Control device for internal combustion engine

Abstract

The purpose of the present invention is to provide an internal combustion engine control device that makes it possible both to achieve stable combustion of an air-fuel mixture and to prevent damage to an ignition coil caused by heat production. A control device 200 for an internal combustion engine 100 that comprises an ignition plug 105 and an ignition coil 150 comprises: a temperature estimation unit 210 that estimates a coil temperature that is the temperature in and around the ignition coil 150 of the internal combustion engine 100; and an ignition control unit 220 that controls energization of the ignition coil 150 and thereby controls the current supplied to the ignition plug 105. The ignition coil 150 has an increase mechanism that increases the current being supplied to the ignition plug 105. The ignition control unit 220 controls the increase in current by the increase mechanism such that the increase is smaller the higher the estimated coil temperature.

Description

Technical Field

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

Background Art

[0002] For further improvement of fuel efficiency and exhaust gas purification of automobiles, there are known control devices for internal combustion engines that introduce technologies such as burning a mixture supplied into the cylinder of an internal combustion engine leaner than the stoichiometric air-fuel ratio and technologies using exhaust gas recirculation (EGR) that recirculates exhaust gas.

[0003] Due to the ultra-leaning of the air-fuel mixture and the increase in the EGR rate, the energy to be supplied to the spark plug for stably burning the air-fuel mixture increases. As a technology for increasing the energy supplied to the spark plug, there is Patent Document 1.

[0004] In the internal combustion engine disclosed in Patent Document 1, a main primary coil and a secondary primary coil are arranged on the primary side of an ignition coil that gives energy to the spark plug. And in the control device for the internal combustion engine disclosed in Patent Document 1, in order to increase the energy supplied to the spark plug, after cutting off the energization of the main primary coil, the secondary primary coil is energized.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] If the energization amount of the ignition coil is increased too much to increase the energy supply amount to the spark plug, the temperature of the ignition coil will rise excessively due to the heat generated by the ignition coil, and the ignition coil may malfunction. Therefore, it is necessary to set an upper limit value for the energization amount of the ignition coil so that the ignition coil does not exceed the upper limit temperature even when used in the most severe operating environment. The upper limit value of the energization amount of the ignition coil is set with a margin. If this margin is too large, the energization amount of the ignition coil will be greatly restricted, and the energy supply amount to the spark plug will also be greatly restricted. Due to this restriction, in the ignition coil having a primary coil and a secondary primary coil as in Patent Document 1, when it is desired to energize the secondary primary coil to assist the energization amount of the primary coil, there may be a case where the secondary primary coil cannot be energized. As a result, in the control device for an internal combustion engine disclosed in Patent Document 1, there may be a case where the energy supply amount to the spark plug necessary for stable combustion of the air-fuel mixture cannot be ensured. Therefore, the control device for an internal combustion engine disclosed in Patent Document 1 has room for improvement in achieving both stable combustion of the air-fuel mixture and prevention of failure due to heat generation of the ignition coil.

[0007] The present invention has been made in view of the above, and an object thereof is to provide a control device for an internal combustion engine capable of achieving both stable combustion of an air-fuel mixture and prevention of failure due to heat generation of an ignition coil.

Means for Solving the Problems

[0008] In order to solve the above problems, a control device for an internal combustion engine according to the present invention is a control device for an internal combustion engine including a spark plug and an ignition coil, and includes a temperature estimation unit that estimates a coil temperature that is the temperature inside or around the ignition coil, and an ignition control unit that controls the current supplied to the spark plug by controlling the energization of the ignition coil. The ignition coil has an increasing mechanism that increases the current while supplying the current to the spark plug, and the ignition control unit controls the increase amount so that the higher the estimated coil temperature, the smaller the increase amount of the current by the increasing mechanism.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a control device for an internal combustion engine that can achieve both stable combustion of an air-fuel mixture and prevention of failures due to heat generation of an ignition coil. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For components with the same reference numerals in each embodiment, unless otherwise specified, they have the same functions in each embodiment, and the description thereof will be omitted.

[0012] [Embodiment 1] The control device 200 of the internal combustion engine 100 according to Embodiment 1 will be described with reference to FIGS. 1 to 7.

[0013] FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine system 1 including the control device 200 of the present embodiment.

[0014] The internal combustion engine 100 is controlled by a control device (Engine Control Unit: ECU) 200 and an accelerator opening sensor 140 that detects the accelerator opening. The internal combustion engine 100 includes a piston 101, an intake valve 102, and an exhaust valve 103 in a cylinder. As an example, the internal combustion engine 100 can be an internal combustion engine having a plurality of, for example, four cylinders. However, FIG. 1 illustratively shows only one cylinder out of the plurality of cylinders.

[0015] The piston 101 is connected to a crankshaft (not shown). The crankshaft is composed of a main shaft and a sub-shaft. The sub-shaft is connected to the piston 101 via a connecting rod. The crankshaft may be provided with a variable compression ratio mechanism that makes the distance between the main shaft and the sub-shaft or the length of the connecting rod variable. By providing the internal combustion engine 100 with a variable compression ratio mechanism, the stroke amount of the piston 101 can be changed, and the pressure in the combustion chamber R1 can be made variable.

[0016] The cylinder head is provided with a spark plug 105 and an ignition coil 150. Further, the cylinder head is provided with a fuel injection valve 107 for directly injecting fuel into the combustion chamber R1 in the cylinder. Although not shown, the water jacket of the cylinder is provided with a water temperature sensor for detecting the temperature of the cooling water.

[0017] Also, an intake pipe 110 for introducing air inhaled into the internal combustion engine 100 is provided upstream of the intake valve 102. An exhaust pipe 111 for discharging the exhaust gas discharged from the cylinder to the outside is provided downstream of the exhaust valve 103. The intake pipe 110 is provided with an intercooler 112 for cooling the intake gas, a throttle valve 113 for adjusting the intake air volume according to the accelerator opening, a surge tank 114 for adjusting the flow of the intake gas, and a tumble control valve (TCV) 115 for narrowing a part of the intake pipe 110 to generate turbulence (tumble) in the intake gas flow.

[0018] Also, the exhaust pipe 111 communicates with an exhaust passage 121. The exhaust passage 121 is provided with a three-way catalyst 123, an air-fuel ratio sensor 124, and a turbine 125b. The three-way catalyst 123 is for purifying the exhaust gas. The air-fuel ratio sensor 124 is a sensor for detecting the air-fuel ratio of the exhaust gas. Also, the turbine 125b generates a driving force for driving the compressor 125a by utilizing the energy of the exhaust gas.

[0019] Note that the exhaust passage 121 branches into an EGR pipe 126 on the downstream side of the three-way catalyst 123. The EGR pipe 126 is a pipe for recirculating the exhaust gas as EGR gas to the intake side. The EGR pipe 126 is connected to an intake passage 130 that communicates with the intake pipe 110. The EGR pipe 126 is provided with an EGR cooler 127 for cooling the EGR gas, an EGR valve 128 for adjusting the amount of the EGR gas, and a pressure sensor 133 for detecting the pressures before and after the EGR valve 128. Also, a three-way catalyst 129 different from the three-way catalyst 123 is provided further downstream of the branch point of the exhaust passage 121 and the EGR pipe 126.

[0020] The intake pipe 110 communicates with the intake passage 130 on the compressor 125a side. An air flow sensor 131 for measuring the air flow rate and a pressure regulating valve 132 for adjusting the intake pressure are provided in the intake passage 130. Further, an oxygen concentration sensor 134 for detecting the oxygen concentration of the intake gas (a gas obtained by mixing the intake air supplied from the intake passage 130 and the EGR gas) is provided in the intake pipe 110.

[0021] The intake gas flows into the combustion chamber R1 through the intercooler 112, the intake pipe 110, the surge tank 114, the tumble valve 115, and the intake valve 102. Fuel is injected from the fuel injection valve 107 into the intake gas that has flowed into the combustion chamber R1 to form an air-fuel mixture. The air-fuel mixture is ignited and combusted by a spark generated from the spark plug 105 at a predetermined ignition timing. The combustion pressure generated by the combustion of this air-fuel mixture pushes down the piston 101, whereby the internal combustion engine 100 generates power.

[0022] The exhaust gas after combustion passes through the exhaust valve 103, the exhaust pipe 111, and the turbine 125b and is sent to the three-way catalyst 123, where the NOx, CO, and HC components are purified. Thereafter, the exhaust gas passes through the exhaust passage 121 and is sent to the three-way catalyst 129, where it is purified again and discharged to the outside.

[0023] Also, a part of the exhaust gas is introduced as EGR gas into the intake passage 130 through the EGR pipe 126, the EGR cooler 127, and the EGR valve 128. The EGR gas introduced into the intake passage 130 merges with the intake air to form an intake gas in which the intake air and the EGR gas are mixed. The intake gas passes through the intake pipe 110 and the like and reaches the combustion chamber R1.

[0024] The control device 200 is composed of an electronic control unit including a processor such as a CPU and a storage device such as a ROM and a RAM. The control device 200 realizes its functions by the CPU executing the program stored in the ROM. Specifically, the control device 200 calculates a required torque based on the detection signal of the accelerator opening sensor 140 and various sensor signals. The control device 200 calculates the opening degree of the pressure regulating valve 132, the opening degree of the throttle valve 113, the injection pulse period of the fuel injection valve 107, the ignition timing of the ignition plug 105, the opening and closing timing of the intake valve 102 and the exhaust valve 103, and the opening degree of the EGR valve 128, etc., which are the main operating amounts of the internal combustion engine 100, based on the operating state of the internal combustion engine 100 obtained from the detection signals of various sensors and the operating conditions of the internal combustion engine 100.

[0025] FIG. 2 is a diagram showing a schematic configuration of the ignition coil 150 and the ignition coil energization circuit 160 shown in FIG. 1. FIG. 3 is a diagram for explaining the operation of the ignition coil 150 and the ignition coil energization circuit 160.

[0026] The ignition coil 150 constitutes a transformer that supplies the ignition plug 105 with the current (energy) necessary for the ignition plug 105 to ignite the air-fuel mixture and burn the air-fuel mixture. The ignition coil 150 has a primary coil 151 disposed on the primary side of the transformer, a secondary coil 152 disposed on the secondary side of the transformer and connected to the ignition plug 105, and a tertiary coil 153 disposed on the primary side of the transformer. The primary coil 151, the secondary coil 152, and the tertiary coil 153 are wound around the same core. The number of turns of the secondary coil 152 is larger than the total number of turns of the primary coil 151 and the tertiary coil 153.

[0027] The ignition coil energization circuit 160 has a primary coil energization circuit 161, a tertiary coil energization circuit 162, and a tertiary current monitoring circuit 163.

[0028] The primary coil energization circuit 161 is a circuit that energizes the primary coil 151 based on a primary coil energization signal from the control device 200. The tertiary coil energization circuit 162 is a circuit that energizes the tertiary coil 153 based on a tertiary coil energization signal from the control device 200. Each of the primary coil energization circuit 161 and the tertiary coil energization circuit 162 is configured to include, for example, an igniter or the like.

[0029] The tertiary current monitoring circuit 163 monitors the current flowing through the tertiary coil 153 (also referred to as "tertiary current"). Specifically, the tertiary current monitoring circuit 163 detects the current flowing through the tertiary coil 153 and also detects a return signal from the tertiary coil 153, and outputs the detected signals to the control device 200. The return signal is a signal output from the ignition coil 150 side to the control device 200 side in response to the energization of the ignition coil 150. The return signal of the present embodiment is output when the energization of the tertiary coil 153 stops, particularly when the energization abnormally stops. Therefore, the return signal of the present embodiment can be said to be a signal indicating the diagnostic result of the tertiary coil 153 (also referred to as a "diagnostic signal").

[0030] When the ignition plug 105 is ignited, the control device 200 outputs a primary coil energization signal to the primary coil energization circuit 161 to energize the primary coil 151. The primary coil energization signal may be a pulse signal that indicates a high level during the energization period of the primary coil 151 and a low level during the non-energization period of the primary coil 151, as shown in the upper part of FIG. 3. The energization period of the primary coil 151 is set according to the energization amount of the primary coil 151 and conforms to the dwell angle.

[0031] When the primary coil 151 is energized (when the energization starts and stops), a current is generated in the secondary coil 152 by electromagnetic induction, and the generated current is supplied to the ignition plug 105. The generated current of the secondary coil 152 becomes a large current according to the energization period of the primary coil 151, as shown in the lower part of FIG. 3, and decreases over time.

[0032] Depending on the operating conditions of the internal combustion engine 100 and the dilution ratio of the air-fuel mixture (EGR rate and / or air-fuel ratio), the amount of energy supplied to the spark plug 105 necessary for stable combustion of the air-fuel mixture may be insufficient only by energizing the primary coil 151. In this case, while supplying current to the spark plug 105 by energizing the primary coil 151, the control device 200 outputs a tertiary coil energization signal to the tertiary coil energization circuit 162 to energize the tertiary coil 153. As shown in the middle row of FIG. 3, the tertiary coil energization signal may be a pulse signal that indicates a high level during the energization period of the tertiary coil 153 and a low level during the non-energization period of the tertiary coil 153. The energization period of the tertiary coil 153 is set according to the energization amount of the tertiary coil 153. The energization amount and energization timing of the tertiary coil 153 are set according to the amount and timing when the amount of energy supplied to the spark plug 105 is insufficient. Since the energization period of the tertiary coil 153 overlaps the energization of the primary coil 151, it is also referred to as an overlap period.

[0033] When the tertiary coil 153 is energized while supplying current to the spark plug 105 by energizing the primary coil 151, a current is generated in the secondary coil 152 by electromagnetic induction, and the generated current is supplied to the spark plug 105. As shown in the lower row of FIG. 3, the current generated in the secondary coil 152 is superimposed with a current corresponding to the energization of the primary coil 151 and a current corresponding to the energization of the tertiary coil 153. Thereby, the current supplied to the spark plug 105 increases.

[0034] As described above, the ignition coil 150 of the present embodiment has a tertiary coil 153 as an increasing mechanism for increasing the current while supplying current to the spark plug 105. However, this increasing mechanism is not limited to the tertiary coil 153.

[0035] FIG. 4 is a block diagram showing a functional configuration of the control device 200 according to Embodiment 1. FIG. 5 is a block diagram showing a detailed configuration of the temperature estimation unit 210 shown in FIG. 4. FIG. 6(a) is a diagram for explaining a map showing the relationship between the energization amount of the primary coil 151, the dilution degree of the air-fuel mixture, and the rotational speed of the internal combustion engine 100. FIG. 6(b) is a diagram for explaining a map showing the relationship between the energization amount of the tertiary coil 153, the dilution degree of the air-fuel mixture, and the rotational speed of the internal combustion engine 100. FIG. 7(a) is a diagram for explaining a control example of the energization amount of the tertiary coil 153 according to the coil temperature. FIG. 7(b) is a diagram for explaining a control example of the energization amounts of the primary coil 151 and the tertiary coil 153 according to the coil temperature.

[0036] As shown in FIG. 4, the control device 200 includes a temperature estimation unit 210 and an ignition control unit 220.

[0037] The temperature estimation unit 210 estimates the coil temperature, which is the temperature inside or around the spark plug 105. The temperature estimation unit 210 estimates the coil temperature based on the operating conditions of the internal combustion engine 100, the coolant temperature of the internal combustion engine 100, and the energization amount of the ignition coil 150.

[0038] As shown in FIG. 5, the temperature estimation unit 210 includes a heat generation amount calculation unit 211, a heat dissipation amount calculation unit 212, a temperature calculation unit 213, and a temperature update unit 214.

[0039] The heat generation amount calculation unit 211 calculates the heat generation amount Qc (J) of the ignition coil 150 based on the energization amount of the ignition coil 150 and the operating conditions of the internal combustion engine 100. Specifically, as shown in FIG. 5, a heat generation amount map showing the relationship between the energization amounts of the primary coil 151 and the tertiary coil 153 and the heat generation amount of the ignition coil 150 per ignition is provided in advance in the heat generation amount calculation unit 211. The heat generation amount calculation unit 211 specifies the heat generation amount of the ignition coil 150 per ignition from the energization amounts of the primary coil 151 and the tertiary coil 153 using this heat generation amount map. Then, the heat generation amount calculation unit 211 calculates the heat generation amount Qc (J) of the ignition coil 150 using Equation (1). Heat generation amount Qc (J) = qc (J / ignition) × Δt × rotational speed (rpm) / 120 …(1) In Equation (1), qc (J / ignition) is the calorific value of the ignition coil 150 per ignition. Δt is the calculation interval (s) of the coil temperature.

[0040] The heat dissipation calculation unit 212 calculates the heat dissipation Ql (J) of the ignition coil 150 based on the cooling water temperature (or engine room temperature) of the internal combustion engine 100 and the previously calculated coil temperature. Specifically, the heat dissipation calculation unit 212 calculates the heat dissipation Ql (J) of the ignition coil 150 using Equation (2). Heat dissipation Ql (J)=Ah(Tc - Tr)×Δt …(2) In Equation (2), A is the surface area (m 2 ) of the ignition coil 150. h is the heat transfer coefficient (J / s / m 2 ). The heat transfer coefficient h is determined in advance by experiments or the like. Tc is the previously calculated coil temperature (°C). Tr is the cooling water temperature (or engine room temperature) (°C).

[0041] The temperature calculation unit 213 calculates the coil temperature Tc’ from the calorific value Qc (J) and the heat dissipation Ql (J) of the ignition coil 150. Specifically, the temperature calculation unit 213 calculates the coil temperature Tc’ using Equation (3). Coil temperature Tc’ = Tc+(Qc - Ql) / C …(3) In Equation (3), C is the heat capacity (J / kg) of the ignition coil 150.

[0042] The temperature update unit 214 updates and stores the previously calculated coil temperature Tc using the coil temperature Tc’ calculated this time by the temperature calculation unit 213.

[0043] In this way, the temperature estimation unit 210 can estimate the coil temperature based on the operating conditions of the internal combustion engine 100, the cooling water temperature of the internal combustion engine 100, and the energization amount of the ignition coil 150.

[0044] As a result, the control device 200 can grasp the temperature of the ignition coil 150 without adding hardware such as a temperature sensor and a temperature detection circuit. Therefore, the control device 200 can easily prevent a failure due to heat generation of the ignition coil 150 while ensuring the amount of energy supplied to the spark plug 105 necessary for stable combustion of the air-fuel mixture.

[0045] The ignition control unit 220 controls the current supplied to the spark plug 105 by controlling the energization of the ignition coil 150. Specifically, the ignition control unit 220 sets the energization amount of the primary coil 151 based on the operating conditions of the internal combustion engine 100 and the dilution degree of the air-fuel mixture. For example, as shown in FIG. 6(a), a map showing the relationship between the energization amount of the primary coil 151, the dilution degree of the air-fuel mixture, and the rotational speed of the internal combustion engine 100 is provided in advance in the ignition control unit 220. The ignition control unit 220 sets the energization amount of the primary coil 151 used for the current energization from the rotational speed of the internal combustion engine 100 and the dilution degree of the air-fuel mixture using the map shown in FIG. 6(a). The ignition control unit 220 generates a primary coil energization signal according to the set energization amount of the primary coil 151 and outputs it to the primary coil energization circuit 161.

[0046] Further, the ignition control unit 220 sets the energization amount of the tertiary coil 153 based on the operating conditions of the internal combustion engine 100 and the dilution degree of the air-fuel mixture. Specifically, as shown in FIG. 6(b), a map showing the relationship between the energization amount of the tertiary coil 153, the dilution degree of the air-fuel mixture, and the rotational speed of the internal combustion engine 100 is provided in advance in the ignition control unit 220. The ignition control unit 220 sets the energization amount of the tertiary coil 153 used for the current energization from the rotational speed of the internal combustion engine 100 and the dilution degree of the air-fuel mixture using the map shown in FIG. 6(b). The ignition control unit 220 generates a tertiary coil energization signal according to the set energization amount of the tertiary coil 153 and outputs it to the tertiary coil energization circuit 162.

[0047] When setting the energization amount of the tertiary coil 153, as shown in Fig. 7(a), the ignition control unit 220 controls the energization amount of the tertiary coil 153 such that the higher the estimated coil temperature, the smaller the energization amount of the tertiary coil 153. Specifically, the ignition control unit 220 sets the upper limit value of the energization amount of the tertiary coil 153 such that the higher the estimated coil temperature, the smaller the energization amount of the tertiary coil 153. And the ignition control unit 220 may set the energization amount of the tertiary coil 153 to be equal to or less than this upper limit value.

[0048] Thereby, the ignition control unit 220 can limit (reduce) the energization amount of the tertiary coil 153 within the range of the energization amount at which the ignition coil 150 does not fail due to heat generation. Therefore, the control device 200 can prevent the failure of the ignition coil 150 due to heat generation while ensuring the energy supply amount to the spark plug 105 necessary for the stable combustion of the air-fuel mixture.

[0049] When the estimated coil temperature exceeds a predetermined temperature, as shown in Fig. 7(a), the ignition control unit 220 stops the energization of the tertiary coil 153. The predetermined temperature may be a temperature (for example, 150°C) at which the ignition coil 150 does not fail due to heat generation even when used in the most severe usage environment. The most severe usage environment of the ignition coil 150 is, for example, an environment where heat accumulates in the engine room, such as after a rapid acceleration of an automobile. In the most severe usage environment of the ignition coil 150, the engine room temperature or the coolant water temperature may be, for example, 120°C.

[0050] Thereby, the control device 200 can surely prevent the failure of the ignition coil 150 due to heat generation while ensuring the energy supply amount to the spark plug 105 necessary for the stable combustion of the air-fuel mixture.

[0051] Note that the ignition control unit 220 can control not only the energization amount of the tertiary coil 153 but also the energization amount of the primary coil 151 according to the coil temperature. For example, as shown in FIG. 7(b), when the rotational speed of the internal combustion engine 100 is high, it is required to supply a large current to the spark plug 105, so it is difficult to limit the energization amount of the primary coil 151. Therefore, when the rotational speed of the internal combustion engine 100 is high, the ignition control unit 220 preferentially limits (reduces) the energization amount of the tertiary coil 153 rather than the energization amount of the primary coil 151. On the other hand, when the rotational speed of the internal combustion engine 100 is low, long-term discharge of the spark plug 105 is effective for combustion stabilization. Therefore, when the rotational speed of the internal combustion engine 100 is low, the ignition control unit 220 preferentially limits (reduces) the energization amount of the primary coil 151 rather than the energization amount of the tertiary coil 153.

[0052] Thereby, even when the internal combustion engine 100 operates under various operating conditions, the control device 200 can prevent a failure due to heat generation of the ignition coil 150 while reliably and efficiently securing the amount of energy supplied to the spark plug 105 necessary for stable combustion of the air-fuel mixture.

[0053] As described above, the control device 200 according to the first embodiment is a control device for an internal combustion engine 100 including a spark plug 105 and an ignition coil 150, and includes a temperature estimation unit 210 that estimates a coil temperature, which is the temperature inside or around the ignition coil 150, and an ignition control unit 220 that controls the current supplied to the spark plug 105 by controlling the energization of the ignition coil 150. The ignition coil 150 has an increasing mechanism that increases the current while supplying the current to the spark plug 105. The ignition control unit 220 controls the increase amount such that the higher the estimated coil temperature, the smaller the increase amount of the current by the increasing mechanism.

[0054] As a result, the control device 200 of Embodiment 1 can limit (reduce) the amount of current increase by the increasing mechanism within the range of the energization amount at which the ignition coil 150 does not fail due to heat generation. Therefore, the control device 200 of Embodiment 1 can prevent failure due to heat generation of the ignition coil 150 while ensuring the amount of energy supplied to the spark plug 105 necessary for stable combustion of the air-fuel mixture. Thus, the control device 200 of Embodiment 1 can achieve both stable combustion of the air-fuel mixture and prevention of failure due to heat generation of the ignition coil 150.

[0055] [Embodiment 2] The control device 200 of the internal combustion engine 100 according to Embodiment 2 will be described with reference to FIGS. 8 to 12. Regarding the same configuration and operation as those of Embodiment 1 in the control device 200 of the internal combustion engine 100 according to Embodiment 2, the description will be omitted.

[0056] FIG. 8 is a block diagram showing the functional configuration of the control device 200 according to Embodiment 2. FIG. 9(a) is a diagram for explaining the relationship between the length of the return signal and the coil temperature. FIG. 9(b) is a diagram for explaining the length of the return signal. FIG. 10 is a diagram for explaining a map showing the relationship between the energization amount of the primary coil 151 or the tertiary coil 153 and the generated current (energy) of the secondary coil 152. FIG. 11 is a diagram for explaining a map showing the relationship between the upper limit value of the generated current (energy) of the secondary coil 152 and the target value of the EGR rate and / or the target value of the air-fuel ratio of the air-fuel mixture. FIG. 12 is a diagram for explaining the temperature characteristic diagnosis unit 250.

[0057] The control device 200 according to Embodiment 2 includes a temperature estimation unit 210, an ignition control unit 220, a generated current estimation unit 230, a dilution degree setting unit 240, and a temperature characteristic diagnosis unit 250. Note that since the ignition control unit 220 of Embodiment 2 is the same as that of Embodiment 1, the description thereof will be omitted.

[0058] The temperature estimation unit 210 in Embodiment 2 estimates the coil temperature based on a return signal output from the ignition coil 150 side to the control device 200 side in response to energization of the ignition coil 150. As described above, the return signal is output when the energization of the tertiary coil 153 stops, particularly when the energization abnormally stops. Due to the characteristics of the components of the ignition coil 150, the length of the return signal changes. As shown in FIG. 9(a), the length of the return signal becomes longer as the coil temperature is higher. The length of the return signal may be the time width of the return signal itself, or as shown in FIG. 9(b), it may be the time widths of the return signal and the tertiary coil energization signal. That is, the length of the return signal may be the time from the rise of the tertiary coil energization signal to the fall of the return signal.

[0059] As shown in FIG. 9(a), a map showing the relationship between the length of the return signal and the coil temperature is provided in advance in the temperature estimation unit 210 of Embodiment 2. The temperature estimation unit 210 in Embodiment 2 estimates the coil temperature from the length of the return signal using the map shown in FIG. 9(a).

[0060] Thereby, since the temperature estimation unit 210 in Embodiment 2 can estimate the coil temperature according to the temperature characteristics of the ignition coil 150, the estimation accuracy of the coil temperature can be improved more than in Embodiment 1. Therefore, the control device 200 in Embodiment 2 can more reliably prevent a failure due to heat generation of the ignition coil 150 while ensuring the amount of energy supplied to the spark plug 105 necessary for stable combustion of the air-fuel mixture.

[0061] The generated current estimation unit 230 estimates the upper limit value of the generated current (energy) of the secondary coil 152 based on the energization amount of the primary coil 151 and the energization amount of the tertiary coil 153. Specifically, as shown in FIG. 10, a map showing the relationship between the energization amount of the primary coil 151 and the generated current (energy) of the secondary coil 152 and the relationship between the energization amount of the tertiary coil 153 and the generated current (energy) of the secondary coil 152 is provided in advance in the generated current estimation unit 230. The generated current estimation unit 230 identifies the generated current (energy) of the secondary coil 152 from the energization amount of the primary coil 151 and the tertiary coil 153 using the map shown in FIG. 10. Then, the generated current estimation unit 230 calculates the generated current (energy) of the secondary coil 152 from the sum of the generated current (energy) of the secondary coil 152 due to the energization of the primary coil 151 and the generated current (energy) of the secondary coil 152 due to the energization of the tertiary coil 153 and the conversion efficiency. And the generated current estimation unit 230 can use this calculated value as the upper limit value of the generated current (energy) of the secondary coil 152.

[0062] The dilution ratio setting unit 240 sets a target value for the dilution ratio of the air-fuel mixture supplied into the cylinder of the internal combustion engine 100 based on the upper limit value of the generated current (energy) of the secondary coil 152 estimated by the generated current estimation unit 230. The dilution ratio of the air-fuel mixture is the EGR rate of the air-fuel mixture and / or the air-fuel ratio of the air-fuel mixture. As shown in FIG. 11, a map showing the relationship between the upper limit value of the generated current (energy) of the secondary coil 152 and the target value of the EGR rate of the air-fuel mixture and / or the relationship between the upper limit value of the generated current (energy) of the secondary coil 152 and the target value of the air-fuel ratio is provided in advance in the generated current estimation unit 230. The dilution ratio setting unit 240 sets the target value of the EGR rate of the air-fuel mixture and / or the target value of the air-fuel ratio from the estimated upper limit value of the generated current (energy) of the secondary coil 152 using the map shown in FIG. 11.

[0063] That is, as shown in FIG. 11, when the upper limit value of the generated current (energy) of the secondary coil 152 estimated by the dilution ratio setting unit 240 is small, the dilution ratio setting unit 240 uses the relationship of reducing the target value of the EGR rate of the air-fuel mixture and / or the target value of the air-fuel ratio to set the target value of the EGR rate of the air-fuel mixture and / or the target value of the air-fuel ratio.

[0064] Accordingly, when the control device 200 of Embodiment 2 limits (decreases) the energization amount of the tertiary coil 153 and cannot secure the energy supply amount to the spark plug 105 necessary for the stable combustion of the air-fuel mixture, it can stably burn the air-fuel mixture by controlling the target value of the EGR rate and / or the target value of the air-fuel ratio. Therefore, the control device 200 of Embodiment 2 can achieve both the stable combustion of the air-fuel mixture and the prevention of failures due to heat generation of the ignition coil 150. Note that the generated current estimation unit 230 and the dilution degree setting unit 240 may be provided in the control device 200 of Embodiment 1.

[0065] The temperature characteristic diagnosis unit 250 diagnoses the temperature characteristics of the ignition coil 150 in which the length of the return signal changes according to the coil temperature. Specifically, the temperature characteristic diagnosis unit 250 collects in advance the outside air temperature and the length of the return signal in association with each other when it is assumed that the outside air temperature and the coil temperature are equal. The time when it is assumed that the outside air temperature and the coil temperature are equal is, for example, the timing immediately after the start of the internal combustion engine 100 when the internal combustion engine 100 has stopped for a long time and the cooling water temperature and the outside air temperature have become equal. In addition, the temperature characteristic diagnosis unit 250 regards the relationship between the median (or average value) of the collected outside air temperature and the median (or average value) of the length of the return signal as the relationship between the median (or average value) of the coil temperature and the median (or average value) of the length of the return signal, and stores it in advance. The relationship between the median (or average value) of the coil temperature and the median (or average value) of the length of the return signal is such that the length of the return signal increases as the coil temperature increases, and is represented as a linear relationship as shown by the broken line in FIG. 12.

[0066] Then, when the temperature characteristic diagnosis unit 250 acquires the outside air temperature and the length of the return signal in this diagnosis, it specifies a straight line (solid line in FIG. 12) having the same slope as the slope of the broken line shown in FIG. 12 stored in advance passing through the acquired outside air temperature and the length of the return signal. The temperature characteristic diagnosis unit 250 sets the relationship between the coil temperature and the length of the return signal indicated by the specified straight line as the temperature characteristics of the ignition coil 150 obtained by this diagnosis.

[0067] The temperature estimation unit 210 of the control device 200 including the temperature characteristic diagnosis unit 250 can estimate the coil temperature based on the temperature characteristics obtained by the current diagnosis by the temperature characteristic diagnosis unit 250.

[0068] Accordingly, since the temperature estimation unit 210 can estimate the coil temperature in consideration of the temperature characteristics of the different ignition coils 150 by the individual ignition coils 150, the estimation accuracy of the coil temperature can be further improved. Therefore, the control device 200 including the temperature characteristic diagnosis unit 250 can more reliably prevent a failure due to heat generation of the ignition coil 150 while ensuring the energy supply amount to the spark plug 105 necessary for stable combustion of the air-fuel mixture.

[0069] In addition, in each of the above embodiments, the return signal is a signal output when the energization of the tertiary coil 153 stops as described above. However, the return signal may be a signal output when the energization of the primary coil 151 stops. That is, the return signal includes a primary return signal output from the primary coil 151 side to the control device 200 side in response to the energization of the primary coil 151, and a tertiary return signal output from the tertiary coil 153 side to the control device 200 side in response to the energization of the tertiary coil 153. And the temperature estimation unit 210 can estimate the coil temperature based on at least one of the primary return signal and the tertiary return signal.

[0070] Accordingly, the temperature estimation unit 210 can estimate the coil temperature based on the primary return signal from the primary coil 151 even when the tertiary return signal from the tertiary coil 153 is not output due to an unexpected situation. Therefore, the control device 200 can surely and stably prevent a failure due to heat generation of the ignition coil 150 while ensuring the energy supply amount to the spark plug 105 necessary for stable combustion of the air-fuel mixture.

[0071] In addition, in each of the above embodiments, the return signal is a signal output when the energization of the ignition coil 150 stops. However, the return signal may be a detection signal of a temperature sensor that detects the coil temperature of the ignition coil 150. When estimating the coil temperature based on the return signal, the temperature estimation unit 210 can estimate the coil temperature based on the detection signal of this temperature sensor.

[0072] Thereby, the temperature estimation unit 210 can acquire an accurate coil temperature. Therefore, the control device 200 can more reliably prevent a failure due to heat generation of the ignition coil 150 while ensuring the energy supply amount to the spark plug 105 necessary for stable combustion of the air-fuel mixture.

[0073] [Others] The present invention is not limited to the above embodiments and includes various modifications. For example, the above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Also, for a part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

[0074] In addition, each of the above configurations, functions, processing units, processing means, etc. may be realized by hardware, for example, by designing a part or all of them with an integrated circuit. Also, each of the above configurations, functions, etc. may be realized by software by a processor interpreting and executing a program that realizes each function. Information such as a program, tape, file, etc. that realizes each function can be placed in a memory, a recording device such as a hard disk or SSD (solid state drive), or a recording medium such as an IC card, SD card, or DVD.

[0075] In addition, the control lines and information lines show those considered necessary for explanation, and not all control lines and information lines are necessarily shown on the product. In fact, it may be considered that almost all components are interconnected.

Explanation of Signs

[0076] 100…Internal combustion engine, 105…Spark plug, 150…Ignition coil, 151…Primary coil, 152…Secondary coil, 153…Tertiary coil (boost mechanism), 200…Control device, 210…Temperature estimation unit, 220…Ignition control unit, 230…Generated current estimation unit, 240…Dilution setting unit, 250…Temperature characteristic diagnosis unit

Claims

1. A control device for an internal combustion engine including a spark plug and a spark coil, comprising: a temperature estimation unit that estimates a coil temperature which is a temperature inside or around the spark coil; a spark control unit that controls a current supplied to the spark plug by controlling energization of the spark coil, wherein the spark coil has an increasing mechanism that increases the current while supplying the current to the spark plug, and the spark control unit controls the increase amount such that the higher the estimated coil temperature, the smaller the increase amount of the current by the increasing mechanism. A control device for an internal combustion engine, characterized by the above.

2. The spark coil has a primary coil disposed on the primary side, a secondary coil disposed on the secondary side and connected to the spark plug, and a tertiary coil disposed on the primary side, wherein the increasing mechanism is the tertiary coil, and the spark control unit controls the energization amount of the tertiary coil such that the higher the estimated coil temperature while supplying the current to the spark plug by energization of the primary coil, the smaller the energization amount of the tertiary coil. The control device for an internal combustion engine according to claim 1, characterized by the above.

3. The temperature estimation unit estimates the coil temperature based on an operating condition of the internal combustion engine, a cooling water temperature of the internal combustion engine, and an energization amount of the spark coil. The control device for an internal combustion engine according to claim 2, characterized by the above.

4. The temperature estimation unit estimates the coil temperature based on a return signal output from the spark coil side to the control device side in response to energization of the spark coil. The control device for an internal combustion engine according to claim 2, characterized by the above.

5. When the estimated coil temperature exceeds a predetermined temperature, the spark control unit stops energization of the tertiary coil. The control device for an internal combustion engine according to claim 2, characterized by the above.

6. a generated current estimation unit that estimates an upper limit value of a generated current of the secondary coil based on an energization amount of the primary coil and an energization amount of the tertiary coil; a dilution ratio setting unit that sets a target value of a dilution ratio of an air-fuel mixture supplied into a cylinder of the internal combustion engine based on the estimated upper limit value of the generated current. The control device for an internal combustion engine according to claim 2, further comprising the above.

7. The control device further includes a temperature characteristic diagnosis unit that diagnoses a temperature characteristic of the spark coil in which a length of the return signal changes according to the coil temperature. The temperature estimation unit estimates the coil temperature based on the diagnosed temperature characteristics. The control device for an internal combustion engine according to claim 4, characterized in that.

8. The return signal includes a primary return signal output from the primary coil side to the control device side in response to energization of the primary coil, and a tertiary return signal output from the tertiary coil side to the control device side in response to energization of the tertiary coil. The temperature estimation unit estimates the coil temperature based on at least one of the primary return signal and the tertiary return signal. The control device for an internal combustion engine according to claim 4, characterized in that.

Images