WO2014010465A1

WO2014010465A1 - Rankine cycle device

Info

Publication number: WO2014010465A1
Application number: PCT/JP2013/068105
Authority: WO
Inventors: 耕二郎田丸; 井口　雅夫; 英文森; 榎島　史修
Original assignee: 株式会社豊田自動織機
Priority date: 2012-07-10
Filing date: 2013-07-02
Publication date: 2014-01-16
Also published as: JP2014016115A

Abstract

A Rankine cycle device, provided with: a pump for pumping the working fluid; a heat exchanger for exchanging heat between the working fluid pumped by the pump and a fluid from the heat discharge source; an expander for causing the working fluid heat-exchanged by the heat exchanger to expand and outputting the mechanical energy; a condenser for causing the working fluid caused to expand in the expander to condense, the pump, the heat exchanger, the expander, and the condenser being connected in sequence so as to form a working fluid circuit in which the working fluid circulates; a pressure detection device for detecting the low-pressure-side pressure, which is the pressure of the working fluid flowing from the exit of the expander to the entrance of the pump; and a pressure control device for controlling the high-pressure-side pressure, which is the pressure of the working fluid flowing from the exit of the pump to the entrance of the expander. The pressure control device is constituted so as to control the high-pressure-side pressure so that the high-pressure-side pressure remains constant, even if the low-pressure-side pressure decreases, as long as the difference between the high-pressure-side pressure and the low-pressure-side pressure does not exceed a maximum control limit set in advance.

Description

Rankine cycle equipment

The present invention relates to a Rankine cycle device.

The Rankine cycle device includes a pump that pumps the working fluid, a heat exchanger that exchanges heat with the fluid from the exhaust heat source, and a working fluid that is heat-exchanged by the heat exchanger. And an expander that outputs dynamic energy and a condenser that condenses the working fluid expanded by the expander. A pump, a heat exchanger, an expander, and a condenser are sequentially connected to form a working fluid circuit in which the working fluid circulates.

In the above working fluid circuit, the pressure of the working fluid flowing from the outlet of the pump to the inlet of the expander is “high pressure side pressure (evaporation pressure)”, and the pressure of the working fluid flowing from the outlet of the expander to the inlet of the pump is The “low pressure side pressure (condensation pressure)” is lower than the high pressure side pressure. The smaller the difference between the high-pressure side pressure and the low-pressure side pressure is, the more the expander cannot effectively convert the thermal energy of the working fluid into mechanical energy such as rotational energy. The mechanical energy cannot be output.

Therefore, in Patent Document 1, a pressure difference detection device that detects a difference between a high-pressure side pressure and a low-pressure side pressure of the working fluid flowing in the working fluid circuit, and a pressure difference detected by the pressure difference detection device are determined in advance. A Rankine cycle device is disclosed that includes a pressure difference increasing device that increases a pressure difference so as to be a predetermined pressure difference when the pressure difference falls below a predetermined pressure difference. Patent Document 2 discloses that control is performed such that the difference between the high-pressure side pressure and the low-pressure side pressure of the working fluid flowing in the working fluid circuit is kept constant. According to these, the difference between the high-pressure side pressure and the low-pressure side pressure is prevented from becoming too small, and the expander can output stable mechanical energy.

JP 2007-255327 A JP 2008-297961 A

However, for example, when the working fluid expanded by the expander is cooled by outside air in the condenser and condensed, the lower the temperature of the outside air, the easier the working fluid is cooled and the lower the condensation pressure of the working fluid. . Under such circumstances, in the technique of Patent Document 1, the difference between the evaporation pressure and the condensation pressure becomes too large, and the reliability of the expander and the pump may be reduced.

On the other hand, in the technique of Patent Document 2, the difference between the evaporation pressure and the condensation pressure is controlled to be kept constant. For this reason, for example, when the condensing pressure is lowered, the evaporation pressure is lowered even when the pressure difference is in a range where the reliability of the expander and the pump is maintained. That is, the difference between the evaporation pressure and the condensation pressure cannot be made larger than a certain value, and as a result, the mechanical energy output from the expander cannot be made as large as possible.

An object of the present disclosure is to provide a Rankine cycle device that can ensure the reliability of the expander and the pump and can increase the mechanical energy output from the expander as much as possible.

The Rankine cycle device for achieving the above object includes a pump that pumps a working fluid, a heat exchanger that exchanges heat between the working fluid pumped by the pump and a fluid from an exhaust heat source, and heat exchange using the heat exchanger. An expander that expands the generated working fluid to output mechanical energy, and a condenser that condenses the working fluid expanded by the expander, the pump, the heat exchanger, the expander, and the The condenser is connected in series to form a working fluid circuit through which the working fluid circulates, and a low pressure side pressure that is a pressure of the working fluid flowing from the outlet of the expander to the inlet of the pump. And a pressure control device that controls a high-pressure side pressure that is a pressure of a working fluid that flows from the outlet of the pump to the inlet of the expander. The pressure control device keeps the high-pressure side pressure constant even when the low-pressure side pressure is reduced, as long as the difference between the high-pressure side pressure and the low-pressure side pressure does not exceed a preset control upper limit value. Configured to control.

The schematic diagram which shows the Rankine cycle apparatus in embodiment. The graph which shows the change of a high pressure side pressure and a low pressure side pressure. The graph which shows the change of the high voltage | pressure side pressure in another embodiment, and a low voltage | pressure side pressure. The schematic diagram which shows the Rankine-cycle apparatus in another embodiment. The schematic diagram which shows the Rankine-cycle apparatus in another embodiment.

Hereinafter, a Rankine cycle device mounted on a vehicle according to an embodiment will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the Rankine cycle device 10 includes a working fluid circuit 11 through which a working fluid circulates. The working fluid circuit 11 includes an expander 20, a condenser 30, a pump 40, and a heat exchanger 50 that are sequentially connected. The working fluid flows along the arrangement order of the expander 20, the condenser 30, the pump 40, and the heat exchanger 50 and circulates in the working fluid circuit 11.

The heat exchanger 50 includes a heat absorber 50a and a heat radiator 50b. The heat absorber 50 a is connected to the outlet of the pump 40 through the first passage 21. The radiator 50b is provided around the exhaust passage E1 connected to the engine E as an exhaust heat source. The exhaust of the engine E is exhausted from the muffler E2 after being radiated by the radiator 50b.

The heat absorber 50 a of the heat exchanger 50 and the inlet of the expander 20 are connected via the second passage 22. The outlet of the expander 20 and the inlet of the condenser 30 are connected via a third passage 23. The outlet of the condenser 30 and the inlet of the pump 40 are connected via the fourth passage 24. The heat exchanger 50 changes the working fluid in a low-temperature and high-pressure liquid state pumped by the pump 40 into a high-temperature and high-pressure working fluid by exchanging heat with the exhaust flowing through the exhaust passage E1 of the engine E. . The condenser 30 changes the working fluid that has been expanded in the expander 20 and turned into a high-temperature and low-pressure gas state into a low-temperature and low-pressure liquid-state working fluid by exchanging heat with the outside air.

Rankine cycle device 10 includes a drive shaft 60 a that functions as both a pump shaft of pump 40 and an output shaft of expander 20. A pulley 60b is fixed to the end of the drive shaft 60a. A belt 60c is wound around the pulley 60b. The belt 60c is wound around a pulley E4 fixed to a crankshaft E3 that is a rotation output shaft of the engine E. The crankshaft E3 is connected to the drive shaft 60a via a pulley E4, a belt 60c, and a pulley 60b.

The working fluid circuit 11 has one end connected to the first passage 21 (that is, a passage extending between the outlet of the pump 40 and the heat exchanger 50) and the other end connected to the third passage 23 (that is, the expander 20). A bypass passage 71 connected to an outlet of the condenser 30 and an inlet of the condenser 30. The bypass passage 71 is provided with a flow rate adjusting valve 71a that changes the flow rate of the working fluid flowing from the pump 40 to the bypass passage 71 and the heat exchanger 50, respectively. The flow rate adjustment valve 71 a is connected to the control unit 75. The control unit 75 transmits a signal to the flow rate adjusting valve 71a in order to adjust the opening degree of the flow rate adjusting valve 71a.

In the fourth passage 24 (that is, the passage between the outlet of the condenser 30 and the inlet of the pump 40), pressure detection for detecting a low-pressure side pressure (condensation pressure) that is the pressure of the working fluid that has passed through the condenser 30. A first pressure sensor 72 as a device is provided. The first pressure sensor 72 is connected to the control unit 75 so that a signal can be transmitted to the control unit 75. The first pressure sensor 72 sends a signal indicating the detection result to the control unit 75.

In the second passage 22 (that is, a passage extending between the heat exchanger 50 and the inlet of the expander 20), a high-pressure side pressure (evaporation pressure) that is the pressure of the working fluid that has passed through the heat exchanger 50 is detected. A second pressure sensor 73 is provided. The second pressure sensor 73 is connected to the control unit 75 so that signals can be transmitted to the control unit 75. The second pressure sensor 73 sends a signal indicating the detection result to the control unit 75.

Next, the operation of this embodiment will be described.

When the pump 40 is driven, the working fluid is pumped by the pump 40 and circulates in the working fluid circuit 11. When the working fluid sent from the pump 40 to the heat exchanger 50 through the first passage 21 passes through the heat exchanger 50, it is heat-exchanged with the exhaust gas and becomes a high-temperature and high-pressure gas state. The working fluid that has passed through the heat exchanger 50 and is in a high-temperature and high-pressure gas state is sucked into the expander 20 from the inlet of the expander 20 via the second passage 22. The working fluid sucked into the expander 20 is expanded by the expander 20, and part of the thermal energy of the working fluid is taken out as mechanical energy through the expander 20 to assist the rotational output of the engine E. Used for. The working fluid whose temperature has been lowered and reduced in pressure in the expander 20 is sucked into the condenser 30 from the outlet of the expander 20 via the third passage 23. The working fluid sucked into the condenser 30 is condensed and liquefied by the condenser 30, and is returned to the pump 40 through the fourth passage 24.

Here, the pressure detected by the first pressure sensor 72 is greatly affected by the temperature of the outside air that exchanges heat with the working fluid in the condenser 30. For example, the higher the temperature of the outside air, the harder the working fluid is cooled (condensed) in the condenser 30 and the lower the pressure of the working fluid. Further, for example, the lower the temperature of the outside air, the easier the working fluid is cooled (condensed) in the condenser 30 and the pressure of the working fluid tends to be low.

FIG. 2 shows changes in pressure (changes in low-pressure side pressure and high-pressure side pressure) detected by the first pressure sensor 72 and the second pressure sensor 73, respectively. Between time T1 and time T2, the pressure difference Z1 between the pressure P11 detected by the first pressure sensor 72 and the pressure P21 detected by the second pressure sensor 73 is constant, and a preset control is performed. It is smaller than the upper limit. Here, the “control upper limit value Z” is the high pressure side pressure and the low pressure side pressure at which the expander 20 and the pump 40 do not impair the reliability of the equipment due to the load received by the difference between the high pressure side pressure and the low pressure side pressure. This is the upper limit of the difference.

Suppose that the temperature of the outside air gradually decreases from time T1 to time T2 from time T2 to time T3. Then, the working fluid is cooled to a temperature lower than the temperature at the time T1 to the time T2 in the condenser 30 from the time T2 to the time T3, and the pressure of the working fluid gradually decreases. The pressure P12 detected by the first pressure sensor 72 at time T3 is lower than the pressure P11 detected by the first pressure sensor 72 at time T2.

Here, it is assumed that the pressure difference Z2 between the pressure P12 detected by the first pressure sensor 72 and the pressure P21 detected by the second pressure sensor 73 has reached a preset control upper limit value. At this time, the control unit 75 determines that the flow rate of the working fluid flowing from the first passage 21 through the bypass passage 71 to the third passage 23 is within a range where the difference between the high pressure side pressure and the low pressure side pressure does not exceed the control upper limit value. The opening degree of the flow rate adjustment valve 71a is controlled so as to decrease. As a result, the high-pressure side pressure is maintained at a constant value without gradually decreasing following the low-pressure side pressure, and the difference between the high-pressure side pressure and the low-pressure side pressure becomes as large as possible within the range not exceeding the control upper limit value. ing. Therefore, in the present embodiment, the control unit 75 functions as a pressure control device that controls the high-pressure side pressure.

Between time T3 and time T4, the pressure difference Z2 between the pressure P12 detected by the first pressure sensor 72 and the pressure P21 detected by the second pressure sensor 73 is constant. It is assumed that the temperature of the outside air further gradually decreases from the time T3 to the time T4 between the time T4 and the time T5. Then, the working fluid is cooled to a temperature further lower than the temperature between time T3 and time T4 in the condenser 30 between time T4 and time T5, and the pressure of the working fluid gradually decreases. Go. The pressure P13 detected by the first pressure sensor 72 at time T5 is lower than the pressure P12 detected by the first pressure sensor 72 at time T4.

At this time, the controller 75 controls the opening degree of the flow rate adjusting valve 71a so that the flow rate of the working fluid flowing from the first passage 21 through the bypass passage 71 to the third passage 23 increases. As a result, the flow rate of the working fluid flowing from the outlet of the pump 40 to the inlet of the expander 20 decreases, and the pressure P22 detected by the second pressure sensor 73 at time T5 is the second pressure at time T4. It becomes lower than the pressure P21 detected by the sensor 73.

Here, the pressure difference Z3 between the pressure P13 detected by the first pressure sensor 72 and the pressure P22 detected by the second pressure sensor 73 is a preset control upper limit value. That is, the flow rate adjustment is performed so that the pressure difference Z3 between the pressure P13 and the pressure P22 becomes the control upper limit value by changing the flow rate of the working fluid flowing from the first passage 21 to the third passage 23 via the bypass passage 71. The opening degree of the valve 71 a is adjusted by the control unit 75. As a result, the high pressure side pressure decreases from time T4 to time T5 so that the difference between the high pressure side pressure and the low pressure side pressure does not exceed the control upper limit value, so the difference between the high pressure side pressure and the low pressure side pressure. Is prevented from becoming too large.

In the above embodiment, the following effects can be obtained.

(1) The Rankine cycle apparatus 10 includes a first pressure sensor 72 that detects a low-pressure side pressure that is a pressure of a working fluid that flows from the outlet of the expander 20 to the inlet of the pump 40. In the working fluid circuit 11, the bypass passage 71 having one end connected to the first passage 21 and the other end connected to the third passage 23 is disposed, and the operation flows through the bypass passage 71 through the bypass passage 71. A flow rate adjusting valve 71a for changing the flow rate of the fluid and the flow rate of the working fluid flowing through the heat exchanger 50 is provided. And the control part 75 changes the flow volume of the working fluid which flows into the 3rd channel | path 23 from the 1st channel | path 21 through the bypass channel | path 71, and thereby the working fluid which flows from the outlet of the pump 40 to the inlet of the expander 20 is changed. The high-pressure side pressure that is the pressure is controlled.

For example, even if the low-pressure side pressure detected by the first pressure sensor 72 gradually decreases, the control unit 75 causes the difference between the high-pressure side pressure and the low-pressure side pressure to exceed a preset control upper limit value. In the absence range, the flow rate of the working fluid flowing from the first passage 21 through the bypass passage 71 to the third passage 23 is decreased. Therefore, the high-pressure side pressure can be controlled so that the high-pressure side pressure is maintained at a constant value without gradually decreasing following the low-pressure side pressure. As a result, the difference between the high pressure side pressure and the low pressure side pressure can be increased as much as possible within a range not exceeding the control upper limit value. Further, for example, when the low-pressure side pressure detected by the first pressure sensor 72 is excessively low, the amount of working fluid flowing from the first passage 21 to the third passage 23 through the bypass passage 71 is increased. Thus, the flow rate of the working fluid flowing from the outlet of the pump 40 to the inlet of the expander 20 can be reduced. As a result, the high pressure side pressure can be lowered so that the difference between the high pressure side pressure and the low pressure side pressure does not exceed the control upper limit value, so the difference between the high pressure side pressure and the low pressure side pressure becomes too large. This can be prevented. As a result, the reliability of the expander 20 and the pump 40 can be ensured, and the mechanical energy output from the expander 20 can be maximized.

(2) In the present embodiment, the high pressure side pressure is controlled by changing the flow rate of the working fluid flowing from the first passage 21 to the third passage 23 through the bypass passage 71. Therefore, for example, in order to control the high-pressure side pressure, there is no need to control the rotation speed of the motor that drives the pump 40 or the rotation speed of the expander 20, and the single drive shaft 60a can be controlled. It becomes possible to function as both the pump shaft of the pump 40 and the expander 20, and the configuration of the Rankine cycle apparatus 10 can be simplified.

Note that the above embodiment may be modified as follows.

In the embodiment, an upper limit value of the high pressure side pressure may be set in advance. For example, as shown in FIG. 3, the pressure difference Z4 between the pressure P14 detected by the first pressure sensor 72 and the pressure P23 detected by the second pressure sensor 73 is constant between time T6 and time T7. It is. At this time, it is assumed that the pressure P23 detected by the second pressure sensor 73 has already reached the upper limit value of the high-pressure side pressure. Then, it is assumed that the temperature of the outside air gradually rises from time T6 to time T7 from time T7 to time T8. Then, the working fluid is condensed to a temperature higher than that at the time T6 to the time T7 in the condenser 30 from the time T7 to the time T8, and the pressure of the working fluid is gradually increased. The pressure P15 detected by the first pressure sensor 72 at time T8 is higher than the pressure P14 detected by the first pressure sensor 72 at time T7, and the high pressure side pressure and the low pressure side pressure are detected. The difference with is small. Here, the control unit 75 controls the high pressure side pressure so that the high pressure side pressure does not exceed the upper limit value. Specifically, the control unit 75 controls the rotational speed of the motor that drives the pump 40, thereby changing the flow rate of the working fluid pumped from the pump 40 to the heat exchanger 50, and the high-pressure side pressure reaches the upper limit value. Do not exceed. According to this, a situation in which the high pressure side pressure becomes excessively high due to an attempt to increase the difference between the high pressure side pressure and the low pressure side pressure as much as possible within a range not exceeding the control upper limit value. Can be prevented. As a result, the reliability of the expander 20 and the pump 40 can be further ensured.

The drive shaft 60a may not function as both the pump shaft of the pump 40 and the output shaft of the expander 20. For example, as shown in FIG. 4, the Rankine cycle apparatus 10 may include a motor 40 a that drives the pump 40. A pulley 201b is fixed to the output shaft 20b of the expander 20. A belt 60c is wound around the pulley 201b. The belt 60c is wound around a pulley E4 fixed to the crankshaft E3 of the engine E. The crankshaft E3 is connected to the output shaft 20b via a pulley E4, a belt 60c, and a pulley 201b. The mechanical energy output from the expander 20 assists the rotational output of the engine E.

The pump 40 is driven by the rotation of the motor 40a to pump the working fluid to the heat exchanger 50. For example, even if the pressure detected by the first pressure sensor 72 gradually decreases, the control unit 75 has a range in which the difference between the high pressure side pressure and the low pressure side pressure does not exceed a preset control upper limit value. Then, the flow rate of the working fluid can be adjusted through the rotation speed control of the motor 40a so that the high-pressure side pressure is maintained at a constant value. As a result, the difference between the high pressure side pressure and the low pressure side pressure can be increased as much as possible within a range not exceeding the control upper limit value. For example, when the pressure detected by the first pressure sensor 72 is excessively low, the control unit 75 controls the motor 40a so that the rotation speed of the motor 40a decreases. According to this, the flow rate of the working fluid pumped to the heat exchanger 50 by the pump 40 can be reduced, and as a result, the difference between the high pressure side pressure and the low pressure side pressure is set to a preset control upper limit value. The high pressure side pressure can be lowered so as not to exceed. Therefore, it is possible to prevent the difference between the high pressure side pressure and the low pressure side pressure from becoming too large.

Further, as shown in FIG. 5, a power generator 20 a may be connected to the expander 20. For example, even if the pressure detected by the first pressure sensor 72 gradually decreases, the control unit 75 causes the difference between the high pressure side pressure and the low pressure side pressure to exceed the preset control upper limit value. In the absence range, the rotational speed of the generator 20a is controlled to keep the high-pressure side pressure at a constant value. Thereby, the difference between the high pressure side pressure and the low pressure side pressure can be increased as much as possible within a range not exceeding the control upper limit value. For example, when the pressure detected by the first pressure sensor 72 is excessively low, the control unit 75 controls the generator 20a so that the rotational speed of the generator 20a increases. According to this, it controls so that the rotation speed of the expander 20 driven with the generator 20a rises, and it can make a high voltage | pressure side pressure low. As a result, it is possible to prevent the difference between the high-pressure side pressure and the low-pressure side pressure from exceeding a preset control upper limit value, and the difference between the high-pressure side pressure and the low-pressure side pressure becomes too large. Can be prevented.

One end of the bypass passage 71 may be connected to the second passage 22. Further, the other end of the bypass passage 71 may be connected to the fourth passage 24. The point is that a part of the working fluid flowing through the passage extending from the outlet of the pump 40 to the inlet of the expander 20 is transferred by the bypass passage 71 to the passage extending from the outlet of the expander 20 to the inlet of the pump 40. What is necessary is just to be able to bypass.

The first pressure sensor 72 may be provided in the third passage 23.

A temperature sensor for detecting the temperature of the working fluid condensed and liquefied in the condenser 30 (specifically, the temperature of the working fluid flowing from the outlet of the condenser 30 to the subcooler) may be provided. Then, the control unit 75 may calculate the pressure of the working fluid based on the temperature of the working fluid detected by the temperature sensor. In this case, the temperature sensor and the control unit 75 constitute a pressure detection device that detects the low-pressure side pressure.

As the fluid from the exhaust heat source, for example, engine cooling water, supercharged air, EGR gas, or the like flowing through a cooling water circulation path connected to the engine E may be used.

Claims

A pump for pumping the working fluid;
A heat exchanger that exchanges heat between the working fluid pumped by the pump and the fluid from the exhaust heat source;
An expander that expands the working fluid heat-exchanged by the heat exchanger and outputs mechanical energy;
A condenser that condenses the working fluid expanded by the expander, wherein the pump, the heat exchanger, the expander, and the condenser sequentially form a working fluid circuit through which the working fluid circulates. Connected to the condenser;
A pressure detection device that detects a low-pressure side pressure that is a pressure of a working fluid flowing from an outlet of the expander to an inlet of the pump;
A pressure control device that controls a high-pressure side pressure that is a pressure of a working fluid that flows from an outlet of the pump to an inlet of the expander,
The pressure control device keeps the high-pressure side pressure constant even when the low-pressure side pressure is reduced, as long as the difference between the high-pressure side pressure and the low-pressure side pressure does not exceed a preset control upper limit value. A Rankine cycle device configured to be controlled.
The Rankine cycle device according to claim 1, wherein the pressure control device is configured to control the high-pressure side pressure so that the high-pressure side pressure does not exceed a preset upper limit value.
The working fluid circuit includes a bypass passage connecting a portion between the outlet of the pump and the inlet of the expander to a portion between the outlet of the expander and the inlet of the pump;
The Rankine cycle device according to claim 1 or 2, wherein the pressure control device is configured to control the high-pressure side pressure by changing a flow rate of the working fluid flowing through the bypass passage.
The Rankine cycle device according to claim 1 or 2, wherein the pressure control device is configured to control the high-pressure side pressure by controlling a rotation speed of a motor that drives the pump.
The Rankine cycle device according to claim 1 or 2, wherein the pressure control device is configured to control the high-pressure side pressure by controlling a rotation speed of the expander.