CN110719993B - Reliability Test of Air Quality Measuring Devices - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (1), wherein a mass flow m of the intake combustion air (11) is measured by an air mass measuring device _A Wherein a pressure-based air mass measuring device (13) is selected, wherein the mass flow m relative to the mass flow through an intake pipe (15) connected between the air mass measuring device (13) and at least one combustion chamber (20) of the internal combustion engine (1) is selected _s To m is aligned with _A Is checked for plausibility (140), wherein the mass flow m is determined in the following operating state _s : in the operating state, the mass flow m of the exhaust gas (12) _R Is recirculated into the intake pipe (15), wherein a mass flow m is additionally determined (130) _R . The invention also relates to an air supply system for an internal combustion engine (1) and to a computer program product.

Description

Reliability Test of Air Quality Measuring Devices

technical field

The invention relates to a method for operating an internal combustion engine, in which a malfunction of an air mass measuring device can be detected, and also to an air supply system for an internal combustion engine which is provided for this purpose.

Background technique

Air mass measuring devices are used in the intake ducts of internal combustion engines in order to ensure optimum filling of the combustion chambers and thus optimum combustion. The power delivered by a petrol engine is proportional to the air mass flow in. The correct measurement of the air mass flow is of great safety relevance. Therefore, the law stipulates that the correct function of the air quality measuring devices should be monitored.

From US 5 291 803 A, DE 199 46 874 A1 and DE 10 2010 044 164 A1 it is known to carry out a plausibility check of the air mass flow determined by the air quality measuring device by means of a comparison value which is determined independently of the air Other sensors of the mass measuring device are obtained. If the air mass flow deviates too far from the comparison value, this can be evaluated as a sign of a malfunction.

Contents of the invention

A method for operating an internal combustion engine has been developed within the scope of the present invention. The mass flow m _A of the intake combustion air (Verbrennungsluft) is measured by an air mass measuring device.

According to the invention, a pressure-based air quality measurement device is selected. A plausibility check of the value of _mA with respect to the mass flow m _S flowing through an intake manifold which is connected between the air mass measuring device and at least one combustion chamber of the internal combustion engine is carried out. In this case, the mass flow m _S is ascertained in the operating state, wherein in the operating state the mass flow m _R of the exhaust gas is recirculated into the intake tract, wherein the mass flow m _R is additionally ascertained.

It has been recognized that the mass flow m _S should nominally be equal to the sum of the mass flow m _A and the recirculated exhaust gas mass flow m _R regardless of the position of the throttle valve arranged between the air mass measuring device and the intake manifold . Furthermore, it has been found that both the mass flow m _S and the exhaust gas mass flow m _R flowing through the intake tract can be provided by the sensors normally present in internal combustion engines (at least with sufficient accuracy for a plausibility test) derived. Thus, redundant sensors can be dispensed with. This provision for monitoring the correct function of the air quality measuring device can thus be fulfilled with little effort.

According to the prior art, for example, the pressure and the temperature of the air before the pressure is relieved by the throttle valve are measured by means of a boost pressure sensor, and this relief pressure is already modeled by means of a throttle equation. By measuring the intake manifold pressure, the mass flow through the throttle valve can then be determined as a comparison value for _mA . In contrast, the plausibility check according to the invention has the advantage that no boost pressure sensor is required, thus saving costs.

Particularly advantageous is the combination with a pressure-based air quality measuring device, for example of the PFM (Pressure-based Flow Meter) type. This air mass measuring device measures the static pressure as a reference pressure, as well as the pressure difference caused by the mass flow, and also measures the temperature of the air. This therefore involves a complex sensor which can simultaneously assume the function of a charge pressure sensor for this purpose, since the static pressure corresponds to the charge pressure and the temperature corresponds to the charge air temperature. Obviously, the additionally present boost pressure sensor can be used for plausibility checking of the air mass measuring device. However, boost sensors are too expensive to be used only as such a control mechanism.

Instead of ascertaining the recirculated exhaust gas mass flow m _R , the exhaust gas mass flow can in principle be set to zero by temporarily disabling the exhaust gas recirculation. However, even with active exhaust gas recirculation, this has significant disadvantages compared to the plausibility check implemented according to the invention. Especially in natural gas engines for commercial vehicles, it is not possible to switch off the exhaust gas recirculation at every operating point of the engine, because the exhaust gas recirculation is used there mainly to reduce the temperature of the combustion chamber or the engine outlet temperature and to protect the turbocharger. Necessary for presses and other components. Operating states in which exhaust gas recirculation is temporarily not required rarely occur during driving operation. In order to carry out a prescribed plausibility check of the air quality measuring device, it may therefore be necessary to briefly force an operating state in which the exhaust gas recirculation is temporarily disabled. This can mean, for example, that the engine torque must be reduced in order to avoid overheating of the internal combustion engine or the exhaust system. On the one hand, this can be unpleasant for the driver, since the full requested engine torque is sometimes not available. On the other hand, when exhaust gas recirculation is disabled, the ignition angle also needs to be adjusted later if necessary, which reduces combustion efficiency and increases fuel consumption.

In a particularly advantageous embodiment of the invention, the mass flow m _S is determined from the air mass in the combustion chamber and the rotational speed n of the internal combustion engine. The mass flow m _S can be obtained, for example, according to the following formula:

Here, the fraction represents the air mass in the combustion chamber under the approximation that air is considered an ideal gas. p _c , V _c and T _c are the pressure, volume and temperature of the air in the combustion chamber, respectively, R _c is the specific gas constant of the air in the combustion chamber, n is the engine speed, and F(n) is multiplication factor.

It is particularly easy to determine p _c , V _c and T _c at the instant when the inlet valve of the combustion chamber is open. V _c then corresponds to the effective working volume of the internal combustion engine, and p _c approximately corresponds to the pressure in the intake manifold measured under standard conditions.

As standard, the temperature is measured in the intake manifold in addition to the pressure. If the inlet valve of the combustion chamber is open, the temperature T _c in the combustion chamber results at least approximately from the temperature in the intake tract and the cooling water temperature T _K of the internal combustion engine, which is also measured under standard conditions. Advantageously, the mass flow m _S is therefore ascertained on the basis of the temperature T _c in the combustion chamber from which the temperature in the intake manifold _TM is ascertained in conjunction with the cooling water temperature T _K of the internal combustion engine.

Exhaust gas recirculation usually does not take place with a constant flow resistance, but is controlled by an exhaust gas recirculation valve, which can be either open or closed. The exhaust gas recirculation valve also has a flow resistance in the open state, so that the exhaust gas recirculation acts as a throttle. The most important variables by which the mass flow m _R of the recirculated exhaust gas can be determined at least approximately are: the pressure and the temperature of the exhaust gas before and after the restrictor. It is therefore advantageous to control the mass flow m _R of the exhaust gas via the exhaust gas recirculation valve and to determine the mass flow m _R taking into account the pressure pv and the temperature T _v of the exhaust gas upstream of the exhaust gas recirculation valve in the direction of flow.

For example, the pressure pv and the temperature T _v of the exhaust gas can be measured. Corresponding sensors can be present, for example, in the context of exhaust gas aftertreatment. However, for the purpose of exhaust gas aftertreatment there are also many characteristic diagrams or calculation models of internal combustion engines which describe the pressure pv and the temperature T _v of the exhaust gas as a function of the operating point of the internal combustion engine. Advantageously, therefore, the pressure pv and the temperature T _v of the exhaust gas are called from a characteristic diagram or a calculation model depending on the operating point of the internal combustion engine.

Advantageously, the ascertainment of the mass flow m _R of the exhaust gas can be significantly simplified by assuming the exhaust gas recirculation valve as a throttle for the ascertainment of the mass flow m _R . Since the pressure and temperature of the recirculated exhaust gas in the intake manifold downstream of the exhaust gas recirculation valve are measured as standard, and at the same time the pressure pv and temperature of the exhaust gas upstream of the exhaust gas recirculation valve in the flow direction are known T _v , so m _R can be directly calculated when additionally knowing the opening cross-section and the emission coefficient of the exhaust gas recirculation valve. The opening cross section and the discharge coefficient of the exhaust gas recirculation valve are known as a function of the valve opening or can be determined, for example, on a test bench.

For example m _R can be calculated using the following throttling equation:

其中

in

Here, A is the opening cross section of the exhaust gas recirculation valve and μ is the discharge coefficient of the exhaust gas recirculation valve. p _M is the pressure in the intake manifold measured under standard conditions, ρ _v is the density of the recirculated exhaust gas upstream of the exhaust gas recirculation valve in the direction of flow. In the approximation that the exhaust gas is an ideal gas, the pressure p _v and the temperature T _v in the flow direction before the exhaust gas recirculation valve are related by the following formula:

p _V ·v _V ＝R _V ·T _V

Here, ν _v is the specific volume of the recirculated exhaust gas, and R _v is the specific gas constant of the recirculated exhaust gas. By means of ν _v =1/ρ _v we get:

Now, for a plausibility check of _mA , in the above-derived formula for the mass flow m _s through the intake pipe with the inlet valve open, the pressure pc can be replaced by the intake pipe pressure, and the pressure pc can be replaced by (air and re The gas constant Rv of the mixture composed of circulating exhaust gas is replaced by the gas constant _Rc . Then, m _A should correspond to the difference between m _s and m _R . If the magnitude of the deviation of _mA from this value exceeds a predetermined limit value, it can be concluded that the mass flow _mA measured by means of the air mass measuring device is faulty. For pressure-based air quality measuring devices which measure static pressure, pressure difference due to mass flow and temperature by means of separate sensors, this also means that at least one of these sensors is defective . One possible cause for this is a change in the sensor characteristic curve due to environmental influences or aging.

As mentioned above, the invention also relates to an air supply system for an internal combustion engine. The air supply system comprises: a turbocharger, an air quality measuring device arranged downstream of the turbocharger in flow direction, a throttle valve arranged downstream of the air quality measuring device in flow direction, The intake manifold after the throttle valve and before the combustion chamber of the internal combustion engine. In addition, an exhaust gas recirculation line (for the exhaust gases of the internal combustion engine) opens into the intake tract.

According to the invention, the air mass measuring device is a pressure-based air mass measuring device and is provided as the sole sensor for measuring charge pressure and charge air temperature.

It has been recognized that the method according to the invention enables in this configuration to carry out a plausibility check of the mass flow _mA of the combustion air measured by the air mass measuring device without the need for a charge pressure sensor as other redundant sensors. Therefore, a boost pressure sensor can be omitted. This omission in turn results in the use of higher-quality pressure-based air quality measuring devices without ultimately incurring any additional costs in production.

In a further advantageous embodiment of the invention, a sensor is connected in the exhaust gas recirculation line for the direct measurement of the mass flow m _R of the exhaust gas conducted through the exhaust gas recirculation line. This can be a relatively cheap sensor since only sufficient accuracy is required for plausibility checks.

As already mentioned above, there are embodiments of the method according to the invention which individually process data which can be measured by sensors which are present anyway or which can be called up from characteristic diagrams. In particular, an embodiment of this kind can thus be realized entirely in software running on the control unit. Other embodiments may be implemented at least in part in software on the control device. Such software can be sold, for example, as an update to existing control devices and is thus a separate product. Therefore, the invention also relates to a computer program product having machine-readable instructions which, when executed on a computer and/or a control device, cause the computer and/or a control device to carry out the method according to the invention.

Description of drawings

Further measures for improving the invention will be shown in more detail below in conjunction with the description of preferred embodiments of the invention with reference to the drawings.

The accompanying drawings show:

Figure 1 shows a schematic diagram of an embodiment of the air supply system and of the method;

FIG. 2 shows an exemplary illustration of an exhaust gas recirculation valve 25 that can be used in the air supply system or in the method.

Detailed ways

According to FIG. 1 , combustion air 11 is drawn in via an exhaust gas turbocharger 26 which is driven by exhaust gas 12 of internal combustion engine 1 . The mass flow _mA of the combustion air 11 is measured by a pressure-based air mass measuring device 13 .

Combustion air 11 is supplied via throttle valve 14 to intake manifold 15 and from there via inlet valve 21 into combustion chamber 20 of cylinder 16 of internal combustion engine 1 , shown as an example in FIG. 1 . Combustion of petrol or gaseous fuel drives a piston 17 which is coupled via a connecting rod 1 to a crankshaft not shown in Figure 1, the delivery of which is not shown for clarity. Exhaust gas 12 is discharged from combustion chamber 20 via discharge valve 22 . The cylinder 16 is surrounded by a cooling water jacket 19, and the temperature T _K of the cooling water jacket 19 is measured.

A portion of the exhaust gas 12 is recirculated into the intake pipe 15 via an exhaust gas recirculation line 28 . Connected in the exhaust gas recirculation line 28 is a temperature sensor 23 which measures the temperature T _v of the exhaust gas 12 upstream of the exhaust gas recirculation valve 25 in the direction of flow. Also connected in the exhaust gas recirculation line 28 is a pressure sensor 24 which measures the pressure p _v of the exhaust gas 12 upstream of the exhaust gas recirculation valve 25 in the direction of flow. Temperature T _v and pressure p _v can optionally also be called up from characteristic map 27 as a function of the operating point of internal combustion engine 1 .

The plausibility check of the mass flow _mA measured by the air mass measuring device is now carried out in several steps. First, in step 110, the temperature _Tc in the combustion chamber 20 is derived from: the intake manifold temperature T _M measured by means of the intake manifold temperature sensor 15b, the temperature T _K of the cooling water jacket 19 and (optionally) Further operating variables of internal combustion engine 1 . In a next step 120, the total mass flow m _S through the intake manifold 15 is determined from the temperature _Tc in combination with the pressure _pM in the intake manifold, which is determined by the intake manifold pressure sensor 15a, and the rotational speed n of the internal combustion engine 1 measured.

In active exhaust gas recirculation, this mass flow m _S consists of a mixture of combustion air 11 and recirculated exhaust gas 12 . Thus, in step 130 the mass flow of recirculated exhaust gas 12 is ascertained from: temperature T _v and pressure p _v of recirculated exhaust gas 12 upstream of exhaust gas recirculation valve 25 in flow direction, intake manifold pressure p _M. Alternatively, this mass flow m _R can also be ascertained directly via the sensor 29 in the exhaust gas recirculation line 28 .

Finally, in step 140 a comparison value m _{A *} of the mass flow m A of combustion air 11 is determined by the difference between the total mass flow m _S in the intake manifold 15 and the mass flow m _R of the recirculated exhaust gas 12 . In the case of normal functioning of the air quality measuring device 13 , _mA * should be the same as _mA except for inaccuracies caused by the approximation. If the magnitude of the deviation between _mA and _mA * is greater than a predetermined limit value, it is concluded that air mass measuring device 13 has a faulty state.

FIG. 2 schematically shows an exhaust gas recirculation valve 25 which can be used in the air supply system shown in FIG. 1 . The valve 25 is formed by a valve body 25a which is passed through by a channel 25b. The channel 25b is connected on the input side to the exhaust gas recirculation line 28 and the channel is connected on the output side to the intake pipe 15 .

The channel 25b can be closed by a valve disk 25d interacting with the valve seat 25c. The valve disk can be moved by a valve rod 25e, which can be moved by means of a servomotor 25f. In the open state of the valve 25, the exhaust gas 12 can pass through the opening area A determined by the position of the valve disk 25d. This position is measured by a travel measurement 25g on the valve stem 25e. The valve 25 is connected to the engine control unit via an electronic connection 25h.

Claims (9)

1. A method for operating an internal combustion engine (1), in which method a malfunction of an air mass measuring device is detected, wherein a mass flow of drawn-in combustion air (11) is measured by the air mass measuring device mA, where a pressure-based air mass measurement device (13) is chosen and the value of mA is plausibly checked against the mass flow mS flowing through the intake duct (15) connected to the air Between a mass measuring device (13) and at least one combustion chamber (20) of the internal combustion engine (1), wherein the mass flow mS is determined in an operating state, wherein the mass of the exhaust gas (12) is determined in the operating state The flow mR is recirculated into the intake pipe (15), wherein the mass flow mR is additionally ascertained, wherein the difference between the mass flow and the mS mass flow mR is ascertained and the difference is calculated with the mass The current mA is compared, wherein a malfunction of the air quality measuring device is detected if the comparison value is greater than a predefined limit value. 2 . The method according to claim 1 , characterized in that the mass flow mS is ascertained from the air mass in the combustion chamber ( 20 ) and the rotational speed n of the internal combustion engine. 3 . 3. The method according to claim 1 or 2, characterized in that the mass flow mS is obtained based on the temperature TC in the combustion chamber (20), and the temperature TM in the intake pipe is combined with the The temperature TC in the combustion chamber is obtained from the cooling water temperature TK of the internal combustion engine (1). 4. The method as claimed in claim 1 or 2, characterized in that the mass flow mR of the exhaust gas is controlled by means of an exhaust gas recirculation valve (25), wherein the position of the exhaust gas (12) in the flow direction is taken into account The mass flow mR is ascertained from the pressure pv upstream of the exhaust gas recirculation valve ( 25 ) and the temperature Tv. 5 . The method according to claim 4 , characterized in that the pressure pv and the temperature Tv of the exhaust gas ( 12 ) are called from a characteristic map or a calculation model ( 27 ) as a function of the operating point of the internal combustion engine ( 1 ). 6 . The method as claimed in claim 4 , characterized in that the exhaust gas recirculation valve ( 25 ) is identified as a throttle for ascertaining the mass flow mR. 7. An air supply system for an internal combustion engine (1), said air supply system comprising: a turbocharger (26), an air mass measuring device (13), a throttle valve (14) and an intake duct (15) , the air quality measuring device is arranged after the turbocharger (26) in the flow direction, the throttle valve is arranged after the air quality measuring device (13) in the flow direction, the intake pipe Arranged downstream of the throttle valve (14) in flow direction and upstream of the combustion chamber (20) of the internal combustion engine (1), wherein the exhaust gas for the exhaust gas (12) of the internal combustion engine (1) is regenerated A circulation line (28) opens into the intake duct (15), wherein the air quality measurement device (13) is a pressure-based air quality measurement device (13), and the air quality measurement device is arranged to use A single sensor for measuring charge pressure and charge air temperature, wherein the air supply system is configured for carrying out the method according to any one of claims 1 to 6 . 8. Air supply system according to claim 7, characterized in that a sensor (29) is connected in the exhaust gas recirculation line (28) for the direct measurement of The mass flow mR of the exhaust gas ( 12 ) in line ( 28 ). 9. A machine-readable storage medium having stored thereon a computer program product comprising machine-readable instructions, which when implemented on a computer and/or on a control device , the machine-readable instructions cause the computer and/or the control device to implement the method according to any one of claims 1-6.

Images