Control device of internal combustion engine

Abstract

The present invention comprises: a combustion chamber wall temperature estimation unit that obtains estimated values of combustion chamber wall temperatures which include a combustion chamber wall surface temperature and a combustion chamber wall internal temperature; and an ignition timing control unit that retards an ignition timing and advances the ignition timing after retarding the ignition timing, wherein, in ignition timing retardation control for retarding the ignition timing when a knock is detected, the ignition timing control unit sets an ignition timing retardation amount on the basis of at least the estimated value of the combustion chamber wall internal temperature.

Description

Control device for internal combustion engine

[0001] The present invention relates to a control device for an internal combustion engine.

[0002] In recent years, regulations regarding fuel economy and exhaust emissions for automobiles and other vehicles have been strengthened. Such regulations are expected to become even stricter in the future. In particular, regulations regarding fuel economy are an issue of great concern due to the recent rise in fuel prices, the impact on global warming, the depletion of energy resources, and other issues.

[0003] Under these circumstances, for example, in the automotive industry, various technological developments are being made with the aim of improving the fuel economy and exhaust performance of vehicles. One example of such development technologies aimed at improving fuel economy is a high compression ratio technology that increases the compression ratio of an internal combustion engine. Another example of development technologies aimed at improving exhaust performance is a multi-stage injection technology that injects fuel multiple times during the intake stroke, reducing the amount of fuel injected per injection and thereby reducing the particulate number (PN).

[0004] While the above-mentioned high compression ratio technology improves thermal efficiency and fuel economy by increasing the compression ratio of an internal combustion engine, it is known that the temperature inside the combustion chamber increases, making knocking (hereinafter sometimes referred to as "knock"). Therefore, in conventional internal combustion engines, knocking is detected by detecting engine block vibrations or an increase in a specific frequency signal level of in-cylinder pressure when knocking occurs. The occurrence of knocking is detected, for example, by attaching a vibration-type knock sensor to the engine block and analyzing signals output from the knock sensor over a predetermined period (knock window) using FFT (fast Fourier transform). Based on this detection information, conventional internal combustion engines retard the ignition timing after knocking has occurred to prevent subsequent knocking.

[0005] A prior art method for controlling ignition timing to prevent knocking is disclosed, for example, in Patent Document 1. The technology described in Patent Document 1 uses a means for setting the amount of ignition retard for ignition retard control that is implemented after knocking occurs, based on an estimated value of the surface temperature of the combustion chamber wall (hereinafter referred to as surface temperature), which is one of the factors that influence the occurrence of knocking.

[0006] Japanese Patent Application Laid-Open No. 2022-032184

[0007] However, it was newly discovered that, for example, when two conditions are assumed in which the surface temperature of the combustion chamber wall is the same but the internal temperature of the combustion chamber wall is different, if the same ignition retard amount is set, the surface temperature after the ignition retard will be different under the two conditions. In other words, the technology described in Patent Document 1 posed a new problem in that if the ignition timing manipulation amount, including the ignition retard amount after knocking occurs, is determined based only on the surface temperature, the surface temperature may be cooled excessively or insufficiently.

[0008] The present invention has been made in consideration of this problem, and an object of the present invention is to provide a control device for an internal combustion engine that can appropriately control ignition timing after knocking occurs while suppressing deterioration in efficiency.

[0009] The control device for an internal combustion engine of the present invention includes a combustion chamber wall temperature estimator that calculates an estimated value of the combustion chamber wall temperature, including the combustion chamber wall surface temperature and the combustion chamber wall internal temperature, and an ignition timing control unit that retards the ignition timing and advances the ignition timing after the retardation. In retard control that retards the ignition timing when knock is detected, the ignition timing control unit sets the retard amount based on at least the estimated value of the combustion chamber wall internal temperature.

[0010] According to the present invention, it is possible to provide a control device for an internal combustion engine that can appropriately control ignition timing after knocking occurs while suppressing deterioration in efficiency. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments.

[0011] FIG. 1 is a schematic diagram illustrating an example of a system configuration of an internal combustion engine mounted on an automobile according to a first embodiment of the present invention, together with related configurations. FIG. 2 is a block diagram illustrating a hardware configuration of an ECU according to the first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a portion of a liner and a piston in contact with a combustion chamber of the internal combustion engine according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating time changes in surface temperature and internal temperature when ignition timing is manipulated according to the first embodiment of the present invention. FIG. 5 is a functional block diagram illustrating processing details of combustion chamber temperature estimation and an ignition timing control unit according to the first embodiment of the present invention. FIG. 6 is a graph illustrating a schematic diagram of an ignition timing manipulation amount according to the first embodiment of the present invention. FIG. 7 is a flowchart illustrating processing details of a combustion chamber wall temperature estimator according to the first embodiment of the present invention. FIG. 8 is a schematic diagram illustrating a combustion chamber wall transfer ratio according to the first embodiment of the present invention. FIG. 9 is a flowchart illustrating processing details of a retard amount calculator according to the first embodiment of the present invention. FIG. 1 is a schematic diagram showing a map for calculating a retardation margin based on the combustion chamber wall internal temperature or knock frequency in the first embodiment of the present invention. FIG. 2 is a chart for explaining an example of a procedure for determining an advance amount in the first embodiment of the present invention. FIG. 3 is a flowchart showing processing details of an advance rate calculation unit in the first embodiment of the present invention. FIG. 4 is a diagram for explaining the relationship between the ignition timing convergence time and the knock frequency in the first embodiment of the present invention. FIG. 5 is a diagram showing time changes indicating operation of the ignition timing according to the first embodiment of the present invention, where (a) shows a case where the difference between the internal temperature and the surface temperature of the combustion chamber wall is small, and (b) shows a case where the difference between the internal temperature and the surface temperature is large. FIG. 6 is a flowchart showing processing details of combustion chamber temperature estimation based on knock intensity and knock frequency in the second embodiment of the present invention. FIG. 7 is a schematic diagram showing the relationship between knock intensity and surface temperature in the second embodiment of the present invention.Fig. 10 is a flowchart showing the processing contents of a delay amount calculation unit, an advance angle amount calculation unit, and an advance angle speed calculation unit in a second embodiment of the present invention. Fig. 11 is a schematic diagram showing a map of delay angle amounts with surface temperature and internal temperature as axes in a second embodiment of the present invention. Fig. 12 is a schematic diagram showing the difference between delay angle amounts and advance angle amounts with surface temperature and internal temperature as axes in a second embodiment of the present invention. Fig. 13 is a schematic diagram showing the relationship between the difference between surface temperature and internal temperature and the advance angle speed in a second embodiment of the present invention.

[0012] An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, an internal combustion engine that is mounted on an automobile or the like and uses gasoline as fuel will be described as an example, but the present invention can also be applied to other internal combustion engines that use different types of fuel, specifications, or uses.

[0013] First Embodiment First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 17. FIG. 1 is a schematic diagram illustrating an example of the system configuration of an internal combustion engine mounted on an automobile, along with related components. The internal combustion engine ENG illustrated in FIG. 1 is a direct-injection internal combustion engine for an automobile that is driven by spark ignition combustion. For simplicity, FIG. 1 shows only one of multiple cylinders along with related components. This internal combustion engine ENG employs variable valve timing control (VTC), which continuously adjusts the opening and closing timing of the intake valves in accordance with the engine speed and load.

[0014] The internal combustion engine ENG of this embodiment includes an internal combustion engine body, an intake mechanism, an in-cylinder fuel injection mechanism, an ignition mechanism, an exhaust mechanism, a cooling mechanism, etc., as well as an ECU (Electronic Control Unit) 100 that controls each of these components. The ECU 100 is a control device that controls the operation of the internal combustion engine ENG. The ECU 100 calculates and controls major operating variables of the internal combustion engine ENG, such as the air flow rate, fuel injection amount, ignition timing, and fuel pressure, based on the operating state of the internal combustion engine ENG obtained from output information from various sensors.

[0015] The internal combustion engine body includes an engine block 30, a liner 32 that constitutes the cylinder 14, a piston 33 inside the cylinder 14, and a cylinder head 34 at the top of the cylinder 14. A crank angle sensor 19 is disposed in the crank section to detect the position of the piston 33. The crank angle sensor 19 transmits its detection result (output information) to the ECU 100. The ECU 100 calculates the rotation speed of the internal combustion engine based on the output information of the crank angle sensor 19. The engine block 30 also includes a knock sensor 21. The knock sensor 21 detects vibrations of the engine block 30. The knock sensor 21 converts the detected vibrations into an electrical signal and transmits it to the ECU 100. The ECU 100 determines whether knocking (abnormal combustion) has occurred based on the intensity of the output signal from the knock sensor 21 from the engine block 30, etc.

[0016] The internal combustion engine ENG is equipped with an accelerator position sensor 12. The accelerator position sensor 12 detects the amount of depression of the accelerator pedal, i.e., the accelerator position. The accelerator position sensor 12 transmits the detection result (output information) to the ECU 100. The ECU 100 calculates the required torque based on the output information from the accelerator position sensor 12. In other words, the accelerator position sensor 12 can also be considered a required torque detection sensor that detects the required torque to the internal combustion engine ENG.

[0017] The intake mechanism supplies air into multiple cylinders. This intake mechanism includes an air flow sensor 1 (AFS: Air Flow Sensor), an intake pressure sensor 3 (MAP: Manifold Absolute Pressure sensor), and an intake pipe 7 having a collector 6. The air flow sensor 1 measures the intake air amount (air flow rate) and intake air temperature. The intake pressure sensor 3 measures the intake pipe pressure (intake pressure). The various sensors, such as the air flow sensor 1 and the intake pressure sensor 3, send their detection results to the ECU 100.

[0018] The ECU 100 calculates the throttle opening and sends the calculated throttle opening as a throttle drive signal to the electronically controlled throttle 2. The electronically controlled throttle 2 adjusts the intake pipe pressure (in other words, the air flow rate). The cylinder head 34 is equipped with a variable valve 5 for adjusting the air-fuel mixture flowing into the cylinder or the exhaust gas discharged from the cylinder. The variable valve 5 adjusts the intake air amount and internal EGR amount for each cylinder.

[0019] The in-cylinder fuel injection mechanism includes a fuel injection device (hereinafter also referred to as an injector) 13 for each cylinder, which directly injects gasoline fuel into each of the cylinders. A high-pressure fuel pump (not shown) for supplying high-pressure fuel and a fuel pipe are connected to the injector 13. A fuel pressure sensor for measuring the fuel injection pressure is provided in the fuel pipe, and the detection result (output information) of the fuel pressure sensor is sent to the ECU 100. The fuel injection amount calculated by the ECU 100 is converted into a valve-opening pulse signal and sent to the injector 13.

[0020] The ignition mechanism includes an ignition coil 16 for igniting the mixture of gasoline fuel and air injected into the cylinder, and an ignition plug 17 for supplying ignition energy to the ignition coil 16, for each cylinder. In the ignition mechanism of this embodiment, the ignition timing is controlled by the ECU 100. An ignition signal is sent to the ignition coil 16 so that ignition occurs at the ignition timing controlled by the ECU 100. When the ignition signal is sent from the ECU 100 to the ignition coil 16, the mixture is combusted in the cylinder.

[0021] The exhaust mechanism includes an exhaust pipe 15 that exhausts air after combustion in the cylinders. The exhaust pipe 15 includes a three-way catalyst 10 that purifies the exhaust gas, and an air-fuel ratio sensor 9 that detects the air-fuel ratio of the exhaust gas. The air-fuel ratio sensor 9 transmits the detection result (output information) to the ECU 100. An external EGR unit 24 is provided downstream of the three-way catalyst 10 between the three-way catalyst 10 and the intake pipe 7.

[0022] The cooling mechanism includes a cooling water system (not shown) for lowering the temperatures of the engine block 30, liner 32, cylinder head 34, etc., and an oil jet system 20 for lowering the temperatures of the piston 33, crank, etc. The oil jet system 20 is connected to a variable displacement (variable oil pressure) oil pump 20a.

[0023] The cooling mechanism includes a temperature sensor 18 that measures the temperature of the coolant circulating around the internal combustion engine ENG. The temperature sensor 18 transmits the detection result (output information) to the ECU 100. The oil pump 20a also adjusts the output (flow rate, oil pressure) to adjust the amount of oil injected from the oil jet system 20 toward the back of the piston 33 of each cylinder.

[0024] In this type of internal combustion engine ENG, fuel injected from an injector 13 is added to air that flows into a cylinder 14 from an intake pipe 7 via an intake valve to form an air-fuel mixture. The air-fuel mixture is ignited (exploded) by a spark generated by a spark plug 17 at a predetermined ignition timing. The combustion pressure of the air-fuel mixture then pushes a piston downward, rotating a rotating shaft (crankshaft) connected to the piston via a connecting rod. This generates driving force for the internal combustion engine ENG. Exhaust gases after the explosion are sent to a three-way catalyst 10 via an exhaust pipe 15. The exhaust gases are purified of exhaust components within the three-way catalyst 10 and then discharged to the outside.

[0025] FIG. 2 is a block diagram showing a schematic hardware configuration of the ECU 100. In FIG. 2, information from various sensors is input to an input circuit 121 of the ECU 100, which is a control device for the internal combustion engine ENG. The information input to the input circuit 121 includes the following: air flow rate (intake flow rate) from the air flow sensor 1; intake manifold pressure (intake pressure) from the intake pressure sensor 3; coil primary or secondary voltage from a voltage sensor of the ignition coil 16; fuel injection pressure from a fuel pressure sensor of the fuel injector 13; crank angle from the crank angle sensor 19; exhaust gas air-fuel ratio (exhaust air-fuel ratio) from the air-fuel ratio sensor 9; coolant temperature from the temperature sensor 18; accelerator opening from the accelerator opening sensor 12; rotational speed of the rotating shaft (crankshaft); various VTC setting values ​​(VTC settings); and knock sensor signals. However, the information input to the ECU 100 is not limited to these.

[0026] Information input to the input circuit 121 of the ECU 100 is sent to the input port side of the input / output port 122. The input information sent to the input / output port 122 is temporarily stored in the RAM 123c and is processed by the CPU 123a in accordance with a predetermined control program. The control program, which describes the details of the processing, is written in the ROM 123b in advance. The input information is processed in accordance with the control program to generate output information for controlling the internal combustion engine ENG.

[0027] Output information indicating the amount of actuation of the ignition coil 16 is temporarily stored in RAM 123c, and then sent to the output port side of the input / output port 122, and then sent to the ignition control unit 124, fuel injection control unit 125, etc. Note that various actuators other than those mentioned above are used in the internal combustion engine ENG, but their description will be omitted here.

[0028] In this embodiment, the ECU 100 has an ignition control unit 124 as a drive circuit. The ignition control unit 124 acquires information (operation amount) related to the timing and duration of energization of the ignition coil 16 as an operation amount of the associated actuator. The ignition control unit 124 controls the timing and duration of energization of the ignition coil 16 based on the acquired operation amount. Note that in this embodiment, a part of the ignition control unit 124 for controlling the duration of energization and the amount of discharge energy of the ignition coil may be implemented in a device separate from the ECU 100.

[0029] Next, heat transfer in the combustion chamber wall of an internal combustion engine ENG will be described. Figure 3 is a schematic diagram showing a part of the combustion chamber wall in contact with the combustion chamber. The combustion chamber 31 is a space where combustion of a fuel-air mixture takes place, and the wall in contact with the combustion chamber 31 is the combustion chamber wall. The combustion chamber walls shown in Figure 3 are a liner 32, a piston 33, and a cylinder head 34.

[0030] The surfaces of the combustion chamber wall are surfaces 32a, 33a, and 34a of the liner 32, piston 33, and head 34. The surfaces 32a, 33a, and 34a are the surfaces that come into contact with gas inside the combustion chamber 31. The interior of the combustion chamber wall is interiors 32b, 33b, and 34b of the liner 32, piston 33, and head 34. The combustion chamber wall usually comes into contact with cooling water, air, oil jets, and the like on the side opposite to the surface facing the combustion chamber (back side). The temperature of the combustion chamber wall is controlled by exchanging energy with these elements through heat transfer.

[0031] The temperature inside the combustion chamber wall changes more slowly than the temperature change on the surface of the combustion chamber wall due to the heat capacity of the combustion chamber wall and the heat transfer and heat exchange with the back side. On the other hand, the temperature on the surface of the combustion chamber wall tends to change more easily in response to changes in the conditions of the combustion chamber 31 than the temperature change inside the combustion chamber wall. This difference in responsiveness can lead to situations where the internal temperature of the combustion chamber wall is different even if the surface temperature is the same.

[0032] In Figure 4, the upper part shows a signal that detects whether or not knock has occurred (hereinafter referred to as a knock flag), the middle part shows the operation of the ignition timing, and the bottom part shows the change in combustion chamber wall temperature over time when the ignition timing is operated. Figure 4 shows examples of combustion chamber wall temperature under two conditions. Under the two conditions, Condition L and Condition H, the surface temperature when knock occurs is the same, but the internal temperature when knock occurs is higher under Condition H than under Condition L.

[0033] As shown in the middle part of Figure 4, the lower part of Figure 4 shows the history of the surface temperature Tsf and the internal temperature Tin when the same ignition timing operation is performed under conditions L and H. In the lower part of Figure 4, the change in the combustion chamber wall temperature is shown by the solid lines for the surface temperature TsfL and the internal temperature TinL under condition L, and by the dashed lines for the surface temperature TsfH and the internal temperature TinH under condition H.

[0034] The two dashed dotted lines in the lower row indicate the steady-state values ​​of the surface temperature Tsf and the internal temperature Tin that are reached when the ignition timing is maintained at ADV1 and a constant rotation speed is maintained. The horizontal axis indicates time, with t1 indicating the timing when a knock occurred and t2 indicating the timing when the ignition timing was retarded. Also, t3 indicates the timing when the ignition timing was advanced after the retard operation to return to the ignition timing before the knock occurred. t4 indicates the timing when the surface temperature TsfH almost converges to the steady-state value under condition H. t5 indicates the timing when the surface temperature TsfL converges under condition L.

[0035] 4, the ignition timing is set to ADV1 at time t1 when knock occurs, and is then temporarily retarded after the knock occurs, and then gradually advanced back to the original ignition timing ADV1, and the ignition timing is controlled so that this ignition timing ADV1 is maintained. If the ignition timing is retarded at time t2, which is the next combustion cycle after knock occurs at time t1, the amount of heat transferred from the gas in the combustion chamber 31 to the surfaces (32a, 33a, 34a) of the combustion chamber walls (liner 32, piston 33, and head 34) decreases, and the surface temperatures TsfL and TsfH decrease.

[0036] On the other hand, when the amount of heat conduction to the interior (32b, 33b, 34b) decreases due to a decrease in the surface temperatures TsfL and TsfH, the internal temperatures TinL and TinH decrease. Therefore, the decrease in the internal temperatures TinL and TinH occurs with a delay from the decrease in the surface temperatures TsfL and TsfH.

[0037] Under condition H, where the internal temperature is high, the amount of heat conducted to the interior of the combustion chamber wall is smaller than under condition L, and therefore, as shown by A in the figure, the decrease in surface temperature TsfH after retarding the ignition timing is smaller than under condition L. Thereafter, by advancing the ignition timing, the amount of heat conducted from the combustion gas in the combustion chamber to the surface of the combustion chamber wall increases, so the surface temperatures TsfL and TsfH increase, and after a slight delay, the internal temperatures TinL and TinH also increase.

[0038] As shown in the middle of Figure 4, if the ignition timing is advanced at a predetermined rate over multiple combustion cycles, and then returned to the original ignition timing ADV1 and operation is continued at a constant value, the internal temperatures TinL and TinH will eventually converge to a steady state. The state in which the internal temperature TinH drops after a retard operation under condition H is closer to this steady state than the internal temperature TinL under condition L. Therefore, condition H converges to the steady state at time t4, earlier than condition L. On the other hand, condition L converges to the steady state at time t5, later than condition H. This difference in convergence time is indicated by B in the figure.

[0039] Thus, even if the surface temperatures TsfL and TsfH are the same at the time that knock occurs, if the internal temperatures TinL and TinH are different, the change in surface temperature in response to the operation of the ignition timing will differ. Therefore, the control device for the internal combustion engine ENG of this embodiment operates the ignition timing taking into account not only the surface temperature of the combustion chamber wall but also the internal temperature, thereby suppressing knocking while suppressing deterioration in efficiency such as fuel economy and output.

[0040] 5 is a functional block diagram showing the processing performed by the combustion chamber wall temperature estimation unit and ignition timing control unit in the CPU. The combustion chamber wall temperature estimation unit 501 and ignition timing control unit 502 are functions realized by a program executed by the CPU 123a in the ECU 100. The CPU 123a performs arithmetic processing using various inputs from the input circuit 121. For example, the inflow air flow rate of each cylinder is calculated using input values ​​such as the air flow sensor measurement value, engine speed, and coolant temperature. The intake air pressure is calculated using the energy conservation equation and the gas state equation based on the mass within the volume from the throttle to the engine, etc.

[0041] 5 estimates combustion chamber wall temperatures, including the combustion chamber wall surface temperature and the combustion chamber internal temperature, when knock occurs and at various assumed times, based on operating condition parameters, temperature condition parameters, ignition timing, etc. Ignition timing control unit 502 controls the ignition timing using the estimated results of the combustion chamber wall surface temperature and internal temperature when knock occurs and at various assumed times.

[0042] The ignition timing control unit 502 performs retard control to retard the ignition timing, and advance control to advance the ignition timing immediately after the retard control. The ignition timing control unit 502 of this embodiment may perform advance control all at once immediately after the retard control, or may perform advance control separately into first advance control and second advance control that advances the ignition timing at an advance speed slower than the first advance control.

[0043] This ignition timing control unit 502 includes a retard amount calculation unit 503, an advance amount calculation unit 504, and an advance rate calculation unit 505. The retard amount calculation unit 503 calculates the retard amount in the retard control after knock detection. The advance amount calculation unit 504 calculates the advance amount after the ignition retard implemented after knock detection, i.e., the advance rate in the first advance control. The advance rate calculation unit 505 calculates the speed (advance rate) at which the ignition timing is advanced after the ignition advance in the first advance control, i.e., the advance rate in the second advance control.

[0044] Fig. 6 is a chart for explaining the amount of ignition timing manipulation. The knock flag shown in the upper part of Fig. 6 indicates whether or not knock has occurred. The lower part of Fig. 6 shows the change in ignition timing over time when ignition timing manipulation is performed using the retard amount, advance amount, and advance rate calculated by the combustion chamber wall temperature estimation unit 501 and the ignition timing control unit 502 in Fig. 5.

[0045] When the ignition timing control unit 502 detects the occurrence of knock, it performs retard control to retard the ignition timing using the estimated values ​​of the surface temperature and internal temperature of the combustion chamber wall estimated by the combustion chamber wall temperature estimation unit 501. Here, the retard amount indicates how much the ignition timing is retarded relative to the ignition timing at the time of the knock occurrence or a preset reference ignition timing. This retard amount is an amount by which the ignition timing is rapidly retarded in a short combustion cycle immediately after the knock occurrence. For example, it may be the retard amount in the next combustion cycle immediately after the knock occurrence.

[0046] After performing the retard control, the ignition timing control unit 502 performs a first advance control of the ignition timing. The advance amount indicates how much the ignition timing is advanced relative to the ignition timing that was retarded after the occurrence of knock. This advance amount is the amount advanced in a predetermined short combustion cycle immediately after the retard control of the ignition timing. For example, it may be the advance amount in the next combustion cycle immediately after the retard control. This advance amount is preferably equal to or smaller than the retard amount in the retard control, and in this embodiment, it is an angle smaller than the retard amount in the retard control.

[0047] After the first advance control is performed, if there is room to advance the ignition timing, for example, if the advance amount is smaller than the delay amount in the delay control, a second advance control is performed to gradually advance the ignition timing at an advance rate slower than that in the first advance control. Here, the advance rate can be expressed as the amount by which the ignition timing is gradually advanced per unit time. For example, the advance rate may be the amount by which the ignition timing is advanced over a predetermined number of combustion cycles immediately after the first advance control.

[0048] In this embodiment, the sum of the advance amounts in the first advance control and the second advance control may be set to be equal to the delay amount in the delay control. In this way, the first advance control and the second advance control return the ignition timing to the value before the delay control, such as the ignition timing at the time of knocking or a preset reference ignition timing.

[0049] Next, a process for operating the ignition timing by calculation in the control device for the internal combustion engine ENG will be described. First, a combustion chamber wall temperature estimation unit 501 estimates the combustion chamber wall surface temperature and the combustion chamber wall internal temperature, and then an ignition timing control unit 502 controls the ignition timing based on the estimated values.

[0050] 7 is a flowchart showing the processing contents of the combustion chamber wall temperature estimation unit. In step S701, the combustion chamber wall temperature estimation unit 501 calculates the amount of energy dQinput / dt [J / s] to be input to the engine. For example, as shown in equation 1, the amount of energy can be calculated using the air flow rate mair [kg / s] detected by the air flow sensor 1, the exhaust air-fuel ratio AbF [-] detected by the air-fuel ratio sensor 9, and the calorific value Qfuel [J / kg] of the fuel.

[0051]

[0052] After calculating the amount of energy input, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S702. In step S702, the combustion chamber wall temperature estimation unit 501 calculates the energy transfer rate dQwall / dt [J / s] due to heat transfer to the combustion chamber wall using the ignition timing. For example, as shown in equation 2, the energy transfer rate can be calculated using the ratio of the amount of energy transferred to the combustion chamber wall from the amount of input energy (combustion chamber wall transfer rate) Rwall [-].

[0053]

[0054] Here, the combustion chamber wall transfer fraction Rwall changes continuously depending on the ignition timing. FIG. 8 is a graph schematically showing the combustion chamber wall transfer fraction. As shown in FIG. 8, when the ignition timing is retarded, the combustion chamber wall transfer fraction decreases from the optimal ignition timing (MBT in the figure). In this case, the combustion chamber wall transfer fraction can be evaluated as a function of the ignition timing. In FIG. 8, the combustion chamber wall transfer fraction can be expressed as a quadratic function of the ignition timing, as shown in Equation 3, for example.

[0055] Here, θ is the ignition timing (deg), α (-), β (-), and θref (deg) are coefficients in the approximation formula, and are parameters identified from the results of prior experiments and simulations. By specifying the ignition timing, the combustion chamber wall transfer fraction can be calculated. In addition to the ignition timing, the combustion chamber wall transfer fraction can also include changes in the combustion chamber surface temperature and combustion gas temperature.

[0056] After calculating the energy transfer rate dQwall / dt due to heat conduction to the surface of the combustion chamber wall in step S702, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S703. In step S703, the combustion chamber wall temperature estimation unit 501 calculates the energy transfer rate due to heat conduction between the surface of the combustion chamber wall and the interior of the combustion chamber wall, where the walls are in contact. The calculation formulas for the energy transfer rate due to heat conduction can be generalized as the following formulas 4 to 7.

[0057]

[0058] In Equations 4 to 7, dQsfc / dt is the energy transfer rate [J / s] due to heat conduction between the surface of the combustion chamber wall and the wall it contacts, and dQinc / dt is the energy transfer rate [J / s] due to heat conduction between the interior of the combustion chamber wall and the wall it contacts. Here, heat conduction is calculated assuming that the combustion chamber wall consists of two walls: the surface and the interior. i is the number assigned to the contacting wall (i = 1, 2, ...). For the i-th wall, one of the i-th walls facing the surface is the interior, and conversely, one of the i-th walls facing the interior is the surface.

[0059] In addition, in Equations 4 to 7, dQsfc,i / dt is the energy transfer rate by heat conduction to the i-th wall that the surface contacts [J / s], and dQinc,i / dt is the energy transfer rate by heat conduction to the i-th wall that the interior contacts [J / s]. λsf,i is the thermal conduction coefficient between the i-th wall and the surface [W / m2 / K], λin,i is the thermal conduction coefficient between the i-th wall and the interior [W / m2 / K], Ti is the temperature of the i-th wall [K], Tsf is the surface temperature [K], Tin is the interior temperature [K], Lsf,i is the distance between the surface and the i-th wall [m], Lin,i is the distance between the interior and the i-th wall [m], Ssf,i is the contact area between the surface and the i-th wall [m2], and Sin,i is the contact area between the interior and the i-th wall [m2].

[0060] 3, examples of walls that come into contact with the surface 32a of the liner 32 include the interior 32b of the liner 32, the surface 33a of the piston 33, the interior 33b of the piston 33, and the surface 34a of the head 34. Examples of walls that come into contact with the interior 32b of the liner 32 include the surface 32a of the liner 32. Similarly, examples of walls that come into contact with the surface 34a of the head 34 include the interior 34b of the head 34 and the surface 32a of the liner 32, and examples of walls that come into contact with the interior 34b of the head 34 include the surface 34a of the head 34. Furthermore, examples of walls that come into contact with the surface 33a of the piston 33 include the interior 33b of the piston 33 and the surface 32a of the liner 32, and examples of walls that come into contact with the interior 33b of the piston 33 include the surface 33a of the piston 33 and the surface 32a of the liner 32.

[0061] The thermal conductivity coefficient, wall distance, and contact area are often determined by physical properties and design values. However, if they cannot be determined from physical properties and design values ​​because multiple materials are sandwiched in the contact area or the shape is complex, appropriate values ​​determined in advance through prior experiments or simulations can be used.

[0062] After calculating the energy transfer rate due to heat conduction in step S703, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S704. In step S704, the energy transfer rate due to heat transfer between the inside of the combustion chamber wall and a fluid in contact with the inside is calculated. The fluid in contact with the inside of the combustion chamber wall is, for example, cooling water, an oil jet, air, etc., as shown in FIG. 3. The formula for calculating the energy transfer rate due to heat conduction can be generalized to the following equations 8 and 9.

[0063]

[0064] Here, dQint / dt [J / s] is the energy transfer rate due to heat transfer between the interior and the fluid. i is the number assigned to the contacting fluid (i = 1, 2, ...). Examples of fluids that come into contact with the interior of the liner include cooling water and air. Examples of fluids that come into contact with the interior of the piston include oil jets and air. Examples of fluids that come into contact with the interior of the head include cooling water and air.

[0065] In Equations 8 and 9, dQint,i / dt is the energy transfer rate due to heat transfer between the interior and the i-th fluid with which it is in contact. hint,i is the heat transfer coefficient [W / m2 / K] between the interior and the i-th fluid, Tl,i is the temperature of the i-th fluid, and Sinl,i is the contact area between the interior and the i-th fluid. If the heat transfer coefficient and contact area cannot be determined from the physical property values ​​and design values, appropriate values ​​obtained in advance through prior experiments or simulations can also be used.

[0066] In step S704, once the energy transfer rate due to heat transfer between the interior and the fluid has been calculated, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S705. In step S705, the combustion chamber wall temperature estimation unit 501 calculates an estimated surface temperature value and an estimated internal temperature value of the combustion chamber wall using equations 10 and 11.

[0067]

[0068] where Tsf,now is the current estimated surface temperature value [K], Tin,now is the current estimated internal temperature value [K], Msf is the surface mass [kg], Min is the internal mass [kg], Csf is the surface specific heat [J / kg / K], Cin is the internal specific heat [J / kg / K], and Δt is the calculation period [s]. If the mass and specific heat cannot be determined from the physical property values ​​and design values, appropriate values ​​obtained in advance through prior experiments or simulations can also be used.

[0069] Next, a description will be given of the processing in the ignition timing control unit 502. The processing in the ignition timing control unit 502 includes a delay amount calculation unit 503 calculating the delay amount, a lead amount calculation unit 504 calculating the lead amount, and a lead speed calculation unit 505 calculating the lead speed.

[0070] First, the calculation process of the delay amount by delay amount calculation unit 503 will be described. FIG. 9 is a flowchart showing the process performed by the delay amount calculation unit. In step S901, delay amount calculation unit 503 sets a target surface temperature decrease amount based on knock recurrence temperature Tkc. Delay amount calculation unit 503 may start the process when the estimated surface temperature reaches a predetermined temperature. In this embodiment, delay amount calculation unit 503 can start the process when knock recurrence temperature Tkc reaches a temperature that is provided with a margin, which will be described later.

[0071] Here, the knock recurrence temperature Tkc is a reference temperature at which knock is expected to occur, in other words, the expected knock occurrence temperature. This knock recurrence temperature Tkc is a parameter that can be determined in advance. The knock recurrence temperature Tkc may be calculated assuming a standard fuel. Furthermore, the retard amount and the advance amount (described later) may be calculated based on fuel properties determined based on at least one of a fuel injection parameter and the ratio of the fuel amount to the air amount that results in a stoichiometric mixture ratio.

[0072] The knock recurrence temperature Tkc may be a value that is adapted using a map that is obtained in advance through prior experiments, simulations, etc. For example, because the knock recurrence temperature Tkc varies depending on the engine speed, engine load, and coolant temperature, a map based on these factors may be stored in advance, and an adapted value may be used when calculating the retard amount.

[0073] FIG. 10 is a schematic diagram showing a map of knock recurrence temperature with engine load and engine speed as axes, with each solid line indicating the knock recurrence temperature Tkc. Because this relationship varies depending on the coolant temperature, in this embodiment, a map like the one shown in FIG. 10 is created for each coolant temperature. In this map, the higher the engine speed, the higher the knock recurrence temperature Tkc. The higher the engine load, the higher the knock recurrence temperature Tkc. Furthermore, the higher the coolant temperature, the higher the knock recurrence temperature Tkc.

[0074] Using the knock recurrence temperature Tkc obtained from the map, the target temperature decrease amount ΔTsf[K] can be determined from the current estimated surface temperature value Tsf,now as shown in Equation 12.

[0075]

[0076] Here, ΔTsf,mar is a retard margin [K] provided between the temperature reached when the timing is retarded and the knock recurrence temperature. In this embodiment, the retard margin may be a preset constant value, but it can also be set according to the internal temperature of the combustion chamber wall or the knock frequency. The knock frequency, which will be described later, is the number of knock occurrences per combustion cycle calculated based on the number of knocks that occurred in a predetermined number of combustion cycles immediately preceding the retard margin. In this embodiment, as will be described later, the knock frequency may be calculated from a weighted value obtained by using a weighted average of a single knock flag.

[0077] FIG. 11 is a schematic diagram showing a map for determining the retard margin based on the combustion chamber wall internal temperature or knock frequency. It is assumed that the surface temperature of the combustion chamber wall is difficult to decrease when the internal temperature is high and difficult to decrease when the knock frequency is high. Therefore, the retard amount calculation unit 503 can determine the retard margin ΔTsf,mar using a map that indicates the retard margin corresponding to the estimated internal temperature or the knock frequency. These maps can be set in advance through experiments or simulations.

[0078] After the target surface temperature decrease amount is determined in step S901, the process of the delay amount calculation unit 503 proceeds to step S902. In step S902, the delay amount calculation unit 503 determines the delay target surface temperature from the target surface temperature decrease amount and the surface temperature estimate value. For example, the delay target surface temperature can be calculated using equation 13 from the current value Tsf,now of the surface temperature estimate value and the target temperature decrease amount ΔTsf.

[0079]

[0080] Here, Tsf, tar is the retard angle target surface temperature [K]. Once the retard angle target surface temperature is determined in step S902, the process of the retard angle calculation unit 503 proceeds to step S903.

[0081] In step S903, the retard amount calculation unit 503 sets the retard target ignition timing based on the retard target surface temperature, the estimated surface temperature, and the estimated internal temperature. The retard target ignition timing can be set using, for example, Equation 14, which is derived using Equations 1 to 11.

[0082]

[0083] Here, θtar is the retarded target ignition timing [deg], θref is the coefficient [deg] of Equation 3, Tsf,tar is the target value of the surface temperature [K], Tsf,now is the current value of the estimated surface temperature [K], and Ti,now is the current value of the estimated temperature of the i-th wall with which the surface contacts [K], and one of the i-th walls is the interior.

[0084] After the target ignition timing is determined in step S903, the process of the delay amount calculation unit 503 proceeds to step S904. In step S904, the delay amount calculation unit 503 calculates the delay amount from the current ignition timing and the target ignition timing. If the current ignition timing is θnow, the delay amount ΔθR can be calculated using equation 15.

[0085] The delay amount calculation unit 503 sets ΔθR [deg] calculated by the formula 15 as the delay amount.

[0086] In setting the above retard amount, as shown in Equation 14, the ignition timing retard amount is determined taking into account the current estimated value of the combustion chamber wall internal temperature. For example, the internal estimated value is taken into account as the current estimated value of the temperature of the i-th wall in contact with the surface. Furthermore, as shown in FIG. 11, the higher the estimated internal temperature, the smaller the difference with the surface temperature and the more difficult it is for the surface temperature to drop, so the retard margin is set to be larger. As a result, the ignition timing can be determined to satisfy the target surface temperature by taking into account the estimated internal temperature, so an appropriate ignition retard amount can be set.

[0087] Next, the calculation process of the advance amount by advance amount calculation unit 504 will be described. FIG. 12 is a flowchart showing the processing content of the advance amount calculation unit. In step S1201, advance amount calculation unit 504 compares the current value of the estimated surface temperature with the knock recurrence temperature. If the current value of the estimated surface temperature is higher than the knock recurrence temperature, this indicates that the amount of ignition timing retard may be insufficient. If the determination is YES, the processing by advance amount calculation unit 504 proceeds to step S1205. If the determination is NO, the processing by advance amount calculation unit 504 proceeds to step S1202.

[0088] In step S1202, advance amount calculation unit 504 sets an advance target surface temperature with a margin from the knock recurrence temperature. For example, advance target surface temperature Tsf,tar,a can be set by Expression 16 as a value with a margin from the knock recurrence temperature.

[0089]

[0090] Here, Tkc is the knock recurrence temperature, and ΔTsf,a is the advance margin [K] that is provided between the temperature reached when the advance is made and the knock recurrence temperature. In this embodiment, the advance margin ΔTsf,a may be a preset constant value, but it can also be set in accordance with the internal temperature of the combustion chamber wall or the knock frequency. The knock frequency, which will be described later, is the number of knock occurrences per combustion cycle calculated based on the number of knocks that occurred in a predetermined number of combustion cycles immediately preceding the advance. In this embodiment, as will be described later, the knock frequency may be determined from a value weighted using a weighted average from a single knock flag.

[0091] FIG. 13 is a schematic diagram showing a map for determining the advance margin based on the combustion chamber wall internal temperature or knock frequency. It is assumed that the surface temperature of the combustion chamber wall is difficult to decrease when the internal temperature is high. This also suggests that the surface temperature of the combustion chamber wall is difficult to decrease when the knock frequency is high. Therefore, the advance amount calculation unit 504 can determine the advance margin ΔTsf,a using a map that indicates the advance margin corresponding to the estimated internal temperature or the knock frequency. These maps can be set in advance through prior experiments or simulations.

[0092] After the target surface temperature is determined in step S1202, the process of the advance angle calculation unit 504 proceeds to step S1203. In step S1203, the advance angle calculation unit 504 sets the target ignition timing based on the target surface temperature, the estimated surface temperature, and the estimated internal temperature. For example, this can be determined by equation 17, which is similar to equation 14, which is derived from equations 1 to 11.

[0093] where θtar,a is the target ignition timing after advance [deg], and Tsf,tar,a is the target surface temperature value after advance [K]. The other coefficients are the same as in Equation 14.

[0094] After the target ignition timing is set in step S1203, the process of the advance amount calculation unit 504 proceeds to step S1204. In step S1204, the advance amount is calculated from the current ignition timing and the target ignition timing using equation 18. For example, the advance amount can be calculated from the current ignition timing and the target ignition timing after the advance calculated in step S1003.

[0095] Here, Δθa is the advance angle [deg].

[0096] In this embodiment, instead of steps S1203 and S1204, the target value of the advance angle can be searched for by repeatedly calculating the surface temperature attainment values ​​for a plurality of advance angles.

[0097] FIG. 14 is a chart illustrating an example of a procedure for determining the advance amount. In FIG. 14, the knock recurrence temperature Tkc is indicated by a solid line, and the target surface temperature value Tsf,tar,a, to which an advance margin ΔTsf,a is added, is indicated by a dashed line. In step S1203, advance amount calculation unit 504 calculates target surface temperature values ​​Tsfθ1...Tsfθn for multiple advance amounts for the ignition retard amount after retardation performed by retard amount calculation unit 503. A search is made for an advance amount such that the target temperatures Tsfθ1...Tsfθn for each calculated advance amount are temperatures suitable for the current conditions.

[0098] The temperature reached when the internal temperature is TinL differs from that reached when the internal temperature is TinH, which is higher than TinL. When the internal temperature is TinH, that is, when the difference between the internal temperature and the surface temperature is small, the target surface temperature is reached with a small amount of advance. Therefore, the target ignition timing θtar,a varies depending on the difference between the internal temperature and the surface temperature. Therefore, the target ignition timing θtar,a can be determined by calculating the amount of advance that will result in the surface temperature reached by multiple amounts of advance at the current internal temperature being the target surface temperature value (dashed line) with an advance margin.

[0099] On the other hand, if it is determined in step S1202 that the cooling is insufficient, then in step S1205, the amount of ignition advance is set so as to retard the ignition by a predetermined value, as shown in the following equation (19).

[0100] Here, Δθa,e is a predetermined value [deg] of the retard angle.

[0101] As described above, by setting the amount of ignition advance, the ignition can be advanced within a range that prevents the surface temperature from exceeding a predetermined value, and by taking the internal temperature into consideration, the ignition timing can be advanced to avoid being over or under advanced. As a result, the period during which the ignition timing is retarded can be minimized, and deterioration of fuel economy due to continued ignition timing retardation can be suppressed.

[0102] Next, the calculation process of the advance angular speed by advance angular speed calculation unit 505 will be described. Fig. 15 is a flowchart showing the processing content of advance angular speed calculation unit 505. In step S1501, advance angular speed calculation unit 505 calculates the amount of change in the amount of heat conduction based on the estimated value of the surface temperature of the combustion chamber wall and the estimated value of the internal temperature. The rate of energy transfer due to heat conduction between the surface and internal of the combustion chamber wall can be written as shown in the following equation 20 from equations 4 to 7.

[0103]

[0104] Here, dQcinsf / dt is the rate of energy transfer due to heat conduction from the surface to the interior [J / s], λinsf is the thermal conductivity between the surface and the interior [W / m2 / K], Tsf is the estimated surface temperature [K], Tin is the estimated internal temperature [K], Linsf is the distance between the surface and the interior [m], and Sinsf is the contact area between the surface and the interior [m2].

[0105] The amount of change in the rate of energy transfer due to thermal conduction can be calculated, for example, by using the current values ​​of Tin and Tsf and the values ​​several steps before in equation (21).

[0106]

[0107] Here, ΔdQcinsf / dt is the change in the energy transfer rate due to thermal conduction [J / s], dQcinsf / dt(tnow) is the change in the energy transfer rate due to thermal conduction [J / s] calculated by inputting the current estimated surface temperature and estimated internal temperature values ​​into equation 20, and dQcinsf / dt(tpast) is the change in the energy transfer rate due to thermal conduction [J / s] calculated by inputting the past estimated surface temperature and estimated internal temperature values ​​into equation 20.

[0108] After calculating the amount of change in the energy transfer rate due to heat conduction in step S1501, the processing of the advance angular velocity calculation unit 505 proceeds to step S1502. In step S1502, the advance angular velocity calculation unit 505 calculates the energy transfer rate due to heat conduction from the gas in the combustion chamber to the surface of the combustion chamber wall, which is required to maintain the surface temperature.

[0109] The advance angular velocity calculation unit 505 can calculate the required energy transfer velocity, for example, by calculating the energy transfer velocity due to heat conduction from the gas in the combustion chamber to the surface of the combustion chamber wall at the current ignition timing from equations 2 and 3, and adding this to the change in the energy transfer velocity due to heat conduction calculated in step S1501 using equation 22.

[0110]

[0111] Here, dQwall,tar / dt is the energy transfer rate [J / s] due to heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall required to maintain the surface temperature, and dQwall,now / dt is the energy transfer rate [J / s] due to heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall calculated from Equation 2 and Equation 3 and the current ignition timing setting.

[0112] After calculating the energy transfer rate by heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall, which is necessary to maintain the surface temperature, in step S1502, the processing of the advance angular velocity calculation unit 505 proceeds to step S1503. In step S1503, the advance angular velocity calculation unit 505 calculates the ignition timing that achieves the target energy transfer rate by heat transfer to the surface of the combustion chamber wall. For example, assuming that dQwall,tar / dt calculated in step S1202 is equal to the values ​​of Equation 2 and Equation 3, Equation 23 is derived.

[0113]

[0114] Here, θtar, a2 is the target ignition timing [deg]. By solving Equation 19 for θtar, a2, the target ignition timing is derived as shown in Equation 24.

[0115]

[0116] In step S1504, the advance angular velocity calculation unit 505 converts the time required to converge to the target ignition timing into an advance angular velocity θdot [s]. The advance angular velocity is determined by the following equation (25).

[0117]

[0118] Note that the time it takes for the ignition timing to converge affects the knock frequency. Therefore, in this embodiment, the time tdel required for the ignition timing to converge to the target ignition timing is set based on the time required to achieve the target knock frequency.

[0119] 16 is a diagram illustrating the relationship between the ignition timing convergence time and the knock frequency. The horizontal axis represents the ignition timing convergence time, and the vertical axis represents the knock frequency. When the operating conditions of the internal combustion engine ENG, such as the torque and rotation speed, are constant, the knock frequency decreases as the ignition timing convergence time increases. Therefore, in this embodiment, the ignition timing convergence time that results in a preset target knock frequency, as indicated by the dashed line, can be used as the target ignition timing convergence time tdel.

[0120] By determining the advance rate of the ignition timing as described above, advance rate calculation unit 505 can appropriately set the advance rate of the ignition timing in accordance with changes in the amount of heat conduction from the surface to the interior, which changes with changes in the internal temperature. As a result, advance rate calculation unit 505 can control the surface temperature to an appropriate temperature range while taking the internal temperature into consideration, thereby achieving both suppression of knock recurrence and suppression of deterioration in fuel economy due to retardation of the ignition timing.

[0121] According to the internal combustion engine control device of this embodiment, when controlling the ignition timing after a knock occurs, the ignition timing can be controlled while appropriately managing the surface temperature of the combustion chamber at a temperature close to the knock recurrence temperature. Here, by taking the internal temperature into consideration, appropriate ignition retard amounts, advance amounts, and advance speeds can be set.

[0122] 17A and 17B are diagrams showing changes over time in an example of ignition timing control in this embodiment. Fig. 17A shows a case where the difference between the internal temperature and the surface temperature of the combustion chamber wall is small, and Fig. 17B shows a case where the difference between the internal temperature and the surface temperature of the combustion chamber wall is large. In this embodiment, when the internal temperature is high and the difference between the internal temperature and the surface temperature is small, the delay amount in the delay control and the advance amount in the first advance control can both be set larger than when the internal temperature is low and the difference between the internal temperature and the surface temperature is large.

[0123] Conversely, when the internal temperature is low and the difference between the internal temperature and the surface temperature is large, the delay amount in the delay control and the advance amount in the first advance control can both be set smaller than when the internal temperature is high and the difference between the internal temperature and the surface temperature is small. Therefore, the ignition timing control unit 502 of this embodiment can set the delay amount so that it has a negative correlation with the difference between the surface temperature and the internal temperature. Furthermore, the ignition timing control unit 502 of this embodiment can set the advance amount so that it has a negative correlation with the difference between the surface temperature and the internal temperature.

[0124] Furthermore, in this embodiment, when the internal temperature is high and the difference between the internal temperature and the surface temperature is small, the advance time in the second advance control can be set longer than when the internal temperature is low and the difference between the internal temperature and the surface temperature is large. Therefore, the ignition timing control unit 502 in this embodiment can set the advance speed in the second advance control so that it has a positive correlation with the difference between the surface temperature and the internal temperature.

[0125] Therefore, the control device of this embodiment can appropriately suppress the recurrence of knock in various situations while controlling the ignition timing by avoiding excessive ignition timing retardation or an excessively long period of ignition timing retardation. As a result, it is possible to appropriately control the ignition timing while suppressing deterioration in efficiency, such as fuel economy and output, after the occurrence of knock during engine operation.

[0126] [Second Embodiment] The second embodiment is an example in which the combustion chamber wall temperature is estimated by a process different from that of the first embodiment to control the ignition timing. Fig. 18 is a flowchart showing the process of estimating the combustion chamber temperature based on the knock intensity and knock frequency. The process described in Fig. 7 is an estimation method based on a physical formula. In Fig. 18, a combustion chamber wall temperature estimation unit 501 simply estimates the combustion chamber wall temperature based on the knock frequency and knock intensity.

[0127] In step S1801, the combustion chamber wall temperature estimator 501 calculates the knock frequency based on the knock flag. Here, the knock frequency is a value calculated based on the number of knocks that occurred in the most recent predetermined number of combustion cycles, and represents the number of knocks that occurred per combustion cycle. For example, this can be expressed as in Equation 26.

[0128] Here, R(k) is the knock frequency (average value of the knock flag) in a predetermined number of combustion cycles up to the kth cycle, R(k-1) is the knock frequency (average value of the knock flag) in the k-1th combustion cycle, and f(k) is the presence or absence of the knock flag in the kth cycle (True=1, False=0).

[0129] For example, the combustion chamber wall temperature estimation unit 501 starts counting the number of combustion cycles when the engine load state reaches a preset condition under which knocking is expected to occur. After counting the number of knocks that have occurred in the combustion cycles up to just before the predetermined number of cycles is reached, when a knock flag for the predetermined number of combustion cycles is detected, the combustion chamber wall temperature estimation unit 501 can calculate the knock frequency based on the weighted average equation in Equation 26.

[0130] When the engine load condition reaches a preset condition, for example, when the condition is reached where the occurrence of knock is not expected, combustion chamber wall temperature estimator 501 can stop or reset counting the number of combustion cycles. Furthermore, considering that the sum of the coefficients R(k-1) and f(k) is 1, Equation 26 can be simplified to obtain the knock frequency using a weighted average equation such as Equation 27.

[0131] Here, α is a coefficient of the weighted average, and (1-α) is the weighting value. For example, if the time is used as the basis, α can be calculated using equation 28.

[0132] Here, τ is a predetermined time (s) and Ne is the engine speed (rpm). In this case, a value of about 10 seconds can be selected for τ. α may be a fixed value; for example, if the frequency is to be calculated for 100 combustion cycles, α may be set to 0.99.

[0133] In this embodiment, instead of calculating the knock frequency based on the number of knocks that occurred in the most recent predetermined number of combustion cycles, the knock frequency may be calculated using a weighting value for a single detected knock flag. This eliminates the need to store the number of recent predetermined number of knocks. In this case, for example, knock frequencies when knock flags are detected under various operating conditions are obtained in advance through simulation, experiment, or the like, and a weighting value for a single knock flag is set in advance using a weighted average.

[0134] Furthermore, by using the weighting value, when one knock flag is detected, for example, combustion chamber wall temperature estimation unit 501 can calculate the knock frequency from equation (29).

[0135]

[0136] Here, KFR is the knock frequency [-], KnockFlag is the knock flag [-], and is a flag that is set to 1 (True) when a knock occurs and to 0 (False) when a knock does not occur. W is a preset weighting value for weighted averaging and is set between 0 and 1.

[0137] After calculating the knock frequency, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S1802, where the surface temperature is estimated from the knock intensity. FIG. 19 is a schematic diagram showing a map indicating the relationship between the knock intensity and the surface temperature of the combustion chamber wall. As the surface temperature increases, the amount of unburned air-fuel mixture that self-ignites increases, and therefore the knock intensity increases. From this relationship, there is a positive correlation between the knock intensity and the surface temperature. By specifying the relationship between the knock intensity and the surface temperature in advance through simulation or experiment, the surface temperature can be found from the knock intensity while the internal combustion engine is operating.

[0138] Next, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S1803, where the difference between the internal temperature and the surface temperature of the combustion chamber wall is estimated from the knock frequency. FIG. 20 is a schematic diagram showing a map showing the relationship between the knock frequency and the difference between the surface temperature and the internal temperature. The difference between the internal temperature and the surface temperature can be obtained using this map. As shown in FIG. 20, there is a negative correlation between the knock frequency and the surface temperature and the internal temperature.

[0139] The negative correlation between knock frequency and the difference between the surface temperature and the internal temperature can be explained as follows. As shown in Figure 4, when the difference between the surface temperature and the internal temperature is large, it takes longer for the surface temperature to reach a steady-state value than when the difference between the two is small. This change suggests that when the difference between the surface temperature and the internal temperature is large, it takes longer for the surface temperature to reach the knock recurrence temperature than when the difference between the two is small, and the knock occurrence frequency decreases. In this way, it can be said that there is a negative correlation between knock frequency and the difference between the surface temperature and the internal temperature.

[0140] Therefore, by defining the relationship between the knock frequency and the difference between the surface temperature and the internal temperature in advance through simulation or experiment, as shown in Figure 20, the relationship between the surface temperature and the internal temperature can be obtained from the knock frequency that occurs during operation.

[0141] Next, the process of the combustion chamber wall temperature estimation unit 501 proceeds to step S1804, where the internal temperature of the combustion chamber wall is estimated. The internal temperature can be calculated from the sum of the surface temperature calculated in step S1802 and the difference between the surface temperature and the internal temperature calculated in step S1803.

[0142] After the combustion chamber wall temperature estimation unit 501 estimates the internal temperature of the combustion chamber wall, the ignition timing control unit 502 controls the ignition timing based on the estimated value. Fig. 21 is a flowchart showing the processing contents of the retard amount calculation unit, advance amount calculation unit, and advance angle speed calculation unit. The retard amount calculation unit 503 performs the processing of step S2101, the advance angle amount calculation unit 504 performs the processing of step S2102, and the advance angle speed calculation unit 505 performs the processing of step S2103.

[0143] That is, in step S2101, the delay amount calculation unit 503 sets the delay amount based on the surface temperature and the internal temperature. At this time, a map that has been previously adapted based on experiments or simulations can be used.

[0144] 22 is a schematic diagram showing a map of the ignition retard amount, with the surface temperature of the combustion chamber wall and the internal temperature as axes. The map of the ignition retard amount has a relationship in which the retard amount increases as the surface temperature increases, and also increases as the internal temperature increases.

[0145] In step S2102, advance amount calculation unit 504 calculates the ignition advance amount in the first advance control. For example, the ignition advance amount is calculated by using a map of the difference between the advance amount and the retard amount (the difference is set to 0 when returning to the ignition timing immediately before the ignition retard) that has been adapted in advance based on experiments or simulations to calculate the difference between the advance amount and the retard amount based on the surface temperature and the internal temperature, and then the ignition timing advance amount is determined from the calculated value.

[0146] 23 is a map showing the difference between the retard amount and the advance amount, with the surface temperature and the difference between the surface temperature and the internal temperature as axes. The lower the surface temperature, the smaller the difference between the retard amount and the advance amount, and the larger the difference between the surface temperature and the internal temperature, the smaller the difference between the retard amount and the advance amount. The reason for this is that when the surface temperature is low, it can be assumed that there is a low probability that knock will recur even if the original ignition timing is returned to after the ignition retard.

[0147] Furthermore, when the difference between the surface temperature and the internal temperature is large (which is essentially the same as a low internal temperature), it can be assumed that the surface temperature is unlikely to rise even if the original ignition timing is returned to after the ignition timing is retarded, and the probability of knock recurring is low. Once the difference between the retard amount and the advance amount is determined using the map in Figure 23, the advance amount can be calculated by subtracting the difference between the retard amount and the advance amount determined using the map from the retard amount.

[0148] In step S2103, the advance speed calculation unit 505 calculates the ignition timing advance speed in the second advance control. The ignition timing advance speed can be calculated based on the difference between the surface temperature and the internal temperature. FIG. 24 is a schematic diagram showing the relationship between the difference between the surface temperature and the internal temperature of the combustion chamber wall and the advance speed. This relationship between the difference between the surface temperature and the internal temperature and the advance speed is previously determined through experiments and simulations.

[0149] The larger the difference between the surface temperature and the internal temperature, the less likely the surface temperature will rise, so the ignition timing can be returned earlier and the advance rate can be increased. On the other hand, the smaller the difference between the surface temperature and the internal temperature, the more likely the surface temperature will rise, making it necessary to cool the internal temperature, so the advance rate must be reduced. For this reason, the advance rate is set so that it has a positive correlation with the difference between the surface temperature and the internal temperature.

[0150] As with the first embodiment, the internal combustion engine control device of the second embodiment can appropriately control ignition timing while suppressing deterioration in fuel economy and output efficiency after knock occurs during engine operation. Furthermore, in the second embodiment, the combustion chamber wall temperature estimator 501 simply estimates the combustion chamber wall temperature based on the knock intensity and knock frequency. Furthermore, the ignition timing control unit 502 uses maps to determine the retard amount in the retard control, the advance amount in the first advance control, and the advance rate in the second advance control. Therefore, the internal combustion engine control device of the second embodiment can easily appropriately control ignition timing.

[0151] The above-described embodiments can be modified as appropriate within the scope of the claims of the present invention. For example, in each embodiment, the ignition timing control unit 502 can estimate the state of fuel and reflect this in the operation of the ignition timing. The state of the fuel supplied to the engine (supplied fuel) can be estimated from the relationship between the estimated surface temperature when knock occurred and the knock recurrence temperature.

[0152] For example, if the estimated surface temperature when knock occurs is higher than the knock recurrence temperature, this suggests that the supplied fuel is less likely to cause knock than the fuel used to predetermine the knock recurrence temperature. In this case, the greater the difference between the estimated surface temperature and the knock recurrence temperature, the less likely it is that knock will occur with the supplied fuel. Therefore, the ignition timing control unit 502 may correct the ignition retard amount set in each embodiment so that it has a negative correlation with this difference. Alternatively, the ignition timing control unit 502 may correct the advance amount set in each embodiment so that it has a positive correlation with this difference. In this way, the control device for an internal combustion engine in each embodiment can suppress excessive ignition retard and insufficient ignition advance, thereby suppressing deterioration in fuel economy and output efficiency.

[0153] Conversely, if the estimated surface temperature at the time of knock occurrence is lower than the knock recurrence temperature, this suggests that the supplied fuel is more likely to cause knock than the fuel used to predetermine the knock recurrence temperature. In this case, the greater the difference between the knock recurrence temperature and the estimated surface temperature, the more likely it is that knock will occur with the supplied fuel. Therefore, the ignition timing control unit 502 may correct the ignition retard amount set in each embodiment so that it has a positive correlation with this difference. Alternatively, the ignition timing control unit 502 may correct the advance amount set in each embodiment so that it has a negative correlation with this difference. In this way, the control device for an internal combustion engine in each embodiment can suppress insufficient ignition retard and excessive ignition advance, thereby suppressing deterioration in fuel economy and output efficiency.

[0154] In addition, in each of the above embodiments, an example has been described in which the operation of the ignition timing is started when the knock sensor 21 detects a knock flag, but this is not particularly limited. For example, it is also possible to detect a knock when the estimated value of the surface temperature of the combustion chamber wall or the estimated value of the internal temperature reaches a predetermined value, and have the ignition timing control unit start operating the ignition timing in the same way as when a knock flag is detected.

[0155] In this case, the predetermined value may be, for example, a value that includes a margin from the knock recurrence temperature. Furthermore, ignition timing control may be initiated when the difference between the estimated surface temperature of the combustion chamber wall and the estimated internal temperature reaches a predetermined value. The estimated surface and internal temperatures used in steps S2101 to S2103 in the flow chart of FIG. 21 may be the surface and internal temperatures calculated in the flow chart of FIG. 18, or may be values ​​estimated using the flow chart of FIG. 7.

[0156] 1...Air flow sensor, 2...Electronically controlled throttle, 3...Intake pressure sensor, 5...Variable valve, 6...Collector, 7...Intake pipe, 9...Air-fuel ratio sensor, 10...Three-way catalyst, 11...External EGR section, 12...Accelerator opening sensor, 13...Fuel injection device (injector), 14...Cylinder, 15...Exhaust pipe, 16...Ignition coil, 17...Spark plug, 18...Temperature sensor, 19...Crank angle sensor, 20...Oil jet system, 20a...Oil pump, 100...ECU, 121...Input circuit, 122...Input / output port, 124...Ignition control section, 125...Fuel injection control section, 501...Combustion chamber wall temperature estimation section, 502...Ignition timing control section, 503...Retard amount calculation section, 504...Advance amount calculation section, 505...Advance angle speed calculation section, ENG...Internal combustion engine

Claims

1. A control device for an internal combustion engine, comprising: a combustion chamber wall temperature estimation unit that calculates an estimated value of the combustion chamber wall temperature, including the combustion chamber wall surface temperature and the combustion chamber wall internal temperature; and an ignition timing control unit that retards the ignition timing and advances the ignition timing after said retardation, wherein the ignition timing control unit, in retard control that retards the ignition timing when knock is detected, sets the amount of retard based on at least the estimated value of the combustion chamber wall internal temperature.

2. The control device for an internal combustion engine according to claim 1, wherein the ignition timing control unit sets the amount of retardation based on estimated values ​​of the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

3. A control device for an internal combustion engine as described in claim 2, wherein the ignition timing control unit sets the amount of retardation so that the amount of retardation has a negative correlation with the difference between the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

4. A control device for an internal combustion engine as set forth in claim 1, wherein the ignition timing control unit, in advance angle control for advancing the ignition timing after the retardation, sets the advance angle amount based on at least an estimated value of the temperature inside the combustion chamber wall.

5. The control device for an internal combustion engine according to claim 4, wherein the ignition timing control section sets the advance amount based on estimated values ​​of the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

6. A control device for an internal combustion engine as set forth in claim 5, wherein the ignition timing control unit sets the advance amount so that the advance amount has a negative correlation with the difference between the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

7. The control device for an internal combustion engine according to claim 4, wherein in the advance angle control, the advance angle speed is set based on at least the estimated value of the temperature inside the combustion chamber wall.

8. The control device for an internal combustion engine according to claim 7, wherein in the advance angle control, the advance angle speed is set based on the estimated value of the combustion chamber wall surface temperature and the estimated value of the combustion chamber wall internal temperature.

9. The control device for an internal combustion engine according to claim 8, wherein the ignition timing control unit sets the advance angular speed so as to have a positive correlation with the difference between the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

10. A control device for an internal combustion engine as described in claim 1, wherein the ignition timing control unit retards the ignition timing by a predetermined retard amount and then advances it by a predetermined advance amount when the estimated value of the combustion chamber wall surface temperature reaches a predetermined value.

11. The control device for an internal combustion engine according to claim 1, wherein the retard amount is set based on a retard target surface temperature that is a predetermined retard margin from the knock recurrence temperature.

12. The control device for an internal combustion engine according to claim 4, wherein the advance amount is set based on an advance target surface temperature that is a predetermined advance margin from the knock recurrence temperature.

13. A control device for an internal combustion engine as described in claim 4, wherein the ignition timing control unit performs retard control to retard the ignition timing, first advance control to advance the ignition timing by an angle smaller than the retard amount in the retard control immediately after the retard control, and second advance control to advance the ignition timing by an advance rate slower than that in the first advance control immediately after the first advance control.

14. The control device for an internal combustion engine according to claim 1, wherein the combustion chamber wall temperature estimation unit estimates the combustion chamber wall surface temperature based on at least knock intensity, and estimates the combustion chamber wall internal temperature based on at least knock frequency.

15. A control device for an internal combustion engine as described in claim 1, wherein a plurality of estimated knock occurrence temperatures under specified operating conditions and the retard amount for each of the plurality of estimated knock occurrence temperatures are set in advance, and the ignition timing control unit: if the estimated value of the combustion chamber wall temperature when the knock is detected is higher than the estimated knock occurrence temperature under the operating conditions when the knock is detected, sets the retard amount so that there is a negative correlation between the estimated value and the estimated knock occurrence temperature, or sets the advance amount so that there is a positive correlation between the estimated value and the estimated knock occurrence temperature, and if the estimated value of the combustion chamber wall temperature when the knock is detected is lower than the estimated knock occurrence temperature under the operating conditions when the knock is detected, sets the retard amount so that there is a positive correlation between the estimated value and the estimated knock occurrence temperature, or sets the advance amount so that there is a negative correlation between the estimated value and the estimated knock occurrence temperature.

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