JP2024077669A - Vehicle control method and vehicle control device - Google Patents

Abstract

An appropriate rich spike is performed for both of two exhaust gas purification catalysts arranged in series in the exhaust passage of an internal combustion engine.
[Solution] A control unit 21 controls a first rich spike and a second rich spike to promote regeneration of the exhaust purification capacity of a manifold catalyst 14 and an underfloor catalyst 15 immediately after a fuel cut is performed. The first rich spike and the second rich spike temporarily increase the fuel injection amount so that the equivalence ratio becomes richer than the theoretical equivalence ratio. The first rich spike promotes regeneration of the exhaust purification capacity of the manifold catalyst 14. The second rich spike promotes regeneration of the exhaust purification capacity of the underfloor catalyst 15.
[Selected Figure] Figure 1

Description

The present invention relates to a method and device for controlling a vehicle in which two exhaust purification catalysts are arranged in series in the exhaust passage of an internal combustion engine.

Internal combustion engines that perform a fuel cut to stop fuel injection from the fuel injection valve when a specific fuel cut condition is met while the vehicle is running are widely known.

For example, Patent Documents 1 and 2 disclose a technique for estimating the amount of oxygen storage in an exhaust purification catalyst after such a fuel cut is performed, and performing a rich spike in which the fuel injection amount is temporarily increased according to the catalyst temperature of the exhaust purification catalyst and the estimated amount of oxygen storage.

JP 2005-140011 A JP 2013-15065 A

However, when two exhaust purification catalysts are arranged in series in the exhaust passage, there is a problem in that the temperature of the downstream exhaust purification catalyst located downstream cannot be estimated with as much accuracy as the temperature of the upstream exhaust purification catalyst located upstream. In other words, in a vehicle in which two exhaust purification catalysts are arranged in series in the exhaust passage of an internal combustion engine, when performing a rich spike according to the catalyst temperature to reduce the amount of oxygen storage, there is room for further improvement in performing an appropriate rich spike for both the upstream exhaust purification catalyst and the downstream exhaust purification catalyst.

The vehicle of the present invention is characterized in that, after the fuel cut ends, a first rich spike is performed to temporarily increase the fuel injection amount based on the oxygen storage amount of the first catalyst located upstream, and a second rich spike is performed to temporarily increase the fuel injection amount after the first rich spike is performed in accordance with the catalyst supply heat amount supplied to the second catalyst located downstream.

According to the present invention, it is possible to perform appropriate rich spikes for both the first and second catalysts, and the amount of oxygen storage in the first and second catalysts can be appropriately reduced to prevent deterioration of exhaust performance.

1 is an explanatory diagram showing a schematic overview of a system configuration of a vehicle to which the present invention is applied; 6 is a timing chart showing a case where only a first rich spike is performed after a fuel cut. 6 is a timing chart showing a case where a second rich spike is performed after a fuel cut. 6 is a timing chart showing a case where a second rich spike is not performed after a fuel cut. 4 is a flowchart showing a flow of control of a vehicle according to the present invention. FIG. 2 is a block diagram showing a control flow of the vehicle according to the present invention.

Below, one embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 is an explanatory diagram that shows a schematic overview of the system configuration of a vehicle to which the present invention is applied.

The internal combustion engine 1 is, for example, an in-line multi-cylinder spark ignition internal combustion engine that uses gasoline as fuel and is mounted as a drive source in a vehicle such as an automobile. In other words, the internal combustion engine 1 drives the drive wheels (not shown) of the vehicle in which the internal combustion engine 1 is mounted.

The downstream end of the intake port 4 is connected to the combustion chamber 2 of the internal combustion engine 1 via the intake valve 3, and the upstream end of the exhaust port 6 is connected to the combustion chamber 2 via the exhaust valve 5.

A fuel injection valve 7 is disposed in the intake port 4 to inject fuel (e.g., gasoline) into the intake port 4. The fuel injected from the fuel injection valve 7 is ignited by a spark plug 8 in the combustion chamber 2.

The upstream end of the intake port 4 is connected to an intake passage 9. In the intake passage 9, there are arranged, in order from the upstream side in the direction of intake (air) flow, an air cleaner 10, an air flow meter 11 that detects the amount of intake air, and an electric throttle valve 12 whose opening is controlled by a control signal from a control unit 21 (described later).

The downstream end of the exhaust port 6 is connected to an exhaust passage 13. In the exhaust passage 13, a manifold catalyst 14 as a first catalyst and an underfloor catalyst 15 as a second catalyst are arranged in that order from the upstream side in the exhaust flow direction. The manifold catalyst 14 and the underfloor catalyst 15 are, for example, three-way catalysts. A three-way catalyst can simultaneously purify NOx, HC, and CO in the exhaust with maximum conversion efficiency when the air-fuel ratio is in a so-called window centered on the theoretical air-fuel ratio.

The manifold catalyst 14 is provided at the assembly portion of the exhaust manifold. The underfloor catalyst 15 is disposed, for example, under the floor of the vehicle.

The exhaust passage 13 is provided with an air-fuel ratio sensor 16 and an oxygen sensor 17. The air-fuel ratio sensor 16 is disposed upstream of the manifold catalyst 14. In other words, the air-fuel ratio sensor 16 detects the air-fuel ratio of the exhaust gas at the inlet side of the manifold catalyst 14. The air-fuel ratio sensor 16 has an output characteristic that is approximately linear according to the air-fuel ratio. The oxygen sensor 17 is disposed downstream of the manifold catalyst 14 and upstream of the underfloor catalyst 15. The oxygen sensor 17 detects only the rich/lean exhaust air-fuel ratio. In other words, the oxygen sensor 17 detects the rich/lean exhaust air-fuel ratio at the outlet side of the manifold catalyst 14. In other words, the oxygen sensor 17 detects the rich/lean exhaust air-fuel ratio at the inlet side of the underfloor catalyst 15.

The internal combustion engine 1 also includes various sensors, such as a crank angle sensor 18 that detects the crank angle of the crankshaft (not shown) and an accelerator opening sensor 19 that detects the amount of depression of the accelerator pedal operated by the driver. The crank angle sensor 18 is capable of detecting the engine speed of the internal combustion engine 1.

The detection signals from the various sensors described above are input to the control unit 21.

The control unit 21 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input/output interface.

The control unit 21 optimally controls the amount and timing of fuel injected from the fuel injection valve 7, the ignition timing of the internal combustion engine 1 (spark plug 8), the amount of intake air, etc., based on detection signals from various sensors.

When a predetermined fuel cut condition is met, the control unit 21 performs a fuel cut to stop the fuel supply to the internal combustion engine 1. The fuel cut condition is met, for example, during deceleration after warm-up is complete, when the engine speed is equal to or greater than a predetermined fuel cut speed and the accelerator opening is equal to or less than a predetermined opening. When a predetermined fuel cut recovery condition is met during fuel cut, the control unit 21 resumes the fuel supply to the internal combustion engine 1. The fuel cut recovery condition is met, for example, when the accelerator opening becomes larger than the predetermined opening, or when the engine speed becomes equal to or less than a predetermined fuel cut recovery speed without the accelerator pedal being depressed. In other words, the control unit 21 corresponds to a first control unit.

In addition, the manifold catalyst 14 and underfloor catalyst 15 have absorbed a large amount of oxygen due to the fuel cut, making it difficult to reduce NOx.

The control unit 21 therefore controls the first and second rich spikes, which are performed immediately after a fuel cut is performed, to promote regeneration of the exhaust purification ability (NOx reduction ability) of the manifold catalyst 14 and the underfloor catalyst 15. The first and second rich spikes temporarily increase the fuel injection amount so that the equivalence ratio becomes richer than the stoichiometric equivalence ratio. In other words, the first and second rich spikes temporarily increase the fuel injection amount so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. In other words, the control unit 21 corresponds to the second control unit and the third control unit.

The first rich spike is performed after the fuel cut described above ends, based on the temperature of the manifold catalyst 14 and the amount of oxygen storage in the manifold catalyst 14. In other words, the first rich spike promotes the regeneration of the exhaust purification ability (NOx reduction ability) of the manifold catalyst 14.

The catalyst temperature of the manifold catalyst 14 is estimated, for example, using a physical model from the internal combustion engine 1 to the manifold catalyst 14, based on the operating state of the internal combustion engine 1, such as the intake air volume of the internal combustion engine 1, the torque of the internal combustion engine 1, and the air-fuel ratio of the internal combustion engine 1. The temperature of the manifold catalyst 14 may be detected by a temperature sensor.

The amount of oxygen storage in the manifold catalyst 14 can be calculated (estimated), for example, using the output signal of the oxygen sensor 17. The calculation of the amount of oxygen storage is performed by the control unit 21.

The first rich spike is performed according to a first rich spike amount (first rich spike execution time) obtained by multiplying the basic first rich spike amount (basic first rich spike execution time) by the first rich spike temperature correction function. In other words, the first rich spike is performed for the first rich spike execution time corresponding to the first rich spike amount. The first rich spike amount is calculated taking into account the oxygen storage amount and the catalyst temperature of the manifold catalyst 14.

The basic first rich spike amount (basic first rich spike execution time) is calculated based on the amount of oxygen storage accumulated in the manifold catalyst 14 during fuel cut. The basic first rich spike amount (basic first rich spike execution time) becomes larger (longer) as the amount of oxygen storage increases.

The first rich spike temperature correction function is a function that depends on the catalyst temperature of the manifold catalyst 14, and corrects the basic first rich spike amount (basic first rich spike implementation time) so that the higher the catalyst temperature of the manifold catalyst 14, the larger the first rich spike amount (the longer the first rich spike implementation time).

The first rich spike takes longer to execute as the catalyst temperature of the manifold catalyst 14 increases and the amount of oxygen storage increases.

The first rich spike amount is calculated with high accuracy by taking into account the oxygen storage amount and the catalyst temperature of the manifold catalyst 14.

The second rich spike is performed immediately following the first rich spike. The second rich spike promotes regeneration of the exhaust purification ability (NOx reduction ability) of the underfloor catalyst 15.

Here, the catalyst temperature of the underfloor catalyst 15 can be estimated based on the operating state of the internal combustion engine 1, such as the intake air volume of the internal combustion engine 1, the torque of the internal combustion engine 1, and the air-fuel ratio of the internal combustion engine 1, using a physical model from the internal combustion engine 1 to the underfloor catalyst 15, for example. However, when estimating using a physical model from the internal combustion engine 1 to the underfloor catalyst 15, the distance from the internal combustion engine 1 to the underfloor catalyst 15 becomes long, so the estimation error of the amount of decrease in the exhaust temperature that decreases between the internal combustion engine 1 and the underfloor catalyst 15 becomes large, and there is a risk that the temperature of the underfloor catalyst 15 cannot be estimated accurately overall. In other words, when estimating the catalyst temperature of the underfloor catalyst 15 using a physical model from the internal combustion engine 1 to the underfloor catalyst 15, the underfloor catalyst 15 may be erroneously determined to be activated when it is not activated, and a second rich spike may be performed, which may deteriorate the exhaust performance.

The second rich spike is therefore performed when it is determined that the underfloor catalyst 15 is in an activated state if the amount of catalyst supply heat supplied to the underfloor catalyst 15 is equal to or greater than a predetermined value Q. In other words, the second rich spike is not performed if the amount of catalyst supply heat is less than the predetermined value Q. The predetermined value Q is set in advance to ensure activation of the underfloor catalyst 15.

The second rich spike is performed for a preset period of time regardless of the amount of heat supplied to the catalyst, as long as the amount of heat supplied to the catalyst is equal to or greater than a predetermined value Q. In other words, the second rich spike is performed for a fixed period of time regardless of the catalyst temperature of the underfloor catalyst 15. The second rich spike is performed so that, assuming that the oxygen storage amount of the underfloor catalyst 15 is at its maximum value, the oxygen storage amount is reduced to, for example, 50% of the maximum value.

The amount of heat supplied to the catalyst can be calculated (estimated) based on, for example, the engine speed, ignition timing, intake air volume, and fuel injection volume of the internal combustion engine 1. The amount of heat supplied to the catalyst is calculated by the control unit 21. The amount of heat supplied to the catalyst is the cumulative value of the amount of heat supplied to the inlet side of the underfloor catalyst 15.

Figure 2 is a timing chart showing the case where only the first rich spike is performed after a fuel cut.

Time t1 in Figure 2 is the timing when the fuel cut condition is met and fuel cut begins.

Time t2 in FIG. 2 is the timing when the fuel cut recovery condition is met and the fuel cut ends. The first rich spike request flag, which is turned on (ON) when the first rich spike is performed, switches from off (OFF) to on at time t2 in FIG. 2. The first rich spike is performed for a period according to the first rich spike amount at time t2. Time t3 in FIG. 2 is the timing when the first rich spike request flag switches from on to off. In other words, the first rich spike is performed between time t2 and time 3 in FIG. 2. Time t3 in FIG. 2 is set according to the first rich spike amount at time t2 in FIG. 2. FIG. 3 is a timing chart showing the case where a second rich spike is performed after a fuel cut.

Time t1 in Figure 3 is the timing when the fuel cut condition is met and fuel cut begins.

Time t2 in Figure 3 is the timing when the fuel cut recovery condition is met and the fuel cut ends. The first rich spike request flag switches from off (OFF) to on at the timing of time t2 in Figure 3.

Time t3 in Figure 3 is the timing when the first rich spike request flag switches from on to off. The second rich spike request flag, which is turned on (ON) when the second rich spike is performed, switches from off (OFF) to on at time t3 in Figure 3. In the example in Figure 3, the catalyst supply heat amount is equal to or greater than the predetermined value Q at time t2, so the second rich spike request flag is on at time t3.

By performing the second rich spike consecutively with the first rich spike, it is possible to suppress deterioration of exhaust performance (generation of NOx). If the first rich spike and the second rich spike are not performed consecutively, there is a risk that exhaust performance will deteriorate (generation of NOx) during that time.

Time t4 in FIG. 3 is the timing when a preset predetermined time has elapsed from time t3 in FIG. 3. Time t4 in FIG. 3 is the timing when the second rich spike request flag switches from on to off. The second rich spike is carried out between time t3 and time t4 in FIG. 3.

Figure 4 is a timing chart showing the case where the second rich spike is not performed after the fuel cut.

Time t1 in Figure 4 is the timing when the fuel cut condition is met and fuel cut begins.

Time t2 in Figure 4 is the timing when the fuel cut recovery condition is met and the fuel cut ends. The first rich spike request flag switches from off (OFF) to on at the timing of time t2 in Figure 4.

Time t3 in Figure 4 is the timing when the first rich spike request flag switches from on to off. In the example of Figure 4, because the amount of heat supplied to the catalyst is less than the predetermined value Q at time t2, the second rich spike request flag does not turn on at time t3, and the second rich spike is not performed.

Figure 5 is a flowchart showing the control flow of the internal combustion engine 1 mounted on the vehicle of the above-mentioned embodiment.

In step S1, it is determined whether or not the fuel cut conditions are met. If it is determined in step S1 that the fuel cut conditions are met, the process proceeds to step S2, where fuel cut is implemented (started). If it is not determined in step S1 that the fuel cut conditions are met, the current routine is terminated.

In step S3, it is determined whether or not the fuel cut recovery condition is satisfied. If it is determined in step S3 that the fuel cut recovery condition is satisfied, the process proceeds to step S4, where the fuel cut is terminated. If it is determined in step S3 that the fuel cut recovery condition is not satisfied, the process proceeds to step S2, where the fuel cut is continued.

In step S5, it is determined whether the amount of heat supplied to the catalyst is equal to or greater than a predetermined value Q. If it is determined in step S5 that the amount of heat supplied to the catalyst is equal to or greater than the predetermined value Q, the process proceeds to step S6, and then to step S7. If it is determined in step S5 that the amount of heat supplied to the catalyst is less than the predetermined value Q, the process proceeds to step S8.

In step S6, the first rich spike is performed. In step S7, the second rich spike is performed. In step S8, the first rich spike is performed.

Figure 6 is a block diagram showing the control flow of the internal combustion engine 1 mounted on the vehicle of the above-mentioned embodiment.

In step S11, the catalyst temperature of the manifold catalyst 14 is estimated. In step S12, the amount of heat supplied to the catalyst is calculated. In step S13, the first rich spike amount is calculated at a predetermined timing using the catalyst temperature of the manifold catalyst 14, the detection signal from the oxygen sensor 17, the intake air volume which is the detection signal from the air flow meter 11, fuel cut information, etc., and the first rich spike is performed.

In step S14, a target air-fuel ratio is calculated based on the first rich spike amount calculated in step S13 or the second rich spike amount calculated in step S16 described below. In step S15, a fuel injection amount from the fuel injection valve 7 is calculated so that the air-fuel ratio of the internal combustion engine 1 becomes the target air-fuel ratio calculated in step S14. In step S16, a second rich spike amount is calculated at a predetermined timing using the catalyst supply heat amount and the on/off information of the first rich spike request flag from step S13.

As explained above, after a fuel cut is performed, the vehicle is able to perform appropriate rich spikes (a first rich spike for the manifold catalyst 14 and a second rich spike for the underfloor catalyst 15) on the manifold catalyst 14 and the underfloor catalyst 15, respectively. Therefore, after a fuel cut is performed, the vehicle is able to appropriately reduce the amount of oxygen storage in the manifold catalyst 14 and the underfloor catalyst 15, respectively, and is able to suppress deterioration of the exhaust performance of the internal combustion engine 1.

Although specific examples of the present invention have been described above, the present invention is not limited to the above examples, and various modifications are possible without departing from the spirit of the present invention.

For example, the second rich spike may be performed if the amount of heat supplied to the catalyst is equal to or greater than a predetermined value Q when the first rich spike is completed. In other words, the second rich spike may not be performed if the amount of heat supplied to the catalyst is less than the predetermined value Q when the first rich spike is completed.

The above-described embodiments relate to a vehicle control method and a vehicle control device.

Reference Signs List 1 internal combustion engine 2 combustion chamber 3 intake valve 4 intake port 5 exhaust valve 6 exhaust port 7 fuel injection valve 8 spark plug 9 intake passage 10 air cleaner 11 air flow meter 12 throttle valve 13 exhaust passage 14 manifold catalyst 15 underfloor catalyst 16 air-fuel ratio sensor 17 oxygen sensor 18 crank angle sensor 19 accelerator opening sensor 21 control unit

Claims (7)

A method for controlling a vehicle in which two exhaust gas purification catalysts are arranged in series in an exhaust passage of an internal combustion engine, comprising:
a fuel cut is performed to stop fuel injection from a fuel injection valve that supplies fuel to the internal combustion engine when a predetermined fuel cut condition is satisfied while the vehicle is running, and when a predetermined fuel cut recovery condition is satisfied during the fuel cut, fuel injection from the fuel injection valve is resumed;
A vehicle control method characterized by implementing a first rich spike in which the fuel injection amount is temporarily increased based on the oxygen storage amount of a first catalyst located upstream after the fuel cut is completed, and implementing a second rich spike in which the fuel injection amount is temporarily increased after the first rich spike is implemented in accordance with the amount of catalyst supply heat supplied to a second catalyst located downstream. The vehicle control method according to claim 1, characterized in that the second rich spike is performed after the first rich spike is performed. The vehicle control method according to claim 2, characterized in that the second rich spike is performed for a predetermined time period regardless of the temperature of the second catalyst. The vehicle control method according to claim 3, characterized in that the second rich spike is not performed when the amount of heat supplied to the catalyst is less than a predetermined value. The vehicle control method according to claim 1, characterized in that the first rich spike is performed for a longer period of time as the catalyst temperature of the first catalyst increases. The vehicle control method according to claim 1, characterized in that the first rich spike is performed for a longer period of time as the amount of oxygen storage increases. A first catalyst for purifying exhaust gas is disposed in an exhaust passage of the internal combustion engine;
a second catalyst for purifying exhaust gas, the second catalyst being disposed downstream of the first catalyst;
a first control unit that performs a fuel cut to stop fuel injection from a fuel injection valve that supplies fuel to the internal combustion engine when a predetermined fuel cut condition is satisfied while the vehicle is traveling, and resumes fuel injection from the fuel injection valve when a predetermined fuel cut recovery condition is satisfied during the fuel cut;
a second control unit that controls a first rich spike that temporarily increases a fuel injection amount based on an oxygen storage amount of the first catalyst after the fuel cut is completed;
and a third control unit that controls a second rich spike that temporarily increases the fuel injection amount after the first rich spike is performed in accordance with the amount of catalyst supply heat supplied to the second catalyst.

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