Method for functional testing of a ventilation system in an evaporative system of a motor vehicle and control unit

Abstract

Method for functional testing of a ventilation system (119) in an evaporative system (100) of a motor vehicle, wherein the evaporative system (100) has an inlet valve (106), a negative pressure generating connection piece (109, 117) and a vent line (114, 115) between the inlet valve (106) and the connection piece (109, 117), comprising the following steps: - controlling the inlet valve (106) such that the inlet valve (106) is opened and the open state is maintained for a first predetermined time (127), and / or controlling the inlet valve (106) such that the inlet valve (106) is closed and the closed state is maintained for a second predetermined time (128); - receiving a quantity representative of a pressure gradient (122) prevailing in the vent line (114, 115) between the inlet valve (106) and the connector (109, 117); and - Assessing the functionality of the venting system (119) based on the pressure gradient (122), wherein the functionality of the venting system is assessed based on a maximum value (125) of the pressure gradient (122) during the first predetermined time (127) and / or based on a minimum value (126) of the pressure gradient (122) during the second predetermined time (128).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to evaporative systems, for example, of a fuel tank, and methods for testing them. Specifically, it relates to a method for functional testing of a ventilation system and a corresponding control unit. BACKGROUND OF THE INVENTION

[0002] According to various country-specific legal regulations and for safety reasons, it is necessary to ensure the functionality of fuel evaporation systems, which ensure adequate venting of a fuel tank without releasing pollutants into the environment. Such evaporation systems typically use activated carbon canisters to capture hydrocarbons escaping from the tank. The fuel vapors temporarily stored in the activated carbon canister can be fed into the combustion chamber at a later time via a venting system, such as a purge line system, depending on the degree of loading of the activated carbon canister. To keep hydrocarbon emissions from the fuel evaporation system as low as possible, a sufficiently large mass flow rate must be achieved from the activated carbon canister to the intake tract of the combustion engine.Accordingly, regular inspection of the flushing line system is required, which typically involves analyzing the pressure in the flushing line system and comparing it with reference values. However, such procedures do not always provide reliable results.

[0003] For example, document DE 10 2019 217 408 A1 discloses a method for diagnosing a failure situation of a vacuum generation line using a tank pressure sensor. The pressure in the fuel tank is measured by a fuel tank pressure sensor while a turbocharger is operating for charging and a purge valve is actuated. A failure situation is diagnosed when an engine vacuum generation line remains open when a pressure change value calculated based on the pressure difference of the fuel tank exceeds a reference value.

[0004] Furthermore, document DE 10 2021 200 667 B4 discloses a method for pressure sensor diagnosis in a tank ventilation system of a motor vehicle, wherein the tank ventilation system has an activated carbon filter, a purge line, a tank ventilation valve arranged in the purge line, and a pressure sensor arranged in the purge line. Within the scope of the method, a pressure prevailing in the purge line is measured using the pressure sensor to determine a starting pressure, the starting pressure is classified into one of several pressure ranges depending on the amplitude of the starting pressure, and a pressure sensor diagnosis is performed using a diagnostic algorithm that is assigned to the pressure range in which the starting pressure lies. SUMMARY AND EMBODIMENTS

[0005] It is therefore an object of the present disclosure to enable a particularly reliable diagnosis of a ventilation system of an evaporative system of a motor vehicle.

[0006] This problem is solved by a method for functional testing of a ventilation system and a control unit according to the independent patent claims. Advantageous embodiments and further developments emerge from the respective dependent claims, the following description, and the drawings.

[0007] Thus, according to a first aspect, a method for functionally testing a ventilation system in an evaporative system of a motor vehicle is provided. The evaporative system, in particular the ventilation system, has an inlet valve, a vacuum-generating connector, and a vent line between the inlet valve and the connector.The method comprises the following steps: (i) controlling the inlet valve such that the inlet valve is opened and the open state is maintained for a first predetermined time, and / or controlling the inlet valve such that the inlet valve is closed and the closed state is maintained for a second predetermined time; (ii) receiving a variable representative of a pressure gradient prevailing in the vent line between the inlet valve and the connector; and (iii) assessing the functionality of the venting system based on the pressure gradient. The method is inventively characterized in that the functionality of the venting system is assessed based on a maximum value of the pressure gradient during the first predetermined time and / or based on a minimum value of the pressure gradient during the second predetermined time.

[0008] According to a further aspect, a control unit for a motor vehicle is provided, wherein the control unit is configured to carry out the method described above.

[0009] According to a further aspect, a computer program is provided which comprises instructions which, when executed by a computer, cause the computer to carry out the method described above.

[0010] In the context of the present disclosure, the term "evaporative system" can be defined as a system configured to discharge vent gases, for example, from a tank, in particular a fuel tank, and / or from a crankcase. The evaporative system can be configured to supply the vent gases to a retention filter, in particular a fuel vapor retention filter, and / or to an intake tract of an internal combustion engine via at least one vent line. The retention filter can be, for example, an activated carbon filter. The evaporative system has a vent system.

[0011] In the context of the present disclosure, the term "venting system" can be defined as a system by which venting gases are supplied to an intake tract of an internal combustion engine, for example, venting gases from a retention filter. The venting system can comprise an inlet valve, for example, a tank venting valve. The inlet valve can be arranged downstream of the retention filter. The venting system can comprise at least one vent line, in particular at least two, in particular at least three. Each vent line can connect the inlet valve to different regions of an intake tract of an internal combustion engine. Each vent line can be a purge line via which venting gases are supplied to the intake tract of the internal combustion engine, in particular, venting gases from the retention filter.One of the vent lines can, for example, be connected to an inlet point in the intake tract, which is located downstream of an air filter in the intake tract and / or upstream of a turbocharger in the intake tract. This vent line can represent a full-load venting path. Another vent line can, for example, be connected to another inlet point in the intake tract, which is located downstream of a throttle valve and / or upstream of an inlet point of an exhaust gas recirculation path in the intake tract. This additional vent line can represent a part-load venting path.

[0012] In the context of the present disclosure, the term "intake valve" can be defined as a controllable valve configured to adjust the gas flow through the ventilation system to the intake tract of the internal combustion engine. The intake valve can be arranged downstream of the retention filter. The intake valve can be configured to adjust the gas flow from the retention filter to the intake tract of the internal combustion engine. For this purpose, the intake valve can be controllable by means of a control unit. The intake valve can be controlled by means of a pulse-width modulated (PWM) signal. The intake valve can be a tank ventilation valve or a crankcase ventilation valve.

[0013] In the context of the present disclosure, a variable representative of a pressure gradient can be any variable from which the pressure gradient can be derived, in particular at least approximately. The variable can be a pressure, for example. The pressure can be measured by means of a pressure sensor arranged in the venting system. The pressure sensor can be arranged in the venting line or in the further venting line. A pressure sensor can be arranged in each of the venting line and the further venting line. The pressure sensor can be arranged between the negative pressure-generating connection piece and a check valve. The received variable can also already be a pressure gradient.

[0014] In the context of the present disclosure, the term "vacuum-generating connector" can mean any type of connection between the venting system and the intake tract that creates a pressure gradient in the venting system, in particular the associated vent line, such that vent gases from the venting system are supplied to the intake tract. The pressure gradient can be created or at least increased, for example, by the Bernoulli effect. The vacuum-generating connector can be or comprise a Venturi nozzle. The vacuum generated by the connector can depend on a boost pressure in the intake tract, in particular a boost pressure downstream of the turbocharger.

[0015] In the context of the present disclosure, the term "Venturi nozzle" can mean a pipe section with a cross-sectional constriction. The cross-sectional constriction can be realized, for example, by two opposing cones. The associated vent line can open into the Venturi nozzle in the region of the cross-sectional constriction, in particular in a region of the smallest cross-section. The Venturi nozzle can be connected on one side to the intake tract upstream of or in front of a turbocharger and on the opposite side to the intake tract downstream of or after the turbocharger, for example upstream or downstream of a charge cooler.

[0016] The described method and the corresponding control unit can be advantageous for enabling a reliable functional test of a venting system. The opening and / or closing of the inlet valve can cause pressure changes in the venting system, which can be indicative of the venting system's functionality, for example, indicative of a stuck-closed inlet valve, a stuck-closed check valve, and / or an at least partially blocked vent line. An evaluation of the pressure gradient, rather than the pressure, can be particularly advantageous because the pressure gradient represents a suitable variable for detecting pressure changes in the venting system, for example, due to the aforementioned opening and / or closing of the inlet valve.

[0017] A diagnosis of the ventilation system can be performed by comparing a pressure curve after the intake valve has opened and / or closed with a reference pressure curve or target pressure curve. Such a diagnosis can be complicated if the vacuum generated by the connector in the ventilation line depends on the boost pressure in the intake tract, and the boost pressure in the intake tract changes. Under these circumstances, incorrect diagnostic results can occur, for example, a defective ventilation system may be falsely identified as functional.

[0018] In other words, the pressure curve, for example in a full-load ventilation line, can be directly dependent on the currently prevailing boost pressure of the combustion engine or an inlet pressure in the Venturi nozzle in an inlet line of the Venturi nozzle. Accordingly, any pressure dynamics in the boost pressure lead to a pressure change at the sensor. In certain situations, e.g., vehicle acceleration with the associated boost pressure buildup, these pressure changes can lead to the pressure change in the ventilation line caused by the boost pressure change being misinterpreted within the diagnostic evaluation algorithm when the diagnostic function is simultaneously active, in particular when testing the full-load ventilation line. A misinterpretation occurs when, for example,If the vent line is blocked, the check valve is stuck closed, or the tank vent valve is stuck closed, the boost pressure dynamics result in a pressure curve in the vent line that correlates with the reference or expected pressure curve considered during the diagnosis. The result is an incorrect "good" test of the vent system.

[0019] Under these circumstances, a functional test of a ventilation system based on a pressure gradient can be more reliable than a comparison with a reference pressure curve. For example, at least some of the aforementioned erroneous "good" tests can be avoided, i.e., a faulty ventilation system can be correctly identified as such. Functional testing based on the pressure gradient can therefore, at least in such cases, be more robust and less error-prone than a comparison with a reference pressure curve. This may be due, among other things, to the fact that the dynamics of pressure changes in the ventilation system after the intake valve opens or closes are greater than typical boost pressure dynamics.

[0020] The boost pressure dynamics present during a functional test of the ventilation system are limited, on the one hand, by system inertia, e.g., when boost pressure builds up via the compression unit, and, on the other hand, by downstream application interventions via the engine control software. Consequently, due to the direct dependency, the purge line pressure dynamics are also limited without actively changing the tank vent valve control. Since the geometric distance between the tank vent valve and the pressure sensor is generally very short, an abrupt change in the tank vent valve control generates a significant purge line pressure change compared to the maximum boost pressure dynamics possible during diagnostic execution and the resulting purge line pressure gradient.An evaluation of the resulting purge line pressure gradient after changing the control of the tank venting valve can thus allow the determination of a properly opening or closing tank venting valve with sufficient selectivity.

[0021] In other words, the pressure gradient-based diagnostic function can ensure robust result generation, even under the influence of pressure dynamics in the vacuum-generating connection or junction of the vent line. Due to the reduced dependence on boost pressure dynamics, diagnostic activation can occur over a wider range, which can lead to improved activation frequency. The two aforementioned advantages combined can lead to a more rapid diagnostic result generation during the driving cycle and a lower number of aborted diagnostic processes, which ultimately contributes to increasing the activated carbon filter purge rate, as the tank venting function needs to be interrupted less frequently.

[0022] The functional test can be performed actively or at least partially passively. With a passive diagnosis, the intake valve can be controlled at least partially by a process function, in particular a tank venting function. Thus, the control can be performed at least partially outside of a diagnostic function.

[0023] Such a passive diagnosis can, for example, comprise one or more of the following steps: (i) checking the basic physical activation conditions analogous to the active test; (ii) observing the control conditions of the intake valve brought about by the process function, in particular the tank ventilation function; (iii) if an opening intake valve is detected on the control side for a given boost pressure criterion, the diagnosis can start at the opening time that corresponds to the start of the first predetermined time, without actively requesting the intake valve control from the diagnostic function; (iv) if a closing intake valve is detected on the control side for a given boost pressure criterion, the diagnosis can start at the closing time that corresponds to the start of the second predetermined time, without actively requesting the intake valve control from the diagnostic function.

[0024] According to one embodiment, the ventilation system comprises at least one, in particular all, of the following components: an intake valve, at least one ventilation line, a pressure sensor arranged in the ventilation line, and a vacuum-generating connector that connects the ventilation line to an intake tract of an internal combustion engine. The ventilation system can comprise the intake valve and a region of the evaporative system downstream of the intake valve, wherein the intake tract of the internal combustion engine is not part of the evaporative system.

[0025] According to one embodiment, the negative pressure generated by the connecting piece depends on a boost pressure in the intake tract of the internal combustion engine.

[0026] According to one embodiment, the intake valve is controlled such that it is first opened for the first predetermined time and then closed for the second predetermined time. Such an embodiment can be advantageous because, in the case of two consecutive, different changes in the state of the intake valve, the resulting pressure gradient profile can be analyzed to determine whether a functioning venting system is present.

[0027] According to one embodiment, the intake valve is controlled such that it is first closed and then opened. In this embodiment, too, the pressure gradient can be analyzed during two consecutive, different changes in the intake valve's state.

[0028] According to one embodiment, the intake valve is controlled before opening the intake valve such that it is closed for at least a third predetermined time. If the intake valve is already closed, the control may also not require any control signals from the control unit to the intake valve. Keeping the intake valve closed before opening may be advantageous, for example, so that a pressure equilibrium is established before opening and / or so that the pressure in the ventilation system before opening depends only on the negative pressure generated by the connection piece or the boost pressure in the intake tract.

[0029] According to one embodiment, assessing the functionality of the venting system includes assessing the functionality of the venting line. Before activating the intake valve, in particular before all previously described activation steps, in particular at the beginning of the third predetermined time, it is checked whether the venting line is exclusively activated. The venting line can be activated, for example, by opening a check valve arranged in the venting line. At the same time, respective check valves in other venting lines can be closed, in particular so that all venting gases are supplied to the intake tract via the first-mentioned venting line. Such an embodiment can be advantageous in order to enable a comprehensible functional test of the venting line.

[0030] According to one embodiment, the vacuum-generating connector is a Venturi nozzle. A Venturi nozzle can be particularly suitable for generating the necessary differential pressure across the vent line, particularly a full-load vent path, at boost pressures above ambient pressure and / or during unthrottled engine operation. When using a Venturi nozzle, the pressure in the vent line can depend significantly on the boost pressure, particularly when the boost pressure changes. Under such circumstances, assessing the functionality of the vent system based on the pressure gradient can enable particularly robust results.

[0031] According to one embodiment, a vent line to be tested for functionality, in particular a full-load vent path, is activated if the Venturi nozzle used to generate a sufficient purge air pressure gradient generates a higher pressure difference to the ambient air at high engine loads than the pressure difference that exists between the branch point after the throttle valve and the ambient air. Such an embodiment can be advantageous because, depending on the respective legal regulation, the full-load purge path in the tank ventilation system must be diagnosed if the ratio of the full-load purge air quantity to the total purge quantity exceeds a specified threshold in a defined homologation cycle.

[0032] According to one embodiment, when assessing the functionality of the venting system, the functionality of at least one of the following components is assessed: the inlet valve, the vacuum-generating connector, the vent line connecting the inlet valve to the connector, and a check valve arranged in the vent line. For example, it may be possible to detect at least one of the following malfunctions: a stuck-closed inlet valve, a stuck-closed check valve, a clogged or blocked vent line, and a clogged or blocked connector. Such malfunctions can change the pressure conditions in the venting system in such a way that the pressure gradient deviates from the expected behavior in a functioning venting system.

[0033] According to one embodiment, the motor vehicle has an internal combustion engine with an intake tract, and the connecting piece opens into the intake tract. The method comprises a further step in which a change in boost pressure in the intake tract is determined, and the functionality of the ventilation system is assessed, in particular only if the amount of the determined change in boost pressure in the intake tract exceeds a predetermined threshold value. The change in boost pressure can be positive or negative. Such an embodiment can be advantageous because, in the event of a significant change in boost pressure, conventional methods for testing the functionality of ventilation systems can be prone to errors, whereas a functional test based on the analysis of a pressure gradient can be particularly robust and reliable in these cases.

[0034] According to one embodiment, the boost pressure is determined by means of a further pressure sensor which is arranged in a line, in particular a high-pressure line, which connects the negative pressure generating connector to the intake tract, in particular to a region of the intake tract downstream of a turbocharger, for example to a region between the turbocharger and a charge cooler of the intake tract or to a region downstream of the charge cooler.

[0035] According to the invention, the functionality of the venting system is assessed based on a maximum value of the pressure gradient during the first predetermined time and / or based on a minimum value of the pressure gradient during the second predetermined time. From the maximum value and / or minimum value, for example, a sufficiently pronounced change in the pressure in the venting line in response to the opening or closing of the inlet valve can be inferred. Such a pressure change can be indicative of a functioning venting system.

[0036] According to one embodiment, the maximum value and / or the minimum value are compared with respective starting values ​​at the beginning of the first predetermined time or at the beginning of the second predetermined time, and the functionality of the venting system is assessed based on this comparison.

[0037] According to one embodiment, the functionality of the venting system is assessed based on a quotient between the maximum value of the pressure gradient and a starting value and / or based on a difference between the maximum value and the starting value. The starting value can be a value of the pressure gradient at the beginning of the first predetermined time and / or a value of the pressure gradient at a predetermined time after the inlet valve opens. Such a quotient and / or such a difference can be particularly meaningful with regard to the functionality of the venting system.

[0038] According to one embodiment, a necessary condition for a functioning venting system is that the maximum value is positive. According to a further development, the starting value can be positive or negative.

[0039] According to one embodiment, the quotient and / or the difference are compared with a respective threshold value to assess functionality. Such a comparison with a threshold value has proven particularly meaningful for conducting the functional test reliably and comprehensibly.

[0040] According to one embodiment, the functionality is assessed based on a further quotient between the minimum value and a further starting value and / or based on a further difference between the minimum value and the further starting value. The further starting value can be a value of the pressure gradient at the beginning of the second predetermined time and / or a value of the pressure gradient at a predetermined point in time after the intake valve has closed. Such a further quotient and / or such a further difference can be particularly meaningful with regard to the functionality of the venting system. By taking into account the further quotient and / or the further difference, it may be possible to verify the plausibility of the functional test based on the quotient and / or the difference, and vice versa.

[0041] According to one embodiment, a necessary condition for a functioning venting system is that the minimum value is negative. According to a further development, the additional starting value can be positive or negative.

[0042] According to one embodiment, to assess functionality, the further quotient and / or the further difference are compared with a respective further threshold value. Such a comparison with a threshold value has proven particularly reliable for conducting the functional test in a reliable and traceable manner.

[0043] According to one embodiment, to assess functionality, a correlation of the pressure curve during the first predetermined time and / or the second predetermined time with an expected curve is additionally considered. The expected curve can be a reference curve of a properly functioning venting system. Such an embodiment can be advantageous because a further criterion for testing functionality is taken into account. This allows the functional test based on the pressure gradient to become more robust and / or be validated.

[0044] According to one embodiment, a height of a gradient reversal is determined based on the minimum value and the maximum value, and the functionality of the venting system is assessed based on the height of the gradient reversal.

[0045] According to one embodiment, during the functional test, in particular during the first predetermined time and / or the second predetermined time, a boost pressure and / or an inlet pressure into the Venturi nozzle must monotonically increase or monotonically decrease.

[0046] According to one embodiment, the functional test is aborted if a change in the boost pressure and / or the inlet pressure into the Venturi nozzle exceeds a predetermined threshold value. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further advantages and advantageous embodiments and further developments of the method and of the control device emerge from the following exemplary embodiments shown in conjunction with the figures.

[0048] They show: Fig. 1 shows an internal combustion engine with an embodiment of a control unit according to the present disclosure; Fig. 2 shows the profile of a pressure gradient in a vent line as a function of a boost pressure and a control profile of an intake valve during the implementation of an embodiment of a method according to the present disclosure in a properly functioning vent system; and Fig. 3 shows the course of a pressure gradient in a vent line as a function of a boost pressure and a control profile of an intake valve during the implementation of the exemplary embodiment of the method according to the present disclosure in a faulty vent system.

[0049] Identical, similar, or functionally identical elements are provided with the same reference symbols in the figures. In some figures, individual reference symbols have been omitted for clarity. The figures and the relative sizes of the elements depicted in the figures are not to scale. Rather, individual elements may be exaggerated for clarity and / or clarity. DETAILED DESCRIPTION OF EMBODIMENTS

[0050] An embodiment of a control device 150 according to the present disclosure is described in connection with Fig. 1 described.

[0051] Fig. 1 shows an internal combustion engine 160 of a motor vehicle with an evaporative system 100, an intake tract 140 having a throttle valve 144 and a turbocharger 142, and with the control unit 150. The evaporative system 100 includes, among other things, a ventilation system 119 and a retention filter 103, here an activated carbon filter. The control unit 150 is an engine control unit for the internal combustion engine 160. The control unit 150 is configured to implement a method for functional testing of a ventilation system 119 in an evaporative system 100 of a motor vehicle according to a method described below in connection with the Fig. 2 and Fig. 3 described embodiment.

[0052] The venting system 119 comprises an inlet valve 106, here a tank venting valve, and two venting lines 114, 115 that branch off from one another downstream of the inlet valve 106. In this case, the venting lines 114, 115 are purge lines assigned to a full-load venting path and a partial-load venting path, respectively. A check valve 107, 108 is arranged in each of the venting lines 114, 115 downstream of—i.e., particularly downstream of—the branching point. In addition, the venting system 119 has two inlet points 109, 117, at which gas flow from the venting system 119 is introduced into the intake tract 140. The check valves 107, 108 direct the gas flow either to the inlet point 117 after the throttle valve 144 (vent line 115 of the part-load venting path) or to the inlet point 109 before the turbocharger 142 (vent line 114 of the full-load venting path).

[0053] The venting system 119 further includes a vacuum-generating connector 109, in this case a Venturi nozzle, which generates the necessary differential pressure across the full-load venting path 107, 109, 114, 116 at boost pressures above ambient pressure and unthrottled engine operation. A pressure sensor 104 is located in the vent line 114 of the full-load venting path for performing the line diagnostics of the full-load venting path.

[0054] The control unit 150 is designed to control the inlet valve 106 by means of a pulse width modulated (PWM) signal and to regulate a gas flow from the retention filter 103 to the inlet points 109, 117.Furthermore, the control unit 150 is configured, among other things, to: (a) determine a target value for the purge flow for the current operating state; (b) determine an intake manifold pressure using a pressure sensor 117 in the intake tract 140; (c) determine a PWM value for controlling the tank venting valve 106 from the pressure gradient between ambient pressure and the pressure at the respective inlet point 109, 117 in the intake tract 140 from the specified purge flow; (d) calculate the fuel quantity to be injected for the current operating state of the engine; (e) calculate the delay time of the gas flow supplied to the combustion through the opening of the tank venting valve 106 for the two above-mentioned inlet points 109, 117 of the tank venting; and (f) calculate a fuel correction based on the hydrocarbon concentration of the purge mass flow learned by means of the lambda controller deviation.

[0055] Fig. Figure 2 shows the temporal progression of pressure 121, measured by pressure sensor 104 in vent line 114, and the associated pressure gradient 122 as a function of the control 123 of intake valve 106 during implementation of an embodiment of the method for the case of a properly functioning venting system. Also shown is the temporal progression of boost pressure 120, as measured, for example, in high-pressure line 116 to Venturi nozzle 109.

[0056] In principle, an increasing inlet pressure into the Venturi nozzle 109 leads to an increase in the vacuum generated within the nozzle 109. Conversely, a decreasing inlet pressure into the Venturi nozzle 109 leads to a decrease in the vacuum generated within the nozzle 109. As a necessary precondition for starting the diagnosis, the exclusive release or activation of the full-load vent line 114 must be checked in advance using suitable functional logic.

[0057] In the method according to the present embodiment, the exclusive activation of the full-load vent line is therefore checked in a first step S1, ie it is checked whether the check valve 107 is open and the check valve 108 is closed, whereby a minimum inlet pressure in the Venturi nozzle 109 must be present.

[0058] In a second, subsequent step S2, the inlet valve 106 is controlled in the closed state for a third predetermined time 129.

[0059] In a third step S3, following the actuation in the sense of the closed state for the third predetermined time 129, the intake valve 106 is actuated such that the intake valve 106 is opened and the open state is maintained for a first predetermined time 127. In other words, it is actuated in the sense of the open state for a first predetermined time 127.

[0060] In a fourth step S4, following the actuation in the open state for the first predetermined time 129, the intake valve 106 is actuated in the closed state for a second predetermined time 128. In other words, in this step S4, the intake valve 106 is actuated such that the intake valve 106 is closed and the closed state is maintained for a second predetermined time 128.

[0061] After the second predetermined time 128, the method is terminated in a step S5.

[0062] To assess the functionality of the venting system based on the pressure gradient 122, in the present exemplary embodiment of the method, the currently prevailing pressure gradient 122 is first stored as the starting value 130 during the third step S3. As the third step S3 continues, the maximum value (formation of a trailing pointer) of the quotient between the current pressure gradient 122 and the stored starting value 130 is continuously calculated. In the present case, the maximum value of the quotient results from the maximum of the gradient 125 during the first predetermined time 127 divided by the starting value 130.

[0063] The absolute value of the determined maximum value of the quotient is then compared with an adjustable threshold. If the determined absolute value of the maximum value exceeds the threshold, this indicates that the inlet valve 106 is opening on demand, and the full-load vent line 114 can be declared functional. To finalize a pass test of the full-load vent line 114, the sign of the pressure gradient 122 must be positive during the formation of the maximum value. If the sign of the pressure gradient 122 is negative during the formation of the maximum value, or if the determined absolute value of the maximum value does not exceed the adjustable threshold, the full-load vent line 114 is declared non-functional.

[0064] In a method according to a variant of this exemplary embodiment, during step S3, in which the intake valve 106 is opened and the open state is maintained for a first predetermined time 127, the change in the pressure gradient 122 is directly used with an additional check of the sign (as previously described). In this variant, the difference between the maximum pressure gradient 125 (trailing indicator) during the first predetermined time 127 and the starting value 130 indicated above is calculated, and the absolute value of the difference is subsequently compared with an adjustable threshold. If the determined absolute value of the difference exceeds the threshold, this is an indication of an intake valve 106 opening on demand, and the full-load vent line 114 can be declared functional.

[0065] In a further variant of the method according to the present exemplary embodiment, the functionality of the full-load vent line 114 is determined, in addition to or alternatively to the previously described variants, during step S4 after the intake valve 106 closes. A further starting value 131 is formed at the start of the second predetermined time 128. The determined maximum value during the second predetermined time 128 of the absolute value of a quotient of the pressure gradient 122 and the further starting value 131 is also compared with an adjustable threshold. If the determined maximum value exceeds the threshold, this is an indication of an intake valve 106 closing on request, and the full-load vent line 114 can be declared functional. To finalize a pass test of the full-load vent line 114, the sign of the pressure gradient 122 must be negative during the formation of the maximum value.If the sign of the pressure gradient 122 is positive during the formation of the maximum value, or if the determined maximum value does not exceed the adjustable threshold, the full-load vent line is declared non-functional.

[0066] In a third variant of the present exemplary embodiment of the method, instead of the determined maximum value of the previously described variant, the change in the pressure gradient 122 during the second predetermined time 128 is used directly, with an additional check of the sign (as described above). The difference between the minimum 126 of the pressure gradient 122 (trailing indicator) during the second predetermined time 128 and the further starting value 131 is calculated, and the absolute value of the difference is then compared with an adjustable threshold. If the determined absolute value of the difference exceeds the threshold, this is an indication of an intake valve 106 closing on demand, and the full-load vent line 114 can be declared functional.

[0067] Fig. For comparison, Fig. 3 shows the time profiles of the pressure 121, the pressure gradient 122, the boost pressure 120 and the control 123 of the inlet valve 106 when carrying out an embodiment of the method described above for a faulty ventilation system, in this case a stuck closed inlet valve 106. The gradient of the pressure gradient 122 during the first predetermined time 127 is smaller than in the properly functioning system, which in Fig.2. The maximum value 125 of the pressure gradient 122 is also found at the end of the first predetermined time 127. During the second predetermined time 128, the minimum value 126 of the pressure gradient 122 and the further starting value 131 coincide, so that the corresponding quotient is 1 and the corresponding difference is 0. Corresponding threshold values ​​are not exceeded, at least in this step S4. Furthermore, the pressure gradient 122 is not negative at the minimum value 126. Consequently, the faulty venting system is correctly identified as such according to the previously described evaluation method. REFERENCE SYMBOL 100 evaporation system 101 Air filter purge air line 102 Leak diagnosis pump 103 retention filters 104 Pressure sensor 105 Tank level sensor 106 Intake valve 107 Check valve 108 additional check valve 109 Vacuum-generating connector 110 Fresh air line 111 Fresh air line to the retention filter 112 Tank ventilation line to the retention filter 113 Tank ventilation line to the inlet valve 114 Vent line (full load vent path) 115 additional vent line (low pressure path) 116 High pressure line 117 Pressure sensor collector 118 tanks 119 Ventilation system 120 boost pressure 121 Pressure in vent line 122 Pressure gradient in vent line 123 Control of the intake valve 124 Time 125 Maximum value of the pressure gradient 126 Minimum value of the pressure gradient 127 first predetermined time 128 second predetermined time 129 third predetermined time 130 starting value 131 additional starting value 140 intake tract 141 Air filter 142 turbochargers 143 Charge cooler 144 Throttle valve 145 Inlet for exhaust gas recirculation 150 control unit 160 combustion engine

Claims

[1] Method for functional testing of a ventilation system (119) in an evaporative system (100) of a motor vehicle, wherein the evaporative system (100) has an inlet valve (106), a negative pressure generating connection piece (109, 117) and a vent line (114, 115) between the inlet valve (106) and the connection piece (109, 117), comprising the following steps: - controlling the inlet valve (106) such that the inlet valve (106) is opened and the open state is maintained for a first predetermined time (127), and / or controlling the inlet valve (106) such that the inlet valve (106) is closed and the closed state is maintained for a second predetermined time (128); - receiving a quantity representative of a pressure gradient (122) prevailing in the vent line (114, 115) between the inlet valve (106) and the connector (109, 117); and - Assessing the functionality of the venting system (119) based on the pressure gradient (122), wherein the functionality of the venting system is assessed based on a maximum value (125) of the pressure gradient (122) during the first predetermined time (127) and / or based on a minimum value (126) of the pressure gradient (122) during the second predetermined time (128). [2] The method according to the preceding claim, wherein the inlet valve (106) is controlled such that it is first opened for the first predetermined time (127) and then closed for the second predetermined time (128). [3] The method according to any one of the preceding claims, wherein before opening the inlet valve (106), the inlet valve (106) is controlled such that it is closed for a third predetermined time (129). [4] The method according to one of the preceding claims, wherein assessing the functionality of the venting system (119) comprises assessing the functionality of the venting line (114, 115) and checking whether the venting line (114, 115) is exclusively activated before controlling the inlet valve (106). [5] The method according to any one of the preceding claims, wherein the negative pressure generating fitting (109) is a venturi nozzle. [6] The method according to one of the preceding claims, wherein, in assessing the functionality of the venting system (119), a functionality of at least one of the following components is assessed: the inlet valve (106), the negative pressure generating connector (109, 117), the vent line (114, 115) connecting the inlet valve (106) to the connector (109, 117), and a check valve (107, 108) arranged in the vent line (114, 115). [7] The method according to one of the preceding claims, wherein the motor vehicle has an internal combustion engine with an intake tract (140) and the connecting piece (109, 117) opens into the intake tract (140), the method comprising a further step in which a charge pressure change in the intake tract (140) is determined, and the functionality of the ventilation system is assessed if the amount of the determined charge pressure change in the intake tract (140) exceeds a predetermined threshold value. [8] The method according to any one of the preceding claims, wherein the functionality of the venting system is assessed based on a quotient between the maximum value (125) of the pressure gradient (122) and a starting value (130) and / or based on a difference between the maximum value (125) and the starting value (130). [9] The method according to the preceding claim, wherein the quotient and / or the difference are compared with a respective threshold value to assess the functionality. [10] The method according to one of claims 8 to 9, wherein the functionality is assessed based on a further quotient between the minimum value (126) of the pressure gradient (122) and a further starting value (131) and / or based on a further difference between the minimum value (126) and the further starting value (131). [11] The method according to the preceding claim, wherein, in order to assess the functionality, the further quotient and / or the further difference are compared with a respective further threshold value. [12] The method according to one of claims 8 to 11, wherein, in order to assess the functionality, a correlation of a pressure curve (121) during the first predetermined time (127) and / or the second predetermined time (128) with an expected curve is additionally taken into account. [13] A control device (150) for a motor vehicle, which is configured to carry out the method according to one of the preceding claims. [14] A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 12.

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