JP2011001876A - Exhaust control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control HC desorption rate at HC desorption, thereby enhancing exhaust performance.SOLUTION: An exhaust control device 100 of an internal combustion engine 1 includes an exhaust passage 31, an exhaust heat recoverer 221 for recovering exhaust heat of exhaust gas, a first catalyst 311 that adsorbs HC until it reaches an HC desorption temperature, and when it has reached the HC desorption temperature, desorbs the adsorbed HC and purifies itself, and a second catalyst 312 that purifies HC when it has reached an activation temperature. The exhaust control device 100 further includes an exhaust heat recovered amount control means (S52, S54, S55) for controlling an exhaust heat recovered amount by the exhaust heat recoverer 221, when the first catalyst 311 reaches the HC desorption temperature, and the second catalyst 312 reaches the activation temperature.

Description

  The present invention relates to an exhaust control device for an internal combustion engine.

  As a conventional exhaust control device for an internal combustion engine, an exhaust passage is branched into a first passage and a second passage, an exhaust cooling promotion portion and a hydrocarbon (hereinafter referred to as “HC”) adsorbent are provided in the first passage, There is one in which a three-way catalyst is provided in an exhaust passage after the passage and the second passage are joined again (see, for example, Patent Document 1).

JP 2001-214734 A

  However, in the above-described conventional exhaust control device for an internal combustion engine, the temperature raising property of the HC adsorbent can be lowered by the exhaust cooling promotion unit, but the HC desorption rate at the time of HC desorption cannot be controlled. There was a problem that the exhaust performance deteriorated.

  The present invention has been made paying attention to such conventional problems, and an object of the present invention is to improve exhaust performance by controlling the HC desorption rate during HC desorption.

  The present invention solves the above problems by the following means. In order to facilitate understanding, reference numerals corresponding to the embodiments of the present invention are given, but the present invention is not limited thereto.

  The present invention includes an exhaust passage (31) through which exhaust flows, an exhaust heat recovery device (221) provided in the exhaust passage (31) for recovering exhaust heat of the exhaust, and downstream of the exhaust heat recovery device (221). A first catalyst (311) provided in the exhaust passage (31) for adsorbing HC until the HC desorption temperature is reached and desorbing and purifying the adsorbed HC when the HC desorption temperature is reached; An exhaust control device (100) for an internal combustion engine (1) comprising a second catalyst (312) provided in an exhaust passage (31) downstream of the catalyst (311) and purifying HC when an activation temperature is reached. Thus, when the first catalyst (311) reaches the HC desorption temperature and the second catalyst (312) reaches the activation temperature, the exhaust heat recovery amount that controls the exhaust heat recovery amount by the exhaust heat recovery device (211) is controlled. Control means (S52, S54, S55) are provided.

  According to the present invention, since the amount of exhaust heat recovered by the exhaust heat recovery device is controlled, the temperature of the exhaust gas flowing into the first catalyst provided downstream of the exhaust heat recovery device can be controlled. Therefore, since the HC desorption rate during HC desorption can be controlled, exhaust performance can be improved.

1 is a schematic configuration diagram of an engine exhaust control device according to an embodiment. FIG. It is a flowchart explaining the exhaust control of the engine by this embodiment. It is a flowchart explaining an exhaust heat recovery process.

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

  FIG. 1 is a schematic configuration diagram of an exhaust control device 100 for an engine 1 according to the present embodiment.

  The exhaust control device 100 of the engine 1 includes a cooling device 2, an exhaust device 3, and a controller 4.

  The cooling device 2 is a device that circulates cooling water that recovers exhaust heat of the engine 1, and includes a first circulation passage 21 and a second circulation passage 22.

  The first circulation passage 21 is a passage through which the cooling water that has flowed through the water jacket formed inside the engine 1 flows into the radiator 211 and is returned to the engine 1 again. In the present embodiment, for convenience of explanation, the side from which the cooling water flows out from the engine 1 is the upstream side, and the side from which the cooling water flows into the engine 1 is the downstream side.

  In the first circulation passage 21, a radiator 211, a thermostat valve 212, and a first water pump 213 are provided in order from the upstream. The first circulation passage 21 is provided with a radiator bypass passage 214 for bypassing the radiator 211 and returning the cooling water to the engine 1.

  The radiator 211 cools the cooling water that has flowed into the interior by the traveling wind, and lowers the cooling water temperature and discharges it.

  The thermostat valve 212 detects the coolant temperature and opens and closes the first circulation passage 21. When the coolant temperature is lower than a predetermined temperature, such as when the engine is started, the thermostat valve 212 is closed. When the thermostat valve 212 is in the closed state, the cooling water flows through the radiator bypass passage 214 without passing through the radiator 211. Further, when the engine 1 is warmed up and the cooling water reaches a predetermined temperature or higher, the thermostat valve 212 is opened. When the thermostat valve 212 is in the open state, the cooling water is cooled by the radiator 211 and flows into the engine 2 again.

  The first water pump 213 is driven by the engine 1 to circulate the cooling water in the first circulation passage 21.

  The second circulation passage 22 is a passage that branches from the middle of the first circulation passage 21, flows the cooling water that has flowed through the water jacket of the engine 1 to the exhaust heat recovery device 221, and returns it to the engine 1 again.

  The second circulation passage 22 is provided with an exhaust heat recovery device 221 and a second water pump 222 in order from the upstream.

  The exhaust heat recovery unit 221 performs heat exchange between the exhaust gas that passes through the exhaust heat recovery unit 221 and the cooling water that circulates through the second circulation passage 22.

  The second water pump 222 is driven by an electric motor to circulate the cooling water in the second circulation passage 22. The discharge amount of the second water pump 222 can be arbitrarily changed, and the exhaust heat recovery amount in the exhaust heat recovery unit 221 can be controlled by controlling the discharge amount of the second water pump 222. The amount of exhaust heat recovered here is the amount of heat exchange between the exhaust gas and the cooling water. The greater the amount of exhaust heat recovered, the greater the degree of temperature reduction of the exhaust that has passed through the exhaust heat recovery unit 221.

  The exhaust device 3 is a device that converts harmful substances in the exhaust exhausted from the engine 1 into harmless substances and reduces them into the outside air, and then exhausts them to the outside. The exhaust passage 31, the bypass passage 32, and the flow switching And a valve 33.

  In the exhaust passage 31, the exhaust heat recovery device 221, the first catalyst 311, the second catalyst 312, the first temperature sensor 313, and the second temperature sensor 314 are provided in order from the upstream.

  The first catalyst 311 adsorbs HC when the catalyst temperature is lower than the HC desorption temperature (approximately 150 ° C.) and desorbs HC when the catalyst temperature is equal to or higher than the HC desorption temperature, and the catalyst temperature is the active temperature ( It is an HC trap catalyst that combines a three-way catalyst that is activated to oxidize HC when the temperature is about 300 ° C. or higher. The HC adsorbent is supported on the surface of the catalyst carrier, and the three-way catalyst is supported on the surface of the HC adsorbent. With such a configuration, first, the lower layer HC adsorbent is warmed after the surface three-way catalyst is warmed by exhaust. Thereby, the first catalyst 311 can adsorb HC when the catalyst temperature is low, and can oxidize to carbon dioxide and water while desorbing the adsorbed HC as the catalyst temperature increases.

  The second catalyst 312 is a three-way catalyst that is activated to oxidize HC when the catalyst temperature becomes equal to or higher than the activation temperature.

  The first temperature sensor 313 is provided in the first catalyst 311 and detects the internal temperature of the first catalyst 311.

  The second temperature sensor 314 is provided in the second catalyst 312 and detects the internal temperature of the second catalyst 312.

  The bypass passage 32 is a passage through which the exhaust discharged from the engine 1 flows into the second catalyst 312 while bypassing the exhaust heat recovery device 221 and the first catalyst 311. The bypass passage 32 branches from the exhaust passage 31 upstream of the exhaust heat recovery device 221 and joins the exhaust passage 31 between the first catalyst 311 and the second catalyst 312.

  The flow path switching valve 33 is provided at a branch portion between the exhaust passage 31 and the bypass passage 32, and switches whether the exhaust discharged from the engine 1 flows into the exhaust passage 31 or the bypass passage 32.

  The controller 4 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). In addition to the first temperature sensor 313 and the second temperature sensor 314, the controller 4 receives signals from various sensors that detect the operating state of the engine 1 such as an accelerator stroke sensor 41 that detects an accelerator pedal depression amount. Entered. And according to the detected driving | running state of the engine 1, the 2nd water pump 222 and the flow-path switching valve 33 are controlled, and the exhaust performance of the exhaust apparatus 3 is improved. Hereinafter, the exhaust control according to the operating state of the engine 1 will be described.

  FIG. 2 is a flowchart illustrating the exhaust control of the engine 1 according to the present embodiment. The controller 4 executes this routine at a predetermined calculation cycle (for example, 10 ms) while the engine 1 is operating.

  In Step S1, the controller 4 determines whether or not the HC adsorbent of the first catalyst 311 is adsorbing HC. Specifically, it is determined whether the temperature detected by the first temperature sensor 313 is lower than a first predetermined temperature at which it can be determined that the HC adsorbent of the first catalyst has reached the HC desorption temperature. When the controller 4 determines that the HC adsorbent of the first catalyst 311 is being HC adsorbed, the controller 4 proceeds to step S2. On the other hand, when it is determined that the HC adsorbent of the first catalyst 311 has desorbed HC, the process proceeds to step S3.

  In step S <b> 2, the controller 4 controls the flow path switching valve 33 so that the exhaust discharged from the engine 1 flows through the exhaust passage 31.

  In step S3, the controller 4 determines whether or not the second catalyst 312 is activated. Specifically, it is determined whether or not the temperature detected by the second temperature sensor 314 is equal to or higher than a second predetermined temperature at which it can be determined that the second catalyst has reached the activation temperature. When the controller 4 determines that the second catalyst 312 is activated, the process proceeds to step S4. On the other hand, when it is determined that the second catalyst 312 is not activated, the process proceeds to step S6.

  In step S <b> 4, the controller 4 controls the flow path switching valve 33 so that the exhaust discharged from the engine 1 flows through the exhaust passage 31.

  In step S <b> 5, the controller 4 performs an exhaust heat recovery process for controlling the amount of exhaust heat recovery by controlling the flow rate of the cooling water circulating through the second circulation passage 22. Specific contents will be described later with reference to FIG.

  In step S <b> 6, the controller 4 controls the flow path switching valve 33 so that the exhaust discharged from the engine 1 flows through the bypass passage 32.

  FIG. 3 is a flowchart for explaining the exhaust heat recovery process.

  In step S51, the controller 4 determines whether or not it is idle. Specifically, it is determined whether or not the idle switch is turned on. The idle switch is a switch that is turned on when the accelerator pedal depression amount is zero and turned off when the accelerator pedal is depressed. If the controller 4 is idling, the process proceeds to step S52. On the other hand, if not idle, the process proceeds to step S53.

  In step S52, the controller 4 fixes the discharge flow rate of the electric water pump and fixes the flow rate of the cooling water circulating in the second circulation passage 22 to the first flow rate.

  In step S53, the controller 4 determines whether the vehicle is traveling normally or operating under a high load. Specifically, it is determined whether the engine load is equal to or less than a predetermined load. If the engine load is equal to or less than the predetermined load, the controller 4 determines that the vehicle is traveling normally and proceeds to step S54. On the other hand, if the engine load is greater than the predetermined load, it is determined that the high load operation is being performed, and the process proceeds to step S55.

  In step S54, the controller 4 changes the discharge flow rate of the electric water pump according to the engine load, and changes the flow rate of the cooling water circulating in the second circulation passage 22 from the second flow rate to the third flow rate. (2nd flow rate <3rd flow rate). The discharge flow rate of the electric water pump is controlled to be the third flow rate when the engine load becomes a predetermined load. The discharge flow rate is decreased as the engine load becomes smaller, and finally becomes the second flow rate. To be controlled. The second flow rate is lower than the first flow rate, and the third flow rate is higher than the first flow rate (second flow rate <first flow rate <third flow rate).

  In step S55, the controller 4 fixes the discharge flow rate of the electric water pump, and fixes the flow rate of the cooling water circulating in the second circulation passage 22 to the fourth flow rate. The fourth flow rate is larger than the first flow rate and smaller than the third flow rate (second flow rate <first flow rate <fourth flow rate <third flow rate).

  Next, the effect of the exhaust control of the engine 1 according to this embodiment will be described. In addition, in order to clarify the correspondence with the flowcharts of FIGS. 2 and 3, the step numbers of the flowcharts will be described together.

  When the engine 1 is started, the controller 4 first detects the catalyst temperatures of the first catalyst 311 and the second catalyst 312. Then, when the catalyst temperature of the first catalyst 311 is lower than the first predetermined temperature, such as immediately after the engine is started (Yes in S1), the flow path switching valve 33 is switched to the exhaust passage 31 side (S2). Accordingly, the HC in the exhaust is trapped by the HC adsorbent of the first catalyst 311 and the exhaust performance can be improved.

  Further, when the catalyst temperature of the first catalyst 311 becomes equal to or higher than the first predetermined temperature after a while since the engine 1 is started (No in S1 and No in S3), the activation of the second catalyst 312 is promoted. Therefore, the flow path switching valve 33 is switched to the bypass passage 32 side (S6). Thereafter, when the second catalyst 312 is activated (No in S1, Yes in S3), the flow path switching valve 33 is switched again to the exhaust passage 31 side (S4), and exhaust heat is discharged according to the operating state as follows. Exhaust heat recovery by the recovery unit 221 is performed to improve exhaust performance (S5).

  First, the exhaust heat recovery process during normal traveling will be described (No in S51, Yes in S53, S54).

  During normal travel, the flow rate of the cooling water circulating through the second circulation passage 22 is reduced when the engine load is small, and the flow rate of the cooling water circulating through the second circulation passage 22 is increased as the engine load increases. That is, when the exhaust flow rate (heat amount) is small, the flow rate of the cooling water circulating through the second circulation passage 22 is reduced, and the flow rate of the cooling water circulating through the second circulation passage 22 is increased as the exhaust flow rate increases.

  As a result, the temperature of the exhaust gas flowing into the first catalyst 311 provided downstream of the exhaust heat recovery unit 221 can be maintained at a predetermined temperature, so that the unit of HC desorbed from the HC adsorbent of the first catalyst 311 The amount of desorption (desorption rate) per time can be kept constant. That is, the amount of HC supplied to the three-way catalyst of the first catalyst 311 and the second catalyst 312 can be set to an appropriate amount while promoting the activation of the three-way catalyst of the first catalyst 311. Therefore, it is possible to suppress the exhaust performance from being deteriorated by supplying a large amount of HC that cannot be oxidized to the three-way catalyst of the first catalyst 311 and the second catalyst 312.

  Next, the exhaust heat recovery process during idling will be described (Yes in S51, S52).

  During idling, the exhaust gas flow rate is lower than during normal travel, so that the activation of the three-way catalyst of the first catalyst 311 can be promoted even if the flow rate of the cooling water circulating through the second circulation passage 22 is reduced. It is difficult to expect oxidation of HC in the first catalyst 311.

  Therefore, during idling, the amount of exhaust heat recovery can be increased by increasing the flow rate of the cooling water that circulates through the second circulation passage 22 than when operating at a relatively low load during normal traveling. The temperature of the exhaust gas flowing into the first catalyst 311 provided downstream of the exhaust heat recovery unit 221 is lowered. Thereby, the desorption amount per unit time of HC desorbed from the HC adsorbent of the first catalyst 311 can be reduced. Therefore, a large amount of HC can be prevented from being desorbed when the activity of the three-way catalyst of the first catalyst 311 is low.

  Finally, the exhaust heat recovery process during high-load traveling will be described (No in S51, No in S53, S55).

  Since the exhaust gas flow rate is higher during high load travel than during normal travel, the first catalyst provided downstream of the exhaust heat recovery unit 221 even if the flow rate of the cooling water circulating through the second circulation passage 22 is reduced. It becomes difficult to maintain the temperature of the exhaust gas flowing into 311 at a predetermined temperature. That is, it becomes difficult to keep the desorption amount per unit time of HC desorbed from the HC adsorbent of the first catalyst 311 constant.

  Therefore, if the vehicle is traveling under a high load, the amount of exhaust heat recovery can be reduced by reducing the flow rate of the cooling water circulating through the second circulation passage 22 compared to when operating at a relatively high load during normal traveling. Thus, the temperature of the exhaust gas flowing into the first catalyst 311 provided downstream of the exhaust heat recovery device 221 is increased. Thereby, since the activity of the three-way catalyst of the first catalyst 311 can be increased, the oxidation of HC in the first catalyst 311 can be promoted.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  For example, in the above-described embodiment, when the first catalyst 311 is lower than the first predetermined temperature, all the exhaust flows through the exhaust passage 31, but the flow rate of the exhaust flowing through the exhaust passage 31 is the amount of the exhaust flowing through the bypass passage 32. If there is more than the flow rate, there is no problem. The same applies when the second catalyst 312 is at or above the second predetermined temperature.

  Further, when the second catalyst 312 is lower than the second predetermined temperature, all the exhaust gas flows through the bypass passage 32. However, if the flow rate of the exhaust gas flowing through the exhaust passage 31 is less than the flow rate of the exhaust gas flowing through the bypass passage 32, no problem.

  Furthermore, although the active states of the first catalyst 311 and the second catalyst 312 are detected by the temperature sensors 313 and 314, they may be estimated from the elapsed time from the start of the engine 1 or the total exhaust amount.

1 engine (internal combustion engine)
22 Second circulation passage (cooling water circulation passage)
31 Exhaust passage 32 Bypass passage 221 Waste heat recovery device 222 Second water pump (flow rate controller)
311 1st catalyst 312 2nd catalyst S2 Bypass flow rate control means S4 Bypass flow rate control means S6 Bypass flow rate control means S52 Waste heat recovery amount control means S54 Waste heat recovery amount control means S55 Waste heat recovery amount control means

Claims (7)

An exhaust passage through which exhaust flows;
An exhaust heat recovery unit provided in the exhaust passage and recovering exhaust heat of exhaust;
A first catalyst that is provided in the exhaust passage downstream of the exhaust heat recovery device and adsorbs HC until the HC desorption temperature is reached, and desorbs and purifies the adsorbed HC when the HC desorption temperature is reached. When,
A second catalyst provided in the exhaust passage downstream of the first catalyst and purifying HC when the activation temperature is reached;
An exhaust control device for an internal combustion engine comprising:
Characterized in that it comprises exhaust heat recovery amount control means for controlling the amount of exhaust heat recovered by the exhaust heat recovery device when the first catalyst reaches the HC desorption temperature and the second catalyst reaches the activation temperature. An exhaust control device for an internal combustion engine. A cooling water circulation passage in which the exhaust heat recovery device is provided in the middle of the passage and in which cooling water for cooling the internal combustion engine circulates;
A flow rate controller provided in the cooling water circulation passage for controlling the flow rate of the cooling water circulating in the cooling water circulation passage,
The exhaust heat recovery amount control means includes:
The exhaust control device for an internal combustion engine according to claim 1, wherein the exhaust heat recovery amount is controlled by controlling a flow rate of the cooling water circulating in the cooling water circulation passage. The exhaust heat recovery amount control means includes:
The exhaust control device for an internal combustion engine according to claim 1 or 2, wherein the exhaust heat recovery amount is controlled so that an HC desorption rate from the first catalyst is constant. The exhaust control device for an internal combustion engine according to claim 3, wherein the exhaust heat recovery amount is controlled when the load of the internal combustion engine is in a normal running state where the load is not more than a predetermined load. The exhaust heat recovery amount control means includes:
The exhaust gas of the internal combustion engine according to any one of claims 1 to 4, wherein the exhaust heat recovery amount is controlled so that an HC desorption rate from the first catalyst decreases during an idle operation. Control device. The exhaust heat recovery amount control means is:
6. The exhaust heat recovery amount is controlled so that the activity of the second catalyst is increased during high-load traveling where the load of the internal combustion engine is greater than a predetermined load. 6. An exhaust control device for an internal combustion engine according to claim 1. A bypass passage provided in the exhaust passage such that exhaust gas bypasses the exhaust heat recovery device and the first catalyst and flows into the second catalyst;
When the first catalyst reaches the HC desorption temperature and the second catalyst reaches the activation temperature, the bypass passage is configured so that the flow rate of the exhaust gas flowing through the bypass passage is smaller than the flow rate of the exhaust gas flowing through the exhaust passage. Bypass flow rate control means for controlling the flow rate of the exhaust gas flowing through,
An exhaust control device for an internal combustion engine according to any one of claims 1 to 6, further comprising:

Images