The present invention concerns a method of cooling fuel for a combustion engine, where the fuel is pressurised by means of pressurisation and lead to one or more fuel in- jection valves. The invention also includes a device for implementing said method of cooling fuel.

US 4,385, 615"Fuel system for diesel engines"discloses a cooling system for fuel. Fuel is pumped from a fuel tank via an intermediate fuel tank to the engine in a higher amount than consumed by the engine. The system comprises means for leading the excess fuel through a cooling unit and back to the intermediate fuel tank, wherefrom the fuel is recycled to the engine. The purpose of this fea- ture of the fuel system is to avoid overheating of the fuel. Overheating can be caused due to the mechanical work/energy induced by the fuel pump and heat transferred from the engine. The downside of the disclosed system is the complexity of the system and the considerable number of extra components needed, which are costly and energy consuming. Also it is necessary to recycle a high amount of fuel in order to achieve an adequate temperature. In the document is mentioned that around 3 times the con- sumed amount of fuel is to be recycled. This leads to an oversized fuel pump and increased energy consumption.

Systems are also known where the fuel is recycled to a normal fuel tank without the intermediate tank and the cooling means. These systems, however, have some of the same disadvantages as the system disclosed in US 4,385, 615. One is the fact that, when the engine has been running for some time, the entire content of the fuel

tank can be overheated, especially in hot weather and/or by low fuel level in the tank.

The object of the invention is to provide a method of and a device for cooling fuel in a simple and efficient man- ner, where overheating of the fuel is avoided, and where the use of energy for recycling the fuel is kept at a minimum. Another object is to ensure constant temperature of the fuel where fluctuations are minimised, in order to enhance engine performance.

The new aspects comprised in the invention are that the fuel between the means of pressurisation and the one or more fuel injection valve (s) is conveyed through at least one first channel, which first channel is in heat trans- ferable contact with at least one separate second chan- nel, in which second channel a coolant is conveyed, and where heat is transferred from the first channel to the second channel.

The technical effect hereby obtained, is that the fuel is cooled and that it is cooled just before entering the en- gine, whereby it is ensured that the fuel is not over- heated and that any unwanted heating effects do not have opportunity to influence the temperature of the fuel be- fore it enters the engine.

The at least one first channel may comprise at least two outlets of which at least one outlet is connected to an excess-pressure valve, which excess-pressure valve is connected to a fuel tank. Hereby it is obtained that overheating of the fuel in the means of pressurisation, e. g. fuel pump, can be avoided. The natural lubricating ability of fuel is lost above a certain temperature, which temperature can be reached e. g. when running the engine at idle speed for longer periods.

At least one of the at least two outlets may be connected to a fuel injection valve. Hereby it is obtained that cooled or temperature controlled fuel can be introduced directly into the engine.

The at least one first channel may be placed inside the at least one second channel. Hereby an advantageous way of transferring heat from the at least one first channel to the at least one second channel is obtained. Also ob- tained is that the at least one first channel is insu- lated from heat radiated from other engine components.

In a further embodiment the at least one second channel may comprise a number of wall sections, which divides the at least one second channel into a number of sub chan- nels. In this way a large contact area between the cool- ant and the wall sections is obtained, which enhances heat transfer. Also obtained is a way of guiding the flow of the coolant in the at least one second channel, which also can enhance heat transfer enabling a more compact and space saving design.

Also, the at least one first channel may comprise a num- ber of inwardly directed fins. This feature enhances heat transfer, due to an increased contact area between the fuel and the fins.

Preferably, the at least one first channel and the at least one second channel is mainly produced from a single piece of extruded material, whereby a cost saving design is obtained.

In a further embodiment fuel enters the at least one first channel coaxial in one end and exits from the at least two outlets in radial direction, whereby an appro-

priate distance between the outlets can be chosen, which distance or distances match corresponding distance or distances between the fuel injection valves.

Preferably, the at least one first channel and the at least one second channel are parallel in order to provide a large common contact area between the channels, whereby heat transfer may be improved.

In a preferred embodiment coolant enters and exits the at least one second channel substantially in the same end, whereby the opposite end can be used for fuel entry only, whereby said opposite end e. g. can be screwed directly on to a fuel pump. It is also obtained that the coolant is easily lead in e. g. parallel hoses to and from the at least one second channel to a separate cooler.

A further embodiment comprises a device for cooling fuel for a combustion engine, where the fuel is pressurised by means of pressurisation and lead to one or more fuel in- jection valves, where the device comprises at least one first channel for conveying fuel, which first channel is in heat transferable contact with at least one second channel, in which second channel a coolant is conveyed, and where heat is transferred from the first channel to the second channel. Hereby it is obtained that the fuel is cooled and that it is cooled just before entering the engine, so that it is ensured that the fuel is not over- heated and that any unwanted heating effects will not have opportunity to influence the temperature of the fuel before it enters the engine.

The device may further comprise: - at least one inlet for fuel, - at least two outlets for fuel,

- at least one inlet for coolant and - at least one outlet for coolant, whereby it is provided that fuel can enter the device and after cooling be distributed through more outlets, and that coolant can be entered and circulated separately in the device before it is recycled to a separate cooler.

The at least one first channel may be placed inside the at least one second channel. This leads toan advantageous way of transferring heat from the at least one first channel to the at least one second channel. Also obtained is that the at least one first channel is insulated from heat radiated from other engine components.

The at least one second channel may comprise at least one wall section, said wall section being connected to the outer wall of the at least one first channel, whereby an improved heat transfer from the fuel in contact with the outer wall of the at least one first channel to the cool- ant in the at least one second channel via the said at least one wall section may be obtained.

Preferably, at least one wall section is extending be- tween the outer wall of the at least one second channel and the outer wall of the at least one first channel.

Hereby it is obtained, that the at least one first chan- nel and the at least one second channel are connected, so that the channels can be extruded in one piece and that a connection can be established from the inside of the at least one first channel to the outside of the at least one second channel.

Fuel may be exited from the at least one first channel to the at least two outlets through passages in the at least

one wall section, whereby it is obtained that the pas- sages are tight and separated from the coolant.

In a further embodiment the at least one first channel, the at least one second channel and the at least one wall section are preferably made in one piece by extrusion, whereby handling and production can be done at a rela- tively low cost.

The following figures show examples of embodiments of the present invention. The invention will be explained in de- tail below with reference to the figures.

-Fig. 1 is an embodiment seen in a view from the side and above.

- Fig. 2 is a top view showing 3 sections, D-D, E-E and F-F.

- Fig. 3 is a sectional view along the line D-D on fig.

2.

Fig. 4 is a sectional view along the line E-E on fig.

2.

- Fig. 5 is a sectional view along the line F-F on fig.

2.

The following numbering is used on the figures: 6 First channel - 8 Second channel -10 Outlet for fuel - 14 Wall section - 16 Sub channel - is Fins - 20 Fuel cooler

22 Inlet for fuel - 24 Inlet for coolant -26 Outlet for coolant 28 Outer wall of first channel 30 Outer wall of second channel 32 Passage 33 Return opening - 34 End cover 35 Distribution opening 36 End cover 37 Separation wall Fig. 1 shows a fuel cooler 20. Fuel enters via an inlet for fuel 22 and exits via a number of outlets for fuel 10. Coolant enters the fuel cooler 20 via an inlet for coolant 24 and exits via an outlet for coolant 26. Fur- ther details are explained in the following.

Fig. 2 shows the same features as fig. 1. Also shown is 3 sectional views D-D, E-E and F-F. D-D is a longitudinal section through the centre of the fuel cooler 20. E-E is a longitudinal section through the centre of the outlet for coolant 26. F-F is a cross section through the centre of an outlet for fuel 10.

Fig. 3 shows an inlet for fuel 22 placed in an end cover 34. The inlet for fuel 22 is connected to a channel 6.

From the channel 6 a number of passages 32, which are placed in a wall section 14, lead to outlets for fuel 10.

The channel 6 is closed in the end opposite the inlet for fuel 22 with an end cover 36. In the end cover 36 are also placed an inlet for coolant 24 and an unshown outlet

for coolant 26. The end cover 34 comprises a circumferen- tial return opening 33, which use is explained below. The fuel cooler is preferably made from a piece of extruded and following machined material with end covers 34 and 36 brazed, glued or welded on to it.

In operation the means of pressurisation (not shown) are connected to the inlet for fuel 22, whereto fuel is lead under high pressure and further lead to the channel 6.

The mechanical work to build the pressure creates heat, leading to increased temperatures of the fuel. Normally the temperature of the fuel is preferred to be kept con- stant. Also, the fuel is normally used to lubricate the means of pressurisation, e. g. a fuel pump, whereby the temperature must be kept under a certain limit above which the fuel looses its lubricating capacity. From the channel 6 the fuel is distributed and exited via the pas- sages 32 to the outlets 10. The outlets are connected to fuel injection valves (not shown), from which the fuel is fed to a combustion engine (not shown). Also not shown is that one of the outlets for fuel 10 can be connected to the fuel tank via an excess-pressure valve. This is used e. g. if the means of pressurisation is a pump of the type which supplies a fixed flow of fuel. In that case the flow must be higher than the maximum fuel consumption of the engine, whereby, especially when the engine is run- ning idle, a large amount of unused fuel must be e. g. lead to the fuel tank. In order to maintain a desired pressure to the injection valves, an excess-pressure valve is inserted in the connection between the outlet for fuel 10 and the fuel tank. The fuel cooler 20 may be connected directly on a fuel pump, in which case it is advantageous to place the inlet for fuel 22 in one end and to place both inlet and outlet for coolant 24 and 26 in the opposite end. Another possibility is to place at least one of the inlets or outlets for coolant 24 or 26

in radial direction on the fuel cooler. In that case they can be placed in any end.

Fig. 4 shows an inlet for fuel 22 and a first channel 6 encircled by an outer wall 28. Outside the first channel 6 is a second channel 8 in which coolant is lead. In this case the second channel 8 is divided into two separate sub channels 16, so that coolant can be lead longitudi- nally from one end to the other, and returned in the op- posite direction, thereby entering and exiting in the same end. The second channel 8 is encircled by an outer wall 30. End covers 34 and 36 are attached among others to the outer wall 30. The second channel 8 is divided into two sub channels 16 by the wall sections 14, which extends between the end covers 34 and 36. The wall sec- tions 14 extend between the outer wall 28 of the first channel 6 and the outer wall 30 of the second channel 8.

Coolant enters via an inlet 24 and flows to the opposite end, where it is stopped and returned to an outlet for coolant 26. In the end cover 36 is placed a separation wall 37, which separates the flows through the inlet 24 and the outlet 26. The separation wall forms a tight con- nection to the wall sections 14. The end cover 36 can comprise a distribution opening 35 in case of multiple sub channels 16, see e. g. fig. 5. This is to couple mul- tiple sub channels 16 to one inlet 24 respective one out- let 26. The end cover 34 comprises a return opening, which allows coolant forwarded in sub channels 16 con- nected to the inlet 26 to be returned via other sub chan- nels 16 connected to the outlet 26, whereby a circuit is formed. In a different embodiment, the coolant could be lead into the channel 8 in one end and exited in the op- posite end, e. g. in radial direction. After leaving the fuel cooler, the coolant is lead to a separate cooling unit, cooled to suitable temperature, and recycled to the fuel cooler. This is a normal cooling circuit and there-

fore known to the skilled person. In case of low ambient temperature or otherwise caused low temperature of the fuel, the fuel cooler may also be used to heat the fuel.

This may be done e. g. by inserting an electrical heating element into the fuel cooler, which is then activated when needed. The temperature of the fuel should then be monitored with a temperature gauge.

Fig. 5 shows a first channel 6 for fuel, which in this case is also placed in the centre as the example in fig.

3 and 4, but could as well be placed off centre. The channel 6 is encircled by an outer wall 28. On the inside of the outer wall 28 a number of inwardly extending fins 18 are placed. The purpose of the fins 18 is to provide an enlarged internal surface area, whereby heat transfer from the fuel is enhanced. The outer wall 28 is connected to a number of wall sections 14, which extend outwardly to an outer wall 30. Between the outer walls 28 and 30 a second channel 8 for coolant is formed, which channel is subdivided into a number of sub channels 16. Increasing the number of wall sections 14 increases the surface area, which improves heat transfer to the coolant. Heat is transferred from the fuel to the fins 18-to the outer wall 28-to the wall sections 14 and to the outer wall 30, where it is transferred to the coolant via the surfaces in contact with the coolant. Coolant enter via an inlet 24 and exits via an outlet 26. The forward flow is distributed via a distribution opening 35.1 to the sub channels 16 in the left part, and is separated from the return flow in the right part to an accumulating opening 35.2 by a separation wall section 37. Both openings 35.1 and 35.2 are placed in the end cover 36. One of the wall sections 14 is preferably made with a thickness adequate to provide passages 32 from the first channel 6 to the outlet 10 as well as adequate wall thickness for e. g. a treading in the outlet 10, where a connection is to be

made to the fuel injection valves and/or excess-pressure valve. The shown embodiment is well suited for an extru- sion process after which the passages 32 and outlets 10 are machined, e. g. by drilling.

The fuel cooler and its components can be made from a number of materials or combinations of materials, e. g. aluminium, steel alloy, brass, magnesium, titanium, and may be assembled by welding, brazing, clad brazing, glu- ing etc. as appropriate. The coolant may e. g. be of the same type as used for cooling the engine. The fuel may be of any type e. g. diesel, gasoline, kerosene etc.

The present invention extends beyond the embodiments shown in the figures, which are to be seen merely as ex- amples. A large number of similar ways to achieve the same. performance are within easy reach of the person skilled in the art, based on the present disclosed inven- tion.