Fuel injection system for internal combustion engines and method for operating a fuel injection system for internal combustion engines

Abstract

The invention relates to a fuel injection system (17) for internal combustion engines, comprising a high-pressure fuel pump (6), a common rail (8), at least two injection valves (9), at least one leakage line (10), an injection valve discharge line (11), and a return line (15), wherein the injection valves (9) can be supplied with a high-pressure fuel (16) by means of the high-pressure fuel pump (6) via the common rail (8), at least two injection valves (9) being fluidically connected to one another by means of the leakage line (10), one of the injection valves (9) being fluidically connected to the return line (15) by means of the injection valve discharge line (11), so that fuel (16) can be discharged from the injection valves (9) via the leakage line (10), via the injection valve discharge line (11), and via the return line (15), in particular into a preferably unpressurized tank (1), can be discharged.The invention further relates to a method for operating a fuel injection system (17) for internal combustion engines. Fuel consumption and pollutant emissions during operation of the internal combustion engine can be reduced and delays and uncomfortable jerking when starting the internal combustion engine can be prevented by making the leakage line (10) and the injection valve drain line (11) high-pressure resistant.

Description

[0001] The invention relates to a fuel injection system for internal combustion engines having the features of the preamble of patent claim 1 and a method for operating a fuel injection system for internal combustion engines having the features of the preamble of patent claim 8.

[0002] Such a fuel injection system for internal combustion engines has a high-pressure fuel pump, a common rail, at least two injectors, at least one leakage line, an injector drain line, and a return line. The injectors can be supplied with high-pressure fuel via the common rail by means of the high-pressure fuel pump. At least two injectors are fluidly connected to one another via the leakage line. The absolute value of this high pressure depends on an operating point of the internal combustion engine, e.g. its torque, speed, etc. In order to be able to inject more fuel into the cylinders of the internal combustion engine in a shorter time in order to achieve a high torque and / or a high speed of the internal combustion engine, the high pressure has higher values ​​than if a lower torque and / or a lower speed is to be achieved.One of the injectors is fluidically connected to the return line via the injector drain line. The connections are designed such that fuel can be discharged from the injectors via the leakage line, the injector drain line, and the return line, in particular into a preferably unpressurized tank. The common rail is a usually tubular distributor to which the injectors are connected for supplying fuel to the cylinders of the internal combustion engine. The common rail is therefore also referred to as a distributor pipe. The common rail is also used in particular for the (intermediate) storage of high-pressure fuel. The common rail thus functions as a high-pressure fuel reservoir.

[0003] The method for operating such a fuel injection system for internal combustion engines has various operating states. When the internal combustion engine is running or idling, the injectors are supplied with high-pressure fuel via the common rail by means of the high-pressure fuel pump. Fuel is also discharged from the injectors, particularly into a preferably depressurized tank, via the leakage line, the injector drain line, and the return line during the running or idling state of the internal combustion engine.

[0004] US 2003 / 0111050 A1 discloses such a fuel injection system for internal combustion engines, comprising a high-pressure fuel pump, a common rail, at least one injector, the high-pressure fuel pump supplying fuel to the at least one injector via the common rail, a pre-feed pump that feeds fuel from a tank to the high-pressure fuel pump, a pressure regulator for the feed pressure of the pre-feed pump, a return line for discharging fuel from the at least one injector and / or the high-pressure fuel pump, and a pressure regulator in the return line. The pressure in the return line is regulated as a function of the feed pressure of the pre-feed pump. The injectors can also be referred to as injection valves.

[0005] The pressure in the common rail and in the injectors drops when the internal combustion engine is at a standstill because the fuel is drained from the injectors via the leakage line, the injector drain line and the return line, in particular into a preferably depressurised tank, even when the internal combustion engine is at a standstill, without new fuel being fed to the common rail. This means that when the internal combustion engine is restarted after it has been at a standstill, the fuel is initially only at low pressure at the injectors. It takes a certain amount of time until the desired high pressure can be provided by the high-pressure fuel pump and until the fuel then reaches the injectors at this desired high pressure. This leads to high fuel consumption and high pollutant emissions precisely during the time in which the fuel is at too low a pressure at the injectors.Furthermore, due to the pressure being too low, there may be delays in starting the engine and an uncomfortable jerking sensation when the engine starts.

[0006] The invention is therefore based on the object of designing and / or developing the fuel injection system for internal combustion engines and the method for operating a fuel injection system for internal combustion engines in such a way that the problems of the prior art are avoided or at least reduced.

[0007] This problem underlying the invention is now initially solved by a fuel injection system for internal combustion engines having the features of patent claim 1.

[0008] One aspect of the invention is essentially that the leakage line and the injector drain line are designed to be high-pressure resistant. High-pressure resistant means that the corresponding lines can withstand the high-pressure fuel and are therefore not mechanically damaged. Furthermore, high-pressure resistant means that undesired leakages of the high-pressure fuel, e.g. at connection points, are avoided with appropriate seals, or at least kept to a minimum. The high-pressure resistant leakage line and the high-pressure resistant injector drain line then keep the fuel in the injectors under high pressure, even when the internal combustion engine is at a standstill. The high-pressure resistant leakage line and the high-pressure resistant injector drain line thus successfully prevent the injectors from having too little pressure.This means that the overall fuel consumption of the internal combustion engine and its pollutant emissions can be reduced.

[0009] According to a preferred embodiment of the fuel injection system, a first shut-off valve is fluidically arranged between the injector drain line and the return line. The shut-off valve is designed, for example, as a solenoid valve. In particular, the first shut-off valve maintains the high-pressure fuel in the leakage line, the injector drain line, the common rail, and the injectors.

[0010] According to a further advantageous embodiment of the fuel injection system, the first shut-off valve is designed as a flow-closing valve. In a flow-closing valve, a valve body of the valve is pressed against a valve seat when the valve is closed, in the direction of the fuel flow, which is established by the valve when it is open. Thus, the valve body is pressed into the valve seat by the high-pressure fuel in the injection valve outlet line when the valve is closed, so that a particularly good seal can be achieved by means of the valve.

[0011] Preferably, a second shut-off valve, which preferably closes against the flow, is fluidically arranged between the tank and the high-pressure fuel pump. In a valve that closes against the flow, a valve body of the valve is pressed against a valve seat when the valve is closed, counter to the direction of the fuel flow that is established by the valve when it is open. The valve body is thus pressed into the valve seat by the fuel, which is under the pressure prevailing in the area of ​​the inlet of the high-pressure fuel pump when the valve is closed, so that a particularly good seal can be achieved by means of the valve. The high-pressure fuel pump itself already achieves a seal against its delivery direction, and this sealing effect is further improved by the second shut-off valve.Thus, the second shut-off valve, in particular, ensures that the high-pressure fuel is retained in the leakage line, the injector drain line, the common rail, and the injectors. In particular, overflow of the high-pressure fuel pump in the opposite direction of its delivery direction will not lead to a reduction in pressure in the leakage line, the injector drain line, the common rail, and the injectors, or will only lead to a significantly reduced reduction in pressure in the leakage line, the injector drain line, the common rail, and the injectors, due to the then-closed second shut-off valve.

[0012] Further preferably, a significantly shorter line section is arranged and / or formed between the second shut-off valve and an inlet of the high-pressure fuel pump than between the tank and the second shut-off valve. In particular, a first intermediate line of minimal length is arranged and / or formed between the second shut-off valve and an inlet of the high-pressure fuel pump. A second intermediate line is arranged and / or formed fluidically between an outlet of the high-pressure fuel pump and an inlet of the common rail. In particular, the second shut-off valve is arranged and / or formed immediately upstream of an inlet of the high-pressure fuel pump. Thus, the seal via the high-pressure fuel pump and the second shut-off valve can be further improved.In this case, overflows of the high-pressure fuel pump in the opposite direction to its delivery direction lead to particularly low pressure losses in the leakage line, the injector drain line, the common rail, and the injectors. This is because very little fuel can then overflow the high-pressure fuel pump in the opposite direction to its delivery direction until it reaches the second shut-off valve.

[0013] To control and / or regulate the pressure within the common rail, a relief valve is connected to the common rail via a common rail drain line and to the return line. The pressure within the common rail is controlled and / or regulated, in particular, by controlling and / or regulating the high-pressure fuel pump.

[0014] Advantageously, the common rail drain line and the injector drain line are fluidically connected to each other by a high-pressure-resistant connecting line. This ensures that the pressure in the injector drain line is essentially the same as in the common rail. The injector drain line could also be fluidically connected directly to the common rail, which is particularly useful if the relief valve is mounted on or in the common rail without the common rail drain line.

[0015] The object underlying the invention is also achieved by a method for operating a fuel injection system for internal combustion engines with the features of patent claim 8.

[0016] One aspect of the invention essentially lies in the fact that, while the internal combustion engine is at a standstill, the fuel is held under high pressure in the leakage line, in the injector drain line, in the common rail, and in the injectors. Thus, when the internal combustion engine is restarted after it has come to a standstill, the fuel is directly applied to the injectors at the desired high pressure. This leads to low fuel consumption and pollutant emissions, particularly during the time until the fuel is applied to the injectors at the pressure provided by the high-pressure fuel pump. Furthermore, delays in starting the internal combustion engine and uncomfortable jerking when starting the internal combustion engine are thus successfully avoided.

[0017] Preferably, when the high-pressure fuel pump is switched off, the first shut-off valve is closed when high pressure is still essentially present in the leakage line, the injector drain line, the common rail, and the injectors. For this purpose, the first shut-off valve is controlled accordingly by a control device of the fuel injection system. The switching off of the high-pressure fuel pump and the first shut-off valve are coordinated accordingly. This ensures in a simple manner that after the high-pressure fuel pump and the internal combustion engine are switched off, i.e. when the internal combustion engine is at a standstill, the fuel is present under high pressure in the leakage line, the injector drain line, the common rail, and the injectors.This pressure is then maintained in the leakage line, the injector drain line, the common rail and the injectors by the high-pressure-resistant design of the lines and in particular by the shut-off valves until the engine is restarted.

[0018] According to a preferred embodiment of the method, the pressure in the leakage line, the injector drain line, the common rail, and the injectors is increased during the shutdown process of the internal combustion engine, in particular by briefly increasing the engine speed and thus increasing the pressure provided by the high-pressure fuel pump shortly before the first shut-off valve closes. This ensures that when the internal combustion engine is restarted after it has been at a standstill, the fuel is applied to the injectors at optimal pressure. If the pressure increase is selected to a correspondingly higher value, small leaks or pressure losses during standstill are tolerable without an increase in the engine's fuel consumption and its pollutant emissions and / or delayed and / or uncomfortable starting being expected.The increase in the pressure provided by the high-pressure fuel pump by increasing the engine speed occurs indirectly through the corresponding dependence of the high-pressure fuel pump control on the engine speed. This indirect increase in the pressure provided by the high-pressure fuel pump can successfully prevent unfavorable operating conditions of the engine.

[0019] There are now a multitude of possibilities for advantageously designing and developing the fuel injection system for internal combustion engines according to the invention and the method for operating a fuel injection system for internal combustion engines according to the invention. Reference is made in this regard to the claims subordinate to claim 1 and the claims subordinate to claim 8. A preferred embodiment of the fuel injection system for internal combustion engines according to the invention and the method for operating a fuel injection system for internal combustion engines according to the invention will now be explained and described in more detail with reference to the drawing and the associated description. The drawing shows: Fig. 1 a flow diagram of a fuel injection system.

[0020] Fig. 1 shows a flow diagram of a fuel injection system 17 for internal combustion engines, including a high-pressure fuel pump 6, a common rail 8, at least two injectors 9, at least one leakage line 10, an injector drain line 11, and a return line 15. The injectors 9 can be supplied with high-pressure fuel 16 by means of the high-pressure fuel pump 6 via the common rail 8. At least two injectors 9 are fluidically connected to one another by means of the leakage line 10. One of the injectors 9 is fluidically connected to the return line 15 by means of the injector drain line 11, so that fuel 16 can be discharged from the injectors 9, in particular into a preferably unpressurized tank 1, via the leakage line 10, the injector drain line 11, and the return line 15.

[0021] The term "unpressurized tank 1" means that the ambient pressure prevails in the tank 1. The tank 1 is preferably only partially filled with fuel 16. By means of a fuel feed pump 2, the fuel 16 can be fed from the tank 1 to the high-pressure fuel pump 6 via a fuel feed line 3. The fuel feed pump 2 is preferably arranged in the tank 1 and immersed in the fuel 16. One end of the return line 15 is also preferably arranged in the tank 1 and immersed in the fuel 16.

[0022] The injection valves 9 are according to Fig. 1 are arranged in a row, with two adjacent injectors 9 always being fluidically connected to a leakage line 10. A last injector 9 of this row of injectors 9 is fluidically connected to the return line 15 via the injector drain line 11. Four injectors 9 are shown here as an example. However, more or fewer injectors 9 could also be provided, particularly depending on the number of cylinders of the internal combustion engine.

[0023] The leakage line 10 and the injection valve drain line 11 are designed to be high-pressure resistant. The leakage lines 10 can be designed as hoses, as pipes, and / or as flow channels formed in housing components. In principle, all lines described in this publication can be designed as hoses, as pipes, and / or as flow channels formed in housing components. The seals at the connection points of the leakage lines 10, for example, to the adjacent injection valve 9, are just as high-pressure resistant as the leakage lines 10 themselves. In particular, appropriate seals are used for this purpose.

[0024] A first shut-off valve 13 is fluidically arranged between the injection valve outlet line 11 and the return line 15. The return line 15 is then, in particular, not designed to be high-pressure resistant, or does not need to be, since the fuel 16, as seen from the injection valves 9, is only under high pressure up to the first shut-off valve 13. The first shut-off valve 13 is designed, in particular, as a solenoid valve. An actuator of the first shut-off valve 13 is connected for control purposes to a control device of the fuel injection system 17 and can thus be controlled using control commands generated by the control device.

[0025] The first shut-off valve 13 is designed as a flow-closing valve. The use of other types of valves is conceivable, as long as it is ensured that high-pressure fuel 16 from the injection valve outlet line 11 is successfully prevented from flowing through the first shut-off valve 13 in the closed state.

[0026] A second shut-off valve 4, which preferably closes against the flow, is fluidically arranged between the tank 1 and the high-pressure fuel pump 6. Here, too, the use of other types of valves is conceivable, as long as it is ensured that flow through the second shut-off valve 4 in the closed state by the high-pressure fuel 16 from the high-pressure fuel pump 6 is successfully avoided.

[0027] A significantly shorter line section is arranged and / or formed between the second shut-off valve 4 and an inlet of the high-pressure fuel pump 6 than between the tank 1 and the second shut-off valve 4. In particular, a first intermediate line 5 of minimal length is arranged and / or formed between the second shut-off valve 4 and an inlet of the high-pressure fuel pump 6. A second intermediate line 7 is arranged and / or formed fluidically between an outlet of the high-pressure fuel pump 6 and an inlet of the common rail 8. The first and / or the second intermediate line 5, 7 are also preferably designed to be high-pressure resistant. The second shut-off valve 4 is preferably connected directly to the inlet of the high-pressure fuel pump 6, e.g. screwed in here. The first intermediate line 5 is then functionally formed by means of the housing of the second shut-off valve 4 and the housing of the high-pressure fuel pump 6.

[0028] A relief valve 14 is connected, on the one hand, to the common rail 8 via a common rail drain line 18 and, on the other hand, to the return line 15. The common rail drain line 18 is also preferably designed to be high-pressure resistant. It is also conceivable for the relief valve to be connected directly to the common rail without the common rail drain line. The control device is also connected for control purposes to an actuator of the relief valve 14 and to a motor of the high-pressure fuel pump 6. The pressure within the common rail 8 can be controlled and / or regulated by corresponding control commands generated by the control device and transmitted to the high-pressure fuel pump 6 and the relief valve 14.

[0029] The common rail drain line 18 and the injection valve drain line 11 are fluidly connected to each other by a high-pressure-resistant connecting line 12. To filter the fuel 16, at least one filter (shown here) is interposed in one of the lines.

[0030] In the following, a method for operating the fuel injection system 17 for internal combustion engines according to Fig.1 in various operating states. When the internal combustion engine is running or idling, the injection valves 9 are supplied with high-pressure fuel 16 by means of the high-pressure fuel pump 6 via the common rail 8. When the internal combustion engine is running or idling, fuel 16 is discharged from the injection valves 9, in particular into a preferably unpressurized tank 1, via the leakage line 10, the injection valve drain line 11, and the return line 15. The high-pressure fuel pump 6 itself is supplied with fuel 16 from the tank 1 by means of the fuel feed pump 2. When the internal combustion engine is running or idling, the first shut-off valve 13 and the second shut-off valve 4 are open.

[0031] While the internal combustion engine is at a standstill, the fuel 16 is held under high pressure in the leakage line 10, in the injector drain line 11, in the common rail 8, and in the injectors 9. When the internal combustion engine is at a standstill, the first shut-off valve 13 and the second shut-off valve 4 are closed. This is an important prerequisite for ensuring that the fuel 16 is held under high pressure in the leakage line 10, in the injector drain line 11, in the common rail 8, and in the injectors 9 while the internal combustion engine is at a standstill.Furthermore, the leakage line 10, the injection valve drain line 11, the common rail 8 and the injection valves 9 must be designed to be high-pressure resistant in order to ensure that the fuel 16 is kept under high pressure in the leakage line 10, in the injection valve drain line 11, in the common rail 8 and in the injection valves 9 while the internal combustion engine is at a standstill.

[0032] When the high-pressure fuel pump 6 is switched off, the first shut-off valve 13 is closed when the high pressure is still essentially present in the leakage line 10, the injector drain line 11, the common rail 8, and the injectors 9. When the high-pressure fuel pump 6 is switched off, the second shut-off valve 4 is also closed when the high pressure is still essentially present in the leakage line 10, the injector drain line 11, the common rail 8, and the injectors 9.

[0033] During the engine shutdown process, the pressure in the leakage line 10, the injector drain line 11, the common rail 8, and the injectors 9 is increased, in particular by briefly increasing the engine speed and thus increasing the pressure provided by the high-pressure fuel pump 6 shortly before the first shut-off valve 13 closes. The pressure is thereby increased to a value that is optimal for restarting the engine after it has been shut down. It is particularly important for restarting the engine that the fuel 16 is present in the injectors 9 at this optimal pressure.The pressure can also be set to a value slightly higher than the optimal value for restarting the internal combustion engine, so that a corresponding leakage / pressure loss during the standstill of the internal combustion engine until restarting is tolerable in the sense of an optimal starting process.

[0034] By means of the fuel injection system 17 described above and the method for operating the fuel injection system 17 described above, the starting of the internal combustion engine after a standstill of the internal combustion engine can be successfully improved. List of reference symbols 1 tank 2 fuel feed pump 3 Fuel supply line 4 second shut-off valve 5 first intermediate line 6 High-pressure fuel pump 7 second intermediate line 8 Common Rail 9 Injector 10 Leakage line 11 Injector drain line 12 connecting line 13 first shut-off valve 14 Relief valve 15 Return line 16 Fuel 17 Fuel injection system 18 Common rail drain line QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2003 / 0111050 A1

[0004]

Claims

[1] Fuel injection system (17) for internal combustion engines, comprising a high-pressure fuel pump (6), a common rail (8), at least two injection valves (9), at least one leakage line (10), an injection valve discharge line (11), and a return line (15), wherein the injection valves (9) can be supplied with a high-pressure fuel (16) by means of the high-pressure fuel pump (6) via the common rail (8), at least two injection valves (9) being fluidically connected to one another by means of the leakage line (10), one of the injection valves (9) being fluidically connected to the return line (15) by means of the injection valve discharge line (11), so that fuel (16) can be discharged from the injection valves (9) via the leakage line (10), via the injection valve discharge line (11), and via the return line (15), in particular into a preferably unpressurized tank (1), is deductible, characterized bythat the leakage line (10) and the injection valve drain line (11) are designed to be high-pressure resistant. [2] Fuel injection system (17) according to claim 1, characterized by that a first shut-off valve (13) is fluidically arranged between the injection valve drain line (11) and the return line (15). [3] Fuel injection system (17) according to claim 2, characterized by that the first shut-off valve (13) is designed as a valve that closes with the flow. [4] Fuel injection system (17) according to one of the preceding claims, characterized by that a second shut-off valve (4), which preferably closes against the flow, is arranged fluidically between the tank (1) and the high-pressure fuel pump (6). [5] Fuel injection system (17) according to the preceding claim, characterized bythat a substantially shorter line section is arranged and / or formed between the second shut-off valve (4) and an inlet of the high-pressure fuel pump (6) than between the tank (1) and the second shut-off valve (4), in particular a first intermediate line (5) of minimal length is arranged and / or formed between the second shut-off valve (4) and an inlet of the high-pressure fuel pump (6). [6] Fuel injection system (17) according to one of the preceding claims, characterized by that a relief valve (14) is connected on the one hand to the common rail (8) by means of a common rail discharge line (18) and on the other hand to the return line (15). [7] Fuel injection system (17) according to the preceding claim, characterized by that the common rail drain line (18) and the injection valve drain line (11) are fluidically connected to one another by means of a high-pressure-resistant connecting line (12). [8] A method for operating a fuel injection system (17) for internal combustion engines, in particular according to one of the preceding claims, in different operating states, wherein the fuel injection system (17) has a high-pressure fuel pump (6), a common rail (8), at least two injection valves (9), at least one leakage line (10), an injection valve discharge line (11), and a return line (15), wherein the injection valves (9) are supplied with a high-pressure fuel (16) by means of the high-pressure fuel pump (6) via the common rail (8) in a driving or idling state of the internal combustion engine, wherein at least two injection valves (9) are fluidically connected to one another by means of the leakage line (10), wherein one of the injection valves (9) is fluidically connected to the return line (15) by means of the injection valve discharge line (11),wherein fuel (16) is discharged from the injection valves (9), in particular into a preferably pressureless tank (1), in the driving or idling state of the internal combustion engine via the leakage line (10), via the injection valve discharge line (11) and via the return line (15), characterized by that the fuel (16) is kept under high pressure in the leakage line (10), in the injection valve drain line (11), in the common rail (8) and in the injection valves (9) when the internal combustion engine is at a standstill. [9] Method according to claim 8, characterized by that when the high-pressure fuel pump (6) is switched off, the first shut-off valve (13) is closed when the high pressure is still essentially present in the leakage line (10), the injection valve drain line (11), in the common rail (8) and in the injection valves (9). [10] Method according to one of claims 8 or 9, characterized bythat when the internal combustion engine is switched off, the pressure in the leakage line (10), the injection valve drain line (11), in the common rail (8) and in the injection valves (9) is increased, in particular by a brief increase in the speed of the internal combustion engine and thus the increase in the pressure provided by the high-pressure fuel pump (6) shortly before the first shut-off valve (13) closes.

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