JP2013113192A - Waste heat regeneration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste heat regeneration system 100 capable of promptly stopping a Rankine cycle circuit 30 after stopping an engine 10 while preventing a temperature rise of a high-temperature boiler 34 and working fluid and the runaway of rotating speed of an expander 36.SOLUTION: The waste heat regeneration system 100 includes: the Rankine cycle circuit 30 which includes a pump 32, the high-temperature boiler 34, the expander 36 and a capacitor 38; an expander bypass flow passage 31 which bypasses the expander 36 and has an on-off valve 33; and a control means 60 which circulates, when the operation of the engine 10 is stopped, refrigerant to the expander bypass flow passage 31 with the on-off valve 33 being opened, and also force-feeds refrigerant to the pump 32 at a flow rate larger than in an idling state.

Description

  The present invention relates to a waste heat regeneration system, and more particularly to a vehicle waste heat regeneration system using a Rankine cycle.

  Waste heat regeneration systems for vehicles have been developed that use Rankine cycle to recover mechanical energy (power) from engine waste heat. A general Rankine cycle circuit includes a pump that pumps a working fluid, a boiler that heats the working fluid by exchanging heat with engine waste heat, and an expander that expands the heated working fluid to recover mechanical energy. And a condenser for cooling and condensing the expanded working fluid, which are sequentially connected to form a closed circuit.

  Normally, in a waste heat regeneration system mounted on a vehicle, when the engine is stopped, the operation of the Rankine cycle is stopped, and mechanical energy is not recovered by the expander. However, if the expander is freely rotated (free-run) without load by the high-temperature / high-pressure steam remaining in the boiler, the rotation speed of the expander may rapidly increase and damage the expander. Further, if the Rankine cycle operation is stopped immediately after the engine is stopped, the working fluid does not circulate through the Rankine cycle circuit, and therefore stays in the boiler. Therefore, there is a possibility that the working fluid and the oil contained in the working fluid are overheated due to the residual heat remaining in the boiler and thermally decomposed or carbonized.

  In the Rankine cycle apparatus of Patent Document 1, the operation of the Rankine cycle apparatus is continued even after the engine is stopped, and a load is continuously applied to the expander in order to recover mechanical energy. Can be prevented. That is, by continuously supplying water as a working fluid to the boiler, the generation of steam is continued and the steam continues to flow into the expander. The amount of water supply at this time is decreased according to the decrease in the internal energy of the boiler. Then, when the steam temperature and the steam pressure of the working fluid become such a temperature and pressure that the expander does not generate an output, the operation of the Rankine cycle device is stopped.

  In the exhaust heat regeneration system of Patent Document 2, a condenser is provided vertically above the boiler, and a bypass flow path is opened when the engine is stopped, and a heat pump cycle is created between the condenser and the boiler. That is, a working circuit liquefied by the condenser moves to the boiler via the bypass flow path due to gravity, and a closed circuit is formed in which the working fluid vaporized by the boiler returns to the condenser again via the bypass flow path. Therefore, even after the engine is stopped, the working fluid continues to circulate in the boiler by the heat pump cycle, and the working fluid in the boiler is prevented from being heated at a high temperature, so that the power supply to the pump can be stopped early.

JP 2006-250075 A JP 2011-12625 A

  However, in the Rankine cycle device of Patent Document 1, runaway is prevented by continuing to apply a load for recovering mechanical energy to the expander, but the temperature and pressure of the working fluid does not generate an output from the expander. It is necessary to continue the operation until the value reaches a certain level. Further, since the flow rate of the working fluid is gradually reduced according to the internal energy of the boiler, it takes more time to lower the temperature of the working fluid. Therefore, the Rankine cycle device cannot be stopped early. In addition, the user feels uncomfortable with the Rankine cycle device operating for a long time after the engine is stopped.

  On the other hand, in Patent Document 2, although the operation of the Rankine cycle circuit can be stopped immediately after the engine is stopped, the boiler when the engine is stopped has a high temperature and a large heat capacity. It is insufficient to prevent the oil from becoming hot.

  In order to solve such a problem, the present invention can quickly stop the operation of the Rankine cycle circuit while preventing the temperature rise of the boiler and the working fluid and the runaway of the expander after the engine is stopped. The purpose is to provide a waste heat regeneration system.

  In order to solve the above problems, a waste heat regeneration system according to the present invention uses waste heat of a vehicle engine, and includes a pump that pumps a working fluid, a boiler that heats the working fluid with waste heat, An expander that expands the working fluid heated by the boiler and recovers mechanical energy, and a Rankine cycle circuit that is configured by sequentially connecting a condenser that cools and condenses the expanded working fluid; Working fluid detecting means for detecting the state of the working fluid at the inlet of the expander, a first branch point provided on the downstream side of the working fluid detecting means and on the upstream side of the expander, and the expander An expander bypass flow path connecting a second branch point provided on the downstream side of the condenser and the upstream side of the condenser, and an expansion for controlling whether or not the working fluid flows into the expander bypass flow path Comprising a machine bypass flow path control means, at the time of deactivation of the engine, and control means for circulating the working fluid in the expander bypass flow passage to the expander bypass flow path control means. Thereby, the expander can be bypassed and the working fluid having a larger flow rate than that in the idling state can be pumped.

  The waste heat regeneration system according to the present invention includes a working fluid detection means provided downstream of the boiler and upstream of the condenser, the working fluid detection means detects the state of the working fluid at the outlet of the boiler, and the control means includes The pump can also stop the pumping of the working fluid based on the state of the working fluid.

  The state of the working fluid detected by the working fluid detection means may be temperature.

  In the waste heat regeneration system according to the present invention, the boiler is further provided between a high-temperature boiler provided downstream of the pump and the pump and the high-temperature boiler, and includes a heat medium and working fluid having a temperature lower than that of the high-temperature boiler. A first branch point provided downstream of the pump and upstream of the low-temperature boiler, and a second branch point provided downstream of the low-temperature boiler and upstream of the high-temperature boiler. And a low temperature boiler bypass flow path control means for controlling whether or not the working fluid flows into the low temperature boiler bypass flow path. The working fluid can also be circulated through the low temperature boiler bypass flow path through the low temperature boiler bypass flow path control means.

  The capacitor may include a capacitor fan, and the control unit may operate the capacitor fan when the engine is stopped.

  According to the waste heat regeneration system of the present invention, after the engine is stopped, the Rankine cycle circuit can be stopped at an early stage while preventing the temperature of the boiler and the working fluid from rising and the rotational speed of the expander from running away.

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 flowchart which shows control of the Rankine cycle circuit of FIG. It is a graph which shows the change of the refrigerant | coolant flow rate in the Rankine cycle circuit of FIG. It is a figure which shows the structure of the waste-heat regeneration system which concerns on Embodiment 2 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 includes a pump 32, a high-temperature boiler 34 as a boiler, an expander 36, and a condenser 38, which are sequentially connected to form a Rankine cycle circuit 30 that is a closed circuit. The pump 32 is connected to the motor 35. A temperature sensor 37 is provided downstream of the high temperature boiler 34 and upstream of the expander 36. One end of the expander bypass channel 31 is connected to the first branch point 31a downstream of the temperature sensor 37 and upstream of the expander 36, and the other end of the expander bypass channel 31 is connected to the expander 36. Is connected to the second branch point 31b on the downstream side of the capacitor 38 and on the upstream side of the capacitor 38. An expander side opening / closing valve 33 is provided in the middle of the expander bypass passage 31.

  The pump 32 is driven by a motor 35 and pumps a refrigerant as a working fluid in the Rankine cycle circuit 30 in the waste heat regeneration system 100. The motor 35 is electrically connected to the ECU 60, and the flow rate of the refrigerant pumped by the pump 32 can be appropriately increased or decreased by changing the rotation speed in accordance with an instruction from the ECU 60. Exhaust gas from the engine 10 is supplied to the high-temperature boiler 34, and the refrigerant is heated by exchanging heat between the exhaust gas and the refrigerant. The expander 36 expands the refrigerant heated and vaporized in the high-temperature boiler 34 to generate mechanical energy. The condenser 38 cools and condenses the vaporized refrigerant by exchanging heat with the outside air.

  The ECU 60 is electrically connected to the engine operating state detector 61, the expander side opening / closing valve 33, the motor 35, and the temperature sensor 37. The ECU 60 controls the opening and closing of the expander side opening / closing valve 33 and the rotation of the motor 35 based on information acquired from the engine operating state detector 61 and the temperature sensor 37. The engine operating state detector 61 is attached to the engine 10 and detects the operating state of the engine (whether the engine 10 is operating). Here, the engine operating state detector 61 is a rotation sensor that detects the rotational speed of the engine 10.

  The engine 10 has a drive shaft 42, and the expander 36 has a drive shaft 43. The belt 41 connects the drive shaft 42 of the engine 10 and the drive shaft 43 of the expander 36, and transmits mechanical energy (expander output) generated by the expander 36 to the drive shaft 42.

  An exhaust pipe 11 is connected to the engine 10, and exhaust gas generated from the engine 10 is exhausted outside the vehicle through the exhaust pipe 11. A high-temperature boiler 34 is provided in the middle of the exhaust pipe 11. In the high-temperature boiler 34, heat exchange is performed between the exhaust gas flowing through the exhaust pipe 11 and the refrigerant flowing through the Rankine cycle circuit 30. That is, the refrigerant in the Rankine cycle circuit 30 is heated by the waste heat of the exhaust gas.

The operation of the waste heat regeneration system 100 according to the first embodiment will be described with reference to FIGS.
FIG. 2 shows a flowchart of ECU 60 according to Embodiment 1 of the present invention.
First, in step S <b> 1, the ECU 60 determines whether or not the engine 10 is operating based on information from the engine operating state detector 61. Note that “when the engine is operating” means when the engine speed is equal to or higher than the engine speed in the idle state.

If the engine 10 is operating, the process proceeds to step S6 to determine whether or not the vehicle is in an idling state. If the vehicle is in an idling state, the expander side opening / closing valve 33 is opened (step S7). That is, in the idling state, since it is not necessary to generate the expander output, the expander 36 is bypassed and the refrigerant is circulated through the expander bypass flow path 31. At this time, since the differential pressure between the refrigerant pressure on the upstream side of the expander 36 and the refrigerant pressure on the downstream side becomes 0, the expander output by the expander 36 is not generated. Next, in step S8, the refrigerant flow rate (Q ₂ ) pumped by the pump 32 is adjusted by the ECU 60 so that the refrigerant is not overheated in the high-temperature boiler 34.

Further, during normal travel, the expander side opening / closing valve 33 is closed (step S9). Next, in step S10, the refrigerant flow rate (Q ₁ ) pumped by the pump 32 is adjusted so that the necessary expander output is generated in the expander 36. The expander output is transmitted to the drive shaft 42 of the engine 10 via the drive shaft 43 and the belt 41 of the expander 36.

  On the other hand, when the engine 10 is stopped, that is, when the operation of the engine 10 is stopped, the expander side on-off valve 33 on the expander bypass flow path 31 is opened and the expander bypass flow path 31 is opened as in step S7. A refrigerant is introduced (step S2). At this time, since the differential pressure between the refrigerant pressure on the upstream side of the expander 36 and the refrigerant pressure on the downstream side becomes 0, the expander output by the expander 36 is not generated.

Then, ECU 60 in step S3, by increasing the rotational speed of the motor 35, increases the flow rate of the refrigerant pump 32 for pumping, to maintain the large flow rate Q ₃ from the refrigerant flow rate Q ₂ at the time of idling (see FIG. 3) . The high temperature boiler 34 can be cooled more quickly by increasing the refrigerant flow rate.

  Next, in step S <b> 4, the ECU 60 determines the refrigerant temperature T at the outlet of the high temperature boiler 34. Here, when the refrigerant temperature T is equal to or lower than the predetermined temperature t, the ECU 60 stops the operation of the pump 32. The predetermined temperature t is an upper limit value of the temperature at which it is determined that the operation of the Rankine cycle circuit 30 can be stopped without increasing the temperature of the refrigerant staying in the high temperature boiler 34.

Next, a change in the refrigerant flow rate in the waste heat regeneration system 100 according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 3 is a graph showing changes in the flow rate of the refrigerant in the Rankine cycle circuit according to the first embodiment of the present invention.
In A _ON when operated at and for the expander output needs of the engine 10, the pump 32 pumps the refrigerant normal control flow Q _1. Here, the normal control flow Q _1, a state in which operating time and the expander output refrigerant expander 36 in A _ON inhales aim when necessary state of the engine 10, i.e. the required expander output is obtained ( This is the refrigerant flow rate necessary for maintaining the temperature. Further, when provided and the expander output engine 10 is operated is not required A _{i (idling),} the pump 32 pumps the refrigerant idling flow Q _2. Idling flow Q ₂ is a refrigerant flow rate required to ensure that a high temperature boiler 34 and the refrigerant is not overheated in the operation time and the expander output required when A _i of the engine 10. Idling flow Q ₂ is smaller than the normal control flow Q _1. The idling time A _i is when the vehicle is idling when waiting for a signal or the like. Then, in the stop _{A OFF} after the engine 10, the pump 32 pumps the coolant of the engine after stopping the flow _{Q 3.} The engine 10 stops operation of the engine 10 through the idling A _i, but the refrigerant flow rate is increased at the same time as the stop of the engine 10. That is, the engine is stopped after the flow rate Q ₃ are larger than the idling flow rate Q _2.

  As described above, in the waste heat regeneration system 100 according to the first embodiment, the refrigerant is circulated through the expander bypass flow path 31 after the engine 10 is stopped, thereby circulating the refrigerant in the Rankine cycle circuit 30 for a while. You can stay without stopping. Therefore, it is possible to prevent the refrigerant and the oil in the refrigerant from becoming hot due to the residual heat of the high-temperature boiler 34. Moreover, since the differential pressure before and after the expander 36 becomes 0 by opening the expander bypass flow path 31, the output of the expander 36 is not generated, and the rotation speed of the expander 36 is prevented from running out of control. You can also. Furthermore, after the engine 10 is stopped, the refrigerant flow rate is increased, so that the high-temperature boiler 34 can be cooled earlier, and the operation of the Rankine cycle circuit 30 can be stopped earlier.

Embodiment 2. FIG.
FIG. 4 shows the configuration of a waste heat regeneration system 200 according to Embodiment 2 of the present invention.
The waste heat regeneration system 200 according to the second embodiment is the waste heat regeneration system 100 according to the first embodiment, in which a low temperature boiler 74 is added as a boiler, and further, a low temperature boiler bypass passage 71, a low temperature boiler side on-off valve. 73, a cooling water circuit 17 and a condenser fan 39 are added. On the Rankine cycle circuit 30, the low temperature boiler 74 is provided on the downstream side of the pump 32 and on the upstream side of the high temperature boiler 34. The low-temperature boiler 74 can circulate the cooling water for cooling the engine that flows through the cooling water circuit 17 of the engine 10 and the refrigerant to exchange heat with each other, and can heat the refrigerant by the waste heat from the engine 10. The temperature of the cooling water for engine cooling in the low temperature boiler 74 is lower than the temperature of the exhaust gas in the high temperature boiler 34. One end of the low-temperature boiler bypass passage 71 is connected to the first branch point 71a on the downstream side of the pump 32 and the upstream side of the low-temperature boiler 74, and the other end of the low-temperature boiler bypass passage 71 is connected to the low-temperature boiler. 74 is connected to the second branch point 71b on the downstream side of 74 and on the upstream side of the high-temperature boiler 34. A low temperature boiler side on-off valve 73 is provided in the middle of the low temperature boiler bypass flow path 71 and is electrically connected to the ECU 60.
Further, a condenser fan 39 for sending outside air to the condenser 38 is provided adjacent to the condenser 38 on the Rankine cycle circuit 30.
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.

Regarding the operation of the waste heat regeneration system 200, the control of the ECU 60 is substantially the same as the control of the ECU 60 in the first embodiment. However, in the waste heat regeneration system 200, in the control corresponding to step S2, the low temperature boiler side on / off valve 73 is opened together with the expander side on / off valve 33, and the condenser fan 39 is put in an operating state.
Moreover, since the change of the refrigerant | coolant flow rate in the waste heat regeneration system 200 is also the same as that of FIG. 3, the detailed description is abbreviate | omitted.

  According to the waste heat regeneration system 200, the refrigerant flows into the low-temperature boiler bypass passage 71 after the engine 10 is stopped, and the low-temperature boiler 74 prevents the refrigerant from exchanging heat with the cooling water, so that the high-temperature boiler 34 is more efficiently used. Can be cooled. Further, since the temperature of the refrigerant circulating in the Rankine cycle circuit 30 can be kept low by the condenser fan 39, the high-temperature boiler can be cooled earlier.

In Embodiments 1 and 2, the flow rate of the refrigerant may be adjusted based on the refrigerant pressure detected using a pressure sensor instead of the temperature sensor 37. Further, by combining the temperature sensor and the pressure sensor, both the temperature and pressure of the refrigerant can be detected, and the flow rate of the refrigerant can be adjusted based on the detected temperature and pressure.
In the first and second embodiments, the operation of the pump 32 is stopped based on the refrigerant temperature T. However, the operation is not limited to this, and the operation of the pump 32 may be stopped when a certain time has elapsed after the engine 10 is stopped. .
Furthermore, the valves for controlling the inflow of the refrigerant into the expander bypass passage 31 and the low temperature boiler bypass passage 71 are not limited to the on-off valves 33 and 73, and a three-way valve may be provided at the first branch points 31a and 71a. Good.
In the first and second embodiments, when the engine 10 is in the idling state, the expander side on-off valve 33 is opened in step 7 so that the output of the expander 36 is not generated. May be closed to generate the output of the expander 36.
The temperature sensor or pressure sensor as the working fluid detection means may be provided at an appropriate location between the outlet of the high temperature boiler 34 and the inlet of the condenser 38.
Instead of the ECU 60 detecting the rotational speed of the engine 10 by the engine operating state detector 61, the ECU 60 may obtain engine rotational speed information from the engine ECU.

  100,200 Waste heat regeneration system, 10 engine, 30 Rankine cycle circuit, 31 expander bypass flow path, 32 pump, 33 expander side opening / closing valve (expander expander bypass flow control means), 34 high temperature boiler (boiler), 36 Expander, 37 temperature sensor (working fluid detection means), 38 condenser, 39 condenser fan, 60 ECU (control means), 71 low temperature boiler bypass flow path, 73 low temperature boiler side on-off valve (low temperature boiler bypass flow path control means), 74 Low temperature boiler.

Claims (5)

A waste heat regeneration system that uses waste heat from a vehicle engine,
A pump that pumps the working fluid, a boiler that heats the working fluid with the waste heat, an expander that recovers mechanical energy by expanding the working fluid heated by the boiler, and cools the working fluid after expansion A Rankine cycle circuit configured by sequentially connecting condensers to be condensed;
An expander bypass flow connecting a first branch point provided downstream of the boiler and upstream of the expander and a second branch point provided downstream of the expander and upstream of the condenser. Road,
Expander bypass flow path control means for controlling the presence or absence of inflow of the working fluid into the expander bypass flow path;
When the operation of the engine is stopped, the working fluid is caused to flow through the expander bypass flow path to the expander bypass flow path control means, and the working fluid having a larger flow rate than that when the engine is idling is supplied to the pump. A waste heat regeneration system comprising control means for pumping. A working fluid detection means provided on the downstream side of the boiler and the upstream side of the condenser;
The working fluid detection means detects the state of the working fluid at the outlet of the boiler,
The waste heat regeneration system according to claim 1, wherein the control unit causes the pump to stop pumping the working fluid based on a state of the working fluid.   The waste heat regeneration system according to claim 2, wherein the state of the working fluid detected by the working fluid detection means is temperature. The boiler is a high-temperature boiler provided on the downstream side of the pump, and a low temperature that is provided between the pump and the high-temperature boiler, and exchanges heat between a heat medium and a working fluid that are cooler than the high-temperature boiler. Consisting of a boiler,
A low temperature boiler bypass connecting a first branch point provided downstream of the pump and upstream of the low temperature boiler and a second branch point provided downstream of the low temperature boiler and upstream of the high temperature boiler. A flow path;
Comprising low temperature boiler bypass flow path control means for controlling the presence or absence of inflow of the working fluid to the low temperature boiler bypass flow path;
The said low temperature boiler bypass flow path control means makes the said low temperature boiler bypass flow path control means distribute | circulate the said working fluid to the said low temperature boiler bypass flow path at the time of the operation stop of the said engine. Waste heat regeneration system. The capacitor has a capacitor fan;
The waste heat regeneration system according to any one of claims 1 to 4, wherein the control means operates the condenser fan when the operation of the engine is stopped.

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