WO2005116427A1

WO2005116427A1 - Method for run-off control of fuel tank ventilation and mixture adaptation phrases in an internal combustion engine and internal combustion engine provided with run-off control

Info

Publication number: WO2005116427A1
Application number: PCT/EP2004/004628
Authority: WO
Inventors: Axel Lang
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2004-04-30
Filing date: 2004-04-30
Publication date: 2005-12-08

Abstract

The invention relates to a method for the run-off control of fuel tank ventilation and mixture adaptation phrases in an internal combustion engine comprising a fuel tank ventilation system, which can be operated at least in a lambda =1 and a weak operating mode. Said operating system can be switched between operating modes according to a desired operating mode which is determined by a plurality of operating mode requirements. Each operating mode requirement is allocated a priority and the determination of the desired operating mode is carried out according to the priorities of the operating mode requirements. A mixture adaptation phase with lambda = 1 can be requested in the presence of a mixture adaptation release and a fuel tank ventilation phase can be requested in the presence of a fuel tank ventilation release. According to the invention, the operating mode requests are prioritised according to at least one rule from the following groups: fuel tank ventilation and mixture adaptation phases have a time interval provided with a maximum length of T < TTE and/or TGA, which must not be completely used; the request of a mixture adaptation phase with a lambda = 1 operating mode occurs in the presence of a lambda =1 operating mode after discharge of TTE or to a time interval, whereby a lambda =1 operating mode and a mixture adaptation release is present; a mixture adaptation phase ends when the corresponding adaptation values are built up; a request for a mixture adaptation phase is forbidden for a given drive cycle, when a preferred tested adaptation for a predetermined amount of adaptation regions occurs, unless a lambda =1 operating mode and a mixture adaptation release is present. The invention also relates to an internal combustion engine which can be operated according to said method.

Description

Process for the sequential control of tank ventilation and mixture adaptation phases in an internal combustion engine and internal combustion engine with sequential control

The invention relates to a method for sequence control of tank ventilation and mixture adaptation phases in an internal combustion engine and an internal combustion engine according to the preambles of the independent claims.

In the conventional internal combustion engines of today's motor vehicles, fuel can also be supplied to the engine from a tank ventilation system during so-called tank ventilation phases. It is already known from EP 0 208 069 A to alternate tank ventilation phases and phases in which errors or tolerances of a mixture pre-control are compensated for by adaptation, according to a fixed time grid. The mixture adaptation takes place due to the higher accuracy of the lambda probes used for sensing the fuel mixture in homogeneous operation or in lambda = 1 operation. Since the other phase is only requested after a time interval assigned to the respective phase has elapsed, this leads to lambda-running internal combustion engines being forced to operate at lambda at fixed times and thus generally interrupting the more fuel-efficient lean operation.

It has been proposed in EP 0 576 448 E1 not to use a predefined time grid for the tank ventilation or mixture adaptation phase, but to vary the ratio of tank ventilation to adaptation periods depending on the amount of fuel generated during tank ventilation by means of a sequence control.

Furthermore, DE 100 43 072 A1 describes a method for compensating for mismatches in the pilot control of a fuel metering of an internal combustion engine, which is operated in at least two different operating modes, homogeneous or stratified. Mixture control and adaptation of the mixture control only take place in homogeneous operation. Switching between the operating modes depends on a target operating mode, which is determined from a plurality of operating mode requirements. Each of the operating mode requirements is assigned a priority. The target operating mode is determined depending on the priorities of the operating mode requirements. The physical urgency of the adaptation is increased in different time frames and a switchover to homogeneous operation is required.

If there is no error or suspected error, no mixture adaptation is required for a long time in the order of half an hour. If an error is detected via a diagnostic function during this time or if the error was known from the last trip through the diagnostics, the time grid is reduced to a few minutes. Furthermore, after an initialization time, when the mixture adaptation has been checked, no mixture adaptation is required for a long time in the order of ten minutes. The mixture adaptation is requested and prohibited depending on the loading of an activated carbon filter in the tank ventilation system after additive or multiplicative adaptation correction has been carried out. A request for mixture adaptation can be activated either only for homogeneous operation or for all operating modes. If the activated carbon filter is heavily loaded with fuel and the mixture adaptation has been completed, a mixture adaptation request is prohibited.

The object of the present invention is to provide a method for sequence control of tank ventilation and mixture adaptation phases in an internal combustion engine which can be operated at least with a lambda value = 1 and lean, in which an optimal interplay between the two phases achieves a more fuel-efficient behavior of the internal combustion engine can. Another aspect of this task is the creation of a corresponding internal combustion engine.

The object is achieved by the features of the independent claims. According to the invention, operating mode requirements are set according to at least one of the following rules:

Tank ventilation and mixture adaptation phases each have time windows with a maximum length T <T _TE or T _G A, which, however, do not have to be fully used if a Lambda ≠ 1 operating mode is present, the request for a mixture adaptation phase with a Lambda = 1 operating mode can be delayed , until the expiry of T _T E or until a point in time when there is a lambda = 1 operating mode and a mixture adaptation release - a mixture adaptation phase is ended if the corresponding adaptation values have settled A request for a mixture adaptation phase no longer occurs for a given driving cycle if a preferably checked adaptation takes place for a predetermined amount of adaptation areas, unless a lambda = 1 operating mode and a mixture adaptation release are present

Through the use of variable time slots with a maximum duration, a flexible and needs-based process of tank ventilation and mixture adaptation can be achieved when a mixture adaptation phase is ended, if the corresponding adaptation values have settled or if a request for a mixture adaptation phase no longer occurs if for a specified quantity Adaptation areas have already been adapted and there is not a lambda = 1 operating mode and a mixture adaptation release, the requirement for mixture adaptation phases can be reduced or the length of mixture adaptation phases can be reduced without the function of the mixture adaptation being impaired. The safe implementation of a tank ventilation phase and mixture adaptation phase is achieved by the introduction according to the invention of a minimum time during which a request for the other phase is prohibited 0 further advantages and aspects of the invention result itself, regardless of their summary in the claims, from the following illustration of exemplary embodiments with the aid of drawings

FIG. 1 shows an internal combustion engine with a fuel tank and a tank ventilation system. FIG. 2 shows a sequence of tank ventilation and mixture adaptation phases according to the prior art. FIG. 3 shows time slots for the method according to the invention. FIG. 4 shows another time slots for the method according to the invention

FIG. 1 shows a schematic representation of an internal combustion engine which is lean-running and has a tank ventilation system, for example a direct-injection gasoline engine, preferably also capable of stratified charging, with an intake pipe 2 and an exhaust tract 3. A throttle valve 5 is arranged in the intake pipe 2 by means of a fuel pump 7 and one Injection valve 4, fuel is transported from a fuel tank 6 into the intake pipe 2. The tank ventilation system comprises a tank ventilation line 10, via which outgassed fuel can be conducted from the tank 6 into the intake pipe 2. To control the ventilation, an absorption filter 8 and a ventilation valve 9 are also arranged in the ventilation line 10. An engine control unit MSG uses sensors, in particular a lambda sensor 11 in the exhaust tract 3, tank sensors 12 in the area of the fuel tank 6, a NOx sensor 13, which is arranged downstream of a NOx storage catalytic converter 14 in the exhaust tract 3, a sensor for detecting the position the throttle valve 5 and a sensor for detecting the state of the ventilation valve 9, operating parameters of the internal combustion engine. On the other hand, operating parameters of internal combustion engine 1 are influenced by engine control unit MSG via actuators (not shown).

The engine control unit MSG comprises a lambda control device for controlling the oxygen concentration of the lambda value or in the exhaust gas. In a manner known per se, a mixture precontrol is overlaid with a regulation. Correction variables are derived from the behavior of the control manipulated variable during mixture adaptation phases in order to compensate for mismatching of the pilot control to changed operating conditions.

Different adaptation variables are preferably adapted in different adaptation areas of the operation of the internal combustion engine. The intervention of the lambda control for setting lambda = 1 is preferably used, if necessary after filtering, to form an adaptation variable, since the accuracy of the lambda probe 11 is highest at lambda = 1. As is known per se, instead of the exact value Lambda = 1, a value deviating from it by a few percent can also be selected. At least two separate areas are preferably used for the selection of the errors, an additive and a multiplicative error. In order to carry out the mixture adaptation, mixture adaptation release conditions must be fulfilled, in the presence of which there is a mixture adaptation release. These relate, for example, to the engine temperature, the operational readiness of the lambda sensor and certain load and speed values of the engine 1. Furthermore, in order to carry out a mixture adaptation, it is necessary that the tank ventilation system, in particular the absorption filter 8, has only a low load of fuel gas.

Depending on the necessary flushing rates, a tank ventilation phase can take place either in throttled mode or in unthrottled lean mode, depending on the pressure drop between the intake pipe 2 and the tank system 6. The tank ventilation system system is preferably activated when there is a high load of fuel outgassing. Further conditions for activating the tank ventilation system can be, for example, certain speed and load values of the internal combustion engine 1.

The tank ventilation can be carried out in different intensities, which in turn can be selected depending on various operating parameters, in particular the operating mode and the current load / speed values of the internal combustion engine of the internal combustion engine 1.

The internal combustion engine 1 is switched in a manner known per se by the engine control unit MSG between different operating modes depending on a target operating mode. The internal combustion engine 1 can preferably also be operated in a stratified charge mode in addition to a lambda = 1 and a lean operating mode. The requested operating modes include, in particular, tank ventilation and mixture adaptation phases. The tank ventilation phase can basically take place at any lambda value and, if necessary, in stratified charge mode. The mixture adaptation phase requires lambda = 1 operation. The target operating mode is determined from a plurality of operating mode requests. A priority is assigned to each operating mode request, the target operating mode being determined as a function of the priorities of the operating mode requests. Corresponding software or circuit arrangements are implemented in the engine control unit MSG. In particular, the engine control unit MSG has a device 15 for sequence control.

Since no mixture adaptation should take place during a tank ventilation phase in order not to impair the accuracy of the error correction, mixture adaptation and tank ventilation phases alternate in time.

FIG. 2 shows a time sequence of tank ventilation and mixture adaptation phases, TE or GA, according to the prior art. A mixture adaptation takes place during a first time interval T1, which is activated by a corresponding request of a corresponding operating mode. Finally, there is an alternating request or activation of tank ventilation phases TE during the time intervals T2 or of mixture adaptation phases GA during time intervals T3 in a fixed time grid. The time grid T2, T3 used is constant. The time interval T1 can be somewhat longer than the subsequent time intervals T3 for carrying out a basic adaptation. FIG. 3 shows a time grid with a sequence of time intervals for the sequence control of tank ventilation and mixture adaptation phases according to the invention. The mixture adaptation phase GA can last a maximum of one time window with the length T _{GA and} the tank ventilation phase can last a maximum of one time window with the length T _T E. However, these maximum times do not have to be fully utilized by the respective function, so that a reduction in the frequency of requests for mixture adaptation phases and the average duration of mixture adaptation phases is achieved. In addition to the use of time windows with a maximum length of T _GA and T _TE , the following rules are used: if a Lambda ≠ 1 operating mode is present, the request for a mixture adaptation phase with a Lambda = 1 operating mode can be requested after T _{TE has} expired or in which there is a lambda = 1 operating mode and a mixture adaptation release - a mixture adaptation phase is ended, if the corresponding adaptation values have settled, a request for a mixture adaptation phase has been made for a given driving cycle is prohibited, if a preferably tested adaptation takes place for a predetermined amount of adaptation ranges unless there is a lambda = 1 operating mode and a mixture adaptation release.

FIG. 3 shows how, when there is a mixture adaptation release and lambda = 1 operation, a tank ventilation phase TE can be terminated in order to activate a mixture adaptation phase GA. In this case, the lambda = 1 operation is not triggered by a separate request for a mixture adaptation phase, but by different operating mode requirements. Such a lambda = 1 operation can be requested, for example, if the required load / speed values can only be represented in a lambda = 1 operation or if lean operation is blocked for other reasons. The latter can be the case, for example, if the NOx storage catalytic converter 14 is outside a permissible temperature window or the NOx sensor 13 is not ready for operation.

According to the invention, such lambda = 1 phases are used in order to avoid the requirement of low-consumption lambda = 1 operation during lean operation. Such a prematurely terminated tank ventilation phase is restarted after the mixture adaptation phase has ended and is ended after T _{TE has} expired. This tank ventilation phase is followed by a new mixture adaptation phase. FIG. 3 also shows that a mixture adaptation phase is ended if the corresponding adaptation values have settled into the respective adaptation range. Therefore T _GA ι <T _GA •

The maximum time during which the mixture adaptation phase is active, T _GA , is selected because, for example, in the case of driving conditions such as overrun or high driving dynamics, the mixture adaptation release conditions can no longer exist temporarily. In order to enable an adaptation, time must be reserved accordingly. This time must be long enough to allow errors to be adapted even with larger errors. In the case of an error, the mixture adaptation phase must last a minimum time so that it can be recognized whether an adaptation must follow. The time grid can also be selected depending on whether an error or an error is suspected. The mixture adaptation phase is advantageously not terminated before the minimum learning time of the mixture adaptation control has expired.

Since it can happen that the mixture pre-control has been adapted in all adaptation areas and has additionally been successfully tested, it is advisable to optionally request further mixture adaptation phases for a given driving cycle, unless there is a lambda = 1 operation together with a mixed adaptation release.

FIG. 4 shows a temporal structuring of a tank ventilation phase TE according to the invention. After a mixture adaptation phase GA with the time T _GA , a tank ventilation phase TE begins with a total time T _TE . The total time T _TE comprises a first sub-area T _TE1 during which the request for a mixture _{adaptation phase} is prohibited. This ensures a minimal fuel flushing of the tank ventilation system. After this minimum time T _TE ι, a mixture _adaptation phase can be requested during the remaining time T _TE2 if lambda = 1 operation is present and the mixture adaptation has been released. A mixture adaptation _phase is forcibly requested at the latest after the maximum time T _TE has expired. LIST OF REFERENCE NUMBERS

1 Internal combustion engine 2 Intake pipe 3 Exhaust tract 4 Injector 5 Throttle valve 6 Fuel tanks 7 Fuel pump 8 Absorber filter 9 Tank vent valve 10 Vent line 1 1 Lambda sensor 12 Tank sensor system 13 NOx sensor 14 NOx storage catalytic converter

20 15 Device for sequence control

Claims

claims

1. Method for sequence control of tank ventilation and mixture adaptation phases in an internal combustion engine with a tank ventilation system that can be operated at least in a lambda = 1 and a lean operating mode, wherein switching between operating modes depends on a target operating mode, which is determined from a plurality i θ of operating mode requirements where each operating mode request is assigned a priority and the target operating mode is determined as a function of the priorities of the operating mode requirements and if there is a mixture adaptation release a mixture adaptation phase with lambda = 1 can be requested and if there is a tank ventilation release a tank

15 ventilation phase can be requested, characterized in that the operating mode requirements are prioritized according to at least one of the group of the following rules:

Tank ventilation and mixture adaptation phases each have time windows with a maximum length of 20 T <T _TE or T _GA , which, however, do not have to be fully used if a Lambda ≠ 1 operating mode is present, a mixture adaptation phase with a Lambda = 1 operating mode is requested after T has elapsed _TE or already at a time when there is a lambda = 1 operating mode and a mixture adaptation release - a mixture adaptation phase is ended if the corresponding adaptation values have settled. A request for a mixture adaptation phase is prohibited for a given driving cycle, if for one predetermined amount of adaptation areas, a preferably tested adaptation has taken place, unless there is a lambda = 1 operating mode and a mixture adaptation release.

2. The method according to claim 1, characterized in that after requesting a tank ventilation phase for a minimum time T _TE ι a request for a mixture adaptation phase is prohibited. Method according to claim 1 or 2, characterized in that a mixture adaptation phase is only requested if a predetermined loading value B1 of the tank ventilation system with fuel outgassing has not been exceeded

Method according to at least one of the preceding claims, characterized in that a tank ventilation release takes place as a function of a predetermined loading value B2 of the tank ventilation system with fuel outgassing

Method according to at least one of the preceding claims, characterized in that at least two separate adaptation areas are used for the mixture adaptation

Internal combustion engine, preferably for a motor vehicle, which can be operated at least in a lambda = 1 and lean operating mode, with a tank ventilation system and an engine control unit with an adaptable mixture pilot control, with switching between operating modes depending on a desired operating mode, which consists of a plurality of Operating mode request is determined, with each of the operating mode requirements being assigned a priority and the target operating mode being determined as a function of the priorities of the operating mode requirements, wherein a mixture adaptation phase with lambda = 1 operation can be requested if there is a mixture adaptation release and one if there is a tank ventilation release Tank ventilation phase can be requested, characterized in that a device for sequence control with a Pπoπsierung the operating mode requirements according to at least one from the group of the following n rules is provided

- Tank ventilation and mixture adaptation phases each have time windows with a maximum length T <T _TE or T _G A, which, however, do not have to be fully used if a Lambda ≠ 1 operating mode is present, the request for a mixture adaptation phase with a Lambda = 1 operating mode after the expiration of T _T ε or at a point in time when there is a lambda = 1 operating mode and a mixture adaptation release - a mixture adaptation phase is ended if the corresponding adaptation values have settled A request for a mixture adaptation phase is prohibited for a given driving cycle if a preferably tested adaptation has been carried out for a predetermined number of adaptation areas, unless there is a lambda = 1 operating mode and a mixture adaptation release.