DE19833932C2 - Fuel supply system for an internal combustion engine - Google Patents

Description

The invention relates to a fuel supply system for an internal combustion engine with a fuel tank and one to the fuel via a fuel line fuel tank connected to the tank.

The fuel delivery device at a fuel supplier system for internal combustion engines generally has one mechanically from the crankshaft of the internal combustion engine driven high-pressure pump on, from an upstream Pre-feed pump from the fuel tank with force material is supplied. The pre-feed pump can be electrical driven or mechanically like the high pressure pump be coupled to the crankshaft of the internal combustion engine. The mechanically driven pre-feed pump delivers accordingly their stroke volume is the speed of the internal combustion engine corresponding fuel volume flow. Advantageous at the mechanical feed pump compared to the electric feed pump feed pump is the higher overall efficiency and the ge lower manufacturing costs.

Problems when starting the internal combustion engine can in particular special occur when the fuel tank was driven empty. In such a dry run the As long as there is air through the pre-fuel tank feed pump sucked in until it enters the internal combustion engine injected fuel no longer to maintain the Combustion is sufficient and the internal combustion engine is stopped remains. If the fuel tank then with force is refilled and the internal combustion engine ge again starts, it must first run dry from the pre-conveyor air in the fuel supply system be urged to add new fuel to the internal combustion engine to be able to lead. This necessary venting of the fuel supply system leads to the mechanical feed pump, the because of their high overall efficiency and low  Manufacturing costs are preferred to a strong delayed starting of the internal combustion engine because the mecha African pre-feed pump due to the low speed of the Internal combustion engine in the starting phase only a low För the volume flow generated so that the displacement of the suction air from the fuel supply system takes a very long time ert.

To avoid the need when using the mechanical feed pump maneuverable time to bleed the fuel supply system to shorten, there is the possibility of the stroke volume of the Pre-feed pump to enlarge to a higher fuel volume to promote lumen flow. Such an enlarged pre-feed pump can then be used for normal operation of the internal combustion engine seem to be oversized so that the excess Fuel volume flow of the pre-feed pump can be regulated must result in undesirable deterioration of the system efficiency and increased fuel heating leads.

In the generic DE 195 47 097 A1 is a Fuel supply system shown in which by means of egg ner shut-off device is prevented that when drying air into the fuel tank inflows care system. To determine the cut-off time tes is suggested, the level in the fuel to collect the container continuously using a measuring device sen and with a defined emptying state over Control unit to switch off the engine or the fuel pump. The additional monitoring and control system required however, significantly increases the manufacturing cost of the force supply system and deteriorates due to its The system efficiency. Beyond that it is not possible to fill the fuel tank at a to completely drain such shut-off device. Alternatively is further proposed in DE 195 47 097 A1 as Ab locking device a float valve in the suction line to use the fuel pump at a defined Emptying the fuel tank closes the suction line.  The float valve is with an additional direction, which ensures that the shimmer valve remains in the closed state after closing. However, this additional device leads to a complex and thus expensive float valve construction. Furthermore, at the float valves used as shut-off devices also be prevented that the fuel tank completely emptied before shutting off, otherwise air will escape the suction line enters the engine before it is switched off. The object of the present invention is a fuel ver care system with an improved start function after Provide dry running of the fuel tank, in which it is possible to fill the fuel tank emptying plett and that continues through an easy Chen and inexpensive construction.

This object is ge by the features of claim 1 solves. Preferred embodiments are in the dependent An sayings revealed.

The fuel supply system according to the invention has an egg ne shut-off device between the fuel line and the fuel tank arranged and designed  is that when it falls below a minimum level in the Fuel tank the fuel line automatically cordoned off. This shut-off device enables the force fabric line in good time before the power runs dry to interrupt the fabric storage container and thus prevent that air gets into the fuel supply system. If the Fuel tank is then refilled and up the shut-off device opens, the internal combustion engine be started without a long venting process.

The shut-off device according to the invention also enables also to use a mechanical pre-feed pump that compared to an electric feed pump a height overall efficiency and lower manufacturing costs. There is then no such mechanical pre-feed pump Increased stroke volume for quick air displacement necessary. The automatic design of the shut-off direction continues to have a shutdown of the burning engine by actively evaluating the level in the Fuel storage tank the advantage that no additional Control unit and therefore no additional power supply necessary is agile.

The invention is explained in more detail with reference to the figures. It demonstrate:

Figure 1 shows a fuel supply system according to the inven tion.

2A and 2B according guide die was a shut-off valve in a first one of open and closed Ventilzu.

Fig. 3 is a check valve according to a second embodiment form;

Fig. 4 is a shut-off valve according to a third embodiment; and

Fig. 5 is a shut-off valve according to a fourth embodiment.

Fig. 1 shows schematically the structure of an inventive fuel supply system for an internal combustion engine, which is particularly suitable for use in a diesel engine. The fuel supply system essentially has a fuel tank 1 , a mechanical Vorför derpump 5 and a mechanical high pressure pump 7 , both of which are coupled to the internal combustion engine and are driven by it. The mechanical pre-feed pump 5 draws fuel from the fuel tank 1 via a fuel filter 4 arranged in a fuel line 3 and delivers the fuel further to the high-pressure pump 7 . The high-pressure pump 7 compresses the fuel and then feeds it under high pressure, for example into a high-pressure accumulator, from which the fuel can be injected into the combustion chambers of the internal combustion engine via injectors. The fuel can, however, also be applied directly from the high-pressure pump 7 to injectors or fed into another known fuel distributor device.

The mechanically driven high-pressure pump 7 must be continuously cooled and lubricated during its operation. For this purpose, fuel from the fuel line 3 is branched off via a flushing line 8 in the area between the prefeed pump 5 and the high-pressure pump 7 and passed through the high-pressure pump for lubrication and cooling, in order then to be returned to the fuel reservoir 1 . In order to keep the pressure upstream of the high-pressure pump 7 constant, a pressure regulator 6 is arranged after the pre-feed pump 5 , which adjusts the pressure in the fuel feed to the high-pressure pump 7 and controls it with excess fuel.

At the connection point between the fuel line 3 and the fuel tank 1 , which is preferably located at the lowest point in the fuel tank or in egg nem pot of the fuel tank, a shut-off valve 2 is arranged. This shut-off valve 2 is designed so that it automatically runs when the fuel tank 1 dries dry, ie its completely emptying, or alternatively closes when the fuel tank falls below a minimum level and thus blocks the fuel line 3 . This shut-off prevents that after suction of the last fuel from the fuel tank 1 by the Vorför derpump 5 air flows into the fuel line 3 . By further suction of the pre-feed pump 5 after shutting off the fuel line 3 , however, a negative pressure builds up in the fuel line 3 and in the fuel filter 4 , which leads to the formation of vapor bubbles in the fuel. The flow resistance in the fuel line 3 and in the fuel filter 4 ensure that when the fuel tank 1 is not significantly higher than the pre-feed pump 5 , the lowest pressure in the fuel supply system immediately before the pre-feed pump 5 , so that the gas bubble forms at this point. After the gas bubble has formed, fuel no longer passes from the pre-feed pump 5 to the high-pressure pump 7 , so that the supply of the internal combustion engine with fuel is interrupted and then dies.

The shut-off valve 2 is also designed so that it opens automatically after refilling the fuel tank 1 . Since no air has got into the fuel system by shutting off the fuel line 3 when the fuel tank 1 runs dry, the internal combustion engine can then be started again immediately without having to carry out a long ventilation process. The automatic execution of the shut-off valve also enables cost-effective production, since no additional energy-consuming control devices have to be provided.

Figs. 2A and 2B shows a first embodiment 1 of such an automatic shut-off valve, as in the fuel supply system of FIG. Can be used. The shut-off valve has a float chamber 20 with a float mer 21 which is arranged at the lowest point in the fuel tank 1 or alternatively also in a swirl pot of this fuel tank 1 and connects the fuel tank 1 to the fuel line 3 . A valve seat 23 is also formed between the float chamber 20 and the fuel line 3 , the float 21 and the valve seat 23 being designed in their outer surfaces such that the inlet to the fuel line 3 is completely sealed when the float 21 is placed on the valve seat 23 . Here, with respect to the geometry of the float 21 and the valve seat 23, in principle all known embodiments can be used.

The float 21 is also formed from a material which has a lower density than the fuel used, so that the float 21 floats in the fuel due to its buoyancy. To prevent the float 21 while escaping from the float chamber 20, the Swim is limited merraum 20 upwardly to the fuel tank 1 side by a fuel-permeable cage 22nd In parallel to the float chamber 20 , the shut-off valve also has a fuel reservoir 24 , the lowest point of which is below the valve seat 23 . This fuel accumulator 24 is connected via a throttle point 25 to the fuel line 3 .

Fig. 2A shows a position of the check valve when fuel det sufficiently befin in the fuel storage container 1. The float 21 is pressed against the cage 22 by the buoyancy forces acting on it in the fuel. During operation of the internal combustion engine, fuel can then be sucked in by the Vorför pump 5 from the fuel tank 1 through the cage 22 via the float chamber 20 and the fuel line 3 and conveyed to the high-pressure pump 7 . Fuel also flows from the fuel reservoir 1 via the fuel accumulator 24 and the throttle point 25 into the fuel line 3 . When the fuel tank 1 empties, the float 21 floating on the fuel moves downward in the direction of the valve seat 23 due to its gravity in the float chamber 20 .

When the fuel level in the fuel tank 1 as shown in Fig. 2B, has dropped to the valve seat 23 in the float chamber 20 , the float 21 sits on the valve seat 23 and seals the float chamber 20 and thus the fuel tank 1 against the fuel line 3 . From the fuel accumulator 24 , the bottom of which is lower than the valve seat 23 , however, fuel continues to flow via the Dros selstelle 25 into the fuel line 3 . The throttle point 25 is, however, dimensioned such that only a very low fuel volume flow flows through, which is substantially below the delivery volume of the pre-feed pump 5 . However, since the pre-feed pump 5 , which is mechanically driven by the internal combustion engine, continues to suck fully, a negative pressure builds up in the fuel line 3 and in the fuel filter 4 , which leads to the formation of a gas bubble from the fuel in front of the feed pump 5 . This gas bubble then prevents white fuel from reaching the high-pressure pump 4 , whereby the injection of fuel into the combustion chambers of the internal combustion engine is interrupted. The internal combustion engine and the coupled with the pre-feed pump 5 then stops. Because of the negative pressure prevailing in the fuel line 3 , however, fuel flows from the fuel accumulator 24 into the fuel line 3 via the throttle point 25 until this negative pressure is completely reduced. The volume of the fuel storage space is dimensioned such that after the engine was at a standstill there is sufficient fuel for pressure reduction, so that no air flows through the fuel reservoir 24 into the fuel line 3 .

In the event that the internal combustion engine is used as a motor in a motor vehicle, dimensioning of the fuel accumulator 24 also takes into account the fact that even after the motor has died, the motor vehicle generally performs a coasting operation in which the motor rotates and thus the pre-feed pump continues to draw fuel. The fuel volume in the fuel tank 24 is then dimensioned such that fuel can flow in during this coasting process and also sufficient fuel remains after the pre-feed pump has come to a complete standstill in order to be able to build the negative pressure in the fuel line 3 .

Characterized in that the negative pressure in the fuel line 3 is reduced by the fuel from the fuel accumulator 24 after the internal combustion engine has come to a standstill, the float 21 seated on the valve seat 23 can float without any resistance after the refueling of the fuel reservoir 1 due to its drive and the connection Release between fuel tank 1 and fuel line 3 via the float chamber 20 again. The internal combustion engine can then be started immediately. The embodiment shown in FIGS . 2A and 2B of the shut-off valve according to the invention thus reliably ensures that no air enters the fuel supply system when the fuel reservoir is dry and the internal combustion engine also starts up again quickly.

Fig. 3 shows a further embodiment of the check valve according to the Invention. In this embodiment, in contrast to the embodiment shown in FIG. 2, no additional fuel reservoir is provided, but only a float chamber 120 is formed between the fuel line 3 and the fuel tank 1 , which has a valve seat 123 toward the fuel line 3 . In the float chamber 120 , a fuel-permeable cage 122 is also arranged, which limits the float chamber to the top of the fuel tank 1 and in which the float 121 leads. In Fig. 3, the float 121 is provided with a flat bottom surface, which provides for sealing of the fuel line 3 on the valve seat 123 upon contact. With regard to the valve seat 123 and the float shape 121 , however, any geometries can be used.

When the float 121 is seated on the valve seat 123 when the fuel reservoir 1 is dry, the fuel line 3 is sealed off from the float chamber 120 so that no air can flow in. However, since, as already shown in connection with the embodiment in FIG. 1, the fuel delivery system in the fuel supply system runs after the fuel supply has been shut off until the internal combustion engine has died and the vehicle containing the internal combustion engine comes to a standstill, builds up the fuel line 3 has a negative pressure which holds the float 121 on the valve seat 123 . So that the float 121 is then released automatically after refilling the fuel tank against the suction by the negative pressure in the fuel line 3 , the float volume 121 is dimensioned such that the buoyancy force acting on it acts on the force acting on the float due to the negative pressure , exceeds. The embodiment shown in Fig. 3 is characterized by a particularly simple structure, since only a few components are required.

Fig. 4 shows a further embodiment of a shut-off valve according to the invention, which in comparison to the embodiment shown in Fig. 3 allows a reduction in the Schwimmervo lumens and thus the required space for the shut-off valve. In the embodiment shown in FIG. 3, the float volume 121 depends essentially on the opening cross section of the fuel line 3 to the float chamber 120 , since this opening cross section determines the force acting on the float 121 due to the negative pressure in the fuel line 3 . Since the opening cross-section of the fuel line 3 must continue to allow a sufficient fuel volume flow for a needs-based supply of the internal combustion engine, a large floating volume 121 is generally necessary in the embodiment shown in FIG. 3, which leads to a large space requirement.

In order to reduce the float volume, in the embodiment shown in FIG. 4, the fuel line 3 is connected by an additional secondary line 227 to a float chamber 220 of the shut-off valve, the opening cross section of the secondary line being designed to be relatively small compared to the opening cross section of the fuel line 3 . The opening of the fuel line 3 and the opening of the secondary line 227 to the float chamber 220 are closed when the fuel storage container 1 is emptied by a separate float 221 , 222 , which are seated on separate valve seats 225 , 226 around the respective openings and preferably in separate fuel-permeable cages 223 , 224 in the swimming pool room 220 .

When the internal combustion engine is operating, if there is sufficient fuel in the fuel tank 1 , the fuel is sucked in by the pre-feed pump 5 predominantly over the large opening cross section of the fuel line 3 . Secondary line 227 is also open; however, due to the small opening cross-section and the high flow losses in the secondary line, the fuel line 3 is hardly supplied with fuel. Then, when material reservoir when emptying of the motor both floats 221, are seated on their depending weiligen valve seats 225, 226 222, they are firmly held th by the generated from the pre-feed pump 5 under pressure. Since the float 221 firmly holding force but due to the small opening cross-section of the secondary line 227 is relatively small, a small float volume is already sufficient to open the secondary line 227 after the fuel tank 1 has been refilled by the buoyancy forces acting on the float 221 .

The float 222 , which preferably also has only a small float volume, is held against it by the vacuum on its valve seat 226 . By opening the secondary line 227 , however, fuel can flow into the fuel line 3 , so that the negative pressure in the fuel line is released very quickly and the float 222 is released from its valve seat 226 , so that the full fuel volume flow required for a restart of the internal combustion engine Pre-feed pump 5 is supplied. Since both floats 221 , 222 , as shown, only have to have a small volume, the space required for the shut-off valve can be significantly reduced.

This also applies in particular to the further embodiment of the shut-off valve according to the invention shown in FIG. 5, which works on the same principle as the embodiment according to FIG. 4, but enables a further reduction in the space requirement. In this shut-off valve, a preferably pot-shaped float 322 sits when the fuel reservoir 1 runs dry on a valve seat 324 which is formed around the opening of the fuel line 3 towards a float chamber 320 . The float 322 is guided in a fuel-permeable cage 323 delimiting the float space 320 . Within the float 322 a continuous bore 326 with a small opening cross-section is also provided centrally above the opening of the fuel line 3 . This bore is closed by a small volume provided in the float 322 gene further float 321 , which is seated on a valve seat 327 around the opening of the bore 326 .

When the fuel tank 1 is filled with fuel and the engine is in operation, the two floats 321 and 322 float in the cage 323 . When driving dry, the float 322 then contacts the valve seat 324 and the float 321 contacts the valve seat 327 . When the fuel tank 1 is filled with fuel again, the float 321 lifts off from the valve seat 327 in the float 322 due to the buoyancy forces, so that the prevailing pressure in the fuel line 3 is reduced by a fuel flow through the bore 326 and also the float 322 leaves its valve seat 324 , so that the pre-feed pump 5 for the suction of fuel then has the full opening cross-section of the fuel line 3 again. So that after refilling the fuel tank 1, there is sufficient contact surface for the fuel on the float 321 to exert driving forces, between the inside of the float 322 and the outside of the float 321 is provided from a sufficient game. Alternatively, lateral bores in the float 322 or grooves on the outside of the float 321 and / or the inside of the float 322 can also be arranged.

Claims (7)

1. A fuel supply system for an internal combustion engine with a fuel reservoir ( 1 ), a fuel delivery device connected via a fuel line ( 3 ) to the fuel reservoir, which has a pre-feed pump ( 5 ) and a high-pressure pump ( 7 ), and a shut-off device ( 2 ), which a float volume ( 20 , 22 ; 120 , 122 ; 220 , 223 , 224 ; 320 , 323 ), which is arranged between the fuel reservoir ( 1 ) and the fuel line ( 3 ), and a float device ( 21 ; 121 ; 221 , 222; 321, 322) and is designed so that the Schwimmereinrich tung when falling below a minimum filling level in the fuel tank (1) shuts off the fuel line (3) selbsttä kind, characterized in that the prefeed pump (5) is mechanically driven by the internal combustion engine and the fuel tank ( 1 ) is not significantly higher than the prefeed pump ( 5 ) in the fuel supply care system is arranged so that by further suction of the pre-feed pump after the fuel line ( 3 ) is shut off by the float device ( 21 ; 121 ; 221 , 222 ; 321 , 322 ) of the shut-off device ( 2 ) in the fuel line ( 3 ) builds up a negative pressure, which leads to vapor formation of the fuel in the fuel line ( 3 ) upstream of the pre-feed pump ( 5 ). 2. Fuel supply system according to claim 1, characterized in that the shut-off device ( 2 ) is designed such that it automatically releases the fuel line ( 3 ) when the amount of fuel in the fuel tank exceeds the minimum fill level again. 3. Fuel supply system according to claim 2, characterized in that a throttle point ( 25 ), which binds the fuel tank ( 1 ) with the fuel line ( 3 ) ver, is arranged parallel to the shut-off device ( 2 ). 4. Fuel supply system according to claim 2, characterized in that the float device ( 121 ; 221 , 222 ; 321 , 322 ) of the shut-off device ( 2 ) is designed so that the buoyancy force of the fuel acting on the float device by the fuel delivery device ( 5 to 8 ) generated suction force on the float device via the fuel line exceeds. 5. Fuel supply system according to claim 4, characterized in that the float volume ( 220 , 223 , 224 ) with the fuel line ( 3 ) verbun via two inflow openings and the float device has two float bodies ( 221 , 222 ), the two inflow openings un have different cross-sections and are separated from each other by a float. 6. Fuel supply system according to claim 4, characterized in that the float device has a first and a second float body ( 321 , 322 ), the first float body ( 322 ) with a recess ( 326 ) hen and for shutting off the fuel line ( 3 ) is designed up to this recess, and wherein the second float body ( 321 ) is designed to shut off the recess ( 326 ) in the first float body ( 322 ). 7. The fuel supply system according to claim 6, characterized in that the first float body ( 322 ) is pot-shaped and the recess is a central bore ( 326 ) which, when the first float body sits on its valve seat ( 324 ) around the opening of the fuel line ( 3 ) comes to rest over this opening.