JP5125298B2 - Fuel supply control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel supply control device for an internal combustion engine that reduces and removes oxides such as NOx trapped (collected) in an exhaust purification catalyst by supplying fuel (HC) into exhaust gas as a reducing agent.

  In Patent Document 1, the air-fuel mixture is discharged unburned when a misfire occurs, and an increase in the oxygen concentration in the exhaust at that time is detected by an air-fuel ratio sensor, or the increase in the HC concentration in the exhaust is detected by the HC sensor. It is disclosed that a misfire determination is performed by detecting the above.

In Patent Document 2, the detection value shifts to the lean side when high molecular weight HC is present in the exhaust gas when detecting with a wide-area air-fuel ratio sensor, so that the exhaust gas calculated based on the air-fuel ratio detection value is entered. Is corrected in consideration of the deviation of the air-fuel ratio detection value.
JP 2001-289111 A JP 2005-146900 A

  However, Patent Document 1 does not detect the amount of HC in the exhaust gas, and Patent Document 2 also predicts the deviation of the air-fuel ratio sensor from the attached fuel amount, and the actual amount of HC in the exhaust gas. Cannot be detected accurately.

  Therefore, the amount of fuel as a reducing agent supplied to the NOx trap catalyst or the like cannot be adjusted.

  The present invention has been made paying attention to such a conventional problem, and aims to accurately estimate the amount of HC in the exhaust gas. Further, the estimated amount of HC traps the NOx trap catalyst or the like. Another object is to appropriately adjust the amount of fuel as a reducing agent used when desorbing oxides such as NOx.

For this reason, the first invention provides an exhaust purification catalyst having a function of accumulating oxides in the exhaust in the exhaust passage of the engine,
Reducing fuel supply control means for controlling the supply of reducing fuel for reducing and purifying the oxide accumulated in the exhaust purification catalyst;
Intake air amount detection means for detecting the amount of air sucked into the engine;
An excess air ratio detecting means for detecting an excess air ratio in the engine exhaust;
The excess air ratio calculated from the detected value of the intake air amount and the set value of the fuel amount supplied upstream from the excess air ratio detection unit, and the excess air ratio detected by the excess air ratio detection means Exhaust HC amount estimation means for estimating the HC amount present in the exhaust based on the deviation amount obtained by the ratio or difference with the detected value, and correcting the HC amount in the exhaust based on the detected value of the exhaust temperature When,
Reducing fuel supply amount correction means for correcting the supply amount of the reducing fuel based on the exhaust HC amount estimated by the exhaust HC amount estimating means;
Including
The reducing fuel supply control means supplies the reducing fuel by fuel injection in the exhaust stroke to the engine combustion chamber or fuel injection into the exhaust passage ,
The excess air ratio detection means is provided downstream of the reducing fuel supply unit and upstream and downstream of the exhaust purification catalyst,
The exhaust HC amount estimation means estimates the exhaust HC amount upstream of the exhaust purification catalyst based on the detection value of the upstream excess air ratio detection means and the calculated excess air ratio, and the downstream air Estimating the amount of HC in the exhaust downstream of the exhaust purification catalyst based on the detected value of the excess ratio detection means and the calculated excess air ratio,
The reduction fuel supply amount correction means is consumed for the reduction of NOx trapped in the exhaust purification catalyst due to the difference between the exhaust HC amount upstream of the exhaust purification catalyst and the exhaust HC amount downstream of the exhaust purification catalyst. Estimating the HC amount, and correcting the supply amount of the reducing fuel based on the estimated value and the target value of the consumed HC amount,
It is characterized by that.

  According to the first invention, when the amount of HC in the exhaust gas increases, as shown in FIG. 5, it has been found that the detection value of the excess air ratio detecting means shifts to the lean side due to the liquid HC occupying a large proportion thereof. Therefore, using this characteristic, the amount of HC in the exhaust gas can be estimated based on the amount of deviation between the calculated excess air ratio calculated value and the detected value.

  According to the second invention, the amount of fuel (HC) supplied as a reducing agent for reducing and removing oxide (NOx) accumulated in an exhaust purification catalyst such as a NOx trap catalyst is set as described above. By correcting according to the estimated amount of HC in the exhaust gas, it is possible to adjust to an appropriate supply amount.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a system configuration of a diesel engine 1 as an internal combustion engine provided with a fuel supply control device according to the present invention.

  A compressor 3a of a variable displacement turbocharger 3 such as a variable nozzle type is disposed upstream of the intake passage 2 of the engine 1, and the intake air is supercharged by the compressor 3a and then cooled by an intercooler 4 to be electronic After passing through the control type intake throttle valve 5, it flows into the combustion chamber of each cylinder through the collector 6.

  The fuel is increased in pressure by the fuel injection pump 7 and sent to the common rail 8 and is directly injected into the combustion chamber from the fuel injection valve 9 of each cylinder. The air that has flowed into the combustion chamber and the injected fuel are combusted by compression ignition, and the exhaust gas flows out into the exhaust passage 10. The fuel injection pump 7, the common rail 8, and the fuel injection valve 9 constitute a common rail fuel injection device.

  Here, downstream of the exhaust turbine 3b in the exhaust passage 10, NOx in the exhaust is trapped when the exhaust air-fuel ratio is lean (oxidizing atmosphere), and the trapped NOx is desorbed and purified when the exhaust air-fuel ratio is rich. A possible NOx trap catalyst 12 is arranged. Further, a diesel particulate filter (hereinafter referred to as DPF) 13 that collects PM (Particulate Matter) that is particulate matter (exhaust particulate) in the exhaust is disposed downstream of the NOx trap catalyst 12.

  An EGR passage 14 is provided for returning a part of the exhaust gas flowing out to the exhaust passage 10 from the upstream side of the exhaust turbine 3a to the intake side as EGR gas, and the EGR passage 14 is provided with an EGR gas cooler 15 for cooling the EGR gas. And an EGR valve 16 for adjusting the EGR amount is interposed.

  For control of the engine 1, the control unit 20 includes a rotational speed sensor 21 for detecting the engine rotational speed Ne, an accelerator opening sensor 22 for detecting the accelerator opening APO, an air flow meter 23 for detecting the intake air amount Qac, an intake air Signals are input from the intake air temperature sensor 24 for detecting the temperature Ta and the water temperature sensor 25 for detecting the engine cooling water temperature Tw.

  The exhaust passage 10 also has an upstream air-fuel ratio sensor 26 that detects an exhaust air-fuel ratio (hereinafter referred to as exhaust λ, expressed as an excess air ratio) on the upstream side and downstream side of the NOx trap catalyst 12 and a downstream side. A side air-fuel ratio sensor 27, an exhaust temperature sensor 28 for detecting the exhaust temperature upstream of the NOx trap catalyst 12, and DPF temperature sensors 29, 30 for detecting temperatures on the upstream and downstream sides of the DPF 14 (DPF temperatures). The signal is also input to the control unit 20.

  Based on these input signals, the control unit 20 controls the fuel injection amount of the fuel injection by the fuel injection valve 9 and the fuel injection command signal to the fuel injection valve 9 for injection timing control, and the opening to the intake throttle valve 5. A command signal, an opening command signal to the EGR valve 16 and the like are output. Further, the supercharging pressure is feedback-controlled by controlling the variable nozzle based on a signal from a variable nozzle sensor (not shown) of the turbocharger 3.

  Here, the control unit 20 performs exhaust purification control such as desorption purification of NOx trapped by the NOx trap catalyst 13 and regeneration of the DPF 14 by combustion removal of PM collected and accumulated in the DPF 14.

  NOx desorption purification is performed by supplying fuel as a reducing agent by post-injection in the exhaust stroke of the fuel injection valve 9 or by providing a dedicated injector separately from the fuel injection valve 9 in the exhaust. This is done by supplying fuel directly.

  During the NOx desorption purification, the amount of fuel as a reducing agent is feedback-corrected and adjusted to an appropriate amount while estimating the amount of HC in the exhaust gas.

  Such NOx desorption purification control will be described in detail below.

  FIG. 2 is a flowchart showing a main routine of NOx desorption purification control.

  In step S1, detection values from various sensors are read.

  In step S2, the NOx deposition amount trapped and deposited on the NOx trap catalyst is calculated based on these detected values. For example, it may be estimated from the integrated value of the engine speed, or may be estimated from the travel distance. When the integrated value is used, the integrated value is reset when NOx desorption purification is completed.

  In step S3, it is determined whether or not a rich spike control timing for desorbing and purifying NOx by air-fuel ratio enrichment is reached, depending on whether or not the accumulation amount has reached a predetermined value.

  When it is determined that the rich spike control time has been reached, the process proceeds to step S4, and the rich spike determination flag is set to 1.

  In step S5, the reducing agent supply amount in the rich spike control is calculated. Specific calculation will be described later.

  In step S6, the amount of fuel injected in the exhaust stroke of the fuel injection valve 9 or the amount of fuel directly injected into the exhaust by the dedicated injector is controlled based on the reducing agent supply amount.

  FIG. 3 shows a first embodiment of the subroutine for calculating the reducing agent supply amount in step S5, that is, the control for estimating the HC amount in the exhaust during the rich spike control and feedback correcting the reducing agent supply amount. The form is shown.

  In the first embodiment, the detected values of the upstream air-fuel ratio sensor 25 and the downstream air-fuel ratio sensor 26 provided on the upstream side and the downstream side of the NOx trap catalyst are used.

  In step S11, a target reducing agent supply amount commensurate with the NOx accumulation amount is calculated based on the operating state (rotation speed, load) of the engine 1, the water temperature Tw, the intake air temperature Ta, the exhaust gas temperature Tex, and the like. This is because even if the NOx accumulation amount is determined, the reduction efficiency of the fuel (HC), which is a reducing agent, and NOx varies depending on the operating state and temperature state of the engine.

  In step S12, the calculated excess air ratio λcal is calculated from the intake air amount Qa detected by the air flow meter 22 and the fuel amount Qf supplied to the upstream side of the NOx trap catalyst by the following equation. Here, the fuel amount Qf is the amount of combustion fuel injected for combustion in the combustion chamber from the fuel injection valve 9 and the amount of fuel for reduction supplied as a reducing agent for NOx (from the fuel injection valve 9 to the exhaust stroke). The amount of fuel injected or the amount of fuel supplied into the exhaust gas from a dedicated injector) is taken as the total amount of fuel.

λcal = Qa / (Qf × 14.6)
In step S13, the difference Δλf between the calculated excess air ratio λcal and the detected value λfs of the upstream air-fuel ratio sensor 25, and the difference Δλr between the excess air ratio λcal and the detected value λfr of the downstream air-fuel ratio sensor 26 are calculated. Is calculated as follows.

Δλf = λfs / λcal
Δλr = λrs / λcal
In step S14, based on the deviations Δλf and Δλr, HCf0 and HCr0, which are HC amounts in the exhaust gas in the respective sensor detection units, are calculated (searched) from a characteristic table of Δλ-HC amount in exhaust gas shown in FIG. To do.

  FIG. 4 shows a characteristic in which the amount of HC in the exhaust gas increases as the deviation Δλ increases. As shown in FIG. 5, the deviation Δλr on the downstream side is larger than the deviation Δλf on the upstream side. Thus, the upstream HC amount HCf0 is larger than the downstream HC amount HCr0.

  Here, the relationship between the deviation amount of the air-fuel ratio (excess air ratio) detected value by the air-fuel ratio sensor and the HC amount in exhaust gas will be considered.

  If the HC in the exhaust exists in a liquid state (including a high-density state close to the liquid state), the air-fuel ratio sensor cannot detect the liquid HC, and the detected value of the air-fuel ratio is on the lean side accordingly. Shift.

  Therefore, if the amount of deviation Δλ of the air-fuel ratio detection value to the lean side is known, the amount of liquid HC in the exhaust can be estimated.

  Further, the ratio of the supplied reducing agent (HC) to the total amount of HC present in liquid form in the exhaust gas is large, and the ratio is the post injection timing when the reducing agent is supplied by post injection. If conditions such as temperature are constant, it is determined to be substantially constant, so that the total amount of HC in exhaust including non-liquid (vaporized) HC can be estimated from the amount of liquid HC in exhaust.

  Therefore, the relationship between the deviation Δλ and the amount of HC in the exhaust gas is experimentally obtained under the constant conditions as described above, and the characteristic table shown in FIG. 4 is created.

  Note that, if the supply amount of the reducing agent (HC) is increased, the amount of liquid HC also increases, and the amount of deviation to the lean side also increases. Therefore, in Patent Document 2, the air-fuel ratio sensor is calculated from the supply amount of the reducing agent. Although the air-fuel ratio correction is performed by estimating the lean deviation, the actual lean deviation amount is not detected to estimate the HC amount in the exhaust gas. Further, it is described that the actual HC amount (concentration) is detected separately from the air-fuel ratio sensor (with another dedicated sensor).

  Returning to FIG. 3, in step S15, HCf0 and HCr0, which are the upstream and downstream HC amounts in the exhaust, are corrected by the exhaust temperature Tex, respectively. For example, it is considered that the higher the exhaust gas temperature Tex, the higher the proportion of the HC amount in the vaporized state that is not liquid, so that it is corrected to increase to HCf1 and HCr1. This correction may be performed based on an arithmetic expression or a correction table corresponding to the exhaust gas temperature Tex.

  The downstream HC amount HCr1 corrected in this way is smaller than the upstream HC amount HCf1, and this difference is caused by reducing NOx trapped in the NOx trap catalyst 12 with a reducing agent (HC). .

  In step S16, the amount of HC consumed by the NOx trap catalyst 12 during this period is calculated by subtracting the downstream HCr0 from the upstream HCf0.

In step S17, the reducing agent supply amount is corrected based on the HC amount actually consumed by the catalyst. Specifically, when the actual consumption amount is too much relative to the target consumption amount of the reducing agent (HC) per unit time (air-fuel ratio detection cycle), the target reducing agent supply amount is corrected to be increased and the actual consumption amount is corrected. If the amount is too small, the target reducing agent supply amount is corrected to decrease .

  In this way, the HC consumption in the NOx trap catalyst decreases due to deterioration of the catalyst or the like, but in this embodiment, the HC amount in the exhaust on the upstream side and downstream side of the NOx trap catalyst is determined by the air-fuel ratio sensor. While estimating based on the deviation Δλ of the detected value of the fuel ratio (excess air ratio) from the calculated air-fuel ratio, the HC consumption amount in the NOx trap catalyst can be estimated from the difference between the two HC amounts.

  As described above, based on the estimated value of the actual consumption amount, the reducing agent supply amount can be adjusted so as to be an appropriate target consumption amount regardless of the deterioration of the NOx trap catalyst. The NOx desorption reduction process can be completed in a short time while suppressing the HC emission, and the HC purification performance can be maintained optimally as a total.

  As described above, when the reducing agent is supplied by the post injection at the fuel injection valve, the amount of HC in the exhaust gas varies depending on the post injection timing. Specifically, the injection is performed even if the post injection amount is the same. When the timing is early, since the combustion chamber temperature at the time of injection is relatively high, the fuel vaporization rate is large, and the amount of liquid HC decreases, so Δλ becomes small.

  Therefore, when changing the injection timing of post-injection according to the conditions at the time of rich spike, if the injection timing is earlier than the reference timing, the decrease in the exhaust HC amount estimated by Δλ should be corrected. Good. Alternatively, the post-injection timing can be corrected instead of or in combination with the correction of the target reducing agent supply amount.

  Further, in the present embodiment, a configuration is added in which it is determined that the NOx trap catalyst has deteriorated when the HC consumption amount in the NOx trap catalyst estimated as described above becomes equal to or less than a threshold for catalyst deterioration diagnosis. May be.

  Next, a second embodiment will be described.

  In the present embodiment, as shown in FIG. 6, an air-fuel ratio sensor 26 is provided only on the upstream side of the NOx trap catalyst 12, and the amount of HC in the exhaust gas on the upstream side is estimated. As shown in FIG. The feed amount is corrected by feedback.

  In FIG. 7, in steps S21 to S25, the exhaust HC amount HCf1 in the upstream portion of the NOx trap catalyst 12 is estimated by Δλf and calculated by correcting the temperature with the exhaust temperature Tex, as in the first embodiment. .

  In step S26, the exhaust HC amount HCf1 in the upstream portion of the NOx trap catalyst 12 is compared with the target reducing agent supply amount calculated in step S4 of FIG. 2 to correct the reducing agent supply amount.

  The exhaust HC amount HCf1 is the amount of HC before HC (reducing agent) is consumed by the NOx trap catalyst 12 and should be equal to the target reducing agent supply amount. Therefore, HCf1 is greater than the target reducing agent supply amount. When it is large, the reducing agent supply amount is corrected to decrease, and when it is less than the target reducing agent supply amount, the reducing agent supply amount is corrected to increase.

  In this way, it is possible to supply an appropriate amount of reducing agent without being affected by the fuel injection valve 9 that performs post-injection and the variation in injectors that inject fuel into exhaust gas.

  Next, a third embodiment will be described.

  In the present embodiment, as shown in FIG. 8, an air-fuel ratio sensor 26 is provided only on the downstream side of the NOx trap catalyst 12, and the upstream HC amount in the exhaust is estimated. As shown in FIG. The feed amount is corrected by feedback.

  In FIG. 9, in steps S31 to S35, the exhaust HC amount HCr1 in the downstream portion of the NOx trap catalyst 12 is estimated by Δλr and calculated by correcting the temperature with the exhaust temperature Tex, as in the first embodiment. .

  In step S26, the exhaust HC amount HCr1 in the downstream portion of the NOx trap catalyst 12 is compared with the allowable HC amount HCout. When HCr1 is less than or equal to the allowable HC amount HCout, the process returns to step S22 to correct the reducing agent supply amount. This control is continued without performing the control, but when the HCr1 exceeds the allowable HC amount HCout, the process proceeds to step S27 to reduce the reducing agent supply amount.

  According to this embodiment, it is possible to suppress discharge (slip) of HC to the downstream side by reducing HC consumption due to deterioration of the NOx trap catalyst or the like.

  Further, the present invention can also be applied to a case where the oxidation catalyst 11 is provided on the upstream side of the NOx trap catalyst 12 as shown in FIG. 10, and the upstream air-fuel ratio sensor 26 is connected to the upstream side of the oxidation catalyst 11. May be provided. In this case, correction may be performed in consideration of the amount of reducing agent that is oxidized and consumed by the oxidation catalyst 11.

  Further, the difference Δλ from the air-fuel ratio calculated value of the air-fuel ratio detected by the air-fuel ratio sensor may be a difference instead of the ratio shown in the embodiment.

  In addition, when a fuel containing sulfur (S) is used, the NOx trap catalyst may cause sulfur poisoning, and the fuel is used as a reducing agent to remove this sulfur poisoning (sulfur oxide). In addition, the present invention can be similarly applied.

  Of course, the present invention is applicable not only to diesel engines but also to gasoline engines.

Engine system diagram showing an embodiment of the present invention A flowchart showing a main routine of NOx desorption purification control Flowchart of a subroutine for calculating the reducing agent supply amount Δλ—Characteristics of exhaust HC amount The figure which shows the exhaust lambda detection value before and behind the NOx trap catalyst, the exhaust lambda calculation value and the reducing agent supply amount System diagram of the engine in the second embodiment Flowchart of a subroutine for calculating a reducing agent supply amount in the second embodiment. System diagram of the engine in the third embodiment Flowchart of a subroutine for calculating a reducing agent supply amount in the third embodiment. System diagram of the engine in the fourth embodiment

Explanation of symbols

1 Diesel engine
2 Intake passage
5 Inlet throttle valve
9 Fuel injection valve
10 Exhaust passage
11 Oxidation catalyst
12 NOx trap catalyst
20 Control unit
21 Rotational speed sensor
22 Accelerator position sensor
23 Air Flow Meter
24 Intake air temperature sensor
25 Water temperature sensor
26 Upstream air-fuel ratio sensor
27 Downstream air-fuel ratio sensor
27 Catalyst temperature sensor
28 Exhaust temperature sensor

Claims (6)

An exhaust purification catalyst having a function of accumulating oxides in the exhaust in the exhaust passage of the engine;
Reducing fuel supply control means for controlling the supply of reducing fuel for reducing and purifying the oxide accumulated in the exhaust purification catalyst;
Intake air amount detection means for detecting the amount of air sucked into the engine;
An excess air ratio detecting means for detecting an excess air ratio in the engine exhaust;
The excess air ratio calculated from the detected value of the intake air amount and the set value of the fuel amount supplied upstream from the excess air ratio detection unit, and the excess air ratio detected by the excess air ratio detection means Exhaust HC amount estimation means for estimating the HC amount present in the exhaust based on the deviation amount obtained by the ratio or difference with the detected value, and correcting the HC amount in the exhaust based on the detected value of the exhaust temperature When,
Reducing fuel supply amount correction means for correcting the supply amount of the reducing fuel based on the exhaust HC amount estimated by the exhaust HC amount estimating means;
Including
The reducing fuel supply control means supplies the reducing fuel by fuel injection in the exhaust stroke to the engine combustion chamber or fuel injection into the exhaust passage ,
The excess air ratio detection means is provided downstream of the reducing fuel supply unit and upstream and downstream of the exhaust purification catalyst,
The exhaust HC amount estimation means estimates the exhaust HC amount upstream of the exhaust purification catalyst based on the detection value of the upstream excess air ratio detection means and the calculated excess air ratio, and the downstream air Estimating the amount of HC in the exhaust downstream of the exhaust purification catalyst based on the detected value of the excess ratio detection means and the calculated excess air ratio,
The reduction fuel supply amount correction means is consumed for the reduction of NOx trapped in the exhaust purification catalyst due to the difference between the exhaust HC amount upstream of the exhaust purification catalyst and the exhaust HC amount downstream of the exhaust purification catalyst. Estimating the HC amount, and correcting the supply amount of the reducing fuel based on the estimated value and the target value of the consumed HC amount,
A fuel supply control apparatus for an internal combustion engine. In the case where the supply of the fuel for reduction is performed by fuel injection in the exhaust stroke, instead of the correction of the supply amount of the reduction fuel or the correction of the supply amount of the reduction fuel based on the estimated HC amount in the exhaust gas fuel supply control apparatus for an internal combustion engine according to claim 1, characterized in that for correcting the injection timing of the combination with the fuel injection in the exhaust stroke and. The fuel supply control device for an internal combustion engine according to claim 1 or 2 , wherein the exhaust purification catalyst is a NOx trap catalyst that traps NOx as an oxide in the exhaust gas. 4. The apparatus according to claim 3 , further comprising means for determining that the NOx trap catalyst has deteriorated when an estimated value of the amount of HC consumed by the NOx trap catalyst becomes equal to or less than a threshold value for catalyst deterioration diagnosis. Fuel supply control device for internal combustion engine. The fuel supply control device for an internal combustion engine according to claim 4 , wherein the threshold value for diagnosing the catalyst deterioration is calculated based on an operating state and a temperature state of the engine. Wherein the target value of the supply amount of the reducing fuel, the engine operating condition, the fuel supply control for an internal combustion engine according to any one of claims 1 to 5, characterized in that calculated on the basis of the temperature state apparatus.

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