Method And Device For Ascertaining The Flow Through A Timer Valve

Abstract

The disclosure relates to a method for ascertaining the flow through a timer valve. The method includes detecting the pressure upstream of the timer valve during an evacuation of a container arranged upstream of the timer valve, ascertaining the flow through the timer valve based on the detected pressure upstream of the timer valve and based on the temperature and the volume of the gas in the container. The method also includes comparing the flow ascertained during the evacuation and a modeled flow and/or comparing a variable dependent on the ascertained flow and a variable dependent on the modeled flow. Additionally, the method includes adapting the model in the event of a discrepancy between the flow ascertained during the evacuation and the modeled flow and/or in the event of a discrepancy between the variable dependent on the ascertained flow and the variable dependent on the modeled flow.

Claims

1. A method for ascertaining a flow through a timer valve, the method comprising: detecting a pressure upstream of the timer valve during an evacuation of a container arranged upstream of the timer valve; ascertaining the flow through the timer valve based on the detected pressure upstream of the timer valve and based on a temperature and a volume of a gas in the container; comparing the flow ascertained during the evacuation and a modeled flow and/or comparing a variable dependent on the ascertained flow and a variable dependent on the modeled flow; and adapting the model when a discrepancy between the flow ascertained during the evacuation and the modeled flow and/or in when a discrepancy between the variable dependent on the ascertained flow and the variable dependent on the modeled flow.

2. The method of claim 1, wherein the ascertainment of the flow through the timer valve during the evacuation is carried out based on the following relationship: ${\stackrel{.}{m}}_{\mathrm{out}\mathrm{of}\mathrm{tank}}=\frac{V_{\mathrm{gas}\mathrm{in}\mathrm{tank}}}{R_{\mathrm{gas}\mathrm{in}\mathrm{tank}}.Math.T_{\mathrm{gas}\mathrm{in}\mathrm{tank}}}.Math.{\stackrel{.}{p}}_{\mathrm{tank}}$ where {dot over (m)}.sub.out of tank is the flow through the timer valve during the evacuation, V.sub.gas in tank is the volume of the gas in the container, R.sub.gas in tank is a specific gas constant of the gas in the container, T.sub.gas in tank is the temperature of the gas in the container, {dot over (p)}.sub.tank is a pressure gradient in the container.

3. The method of claim 1, wherein an amount of flow that has flowed through the timer valve in a predetermined period of time is determined from the flow ascertained during the evacuation according to the following relationship:
m.sub.out of tank=∫.sub.t.sub.0.sup.t.sup.end{dot over (m)}.sub.out of tankdt where {dot over (m)}.sub.out of tank is the flow through the timer valve during the evacuation and m.sub.out of tank is the amount of flow that has flowed through the timer valve in the time period from t.sub.0 to t.sub.end.

4. The method of claim 1, wherein one or more of the following parameters are included in the model on which the modeled flow is based: a detected pressure upstream of the timer valve, a detected pressure downstream of the timer valve, a cross-sectional area of the timer valve through which the flow passes, an ascertained opening time of the timer valve, an ascertained closing time of the timer valve.

5. The method of claim 4, wherein the modeling of the flow through the timer valve is performed by ascertaining the flow through the timer valve while taking into account a detected pressure upstream of the timer valve, a detected pressure downstream of the timer valve, an ascertained opening time of the timer valve and an ascertained closing time of the timer valve.

6. The method of claim 5, wherein the following relationship is used for the modeling of the flow through the timer valve: ${\stackrel{.}{m}}_{\mathrm{TW}}=A.Math.\Psi \left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}},\kappa \right).Math.\frac{P_{\mathrm{up},\mathrm{TW}}}{\sqrt{R_s.Math.T_{\mathrm{up},\mathrm{TW}}}}$ where {dot over (m)}.sub.TVV is the flow through the timer valve, A.sub.r is a reduced cross-sectional area of the timer valve through which the flow passes, Ψ is a flow parameter, P.sub.down,TVV is the detected pressure downstream of the timer valve, P.sub.up,TVV is the detected pressure upstream of the timer valve, k is an isentropic exponent of a mass flow through the timer valve, and R.sub.s is a specific gas constant of the mass flow through the timer valve.

7. The method of claim 6, wherein the flow parameter is ascertained based on the following relationship: $\Psi =\{\begin{array}{cc}\sqrt{\frac{2\kappa }{\kappa -1}}.Math.\sqrt{{\left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\right)}^{\frac{2}{\kappa }}-{\left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\right)}^{\frac{\kappa +1}{\kappa }}},& \frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}>p_{\mathrm{cr}}\\ \sqrt{\frac{2\kappa }{\kappa -1}}.Math.{\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}},& \frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\le p_{\mathrm{cr}}\end{array}$ where p.sub.cr is a critical pressure ratio.

8. The method of claim 1, further comprising modeling the flow through the timer valve and/or modeling a variable that is dependent on the flow.

9. The method of claim 1, further comprising: evacuating the container by a flushing pump arranged between the container and the timer valve or by a negative pressure in an intake tract arranged downstream of the timer valve.

10. The method of claim 9, wherein the pressure upstream of the timer valve is ascertained during the evacuation by a pressure sensor arranged in the container or in a line running between the container and the timer valve.

11. The method of claim 1, wherein the timer valve is a tank vent valve.

12. A device for ascertaining a flow through a timer valve, the device comprising: a control unit carrying out a method comprising: detecting a pressure upstream of the timer valve during an evacuation of a container arranged upstream of the timer valve; ascertaining the flow through the timer valve based on the detected pressure upstream of the timer valve and based on a temperature and a volume of a gas in the container; comparing the flow ascertained during the evacuation and a modeled flow and/or comparing a variable dependent on the ascertained flow and a variable dependent on the modeled flow; and adapting the model when a discrepancy between the flow ascertained during the evacuation and the modeled flow and/or when of a discrepancy between the variable dependent on the ascertained flow and the variable dependent on the modeled flow.

13. The device of claim 12, wherein the ascertainment of the flow through the timer valve during the evacuation is carried out based on the following relationship: ${\stackrel{.}{m}}_{\mathrm{out}\mathrm{of}\mathrm{tank}}=\frac{V_{\mathrm{gas}\mathrm{in}\mathrm{tank}}}{R_{\mathrm{gas}\mathrm{in}\mathrm{tank}}.Math.T_{\mathrm{gas}\mathrm{in}\mathrm{tank}}}.Math.{\stackrel{.}{p}}_{\mathrm{tank}}$ where {dot over (m)}.sub.out of tank is the flow through the timer valve during the evacuation, V.sub.gas in tank is the volume of the gas in the container, R.sub.gas in tank is a specific gas constant of the gas in the container, T.sub.gas in tank is the temperature of the gas in the container, {dot over (p)}.sub.tank is a pressure gradient in the container.

14. The device of claim 12, wherein an amount of flow that has flowed through the timer valve in a predetermined period of time is determined from the flow ascertained during the evacuation according to the following relationship:
m.sub.out of tank=∫.sub.t.sub.0.sup.t.sup.end{dot over (m)}.sub.out of tankdt where {dot over (m)}.sub.out of tank is the flow through the timer valve during the evacuation and m.sub.out of tank is the amount of flow that has flowed through the timer valve in the time period from t.sub.0 to t.sub.end.

15. The device of claim 12, wherein one or more of the following parameters are included in the model on which the modeled flow is based: a detected pressure upstream of the timer valve, a detected pressure downstream of the timer valve, a cross-sectional area of the timer valve through which the flow passes, an ascertained opening time of the timer valve, an ascertained closing time of the timer valve.

16. The device of claim 15, wherein the modeling of the flow through the timer valve is performed by ascertaining the flow through the timer valve while taking into account a detected pressure upstream of the timer valve, a detected pressure downstream of the timer valve, an ascertained opening time of the timer valve and an ascertained closing time of the timer valve.

17. The device of claim 16, wherein the following relationship is used for the modeling of the flow through the timer valve: ${\stackrel{.}{m}}_{\mathrm{TW}}=A.Math.\Psi \left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}},\kappa \right).Math.\frac{P_{\mathrm{up},\mathrm{TW}}}{\sqrt{R_s.Math.T_{\mathrm{up},\mathrm{TW}}}}$ where {dot over (m)}.sub.TVV is the flow through the timer valve, A.sub.r is a reduced cross-sectional area of the timer valve through which the flow passes, Ψ is a flow parameter, P.sub.down,TVV is the detected pressure downstream of the timer valve, P.sub.up,TVV is the detected pressure upstream of the timer valve, k is an isentropic exponent of a mass flow through the timer valve, and R.sub.s is a specific gas constant of the mass flow through the timer valve.

18. The device of claim 17, wherein the flow parameter is ascertained based on the following relationship: $\Psi =\{\begin{array}{cc}\sqrt{\frac{2\kappa }{\kappa -1}}.Math.\sqrt{{\left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\right)}^{\frac{2}{\kappa }}-{\left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\right)}^{\frac{\kappa +1}{\kappa }}},& \frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}>p_{\mathrm{cr}}\\ \sqrt{\frac{2\kappa }{\kappa -1}}.Math.{\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}},& \frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\le p_{\mathrm{cr}}\end{array}$ where p.sub.cr is a critical pressure ratio.

19. The device of claim 12, wherein the method further comprises: evacuating the container by a flushing pump arranged between the container and the timer valve or by a negative pressure in an intake tract arranged downstream of the timer valve.

20. The device of claim 19, wherein the pressure upstream of the timer valve is ascertained during the evacuation by a pressure sensor arranged in the container or in a line running between the container and the timer valve.

Description

DESCRIPTION OF DRAWINGS

[0026] FIG. 1 shows a device for carrying out a method according to the disclosure.

[0027] FIG. 2 shows diagrams of the variation in pressure and mass flow through a timer valve.

[0028] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0029] FIG. 1 shows a device according to the disclosure in which the flow through a tank vent valve of a motor vehicle is ascertained and adapted. The device shown in FIG. 1 forms a tank venting system with a fuel tank 6 as a container. An activated carbon canister 1, to which fresh air is supplied via an air filter 9 through a shut-off valve 7, is connected to the fuel tank 6. Furthermore, the activated carbon canister 1 is connected to a tank vent valve 5 via an optionally provided flushing pump 2. A pressure sensor 3 is arranged in the line between the flushing pump 2 and the tank vent valve 5. If the flushing pump 2 is missing, the pressure sensor 3 is arranged between the activated carbon canister 1 and the tank vent valve 5. A further pressure sensor 8 is arranged in the fuel tank 6 upstream of the tank vent valve 5. In addition, a further pressure sensor 4 is located upstream of the tank vent valve 5 before the flushing pump 2. An intake tract 10 with a compressor 11 and an air filter 9 is located downstream of the tank vent valve 5.

[0030] A mass flow flowing from the fuel tank 6 to the tank vent valve 5 is directed downstream of the tank vent valve 5 into the intake tract 10 and mixed there with fresh air to be compressed, which is fed to the intake tract 10 through the air filter 9. The compressor 11 may be part of an exhaust gas turbocharger.

[0031] To control the combustion process, an engine control 12 is provided as a control unit, which provides output signals 21 based on input signals 20 fed to it and stored working software. The input signals 20 fed to the engine control 12 may be sensor signals and/or data signals provided by a higher-level control. The sensor signals include, for example, pressure sensor signals, temperature sensor signals and gas-pedal position signals. The output signals 21 include control signals for the injection valves and the tank vent valve 5.

[0032] The flow through the tank vent valve 5 is first calculated using a physical model, according to the following relationship:

[00005]${\stackrel{.}{m}}_{\mathrm{TW}}=A.Math.\Psi \left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}},\kappa \right).Math.\frac{P_{\mathrm{up},\mathrm{TW}}}{\sqrt{R_s.Math.T_{\mathrm{up},\mathrm{TW}}}}$

where {dot over (m)}.sub.TVV is the flow through the tank vent valve, A.sub.r is a reduced cross-sectional area of the tank vent valve through which the flow passes, Ψ is a flow parameter, P.sub.down,TVV is the detected pressure downstream of the tank vent valve, P.sub.up,TVV is the detected pressure upstream of the tank vent valve, k is an isentropic exponent of the mass flow through the tank vent valve, and R.sub.s is a specific gas constant of the mass flow through the tank vent valve.

[0033] For the flow parameter, the following may apply:

[00006]$\Psi =\{\begin{array}{cc}\sqrt{\frac{2\kappa }{\kappa -1}}.Math.\sqrt{{\left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\right)}^{\frac{2}{\kappa }}-{\left(\frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\right)}^{\frac{\kappa +1}{\kappa }}},& \frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}>p_{\mathrm{cr}}\\ \sqrt{\frac{2\kappa }{\kappa -1}}.Math.{\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}},& \frac{P_{\mathrm{down},\mathrm{TW}}}{P_{\mathrm{up},\mathrm{TW}}}\le p_{\mathrm{cr}}\end{array}$

where p.sub.cr is a critical pressure ratio.

[0034] Therefore, the pressure measured at the sensor 3 as well as geometrical variables, such as the cross-sectional area of the tank vent valve 5 through which the flow passes, are important input parameters. Such a model is always subject to certain assumptions and does not necessarily reflect the real flow through the tank vent valve exactly. For example, the area through which the flows passes may change over time due to component aging.

[0035] To check the plausibility, and if necessary to adapt the model, the change in state, i.e. the change in pressure and/or temperature, of the gas in the fuel tank 6 during an evacuation of the fuel tank 6 is therefore considered in a first step. The tank 6 is consequently evacuated, for example by way of the electric flushing pump 2 or, on account of a pressure gradient generated in some other way, by way of the tank vent valve 5, such as as a result of a negative pressure in the intake tract 10. Here, the supply of fresh air to the fuel tank 6 is prevented by way of the shut-off valve 7.

[0036] During the evacuation of the fuel tank 6, a pressure upstream of the tank vent valve 5 is detected by evaluating the data of the pressure sensor 8 in the tank 6. A pressure gradient is thus detected over the period of time of the evacuation process. The flow through the tank vent valve 5 from the fuel tank 6 to the intake tract 10 is then ascertained from the detected pressure/pressure gradient. The following relationship may be used for this:

[00007]${\stackrel{.}{m}}_{\mathrm{out}\mathrm{of}\mathrm{tank}}=\frac{V_{\mathrm{gas}\mathrm{in}\mathrm{tank}}}{R_{\mathrm{gas}\mathrm{in}\mathrm{tank}}.Math.T_{\mathrm{gas}\mathrm{in}\mathrm{tank}}}.Math.{\stackrel{.}{p}}_{\mathrm{tank}}$

where {dot over (m)}.sub.out of tank is the flow through the tank vent valve, V.sub.gas in tank is the volume of the gas in the tank, R.sub.gas in tank is the specific gas constant of the gas in the tank, T.sub.gas in tank is the temperature of the gas in the tank, {dot over (p)}.sub.tank is the pressure gradient in the tank.

[0037] As can be seen, the pressure gradient as well as the volume and the temperature of the gas in the fuel tank 6 are included in the flow, that is to say the mass flow from the fuel tank 6. By means of integration, an amount of flow, i.e. a mass that has escaped from the fuel tank 6 over the period of time of the evacuation process, can be determined from the flow, according to the following relationship:

m.sub.out of tank=∫.sub.t.sub.0.sup.t.sup.end{dot over (m)}.sub.out of tankdt

where {dot over (m)}.sub.out of tank is the flow through the tank vent valve and m.sub.out of tank is the amount of flow that has flowed through the tank vent valve in the time period from t.sub.0 to t.sub.end.

[0038] In parallel with this, the flow through the tank vent valve 5 may take place in accordance with the model explained. Also, a modeled amount of flow can be correspondingly determined from the modeled flow by integration.

[0039] FIG. 2 is discussed for the purpose of illustration. FIG. 2 shows three diagrams one above the other, the upper diagram showing the two states of the shut-off valve 7, namely open and closed, over a time axis, the middle diagram showing the relative pressure at the sensor 4 over a corresponding time scale and the lower diagram showing the mass flow through the tank vent valve 5 over a corresponding time scale.

[0040] As can be seen, the shut-off valve 7 is closed in the time periods from approximately 30 seconds to 90 seconds and from 130 seconds, which represents an evacuation of the fuel tank 6. During these time periods, the measured relative pressure at the sensor 4 drops accordingly. In the lowest diagram of FIG. 2, both the modeled flow {dot over (m)}.sub.TVV and the flow {dot over (m)}.sub.out of tank through the tank vent valve 5 detected at the pressure sensor 8 during the evacuation are represented. These variables have been determined according to the relationships explained above, but according to the disclosure the flow {dot over (m)}.sub.out of tank is only determined during the closed phases of the shut-off valve 7—that is to say only during the evacuation.

[0041] A comparison of the flow ascertained during the evacuation and the modeled flow or a comparison of the corresponding amounts of flow represents the step which then follows. The result of this comparison, for example having the formation of a relative discrepancy between the modeled flow {dot over (m)}.sub.TVV and the ascertained flow {dot over (m)}.sub.out of tank during the evacuation, may be recorded in an adaptation factor C.sub.AD. The adaptation factor C.sub.AD can henceforth be used in the calculation of the flow through the tank vent valve 5 according to the following relationship:

{dot over (m)}.sub.TVV,ad=C.sub.ad.Math.{dot over (m)}.sub.TVV

[0042] The model on which the modeled flow is based can therefore be adapted in this sense.

[0043] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.