Fuel injection control device for multi-cylinder engine

Abstract

To provide a fuel injection control device of a multicylinder engine which is suppressed in the lowering of a port injection amount after a finish of temperature raising processing.SOLUTION: In a fuel injection control device of a multicylinder engine having an in-cylinder injection valve and a port injection valve, and purified in exhaust emission by an exhaust emission purification device, the fuel injection control device comprises: a temperature raising processing part for performing temperature raising processing for raising the temperature of the exhaust emission purification device by performing a fuel cut to at least one cylinder, and performing in-cylinder injection to the other remaining cylinder by stopping port injection, and a temperature lowering processing part for performing temperature lowering processing for lowering the temperature of the port injection valve by raising a port injection rate after a finish of the temperature raising processing to be higher than a port injection rate which is preset according to an operation state of the engine.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] A known example of such a temperature-raising process is to raise the temperature of an exhaust gas purification device provided in a multi-cylinder engine. One such temperature-raising process involves cutting fuel in at least one cylinder, stopping port injection in the remaining cylinders, and performing in-cylinder injection (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-115313 Summary of the Invention [Problem to be solved by the invention]

[0004] During the heating process, port injection is stopped, and some of the high-temperature combustion gas returns from the cylinder to the intake port. This can cause the tip of the port injection valve to become hot, expanding the tip and narrowing the injection hole. This can result in a decrease in the port injection volume after the heating process is complete. Furthermore, the fuel stored at the tip of the port injection valve expands, reducing the density of the fuel after the heating process is complete, which can also reduce the port injection volume.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fuel injection control device for a multi-cylinder engine that suppresses a decrease in the port injection amount after the end of the temperature raising process. [Means for solving the problem]

[0006] The above object can be achieved by a fuel injection control device for a multi-cylinder engine having an in-cylinder injection valve and a port injection valve, and in which exhaust is purified by an exhaust purification device, comprising: a temperature rise processing unit that performs a temperature rise process to raise the temperature of the exhaust purification device by cutting fuel in at least one cylinder and stopping port injection and performing in-cylinder injection in the remaining cylinders; and a temperature fall processing unit that performs a temperature fall process to lower the temperature of the port injection valve by raising the port injection rate after the temperature rise process to a value higher than a port injection rate that is predetermined depending on the operating state of the engine.

[0007] The temperature lowering processing unit may increase the pressure of the fuel supplied to the port injection valve during the temperature lowering process from a pressure of the fuel that is predetermined depending on an operating state of the engine.

[0008] The temperature lowering processing unit may start increasing the pressure of the fuel supplied to the port injection valve when the duration of the temperature raising process reaches or exceeds a predetermined time required for lowering the temperature of the port injection valve.

[0009] The temperature rise processing unit may temporarily suspend the temperature rise processing when the duration of the temperature rise processing reaches or exceeds a predetermined time required to lower the temperature of the port injection valve, and the temperature drop processing unit may execute the temperature drop processing after temporarily suspending the temperature rise processing. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a fuel injection control device for a multi-cylinder engine that suppresses a decrease in the port injection amount after the end of the temperature raising process. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic configuration diagram of an engine. [Figure 2] 10 is a flowchart illustrating a temperature lowering process. [Figure 3] 10 is a timing chart illustrating a temperature lowering process. [Figure 4]10 is a flowchart illustrating a modified example of the temperature lowering process. [Figure 5] 10 is a timing chart illustrating a modified example of the temperature lowering process. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Engine outline] FIG. 1 is a schematic diagram of an engine 10. The engine 10 is mounted on a vehicle, for example, as a power source for driving. The engine 10 is an in-line four-cylinder gasoline engine, but may also be a multi-cylinder diesel engine. The engine 10 has cylinders 30, pistons 31, connecting rods 32, a crankshaft 33, an intake passage 35, intake valves 36, an exhaust passage 37, and exhaust valves 38. FIG. 1 shows only one of the four cylinders 30 of the engine 10. An air-fuel mixture is combusted in the cylinder 30. A piston 31 is reciprocally housed in each cylinder 30 and is connected to the crankshaft 33, which is the output shaft of the engine 10, via a connecting rod 32. The connecting rod 32 converts the reciprocating motion of the pistons 31 into the rotational motion of the crankshaft 33.

[0013] The intake passage 35 is connected to the intake port of each cylinder 30 via an intake valve 36. The exhaust passage 37 is connected to the exhaust port of each cylinder 30 via an exhaust valve 38. An air flow meter 75 and a throttle valve 40 that adjusts the amount of intake air are provided in the intake passage 35. An air-fuel ratio sensor 76 and a three-way catalyst 43 for exhaust purification are provided in the exhaust passage 37. The three-way catalyst 43 contains catalytic metal, has oxygen storage capacity, and purifies NOx, HC, and CO. The three-way catalyst 43 is an example of an exhaust purification device. Note that a filter that captures exhaust particulates in the exhaust gas may be provided instead of the three-way catalyst 43 or downstream of the three-way catalyst 43. Furthermore, a filter supporting a three-way catalyst with oxygen storage capacity may be provided instead of the three-way catalyst 43.

[0014] Each cylinder 30 is provided with an in-cylinder injection valve 41d. The in-cylinder injection valve 41d injects fuel directly into the cylinder 30. The intake passage 35 is provided with a port injection valve 41p that injects fuel toward the intake port. Note that as long as the in-cylinder injection valve 41d is provided, the port injection valve 41p does not have to be provided. Each cylinder 30 is provided with an ignition plug 42 that ignites, by spark discharge, a mixture of intake air introduced through the intake passage 35 and fuel injected by the in-cylinder injection valve 41d and the port injection valve 41p.

[0015] The port injection valve 41p is connected to a low-pressure delivery pipe 52. Fuel pumped up from a fuel tank 50 by a low-pressure pump 51 is supplied to the low-pressure delivery pipe 52. Because a relatively low fuel pressure is maintained inside the low-pressure delivery pipe 52, the port injection valve 41p injects a relatively small amount of fuel. The low-pressure pump 51 is an electric pump that is driven by a supply of electricity. The pressure of the fuel supplied to the port injection valve 41p by the low-pressure pump 51 is referred to as low fuel pressure.

[0016] The in-cylinder injection valve 41d is connected to a high-pressure delivery pipe 54. The high-pressure delivery pipe 54 stores fuel that has been pumped up from a fuel tank 50 by a low-pressure pump 51 and then pressurized by a high-pressure pump 53. Because a relatively high fuel pressure is maintained inside the high-pressure delivery pipe 54, the in-cylinder injection valve 41d injects a relatively large amount of fuel. The high-pressure pump 53 is a mechanical pump that is driven in conjunction with the rotation of the engine 10.

[0017] The ECU (Electronic Control Unit) 100 is an electronic control unit that performs control processing related to the engine 10. The ECU 100 is mainly composed of a computer including a CPU (Central Processing Unit) and volatile and non-volatile memories such as RAM (Random Access Memory) and ROM (Read Only Memory). The ECU 100 executes programs installed in the memory on the CPU to perform various control processing related to the engine 10. Various sensors are connected to the ECU 100, which will be described in detail later. The ECU 100 is an example of a fuel injection control device, and functionally realizes a temperature increase processing unit and a temperature decrease processing unit, which will be described in detail later.

[0018] The ECU 100 receives signals from an ignition switch 71, a crank angle sensor 72, an accelerator opening sensor 74, an air flow meter 75, an air-fuel ratio sensor 76, and a water temperature sensor 77. The crank angle sensor 72 detects the rotation speed of the crankshaft of the engine 10. The accelerator opening sensor 74 detects the accelerator pedal opening, which is the amount of depression of the accelerator pedal by the driver. The air flow meter 75 detects the amount of intake air of the engine 10. The air-fuel ratio sensor 76 detects the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 43. The water temperature sensor 77 detects the temperature of the coolant for the engine 10.

[0019] The ECU 100 calculates the engine speed based on the detection value of the crank angle sensor 34, and calculates the engine load based on the engine speed and the intake air amount. The ECU 100 calculates the target engine speed and target load based on the accelerator opening, and controls the fuel injection amount, intake air amount, ignition timing, port injection rate, and in-cylinder injection rate so that the engine speed and load become the target engine speed and target load, respectively.

[0020] When a predetermined condition is met, the ECU 100 executes a temperature-raising process to raise the temperature of the three-way catalyst 43 to its activation temperature. During the temperature-raising process, fuel is cut off for one cylinder, and port injection is stopped and in-cylinder injection is performed for the remaining cylinders. Hereinafter, this control is referred to as a single-cylinder fuel cut. By executing the single-cylinder fuel cut, oxygen and unburned fuel are supplied to the three-way catalyst 43 to promote the combustion of the unburned fuel, thereby raising the temperature of the three-way catalyst 43. Furthermore, in-cylinder injection is performed for the other cylinders, which provides better air-fuel ratio stability, responsiveness, and controllability than port injection. This allows the air-fuel ratio and combustion state of the other cylinders to be stabilized even when one-cylinder fuel cut is being executed, and the temperature-raising process is executed appropriately. As described above, there is a risk that the port injection amount will decrease after the temperature-raising process is completed. Therefore, the ECU 100 of this embodiment executes a temperature-lowering process to lower the tip temperature of the port injection valve 41p.

[0021] [Cooling treatment] Fig. 2 is a flowchart illustrating the temperature drop process. Fig. 3 is a timing chart illustrating the temperature drop process. Fig. 3 shows the transitions of the temperature rise process execution flag, injection method, temperature rise process duration, low-pressure fuel pressure increase flag, and port injection duration. The process shown in Fig. 2 is repeatedly executed at predetermined intervals while the ignition is on.

[0022] The ECU 100 determines whether or not there is a request for temperature increase processing (step S1). If the answer is Yes in step S1, the ECU 100 executes the temperature increase processing described above (step S2). This switches the temperature increase processing execution flag from OFF to ON, and the one-cylinder fuel cut and in-cylinder injection described above are executed (time t1). Step S2 is an example of processing executed by the temperature increase processing unit.

[0023] Next, ECU 100 determines whether the duration of the temperature increase process is equal to or longer than a predetermined time (step S3). The predetermined time is set to the time required to decrease the temperature of port injection valve 41p. Specifically, the predetermined time is set to the shortest time until the tip temperature of port injection valve 41p increases beyond the allowable range due to the continuation of the temperature increase process and the port injection amount decreases beyond the allowable range after the temperature increase process is completed. This predetermined time is determined in advance based on experimental results and simulation results. If the answer is No in step S3, this control ends.

[0024] If the answer to step S3 is Yes, the ECU 100 increases the low-pressure fuel pressure, which is the pressure of the fuel supplied to the port injection valve 41p (step S4, time t2). Specifically, the low-pressure fuel pressure is increased by a predetermined value from the low-pressure fuel pressure, which is predetermined according to the current operating state of the engine 10. The low-pressure fuel pressure is increased by increasing the power supplied to the low-pressure pump 51. By starting to increase the low-pressure fuel pressure while the temperature increase process is being performed in this way, the temperature decrease process, which will be described later, can be effectively performed after the temperature increase process is completed. Step S4 is an example of the process executed by the temperature decrease processing unit.

[0025] If the answer is No in step S1, the ECU 100 determines whether the low fuel pressure is being increased in step S4 (step S5). If the answer is No in step S5, the control ends.

[0026] If step S5 returns Yes, i.e., if the temperature increase process has ended and the low-pressure fuel pressure is being increased, the ECU 100 executes a temperature decrease process to decrease the temperature of the port injection valve 41p (step S6, time t3). The temperature decrease process increases the port injection rate from a rate predetermined according to the current operating state of the engine 10. In the temperature decrease process of this embodiment, the port injection rate is controlled to 100% and the in-cylinder injection rate to 0%. Therefore, after the temperature increase process ends, only port injection is performed. This allows the tip temperature of the port injection valve 41p to decrease immediately after the temperature increase process ends. Furthermore, because the low-pressure fuel pressure is increased during the temperature increase process as described above, the amount of fuel injected from the port injection valve 41p increases, effectively decreasing the tip temperature of the port injection valve 41p. In this way, a decrease in the port injection amount after the temperature increase process ends can be suppressed. Step S6 is an example of a process executed by the temperature decrease processing unit.

[0027] The ECU 100 determines whether the duration of the temperature-lowering process is equal to or longer than a predetermined time (step S7). The predetermined time is set to a time during which the temperature of the port injection valve 41p no longer needs to be lowered. Specifically, the predetermined time is set to the shortest time during which the tip temperature of the port injection valve 41p falls to an allowable range as a result of the temperature-lowering process being continued and the port injection amount increases to an allowable range. This predetermined time is determined in advance based on experimental results and simulation results. If the determination in step S7 is No, the process of step S6 is continued again.

[0028] If the answer to step S7 is Yes, the ECU 100 determines that the tip temperature of the port injection valve 41p has dropped to within the allowable range, and stops increasing the low-pressure fuel pressure and executes normal injection control (step S8, time t4). That is, fuel injection is executed at a port injection rate and an in-cylinder injection rate that are predetermined according to the operating state of the engine 10. In this way, it is possible to suppress a decrease in output of the engine 10 due to unnecessary continuation of the temperature drop process.

[0029] The low-pressure fuel pressure may be increased continuously or in stages.

[0030] [Modification of temperature-lowering treatment] Next, a modified example of the temperature drop process will be described. In this modified example, the low fuel pressure is not increased. FIG. 4 is a flowchart illustrating a modified example of the temperature drop process. FIG. 5 is a timing chart illustrating a modified example of the temperature drop process. FIGS. 4 and 5 correspond to FIGS. 2 and 3, respectively. FIG. 5 shows the transitions of the temperature rise process execution flag, injection method, temperature rise process duration, and port injection duration. Note that duplicated explanations will be omitted for processes that are the same as those in the above-described embodiment.

[0031] If the answer is No in step S1, this control ends. If the answer is Yes in step S1, ECU 100 determines whether the temperature increase process is temporarily stopped (step S1a). If the answer is No in step S1a, ECU 100 executes the temperature increase process (step S2, time t1). If the answer is Yes in step S3, ECU 100 temporarily stops the temperature increase process (step S4a, time t2a). Step S4a is an example of a process executed by the temperature increase processing unit.

[0032] If the answer to step S1a is Yes, step S6 is executed. If the answer to step S7 is Yes, ECU 100 resumes the pause of the temperature increase process (step S8a). As a result, the paused temperature increase process is executed again (time t3a). As described above, in this modification, the temperature decrease process is executed without increasing the low-pressure fuel pressure, making this modification easy to implement. Furthermore, an increase in power consumption of low-pressure pump 51 is also suppressed.

[0033] In the temperature reduction process in the above-described embodiment and modified example, the port injection rate is increased to 100%, but the port injection rate may be other than 100% as long as it is increased above a port injection rate that is predetermined according to the operating state of the engine 10. This is because the port injection rate also increases, making it possible to reduce the tip temperature of the port injection valve 41p and suppress the effect on the operating state.

[0034] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0035] 10 Engine (multi-cylinder engine) 41d Direct injection valve 41p Port injection valve 51 Low-pressure pump 100 ECU (fuel injection control device, temperature increase processing unit, temperature decrease processing unit)

Claims

1. A fuel injection control device for a multi-cylinder engine having an in-cylinder injection valve and a port injection valve, and whose exhaust gas is purified by an exhaust gas purification device, a temperature increase processing unit that performs a temperature increase process to increase the temperature of the exhaust gas purification device by cutting fuel in at least one cylinder and stopping port injection and performing in-cylinder injection in the remaining cylinders; a temperature reduction processing unit that executes a temperature reduction process to reduce the temperature of the port injection valve by increasing the port injection rate after the temperature increase process to a rate higher than a port injection rate that is predetermined in accordance with the operating state of the engine.

2. 2. The fuel injection control device for a multi-cylinder engine according to claim 1, wherein the temperature lowering processing unit raises the pressure of the fuel supplied to the port injection valve from a pressure of the fuel that is predetermined depending on the operating state of the engine during the temperature lowering processing.

3. 3. The fuel injection control device for a multi-cylinder engine according to claim 2, wherein the temperature lowering processing unit starts increasing the pressure of the fuel supplied to the port injection valve when the duration of the temperature raising processing reaches or exceeds a predetermined time required for lowering the temperature of the port injection valve.

4. the temperature increase processing unit temporarily suspends the temperature increase process when a duration of the temperature increase process reaches or exceeds a predetermined time required for decreasing the temperature of the port injection valve; 2. The fuel injection control device for a multi-cylinder engine according to claim 1, wherein the temperature lowering processing unit executes the temperature lowering processing after temporarily suspending the temperature increasing processing.

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