US20090183697A1

US20090183697A1 - Exhaust heat recovery system

Info

Publication number: US20090183697A1
Application number: US12/300,811
Authority: US
Inventors: Kiwamu Inui
Original assignee: Individual
Current assignee: Toyota Motor Corp
Priority date: 2006-05-15
Filing date: 2007-05-11
Publication date: 2009-07-23
Also published as: JP2007303435A; EP2018285A1; CN101443205A; WO2007132326A1; JP4197005B2

Abstract

An exhaust heat recovery system (10) includes an exhaust heat recovery heat exchanger (18) in which heat is transferred from exhaust gas discharged from an internal combustion engine (12) to an engine coolant for cooling the internal combustion engine (12), and a heat pump system (22) for recovering exhaust heat of exhaust gas. The heat pump system (22) includes a refrigerant circulation passage (24) for circulating CO2 refrigerant, a heat-absorbing heat exchanger (32) in which heat is transferred from exhaust gas to the CO2 refrigerant, and a heat-releasing heat exchanger (28) in which the exhaust heat recovered by heat transfer to the CO2 refrigerant in the heat-releasing heat exchanger (32) is recovered.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an exhaust heat recovery system applied to a vehicle, such as an automobile, to supply heat to heat the vehicle cabin and warm up the engine.
2. Description of the Related Art
A vehicle heat pump system having the following features is available (e.g. heat pump system disclosed in Japanese Patent Application Publication No. H3-90430 (JP-A-3-90430)). The heat pump system includes an exhaust gas heat exchanger and a heat pump circuit. In the exhaust gas heat exchanger, heat of exhaust gas discharged from an internal combustion engine is recovered, and transferred to a coolant of the engine. The heat pump circuit uses, as a heat source, the outside air and the engine coolant heated in the exhaust gas heat exchanger. If the heating mode is selected when the temperature of the engine coolant is low, the supply of the engine coolant to a heater core is stopped, and the vehicle cabin is heated using the heat pump circuit.
However, in the aforementioned technology, since the heat pump uses, as the heat source, the outside air and engine coolant heated in the exhaust gas heat exchanger, further improvement of the heat pump efficiency for effective heating is desired.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an exhaust heat recovery system in which the exhaust heat can be effectively recovered.
An exhaust heat recovery system according to an aspect of the invention includes an exhaust heat recovery heat exchanger in which heat is transferred from exhaust gas discharged from an internal combustion engine to a coolant for cooling the internal combustion engine. The exhaust heat recovery system also includes a heat pump. The heat pump includes a circulation passage for a refrigerant, a heat-absorbing heat exchanger in which the heat is transferred from the exhaust gas to the refrigerant, and a heat-releasing heat exchanger in which the heat is recovered from the refrigerant.
In the exhaust heat recovery system according to the aforementioned aspect, exhaust heat (energy) of exhaust gas discharged from the internal combustion engine is recovered and transferred to the coolant in the exhaust heat recovery heat exchanger for quickly warming up the internal combustion engine, heating the vehicle cabin, and the other purposes. Further, the exhaust heat of exhaust gas is recovered and transferred to the refrigerant in the heat-absorbing heat exchanger and used as the heat source to operate the heat pump. The internal combustion engine is quickly warmed up and the vehicle cabin is heated by, for example, heat transfer from the refrigerant in the heat-releasing heat exchanger.
Since the heat pump uses exhaust gas as the heat source of the heat pump, that is, since the heat pump uses high-temperature fluid as the heat source, the heat pump efficiency is high. Therefore, exhaust heat is not discharged to the outside of the vehicle when exhaust gas is discharged, and can be efficiently recovered. The heat pump according to the invention thus has higher performance than that of the conventional configuration in which the outside air or fluid, such as coolant, at relatively low temperature is employed as the heat source. Thus, the thermal efficiency of the entire vehicle is improved.
Thus, in the exhaust heat recovery system according to the aforementioned aspect, exhaust heat can be effectively recovered. Further, since exhaust gas is used as the heat source of the heat pump, frost formation is prevented.
In the exhaust heat recovery system according to the aforementioned aspect, the heat-absorbing heat exchanger of the heat pump may be disposed downstream of the exhaust heat recovery heat exchanger in a flowing direction of the exhaust gas.
In the exhaust heat recovery system according to the aforementioned aspect, exhaust heat of exhaust gas is first recovered and transferred to the coolant in the exhaust heat recovery heat exchanger, and then the exhaust heat that is not recovered in the exhaust heat recovery heat exchanger is recovered in the heat pump. Further, since the remaining heat is transferred from exhaust gas at relatively low temperature to the refrigerant in the heat-absorbing heat exchanger after the heat of the exhaust gas is transferred to the coolant in the exhaust heat recovery heat exchanger, overheating (i.e. excessive pressure increase) of the refrigerant can be prevented. Thus, the heat pump is protected against high temperature by employing the simple configuration, and the exhaust heat can be effectively recovered using the more compact system compared to the system in which, for example, the heat transfer area in the exhaust heat recovery heat exchanger is expanded.
In the exhaust heat recovery system according to the aforementioned aspect, the coolant may be circulated by a pump driven by a power from the internal combustion engine.
The exhaust heat recovery system according to the aforementioned aspect may further include an exhaust heat recovery switching device that is switched between an exhaust heat recovery state where exhaust heat of the exhaust gas is recovered and a discharge state where the exhaust gas is discharged to an outside. In the exhaust heat recovery system, the exhaust gas may flow through the exhaust heat recovery heat exchanger and the heat-absorbing heat exchanger by switching the exhaust heat recovery switching device from the discharge state to the exhaust heat recovery state.
The exhaust heat recovery system according to the aforementioned aspect may further include a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state when a temperature of the coolant is lower than a predetermined temperature, and switches the exhaust heat recovery switching device to the discharge state when the temperature of the coolant is equal to or higher than the predetermined temperature.
In the exhaust heat recovery system according to the aforementioned aspect, the heat pump may include a compressor that compresses the refrigerant to which the heat has been transferred in the heat-absorbing heat exchanger. The exhaust heat recovery system may further include a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state and operates the compressor when the temperature of the coolant is lower than the predetermined temperature.
In the exhaust heat recovery system according to the aforementioned aspect, when the temperature of the coolant is equal to or higher than the predetermined temperature, the control device may control the exhaust heat recovery switching device to the discharge state and control the compressor to a stopped state.
In the exhaust heat recovery system according to the aforementioned aspect, the heat-releasing heat exchanger of the heat pump may be configured so that the heat is transferred from the refrigerant to the coolant therein.
In the exhaust heat recovery system according to the aforementioned aspect, heat is released into the coolant in the heat-releasing heat exchanger of the heat pump, and therefore all the heat recovered from exhaust gas is transferred to the coolant. In this way, using the coolant, the internal combustion engine can be quickly warmed up and air heating (heating of the air for air conditioning) can be achieved.
In the exhaust heat recovery system according to the aforementioned aspect, the heat-releasing heat exchanger of the heat pump may be disposed upstream of the exhaust heat recovery heat exchanger in the circulation passage for the coolant.
In the exhaust heat recovery system according to the aforementioned aspect, the exhaust heat is released into the coolant in the heat-releasing heat exchanger of the heat pump system. Since the heat is released into the coolant at relatively low temperature before the coolant is heated in the exhaust heat recovery heat exchanger, the heat pump efficiency is high, thus contributing to improvement of the entire heat recovery efficiency.
The exhaust heat recovery system according to the aforementioned aspect may further include a heater core that is disposed upstream of the exhaust heat recovery heat exchanger in the circulation passage for the coolant and heats air for air conditioning. In addition, the heat-releasing heat exchanger of the heat pump may be disposed downstream of the heater core in the circulation passage for the coolant.
In the exhaust heat recovery system according to the aforementioned aspect, since the heat is released into the coolant at the lowest temperature in the circulation passage, that is, the heat is released into the coolant after the heat is released from the coolant to the air in the heater core but before the coolant is heated in the exhaust heat recovery heat exchanger, the heat pump efficiency is further improved, thus contributing to further improvement of the entire heat recovery efficiency.
In the exhaust heat recovery system according to the aforementioned aspect, a heat-releasing heat exchanger of the heat pump may be configured so that the heat is transferred from the refrigerant to the air for air conditioning therein.
In the exhaust heat recovery system according to the aforementioned aspect, the air for air conditioning is heated in the heat-releasing heat exchanger of the heat pump so that the recovered heat is used for the vehicle cabin heating. Since the air is directly heated in the heat-releasing heat exchanger, heating start-up time can be shorter than in the case where the engine coolant is used for heating.
The exhaust heat recovery system according to the aforementioned aspect may further include a heater core that is provided in the circulation passage for the coolant and heats the air for air conditioning, and a heater core switching device that is switched between an air supply state where the air for air conditioning is supplied to the heater core and a heater core bypass state where the air for air conditioning is not supplied to the heater core.
In the exhaust heat recovery system according to the aforementioned aspect, when the heater core switching device stops air supply to the heater core, heat is not released from the heater core so as to heat the air. Therefore, the temperature of the coolant staying in the heater core does not decrease, and warm-up time for the internal combustion engine can be shortened.
The exhaust heat recovery system according to the aforementioned aspect may further include a heat pump switching device that is switched between an air supply state where the air for air conditioning is supplied to the heat-releasing heat exchanger and a heat pump bypass state where the air for air conditioning is not supplied to the heat-releasing heat exchanger.
In the exhaust heat recovery system according to the aforementioned aspect, the heater core switching device is switched to the heater core bypass state when the heat pump is operated, and the heat pump switching device is switched to the heat pump bypass state when the heat pump is stopped.
The exhaust heat recovery system according to the aforementioned aspect may further include: an exhaust heat recovery switching device that is switched between an exhaust heat recovery state where the exhaust heat of the exhaust gas is recovered, and a discharge state where the exhaust gas is discharged to an outside; and a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state and switches the heater core switching device to the heater core bypass state when a temperature of the coolant is lower than a predetermined temperature.
The exhaust heat recovery system according to the aforementioned aspect, which includes the heat pump having a compressor that compresses the refrigerant to which the heat has been transferred in the heat-absorbing heat exchanger. The exhaust heat recovery system may further include an exhaust heat recovery switching device that is switched between an exhaust heat recovery state where exhaust heat of the exhaust gas is recovered and a discharge state where the exhaust gas is discharged to an outside, and a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state and operates the compressor, if a request for heating the air for air conditioning is made when a temperature of the coolant is lower than a predetermined temperature.
In the exhaust heat recovery system according to the aforementioned aspect, if the request for heating is made when the temperature of the coolant is lower than the predetermined temperature, the control device may switch the heater core switching device to the heater core bypass state.
In the exhaust heat recovery system according to the aforementioned aspect, when the temperature of the coolant is equal to or higher than the predetermined temperature, the control device may control the exhaust heat recovery switching device to the discharge state and control the compressor to a stopped state.
In the exhaust heat recovery system according to the aforementioned aspect, when the temperature of the coolant is equal to or higher than the predetermined temperature, the control device may control the heat pump switching device to the heat pump bypass state.
As described above, the exhaust heat recovery system according to the aspect of the invention has a great advantage that exhaust heat is effectively recovered.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and/or further objects, features and advantages of the invention will become more apparent from the following description of preferred embodiment with reference to the accompanying drawings, in which numerals are used to represent like elements and wherein:

FIG. 1 is a system block diagram showing an exhaust heat recovery system according to a first embodiment of the invention.

FIG. 2 is a system block diagram showing an exhaust heat recovery system according to a second embodiment of the invention.

FIG. 3 is a side sectional view schematically showing arrangement of a heat-releasing heat exchanger that constitutes a part of the exhaust heat recovery system according to the second embodiment of the invention in an air conditioner case.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

An exhaust heat recovery system 10 as an exhaust heat recovery system according to a first embodiment of the invention will be described with reference to FIG. 1. FIG. 1 shows a system block diagram (system flowsheet) of the exhaust heat recovery system 10. As shown in FIG. 1, the exhaust heat recovery system 10 includes a coolant circulation passage 14 through which an engine coolant is circulated and supplied to an internal combustion engine 12 that produces driving force of a vehicle. In the embodiment, a mechanical pump 15 driven by the power output from the internal combustion engine 12 circulates the engine coolant in the coolant circulation passage 14. Note that, an electric pump may be employed instead of the mechanical pump.
A heater core 16 is provided in the coolant circulation passage 14. The heater core 16 serves as a heat exchanger that provides hot air for heating the vehicle cabin. In the heater core 16, the engine coolant is used as a heat source. More specifically, the heater core 16 is provided in an air conditioner case (not shown). In the heater core 16, the air introduced into the air conditioner case is heated by heat transferred from the engine coolant so that the heated air is used for heating the vehicle cabin. The vehicle cabin is heated by the heated air introduced into the vehicle cabin by a blower (not shown), such as a fan.
Further, an exhaust heat recovery heat exchanger 18 is provided in the coolant circulation passage 14. In the exhaust heat recovery heat exchanger 18, the exhaust heat (energy) of exhaust gas discharged from the internal combustion engine 12 is recovered and transferred to the engine coolant. More specifically, in the exhaust heat recovery heat exchanger 18, the exhaust heat of exhaust gas flowing through an exhaust pipe 20, which is connected to an exhaust manifold 12A of the internal combustion engine 12, is transferred to the engine coolant circulating in the coolant circulation passage 14. A downstream edge (not shown) of the exhaust pipe 20 is opened to atmosphere.
The exhaust heat recovery system 10 further includes a heat pump system 22 for recovering the exhaust heat of exhaust gas. In the embodiment, the heat pump system 22 is configured such that the exhaust heat is recovered and transferred to the engine coolant. The detailed description will be given below.
The heat pump system 22 includes a refrigerant circulation passage 24 through which a refrigerant is circulated. In the refrigerant circulation passage 24, a compressor 26, a heat-releasing heat exchanger 28, an expansion valve 30, and a heat-absorbing heat exchanger 32 are provided in this order. In the embodiment, CO2 refrigerant is employed as the refrigerant circulating through the refrigerant circulation passage 24.
The heat-releasing heat exchanger 28 serves as a refrigerant radiator of the heat pump system 22, and as a heat exchanger in which heat is transferred from the CO2 refrigerant to the engine coolant. More specifically, in the heat-releasing heat exchanger 28, heat is released from the CO2 refrigerant circulating through the refrigerant circulation passage 24 to the engine coolant. The heat-absorbing heat exchanger 32 serves as a heat exchanger in which heat is transferred from exhaust gas to the CO2 refrigerant, and is configured so that the CO2 refrigerant absorbs exhaust heat from exhaust gas (that is, exhaust heat is recovered and transferred to the CO2 refrigerant). In addition, in the heat pump system 22, the CO2 refrigerant is evaporated in the heat-absorbing heat exchanger 32 so as to recover exhaust heat as latent heat and reduce the temperature and pressure of the CO2 refrigerant. Then the compressor 26 compresses the low-temperature, low-pressure CO2 refrigerant to increase the temperature and pressure of the CO2 refrigerant, and sends the high-temperature, high-pressure CO2 refrigerant to the heat-releasing heat exchanger 28. In the heat-releasing heat exchanger 28, the exhaust heat carried by the high-temperature, high-pressure CO2 refrigerant is recovered and transferred to the engine coolant. The expansion valve 30 expands the CO2 refrigerant to transform the refrigerant into the low-pressure liquid before the refrigerant is supplied to the heat-absorbing heat exchanger 32.
In this way, in the heat pump system 22, exhaust heat of exhaust gas is recovered and transferred to the engine coolant (i.e., exhaust heat is stored in the engine coolant). In the embodiment, the heat-releasing heat exchanger 28 is disposed, in the coolant circulation passage 14, between the heater core 16 and the exhaust heat recovery heat exchanger 18, that is, disposed downstream of the heater core 16 and upstream of the exhaust heat recovery heat exchanger 18 in the flowing direction of the engine coolant.
The heat-absorbing heat exchanger 32 is disposed downstream of the exhaust heat recovery heat exchanger 18 in the flowing direction of exhaust gas in the exhaust pipe 20. In addition, a bypass exhaust passage 20A is provided in the exhaust pipe 20 so as to bypass the exhaust heat recovery heat exchanger 18 and the heat-absorbing heat exchanger 32. An on-off valve 34 is disposed in the bypass exhaust passage 20A. When the on-off valve 34 opens, exhaust gas mainly flows through the bypass exhaust passage 20A and is discharged to the outside. When the on-off valve 34 closes, exhaust gas flows through the exhaust heat recovery heat exchanger 18 and heat-absorbing heat exchanger 32 in this order, so that the exhaust gas is recovered in the aforementioned manner. Note that, the on-off valve 34 functions as an exhaust heat recovery switching device according to the invention.
The exhaust heat recovery system 10 further includes an ECU (not shown) as a control device of the system. The ECU is electrically connected to the compressor 26 and the on-off valve 34 so as to operate and stop the compressor 26, and open and close the on-off valve 34. The ECU receives output signals corresponding to the temperature of the engine coolant from a temperature sensor and signals indicative of heating load from an air-conditioning ECU. The ECU controls the compressor 26 and the on-off valve 34 based on the received signals.
Next, the effects and advantages of the first embodiment will be described.
In the exhaust heat recovery system 10 configured as above, for example, when the temperature of the engine coolant is lower than a predetermined temperature (e.g., when the internal combustion engine has just started), the ECU closes the on-off valve 34 and operates the compressor 26. Then exhaust gas from the internal combustion engine 12 flows into the exhaust heat recovery heat exchanger 18 and heat-absorbing heat exchanger 32. In the exhaust heat recovery heat exchanger 18, the engine coolant is directly heated by heat transfer from the high-temperature exhaust gas to the engine coolant. Further, in the heat pump system 22, the exhaust heat of the exhaust gas recovered in the heat-absorbing heat exchanger 32 is transferred to the CO2 refrigerant, and then the heat is supplied to the engine coolant from the CO2 refrigerant. As a result, the engine coolant is heated.
For example, when the temperature of the engine coolant becomes equal to or higher than the predetermined temperature, the ECU opens the on-off valve 34 and stops the compressor 26 (to stop the heat pump system 22). In this case, exhaust gas mainly flows through the bypass exhaust passage 20A and is discharged to the outside.
Since the exhaust heat recovery system 10 is provided with the heat pump system 22, the exhaust heat (thermal energy) that is not recovered in the exhaust heat recovery heat exchanger 18 can be recovered in the heat pump system 22 and supplied to the engine coolant (that is, to the heater core 16). Further, since the heat pump system 22 is provided with the heat-absorbing heat exchanger 32 using exhaust gas as a heat source, in other words, the heat source of the heat-absorbing heat exchanger 32 is fluid at higher temperature than that of the conventional configuration in which, for example, the outside air or the engine coolant is used as the heat source, the heat pump efficiency of the heat pump system 22 is high. As a result, exhaust heat of exhaust gas that is not recovered in the exhaust heat recovery heat exchanger 18 can be efficiently recovered in the heat pump system 22.
The heat-absorbing heat exchanger 32 is disposed downstream of the exhaust heat recovery heat exchanger 18 in the flowing direction of exhaust gas. Therefore, the CO2 refrigerant can be prevented from being overheated, i.e. overexpanded due to the high-temperature exhaust gas. In other words, the heat pump system 22 having high heat recovery efficiency is protected against the high temperature. Further, since the heat-absorbing heat exchanger 32 uses exhaust gas as the heat source, there will be no problem of frost formation, which is a concern when the outside air is employed as the heat source, for example.
In the exhaust heat recovery system 10, since the exhaust heat recovered in the heat pump system 22 is used to increase the engine coolant temperature, the internal combustion engine 12 is quickly warmed up, and heating performance using the heater core 16 can be improved. Thus, even immediately after the start of the internal combustion engine 12, good heating performance can be achieved.
Moreover, in the heat pump system 22, the heat-releasing heat exchanger 28 is disposed so as to release the exhaust heat into the engine coolant at the lowest temperature, that is, the coolant before the exhaust heat is recovered in the exhaust heat recovery heat exchanger 18 provided in the coolant circulation passage 14 and after the exhaust heat is released from the coolant in the heater core 16. Therefore, the heat pump efficiency is high, and the exhaust heat can be more efficiently recovered. Thus, the entire exhaust heat recovery system 10 has improved heat recovery efficiency.
Based on what is described above, in the vehicle to which the exhaust heat recovery system 10 is applied, the heating performance is improved while maintaining good fuel efficiency. That is, the heating performance can be improved without deteriorating fuel efficiency. More specifically, in the conventional heat recovery system configured without the exhaust heat recovery heat exchanger 18 and the heat pump system 22, it is necessary to increase the idling engine speed to quickly heat the coolant in the coolant circulation passage 14 or to change the shift timing of the transmission in order to improve the heating performance (increase the temperature of the engine coolant). However, in the exhaust heat recovery system 10, since the exhaust heat is efficiently recovered and supplied to the engine coolant, it is no longer necessary to increase the idling engine speed nor change the shift timing, thus contributing to improvement of the heating performance without deteriorating fuel efficiency. At the same time, the engine is further quickly warmed up while maintaining good fuel efficiency.
Thus, in the exhaust gas heat recovery system 10 according to the first embodiment, the exhaust heat can be efficiently recovered.
Next, an exhaust heat recovery system 50 according to a second embodiment of the invention will be described with reference to FIGS. 2 and 3. The same components and portions in the second embodiment as those in the first embodiment will be denoted by the same reference numerals, and therefore the detailed description thereof will not be repeated.
FIG. 2 shows a system block diagram (system flowsheet) of the exhaust heat recovery system 50 according to the second embodiment of the invention. As shown in FIG. 2, the exhaust heat recovery system 50 includes a heat pump system 52, instead of the heat pump system 22. This distinguishes the exhaust heat recovery system 50 from the exhaust heat recovery system 10 according to the first embodiment.
The heat pump system 52 is basically the same as the heat pump system 22, except that the heat pump system 52 includes a heat-releasing heat exchanger 54 in which heat is transferred from the CO2 refrigerant to the air used for air conditioning, instead of the heat-releasing heat exchanger 28 in which heat is transferred from the CO2 refrigerant to the engine coolant. Hence, in the heat pump system 52, the exhaust heat recovered in the heat-absorbing heat exchanger 32 is released into the air in the heat-releasing heat exchanger 54 so as to produce hot air for heating the vehicle cabin. In the embodiment, air heating does not require heat transfer through the engine coolant nor the heater core 16.
As shown in FIG. 3, the heat-releasing heat exchanger 54 and the heater core 16 are disposed in the air conditioner case 56. The heat-releasing heat exchanger 54 and the heater core 16 form a vehicle air conditioner 58. An example of the vehicle air conditioner 58 will be supplementarily described below.
As shown in FIG. 3, the air conditioner case 56 opens at its both ends. An outside air door 62 and recirculating air doors 64 are formed on one end of the air conditioner case 56. The outside air door 62 and the recirculating air doors 64 are open and closed by recirculation/ventilation switching dampers 60. On the other end of the air conditioner case 56, a plurality of air outlets 68 are provided to open toward the vehicle cabin, and opened and closed by mode selector dampers 66 when appropriate. The air outlets 68 include, for example, a defroster outlet 68A, a side/center resister air outlet 68B, and a floor air outlet 68C. Thus, the heated air is allowed to blow into the vehicle cabin through at least one of the air outlets 68 at the desired position(s) using the mode selector dampers 66.
Further, a blower 70 is provided downstream of the outside air door 62 and the recirculating air doors 64 in the air conditioner case 56. The blower 70 sucks in the air into the air conditioner case 56 through the outside air door 62 or the recirculating air doors 64 and sends the sucked air toward the air outlets 68. An evaporator 72 for cooling the air for air conditioning is provided downstream of the blower 70 in the air conditioner case 56. The evaporator 72 may constitute a refrigeration cycle (not shown). When the refrigeration cycle is performed, the refrigerant is evaporated in the evaporator 72 by heat transfer from the air to the refrigerant so as to get rid of latent heat from the air.
An air mix damper 74 and the heater core 16 are provided downstream of the evaporator 72 in the air conditioner case 56. The air downstream of the evaporator 72 is guided into the heater core 16 based on, for example, the opening degree of the air mix damper 74, and then the air is heated. Then, after being mixed with the unheated air that has not passed through the heater core 16, the heated air is sent toward the air outlets 68. The air mix damper 74 can adjust the ratio of the amount of air that flows through the heater core 16 to the amount of air that does not flow through the heater core 16 between the ratio in the state where substantially all the air from the evaporator 72 flows through the heater core 16, and the ratio in the state where substantially all the air from the evaporator 72 does not flow through the heater core 16 (the latter state will be hereinafter referred to as “heater core bypass state”). Note that, the air mix damper 74 functions as a heater core switching device according to the invention.
An air mix damper 76 and a heat-releasing heat exchanger 54 are provided downstream of the heater core 16 in the air conditioner case 56. The air downstream of the evaporator 72 (the heater core 16) is guided into the heat-releasing heat exchanger 54 based on, for example, the opening degree of the air mix damper 76, and then, the air is heated. Then, after being mixed with the unheated air that has not passed through the heat-releasing heat exchanger 54, the heated air is sent toward the air outlets 68. The air mix damper 76 can adjust the ratio of the amount of air that flows through the heat-releasing heat exchanger 54 to the amount of air that does not flow through the heat-releasing heat exchanger 54 between the ratio in the state where substantially all the air from the evaporator 72 flows through the heat-releasing heat exchanger 54 and the ratio in the state where substantially all the air from the evaporator 72 does not flow through the heat-releasing heat exchanger 54 (the latter state will be hereinafter referred to as “heat pump bypass state”). Note that, the air mix damper 76 functions as a heat pump switching device according to the invention.
The aforementioned exhaust heat recovery system 50 and the vehicle air conditioner 58 are integrally (synchronously) controlled by a control device (not shown). When the heat pump system 52 is operated, the air mix damper 74 is placed in the heater core bypass state where the air is not heated in the heater core. When the heat pump system 52 stops, the air mix damper 76 is placed in the heat pump bypass state.
The configurations of other parts of the exhaust heat recovery system 50 are the same as those of the exhaust heat recovery system 10. Next, the effects and advantages of the exhaust heat recovery system 50 according to the second embodiment will be described below.
In the exhaust heat recovery system 50 configured as above, for example, when the temperature of the engine coolant is lower than a predetermined temperature (e.g., when the internal combustion engine 12 has just started), the ECU closes the on-off valve 34. With the on-off valve 34 closed, the exhaust heat of exhaust gas is recovered and transferred to the engine coolant in the exhaust heat recovery heat exchanger 18. Accordingly, the internal combustion engine 12 is quickly warmed up. In particular, if the air mix damper 74 is switched to the heater core bypass state, heat release from the heater core 16 is suppressed, and the internal combustion engine 12 is further quickly warmed up. When the temperature of the engine coolant becomes equal to or higher than the predetermined temperature, for example, the ECU opens the on-off valve 34. In this case, the exhaust gas mainly flows through the bypass exhaust passage 20A and is discharged to the outside.
Further, in the exhaust heat recovery system 50, for example, if a request for heating the vehicle cabin is made when the engine coolant temperature is lower than the predetermined temperature (e.g., when the internal combustion engine 12 has just started), the ECU closes the on-off valve 34 and operates the compressor 26. Then, exhaust gas from the internal combustion engine 12 flows into the exhaust heat recovery heat exchanger 18 and the heat-absorbing heat exchanger 32. In the exhaust heat recovery heat exchanger 18, the engine coolant is directly heated by heat transfer from the high-temperature exhaust gas. Thus, the internal combustion engine 12 is further quickly warmed up.
In the heat pump system 52, the exhaust heat of exhaust gas recovered in the heat-absorbing heat exchanger 32 is transferred to the CO2 refrigerant, and is then supplied from the CO2 refrigerant to the air introduced into the air conditioner case 56. Thus, the air used for heating the vehicle cabin is heated. In this case, the air mix damper 74 is placed in the heater core bypass state, and the air is not heated in the heater core 16. The air is further heated by heat transferred from the CO2 refrigerant in the heat-releasing heat exchanger 54, and used for heating the vehicle cabin.
For example, when the temperature of the engine coolant becomes equal to or higher than the predetermined temperature, the ECU opens the on-off valve 34 and stops the compressor 26 (to stop the heat pump system 52). In this case, exhaust gas mainly flows through the bypass exhaust passage 20A and is discharged to the outside. The air mix damper 74 is switched to the state where the air is introduced to the heater core 16, and the air mix damper 76 is switched to the heat pump bypass state. Therefore, after the engine coolant temperature increases, the heater core 16 (the engine coolant) is used as the heat source for heating the vehicle cabin.
Since the exhaust heat recovery system 50 is provided with the heat pump system 52, the exhaust heat unrecovered in the exhaust heat recovery heat exchanger 18 can be recovered in the heat pump system 52. Further, since the heat pump system 52 includes the heat-absorbing heat exchanger 32 having exhaust gas as a heat source, in other words, the heat source of the heat-absorbing heat exchanger 32 is fluid at higher temperature than that of the conventional construction in which, for example, the outside air and engine coolant are used as heat sources, the heat pump efficiency is high. As a result, exhaust heat of exhaust gas unrecovered in the exhaust heat recovery heat exchanger 18 can be efficiently recovered in the heat recovery system 50.
In the exhaust heat recovery system 50, the exhaust heat recovered in the heat-absorbing heat exchanger 32 is supplied to the air used for air conditioning (the heat-releasing heat exchanger 54). In the heat-releasing heat exchanger 54, the air is directly heated without heat transfer through the engine coolant (the heater core 16). Therefore, the heated air, that is, hot air for air conditioning can be provided before the temperature of the engine coolant is increased. That is, at the cold start, etc., hot air can be provided within a short period of time from the engine start, thus contributing to improvement of quick heating performance.
When the heat pump system 52 is operated in the manner described above, the air mix damper 74 suppresses heat release from the heater core 16 into the air. Therefore, the temperature of the engine coolant in the heater core 16 is prevented from decreasing, and is increased within a short period of time. That is, the internal combustion engine 12 can be quickly warmed up without deteriorating (and while improving) the heating performance of the vehicle air conditioner.
Since the heat-absorbing heat exchanger 32 is disposed downstream of the exhaust heat recovery heat exchanger 18 in the flowing direction of exhaust gas, the CO2 refrigerant is prevented from being overheated, i.e. overexpanded due to the high-temperature exhaust gas. In other words, the heat pump system 52 having high heat recovery efficiency is protected against the high temperature. Further, since exhaust gas is used as the heat source in the heat-absorbing heat exchanger 32, there will be no problem of frost formation, which is a concern when the outside air is employed as the heat source, etc.
Based on what is described above, in the vehicle to which the exhaust heat recovery system 50 is applied, the heating performance is improved while maintaining good fuel efficiency, as in the case of the exhaust heat recovery system 10 according to the first embodiment. Thus, the exhaust heat can be efficiently recovered in the exhaust heat recovery system 50 according to the second embodiment.

Claims

1. An exhaust heat recovery system comprising:

an exhaust heat recovery heat exchanger in which heat is transferred from exhaust gas discharged from an internal combustion engine to a coolant for cooling the internal combustion engine; and

a heat pump including:

a circulation passage for a refrigerant;

a heat-absorbing heat exchanger in which the heat is transferred from the exhaust gas to the refrigerant; and

a heat-releasing heat exchanger in which the heat is transferred from the refrigerant to the coolant, directly to a circulation passage for the coolant,

wherein said heat-releasing heat exchanger is disposed upstream of exhaust heat recovery heat exchanger in the circulation passage for the coolant.

2. The exhaust heat recovery system according to claim 1, wherein the heat-absorbing heat exchanger of the heat pump is disposed downstream of the exhaust heat recovery heat exchanger in a flowing direction of the exhaust gas.

3. The exhaust heat recovery system according to claim 1, wherein the coolant is circulated by a pump driven by a power from the internal combustion engine.

4. The exhaust heat recovery system according to claim 1, further comprising:

an exhaust heat recovery switching device switchable between an exhaust heat recovery state where exhaust heat of the exhaust gas is recovered and a discharge state where the exhaust gas is discharged to an outside,

wherein the exhaust gas flows through the exhaust heat recovery heat exchanger and the heat-absorbing heat exchanger by switching the exhaust heat recovery switching device from the discharge state to the exhaust heat recovery state.

5. The exhaust heat recovery system according to claim 4, further comprising:

a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state when a temperature of the coolant is lower than a predetermined temperature, and switches the exhaust heat recovery switching device to the discharge state when the temperature of the coolant is equal to or higher than the predetermined temperature.

6. The exhaust heat recovery system according to claim 4, wherein the heat pump includes a compressor that compresses the refrigerant to which the heat has been transferred in the heat-absorbing heat exchanger,

said exhaust heat recovery system further comprising:

a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state and operates the compressor when the temperature of the coolant is lower than the predetermined temperature.

7. The exhaust heat recovery system according to claim 6, wherein the control device controls the exhaust heat recovery switching device to the discharge state and controls the compressor to a stopped state when the temperature of the coolant is equal to or higher than the predetermined temperature.

8. The exhaust heat recovery system according to claim 1, further comprising:

a heater core that is disposed upstream of the exhaust heat recovery heat exchanger in the circulation passage for the coolant and heats air for air conditioning,

wherein the heat-releasing heat exchanger of the heat pump is disposed downstream of the heater core in the circulation passage for the coolant.

9. An exhaust heat recovery system comprising:

a heat pump including:

a circulation passage for a refrigerant;

a heat-releasing heat exchanger in which the heat is transferred from the refrigerant to an air for air conditioning,

wherein said exhaust heat recovery system further comprises:

a heat pump switching device switchable between an air supply state where the air for air conditioning is supplied to the heat-releasing heat exchanger and a heat pump bypass state where the air for air conditioning is not supplied to the heat-releasing heat exchanger.

10. The exhaust heat recovery system according to claim 9, further comprising:

a heater core that is provided in the circulation passage for the coolant and heats the air for air conditioning; and

a heater core switching device switchable between an air supply state where the air for air conditioning is supplied to the heater core and a heater core bypass state where the air for air conditioning is not supplied to the heater core.

11. The exhaust heat recovery system according to claim 9, wherein the heater core switching device is switched to the heater core bypass state when the heat pump is operated, and the heat pump switching device is switched to the heat pump bypass state when the heat pump is stopped.

12. The exhaust heat recovery system according to claim 9, further comprising:

an exhaust heat recovery switching device switchable between an exhaust heat recovery state where the exhaust heat of the exhaust gas is recovered and a discharge state where the exhaust gas is discharged to an outside; and

a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state and switches the heater core switching device to the heater core bypass state when a temperature of the coolant is lower than a predetermined temperature.

13. The exhaust heat recovery system according to claim 9, wherein the heat pump includes a compressor that compresses the refrigerant to which the heat has been transferred in the heat-absorbing heat exchanger, said exhaust heat recovery system further comprising:

an exhaust heat recovery switching device switchable between an exhaust heat recovery state where exhaust heat of the exhaust gas is recovered and a discharge state where the exhaust gas is discharged to an outside; and

a control device that switches the exhaust heat recovery switching device to the exhaust heat recovery state and operates the compressor if a request for heating the air for air conditioning is made when a temperature of the coolant is lower than a predetermined temperature.

14. The exhaust heat recovery system according to claim 13, wherein the control device switches the heater core switching device to the heater core bypass state if the request for heating is made when the temperature of the coolant is lower than the predetermined temperature.

15. The exhaust heat recovery system according to claim 13, wherein the control device controls the exhaust heat recovery switching device to the discharge state and controls the compressor to a stopped state when the temperature of the coolant is equal to or higher than the predetermined temperature.

16. The exhaust heat recovery system according to claim 15, wherein the control device controls the heat pump switching device to the heat pump bypass state when the temperature of the coolant is equal to or higher than the predetermined temperature.