Description: Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed

Field of the invention
The present disclosure relates to calibration of an air mass flow sensor and more specifically to a method of correction and adaptation of a pressure-based air mass flow sensor (PFM).
Background of the invention
[0002] The pressure-based air mass flow sensor (PFM) measures an air mass flow within the air intake system of an internal combustion engine or a fuel cell system. The PFM is typically installed between the charge air cooler and the EGR throttle valve. A deviation between the air flow value read by the air flow meter and a reference air flow exists because of the air channel and air mass pulsation in the path. Pulsation correction function has to be calibrated to compensate for these pulsations and to ensure this, accurate air mass flow reading from the PFM is compared to a reference air flow across all engine speed and torque zones.

[0003] Generally, charge air cooler used in engine test bed is different from that of vehicle or machine charge air cooler. This is due to packaging and coolant flow constraints at engine test bed. Hence, air system layout difference between engine test bed and vehicle/machine is expected (mainly downstream of the charge air cooler). This leads to variations in air flow measurements by PFM, impacting variation in the exhaust gas recirculation, and further leads to inconsistency in engine emissions.

[0004] Since the PFM cannot detect backflow in a proper way, the deviation between a reference air mass and the value read by PFM without corrections is very high. But with a suitable correction function based on engine speed and the relative pulsation amplitude, the same can be corrected.

[0005] In the prior art US7286925B2 discloses A method and a device for the pulsation correction of measured values of a flow device, which is used to measure pulsating gas flows in internal combustion engines. A raw signal of the flow sensor is fed to an adder of a compensation circuit. The raw signal is at the same time fed to a multiple frequency filter, which has at least one high-pass filter, at least one low-pass filter and at least one band-pass filter. The filtered signals are written into addresses of a correction characteristics map. The values stored in addresses are added to the raw signal by the adder.

[0006] The prior art US20210148296 A1 discloses in an intake air flow rate calculation process, a pulsation correction coefficient calculation process is executed to calculate a pulsation correction coefficient, which is used to compensate for an output error of the air flow meter resulting from an intake air pulsation, based on an engine rotation speed, a throttle opening degree, and an atmospheric pressure, and the intake air flow rate is calculated by correcting the intake air flow rate with the pulsation correction coefficient.
[0007] The prior arts suggests that pulsation amplitude and ratio of pulsation amplitude with respect to engine speed-based correction is available. The available correction factors are specific to engine speed and hence these factors cannot help in the deviation spread reduction further. There are no corrections available based on the absolute air mass, engine speed and injection quantity. Further, there is no adaptive learning function available to accommodate layout changes on the vehicle/machine. Therefore, it calls for a robust improvement measure.

Brief description of the accompanying drawings
An embodiment of the invention is described with reference to the following accompanying drawings:
Figure 1 depicts a system layout for correction and adaptation of a pressure-based air mass flow sensor (PFM).
Figure 2 depicts a flow chart for a method of correction and adaptation of a pressure-based air mass flow sensor PFM
Figure 3 depicts a logic for PFM air mass flow correction
Figure 4 depicts a logic for PFM adaptation on a vehicle/machine layout

Detailed description of the drawings

Figure 1 depicts a depicts a system layout for correction and adaptation of a pressure-based air mass flow sensor (PFM). In the system layout, the cooled air coming from the intercooler is sensed by the PFM. A throttle valve is present at the engine intake passage to control the amount of air flowing to detect a fuel injection amount based on it. The exhaust gas from the engine is recirculated by the Exhaust gas recirculation (EGR) unit. The exhaust manifold is connected to the intake manifold by EGR valve. A control unit regulates the opening and closing of these valves.

Referring to Fig 1, disclosed is a control unit 1 for correction and adaptation of a pressure-based air mass flow sensor (PFM) 2 positioned upstream of a throttle valve 4 and downstream of an intercooler 6, the said control unit 1 configured to: communicate with the PFM 2; obtain a modelled reference air mass (m22) based on a known volumetric efficiency of an engine 7; correct the air mass observed from the PFM 2 based on engine speed and pulsation amplitude; further correct the pulsation corrected air mass observed (M) from the pressure based air mass flow sensor (PFM) 2 by an additional correction based on engine speed, injection quantity and absolute air mass; compute a relative air mass factor (R), an adaptation factor (f) and obtain a dynamic adaptation factor curve by plotting the relative air mass values (R) on axis and adaptation factor (f) on Y axis until the deviation between modelled air mass (m22) and air mass observed (M) from PFM is within a threshold; deactivate an engine gas recirculation (EGR) unit 5 by closing the EGR valve 3; and close a throttle valve 4.
The said control unit calculates the relative air mass (R) by dividing the air mass observed (M) from the PFM 2 with a Maximum air mass flow observed on the engine test bench (M0). The said control unit calculates the adaptation factor (f ) by dividing the modelled reference air mass (m22) with the air mass observed (M) from the PFM.
The control unit 1 comprises of a computation processor to execute the stored programs and a storage unit. The storage unit stores the programs, reference values and inputs from the sensors to execute the invention. The same is in communication with the PFM. The pressure based air mass flow sensor (PFM ) 2 is placed upstream of the throttle valve (that controls the intake of air mass into the engine) 4 and downstream of the intercooler (to reduce the temperature of intake air) 6. To calibrate the PFM 2, the reference air mass (m22) is measured on the engine test bench as a part of initial calibration at a defined standard pressure or temperature by means of a sensor device which may be a rotatory piston gas meter or a thermal air-mass flowmeter or ultrasonic delay time air mass measuring device.
As the air flows through the PFM downstream the intercooler, the deviation in the value read by the PFM and a modelled reference air flow is corrected by the calibrated pulsation correction functions based on engine speed and pulsation amplitude, the same being existing (prior art) logics.
Since these correction factors are specific to engine speed, they do not help in reduction of PFM sensed air mass deviation between the engine test bed (where calibration happens) and the vehicle machine/layout. When these deviations go beyond a set threshold (preferably ± 5%), the control unit intrusively deactivates the Exhaust gas recirculation unit by closing the EGR valves and further closes the throttle valve to initiate an additional correction and adaptation of PFM based on absolute air mass, engine speed and injection quantity. Therefore, an additional correction is done based on the engine speed, injection quantity and absolute air mass. The absolute air mass for the purpose of this specification is the pulsation corrected air mass observed by the PFM sensor. The additional correction and adaptation of PFM are further described herein.
Referring to Figure 2, Fig 2 depicts a flow chart for a method of correction and adaptation of a pressure-based air mass flow sensor (PFM).
Disclosed is a method for correction and adaptation of a pressure-based air mass flow sensor (PFM) positioned upstream of a throttle valve and downstream of an intercooler, the method comprising the steps of: obtaining a modelled reference air mass (m22) 100 based on a known volumetric efficiency of an engine; correcting the air mass observed from a PFM based on engine speed and pulsation amplitude 101; a further correction of pulsation corrected air mass observed from PFM characterized by an additional correction based on engine speed, injection quantity and absolute air mass 102 ; and adaptation of PFM on a vehicle such that air mass observed (M) from the PFM is close to the modelled reference air mass (m22) 103.
The pulsation correction of air mass observed from PFM comprises the steps of : correction of the air mass observed from PFM based on engine speed and pulsation amplitude 101; mapping corrected air mass observed (M) from the PFM versus engine speed 102 a; mapping corrected air mass observed (M) from the PFM versus injection quantity 102b; and further correcting the corrected air mass by multiplying mapped corrected air mass observed (M) from the PFM versus engine speed with mapped corrected air mass observed (M) from the PFM versus injection quantity 102c.
The adaptation of PFM on vehicle comprises the steps of: deactivation of Exhaust gas recirculation valve and throttle valve 103x; Calculating a relative air mass (R) by dividing the air mass observed (M) from the PFM with the Maximum air mass flow observed on the engine test bench 103a; calculating an adaptation factor (f) by dividing the modelled reference air mass (m22) with the air mass observed (M) from the PFM 103b; and obtaining a dynamic adaptation factor curve by plotting the relative air mass values (R) on axis and adaptation factor (f) on Y axis until the deviation between modelled reference air mass and air mass observed (M) from PFM is within a threshold 103c.
The modelled reference air mass (m22) obtained in step 100 is measured on the engine test bench as a part of initial calibration at a defined standard pressure or temperature by means of a sensor device which may be a rotatory piston gas meter or a thermal air-mass flowmeter or ultrasonic delay time air mass measuring device. The step 101 of correcting the air mass observed from a PFM based on engine speed and pulsation amplitude are known in the art. A pulsation correction coefficient may be based on engine speed and pulsation amplitude in order to compensate for an output error of the PFM. The further correction of corrected air mass based on engine speed, injection quantity and absolute air in step 102 is a characteristic step. The same consists of mapping corrected air mass observed (M) from the PFM versus engine speed 102 a; mapping corrected air mass observed (M) from the PFM versus injection quantity 102b. The input values of corrected air mass observed from the PFM and engine speed are mapped. Similarly, the corrected air mass observed from the PFM versus the injection quantity is mapped. A further corrected air mass is thus computed based on the two maps.
The same is followed by adaptation on vehicle 103. The Maximum air mass flow observed on the engine test bench (M0) is project specific and is taken as an input from the engine testbench in step 103x from the reference air mass sensor and the value is fed into the calibration label. Further a relative air mass (R) is obtained by dividing the air mass observed (M) from the PFM with the Maximum air mass flow observed on the engine test bench (M0) 103a followed by calculating an adaptation factor (f) by dividing the modelled reference air mass (m22) with the air mass observed (M) from the PFM 103b. The dynamic adaptation factor curve obtained allows to compute a value such that the further corrected air mass becomes equal to (or becomes close to) the modelled reference air mass. The relative factor ‘R’ between modelled air mass and PFM sensed air mass is calibrated in the ‘X’ axis and correction factors are adapted in the ‘Y’ axis until deviation between modelled air mass and PFM sensed air mass becomes nearly 0 under pre-defined release conditions.

Referring to Figure 3, Figure 3 depicts a logic for PFM air mass flow correction. The input values of corrected air mass observed 50 from the PFM and engine speed 51 are mapped. Similarly, the corrected air mass 50 observed from the PFM versus the injection quantity 53 is mapped. A further corrected air mass 54 is thus computed based on the two maps.
Referring to Figure 4, a logic for PFM adaptation on a vehicle/machine layout. Once the pre-defined release conditions 60 (such as no backflow, closed actuators, shut off air circulation) are satisfied, the control unit obtains the relative air mass (R) 63 by dividing the air mass observed (M) 61 by the PFM with the Maximum air mass flow observed on the engine test bench (M0) 62. The Adaptation factor (f) 64 is calculated by diving the modelled reference air mass m22 with the air mass observed by the PFM.
A dynamic adaptation factor curve is obtained by plotting the relative air mass values (R) 63 on X axis and adaptation factor (f) 64 on Y axis. The deviation between the observed air mass from the PFM 65 and the modelled reference air mass (m22) is observed. If the deviation is close to zero or zero, a final air mass 66 is obtained, if not, then the value is again fed into the X-Axis (R) until the dynamic adaptation factor (f) becomes 1(or close to 1), that is, the PFM observed air mass becomes equal (or close to equal) to the modelled reference air mass.

, Claims:We Claim:
1. A method for correction and adaptation of a pressure-based air mass flow sensor (PFM) positioned upstream of a throttle valve and downstream of an intercooler, the method comprising the steps of:
-obtaining a modelled reference air mass (m22) 100 based on a known volumetric efficiency of an engine;
- correcting the air mass observed from the PFM based on engine speed and pulsation amplitude 101;
-a further correction of pulsation corrected air mass observed (M) from PFM characterized by an additional correction based on engine speed, injection quantity and absolute air mass 102; and
-adaptation of PFM on a vehicle such that the air mass observed (M) from PFM is close to the modelled reference air mass (m22) 103.

2. The method for correction and adaptation of a pressure-based air mass flow (PFM) sensor as claimed in claim 1, wherein, the pulsation correction of air mass observed (M) from the PFM comprises the steps of :
-correction of the air mass observed from PFM based on engine speed and pulsation amplitude 101;
-mapping corrected air mass observed (M) from the PFM versus engine speed 102a;
-mapping corrected air mass observed (M) from the PFM versus injection quantity 102b; and
-further correcting the corrected air mass by multiplying mapped corrected air mass observed from the PFM (M) versus engine speed with mapped corrected air mass observed (M) from the PFM versus injection quantity 102c.

3. The method for correction and adaptation of a pressure-based air mass flow sensor (PFM) as claimed in claim 1, wherein, adaptation of PFM on vehicle comprises the steps of:
- deactivation of Exhaust gas recirculation valve and throttle valve 103x;
-Calculating a relative air mass (R) by dividing the air mass (M) observed from the PFM with the Maximum air mass flow observed on the engine test bench (M0) 103a;
-calculating an adaptation factor (f ) by dividing the modelled reference air mass with the air mass observed (M) from the PFM 103b; and
-obtaining a dynamic adaptation factor curve by plotting the relative air mass values (R) on axis and adaptation factor (f) on Y axis until the deviation between modelled reference air mass (m22) and air mass observed (M) from PFM is within a threshold 103c.

4. A control unit 1 for correction and adaptation of a pressure-based air mass flow sensor (PFM) positioned upstream of a throttle valve 4 and downstream of an intercooler 6, the said control unit configured to:
-communicate with a pressure-based mass flow sensor (PFM) 2 ;
-obtain a modelled reference air mass (m22) based on a known volumetric efficiency of an engine 7;
-correct the air mass observed from a PFM 2 based on engine speed and pulsation amplitude;
- further correct the pulsation corrected air mass observed (M) from a PFM by an additional correction based on engine speed, injection quantity and absolute air mass;
- compute a relative air mass factor (R), an adaptation factor (f) and obtain a dynamic adaptation factor curve by plotting the relative air mass values (R) on axis and adaptation factor (f) on Y axis until the deviation between modelled air mas (m22) and air mass observed (M) from PFM is within a threshold;
- deactivate an engine gas recirculation (EGR) unit 5 by closing the EGR valve 3; and
- close a throttle valve 4;

5. A control unit for correction and adaptation of a pressure-based air mass flow sensor (PFM), as claimed in Claim 6, wherein, the said control unit corrects the air mass observed from the PFM by:
-correcting the air mass observed (M) from PFM based on engine speed and pulsation amplitude;
-mapping corrected air mass observed (M) from the PFM 50 versus engine speed 51;
-mapping corrected air mass observed (M) from PFM 50 versus injection quantity 53; and
-further correcting the corrected air mass by multiplying mapped corrected air mass observed (M) from the PFM versus engine speed with mapped corrected air mass observed (M) from the PFM versus injection quantity.

6. A control unit for correction and adaptation of a pressure-based air mass flow sensor (PFM), as claimed in Claim 6, wherein, the said control unit calculates the relative air mass (R) 63 by dividing the air mass observed (M) 61 from the PFM with the Maximum air mass flow observed on the engine test bench (M0) 62.

7. A control unit for correction and adaptation of a pressure-based air mass flow sensor (PFM), as claimed in Claim 6, wherein, the said control unit calculates an adaptation factor (f) 64 by dividing the modelled reference air mass (m22) with the air mass observed (M) from the PFM.