Control device for internal combustion engine

Abstract

To accurately calculate a wall surface temperature of a cylinder bore.SOLUTION: A control device 100 executes processing of: acquiring a flow rate of cooling water flowing in a water jacket 70 provided in a cylinder block 2 of an internal combustion engine 1; acquiring a cooling water temperature that is a temperature of cooling water; calculating heat generation amount when fuel supplied into a cylinder of the internal combustion engine 1 is burned; and calculating a wall surface temperature of a cylinder bore 4b of the internal combustion engine 1 on the basis of the flow rate of the cooling water, the cooling water temperature and the heat generation amount when the fuel is burned.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] For example, the control device described in Patent Document 1 estimates the wall temperature of a cylinder bore based on the coolant temperature at engine startup and the integrated air quantity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the actual behavior of the wall temperature is not correctly reflected in the integrated air quantity used for estimating the wall temperature. Therefore, there is a limit to the estimation accuracy when estimating the wall temperature of the cylinder bore, and further improvement in accuracy is required.

Means for Solving the Problems

[0005] The control device for an internal combustion engine that solves the above problems executes a process of acquiring the flow rate of coolant flowing through a water jacket provided in a cylinder block of the internal combustion engine, a process of acquiring the coolant temperature that is the temperature of the coolant, a process of calculating the calorific value when fuel supplied into a cylinder of the internal combustion engine burns, and a process of calculating the wall temperature of a cylinder bore of the internal combustion engine based on the flow rate, the coolant temperature, and the calorific value.

[0006] The wall temperature of the cylinder bore is a value correlated with the calorific value when the fuel supplied into the cylinder of the internal combustion engine burns, the temperature of the cooling water that cools the cylinder, and the thermal resistance between the cylinder and the cooling water. Here, the inventor has found that the thermal resistance is correlated with the flow rate of the cooling water flowing through the water jacket. Therefore, in the same configuration, the wall temperature of the cylinder bore is calculated based on the flow rate of the cooling water flowing through the water jacket, the cooling water temperature, and the calorific value when the fuel burns. Therefore, the wall temperature can be accurately calculated.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0008] Hereinafter, an embodiment of a control device for an internal combustion engine will be described with reference to FIGS. 1 to 5. <Configuration of the Internal Combustion Engine> As shown in FIG. 1, a cylinder 4 is provided in a cylinder block 2 of an internal combustion engine 1. The inner wall of the cylinder 4 is hereinafter referred to as a cylinder bore 4b. A piston 5 is provided in the cylinder 4, and the piston 5 is connected to a crankshaft 7 via a connecting rod 6.

[0009] Further, a water jacket 70 through which the cooling water supplied from a water pump 60 flows is formed in the cylinder block 2. A cylinder head 3 is assembled on the upper part of the cylinder block 2. A combustion chamber 8 is formed between the top surface of the piston 5 and the cylinder head 3 in the cylinder 4. Further, in the cylinder head 3, an in-cylinder injection valve 35 for directly injecting fuel into the combustion chamber 8 and a spark plug 11 for spark-igniting the air-fuel mixture in the combustion chamber 8 are provided for each cylinder of the internal combustion engine 1.

[0010] Further, the cylinder head 3 is provided with an intake port 9 for introducing intake air into the combustion chamber 8 and an exhaust port 10 for discharging exhaust from the combustion chamber 8. The intake port 9 is connected to an intake passage 20 provided with a throttle valve 14 for adjusting the intake air amount. Further, an intake valve 12 for opening and closing the intake port 9 is provided in the intake port 9. Also, a port injection valve 36 for injecting fuel into the intake port 9 is provided for each cylinder of the internal combustion engine 1 in the cylinder head 3.

[0011] An exhaust valve 13 for opening and closing the exhaust port 10 is provided in the exhaust port 10. The exhaust port 10 is connected to an exhaust passage 30. A catalyst 32 for purifying exhaust is provided in the exhaust passage 30. This catalyst 32 purifies the exhaust by controlling the air-fuel ratio of the air-fuel mixture to a target air-fuel ratio.

[0012] Note that as the fuel for the internal combustion engine 1, only alcohol fuel (fuel with an alcohol fuel ratio of "100%"), only gasoline fuel (fuel with an alcohol fuel ratio of "0%"), and a mixed fuel in which alcohol fuel and gasoline fuel are mixed can be used.

[0013] <Regarding the control device> The control device 100 includes a central processing unit (hereinafter referred to as CPU) 110, a memory 120 in which control programs and data are stored, and the like. Then, by the CPU 110 executing the programs stored in the memory 120, various engine controls are executed.

[0014] The control device 100 is connected to various sensors. For example, the control device 100 is connected to a crank angle sensor 41 that detects the rotation angle of the crankshaft 7, an air flow meter 44 that detects the intake air amount GA, and a water temperature sensor 45 that detects the cooling water temperature Tw, which is the temperature of the cooling water after heat exchange in the internal combustion engine 1. Further, the control device 100 is connected to an air-fuel ratio sensor 46 that is provided in the exhaust passage 30 upstream of the catalyst 32 and detects the air-fuel ratio AF, and a pump speed sensor 47 that detects the pump rotation speed Np, which is the rotation speed of the water pump 60.

[0015] The control device 100 calculates the engine rotation speed Ne based on the output signal Scr of the crank angle sensor 41. Further, the control device 100 calculates the engine load factor KL based on the engine rotation speed Ne and the intake air amount GA. The engine load factor KL represents the ratio of the current cylinder intake air amount to the cylinder intake air amount when the internal combustion engine 1 is in steady operation with the throttle valve fully open at the current engine rotation speed Ne. Note that the cylinder intake air amount is the amount of air flowing into each cylinder during the intake stroke. Further, the control device 100 calculates the flow rate V of the cooling water flowing through the water jacket 70 based on the pump rotation speed Np.

[0016] <Regarding fuel injection> As one of various controls of the internal combustion engine 1, the control device 100 executes a process of switching three types of fuel injection modes according to the engine operating state. One of the fuel injection modes that can be switched in this embodiment is an in-cylinder injection mode in which fuel is injected only from the in-cylinder injection valve 35. Another fuel injection mode that can be switched in this embodiment is a port injection mode in which fuel is injected only from the port injection valve 36. And one of the fuel injection modes that can be switched in this embodiment is a dual injection mode in which fuel is injected from both the in-cylinder injection valve 35 and the port injection valve 36.

[0017] The switching of the fuel injection mode described above is executed by variously changing the port injection ratio Rp indicating the ratio of the fuel amount injected from the port injection valve 36 out of the fuel injection amount Q set based on the engine operating state.

[0018] The port injection ratio Rp is variably set within the range of "0 ≦ Rp ≦ 1" based on the engine operating state such as the engine load factor KL and the engine rotational speed Ne, and the fuel amount obtained by multiplying the fuel injection amount Q by the port injection ratio Rp is set as the fuel injection amount of the port injection valve 36. On the other hand, the value obtained by subtracting the port injection ratio Rp from "1" is calculated as the in-cylinder injection ratio Rd indicating the ratio of the fuel amount injected from the in-cylinder injection valve 35 out of the fuel injection amount Q (Rd = 1 - Rp). Then, the fuel amount obtained by multiplying the fuel injection amount Q by the in-cylinder injection ratio Rd is set as the fuel injection amount of the in-cylinder injection valve 35.

[0019] <Regarding air-fuel ratio feedback control> Further, as one of various controls of the internal combustion engine 1, the control device 100 performs air-fuel ratio feedback control. This air-fuel ratio feedback control is a control for correcting the fuel injection amount Q based on the air-fuel ratio AF detected by the air-fuel ratio sensor 46 in order to make the air-fuel ratio of the air-fuel mixture the target air-fuel ratio AFt (for example, the stoichiometric air-fuel ratio, etc.). The control device 100 calculates an air-fuel ratio correction value FAF so that the deviation between the air-fuel ratio AF and the target air-fuel ratio AFt is reduced. Specifically, the control device 100 calculates the sum of a proportional element, an integral element, and a differential element with the deviation between the target air-fuel ratio AFt and the air-fuel ratio AF as an input as the air-fuel ratio correction value FAF. Then, by correcting the fuel injection amount Q with the air-fuel ratio correction value FAF, the air-fuel ratio of the air-fuel mixture is converged to the target air-fuel ratio AFt.

[0020] <Regarding the estimation of alcohol concentration> Further, the control device 100 executes a process of estimating the alcohol concentration AD of the fuel. That is, in the internal combustion engine 1, the air-fuel ratio feedback control described above is performed. Here, as the alcohol concentration in the fuel increases, the value of the air-fuel ratio correction value FAF required to obtain the target air-fuel ratio AFt tends to increase on the rich side. Therefore, for example, the control device 100 of the present embodiment executes a process of estimating the alcohol concentration AD in the fuel based on the air-fuel ratio correction value FAF calculated to maintain the target air-fuel ratio AFt. In this estimation, the control device 100 calculates the alcohol concentration AD such that the calculated alcohol concentration AD becomes a higher value as the value of the air-fuel ratio correction value FAF is more on the rich side. Incidentally, when estimating the alcohol concentration AD, it is possible to improve the estimation accuracy of the alcohol concentration AD by performing the estimation when the degree of deviation between the actual air-fuel ratio AF and the target air-fuel ratio AFt is sufficiently small and such a state continues for a certain period of time.

[0021] Note that the alcohol concentration AD of the fuel may be estimated in other manners. Further, for example, it may be directly detected using a sensor that detects the alcohol concentration based on the electrical conductivity, capacitance, etc. of the fuel.

[0022] <Regarding the estimation of the bore temperature> The control device 100 executes a process of estimating the bore temperature Tb, which is the wall temperature of the cylinder bore 4b.

[0023] FIG. 2 shows the procedure of the bore temperature calculation process executed by the control device 100. The control device 100 repeatedly executes this process at every predetermined calculation cycle. Hereinafter, the step numbers are represented by numbers preceded by "S".

[0024] When starting the process shown in FIG. 2, the control device 100 acquires the coolant water temperature Tw, the flow rate V, the target air-fuel ratio AFt, the intake air amount GA, the fuel injection amount Q, and the alcohol concentration AD, respectively (S100).

[0025] Next, the control device 100 calculates the thermal resistance R based on the flow rate V (S110). The thermal resistance R is the thermal resistance between the cylinder bore 4b and the cooling water in the water jacket 70. The inventor of the present invention has found that the thermal resistance R correlates with the flow rate V of the cooling water flowing through the water jacket 70. Therefore, in the present embodiment, the relationship between the flow rate V and the thermal resistance R is stored in advance in the memory 120 as map data. Then, the control device 100 calculates the thermal resistance R based on the map data.

[0026] As shown in FIG. 3, in the map data of the thermal resistance R, the value of the thermal resistance R is set such that as the flow rate V increases, the calculated value of the thermal resistance R decreases. Next, the control device 100 calculates the equivalence ratio ER based on the target air-fuel ratio AFt, the intake air amount GA, and the fuel injection amount Q (S120). The fuel injection amount Q is the final fuel injection amount corrected by air-fuel ratio feedback control. The equivalence ratio ER is a value obtained by dividing the fuel injection amount Q by the fuel injection amount required to obtain the stoichiometric air-fuel ratio at the current intake air amount GA. Therefore, when the target air-fuel ratio AFt is smaller than the stoichiometric air-fuel ratio, the equivalence ratio ER becomes a value smaller than "1". Note that the equivalence ratio ER may be calculated by dividing the stoichiometric air-fuel ratio by the detected air-fuel ratio AF.

[0027] Next, the control device 100 calculates a fuel correction coefficient Kf based on the equivalence ratio ER (S130). Generally, the calorific value per unit mass when fuel burns changes according to the air-fuel ratio of the air-fuel mixture. Therefore, the control device 100 calculates the fuel correction coefficient Kf as a correction value multiplied by the fuel injection amount Q in order to correct the difference in calorific value due to the difference in air-fuel ratio with reference to the calorific value per unit mass when the air-fuel mixture of the stoichiometric air-fuel ratio burns.

[0028] In the present embodiment, the relationship between the equivalence ratio ER and the fuel correction coefficient Kf is stored in advance in the memory 120 as map data. Then, the control device 100 calculates the fuel correction coefficient Kf based on the map data.

[0029] As shown in FIG. 4, in the map data of the fuel correction coefficient Kf, when the equivalence ratio ER is "1", the value is set so that the fuel correction coefficient Kf becomes "1". Also, as the equivalence ratio ER becomes smaller than "1", the value of the fuel correction coefficient Kf is set to gradually become smaller than "1". Further, as the equivalence ratio ER becomes larger than "1", the value of the fuel correction coefficient Kf is set to gradually become larger than "1". By correcting the fuel injection amount Q with such a fuel correction coefficient Kf, when the equivalence ratio ER is smaller than "1", that is, when the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, the fuel amount when calculating the calorific value of the fuel becomes less than the fuel injection amount Q. On the other hand, when the equivalence ratio ER is larger than "1", that is, when the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio, the fuel amount when calculating the calorific value of the fuel becomes more than the fuel injection amount Q.

[0030] Next, the control device 100 calculates the lower calorific value LC of the fuel based on the alcohol concentration AD (S140). In the present embodiment, the relationship between the alcohol concentration AD and the lower calorific value LC is stored in advance in the memory 120 as map data. Then, the control device 100 calculates the lower calorific value LC based on the map data.

[0031] As shown in FIG. 5, in the map data of the lower calorific value LC, the value of the lower calorific value LC is set so that the value of the lower calorific value LC calculated increases as the alcohol concentration AD increases.

[0032] Next, the control device 100 calculates the calorific value Qburn per unit time when the fuel supplied into the cylinder of the internal combustion engine 1 burns based on the following formula (1) (S150). Qburn = Ne·(Q·Kf)·LC·α…(1) Ne: Engine rotational speed Q: Fuel injection amount Kf: Fuel correction coefficient LC: Lower calorific value α: Constant for adjusting the unit Note that the value obtained from "Q·Kf" in Equation (1) is a value obtained by correcting the fuel injection amount Q in the calculation of the calorific value in order to correct the calorific value per unit mass of the fuel that changes according to the air-fuel ratio of the air-fuel mixture, as described above.

[0033] Next, the control device 100 calculates the heat flow rate Qw (S160). The heat flow rate Qw is the amount of heat transferred per unit time from the cylinder bore 4b to the cooling water in the water jacket 70. The control device 100 substitutes a value obtained by multiplying the above calorific value Qburn by a coefficient K into the heat flow rate Qw. The coefficient K is an adaptation value for converting the calorific value Qburn into the above heat flow rate Qw. Note that in this embodiment, the coefficient K is a fixed value, but it may be a variable value that changes according to, for example, the engine operating state.

[0034] Next, the control device 100 calculates the bore temperature Tb from the following Equation (2) based on the heat resistance R calculated according to the flow rate V, the heat flow rate Qw calculated from the calorific value of the fuel, and the cooling water temperature Tw (S170).

[0035] Tb = R·Qw + Tw…(2) R: Heat resistance Qw: Heat flow rate Tw: Cooling water temperature Then, when the process of S170 is executed, the control device 100 ends the execution of this process in the current calculation cycle.

[0036] <Function and effect> The function and effect of this embodiment will be described. (1) The bore temperature Tb is a value correlated with the calorific value when the fuel supplied into the cylinder of the internal combustion engine 1 burns, the temperature of the cooling water that cools the cylinder 4, and the heat resistance between the cylinder 4 and the cooling water. Here, the inventor has found that the heat resistance is correlated with the flow rate V of the cooling water flowing through the water jacket 70. Therefore, in this embodiment, the bore temperature Tb is calculated based on the flow rate V of the cooling water flowing through the water jacket 70, the cooling water temperature Tw, and the calorific value Qburn when the fuel burns. Therefore, the bore temperature Tb can be calculated accurately.

[0037] (2) When calculating the calorific value Qburn, the fuel injection amount Q is corrected by the fuel correction coefficient Kf. Therefore, the calorific value Qburn is calculated in consideration of the calorific value per unit mass of the fuel that changes according to the air-fuel ratio of the air-fuel mixture. Therefore, the estimation accuracy of the bore temperature Tb is improved as compared with the case where such correction by the fuel correction coefficient Kf is not performed.

[0038] (3) When calculating the calorific value Qburn, the lower calorific value LC of the fuel is calculated based on the alcohol concentration AD of the fuel. Therefore, the calorific value Qburn is calculated in consideration of the lower calorific value that changes according to the alcohol concentration AD. Therefore, the estimation accuracy of the bore temperature Tb is improved as compared with the case where such calculation of the lower calorific value according to the alcohol concentration AD is not performed.

[0039] <Modification example> Note that the above embodiment can be implemented with the following modifications. The above embodiment and the following modification examples can be implemented in combination with each other within a technically non-conflicting range.

[0040] · The correction of the fuel injection amount Q by the fuel correction coefficient Kf may be omitted. Even in this case, the operations and effects other than those in the above (2) can be obtained. · The calculation of the lower calorific value LC according to the alcohol concentration AD may be omitted. Even in this case, the operations and effects other than those in the above (3) can be obtained.

[0041] · The execution order of each process shown in FIG. 2 may be appropriately changed. · Any one of the thermal resistance R, the fuel correction coefficient Kf, and the lower calorific value LC may be calculated by a functional formula.

[0042] · The control device 100 includes a CPU 110 and a memory 120, and is not limited to executing software processing. For example, it may include a dedicated hardware circuit (such as an ASIC, etc.) that processes at least a part of the software processing executed in the above embodiment. That is, the control device 100 may have any of the following configurations (a) to (c). (a) It includes a processing device that executes all of the above processing according to a program, and a program storage device such as a memory that stores the program. (b) It includes a processing device and a program storage device that execute a part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) It includes a dedicated hardware circuit that executes all of the above processing. Here, there may be a plurality of software processing circuits and dedicated hardware circuits including a processing device and a program storage device. That is, the above processing may be executed by a processing circuit including at least one of one or more software processing circuits and one or more dedicated hardware circuits.

Explanation of Signs

[0043] 1…Internal combustion engine 2…Cylinder block 3…Cylinder head 4…Cylinder 4b…Cylinder bore 9…Intake port 10…Exhaust port 11…Spark plug 11…Internal combustion engine 12…Intake valve 13…Exhaust valve 14…Throttle valve 20…Intake passage 22…Port injection valve 30…Exhaust passage 35…In-cylinder injection valve 36…Port injection valve 41…Crank angle sensor 44…Air flow meter 45…Water temperature sensor 46…Air-fuel ratio sensor 47…Pump speed sensor 60…Water pump 70…Water jacket 100…Control device

Claims

【Claim 1】 a process of obtaining the flow rate of cooling water flowing through a water jacket provided in a cylinder block of an internal combustion engine; a process of obtaining the cooling water temperature, which is the temperature of the cooling water; a process of obtaining a target air-fuel ratio, which is the target air-fuel ratio of the internal combustion engine; a process of obtaining an intake air amount, which is the amount of air inhaled by the internal combustion engine; a process of obtaining a fuel injection amount, which is the amount of fuel injected by the internal combustion engine; a process of obtaining the alcohol concentration of the fuel; a process of calculating an equivalence ratio based on the target air-fuel ratio, the intake air amount, and the fuel injection amount; a process of calculating the calorific value when the fuel supplied into the cylinder of the internal combustion engine burns; a process of calculating the wall temperature of the cylinder bore of the internal combustion engine based on the flow rate, the cooling water temperature, and the calorific value, and executing; In the process of calculating the calorific value, the calorific value is calculated such that the larger the equivalence ratio is, the larger it is, and the higher the alcohol concentration is, the smaller it is. A control device for an internal combustion engine.

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