JP7493885B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device that controls an internal combustion engine mounted on a vehicle.

In general, a three-way catalyst is installed in the exhaust passage of an internal combustion engine to oxidize/reduce harmful substances HC, CO, and _NOx contained in the exhaust gas discharged from the cylinders to render them harmless. In order to efficiently purify all of HC, CO, and _NOx , it is necessary to keep the air-fuel ratio of the mixture within a certain range near the theoretical air-fuel ratio, called a window.

For this reason, conventionally, an air-fuel ratio sensor is installed in the exhaust passage of an internal combustion engine, and the air-fuel ratio of the gas flowing through the exhaust passage is feedback-controlled to the theoretical air-fuel ratio or a target air-fuel ratio close to the theoretical air-fuel ratio by referring to the output signal of the air-fuel ratio sensor. The ECU (Electronic Control Unit), which is the control device that controls the operation of the internal combustion engine, determines the amount of fuel injected from the injector by multiplying the basic injection amount, which is proportional to the amount of air (fresh air) drawn into the cylinder, by a feedback correction coefficient that varies according to the actual air-fuel ratio of the gas (see, for example, the following patent document).

JP 2010-138791 A

Current three-way catalysts have the ability to store oxygen internally, releasing the stored oxygen when rich air-fuel gas flows in, and absorbing excess oxygen when lean air-fuel gas flows in.

This type of catalyst has the property that its purification efficiency for harmful substances decreases if the air-fuel ratio of the gas does not fluctuate to a certain extent. For example, if a vehicle continues to run steadily at a constant vehicle speed or engine speed and the accelerator pedal depression is stable, the air-fuel ratio will continue to converge near the stoichiometric air-fuel ratio, and as a result (especially when the air-fuel ratio stabilizes near the stoichiometric air-fuel ratio after a history of being rich or lean), the amount of harmful substances emitted may increase.

To avoid such an occurrence, vibration control is implemented, which temporarily forces the gas air-fuel ratio to oscillate between rich and lean so that it crosses the theoretical air-fuel ratio, optimizing the amount of oxygen stored in the catalyst and maintaining a high purification efficiency of harmful substances by the catalyst.

However, the magnitude of the engine torque output by the internal combustion engine increases or decreases due to vibration control of the air-fuel ratio. This fluctuation in engine torque may become large enough to be felt by the vehicle occupants, including the driver, and there is a concern that this may degrade the vehicle's noise and vibration (NV) performance or drivability.

The present invention, which was developed for the first time with an eye on the above problems, aims to minimize the adverse effects of vibration control of the air-fuel ratio.

The present invention provides a control device for controlling an internal combustion engine mounted on a vehicle, and when performing vibration control to forcibly increase or decrease the air-fuel ratio of gas discharged from a cylinder and flowing into an exhaust purification catalyst, the control device for the internal combustion engine is configured to gradually change the air-fuel ratio by setting the amount of change in the air-fuel ratio per combustion opportunity in the cylinder or per unit time to a required value or less that is considered to keep the amount of fluctuation in the engine torque output by the internal combustion engine within an acceptable range.

As a side effect of gradually increasing and decreasing the air-fuel ratio in vibration control, it is also possible to promote early heating of the catalyst, for example, immediately after a cold start of the internal combustion engine.

When performing the vibration control, it is also preferable to retard the ignition timing of the mixture in the cylinder during the period in which the air-fuel ratio is changed to the rich side, compared to the other periods. In this way, it is possible to suppress unnecessary increases in engine torque due to the enrichment of the air-fuel ratio, and to further reduce the fluctuations in engine torque. In addition, in the vibration control, the absolute value of the amount of change in the air-fuel ratio per combustion opportunity or per unit time during the period in which the air-fuel ratio is reduced to the lower limit on the rich side may be set to be greater than the absolute value of the amount of change in the air-fuel ratio per combustion opportunity or per unit time during the period in which the air-fuel ratio is increased to the upper limit on the lean side.

The present invention makes it possible to minimize the adverse effects of vibration control of the air-fuel ratio.

1 is a diagram showing a schematic configuration of a vehicle internal combustion engine and a control device according to an embodiment of the present invention; FIG. 4 is a flowchart showing an example of a procedure of a process executed by the control device according to the embodiment in accordance with a program. FIG. 4 is a timing chart illustrating the contents of control performed by the control device according to the embodiment. FIG. 4 is a timing chart illustrating the contents of control performed by the control device according to the embodiment.

One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overview of an internal combustion engine for a vehicle in this embodiment. The internal combustion engine in this embodiment is a spark-ignition four-stroke engine, and is equipped with multiple cylinders 1 (one of which is shown in FIG. 1). An injector 11 for injecting fuel is provided near the intake port of each cylinder 1. In addition, an ignition plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The ignition plug 12 generates a spark discharge between a center electrode and a ground electrode when an induced voltage generated by an ignition coil is applied to the ignition plug 12.

The intake passage 3 for supplying intake air takes in air from the outside and directs it to the intake port of each cylinder 1. An air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream on the intake passage 3.

The exhaust passage 4 for discharging exhaust gases guides exhaust gases generated as a result of burning fuel in the cylinders 1 from the exhaust ports of each cylinder 1 to the outside. An exhaust manifold 42 and a three-way catalyst 41 for purifying exhaust gases are arranged on this exhaust passage 4.

Air-fuel ratio sensors 43, 44 for detecting the air-fuel ratio of the gas flowing through the exhaust passage 4 are installed upstream and downstream of the catalyst 41 in the exhaust passage 4. The air-fuel ratio sensors 43, 44 may each be an _O2 sensor having a nonlinear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A/F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas.

The exhaust gas recirculation device 2 includes an external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a predetermined location downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3 (in particular, the surge tank 33 or the intake manifold 34).

The ECU0, which is the control device for the internal combustion engine in this embodiment, is a microcomputer system having a processor, memory, an input interface, an output interface, etc. The ECU0 may be configured by connecting multiple ECUs or controllers so that they can communicate with each other via an electrical communication line such as a CAN (Controller Area Network).

The input interface of the ECU0 receives inputs such as a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft of the internal combustion engine and the engine speed, an accelerator opening signal c output from a sensor that detects the accelerator pedal depression amount or the opening of the throttle valve 32 as the accelerator opening (in other words, the engine load rate or engine torque required for the internal combustion engine), an intake air temperature/intake pressure signal d output from a temperature/pressure sensor that detects the intake air temperature and intake pressure in the intake passage 3 (particularly the surge tank 33 or the intake manifold 34), a cooling water temperature signal e output from a water temperature sensor that detects the cooling water temperature of the internal combustion engine, a signal f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41, a signal g output from an air-fuel ratio sensor 44 that detects the air-fuel ratio of the exhaust gas downstream of the catalyst 41, and an atmospheric pressure signal h output from an atmospheric pressure sensor that detects the atmospheric pressure.

The output interface of ECU0 outputs an ignition signal i to the igniter 13 of the spark plug 12, a fuel injection signal j to the injector 11, an opening operation signal k to the throttle valve 32, an opening operation signal l to the EGR valve 23, etc.

The processor of ECU0 interprets and executes programs stored in memory in advance, and calculates operating parameters to control the operation of the internal combustion engine. ECU0 acquires various pieces of information a, b, c, d, e, f, g, and h necessary for controlling the operation of the internal combustion engine via the input interface, and determines the engine speed and estimates the amount of air (fresh air) drawn into cylinder 1. Then, based on the engine speed and intake air volume, etc., it determines various operating parameters such as the required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, required EGR rate (or EGR gas amount), ignition timing (including the number of spark ignitions per combustion), etc. ECU0 applies various control signals i, j, k, and l corresponding to the operating parameters via the output interface.

In determining the fuel injection amount, the ECU 0 first obtains the amount of air taken into the cylinder 1, and then determines a basic amount TP of fuel injection amount that can realize a target air-fuel ratio for that amount of intake air. The amount of intake air is estimated based on the engine speed and intake pressure. If necessary, the estimated value can be corrected according to the intake temperature, atmospheric pressure, etc. If an airflow meter is installed in the intake passage 3, it is possible to directly measure the amount of intake air via the airflow meter.

Next, this basic injection amount TP is corrected by a feedback correction coefficient FAF corresponding to the deviation between the measured air-fuel ratio of the gas flowing into the catalyst 41 and the target air-fuel ratio, and various correction coefficients K determined according to environmental conditions and the like. The correction coefficients FAF and K are each a positive number that increases or decreases from 1. Furthermore, the final fuel injection time T, i.e., the time for which current is supplied to the injector 11 to open it, is calculated taking into account the invalid injection time TAUV during which no fuel is injected even when the injector 11 is opened. The fuel injection time T is calculated as follows:
T = TP x FAF x K + TAUV
The ECU 0 inputs a signal j to the injector 11 for the fuel injection time T, and opens the valve of the injector 11 to inject fuel.

In principle, ECU0 sets the target air-fuel ratio to the theoretical air-fuel ratio or an air-fuel ratio close to that, and adjusts the fuel injection amount so that such an air-fuel ratio can be achieved. In an internal combustion engine that uses gasoline as fuel, the normal target air-fuel ratio is 14.6 or a value close to that.

However, if the air-fuel ratio of the gas flowing into the three-way catalyst 41 does not fluctuate by more than a certain amount, the purification efficiency of harmful substances will actually decrease. Therefore, as shown in FIG. 2, when a situation arises in which it is necessary to fluctuate the air-fuel ratio (step S1), the ECU 0 of this embodiment performs vibration control to temporarily forcibly increase or decrease the air-fuel ratio of the gas flowing into the catalyst 41 (step S2).

The situation in step S1 where the air-fuel ratio should be changed typically occurs when steady driving continues for a certain period of time or more, in which the absolute value of the amount of change per unit time in the vehicle speed or engine speed is smaller than a threshold value, and the absolute value of the amount of change per unit time in the accelerator opening is smaller than a threshold value. In such a situation, the gas air-fuel ratio continues to converge near the theoretical air-fuel ratio, which can result in an increase in the amount of harmful substance emissions.

In the vibration control of step S2, the air-fuel ratio of the gas is oscillated between rich and lean so as to straddle the theoretical air-fuel ratio. In the case of an internal combustion engine that uses gasoline as fuel, for example, a period is provided in which the air-fuel ratio is reduced to about 13.3, which is richer than the theoretical air-fuel ratio, and a period is provided in which the air-fuel ratio is increased to about 16, which is leaner than the theoretical air-fuel ratio.

In addition, as shown in FIG. 3 or FIG. 4, in this embodiment, in the air-fuel ratio oscillation control, the amount of change in the air-fuel ratio for each combustion opportunity (i.e., cycle) or per unit time in each cylinder 1 is set to a required value or less that is considered to be within an acceptable range in which the amount of engine torque fluctuation does not degrade the vehicle's NV performance and drivability, and the air-fuel ratio is changed gradually without being changed suddenly. At this time, the amount of change in the fuel injection amount T for each combustion opportunity or per unit time is also set to a required value or less that is within an acceptable range in which the amount of engine torque fluctuation falls.

The amount of change ΔR in the air-fuel ratio per combustion opportunity or per unit time during the period when the air-fuel ratio decreases to the lower limit on the rich side (e.g., 13.3), and the amount of change ΔL in the air-fuel ratio per combustion opportunity or per unit time during the period when the air-fuel ratio increases to the upper limit on the lean side (e.g., 16) may each be variably adjusted according to one or more of the vehicle speed, engine speed, engine load factor, etc. at that time.

The magnitude of the absolute value of the former change amount ΔR and the magnitude of the absolute value of the latter change amount ΔL are not necessarily equal. The example shown in FIG. 4 is a correction to the timing of spark ignition to the mixture in each cylinder 1 during the vibration control of the air-fuel ratio. In order to maximize the thermomechanical conversion efficiency of the internal combustion engine, the ignition timing is usually set to MBT (Minimum advance for Best Torque), or is as close to MBT as possible as long as it does not cause abnormal combustion such as knocking. In the example shown in FIG. 4, during the period in which the air-fuel ratio is changed to rich, the ignition timing is retarded from such normal timing to offset the increase in engine torque due to the enrichment of the air-fuel ratio. Accordingly, the absolute value of the change amount ΔR of the air-fuel ratio during the period in which the air-fuel ratio is changed to rich is allowed to be larger than the absolute value of the change amount ΔL of the air-fuel ratio during the period in which the air-fuel ratio is changed to lean. In other words, during the period when the air-fuel ratio is changed to a richer state, the air-fuel ratio may be changed more quickly.

In this embodiment, the control device 0 controls an internal combustion engine mounted on a vehicle, and when performing vibration control to forcibly increase or decrease the air-fuel ratio of gas discharged from cylinder 1 and flowing into an exhaust purification catalyst 41, the control device 0 for the internal combustion engine is configured to gradually change the air-fuel ratio by setting the amount of change in the air-fuel ratio per combustion opportunity or per unit time in cylinder 1 to a required value or less that is considered to keep the amount of change in the engine torque output by the internal combustion engine within an acceptable range. According to this embodiment, the fluctuation in engine torque caused by the vibration control becomes sufficiently gentle, making it possible to maintain high NV performance and drivability of the vehicle.

In addition, when the temperature of the catalyst 41 is low, such as immediately after a cold start of the internal combustion engine, by implementing vibration control of the air-fuel ratio and gradually changing the air-fuel ratio as described above, it is possible to heat the catalyst 41 early and promote its activation. If the catalyst 41 is activated early, the amount of harmful substances emitted will be reduced accordingly.

In addition, when implementing the vibration control, it is also possible to retard the ignition timing of the mixture in cylinder 1 during the period in which the air-fuel ratio is changed to rich, compared to other periods. This can suppress unnecessary increases in engine torque due to the enrichment of the air-fuel ratio, and further reduce fluctuations in engine torque.

The present invention is not limited to the embodiment described above in detail. For example, in step S2, the vibration control of the air-fuel ratio may be performed simultaneously for all of the multiple cylinders 1 of the internal combustion engine, or the vibration control may be performed only for some of the cylinders 1, and the air-fuel ratio of the remaining cylinders 1 may still be maintained at or near the theoretical air-fuel ratio.

In addition, the specific configuration of each part and the processing procedures can be modified in various ways without departing from the spirit of the present invention.

The present invention can be applied to the control of an internal combustion engine mounted on a vehicle.

0...Control unit (ECU)
REFERENCE SIGNS LIST 1 cylinder 11 injector 12 spark plug 3 intake passage 4 exhaust passage 41 catalyst 43, 44 air-fuel ratio sensor a vehicle speed signal b crank angle signal c accelerator opening signal f, g air-fuel ratio signal i ignition signal j fuel injection signal

Claims (1)

A control device for controlling an internal combustion engine mounted on a vehicle,
When performing vibration control to forcibly increase or decrease the air-fuel ratio of gas discharged from a cylinder and flowing into an exhaust gas purification catalyst, the amount of change in the air-fuel ratio for each combustion opportunity in the cylinder or per unit time is set to a required value or less that is considered to cause the amount of fluctuation in the engine torque output by the internal combustion engine to fall within an acceptable range , thereby gradually changing the air-fuel ratio,
When the vibration control is performed, the ignition timing of the mixture in the cylinder is retarded during a period in which the air-fuel ratio is changed to a richer value compared to other periods,
A control device for an internal combustion engine, in which, in the vibration control, an absolute value of an amount of change in the air-fuel ratio per combustion opportunity or per unit time during a period in which the air-fuel ratio is reduced to a lower limit on the rich side is set to be larger than an absolute value of an amount of change in the air-fuel ratio per combustion opportunity or per unit time during a period in which the air-fuel ratio is increased to an upper limit on the lean side.

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