Method and apparatus for diagnosing the coolant injection of an internal combustion engine

Abstract

Method for diagnosing the coolant injection of an internal combustion engine, characterized in that smoothness or roughness of running is determined from the fluctuations in the speed of several combustion processes, wherein the roughness of running indicates how much the individual combustion processes differ from each other and the smoothness of running indicates how much the individual combustion processes are similar, and from the smoothness of running or roughness of running a functioning or non-functioning of the coolant injection is determined.

Description

State of the art

[0001] The invention relates to a method or device for diagnosing a coolant injection system of an internal combustion engine according to the preamble of the independent patent claims.

[0002] From DE 31 42 729 A1 a method and a device are already known in which water is injected into an internal combustion engine to improve the quality of combustion or to suppress knocking of the internal combustion engine.

[0003] DE 31 42 729 A1 discloses a device for controlling an internal combustion engine in which an actual signal dependent on knocking processes is compared with a signal specifying a permissible knock setpoint in order to control an actuator to reduce the tendency to knock on the basis of the control deviation.

[0004] DE 10 2014 222 474 A1 discloses a method for controlling combustion in which, depending on a detected knock intensity and while maintaining a target exhaust gas temperature, fluid mixing into the cylinder is controlled by setting a target ignition angle. Advantages of the invention Disclosure of the invention

[0005] In contrast, the inventive method or device with the features of the independent claims has the advantage that the smoothness or roughness of the engine's operation allows conclusions to be drawn about whether the coolant injection system is functioning or not. This makes it possible to determine during the operation of the internal combustion engine whether the method is actually being carried out, i.e., whether the injection means are functioning reliably. If reliable coolant injection is confirmed, the ongoing operation can be optimized, taking into account the improved combustion resulting from the coolant injection.If a malfunction of the coolant injection system is detected, appropriate countermeasures must be initiated, in particular measures to protect the internal combustion engine, especially to prevent overheating or severe knocking. This ensures safe engine operation over a wide range.

[0006] Further advantages and improvements result from the features of the dependent patent claims. Since the smoothness or roughness of running depends on the operating parameters of the internal combustion engine, the respective operating point of the engine must be taken into account when evaluating the smoothness or roughness. A particularly simple method compares the smoothness or roughness of running with a reference value. If it is determined that the smoothness is below a reference value or that the roughness is above a reference value, the coolant injection is diagnosed as faulty. This method is particularly simple and requires only a map of reference values. These reference values ​​are stored in a map, specifically depending on the operating points of the internal combustion engine.An improved method for diagnosing coolant injection problems involves measuring engine smoothness or roughness, once with coolant injection activated and once with it deactivated. This direct comparison allows for higher diagnostic accuracy and enables reliable diagnosis even in operating ranges where the differences between activated and deactivated coolant injection are not significant. With the coolant injection system activated and functioning correctly, an improvement in engine smoothness or a reduction in roughness is expected. Conversely, the coolant injection system is diagnosed as faulty if the engine smoothness with the coolant injection system activated does not show a sufficient improvement compared to the smoothness with the coolant injection system deactivated.Alternatively, the coolant injection system can also be diagnosed as faulty if the engine roughness with coolant injection deactivated does not show a sufficiently high increase compared to the roughness with coolant injection activated. Another alternative is a two-stage procedure in which the engine smoothness or roughness is first compared to a reference value. Only if this comparison suggests a potential malfunction of the coolant injection system is a procedure used that actively switches between activated and deactivated coolant injection and compares the smoothness or roughness values. This procedure therefore initially requires less effort, only activating a more complex and improved method for diagnosing the coolant injection system if necessary.This allows for both minimal effort and highly reliable diagnosis. Drawings

[0007] Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description. They show: Fig. 1. a coolant injection into an intake manifold of an internal combustion engine, Fig. 2. A coolant injection directly into the combustion chamber of an internal combustion engine, Fig. 3. An engine map with areas for activated and deactivated water injection and Fig. 4a the running roughness with a functioning coolant injection system, once with water injection activated and once with water injection deactivated and Fig. 4b the running instability signal with water injection activated and deactivated in the case of a non-functional water injection system. Description of the exemplary implementations

[0008] In the Fig. Figure 1 schematically shows an engine, i.e., an internal combustion engine with one cylinder 10. A combustion chamber 101 is defined within the cylinder 10 by a piston 100. Air for combustion is supplied to the cylinder 10, or rather the combustion chamber 101, via an intake manifold 11, and fuel for combustion in the cylinder 10 is supplied via a fuel injector 13. The resulting exhaust gases are carried away from the cylinder 10 via the exhaust pipe 12. This is a typical gasoline or diesel engine, which is used in the Fig. Figure 1 is shown only schematically. In particular, further control elements such as air intake and exhaust outlet valves, means for influencing the airflow through the intake manifold 11 (such as a throttle valve), a spark plug or a glow plug and other elements of conventional gasoline and diesel engines are not shown, as they are not important for understanding the invention.

[0009] Furthermore, in the Fig. Figure 1 shows a coolant injection system, typically water injection into the intake manifold 11. Besides water as a coolant, mixtures of water and alcohol are particularly suitable. In the following, the terms coolant injection and water injection are used interchangeably to describe a coolant injection system. The water injection system consists of a water tank 2, which is connected to an electric pump 1 via a connecting line 5. Water can flow from the tank 2 to the electric pump 1 through the connecting line 5, or be drawn from the tank by the electric pump 1. The side of the electric pump 1 that is connected to the water tank 2 via the connecting line 5 is referred to as the inlet. Furthermore, the electric pump 1 has a high-pressure outlet that is connected to a water rail 3 via the connecting line 5.The water rail 3 is a pressure accumulator that can be filled with water from the electric pump and pressurized. The pressure is relatively low, especially during injection into the suction pipe, so the water rail 3 can also be designed as a simple hose or a hose distributor. The water rail 3 is then connected via a further connecting line 5 to a water injector 4, which opens into the suction pipe 11. The water in the tank 2 is thus supplied via the inlet of the electric pump 1 and made available at the high-pressure outlet of the pump 1 at increased pressure. This water is then temporarily stored in the water rail 3 until it is injected into the suction pipe 11 through a corresponding opening in the water injector 4.

[0010] A large number of water injectors 4 can also be connected to the water rail 3, supplying a plurality of cylinders 10 with water. This is a particularly useful design for multi-cylinder engines, as are common in modern motor vehicles, allowing each cylinder to be individually supplied with a quantity of water tailored to its specific needs.

[0011] By injecting water into the intake manifold 11, a mixture of air, fuel, and water is created in the combustion chamber 101 of cylinder 10, together with the fuel injected by the fuel injector 13. This mixture is then ignited, either by a spark plug or, in the case of a diesel engine, by a self-ignition process, resulting in combustion of the fuel-air mixture in the combustion chamber of cylinder 10. The water contained in this air-fuel mixture effectively cools the combustion chamber 101 in cylinder 10, thereby reducing the combustion temperature and, in the case of gasoline engines, decreasing the tendency to knock. This allows for an optimized ignition timing, which has a positive effect on the efficiency and fuel consumption of the gasoline engine. Furthermore, the formation of harmful exhaust gases can also be reduced in both gasoline and diesel engines.Introducing water into a combustion chamber is therefore a measure that can positively influence the combustion quality in the combustion chamber of cylinder 10. This measure can positively affect the exhaust gas quality, the thermal load on cylinder 10, the engine's performance, and fuel consumption. Furthermore, a control unit 200 is shown, which is a microcontroller for controlling all engine components. For this purpose, signals from the corresponding engine sensors are read, and appropriate engine control signals are calculated. The control unit 200 thus serves as a means of monitoring all operating states of the engine.

[0012] In the Fig. Figure 2 also shows an engine with water injection into the combustion chamber of cylinder 10. The reference numbers 10, 11, 12, 13, 1, 2, 3, 4, 5, 100, 101 again denote the same objects as in the Fig. 1. Unlike the Fig. However, in this case, the water injector 4 is not positioned so that it opens into the intake manifold 11, but directly into the combustion chamber 101 of cylinder 10. Injecting water directly into the combustion chamber of cylinder 10 requires significantly higher pressures than injecting it into the intake manifold. For injecting water into the intake manifold 11, a water pressure of just a few bar is sufficient. Since injection into the combustion chamber of cylinder 10 can occur when the air intake valve towards the intake manifold 11 is already closed and the cylinder is in a compression phase, a significantly higher pressure, up to the order of 200 bar, is required for injecting water into a combustion chamber. Therefore, water must be stored in the water rail 3 at a significantly higher pressure to enable direct injection into the combustion chamber of cylinder 10. For this purpose, a high-pressure pump 6 is connected downstream of the electric pump 1.The inlet of the high-pressure pump 6 is connected to the high-pressure outlet of the electric pump 1 via a connecting line 5. The high-pressure outlet of the high-pressure pump 6 is connected to the water rail 3 via a connecting line 5. This arrangement creates a sufficiently high pressure to allow water to be injected directly into the combustion chamber of the engine.

[0013] In the Fig. Figure 3 shows a characteristic map in which the load L and the rotational speed N, as well as the operating ranges in which coolant injection is activated or deactivated, are shown. As can be seen, in the larger range 32, particularly in the range of lower load and lower rotational speed, coolant injection is not activated. In a further range 31, particularly at higher load and higher rotational speed, water injection is activated to minimize thermal overload of the internal combustion engine or engine knocking. According to the invention, a method and a device are now proposed by which the functioning or non-functioning of the coolant injection can be determined. If it turns out that the coolant injection is functioning, improved operation of the internal combustion engine with coolant injection is possible.In this process, the combustion engine operates in an optimized operating range, which can increase fuel consumption and / or power output. If it is determined that the coolant injection system is not functioning, a protective mode for the combustion engine must be implemented, as the optimized operation with coolant injection is then not possible. This protective mode increases fuel consumption and reduces engine power.

[0014] In the Fig. Figure 4a illustrates the engine roughness of a system with functioning coolant injection. The roughness is plotted against time. This roughness results from fluctuations in engine speed, both between individual cylinders of a multi-cylinder internal combustion engine and between successive combustion cycles in the same cylinder. Depending on the composition of the fuel-air mixture in a combustion chamber of the internal combustion engine, there are differences in the combustion process, which manifest themselves in varying torque contributions from the respective combustion cycles. This can be detected, for example, by analyzing the engine speed immediately after each combustion cycle.By injecting coolant, the individual combustion processes in the cylinders are better controlled, and the differences in the combustion processes of the individual cylinders are reduced.

[0015] Two different evaluation criteria can then be implemented: running roughness and running smoothness. Running roughness indicates how much the individual combustion processes differ from one another. Running smoothness indicates how similar the combustion processes are in the individual cylinders. Both, however, describe the same phenomenon, only with a different sign. This means that high running roughness corresponds to low running smoothness, and low running roughness corresponds to high running smoothness. Essentially, both measures convey the same information; however, in the past, both running roughness and running smoothness were used to evaluate the uniformity of combustion processes in internal combustion engines.

[0016] In the Fig. Figure 4a shows the engine roughness with a functioning coolant injection system. The first section (401) shows the roughness with the coolant injection system activated. The second section (402) shows the roughness with the coolant injection system deactivated, i.e., switched off. As can be clearly seen, the roughness is significantly higher with the coolant injection system switched off than with it switched on (401). It is therefore possible to clearly distinguish whether the internal combustion engine is currently operating with water injection or not.

[0017] In the Fig. Figure 4b shows the same measurement with faulty coolant injection. Since the coolant injection is not functioning, switching it on or off has no effect on the combustion process, as no coolant is introduced into the combustion chamber in either state. Therefore, both roughness curves fall within range 402, which corresponds to a deactivated coolant injection system.

[0018] Depending on the operating range in map 3, different analysis methods can now be used. At operating point 301, the internal combustion engine is in a state where coolant injection is activated. By simply observing the engine's smoothness or roughness, it can be determined whether water is actually being injected or not, i.e., whether the water injection system is functioning correctly. However, the smoothness or roughness signal is also influenced by the operation of the internal combustion engine or the vehicle in which it is installed. An internal combustion engine is generally not operated continuously at a static level; rather, the speed and load change, and thus the engine's operating points also change. It is therefore necessary to store the different smoothness or roughness ranges 401 and 402 as a function of the respective operating points of the internal combustion engine.Especially at higher loads and speeds, greater fluctuations can occur than at lower loads and speeds. In particular, the idle operation of the internal combustion engine should be characterized by low or high smoothness. Due to the constantly changing operating conditions of the engine, a simple distinction between ranges 401 and 402, as described in the [reference], is not possible. Fig. As shown in Figure 4a, this can be difficult. In particular, these areas can overlap significantly during actual operation of the combustion engine, making it hard to determine whether the coolant injection is working or not.

[0019] Improved diagnostics can therefore be achieved by performing two consecutive measurements of engine roughness or smoothness. For one state, coolant injection is activated and then deactivated shortly afterward, and the roughness is measured in both states. A clear difference will be detectable, especially if the operating conditions of the combustion engine have not changed significantly between these two measurements.

[0020] At operating point 301, where water injection is activated, a simple evaluation of the engine roughness can detect a malfunction in the coolant injection system. Alternatively, at operating point 301, active diagnostics can be performed by selectively activating and deactivating the water injection system to check whether there is a significant change in engine roughness or smoothness, thus indicating whether the coolant injection system is functioning correctly or not.

[0021] At operating point 302, water injection is not activated, meaning that comparing the engine's roughness or smoothness to a stored reference value is meaningless. However, active diagnostics can still be performed at operating point 302 by selectively activating and deactivating water injection and comparing the engine's roughness or smoothness in each case. Even in this operating range, where coolant injection is not normally intended, its influence on engine roughness or smoothness can still be detected, allowing for diagnostics of the coolant injection system. This procedure at operating point 302 results in a slight increase in coolant consumption, which is not problematic since the active diagnostics are only performed occasionally.

[0022] Furthermore, a two-stage diagnostic procedure can be implemented in which the engine roughness or smoothness is continuously evaluated at the operating point where water injection 301 is activated. If this diagnostic procedure does not clearly determine whether the coolant injection is functioning reliably, an active diagnosis is performed by controlled switching of the coolant injection on and off. The advantage of this two-stage procedure is that the effort required for simple, continuous monitoring of engine roughness or smoothness during operation with coolant injection is particularly low. In particular, it is then unnecessary to briefly switch off the coolant injection for diagnostic purposes in this operating range, where coolant injection is actually required.This more complex procedure is only performed if simple monitoring of engine roughness or smoothness indicates a potential malfunction in the water injection system, allowing for more extensive active diagnostics. This two-stage process thus minimizes the initial diagnostic effort, with more complex active diagnostics only being carried out when necessary. An advantage of this method is that additional coolant consumption for purely diagnostic purposes only occurs when a fault is suspected.

Claims

[1] Method for diagnosing coolant injection in an internal combustion engine, characterized by , that smoothness or roughness of running is determined from the fluctuations in the speed of several combustion processes, whereby roughness of running indicates how much the individual combustion processes differ from each other and smoothness of running indicates how much the individual combustion processes are similar, and from smoothness or roughness of running a functioning or non-functioning of the coolant injection is determined. [2] Method according to claim 1, characterized by , that the smoothness or roughness of running is determined at an operating point of the internal combustion engine. [3] Method according to claim 1 or 2, characterized by , that the smoothness or unevenness of running is compared with a reference value. [4] Method according to claim 3, characterized by, that the coolant injection is diagnosed as faulty if the running smoothness is below the reference value or the running roughness is above the reference value. [5] Method according to claim 1 or 2, characterized by , that the smoothness or roughness of running is determined once with coolant injection activated and once with coolant injection deactivated, and that the two values ​​for smoothness or roughness of running are compared with each other. [6] Method according to claim 5, characterized by , that the coolant injection is diagnosed as faulty if the running smoothness with coolant injection activated is lower than the running smoothness with coolant injection deactivated, or that the coolant injection is diagnosed as faulty if the running roughness with coolant injection activated is greater than the running roughness with coolant injection deactivated. [7] Method according to claim 1 or 2, characterized by, that the coolant injection is diagnosed as potentially faulty if the smoothness of running is below a reference value or the roughness of running is above a reference value, and that the coolant injection is diagnosed as definitively faulty if the smoothness of running with coolant injection activated is less than the smoothness of running with coolant injection deactivated, or that the coolant injection is diagnosed as definitively faulty if the roughness of running with coolant injection activated is greater than the roughness of running with coolant injection deactivated. [8] Device for diagnosing the coolant injection of an internal combustion engine, characterized by, that means are provided which determine the smoothness or roughness of the running of the internal combustion engine from the fluctuations in the speed of several combustion processes, wherein the roughness indicates how much the individual combustion processes differ from each other and the smoothness indicates how much the individual combustion processes are similar, and determine from the smoothness or roughness of the running whether the coolant injection is functioning or not.

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