Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1999-04-05
2002-04-30
Grimley, Arthur T. (Department: 2852)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C073S118040, C073S202000
Reexamination Certificate
active
06381548
ABSTRACT:
TECHNICAL FIELD
The invention concerns a method and a device for measuring a fluid flow, in particular an air flow, flowing in a flow canal to an engine or from an engine, by means of a fluid mass measuring means connected to an evaluation means. Methods and devices of this kind serve for example during operation of an internal combustion engine to measure the air instantaneously drawn in by the engine.
BACKGROUND OF THE INVENTION
Control means which allow optimum possible operation of the engine as a function of the varying requirements of the vehicle driver are used to control modem internal combustion engines, in particular those which are used in motor vehicles. The control means for this purpose record all essential operational parameters of the engine and, depending on the standards of the vehicle driver and taking the properties of the engine into account, transmit control commands to the engine and the associated supply units, which are adapted to the respective operating status. One aim of this so-called “engine management” is to provide optimum performance with low fuel consumption and low emission of noxious substances in every operating situation.
The fuel consumption and emission of noxious substances in an internal combustion engine are essentially determined by the ratio of the air mass and the fuel mass which are drawn in by the engine. Here the air mass flowing to the engine is directly influenced by the vehicle driver who causes adjustment of the choke valve in the air intake. If the choke valve is closed, only a low air mass flows through the intake. With the choke valve fully open, on the other hand, nearly the whole intake cross-section is available for the air flow.
In order to provide a performance which meets the respective requirements of the vehicle driver, a fuel mass corresponding to the air mass flowing to the engine must be supplied to the combustion chamber of the engine which is active at any given time. For this purpose the air mass flowing through the intake is recorded, and the fuel mass which is sufficient for low-exhaust combustion is determined by means of the engine control device. The precision with which the optimum ratio of fuel mass provided for combustion to air mass drawn in is maintained here, depends directly on the exactness with which the air mass flow is measured. It has been established that even minor deviations of the measurement result from the air mass actually supplied lead to a multiplication of the proportion of certain noxious components of the combustion gases. With respect to the legal requirements for the reduction of pollutant emissions, which are getting stricter and stricter, higher and higher demands are therefore being made on the accuracy of measurement of devices with which the air flow in the intake of an internal combustion engine is recorded.
A basic problem in the measurement of a fluid flow which is drawn in by an engine or discharged from it lies in that the curve of the flow is not constant. This is caused inter alia by the fact that as a rule the fluid is not drawn in or conveyed through the engine in a continuous operation. Instead this operation is usually performed in pulsed fashion. As a result, the flow of the fluid is not constant. Added to this is the fact that the resonance properties of the canals through which the fluid flows lead to reverse flows of the fluid.
The flow behaviour of an air stream which is drawn in through an intake common to the combustion chambers of an internal combustion engine is particularly problematic. Since it is not only the combustion chamber which is to be supplied with air and fuel at any given time and which is active with respect to the air intake, but also the other combustion chambers which are connected to this flow canal, due to for example the movement of the inlet valves which control access to the combustion chambers, due to movements of the cylinders in the combustion chambers, due to exhaust gas recirculation, etc. there are pressure pulses which trigger a pulsed air flow in a direction opposite the intake direction. Here the maximum pulsation occurs with maximum choke valve opening or maximum exhaust gas recirculation. The non-uniformity of flow caused inter alia by this disturbance leads for example to considerable impairment of the accuracy of the measurement results in air mass measurement.
Attempts have been made to solve the problems described above in the measurement of a fluid flow by compensating for the pulsation with a corresponding structural arrangement of the measuring sensors. Thus for example a so-called “bidirectional air mass measuring means” in which a temperature sensor is arranged both in front of and behind a heating element in the direction of flow, is known from practical experience for the measurement of an air mass flow drawn in by a motor vehicle internal combustion engine. The heating element is maintained at a constant temperature. If there is no air flow, the same temperature occurs at both temperature sensors. If on the other hand the flow approaches from a certain direction of flow, a temperature difference arises between the sensors. This temperature difference delivers not only information on the mass flow of the air, but also on its direction of flow.
With the fluid mass measuring means described above, of course an improvement in quality of the measurement result can be obtained in comparison with a conventional hot-wire or hot-film air mass measuring means. In practice however it turns out that this improvement is not sufficient to meet the requirements which are getting stricter and stricter.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a method and a device which allow sufficiently precise measurement of a fluid stream flowing through a canal.
With reference to the method, this object is achieved by a method of the kind mentioned hereinbefore, in which in a regularly performed cycle
an operational parameter characterizing the operating status of the engine is recorded,
the data supplied by the fluid mass measuring means are recorded,
at least one extreme value is determined from the data recorded since the beginning of a time period,
an average value is determined from the recorded data,
a pulsation amplitude is determined by dividing the extreme value by the average value, and
the average value is corrected by multiplying it by a correction factor which is selected in dependence on the operational parameter and the pulsation amplitude, from a plurality of correction factors stored in a memory of the evaluation means and being determined in an operation test for the type of fluid mass measuring means in relation to the type of engine.
The invention is based on the concept of reducing the error in the measurement of a mass flow of a fluid by the fact that first an average value is formed from the data recorded within a given time period and then a correction of this average value, which is still subject to error, is made in dependence on certain parameters which characterize the respective operating status of the engine, the properties of the air mass measuring means and the behaviour of the measured fluid flow during the measuring period. The average value corrected in this way is available as the result of fluid mass flow measurement for further processing. In this way the method according to the invention delivers, without elaborate structural alterations to the flow canal, the fluid mass measuring means, the evaluation means or other components which influence the measurement, a measurement result which can be used for example for control of an engine and which lies within the required narrow error tolerance limits.
To prepare for the correction of the previously determined average value, with the method according to the invention an extreme value is recorded. This extreme value is standardised by means of the average value. In this way, according to the invention a quantity referred to as the “pulsation amplitude” is available, which makes a statement about the behaviour of the fluid
Mafrica Sebastien
Ritz Tom
Van Marion Willem
Charioui Mohamed
Cichosz Vincent A.
Delphi Technologies Inc.
Grimley Arthur T.
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