Control device for internal combustion engines

Abstract

To provide a control device for an internal combustion engine that can stably control the injection mode. [Solution] A control device having a first fuel injection valve for injecting fuel into a cylinder and a second fuel injection valve for injecting fuel into an intake manifold, comprising: a first setting unit for determining the first fuel injection amount; a second setting unit for determining a threshold value and a hysteresis width for the fuel injection amount; and an injection control unit for switching between a first mode in which the fuel is injected from the first fuel injection valve and a second mode in which the fuel is injected from the second fuel injection valve, wherein the second setting unit sets the hysteresis width to a constant multiple of the first fuel injection amount, the injection control unit selects the second mode when the first fuel injection amount is less than the threshold value, selects the first mode when the first fuel injection amount is greater than or equal to the sum of the threshold value and the hysteresis width, and maintains the previous injection mode when the first fuel injection amount is greater than or equal to the threshold value and less than the sum of the threshold value and the hysteresis width.

Description

Technical Field

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

Background Art

[0002] Fuel is injected from a fuel injection valve into an internal combustion engine. There is known a technique for controlling the lift amount of the fuel injection valve and performing full-lift injection and partial-lift injection (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In one injection cycle, single injection refers to injecting the required injection amount in one injection. In one injection cycle, multi-injection refers to injecting the required injection amount in multiple injections. Multi-injection including partial-lift injection is called partial-lift multi-injection. There may be a switch between single port injection and partial-lift multi-injection for the injection mode. However, if the switching is performed frequently, the air-fuel ratio (A / F) becomes unstable. Therefore, an object is to provide a control device for an internal combustion engine capable of stably controlling the injection mode.

Means for Solving the Problems

[0005] The above objective can be achieved by a control device for an internal combustion engine that controls an internal combustion engine having a first fuel injection valve for injecting fuel into the cylinders of the internal combustion engine and a second fuel injection valve for injecting fuel into the intake manifold, comprising: a first setting unit for determining a first fuel injection amount; a second setting unit for determining a threshold value and a hysteresis width for the fuel injection amount; and an injection control unit for switching the fuel injection mode between a first mode in which the fuel is injected from the first fuel injection valve and a second mode in which the fuel is injected from the second fuel injection valve, wherein the second setting unit sets the hysteresis width to a constant multiple of the first fuel injection amount, the injection control unit selects the second mode when the first fuel injection amount is less than the threshold value, the injection control unit selects the first mode when the first fuel injection amount is greater than or equal to the sum of the threshold value and the hysteresis width, and the injection control unit maintains the previous injection mode when the first fuel injection amount is greater than or equal to the threshold value and less than the sum of the threshold value and the hysteresis width.

[0006] The injection control unit may cause the first fuel injector to perform multi-injection in the first mode.

[0007] The second setting unit may set the hysteresis width to 0.5 times or less the first fuel injection amount.

[0008] The first fuel injection amount may also be the amount of fuel injected so that the air-fuel ratio of the internal combustion engine is the stoichiometric air-fuel ratio.

[0009] The threshold may also be the minimum injection amount injected by the second fuel injector. [Effects of the Invention]

[0010] This invention provides a control device for an internal combustion engine that can stably control the injection mode. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram illustrating an internal combustion engine. [Figure 2]Figure 2 is a flowchart illustrating the process in the embodiment. [Figure 3] Figure 3 is a schematic diagram illustrating the injection modes. [Modes for carrying out the invention]

[0012] The control device for the internal combustion engine of this embodiment will be described below with reference to the drawings. Figure 1 is a schematic diagram illustrating an internal combustion engine 10, showing one cylinder. The internal combustion engine 10 burns fuel to produce power. The fuel is, for example, gasoline or alcohol. The internal combustion engine 10 has a cylinder head 30 and a cylinder block 32. The cylinder head 30 is mounted on top of the cylinder block 32. A piston 33 is housed in the cylinder block 32. In each cylinder, the combustion chamber 34 is partitioned by the piston 33, the cylinder block 32 and the cylinder head 30.

[0013] The cylinder head 30 is equipped with a fuel injector 22 (first fuel injector), an intake valve 25, an exhaust valve 26, and a spark plug 27. The fuel injector 22 is a direct injection injector that injects fuel directly into the cylinder. An intake pipe 12 and an exhaust pipe 14 are connected to the cylinder head 30.

[0014] The intake manifold 12 is equipped with, in order from upstream, an air cleaner 15, an airflow meter 16, a throttle valve 18, and a fuel injector 24 (second fuel injector). The fuel injector 24 is a port injection injector that injects fuel into the intake manifold 12.

[0015] The air cleaner 15 removes dust and debris from the air. The airflow meter 16 detects the airflow rate. The throttle valve 18 regulates the airflow rate. The larger the opening of the throttle valve 18, the greater the airflow rate. The smaller the opening, the greater the airflow rate.

[0016] When the intake valve 25 opens, air flows from the intake pipe 12 into the combustion chamber 34. The fuel injected from the fuel injection valve 22 or 24 is also introduced into the combustion chamber 34. Air and fuel form an air-fuel mixture. The ignition plug 27 ignites the air-fuel mixture. Driving force is generated by the combustion of the air-fuel mixture.

[0017] The exhaust gas generated by combustion is discharged into the exhaust pipe 14 when the exhaust valve 26 opens. The catalyst 20 provided in the exhaust pipe 14 purifies PM, carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NOx), etc. in the exhaust gas.

[0018] An air-fuel ratio sensor 29 is provided upstream of the catalyst 20 in the exhaust pipe 14. The air-fuel ratio sensor 29 detects the air-fuel ratio. The temperature sensor 52 detects the temperature of the cooling water of the internal combustion engine 10 or the outside air temperature. The rotational speed sensor 54 detects the rotational speed of the internal combustion engine 10.

[0019] Fuel is stored in the fuel tank 40. The fuel system 48 includes a fuel passage 42 and a fuel pipe 46. The fuel system 47 includes a fuel passage 43, a high-pressure pump 44, and a fuel pipe 45.

[0020] A feed pump 41 is provided in the fuel tank 40. The feed pump 41 pumps up fuel from the fuel tank 40 and supplies it to the fuel passages 42 and 43. The fuel passage 42 is connected to the fuel pipe 46. The fuel pipe 46 is connected to the fuel injection valve 24 of each cylinder. Fuel passes through the fuel passage 42 and the fuel pipe 46 and is supplied to the fuel injection valve 24.

[0021] The fuel passage 43 branches off from the fuel passage 42 and is connected to the fuel pipe 45. The fuel pipe 45 is connected to the fuel injection valve 22 of each cylinder. A high-pressure pump 44 is provided in the fuel passage 43. Fuel is pressurized by the high-pressure pump 44, flows through the fuel passage 43 and the fuel pipe 45, and is supplied to the fuel injection valve 22.

[0022] The ECU (Electronic Control Unit) 50 is a control device for the internal combustion engine 10 and includes an arithmetic unit such as a CPU (Central Processing Unit) and storage devices such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0023] The ECU 50 controls the opening degree of the throttle valve 18 and controls the valve timing of the intake valve 25 and the exhaust valve 26. The ECU 50 acquires the air flow rate detected by the air flow meter 16. The ECU 50 acquires the air-fuel ratio detected by the air-fuel ratio sensor 29. The ECU 50 acquires the temperature detected by the temperature sensor 52. The ECU 50 acquires the rotational speed detected by the rotational speed sensor 54. The ECU 50 controls the feed pump 41 and the high-pressure pump 44 and adjusts the fuel discharge amount in these pumps.

[0024] The ECU 50 controls the fuel injection valves 22 and 24 and controls the injection timing, the number of injections, and the injection amount. The ECU 50 can execute both direct injection using the fuel injection valve 22 and port injection using the fuel injection valve 24, and can also perform only one of them.

[0025] A needle is provided in the housing of the fuel injection valve. The ECU 50 energizes the fuel injection valve and controls the lift amount of the needle. If the lift amount of the needle is zero, the fuel injection valve is closed. When the needle lifts, the fuel injection valve opens. When the lift amount is maximum (100%), the fuel injection valve is fully open. The fuel injection performed at full open is described as full-lift injection. The injection performed in a state where the lift amount is greater than zero and less than the maximum lift amount is described as partial-lift injection.

[0026] In one injection cycle, injecting the required fuel injection amount at once is called single injection. In one injection cycle, dividing the required fuel injection amount and injecting it is called multi-injection.

[0027] A multi-injection that includes a partial-lift injection is called a partial-lift multi-injection. A multi-injection includes multiple injections. If at least one of the multiple injections is a partial-lift injection, the multi-injection is a partial-lift multi-injection. All of the multiple injections may be partial-lift injections. If all of the multiple injections are full-lift injections, the multi-injection is not a partial-lift multi-injection. The fuel injector 22 may perform single injections and multi-injections, and may also perform full-lift injections, partial injections, and partial-lift multi-injections. The fuel injector 24 performs full-lift injections.

[0028] The ECU 50 functions as an injection control unit that switches the injection mode between the first mode and the second mode. In the first mode, the fuel injector 22 performs direct injection, and sometimes the fuel injector 24 also injects fuel together with the fuel injector 22. That is, fuel can be injected using both the fuel injectors 22 and 24. In the first mode, the fuel injector 22 may also perform multi-injection and partial-lift multi-injection. By performing multi-injection using the fuel injector 22, combustion can be improved and particulate matter (PM) in the exhaust can be reduced. In the second mode, port injection is performed using the fuel injector 24. The fuel injector 22 does not inject fuel.

[0029] ECU50 functions as a first setting unit, setting the basic injection amount Qb (first fuel injection amount), the in-cylinder required injection amount Qd, and the port required injection amount Qp. ECU50 also functions as a second setting unit, determining the fuel injection amount threshold Qmip and the hysteresis width H.

[0030] The basic injection amount Qb is the theoretical injection amount required to make the air-fuel ratio of the internal combustion engine 10 the stoichiometric air-fuel ratio. The in-cylinder required injection amount Qd is the injection amount required by the fuel injector 22. The port required injection amount Qp is the injection amount required by the fuel injector 24.

[0031] The port-required injection amount Qp is calculated, for example, by the following equation (1), where k is the feedback rate, which is determined based on the air-fuel ratio, etc. Qm is the amount of fuel that did not contribute to combustion. Qp = (Qb × (1 + k / 100)) + Qm (1)

[0032] Uncontributed fuel refers to fuel injected from the fuel injector 24 that adheres to the intake port or other parts and is not burned. When uncontributed fuel is generated, the injection amount is increased to compensate for the uncontributed amount. In other words, Qm becomes a positive value. On the other hand, uncontributed fuel generated in the previous injection cycle may detach from the adhered parts and be introduced into the combustion chamber 34. In this case, Qm becomes a negative value.

[0033] The ECU50 switches the injection mode between the first mode and the second mode based on the threshold Qmip and the hysteresis width H. The threshold Qmip is the minimum injection amount in port injection. The hysteresis width H is a constant multiple of the basic injection amount Qb, as shown in equation (3) below. H = c × Qb (3) c is a constant, for example, less than or equal to 0.5, but it could also be less than or equal to 0.4, less than or equal to 0.3, or less than or equal to 0.2. For example, c could be 0.1 or 0.2.

[0034] Figure 2 is a flowchart illustrating the processing in the embodiment. The ECU 50 determines whether the port request injection amount Qp is greater than or equal to the sum of the threshold Qmip and the hysteresis width H (Qmip + H) (step S10). If the determination is positive (Yes), the ECU 50 sets the injection mode to the first mode (step S12).

[0035] If the result in step S10 is negative (No), the ECU 50 determines whether the port request injection amount Qp is less than the threshold Qmip (step S14). If the result is positive, the ECU 50 sets the injection mode to the second mode (step S16). If the result is negative, the ECU 50 maintains the injection mode of the previous injection cycle (step S18). The process then ends.

[0036] Figure 3 is a schematic diagram illustrating injection modes. The horizontal axis represents the fuel injection amount, which increases from left to right. The sum of these amounts, Qmip+H, is set at a position to the right of the threshold Qmip by a hysteresis width H.

[0037] As shown in Figure 3, in the portion where the port-requested injection amount Qp is below the threshold Qmip, the injection mode is the second mode (step S16 in Figure 2). In the portion where the port-requested injection amount Qp is greater than or equal to the sum Qmip + H, the injection mode is the first mode (step S12 in Figure 2). In the portion where the port-requested injection amount Qp is greater than or equal to the threshold Qmip and less than the sum Qmip + H, the previous injection mode is maintained (step S18).

[0038] For example, if the system switches between the first and second modes at a threshold Qmip, the injection mode changes frequently, leading to an unstable air-fuel ratio.

[0039] According to the embodiment, the ECU 50 determines the hysteresis width H as a constant multiple of the basic injection amount Qb (H = c × Qb). The ECU 50 switches the injection mode based on the threshold Qmip and the hysteresis width H. Frequent switching of the injection mode is suppressed and stable control is achieved.

[0040] As shown in Figures 2 and 3, when the port-required injection amount Qp is less than the threshold Qmip, the injection mode is the second mode. When the port-required injection amount Qp is greater than or equal to the sum Qmip + H, the injection mode is the first mode. When the port-required injection amount Qp is greater than or equal to the threshold Qmip and less than the sum Qmip + H, the previous injection mode is maintained. For example, once the injection mode is in the first mode, the first mode is maintained even if the port-required injection amount Qp is in the range of Qmip to Qmip + H. The frequency of switching to the second mode decreases. In other words, the first mode is more likely to be maintained. The air-fuel ratio becomes stable.

[0041] The basic injection amount Qb changes depending on the load factor of the internal combustion engine 10. If the hysteresis width H is kept constant, the hysteresis width H does not change even if the basic injection amount Qb changes. Because the hysteresis width H does not follow the change in the basic injection amount Qb, it is difficult to control the injection mode. If the hysteresis width H is relatively large compared to the basic injection amount Qb, switching of the injection mode is less likely to occur. Switching from the second mode to the first mode is less likely to occur, and there is a risk that PM in the exhaust will worsen. If the hysteresis width H is relatively small compared to the basic injection amount Qb, switching of the injection mode occurs frequently, and the air-fuel ratio becomes unstable.

[0042] According to the embodiment, the hysteresis width H is a constant multiple of the basic injection amount Qb, and is smaller than Qb. The hysteresis width H changes in accordance with the basic injection amount Qb. In other words, the hysteresis width H maintains a constant ratio with respect to the basic injection amount Qb. The frequency of switching between injection modes is controlled to an appropriate number of times. The coefficient c is less than 1, for example, 0.7 or less, 0.5 or less, 0.3 or less, 0.2 or less, 0.1 or less, etc. When the coefficient c is 0.1, the hysteresis width H is 0.1 times the basic injection amount Qb (10% of Qb).

[0043] In the first mode, the ECU 50 causes the fuel injector 22 to perform multi-injection. Multi-injection makes it easier for the fuel to vaporize, improving combustion. PM in the exhaust is reduced. According to this embodiment, by setting the hysteresis width H to c × Qb, the first mode is more easily maintained. Combustion is effectively improved. The number of injections included in the multi-injection within one cycle is set to the maximum number within the range where the sum of the injection amounts is less than or equal to the total injection amount Q of one cycle. Combustion is further improved.

[0044] The basic injection amount Qb is the amount injected so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. The hysteresis width H is a constant multiple of Qb. The basic injection amount Qb changes according to the operating conditions of the internal combustion engine 10. The hysteresis width H changes in accordance with Qb. By maintaining an appropriate size for the hysteresis width H, the injection mode can be stably controlled.

[0045] The minimum injection volume Qmip for port injection is a threshold for switching injection modes. In this embodiment, the injection mode is switched based on the threshold Qmip and the sum of Qmip and the hysteresis width H, Qmip+H (Figure 3). This allows for stable control of the injection mode.

[0046] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of Symbols]

[0047] 10 Internal combustion engine, 12 Intake pipe, 14 Exhaust pipe, 15 Air cleaner, 16 Airflow meter, 18 Throttle valve, 20 Catalytic converter, 22, 24 Fuel injectors, 25 Intake valve, 26 Exhaust valve, 27 Spark plug, 29 Air-fuel ratio sensor, 30 Cylinder head, 32 Cylinder block, 33 Piston, 34 Combustion chamber, 40 Fuel tank, 41 Feed pump, 42, 43 Fuel passages, 44 High-pressure pump, 45, 46 Fuel piping, 47, 48 Fuel system, 50 ECU, 52 Temperature sensor, 54 Rotation speed sensor

Claims

1. A control device for an internal combustion engine having a first fuel injection valve for injecting fuel into the cylinders of the internal combustion engine and a second fuel injection valve for injecting fuel into the intake manifold, A first setting unit for determining the first fuel injection amount, A second setting unit that determines the threshold and hysteresis width of the fuel injection amount, The system comprises an injection control unit that switches the fuel injection mode between a first mode in which the fuel is injected from the first fuel injection valve and a second mode in which the fuel is injected from the second fuel injection valve, The second setting unit sets the hysteresis width to a constant multiple of the first fuel injection amount. If the first fuel injection amount is less than the threshold, the injection control unit selects the second mode. If the first fuel injection amount is greater than or equal to the sum of the threshold and the hysteresis width, the injection control unit selects the first mode. When the first fuel injection amount is greater than or equal to the threshold and less than the sum of the threshold and the hysteresis width, the injection control unit maintains the previous injection mode. This is a control device for an internal combustion engine.

2. The control device for an internal combustion engine according to claim 1, wherein the injection control unit causes the first fuel injector to perform multi-injection in the first mode.

3. The control device for an internal combustion engine according to claim 1 or 2, wherein the second setting unit sets the hysteresis width to 0.5 times or less the first fuel injection amount.

4. The control device for an internal combustion engine according to claim 1 or 2, wherein the first fuel injection amount is the amount of fuel injected so that the air-fuel ratio of the internal combustion engine is the stoichiometric air-fuel ratio.

5. The control device for an internal combustion engine according to claim 1 or 2, wherein the threshold is the minimum injection amount injected by the second fuel injector.

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