JP2012241548A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system that prevents cracks in a filter or runaway regeneration to be caused by a temperature difference in the filter by uniformly adjusting the temperature in the filter.SOLUTION: In the exhaust emission control system, the temperature in a filter center part is controlled by regeneration control to a temperature at which the filter can be regenerated. The temperature is different between the filter center part and an outer circumferential part, and the temperature is different between a filter entrance side and an exit side. When the temperature difference between the filter center part and the outer circumferential part is larger than a set value, an electric heater 61 starts to supply heat to the outer circumference of a DPF (diesel particulate filter) 30. Heating wires 63 of the electric heater 61 are arranged while increasing the distance from an entrance side of the DPF to an exit side. When electric energy is supplied, the electric heater 61 supplies heat in such a manner that the heating quantity decreases from the entrance side to the exit side of the DPF. By heating the filter with heating gradient, the temperature difference between the filter center part and the outer circumferential part and the temperature difference between the entrance side and the exit side of the filter are eliminated.

Description

  The present invention relates to an exhaust gas purification device, and in particular, collects particulate matter contained in exhaust gas by a filter to purify the exhaust gas, and appropriately incinerates and removes the particulate matter collected in the filter. The present invention relates to an exhaust purification device that regenerates exhaust gas.

  2. Description of the Related Art Conventionally, as a diesel engine exhaust purification device, a DPF (diesel particulate filter) is provided in the middle of an exhaust passage in order to prevent particulates (PM) in exhaust gas from being released into the atmosphere. Well known from. This filter is composed of a number of elongated cells defined by, for example, a porous ceramic material partition wall, and one end of each cell is closed by a plug (plug member). Therefore, at the time of particulate collection, the exhaust gas flowing in from the cell opened on the exhaust upstream side passes through the partition wall to the cell opened on the exhaust downstream side, and passes through the filter. During the passage through the partition, the particulates in the exhaust gas are collected by the partition.

  By the way, with the use of the filter, when the amount of particulates accumulated in the filter increases, the filter becomes clogged. As a result, the exhaust pressure of the engine rises and fuel consumption deteriorates, etc., so that PM trapped in the filter is appropriately burned to remove clogging of the filter, and the filter is regenerated (for example, Patent Documents). 1).

JP 2009-79501 A

  During regeneration, the inside of the filter becomes hot due to combustion. A part of the heat in the filter escapes from the filter outer periphery to the outside, so that the temperature of the filter outer peripheral portion is lower than the temperature of the filter central portion. If a temperature difference occurs inside the filter, the filter may be cracked due to thermal stress.

  Furthermore, unburned residue is generated at the filter outer periphery where the filter temperature is low. The unburned PM may burn rapidly at a high temperature, causing the filter to be damaged (so-called runaway regeneration).

  Further, during regeneration, the PM accumulated on the filter inlet side burns first, and the combustion heat is sent to the outlet side. Therefore, the temperature on the filter outlet side is higher than the temperature on the filter inlet side. That is, in addition to the temperature difference between the filter center portion and the outer peripheral portion, a temperature difference between the filter inlet side and the outlet side occurs, which may cause filter cracking.

  An object of the present invention is to provide an exhaust emission control device that can prevent filter cracking and runaway regeneration due to a temperature difference inside a filter by making the temperature inside the filter uniform.

  (1) In order to achieve the above object, the present invention provides a filter that is disposed in an exhaust system of an engine and collects particulate matter contained in exhaust gas, and removes the particulate matter deposited on the filter by incineration. In the exhaust gas purification apparatus comprising a regeneration device that regenerates the filter and a regeneration control device that controls operation start / stop of the regeneration device, first temperature detecting means for detecting the temperature of the filter center portion, A second temperature detecting means for detecting the temperature of the outer periphery of the filter, an insufficient heat amount calculating means for calculating an amount of heat insufficient for regeneration based on the detected temperatures of the first temperature detecting means and the second temperature detecting means, and the filter Heating means for supplying the heat quantity obtained by the insufficient heat quantity calculating means.

  In the present invention configured as described above, the heating means supplies the heat amount to the outer periphery of the filter without excess or deficiency, thereby eliminating the temperature difference between the filter center portion and the outer periphery portion. Thereby, the temperature in a filter can be made uniform and the filter crack and runaway reproduction resulting from the temperature difference inside a filter can be prevented.

  (2) In the above (1), preferably, the heating means has a heating gradient imparting function for supplying a heat amount so as to reduce a heat amount from the filter inlet side toward the outlet side.

  The heating gradient imparting function eliminates the temperature difference between the filter center and the outer periphery by supplying heat so that the amount of heating is reduced from the filter inlet side toward the outlet side. The temperature difference is also eliminated. Thereby, the temperature in the filter can be made more uniform, and the filter cracking due to the temperature difference inside the filter can be prevented.

  (3) In the above (2), preferably, the heating means has heating wires arranged at dense to sparse intervals from the filter inlet side to the outlet side, and the heating gradient applying function is The amount of heat is supplied when the heating wire generates heat.

  Thereby, the heating gradient provision function can supply the amount of heat so as to reduce the amount of heating from the filter inlet side toward the outlet side.

  (4) In the above (3), preferably, the heating wire generates heat using regenerative energy.

  In the present invention, energy efficiency can be improved by the heating means supplying heat to the outer periphery of the filter without excess or deficiency. By using regenerative energy, energy efficiency can be further improved.

  According to the present invention, by making the temperature in the filter uniform, it is possible to prevent filter cracking and runaway regeneration due to the temperature difference inside the filter.

1 is a system configuration diagram of an engine to which an exhaust emission control device is applied. 2A is a schematic sectional view of the DPF, and FIG. 2B is a schematic plan view of the DPF. It is a control flow which shows the process concerning the reproduction | regeneration control of a controller. It is a conceptual diagram explaining the operation | movement which concerns on a heating. It is a schematic plan view of DPF which shows the structure concerning a modification.

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

~Constitution~
FIG. 1 shows a system configuration diagram of a diesel engine (hereinafter referred to as an engine) to which an exhaust emission control device 19 according to an embodiment of the present invention is applied. The internal combustion engine 10 includes a common rail 2 common to each cylinder, and supplies high-pressure fuel (light oil) stored in the common rail 2 to the injectors 4 provided in the respective cylinders. Be injected.

  The intake passage 6 is equipped with a turbocharger 8. The intake air drawn from an air cleaner (not shown) flows into the compressor 8a of the turbocharger 8 from the intake passage 6, and the intake air supercharged by the compressor 8a is intercooler. 11 and the intake control valve 12 are introduced into the intake manifold 14.

  On the other hand, the exhaust gas from the internal combustion engine 10 flows into the exhaust pipe 16 after passing through the exhaust manifold 15. Note that an EGR passage 17 is provided between the exhaust manifold 15 and the intake manifold 14 to communicate the exhaust manifold 15 and the intake manifold 14 via an EGR valve 18. The exhaust pipe 16 is connected to the exhaust aftertreatment device 19 via the turbine 8 b of the turbocharger 8. The rotating shaft of the turbine 8b is connected to the rotating shaft of the compressor 8a, and the turbine 8b receives the exhaust flowing in the exhaust pipe 16 and drives the compressor 8a.

  The exhaust aftertreatment device 19 includes an oxidation catalyst 20 and a particulate filter (hereinafter referred to as DPF) 30 in order from the upstream. The oxidation catalyst 20 oxidizes NO in the exhaust to generate NO2, and supplies the NO2 as an oxidant to the DPF 30. The DPF 30 is made of a honeycomb cordierite carrier.

  By disposing the oxidation catalyst 20 and the DPF 30 in this manner, the particulates collected and deposited in the DPF 30 react with NO2 supplied from the oxidation catalyst 20 at a relatively low temperature (for example, 250 ° C.). It is oxidized.

  Between the oxidation catalyst 20 and the DPF 30, exhaust temperature sensors 40 and 41 for detecting the exhaust temperature, and a differential pressure sensor 42 for detecting the exhaust differential pressure before and after the DPF 30 are provided.

  As a characteristic configuration, the present embodiment includes an electric heater 61 provided to cover the outer periphery of the DPF 30 (described later).

  The engine system includes a power supply control system. The power supply control system includes an alternator 50, a battery 60, a relay switch 62, a controller 70, and the like. The controller 70 includes various sensors such as temperature sensors 40 and 41, a differential pressure sensor 42, a load sensor 43, and a rotation sensor 44. It is connected.

  The battery 60 stores electrical energy, such as energy necessary for causing the electric heater 61 to generate heat. Note that electric energy may be supplied directly from the alternator 50 to the electric heater 61. The battery 60 may store the regenerative energy of the hybrid vehicle.

  The controller 70 is configured by a CPU, a ROM, and the like, and stores information (map information) of exhaust gas temperature in accordance with the engine operating status (load and engine speed) in advance. And the estimated value of exhaust gas temperature is calculated based on the information from each connected sensor (center part temperature sensor 40, outer peripheral part temperature sensor 41, load sensor 43, rotation sensor 44, etc.). Further, the PM collection estimated amount is calculated based on information from the differential pressure sensor 42, and control related to the start / stop of regeneration is performed.

  Further, the controller 70 calculates the amount of electrical energy (shortage energy amount during regeneration) to be supplied to the electric heater 61 based on the detected temperature information from the center temperature sensor 40 and the exhaust outer periphery temperature sensor 41. The controller 70 controls the relay switch 62, adjusts the energization time by turning the contact of the relay switch 62 on and off, or adjusts the current or voltage, thereby adjusting the electric energy amount to be supplied to the electric heater 61. adjust.

  FIG. 2A is a schematic cross-sectional view of the DPF 30, and FIG. 2B is a schematic plan view of the DPF 30. The DPF 30 includes a catalyst carrier 31, a DPF support member 32, and a metal casing 33. Brackets 34 and 35 are welded to the metal casing 33. Two semicircular brackets 36 are attached to the brackets 34 and 35, and an electric heater 61 is provided on the bracket 36 so as to correspond to the shape of the bracket 36. Thereby, the electric heater 61 covers the outer periphery of the DPF 30.

  In the electric heater 61, the heating wire 63 is embedded in the heat insulating material, and the heating wire 63 and the heat insulating material are integrated to form a semi-cylindrical shape. As the type of heat insulating material, alumina-silicate ceramic fiber, alumina fiber, zirconia fiber, silica fiber, mineral fiber such as rock wool, asbestos, nylon, organic fiber such as Kevlar, foamed molded product such as urethane, or Combinations of these can be used.

  The heating wires 63 are arranged from dense to sparse intervals from the DPF inlet side to the outlet side, and generate heat so as to reduce the heating amount from the DPF inlet side to the outlet side.

  FIG. 3 is a control flow showing processing related to the reproduction control of the controller 70.

  The controller 70 calculates the PM collection estimated amount based on the information from the differential pressure sensor 42 (step S11), and determines whether the PM collection estimated amount is equal to or greater than a set amount (start) (step S12). If the PM collection estimated amount is equal to or greater than the set amount (start), it is determined that the DPF 30 is clogged, and regeneration control is started (step S13). If the PM collection estimated amount is less than the set amount (start), the processes of S11 and S12 are repeated.

  In regeneration control, the amount of heat required for regeneration is calculated based on detected temperatures Tcet, Tout (described later) and the estimated temperature, and the injection amount of exhaust heating fuel (post injection amount) is calculated based on the required amount of heat. . Based on the calculation result, the engine speed, load, fuel injection amount, and the like are controlled to adjust the exhaust temperature.

  Further, it is determined whether or not heating control is necessary (whether or not the internal / external temperature difference ΔTa is equal to or less than the set value) (step S14) (described later). It is determined whether or not the following (step S15). If the estimated PM collection amount is equal to or less than the set amount (stop), it is determined that PM is burned and removed, and regeneration control is stopped (step S16). When the PM collection estimated amount is larger than the set amount (stop), the processes of S13 to S15 are repeated.

  The controller 70 performs control related to heating in conjunction with the regeneration control. Based on the detected temperature Tcet from the center temperature sensor 40 and the detected temperature Tout from the outer periphery temperature sensor 41, an internal / external temperature difference ΔTa (Tcet−Tout) is calculated to determine whether heating control is necessary (step S14). ). If the internal / external temperature difference ΔTa is larger than the set value and it is determined that heating control is necessary, the amount of heat Q that is insufficient for regeneration is calculated based on the detected temperatures Tcet, Tout, the volume of the filter, etc., and the energy is supplied to the electric heater 61. Start (step S17).

  Further, the heating time T (Q / W) is calculated from the required heat quantity Q and the electric power W supplied from the electric heater 61, and heating is performed for a predetermined time T (step S18). During heating, it is determined whether or not heating control is necessary (step S19), and if the internal / external temperature difference ΔTa becomes equal to or smaller than the set value and it is determined that heating control is not necessary, the supply of energy to the electric heater 61 is stopped (step S20). When the internal / external temperature difference ΔTa is larger than the set value, the processes of S17 to S20 are repeated.

  In step S19, the controller 70 performs feedback control based on the internal / external temperature difference ΔTa. That is, when the internal / external temperature difference ΔTa approaches the set value, the relay switch 62 is turned off and the rate of temperature increase is slowed. After that, when the internal / external temperature difference ΔTa does not reach the set value, the relay switch 62 is turned on and heated. The supply power W and the heating time T are adjusted while repeating ON-OFF control of the relay switch 62.

-Correspondence with claims-
The DPF 30 is disposed downstream of the exhaust pipe 16 and constitutes a filter that collects PM. The injector 4 and the oxidation catalyst 20 constitute a regenerator that incinerates and removes PM to regenerate DPF, and a differential pressure sensor 42. The processes of S11, S12, S13, S15, and S16 of the controller 70 are configured as a regeneration control device that controls the start / stop of the operation of the regeneration device.

  A part of the processing of S17 of the controller 70 constitutes an insufficient heat amount calculating means for calculating the heat amount Q insufficient for regeneration based on the detected temperatures of the center temperature sensor 40 and the outer peripheral temperature sensor 41, and the electric heater 61 The heating means for supplying the heat quantity Q to the outer periphery of the DPF 30 is configured.

  The arrangement interval of the heating wires 63 of the electric heater 61 constitutes a heating gradient imparting function for supplying an amount of heat so as to reduce the amount of heating from the DPF 30 inlet side toward the outlet side.

~ Operation ~
The operation related to reproduction (S11 → S12 → S13 → S14 → S15 → S16) will be described.

The exhaust gas flowing into the downstream portion of the exhaust pipe 16 first passes through the oxidation catalyst 20. At this time, nitric oxide (NO) contained in the exhaust gas is oxidized into nitrogen dioxide (NO2) by the reaction (R1) by the action of the catalyst. In addition, HC and CO in the exhaust are also oxidized by the reaction (R2, R3). The exhaust temperature is raised by the oxidation reaction (R2) of the fuel added to the exhaust by post injection.
4NO + O2 → 2NO2 (R1)
HC + O2 → CO2 + H2O (R2)
C0 + 1/2 O2 → CO2 (R3)

The solid carbonaceous material (C), which is the main component of PM deposited on the DPF 30, is oxidized by the reaction (R4, R5), and the DPF 30 is regenerated.
C + O2 → CO2 (R4)
C + 2 NO2 → CO2 + 2 NO (R5)

  During regeneration, part of the heat in the DPF 30 escapes from the outer periphery of the DPF 30 to the outside, so that the temperature at the outer periphery of the filter is lower than the temperature at the center of the filter. Due to the temperature difference inside the filter, there is a risk of filter cracking and runaway regeneration due to thermal stress.

  Therefore, when a temperature difference occurs inside the filter, heating control is performed (S14 → S17 → S18 → S19 → S20).

  FIG. 4 is a conceptual diagram illustrating an operation related to heating. By appropriate regeneration control, the detected temperature Tcet at the center of the filter becomes t (temperature that is sufficient and sufficient for regeneration). On the other hand, the detected temperature Tout at the outer periphery of the filter is t−a, and an internal / external temperature difference ΔTa = a occurs. The electric heater 61 supplies heat to the outer periphery of the DPF 30 so as to eliminate the internal / external temperature difference ΔTa.

  By the way, at the time of regeneration, PM staying on the filter inlet side burns first, and the combustion heat is sent to the outlet side. Therefore, the temperature on the filter outlet side is higher than the temperature on the filter inlet side. If the detected temperature Tout of the filter outer peripheral portion on the filter inlet side is ta, the temperature of the filter outer peripheral portion on the filter inlet side is ta-b. The temperature difference between the filter inlet side and the outlet side can cause filter cracking.

  If the electric heater 61 is heated uniformly (temperature increase + a) so as to eliminate the internal / external temperature difference ΔTa = a, the temperature of the filter outer peripheral portion on the filter inlet side becomes t, and the filter central portion and the outer periphery The temperature difference of the part is eliminated. However, the temperature of the filter outer peripheral portion on the filter inlet side is t + b, and the temperature difference between the filter inlet side and the outlet side is not eliminated. Furthermore, excessive heating is uneconomical.

  The heating wire 63 of the electric heater 61 of this embodiment is arrange | positioned from the DPF entrance side to the exit side at the spacing from dense to sparse. When electric energy is supplied, the electric heater 61 supplies heat so as to reduce the amount of heating from the DPF inlet side toward the outlet side. That is, heating is performed so as to increase the temperature by + a on the DPF inlet side, while heating is performed so that the temperature is increased by + a−b on the DPF outlet side.

  When heating is performed with such a heating gradient, the temperature from the filter inlet side to the outlet side is uniformly t in the outer periphery of the filter, and the temperature difference between the filter inlet side and the outlet side is also eliminated.

  In FIG. 4, for convenience of explanation, both the temperature gradient and the heating gradient are expressed as linear functions as an example. However, the present invention is not limited to this.

~effect~
In the present embodiment, by making the temperature in the filter uniform, it is possible to prevent filter cracking and runaway regeneration due to the temperature difference inside the filter. Moreover, the following effects accompanying this can be obtained.

  PM remaining in the filter can be prevented and DPF regeneration can be performed more reliably. By ensuring proper regeneration, the DPF is not damaged and contributes to a longer life of the DPF. In addition, by properly performing appropriate regeneration, the regeneration time can be shortened, resulting in improved fuel efficiency.

  In this embodiment, other effects can be obtained.

  The electric heater 61 can supply the amount of heat necessary for regeneration without excess or deficiency. By eliminating unnecessary heating, it contributes to improving energy efficiency. Furthermore, if the regenerative energy of the hybrid vehicle is used, further energy efficiency can be improved.

  The controller 70 sets the heating time T in step S18 and performs feedback control in step S19. Thereby, excessive temperature rise can be prevented.

  The electric heater 61 is provided so as to cover the outer periphery of the DPF 30 via the brackets 34, 35, and 36, and the electric heating wire 63 is embedded in a heat insulating material. When the heating wire 63 is disconnected, the bracket 36 is removed and the heating heater 61 is replaced. This contributes to improvement in maintenance.

~ Modification ~
In the present embodiment, the heating wires 63 are arranged from dense to sparse intervals from the DPF inlet side to the outlet side, and the arrangement intervals of the heating wires 63 constitute a heating gradient imparting function, but the present invention is limited to this. Is not to be done.

  FIG. 5 is a schematic plan view of the DPF 30 showing the configuration according to the modification. The heating wires 63 are arranged at uniform intervals from the DPF inlet side to the outlet side. On the other hand, the resistance value Ω of the heating wire 63 is set from a high value to a low value from the DPF inlet side to the outlet side. For example, the resistance value of the heating wire 63 on the DPF inlet side is Ω1, the resistance value of the heating wire 63 in the center of the DPF is Ω2, and the resistance value of the heating wire 63 on the DPF outlet side is Ω3, so that Ω1> Ω2> Ω3. Set as follows. When electric energy is supplied, the electric heater 61 supplies heat so as to reduce the amount of heating from the DPF inlet side toward the outlet side.

  That is, the setting of the resistance value Ω of the heating wire 63 constitutes a heating gradient imparting function. With this configuration, the same effect as in the present embodiment can be obtained.

2 Common rail 4 Injector 6 Intake passage 10 Internal combustion engine 8 Turbocharger 11 Intercooler 12 Intake control valve 14 Intake manifold 15 Exhaust manifold 16 Exhaust pipe 18 EGR valve 19 Exhaust purification device 20 Oxidation catalyst 30 DPF
31 catalyst carrier 32 DPF support 33 casing 34, 35, 36 bracket 40 center temperature sensor 41 outer periphery temperature sensor 42 differential pressure sensor 43 load sensor 44 rotation sensor 50 alternator 60 battery 61 electric heater 62 relay switch 63 heating wire 70 controller

Claims (4)

A filter that is disposed in the exhaust system of the engine and collects particulate matter contained in the exhaust gas, a regeneration device that regenerates the filter by burning and removing particulate matter accumulated on the filter, and operation of the regeneration device In an exhaust emission control device comprising a regeneration control device for controlling start / stop,
First temperature detection means for detecting the temperature of the filter center,
Second temperature detection means for detecting the temperature of the filter outer periphery,
An insufficient heat amount calculating means for calculating an amount of heat insufficient for regeneration based on the detected temperatures of the first temperature detecting means and the second temperature detecting means;
An exhaust emission control device comprising: heating means for supplying heat obtained by the insufficient heat quantity calculating means to an outer periphery of the filter. The exhaust emission control device according to claim 1,
The heating means includes
An exhaust emission control device having a heating gradient imparting function for supplying a heat amount so as to reduce a heat amount from the filter inlet side toward the outlet side. The exhaust emission control device according to claim 2,
The heating means has heating wires arranged at dense to sparse intervals from the filter inlet side to the outlet side,
The exhaust gas purification apparatus according to claim 1, wherein the heating gradient providing function supplies heat when the heating wire generates heat. The exhaust emission control device according to claim 3,
The exhaust heating device, wherein the heating wire generates heat using regenerative energy.

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