EP1317611B1 - Method for generating the time-delay of an electromagnetic tank bleeder valve - Google Patents

Abstract

The invention relates to a method for the cyclically timed control of a flow control valve, whose opening diameter follows its control signal with a time-delay tv. According to said method, a value for the time-delay is taken into consideration during the generation of the control signal, whereby the intake manifold pressure is taken into account for the time-delay during the generation of the value.

Description

State of the art

The invention relates to a method for forming the delay time of electromagnetic tank vent valves. Internal combustion engines powered by motor vehicles are often equipped with so-called tank ventilation systems that help prevent emission of fuel vapor from the storage tank into the environment. The fuel evaporating in the tank is stored in an activated carbon filter and supplied to the intake manifold of the internal combustion engine and thus the combustion during operation of the motor vehicle via a pulsed controllable electromagnetic tank vent valve.

Such valves are designed to have a delay time (see, e.g., U.S. Patent No. 5,476,081).

Tank ventilation valves (TEV) are generally designed as cyclically actuated solenoid valves and arranged between the activated carbon filter (AKF) and the intake manifold. With electrical control of such valves, the magnetization of a core takes place, which causes the valve armature is attracted by the core against a spring force and opens the valve. When closing, this is done inverse process. The movement of the armature follows the electrical control with a time delay (= delay time), which depends on the structure of the magnetic field and thus also on the applied battery voltage, the inertia of the armature and the forces acting on these.

The actual open time of the valve is shortened by this delay time. As a result, the amount of gas flowing through the tank ventilation valve decreases, which has a strong effect, especially with short activation times.

In tank venting systems, the amount of gas flowing through the tank vent valve may be varied within a controlled or regulated manner depending on its fuel concentration and also on the current load speed operating point of the engine within wide limits. Even with a comparatively small total air flow drawn by the internal combustion engine, for example when idling, a sufficient accuracy of the meterability of the gas flow flowing through the tank ventilation valve must be ensured. This requires in any case the consideration of the delay time.

It is known to take into account the influence of the battery voltage on the delay time in the control of solenoid valves.

Against this background, the object of the invention in a mathematical formation of the delay time, the actual delay time in the operation of the tank vent valve even closer and corresponds to it as closely as possible.

This object is achieved with the feature combination of the independent claim.

Specifically, in a method for periodically timed control of a flow control valve whose opening cross section follows its drive signal by a delay time tv followed and in which a value for the delay time in the formation of the drive signal is taken into account, the intake manifold pressure in the formation of the value for the delay time ,

An embodiment of the invention is characterized in that in tank vent valves whose real delay time increases at higher Saugrohrunterdruck, the calculated delay time is also increased.

A further embodiment provides that, in the case of tank-venting valves whose actual delay time decreases at higher intake manifold vacuum, the calculated delay time is likewise reduced.

According to a further embodiment, the influence of the intake manifold pressure by means of a characteristic curve to be modeled separately, by means of a multi-dimensional characteristic map or on the basis of a mathematical modeling is taken into account.

• die Werte des Saugrohrdrucks und des Umgebungsdrucks oder die Werte des Saugrohrdrucks und des Drucks auf der dem Saugrohr abgewandten Seite des Tankentlüftungsventils
• oder die daraus zu bestimmenden Werte der Druckdifferenz
• oder die daraus zu bestimmenden Werte des Druckverhältnisses

als Eingangsgröße der Kennlinie, des Kennfeldes oder der rechnerischen Modellierung dienen.Another embodiment is characterized in that

• the values of the intake manifold pressure and the ambient pressure or the values of the intake manifold pressure and the pressure on the side of the tank ventilation valve facing away from the intake manifold
• or the values of the pressure difference to be determined from this
• or the values of the pressure ratio to be determined from this

serve as an input variable of the characteristic curve, the characteristic diagram or the computational modeling.

The invention is also directed to an electronic control device for carrying out at least one of the above-mentioned methods and embodiments.

Essential to the invention is the consideration of the dependence of the delay time of the tank venting valve of the intake manifold pressure in the arithmetic formation of the delay time. The invention is thus based on the recognition that one of the forces which counteract the opening of the valve comes from Saugrohrunterdruck, the suction pipe side is at the anchor; this force increases with the Saugrohrunterdruck and leads to a corresponding change in the delay time, which must be considered in the control of the tank vent valve. The activated charcoal filter facing side of the tank venting valve is in good approximation to ambient pressure.

When used in a fuel vapor retention system, also referred to as a tank ventilation system, the following advantage results:

The increase in the accuracy of the calculated delay time reduces the error in the formation of the drive signal for the tank vent valve. The invention essential consideration of the influence of the intake manifold pressure on the TEV delay time is particularly advantageous and necessary for the accurate dosage of small mass flows through the tank vent valve. A disregard of this influence can be too great relative errors in the tank ventilation and thus lead to undesirably high mixture deviations. An example is shown below.

• Figur 1 zeigt eine Brennkraftmaschine mit einer Tankentlüftungsanlage.
• Figur 2 stellt den zeitlichen Verlauf des Ansteuersignals zur Verdeutlichung des technischen Hintergrundes des erfindungsgemäßen Verfahrens dar. Fig. 3 zeigt ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens.

An embodiment of the invention is illustrated in the drawing and will be described in more detail below.

• FIG. 1 shows an internal combustion engine with a tank ventilation system.
• Figure 2 illustrates the timing of the drive signal to illustrate the technical background of the method according to the invention. Fig. 3 shows an embodiment of the method according to the invention.

1 shows an internal combustion engine 1 with a suction pipe 2, an exhaust tract 3, a tank ventilation system 4, a tank 5, a control unit 6, an exhaust gas sensor 7, a sensor 8, which is representative of a variety of sensors used in the operation of the internal combustion engine Operating parameters such as speed n, intake air quantity L, temperature T, intake air temperature, throttle valve opening angle, intake manifold pressure, ambient pressure, etc., and a fuel metering device 9, which may be implemented, for example, as an arrangement of one or more injectors. The control signals ti for the injectors are generated by a combination of a pilot control and a control intervention. In this case, the feedforward control essentially comprises the formation of a base value for the drive signal as a function of rotational speed n and load L of the internal combustion engine. This basic value is then corrected multiplicatively in a closed control loop as a function of the exhaust gas composition which is detected by the exhaust gas sensor system 7. Further corrections take into account the temperature influences of the internal combustion engine or the intake air and the influence of the tank ventilation or the battery voltage.

The tank ventilation system 4 consists of an activated carbon filter 10, which communicates via corresponding lines or connections to the tank, the ambient air and the intake manifold of the internal combustion engine, wherein a tank vent valve 11 is arranged in the line to the intake manifold. The activated carbon filter 10 stores in the tank 5 evaporating fuel. When the tank venting valve 11 is opened by the control unit 6, air is sucked from the environment through the activated carbon filter, which discharges the stored fuel into the air. This fuel-air mixture, which is also referred to as a tank venting mixture or else as a regeneration gas, influences the composition of the mixture as a whole supplied to the internal combustion engine, which is co-determined by metering of fuel via the fuel metering device 9, which is adapted to the intake air quantity. In this case, the fuel sucked in via the tank ventilation system can correspond in extreme cases to a proportion of approximately one third to half of the total fuel quantity.

The following calculation example illustrates the influence of tank ventilation on the mixture formation on the basis of typical values, as they occur in the field of tank ventilation of motor vehicles. In this example, the idle air requirement of the engine is about 10 cubic meters per hour. Through the permanently open tank vent valve flow about 4 cubic meters per hour. The tank vent valve is not permanently open, but is driven, for example, with a duty cycle of 1.67%. In other words, the ratio of the times when it is opened to the times when it closes In the following it is assumed that the regeneration gas flowing through the opened tank ventilation valve consists of 100% fuel vapor. This burns approximately in the volume ratio 1: 30 stoichiometrically with air. The amount of air required to burn the fuel vapor passing through the tank vent valve at these values is calculated to be 30 * 1.67: 100 * 4 cubic meters per hour to 2 cubic meters per hour. In other words, since the amount of intake air is 10 cubic meters per hour, 20% thereof, or 2 cubic meters per hour but already get their fuel content through the tank ventilation, only 80% of the fuel quantity required without tank ventilation need to be injected. In order to correct the tank venting influence on the mixture balance, a mixture correction corresponding to the above 20% is necessary. This mixture correction is effective in the mixture control loop from the exhaust gas probe 7 (control sensor), control unit 6 (controller) and injection valve 9 (control actuator).

This calculation example is valid for the ideal case, which is characterized by a tank vent valve without delay time or with precisely considered delay time. The following section shows how the delay time occurring in real tank ventilation valves has an effect. The period duration of the trigger duty ratio, which is initially the basis of the calculation example, amounts to 100 milliseconds. The actual pull-in delay is 3 milliseconds. The start delay should be compensated by including an assumed delay time of 4 milliseconds.

The tank vent valve in this case becomes 1.67 milliseconds + 4 milliseconds = 5.67 milliseconds opening controlled. The above mentioned duty ratio of 1.67% has been used. The actual open time is the difference of 5.67 milliseconds and 3 milliseconds to 2.67 milliseconds. In the calculation of the mixture correction, however, the opening time is 1.67 milliseconds. This results in a calculated fuel fraction of 20%, which is the actual fuel fraction of 32%.

This demonstrates the importance of forming the value for the delay time as accurately as possible. An increase in accuracy in this context means an improved approximation of the calculated value to the actual conditions.

According to the invention, in addition to the dependence of the delay time on the battery voltage, the dependence on the intake manifold pressure in the control of the TEVs is taken into account.

This can be done by means of a characteristic to be modeled separately, by means of a multi-dimensional map or on the basis of an analytical modeling.

In addition to the battery voltage, both the values of the intake manifold and the ambient pressure as well as the values of the differential pressure or the pressure ratio to be determined from this are conceivable as input variables.

Saugrohr- and ambient pressure, for example, supplied by the sensor 8. But you can also be calculated from other operating parameters of the engine, such as intake air and intake air temperature.

The differential pressure refers, for example, to the difference between ambient pressure and intake manifold pressure. Analogous the pressure ratio refers to the ratio of the ambient pressure to the intake manifold pressure. If a pressure sensor is used in the tank ventilation system, for example for diagnosis, it can replace the ambient pressure. Of course, the pressure difference (or the pressure ratio) directly above the tank vent valve, ie measured from the pressures on both sides of the tank venting valve and used.

In today normally closed tank vent valves, a higher Saugrohrunterdruck (lower absolute intake manifold pressure) acts closing on the movable armature of the tank venting valve. In this design, the higher intake manifold vacuum counteracts the valve opening and thus increases the delay time.

According to the invention this is taken into account by the fact that at higher intake manifold vacuum, the calculated delay time is also increased.

In another type of valve in which a higher intake manifold vacuum reduces the real delay time, then the calculated delay time must be reduced.

An example of the drive signal formation is shown in the flowchart of FIG.

The extent of the magnification as a function of the stated pressures is taken into account by means of a characteristic to be modeled separately, by means of a multi-dimensional characteristic map or on the basis of a computational modeling. These are measures familiar to the person skilled in the art, which require no detailed explanation.

The named characteristic and / or the characteristic map is stored in the control unit. The control unit further contains a program for controlling the tank ventilation valve as a function of further operating parameters such as intake air quantity, speed, etc. Such a control is described, for example, in US Pat. No. 4,683,861. With a period duration of the drive duty cycle of, for example, 100 milliseconds and the desired real duty cycle of 1.67% already mentioned above as an example, this results in a desired real opening duration OD of 1.67 ms. The actual drive signal AS is determined, for example, in the following way: $$\mathrm{A}\mathrm{S}=1.67\mathrm{m}\mathrm{s}+\mathrm{t}\mathrm{v},$$

In Fig. 3, the desired opening duration OD is determined in step 1. In step 2, the delay time tv is determined by map access, characteristic access or by calculation. For example, the map or characteristic curve or the dependencies that are essential for the calculation are determined once for a vehicle type. They can also be corrected on board, as is known from US 5,873,350.

In the case of a map that can be addressed by several parameters, the influence of the intake manifold pressure and the battery voltage can be taken into account in a common map, which is addressed with the intake manifold pressure and the battery voltage as input variables. In addition to the intake manifold pressure, the value of the ambient pressure can be used as the input variable. Values for the difference or the ratio of the pressures on both sides of the tank venting valve can serve as an input variable as an alternative to the intake manifold pressure. The tv value determined in this way then contains already a battery voltage correction (tv = tv (Ubatt, print sizes).

In the case of a characteristic
tv = tv (intake manifold pressure influence), which is addressed only by the intake manifold pressure influence, the battery voltage by a separate correction is taken into account.

In step 3, the real drive duty cycle is then determined as the sum AS = OD + tv.

Claims (6)

1. Method for the periodically clocked actuation of a flow control valve, the opening cross section of which follows its actuation signal with a delay by a delay time tv, and in which a value for the delay time is taken into account when forming the actuation signal, characterized in that the induction pipe pressure is taken into account when forming the value for the delay time.
2. Method according to Claim 1, characterized in that in the case of tank vent valves with a real delay time which increases in the event of a higher induction pipe subatmospheric pressure, the delay time formed by calculation is likewise increased.
3. Method according to Claim 1, characterized in that in the case of tank vent valves with a real delay time which reduces in the event of a higher induction pipe subatmospheric pressure, the delay time formed by calculation is likewise reduced.
4. Method according to Claim, 1, 2 or 3, characterized in that the influence of the induction pipe pressure is taken into account by means of a characteristic curve which can be separately modelled, by means of a multidimensional characteristic diagram or on the basis of computer modelling.
5. Method according to Claim 4, characterized in that

   - the values for the induction pipe pressure and the ambient pressure or the values for the induction pipe pressure and the pressure on the side of the tank vent valve which faces away from the induction pipe,

   - or the values for the pressure difference which can be determined therefrom,

   - or the values for the pressure ratio which can be determined therefrom,

   all serve as input variables for the characteristic curve, the characteristic diagram or the computer modelling.
6. Electronic control device for carrying out at least one of the methods according to Claims 1-5.

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