This invention relates to a finned heat exchanger and an engine incorporating the finned heat exchanger which has advantageous application to engine cooling.

In engines, especially engines designed as the power source for motorcycles and the like, it is well known that a fuel combustion process occurring in an engine cylinder, as well as providing motive force for a vehicle, also produces waste heat. This waste heat must be removed or the engine will overheat. The amount of heat generated corresponds to a large degree to the power being produced by the engine which in turn relates at least to some degree to the acceleration or speed that the vehicle is operating at. To this end, engines are usually provided with cooling systems, which might be quite complex, to assist with heat removal. For example, an engine may be provided with a liquid cooling system, such as a water cooling system, this results in increased cost due to the fabrication of water distribution ducts to cool the engine. A water pump is an additional cost item. In such case, air cooled engines have a cost advantage. In such case means may be provided to enhance heat transfer from the engine into the surrounding air by convection, which takes advantage of the fact that the vehicle will be moving through the air. In the case where the engine is an air cooled engine, convective heat transfer from the engine to the air is the predominant mechanism by which such heat transfer occurs and this is typically enhanced by forced convection through use of cooling fans. Some radiative heat transfer may also occur.

To this end, the engine - or more specifically the engine block and/or cylinder head - are typically provided with a finned heat exchanger in the form of a cooling fin structure incorporating a number of cooling fins to enhance such convective heat transfer. The fins typically take the form of elongate fins of planar geometry protruding from the engine block or cylinder head approximately perpendicular to a major axis of an engine block or cylinder head. Perhaps six such fins might be provided for one form of engine. Such a cooling arrangement is effective for most types of engine application. One example is disclosed in Japan Patent Publication JP 62-186042 which discloses a cooling fin structure with fins incorporating a single sweeping curve provided to increase fin rigidity and dampen vibration or resonance of each fin. Figure 1 shows the geometry of the cooling fin(s) of JP 62-186042.

However, there may be certain engine applications where higher heat outputs from the engine cylinder(s) may be anticipated. Such applications may include the cooling of higher performance 4-valve single cylinder 4 stroke engines, including those with twin spark plugs, as are being developed by the Applicant. With the increased specific power output of the engine (that is more power output per unit engine displacement or capacity) there is more heat generated and therefore a need for increased heat transfer, in this case cooling, efficiency.

It is an object of the present invention to provide a finned heat exchanger with an improved heat transfer efficiency which may be applied to engine cooling but also to other heat transfer applications.

It is a further object of the invention to provide an air-cooled engine with a finned heat exchanger having a cooling fin structure which enhance{s) convective heat transfer away from the engine as compared to conventional cooling fin structures or finned heat exchangers.

In a first aspect, the present invention provides a finned heat exchanger having a fin structure in heat transferable contact with a body for which heat is to be exchanged and comprising a plurality of fins of planar geometry extending away from said body for transferring heat between the body and a surrounding heat transfer fluid wherein said fins are configured with a surface profile to promote turbulent flow of the surrounding heat transfer fluid across said fins such that heat transfer between said body and said surrounding fluid is promoted.

The fins are advantageously configured with a surface profile comprising a plurality of corrugations or undulations. These corrugations or undulations may usefully run the whole or a major portion of the distance between an edge of a fin distal from the body and the edge of the fin proximal to the body.

The corrugations or undulations may be configured with respect to at least two parameters selected from the group consisting of number, shape, depth and orientation of corrugations to enhance turbulence in fluid flow passing over the fins and convective heat transfer between the fins and surrounding heat transfer fluid.

The corrugations or undulations may have a flattened base with walls extending at a constant or slightly varied ramp angle away from a line passing along the base.

Desirably, each fin has a tapered construction in a direction outward from said body having greater cross-sectional area at the connection between fin and body than at the edge of the fin distal from the body.

The heat transfer operation of predominant importance is convection which may be natural or forced. Desirably, to reduce cost, convection between the body and surrounding fluid is unforced by a fan.

The body may, advantageously, be an engine and the heat transfer fluid may be air. However, other bodies and fluids, and other heat transfer applications, are not excluded.

The following description is applicable mutatis mutandis to those other applications. Importantly, the finned heat exchanger has the structural characteristics described below.

In a second aspect, the present invention provides an air cooled engine comprising:
(a) an engine block;
(b) a cylinder head;
(c) at least one cylinder accommodated by the engine block and cylinder head which generates heat when the engine is operating; and

a finned heat exchanger having a cooling fin structure comprising a plurality of cooling fins of planar geometry extending away from at least one of the engine block and cylinder head for transferring heat away from the engine wherein said cooling fins are configured with a surface profile to promote turbulent flow of surrounding air across said cooling fins when said engine is operating such that heat transfer from engine to surrounding air is promoted.

By the requirement that the engine be "air cooled" is intended that convective heat transfer is the dominant mechanism for transfer of heat from the to surrounding air. Such convective heat transfer may be natural or forced, for example by a cooling fan which generates an air flow across each cooling fin. In a particularly preferred embodiment, no cooling fan is provided; the air flow past the engine and convection is unforced by a cooling fan in which case cooling flow of air may be generated simply through motion of a vehicle including the engine through the air. This saves cost of a cooling fan. Further, while preferably avoided, the provision of water or other liquid cooling is not precluded.

Typically, the engine or other body may be provided with a fin structure comprising a plurality of fins which may be configured with surface profile and area dependent on engine design criteria such as capacity, power output and application. Advantageously, the engine is a four stroke valve in head engine for a motorcycle. Such engine may comprise multiple, advantageously two spark plugs.

The fins of the fin structure are efficiently arranged in banks of fins and may have a stacked wavy appearance when viewed side on. These fins are advantageously provided for both the engine block and cylinder head in an engine application and extend approximately perpendicularly away from a vertical axis of engine block and/or cylinder head.

Each fin may advantageously be configured with a surface profile comprising a plurality of corrugations or undulations, for example as viewed from a side of a fin, irrespective of whether the engine is a single or multi-cylinder engine. Provision of such corrugations and undulations provides each fin with a wavy appearance forming an approximately serpentine flow path for air passing between adjacent cooling fins, corrugations on adjacent fins forming surfaces confining cooling air flow. Each fin is not simply curved to increase rigidity and dampen vibration or resonance. On the other hand, the corrugations are not V notched with sharp change in angle at a base of a corrugation or undulation which complicates manufacture and which is not necessary to impart the necessary degree of turbulence. The depth of corrugations or undulations is sufficient to induce a turbulent flow in air crossing cooling fins.

The corrugations or undulations may run the whole or major portion of the distance between an edge of the fin distal from the engine and the edge of the fin proximal to the engine. The proximal edge of each fin is connected to the engine block and/or cylinder head, at a connection, so that heat may be transferred from engine block/cylinder head ("engine body") through the connection to the bulk of the cooling fin. The surface area of the connection is optimized to maximize heat transfer between the body and each fin, for example from the engine to each cooling fin, this being dependent on the surface area of the connection. It may also be appreciated that forming each fin with a plurality of corrugations or undulations increases the surface area at the connection to the engine and so, consequently, the heat transfer area. Later in this specification, the term "corrugations" rather than the expression "corrugations or undulations" is used.

Each fin advantageously has a tapered construction in an outward direction from the body, such as the engine block or cylinder head, having greater cross-sectional area at the connection between the body than at the edge of the fin distal from the body. In an engine application, each fin has greater cross-sectional area at the connection between the engine block or cylinder head and fin than at the edge of the fin distal from the engine block or cylinder head.

The engine block and cylinder head may be formed in one piece, that is integrally, or in a number of pieces, being cast together or separately as determined best from a manufacturing point of view. In assembly, or integrally, the engine block and cylinder head form the "engine body" where referred to in this specification.

The corrugations of the fins are themselves configured with respect to at least two parameters selected from the group consisting of number, shape, depth and orientation of corrugations to enhance turbulence in airflow passing over the fins and convective heat transfer between the fins and surrounding air. Depth needs to be sufficient to induce turbulence, this - in combination with a suitable corrugation shape - imparting a wavy appearance to the fins and a serpentine and eddying flow path for heat transfer fluid, typically air, between adjacent fins.

The orientation of the corrugations may be an orientation intersecting, for example being perpendicular or substantially perpendicular, with a predominant direction of airflow over the fins while the engine is in operation. The corrugations, while they may take sinusoidal form, more advantageously take a slightly sharper geometrical form as this may enhance turbulence and convective heat transfer.

To that end, the corrugations may have a flattened base with walls extending at a constant or slightly varied ramp angle away from a line passing along the base. That is, it is desirable if the corrugations are not simply curved or sinusoidal as this increases contact length between engine body and each fin and heat transfer surface area both as exposed to air and at the connection with the engine body. Squared corners for the corrugations, taken with sufficient depth, may also assist in promoting turbulence and convective heat transfer.

The corrugations are also selected in number to enhance surface area of the fins and convective heat transfer. The number of corrugations is greater, advantageously significantly greater, than the number of cylinders in the engine. Therefore, for a single cylinder engine having an engine block, viewed schematically to have four sides, the number of corrugations per side of the engine block would be significantly greater than one, preferably greater than four, more preferably greater than eight and most preferably greater than twelve. For a two cylinder engine having an engine body schematically viewed as having four sides, the number of corrugations per side of the engine block would also be significantly greater than two, preferably greater than eight and most preferably greater than twelve. Analogous multiples of corrugations over number of cylinders may be envisaged for other geometries of engine body.

Viewed geometrically, a graphic projection from each cylinder toward a side of the engine body may form a plane intersecting each fin. Viewed against this plane will be a plurality of corrugations or undulations, each fin effectively being viewed in cross-section. This plurality of corrugations promotes heat transfer from the or each cylinder through promoting surface area and turbulent air flow over the fins which also promotes convective heat transfer between the engine body and surrounding air.

Where the engine block generally takes the shape of a rhomboid or parallelepiped, tapered in longitudinal extent or not, it may be understood that corrugations may be omitted or changed in configuration in corner regions of the parallelepiped for purposes of manufacturing convenience. In a cooling duty, the flatter configuration In corner regions, which form Inlet and exit regions for a cooling air flow path between adjacent cooling fins, also causes a change away from the preferred serpentine and eddying flow path between adjacent cooling plates.

The corrugated structure of each fin also promotes stiffness which is increased over the flat non-corrugated fin construction used in prior art engines. Accordingly, rubber isolators between the cooling fins may not be necessary and may be excluded with potential cost advantage. This also increases the cooling effect since these isolators reduce the surface area in contact with air and also impede the airflow over other parts of the cooling fins. In some constructions, this may enable fewer cooling fins to be provided than following a flat fin construction. For example, in one engine cooling application, the Applicant required 6 flat cooling fins. With the corrugated construction, the number of cooling fins was reduced to 5.

The finned heat exchanger as above described is suitable for air cooled engines including spark ignited engines and particularly those of four stroke type as above mentioned. Such engine may have 2, 3 or 4 valves dependent on the desired performance characteristics of the engine. Higher performance four stroke engines as being developed by the Applicant have 4 valves and a demonstrably significant heat output. The cooling system may particularly beneficially be applied to small bore engines, that is engines having a capacity of between 70 cc and 250 cc and cylinder bore diameter of between 45mm and 70mm, where the engine has two, three or more valves. The engine may be fuel injected or carbureted. The engine provided with cooling fins as described above may be advantageous from a weight reduction point of view being applicable with cast iron liner and aluminium cylinders.

In a final aspect, the present invention provides a method of transferring heat between a body and surrounding heat transfer fluid using the finned heat exchanger as above described. A most advantageous application is in the air cooling of an engine by convective heat transfer.

The finned heat exchanger and engine of the present invention may be more fully understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:

Figure 1 is side view of an engine block of an engine according to prior art.

Figure 2 is a side view of a cylinder head of an engine having a finned heat exchanger having a cooling fin structure with fins configured with a plurality of corrugations according to a preferred embodiment of the invention.

Figure 3 is a side view of an engine block of an engine having a finned heat exchanger having a cooling fin structure with fins configured with a plurality of corrugations according to a preferred embodiment of the invention.

Figure 4 illustrates an assembly of the cylinder head and engine block of an engine as respectively shown in Figures 2 and 3.

Figure 5 illustrates mounting of assembly of cylinder head and cylinder block incorporating the finned heat exchanger of a preferred embodiment of the invention on a motorcycle.

Figure 6 is an isometric view of an engine according to a preferred embodiment of the invention showing cylinder head (upper box) and engine block (lower box).

With reference to Figures 2, 3 and 4, there is shown an engine in the form of a four valve single cylinder 4 stroke small bore engine 100, for a motorcycle 200, having an engine block 10 and cylinder head 11. As the engine has valves located in the cylinder head 11, it is a valve in head engine. As the engine 100 produces a significant heat output, a finned heat exchanger is provided to enhance heat transfer between engine 100 and surrounding air. Heat is exchanged during air cooling of the engine 100 with cooling occurring predominantly by the mechanism of convective transfer of heat away from the engine 100 to the surrounding air which thereby acts as a heat transfer fluid.

The finned heat exchanger comprises a cooling fin structure and, as will be observed, both engine block 10 and cylinder head 11 of engine 100 are respectively provided with banks of cooling fins 12 and 13 extending away from the engine body comprised by engine block 10 and cylinder head 11. The cooling fins 12, 13 are not formed integrally, say by forging, with cylinder walls for ease and lowered cost of engine manufacture.

Each cooling fin, as may be seen in Figures 2 to 4, has a tapered construction in an outward direction from engine block 10 and cylinder head 11 having greater cross-sectional area at the connection 127 between engine block 10 or cylinder head 11 and fin than at the edge 126 of the fin 125 distal from engine block 10 or cylinder head 11 (please note dimension A in comparison in. dimension B in Figure 4).

Each bank 12 and 13 of cooling fins comprises 6 fins for the cylinder head 11 and 5 fins for the engine block 10. These fins are used to promote convective heat transfer for dissipation of heat from engine 100 to the atmosphere.

Each cooling fin 125 in the bank of fins 12 and 13 has planar geometry and is configured with a surface profile comprising a plurality of corrugations 1 such that each fin has an undulating or wavy form when viewed from the side as demonstrated by the drawings.

There are a number of corrugations - that is four to five corrugations, when viewed In a side projection illustrating the corrugations in an imaginary plane projected from engine 100. As may be noted from Fig. 1, there are no corrugations 14 to enhance turbulence provided at corners 105 of the engine block 10 and cylinder head 11. In addition, intake manifold 111 and other engine ducts are not obstructed by, or needful of, provision of the cooling fins 12 and 13. Port 117 to accommodate a spark plug is likewise positioned proximate an uncorrelated portion of cooling fin 1260 (see Figure 6).

The shape and depth of each corrugation 14 impacts on the convective heat transfer efficiency because it increases the heat transfer area of the fins in the cooling fin structure made up of banks of cooling fins 12 and 13. The depth of corrugations 14 is sufficient to impart a wavy appearance to the banks of cooling fins 12 and 13 and a serpentine and eddying flow for cooling air passing through the passage formed between adjacent fins, this flow path being shown in Figures 2 and 4. Each cooling fin is of conventional material of construction for a cooling fin structure for an engine. A metallic material is preferred. A tapering construction for the fins in each of fin banks 12 and 13 may also be observed from the drawings.

That is, each cooling fin has a greater cross-section at the connection 127 between
the engine 100 and fin 120 than at the edge 126 of each fin distal from the engine.

This provides greater heat transfer area to induce heat flow away from the engine. Each corrugation 14 runs the whole of the distance between an edge of each fin distal from the engine 100 and the edge of each fin proximal the engine 100 as shown in Figures 4 and 6.

Figure 4 illustrates assembly of cylinder head 11 and engine block 10 In the complete engine 100. This assembly is mounted on to a frame 201 of a motorcycle 200 as also illustrated in Figure 5. The engine 100, with engine block 10 and cylinder head 11, is oriented such that the corrugations 14 of each fin in each bank of fins 12 and 13 is perpendicular or substantially perpendicular with an expected predominant vector of airflow over the fins while the motorcycle 200 is moving or in operating condition. It may be noted that motorcycle 200 does not incorporate a cooling fan or rely on fan forced convection providing cost advantage. Cooling air is caused to flow past cooling fins simply by motion of air past motorcycle 200 as it moves through the air.

The flow of the air in this situation is represented by arrows 202. As the corrugations have a rounded form, with a flattened base, they have more surface area compared to straight fins, while having shape and depth to enhance turbulence in the air flow 202, as it is forced to flow into the corrugations or undulations 14, through a serpentine flow path` with resulting eddying or circulating turbulent flow promoting a better convective heat transfer which leads to better cooling of engine 100. The outflow of the air through the cooling fins is represented by arrows 203. There is no appreciable change in direction of airflow between that at an inlet region and that at an exit region of a passage formed by surfaces of adjacent cooling fins. Inlet and exit regions are indicated by the horizontal arrows at the left and right of the engine body of Figures 2 and 4.

The corrugated structure of each cooling fin also provides stiffness and makes the cooling fin structure less susceptible to vehicle vibration as compared to a flat or straight fin construction. Hence, rubber isolators between the cooling fins are excluded. This improves the cooling effect since these isolators reduce the surface area of fins in contact with air. In addition, a cost saving may be achieved by omitting requirement for such isolators.

The Applicant has compared cooling performance of an engine being cooled by use of a heat exchanger having corrugated fins, of particular structure and layout, according to the invention, and such as is incorporated in motorcycle 200, and an engine having non-corrugated flat fins. The experiment conducted on four valve four stroke motorcycle engines having same heat Input, size and same wind speed or air flow rate was maintained. The following results have been observed:

1. The increase in surface area of corrugated fin, as opposed to a straight or flat fin, is on the order of 4.5%.

2. The convective heat transfer co-efficient increases by 14.5% with a corrugated fin structure as opposed to a straight or flat fin structure.

3. The heat dissipated over unit pitch along the length of liner increases by 16,3%.
The number of cooling fins required with such an arrangement is less as compared that of fins having conventional flat/straight shape due to increased heat transfer efficiency. This would contribute to reduction In engine weight.

As an alternative, the engine 100 may be provided with an engine block with corrugated or undulating fins and cylinder head with straight fins or vice versa.

Modifications and variations to the finned heat exchanger and engine of the present invention will be understood by the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present disclosure. For example, it is to be understood that a finned heat exchanger in accordance with the invention may be used in applications other than automotive applications.

CLAIM:

1. A finned heat exchanger having a fin structure in heat transferable contact with a body for which heat is to be exchanged and comprising a plurality of fins of planar geometry extending away from said body for transferring heat between the body and a surrounding heat transfer fluid wherein said fins are configured with a surface profile to promote turbulent flow of the surrounding heat transfer fluid across said fins such that heat transfer between said body and said surrounding fluid is promoted.

2. The heat exchanger of claim 1 wherein said fins are configured with a surface profile comprising a plurality of corrugations or undulations.

3. The heat exchanger of claim 1 or 2 wherein each fin has a tapered construction in a direction outward from said body having greater cross-sectional area at the connection between fin and body than at the edge of the fin distal from the body.

4. The heat exchanger of any one of the preceding claims wherein convection between the body and surrounding fluid is unforced by a fan.

5. The heat exchanger of any one of claims 2 to 4 wherein said corrugations or undulations run the whole or a major portion of the distance between an edge of a fin distal from the body and the edge of the fin proximal to the body.

6. The heat exchanger of any one of claims 2 to 5 wherein said corrugations or undulations are configured with respect to at least two parameters selected from the group consisting of number, shape, depth and orientation of corrugations to enhance turbulence in fluid flow passing over the fins and convective heat transfer between the fins and surrounding heat transfer fluid.

7. The heat exchanger of claim 6 wherein said corrugations or undulations (14) have a flattened base with walls extending at a constant or slightly varied ramp angle away from a line passing along the base.

8. An air cooled engine (100) comprising:

(a) an engine block (10);

(b) a cylinder head (11);

(c) at least one cylinder accommodated by the engine block (10) and cylinder head (11) which generates heat when the engine (100) is operating; and

(d) a finned heat exchanger having a cooling fin structure comprising a plurality of cooling fins (12, 13) of planar geometry extending away from at least one of the engine block (10) and cylinder head (11) for transferring heat away from the engine (100) wherein said cooling fins (12, 13) are configured with a surface profile to promote turbulent flow of surrounding air across said cooling fins (12, 13) when said engine (100) is operating such that heat transfer from engine (100) to surrounding air is promoted.

9. The engine of claim 8 wherein said fins (12, 13) are configured with a surface profile comprising a plurality of corrugations or undulations (14).

10. The engine of claim 8 or 9 wherein each cooling fin has a tapered construction in a direction outward from engine block or cylinder head having greater cross-sectional area at the connection between fin and engine block or cylinder head than at the edge of the fin distal from the engine block or cylinder head.

11. The engine of any one of claims 8 to 10 wherein convection from the engine is unforced by a cooling fan.

12.The engine of any one of claims 8 to 11 wherein said corrugations or undulations (14) run the whole or a major portion of the distance between an edge of a cooling fin distal from the engine (100) and the edge of the cooling fin proximal to the engine (100).

13. The engine of any one of claims 8 to 12 wherein said corrugations or undulations (14) are configured with respect to at least two parameters selected from the group consisting of number, shape, depth and orientation o. corrugations to enhance turbulence in airflow passing over the fins and convective heat transfer from the fins to surrounding air.

14. The engine of claim 13 wherein said corrugations or undulations (14) have a flattened base with walls extending at a constant or slightly varied ramp angle away from a line passing along the base.

15.The engine of claim 13 or 14 wherein said corrugations or undulations (14) are selected in number to be significantly greater than the number of cylinders in the engine (100).

16. The engine of claim 15 wherein corrugations or undulations (14) are omitted or changed in configuration in corner regions of the cylinder block (10) and cylinder head (11).

17. The engine of any one of claims 8 to 16 being a four stroke valve in head engine.

18. The engine of claim 17 being a small bore engine.

19. A method of transferring heat between a body and surrounding heat transfer fluid using the finned heat exchanger as claimed in any one of claims 1 to 7.

20. A method of air cooling an engine using the finned heat exchanger as claimed in any one of claims 8 to 18.