Data processing: measuring – calibrating – or testing – Measurement system – Temperature measuring system
Reexamination Certificate
2002-08-27
2004-12-07
Bui, Bryan (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Temperature measuring system
C702S051000, C702S099000, C702S131000, C702S136000
Reexamination Certificate
active
06829555
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to monitoring the emissions of a supply vessel for storing a volatile medium including a fuel tank system mounted in a motor vehicle. The invention relates especially to a method, a circuit as well as a control apparatus for monitoring the emissions of such a supply vessel during operation.
BACKGROUND OF THE INVENTION
In various areas of technology, supply vessels of the above-mentioned kind have to be checked with respect to their tightness. Accordingly, it is important, for example, in chemical processing technology to check the tightness of tanks for keeping volatile chemical substances for reasons of emission protection. The necessity is especially present in the area of motor vehicle technology to regularly carry out tightness checks on fuel tanks or fuel tank systems utilized in motor vehicles.
In the last-mentioned context, reference is made to the statutory regulations present in parts of the United States for the operation of internal combustion engines. According to these regulations, it is necessary that motor vehicles, which utilize volatile fuels such as gasoline, have a device for monitoring the emission of fuel which can detect a non-tightness or leakage of the size of 0.5 mm in the tank system utilizing only on-board equipment.
U.S. Pat. No. 6,234,152 discloses a method for checking the tightness of a vehicle tank system. Here, an overpressure relative to ambient pressure is introduced into the tank system and a conclusion as to a leakage is made from the subsequent trace of the pressure. Similar methods for checking a tank-venting system of a motor vehicle are presented in U.S. Pat. Nos. 5,890,474 and 6,131,550.
SUMMARY OF THE INVENTION
In the above-mentioned monitoring of emissions and especially the detection of the smallest leakages of the above-mentioned cross section of 0.5 mm, the invention is based on the recognition that the temperature of the volatile medium has a considerable influence on the measuring accuracy in a tightness check (leakage diagnosis). On the one hand, the above-mentioned operational checks, especially in tank systems, should be carried out only within a specific temperature range because, with increasing fuel temperature, the vaporization of the medium increases and, starting at a specific temperature, an overpressure develops in the supply vessel because of vaporization and this overpressure increases the overpressure generated in the tightness check or counters the generated underpressure. In this way, incorrect assumptions with respect to the pressure conditions define a reason for incorrect diagnoses. Accordingly, in the case of a diagnosis carried out with overpressure, an un-tight supply vessel is diagnosed as “tight” and in a diagnosis carried out with an underpressure, a vessel which is indeed tight is erroneously diagnosed as “un-tight”.
In addition, especially for vessels manufactured of plastic, the thermal expansion of the material is to be considered. Based on the expansion characteristic of the plastic, which occurs with increasing temperature, uncontrollable volume changes of the interior vessel space occur and therefore, in turn, incorrect assumptions with respect to the existing internal pressure conditions result.
It is further noted that the term “supply vessel” (for example, in the case of motor vehicle tank systems) includes also function elements, which are significant for the entire tank system, such as lines and seals.
In view of the foregoing, it is an object of the invention to provide a method, a circuit and a control apparatus of the kind set forth initially herein which make possible a monitoring of emissions in supply vessels which is improved compared to the state of the art. Especially, this improvement should be achieved by detecting the actual temperature of the supplied medium with the least possible technical complexity especially by avoiding the use of costly temperature sensors in the supply vessel in order to increase the accuracy of a tightness check carried out on the supply vessel.
The method of the invention is for monitoring the emissions of a supply vessel storing a volatile medium during operation including a fuel supply tank of a motor vehicle. The method includes the steps of: carrying out a tightness check of the supply vessel from time-to-time; determining the temperature of the medium based on at least one characteristic variable utilizing a model computation from time-to-time or cyclically; and, either utilizing the temperature in the tightness check or carrying out the tightness check only when the determined temperature of the medium lies within a pregivable temperature interval.
The invention is based on the idea to include the temperature of the volatile medium in a function check described initially herein as a corrective quantity and model this corrective quantity based on additional characteristic variables, that is, determine this corrective quantity based on a model computation. The additional characteristic variables include variables such as the ambient temperature, the fill level of the supply vessel or, in the case of a motor vehicle, additionally, operating data of the vehicle (vehicle speed or the like) or of the vehicle engine (duration of operation, the length of time an engine has been switched off, engine temperature or the like).
According to a first variation, the invention provides to mathematically determine the real temperature of the medium (T_ktm) from these characteristic variables and to include the value of T_ktm which is so computed as a corrective quantity in the check of the operability of the supply vessel as mentioned above. In a second variation, a check as to operability of the supply vessel is only carried out when the computed value of T_ktm lies within a pregivable temperature interval.
In the above-mentioned variations, the corrective quantity can be determined by means of the model computation before each execution of an operational check or from time-to-time, for example, cyclically. Alternatively, the characteristic variables, which are necessary for the computation of T_ktm, can be stored after a one-time executed model computation in the form of a characteristic variable diagram or in a corresponding table especially for a given construction type of the supply vessel or of a motor vehicle. In this way, the characteristic variables are directly available for subsequent determinations of T_ktm without it being necessary to carry out the above-mentioned model computation anew.
For further refining the suggested method, characteristic variables can be included in the model computation and these characteristic variables include the operation duration or switch-off duration of an internal combustion engine, which is supplied by the supply vessel, as well as, in the case of a vehicle, the road speed, the fuel level in dependence upon the vehicle speed and/or the elevation of the supply vessel or a vehicle having such a vessel. For falling ambient temperatures at a simultaneously relatively high geographic elevation of the vehicle (for example, during travel through mountain passes), one can assume a reduced rate of cooling because of the reduced air pressure. In addition, for vehicles, the characteristic data concerning the particular vehicle manufacturing series can be included such as the type of chassis and/or type of engine. In this way, the following can advantageously form a basis: different flow conditions for a moving vehicle and a different underflow of a vehicle tank caused thereby as well as different mounting positions of the fuel tank and/or of the engine in the vehicle chassis in dependence upon the chassis form. When a shut-down duration of the engine is included in the model computation, it can be provided to store a cool-down curve specific to the model series and to apply this curve as a starting value for the engine temperature when the engine is started again.
It is noted that the warming curve and/or the cool-down curve of the medium in the supply vessel, which is to be consider
Dworzak Uwe
Penschuck Juergen
Bui Bryan
Ottesen Walter
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