Method and arrangement for checking the operability of a tank-venting system

The invention is directed to a method and arrangement for checking the operability of a vessel. Pressure is introduced into the vessel utilizing a pressure source having operating variables which vary during operation of the pressure source. These operating variables are detected while the pressure is introduced into the vessel and a conclusion as to a presence of a leak in the vessel is drawn from the operating variables. By utilizing the operating variables, a statement as precise as possible is provided as to the presence of the leak with as little additional equipment as possible.

FIELD OF THE INVENTION 
The invention relates to a method for checking the operability of a vessel 
such as a venting system including a tank, an adsorption filter and a 
tank-venting valve. The adsorption filter has a venting line and is 
connected via a tank-connecting line to the tank. The tank-venting valve 
is connected to the adsorption filter via a valve line with which a 
pressure is introduced into the vessel by means of a pressure source. The 
presence of a leak is concluded from the course of the pressure and/or 
pumped volume flow. 
BACKGROUND OF THE INVENTION 
Vessels must be checked in different areas of technology with respect to 
their operability, that is, with respect to tightness. Thus, in the 
chemical industry or in the process industry for example, it is important 
that the tightness of vessels be checked. Furthermore, it is however also 
necessary to check the tightness, especially of tank systems, in the motor 
vehicle industry. 
For example, the California Environmental Authority (CARB) as well as the 
Environmental Protection Agency (EPA) require a check of the operability 
of tank-venting systems in motor vehicles utilizing on-board diagnostic 
means (On-board Diagnosis, OBD II). Starting with the model year 1996, 
leaks of the size of 1 mm or more must be detected and starting with the 
model year 2000, the detection of leaks starting with a size of 0.5 mm is 
required. Such leaks must, for example, be indicated in the motor vehicle 
and be stored in a memory. 
U.S. Pat. No. 5,349,935 discloses a method and an arrangement for checking 
the operability of a tank-venting system wherein an overpressure is 
introduced into the tank-venting system by means of a secondary air pump. 
The presence of a leak is subsequently concluded from an evaluation of the 
course of the pressure. 
It is disadvantageous with respect to this method and this arrangement that 
a secondary air pump is not present in all vehicles. Furthermore, a 
pressure sensor is necessary to evaluate the course of the pressure. The 
sensor is not only an additional element of the tank-venting system which 
can malfunction but also makes the system more expensive. 
Furthermore, an arrangement for checking the operability of a tank-venting 
system is known wherein the overpressure is introduced into the 
tank-venting system by means of a pump or pressure source. The volume flow 
introduced is measured at a diaphragm by means of a difference pressure 
measurement and, thereafter, a decision is made as to whether a leak is 
present or not from a comparison with a programmable threshold. 
It is a disadvantage of this arrangement that a measurement of an absolute 
volume flow is required which is compared to a threshold. This absolute 
measurement of the volume flow is problematic for the reason that the 
total of tolerances of the flow machine go into the measurement, for 
example, the tolerance of the output volume flow. In addition, a pressure 
sensor for measuring the pressure is required even in this arrangement. 
This sensor not only makes the entire method and arrangement more complex 
but also more expensive. 
A further method is known for checking the operability of a tank-venting 
system wherein a reference leak is switched into the tank-venting system 
and wherein a statement as to the presence of a leak is made from a 
comparison of the measurements with and without the reference leak. 
Also, U.S. Pat. No. 5,347,971 discloses a method for checking the 
operability of a tank-venting system wherein a conclusion as to the 
tightness of the system is reached from a comparison of the measurements 
with and without a reference leak. 
In the two last-mentioned methods, it is problematical that a proper 
reference measurement is not possible between a reference leak and a leak 
present in the tank-venting system because a leak, which is possibly 
present in the tank-venting system, always affects the measurement, even 
when the reference leak is switched in. The reference leak is accordingly 
not a proper reference leak and, instead, should rather be characterized 
as an "offset" leak. With this offset leak, measurement inaccuracies can 
be expected in the check of the operability of a tank-venting system. 
A method wherein the check of the operability of a tank-venting system 
takes place with the aid of a proper reference leak is disclosed in U.S. 
Pat. No. 5,390,645. In this method, the volume flow of a blower motor is 
split so that it simultaneously flows through a reference leak and into 
the tank-venting system. A conclusion as to the presence of the leak is 
reached from a comparison of the flow in the two flow paths wherein the 
flows are detected by through-flow sensors mounted in the respective 
paths. 
However, a disadvantage of this method is that two relatively complex 
through-flow sensors are required to carry out the method. Furthermore, it 
is a disadvantage in this method that the overpressure source is mounted 
in the flow path of the regeneration air of an adsorption filter because 
this regeneration air often contains dirt and water mist, salt water and 
the like which can disadvantageously affect the function of the 
overpressure source. This operates unfavorably on the service life of the 
overpressure source. 
SUMMARY OF THE INVENTION 
It is an object of the invention to improve upon a method for checking the 
operability of a vessel and especially a tank-venting system of the kind 
described above by providing the most precise statement as to the presence 
of a leak in the vessel with the least possible additional equipment. 
Also, a genuine reference measurement is carried out. 
The method of the invention is for checking the operability of a vessel. 
The method includes the steps of: introducing a pressure into the vessel 
utilizing a pressure source having operating variables which vary during 
operational use thereof; detecting the operating variables while 
introducing the pressure into the vessel; and, drawing a conclusion as to 
a presence of a leak in the vessel from the operating variables. 
The detection of the operating variables of the pressure source when 
introducing the pressure and the conclusion as to the presence of a leak 
on the basis of these operating variables affords the special advantage 
that additional equipment such as pressure sensors, through-flow sensors 
and the like are completely unnecessary because a conclusion as to the 
presence of a leak is based solely on the operating variables of the 
pressure source. This additional equipment would, in part, be technically 
complex, subject to malfunction and expensive. 
In principle, it would be possible to detect the operating variables of the 
pressure source initially based on a comparison leak and to store these 
variables in a memory. Then, these operating variables are compared to 
operating variables detected in later measurements and a conclusion as to 
the presence of a leak is drawn. In this way, a conclusion as to the 
presence of a leak can be drawn with relative accuracy. However, it is not 
possible in such a method to consider, for example, the deterioration 
effects of the tank-venting system or of the motor vehicle or to consider 
additional variables, which influence the measurement, such as 
temperature, air pressure of the atmosphere and the like. 
For this reason, an especially advantageous embodiment considers especially 
different operating conditions of the vehicle and especially also 
operating conditions which are caused by deterioration. In this 
embodiment, the tank-venting system and a reference leak are alternately 
charged with an overpressure and the operating variables of the pressure 
source are detected when introducing the pressure into the tank-venting 
system and when introducing the pressure into the reference leak. These 
operating variables are then compared to each other and a conclusion as to 
the presence of a leak is drawn therefrom. 
The presence of a reference leak has the substantial advantage that, on the 
one hand, representative comparison operating variables for an existing 
leak must not be stored in a memory and the memory is therefore not needed 
and, on the other hand, all operating conditions of the vehicle, 
temperature, deterioration and the like can be considered. 
Various embodiments are conceivable with respect to the arrangement of the 
reference leak. 
An especially advantageous embodiment of the invention provides that the 
reference leak is arranged parallelly to the tank-venting system. This 
embodiment makes possible especially an accurate reference measurement as 
described above. 
Another advantageous embodiment provides that the reference leak is 
simulated by a controlled partial opening of the tank-venting valve. In 
this way, an additional reference leak branch in the tank-venting system 
can be omitted. In an especially advantageous manner, and in addition to 
the foregoing, any desired leak size can be realized with the controlled 
partial opening of the tank-venting valve. 
The arrangement of the invention is for checking the operability of a 
vessel and the arrangement includes: a pressure source for charging the 
vessel with a pressure; the pressure source having operating variables 
which vary during operational use thereof; and, a circuit unit for 
detecting and evaluating the operating variables as the pressure is 
introduced into the vessel. 
The operating variables of the pressure source change with the presence of 
a leak. For this reason, a conclusion can be drawn in a simple manner as 
to the presence of a leak by detecting and evaluating the operating 
variables of the pressure source in the circuit unit. This detection and 
evaluation is without additional equipment such as pressure sensors, flow 
sensors and the like. 
To precisely check the operability of a vessel, it has been shown to be 
especially advantageous to mount a reference leak parallel to the vessel. 
A pressure source can be alternately connected to the vessel and to the 
reference leak via a switching device. This is especially the case with 
respect to a tank-venting system and where operating conditions change 
which changes, for example, are caused by changing environmental 
influences or by deterioration. 
Different valves can be used with respect to the switching device. 
Preferably, the switching device is a 3/2-way valve or a 4/2-way valve. 
Another possibility provides that, in the case of a tank-venting system, 
the tank-venting valve is, for example, driven so that it opens, for 
example, via a clocked drive; whereas, the tank-venting system is charged 
by the pressure source with pressure. 
A desired reference leak is simulated by the controlled opening of the 
tank-venting valve whereby the reference leak arranged in the tank-venting 
system can be omitted. Furthermore, in this case, the above-mentioned 
switching device in the form of a 3/2-way valve or a 4/2-way valve can be 
omitted and replaced by a conventional check valve which is mounted 
parallel to the line branch leading to the pressure source. 
With respect to the pressure source, the most different embodiments are 
possible. An advantageous embodiment provides that the pressure source is 
an electrically-driven pump. 
The current consumed and/or the rpm of the pump and/or the voltage applied 
to the pump can be detected as operating variables and be evaluated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
The method and the arrangement of the invention are explained below in the 
context of a tank-venting system. It is understood that the invention 
applies to any desired vessel which is intended to be checked as to 
operability, namely, tightness. 
A tank-venting system of a motor vehicle tank system is shown in FIG. 4 and 
includes: a tank 10, an adsorption filter 20 as well as a tank-venting 
valve 30. The adsorption filter 20 can, for example, be an active charcoal 
filter which is connected to the tank 10 via a tank connecting line 12 and 
has a venting line 22 connected to the ambient. The tank-venting valve is, 
on the one hand, connected to the adsorption filter 20 via a valve line 24 
and, on the other hand, to an intake pipe 40 of an internal combustion 
engine via a valve line 42. 
Hydrocarbons form in the tank 10 by vaporization and deposit in the 
adsorption filter 20. The tank-venting valve 30 is opened to regenerate 
the adsorption filter 20 so that, because of an underpressure present in 
the intake pipe 40, air of the atmosphere is drawn by suction through the 
adsorption filter 20 whereby the hydrocarbons, which had deposited on the 
adsorption filter 20, are drawn by suction into the intake pipe 40 and 
supplied to the internal combustion engine (not shown). 
A first embodiment of the arrangement of the invention for checking the 
operability of a tank-venting system is shown in FIG. 1. 
As shown in FIG. 1, such an arrangement includes a pump 50 which is 
connected to a circuit unit 60. A switchover valve is connected downstream 
of the pump 50 and is in the form of a 4/2-way valve 70. On the one hand, 
the adsorption filter 20 is connected downstream of the 4/2-way valve 70 
via the venting line 22 while, on the other hand, a reference leak 80 is 
connected downstream of the 4/2-way valve. In its first switch position, a 
connection between the pump 50 and the tank-venting system is established 
via the venting line 22 and the adsorption filter 20 so that the 
tank-venting system can be charged with pressure by the pump 50. In its 
other switch position, the reference leak 80 can be charged with pressure 
by the pump. 
During the introduction of a pressure, the current input of the pump can, 
for example, be detected by the circuit shown in FIG. 1 which is part of 
the circuit unit 60. The current input of the pump can be detected by 
tapping the voltage at a measurement resistor R.sub.meas, which is 
connected in the emitter line of a transistor driving the pump 50. The 
current input is a measure for the pump volume flow of the pump 50. 
This pump volume flow is, on the one hand, determined when the tank-venting 
system is charged with pressure by the pump 50 and, on the other hand, 
when the reference leak 80 is charged by the pump 50 with pressure. A 
comparison of the two quantities facilitates a determination as to the 
presence of a leak in the tank-venting system in a manner described 
hereinafter. 
In FIG. 2, another embodiment of the arrangement of the invention is shown 
which differs from the arrangement shown in FIG. 1 only in that a 3/2-way 
valve 72 is used in lieu of a 4/2-way valve 70. In this case, the 
reference leak 80 is arranged parallel to the 3/2-way valve. 
It is understood that the size of the reference leak 80 is so selected that 
it corresponds precisely to the size of the leak to be detected. 
The reference leak 80 can then, for example, also be a part of the 
switchover valve (70, 72) such as a narrowing 82 of a channel 84 as shown 
schematically in FIG. 1a so that an additional reference component branch 
can be omitted in this case. 
The method for checking the operability of a tank-venting system is 
explained with respect to the flowchart shown in FIG. 3. After the start 
of the program in step 100 and the switch-on of the pump motor in step 
110, a time delay of approximately three seconds first elapses in step 
120. This step serves to adjust the steady-state condition. Thereafter, in 
step 130, the pump current v.sub.p is determined from an operating 
characteristic variable of the pump motor 50 and stored as a reference 
pump flow v.sub.o. Steps 110 to 130 define a reference measurement for a 
pregiven leak 80. 
In step 140, the tank-venting valve 30 is closed and the 4/2-way valve 70 
shown in FIG. 1 or the 3/2-way valve 72 shown in FIG. 2 is actuated (step 
150) so that the tank-venting system can be subjected to a pressure. 
Thereafter, in step 160, a further delay time of approximately 20 seconds 
elapses which serves to fill the tank and to await the adjustment of a 
steady-state condition. Thereafter, in step 170 the pump flow v.sub.p of 
the pump 50 is determined again from motor operating variables and stored 
as a measurement pump flow v.sub.1. 
Thereafter, in method step 180, a comparison is made of the reference pump 
flow v.sub.o of step 130 and the measurement pump flow v.sub.1 of step 
170. A comparison is made as to whether the reference pump flow v.sub.o, 
(step 130) is less or equal to the measurement pump flow v.sub.1 of the 
tank-venting system (step 170). If this is the case, then a fault 
announcement is outputted in step 190 (for example, a leak announcement) 
and the switchover valve is switched back in step 210 and the pump motor 
50 is switched off in step 220. If this is not the case, then an 
announcement of the content "system tight" (step 200) is outputted and 
then, in step 210, the switchover valve is switched back and the motor 50 
is switched off (step 220). The method is then ended in step 230. 
The advantage of this method is a genuine reference measurement with a 
reference leak 80. Additional pressure sensors, flow sensors or the like 
become unnecessary because of the detection of the pump flow of the pump 
50 via operating variables of the pump, such as the current input or the 
rpm, voltage at the pump and the like. 
A further embodiment is shown in FIG. 5 and provides that the tank-venting 
valve 30 can be controlled to be openable to simulate a leak of any 
desired size. In this case, switchover valves such as the 4/2-way valve 
(shown in FIG. 1) or the 3/2-way valve (shown in FIG. 2) can be omitted 
and it is only necessary to provide a shutoff valve 86 in a line branch 
parallel to the pressure source, which is closed when a check as to 
operability of the tank-venting system is undertaken, and which is open in 
the remaining cases. In FIG. 5, a control unit 88 contains a 
microprocessor and outputs control signals to the tank-venting valve 30 
and the shutoff valve 86. 
It is emphasized that it is irrelevant in which sequence the measurement of 
the pump flows takes place. It is unimportant as to the quality of the 
measurement whether the reference measurement is first made or the 
measurement of the tank-venting system or vice versa. 
It is emphasized also that the pressure source is not mounted in the flow 
path of the regeneration air of the adsorption filter 20 when no check as 
to operability of the tank-venting system is undertaken so that dirt, 
water, vapor, salt water and the like (which can be constituents of the 
regeneration air) cannot disadvantageously affect the pump 50, for 
example, by shortening the service life thereof. 
It is understood that the foregoing description is that of the preferred 
embodiments of the invention and that various changes and modifications 
may be made thereto without departing from the spirit and scope of the 
invention as defined in the appended claims.