WO2004013466A1

WO2004013466A1 - Rankine cycle apparatus

Info

Publication number: WO2004013466A1
Application number: PCT/JP2003/009223
Authority: WO
Inventors: Akihisa Sato; Shigeru Ibaraki
Original assignee: Honda Giken Kogyo Kabushiki Kaisha
Priority date: 2002-07-24
Filing date: 2003-07-22
Publication date: 2004-02-12
Also published as: AU2003248086A1; EP1536104A4; JP3901608B2; EP1536104A1; US20060086091A1; JP2004052738A

Abstract

In a Rankine cycle apparatus, the amount of water supply to an evaporator (12) is regulated and the number of revolution of an expander (13) is regulated so that a vapor temperature at the outlet of the evaporator (12) corresponds to a target vapor temperature. When the amount of water supply to the evaporator (12) is reduced in a stepped manner, a vapor temperature at the outlet of the evaporator (12) rises slowly and converges to a predetermined temperature. When the number of rotation of the expander (13) is reduced in a stepped manner, the vapor temperature rises quickly, though temporarily. Accordingly, simultaneous regulation of the amount of water supply to the evaporator (12) and the number of rotation of the expander (13) enables a vapor temperature at the outlet of the evaporator (12) to correspond to a target vapor temperature with excellent response and high accuracy, so that combined efficiency, a combination of the efficiency of the evaporator (12) and the efficiency of the expander (13), can be made to maximum. This enables to regulate the temperature of a vapor phase medium produced in the evaporator (12) to a target temperature with excellent response and high accuracy.

Description

Specification

Field of the invention

The present invention relates to an evaporator that generates a gas-phase working medium by heating a liquid-phase working medium with exhaust gas of an engine, and a positive displacement type that converts heat energy of the gas-phase working medium generated by the evaporator into mechanical energy. And a Rankine cycle device comprising the expander.

Background art

In Japanese Unexamined Patent Publication No. 2-38181, the steam temperature at the outlet of a waste heat flow-through poiler, which uses the exhaust gas of an engine rotating at a constant speed as a heat source, is compared with the target steam temperature. Feed-back control the amount of water supplied to the waste heat once-through boiler so that it matches the target steam temperature. This document describes that the control of steam temperature is improved by compensating engine load fluctuations.

As shown in Fig. 12, in the Rankine cycle device, the steam temperature at the outlet of the evaporator is controlled to be higher than the saturated steam temperature in order for the output of the expander to become positive, that is, to extract mechanical energy from the expander. There is a need to. Also, as shown in Fig. 13, the efficiency of the evaporator and the efficiency of the expander vary depending on the steam temperature, and to maximize the combined efficiency of the two, it is necessary to control the steam temperature to the optimum temperature. is there. However, as shown in Fig. 4A, when the amount of water supplied to the evaporator is changed stepwise, it takes several tens to several hundreds of seconds to reach a steady state due to the low response of the change in steam temperature. Therefore, in a Rankine cycle system for vehicles with a high engine load fluctuation speed, the steam temperature at the outlet of the evaporator is improved with high responsiveness and accuracy by changing the amount of water supplied to the evaporator. It is difficult to control.

In order to control the steam temperature with high responsiveness by increasing or decreasing the amount of water supply, it is necessary to reduce the heat mass of the evaporator. However, in this case, there is a problem that the amount of steam generated by the evaporator is insufficient or the efficiency of the evaporator is reduced. Disclosure of the invention

The present invention has been made in view of the above circumstances, and has as its object to control the temperature of a gas-phase working medium generated in an evaporator to a target temperature with good responsiveness and high accuracy in a Rankine cycle device.

To achieve the above object, according to the present invention, an evaporator for heating a liquid-phase working medium with exhaust gas of an engine to generate a gas-phase working medium, and a heat energy of the gas-phase working medium generated in the evaporator, In a Rankine cycle device equipped with a positive displacement expander that converts gas into mechanical energy, the temperature of the gas phase working medium at the outlet of the evaporator matches the target temperature. There is proposed a Rankine cycle device characterized by comprising a control means for controlling the supply amount of water and controlling the rotation speed of the expander.

According to the above configuration, the supply amount of the liquid-phase working medium to the evaporator for generating the gas-phase working medium by heating the liquid-phase working medium with the exhaust gas of the engine is controlled, and the gas generated in the evaporator is controlled. By controlling the number of revolutions of a positive displacement expander that converts the thermal energy of the phase working medium into mechanical energy, the temperature of the gas phase working medium generated in the evaporator is responsively and accurately matched to the target temperature. Thus, the combined efficiency of the evaporator and the expander can be maximized.

Incidentally, the controller 20 of the embodiment corresponds to the control means of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

1 to 9 show a first embodiment of the present invention, FIG. 1 is an overall configuration diagram of a Rankine cycle device, and FIGS. 2A to 2D are diagrams showing a temperature distribution of a working medium inside an evaporator. Fig. 3 is a graph showing changes in steam pressure and steam temperature when the expander rotation speed is changed stepwise.Figs. 4A to 4C show the results when the water supply amount and the expander rotation speed are simultaneously changed. Fig. 5 is a flowchart of a main routine for controlling steam temperature, Fig. 6 is a flowchart of a routine for calculating a feedwater feedforward value, Fig. 7 is a flowchart of a routine for calculating a target expander speed, Figure 8 is the map to find the fuel flow rate G _F from the engine operating condition such as Enji down speed N e and the intake negative pressure P b, 9 water supply feedforward from the exhaust gas flow rate G _gAS and exhaust gas temperature T g to search for value Q _FF Is a map. FIGS. 10 and 11 show the second embodiment of the present invention. FIGS. 10A and 10B show a flow chart of a main routine of a steam temperature control according to a second embodiment, and FIG. 11 shows a steam flow rate and a deviation T. FIG. FIG. 6 is a map for searching for an increase / decrease in rotation speed Δ _{一一} from FIG. Fig. 12 is a graph showing the relationship between the steam temperature and the output of the expander, and Fig. 13 is a graph showing the relationship between the optimum steam temperature and the maximum efficiency of the evaporator and the expander.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described based on embodiments of the present invention shown in the accompanying drawings.

As shown in Fig. 1, the Rankine cycle device for recovering the thermal energy of the exhaust gas from the engine 11 of the vehicle uses a high-temperature and high-pressure gas by heating the liquid-phase working medium (water) with the exhaust gas from the engine 11. Evaporator 12 to generate phase working medium (steam), positive displacement expander 13 to convert thermal energy of high-temperature and high-pressure steam generated by evaporator 12 to mechanical energy, and discharge from expander 13 A condenser 14 for cooling the condensed steam and condensing it into water; a tank 15 for storing the water discharged from the condenser 14; a water supply pump 16 for sucking the water in the tank 15; An injector 17 for injecting the water sucked by the water supply pump 16 into the evaporator 12 is arranged on a closed circuit.

The motor generator 18 connected to the expander 13 is disposed, for example, between the engine 11 and the driving wheels, and assists the output of the engine 11 by causing the motor generator 18 to function as a motor. At the same time, when the vehicle decelerates, the motor / generator 18 can function as a generator to recover the kinetic energy of the vehicle as electric energy. The motor generator 18 may be connected to the expander 13 by itself and have only the function of generating electric energy. In the present invention, the load applied to the expander 13 from the motor / generator 18 is adjusted by adjusting the load (power generation amount) of the motor 18 so that the number of rotations of the expander 13 is reduced. Control. The operating state of the engine 11, that is, the engine speed Ne, the intake negative pressure Pb, the exhaust gas temperature Tg, the air-fuel ratio A / F, and the output of the evaporator 12 detected by the steam temperature sensor 19 The controller 20 to which the steam temperature T of the motor 17 is input, determines the amount of water supplied to the injector 17 (or the rotation speed of the water supply pump 16) and the load generated by the motor generator 18, ie, the expander 13 To control the number of rotations. Next, the reason why the steam temperature at the outlet of the evaporator 12 can be controlled by adjusting the rotation speed of the expander 13 will be described.

FIG. 2A schematically shows the structure of the evaporator 12. The heat transfer tube 22 arranged inside the casing 21 of the evaporator 12 is provided with a water inlet 2 2 a connected to the injector 17. And a steam outlet 2 2 b connected to the expander 13 .The casing 21 has an exhaust gas inlet 21 a on the steam outlet 22 b side and an exhaust gas outlet 2 lb on the water inlet 22 a side. Is provided. Therefore, the working medium and the exhaust gas flow in opposite directions.

As shown in Fig. 2B, the temperature of the water supplied to the water inlet 22a of the heat transfer tube 22 gradually rises in the liquid phase, and when the temperature reaches the saturation temperature at point a, the water and steam coexist. It becomes vapor (two-phase state) and is maintained at the saturation temperature. At point b, all the water becomes superheated steam in a gaseous state, and the temperature of the steam rises from the saturation temperature. As shown in Fig. 3, while keeping the steam supply to the expander 13 constant, the load on the motor * generalizer 18 was reduced and the rotational speed of the expander 13 was increased stepwise. The steam pressure decreases, and the steam temperature temporarily drops due to the latent heat of vaporization and the heat of expansion of the water. That is, as shown in FIG. 2C, the saturation temperature decreases, points a and b shift to the water inlet 22 a side, and the temperature of the steam discharged from the steam outlet 22 b temporarily drops. The rate of decrease in steam temperature is proportional to the rate of decrease in steam pressure, and is on the order of several seconds. Thereafter, as shown in FIG. 2D, the working medium in the heat transfer tube 22 continues to receive the thermal energy of the exhaust gas and rises in temperature, and as shown in FIG. 3, before the rotational speed of the expander 13 is increased. Return to the temperature of Since this temperature change is affected by the heat mass of the evaporator 12, it is on the order of tens to hundreds of seconds. As described above, by increasing or decreasing the number of revolutions of the expander 13, the steam temperature at the outlet of the evaporator 12 can be temporally controlled with good responsiveness.

As described above, a change in the steam temperature due to an increase or decrease in the number of revolutions of the expander 13] is temporary, and the steam temperature returns to its original value over time. At the same time, the amount of water supplied from the injector 17 to the evaporator 12 is controlled. For example, increasing the steam temperature at the outlet of the evaporator 12, as shown in FIG. steam The temperature slowly rises on the order of several tens to several hundreds of seconds and converges to a predetermined temperature. As described above, the control of steam temperature by increasing or decreasing the amount of supplied water has extremely low responsiveness, but at the same time, the rotational speed of the expander 13 is increased stepwise as shown in Fig. 4B. By reducing the temperature and temporarily increasing the steam temperature, the steam temperature can be controlled to the target steam temperature with good responsiveness and high accuracy, as shown in Fig. 4C. It is possible to maximize the overall efficiency combining the efficiency and the expander efficiency.

Next, the above operation will be further described with reference to the flowcharts of FIGS.

First, in step S1, the steam temperature T at the outlet of the evaporator 12 is detected by the steam temperature sensor 19, and in step S2, the operating state of the engine 11, that is, the engine speed Ne, the intake negative pressure Pb, and the exhaust detecting the gas temperature Tg and the air-fuel ratio AZF, and out calculation based on the amount of water supplied Fidofowa one de value Q _FF in step S 3 Ne, Pb, Tg, the a / F.

FIG. 6 shows the subroutine of step S3. In step S11, the engine speed Ne and the intake negative pressure Pb are applied to the map shown in FIG. 8 to find the fuel flow rate G _F of the engine 11. I do. As the fuel flow rate G _F is larger engine speed Ne, the larger is higher or intake negative pressure Pb. Incidentally, the fuel flow rate G _F sharply increases the intake negative pressure Pb is high region, a because the fuel is made rich at the time of high load of the engine 1 1. In the following step _S12 , the exhaust gas flow rate G _GAS is calculated by (A / F + 1) XG _F using the air-fuel ratio AZF and the fuel flow rate G _F. Then the exhaust gas flow rate G _GAS and exhaust gas temperature Tg in Step S 1 3 is applied to the map of FIG. 9 searches the water supply amount Fidofowa one de value Q _FF. The feedwater feedforward value Q _FF increases as the exhaust gas flow rate GGAS increases and the exhaust gas temperature Tg increases. The feedwater feedforward value Q _FF is the target steam temperature T. It is corrected to increase slightly according to the rise of.

When the feedwater feedforward value Q _FF is calculated in this manner, the flow returns to the flowchart of FIG. Calculated from feedwater feedforward value _QFF . Since the amount of water supply changes according to the rotation speed of the water supply pump 16, Instead of S 4, the water supply command value of the injector 1 7 Step S 4 ', i.e. the rotational speed N of the water supply pump 1 6 may be calculated from the amount of water supply Fidofowa one de value Q _FF. In the following step S5, the steam temperature T is set to the target steam temperature T. Calculate the target rotation speed Ν _{膨張} of the expander 13 for controlling the rotation speed. FIG. 7 shows the subroutine of step S5. If the steam temperature を exceeds the target steam temperature T _Q in step _S21 , the rotation speed is increased or decreased to the target expander rotation speed N _EXP in step S22. the amount _Δ Ν ΕΧΡ to the summing, steam temperature T conversely if the target steam temperature T ₀ or less, subtracts the rotational speed decrease amount _Δ Ν ΕΧΡ from targets expander rotational speed N _EXP step S 2 3. Then, in step _S6 of the flowchart in FIG. 5, the target expander rotation speed Ν is output as a command value, and the load generated by the motor generator 18 is changed to control the rotation speed of the expander 13.

Next, a second embodiment of the present invention will be described based on FIG. 10 and FIG. The flow chart of FIG. 10 is obtained by adding steps S 3 A and S 3 B after step S 3 (calculating the water supply amount feedforward value) of the flow chart of FIG. 5 (first embodiment). Substantially the same. That is, the deviation T. of the water supply feedback value Q _FB target steam temperature T ₀ and the steam temperature T in step S 3 A Calculated as a single PID calculation value. Then Step S 3 water supply amount by adding the amount of water supply feedback value Q _FB water supply amount Fidofowa one de value Q _FF in beta Q. Calculate the water supply amount Q in step S 4 (or step S 4 ′). Calculate the water supply command value based on.

When calculating the target expander rotational speed N _EXP in step S5 (see FIG. 7), as shown in FIG. 11, when the steam flow rate is small, the rotational speed increase / decrease Δ Ν _目標 of the target expander rotational speed N _EXP is _reduced. Although the steam temperature can be changed even if it is small, when the steam flow rate is large, the steam temperature cannot be changed without increasing the rotation speed increase / decrease AN _EXP of the target expander speed Ν _ΕΧΡ . Also target steam temperature T. _{蒸気} ₀ — When T is large, increase or decrease the rotation speed Δ Ν 、 and increase the deviation Τ. When Τ is small, the expander speed can be quickly converged to the target expander speed N _EXP by reducing the rotational speed increase / decrease amount AN _EXP . As described above, according to the second embodiment, the feedforward control and the feedback By using this control together with the expansion control, it is possible to converge the expander rotational speed more precisely to the target expander rotational speed N _EXP .

Although the embodiments of the present invention have been described in detail, various design changes can be made in the present invention without departing from the gist thereof.

For example, in the flowchart of FIG. 6, the feedwater feedforward value _QFF is calculated based on Ne, Pb, Tg, and AZF, but the flowrate sensor may directly detect the exhaust gas flow rate.

Although Matsupu are retrieved in step S 1 1 of the flowchart of FIG. 6 fuel flow G _F of the engine 1 1 from the engine speed N e and the intake negative pressure P b, then from the fuel injection amount of E engine 1 1 It may be calculated.

The working medium is not limited to water (steam), and any other suitable working medium can be used.

Claims

The scope of the claims

The evaporator (12), which heats the liquid-phase working medium with the exhaust gas of (11) to generate a gas-phase working medium, and converts the heat energy of the gas-phase working medium generated by the evaporator (12) into mechanical energy Rankine cycle device equipped with a positive displacement expander (13)

In order to match the temperature of the gas-phase working medium at the outlet of the evaporator (12) with the target temperature, control the supply amount of the liquid-phase working medium to the evaporator (12), and rotate the expander (13). Rankine cycle device comprising control means (20) for controlling the number