Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
2002-09-05
2004-10-12
McCall, Eric S. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
Reexamination Certificate
active
06802209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an arrangement for calibrating a pressure sensor of a fuel-metering system of an internal combustion engine. The fuel-metering system includes: a high-pressure pump for moving fuel from a low-pressure region into a high-pressure region; injectors, which are controllable in dependence upon operating characteristic variables, for metering fuel from the high-pressure region into combustion chambers of the engine; and, the pressure sensor for measuring the pressure in the high-pressure region.
BACKGROUND OF THE INVENTION
The fuel-metering system is, for example, configured as a common-rail fuel direct-injection system with a presupply pump and a high-pressure pump controlled (open loop and/or closed loop) by demand. The presupply pump is, for example, configured as an electric fuel pump and moves fuel from a fuel supply vessel into the low-pressure region of the fuel-metering system. A prepressure of, for example, 4 bar is present in the low-pressure region. The high-pressure pump pumps the fuel from the low-pressure region into a high-pressure store in the high-pressure region of the fuel-metering system. In the high-pressure store, a pressure of 150 to 200 bar is, for example, present for gasoline fuel and a pressure of, for example, 1,500 to 2,000 bar is present for diesel fuel. Several injectors branch from the high-pressure store and, with a corresponding driving control, inject the fuel from the high-pressure store into the combustion chambers of the engine at the injection pressure present at the high-pressure store. The injectors are drivable in dependence upon specific operating characteristic variables. In the high-pressure store, a pressure sensor is furthermore mounted via which the injection pressure, which is present in the high-pressure store, is determined and a corresponding electrical signal is conducted to a control apparatus of the engine. Finally, a pressure control line branches from the high-pressure region of the fuel-metering system and this pressure control line opens via a pressure control valve into the low-pressure region. A low-pressure line branches from the low-pressure region of the fuel supply system and this low-pressure line leads via a low-pressure controller back into the fuel supply vessel.
Pressure sensors, as they are also utilized in fuel-metering systems, conventionally include a static offset error, that is, the zero point is not reliably indicated. An offset error leads to the situation that the measured value of pressure sensors, especially in the low-pressure region, can have large relative deviations to the actual pressure value.
As a rule, a low pressure is present at the starter phase of direct-injecting rail internal combustion engines. The internal combustion engine is mostly started with a low prepressure generated by the presupply pump and, only later is there a switchover to the high pressure. The fuel mass, which is injected into the combustion chambers by the injectors, is greatly dependent upon the injection pressure present in the high-pressure store. For this reason, this injection pressure should be taken into account in the computation of the injection time in the starting phase. Because of the above-described inaccuracies of the pressure sensor (especially at low pressures), the above is, however, mostly not possible. For this reason and according to the state of the art, the start of a direct-injecting engine, as a rule, takes place without considering the actual pressure present in the high-pressure region.
SUMMARY OF THE INVENTION
From the above-mentioned disadvantages of the state of the art, the task of the present invention results to so calibrate a pressure sensor of a fuel-metering system of an internal combustion engine that the offset error is minimized.
Starting from the method of the above-mentioned state of the art, the invention suggests to solve this task in that a pressure, which is present in the high-pressure region, is applied as a reference pressure and that the pressure, which is present in the high-pressure region, is measured as a sensor pressure by the pressure sensor and that the characteristic line of the pressure sensor is corrected in such a manner that the difference of reference pressure and sensor pressure is minimized.
Advantages of the Invention
The offset error exhibits a large scattering from pressure sensor to pressure sensor. For this reason, no generally valid application is possible for minimizing an offset error for pressure sensors; instead, each pressure sensor must be calibrated individually.
Therefore, according to the invention, an adaptation of the sensor characteristic line is carried out individually for each pressure sensor. The method according to the invention is based on the concept that in the measuring range wherein the pressure sensor exhibits the largest offset error, the reference pressure is determined with a higher accuracy than the sensor pressure can be measured by the pressure sensor. When the sensor characteristic line is so corrected that the difference of difference pressure and sensor pressure is minimized (preferably set to equal zero), then it can be assumed that the pressure sensor, which is calibrated in accordance with the method of the invention, has a higher measuring accuracy than a pressure sensor having a non-adapted sensor characteristic line.
According to an advantageous further embodiment of the present invention, it is suggested that, after measuring the sensor pressure with the pressure sensor and before the correction of the characteristic line of the pressure sensor, a check is made as to whether the measured sensor pressure is within pregiven plausibility limits. If the sensor pressure lies outside of the plausibility limit, then it is assumed that the pressure sensor is defective. In this case, an adaptation of the sensor characteristic line serves no purpose and the calibration of the pressure sensor is interrupted and a corresponding fault announcement is outputted.
Various pressures can be applied as a reference pressure. However, a precondition is that the reference pressure can be determined with a higher accuracy than the sensor pressure can be measured by the pressure sensor.
According to a preferred embodiment of the present invention, it is suggested that the pressure in the high-pressure region is generated in that a presupply pump of the fuel-metering system is activated to generate the low pressure in the low-pressure region and the low pressure is conducted into the high-pressure region. In this way, the prepressure, which is generated by the presupply pump, is also present in the high-pressure region of the fuel-metering system.
The low-pressure controller of the fuel-metering system exhibits, for example, an accuracy of approximately ±6% which corresponds to ±240 mbar for a prepressure of approximately 4 bar. A pressure, which is adjusted at the low-pressure controller, can therefore be determined with a higher accuracy than the sensor pressure can be measured by the pressure sensor in the high-pressure region. The pressure, which is present in the low-pressure region, can, for example, be conducted into the high-pressure region via additional pressure compensating lines or by opening connecting lines already present between the low-pressure region and the high-pressure region. As a reference pressure, the pressure can then advantageously be applied which is adjusted at a low-pressure controller of the fuel-metering system in the low-pressure region.
According to a further embodiment of the present invention, it is suggested that the pressure from the low-pressure region is conducted into the high-pressure region through opened inlet valves and outlet valves. The pressure, which is adjusted at a low-pressure controller of the fuel-metering system in the low-pressure region, is applied as a reference pressure while considering the opening pressure of the inlet valves and outlet valves of the high-pressure pump. This embodiment affords the
Amler Markus
Bochum Hansjoerg
Frenz Thomas
Joos Klaus
Kuesell Matthias
McCall Eric S.
Ottesen Walter
Robert & Bosch GmbH
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