Exhaust purification device

Abstract

To improve HC purification performance by making suppression of oxygen poisoning of a catalyst and suppression of deterioration of oxidation reaction compatible.SOLUTION: The exhaust emission control device includes an exhaust passage 30 connected to a combustion chamber 4 of an engine 1, a second purification catalyst 33 disposed in the exhaust passage and including an adsorbent for adsorbing HC discharged from the engine and an oxidation catalyst capable of oxidizing HC, a secondary air supply passage 40 connected to the exhaust passage upstream of the second purification catalyst 33, an air pump 41 for supplying secondary air to the secondary air supply passage, a secondary air control valve 42 disposed in the secondary air supply passage for imparting periodicity to the secondary air, and an ECU100 electrically connected to the secondary air control valve. The ECU alternately executes a supply time for supplying the secondary air by opening the secondary air control valve and a stop time for stopping the secondary air by closing the secondary air control valve, the supply time is 2 seconds or more and 16 seconds or less, and the stop time is longer than 0 second and 16 seconds or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to an exhaust gas purification device. [Background technology]

[0002] Engine exhaust contains harmful components such as HC (hydrocarbons), CO (carbon monoxide), NOx (nitrogen oxides), and soot. To prevent these harmful components from being emitted to the outside, the exhaust path is equipped with purification catalysts, oxygen storage materials (OSC materials), catalyst-loaded filters, and other devices. Furthermore, because catalyst activity is low when the engine temperature is low, such as during a cold start, an adsorbent is also used to suppress harmful components when the engine is cold. The adsorbent adsorbs harmful components in the exhaust when the engine is cold and releases the adsorbed harmful components when the engine temperature rises.

[0003] A method of supplying oxygen to a catalyst by introducing secondary air into the exhaust path to promote catalyst activation when the catalyst temperature is low, etc. Patent Document 1 discloses an exhaust purification device that is equipped with a device that periodically introduces secondary air upstream of the catalyst and changes the secondary air period based on the operating state of the engine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-92713 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, when a mixture of air and fuel with a stoichiometric air-fuel ratio (λ=1) is supplied to the engine, it is possible to activate the catalyst by introducing secondary air into the exhaust path and supplying additional oxygen. However, if secondary air is continuously supplied to the catalyst, excessive oxygen will be adsorbed onto the precious metals on the catalyst surface, resulting in a state known as oxygen poisoning, which reduces catalytic activity. This problem can be addressed by periodically supplying secondary air to the catalyst.

[0006] By periodically supplying secondary air to the catalyst during shutdown periods, alternating between periods when oxygen is not supplied (shutdown periods) and periods when oxygen is supplied (supply periods), oxygen poisoning on the catalyst surface can be eliminated during shutdown periods. The oxygen storage material releases its stored oxygen during shutdown periods when the oxygen concentration is low. Therefore, during shutdown periods, both the oxygen on the catalyst surface and the oxygen released from the OSC material can be used to oxidize the exhaust gas in the order of most reactive: H2, CO, and HC. The heat generated by this oxidation reaction further activates the catalyst surface, further promoting the supply of oxygen from the oxygen storage material.

[0007] However, if the shutdown time is too long, the amount of oxygen released from the oxygen storage material gradually becomes insufficient, suppressing the oxidation reaction and heat generation.If the exhaust gas purification device includes an HC adsorbent, when the oxygen released from the OSC runs out during the shutdown time and the air-fuel ratio returns to λ=1, there is a problem that there is insufficient oxygen to oxidize the HC desorbed from the adsorbent, resulting in a decrease in HC purification performance.

[0008] The technology disclosed herein has been developed in light of these points, and its purpose is to supply secondary air at an appropriate cycle in order to simultaneously suppress oxygen poisoning of the catalyst and suppress a decline in the oxidation reaction, thereby improving HC purification performance. [Means for solving the problem]

[0009] As a result of extensive research, the inventors of the present application have succeeded in suppressing both oxygen poisoning of the catalyst and a decrease in the oxidation reaction by appropriately setting the period when oxygen is not supplied and the period when oxygen is supplied in the periodic secondary air supply.

[0010] Specifically, the technology disclosed here is an exhaust passage connected to a combustion chamber of the engine; a purification catalyst disposed in the exhaust passage and including an adsorbent for adsorbing HC emitted from the engine and an oxidation catalyst capable of oxidizing HC; a secondary air supply passage connected to the exhaust passage upstream of the purification catalyst; a secondary air supply device that supplies secondary air to the secondary air supply passage; a secondary air control valve disposed in the secondary air supply passage and providing periodicity to the secondary air; a controller electrically connected to the secondary air control valve; the controller alternately executes a supply period in which the secondary air control valve is opened to supply secondary air and a stop period in which the secondary air control valve is closed to stop the secondary air, The supply time is 2 seconds or more and 16 seconds or less, and the stop time is more than 0 seconds and 16 seconds or less.

[0011] With this configuration, when the exhaust gas is at a low temperature, such as during engine startup, secondary air can be supplied upstream of the purification catalyst to increase its activity. The secondary air is periodically supplied to the purification catalyst by alternately repeating supply and stop periods. By providing a predetermined stop period rather than a steady supply of secondary air, it is possible to prevent excessive adsorption of oxygen onto the surface of the purification catalyst, resulting in oxygen poisoning. Furthermore, by alternately repeating supply and stop periods for appropriate periods, a good balance is achieved between the release of HC from the adsorbent and the purification of HC through oxidation reactions, making it possible to maintain a high HC purification rate.

[0012] It is more preferable that the supply time is 2 seconds or more and less than 8 seconds, and the stop time is 2 seconds or more and 6 seconds or less.

[0013] This configuration makes it possible to further increase the HC purification rate.

[0014] The purification catalyst preferably contains an oxygen storage material (OSC material) that has the function of storing and releasing oxygen.

[0015] A purification catalyst containing an oxygen storage material generates heat of adsorption by adsorbing O2 when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and generates heat of oxidation by oxidizing HC and CO using the adsorbed O2 when the exhaust air-fuel ratio is non-lean. Thus, the purification catalyst is characterized by repeating adsorption and oxidation reactions through a cycle of lean and non-lean states. If secondary air is constantly supplied to the purification catalyst, the catalyst will always be in a lean state, and no cycle of lean and non-lean states will occur, which will cause a drop in catalyst temperature and a decrease in activity. According to the configuration of the present disclosure, periodic secondary air can create the above-mentioned cycle of lean and non-lean states. The purification catalyst generates a cycle of adsorption heat and oxidation heat due to the periodic secondary air, making it possible to maintain a high temperature and promote combustion function.

[0016] Furthermore, by setting the secondary air stop time to an appropriate period, the stop time can be ended and the supply time can be started when the oxygen released from the OSC material runs out. During the stop time, the oxidation reaction and heat generation are not suppressed, and there is no shortage of oxygen to oxidize the HC released from the adsorbent, so catalytic activity can be increased very efficiently.

[0017] The adsorbent may include zeolite, and the oxidation catalyst may include at least one selected from palladium, rhodium, and platinum.

[0018] The air-fuel ratio of the mixture supplied to the engine may be set to λ=1, which is approximately equal to the stoichiometric air-fuel ratio. [Effects of the Invention]

[0019] As explained above, the exhaust gas purification device disclosed herein can suppress oxygen poisoning of the catalyst and suppress a decrease in oxidation reaction, thereby improving HC purification performance. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram illustrating an engine system to which an exhaust purification device is applied. [Figure 2] FIG. 2 is a block diagram of an engine system to which the exhaust purification device is applied. [Figure 3] FIG. 3 is a schematic diagram for explaining the periodicity of the secondary air. [Figure 4] FIG. 4 is a graph showing the HC purification rate when the supply time of secondary air is fixed at 1 second and the stop time is set to various times. [Figure 5] FIG. 5 is a graph showing the HC purification rate when the supply time of secondary air is fixed at 2 seconds and the stop time is set to various times. [Figure 6] FIG. 6 is a graph showing the HC purification rate when the supply time of secondary air is fixed at 16 seconds and the stop time is set to various times. [Figure 7] FIG. 7 is a graph showing the HC purification rate when the secondary air stop time is fixed at 4 seconds and the supply time is set to various times. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of an engine system to which an exhaust gas purification device is applied will be described with reference to the drawings. The exhaust gas purification device described here is an example.

[0022] Fig. 1 is a schematic diagram illustrating an engine system to which an exhaust gas purification device is applied, and Fig. 2 is a block diagram illustrating an engine system to which an exhaust gas purification device is applied.

[0023] The engine system has an engine 1. The engine 1 is mounted on a four-wheeled automobile. The automobile runs when the engine 1 is driven. The fuel for the engine 1 is gasoline in this configuration example.

[0024] <Engine configuration> Engine 1 has a cylinder 2 and a piston 3 inserted into cylinder 2. The piston 3 reciprocates due to combustion of an air-fuel mixture in a combustion chamber 4 inside cylinder 2, and an intake stroke, compression stroke, expansion stroke, and exhaust stroke are repeated within cylinder 2. Engine 1 has a fuel injection valve 5 that supplies fuel to combustion chamber 4, and an intake passage 20 and an exhaust passage 30 that are connected to combustion chamber 4. Air supplied from intake passage 20 is introduced into combustion chamber 4 by an intake valve 21. Exhaust gas generated by combustion of the air-fuel mixture in combustion chamber 4 is discharged into exhaust passage 30 by an exhaust valve 31.

[0025] The intake valve 21 and the exhaust valve 31 are controlled to open and close by a valve control device. The valve control device adjusts the amount of air introduced into the cylinder 2 and the amount of burned gas introduced into the cylinder 2 by controlling the opening and closing of the intake valve 21 or the exhaust valve 31. The valve control device is a variable valve mechanism that varies the valve timing and / or valve lift, and as shown in FIG. 2, is, for example, an electric or hydraulic intake S-VT (Sequential-Valve Timing) 11 and an exhaust S-VT 12. The intake S-VT 11 and the exhaust S-VT 12 continuously change the rotational phase of the intake camshaft and the exhaust camshaft, respectively, within a predetermined angle range.

[0026] <Exhaust gas purification device> An exhaust purification device 10 is arranged downstream of the exhaust passage 30. The exhaust purification device 10 includes purification catalysts 32, 33, and 34 that purify the exhaust gas, and a secondary air supply device 41 that supplies secondary air. In the exhaust passage 30, a first purification catalyst 32, a second purification catalyst 33, and a third purification catalyst 34 are arranged in this order from upstream.

[0027] (purifying catalyst) The first purification catalyst 32 and the third purification catalyst 34 are three-way catalysts. The first purification catalyst 32 and the third purification catalyst 34 are exhaust purification catalysts that become activated at a predetermined temperature or higher, and that purify mainly nitrogen oxides (NOx) out of the harmful substances in the exhaust gas by reducing them, and purify hydrocarbons (HC) and carbon monoxide (CO) by oxidizing them. The first purification catalyst 32 and the third purification catalyst 34 are formed with a catalyst layer inside a cylindrical case, and the catalyst layer is supported on a carrier, with precious metal particles such as Rh (rhodium), Pd (palladium), Pt (platinum), etc., and OSC materials or the like as promoters. The first purification catalyst 32 and the third purification catalyst 34 have a high NOx purification rate when the exhaust air-fuel ratio (air-fuel ratio: A / F) is rich. When the first purification catalyst 32 and the third purification catalyst 34 are exposed to oxygen, the supported catalytic metal is oxidized, causing a decrease in activity and a decrease in the NOx purification rate. The first purification catalyst 32 and the third purification catalyst 34 have an oxygen storage capacity (OSC) function, and when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, they generate heat of adsorption by adsorbing O2, and when the air-fuel ratio of the exhaust gas is not lean, they use the adsorbed O2 to oxidize HC and CO.

[0028] The second purification catalyst 33 includes an adsorbent that adsorbs HC emitted from the engine and an oxidation catalyst that can oxidize the HC. The second purification catalyst 33 corresponds to the "purification catalyst" in the claims. The second purification catalyst 33 is, for example, formed by stacking an HC adsorption layer and a catalyst layer inside a cylindrical case. The second purification catalyst 33 has an HC adsorption layer containing zeolite on a carrier, and a catalyst layer containing precious metal particles such as Rh (rhodium), Pd (palladium), or Pt (platinum) as an oxidation catalyst on the HC adsorption layer. The catalyst layer may contain an OSC material. The oxidation catalyst of the second purification catalyst 33 is, for example, a diesel oxidation catalyst (DOC). The HC adsorbent is more preferably β-zeolite with SiO2 / Al2O3=25-300. The HC adsorbent can temporarily adsorb HC when the oxidation catalyst is not sufficiently activated. When the temperatures of the HC adsorbent and the oxidation catalyst become high, HC are released from the HC adsorbent, and the HC can be oxidized by the oxidation catalyst. A catalyst temperature sensor SW1 is arranged near the inlet or outlet of the second purification catalyst 33. The catalyst temperature sensor SW1 is capable of detecting the temperature of the exhaust gas passing through the second purification catalyst 33. The temperature of the second purification catalyst 33 can be estimated from the temperature detected by the catalyst temperature sensor SW1. An exhaust sensor SW2 may be arranged in the exhaust passage 30, between the second purification catalyst 33 and the third purification catalyst 34. The exhaust sensor SW2 is capable of detecting the concentrations of exhaust components such as HC, CO, and NOx.

[0029] (Secondary air supply type) A secondary air supply passage 40 is connected to the exhaust passage 30 between the first purification catalyst 32 and the second purification catalyst 33. Secondary air is supplied to the secondary air supply passage 40 from a secondary air supply device 41. The secondary air supply device 41 is, for example, an air pump that sends outside air to the secondary air supply passage 40. The secondary air is not limited to outside air, and may be air supplied from the intake passage or the exhaust passage by providing a branch passage in the intake passage or the exhaust passage. A secondary air control valve 42 is arranged in the secondary air supply passage 40 between the secondary air supply device 41 and the exhaust passage 30. The secondary air control valve 42 imparts periodicity to the secondary air supplied from the secondary air supply device 41. The secondary air control valve 42 is electrically connected to the ECU 100.

[0030] Under the control of the ECU 100, the secondary air control valve 42 opens to supply secondary air and closes to stop the secondary air. For example, as shown in FIG. 3, when a mixture of air and fuel at a stoichiometric air-fuel ratio (λ=1) is supplied to the engine, a supply period in which the secondary air control valve is opened to supply secondary air and a stop period in which the secondary air control valve is closed to stop the secondary air are alternately executed, thereby periodically supplying secondary air to the exhaust passage 30. When secondary air is not supplied, the oxygen concentration in the exhaust passage is in a steady state of λ=1, as indicated by the dashed line L1 in FIG. 3. When secondary air is constantly supplied rather than periodically, the oxygen concentration in the exhaust passage is in a steady state, as indicated by the dashed line L2 in FIG. 3. Note that FIG. 3 is a schematic diagram for ease of explanation, and the waveform of the actually measured oxygen concentration may be curved.

[0031] (Secondary air supply time and stop time) The supply time and stop time of secondary air can be set arbitrarily, and may be maintained at a constant cycle or may be varied. The supply time of secondary air is preferably between 2 and 16 seconds, and more preferably between 2 and 8 seconds. If the supply time of secondary air is 1 second or less, the oxygen storage capacity cannot be fully utilized, and the catalyst activity cannot be promoted. The stop time of secondary air is preferably between 0 and 16 seconds. More preferably, the stop time of secondary air is between 2 and 6 seconds. By supplying secondary air, it is possible to increase the HC purification rate compared to when secondary air is not supplied, but if there is no stop time for secondary air or if the supply time is long, there is a risk of oxygen poisoning of the catalyst. If the stop time is longer than 16 seconds, the HC purification rate cannot be significantly improved. If the stop time is too long, there is a risk of oxygen shortage, and the exhaust gas cannot be sufficiently purified.

[0032] As described above, by alternating between supply and stop periods for a predetermined period of time, HC desorption from the adsorbent and HC purification through oxidation reactions are achieved in a balanced manner, making it possible to maintain a high HC purification rate. Furthermore, a purification catalyst containing an oxygen storage material generates adsorption heat by adsorbing O2 when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio. When the exhaust air-fuel ratio is non-lean, it generates oxidation heat by oxidizing HC and CO using the adsorbed O2. Periodic secondary air can create a cycle of lean and non-lean states. By supplying such secondary air, a cycle of adsorption heat and oxidation heat occurs in the exhaust purification catalyst supported on the filter, making it possible to maintain a high temperature and promote combustion function. Furthermore, by adjusting the stop and supply periods so that oxygen is supplied again immediately after the oxygen stored in the oxygen storage material has been fully released, it is possible to generate adsorption heat and oxidation heat most efficiently and further activate the catalyst.

[0033] <Control system> Next, a control system of the exhaust purification device will be described with reference to Fig. 2. The engine system of this embodiment is controlled by an ECU (Engine Control Unit) 100 provided in a vehicle. The ECU 100 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) 101, a memory 102, and an I / F circuit 103. The CPU 101 executes programs. The memory 102 is configured, for example, by a RAM (Random Access Memory) or a ROM (Read Only Memory), and stores programs and data. The I / F circuit 103 inputs and outputs electrical signals. The ECU 100 is an example of a controller.

[0034] 1 and 2, various sensors SW1 to SW4 are electrically connected to the ECU 100. The sensors SW1 to SW4 output signals to the ECU 100. The sensors include the following sensors. Catalyst temperature sensor SW1: arranged in the exhaust passage 30 near the purification catalyst 33, and detects the temperature of the air flowing through the exhaust passage 30. Exhaust sensor SW2: Detects the concentration of exhaust components such as HC, CO, and NOx. Accelerator opening sensor SW3: Attached to the accelerator pedal mechanism, it detects the amount of accelerator pedal depression (accelerator opening). Engine revolution speed sensor SW4: attached to engine 1 and detects the revolution speed of engine 1.

[0035] The ECU 100 determines the operating state of the engine 1 based on signals from sensors SW1 to SW4, etc., and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in a memory 102. The control logic includes calculating a target amount and / or a control amount using a map stored in the memory 102.

[0036] The ECU 100 is electrically connected to devices such as the fuel injection valve 5, intake S-VT 11, exhaust S-VT 12, secondary air supply device 41, and secondary air control valve 42. The ECU 100 outputs an electrical signal related to the calculated control amount to the fuel injection valve 5, intake S-VT 11, exhaust S-VT 12, secondary air supply device 41, secondary air control valve 42, etc.

[0037] (Control when catalyst temperature drops) As a controller of the exhaust gas purification device, when the temperature of the exhaust gas purification catalyst drops, the ECU 100 opens the secondary air control valve 42 and supplies secondary air to the exhaust gas purification catalyst to activate it. Specifically, the ECU 100 determines whether the temperature detected by the catalyst temperature sensor SW1 is equal to or higher than a predetermined temperature stored in the memory 102. If it is lower than the predetermined temperature, a control signal is output to the secondary air supply device 41 and the secondary air control valve 42 to periodically supply secondary air from the secondary air supply passage 40 to the exhaust passage 30. In this way, by periodically supplying secondary air to the purification catalyst 34, the release of HC from the adsorbent and the oxidation of HC, and the cycle of adsorption heat and oxidation heat occur efficiently, keeping the catalyst activity high and promoting the purification function. The predetermined temperature is the temperature range in which the exhaust gas purification catalyst can exhibit a purification effect, for example, 200°C or higher and 400°C or lower. Note that the secondary air is supplied not only according to the temperature detected by the catalyst temperature sensor SW1, but may also be supplied according to the operating state of the engine 1 and the concentration of exhaust components determined by signals from other sensors.

[0038] (Evaluation of HC purification rate) In order to verify that the catalyst activity can be improved by periodically supplying secondary air to the purification catalyst, the following evaluation was conducted.

[0039] (Purification catalyst) A diesel oxidation catalyst (DOC) equipped with an HC adsorbent and a three-way catalyst were mixed and used as the purification catalyst. The diesel oxidation catalyst equipped with an HC adsorbent used platinum and palladium as precious metal particles, and cerium-zirconium composite oxide and alumina as promoters. Beta zeolite was used as the HC adsorbent. The substrate was made of cordierite and was a flow-through type. The three-way catalyst used rhodium and palladium as precious metal particles, and cerium-zirconium composite oxide and alumina as promoters. The substrate was made of cordierite and was a flow-through type.

[0040] (Evaluation conditions) The composition of the model gas is shown in Table 1. The model gas was a mixture with a stoichiometric air-fuel ratio (λ = 1). 1% oxygen was added to the model gas as secondary air. The gas flow was controlled at a space velocity of 11,000 (1 / h) and a temperature increase rate of 30°C / min to 600°C. The secondary air was introduced at a predetermined interval, with set supply and stop times. After the introduction of the model gas and secondary air began, the gas temperature was increased, and the total HC concentration (THC) in the gas was measured downstream of the purification catalyst. The HC reduction efficiency was calculated by dividing the measured total HC concentration downstream by the total HC concentration of the original model gas. Considering the required function of a purification catalyst containing an HC adsorbent, which is to simultaneously desorb and oxidize HC once adsorbed during temperature increase, the HC reduction efficiency was calculated as an average over an inlet gas temperature range of 80°C to 300°C.

[0041] [Table 1]

[0042] (Comparative Example 1) The HC purification rate was calculated for secondary air supplied at various cycles with a fixed supply time of 1 second and stop times of 2, 4, 6, and 16 seconds. The results are shown in Figure 4. Note that in Figures 4 to 6, the data for a stop time of 0 seconds represents the purification rate when secondary air was introduced steadily rather than periodically, and the data marked [λ=1] represents the purification rate when only the model gas (λ=1) was introduced without introducing secondary air. As shown in Figure 4, when the supply time was 1 second and the stop times were 2, 4, 6, and 16 seconds, the purification rate was lower than the purification rate when secondary air was introduced steadily.

[0043] Example 1 The HC purification rate was calculated for secondary air supply cycles with a fixed supply time of 2 seconds and stop times of 2, 4, 6, and 16 seconds. The results are shown in Figure 5. When the supply time was 2 seconds and the stop times were 2, 4, 6, and 16 seconds, a higher purification rate was obtained than when secondary air was constantly introduced. In particular, the purification rate was significantly higher than when secondary air was constantly introduced in cycles with a supply time of 2 seconds and a stop time of 2 seconds, a supply time of 2 seconds and a stop time of 4 seconds, and a supply time of 2 seconds and a stop time of 6 seconds. Among these, the cycle with a supply time of 2 seconds and a stop time of 4 seconds showed a significantly higher purification rate.

[0044] Example 2 The HC purification rate was calculated for secondary air supplied at each cycle with a fixed supply time of 16 seconds and a stop time of 2, 4, 6, or 16 seconds. The results are shown in Fig. 6. When the supply time was 16 seconds and the stop time was 2, 4, 6, or 16 seconds, a higher purification rate was obtained than when secondary air was constantly introduced. When the supply time was 16 seconds, the purification rate improved as the stop time was longer.

[0045] Example 3 The HC purification rate was calculated for the case where the stop time was fixed at 4 seconds and secondary air was supplied at intervals of 1, 2, 4, 8, and 16 seconds. The results are shown in Figure 7. In Figure 7, the data for a supply time of 0 seconds represents the purification rate when only the model gas (λ=1) was introduced without secondary air being introduced, and the data marked "Steady" represents the purification rate when secondary air was introduced steadily rather than periodically. As shown in Figure 7, the 2-second supply time showed the highest purification rate, and the next highest supply time of 4 seconds also showed a purification rate of over 90%, significantly improving the purification rate compared to when secondary air was introduced steadily. Although improvements in purification rate were also observed with supply times of 8 and 16 seconds, the purification rates were not as significantly high as those with supply times of 2 and 4 seconds. [Explanation of symbols]

[0046] 1 engine 4 Combustion chamber 10 Exhaust gas purification device 20 Intake passage 30 Exhaust passage 32 First purification catalyst 33 Second purification catalyst 34 Third purification catalyst 40 Secondary air supply passage 41 Air pump (secondary air supply device) 42 Secondary air control valve 100 ECU (Controller) SW1 catalyst temperature sensor

Claims

1. an exhaust passage connected to a combustion chamber of the engine; a purification catalyst disposed in the exhaust passage and including an adsorbent for adsorbing HC emitted from the engine and an oxidation catalyst capable of oxidizing HC; a secondary air supply passage connected to the exhaust passage upstream of the purification catalyst; a secondary air supply device that supplies secondary air to the secondary air supply passage; a secondary air control valve disposed in the secondary air supply passage and providing periodicity to the secondary air; a controller electrically connected to the secondary air control valve; the controller alternately executes a supply period in which the secondary air control valve is opened to supply secondary air and a stop period in which the secondary air control valve is closed to stop the secondary air, The exhaust gas purification device is characterized in that the supply time is 2 seconds or more and 16 seconds or less, and the stop time is more than 0 seconds and 16 seconds or less.

2. The exhaust gas purification device according to claim 1, The exhaust gas purification device is characterized in that the supply time is 2 seconds or more and less than 8 seconds, and the stop time is 2 seconds or more and 6 seconds or less.

3. The exhaust gas purification device according to claim 1, An exhaust gas purification device, wherein the adsorbent contains zeolite, and the oxidation catalyst contains at least one selected from the group consisting of palladium, rhodium, and platinum.

4. The exhaust gas purification device according to claim 1, The exhaust gas purification device is characterized in that the purification catalyst includes an oxygen storage material having a function of storing and releasing oxygen.

5. The exhaust gas purification device according to claim 1, An exhaust gas purification device characterized in that the air-fuel ratio of the mixture supplied to the engine is λ=1, which is approximately equal to the stoichiometric air-fuel ratio.

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