JP2024071857A - Waste heat recovery device for internal combustion engine - Google Patents

Abstract

To provide a waste heat recovery device for an internal combustion engine capable of recovering exhaust heat as much as possible while appropriately radiating heat in accordance with load of the internal combustion engine.SOLUTION: A waste heat recovery device for an internal combustion engine includes: a cooling water circuit 3 in which cooling water for cooling an internal combustion engine 2 circulates and that has a radiator 33 for radiating heat; a Rankine cycle circuit 5 in which a working medium with a low-boiling point circulates and that has an evaporator 53, an expander 54 and a power generator 56; an exhaust heat recovery circuit 4 branched from a branch part of the cooling water circuit 3, passing through an exhaust heat recovery device 22 and the evaporator 53 and merging with a portion between the branch part of the cooling water circuit 3 and the radiator 33; a first selector valve 44 that switches a flow of the cooling water from the branch part side to the exhaust heat recovery device 22 side or the side bypassing the same; and a second selector valve 58 that switches a flow of the working medium from the evaporator 53 side to the expander 54 side or the side bypassing the same. The first and second selector valves 44, 58 are switched in accordance with a load of the internal combustion engine 2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a waste heat recovery device for an internal combustion engine for recovering waste heat generated by combustion in the internal combustion engine.

A conventional waste heat recovery device for an internal combustion engine is disclosed in, for example, Patent Document 1. This waste heat recovery device includes a cooling water circuit (radiator cooling water circuit) through which the cooling water of the internal combustion engine circulates and which has a radiator, a Rankine cycle (ORC) circuit through which an organic medium with a lower boiling point than the cooling water circulates and which has an evaporator, an expander, and a condenser, an exhaust heat recovery device that recovers exhaust heat from the internal combustion engine, a Rankine cycle cooling water circuit (ORC cooling water circuit) that branches off from the radiator cooling water circuit downstream of the internal combustion engine, passes through the exhaust heat recovery device and the evaporator, and merges with the cooling water circuit upstream of the internal combustion engine, and a switching means that switches the flow of cooling water in the ORC cooling water circuit between a flow that passes through the exhaust heat recovery device and the evaporator, or a flow that passes only through the evaporator.

In this waste heat recovery system, when the detected coolant temperature, for example the coolant temperature downstream of the internal combustion engine, is within an appropriate temperature range (for example, 80 to 95°C), the flow of coolant in the ORC coolant circuit is switched to a flow that passes through the exhaust heat recovery device and the evaporator. As a result, the coolant in the ORC coolant circuit receives exhaust heat in the exhaust heat recovery device, and then transfers heat to the low-boiling organic medium in the ORC circuit in the evaporator, causing it to be vaporized. The vaporized organic medium drives the expander, converting the thermal energy of the organic medium into mechanical energy, which is then recovered (regenerated) as electrical energy by the generator connected to the expander.

When the cooling water temperature is higher than the above-mentioned optimum temperature range, the flow of the cooling water is switched to flow only through the evaporator. As a result, the temperature of the cooling water in the RC cooling water circuit is reduced by transferring heat to the organic medium in the evaporator without receiving exhaust heat in the exhaust heat recovery device.

JP 2010-138697 A

When regenerating using a Rankine cycle circuit, the more heat input, the greater the amount of regeneration that can be obtained. Therefore, when exhaust heat is used as the heat source as described above, it is desirable to transfer as much of the exhaust heat as possible to the coolant. However, in conventional waste heat recovery devices, the coolant that flows out of the evaporator is configured to merge with the radiator coolant circuit and then flow into the internal combustion engine before the radiator. For this reason, if the amount of exhaust heat transferred to the coolant is increased, the high-temperature coolant will flow into the internal combustion engine without being dissipated, which will cause the coolant temperature to rise and fall outside the optimum temperature range. This makes it necessary to limit the amount of exhaust heat, and it is not possible to obtain a sufficient amount of regeneration.

The present invention was made to solve these problems, and aims to provide a waste heat recovery device for an internal combustion engine that can recover as much exhaust heat as possible while appropriately dissipating heat according to the load of the internal combustion engine. This will ultimately promote the reuse of energy and contribute to improving energy efficiency.

In order to achieve this object, the invention according to claim 1 is a waste heat recovery device for an internal combustion engine for recovering waste heat generated by combustion in the internal combustion engine, comprising a cooling water circuit 3 having a cooling water pump (first pump 32 in the embodiment (hereinafter the same in this paragraph)) through which cooling water for cooling the internal combustion engine 2 circulates and which delivers the cooling water, and a radiator 33 for dissipating heat from the cooling water, a working medium pump (second pump 52) through which a working medium having a lower boiling point than the cooling water circulates and which delivers the working medium, an evaporator 53 which heats and vaporizes the working medium by heat exchange with the cooling water, an expander 54 which expands and decompresses the vaporized working medium and converts the thermal energy of the working medium into mechanical energy, a generator 56 which generates electricity by the mechanical energy, and a condenser 55 which cools and liquefies the working medium flowing out of the expander 54 by heat exchange with outside air, and a Rankine cycle circuit 5 which is provided in an exhaust passage 21 of the internal combustion engine 2 and has a condenser 55 for cooling and liquefying the working medium flowing out of the expander 54, and an exhaust heat recovery circuit 4 that branches off from a branch portion of the coolant circuit 3 downstream of the internal combustion engine 2, passes through the exhaust heat recovery device 22 to receive heat, passes through an evaporator 53 to transfer heat, and joins a joining portion between the branch portion of the coolant circuit 3 and a radiator 33, the exhaust heat recovery circuit 4 including a first bypass passage 42 that bypasses the exhaust heat recovery device 22, and a first switching valve 44 that switches the flow of coolant from the branch portion side to the exhaust heat recovery device 22 side or the first bypass passage 42 side. The Rankine cycle circuit 5 has a second bypass passage 57 that bypasses the expander 54, and a second switching valve 58 that switches the flow of the working medium from the evaporator 53 side to the expander 54 side or the second bypass passage 57 side, and is further characterized by having a load acquisition means (accelerator opening sensor 65) that acquires the load (accelerator opening AP) of the internal combustion engine 2, and a control means (ECU 6) that controls the first switching valve 44 and the second switching valve 58 according to the acquired load of the internal combustion engine 2.

As described above, the waste heat recovery device for an internal combustion engine of the present invention includes a coolant circuit through which the coolant for the internal combustion engine circulates and which has a radiator for dissipating heat from the coolant, a Rankine cycle circuit through which a working medium with a boiling point lower than that of the coolant circulates and which has an evaporator, an expander, a generator, and the like, an exhaust heat recovery device that recovers heat from the exhaust, an exhaust heat recovery circuit that branches off from a branch point downstream of the internal combustion engine of the coolant circuit, passes through the exhaust heat recovery device and the evaporator in order, and merges into a junction between the branch point of the coolant circuit and the radiator, a first switching valve that switches the flow of the coolant from the branch point side to the exhaust heat recovery device side or a first bypass passage side that bypasses it, and a second switching valve that switches the flow of the working medium from the evaporator side to the expander side or a second bypass passage side that bypasses it.

According to the present invention, the load of the internal combustion engine is acquired. In this case, the load of the internal combustion engine represents the degree of heat dissipation required to dissipate the heat generated in the cooling water due to the combustion in the internal combustion engine. Then, the first switching valve and the second switching valve are switched according to the acquired load of the internal combustion engine.

For example, when the load on the internal combustion engine is relatively small (when the heat dissipation requirement is relatively small), the first switching valve of the cooling water circuit is switched to the exhaust heat recovery device side, and the second switching valve of the Rankine cycle circuit is switched to the expander side. As a result, the cooling water receives exhaust heat in the exhaust heat recovery device, and then transfers heat to the working medium in the evaporator. The expander is driven by the vaporized working medium, and the generator generates electricity, converting the exhaust heat into electrical energy and recovering (regenerating). In this case, since the original heat dissipation requirement is small, the cooling water appropriately dissipates heat by the radiator, combining this heat dissipation requirement with the heat received from the exhaust heat.

On the other hand, for example, when the load on the internal combustion engine is relatively large (when the heat dissipation requirement is relatively large), the first switching valve is switched to the first bypass passage side, and the second switching valve is switched to the second bypass passage side. As a result, the coolant does not receive exhaust heat and the expander is not driven, and the coolant transfers heat to the working medium in the evaporator, and then the heat is appropriately dissipated by the radiator. As described above, it is possible to recover as much exhaust heat as possible while appropriately dissipating heat according to the load on the internal combustion engine, i.e., the heat dissipation requirement.

The invention according to claim 2 is characterized in that in the waste heat recovery device for an internal combustion engine described in claim 1, the control means switches the first switching valve 44 to the exhaust heat recovery device 22 side and switches the second switching valve 58 to the expander 54 side when the internal combustion engine 2 is in a low to medium load state (steps 1 and 2 in FIG. 2).

According to this configuration, when the internal combustion engine is in a low to medium load state and the amount of heat of the cooling water flowing out of the internal combustion engine is not excessive (when the heat dissipation requirement is small), the first and second switching valves are switched as described above, so that the cooling water flows to the exhaust heat recovery device and the working medium flows to the expander. As a result, exhaust heat is transferred to the cooling water in the exhaust heat recovery device, the expander is driven by the vaporized working medium, and electricity is generated by the generator, so that the maximum amount of exhaust heat can be recovered and energy efficiency can be improved. In addition, the heat dissipation of the cooling water can be appropriately performed by the radiator, combining the original heat dissipation requirement and the heat received from the exhaust heat.

The invention according to claim 3 is characterized in that in the waste heat recovery device for an internal combustion engine described in claim 1, the control means switches the first switching valve 44 to the first bypass passage 42 side and switches the second switching valve 58 to the second bypass passage 57 side when the internal combustion engine 2 is in a high load state (steps 1 and 3 in FIG. 2).

According to this configuration, when the internal combustion engine is in a high load state and the heat amount of the cooling water flowing out of the internal combustion engine is excessive (when the heat dissipation demand is large), the first and second switching valves are switched as described above, so that the cooling water does not flow to the exhaust heat recovery device and the working medium does not flow to the expander. As a result, the cooling water does not receive exhaust heat and the expander is not driven, and the cooling water flows into the radiator after transferring heat to the working medium in the evaporator, so that the radiator can properly dissipate heat from the cooling water.

The invention according to claim 4 is characterized in that, in the waste heat recovery device for an internal combustion engine according to any one of claims 1 to 3, it further comprises a flow control valve 43 provided at the branch of the cooling water circuit 3 for controlling the flow rate ratio RQW between the cooling water flow rate flowing from the branch to the radiator 33 side and the cooling water flow rate flowing to the exhaust heat recovery circuit 4 side, and a heat radiation amount calculation means (ECU 6, step 4 in FIG. 2) for calculating the heat radiation amount QHR of the radiator 33, and the control means controls the flow control valve 43 so that the calculated heat radiation amount QHR becomes the maximum heat radiation capacity QHMAX of the radiator 33 (steps 5 and 6 in FIG. 2).

According to this configuration, a flow control valve is provided at the branch of the cooling water circuit, and this flow control valve controls the flow ratio between the flow rate of the cooling water flowing from the branch to the radiator side and the flow rate of the cooling water flowing to the exhaust heat recovery circuit side. In addition, the amount of heat dissipation of the radiator is calculated, and the flow control valve is controlled so that the calculated amount of heat dissipation is the maximum heat dissipation capacity of the radiator. As a result, the maximum heat dissipation capacity of the radiator is always exerted, and exhaust heat can be recovered to the maximum while satisfying the heat dissipation requirements as much as possible. In addition, when the internal combustion engine is in a high load state and the heat dissipation requirements exceed the maximum heat dissipation capacity of the radiator, the shortage of heat dissipation capacity is compensated for by heat dissipation through the Rankine cycle circuit, so there is no need to increase the maximum heat dissipation capacity of the radiator, and it is possible to reduce its size.

1 is a diagram illustrating a schematic diagram of a waste heat recovery device for an internal combustion engine according to an embodiment of the present invention. 4 is a flowchart showing a waste heat recovery control process executed by the ECU of FIG. 1 . FIG. 4 is a diagram showing the operation of the waste heat recovery device when the internal combustion engine is in a low to medium load state. FIG. 4 is a diagram illustrating the operation of the waste heat recovery device when the internal combustion engine is in a high load state. FIG. 4 is a diagram showing the relationship between the load range of the internal combustion engine and waste heat recovery control according to the embodiment, together with a comparative example.

Below, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an internal combustion engine waste heat recovery device 1 according to an embodiment. The waste heat recovery device 1 recovers waste heat generated by combustion in an internal combustion engine (hereinafter referred to as "engine") 2 mounted as a power source in, for example, a vehicle (not shown).

As shown in FIG. 1, the waste heat recovery device 1 includes a cooling water circuit 3 through which cooling water for cooling the engine (ENG) 2 circulates, an exhaust heat recovery circuit 4 that branches off from the cooling water circuit 3 and through an exhaust heat recovery device 22 (described later) through which the cooling water circulates, a Rankine cycle (ORC) circuit 5 through which an organic medium (e.g., silicon oil) as a working medium circulates and which constitutes a Rankine cycle, and an ECU (electronic control unit) 6 that controls the operation of these circuits. Note that in FIG. 1 and FIGS. 3 and 4 described later, the flow paths through which the cooling water or exhaust (exhaust gas) flows are indicated by thick lines, and the flow paths through which the organic medium flows are indicated by thin lines.

An exhaust heat recovery device 22 is provided in the exhaust passage 21 of the engine 2 to recover the heat (exhaust heat) of the exhaust gas discharged from the engine 2.

The cooling water circuit 3 has a ring-shaped cooling water passage 31 that passes through the engine 2, and a first pump 32 and a radiator (RAD) 33 that are provided along the cooling water passage 31. The first pump 32 is disposed upstream of the engine 2 and sends the cooling water to the engine 2 side. The radiator 33 is disposed downstream of the engine 2 and cools the cooling water by heat exchange with the outside air and dissipates heat. The cooling water circuit 3 also has a radiator bypass passage 34 that is connected to the cooling water passage 31 so as to bypass the radiator 33, and a thermostat 35 is provided at the connection part downstream of the radiator 33. The thermostat 35 is configured to be maintained in a closed state when the temperature of the cooling water is equal to or lower than a predetermined temperature (e.g., 80°C), so that the cooling water flows to the radiator bypass passage 34 side, and to open the valve when the temperature exceeds the predetermined temperature, so that the cooling water flows to the radiator 33 side.

The exhaust heat recovery circuit 4 has an annular exhaust heat recovery passage 41 and a first bypass passage 42. The exhaust heat recovery passage 41 branches from a branch downstream of the engine 2 of the cooling water passage 31, passes through the exhaust heat recovery device 22 and an evaporator 53 of the Rankine cycle circuit 5, and merges with the junction 36 between the branch of the cooling water passage 31 and the radiator 33. A flow control valve 43 is provided at this branch. The flow control valve 43 is capable of continuously adjusting the flow rate ratio RQW between the cooling water flow rate flowing from the engine 2 through the branch to the radiator 33 side and the cooling water flow rate flowing to the exhaust heat recovery circuit 4 side according to the valve opening degree, and its operation is controlled by the ECU 6.

The first bypass passage 42 is connected to the exhaust heat recovery flow path 41 so as to bypass the exhaust heat recovery device 22, and a first switching valve 44 is provided at the connection part upstream of the exhaust heat recovery device 22. The first switching valve 44 switches the flow of cooling water from the branch part side to either the exhaust heat recovery device 22 side or the first bypass passage 42 side.

The Rankine cycle circuit 5 has a ring-shaped organic medium flow path 51 through which the organic medium circulates, a second pump 52, an evaporator 53, an expander 54, and a condenser 55 arranged in sequence along the organic medium flow path 51, and a generator 56 connected to the expander 54. The second pump 52 sends the liquid organic medium to the evaporator 53. The evaporator 53 heats the organic medium by heat exchange with the cooling water and vaporizes (evaporates). The expander 54 expands and decompresses the vaporized organic medium, and converts the thermal energy of the organic medium into mechanical energy. The generator 56 generates electricity using the mechanical energy of the expander 54, and recovers (regenerates) it as electrical energy in a battery (not shown). The condenser 55 cools the organic medium flowing out of the expander 54 by heat exchange with the outside air, and liquefies (condenses).

The Rankine cycle circuit 5 also has a second bypass passage 57 connected to the organic medium flow path 51 so as to bypass the expander 54, and a second switching valve 58 is provided at the connection on the evaporator 53 side. The second switching valve 58 switches the flow of the organic medium from the evaporator 53 side to either the expander 54 side or the second bypass passage 57 side. The second bypass passage 57 also has a pressure control valve 59 that controls the pressure of the organic medium.

A first water temperature sensor 61 is provided upstream of the evaporator 53 in the exhaust heat recovery passage 41, and second and third water temperature sensors 62, 63 are provided upstream and downstream of the radiator 33 in the cooling water passage 31, respectively. The first to third water temperature sensors 61 to 63 detect the temperature of the cooling water at their respective positions as first to third water temperatures TW1 to TW3, and output the detection signals to the ECU 6.

A flow sensor 64 is provided upstream of the radiator 33. The flow sensor 64 detects the coolant flow rate QW flowing into the radiator 33 and outputs a detection signal to the ECU 6. The ECU 6 also receives a detection signal from an accelerator position sensor 65 indicating the amount of depression of the accelerator pedal (not shown) of the vehicle (hereinafter referred to as "accelerator position") AP.

The ECU 6 is composed of a microcomputer that includes a CPU, RAM, ROM, and an I/O interface (none of which are shown). The ECU 6 controls the recovery of waste heat generated by combustion in the engine 2 in response to detection signals from the various sensors 61 to 65 described above.

Figure 2 shows the waste heat recovery control process executed by the ECU 6. This process is executed repeatedly, for example, at a predetermined cycle. First, in step 1 (shown as "S1"; the same applies below), it is determined whether the engine 2 is in a low to medium load state. This determination is made, for example, by determining whether the detected accelerator opening AP is equal to or smaller than a predetermined opening APREF, which corresponds to a low to medium load state of the engine 2.

If the result of this determination is YES and the engine 2 is in a low to medium load state, the process proceeds to step 2, where the first switching valve 44 is switched to the exhaust heat recovery device 22 side and the second switching valve 58 is switched to the expander 54 side.

Next, in step 4, the amount of heat radiation QHR from the radiator 33 is calculated. This calculation is performed, for example, based on the second and third water temperatures TW2, TW3 upstream and downstream of the radiator 33 detected by the water temperature sensors 62, 63, and the cooling water flow rate QW detected by the flow rate sensor 64.

Next, the target flow ratio RQWCMD is calculated (set) so that the calculated heat radiation amount QHR becomes the predetermined maximum heat radiation capacity QHMAX of the radiator 33 (the maximum amount of heat that the radiator 33 can dissipate). This target flow ratio RQWCMD is the target value of the flow ratio RQW (the flow ratio between the cooling water flow rate flowing from the flow control valve 43 to the radiator 33 side and the cooling water flow rate flowing to the exhaust heat recovery circuit 4 side) controlled by the flow control valve 43.

The target flow ratio RQWCMD is set, for example, when the heat dissipation amount QHR is smaller than the maximum heat dissipation capacity QHMAX and there is a margin of heat dissipation capacity, by changing the target flow ratio RQWCMD in accordance with the difference so that the proportion of the cooling water flow to the exhaust heat recovery circuit 4 side increases, and by maintaining the target flow ratio RQWCMD when the heat dissipation amount QHR is approximately equal to the maximum heat dissipation capacity QHMAX.

Next, based on the calculated target flow ratio RQWCMD, the valve opening of the flow control valve 43 is controlled so as to obtain the target flow ratio RQWCMD, and this process ends.

Figure 3 shows the operation obtained by the above-mentioned control when the engine 2 is in a low to medium load state. In Figures 3 and 4, the flow paths through which the coolant and organic medium flow are indicated by solid lines, and the flow paths through which they do not flow are indicated by dotted lines. First, in the coolant circuit 3, the coolant flows clockwise through the coolant flow path 31 by the operation of the first pump 32. The high-temperature coolant flowing out of the engine 2 is distributed to the radiator 33 side and the exhaust heat recovery circuit 4 side by the control of the flow control valve 43 so as to achieve the target flow ratio RQWCMD set in step 5.

The coolant distributed to the exhaust heat recovery circuit 4 flows into the exhaust heat recovery device 22 by switching the first switching valve 44 in step 2, and receives heat through heat exchange with the exhaust gas. The heated coolant then flows into the evaporator 53 of the Rankine cycle circuit 5, where it transfers heat to the organic medium through heat exchange, vaporizing (evaporating) the organic medium while being cooled. The coolant then merges with the high-temperature coolant sent directly from the engine 2 at the junction 36 of the coolant flow path 31, and then exchanges heat with the outside air in the radiator 33, dissipating heat.

Meanwhile, in the Rankine cycle circuit 5, the organic medium flows clockwise through the organic medium flow path 51 by the operation of the second pump 52, and is vaporized in the evaporator 53 by heat exchange with the cooling water that has been heated by the exhaust heat recovery device 22. The vaporized organic medium is sent to the expander 54 by switching the second switching valve 58 in step 2, and is reduced in pressure and cooled in the expander 54. The thermal energy of the reduced-pressure, reduced-temperature organic medium is converted into mechanical energy in the expander 54, and is further used to generate electricity in the generator 56, and is recovered (regenerated) as electrical energy in the battery. The organic medium is then cooled by heat exchange with the outside air in the condenser 55, liquefied, and returned to the second pump 52.

As described above, in low to medium load conditions where the heat dissipation requirement of the engine 2 is small, as shown in FIG. 5(b), the amount of heat equivalent to the surplus capacity obtained by subtracting the heat dissipation requirement from the maximum heat dissipation capacity of the radiator 33 is transferred from the exhaust gas (exhaust) to the coolant, and power is generated in the Rankine cycle circuit 5, so that the maximum amount of exhaust heat can be recovered as electrical energy, improving energy efficiency. Also, unlike the conventional case (a) where heat dissipation is performed only by the radiator, by controlling the flow rate ratio RQW using the flow control valve 43, the maximum heat dissipation capacity of the radiator 33 is always exerted, and heat dissipation from the coolant can be appropriately performed by combining the original heat dissipation requirement and the heat received from the exhaust heat.

Returning to the waste heat recovery control process in FIG. 2, if the determination result in step 1 is NO and the engine 2 is in a high load state, the process proceeds to step 3, where the first switching valve 44 is switched to the first bypass passage 42 side and the second switching valve 58 is switched to the second bypass passage 57 side.

The processing after step 3 is the same as when the engine 2 is in a low to medium load state described above, and by executing steps 4 to 6, the calculation of the heat dissipation amount QHR of the radiator 33, the calculation of the maximum heat dissipation capacity QHMAX of the radiator 33 and the target flow ratio RQWCMD according to the heat dissipation amount QHR, and the control of the flow control valve 43 based on the target flow ratio RQWCMD are performed in the same manner.

Figure 4 shows the operation obtained by the above-mentioned control when the engine 2 is in a high load state. First, the operation in the cooling water circuit 3 is the same as when the engine 2 is in a low to medium load state, and the cooling water flows clockwise through the cooling water passage 31 and, after flowing out of the engine 2, is distributed to the radiator 33 side and the exhaust heat recovery circuit 4 side by the control of the flow control valve 43 so as to achieve the target flow ratio RQWCMD set in step 5.

The cooling water distributed to the exhaust heat recovery circuit 4 does not flow to the exhaust heat recovery device 22 but flows into the first bypass passage 42 due to the switching of the first switching valve 44 in step 3. Therefore, the cooling water flows directly into the evaporator 53 without receiving heat from the exhaust heat. The operation thereafter is the same as in the low to medium load state, and the cooling water transfers heat to the organic medium through heat exchange in the evaporator 53 while being cooled itself. The cooling water then flows into the confluence 36 of the cooling water flow path 31, where it merges with the high-temperature cooling water sent directly from the engine 2, and is then heat-exchanged with the outside air in the radiator 33, where heat is dissipated.

On the other hand, in the Rankine cycle circuit 5, the organic medium flows in the organic medium flow path 51 in a clockwise direction, and in the evaporator 53, the organic medium is heat-exchanged with the cooling water that has been heated by the exhaust heat recovery device 22. In this case, by switching the second switching valve 58 in step 3, the organic medium does not flow to the expander 54 side, but flows into the second bypass passage 57, and the pressure control valve 59 is operated. As a result, the pressure in the Rankine cycle circuit 5 decreases, and the boiling point of the organic medium decreases, so that the temperature difference between the high-temperature cooling water flowing into the evaporator 53 and the organic medium increases, and the cooling capacity (heat dissipation capacity) of the cooling water in the evaporator 53 can be increased. The cooling water thus cooled merges with the high-temperature cooling water sent directly from the engine 2 at the junction 36 of the cooling water flow path 31, and then exchanges heat with the outside air in the radiator 33 and dissipates heat. The organic medium also flows into the condenser 55, where it is cooled by heat exchange with the outside air, liquefied, and then returns to the second pump 52.

As described above, when the engine 2 is under high load and the heat dissipation requirement is high, the coolant does not receive exhaust heat and the expander 54 is not driven, and the coolant flows into the radiator 33 after transferring (dissipating) heat to the organic medium in the evaporator 53, so that the heat dissipation from the coolant can be appropriately performed by the radiator 33. Also, as shown in FIG. 5, the amount of heat that exceeds the maximum heat dissipation capacity of the radiator 33 is dissipated in the Rankine cycle circuit 5, so that the maximum heat dissipation capacity of the radiator 33 can be reduced by that amount, and the radiator 33 can be made smaller.

The present invention is not limited to the embodiment described above, and can be implemented in various ways. For example, in the embodiment, the accelerator opening AP is used as the load that indicates the degree of heat dissipation requirement of the engine 2, but this is not limiting, and other parameters that appropriately indicate the load of the engine 2, such as the fuel injection amount, the intake air amount, or the cooling water temperature near the outlet of the engine 2, may be used.

In the embodiment, the calculation of the heat radiation amount QHR of the radiator 33 is described as being performed based on the second and third water temperatures TW2, TW3 upstream and downstream of the radiator 33 and the cooling water flow rate QW, but any calculation method may be used as long as the calculation accuracy can be ensured.

In addition, in the embodiment, the determination of whether the engine 2 is in a low to medium load state is made by comparing the detected accelerator opening AP with a single predetermined opening APREF, but control hunting according to the comparison result may be avoided by setting hysteresis in this predetermined opening APREF. In addition, the specific configurations and numerical values shown in the embodiment are merely examples, and the detailed configurations can be changed within the scope of the spirit of the present invention.

1 Waste heat recovery device 2 Internal combustion engine
3 Cooling water circuit 4 Exhaust heat recovery circuit 5 Rankine cycle circuit 6 ECU (control means, heat radiation amount calculation means)
21 exhaust passage 22 exhaust heat recovery device 32 first pump (cooling water pump)
33 Radiator 36 Junction 42 First bypass passage 44 First switching valve 52 Second pump (working medium pump)
53 Evaporator 54 Expander 55 Condenser 57 Second bypass passage 58 Second switching valve 65 Accelerator opening sensor (load acquisition means)
AP Accelerator opening (load on internal combustion engine)
RQW Flow ratio QHR Radiator heat dissipation amount QHMAX Radiator maximum heat dissipation capacity

Claims (4)

A waste heat recovery device for an internal combustion engine for recovering waste heat generated by combustion in the internal combustion engine,
a cooling water circuit through which cooling water for cooling the internal combustion engine circulates, the cooling water circuit having a cooling water pump for delivering the cooling water and a radiator for dissipating heat from the cooling water;
a Rankine cycle circuit including a working medium pump through which a working medium having a boiling point lower than that of cooling water circulates and which delivers the working medium, an evaporator which heats and vaporizes the working medium by heat exchange with the cooling water, an expander which expands and reduces the pressure of the vaporized working medium and converts the thermal energy of the working medium into mechanical energy, a generator which generates electricity using the mechanical energy, and a condenser which cools and liquefies the working medium flowing out of the expander by heat exchange with outside air;
an exhaust heat recovery device provided in an exhaust passage of the internal combustion engine and configured to recover heat from exhaust gas;
an exhaust heat recovery circuit that branches off from a branching portion of the cooling water circuit downstream of the internal combustion engine, passes through the exhaust heat recovery device to receive heat, passes through the evaporator to transfer heat, and joins between the branching portion of the cooling water circuit and the radiator,
the exhaust heat recovery circuit includes a first bypass passage that bypasses the exhaust heat recovery device, and a first switching valve that switches a flow of cooling water from the branching portion side to the exhaust heat recovery device side or the first bypass passage side,
the Rankine cycle circuit includes a second bypass passage that bypasses the expander, and a second switching valve that switches a flow of the working medium from the evaporator side to the expander side or the second bypass passage side,
A load acquisition means for acquiring a load of the internal combustion engine;
a control unit that controls the first changeover valve and the second changeover valve in accordance with the acquired load of the internal combustion engine. The waste heat recovery device for an internal combustion engine according to claim 1, characterized in that the control means switches the first switching valve to the exhaust heat recovery device side and the second switching valve to the expander side when the internal combustion engine is in a low to medium load state. The waste heat recovery device for an internal combustion engine according to claim 1, characterized in that the control means switches the first switching valve to the first bypass passage side and switches the second switching valve to the second bypass passage side when the internal combustion engine is in a high load state. a flow control valve provided at the branching portion of the cooling water circuit for controlling a flow rate ratio between a flow rate of the cooling water flowing from the branching portion to the radiator side and a flow rate of the cooling water flowing to the exhaust heat recovery circuit side;
and a heat radiation amount calculation means for calculating a heat radiation amount of the radiator.
4. The waste heat recovery device for an internal combustion engine according to claim 1, wherein the control means controls the flow control valve so that the calculated amount of heat radiation becomes equal to a maximum heat radiation capacity of the radiator.