Thermoelectric generating device

A thermoelectric generating device has a thermoelectric element which utilizes an exhaust gas from an engine as a high temperature heat source and an engine coolant as a low temperature heat source in order to generate electricity. An introducing passage introduces a part of the exhaust gas passed through the thermoelectric element into an intake of the engine. An introducing valve opens and closes the introducing passage. A controller controls an opening degree of the introducing valve according to a load of the engine.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2003-128301 filed on May 6, 2003, Japanese Patent Application No. 2003-132234 filed on May 9, 2003 and Japanese Patent Application No. 2004-92699 filed on Mar. 26, 2004 the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a thermoelectric generating device which converts a heat energy of an exhaust gas of an engine into an electric energy.

BACKGROUND OF THE INVENTION

A conventional thermoelectric generating device is shown in JP-U-63-162916A. The conventional thermoelectric generating device has a thermoelectric element which utilizes an exhaust gas as a high temperature heat source and an ambient air as a low temperature heat source in order to generate electricity. A bypass pipes branched from an exhaust pipe of an engine through a plurality of branch pipes. Each of the branch pipes has an electric valve which opens and closes the branch pipes. The electric valve closes the bypass pipe respectively when the temperature of the exhaust gas exceeds a predetermined value to control an amount of the exhaust gas flowing in the bypass pipe so that the temperature of the thermoelectric element at the high temperature side is kept under the resisting temperature.

JP-2000-297699A shows another conventional thermoelectric generating device which utilizes an engine coolant as a low temperature heat source.

In the thermoelectric generating device shown in JP-U-63-162916A, an amount of generated current depends on a temperature difference between the exhaust gas and the ambient air when the temperature of the exhaust gas is lower than a predetermined value. Since the temperature difference fluctuates in each situation, there is no technical concept to generate current effectively in a positive way.

In the thermoelectric generating device shown in JP-2000-297699A, since the heat of the exhaust gas is absorbed by the engine coolant, the temperature of the engine coolant may increase over a threshold so that overheating of the engine may be caused. To prevent the overheating, it is necessary to upsize a radiator.

SUMMARY OF THE INVENTION

The present invention is made in view of the foregoing matter and it is an object of the present invention to provide a thermoelectric generating device which utilize an engine coolant as a low temperature heat source and generates maximum electricity according to a load of the engine without upsizing of the radiator.

According to the present invention, a thermoelectric generating device has a thermoelectric element which utilize an exhaust gas of an engine as a high temperature heat source and an engine coolant as a low temperature heat source. The thermoelectric generating device has an introducing passage for introducing a part of the exhaust gas into a suction pipe, a introducing valve for opening and closing the introducing passage, and a controller for controlling the opening degree of the introducing valve.

Accordingly, the thermoelectric element generates an electricity by utilizing the exhaust gas which is re-circulated to the suction pipe with applying a heat to the thermoelectric element according to the load of the engine. Thus, it is unnecessary to provide a heat exchanger particularly only to cool the exhaust gas which is re-circulated into the suction pipe.

DETAILED DESCRIPTION OF EMBODIMENT

First Embodiment

A thermoelectric generating device100of the present invention is used for an automobile having a water-cooled engine10. A thermoelectric element111of the device100has a function of generating an electricity and a function of cooling an exhaust gas for re-circulation, which is referred to as EGR.

Referring toFIG. 1, an engine10is provided with an intake pipe12for introducing an air for combustion and an exhaust pipe11for introducing the exhaust gas. A throttle valve12ais disposed in the intake pipe12which varies an opening degree to adjust an amount of intake air.

The engine10is provided with an engine-coolant circuit20. An engine coolant is circulated in the engine-coolant circuit20through a radiator21by a water-pump13. The water pump13is driven by the engine10. The coolant is cooled by the radiator21and the temperature of the engine10is kept in a proper range. The engine-coolant circuit20is provided with a bypass passage22and a thermostat23which controls the amount of the coolant which flows into the radiator21and the bypass passage22. When the temperature of the coolant is less than a predetermined value (for example 90° C.), the thermostat23closes the passage toward the radiator21so that the coolant flows in the bypass passage22to restrict a super cooling of the coolant. Thereby, a warming up of the engine is expedited when the coolant is in a low temperature.

A heater core31is arranged in the engine-coolant circuit20in parallel with the radiator21which forms the heater circuit30. The heater core31is a heat exchanger for warming an air by a heat derived from the warmed coolant.

The thermoelectric generating device100is comprised of a thermoelectric generator110and a controller120, and utilizes the exhaust gas from the engine10and the coolant in the engine-coolant circuit20.

The thermoelectric generator110has the thermoelectric element111to which a branched passage112and a coolant pipe114are connected, the element111generating the electricity by Seebeck effect.

The branched passage112diverges from and converges on the exhaust pipe11which is referred to as exhaust passage in the present invention. The exhaust gas flows in the branched passage112. One side surface of the thermoelectric element111is in contact with the branched passage112. At upstream of the thermoelectric element111in the branched passage112, a branch valve (an electric valve)112ais disposed.

The coolant pipe114diverges from the engine-coolant circuit20at upstream from the radiator21and is connected with the engine-coolant circuit20at upstream from the water-pump13through the thermoelectric generator110. The other side surface of the thermoelectric element11is in contact with the coolant pipe114.

One end of an introducing passage113is connected at downstream of the generator110in the branched passage and the other end of the introducing passage113is connected with the intake pipe12. An introducing valve113ais disposed in the branched passage112for opening and closing the branched passage112.

An exhaust gas temperature sensor130is disposed in the exhaust pipe11to detect the temperature of the exhaust gas, and the sensor130outputs the signal indicative of the temperature to the controller120. The temperature of the exhaust gas represents a characteristic of the load of the engine10. That is, the lower the temperature of the engine10becomes, the lower the load of engine becomes. The higher the temperature of the engine10becomes, the higher the load of the engine becomes.

The controller controls the opening degree of the branch valve112aand the introducing valve113aaccording to the signal from the exhaust temperature sensor130. As the detected temperature is lower, the opening degree of the valves112aand113abecomes larger. As the detected temperature is higher, the opening degree of the valve112aand113abecomes smaller.

An operation of this embodiment is described hereinafter. The function of generating the electricity is explained as follows.

Under the operation of the engine10, the fresh air is introduced into intake pipe12based on the opening degree of the throttle valve12aand the introduced air is mixed with a fuel injected by an injector (not shown). The mixed air and fuel is introduced into the combustion chamber and is ignited to be combusted. The exhaust gas is purified by a catalyst (not shown) and is discharged into the air. The engine coolant is circulated in the engine-coolant circuit20, heater circuit30, and the coolant pipe114by the operation of the water-pump13.

The controller120controls the opening degree of the branch valve112aand introducing valve113aaccording to the signal from the exhaust temperature sensor130, which is indicative of the temperature of the exhaust gas. When the load of the engine is low and the temperature of the exhaust gas is low, the controller120raises the opening degree of the branch valve112a. Then, amount of an exhaust gas flowing into the branch passage112is increased. The thermoelectric element111generates the electricity according to the temperature difference between the exhaust gas in the branch passage112and the engine coolant in the coolant pipe114. The generated electricity is charged in a battery and is supplied to devices and systems300.

As the load of the engine increases and the temperature of the exhaust gas rise, the controller120lowers the opening degree of the branch valve112a. Then, the amount of the exhaust gas flowing into the branched passage112is decreased and amount of electricity generated by the thermoelectric element111is restrained.

The function of cooling the EGR gas is described herein after.

When the thermoelectric element111generates the electricity at the one side of the element111, the exhaust gas is cooled down at the other side of the element11by the coolant flowing in the coolant pipe114. The cooled exhaust gas flows in the introducing passage113toward the intake pipe12via the introducing valve113a.

Such a function described above is almost equal to a function of an EGR system in which the exhaust gas is cooled by a particular heat exchanger and the cooled exhaust gas is introduced into the intake pipe. The temperature of the combustion is lowered and the concentration of NOxis reduced without deteriorating the performance of the engine10.

As the temperature of the exhaust gas increases according to the load of the engine10, the controller120lowers the opening degree of branch valve112aand the introducing valve113a. Then, the amount of the exhaust gas flowing in the introducing passage113decreases, and the cooling function of the EGR gas is restrained.

When the engine10is started and the temperature of the exhaust gas is lower than a predetermined value so that the catalyst is not activated, the controller120closes the branch valve112aand stops the generation of the thermoelectric element111. That is, a decreasing of the exhaust gas temperature is restrained and the catalyst is activated at first.

As described above, in the present invention, it is possible to generate the electricity by the thermoelectric element111with utilizing the exhaust gas. Since the exhaust gas flowing in the introducing passage113toward the intake pipe12is cooled by the thermoelectric element111with the coolant flowing in the coolant pipe114, it is possible to cool the EGR gas without a specific heat exchanger.

A load of an alternator equipped on the engine10is reduced by the generation of the thermoelectric element111. A pumping loss of the engine10is also reduced by introducing the exhaust gas into the intake pipe12. The warming up of the engine10is expedited by the coolant in the coolant pipe, the coolant absorbing the heat from the exhaust gas. And it makes possible to reduce the friction loss and to improve a fuel economy figure.

A rising character of the heater core31is improved by the coolant absorbing the heat from the exhaust gas.

As the load of the engine decreases, the controller120rises the opening degree of the branch valve112aand the introducing valve113a. Therefore, the function of generating electricity and the function of cooling the EGR gas are executed at the same time.

When the temperature of the exhaust gas is low and the catalyst is not activated, the controller12controls the branch valve112ainto the closed position. The exhaust gas does not flow in the branched passage112so that the heat of the exhaust gas is not treated by the thermoelectric element111. Therefore, the temperature of the exhaust gas does not decrease and the activation of the catalyst is not deteriorated.

Second Embodiment

FIG. 2shows a second embodiment. In the second embodiment, the thermoelectric generating device is applied to a hybrid vehicle which includes the engine10and a driving motor40for driving the hybrid vehicle.

The driving motor40is driven with receiving the electricity from the battery and is controlled the rotational speed thereof by an inverter50. The engine10and the driving motor40are selectively driven according to the driving condition of the vehicle. The inverter50, the driving motor40, and the battery (not shown) are provided with an inverter coolant circuit60for cooling components which are under the operation.

The inverter coolant circuit60is provided with a radiator61and a coolant in the circuit60is circulated by an electric pump63. The coolant pipe114is connected with the inverter coolant circuit60at positions upstream and downstream from the electric pump63. A second radiator62which radiates the heat absorbed from the exhaust gas is arranged at upstream from the electric pump63in the coolant pipe114. A reservoir64for absorbing an expansion and contraction of the coolant is disposed at upstream from the radiator61in the circuit60.

The operation of the second embodiment is substantially the same as the first embodiment. In the second embodiment, the amount of the generated electricity is increased by utilizing the coolant for cooling the inverter50.

The temperature of the engine coolant is between 90° C. and 110° C. by adjusting capacities of the radiator21and the thermostat23to operate the engine10under a proper condition. The temperature of the inverter coolant is kept around 60° C. to ensure lives of the inverter50, the driving motor40and the battery.

Compared with the first embodiment, the temperature difference between the inverter coolant and the exhaust gas becomes larger. Thus, the amount of the generated electricity in the second embodiment becomes larger than that in the first embodiment.

The radiator61and second radiator62can be integrated together. Thereby, the number of radiator tanks is reduced, and a dead space between the radiator61and the second radiator62does not exist. The radiator has a high heat exchanging efficiency and is constructed in a low cost.

In the first and second embodiments, the load condition of the engine10is detected by means of the exhaust temperature sensor130. The load condition of the engine10can be detected by detecting a concentration of oxide contained in the exhaust gas or detecting the pressure in the intake pipe12.

The engine coolant and the inverter coolant can be replaced by the ambient air.

Third Embodiment

In the third embodiment, the same parts and components as those in the first embodiment are indicated with the same reference numerals and same description will not be reiterated.

Referring toFIG. 3, the engine10is controlled by an engine controller14. The engine controller14receives signals such as an engine speed signal, a throttle opening degree signal, a vehicle velocity signal and the like. The engine controller14has a map in which an amount of fuel injection is memorized. The amount of fuel injection is based on the engine speed signal and the throttle opening degree signal. The fuel is injected into the intake pipe12according to the map. The engine controller14sends signals to and receives signals from the controller120.

The coolant pipe114diverges from the engine-coolant circuit20at downstream from the radiator21and converges on the engine-coolant circuit20at upstream from the water-pump13through the thermoelectric generator110. The coolant passed through the radiator21flows into the one side surface of the thermoelectric element111. This coolant is a low temperature heat source for the thermoelectric element111.

The controller120memorizes an axial torque map, a cooling loss map of the engine10, a coolant amount map of the engine10, a standard radiation map of the radiator21, an opening degree map of the branch valve112aand various equations for calculation. The controller120controls the opening degree of the branch valve112a. The opening degree of the introducing valve113ais controlled according to the exhaust temperature signal from the exhaust temperature sensor130.

In this embodiment, variable means is comprised of the branched passage112, branch valve112aand the controller120. The variable means varies the supplying condition of the exhaust gas to the thermoelectric element111.

The function of the maps and the equations are described hereinafter.

FIG. 4is a map showing the relation between the amount of the fuel injection L and the axial torque T. The axial torque T under the operation of the engine is derived from this axial torque map. And the shaft horsepower P is calculated by a following equation based on the axial torque T and an engine speed Ne.

FIG. 5is the cooling loss map showing the relation between the engine speed Ne and a cooling loss amount Qe of the engine10. In the cooling loss map, the shaft horsepower P is varied from P1to P7as a parameter. When the shaft horsepower P is P1, no load is applied to the shaft. When the shaft horsepower P is P7, full load is applied to the shaft. The cooling loss amount Qe under the operation of the engine10is derived from this map. The cooling loss amount Qe is a heat amount radiated by the radiator21and is derived by multiplying the whole heat of combustion and the cooling loss coefficient.

FIG. 6is the coolant amount map to derive the engine coolant amount Ve, in which the engine speed Ne is a parameter. The coolant amount map shows a relation between a water-pump character Δhp, a fluid resistant character Δht, and an engine coolant amount Ve. The engine speed Ne1–Ne4is in proportion to the speed of the water-pump. The fluid resistant character Δht includes fluid resistance in the engine coolant circuit20, the heater circuit30and the coolant pipe114.

The amount of coolant Vw flowing through the radiator21is calculated from the following equation based on the engine coolant amount Ve.
Vw=K×Ve

K is a constant which is derived based on the resistant coefficient of the radiator21, the bypass passage22, the thermostat23, the heater core31and coolant pipe114.

FIG. 7is the standard radiation map of the radiator21, in which the amount of coolant Vw flowing through the radiator21is a parameter. This map shows a relation between the velocity Va of the air flowing into the front surface of the radiator21and a standard radiation amount Qr of the radiator21under the operation of the engine. The air velocity Va is calculated based on the vehicle speed V derived by the engine controller14with considering the resistance of a bumper and a grille of the vehicle according to the following equation.
Va=b×V

“b” is a constant, for example, 1/5.

FIG. 8is an opening degree map showing the relation between the radiation amount from the exhaust gas Qex and the opening degree of the branch valve112a. The radiation amount Qex is equal to the amount of surplus capacity ΔQx of the radiator21. ΔQx is derived from the following equation.

Surplus capacity ΔQx=Standard radiation amount Qr−Cooling loss amount Qe=Radiation amount from the exhaust gas Qex.

As the radiation amount Qex becomes larger, the opening degree of the branch valve112abecomes larger.

The operation of the embodiment is described hereinafter.

The controller120controls the opening degree of the branch valve112aaccording to the maps and aforementioned equations.

FIG. 9is a flowchart for explaining the operation. In step S100, the data such as the fuel injection amount L, the engine speed Ne, the throttle valve opening degree Bk, vehicle speed V and the like are read. In step S110, the cooling loss amount Qe is calculated. That is, from the axial torque map shown inFIG. 4, the axial torque corresponding to a present amount of fuel injection is derived, and then the shaft horsepower P is calculated with the aforementioned equation. Then, according to the cooling loss map shown inFIG. 5, the cooling loss amount Qe is derived based on the present engine speed Ne and the present shaft horsepower P.

In step S120, the standard radiation amount Qr is calculated. The engine coolant amount Ve is derived from a crossing point of the pump character Δhp and the fluid resistant character Δht at the present engine speed Ne as shown inFIG. 6. The amount of radiator coolant Vw is calculated based on the engine coolant amount Ve. According to the standard radiation map shown inFIG. 7, the standard radiation amount Qr is calculated.

In step S130, surplus capacity ΔQx is calculated based on the cooling loss amount Qe and the standard radiation amount Qr.

In step S140, it is determined whether the surplus capacity ΔQx is more than zero. When it is “NO” in step S140, the branch valve112ais closed in step S150and the processing is returned to step S100. In this situation, the load of the engine is highest and the cooling loss amount Qe is radiated in the standard radiation amount Qr. The exhaust gas is not supplied to the thermoelectric element111to restrain an elevation of the coolant temperature in coolant pipe114and the overheating of the radiator21.

When it is “Yes” in step S140, the exhaust radiation amount Qex is calculated in step S160. The exhaust radiation amount Qex is established as an equal amount to the surplus capacity ΔQx. When the surplus capacity ΔQx is more than zero, the load of the engine is relatively low and the radiator21radiates the cooling loss amount Qe and also have a radiation capacity corresponding to the surplus capacity ΔQx.

In step S170, the opening degree of branch valve112ais adjusted. As the exhaust radiation amount Qex becomes larger, the opening degree of the branch valve112abecomes larger, the amount of exhaust gas flowing into the branched passage112is increased, and the temperature difference between the coolant in the coolant pipe114and exhaust gas becomes larger in order to increase the amount of the generated electricity. The generated electricity is supplied to the battery and other electric components. The coolant absorbs a heat from the exhaust gas, however, the absorbed heat is radiated by the radiator21in the surplus capacity thereof.

The controller120controls the opening degree of the introducing valve113ain such a manner that as the exhaust temperature is lower, that is, as the load of the engine is lower, the opening degree of the introducing valve113ais increased. The exhaust gas is cooled by the coolant in the coolant pipe114. The cooled exhaust gas flows in the introducing passage113through the introducing valve113atoward the intake pipe12.

The embodiment described above has a same function of the EGR gas cooling system which includes a particular heat exchanger for cooling the EGR gas so that the combustion temperature is decreased and concentration of NOxin exhaust gas is reduced.

In this embodiment, since the opening degree of the branch valve112abecomes larger as the surplus capacity ΔQx of the radiator becomes larger, the heat absorbed by the coolant from the exhaust gas is radiated in the surplus capacity ΔQx. It is possible to generate a maximum electricity by introducing the exhaust gas into the branched passage112, and a transferred heat from the exhaust gas to the coolant is radiated in the surplus capacity ΔQx of the radiator21.

Since the thermoelectric element111reduces a load of an alternator, a fuel economy of the engine10is improved.

The thermoelectric element111generates the electricity according to the temperature difference between the exhaust gas and the engine coolant cooled by the radiator.

The coolant pipe114can be diverged from the engine coolant circuit20at the downstream from the thermostat23.

As shown inFIG. 8, the coolant pipe114can be arranged in a series with the radiator21.

The introducing passage113and the introducing valve113acan be eliminated according to the horsepower of the engine10and the concentration of NOxin the exhaust gas.

Fourth Embodiment

FIG. 11shows a fourth embodiment. In this embodiment, the amount of the engine coolant is varied.

A coolant pipe114diverges from the engine coolant circuit20at downstream from the radiator21and converges on the engine coolant circuit20at upstream of the water-pump13.

A fluid control valve114ais disposed on a diverging point of the coolant pipe114. The fluid control valve114acontrols the amount of coolant flowing in the engine coolant circuit20and in the coolant pipe114. The opening degree of the fluid control valve114ais controlled by the controller120. The variable means for varying the supply condition of the coolant to the thermoelectric element111is comprised of the coolant pipe114, the fluid control valve114a, and the controller120.

As the surplus capacity of the radiator21increases, the opening degree of the fluid control valve114aincreases so that the amount of the coolant flowing through the coolant pipe114increases. Thus, the temperature difference between the coolant and the exhaust gas increases so that the amount of generated electricity is increased.

It is possible to generate a maximum electricity by introducing the coolant into the coolant passage114, and a transferred heat from the exhaust gas to the coolant is radiated in the surplus capacity ΔQx of the radiator21.

Fifth Embodiment

FIGS. 12–14shows a fifth embodiment in which the thermostat23is replaced by a changing valve24. The controller120controls the opening degree of the changing valve24.

As shown inFIGS. 13A–13D, the valve body is rotated in four positions by the signal from the controller120. Three positions shown inFIGS. 13A–13Care conventional positions. The valve head can be positioned as shown inFIG. 13Din which the bypass passage22is connected with the radiator21.

Right after the engine10is started, the changing valve24is positioned as shown inFIG. 13Dand the fluid control valve114aopens the coolant pipe114and the coolant circuit20. The coolant flows like arrows shown inFIG. 14. Thus, the thermoelectric element111generates the electricity and the coolant absorbs a heat generated by the element111so that engine10is warmed up rapidly. The changing valve24controls the flowing of the coolant more precisely than the thermostat23so that precise controls of the generation, the warming up and the cooling the engine are executed.

FIG. 15shows a modification of the fifth embodiment. The fluid control valve114aand the changing valve24are integrated into a switching valve24a. The switching valve24ahas four connecting portions for opening and closing independently. Each of four connecting portions is confronting to the radiator21, bypass passage22, the engine10and the coolant pipe114.

Sixth Embodiment

FIGS. 16–18show a sixth embodiment. The branched passage112is not shown inFIGS. 16–18. In this embodiment, the temperature of the coolant flowing into the thermoelectric element111is varied.

As shown inFIG. 16, the radiator21is divided into a first radiator211aand a second radiator211b.

The first radiator211ais configured that the radiation performance is maximum when the load of the vehicle is middle band.

An outlet tank of the radiator21is provided with a partition212cat a boundary between the first radiator211aand the second radiator211b. The first outlet212ais provided on the outlet tank212corresponding to the first radiator211aand the second outlet212bis provided on the outlet tank212corresponding to the second radiator211b. The coolant flowing through the radiator21is divided into one flow from the first radiator211ato the first outlet212aand the other flow from the second radiator211bto the second outlet.212b.

The first outlet212a is connected with the engine coolant circuit20between the fluid control valve114aand the thermostat23, and the second outlet212bis connected with the fluid control valve114a.

An operation and a function of the embodiment are described hereinafter.

1. In Low Load

When the engine10is under the low load, for example, under an idling or an ordinal driving, the temperature of the coolant at the outlet of the engine is relatively low (less than 82° C., for example) so that the thermostat23closes the side of the radiator21as shown inFIG. 16. The controller120controls the fluid control valve114ato open the side of the engine10and the side of the coolant passage114.

The coolant flowing out from the engine10is divided into one flow heading to the bypass passage22and the other flow heading to the radiator21. The coolant flowing out from the bypass passage22returns to the engine10. The coolant flowing out from the radiator21flows through the first radiator211aand the second radiator211b.

The coolant flowing out from the first radiator211athrough the first outlet212aflows into the fluid control valve114a. The coolant flowing out from the second radiator211bthrough the second outlet212bflows into the fluid control valve114aand returns to the engine10through the coolant passage114. The thermoelectric element111generates the electricity.

The coolant is cooled down by the radiator21and thermoelectric element111is cooled by the coolant of low temperature. Thus the temperature difference between the coolant and the exhaust gas is increased so that sufficient electricity is generated. The coolant is cooled by the radiator21and absorbs the heat from exhaust gas through the thermoelectric element111. A deterioration of the warming up is restrained.

2. In Middle Load

When the engine10is under the middle load, the temperature of the coolant at the outlet of the engine10is between 82° C. and 100° C. for example. As shown inFIG. 17, the thermostat23opens the side of the radiator21and the side of the bypass passage22. The fluid control valve114aopens the coolant passage114according to a signal from the controller120.

The coolant flowing out from the engine10is divided into one stream heading to the bypass passage22and the other stream heading to the radiator21. The coolant flowing out from the bypass passage22is returned to the engine10. The coolant flowing into the radiator22flows through the first radiator211aand the second radiator211b.

The coolant flowing out from the first radiator211athrough the first outlet212areturns to the engine10through the thermostat23. The coolant flowing out from the second radiator211bthrough the second outlet212bflows into the fluid control valve114aand returns to the engine10through the coolant pipe114. The thermoelectric element111generates the electricity.

Since the fluid resistance of the coolant pipe114is larger than that of the engine coolant circuit20, the amount of the coolant Vw2passing through the second radiator211bis less than the amount of the coolant Vw3passing through the first radiator211a. The temperature of the coolant Tw2at the outlet of the second radiator211bis less than that of the coolant Tw3at the outlet of the first radiator211a. Therefore, the electricity generated by the thermoelectric element111is increased.

A sample of the calculation by the inventors is described below.

When the radiator21is not divided, the temperature Tw1of the coolant at the outlet of the engine10is 100° C., the amount of the coolant is 40 L/min., the air velocity at the front of the radiator21is 3 m/s, and the inlet air temperature of the radiator21is 30° C., the temperature of the coolant at the outlet of the radiator21is 93° C. The coolant at 93° C. and the exhaust gas at 400° C. are supplied to the thermoelectric element111, and the element111generates the electricity based on the temperature difference 307° C.

When the radiator21is divided into the first and second radiator, the amount Vw2of the coolant passing through the second radiator211bis 5 L/min. The temperature Tw2of the coolant flowing out from the second radiator211bthrough the second outlet212bis 82° C. The coolant at 82° C. and the exhaust gas at 400° C. are supplied to the thermoelectric element111, and the element111generates the electricity based on the temperature difference 318° C.

The maximum electricity Emaxgenerated by the element111is in proportion to the square number of the temperature difference between the temperature TH of the exhaust gas and the temperature TL of the coolant as following equation.
Emax=¼×pf×(TH−TL)2

“Pf” is a Seebeck coefficient.

3. In High Load

When the temperature of the coolant at the outlet of the engine10is high (100° C., for example), the thermostat23opens the side of the radiator21as shown inFIG. 18. The fluid control valve114aopens the engine coolant circuit20according to a signal from the controller120.

The coolant flowing out from the engine10flows into the radiator21and flows through the first radiator211aand the second radiator211b.

The coolant flowing out from the first radiator211areturns to the engine10through the first outlet212aand the thermostat23. The coolant flowing out from the second radiator211breturns to the engine10through the fluid control valve114a. In such a construction, since the coolant is not supplied to the element111, the generation of the electricity is stopped.

In this embodiment, the amount of the coolant supplied to the thermoelectric element111is varied, and the temperature of coolant at the outlet of the radiator21is decreased according to the load of the engine10(surplus capacity ΔQx). Thus, the electricity is generated efficiently.

In the third embodiment, the amount of the exhaust gas is controlled. In the fourth through sixth embodiments, the amount or the temperature of the coolant is controlled. The amount of the exhaust gas and the coolant and the temperature of the coolant can be controlled at the same time.