Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2003-03-10
2004-06-08
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S049700, C073S011040
Reexamination Certificate
active
06745614
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention proceeds from a motor vehicle air spring system having a level control arrangement. Air spring systems with level control arrangements are known in various configurations.
U.S. Pat. No. 5,142,897 discloses an arrangement for level control for a vehicle having air springs. The elevation signals of the elevation sensors are filtered at a time constant in order to improve the control performance of the arrangement. An elevation change is either caused by a load change or by a leak in an air spring. In control operations, usually there is no differentiation as to whether a control request takes place because of a changed load state or because of a leakage.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for detecting especially medium size leaks in a motor vehicle air spring system, that is, with a control, for example, the desired level can still be reached.
The essence of the arrangement according to the invention is a function logic for detecting leakages in the level-controlled air spring system. This function logic is part of the level control arrangement. The operation of this logic is based on a separate treatment of the level control in different driving states.
The operation of the function logic will now be described.
(a) Ignition is Switched Off.
In this state, the level control apparatus switches off after an after-run time of, for example, five minutes. Thereafter, the control apparatus (SG) awakens time controlled, for example, after two hours, and then, for example, after five hours again in order to evaluate the control deviation. If it is detected that the vehicle is too low at least at one vehicle corner (lower threshold value elevation level reached or there is a drop therebelow), the vehicle is controlled at all vehicle corners to the desired level within the tolerance limits or threshold values. Thereafter, the control apparatus switches into the sleep mode.
(b) Ignition of the Vehicle is Switched On.
A continuous level monitoring takes place by the control apparatus (SG). If the tolerance limits are exceeded (for example, there is a drop below the threshold value h
su
) the vehicle is again controlled to the desired level.
With respect to (a), the detection logic according to the invention for detecting leakages in the individual air springs during control apparatus after-run.
When the ignition is switched off (KL15-off) and after the elapse of a fixed time span (for example, five minutes), the control apparatus goes into the sleep mode (current save mode). Before the control apparatus goes into the sleep mode, the air pressure p
1
for each air spring (VL, VR, HL, HR) and the distance h
1
(VL, VR, HL, HR) is measured in the air springs from wheel to wheel at time point t
1
in accordance with the method of the invention and is stored together with the time t
1
. With a renewed awakening of the control apparatus (movement out of the current save mode), only with the detection of an up control requirement at time point t
2
(that is, there is a drop below the lower threshold value h
su
), the air pressures p
2
(VL, VR, HL, HR) are measured in the individual air springs.
For specific circuit arrangements, it is especially advantageous to only then determine the air pressures p
2
when there is a drop below the lower threshold value h
su
of the elevation level at least one vehicle corner. In these circuit arrangements, an air exchange can take place with the corresponding lines and, if required, with the connected air drive for each pressure measurement in an air spring insofar as a pressure drop exists between the pressure in the air spring bellows and the components connected for the pressure measurement. The volume of an air dryer amounts normally to approximately 200 to 300 cm
3
. If the air dryer, for example, has a pressure close to atmospheric pressure, then a drop of the elevation level at the vehicle corner of this air spring bellows is possible when there is an air exchange and a pressure compensation with the connected air spring bellows. In an unfavorable case, a drop of the vehicle corner could take place and lead to a detection of leakage during the determination of a leakage in the sequence of first carrying out a pressure measurement and then determining the elevation level because of the above-described air exchange and pressure compensation with the connected lines and components. In the determination of the leakage in the reverse sequence, this is reliably avoided (first determining the elevation level and then, when necessary, making the pressure measurement) whereby pressurized air and energy are saved.
For evaluating the condition, that air spring is used for the evaluation at whose axle a control requirement was detected and that air spring is selected which lies the lowest, that is, which has the lowest value of h
2
. The conditions for the air spring selected in this manner are as follows:
Condition 1: (p
1
−p
2
)>K
1
wherein K
1
≧0 (Wheel load has not increased, for example, K
1
=0 bar) and
Condition 2: {h(t
1
)−h(t
2
)}*K
3
/(t
2
−t
1
)>K
2
wherein K
2
>0 and K
3
>0 (Elevation level at the corresponding air spring has not decreased, for example, K
2
=1/s and K
3
=10/mm) and,
Condition 3: (t
2
−t
1
)<T
Limit
(Time condition in which a leak can be detected).
If the above conditions are satisfied, a leakage at this air spring is detected and a wheel-specific counter Z
T
is incremented. If, in contrast, no control requirement is detected at t
2
(that is, there is no drop below threshold value h
su
of the corresponding air spring), the corresponding wheel-specific counters Z
T
(VL, VR, HL, HR) are decremented, preferably, minimally to the value 0.
At T
Limit
, it can be inputted how large the leak should be so that this leak can still be detected. The greater T
Limit
is, the lower the leakage values which still can be detected and the lower T
Limit
is, the greater the leakage has to be in order to still be detected via the conditions.
If a wheel-specific counter Z
T
exceeds a threshold value K
4
(for example, the value 4), a leakage fault is detected. A leakage fault is displayed optically and/or acoustically in the interior of the vehicle. The particular leakage fault can be displayed wheel-specifically and/or as a fault for the entire air spring system. A leakage fault is preferably stored in the control apparatus in a permanent memory in order to make it available for later analysis and repair purposes.
For multiple awakening operations, the method is correspondingly repeated in that the values at the instantaneous time point are again assigned to the time point t
2
and to the past time point, the time point t
1
. That is, as a new time point t
1
, the last time point t
2
is selected at which the control apparatus was transferred from the active state into the sleep mode. The new time point t
2
is selected time-controlled after a pregiven time span of, for example, three hours when the control apparatus is again transferred out of the sleep mode into the active state.
Variations:
The time point t
1
does not have to be necessarily determined with the first transfer of the control apparatus after the switchoff of the ignition (KL15=off) into the sleep mode; instead, the time point t
1
can be determined also, for example, with the first awakening of the control apparatus (leaving the sleep mode) and the detection of a control need, that is, there is a drop below the threshold value h
su
of at least one air spring. The time point t
2
shifts then to the next awakening of the control apparatus. The reason is that a separately initiated pressure measurement causes disturbing noises. At the start of each control operation, however, a pressure measurement is anyway carried out. With this variation, no additional pressure measurements (valve switching) are therefore necessary. Furthermore, effects because of the cooling of the air springs can be precluded in that t
1
is so se
Continental Aktiengesellschaft
Frank Rodney
Ottesen Walter
LandOfFree
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