Internal combustion engine and method for operating such an internal combustion engine with reduced tank pressure

Abstract

Internal combustion engine (1) with - an internal combustion engine (2), - an intake manifold(6) for supplying a gas mixture to the internal combustion engine (2) and - a fuel tank system that - a fuel tank (8), - a fuel vapor filter (9) which is in fluid-conducting communication with the environment, - a vent line (10) leading from the fuel tank (8) to the fuel vapor filter (9) and - a purge gas line (11, 19) leading from the fuel vapor filter (9) to the intake tract (6), comprising an evacuation line (15) connecting the fuel tank (8) to the intake tract (6), and a gas supply device (16) designed to reduce the tank pressure in the fuel tank (8) as required.

Description

[0001] The invention relates to an internal combustion engine with a fuel tank system that can be vented. The invention also relates to a method for operating such an internal combustion engine. The internal combustion engine can, in particular, be part of a motor vehicle.

[0002] A fuel tank system for an internal combustion engine of a motor vehicle typically has a vent line that allows pressure buildup in the fuel tank to be released into the environment. This pressure can occur, for example, due to fuel evaporating at relatively high ambient temperatures (see, for example, DE 10 2013 109 459 A1 or DE 10 2016 010 837 A1). Due to emission regulations, it is essential that as few fuel vapors as possible escape into the environment. This is prevented by integrating a fuel vapor filter into the vent line, which absorbs the fuel vapors. Such a fuel vapor filter is usually in the form of an activated carbon filter.

[0003] To regenerate such a fuel vapor filter, the corresponding fuel tank system is typically equipped with a purge gas line, which is connected to the fuel vapor filter on one side and to the intake manifold of the internal combustion engine on the other. During engine operation, ambient air can be drawn in through a connection between the fuel vapor filter and the environment by means of a vacuum created at the point where the purge gas line enters the intake manifold, compared to the ambient pressure. This ambient air flows through the fuel vapor filter, thus purging it. The fuel vapors from the fuel vapor filter are then fed into the combustion chambers of the internal combustion engine via the intake manifold.

[0004] To prevent fuel vapors from escaping the fuel tank system due to a saturated fuel vapor filter, even during extended periods of non-use of the internal combustion engine, especially at relatively high ambient temperatures and / or relatively low ambient pressures, the fuel vapor filter must be adequately sized. This entails correspondingly high costs and a correspondingly large installation space requirement.

[0005] Furthermore, it is generally advisable to regenerate the fuel vapor filter of the associated fuel tank system immediately after starting a motor vehicle's internal combustion engine, as the operation of the engine and / or the vehicle can only last for a short time. This ensures that the fuel vapor filter is regenerated as much as possible when the engine is switched off, in order to have sufficient capacity to absorb fuel vapors.Introducing fuel vapors into the combustion chambers of the internal combustion engine during fuel vapor filter regeneration can, however, cause difficulties. This is because it must be taken into account when metering the amount of fuel injected via the fuel injectors, which are actually intended for supplying fuel to the combustion chambers, in order to continue operating the internal combustion engine with a defined fuel-oxygen ratio. If the fuel vapor filter has only a small amount of soot when the internal combustion engine is started, regeneration of the fuel vapor filter involving the introduction of fuel vapors into the intake manifold can be carried out more selectively and, if necessary, limited to specific operating conditions of the internal combustion engine where the associated problems are relatively minor.

[0006] DE 101 01 257 A1 and DE 10 2009 036 263 A1 each disclose a method for leak testing a fuel tank system of an internal combustion engine, in which a vacuum is generated in the fuel tank system during operation of an internal combustion engine of the internal combustion engine by evacuating the fuel tank through a corresponding vacuum prevailing in the intake tract of the internal combustion engine via an evacuation line that connects the intake tract to a fuel tank and in which a valve is integrated.

[0007] US patent 2014 / 0277927 A1 discloses an internal combustion engine with a fuel tank system in which a pump may be integrated into the purge gas line and / or into an ambient air line connecting a fuel vapor filter to the environment.

[0008] The invention is based on the objective of minimizing the loading of the fuel vapor filter with fuel vapors during periods when the internal combustion engine is not in operation.

[0009] This problem is solved by an internal combustion engine according to claim 1 and by a method according to claim 4. Advantageous embodiments of the internal combustion engine according to the invention and preferred embodiments of the method according to the invention are the subject of further claims and / or will become apparent from the following description of the invention.

[0010] According to the invention, an internal combustion engine is provided, comprising at least one internal combustion engine (in particular a spark-ignition engine or another internal combustion engine, at least intermittently spark-ignited), an intake manifold for supplying a gas mixture to the internal combustion engine, and a fuel tank system. The fuel tank system includes at least one fuel tank, a fuel vapor filter in fluid-conducting communication with the environment, a vent line leading from the fuel tank to the fuel vapor filter, and a purge gas line leading from the fuel vapor filter to the intake manifold of the internal combustion engine. Furthermore, a tank vent valve may be provided for adjusting the mass flow rate of the purge gas introduced from the purge gas line into the intake manifold.According to the invention, an evacuation line, which may be identical to the purge gas line in sections and connects the fuel tank to the intake manifold, and a gas supply device, which is designed to reduce the tank pressure in the fuel tank as needed, are also provided. The gas supply device can preferably be integrated into the evacuation line.

[0011] The resulting ability to reduce the tank pressure in the fuel tank as needed allows for the targeted evaporation of particularly volatile fuel components or hydrocarbons by lowering their evaporation temperatures according to their respective vapor pressure curves. This enables the volatile hydrocarbons to be selectively introduced into the intake manifold via the evacuation line at a suitable time. This can preferably be done during (fired) operation of the combustion engine, as this allows for the thermal utilization of the gaseous hydrocarbons in the combustion chamber(s) of the engine.According to the invention, a targeted evaporation of volatile hydrocarbons in the fuel can therefore be achieved during the operation of the internal combustion engine, which prevents these hydrocarbons from still being present when the internal combustion engine or the entire internal combustion engine or, in particular, a motor vehicle comprising the internal combustion engine is taken out of service.If, during or after such a shutdown, the tank pressure in the fuel tank is no longer reduced by means of the gas delivery device, the evaporation of hydrocarbons in the fuel during non-operation can consequently be largely avoided, because not only has a relatively large quantity of the volatile hydrocarbons already evaporated and been carried away during the previous operation of the internal combustion engine, but also the tendency of the fuel components remaining in the tank to evaporate is reduced as a result of an increased tank pressure.

[0012] Accordingly, according to a method according to the invention for operating an internal combustion engine according to the invention, it is provided that for commissioning and / or at least temporarily during (fired) operation of the internal combustion engine, optionally directly with the commissioning of the internal combustion engine, a lower tank pressure is set in the fuel tank compared to when the internal combustion engine is not in operation by means of the gas supply device and fuel vapors from the fuel tank are introduced into the intake tract via the evacuation line of the fuel tank system.

[0013] Setting a relatively low tank pressure in the fuel tank by means of the gas delivery device for starting the internal combustion engine is to be understood as initiating this measure if a subsequent start-up of the internal combustion engine will be safe or unavoidable.

[0014] In carrying out a method according to the invention, it is preferably provided that, during operation of the internal combustion engine, a tank pressure below ambient pressure, i.e., a tank vacuum, and particularly preferably a maximum permissible tank vacuum limited by the vacuum resistance of the fuel tank, is set by means of the gas supply device, which makes it possible to maximize the targeted evaporation of volatile hydrocarbons in the fuel. As a result, this prevents these hydrocarbons from evaporating further during a subsequent period of non-operation of the internal combustion engine and thus from leading to an increasing load on the fuel vapor filter.

[0015] When the internal combustion engine, and in particular the entire internal combustion engine or the motor vehicle comprising it, is taken out of service, a tank pressure corresponding (essentially) to the ambient pressure and / or at least temporarily exceeding the ambient pressure can be set. This increase in tank pressure can be achieved by pressure equalization with the surroundings (for example, via a valve provided for this purpose) and / or by means of the gas supply device, in particular by reversing the direction of delivery of the gas supply device. Alternatively, a different gas supply device can be used to increase the tank pressure when the internal combustion engine or motor vehicle is not in operation.

[0016] According to a preferred embodiment of an internal combustion engine according to the invention, the evacuation line may bypass the fuel vapor filter or at least the component of the fuel vapor filter responsible for the filtering effect, which may in particular comprise activated carbon. The transfer of fuel vapors from the fuel tank to the intake manifold via the evacuation line, which is intended to occur at least temporarily during operation of the internal combustion engine, should therefore preferably not pass through the fuel vapor filter in order to ensure the most unimpeded flow of fuel vapors possible.

[0017] According to a further preferred embodiment of an internal combustion engine according to the invention, it can be provided that the gas supply device is also integrated into the purge gas line, which makes it possible to use the gas supply device even during a regeneration of the fuel vapor filter in order to realize a sufficient pressure gradient across the purge gas line.

[0018] Preferably, it can be provided that during operation of the combustion engine, the gas supply device for generating a relatively low tank pressure is only used for as long as this allows for the evaporation of volatile hydrocarbons in the fuel to a relevant extent. Accordingly, within the framework of a method according to the invention, it can be provided that - from a quantity of fuel in the fuel tank (fuel quantity) and a proportion of volatile fuel components in this fuel quantity, an initial quantity of volatile fuel components is determined and - an evacuation quantity of the volatile fuel components, which is directed from the fuel tank into the intake tract via the evacuation line, is determined and - the operation of the gas delivery device is terminated or its power is reduced with regard to pressure reduction in the fuel tank if the difference between the output quantity and the evacuation quantity is below a defined limit.

[0019] According to a further preferred embodiment of the method according to the invention, it can also be provided that an actual value of the tank pressure is regulated as a function of a setpoint value of the tank pressure, which enables particularly precise control of the execution of a method according to the invention. The setpoint value of the tank pressure can also be varied, in particular as a function of the temperature of the fuel and / or the ambient temperature and / or the ambient pressure and / or the operating state of the internal combustion engine.

[0020] The invention also relates to a motor vehicle with an internal combustion engine according to the invention. The internal combustion engine of the internal combustion engine can be provided, in particular, for the direct or indirect provision of drive power to the motor vehicle. A motor vehicle according to the invention can, in particular, be a wheeled and not rail-bound motor vehicle (preferably a passenger car or a truck).

[0021] According to the invention, the term "fuel vapor filter" does not imply that it must filter the volatile fuel in gaseous form. Rather, the fuel may already be (partially) condensed again during the filtration process.

[0022] The present invention is explained in more detail below with reference to embodiments illustrated in the drawings. The drawings show, in simplified form: Fig. 1: an internal combustion engine according to the invention in a first embodiment; and Fig. 2: an internal combustion engine according to the invention in a second embodiment.

[0023] The Fig. Figure 1 shows a simplified representation of an internal combustion engine 1 according to the invention. This engine comprises a combustion engine 2 in which a plurality of combustion chambers 3 are formed. During operation of the internal combustion engine 1, mixture quantities are burned in a known manner and in a defined sequence in the combustion chambers 3, which are partially delimited by cylinders 4 of the combustion engine 2 and by pistons 5 movably guided therein. The pressure increases thus generated in the combustion chambers 3 are used to move the pistons 5. These movements of the pistons 5 are converted into a rotary movement of a crankshaft (not shown) via connecting rods (not shown). The guidance of the pistons 5 by the connecting rods via the crankshaft simultaneously results in a cyclic reciprocating movement of the pistons 5.

[0024] The mixture quantities intended for combustion in the combustion chambers 3 comprise, on the one hand, a gas mixture consisting entirely or mainly of ambient air drawn in from the surroundings, and optionally also partially of recirculated exhaust gas, which is supplied to the combustion engine 2 via an intake manifold 6. The gas mixture can be passed through a compressor of an exhaust gas turbocharger (not shown) integrated into the intake manifold 6, by means of which the gas mixture can be compressed. The mixture quantities also include fuel, which can be introduced directly into the combustion chambers 3, for example, by means of injection valves (not shown). The exhaust gas produced during the combustion of the gas-fuel mixture quantities in the combustion chambers 3 is discharged via an exhaust manifold 7 and can flow through an exhaust turbine of the exhaust gas turbocharger.

[0025] The fuel to be introduced into the combustion chambers 3 by means of the fuel injectors originates from a fuel tank 8 of a fuel tank system of the internal combustion engine 1. This fuel tank system comprises, in addition to the fuel tank 8, a fuel vapor filter 9, which may be designed as or include an activated carbon filter and is connected to the fuel tank 8 via a vent line 10. The fuel vapor filter 9 is further connected to the intake manifold 6 of the internal combustion engine 1 via a purge gas line 11. If the internal combustion engine 1 includes an exhaust gas turbocharger, the purge gas line 11 can open into the intake manifold 6 upstream of the compressor (with respect to the flow direction of the gas mixture in the intake manifold 6 towards the combustion engine 2).Furthermore, the fuel vapor filter 9 is in gas-conducting contact with the environment via an ambient air line 12 on the side facing away from the vent line 10 and the purge gas line 11 (with regard to its filtering effect for fuel vapors).

[0026] Fuel tank 8 is partially filled with fuel, some of which is normally liquid and has usually evaporated, so that fuel in fuel tank 8 is also present in a gaseous state. Such evaporation of fuel in fuel tank 8 occurs particularly at relatively high ambient temperatures and relatively low ambient pressure, for example, as a result of a vehicle with an internal combustion engine 1 driving uphill, because a decrease in ambient pressure reduces the evaporation temperatures of the various fuel components according to their respective vapor pressure curves.To avoid an impermissibly high overpressure in the fuel tank 8 caused by such evaporation, the possibility of pressure equalization with the ambient pressure is provided via the vent line 10, the fuel vapor filter 9 and the ambient air line 12, whereby the fuel vapor filter 9 prevents such pressure equalization from leading to the escape of fuel vapors into the environment.

[0027] Such venting of the fuel tank 8, which occurs during a period of non-operation in an internal combustion engine 1 according to the invention, leads to an increasing saturation of the fuel vapor filter 9, which in turn necessitates its periodic regeneration. For this purpose, the fuel vapor filter 9 is purged by drawing in ambient air via the ambient air line 12. This ambient air flows through the fuel vapor filter 9, whereby fuel molecules absorbed in the fuel vapor filter 9 are carried away by the ambient air and introduced into the intake manifold 6 via the purge gas line 11. The mass flow of the purge gas can be selectively adjusted by means of a tank venting valve 13. By introducing the purge gas and the fuel molecules contained therein, these are supplied to the combustion chambers 3 of the internal combustion engine 2 for thermal utilization or combustion.Such purging of the fuel vapor filter 9 is only temporary, but always takes place during the operation of the combustion engine 2, because only then can the fuel introduced into the intake manifold 6 by purging the fuel vapor filter 9 be reliably supplied to the combustion chambers 3 for combustion. Furthermore, a sufficient pressure differential across the purge gas line 11 towards the intake manifold 6 can then be ensured.

[0028] In order to draw in only ambient air via the ambient air line 12 and not additional fuel vapors via the vent line 10 during a purging of the fuel vapor filter 9, the vent line 10 can then be blocked by means of a first shut-off valve 14.

[0029] According to the invention, the internal combustion engine 1 comprises, as described in the Fig. 1. Furthermore, an evacuation line 15 branches off from the vent line 10 in a section located between the fuel tank 8 and the first shut-off valve 14 and opens into a section of the purge gas line 11 located between the tank vent valve 13 and the intake manifold 6. A gas supply device 16 and a second shut-off valve 17 are integrated into this evacuation line 15. The gas supply device 16 is arranged between the branch of the evacuation line 15 and the second shut-off valve 17. Preferably, the gas supply device 16 is arranged as close as possible to the fuel tank 8, since the gas supply device 16 is (also) intended to create a tank vacuum, i.e., a slight vacuum, as needed before and / or during operation of the internal combustion engine 2.The aim is to establish a tank (under)pressure in the fuel tank 8 that is below ambient pressure, which is facilitated by arranging the device as close as possible to the fuel tank 8. The tank underpressure established by means of the gas supply device 16 is also below the gas pressure prevailing, at least temporarily, in the area of ​​the outlet of the purge gas line 11 into the intake tract 6. Preferably, the tank underpressure is maximized, i.e., generated to the greatest extent possible, as permitted by the structural (under-pressure) strength of the fuel tank 8.

[0030] Creating a vacuum in the fuel tank serves to induce the evaporation of relatively volatile hydrocarbons in the fuel. This allows them to be selectively introduced, at least temporarily, into the intake manifold 6 during the operation of the internal combustion engine 2, so that they can be thermally utilized in the combustion chambers 3 of the internal combustion engine 2. This prevents these hydrocarbons from evaporating after the internal combustion engine 2 has been switched off, thus preventing additional loading of the fuel vapor filter 9. The aim is to ensure that the fuel vapor filter 9 is loaded as little as possible when the internal combustion engine 2, and especially when the vehicle containing the internal combustion engine 1, is not in operation.This is further supported by the fact that no vacuum is created in the fuel tank 8 by means of the gas delivery device 16 during the non-operation of the internal combustion engine 2 or the internal combustion engine 1 or the motor vehicle, which results in higher evaporation temperatures of the fuel components and consequently reduces the tendency of the fuel components to evaporate.

[0031] Specifically, such a procedure can include the following steps: First, a potential for reducing the tank pressure is determined depending on the determined boundary conditions, such as the ambient temperature, a pressure reserve (e.g. from component properties of the tank), a determination of whether the fuel tank 8 is currently being refueled or, if not, how much time has passed since such refueling.

[0032] Subsequently, a need for a change in the tank pressure can be determined, which can be done in particular depending on the boundary conditions relating to the fuel tank 8, such as the actual tank pressure, the closed position of the first shut-off valve 14, the temperature of the fuel in the fuel tank 8, the structural pressure resistance of the fuel tank 8 and a suitable quantity, for example in the form of a model value, to represent the proportion of volatile hydrocarbons in the fuel.

[0033] Depending on these boundary conditions, a continuous determination can be made regarding the realization of the greatest possible evaporation of volatile hydrocarbons in the fuel. This can be carried out both before and during a reduction of the tank pressure by means of the gas delivery device 16.

[0034] The one in Fig. The internal combustion engine 1 shown in Figure 2 differs from the one shown in Figure 2. Fig.1. The only difference is that a third shut-off valve 18 is integrated into the section of the vent line 10 located between the fuel tank 8 and the branch of the evacuation line 15. This allows for the formation of a second purge gas line 19 of the fuel tank system, which runs from the fuel vapor filter 9 via the corresponding section of the vent line 10 to the branch of the evacuation line 15, then via the evacuation line 15 and the section of the first purge gas line 11 located between the outlet of the evacuation line 15 and the intake manifold 6. This allows purge gas to be routed to the intake manifold 6 as needed via either the first purge gas line 11 or the second purge gas line 19, the selection being made particularly depending on the gas pressure prevailing in the area of ​​the outlets of the purge gas lines 11 and 19 into the intake manifold 6.If the gas pressure is so high that a sufficient pressure differential cannot be achieved across the first purge gas line 11 to ensure purging of the fuel vapor filter 9, purging can be carried out via the second purge gas line 19. A sufficient pressure differential across this second purge gas line 19 can then be ensured by activating the gas supply device 16 accordingly. Flow control of the purge gas during purging via the second purge gas line 19 can then be achieved by means of appropriate power control of the gas supply device 16 and / or by appropriate control of the first shut-off valve 14 and / or the second shut-off valve 17 (which then function as a tank venting valve).If the purge gas is routed via the first purge gas line 11, at least the first shut-off valve 14 and the second shut-off valve 17, and possibly also the third shut-off valve 18, are kept closed. If, on the other hand, the purge gas is routed via the second purge gas line 19, the tank vent valve 13 and the third shut-off valve 18 are kept closed. REFERENCE MARK LIST 1 internal combustion engine 2 Internal combustion engine 3 Combustion chamber of the internal combustion engine 4 cylinders of the internal combustion engine 5 pistons of the internal combustion engine 6 Intake tract 7 Exhaust system 8 Fuel tank 9 Fuel vapor filters 10 Vent line 11 (first) purge gas line 12 Ambient air duct 13 Tank vent valve 14 first shut-off valve 15 Evacuation line 16 Gas conveying device 17 second shut-off valve 18 third shut-off valve 19 (second) purge gas line

Claims

[1] Internal combustion engine (1) with - an internal combustion engine (2), - an intake manifold(6) for supplying a gas mixture to the internal combustion engine (2) and - a fuel tank system that - a fuel tank (8), - a fuel vapor filter (9) which is in fluid-conducting communication with the environment, - a vent line (10) leading from the fuel tank (8) to the fuel vapor filter (9) and - a purge gas line (11, 19) leading from the fuel vapor filter (9) to the intake manifold (6), comprising, characterized by an evacuation line (15) connecting the fuel tank (8) to the intake tract (6), and a gas delivery device (16) designed to reduce the tank pressure in the fuel tank (8) as required. [2] Internal combustion engine (1) according to claim 1, characterized by , that the evacuation line (15) bypasses the fuel vapor filter (9). [3] Internal combustion engine (1) according to claim 1 or 2, characterized by that the gas conveying device (16) is integrated into the evacuation line (15) and / or into the purge gas line (11). [4] Method for operating an internal combustion engine (1) according to any one of the preceding claims, characterized by , that for commissioning and / or at least temporarily during operation of the internal combustion engine (2) a lower tank pressure is set in the fuel tank (8) compared to when the internal combustion engine (2) is not in operation by means of the gas supply device (16) and fuel vapors from the fuel tank (8) are introduced into the intake tract (6) via the evacuation line (15). [5] Method according to claim 4, characterized by , that during the operation of the internal combustion engine (2) a tank vacuum, which is a tank pressure below the ambient pressure, is set by means of the gas supply device (16). [6] Method according to claim 5, characterized by , that a maximum permissible tank vacuum is set, limited by the vacuum resistance of the fuel tank (8). [7] Method according to any one of claims 4 to 6, characterized by , that when the internal combustion engine (2) is taken out of service, a tank pressure corresponding to the ambient pressure and / or at least temporarily a pressure higher than the ambient pressure is set. [8] Method according to any one of claims 4 to 7, characterized by , that - from a quantity of fuel which is a quantity of the fuel located in the fuel tank (8) and a proportion of volatile fuel components in this quantity of fuel, an initial quantity of the volatile fuel components is determined and - an evacuation quantity of the volatile fuel components, which is directed from the fuel tank (8) to the intake tract (6) via the evacuation line (15) is determined and - the operation of the gas supply device (16) is terminated or its power is reduced with respect to pressure reduction in the fuel tank (8) when the difference between the output quantity and the evacuation quantity is below a defined limit. [9] Method according to any one of claims 4 to 8, characterized by , that an actual value of the tank pressure is regulated depending on a target value of the tank pressure. [10] Method according to claim 9, characterized by , that the target value of the tank pressure is varied.

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