JP7722296B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to an internal combustion engine control device.

Patent Document 1 discloses a control device applied to an internal combustion engine equipped with a catalytic converter that purifies exhaust gas flowing through the exhaust passage. When the internal combustion engine is cold idling, the control device performs ignition timing control to retard ignition timing in order to raise the temperature of exhaust gas discharged from the cylinder into the exhaust passage. Furthermore, when the control device retards ignition timing during cold idling, it reduces the amount of valve overlap compared to when the ignition timing is not retarded. The amount of valve overlap is the length of time during which the intake valve and exhaust valve are simultaneously open.

Japanese Patent Application Laid-Open No. 2003-293801

When the intake valve and exhaust valve are opened simultaneously, exhaust gas from the cylinder flows into the intake passage as internal EGR, raising the temperature of the gas introduced from the intake passage into the cylinder. This promotes fuel vaporization within the cylinder, reducing the amount of particulate matter contained in the exhaust gas discharged from the cylinder into the exhaust passage. However, if the overlap amount is set too high when the internal combustion engine is running cold, the amount of internal EGR may become excessive, causing unstable combustion in the cylinder. Unstable combustion in the cylinder may cause a surge in the internal combustion engine.

An internal combustion engine control device that solves the above problem is applied to an internal combustion engine equipped with an adjustment mechanism that adjusts the valve overlap amount, which is the length of time during which the intake valve and exhaust valve are simultaneously open, and a catalytic converter that purifies exhaust gas discharged from the cylinder into the exhaust passage. This internal combustion engine control device also includes an execution device that controls the operation of the internal combustion engine. The execution device executes a guard value setting process that, when an engine load factor, which is the load factor of the internal combustion engine, is equal to or less than the upper limit of a predetermined load factor range, sets an upper limit guard value for the valve overlap amount to a value that is smaller than when the engine load factor is higher than the upper limit, and an adjustment process that, when the internal combustion engine is operating cold, reduces the amount of particulate matter contained in the exhaust by adjusting the valve overlap amount within a range equal to or less than the upper limit guard value.

The inventors of this invention conducted various experiments and simulations on the relationship between the likelihood of surge occurring in an internal combustion engine during cold operation and the amount of valve overlap, and came to the following conclusion: When the engine load factor is within a predetermined load factor range during cold operation of an internal combustion engine, setting the amount of valve overlap to an appropriate length to reduce the amount of particulate matter contained in the exhaust makes the internal combustion engine more susceptible to surge.

Therefore, when the engine load factor is below the upper limit of a predetermined load factor range, the internal combustion engine control device sets the upper limit guard value to a value that is smaller than when the engine load factor is higher than the upper limit. When the internal combustion engine is running cold, the control device adjusts the valve overlap amount within a range below the upper limit guard value. This makes it possible to reduce the amount of particulate matter contained in the exhaust while suppressing the occurrence of surges when the internal combustion engine is running cold.

FIG. 1 is a block diagram showing a control device that is an embodiment of an internal combustion engine control device, and an internal combustion engine to which the control device is applied. FIG. 2 is a block diagram showing a number of processes executed by the control device. FIG. 3 is a graph showing the relationship between the optimum value of the valve overlap amount and the upper limit guard value when the engine load factor is changed under the condition that the cooling water temperature and engine speed are maintained.

An embodiment of an internal combustion engine control device will be described below with reference to FIGS.
1 illustrates an internal combustion engine 10 and a control device 60 applied to the internal combustion engine 10. The control device 60 corresponds to the "internal combustion engine control device."

<Structure of an internal combustion engine>
The internal combustion engine 10 includes a plurality of cylinders 11, a plurality of pistons 12, and a crankshaft 13. A piston 12 is housed in each of the cylinders 11 so that it can reciprocate. The pistons 12 are each connected to the crankshaft 13 via a connecting rod 14. Therefore, when an air-fuel mixture containing fuel and air burns in the cylinder 11, power corresponding to the combustion of the air-fuel mixture is transmitted to the crankshaft 13 via the piston 12 and the connecting rod 14. This causes the crankshaft 13 to rotate.

The internal combustion engine 10 includes an intake passage 16, a throttle valve 17, an exhaust passage 21, and a catalytic converter 22. The intake passage 16 is a passage through which air flows to be introduced into the multiple cylinders 11. The throttle valve 17 is installed in the intake passage 16. The flow rate of air flowing through the intake passage 16 is adjusted by adjusting the throttle opening, which is the opening degree of the throttle valve 17. The exhaust passage 21 is a passage through which exhaust gas is discharged from the multiple cylinders 11. The catalytic converter 22 purifies the exhaust gas flowing through the exhaust passage 21.

The internal combustion engine 10 is equipped with multiple intake valves 25 and multiple exhaust valves 26. When an intake valve 25 opens, air is introduced from the intake passage 16 into the cylinder 11 corresponding to that intake valve 25. When an exhaust valve 26 opens, exhaust gas is discharged from the cylinder 11 corresponding to that exhaust valve 26 into the exhaust passage 21.

The internal combustion engine 10 is equipped with an intake valve timing adjustment mechanism 27 (hereinafter referred to as the "intake VVT mechanism 27") and an exhaust valve timing adjustment mechanism 28 (hereinafter referred to as the "exhaust VVT mechanism 28"). The intake VVT mechanism 27 adjusts the opening timing of the intake valve 25. The exhaust VVT mechanism 28 adjusts the opening timing of the exhaust valve 26. If the length of time during which the intake valve 25 and the exhaust valve 26 are simultaneously open is defined as the "valve overlap amount," the valve overlap amount can be changed by operating at least one of the intake VVT mechanism 27 and the exhaust VVT mechanism 28. Therefore, the intake VVT mechanism 27 and the exhaust VVT mechanism 28 correspond to "adjustment mechanisms" that adjust the valve overlap amount.

The internal combustion engine 10 is equipped with a plurality of port injection valves 31 and a plurality of in-cylinder injection valves 32 as fuel injection valves, as well as a plurality of spark plugs 35. A port injection valve 31, an in-cylinder injection valve 32, and a spark plug 35 are provided for each of the plurality of cylinders 11. The port injection valves 31 inject fuel into the intake passage 16. The in-cylinder injection valves 32 inject fuel directly into the cylinders 11. The spark plugs 35 ignite a mixture containing fuel and air within the cylinders 11 by spark discharge.

The internal combustion engine 10 is equipped with an exhaust-driven supercharger 40. The supercharger 40 has a turbine 41 and a compressor 42. The turbine 41 is located in the exhaust passage 21 upstream of the catalytic converter 22. The compressor 42 is located in the intake passage 16 upstream of the throttle valve 17. When the turbine 41 is activated by the flow of exhaust gas, the compressor 42 operates in synchronization with the turbine 41. In this way, the supercharger 40 compresses the air flowing through the intake passage 16.

<Detection system for internal combustion engines>
The detection system of the internal combustion engine 10 includes a plurality of sensors that output signals corresponding to the detection results to the control device 60. The plurality of sensors includes a crank angle sensor 51, a water temperature sensor 52, an air flow meter 53, a boost pressure sensor 54, and an intake pressure sensor 55. The crank angle sensor 51 detects the rotation angle of the crankshaft 13 and outputs a signal corresponding to the rotation speed of the crankshaft 13. The water temperature sensor 52 detects the temperature of the coolant circulating within the internal combustion engine 10. The air flow meter 53 detects the flow rate of air flowing through the intake passage 16. The boost pressure sensor 54 detects the pressure in a portion of the intake passage 16 between the compressor 42 and the throttle valve 17. The intake pressure sensor 55 detects the pressure in a portion of the intake passage 16 downstream of the throttle valve 17.

The rotational speed of the crankshaft 13 based on the detection signal of the crank angle sensor 51 is referred to as the "engine speed NE." The coolant temperature based on the detection value of the water temperature sensor 52 is referred to as the "coolant temperature TMPw." The air flow rate based on the detection value of the air flow meter 53 is referred to as the "intake air amount GA." The pressure based on the detection value of the supercharging pressure sensor 54 is referred to as the "supercharging pressure PTC." The pressure based on the detection value of the intake pressure sensor 55 is referred to as the "intake pressure PIM."

<Control device>
The control device 60 includes a CPU 61 and a memory 62. The memory 62 stores various control programs executed by the CPU 61. The CPU 61 executes the control programs to control the operation of the internal combustion engine 10 based on the detection results of the various sensors. Specifically, the CPU 61 adjusts the opening timing of the intake valve 25, the opening timing of the exhaust valve 26, the ignition timing of the spark plug 35, the throttle opening of the throttle valve 17, the fuel injection amount of the port injection valve 31, and the fuel injection amount of the in-cylinder injection valve 32. In other words, the CPU 61 corresponds to an "execution device."

Here, when the internal combustion engine 10 is operating in cold condition, the control device 60 adjusts the valve overlap amount QVO in order to reduce the number of particulate matter (also referred to as "PM") (also referred to as "PN") contained in the exhaust gas discharged from the multiple cylinders 11 into the exhaust passage 21.

The flow of processing for reducing PN during cold operation of the internal combustion engine 10 will be described with reference to FIGS.
2, the CPU 61 executes the control program to perform the following processes: a scavenging rate calculation process M11, a load rate calculation process M13, a load rate selection process M15, a guard value setting process M17, and an adjustment process M19.

In the scavenge rate calculation process M11, the CPU 61 calculates the scavenge rate RS based on the boost pressure PTC and the valve overlap amount QVO. Specifically, the CPU 61 calculates the scavenge rate RS so that the higher the boost pressure PTC, the higher the scavenge rate RS. The CPU 61 calculates the scavenge rate RS so that the higher the valve overlap amount QVO, the higher the scavenge rate RS.

In the load factor calculation process M13, the CPU 61 calculates the engine load factor, which is the load factor of the internal combustion engine 10. The engine load factor is a parameter that determines the amount of air filled into the cylinder 11, and is the ratio of the amount of air inflow per combustion cycle of one cylinder to a reference amount of air inflow. The reference amount of air inflow varies depending on the engine speed NE. The CPU 61 calculates the engine load factor based on the intake air amount GA and the engine speed NE. The engine load factor calculated in the load factor calculation process M13 is referred to as the "calculated engine load factor value KLC."

In the load rate selection process M15, the CPU 61 uses the scavenge rate RS to select the calculated engine load rate KLC or the required load rate KLR. The required load rate KLR is the engine load rate required of the internal combustion engine 10. When the vehicle driver is operating the accelerator, the greater the accelerator operation amount, the larger the value calculated as the required load rate KLR. The CPU 61 selects the calculated engine load rate KLC when the scavenge rate RS is less than the determined scavenge rate RSth, and selects the required load rate KLR when the scavenge rate RS is less than the determined scavenge rate RSth. A value for determining whether scavenging is occurring in the internal combustion engine 10 from the scavenge rate RS is set as the determined scavenge rate RSth. When the scavenge rate RS is equal to or greater than the determined scavenge rate RSth, scavenging is considered to be occurring. On the other hand, if the scavenging rate RS is less than the determined scavenging rate RSth, it is assumed that scavenging is not occurring. Note that the value selected by the CPU 61 from the calculated engine load rate KLC and the required load rate KLR is referred to as the "selected load rate KLS."

In the guard value setting process M17, the CPU 61 sets an upper limit guard value QVOL for the valve overlap amount QVO. The CPU 61 sets the upper limit guard value QVOL based on the cooling water temperature TMPw, engine speed NE, and selected load factor KLS. In this embodiment, the CPU 61 uses map MP to set the upper limit guard value QVOL to a value corresponding to the cooling water temperature TMPw, engine speed NE, and selected load factor KLS.

Incidentally, the lower the cooling water temperature TMPw, the more likely combustion in the cylinder 11 is to become unstable. The lower the engine speed NE, the more likely combustion in the cylinder 11 is to become unstable. If the valve overlap amount QVO is increased when combustion in the cylinder 11 is unstable, surges are more likely to occur in the internal combustion engine 10.

Therefore, the CPU 61 sets a smaller value as the upper limit guard value QVOL as the cooling water temperature TMPw is lower. The CPU 61 sets a smaller value as the engine speed NE is lower.

Now, referring to Figure 3, the relationship between the likelihood of surge occurring in the internal combustion engine 10 during cold operation and the engine load factor KL will be explained. The solid line in Figure 3 shows the relationship between the optimized value QVOCV of the valve overlap amount QVO and the engine load factor KL when the coolant temperature TMPw and engine speed NE are fixed at certain values. The optimized value QVOCV of the valve overlap amount is the valve overlap amount QVO that minimizes the amount of particulate matter contained in the exhaust. If the coolant temperature TMPw or engine speed NE changes, the magnitude of the optimized value QVOCV will change, i.e., the shape of the solid line in Figure 3 will change.

As a result of various experiments and simulations, the inventors of the present invention have come to the following conclusion: When the engine load factor KL is within the predetermined load factor region RKL shown in Figure 3, if the adaptive value QVOCV corresponding to the engine load factor KL at that time is set as the valve overlap amount QVO, a surge is likely to occur in the internal combustion engine 10.

Therefore, when the selected load rate KLS is equal to or lower than the upper limit KLUL of the specified load rate range RKL, the CPU 61 sets the upper limit guard value QVOL to a value that is lower than when the selected load rate KLS is higher than the upper limit KLUL. Specifically, within the range between a first load rate KL1 that is lower than the lower limit KLDL of the specified load rate range RKL and a second load rate KL2 that is higher than the upper limit KLUL, the CPU 61 sets a higher value as the upper limit guard value QVOL the higher the selected load rate KLS. As a result, when the selected load rate KLS is within the specified load rate range RKL, the CPU 61 can set a higher value as the upper limit guard value QVOL the higher the selected load rate KLS. Note that when the selected load rate KLS is equal to or higher than the upper limit KLUL, the CPU 61 sets the upper limit guard value QVOL so that it does not fall below the compatible value QVOCV.

Returning to Figure 2, in adjustment process M19, the CPU 61 reduces the amount of particulate matter contained in the exhaust emitted from the cylinder 11 into the exhaust passage 21 by adjusting the valve overlap amount QVO within a range equal to or less than the upper limit guard value QVOL. Specifically, the CPU 61 sets the smaller of the optimized valve overlap amount value QVOCV and the upper limit guard value QVOL as the valve overlap amount QVO. The CPU 61 then operates the intake VVT mechanism 27 and the exhaust VVT mechanism 28 based on the valve overlap amount QVO.

As described above, when the selected load rate KLS is equal to or greater than the upper limit KLUL of the specified load rate range RKL, the upper limit guard value QVOL does not fall below the adaptive value QVOCV. Therefore, it can be said that the CPU 61 limits the valve overlap amount QVO to the upper limit guard value QVOL, provided that the selected load rate KLS is equal to or less than the upper limit KLUL.

<Action and effect>
The operation of this embodiment will be described.
During cold operation of the internal combustion engine 10, the intake valve 25 and the exhaust valve 26 may be simultaneously opened to promote vaporization of fuel in the cylinder 11. This increases the temperature of the gas introduced into the cylinder 11 from the intake passage 16. As a result, the temperature inside the cylinder 11 can be increased early, promoting vaporization of fuel inside the cylinder 11.

In this embodiment, the upper limit guard value QVOL is set based on the coolant temperature TMPw, engine speed NE, and engine load factor KL. The valve overlap amount QVO is set within a range equal to or less than the upper limit guard value QVOL. Incidentally, when the engine is operating in an operating range where combustion in the cylinder 11 is likely to become unstable, the upper limit guard value QVOL is set to a smaller value than when this is not the case.

In this embodiment, the following effects can be obtained.
(1) When the engine load factor is equal to or lower than the upper limit KLUL of the predetermined load factor range RKL, the control device 60 sets the upper limit guard value QVOL to a value that is smaller than the value when the engine load factor is higher than the upper limit KLUL. Then, when the internal combustion engine 10 is in cold operation, the control device 60 adjusts the valve overlap amount QVO within a range equal to or lower than the upper limit guard value QVOL. This makes it possible to reduce the amount of particulate matter contained in the exhaust gas discharged from the cylinders 11 to the exhaust passage 21 while suppressing the occurrence of surges in the internal combustion engine 10 during cold operation of the internal combustion engine 10.

(2) As shown in Figure 3, when the engine load factor is within a predetermined load factor range RKL, the upper limit guard value QVOL can be gradually increased as the engine load factor increases. This makes it possible to prevent the valve overlap amount QVO from suddenly increasing or decreasing around the upper limit KLUL when the engine is operated such that the engine load factor gradually increases. As a result, it is possible to prevent vibrations in the internal combustion engine 10 caused by sudden changes in the valve overlap amount QVO.

(3) When scavenging occurs in the internal combustion engine 10, a large amount of air introduced into the cylinders 11 from the intake passage 16 is discharged into the exhaust passage 21 without contributing to combustion. As a result, the deviation between the calculated engine load rate KLC and the actual engine load rate KL may be greater than the deviation between the required load rate KLR and the actual engine load rate KL. Therefore, when the control device 60 determines that scavenging is occurring, it sets the upper limit guard value QVOL using the required load rate KLR instead of the calculated engine load rate KLC. On the other hand, when scavenging is not occurring in the internal combustion engine 10, a small amount of air introduced into the cylinders 11 from the intake passage 16 is discharged into the exhaust passage 21 without contributing to combustion. Therefore, a deviation is unlikely to occur between the calculated engine load rate KLC and the actual engine load rate KL. Therefore, when the control device 60 determines that scavenging is not occurring, it sets the upper limit guard value QVOL using the calculated engine load rate KLC. In this way, by using the calculated engine load factor KLC and the required load factor KLR differently depending on whether scavenging is occurring, the upper limit guard value QVOL can be set appropriately regardless of whether scavenging is occurring.

<Example of change>
The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

The CPU 61 may calculate an average value of the engine load factor based on a plurality of selected load factors KLS arranged in chronological order, and set the upper limit guard value QVOL using the average value.
The CPU 61 does not need to differentiate between the calculated engine load factor KLC and the required load factor KLR depending on whether scavenging is occurring in the internal combustion engine 10. That is, the CPU 61 may set the upper limit guard value QVOL using the calculated value KLC, or may set the upper limit guard value QVOL using the required load factor KLR, regardless of whether scavenging is occurring. In this case, the control device can be applied to an internal combustion engine that does not have a supercharger.

When the engine load factor is within the predetermined load factor range RKL, it is not essential to set the upper limit guard value QVOL to a larger value as the engine load factor increases.
The internal combustion engine may be configured to include only one of the intake VVT mechanism 27 and the exhaust VVT mechanism 28 as long as the valve overlap amount QVO can be adjusted.

- When the internal combustion engine 10 is warming up, the guard value setting process M17 does not need to be executed. This is because surges caused by a large valve overlap amount QVO are less likely to occur in the internal combustion engine 10 during warm-up operation.

The control device 60 is not limited to a device that includes a CPU and a ROM and executes software processing. In other words, the control device 60 may have any one of the following configurations (a) to (c):
(a) The control device 60 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., computer-readable medium, includes any available medium that can be accessed by a general-purpose or special-purpose computer.

(b) The control device 60 is equipped with one or more dedicated hardware circuits that perform various processes. Examples of dedicated hardware circuits include application-specific integrated circuits (ASICs) or FPGAs. ASIC is an abbreviation for "Application Specific Integrated Circuit," and FPGA is an abbreviation for "Field Programmable Gate Array."

(c) The control device 60 includes a processor that executes some of the various processes in accordance with a computer program, and dedicated hardware circuits that execute the remaining processes.

10...internal combustion engine, 11...cylinder, 21...exhaust passage, 22...catalytic device, 25...intake valve, 26...exhaust valve, 27...intake VVT mechanism, 28...exhaust VVT mechanism, 40...supercharger, 60...control device, 61...CPU.

Claims (2)

The present invention is applied to an internal combustion engine including an adjustment mechanism for adjusting a valve overlap amount, which is the length of time during which the intake valve and the exhaust valve are simultaneously open, a catalytic converter for purifying exhaust gas discharged from inside the cylinder into an exhaust passage, and a supercharger ,
an execution device for controlling the operation of the internal combustion engine;
The execution device
a guard value setting process for setting, when an engine load factor that is the load factor of the internal combustion engine is equal to or lower than an upper limit of a predetermined load factor region, a value that is smaller than a value that is used when the engine load factor is higher than the upper limit as an upper limit guard value of the valve overlap amount;
an adjustment process for reducing the number of particulate matters contained in the exhaust gas by adjusting the valve overlap amount within a range equal to or less than the upper limit guard value during cold operation of the internal combustion engine;
a scavenging rate calculation process for calculating a scavenging rate based on the boost pressure of the supercharger and the valve overlap amount ;
In the guard value setting process when the scavenge rate is equal to or greater than a determined scavenge rate, the upper limit guard value is set using a required value of the engine load rate;
In the guard value setting process when the scavenge rate is less than the determined scavenge rate, the upper limit guard value is set using the calculated value of the engine load rate.
Internal combustion engine control device. 2. The internal combustion engine control device according to claim 1, wherein, in the guard value setting process, when the engine load factor is within the predetermined load factor range, the execution device sets a larger value as the engine load factor is higher as the engine load factor is higher.