JP2022117654A - internal combustion engine - Google Patents

Abstract

To provide an internal combustion engine that suppresses the lowering of temperature of exhaust when a combustion cycle is changed to a mirror cycle, and that improves fuel consumption.SOLUTION: An internal combustion engine 10 is equipped with a variable valve train 20 that adjusts an opening/closing timing of an intake valve 13, a cooling mechanism 30 that has a water jacket 33 and a cooling water pump 32, and an exhaust emission control device 40 that purifies exhaust discharged through an exhaust valve 14. The variable valve train 20 adjusts the opening/closing timing of the intake valve 13 to change a combustion cycle to a mirror cycle. The internal combustion engine 10 is equipped with a control device 50 that controls the variable valve mechanism 20 and the cooling water pump 32. The control device 50 reduces the discharge amount of the cooling water pump 32 when the combustion cycle is changed to the mirror cycle, thereby reducing a flow rate of cooling water of a water jacket 33.SELECTED DRAWING: Figure 1

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine capable of adjusting the opening/closing timing of intake valves by means of a variable valve mechanism to set the combustion cycle to Miller cycle.

A device has been proposed that adjusts the opening/closing timing of an intake valve to make the combustion cycle a Miller cycle in which the expansion ratio of the cylinder interior gas is greater than the compression ratio (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2020-037905 JP 2020-133591 A

The Miller cycle reduces the amount of intake air introduced into the cylinder by adjusting the opening and closing timing of the intake valve, thereby reducing the compression ratio when compressing the gas inside the cylinder and compressing the gas inside the cylinder. This is a combustion cycle in which the expansion ratio when the cylinder interior gas is burned is relatively large due to the low temperature rise at the time. Thus, by setting the combustion cycle to the Miller cycle, the compression pressure during compression of the cylinder interior gas is reduced, thereby reducing the mechanical load. In addition, heat loss is reduced and the thermal load on the wall of the cylinder is alleviated by lowering the temperature of the gas in the cylinder after combustion. Therefore, fuel consumption can be improved.

However, in an internal combustion engine equipped with an exhaust purification device, the temperature of the exhaust gas decreases as the temperature of the gas in the cylinder decreases by setting the combustion cycle to the Miller cycle. Due to this decrease in the temperature of the exhaust gas, the temperature of the exhaust gas purification device may not reach the desired temperature, and there is a risk that the purification performance of the exhaust gas will deteriorate.

Further, as described above, by setting the combustion cycle to the Miller cycle, the temperature of the cylinder interior gas is reduced, thereby reducing heat loss and improving thermal efficiency. However, there is room for improvement in thermal efficiency when the combustion cycle is the Miller cycle, and further improvement in fuel consumption is required.

An object of the present disclosure is to provide an internal combustion engine that suppresses a decrease in exhaust temperature and improves fuel efficiency when the combustion cycle is set to the Miller cycle.

An internal combustion engine according to one aspect of the present invention that achieves the above object includes a variable valve mechanism that adjusts the opening/closing timing of an intake valve that introduces intake air into a cylinder; a water jacket formed around the cylinder; a cooling mechanism having a cooling water pump that adjusts the flow rate of cooling water flowing through a water jacket; In an internal combustion engine capable of adjusting the opening/closing timing of the intake valve to set the combustion cycle to a Miller cycle in which the expansion ratio of the gas inside the cylinder is greater than the compression ratio, the variable valve mechanism and the A control device for controlling a cooling water pump is provided, and the control device reduces the discharge amount of the cooling water pump and reduces the flow rate of cooling water in the water jacket when the combustion cycle is set to the Miller cycle. It is characterized by being the structure which performs control.

According to one aspect of the present invention, by cooperatively controlling the Miller cycle by the variable valve mechanism and the adjustment of the discharge amount of the cooling water pump, the temperature of the in-cylinder gas when the combustion cycle is the Miller cycle. It becomes advantageous to suppress the decrease, and the temperature of the exhaust gas can be increased. As a result, it is possible to set the temperature of the exhaust gas purifying device to a temperature at which the performance can be exhibited, and prevent deterioration of the exhaust gas purifying performance.

In addition, the reduction in heat transfer from the gas in the cylinder reduces heat loss and improves the thermal efficiency, and the reduction in the discharge amount of the cooling water pump reduces the work of the cooling water pump. As a result, the fuel consumption can be further improved when the combustion cycle is the Miller cycle.

1 is a configuration diagram illustrating an internal combustion engine of an embodiment; FIG. FIG. 2 is a diagram illustrating a correlation between a cam angle and an intake valve lift amount in a reference mode and a mirror cycle mode by the variable valve mechanism of FIG. 1; FIG. 2 is a first control map illustrating the correlation between the rotation speed and the accelerator opening and the fuel injection amount in FIG. 1; FIG. FIG. 2 is a second control map illustrating the correlation between the rotational speed and fuel injection amount in FIG. 1 and the reference discharge amount and reduction amount; FIG. FIG. 2 is a flow diagram illustrating a control flow for adjusting opening/closing timing of an intake valve in a control method for an internal combustion engine according to the embodiment; FIG. 2 is a flow diagram illustrating a control flow for adjusting the discharge amount of a cooling water pump in the method for controlling an internal combustion engine according to the embodiment; FIG. 2 is a flow diagram illustrating a control flow for prohibiting reduction of the discharge amount of a cooling water pump in a control method for an internal combustion engine according to the embodiment;

An embodiment of an internal combustion engine according to the present disclosure will be described below. In FIG. 1, the dashed-dotted line indicates the signal line, the white arrow indicates the flow of gas (intake and exhaust), and the solid arrow indicates the flow of cooling water. In FIG. 1, the arrangement of cooling water and gas flow paths is changed so that the configuration is easy to understand, and does not necessarily correspond to what is actually manufactured. Also, only one cylinder 11 is shown to avoid the complexity of FIG.

As illustrated in FIG. 1 , the internal combustion engine 10 of the embodiment is a diesel engine that uses light oil as fuel, and is an engine that obtains power by reciprocating linear motion of a piston 12 inside a cylinder 11 . The internal combustion engine 10 is a multi-cylinder engine having not only one cylinder but also other cylinders (not shown). The fuel for the internal combustion engine 10 is not limited to light oil, and may be gasoline or liquefied gas. Further, the number of cylinders and cylinder arrangement of the internal combustion engine 10 are not particularly limited. The internal combustion engine 10 includes a variable valve mechanism 20, a cooling mechanism 30, and an exhaust purification device 40. As shown in FIG.

The variable valve mechanism 20 is a mechanism that adjusts the opening and closing timing of the intake valve 13 that introduces intake air into the cylinder 11. It is a cam phase type that advances and retards the phase of rotation of the cam, and a cam that switches between a plurality of cams. A switching type and an actuator type in which the lift amount of the valve itself is varied by an actuator are exemplified.

The variable valve mechanism 20 of this embodiment is of a cam-switching type, and switches the opening/closing timing of the intake valve 13 between the reference mode and the Miller cycle mode. The variable valve mechanism 20 has a first cam that opens and closes the intake valve 13 in the standard mode and a second cam that opens and closes the intake valve 13 in the Miller cycle mode, and switches between these two cams. In addition, the cam switching type has a method of switching the cam in contact with the rocker arm to the first cam or the second cam, and a coupling state of the rocker arm in contact with the first cam and the separate sub-arm in contact with the second cam. A switching method is exemplified.

As illustrated in FIG. 2, in the reference mode, the intake valve 13 begins to open near the top dead center of the piston 12 in the intake stroke of the combustion cycle, and the intake valve 13 closes near the bottom dead center of the piston 12 in the intake stroke. It is the mode to end. In the present disclosure, the vicinity of the top dead center and the vicinity of the bottom dead center are within the range of the period during which the intake charging efficiency is improved. For example, by starting to open the intake valve 13 before the top dead center of the piston 12 and before the exhaust valve 14 closes, the kinetic energy of the exhaust promotes intake. In addition, by closing the intake valve 13 after the piston 12 has passed the bottom dead center, the inertial force of the intake itself promotes intake. Note that the vicinity of the top dead center and the vicinity of the bottom dead center include the top dead center and the bottom dead center.

The Miller cycle mode is a mode in which the opening/closing timing of the intake valve 13 is shifted from that in the reference mode to reduce the amount of intake air introduced into the cylinder 11 . In the present disclosure, the Miller cycle refers to the relative expansion ratio when the cylinder interior gas is combusted because the compression ratio becomes smaller when the cylinder interior gas is compressed and the temperature rise during compression of the cylinder interior gas becomes lower. increases and the expansion ratio of the cylinder interior gas becomes larger than the compression ratio.

In the Miller cycle mode of the present embodiment, the intake valve 13 begins to open after the top dead center of the piston 12 in the intake stroke of the combustion cycle, and after the exhaust valve 14 has finished closing, and the intake valve 13 ends closing in the reference mode. In this mode, the intake valve 13 finishes closing at the retarded timing. In other words, in the Miller cycle mode, the opening/closing timing of the intake valve 13 overlaps with the compression stroke of the combustion cycle, and the gas inside the cylinder 11 is blown back to the intake passage 15 through the intake valve 13 due to the compression stroke.

The opening timing of the intake valve 13 in the Miller cycle mode is not limited to the end of closing of the exhaust valve 14, but may be top dead center. Thus, in the Miller cycle mode, the overlapping period of the intake valve 13 and the exhaust valve 14 is preferably shorter than the overlapping period in the reference mode, and more preferably there is no overlapping period. Overlap in the present disclosure refers to a condition in which both the intake valve 13 and the exhaust valve 14 are open simultaneously.

The timing at which the intake valve 13 in the Miller cycle mode finishes closing is after the bottom dead center of the intake stroke in the combustion cycle and after the end point of the period in which the intake charging efficiency is improved. Further, the closing timing of the intake valve 13 in the Miller cycle mode may be retarded from the middle point from the bottom dead center of the intake stroke to the top dead center of the compression stroke. The closing timing of the intake valve 13 in the Miller cycle mode can be appropriately set after the end point of the period in which the intake charging efficiency is improved after the bottom dead center of the intake stroke. As the closing timing of the intake valve 13 in this Miller cycle mode approaches the bottom dead center, the intake air filling amount increases, and as the timing approaches the top dead center, the intake air filling amount decreases.

The Miller cycle mode is not limited to a configuration in which the closing end timing of the intake valve 13 is retarded from the closing end timing of the reference mode, but can reduce the intake charging efficiency to make the combustion cycle a Miller cycle. Any configuration is acceptable. For example, the closing end timing of the intake valve 13 may be advanced from the closing end timing of the reference mode, or may be set before the bottom dead center of the intake stroke.

As illustrated in FIG. 1, the cooling mechanism 30 includes a cooling circuit 31 through which cooling water circulates. The cooling circuit 31 is a cooling channel in which a cooling water pump 32, a water jacket 33, a thermostat 34, and a radiator 35 are interposed. 36 and a detour 37 that bypasses the cooling passage 36 . In the cooling circuit 31, the cooling water is configured to circulate through the cooling water pump 32, the water jacket 33, the thermostat 34, the cooling path 36 and the detour 37 in this order. The cooling mechanism 30 also includes a cooling fan 38 .

The cooling water pump 32 is a pump that discharges cooling water and circulates the cooling water in the cooling circuit 31 . The cooling water pump 32 may be an electric water pump or a mechanical water pump connected to the crankshaft 16 by a power transmission mechanism capable of adjusting the speed ratio of the rotational power. are exemplified.

The water jacket 33 is a cooling water passage provided around the cylinders 11 , and the passage is formed so as to surround the plurality of cylinders 11 . After passing through the water jacket 33 , the thermostat 34 is arranged at the branch point of the cooling passage 36 and the detour 37 . The radiator 35 is arranged on the front side (left side in FIG. 1) of the vehicle on which the internal combustion engine 10 is mounted, and the cooling fan 38 is arranged on the rear side of the radiator 35 . The radiator 35 is a heat exchanger that uses the vehicle speed wind and the cooling wind from the subsequent cooling fan 38 to cool the cooling water that passes through it. The cooling path 36 is a flow path in which a radiator 35 is provided in the middle thereof and cooling water is cooled by the radiator 35 . A detour 37 is a flow path that bypasses the cooling path 36 so that the cooling water is not cooled by the radiator 35 .

The cooling circuit 31 of this embodiment is of an outlet control type in which a thermostat 34 is arranged in the passage after passing through the water jacket 33 and before passing through the cooling path 36 and the detour 37 in which the radiator 35 is interposed. The outlet control type cooling circuit 31 can improve the air bleeding property and suppress the occurrence of cavitation, so it is advantageous for improving the durability, and is particularly suitable for large vehicles such as trucks. The cooling circuit 31 may be of an inlet control type in which a thermostat 34 is arranged in the flow path after passing through the radiator 35 and before passing through the water jacket 33 instead of the outlet control type. The inlet-controlled cooling circuit is advantageous in adjusting the temperature of the cooling water compared to the outlet-controlled cooling circuit 31 .

The exhaust gas purification device 40 is arranged in the exhaust passage 17 and includes an oxidation catalyst device 41 , a filter device 42 , a reducing agent injection device 43 and a selective reduction catalyst device 44 . The oxidation catalyst device 41 is arranged upstream of the filter device 42 with respect to the flow of exhaust gas and has a catalyst for oxidizing hydrocarbons, carbon monoxide and nitrogen monoxide contained in the exhaust gas. The filter device 42 filters and collects particulate matter contained in the exhaust. The reducing agent injection device 43 is arranged upstream of the selective reduction catalyst device 44 with respect to the flow of exhaust gas, and injects urea water to supply the selective reduction catalyst device 44 with ammonia as a reducing agent. The selective reduction catalyst device 44 has a catalyst that reduces and purifies nitrogen oxides contained in the exhaust gas using ammonia as a reducing agent. Note that the exhaust purification device 40 is arranged upstream of the oxidation catalyst device 41 and is arranged downstream of the exhaust pipe fuel injection device or the selective reduction catalyst device 44 that injects fuel in advance into the exhaust, A reducing agent adsorption catalyst device that adsorbs and removes the reducing agent contained in the exhaust after passing through the selective reduction catalyst device 44 may be provided.

In addition to the above configuration, the internal combustion engine 10 of the present embodiment includes a cooling water temperature acquisition device 51, a rotation speed acquisition device 52, an accelerator opening acquisition device 53, an exhaust temperature acquisition device 54, and a control device 50. Configured. The rotational speed acquisition device 52 and the accelerator opening degree acquisition device 53 function as state parameter acquisition devices, and the cooling water temperature acquisition device 51 and the exhaust temperature acquisition device 54 function as temperature parameter acquisition devices.

The coolant temperature acquisition device 51 is a device that directly acquires the temperature Tw of the coolant after passing through the water jacket 33 and before passing through the thermostat 34 . The cooling water temperature acquisition device 51 can also be configured by a device that indirectly acquires the cooling water temperature Tw, and estimates the cooling water temperature Tw based on the state parameters acquired by the state parameter acquisition device described later. It can be a device.

The state parameter acquisition device is a device that acquires state parameters relating to the operating state of the internal combustion engine 10 . The state parameter may be a combination of the fuel injection amount Qe injected into the cylinder 11 from the fuel injection device 18 per unit time and the rotational speed Ne of the crankshaft 16 of the internal combustion engine 10, or the combination of the fuel injection amount Qe with the rotational speed Ne and A combination of the rotation speed Ne and the accelerator opening Ao is exemplified because it is calculated based on the accelerator opening Ao, which is the depression amount of the accelerator pedal. The state parameter acquisition device of this embodiment is composed of a rotational speed acquisition device 52 and an accelerator opening acquisition device 53 . The rotational speed acquisition device 52 is a device that acquires the rotational speed Ne of the crankshaft 16 of the internal combustion engine 10 . The accelerator opening degree acquiring device 53 is a device for acquiring the accelerator opening degree Ao of the accelerator pedal (not shown). The state parameter acquisition device may be configured to directly detect the state parameter, or may be configured to indirectly calculate the state parameter by detecting a value capable of calculating the state parameter. For example, the rotation speed acquisition device 52 may be a device that directly acquires the rotation speed Ne of the crankshaft 16, or a rotation speed of the crankshaft 16 from the rotation speed of a propeller shaft (not shown) or the rotation speed of the wheels of the vehicle on which the internal combustion engine 10 is mounted. A device that indirectly obtains Ne is exemplified.

The temperature parameter acquisition device is a device that acquires a temperature parameter that can determine whether the operating state of the internal combustion engine 10 is in a low temperature state. Examples of temperature parameters include the cooling water temperature Tw, the oil temperature of the internal combustion engine 10, and the exhaust temperature. The temperature parameter acquisition device of this embodiment is composed of a cooling water temperature acquisition device 51 and an exhaust temperature acquisition device 54 . The exhaust temperature acquisition device 54 is a device that is arranged upstream or downstream of the selective catalytic reduction device 44 or both, and that acquires the temperature of the passing exhaust gas. The temperature parameter acquisition device may be configured to directly detect the temperature parameter, or may be configured to indirectly calculate the temperature parameter by detecting a value that allows the temperature parameter to be calculated. For example, the exhaust temperature acquisition device 54 may be a device that indirectly acquires the exhaust temperature from the fuel injection amount or a sensor that directly acquires the temperature of the selective catalytic reduction device 44 .

The control device 50 is hardware composed of a central processing unit (CPU) that performs various types of information processing, an internal storage device capable of reading and writing programs and information processing results used for performing the various types of information processing, and various interfaces. be. The control device 50 is electrically connected to the variable valve mechanism 20, the cooling water pump 32, and each acquisition device.

The control device 50 has a Miller cycle determination section 55, a valve control section 56, a temperature state determination section 57, a calculation section 58, and a pump control section 59 as functional elements. Each functional element is stored as a program in the internal storage device and executed by the central processing unit at appropriate times. Note that each functional element may be configured by a programmable controller (PLC) or an electric circuit that functions independently of the program.

The Miller cycle determination unit 55 is a functional element that determines whether or not the operating state of the internal combustion engine 10 is in a Miller cycle possible state based on the state parameters acquired by the state parameter acquisition device. Specifically, the Miller cycle determination unit 55 has a first control map M1, and determines whether or not the fuel injection amount Qe based on the rotation speed Ne and the accelerator opening Ao is equal to or less than a preset injection amount threshold Qa. . When it is determined that the fuel injection amount Qe is equal to or less than the injection amount threshold Qa, the Miller cycle determination unit 55 determines that the operating state of the internal combustion engine 10 is in a Miller cycle enabled state, and determines that the fuel injection amount Qe is greater than the injection amount threshold Qa. In this case, it is determined that the operating state of the internal combustion engine 10 is not the Miller cycle enabled state.

The Miller cycle capable state indicates a state in which the fuel injected into the cylinder 11 can be substantially completely combusted when the combustion cycle is set to the Miller cycle. As described above, in the Miller cycle, the filling rate of the cylinder interior gas is low and the amount of oxygen contained in the cylinder interior gas is small. Therefore, when the combustion cycle is the Miller cycle, if the amount of fuel injected into the cylinder 11 is larger than the amount of oxygen contained in the gas in the cylinder, the incomplete combustion of the fuel may deteriorate the exhaust performance, stalls without burning.

As exemplified in FIG. 3, in the first control map M1, correlations between the rotational speed Ne and the accelerator opening Ao and the fuel injection amount Qe are set in advance by experiments, tests, or simulations. The fuel injection amount Qe has a positive correlation with the rotational speed Ne, and increases stepwise as the rotational speed Ne increases. Further, the fuel injection amount Qe has a positive correlation with the accelerator opening Ao, and increases stepwise as the accelerator opening Ao increases.

The injection amount threshold Qa is appropriately set according to the amount of oxygen contained in the cylinder interior gas when the combustion cycle is the Miller cycle. When the combustion cycle is the Miller cycle, the injection amount threshold Qa is set to a larger value as the amount of oxygen contained in the cylinder interior gas increases, and is set to a smaller value as the amount of oxygen decreases. In other words, the injection amount threshold Qa is appropriately set according to the filling amount of the cylinder interior gas defined by the timing at which the intake valve 13 finishes closing. When an exhaust gas recirculation passage that branches off from the exhaust passage 17 and merges with the intake passage 15 is provided, the injection amount threshold Qa should take into account the amount of exhaust gas recirculated.

The valve control unit 56 opens and closes the intake valve 13 in the Miller cycle mode by the variable valve mechanism 20 when the Miller cycle determination unit 55 determines that the operating state of the internal combustion engine 10 is the Miller cycle possible state. is a functional element that opens and closes the intake valve 13 in the reference mode by the variable valve mechanism 20 when it is determined that the operating state of the internal combustion engine 10 is not the Miller cycle possible state.

The temperature state determination unit 57 is a functional element that determines whether the temperature state of the internal combustion engine 10 is a low temperature state based on the temperature parameter acquired by the temperature parameter acquisition device. In the present disclosure, a state in which the temperature of the internal combustion engine 10 is low means a state in which the internal combustion engine 10 is cold-started, or a state in which the catalyst of the selective catalytic reduction device 44 has not reached a temperature at which it is activated.

A cold start indicates a state in which the temperature of each part of the internal combustion engine 10 is equal to or lower than the ambient temperature. Note that the equivalent temperature includes the same temperature, and may be a temperature higher than that temperature within a range that can be regarded as the same temperature. For example, if the temperature difference is less than 10 degrees with respect to the ambient temperature, it is regarded as the same temperature. Examples of the temperature of each part of the internal combustion engine 10 include the temperature of cooling water for cooling the internal combustion engine 10, the temperature of oil in the internal combustion engine 10, and the temperature of the exhaust gas flowing through the exhaust passage 17.

The temperature at which the catalyst is activated is the temperature at which the urea water is injected from the reducing agent injection device 43. The injected urea water hydrolyzes into ammonia, and the selective reduction catalyst device 44 to which the ammonia is supplied produces nitrogen. This is the temperature at which oxide purification begins. Temperatures in the range of 200° C. to 300° C. are exemplified as the temperature at which the catalyst is activated. In other words, the state in which the temperature does not reach the activation temperature of the catalyst is the state in which the purification rate of the selective catalytic reduction device 44 decreases.

A temperature state determination unit 57 determines whether or not the internal combustion engine 10 is in a cold start state based on the cooling water temperature Tw acquired by the cooling water temperature acquisition device 51 . The temperature state determination unit 57 determines that the internal combustion engine 10 is in a cold start state when the coolant temperature Tw is less than the lower limit value Ta of the target coolant temperature range Ta to Tb. In this determination, a device for acquiring the ambient temperature may be used to compare the cooling water temperature Tw with the ambient temperature. Further, in this determination, the oil temperature of the internal combustion engine 10 may be used instead of the cooling water temperature Tw, or a plurality of temperatures including the cooling water temperature Tw and the oil temperature may be used for determination.

The temperature state determination unit 57 determines whether or not the temperature at which the catalyst of the selective catalytic reduction device 44 is activated has reached, based on the temperature Tg of the exhaust gas acquired by the exhaust temperature acquisition device 54 . Note that even if the temperature state determination unit 57 determines that the internal combustion engine 10 is not in the cold start state, if the temperature at which the catalyst of the selective catalytic reduction device 44 is activated has not yet reached, the internal combustion engine 10 It is desirable to determine that the temperature state is the low temperature state.

Further, the temperature state determination unit 57 determines whether the cooling water temperature Tw exceeds the upper limit value Tb of the target cooling water temperature range Ta to Tb when the discharge amount Qw of the cooling water pump 32 reaches the Miller cycle discharge amount Qw2. It is also a functional element that determines whether or not

The calculator 58 is a functional element that calculates the discharge amount Qw of the cooling water pump 32, and is a functional element that calculates the discharge amount based on the state parameter and corrects the discharge amount based on the temperature parameter.

The calculation unit 58 uses the reference discharge amount Qw1 when the combustion cycle is not set to the Miller cycle and the Miller cycle discharge amount Qw2 when the combustion cycle is set to the Miller cycle as state parameters according to the determination result of the Miller cycle determination unit 55. calculated based on Specifically, the calculation unit 58 has a second control map M2, and when the mirror cycle determination unit 55 selects the reference mode, the second control map M2 is referred to to determine the rotation speed Ne and the fuel injection amount Qe. A reference discharge amount Qw1 based on the above is calculated. Further, when the mirror cycle determination unit 55 selects the mirror cycle mode, the calculation unit 58 refers to the second control map M2 to calculate the reference discharge amount Qw1 and the reduction amount ΔQw based on the rotational speed Ne and the fuel injection amount Qe. is calculated, and a discharge amount Qw2 for the mirror cycle is calculated by subtracting the reduction amount ΔQw from the reference discharge amount Qw1.

As exemplified in FIG. 4, the second control map M2 presets correlations between the rotation speed Ne, the fuel injection amount Qe, the reference discharge amount Qw1, and the reduction amount ΔQw through experiments, tests, or simulations. The reference discharge amount Qw1 has a positive correlation with the rotation speed Ne, and increases as the rotation speed Ne increases. Also, the reference discharge amount Qw1 has a positive correlation with the fuel injection amount Qe, and increases as the fuel injection amount Qe increases. The reduction amount ΔQw becomes zero when the fuel injection amount Qe is greater than the injection amount threshold Qa, and becomes a positive value when the fuel injection amount Qe is equal to or less than the injection amount threshold Qa. The reduction amount ΔQw has a positive correlation with the rotational speed Ne within a positive value range, and increases as the rotational speed Ne increases. Further, the reduction amount ΔQw has a positive correlation with the fuel injection amount Qe within a positive value range, and increases as the fuel injection amount Qe increases. It is assumed that the reduction amount ΔQw is a value smaller than the reference discharge amount Qw1, and that the Miller cycle discharge amount Qw2 never becomes zero while the internal combustion engine 10 is running.

The reduction amount ΔQw is such that the fuel cycle becomes the Miller cycle in the operating state of the internal combustion engine 10 based on the state parameters, and the discharge amount Qw of the cooling water pump 32 becomes the Miller cycle discharge amount Qw2, which is lower than the reference discharge amount Qw1. The temperature Tw of the cooling water in this case is set to a value within the target cooling water temperature range Ta to Tb. The reduction amount ΔQw is set to a value such that the cooling water temperature Tw does not exceed the upper limit value Tb of the target cooling water temperature range Ta to Tb when the discharge amount Qw of the cooling water pump 32 becomes the Miller cycle discharge amount Qw2. preferably

The calculation unit 58 prohibits control to decrease when the cooling water temperature Tw when the discharge amount Qw of the cooling water pump 32 reaches the mirror cycle discharge amount Qw2 exceeds the upper limit value Tb of the target cooling water temperature range Ta. do. Specifically, when the temperature state determination unit 57 determines that the cooling water temperature Tw exceeds the upper limit value Tb, the calculation unit 58 corrects the reduction amount ΔQw to zero. When the reduction amount ΔQw becomes zero, the discharge amount Qw of the cooling water pump 32 becomes the reference discharge amount Qw1, and the reduction control is prohibited.

The calculation unit 58 corrects the reduction amount ΔQw when the temperature state determination unit 57 determines that the temperature state of the internal combustion engine 10 is a low temperature state. Specifically, the calculation unit 58 compares the cooling water temperature Tw with the target cooling water temperature range Ta to Tb, and corrects the reduction amount ΔQw so that the cooling water temperature Tw approaches the target cooling water temperature range Ta to Tb. do. For example, when the cooling water temperature Tw when the discharge amount Qw of the cooling water pump 32 reaches the Miller cycle discharge amount Qw2 is lower than the lower limit value Ta of the target cooling water temperature range Ta, the calculation unit 58 calculates the reduction amount Correction is made to increase ΔQw. The calculation unit 58 may use a method of sequentially adding a predetermined correction amount to the reduction amount ΔQw in correcting the reduction amount ΔQw. A control map may be used in which the correlation between the difference ΔTw from either the lower limit value Ta or the upper limit value Tb and the correction amount is set.

The pump control unit 59 is a functional element that adjusts the discharge amount of the cooling water pump 32 based on the discharge amount calculated by the calculation unit 58 . Specifically, the pump control unit 59 adjusts the rotation speed of the cooling water pump 32 to adjust the discharge amount of the cooling water pump 32 to the discharge amount calculated by the calculation unit 58 .

As illustrated in FIGS. 5 to 7, the method of controlling the internal combustion engine 10 is a method that is repeatedly performed at predetermined intervals while the internal combustion engine 10 is running. In the present disclosure, the predetermined cycle is defined as a cycle in which each acquisition device acquires an acquired value. The progress of one cycle in the flow chart is indicated by "return".

FIG. 5 is a control flow for adjusting the opening/closing timing of the intake valve 13. As shown in FIG. The state parameter acquisition device acquires state parameters (S110). In this step S110, the rotation speed acquisition device 52 acquires the rotation speed Ne of the crankshaft 16 and the accelerator opening acquisition device 53 acquires the accelerator opening Ao. Next, the Miller cycle determining unit 55 determines whether or not the operating state of the internal combustion engine 10 is the Miller cycle possible state based on the state parameter (S120). In this step S120, the Miller cycle determination unit 55 refers to the first control map M1 to calculate the fuel injection amount Qe based on the acquired rotation speed Ne and accelerator opening Ao, and the calculated fuel injection amount Qe is injected. It is determined whether or not it is equal to or less than the quantity threshold Qa.

When it is determined that the operating state of the internal combustion engine 10 is the Miller cycle possible state (S120: YES), the valve control unit 56 selects the Miller cycle mode as the opening/closing timing of the intake valve 13 (S130). The Miller cycle mode is a mode in which the intake valve 13 begins to open after the exhaust valve 14 finishes closing, and finishes closing after the bottom dead center and after the end point of the period in which the intake charging efficiency improves. On the other hand, if it is determined that the operating state of the internal combustion engine 10 is not the Miller cycle possible state (S120: NO), the valve control unit 56 selects the reference mode as the opening/closing timing of the intake valve 13 (S140).

Next, the valve control unit 56 instructs the selected mode to the variable valve mechanism 20, the variable valve mechanism 20 adjusts the opening/closing timing of the intake valve 13 according to the instructed mode (S150), and the control flow is started. return.

FIG. 6 is a control flow for adjusting the discharge amount Qw of the cooling water pump 32. As shown in FIG. The temperature parameter acquisition device and the state parameter acquisition device acquire each parameter (S210). In step S210, the coolant temperature acquisition device 51 acquires the coolant temperature Tw, the rotation speed acquisition device 52 acquires the rotation speed Ne of the crankshaft 16, and the accelerator opening acquisition device 53 acquires the accelerator opening Ao. Then, the exhaust temperature acquiring device 54 acquires the exhaust temperature Tg. Next, the calculator 58 determines whether or not the Miller cycle mode has been selected in the control flow of FIG. 5 (S220).

If it is determined that the mirror cycle mode has been selected (S220: YES), the calculator 58 calculates the discharge amount Qw2 for the mirror cycle based on the state parameters (S230). In step S230, the calculation unit 58 refers to the second control map M2 to calculate the reference discharge amount Qw1 and the reduction amount ΔQw based on the rotation speed Ne and the fuel injection amount Qe. is subtracted to calculate the discharge amount Qw2 for the Miller cycle. Next, the temperature state determination unit 57 determines whether the temperature state of the internal combustion engine 10 is a low temperature state based on the acquired temperature parameter (S240). In this step S240, the temperature state determination unit 57 determines whether or not the cooling water temperature Tw is less than the lower limit value Ta, and determines whether or not the exhaust temperature Tg has reached the temperature at which the catalyst is activated. When it is determined that the temperature state of the internal combustion engine 10 is in a low temperature state (S240: YES), the calculator 58 corrects the reduction amount ΔQw (S250). In step S250, the calculator 58 increases the reduction amount ΔQw so that the cooling water temperature Tw falls within the target cooling water temperature range Ta to Tb. On the other hand, if it is determined that the temperature state of the internal combustion engine 10 is not low temperature (S240: NO), the reduction amount ΔQw is not corrected.

On the other hand, if it is determined that the reference mode has been selected instead of the mirror cycle mode (S220: NO), the calculator 58 calculates the reference discharge amount Qw1 based on the state parameters (S260). In this step S240, the calculator 58 refers to the second control map M2 to calculate the reference discharge amount Qw1 based on the rotation speed Ne and the fuel injection amount Qe.

When the discharge amount is calculated in each step, the pump control unit 59 adjusts the rotation speed of the cooling water pump 32 according to the calculated discharge amount (S270), and the control flow returns to the start.

FIG. 7 is a control flow for prohibiting reduction of the discharge amount of the cooling water pump 32 when the combustion cycle is the Miller cycle. The cooling water temperature acquisition device 51 acquires the cooling water temperature Tw (S310). Next, the temperature state determination unit 57 determines whether or not the cooling water temperature Tw exceeds the upper limit value Tb of the target cooling water temperature range Ta to Tb (S320). If it is determined that the cooling water temperature Tw exceeds the upper limit value Tb (S320: YES), the calculator 58 sets the reduction amount ΔQw to zero (S330), and the control flow returns to the start. As a result, reduction of the discharge amount is prohibited in step S270 of FIG. On the other hand, if it is determined that the cooling water temperature Tw is equal to or lower than the upper limit value Tb (S320: YES), the calculation unit 58 does not set the reduction amount ΔQw to zero, and the reduction of the discharge amount is maintained in step S270 of FIG.

As described above, according to the internal combustion engine 10 of the present embodiment, by reducing the discharge amount of the cooling water pump 32 when the combustion cycle is the Miller cycle, the flow rate of the cooling water flowing through the water jacket 33 is reduced. Therefore, the temperature of the wall portion of the cylinder 11 and the water jacket 33 increases, and the heat transfer from the gas inside the cylinder 11 to the wall portion of the cylinder 11 can be reduced. This is advantageous for suppressing a decrease in the temperature of the cylinder interior gas when the combustion cycle is set to the Miller cycle, and the temperature of the exhaust gas can be increased. As a result, it is possible to set the temperature of the exhaust purification device 40 to a temperature at which the performance can be exhibited, and prevent deterioration of the exhaust purification performance.

In addition, the reduction in heat transfer from the cylinder interior gas reduces the heat loss and improves the thermal efficiency, and the reduction in the discharge amount of the cooling water pump 32 reduces the work of the cooling water pump 32 . As a result, the fuel consumption can be further improved when the combustion cycle is the Miller cycle.

By cooperatively controlling the Miller cycle by the variable valve mechanism 20 and the adjustment of the discharge amount of the cooling water pump 32 in this way, a decrease in exhaust temperature when the combustion cycle is the Miller cycle is suppressed. Fuel consumption can be improved.

When the internal combustion engine 10 performs control to reduce the flow rate of cooling water in the water jacket 33 by setting the combustion cycle to the Miller cycle, the cooling water temperature Tw exceeds the upper limit value Tb of the target cooling water temperature range Ta to Tb. Sometimes it is desirable to inhibit control to reduce. As a result, it is possible to avoid physical damage caused by overheating in which the cooling water temperature Tw exceeds the upper limit value Tb.

The internal combustion engine 10 may calculate the reduction amount ΔQw when the combustion cycle is the Miller cycle based on the coolant temperature Tw. In this case, the flow rate of cooling water in the water jacket 33 is adjusted by feedback control. It is preferable that the internal combustion engine 10 calculates the reduction amount ΔQw when the combustion cycle is the Miller cycle, based on the state parameters with reference to the second control map M2. The control using the second control map M2 is feedforward control, which is advantageous for speeding up the response to changes in the flow rate of the cooling water in the water jacket 33 .

When the internal combustion engine 10 is in a low temperature state and the combustion cycle is set to the Miller cycle, it is desirable to increase the reduction amount ΔQw. By further reducing the discharge amount of the cooling water pump 32 when the combustion cycle is set to the Miller cycle in the low temperature state, the flow rate of the cooling water flowing through the water jacket 33 is further reduced. This is advantageous for raising the temperature Tw of the cooling water, and the temperature state of the internal combustion engine 10 can be quickly brought out of the low temperature state to shorten the time required for warming up.

A target cooling water temperature Tc may be used instead of the target cooling water temperature range Ta to Tb. Target cooling water temperature Tc is set within a target cooling water temperature range Ta to Tb. When the target cooling water temperature Tc is used, the reference discharge amount Qw1 is set within a range in which the cooling water temperature Tw is equal to or lower than the target cooling water Tc, and when the temperature Tw exceeds the target cooling water temperature Tc, the cooling water pump 32 is prohibited. Similarly, the reduction amount ΔQw is also set within a range in which the temperature Tw is equal to or higher than the target cooling water temperature Tc.

10 Internal combustion engine 11 Cylinder 13 Intake valve 14 Exhaust valve 20 Variable valve mechanism 30 Cooling mechanism 32 Cooling water pump 33 Water jacket 40 Exhaust purification device 44 Selective reduction catalyst device 50 Control device

Claims (5)

A variable valve mechanism that adjusts the opening and closing timing of an intake valve that introduces intake air into the cylinder, a water jacket formed around the cylinder, and a cooling water pump that adjusts the flow rate of cooling water flowing through the water jacket. and an exhaust purification device for purifying exhaust gas discharged from the cylinder through an exhaust valve, wherein the variable valve mechanism adjusts the opening and closing timing of the intake valve to control the combustion cycle of the cylinder. In an internal combustion engine capable of a Miller cycle in which the expansion ratio of the internal cylinder gas is greater than the compression ratio,
A control device for controlling the variable valve mechanism and the cooling water pump is provided, and the control device reduces the discharge amount of the cooling water pump and cools the water jacket when the combustion cycle is a Miller cycle. An internal combustion engine, characterized in that it is configured to perform control to reduce the flow rate of water. Equipped with a temperature acquisition device that directly or indirectly acquires the temperature of the cooling water,
For the cooling water, the temperature of the cooling water acquired by the temperature acquisition device in the control to decrease is set within a preset target cooling water temperature range or within a range equal to or lower than the target cooling water temperature. The discharge amount of the cooling water pump is reduced below the reference discharge amount of the pump, and the reduction control is prohibited when the temperature of the cooling water exceeds the upper limit value of the target cooling water temperature range or the target cooling water temperature. 2. The internal combustion engine of claim 1, which is a construction. A state parameter acquisition device for acquiring state parameters relating to the operating state of the internal combustion engine,
The control device controls the state parameter acquired by the state parameter acquisition device and the fuel cycle becomes a Miller cycle in an operating state based on the state parameter, and the discharge amount of the cooling water pump is larger than the reference discharge amount. Having a correlation with a reduction amount set to a value at which the cooling water temperature falls within the target cooling water temperature range or is equal to or lower than the target cooling water temperature when the discharge amount for the Miller cycle is reduced;
In the control for reducing, the Miller cycle discharge amount is calculated by subtracting the reduction amount based on the state parameter from the reference discharge amount, and the discharge amount of the cooling water pump is calculated as the Miller cycle discharge amount. 3. An internal combustion engine as claimed in claim 2 in a modulating arrangement. Temperature parameter acquisition for acquiring a temperature parameter capable of determining whether the temperature state of the internal combustion engine is a cold start state or a low temperature state including a state in which the temperature of the exhaust purification device is lower than a preset target device temperature. equipped with a device
When the control device determines that the temperature state of the internal combustion engine is the low temperature state based on the temperature parameter acquired by the temperature parameter acquisition device, the control device increases the reduction amount, and increases the reduction amount by the increased reduction amount. 4. The internal combustion engine according to claim 3, wherein the cooling water pump is configured to reduce the discharge amount. The control device determines whether or not the operating state is a Miller cycle capable state in which the combustion cycle can be changed to the Miller cycle based on the state parameter obtained by the state parameter, and determines whether the operating state is the Miller cycle possible state. 5. The internal combustion engine according to claim 3, wherein when it is determined that the engine is ready, the variable valve mechanism adjusts the opening/closing timing of the intake valve to control the combustion cycle to the Miller cycle.

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