JP3587670B2 - Exhaust gas purification equipment for automobiles - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for an automobile.
[0002]
[Prior art]
As a system for purifying exhaust gas from automobile engines, a carrier carrying a noble metal such as platinum or rhodium as a catalyst is provided in the exhaust passage to oxidize or oxidize / reduce HC, CO, NOx, etc. in the exhaust gas. 2. Description of the Related Art A catalytic converter system that purifies by using a catalyst is known.
[0003]
In this catalytic converter system, purification of exhaust gas requires that the catalyst be heated to an activation temperature, for example, 300 to 400 ° C. or higher, but generally employs a catalyst heating method using exhaust gas. Therefore, immediately after the start of the engine, the catalyst has not reached the activation temperature, and there is a problem that the exhaust gas is hardly purified.
[0004]
Therefore, the above catalyst is arranged near the engine so that the activation temperature is reached as quickly as possible by the heat of the exhaust gas, or the carrier supporting the catalyst is changed from ceramic to a metal having good heat conductivity. Instead, at present, 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, it is expected that the purification rate of harmful gas components such as HC, CO and NOx will be required to be further improved in the future due to the strengthening of so-called exhaust gas regulations. It is necessary to dispose the exhaust gas as close as possible to the engine so that the exhaust gas can be purified immediately after the start of the engine. 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.
[0006]
In order to solve this problem, for example, in the invention described in JP-A-6-93844, the exhaust pipe is branched into two near the engine to form a main flow path and a bypass flow path. Has proposed a system in which an HC adsorbing means is provided, and a main catalyst is disposed downstream of a portion where the bypass flow path joins the main flow path again.
[0007]
According to the present 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 opened. The exhaust gas is passed through 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, and the catalyst is removed. Until the activation temperature is reached, low-temperature HC is adsorbed and held in the adsorbing means of the bypass flow path. After the temperature of the exhaust gas becomes high and the main catalyst is sufficiently warmed by the exhaust gas, the bypass gas is slightly opened by the switching valve to flow the exhaust gas through the bypass gas channel, and the exhaust gas is adsorbed and held by the adsorption means. The HC is thermally desorbed and is purified by the rear main catalyst.
[0008]
In this configuration, the pressure loss increases by passing the exhaust gas through the adsorption means at the time of desorption, and during that time, deterioration in drivability and fuel efficiency cannot be avoided. Further, in order to purify the desorbed HC by the rear catalyst, an amount of oxygen is required to purify the desorbed amount from the adsorbing means in addition to the harmful components originally emitted from the engine. It must be slid to lean (lean) side of the stoichiometric air-fuel ratio). Therefore, the drivability is further deteriorated. In addition, in lean operation, the NOx purification rate is extremely low, so that the time of the desorption stroke needs to be accurate and as short as possible.
[0009]
Therefore, in the above-described conventional HC desorption process, it is necessary to accurately measure physical quantities such as the temperature of the inlet / outlet of the adsorbing means, the temperature of the main catalyst, and the air-fuel ratio. However, there are problems that the control logic becomes complicated and the cost increases. Further, 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.
[0010]
As another prior art, in an exhaust gas purifying apparatus described in Japanese Patent Application Laid-Open No. 6-74021, HC is adsorbed by an adsorber provided in a bypass passage on the upstream side of the catalyst, and the catalyst is activated. By controlling the desorption of HC from the adsorber during the deceleration operation or the idling operation, which is performed later, the amount of NOx emissions is reduced. Since there is no disclosure as to whether or not to perform the desorption, it is questionable whether the desorbed HC can be purified by the catalyst.
[0011]
As still another conventional technique, in an engine control device described in Japanese Patent Application Laid-Open No. Hei 9-112322, harmful components such as HC adsorbed by an adsorbent provided in an exhaust gas bypass passage are desorbed and a catalyst device is used. At the time of recirculation to the upstream side, by reducing the fuel supply amount according to the desorbed amount, the exhaust gas including the desorbed HC is satisfactorily purified. It circulates HC and the like desorbed from the adsorbent provided in the downstream bypass passage to the upstream side of the catalyst, and is different from the basic configuration intended by the present invention from the basic configuration.
[0012]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems of the prior art, and has been developed using means different from the prior art, without deteriorating drivability and increasing costs, and using an adsorption device provided on the upstream side of the catalyst device. Exhaust gas purifying apparatus for automobiles that can start the engine and smoothly perform warm-up operation while preventing harmful exhaust gas emission by quickly desorbing HC and the like adsorbed by the means. It is intended to provide.
[0014]
[Means for Solving the Problems]
The present invention is not limited to the case of deceleration of the vehicle speed, and when performing the desorption control of the adsorbing means, the air-fuel ratio does not uniformly slide to the lean side, but the desorption HC is determined by the engine speed and the intake air amount of the engine. Provided is an exhaust gas purifying apparatus that controls the fuel injection amount by estimating the concentration and taking the desorbed HC concentration into consideration, thereby minimizing the deterioration of drivability and preventing the deterioration of the NOx purification rate. Things.
[0016]
According to the first aspect of the invention, to estimate the desorbed HC concentration desorption stroke from engine operating conditions such as inhaled air amount, and variably controls the amount of fuel supplied to the engine in accordance with the desorbed HC concentration, By keeping the air-fuel ratio downstream of the adsorption means at a stoichiometric ratio, it is possible to obtain good purification characteristics of desorbed HC. Furthermore, since excessive lean control is not performed, deterioration of drivability and emission of NOx can be suppressed. Further, in this case, since a sensor for measuring the HC concentration is not required, an inexpensive configuration can be achieved.
[0017]
According to the second 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 has a small heat capacity immediately downstream of the engine. Because it 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 emission of harmful substances such as HC until the downstream catalyst device is sufficiently activated.
[0018]
According to the third 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]
BEST MODE FOR CARRYING OUT THE INVENTION
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, an adsorber 4 is provided in the exhaust pipe 3 of the engine 1 on the downstream side of the exhaust manifold 31 and on the upstream side of the three-way catalyst 10. The suction device 4 has a cylindrical large-diameter 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. 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 in 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 exhaust gas flow distribution uniform when the exhaust gas flows into the honeycomb body 5 to increase the adsorption efficiency. Note that the partition wall 42 and the current plate 44 may have an integral structure or may be separated. An actuator 7 is provided in the adsorption device 4 to drive the flow path switching valve 6, and the actuator 7 and the switching valve 6 are connected by a shaft 71 and an arm 72.
[0020]
The contact surface of the valve plate 61 of the switching valve 6 with the seat portion is covered with a mesh 62 made of stainless steel in order to reduce noise generated by impact with the seat portion. 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 peripheral 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.
[0021]
The intake pipes 8a and 8b for supplying a negative pressure for operating the actuator 7 are connected to a surge tank 2 which is a part of an 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). As described above, the three-way catalyst 10 is provided downstream of the adsorption device 4. 11 is a control means of the microcomputer built in the engine and the adsorption device, the signal (intake air amount indicating the operating condition of the engine 1 Qn, engine speed Ne, the coolant temperature Tw, other, O ₂ concentration in the exhaust gas, a throttle In addition to controlling the fuel injection amount according to the opening degree, the solenoid valve 9 shown in FIG. 1 is controlled to open and close, thereby controlling the switching valve 6.
[0022]
Next, the operation of the present apparatus will be described with reference to the 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), the control means 11 receives the signal Tw from an engine water temperature sensor (not shown) and 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 cold, and when the engine water temperature Tw (° C.) is lower than the adsorbable temperature Tw 1 (° C.), the solenoid valve (VSV) 9 is opened, and the intake pipes 8 a and 8 b are opened. Communicate. Accordingly, 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 is indicated by a broken line. Move to the position shown, open the honeycomb body 5 and close the flow path 43 (step 2).
[0023]
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 by 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 flows in the honeycomb body 5 with a uniform flow velocity distribution. 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 the temperature of the exhaust gas exceeds a temperature at which zeolite can be adsorbed for a predetermined time t1, 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 cut off, 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.
[0024]
As a result, the flow path of the exhaust gas is switched, and 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.
[0025]
In FIG. 4, before flowing exhaust gas to the honeycomb body 5, first, it is determined whether or not the state of the engine 1 and the catalyst 10 is in a stable active state by determining whether or not the signal Tw from the engine water temperature sensor exceeds a predetermined value Tw2. The control means 11 determines whether or not desorption is possible (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 that the vehicle is decelerating based on whether or not the idle switch is turned 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 allow the exhaust gas to flow into the honeycomb body 5, and the adsorbed HC is desorbed by the exhaust heat (step 9). Then, the integrated 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 integrated valve opening time t exceeds a predetermined time t2 (step 11). . After it is determined that the desorption is completed, the solenoid valve 9 is closed, the honeycomb body 5 is closed by the switching valve 6, the flow path 43 is opened, and the exhaust gas flows into the flow path 43 (step 12). Then, control feedback of normal fuel injection is restarted (step 13), and a series of desorption control ends.
[0026]
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 11 determines whether or not the states of the engine 1 and the catalyst 10 are in a stable active state based on a signal from the engine water temperature sensor. Is determined (step 5 '). When it is determined that the gas 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 allow the exhaust gas to flow into the honeycomb body 5. Then, the desorption of the adsorbed HC is started by the exhaust heat (step 6 '). Thereafter, the control unit 11 determines the concentration of the desorbed HC, and determines the fuel injection amount to be lean-controlled by the amount of the oxygen necessary for purifying the desorbed HC by the catalyst 10 (step 7 '). In addition, 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 method to do.
[0027]
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 and the heat capacity and the desorption temperature characteristics of the honeycomb body 5, the desorption HC concentration in real time can be estimated. 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 deterioration of drivability due to unnecessary lean control and to reduce an increase in NOx emission. When the desorbed HC concentration falls below a 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, normal fuel injection control feedback is restarted (step 11 '), and a series of desorption control is terminated. 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.
[0028]
In this embodiment, the normal fuel injection feedback is stopped at the time of desorption. However, by installing an air-fuel ratio sensor downstream of the adsorber 4, the precise fuel injection feedback by the fuel injection feedback is also performed at the time of desorption. Fuel ratio control can be performed. 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, since a small amount of HC discharged to the upstream side of the catalyst 10 from the end of the adsorption is relatively small and close to the engine 1, the HC is purified by the start catalyst 12, which is activated quickly. It is possible to further reduce HC discharged from the system.
[0029]
Further, an upper limit value of the intake air flow rate Q at which the control can be executed may be set in advance so as not to deteriorate the drivability. Instead of the flow rate Q, the upper limit value is set to the intake air amount Qn (L / rev) per engine revolution, the engine speed Ne (rpm), the engine load Pm (Pa), the vehicle speed V (km / h), and the like. May be set.
[0030]
Further, in the embodiment shown in FIGS. 1 and 7, the exhaust gas flow path switching valve 6 is provided on the outlet side of the adsorption device 4, that is, on the downstream side. It may be provided on the upstream side, and there is no substantial difference in 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 according to the second embodiment.
FIG. 6 is a graph showing the amount of heat received in a desorption process according to 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 Arms 8a and 8b Suction pipe 9 Solenoid valve (VSV)
Reference Signs List 10 three-way catalyst 11 control means 12 start catalyst 61 valve plate 62 mesh 63 ring

Claims (3)

A catalyst device disposed in an exhaust pipe of an engine, and an adsorbing means disposed in the exhaust pipe on the upstream side of the catalyst device and carrying an adsorbent for adsorbing harmful exhaust gas components on a part of an exhaust gas flow path. Exhaust gas flow path switching means installed on at least one of the upstream side and the downstream side of the adsorption means and capable of selectively switching the flow of exhaust gas to a flow path bypassing the adsorption means and the other adsorption means; And control means for controlling the switching means. In the desorption process of the harmful exhaust gas component adsorbed by the adsorption means, the flow path switching means is switched after the engine and the catalyst are warmed up. It desorbs harmful exhaust gas components, estimates the desorption concentration of harmful exhaust components from the engine intake air volume and engine speed, and variably controls the fuel supply to the engine according to the desorption concentration. Automotive exhaust It is purified apparatus. 2. 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. The exhaust gas passage switching means vehicle exhaust gas purification device according to claim 1 or 2, characterized in that it comprises a soundproof type valve plate having a metal mesh contact surface with the seat portion.

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