Intake Air Guide With Intake Air Pressure Ascertainment and Method for Intake Air Pressure Ascertainment

Abstract

An operating method for a fresh-air feed device for an internal combustion engine is configured for feeding fresh air from the environment surrounding the internal combustion engine into at least one combustion chamber of the internal combustion engine. A controllable throttle valve is configured for varying a through-flowable area of the fresh-air feed device and for at least partially shutting off the fresh-air feed device. The device has a compressor which is arranged upstream of the throttle valve in an intended through-flow direction from the environment into the combustion chamber, which is configured for conveying an air mass flow in the intended through-flow direction in the fresh-air feed device. A pre-compressor section of the device is arranged upstream of the compressor, an intermediate section is arranged downstream of the compressor device and upstream of the throttle valve, and a post-throttle section is arranged downstream of the throttle valve. A first air pressure sensor is arranged in the pre-compressor section, and a second air pressure sensor is arranged in the post-throttle section. In a first operating state, a first air pressure is measured via the first air pressure sensor. In a second step in the first operating state, a second air pressure is measured via the second air pressure sensor. Based on the second air pressure, a theoretical air pressure for the intermediate section is ascertained in a manner dependent on a theoretically through-flowable area set by the throttle valve. The theoretical air pressure is compared with the first air pressure or with a comparison value for the first air pressure. In the event of a deviation of the theoretical air pressure from the first air pressure or from the comparison value beyond an error threshold value, a corrective value for the ascertainment of the theoretical air pressure is determined.

Claims

1-4. (canceled)

5. An operating method for a fresh air feed device for an internal combustion engine, wherein the fresh air feed device, which is configured to feed fresh air from an environment surrounding the internal combustion engine into at least one combustion chamber of the internal combustion engine, has a controllable throttle valve, which is configured to change an area through which flow can occur of the fresh air feed device and to at least partially block the fresh air feed device, and wherein the fresh air feed device has a compressor, which is arranged upstream of the throttle valve in a planned flow-through direction from the environment into the combustion chamber and is configured to convey an air mass flow in the planned flow-through direction in the fresh air feed device, and wherein a pre-compressor section of the fresh air feed device is arranged upstream of the compressor, an intermediate section is arranged downstream of the compressor and upstream of the throttle valve, and a post-throttle section is arranged downstream of the throttle valve, the method comprising: in a first operating state of the fresh air feed device, a first air pressure is measured using a first air pressure sensor arranged in the pre-compressor section; in a second step in said first operating state, a second air pressure is measured using a second air pressure sensor arranged in the post-throttle section; and on the basis of said second air pressure, a theoretical air pressure is ascertained for the intermediate section as a function of a theoretical area through which flow can occur, which is set using the throttle valve, comparing the theoretical air pressure to the first air pressure or a comparison value for the first air pressure; and determining a correction value for the ascertainment of the theoretical air pressure in an event of a deviation of the theoretical air pressure from the first air pressure or the comparison value beyond an error threshold value.

6. The operating method according to claim 5, further comprising: in a second operating state of the fresh air feed device, ascertaining a corrected air pressure for the intermediate region, wherein to ascertain the corrected air pressure, the air pressure in said post-throttle section is measured using the second air pressure sensor, and said correction value is used for ascertaining the corrected air pressure.

7. A fresh air feed device for an internal combustion engine configured for feeding fresh air from an environment surrounding the internal combustion engine into at least one combustion chamber of the internal combustion engine, comprising: a controllable throttle valve for changing an area through which flow can occur of the fresh air feed device, which controllable throttle valve is configured to at least partially block the fresh air feed device; and a compressor arranged upstream of the throttle valve in a planned flow-through direction from the environment into the combustion chamber, wherein a pre-compressor section of the fresh air feed device is arranged upstream of the compressor, an intermediate section is arranged downstream of the compressor and upstream of the throttle valve, and a post-throttle section is arranged downstream of the throttle valve; a first air pressure sensor arranged in the pre-compressor section, and a second air pressure sensor arranged in the post-throttle section; and an engine control unit configured to: in a first operating state of the fresh air feed device, measure a first air pressure using the first air pressure sensor arranged in the pre-compressor section; in a second step in said first operating state, measure a second air pressure using the second air pressure sensor arranged in the post-throttle section; and on the basis of said second air pressure, ascertain a theoretical air pressure for the intermediate section as a function of a theoretical area through which flow can occur, which is set using the throttle valve, compare the theoretical air pressure to the first air pressure or a comparison value for the first air pressure; and determine a correction value for the ascertainment of the theoretical air pressure in an event of a deviation of the theoretical air pressure from the first air pressure or the comparison value beyond an error threshold value.

8. An internal combustion engine comprising the fresh air feed device according to claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a part of a schematic fresh air feed device; and

[0022] FIG. 2 is a schematic flow chart for the operating method.

DETAILED DESCRIPTION OF THE DRAWINGS

[0023] Referring to FIG. 1, the fresh air feed device 1 is divided by the compressor device 3 and the throttle valve 6 having the throttle flap 5 into three subsections. The pre-compressor section 2 is located, with respect to the planned flow-through direction 10 through the fresh air feed device 1, thus with respect to an air mass flow from the environment into at least one combustion chamber of an internal combustion engine, before the compressor device 3, which is designed in the present step as the high-pressure stage of an exhaust gas turbocharger. Furthermore, the intermediate section 4 is arranged downstream of the compressor device 3 and upstream of the throttle valve 6 with respect to this planned flow-through direction 10. Furthermore, the post-throttle section 7 is arranged downstream of the throttle valve 6.

[0024] A first air pressure sensor 8, using which the air pressure in the air mass flow in this section is measurable, is arranged in the pre-compressor section 2. Furthermore, a second air pressure sensor 9 is arranged in the post-throttle section 7, using which the air pressure in the air mass flow in this section is measurable. The intermediate section 4 is embodied free of air pressure sensors, a measurement of the air pressure in this region is thus not possible using the proposed fresh air feed device, however, knowing the air pressure in operation of the internal combustion engine improves the control quality of the fresh air feed device.

[0025] Ascertaining the air pressure in operation of the internal combustion engine, thus when the air mass flow flows through the fresh air feed device, is enabled by the measurement of the air pressure using the second air pressure sensor 9. The pressure drop upon flowing through the throttle valve 6 can be determined for the air mass flow 11 passing through the throttle valve via known physical relationships. Such a calculation of the air pressure in the intermediate region 4 presumes the assumption of at least the size of the area through which the air mass flow 11 passes, the so-called effective area. The effective area is dependent here in particular on the degree of opening of the throttle valve. However, if this assumed effective area does not correspond to the actual area through which the air mass flow 11 passes, the calculated air pressure thus also deviates from the actually prevailing air pressure in the intermediate region 11. A deviation of the areas can result due to unavoidable manufacturing tolerances, however, the actual area can also change during the service life, in particular due to deposits, and therefore a calculation calibrated in the new state can deviate from reality after considerable operating time. To avoid an auxiliary air pressure sensor in the intermediate section, the invention therefore proposes a calibration of the determination of the air pressure in the intermediate region 4 which is repeatable in operation. In a first operating state, for this purpose the air pressure is measured in the air mass flow using the first and the second air pressure sensor 8, 9. The first operating state is selected here so that the air pressure in the air mass flow in the pre-compressor section 2 and in the intermediate section 4 is at least approximately equal or deviates by a known pressure difference. Furthermore, the calculation of the air pressure is then carried out for the intermediate region 4, which originates as described from the air pressure measured using the second air pressure sensor 9, and the air pressure thus ascertained is compared to the air pressure ascertained using the first air pressure sensor 8.

[0026] In the event of a deviation in this comparison, the calculation, starting from the air pressure measured using the second air pressure sensor 9, is adapted so that the calculation “matches”, in particular the airflow in the throttle valve is changed. In other words, the calculation of the air pressure for the intermediate section 4 is calibrated in this method sequence.

[0027] If the internal combustion engine is operated in an operating mode different from the first operating mode, thus in a part-load or full-load operating mode, the calibrated calculation method is then applied to determine the air pressure in the intermediate region 4 on the basis of the air pressure measured using the second air pressure sensor 9 and the air pressure for the intermediate section can thus be determined more accurately in this second operating mode than without calibration.

[0028] FIG. 2 shows a flow chart for the proposed operating method. In step 101, the air pressure in the first operating state is measured in the pre-compressor section using the first air pressure sensor 8. In step 102, the air pressure in the first operating state in the post-throttle section is measured using the second air pressure sensor 9. In step 103, the air pressure measured in step 102 is converted in a throttle equation to that in the intermediate region 4 under the assumptions made, in particular the effective area. The air pressure thus ascertained for the intermediate region is compared in step 104 to the air pressure measured in step 101. If this comparison has the result that the two air pressures deviate from one another by more than a predetermined tolerance, the calculation method is thus adapted for the air pressure measured on the basis of the measurement using the second air pressure sensor 9, in particular the size of the effective area is adapted, in particular the actual area through which flow can occur is thus determined.

[0029] Using the adapted calculation method, thus in particular using the calibrated calculation on the basis of the measured value from the second air pressure sensor 9, in step 105, the air pressure is calculated in an operating state deviating from the first operating state.

[0030] In other words, the invention is used in an internal combustion engine in reciprocating piston construction, wherein a throttle flap is installed therein in the fresh air feed device. An air pressure sensor is provided downstream of the throttle flap. However, the air pressure in the air mass flow during the operation of the internal combustion engine upstream of the throttle flap is also relevant for the control of the internal combustion engine or the fresh air feed device. In particular to save costs, this air pressure is not measured using an air pressure sensor, but rather calculated with the aid of a generally known throttle equation. In particular the following parameters are entered in this equation: [0031] air pressure downstream of the throttle valve, [0032] air temperature upstream of the throttle valve, [0033] air mass flow, and [0034] the effective area in the throttle valve through which this air mass flow can flow, this is in particular dependent on a throttle flap position of the throttle valve.

[0035] The effective area is accordingly only indirectly known, since it is unknown in particular whether the throttle valve clogs with contaminants over time, only the set degree of opening or opening angle is known. If the above-mentioned parameters are known, a calculation of the air pressure in the intermediate region is possible. However, deviations can occur between the air pressure ascertained using the proposed calculation method and that actually prevailing in the intermediate region due to sooting/soiling, in particular at the throttle valve, in particular due to soot deposits and due to component variations because of manufacturing tolerances.

[0036] The invention makes use of the principle in an internal combustion engine having an exhaust gas turbocharger such that the air pressure in the intermediate section 4 can be concluded starting from the air pressure measured in the pre-compressor section 2. In the first operating mode, in particular thus in the idle mode of the internal combustion engine, the air pressure is known sufficiently accurately since the compressor device 3 of the exhaust gas turbocharger or the high-pressure stage of the exhaust gas turbocharger hardly builds up charge pressure. An air pressure sensor is provided upstream of this high-pressure stage. The pressure before the throttle flap may be estimated in idle using a simple calculation model. This is not possible in the required accuracy at other operating points of the internal combustion engine. The air pressure in the intermediate region 4 can be determined more accurately with the aid of the calculation method calibrated in idle of the internal combustion engine than without the calibration.

[0037] In other words, an area error (presumed or effective area in the throttle valve in relation to the area through which flow can actually occur) is minimized using the calibration. The area through which flow can occur determined in the first operating mode can be stored in a control unit as the calculation basis and used for air pressure determination in all other operating ranges. In particular, the influence of the component tolerances and the unknown sooting/soiling in the fresh air feed device can be taken into consideration by this method. An air pressure sensor upstream of the throttle valve is not necessary, although an accurate air pressure ascertainment is possible.