JP2016160921A - Combustion control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion control device for an internal combustion engine for controlling fuel injection start timing without using a measurement value from a cylinder inner pressure sensor.SOLUTION: A combustion control device for an internal combustion engine includes: an engine speed sensor 44 for detecting a crank angle; an injection control section 90 (timing determination section 92) for starting fuel injection from an injector 11 into a cylinder at timing when the detected crank angle reaches a predetermined injection start angle; a timing correction amount acquisition section 80 for acquiring correction amount of the injection start timing from a differential value between a target combustion gravity center and an actual combustion gravity center; and an injection control section 90 (injection start timing calculation section 91) for correcting actual injection start timing input as a command value on the basis of the input timing correction amount.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a combustion control device for an internal combustion engine.

  In an internal combustion engine such as a diesel engine, the combustion center of gravity is controlled in order to improve fuel efficiency. For example, the combustion center of gravity in the current cycle is calculated from the pressure in the cylinder by the in-cylinder pressure sensor, the difference between the obtained value of the combustion center of gravity and the target value for the combustion center of gravity, and the calculated maximum slope of the heat release rate A technique for correcting the fuel injection amount and the injection pressure in the pilot injection of the next cycle according to the difference between the value and the target value has been proposed (see, for example, Patent Document 1).

  There is also a technology that measures the combustion center-of-gravity angle based on the in-cylinder pressure change measured by the in-cylinder pressure sensor, obtains the combustion center-of-gravity angle from the target fuel pressure, and determines whether combustion is appropriate from the comparison between the two. It has been proposed (see, for example, Patent Document 2).

  Also, based on the in-cylinder pressure measured by the in-cylinder pressure sensor and the crank angle from the rotational speed sensor, the predicted combustion center of gravity is calculated using the center of gravity of the waveform of the in-cylinder pressure as the combustion center of gravity. A technique for determining a combustion center of gravity correction coefficient has also been proposed (see, for example, Patent Document 3).

JP 2013-160080 A JP 2011-202629 A JP 2011-157892 A

  In each of the conventional techniques described above, the combustion center of gravity is obtained using the in-cylinder pressure measured by the in-cylinder pressure sensor, and the fuel injection start timing is controlled. Here, in view of the problem of simplification of the configuration, it is desirable to omit the in-cylinder pressure sensor. Even if an in-cylinder pressure sensor is provided, if the fuel injection start timing can be controlled without using the detection signal of the in-cylinder pressure sensor, it becomes possible to cope with an abnormality in the detection signal due to disconnection or noise. There are advantages.

  An object of the disclosed combustion control device is to control the fuel injection start timing without using the measured value from the in-cylinder pressure sensor.

  The disclosed combustion control device for an internal combustion engine includes crank angle detection means for detecting a crank angle, and fuel injection from the injector into the cylinder at a timing when the detected crank angle reaches a predetermined injection start angle. An injection control means for starting, a correction amount acquiring means for acquiring a correction amount of an injection start angle from a difference value between a target combustion center of gravity and an actual combustion center of gravity, and correcting the injection start angle based on the correction amount of the injection start angle Correction means.

  According to the disclosed combustion control device, the fuel injection start timing can be controlled without using the measured value from the in-cylinder pressure sensor.

It is a schematic structure figure showing an example of the intake and exhaust system of the diesel engine concerning this embodiment. It is a functional block diagram of ECU which concerns on this embodiment. It is a block diagram explaining the target combustion gravity center acquisition process by a target combustion gravity center acquisition part. It is a block diagram explaining the actual combustion gravity center acquisition process by an actual combustion gravity center acquisition part. It is a block diagram explaining the acquisition process of the correction amount of the injection timing by a timing correction amount acquisition part. It is a graph explaining the linear relationship between the difference value (ΔCOC) of the combustion center of gravity and the correction amount (ΔSOI) of the fuel injection start timing. It is a block diagram explaining the fuel injection control by an injection control part. It is a figure which compares the control of this embodiment, and the control of a comparative example.

  Hereinafter, a combustion control device for an internal combustion engine according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a schematic configuration diagram illustrating an example of an intake / exhaust system of a diesel engine (hereinafter simply referred to as an engine) 10 according to the present embodiment.

  As shown in FIG. 1, each cylinder of the engine 10 is provided with an injector 11 for direct injection into each cylinder. The injector 11 is in communication with the common rail 12 and injects high-pressure fuel that has been pressured by the common rail 12 into the cylinder based on an injection instruction from the ECU 50. A piston 13 is disposed in the cylinder so as to be able to reciprocate. The reciprocating motion of the piston 13 is converted by the crank 14 into the rotational motion of the crankshaft 14A.

  An intake passage 15 for introducing fresh air is connected to the intake manifold 10 </ b> A of the engine 10. In this intake passage 15, an air cleaner 16, a compressor 17 </ b> A of a supercharger 17, and an intercooler 18 are provided in this order from the intake upstream side. An exhaust passage 19 for leading the exhaust to the outside is connected to the exhaust manifold 10B. In the exhaust passage 19, a turbine 17B of the supercharger 17, an exhaust purification device 30 and the like are provided in order from the exhaust upstream side.

  The EGR device 20 includes an EGR passage 21 that connects the exhaust manifold 10B and the intake manifold 10A, an EGR cooler 22 that cools EGR gas, and an EGR valve 23 that adjusts the EGR amount (exhaust gas recirculation amount). The exhaust purification device 30 is configured by arranging, in order from the exhaust upstream side, a NOx occlusion reduction type catalyst 31 for reducing and purifying NOx, and a filter 32 for collecting PM (particulate matter) in a case 30A.

  Various sensors are attached to each part of the engine 10. These sensors together with the ECU 50 are an example of the combustion control device of the present invention.

  For example, a rail pressure sensor 41 that outputs a detection signal corresponding to the fuel pressure (rail pressure) stored in the common rail 12 is attached to the common rail 12. A boost pressure sensor 42 that detects a boost pressure (supercharging pressure) is attached to the intake manifold 10A. The air cleaner 16 is provided with an intake air amount sensor 43 that detects an intake air amount.

  An engine speed sensor 44 for detecting the engine speed is attached to the engine 10. The engine speed sensor 44 reads gear-like irregularities formed on the outer periphery of the disc 14B, and outputs a detection signal whose level changes every time the crank 14 (crankshaft 14A) makes a predetermined angle. Therefore, the engine speed sensor 44 is an example of a crank angle detection unit that detects a crank angle. The accelerator opening sensor 45 outputs a detection signal corresponding to an operation amount of an accelerator pedal (not shown), in other words, a detection signal indicating the fuel injection amount.

  The ECU 50 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, the sensor values of the sensors 41 to 45 are input to the ECU 50.

  The ECU 50 corresponds to a combustion control device for the engine 10, which is an example of an internal combustion engine, together with the various sensors described above. Therefore, as shown in FIG. 2, the ECU 50 includes a target combustion gravity center acquisition unit 60, an actual combustion gravity center acquisition unit 70, a timing correction amount acquisition unit 80, and an injection control unit 90 as some functional elements. . Each of these functional elements will be described as being included in the ECU 50 which is an integral hardware, but any one of these may be provided in separate hardware.

Here, the combustion center of gravity (COC) will be described. The combustion center of gravity is defined as the combustion degree when the fuel injected into the cylinder (combustion chamber) burns in the cylinder and the complete combustion state in which the combustion of all the fuel is completed is assumed to be “100%”. When the degree reaches "50%". The target combustion center of gravity ( _{COC_base} ) is a combustion center of gravity targeted for control, and is determined corresponding to the combination of the engine speed and the fuel injection amount (accelerator opening). On the other hand, the actual combustion center of gravity ( _{COC_act} ) is the actual combustion center of gravity in the engine 10. The actual combustion center of gravity is acquired by a polynomial calculation in the actual combustion center of gravity acquisition unit 70 with reference to the rail pressure, the intake oxygen concentration, the boost pressure, and the fuel injection start timing (SOI) as described later in this embodiment. ing.

  As shown in FIG. 3, the target combustion gravity center acquisition unit 60 has a combustion gravity center map 61. The combustion center-of-gravity map 61 is a map that is referred to based on the engine speed Ne and the accelerator opening Q (fuel injection amount of the engine 10), and is a target corresponding to the engine speed Ne and the accelerator opening Q. The combustion center of gravity is set in advance based on experiments and the like. Therefore, in the target combustion center of gravity acquisition unit 60, the engine rotational speed Ne and the accelerator opening Q are input signals to the combustion center of gravity map 61, and the target combustion center of gravity is read from the combustion center of gravity map 61. It is output to the timing correction amount acquisition unit 80.

  As shown in FIG. 4, the actual combustion center-of-gravity acquisition unit 70 includes a rail pressure correction amount map 71, an intake oxygen concentration correction amount map 72, a boost pressure correction amount map 73, a target boost pressure map 74, an injection timing map 75, and an actual A combustion center-of-gravity calculation unit 76 is provided.

  The rail pressure correction amount map 71 is a map that is referred to based on the engine rotational speed Ne and the accelerator opening Q, and the rail pressure correction amount corresponding to the engine rotational speed Ne and the accelerator opening Q is previously tested. Etc. are set based on the above. Therefore, when the engine speed Ne and the accelerator opening Q are input, the rail pressure correction amount map 71 outputs the corresponding rail pressure correction amount to the actual combustion gravity center calculator 76.

  The intake oxygen concentration correction amount map 72 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and the correction amount of the intake oxygen concentration corresponding to the engine speed Ne and the accelerator opening Q is shown in FIG. It is set based on experiments and the like in advance. Therefore, when the engine speed Ne and the accelerator opening Q are input, the intake oxygen concentration correction amount map 72 outputs the corresponding intake oxygen concentration correction amount to the actual combustion gravity center calculator 76.

  The boost pressure correction amount map 73 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and the correction amount of the boost pressure corresponding to the engine speed Ne and the accelerator opening Q is previously tested. Etc. are set based on the above. Therefore, when the engine speed Ne and the accelerator opening Q are input, the boost pressure correction amount map 73 outputs the corresponding boost pressure correction amount to the actual combustion gravity center calculator 76.

  The target boost pressure map 74 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and the target value of the boost pressure corresponding to the engine speed Ne and the accelerator opening Q is determined in advance by experiments or the like. It is set based on. Therefore, when the engine speed Ne and the accelerator opening Q are input, the target boost pressure map 74 outputs the corresponding target boost pressure to the actual combustion gravity center calculator 76.

  The injection timing map 75 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and the target value of the injection timing corresponding to the engine speed Ne and the accelerator opening Q is previously set in an experiment or the like. Is set based on. This target value is adjusted for calculating the combustion center of gravity. Therefore, when the engine speed Ne and the accelerator opening Q are input, the injection timing map 75 outputs the corresponding target injection timing to the actual combustion gravity center calculator 76.

  The actual combustion center of gravity calculation unit 76 calculates the actual combustion center of gravity based on the detection signals input from the sensors 41 to 45, the correction amounts and target values input from the maps 71 to 75, and other input signals. That is, the actual combustion center of gravity calculation unit 76 includes the correction amount and target value input from each of the above-described maps 71 to 75, the target combustion center of gravity input from the target combustion center of gravity acquisition unit 60, and the rail input from the rail pressure sensor 41. Based on the pressure, the separately acquired rail pressure target value, the intake oxygen concentration, the intake oxygen target value, and the actual injection start timing, an approximate calculation with a polynomial is performed to acquire the actual combustion center of gravity. The acquired actual combustion gravity center is output to the timing correction amount acquisition unit 80.

  The intake oxygen concentration is the intake oxygen concentration after the EGR merge, and is calculated based on the opening degree of the EGR valve 23, the detection signal of the intake air amount sensor 43, and the like. The actual injection start timing is information on the crank angle corresponding to the fuel injection start timing, and is determined in advance by experiments or the like. The actual injection start timing is input as an instruction value to the actual combustion gravity center acquisition unit 70, and serves as a reference for the injection start timing. For this reason, the actual injection start timing is different from the target injection timing input from the injection timing map 75.

As illustrated in FIG. 5, the timing correction amount acquisition unit 80 includes a correction amount calculation unit 81. Correction amount calculation unit 81 obtains the target combustion center (COC _{_base)} and the correction amount of the injection start angle from the difference value (△ COC) of the actual combustion center _{(COC _act) (△ SOI)} . As described above, since the fuel injection start timing is determined by the crank angle, the correction amount of the injection start angle corresponds to the correction amount of the injection start timing. Therefore, the timing correction amount acquisition unit 80 is an example of a correction amount acquisition unit of the present invention.

  As shown in FIG. 6, the difference value ΔCOC between both combustion centers of gravity and the injection start angle correction amount ΔSOI have a linear relationship. FIG. 6 shows two examples of (1) ΔCOC = −α × ΔSOI and (2) ΔCOC = −β × ΔSOI. In the example of (1), the correction amount ΔSOI of the injection start angle is obtained by calculating −1 / α × ΔCOC. Similarly, in the example of (2), the correction amount ΔSOI of the injection start angle is obtained by calculating −1 / β × ΔCOC. Although two examples are shown in FIG. 6, it has been confirmed by experiments that a linear relationship is obtained regardless of the operating conditions.

  The correction amount of the injection start angle calculated by the correction amount calculation unit 81 is output to the injection control unit 90 as a timing correction amount.

  As shown in FIG. 7, the injection control unit 90 includes an injection start timing calculation unit 91 and a timing determination unit 92.

  The injection start timing calculation unit 91 is an example of a correction unit of the present invention, and actual injection start input as an instruction value based on the timing correction amount input from the timing correction amount acquisition unit 80 (correction amount calculation unit 81). Correct the timing.

  If the actual injection start timing is A degree at the crank angle and the timing correction amount is -B degree at the crank angle, the injection start timing calculation unit 91 sets the (A-B) degree as the corrected injection start timing. get. Similarly, when the actual injection start timing is A degree at the crank angle and the timing correction amount is + C degree at the crank angle, the injection start timing calculation unit 91 acquires (A + C) degree as the corrected injection start timing. .

  The timing determination unit 92 is an example of the injection control unit of the present invention, and starts fuel injection from the injector 11 into the cylinder at the corrected injection start timing input from the injection start timing calculation unit 91. That is, the timing determination unit 92 determines the crank angle based on the detection signal input from the engine speed sensor 44, and when the crank angle reaches a crank angle corresponding to the corrected injection start timing, Fuel injection into the cylinder is started.

FIG. 8 is a diagram for comparing the control by the ECU 50 of the present embodiment with the control of the comparative example. The fuel consumption rate (BSFC) when the torque (Torque) of the engine 10 is increased from time t ₁ to time t _2. ), Soot generation amount (Soot), and NOx generation amount.

The solid line in the figure shows the control according to the present embodiment, and the fuel injection start is performed so that the combustion center of gravity (COC) becomes constant over the fluctuation period (t ₁ -t ₃ ) of the excess air ratio (Lambda). Timing (SOI) is corrected. The broken line in the figure shows the control of the comparative example, and the fuel is injected at a constant injection start timing over the fluctuation period of the excess air ratio.

  By performing the control according to the present embodiment, it can be understood that the amount of soot generated and the fuel consumption rate can be significantly reduced while maintaining the amount of NOx generated substantially the same over the fluctuation period of the excess air ratio.

In this embodiment, the engine speed sensor 44 for detecting the crank angle and the fuel injection from the injector 11 into the cylinder are started at the timing when the detected crank angle reaches a predetermined injection start angle. a timing determination unit 92 to the difference value of the target combustion center (COC _{_base)} and the actual combustion center _(COC _act) (△ COC) correction amount of the injection start timing from: Getting (△ SOI correction amount of the injection start angle) Since the timing correction amount acquisition unit 80 and the injection start timing calculation unit 91 that corrects the actual injection start timing (injection start angle) input as the instruction value based on the input timing correction amount are provided, The fuel injection start timing can be controlled without using the measured value. Thereby, the cylinder pressure sensor can be omitted, and even when the cylinder pressure sensor is provided, the fuel injection start timing can be controlled without using the detection signal from the cylinder pressure sensor.

  Further, the timing correction amount acquisition unit 80 acquires a value obtained by multiplying the difference value between the target combustion center of gravity and the actual combustion center of gravity by a constant (−1 / α, −1 / β) as a correction amount of the injection start timing. Therefore, the processing can be simplified and suitable for high-speed processing.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

DESCRIPTION OF SYMBOLS 10 ... Engine, 10A ... Intake manifold, 10B ... Exhaust manifold, 11 ... Injector, 12 ... Common rail, 13 ... Piston, 14 ... Crank, 14A ... Crankshaft, 14B ... Disc, 15 ... Intake passage, 16 ... Air cleaner, 17 DESCRIPTION OF SYMBOLS ... Supercharger, 17A ... Compressor, 17B ... Turbine, 18 ... Intercooler, 19 ... Exhaust passage, 20 ... EGR passage, 21 ... EGR passage, 22 ... EGR cooler, 23 ... EGR valve, 30 ... Exhaust purification device, 30A ... Case, 31 ... NOx occlusion reduction type catalyst, 32 ... Filter, 41 ... Rail pressure sensor, 42 ... Boost pressure sensor, 43 ... Intake air amount sensor, 44 ... Engine speed sensor, 45 ... Accelerator opening sensor, 50 ... ECU, 60 ... target combustion center of gravity acquisition unit, 61 ... combustion center of gravity map, 70 ... actual combustion center of gravity Obtaining unit, 71 ... rail pressure correction amount map, 72 ... intake oxygen concentration correction amount map, 73 ... boost pressure correction amount map, 74 ... target boost pressure map, 75 ... injection timing map, 76 ... actual combustion gravity center calculation unit, 80 ... Timing correction amount acquisition unit, 81 ... Correction amount calculation unit, 90 ... Injection control unit, 91 ... Injection start timing calculation unit, 92 ... Timing determination unit

Claims (2)

Crank angle detecting means for detecting the crank angle;
Injection control means for starting fuel injection from the injector into the cylinder at a timing when the detected crank angle reaches a predetermined injection start angle;
Correction amount acquisition means for acquiring the correction amount of the injection start angle from the difference value between the target combustion center of gravity and the actual combustion center of gravity;
Correction means for correcting the injection start angle based on the correction amount of the injection start angle,
Combustion control device for an internal combustion engine. The correction amount acquisition means acquires a value obtained by multiplying a difference value between the target combustion gravity center and the actual combustion gravity center by a constant as a correction amount of the injection start angle.
The combustion control device for an internal combustion engine according to claim 1.

Images