JP2013181394A - Waste heat recovery device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste heat recovery device of an engine, which can rapidly elevate a cooling water temperature by using Rankine cycle during a warm-up period or the like of the engine and can early complete the warm-up.SOLUTION: An exhaust side heat exchanger 48 installed in an exhaust passage 45 of an engine 2, a cooling water side heat exchanger 51 disposed in a cooling water passage 52, and an expander 64 are connected into a loop through a working fluid passage 63; and a bypass 70 bypassing the expander 64 is disposed. During warming up the engine 2, a working fluid is changed into superheated vapor by heat exchange with exhaust gas in the exhaust side heat exchanger 48, then bypasses the expander 64 by switching of third and fourth valves 68, 69 and circulated into the cooling water side heat exchanger 51. Thus, a temperature of the cooling water can be rapidly elevated by heat exchanging with a working fluid of high temperature and high pressure which is not depressurized nor expanded in the expander 64. After warm-up is completed, the working fluid is circulated into the expander 64 by the switching of the third and fourth valves 68, 69 to extract power which is used to drive an electric power generator 66.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine waste heat recovery device, and more specifically, a so-called Rankine cycle in which a working fluid circulating in a cycle exchanges heat with exhaust gas exhausted from the engine, The present invention relates to a waste heat recovery device for an engine using the above.

Conventionally, an engine waste heat recovery device using a Rankine cycle has been proposed in order to effectively use waste heat of exhaust gas discharged from the engine (see, for example, Patent Document 1).
In the technology disclosed in Patent Document 1, the working fluid circulating in the cycle is heat-exchanged with the exhaust gas of the engine with a steam generator, and the working fluid changed to superheated steam is decompressed and expanded with an expander and taken out as power, A generator is driven by the power to generate electricity. Furthermore, in order to use the heat remaining in the working fluid after decompression and expansion, when the engine starts cold, the working fluid is heated with the engine cooling water to warm up the cooling water. Time is shortened.

JP 2005-42618 A

However, the amount of heat remaining in the working fluid after expansion under reduced pressure is not so much. This means that sufficient heat exchange with the engine cooling water cannot be expected, and there has been a problem that the engine warm-up time can hardly be shortened because the cooling water temperature cannot be quickly raised. Therefore, engine warm-up has been prolonged, unburned hydrocarbons (HC) have increased, and fuel consumption has also deteriorated due to fuel increase, and countermeasures have been conventionally demanded.
The present invention has been made to solve such problems, and the object of the present invention is to quickly raise the cooling water temperature by using the Rankine cycle when the engine is warmed up, etc. It is an object of the present invention to provide a waste heat recovery device for an engine that can be completed and that can achieve reduction of unburned hydrocarbons and improvement of fuel consumption.

  In order to achieve the above object, a first aspect of the present invention provides a pump that circulates a working fluid in a cycle, a first heat exchanger that exchanges heat between exhaust gas discharged from an engine and the working fluid in the cycle, An expander that decompresses and expands the working fluid heat-exchanged by the first heat exchanger, a second heat exchanger that exchanges heat between the engine coolant and the working fluid in the cycle, and expands the working fluid in the cycle A first bypass passage to be bypassed from the vessel, cooling water temperature detecting means for detecting the temperature of the cooling water, and operation when the temperature of the cooling water detected by the cooling water temperature detecting means is equal to or higher than a predetermined determination value. And a first switching means for performing switching control so that the working fluid flows through the first bypass passage when the temperature of the cooling water is lower than the determination value without flowing the fluid through the first bypass passage. .

The invention of claim 2 is mounted on a hybrid vehicle having a travel motor driven by a travel battery together with an engine as a travel drive source in claim 1, and the expander is configured to generate a generator by decompression and expansion of the working fluid. The battery is driven and the generated power is charged to the battery for traveling.
According to a third aspect of the present invention, in the first or second aspect, the high pressure side EGR system for circulating the exhaust gas as EGR gas from the upstream side of the turbine of the turbocharger provided in the engine to the downstream side of the compressor, and the high pressure side EGR system A high-pressure side EGR cooler for exchanging heat between the exhaust gas to be recirculated and the working fluid in the cycle; and a second switching means for circulating the working fluid to the high-pressure side EGR cooler when the temperature of the cooling water is equal to or higher than a determination value. It is provided.

According to a fourth aspect of the present invention, in the third aspect, the low-pressure side EGR system that recirculates the exhaust gas as EGR gas from the downstream side of the turbocharger turbine to the upstream side of the compressor, and the exhaust gas recirculated by the low-pressure side EGR system and the in-cycle A low pressure side EGR cooler for exchanging heat with the working fluid, and a third switching means for circulating the working fluid to the low pressure side EGR cooler when the temperature of the cooling water is equal to or higher than a determination value.
According to a fifth aspect of the present invention, in the fourth aspect, when the temperature of the cooling water is equal to or higher than the determination value, the working fluid that has been decompressed and expanded by the expander is used as the second heat exchanger, the low-pressure side EGR cooler, In order.
A sixth aspect of the present invention provides the second bypass passage for bypassing the exhaust gas recirculated by the low-pressure side EGR system from the low-pressure side EGR cooler and the temperature of the cooling water in the first to fourth aspects when the temperature of the cooling water is equal to or higher than a determination value. And a fourth switching means for performing switching control so that the exhaust gas is allowed to flow through the second bypass passage when the temperature of the cooling water is lower than the determination value without flowing the exhaust gas through the second bypass passage.

As described above, according to the engine waste heat recovery apparatus of the first aspect, the working fluid is circulated in the order of the first heat exchanger, the expander, and the second heat exchanger, and the working fluid is expanded. When the temperature of the cooling water is equal to or higher than the determination value, the first switching means does not allow the working fluid to flow through the first bypass passage, and the temperature of the cooling water is lower than the determination value. In such a case, the working fluid was allowed to flow through the first bypass passage.
Accordingly, when the engine is warmed up when the temperature of the cooling water is less than the determination value, the working fluid flows through the first bypass passage, and the high-temperature and high-pressure working fluid that has not been decompressed and expanded by the expander is cooled by the second heat exchanger. Heat exchanged with water. Therefore, it is possible to quickly raise the temperature of the cooling water and complete warm-up at an early stage, thereby achieving reduction of unburned hydrocarbons and improvement of fuel consumption.
In addition, after the engine warm-up when the temperature of the cooling water is equal to or higher than the determination value, the working fluid can flow through the expander and take out power by decompression expansion. And since the working fluid after decompression expansion is heat-exchanged with the cooling water whose temperature has already increased in the second heat exchanger and preheated, it is possible to promote the generation of superheated steam in the subsequent first heat exchanger, Rankine cycle efficiency can be increased.

According to the engine waste heat recovery apparatus of the second aspect of the present invention, in addition to the first aspect, the generator is driven by the expander to charge the generated power to the traveling battery of the hybrid vehicle. Therefore, the waste heat of the engine can be effectively used for charging the traveling battery.
According to the waste heat recovery device for an engine of the invention of claim 3, in addition to claim 1 or 2, when the temperature of the cooling water is equal to or higher than a determination value, the working fluid is circulated to the high pressure side EGR cooler. Accordingly, the working fluid after decompression and expansion by the expander is preheated by the second heat exchanger, and is also preheated by the heat exchange with the exhaust gas in the high pressure side EGR cooler, and then the superheated steam in the first heat exchanger. Can be further promoted.

According to the waste heat recovery apparatus for an engine of the invention of claim 4, in addition to claim 3, when the temperature of the cooling water is equal to or higher than the determination value, the working fluid is circulated to the low pressure side EGR cooler. Accordingly, the working fluid after decompression expansion by the expander is preheated by the second heat exchanger and the high pressure side EGR cooler, and also preheated by the heat exchange with the exhaust gas in the low pressure side EGR cooler, and then the first heat exchange thereafter. The generation of superheated steam in the vessel can be further promoted.
According to the engine waste heat recovery apparatus of the fifth aspect of the present invention, in addition to the fourth aspect, the relatively low temperature second heat exchanger, the intermediate temperature low pressure side EGR cooler, and the high temperature high pressure side EGR cooler The working fluid was circulated in order. Therefore, the temperature of the working fluid can be shifted stepwise to the high temperature side, and loss during heat exchange can be avoided to obtain the preheating effect of the working fluid to the maximum.

According to the engine waste heat recovery apparatus of the sixth aspect of the present invention, in addition to the first to fourth aspects, the second bypass passage for bypassing the exhaust gas from the low-pressure side EGR cooler is provided, and the temperature of the cooling water is equal to or higher than the determination value. In this case, the exhaust gas is not allowed to flow through the second bypass passage, and when the temperature of the cooling water is lower than the determination value, the exhaust gas is allowed to flow through the second bypass passage.
Therefore, at the time of engine warm-up when the temperature of the cooling water is lower than the determination value, the exhaust gas flows through the second bypass passage without flowing through the low-pressure side EGR cooler. If the exhaust gas is cooled by the low-pressure EGR cooler when the engine is warmed up, the temperature of the intake air flowing into the cylinder decreases, which increases unburned hydrocarbons and prevents warm-up. it can.

1 is an overall configuration diagram showing a hybrid electric vehicle to which an engine waste heat recovery apparatus of an embodiment is applied. It is detail drawing which shows the structure of a waste heat recovery apparatus.

Hereinafter, an embodiment of an engine waste heat recovery apparatus embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing a hybrid electric vehicle to which the engine waste heat recovery apparatus of the present embodiment is applied. Prior to the description of the waste heat recovery apparatus, first, the configuration of the entire vehicle will be described with reference to FIG.
The hybrid electric vehicle 1 is a so-called parallel type hybrid vehicle, and is configured as a truck in this embodiment. In the following description, the hybrid electric vehicle 1 may be referred to as a vehicle.
An input shaft of a travel clutch 4 is connected to an output shaft of a diesel engine (hereinafter referred to as an engine) 2, and the output shaft of the travel clutch 4 is capable of generating power, such as a permanent magnet synchronous motor. The input shaft of the automatic transmission 8 is connected via the rotating shaft of the motor 6 for use. The automatic transmission 8 automates the connection / disconnection operation of the traveling clutch 4 and the shift speed switching operation based on a general manual transmission. In this embodiment, the shift speed of 6 forward speeds and 1 reverse speed is changed. And the second speed is set as the starting stage. Of course, the types of the engine 2 and the transmission 8 are not limited to this, and can be arbitrarily changed. For example, the engine 2 or the transmission 8 may be embodied in a gasoline engine or a normal manual transmission.

The output shaft of the transmission 8 is connected to the left and right drive wheels 16 via a propeller shaft 10, a differential device 12 and a drive shaft 14. Therefore, when the travel clutch 4 is disconnected, only the travel motor 6 is connected to the drive wheel 16 side via the transmission 8, and when the travel clutch 4 is connected, both the engine 2 and the travel motor 6 are connected via the transmission 8. To the drive wheel 16 side.
The traveling motor 6 operates as a motor when DC power stored in the traveling battery 18 is converted into AC power by the inverter 20 and supplied, and is driven after its drive torque is appropriately shifted by the transmission 8. The vehicle 1 is caused to travel by being transmitted to the wheel 16. Further, during coasting operation in which the vehicle 1 decelerates due to the accelerator being off, the traveling motor 6 operates as a generator to generate AC power, while generating regenerative torque and applying braking force to the drive wheels 16, the vehicle 1. Decelerate. Then, the generated AC power is converted into DC power by the inverter 20 and then charged to the battery 18, whereby the deceleration energy of the vehicle 1 is recovered as electric energy, and is then effectively used for traveling by the traveling motor 6. Is done.

  On the other hand, the driving force of the engine 2 is transmitted to the transmission 8 via the rotating shaft of the traveling motor 6 when the traveling clutch 4 is connected, and is transmitted to the drive wheels 16 after being appropriately shifted. . Therefore, when the driving force of the engine 2 is transmitted to the driving wheels 16 and the traveling motor 6 does not operate as a motor, only the driving force of the engine 2 is transmitted to the driving wheels 16 via the transmission 8. When the traveling motor 6 operates as a motor, both the driving force of the engine 2 and the traveling motor 6 are transmitted to the drive wheels 16 via the transmission 8.

When the remaining capacity (SOC) of the battery 18 decreases and the battery 18 needs to be charged, the traveling motor 6 operates as a generator even when the vehicle 1 is traveling, and the engine 2 Electricity is generated by operating the traveling motor 6 using a part of the driving force, and the battery 18 is charged after the generated AC power is converted into DC power by the inverter 20.
The vehicle ECU 22 drives and controls an actuator (not shown) according to the operation state of the vehicle 1 and the engine 2 and information from the engine ECU 24, the inverter ECU 26, and the battery ECU 28, and the connection / disconnection control of the traveling clutch 4 and the transmission 8. And the integrated control for appropriately operating the engine 2 and the traveling motor 6 in accordance with these control states and the traveling state of the vehicle 1 are performed.

For such control, the vehicle ECU 22 receives an accelerator sensor 32 for detecting the operation amount Acc of the accelerator pedal 30, a vehicle speed sensor 34 for detecting the speed V of the vehicle 1, and a rotational speed Ne of the output shaft of the engine 2. Sensors such as an engine rotational speed sensor 35 for detecting, an electric motor rotational speed sensor 36 for detecting the rotational speed Ng of the traveling motor 6 (input rotational speed of the transmission 8), and a brake sensor 40 for detecting the depression operation of the brake pedal 39 Is connected. Based on these pieces of detection information, the vehicle ECU 22 calculates a required torque necessary for traveling of the vehicle 1 and distributes the required torque to the engine 2 side and the traveling motor 6 side.
In parallel with this, the travel mode (engine travel, motor travel, engine / motor travel) is set based on the required torque, the travel state of the vehicle 1, the operation state of the engine 2 and the travel motor 6, or the SOC of the battery 18. A command is output to the engine ECU 24 and the inverter ECU 26 to execute the selected travel mode, and the shift control of the transmission 8 is appropriately executed.
The engine ECU 24 operates the engine 2 by executing injection amount control and injection timing control so as to achieve the travel mode and engine torque set by the vehicle ECU 22.
Further, the inverter ECU 26 drives and controls the inverter 20 so as to achieve the travel mode and the torque of the travel motor 6 set by the vehicle ECU 22, and the motor is operated by the power running control or by the regeneration control. Activate the generator.

Further, the battery ECU 28 detects the temperature of the battery 18, the voltage of the battery 18, the current flowing between the inverter 20 and the battery 18, obtains the SOC of the battery 18 from these detection results, and detects the SOC. At the same time, it is output to the vehicle ECU 22.
The vehicle 1 according to the present embodiment is configured as described above, and the engine 2 is provided with a waste heat recovery device using a Rankine cycle. Hereinafter, the configuration of the waste heat recovery apparatus will be described in detail with reference to FIG.

A compressor 42 a and an intercooler 43 of a turbocharger 42 are disposed in the intake passage 41 of the engine 2 from the upstream side, and a downstream side of the intake passage 41 is connected to an intake manifold 44 of the engine 2. The intercooler 43 functions to cool the intake air whose temperature has been increased by supercharging of the turbocharger 42, but the type may be air-cooled or water-cooled.
Further, an exhaust passage 46 is connected to the exhaust manifold 45 of the engine 2, and a turbine 42 b provided on the same axis as the compressor 42 a of the turbocharger 42 from the upstream side of the exhaust passage 46, an aftertreatment device 47, An exhaust-side heat exchanger 48 (first heat exchanger) that functions as a steam generator and a silencer (not shown) are disposed. In the present embodiment, the post-processing device 47 is configured by DPF (diesel particulate filter) and SCR (selective reduction type NOx catalyst), but is not limited thereto and can be arbitrarily changed.

A cooling fan 49 that is rotationally driven by the crankshaft 2 a is disposed in front of the engine 2 (left side in the figure), and a radiator 50 is disposed in front of the cooling fan 49. The engine 2 and the radiator 50 are connected in a loop through a cooling water passage 52 together with a cooling water side heat exchanger 51 (second heat exchanger).
The cooling water is circulated through the cooling water passage 52 in the order of the engine 2, the cooling water side heat exchanger 51, and the radiator 50 by a pump (not shown). The engine 2 has a cooling action, and the radiator 50 radiates heat. For this reason, after the warm-up of the engine 2 is completed, the temperature of the cooling water flowing through the cooling water side heat exchanger 51 reaches about 100 ° C. Heat exchange takes place at.

One side of the exhaust manifold 45 and the vicinity of the inlet of the intake manifold 44 are connected via an HPL-EGR passage 53, and an HPL-EGR passage 53 is connected to an HPL-EGR valve 54 and an HPL-EGR cooler 55 (high pressure side EGR cooler). Is arranged (high pressure side EGR system). The downstream side of the aftertreatment device 47 of the exhaust passage 46 and the upstream side of the compressor 42a of the intake passage 41 are connected via an LPL-EGR passage 56. The LPL-EGR passage 56 is connected to an LPL-EGR valve 57 and an LPL. -An EGR cooler 58 (low pressure side EGR cooler) is provided (low pressure side EGR system).
The opening degree of the HPL-EGR valve 54 and the LPL-EGR valve 57 is controlled by the engine ECU 24, and the exhaust gas of the engine 2 is recirculated to the intake side as EGR gas through the HPL-EGR passage 53 and the LPL-EGR passage 56 accordingly. Is done. For this reason, after the warm-up of the engine 2 is completed, the temperature of the exhaust gas flowing through the HPL-EGR cooler 55 reaches about 300 to 500 ° C., and the temperature of the exhaust gas flowing through the LPL-EGR cooler 58 reaches about 150 to 200 ° C. As described later, heat exchange is performed with the working fluid of the Rankine cycle.

A first valve 59 (fourth switching means) is interposed on the upstream side of the LPL-EGR passage 58 in the LPL-EGR passage 56, and the upstream side of the first valve 59 and the downstream side of the LPL-EGR cooler 58. Are connected via a bypass passage 61 (second bypass passage), and a second valve 60 (fourth switching means) is interposed in the bypass passage 61.
On the other hand, the exhaust side heat exchanger 48, the cooling water side heat exchanger 51, the LPL-EGR cooler 58, and the HPL-EGR cooler 55 are connected in a loop through the working fluid path 63 of the waste heat recovery apparatus. Yes. An expander 64 and a pump 65 are interposed between the exhaust side heat exchanger 48 and the cooling water side heat exchanger 51, and the working fluid is pumped by the exhaust side heat exchanger 48, the expander 64, and the cooling water side. The working fluid path 63 is circulated in the order of the heat exchanger 51, the LPL-EGR cooler 58, and the HPL-EGR cooler 55. In the following description, the upstream side and the downstream side of the working fluid path 63 are defined according to the circulation direction.

A power generator 66 is connected to the expander 64, and the working fluid that has become superheated steam is decompressed and expanded in the expander 64 to extract power (rotational force) as described later, and the power generator 66 is driven by the power. Driven to generate electricity.
A third valve 68 (first switching means) is interposed on the upstream side (exhaust side heat exchanger 48 side) of the expander 64 in the working fluid path 63, and the upstream side of the third valve 68 and the expander 64. Is connected to the downstream side (pump 65 side) via a bypass passage 70 (first bypass passage), and a fourth valve 69 (first switching means) is interposed in the bypass passage 70.

Further, a fifth valve 71 (third switching means) is interposed on the upstream side of the LPL-EGR cooler 58 in the working fluid path 63, and the upstream side of the fifth valve 71 and the downstream side of the LPL-EGR cooler 58. Is connected via a bypass path 73, and a sixth valve 72 (third switching means) is interposed in the bypass path 73.
Further, a seventh valve 74 (second switching means) is interposed on the upstream side of the HPL-EGR cooler 55 in the working fluid path 63, and the upstream side of the seventh valve 74 and the downstream side of the HPL-EGR cooler 55. Is connected via a bypass path 76, and an eighth valve 75 (second switching means) is interposed in the bypass path 76.

The pump 65 and the first to eighth valves 59, 60, 68, 69, 71, 72, 74, 75 are connected to the engine ECU 24. The engine ECU 24 controls the driving of the pump 65 and the valves 59, 60, 68, 69, Opening / closing control of 71, 72, 74, 75 is performed.
Further, the cooling water side heat exchanger 51 is provided with a water temperature sensor 78 (cooling water temperature detecting means), and detects the temperature Tw of the engine cooling water flowing into the cooling water side heat exchanger 51 to the engine ECU 24. It is designed to output. The position of the water temperature sensor 78 is not limited to this, and can be arbitrarily changed. For example, the water temperature sensor 78 may be provided on one side of the engine 2 or the cooling water channel 52.

Next, the control status of the waste heat recovery device of the engine 2 configured as described above, particularly the control status of each valve 59, 60, 68, 69, 71, 72, 74, 75 will be described.
When engine travel or engine / motor travel is selected as the travel mode by the vehicle ECU 22, the engine ECU 24 that has input an operation command for the engine 2 starts the engine 2 and starts operation, and also drives the pump 65 to operate the working fluid. A working fluid is circulated in the passage 63. In parallel with this, the engine ECU compares the cooling water temperature Tw detected by the water temperature sensor 78 with a preset determination value Tw0, and based on the comparison result, each valve 59, 60, 68, 69 is shown in Table 1 below. , 71, 72, 74 and 75 are switched. In the table, ◯ represents valve opening, and X represents valve closing.

The determination value Tw0 is set to the coolant temperature at the time when the engine 2 has been warmed up. Accordingly, when the cooling water temperature Tw is lower than the determination value Tw0, it can be considered that the engine 2 is warmed up, and when the cooling water temperature Tw is equal to or higher than the determination value Tw0, it can be considered that the engine 2 has been warmed up.
For example, when the cold engine 2 is started to warm up, the cooling water temperature Tw is initially lower than the determination value Tw0, so the engine ECU 24 has the second, fourth, sixth and eighth valves 60, 69, 72, 75 is opened, and the first, third, fifth and seventh valves 59, 68, 71 and 74 are closed.
Since the first valve 59 is closed and the second valve 60 is opened, the exhaust gas is circulated to the intake side of the engine 2 via the bypass passage 61 without flowing through the LPL-EGR cooler 58. When exhaust gas is cooled by the LPL-EGR cooler 58 during warm-up of the engine 2 where the exhaust gas temperature is relatively low, the temperature of the intake air flowing into the cylinder decreases, which increases unburned hydrocarbons and prevents warm-up. Problems can be prevented by bypassing the LPL-EGR cooler 58.

Further, as the engine 2 continues to operate, the temperature of the exhaust gas rises prior to the rise in the coolant temperature Tw. In the exhaust side heat exchanger 48, heat exchange between the exhaust gas and the working fluid is performed, and the working fluid changes from a liquid phase to high-temperature and high-pressure superheated steam.
Since the third valve 68 is closed and the fourth valve 69 is opened, the working fluid that has flowed out of the exhaust-side heat exchanger 48 flows through the bypass 70 without flowing through the expander 64. Thereafter, the working fluid flows through the coolant side heat exchanger 51, the fifth valve 71 is closed, and the sixth valve 72 is opened, so that the bypass path 73 does not flow through the LPL-EGR cooler 58. Circulate. Further, since the seventh valve 74 is closed and the eighth valve 75 is opened, the working fluid flows through the bypass passage 76 without flowing through the HPL-EGR cooler 55 and returns to the exhaust-side heat exchanger 48. The above circulation is repeated in the working fluid path 63.

When the engine 2 is warmed up, the cooling water temperature Tw is still low (<Tw0), and a rapid temperature increase of the cooling water is demanded from the viewpoint of unburned hydrocarbons and fuel consumption. The working fluid heated by the exhaust side heat exchanger 48 bypasses the expander 64 and flows through the cooling water side heat exchanger 51. For this reason, in the cooling water side heat exchanger 51, heat exchange is performed between the high-temperature and high-pressure working fluid that has not been decompressed and expanded by the expander 64 and the cooling water. Therefore, it is possible to quickly raise the temperature of the cooling water and complete warm-up at an early stage, thereby achieving reduction of unburned hydrocarbons and improvement of fuel consumption.
In addition, since the working fluid after passing through the cooling water side heat exchanger 51 bypasses the LPL-EGR cooler 58 and the HPL-EGR cooler 55, the exhaust side heat exchange is not performed by these EGR coolers 58 and 55 without temperature drop. Returned to vessel 48. Therefore, it is easy to raise the temperature of the working fluid when the heat is again exchanged by the exhaust side heat exchanger 48, and in the subsequent heat exchange of the cooling water side heat exchanger 51, the temperature of the cooling water can be raised by a higher temperature working fluid. As a result, warm-up of the engine 2 can be further promoted.

When the cooling water temperature Tw rises and becomes equal to or higher than the determination value Tw0, the engine ECU 24 opens the first, third, fifth, and seventh valves 59, 68, 71, and 74, and the second, fourth, sixth, and eighth valves 60. , 69, 72, 75 are closed.
Since the first valve 59 is opened and the second valve 60 is closed, the exhaust gas is circulated to the intake side of the engine 2 through the LPL-EGR cooler 58 without flowing through the bypass passage 61. Therefore, as described below, the exhaust gas is heat-exchanged with the working fluid by the LPL-EGR cooler 58 and is circulated to the intake side of the engine 2 after cooling.
Further, since the temperature of the exhaust gas at this time has sufficiently increased, the working fluid changes to high-temperature and high-pressure superheated steam in the exhaust-side heat exchanger 48 by heat exchange with the exhaust gas. Since the third valve 68 is opened and the fourth valve 69 is closed, the working fluid flows through the expander 64 without flowing through the bypass 70 and is decompressed and expanded. The generator 66 is driven by the power extracted from the expander 64 to generate power, and the generated power is converted into DC power by the inverter 20 and charged to the battery 18. As a result, the waste heat of the engine 2 is recovered as electric energy and is then effectively used for traveling by the traveling motor 6.

Thereafter, the working fluid flows through the cooling water side heat exchanger 51, the fifth valve 71 is opened, and the sixth valve 72 is closed, so that the LPL-EGR cooler 58 is not flown through the bypass 73. Circulate. Further, since the seventh valve 74 is opened and the eighth valve 75 is closed, the working fluid flows through the HPL-EGR cooler 55 without flowing through the bypass passage 76 and returns to the exhaust-side heat exchanger 48. The above circulation is repeated in the working fluid path 63.
The cooling water temperature Tw has already risen sufficiently after the engine 2 has been warmed up. As described above, the cooling water side heat exchanger 51 is supplied with cooling water of about 100 ° C., and the LPL-EGR cooler 58 has An exhaust gas of about 150 to 200 ° C. is circulated, and an exhaust gas of about 300 to 500 ° C. is circulated through the HPL-EGR cooler 55. The working fluid that has been decompressed and expanded by the expander 64 flows through the cooling water side heat exchanger 51, the LPL-EGR cooler 58, and the HPL-EGR cooler 55, and sequentially performs heat exchange.

Therefore, in the process, the working fluid is preheated and returned to the exhaust-side heat exchanger 48 in a state in which the temperature has risen considerably. Therefore, it is possible to promote the generation of superheated steam when performing heat exchange with the exhaust-side heat exchanger 48 thereafter, and the cooling water-side heat exchanger 51 can drive the generator 66 using higher-temperature and high-pressure superheated steam. As a result, the efficiency of the Rankine cycle can be increased and the waste heat of the engine 2 can be effectively utilized to the maximum extent.
Here, the flow order of the working fluid is set in the order of the relatively low temperature coolant side heat exchanger 51, the intermediate temperature LPL-EGR cooler, and the high temperature HPL-EGR cooler 55. Will gradually shift to the high temperature side. In other distribution sequences, the temperature of the working fluid heated by a certain device is lowered by heat exchange at a lower temperature device, and the effect of preheating is reduced. By adopting the flow order of the working fluid as described above, a loss during heat exchange can be avoided and the preheating effect of the working fluid can be obtained to the maximum. Therefore, generation of superheated steam in the exhaust-side heat exchanger 48 can be promoted, and the Rankine cycle efficiency can be further improved.

This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the present invention is embodied in the waste heat recovery device for the engine 2 mounted on the hybrid truck 1, but the vehicle to be applied is not limited to this and can be arbitrarily changed. For example, the present invention may be applied to a hybrid bus or a passenger car, or may be applied to an engine vehicle including only the engine 2 as a driving source for traveling.
In the above embodiment, the HPL-EGR cooler 55 and the LPL-EGR cooler 58 are provided in the working fluid path 63 of the waste heat recovery apparatus. However, the present invention is not limited to this, and the EGR coolers 55 and 58 are omitted. Alternatively, only one of them may be provided.

In the above embodiment, the first to eighth valves 59, 60, 68, 69, 71, 72, 74, and 75 are completely opened or closed. However, the valve control is not limited. . For example, each valve 59, 60, 68, 69, 71, 72, 74, 75 may be controlled to a predetermined opening.
Moreover, in the said embodiment, although the condenser was not provided in the working fluid path 63 of the waste heat recovery apparatus, you may provide a condenser between the expander 64 and the pump 65, for example.
In the above-described embodiment, the working fluid is decompressed and expanded to drive the generator 66. However, the use of waste heat of the engine 2 is not limited to this. For example, the crankshaft 2a of the engine 2 using the extracted power as auxiliary power. May be recovered.

2 Engine 6 Traveling motor 18 Traveling battery 24 Engine ECU (first to fourth switching means)
42 Turbo 42a Compressor 42b Turbine 48 Exhaust side heat exchanger (first heat exchanger)
51 Cooling water side heat exchanger (second heat exchanger)
53 HPL-EGR passage (high pressure side EGR system)
54 HPL-EGR valve (high pressure side EGR system)
55 HPL-EGR cooler (high pressure side EGR cooler)
56 LPL-EGR passage (low pressure side EGR system)
57 LPL-EGR valve (low pressure EGR system)
58 LPL-EGR cooler (low pressure EGR cooler)
59 First valve (fourth switching means)
60 Second valve (fourth switching means)
61 Bypass (second bypass)
64 expander 65 pump 66 generator 68 third valve (first switching means)
69 Fourth valve (first switching means)
70 Bypass (first bypass)
71 5th valve (3rd switching means)
72 6th valve (3rd switching means)
74 7th valve (second switching means)
75 8th valve (second switching means)
78 Water temperature sensor (cooling water detection means)

Claims (6)

A pump for circulating the working fluid in the cycle;
A first heat exchanger for exchanging heat between the exhaust gas discharged from the engine and the working fluid in the cycle;
An expander that decompresses and expands the working fluid heat-exchanged by the first heat exchanger;
A second heat exchanger for exchanging heat between the engine coolant and the working fluid in the cycle;
A first bypass passage for bypassing working fluid in the cycle from the expander;
Cooling water temperature detecting means for detecting the temperature of the cooling water;
When the temperature of the cooling water detected by the cooling water temperature detecting means is equal to or higher than a preset determination value, the working fluid is not allowed to flow through the first bypass passage, and the temperature of the cooling water is lower than the determination value. And a first switching means for switching and controlling the working fluid to flow through the first bypass passage. Mounted on a hybrid vehicle having a traveling motor driven by a traveling battery together with the engine as a traveling drive source,
The waste heat recovery apparatus for an engine according to claim 2, wherein the expander drives a generator by decompression expansion of the working fluid, and charges the generated battery with the generated power. A high-pressure side EGR system that circulates exhaust gas as EGR gas from an upstream side of a turbine of a turbocharger provided in the engine to a downstream side of the compressor;
A high pressure side EGR cooler for exchanging heat between the exhaust gas recirculated by the high pressure side EGR system and the working fluid in the cycle;
3. The engine waste heat according to claim 1, further comprising: a second switching unit that causes the working fluid to flow to the high-pressure side EGR cooler when the temperature of the cooling water is equal to or higher than the determination value. Recovery device. A low pressure side EGR system for circulating exhaust gas as EGR gas from the downstream side of the turbine of the turbocharger to the upstream side of the compressor;
A low pressure side EGR cooler for exchanging heat between the exhaust gas circulated by the low pressure side EGR system and the working fluid in the cycle;
4. The engine waste heat recovery apparatus according to claim 3, further comprising: a third switching unit that causes the working fluid to flow to the low-pressure side EGR cooler when the temperature of the cooling water is equal to or higher than the determination value. .   When the temperature of the cooling water is equal to or higher than the determination value, the working fluid that has been decompressed and expanded by the expander is circulated in the order of the second heat exchanger, the low-pressure side EGR cooler, and the high-pressure side EGR cooler. The engine waste heat recovery apparatus according to claim 4, wherein A second bypass path for bypassing the exhaust gas circulated by the low pressure side EGR system from the low pressure side EGR cooler;
When the temperature of the cooling water is equal to or higher than the determination value, the exhaust gas is not allowed to flow through the second bypass passage, and when the temperature of the cooling water is lower than the determination value, the exhaust gas is allowed to flow through the second bypass passage. The engine waste heat recovery apparatus according to any one of claims 1 to 4, further comprising fourth switching means for performing switching control.

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