Exhaust heat recovery control device

An exhaust heat recovery control device includes a recovered heat adjusting unit configured to adjust an amount of heat recovered of exhaust gas by an exhaust heat recoverer recovering heat of exhaust gas and a control unit configured to control the recovered heat adjusting unit so as to prevent or suppress freezing in an exhaust pipe based on a traveling history of a vehicle on which the exhaust heat recovery control device is mounted when the freezing in the exhaust pipe is predicted.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2014-019510 filed on Feb. 4, 2014 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust heat recovery control device that controls an exhaust heat recoverer recovering exhaust heat of an exhaust pipe or the like.

2. Description of Related Art

In an exhaust heat recoverer recovering exhaust heat from an exhaust pipe or the like, condensed water may be produced by recovering exhaust heat and thus cooling exhaust gas. The condensed water may cause damage to a catalyst unit for purifying exhaust gas, a switching valve for switching a flow channel of exhaust gas to an exhaust heat recoverer, and the like.

Therefore, Japanese Patent Application Publication No. 2006-161593 (JP 2006-161593 A) proposes an exhaust heat recovery system that prevents condensed water from coming into contact with a catalyst unit, a switching valve, or the like.

Specifically, in the exhaust heat recovery system described in JP 2006-161593 A, a heat exchanger for exhaust heat recovery is arranged in parallel with an exhaust pipe between a branched pipe branched from the exhaust pipe and a merged pipe merging on the downstream side of the branched part of the exhaust pipe. A flow channel switching valve switching a flow channel of exhaust gas to the exhaust pipe or the heat exchanger for exhaust heat recovery is disposed between the branched part and the merged part of the exhaust pipe. A part including a region between the flow channel switching valve and the merged part in the exhaust pipe is provided with a liquid storage part in which liquid can be stored.

However, in an environment below the freezing point, there is a possibility that condensed water produced in the exhaust heat recoverer will be frozen in the exhaust pipe. When the freezing in the exhaust pipe is not released but is kept in some traveling conditions and condensed water is further produced and frozen, the decrease in output power of an engine or the degradation in interior noise due to exhaust sound (also referred to as degradation in noise and vibration (NV) performance) may be caused, which provides room for improvement.

SUMMARY OF THE INVENTION

The invention causes recovery of exhaust heat and suppression of performance degradation due to the freezing of condensed water to be compatible with each other.

According to an aspect of the invention, there is provided an exhaust heat recovery control device including: a recovered heat adjusting unit configured to adjust an amount of heat recovered of exhaust gas by an exhaust heat recoverer recovering heat of exhaust gas; and a control unit configured to control the recovered heat adjusting unit so as to prevent or suppress freezing in an exhaust pipe based on a traveling history of a vehicle on which the exhaust heat recovery control device is mounted when the freezing in the exhaust pipe is predicted.

According to this configuration, the recovered heat adjusting unit adjusts the amount of heat recovered of exhaust gas by the exhaust heat recoverer recovering heat of the exhaust gas.

The control unit controls the recovered heat adjusting unit so as to prevent or suppress freezing in the exhaust pipe based on the traveling history when the freezing in the exhaust pipe is predicted. For example, when it is determined based on the traveling history that the freezing is not released, the freezing in the exhaust pipe can be released by controlling the recovered heat adjusting unit so as to reduce or limit the amount of heat recovered of exhaust gas. On the other hand, when it is determined based on the traveling history that the freezing is released, it is possible to recover exhaust heat by controlling the exhaust heat recoverer so as to recover heat or controlling the recovered heat adjusting unit so as to increase the amount of heat recovered. Accordingly, it is possible to cause the recovery of exhaust heat and the suppression of performance degradation due to the freezing of condensed water.

For example, the control unit may control the recovered heat adjusting unit so as to decrease the amount of heat recovered of exhaust gas by the exhaust heat recoverer when a previous traveling time as the traveling history is equal to or shorter than a predetermined reference time. That is, it can be determined based on the previous traveling time whether the freezing in the exhaust pipe is released. Accordingly, when the previous traveling time is equal to or shorter than a predetermined reference time, there is a high possibility that the inside of the exhaust pipe is frozen and it is thus possible to release the freezing in the exhaust pipe by controlling the recovered heat adjusting unit so as to decrease the amount of heat recovered.

The exhaust heat recoverer may raise the temperature of a coolant for cooling an engine using the recovered heat of exhaust gas, the recovered heat adjusting unit may include a circulation unit configured to circulate the coolant, and the control unit may adjust the amount of heat recovered of exhaust gas by adjusting an amount of coolant circulated by the circulation unit. Alternatively, the recovered heat adjusting unit may adjust the amount of heat recovered by adjusting a flow rate of exhaust gas passing through the exhaust heat recoverer.

As described above, according to the invention, it is possible to cause recovery of exhaust heat and suppression of performance degradation due to freezing of condensed water to be compatible with each other.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an example of an embodiment of the invention will be described in detail with reference to the accompanying drawings.FIG. 1is a block diagram schematically illustrating a configuration of an exhaust heat recovery control device according to an embodiment of the invention.

In an exhaust heat recovery control device10, a recovered heat adjusting unit for adjusting an amount of heat recovered by an exhaust heat recoverer12recovering heat of exhaust gas is connected to a controller14as the control unit.

The exhaust heat recoverer12is disposed in an exhaust pipe through which exhaust gas of an automobile passes, recovers heat of the exhaust gas of the engine of the automobile, and uses the recovered heat for promotion of space heating or warming-up of an engine or the like.

The controller14controls the recovered heat adjusting unit so as to control whether to recover the heat of exhaust gas or an amount of heat recovered through the use of the exhaust heat recoverer12.

The controller14is connected to a water temperature sensor18and an external air temperature sensor20. That is, the detection results of the water temperature sensor18and the external air temperature sensor20are input to the controller14. This embodiment describes an example in which the detection results of the water temperature sensor18and the external air temperature sensor20are directly input to the controller14, but the invention is not limited to this example. For example, the detection result of the water temperature sensor18may be input to the controller14via an engine electronic control unit (ECU) and the detection result of the external air temperature sensor20may be input to the controller14via an air-conditioner ECU.

The controller14controls the recovered heat adjusting unit on the basis of the detection results of the water temperature sensor18and the external air temperature sensor20.

Now, arrangement examples of the exhaust heat recoverer12and specific examples of the recovered heat adjusting unit will be described below.FIGS. 2A to 2Care diagrams illustrating arrangement examples of the exhaust heat recoverer12and specific examples of the recovered heat adjusting unit.

In the example illustrated inFIG. 2A, a catalyst unit34and a main muffler36are disposed sequentially from the upstream side in the discharge path of an exhaust pipe22for discharging exhaust gas from the engine28. A bypass path24is disposed in parallel with the exhaust pipe22between the main muffler36and the catalyst unit34, and the exhaust heat recoverer12is disposed in the bypass path24.

A coolant for cooling the engine28is circulated to the exhaust heat recoverer12by a water pump (W/P)30. The coolant circulated to the exhaust heat recoverer12flows into a heater core32and is returned to the engine28. That is, the flow channel of the coolant is provided with the exhaust heat recoverer12so as to recover the heat of exhaust gas through the use of the exhaust heat recoverer12and to raise the temperature of the coolant, which can be used for a heat source of a heater, promotion of warming-up, or the like.

The exhaust pipe22is provided with a switching valve38so as to adjust an amount of exhaust gas flowing into the bypass path24or to switch the flow channel through the use of the switching valve38. The switching valve38is operated by an actuator40. That is, by causing the controller14to control the operation of the actuator40, the amount of exhaust gas flowing into the exhaust heat recoverer12is adjusted and the amount of exhaust heat recovered is adjusted. Accordingly, the actuator40driving the switching valve38and the water pump30serve as the recovered heat adjusting unit. The opening and shutting of the switching valve38may be controlled so as to control whether to cause exhaust gas to flow into the exhaust heat recoverer12, or the degree of opening of the switching valve38may be controlled so as to control the flow rate of exhaust gas flowing into the exhaust heat recoverer12.

In the example illustrated inFIG. 2B, a catalyst unit34, an exhaust heat recoverer12, and a main muffler36are disposed sequentially from the upstream side in the discharge path of the exhaust pipe22for discharging exhaust gas from the engine28.

Similarly toFIG. 2A, a coolant for cooling the engine28is circulated to the exhaust heat recoverer12by a water pump (W/P)30. The coolant circulated to the exhaust heat recoverer12flows into a heater core32and is returned to the engine28. That is, the flow channel of the coolant is provided with the exhaust heat recoverer12so as to recover the heat of exhaust gas through the use of the exhaust heat recoverer12and to raise the temperature of the coolant, which can be used for a heat source of a heater, promotion of warming-up, or the like.

The circulation path of the coolant is provided with a bypass path supplying the coolant to the heater core32without passing through the exhaust heat recoverer12. That is, the circulation path of the coolant includes a circulation path passing through the exhaust heat recoverer12and a circulation path not passing through the exhaust heat recoverer12.

A switching valve42for switching the circulation path between the two circulation paths is disposed so as to switch the circulation path of the coolant through the use of the switching valve. The switching valve42is operated by an actuator44. That is, by causing the controller14to control the operation of the actuator44, the amount of coolant circulating to the exhaust heat recoverer12is adjusted and the amount of exhaust heat recovered is adjusted. Accordingly, the actuator44driving the switching valve42and the water pump30serve as the recovered heat adjusting unit. The opening and shutting of the switching valve42may be controlled so as to control whether to cause coolant to flow into the exhaust heat recoverer12, or the degree of opening of the switching valve42may be controlled so as to control the flow rate of coolant flowing into the exhaust heat recoverer12.

In the example illustrated inFIG. 2C, similarly toFIG. 2B, a catalyst unit34, an exhaust heat recoverer12, and a main muffler36are disposed sequentially from the upstream side in the discharge path of the exhaust pipe22for discharging exhaust gas from the engine28.

Similarly toFIG. 2A, a coolant for cooling the engine28is circulated to the exhaust heat recoverer12by a water pump (W/P)30. The coolant circulated to the exhaust heat recoverer12flows into a heater core32and is returned to the engine28. That is, the flow channel of the coolant is provided with the exhaust heat recoverer12so as to recover the heat of exhaust gas through the use of the exhaust heat recoverer12and to raise the temperature of the coolant, which can be used for a heat source of a heater.

In the example illustrated inFIG. 2C, the water pump30that is driven by a motor or the like is applied to change the flow rate of the coolant through the use of the water pump30. That is, by controlling the controller14to control the water pump30so as to adjust the flow rate of the coolant flowing into the exhaust heat recoverer12, the amount of exhaust heat recovered is adjusted. Accordingly, the water pump30can be considered as the circulation unit and serves as the recovered heat adjusting unit.

The configurations illustrated inFIGS. 2A to 2Cmay be combined. Alternatively, the water pump30illustrated inFIG. 2Cmay be applied to the configurations illustrated inFIGS. 2A, 2Band the controller14may be configured to control the actuators40,44and the water pump30. Alternatively, the configurations illustrated inFIGS. 2A, 2Bmay be combined.

When the engine is stopped and put in the environment below the freezing point in a state in which condensed water is produced and is not discharged but remains in the exhaust pipe, there is a possibility that the condensed water will be frozen in the exhaust pipe22.

An example of the reason for the remaining of condensed water is that the exhaust pipe22has level differences to avoid other components and the condensed water is not discharged to the downstream side when there is not a certain degree of flow rate of gas (a certain engine rotation speed).

When the condensed water is frozen in the exhaust pipe22, it is considered that the condensed water is not melted and remains depending on the traveling conditions. When the condensed water is frozen and remains and condensed water is further produced and is frozen, there is a possibility that a decrease in output power of the engine due to the degradation in exhaust performance, the degradation in interior noise due to exhaust sound, and the like will be caused.

Accordingly, in this embodiment, the controller14controls the recovered heat adjusting unit on the basis of the traveling history so as to adjust the amount of exhaust heat recovered by the exhaust heat recoverer12.

For example, in the configuration example illustrated inFIG. 2A, the amount of exhaust heat recovered can be adjusted by adjusting the flow rate of exhaust gas flowing into the exhaust heat recoverer12. For example, when the flow rate of exhaust gas flowing into the exhaust heat recoverer12is decreased, the amount of heat recovered is also decreased. In the configuration examples illustrated inFIGS. 2B, 2C, the amount of exhaust heat recovered can be adjusted by adjusting the flow rate of the coolant flowing into the exhaust heat recoverer12. That is, as illustrated inFIG. 3, when the flow rate of the coolant is decreased, the heat transfer coefficient between the coolant and the pipe is decreased and the exhaust heat recovery performance degrades. When the exhaust heat recovery performance degrades, the exhaust gas temperature after the exhaust heat recoverer12rises and the freezing in the exhaust pipe22subsequent to the exhaust heat recoverer12can be released. The production of condensed water is decreased and thus the freezing of the produced condensed water and the enlargement of the frozen part are suppressed.

Specific processes that are performed by the controller14of the exhaust heat recovery control device10according to this embodiment having the above-mentioned configuration will be described below.FIG. 4is a flowchart illustrating an example of the process flow that is performed by the controller14of the exhaust heat recovery control device10according to this embodiment. The process flow illustrated inFIG. 4is started when an ignition switch (IG) not illustrated is turned on, and is ended when the IG is turned off.

First, in step100, the controller14starts the engine28and then the process flow goes to step102.

In step102, the controller14determines whether there is a possibility that the exhaust pipe22will be frozen. Regarding this determination, for example, the controller14determines whether the external air temperature is equal to or lower than a predetermined threshold value on the basis of the detection result of the external air temperature sensor20. The process flow goes to step104when the determination result is negative, and goes to step110when the determination result is positive. It may be determined on the basis of the history of the external air temperature when there is a possibility that the exhaust pipe22will be frozen. For example, when the current external air temperature is not below the freezing point but is temporarily below the freezing point at the time of stopping the engine, it can be determined that there is a possibility of the freezing.

In step104, the controller14determines whether the freezing is released on the basis of the previous traveling history. Regarding this determination, the controller14determines whether the freezing in the exhaust pipe22is released, for example, by determining whether the previous traveling time is equal to or longer than a predetermined reference time. The process flow goes to step106when the determination result is positive, and goes to step110when the determination result is negative. As the traveling history, a maximum amount of exhaust gas discharged, an amount of fuel consumed, a maximum rotation speed of the engine, a maximum vehicle speed, a maximum gas temperature of the exhaust gas temperature, a predicted gas temperature or a predicted catalyst temperature predicted by an engine ECU, and the like may be used in addition to the previous traveling time. That is, regarding the determination, it may be determined on the basis of at least one traveling history among the above-mentioned traveling histories whether the freezing in the exhaust pipe22is released.

In step106, the controller14determines whether the coolant temperature is equal to or lower than a specific temperature on the basis of the detection result of the water temperature sensor18. The process flow goes to step108when the determination result is positive, and goes to step110when the determination result is negative. The specific temperature may be set to different values depending on a space heating request, may be set to A° C. (for example, 60° C.) when the space heating request is given, and may be set to B° C. (for example, 45° C.) when the space heating request is not given.

In step108, an exhaust heat recovery mode is performed by the controller14, the process flow is returned to step106, and the above-mentioned processes are repeatedly performed. In the exhaust heat recovery mode, for example, in the example illustrated inFIG. 2A, the controller14controls the driving of the actuator40so as to drive the switching valve38such that exhaust gas flows into the exhaust heat recoverer12. In the example illustrated inFIG. 2B, the controller14controls the driving of the actuator44so as to drive the switching valve42such that coolant flows into the exhaust heat recoverer12. In the example illustrated inFIG. 2C, the controller14controls the driving of the water pump30so as to increase the flow rate of the coolant flowing in the exhaust heat recoverer12. By performing these processes, the exhaust heat is recovered by the exhaust heat recoverer12, the temperature of the coolant is raised, and it is thus possible to assist the space heating or to promote the warming-up of the engine.

On the other hand, in step110, an exhaust heat non-recovery mode is performed by the controller14and then the process flow goes to step112. In the exhaust heat non-recovery mode, for example, in the example illustrated inFIG. 2A, the controller14controls the driving of the actuator40so as to drive the switching valve38such that the amount of exhaust gas flowing into the exhaust heat recoverer12is decreased or limited. In the example illustrated inFIG. 2B, the controller14controls the driving of the actuator44so as to drive the switching valve42such that the amount of coolant flowing into the exhaust heat recoverer12is decreased or limited. In the example illustrated inFIG. 2C, the controller14controls the driving of the water pump30so as to decrease the flow rate of the coolant flowing into the exhaust heat recoverer12. By performing these processes, the recovery of exhaust heat by the exhaust heat recoverer12is stopped or decreased. Accordingly, as described with reference toFIG. 3, the exhaust gas temperature after the exhaust heat recoverer12is raised, and the freezing in the exhaust pipe22subsequent to the exhaust heat recoverer12is released when the condensed water is frozen. The production of condensed water is decreased and thus the freezing of the produced condensed water and the enlargement of the frozen part are suppressed.

In step112, the controller14determines whether the freezing is released on the basis of the current traveling history. The process flow is returned to step110and the above-mentioned processes are repeatedly performed when the determination result is negative, and the process flow is returned to step106and the above-mentioned processes are repeatedly performed when the determination result is positive. The contents described in step104can be used as the traveling history.

The processes that are performed by the controller14in the above-mentioned embodiment may be stored as a program in a storage medium and the program may be distributed.

The invention is not limited to the above-mentioned details, and can be modified in various forms without departing from the gist thereof.