Method for diagnosing leakage of a water injection system

Abstract

A method for diagnosing leakage of a water injection system 20, a device for carrying out the method according to the invention, and an internal combustion engine 1 with the device according to the in

Description

The present invention relates to a method for diagnosing leakage of a water injection system, a device for carrying out the method according to the invention, and an internal combustion engine with the device according to the invention. Highly turbocharged internal combustion engines develop high temperatures of both the intake gas mixture and the combustion chamber itself. As a result, the knock limit is quickly reached at higher loads, resulting in uncontrolled combustion of the compressed filling of the combustion chamber, which in turn leads to high local temperatures and pressure gradients. In order to prevent this, the ignition timing must be adjusted to take place later, resulting in poorer overall efficiency and increasing exhaust temperatures, and thus lower power and higher emissions. Another approach is to enrich the fuel mixture so that some portion of the injected fuel cannot be burnt but evaporates and thus lowers the exhaust temperature. However, enriching the fuel mixture at least results in more fuel being consumed, wherein, of course, often higher exhaust emissions are also the result because the catalytic converter functions less efficiently due to the enriched fuel mixture. In accordance with another technical approach, water is injected into the combustion chamber or intake pipe to reduce fuel consumption and emissions. Use of a water mixture or other non-combustible liquid with as high an evaporation enthalpy as possible is also conceivable. In the context of the application, water is understood as an obvious example of such a liquid as representative of all usable liquids, which is why water injection, etc. is also specifically referred to. The term "water" in the context of the application thus includes all liquids that can be used. The evaporating water has a cooling effect and thus reduces the temperatures of the air flows, in particular at the inlet of the gas mixture into the combustion chamber and in the combustion chamber itself, which means the knock limit is reached later and controlled combustion can be ensured even at higher loads. Water injections are typically only used in certain high-load ranges, as most internal combustion engines do not require cooling by means of water injection at lower load requirements. However, if water injection is required, a pump transfers the water from a water tank, typically through a filter, into a water injection system. From there, the water is then typically fed into an intake pipe via injection nozzles or directly into the combustion chamber via direct injection. The water injection system can also be referred to as a water rail. The water in the intake pipe can be mixed with the fuel mixture or fed into the combustion chamber in layers. Typically, a shut off valve is provided between the water supply, consisting of the water tank and pump, and the water injection system to be able to keep it completely free of water. This is particularly necessary at negative temperatures, as otherwise the water in the water injection system could freeze when the vehicle is switched off and thus cause damage to the sensitive injector, for example. When using a water injection system in internal combustion engines, care should be taken to ensure that there is not a so-called water hammer. A risk of a water hammer exists when liquid water enters the combustion chamber and does not evaporate. As liquid water is not compressible like gas, it reduces the volume available in the compression stroke, thereby creating excessively high pressures in the compressed combustion chamber, which can cause the connecting rod of the piston to bend in the cylinder and lead to engine damage. In order to prevent this, it is essential to detect a leakage in the water injection system, which could cause too much water to enter the intake pipe, as quickly as possible. Patent document DE 102018204551 B4 proposes a method and device for diagnosing a water injection system with a pressure chamber for water, a water rail, a pressure sensor, a pump and a fuel injector, wherein the pressure in the water rail is detected over a predetermined period of time with the pump switched off. The amount of the pressure drop provides information about the tightness of the system. However, the disadvantage of this approach is that the observation period must be sufficiently long to be able to make a corresponding statement. Patent document DE 102018216411 A1 discloses a device for water injection with, among other sensors, a water rail pressure sensor and a pump, wherein a leakage can be detected in the event of noticeable pressure changes in the water rail. Patent document US 2019120176 A1 discloses a device for water injection with a pressure sensor between the shut-off valve and the fuel injector, i.e. in the water injection system. Based on a determined fill time upon opening of the shut-off valve, the pressure and the known volume of the water injection system, a leakage of the system is subsequently concluded. In light of the described background of the prior art the present invention seeks to propose an alternative way of determining a leakage of the water injection system, a corresponding device for carrying out the method according to the invention, and an internal combustion engine with the device according to the invention. This may be solved by the subject-matters of the independent claims. Advantageous further developments of the invention are included in the dependent claims. In the method according to an aspect of the invention for diagnosing leakage in a water injection system, the water injection system is configured to inject water into an intake pipe of the internal combustion engine and can be separated from a water supply by a shut-off valve. The water supply preferably consists of a water tank and a water pump, which is configured to pump water from the water tank into the water injection system. The shut-off valve can ensure that water does not enter the water injection system when the shut-off valve is closed. According to an aspect of the present invention, prior to filling the water injection system with water from the water supply, a first pressure in the water injection system is continuously measured and compared by means of a first pressure sensor and a second pressure in the intake pipe by means of a second pressure sensor when the shut-off valve is closed and the load of the internal combustion engine changes. A continuous measurement is to be understood to mean multiple measured values are taken over a certain period of time in order to determine a pressure curve of the corresponding parameters. Comparing the pressures is to be understood that the two pressures are related in such a way that a possible dependence of the first pressure on the second pressure can be detected. This can be achieved, for example, by forming the difference between the two pressures. The change in load during the pressure measurements causes the pressure in the intake pipe to change. If the first pressure in the water injection system follows the second pressure in the intake pipe, the injection system is not pressure-tight in relation to the intake pipe, and therefore damage to the water injector is to be assumed in this case. When injecting the water into the intake pipe, this may result in more water entering the intake pipe than intended, or water entering the intake pipe unintentionally after filling the water injection system. In this case, a leakage is therefore diagnosed, which preferably involves the output of a corresponding warning and the deactivation of the water injection system or the deactivation of the shut-off valve so that it cannot be opened. The formulation "the first pressure follows the second pressure" should be understood to mean that a pressure change of the second pressure also has an effect on the measured value of the first pressure, possibly with a slight time delay or smaller magnitude. Ideally, provided the water injection system does not have a leakage, the first pressure should remain constant even if the load and thus the second pressure changes. Possible pressure changes of the first pressure due to temperature differences induced by the load changes are preferably identified and isolated. The method according to aspects of the invention can thus provide a technically comparatively simple and fast way of detecting a possible leakage in the water injection system that could damage the engine. In an advantageous embodiment of the invention, the first pressure and / or the second pressure are / is detected using multiple individual sensors. In this way, the accuracy of the measurement and thus the reliability of the diagnostic method can be further improved. The device according to an aspect of the invention for carrying out the method according to aspects of the invention comprises at least one first pressure sensor for measuring a first pressure in a water injection system of an internal combustion engine and at least one second pressure sensor for measuring a second pressure in an intake pipe of an internal combustion engine. In addition, the device according to an aspect of the invention comprises an evaluation unit, which is configured to continuously compare the first pressure and the second pressure and output a message if the first pressure follows the second pressure. Using such a device, the method according to the invention can be carried out. An internal combustion engine according to an aspect of the invention, in particular for a motor vehicle, comprises at least one device according to an aspect of the invention for carrying out the method according to an aspect of the invention. Various advantageous aspects and embodiments of the invention will be explained in further detail below, making reference to the accompanying drawing. Fig. 1 shows a schematic illustration of an embodiment of an internal combustion engine 1 according to the present invention Fig. 1 shows a schematic illustration of an embodiment of an internal combustion engine 1 according to the present invention. This has a piston 50, which is configured as a combustion chamber for an air-fuel mixture to be combusted. The air-fuel mixture enters the cylinder 50 via an intake pipe 60, wherein a fuel injection system 40 directs the fuel or air-fuel mixture into the intake pipe 60. An exhaust system 70 is provided to discharge combusted exhaust gases from the cylinder 50. In particular, an exhaust gas recovery system and / or a turbocharger system can be provided that connects exhaust system 70 to the fuel injection system 40. Furthermore, water injection is provided by a water injection system 20 and a water supply 10. The water supply 10 consists of a water tank 11 and a pump 12, which directs water from the water tank 11 via water lines 21 to the water injection system 20. The water injection system 20 consists of an injector 23 that injects the water into the intake pipe 60. A shut-off valve 30 is provided between the water supply 10 and the water injection system 20, which is configured to prevent water flowing into the water injection system 20 when closed. Thus, the water injection system 20 can be completely drained, which in particular prevents damage to the water injection system 20. Furthermore, embodiments are conceivable in which a filter or similar water treatment device is provided that filters the water prior to entering the water injection system 20, and thus prevents harmful particles from being present in the water that could clog or damage the injector 23. Furthermore, a water recirculation system can be used, which returns unneeded water from the intake pipe 60 or the water injection system 20 to the water tank 11. If multiple cylinders 50 are provided in one embodiment, multiple injectors 23 are provided in the water injection system 20, which inject water into the respective intake pipes 60 of the individual cylinders 50. Such a water injection system 20 is also referred to as a water rail, wherein the water rail can continue to be fed by only one water supply 10. In the initial state, there is no water in the water injection system 20. If a certain load requirement of the internal combustion engine 1 requires water injection to increase power and reduce emissions, the shut off valve 30 opens, causing the pump 12 to pump water into the water injection system 20. From there, the water passes through the injectors 23 at a fixed point in time before or during the filling of the cylinder 50, i.e., before or during the opening of an intake valve in the combustion chamber, in finely atomised form into the intake pipe 60, where it can mix with the air-fuel mixture. In so doing, it is required that the amount of water is dispensed very accurately so that not too much water is injected into the intake pipe 60 to avoid a water hammer of the engine. If there is leakage in the water injection system 20 and too much water enters the intake pipe during the injection of the water, or if injectors are closed, any water at all, this can have fatal consequences for the engine, as described above. In order to diagnose a leakage according to the method according to an embodiment of the invention, a first pressure sensor 22 is provided in the water injection system 20 for measuring a first pressure p1 and a second pressure sensor 62 in the intake pipe 60 for measuring a second pressure p2. Both pressure sensors 22, 62 measure the corresponding pressures p1, p2 over time in a state in which the shut-off valve 30 is closed and no water is in the water injection system 20. If there is a change in load of the engine, there is also a change in pressure in the intake pipe 60, which is detected by the second pressure sensor 62. If the first pressure p1 also changes during the change in the load in such a way that a connection between the first pressure p1 and the second pressure p2 can be determined, i.e., the first pressure p1 follows the second pressure p2, a leakage is diagnosed and a corresponding warning is output. Ideally, the first pressure p1 remains constant even when the load changes. Preferably, pressure changes of the first pressure p1, which are due to an increase in the temperature in the water injection system 20 due to an increased engine load or other external influences, can be filtered out and ignored when comparing the pressures. The evaluation or comparison of the pressures p1, p2 (measured pressure values) is carried out by an evaluation unit, which collects and evaluates the measured pressures accordingly. The evaluation unit can be implemented by forming a difference, wherein a deviation of the difference of the pressures p1, p2 from a target value specified as a function of other parameters such as outside temperature or load change indicates a leakage, and thus a warning can be output by the evaluation unit and / or the shut-off valve 30 cannot be opened to prevent water from entering the water injection system.

Claims

1. A method for diagnosing leakage of a water injection system of an internal combustion engine, wherein the water injection system is configured to inject water into an intake pipe and can be separated from a water supply by a shut off valve, wherein prior to filling the water injection system, a first pressure in the water injection system and a second pressure in the intake pipe are continuously measured and compared by means of a first pressure sensor in the water injection system and a second pressure sensor in the intake pipe with the shut-off valve closed and a load change of the internal combustion engine and a leakage is diagnosed, as long as the first pressure follows the second pressure.

2. A method according to the preceding claim, wherein multiple first pressure sensors in the water injection system are used to determine the first pressure and / or multiple second pressure sensors in the intake pipe are used to determine the second pressure.

3. A method according to any one of the preceding claims, wherein pressure changes of the first pressure, which are due to an increase in temperature caused by an increased load, are filtered out and ignored when comparing the first pressure with the second pressure.

4. Device for carrying out the method according to any one of the preceding claims, comprisingat least one first pressure sensor for measuring a first pressure in a water injection system of an internal combustion engine,at least one second pressure sensor for measuring a second pressure in an intake pipe of an internal combustion enginean evaluation unit, which is configured to continuously compare the first pressure and the second pressure and output a message if the first pressure follows the second pressure.

5. An internal combustion engine, in particular for a motor vehicle, comprising at least one device according to the preceding claim.