EP1934452B1 - Device for pressure-based load detection - Google Patents

Abstract

The invention relates to a device for intake-pipe-pressure-based determination of the air mass (LM) flowing into the cylinder combustion chamber of an internal combustion engine cylinder of a motor vehicle. Said device comprises a logic unit, by means of which the air mass flowing in can be determined on the basis the intake-pipe pressure by means of a calculation model for load detection. According to the invention, a sensor device (SSD) for directly detecting the intake pipe pressure (PSD) is also provided, which sensor device (SSD) is designed so as to be capable of measuring the intake-pipe pressure only in a lower intake pipe partial region of the internal combustion engine. Also provided is a calculation model (MSD) for indirectly detecting the intake pipe pressure, which calculation model (MSD) is designed so as to be capable of determining, by means of calculation, the intake pipe pressure in an upper intake pipe partial region of the internal combustion engine. According to the invention, the logic unit is designed such that, within the lower intake pipe partial region, the air mass flowing in is determined as a function of the intake pipe pressure measured by means of the sensor device, and that, within the upper intake pipe partial region, the air mass flowing in is determined by means of the intake pipe pressure determined by means of the calculation model.

Description

The invention relates to a device for pressure-based load detection according to the subject-matter of claim 1.

In the load detection is the determination of the air mass, which is sucked for the purpose of combustion in the combustion chamber of a cylinder of an internal combustion engine.

In particular, two methods are to be distinguished here - those based on an immediate measurement of the air mass by means of sensors (eg hot-film air mass sensor, hot-wire air mass sensor or the like), and those which operate without a direct air mass measurement. In methods with direct air mass measurement, the air mass flowing into the intake manifold is measured and the air mass flowing into the cylinder from the intake manifold is calculated by means of a calculation model which describes the intake manifold dynamics. In processes without direct air mass measurement, the measured intake manifold pressure is usually used, from which an air mass model is used to deduce the incoming air mass. These methods are also referred to as pressure-based or suction tube pressure-based methods for load detection. With suction pipe pressure-based methods for load detection, the air mass is determined as a function of the intake manifold pressure and the temperature of the air in the intake manifold. In order to be able to close the intake manifold pressure on the air mass flowing into the combustion chamber complex calculation models are required, which describe the fresh air mass flow from the collector in the intake to the combustion chamber of the cylinder. Parameters to be taken into account here are, in particular, the engine speed, the camshaft position and / or the lift positions and / or lift positions of exhaust and intake valves, the engine temperature and, with supercharged engines: the position of the bypass (Wastegate). The fresh air mass remaining in the cylinders steadily increases with the intake manifold pressure with otherwise identical input parameters (parameters) ( FIG. 2 ).

Known devices for the pressure-based determination of the air mass (load) therefore include suction tube pressure sensors, which can cover or measure the entire intake manifold pressure range.

From the publication WO 03/046356 A2 In the calculation of the air mass flowing into a cylinder in the entire intake manifold pressure range, both a measured and a modeled intake manifold pressure value are jointly considered.

The invention has for its object to provide a device that ensures improved accuracy of the load detection, especially in low load ranges.

The invention is based on the finding that measurement errors occur due to the tolerance of the sensors, which have different effects in the different load ranges. In this case, a distinction between an absolute measurement error, the proportion (amount) over the entire measuring range is always the same and which corresponds to a percentage of the final value, and a relative measurement error, the proportion of which changes depending on the height of the measured value , The relative measurement error increases disproportionately at small intake pipe pressures (loads) and thus has a particularly disadvantageous effect on the accuracy of the load signal. However, especially at low loads, high accuracy of the load signal is extremely important for drivability of a motor vehicle (e.g., in the transition from high loads to idle). The larger the measuring range of a sensor and the greater the gradient of the load over the intake manifold pressure, the stronger the disadvantageous effect described is pronounced. For these reasons, in particular load calculation models of direct-injection supercharged engines are sensitive to existing pressure sensor tolerances. Especially in these engines, the gradient is twice that of non-supercharged engines due to high valve overlaps (i.e., phases in which both intake and exhaust valves are open) and the intake manifold pressure range to be sensed. The device according to the invention is therefore particularly suitable for directly supercharged supercharged internal combustion engines.

According to the invention the object is achieved by the totality of the features of claim 1, while in the dependent claims preferred embodiments of the invention are given. A device according to the invention comprises a

Sensor device (intake manifold pressure sensor) whose measuring range covers only the lower part of the physical intake manifold pressure range of the internal combustion engine. Due to the smaller measuring range, the absolute measuring error is smaller than with a measuring device that covers the entire physical measuring range (total physical intake manifold pressure range). Further, due to the smaller relative measurement error, the error in determining the load as a function of the measured intake manifold pressure is considerably smaller for smaller loads. Outside the pressure range of the pressure sensor used, the intake manifold pressure is determined by means of a calculation model and the required load is calculated on the basis of the calculated intake manifold pressure. The present error due to the calculation model for calculating the intake manifold pressure in the upper intake manifold pressure range is significantly less noticeable, so that clearly outweigh the benefits of increased accuracy in the lower intake manifold pressure range.

In a preferred embodiment, the intake manifold pressure (value) measured in the lower part of the intake manifold pressure range is used directly as an input to a load sensing model to determine the load. Alternatively, the intake manifold pressure can be simulated over the entire intake manifold pressure range via a calculation model, wherein the measured intake manifold pressure is supplied to a regulator device in the lower Saugrohrdruckteilbereich (in which the intake manifold pressure is detected by a sensor device) is adjusted over the modeled intake manifold pressure to the measured intake manifold pressure.

According to one embodiment of the invention for turbocharged engines, the sensor device is preferably designed such that it covers the entire Saugrohrdruckbereich without active supercharger (in this lower pressure range so the intake manifold pressure is determined directly via a measurement), while in the pressure range above the maximum mammoth pressure without active Charger device to intake manifold maximum pressure with active charger device, the intake manifold pressure is determined model-based.

Figur 1:

einen Zylinder einer Brennkraftmaschine mit zugehörigem Ansaug- und Abgastrakt in schematischer Darstellung,

Figur 2:

den schematisch dargestellten Verlauf der der Brennkammer eines Zylinders zugeführten Luftmasse in Abhängigkeit vom Saugrohrdruck,

Figur 3:

die erfindungsgemäße Vorrichtung in einer ersten möglichen Ausführungsform in schematischer Darstellung, und

Figur 4:

die erfindungsgemäße Vorrichtung in einer weiteren möglichen Ausführungsform in schematischer Darstellung.

An embodiment of the invention is illustrated in the drawing and will be described in more detail below. Show it:

FIG. 1:

a cylinder of an internal combustion engine with associated intake and exhaust tract in a schematic representation,

FIG. 2:

the schematically illustrated course of the combustion chamber of a cylinder supplied air mass as a function of intake manifold pressure,

FIG. 3:

the inventive device in a first possible embodiment in a schematic representation, and

FIG. 4:

the device according to the invention in a further possible embodiment in a schematic representation.

In FIG. 1 is schematically shown a cylinder 2 of an internal combustion engine of a motor vehicle together with its associated intake and its associated exhaust tract. In the combustion chamber of the cylinder 2, a piston 4 driven by a crankshaft, not shown, moves up and down. In conjunction with the valve drive represented in simplified form by an inlet valve EV and an outlet valve AV together with the associated valve control, which is preferably designed as a valve control variable with respect to the valve timing and / or the valve strokes, the various cycles of a combustion process are realized.

The intake tract comprises a suction pipe 6 with a collector 6a, wherein in the collector 6a for measuring the intake manifold pressure P _SD is designed as a Saugrohrdrucksensor sensor device S _{SD is} arranged and a controllable throttle 8. In the illustrated embodiment with Ladereihrichtung is seen in the intake further a in the air flow direction In front of the throttle valve 8 arranged boost pressure sensor S _LD , a charge air cooler 10 and a compressor unit 12 of a charger provided.

In the illustrated part of the exhaust system, an exhaust manifold 14 with an integrated turbine unit 16 of the charger and associated controllable bypass 18 (wastegate) is shown.

To control the load or air mass to be supplied due to a load request, it is necessary to know how much air mass actually remains in the combustion chamber of the cylinder for the purpose of combustion. In this case, the air mass flowing into the combustion chamber is not equal to the air mass remaining in the combustion chamber at some operating points, since a so-called over-flushing can occur, especially in supercharger operation due to valve overlaps, in which portions of the air mass supplied to the combustion chamber are still in the intake stroke in the exhaust tract be forwarded and thus not available in the combustion process.

In FIG. 3 a first preferred embodiment of the device according to the invention is illustrated. The device according to the invention is designed such that via the intake manifold pressure P _SD , P _SD 'the incoming air mass LM can be determined by means of a calculation model M _LE for load detection. Furthermore, there is a sensor device S _SD for direct detection of the intake manifold pressure P _SD , which is designed (designed) with respect to its measuring range such that the intake manifold pressure P _SD can only be measured in a lower intake manifold pressure portion of the internal combustion engine. Furthermore, a calculation model M _SD for indirect detection of the intake manifold pressure P _SD 'is present, which is designed such that hereby the intake manifold pressure P _SD ' can be determined by calculation in an upper intake manifold pressure portion of the internal combustion engine. The device is designed such that within the lower Saurohrdruckteilbereichs the incoming air mass LM is determined as a function of the measured by means of sensor S _SD intake manifold pressure P _SD , and that within the upper Saugrohrdruckteilbereichs the incoming air mass LM via the determined by means of calculation model M _SD intake manifold pressure P _SD 'is determined. For this purpose, a monitoring device ÜE is provided, by means of which it is monitored whether the actual intake manifold pressure is within the measuring range of the sensor device S _SD or not. If there is an intake manifold pressure which lies in the measuring range (P _{sensor_min} <x <P _{sensor_max} ) of the sensor device S _SD , the measured intake manifold pressure P _{SD is} forwarded directly to the calculation model M _LE for load _detection for further processing. If there is an intake manifold pressure that is outside the measuring range (x> P _{sensor_max} ) of the sensor device S _SD , an intake manifold pressure P _SD 'is calculated and this forwarded instead of the measured intake manifold pressure P _SD for further processing to the calculation model M _LE for load detection (or for determining the air mass LM). The selection of which intake manifold pressure (measured intake manifold pressure P _SD or model-based calculated intake manifold pressure P _SD ') is relevant and is forwarded is realized via a diverter element W controlled by the monitoring device UE.

Alternatively to the execution according to FIG. 3 the device according to the invention for determining the load can be designed such that it always works with a model-based intake manifold pressure P _SD 'as an input signal for the calculation model M _LE for load detection. For this purpose, for example, a device according to FIG. 4 Use. According to FIG. 4 the intake manifold pressure P _SD 'is always model-based determined, depending on whether the intake manifold pressure is within the measuring range of the sensor device S _SD or not, the calculated intake manifold pressure P _SD ' is adjusted via a correction value K to the measured intake manifold pressure P _SD or calculated intake manifold pressure P _SD 'remains unchanged. In the event that the intake manifold pressure is within the measuring range of the sensor device S _SD , a correction value K for calculating the intake manifold pressure P _SD 'is determined via a balancing regulator R. For this purpose, the correction quantity K is determined by means of a difference between measured intake manifold pressure P _SD and calculated intake manifold pressure P _SD 'fed to balancing regulator R, and the calculated intake manifold pressure P _SD ' is compared to the measured intake manifold pressure P _SD . If the intake manifold pressure value is outside the sensor measurement range, the calculation model M _SD for calculating the intake manifold pressure P _SD 'can not be adjusted to the measured intake manifold pressure P _SD . The unbalanced calculated intake manifold pressure value P _SD 'is then used directly as input to the post-order calculation model M _LE for load detection. For this purpose, the calculation model for load detection instead of the correction value K, a neutral value N is fed to the calculation of the intake manifold pressure is not affected.

Claims (3)

1. A device for determining the air mass (LM) flowing into the cylinder combustion chamber of an internal combustion engine cylinder of a motor vehicle, wherein the inflowing air mass (LM) can be determined by means of a calculation model (M_LE) for detecting the load as a function of the intake manifold pressure (P_SD), and the device contains,

   - a sensor device (S_SD) for the direct detection of the intake manifold pressure (P_SD), with a measurement range, so that the intake manifold pressure (P_SD) can be measured by means of the sensor device (S_SD) exclusively in a lower partial range of the intake manifold pressure of the internal combustion engine,

   - and a calculation model (M_SD) for the indirect detection of the intake manifold pressure (P_SD'), which is configured in such a way that the intake manifold pressure (P_SD') can be determined with this by means of calculation in an upper partial range of the intake manifold pressure of the internal combustion engine,

   - and the device is configured in such a way that, within the lower partial range of the intake manifold pressure, the inflowing air mass (LM) is determined as a function of the intake manifold pressure (P_SD) measured by means of a sensor device (S_SD), and in that within the upper partial range of the intake manifold pressure, the inflowing air mass (LM) is determined by means of the intake manifold pressure (P_SD') determined by means of the calculation model (M_SD).
2. A device according to claim 1, characterised in that the device is configured for a supercharged internal combustion engine, wherein the sensor device (S_SD) has a measurement range, which corresponds to the pressure range up to the maximum intake manifold pressure without an activated supercharger device and the intake manifold pressure (P_SD) in this pressure range can be determined directly by means of the sensor device (S_SD), and wherein the intake manifold pressure (P_SD') in the pressure range above the maximum intake manifold pressure without an activated supercharger device is determined up to the maximum pressure with an activated supercharger device by means of the calculation model (M_SD).
3. A device according to any one of the preceding claims, characterised in that the intake manifold pressure over the entire intake manifold pressure range is determined by means of the calculation model (M_SD) to determine the intake manifold pressure (P_SD'), the determined intake manifold pressure (P_SD') in the lower partial range of the intake manifold pressure being matched to the measured intake manifold pressure (P_SD).

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