Method for controlling the injection characteristics of an engine operatable by means of gaseous fuel

Abstract

The invention relates to a method for controlling the blow-in characteristic of a vehicle engine operated with gaseous fuel: determining a time window defining a first point in time at which an intake valve is opened and a second point in time at which the intake valve is closed; determining an engine-side parameter based on the time window; determining a coupling coefficient, which defines a relative angle value on the basis of the parameter, which relative angle value indicates a first period of time for opening the intake valve, a second period of time for closing the intake valve or a third period of time for firing after closing the intake valve, determining a third point of time at which the injection begins, which is coupled to the second point of time by means of the coupling coefficient, or a fourth point in time at the end of the injection is determined, which is coupled to the first point in time by means of a coupling coefficient, or a fifth point in time at the end of the injection is determined, which is coupled to the ignition point in time by means of a coupling coefficient, the latest end of the injection is determined before a maximum permissible cylinder pressure is reached in the engine cylinder, the actual cylinder pressure is calculated from the cylinder piston position and compared to the maximum allowable cylinder pressure for the blow-in.

Description

Technical Field

[0001] The invention relates to a method for controlling an injection characteristic of an engine for a vehicle which can be operated with gaseous fuel. Background Art

[0002] In the prior art, the control of injection valves for gasoline direct injection of engines has hitherto been implemented with the aid of software. In this case, the start or end of the injection is parameterized relative to the top dead center of the corresponding cylinder of the engine. In this case, multiple injections can be realized. There is also the possibility of linking the end of the last injection to the ignition time. The coupling of the control of the injector with the phase of the intake valve stroke as a function for Otto engines with intake manifold injection is already prior art.

[0003] Unlike liquid fuels, such as gasoline, gaseous fuels, such as H2 or CNG, displace fresh charge when they are introduced due to the volume they occupy. This applies not only to injection into the intake duct (=PFI) but also to direct injection into the cylinder (=DI). In particular, by using direct injection DI, the air consumption and thus the achievable load can be significantly increased in the case of an introduction after closing the intake valve. Therefore, when using gaseous fuels, the relative position of the injection window (injection time window) with respect to the stroke of the intake valve in the vehicle engine is crucial for the operation of the engine. Summary of the invention

[0004] It is therefore an object of the present invention to provide a solution by means of which the injection characteristics of an engine for a vehicle which can be operated with gaseous fuel can be controlled in an efficient and reliable manner.

[0005] This object is achieved by a method according to the invention for controlling an injection behavior of an engine for a vehicle which can be operated with gaseous fuel.

[0006] According to a first aspect, the disclosure relates to a method for controlling an injection characteristic of an engine for a vehicle that can be operated with gaseous fuel, the method comprising the following steps:

[0007] In a first step, a time window is determined which defines a first point in time for opening an intake valve of the engine. and a second time point EVS for closing an intake valve of the engine.

[0008] In a second step, at least one engine-side parameter is determined based on the ascertained time window.

[0009] In a third step, a coupling coefficient is determined which defines a relative angle value based on the engine-side parameter, wherein the relative angle value indicates either a first time period for opening the intake valve, a second time period for closing the intake valve, or a third time period for ignition after closing the intake valve.

[0010] In a fourth step, a third time t3 for the start of the blowing is determined, which is coupled to the second time EVS via the determined coupling coefficient, or in a fifth step, a fourth time t4 for the end of the blowing is determined, which is coupled to the first time EVS via the coupling coefficient. In a sixth step, a fifth time t5 for the end of injection is determined, which is coupled to the ignition time via a coupling factor, wherein the maximum permissible cylinder pressure P is reached in a cylinder of the engine by: 最大允许,气缸 The latest end of the previous blowing ( Ende): Calculate the actual cylinder pressure p according to the piston position of the cylinder 实际,气缸 and compare it with the maximum permissible cylinder pressure P for blowing 最大允许,气缸 Make a comparison.

[0011] The basic idea of ​​the invention is to couple the position of the blowing window to the opening and closing times of the intake valve in a parameterizable manner. The opening and closing times of the intake valve can be freely selected. The coupling is implemented in the software of the engine control unit by corresponding possibilities. When using direct blowing, the parameterizability of the relative position of the start of blowing and the closing of the intake valve (EVS) is important. Optionally, it is also meaningful to link the end of blowing to the ignition time.

[0012] The invention is based on the recognition that, in contrast to liquid fuels, gaseous fuels (e.g. H2, CNG) displace fresh charge when introduced into the cylinders of an engine due to the volume occupied. This applies not only to injection into the intake duct (PFI) but also to direct injection into the cylinder (=DI). In particular, by using direct injection, the air consumption and thus the achievable load can be significantly increased in the case of an introduction after closing the intake valve. Therefore, when using gaseous fuels, it is important for the operation of the engine to determine the relative position of the injection window with respect to the intake valve stroke.

[0013] The proposed solution is implemented by a corresponding function in the software of the controller. Here, the relative angle δ EVS and γ ZWA corresponding characteristic diagram is provided, which can be parameterized accordingly depending on the engine-side parameters. During the opening period of the intake valve, the above-mentioned displacement of the fresh charge by the injection takes place. If this displacement is to be avoided, it is necessary to start the injection after closing the valve. For reasons of fluid dynamics, it is not mandatory to wait until the zero stroke of the intake valve. Engine tests show that the displacement effect is already greatly reduced from an intake valve stroke of less than 1 mm. Since the behavior of the intake valve stroke is engine-dependent, the reference value should be freely selectable.

[0014] A possible configuration of the method provides the following further steps:

[0015] - Determine the pressure ratio, which is represented by the ambient pressure p in the blowing space of the cylinder 环境 and is constituted by a first pressure p1 of the engine and by a second pressure p2 of the fuel blown into the nozzle of this cylinder of the engine,

[0016] - compare (the determined pressure ratio with the defined limit value on the blow-in valve) to determine whether the determined pressure ratio corresponds to the defined limit value on the blow-in valve, and if not,

[0017] The second pressure p2 is increased in order to reach the defined limit value.

[0018] In this way, in particular for technical applications with an intake manifold injection system for cylinders in an engine, the injection window can be adjusted optimally and effectively.

[0019] A possible configuration of the method provides that the ambient pressure is the current pressure value in the cylinder or the current pressure value in the intake pipe of the engine. The following advantage is achieved thereby: the blowing window can be adjusted accurately.

[0020] One possible embodiment of the method provides that the pressure ratio is determined at the time of the end of the fuel injection. This achieves the advantage that the injection window can be adjusted exactly.

[0021] One possible embodiment of the method provides that the minimum injection pressure is determined as a function of the operating point. This achieves the advantage that the optimized injection window can be adjusted flexibly and efficiently.

[0022] A possible embodiment of the method provides that the gaseous fuel is at least one of the following: hydrogen, natural gas, a gaseous fuel mixture. This achieves the advantage that the setting of the optimized blowing window can be flexibly adapted to the respective field of application.

[0023] One possible embodiment of the method provides that an optimal position of an injection window is determined based on the determined phase position of the intake valve and based on the ignition angle, the injection window representing the start and end time for injecting gaseous fuel into an injection space, for example a combustion chamber or an intake manifold of an engine. This achieves the advantage that the injection window can be adjusted in an application-specific and efficient manner.

[0024] According to a second aspect, the disclosure relates to a computer program, which contains machine-readable instructions, which, when executed on one or more computers and / or computer controllers, cause the one or more computers or computer controllers to implement the method according to the invention.

[0025] According to a third aspect, the disclosure relates to a machine-readable data carrier and / or a download product having said computer program.

[0026] According to a fourth aspect, the disclosure relates to one or more computers and / or computer management systems having the computer program and / or having the machine-readable data carrier and / or download product.

[0027] Further measures for improving the invention are shown in more detail below together with the description of preferred exemplary embodiments of the invention with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings show:

[0029] Figure 1 A schematic flow chart of a method 100 for controlling an injection characteristic of an engine for a vehicle that can be operated with gaseous fuel according to one specific embodiment of the present invention is shown;

[0030] Figure 2 A schematic diagram showing the relative positions of a blowing window and an intake valve or an ignition device according to an embodiment of the present invention;

[0031] Figure 3 A schematic flow chart of a method 100 for controlling an injection characteristic of an engine for a vehicle that can be operated with gaseous fuel according to one specific embodiment of the present invention is shown;

[0032] Figure 4 A schematic diagram showing a method for determining an injection position relative to a phase of an intake valve and determining an ignition angle according to an embodiment of the present invention;

[0033] Figure 5A schematic diagram showing a method for calculating a minimum insufflation pressure and a latest insufflation end according to a pressure ratio of a PFI system and a DI system according to an embodiment of the present invention; and

[0034] Figure 6 A schematic curve showing the variation of the flow rate as a function of the pressure ratio is shown. DETAILED DESCRIPTION

[0035] Figure 1 ——Combination Figure 2 and Figure 3 - A schematic flow chart of a method 100 for controlling an injection behavior of an engine 130 for a vehicle 120 that can be operated with gaseous fuel is shown according to one specific embodiment of the present invention.

[0036] In a first step 102 , a time window 10 is determined, which defines a first time point for opening an intake valve 134 of an engine 130 . and a second time point EVS12 for closing an intake valve 134 of the engine 130 .

[0037] In a second step 104, at least one engine-side parameter 18 is determined based on the determined time window 10. The engine-side parameter 18 may be, for example, a rotational speed (n), a relative load (r l ), blowing pressure (P Rail ) or the phase of the intake valve.

[0038] In a third step 106, a coupling coefficient 19 is determined, which defines relative angle values ​​52, 54, 56 based on the engine-side parameter 18. In this case, the relative angle values ​​52, 54, 56 either indicate a first time period for opening the intake valve 134 (=relative angle value 52), a second time period for closing the intake valve 134 (=relative angle value 54), or a third time period for ignition after closing the intake valve 134 (=relative angle value 56). In this case, the coupling coefficient 19 is reflected in Figure 4 The following modes can be selected: Delta Delta EVS and Delta ZW.

[0039] In a fourth step 108, a third time t3 13 is determined for the start of the blowing, which is coupled to the second time EVS12 via the determined coupling coefficient 19, or in a fifth step 110 a fourth time t4 14 is determined for the end of the blowing, which is coupled to the first time EVS12 via the (relative) coupling coefficient 19. 11 is coupled, or in a sixth step 112 a fifth time t5 15 is determined for the end of the injection, which is coupled to the ignition time via a coupling factor 19. Here, the maximum permissible cylinder pressure P is determined in a cylinder 138 of the engine 130. 最大允许,气缸 24 before the latest end of the blowing, which is calculated from the piston position of the cylinder 138 actual cylinder pressure p 实际,气缸 22 and compare it with the maximum permissible cylinder pressure P for this blowing 最大允许,气缸 24 for comparison.

[0040] Depending on the selected mode, steps 108, 110 and 112 can be carried out alternately and therefore do not have to be carried out in sequence (see also Figure 4 ).

[0041] In this context, the invention can be used in systems with intake manifold injection or direct injection of gaseous fuels (eg H 2 , CNG, etc.).

[0042] Figure 2 A schematic diagram showing the relative positions of a blowing window and an intake valve or an ignition device according to an embodiment of the present invention.

[0043] Here, the relative angle δ EVS and γ ZW A corresponding characteristic map is provided which can be parameterized accordingly as a function of the engine-side parameters 18 (eg, rotational speed n, relative load rl and injection pressure Prail) (see also Figure 4 ).

[0044] During the opening duration of the intake valve, the above-mentioned displacement of the fresh charge by the injection takes place. If this displacement is to be avoided, it is necessary to start the injection after closing the valve (in Figure 2 In, δ EVS <0). For reasons of fluid dynamics, it is not absolutely necessary to wait until the zero stroke of the intake valve. Engine tests show that the displacement effect is already strongly reduced from an intake valve stroke of less than 1 mm. Since the behavior of the intake valve stroke is engine-dependent, the reference value should be freely selectable.

[0045] Figure 2 Schematic diagram of the opening of the blow-in window relative to the intake valve and close (δ EVS). In this case, the opening and closing times of the intake valve can be freely selected (for example, an intake valve stroke of 1 mm). This coupling is implemented in the software of the engine control unit via corresponding possibilities. In the case of direct insufflation, the start of insufflation is relative to the closing time of the intake valve (δ EVS ) is important. In addition, the end of injection and the ignition time (γ ZW) ) association or coupling is meaningful, which is Figure 2 It is also schematically shown in FIG.

[0046] Figure 3 A schematic flow chart of a method 100 for controlling an injection behavior of an engine for a vehicle that can be operated with gaseous fuel according to one specific embodiment of the present invention is shown.

[0047] In step 114, the pressure ratio 30 is determined, which is represented by the ambient pressure p in the blowing space 140 of the cylinder 138. 环境 A first pressure p1 36 of the cylinder 132 and a second pressure p2 38 of the fuel in the injection valve 40 of the cylinder 138 of the engine 130 are formed.

[0048] In a next step 116 a comparison is made as to whether the ascertained pressure ratio 30 corresponds to a defined limit value 34 at the injection valve 40 , and if not, in a step 118 the second pressure p2 38 is increased in order to reach the defined limit value or defined condition.

[0049] Here, the ambient pressure 32 may be a current pressure value in the cylinder 138 or a current pressure value in the intake pipe 132 of the engine 130 (see Figure 5 ).

[0050] In this case, the pressure ratio 30 may optionally be ascertained at the point in time when the injection of fuel is completed.

[0051] Alternatively, a minimum blowing pressure can be determined as a function of the operating point.

[0052] Figure 4 A schematic diagram is shown for determining the injection position relative to the phase of the intake valve and determining the ignition angle according to an embodiment of the present invention. As mentioned above, the following corresponding modes are selected here: Delta Delta EVS and Delta ZW.

[0053] Here, the corresponding relative angle is determined based on the engine-side parameters 18 and the corresponding characteristic curve map stored in the control unit. δ EVS and γ ZW, in order to determine the corresponding current phase of the intake valve or the relative angle 52 54 (EVS) or 56 (ZW). These data can then be used to determine the blowing start SOI 14 or the blowing end EOI 13 , 15 or generally the optimal position of the blowing window, depending on the selected mode.

[0054] Therefore, the software side implementation needs to allow the following choice of mode: which coupling ( EVS or ZW) is effective. Accordingly, when using the current phase of the intake valve, consider Figure 4 The corresponding characteristic diagrams (KF) 62 , 64 , 66 shown are used to calculate the blowing position or the position of the blowing window.

[0055] Figure 5 A schematic diagram is shown for calculating a minimum insufflation pressure and a latest end of insufflation as a function of a pressure ratio 30 for a PFI system and a pressure ratio 35 for a DI system according to one specific embodiment of the present invention.

[0056] When injecting gaseous fuel, for stable operation of the injection component (injector), it is necessary to link the level of the injection pressure and the end of the injection process to the pressure ratio. In this case, it is necessary to observe the injection pressure and the pressure in the environment to be injected (intake pipe, cylinder). In this regard, two problems are mentioned.

[0057] 1. Ensure supercritical flow

[0058] In order to optimally meter the fuel, it is necessary to ensure a supersonic flow in the opening cross section of the inlet valve. For this purpose, the currently existing pressure ratio π=p 环境 / p 吹入 Need to be less than or equal to the critical pressure ratio π 临界 (π≤π 临界 ). As a result, a constant flow velocity (close to the speed of sound) occurs in the opening cross section, and the metering becomes linear over the injection time. If a critical pressure ratio is exceeded, i.e. the properties of the fuel to be injected, the flow velocity in the opening cross section decreases nonlinearly and the metering becomes inaccurate. Figure 6 The pressure ratio according to the flow function Ψ is shown, as is the ratio of the mass flow out of the insufflation valve.

[0059] In the case of direct blowing into the cylinder, p 环境 =p 气缸 As the compression process increases, the critical pressure ratio π can be exceeded at a constant blowing pressure. 临界 (For example, for H2π 临界0.528). In the case of inlet pipe blowing, the supercritical pressure ratio can also be exceeded, for example at high filling levels (p 环境 =p 进气管 ↑) and the blowing pressure p 吹入 Low and constant.

[0060] In order to prevent this, the invention proposes to link the end of the injection and the level of the injection pressure to the profile of the cylinder pressure or to the level of the intake manifold pressure. This results in a limitation of the minimum injection pressure and / or a possible latest injection position for reliable metering of the fuel, depending on the operating point. The calculation of the cylinder pressure profile required for this is already performed continuously in the control unit. With the intake manifold pressure and the insufflation pressure also measured continuously, all necessary data are available for implementation.

[0061] 2. Avoid premature closure of the blow-in ejector

[0062] If the insufflation element with the needle is designed to open “outwards” and to be pressure-balanced on the inside, then the pressure 环境 Above a certain level of the injection window, there is the risk that the open needle of the injector can no longer be held by its drive (e.g. coil / magnetic circuit) and the needle closes. In particular, in applications as direct injection into the cylinder, this impairs the accuracy of the fuel metering. This situation is avoided by combining the injection window with a certain limit value for the ambient pressure, in particular a certain limit value for the cylinder pressure.

[0063] As mentioned above, with the help of Figures 1 to 4 The embodiments in describe coupling the injection window (=start and end of injection) to the opening and closing of the intake valve and the position of the ignition time.

[0064] exist Figure 5 In the embodiment shown, this basic concept is now correspondingly expanded or supplemented.

[0065] This is now expanded as follows: the end of the blowing which can be achieved here is linked to applicable values ​​of the ambient pressure and the critical pressure ratio and is thereby limited. That is, in addition, a minimum level of the blowing pressure is determined and monitored as a function of the operating point.

[0066] according to Figure 5 The proposed solution of the specific embodiment of the invention is implemented by corresponding functions in the software of a control unit in the vehicle.

[0067] To parameterize this function, first, the critical pressure ratio π 临界 The value of the ambient pressure p 最大,气缸A fixed value is given: at this ambient pressure, the blow-in valve remains reliably open. This ambient pressure is only relevant when using direct injection (see Figure 5 ).

[0068] The value of the intake manifold pressure or cylinder pressure is taken into account together with the injection pressure at the time of the end of the injection to check the criticality of the current pressure ratio. If the critical pressure ratio is reached or exceeded, the current minimum injection pressure is transmitted to the pressure control system for adjustment.

[0069] This function can therefore also be used to allow operation with a blowing pressure that is always as low as possible. This allows maximum emptying of the gas tank and thus allows the maximum range of the vehicle to be indicated or ascertained.

[0070] In order to avoid the aforementioned premature closing of the injection element, the end of the injection is limited in the direction of delay. At present, this is only necessary for systems with direct injection, because the injection can be carried out after closing the intake valve. During the subsequent further compression, the ambient pressure, that is, the cylinder pressure, rises so that the critical pressure ratio can be exceeded.

[0071] As a functional solution, it is proposed to use the cylinder pressure curve that has been synchronously calculated in the software in order to find the latest current crank angle for the end of injection and use it as EOI 最大 The limits are transmitted to the corresponding blow-in position calculation.

Claims

1. A method (100) for controlling an injection characteristic of an engine (130) for a vehicle (120) which can be operated with gaseous fuel: - determining (102) a time window (10) defining a first time point for opening an intake valve (134) of the engine (130) (11) and a second time point EVS (12) for closing an intake valve (134) of an engine (130); - determining (104) at least one engine-side parameter (18) based on the determined time window (10); - determining (106) a coupling coefficient (19), said coupling coefficient defining relative angle values ​​(52, 54, 56) based on said engine-side parameter (18), wherein: The relative angle values ​​(52, 54, 56) indicate a first time period for opening the intake valve (134), a second time period for closing the intake valve (134), or a third time period for ignition after closing the intake valve (134), - determining (108) a third time t3 (13) for the start of the blowing, which is coupled to the second time EVS (12) via the determined coupling coefficient (19), or - determining (110) a fourth time t4 (14) for the end of the blowing, said fourth time t4 being related to the first time t4 (14) by means of the coupling coefficient (19) (11) coupling, or - determining (112) a fifth time t5 (15) for the end of the injection, the fifth time being coupled to the ignition time via the coupling factor (19), The maximum permissible cylinder pressure P in the cylinder (138) of the engine (130) is determined by: 最大允许,气缸 (24) The latest end of the above-mentioned blowing: Calculate the actual cylinder pressure p according to the piston position of the cylinder (138) 实际,气缸 (22) and compare it with the maximum permissible cylinder pressure P for the blowing 最大允许,气缸 (24) for comparison.

2. The method (100) according to claim 1, comprising the following steps: - determining (114) a pressure ratio (30) which is represented by the ambient pressure p in the blowing space (140) of the cylinder (138) 环境 (32) and is constituted by a first pressure p1 (36) of the fuel injected into a nozzle (142) of a cylinder (138) of the engine (130), - Comparison (116): determine whether the detected pressure ratio corresponds to the defined limit value (34) at the insufflation valve (40); if not, - Increasing (118) the second pressure p2 (38) in order to reach the defined limit value.

3. The method (100) according to claim 2, wherein: The ambient pressure (32) is the current pressure value in the cylinder (138) or the current pressure value in the intake pipe (132) of the engine (130).

4. The method (100) according to claim 2 or 3, wherein: The pressure ratio (30) is determined at a point in time when the injection of the fuel is completed.

5. The method (100) according to any one of the preceding claims, wherein: Determine the minimum blowing pressure according to the operating point.

6. The method (100) according to any one of the preceding claims, wherein: The gaseous fuel is at least one of the following: hydrogen, natural gas, and a gaseous fuel mixture.

7. A computer program comprising machine-readable instructions which, when executed on one or more computers and / or computer-controlled devices, arrange for the one or more computers or computer-controlled devices to implement the method according to any one of claims 1 to 6.

8. A machine-readable data carrier and / or download product having a computer program according to claim 7.

9. One or more computers and / or computer management systems having a computer program according to claim 7 and / or having a machine-readable data carrier and / or a download product according to claim 8.

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