U.S. patent application number 09/958538 was filed with the patent office on 2002-10-31 for method for verifying the tightness of a tank system in a motor vehicle.
Invention is credited to Streib, Martin.
Application Number | 20020157653 09/958538 |
Document ID | / |
Family ID | 7630640 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157653 |
Kind Code |
A1 |
Streib, Martin |
October 31, 2002 |
METHOD FOR VERIFYING THE TIGHTNESS OF A TANK SYSTEM IN A MOTOR
VEHICLE
Abstract
A method for checking the tightness of a tank system, especially
of a tank-venting system of a vehicle, wherein an overpressure or
an underpressure relative to the atmospheric pressure is introduced
into the tank system by means of a pressure source and the
time-dependent trace of at least one operating characteristic
variable of the pressure source is detected when introducing the
overpressure/underpressure up to reaching a first time point or a
first pressure level and is compared to a time-dependent trace of
the operating characteristic value up to this time point or up to
this pressure level (expected diagnostic trace), the time-dependent
trace being expected in the case of a tight tank system, and, a
conclusion as to non-tightness is drawn when the detected
time-dependent trace deviates from the expected diagnostic trace by
at least a pregiven value, characterized in that, when a deviation
is determined, the overpressure/underpressure in the tank-venting
system is further increased up to reaching a second time point or a
second pressure level; the operating characteristic value of the
pressure source continues to be detected and compared to an
expected further time-dependent trace of the operating variable in
the case of a tight system (further diagnostic trace) and, a fault
announcement is only then outputted when the detected
time-dependent trace during the introduction of the further
overpressure/underpressure deviates from the further diagnostic
trace.
Inventors: |
Streib, Martin; (Vaihingen,
DE) |
Correspondence
Address: |
Walter Ottesen
PO Box 4026
Gaithersburg
MD
20885-4026
US
|
Family ID: |
7630640 |
Appl. No.: |
09/958538 |
Filed: |
November 30, 2001 |
PCT Filed: |
January 25, 2001 |
PCT NO: |
PCT/DE01/00287 |
Current U.S.
Class: |
123/520 ;
73/40 |
Current CPC
Class: |
F02M 25/0818 20130101;
G01M 3/32 20130101 |
Class at
Publication: |
123/520 ;
73/40 |
International
Class: |
F02M 033/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 11, 2000 |
DE |
100 06 185.0 |
Claims
1. Method for checking the tightness of a tank system, especially
of a tank-venting system of a vehicle, wherein an overpressure or
an underpressure relative to the atmospheric pressure is introduced
into the tank system by means of a pressure source and the
time-dependent trace of at least one operating characteristic
variable of the pressure source is detected when introducing the
overpressure/underpressure up to reaching a first time point or a
first pressure level and is compared to a time-dependent trace of
the operating characteristic value up to this time point or up to
this pressure level (expected diagnostic trace), the time-dependent
trace being expected in the case of a tight tank system, and, a
conclusion as to non-tightness is drawn when the detected
time-dependent trace deviates from the expected diagnostic trace by
at least a pregiven value, characterized in that, when a deviation
is determined, the overpressure/underpressure in the tank-venting
system is further increased up to reaching a second time point or a
second pressure level; the operating characteristic value of the
pressure source continues to be detected and compared to an
expected further time-dependent trace of the operating variable in
the case of a tight system (further diagnostic trace) and, a fault
announcement is only then outputted when the detected
time-dependent trace during the introduction of the further
overpressure/underpressure deviates from the further diagnostic
trace.
2. Method of claim 1, characterized in that the pump current of an
overpressure pump/underpressure pump is detected as an operating
characteristic variable.
3. Method of claim 2, characterized in that one compares the pumped
current to the expected current values for a tight tank system
after the elapse of the pregiven time intervals and a fault
announcement is only outputted when the detected pump current
deviates from a first expected value in a tight tank system after
the elapse of the first time interval as well as deviates from a
second expected current value for a tight tank system after the
elapse of the second interval.
Description
STATE OF THE ART
[0001] The invention relates to a method for checking the tightness
of a tank system, especially a tank-venting system, in accordance
with the preamble of claim 1.
[0002] A method for checking the tightness of the tank-venting
system of a vehicle is disclosed, for example, in DE 198 09 384 A1
as well as in DE 196 36 431 A1.
[0003] In the above, an overpressure is introduced into a
tank-venting system by means of a pressure source and the
time-dependent trace of at least one operating characteristic
variable of the pressure source is detected while introducing the
overpressure. This time-dependent trace is compared to a
time-dependent trace of the operating characteristic variable
(diagnostic trace), which is expected in the case of a tight tank
system. This expected time-dependent trace is, for example,
previously measured, computed or estimated. A conclusion is then
drawn as to non-tightness when the detected time-dependent trace
deviates from the diagnostic trace by at least a pregiven value.
The pump current of a pump is used, for example, as the diagnostic
trace. The diagnostic trace corresponds to the pump current which
occurs when an overpressure is introduced into a tank-venting
system having a pregiven reference leak having, for example, a
diameter of 0.5 mm. In this case, the current of the pump is
compared to a reference current during introduction of the
overpressure. The absolute current level can vary greatly for the
same leak size because of ambient conditions and tolerances.
Independently of the absolute level, a fine leak having a diameter
of 0.5 mm can, however, be excluded if, during the introduction of
the overpressure by pumping, a current level is reached which is
greater than the reference current. If this current level is not
reached, then a conclusion can be drawn as to a fine leak having a
diameter of .gtoreq.0.5 mm.
[0004] In contrast, a large leak having a diameter of 1 mm or more
cannot be detected from the method of tightness checking of
tank-venting systems known from the state of the art. When pumping
against a reference leak, and when a leak is present having a
diameter of approximately 1 mm, any desired current level can be
reached after a certain pregivable time in dependence upon ambient
conditions and component tolerances. A reliable decision is
therefore not possible in this manner as to whether a large is leak
is present having a diameter of 1 mm or more.
[0005] In view of the above, it is, for example, conceivable that a
pregiven pump current is not yet reached after a pregiven time for
a leak having a diameter of only 0.4 mm (for which no fault output
is required), so that a fault would be outputted in the methods
known from the state of the art.
[0006] On the other hand, for other tolerances, a pregiven current
threshold can be reached also for a leak having a diameter of more
than 1 mm in a time interval, which is less than a pregiven
diagnostic time interval and this would lead to the situation that
a fault output would not take place.
[0007] In view of the above, it is a task of the invention to
improve a method for checking the tightness of a tank system of a
vehicle so that a reliable detection of large leaks having a
diameter of .gtoreq.1 mm is possible independently of
tolerance-caused disturbances and/or environmentally-caused
disturbances of the operating characteristic value during the
introduction of an overpressure into the tank system.
ADVANTAGES OF THE INVENTION
[0008] This task is solved in accordance with the invention with
the features of claim 1 with a method for checking the tightness of
a tank system of the kind described initially herein.
[0009] Advantageous further improvements of the invention are the
subject matter of the dependent claims.
[0010] The advantage of the method of the invention is that, to a
certain extent, it is possible to verify an initially expected
untightness or to show that it is false via the following: a
further diagnostic trace (that is, a further introduction of an
overpressure or underpressure into the tank system); the detection
of the operating variable of the pressure source when introducing
this additional overpressure or underpressure until reaching a
second time point or a second pressure level; a comparison of the
so detected operating characteristic variable to a time-dependent
trace of the operating characteristic variable (expected for a
tight tank system) when introducing the additional overpressure;
and, the output of a fault announcement only when a determination
is made of a deviation of the detected operating characteristic
variable from the diagnostic trace by at least a pregiven value and
when there is a deviation of the operating characteristic variable
from the further diagnostic trace by at least a pregiven value.
With this verification or showing to be false, faults can be
eliminated which are caused especially by ambient influences or
component tolerances.
[0011] With the method of the invention, large leaks having a
diameter of 1 mm or greater than 1 mm can be recognized with high
accuracy. On the other hand, leaks having a diameter of less than 1
mm do not lead to fault announcements.
[0012] The electric current of an overpressure pump/underpressure
pump is advantageously detected as an operating characteristic
variable of the pressure source. For this reason, it is not only
possible to accurately detect significant changes of the operating
state of the pressure source but the detected electric current can
also be directly further processed in evaluation circuits or the
like in an advantageous manner.
[0013] As to the time-dependent trace of the operating
characteristic variable (that is, the electric current), the
current could, in principle, be detected continuously over time and
the functional trace shown in this manner could be compared to a
time-dependent trace which was previously measured, computed or
estimated.
[0014] An especially advantageous embodiment provides that the pump
current is compared to the expected current values for a tight tank
system after the elapse of pregiven time intervals and a fault
announcement is only outputted when the detected pump current,
after the elapse of the first time interval, deviates from an
expected current value for a tight tank system as well as, after
the elapse of the second time interval, deviates from a second
expected current value for a tight tank system.
[0015] With the comparison of these values, a very accurate leak
detection of a tank-venting system is also possible. A
significantly reduced storage complexity is required when compared
to the detection of the time-dependent trace of the current
intensity.
DRAWING
[0016] Further features and advantages of the invention are the
subject matter of the description which follows as a well as the
illustration of some embodiments.
[0017] In the drawings:
[0018] FIG. 1 schematically shows a tank-venting system of a
vehicle known from the state of the art wherein the method, which
makes use of the invention, is applied;
[0019] FIG. 2 schematically shows the time-dependent trace of the
pump current of a pump for introducing an overpressure into the
tank-venting system of a vehicle; and,
[0020] FIG. 3 schematically shows a flowchart of an embodiment of
the method, which makes use of the invention, for checking the
tightness of a tank-venting system of a vehicle.
DESCRIPTION OF AN EMBODIMENT
[0021] The invention is described in the following with respect to
an example of a tank-venting system of a motor vehicle. It is,
however, understood that the method of the invention can be used
not only for a tank-venting system but for any desired tank
system.
[0022] A tank-venting system of a motor vehicle tank system is
shown in FIG. 1 and includes a tank 10, an adsorption filter 20
(for example, an active charcoal filter), a venting line 22
connectable to the ambient and a tank-venting valve 30. The
adsorption filter 20 is connected to the tank 10 via a tank
connecting line 12. The tank-venting valve 30 is connected, on the
one hand, to the adsorption filter 20 via a valve line 24 and, on
the other hand, to an intake manifold 40 of an internal combustion
engine (not shown) via a valve line 42.
[0023] Hydrocarbons develop in the tank 10 because of vaporization
and these hydrocarbons deposit on the adsorption filter 20. To
regenerate the adsorption filter 20, the tank-venting valve 30 is
opened so that air of the atmosphere is drawn by suction through
the adsorption filter 20 because of the underpressure present in
the intake manifold 40. In this way, the hydrocarbons deposited on
the absorption filter 20 are drawn by suction into the intake
manifold 40 and supplied to the engine.
[0024] In order to check the operability of the tank-venting
system, a pump 50 is provided which is connected to a circuit unit
60. A switchover valve 70 is switched downstream of the pump 50 and
this valve can, for example, be in the form of a 3/2 directional
valve. A reference leak 81 is arranged in a separate branch 80
parallel to this switchover valve 70. The size of the reference
leak 81 is so selected that this leak corresponds to the size of
the leak to be detected. The size can, for example, be so selected
that it corresponds to a reference leak having a diameter of 0.5
mm.
[0025] It is understood that the reference leak 81 can, for
example, also be part of the switchover valve 70, that is, as a
channel construction or the like so that, in this case, an
additional reference part can be omitted (not shown).
[0026] The tightness check of the tank-venting system is, for
example, explained in detail in DE 196 36 431 A1 or in DE 198 09
384 A1 incorporated fully herein by reference. By detecting the
current to be supplied to the pump, it can be determined whether
the pumped flow, which is to be introduced into the tank-venting
system by the pump source in the form of the pump 50, deviates from
a pumped flow which is present when introducing an overpressure via
the reference leak. For this purpose, the time-dependent trace of
the current, which results when the voltage is applied to the pump
50, is detected. It is noted that the invention is not limited to
the introduction of an overpressure; rather, the tightness check
can likewise be undertaken by introducing an underpressure. In both
cases, possibly present leaks can be determined.
[0027] The method for checking tightness is explained in greater
detail in the following in connection with FIG. 2 wherein the pump
current is shown schematically as a function of time and in
connection with FIG. 3 which schematically shows a flowchart of the
method.
[0028] First, an overpressure is introduced into the tank-venting
system in step 202 (FIG. 3). Here, the time-dependent pump current
is detected. As shown in FIG. 2, a reference current I.sub.Ref is
first applied to the pump 50. In this state, the switchover valve
70 is in the position identified by I in FIG. 1. In this position
of the switchover valve 70, a pumped flow is introduced by the pump
or pressure source 50 into the tank-venting system via the
reference leak 80. Here, the current I.sub.Ref adjusts as shown
schematically in FIG. 2 and is essentially constant over time. As
soon as the switchover valve 70 is switched over from the position
I into the position II, the pressure source or pump 50 applies an
overpressure (step 202) to the tank-venting system. When switching
over, the motor current first drops rapidly by a value I.sub.stroke
and thereafter increases continuously over time. It can be assumed
that no leak is present when the detected pump current reaches a
current level I.sub.GL1 after a time t.sub.end1 (step 203) which is
less than a pregivable time T.sub.GL1, which current level deviates
by a difference DIGL2 from an idle current I.sub.LL Of the pump
(FIG. 2). Stated otherwise, the pump current reaches in a time
t=t.sub.end1, which is less than a pregiven time T.sub.GL1, a
current level I.sub.GL1, which exceeds the idle current I.sub.LL by
a pregiven threshold DIGL2. In this case, as shown schematically in
FIG. 3, for example, the tightness check can be ended after output
of an announcement "no leak" in step 206. This case is shown
schematically in FIG. 2 by the curve identified by 1. The
continuation of the curve I for a time t>t.sub.end1 shows the
current trace which would result if pumping were continued. As
shown above, the diagnosis is, however, interrupted when the
detected current corresponds to the current I.sub.GL1 which is
determined in step 204.
[0029] However, if the detected current does not correspond to the
pregiven value I.sub.GL1, a leak could be present. On the other
hand, a falsification of the result could also be present because
of ambient conditions and/or tolerances, which can lead to a large
variation of the detected current. Thus, it is for example
conceivable that the current I.sub.GL1 is not yet reached after the
time t.sub.GL1 for a leak of only 0.4 mm (for which no fault need
be indicated) so that a fault announcement would be erroneously
outputted and stored. A case of this kind is shown schematically in
FIG. 2 with respect to the current-time trace identified by 2.
[0030] Oppositely, the threshold T.sub.GL1 could, for example, be
reached in a time t<T.sub.GL1, for example, for other tolerances
and for a leak having a diameter greater than 1 mm, whereby a leak
which would have to be indicated would not be detected.
[0031] In order to exclude errors of this kind and as shown in
connection with the current-time trace identified by 2 in FIG. 2,
the tightness check is continued up to a maximum time
T.sub.GL2>>T.sub.GL1 rather than an immediate fault
announcement and a fault entry in a memory. If a level I.sub.GL2 is
reached after a time t<TGL2 (for example, at a time
t=t.sub.end2), then it can be assumed that no leak having a
diameter .gtoreq.1 mm is present. The original "large leak
suspicion" in step 204 is therefore not confirmed in this case but
was only caused by tolerances and/or the environment. This check
takes place in steps 209, 211 (FIG. 3). It is indicated in this
case that no large leak is present and the tightness check is
interrupted at t.sub.end2. (The continuation of the curve
identified by 2 beyond t.sub.end2 only shows the theoretical
further trace of the current for the case that pumping was
continued).
[0032] If, in contrast, a current-time trace adjusts as shown
schematically in FIG. 2 by the curve identified by 3 (wherein the
level I.sub.GL2 is not yet reached after the time t.sub.GL2), it is
clear that a leak is present for a corresponding application of the
threshold I.sub.GL2 which leak is at least not significantly
smaller than a leak having a diameter of 1 mm. Because of the
higher current level closer to the reference current I.sub.Ref,
tolerances play significantly less of a role in this case. The
"initial suspicion" set at time t=T.sub.GL1 (see step 204) is, in
this case, confirmed and a fault announcement is outputted and
entered in a memory in step 213.
[0033] The applications of the current thresholds I.sub.GL1,
I.sub.GL2 takes place, for example, via earlier measurements,
computations or estimates.
[0034] The current threshold I.sub.GL2 is, for example, specified
as the difference of reference current I.sub.Ref and a value DIGL2.
The value DIGL2 is a function of I.sub.Ref-I.sub.LL. Equivalent to
this, I.sub.GL2 can be determined also as the sum of I.sub.LL and
DIGL2* wherein DIGL2* is likewise a function of
I.sub.Ref-I.sub.LL.
[0035] The advantage of the above-described method is that a leak
can be very precisely detected independently of environmental
conditions or module tolerances. To a certain extent, an "initial
suspicion" as to a leak can be confirmed or disregarded by the
additional introduction of an overpressure into the tank-venting
system.
[0036] The above-described method is explained in combination with
the detection of current values. It is, however, noted that the
method is in no way limited to the detection of current values but
any desired operating characteristic variable of the pump can be
considered especially also the pressure generated thereby for the
detection of leaks in a tank system. The method described above
only sets forth an especially advantageous embodiment.
* * * * *