JP2022135401A - Rankine cycle system and control method therefor - Google Patents

Abstract

To provide a Rankine cycle system that can be made compact and lightweight, and a control method therefor.SOLUTION: In a Rankine cycle system 10, working fluid pumped by driving a pump shaft 12a that is a rotation shaft of a pump 12 flows through an evaporator 14, a turbine 16, and a condenser 18 in order, and is pumped by the pump again. A turbine shaft 16a that is a rotation shaft of the turbine is arranged coaxially with the pump shaft. The Rankine cycle system comprises a transmission 40 arranged between the turbine shaft and the pump shaft, and for converting the rotation speed of the turbine shaft at a predetermined gear ratio, and transmitting it to the pump shaft, and comprises a control part (ECU) 50 for controlling the transmission so that predetermined torque is applied to the pump shaft by changing the rotation speed of the turbine shaft on the basis of respective temperatures and pressures in a working fluid outlet of the pump and a working fluid inlet of the turbine.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a Rankine cycle system and its control method.

The Rankine cycle is well known, and is applied, for example, to recovery of exhaust heat from an in-vehicle engine from the viewpoint of energy saving. A Rankine cycle system mainly has a closed circuit in which a pump, an evaporator, an expander, and a condenser are arranged in order and a working fluid circulates. The pump pumps the working fluid towards the evaporator to circulate the working fluid in the closed circuit of the Rankine cycle system. In an example applied to an in-vehicle engine, the evaporator is configured as a heat exchanger to heat and evaporate the working fluid with waste heat from the engine as a heat source, and the expander is configured to extract power from the working fluid that has passed through the evaporator. and the condenser may be configured as a heat exchanger to condense and liquefy the working fluid that has passed through the expander.

Such a Rankine cycle system includes a generator that receives power from a turbine (expander) and a motor that drives an oil pump (see Patent Document 1).

Japanese Patent Publication No. 2006-506570

By the way, in the Rankine cycle system described in Patent Literature 1, it is necessary to dispose the generator and the motor separately, which increases the size and weight of the system. Moreover, when such a Rankine cycle system is mounted on a vehicle, it is not preferable in that it requires a large space for installing the system.

An object of the present disclosure is to provide a Rankine cycle system and a method of controlling the system that can be made compact and lightweight.

In order to achieve the above objects, the Rankine cycle system in the present disclosure is
In the Rankine cycle system, the working fluid pumped by driving the pump shaft, which is the rotating shaft of the pump, flows through the evaporator, the turbine, and the condenser in order, and is pumped again by the pump,
A turbine shaft, which is a rotating shaft of the turbine, is arranged coaxially with respect to the pump shaft,
a transmission disposed between the turbine shaft and the pump shaft for converting the rotation speed of the turbine shaft with a predetermined gear ratio and transmitting the result to the pump shaft;
The transmission is operated so that a predetermined torque is applied to the pump shaft by changing the rotation speed of the turbine shaft based on the respective temperatures and pressures of the working fluid outlet of the pump and the working fluid inlet of the turbine. It has a control unit for controlling.

The control method in the Rankine cycle system in the present disclosure includes
A control method in a Rankine cycle system in which the working fluid pumped by driving the pump shaft, which is the rotating shaft of the pump, flows through the evaporator, the turbine, and the condenser in order, and is pumped again by the pump,
a transmission that converts the rotation speed of a turbine shaft, which is the rotation shaft of the turbine, at a predetermined gear ratio and transmits the speed to the pump shaft;
the density of the working fluid at the working fluid outlet of the pump and the density of the working fluid at the working fluid inlet of the turbine based on the respective temperatures and pressures of the working fluid outlet of the pump and the working fluid inlet of the turbine; calculating each;
determining whether the turbine shaft torque is greater than the pump shaft torque based on each of the calculated densities;
controlling the transmission to change the speed of the turbine shaft when the torque of the turbine shaft is not greater than the torque of the pump shaft;
including.

According to the present disclosure, the system can be made smaller and lighter.

FIG. 1 is a schematic configuration diagram of a Rankine cycle system according to this embodiment. FIG. 2 is a flow chart showing the operation of the ECU.

Embodiments of the present disclosure will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a Rankine cycle system 10 according to this embodiment. Rankine cycle system 10 includes pump 12 , evaporator 14 , turbine 16 (expander) and condenser 18 . The pump 12, evaporator 14, turbine 16 and condenser 18 are arranged in sequence in an annular passage 20 through which the working fluid flows, forming a closed circuit. Here, a Rankine cycle system 10 mounted on a vehicle will be described. Also, although ethanol is used as the working fluid, the present disclosure does not limit the working fluid to ethanol.

The pump 12 has a pump shaft 12a, and when the pump shaft 12a is driven, the working fluid is pressure-fed to the evaporator 14 side and circulated through the annular passage 20 of the Rankine cycle system 10. As shown in FIG. The pump 12 is driven by the motor generator 12b at startup, but may be driven using the power (driving force) of another power source. The motor generator 12b is controlled by a control unit (described later) to switch between a power supply mode in which power is supplied to the motor to drive the pump 12 and a power generation mode in which power is generated with an amount of power corresponding to surplus torque (described later). be.

The evaporator 14 is configured as a heat exchanger. The evaporator 14 is configured as a counterflow heat exchanger. Here, the heat of the exhaust gas of an internal combustion engine for a vehicle (hereinafter referred to as engine) is used as the heat source. In the evaporator 14, the flow direction of the exhaust gas and the flow direction of the working fluid are generally opposite. The evaporator 14 heats the (liquid phase) working fluid pressure-fed by the pump 12 by exchanging heat with the exhaust gas flowing through the exhaust pipe of the engine as a heat source. The working fluid is vaporized (vaporized) by being heated by the heat (waste heat) of the exhaust gas in the evaporator 14 , and the vaporized working fluid flows into the turbine 16 .

The turbine 16 extracts the expansion energy of the working fluid vaporized by the evaporator 14 as power (mechanical energy) to rotate a turbine shaft 16a.

The condenser 18 cools the working fluid expanded by the turbine 16 to condense and liquefy it. The condenser 18 is configured as a counterflow heat exchanger. Cooling water of the engine (engine cooling water) is used as a cooling source for the working fluid of the condenser 18 . That is, in the condenser 18, the flow direction of the engine cooling water is generally opposite to the flow direction of the working fluid. The condenser 18 cools the (vapor-phase or gaseous) working fluid that has passed through the turbine 16 by exchanging heat with engine cooling water as a cooling source. The working fluid is condensed (liquefied) by being cooled by heat exchange with the engine cooling water in the condenser 18 . Here, the engine cooling water flows into the condenser 18 after passing through the radiator (not shown), but the present disclosure is not limited to such a configuration. It may be cooled.

A tank 30 is positioned between the condenser 18 and the pump 12 . The tank 30 is provided so as to achieve gas-liquid separation of the working fluid. A working fluid channel (upstream channel portion) 22 extending from the condenser 18 side toward the tank 30 is provided so as to communicate with an upper region within the tank 30 . A working fluid channel (downstream channel portion) 24 extending from the tank 30 toward the pump 12 side is provided so as to communicate with a lower region within the tank 30 . That is, the working fluid condensed in the condenser 18 is separated into gas and liquid in the tank 30 , and the liquid-phase working fluid is sucked into the pump 12 and circulated through the annular passage 20 again.

In the Rankine cycle system 10 according to the present embodiment, the pump shaft 12a and the turbine shaft 16a are arranged coaxially. A transmission 40 is arranged between the pump shaft 12a and the turbine shaft 16a. The transmission 40 has a synchronizer (not shown) and an actuator 40a. The actuator 40a establishes a power transmission path with a predetermined gear ratio by shifting a sleeve (not shown) of a synchronizing device and coupling a target transmission gear with an input shaft or an output shaft. As a result, the transmission 40 converts the rotation speed of the turbine shaft 16a by a predetermined gear ratio and transmits the same to the pump shaft 12a. As a result, the output of the turbine 16 is applied to the pump 12 via the transmission 40, so that the pump 12 can be driven independently.

By the way, depending on the characteristics of the pump 12 and the turbine 16, the rotation speed of the pump 12 and the rotation speed of the turbine 16 may not have an appropriate relationship. In this case, the pump 12 cannot obtain the output of the turbine 16, making it difficult to drive the pump 12 independently. Therefore, a suitable speed change is required between the pump 12 and the turbine 16 .

ここで、Ｐは圧力、Ｑは体積流量、Ｔはトルク、ωは回転数、ｍドットは質量流量、ρは密度を表す。 Next, the relationship between the volumetric work by the pump 12 and the axial work by the turbine 16 will be described.
The relationship between the volume work and the axial work is represented by the following formulas (1) to (3).

Here, P is pressure, Q is volumetric flow rate, T is torque, ω is rotation speed, m dots is mass flow rate, and ρ is density.

ここで、Ｐ_ｐはポンプ１２の作動流体出口（以下、出口）の圧力、ρ_Ｐはポンプ１２の出口における作動流体の密度、Ｔ_ｐはポンプ１２のトルク、ω_Ｐはポンプ１２の回転数を表す。なお、密度ρ_Ｐは、ポンプ１２の出口の温度、圧力Ｐ_Ｐ、および、蒸気表データから求められる。ポンプ１２の出口の温度、圧力Ｐ_Ｐは、ポンプ１２の出口に設けられる温度センサ（不図示）および圧力センサ（不図示）のそれぞれから取得される。 In the pump 12, the above formula (3) is represented by the following formula (4).

Here, P _p is the pressure at the working fluid outlet (hereinafter referred to as the outlet) of the pump 12, ρ _P is the density of the working fluid at the outlet of the pump 12, T _p is the torque of the pump 12, and ω _P is the rotation speed of the pump 12. show. Note that the density ρ _P is obtained from the temperature at the outlet of the pump 12, the pressure P _P , and the steam table data. The temperature and pressure _PP at the outlet of the pump 12 are obtained from a temperature sensor (not shown) and a pressure sensor (not shown) provided at the outlet of the pump 12, respectively.

Further, from the above equation (4), the torque T _P of the pump 12 is expressed by the following equation (5).

ここで、Ｐ_Ｔはタービン１６の作動流体入口（以下、入口）の圧力、ρ_Ｔはタービン１６の入口における作動流体の密度、Ｔ_Ｔはタービン１６のトルク、ω_Ｔはタービン１６の回転数を表す。なお、密度ρ_Ｔは、タービン１６の入口の温度、圧力Ｐ_Ｔ、蒸気表データから求められる。タービン１６の入口の温度、圧力Ｐ_Ｔは、タービン１６の入口に設けられる温度センサ（不図示）および圧力センサ（不図示）のそれぞれから取得される。 In the turbine 16, the above equation (3) is represented by the following equation (6).

Here, _PT is the pressure at the working fluid inlet (hereinafter referred to as the inlet) of the turbine 16, _ρT is the density of the working fluid at the inlet of the turbine 16, _TT is the torque of the turbine 16, and _ωT is the rotation speed of the turbine 16. show. Note that the density ρ _T is obtained from the inlet temperature of the turbine 16, the pressure P _T , and the steam table data. The temperature and pressure _PT at the inlet of the turbine 16 are obtained from a temperature sensor (not shown) and a pressure sensor (not shown) provided at the inlet of the turbine 16, respectively.

Also, from the above equation (6), the torque of the turbine 16 is expressed by the following equation (7).

式（８）より、ポンプ１２の回転数ω_ｐとタービン１６の回転数ω_Ｔとの関係は、以下の式（９）、式（１０）で表される。

In order for the pump 12 to be independently driven, the following formula (8) should be established.

From equation (8), the relationship between the rotation speed ω _p of the pump 12 and the rotation speed ω _T of the turbine 16 is expressed by the following equations (9) and (10).

When there is no pressure loss in the evaporator 14, the relationship between the rotation speed _ωp of the pump 12 and the rotation speed _ωT of the turbine 16 is represented by the following equation (11).

From the above, it is necessary to drive the pump 12 with the driving force of the motor generator 12b to start the pump 12, but if there is a sufficient heat source to vaporize the working fluid, the equation (10) or (11) can be used. If the rotation speed ω _T of the turbine 16 is changed so as to satisfy ω T , it becomes possible to drive the pump 12 with the output of the turbine 16 . That is, self-driving of the pump 12 becomes possible.

In the present embodiment, the ECU 50 (Electronic Control Unit: control unit) controls the transmission so as to change the rotational speed ω _T of the turbine 16 (turbine shaft 16a) so as to satisfy the expression (10) or (11). 40 actuators 40a.

Next, control by the ECU 50 including control of the transmission 40 will be described. A pressure sensor is provided at each of the outlet of the pump 12 and the inlet of the turbine 16 for control of the transmission 40 . A temperature sensor is provided at each of the outlet of the pump 12 and the inlet of the turbine 16 . Outputs from these sensors are input to the ECU 50 described above.

The ECU 50 is configured as a so-called computer so as to perform various controls of the Rankine cycle system 10 and the engine, and includes a known arithmetic processing unit (eg, CPU), storage device (eg, ROM, RAM), input port, output port, and the like. configured as follows. The ECU 50 acquires (detects) various values based on outputs from these sensors, performs predetermined calculations based on pre-stored programs and data, and controls the operation of the engine (for example, injectors and throttle valves), motor An actuation signal is output to each of them for driving the generator 12b, driving the actuator 40a for the transmission 40, and the like. In other words, the ECU 50 has functional units corresponding to the control means of the engine, the control means of the motor generator 12b, and the control means of the transmission 40, and these are associated with each other. Note that the ECU 50 is not limited to being one electronic control unit, and may be configured as a complex of a plurality of electronic control units.

Next, control of the transmission 40 by the ECU 50 will be described with reference to FIG. FIG. 2 is a flow chart showing the operation of the ECU 50. As shown in FIG. The flow of FIG. 2 is executed at predetermined time intervals during operation of the Rankine cycle system 10 .

First, in step S100, the ECU 50 acquires the temperature and pressure at the outlet of the pump 12 and acquires the temperature and pressure at the inlet of the turbine 16.

Next, in step S 110 , the ECU 50 calculates the density ρ _P of the working fluid at the outlet of the pump 12 and calculates the density ρ _T of the working fluid at the inlet of the turbine 16 .

Next, in step _S120 , the _ECU 50 _adjusts the _{torque TT} of the turbine 16 to It is determined whether or not the torque is greater than the torque T _P (whether T _T >T _P holds). If T _T >T _P holds (step S120: YES), the process proceeds to step S130. If T _T >T _P does not hold (step S120: NO), the process transitions to step S140.

Next, in step S130, the ECU 50 switches the motor generator 12b to the power generation mode so as to generate power corresponding to surplus torque obtained by subtracting the torque of the pump shaft 12a from the torque of the turbine shaft 16a. After that, the flow shown in FIG. 2 ends.

Next, in step S140, the ECU 50 controls the actuator 40a of the transmission 40 so as to change the rotation speed of the turbine shaft 16a. As a result, the torque of the turbine shaft 16a is transmitted to the pump shaft 12a via the transmission 40. As shown in FIG. As a result, self-driving of the pump 12 becomes possible. After that, the flow shown in FIG. 2 ends.

As described above, in the Rankine cycle system 10 according to the present embodiment, the working fluid pressure-fed by driving the pump shaft 12a, which is the rotating shaft of the pump 12, passes through the evaporator 14, the turbine 16, and the condenser 18 in order. and pumped again by the pump 12, in a Rankine cycle system, the axis of rotation of the turbine 16, the turbine shaft 16a, is coaxially arranged with respect to the pump shaft 12a, and between the turbine shaft 16a and the pump shaft 12a. and is provided with a transmission 40 that converts the rotation speed of the turbine shaft 16a at a predetermined gear ratio and transmits it to the pump shaft 12a. An ECU 50 is provided to control the transmission 40 so that a predetermined torque is applied to the pump shaft 12a by changing the rotation speed of the turbine shaft 16a.

With the above configuration, a predetermined torque is applied to the pump 12 from the turbine shaft 16a via the transmission 40, so a motor for driving the pump 12 is not required. This makes it possible to reduce the size and weight of the system. Moreover, since the transmission 40 is arranged between the turbine shaft 16a and the pump shaft 12a, the space for installing the system can be reduced. This allows the system to be further miniaturized.

In the above embodiment, the motor-generator 12b is provided to generate power corresponding to surplus torque obtained by subtracting the predetermined torque of the pump shaft 12a from the torque of the turbine shaft 16a. This allows the generated power to be stored in the battery. Further, when the pump 12 is started, the pump shaft 12a can be driven by the stored electric power, so that energy can be saved.

In addition, the above-described embodiments are merely examples of specific implementations of the present disclosure, and the technical scope of the present disclosure should not be construed to be limited by these. . That is, the present disclosure can be embodied in various forms without departing from its spirit or key features.

INDUSTRIAL APPLICABILITY The present disclosure is suitably used for vehicles equipped with a Rankine cycle system that requires downsizing and weight reduction of the system.

REFERENCE SIGNS LIST 10 Rankine cycle system 12 pump 12a pump shaft 12b motor generator 14 evaporator 16 turbine 16a turbine shaft 18 condenser 20 annular passage 22, 24 working fluid flow path 30 tank 40 transmission 40a actuator 50 ECU

Claims (3)

In the Rankine cycle system, the working fluid pumped by driving the pump shaft, which is the rotating shaft of the pump, flows through the evaporator, the turbine, and the condenser in order, and is pumped again by the pump,
A turbine shaft, which is a rotating shaft of the turbine, is arranged coaxially with respect to the pump shaft,
a transmission disposed between the turbine shaft and the pump shaft for converting the rotation speed of the turbine shaft with a predetermined gear ratio and transmitting the result to the pump shaft;
The transmission is operated so that a predetermined torque is applied to the pump shaft by changing the rotation speed of the turbine shaft based on the respective temperatures and pressures of the working fluid outlet of the pump and the working fluid inlet of the turbine. A Rankine cycle system comprising a control unit for controlling. a motor generator configured to generate power corresponding to surplus torque obtained by subtracting the predetermined torque of the pump shaft from the torque of the turbine shaft;
The Rankine cycle system according to claim 1. A control method in a Rankine cycle system in which the working fluid pumped by driving the pump shaft, which is the rotating shaft of the pump, flows through the evaporator, the turbine, and the condenser in order, and is pumped again by the pump,
a transmission that converts the rotation speed of a turbine shaft, which is the rotation shaft of the turbine, at a predetermined gear ratio and transmits the speed to the pump shaft;
of the density of the working fluid at the working fluid outlet of the pump and the density of the working fluid at the working fluid inlet of the turbine based on the respective temperatures and pressures of the working fluid outlet of the pump and the working fluid inlet of the turbine; calculating each;
determining whether the turbine shaft torque is greater than the pump shaft torque based on each of the calculated densities;
controlling the transmission to change the speed of the turbine shaft when the torque of the turbine shaft is not greater than the torque of the pump shaft;
control methods, including;

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