GB2437309A

GB2437309A - Vehicle engine cooling using a Stirling Engine

Info

Publication number: GB2437309A
Application number: GB0608011A
Authority: GB
Inventors: Colin Helle-Lorentzen; Jon Edward Caine
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-04-22
Filing date: 2006-04-22
Publication date: 2007-10-24
Anticipated expiration: 2026-04-22
Also published as: GB2437309B; GB0608011D0

Abstract

A cooling system 10 for the engine 1 of a motor vehicle is disclosed in which a radiator 4 is cooled by a fan 8 driven by a Stirling engine 7. The Stirling engine 7 has a hot side heated by coolant circulated through the engine 1 and a cooling circuit by a coolant pump 3 and a cold side cooled by direct air cooling or via a separate cooler.

Description

A Cooling System for an Engine This invention relates to motor vehicles

and in particular to a cooling system for an engine of a motor vehicle.

It is well known to provide a cooling system for the engine of a motor vehicle having an air to liquid heat exchanger normally referred to as a radiator, a pump to circulate coolant through the engine and radiator and a fan to promote the flow of air through the radiator. The fan is normally driven by a belt from the engine or by means of an electric motor.

Both of these fan drive methods require the production of additional power by the engine. In the case of a belt driven fan, power is required to directly drive the fan, and in the case of an electric motor driven fan, power is required to produce the electricity required to power the electric motor.

This additional engine power will have an adverse effect on the fuel economy and emission performance of the engine.

It is an object of this invention to provide a cooling system for the engine of a motor vehicle having a fan which requires little or no additional engine power to drive it.

According to a first aspect of the invention there is provided a cooling system for the engine of a motor vehicle comprising a cooling circuit having a radiator and a coolant pump to circulate coolant through the engine and the radiator and a,fan to produce a flow of air through the radiator wherein the fan is driven by a Stirling engine having a hot side heated by coolant circulating through the cooling circuit.

The hot side of the Stirling engine may have a heat exchanger and the coolant flowing through the cooling circuit may flow through the heat exchanger of the Stirling engine before flowing to the radiator.

The Stirling engine may have a cold side and the cold side may be cooled by air passing over the cold side.

The air may be urged past the cold side of the Stirling engine by a fan driven by the Stirling engine.

The same fan may be used to cool the cold side of the Stirling engine and the radiator.

Alternatively, the Stirling engine may have a cold side and the cold side may be cooled by passing liquid through a cooler attached to the cold side of the Stirling engine.

The liquid passing through the cooler attached to the cold side of the Stirling engine may be cooled by circulation through a cold side air to liquid heat exchanger.

The liquid may be circulated through the cold side cooler and the cold side air to liquid heat exchanger by a pump driven by the Stirling engine.

Air may be urged past the cold side air to liquid heat exchanger by a fan driven by the Stirling engine.

The same fan may be used to cool the cold side air to liquid heat exchanger and the radiator.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.l is a schematic diagram of a cooling system for an engine of a motor vehicle having a fan drive arrangement according to a first embodiment of the invention; Fig.2 is a schematic plan view of a fan drive arrangement according to a second embodiment of the invention for use in the cooling system shown in Fig.l; Fig.3 is a vertical cross-section through a Stirling engine forming part of the fan drive arrangement shown in Fig.2; F'ig.4 is a schematic front view of a fan drive arrangement according to a third embodiment of the invention for use in the cooling system shown in Fig.l; and F'ig.5 is a schematic plan view of the fan drive arrangement shown in Fig.4.

With particular reference to Fig.1 there is shown an internal combustion engine 1 having a number of coolant channels formed therein (not shown) to permit the circulation of coolant through the engine 1.

The engine 1 has a cooling circuit associated therewith to maintain the temperature of the engine 1 below a maximum desired operating temperature.

The main cooling circuit comprises of a coolant circulation pump 3 to circulate coolant around the main cooling circuit, an air to liquid heat exchanger in the form of a radiator 4 to cool the coolant passing therethrough and a Stirling engine 7 to recuperate waste energy from the coolant. Connected to the main cooling circuit is a cabin heater 6 to provide heating for a passenger compartment of the motor vehicle and a degas apparatus 5 to remove entrained gas from the coolant circulating in the main cooling circuit.

The pump 3 is positioned at an inlet to the cooling channels in the engine 1 and urges coolant to flow through the coolant channels in the engine 1 to a valve assembly 2 located at a coolant outlet side of the engine 1.

The valve assembly 2 is operable to distribute the coolant from the engine 1 depending upon the temperature of the coolant to the cabin heater 6 via a supply hose HS', to the radiator 4 via radiator supply hoses RS' and RS2' or back to the pump 3 via a bypass hose BL' connected to a return hose HR' from the cabin heater 6.

The Stirling engine 7 has a hot side heat exchanger connected to the valve assembly 2 by the radiator supply hose RS' and connected to an inlet to the radiator 4 by the radiator supply hose RS2' . The radiator 4 has an outlet connected to an inlet of the pump 3 by a radiator return hose RR' The degas apparatus 5 is connected to a degas supply pipe DS' through which coolant flows to the degas apparatus and a return pipe DR' through which coolant flows back to the main cooling circuit at a position upstream from the coolant circulation pump 3. The degas supply pipe DS' is connected to the highest point in the main cooling circuit by a primary degas supply pipe DSl' and to the highest point in the radiator 4 by a secondary degas supply pipe DS2' General operation of the cooling system will not be described in great detail as it is conventional in nature but basically below a predetermined coolant temperature the coolant is prevented from flowing through the radiator 4 by the valve assembly 2 so as to assist the engine 1 in warming up and in this case the majority of coolant flows back directly to the pump 3 via the bypass hose BL' . When the predetermined coolant temperature is exceeded coolant begins to flow to the radiator 4 via the radiator supply hoses RS' and RS2' The Stirling engine 7 is used to recuperate waste heat from the engine 1 and use this recuperated energy to drive a cooling fan 8.

The cooling fan 8 is, in this case, positioned to the rear side of the radiator 4 so that it draws air through the radiator 4 but it will be appreciated that the fan 8 could be positioned in front of the radiator 4 so that it forces or pushes air through the radiator 4.

The Stirling engine 7 has an output shaft (not shown) to drive a belt drive (not shown) connected between the Stirling engine 7 and the fan 8.

The Stirling engine can be of any form that is to say it can be an alpha Stirling containing two separate power pistons in separate cylinders, one "hot" piston on a hot side of the engine and one "cold" piston on a cold side of the engine. The hot piston cylinder is situated inside a hot side heat exchanger which in this case would be connected to the engine 1 by the radiator supply hose RS' and to the radiator 4 by the radiator supply hose RS2' The cold piston cylinder is situated inside a cold side heat exchanger. The cold side heat exchanger can be a simple air cooled heat exchanger using air flowing over say fins or can be an air to liquid heat exchanger in which coolant is circulated through the cold side heat exchanger or cooler to a separate heat exchanger used to cool the coolant.

Alternatively, the Stirling engine 7 could be a beta Stirling engine having a single power piston arranged within the same cylinder on the same shaft as a displacer piston.

The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot side heat exchanger to the cold side heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston and, when it is pushed to the cold end of the cylinder, it contracts and the momentum of the machine pushes the power piston the other way to compress the gas.

As yet another alternative the Stirling engine 7 could be a gamma Stirling engine which is simply a beta Stirling engine in which the power piston is mounted in a separate cylinder alongside the displacer piston cylinder but is still connected to the same flywheel. The gas in the two cylinders can flow freely between them and remains a single body.

Irrespective of the type of Stirling engine used the method of operation is the same, hot coolant from the engine 1 is used to heat the hot side of the Stirling engine 7 by being circulated through the hot side heat exchanger thereby recuperating energy from the coolant which would otherwise be wasted. The cold side heat exchanger is maintained cool by positioning it in a position where air at ambient temperature can either flow over it or by positioning a separate heat exchanger in such a position. In either case air at ambient temperature can be caused to flow either directly over the cold side or through the separate heat exchanger by a fan which can be the same fan used to cool the radiator 4 or can be a separate fan driven by the Stirling engine 7.

A temperature difference is thereby produced between the temperature of the coolant and the temperature of ambient air and it is this temperature difference which is used to power the Stirling engine 7.

When the engine 1 is started from cold the temperature of the coolant and the temperature of ambient air are substantially the same and so no power can be produced by the Stirling engine 7 but when the valve assembly 2 opens to permit coolant to flow through the radiator 4 there is almost immediately a significant temperature difference produced between the hot and cold sides of the Stirling engine 7. The temperature difference is likely to be initially in the region of 50 degrees Celsius although this will depend upon the ambient air temperature.

Such a temperature difference is sufficient for the Stirling engine 7 to begin producing power and as a consequence the fan 8 will begin to rotate to draw air through the radiator 4. As the engine 1 continues to warm up the temperature difference will tend to increase thereby increasing the rotational speed of the fan 8 as the Stirling engine 7 speeds up.

Even if the ambient temperature is very high there is still sufficient temperature difference to power the Stirling engine 7. When the ambient temperature is very low the fan 8 is not normally required but in such a situation the Stirling engine 7 is unlikely to be operating because the valve assembly 2 will tend to circulate the coolant straight back to the pump 3 or to the heater 6 rather than through the radiator 4.

Although the Stirling engine 7 is shown connected between the engine 1 and the radiator 4 because in that location the maximum possible temperature difference can be achieved it will be appreciated that the invention is not limited to such a positioning of the Stirling engine 7 and that the hot side of the Stirling engine 7 could be connected to the main cooling circuit at a different location.

If required, a small electric motor or other actuating device could be attached to the Stirling engine 7 or the fan 8 to start the fan 8 rotating. However, any such device will only consume a minimal amount of power because it would only be required for a short period of time in order to start the Stirling engine 7.

Alternatively, the Stirling engine could be incorporated as part of the radiator and use the flow of coolant to start it by driving an impellor connected to the output shaft of the Stirling engine. The impellor could be directly connected to the Stirling engine in which case, when operating the Stirling engine would act as an additional coolant circulation pump or could be connected through a one way clutch so that it would not drive the impellor when operating.

As soon as the Stirling engine 7 starts to operate the fan 8 will also begin to rotate and the speed of rotation of the fan 8 is dependant upon the speed of rotation of the Stirling engine 7. One of the significant advantages of the invention is that the cooling of the radiator 4 by the Stirling engine 7 is self governing in that as the temperature of the coolant leaving the engine 1 increases the speed of the Stirling engine 7 increases to provide more cooling to the radiator 4. Conversely, if the coolant from the engine 1 reduces then the Stirling engine 7 will also slow thereby reducing the cooling effect of the fan 8. By careful design of the Stirling engine 7 and the fan 8 it is therefore possible to produce a cooling mechanism for the radiator 4 that requires no additional electronic control and more importantly requires no additional energy or power from the engine 1 as it is driven by the waste energy recuperated from the coolant. It will also be appreciated that the extraction of some heat from the coolant by the Stirling engine 7 will reduce the cooling requirements of the radiator 4 and so a smaller radiator 4 can potentially be used. This is important as it provides additional space in which to package the Stirling engine 7.

By using rejected energy from the engine 1 to power the fan 8, the engine 1 does not need to produce more power to is drive the fan 8 or drive an electric generator to produce electricity to power a fan motor and so the fuel efficiency and hence the emission performance of the engine 1 is improved.

With reference to Figs.2 and 3 there is shown a second embodiment of a fan drive arrangement intended to replace the fan drive arrangement shown in Fig.1.

As before, a supply of hot coolant is supplied to a hot side 11 of a Stirling engine 17 via a radiator supply hose RS' which is connected to an inlet of a hot side heat exchanger 24. The hot coolant flows through the hot side heat exchanger 24 and then flows to an inlet to the radiator 4 via a radiator supply hose RS2' The hot side 11 of the Stirling engine 17 has a piston slidingly supported in a cylinder. The piston 25 is connected via a connecting rod 26 to a common crankshaft 27 which has an output shaft 13. A cold side 12 of the Stirling engine 17 has a cold side piston 28 slidingly supported in a separate cylinder to the hot side piston 25.

-10 -The cold side piston 28 is connected to the common crankshaft 27 by a connecting rod 29.

A number of cooling fins 23 are positioned on an outer surface of the cylinder for the cold side piston 28 in order to improve the transfer of heat from the cold side cylinder.

The hot side piston 25 defines in combination with its cylinder a hot side chamber HSC' and the cold side piston 28 defines in combination with its cylinder a cold side chamber CSC' . The hot and cold side chambers HSC' and CSC' are interconnected via a connecting conduit 33 in which is mounted a regenerator 30. The regenerator 30 is heated when hot gas is pushed from the hot side chamber HSC' to the cold side chamber CSC' and rejects some of the stored heat back into the gas when the gas is pushed from the cold side chamber CSC' to the hot side chamber HSC' thereby improving the efficiency of the Stirling engine 17.

Operation of this alpha type Stirling engine can be considered to comprise of four phases, expansion of the gas on the hot side, transfer of the hot gas to the cold side, contraction of the gas on the cold side and transfer of the cold gas back to the hot side.

In the first or expansion phase most of the gas is located in the hot side chamber HSC' where it is heated by the transfer of heat from the coolant passing through the hot side heat exchanger 24. The expansion of the gas drives the hot side and cold pistons 25, 28 inwards thereby increasing the volume of the hot and cold chambers HRC' and 0SC' In the hot transfer phase the momentum of the crankshaft 27, which has a flywheel (not shown) attached to it, causes rotation of the crankshaft 27 in a clockwise direction so that the hot side piston 25 moves upwardly -11 -thereby reducing the volume of the hot side chamber HRC' and pushing the hot gas through the connecting conduit 33 and the regenerator 30 towards the cold side chamber CSC', at the same time the cold side piston 28 is moved by the crankshaft 27 so as to increase the volume of the cold side chamber CSC' . As the hot gas passes through the regenerator 30 it heats a heat storage medium located in the regenerator 30 so as to store heat for future use.

In the contraction phase the gas is cooled in the cold side chamber CSC' and pulls the cold side and hot side pistons 28 and 25 in directions to reduce their respective chambers CSC' and HSC' however, most of the gas remains in the cold side chamber CSC' during this phase.

In the final cold transfer phase the momentum of the crankshaft 27 is used to transfer the now contracted gas from the cold side chamber CSC' back to the hot side chamber HSC' via the connecting conduit 33 and the regenerator 30 for reheating so as to start the cycle again.

As the cold gas passes through the regenerator 30 it is heated by the heat stored in the regenerator 30.

With particular reference to Fig.2 the output shaft 13 has first and second drive pulleys 14, 20 fastened to it.

The first pulley 14 is used to drive a belt 16 drivingly connected to a first driven pulley 15. The first driven pulley 15 is connected to a fan 19 used to blow air onto the fins 23 on the cold side 12 of the Stirling engine 17 so as to improve the cooling of the gas when it is located in the cold side chamber CSC' The second drive pulley 20 is used to drive a belt 21 drivingly connected to a second driven pulley 22. The second driven pulley 22 is connected to a fan 18 used to blow air onto the radiator 4 so as to cool the coolant passing through the radiator 4.

-12 -Therefore when there is a Bufficient temperature difference between the temperature of the coolant entering the heat exchanger 24 and the temperature of the air passing over the fins 23, the output shaft 13 of the Stirling engine 17 will rotate causing the two fans 18, 19 to be rotated.

Although this embodiment has been described with reference to a specific type of Stirling engine it will be appreciated that a different type of Stirling engine could be used. It will also be appreciated that the cooling fan 18 used to pass air through the radiator 4 could also be used to cool the cold side 12 of the Stirling engine 17 so that only one fan need be driven by the Stirling engine 17.

It will also be appreciated that the fan 8 could be used to draw air through the radiator 4 rather than blow air through it.

With reference to Figs.4 and 5 there is shown a third embodiment of a fan drive arrangement intended to replace the fan drive arrangement shown in Fig.1.

As before, a supply of hot coolant is supplied to a hot side 31 of a Stirling engine 37 via a radiator supply hose RS' which is connected to an inlet of a hot side heat exchanger. The hot coolant flows through the hot side heat exchanger and then flows to an inlet of the radiator 4 via a radiator supply hose RS2' The Stirling engine 37 has an output shaft 53 which drives a coolant pump 50 and a drive pulley 40. The drive pulley 40 is used to drive a belt 41 drivingly connected to a driven pulley 42. The driven pulley 42 is connected to a fan 38 used to blow air onto the radiator 4 and a cold side heat exchanger in the form of a cooler 54.

-13 -Coolant is circulated through the cooler 54 and through a heat exchanger on the cold side 32 of the Stirling engine 37 by the pump 50. The coolant passes from the pump 50 to an inlet side of the cold side heat exchanger via a pipe CS' passes through the cold side heat exchanger where heat from the gas in the cold side 32 is transferred to it, exits the cold side heat exchanger and flows to the cooler 54 via a cooler supply pipe CS2' where heat is extracted from the coolant by the air passing through the cooler 54 and is returned from the cooler 54 to an inlet side of the pump 50 via a coolant return pipe CR'.

Therefore when there is a sufficient temperature difference between the temperature of the coolant entering the hot side heat exchanger and the temperature of the coolant entering the cold side heat exchanger the output shaft 53 from Stirling engine 37 will rotate causing the fan 38 to be rotated.

It will be appreciated that any type of Stirling engine having a hot side and a cold side could be used to power the fan 38. It will also be appreciated that separate cooling fans driven by the Stirling engine 37 could be used to pass air separately through the cooler 54 and radiator 4.

It will also be appreciated that the fan 38 could be used to draw air through the radiator 4 rather than blow the air through it.

Therefore in summary, the invention provides the use of a Stirling engine to recuperate waste heat from a cooling circuit of an engine and use that recuperated heat to drive one or more fans used to cool the coolant passing through a main cooling circuit for an engine.

It will be appreciated by those skilled in the art that although the invention has been described by way of example -14 -with reference to one or more embodiments it is not limited to the disclosed embodiments and that one or more modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

Claims

-15 -Claims 1. A cooling system for the engine of a motor vehicle

comprising a cooling circuit having a radiator and a coolant pump to circulate coolant through the engine and the radiator and a fan to produce a flow of air through the radiator wherein the fan is driven by a Stirling engine having a hot side heated by coolant circulating through the cooling circuit.

2. A system as claimed in claim 1 wherein the hot side of the Stirling engine has heat exchanger and the coolant flowing through the cooling circuit flows through the heat exchanger of the Stirling engine before flowing to the radiator.

3. A system as claimed in claim 1 or in claim 2 wherein the Stirling engine has a cold side and the cold side is cooled by air passing over the cold side.

4. A system as claimed in claim 3 wherein the air is urged past the cold side of the Stirling engine by a fan driven by the Stirling engine.

5. A system as claimed in claim 4 wherein the same fan is used to cool the cold side of the Stirling engine and the radiator.

6. A system as claimed in claim 1 or in claim 2 wherein the Stirling engine has a cold side and the cold side is cooled by passing liquid through a cooler attached to the cold side of the Stirling engine.

7. A system as claimed in claim 6 wherein the liquid passing through the cooler attached to the cold side of the Stirling engine is cooled by circulation through a cold side air to liquid heat exchanger.

-16 - 8. A system as claimed in claim 7 wherein the liquid is circulated through the cold side cooler and the cold side air to liquid heat exchanger by a pump driven by the Stirling engine.

9. A system as claimed in claim 7 or in claim 8 wherein air is urged past the cold side air to liquid heat exchanger by a fan driven by the Stirling engine.

10. A system as claimed in claim 9 wherein the same fan is used to cool the cold side air to liquid heat exchanger and the radiator.

11. A cooling system for the engine of a motor vehicle substantially as described herein with reference to the accompanying drawing.