JPH11159321A - Exhaust emission control device for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate HC or others adsorbed to an adsorber provided at the upstream side of a catalyst without lowering driveability and increasing costs. SOLUTION: During starting an engine 1, exhaust gas is passed through a honeycomb 5 in an adsorber 4, provided in part of the large-diameter portion 41 of an exhaust pipe 3 at the upstream side of a catalytic converter rhodium 10, with an exhaust gas flow passage switch valve 6 switched by an ECU 11 to adsorb harmful HC or others to adsorbent carried on the honeycomb 5. When warm-up operation is completed and the rhodium 10 is activated, the switch valve 6 opens a flow passage 43 but HC and others adsorbed to the adsorber 4 is treated by the catalyst 10 by switching the switch valve 6 again during decelerating operation to carry exhaust gas to the honeycomb 5 for elimination. In this case, a fuel injection amount is reduced corresponding to an elimination amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle exhaust gas purifying apparatus.

[0002]

2. Description of the Related Art As a system for purifying exhaust gas of an automobile engine, a carrier carrying a noble metal such as platinum or rhodium as a catalyst is provided in an exhaust passage, and H in the exhaust gas is provided.
2. Description of the Related Art A catalytic converter system for purifying C, CO, NOx, and the like by an oxidation reaction or an oxidation / reduction reaction is known.

In this catalytic converter system, in order to purify exhaust gas, the catalyst is activated at an activation temperature, for example, 300 to 40.
It is necessary that the catalyst is heated to 0 ° C. or higher, but generally, the catalyst does not reach the activation temperature immediately after the start of the engine because a catalyst heating method using exhaust gas is employed. However, there is a problem that exhaust gas is hardly purified.

[0004] Therefore, the above-mentioned catalyst is arranged in the vicinity of the engine so that the activation temperature can be reached as quickly as possible by the heat of the exhaust gas, or the carrier supporting the catalyst can be made of ceramics having thermal conductivity. At present, instead of a good metal, the activation temperature is reached earlier, or the activation temperature is reached earlier by providing a heater on the carrier and forcibly heating the carrier.

[0005] On the other hand, purifying rates of harmful gas components such as HC, CO, NOx, etc.
It is expected that further improvements will be required in the future, but to achieve this, the catalyst should be placed as close as possible to the engine so that exhaust gas can be purified immediately after the engine starts. It becomes necessary. However, when the catalyst is brought closer to the engine, the catalyst is exposed to high-temperature exhaust gas under normal operating conditions.However, the catalyst generally deteriorates rapidly under high-temperature conditions, so that the purification rate is rather reduced. There's a problem.

In order to solve this problem, for example, in the invention described in JP-A-6-93844, an exhaust pipe is branched into two near an engine to form a main flow path and a bypass flow path. There has been proposed a system in which HC bypass means is provided in a bypass passage, and a main catalyst is disposed downstream of a portion where the bypass passage joins the main passage again.

In this invention, a switching valve (opening / closing device) is provided at a branch portion of the exhaust pipe near the engine, and when the exhaust gas is at a low temperature, such as immediately after starting the engine, the main flow path is closed and the bypass flow path is closed. By opening the exhaust gas, the exhaust gas flows into the bypass flow path to adsorb and remove harmful components at low temperature, especially HC, and after the engine is warmed up and combustion is stabilized, the switching valve is switched to flow exhaust gas to the main flow path side. Until the catalyst reaches the activation temperature, the low-temperature H
C is held by suction. After the temperature of the exhaust gas becomes high and the main catalyst is sufficiently warmed by the exhaust gas, the bypass flow passage is slightly opened by the switching valve to flow the exhaust gas through the bypass flow passage, and is adsorbed and held by the adsorption means. H
A configuration is adopted in which C is thermally desorbed and purified by the rear main catalyst.

In this configuration, the pressure loss is increased by passing the exhaust gas through the adsorption means at the time of desorption, and during that time, deterioration of drivability and fuel efficiency cannot be avoided.
Further, in order to purify the desorbed HC by the rear catalyst, it is necessary to provide an amount of oxygen sufficient to purify the desorbed amount from the adsorbing means in addition to the harmful components originally emitted from the engine. It has to be slid to lean (lean) side than the stoichiometric air-fuel ratio). Therefore, the drivability is further deteriorated. In addition, in lean operation, the NOx purification rate is extremely reduced, so that the time of the desorption stroke needs to be accurately and as short as possible.

Therefore, the temperature of the inlet and outlet of the adsorbing means, the temperature of the main catalyst,
It is necessary to accurately measure a physical quantity such as an air-fuel ratio, and sensors for this purpose are added. However, there are problems that the control logic becomes complicated and the cost increases. Furthermore, it is necessary to adjust the opening of the switching valve according to the engine operating conditions, and there is a problem that it is difficult to quickly remove the engine under any operating conditions.

Another prior art is disclosed in Japanese Patent Application Laid-Open No. 6-7402.
In the exhaust gas purifying apparatus described in Japanese Patent Application Publication No. 1 (1993) -1991, the adsorbing device provided in the bypass passage on the upstream side of the catalyst causes H
Although C is adsorbed and HC is desorbed from the adsorber and processed during deceleration operation or idling operation after the catalyst is activated, NOx emission is suppressed. Since there is no disclosure on how to perform fuel injection control when performing desorption, the desorbed HC
It is questionable whether can be purified by a catalyst.

Still another prior art is disclosed in Japanese Patent Application Laid-Open No. 9-11 / 1991.
In the engine control device described in Japanese Patent No. 2322, when the harmful components such as HC adsorbed by the adsorbent provided in the exhaust gas bypass path desorb and return to the upstream side of the catalyst device, the desorption amount The exhaust gas including the desorbed HC is satisfactorily purified by reducing the fuel supply amount in accordance with the above-mentioned method. However, this method uses an adsorbent provided in a bypass passage downstream of the catalyst. It circulates HC and the like desorbed from the catalyst to the upstream side of the catalyst, and differs from the basic configuration intended by the present invention from the basic configuration.

[0012]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention uses a different means from the prior art without deteriorating drivability and increasing cost. By quickly desorbing HC and the like adsorbed by the adsorption means provided on the upstream side of the device,
It is an object of the present invention to provide an exhaust gas purifying apparatus for a vehicle that can start an engine and smoothly perform a warm-up operation while preventing emission of harmful exhaust gas.

[0013]

According to the present invention, in order to solve the above-mentioned problems, in the desorption process of the adsorbing means provided on the upstream side of the catalyst device, the switching valve is switched at the time of vehicle speed reduction. It is an object of the present invention to provide an exhaust gas purifying apparatus for an automobile in which the fuel injection amount at that time is reduced or cut in accordance with the amount of desorption from the adsorbing means so as to suppress deterioration of drivability.

In the present invention, not only when the vehicle speed is decelerated but also when the desorption control of the adsorbing means is performed, the air-fuel ratio does not always slide to the lean side, but the engine speed and the intake air amount of the engine. The desorbed HC concentration is estimated by
It is an object of the present invention to provide an exhaust gas purifying apparatus that controls the fuel injection amount in consideration of the C concentration to minimize the deterioration of drivability and to prevent the deterioration of the NOx purification rate.

The solution according to the present invention is described in each of the claims as a more specific configuration.
According to the invention described in claim 1, during the desorption process of HC,
The flow path switching valve is switched so that the exhaust gas flows to the adsorbing means, heat from the exhaust gas is given to the adsorbing means to desorb HC, and the desorbed HC is purified by the catalyst behind the adsorbing means. The timing of the desorption stroke is defined as the time of deceleration of the vehicle. By reducing or cutting the amount of fuel supplied to the engine, it is possible to achieve both purification of desorbed HC and prevention of deterioration in drivability.

According to the second aspect of the present invention, in the configuration of the first aspect, the desorbed HC concentration in the desorption stroke is estimated from engine operating conditions such as an intake air amount, and the engine is supplied to the engine in accordance with the desorbed HC concentration. By variably controlling the fuel supply amount and maintaining the stoichiometric air-fuel ratio downstream of the adsorption means, it is possible to obtain good purification characteristics of desorbed HC. Furthermore, since excessive lean control is not performed, drivability deteriorates and N
Ox emission can be suppressed. In this case, H
Since a sensor or the like for measuring the C concentration is not required, an inexpensive configuration can be achieved.

According to the third aspect of the present invention, the start catalyst provided on the upstream side of the adsorber has a small heat capacity because it is a part of the entire catalyst including that on the downstream side, and furthermore, is located immediately downstream of the engine. Since it is located on the side and receives relatively high temperature exhaust gas, it is activated early after starting. Therefore, after the adsorption means is closed, the start catalyst is effective in preventing the emission of harmful substances such as HC until the downstream catalyst device is sufficiently activated.

According to the fourth aspect of the present invention, it is possible to suppress noise when the valve plate is seated on or separated from the valve seat.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 4 and FIG. As shown in FIG. 1, the exhaust pipe 3 of the engine 1 has an exhaust manifold 3
An adsorber 4 is interposed downstream of the three-way catalyst 10 and downstream of the first three-way catalyst 10. The suction device 4 has a large-diameter cylindrical portion 41 of the exhaust pipe 3 in which the honeycomb body 5 is housed. Although not shown, in order to suppress the temperature rise of the honeycomb body 5 due to the exhaust gas, a space is provided between the large diameter portion 41 and the honeycomb body 5 to form an air heat insulating layer, or a heat insulating material is provided therebetween. Heat insulation is performed by a method such as insertion. The honeycomb body 5 is formed by winding a stainless steel foil plate or a porous ceramic molded body such as cordierite, and has a cylindrical shape conforming to the inner surface of the large diameter portion 41, as shown in FIG. It has a large number of parallel through holes 51, and a zeolite-based adsorbent is carried in the through holes 51. The honeycomb body 5 can be formed into a semi-cylindrical shape, an elliptical shape, a rectangular shape, or the like in accordance with the inner surface shape of the large-diameter portion 41. Immediately after the downstream end of the honeycomb body 5, an exhaust gas passage switching valve 6 is provided. The honeycomb body 5 is separated and held by a partition wall 42 provided between the honeycomb body 5 and a flow path 43 formed in other portions. A rectifying plate 44 is provided on the upstream side of the honeycomb body 5 to make the flow velocity distribution of the exhaust gas uniform when the exhaust gas flows into the honeycomb body 5 to increase the adsorption efficiency. Note that the partition wall 42 and the rectifying plate 44 may have an integral structure or may be separated. In addition, the flow path switching valve 6
An actuator 7 is provided in the suction device 4 for driving the actuator. The actuator 7 and the switching valve 6 are connected by a shaft 71 and an arm 72.

The valve plate 61 of the switching valve 6 has a stainless steel mesh 62 at its contact surface with the seat in order to reduce noise generated by impact with the seat. Specifically, as illustrated in FIG. 8, the valve plate 61 is sandwiched between two donut-shaped meshes 62, and the entire outer periphery of the mesh 62 is fixed by seam welding. In order to prevent the inner circumferential corner of the donut-shaped mesh 62 from fraying, a donut-shaped stainless steel ring 63 is fixed to the mesh by welding all around.

The intake pipes 8a and 8b for supplying a negative pressure for operating the actuator 7 are connected to the surge tank 2 which is a part of the intake passage on the upstream side of the engine 1. An electromagnetic valve 9 is interposed between the intake pipes 8a and 8b as a negative pressure switching valve (VSV). Further, the three-way catalyst 10 is provided downstream of the adsorption device 4 as described above. 1
Reference numeral 1 denotes control means for an engine and an adsorbing device built in a microcomputer, and a signal indicating an operation state of the engine 1 (intake air amount Qn, engine speed Ne, water temperature Tw,
Other, O ₂ concentration in the exhaust gas, a throttle opening degree)
And controls the opening and closing of the solenoid valve 9 shown in FIG. 1 to control the switching valve 6.

Next, the operation of this apparatus will be described with reference to FIG.
This will be described with reference to flowcharts of FIGS. FIGS. 3 and 4 show a case where the vehicle travels in the 75 FTP mode, which is a typical travel pattern of US exhaust gas regulations.
When the engine is started (IG ON), a signal Tw from an engine water temperature sensor (not shown) is received, and the control means 11 determines whether or not the adsorption device 4 has the adsorption capability (step 1). At the time of cold start, the honeycomb body 5 is cooled, and when the engine water temperature Tw (° C.) is equal to or lower than the adsorbable temperature Tw 1 (° C.), the solenoid valve (VSV) 9 is opened, and the intake pipe 8 is opened.
a and 8b communicate. As a result, the negative pressure of the surge tank 2 acts on the actuator 7 via the intake valves 8a and 8b to pull the shaft 71, so that the arm 72 rotates and
The switching valve (three-way valve) 6 integrated therewith moves to the position shown by the dashed line, opens the honeycomb body 5, and
Is closed (step 2).

Immediately after the start of the engine 1, the exhaust gas temperature is low, and the engine 1 discharges exhaust gas containing a large amount of cold HC. The cold HC is adsorbed on the zeolite while the exhaust gas flows through the through-hole 51 supporting the zeolite of the honeycomb body 5, and the exhaust gas from which the cold HC has been removed passes through the three-way catalyst 10, and a muffler (not shown) (Muffler) and then released into the atmosphere. At this time, since the rectifying plate 44 rectifies the flow of the exhaust gas, the exhaust gas has a uniform flow velocity distribution and flows in the honeycomb body 5. At this time, the control means 11 counts the elapsed time t after the operation of the solenoid valve 9 (step 3). When the engine 1 is warmed up and a predetermined time t1 at which the temperature of the exhaust gas exceeds the temperature at which zeolite can be adsorbed passes, the electromagnetic valve 9 is closed by a signal from the control means 11. As a result, the supply of the negative pressure to the actuator 7 is interrupted, and instead, the atmospheric pressure is introduced into the actuator, so that the actuator 7 rotates the switching valve 6 via the shaft 71 and the arm 72 by the elasticity of the built-in spring. Then, the honeycomb body 5 is closed, and the channel 43 is opened.

As a result, the flow path of the exhaust gas is switched,
The exhaust gas flows through the flow path 43 where the honeycomb body 5 does not exist (Step 4). At this time, since the combustion state of the exhaust gas discharged from the engine is already stable, the temperature of the exhaust gas is high, and the content of HC is small. During operation for several seconds to several tens of seconds in this state, the three-way catalyst 10 warms up, and thereafter, exhaust gas containing almost no HC is discharged into the atmosphere via the flow path 43 and a muffler (not shown). Thereafter, the honeycomb body 5 proceeds to the detachment process shown in FIG.

In FIG. 4, before flowing exhaust gas to the honeycomb body 5, it is determined whether the state of the engine 1 and the catalyst 10 is in a stable active state when the signal Tw from the engine water temperature sensor exceeds a predetermined value Tw2. The control means 11 makes a determination as to whether or not the desorption is performed (step 5). When the water temperature Tw exceeds the predetermined value Tw2, the desorption process proceeds as follows. First, the control means 11 determines whether or not the engine speed Ne exceeds the detachable speed Ne1 (step 6). Next, it is determined whether the vehicle is decelerating based on whether or not the idle switch is ON. (Step 7). If the vehicle is decelerating, oxygen necessary for purifying the desorbed HC is supplied by the catalyst 10, the feedback control of the normal fuel injection is stopped, and a predetermined fuel reduction or fuel cut is performed (step 8). Then, the solenoid valve 9 is opened, the honeycomb body 5 is opened by the switching valve 6, and the flow path 43 is closed to cause the exhaust gas to flow into the honeycomb body 5, and the adsorbed HC is desorbed by the exhaust heat (step 9). Then, the cumulative valve opening time t of the solenoid valve 9 is counted (step 10), and it is determined whether the desorption is completed based on whether the cumulative valve opening time t exceeds a predetermined time t2 (step 11). . After it is determined that the detachment is completed, the solenoid valve 9 is closed, and the honeycomb body 5 is switched by the switching valve 6.
Is closed and the flow path 43 is opened to exhaust gas
(Step 12). Then, control feedback of normal fuel injection is restarted (step 13), and a series of desorption control ends.

Next, a second embodiment of the present invention will be described with reference to FIG. Since the system configuration of the second embodiment is the same as that of the first embodiment, it will be described with reference to FIG. Further, the suction process of the second embodiment is the same as that of the first embodiment shown in FIG. In the flowchart of FIG. 5 showing the desorption process of the second embodiment, first, the control means 1 determines whether or not the state of the engine 1 and the catalyst 10 is in a stable active state by a signal from an engine water temperature sensor.
1 to determine whether or not desorption is possible (step 5 '). If it is determined that the valve can be removed, the solenoid valve (VSV) 9
Is opened, the honeycomb body 5 is opened by the switching valve (three-way valve) 6, and the flow path 43 is closed to exhaust gas from the honeycomb body 5.
And the desorption of the adsorbed HC is started by the exhaust heat (step 6 '). Thereafter, the concentration of the desorbed HC is determined, and the fuel injection amount to be lean-controlled by the amount of oxygen required for purifying the desorbed HC by the catalyst 10 is controlled by the control means 1.
1 is determined (step 7 '). As a method of determining the desorbed HC concentration, a method of directly measuring the HC concentration by installing an HC sensor on the downstream side of the adsorption device 4 or a method of measuring the temperature of the honeycomb body 5 or the temperature of the gas discharged from the honeycomb body 5 Is measured and the desorbed HC concentration is estimated from this temperature. However, the present inventors estimate the desorbed HC concentration from engine operating conditions mainly including the engine intake air amount Qn and the engine speed Ne. Adopt a way to.

According to the investigation by the present inventors, it has been found that, after the engine 1 and the catalyst 10 are in a stable state, the amount of heat given to the honeycomb body 5 from the exhaust gas depends on the engine intake air amount Q or Qn. (FIG. 6). From this relationship, the heat capacity of the honeycomb body 5 and the desorption temperature characteristics, the desorbed HC concentration can be estimated in real time. Then, the normal fuel injection feedback control is stopped, and the fuel injection control is executed so that the desorbed HC obtained by the above method can be purified (step 8 '). With this method, it is possible to suppress the deterioration of drivability due to the lean control more than necessary, and to reduce the increase in NOx emission. When the desorbed HC concentration becomes equal to or less than the predetermined value, it is determined that the desorption is completed (step 9 '). After it is determined that the desorption is completed, the solenoid valve 9 is closed, the switching valve 6 closes the honeycomb body 5 and opens the flow path 43, and the exhaust gas flows through the flow path 43 (step 10 '). Then, the normal fuel injection control feedback is restarted (step 11 '), and a series of desorption control ends. When a temperature sensor is installed on the downstream side of the above-described honeycomb body 5, it is possible to detect thermal deterioration of the adsorbent by monitoring the temperature history of the exhaust gas.

In this embodiment, normal fuel injection feedback is stopped at the time of desorption, but by installing an air-fuel ratio sensor downstream of the adsorption device 4,
Even at the time of desorption, it is possible to perform precise air-fuel ratio control by fuel injection feedback. Further, in the first and second embodiments, the catalyst 10 is provided on the downstream side of the adsorption device 4 as shown in FIG. 1, but for the purpose of further purification, the catalyst 10 of the third embodiment shown in FIG. As described above, the start catalyst 12 may be provided on the upstream side of the adsorption device 4. In this case, a small amount of HC that has been discharged to the upstream side of the catalyst 10 from the end of the adsorption is purified by the start catalyst 12 which is relatively small and close to the engine 1 and thus is quickly activated. It is possible to further reduce the amount of HC discharged from the system.

Further, an upper limit value of the intake air flow rate Q at which the control can be performed may be set in advance so as not to deteriorate the drivability. Also, instead of the flow rate Q, the intake air amount Qn (L / re
v), engine speed Ne (rpm), engine load P
Upper limits may be set for m (Pa), vehicle speed V (km / h), and the like.

Further, in the embodiment shown in FIGS. 1 and 7, the exhaust gas passage switching valve 6 is connected to the outlet side of the adsorber 4,
That is, although provided on the downstream side, the switching valve 6 may be provided on the inlet side of the adsorption device 4, that is, on the upstream side, and there is no substantial difference in the operation and effect.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing the structure of the suction device.

FIG. 3 is a flowchart illustrating an adsorption process according to the first embodiment.

FIG. 4 is a flowchart showing a desorption process in the first embodiment.

FIG. 5 is a flowchart showing a desorption process in the second embodiment.

FIG. 6 is a graph showing the amount of heat received in a desorption process in the second embodiment.

FIG. 7 is a system configuration diagram of a third embodiment.

8 (a) is a front view, and FIG. 8 (b) is a longitudinal sectional view taken along line AA of FIG. 8 (a), showing a part of the structure in the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Surge tank 3 ... Exhaust pipe 31 ... Exhaust manifold 4 ... Adsorption device 41 ... Exhaust pipe large diameter part 42 ... Partition wall 43 ... Exhaust gas flow path 44 ... Rectifier plate 5 ... Honeycomb body 6 ... Exhaust gas flow path switching Valve (3-way valve) 7 Actuator 71 Shaft 72 Arm 8a, 8b Suction tube 9 Solenoid valve (VSV) 10 Three-way catalyst 11 Control means 12 Start catalyst 61 Valve plate 62 Mesh 63 ring

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 9/04 F02D 9/04 E 41/12 330 41/12 330J (72) Inventor Tatsuo Sakai 1-chome, Showa-cho, Kariya City, Aichi Prefecture No. 1 Inside DENSO Corporation (72) Inventor Takaaki Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hiroshi Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (4)

[Claims] A catalyst device disposed in an exhaust pipe of an engine; and a catalyst device disposed in the exhaust pipe on an upstream side of the catalyst device.
An adsorbing means that carries an adsorbent for adsorbing exhaust gas harmful components in a part of the exhaust gas flow path, and is disposed on at least one of the upstream side and the downstream side of the adsorbing means, so that the exhaust gas flows through the adsorbing means and the other side. Exhaust gas flow path switching means which can be selectively switched to a flow path bypassing the adsorption means, and control means for controlling the switching means, wherein exhaust gas harmful components adsorbed by the adsorption means are removed. An exhaust gas purifying apparatus for an automobile, wherein the desorption process is performed in a decelerating state of the automobile after the engine and the catalyst are warmed up, and at the same time, a fuel reduction or a fuel cut to the engine is performed. A catalyst device disposed in an exhaust pipe of the engine; and a catalyst device disposed in the exhaust pipe on the upstream side of the catalyst device.
An adsorbing means that carries an adsorbent for adsorbing exhaust gas harmful components in a part of the exhaust gas flow path, and is disposed on at least one of the upstream side and the downstream side of the adsorbing means, so that the exhaust gas flows through the adsorbing means and the other side. Exhaust gas flow path switching means which can be selectively switched to a flow path bypassing the adsorption means, and control means for controlling the switching means, wherein exhaust gas harmful components adsorbed by the adsorption means are removed. In the desorption process, after the engine and the catalyst are warmed up, the above-mentioned flow switching means is switched to desorb the exhaust harmful gas component, the desorption concentration of the exhaust harmful component is estimated from the engine intake air amount and the engine speed, An exhaust gas purifying apparatus for an automobile, wherein the amount of fuel supplied to the engine is variably controlled in accordance with the separated concentration. 3. The exhaust gas purifying apparatus for an automobile according to claim 1, further comprising a start catalyst upstream of the adsorbing means, in addition to the catalytic device. 4. An exhaust gas purifying apparatus for an automobile according to claim 1, wherein said exhaust gas passage switching means comprises a soundproof valve plate.