Methods for diagnosing a water injection system and diagnostic system

Abstract

Method for diagnosing a water injection system (1) for an internal combustion engine (2). The water injection system (1) comprises an injection device (3) and a supply device (4) with a pump unit (14) for supplying water to the injection device (3). The injection device (3) comprises a pressurizable pressure rail (23) and at least one water injector (13) connected to the pressure rail (23). During a diagnostic operation to examine the water injection system (1), a load point shift of a load state of the internal combustion engine (2), in particular to a higher load, is automatically and at least temporarily shifted by means of a diagnostic device (5) after a start-up, so that a load state suitable for the examination is present in order to counteract misfires.

Description

[0001] The present invention relates to a method for diagnosing a water injection system for an internal combustion engine of a motor vehicle.

[0002] The water injection system comprises an injection device and a supply device with at least one pump unit for supplying water to the injection device. The injection device comprises at least one pressure rail that can be pressurized by means of the pump unit and at least one water injector connected to the pressure rail.

[0003] When using water injection in combustion engines, it is crucial that the system functions flawlessly and, in particular, that the correct amount of water is injected. If, for example, too much water is injected, there is a risk that liquid water will enter the combustion chamber and not evaporate. This liquid water reduces the volume available during the compression stroke, which in the worst case can lead to engine damage. If too little water is injected, it can result in increased engine temperatures and undesirable exhaust emissions.

[0004] From DE 10 2018 204 551 A1, a method for diagnosing water injection is known in which the static pressure in the pressure rail or water rail is recorded over a predetermined period with the pump switched off and the water injectors closed. The magnitude of the pressure loss provides information about any leaks present. To check the function of the water injectors, the system is pressurized and water is injected several times in a controlled manner using the water injectors. The change in pressure in the pressure chamber depending on the injections is then monitored. The observation period must be sufficiently long to obtain reliable results.

[0005] A disadvantage of this approach, however, is that water is introduced into the combustion chamber during the diagnostic injections, which can undesirably affect the combustion process. This can even lead to misfires while driving. Therefore, DE 10 2018 204 551 A1 proposes that the individual injections be measured so small that they do not impair the combustion process. However, experience has shown that larger injection quantities are advantageous for reliable and reproducible diagnostics.

[0006] From DE 10 2023 106 197 B3, a method for diagnosing a water injection system is known in which the pressure rail is pressurized and subsequently a first pressure in the pressure rail and a second pressure in the intake manifold are measured by sensors. These pressure measurements are continued during a load change of the internal combustion engine. The water injectors are not actuated during this process. If the first pressure in the pressure rail follows the second pressure in the intake manifold during the load change, a leak is diagnosed.

[0007] German patent application DE 10 2017 116 332 A1 discloses a water injection system for a hybrid vehicle, comprising an internal combustion engine, an electric motor, a battery for powering the electric motor, and a hybrid transaxle transmission. A control device executes a control routine to enable water injection, while an engine speed-load profile is set by adjusting the speed ratio of the hybrid transaxle transmission and a battery power offset. This is intended to better utilize the fuel-saving advantages of water injection.

[0008] In contrast, the object of the present invention is to provide an improved method for diagnosing a water injection system.

[0009] This problem is solved by a method having the features of claim 1 and by a diagnostic system having the features of claim 10. Preferred embodiments of the invention are the subject of the dependent claims. Further advantages and features of the present invention will become apparent from the general description and the description of the exemplary embodiment.

[0010] The method according to the invention serves to diagnose a water injection system for an internal combustion engine, in particular a hybrid powertrain of a motor vehicle. The water injection system comprises an injection device and, in particular, a supply device with at least one pump unit for supplying water to the injection device. The injection device comprises, in particular, at least one pressure rail that can be pressurized by means of the pump unit and at least one water injector connected to the pressure rail. In particular, the supply device can be separated from the injection device by means of a shut-off unit.During a diagnostic operation to examine the water injection system (especially automatically after a start), a diagnostic device is used to at least temporarily shift the load point (of a load condition) and / or increase the rotational speed of the internal combustion engine (especially to a higher load and / or rotational speed). This load point shift provides a suitable operating point and, in particular, load condition for the examination, so that, for example, misfires do not occur as a result of the examination and, in particular, due to an intentional or unintentional ingress of water into the internal combustion engine.

[0011] The method according to the invention offers many advantages. A significant advantage is the load point shift during diagnostic operation. This enables a structurally simple yet highly reliable prevention of misfires. Furthermore, it allows for considerably more reliable and faster diagnostics. For example, it enables the injection of a quantity of water comparable to that used in the normal operation of the water injection system. Another particular advantage is that diagnostics can be performed while stationary, in a workshop, or on a production line.

[0012] In a preferred and advantageous embodiment, a negative (braking) torque is applied to the internal combustion engine to shift the load point. This negative torque can also be described as a braking torque. In particular, the load state is thereby shifted to a higher load. Preferably, the load point shift is achieved by means of at least one electric motor of a hybrid powertrain of the vehicle. In other words, the load shift is effected by applying a torque from the electric motor. This enables a structurally simple and, at the same time, very reliable load point shift. The load point shift can also be achieved by means of another suitable component of the hybrid powertrain. A significant advantage is that the load point shift using the electric motor can also be carried out when the vehicle is stationary. However, it is also possible for the load point shift to occur while driving.

[0013] Particularly preferably, the diagnostic procedure is performed automatically after a start. This means, in particular, that an adjustment of the engine speed and / or the load level is carried out automatically. Preferably, a profile for adjusting the engine speed and the load level is predefined (by the tester or workshop tester). In advantageous embodiments, the diagnostic procedure runs automatically after a trigger while the vehicle is stationary. An operating point is understood to be, in particular, a load condition, whereby a (specific) operating point can include not only a (specific) load condition but also a (specific) engine speed. An engine speed shift is understood to be a change in engine speed from a first value to a second, different value.

[0014] In particular, the water injection system comprises at least one electric machine. The water injection system can comprise at least one hybrid powertrain with at least one electric machine. The electric machine is, in particular, a traction motor.

[0015] During load point shifting, the electric machine is preferably operated as a generator to produce electrical energy. The generated electrical energy is then supplied to at least one vehicle consumer and / or stored in a traction battery. In this way, load point shifting has a beneficial effect on the vehicle's energy balance.

[0016] It is possible and advantageous for at least one supply measure to be carried out during diagnostic operation. Preferably, this supply measure includes at least filling the injection system with water and / or venting the injection system. The load point shift occurs at least during the filling and / or venting process. Water may escape from the water injector during such a supply measure. Due to the load point shift, it can be reliably ensured that no misfires occur during this process.

[0017] For filling and / or venting, for example, it is provided that the supply unit is connected to the injection unit by means of the shut-off unit and that water is pumped into the injection unit and in particular into the pressure rail by means of the pump unit.

[0018] It is preferred and advantageous that, during diagnostic operation, at least one water injector is activated at least temporarily, allowing water to enter the internal combustion engine. Preferably, the load point shift occurs at least during the activation of the water injector. This also reliably ensures that no misfires occur during diagnostic operation. It is possible for the load point shift to also occur shortly before and / or shortly after the activation of the water injector. For example, the load point shift occurs a maximum of 30 seconds, 15 seconds, 10 seconds, 5 seconds, or 3 seconds before and / or after.

[0019] It is possible that during diagnostic operation, water may escape from the water injector into the internal combustion engine at least temporarily, even without targeted control of the water injector. Preferably, the load shift also occurs at least when such a water escape is to be expected due to diagnostic reasons.

[0020] It is preferred and advantageous for the diagnostic procedure to be performed while the vehicle is stationary. In other words, the vehicle is at a standstill. Specifically, no gear should be engaged, or in the case of an automatic transmission, P or N should be selected. It is also possible and advantageous for the diagnostic procedure to be performed while driving.

[0021] In an advantageous embodiment, for diagnostic operation (especially when stationary), the idling internal combustion engine is brought to a speed range with a higher speed than its normal idle speed. In particular, this increase in speed occurs before the load point shift. Specifically, the speed increase takes place at the beginning of the diagnostic operation. For example, after starting or triggering the diagnostic operation, the internal combustion engine is brought to a higher speed.

[0022] Preferably, the engine speed increase during diagnostic operation is automated using the diagnostic device. For example, the diagnostic device controls an engine control unit or similar component.

[0023] It is possible for the engine speed to be increased manually. For example, the engine speed can be increased by pressing an accelerator pedal, a foot lever, or a comparable control element for the internal combustion engine. Preferably, the manual engine speed increase is supported by the diagnostic system. Particularly preferably, the engine speed increase is supported by the diagnostic system by means of an optical display of a target engine speed range and / or an actual engine speed range. The optical display is provided, in particular, by a display unit. The display unit can be provided, for example, by the diagnostic system and, in particular, by a workshop tester. It is also possible for the display unit to be provided by the vehicle and, for example, by a (digital) instrument panel.

[0024] In all embodiments, it is preferred that at least one test is performed during diagnostic operation using the diagnostic device. Such a test can also be referred to as a test routine or diagnostic routine. The test comprises, in particular, at least one of the following steps: building up pressure in the pressure rail (using the pump unit with the shut-off unit open); maintaining and measuring pressure in the pressure rail (with the shut-off unit closed) and determining any pressure change over time; activating the water injector at least once so that water is injected into the internal combustion engine and determining the pressure drop caused by the at least one injection. In particular, the pressure is measured before and after injection. In particular, at least one load point shift is performed at least temporarily during such a test.Particularly preferably, a load point shift occurs at least during the injection of water into the internal combustion engine.

[0025] The condition of the water injection system is determined based on the pressure change over time and / or the pressure drop. If the pressure change over time and / or the pressure drop deviates from a predefined value by a certain amount, a defect or leak is assumed. Further investigations may also be carried out. Specifically, the cylinders and / or the water injectors assigned to them are tested sequentially. The test results are stored and / or transmitted to an output device. For example, the test results are displayed on a workshop tester's display unit and / or on a mobile device, such as a smartphone.

[0026] The diagnostic system according to the invention comprises a water injection system for an internal combustion engine, in particular for a hybrid powertrain of a motor vehicle, and a diagnostic device. The diagnostic system is suitable and configured to carry out the method presented here. Such a diagnostic system also solves the previously stated problem particularly advantageously. In particular, the diagnostic system can be operated according to the method presented here. In particular, the diagnostic system comprises the means or the spatial-physical features which are described here for the method and its implementation.

[0027] Preferably, the diagnostic device comprises at least one workshop tester that can be connected to the water injection system. In particular, the workshop tester is mobile. In particular, the workshop tester has a user interface with at least one display unit and at least one control panel. In particular, the workshop tester comprises a mobile and / or portable housing. In particular, the workshop tester includes an interface unit for connecting to the water injection system or to the motor vehicle.

[0028] A workshop tester is understood to be, in particular, a tester for use on a production line during the manufacture of the water injection system or the motor vehicle. In addition to or as an alternative to the workshop tester, a diagnostic device may include at least one control unit that is integrated into the water injection system and / or the motor vehicle.

[0029] The diagnostic device includes, in particular, at least one algorithm for executing the procedure steps. Specifically, the algorithm is stored in the control unit and / or in the workshop tester. The diagnostic device includes, in particular, sensors and / or actuators and functional connections to the components of the water injection system and, in particular, also to the hybrid powertrain. Specifically, the diagnostic device is functionally connected to a control unit of the hybrid powertrain or the vehicle.

[0030] The water injection system may include an internal combustion engine. The water injection system may include a hybrid powertrain with at least one internal combustion engine and at least one electric motor. The water injection system may also include a motor vehicle. The applicant reserves the right to claim a motor vehicle with a water injection system and / or a diagnostic system with a motor vehicle.

[0031] Within the scope of the present invention, the term "water" is understood to include, in particular, aqueous solutions and all other liquids in a water injection system. Specifically, a plurality of water injectors and, for example, at least one water injector per cylinder of the internal combustion engine are provided. In particular, the water injectors are arranged such that they can inject into an intake manifold of the internal combustion engine.

[0032] Further advantages and features of the present invention will become apparent from the exemplary embodiments, which are explained below with reference to the accompanying figures.

[0033] The figures show: Fig. 1 a purely schematic representation of a motor vehicle with a diagnostic system according to the invention in a side view; and Fig. 2 a purely schematic diagram of an examination routine performed by the diagnostic system.

[0034] The Fig. Figure 1 shows a motor vehicle 10 with a hybrid powertrain 12 comprising one or more electric machines 22. The machine 22 can also be referred to as the drive motor and is supplied with electrical energy via a traction battery 32. During deceleration, the machine 22 can be operated as a generator, so that the traction battery 32 can be charged or electrical consumers can be supplied. The hybrid powertrain 12 also includes an internal combustion engine 2 and, for example, a gasoline engine or a diesel engine.

[0035] The motor vehicle 10 is equipped with a water injection system 1, which serves to protect the internal combustion engine 2 and its components, especially under high loads (component protection), and to reduce, for example, the exhaust gas temperature or the tendency to knock.

[0036] The water injection system 1 comprises an injection device 3 for injecting water into the running internal combustion engine 2. In the example shown here, at least one water injector 13 is provided for each cylinder of the internal combustion engine 2. The water injectors 13 are connected to a pressure rail 23 or water rail.

[0037] The pressure rail 23 is supplied with water and pressure by a supply unit 4, which comprises a pump unit 14 and a storage tank 34. The supply unit 4 can be disconnected from and connected to the pressure rail 23 via a controllable shut-off unit 24.

[0038] To ensure proper functioning, the water injection system can be examined as part of an automatic diagnostic procedure. For this purpose, the water injection system is operatively connected to a diagnostic device 5. The diagnostic device 5 is part of a diagnostic system 100, which, in the variant shown here, is integrated both into a control unit 45 of the vehicle 10 and into a mobile workshop tester 15. The workshop tester 15 has a display unit 25 and, for example, a display. Data can be entered via a control panel 35, which includes, for example, a keyboard and a mouse or similar devices.

[0039] During diagnostic operation, the diagnostic device 5 automatically shifts the load point of the internal combustion engine 2 to a higher load. This prevents misfires and other malfunctions if water enters the internal combustion engine 2 unintentionally or intentionally through the water injectors 13 during the test. The load point shift is achieved by means of the electric machine 22. The machine 22 exerts a negative torque or braking torque on the internal combustion engine 2, forcing it to operate at a higher load.

[0040] In an exemplary diagnostic operation sequence, the vehicle 10 is stationary. The diagnostic device 5 then automatically increases the engine speed. The engine speed can also be increased manually, for example, by reaching a visually indicated speed range via the accelerator pedal. Subsequently, the diagnostic device 5 shifts the load point of the internal combustion engine 2 by applying torque from the electric motor 22. The higher load point is maintained during the filling and / or venting of the injection system 3.

[0041] After filling and / or venting, the water injection system is in an operational and diagnostic-ready state. The load point shift can be reversed if necessary. The diagnostic device 5 now begins the examination or examination routine. If the examination requires the injection of water, a suitable load point shift is automatically performed again. Following the examinations, the result is stored in the control unit 45 or displayed on the display unit 25 of the workshop tester 15.

[0042] An example of a routine for such an examination is in the Fig. Figure 2 illustrates this. The test procedure used here is to determine whether there is a defect in the water injection system 1 or whether the replacement of components, such as water injectors 13, is necessary. The test procedure is performed with the vehicle 10 stationary under the boundary conditions shown. Reference symbol list: 1 Water injection system 2 Internal combustion engine 3 Injection system 4 Supply facility 5 Diagnostic device 10 motor vehicle 12 Hybrid powertrain 13 Water injector 14 Pump unit 15 workshop testers 22 machine 23 Pressure rail 24 shut-off unit 25 Display unit 32 traction battery 34 storage containers 35 Control panel 45 Control unit 100 diagnostic system

Claims

[1] Method for diagnosing a water injection system (1) for an internal combustion engine (2) of a motor vehicle (10), wherein the water injection system (1) comprises an injection device (3) and a supply device (4) with at least one pump unit (14) for supplying water to the injection device (3), and wherein the injection device (3) comprises at least one pressure rail (23) which can be pressurized by means of the pump unit (14) and at least one water injector (13) connected to the pressure rail (23), characterized by, that by means of a diagnostic device (5) during a diagnostic operation for the examination of the water injection system (1) after a start, a load point shift and / or a speed shift of the internal combustion engine (2) is carried out automatically at least temporarily, in particular to a higher load and / or a higher speed, so that an operating point suitable for the examination is available at which no misfires occur as a result of the examination. [2] Method according to the preceding claim, wherein, for load point shifting, a negative torque is applied to the internal combustion engine (2) by means of an electric machine (22) of a hybrid powertrain (12) of the motor vehicle (10), so that the load state is shifted to a higher load. [3] Method according to one of the preceding claims, wherein at least one supply measure is carried out in diagnostic operation and wherein the supply measure comprises at least one filling of the injection device (3) with water and / or one venting of the injection device (3) and wherein the load point shift is carried out at least during the filling and / or venting. [4] Method according to one of the preceding claims, wherein in diagnostic mode at least one water injector (13) is activated at least temporarily, so that water enters the internal combustion engine (2), and wherein the load point shift takes place at least during the activation of the water injector (13). [5] Method according to any of the preceding claims, wherein the diagnostic operation is carried out while stationary and / or while driving. [6] Method according to one of the preceding claims, wherein for diagnostic operation the internal combustion engine (2) running at idle is brought into a speed range with a speed increased compared to an idle speed. [7] Method according to the preceding claim, wherein the speed increase is carried out automatically by means of the diagnostic device (5) and / or wherein the speed increase is carried out manually and is preferably supported by the diagnostic device (5) by means of an optical display of a target speed range and / or an actual speed range. [8] A method according to one of the preceding claims, wherein in diagnostic operation at least one examination is carried out using the diagnostic device (5), comprising at least one of the following steps: build up pressure in the pressure rail (23); maintain and measure pressure in the pressure rail (23) and determine a pressure change over time; actuate water injector (13) at least once so that water is injected into the internal combustion engine (2) and determine the pressure drop caused by the at least one injection. [9] Diagnostic system (100) comprising a water injection system (1) for an internal combustion engine (2) of a motor vehicle (10) and a diagnostic device (5) suitable and configured to carry out the method according to one of the preceding claims. [10] Diagnostic system (100) according to the preceding claim, wherein the diagnostic device (5) comprises at least one mobile workshop tester (15) that can be coupled to the water injection system (1).

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