WO2012131787A1

WO2012131787A1 - Exhaust gas purification system for internal combustion engine

Info

Publication number: WO2012131787A1
Application number: PCT/JP2011/001963
Authority: WO
Inventors: 彰紀森島; 健一辻本
Original assignee: トヨタ自動車株式会社
Priority date: 2011-03-31
Filing date: 2011-03-31
Publication date: 2012-10-04

Abstract

An exhaust gas purification system for an internal combustion engine, comprising: a fuel supply device (15) for supplying fuel to exhaust gas flowing into an exhaust gas purification catalyst (13); a heating device (16) for igniting the fuel supplied from the fuel supply device (15); and a controller (50) for controlling the fuel supply device (15). The controller (50) controls the fuel supply device (15) so that the fuel supply device (15) intermittently supplies the fuel and so that, in order to bring the amount of smoke generation into an allowable range, the amount of supply of one set of fuel consisting of one or more shots is below a predetermined upper limit supply amount.

Description

Exhaust gas purification system for internal combustion engine

The present invention relates to an exhaust purification system having an exhaust temperature raising device that is provided in an exhaust passage of an internal combustion engine and raises the temperature of exhaust gas.

Various exhaust purification devices having a function of burning fuel in an exhaust pipe by an ignition device such as a glow plug have been proposed. For example, in the apparatus of Patent Document 1, in an operation region where ignition is possible, a first control state in which fuel is ignited by heating with a glow plug or a third control state in which heating by a glow plug is stopped is selectively performed. In the operation region that is realized and cannot be ignited, the second operation state in which heating by the glow plug is performed but the fuel is not ignited, or the third operation state is selectively realized.

In the apparatus of Patent Document 2, fuel is intermittently supplied from a fuel supply valve to a small oxidation catalyst disposed in an exhaust passage, and a flame is generated intermittently without generating soot.

In the apparatus of Patent Document 3, an amount of fuel necessary for preventing thermal deterioration of the exhaust purification catalyst is intermittently supplied into the exhaust passage.

JP 2010-59886 A JP 2010-48228 A JP 2009-156167 A

However, in the apparatus of Patent Document 1, the liquid fuel film adhering to the wall surface of the exhaust pipe is exposed to high temperature exhaust gas to form a rich mixture and generate a large amount of smoke. In the device of Patent Document 2, the generation of soot is suppressed by intermittently supplying the fuel, but the upper limit supply amount of the fuel supply amount is determined in advance so that the generation of smoke is within the allowable range. Absent. The device of Patent Document 3 supplies fuel intermittently, but does not consider the problem of smoke generation.

An object of the present invention is to effectively suppress the generation of smoke in a system that supplies fuel to an exhaust passage.

One aspect of the present invention is:
An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
A fuel supply device that is provided in the exhaust passage upstream of the exhaust purification catalyst and supplies fuel to the exhaust flowing into the exhaust purification catalyst;
A heating device for igniting the fuel supplied from the fuel supply device;
A controller for controlling the fuel supply device,
The controller is configured to supply the fuel intermittently by the fuel supply device and to supply the fuel in one set of one or more shots in order to keep the amount of smoke generated within an allowable range. The exhaust gas purification system for an internal combustion engine is characterized in that the fuel supply device is controlled so that is less than a predetermined upper limit supply amount.

In this aspect, the fuel supply amount in one set of supply is less than a predetermined upper limit supply amount. Therefore, the generation of smoke can be effectively suppressed.

Preferably, the system further includes a sensor for detecting or estimating a fuel adhesion amount in the exhaust passage, and the controller controls the fuel supply device based on the detected or estimated fuel adhesion amount. In this aspect, the generation of smoke can be more effectively suppressed. The controller may further stop or reduce the fuel supply by the fuel supply device when the fuel adhesion amount detected or estimated by the sensor exceeds a predetermined upper limit adhesion amount.

The controller may stop the fuel supply after the one set of supply and restart the fuel supply after the stop.

In addition, the means for solving the problems in the present invention can be used in combination as much as possible.

FIG. 1 is a conceptual diagram of a first embodiment of the present invention. FIG. 2 is a flowchart showing the fuel supply process to the exhaust passage. FIG. 3 is a timing chart showing the relationship between the fuel supply amount, the adhesion amount, and the smoke amount. FIG. 4 is a graph showing the relationship between the upstream air-fuel ratio and the downstream air-fuel ratio. FIG. 5 is a graph showing an example of setting the upper limit supply amount when the upper limit supply amount is variable. FIG. 6 is a timing chart showing the relationship between the fuel supply amount, the adhesion amount, and the smoke amount before improvement according to the present invention.

Preferred embodiments of the present invention will be described in detail below. FIG. 1 shows a first embodiment of the present invention. In FIG. 1, the engine body 1 is a compression ignition internal combustion engine (diesel engine) using light oil as fuel, but may be another type of internal combustion engine. The engine body 1 has a combustion chamber 2 in each of the four cylinders. Each combustion chamber 2 is provided with an electronically controlled fuel injection valve 3 for injecting fuel. An intake manifold 4 and an exhaust manifold 5 are connected to the combustion chamber 2. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake pipe 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an air flow meter 8.

A throttle valve 10 driven by a step motor (not shown) is disposed in the intake pipe 6. An intercooler 11 for cooling the intake air flowing through the intake pipe 6 is disposed around the intake pipe 6. Engine cooling water is guided into the intercooler 11 and the intake air is cooled by the engine cooling water.

Each fuel injection valve 3 is connected to a common rail 42 via a fuel supply pipe 41, and this common rail 42 is connected to a fuel tank 44 via an electronically controlled fuel pump 43 with variable discharge amount. The fuel stored in the fuel tank 44 is supplied into the common rail 42 by the fuel pump 43, and the fuel supplied into the common rail 42 is supplied to the fuel injection valve 3 through each fuel supply pipe 41.

The exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the exhaust purification catalyst 13 via the exhaust pipe 12. A small oxidation catalyst 14 is arranged in the engine exhaust passage upstream of the exhaust purification catalyst 13, that is, in the exhaust pipe 12. The small oxidation catalyst 14 has a smaller volume and front projection area than the exhaust purification catalyst 13. The front surface projected area of the small oxidation catalyst 14 is smaller than the cross-sectional area of the surrounding exhaust pipe 12, and thus a part of the exhaust gas passing through the exhaust pipe 12 flows through the small oxidation catalyst 14.

The exhaust purification catalyst 13 is composed of, for example, an oxidation catalyst, a three-way catalyst, or a NOx catalyst. The small oxidation catalyst 14 is composed of an oxidation catalyst, and as the catalyst material, for example, Pt / CeO ₂ , Mn / CeO ₂ , Fe / CeO ₂ , Ni / CeO ₂ , Cu / CeO ₂ or the like can be used. A honeycomb body formed of cordierite or metal is used as the base material for the catalysts 13 and 14.

In the exhaust pipe 12 upstream of the small oxidation catalyst 14, a fuel injection valve 15 for supplying fuel to the small oxidation catalyst 14 is arranged with its injection port facing the exhaust pipe 12. The fuel in the fuel tank 44 is supplied to the fuel injection valve 15 via the fuel pump 43.

A glow plug 16 is provided in the exhaust pipe 12 downstream of the fuel injection valve 15. The glow plug 16 is arranged so that the fuel added from the fuel injection valve 15 contacts the tip of the glow plug 16 and can ignite the fuel. The glow plug 16 is connected to a DC power source and a booster circuit (both not shown) for supplying power to the glow plug 16. As a means for ignition, a ceramic heater may be used instead of the glow plug. In order to promote atomization of the fuel, a collision plate for causing the fuel injected from the fuel injection valve 15 to collide may be disposed in the exhaust pipe 12. The small oxidation catalyst 14, the fuel injection valve 15 and the glow plug 16 constitute an exhaust temperature raising device 40, which is controlled by an ECU 50 which will be described later.

In the exhaust pipe 12 upstream of the small oxidation catalyst 14, an exhaust temperature sensor 31 for detecting the exhaust temperature is installed. An A / F sensor 32 for detecting the air-fuel ratio in the exhaust passage is installed in the exhaust pipe 12 downstream of the small oxidation catalyst 14 and upstream of the exhaust purification catalyst 13.

An electronic control unit (ECU) 50, which is a controller, is composed of a well-known digital computer, and is connected to each other by a bidirectional bus, a ROM (read only memory), a RAM (random access memory), a CPU (microprocessor), an input port. And an output port.

The exhaust temperature sensor 31 and the A / F sensor 32 are connected to the ECU 50. The accelerator pedal 51 is provided with a load sensor 52 that generates an output voltage proportional to the amount of depression of the accelerator pedal 51, and the load sensor 52 is connected to the ECU 50. Further, the ECU 50 is connected to a crank angle sensor 53 that generates an output pulse every time the crankshaft of the engine body 1 rotates, for example, 15 °. Further, an intake air temperature sensor 54 installed in the vicinity of the throttle valve 10 and a water temperature sensor 55 installed in a cylinder block of the engine body 1 are connected to the ECU 50. The output signal of each sensor is input to the input port of the ECU 50 via the corresponding AD converter.

On the other hand, the ECU 50 is connected to the stepping motor for driving the fuel injection valve 3, the fuel pump 43, and the throttle valve 10 via the corresponding DA converter and driving circuit, respectively. The operation of these actuators is controlled by the ECU 50. Various programs and reference values / initial values are stored in the ROM of the ECU 50.

The ECU 50 determines the vehicle state including the detection values of the air flow meter 8, the exhaust temperature sensor 31, the A / F sensor 32, the load sensor 52, the crank angle sensor 53, the intake air temperature sensor 54, and the water temperature sensor 55, particularly the engine operating state. Based on the indicated parameter, the fuel supply instruction amount is calculated, and a control signal is output to open the fuel injection valve 3 for a time corresponding to the instruction amount. In accordance with this control signal, an amount of fuel corresponding to the fuel supply instruction amount is supplied from the fuel injection valve 3, and the engine body 1 is operated.

On the other hand, a part or all of the fuel supplied from the fuel injection valve 15 is supplied to the small oxidation catalyst 14. If the small oxidation catalyst 14 is activated at this time, the fuel is oxidized in the small oxidation catalyst 14. The small oxidation catalyst 14 is heated by the oxidation reaction heat generated at this time. Further, when the temperature of the small oxidation catalyst 14 is increased, hydrocarbons having a large number of carbon atoms in the fuel are decomposed to generate hydrocarbons having a small number of carbon atoms and high reactivity, thereby making the fuel a highly reactive fuel. Reformed. In other words, the small oxidation catalyst 14 constitutes a rapid heat generator that rapidly generates heat on the one hand, and a reformed fuel discharger that discharges the reformed fuel on the other hand. Further, part or all of the fuel supplied from the fuel injection valve 15 is heated or ignited by the glow plug 16, thereby promoting the temperature increase of the exhaust gas.

In parallel with the operation control of the engine body 1 described above, the ECU 50 estimates the amount of fuel adhering to the exhaust passage. This adhesion amount estimation process is repeatedly executed every predetermined time Δt during the operation of the engine body 1. In this process, the ECU 50 reads various parameters indicating the operating state of the engine body 1 and calculates the fuel adhesion amount based on these parameters. Such parameters include engine speed Ne, intake air amount Ga, injection amount from in-cylinder fuel injection valve 3, injection amount from fuel injection valve 15, exhaust temperature, engine water temperature, glow plug temperature, and A / The air-fuel ratio AF2 on the downstream side of the exhaust gas temperature raising device 40 detected by the F sensor 32 is included.

The amount of adhesion is estimated by subtracting the downstream air-fuel ratio AF2 from the upstream air-fuel ratio AF1 calculated from the injection amounts from the in-cylinder fuel injection valve 3 and the fuel injection valve 15 and the intake air amount Ga. This is performed by adding up the obtained values while correcting them with the remaining parameters. For example, in FIG. 4, when the downstream air-fuel ratio AF2 is larger than the upstream air-fuel ratio AF1 (ie, lean), the area C of the difference between the two (accumulated value of the difference) is the amount of fuel attached. It can be considered to correlate with the quantity. The estimation can also take into account the tube wall temperature of the exhaust passage 12, and the tube wall temperature can be estimated based on, for example, the exhaust temperature, the intake air amount Ga (that is, the passing gas amount), and the glow plug temperature. In this case, the tube wall temperature can be estimated based on a two-dimensional map of the amount of heat taken away determined by the exhaust gas temperature and the passing gas amount and the glow plug temperature. When a collision plate is used, the temperature of the collision plate may be estimated and used for estimation of the adhesion amount.

In parallel with the above adhesion amount estimation process, the ECU 50 controls the exhaust temperature raising device 40 to supply fuel to the exhaust passage. The processing routine of FIG. 2 is repeatedly executed every predetermined time Δt when the engine body 1 is in operation and there is a fuel supply request to the fuel injection valve 15. The fuel supply request to the fuel injection valve 15 includes a temperature rise of the exhaust purification catalyst 13 at a low temperature such as during cold start, oxidation and combustion of particulate matter (PM) accumulated in the exhaust purification catalyst 13, and (exhaust purification catalyst). When 13 is a NOx occlusion reduction catalyst, it is output by the ECU 50 for the purpose of NOx reduction and SOx poisoning recovery for the exhaust purification catalyst 13. The predetermined conditions for requesting fuel supply are, for example, that the small oxidation catalyst 14 is activated and the temperature detected by the intake air temperature sensor 54 is lower than a predetermined value in the case of temperature rise at low temperatures. In the case of NOx reduction and SOx poisoning recovery for the exhaust purification catalyst 13, for example, the estimated value of the accumulation amount or occlusion amount of each substance exceeds a predetermined reference value, and the temperature of the exhaust purification catalyst 13 Is an estimated value exceeding a predetermined reference value. The required amount of fuel supply (that is, the fuel supply amount set according to the purpose of the fuel supply request) may be a fixed value or a variable value. In the case of the variable value, the required amount can be determined based on, for example, the estimated temperature of the exhaust purification catalyst 13 and / or the estimated value of the accumulation amount or occlusion amount of each substance.

In FIG. 2, when there is a fuel supply request to the fuel injection valve 15, the ECU 50 reads the estimated value of the current adhesion amount calculated by the above-described adhesion amount estimation processing (S100). Next, the ECU 50 determines whether or not the estimated value of the adhesion amount is less than a predetermined upper limit adhesion amount a2 (S110). If negative, that is, if it is greater than or equal to the upper limit adhesion amount a2, the process proceeds to step S190 described later. Transition. If the determination is affirmative, the ECU 50 next calculates an upper limit supply amount b1 in the next set of fuel supply based on the estimated value of the current adhesion amount (S120). The upper limit supply amount b1 is set to a value obtained by subtracting a predetermined margin from a value such that the amount of smoke generated exceeds the allowable range when the fuel supply amount in the next set exceeds this. The upper limit supply amount b1 may be a fixed value or a variable value. In the case of a variable value, the upper limit supply amount b1 can be made larger as the engine speed Ne and the intake air amount KL are higher, as shown in FIG. 5, for example.

Next, the ECU 50 calculates the number of shots so that the total supply amount of one set is less than the upper limit supply amount b1 (S130). The number of shots may be 1 in addition to the case where the number of shots is 2 or more. The valve opening time t1 per shot (see FIG. 3) may be a fixed value or a variable value. In the case of a variable value, the valve opening time t1 is reflected in the calculation of the number of shots. The valve opening time t1 can be set to a larger value as the exhaust gas temperature is higher, for example. When the required amount of fuel supply is 2000 mm ^ 3, for example, if the total supply amount of one set is 1000 mm ^ 3, the number of sets is two.

Next, the ECU 50 controls the fuel injection valve 15 to execute fuel supply for one shot (S140). After the supply of one shot, the fuel supply is suspended over a predetermined shot interval t2 (S150). The shot interval t2 may be a fixed value or a variable value. For example, the shot interval t2 can be made smaller as the exhaust gas temperature is higher.

Shots and pauses are alternately repeated over the supply time t3 as necessary, and when the number of shots calculated in step S130 is completed (S160), a standby time t4 for stopping fuel supply is started (S170). . This standby time t4 is continued until the current adhesion amount (S180) falls below a predetermined supply restart reference value a1 (S190). In a normal case, the waiting time t4 is several seconds.

When the adhesion amount falls below the supply restart reference value a1, it is determined whether the required amount of fuel supply has been completed, and in the case of negative, the processing from step S110 to S190 is repeatedly executed. The processing of this routine is returned when the required amount of fuel has been supplied.

As a result of the above processing, in the present embodiment, the fuel supply over the supply time t3 and the stop over the standby time t4 are repeatedly executed alternately until the required amount of fuel supply ends (S200). .

For example, as in the conventional example shown in FIG. 6, when a required amount of fuel of, for example, 2000 mm ^ 3 is supplied at regular shot intervals t2 and without providing a waiting time, the wall surface of the exhaust pipe The liquid-phase fuel film adhering to the gas is exposed to high-temperature exhaust gas to form a rich air-fuel mixture, and a large amount of smoke exceeding the allowable smoke amount S1 is generated. In contrast, in the present embodiment, the fuel injection valve 15 is composed of one or more shots in order to intermittently supply the fuel and make the amount of smoke generated within an allowable range. The fuel injection valve 15 is controlled so that the fuel supply amount in one set of supply falls below a predetermined upper limit supply amount b1 (S130). Therefore, the generation of smoke can be effectively suppressed.

Further, in this embodiment, the system estimates the current fuel adhesion amount in the exhaust passage by the adhesion amount estimation process, and the ECU 50 controls the fuel injection valve 15 based on the estimated current fuel adhesion amount. Therefore, it is possible to appropriately respond to a delayed change in the air-fuel ratio caused by the fuel adhering to the exhaust passage, and the generation of smoke can be further effectively suppressed.

Further, in the present embodiment, the fuel supply is stopped for the standby time t4 after the supply of one set, and the fuel supply is restarted after the standby time t4. Therefore, the generation of smoke is suppressed by suppressing the amount of adhesion due to the stop of the supply. be able to.

Further, in this embodiment, when the estimated fuel adhesion amount exceeds a predetermined upper limit adhesion amount a2, the fuel supply by the fuel injection valve 15 is stopped until the fuel adhesion amount falls below a predetermined supply resumption reference value. Since (S110) is performed, it becomes possible to set the stop period to the optimum or shortest according to the current fuel adhesion amount.

Although the present invention has been described with a certain degree of specificity, it should be understood that various modifications and changes can be made without departing from the spirit and scope of the claimed invention. Various technical means shown in the above-described embodiment and each modification can be combined with each other as much as possible. In the above embodiment, the system estimates the current fuel adhesion amount in the exhaust passage by the adhesion amount estimation processing, but the adhesion amount may be detected by a sensor.

In the above embodiment, when the estimated fuel adhesion amount exceeds the predetermined upper limit adhesion amount, the fuel supply by the fuel injection valve 15 is stopped until the fuel adhesion amount falls below a predetermined supply restart reference value (t4). However, the fuel supply amount may be reduced and the supply may be continued.

In the above embodiment, the current adhesion amount is monitored for each set of fuel supply, but the adhesion amount may be monitored for each shot.

In order to promote combustion, a conduit for supplying secondary air from the outside into the exhaust pipe 12, a control valve, and a compressor may be provided. In that case, the supply amount of secondary air can also be considered in the estimation of the adhesion amount. The present invention can also be applied to an engine that does not have a small oxidation catalyst or an engine that does not have a turbocharger.

12 Exhaust pipe 13 Exhaust purification catalyst 14 Small oxidation catalyst 15 Fuel injection valve 16 Glow plug 31 Exhaust temperature sensor 32 A / F sensor 40 Exhaust temperature raising device 50 ECU

Claims

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
A fuel supply device that is provided in the exhaust passage upstream of the exhaust purification catalyst and supplies fuel to the exhaust flowing into the exhaust purification catalyst;
A heating device for igniting the fuel supplied from the fuel supply device;
A controller for controlling the fuel supply device,
The controller is configured to supply the fuel intermittently by the fuel supply device and to supply the fuel in one set of one or more shots in order to keep the amount of smoke generated within an allowable range. The exhaust gas purification system for an internal combustion engine is characterized in that the fuel supply device is controlled so that is less than a predetermined upper limit supply amount.
An exhaust purification system for an internal combustion engine according to claim 1,
A sensor for detecting or estimating a fuel adhesion amount in the exhaust passage;
The exhaust gas purification system for an internal combustion engine, wherein the controller controls the fuel supply device based on the detected or estimated fuel adhesion amount.
An exhaust purification system for an internal combustion engine according to claim 1,
The exhaust gas purification system for an internal combustion engine, wherein the controller stops the fuel supply after the one set of supply, and restarts the fuel supply after the stop.
An exhaust purification system for an internal combustion engine according to claim 2,
The controller is configured to stop or reduce the fuel supply by the fuel supply device when the fuel adhesion amount detected or estimated by the sensor exceeds a predetermined upper limit adhesion amount. Purification system.