WO2013002017A1

WO2013002017A1 - Rankine cycle

Info

Publication number: WO2013002017A1
Application number: PCT/JP2012/064991
Authority: WO
Inventors: 榎島　史修; 井口　雅夫; 英文森
Original assignee: 株式会社豊田自動織機
Priority date: 2011-06-30
Filing date: 2012-06-12
Publication date: 2013-01-03
Also published as: EP2728131A1; CN103608548A; JP2013011259A; US20140116051A1; JP5621721B2

Abstract

A Rankine cycle (101) in which a waste-gas boiler (113) that exchanges heat between a refrigerant and an exhaust gas, an expander (114), a condenser (115), and a pump (111) are provided sequentially along a refrigerant circulation path. Said Rankine cycle is also provided with the following: a temperature sensor (131) that measures the temperature of the refrigerant flowing from the waste-gas boiler (113); a pressure sensor (132) that measures the pressure of the refrigerant flowing through the waste-gas boiler (113); a bypass channel (3) and flow control valve (130) that regulate the flow rate of the refrigerant into the waste-gas boiler (113); and an ECU (140) that controls said flow control valve (130) such that the pressure of the refrigerant taken into the expander (114) as a function of the temperature of said refrigerant moves along a target pressure line (TPL) that sets a target pressure such that the density of the refrigerant increases as the temperature thereof increases.

Description

Rankine cycle

The present invention relates to a Rankine cycle.

There has been developed a technology using a Rankine cycle that converts heat emitted from an internal combustion engine of a vehicle into power for a generator or the like.
The Rankine cycle is powered by a heat exchanger that overheats the working fluid by exchanging heat between the heat transfer medium containing heat discharged from the internal combustion engine and the working fluid, and by expanding the working fluid in the superheated steam state. It comprises an expander, a condenser for cooling and liquefying the expanded working fluid, and a pump for pumping the liquefied working fluid to a heat exchanger. Then, the expander rotates the rotating body such as a turbine by expanding the working fluid, thereby converting the energy at the time of expansion of the working fluid into rotational driving force, and the converted rotational driving force is a generator or the like. Transmitted as power.

For example, Patent Document 1 discloses a first heat exchanger that exchanges heat between the refrigerant and the cooling water of the internal combustion engine in the middle of the flow path where the refrigerant pump sends the refrigerant (working fluid) to the expander. There is described a Rankine cycle in which a second heat exchanger for exchanging heat with the exhaust gas (heat medium) is arranged in this order. In the Rankine cycle of Patent Document 1, the refrigerant exchanges heat with the cooling water in the first heat exchanger to become steam, and then exchanges heat with the exhaust gas having a higher temperature in the second heat exchanger to overheat it. It turns into steam and flows into the expander.

JP, 2011-12625, A

In the Rankine cycle of Patent Document 1, the temperature of the exhaust gas greatly fluctuates between about 200 ° C. and 800 ° C. depending on the load of the internal combustion engine and becomes very high temperature, so heat exchange is performed in the second heat exchanger The heat absorption amount of the refrigerant increases as the temperature of the exhaust gas increases and becomes high temperature, and the high temperature refrigerant is sucked into the expander. For this reason, in the Rankine cycle of Patent Document 1, a heat resistant design is required for the expander, the piping of the refrigerant, and the like, and there is a problem that the cost increases.

The present invention has been made to solve such problems. In heat exchange between the refrigerant (working fluid) and the exhaust gas (heat medium), the temperature rise of the refrigerant with respect to the temperature rise of the exhaust gas is suppressed. Intended to provide a Rankine cycle.

In order to solve the above-described problems, the Rankine cycle according to the present invention generates a driving force by expanding a working fluid, a heat exchanger for exchanging heat between the working fluid and a heat medium, in a working fluid circulation path. A fluid expander, a condenser for condensing the working fluid, and a fluid pumping device for transferring the working fluid to the heat exchanger are sequentially provided, and the state of the working fluid after heat exchange with the heat medium in the heat exchanger is In a Rankine cycle that is superheated steam, a temperature detector that detects the temperature of the working fluid flowing out of the heat exchanger, a pressure detector that detects the pressure of the working fluid flowing through the heat exchanger, and operation to the heat exchanger The control device includes a flow control means for controlling the flow rate of the fluid and a control device for controlling the flow control means, and the control device controls the density of the working fluid having flowed out of the heat exchanger as the temperature increases. But Set target pressure to pressure, so that the detected pressure of the pressure detector reaches the target pressure, and controls the flow rate adjusting means.

According to the Rankine cycle of the present invention, in heat exchange between the working fluid and the heat medium, it is possible to suppress the temperature rise of the working fluid with respect to the increase in the heat exchange amount.

It is a schematic diagram which shows the Rankine cycle which concerns on embodiment of this invention, and the structure of the periphery of it. It is a ph diagram which shows the state of the refrigerant | coolant in the Rankine cycle of FIG. It is a figure which shows the modification of the Rankine cycle which concerns on embodiment. It is a figure which shows another modification of the Rankine cycle which concerns on embodiment.

Hereinafter, an embodiment of the present invention will be described based on the attached drawings.
Embodiment First, the configuration of the Rankine cycle 101 according to the embodiment of the present invention and the periphery thereof will be described. In the following embodiment, an example in which a Rankine cycle is used for an internal combustion engine, that is, a vehicle equipped with the engine 10 will be described.
Referring to FIG. 1, a vehicle (not shown) having an engine 10 has a Rankine cycle 101.

The Rankine cycle 101 forms a circulation path that sequentially connects the pump 111, the cooling water boiler 112, the waste gas boiler 113, the expander 114, the condenser 115, the receiver 116, and the subcooler 117 in an annular fashion, and In the embodiment, R134a) is distributed.

The pump 111 is operated to pump fluid, and in this embodiment, it is assumed to pump liquid. The pump 111 shares its drive shaft 119 with the expander 114. Further, a pulley 119 b is connected to the drive shaft 119 via an electromagnetic clutch 119 a. The pulley 119 b is connected by a drive belt 10 c to an engine pulley 10 b connected to an engine drive shaft 10 a extending from the engine 10. The electromagnetic clutch 119a can connect or disconnect the drive shaft 119 and the pulley 119b, and is electrically connected to the ECU 140, which is a control device of the vehicle, to control its connection / disconnection operation. For this reason, the rotational speed of the pump 111 depends on the rotational speed of the engine 10 or the expander 114.
Here, the pump 111 constitutes a fluid pumping device.

Further, the discharge port on the downstream side of the pump 111 is in communication with the refrigerant inlet of the cooling water boiler 112 via the

flow path portions

1a and 1b. Inside the cooling water boiler 112, the cooling water for cooling the engine and the refrigerant flowing through the cooling water circuit 20 of the engine 10 can flow and exchange heat with each other, whereby the refrigerant can be heated.
In the cooling water circuit 20, the radiator 22 is provided in the middle of the water circulation flow passage 20a which is a circulation flow passage extending from the engine 10 and connected to the water pump 21 integral with the engine 10, and branches in the middle of the water circulation flow passage 20a. Then, the cooling water boiler 112 is provided in the middle of the branched water flow passage 20b which joins the water circulation flow passage 20a again. The radiator 22 cools the cooling water by heat exchange between the cooling water flowing inside and the ambient air.

The refrigerant outlet of the cooling water boiler 112 is in communication with the refrigerant inlet of the waste gas boiler 113 via the flow passage portion 1c. Inside the waste gas boiler 113, the refrigerant flowing out of the cooling water boiler 112 and the exhaust gas of the exhaust system 30 of the engine 10 flow and exchange heat with each other, whereby the refrigerant can be heated. The waste gas boiler 113 is provided in the middle of the exhaust flow passage 30a that communicates the engine 10 in the exhaust system 30 with the muffler 30b.
Here, the exhaust gas constitutes a heat medium, and the waste gas boiler 113 constitutes a heat exchanger.

The refrigerant outlet of the waste gas boiler 113 is in communication with the inlet of the expander 114, which is a fluid expander, via the flow passage 1d. The expander 114 rotates the drive shaft 119 together with a rotating body such as a turbine by expanding the high-temperature and high-pressure refrigerant after being heated by the waste gas boiler 113 in its interior, thereby obtaining work by the rotational driving force. It is a device. Further, an alternator 118 having a power generation function is provided between the expander 114 and the pump 111, and the alternator 118 shares the drive shaft 119. Therefore, the rotational drive force generated by the expander 114 can drive the alternator 118 and the pump 111 integrally via the drive shaft 119, and the drive force of the pump 111 applied by the engine 10 is the drive shaft The alternator 118 and the expander 114 can be driven integrally via 119.
The

flow path portions

1a, 1b, 1c and 1d constitute a first flow path 1 which is a high pressure side flow path of the refrigerant.

In addition, alternator 118 is electrically connected to converter 120, and converter 120 is electrically connected to battery 121. Then, when the expander 114 rotationally drives the drive shaft 119, the alternator 118 generates alternating current and sends it to the converter 120, and the converter 120 converts the sent alternating current into direct current and supplies it to the battery 121 for charging. Let

Further, the outlet of the expander 114 is in communication with the inlet of the condenser 115 via the flow passage 2a. Inside the condenser 115, the refrigerant flows to exchange heat with the air around the condenser 115, whereby the refrigerant can be cooled and condensed.
Here, the condenser 115 constitutes a condenser.

The outlet of the condenser 115 is in communication with the inlet of the receiver 116 via the flow passage 2b, and the outlet of the receiver 116 is in communication with the inlet of the subcooler 117 via the flow passage 2c.
The receiver 116 is a gas-liquid separator containing a liquid refrigerant inside, and removes the vapor component, water, foreign matter, etc. of the refrigerant contained in the refrigerant.
Inside the subcooler 117, the liquid refrigerant sent from the receiver 116 flows and exchanges heat with the air around the subcooler 117, whereby the refrigerant can be subcooled.

The outlet of the subcooler 117 communicates with the suction port of the pump 111 via the flow path 2 d, and the refrigerant flowing out of the subcooler 117 is sucked by the pump 111 and pumped again to circulate in the Rankine cycle 101.
The

flow path portions

2a, 2b, 2c and 2d constitute a second flow path 2 which is a low pressure side flow path of the refrigerant.

In addition, the Rankine cycle 101 has a bypass flow passage 3 communicating the flow passage portion 1 a of the first flow passage 1 with the second flow passage 2. In the present embodiment, one end of the bypass flow path 3 is connected to the connecting portion of the flow path portion 1a and the flow path portion 1b of the first flow path 1, and the other end of the bypass flow path 3 is , And the flow path portion 2 b of the second flow path 2. Furthermore, the Rankine cycle 101 has a flow rate adjusting valve 130 which can open or close the bypass flow passage 3 and adjust the flow passage cross-sectional area of the bypass flow passage 3 in the middle of the bypass flow passage 3. There is. The flow rate adjustment valve 130 is electrically connected to the ECU 140 and its operation is controlled.
Here, the bypass flow path 3 and the flow control valve 130 constitute a flow control means.

In addition, the Rankine cycle 101 circulates the temperature sensor 131 for detecting the temperature of the refrigerant flowing in the flow passage 1 d and the flow passage 1 d in the vicinity of the inlet of the expander 114 in the flow passage 1 d of the first flow passage 1. And a pressure sensor 132 for detecting the pressure of the refrigerant. The temperature sensor 131 detects the temperature of the refrigerant at the inlet of the expander 114, that is, the temperature of the refrigerant flowing out of the waste gas boiler 113, and sends the detected temperature information of the refrigerant to the electrically connected ECU 140. Further, the pressure sensor 132 detects the pressure of the refrigerant at the inlet of the expander 114, that is, the pressure of the refrigerant flowing through the waste gas boiler 113, and sends the detected pressure information of the refrigerant to the electrically connected ECU 140. In the flow path portions 1a to 1d of the first flow path 1, the pressure of the refrigerant is equal between the flow path portions regardless of the opening and closing of the flow rate adjustment valve 130. It may be provided in any of 1a to 1c.
Here, the temperature sensor 131 constitutes a temperature detector, and the pressure sensor 132 constitutes a pressure detector.

Next, the operation of the Rankine cycle 101 according to the embodiment of the present invention will be described.
Referring to FIG. 1, while the engine 10 is in operation, the water pump 21 is also operated to pump cooling water. The coolant water pumped from the engine 10 to the outside circulates through the coolant boiler 112 and the radiator 22 in the coolant circuit 20 so as to return to the engine 10 again.

Further, exhaust gas is discharged from the engine 10 in operation to the exhaust system 30. The exhausted exhaust gas flows through the inside of the waste gas boiler 113 and is then discharged from the muffler 30 b to the outside of the vehicle.
In addition, when the engine 10 operates, the ECU 140 connects the electromagnetic clutch 119a. Thereby, the rotational drive force of the engine 10 is transmitted to the drive shaft 119 via the engine drive shaft 10a, the engine pulley 10b, the drive belt 10c, the pulley 119b and the electromagnetic clutch 119a, whereby the drive shaft 119 is a pump 111 drives the alternator 118 and the expander 114 together.

The driven pump 111 pumps the refrigerant in the liquid state toward the cooling water boiler 112, and the driven expander 114 rotates the rotating body such as a turbine, thereby the flow path of the first flow path 1 The refrigerant in the portion 1 d is depressurized and sent to the flow path portion 2 a of the second flow path 2. The refrigerant is pressure-fed by the pump 111 to receive the adiabatic pressurization action.
The refrigerant in the liquid state, which is pressure-fed by the pump 111, passes through the

flow path portions

1a and 1b, flows into the cooling water boiler 112, and is isostatically heated by rising heat exchange with the cooling water flowing therethrough. Warm and drain. When the flow rate adjustment valve 130 is opened, a part of the refrigerant in the flow path portion 1 a joins the flow path portion 2 b of the second flow path 2 through the bypass flow path 3.

The refrigerant that has flowed out of the cooling water boiler 112 passes through the flow path portion 1c and flows into the waste gas boiler 113, and is isobarically heated by exchanging heat with the exhaust gas flowing inside, thereby raising the temperature and temperature Flow out as superheated steam.
Furthermore, the refrigerant in the high temperature / high pressure superheated vapor state, which has flowed out of the waste gas boiler 113, passes through the flow path portion 1d and is drawn into the expander 114. The refrigerant is adiabatically expanded using the pressure difference of the refrigerant between the upstream flow passage portion 1 d and the downstream flow passage portion 2 a in the expander 114, and then flows out in a high temperature and low pressure superheated vapor state. Then, in the expander 114, the expansion energy of the refrigerant is converted to rotational energy as regenerative energy and transmitted to the drive shaft 119.

The regenerative energy transmitted to the drive shaft 119 is not only applied to the alternator 118 and the pump 111 as a rotational drive force, but is also transmitted to the engine 10 to assist the rotational drive. In addition, the alternator 118 is operated by the applied rotational driving force to generate an alternating current, and the generated alternating current is converted to a direct current by the converter 120 and then charged to the battery 121.

The refrigerant in the superheated vapor state, which has flowed out of the expander 114, passes through the flow path 2a and flows into the condenser 115, and is isobarically cooled and condensed by conducting heat exchange with the surrounding air, that is, the outside air in the condenser 115, Out in liquid state.
Further, the refrigerant in the liquid state, which has flowed out of the condenser 115, passes through the flow passage 2b and flows into the receiver 116, passes through the liquid refrigerant stored in the receiver 116, and flows out to the flow passage 2c. When the refrigerant passes through the inside of the receiver 116, the vapor component, the moisture, the foreign matter, and the like of the contained refrigerant are removed.

Then, the refrigerant flowing out of the receiver 116 passes through the flow path portion 2c and flows into the subcooler 117, and is subjected to heat exchange with the outside air in the subcooler 117 to be further equal-pressure cooled and turned into a supercooling liquid state. It leaks to part 2d. Further, the refrigerant in the flow path 2 d is sucked into the pump 111 and pumped again, and circulates through the Rankine cycle 101.

Here, in FIG. 2, the state change of the refrigerant in the circulation process of the Rankine cycle 101 is shown on the ph diagram of the refrigerant. The ph diagram has an orthogonal coordinate system in which the ordinate is the pressure of the refrigerant (unit: MPa) and the abscissa is enthalpy of the refrigerant (unit: kJ / kg). Furthermore, a region in which the refrigerant is in the supercooled liquid state is indicated by the supercoolant region SL, a region in which the refrigerant is in the wet vapor state is indicated by the wet vapor region WS, and a region in which the refrigerant is in the superheated vapor state is the overheated vapor region. It is indicated by SS. A saturated liquid line α is shown at the boundary between the supercooled liquid region SL and the wet steam region WS, and a dried saturated vapor line β is shown at the boundary between the wet steam region WS and the superheated steam region SS.

Furthermore, in FIG. 2, the engine 10 (see FIG. 1) has a medium load and the exhaust gas temperature during operation of the Rankine cycle 101 circulates the Rankine cycle 101 in an average state (for example, about 500 to 600 ° C.). The change of state of the refrigerant proceeds along a trapezoidal cycle S with the points A, B, C and D as apexes.
Referring also to FIG. 1, in the cycle S, the process from the point A to the point B indicates the adiabatic pressurization process of the refrigerant by the pumping of the pump 111. In this step, the refrigerant raises the pressure from the pressure Pa to the pressure Pb and raises the temperature, and the state maintains a liquid state (supercooled liquid state) in the subcooled liquid region SL.

In the process from point B to point C, the process from point B to point E indicates an equal pressure heating process in the cooling water boiler 112, and the process from point E to point C indicates an equal pressure heating process in the waste gas boiler 113. In the process from point B to point E, the refrigerant raises the temperature while maintaining the pressure at Pb by heat exchange with the cooling water, and in the process from point E to point C, the pressure is Pb by heat exchange with the exhaust gas. remains to further raise the temperature was maintained at it to a temperature T _0. The temperature T ₀ is set to 120 ° C. in this embodiment. At this time, the state of the refrigerant maintains the supercooled liquid state in the supercooled liquid region SL in the process from point B to point E, and the supercooling in the supercooled liquid region SL in the process from point E to point C The liquid state changes to the superheated steam state in the superheated steam region SS through the wet steam region WS.

The process from point C to point D shows the adiabatic expansion process by the expander 114. In this process, the refrigerant lowers the pressure from pressure Pb to pressure Pa and lowers the temperature, and the state maintains the superheated vapor state in the superheated vapor region SS.

In the process from point D to point A, the process from point D to point F indicates an equal pressure cooling process in the capacitor 115, and the process from point F to point A indicates an equal pressure cooling process in the subcooler 117. In the process from point D to point F, the refrigerant lowers the temperature while maintaining the pressure at Pa by heat exchange with the open air, and at the process from point F to point A, the pressure is maintained at Pa by heat exchange with the open air Further reduce the temperature. At this time, the state of the refrigerant changes from the superheated vapor state in the superheated vapor region SS to a saturated liquid in the process from point D to point F, and in the process from point F to point A in the supercooled liquid region SL. Change to supercooled liquid state.

Further, when the load of the engine 10 increases and the heat quantity of the exhaust gas increases and the temperature rises, the quantity of heat absorbed by the refrigerant from the exhaust gas in the waste gas boiler 113 increases, and the enthalpy of the refrigerant after heat exchange with the exhaust gas To increase. Then, since the rotational speeds of the pump 111 and the expander 114 are linked with the engine 10 and are constant, the state of the refrigerant at point C after heat exchange in the waste gas boiler 113 is, for example, an isopycnic line passing through point C The (identical volume line) d0 is going to transition to the increase direction of enthalpy, that is, to the point C1 which is the increase direction of temperature. The state change from point C to point C1 has a large temperature rise. Therefore, in the Rankine cycle 101, the temperature rise of the refrigerant after heat exchange in the waste gas boiler 113, that is, the refrigerant sucked into the expander 114 is suppressed with respect to the temperature rise of the exhaust gas, and the amount of heat applied to the expander 114 is reduced. In order to do this, the following control is performed.

From the isodensity lines d0, d1, d2, d3, d4 and d5 in FIG. 2, the density increases from d0 to d5, but the specific volume decreases. Further, a curve T _{0 in} FIG. 2 shows an isotemperature line of the temperature T ₀ . The temperature of the isotemperature line increases by 10 ° C. as it goes from the isotemperature line T ₀ toward the isotemperature lines T ₁ , T ₂ , T ₃ , T ₄ , T ₅ , T ₆ , and T _7. The temperature decreases by 10.degree. C. from ₀ toward the isotemperature lines T.sub.- ₁ , T.sub.- ₂ , T.sub.- ₃ , T.sub.- ₄ and T.sub.- ₅ .

At this time, the ECU 140 determines the temperature of the refrigerant after heat exchange in the waste gas boiler 113 and the pressure of the refrigerant flowing through the waste gas boiler 113, that is, the temperature and pressure of the refrigerant sucked into the expander 114 on the target pressure line TPL. It controls to satisfy the relationship along and transition. That is, the ECU 140 adjusts the pressure of the refrigerant drawn into the expander 114 according to the temperature of the refrigerant drawn into the expander 114 so that the temperature and pressure of the refrigerant are on the target pressure line TPL. Control to meet As described above, when the amount of heat absorbed by the refrigerant from the exhaust gas in the waste gas boiler 113 increases and the state of the refrigerant tries to transition from point C to point C1, the refrigerant state is controlled from point C to point C1 'by control of the ECU 140. To change. The refrigerant at point C1 'is smaller in enthalpy and lower in refrigerant temperature than in the case of point C1, but the refrigerant flow rate is increased to control the pressure high, and the exhaust gas (heat medium) to the refrigerant (working fluid) The amount of heat received) is approximately equal to that at point C1.

The target pressure line TPL is a straight line set so that the refrigerant density increases with the temperature rise of the refrigerant. The target pressure is proportional to the enthalpy of the refrigerant. The target pressure line TPL is determined to be located in the overheated steam region SS even when the engine 10 has a low load and the exhaust gas temperature is low (close to the left end on the target pressure line TPL in FIG. 2). If the amount of increase in the refrigerant density (increase in the flow rate of the refrigerant) accompanying the temperature rise is small, the effects of the present invention become small, and if it is too large, hunting becomes easy and control becomes difficult.
As described above, in the control in which the temperature and the pressure satisfy the relationship along the target pressure line TPL, the temperature and the pressure accompany the rise in the refrigerant temperature more than the non-control state in which the relationship satisfies the relationship along the isodensity line d0. Since the rate of rise of the refrigerant pressure is increased, the refrigerant flow rate is increased in order to increase the density of the refrigerant flowing through the waste gas boiler 113 as the refrigerant temperature rises. Therefore, the temperature rise of the refrigerant after heat exchange in the waste gas boiler 113 is suppressed with respect to the increase of the heat quantity of the exhaust gas.

Then, the ECU 140 uses the refrigerant temperature detected by the temperature sensor 131 at the inlet of the expander 114 in the flow path portion 1 d and the refrigerant pressure detected by the pressure sensor 132 to adjust the flow rate adjustment valve 130 to By controlling the refrigerant flow rate, the temperature and pressure of the refrigerant drawn into the expander 114 are controlled to match the target pressure line TPL.

Specifically, the target pressure (target pressure line TPL) of the refrigerant with respect to the temperature detected by the temperature sensor 131 is stored in the ECU 140 in advance. Then, the ECU 140 adjusts the flow rate adjustment valve 130 such that the pressure detected by the pressure sensor 132 becomes the target pressure. That is, when the pressure detected by the pressure sensor 132 is lower than the target pressure, the ECU 140 decreases the degree of opening of the flow rate adjustment valve 130 to increase the flow rate of the refrigerant in the flow passage portion 1d, thereby the refrigerant in the flow passage portion 1d. The pressure (the pressure of the refrigerant drawn into the expander 114) is increased. Further, when the pressure detected by the pressure sensor 132 is higher than the target pressure, the ECU 140 increases the degree of opening of the flow rate adjustment valve 130 to decrease the flow rate of the refrigerant in the flow passage 1 d, thereby reducing the refrigerant in the flow passage 1 d. The pressure (the pressure of the refrigerant drawn into the expander 114) is reduced. Furthermore, the ECU 140 controls the refrigerant pressure in accordance with the temperature received from the temperature sensor 131 over time as needed.
The ECU 140 may calculate the target pressure line TPL from the temperature or the like of the refrigerant at the point C.

Further, in the Rankine cycle 101, the design upper limit pressure of the flow path piping of the first flow path 1 which is the high pressure side flow path, and the expander 114, the cooling water boiler 112 and the waste gas boiler 113 which are components on the first flow path 1 The upper limit pressure Pc may be set as In this case, when the refrigerant temperature rises above the temperature T5 corresponding to the upper limit pressure Pc in the target pressure line TPL, the target pressure is fixed to the upper limit pressure Pc as indicated by a broken line TPL '.

Further, even when the temperature of the exhaust gas decreases and the temperature of the refrigerant sucked into the expander 114 falls below the temperature T ₀ at the point C, the ECU 140 responds to the temperature of the refrigerant falling at the temperature sensor 131. Then, the refrigerant pressure in the pressure sensor 132 is controlled so that the relationship between the temperature and the pressure of the refrigerant transitions along the target pressure line TPL. In control in which the temperature and pressure satisfy the relationship along the target pressure line TPL, the ECU 140 decreases the refrigerant temperature more than the state of the refrigerant in which the temperature and pressure decrease while satisfying the relationship on the isodensity line d0. In order to reduce the density of the refrigerant flowing through the waste gas boiler 113, the flow rate of the refrigerant is reduced. Therefore, the temperature drop of the refrigerant after heat exchange in the waste gas boiler 113 is suppressed with respect to the reduction of the heat quantity of the exhaust gas, and the liquid back in the expander 114 is suppressed.

As described above, the Rankine cycle 101 according to the embodiment of the present invention includes the waste gas boiler 113 which causes the refrigerant and the exhaust gas to exchange heat between the refrigerant and the exhaust gas, and the expander which generates driving force by expanding the refrigerant. 114, a condenser 115 for condensing the refrigerant, and a pump 111 for transferring the refrigerant to the waste gas boiler 113 are sequentially provided, and the state of the refrigerant after heat exchange with the exhaust gas in the waste gas boiler 113 is superheated steam. The Rankine cycle 101 adjusts the flow rate of the refrigerant to the waste gas boiler 113, the temperature sensor 131 for detecting the temperature of the refrigerant flowing out of the waste gas boiler 113, the pressure sensor 132 for detecting the pressure of the refrigerant flowing through the waste gas boiler 113, The bypass flow path 3 and the flow control valve 130 and the ECU 140 for controlling the flow control valve 130 are provided. The ECU 140 controls the flow rate adjustment valve 130 so that the refrigerant density increases with the temperature rise of the refrigerant when the temperature detected by the temperature sensor 131 rises.

At this time, the refrigerant in the superheated vapor state after heat exchange in the waste gas boiler 113 increases in heat absorption (enthalpy) as the temperature of the exhaust gas performing heat exchange rises, and along with that, is drawn into the expander 114 The pressure and temperature of the refrigerant tend to increase along the isopyth line d0 in the superheated steam region SS. The ECU 140 makes the transition such that the temperature and pressure of the refrigerant drawn into the expander 114 satisfy the relationship along the target pressure line TPL that sets the target pressure so that the refrigerant density increases with the temperature rise of the refrigerant. Control. Therefore, when the temperature of the exhaust gas rises, the flow rate of the refrigerant flowing through the waste gas boiler 113 is controlled to increase in order to increase the density of the refrigerant, so the exhaust gas in the waste gas boiler 113 is suppressed while suppressing the rise in the refrigerant temperature. Endothermic heat from the can be increased. That is, the Rankine cycle 101 makes it possible to suppress the temperature rise of the refrigerant with respect to the temperature rise of the exhaust gas (the increase of the heat exchange amount) in the heat exchange between the refrigerant and the exhaust gas.

Further, in the Rankine cycle 101, when the temperature detected by the temperature sensor 131 decreases, the ECU 140 controls the flow rate adjustment valve 130 so that the refrigerant density decreases with the temperature decrease of the refrigerant. At this time, the ECU 140 controls the temperature and the pressure of the refrigerant drawn into the expander 114 so as to make a transition by satisfying the relationship along the target pressure line TPL. Therefore, the temperature drop of the refrigerant after heat exchange in the waste gas boiler 113 is suppressed with respect to the reduction of the heat quantity of the exhaust gas, and the liquid back in the expander 114 is suppressed.

Further, in the Rankine cycle 101, when the temperature detected by the temperature sensor 131 rises above the temperature T5 corresponding to the upper limit pressure Pc, the ECU 140 maintains the waste gas boiler 113 so that the pressure detected by the pressure sensor 132 maintains the upper limit pressure Pc. Control the flow rate of the refrigerant flowing through to reduce the refrigerant density. As a result, the flow path piping of the first flow path 1, which is the high pressure side flow path, and the expander 114, the cooling water boiler 112, the waste gas boiler 113, etc. which are components on the first flow path 1 are exposed to abnormal high pressure. It can prevent.

Further, in the Rankine cycle 101, the bypass flow passage 3 communicates the flow passage portion 1a of the refrigerant traveling from the pump 111 to the waste gas boiler 113 to the second flow passage 2 of the refrigerant traveling from the expander 114 to the pump 111. As a result, all the refrigerant heated by the waste gas boiler 113 flows into the expander 114, so the thermal energy of the refrigerant acquired by the waste gas boiler 113 is converted into expansion energy by the expander 114 without being discarded halfway Can be used. Therefore, the Rankine cycle 101 makes it possible to efficiently use the heat energy acquired by the waste gas boiler 113.

Furthermore, in the Rankine cycle 101, the bypass flow path 3 is connected between the condenser 115 and the pump 111 in the second flow path 2 of the refrigerant traveling from the expander 114 to the pump 111. As a result, the refrigerant flowing through the bypass flow path 3 flows downstream of the condenser 115, so the pressure loss of the condenser 115 does not increase, and the pressure of the refrigerant in the flow path portion 2a between the expander 114 and the condenser 115 You can control the rise of Therefore, since the differential pressure of the refrigerant between the flow passage portion 1d on the upstream side of the expander 114 and the flow passage portion 2a on the downstream side can be maintained high, the regenerative energy obtained by the expander 114 is sufficiently ensured. It will be possible to In addition, the bypass flow path 3 connected between the condenser 115 and the sub cooler 117 is a pump cavitation (a bubble of refrigerant generated when the flow path portion 1 a is bypassed to the flow path portion 2 d between the sub cooler 117 and the pump 111 ) Can be prevented. Further, the bypass flow path 3 connected between the condenser 115 and the pump 111 is a refrigerant flowing into the condenser 115 which occurs when the flow path part 1 a is bypassed to the flow path part 2 a between the expander 114 and the condenser 115. Thus, it is possible to prevent the temperature decrease of the inflowing refrigerant and to suppress the decrease of the heat release amount of the condenser 115 due to the temperature decrease of the inflowing refrigerant. The decrease in the amount of heat release in the condenser 115 causes the pressure in the second flow passage 2 to rise, and the differential pressure of the refrigerant between the flow passage portion 1 d on the upstream side of the expander 114 and the flow passage portion 2 a on the downstream side As a result, the regenerative energy obtained by the expander 114 is reduced.

In the Rankine cycle 101 according to the embodiment, the target pressure line TPL is a straight line in which the target pressure is proportional to the enthalpy of the refrigerant, but is not limited to the straight line.

Further, in the embodiment, the pressure detected by the pressure sensor 132 (the pressure of the refrigerant flowing through the waste gas boiler 113) is adjusted by adjusting the flow passage cross-sectional area of the bypass flow passage 3 using the flow rate adjustment valve 130. It is not limited to this.
As in the Rankine cycle 201 shown in FIG. 3, the pump 111 may be driven by the motor 222 without being connected to the engine 10, the alternator 118 and the expander 114. In this case, by controlling the rotational speed of the motor 222, the rotational speed of the pump 111 can be adjusted, whereby the pressure detected by the pressure sensor 132 can be adjusted. At this time, in the expander 114, the drive shaft 114a and the pulley 119b rotationally driven by the engine 10 are connected via the electromagnetic clutch 119a, and the alternator 118 shares the drive shaft 114a.

Also, as in the Rankine cycle 301 shown in FIG. 4, the pump 111 is driven by the motor 222 without being connected to the engine 10, the alternator 118 and the expander 114, and the expander 114 and the alternator 118 are not connected to the engine 10. You may make it mutually be connected by the drive shaft 114a. At this time, the rotational speed of the pump 111 is adjusted by adjusting the rotational speed of the motor 222, or the load of the alternator 118 is controlled to adjust the rotational speed of the expander 114, thereby detecting the pressure sensor 132. The pressure can be adjusted.
In addition, the expander 114 may have an arbitrary change in suction volume. By changing the suction volume, the flow rate (volume flow rate) of the refrigerant transferred by the expander 114 is changed, and the refrigerant pressure in the upstream flow passage of the expander 114 is changed. The pressure can be adjusted.

Further, in the Rankine cycle 101 according to the embodiment, the bypass flow passage 3 communicates the flow passage portion 1 a of the first flow passage 1 with the flow passage portion 2 b of the second flow passage 2, but is limited thereto Not The bypass flow channel 3 may be connected to any of the

flow channel portions

2 a, 2 c and 2 d with respect to the second flow channel 2.
In the Rankine cycle 101 according to the embodiment, a plurality of bypass flow paths 3 may be provided.

Moreover, although the Rankine cycle 101 of embodiment was provided with two heat exchangers, the cooling water boiler 112 and the waste gas boiler 113, it is not limited to this, You may provide three or more. The Rankine cycle 101 may have a heat exchanger for the air conditioner refrigerant and the Rankine cycle 101 refrigerant, and has a heat exchanger for the motor coolant used in the hybrid car and the Rankine cycle 101 refrigerant. May be

DESCRIPTION OF SYMBOLS 3 bypass flow path (flow rate adjustment means), 101, 201, 301 Rankine cycle, 111 pump (fluid pumping device), 113 waste gas boiler (heat exchanger), 114 expander (fluid expander), 115 condenser (condenser) , 130 flow control valve (flow control means), 131 temperature sensor (temperature sensor), 132 pressure sensor (pressure sensor), 140 ECU (control device).

Claims

A heat exchanger for heat exchange between the working fluid and the heat medium, a fluid expander for generating a driving force by expanding the working fluid, a condenser for condensing the working fluid, and a working fluid In the Rankine cycle in which the fluid pumping device for transferring to the heat exchanger is sequentially provided, and the state of the working fluid after heat exchange with the heat medium in the heat exchanger is superheated steam,
A temperature detector for detecting the temperature of the working fluid flowing out of the heat exchanger;
A pressure detector that detects the pressure of the working fluid flowing through the heat exchanger;
Flow control means for controlling the flow of working fluid to the heat exchanger;
And a controller for controlling the flow rate adjusting means.
The control device sets a target pressure such that the density of the working fluid flowing out of the heat exchanger increases with an increase in temperature detected by the temperature detector, and the detected pressure of the pressure detector is the pressure detected by the pressure detector. The Rankine cycle which controls the said flow volume adjustment means so that it may become target pressure.
The Rankine cycle according to claim 1, wherein the control device controls the flow rate adjusting means as the temperature detected by the temperature detector rises, to increase the flow rate of the working fluid to the heat exchanger.
An upper limit pressure is set to the target pressure, and when the temperature detected by the temperature detector is equal to or higher than a predetermined temperature, the flow rate adjusting unit is controlled such that the detected pressure of the pressure detector becomes the upper limit pressure. The Rankine cycle of Claim 2.
The Rankine cycle according to any one of claims 1 to 3, wherein the target pressure is proportional to an enthalpy of the working fluid flowing out of the heat exchanger.
The flow rate adjusting means is
A bypass that communicates a flow path of working fluid from the fluid pumping device to the heat exchanger with a flow path of working fluid from the fluid expander to the fluid pumping device;
The Rankine cycle according to any one of claims 1 to 4, which is a flow control valve capable of adjusting the flow rate of the working fluid in the bypass.
6. The Rankine cycle according to claim 5, wherein the bypass is connected between the condenser and the fluid pumping device in a flow path of working fluid from the fluid expander to the fluid pumping device.