JP5868073B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to control of an internal combustion engine mounted on a vehicle or the like.

  If each part of the internal combustion engine is cold, such as during a cold start, the friction loss increases. In addition, if the exhaust gas purification catalyst is cold, the ability to purify harmful components contained in the exhaust gas is reduced. Therefore, for a while after the start of the internal combustion engine, it is usual to warm up the parts of the engine and the catalyst to raise the temperature by increasing the fuel injection amount or increasing the idle speed. (For example, refer to the following patent document).

  By increasing the fuel injection amount for warm-up, the atmosphere in the catalyst tends to be rich in air-fuel ratio, that is, oxygen deficient. For this reason, after the internal combustion engine is started, the purification rate of HC temporarily decreases and the amount of HC emission increases.

JP 2006-283640 A

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and an object of the present invention is to further reduce the HC emission amount after starting the internal combustion engine.

In the present invention, immediately after the internal combustion engine is started, the fuel increase correction is performed to enrich the air-fuel ratio, and it is determined whether or not the exhaust gas purification catalyst has been warmed up to some extent. If this is the case, the fuel cut control is performed to cut the fuel supply at least once by lowering the fuel cut permission rotation speed from the normal level. The control apparatus for the internal combustion engine is configured such that the higher the cooling water temperature of the internal combustion engine is, the lower the temperature is .

  In other words, when the catalyst is warmed up to some extent, the fuel is intentionally cut to send air containing no fuel component to the catalyst.

  According to the present invention, it is possible to further reduce the HC emission amount after starting the internal combustion engine.

The figure which shows the whole structure of the internal combustion engine in one Embodiment of this invention. The figure which shows the relationship between the engine temperature and fuel cut permission rotation speed in control by the control apparatus of the embodiment. The figure which shows the relationship between the engine temperature at the time of starting in the control by the control apparatus of the embodiment, and the threshold value of an integrated intake air amount. The flowchart which shows the example of a procedure of the process which the control apparatus of the embodiment performs in control after starting. The timing chart which shows the example of control by the control apparatus of the embodiment.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine of the present embodiment is, for example, a three-cylinder four-stroke engine, a plurality of cylinders 1 (one of which is shown in FIG. 1), and an injector 11 that injects fuel into each cylinder 1. And an intake passage 3 for supplying intake air to each cylinder 1 and an exhaust passage 4 for discharging exhaust gas from each cylinder 1.

  The intake passage 3 takes in air from the outside and guides it to the intake port of the cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 33, a surge tank 34, and an intake manifold 35 are arranged in this order from the upstream.

  The exhaust passage 4 guides exhaust generated as a result of burning fuel in the cylinder 1 from the exhaust port of the cylinder 1 to the outside. An exhaust manifold 42 and a three-way catalyst 41 are disposed on the exhaust passage 4.

  An ECU (Electronic Control Unit) 2 that controls operation of the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like. The input interface outputs a vehicle speed signal a output from a vehicle speed sensor that detects the vehicle speed, a rotation speed signal b output from a rotation speed sensor that detects the engine rotation speed, and an accelerator sensor that detects the amount of depression of the accelerator pedal. Accelerator opening request signal c, temperature / pressure signal d output from a temperature / pressure sensor for detecting intake air temperature and intake pressure in intake passage 3 (especially surge tank 34), and cooling water temperature of the internal combustion engine are detected. The coolant temperature signal e output from the water temperature sensor, the crank angle signal and cylinder discrimination signal f output from the timing sensor at the end of the intake camshaft, and the predetermined crank angle from the timing sensor at the end of the exhaust camshaft. An exhaust cam signal g or the like output every rotation is input. From the output interface, the fuel injection signal h is output to the injector 11, the ignition signal i is output to the ignition plug (ignition coil thereof), the opening operation signal j is output to the throttle valve 33, and the like. The amount of depression of the accelerator pedal can be considered as a required load (engine output) commanded by the driver.

  The processor of the ECU 2 interprets and executes a program stored in advance in the memory, and controls the operation of the internal combustion engine. The ECU 2 acquires various information a, b, c, d, e, f, and g necessary for operation control of the internal combustion engine via the input interface, and based on them, the intake air amount, the required fuel injection amount, the ignition timing, etc. Is calculated. Then, various control signals h, i, j corresponding to the calculation result are applied via the output interface. Since the calculation method of the control inputs h, i, j can be the same as that of the known operation control of the internal combustion engine, a detailed explanation is omitted.

  The ECU 2 that is the control device of the present embodiment performs an increase correction of the fuel injection amount that controls the air-fuel ratio of the gas charged in the cylinder 1 to be richer than the stoichiometric air-fuel ratio immediately after the start (complete explosion) of the internal combustion engine. Do. This start-up increase correction is intended to warm up each part of the internal combustion engine and the catalyst 41 and quickly increase their temperature.

  However, the increase correction at start is disadvantageous in terms of fuel consumption, so I want to reduce it as much as possible. In addition, the atmosphere in the catalyst 41 becomes rich in the air-fuel ratio, the amount of oxygen stored in the catalyst 41 decreases due to the lack of oxygen, and the purification rate of HC, which is a kind of harmful substance, decreases.

  In view of the above, in this embodiment, when it is determined that the temperature of the catalyst 41 has increased to some extent, a fuel cut is performed in one or a few cycles, and air containing no fuel component is removed from the catalyst. 41.

  Originally, the in-vehicle ECU 2 earns fuel by cutting fuel during deceleration. The ECU 2 starts a fuel cut that stops fuel injection from the injector 11 (and ignition by the spark plug) when a predetermined fuel cut condition is satisfied. The fuel cut condition is that the amount of depression of the accelerator pedal is 0 or less than a threshold value close to 0, and the engine speed is equal to or higher than the fuel cut permission speed.

  During the fuel cut, when a predetermined fuel cut end condition is satisfied, the fuel is returned from the fuel cut and the fuel injection (and ignition) from the injector 11 is resumed. The fuel cut end condition is that the amount of depression of the accelerator pedal exceeds a threshold value, or the engine speed has decreased to the fuel cut return speed.

  In addition, if the ECU 2 determines that the catalyst 41 has been warmed to some extent during the period when the start-up increase correction is performed, the ECU 2 lowers the fuel cut permission rotational speed to near the limit that does not cause engine stall temporarily. In this way, the fuel cut is forcibly induced halfway.

  FIG. 2 shows the relationship between the temperature of the internal combustion engine, the fuel cut permission rotational speed, and the fuel cut return rotational speed. In FIG. 2, the solid line indicates the normal fuel cut permission rotational speed after completion of warm-up, and the broken line indicates the fuel cut return rotational speed. In both the fuel cut permission rotation speed and the return rotation speed, the lower the coolant temperature, the higher the rotation speed. That is, the lower the coolant temperature, the more difficult it is to enter the fuel cut even if the driver depresses the accelerator pedal, and it is easier to return from the fuel cut.

  The chain line in FIG. 2 represents the fuel cut permission rotational speed when it is determined that the catalyst 41 has been warmed to some extent during the start-up increase correction. This permitted rotational speed is lower than the normal permitted rotational speed and higher than the return rotational speed.

  In this embodiment, the ECU 2 refers to the integrated amount of intake air charged in the cylinder 1 as an index indicating the degree of warming up of the catalyst 41. The ECU 2 determines that the temperature of the catalyst 41 has increased to some extent as a result of the accumulated intake air amount immediately after starting the internal combustion engine reaching the threshold value. The intake air amount that fills the cylinder 1 for each cycle can be estimated based on the intake air temperature, the intake air pressure, and the engine speed.

  As shown in FIG. 3, the threshold value to be compared with the integrated intake air amount depends on the temperature of the engine when the internal combustion engine is started. The threshold value is set higher as the cooling water temperature at the start is lower. This is because even if the integrated intake air amount is the same, literally cold start that has passed one day and night since the previous engine stop and a short time that only about ten minutes have passed since the previous engine stop. This is because the temperature condition of the catalyst 41 is different from the time restart.

  FIG. 4 shows a procedure example of processing executed by the ECU 2 after the internal combustion engine is started. The ECU 2 increases the fuel injection amount as a start-up increase correction immediately after the internal combustion engine is completely detonated (step S1) (step S2). Further, immediately after the internal combustion engine is completely exploded, counting of the integrated value of the intake air amount filled in the cylinder 1 is started (step S4). At the same time, a threshold value to be compared with the counted intake air amount is determined based on the coolant temperature immediately after the complete explosion of the internal combustion engine (step S3).

  Then, the determined threshold value is compared with the counted integrated intake air amount (step S5), and if the integrated intake air amount reaches the threshold value, a fuel cut is executed to stop fuel injection in one or a few cycles. (Step S6). Specifically, the fuel cut is induced by lowering the fuel cut permission rotational speed.

  When one or a few fuel cuts are completed (step S7), fuel injection is resumed (step S8). Thereafter, the reduced fuel cut permission rotational speed is returned to the original value.

  It should be noted that the fuel injection amount increase correction at the time of start often ends before the integrated intake air amount exceeds the threshold value. After the start-up increase correction is completed, in principle, the fuel injection amount is controlled so that the air-fuel ratio of the gas charged in the cylinder 1 converges to the target air-fuel ratio, particularly the stoichiometric air-fuel ratio.

  FIG. 5 shows an example of control after the internal combustion engine is started by the ECU 2 of the present embodiment. In the illustrated example, the air-fuel ratio is controlled to be rich by start-up fuel correction for a while immediately after the start, and then the control shifts to the stoichiometric air-fuel ratio. Then, the fuel cut is performed when it is determined that the integrated intake air amount after the start exceeds the threshold value and the catalyst 41 has been warmed to some extent. Due to the start-up increase correction, the oxygen storage amount in the catalyst 41 after the start-up decreases and the HC purification rate decreases, but the oxygen storage amount is restored by the fuel cut, and the HC purification rate also increases. improves. In addition, the oxygen sent to the catalyst 41 by the fuel cut reacts with the fuel component remaining in the catalyst 41 to raise the temperature, so that the temperature of the catalyst 41 can be increased quickly.

  In the present embodiment, immediately after the internal combustion engine is started, the fuel increase correction is performed to enrich the air-fuel ratio, and it is determined whether the exhaust gas purification catalyst 41 has been warmed up to a certain extent. When it is determined that the fuel supply has been performed, the control device 2 for the internal combustion engine is configured to perform the fuel cut control that cuts off the fuel supply at least once.

  According to the control device 2 of the present embodiment, not only can the reduction in the amount of oxygen in the catalyst 41 caused by the start-up increase correction be compensated to improve the HC purification rate after start-up, but also oxygen, fuel components, and the like. It is also possible to raise the temperature of the catalyst 41 using this reaction. Accordingly, it is possible to reduce the increase in the fuel injection amount and the increase in the idle speed after the start, which contributes to the improvement of fuel consumption.

  The fuel cut control is less harmful than the air-fuel ratio lean control, is simple as control, and requires less cost for designing the control device 2. Further, it is not necessary to add other members and mechanisms to the internal combustion engine.

  The present invention is not limited to the embodiment described in detail above. For example, in the above embodiment, the integrated air amount is referred to as an index indicating the degree of warming up of the catalyst 41. However, instead of the integrated air amount, the current catalyst temperature is determined from the engine speed and / or the cooling water temperature or the like. The fuel cut may be executed assuming that the catalyst 41 has been warmed up to some extent when the estimated temperature reaches a threshold value. Alternatively, a sensor for measuring the temperature of the catalyst 41 may be mounted, and the fuel cut may be executed by comparing the actually measured temperature of the catalyst 41 with a threshold value.

  In addition, the specific configuration of each unit, the processing procedure, and the like can be variously modified without departing from the spirit of the present invention.

  The present invention can be used for an internal combustion engine mounted on a vehicle or the like.

DESCRIPTION OF SYMBOLS 1 ... Cylinder 11 ... Injector 2 ... Control apparatus (ECU)
41 ... Catalyst

Claims (1)

Immediately after starting the internal combustion engine, the fuel increase correction for enriching the air-fuel ratio is performed,
Determine if the exhaust gas purification catalyst has warmed up to some extent,
When it is determined that the catalyst has been warmed up to some extent, the fuel cut control is performed to cut off the fuel supply at least once by lowering the fuel cut permission rotation speed from the normal level .
A control device for an internal combustion engine that sets a fuel cut permission rotational speed when it is determined that the catalyst has been warmed to a certain degree or higher as the cooling water temperature of the internal combustion engine is lower .

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