Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M25/00—Engine-pertinent apparatus for adding non-fuel substances or small quantities of secondary fuel to combustion-air, main fuel or fuel-air mixture
  • F02M25/08—Engine-pertinent apparatus for adding non-fuel substances or small quantities of secondary fuel to combustion-air, main fuel or fuel-air mixture adding fuel vapours drawn from engine fuel reservoir
  • F02M25/0809—Judging failure of purge control system

Definitions

• the invention relates to a tank ventilation system for an internal combustion engine in a motor vehicle, in which statements about the state of the tank ventilation system are derived from the result of measurements of the pressure in the tank ventilation system.
• statements about the state of the tank ventilation system statements about the filling state of the fuel tank or statements about the functionality of the tank ventilation system can serve.
• REPLACEMENT LEAF A diagnostic method is known from DE P41 32 055.7, in which a vacuum is first generated in the tank ventilation system when the connection to the intake manifold is open. After the connection to the intake manifold has been closed, the loss of vacuum, ie the pressure increase, is used to determine the tightness and thus the functionality of the tank ventilation system. A leak can be identified by comparing the speed of the pressure rise (pressure gradient) with a threshold value. It is noticeable by a comparatively rapid increase in pressure, that is to say by a threshold being exceeded.
• Both methods are sensitive to the evaporation of fuel in the tank ventilation system (TE system), which in a way influences the pressure measurements as an additional gas source.
• TE system tank ventilation system
• a strong outgassing is noticeable, for example, by enriching the air / fuel mixture of the internal combustion engine. If the outgassing is detected, the respective process is terminated. Since the outgassing occurs frequently, the diagnosis or the level determination is often aborted.
• the object of the invention is to provide methods which provide information on the condition of a tank ventilation system which is independent of the influence of the outgassing of fuel, the information being derived from measured tank pressure profiles.
• the invention solves this problem with the features of claim 1, in particular taking into account the influence of the evaporation of fuel on pressure changes within the tank ventilation system.
• Advantageous developments of the invention are the subject of the dependent claims.
• Advantages of the method according to the invention are that both the diagnosis and the level measurement can be carried out more frequently without the risk of false statements, because they do not have to be stopped even when the fuel is strongly gassing. Compared to disregarding the outgassing (evaporation), there is a higher level of measurement certainty when determining the fill level and a higher level of diagnostic certainty in the diagnosis.
• Fig.l shows a known device which is suitable for performing an embodiment of the method according to the invention.
• FIG 2 shows, by way of example, the time course of the pressure in the tank ventilation system in connection with the opening states of the valves according to the prior art.
• FIG. 5 shows a flow chart for the first exemplary embodiment of the method according to the invention.
• Fig. 6 shows waveforms as they occur in connection with a second embodiment of the invention.
• Fig. 7 discloses a flow chart for the second embodiment.
• Fig. 8 shows waveforms as they occur in a modification of the second embodiment.
• a tank ventilation system which here has an activated carbon filter 5, a shut-off valve 6 (AV) arranged in the ventilation line of the activated carbon filter and a tank ventilation valve arranged in the line between the activated carbon filter and intake manifold 7 (TEV). Fuel vaporizing in the tank is stored in the activated carbon filter and fed to the combustion via the open tank ventilation valve and the intake manifold during operation of the internal combustion engine. Because of the pressure conditions that arise, the activated carbon filter is simultaneously flushed with fresh air when the shut-off valve is open.
• a control device 8 is used to control the tank ventilation by opening and closing the aforementioned valves.
• a pressure sensor 9 supplies a signal about the pressure inside the tank ventilation system, as is used to carry out the methods described above for determining statements about the state of the Tank ventilation system is required.
• the control device is also supplied with signals which indicate the operating state of the internal combustion engine and the composition of the fuel / air mixture supplied to the internal combustion engine.
• the number 10 represents the detection of the speed, the load and, if appropriate, other variables
• the number 11 represents a sensor for detecting the exhaust gas composition in the exhaust pipe 12 of the internal combustion engine.
• the control unit forms 8 integrated control functions, a fuel metering signal ti with which the fuel metering device 3 in the intake pipe of the internal combustion engine is controlled.
• 2 a and b illustrate the opening and closing state of the tank ventilation valve (FIG. 2 a) and the shut-off valve (FIG. 2 b) over time t in processes known from the prior art.
• FIG. 2 c shows the Corresponding course of the tank pressure, or the difference between the ambient and tank pressure.
• the tank ventilation valve When the tank ventilation valve is open, the shut-off valve is closed and the supply of air to the tank ventilation system is thus interrupted. As a result, the tank pressure gradually drops until, for example, the tank ventilation valve is closed at a pressure difference of 10 hPa from the ambient pressure.
• the slope of the pressure drop i.e. the extent of the rate of change in pressure, a measure of the level in the tank.
• the extent of the pressure change that occurs further to the right when the shut-off and tank ventilation valve is closed is a measure of the tightness of the tank ventilation system.
• the pressure In the ideal case of a completely sealed system, the pressure remains constant, as is illustrated by the continuous pressure curve in the time range t greater than t2.
• a leaky system is characterized by the pressure increase shown in dashed lines. However, such an increase in pressure when the valves are closed can also be caused by the vaporization of fuel.
• the outgassing weakens to a certain extent the suction pipe negative pressure acting on the tank when the tank ventilation valve is open, and between times t2 and t3, the outgassing accelerates the pressure equalization between the tank and ambient atmosphere when the valves are closed.
• the influence of outgassing on the measured tank pressure curve is determined in a first step by determining the gradient gradO of the tank pressure curve between the times to and tl. In a second step, this gradO (positive) is subtracted from the gradl (negative) determined between times t1 and t2.
• a third step the process of increasing the pressure is characterized
• the gradient of the gradient of the tank pressure grad2 between times t2 and t3 is determined.
• the value grad2corr, corrected for the influence of the outgassing, results from the difference between grad2 and gradO. Only when the corrected gradient value grad2corr " exceeds a threshold value SW to be matched to the tank ventilation system, is the system considered to be leaking.
• This procedure is based on the knowledge that the size of the detectable leaks increases when the fuel is outgassed (grad0> 0). In other words, smaller leaks can be detected without outgassing than with outgassing.
• Another design option is to divide the compensation gradient gradO into classes (0 ⁇ grad0 ⁇ SGl; SGl ⁇ gradO ⁇ SG2; ...) and to select the leak detection threshold SW depending on the assigned class and the level FS of the tank.
• step S1 the pressure PO is detected with the tank ventilation valve closed and the shutoff valve open, before the shutoff valve is also closed in step S2.
• gradO is a measure of the outgassing of the fuel.
• step S5 values for gradl from the time interval t2-tl (step S5) and grad2 from the time interval t3-t2 can be used for the opening and closing states of the shut-off and tank ventilation valve explained in connection with FIG. 3 ⁇ vote (step S6).
• step S7 gradl and grade 2 are corrected with gradO and in step 8 the fill level of the tank is read out from the characteristic curve according to FIG. 4 via gradlkorr.
• step S9 is used to compare grad2korr with a threshold value SW. If this is exceeded, an error message is issued in step S10, which signals a leak. Otherwise the end of the procedure is reached.
• FIG. 6a shows the time profile of a manipulated variable FR from a lambda control loop. It comes about by first comparing the signal L of the exhaust gas probe with a target value. If the comparison result reflects a fuel mixture that is too lean, FR is increased, which ultimately goes into the ti formation in such a way that the fuel portion is increased. If, on the other hand, the comparison result reflects a mixture that is too rich, FR is reduced.
• the time course of the control factor FR shown in FIG. 6a is established. From the course of this control factor, as will be shown in the following, the influence of the outgassing of fuel on the course of the tank pressure can be concluded.
• the flowchart in FIG. 7 shows examples of step sequences for obtaining the statements mentioned.
• FR1 can be determined as the mean value of FR or also as the value of FR immediately before a proportional jump.
• Steps S2 and S3 serve to open the tank ventilation valve and to close the shut-off valve.
• a value FR2 is determined in a step S4 in a manner analogous to the determination of FR1.
• dFR ⁇ 0 and thus the amount of gradlkorr becomes larger than gradl. As already described above, this compensates for the output falsifying the pressure measurement.
• Grad2korr can be determined in a similar way.
• the leak detection threshold SW can be changed as a function of the determined outgassing dFR, as is disclosed by FIG. In FIG. 4a, only the gradO would have to be replaced by dFR.
• This process can be followed by a leak test and a second test of the outgassing. See FIG. 8, in which, at time t3, the tank ventilation valve is closed with the shutoff valve still closed and the subsequent pressure change is observed until time t4.
• a degree 2 can be formed from the pressure values at times t4 and t3.
• the influence of the outgassing on this gradient can be measured from the FR values at times t2 and t3. Opening the tank vent valve at time t4 with the shut-off valve still closed serves to safeguard the results obtained by the previous process sequence. If the pressure rises rapidly in the interval (t3, t4), this indicates a leak on the one hand.
• an increased outgassing of fuel in the negative pressure phase can also be responsible for this.
• a second outgassing test is carried out starting at t4.
• the shut-off valve is also closed at the beginning of the second outgassing test.
• the activated carbon filter is therefore not flushed with fresh air and as As a result, any remaining loading of the Aktov carbon filter with fuel has no influence on the following outgassing test. Otherwise, the conditions for the control factor FR for times t> t4 are analogous to those in FIG. 6a from time t1.
• the fuel vapor generated during the vacuum reduction by sloshing the fuel to increase the amount of the vacuum reduction gradient, which incorrectly indicates a leak.
• the test result is to be rejected.
• the difference between the amounts of the dFR values is formed in the first vacuum build-up (dFRl) and the second vacuum build-up (dFR2) (FIG. 8d). If the difference exceeds a threshold value, the test result is rejected.

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Citations (8)

• 1993
  • 1993-12-11 DE DE19934342431 patent/DE4342431A1/de not_active Ceased
• 1994
  • 1994-11-29 WO PCT/DE1994/001411 patent/WO1995016122A1/de active Application Filing

Patent Citations (8)

Non-Patent Citations (1)

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