JP2009144634A - Fuel cetane number estimation device for compression ignition type internal combustion engine, and control device for compression ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more accurately estimate a cetane number of a fuel of a compression ignition type internal combustion engine with a less operation amount. <P>SOLUTION: In step S101, a cetane number estimation injection control mode for searching a fuel injection timing Tinj in which ΔP/ΔCA=a is effected is executed where difference of an in-cylinder pressure peak value P2 after compression top dead center caused by combustion by fuel injection (main injection) and an in-cylinder pressure peak value P1 at the compression top dead center caused by compression of an in-cylinder gas by piston motion or combustion by pilot injection before the main injection or its neighborhood is represented by ΔP and difference of crank angles CA2, CA1 corresponding to the respective in-cylinder pressure peak values P2, P1 is represented by ΔCA. In step S102, the cetane number CN of the fuel is estimated based on the fuel injection timing Tinj in which ΔP/ΔCA=a searched in execution of the cetane number estimation injection control mode is effected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a device for estimating the cetane number of a fuel of a compression ignition type internal combustion engine, and a control device for a compression ignition type internal combustion engine including the device.

  A technique for estimating the cetane number of fuel of a compression ignition type internal combustion engine is disclosed in Patent Document 1 below. In Patent Document 1, fuel injection into a cylinder is divided into main injection and pilot injection preceding this main injection. Then, the heat generation rate due to the combustion of the pilot-injected fuel is calculated using the in-cylinder pressure, and the cetane number of the fuel is estimated based on the time when the maximum value of the heat generation rate is shown or when the heat generation rate starts to rise. . The heat generation rate dQ / dθ used for estimating the cetane number can be calculated by the following equation (1) using the in-cylinder pressure P. In equation (1), A is a constant, κ is a specific heat ratio, θ is a crank angle, and V is a combustion chamber volume (determined by the crank angle θ).

  dQ / dθ = A / (κ−1) · (V · dP / dθ + κ · P · dV / dθ) (1)

JP 2006-226188 A

  In Patent Document 1, since the amount of calculation when calculating the heat release rate dQ / dθ using the in-cylinder pressure P increases, the amount of calculation necessary for estimating the cetane number of the fuel increases and the calculation time increases. To do. Further, when calculating the heat generation rate dQ / dθ using the in-cylinder pressure P, it is necessary to calculate the differential value dP / dθ of the in-cylinder pressure, and therefore included in the calculated heat generation rate dQ / dθ. As a result, the estimation accuracy of the cetane number of the fuel decreases. When the estimation accuracy of the cetane number of the fuel decreases, the combustion noise of the compression ignition type internal combustion engine increases or the combustion tends to become unstable.

  An object of the present invention is to estimate the cetane number of a fuel of a compression ignition type internal combustion engine more accurately with a smaller calculation amount. Another object of the present invention is to realize reduction of combustion noise and stabilization of combustion in a compression ignition type internal combustion engine.

  The fuel ignition cetane number estimation device for a compression ignition type internal combustion engine and the control device for a compression ignition type internal combustion engine according to the present invention employ the following means in order to achieve at least a part of the above-described object.

  A fuel cetane number estimation device for a compression ignition type internal combustion engine according to the present invention is a device for estimating the fuel cetane number of a compression ignition type internal combustion engine that injects fuel into a cylinder and self-ignites, An in-cylinder pressure detection unit that detects a crank angle; a fuel injection control unit that performs fuel injection control; and a cetane number estimation unit that estimates a cetane number of fuel. When estimating the cetane number, the fuel injection control unit determines that the cylinder pressure peak value after compression top dead center due to combustion by fuel injection and the cylinder gas compression by piston motion or the pilot before fuel injection. The difference from the cylinder top pressure peak value at or near the compression top dead center due to combustion by injection is ΔP, the crank angle difference corresponding to each cylinder pressure peak value is ΔCA, and a is a predetermined value. Then, in the cylinder A cetane number estimation injection control mode for searching for the fuel injection timing at which ΔP / ΔCA = a is substantially satisfied is executed based on the in-cylinder pressure detected by the pressure detector and the crank angle detected by the crank angle detector. The cetane number estimation unit estimates the cetane number of the fuel based on the fuel injection timing at which ΔP / ΔCA = a found when the cetane number estimation injection control mode is executed. .

  According to the present invention, based on the fuel injection timing at which ΔP / ΔCA = a is substantially established by utilizing the fact that the fuel injection timing at which ΔP / ΔCA = a is substantially established changes according to the cetane number of the fuel. By estimating the cetane number of the fuel, the cetane number of the fuel can be estimated without calculating the differential value of the in-cylinder pressure and the heat generation rate. Even if there is a shift in the mounting position of the crank angle sensor, there is almost no error due to the shift in the mounting position of the sensor in the difference in the crank angle, so the crank angle corresponding to each in-cylinder pressure peak value that is easier to detect By calculating the difference ΔCA, it is possible to estimate the cetane number that is hardly affected by the displacement of the mounting position of the crank angle sensor. Therefore, the cetane number of the fuel of the compression ignition type internal combustion engine can be estimated more accurately with a smaller amount of calculation.

  In one aspect of the present invention, by setting the predetermined value a to a negative value, it is possible to increase the sensitivity of the fuel injection timing at which ΔP / ΔCA = a is substantially satisfied with respect to the change in the cetane number. The estimation accuracy of the price can be further increased.

  In one aspect of the present invention, a cetane number characteristic storage unit that stores the relationship between the cetane number of fuel and the fuel injection timing at which ΔP / ΔCA = a is substantially satisfied is provided, and the cetane number estimation unit stores the cetane number characteristic storage. It is preferable to estimate the cetane number of the fuel by calculating the cetane number of the fuel corresponding to the timing of the fuel injection searched during the execution of the cetane number estimation injection control mode. is there.

  A fuel cetane number estimation device for a compression ignition type internal combustion engine according to the present invention is a device for estimating the fuel cetane number of a compression ignition type internal combustion engine that injects fuel into the cylinder and ignites itself, An in-cylinder pressure detection unit that detects pressure, a fuel injection control unit that performs fuel injection control, and a cetane number estimation unit that estimates the cetane number of the fuel. The injection control unit has a cylinder pressure peak value after compression top dead center due to combustion by fuel injection and compression top dead center due to compression of cylinder gas by piston motion or combustion by pilot injection before fuel injection. If the difference from the in-cylinder pressure peak value at or near the point is ΔP, a cetane for searching for the fuel injection timing at which ΔP = 0 is substantially established based on the in-cylinder pressure detected by the in-cylinder pressure detecting unit. Injection control mode for price estimation The cetane number estimating unit estimates the cetane number of the fuel based on the fuel injection timing at which ΔP = 0, which is found when the cetane number estimation injection control mode is executed, is substantially satisfied.

  According to the present invention, by utilizing the fact that the fuel injection timing at which ΔP = 0 is substantially satisfied changes according to the cetane number of the fuel, the fuel cetane is based on the fuel injection timing at which ΔP = 0 is approximately satisfied. By estimating the value, the cetane number of the fuel can be estimated without calculating the differential value of the in-cylinder pressure and the heat generation rate. The fuel injection timing at which the difference ΔP of the in-cylinder pressure peak value becomes substantially zero even if the gain of the in-cylinder pressure sensor is deviated and an error occurs in the in-cylinder pressure detected by the in-cylinder pressure sensor. By searching for cetane, it is possible to estimate the cetane number that is hardly affected by the gain deviation of the in-cylinder pressure sensor. Therefore, the cetane number of the fuel of the compression ignition type internal combustion engine can be estimated more accurately with a smaller amount of calculation.

  In one aspect of the present invention, a cetane number characteristic storage unit is provided that stores a relationship between the cetane number of fuel and the fuel injection timing at which ΔP = 0 is substantially satisfied, and the cetane number estimation unit is provided in the cetane number characteristic storage unit. In the stored relationship, it is preferable to estimate the cetane number of the fuel by calculating the cetane number of the fuel corresponding to the fuel injection timing searched when the cetane number estimation injection control mode is executed.

  A control device for a compression ignition type internal combustion engine according to the present invention is a control device for a compression ignition type internal combustion engine comprising the fuel cetane number estimation device for a compression ignition type internal combustion engine according to the present invention. The gist is to control at least one of the fuel injection timing, pilot injection amount, and EGR rate based on the estimated cetane number of the fuel.

  According to the present invention, the compression ignition internal combustion engine is controlled by controlling any one or more of the fuel injection timing, the pilot injection amount, and the EGR rate based on the cetane number of the fuel estimated by the cetane number estimation unit. Reduction of engine combustion noise and stabilization of combustion can be realized.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a control device including a fuel cetane number estimation device according to an embodiment of the present invention, together with a compression ignition type internal combustion engine 10. Fuel used in the compression ignition internal combustion engine 10 is stored in the fuel tank 12. As the fuel here, for example, light oil can be used. The fuel stored in the fuel tank 12 is pumped up by a fuel pump and supplied to the compression ignition internal combustion engine 10. The compression ignition type internal combustion engine 10 can be constituted by a known diesel engine using a piston-crank mechanism, for example. In the compression ignition type internal combustion engine 10 (diesel engine), for example, when the piston is located near the compression top dead center, the fuel in the cylinder is directly ignited and burned by directly injecting the fuel from the fuel injection valve into the cylinder. (Diesel combustion). The compression ignition internal combustion engine 10 is provided with an in-cylinder pressure sensor 22 for detecting the in-cylinder pressure P and a crank angle sensor 24 for detecting the crank angle CA. The signal indicating the in-cylinder pressure P of the compression ignition internal combustion engine 10 detected by the in-cylinder pressure sensor 22 and the signal indicating the crank angle CA of the compression ignition internal combustion engine 10 detected by the crank angle sensor 24 are electronically controlled. Input to an apparatus (ECU) 40.

  Since the cetane number of fuel (for example, light oil) marketed in the market is not always constant, fuel having a cetane number different from the assumed cetane number may be supplied into the fuel tank 12. When the cetane number of the fuel used in the compression ignition type internal combustion engine 10 is lower than the assumed cetane number, the ignition delay period of the fuel injected in the cylinder becomes long, and the fuel combustion tends to become unstable. On the other hand, when the cetane number of the fuel is higher than the assumed cetane number, combustion becomes active and combustion noise tends to increase. Therefore, in the present embodiment, the electronic control unit 40 estimates the cetane number CN of the fuel used in the compression ignition internal combustion engine 10, and performs fuel injection control based on the estimated cetane number CN.

  The electronic control unit 40 can be configured to include, for example, the functional blocks shown in FIG. The fuel injection control unit 42 outputs an injection control signal generated based on the operation state such as the rotational speed and load of the compression ignition type internal combustion engine 10 to the fuel injection valve of the compression ignition type internal combustion engine 10, so that the compression ignition type Fuel injection control of the internal combustion engine 10 is performed. The cetane number estimation unit 44 estimates the cetane number CN of the fuel used in the compression ignition internal combustion engine 10. Hereinafter, the process (cetane number estimation process) executed when the electronic control unit 40 estimates the cetane number CN of the fuel will be described with reference to the flowchart of FIG.

  In step S101, the fuel injection control unit 42 satisfies ΔP / ΔCA = a described below based on the in-cylinder pressure P detected by the in-cylinder pressure sensor 22 and the crank angle CA detected by the crank angle sensor 24. A cetane number estimation injection control mode for searching for the fuel injection timing Tinj where the condition is satisfied (or substantially satisfied) is executed. Here, as shown in FIG. 3, ΔP depends on the in-cylinder pressure peak value P2 after compression top dead center (expansion stroke) due to combustion (heat generation) by fuel injection (main injection) and piston motion. This is a difference P2−P1 from the in-cylinder pressure peak value P1 at or near the compression top dead center due to combustion (heat generation) due to in-cylinder gas compression or pilot injection before main injection. ΔCA is a difference CA2−CA1 between crank angles CA2 and CA1 corresponding to the in-cylinder pressure peak values P2 and P1, as shown in FIG. Further, a is a predetermined value, and for example, a positive value can be set or a negative value can be set.

  When the cetane number estimation injection control mode is executed, the lower the cetane number CN of the fuel, the longer the ignition delay period of the fuel. Therefore, the peak value of the heat generation rate in the expansion stroke decreases, and the cylinder at the crank angle CA2 decreases. As the internal pressure peak value P2 decreases, the value of ΔP / ΔCA decreases. Here, FIG. 4 shows the result of examining the change in the heat generation rate and the in-cylinder pressure by calculation when the cetane number CN of the fuel is changed. In the calculation, the engine speed is 1400 rpm, the pilot injection start timing is 15 ° before compression top dead center (−15 ° ATDC), the pilot injection amount is 2.5 mg, and the main injection start timing is 5 after compression top dead center. ° (+ 5 ° ATDC), the main injection amount is 5 mg, and the cetane number CN of the fuel is changed from 52 to 38. As shown in FIG. 4, it can be seen that when the cetane number CN of the fuel decreases, the peak value of the heat generation rate in the expansion stroke decreases and the in-cylinder pressure peak value P2 decreases. That is, it can be seen that when the cetane number CN of the fuel decreases, the value of ΔP / ΔCA decreases.

  Further, when the cetane number estimation injection control mode is executed, as the fuel injection (main injection) start timing Tinj is advanced (advanced), the fuel by the main injection becomes more likely to self-ignite, and the heat generation rate in the expansion stroke Increases in the cylinder pressure peak value P2 at the crank angle CA2, thereby increasing the value of ΔP / ΔCA. Here, FIG. 5 shows the result of examining the change in the heat generation rate and the in-cylinder pressure when the main injection start timing Tinj is changed while maintaining the cetane number CN of the fuel at a constant value. In the calculation, the fuel cetane number CN is 52, the engine speed is 1400 rpm, the pilot injection start timing is 15 ° before compression top dead center (−15 ° ATDC), the pilot injection amount is 2.5 mg, the main injection amount The main injection start timing Tinj is 3.6 ° after compression top dead center (+ 3.6 ° ATDC), 5 ° after compression top dead center (+ 5 ° ATDC), and 7.3 ° after compression top dead center ( + 7.3 ° ATDC). As shown in FIG. 5, it can be seen that as the main injection start timing Tinj is advanced, the peak value of the heat generation rate in the expansion stroke increases and the in-cylinder pressure peak value P2 increases. That is, it can be seen that the value of ΔP / ΔCA increases as the start timing Tinj of fuel injection (main injection) is advanced. In the example shown in FIG. 5, ΔP / ΔCA = −0.046 MPa / deg when the main injection start timing Tinj is 7.3 ° after the compression top dead center, and the main injection start timing Tinj is 5 after the compression top dead center. ΔP / ΔCA = 0 when it is °, and ΔP / ΔCA = 0.032 MPa / deg when the main injection start timing Tinj is 3.6 ° after compression top dead center.

  Therefore, in order to keep the value of ΔP / ΔCA at a predetermined value (constant value) a as the fuel cetane number CN decreases, it is necessary to advance the start timing Tinj of fuel injection (main injection). That is, when the cetane number estimation injection control mode is executed, the fuel injection (main injection) start timing Tinj that satisfies ΔP / ΔCA = a becomes earlier as the fuel cetane number CN is lower. FIG. 6 shows the result of examining the relationship between the cetane number CN of fuel and the start timing Tinj of fuel injection (main injection) where ΔP / ΔCA = a is established. FIG. 6 shows the relationship when a = 0, the relationship when a = 0.032 MPa / deg, and the relationship when a = −0.046 MPa / deg. The engine speed is 1400 rpm, The pilot injection start timing is 15 ° before compression top dead center (−15 ° ATDC), the pilot injection amount is 2.5 mg, and the main injection amount is 5 mg. As shown in FIG. 6, the main injection start timing Tinj at which ΔP / ΔCA = a is established changes according to the cetane number CN of the fuel, and the main injection at which ΔP / ΔCA = a is established as the cetane number CN of the fuel is lower. It can be seen that the start timing Tinj is earlier (the higher the cetane number CN of the fuel, the later the main injection start timing Tinj at which ΔP / ΔCA = a is established). Therefore, the cetane number CN of the fuel can be estimated by searching for the fuel injection (main injection) start timing Tinj where ΔP / ΔCA = a is satisfied (or substantially satisfied). The fuel injection control unit 42 calculates the value of ΔP / ΔCA based on the in-cylinder pressure P and the crank angle CA when searching for the start timing Tinj of fuel injection (main injection) where ΔP / ΔCA = a is established. When the value ΔP / ΔCA is larger than the predetermined value a, the start timing of fuel injection (main injection) is retarded, and when the value ΔP / ΔCA is smaller than the predetermined value a, fuel injection (main injection). Advance the start time of.

  Note that pilot injection is not necessarily performed when the cetane number estimation injection control mode is executed. ΔP when pilot injection is not performed is the in-cylinder pressure peak value P2 after compression top dead center (expansion stroke) due to combustion (heat generation) by fuel injection (main injection) and in-cylinder gas due to piston motion. This is expressed by a difference P2-P1 from the in-cylinder pressure peak value P1 at the compression top dead center due to the compression of.

  In step S102, the cetane number estimation unit 44 sets the fuel cetane number CN based on the fuel injection timing Tinj that satisfies (or substantially satisfies) ΔP / ΔCA = a searched for when the cetane number estimation injection control mode is executed. Is estimated. In this case, as shown in FIG. 6, for example, a characteristic map representing the relationship between the cetane number CN of fuel and the start timing Tinj of fuel injection (main injection) where ΔP / ΔCA = a is established (or substantially established) Is created in advance and stored in the cetane number characteristic storage unit 46 (storage device) in the electronic control unit 40. The cetane number estimation unit 44 corresponds to the fuel injection (main injection) start timing Tinj searched for in the execution of the cetane number estimation injection control mode in step S101 in the characteristic map stored in the cetane number characteristic storage unit 46. The cetane number CN of the fuel is estimated by calculating the cetane number CN of the fuel.

  Note that, when the cetane number estimation injection control mode is executed, the fuel injection control unit 42 preferably keeps the fuel injection amount (main injection amount) at a constant value. When pilot injection is performed prior to main injection, the fuel injection control unit 42 preferably keeps the pilot injection start timing and the pilot injection amount at constant values. When performing EGR (exhaust gas recirculation), it is preferable to keep the EGR rate at a constant value. In addition, the fuel injection amount (main injection amount), the pilot injection start timing, and the pilot injection amount (pilot) when the characteristic map stored in the cetane number characteristic storage unit 46 is created and when the cetane number estimation injection control mode is executed. It is preferable to align the EGR rate (when performing injection) and the EGR rate (when performing EGR).

  The cetane number estimation process shown in the flowchart of FIG. 2 can be executed, for example, at idling immediately after the compression ignition type internal combustion engine 10 is started. Alternatively, the cetane number estimation process can be executed immediately after the compression ignition internal combustion engine 10 is started after the fuel is supplied into the fuel tank 12. At this time, whether or not the fuel is supplied into the fuel tank 12 is determined based on a detection value of a sensor attached to the fuel tank 12 for detecting the remaining amount of fuel in the fuel tank 12, for example. Can do. In addition, when a load (for example, a vehicle) is driven by the power of the compression ignition type internal combustion engine 10, the cetane number estimation process can be executed when the load (vehicle) is decelerated. At that time, whether or not the load (vehicle) is in a decelerating state can be determined based on, for example, the accelerator opening. When the injection control mode for estimating the cetane number is executed when the load (vehicle) is decelerated, the torque of the compression ignition internal combustion engine 10 is almost suppressed from the compression ignition internal combustion engine 10 to the load (vehicle). It is preferable to keep the fuel injection amount small so that it is not transmitted.

  Further, when the compression ignition type internal combustion engine 10 is a multi-cylinder engine having a plurality of cylinders and the fuel injection control can be performed independently for each cylinder, all of the cetane number estimation injection control modes are not necessarily performed. For example, the cetane number estimation injection control mode can be applied to some cylinders (for example, one cylinder). By performing the cetane number estimation injection control mode for one of the multi-cylinder cylinders, the cetane number estimation injection has almost no effect on the operation state (transfer torque to the load) of the compression ignition type internal combustion engine 10. Since the control mode can be executed, the degree of freedom in executing the cetane number estimation process (cetane number estimation injection control mode) can be increased.

  After the estimation of the cetane number CN of the fuel by the cetane number estimation process, the fuel injection control unit 42 controls the fuel injection timing based on the cetane number CN of the fuel estimated by the cetane number estimation unit 44. For example, when the cetane number CN estimated by the cetane number estimating unit 44 is lower than the predetermined value CN0, the fuel injection control unit 42 performs fuel injection (main injection) (when the cetane number CN is the predetermined value CN0). ) Start time. Thereby, the combustion of the compression ignition type internal combustion engine 10 is stabilized. On the other hand, when the cetane number CN estimated by the cetane number estimation unit 44 is higher than the predetermined value CN0, the fuel injection control unit 42 performs fuel injection (main injection) (when the cetane number CN is the predetermined value CN0). ) Is delayed. Thereby, the combustion noise of the compression ignition type internal combustion engine 10 is reduced.

  In addition, when pilot injection is performed, the fuel injection control unit 42 can also control the pilot injection amount based on the cetane number CN of the fuel estimated by the cetane number estimation unit 44. For example, when the cetane number CN estimated by the cetane number estimation unit 44 is lower than the predetermined value CN0, the fuel injection control unit 42 increases the pilot injection amount (than when the cetane number CN is the predetermined value CN0). It can also be made. This also makes it possible to stabilize the combustion of the compression ignition type internal combustion engine 10. On the other hand, when the cetane number CN estimated by the cetane number estimation unit 44 is higher than the predetermined value CN0, the fuel injection control unit 42 reduces the pilot injection amount (than when the cetane number CN is the predetermined value CN0). It can also be made. Also by this, the combustion noise of the compression ignition type internal combustion engine 10 can be reduced.

  In addition, when performing EGR (exhaust gas recirculation) in which a part of the exhaust gas after combustion is supplied to the intake side as EGR gas, the electronic control unit 40 uses the cetane number CN of the fuel estimated by the cetane number estimation unit 44. The EGR rate (the amount of EGR gas supplied to the intake side) can also be controlled based on the above. For example, when the cetane number CN estimated by the cetane number estimation unit 44 is lower than the predetermined value CN0, the electronic control unit 40 decreases the EGR rate (than when the cetane number CN is the predetermined value CN0). You can also. This also makes it possible to stabilize the combustion of the compression ignition type internal combustion engine 10. On the other hand, when the cetane number CN estimated by the cetane number estimation unit 44 is higher than the predetermined value CN0, the electronic control unit 40 increases the EGR rate (in comparison with the case where the cetane number CN is the predetermined value CN0). You can also. Also by this, the combustion noise of the compression ignition type internal combustion engine 10 can be reduced. The control of the EGR rate can be performed, for example, by controlling the opening degree of the EGR control valve provided in the recirculation passage connecting the exhaust passage and the intake passage of the compression ignition type internal combustion engine 10. As described above, the electronic control unit 40 is based on the cetane number CN of the fuel estimated by the cetane number estimation unit 44, and any one of the start timing of fuel injection (main injection), the pilot injection amount, and the EGR rate. The above can be controlled.

  When estimating the cetane number of the fuel based on the heat generation rate dQ / dθ calculated using the in-cylinder pressure P as in Patent Document 1, the amount of calculation when calculating the heat generation rate dQ / dθ Therefore, the amount of calculation required for estimating the cetane number of the fuel increases and the calculation time increases. Further, when calculating the heat generation rate dQ / dθ using the in-cylinder pressure P according to the above-described equation (1), it is necessary to calculate the differential value dP / dθ of the in-cylinder pressure. The noise included in the occurrence rate dQ / dθ increases. Further, when the combustion chamber volume V in equation (1) is obtained from the crank angle θ, if there is a shift in the mounting position of the crank angle sensor (if there is an error in the detected crank angle θ), the combustion chamber An error also occurs in the value of the volume V, and an error also occurs in the value of the heat generation rate dQ / dθ. As a result, the estimation accuracy of the cetane number of the fuel decreases.

  On the other hand, in the present embodiment, the fuel injection start timing at which ΔP / ΔCA = a is satisfied by utilizing the fact that the fuel injection start timing Tinj at which ΔP / ΔCA = a is satisfied changes according to the cetane number CN of the fuel. By estimating the cetane number CN of the fuel based on the timing Tinj, the cetane number CN of the fuel can be estimated without calculating the differential value dP / dθ of the in-cylinder pressure and the heat generation rate dQ / dθ. Therefore, the calculation amount required for estimating the cetane number CN of the fuel can be greatly reduced, and the calculation time can be greatly shortened. Even if the mounting position of the crank angle sensor 24 is deviated, an error due to the deviation of the sensor mounting position hardly occurs in the difference in the crank angle CA. Therefore, by calculating the difference ΔCA between the crank angles CA2 and CA1 corresponding to the in-cylinder pressure peak values P2 and P1 that are easier to detect, it is hardly affected by the mounting position shift of the crank angle sensor 24 and is highly accurate. The cetane number CN can be estimated. Based on the estimated cetane number CN, the combustion timing of the compression ignition internal combustion engine 10 is controlled by controlling any one or more of the fuel injection (main injection) start timing, the pilot injection amount, and the EGR rate. Noise reduction and combustion stabilization can be realized.

  Furthermore, in the characteristic map shown in FIG. 6, the smaller the predetermined value a, the greater the slope of the fuel injection start timing Tinj with respect to the cetane number CN, and the higher the sensitivity of the fuel injection start timing Tinj with respect to changes in the cetane number CN. Become. If the value of the predetermined value a is small and negative, the combustion becomes more unstable because of retarded combustion in the retard injection, and even if the cetane number CN slightly changes, the combustion greatly fluctuates, so the change in the cetane number CN The fuel injection start timing Tinj is more sensitive to the cetane number CN, and the cetane number CN can be easily detected. Therefore, the estimation accuracy of the cetane number CN of the fuel can be further increased by setting the predetermined value a to a negative value.

  Further, as shown in the cetane number estimation process according to the flowchart of FIG. 7, in step S201, the fuel injection control unit 42 satisfies the condition of ΔP = 0 based on the in-cylinder pressure P detected by the in-cylinder pressure sensor 22. It is also possible to execute the cetane number estimation injection control mode for searching for the fuel injection timing Tinj that is established (or substantially established). That is, the predetermined value a can be set to 0. ΔP here is also the in-cylinder pressure peak value P2 after compression top dead center (expansion stroke) due to combustion (heat generation) by fuel injection (main injection), and compression or main compression of in-cylinder gas by piston motion. FIG. 8 shows the difference P2-P1 from the in-cylinder pressure peak value P1 at or near the compression top dead center caused by combustion (heat generation) by pilot injection before injection, and when ΔP = 0 holds. As shown, the cylinder pressure peak value P2 and the cylinder pressure peak value P1 are equal. As shown in the relationship in the case of a = 0 in FIG. 6, the main injection start timing Tinj at which ΔP = 0 is established changes according to the cetane number CN of the fuel, and ΔP = 0 becomes lower as the cetane number CN of the fuel is lower. It can be seen that the established main injection start timing Tinj is earlier (the higher the cetane number CN of the fuel, the later the main injection start timing Tinj at which ΔP = 0 is established). Therefore, the cetane number CN of the fuel can also be estimated by searching for the fuel injection (main injection) start timing Tinj where ΔP = 0 is satisfied (or substantially satisfied). Then, in step S202 of the flowchart of FIG. 7, the cetane number estimating unit 44 is based on the fuel injection timing Tinj that satisfies ΔP = 0 that is found when the cetane number estimation injection control mode is executed. The cetane number CN of the fuel can be estimated. In that case, a characteristic map representing the relationship between the fuel cetane number CN and the start timing Tinj of fuel injection (main injection) where ΔP = 0 is satisfied (or substantially satisfied) is created in advance in the electronic control unit 40. Is stored in the cetane number characteristic storage unit 46 (storage device). The cetane number estimation unit 44 uses the characteristic map stored in the cetane number characteristic storage unit 46 to search for the fuel corresponding to the start timing Tinj of the fuel injection (main injection) searched during the execution of the cetane number estimation injection control mode. The cetane number CN of the fuel is estimated by calculating the cetane number CN.

  The fuel cetane number CN is estimated based on the fuel injection start timing Tinj at which ΔP = 0 is established by using the fact that the fuel injection start timing Tinj at which ΔP = 0 is established changes according to the cetane number CN of the fuel. Even in this case, the cetane number CN of the fuel can be estimated without calculating the differential value dP / dθ of the in-cylinder pressure and the heat generation rate dQ / dθ. Therefore, the calculation amount required for estimating the cetane number CN of the fuel can be greatly reduced, and the calculation time can be greatly shortened. Furthermore, in this case, the cetane number CN of the fuel can be estimated without necessarily using the crank angle CA. Furthermore, in this case, the gain of the in-cylinder pressure sensor 22 (ratio between the output signal level of the sensor 22 and the actual in-cylinder pressure) is shifted due to variations in the in-cylinder pressure sensor 22, changes with time, and the like. Even if there is an error in the in-cylinder pressure P detected by the pressure sensor 22, the in-cylinder pressure sensor 22 is detected by detecting the fuel injection start timing Tinj at which the difference ΔP between the in-cylinder pressure peak values P2 and P1 is zero. Thus, it is possible to estimate the cetane number CN with high accuracy, which is hardly affected by the gain deviation.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

It is a figure which shows schematic structure of a control apparatus provided with the fuel cetane number estimation apparatus which concerns on embodiment of this invention with a compression ignition type internal combustion engine. It is a flowchart explaining the process performed when an electronic controller estimates the cetane number CN of a fuel. It is a figure explaining the conditions which search the start time Tinj of fuel injection at the time of execution of the injection control mode for cetane number estimation. It is a figure which shows the result of having investigated by calculation the change of the heat release rate and cylinder pressure in the case of changing the cetane number CN of fuel. It is a figure which shows the result of having investigated by calculation the change in the heat release rate and the cylinder pressure when changing the fuel injection start timing Tinj while maintaining the cetane number CN of the fuel at a constant value. It is a figure which shows the result of having investigated the relationship between the cetane number CN of fuel, and the fuel injection start timing Tinj in which (DELTA) P / (DELTA) CA = a is materialized. It is a flowchart explaining the other process performed when an electronic controller estimates the cetane number CN of a fuel. It is a figure explaining the other conditions which search the fuel injection start time Tinj at the time of execution of the injection control mode for cetane number estimation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Compression ignition type internal combustion engine, 12 Fuel tank, 22 In-cylinder pressure sensor, 24 Crank angle sensor, 40 Electronic control unit, 42 Fuel injection control part, 44 Cetane number estimation part, 46 Cetane number characteristic storage part

Claims (6)

An apparatus for estimating the cetane number of a fuel of a compression ignition type internal combustion engine that injects fuel into a cylinder and self-ignites,
An in-cylinder pressure detector for detecting the in-cylinder pressure;
A crank angle detector for detecting the crank angle;
A fuel injection control unit for performing fuel injection control;
A cetane number estimation unit for estimating the cetane number of the fuel;
With
When estimating the cetane number of fuel,
The fuel injection control unit includes an in-cylinder pressure peak value after compression top dead center caused by combustion by fuel injection, and compression increase caused by compression of in-cylinder gas by piston motion or combustion by pilot injection before the fuel injection. When the difference from the in-cylinder pressure peak value at or near the dead point is ΔP, the difference in crank angle corresponding to each in-cylinder pressure peak value is ΔCA, and a is a predetermined value, the in-cylinder pressure detection unit Executing the cetane number estimation injection control mode for searching for the fuel injection timing at which ΔP / ΔCA = a is substantially established based on the detected in-cylinder pressure and the crank angle detected by the crank angle detector;
The cetane number estimating unit estimates the cetane number of the fuel based on the fuel injection timing at which ΔP / ΔCA = a searched for when executing the cetane number estimation injection control mode is substantially satisfied. Fuel cetane number estimation device. A fuel cetane number estimation device for a compression ignition internal combustion engine according to claim 1,
The fuel cetane number estimation device for a compression ignition type internal combustion engine, wherein the predetermined value a is a negative value. A fuel cetane number estimation device for a compression ignition type internal combustion engine according to claim 1 or 2,
A cetane number characteristic storage unit for storing a relationship between the cetane number of the fuel and the fuel injection timing at which ΔP / ΔCA = a is substantially established;
The cetane number estimation unit calculates a fuel cetane number corresponding to the fuel injection timing searched during execution of the cetane number estimation injection control mode in the relationship stored in the cetane number characteristic storage unit. An apparatus for estimating the fuel cetane number of a compression ignition type internal combustion engine for estimating the cetane number of the engine. An apparatus for estimating the cetane number of a fuel of a compression ignition type internal combustion engine that injects fuel into a cylinder and self-ignites,
An in-cylinder pressure detector for detecting the in-cylinder pressure;
A fuel injection control unit for performing fuel injection control;
A cetane number estimation unit for estimating the cetane number of the fuel;
With
When estimating the cetane number of fuel,
The fuel injection control unit includes an in-cylinder pressure peak value after compression top dead center caused by combustion by fuel injection, and compression increase caused by compression of in-cylinder gas by piston motion or combustion by pilot injection before the fuel injection. If the difference from the in-cylinder pressure peak value at or near the dead point is ΔP, the fuel injection timing at which ΔP = 0 is substantially satisfied is searched based on the in-cylinder pressure detected by the in-cylinder pressure detector. Execute cetane number estimation injection control mode,
The cetane number estimation unit estimates the cetane number of the fuel based on the fuel injection timing at which ΔP = 0, which is found when executing the cetane number estimation injection control mode, is substantially satisfied. Price estimation device. A fuel cetane number estimation device for a compression ignition type internal combustion engine according to claim 4,
A cetane number characteristic storage unit for storing a relationship between the cetane number of the fuel and the fuel injection timing at which ΔP = 0 is substantially satisfied;
The cetane number estimation unit calculates a fuel cetane number corresponding to the fuel injection timing searched during execution of the cetane number estimation injection control mode in the relationship stored in the cetane number characteristic storage unit. An apparatus for estimating the fuel cetane number of a compression ignition type internal combustion engine for estimating the cetane number of the engine. A control device for a compression ignition internal combustion engine comprising the fuel cetane number estimation device for a compression ignition internal combustion engine according to any one of claims 1 to 5,
A control device for a compression ignition type internal combustion engine that controls at least one of the fuel injection timing, pilot injection amount, and EGR rate based on the cetane number of the fuel estimated by the cetane number estimation unit.

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