WO2008054315A1

WO2008054315A1 - Arrangement for supplying a combustion engine with fuel.

Info

Publication number: WO2008054315A1
Application number: PCT/SE2007/050793
Authority: WO
Inventors: Kim KYLSTRÖM; Marcus Segerstedt; Pontus Kihlsten
Original assignee: Scania Cv Ab (Publ)
Priority date: 2006-10-31
Filing date: 2007-10-30
Publication date: 2008-05-08
Also published as: SE530451C2; SE0602289L; DE112007002595T5

Abstract

The present invention relates to an arrangement for supplying fuel to a combustion engine (1). The arrangement comprises at least one fuel line (2) which has an extent from a fuel tank (3) to at least one injection means (14) for injection of fuel in the combustion engine (1), a fuel pump (4) adapted to transferring fuel in the fuel line (2), a fuel filter (6) adapted to filtering the fuel in the fuel line (2), and a warming unit (7) adapted to making warming of the fuel in the fuel line (2) possible. The arrangement also comprises a return line (12) connected to the fuel line (2) in a first region (2a') which is situated upstream from the warming unit (7) with respect to the intended direction of fuel flow through the fuel line (2), and in a second region (2b') which is situated downstream of the warming unit (7), and control means (13, 19) which are adapted to making possible a flow of fuel from the second region (2b') of the fuel line back to the first region (2a') via the return line (12).

Description

Arrangement for supplying a combustion engine with fuel

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The present invention relates to an arrangement for supplying fuel to a combustion engine according to the preamble of claim 1.

Fuels for operation of combustion engines are available in many grades and with different characteristics. In particular, certain grades of diesel oil may have the characteristic that wax precipitates at low temperatures. If cold diesel oil containing wax precipitations is led into a fuel line to a diesel engine, the wax is retained in the fuel filter which is adapted to filtering particles and other impurities out from the fuel before it reaches the diesel engine. The wax thereupon obstructs the fine passages of the fuel filter. When a fuel filter becomes obstructed to a certain degree, the fuel pump adapted to feeding fuel to the diesel engine can no longer push enough fuel through the fuel filter to maintain the operation of the diesel engine. A known way of solving this problem is to use various kinds of heater for warming the diesel oil close to the fuel filter during cold starts of diesel engines. Such heaters warm the cold diesel oil to a temperature at which the risk of wax precipitations is substantially eliminated.

JP 57-119157 refers to a device for preventing a fuel filter from being obstructed by precipitations in the fuel. The device comprises a fuel line with a fuel filter and a fuel pump for transfer of fuel from a fuel tank to a combustion engine. The fuel undergoes a certain warming in the fuel pump. The device comprises a return line adapted to recirculating part of the fuel in the fuel line after it has passed through the fuel filter and has undergone warming by the fuel pump. The fuel is recirculated through the return line to a location upstream of these components in the fuel line where it mixes with fuel from the fuel tank. Since the recirculating fuel has undergone warming by the fuel pump, the fuel which is led to the combustion engine will assume a progressively rising temperature. The presence in the fuel of precipitations that would obstruct the fuel filter can thereby be reduced. GB 2 031 994 refers to a device for filtering of fuel which is led to a diesel engine. The device comprises a fuel line with a fuel filter and a fuel pump for transferring fuel from a fuel tank to a diesel engine. A recirculating fuel flow from the diesel engine is led back to the fuel line at a location upstream of the fuel filter and the fuel pump where it mixes with fuel from the fuel tank before being led back to the combustion engine. Since the recirculating fuel will have received a certain warming in the combustion engine, the fuel which is led through the fuel filter assumes a raised temperature. The presence in the fuel of precipitations can thus be reduced and obstruction of the fuel filter be prevented.

The solutions indicated above work for fuel supply systems in which relatively small fuel flows are led to a combustion engine. In fuel supply systems in which fuel is to be used not only for injection at high pressure in the combustion engine by injection means but also to control the injection means, a relatively large fuel flow has to led to the combustion engine. In such cases the fuel flow may be of the order of 12 litres per minute. With the known solutions it is not possible to impart to a fuel flow of such a magnitude a necessary temperature rise, which may be about 1O⁰C.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement for supply of fuel to a combustion engine whereby relatively large flows of cold fuel can relatively quickly be warmed to an acceptable temperature at which the presence of precipitations in the fuel and the consequence risk of the precipitations obstructing the fuel filter are eliminated.

The object indicated above is achieved with the arrangement of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. The heater is thus arranged in the fuel line at a location between the connections of the return line to the fuel line. Fuel warmed in the heater can thus be recirculated through the return line to a location upstream of the heater. The fuel returned through the return line will thus have already been warmed at least once by the warming unit. The returned fuel will therefore be at a higher temperature than the fuel which comes directly from the fuel tank. A mixture of warmed fuel from the return line and fuel from the fuel tank is thereafter led together through the warming unit. As this recirculation of fuel proceeds, the temperature of the fuel leaving the warming unit will be progressively higher. The fuel reaching and flowing through the fuel filter will thus become increasingly warm. The remaining precipitations in the fuel will melt and the warm fuel flowing through the fuel filter will melt the precipitations retained therein. Since substantially all that is required is that the return line is connected to the fuel line upstream and downstream of the heater, such a return line may be quite short, making it possible for fuel to be recirculated a number of times through the return line during a relatively short period of time. Accordingly, relatively large fuel flows can be provided with rapid warming to an acceptable temperature by means of a heater of conventional capacity. Fuel pumps usually have a relatively large overcapacity. With such a fuel pump, a large proportion of the amount of the fuel supplied from the fuel pump can be recirculated, thereby reducing the supply of fuel from the fuel tank and the supply of precipitations.

According to an embodiment of the present invention, the return line is connected to the fuel line in a first region situated upstream of the fuel pump, and in a second region situated downstream of the fuel pump, with respect to the intended direction of fuel flow in the fuel line. The return line is thus connected to the fuel line in a first region situated on the suction side of the fuel line and in a second region situated on the pressure side of the fuel line. The pressure difference between the pressure side of the fuel line and the suction side of the fuel line can here be used for providing a recirculating flow of fuel in the return line. The return line is preferably connected to the fuel line in a second region situated substantially immediately upstream of the fuel filter, making it unnecessary for the fuel which is returned through the return line to pass through the fuel filter. The fuel need therefore only pass through the fuel filter once, i.e. when it is led to the combustion engine.

According to another embodiment of the present invention, the arrangement comprises control means adapted to providing a fuel flow through the return line when the fuel pressure substantially immediately upstream of the fuel filter in the fuel line exceeds a predetermined pressure value. If cold fuel containing precipitations is led through the fuel filter, the precipitations are retained in the fuel filter and obstruct its fine passages. The fuel pump will then find it increasingly difficult to push fuel through the fuel filter. The fuel pressure upstream of the fuel filter will therefore increase. The fuel pressure upstream of the fuel filter is thus a parameter which can with advantage be used for detecting whether the fuel filter is about to become obstructed. Said control means may comprise a pressure-controlled valve means arranged in the return line and adapted to being placed in an open position when the fuel pressure substantially immediately upstream of the fuel filter in the return line exceeds said predetermined pressure value. A simple such pressure-controlled valve means may take the form of a spring-loaded check valve which opens when the fuel pressure exceeds the predetermined pressure value.

According to another embodiment of the present invention, said control means is adapted to providing a fuel flow through the return line when the fuel reaching the fuel filter is at a lower temperature than a predetermined temperature value. The temperature of the fuel is another parameter which can be used for indicating whether the fuel may contain precipitations. Said control means may thus comprise at least one temperature-controlled valve means arranged in the return line and adapted to being placed in an open position when the fuel reaching the fuel filter is at a lower temperature than said predetermined temperature value. However, such an indication is less reliable in that substantially only poor quality fuel will contain precipitations at temperatures below the predetermined temperature value. If the return line contains only a temperature-controlled valve means, the fuel, whatever its quality, will undergo warming when it is at a temperature below the specified temperature value. The return line may with advantage comprise both a pressure-controlled valve means and a temperature-controlled valve means. If the temperature of the fuel is below the specified temperature value and the fuel pressure upstream of the fuel filter is above the specified pressure value, this is a very reliable indication that the fuel filter is about to become obstructed by precipitations. According to another embodiment of the present invention, the arrangement comprises an overpressure line which has an extent between the fuel line and the fuel tank, and a pressure-controlled valve which is arranged in the overpressure line and is adapted to opening when the fuel pressure in the fuel line close to the overpressure line exceeds a specified pressure value. With advantage, such an overpressure line is connected to the fuel line upstream of the fuel filter in a region in the vicinity of the connection of the return line to the fuel line. With such a connection of the overpressure line, the pressure-controlled valve in the overpressure line has to be adapted to opening at a higher pressure than the pressure at which the pressure-controlled valve in the return line opens, in order to avoid preventing the recirculation of fuel through the return line. As well as when the fuel filter is obstructed, high fuel pressure may also occur in this region of the fuel line when, for example, a shutoff valve in the fuel line closes. To protect the components in the fuel line against such high fuel pressure, the pressure- controlled valve in the overpressure line is adapted to opening so that pressurised fuel can be led out from the fuel line to the fuel tank.

According to another embodiment of the present invention, said warming unit is an electric heater. An electric heater has the advantage that it can provide rapid and substantially immediate warming of the fuel which is led through the fuel line during a cold start of a combustion engine. The arrangement comprises preferably a control unit adapted to controlling the activation of the warming unit. The control unit may be adapted to receiving information from a temperature sensor which detects the temperature of the fuel in the fuel line or the fuel tank, and/or from a pressure sensor which detects the fuel pressure in the fuel line in a region substantially immediately upstream of the fuel filter. When the fuel is at a temperature below a specified temperature value and/or the fuel pressure exceeds a specified pressure value, the control unit will activate the warming unit so that it warms the fuel in the fuel line. Alternatively, the warming unit may be activated manually via a suitable button or other control means. 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 an arrangement for supplying fuel to a combustion engine according to a first embodiment of the invention, and Fig. 2 depicts an arrangement for supplying fuel to a combustion engine according to a second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 depicts an arrangement for supplying fuel to a combustion engine. The combustion engine is here exemplified as a diesel engine 1 which is schematically represented in Fig. 1. The diesel engine 1 may be fitted in a heavy vehicle. The arrangement comprises a fuel line 2 adapted to leading fuel from a fuel tank 3 to the combustion spaces of the diesel engine 1. A fuel pump 4 is adapted to conveying fuel in the fuel line 2. A first section 2a of the fuel line 2 is situated on the suction side of the fuel pump 4, and a second section 2b of the fuel line 2 is situated on the pressure side of the fuel pump 4. The fuel will be at a higher pressure in the second section 2b of the fuel line than in the first section 2a. The fuel pump 4 may be a gear pump. The fuel line 2 is provided, at an inlet aperture in the fuel tank 3, with a first coarse filter 5 adapted to filtering relatively large particles out of the fuel when the latter is sucked into the fuel line 2. The arrangement also comprises a second considerably finer fuel filter 6 adapted to filtering out remaining finer particles and other impurities, e.g. water, which may be present in the fuel. The second fuel filter 6 is situated in the second section 2b of the fuel line, i.e. downstream of the fuel pump 4.

A warming unit 7, which in this case is electrical, is arranged in the fuel line 2 to provide warming of the fuel as necessary. The warming unit 7 is here arranged in the first section 2a of the fuel line but may also be arranged in the second section 2b of the fuel line. The warming unit 7 is here controlled by an electrical control unit 8 which may be a computer unit provided with suitable software. The control unit 8 is adapted to controlling the warming unit 7 on the basis of information from a temperature sensor 9 which is intended to detect the temperature of the fuel at a suitable location in the fuel line 2. In this case, the temperature sensor 9 detects the temperature of the fuel in the fuel line 2 in a region between the fuel pump 4 and the fuel filter 6. The control unit 8 is adapted to activating the warming unit 7 when the temperature sensor 9 indicates that the fuel is at a temperature below the minimum acceptable temperature value. The fuel line 2 comprises a shutoff valve 10 situated at a location downstream of the fuel filter 6. When the shutoff valve 10, which may be a solenoid valve, is placed in a closed position, the fuel flow to the diesel engine 1 is interrupted. The shutoff valve 10 is likewise controlled by the control unit 8. A pressure-regulating one-way valve 11 is arranged to monitor the pressure in the second section 2b of the fuel line. If the pressure in the second section 2b of the fuel line exceeds a maximum acceptable pressure value, the pressure-regulating one-way valve 11 is adapted to opening so that fuel from the second section 2b of the fuel line is led to the fuel tank 3 via a line 11a and the first section 2a of the fuel line.

A return line 12 is connected to the fuel line in a first region 2a' situated in the first section 2a of the fuel line, and to the fuel line in a second region 2b' situated in the second section 2b of the fuel line. The connection of the return line 12 to the first region 2a' of the fuel line is situated upstream of the fuel pump 4 and the warming unit 7 with respect to the intended direction of fuel flow through the fuel line 2. The connection of the return line 12 to the second region 2b' of the fuel line is situated downstream of the warming unit 7 and the fuel pump 4. The connection of the return line 12 to the second region 2b' of the fuel line is situated substantially immediately upstream of the fuel filter 6. The return line 12 comprises a pressure-controlled valve 13. If the fuel is at a pressure which exceeds a specified value in the second region 2b' of the fuel line, the pressure-controlled valve 13 is adapted to opening so that fuel can be recirculated in the return line 12 from the second region 2b' of the fuel line to the first region 2a'. Since the fuel pressure will be higher in the second region 2b' of the fuel line, which is situated on the pressure side 2b of the fuel line, than in the first region 2a', which is situated on the suction side 2a of the fuel line, the result is a natural flow of fuel in the return line 12 when the pressure-controlled valve 13 opens, without the assistance of any extra equipment. With such a return line 12, it is possible to lead fuel which has already been warmed in the warming unit 7 and is situated in the second region 2b' of the fuel line back to the first region 2a', after which the fuel can be led back to the warming unit 7 in order to be warmed further.

The diesel engine 1 comprises injection means 14 adapted to injecting fuel at high pressure into the respective combustion spaces of the engine. The control unit 8 is adapted to controlling the flow of the fuel which is to be burned in the cylinders by means of two solenoid valves 15a, b. The diesel engine comprises ducts 15a', b' for leading the fuel which is to be burned to the respective injection means 14. In this type of injection system, the fuel is also used for controlling the injection means 14 so that they open and close at desired times. The control unit 8 is at the same time also adapted to controlling the flow of fuel for this control by means of two solenoid valves 16a, b. The diesel engine comprises ducts 16a', b' for leading the fuel for this control to the respective injection means 14. Substantially all of the fuel which is led to the injection means 14 for this control and a small proportion of left-over fuel which is led to the injection means 14 in order to be burned are returned back to the fuel tank 3 via a recirculation line 17. A constriction 18 is arranged in a line 18' which connects the second section 2b of the fuel line downstream of the shutoff valve 10 to the recirculation line 17. By means of the constriction 18, the fuel pressure in the fuel line 2 can be reduced when the shutoff valve 10 is placed in a closed position.

During operation of the diesel engine 1, the fuel pump 4 sucks fuel from the fuel tank 3 through the first section 2a of the fuel line. The fuel sucked into the first section 2a of the fuel line undergoes coarse filtration in the first filter 5. During its passage through the first section 2a of the fuel line, the fuel passes the warming unit 7 before it reaches the fuel pump 4. Thereafter, the fuel pump 4 pushes the fuel on through the second section 2b of the fuel line, in which the fuel passes the second fuel filter 6 and the shutoff valve 10 before it is led via the solenoid valves 15a, b, 16a, b to the injection means 14 in order to be burned or to control the opening times of the injection means. Left-over fuel is returned to the fuel tank 3 via the recirculation line 17.

During a cold start of the diesel engine 1, the temperature sensor 9 may indicate that the fuel is at a lower temperature than a specified minimum temperature value which may for example be 5⁰C. If such is the case, the control unit 8 activates the warming unit 7 so that it provides warming of the fuel in the fuel line 2. If the fuel is of poor quality, it may contain paraffin precipitations when it is at a temperature below that temperature value. If the fuel contains wax precipitations, they will be retained in and obstruct the second fuel filter 6. The fuel pump 4 will therefore find it increasingly difficult to push fuel through the fuel filter 6 and the fuel pressure upstream of the fuel filter 6 will rise. If the fuel filter 6 becomes obstructed to such an extent that the pressure rises above a predetermined pressure value, the pressure-controlled valve 13 is adapted to opening. Part of the fuel in the region upstream of the fuel filter 6 will then return through the return line 12 from the second region 2b' of the fuel line to the first region 2a'. The fuel which is returned through the return line 12 will thus have already been warmed by the warming unit. The returned fuel will thus be at a higher temperature than the fuel which comes directly from the fuel tank 3. A mixture of warmed fuel from the return line 12 and fuel from the fuel tank 3 is thereafter led through the warming unit 7. As this recirculation of fuel proceeds, the temperature of the fuel leaving the warming unit 7 will be progressively higher. The fuel reaching and flowing through the fuel filter 6 will therefore be increasingly warm. The remaining wax precipitations in the fuel will melt and the warm fuel flowing through the fuel filter 6 will melt the wax precipitations retained in the fuel filter 6. The pressure of the fuel upstream of the fuel filter 6 will drop. When the fuel pressure has dropped to a value below the specified pressure value, the pressure-controlled valve 13 will close and the fuel flow through the return line 12 will cease. When the temperature sensor 9 also indicates that the fuel temperature has risen above the predetermined value, the control unit 8 will switch off the warming unit 7. The fuel in the fuel tank 3 will then have been warmed by warm fuel from the recirculation line 17, with the result that it no longer contains any wax precipitations. Fig. 2 depicts an alternative arrangement for supplying fuel to a combustion engine 1. Here again, the arrangement comprises a return line 12 adapted to recirculating fuel when the fuel is at such a low temperature that it may contain wax precipitations. The return line 12 in this case is provided not only with the pressure-controlled valve 13 but also a temperature-controlled valve 19. The sole object of the temperature- controlled valve 19 is to make a fuel flow through the return line 12 possible when the fuel is at a temperature below the temperature value at which there is risk of wax precipitations occurring in the fuel. The temperature-controlled valve 19 in this case is controlled by the control unit 8 on the basis of information from the temperature sensor 9 about the temperature of the fuel. Alternatively, the temperature-controlled valve 19 may be a thermostat which itself detects the temperature of the fuel and places itself in an intended position. When the fuel is at a temperature above the specified temperature value at which wax precipitations may occur, the temperature-controlled valve 19 is intended to be in a closed position. Even if the pressure in the second region 2b' of the fuel line exceeds the specified pressure value and the pressure- controlled valve 13 opens, the temperature-controlled valve 19 will prevent a return flow of fuel in the return line 12. This situation may occur when the shutoff valve 10 closes. The closed temperature-controlled valve 19 will therefore prevent a powerful pressure surge from propagating from the second section 2b of the fuel line to the first section 2a of the fuel line via the return line 12. Such a pressure surge would entail risk of damage to the fuel pump 4 and other components situated in the first section 2a of the fuel line. During a cold start of the combustion engine 1, when the fuel is at a lower temperature than a specified value, the control unit 8 will keep the temperature- controlled valve 19 in an open position. If the fuel pressure upstream of the fuel filter 6 rises above the specified pressure value, the pressure-controlled valve means 13 will open so that fuel is recirculated through the return line 12. This recirculation of fuel through the return line 12 works in a manner corresponding to the embodiment depicted in Fig. 1.

The arrangement depicted in Fig. 2 also comprises an overpressure line 20 which has an extent between a third region 2b" of the fuel line 2 and the fuel tank 3. The third region of the fuel line is situated in the immediate vicinity of the second region 2b' of the fuel line where the return line is connected. A pressure-controlled valve 21 is arranged in the overpressure line 20. The pressure-controlled valve 21 is adapted to opening when the fuel pressure in the third region 2b" of the fuel line exceeds a specified pressure value. The pressure-controlled valve 21 is adapted to opening at a higher pressure than the pressure at which the pressure-controlled valve 13 is adapted to opening. The pressure-controlled valve 21 valve can therefore substantially only be opened when the temperature-controlled valve 19 is closed. The pressure in the third region 2b" of the fuel line when the overpressure line 20 is connected may rise above the specified pressure value when, for example, the shutoff valve 10 closes. The pressure surge which may then occur cannot be propagated through the return line 12 when the temperature-controlled valve 19 is closed. The high pressure downstream of the shutoff valve 10 will open the pressure-controlled valve 21 so that fuel can be led back to the fuel tank 3 via the overpressure line 20. The high pressure in this section of the fuel line can thus be reduced without stressing of pressure-sensitive components.

The invention is in no way limited to the embodiments described but may be varied freely within the scopes of the claims.

Claims

1. An arrangement for supplying fuel to a combustion engine (1), which arrangement comprises at least one fuel line (2) which has an extent from a fuel tank (3) to at least one injection means (14) for injection of fuel in the combustion engine (1), a fuel pump (4) adapted to transferring fuel in the fuel line (2), a fuel filter (6) adapted to filtering the fuel in the fuel line (2), and a warming unit (7) adapted to making warming of the fuel in the fuel line (2) possible, characterised in that arrangement comprises a return line (12) connected to the fuel line (2) in a first region (2a') which is situated upstream from the warming unit (7) with respect to the intended direction of fuel flow through the fuel line (2), and in a second region (2b') which is situated downstream of the warming unit (7), and control means (13, 19) which are adapted to making possible a flow of fuel from the second region (2b') of the fuel line back to the first region (2a') via the return line (12).

2. An arrangement according to claim 1, characterised in that the return line (12) is connected to the fuel line (2) in a first region (2a') which is situated upstream of the fuel pump (4), and in a second region (2b') which is situated downstream of the fuel pump (4), with respect to the intended direction of fuel flow in the fuel line (2).

3. An arrangement according to claim 1, characterised in that the return line (12) is connected to the fuel line (2) in a second region (2b') which is situated upstream of the fuel filter (6).

4. An arrangement according to any one of the foregoing claims, characterised in that said control means (13) is adapted to providing a fuel flow through the return line (12) when the fuel pressure substantially immediately upstream of the fuel filter (6) in the fuel line (2) exceeds a predetermined pressure value.

5. An arrangement according to claim 4, characterised in that said control means comprises a pressure-controlled valve means (13) arranged in the return line (12) and adapted to being placed in an open position when the fuel pressure substantially immediately upstream of the fuel filter (6) in the fuel line (2) exceeds said predetermined pressure value.

6. An arrangement according to any one of the foregoing claims, characterised in that said control means (13, 19) are adapted to providing a fuel flow through the return line

(12) when the fuel reaching the fuel filter (6) is at a lower temperature than a predetermined temperature value.

7. An arrangement according to claim 6, characterised in that said control means comprises at least one temperature-controlled valve means (19) arranged in the return line (12) and adapted to being placed in an open position when the fuel reaching the fuel filter (6) is at a lower temperature than said predetermined temperature value.

8. An arrangement according to any one of the foregoing claims, characterised in that the arrangement comprises an overpressure line (20) which has an extent between the fuel line (2) and the fuel tank (3), and a pressure-controlled valve (21) which is arranged in the overpressure line (20) and is adapted to opening when the fuel pressure in the fuel line (2) close to the overpressure line (20) exceeds a specified pressure value.

9. An arrangement according to any one of the foregoing claims, characterised in that said warming unit is an electric heater (7).

10. An arrangement according to any one of the foregoing claims, characterised in that the arrangement comprises a control unit (8) adapted to controlling the activation of the warming unit (7).