger chamber pressure Proom due to the increase in the plunger 51 occurs while being offset by the decrease in the plunger chamber pressure Proom due to the fuel discharge. However, the calculation error due to the difference between the actual behavior and the model can be made sufficiently small by appropriately setting the time interval of calculation processing (in this example, every 10 microseconds) to a small value. Thereby, the calculation formulas F2 and F3 are simplified to realize simple integration.

  Such calculation processing (steps S2 to S7) is continuously executed until the plunger 51 reaches the top dead center, and all the numerical values calculated when the top dead center is reached are cleared. Since this calculation process can be executed before the fuel discharge from the high-pressure pump 50 to the common rail 60 is actually started, the feed-forward control process for the fuel injection from the injectors 71 to 74 as described below. It can also be used.

  As described above, the discharge amount calculation process of the present embodiment calculates the amount of fuel that leaks from the cylindrical gap (clearance amount Cr) between the outer peripheral surface 55 and the cylinder wall surface 54, and supplies the leakage to the common rail 60. It is possible to calculate the fuel pumping amount (total discharge amount). Thereby, even if a leak increases as the injection pressure (accumulated pressure) of the common rail 60 increases, the calculation accuracy of the discharge amount (pressure feed amount) can be maintained.

  Furthermore, since the discharge amount calculation process of the present embodiment can calculate the instantaneous discharge amount ΔQ1 using the differential pressure between the plunger chamber pressure Proom and the rail pressure Pout that is the internal pressure of the common rail 60, the rail pressure Pout is It is possible to accurately calculate the discharge during the changing injection period. The inventor of the present invention has newly created an injection amount correction process utilizing such characteristics.

(Details of injection amount correction processing)
FIG. 5 is an explanatory diagram showing a state in which the injection amount increases due to the overlap of the injection period of the injector and the pressure feeding period (discharge period) to the common rail. FIG. 5 (a) shows a synchronous system in which a pumping overlap period that is an overlap of both periods does not occur. FIG. 5 (b) shows an asynchronous system in which a pumping overlap period occurs. In the drawing, # 1, # 2, # 3, and # 4 are numbers of the cylinders of the engine 80.

  In this embodiment, synchronous and asynchronous are concepts that focus on the synchronism between the injection period of the injectors 71 to 74 and the pumping period to the common rail 60. On the other hand, the cam 52 that drives the high-pressure pump 50 is driven by a crankshaft (not shown) of the engine 80, and the rotation of the cam 52 and the crankshaft is synchronized. Thereby, ECU70 can predict the relationship between the timing of an injection period and a pumping period also in an asynchronous system.

  In the synchronous system shown in FIG. 5A, the number of pumping pumps is four while the cycle of the engine 80 is completed and the injection of all four cylinders is completed. In FIG. 5A, for example, two high-pressure pumps 50 having a well-known configuration are sandwiched from both sides of the cam 52, and four times of pumping is performed by two rotations of the cam 52. On the other hand, since the engine 80 is a four-stroke internal combustion engine, one cycle is completed every time the crankshaft rotates twice, and the injection of all cylinders is completed. That is, the rotation ratio between the pump speed NP and the engine speed Ne is 1: 1, and the crankshaft makes one revolution every time the cam 52 makes one revolution.

  The ECU 70 can adjust the timing of the drive current waveform based on the cam lift of the pump to synchronize the injection period and the pumping period of the pump. Thereby, since the pumping period of the pump can be excluded from the injection period, it is possible to eliminate the variation in the injection amount due to the overlap of the injection period and the pumping period of the pump (pressure overlapping period).

  In the synchronous system shown in FIG. 5B, the rotation ratio between the pump rotational speed NP and the engine rotational speed Ne is 3: 4, and each time the cam 52 rotates three times, the crankshaft rotates four times. In this example, while the cycle of the engine 80 is completed and the injection of all four cylinders is completed, the pumping frequency is 3 times. Such an example occurs, for example, by reducing the number of pumping operations in consideration of the excessive capacity of the high-pressure pump 50 when the high-pressure pump 50 is shared by a relatively small engine.

  In such an asynchronous system, the ECU 70 cannot synchronize the injection period and the pumping period by adjusting the timing of the drive current waveform based on the cam lift of the pump. As a result, the injection amount variation (increase) due to the overlap of the pumping periods (pressure overlap) occurs, resulting in a difference in the injection amount between the cylinders.

  FIG. 6 is an explanatory diagram showing the content of the injection correction of this embodiment in comparison with a comparative example (the above-described example). As shown in the comparative example, in the asynchronous system, it can be seen that the injection amount is increased due to the overlap of pumping. This increase is due to the fact that the rail pressure rises due to the pumping of fuel from the high-pressure pump 50 in spite of the assumption that the rail pressure drops due to the fuel injection when the drive current waveform is injected. Due to

  In the present embodiment, this is realized by suppressing the overlapping discharge amount by performing waveform correction (TQ correction, that is, correction for accelerating the valve closing timing) that assumes an increase in rail pressure due to pump pumping. . The overlapping discharge amount means an increase in the injection amount due to pumping by the pump.

  FIG. 7 is a flowchart showing the processing contents for executing the injection amount correction. FIG. 8 is a block diagram showing the contents of the main processing of this processing. FIG. 9 is a diagram illustrating a calculation formula used for injection amount correction. This calculation process is executed by the ECU 70. This process is a process performed at a constant cycle for each cylinder of the engine 80.

  In step S11, the ECU 70 determines whether or not the operating state of the engine 80 is steady. As a result of the processing, if it is determined that the vehicle is in an unsteady state where the accelerator is depressed and the vehicle is accelerating, the processing proceeds to step S12 and all correction processing is skipped. This is because, in the unsteady state, the injection timing fluctuates every moment, so that the prediction that is the premise of the feedforward control process may be disrupted and a negative effect may be caused by the correction process. On the other hand, if it is determined to be steady, the process proceeds to step S13 and step S14.

  ECU70 performs the process of step S13 and step S14 in parallel. In step S13, an injection period is calculated. The injection period is determined by the rotational speed Ne of the engine 80 and the load. Specifically, for example, the start of the injection period is determined by the rotational speed Ne of the engine 80, and the end of the injection period is determined by the load. On the other hand, in step S14, a pump discharge period is calculated. The start of the pump discharge period is determined based on the discharge amount of the high-pressure pump 50 (see step S14 in FIG. 8).

  In step S15, the ECU 70 determines whether or not there are an injection period and a discharge period. In the present embodiment, the cylinders # 1, # 2, and # 3 always overlap. On the other hand, the # 4 cylinder does not overlap. Therefore, in the engine 80 of the present embodiment, step S15 may be considered unnecessary, but is a necessary step depending on the rotation ratio between the cam 52 and the crankshaft and the injection characteristics of the engine 80.

  In step S16, the ECU 70 calculates an overlap period. The overlap period is calculated using the calculated values in step S13 and step S14. Thereby, the start and end of the overlap period are calculated.

  In step S <b> 17, the ECU 70 calculates an overlapping discharge amount Qout. The overlapping discharge amount Qout can be calculated by using the calculation method F5 (see FIG. 9) and the processing method described above (FIGS. 3 and 4). At this time, the calculation accuracy may be improved by calculation that also takes into account the fluctuation (rise) of the rail pressure Pout caused by the overlapping discharge amount Oout, or the rail pressure Pout caused by the overlapping discharge amount Oout. It is also possible to use a simple calculation method that does not take into account fluctuations (rise).

  In step S18, the ECU 70 determines whether there is feedback. This determination is made based on a feedback flag described later. If there is feedback, the process proceeds to step S21 after the feedback amount Qfb is added (step S19). On the other hand, if there is no feedback, the feedback amount Qfb is not added (step S20), and the process proceeds to step S21.

  In step S21, the ECU 70 calculates the rail pressure change amount ΔPout. The rail pressure change amount ΔPout can be calculated using a calculation formula F6 (see FIG. 9). The calculation formula F6 is a formula based on the same concept as the calculation formula F2 described above. The rail pressure change amount ΔPout can be calculated, for example, based on the addition amount (or non-addition) of the overlap discharge amount Oout and the feedback amount Qfb (see FIG. 8).

  In step S22, the ECU 70 determines a correction amount TQc for the injection period TQ. The correction amount TQc is determined using a map prepared in advance (see step S22 in FIG. 8). This map is obtained by experiments. As a result, preparation for the injection amount correction processing by feedforward control is completed before injection.

  In step S23, the ECU 70 executes an injection process. The injection process is executed by driving using the drive current waveform corrected using the correction amount TQc. The correction amount TQc is used for determining the shortening amount of the injection period.

  In step S24, the ECU 70 measures the rail pressure before and after injection. The actual measurement of the rail pressure is performed using the rail pressure sensor 61. The actual measurement of the rail pressure is executed to realize a feedback process (see steps S24 and S25 in FIG. 8) for the injection amount correction in the next cycle.

  In step S25, the ECU 70 executes a cylinder difference detection process. In the cylinder difference detection process, the measured value Qi (reference injection amount) of the cylinder # 4 that does not overlap the pumping period (discharge period) to the high-pressure pump 50 and the injection period, and other # 1 to # 1 that overlap. This is a process of comparing the measured value Q′i (corrected injection amount) of the injection amount of the cylinder # 3 and detecting the cylinder difference in the injection amount due to the presence or absence of overlap. The injection amount of each cylinder is calculated based on the measured value of the pressure drop of the internal fuel in the common rail 60.

FIG. 10 is a chart showing the pressure drop of the internal fuel in the common rail 60 during the non-overlapping and overlapping injections. When there is no overlap, the internal fuel pressure in the common rail 60 drops from the injection pressure P1 at the start of injection to the injection pressure P2 at the end of injection. Since this pressure is caused by the injection, the injection amount can be measured using this pressure drop amount. Specifically, the injection amount Qi of the cylinder # 4 that does not overlap is calculated by the ECU 70 using the calculation formula F7 of FIG.
On the other hand, at the time of duplication, the internal fuel pressure in the common rail 60 drops from the injection pressure P′1 at the start of injection to the injection pressure P′2 at the end of injection. However, since the pressure drop amount is reduced by ΔPout caused by the overlapping discharge amount Oout, ΔPout is added. As a result, the actual measured value Q′i of the cylinders # 1 to # 3 with the overlap is calculated by the ECU 70 using the calculation formula F8 of FIG.

  The cylinder difference detection process is based on the injection amount Qi of the cylinder # 4 that has no overlap, and detects a difference between the reference value and each of the injection amounts Q′i of the cylinders # 1 to # 3 that have an overlap (see FIG. 9 is a process for calculating the feedback amount Qfb. As a result, the feedback amount Qfb is calculated for each of the cylinders # 1 to # 3. The injector 74 that injects fuel into the # 4 cylinder that does not overlap is also referred to as a reference injector. It is also called the injectors 71 to 73 for injecting fuel into the # 1 to # 3 cylinders that overlap, and the correction target injector.

  In step S26, the ECU 70 determines whether or not the feedback amount Qfb is within a threshold value (that is, within a predetermined range). As a result of the determination, when the feedback amount Qfb is within the threshold value, the feedback flag is set to “with feedback”, and the feedback amount Qfb is stored in a memory (not shown) of the ECU 70. On the other hand, when the feedback amount Qfb is other than the threshold value, the feedback flag is set to “no feedback”.

  The feedback flag is used in the above-described step S18 (determination of presence / absence of feedback). The feedback amount ΔQfb is used in step S19 (feedback amount addition) described above. Thereby, in the next injection, it is possible to inject with a drive current waveform corrected based on the actual measurement value by using the feedback amount ΔQfb.

  The present inventor has found that the correction using the feedback amount ΔQfb has a remarkable effect that it can be used to compensate for the deviation of the feedforward correction amount due to the change in the actual usage environment (fuel viscosity).

  As described above, the injection amount correction processing according to the present embodiment predicts the pumping amount (discharge amount) to the common rail 60 even if the pumping period to the common rail 60 and the injection period overlap, and performs feedforward correction to overlap. It is possible to compensate for the injection error caused by the pressure feeding. Furthermore, since the injection amount correction process of the present embodiment can generate the feedback amount ΔQfb by the cylinder difference detection process by monitoring the injection pressure at the time of injection, it also compensates for the prediction error of the feedforward correction. It has also succeeded in achieving highly reliable and accurate correction.

(Other embodiments)
The present invention is not limited to the above embodiment, and may be implemented as follows, for example.

  (1) In the above embodiment, the rotation ratio between the pump rotational speed NP and the engine rotational speed Ne is a system of 3: 4. However, the present invention is not limited to this, and the present invention provides an injection period of the injector and a pumping period of the pump. Can be widely applied to overlapping systems.

  (2) In the above embodiment, the metering method of the high-pressure pump is throttling adjustment, but it can also be applied to other metering methods such as an overflow method.

  DESCRIPTION OF SYMBOLS 10 ... Common rail type fuel injection system, 16 ... High pressure supply piping, 20 ... Fuel tank, 30 ... Feed pump, 40 ... Supply control valve, 50 ... High pressure pump, 51 ... Plunger, 52 ... Cam, 53 ... Pressure chamber, 54 ... Cylinder wall surface, 60 ... common rail, 61 ... rail pressure sensor, 70 ... ECU.

Claims (3)

A pressure accumulator for accumulating fuel;
A cylinder having a pressure chamber formed therein;
A plunger that performs a pressurization movement that is a movement in a pressurization direction in the cylinder, and that pumps fuel to the pressure accumulating unit by causing a volume change in the pressure chamber by the pressurization movement;
A control unit for controlling the pumping amount of fuel to the pressure accumulating unit;
With
The controller estimates the amount of fuel leakage from the gap between the inner circumferential surface of the pressure chamber and the outer circumferential surface of the plunger, and the estimated leakage amount and the stroke of the plunger during the pressurizing movement the use and change in volume of the pressure chamber, the have a pumping quantity calculation unit configured to calculate the pumping amount in accordance with,
The pumping amount calculation unit is a fuel pumping system that calculates a pumping speed to the pressure accumulating unit based on a difference between a plunger chamber pressure that is a pressure in the pressure chamber at the time of pressurization and a pressure of the pressure accumulating unit .   2. The fuel pumping system according to claim 1, wherein the pumping amount calculation unit calculates a resistance value with respect to a flow of fuel flowing through the gap based on the stroke, and estimates the leakage amount using the resistance value. The pumping amount calculation unit regards the fuel as a predetermined compressive fluid, and uses the bulk elastic modulus of the predetermined compressive fluid to indicate the pressure in the pressure chamber during the pressurization caused by the pressurization movement. Calculate the increase in plunger chamber pressure,
It said predetermined compressible fluid, at least one of the elastic deformation of the cylinder and the plunger, according to claim 1 or 2 having a bulk modulus that is previously determined based on at least one of the volume elastic deformation of the fuel Fuel pumping system.

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