WO2000064694A1

WO2000064694A1 - Fuel tank

Info

Publication number: WO2000064694A1
Application number: PCT/SE2000/000768
Authority: WO
Inventors: Jan-Olof Larsson
Original assignee: Scania Cv Aktiebolag (Publ)
Priority date: 1999-04-22
Filing date: 2000-04-20
Publication date: 2000-11-02
Also published as: SE512730C2; SE9901437L; SE9901437D0

Abstract

A fuel tank (1) incorporates a casing (2) which forms a substantially enclosed space. The casing (2) is connected to a line (3) for conveying fuel from the tank (1) and to a return line (5) for conveying fuel back to the tank (1). The fuel tank (1) incorporates means designed to guide the return fuel in such a way that it comes into contact with and is cooled by the casing (2) of the fuel tank (1) before it mixes with the fuel (4) stored in the tank.

Description

Fuel tank

Background to the invention, and state of the art

The present invention relates to a fuel tank according to the preamble to patent claim 1, intended, for example, for a motor vehicle.

In order to supply fuel to a combustion engine in a motor vehicle, a pump is commonly used for feeding fuel from a fuel tank to the combustion engine. Such a pump is often driven by the combustion engine and the quantity of fuel pumped from the tank varies with the speed of the engine. In order to ensure that the pump does in all situations supply a necessary fuel quantity to the engine, it has in normal engine operation a certain overcapacity. During a normal assortment of conditions encountered when driving a motor vehicle, approximately one-third of the fuel pumped from the tank is led back in the form of a return flow. A large fuel return flow arises when the engine is operating with little or no gas mobilisation, e.g. on downhill runs and during no-load running.

New injection systems which operate with high injection pressures result in a relatively high return fuel temperature, usually of the order of 80°C. When the fuel reaches such temperatures, there is risk of resin precipitation which may block fuel lines and cause breakdowns.

GB 2 246 988 makes known a fuel system for a motor vehicle which includes a fuel tank with a line for conveying fuel from the tank and a return line for conveying return fuel to the tank. In order to cool it, the return fuel is led through a heat exchanger arranged inside the fuel tank before it mixes with the fuel stored in the tank. Such cooling of return fuel causes a corresponding heating of the fuel stored in the tank. Cases where there is a large fuel return flow to the tank and a small quantity of fuel stored in the tank result in high temperature of the fuel stored in the tank and ineffective cooling of the return fuel.

US 4 283 067 makes known a motor vehicle in the form of a passenger car which has a fuel tank situated behind the rear seat. The air supplied by an air-conditioning system in the passenger compartment of the car is intended, after passing through the passenger compartment, to flow past the outside of the fuel tank. Such a fuel tank location is often not appropriate and the air flow past the fuel tank is unlikely to provide sufficient cooling to cool a large quantity of fuel returning at a high temperature.

Summary of the invention

The object of the present invention is to provide a fuel tank according to the preamble to the patent claim, which by uncomplicated means causes effective cooling of a fuel return flow to the tank.

This object is achieved by the fuel tank mentioned in the introduction, which is characterised by the features indicated in the characterising part of claim 1. As fuel tanks are generally situated in an environment which has a significantly lower temperature than the return fuel and as the fuel tank casing usually consists of a relatively thin layer of a metallic material with good thermally conducting characteristics, the return fuel is effectively cooled by contact with the casing. The location of fuel tanks in motor vehicles is often also such that at least some areas of their casing form an outer delineating surface for the vehicle. Such a delineating surface is subject to effective cooling by the air flowing past it while the vehicle is in motion. There is usually also good cooling of other outer delineating surfaces of a fuel tank arranged in a vehicle. Guidance of the return fuel so that it flows in contact with and is cooled by the casing can be implemented by simple means and is therefore not expensive. For example, the design of the return line at the inlet to the tank may be such that the return fuel flows to and in contact with the casing before it mixes with the fuel stored in the tank.

According to a preferred embodiment of the invention, said means are designed to guide the return fuel so that it is caused to flow along an area of an inside wall surface of the casing. Such an area represents with advantage a large proportion of the total inside wall surface of the casing and should preferably extend over more than 25% of the total inside wall surface of the casing in order to achieve effective cooling of the return fuel. Advantageously, said means are designed to spread return fuel substantially uniformly over said area. This results in uniform cooling of the return fuel. Said means may include a device which is enclosed in the casing and which incorporates a guiding surface for directing return fuel in contact with the inside wall surface of the casing. Such a device may be used to achieve reliable guidance of the return fuel all the way from its inlet into the fuel tank to its contact with the inside wall surface of the casing.

According to another preferred embodiment of the invention, the guiding surface of said device extends substantially parallel with and at a short distance from at least part of the inside wall surface of the casing so as to form a slit-shaped passage through which the return fuel is intended to flow. With such a slit-shaped passage, the return flow may be caused to flow in the form of a thin flow along a relatively large area of the inside wall surface of the casing. This provides the return fuel with prolonged cooling contact with the casing before it mixes with the fuel stored in the tank.

According to another preferred embodiment of the invention, said device may have a tanklike shape with an outer wall surface which forms said guiding surface ana^* an inner wall surface which forms a second space within the first space, and the device may incorporate an aperture to allow return fuel to pass from said passage into the second space. In such cases, the tanklike device has with advantage a shape and size such that an outer wall surface of it can be arranged substantially immediately within the inside wall surface of the casing during the forming of the slit-shaped passage. The passage extends with advantage along as large a proportion of the total inside wall surface of the casing as possible and the return fuel is caused to flow a long distance before it mixes with the fuel stored in the tank. Said tanklike device may be arranged in the casing with its aperture directed upwards, in which case the return fuel is led into the tank via an orifice of the return line, which orifice is arranged at a lower portion of the casing. The tanklike device may incorporate side portions which with advantage extend almost up to the upper portion of the casing. This means that the return fuel can spread over a very large area before it flows over an upper edge of the side portions of the device and in through the aperture of the device. The return fuel is thus led into the second space, where it mixes with the fuel stored in the tank. According to an alternative positioning of the tanklike device, it is arranged in the casing with the aperture directed downwards and the return fuel is led into the tank via an orifice of the return line, which orifice is arranged at an upper portion of the casing. In this case the side portions of the tanklike device may extend only a short distance downwards, since the return fuel, even without guiding surfaces, can be caused to flow downwards along the side portions of the casing until it reaches the fuel stored in the tank.

According to another preferred embodiment of the invention, said device incorporates a tubular line designed to lead the return fuel to the inside wall surface of the casing in such a way that the return fuel flows in contact with the inside wall surface of the casing in an area situated above the level of the fuel stored in the tank. Such a pipeline provides reliable guidance of the return fuel to the inside wall surface of the casing. Thereafter the return fuel runs downwards and is cooled by the inside wall surface of the casing until it reaches the fuel stored in the casing. With advantage, the tubular line extends in a path within the inside wall surface of the casing and incorporates holes through which the fuel is intended to flow to said area of the inside wall surface of the casing. Such a pipeline, which with advantage incorporates holes arranged at constant spacing along the extent of the pipe, makes it possible for the return fuel to spread substantially uniformly over the whole inside wall surface of the side portions of the casing. The result is effective cooling of the return fuel.

Brief description of the drawings

Preferred embodiments of the invention are described below by way of examples with reference to the attached drawings, in which:

Fig. 1 depicts a fuel tank according to a first embodiment of the invention. Fig. 2 depicts a fuel tank according to a second embodiment of the invention. Fig. 3 depicts a fuel tank according to a third embodiment of the invention.

Detailed description of preferred embodiments of the present invention

Fig. 1 depicts a first embodiment of a fuel tank 1 of a motor vehicle, which tank is intended to accommodate liquid fuel such as diesel oil for driving the motor vehicle's combustion engine. The fuel tank 1 incorporates a casing 2 which consists of a relatively thin metal material (sheetmetal material) with good thermally conducting characteristics. The casing 2 incorporates an inside wall surface 2a which forms a substantially enclosed space, and an outside wall surface 2b which is in contact with an environment. Such an environment may be adjacent portions of the motor vehicle or ambient air. In cases where the motor vehicle consists of a truck, the tank is advantageously mounted on the vehicle's frame side-members in a conventional manner at a point where relatively good air flow is possible. With ambient air it is possible to achieve a cooling air flow past the outside wall surface 2b of the casing while the motor vehicle is in motion. The casing 2 is connected to a line 3 for conveying fuel 4 stored in a fuel tank 1 to a combustion engine by means, for example, of a pump. Depending on the vehicle's operating situation, unburnt fuel is led back to the fuel tank 1 via a return line 5. In Fig. 1, the return line 5 leads into the lower portion of the casing 2. The casing 2 encloses a device 6 with a tanklike shape with an inner wall surface 6a which forms a second space inside the enclosed space of the casing, and an outer wall surface 6b which forms a guiding surface for the return fuel. The tanklike device 6 incorporates an aperture 7 to allow return fuel to enter the second space. The tanklike device 6 is arranged with its bottom portion 6c a short distance above a corresponding lower portion of the casing 2 and with side portions 6d arranged a short distance within corresponding side portions of the casing 2. The outer wall surface 6b of the tanklike device 6 thus forms in conjunction with the inside wall surface 2a of the casing a slit-shaped passage 8. The passage 8 thus extends along a large proportion of the whole of the inside wall surface 2a of the casing.

In Fig. 1, the return fuel, which may be at a temperature of about 80°C, is led into the lower portion of the casing 2 via the return line 5. Immediately after the fuel enters the casing 2 it comes into contact with the bottom portion 6c of the device 6. The outer wall surface 6b of this bottom portion 6c serves as a guiding surface which leads the return fuel into contact with the inside wall surface 2a of the casing. The return fuel spreads substantially uniformly in the slit-shaped passage 8, which initially extends mainly in a horizontal plane. When the return fuel reaches the side portions of the casing 2, it flows upwards in the passage 8. This flow upwards in the slit-shaped passage 8 continues until the return fuel reaches a level situated above the upper edges of the side portions 6d of the device 6. The return fuel then flows in through the opening 7 of the device 6 and down into the space of the tanklike device. In that space it mixes with the fuel 4 stored there. While the fuel is passing through the slit-shaped passage 8, it is cooled by the casing 2, which is in contact with an environment which is at a considerably lower temperature than the return fuel. Advantageously, at least some parts of the outside wall surface 2b of the casing 2 are in contact with ambient air. The casing and the return fuel are thus subject to very effective cooling by the air stream which flows past the outside wall surface 2b of the casing when the vehicle is in motion. The upper edges of the side portions 6d of the device 6 are with advantage situated at a level immediately below the upper portion of the inside wall surface 2a of the casing. This results in the return fuel flowing along a very large area of the inside wall surface 2a of the casing before it mixes with the fuel 4 stored in the space of the tanklike device 6. The result is very effective cooling of the return fuel.

Fig. 2 depicts a fuel tank 1 according to another alternative embodiment. Here too the fuel tank 1 incorporates a casing 2 with an inside wall surface 2a and an outer wall surface 2b, a line 3 for conveying fuel from the tank 1 and a return line 5 for supply of return fuel. The difference is that in this embodiment the return line 5 leads into an upper portion of the casing 2. Here again, a tanklike device 6 which is provided with a bottom portion 6c and side portions 6d and an aperture 7 is arranged inside the casing 2, but the tanklike device 6 is placed with its aperture 7 directed downwards and with the outer wall surfaces 6b of its bottom portion 6c and of its side portions 6d arranged parallel with and at a short distance from the inside wall surface 2a of the casing during the formation of the slit-shaped passage 8. Here the fuel 4 stored in the fuel tank 1 is mainly stored in the casing 2 but when a large quantity of fuel is stored in the tank the fuel level extends into the space of the tanklike device.

The return fuel is led via the return line 2 into the fuel tank 1 at an upper portion of the casing 2. Substantially immediately inside the casing 2, it is guided and spread sideways by the outer wall surface 6b of the tanklike device so that it comes into contact with the inside wall surface 2a of the casing. The return fuel spreads substantially uniformly in the slit-shaped passage 8 between the bottom portion 6a of the tanklike device and the inside wall surface 2a of the casing. The passage 8 is so narrow that the retum fuel is in contact all the time with the inside wall surface 2a of the casing. The temperature of the return fuel is usually considerably higher than that of the casing 2 which is cooled by the environment, which means that the fuel is continuously cooled on its way through the passage 8. The return fuel is thereafter led through part of the passage 8 which extends vertically between the side portions 6d of the tanklike device and the side portions of the casing 2. Here the return fuel flows downwards along the side portions of the casing 2 until it mixes with the fuel 4 stored in the fuel tank 1. The side portions 6d of the tanklike device need not necessarily extend right down to the lower portion of the casing 2, since the return fuel is likely to flow downwards along the inside wall surface 2a of the casing even without such a guiding surface.

Fig. 3 depicts a third alternative embodiment of a fuel tank 1 which is designed to cool a fuel return flow to the tank 1. Here too the fuel tank 1 incorporates a casing 2, a line 3 for conveying fuel from the tank 1 and a return line 5 which conveys return fuel to the tank 1. The return line 5 leads within the casing 2 into an annular line 9. The line 9 is situated in an upper portion of the casing 2 and extends in a closed path a short distance within the inside wall surface 2a of the casing. The line 9 incorporates a multiplicity of holes arranged at intervals along its extent, each of them with an orifice directed towards the inside wall surface 2a of the casing. The return fuel is thus led from the line 9^"through the holes to the inside wall surface 2a of the casing in such a way that it flows in contact with the inside wall surface 2a of the casing in a region situated above the level of the fuel 4 stored in the tank. Thereafter the return fuel flows downwards along the inside wall surface 2a of the casing until it reaches the fuel 4 stored in the casing 2. The apertures of the line 9 are with advantage distributed evenly along its extent so that the return fuel is distributed substantially uniformly over the inside wall surface 2a of the casing. The result is uniform and efficient cooling of the return fuel before it mixes with the fuel 4 stored in the tank.

The present invention is not limited to the embodiments depicted in the drawings but may be varied freely within the scopes of the patent claims. For example, the casing 2 described may be of substantially any desired shape. Should the tank be designed with a substantially parallelepipedic or cylindrical shape, the tank can easily replace existing conventional tanks on existing motor vehicles where there is risk of the problems mentioned in the introduction. Similarly, the device for guiding the return fuel need not be tanklike in shape but may be of any desired shape provided that it is functional in a manner appropriate to leading the return fuel to the inside wall surface 2a of the casing.

Claims

Patent claims

1. Fuel tank (1) incorporating a casing (2) which forms a first substantially enclosed space, which casing (2) is connected to a line (3) for conveying fuel from the tank (1) and to a return line (5) for conveying fuel back to the tank (1), characterised in that the fuel tank (1) incorporates means designed to guide the return fuel in such a way that it comes into contact with and is cooled by the casing (2) of the fuel tank (1) before it mixes with the fuel (4) stored in the tank.

2. Fuel tank according to claim 1, characterised in that said means are designed to guide the return fuel so that it is caused to flow along an area of an inside wall surface (2a) of the casing.

3. Fuel tank according to claim 2, characterised in that said means are designed to spread the return fuel substantially uniformly over said area. ^~"

4. Fuel tank according to any one of the foregoing claims, characterised in that said means include a device (6,9) which is enclosed in the casing and which incorporates a guiding surface for conveying the return fuel in contact with the inside wall surface (2a) of the casing.

5. Fuel tank according to claims 2 and 4, characterised in that the guiding surface of said device (6) extends substantially parallel with and at a short distance from at least part of the inside wall surface (2a) of the casing so as to form a slit-shaped passage (8) through which the return fuel is caused to flow.

6. Fuel tank according to claim 5, characterised in that said device (6) is tanklike in shape with an outer wall surface (6b) which forms said guiding surface, and an inner surface (6a) which forms a second space inside the first space, and that the device (6) incorporates an aperture to allow return fuel to pass from said passage (8) into the second space.

7. Fuel tank according to claim 6, characterised in that said tanklike device (6) is arranged in the casing (2) with its aperture directed upwards and the return fuel is intended to be led into the tank via an orifice of the return line (5), which orifice is arranged at a lower portion of the casing (2).

8. Fuel tank according to claim 6, characterised in that said tanklike device (6) is arranged in the casing (2) with its aperture directed downwards and the return fuel is intended to be led into the tank via an orifice of the return line (5), which orifice is arranged at a upper portion of the casing (2).

9. Fuel tank according to claims 2 and 4, characterised in that said device includes a tubular line (9) designed to lead the return fuel to the inside wall surface (2a) of the casing in such a way that the return fuel flows in contact with the inside wall surface (2a) of the casing in the region situated above the level of the fuel (4) stored in the tank.

10. Fuel tank according to claim 9, characterised in that the tubular line (9) extends in a path within the inside wall surface (2a) of the casing and incorporates holes through which the return fuel is intended to flow so that it comes into contact with the inside wall surface (2a) of the casing.