EP1317611A1

EP1317611A1 - Method for generating the time-delay of an electromagnetic tank bleeder valve

Info

Publication number: EP1317611A1
Application number: EP01971684A
Authority: EP
Inventors: Gholamabas Esteghlal; Dieter Lederer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-09-04
Filing date: 2001-09-03
Publication date: 2003-06-11
Anticipated expiration: 2021-09-03
Also published as: DE10043698A1; EP1317611B1; WO2002020962A1; DE50110408D1

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

Process for forming the delay time of an electromagnetic tank ventilation valve

State of the art

The invention relates to a method for forming the

Delay time of electromagnetic tank ventilation valves. Motor vehicles powered by internal combustion engines are often equipped with so-called tank ventilation systems, which help to prevent emission of fuel vapor from the storage tank into the environment. The one evaporating in the tank

Fuel is stored in an activated carbon filter and fed to the intake manifold of the internal combustion engine and thus the combustion during operation of the motor vehicle via an electromagnetic tank ventilation valve which can be controlled in a timed manner.

Such valves have a delay due to the design.

Tank ventilation valves (TEV) are generally executed as clocked solenoid valves and between the

Activated carbon filter (AKF) and the intake manifold. When such valves are electrically actuated, the magnetization of a core takes place, which leads to the valve armature being attracted to the core against a spring force and the valve opening. This is done when closing 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 battery voltage, the inertia of the armature and the forces acting on it.

The actual open time of the valve is reduced by this delay time. This reduces the amount of gas flowing through the tank ventilation valve, which has a particularly strong effect on short activation times.

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

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

Against this background, the object of the invention is to calculate the delay time, which is the actual delay time in the operation of the

Tank vent valve comes even closer and corresponds as closely as possible. This object is achieved with the combination of features of the independent claim.

Specifically, in a method for periodically 5-cycle control of a flow control valve, the opening cross-section of which follows its control signal delayed by a delay time tv and in which a value for the delay time is taken into account in the formation of the control signal, the intake manifold pressure in the formation of the L0 value for the Delay time taken into account.

One embodiment of the invention is characterized in that, in the case of tank ventilation valves, the real delay time of which increases with a higher intake manifold vacuum, L5 the calculated delay time is also increased.

A further embodiment provides that in the case of tank ventilation valves, the real delay time of which decreases with a higher intake manifold vacuum, the arithmetically formed delay time is also reduced.

According to a further embodiment, the influence of the intake manifold pressure is taken into account by means of a! 5 characteristic curve to be modeled separately, by means of a multi-dimensional characteristic map or on the basis of a computational modeling.

Another embodiment is characterized in that SO - 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 15 pressure difference to be determined therefrom - or the values of the

Pressure ratio serve as the input variable of the characteristic curve, the map or the mathematical modeling.

The invention also relates to an electronic control device for performing at least one of the above-mentioned methods and embodiments.

L0

Essential to the invention is the consideration of the dependency of the delay time of the tank ventilation valve on the intake manifold pressure when calculating the delay time. The invention is therefore based on the knowledge that a

L5 the forces that counteract the opening of the valve come from the intake manifold vacuum, which is on the intake manifold side at the armature; this force increases with the intake manifold vacuum and leads to a corresponding change in the delay time, which increases when the tank ventilation valve is activated

.0 is taken into account. The side of the tank ventilation valve facing the activated carbon filter is a good approximation of the ambient pressure.

When used in a fuel vapor retention system, also referred to as a tank ventilation system 25, the following advantage results:

Increasing the accuracy of the calculated delay time reduces the error in the formation of the

50 control signals for the tank ventilation valve. The consideration of the influence of the intake manifold pressure on the TEV delay time, which is essential to the invention, is particularly advantageous and necessary for the precise metering of small mass flows via the tank ventilation valve. A

$ 5 Ignoring this influence can be too big relative errors in the tank ventilation and thus lead to undesirably high mixture deviations. An example is shown below.

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

Figure 1 shows an internal combustion engine with a tank ventilation system. L0 Figure 2 shows the time course of the control signal to clarify the technical background of the inventive method. Fig. 3 shows an embodiment of the inventive method.

L5 In detail, FIG. 1 shows an internal combustion engine 1 with an intake manifold 2, an exhaust tract 3, a tank ventilation system 4, a tank 5, a control unit 6, an exhaust gas sensor system 7, a sensor system 8, which is representative of a large number of when the internal combustion engine is operating

-0 sensors used for 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, for example as an arrangement of one or more

.5 injectors can be realized. The control signals ti for the injection valves are generated by a combination of a pilot control and a control intervention. The precontrol essentially comprises the formation of a basic value for the control signal as a function of speed n and load L der

Internal combustion engine. This base value is then multiplicatively corrected 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

15 take into account 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 a 5 activated carbon filter 10, which communicates with the tank, the ambient air and the intake manifold of the internal combustion engine via corresponding lines or connections, a tank ventilation valve 11 being arranged in the line to the intake manifold. The activated carbon filter 10 stores in the tank 5

L0 evaporating fuel. When the tank ventilation valve 11 is activated by the control unit 6, air is drawn in from the surroundings through the activated carbon filter, which releases the stored fuel into the air. This also as a tank ventilation mixture or as a regeneration gas

L5 designated fuel-air mixture influences the composition of the mixture supplied to the internal combustion engine as a whole, which is also determined by a metering of fuel adjusted to the intake air quantity via the fuel metering device 9.

! 0 In extreme cases, the fuel drawn in via the tank ventilation system can correspond to a share of approx. One third to half of the total fuel quantity.

15 The following calculation example illustrates the influence of tank ventilation on the mixture formation based on typical values that occur in the area of tank ventilation in motor vehicles. In this example, the engine's idle air requirement is approximately 10 cubic meters per hour.

0 Approx. 4 cubic meters per hour flow through the permanently open tank ventilation valve. However, the tank ventilation valve is not permanently open, but is controlled, for example, with a duty cycle of 1.67%. In other words: the ratio of the times when it's opening

5 is controlled at the times when it closes is controlled, is 1.67: 100. It is further assumed that this is due to the open

Tank vent valve flowing regeneration gas consists of 100% fuel vapor. This burns in a 5: 1 ratio by volume stoichiometric with air. The amount of air required to burn the fuel vapor that flows through the tank ventilation valve at these values is calculated at 30 * 1.67: 100 * 4 cubic meters per hour at 2 cubic meters

L0 per hour. In other words, since the amount of intake air 10

Cubic meters per hour, 20% of it, or 2 cubic meters per hour, however, already receive their fuel share via the tank ventilation, only 80% of the fuel quantity required without tank ventilation has to be injected

Be L5. In order to correct the influence of the tank ventilation on the mixture balance, a mixture correction that corresponds to the 20% specified above is necessary. This mixture correction is made up of the exhaust gas probe 7 (control sensor), control unit 6 (controller) and injection valve 9 in the mixture control loop

20 (control actuator) effective.

This calculation example is valid for the ideal case, which is characterized by a tank ventilation valve without delay time or with exactly correct delay time taken into account

! 5 awards. The following shows how the delay time that occurs with real tank ventilation valves has an effect. The period of the control pulse duty factor, which is the basis of the calculation example, is 100 milliseconds. The actual

10 pull-in delay is 3 milliseconds. The delay is to be compensated by including an assumed delay time of 4 milliseconds.

In this case, the tank vent valve becomes 1.67.5 milliseconds + 4 milliseconds = 5.67 milliseconds controlled opening. The duty cycle of 1.67% specified above was used as a basis. The actual open time is the difference of 5.67 milliseconds and 3 milliseconds to 2.67 milliseconds. In 5 the calculation of the mixture correction goes however

Opening time 1.67 milliseconds on. This results in a calculated fuel share of 20%, which is compared to the actual fuel share of 32%.

L0 This proves the importance of forming the value for the delay time as precisely as possible. In this context, an increase in accuracy means an improved approximation of the calculated value to the actual conditions.

L5

According to the invention, in addition to the dependency of the delay time on the battery voltage, the dependence on the intake manifold pressure is taken into account when driving the TEV.

20 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 analytical modeling.

In addition to the battery voltage, the values of the Ϊ5 intake manifold and ambient pressure as well as the values of the differential pressure or the pressure ratio to be determined therefrom are conceivable as input variables.

The intake manifold and ambient pressure are supplied by the SO sensor system 8, for example. However, as is known, they can also be calculated from other operating parameters of the engine, such as intake air quantity and intake air temperature.

The differential pressure relates, for example, to the! 5 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, this can replace the ambient pressure. Of course, the pressure difference (or the pressure ratio) can also be measured and used directly above the tank ventilation valve, ie from the pressures on both sides of the tank ventilation valve.

.0

With currentless closed today

Tank breather valves a higher intake manifold vacuum (lower absolute intake manifold pressure) has a closing effect on the movable armature of the tank breather valve. With this .5 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 the computed! 0 delay time is also increased at a higher intake manifold vacuum.

In another type of valve, in which a higher intake manifold vacuum reduces the real delay time, the calculated delay time must also be reduced 15.

An example of the control signal formation is shown in the flow diagram of FIG. 3.

0 The extent of the enlargement as a function of the pressures mentioned is taken into account by means of a characteristic to be modeled separately, by means of a multi-dimensional map or on the basis of a computational modeling. These are measures familiar to the expert,

5 which do not require a detailed explanation. The named characteristic and / or the characteristic diagram is stored in the control unit. The control unit also contains a program for controlling the tank ventilation valve in dependence on 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 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, a desired real opening duration OD of 1.67 ms results. The actual control signal AS is determined, for example, in the following way:

L5 AS = 1.67ms + tv.

3 is the desired step 1

Opening duration OD determined. In step 2, the delay time tv is due to map access, access to the characteristic curve

20 or determined by calculation. The characteristic diagram or the characteristic curve or the dependencies that are important for the calculation are determined, for example, once for a vehicle type. They can also be corrected on board, as is known from US 5 873 350.

25

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 related to the intake manifold pressure and the

SO battery voltage is addressed as input variables.

In addition to the intake manifold pressure, the value of the ambient pressure can be used as an input variable. As an alternative to the intake manifold pressure, values for the difference or the ratio of the pressures on both sides of the tank ventilation valve can be used as

15 input variable serve. 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 curve tv = tv (intake manifold pressure influence), which is only from

Intake manifold pressure is addressed, the battery voltage must be taken into account by a separate correction.

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

Claims

L0 claims

1. Method for periodically actuating a

Flow control valve whose opening cross section delays its control signal by a delay time tv

L5 follows and in which a value for the delay time is taken into account when forming the control signal, characterized in that the intake manifold pressure is taken into account when forming the value for the delay time.

-0

2. The method according to claim 1, characterized in that in tank ventilation valves, the real delay time increases with higher intake manifold pressure, the calculated delay time also increases

.5 will.

3. The method according to claim 1, characterized in that in the case of tank ventilation valves, the real delay time of which decreases with a higher intake manifold vacuum, the

50 calculated delay time is also reduced.

4. The method according to claim 1, 2 or 3, characterized in that the influence of the intake manifold pressure

55 by means of a characteristic curve to be modeled separately, is taken into account by means of a multi-dimensional map or on the basis of a computational modeling.

5. The method according to claim 4, 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 pressure difference values to be determined therefrom

- or the values of the pressure ratio to be determined therefrom serve as the input variable of the characteristic curve, the characteristic diagram or the mathematical modeling.

6. Electronic control device for performing at least one of the methods according to claims 1-5.