JP2013100758A - Exhaust heat recovery device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust heat recovery device for efficiently recovering heat, without impairing activation of an oxidation catalyst.SOLUTION: This exhaust heat recovery device of an engine 1 includes: a DPF 21 for collecting PM in exhaust gas in an exhaust passage 20; and a DOC 22 having oxidation capacity with respect to a component in the exhaust gas in the exhaust passage 20 on the upstream side of the DPF 21. The exhaust heat recovery device includes: a bypass passage 52 connected in parallel to a main exhaust passage 51 between the DOC 22 and the DPF 21; a heat exchanger 53 provided in the bypass passage 52 and exchanging heat between the exhaust gas passing through the bypass passage 52 and a heating medium; an opening-closing valve 54 for opening-closing the main exhaust passage 51 arranged in parallel to the bypass passage 52; and an ECU 40 for controlling operation of at least the opening-closing valve.

Description

  The present invention relates to an exhaust heat recovery apparatus for an engine, and more particularly, to a heat recovery technique using a heat exchanger provided in an exhaust passage.

  2. Description of the Related Art Diesel particulate filters (hereinafter referred to as DPFs) are known as exhaust aftertreatment devices that purify exhaust from engines that can be operated by lean combustion, for example, diesel engines. The DPF is provided in the exhaust passage and collects particulate matter (particulate matter, hereinafter referred to as PM) in the exhaust. In addition, an oxidation catalyst is provided in the exhaust passage, and an unburned fuel is caused to flow into the oxidation catalyst to cause an oxidation reaction. The reaction heat accompanying this raises the exhaust temperature, which is collected by PM or DPF in the exhaust. A technique for burning and removing PM is known.

  Further, a technique is known in which a heat exchanger is provided in the exhaust passage of the engine, and the warm-up operation time is shortened by collecting the exhaust heat and warming the cooling water. Specifically, a bypass passage is provided in the exhaust passage, a heat exchanger is disposed in the exhaust passage, a flow switching valve is provided at a connection portion between the exhaust passage and the bypass passage, and the exhaust discharged from the engine exchanges heat. It has a function of switching so as to pass or not pass through the vessel (Patent Document 1).

  By configuring in this way, for example, by preventing the exhaust from passing through the heat exchanger after completion of warm-up, the temperature of the cooling water is prevented from being increased more than necessary, and provided downstream of the heat exchanger. The exhaust purification performance is improved by suppressing the decrease in the exhaust temperature flowing into the three-way catalyst.

JP 2009-127435 A

  In Patent Document 1, exhaust heat from a normal combustion gasoline engine can be recovered, but a diesel engine is also required to shorten the warm-up operation time. However, in general, an exhaust passage of a diesel engine is not provided with a three-way catalyst but is provided with an oxidation catalyst and a DPF as described above, and an appropriate arrangement of a heat exchanger has not been studied. For example, when the heat exchanger is disposed downstream of the exhaust passage, the heat exchange rate is reduced, and when it is disposed upstream, it becomes a factor that hinders early activation of the downstream catalyst during cold start.

  The present invention has been made to solve such a problem, and the object of the present invention is, in a lean combustion engine provided with an oxidation catalyst and a DPF in an exhaust passage, without impairing the activation of the oxidation catalyst. An object of the present invention is to provide an exhaust heat recovery device capable of efficiently performing heat recovery.

  In order to achieve the above object, an exhaust heat recovery apparatus for an engine according to claim 1 is provided with a first filter for collecting particulate matter in exhaust gas in an exhaust passage, and on the upstream side of the first filter. An exhaust heat recovery apparatus for an engine having an oxidation catalyst capable of oxidizing components in exhaust gas in an exhaust passage, wherein the bypass passage is connected in parallel to the exhaust passage between the oxidation catalyst and the first filter. And a heat exchange means provided in the bypass passage for exchanging heat between the exhaust passing through the bypass passage and the heat medium, and an exhaust passage and a bypass passage in parallel with the bypass passage through which the exhaust gas has passed through the oxidation catalyst. Switching means for switching between and a control means for controlling the operation of at least the switching means.

According to a second aspect of the present invention, there is provided an exhaust heat recovery apparatus for an engine according to the first aspect, wherein the control means is configured such that when the first filter is regenerated, the exhaust gas that has passed through the oxidation catalyst passes through an exhaust passage parallel to the bypass passage. The switching means is controlled to operate.
According to a third aspect of the present invention, there is provided an exhaust heat recovery apparatus for an engine according to the second aspect, further comprising a heat exchange rate detection means for detecting a heat exchange rate of the heat exchange means, wherein the control means can control the heat exchange rate. In the regeneration of the first filter, when the exhaust gas that has passed through the oxidation catalyst is controlled by operating the switching means and is passed through the bypass passage, the heat exchange rate detected by the heat exchange rate detection means is set to a predetermined value or less. It is characterized by doing.

According to a fourth aspect of the present invention, there is provided an exhaust heat recovery apparatus for an engine according to the third aspect, wherein the heat exchange means carries a noble metal.
An engine exhaust heat recovery device according to a fifth aspect of the present invention is the engine exhaust heat recovery device according to any one of the first to fourth aspects, wherein the particulate matter in the exhaust gas is collected in the bypass path upstream of the heat exchange means. It is characterized by comprising the filter.

  According to a sixth aspect of the present invention, there is provided an exhaust heat recovery apparatus for an engine according to the fifth aspect of the present invention, further comprising a deposition amount detecting means for detecting the amount of particulate matter deposited on the second filter. When the deposited amount of the particulate matter is greater than or equal to a predetermined amount, the switching means is controlled to operate so that the exhaust gas that has passed through the oxidation catalyst passes through the bypass when the first filter is regenerated. And

According to a seventh aspect of the present invention, there is provided an exhaust heat recovery apparatus for an engine according to the sixth aspect, wherein the control means opens the switching means from the fully open state to the fully closed state when the exhaust gas that has passed through the oxidation catalyst is allowed to pass through the bypass passage. It is characterized in that the degree is continuously and gradually changed.
An engine exhaust heat recovery apparatus according to claim 8 is characterized in that, in claim 6, noble metal is supported on the second filter.

  According to the first aspect of the present invention, the bypass passage having the heat exchange means is provided in the exhaust passage between the oxidation catalyst provided in the exhaust passage of the engine and the first filter, so that the exhaust passes through the bypass passage. By controlling the operation of the switching means as described above, the exhaust heat can be recovered by the heat exchange means. Therefore, for example, when the heat medium is engine cooling water, the cooling water is warmed by the heat energy of the exhaust, and the warm-up operation time can be shortened.

  In particular, since the heat exchanging means is arranged downstream of the oxidation catalyst, for example, at the time of cold start, the oxidation catalyst can be activated with priority, and the exhaust gas purification performance can be secured quickly. It is possible to promote an increase in exhaust gas temperature on the downstream side. In addition, since the heat exchange means is disposed on the upstream side of the first filter, the exhaust heat recovery efficiency in the heat exchange means can be improved. In general, the filter has a relatively small reduction in the collection efficiency due to a temperature drop, and therefore, there is little possibility that the function of the first filter will be lowered by arranging the filter on the downstream side.

By providing the heat exchanging means between the oxidation catalyst and the first filter in this way, it is possible to improve the exhaust heat recovery efficiency in the heat exchanging means while suppressing deterioration of the functions of the oxidation catalyst and the first filter. it can.
According to the second aspect of the present invention, when the first filter is regenerated, the exhaust gas that has passed through the oxidation catalyst passes through the exhaust gas passage in parallel with the bypass passage, so that the temperature of the exhaust gas flowing into the first filter is hot. The reduction by the exchange means is avoided, and the regeneration time of the first filter can be reduced.

According to the invention of claim 3, when the particulate matter in the exhaust is deposited on the heat exchange means and the heat exchange rate is reduced, the exhaust that has passed through the oxidation catalyst during regeneration of the first filter. Passes through the bypass, so that the particulate matter deposited on the heat exchange means can be burned and removed, and the heat exchange rate of the heat exchange means can be recovered.
According to the invention of claim 4, since the noble metal is supported on the heat exchanging means, combustion removal of the particulate matter deposited on the heat exchanging means can be promoted.

According to the invention of claim 5, since the second filter for collecting the particulate matter in the exhaust gas is provided in the bypass path upstream of the heat exchange means, the particulate matter is deposited on the heat exchange means. It can be prevented and the heat exchange rate of the heat exchange means can be maintained.
Further, according to the invention of claim 6, when the particulate matter is accumulated in the second filter in a predetermined amount or more, the exhaust gas that has passed through the oxidation catalyst during the regeneration of the first filter passes through the bypass path. The particulate matter deposited on the second filter can be burned and removed to regenerate the second filter. Thereby, the pressure loss in the 2nd filter at the time of exhaust heat recovery can be reduced, and a fuel consumption fall can be controlled. In addition, it is possible to prevent the second filter from being burned out, which may occur when burning in a state where PM is excessively accumulated.

  According to the invention of claim 7, when the exhaust gas that has passed through the oxidation catalyst is allowed to pass through the bypass passage, the opening degree of the switching means is continuously gradually controlled from the fully open state to the fully closed state. Immediately after the start of regeneration of the filter, the flow rate of the exhaust gas passing through the second filter is suppressed to suppress a significant increase in pressure loss, the regeneration proceeds and particulate matter is removed from the second filter, and the pressure loss decreases. Along with this, the flow rate of the exhaust gas passing through the second filter can be increased, so that rapid regeneration can be completed.

  According to the eighth aspect of the invention, since the noble metal is supported on the second filter, it is possible to promote combustion removal of the particulate matter in the second filter.

1 is a configuration diagram of an intake / exhaust system of a diesel engine to which an exhaust heat recovery apparatus according to a first embodiment of the present invention is applied. 1 is a structural diagram of an exhaust heat recovery apparatus according to a first embodiment of the present invention. It is a structural diagram of the exhaust heat recovery device of the second embodiment of the present invention. It is a graph which shows transition of the opening degree of the on-off valve at the time of PM filter reproduction | regeneration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an intake / exhaust system of a diesel engine (hereinafter referred to as an engine 1) to which an exhaust heat recovery apparatus according to a first embodiment of the present invention is applied.
The engine 1 is, for example, a common rail type in-line multi-cylinder diesel engine mounted on a vehicle. The cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 4 for injecting fuel into the combustion chamber 3 for each cylinder. Each fuel injection valve 4 is connected to a common rail (not shown), and high-pressure fuel is supplied from the common rail.

An intake passage 10 of the engine 1 is provided with an electromagnetic intake throttle valve 11 that adjusts the intake air amount, and an airflow sensor 12 that detects an intake air flow rate upstream thereof.
The exhaust passage 20 of the engine 1 is provided with a diesel particulate filter (DPF21: corresponding to the first filter of the present invention) that collects particulate matter (PM) in the exhaust. For example, the DPF 21 is formed by alternately closing the upstream and downstream sides of the passage of the honeycomb carrier with plugs, and a catalytic noble metal such as platinum (Pt), palladium (Pd), and rhodium (Rh) on the porous wall forming the passage. Is formed.

The exhaust passage 20 upstream of the DPF 21 is provided with an oxidation catalyst (hereinafter referred to as DOC22). The DOC 22 is formed, for example, by supporting a catalyst noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh) on a porous wall forming a passage, and oxidizes CO and HC in the exhaust. together is converted to CO ₂ and H ₂ O Te has a function of NO in the exhaust is oxidized to generate NO _2.

Further, an exhaust gas temperature sensor 30 that detects the exhaust gas temperature immediately after passing through the oxidation catalyst 22 is provided on the downstream side of the oxidation catalyst 22. An exhaust gas temperature sensor 31 that detects the exhaust gas temperature immediately after passing through the DPF 21 is provided on the downstream side of the DPF 21. Further, a differential pressure sensor 32 that detects a differential pressure between the upstream side and the downstream side of the DPF 21 is provided.
An electronic control unit (hereinafter referred to as ECU 40) (control means, heat exchange rate detection means, accumulation amount detection means) is a control device for performing comprehensive control including operation control of the engine 1, and an input / output device. And a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), and the like.

On the input side of the ECU 40, in addition to the air flow sensor 12, the exhaust temperature sensors 30, 31 and the differential pressure sensor 32 described above, a crank angle sensor 33 for detecting the crank angle, and an accelerator position sensor 34 for detecting the depression amount of the accelerator pedal. , And a vehicle speed sensor 35 for detecting the vehicle speed are connected, and detection information from these sensors is input.
On the other hand, various output devices such as the fuel injection valve 4 and the intake throttle valve 11 are connected to the output side of the ECU 40, and the fuel calculated by the ECU 40 based on detection information from various sensors is connected to these various output devices. The injection amount, the fuel injection timing, and the like are output, and thereby the intake throttle valve 11 and the fuel injection valve 4 are controlled at an appropriate timing.

When the DOC 22 is arranged upstream of the DPF 21 as described above, NO ₂ generated in the DOC 22 flows into the DPF 21 during normal engine operation, and is a carbon component in PM collected and accumulated in the DPF 21. It reacts with a certain trap to oxidize it. Oxidized soot becomes CO _{2 and} is removed from the DPF 21, whereby continuous regeneration is performed in which the DPF 21 is continuously regenerated.

On the other hand, depending on the operating condition of the engine 1, the DPF 21 may not be sufficiently regenerated only by the continuous regeneration. Therefore, the ECU 40 has a function of forcibly regenerating the DPF 21 by controlling the operation of the engine 1.
Specifically, the ECU 40 calculates the PM accumulation amount in the DPF 21 from the differential pressure detected by the differential pressure sensor 32. When the calculated accumulation amount is equal to or greater than the allowable accumulation amount set in advance in the experiment, the exhaust temperature after passing through the DPF 21 detected by the exhaust temperature sensor 31, that is, the temperature of the DPF 21, is a target regeneration whose target value is the forced regeneration temperature. The forced regeneration temperature is raised so as to reach the temperature.

  In the forced regeneration, post-injection (sub-injection) of fuel is performed so that the forced regeneration temperature is reached after, for example, the expansion stroke after the main injection of fuel during operation of the engine 1, and unburned fuel (HC, CO, etc.) Exhaust gas containing the gas is discharged into the exhaust passage 20. The unburned fuel mixed in the exhaust flows into the DOC 22 and is oxidized, and the exhaust temperature is raised by the reaction heat of oxidation. As a result, the high-temperature exhaust gas flows into the DPF 21 on the downstream side of the exhaust gas, and the PM deposited on the DPF 21 can be heated and burned to forcibly regenerate the DPF 21.

Further, in the present embodiment, an exhaust heat recovery device 50 for recovering and effectively using the exhaust heat is provided.
The exhaust heat recovery device 50 includes a bypass passage 52 provided in parallel to the main exhaust passage 51 that is a part of the exhaust passage 20 between the DOC 22 and the DPF 21, and a heat exchanger 53 provided in the bypass passage 52. (Heat exchange means) and an on-off valve 54 (switching means) provided at a branch portion between the main exhaust passage 51 and the bypass passage 52.

The heat exchanger 53 is introduced with cooling water of the engine 1 and has a function of exchanging heat between the exhaust gas passing through the bypass passage 52 and the cooling water.
The on-off valve 34 is controlled by the ECU 40 and has a function of opening and closing the main exhaust passage 51, and is between a fully open state in which the main exhaust passage 51 is fully opened and a fully closed state in which the main exhaust passage 51 is fully closed. Switching is possible. The bypass passage 52 has a smaller flow passage cross-sectional area than the main exhaust passage 51 and is provided with a heat exchanger 53. Therefore, the bypass passage 52 has a larger flow passage resistance, so that the exhaust discharged from the oxidation catalyst 22 when the on-off valve 54 is fully opened. Most of them pass through the main exhaust passage 51. On the other hand, when the on-off valve 54 is fully closed, all the exhaust discharged from the oxidation catalyst 22 passes through the bypass passage 52. Therefore, the on-off valve 54 has a function equivalent to the function of switching the flow path so that the exhaust discharged from the oxidation catalyst 22 passes through either the bypass path 52 or the main exhaust path 51.

Then, the ECU 40 controls the opening / closing valve 54 so that the exhaust gas passes through the bypass passage 52, so that heat exchange is performed between the exhaust gas passing through the bypass passage 52 and the cooling water by the heat exchanger 53. Exhaust heat can be recovered.
The ECU 40 controls the closing of the on-off valve 34 so that the exhaust gas passes through the bypass 52 when the engine 1 is cold-started (for example, when the coolant temperature is equal to or lower than a predetermined temperature). Thereby, since the cooling water of the engine 1 is warmed, when the engine 1 is cold-started, warm-up can be promoted using exhaust heat, and the warm-up operation time can be shortened.

  Further, the ECU 40 has a function of monitoring the heat exchange rate of the heat exchanger 53 when the exhaust valve heat is recovered by operating the on-off valve 54 so that the exhaust gas passes through the bypass passage 52. . The heat exchange rate is an index representing the heat exchange performance in the heat exchanger 53. For example, the flow rate of the cooling water flowing through the heat exchanger 53, the cooling water temperature upstream of the heat exchanger 53, and the cooling water temperature downstream. What is necessary is just to judge from the heat recovery amount calculated | required by integrating | accumulating the difference of these.

When the heat exchange rate of the heat exchanger 53 is equal to or less than a predetermined value close to the lower limit value of the allowable range, the ECU 40 causes the exhaust to pass through the bypass passage 52 for a predetermined time at the next forced regeneration of the DPF 21. Thus, the on-off valve 54 is controlled.
As a result, high-temperature exhaust gas flows from the oxidation catalyst 22 into the heat exchanger 53 at the time of forced regeneration with respect to the heat exchanger 53 having a reduced heat exchange rate, and the PM deposited on the heat exchanger 53 is burned and removed. The heat exchanger 53 can be regenerated and the heat exchange rate of the heat exchanger 53 can be recovered.

Furthermore, a flow rate control valve for controlling the flow rate of the cooling water that passes through the heat exchanger 53 may be provided, and the flow rate of the cooling water may be limited when the heat exchanger 53 is regenerated. In this way, the amount of heat exchange in the heat exchanger 53 can be suppressed, so that the regeneration time of the heat exchanger 53 can be shortened.
Further, by regenerating the heat exchanger 53, the exhaust temperature at the inlet of the DPF 21 changes compared to when the heat exchanger 53 is not regenerated, so that the DPF 21 is also regenerated when the heat exchanger 53 is regenerated. It is good to control the injection quantity of post injection so that it may become suitable temperature. In this way, when the heat exchanger 53 is regenerated, the DPF 21 can be regenerated at the same time, and the total regeneration time of the heat exchanger 53 and the DPF 21 can be shortened.

Next, a second embodiment of the present invention will be described with reference to FIG.
The exhaust heat recovery device 60 according to the second embodiment of the present invention has a PM filter 61 (second filter) in the bypass path 52 upstream of the heat exchanger 53 with respect to the exhaust heat recovery device 50 according to the first embodiment. The filter is different.
The PM filter 61 has a function of collecting PM like the DPF 21, is smaller than the DPF 21, and has a lower capacity.

In the present embodiment, since the PM filter 61 is provided on the upstream side of the heat exchanger 53, PM hardly accumulates in the heat exchanger 53, and the heat exchange rate of the heat exchanger 53 can be maintained. However, since PM accumulates on the PM filter 61, it is necessary to regenerate the PM filter 61 instead of regenerating the heat exchanger 53.
The regeneration of the PM filter 61 is executed when the accumulated amount of PM in the PM filter 61 is estimated by the ECU 40 and the estimated value of the accumulated amount becomes equal to or larger than a predetermined amount close to the upper limit value of the allowable range. The estimated value of the PM accumulation amount in the PM filter 61 may be estimated based on, for example, the integrated value of the exhaust flow rate that has passed through the PM filter 61 since the previous regeneration of the PM filter 61. The integrated value of the exhaust flow rate may be calculated based on the exhaust flow rate calculated based on the intake flow rate detected by the air flow sensor 12 and the fuel injection amount injected from the fuel injection valve, and the opening degree of the on-off valve 54. . Alternatively, the start of regeneration of the PM filter 61 may be simply determined based on the operation time of the engine 1 since the previous regeneration of the PM filter 61.

Then, the ECU 40 closes the on-off valve 54 so that the exhaust gas passes through the bypass passage 52 for a predetermined time during the next forced regeneration of the DPF 21 when the amount of accumulated PM in the PM filter 61 exceeds a predetermined amount. Control the operation.
As a result, high temperature exhaust gas flows from the oxidation catalyst 22 into the PM filter 61 during the forced regeneration with respect to the PM filter 61 on which PM has accumulated a predetermined amount or more, and the PM deposited on the PM filter 61 is burned and removed. 61 can be reproduced. Therefore, the pressure loss in the PM filter 61 can be reduced, and fuel consumption reduction at the time of cold start can be suppressed. Further, it is possible to prevent burning of the PM filter 61 that may occur when PM is burned in a state where PM is excessively accumulated.

  Further, in the exhaust heat recovery device 60, the opening degree of the on-off valve 54 may be continuously controlled. Specifically, the opening degree of the on-off valve 54 can be continuously controlled by the ECU 40 from the fully open state to the fully closed state. As for the transition from the fully open state to the fully closed state, it is desirable to continuously control the opening degree based on the PM accumulation amount accumulated on the PM filter 61, but for simplification, it may be controlled based on the elapsed time. .

FIG. 4 is a graph showing the transition of the opening degree of the on-off valve 54 during regeneration of the PM filter 61.
When the PM filter 61 is regenerated, the ECU 40 gradually decreases the opening rather than fully closing from the start of regeneration as shown in FIG.
This is because if a large amount of exhaust gas is allowed to pass through the PM filter 61 having a relatively small capacity, the pressure loss increases significantly, so that the output of the engine 1 changes greatly, the drivability is reduced and the fuel consumption is reduced. This is because there is a risk of lowering. In addition, it is considered that the accumulated PM may burn rapidly and may cause melting of the PM filter 61.

By gradually closing the opening of the on-off valve 54 in this way, immediately after the start of regeneration of the PM filter 61, the flow rate of the exhaust gas passing through the PM filter 61 is suppressed, and a significant increase in pressure loss is suppressed and regeneration is performed. As the pressure advances and PM is removed from the PM filter 61 and the pressure loss is reduced, the flow rate of the exhaust gas passing through the PM filter 61 is increased, so that rapid regeneration can be completed.
Further, in the above embodiment, the heat exchanger 53 and the PM filter 61 may be loaded with a noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh). In this way, it is possible to promote combustion removal of PM during regeneration of the heat exchanger 53 and the PM filter 61, and to shorten the regeneration time. Furthermore, it is preferable that the heat exchanger 53 and the PM filter 61 carry a rare earth such as cerium (Ce). Thereby, it is possible to stably supply oxygen during regeneration by utilizing the oxygen storage capacity of rare earth, and further shorten the regeneration time.

Although the description of the embodiment of the invention is finished as above, the embodiment of the present invention is not limited to the above embodiment.
For example, in the above embodiment, the exhaust flow path is switched by the open / close valve 54 that opens and closes the main exhaust passage 51, but an open / close valve may be provided in the bypass passage 52, or the main exhaust passage 51 and the bypass passage 52 may be provided. You may provide an on-off valve in the connection part with a downstream.

  In this embodiment, the cooling water of the engine 1 is warmed by the heat exchanger 53, and the heat of the exhaust is used for warming up at the time of cold start. The heat energy of the exhaust gas may be used for other devices and applications through a heat medium other than cooling water.

1 Engine 20 Exhaust passage 21 DPF
22 DOC
40 ECU
50, 60 Exhaust heat recovery device 52 Bypass path 53 Heat exchanger 54 On-off valve 61 PM filter

Claims (8)

The exhaust passage is provided with a first filter for collecting particulate matter in the exhaust gas, and the exhaust passage upstream of the first filter is provided with an oxidation catalyst capable of oxidizing components in the exhaust gas. An exhaust heat recovery device for an engine,
A bypass path connected in parallel to the exhaust passage between the oxidation catalyst and the first filter;
A heat exchanging means provided in the bypass passage for exchanging heat between the exhaust gas passing through the bypass passage and the heat medium;
Switching means for switching an inflow destination of the exhaust gas that has passed through the oxidation catalyst between the exhaust passage and the bypass passage in parallel with the bypass passage;
Control means for controlling the operation of at least the switching means;
An exhaust heat recovery device for an engine characterized by comprising:   The control means controls the operation of the switching means so that, when the first filter is regenerated, the exhaust gas that has passed through the oxidation catalyst passes through the exhaust gas passage in parallel with the bypass passage. Item 2. An exhaust heat recovery apparatus for an engine according to Item 1. A heat exchange rate detecting means for detecting a heat exchange rate of the heat exchange means;
The control means is capable of controlling the heat exchange rate and, when regenerating the first filter, controlling the operation of the switching means to pass the exhaust gas that has passed through the oxidation catalyst to the bypass passage. The exhaust heat recovery device for an engine according to claim 2, wherein the heat exchange rate detected by the heat exchange rate detection means is set to a predetermined value or less.   The exhaust heat recovery apparatus for an engine according to claim 3, wherein a precious metal is supported on the heat exchange means.   The engine according to any one of claims 1 to 4, wherein a second filter that collects particulate matter in the exhaust gas is provided in the bypass passage upstream of the heat exchange means. Exhaust heat recovery device. A deposition amount detecting means for detecting a deposition amount of the particulate matter in the second filter;
When the accumulation amount of the particulate matter detected by the accumulation amount detection unit is equal to or greater than a predetermined amount, the control unit causes the exhaust gas that has passed through the oxidation catalyst during the regeneration of the first filter to pass through the bypass path. 6. The engine exhaust heat recovery apparatus according to claim 5, wherein the operation of the switching means is controlled so as to pass through the engine.   The control means, when allowing the exhaust gas that has passed through the oxidation catalyst to pass through the bypass passage, continuously and gradually controls the opening degree of the switching means from a fully open state to a fully closed state. Item 7. An exhaust heat recovery apparatus for an engine according to Item 6.   The exhaust heat recovery apparatus for an engine according to claim 6, wherein a precious metal is supported on the second filter.

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