Internal combustion engine control device and internal combustion engine control method

Abstract

One aspect of the present invention is an internal combustion engine control device designed to control an internal combustion engine comprising an oil pump ejecting a lubricant at a specified flow rate and an oil jet system spraying the lubricant ejected by the oil pump against a supply receiving portion of a piston, wherein the internal combustion engine control device includes a control device which performs a control to interrupt the injection of the lubricant from the oil jet system or to reduce the flow rate of the lubricant to below a flow rate in a previous cycle when the temperature of a piston crown surface falls below a lower limit temperature of a temperature range in which the amount of deposits accumulated on the piston crown surface falls below a threshold.

Description

Internal combustion engine control device and internal combustion engine control method

[0001] The present invention relates to an internal combustion engine control device and an internal combustion engine control method for controlling an internal combustion engine that injects an oil jet onto a piston.

[0002] In the control system of an internal combustion engine, it is known that the accumulation of deposits in the combustion chamber can lead to a deterioration in fuel economy and exhaust performance. When deposits accumulate, one method of reducing the deposits in the combustion chamber is to operate the internal combustion engine at a higher load, thereby burning off the deposits. However, if the amount of deposits increases, the deposits may harden, which can lead to problems such as the deposit accumulation not being suppressed even when deposit burning is performed.

[0003] Patent Document 1 discloses a method for controlling the ON / OFF of an oil jet to prevent the piston temperature from entering the temperature range where deposit accumulation increases, in order to suppress the buildup of deposits in the cooling channel. In this way, by controlling the piston temperature so that it does not enter the temperature range where deposit accumulation increases, it is possible to suppress deposit accumulation.

[0004] Japanese Patent Application Laid-Open No. 2017-145757

[0005] However, in the technology described in Patent Document 1, when the oil jet is turned on to lower the piston temperature in order to suppress deposit buildup, the engine displacement increases. As a result, the levels of exhaust gas regulated substances such as THC (Total Hydrocarbon) and PN (Particulate Number) increase. Furthermore, when there are multiple temperature ranges in which deposits increase, it is difficult to maintain the piston temperature at a level that suppresses deposit buildup simply by controlling the oil jet on and off, and deposit buildup can sometimes result in increases in THC and PN.

[0006] Given the above situation, there was a demand for a method that could simultaneously suppress deposit accumulation and reduce emissions of regulated exhaust gas substances.

[0007] In order to solve the above problems, one embodiment of the present invention provides an internal combustion engine control device that controls an internal combustion engine having an oil pump that discharges a specified flow rate of lubricating oil and an oil jet system that injects the lubricating oil discharged from the oil pump toward a supply portion of the piston, and is equipped with a control unit that stops the injection of lubricating oil from the oil jet system or controls the flow rate of lubricating oil to be lower than the flow rate in the previous cycle when the temperature of the piston crown surface is below the lower limit temperature of the temperature range in which the amount of deposit accumulation on the piston crown surface is less than a threshold value.

[0008] According to at least one aspect of the present invention, it is possible to suppress the accumulation of deposits and the emission of substances subject to exhaust gas regulation at the same time. Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments.

[0009] FIG. 1 is a schematic diagram showing an example of a system configuration of an internal combustion engine controlled by an internal combustion engine control device according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a variable displacement oil pump used in an internal combustion engine. FIG. 3 is a block diagram showing an example of the configuration of an internal combustion engine control device according to the first embodiment of the present invention. FIG. 4 is a control block diagram showing an overview of control executed by the internal combustion engine control device according to the first embodiment of the present invention. FIG. 5 is a map (graph) showing an example of the relationship between oil pressure and oil jet flow rate. FIG. 6 is a map showing an example of the relationship between the oil jet flow rate and the heat transfer coefficient between the piston and the oil jet. FIG. 7 is a diagram showing an example of the relationship between the engine operating time of an internal combustion engine and THC. FIG. 8 is a diagram showing an example of the relationship between the piston crown surface temperature and the deposit accumulation amount. FIG. 9 is a flowchart showing an example of the operation of the oil pressure setting unit of the internal combustion engine control device according to the first embodiment of the present invention. FIG. 10 is a map (graph) showing an example of the relationship between oil temperature and oil jet injection possible pressure. FIG. 10 is a block diagram showing an outline of control by an internal combustion engine control device according to a fourth embodiment of the present invention.

[0010] Hereinafter, examples of modes for carrying out the present invention (hereinafter referred to as "embodiments") will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, identical components or components having substantially the same functions are designated by the same reference numerals, and redundant description will be omitted.

[0011] First Embodiment First, a system configuration of an internal combustion engine controlled by an internal combustion engine control device according to a first embodiment of the present invention will be described with reference to FIG.

[0012] [Configuration of Internal Combustion Engine] Fig. 1 is a schematic diagram showing an example of the system configuration of an internal combustion engine controlled by an internal combustion engine control device according to this embodiment. The internal combustion engine 100 shown in Fig. 1 shows the system configuration of a spark-ignition internal combustion engine used in an automobile, and is equipped with an in-cylinder fuel injection valve that directly injects fuel made of gasoline into a cylinder. Note that the internal combustion engine 100 is not limited to an in-cylinder injection type internal combustion engine (direct injection engine), and a port injection type internal combustion engine that injects fuel into an intake port may also be used.

[0013] The internal combustion engine 100 is a four-stroke engine that repeats four strokes: an intake stroke, a compression stroke, a combustion (expansion) stroke, and an exhaust stroke. The internal combustion engine 100 is a multi-cylinder engine with, for example, four cylinders. The number of cylinders that the internal combustion engine 100 has is not limited to four, and the internal combustion engine 100 may have six, eight, or more cylinders. The number of cycles of the internal combustion engine 100 is not limited to four.

[0014] 1, the internal combustion engine 100 includes an air flow sensor 1, an electronically controlled throttle valve 2, an intake pressure sensor 3, a compressor 4a, an intercooler 7, and a cylinder 14. The air flow sensor 1, the electronically controlled throttle valve 2, the intake pressure sensor 3, the compressor 4a, and the intercooler 7 are arranged in the intake pipe 6 at positions up to the cylinder 14.

[0015] Furthermore, the air flow sensor 1 measures the intake air volume and intake air temperature. The electronically controlled throttle valve 2 is driven to be able to open and close by a drive motor (not shown). The opening of the electronically controlled throttle valve 2 is adjusted based on the accelerator operation by the driver. This adjusts the intake air volume and the pressure in the intake pipe 6. The intake pressure sensor 3 measures the pressure in the intake pipe 6.

[0016] The compressor 4a compresses the intake air to be supercharged in the supercharger. Rotational force is transmitted to the compressor 4a by a turbine 4b (described later). The intercooler 7 is disposed upstream of the cylinder 14 and cools the intake air.

[0017] The internal combustion engine 100 is also provided with an ignition device for each cylinder 14, which includes a fuel injector 13 that injects fuel into the cylinder 14, and an ignition device that includes an ignition coil 16 and a spark plug 17 that supply ignition energy. Under the control of an internal combustion engine control device 30, the ignition coil 16 generates a high voltage and applies it to the spark plug 17. This generates a spark in the spark plug 17. The spark generated in the spark plug 17 then combusts and explodes the air-fuel mixture in the cylinder. For example, an ECU (Engine Control Unit) can be used as the internal combustion engine control device 30.

[0018] In addition, a voltage sensor (not shown) is attached to the ignition coil 16. The voltage sensor measures the primary side voltage or secondary side voltage of the ignition coil 16. Voltage information measured by the voltage sensor is sent to the internal combustion engine control device 30.

[0019] Additionally, variable valves 5a and 5b are provided in the cylinder head 20 of each cylinder 14. Variable valve 5a adjusts the air-fuel mixture flowing into each cylinder 14, while variable valve 5b adjusts the exhaust gas discharged from each cylinder. By adjusting variable valves 5a and 5b, the intake air volume and internal exhaust gas recirculation (EGR) volume for each cylinder 14 can be adjusted.

[0020] Furthermore, a piston 21 is slidably disposed within the cylinder 14. The piston 21 compresses the mixture of fuel and gas that flows into the cylinder 14. The piston 21 reciprocates within the cylinder 14 due to the combustion pressure generated within the cylinder. The internal combustion engine 100 is also equipped with a crank angle sensor 19 for detecting the position of the piston 21. Crank angle information (rotation information) measured by the crank angle sensor 19 is sent to the internal combustion engine control device 30.

[0021] The fuel injection device 13 is controlled by an internal combustion engine control unit (ECU) 30 and injects fuel into the cylinder 14. As a result, an air-fuel mixture is generated in the cylinder 14. A high-pressure fuel pump (not shown) is also connected to the fuel injection device 13. Fuel pressurized by the high-pressure fuel pump is supplied to the fuel injection device 13. Furthermore, a fuel pressure sensor for measuring the fuel injection pressure is provided in a fuel pipe connecting the fuel injection device 13 and the high-pressure fuel pump.

[0022] The cylinder 14 is also provided with a temperature sensor 18. The temperature sensor 18 measures the temperature of the coolant circulating through the cylinder 14. The coolant device includes a water pump (not shown), which adjusts the flow rate of the coolant circulating through the cylinder 14. The water pump may be one that is driven by the output of the internal combustion engine or an electric water pump (electric water pump). Although not shown, other devices that adjust the coolant may include a thermostat that controls the coolant flowing into the cylinder, and valves that switch the flow direction to each component of the internal combustion engine, such as a heat exchanger or cylinder.

[0023] Furthermore, each cylinder 14 of the internal combustion engine 100 is provided with an oil jet system 101 (piston cooling device). The oil jet system 101 is connected to a variable displacement oil pump 54 (see FIG. 2), and oil (lubricating oil) for cooling and lubrication is supplied from the oil pump 54. The oil jet system 101 is provided with a throttle portion 103 that increases the flow rate of the lubricating oil. Engine oil is generally used as the lubricating oil.

[0024] The oil jet system 101 injects lubricating oil from the throttle portion 103 onto the underside of the piston 21 to lower the temperature of the piston 21. The oil jet system 101 allows the lubricating oil to be appropriately applied to the underside (backside) of the piston 21, and the temperature of the piston crown surface can be accurately controlled. Furthermore, the internal combustion engine control device 30 adjusts the output (flow rate, oil pressure) of the oil pump 54, thereby changing the amount of lubricating oil injected from the oil jet system 101 toward the piston 21.

[0025] A valve 102 is provided in the oil flow path of the oil jet system 101. The valve 102 is provided between the oil main gallery 110 and the oil jet nozzle outlet. In this example, the valve 102 is disposed between the oil pump 54 and the oil jet nozzle outlet.

[0026] Furthermore, an exhaust pipe 15 is connected to the exhaust port of the cylinder 14. The exhaust pipe 15 is provided with a turbine 4b, an electronically controlled wastegate valve 11, a three-way catalyst 10, and an air-fuel ratio sensor 9. The turbine 4b is rotated by the exhaust gas passing through the exhaust pipe 15 and transmits rotational force to the compressor 4a. The electronically controlled wastegate valve 11, which is connected to connect the upstream and downstream sides of the turbine 4b, adjusts the exhaust flow rate that flows to the turbine 4b.

[0027] The three-way catalyst 10 is disposed downstream of the turbine 4b. The three-way catalyst 10 purifies harmful substances contained in the exhaust gas through oxidation-reduction reactions. The air-fuel ratio sensor 9 is disposed upstream of the three-way catalyst 10. The air-fuel ratio sensor 9 detects the air-fuel ratio of the exhaust gas passing through the exhaust pipe 15.

[0028] Signals detected by the air flow sensor 1, intake pressure sensor 3, voltage sensor, and other sensors are sent to the internal combustion engine control device 30. A signal detected by an accelerator position sensor 12 that detects the amount of depression of the accelerator pedal, i.e., the accelerator position, is also sent to the internal combustion engine control device 30.

[0029] The internal combustion engine control device 30 calculates the required torque based on the output signal of the accelerator position sensor 12. That is, the accelerator position sensor 12 is used as a required torque detection sensor that detects the torque required for the internal combustion engine 100. The internal combustion engine control device 30 also calculates the rotation speed of the internal combustion engine 100 based on the output signal of the crank angle sensor 19. Then, the internal combustion engine control device 30 optimally calculates the main operation variables of the internal combustion engine 100, such as the air flow rate (intake flow rate), fuel injection amount, ignition timing, throttle opening, and fuel pressure, based on the operating state of the internal combustion engine 100 obtained from the output signals of various sensors.

[0030] The fuel injection amount calculated by the internal combustion engine control device 30 is converted into a valve-opening pulse signal and output to the fuel injector 13. In addition, the ignition timing calculated by the internal combustion engine control device 30 is output as an ignition signal to the spark plug 17. Furthermore, the throttle opening calculated by the internal combustion engine control device 30 is output as a throttle drive signal to the electronically controlled throttle valve 2.

[0031] In the internal combustion engine 100 configured as described above, fuel is injected from the fuel injector 13 into air that flows into the cylinder 14 from the intake pipe 6 through the intake valve (variable valve 5a), forming an air-fuel mixture in the cylinder. The air-fuel mixture explodes at a predetermined ignition timing due to a spark generated by the spark plug 17, and the resulting combustion pressure pushes the piston 21 down, providing driving force for the internal combustion engine 100. Furthermore, exhaust gas after the explosion passes through the exhaust pipe 15 and is sent to the three-way catalyst 10, where the exhaust components are purified and then discharged to the outside.

[0032] The internal combustion engine 100 may be provided with an EGR pipe (not shown) that connects the intake pipe 6 and the exhaust pipe 15. A portion of the exhaust gas passing through the exhaust pipe 15 may be returned to the intake pipe 6 through this EGR pipe.

[0033] [Configuration of Oil Pump] Next, an outline of the configuration of the variable displacement oil pump 54 used in the internal combustion engine 100 will be described with reference to FIG.

[0034] 2 is a schematic cross-sectional view showing an example of the configuration of a variable displacement oil pump 54 used in the internal combustion engine 100. The oil pump unit (oil pump 54) is a variable displacement pump including a pump housing 161 having a storage portion, a rotor 164 disposed within the storage portion and connected to the rotary shaft of the internal combustion engine 100 so as to transmit driving force, a cam ring 165 whose eccentricity between the center of rotation of the rotor 164 and its own center changes between a high discharge rate position and a low discharge rate position, and a control valve (proportional solenoid 171a in an oil control valve 171, a substantially cylindrical valve element not shown) that changes the eccentricity of the cam ring 165 under control of a control unit (oil jet control unit 36 ​​of the internal combustion engine control device 30). The configuration of the oil pump 54 will be described in more detail below.

[0035] The variable displacement oil pump 54 is capable of variably controlling the pressure (hydraulic pressure) of the oil being discharged. The oil pump 54 has an intake port and an outlet port on both sides of a pump housing 161. A drive shaft 162, to which rotational force is transmitted from the crankshaft of the internal combustion engine 100, is disposed and passes through the oil pump 54 approximately in the center.

[0036] A rotor 164 and a cam ring 165 are housed and arranged inside the pump housing 161. The rotor 164 is coupled to the drive shaft 162. That is, the rotor 164 is configured to be able to transmit the driving force of the rotary shaft of the internal combustion engine 100. The rotor 164 holds a plurality of vanes 163 on its outer periphery so that the vanes 163 can move back and forth approximately in the radial direction.

[0037] Cam ring 165 is provided on the outer periphery of rotor 164 so as to be able to swing eccentrically. The tips of each vane 163 are in sliding contact with the inner periphery of cam ring 165. A pair of vane rings 150 are slidably disposed on both side surfaces of the inner periphery of rotor 164.

[0038] Operating chambers 167 and 168 are formed on the outer periphery of cam ring 165, separated by seal members 166a and 166b. Cam ring 165 swings around pivot pin 169 in a direction that reduces the amount of eccentricity in response to the discharge pressure of oil introduced into operating chambers 167 and 168. Cam ring 165 also has lever portion 165a formed integrally with the outer periphery. Lever portion 165a is formed so as to protrude toward the outer periphery of cam ring 165. Cam ring 165 swings in a direction that increases the amount of eccentricity due to the spring force of coil spring 151, which presses lever portion 165a in a direction approximately perpendicular to the direction of rotation of the crankshaft.

[0039] In the initial state, the internal combustion engine control device 30 urges the cam ring 165 in the direction that maximizes the amount of eccentricity using the spring force of the coil spring 151, thereby increasing the discharge pressure of the oil pump 54. On the other hand, when the oil pressure in the working chamber 167 reaches or exceeds a predetermined value, the internal combustion engine control device 30 causes the cam ring 165 to swing against the spring force of the coil spring 170 in the direction that reduces the amount of eccentricity, thereby reducing the discharge pressure.

[0040] Oil (lubricating oil) is supplied to the working chamber 167 of the oil pump 54 from the oil main gallery 110, and oil is supplied to the working chamber 168 via an oil control valve 171 made up of a proportional solenoid valve. The oil discharged from the oil pump 54 is supplied to a hydraulic VTC (Valve Timing Control) mechanism that controls the above-mentioned variable valves 5a and 5b (see FIG. 1) of the internal combustion engine 100, an oil jet mechanism that cools the piston 21, and the like.

[0041] The oil control valve 171 has a first opening 172 and a second opening 173 formed in its body. The oil control valve 171 also has a proportional solenoid 171a and a substantially cylindrical valve element (not shown) that moves in response to the thrust generated in the proportional solenoid 171a when energized. Grooves designed in consideration of the positions of the first opening 172 and the second opening 173 are formed on the circumferential surface of the substantially cylindrical valve element. The valve element moves in the axial direction of the oil control valve 171 (left-right direction in FIG. 2 ) in response to the thrust generated by the proportional solenoid 171a. Depending on the position of the valve element, the relative positional relationship between the grooves in the valve element and the first and second openings 172 and 173 changes, thereby changing the flow path. When the valve element is in the first position, the oil pump operating chamber 168 communicates with the oil pan through the first opening 172. Also, when the valve body is in the second position, the working chamber 168 of the oil pump communicates with the oil main gallery 110 through the first opening 172 and the second opening 173 .

[0042] The oil control valve 171 is duty-controlled by a drive signal (PWM (Pulse Width Modulation) signal) from the internal combustion engine control device 30. A proportional solenoid 171a in the oil control valve 171 is excited in accordance with the duty ratio of the drive signal, and the valve element is driven to a target control position.

[0043] The oil pump 54 is a mechanism for manipulating the oil pressure of the discharge oil (hereinafter also referred to as "discharge oil pressure") by controlling the eccentricity of the vane 163 in accordance with the oil pressure difference between the working chambers 167 and 168. The oil pump 54 performs the following controls: [a] When the oil pressure difference between the working chambers 167 and 168 is large, the eccentricity of the vane 163 (cam ring 165) is reduced to reduce the discharge oil pressure. [b] When the oil pressure difference between the working chambers 167 and 168 is small, the eccentricity of the vane 163 (cam ring 165) is increased to increase the discharge oil pressure.

[0044] The hydraulic pressure in the working chamber 168 can be controlled by controlling the introduction and discharge of oil into and from the working chamber 168. That is, the hydraulic pressure in the working chamber 168 is controlled by the duty ratio of the drive signal supplied to the oil control valve 171. The relationship between the duty ratio of the drive signal and the discharge hydraulic pressure is as follows: [a] When the duty ratio is 100%, the valve element in the oil control valve 171 moves to a position where the working chamber 168 communicates with the oil pan, and the hydraulic pressure in the working chamber 168 decreases (= the hydraulic pressure in the working chamber 168 is equivalent to that of the oil pan (1 atmosphere)). This minimizes the eccentricity of the vane 163 (cam ring 165) of the oil pump 54, and the discharge hydraulic pressure becomes minimum. [b] When the duty ratio is 0%, the valve element in the oil control valve 171 moves to a position where the working chamber 168 communicates with the oil main gallery 110, and the hydraulic pressure in the working chamber 168 increases (= the hydraulic pressure in the working chamber 168 is equivalent to that of the oil main gallery 110). As a result, the amount of eccentricity of the vane 163 (cam ring 165) of the oil pump 54 becomes maximum, and the discharge oil pressure becomes maximum.

[0045] In this way, when the duty ratio of the drive signal is large, the working chamber 168 communicates with the drain (oil pan) via the oil control valve 171. As a result, the oil discharged from the oil pump 54 is in a low-pressure state. On the other hand, when the duty ratio of the drive signal is small, the oil main gallery 110 and the working chamber 168 communicate with each other via the oil control valve 171, and hydraulic pressure is applied to the working chamber 167. As a result, the oil discharged from the oil pump 54 is in a high-pressure state. Then, by adjusting the duty ratio of the drive signal between 100% and 0%, it is possible to adjust the pressure of the oil discharged from the oil pump 54 within a range from maximum to minimum.

[0046] In addition, an oil pressure sensor 111 is disposed in the oil main gallery 110. The oil pressure sensor 111 measures the pressure of the oil in the oil main gallery 110 and outputs a signal corresponding to the oil pressure. The oil pressure in the oil main gallery 110 correlates with the pressure of the oil discharged by the oil pump 54 (discharge oil pressure). In this embodiment, the discharge oil pressure of the oil pump 54 is detected by acquiring the output signal of the oil pressure sensor 111. The output signal of this oil pressure sensor 111 is input to the internal combustion engine control device 30 and used for feedback control of the discharge oil pressure of the oil pump 54 to a target discharge oil pressure. Of course, it goes without saying that the oil pressure obtained from the output signal of the oil pressure sensor 111 can also be used for other control purposes. Hereinafter, when simply referred to as "oil pressure," it means the discharge oil pressure of the oil pump 54.

[0047] The oil supplied and injected to each mechanism and the oil discharged from the oil control valve 171 are collected in the oil pan and then supplied again to the oil main gallery 110, from where they are supplied and injected to each of the above-mentioned mechanisms.

[0048] 2, the oil jet system 101 can adjust the amount of oil supplied to the oil jet by arbitrarily setting the discharge oil pressure of the oil pump 54. Therefore, compared to simply switching the oil jet ON / OFF, this embodiment makes it easier to maintain the piston crown temperature in a temperature range 802 (between a lower limit temperature 805 and an upper limit temperature 806) where the amount of deposit buildup is equal to or less than a threshold value 804, as shown in FIGS.

[0049] It should be noted that instead of the variable displacement oil pump 54 described above, an oil pump in which the oil pressure increases in proportion to the rotation speed may be used. Generally, such oil pumps are unable to reduce the oil pressure sufficiently under low temperature conditions, and the pump alone cannot stop the oil jet. Therefore, a solenoid valve for stopping the oil jet must be provided to stop the oil jet. When a variable displacement oil pump 54 is used, hydraulic pressure control is possible over the entire temperature range, including low temperatures, so a solenoid valve for switching between on and off oil jet injection is not required.

[0050] If the oil jet system 101 is configured using a variable displacement oil pump 54, it is possible to control the amount of oil supplied to the oil jet even when the ambient temperature is low, making it easier to control the temperature of the piston crown surface and increasing the effect of reducing THC and PN.

[0051] [Configuration of Internal Combustion Engine Control Device] Next, an example of the configuration of an internal combustion engine control device 30 to which the present invention is applied will be described with reference to FIG.

[0052] Fig. 3 is a block diagram showing an example of the configuration of the internal combustion engine control device 30. As shown in Fig. 3, the internal combustion engine control device 30, which is an ECU, has an input circuit 31, an input / output port 32, a CPU (Central Processing Unit) 33a, a RAM (Random Access Memory) 33c, and a ROM (Read Only Memory) 33b. The internal combustion engine control device 30 also has an oil jet control unit 36.

[0053] For example, the input circuit 31 receives an air flow rate signal from the air flow sensor 1 (see FIG. 1), an intake pressure signal from the intake pressure sensor 3, and a coil primary voltage or secondary voltage signal from a voltage sensor. The input circuit 31 also receives a crank angle (rpm) from the crank angle sensor 19 and oil pressure (oil pressure) and oil temperature (oil temperature) signals from the sensors provided in the oil jet system 101. In addition to this information, the input circuit 31 also receives information measured by various sensors, such as the throttle opening and exhaust air-fuel ratio.

[0054] The input circuit 31 performs signal processing such as noise removal on the input signal and sends the signal to the input / output port 32. The value of the signal input to the input port of the input / output port 32 is temporarily stored in the RAM 33c.

[0055] The ROM 33b stores a control program describing the contents of various arithmetic processes executed by the CPU 33a, as well as maps and data tables used in each process. The control program and the maps and data tables used in each process may be stored in a non-volatile storage (not shown). The RAM 33c has a storage area for storing values ​​input to the input ports of the input / output port 32 and values ​​representing the manipulated variable of each actuator calculated according to the control program. The values ​​representing the manipulated variable of each actuator stored in the RAM 33c are sent to the output ports of the input / output port 32.

[0056] The operation amount of the oil pump 54 set in the output port of the input / output port 32 is sent to the oil jet control unit 36. The oil jet control unit 36 ​​generates a control signal based on the operation amount of the oil pump 54, and a drive circuit (not shown) supplies a drive signal based on the control signal to the oil pump 54. In this way, the oil jet control unit 36 ​​controls the pressure (hydraulic pressure) of the oil output by the oil pump 54, which supplies oil to the oil jet system 101 (see FIG. 1). Then, by controlling the hydraulic pressure of the oil pump 54, the oil jet control unit 36 ​​adjusts the amount of oil sprayed from the oil jet system 101, thereby controlling the temperature change of the piston 21.

[0057] Note that the internal combustion engine 100 also uses actuators other than these, and the internal combustion engine control device 30 is equipped with an ignition control unit, a fuel injection control unit, etc. (not shown) that control these actuators, but a description thereof will be omitted here. In the present embodiment, an example has been described in which the internal combustion engine control device 30 is equipped with the oil jet control unit 36, but this is not limited to this. For example, the oil jet control unit 36 ​​may be implemented in a control device different from the internal combustion engine control device 30.

[0058] [Outline of Control of Internal Combustion Engine Control Device] Next, an outline of the control executed by the internal combustion engine control device 30 will be described with reference to Fig. 4. Fig. 4 is a control block diagram showing an outline of the control executed by the internal combustion engine control device 30. In the internal combustion engine control device 30, the oil jet control unit 36 ​​includes a piston crown surface temperature correlation index estimation unit 41 and an oil pressure setting unit 42. The CPU 33a (see Fig. 3) executes a control program recorded in the ROM 33b or the like, thereby realizing the function of each processing block.

[0059] [Piston Crown Surface Temperature Correlation Index Estimation Unit] The piston crown surface temperature correlation index estimation unit 41 (an example of a correlation index estimation unit) is a processing block that estimates a piston crown surface temperature correlation index that is correlated with the temperature of the piston 21, based on operating condition parameters and oil jet parameters of the internal combustion engine 100. In the example of FIG. 4 , the air flow rate in the intake pipe 6 and the engine speed (crank angle) are input as operating condition parameters, and the discharge oil pressure of the oil pump 54 and the oil temperature of the oil jet are input as oil jet parameters. For example, an oil temperature sensor is provided in an oil pan (not shown), and the oil temperature sensor measures the temperature of oil flowing into the oil pan. Note that the location at which the oil temperature is measured is not limited to the oil pan, and it may be a location closer to the oil pump 54.

[0060] For example, the piston crown surface temperature correlation index estimating unit 41 may estimate the piston temperature itself as the piston crown surface temperature correlation index. For example, the piston temperature change can be successively estimated from the balance between the energy input to the piston and the energy released. For example, the following equation 1 may be calculated. The energy is assumed to be thermal energy.

[0061] [Math. 1] Tpis = (Tpis, 0) + (Qinp - (Qout, 1) - (Qout, oj) - (Qout, res)) ÷ (Mpis x Cpis)

[0062] Here, Tpis is the updated (estimated) value of the piston temperature, and (Tpis, 0) is the current value of the piston temperature. Qinp is the energy [J] transferred from the combustion gas to the piston, and (Oout, l) is the energy [J] transferred from the piston to the cylinder liner through the piston ring and piston skirt (the part in contact with the inner wall of the cylinder). (Qout, oj) is the energy [J] transferred from the piston to the oil jet, and (Qout, res) is the energy [J] flowing from the piston to the outside through the crankshaft or the like. Furthermore, Mpis is the mass of the piston (kg), and Cpis is the specific heat [J / kg / K] of the piston. For example, Qinp, (Qout, l), and (Qout, oj) can be calculated using the following equations 2, 3, and 5.

[0063] [Math. 2] Qinp = (Mdot, f) x Qf x ηpis x Δτ [Math. 3] (Qout, l) = Spl x λpl x ((Tpis, 0) - Tc) x Δτ [Math. 4] (Qout, oj) = Spo x hpis x ((Tpis, 0) - Toil) x Δτ

[0064] Here, (Mdot, f) is the fuel flow rate [kg / s], Qf is the lower heating value of the fuel [J], ηpis is the rate of energy transferred to the piston (-), and Δτ is the calculation period [s]. Spl is the contact area between the piston and the liner [m2], λpl is the thermal conductivity between the piston and the liner [W / (m·K)], and Tc is the coolant temperature [°C]. Spo is the contact area between the oil jet and the piston [m2], hpis is the heat transfer coefficient of the oil jet, and Toil is the oil temperature of the oil jet [°C].

[0065] Qf can be set in advance assuming, for example, gasoline. Spl can be given by the contact area between the piston ring and the liner portion and can be easily set based on geometric information such as the piston ring thickness and bore diameter (e.g., piston ring thickness × bore diameter × pi). Spo can be set based on the piston's geometric information (e.g., bore diameter × bore diameter × pi ÷ 4). ηpis can be given by a map based on operating conditions, piston temperature, cooling temperature, and oil temperature, and this map must be determined in advance through experiments or simulations. hpis is a parameter that depends on the oil jet shape and oil jet flow rate. Therefore, hpis can be identified in advance through measurements such as experiments or simulations, and a map can be created. For example, the relationship between oil pressure and oil jet flow rate shown in Figure 5 and the relationship between oil jet flow rate and heat transfer coefficient hpis shown in Figure 6 can be used.

[0066] Fig. 5 is a map (graph) showing an example of the relationship between oil pressure and oil jet flow rate. The vertical axis of Fig. 5 represents the oil jet flow rate, and the horizontal axis represents the oil pressure. Fig. 6 is a map showing an example of the relationship between the oil jet flow rate and the heat transfer coefficient hpis between the piston and the oil jet. The vertical axis of Fig. 6 represents the heat transfer coefficient (hpis), and the horizontal axis represents the oil jet flow rate.

[0067] As shown in FIG. 5, the oil jet flow rate is greater than or equal to 0 when the oil pressure is equal to or greater than the valve opening pressure of the valve 102, and the flow rate increases as the oil pressure increases. Furthermore, when compared at the same oil pressure, the higher the oil temperature, the lower the oil viscosity and the higher the oil jet flow rate. Furthermore, as shown in FIG. 6, the heat transfer coefficient hpis has a positive correlation with the oil jet flow rate. Therefore, the higher the oil jet flow rate, the higher the heat transfer coefficient hpis. The current oil jet flow rate can be calculated from the oil pressure, oil temperature, and the relationship shown in FIG. 5, and the heat transfer coefficient hpis can be calculated from the calculated oil jet flow rate and the relationship shown in FIG. 6. Furthermore, the fuel flow rate (Mdot, f) can be calculated, for example, using the air flow rate (Mdot, a) measured by the air flow sensor 1 and the exhaust air-fuel ratio AbF(-) detected by the air-fuel ratio sensor 9, as shown in Equation 5.

[0068] (Mdot, f)=(Mdot, a)÷AbF [Equation 5] From the above, the piston crown surface temperature correlation index can be calculated.

[0069] (Another Calculation Method of the Piston Crown Surface Temperature Correlation Index) It is clear that the piston temperature has a qualitative tendency to rise as the combustion operation of the internal combustion engine continues and to fall when the combustion operation of the internal combustion engine stops. For this reason, the time during which the combustion operation of the internal combustion engine continues (combustion operation duration) may be used to calculate the piston crown surface temperature correlation index. For example, this can be given by the following equation.

[0070] [Equation 6] tcomb = (tcomb, 0) + Δτ (during combustion operation) [Equation 7] tcomb = (tcomb, 0) - Δτstop (during fuel cut, engine stop)

[0071] Here, tcomb is the updated value [s] of the time that the combustion operation of the engine has continued, and (tcomb, 0) is the current value [s] of the time that the combustion operation of the internal combustion engine 100 has continued. Equation 7 is an equation that expresses both the state immediately after the internal combustion engine 100 has stopped and the state after the internal combustion engine 100 has stopped for a while. In addition, in the case of Equation 7, if the time after the internal combustion engine has stopped is long, the value of tcomb (combustion operation duration) becomes negative, so as a general rule, tcomb≧0.

[0072] Δτstop is a parameter used to express the decrease in piston temperature during fuel cut or engine shutdown as a decrease in the duration of combustion operation of the internal combustion engine. In other words, "-Δτstop" represents a temperature decrease. In its simplest form, Δτstop may be set to the calculation period. Furthermore, because the decrease in piston temperature is affected by fuel cut, engine shutdown, water temperature, and oil temperature, Δτstop can be given as a map with water temperature, oil temperature, and engine speed as its axes. The lower the water temperature and oil temperature, the larger Δτstop becomes. On the other hand, the higher the engine speed, the larger Δτstop becomes. This reflects the fact that the lower the water temperature and oil temperature, the greater the amount of energy flowing from the piston to the liner, resulting in improved cooling. Furthermore, the higher the engine speed, the greater the heat transfer with the air introduced into the cylinder, resulting in improved piston cooling.

[0073] The initial value of the duration of combustion operation, which is necessary for calculating the duration of engine combustion operation, can be set based on the oil temperature and water temperature at engine start. For example, a reference value for the coolant temperature is set, and the initial value is set to 0 if the coolant temperature at the start of engine combustion is equal to or greater than the reference value. On the other hand, if the coolant temperature at the start of engine combustion is equal to or greater than the reference value, the initial value is set to a value greater than 0. Conversely, if the coolant temperature at the start of engine combustion is less than the reference value, the initial value is set to a value less than 0. By setting the initial value in this manner, it is possible to reproduce a situation in which differences in the initial temperature result in differences in the time it takes to reach a predetermined temperature. Note that the initial value of the duration of combustion operation is also required to be determined in advance through simulations or engine operation tests.

[0074] (Another Calculation Method for the Piston Crown Surface Temperature Correlation Index) In the process of increasing piston temperature, the greater the engine output (e.g., engine torque or engine speed), the greater the amount of heat transferred to the piston, and therefore the greater the temperature increase. Furthermore, because oil jet injection causes energy to flow from the piston to the oil, it is desirable to incorporate this influence into the index. It is difficult to reflect the operating conditions and the oil jet operating state in the combustion operation duration described above. Therefore, the equation for the combustion operation duration shown in Equation 6 was improved, and an index correlated with the piston crown surface temperature is defined as shown in Equation 8 below. While Equation 6 simply integrates the engine operating time, Equation 8 weights the operating conditions and the presence or absence of an oil jet when integrating the operating time, thereby allowing the influence of the operating conditions and the oil jet to be reflected.

[0075] [Equation 8] tcomb = (tcomb, 0) + (αout - αoj) Δτ (during combustion operation)

[0076] Here, tcomb is the updated value [s] of the index correlated with the piston crown surface temperature, (tcomb, 0) is the current value [s] of the index correlated with the piston crown surface temperature, and αout is a coefficient for reflecting the influence of operating conditions and is an index positively correlated with output. For example, the value of αout at the reference output may be set to 1, and αout may be set to a value positively correlated with output. Furthermore, when the output is 0, the coefficient is set to a negative value. This makes it possible to express the change in piston temperature that occurs when the engine is stopped or fuel is cut. For example, if αout is set to -1 when the output is 0, then Equation 8 is equivalent to Equation 7.

[0077] Furthermore, αoj is a coefficient for reflecting the influence of the oil jet and is given as an index having a positive correlation with the oil jet flow rate or oil pressure. For example, when the oil jet flow rate is 0, αoj is set to 0, and αoj is set to be proportional to the oil jet flow rate. Furthermore, when the value of αoj is given based on oil pressure, αoj is set to 0 when the oil pressure is less than the valve opening pressure of the valve 102, and αoj is set to be positively correlated with the oil pressure in the range where the oil pressure is equal to or greater than the valve opening pressure. This makes it possible to apply an index that is closer to the behavior of the piston temperature than the combustion operation duration (Equations 6 to 7) and that can be calculated more easily than the piston crown surface temperature estimation (Equations 1 to 5).

[0078] The temperature of the crown surface of the piston 21 may also be measured directly by providing a temperature sensor 105 for temperature measurement near the crown surface of the piston 21. In Fig. 1, an example is shown in which the temperature sensor 105 is provided in a portion of the outer wall of the cylinder 14 that corresponds to the region in which the piston 21 reciprocates.

[0079] [Hydraulic Pressure Setting Unit] The hydraulic pressure setting unit 42 (see FIG. 4) is a processing block that sets the oil pressure generated by the variable displacement oil pump 54. The hydraulic pressure setting unit 42 sets the hydraulic pressure (target hydraulic pressure) when oil jet injection is performed, based on the piston crown surface temperature correlation index estimated by the piston crown surface temperature correlation index estimation unit 41. The hydraulic pressure is determined by branching processing shown in FIG. 9 based on the piston crown surface temperature correlation index, and as a result, the oil jet flow rate can be controlled.

[0080] As described above, in this embodiment, it is possible to control the oil jet flow rate based on an index correlated with the piston crown surface temperature by providing the piston crown surface temperature correlation index estimating unit 41 and the oil pressure setting unit 42. Also, the oil pressure setting unit 42 may be configured to use the measurement value of the temperature sensor 105 (see FIG. 1 ) as the piston crown surface temperature instead of the piston crown surface temperature correlation index.

[0081] [Engine Operating Time and THC Emissions] Here, the relationship between engine operating time of an internal combustion engine and THC emissions will be described. FIG. 7 is a diagram showing an example of the relationship between engine operating time [h] of an internal combustion engine and THC emissions [ppmC]. PN also shows a similar trend to THC emissions. As the engine operating time increases, substances (combustion products) resulting from unburned or incomplete combustion of fuel and lubricating oil accumulate as deposits inside the engine cylinder. The deposits repeatedly adhere to and peel off the combustion chamber walls, and the amount of accumulation increases over time. The deposits absorb fuel or lubricating oil, causing partial misfires or incomplete combustion, resulting in increases in THC and PN emissions from the engine. FIG. 7 shows an example in which THC emissions increase from an initial value 701 over engine operating time, exceeding the allowable THC increase limit 702.

[0082] Deposits accumulate on the walls of the cylinder head 20, piston 21, cylinder 14, intake variable valve 5a, exhaust variable valve 5b, and fuel injector 13. The inner wall of the cylinder 14 is the sliding part with the piston 21, and near the ignition timing, the piston 21 is positioned close to top dead center. Therefore, near the ignition timing, the surface area of ​​the inner wall of the cylinder 14, which forms the combustion chamber, is smaller than the crown surface of the piston 21, and deposits are more likely to accumulate on the crown surface of the piston 21 than on the cylinder 14.

[0083] [Piston Crown Surface Temperature and Deposit Amount] Next, the relationship between the piston crown surface temperature (°C) of the piston 21, which is the main component on which deposits accumulate, and the deposit accumulation amount will be described. FIG. 8 is a graph showing an example of the relationship between piston crown surface temperature (°C) and deposit accumulation amount (mg). Note that FIG. 8 shows the deposit accumulation amount after a certain period of engine operation has elapsed. Deposits are likely to accumulate when the piston crown surface temperature is in a low temperature range 801 and a high temperature range 803. Therefore, in order to suppress deposit accumulation, it is preferable to maintain the piston crown surface temperature in a temperature range 802 between temperature ranges 801 and 803, where the deposit accumulation amount is "low." As a result, increases in THC and PN due to deposit accumulation can be suppressed.

[0084] 8 shows an example in which the lower limit temperature 805 of the temperature range 802 is set to approximately 150°C and the upper limit temperature 806 is set to approximately 215°C based on the deposit accumulation amount threshold value 804 (tolerance value). The deposit accumulation amount threshold value 804 (tolerance value) may be set in advance by the ECU 30 based on the allowable amount 702 of THC increase from the initial value 701 of the emission amount of exhaust gas regulated substances such as THC shown in FIG.

[0085] [Operation of Oil Pressure Setting Unit] Next, the operation of the oil pressure setting unit 42 of the internal combustion engine control device 30 will be described with reference to Fig. 9. Fig. 9 is a flowchart showing an example of the operation of the oil pressure setting unit 42 of the internal combustion engine control device 30.

[0086] First, in step S901, the oil pressure setting unit 42 determines whether the lubricity of the piston 21 and the cylinder 14 has decreased, i.e., whether the piston lubricity is low. For example, if the duration of combustion operation of the internal combustion engine 100 calculated using equations 6 and 7 is shorter than a predetermined value, it can be determined that the piston lubricity is low. If the determination in step S901 is YES, the oil pressure setting unit 42 proceeds to step S902, and if the determination is NO, the oil pressure setting unit 42 proceeds to step S903.

[0087] If the duration of combustion operation of the internal combustion engine 100 is less than a predetermined value (YES in S901), in step S902, the oil pressure setting unit 42 sets the target oil pressure of the oil pump 54 to a pressure at which oil jet injection is possible. The oil pressure at which oil jet injection is possible is determined according to the specifications of the oil jet nozzle and valve 102 (see FIG. 1) and the oil temperature. Qualitatively, the lower the oil temperature, the higher the oil pressure at which oil jet injection is possible. The valve 102 is a check valve (non-return valve) configured to open when the oil pressure in the oil main gallery 110 reaches or exceeds a predetermined value. For example, a ball valve can be used as the valve 102.

[0088] The relationship between the oil temperature and the pressure at which oil jet injection is possible will now be described with reference to Fig. 10. Fig. 10 is a map (graph) showing an example of the relationship between the oil temperature and the pressure at which oil jet injection is possible. The vertical axis of Fig. 10 represents the pressure at which oil jet injection is possible, and the horizontal axis represents the oil temperature.

[0089] As shown in Figure 10, under conditions of high oil temperature, the injection pressure is determined by the valve opening pressure of the valve 102. At low temperatures, the oil viscosity increases, resulting in increased pressure loss in the oil jet nozzle. Therefore, the pressure required to inject oil from the nozzle tip may be much greater than the injection pressure (oil jet cut pressure Pc) determined by the valve 102. The oil pressure setting unit 42 determines the oil pressure setting value (target oil pressure 62) based on the current oil temperature and the relationship shown in Figure 10. The target oil pressure 62 may be set to a value equal to or greater than the pressure at which the oil jet can be injected (oil jet injection pressure 61). Hereinafter, the mode in which the processing in step S902 is performed is referred to as the "lubrication mode."

[0090] By setting in this way, the oil pressure setting unit 42 can determine when piston lubrication is low and set the oil pressure at which oil jet injection is possible. Therefore, when piston lubrication is low, oil is supplied by the oil jet to improve lubrication, and the deterioration of fuel consumption in a situation where piston lubrication is low can be reduced.

[0091] As described above, the oil pressure setting unit 42 is configured to set the target value of the oil pressure of the oil jet (oil jet system 101) to an oil pressure that allows oil jet injection, and to set an oil pressure that allows oil to be impregnated into each part of the internal combustion engine.

[0092] In addition, the oil pressure setting unit 42 sets the target oil pressure value of the oil jet (oil jet system 101) to a oil pressure at which oil jet injection can be stopped or a oil pressure at which the oil jet can be injected, based on the oil pressure at which the valve 102 responding to the oil pressure provided between the oil pump 54 and the oil jet nozzle opens and closes.

[0093] If the duration of combustion operation of the internal combustion engine 100 is equal to or longer than the predetermined value (NO in S901), the oil pressure setting unit 42 determines whether the piston crown surface temperature correlation index is smaller than a first predetermined value in step S903 of Fig. 9. The first predetermined value is set to be the lower limit temperature 805 of the temperature range 802 in Fig. 6 where the deposit amount is small.

[0094] In this way, when the crown surface temperature of the piston 21 is less than the first predetermined value, the oil pressure setting unit 42 sets the oil pressure of the oil jet (oil jet system 101) to a pressure at which oil jet injection can be stopped.

[0095] If the crown surface temperature of piston 21 is lower than the first predetermined value (YES in S903), oil pressure setting unit 42 proceeds to step S904. If the crown surface temperature of piston 21 is equal to or higher than the first predetermined value (NO in S903), oil pressure setting unit 42 proceeds to step S905.

[0096] In step S904, the oil pressure setting unit 42 sets the target oil pressure of the oil pump 54 to a pressure at which the oil jet can be stopped, based on the relationship shown in Fig. 5. Specifically, the target oil pressure can be set to a pressure lower than the valve opening pressure of the valve 102 provided between the oil main gallery 110 and the oil jet nozzle. Hereinafter, the mode in which the processing in step S904 is performed after a YES determination in step S903 is referred to as the "warm-up promotion mode."

[0097] In step S905, the oil pressure setting unit 42 determines whether the crown surface temperature of the piston 21 is greater than a second predetermined value. If the crown surface temperature of the piston 21 is greater than the second predetermined value (YES in S905), the oil pressure setting unit 42 proceeds to step S906. Then, in step S906, the oil pressure setting unit 42 sets the target oil pressure of the oil pump 54 to a pressure that enables oil jet injection, and performs control to suppress the crown surface temperature of the piston 21. The second predetermined value is set to be the upper limit temperature 806 of the temperature range 802 in FIG. 8 where the amount of deposit accumulation is small.

[0098] On the other hand, if the crown surface temperature of the piston 21 is equal to or lower than the second predetermined value (NO in S905), the oil pressure setting unit 42 proceeds to step S907 and determines whether there is an increase in the change over time in the crown surface temperature of the piston 21. The ECU 30 stores in the RAM 33 the direction and amount of change in the crown surface temperature as the change over time in the crown surface temperature of the piston 21.

[0099] In step S907, if the change over time in the piston crown surface temperature is increasing (YES in step S907), the oil pressure setting unit 42 proceeds to step S908. Then, in step S908, the oil pressure setting unit 42 controls the amount of oil in the oil jet (oil jet flow rate) to be greater than the amount of oil in the previous cycle, thereby lowering the temperature of the piston crown surface.

[0100] On the other hand, if the change over time in the crown surface temperature of the piston 21 is not increasing (is constant or is decreasing) (NO in step S907), the oil pressure setting unit 42 proceeds to step S904. Then, the oil pressure setting unit 42 increases the crown surface temperature of the piston 21 by setting an oil pressure that allows the oil jet to be stopped or by reducing the oil amount (S904). Thereafter, the mode in which the processes of steps S905, S906, S907, S908, and S904 are performed is referred to as the "deposit reduction mode."

[0101] The deposit reduction mode makes it easier to maintain the crown temperature of piston 21 between a first predetermined value (e.g., lower limit temperature 805) and a second predetermined value (e.g., upper limit temperature 806). As a result, the crown temperature of piston 21 is maintained within temperature range 802 where the amount of deposit buildup is small, thereby reducing deposit buildup and suppressing increases in THC and PN.

[0102] When the processing of step S902, S904, S906, or S908 is completed, this processing by the oil pressure setting unit 42 is terminated. As shown in Fig. 12, the oil pressure setting unit 42 can also be said to have a function of selecting one of the "lubrication mode," "warm-up promotion mode," and "deposit suppression mode" based on the piston crown surface temperature correlation index or the measured value of the piston crown surface temperature, and executing the selected mode.

[0103] For example, the oil pressure setting unit 42 may select and execute the "warm-up acceleration mode" within a first temperature range that includes a pre-identified temperature state of the piston crown surface where the deposit accumulation amount on the piston crown surface exceeds a threshold value (threshold value 804), as shown by a solid line 1202 in FIG. 12 (described later). The first temperature range is a temperature range (temperature range 801 in FIG. 4 ) where the piston crown surface temperature is lower than the lower limit (lower limit temperature 805) of the temperature state of the piston crown surface where the deposit accumulation amount is less than the threshold value. When the piston crown surface temperature is within the first temperature range where the deposit accumulation amount exceeds the threshold value, the oil pressure setting unit 42 selects the "warm-up acceleration mode" and executes oil jet injection (S904). This facilitates an increase in the piston crown surface temperature, thereby reducing the time spent in the temperature range 801 where the deposit accumulation amount exceeds the threshold value. As a result, THC and PN can be suppressed.

[0104] The oil pressure setting unit 42 also selects and executes the "deposit reduction mode" when the temperature of the piston crown surface is in a second temperature range (temperature ranges 802 and 803 in FIG. 4 ) higher than the first temperature range, as indicated by a solid line 1202 in FIG. 12 . In the deposit reduction mode under the second temperature range, if the piston crown surface temperature is lower than the upper limit (upper limit temperature 806) of the piston crown surface temperature at which the amount of deposits on the piston crown surface is less than the threshold value (threshold value 804) (NO in S905), the oil pressure setting unit 42 reduces or cuts off the oil jet flow rate (S904). However, if the piston crown surface temperature is lower than the upper limit (upper limit temperature 806) of the piston crown surface temperature at which the amount of deposits on the piston crown surface is less than the threshold value and the change in the piston crown surface temperature over time is increasing (YES in S907), the oil pressure setting unit 42 increases the oil jet flow rate (S908).

[0105] On the other hand, if the temperature of the piston crown surface is higher than the upper limit of the temperature at which the amount of deposit buildup becomes less than the threshold value (threshold value 804) (YES in S905), the oil pressure setting unit 42 executes oil jet injection (S906). This control makes it easier to maintain the temperature of the piston crown surface within the temperature range (between the lower limit temperature 805 and the upper limit temperature 806) at which the amount of deposit buildup becomes small. This makes it possible to suppress deposit buildup on the piston crown surface, thereby reducing THC and PN.

[0106] Here, the control of oil jet injection (flow rate) has been described using the solid line 1202 in FIG. 12 as an example, but similar control is also possible using the dashed line 1201 in FIG.

[0107] As described above, the internal combustion engine control device (internal combustion engine control device 30) according to this embodiment is an internal combustion engine control device that controls an internal combustion engine (internal combustion engine 100) having an oil pump (oil pump 54) that discharges lubricating oil at a specified flow rate and an oil jet system (oil jet system 101) that sprays the lubricating oil discharged from the oil pump toward a supply portion (back surface) of a piston (piston 21). The internal combustion engine control device also includes a control unit (CPU 33 a, oil jet control unit 36) that stops the injection of lubricating oil from the oil jet system or controls the lubricating oil flow rate to be lower than the flow rate in the previous cycle when the temperature of the piston crown surface is below a lower limit temperature (lower limit temperature 805) of a temperature range (temperature range 802) in which the amount of deposits on the piston crown surface is less than a threshold value (threshold value 804) (corresponding to a warm-up acceleration mode).

[0108] According to the internal combustion engine control device of the present embodiment described above, when the temperature of the piston crown surface is below the lower limit temperature of the temperature range in which the amount of deposits on the piston crown surface becomes less than the threshold, control is executed to reduce the injection of lubricating oil from the oil jet or the flow rate. This oil jet control allows the temperature of the piston crown surface to quickly pass through a temperature state in which the amount of deposits on the piston crown surface becomes greater than the threshold and transition to a temperature range in which the amount of deposits becomes small. This suppresses deposit accumulation and reduces emissions of substances subject to exhaust gas regulations. In other words, it is possible to achieve both suppression of deposit accumulation and suppression of emissions of substances subject to exhaust gas regulations.

[0109] The control unit (oil jet control unit 36) is configured to stop the injection of lubricating oil from the oil jet system or to control the flow rate of lubricating oil to be lower than the flow rate in the previous cycle when the temperature of the piston crown surface is higher than the lower limit temperature (lower limit temperature 805) and lower than the upper limit temperature (upper limit temperature 806) of the temperature range (temperature range 802) in which the amount of deposit accumulation on the piston crown surface becomes less than a threshold value (threshold value 804) (corresponding to the deposit suppression mode).

[0110] By controlling the oil jet in the above manner, the temperature of the piston crown surface is maintained within a temperature range in which the amount of deposit buildup is small, thereby suppressing deposit buildup and preventing increases in THC and PN.

[0111] The control unit (oil jet control unit 36) is configured to increase the flow rate of lubricating oil from the flow rate in the previous cycle when the temperature of the piston crown surface is higher than the lower limit temperature (lower limit temperature 805) and lower than the upper limit temperature (upper limit temperature 806) of the temperature range (temperature range 802) in which the amount of deposit accumulation on the piston crown surface is less than a threshold value (threshold value 804) (corresponding to the deposit suppression mode), and when the change in the temperature of the piston crown surface over time tends to increase.

[0112] By controlling the oil jets as described above, the temperature of the piston crown surface is maintained within a temperature range where the amount of deposit buildup is small, thereby suppressing deposit buildup and preventing increases in THC and PN. In particular, when the temperature of the piston crown surface is on an increasing trend over time, the amount of deposit buildup increases (see Figure 8). However, by increasing the flow rate of the lubricating oil injected, the temperature rise on the piston crown surface can be prevented, and the increase in the amount of deposit buildup can be suppressed.

[0113] The control unit (oil jet control unit 36) is configured to inject lubricating oil from the oil jet system when the temperature of the piston crown surface exceeds the upper limit temperature of the temperature range in which the amount of deposit accumulation on the piston crown surface is less than a threshold value (corresponding to the deposit suppression mode).

[0114] The above-described oil jet control quickly reduces the temperature of the piston crown surface, and by keeping the piston crown surface temperature within the temperature range where the amount of deposit buildup is small, deposit buildup is suppressed and an increase in THC and PN is suppressed.

[0115] The control unit (oil jet control unit 36) is configured to determine the lubricity between the piston and the cylinder of the internal combustion engine before comparing the temperature of the piston crown surface with the lower limit temperature (lower limit temperature 805) of the temperature range (temperature range 802) in which the amount of deposit accumulation on the piston crown surface becomes less than a threshold value (threshold value 804), and if it determines that the lubricity is insufficient (corresponding to the lubrication mode), to execute injection of lubricating oil from the oil jet system.

[0116] The oil jet control configured as described above can improve the lubrication between the piston and the cylinder of the internal combustion engine, thereby reducing the deterioration of fuel consumption in situations where the piston lubrication is low.

[0117] The temperature of the piston crown surface is a piston crown surface temperature correlation index correlated with the temperature of the piston crown surface, which is estimated based on operating condition parameters of the internal combustion engine and oil jet parameters for injecting lubricating oil onto the back surface of the piston, or a measurement value of a temperature sensor (temperature sensor 105) that measures the temperature of the piston crown surface.

[0118] Second Embodiment A second embodiment of the present invention is an example in which the controllability of the piston crown surface temperature is enhanced by improving the piston 21 in the internal combustion engine 100 of the first embodiment. The configuration of a control system in the second embodiment of the present invention will be described below with reference to FIGS. 11 and 12 .

[0119] Fig. 11 is a schematic diagram showing an example of the configuration of a piston in this embodiment. Fig. 12 is a diagram showing time-series changes in vehicle speed [km / h], oil jet flow rate ("OJ flow rate" in the figure) [L / min], piston crown surface temperature [°C], and oil temperature [°C] at engine start in this embodiment. In Fig. 12, the oil jet flow rate, piston crown surface temperature, and oil temperature are shown by dashed lines 1201 for the first embodiment and by solid lines 1202 for the second embodiment. Note that in Fig. 12, (1) lubrication mode, (2) accelerated warm-up mode, and (3) deposit suppression mode are assumed to be examples applied to the second embodiment.

[0120] The piston 21A according to the second embodiment differs from the piston 21 according to the first embodiment in that the piston 21A comprises a base material 1101 and a piston crown surface 1102 made of a material having a lower thermal conductivity than the base material 1101 and facing the combustion chamber of the internal combustion engine 100.

[0121] The operation and effect of the piston 21A according to the second embodiment will be described with reference to FIGS. 11 and 12 . By providing the piston crown surface 1102 with a material having a lower thermal conductivity than the base material 1101, heat loss from the combustion chamber to the lubricating oil through the base material 1101 of the piston 21A and the piston rings disposed on the side of the piston 21A can be suppressed. As a result, as shown at time 1203 in FIG. 12 , the rate of temperature rise of the piston crown surface 1102 during engine start-up can be increased compared to the first embodiment. As a result, the time required to reach the lower limit temperature 805 (see FIG. 8 ), at which the amount of deposit accumulation becomes small, can be shortened from time 1204 to time 1205. Because the engine repeatedly stops and starts, the configuration of the piston 21A according to the second embodiment allows the piston crown surface temperature to remain in the temperature range 802 at which the amount of deposit accumulation becomes small, for a longer period compared to the first embodiment, thereby suppressing deposit accumulation. As a result, increases in THC and PN can be suppressed.

[0122] Furthermore, it is preferable to set the thickness 1104 of the piston crown surface 1102, which is provided with a material having a lower thermal conductivity than the base material 1101, to be sufficiently smaller than the thickness 1103 of the base material 1101. Since thermal conductivity is determined by the "heat transfer coefficient" and "heat capacity" of the material, reducing the thickness 1104 of the piston crown surface 1102 makes it easier for the temperature of the piston crown surface 1102 to rise. This increases the time the piston crown surface temperature remains in the temperature range 802 where the amount of deposit buildup is small, thereby suppressing deposit buildup. In order to reduce the thickness of the piston crown surface 1102, the piston crown surface 1102 may be formed by coating the base material 1101.

[0123] In the piston 21A, for example, aluminum is used for the base material 1101 and a ceramic material is used for the piston crown surface 1102, and it is preferable to set the thermal conductivity of the base material 1101 to 135 [W / mK] and the thermal conductivity of the piston crown surface 1102 to 10 [W / mK] or less. In this way, by designing the thermal conductivity of the piston crown surface 1102 to be sufficiently smaller than the thermal conductivity of the base material 1101, the temperature rise rate of the piston crown surface 1102 can be increased, and the effect of suppressing deposit accumulation can be improved.

[0124] Furthermore, by using the configuration and control of the second embodiment, the timing for starting oil jet injection or increasing the amount of oil in the oil jet can be accelerated after the warm-up acceleration mode. By injecting the oil jet onto the underside of the piston 21A, heat is transferred from the piston 21A to the lubricating oil, increasing the rate at which the oil temperature rises. As a result, it is possible to accelerate the time it takes to stop the oil jet or for the oil temperature of the oil jet to reach the warm-up judgment temperature Twj, from time 1206 to time 1207. The warm-up judgment temperature Twj is a temperature threshold for determining whether the internal combustion engine 100 has warmed up to a set temperature. As a result, the fuel injected into the engine cylinder is more likely to vaporize, enhancing the suppression effect of THC and PN.

[0125] <Modification of Second Embodiment> In the control system according to the second embodiment, the oil pressure setting unit 42, which selects one of the “lubrication mode,” “warm-up promotion mode,” and “deposit suppression mode,” may have a function of executing the selected mode by taking into account the thermal conductivity of the piston crown surface to the measured value of the piston crown surface temperature correlation index or the piston crown surface temperature.

[0126] For example, after the oil jet is turned on, a time delay occurs depending on the thermal conductivity (heat transfer rate and heat capacity) of the piston crown surface 1102 until the temperature of the piston crown surface 1102 drops. For this reason, it is advisable to predict the piston crown surface temperature in advance by taking the thermal conductivity into account in the temperature change of the piston 21A, and select one of the "lubrication mode," "warm-up promotion mode," and "deposit suppression mode" depending on the predicted value of the piston crown surface temperature.

[0127] This makes it easier to control the piston crown surface temperature within a predetermined range in this embodiment, thereby enhancing the effect of suppressing THC and PN. That is, the oil jet is switched earlier or later, taking into account the delay in the effect of increasing or decreasing the oil jet. For example, when the thermal conductivity is greater than a predetermined value, the temperature change on the piston crown surface is rapid, so the oil jet is turned on / off or the flow rate is switched later. On the other hand, when the thermal conductivity is equal to or less than the predetermined value, the temperature change on the piston crown surface is gradual, so the oil jet is turned on / off or the flow rate is switched earlier.

[0128] In one example of the control system according to the second embodiment, when the temperature of the piston crown surface 1102 reaches the upper limit temperature 806 at which the amount of deposit buildup becomes small, the oil jet flow rate is increased to cool the piston 21A. However, there is a delay due to the thermal conductivity between the time when the oil jet flow rate is increased (e.g., time 1208) and the time when the temperature of the piston crown surface 21A actually starts to decrease (e.g., time 1209).

[0129] Therefore, the change in piston crown surface temperature over time is stored in the ECU 30. Then, taking into account the time delay due to thermal conductivity, the oil pressure setting unit 42 preferably increases the oil jet flow rate in advance when it is predicted that the piston crown surface temperature after a certain time period, calculated from the change in piston crown surface temperature over time, will exceed the upper limit temperature 806 at which the amount of deposit accumulation becomes small. This shortens the time during which the piston crown surface temperature exceeds the upper limit temperature 806 at which the amount of deposit accumulation becomes small, thereby suppressing deposit accumulation.

[0130] Furthermore, if it is predicted that the piston crown surface temperature will fall below the lower limit temperature 805 at which the amount of deposit buildup becomes small, it is advisable to reduce the oil jet flow rate in advance or stop the oil jet. This makes it possible to shorten the time that the piston crown surface temperature falls below the lower limit temperature 805 at which the amount of deposit buildup becomes small, thereby suppressing the buildup of deposits.

[0131] Here, the control of the oil jet flow rate has been explained using the second embodiment (solid line 1202 in Figure 12) as an example, but similar control is also possible in the first embodiment (dashed line 1201).

[0132] <Third embodiment> A third embodiment of the present invention is an example in which the ignition timing of the mixture in the combustion chamber is controlled based on mode information notified from the oil jet control unit 36. The configuration of the control system in the third embodiment of the present invention will be described below with reference to Figures 13 and 14.

[0133] Fig. 13 is a block diagram showing an example of the configuration of an internal combustion engine control device according to this embodiment. As shown in Fig. 13, an internal combustion engine control device 30A according to this embodiment has a configuration in which an ignition timing control unit 1300 is added to the internal combustion engine control device 30 according to the first embodiment. The CPU 33a executes a control program recorded in the ROM 33b or the like, thereby realizing the function of each processing block.

[0134] The piston crown surface temperature correlation index estimating section 41 and the oil pressure setting section 42 have the same functions as the piston crown surface temperature correlation index estimating section 41 and the oil pressure setting section 42 (FIG. 4) according to the first embodiment.

[0135] The ignition timing control unit 1300 adjusts the timing of sending an ignition signal to the ignition coil 16 based on the mode information (or the state of the piston crown surface temperature) notified by the oil jet control unit 36, and controls the ignition timing of the air-fuel mixture.

[0136] 14 is a control block diagram showing an overview of the control executed by the internal combustion engine control device 30A. When the mode information notified from the hydraulic pressure setting unit 42 is "(2) accelerated warm-up mode," the ignition timing control unit 1300 advances or retards the ignition timing of the air-fuel mixture, which is set based on the load of the internal combustion engine 100, thereby performing control to increase the piston crown temperature. The load information of the internal combustion engine 100 includes, for example, the intake air flow rate and the engine speed.

[0137] If the ignition timing is advanced beyond the timing that optimizes fuel economy, i.e., the optimal ignition timing at which the combustion speed is increased, the in-cylinder pressure increases, causing the in-cylinder temperature to rise and increasing the amount of heat that moves from the inside of the cylinder to the piston crown surface. This increases the piston crown surface temperature and shortens the time it takes for the piston crown surface temperature to reach the lower limit temperature 805. As a result, the effect of reducing THC and PN is enhanced.

[0138] 12 , when the piston crown surface temperature exceeds the upper limit temperature 806, the amount of heat transferred from inside the cylinder to the piston crown surface can be suppressed by retarding the ignition timing from the optimal ignition timing. This shortens the time it takes for the piston crown surface temperature to fall below the upper limit temperature 806, thereby enhancing the deposit suppression effect.

[0139] Furthermore, when the mode information notified from the hydraulic pressure setting unit 42 is "(3) Deposit Reduction Mode," the ignition timing control unit 1300 adjusts the piston crown surface temperature by advancing or retarding the ignition timing of the air-fuel mixture, which is set based on the load of the internal combustion engine 100. Load information on the internal combustion engine 100 includes, for example, the intake air flow rate and engine speed. For example, when a high engine speed is required, the ignition timing is advanced to quickly increase the engine speed. On the other hand, when a high engine speed is not required, the ignition timing is retarded to quickly decrease the engine speed. This makes it easier to change the piston crown surface temperature, and can lengthen the time the piston crown surface temperature remains in a temperature range where deposits are small. This can suppress deposits and enhance the effects of reducing THC and PN.

[0140] As described above, the internal combustion engine control device (internal combustion engine control device 30A) according to this embodiment includes an ignition timing control unit (ignition timing control unit 1300) that advances the ignition timing that is set based on the load of the internal combustion engine when the temperature of the piston crown surface is below the lower limit temperature (lower limit temperature 805) of the temperature range in which the amount of deposits on the piston crown surface becomes less than the threshold value (threshold value 804). For example, the ignition timing is the optimal ignition timing that increases the combustion speed of the air-fuel mixture in the combustion chamber.

[0141] The internal combustion engine control device (internal combustion engine control device 30A) according to this embodiment also includes an ignition timing control unit (ignition timing control unit 1300) that advances or retards the ignition timing, which is set based on the load of the internal combustion engine, when the temperature of the piston crown surface is equal to or higher than a lower limit temperature (lower limit temperature 805) of a temperature range in which the amount of deposits on the piston crown surface becomes smaller than a threshold value (threshold value 804). For example, the ignition timing control unit advances the ignition timing when a target rotation speed of the internal combustion engine is higher than a first rotation speed, and retards the ignition timing when the target rotation speed of the internal combustion engine is lower than a second rotation speed that is lower than the first rotation speed.

[0142] <Fourth embodiment> A fourth embodiment of the present invention is an example in which an oil jet control unit includes a mode selection unit separate from the oil pressure setting unit 42. The configuration of a control system in the fourth embodiment of the present invention will be described below with reference to FIG.

[0143] 15 is a block diagram showing an outline of control of the internal combustion engine control device according to this embodiment. As shown in FIG. 15, the oil jet control unit 36A according to this embodiment includes a piston crown surface temperature correlation index estimating unit 41, a mode selecting unit 1500, and an oil pressure setting unit 42A. The CPU 33a executes a control program recorded in the ROM 33b or the like, thereby realizing the function of each processing block.

[0144] The piston crown surface temperature correlation index estimating unit 41 has the same function as the piston crown surface temperature correlation index estimating unit 41 (FIG. 4) according to the first embodiment. The piston crown surface temperature correlation index estimating unit 41 sends the estimated piston crown surface temperature correlation index to the oil pressure setting unit 42A and the mode selecting unit 1500.

[0145] The mode selection unit 1500 selects one of the "lubrication mode," "warm-up promotion mode," or "deposit reduction mode" based on the piston crown surface temperature correlation index or the measured value of the piston crown surface temperature, and sends the selection result (mode information) to the oil pressure setting unit 42A. Note that, as in the first embodiment, the mode selection unit 1500 may determine that the piston lubricity is low when the combustion operation duration of the internal combustion engine 100 is shorter than a predetermined value, and select the "lubrication mode." Furthermore, when the combustion operation duration is equal to or longer than a predetermined value, the mode selection unit 1500 selects the "warm-up promotion mode" or the "deposit reduction mode" based on the piston crown surface temperature.

[0146] The oil pressure setting unit 42A has functions excluding the mode selection function from the oil pressure setting unit 42 according to the first embodiment. The oil pressure setting unit 42A sets the oil pressure (target oil pressure) when oil jet injection is performed according to the flowchart of Fig. 9 based on the measured value of the piston crown surface temperature correlation index or the piston crown surface temperature and the mode information notified from the mode selection unit 1500.

[0147] <Modification of Fourth Embodiment> Note that, similar to the oil pressure setting unit 42 according to the modification of the second embodiment, the mode selection unit 1500 may have a function of selecting a mode by taking into account the piston crown surface temperature correlation index or the piston crown surface temperature and the thermal conductivity. This makes it easier to control the piston crown surface temperature within a predetermined range, and can enhance the effects of suppressing THC and PN in this embodiment as well.

[0148] <Example of a Vehicle Equipped with a Control System> The control system in each of the above-described embodiments is effective for an internal combustion engine equipped with an engine, but may also be used in a series hybrid vehicle that uses the engine as a generator or a plug-in hybrid electric vehicle (PHEV) that allows the timing of engine operation to be selected. Compared to an internal combustion engine equipped with an engine, a series hybrid or PHEV can secure the power for running the vehicle using an electric motor. Therefore, by combining this with the present invention, the start timing of the internal combustion engine can be set arbitrarily. For example, if the piston crown temperature rises too much and exceeds the upper limit temperature 806, in the case of a series hybrid or PHEV, stopping the engine (idling stop) can suppress deposit accumulation and the increase in THC and PN.

[0149] Furthermore, the present invention is not limited to the above-described embodiments, and various other applications and modifications are possible without departing from the spirit of the present invention as defined in the claims. For example, the above-described embodiments have been described in detail and specifically to clearly explain the present invention, and are not necessarily limited to those including all of the components described. Furthermore, it is possible to replace part of the configuration of one embodiment with a component of another embodiment. It is also possible to add a component of another embodiment to the configuration of one embodiment. It is also possible to add, replace, or delete other components from part of the configuration of each embodiment.

[0150] Furthermore, some or all of the above-described configurations, functions, processing units, etc. may be implemented in hardware, for example, by designing them as integrated circuits, etc. As the hardware, a broad processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used.

[0151] In the above-described embodiment, the control lines and information lines are those that are considered necessary for the explanation, and not all control lines and information lines in the product are necessarily shown. In reality, it can be considered that almost all components are connected to each other.

[0152] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0153] 21, 21A... Piston, 30, 30A... Internal combustion engine control unit (ECU), 36, 36A... Oil jet control unit, 41... Piston crown surface temperature correlation index estimation unit, 42, 42A... Oil pressure setting unit, 54... Oil pump, 101... Oil jet system, 701... Initial value, 702... Increase amount, 801 to 803... Temperature range, 804... Threshold value, 805... Lower limit temperature, 806... Upper limit temperature, 1101... Base material, 1102... Piston crown surface, 1300... Ignition timing control unit

Claims

1. An internal combustion engine control device that controls an internal combustion engine having an oil pump that discharges lubricating oil at a specified flow rate and an oil jet system that injects the lubricating oil discharged from the oil pump toward a portion of a piston that receives the lubricating oil, and that includes a control unit that stops the injection of the lubricating oil from the oil jet system or controls the flow rate of the lubricating oil to be lower than the flow rate in the previous cycle when the temperature of the piston crown surface is below the lower limit temperature of a temperature range in which the amount of deposits accumulated on the piston crown surface is less than a threshold value.

2. An internal combustion engine control device as described in claim 1, wherein the control unit stops the injection of the lubricating oil from the oil jet system or controls the flow rate of the lubricating oil to be lower than the flow rate in the previous cycle when the temperature of the piston crown surface is above the lower limit temperature and below the upper limit temperature of the temperature range in which the amount of deposits accumulated on the piston crown surface becomes less than the threshold value.

3. The internal combustion engine control device according to claim 2, wherein the control unit increases the flow rate of the lubricating oil from the flow rate in the previous cycle when the temperature of the piston crown surface is equal to or higher than the lower limit temperature and equal to or lower than the upper limit temperature of the temperature range in which the amount of deposits on the piston crown surface becomes less than the threshold value and when the temperature of the piston crown surface is showing an increasing trend over time.

4. An internal combustion engine control device as described in claim 3, wherein the control unit executes injection of the lubricating oil from the oil jet system when the temperature of the piston crown surface exceeds an upper limit temperature of a temperature range in which the amount of deposits accumulated on the piston crown surface becomes less than the threshold value.

5. An internal combustion engine control device as described in claim 1, wherein the control unit determines the lubricity between the piston and the cylinder of the internal combustion engine before comparing the temperature of the piston crown surface with the lower limit temperature of the temperature range at which the amount of deposit accumulation on the piston crown surface becomes less than the threshold value, and if it determines that the lubricity is insufficient, it executes injection of the lubricating oil from the oil jet system.

6. An internal combustion engine control device according to claim 1, wherein the piston comprises a base material that forms the supplied portion, and the piston crown surface that faces the combustion chamber of the internal combustion engine and is made of a material that has a lower thermal conductivity than the base material.

7. The internal combustion engine control device according to claim 6, wherein the control unit predicts the temperature of the piston crown surface by taking into account a thermal conductivity of the piston crown surface in relation to a temperature change of the piston crown surface, and controls injection of the lubricating oil from the oil jet system based on the predicted value of the temperature of the piston crown surface.

8. An internal combustion engine control device according to claim 1, wherein the oil pump is a variable displacement pump comprising: a pump housing having a storage section; a rotor disposed within the storage section and connected to the rotary shaft of the internal combustion engine so as to be able to transmit driving force; a cam ring whose eccentricity between the center of rotation of the rotor and its own center changes between a high discharge position and a low discharge position; and a control valve section which changes the eccentricity of the cam ring under the control of the control section.

9. An internal combustion engine control device as set forth in claim 1, further comprising an ignition timing control unit that advances the ignition timing set based on the load of the internal combustion engine when the temperature of the piston crown surface is below the lower limit temperature of a temperature range in which the amount of deposits on the piston crown surface becomes less than a threshold value, wherein the ignition timing is the optimum ignition timing that increases the combustion speed of the air-fuel mixture in the combustion chamber.

10. An internal combustion engine control device according to claim 2, further comprising an ignition timing control unit that advances or retards the ignition timing that is set based on the load of the internal combustion engine when the temperature of the piston crown surface is equal to or higher than the lower limit temperature of a temperature range in which the amount of deposits on the piston crown surface becomes smaller than the threshold value, wherein the ignition timing control unit advances the ignition timing when a target rotation speed of the internal combustion engine is higher than a first rotation speed, and retards the ignition timing when the target rotation speed of the internal combustion engine is lower than a second rotation speed that is smaller than the first rotation speed.

11. The internal combustion engine control device according to claim 1, wherein the threshold value of the deposit accumulation amount is set based on an allowable increase in the amount of emissions of exhaust gas regulated substances from an initial value.

12. The internal combustion engine control device according to claim 1, wherein the temperature of the piston crown surface is a piston crown surface temperature correlation index correlated with the temperature of the piston crown surface, estimated based on operating condition parameters of the internal combustion engine and oil jet parameters for injecting the lubricating oil onto the back surface of the piston, or a value measured by a temperature sensor that measures the temperature of the piston crown surface.

13. A method for controlling an internal combustion engine in an internal combustion engine control device that controls an internal combustion engine having an oil pump that discharges a specified flow rate of lubricating oil and an oil jet system that injects the lubricating oil discharged from the oil pump toward a portion of a piston that is supplied with the lubricating oil, the method comprising: a process for determining whether the temperature of a piston crown surface is below a lower limit temperature of a temperature range in which the amount of deposits accumulated on the piston crown surface becomes less than a threshold value; and a process for stopping the injection of the lubricating oil from the oil jet system or reducing the flow rate of the lubricating oil below that of the previous cycle when the temperature of the piston crown surface is below the lower limit temperature of the temperature range in which the amount of deposits accumulated becomes less than the threshold value.

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