JP5181972B2 - Engine exhaust gas purification device - Google Patents

Description

    The present invention relates to an exhaust gas purification device for an engine.

    From the viewpoints of reducing environmental burden and reducing fuel consumption of automobiles, hybrid cars and automobiles using hydrogen as fuel are attracting attention.

    Gasoline engines that are widely used in passenger cars are generally less efficient at light loads. On the other hand, in the case of a hybrid vehicle, in a low speed range and a light load range, it is possible to drive with an electric motor instead of an engine with low efficiency, so that fuel efficiency can be improved and harmful emissions are also low. It is advantageous for reducing the environmental load.

    On the other hand, in the case of an automobile that uses only hydrogen as a fuel, unlike an automobile that uses an HC (hydrocarbon) component such as gasoline, light oil, or alcohol as fuel, it is possible to avoid exhausting HC as exhaust gas. it can. However, hydrogen fuel is disadvantageous in terms of travel distance because it generates less heat than gasoline and is disadvantageous in terms of output, and it is difficult to mount a large amount of hydrogen in an automobile.

Therefore, it has been proposed to use hydrogen and gasoline as fuel. For example, Patent Documents 1 to 3 disclose a system in which hydrogen and gasoline are switched and supplied to an engine combustion chamber. In these patent documents, when gasoline is used as fuel, the engine is usually stoichiometrically operated. Therefore, in order to purify HC, CO and NOx (nitrogen oxides) in the exhaust gas, a three-way catalyst is provided in the exhaust gas passage. It is described that it arrange | positions. Further, when hydrogen is used as fuel, NOx is discharged from the engine. However, Patent Document 3 discloses that a three-way catalyst, a NOx storage reduction catalyst, and a NOx selective reduction catalyst are used in combination.
JP 2007-51583 A JP 2007-51596 A JP 2007-269227 A

    However, when hydrogen and gasoline are used as fuel, HC is discharged without being purified even if only a three-way catalyst is used, or if a three-way catalyst is combined with a NOx storage reduction catalyst or a NOx selective reduction catalyst. Sometimes.

    That is, a canister containing an adsorbent such as activated carbon is connected to the gasoline tank in order to prevent the evaporated fuel generated in the tank from being released into the atmosphere. Since the adsorption capacity of the adsorbent is limited, it is necessary to perform a purge process in which the atmosphere is taken into the canister before the adsorption is saturated, the fuel component is released from the adsorbent, and introduced into the intake system of the engine. However, when the engine uses hydrogen as the fuel, the lean burn operation is performed and the combustion chamber temperature is low. Therefore, the evaporated fuel purged to the intake system does not completely burn in the combustion chamber, and the amount of HC discharged to the exhaust system is small. Become more. At that time, since the exhaust gas temperature is low, the three-way catalyst is also in a state where the temperature is low and not sufficiently activated, so that the HC caused by the evaporated fuel in the exhaust gas is not oxidized and purified, Will be discharged inside.

    Therefore, the present invention purges the evaporated fuel when the engine is lean-burned with hydrogen as fuel while purifying exhaust gas efficiently when the engine is stoichiometrically run with gasoline as fuel. However, it is an issue to prevent emission from deteriorating.

    In order to solve the above problems, the present invention branches an engine exhaust passage into a first passage and a second passage, and the first passage has a catalyst with good HC purification performance when the exhaust gas is lean and low in temperature. In the second passage, a second catalyst having good performance as a three-way catalyst is arranged, and the flow rate of exhaust gas flowing into the first passage and the second passage according to the properties of the exhaust gas discharged from the engine is set. I tried to control it.

The invention according to claim 1 is an engine exhaust gas purifying apparatus for performing an operation using a fuel containing gasoline and an operation using hydrogen fuel,
A canister that adsorbs the evaporated fuel generated in a fuel tank that stores the fuel containing gasoline, and a purge passage that purges the evaporated fuel adsorbed by the canister to the intake system of the engine;
The engine exhaust passage branches into a first passage and a second passage, the first catalyst is disposed in the first passage, the second catalyst is disposed in the second passage,
The first catalyst is selected from the group consisting of Pt-supported alumina in which Pt is supported on an alumina-based support material, and Pt-supported CeZr-based composite oxide in which Pt is supported on a CeZr-based composite oxide support material. Including at least one species,
The second catalyst includes Pd-supported alumina in which Pd is supported on an alumina support material, Rh-supported CeZr-based composite oxide in which Rh is supported on a CeZr-based composite oxide support material, and Rh on active alumina particles . hints and Rh supported alumina obtained by carrying, at least one selected from the group consisting of Pd supported CeZr-based mixed oxide obtained by supporting Pd on CeZr-based mixed oxide support material,
Of the fuel containing gasoline and hydrogen fuel, at least hydrogen fuel is used, the engine is lean burned, and the temperature of the exhaust gas is below a predetermined temperature, the exhaust gas has priority over the first passage. In the lean burn operation, when the temperature of the exhaust gas is higher than the predetermined temperature, the exhaust gas flows into the first passage and the second passage and the exhaust gas temperature When the engine is stoichiometrically operated using the fuel containing gasoline so that the flow rate of the exhaust gas flowing into the second passage increases as the value of the exhaust gas increases , the exhaust gas is given priority to the second passage. Control means for controlling the flow rate of the exhaust gas flowing into the first passage and the second passage so as to flow into the first passage.

    Here, Pt-supported alumina and Pt-supported CeZr-based composite oxide, which are catalyst materials belonging to the first catalyst group, and Pd-supported alumina, Rh-supported CeZr-based composite oxide, which belong to the second catalyst group. When the Rh-supported alumina and the Pd-supported CeZr-based composite oxide are compared with respect to the exhaust gas purification performance, it will be clarified later by experimental data as follows.

    That is, since the catalyst material of the first catalyst group has Pt as the catalyst metal, the HC purification performance and the NOx purification performance in the low temperature region are higher than the catalyst material of the second catalyst group using Pd and Rh as the catalyst metal. high. In particular, regarding the purification of HC and NO in the low temperature range when the air-fuel ratio of the exhaust gas is lean, the catalyst material of the first catalyst group is excellent. Below ℃, the catalyst material of the first catalyst group has better purification performance than the catalyst material of the second catalyst group.

    On the other hand, regarding the purification of HC and NO when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio, the catalyst material of the second catalyst group has better purification performance than the catalyst material of the first catalyst group. In particular, the catalyst material of the second catalyst group has a characteristic that the light-off temperature is lower than that of the catalyst material of the first catalyst group.

    Thus, in the present invention, when at least hydrogen fuel is used and the engine is lean burn-operated and the temperature of the exhaust gas is lower than a predetermined temperature, the exhaust gas preferentially flows into the first passage. Therefore, HC and NO in the exhaust gas are efficiently purified by the catalyst material of the first catalyst group. That is, HC contained in the exhaust gas by purging the evaporated fuel to the intake system is purified by the catalyst material of the first catalyst group, and is prevented from being discharged into the atmosphere without being purified. Further, NO that is likely to be generated during the lean burn operation using the hydrogen fuel is purified by the catalyst material of the first catalyst group, and is prevented from being discharged into the atmosphere without being purified.

On the other hand, when the fuel containing gasoline is used and the engine is stoichiometrically operated, the exhaust gas preferentially flows into the second passage. Therefore, the catalyst material of the second catalyst group causes the HC in the exhaust gas to be exhausted. And NO is efficiently purified and is prevented from being discharged into the atmosphere without being purified.

    The above-mentioned Pd-supported alumina, Rh-supported CeZr-based composite oxide, Rh-supported alumina, and Pd-supported CeZr-based composite oxide have an exhaust gas temperature of about HC purification when the air-fuel ratio of the exhaust gas is lean. When it becomes higher, the HC purification performance becomes higher than the catalyst material of the first catalyst group. Therefore, HC in exhaust gas is efficiently purified from low temperature to high temperature by using the first catalyst and the second catalyst by controlling the flow rate of exhaust gas flowing into the second passage as the exhaust gas temperature increases. can do.

The invention according to claim 2 is the invention according to claim 1,
The second catalyst is at least one selected from the Pd-supported alumina and the Rh-supported CeZr composite oxide.

    That is, among the four types of catalyst materials belonging to the second catalyst group, the Pd-supported alumina and the Rh-supported CeZr-based composite oxide are HC and NO when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio. Since the light-off temperature relating to purification is low, it is advantageous for purification of HC and NO at low temperatures when fuel containing gasoline is used and the engine is operating stoichiometrically.

The invention according to claim 3 is the invention according to claim 1 or claim 2,
The second catalyst is supported on a carrier such that the Pd-supported alumina or the Pd-supported CeZr-based composite oxide is a lower layer, and the Rh-supported alumina or the Rh-supported CeZr-based composite oxide is an upper layer. Features.

According to a fourth aspect of the present invention, in any one of the first to third aspects,
The engine is mounted on a hybrid vehicle that can be driven by an electric motor, and is used for driving a generator for the electric motor.

    Therefore, when the engine of the hybrid vehicle is lean burned with hydrogen fuel, HC contained in the exhaust gas can be efficiently purified by the first catalyst by purging the evaporated fuel to the intake system. , It is suppressed to be discharged into the atmosphere without being purified.

As described above, according to the present invention, the engine exhaust passage is branched into the first passage and the second passage, and the first passage is made of the group consisting of Pt-supported alumina and Pt-supported CeZr-based composite oxide. A first catalyst containing at least one selected is disposed, and the second passage is at least selected from the group consisting of Pd-supported alumina, Rh-supported CeZr-based composite oxide, Rh-supported alumina, and Pd-supported CeZr-based composite oxide. When a second catalyst including one kind is arranged, and at least hydrogen fuel is used among fuels including gasoline and hydrogen fuel, the engine is lean burn-operated, and the exhaust gas temperature is lower than a predetermined temperature, exhaust gas as gas is preferentially flow into the first passage, in the lean-burn operation, when the temperature of the exhaust gas is higher than the predetermined temperature, the exhaust Scan is so that the exhaust gas flow rate flowing into the second passage about the first passage and the flow into the second passage and the exhaust gas temperature rises is increased, the fuel is used engine stoichiometric operation or gasoline Since the exhaust gas preferentially flows into the second passage when it is being operated, the HC contained in the exhaust gas by the purge of the evaporated fuel to the intake system during the lean burn operation, or the lean burn Can be efficiently purified, and HC and NO can be efficiently purified during the stoichiometric operation. Further, during the lean burn operation, the first catalyst and the second catalyst are separated from each other. It is possible to efficiently purify HC in the exhaust gas from low temperature to high temperature.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

<Schematic configuration of hybrid vehicle>
FIG. 1 is a schematic configuration diagram of a hybrid vehicle according to an embodiment of the present invention. This vehicle is provided with an engine 1 and a motor 2 as power sources, but the engine 1 is a so-called series hybrid vehicle that uses only the power generation and the power for moving the vehicle depends entirely on the motor 2. The engine 1 is a dual fuel engine configured to use gasoline as a fuel by switching between gasoline and hydrogen and further mixing gasoline and hydrogen.

    The hybrid vehicle includes a gasoline fuel tank 3 for supplying gasoline to the engine 1, a hydrogen fuel tank 4 for supplying hydrogen to the engine 1, a generator (generator) 6 driven by the output shaft 5 of the engine 1, and a motor drive A battery (high voltage battery) 7 for storing electric power is provided.

    The battery 7 is connected to the motor 2 and the generator 6 via the DC-AC converter 11 and the AC-DC converter 12, respectively, so that the generated power from the generator 6 and the regenerative power from the motor 2 are supplied. Charged. The battery 7 supplies power to the motor 2 and the generator 6. The output shaft of the motor 2 is connected to the drive wheel 13 via a differential gear 14.

    AC power generated by the generator 6 is converted into DC power by the AC-DC converter 12, further converted into AC power by the DC-AC converter 11, and supplied to the motor 2. The DC power of the battery 7 is converted into AC power having a predetermined frequency by the DC-AC converter 11 and supplied to the motor 2. AC power generated by the generator 6 is converted into DC power by the AC-DC converter 12 and supplied to the battery 7.

    A canister 15 that adsorbs evaporated fuel (gasoline) generated in the tank is connected to the gasoline fuel tank 3 via an evaporated fuel passage 16. The canister 15 has an air intake at the bottom and is made of a breathable member filled with activated carbon or the like. The canister 15 is connected to an intake passage on the downstream side of the throttle valve of the engine 1 via a purge passage 17, and a purge control valve 18 is disposed in the middle of the purge passage 17. The purge control valve 18 is electromagnetically controlled in its opening / closing operation, and the evaporated fuel supplied to the canister 15 is supplied (purged) together with air to the intake passage.

    In this case, the amount of evaporated fuel adsorbed by the canister 15 is estimated based on the temperature of the gasoline fuel tank 3, the time during which purging is not performed, and the purge control valve 18 is turned on when the estimated amount exceeds a predetermined value. The valve is opened for a predetermined time. The purge control valve 18 may be periodically opened for a predetermined time without estimating the evaporated fuel adsorption amount.

    The exhaust passage 21 of the engine 1 branches into a first passage 22 and a second passage 23, a first catalyst 24 is disposed in the first passage 22, and a second catalyst 25 is disposed in the second passage 23. A flow rate control valve 26 that controls the flow rate of exhaust gas flowing through the first passage 22 and the second passage 23 is disposed at a branch portion of the exhaust passage 21. In the exhaust passage 21 upstream of the flow control valve 26, a temperature sensor 27 for detecting the temperature of the exhaust gas flowing into the first catalyst 24 or the second catalyst 25, and an oxygen sensor for detecting the oxygen concentration of the exhaust gas. 28 are arranged. Specific configurations of the first catalyst 24 and the second catalyst 25 will be described later.

<Engine and control system configuration>
As shown in FIG. 2, the engine 1 of the present example includes a pair of rotor housings 31 and 32, two rotors 33 and 34 that are supported by an output shaft (eccentric shaft) 5 and rotate along the inner peripheral surface thereof. Is a two-rotor rotary piston engine. In FIG. 2, the pair of rotor housings 31 and 32 are schematically shown as being developed left and right.

    An intake passage 35 of the engine 1 is provided with a throttle valve 36 driven by an actuator 37 in a common passage portion on the upstream side. Two independent passage portions branched downstream of the intake passage 35 are provided with gasoline fuel injection valves 38 and 39 for performing port injection, and hydrogen for injecting fuel into the combustion chambers in the rotor housings 31 and 32. Fuel injection valves 40 and 41 are installed. In addition, two spark plugs 42 to 45 are installed in each of the rotor housings 31 and 32. The throttle valve actuator 37, the fuel injection valves 38 to 41, the spark plugs 42 to 45, the DC-AC converter 11, the AC-DC converter 12, and the flow control valve 26 are control means (PCM (powertrain control) using a computer. Module)) 46.

    For the above control, the control means 46 includes a battery current / voltage sensor 47, a fuel sensor 48 for detecting the remaining amount of gasoline in the gasoline fuel tank 3, a pressure sensor 49 for detecting the remaining amount of hydrogen in the hydrogen fuel tank 4, and an automobile. The detection signals of the fuel use switch 50, the vehicle speed sensor 51, the accelerator opening sensor 52, the temperature sensor 27, the oxygen sensor 28, and the like provided in the instrument panel are input. The battery current / voltage sensor 47 is attached to the battery 7 and is used to determine the electric power that enters the battery 7 and the electric power that leaves the battery 7 from the current and voltage, and detects the storage amount of the battery 7. belongs to.

    Hereinafter, the control will be specifically described. Regarding the operation of the engine 1, when the output torque required for the motor 2 (hereinafter referred to as “requested torque”) is greater than or equal to a predetermined value based on the detection signals of the vehicle speed sensor 51 and the accelerator opening sensor 52. Further, based on the detection signal of the battery current / voltage sensor 47, it is determined that the operation of the engine 1 is necessary when the storage amount of the battery 7 is equal to or less than a predetermined value. The required engine torque is calculated based on the required torque of the motor 2 and the amount of electricity stored in the battery 7, and the engine 1 is operated.

    The fuel switching between gasoline and hydrogen used in the engine 1 includes the temperature of the second catalyst 25 (catalyst activity) detected by the temperature sensor 27, the gasoline remaining amount in the gasoline fuel tank 3 detected by the fuel sensor 48, This is executed based on the remaining amount of hydrogen in the hydrogen fuel tank 4 detected by the pressure sensor 49 and the type of fuel selected by the driver by the changeover switch 50 for the used fuel. That is, when the engine is started, hydrogen is automatically used until the second catalyst 25 is activated in order to improve the exhaust emission performance. After the activation of the second catalyst 25, gasoline is used when the driver selects gasoline, and hydrogen is used when hydrogen is selected. However, when the remaining amount of either hydrogen or gasoline becomes less than the predetermined value, hydrogen and gasoline are used together at a predetermined mixing ratio. In addition, hydrogen is used when gasoline is used and gasoline is running out of fuel.

    The target air-fuel ratio (target excess air ratio λ) of the engine 1 is different between when gasoline is used and when hydrogen is used. When gasoline is used, λ = 1 is set (stoichiometric operation). It is set to near λ = 2.0, which is the closest to the optimum fuel efficiency at zero (lean burn operation), and lean burn operation is also performed when hydrogen and gasoline are used together. By performing lean burn operation of the engine 1 when using hydrogen, an increase in combustion temperature is suppressed and NOx emission is suppressed. However, even when hydrogen is used, when the required torque for the engine 1 is large (when the battery 7 is charged or when the vehicle electrical load is large), the lean burn operation is performed by appropriately reducing the lean degree of the target air-fuel ratio. The air-fuel ratio of the engine 1 is feedback controlled based on the detection signal of the oxygen sensor 28.

    The control means 46 controls the DC-AC converter 11 and the AC-DC converter 12, and controls power transfer and conversion among the battery 7, the generator 13, and the motor 17. In this case, the motor 2 is driven by the electric power supplied from the battery 7 at the time of low torque operation where the required torque is low, such as at the time of constant speed operation of the automobile or at the start of the automobile, and is driven by the engine 1 at the time of medium torque operation. It is driven by electric power supplied from the generator 6, and is driven by electric power supplied from both the generator 6 and the battery 7 during high torque operation with a high required torque such as during rapid acceleration. When the amount of power stored in the battery 7 is small, the engine 1 causes the generator 6 to generate electric power larger than that required for the motor 2, and extra power is supplied to the battery 7 for charging.

    The control of the flow control valve 26 by the control means 46 will be described in detail after the configuration of the catalyst is described.

<About the catalyst material used for the first catalyst and the second catalyst>
The following 12 types of catalyst materials were prepared, and the saturation HC purification rate and NOx purification rate at each exhaust gas air-fuel ratio lean were measured. Here, since the saturated fuel (evaporative gas) contains a lot of saturated hydrocarbons (HC), the saturated HC purification rate was measured. Saturated hydrocarbons are less likely to be oxidized than unsaturated hydrocarbons due to the stability of their chemical structure. Therefore, if saturated hydrocarbons are oxidized, it may be considered that unsaturated hydrocarbons are also oxidized.

-Three kinds of catalyst materials whose support material is OSCI-
This OSC (oxygen storage / release material) I is a CeZrNd composite oxide (CeZr-based composite oxide) in which Ce, Zr and Nd constitute crystals, and its composition is 10% CeO ₂ -80% ZrO ₂ -10. % Nd ₂ O ₃ (mass%).

    Pd / OSCI catalyst material (Pd-supported CeZr-based composite oxide catalyst material) in which Pd is supported on the OSCI particles as a CeZr-based composite oxide support material, and Rh / OSCI catalyst material in which Rh is supported on OSCI particles ( Rh-supported CeZr-based composite oxide catalyst material) and Pt / OSCI catalyst material (Pt-supported CeZr-based composite oxide catalyst material) in which Pt is supported on OSCI particles were prepared. The catalyst metals Pd, Rh, and Pt were supported on the OSCI particles by using an evaporation to dryness method, followed by firing at a temperature of 500 ° C. for 2 hours to obtain each catalyst material. The amount of each catalyst metal supported was constant at 1.0% by mass with respect to each support material.

-3 types of catalyst materials with support material OSCII-
This OSC (oxygen storage / release material) II is a CeZrNd composite oxide (CeZr composite oxide) in which Ce, Zr and Nd constitute crystals as a CeZr composite oxide, and its composition is 35% CeO. is _{2 -55% ZrO 2 -10% Nd} 2 O 3 ( wt%).

    Pd / OSCII catalyst material (Pd-supported CeZr-based composite oxide catalyst material) in which Pd is supported on the OSCII particles as a CeZr-based composite oxide support material, and Rh / OSCII catalyst material (in which Rh is supported on OSCII particles) Rh-supported CeZr-based composite oxide catalyst material) and Pt / OSCII catalyst material (Pt-supported CeZr-based composite oxide catalyst material) in which Pt is supported on OSCII particles were prepared. The catalyst metals Pd, Rh, and Pt were supported on the OSCII particles by an evaporation-drying method, and each catalyst material was obtained by firing at a temperature of 500 ° C. for 2 hours. The amount of each catalyst metal supported was constant at 1.0% by mass with respect to each support material.

-Three kinds of catalyst materials whose support material is activated alumina-
Pd / Al ₂ O ₃ catalyst material (Pd-supported alumina catalyst material) in which Pd is supported on activated alumina particles as an active alumina support material, and Rh / Al ₂ O ₃ catalyst material (in which Rh is supported on activated alumina particles) Rh-supported alumina catalyst material) and Pt / Al ₂ O ₃ catalyst material (Pt-supported alumina catalyst material) in which Pt is supported on activated alumina particles were prepared. The catalyst metals Pd, Rh, and Pt were supported on the activated alumina particles by using an evaporation to dryness method and calcination at a temperature of 500 ° C. for 2 hours to obtain each catalyst material. The amount of each catalyst metal supported was constant at 1.0% by mass with respect to each support material.

- support material catalyst material three a ZrO ₂ coating La-containing alumina -
ZrO ₂ -coated La-containing alumina is obtained by coating the surface of activated alumina particles containing 4% by mass of La ₂ O ₃ with 10% by mass of zirconium oxide. Pd / ZrLa—Al ₂ O ₃ catalyst material (Pd-supported ZrO ₂ -coated alumina catalyst material) in which Pd is supported on ZrO ₂ -coated La-containing alumina particles as the active alumina-based support material, ZrO ₂ -coated La-containing alumina particles Rh / ZrLa—Al ₂ O ₃ catalyst material supporting Rh (Rh-supported ZrO ₂ coated alumina catalyst material), and Pt / ZrLa—Al ₂ O ₃ catalyst material supporting Pt on ZrO ₂ coated La-containing alumina particles Three types of (Pt-supported ZrO ₂ -coated alumina catalyst material) were prepared. These catalyst materials were obtained by dropping a nitric acid solution of each of the catalyst metals Pd, Rh, and Pt onto the ZrO ₂ -coated La-containing alumina powder, followed by drying and firing at 500 ° C. The amount of each catalyst metal supported was constant at 1.0% by mass with respect to each support material.

-Measurement of saturated HC purification rate and NOx purification rate-
A catalyst sample in which each of the 12 kinds of catalyst materials is supported on a cordierite honeycomb carrier (capacity: 25 mL; diameter: 25.4 mm, length: 50 mm) was prepared using a simulated exhaust gas flow reactor and an exhaust gas analyzer. Then, the saturation HC purification rate and NOx purification rate at the air-fuel ratio lean were measured. The composition of the simulated exhaust gas is as follows: O ₂ = 9.6%, CO ₂ = 0.56%, CO = 0.01%, H ₂ = 1.0%, C ₄ H ₁₀ (butane) = 0.05% NO = 0.001%, H ₂ O = 18.6%, and the remaining N ₂ . In this case, C ₄ H ₁₀ (butane) is a saturated hydrocarbon. The space velocity was 60000 / h, and the temperature increase rate of the catalyst inlet gas temperature was 30 ° C./min.

-Purification characteristics of HC and NOx-
FIG. 3 shows the measurement result of the lean saturated HC purification rate. According to the figure, the above 12 types of catalyst materials begin to purify saturated HC before the catalyst inlet gas temperature reaches 200 ° C., and the group A has a high activity at 400 ° C. or lower, and the gas temperature is 300 ° C. Saturated HC purification begins after the temperature exceeds 400 ° C., and Group B has higher activity in the high temperature range exceeding 400 ° C. than Group A, and Group C begins to purify saturated HC from around 400 ° C. Can be divided.

Group A includes Pt / OSCI and Pt / OSCII catalyst materials as Pt-supported CeZr-based composite oxide catalyst materials, and Pt / Al ₂ O ₃ catalyst materials and Pt / ZrLa-Al as Pt-supported alumina catalyst materials. ₂ O ₃ catalyst material belongs, and Group B includes Rh / OSCI catalyst material and Rh / OSC II catalyst material as Rh-supported CeZr-based composite oxide catalyst materials, and Pd / Al ₂ O ₃ as Pd-supported alumina catalyst material. Catalyst material and Pd / ZrLa—Al ₂ O ₃ catalyst material belong to group C, Pd / OSCI catalyst material and Pd / OSCII catalyst material as Pd-supported CeZr-based composite oxide catalyst material, and Rh-supported alumina catalyst material Rh / Al ₂ O ₃ catalyst material and Rh / ZrLa—Al ₂ O ₃ catalyst material as

4 to 7 show the measurement results of the lean NO purification rate. Looking at the group A catalyst material, the Pt / Al ₂ O ₃ catalyst material shows a decline in the NO purification rate around 350 ° C. (FIG. 6), but the other three types all range from the low temperature range to the high temperature range. It shows a relatively high NO purification rate over a wide temperature range (see FIGS. 4, 5 and 7). In particular, the NOx purification performance of the Pt / OSCI catalyst material and the Pt / OSCII catalyst material is high. Looking at the catalyst material of Group B, the NO purification rate tends to be relatively high at 250 to 500 ° C. A decrease in the NO purification rate in the vicinity of 100 ° C. to 200 ° C. is considered to be caused by the release of NOx adsorbed at low temperatures. Looking at the catalyst material of Group C, a decrease in the NO purification rate is observed around 300 ° C. to 400 ° C., which is considered to be caused by the release of NOx adsorbed on the low temperature side. Further, the NO purification rate at 300 ° C. or less for all the catalyst materials of group A is higher than that of the catalyst materials of groups B and C.

    From the saturated HC and NO purification rate data described above, the saturated HC purification start temperature of the groups B and C is higher than that of the catalytic metals Pd or Rh of the groups B and C compared to Pt. This is probably because NOx adsorbed on the active sites effective for saturated HC purification hinders the purification of saturated HC. In the case of group B, since the release of adsorbed NOx ends at around 300 ° C., the purification start temperature of saturated HC shifts to a higher temperature than 300 ° C., and in the case of group C, the release of adsorbed NOx is 400 It is considered that the saturation HC purification start temperature is shifted further to the higher temperature side because the process is completed at around 0 ° C.

    On the other hand, in group A, although NOx adsorption occurs in a low temperature range of 150 ° C. or lower, the catalyst metal Pt has a relatively low light-off temperature for NOx purification in the presence of saturated HC. It is considered that the adsorbed NOx is decomposed relatively early and the purification start temperature of the saturated HC is lowered as described above.

    Table 1 summarizes the saturated HC purification start temperatures and NO release temperatures of the 12 types of catalyst materials.

<Exhaust gas purification performance near the theoretical air-fuel ratio of group A to C catalyst materials>
-Catalyst sample according to Group A-
Cordierite honeycomb carrier (capacity 25 mL; diameter 25.4 mm, length 50 mm) with Group A Pt / OSCI catalyst material and Pt / Al ₂ O ₃ catalyst material, the former being the upper layer and the latter being the lower layer A catalyst sample supported on the catalyst was prepared. The supported amount per liter of the carrier is 50 g / L for both OSCI and Al ₂ O ₃ , and Pt is 2.5 g / L for both the upper and lower layers (total of 5 g / L).

-Catalyst sample according to Group B-
Prepare a catalyst sample in which Rh / OSCI catalyst material and Pd / Al ₂ O ₃ catalyst material of Group B are supported on the same honeycomb carrier as the catalyst sample of Group A so that the former is the upper layer and the latter is the lower layer. did. The supported amount per liter of the carrier is 50 g / L for both OSCI and Al ₂ O ₃ , 1.0 g / L for the upper layer Rh, and 4 g / L for the lower layer Pd (total of 5 g / L).

-Catalyst sample according to Group C-
Prepare a catalyst sample in which Rh / Al ₂ O ₃ catalyst material and Pd / OSCI catalyst material of group C are supported on the same honeycomb carrier as the catalyst sample of group A so that the former is the upper layer and the latter is the lower layer. did. The supported amount per liter of the carrier is 50 g / L for both OSCI and Al ₂ O ₃ , 1.0 g / L for the upper layer Rh, and 4 g / L for the lower layer Pd (total of 5 g / L).

−Measurement of exhaust gas purification performance−
Each catalyst sample of the above groups A to C was set in a model exhaust gas flow reactor, and the exhaust gas purification performance (light-off temperature T50 and exhaust gas purification rate C400) was evaluated. The model exhaust gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. Table 2 shows the gas composition when A / F = 14.7, A / F = 13.8 and A / F = 15.6. The space velocity SV was 60000 / h, and the temperature elevation rate was 30 ° C./min.

    In the light-off temperature T50, as the model exhaust gas temperature rises, the concentration of each component (HC and NO) of the gas detected downstream of the catalyst becomes half of the concentration of each component (HC and NO) of the gas flowing into the catalyst. This is the catalyst inlet gas temperature at the time (that is, when the purification rate reaches 50%). The exhaust gas purification rate C400 is the purification rate of each component (HC and NO) of the gas when the model exhaust gas temperature at the catalyst inlet is 400 ° C. The result of T50 is shown in FIG. 8, and the result of C400 is shown in FIG.

    Looking at the light-off temperature T50 (FIG. 8), group B is the best, followed by group C and group A in sequence. Regarding the exhaust gas purification rate C400 (FIG. 9), group B is the best, followed by group C and group A in order.

<Configuration of first catalyst and second catalyst and flow path control of exhaust gas>
Based on the performance evaluation results for the group A to C catalyst materials, the first catalyst 24 disposed in the first passage 22 employs the group A catalyst material and is disposed in the second passage 23. In 25, at least one kind of catalyst material selected from the above-mentioned group B and group C (however, Pd / OSCI catalyst material, Pd / OSCII catalyst material and Rh / Al ₂ O ₃ catalyst material) is adopted.

In a preferred embodiment, the second catalyst 25 is made of at least one of a Pd / Al ₂ O ₃ catalyst material and a Pd / ZrLa—Al ₂ O ₃ catalyst material in which Pd is supported on an alumina-based support material of group B, and an OSC. It is a combination of at least one of an Rh / OSCI catalyst material and an Rh / OSCII catalyst material in which Rh is supported on a system support material (a layered structure in which the former is a lower layer and the latter is an upper layer). Alternatively, the second catalyst 25 may be a combination of a group B Pd catalyst material and a group C Rh / Al ₂ O ₃ catalyst material , or a combination of a group B Rh catalyst material and a group C Pd catalyst material. Is also a preferred embodiment (the Pd-based catalyst material is the lower layer and the Rh-based catalyst material is the upper layer).

Even when only the group C catalyst material is employed for the second catalyst 25, it is preferable that the Pd-based catalyst material is the lower layer and the Rh / Al ₂ O ₃ catalyst material is the upper layer.

    Then, according to the type of fuel used in the engine 1, the exhaust gas temperature detected by the temperature sensor 27, and the air-fuel ratio of the exhaust gas obtained by the oxygen sensor 28, the control means 46 controls the flow control valve 26. I tried to control it.

    FIG. 10 is a flowchart showing the control mode. In step S1 after the start, it is determined whether or not the fuel used in the engine 1 is only hydrogen. When only hydrogen is used as the fuel, the process proceeds to step S2, and it is determined whether or not the exhaust gas is equal to or lower than a predetermined temperature. This predetermined temperature is based on the temperature characteristics of the saturated HC purification of the catalyst material used for the first catalyst 24 and the second catalyst 25, and the saturated HC purification rate of the first catalyst 24 and the saturated HC purification rate of the second catalyst 25. Set the temperature so that becomes the same. For example, when the group B catalyst material is used for the second catalyst 25, the predetermined temperature may be set to around 400 ° C., and when the group C catalyst material is used for the second catalyst 25, the predetermined temperature is set to 500. What is necessary is just to set around ℃.

    When it is determined in step S2 that the exhaust gas temperature is equal to or lower than the predetermined temperature, the flow proceeds to step S3 and the flow control valve 26 is controlled so that the entire amount of exhaust gas flows into the first passage 22. When it is determined in step S2 that the exhaust gas temperature is higher than the predetermined temperature, the process proceeds to step S4, and the flow control valve 26 is controlled so that a part of the exhaust gas flows into the second passage 23. In this case, the flow rate control valve 26 is controlled so that the flow rate of the exhaust gas flowing into the second passage 23 increases as the exhaust gas temperature increases. Note that the predetermined temperature, which is a condition for proceeding to step S4, may not reach the 400 ° C. or 500 ° C. at the time when the second catalyst 25 starts flowing the exhaust gas through the second passage 23. The temperature may be set several tens of degrees Celsius higher (for example, about 50 degrees Celsius higher).

    When the fuel used in the engine 1 is not only hydrogen in step S1, the process proceeds to step S5, and it is determined whether or not the air-fuel ratio of the exhaust gas is lean. The air-fuel ratio is lean when hydrogen and gasoline are used together as fuel. At this time, the flow proceeds to hydrogen step S2, and the flow rate control valve is the same as when only hydrogen is used as fuel. 26 is used to control the exhaust gas flow path. When the air-fuel ratio is not lean, that is, stoichiometric operation using only gasoline as fuel, the process proceeds to step S6, and the flow rate control valve 26 is set so that the entire amount of exhaust gas flows into the second passage 23. Control.

    In the above configuration, when the engine 1 is lean-burned using only hydrogen as fuel, or when lean-burning is performed using both hydrogen and gasoline as fuel, the combustion chamber temperature is low. For this reason, when the evaporated fuel is purged from the canister 15 to the intake passage 35, the evaporated fuel is not completely burned in the combustion chamber, and the amount of HC discharged to the exhaust passage increases. At that time, the exhaust gas temperature is also low.

    On the other hand, in the preferred embodiment, when the exhaust gas temperature is equal to or lower than a predetermined temperature (for example, 400 ° C.) in the lean burn operation, the entire amount of exhaust gas flows into the first passage 22. The first catalyst 24 provided in the first passage 22 employs a group A catalyst material having a high saturation HC purification rate at a low temperature as shown in FIG. The saturated HC therein is efficiently purified by the catalyst material of Group A, and the amount of HC resulting from the evaporated fuel is discharged into the atmosphere without being purified. Further, since the catalyst material of Group A has a relatively high NOx purification rate at a low temperature, emission of NOx into the atmosphere is also suppressed.

    In the lean burn operation, when the exhaust gas temperature exceeds a predetermined temperature, a part of the exhaust gas flows into the second passage 23. The second catalyst 25 provided in the second passage 23 employs a group B catalyst material having a high saturated HC purification rate at high temperature as shown in FIG. This is advantageous in suppressing HC from being discharged into the atmosphere without being purified. Further, as the exhaust gas temperature rises above the predetermined temperature, the exhaust gas inflow amount into the second passage 23 increases, which is further advantageous for the purification of HC by the evaporated fuel. Further, since the exhaust gas also flows into the first passage 22, NOx purification by the group A catalyst material can be achieved.

Even when only the Group C catalyst material (however, Pd / OSCI catalyst material, Pd / OSCII catalyst material, Rh / Al ₂ O ₃ catalyst material) is adopted as the second catalyst 25, the predetermined temperature is set to around 500 ° C. Then, the same effect as that obtained when the group B catalyst material is employed for the second catalyst 25 can be obtained.

On the other hand, when the engine 1 is stoichiometrically operated using gasoline as fuel, the entire amount of exhaust gas flows into the second passage 23. The second catalyst 25 of the second passage 23 includes a Pd catalyst selected from Group B and Group C (however, Pd / OSCI catalyst material, Pd / OSCII catalyst material, and Rh / Al ₂ O ₃ catalyst material). Since the material and the Rh-based catalyst material are used in combination, the exhaust gas is efficiently purified by the second catalyst 25. Even when only the group C catalyst material (however, Pd / OSCI catalyst material, Pd / OSCII catalyst material, Rh / Al ₂ O ₃ catalyst material) is adopted as the second catalyst 25, the stoichiometric operation is performed by the group A catalyst material. As compared with the case of purifying the exhaust gas, the exhaust gas can be purified efficiently.

    In addition, although the engine of the said embodiment is a rotary piston engine, this invention is not limited to this, A reciprocating engine may be sufficient.

    Moreover, although the said embodiment concerns a series hybrid vehicle, this invention is applicable also to a parallel hybrid vehicle, a series parallel hybrid vehicle, and the motor vehicle driven only by an engine irrespective of a motor. .

It is a block diagram of the hybrid vehicle which concerns on this invention. It is a block diagram of the engine and control system of the vehicle. It is a graph which shows the relationship between the lean saturation HC purification rate of various catalyst materials, and exhaust gas temperature. It is a graph which shows the relationship between the lean NO purification rate of 3 types of catalyst materials whose support material is OSCI, and exhaust gas temperature. It is a graph which shows the relationship between the lean NO purification rate of 3 types of catalyst materials whose support material is OSCII, and exhaust gas temperature. It is a graph which shows the relationship between the lean NO purification rate of 3 types of catalyst materials whose support material is activated alumina, and exhaust gas temperature. Support material is a graph showing the relationship between the ZrO ₂ coated La-containing catalyst material three lean NO purification rate is alumina and the exhaust gas temperature. It is a graph which shows the light-off temperature T50 regarding the purification | cleaning of the exhaust gas in the vicinity of the theoretical air fuel ratio of each catalyst of group AC. It is a graph which shows the exhaust gas purification rate in the exhaust gas temperature of 400 degreeC in the vicinity of the theoretical air fuel ratio of each catalyst of group AC. It is a flowchart of control concerning the present invention.

1 Engine 2 Motor 3 Gasoline fuel tank 4 Hydrogen fuel tank 6 Generator (generator)
15 canister 16 evaporative fuel passage 17 purge passage 21 exhaust passage 22 first passage 23 second passage 24 first catalyst 25 second catalyst

Claims (4)

An exhaust gas purifying device for an engine in which an operation using fuel including gasoline and an operation using hydrogen fuel are performed,
A canister that adsorbs the evaporated fuel generated in a fuel tank that stores the fuel containing gasoline, and a purge passage that purges the evaporated fuel adsorbed by the canister to the intake system of the engine;
The engine exhaust passage branches into a first passage and a second passage, the first catalyst is disposed in the first passage, the second catalyst is disposed in the second passage,
The first catalyst is selected from the group consisting of Pt-supported alumina in which Pt is supported on an alumina-based support material, and Pt-supported CeZr-based composite oxide in which Pt is supported on a CeZr-based composite oxide support material. Including at least one species,
The second catalyst includes Pd-supported alumina in which Pd is supported on an alumina support material, Rh-supported CeZr-based composite oxide in which Rh is supported on a CeZr-based composite oxide support material, and Rh on active alumina particles . hints and Rh supported alumina obtained by carrying, at least one selected from the group consisting of Pd supported CeZr-based mixed oxide obtained by supporting Pd on CeZr-based mixed oxide support material,
Of the fuel containing gasoline and hydrogen fuel, at least hydrogen fuel is used, the engine is lean burned, and the temperature of the exhaust gas is below a predetermined temperature, the exhaust gas has priority over the first passage. In the lean burn operation, when the temperature of the exhaust gas is higher than the predetermined temperature, the exhaust gas flows into the first passage and the second passage and the exhaust gas temperature When the engine is stoichiometrically operated using the fuel containing gasoline so that the flow rate of the exhaust gas flowing into the second passage increases as the value of the exhaust gas increases , the exhaust gas is given priority to the second passage. Engine exhaust gas purification comprising control means for controlling the flow rate of exhaust gas flowing into the first passage and the second passage so as to flow into the first passage Location. In claim 1,
The engine exhaust gas purification apparatus, wherein the second catalyst is at least one selected from the Pd-supported alumina and the Rh-supported CeZr-based composite oxide. In claim 1 or claim 2,
The second catalyst is supported on a carrier such that the Pd-supported alumina or the Pd-supported CeZr-based composite oxide is a lower layer, and the Rh-supported alumina or the Rh-supported CeZr-based composite oxide is an upper layer. An exhaust gas purification device for an engine that is characterized. In any one of Claim 1 thru | or 3,
The engine is mounted on a hybrid vehicle that can be driven by an electric motor, and is used for driving a generator for the electric motor.

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