JP2014190170A - Waste heat regeneration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive cooling of EGR gas while efficiently collecting waste heat from an engine.SOLUTION: A waste heat regeneration system 100 includes a Rankine cycle circuit 10 which is formed by sequentially connecting a pump 2 for pressure-feeding a refrigerant, an EGR boiler 4, a compressed air boiler 3 and an exhaust gas boiler 5 for heating the refrigerant, an expander 6 for collecting mechanical energy by expanding the heated refrigerant, and a condenser 8 for cooling and condensing the refrigerant after expansion. The EGR boiler 4 and the compressed air boiler 3 are connected in series so that the compressed air boiler 3 is disposed in the upstream side, and the exhaust gas boiler 5 is connected in parallel to the EGR boiler 4 and the compressed air boiler 3.

Description

  The present invention relates to a waste heat regeneration system, and more particularly to a waste heat regeneration system that uses waste heat of an internal combustion engine of a vehicle using a Rankine cycle.

  A waste heat regeneration system for a vehicle using a Rankine cycle circuit that recovers mechanical energy (power) from waste heat of an internal combustion engine has been developed. A general Rankine cycle circuit includes a pump that pumps refrigerant, a heat exchanger that heats the refrigerant by exchanging heat with engine waste heat, and an expander that expands the heated refrigerant to recover mechanical energy. And a condenser that cools and condenses the expanded refrigerant, and these are sequentially connected to form a closed circuit.

  Here, in FIG. 6 of Patent Document 1, as a heat exchanger, an EGR cooler in which heat is exchanged between the refrigerant and the EGR gas that is recirculated exhaust, and an exhaust gas boiler in which heat is exchanged between the refrigerant and the exhaust gas are arranged in parallel. A provided Rankine cycle circuit is disclosed. Since the EGR gas and the exhaust gas are high in temperature, the refrigerant can receive a larger amount of heat by circulating the refrigerant through each of the EGR boiler and the exhaust gas boiler arranged in parallel as in the Rankine cycle circuit of Patent Document 1. Therefore, the waste heat recovery efficiency of the Rankine cycle circuit as a whole is improved.

JP 2009-236014 A

  However, the refrigerant cooled and condensed by the condenser and pumped by the pump has a low temperature, and when such a low-temperature refrigerant flows into the EGR boiler, the EGR gas may be overcooled and condensed water may be generated in the EGR circuit. there were. If such condensed water is generated, the condensed water may enter the combustion chamber and hinder combustion of the internal combustion engine.

  In order to solve such problems, an object of the present invention is to provide a waste heat regeneration system that can efficiently recover waste heat from an internal combustion engine and prevent excessive cooling of EGR gas.

  In order to solve the above problems, a waste heat regeneration system according to the present invention uses waste heat of an internal combustion engine, and includes a pump that pumps a refrigerant, a refrigerant heating means that heats the refrigerant, and a refrigerant heating means. An expander that expands the heated refrigerant and recovers mechanical energy and a condenser that cools and condenses the expanded refrigerant are sequentially connected, and the refrigerant heating means is an exhaust gas recirculated to the internal combustion engine. An EGR boiler that exchanges heat with the refrigerant using EGR gas as a heat source, and a compressed air boiler that exchanges heat with the refrigerant using compressed air supplied to the internal combustion engine by the supercharger as a heat source An exhaust gas boiler that exchanges heat with the refrigerant using the exhaust gas of the internal combustion engine as a heat source, and the EGR boiler and the compressed air boiler are connected in series so that the compressed air boiler is on the upstream side , Exhaust gas boiler is connected in parallel with the EGR boiler and compressed air boiler.

The waste heat regeneration system according to the present invention may include a flow rate adjusting unit capable of adjusting a distribution ratio between a flow rate of the refrigerant flowing through the EGR boiler and the compressed air boiler and a flow rate of the refrigerant flowing through the exhaust gas boiler. .
Further, the flow rate adjusting means can make the flow rate of the refrigerant flowing through the exhaust gas boiler zero.

  According to the waste heat regeneration system of the present invention, excessive cooling of the EGR gas can be prevented while efficiently recovering mechanical energy.

It is a figure which shows the structure of the waste-heat regeneration system which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the waste-heat regeneration system which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of the waste-heat regeneration system which concerns on Embodiment 3 of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
A configuration of a waste heat regeneration system 100 according to Embodiment 1 of the present invention is shown in FIG.
The waste heat regeneration system 100 uses waste heat of the engine 12 as an internal combustion engine, and includes a pump 2, a compressed air boiler 3, an EGR boiler 4, an exhaust gas boiler 5, an expander 6, and a condenser. And a Rankine cycle circuit 10. Here, the Rankine cycle circuit 10 includes a main circuit 10a and a sub circuit 10b. The main circuit 10a is a closed circuit configured by sequentially connecting the pump 2, the compressed air boiler 3, the EGR boiler 4, the expander 6, and the condenser 8. The slave circuit 10b is a closed circuit configured by sequentially connecting the pump 2, the exhaust gas boiler 5, the expander 6, and the condenser 8. That is, the compressed air boiler 3 and the EGR boiler 4 are connected in series to the main circuit 10a downstream of the pump 2 and upstream of the expander 6. The compressed air boiler 3 is provided downstream of the pump 2 and upstream of the EGR boiler 4. On the other hand, the slave circuit 10b branches from the main circuit 10a at a first branch point 13a downstream of the pump 2 and upstream of the compressed air boiler 3, and is downstream of the EGR boiler 4 and upstream of the expander 6. Join at 13b. Therefore, the main circuit 10a and the sub circuit 10b have a common configuration downstream of the second branch point 13b and upstream of the first branch point 13a. Moreover, the compressed air boiler 3 and the EGR boiler 4 and the exhaust gas boiler 5 are connected in parallel by the configuration of the Rankine cycle circuit 10. Further, a flow rate adjusting valve 15 is provided on the slave circuit 10b downstream of the first branch point 13a and upstream of the exhaust gas boiler 5.
The compressed air boiler 3 exchanges heat with the refrigerant using compressed air supplied to the engine 12 by a supercharger 14 to be described later, that is, compressed intake air as a heat source. The EGR boiler 4 exchanges heat with the refrigerant using EGR gas, which is part of the exhaust gas recirculated to the engine 12, as a heat source. Further, the exhaust gas boiler 5 performs heat exchange with the refrigerant using the exhaust gas as a heat source. And these compressed air boiler 3, EGR boiler 4, and exhaust gas boiler 5 comprise a refrigerant heating means.
The flow rate adjusting valve 15 constitutes a flow rate adjusting means.

The flow of the refrigerant in the Rankine cycle circuit 10 will be described.
The refrigerant in the Rankine cycle circuit 10 in the waste heat regeneration system 100 is pumped by the pump 2. When the flow rate adjustment valve 15 on the slave circuit 10b is in a fully open state, the refrigerant pumped by the pump 2 partially flows into the compressed air boiler 3 according to the main circuit 10a when passing through the first branch point 13a. The rest flows into the exhaust gas boiler 5 according to the subcircuit 10b. The refrigerant flowing into the compressed air boiler 3 on the main circuit 10a is heated and vaporized by the compressed air boiler 3 and the EGR boiler 4 arranged in series. Moreover, the refrigerant | coolant which flows in into the exhaust gas boiler 5 on the subcircuit 10b is heated by the exhaust gas boiler 5, and is vaporized. Then, the refrigerant vaporized in the compressed air boiler 3 and the EGR boiler 4 on the main circuit 10a and the refrigerant vaporized in the exhaust gas boiler 5 on the sub circuit 10b merge at the second branch point 13b and flow into the expander 6. . The expander 6 expands the refrigerant to generate mechanical energy. Here, the mechanical energy generated in the expander 6 assists the rotation of the engine 12. The refrigerant that has passed through the expander 6 flows into the condenser 8 and is cooled and condensed to be liquefied. The liquefied refrigerant flows into the pump 2 and is pumped again.

  The flow rate adjusting valve 15 is in a fully open state during normal travel, and at this time, the ratio of the flow rate of the refrigerant flowing into the compressed air boiler 3 and the flow rate of the refrigerant flowing into the exhaust gas boiler 5 is 1: 1. . The flow rate adjustment valve 15 is controlled to be opened and closed by an ECU (not shown). Here, when the flow rate adjustment valve 15 is gradually brought close to the closed state, the flow rate of the refrigerant flowing into the exhaust gas boiler 5 decreases accordingly, and the flow rate of the refrigerant flowing into the compressed air boiler 3 increases. . When the flow rate adjustment valve 15 is completely closed, the flow rate of the refrigerant flowing into the exhaust gas boiler 5 becomes 0, and all the refrigerant passing through the first branch point 13a flows into the compressed air boiler 3. That is, the flow rate adjusting valve 15 adjusts the distribution ratio between the flow rate of the refrigerant flowing through the compressed air boiler 3 and the EGR boiler 4 and the flow rate of the refrigerant flowing through the exhaust gas boiler 5.

  The engine 12 is connected to the intake system 16 and the exhaust system 11. In addition, the intake system 16 and the exhaust system 11 are each connected to a supercharger 14. Further, an EGR passage 18 is connected to the intake system 16 and the exhaust system 11, and one end of the EGR passage 18 is connected to the intake system 16 and the other end is connected to the exhaust system 11. The compressed air boiler 3 is connected to the intake system 16, the exhaust gas boiler 5 is connected to the exhaust system 11, and the EGR boiler 4 is connected to the EGR passage 18.

  Air sucked from the intake system 16 is compressed by the supercharger 14. Compressed air, which is pressurized air that has been pressurized at that time, is cooled by exchanging heat with the refrigerant in the main circuit 10 a of the Rankine cycle circuit 10 in the compressed air boiler 3, and then flows into the engine 12. The air burns in the engine 12 and then flows through the exhaust system 11 as exhaust gas. The exhaust gas flowing through the exhaust system 11 passes through the supercharger 14 and drives the supercharger 14. Then, after the exhaust gas exchanges heat with the refrigerant in the slave circuit 10b of the Rankine cycle circuit 10 in the exhaust gas boiler 5, the exhaust gas passes through a muffler (not shown) and is discharged outside the vehicle. A part of the exhaust gas flowing out from the engine 12 flows into the EGR passage 18 as EGR gas. The EGR gas flowing through the EGR passage 18 is cooled by exchanging heat with the refrigerant in the main circuit 10a of the Rankine cycle circuit 10 in the EGR boiler 4. The cooled EGR gas joins the intake system 16 from the EGR passage 18 and is recirculated to the engine 12 again.

As described above, in the waste heat regeneration system 100 according to the first embodiment, the compressed air boiler 3 is provided downstream of the pump 2 and upstream of the EGR boiler 4, so that the refrigerant before flowing into the EGR boiler 4 is compressed air. Heated by the boiler 3. Therefore, excessive cooling of the EGR gas due to the low-temperature refrigerant pumped by the pump 2 directly flowing into the EGR boiler 4 is prevented. As a result, the generation of condensed water in the EGR passage 18 is also prevented.
In addition, since the exhaust gas boiler 5 is provided in parallel to the EGR boiler 4, the Rankine cycle circuit 10 can recover both waste heat from the EGR gas and waste heat from the exhaust gas. Heat recovery efficiency is improved.
Further, the exhaust gas boiler 5 of the sub circuit 10b is provided in parallel with the compressed air boiler 3 of the main circuit 10a. Therefore, since the refrigerant flowing into the exhaust gas boiler 5 does not flow through the compressed air boiler 3 but is pumped by the pump 2 and then directly flows into the exhaust gas boiler 5 at a low temperature, a large amount of waste heat is recovered from the exhaust gas accordingly. be able to.
Furthermore, in the compressed air boiler 3, since the compressed air from the supercharger 14 is cooled by the refrigerant of the Rankine cycle circuit 10, it is not necessary to separately provide an air-cooled intercooler for cooling the compressed air.

  Further, by providing the flow rate adjusting valve 15 downstream of the first branch point 13a and upstream of the exhaust gas boiler 5 on the slave circuit 10b, the compressed air is used in response to an increase in demand for cooling the intake air, such as during acceleration. The cooling function of the boiler 3 can be improved immediately. That is, when the amount of intake air sucked into the engine 12 increases and the necessity of cooling the intake air becomes high, the refrigerant flowing into the exhaust gas boiler 5 on the subcircuit 10b by restricting the flow rate adjusting valve 15 The flow rate is limited. And the flow volume of the refrigerant | coolant which flows into the compressed air boiler 3 on the main circuit 10a increases correspondingly, and the compressed air boiler 3 can cool the intake air which became high temperature compressed by the supercharger 14 more efficiently. Here, if the flow control valve 15 is further completely closed, the refrigerant flowing through the exhaust gas boiler 5 of the subcircuit 10b becomes 0, and all the refrigerant flows into the compressed air boiler 3 to cool the intake air. Can be used.

  Even when the flow rate adjustment valve 15 is completely closed, the EGR boiler 4 is arranged in series with the compressed air boiler 3 on the main circuit 10a, so that refrigerant flows through the EGR boiler 4. Then, the EGR gas in the EGR passage 18 can be continuously cooled.

Embodiment 2. FIG.
FIG. 2 shows the configuration of a waste heat regeneration system 200 according to Embodiment 2 of the present invention. In the following description, the same reference numerals as those in FIG. 1 are the same or similar components, and thus detailed description thereof is omitted.
The waste heat regeneration system 200 according to the second embodiment is the waste heat regeneration system 100 according to the first embodiment, and further includes a Rankine cycle circuit 20 having an internal heat exchanger 7. The Rankine cycle circuit 20 includes a main circuit 20a and a slave circuit 20b, similarly to the Rankine cycle circuit 10 of the first embodiment. That is, the secondary circuit 20b branches from the main circuit 20a at the first branch point 23a downstream of the pump 2 and upstream of the compressed air boiler 3, and the second branch point downstream of the EGR boiler 4 and upstream of the expander 6. Merge at 23b.

  In the Rankine cycle circuit 20, the internal heat exchanger 7 is connected downstream of the flow rate adjustment valve 15 on the slave circuit 20 b and upstream of the exhaust gas boiler 5, and is also connected downstream of the expander 6 and upstream of the condenser 8. The That is, the low-temperature refrigerant that is pumped to the pump 2 and passes through the first branch point 23a and flows through the subcircuit 20b, and the high-temperature refrigerant that has expanded in the expander 6 exchange heat in the internal heat exchanger 7. Configured to do.

  As described above, the waste heat regeneration system 200 according to the second embodiment has the internal heat exchanger 7 so that the high-temperature refrigerant flowing out of the expander 6 is cooled in the internal heat exchanger 7 before flowing into the condenser 8. Is done. Accordingly, since the temperature of the refrigerant flowing into the condenser 8 is lower than that of the conventional one, the refrigerant condensing pressure is lowered correspondingly, and as a result, the load on the condenser 8 is reduced and the efficiency of cooling condensation is improved. Further, by arranging the compressed air boiler 3 and the internal heat exchanger 7 having a relatively low temperature of the heat source in parallel rather than in series, heat recovery can be efficiently performed in both.

Embodiment 3 FIG.
FIG. 3 shows the configuration of a waste heat regeneration system 300 according to Embodiment 3 of the present invention.
In the following description, the same reference numerals as those in FIG. 1 or 2 are the same or similar components, and detailed description thereof will be omitted.
The waste heat regeneration system 300 includes the Rankine cycle circuit 30 including the main circuit 30a and the sub circuit 30b, similarly to the waste heat regeneration systems 100 and 200 of the first or second embodiment. That is, the secondary circuit 30b branches from the main circuit 30a at the first branch point 33a downstream of the pump 2 and upstream of the compressed air boiler 3, and the second branch point downstream of the EGR boiler 4 and upstream of the expander 6. Merge at 33b. Furthermore, a third branch point 33c is set downstream of the compressed air boiler 3 and upstream of the EGR boiler 4 on the main circuit 30a of the Rankine cycle circuit 30, and downstream of the internal heat exchanger 7 of the slave circuit 30b and exhaust gas boiler. A fourth branch point 33 d is set upstream of 5. The Rankine cycle circuit 30 is provided with a bypass passage 30c having one end connected to the third branch point 33c and the other end connected to the fourth branch point 33d. A second flow rate adjustment valve 37 is provided downstream of the third branch point 33 c on the main circuit 30 a and upstream of the EGR boiler 4.

  When the second flow rate adjustment valve 37 is fully opened, the refrigerant flowing through the main circuit 30 a flows through the compressed air boiler 3 and then passes through the second flow rate adjustment valve 37 and flows into the EGR boiler 4. The second flow rate adjusting valve 37 is controlled to be opened and closed by an ECU (not shown). Here, when the second flow rate adjusting valve 37 is throttled to approach the closed state, the flow rate of the refrigerant flowing into the EGR boiler 4 gradually decreases, and the remaining refrigerant passes through the third branch point 33c accordingly. It distribute | circulates to the bypass flow path 30c. And the refrigerant | coolant which distribute | circulates the bypass flow path 30c merges with the refrigerant | coolant of the subcircuit 30b in the 4th branch point 33d, and flows in into the exhaust gas boiler 5 after that. Further, when the second flow rate adjusting valve 37 is completely closed, the flow rate of the refrigerant flowing into the EGR boiler 4 becomes 0, and the total amount of the refrigerant on the main circuit 30a flowing out from the compressed air boiler 3 on the main circuit 30a is reduced. The refrigerant flows through the bypass flow path 30c and merges with the refrigerant of the slave circuit 30b.

  As described above, in the waste heat regeneration system 300 according to this embodiment, excessive cooling of the EGR gas is further performed by adjusting the flow rate of the refrigerant flowing into the EGR boiler 4 by the bypass flow path 30c and the second flow rate adjustment valve 37. Can be prevented. That is, when the flow rate adjustment valve 15 is closed and a large amount of refrigerant flows into the compressed air boiler 3 of the main circuit 30a, there is a possibility that the refrigerant is still at a low temperature even when heated in the compressed air boiler 3. In such a case, if the entire amount of the refrigerant that has flowed out of the compressed air boiler 3 flows into the EGR boiler 4, the EGR gas is overcooled and condensed water may be generated in the EGR passage 18. Therefore, the second flow rate adjusting valve 37 is throttled to reduce or reduce the flow rate of the refrigerant flowing through the EGR boiler 4, thereby preventing excessive cooling of the EGR gas and generation of condensed water in the EGR passage 18.

In the first to third embodiments, the flow rate adjusting valve 15 is used as the flow rate adjusting means.
Also in the third embodiment, the means for adjusting the flow rate of the refrigerant flowing through the EGR boiler 4 is not limited to the second flow rate adjustment valve 37, and a three-way valve may be provided at the third branch point 33c.

  100, 200, 300 Waste heat regeneration system, 2 pump, 3 compressed air boiler (refrigerant heating means), 4 EGR boiler (refrigerant heating means), 5 exhaust gas boiler (refrigerant heating means), 6 expander, 8 condenser, 10, 20, 30 Rankine cycle circuit, 12 engine, 14 supercharger, 15 flow rate adjusting valve (flow rate adjusting means).

Claims (3)

A waste heat regeneration system that uses waste heat of an internal combustion engine,
A pump that pumps the refrigerant; a refrigerant heating means that heats the refrigerant; an expander that expands the refrigerant heated by the refrigerant heating means to recover mechanical energy; and a condenser that cools and condenses the refrigerant after expansion. It is equipped with a Rankine cycle circuit that is configured to be sequentially connected,
The refrigerant heating means includes
An EGR boiler that exchanges heat with the refrigerant using EGR gas that is part of exhaust gas recirculated to the internal combustion engine as a heat source;
A compressed air boiler for exchanging heat with the refrigerant using compressed air supplied to the internal combustion engine by a supercharger as a heat source;
An exhaust gas boiler for exchanging heat with the refrigerant using the exhaust gas of the internal combustion engine as a heat source;
Have
The EGR boiler and the compressed air boiler are connected in series so that the compressed air boiler is on the upstream side,
The exhaust gas boiler is a waste heat regeneration system connected in parallel with the EGR boiler and the compressed air boiler.   The waste heat according to claim 1, further comprising a flow rate adjusting unit capable of adjusting a distribution ratio between a flow rate of the refrigerant flowing through the EGR boiler and the compressed air boiler and a flow rate of the refrigerant flowing through the exhaust gas boiler. Regenerative system.   The waste heat regeneration system according to claim 2, wherein the flow rate adjusting unit can reduce the flow rate of the refrigerant to be circulated through the exhaust gas boiler.

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