Method for detecting a sticking tank vent valve

Abstract

A method for detecting a sticking tank vent valve in a motor vehicle, a temperature sensor being situated in a tank vent line between the tank vent valve and an inlet point into an intake manifold or into a turbocharger and sticking of the tank vent valve being detected when the absolute value of a correlation of a calculated tank ventilation mass flow and of a signal value of the temperature sensor violates a predefinable threshold value.

Claims

1. A method for detecting a sticking tank vent valve in a motor vehicle, a temperature sensor being situated in a tank vent line between the tank vent valve and an inlet point into an intake manifold or into a turbocharger, the method comprising: detecting a sticking of the tank vent valve when the absolute value of a correlation of a computed tank ventilation mass flow and of a signal value of the temperature sensor violates a predefinable threshold value.

2. The method as recited in claim 1, wherein when the tank vent valve is being activated, a closed sticking of the tank vent valve is detected if the absolute value of the correlation of a computed tank ventilation mass flow and of the signal value of the temperature sensor falls below a predefinable threshold value.

3. The method as recited in claim 1, wherein when the tank vent valve is not being activated, an open sticking of the tank vent valve is detected if the absolute value of the correlation of a computed tank ventilation mass flow and of the signal value of the temperature sensor exceeds a predefinable threshold value.

4. The method as recited in claim 1, wherein diagnosing of the tank vent valve is discontinued when at least one operating condition of the motor vehicles changes by more than an applicable threshold value.

5. The method as recited in claim 4, wherein the changing operating condition is at least one of a motor vehicle speed and an internal combustion engine speed.

6. The method as recited in claim 1, wherein a signal of a reference temperature sensor, which is situated outside of the tank vent line, is taken into account when detecting a sticking tank vent valve.

7. A non-transitory machine-readable memory medium on which is stored a computer program for detecting a sticking tank vent valve in a motor vehicle, a temperature sensor being situated in a tank vent line between the tank vent valve and an inlet point into an intake manifold or into a turbocharger, the computer program, when executed by a control unit, causing the control unit to perform: detecting a sticking of the tank vent valve when the absolute value of a correlation of a computed tank ventilation mass flow and of a signal value of the temperature sensor violates a predefinable threshold value.

8. An electronic control unit for detecting a sticking tank vent valve in a motor vehicle, a temperature sensor being situated in a tank vent line between the tank vent valve and an inlet point into an intake manifold or into a turbocharger, the control unit configured to: detecting a sticking of the tank vent valve when the absolute value of a correlation of a computed tank ventilation mass flow and of a signal value of the temperature sensor violates a predefinable threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic illustration of a tank ventilation system, an internal combustion engine, as well as a control unit of a motor vehicle according to the related art.

(2) FIG. 2 shows a schematic illustration of the intensity of the tank ventilation mass flow and the intensity of the temperature sensor signal over time.

(3) FIG. 3 shows a schematic illustration of an internal combustion engine, a control unit, as well as another tank ventilation system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(4) FIG. 1 schematically shows a tank ventilation system of a motor vehicle (not shown), an internal combustion engine 5, and a control unit 9 of the motor vehicle according to the related art. The tank ventilation system includes a fuel tank 1, an adsorption filter 2, as well as a tank vent valve 3. In this device for tank venting shown in FIG. 1 as well as in the device for tank-venting shown in FIG. 3, adsorption filter 2 is designed as an activated carbon filter. Between tank vent valve 3 and an inlet point 15 into an intake manifold 8 and into a turbocharger 7 is a tank vent line 14, within which a temperature sensor 10 is situated in such a way that it is heated by the waste heat of internal combustion engine 5. The tank ventilation system furthermore includes two one-way valves 12 and 13 as well as a Venturi nozzle 4. Internal combustion engine 5 is a charged engine including turbocharger 7 and an intercooler 6. Intake manifold 8 connects internal combustion engine 5 and intercooler 6.

(5) The method for detecting a sticking of tank vent valve 3 proceeds as follows. Initially, temperature sensor 10 is heated by internal combustion engine 5 to a temperature T.sub.0 above ambient temperature T.sub.R by an applicatively predefinable T. Thereafter, a tank venting is carried out, meaning that tank vent valve 3 is opened and a tank ventilation mass flow m.sub.reg streams through tank vent line 14. Since tank ventilation mass flow m.sub.reg exhibits only a temperature that corresponds to ambient temperature T.sub.R, temperature sensor 10 experiences a temperature decrease T.sub.2 due to tank ventilation mass flow m.sub.reg flowing by so that the tank vent valve then exhibits a temperature of T.sub.1=T.sub.0T.sub.2. This process is illustrated in FIG. 2.

(6) FIG. 2 schematically shows the chronological sequence of a tank ventilation mass flow m.sub.reg in kg/h as well as the chronological sequence of a signal s.sub.temp of temperature sensor 10 in C. At points in time t.sub.1, t.sub.2, and t.sub.4, a clear correlation between tank ventilation mass flow m.sub.reg and the absolute value of temperature signal s.sub.temp is apparent. When tank ventilation mass flow m.sub.reg rises, signal s.sub.temp of temperature sensor 10 drops. As soon as tank ventilation mass flow m.sub.reg has fallen to zero, i.e., at point in time t.sub.3, signal s.sub.temp of temperature sensor 10 begins to rise again because internal combustion engine 5 heats up temperature sensor 10 again and no cooling through a tank ventilation mass flow takes place. Due to temperature decrease T.sub.2, presence of tank ventilation mass flow m.sub.reg is deduced and it is assumed that tank vent valve 3 is operational.

(7) In this first specific embodiment of the method, when tank vent valve 3 is being activated, a closed sticking of tank vent valve 3 is detected. In this case, due to closed sticking tank vent valve 3, the real tank ventilation mass flow via tank vent valve 3 is zero kg/h and no cooling of temperature sensor 10 takes place. However, a tank ventilation mass flow m.sub.reg,b is calculated from the environmental conditions, i.e., with the aid of the setpoint activation. This calculated tank ventilation mass flow m.sub.reg,b is correlated in the following with the signal of temperature sensor 10. If the absolute value of this correlation falls below a predefinable threshold value s.sub.1, in the present case |s.sub.1|=0.75, a closed sticking of tank vent valve 3 is detected.

(8) In a second specific embodiment of the method, when tank vent valve 3 is not being activated, an open sticking of tank vent valve 3 is detected. In this second case, the calculated tank-ventilation mass flow m.sub.reg,b is zero kg/h via the tank vent valve 3 since tank vent valve 3 is expected to be closed. The real tank ventilation mass flow via tank vent valve 3 is greater than zero kg/h, however, due to the defect of tank vent valve 3. In this second case as well, the calculated tank ventilation mass flow m.sub.reg,b is correlated with the signal of temperature sensor 10. If the absolute value of the correlation exceeds a second predefinable threshold value s.sub.2, in the present case |s.sub.2|=0.3, an open sticking of tank vent valve 3 is detected.

(9) The method for detecting a sticking tank vent valve 3 is discontinued when the speed of the motor vehicle and/or the speed of internal combustion engine 5 changes by more than an applicable threshold value. In both cases, a clear change in the particular operating condition results in a drastic change in the temperature of tank vent line 14, which directly affects temperature sensor 10. Since this may result in a misinterpretation of the signal of temperature sensor 10, the method is discontinued.

(10) FIG. 3 shows a schematic illustration of an internal combustion engine, of a control unit, as well as of another tank ventilation system. The difference to the tank ventilation system shown in FIG. 1 is that in the tank ventilation system in FIG. 3, a reference temperature sensor 11 is situated outside of tank vent line 14. The signal of this reference temperature sensor 11 may be taken into account in both specific embodiments of the method described above to detect a sticking tank vent valve 3 in order to deduce the presence of a tank ventilation mass flow m.sub.reg. Since reference temperature sensor 11 is positioned outside of tank vent line 14, the signal of reference temperature sensor 11 is not affected by the tank ventilation mass flow m.sub.reg flowing by. In the tank ventilation system shown in FIG. 3, however, reference temperature sensor 11 is situated outside of the tank vent line, facing temperature sensor 10. This means that initially, temperature sensor 10 as well as reference temperature sensor 11 is heated by internal combustion engine 5 to a temperature T.sub.0 above ambient temperature T.sub.R by a predefinable T. While temperature sensor 10 experiences a decrease in temperature T.sub.2 due to tank ventilation mass flow m.sub.reg flowing by, reference temperature sensor 11 remains at temperature T.sub.0. The difference in temperature is obtained by comparing the signals of temperature sensor 10 and of reference temperature sensor 11, on account of which the presence of tank ventilation mass flow m.sub.reg may be deduced.

(11) If reference temperature sensor 11 is used, it no longer necessary to discontinue the method for detecting the sticking of tank vent valve 3 when the motor vehicle speed or the speed of internal combustion engine 5 changes quickly since the effect of a change in the temperature of tank vent line 14 is nullified by the use of reference temperature sensor 11.