Claims:We Claim:
1. A method of calibrating a pressure-based air mass flow (PFM) sensor, the PFM sensor (104) positioned upstream of throttle valve (103) and downstream of an intercooler (105) in a system vehicle layout, the PFM sensor (104) comprising pressure sensing elements and at least a temperature sensing element, the method steps comprising:
computing (201) a modelled reference air mass (m22) for the vehicles based on known volumetric efficiency of the engine;
calculating (202) an air mass (m21) observed at the PFM sensor based on a differential pressure measured by the pressure sensing element and a temperature measured by temperature sensing element respectively;
determining (203) a dynamic tolerance factor by comparing the modelled reference air mass (m22) with calculated air mass (m21) across range of air mass flow regions;
remodeling (204) the dynamic tolerance factor in accordance with the vehicle layout to calibrate the pressure-based air mass flow sensor.

2. The method of calibrating a pressure-based air mass flow sensor in a Vehicle as claimed in claim 1, wherein the modelled reference air mass (m22) is calculating using input from an intake manifold pressure sensor (102) positioned downstream of the throttle valve (103) and the temperature sensing element of the PFM in dependance of ideal gas equation.
3. The method of calibrating a pressure-based air mass flow sensor for a Vehicle as claimed in claim 1, wherein remodeling the dynamic tolerance factor comprises;
Comparing the modelled reference air mass (m22) with the observed air mass as derived from the PFM sensor (104) to derive a relative air mass flow;
Interpolating the dynamic tolerance factor according to a slope between the defined relative mass-flow points to remodel the dynamic tolerance factor.

4. A control unit (107) adapted to calibrate a pressure-based air mass flow (PFM) sensor in a system, the control unit (107) in communication with an intake manifold pressure sensor (102) positioned downstream of the throttle valve (103) and at least the PFM sensor (104) , the PFM sensor (104) positioned upstream of a throttle valve (103) and downstream of an intercooler (105) in the system layout, the PFM sensor (104) comprising pressure sensing elements and at least a temperature sensing element, the control unit (107) adapted to:
compute a modelled reference air mass (m22) for the system based on known volumetric efficiency of engine;
calculate air mass (m21) observed at the PFM sensor based on a differential pressure input received from the pressure sensing elements, a temperature input received from the temperature sensing element respectively and a pre-determined dynamic tolerance factor for range of air mass flow regions retrieved from a memory of the control unit (107);
remodel the dynamic tolerance factor in accordance with the vehicle layout to calibrate the pressure-based air mass flow sensor.

5. The control unit (107) adapted to calibrate a pressure-based air mass flow (PFM) sensor in a Vehicle as claimed in claim 4, wherein the control unit (107) calculates reference air mass (m22) using input received from a intake manifold pressure sensor (102) positioned downstream of the throttle valve (103) and the temperature sensing element of the pressure-based air mass flow sensor in dependance of ideal gas equation.
6. The control unit (107) adapted to calibrate a pressure-based air mass flow (PFM) sensor in a Vehicle as claimed in claim 4, wherein the control unit (107) is further configured to;
Compare the reference air mass (m22) with the observed air mass as derived from the PFM sensor (104) to derive a relative air mass flow;
Interpolate the dynamic tolerance factor according to a slope between the defined relative mass-flow points to remodel the dynamic tolerance factor.
, 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
[0001] The present disclosure relates to a control unit and a method of calibrating a pressure-based air mass flow (PFM) sensor in a Vehicle.

Background of the invention
[0002] The amount of fresh air or the mass flow rate of air entering a fuel-injected internal combustion engine is an important parameter for operation an engine control unit (ECU) to balance and deliver the correct fuel mass to the engine (Torque control) and also ensure compliance with the emission norms by actuation of the Exhaust Gas Recirculation (EGR) valve and throttle valve along with engine related calibrations. A pressure-based air flow meter or alternatively called pressure-based air mass flow sensor (PFM) registers the mass flow of fresh air drawn in by the engine and it is robust for the pulsations caused by opening and closing of the inlet and outlet valves. The PFM is mounted between the charge air cooler and intake throttle valve.

[0003] The PFM is a plug-in sensor assembled into the measuring tube. The PFM, measures the static and dynamic pressures and temperature. PFM calibration contains corrective functions which are available for very large air-flow ranges due to strong engine pulsations. The air mass is calculated directly in the engine control unit. PFM sensor is robust particularly for commercial vehicle application due to the high mass-flows and intake pressures. However, due to the pressure-based approach there is always a trade-off of measurement range with required tolerances and admissible pressure losses. This means that PFM has low tolerance in the full load region and has high tolerances in low loads over lifetime. PFM air mass is calculated by the Bernoulli equation, Ideal gas equation and Conservation of mass. PFM air mass is function of effective cross section area, differential pressure, static pressure, and temperature. Both pressure and temperature are measured by sensors in the vehicle PFM, but the effective cross section area is a calibratable variable that contributes to varying tolerance value. Hence there is a need for an accurate and effective method to calibrate the PFM sensor in a system layout.

[0004] Patent Application DE102016220029A1 titled “Method and apparatus for monitoring a mass air flow sensor of an internal combustion engine with exhaust gas recirculation” discloses a method and apparatus for monitoring a mass air flow sensor of an internal combustion engine (10) having an exhaust-gas recirculation, wherein, in an operating state of the internal combustion engine (10), in which the exhaust-gas recirculation opened, modeled air mass flow value m and #x307;mod() with a measured mass air flow value and, in dependence of the comparison of the modeled air mass flow value (m and #x307;mod) and the measured mass air flow value a fault reaction is triggered.

Brief description of the accompanying drawings
[0005] An embodiment of the invention is described with reference to the following accompanying drawings:
[0006] Figure 1 depicts a portion (100) of a vehicle layout;
[0007] Figure 2 illustrates method steps (200) for calibrating a pressure-based air mass flow (PFM) sensor in a vehicle.

Detailed description of the drawings

[0008] Figure 1 depicts a portion of a system layout. The system layout comprises an internal combustion engine (101), an intercooler (105), a turbocharger (106), a throttle valve (103), a intake manifold pressure sensor (102), a pressure based mass flow meter (PFM (104), in common parlance also called a pressure based air mass flow sensor) along with other components and sensors. For the purposes of this invention, only components and sensors having a bearing on the working of the invention have been elucidated.

[0009] Internal combustion engine (101) uses fuel which combusts inside a combustion chamber with the help of an oxidizer (typically oxygen from the air). These include petrol, diesel, jet fuel, and compressed natural gas. The amount of fresh air entering the internal combustion engine (101) is measured by means of the PFM sensor (104) in the Diesel applications. The PFM sensor (104) is placed proximate to the intake manifold of the internal combustion engine (101).

[0010] The turbocharger (106) is a turbine-driven forced induction device that increases an internal combustion engine (101)’s efficiency and power output by forcing extra air into the combustion chamber. A conventional turbocharger (106) has two principal components a turbine and a compressor. The turbocharger (106)’s compressor draws in ambient air and compresses it before it enters the intake manifold at increased pressure. The intake manifold of the internal combustion engine (101) is in fluid communication with the intercooler (105). The intake manifold receives an extra mass of compressed air from the turbocharger (106) via the intercooler (105). The throttle valve (103) is mounted between the intercooler and the intake manifold and regulates the supply of this extra mass of compressed air to the internal combustion engine (101).

[0001] The intake manifold pressure sensor (102) is positioned downstream of the throttle valve (103). A control unit (107) is in communication with the intake manifold pressure sensor (102) position downstream of the throttle valve (103) and at least the PFM sensor (104). The control unit (107) is adapted to calibrate a pressure-based air mass flow (PFM) sensor, the PFM sensor (104) positioned downstream of a throttle valve (103) and upstream of an intercooler (105) in a system layout. The control unit (107) is logic circuitry implemented as any or a combination of: one or more microchips or integrated circuits interconnected using a parent board, hardwired logic, software stored by a memory device and executed by a microprocessor, firmware, an application specific integrated circuit (ASIC), and/or a field programmable gate array (FPGA).

[0002] The PFM sensor (104) comprises a pressure sensing elements and at least a temperature sensing element. PFM calculates air mass using the Bernoulli equation, Ideal gas equation and Conservation of mass. In accordance with these equations, PFM air mass is function of effective cross section area (Aeff), differential pressure, static pressure, and temperature. Effective cross section area (Aeff) is the only calibratable variable.

This Effective cross section area contributes to a tolerance factor. The Aeff varies for the test bench to when the sensor is actually mounted on the vehicles. Hence the tolerance factor requires remodeling after the PFM sensor (104) is mounted on the vehicle.

[0003] It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0004] Figure 2 illustrates method steps for calibrating a pressure-based air mass flow (PFM) sensor. The system layout has been described in accordance with figure 1. The method of calibrating a pressure-based air mass flow (PFM) sensor in a Vehicle, the PFM sensor (104) positioned downstream of throttle valve (103) and upstream of intercooler (105) in the vehicle layout as described in accordance with figure 1. The PFM sensor (104) comprises a pressure sensing element and at least a temperature sensing element.

[0005] Method step 201 comprises computing a reference air mass (m22) for the vehicles based on known volumetric efficiency of the engine. The reference air mass (m22) is calculated using input from a intake manifold pressure sensor (102) positioned downstream of the throttle valve (103) and the temperature sensing element of the PFM in dependance of ideal gas equation (PV=nRT). For a known volumetric efficiency “V” for the vehicle design or on the test bench, input pressure “P” from the intake manifold pressure sensor (102) and input temperature “T”, ideal gas constant “R” the value of “n” or amount of substance is calculated in terms of the air mass. This calculation happens in the control unit (107) when the PFM sensor (104) is mounted on the vehicle.

[0006] Method step 202 comprises calculating an air mass (m21) observed at the PFM based on a differential pressure, static pressure measured by the pressure sensing elements and temperature measured by temperature sensing element respectively. PFM air mass is calculated by the Bernoulli equation, Ideal gas equation and Conservation of mass. PFM air mass is function of effective cross section area, differential pressure, static pressure, and temperature. Effective cross section area is the only calibratable variable. This Effective cross section area contributes to a tolerance factor.

[0007] Method step 203 comprises determining a dynamic tolerance factor by comparing the reference air mass (m22) with calculated air mass (m21) across range of air mass flow regions. Effective flow area calibrated at a single point [highest mass flow] will not hold good for the lower mass-flow regions because of lesser differential pressures and tolerance of the PFM. This creates higher deviations in air mass sensed compared to reference, mainly at lower air mass flow regions. Hence, multipoint effective area calibration on engine is done to keep the tolerance of the mass flow within the thresholds defined and calculate a dynamic tolerance factor that varies for different mass flow regions.

[0008] Method step 204 comprises remodeling the dynamic tolerance factor in accordance with the vehicle layout to calibrate the pressure-based air mass flow sensor. Remodeling the dynamic tolerance factor comprises comparing the reference air mass (m22) with the observed air mass as derived from the PFM sensor (104) to derive a relative air mass flow. After that the dynamic tolerance factor is interpolated according to a slope between the lowest and highest relative mass-flows to remodel the dynamic tolerance factor.

[0009] In detail the procedure for the adaptation involves multiple steps which are performed by the control unit (107). The relative mass flow threshold which requires adaptation is pre-defined in the control unit (107). Then release conditions such like engine speed gradient, mass-flow gradient, injection quantity gradient, pressure offset of the sensor etc. are also pre-defined and stored in a memory of the control unit (107). When the relative air mass is within the calibrated threshold and all the release conditions are satisfied, intrusive shut-off of the EGR valve, Throttle valve (103) or Exhaust flap is ensured via status monitoring. Following this, the control unit (107) compares the air mass flow read from PFM (m21) with the reference modelled air mass at the intake manifold m22. If the deviation of the mass-flow is more than the calibrated threshold, the deviation is corrected by a factor. The slope gets calculated between the defined relative mass-flow points and the factor gets interpolated

[0010] A person skilled in the art will appreciate that while these method steps describe only a series of steps to accomplish the objectives, these methodologies may be implemented via a specific control unit (107) in the vehicle or centrally through the engine control unit (107). The control unit (107) is adapted to calibrate a pressure-based air mass flow (PFM) sensor in a vehicle. The vehicle layout is elaborated in accordance with figure 1. For clarity it is reiterated that the control unit (107) is in communication with a intake manifold pressure sensor (102) position upstream downstream of the throttle valve (103) and at least the PFM sensor (104) , the PFM sensor (104) positioned upstream of a throttle valve (103) and downstream of an intercooler (105) in a vehicle layout, the PFM sensor (104) comprising a pressure sensing element and at least a temperature sensing element.

[0011] The control unit (107) adapted to compute a modelled reference air mass (m22) for the vehicles based on known volumetric efficiency of the engine; calculate an air mass (m21) observed at the PFM based on a differential pressure, static pressure input received from the pressure sensing elements, a temperature input received from the temperature sensing element respectively and a pre-determined dynamic tolerance factor for range of air mass flow regions retrieved from a memory of the control unit (107); remodel the dynamic tolerance factor in accordance with the vehicle layout to calibrate the pressure-based air mass flow sensor.

[0012] The control unit (107) calculates reference air mass (m22) using input received from a intake manifold pressure sensor (102) positioned downstream of the throttle valve (103) and the temperature sensing element of the PFM pressure-based air mass flow sensor in dependance of ideal gas equation. The control unit (107) is further configured to; compare the reference air mass (m22) with the observed air mass as derived from the PFM sensor (104) to derive a relative air mass flow; interpolate the dynamic tolerance factor according to a slope between the defined relative mass-flows to remodel the dynamic tolerance factor.

[0013] This idea to develop a control unit (107) and a method of calibrating a pressure-based air mass flow (PFM) sensor in a vehicle provides an accurate, robust and closed loop method of calibration for the PFM sensor (104). The present invention not only considers a dynamic tolerance factor due to effective flow area at multiple mass flow regions based on relative mass flow but also adapting the effective area in accordance with the machine/vehicle layout to remodel the dynamic tolerance factor.

[0014] It must be understood that the embodiments explained in the above detailed description are only illustrative and do not limit the scope of this invention. Any modification a control unit (107) and a method (200) of calibrating a pressure-based air mass flow (PFM) sensor in a vehicle are envisaged and form a part of this invention. The scope of this invention is limited only by the claims.