Fuel injection control device for diesel engines

Abstract

To provide a fuel injection control device for a diesel engine capable of shortening a combustion period.SOLUTION: A fuel injection control device 1 for a diesel engine includes: the diesel engine 2; and a fuel injection control part 3 causing a fuel injection valve 11 of the diesel engine 2 to execute fuel injection. The fuel injection control part 3 causes the fuel injection valve 11 to execute main injection M and a plurality of times of after-injection A after the main injection M as injection. In the fuel injection control part 3, an injection amount of each of the plurality of times of after-injection A is set smaller than that of the previous injection.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel injection control device for a diesel engine. [Background technology]

[0002] Patent Document 1 describes a control device for a diesel engine. In order to suppress the generation of soot, this control device for a diesel engine executes a main injection in which fuel is injected, and an after-injection in which a smaller amount of fuel than the main injection is injected after the main injection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-042703 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the fuel injected in the latter half of the combustion period is not disturbed by the subsequent fuel injection, it tends to become inactive fuel that is not burned early. As a result, the fuel injected in the latter half of the combustion period prolongs afterburning in the latter half of the injection, which reduces thermal efficiency and prevents sufficient reduction in fuel consumption.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fuel injection control device for a diesel engine that can reduce the combustion period. [Means for solving the problem]

[0006] The fuel injection control device for a diesel engine according to the present invention includes a fuel injection control unit that causes a fuel injection valve to inject fuel, and the fuel injection control unit causes the fuel injection valve to perform a main injection and multiple after-injections following the main injection, with the injection amount of each of the multiple after-injections being smaller than the injection amount of the previous injection.

[0007] This diesel engine fuel injection control device executes multiple after-injections after a main injection. As a result, the fuel in the latter half of the main injection is disturbed and activated by the momentum of the after-injections. Also, in the multiple after-injections, the fuel in the latter half of an earlier after-injection is disturbed and activated by the momentum of the later after-injection. Moreover, the injection amount of each of the multiple after-injections is smaller than the injection amount of the earlier injection. Therefore, the amount of inactivated fuel in the latter half of each of the multiple after-injections can be reduced. This shortens the combustion period, thereby improving thermal efficiency and fuel economy.

[0008] The fuel injection control unit may cause the fuel injection valve to perform the main injection and the multiple after injections so that the interval between each of the main injection and the multiple after injections is 300 μs or less. In this diesel engine fuel injection control device, because the interval between each of the main injection and the multiple after injections is 300 μs or less, the later injections can be injected before the inactive fuel from the earlier injection has diffused over a wide area. This reduces the amount of inactive fuel in the latter half of the injection.

[0009] The fuel injection control unit completes the main injection and the multiple after-injections of the fuel injection valve by the time the rotation angle of the crankshaft reaches 20 degrees after top dead center of the compression stroke. In this fuel injection control device for a diesel engine, the main injection and the multiple after-injections are completed by the time the rotation angle of the crankshaft reaches 20 degrees after top dead center of the compression stroke, so that the lengthening of the combustion period due to the after-injections can be suppressed. [Effects of the Invention]

[0010] According to the present invention, the combustion period can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a schematic diagram showing a fuel injection control device for a diesel engine according to an embodiment; [Figure 2] 3 is a diagram showing an example of an injection pattern of injection that a fuel injection control unit causes a fuel injection valve to perform; FIG. [Figure 3] FIG. 10 is a schematic diagram for explaining the injection amount of the first after-injection. [Figure 4] FIG. 10 is a schematic diagram for explaining the injection amount of the second and subsequent after-injections. [Figure 5] 10 is a graph showing an example of the relationship between the in-cylinder pressure and the heat release rate for each injection pattern. [Figure 6] 10 is a graph showing an example of energy balance in each injection pattern. [Figure 7] 10 is a table showing an example of energy balance in each injection pattern. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted.

[0013] Fig. 1 is a schematic diagram showing a diesel engine fuel injection control device 1 according to an embodiment. As shown in Fig. 1, the diesel engine fuel injection control device 1 according to this embodiment is mounted on a vehicle (not shown) equipped with a diesel engine 2, and includes a fuel injection control unit 3 that controls the injection of fuel into the diesel engine 2.

[0014] The diesel engine 2 is an internal combustion engine that uses diesel fuel. The diesel engine 2 has multiple cylinders 4. Pistons 5 are slidably housed in the cylinders 4. The pistons 5 are connected to a crankshaft 7 via connecting rods 6, and the pistons 5 slide as the crankshaft 7 rotates. Attached to the cylinders 4 are intake manifolds 9 that supply air to combustion chambers 8, exhaust manifolds 10 that discharge exhaust gas from the combustion chambers 8, and fuel injection valves 11 that inject fuel into the combustion chambers 8. The fuel injection valves 11 inject fuel based on instructions from a fuel injection control unit 3.

[0015] The fuel injection control unit 3 is a control device that causes the fuel injection valve 11 to inject fuel. The fuel injection control unit 3 is, for example, an electronic control unit (ECU) having a central processing unit (CPU), read only memory (ROM), random access memory (RAM), etc. The fuel injection control unit 3 performs various controls, for example, by loading a program stored in the ROM into the RAM and executing it on the CPU. The fuel injection control unit 3 may be configured by a single electronic control unit or multiple electronic control units.

[0016] The fuel injection control unit 3 causes the fuel injection valve 11 to perform a main injection M and a plurality of after-injections A as injections of fuel into the combustion chamber 8.

[0017] FIG. 2 is a diagram showing an example of an injection pattern of injections that the fuel injection control unit 3 causes the fuel injection valve 11 to perform. As shown in FIG. 2, the main injection M is an injection that is performed, for example, when the piston 5 is at top dead center (TDC). However, the main injection M may be an injection that is not performed when the piston 5 is at top dead center. The multiple after injections A are auxiliary injections that are performed after the main injection M. More specifically, the multiple after injections A are injections that are performed after the main injection M. The torque requested by the driver is output by the main injection M and the multiple after injections A. In other words, the total injection amount for outputting the torque requested by the driver is divided and injected into the main injection M and the multiple after injections A.

[0018] The multiple after-injections A are performed to shorten the combustion period. In the main injection M, fuel is injected into the combustion chamber 8, where it ignites and burns. However, the fuel in the latter half of the injection is not disturbed by the subsequent fuel injection, and therefore tends to become inactive fuel that is not burned early. As a result, the fuel in the latter half of the combustion prolongs afterburning in the latter half of the injection, which reduces thermal efficiency and prevents sufficient reduction in fuel consumption. Therefore, by performing multiple after-injections A after the main injection M, the fuel in the latter half of the injection of the main injection M is disturbed and activated by the momentum of the after-injections A. This reduces afterburning in the latter half of the combustion of the main injection M, and shortens the combustion period of the main injection M.

[0019] Here, in the multiple after injections A, as with the main injection M, the fuel in the latter half of the injection is not disturbed by the subsequent fuel injection, and therefore tends to become inactive fuel that is not burned early. Therefore, the fuel injection control unit 3 makes the injection amount of each of the multiple after injections A less than the injection amount of the previous injection. Specifically, the fuel injection control unit 3 makes the injection amount of the first after injection A less than the injection amount of the main injection M, the injection amount of the second after injection A less than the injection amount of the first after injection A, and the injection amount of the n-th after injection A less than the injection amount of the (n-1)-th after injection A.

[0020] Similarly, the fuel injection control unit 3 reduces the maximum injection rate of each of the multiple after injections A below the maximum injection rate of the previous injection. Specifically, the fuel injection control unit 3 reduces the maximum injection rate of the first after injection A below the maximum injection rate of the main injection M, reduces the maximum injection rate of the second after injection A below the maximum injection rate of the first after injection A, and reduces the maximum injection rate of the nth after injection A below the maximum injection rate of the (n-1)th after injection A.

[0021] FIG. 3 is a schematic diagram illustrating the injection amount of the first after-injection A. As shown in FIG. 3, it is preferable that the first after-injection A injects an amount of fuel that is sufficient to activate the unburned fuel UM from the main injection M. For example, when the first after-injection A is performed, it is considered that the unburned fuel UM from the main injection M spreads throughout the combustion chamber 8 toward the inner wall surface 41 of the cylinder 4 that forms the combustion chamber 8. On the other hand, if fuel is injected up to the inner wall surface 41 of the cylinder 4, the combustion of the fuel near the inner wall surface 41 may increase cooling loss and reduce thermal efficiency. Therefore, in the first after-injection A, fuel is injected so that the fuel spreads throughout the combustion chamber 8 without reaching the inner wall surface 41.

[0022] FIG. 4 is a schematic diagram illustrating the injection amount of the second or subsequent after injection A. As shown in FIG. 4, in the second or subsequent after injection A, it is preferable to inject an amount of fuel that can activate the unburned fuel UA from the previous after injection A. For example, when the second or subsequent after injection A is performed, it is considered that the unburned fuel UA from the previous after injection A spreads into the combustion chamber 8 toward the inner wall surface 41 of the cylinder 4. However, because the injection amount of each of the multiple after injections A is smaller than the injection amount of the previous injection, the range of the unburned fuel UA remaining in the combustion chamber 8 when the second or subsequent after injection A is performed is narrower than the range of the unburned fuel UM remaining in the combustion chamber 8 when the first after injection A is performed. Furthermore, the range of the unburned fuel UA remaining in the combustion chamber 8 when the n+1th after injection A is performed is narrower than the range of the unburned fuel UA remaining in the combustion chamber 8 when the nth after injection A is performed. Therefore, in the second and subsequent after-injections A, fuel is injected so that the fuel does not reach the inner wall surface 41 and spreads over the entire range of the unburned fuel UA from the previous after-injection A.

[0023] The injection time of each of the multiple after-injections A may be shorter than the injection time of the main injection M. The injection time of each of the multiple after-injections A is not particularly limited, but may be shorter than the injection time of the previous injection. Specifically, the injection time of the first after-injection A may be shorter than the injection time of the main injection M, the injection time of the second after-injection A may be shorter than the injection time of the first after-injection A, and the injection time of the nth after-injection A may be shorter than the injection time of the (n-1)th after-injection A.

[0024] The total injection amount and total injection time of the multiple after-injections A may be less than the injection amount and injection time of the main injection M. The total injection amount of the multiple after-injections A is the sum of the injection amounts of the multiple after-injections A, and the total injection time of the multiple after-injections A is the sum of the injection times of the multiple after-injections A.

[0025] Although there are no particular limitations on the interval between the main injection M and each of the multiple after-injections A, the shorter the interval, the better. For example, the fuel injection control unit 3 causes the fuel injection valve 11 to perform the main injection M and each of the multiple after-injections A so that the interval between the main injection M and each of the multiple after-injections A is 300 μsec or less.

[0026] The time from when the main injection M is performed until the multiple after injections A are performed is not particularly limited, but is preferably set to a time that does not lengthen the combustion time. For example, the fuel injection control unit 3 completes the main injection M and the multiple after injections A of the fuel injection valve 11 by the time the rotation angle of the crankshaft 7 reaches 20 degrees after the compression top dead center (ATDC) or 30 degrees after the compression top dead center. The rotation angle of the crankshaft 7 can be detected, for example, by a crank angle sensor (not shown) installed on or near the crankshaft 7.

[0027] The fuel injection control device 1 for a diesel engine may be provided with an injection map that registers the injection timing, injection time, injection amount, injection interval, etc. of the above-mentioned main injection M and the multiple after-injections A. In this case, the fuel injection control unit 3 can refer to this injection map to cause the fuel injection valve 11 to execute the main injection M and the multiple after-injections A.

[0028] As described above, the fuel injection control device 1 for a diesel engine according to this embodiment executes multiple after-injections A after a main injection M. As a result, the fuel in the latter half of the injection of the main injection M is disturbed and activated by the momentum of the after-injections A. Also, in the multiple after-injections A, the fuel in the latter half of the injection of an earlier after-injection A is disturbed and activated by the momentum of the later after-injection A. Moreover, the injection amount of each of the multiple after-injections A is smaller than the injection amount of the earlier injection. Therefore, in each of the multiple after-injections A, the amount of inactivated fuel in the latter half of the injection can be reduced. This makes it possible to shorten the combustion period, thereby improving thermal efficiency and fuel economy.

[0029] Furthermore, in the diesel engine fuel injection control device 1 according to this embodiment, the interval between each of the main injection M and the multiple after injections A is 300 μs or less, so that the after injections can be injected before the inactive fuel from the previous injection has diffused over a wide area, thereby reducing the amount of inactive fuel in the latter half of the injection.

[0030] Furthermore, in the fuel injection control device 1 for a diesel engine according to this embodiment, the main injection M and multiple after-injections A are completed by the time the rotation angle of the crankshaft 7 reaches 20 degrees after top dead center of compression or 30 degrees after top dead center of compression, thereby preventing the combustion period from being prolonged by the after-injections A.

[0031] The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment, and may be modified or applied to other things within the scope that does not change the gist described in each claim.

[0032] Here, the cylinder pressure, heat generation amount, and energy balance were measured for Comparative Examples 1 and 2 and Examples 1 and 2, in which the fuel injection pattern was changed. The measurement conditions were as follows.

[0033] In Comparative Example 1, the injection pattern was set to execute only the main injection. 3 of fuel was injected.

[0034] In Comparative Example 2, an injection pattern was used in which one after-injection was performed after the main injection. In Comparative Example 2, the main injection was set to 96 mm so that the total injection amount was the same as in Comparative Example 1. 3 of fuel is injected, and 9mm is used as after-injection. 3 of fuel was injected.

[0035] In Example 1, an injection pattern was used in which two after-injections were performed after the main injection. In Example 1, the main injection was performed for 90 mm so that the total injection amount was the same as in Comparative Example 1.3 of fuel is injected, and 9mm is injected as the first after-injection. 3 of fuel is injected, and a second after-injection of 6mm 3 of fuel was injected.

[0036] In Example 2, an injection pattern was used in which three after-injections were performed after the main injection. In Example 3, the main injection was performed at 87 mm so that the total injection amount was the same as in Comparative Example 1. 3 of fuel is injected, and 9mm is injected as the first after-injection. 3 of fuel is injected, and a second after-injection of 6mm 3 of fuel is injected, and then 3mm is injected as a third after-injection. 3 of fuel was injected.

[0037] The measurement results are shown in Figures 5 to 7. Figure 5 is a graph showing an example of the relationship between in-cylinder pressure and heat release rate for each injection pattern. Figure 6 is a graph showing an example of energy balance for each injection pattern. Figure 7 is a table showing an example of energy balance for each injection pattern. As shown in Figures 6 and 7, the indicated thermal efficiency, exhaust loss, and cooling loss were measured as the energy balance for each injection pattern.

[0038] As shown in Figure 5, the in-cylinder pressure and heat release rate changed depending on the injection pattern. Furthermore, as shown in Figures 6 and 7, in Examples 1 and 2, in which multiple after-injections were performed after the main injection, the indicated thermal efficiency was higher than in Comparative Example 1, in which only the main injection was performed, and Comparative Example 2, in which one after-injection was performed after the main injection. Furthermore, in both Examples 1 and 2, in which multiple after-injections were performed after the main injection, the indicated thermal efficiency exceeded 50%.

[0039] From these results, it is inferred that by performing multiple after-injections after the main injection and making the injection amount of each of the multiple after-injections less than the injection amount of the previous injection, the combustion period is shortened due to the reduction in afterburning, thereby improving thermal efficiency. [Explanation of symbols]

[0040] 1...fuel injection control device, 2...diesel engine, 3...fuel injection control section, 4...cylinder, 5...piston, 6...connecting rod, 7...crankshaft, 8...combustion chamber, 9...intake manifold, 10...exhaust manifold, 11...fuel injection valve, 41...inner wall surface, M...main injection, A...after injection, UM...unburned fuel, UA...unburned fuel.

Claims

1. a fuel injection control unit that causes the fuel injection valve to inject fuel; The fuel injection control unit causing the fuel injection valve to perform a main injection and a plurality of after-injections following the main injection as the injection; The injection amount of each of the plurality of after-injections is made smaller than the injection amount of the preceding injection, causing the fuel injection valve to perform a main injection and a plurality of after-injections so that the interval between each of the main injection and the plurality of after-injections is 300 μsec or less; Fuel injection control device for diesel engines.

2. a fuel injection control unit that causes the fuel injection valve to inject fuel; The fuel injection control unit causing the fuel injection valve to perform a main injection and a plurality of after-injections following the main injection as the injection; The injection amount of each of the plurality of after-injections is made smaller than the injection amount of the preceding injection, The main injection and the plurality of after-injections of the fuel injection valve are completed by the time the rotation angle of the crankshaft reaches 20 degrees after the top dead center of compression. Fuel injection control device for diesel engines.

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