Fuel metering for the operation of an internal combustion engine

Abstract

For an optimized metering of fuel and water for the operation of an internal combustion engine in which a direct injection and an intake manifold injection are provided for metering fuel into the internal combustion engine, and in which the internal combustion engine is assigned a system for water injection, a same intake manifold injector is used for both water and fuel injection.

Claims

1. A method for operating an internal combustion engine that is arranged for receiving both direct and intake manifold injections, the method comprising: using a same intake manifold injector, injecting water and fuel into the internal combustion engine as part of the intake manifold injection; wherein, after terminating an operating mode in which the water injection takes place, the fuel is metered via the intake manifold injector such that water present in a low-pressure accumulator, which is used for both the water injection and the fuel injection, is consumed.

2. The method of claim 1, wherein a duration of an activation of the fuel injection is determined as a function of a PFI portion in a split operation and a quantity of water still present in the low-pressure accumulator when the fuel injection is performed.

3. The method of claim 1, further comprising executing at least one of a start/stop function and a coasting function by which a stop of the internal combustion engine is prevented until the water present in the low-pressure accumulator is consumed.

4. The method of claim 1, wherein, after terminating an operating mode in which the water injection takes place, the injection of the fuel is controlled based on a quantity of water still present in a low-pressure accumulator.

5. The method of claim 1, further comprising: operating the internal combustion engine using the direct injection and an adjusted lambda value; connecting the intake manifold injector for the intake manifold injection; determining a resultant enrichment of an overall mixture by evaluating a lambda signal; determining at least one of a water portion and a fuel portion in a water/fuel mixture to be metered via the intake manifold injector.

6. The method of claim 1, further comprising: operating the internal combustion engine using the direct injection and an adjusted lambda value; connecting the intake manifold injector for the intake manifold injection; comparing a lambda signal representing a resultant enrichment of an overall mixture to an enrichment value that corresponds to an intake manifold injection; and detecting that no water is present in the low-pressure accumulator when the lambda signal matches the enrichment value.

7. The method of claim 1, further comprising, during or after activating the water injection, determining at least one of when and what extent a change in an ignition angle takes place.

8. The method of claim 7, wherein the determination is based on at least one of a geometry of a fuel line via which the fuel is fed to the intake manifold injector, a geometry of a low-pressure accumulator via which the fuel and the water are fed to the intake manifold injector, a fluid quantity injected via the intake manifold injection, an instantaneous fuel pressure, an instantaneous position of a valve that controls respective quantities of the fuel and the water fed to the intake manifold injector, a control of a water pump that pumps the water to the intake manifold injector, and a control of a fuel pump that pumps the fuel to the intake manifold injector.

9. The method of claim 1, further comprising detecting a knock sensor signal following an activation of the water injection and determining, based on the detected knock sensor signal, whether a sufficient quantity of water is meterable via the intake manifold injection.

10. The method of claim 1, further comprising, during or after activating the water injection and operating the internal combustion engine in an operation in which both the intake manifold injection and the direct injection take place: temporarily increasing a portion of the fuel metered via the intake manifold injection; determining a resultant enrichment of an overall mixture of the water and fuel by evaluating a lambda signal; based on the determined resultant enrichment, determining a modification of the portion of the fuel and a portion of the water in the overall mixture to be metered via the intake manifold injection.

11. The method of claim 1, wherein a portion of the fuel metered via the intake manifold injection is increased during or after activating the water injection and operating the internal combustion engine in a mode in which both the intake manifold injection and the direct injection occur.

12. The method of claim 11, further comprising: using a software model, computing the respective portions of the fuel and of the water present in a rail; and based on the computed portions, determining when an increase in the fuel portion metered via the intake manifold injection is to be terminated.

13. The method of claim 1, wherein the water injection occurs in a full-load range.

14. The method of claim 1, wherein, in the water injection, the water is injected under low pressure.

15. The method of claim 1, wherein, using a mixing or 3/2-way valve that is arranged in low-pressure circuits of a source of the water and of a source of the fuel, a switchover takes place between at least two of the injection of the water, the injection of the fuel, and a mix of the injection of the water and the fuel.

16. The method of claim 15, wherein: the valve is a mixing valve; the method further comprises, based on a signal of a lambda sensor, controlling the mixing valve to form a mixture of the water and the fuel; and the injecting of the water and the fuel includes metering the mixture via the intake manifold injector.

17. The method of claim 1, wherein a respective check valve is situated in each of a low-pressure circuit of a source of the fuel and a low-pressure circuit of a source of the water injection, upstream from at least one of (a) a shared fuel low-pressure line to which both the water and the fuel are fed and (b) respective inputs to a shared valve.

18. The method of claim 17, further comprising controlling whether the water is guided into the intake manifold injector using a water pump and controlling whether the fuel is guided into the intake manifold injector using a low-pressure gasoline pump.

19. The method of claim 1, wherein supply systems for metering the fuel and the water in a low-pressure range are demand-controlled.

20. A fuel metering system for an internal combustion engine, the system comprising: a direct fuel injector via which a direct fuel injection into the internal combustion engine can be performed; a water source; a fuel source; an intake manifold injector to which water is suppliable from the water source and fuel is suppliable from the fuel source for an injection of water and fuel into the internal combustion engine via the intake manifold injector; wherein, after terminating an operating mode in which the water injection takes place, the intake manifold injector is configured to meter the fuel such that water present in a low-pressure accumulator, which is used for both the water injection and the fuel injection, is consumed.

21. A control unit for operating an internal combustion engine that is arranged for receiving both direct and intake manifold injections, the control unit comprising: a processor coupled to a metering circuit and that is configured to control the metering circuit to inject water and fuel into the internal combustion engine as part of the intake manifold injection using a same intake manifold injector of the metering circuit; wherein, after terminating an operating mode in which the water injection takes place, the processor is configured to meter the fuel via the intake manifold injector such that water present in a low-pressure accumulator, which is used for both the water injection and the fuel injection, is consumed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic representation of an internal combustion engine that is operable with a gasoline direct injection, an intake manifold fuel injection, and a water injection, according to an example embodiment of the present invention.

(2) FIG. 2 is a flowchart including possible method steps for flushing out injectors according to an example embodiment of the present invention.

(3) FIG. 3 is a flowchart including several method steps for determining the water portion in the gasoline/water mixture in the low-pressure accumulator according to an example embodiment of the present invention.

(4) FIG. 4 is a flowchart including method steps that can be carried out at the beginning of the water injection in order to obtain a rapid response of the overall system according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(5) A vehicle 1 that includes an internal combustion engine 2 for driving vehicle 1 is schematically illustrated in FIG. 1. In vehicle 1, a control unit 3 is situated which enables a control and/or regulation of internal combustion engine 2 and, in particular, a control of the mixture formation. Internal combustion engine 2 includes cylinders 4. Each cylinder 4 is assigned at least one direct injector 5. Each direct injector 5 is connected to control unit 3 via a signal line 6.

(6) Direct injectors 5 are connected to a fuel high-pressure pump 8 via a high-pressure accumulator 7 (high-pressure rail). Fuel high-pressure pump 8 is connected to control unit 3 via a data line 9.

(7) A fuel tank 10 which is assigned a fuel low-pressure pump 11 is further shown in FIG. 1. Fuel low-pressure pump 11 is connected to control unit 3 via a data line 12.

(8) The fuel supplied by fuel low-pressure pump 11 from fuel tank 10 reaches fuel high-pressure pump 8, which generates the pressure necessary for the gasoline direct injection, via a fuel low-pressure line 13. In the exemplary embodiment shown in FIG. 1, fuel low-pressure pump 11 moreover makes available the pressure necessary for the intake manifold injection. For this purpose, the fuel reaches a fuel low-pressure accumulator 15 (fuel low-pressure rail) via fuel low-pressure line 13 and a valve 14 which can be designed as a 3/2-way valve or as a mixing valve. Fuel low-pressure accumulator 15 is connected to intake manifold injectors 16 (PFI injectors).

(9) In FIG. 1, a water injection system is further shown which includes a water tank 17 and an electric water pump 18 connected to valve 14 via a line 19. Electric water pump 18 and valve 14 are connected to control unit 3 via data lines 20 and 21. The example embodiment shown in FIG. 1 further includes check valves 29 and 30 which are situated in the water low-pressure circuit and the fuel low-pressure circuit.

(10) Control unit 3 includes a processor 22 and a memory element 23. In memory element 23, a computer program 24 is stored, for example, which is programmed to carry out the method according to the present invention. The method according to the present invention is then carried out with the aid of control unit 3 when computer program 24 runs on processor 22.

(11) Internal combustion engine 2 is connected to an exhaust tract 25 which includes an exhaust gas catalytic converter 26 and a lambda sensor 27. Internal combustion engine 2 is further assigned a knock sensor 28.

(12) FIG. 2 is a flowchart of steps that take into account the water portion present in the fuel low-pressure accumulator 15 following a water injection that took place for the further operation of the internal combustion engine.

(13) In a step 100, the water injection is terminated. This can be the case, for example, when an instantaneous performance requirement leaves the full-load range. In a step 101, the water portion which is still present in fuel low-pressure accumulator 15 is flushed out. For this purpose, valve 14 is adjusted in such a way that up to 100% fuel is metered via the intake manifold injection. As a result, the water which is still present in the intake manifold injection system is consumed particularly quickly. If the vehicle is in a DI/PFI split operation, the portion of the intake manifold injection (PFI) can be adjusted to up to 100%. In systems in which no valve 14, i.e., neither a mixing nor a switching valve, is present, the water pressure can be alternatively reduced by appropriately controlling electric water pump 18, so that only fuel is delivered into the low-pressure accumulator.

(14) In a step 102, the water portion present in the low-pressure accumulator is determined to ascertain how long the water emptying function should be active. This preferably takes place by using a software model. This software model computes the fuel quantity already injected and uses same to ascertain the quantity of water which is still present in the low-pressure accumulator.

(15) In a step 103, the internal combustion engine is operated taking into account the water portion still present in the low-pressure accumulator.

(16) In a step 104, it is checked whether water is still present in the low-pressure accumulator. If this is the case, the internal combustion engine is continued to be operated in such a way that a flushing is achieved preferably rapidly and the water portion is taken into account during the operation of the internal combustion engine. If there is no more water in the fuel low-pressure accumulator or if the water portion is below a certain minimal threshold value, the process returns to a normal operation of the internal combustion engine in a step 105.

(17) In FIG. 3, method steps are shown which make it possible to determine the water portion in the fuel/water mixture, for example to determine the water portion in the low-pressure accumulator (step 103 in FIG. 2) or to carry out a diagnosis of the overall system. The method starts in a step 110 in which the water portion is to be determined. In a step 111, the internal combustion engine is operated only via the direct injection. In a step 112, the intake manifold injection is temporarily connected, however without adjusting this fuel metering as is usually the case in the DI/PFI split operation. Instead, in a step 113, the lambda signal is detected and evaluated by lambda sensor 27. The evaluation initially shows whether there is an enrichment and/or how strong same is due to the temporary connection of the intake manifold injection. The degree of the enrichment can then be used to determine the water portion and/or the fuel portion in the fuel/water mixture which was metered via the intake manifold injection. This evaluation takes place in a step 114. Here, the lambda value can be compared to a corresponding enrichment value of an intake manifold injection without a preceding water injection. If the measured lambda value matches this enrichment value, a water portion ascertained in a method step 115 can be determined as zero and the state of the system may be detected as water emptied.

(18) FIG. 4 shows method steps which can be carried out when a water filling function is carried out during which the water is to displace the fuel present in the fuel supply system in fuel low-pressure accumulator 15 preferably rapidly.

(19) In general, the ignition angle can only be shifted as a function of the incrementally increasing water portion toward early to the optimal ignition angle for this operation in the case of the activation of the water injection due to the load jump toward full load and in the case of an excessively low water portion or a state in which only fuel is present in the low-pressure accumulator, as otherwise knocking effects would occur. Various measures or combinations thereof can be implemented to already take into account the excessively low injected water quantity with regard to the efficiency of shifting the ignition angle forward in this transition state, on the one hand, and to prevent knocking, on the other hand. Different embodiments and refinements of this functionality are explained based on the flowchart shown in FIG. 4.

(20) In a step 120, the water filling function is activated. According to an example embodiment, the instantaneous water portion in the fuel low-pressure system is determined in a step 121. This can take place, for example, through the evaluation of a knock signal by knock sensor 28. Alternatively and/or additionally, the changing increasing water portion can be determined in step 121 from a model or incrementally continuously taken into account when metering the fuel. Alternatively or additionally, a diagnosis can be carried out in steps 122, 123, and 124 in order to establish whether a sufficient quantity of water is already present in the intake manifold supply system. For example, the water quantity present in low-pressure accumulator 15 can be determined by evaluating the lambda signal. For this purpose, the fuel quantity metered via the intake manifold injection is temporarily increased in step 122. In step 123, the degree of the enrichment is ascertained based on the lambda signal. In step 124, the water portion present in low-pressure accumulator 15 is inferred from the degree of the enrichment. This occurs similarly to the diagnostic procedure described in FIG. 3.

(21) According to an example embodiment, the portion of the fuel metered via the intake manifold injection was increased in step 121 for the purpose of preferably rapidly increasing the water portion metered via the intake manifold injection. It can be provided to check in a step 125, whether the water portion has reached the maximum value. If this is the case, the ignition angle is set to early in a step 126, which is the ignition angle provided for the optimal quantity of injected water. According to another example embodiment, the ignition angle is successively shifted to early depending on the instantaneous water/fuel ratio in the low-pressure accumulator or the increase of the water portion in the low-pressure accumulator.

(22) It can be achieved with the aid of the method described in FIG. 4 that the maximum advantages of the supplementing water injection, in particular in the case of an operation under full-load conditions, can be used preferably rapidly, since on the one hand, a rapid and controlled filling of the low-pressure accumulator with water after an activated water injection is possible and, on the other hand, the delayed filling of the low-pressure accumulator with water is taken into account when adjusting the ignition angle to early.