Patent Application
20070277509
The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
One embodiment of the invention will be described below with reference to the drawings. A general configuration of a diesel engine using a fuel supply apparatus of the invention is described with reference to
In this embodiment, the diesel engine 1 (hereinafter referred to as “engine 1”) may be a common rail in-cylinder direct-injection four-cylinder engine. The engine 1 includes, as main components, a fuel supply system 2, combustion chambers 3, an intake system 6 and an exhaust system 7.
The fuel supply system 2 includes a fuel supply pump 21, a common rail 22, injectors (fuel injection valves) 23, a supplemental fuel valve 25, an engine fuel passage 26 and a fuel passage 27.
The fuel supply pump 21 draws fuel from the fuel tank and pressurizes the fuel to supply the pressurized fuel to the common rail 22 through the engine fuel passage 26. The common rail 22 functions as an accumulator for maintaining the pressure of fuel supplied from the fuel supply pump 21 at a prescribed level (accumulating the high-pressure fuel supplied from the fuel supply pump 21). The common rail 22 distributes the accumulated fuel to the injectors 23. Each injector 23 is an electromagnetically driven valve designed to open when a specified voltage is applied and spray fuel into the associated combustion chamber 3.
The fuel supply pump 21 is designed to supply part of the fuel drawn from the fuel tank to the supplemental fuel valve 25 through the fuel passage 27. The supplemental fuel valve 25 is an electromagnetically driven valve designed to open when a specified voltage is applied and supply fuel to the exhaust system 7 (from exhaust ports 71 to an exhaust manifold 72). An injection hole of the supplemental fuel valve 25 is exposed to the interior of the exhaust system 7.
The intake system 6 has an intake manifold 63 connected to intake ports formed in the cylinder head. An intake pipe 64, included in the intake passage, is connected to the intake manifold 63. An air cleaner 65, an airflow meter 32 and a throttle valve 62 are disposed in the intake passage in order from the upstream side. The airflow meter 32 is designed to output an electric signal that indicates the volume of airflow into the intake passage through the air cleaner 65.
The exhaust system 7 has an exhaust manifold 72 connected to the exhaust ports 71 formed on the cylinder head. Exhaust pipes 73 and 74, included in the exhaust passage, are connected to the exhaust manifold 72. A catalytic converter 4 is also disposed in the exhaust passage.
The catalytic converter 4 includes a NOX storage reduction catalyst 4a and a DPNR catalyst 4b. The NOX storage reduction catalyst 4a is designed to absorb NOX in the presence of a high oxygen concentration in exhaust gas when the oxygen concentration in the exhaust gas is high and to reduce NOX to NO2 or NO as emissions in the presence of a low oxygen concentration and a large amount of reduction component (unburnt component of fuel, such as HC) in exhaust gas when the oxygen concentration is low and an excess of reductant (e.g., unburned fuel, such as HC) in exhaust gas. The NOX emissions in the form of NO2 or NO react immediately with HC or CO contained in exhaust gas, so that the NO2 or NO is reduced to N2. The reduction of NO2 or NO to N2 causes HC or CO to be oxidized to H2O or CO2.
In one example, the DPNR catalyst 4b employs a porous ceramic structure that contains the NOX storage reduction catalyst. The PM in exhaust gas is trapped when passing through the porous wall. When the air-fuel ratio of the exhaust gas is lean, the NOX storage reduction catalyst absorbs NOX contained in exhaust gas. When the air fuel ratio is rich, the stored NOX is reduced. The DPNR catalyst 4b also oxidizes and burns the trapped PM.
The exhaust gas purification system includes the catalytic converter 4, the supplemental fuel valve 25, and the fuel passage 27 as well as an electronic control unit (ECU) 100. The ECU 100 controls the operation of the supplemental fuel valve 25.
The engine 1 has a turbocharger (compressor) 5. The turbocharger 5 includes a turbine shaft 5a, a turbine wheel 5b and a compressor impeller 5c, the turbine wheel 5b and the compressor impeller 5c are connected to each other via the turbine shaft 5a. The compressor impeller 5c faces the interior of the intake pipe 64, while the turbine wheel 5b exposes the interior of the exhaust pipe 73. The turbocharger 5 thus configured utilizes an exhaust flow (exhaust pressure) received by the turbine wheel 5b to rotate the compressor impeller 5c in order to forcibly induct air into the engine. In this embodiment, the turbocharger 5 is a variable nozzle turbocharger having a variable nozzle vane mechanism 5d on the side of the turbine wheel 5b. The boost pressure of the engine 1 may be regulated by controlling the opening degree of the variable nozzle vane mechanism 5d.
The intake system 6 has an intercooler 61 provided on the intake pipe 64. The intercooler 61 is designed to cool intake air whose temperature has increased due to the forced induction by the turbocharger 5. The throttle valve 62 is also provided in the intake pipe 64 downstream of the intercooler 61. The throttle valve 62 is an electronically controlled valve whose opening varies continuously. The throttle valve 62 reduces the cross-section of the intake air passage under certain conditions to control (decrease) the volume of intake air.
The engine 1 has an exhaust gas recirculation (EGR) passage 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 recirculates some exhaust gas to the intake system 6 as required and supply such exhaust gas back to the combustion chambers 3 to lower the combustion temperature. This decreases the amount of NOX emissions. The EGR passage 8 has an EGR valve 81 and an EGR cooler 82 that cools exhaust gas passing (recirculating) through the EGR passage 8. The volume of EGR to be introduced from the exhaust system 7 to the intake system 6 (volume of exhaust gas to be recirculated) may be adjusted by controlling the opening degree of the EGR valve 81.
The sensors will now be described. The engine 1 has several types of sensors installed at specific locations thereof. The sensors output signals that indicate the environmental conditions of the specific locations as well as signals indicating the operating conditions of the engine 1.
For instance, the airflow meter 32, upstream of the throttle valve 62 in the intake system 6, outputs a signal that indicates the detected flow rate of the intake air (intake air volume). The intake temperature sensor 33, provided on the intake manifold 63, outputs a signal that indicates the detected temperature of the intake air. The intake pressure sensor 34, provided on the intake manifold 63, outputs a signal that indicates the detected pressure of the intake air. An A/F (air-fuel ratio) sensor 35, downstream of the catalytic converter 4 in the exhaust system 7, outputs a detection signal, which continuously varies depending on the oxygen concentration in exhaust gas. An exhaust gas temperature sensor 36, downstream of the catalytic converter 4 in the exhaust system 7, outputs a that indicates the detected exhaust gas temperature. A rail pressure sensor 37 outputs a signal that indicates the detected pressure of the fuel stored in the common rail 22. A fuel pressure sensor 38 outputs a signal that indicates the detected pressure of fuel flowing through the fuel passage 27 (fuel pressure).
The ECU will now be described. As shown in
The ROM 102, the CPU 101, the RAM 103 and the backup RAM 104 are connected to each other via a bus 107, while being connected to an input interface 105 and an output interface 106.
The input interface 105 connects to the airflow meter 32, the intake temperature sensor 33, the intake pressure sensor 34, the A/F sensor 35, the exhaust gas temperature sensor 36, the rail pressure sensor 37, and the fuel pressure sensor 38. In addition, the input interface 105 connects to a water temperature sensor 31, an atmospheric pressure sensor 39, an accelerator depression sensor 40 and a crankshaft position sensor 41. The water temperature 31 outputs a signal that indicates the detected coolant temperature in the engine 1. The atmospheric pressure sensor 39 detects the atmospheric pressure variable due to environmental conditions, including altitude. The accelerator depression sensor 40 outputs a signal that indicates the detected displacement of the accelerator pedal. The crankshaft position sensor 41 outputs a pulse when the output shaft (crankshaft) of the engine 1 rotates by a given angle. In turn, the output interface 106 connects to the injector 23, the supplemental fuel valve 25, the variable nozzle vane mechanism 5d, the throttle valve 62, the EGR valve 81 and others.
The ECU 100 executes the respective controls in the engine 1 based on the outputs from the aforementioned sensors. The ECU 100 also executes PM catalyst regeneration control and a correction process of fuel supply interval, which will be described later.
Next, the PM catalyst regeneration control will be described. The ECU 100 first estimates the amount of PM deposits in the DPNR catalyst 4b. One approach to estimating the amount of PM deposits is to use a map plotted with experimental data on the amount of PM adhesion that varies depending on the operating conditions of the engine 1 (e.g. exhaust gas temperature, fuel injection amount and engine speed). The amounts of PM adhesion read from the map are summed to obtain the amount of PM deposits. Another approach would be to estimate the amount of PM deposits based on the vehicle driving distance or driving duration. Still another alternative is to use a pressure differential sensor, disposed in the catalytic converter 4, to detect the pressure differential between upstream and downstream of the DPNR catalyst 4b. The amount of PM deposits trapped by the DPNR catalyst 4b is calculated based on the output from the differential pressure sensor.
If the estimate amount of PM deposits is equal to or larger than a specified reference value, the ECU 100 determines to start regeneration of the DPNR catalyst 4b and executes the PM catalyst regeneration control. More specifically, the ECU 100 calculates a required fuel supply amount and supply interval based on the engine speed output from the crankshaft position sensor 41 with reference to the map previously plotted with the experimental results. According to the calculation result, the ECU 100 controls the operation of the supplemental fuel valve 25, through which fuel is supplied to the exhaust system 7 continuously. The fuel supply results in a rise in temperature of the DPNR catalyst 4b, which promotes oxidization of the PM deposits in the DPNR catalyst 4b to H2O and CO2 emissions.
Other than the PM catalyst regeneration control, the ECU 100 may execute sulfur poisoning recovery control or NOX reduction control. The sulfur poisoning recovery control releases sulfur from the NOX storage reduction catalyst 4a and the DPNR catalyst 4b. This is achieved by increasing the catalyst temperature by continuously supplying fuel from the supplemental fuel valve 25, while controlling the air-fuel ratio of exhaust gas to the stoichiometric or richer ratio. The NOX reduction control is intended to reduce the NOX stored in the NOX storage reduction catalyst 4a and the DPNR catalyst 4b to N2, CO2 and H2O by intermittently supplying fuel from the supplemental fuel valve 25.
The PM catalyst regeneration control, the sulfur poisoning recovery control and the NOX reduction control are performed individually as appropriate. When it is necessary to perform all three control simulataneously, these controls may be performed in the sequence described above.
Next, the correction process of fuel supply interval will be described. As stated previously, the volume of intake air to the engine 1 mounted on the vehicle decreases following certain environmental changes, such as atmospheric pressure change, or upon a shift from normal to transient driving. This increases the amount of PM emissions. As the amount of PM emissions increases, the amount of PM adhering and entering the injection hole of the supplemental fuel valve 25 increases, which helps PM deposits build up. The PM deposits may clog the injection hole of the supplemental fuel valve 25. As the exhaust gas temperature at the distal end of the supplemental fuel valve 25 increases from the reference preset temperature, the temperature of the distal end itself of the supplemental fuel valve 25 also increases, producing PM deposits. The PM deposits may clog the injection hole of the supplemental fuel valve 25.
In order to solve this problem, in this embodiment, a correction coefficient of the fuel supply interval, eminttemp, which is used for correcting the fuel supply interval, is calculated based on the temperature of the distal end of the supplemental fuel valve 25. In addition, a correction coefficient of the fuel supply interval, emintpm, which is used for correcting the fuel supply interval, is calculated based on the variation in amount of PM emissions due to environmental changes or during transient driving conditions. Between eminttemp and emintpm, the correction coefficient of the fuel supply interval that results in a larger amount of fuel supply per unit time, is selected as an target fuel supply interval. This provides the feature of maintaining fuel economy, while preventing clogging of the injection hole of the supplemental fuel valve 25.
A specific example of the correction process of fuel supply interval is described below with reference to the flowchart in
In step ST1, the engine speed Ne is read from the output of the crankshaft position sensor 41 to calculate a required fuel supply amount Q based on the engine speed Ne with reference to a map, such as that shown in
In step ST2, a reference fuel supply interval Tb (see
In step ST3, the correction coefficient of the fuel supply interval, eminttemp, which is used to correct the fuel supply interval, is calculated based on the temperature of the distal end of the supplemental fuel valve 25.
More specifically, based on the difference between the reference exhaust gas temperature obtained in step ST2 and the current exhaust gas temperature (change in exhaust gas temperature ΔTh), the correction coefficient of fuel supply interval, eminttemp, is calculated with reference to the map shown in
It should be understood that the exhaust gas temperature (ambient temperature of the supplemental fuel valve 25) may be calculated using a specific map for calculating the exhaust gas temperature. The map may use experimental and calculation data on engine speed Ne, intake temperature, atmospheric pressure and so forth as parameters. The ROM 102 in the ECU 100 may store this map in advance. Alternatively, an exhaust gas temperature sensor may be provided to detect and output the exhaust gas temperature upstream of the turbocharger 5.
In step ST4, the correction coefficient of fuel supply interval, emintpm, used to correct the fuel supply interval is calculated based the variation in amount of PM emissions due to environmental changes or during transient driving conditions.
More specifically, first an air volume ratio and a λ (excess air ratio) correction coefficient for amount of PM emissions are calculated.
The air volume ratio will now be described. The air volume ratio, gnr, is calculated by dividing the actual intake air volume to the engine 1, which is obtained from the output signal of the airflow meter 32, by the reference intake air volume on a flat driving condition (air volume ratio gnr=intake air volume divided by reference intake air volume).
Next the calculation of the λ correction coefficient for amount of PM emissions will be described. Based on the air volume ratio gnr calculated in the aforementioned process, and the atmospheric pressure (detected value), obtained from the output signal of the atmospheric pressure sensor 39, the λ correction coefficient, emgpmlmd, for amount of PM emissions is calculated with reference to a map of
Based on the λ correction coefficient, emgpmlmd, thus calculated, the correction coefficient of fuel supply interval, emintpm, is calculated with reference to a map of
In steps ST5 to ST7, the correction coefficient of fuel supply interval, eminttemp, calculated in step ST3, is compared with the correction coefficient of fuel supply interval, emintpm, calculated in step ST4. The smaller value of the two is selected, that is the one which results in a larger amount of fuel supply per unit time. More specifically, if the correction coefficient of fuel supply interval, eminttemp, which depends on the temperature of the distal end of the supplemental fuel valve, is smaller than the correction coefficient of fuel supply interval, emintpm, which depends on the variation in amount of PM emissions (if the result of the determination in step ST5 is true), the correction coefficient, eminttemp, is selected as a correction coefficient of the target fuel supply interval, emintad (step ST6). In contrast, if the correction coefficient of fuel supply interval, emintpm, is smaller than the correction coefficient of fuel supply interval, eminttemp (if the result of the determination in step ST5 is false), the correction coefficient, emintpm, is selected as a correction coefficient of the target fuel supply interval, emintad (step ST7).
In step ST8, the correction coefficient of the target fuel supply interval, emintad, selected in step ST6 or ST7, is multiplied by the reference fuel supply interval, calculated in step ST2, to obtain an target fuel supply interval (target fuel supply interval=[reference fuel supply interval prior to correction]×emintad). Then, the routine ends.
In accordance with the correction process of fuel supply interval, either the correction coefficient of fuel supply interval, eminttemp or emintpm, is selected to correct the target fuel supply interval. In particular, the correction coefficient that results in a shorter fuel supply interval (a larger amount of fuel supply per unit time) is selected. This allows the fuel supply interval to be appropriately corrected for either one of condition changes that is more likely to cause clogging of the injection hole of the supplemental fuel valve 25; where the temperature of the distal end of the supplemental fuel valve 25 rises or the amount of PM emissions increases due to environmental changes or during transient driving conditions. Thereby, clogging of the injection hole of the supplemental fuel valve 25 is effectively prevented. Also, in accordance with the correction process of fuel supply interval, a fuel supply amount (fuel supply amount per unit time) appropriate to the foregoing specific condition change is provided. This maintains fuel economy in contrast to the case where the fuel supply amount is adjusted when the amount of PM emissions reaches the maximum in the allowable fluctuation.
Although increasing the fuel supply amount per unit time prevents clogging of the injection hole of the supplemental fuel valve 25, the fuel also reacts with oxygen in the catalyst, which can cause the catalyst temperature to exceed a certain range of values (e.g. 750° C.). One approach to avoid such situation is offered as follows. The temperature of the DPNR catalyst 4b is estimated based on the exhaust gas temperature detected by the exhaust gas temperature sensor 35. If the estimated catalyst temperature is equal to or higher than a prescribed temperature, the fuel supply amount per unit time is reduced according to the estimated catalyst temperature (more specifically, variation in catalyst temperature relative to a preset value). Therefore, an excessive rise in catalyst temperature is prevented. It should be understood that the prescribed temperature for the catalyst temperature may be obtained empirically by taking the certain range of the catalyst temperature (e.g. 750° C.) into consideration.
One approach to reducing the fuel supply amount per unit time, the fuel supply duration per interval shown in
To prevent an excessive increase in catalyst temperature, the following approach may also be taken. The temperature of the DPNR catalyst 4b may be estimated based on the exhaust gas temperature detected by the exhaust gas temperature sensor 35. Then, based on the estimated current catalyst temperature and the target fuel supply interval the increase in catalyst temperature, resulting from the fuel supplies at the target fuel supply interval, is estimated. A restrictive correction or increase of the fuel supply amount per unit time is performed so that the estimated catalyst temperature does not exceed a prescribed value (a value determined based on the maximum allowable catalyst temperature).
Another embodiment of the invention is further described. In the embodiment described above, one of either the correction coefficient of fuel supply interval, eminttemp or emintpm, is used to determine the target fuel supply interval. However, the invention is not limited to the aforementioned embodiment. Instead, the target fuel supply interval may be calculated using only the correction coefficient of fuel supply interval, emintpm.
Also in the embodiment described above, the reference fuel supply interval Tb is multiplied by the correction coefficient of fuel supply interval, eminttemp or emintpm, to correct the fuel supply amount. Alternatively, the reference fuel supply duration per interval (see
In the above-described embodiment, the correction coefficient of fuel supply interval, eminttemp, which depends on the temperature of the distal end of the supplemental fuel valve 25, is calculated based on the variation in exhaust gas temperature ΔTh. Alternatively, the correction coefficient of fuel supply interval, eminttemp, may be calculated based on the coolant temperature in the engine 1, obtained from a signal output by the water temperature sensor 31, with reference to a map of
In the above-described embodiment, a direct-injection four-cylinder diesel engine is equipped with the exhaust gas purification system of the invention. However, the invention is not limited to this embodiment. Alternatively, other diesel engines having any number of cylinders, such as a direct-injection six-cylinder diesel engine, may be equipped with the exhaust gas purification system of the invention as well. In addition, the invention is limited to use with direct-injection diesel engines, but may also be applied to other types of diesel engines. Further, the invention may be used not only with vehicle engines, but also for engines designed for other purposes.
In the embodiment previously described, the catalytic converter 4 includes the NOX storage reduction catalyst 4a and the DPNR catalyst 4b. Alternatively, the catalytic converter 4 may include a DPF in addition to the NOX storage reduction catalyst 4a or an oxidation catalyst.
While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the embodiments are shown in various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-149654 | May 2006 | JP | national |
