Control device for internal combustion engines

Abstract

To provide a control device for an internal combustion engine capable of suppressing increase in unburned HC and expansion of an air-fuel ratio difference between cylinders, etc. even when variation of cylinder inner wall surface temperatures occurs due to warming-up processing in a cooler.SOLUTION: A control device for an internal combustion engine acquires information on cylinder inner wall surface temperatures that vary according to portions due to warming-up processing, and differentiates injection patterns of fuel injection valves between the plurality of fuel injection valves provided in the same cylinder or cylinders in accordance with the cylinder inner wall surface temperature of a portion supplied with fuel by the fuel injection valve.SELECTED DRAWING: Figure 12

Description

Technical Field

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

Background Art

[0002] In the cooling structure of an internal combustion engine disclosed in Patent Document 1, a movable partition member that can take a closed position for partitioning the block-side water jacket formed annularly so as to surround the cylinder in the circumferential direction and an open position for opening in the circumferential direction is provided between a cooling water inlet and a main cooling water outlet. In the open state where the movable partition member is in the open position, early warm-up is achieved by allowing the cooling water to flow directly to the main cooling water outlet. In the closed state where the movable partition member is in the closed position, the cooling water flows around the movable partition member to effect effective cooling.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when a warm-up process for reducing the circulation amount of cooling water to a part of the water flow path formed around the cylinder is performed by the cooling device in the cold state, in one cylinder and also between cylinders, variations in the cylinder inner wall surface temperature (liner wall surface temperature), that is, differences in temperature depending on the part of the cylinder inner wall surface occur. Then, the amount of vaporization of fuel adhering to the part with a low cylinder inner wall surface temperature decreases, increasing the unburned HC. Also, when the cylinder inner wall surface temperature varies between cylinders, the air-fuel ratio difference between cylinders may widen, possibly deteriorating knocking.

[0005] This invention has been made in view of the conventional situation, and its purpose is to provide a control device for an internal combustion engine that can suppress the increase of unburned HC and the widening of the air-fuel ratio difference between cylinders, even if variations in cylinder wall surface temperature occur due to warm-up treatment by the cooling device. [Means for solving the problem]

[0006] In one embodiment, the control device for an internal combustion engine according to the present invention acquires information on the cylinder wall surface temperature which varies depending on the location due to warm-up, and makes the fuel injection pattern of the fuel injection valves different among multiple fuel injection valves provided in the same cylinder, or between cylinders, according to the cylinder wall surface temperature of the location where fuel is supplied by the fuel injection valves. The system is configured such that an injection pattern is selected in which an index based on the fuel vaporization rate and the homogeneity of the fuel-air mixture reaches a peak value at the cylinder wall temperature in the part where fuel is supplied by the fuel injector. . [Effects of the Invention]

[0007] According to the above invention, even if variations in cylinder wall surface temperature occur due to warm-up treatment in the cooling device, it is possible to suppress the increase of unburned HC and the widening of the air-fuel ratio difference between cylinders. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the configuration of the cooling system for an internal combustion engine. [Figure 2] This is a diagram showing the warm-up process of a cooling system. [Figure 3] This diagram shows the control system for intake and exhaust valves and fuel injection. [Figure 4] This diagram shows the positional relationship between the intake and exhaust valves and the cooling system in the first cylinder. [Figure 5] This is a diagram showing the vaporization rate map. [Figure 6] This is a figure showing a homogeneity map. [Figure 7] This is a diagram showing the HC reduction index map. [Figure 8] This figure shows an example of the placement of water temperature sensors. [Figure 9] This figure shows an example of the placement of water temperature sensors. [Figure 10] This figure shows an example of the placement of water temperature sensors. [Figure 11] It is a diagram illustrating the temperature state immediately after the cold engine starts. [Figure 12] It is a diagram showing the setting process of the injection timing immediately after the cold engine starts. [Figure 13] It is a diagram showing the injection pulse signal immediately after the cold engine starts. [Figure 14] It is a diagram illustrating the temperature state during warm-up. [Figure 15] It is a diagram showing the setting process of the injection timing during warm-up. [Figure 16] It is a diagram showing the injection pulse signal during warm-up. [Figure 17] It is a diagram illustrating the temperature state after warm-up is completed. [Figure 18] It is a diagram showing the setting process of the injection timing after warm-up is completed. [Figure 19] It is a diagram showing the injection pulse signal after warm-up is completed.

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the present invention will be described with reference to the attached drawings. FIG. 1 is a schematic diagram showing the structure of the cooling device 20 of the internal combustion engine 10. The internal combustion engine 10 is a three-cylinder in-line engine in which the first cylinder #1, the second cylinder #2, and the third cylinder #3 are arranged in a straight line in the crankshaft direction. However, the number of cylinders of the internal combustion engine 10 is not limited to three cylinders.

[0010] The cooling device 20 is a water-cooled type that cools the internal combustion engine 10 using cooling water (coolant). And the cooling device 20 includes a block-side water jacket 21 formed in the cylinder block 11, a radiator 22, a water pump 23, a first thermostat 24, a second thermostat 25, and further includes a cooling water pipe connecting these to each other.

[0011] The block-side water jacket 21 is a water passage formed around the cylinder, and is formed to surround the cylinder bores from the first cylinder #1 to the third cylinder #3. The coolant inlet and outlet of the block-side water jacket 21 are positioned opposite each other across the cylinder axis of the first cylinder #1.

[0012] The first thermostat 24 switches, depending on the temperature of the coolant, whether to circulate the coolant after it has cooled the internal combustion engine 10 through the radiator 22 or to circulate it by bypassing the radiator 22. The water pump 23 is a liquid pump driven by the internal combustion engine 10 and is located in the cooling water piping downstream of the first thermostat 24 and radiator 22, and upstream of the block-side water jacket 21. The water pump 23 then pressurizes and pumps the cooling water towards the block-side water jacket 21.

[0013] In this configuration, when the cooling water temperature is below a threshold in a cold state, the cooling water circulates via the water pump 23, the block-side water jacket 21, and the first thermostat 24. Furthermore, in the warmed-up state where the coolant temperature is higher than the threshold, the coolant circulates via the water pump 23, the block-side water jacket 21, and the radiator 22.

[0014] Here, the block-side water jacket 21 is composed of a first system 21A and a second system 21B. The first system 21A is provided along the side of the cylinder bore of the first cylinder #1 that is not adjacent to the second cylinder #2, and is a route that directly connects the coolant inlet and coolant outlet of the block-side water jacket 21, and does not pass through the cylinder bore of the second cylinder #2 or the cylinder bore of the third cylinder #3.

[0015] On the other hand, the second system 21B is separated from the first system 21A and is a route that circles around the cylinder bore of the second cylinder #2 and the cylinder bore of the third cylinder #3. Therefore, when cooling water is circulated through the first system 21A and the second system 21B, the cylinder liners of all three cylinders, from cylinder #1 to cylinder #3, are cooled. In contrast, if coolant is normally circulated to the first system 21A, but the circulation of coolant to the second system 21B is stopped or reduced, the cooling capacity for the second cylinder #2 and the third cylinder #3 will decrease compared to the first cylinder #1.

[0016] The second thermostat 25 is a device that adjusts the amount of coolant circulated to the second system 21B according to the temperature of the coolant. When the temperature of the coolant is below a threshold, it reduces the amount of coolant circulated to the second system 21B compared to when the temperature of the coolant is above the threshold, circulating only the minimum necessary amount of coolant to the second system 21B. The minimum required amount is the amount of circulation that effectively stops the cooling function, and the state in which the minimum required amount of cooling water is circulated can be called a water-stopped state.

[0017] According to the cooling device 20, in a cold state where the coolant temperature is low, the coolant bypasses the radiator 22 and circulates exclusively for the cooling of the first cylinder #1, while the cooling functions of the second cylinder #2 and the third cylinder #3 are hardly performed. Therefore, compared to a cooling system that circulates coolant to all cylinders #1 through #3 in a cold state, this system can accelerate the warming up of the internal combustion engine 10.

[0018] In other words, the cooling device 20 performs a warm-up process that reduces the amount of cooling water circulating to a portion of the water passages formed around the cylinder when the engine is cold. Figure 2 shows the difference in the circulation rate (flow rate) of cooling water in the block-side water jacket 21 when the warm-up process is being performed. It shows that the circulation rate of the second system 21B is reduced compared to the first system 21A, and the temperature of the cooling water in the second system 21B is higher than that of the first system 21A.

[0019] The internal combustion engine 10 equipped with the above-described cooling device 20 is an intake port injection type spark-ignition gasoline engine equipped with a fuel injection valve that injects fuel into the intake port. Figure 3 shows the configuration of the intake and exhaust valves and the arrangement of the fuel injection valves of the internal combustion engine 10, and is a view of one of the three cylinders from above along the cylinder axis. Note that the intake and exhaust valve configuration and fuel injection valve arrangement shown in Figure 3 are common to all three-cylinder engines.

[0020] The internal combustion engine 10 is a four-valve engine equipped with a first intake valve 12A, a second intake valve 12B, a first exhaust valve 13A, and a second exhaust valve 13B per cylinder. A first intake port 14A, which communicates with the combustion chamber via a first intake valve 12A, is provided with a first fuel injection valve 15A.

[0021] Furthermore, a second fuel injection valve 15B is provided in the second intake port 14B, which communicates with the combustion chamber via the second intake valve 12B. Then, the first fuel injector 15A injects fuel into the first intake port 14A, and the second fuel injector 15B injects fuel into the second intake port 14B.

[0022] Figure 4 shows the positional relationship between the intake and exhaust valves and the first system 21A of the block-side water jacket 21 in the first cylinder #1. In the first cylinder #1, a first system 21A is provided on the side where the first intake valve 12A and the first exhaust valve 13A are positioned opposite each other, and a second system 21B is provided on the side where the second intake valve 12B and the second exhaust valve 13B are positioned opposite each other.

[0023] The control device 30 includes a microcomputer 30A as a control unit that outputs the results of calculations based on the acquired information, and controls fuel injection by the fuel injectors 15A and 15B of each cylinder. The microcomputer 30A includes an MPU (Microprocessor Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., which are not shown in the diagram.

[0024] The microcomputer 30A acquires signals output by various sensors that detect the operating state of the internal combustion engine 10, and outputs injection pulse signals to control the fuel injection of the fuel injectors 15A and 15B of each cylinder through calculation processing based on the acquired signals. The various sensors mentioned above include a flow sensor 41 for detecting the intake air flow rate of the internal combustion engine 10, a crank angle sensor 42 for detecting the rotation angle of the crankshaft of the internal combustion engine 10, a water temperature sensor 43 for detecting the temperature of the coolant of the internal combustion engine 10, and an air-fuel ratio sensor 44 for detecting the exhaust air-fuel ratio of the internal combustion engine 10.

[0025] The microcomputer 30A determines the engine rotation speed based on the crankshaft rotation angle detected by the crank angle sensor 42, and determines the basic injection pulse width (basic fuel injection amount) based on the intake air flow rate detected by the flow sensor 41 and the engine rotation speed. Furthermore, the microcomputer 30A applies correction processing to the basic injection pulse width based on the coolant temperature detected by the water temperature sensor 43 and correction processing based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor 44 to determine the final injection pulse width (final fuel injection amount). The microcomputer 30A then outputs an injection pulse signal with the final injection pulse width to the fuel injection valves 15A and 15B of each cylinder at a timing corresponding to the combustion cycle of each cylinder.

[0026] Incidentally, the above-mentioned cooling device 20 performs a warm-up process in a cold state by reducing the amount of cooling water circulating to the second system 21B, thereby reducing the amount of cooling water circulating to a portion of the block-side water jacket 21, which causes variations in the cylinder wall temperature (in other words, the cylinder liner temperature). In other words, the cylinder wall temperature of cylinder #1 is lower than that of cylinders #2 and #3, and the cylinder wall temperature of cylinder #1 on the first system 21A side (the side where the first intake valve 12A and the first exhaust valve 13A are located, see Figure 4) is lower than that of cylinder #1 on the second system 21B side (the side where the second intake valve 12B and the second exhaust valve 13B are located).

[0027] Furthermore, if there are variations in the cylinder wall temperature, the amount of fuel vaporized from the cylinder wall will differ according to the differences in the cylinder wall temperature. Therefore, variations in cylinder wall temperature between cylinders (specifically between cylinder #1, cylinder #2, and cylinder #3) result in variations in the air-fuel ratio between cylinders, leading to an increase in unburned HC and worsening knocking.

[0028] Furthermore, in a cylinder equipped with two fuel injectors 15A and 15B, if there is a variation in the cylinder wall temperature between the side to which the fuel injected by the first fuel injector 15A reaches and the side to which the fuel injected by the second fuel injector 15B reaches, the amount of fuel vaporized from the side with the lower cylinder wall temperature will be lower than the amount of fuel vaporized from the side with the higher cylinder wall temperature, leading to an increase in unburned HC. In this embodiment, during the warm-up process, in the first cylinder #1, the cylinder wall temperature on the side of the first fuel injector 15A becomes lower than the cylinder wall temperature on the side of the second fuel injector 15B, and the amount of vaporization from the fuel injected from the first fuel injector 15A and adhering to the cylinder wall decreases.

[0029] Therefore, in a cold state where the cooling device 20 performs a warm-up process and variations in cylinder wall temperature occur, the microcomputer 30A makes the injection patterns of the fuel injectors 15A and 15B differ between the fuel injectors 15A and 15B, or between cylinders, depending on the cylinder wall temperature at the point where fuel is supplied by the fuel injectors 15A and 15B, which are located in the same cylinder (first cylinder #1). In other words, the microcomputer 30A suppresses the increase in unburned HC due to variations in cylinder wall temperature by switching the injection patterns of the fuel injectors 15A and 15B according to the variations in cylinder wall temperature. The injection pattern refers to at least one of the following: fuel injection timing, fuel injection volume distribution ratio, and the number of divisions in a split injection.

[0030] The following section will describe in detail how the microcomputer 30A controls the injection pattern according to the cylinder wall temperature. The microcomputer 30A acquires information on the cylinder wall temperature at the point where fuel is supplied by the fuel injectors 15A and 15B, and selects an injection pattern in which the HC reduction index reaches its peak value (maximum value) at the acquired cylinder wall temperature, that is, an injection pattern that minimizes unburned HC.

[0031] The HC reduction index is determined from the vaporization rate and homogeneity, and the microcomputer 30A suppresses the increase in unburned HC even if the cylinder wall temperature varies by selecting an injection pattern that maximizes the vaporization rate and homogeneity in an optimal balance. In this embodiment, "vaporization rate" and "homogeneity" are defined as follows.

[0032] In this embodiment, the "vaporization rate" is defined as follows: when FS is the amount of fuel injected from the fuel injectors 15A and 15B during one cycle of the internal combustion engine 10, and FV is the amount of vaporized fuel present in the cylinder at compression TDC out of the total fuel amount FS, the vaporization rate [%] = 100 × FV / FA. Furthermore, in this embodiment, the "homogeny" is defined as follows: VM is the volume of the air-fuel mixture present in the cylinder at compression TDC, and VC is the volume of the combustible air-fuel mixture present in the cylinder at compression TDC, specifically the volume of the air-fuel mixture with an air-fuel ratio of 12 to 16, where homogeneity [%] = 100 × VC / VM.

[0033] Unburned HC is generated based on the above-mentioned "vaporization rate" and "homogeneity," and unburned HC is reduced by improving the "vaporization rate" through a reduction in the amount of fuel adhering to the inner wall of the cylinder. Furthermore, the reduction of localized rich mixtures within the cylinder improves "homogeneity," thereby reducing unburned HC.

[0034] Therefore, the microcomputer 30A is configured to select an injection pattern that can reduce unburned HC as much as possible given the conditions of the cylinder wall temperature, by taking into account an injection pattern that uses "vaporization rate" as an indicator and an injection pattern that uses "homogeneity" as an indicator. In detail, the microcomputer 30A is configured to select an injection pattern in which the HC reduction index, determined by weighting "vaporization rate" and "homogeneity," reaches a peak value for the given conditions of the cylinder wall temperature.

[0035] Figures 5-7 illustrate the characteristics of control that selects an injection pattern based on an HC reduction index, and show the case where the injection timing (specifically, the injection termination timing) as part of the injection pattern is switched according to the cylinder wall temperature. Figure 5 is a map that stores vaporization rate [%] data for each combination of injection termination timing and water temperature. Figure 6 is a map that stores homogeneity [%] data for each combination of injection termination timing and water temperature. Figure 7 is a map that stores the HC reduction index [%] for each combination of injection termination timing and water temperature.

[0036] During the development and design phase to define the control specifications for the microcomputer 30A, the vaporization rate for each combination of injection termination timing and water temperature (representing the cylinder wall temperature) is determined through experiments and simulations, and these relationships are mapped as shown in Figure 5. Similarly, during the development and design phases in which control specifications are defined, the degree of homogeneity for each combination of injection termination timing and water temperature (representing the cylinder wall temperature) is determined through experiments and simulations, and these relationships are mapped as shown in Figure 6.

[0037] Furthermore, if the target internal combustion engine 10 is equipped with a variable valve timing device (VTC) that varies the valve timing of the intake valves 12A and 12B, the valve overlap changes depending on the valve timing of the intake valves 12A and 12B, which in turn changes the amount of blowback to the intake ports 14A and 14B when the intake valves 12A and 12B are open. Furthermore, the amount of air blown back into intake ports 14A and 14B changes, which alters the vaporization rate and homogeneity. Therefore, if the internal combustion engine 10 is equipped with a variable valve timing device (VTC), a vaporization rate map and a homogeneity map are defined for each valve timing (in other words, for each conversion angle of the variable valve timing device VTC).

[0038] Once the vaporization rate map and homogeneity map are obtained, an HC reduction index is calculated for each combination of injection termination timing and water temperature by weighting the vaporization rate and homogeneity, and a map (see Figure 7) is created to store the HC reduction index for each combination of injection termination timing and water temperature. In other words, the HC reduction index [%] value stored in each grid cell of the HC reduction index map is obtained by weighting the vaporization rate [%] stored in the same grid cell of the vaporization rate map and the homogeneity [%] stored in the same grid cell of the homogeneity map. The microcomputer 30A then sets the injection termination timing at which the HC reduction index is greatest relative to the detected cylinder wall temperature (water temperature) as the set value for the injection control of the fuel injectors 15A and 15B, based on the characteristics of the HC reduction index in the HC reduction index map, and varies the injection termination timing according to the difference in cylinder wall temperature (water temperature).

[0039] Here, the HC reduction index is calculated using the following formula, with contribution C1 being the degree to which the vaporization rate contributes to the reduction of unburned HC, and contribution C2 being the degree to which homogeneity contributes to the reduction of unburned HC. HC reduction index = vaporization rate × C1 + homogeneity × C2

[0040] The contributions C1 and C2 are C1 + C2 = 1.0, and are values ​​that are adapted based on measurement results of unburned HC in actual equipment. Furthermore, to reduce unburned HC, it is more effective to calculate the HC index by giving greater weight to homogeneity (contribution C2) than to vaporization rate (contribution C1). For example, C1 = 0.3 and C2 = 0.7.

[0041] When the cooling system 20 performs a warm-up process and the cylinder wall temperature at the point where the fuel injected by the fuel injectors 15A and 15B adheres varies between cylinders or within the same cylinder, the microcomputer 30A sets individual injection termination timings according to the differences in cylinder wall temperature. Here, the microcomputer 30A detects variations in the cylinder wall temperature by acquiring information on the water temperature TW1 in the first system 21A and the water temperature TW2 in the second system 21B.

[0042] More specifically, the microcomputer 30A, for the first fuel injector 15A (see Figure 4) located on the first system 21A side in the first cylinder #1, sets the water temperature TW1 in the first system 21A to the cylinder wall surface temperature at the point where the fuel injected by the first fuel injector 15A adheres. Furthermore, the microcomputer 30A determines that for the second fuel injector 15B located on the second system 21B side in the first cylinder #1, the water temperature TW2 in the second system 21B is the cylinder wall surface temperature at the point where the fuel injected by the second fuel injector 15B adheres. Furthermore, for the second cylinder #2 and the third cylinder #3, the microcomputer 30A represents both the cylinder wall temperature at the point where fuel injected by the first fuel injector 15A adheres and the cylinder wall temperature at the point where fuel injected by the second fuel injector 15B adheres, using the water temperature TW2 in the second system 21B.

[0043] Here, we will explain how to determine the water temperature TW1 in the first system 21A and the water temperature TW2 in the second system 21B. Figure 8 shows a configuration in which the water temperature sensor 43 includes a first water temperature sensor 43A that detects the water temperature TW3 in the water passage after the first system 21A and the second system 21B merge, and a second water temperature sensor 43B that detects the water temperature TW1 in the first system 21A. In this configuration, the microcomputer 30A estimates the water temperature TW2 in the second system 21B from the water temperature TW3 after the confluence and the water temperature TW1 in the first system 21A.

[0044] Figure 9 shows a configuration in which the water temperature sensor 43 includes a first water temperature sensor 43A that detects the water temperature TW3 in the water flow passage after the first system 21A and the second system 21B merge, and a third water temperature sensor 43C that detects the water temperature TW2 in the second system 21B. In this configuration, the microcomputer 30A estimates the water temperature TW1 in the first system 21A from the water temperature TW3 after the confluence and the water temperature TW2 in the second system 21B.

[0045] Figure 10 shows a configuration in which the water temperature sensor 43 includes a first water temperature sensor 43A that detects the water temperature TW3 in the water passage after the first system 21A and the second system 21B merge, a second water temperature sensor 43B that detects the water temperature TW1 in the first system 21A, and a third water temperature sensor 43C that detects the water temperature TW2 in the second system 21B. In this case, since the water temperature TW1 in the first system 21A and the water temperature TW2 in the second system 21B are directly detected by sensors, the control accuracy is higher compared to when water temperature is estimated, but the number of water temperature sensors 43 increases. In contrast, the configuration shown in Figure 8 or Figure 9 allows for a reduction in the number of water temperature sensors 43 while simultaneously enabling control of the injection pattern in response to variations in the cylinder wall temperature.

[0046] Next, we will explain in more detail the differences in injection termination timing due to variations in the temperature of the cylinder wall surface. Figures 11-19 illustrate the differences in injection termination timing due to variations in cylinder wall temperature in the first cylinder #1, at each stage of warm-up. Figures 11-13 show the state immediately after cold start, Figures 14-16 show the state after some warm-up has progressed, and Figures 17-19 show the state after warm-up is complete.

[0047] Figure 11 illustrates the variation in cylinder wall temperature immediately after cold start-up when the amount of coolant circulation in the second system 21B is suppressed (when the water flow in the second system 21B is stopped), showing a state where the water temperature of the first system 21A, which is on the side of the first fuel injection valve 15A, is 20°C, and the water temperature of the second system 21B, which is on the side of the second fuel injection valve 15B, is 40°C. Figure 12 shows how the injection termination timings for the first fuel injector 15A and the second fuel injector 15B are retrieved from the HC reduction index map under the water temperature (cylinder wall temperature) conditions shown in Figure 11. Figure 12 shows the process of searching for the injection termination timing from the HC reduction index map when the conversion angle of the variable valve timing device (VTC) is 0 degrees. The same applies to Figures 15 and 18, which will be explained later.

[0048] The water temperature of the first system 21A, which is on the side of the first fuel injector 15A, is 20°C. The temperature of the cylinder wall surface to which the fuel injected from the first fuel injector 15A adheres is also around 20°C. Therefore, the injection termination timing at which the HC reduction index reaches its peak value in the 20°C row of the HC reduction index map is set as the injection termination timing of the first fuel injector 15A. In the example shown in Figure 12, in the 20°C row of the HC reduction index map, the injection termination timing at which the HC reduction index is highest (in other words, the degree of reduction of unburned HC is highest) is 90 degrees before intake top dead center (-90 degrees ATDC), where the HC reduction index is 72. Therefore, the injection termination timing of the first fuel injector 15A is set to 90 degrees before intake top dead center.

[0049] On the other hand, the water temperature of the second system 21B, which is on the side of the second fuel injector 15B, is 40°C, and the temperature of the cylinder wall surface to which the fuel injected from the second fuel injector 15B adheres is approximately 40°C, so refer to the 40°C row on the HC reduction index map. Here, in the 40°C row of the HC reduction index map, the highest value for the HC reduction index is 75, and the injection termination timings at which the HC reduction index reaches 75 are 30 degrees before intake top dead center (-30 degrees ATDC) and intake top dead center (0 degrees ATDC).

[0050] However, when calculating the HC reduction index from the vaporization rate and homogeneity, homogeneity takes precedence, and the homogeneity map (see Figure 6) shows that when the water temperature is 40°C, homogeneity tends to increase as the injection termination timing is delayed. Therefore, the injection termination timing for the second fuel injector 15B is set to the intake top dead center, which is a later timing than the injection termination timing 30 degrees before intake top dead center, where the HC reduction index shows the maximum value, and where the homogeneity is likely to be slightly higher. Furthermore, if the water temperature grid in the HC reduction index map is set in 20°C increments, for example, 0°C, 20°C, and 40°C, and the actual water temperature is an intermediate value such as 25°C or 30°C, the injection termination timing that matches the intermediate water temperature can be determined through interpolation.

[0051] Figure 13 shows the output timing of the injection pulse signals of each fuel injector 15A and 15B of cylinder #1 when the water temperature of the first system 21A, which is on the side of the first fuel injector 15A, is 20°C and the water temperature of the second system 21B, which is on the side of the second fuel injector 15B, is 40°C. As mentioned above, the injection termination timing of the first fuel injector 15A is set to 90 degrees before intake top dead center. Therefore, an injection pulse signal is output to the first fuel injector 15A so that fuel injection from the first fuel injector 15A starts at a timing equal to the injection pulse width 90 degrees before intake top dead center. On the other hand, since the injection termination timing of the second fuel injector 15B is set to intake top dead center, an injection pulse signal is output to the second fuel injector 15B so that fuel injection from the second fuel injector 15B starts at a timing equal to the injection pulse width from intake top dead center.

[0052] In other words, in the first cylinder #1, the injection timing of the fuel injector (first fuel injector 15A), where the cylinder wall temperature at the fuel supply point is relatively low, is set to be earlier than the injection timing of the fuel injector (second fuel injector 15B), where the cylinder wall temperature at the fuel supply point is relatively high. By setting the injection timing in this manner, the vaporization period of the fuel injected from the first fuel injection valve 15A, which injects fuel to the side with the lower cylinder wall temperature, can be extended, thereby reducing unburned HC. In the example shown in Figure 13, the fuel injection volume sharing ratio between the first fuel injector 15A and the second fuel injector 15B is 50:50, and the pulse width of the injection pulse signal supplied to the first fuel injector 15A is the same as the pulse width of the injection pulse signal supplied to the second fuel injector 15B.

[0053] On the other hand, the injection termination timing for the fuel injectors 15A and 15B of the second cylinder #2 and third cylinder #3 is uniformly set to 90 degrees before intake top dead center, based on the water temperature of the second system 21B, which is 40°C. In other words, during the warm-up process, the microcomputer 30A controls the injection timing (injection pattern) to differ between multiple fuel injectors in the same cylinder, or between cylinders, in accordance with variations in the cylinder wall temperature.

[0054] Figure 14 illustrates the variation in cylinder wall temperature in cylinder #1 of the first cylinder when the engine has warmed up more than in Figure 11, showing a state where the water temperature of the first system 21A is 40°C and the water temperature of the second system 21B is 80°C. Furthermore, the water temperature of the second system 21B, which is 80°C, is within the appropriate range after warm-up is complete and is roughly equivalent to the water temperature at which warm-up is complete.

[0055] Figure 15 shows how the injection termination timing is determined from the HC reduction index map according to the water temperature conditions described above. The water temperature of the second system 21B is 80°C, and the HC reduction index reaches its maximum value at a water temperature of 80°C when the injection termination timing is 30 degrees after intake top dead center (30 degrees ATDC). Therefore, the injection termination timing of the second fuel injector 15B of the first cylinder #1 is set to 30 degrees after intake top dead center.

[0056] Furthermore, the injection termination timing for the fuel injectors 15A and 15B of the second cylinder #2 and third cylinder #3 is uniformly set to 30 degrees after intake top dead center, based on the water temperature of the second system 21B, which is 80°C. On the other hand, the water temperature of the first system 21B is 40°C, and the HC reduction index reaches its maximum value at a water temperature of 40°C when the injection termination timing is 30 degrees before intake top dead center (-30 degrees ATDC) and when it is at intake top dead center (0 degrees ATDC). As mentioned above, when the water temperature is 40°C, homogeneity tends to be higher with later injection termination timings. Therefore, here, the intake top dead center, which is the later of the two injection termination timings, is set as the injection termination timing for the first fuel injector 15A of the first cylinder #1.

[0057] Figure 16 shows the injection pulse signals of the fuel injectors 15A and 15B of cylinder #1 when the water temperature of the first system 21A is 40°C and the water temperature of the second system 21B is 80°C. As mentioned above, the injection termination timing of the first fuel injector 15A is set to intake top dead center. Therefore, an injection pulse signal is output to the first fuel injector 15A so that fuel injection from the first fuel injector 15A begins at a timing equal to the injection pulse width before intake top dead center. On the other hand, since the injection termination timing of the second fuel injector 15B is set to 30 degrees after intake top dead center, an injection pulse signal is output to the second fuel injector 15B so that fuel injection from the second fuel injector 15B starts at a timing equal to the injection pulse width from 30 degrees after intake top dead center.

[0058] In other words, as the engine warms up from a cold start state, the injection termination timing in cylinder #1 is retarded by both the first fuel injector 15A and the second fuel injector 15B compared to the initial timing at the start of warm-up (see Figure 13). However, the temperature conditions in Figures 14-16 still show a difference between the cylinder wall temperature on the first fuel injector 15A side and the cylinder wall temperature on the second fuel injector 15B side, with the first fuel injector 15A side being at a lower temperature. Therefore, in order to ensure a vaporization period for the fuel injected from the first fuel injector 15A, the injection termination timing of the first fuel injector 15A is set to be earlier than the injection termination timing of the first fuel injector 15A.

[0059] Figure 17 illustrates the cylinder wall temperature in cylinder #1 of the internal combustion engine 10 when it has almost completed warming up. The water temperature of both the first system 21A and the second system 21B are 80°C, and the variation in cylinder wall temperature in cylinder #1 has been eliminated. Figure 18 shows how the injection termination timing is retrieved from the HC reduction index map according to the water temperature conditions described above.

[0060] The water temperature of both the first system 21A and the second system 21B is 80°C. The HC reduction index on the HC reduction index map reaches its maximum value at a water temperature of 80°C when the injection termination timing is 30 degrees after intake top dead center (30 degrees ATDC). Therefore, the injection termination timing for each fuel injector 15A and 15B of cylinder #1 is set to 30 degrees after intake top dead center. Furthermore, the fuel injection termination timing for the second cylinder #2 and third cylinder #3 fuel injection valves 15A and 15B is set to 30 degrees after top dead center, thus unifying the injection termination timing to 30 degrees after top dead center for all fuel injection valves 15A and 15B.

[0061] Figure 19 shows the injection pulse signals of the fuel injectors 15A and 15B of cylinder #1 when the water temperature of the first system 21A is 80°C and the water temperature of the second system 21B is 80°C. Upon completion of warm-up, the water temperature of both the first system 21A and the second system 21B reaches 80°C, eliminating variations in the cylinder wall temperature in the first cylinder #1. As a result, the injection termination timing of each fuel injector 15A and 15B in the first cylinder #1 is uniformly set to 30 degrees after intake top dead center, and the same injection pulse signal is supplied to each fuel injector 15A and 15B at the same timing. In addition, injection pulse signals are supplied to the fuel injectors 15A and 15B of the second cylinder #2 and the third cylinder #3, respectively, at the same timing as shown in Figure 19.

[0062] In the above embodiment, the injection timing as an injection pattern is varied among multiple fuel injectors provided in the same cylinder, or between cylinders, according to variations in the cylinder wall surface temperature. However, the injection pattern is not limited to injection timing, and the fuel injection amount distribution ratio or the number of divisions in the divided injection can be varied. Furthermore, several of the injection timing, fuel injection volume distribution ratio, and number of divisions in split injection can be varied among multiple fuel injection valves installed in the same cylinder, or between cylinders, according to variations in cylinder wall temperature.

[0063] The following outlines injection control when the fuel injection volume distribution ratio is varied among multiple fuel injection valves installed in the same cylinder, according to variations in cylinder wall temperature. When the cylinder wall temperature is low, the amount of fuel adhering to the wall that vaporizes decreases, resulting in an increase in unburned HC. Therefore, the fuel injection ratio is set to reduce the amount of fuel injected by the fuel injector that injects to the side with the lower cylinder wall temperature (the first fuel injector 15A of cylinder #1), and relatively increase the amount of fuel injected by the fuel injector that injects to the side with the higher cylinder wall temperature (the second fuel injector 15B of cylinder #1), by switching the fuel injection ratio.

[0064] Then, once the engine has warmed up and the variation in cylinder wall temperature has been eliminated, the fuel injection ratio between the two fuel injectors is restored to 50:50. Here, the vaporization rate and homogeneity are determined for each combination of the distribution ratio and water temperature. An HC reduction index is then set for each combination of the distribution ratio and water temperature to create an HC reduction index map, and the system can be configured to select the distribution ratio that yields the highest HC reduction index under the water temperature conditions during control.

[0065] Furthermore, by using split injection, which divides the fuel injection amount per cycle into multiple injections, the amount of fuel adhering to the inner wall of the cylinder can be reduced, and the fuel inside the cylinder can be made more homogenized. Therefore, the lower the temperature of the cylinder wall surface to which the fuel injected from the fuel injector adheres, the more times the injection is divided, making it possible to vary the number of divisions between multiple fuel injectors in the same cylinder, or between cylinders.

[0066] The number of divisions, which is set according to the cylinder wall temperature, is a natural number. A division of 1 indicates that the fuel injection amount per cycle is injected in one go without being divided. Here too, the vaporization rate and homogeneity are determined for each combination of the number of divisions and water temperature. An HC reduction index is then set for each combination of the distribution ratio and water temperature to create an HC reduction index map, and the system can be configured to select the number of divisions that yields the highest HC reduction index under the water temperature conditions during control.

[0067] The technical concepts described in the above embodiments can be used in appropriate combinations, as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it will be obvious to those skilled in the art that various modifications can be taken based on the basic technical concept and teachings of the present invention.

[0068] For example, in the internal combustion engine 10 shown in Figures 1 and 3, the cylinder wall temperature of the first cylinder #1 is represented by the water temperature of the first system 21A, and the injection patterns of the first fuel injector 15A and the second fuel injector 15B of the first cylinder #1 are set to the same injection pattern corresponding to the water temperature of the first system 21A, while the injection patterns of the second cylinder #2 and the third cylinder #3 are set according to the water temperature of the second system 21B, thereby making the injection patterns different between cylinders.

[0069] Furthermore, although the internal combustion engine 10 shown in Figure 3 has two intake ports and two fuel injection valves per cylinder, it can be a port injection engine with one intake port and one fuel injection valve per cylinder. Furthermore, in the case of a port injection engine equipped with one fuel injection valve per cylinder, the injection pattern can be varied between cylinders in accordance with the variation in cylinder wall surface temperature between cylinders.

[0070] Furthermore, the number of cylinders in the internal combustion engine is not limited to three; it may also be a two-cylinder engine or an internal combustion engine with four or more cylinders. In internal combustion engines with three or more cylinders, the number of cylinders through which water flows continuously (in other words, through which water flows both when the engine is cold and after it has warmed up) can be two or more.

[0071] Furthermore, instead of using the cooling water temperature to represent the cylinder wall temperature, a wall temperature sensor (cylinder liner temperature sensor) that directly detects the cylinder wall temperature can be provided, and the injection pattern can be varied according to the detection result of the wall temperature sensor. Furthermore, instead of varying the injection termination timing as part of the injection pattern, the injection start timing can be varied according to the variation in the cylinder wall temperature.

[0072] Furthermore, the structure in the cooling device 20 that reduces the amount of cooling water circulating to a portion of the water passages formed around the cylinder when the engine is cold is not limited to that shown in Figure 1. For example, in a cooling system in which only one block-side water jacket is provided, the cooling system may have a structure that changes the amount of cooling water circulated to a portion of the system by switching the position of the partition plate according to the cooling water temperature. Furthermore, instead of the thermostats 24 and 25 of the cooling device 20, a valve device driven by an actuator can be provided, and the microcomputer 30A can be configured to electronically control the valve device based on water temperature information. [Explanation of symbols]

[0073] 10...Internal combustion engine, 11...Cylinder block, 12A...First intake valve, 12B...Second intake valve, 14A...First intake port, 14B...Second intake port, 15A...First fuel injector, 15B...Second fuel injector, 20...Cooling system, 21...Block-side water jacket (water flow passage), 21A...First system, 21B...Second system, 22...Radiator, 23...Water pump, 24...First thermostat, 25...Second thermostat, 30...Control unit, 30A...Microcomputer

Claims

1. A control device for an internal combustion engine, The aforementioned internal combustion engine is A fuel injector that injects fuel into the intake port, A cooling device that performs a warm-up process to reduce the amount of cooling water circulating to a portion of the water passages formed around the cylinder while the engine is cold, Equipped with, The control device is The warm-up process described above provides information on the cylinder wall surface temperature, which varies depending on the location. The fuel injection pattern of the fuel injection valve is configured to differ between multiple fuel injection valves in the same cylinder, or between cylinders, depending on the cylinder wall temperature at the point where fuel is supplied by the fuel injection valve. The injection pattern is selected such that an index based on the fuel vaporization rate and the homogeneity of the mixture reaches a peak value at the cylinder wall temperature in the part where fuel is supplied by the fuel injector. Control device for internal combustion engines.

2. A control device for an internal combustion engine according to claim 1, The injection pattern is at least one of the following: injection timing, fuel injection amount distribution ratio, and number of divisions in the divided injection. Control device for internal combustion engines.

3. A control device for an internal combustion engine according to claim 1, The injection timing of the fuel injector in which the cylinder wall temperature in the fuel supply area is relatively low is set earlier than the injection timing of the fuel injector in which the cylinder wall temperature in the fuel supply area is relatively high. Control device for internal combustion engines.

4. A control device for an internal combustion engine according to claim 1, The aforementioned index is determined by giving greater weight to the homogeneity than to the vaporization rate. Control device for internal combustion engines.

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