JP2011085081A - Method for determining engine misfire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently execute operation control such as on exhaust gas, fuel economy, combustion noise of an engine, and the like by improving accuracy of engine misfire determination. <P>SOLUTION: Temperature of an inside of a cylinder corresponding to crank angle is calculated by using compression pressure provided by a cylinder pressure sensor and differential value to crank angle change by using the temperature of the inside of the cylinder is calculated as change quantity of the temperature of the inside of the cylinder. Then, an engine misfire criterion value preset for each operation condition is calculated, and engine misfire is determined by comparing the change quantity of the temperature of the inside of the cylinder determined with the engine misfire determination threshold. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for performing misfire determination using an in-cylinder temperature of an engine.

  2. Description of the Related Art Conventionally, various methods for performing engine misfire determination in internal combustion engines (hereinafter referred to as “engines”) mounted on vehicles are known.

  For example, in Patent Document 1, the in-cylinder temperature of a gasoline engine is measured, the maximum value and the crank angle at the time when the maximum value is detected are compared with a threshold value for misfire determination, and they are within the threshold value. If it is, it is determined that there is a misfire.

  It is also conceivable to perform correction control such as the fuel injection timing of the engine when it is determined that a misfire has occurred, using such a misfire determination of the engine.

  However, in the misfire determination described in Patent Document 1, since the combustion temperature is relatively low depending on the operating state of the engine, it may be erroneously determined to be misfire, and correction control such as injection timing may be performed.

  As described above, the conventional engine misfire determination and control method has a low misfire determination accuracy, and there has been a problem that appropriate correction control cannot be performed based on such misfire determination.

  In particular, in a diesel engine, it is difficult to predict misfire (combustion instability) in advance. Therefore, advance the injection timing in advance and reduce the EGR amount (EGR rate) accordingly. I try to suppress misfire by putting it on.

  However, the combustion noise worsens with an increase in the amount of advancement of the injection timing and a decrease in the EGR rate, and there is a possibility that the emission of nitrogen oxides will increase.

  In addition, the ease of misfire also varies depending on the cetane number of the fuel used in the engine. A general engine is misfire-matched to the lowest cetane number in the input market in order to prevent misfire even when fuel with a wide range of cetane numbers distributed in the market is used. Therefore, even when fuel with a high cetane number is used, the injection timing is advanced in advance so that the engine does not misfire, or the EGR rate is reduced. Therefore, even in this case, problems such as deterioration of combustion noise and increased emission of nitrogen oxides may occur.

Japanese Patent Laid-Open No. 3-206361

  An object of the present invention is to improve the accuracy with which misfire determination is performed in order to eliminate the above-described problems, and to efficiently perform engine operation control.

  The present invention takes the following means in order to solve the above-described problems. That is, the engine misfire determination method according to the present invention includes an in-cylinder temperature detecting means for detecting an in-cylinder temperature and a crank angle detecting means for detecting a crank angle. The amount of change in the in-cylinder temperature with respect to the change in the crank angle calculated by the angle is compared with a predetermined misfire determination threshold value to perform misfire determination.

  If this is the case, the misfire of the engine is more reliably determined from the amount of change in the in-cylinder temperature with respect to the change in the crank angle calculated using the in-cylinder temperature and the crank angle, that is, the differential coefficient indicating the temperature change in the cylinder. Can be judged. And the misfire tendency of an engine can be determined uniquely and, therefore, an engine can be controlled efficiently. In addition, the engine misfire determination can be performed regardless of the fuel property, that is, the high cetane number of the fuel.

  As a result of various experiments conducted by the inventors to improve the accuracy of performing the misfire determination, in other words, data as shown in FIG. 3 was obtained. The data shown in FIG. 3 is obtained by taking the crank angle (° C. A) with 0 ° C. as the top dead center on the horizontal axis and the temperature (° C.) on the vertical axis. The temperature history in a cylinder in the combustion state when each parameter of is changed is shown. In this figure, the solid line shows the in-cylinder temperature change when each parameter is given a constant that does not misfire in the actual vehicle worst specifications, and the broken line shows the in-cylinder temperature when the constant that gives misfire in the actual vehicle is given to each parameter. It shows a change. The actual vehicle's worst specifications here use the fuel that is likely to misfire, and further assume the conditions that are most likely to misfire, taking into account variations in compression ratio, fuel injection timing, fuel injection amount, turbocharger, air flow meter, etc. It is.

  When these solid lines are compared with the broken line, the differential coefficient dt / dθ according to the crank angle of the in-cylinder temperature is always 0 or more in the solid line. On the other hand, the broken line always has a region where the differential coefficient dt / dθ due to the crank angle of the in-cylinder temperature is less than zero. That is, even if there are variations among individuals such as engine water temperature, oil temperature, intake air temperature, compression ratio, fuel injection, fuel injection timing, intake air pressure, and / or internal and external EGR rate, It has become clear that it is possible to correctly determine whether or not the fire has misfired.

  That is, since the misfire determination method according to the present invention is as described above, it is possible to improve the accuracy of performing the misfire determination without being affected by changes in the engine environment. Therefore, since it is not necessary to greatly reduce the EGR rate or advance the injection timing with an expectation, it is possible to improve the fuel efficiency and to efficiently control the engine operation after the misfire determination, such as suppressing the generation of harmful substances. It can be carried out.

  ADVANTAGE OF THE INVENTION According to this invention, the precision which performs misfire determination can be improved and, therefore, engine operation control can be performed efficiently.

1 is a schematic configuration diagram of an engine according to an embodiment of the present invention. The flowchart which shows the control procedure of the embodiment. The graph which shows the temperature course in the cylinder of the same embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a configuration of a diesel engine (hereinafter referred to as “engine”) 1 which is an internal combustion engine in the present embodiment. The engine 1 mounted on a vehicle or the like includes a plurality of cylinders 7 (only one cylinder is shown in the figure), an injector 73 that injects fuel into each cylinder 7, and intake air to each cylinder 7. An intake path 3 for supplying, an exhaust path 4 for discharging exhaust gas from each cylinder 7, a variable capacity turbocharger 2 that is a set of a drive turbine 22 and a compressor 21, an intake path 3 and an exhaust path 4 And an EGR device 5 that recirculates the exhaust gas.

  In the vicinity of a crankshaft (not shown) that rotates in synchronization with a camshaft (not shown) provided in the cylinder 7, a crank angle sensor 85 for detecting the rotation angle is attached. An in-cylinder pressure sensor 86 for detecting the in-cylinder pressure at the time of combustion is attached to the combustion chamber provided in the cylinder 7.

  The intake path 3 takes in air from the outside and guides it to the intake port 71 of the cylinder 7. On the intake path 3, an air cleaner 31, a compressor 21, an intercooler 32, and a surge tank 33 are arranged in this order from the upstream. In addition, an intake pressure sensor 81 for detecting the pressure in the surge tank 33 and an intake air temperature sensor 82 for detecting the temperature of intake air are provided on the intake path 3.

  The exhaust path 4 guides exhaust gas generated as a result of burning fuel in the cylinder 7 from the exhaust port 72 of the cylinder 7 to the outside.

  The turbocharger 2 is configured such that the drive turbine 22 and the compressor 21 are connected coaxially and interlocked. Then, the drive turbine 22 is rotationally driven by using the energy of the exhaust gas, and the compressor 21 is pumped by using the rotational force, whereby the intake air is pressurized and compressed, that is, supercharged and sent to the cylinder 7. .

  The EGR device 5 includes an EGR passage 51 through which exhaust gas flows and an EGR valve 52 that opens and closes the EGR passage 51. An EGR cooler 53 is disposed on the EGR passage 51.

  An electronic control unit (ECU) 6 that controls the engine 1 is a microcomputer system having a CPU 61, a memory 62, an input interface 63, an output interface 64, and the like. The input interface 63 includes a boost pressure signal a output from a sensor 81 that detects the pressure in the intake pipe, an intake air temperature signal b output from the intake temperature sensor 82 that detects the temperature in the intake pipe, and a sensor that detects the engine speed. 83, an accelerator signal d output from a sensor 84 for detecting the accelerator opening, that is, an accelerator pedal depression amount, and a crank angle sensor 85 for detecting the rotational state of the engine 1. A crank angle signal e, a combustion pressure signal f output from the in-cylinder pressure sensor 86, and the like are input. On the other hand, from the output interface 64, a fuel injection signal g corresponding to the injection amount determined from various conditions such as the detected engine speed NE and the accelerator pedal depression amount is output to the injector 73 and to the EGR valve 52. Thus, an open / close signal h is output.

  The CPU 61 interprets and executes a program stored in the memory 62 in advance, and controls the operation of the engine 1. The CPU 61 obtains various information a, b, c, d, e, f and the like necessary for operation control of the engine 1 through the input interface 63, and based on them, the fuel injection amount, the fuel injection timing, the EGR valve 52, and the like. The valve opening time is calculated and various control signals g, h, etc. corresponding to the calculation result are applied via the output interface 64.

  In the fuel injection, the injector 73 divides the injection into a plurality of times during one cycle, that is, the pilot injection that injects a small amount of fuel at an early stage to smooth the start of combustion and the pressure rise, and the subsequent main injection. Combustion control is performed to perform injection.

  In the engine misfire determination method and the control based on the determination in this embodiment, the misfire determination is performed using the amount of change in the in-cylinder temperature with respect to the change in the crank angle, that is, the differential coefficient dt / dθ depending on the crank angle of the in-cylinder temperature. Is. If misfire is determined, correction control is performed on the injection timing, etc., so that misfire determination can be performed accurately due to variations in engine operating conditions, and exhaust emissions, fuel consumption, combustion noise, etc. It allows you to drive with value. Hereinafter, the engine misfire determination method and the outline procedure of the correction control based on the determination will be described with reference to the flowchart shown in FIG.

  The misfire determination and control program is repeatedly executed when the engine 1 is operating.

  First, the in-cylinder temperature t (θ) at each crank angle θ is calculated (step S1). Specifically, the in-cylinder temperature t (θ) before main fuel injection is performed from the injector 73 is calculated. A crank angle sensor 85 is used as a crank angle detecting means for detecting the crank angle θ at that time, and a cylinder pressure sensor 86 attached to the combustion chamber is used as a cylinder temperature detecting means for detecting a cylinder temperature t (θ). The in-cylinder temperature t (θ) when the crank angle is θ ° C. A is calculated using the combustion pressure obtained from the in-cylinder pressure sensor 86.

  Thereafter, using the in-cylinder temperature t (θ) calculated in step S1, a change amount dt / dθ of the in-cylinder temperature t (θ) with respect to the change in the crank angle θ is calculated (step S2). Specifically, a value obtained by differentiating the in-cylinder temperature t (θ) by the crank angle θ is calculated.

  Next, a misfire determination threshold value K is calculated (step S3). This misfire determination threshold value K is preset for each operating condition, and is expressed by the following equation.

K = KEGR * KQN * KTP (Formula 1)
KEGR in (Expression 1) is a value that is determined one-dimensionally depending on the value of the EGR rate (%). When this EGR rate increases, the engine 1 tends to misfire more easily. Therefore, there is a relationship that when the value of KEGR increases, the misfire determination threshold value K also increases.

Further, KQN in (Equation 1) is a value determined depending on two values of the fuel injection amount Qv (mm ³ / time) per one fuel injection and the engine speed NE (rpm). The fuel injection amount Qv is determined from various conditions such as the engine speed NE detected using the sensor 83.

  Similarly, KTP in (Equation 1) is a value determined depending on two values of the intake pipe pressure PIM (kpa) and the intake air temperature THA (K). The intake pipe pressure PIM is measured using an intake pressure sensor 81 provided on the intake path 3, and the intake air temperature THA is measured using an intake temperature sensor 82 provided on the intake path 3.

  Next, the change amount dt / dθ of the in-cylinder temperature t (θ) with respect to the change in the crank angle θ calculated in step S2 is compared with the misfire determination threshold value K calculated in step S3 (step S4). As a result, when the change amount dt / dθ is smaller than the misfire determination threshold value K, it is determined that the engine 1 has misfired. Therefore, the process proceeds to step S5 and subsequent steps described below. On the other hand, when the change amount dt / dθ is equal to or larger than the misfire determination threshold value K, it is determined that the engine 1 has not misfired. Therefore, correction control such as injection timing is not performed.

  Steps S5 to S8 described below are steps for calculating a correction coefficient for correcting a normal calculation value in step S9.

  In step S5, the fuel injection timing advance correction coefficient AK is calculated from the one-dimensional map. The fuel injection timing advance correction coefficient AK is used to advance the normal calculated value aINJ calculated based on the engine speed NE, the required load, and the like.

  Similarly, in step S6, the EGR reduction coefficient AE is calculated from the one-dimensional map. The EGR reduction coefficient AE is used to reduce the normal calculated value aEGR.

  In step S7, the boost pressure increase coefficient AP is calculated from the one-dimensional map. The supercharging pressure increase coefficient AP is used to increase and correct the normal calculated value aPIM.

  In step S8, the pilot amount increase coefficient APL is calculated from the one-dimensional map. This pilot amount increase coefficient APL is used to increase the normal calculation value aPL.

  After the determination steps of steps S5 to S8 are completed, final values FINJ, FEGR, FPIM, FPL is obtained, and the fuel injection timing, EGR rate, supercharging pressure, and / or pilot amount are corrected based on this final value (step S9). Specifically, the final values are calculated as FINJ = aINJ * AK, FEGR = aEGR * AE, FPIM = aPIM * AP, and FPL = aPL * APL. If it is determined that the engine 1 has misfired, the fuel injection timing is advanced (advanced). Further, correction control is performed so that the EGR rate is decreased, the supercharging pressure is increased, and the pilot amount is increased.

  Thus, as a misfire determination method of the engine 1, the change amount dt / dθ of the in-cylinder temperature with respect to the change in the crank angle calculated by the in-cylinder temperature and the crank angle is set to the misfire determination threshold value determined in advance by the fuel injection amount or the like. Since misfire determination is performed in comparison with K, the determination accuracy can be improved.

  Moreover, since the problem that the misfire determination accuracy is low in the diesel engine 1 can be solved, it is not necessary to reduce the EGR rate or to advance the injection timing greatly, so that the fuel consumption is improved and the generation of harmful substances. It is possible to efficiently control the operation of the engine 1 after the misfire determination.

  Furthermore, by incorporating misfire determination with reference to the value of dt / dθ into the automatic calibration program using the design of experiment, optimum parameters that do not cause misfire (EGR valve opening, injection timing, injection pressure, pilot injection amount, pilot interval) Etc.) can be determined. Similar values can also be used to adapt map values.

  The present invention is not limited to the embodiment described above.

  The internal combustion engine is not limited to the diesel engine described above. This misfire determination method and control method can be applied to a gasoline engine, in particular, a direct injection gasoline engine or the like.

  The in-cylinder temperature detection means is not limited to the in-cylinder pressure sensor. For example, even if the in-cylinder temperature is detected by a CARS temperature measurement method (a method of measuring the CARS spectrum of the target molecule and obtaining the vibration and rotation temperature of the target molecule from the spectrum shape) of measuring the inside of the cylinder with a laser. Good. Further, a temperature sensor for detecting the in-cylinder temperature may be provided in the cylinder, and thereby the in-cylinder temperature may be directly measured.

  The correction target is not limited to correcting all of the injection timing, EGR rate, boost pressure, and pilot injection amount calculation values as described in the present embodiment, and one or a plurality of calculation values among these are calculated. You may correct | amend.

  Furthermore, the calculation method of the misfire determination threshold value K is not limited to that of the present embodiment, and various changes can be made.

  In addition, various changes may be made without departing from the spirit of the present invention.

  1 ... Diesel engine

Claims (1)

In an engine comprising an in-cylinder temperature detecting means for detecting an in-cylinder temperature and a crank angle detecting means for detecting a crank angle,
A misfire determination method for an engine, wherein a misfire determination is performed by comparing a change amount of the in-cylinder temperature with respect to a change in the crank angle calculated based on the in-cylinder temperature and the crank angle with a predetermined misfire determination threshold value.

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