JP3702798B2 - Catalyst deterioration suppressing device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst deterioration device for an internal combustion engine that generates engine braking force while suppressing deterioration of the catalyst.
[0002]
[Prior art]
In an engine (internal combustion engine) mounted on an automobile (vehicle), a catalyst such as a three-way catalyst, a lean NOx catalyst, or an HC adsorption catalyst is attached to an exhaust path in order to purify exhaust gas.
[0003]
Such a catalyst tends to deteriorate when it is in a high temperature state and in an oxidizing atmosphere. Specifically, a situation where the catalyst is in a high temperature state is, for example, a high speed operation (high load rich operation). In this state, the catalyst is not in an oxidizing atmosphere, but when the state becomes an oxidizing atmosphere thereafter, the catalyst undergoes thermal degradation.
[0004]
In order to suppress such thermal deterioration of the catalyst, an automobile engine is restricted when decelerating from high-speed operation.
[0005]
In this respect, the engine is normally operated in a fuel cut operation in which the fuel supplied to the cylinder is cut in order to accelerate the deceleration and obtain a feeling of deceleration during the deceleration operation when the automobile decelerates. This is because if the engine fuel cut is not performed during deceleration, torque is generated from the engine even during deceleration, and the engine braking force is reduced.
[0006]
However, when the engine is decelerated from high speed operation (high load operation), the catalyst is in an oxidizing atmosphere in addition to being in a high temperature state, so that thermal degradation is promoted. End up.
[0007]
For this reason, when decelerating from high-speed operation (high load operation), to protect the catalyst (suppression of deterioration), forbid the operation that cuts the fuel so that it does not become an oxidizing atmosphere, The means is required to generate a large engine braking force that can compensate for the decrease in engine braking caused by the fuel supply.
[0008]
For this reason, conventionally, the throttle valve in the intake passage is throttled during the intake stroke of the engine, and the throttle loss at this time, that is, the intake loss causes the engine braking force to be reduced when decelerating from high speed operation, and the engine is reduced. Compensation for braking performance has been made.
[0009]
[Problems to be solved by the invention]
By the way, in order to generate a large engine braking force that compensates for the decrease in engine braking caused by the fuel supply only by the throttle loss in the intake stroke, the throttle valve has to increase the throttle amount considerably.
[0010]
However, when the throttle amount increases, the pressure in the manifold, which serves as the intake port of the engine, decreases, and the engine burns at a low pressure, which may deteriorate the combustion state.
[0011]
For this reason, it is difficult to set the throttle amount large in order to ensure good combustion, and there is a situation in which satisfactory engine brake performance cannot be ensured.
[0012]
The present invention has been made paying attention to the above-described circumstances, and an object of the present invention is to provide an internal combustion engine for a vehicle that can secure a large engine braking force that can compensate for engine brake drop caused by prohibition of fuel cut while suppressing thermal deterioration of the catalyst. An object of the present invention is to provide a catalyst deterioration suppressing device for an engine.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a catalyst deterioration suppressing device according to claim 1 includes a sensor that detects a temperature of a catalyst of an internal combustion engine that has a catalyst in an exhaust passage and that can be operated with the fuel cut off during vehicle deceleration. The exhaust throttle can be controlled and the exhaust throttle is controlled when the fuel supply is cut when the vehicle is decelerated. When the vehicle is decelerated, the fuel cut is prohibited and exhausted when the temperature of the catalyst is higher than the specified temperature. The throttle part has a structure having a control means for controlling the throttle with a throttle opening smaller than that at the time of the fuel supply cut operation so that a large engine braking force can be obtained against the torque generated by combustion.
[0014]
As a result, a large engine braking force that compensates for a decrease in engine braking performance caused by the fuel cut prohibition is ensured while suppressing thermal deterioration of the catalyst.
[0015]
In addition to the above object, the catalyst deterioration suppression device according to claim 2 further has a structure in which the intake passage of the internal combustion engine is throttled and controlled together with the exhaust passage so as to suppress the deterioration of combustion under low pressure. The large engine brake is easily secured while ensuring the performance.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the first embodiment shown in FIG. 1 and FIG.
[0017]
FIG. 1 shows a peripheral structure of an internal combustion engine for a vehicle, for example, mounted on an automobile to which the present invention is applied. In FIG. 1, reference numeral 1 denotes an internal combustion engine, for example, a cylinder-injected spark-type reciprocating gasoline engine (hereinafter simply referred to as a reciprocating gasoline engine). Engine).
[0018]
The engine body 1 includes a cylinder block 2 in which a cylinder 2 a is formed, a cylinder head 3 mounted on the upper end of the block 2, and an oil pan 4 attached to the lower end of the cylinder block 2. is there.
[0019]
Of these, the piston 5 is reciprocally accommodated in the cylinder 2a of the cylinder block 2. A combustion chamber 6 is formed on the lower surface of the cylinder head 3 to be combined with the cylinder 2a. A spark plug 3 a is incorporated in the center of the combustion chamber 6. An upright intake port 8 extending from the combustion chamber 6 to the upper end of the cylinder head 3 is formed on one side of the combustion chamber 6 sandwiching the ignition plug 3a, and on the other side of the cylinder block 2 from the combustion chamber 6. An exhaust port 7 extending to one side in the width direction is formed. Camshaft driven intake valves 9 and exhaust valves 10 are incorporated at the ends of the combustion chambers 6 of the intake and exhaust ports 7 and 8, respectively. Further, an electronically controlled injector 11 for injecting fuel into the cylinder 2a is incorporated in a portion near the intake port 8. A predetermined combustion cycle (for example, four cycles of intake, compression, explosion, and exhaust) is performed in the cylinder 2a from the operation of each intake valve 9, exhaust valve 10, and injector 11.
[0020]
The inlet of the intake port 8 is formed by an intake manifold 13, a surge tank 14, an electronically controlled throttle valve 15, an air flow sensor (not shown), and an air cleaner (not shown: all of which constitute an intake passage together with the intake port). Are sequentially opened to the atmosphere so that the combustion air necessary for combustion can be taken into the cylinder 2a. The outlet of the exhaust port 7 is formed by an exhaust manifold 17, an exhaust pipe 18, a catalyst 19 (three-way catalyst, lean NOx catalyst, HC adsorption catalyst, etc.), and a tail pipe 20 (all of which constitute an exhaust path together with the exhaust port). The exhaust gas exhausted from the engine is exhausted to the atmosphere through the passages in order and opened to the atmosphere. Reference numeral 24 denotes a temperature sensor (for example, installed at the catalyst inlet) for detecting the temperature of the catalyst 19.
[0021]
Electronic control devices (an injector 11, a throttle valve 15, an air flow sensor, etc.) for each part of the engine are connected to an ECU 21 (corresponding to a control means) constituted by, for example, a microcomputer. The ECU 21 includes an accelerator position signal from an accelerator position sensor (not shown), an engine speed signal from an engine speed sensor (not shown) for detecting the engine speed, an intake air flow signal from an air flow sensor, and the like. Various target values corresponding to the operating state of the engine are calculated, and a function for controlling the opening degree of the throttle valve 15, the fuel injection amount of the injector 11 and the injection timing is set according to these values.
[0022]
In addition, the ECU 21 can reduce deceleration from, for example, medium / high speed operation by using an accelerator opening signal, an engine speed signal, and a brake signal (not shown) of a brake switch (not shown) that is turned on and off in conjunction with brake pedal operation. Upon detection, a fuel cut function (fuel cut mode) for stopping fuel injection of the injector 11 and a deceleration operation in which the catalyst 19 that causes catalyst deterioration becomes a high temperature state among the deceleration operations (for example, from a high speed operation (high load operation)) In the “deceleration”, a function of prohibiting fuel cut to protect the catalyst 19 from thermal deterioration, that is, a function of continuing fuel injection (fuel cut prohibition mode) is set. The fuel cut is canceled when the engine speed decreases to a predetermined recovery injection start speed.
[0023]
On the other hand, an exhaust passage, for example, a tail pipe 20 downstream of the catalyst 19 is provided with, for example, a normally open electronically controlled throttle valve 25 (corresponding to an exhaust throttle unit) that constitutes the catalyst deterioration suppressing device 23. The throttle of the throttle valve 25 is changed, for example, from a position where the passage of the tail pipe 20 is fully opened to a position where the tail pipe 20 is almost fully closed. The throttle of the throttle valve 25 enables an increase in engine exhaust loss.
[0024]
The throttle valve 25 is operated by the ECU 21 during a deceleration operation in which the catalyst 19 is in a high temperature state (fuel cut prohibition operation), that is, the catalyst temperature detected by the temperature sensor 24 is a predetermined temperature (for example, the heat resistance temperature of the catalyst 23). When the value is greater than or equal to the optimal value determined in a timely manner, it is controlled to the aperture side greatly.
[0025]
Specifically, the ECU 21 has a predetermined value A1 that defines the opening degree of the throttle valve 25 used in the fuel cut prohibition mode and a predetermined value A2 that defines the opening degree of the throttle valve 25 used in the fuel cut mode. It has been determined. These predetermined values A1 and A2 are all determined based on engine operating conditions (engine speed, volumetric efficiency, net average effective pressure, intake air amount, manifold pressure, exhaust volume flow rate, exhaust mass flow rate, fuel cut duration, exhaust pressure) Or a map value (including a fixed value) optimized in advance according to the condition obtained from one or more of the indicators having a correlation therewith. For example, the predetermined value A1 is an opening degree that causes exhaust loss that performs deceleration suitable for the deceleration state while canceling torque generated by combustion during deceleration operation, specifically, a fully closed position or a closed position near the fully closed state. Is set. The predetermined value A2 is set to an opening degree that causes exhaust loss that performs deceleration suitable for the deceleration state in combination with the fuel cut, specifically, for example, a value that is a position opened from the predetermined value A1 (A1 ≦ A2). ). A2 may be fully open.
[0026]
The ECU 21 controls the throttle valve 25 according to the predetermined value A2 during normal deceleration operation, that is, in the fuel cut mode, and predetermined during the deceleration operation with protection of the catalyst 19, that is, in the fuel cut prohibition mode. A function for controlling the throttle valve 25 according to the value A1 is set.
[0027]
This control makes it possible to generate a sufficient engine braking force without forcing a burden on the intake system to deteriorate the combustion in the fuel cut prohibition mode for protecting the catalyst 19 by utilizing the exhaust loss of the engine. I have to. FIG. 2 shows an engine brake control flow using the exhaust loss.
[0028]
If the engine brake control is described with reference to this control flow, it is assumed that the automobile is currently traveling steadily.
[0029]
At this time, the ECU 31 monitors the accelerator opening, the engine speed, the brake switch signal, and the like (step S1), and if not decelerating operation, the injector 11 is in accordance with various target values obtained according to the engine operating state. The fuel injection amount, the injection timing, and the throttle valve 15 are controlled (step S2; normal control). At this time, the throttle valve 25 is fully opened.
[0030]
On the other hand, it is assumed that the driver performs a brake operation during traveling and shifts to a deceleration traveling operation.
[0031]
During this deceleration, if the catalyst temperature falls below a predetermined temperature value (for example, 800 ° C.) (step S3) and the ECU 21 determines that the situation does not cause thermal degradation, the ECU 21 switches to the fuel cut mode (step S4). Stop fuel injection. Then, the throttle valve 25 is controlled to have a throttle opening of a predetermined value A2 determined from the map value corresponding to the operating condition (step S5).
[0032]
On the other hand, if the deceleration travel is deceleration from high speed travel (high load operation), for example, and the temperature of the catalyst 19 rises to a predetermined temperature (for example, 800 ° C.) or higher, the ECU 21 determines that the situation will cause thermal degradation and Switch to the cut inhibition mode (step S6) and continue fuel injection. Then, the throttle valve 25 is controlled so as to have a throttle opening of a predetermined value A1 determined from a map value corresponding to the operating condition (step S7).
[0033]
Then, the exhaust pressure increases (due to the restriction of the exhaust passage) while the engine continues to burn. The engine now exhibits the behavior of increasing exhaust loss.
[0034]
Here, the predetermined value A1 is set to a throttle value (for example, fully closed) at which an exhaust loss necessary for canceling the torque generated by combustion and generating more engine braking force is ensured.
[0035]
In other words, the automobile is decelerated while the engine braking force caused by the exhaust loss is applied (decelerated running without fuel cut).
[0036]
Therefore, a satisfactory engine brake can be obtained.
[0037]
FIG. 3 shows a second embodiment of the present invention.
[0038]
In the present embodiment, not only exhaust loss but also throttle control of the intake passage, for example, throttle control of the throttle valve 15 (corresponding to the intake throttle portion) is used together so as to ensure a larger engine braking force. .
[0039]
Specifically, the ECU 21 has a predetermined value B1 that defines the opening of the throttle valve 15 used in the fuel cut prohibition mode and a predetermined value B2 that defines the opening of the throttle valve 15 used in the fuel cut mode. It has been determined. These predetermined values B1 and B2 are also set from map values (including fixed values) optimized according to the engine operating conditions, as in the case of the predetermined values A1 and A2. For example, the predetermined value B1 is set to an opening that causes an intake loss that performs deceleration suitable for the deceleration state in combination with the exhaust loss within a range in which the combustion state does not deteriorate. The predetermined value B2 is set to an opening degree that causes an intake loss that performs deceleration suitable for the deceleration state in combination with fuel cut and exhaust loss.
[0040]
In the fuel cut mode, the throttle of the throttle valve 25 performed in step S5 is mainly used in combination with this, and the throttle valve 15 is throttled according to the predetermined value B2 shown in step S8 as a sub. Thus, a sufficiently large engine braking force is generated from both the generated intake loss and the exhaust loss.
[0041]
In the fuel cut prohibition mode, the throttle of the throttle valve 25 performed in step S7 is mainly used in combination with this, and the throttle in a range in which the combustion does not deteriorate according to the predetermined value B1 shown in step S9 as a sub. The valve 15 is throttled so that a sufficiently large engine braking force is generated from both the intake loss and the exhaust loss that occur.
[0042]
A structure that secures the engine braking force by combining the intake loss and the exhaust loss has the same effect as the first embodiment. In particular, the structure combining the intake loss and the exhaust loss produces engine braking force due to intake loss due to the restriction of the intake passage that does not cause combustion under low pressure. Furthermore, there is an advantage that a large engine braking force can be secured while suppressing deterioration of combustion and supplementing the engine braking performance brought about by the fuel cut prohibition. Needless to say, even in the fuel cut mode, a larger engine braking force can be secured.
[0043]
In the control flow shown in FIG. 3, the steps other than steps S8 and S9 are the same as the control flow shown in FIG.
[0044]
FIG. 4 shows a third embodiment of the present invention.
[0045]
In the present embodiment, a cooling part, for example, a heat dissipating part 27 provided with a bellows pipe 27a on a part of the tail pipe 20 is formed in the tail pipe 20 part on the upstream side of the throttle valve 25, and immediately before the throttle valve 26. In this structure, the heat of the exhaust gas is dissipated from the heat dissipating part 27.
[0046]
With this structure, the thermal burden on the throttle valve 25 is reduced by the heat radiation of the heat radiating portion 27 performed upstream of the throttle valve 25. Even in the throttle valve 25 having a low heat-resistant temperature, exhaust loss is used. There is an advantage that the engine braking force can be secured. Of course, the cooling part may have a structure in which the heat radiation area is enlarged by a structure other than the heat radiation part 27, for example, a structure in which fins are attached to the outer peripheral surface of the pipe, or a structure in which the fins and the bellows pipe 27a are used in combination. Other structures may also be used.
[0047]
However, in FIG. 4, the same parts as those in FIG.
[0048]
The present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the spirit of the present invention. For example, in the above-described embodiment, an example in which a throttle valve is provided in the exhaust pipe as the exhaust throttle unit has been described. However, the present invention is not limited thereto, and a structure in which a valve is provided in another exhaust passage portion may be used. Of course, the intake throttle portion may be a valve provided in another intake passage portion instead of the throttle valve. In the above-described embodiment, the example in which the throttle valve is provided on the downstream side of the catalyst has been described. However, the present invention is not limited to this, and the throttle valve may be provided on the upstream side of the catalyst. Since the road volume is reduced, there is an advantage that the responsiveness of the fuel cut mode and the fuel cut prohibition mode is improved. In the above-described embodiments, the cylinder injection type gasoline engine is used as the internal combustion engine. However, the present invention is not limited to this, and a gasoline engine or a diesel engine having a structure in which fuel is injected into the intake manifold may be used.
[0049]
【The invention's effect】
As described above, according to the first aspect of the present invention, it is possible to secure a large engine braking force against the torque generated by combustion with the exhaust loss caused by the throttle during vehicle deceleration operation with fuel cut prohibition. it can.
[0050]
Accordingly, it is possible to secure a large engine brake that suppresses the deterioration of the engine brake performance caused by the fuel cut prohibition while suppressing the thermal deterioration of the catalyst.
[0051]
According to the second aspect of the present invention, in addition to the above-described effect, the synergistic effect of the engine braking force caused by the intake air loss while suppressing the deterioration of combustion under low pressure can easily secure a larger engine brake. Play.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration around an engine in which a catalyst deterioration suppressing device according to a first embodiment of the present invention is incorporated.
FIG. 2 is a flowchart showing control during deceleration traveling in the catalyst deterioration device.
FIG. 3 is a flowchart showing control during deceleration traveling, which is a main part of the second embodiment of the present invention.
FIG. 4 is a diagram showing a configuration around an engine which is a main part of a third embodiment of the present invention.
[Explanation of symbols]
1 ... Engine body 15 ... Electronically controlled throttle valve (intake throttle part)
29 ... Catalyst 21 ... ECU (control means)
24 ... temperature sensor 25 ... throttle valve (exhaust throttle part).

Claims (2)

A sensor for detecting the temperature of the catalyst of the internal combustion engine capable of operating with a catalyst in the exhaust path and cutting off the supply of fuel when the vehicle decelerates;
An exhaust throttle unit capable of throttle control of the exhaust passage, and throttled when the fuel supply cut operation at the time of deceleration of the vehicle ;
Control means for prohibiting the fuel cut and controlling the exhaust throttle with a throttle opening smaller than that during the fuel supply cut operation when the temperature of the catalyst is equal to or higher than a predetermined temperature when the vehicle is decelerated. An apparatus for suppressing catalyst deterioration of an internal combustion engine, characterized by comprising: The internal combustion engine has an intake throttle portion that can be throttled in the intake passage,
The control means prohibits the fuel cut and performs both the throttle control of the intake throttle unit and the throttle control of the exhaust throttle unit when the temperature of the catalyst is equal to or higher than a predetermined temperature during vehicle deceleration. 2. The catalyst deterioration suppressing apparatus for an internal combustion engine according to claim 1, wherein

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