METHOD FOR DETERMINING THE MASS FLOW IN AN INTERNAL COMBUSTION ENGINE

Description

[0001] The invention relates to a method for determining the mass flow in an internal combustion engine using the differential pressure method. A mass flow meter, preferably a combination of one or more sensors for differential pressure, absolute pressure, temperature, humidity, and gas composition, and a computing unit are used to calculate a mass flow signal. The mass flow signal is calculated and filtered by the evaluation unit from the sensor measurements, and the filtered mass flow signal is sent to the engine control unit. Furthermore, the invention relates to an evaluation unit for determining the mass flow in an internal combustion engine, in particular for carrying out a method according to one of the preceding claims. The evaluation unit comprises an interface to a data bus system of an engine control unit of the internal combustion engine.

[0002] Mass flow meters that measure air mass or exhaust gas mass (EGR) in internal combustion engines have to contend with a multitude of disturbances. Gas mass flows in internal combustion engines are subject to massive pressure and flow fluctuations, known as pulsations, as well as rapid changes in temperature and composition. The closer the measurement is taken to the cylinder, the greater these pulsations and measured value fluctuations become. Measuring exhaust gas that is to be fed back into the combustion air, known as exhaust gas recirculation (ARG or EGR), is particularly difficult in this regard.

[0003] The EGR and combustion air flow in many internal combustion engines are measured using the differential pressure principle. With the differential pressure principle, kinetic energy, i.e., the flow velocity, is converted into potential energy, i.e., a pressure gradient (differential pressure). The measured differential pressure is thus a measure of the flow velocity of the mass flow. Due to the quadratic nature of kinetic energy, the resulting pressure gradient is very small, especially at low mass flow velocities and the associated low flow rates.

[0004] Unfortunately, pressure and flow pulsations in combustion engines are also very high, especially at low EGR flow rates. Due to the low engine speeds, which may also be combined with high load values, particularly pronounced pulsations occur. The useful signal to noise ratio is therefore very unfavorable for differential pressure (dp) measurements at these points. Currently, attempts are being made to equalize this using suitable filters that dampen the measurement signal.

[0005] DE 10 2013 106723 A1 discloses a mass flow sensor for determining the mass flow through a line using differential pressure. US 5 646 344 A discloses an engine control system that adjusts the filtering of a pulsating measurement signal of an air mass flow, for example, based on the engine speed. US 2006 / 224298 A1 discloses filtering of a measurement signal of a gaseous mass flow based on an analysis of the pulsations of the current measured values.

[0006] Such filters and their underlying filter parameters are very complex in differential pressure measurement and relate in particular to the filtering of absolute pressure (pabs), differential pressure (dp), temperature (temp), and gas composition before and after the mass flow calculation, as well as to the filtering of the calculated mass flow signal and the calculated medium density. Depending on the type, frequency, and magnitude of the pulsations, an optimal measurement result is achieved through different filtering methods. Such a multipolar filter, which is adapted to the current pulsation characteristics of the motor, offers significant advantages over a fixed filter.

[0007] A multipolar filter performs self-adaptive filtering, the result of which depends on the measurement dynamics: To achieve optimal control performance, the multipolar filter must be adapted to the current measurement situation. This can be achieved through intelligent analysis of the pulsations of the current measured values ​​(dp, pabs, temp, gas composition). For this purpose, the pulsation height and frequency of the raw measured values ​​are analyzed, and the filter parameters for the various filters are then optimized.

[0008] The disadvantage of self-adaptive filtering is that a number of pulsations caused by the valve openings in the cylinder must first be analyzed to determine new filter parameters. These are typically 2-3 ignition timings of all cylinders or 4-6 engine revolutions (at 800 rpm, for example, 4 revolutions correspond to 300 ms). Especially in dynamic load-change operation and at low engine speeds, as is often the case with commercial vehicle engines, this can be too slow to achieve sufficient control quality during load changes.

[0009] However, for emissions-optimized control of combustion engines, high air mass measurement accuracy, high signal quality, and stability of the measured values, coupled with high measurement dynamics, are required. However, according to the current state of the art, these measurement parameters are mutually exclusive. A poor signal-to-noise ratio leads to poor accuracy, while high attenuation and thus control quality leads to low signal dynamics.

[0010] This application aims to optimize the control of internal combustion engines. To this end, it proposes a method according to claim 1 and a mass flow meter according to claim 6. Some preferred embodiments of the invention are recited in the respective subclaims.

[0011] A key fundamental idea of ​​the invention is to propose a method in which the filter parameters of the evaluation unit are matched to a measurement situation, wherein in a first measurement situation the filter parameters are set based on an analysis of pulsations of the current measured values, and wherein in a second measurement situation the filter parameters are set based on current status data of the internal combustion engine transmitted by the engine control unit. Another key fundamental idea is to propose a mass flow meter for determining the mass flow in an internal combustion engine, in which the filter parameters of the mass flow signal are determined based on status data of the internal combustion engine that is available in the engine control unit. Such a mass flow meter preferably has a combination of one or more sensors for differential pressure, absolute pressure, temperature, humidity, and gas composition, and an evaluation unit.Alternatively or additionally, the gas composition can also be calculated by the evaluation unit from a model that determines the EGR rate from a ratio of EGR mass to air mass.

[0012] These basic ideas make it possible to provide a second measurement situation for determining mass flow, using an engine-dynamically adaptive filter. In the second measurement situation, the sensor does not determine filter parameters self-adaptively; instead, they are optimized by a status signal transmitted by the combustion engine, specifically by the engine control unit. At the moment of a load or speed change, the sensor can therefore immediately reset the filter parameters to their optimal values. This ensures optimal control quality of the measured values ​​even in the second measurement situation.

[0013] These features enable an intelligent mass flow meter that internally measures at least the pressure, temperature, and differential pressure and communicates with the engine control unit (ECU) of the combustion engine via a data bus, particularly digitally, for example via CAN bus. The evaluation unit according to the invention not only sends its measured values ​​to the ECU but also receives relevant engine characteristics or status data from it, such as engine speed, load, and the position of the EGR or throttle valve. A status signal or status data of the combustion engine therefore includes data from the combustion engine relating to its current status.In a particularly preferred embodiment, these signals or data also relate to imminent changes in the state of the internal combustion engine, for example due to control signals currently given to the internal combustion engine, which will result in a change in the state of the engine (e.g. load request by the driver).

[0014] Especially at low engine speeds, it is advantageous to filter the values ​​measured by the sensors before calculating the mass flow signal, and to subject the result of the mass flow calculation to further filtering. This allows for the generation of a stable signal for control purposes.

[0015] In addition to measuring flow rates, it is also possible to simulate such flows (regardless of whether EGR or air) using engine models, so-called filling models. This is difficult for engine management because the engine characteristics change during operation. In particular, the aging of EGR coolers and wear on cylinders and seals cause the filling model to become noticeably worse. However, the evaluation unit according to the invention opens up the possibility of integrating a filling model and continuously adapting it. A filling model is particularly interesting where the evaluation unit itself functions poorly, for example with small flow rates and high pulsations due to, for example, low engine speed, high load, or an unfavorable signal-to-noise ratio. In this case, the evaluation unit can switch to a load / engine speed / valve position-based model.

[0016] It is particularly advantageous if the filling model is adapted to the wear of combustion engine components. For this measurement situation, the evaluation unit can ideally optimize itself based on the data obtained in the favorable load range, such as high engine speed and high load, and continuously adapt to the changing engine characteristics due to aging during vehicle operation.

Claims

1. A method for determining the mass flow according to the differential pressure method in an internal combustion engine, wherein a mass flowmeter measures a differential pressure (dp), an absolute pressure (pabs) and the temperature (temp) of the mass flow by means of sensors in order to calculate a mass flow signal, wherein the mass flowmeter communicates with the engine control of the internal combustion engine via a data bus, wherein the mass flow signal is filtered by an evaluation unit of the mass flowmeter and wherein the filtered mass flow signal is sent to the engine control, characterised in that the filtering parameters are calibrated by the evaluation unit to a measurement situation, wherein in a first measurement situation the filtering parameters are set on the basis of an analysis of pulsations of the current measured values and wherein in a second measurement situation the filtering parameters are set on the basis of status data of the internal combustion engine transferred from the engine control and received by the evaluation unit.

2. The method according to claim 1, characterised in that the current status data of the internal combustion engine include a load state and / or a speed of the internal combustion engine and / or a flap setting of the exhaust gas recirculation of the internal combustion engine.

3. The method according to claim 1 or 2, characterised in that a change from the first measurement situation to the second measurement situation takes place with a load change of the internal combustion engine.

4. The method according to any one of the preceding claims, characterised in that in third measurement situation a filling model of the internal combustion engine is used to determine the filtering parameters.

5. The method according to claim 4, characterised in that the filling model is adapted to wear on components of the internal combustion engine.

6. A mass flowmeter for performing a method according to any one of the preceding claims, which performs the method during operation, wherein the mass flowmeter includes sensors for measuring a differential pressure (dp), an absolute pressure (pabs) and the temperature (temp) of the mass flow, wherein the mass flowmeter includes an evaluation unit for calculating a mass flow signal and wherein the mass flowmeter includes an interface with a data bus system of an engine control of the internal combustion engine, characterised in that the parameters for the filtering of the mass flow signal contain status data of the internal combustion engine.

7. A probe according to claim 6, characterised in that the status data include a load state and / or a speed of the internal combustion engine and / or a flap setting of the exhaust gas recirculation of the internal combustion engine.