JP2009085079A - Catalyst deterioration detection device for internal combustion engine - Google Patents

Abstract

An apparatus for detecting catalyst deterioration of an internal combustion engine capable of more precisely detecting catalyst deterioration.
A catalyst deterioration detection device for an internal combustion engine for detecting deterioration of a catalyst by causing the catalyst to generate heat by supplying the added fuel, and calculating a heat generation amount of the added fuel (step S2) to generate heat generated in the catalyst. Is calculated (step S3), and deterioration of the catalyst is detected based on the calculated calorific value of the added fuel and the amount of heat generated in the catalyst (steps S5 and S6). According to this, even if the fuel properties of the added fuel change, the calorific value of the added fuel is calculated, and this is used as one of the judgment materials for detecting the deterioration of the catalyst. Is possible.
[Selection] Figure 2

Description

  The present invention relates to a catalyst deterioration detection device for an internal combustion engine.

  In general, in an internal combustion engine, a catalyst is disposed in an exhaust passage in order to oxidize unburned components in exhaust gas and purify them so that they are not released into the atmosphere. It is necessary to detect the oxidation ability of such a catalyst while traveling and notify the driver in the event of a failure.

  Therefore, as a method of detecting the oxidation ability of the catalyst while traveling, a method of adding a fixed amount of fuel into the exhaust pipe and oxidizing it on the oxidation catalyst, and detecting the amount of heat obtained as a result and diagnosing the degree of deterioration of the catalyst Is known (see, for example, Patent Document 1).

  Recently, however, the fuel used in a single vehicle has been diversified in addition to gasoline, such as alcohol fuel and biodiesel fuel, so that when the fuel is switched to a fuel with a different calorific value, the catalyst functions normally. However, the amount of heat obtained with the catalyst is different. In recent years, since various mixed fuels including biofuels are becoming mainstream, the calorific value of the fuel is not always constant. For this reason, for example, Patent Document 2 discloses a technique for detecting a calorific value related value related to the calorific value of the fuel and reflecting the calorific value related value in the control of the internal combustion engine, thereby responding to a change in fuel properties. Disclosure.

JP 2006-291742 A JP 2004-239173 A

  By the way, in the method of adding a fixed amount of fuel into the exhaust pipe and oxidizing it on the oxidation catalyst, and detecting the amount of heat obtained and diagnosing the degree of deterioration of the catalyst, the fuel properties of the fuel added to the catalyst change. There is a possibility that the amount of heat generated in the catalyst changes and erroneous detection of catalyst deterioration occurs. In other words, if the fuel property changes, the amount of heat generated by the added fuel that has been added as an oxidizer when the deterioration of the oxidation catalyst is detected is unknown, so even if the amount of heat generated by the catalyst is detected, the amount of heat generated per unit fuel cannot be determined. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalyst deterioration detection device for an internal combustion engine capable of more accurately detecting catalyst deterioration.

  An internal combustion engine catalyst deterioration detection device according to the present invention is a catalyst deterioration detection device for an internal combustion engine that detects the deterioration of the catalyst by causing the catalyst to generate heat by supplying the additional fuel, and calculates the heat generation amount of the additional fuel. A catalyst calorific value calculating means for calculating the calorific value generated in the catalyst, a calorific value generated in the catalyst, and a deterioration of the catalyst based on the calorific value of the added fuel and the calorific value generated in the catalyst. And a deterioration detecting means for detecting.

  According to this configuration, even if the fuel properties of the added fuel change, the calorific value of the added fuel is calculated, and this is used as one of judgment materials for detecting the deterioration of the catalyst. Detection is possible.

  In the above configuration, the added fuel heat generation amount calculating means may employ a configuration in which the heat generation amount of the added fuel is calculated from the combustion state of the fuel in the internal combustion engine.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst deterioration detection apparatus of the internal combustion engine which can detect a catalyst deterioration more precisely is obtained.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Embodiments of the invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram illustrating an example of an internal combustion engine to which a catalyst deterioration detection device according to an embodiment of the present invention is applied. As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 is a vehicular multi-cylinder engine (only one cylinder is shown), and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

  In the cylinder head of the internal combustion engine 1, an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port are provided for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder. An in-cylinder pressure sensor 50 that detects the pressure in the combustion chamber 3 is provided adjacent to the spark plug 7. Further, an injector (fuel injection valve) 12 is disposed in the cylinder head for each cylinder so that fuel is directly injected into the combustion chamber 3. The piston 4 is configured as a so-called deep dish top surface type, and a concave portion 4a is formed on the upper surface thereof. In the internal combustion engine 1, fuel is directly injected from the injector 12 toward the concave portion 4 a of the piston 4 in a state where air is sucked into the combustion chamber 3. As a result, a layer of a mixture of fuel and air is formed (stratified) in the vicinity of the spark plug 7 and separated from the surrounding air layer, and stable stratified combustion is executed.

  The intake port of each cylinder is connected to a surge tank 8 serving as an intake air collecting chamber via a branch pipe for each cylinder. An intake pipe 13 that forms an intake manifold passage is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13.

  An air flow meter 5 for detecting the intake air amount and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side. An intake passage is formed by the intake port, the surge tank 8 and the intake pipe 13.

  On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder, and a catalyst 11 is attached to the exhaust pipe 6. An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. An addition fuel valve 60 for adding fuel to the catalyst 11 is installed on the upstream side of the catalyst 11, and an exhaust temperature sensor 18 for detecting the temperature of the exhaust gas is installed on the downstream side. The added fuel supplied by the added fuel valve 60 is supplied from a tank that stores fuel injected from the injector 12.

  The spark plug 7, the throttle valve 10, the injector 12, the added fuel valve 60, and the like are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as a control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 5 and the exhaust temperature sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the internal combustion engine 1, an accelerator opening sensor 15 that detects the accelerator opening, Various other sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and the ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc. The ECU 20 also functions as a catalyst deterioration detection device.

The catalyst 11 is composed of an oxidation catalyst having oxidation ability. For example, a catalyst using a noble metal such as platinum or palladium as a catalyst component is used. By using this catalyst 11, carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas are oxidized and removed in the presence of oxygen (O ₂ ).

  In the new catalyst 11, a large number of fine particulate catalyst components are uniformly distributed, and the contact probability between the exhaust gas and the catalyst component is maintained high. However, when the catalyst 11 deteriorates, some of the catalyst components disappear, and some of the catalyst components are baked and solidified by exhaust heat and become sintered. In this case, the contact probability between the exhaust gas and the catalyst component is lowered, and the purification rate is lowered.

  Hereinafter, the catalyst deterioration detection process by the ECU 20 will be described with reference to a flowchart shown in FIG. Note that the process shown in FIG. 2 is repeatedly executed at predetermined intervals.

  First, as shown in FIG. 2, it is determined whether the current state is the catalyst deterioration detection mode (step S1). The catalyst deterioration detection mode is a mode that specifies whether or not the deterioration of the catalyst 11 is to be detected. For example, the catalyst deterioration detection mode is turned on only once every time the internal combustion engine 1 is driven to detect the catalyst deterioration. . At this time, a predetermined amount of added fuel is supplied to the catalyst 11 in order to detect deterioration of the catalyst 11. Note that the detection frequency of the catalyst deterioration detection is not limited to this, and can be changed as appropriate.

Next, the heat generation amount q per unit fuel injection amount of the internal combustion engine is detected (step S2). Here, when the fuel injection amount is τ and the heat generation amount of the internal combustion engine is Q, the heat generation amount q per unit fuel injection amount is calculated by the following equation (1).
q = Q / τ (1)

  FIG. 3 is a graph showing the relationship between the alcohol concentration of the alcohol-mixed fuel obtained by mixing alcohol (ethanol) with gasoline and the fuel injection amount τ / heat generation amount Q.

  As can be seen from FIG. 3, when the fuel property (alcohol concentration in this case) changes, the calorific value Q also changes, and the fuel injection amount τ / heat value Q changes linearly.

  Since the fuel injection amount τ is substantially proportional to the injection time of the injector 12, it can be obtained from the injection time of the injector 12.

Further, the heat generation amount Q of the internal combustion engine can be approximately obtained from the following equation (2) from, for example, the pressure P obtained from the in-cylinder pressure sensor 50, the volume V obtained from the crank angle, and the specific heat ratio κ.
Q = ΔPV ^κ (2)

  When the amount of heat Q is obtained by the equation (2), the calculation formula is simple, so that on-board failure detection is possible.

  As another method for obtaining the heat quantity Q, for example, the heat quantity Q can be estimated by installing an ion sensor in the internal combustion engine 1 and detecting the ion current from the ion sensor. In addition, since it is a well-known technique, detailed description is abbreviate | omitted.

  It is also possible to calculate the heat quantity Q by integrating the heat generation rate in the internal combustion engine 1.

Next, the calorific value Q _cat of the catalyst 11 is detected (step S3).
For example, as shown in FIG. 4, the calorific value Q _cat of the catalyst 11 is approximately proportional to the temperature gradient of the exhaust temperature that has passed through the catalyst 11, that is, the temperature rise value. Therefore, by monitoring the temperature detected by the exhaust temperature sensor 18 and detecting the temperature rise value, the calorific value Q _cat of the catalyst 11 is detected.
Can be requested.

Here, the calorific value Q _cat of the catalyst 11 is substantially proportional to the amount of fuel added to the catalyst 11 as shown in FIG. Further, when the catalyst 11 deteriorates for some reason, the calorific value Q _cat of the catalyst 11 decreases. Therefore, the detected calorific value Q _cat is compared with a predetermined threshold, and if the calorific value Q _cat is lower than the threshold, it can be determined that the catalyst 11 has deteriorated.

However, the calorific value Q _cat varies depending not only on the deterioration of the catalyst 11 but also on the properties of the added fuel (calorific value).

For this reason, in the present embodiment, the value of the detected heat generation amount Q _cat is normalized using the heat generation amount q per unit fuel injection amount obtained in step S2 (step S4). In other words, the detected value of the heat generation amount Q _cat is corrected using the heat generation amount q per unit fuel injection amount. The normalized calorific value Q ′ is expressed by the following equation (3).
Q ′ = Q _cat / q (3)

Next, the normalized heat quantity Q ′ is compared with a predetermined threshold value α (step S5). If the heat quantity Q ′ is lower than the threshold value α, it is determined that the catalyst 11 has failed (step S6). That is, the deterioration of the catalyst 11 is detected based on the calculated calorific value q of the added fuel and the calorific value Q _cat generated in the catalyst 11.

  In the above-described embodiment, the case where the added fuel is supplied to the catalyst 11 by the added fuel valve has been described. However, the present invention is not limited to this, and the present invention is also applied to the case of so-called post injection from the injector (fuel injection valve) 12. Can be applied.

  In the above embodiment, the gasoline engine is exemplified as the internal combustion engine. However, the present invention is not limited to this, and the present invention is naturally applicable to a diesel engine or the like.

1 is a schematic diagram illustrating an example of an internal combustion engine to which a catalyst deterioration detection device according to an embodiment of the present invention is applied. It is a flowchart which shows the catalyst deterioration detection process by ECU20. It is a graph which shows the relationship between the alcohol density | concentration of the alcohol mixed fuel which mixed alcohol with gasoline, and fuel injection quantity (tau) / calorific value Q. 3 is a graph showing a relationship between a calorific value Q _cat of a catalyst 11 and a temperature rise value. 3 is a graph showing a relationship between a calorific value Q _cat of a catalyst 11 and a fuel addition amount supplied to the catalyst 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Air flow meter 6 ... Exhaust pipe 11 ... Catalyst 12 Injector 17 Pre-catalyst sensor 18 Post-catalyst sensor 20 Electronic control unit (ECU)
50 ... In-cylinder pressure sensor 60 ... Addition fuel valve Ve ... Exhaust valve Vi ... Intake valve Q ... Heat generation amount _Qcat of internal combustion engine ... Heat generation amount τ of catalyst ... Fuel injection amount q of injector q ... Heat generation per unit fuel injection amount the amount of heat the amount Q '... Q _cat was normalized by q

Claims (3)

A catalyst deterioration detection device for an internal combustion engine that detects the deterioration of the catalyst by causing the catalyst to generate heat by supplying the added fuel,
An added fuel heating value calculating means for calculating a heating value of the added fuel;
A catalyst calorific value calculating means for calculating a calorific value generated in the catalyst;
A deterioration detecting means for detecting deterioration of the catalyst based on the calculated calorific value of the added fuel and the calorific value generated in the catalyst;
A catalyst deterioration detection device for an internal combustion engine, comprising: The added fuel heating value calculating means calculates the heating value of the added fuel from the combustion state of the fuel in the internal combustion engine.
The catalyst deterioration detecting device for an internal combustion engine according to claim 1.   3. The catalyst deterioration detection device for an internal combustion engine according to claim 1, wherein the catalyst is an oxidation catalyst, and the added fuel is added to the catalyst as an oxidant.

Images