Control device for internal combustion engine

Abstract

To improve the fuel consumption performance of an internal combustion engine having an oil jet mechanism.SOLUTION: A control device of an internal combustion engine including an oil jet mechanism having a piston oil jet nozzle for injecting oil toward a piston comprises: a piston temperature calculation part for calculating a piston temperature after the rotational speed deceleration at which the rotational speed of the internal combustion engine lowers; and a piston oil jet execution part for executing a piston oil jet by the oil jet mechanism when the piston temperature calculated by the piston temperature calculation part is higher than a preset threshold.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Conventionally, a cooling device for an internal combustion engine equipped with an oil jet mechanism that injects oil from a piston oil jet nozzle toward the piston to cool the piston is known (see, for example, Patent Document 1). In an internal combustion engine, when an air-fuel mixture burns in a combustion chamber, the temperature of the piston rises due to the heat of combustion. Therefore, it may be determined whether or not to perform oil injection (piston oil jet) by the oil jet mechanism based on the temperature of the piston.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an internal combustion engine, the intake air amount and the fuel injection amount change depending on how the accelerator is depressed. Along with this, the combustion state of the air-fuel mixture in the combustion chamber changes, and the temperature of the piston also changes. Thus, although the temperature of the piston changes moment by moment, if it is determined whether or not to perform piston oil jet based on the temperature of the piston acquired at a certain point in time, there may be inconveniences. For example, assume that the temperature of the piston is acquired and it is determined that the piston oil jet is to be performed based on that temperature, and then the accelerator is turned off and the fuel supply is cut off after the temperature of the piston is acquired. In this case, the air-fuel mixture in the combustion chamber is not combusted, and although the temperature of the piston decreases, the piston oil jet is to be performed. In such a case, when the accelerator is depressed again and the vehicle returns from the fuel cut state, the temperature of the piston is lower than the temperature for performing proper combustion, and as a result, it is assumed that the fuel consumption deteriorates. Conventionally, no measures have been taken against such a phenomenon, and the same is true in Patent Document 1, leaving room for improvement.

[0005] Therefore, the control device for an internal combustion engine disclosed in this specification aims to improve the fuel consumption performance in an internal combustion engine equipped with an oil jet mechanism.

Means for Solving the Problems

[0006] The control device for an internal combustion engine disclosed in this specification is a control device for an internal combustion engine equipped with an oil jet mechanism having a piston oil jet nozzle that injects oil toward the piston, and the control device includes a piston temperature calculation unit that calculates the piston temperature after the rotational speed reduction when the rotational speed of the internal combustion engine decreases, and a piston oil jet execution unit that executes a piston oil jet by the oil jet mechanism when the piston temperature calculated by the piston temperature calculation unit is higher than a preset threshold value.

[0007] In the control device for an internal combustion engine having the above-described configuration, the control device further includes a warm-up determination unit that determines whether or not the warm-up of the internal combustion engine has been completed, and the piston oil jet execution unit sets the number of executions of the piston oil jet before the warm-up completion determination by the warm-up determination unit to be larger than the number of executions of the piston oil jet after the warm-up completion determination by the warm-up determination unit.

[0008] Furthermore, in the control device for an internal combustion engine having the above-described configuration, the piston temperature calculation unit may calculate the piston temperature after the rotational speed reduction based on the temperature of the oil injected by the oil jet mechanism and the temperature of the cooling water circulating in the internal combustion engine.

[0009] Also, in the control device for an internal combustion engine having the above-described configuration, the temperature of the cooling water may be the cooling water outlet temperature at the outlet where the cooling water flows out from the engine body included in the internal combustion engine.

Advantages of the Invention

[0010] The control device for an internal combustion engine disclosed in this specification aims to improve the fuel consumption performance in an internal combustion engine equipped with an oil jet mechanism.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, etc. of each part may not be illustrated so as to be exactly the same as the actual ones. Also, depending on the drawings, details may be omitted.

[0013] (Embodiment) [Configuration of Engine System] First, referring to FIG. 1, the schematic configuration of the engine system 50 according to the embodiment will be described. The engine system 50 includes an engine 1 which is an example of an internal combustion engine, and a control device for the engine 1. The control device includes an ECU (Electronic Control Unit), a coolant water temperature sensor 101, an oil temperature sensor 102, an accelerator opening sensor 103, a vehicle speed sensor 104 (see FIG. 2), and the like. The control device will be described in detail later.

[0014] The engine 1 uses gasoline as fuel and includes a cylinder block 11 and a cylinder head 20 that form the engine body 10. In the cylinder block 11, cylinders are formed by cylinder bore walls 11a. An open deck type water jacket 12 is provided in the cylinder bore wall 11a. The water jacket 12 is connected to a coolant water circulation path 13 of the engine 1. A water pump 14 is disposed in the coolant water circulation path 13. The water pump 14 is electric and is electrically connected to the ECU 100 and is driven at an arbitrary rotational speed based on a command from the ECU 100. Note that the water jacket 12 may be of a closed deck type. Although a radiator is equipped in the coolant water circulation path 13, it is omitted in FIG. 1.

[0015] Although Figure 1 shows a single cylinder, the engine 1 of this embodiment is an in-line four-cylinder internal combustion engine, and four cylinders are provided along the direction perpendicular to the plane of the paper. Inside each cylinder, a piston 15 is slidably housed along the axial direction of the cylinder. The piston 15 is connected to a crankshaft 17 via a connecting rod 16. The number of cylinders of the internal combustion engine to which this embodiment can be applied is not limited to four cylinders, and other numbers of cylinders may also be used. Further, the arrangement method thereof is not limited to in-line, and a conventionally known arrangement method such as V-type may also be used.

[0016] The cylinder head 20 is mounted on the upper side of the cylinder block 11. The cylinder head 20 is provided with an intake port 22a to which an intake valve 21a is attached and an exhaust port 22b to which an exhaust valve 21b is attached. Further, the cylinder head 20 is provided with a combustion chamber 23. An ignition plug 24 is provided in the combustion chamber 23. Although a water jacket is also formed in the cylinder head 20, it is omitted in Figure 1.

[0017] Below the cylinder block 11, an oil pan 25 is provided. In the oil pan 25, oil used for lubricating and cooling each part of the engine 1 is stored. In the oil pan 25, an oil strainer 26 is disposed. The oil strainer 26 has an oil suction port 26a and is connected to an oil gallery 27 via a connection pipe 26b. An oil pump 28 is provided in the oil gallery 27, and an oil filter 29 is provided on the downstream side of the oil pump 28. The oil pump 28 is electric and is electrically connected to the ECU 100 and is driven at an arbitrary rotational speed based on a command from the ECU 100. When the rotational speed of the oil pump 28 increases, the oil pressure in the oil gallery 27 rises. Note that the oil pump 28 may be a mechanical oil pump capable of changing the discharge amount and the discharge pressure (oil pressure). Such a mechanical oil pump includes, for example, an oil pump using a trochoid gear and an oil pump using a vane. In short, any pump that can control the oil discharge amount and the discharge pressure can be adopted.

[0018] The oil gallery 27 runs through the engine 1 and branches out in the engine 1 toward locations where oil supply is required as a lubricant and locations where oil supply is required as a coolant.

[0019] The engine 1 is provided with an oil jet mechanism 30 branched from the oil gallery 27 and supplied with oil. The oil jet mechanism 30 includes a piston oil jet nozzle 31 that injects oil toward the lower surface of each piston 15. A check valve 32 is incorporated at the base end of the piston oil jet nozzle 31. When the rotational speed of the oil pump 28 increases and the oil pressure in the oil gallery 27 rises to a predetermined value, the check valve 32 opens, and oil is injected from the piston oil jet nozzle 31 toward the lower surface of the piston 15, cooling the piston 15. Note that the oil jet mechanism 30 not only cools the piston 15 but also distributes the heat taken from the piston 15 to each part of the engine 1 by using the oil injected toward the piston 15 as a heat medium. That is, the oil jet mechanism 30 also has a function of promoting the warm-up of the engine 1.

[0020] The engine 1 can use conventionally known gasoline alternative fuels such as ethanol and natural gas instead of gasoline. Further, the internal combustion engine may be a diesel engine. Further, a dry sump system in which oil is stored in an oil tank instead of the oil pan 25 may be adopted.

[0021] Next, with reference to FIG. 2, the various sensors included in the control device and the functions of the ECU 100 will be described. The control device includes various sensors installed in the engine 1 and various sensors installed in each part of the vehicle equipped with the engine 1. Specifically, the various sensors include a water temperature sensor 101, an oil temperature sensor 102, an accelerator opening sensor 103, and a vehicle speed sensor 104. As shown in FIG. 1, the water temperature sensor 101 is mounted near the outlet 12a of the water jacket 12 and detects the outlet temperature of the cooling water. The reason for detecting the outlet temperature is that the detection accuracy of the water temperature reflecting the temperature state of the bore wall is high. The oil temperature sensor 102 is mounted on the oil pan 25 and detects the temperature of the oil stored in the oil pan 25. The value of the water temperature detected by the water temperature sensor 101 and the temperature of the oil detected by the oil temperature sensor 102 are used for calculating the piston temperature, which will be described later. The accelerator opening sensor 103 detects the amount of depression of the accelerator pedal by the driver. The vehicle speed sensor 104 detects the traveling speed of the vehicle equipped with the engine 1.

[0022] Note that the engine 1 includes various other sensors, but the description of these various sensors is omitted here.

[0023] The ECU 100 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a backup RAM, and other storage devices. It executes arithmetic processing based on programs and maps stored in the CPU, ROM, and other storage devices. The RAM is a memory that temporarily stores the arithmetic results by the CPU and data input from various sensors, and the backup RAM is a non-volatile memory that stores data to be saved when the engine 1 stops, etc.

[0024] The ECU 100 functions as a timing unit 100a, a first piston temperature calculation unit 100b, an oil temperature acquisition unit 100c, a second piston temperature calculation unit 100d, and a driving state determination unit 100e shown in FIG. 2. The ECU 100 also functions as a warm-up determination unit 100f, a piston oil jet execution unit 100g, and an oil pump control unit 100h.

[0025] The timing unit 100a measures a control execution interval s1 for performing piston oil jet control to be described later, and measures an injection execution interval s2 from the previously executed piston oil jet. The control execution interval s1 and the injection execution interval s2 will be described in detail later.

[0026] The first piston temperature calculation unit 100b calculates a piston estimated temperature Tp for performing piston oil jet control. The oil temperature acquisition unit 100c acquires the value of the oil temperature detected by the oil temperature sensor 102. The second piston temperature calculation unit 100d calculates an assumed piston temperature Tpx at the time of FC (Fuel Cut) return based on the piston estimated temperature Tp calculated by the first piston temperature calculation unit 100b and the oil temperature Toil acquired by the oil temperature acquisition unit 100c. The first piston temperature calculation unit 100b and the second piston temperature calculation unit 100d function as a piston temperature calculation unit that collaboratively calculates the piston temperature after the engine speed deceleration when the engine speed of the engine 1 decreases. Here, the engine speed deceleration refers to a phenomenon in which when the accelerator is turned off and the fuel is cut, the air-fuel mixture in the combustion chamber of the engine 1 does not burn and the engine speed of the engine 1 decreases. Therefore, for example, a state in which the engine speed of the engine 1 decreases due to an increase in load while the vehicle equipped with the engine 1 is traveling on an uphill road is not included. The calculation of the piston temperature after the engine speed deceleration of the engine 1 will be described in detail later.

[0027] The driving state determination unit 100e determines the state of the drive system of a vehicle equipped with the engine 1. That is, it determines whether the vehicle is in a driving state (power running state) or a driven state. Referring to FIG. 3, in the drive system of a vehicle equipped with the engine 1, the crankshaft 17 provided in the engine 1 is connected to the wheels 43 via the transmission 41 and the drive shaft 42. Therefore, the rotational output of the crankshaft 17 is transmitted to the wheels 43 via the transmission 41 and the drive shaft 42. The crankshaft 17 is also connected to the alternator 51 via a drive belt. The alternator 51 rotates and generates electricity by the rotational output of the crankshaft 17. The alternator 51 is electrically connected to the battery 52, and the electric power generated by the alternator 51 is stored in the battery 52. The battery 52 is connected to each part of the vehicle that requires electric power, and the electric oil pump 28, which is electric, is also connected to the battery 52 and receives electric power supply. Although a clutch device may be interposed in the drive system, its description is omitted here.

[0028] Such a drive system forms a recovery path for inertial driving force from the wheel 43 to the crankshaft 17 as indicated by the arrow in FIG. 3 when, for example, the driven state with the accelerator off. When the vehicle is running and the wheel 43 is rotating, if the accelerator is turned off and the rotational output of the crankshaft 17 is not exerted, the inertial driving force of the wheel 43 is transmitted to the crankshaft 17. That is, the crankshaft 17 rotates without newly consuming fuel. Even when the crankshaft 17 is rotating due to inertial driving force, the alternator 51 generates electricity, and the electric power is recovered and stored in the battery 52. If the oil pump 28 is operated using the electric power stored in the battery 52 in this way, it is advantageous in terms of fuel consumption. When the oil pump is mechanical, the oil pump is driven by the inertial driving force of the crankshaft 17, and this is also advantageous in terms of fuel consumption. In this way, when the vehicle is in a driven state, by driving the oil pump 28 using the energy that operates the drive system, the energy utilization efficiency can be improved, and the fuel consumption of the vehicle can be improved.

[0029] The warm-up determination unit 100f determines whether or not the warm-up of the engine 1 is completed. The piston oil jet execution unit 100g executes a piston oil jet by the oil jet mechanism 30 when a predetermined condition is satisfied.

[0030] When the piston oil jet execution unit 100g executes a piston oil jet, the oil pump control unit 100h drives the oil pump 28 and raises the oil pressure to a state where the piston oil jet is executed. Specifically, the rotational speed of the oil pump 28 is increased. When the oil pump is mechanical, the discharge pressure is switched from the low pressure side to the high pressure side.

[0031] [Piston Oil Jet Control] Next, piston oil jet control will be described with reference to FIGS. 4 to 6. The ECU 100 performs piston oil jet control illustrated in the flowchart shown in FIG. 4. The piston oil jet control is repeatedly executed as a control execution interval s1 after the engine 1 is started.

[0032] In step S1, the ECU 100 acquires the piston estimated temperature Tp and the oil temperature Toil. The piston estimated temperature Tp is the piston temperature at the time of performing the process of step S1, and is calculated by the first piston temperature calculation unit 100b. The oil temperature Toil is obtained by the oil temperature acquisition unit 100c acquiring the detection value of the oil temperature sensor 102.

[0033] Here, the piston estimated temperature Tp can be expressed as in the following formula (1).

Equation

[0034] The formula (1) includes the piston convergence destination temperature Tp∞. That is, the piston estimated temperature Tp represented by the formula (1) is expressed in the form of a transfer function using Laplace transform as the value of the first-order lag of the piston convergence destination temperature Tp∞.

[0035] The piston convergence destination temperature Tp∞ is the temperature at which the piston 15 converges based on the heat balance among the elements included in the engine 1, and can be calculated based on an equation derived using the thermal circuit model illustrated in FIG. 5. The thermal circuit model is a model for simulating the heat transfer in the engine 1. Here, the meanings of the capital letters used in the thermal circuit model will be explained. In FIG. 5, the capital letter T indicates the temperature (K) of each element, and the capital letter Q indicates the heat transfer amount (W) of each element. Also, the capital letter R indicates the thermal resistance (K / W) of each element, and the capital letter C indicates the heat capacity (J / K) of each element. Next, the meanings of the subscripts used in the thermal circuit model will be explained. Each subscript in FIG. 5 indicates the type of element included in the thermal circuit model, where g represents combustion gas, p represents the piston 15, b represents the cylinder bore wall 11a, w represents cooling water, and pj represents the piston oil jet (oil). Therefore, Tg indicates the combustion gas temperature. Also, Qp represents the heat transfer amount in the piston 15, Rp represents the thermal resistance of the piston 15, Tp represents the temperature of the piston 15, and Cp represents the heat capacity of the piston 15. Also, Qb represents the heat transfer amount in the cylinder bore wall 11a, Rb represents the thermal resistance of the cylinder bore wall 11a, Tb represents the temperature of the cylinder bore wall 11a, and Cb represents the heat capacity of the cylinder bore wall 11a. Also, Qw represents the heat transfer amount in the cooling water, Rw represents the thermal resistance of the cooling water, and Tw represents the temperature of the cooling water. Furthermore, Qpj represents the heat transfer amount by the oil injected by the piston oil jet, Rpj represents the thermal resistance of the oil injected by the piston oil jet, and Tpj represents the temperature of the oil injected by the piston oil jet. Equation (1) is expressed using these letters. Note that the temperature Tpj = the temperature Toil.

[0036] The piston convergence destination temperature Tp∞ is represented by different equations depending on whether the piston oil jet is executed or not. Specifically, the piston convergence destination temperature Tp∞ when the piston oil jet is executed is represented by the following equation (2-1), and the piston convergence destination temperature Tp∞ when the piston oil jet is not executed is represented by the following equation (2-2).

Equation

[0037] In the piston oil jet control according to this embodiment, the piston oil jet is executed within a range where the piston temperature when the piston oil jet is executed does not fall below the temperature for proper combustion in Engine 1. Therefore, the formula (2-1) indicating the piston convergence destination temperature Tp∞ when the piston oil jet is executed is considered. In formula (2-1), Qp∞ indicates the heat transfer amount in piston 15 when combustion occurs in the combustion chamber, and is shown as the value obtained by multiplying the combustion heat Qburn by the first coefficient K1. The first coefficient K1 can be obtained in advance through simulation or conformity experiments using an actual machine.

[0038] Here, assume a case where the accelerator is off and the fuel supply is cut off. When the fuel supply is cut off, the mixture in the combustion chamber does not burn, and the temperature of the piston decreases. If the piston oil jet is executed in such a state, the piston temperature may become too low. Therefore, assume a case where the fuel supply is cut off. When the fuel supply is cut off, the heat input disappears, and it can be considered that Qp∞ = 0. Therefore, in formula (2-1), when Qp∞ = 0, formula (2-1) is arranged as the following formula (3).

Equation

[0039] By substituting this formula (3) into the piston convergence destination temperature Tp∞ in formula (1), the piston estimated temperature Tp at that time can be obtained.

[0040] In step S2 that is executed following step S1, the second piston temperature calculation unit 100d calculates the assumed piston temperature Tpx at the time of FC return. The assumed piston temperature Tpx at the time of FC return corresponds to the piston temperature after the rotational speed deceleration. Here, the method for calculating the assumed piston temperature Tpx at the time of FC return will be described. When the accelerator is turned off and the fuel supply is cut off, the piston temperature converges to the coolant water temperature. Also, although the coolant water temperature also decreases, the convergence destination is at least the oil temperature. That is, the coolant water temperature Tw is expressed as in the following formula (4).

Equation

[0041] Therefore, the assumed piston temperature Tpx at the time of FC return will exist between the estimated piston temperature Tp that sequentially changes from the time when the fuel cut is executed and the oil temperature Tpj (= Toil). Accordingly, due to the fuel cut (FC), the assumed piston temperature decrease width ≤ (Tp - Tpj), and when using the second coefficient K2 which is a number between 0 and less than 1, the assumed piston temperature decrease width can be expressed as K2(Tp - Tpj). Therefore, the assumed piston temperature Tpx at the time of FC return can be expressed by the following formula (5).

Equation

[0042] Thus, in step S2, the assumed piston temperature Tpx at the time of FC return is calculated using formula (5).

[0043] In step S3 that is executed following step S2, the ECU 100 determines whether or not the engine 1 is in a driven state and the assumed piston temperature Tpx at the time of FC return is equal to or higher than the allowable piston temperature which is a preset threshold value.

[0044] The condition that the engine 1 is in the driven state is for driving the oil pump 28 by the energy recovered by the inertial driving force of the crankshaft 17. Whether it is in the driven state or not can be determined, for example, by whether the vehicle speed measured by the vehicle speed sensor 104 is equal to or higher than a predetermined vehicle speed (for example, 20 km / h or higher) and whether the condition that the accelerator is off is satisfied. The ECU 100 determines that it is in the driven state when these conditions are satisfied. Whether the accelerator is off or not is determined by the detected value of the accelerator opening sensor 103. When the piston oil jet is executed when the engine 1 is in the driven state, it is advantageous in terms of fuel consumption.

[0045] The allowable piston temperature is a threshold value used for determining whether to execute the piston oil jet, and is set as the lower limit of the piston temperature at which proper combustion can be performed in the engine 1.

[0046] Here, referring to FIG. 6, for example, between time t1 and time t2, between time t3 and time t4, and at the timing after time t5, the assumed piston temperature Tpx at the time of FC recovery is equal to or higher than the allowable piston temperature. Therefore, the ECU 100 determines that the assumed piston temperature Tpx at the time of FC recovery is equal to or higher than the allowable piston temperature, which is a preset threshold value, at these timings. The assumed piston temperature Tpx at the time of FC recovery is the piston temperature after the rotational speed deceleration considering the assumed piston temperature decrease width K2(Tp - Tpj) as shown in Equation (5). For this reason, when the temperature of the piston decreases due to the cut-off of fuel supply, the piston oil jet is not executed, so the temperature of the piston 15 at which proper fuel can be supplied is maintained. As a result, the fuel consumption performance of the engine 1 can be improved. Referring to FIG. 6, it can be seen that the assumed piston temperature Tpx at the time of FC recovery decreases at the timing when the accelerator is off (OFF), and there is a correlation between the degree of depression of the accelerator and the assumed piston temperature Tpx at the time of FC recovery.

[0047] When the ECU 100 makes an affirmative determination (Yes determination) in step S3, it proceeds to step S4. When the ECU 100 makes a negative determination (No determination) in step S3, it repeats the process from step S2.

[0048] In step S4, the ECU 100 determines whether the warm-up of engine 1 is complete. Specifically, the ECU 100 determines whether the warm-up of engine 1 is complete based on whether the coolant water temperature is equal to or higher than a predetermined warm-up determination threshold value. If the warm-up is complete, the ECU 100 makes an affirmative determination in step S4 and proceeds to step S5. On the other hand, if the warm-up is not complete, the ECU 100 makes a negative determination in step S4 and proceeds to step S6.

[0049] In step S5, the ECU 100 determines whether the injection execution interval s2 from the piston oil jet executed last time has elapsed. Here, the control execution interval s1 < the injection execution interval s2. When the ECU 100 makes an affirmative determination in step S5, it proceeds to step S6. When the ECU 100 makes a negative determination in step S5, it repeats the process from step S2.

[0050] In step S6, the piston oil jet execution unit 100g increases the discharge pressure by the oil pump 28 and issues a signal to the oil pump control unit 100h so that the piston oil jet is executed. After step S6, the process returns. The timing unit 100a starts timing the control execution interval s1 from the point when this return occurs.

[0051] Here, the relationship between the control execution interval s1 and the injection execution interval s2 will be described in detail. As described above, the control execution interval s1 and the injection execution interval s2 have a relationship where the control execution interval s1 < the injection execution interval s2. For this reason, the number of executions of the piston oil jet before the warm-up completion determination is set to be larger than the number of executions of the piston oil jet after the warm-up completion determination.

[0052] Thus, setting the number of executions of the piston oil jet to be larger before the warm-up completion determination is to promote the warm-up of Engine 1. In Engine 1, the temperature of Piston 15 is likely to rise compared to the temperatures of other parts. Therefore, in order to utilize oil as a heat medium, the piston oil jet is actively executed to transfer the heat of Piston 15 to other parts, such as the crank journal, etc., thereby promoting the warm-up of Engine 1. Note that as a result, Piston 15 itself will be cooled, and this acts in the direction of reducing the diameter of Piston 15. As a result, the clearance with the inner circumference of the cylinder bore is optimized, which is also advantageous in terms of fuel consumption in this regard. On the other hand, after the warm-up completion determination, the frequency of the piston oil jet can be reduced to suppress the oil consumption. That is, if the piston oil jet is frequently executed, the chance of oil consumption will increase accordingly, but by suppressing the frequency of the piston oil jet, oil consumption, and thus, the amount of oil consumed can be suppressed.

[0053] [Effect] According to the present embodiment, in order to determine whether to execute the piston pill jet based on the piston temperature after the rotational speed deceleration, when the temperature of the piston decreases due to the cut-off of fuel supply, the piston oil jet is not executed, and the temperature of Piston 15 at which appropriate fuel can be supplied is maintained. As a result, the fuel consumption performance of Engine 1 can be improved.

[0054] Also, according to the present embodiment, since the number of executions of the piston jet before the warm-up completion determination is set to be larger than the number of executions of the piston jet after the warm-up completion determination, it is possible to achieve both the promotion of the warm-up of Engine 1 and the suppression of oil consumption.

[0055] According to the present embodiment, when calculating the estimated piston temperature, the cooling water outlet temperature is used, so the estimated piston temperature, and thus, the assumed piston temperature at the time of FC return can be accurately calculated.

[0056] The above embodiments are merely examples for carrying out the present invention, and the present invention is not limited thereto. Modifying these examples in various ways is within the scope of the present invention. Further, it is obvious from the above description that various other embodiments are possible within the scope of the present invention.

Explanation of Reference Numerals

[0057] 1 Engine 11 Cylinder Block 11a Cylinder Bore Wall 12 Water Jacket 13 Cooling Water Circulation Path 14 Water Pump 15 Piston 17 Crankshaft 28 Oil Pump 30 Oil Jet Mechanism 31 Piston Oil Jet Nozzle 32 Check Valve 50 Engine System 100 ECU

Claims

1. A control device for an internal combustion engine, comprising an oil jet mechanism having a piston oil jet nozzle for injecting oil toward a piston, wherein the control device includes a piston temperature calculation unit, a warm-up determination unit, and a piston oil jet execution unit, the piston temperature calculation unit determines whether the accelerator of the internal combustion engine has been turned off after the start of the internal combustion engine, and when the accelerator is off and fuel is cut off, calculates the piston temperature in a state where the rotational speed of the internal combustion engine has decreased due to the accelerator being turned off, the warm-up determination unit determines whether the warm-up of the internal combustion engine has been completed, the piston oil jet execution unit executes piston oil jet by the oil jet mechanism only when the piston temperature calculated by the piston temperature calculation unit is higher than a preset threshold value, avoids executing the piston oil jet when the piston temperature is lower than the threshold value, and sets the number of executions of the piston oil jet before the warm-up completion determination by the warm-up determination unit to be greater than the number of executions of the piston oil jet after the warm-up completion determination by the warm-up determination unit, A control device for an internal combustion engine.

2. The piston temperature calculation unit calculates the piston temperature in a state where the rotational speed of the internal combustion engine has decreased due to the accelerator being turned off based on the temperature of the oil injected by the oil jet mechanism and the temperature of the cooling water circulating in the internal combustion engine, The control device for an internal combustion engine according to claim 1.

3. The temperature of the cooling water is the cooling water outlet temperature at the outlet where the cooling water flows out from the engine body included in the internal combustion engine, The control device for an internal combustion engine according to claim 2.

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