METHOD TO ESTIMATE COMPRESSOR INLET PRESSURE FOR A TURBOCHARGER

A method of estimating a compressor inlet pressure for a turbocharger includes: measuring an ambient temperature of air flowing into the compressor; measuring a flow rate of the air into the compressor; measuring a boost pressure of the air from the compressor to an engine; determining a speed of a turbine of the turbocharger; defining a pressure ratio as the ratio of the boost pressure to the compressor inlet pressure; defining a function as the function of the compressor flow rate, the ambient temperature, the compressor inlet pressure and the turbine speed; and equating the pressure ratio and the function and recursively solving for the compressor inlet pressure.

INTRODUCTION

The present disclosure relates to a method of estimating ambient pressure. More specifically, the present disclosure relates to a method of estimating inlet pressure of a compressor for a turbocharger.

Internal combustion engines are supplied with a mixture of air and fuel for combustion within the engine that generates mechanical power. To maximize the power generated by this combustion process, the engine can be equipped with a turbocharger.

A turbocharger includes a turbine that utilizes exhaust from the engine to drive a compressor to compress air flowing into the engine, which forces more air into a combustion chamber of the engine than a naturally aspirated engine. To monitor the performance of the turbocharger, a pressure sensor is employed to measure the ambient pressure of the airflow into the compressor. Such a sensor requires full time on-board diagnostics. Existing diagnostics, however, are complicated and are also very difficult to calibrate. Accordingly, two pressure sensors have been utilized so that the sensors can diagnose each other.

Thus, while current ambient pressure sensors for turbochargers achieve their intended purpose, there is a need for a new and improved method for determining the ambient pressure of the airflow into a compressor of a turbocharger.

SUMMARY

According to several aspects, a method of estimating a compressor inlet pressure for a turbocharger includes: measuring an ambient temperature of air flowing into the compressor; measuring a flow rate of the air into the compressor; measuring a boost pressure of the air from the compressor to an engine; determining a speed of a turbine of the turbocharger; defining a pressure ratio as the ratio of the boost pressure to the compressor inlet pressure; defining a function as the function of the compressor flow rate, the ambient temperature, the compressor inlet pressure and the turbine speed; and equating the pressure ratio and the function and recursively solving for the compressor inlet pressure.

In an additional aspect of the present disclosure, the method further includes measuring an exhaust flow rate of exhaust gas from the engine, measuring an exhaust temperature of the exhaust gas, measuring a wastegate position that controls the flow rate of the exhaust gas that bypasses the turbine, and determining the turbine speed as a function of the exhaust flow rate, the exhaust temperature, the compressor inlet pressure, and the wastegate position.

In another aspect of the present disclosure, recursively solving is based on a linear parameter varying (LPV) dynamic model.

In another aspect of the present disclosure, the LPV dynamic model employs a Kalman filter, the estimated compressor inlet pressure being an output of the Kalman filter.

In another aspect of the present disclosure, the method further includes measuring an ambient pressure with a sensor, and determining a residual as the difference between the estimated compressor inlet pressure and the ambient pressure, the residual providing fault detection isolation.

In another aspect of the present disclosure, the turbine is a variable geometry turbine.

In another aspect of the present disclosure, when the estimated compressor inlet pressure has abrupt changes within a specified time and is greater than the ambient pressure, the fault detection isolation indicates that the variable geometry turbine is stuck open.

In another aspect of the present disclosure, when the estimated compressor inlet pressure has abrupt changes within a specified time and is less than the ambient pressure, the fault detection isolation indicates that the variable geometry turbine is stuck closed.

In another aspect of the present disclosure, when the estimated compressor inlet pressure is less than the ambient pressure, the fault detection isolation indicates that there is a fault in a sensor measuring the boost pressure.

According to several aspects, a method of estimating a compressor inlet pressure for a turbocharger includes: measuring an ambient temperature of air flowing into the compressor; measuring a flow rate of the air into the compressor; measuring a boost pressure of the air from the compressor to an engine; determining a speed of a turbine of the turbocharger; defining a pressure ratio as the ratio of the boost pressure to the compressor inlet pressure; defining a function as the function of the compressor flow rate, the ambient temperature, the compressor inlet pressure and the turbine speed; and equating the pressure ratio and the function and recursively solving for the compressor inlet pressure, wherein recursively solving is based on a linear parameter varying (LPV) dynamic model that employs a Kalman filter, the estimated compressor inlet pressure being an output of the Kalman filter.

In additional aspect of the present disclosure, the method further includes measuring an exhaust flow rate of exhaust gas from the engine, measuring an exhaust temperature of the exhaust gas, measuring a wastegate position that controls the flow rate of the exhaust gas that bypasses the turbine, and determining the turbine speed as a function of the exhaust flow rate, the exhaust temperature, the compressor inlet pressure, and the wastegate position.

In another aspect of the present disclosure, the method further includes measuring an ambient pressure with a sensor, and determining a residual as the difference between the estimated compressor inlet pressure and the ambient pressure, the residual providing fault detection for the ambient pressure sensor or fault isolation to other boosting system failure modes.

In another aspect of the present disclosure, the turbine is a variable geometry turbine.

In another aspect of the present disclosure, when the estimated compressor inlet pressure has abrupt changes within a specified time and is greater than the ambient pressure, the fault detection isolation indicates that the variable geometry turbine is stuck open.

In another aspect of the present disclosure, when the estimated compressor inlet pressure has abrupt changes within a specified time and is less than the ambient pressure, the fault detection isolation indicates that the variable geometry turbine is stuck closed.

In another aspect of the present disclosure, when the estimated compressor inlet pressure is less than the ambient pressure, the fault detection isolation indicates that there is a fault in a sensor measuring the boost pressure.

According to several aspects, a method of estimating a compressor inlet pressure for a turbocharger includes: measuring an ambient temperature of air flowing into the compressor; measuring a flow rate of the air into the compressor; measuring a boost pressure of the air from the compressor to an engine; measuring an exhaust flow rate of exhaust gas from the engine to a turbine; measuring an exhaust temperature of the exhaust gas; measuring a wastegate position that controls the flow rate of the exhaust gas that bypasses the turbine; determining a speed of the turbine as a function the exhaust flow rate, the exhaust temperature, the compressor inlet pressure, and the wastegate position; defining a pressure ratio as the ratio of the boost pressure to the compressor inlet pressure; defining a function as the function of the compressor flow rate, the ambient temperature, the compressor inlet pressure and the exhaust flow, the exhaust temperature, the wastegate position; and equating the pressure ratio and the function and recursively solving for the compressor inlet pressure.

In an additional aspect of the present disclosure, recursively solving is based on a linear parameter varying (LPV) dynamic model.

In another aspect of the present disclosure, the LPV dynamic model employs a Kalman filter, the estimated compressor inlet pressure being an output of the Kalman filter.

In another aspect of the present disclosure, the method further includes measuring an ambient pressure with a sensor, and determining a residual as the difference between the estimated compressor inlet pressure and the ambient pressure, the residual providing fault detection isolation.

DETAILED DESCRIPTION

Referring toFIG. 1, there is shown a turbocharger system10in accordance with the principles of the present disclosure. The turbocharger system10includes a turbocharger12with a turbine14connected to a compressor16with a drive link or shaft18. The turbocharger system10further includes one or more sensors20that measures the flow rate of air, Wc, into the compressor16, the ambient temperature Taand the ambient pressure paof the air flowing into the compressor16, an air cooler22, a pressure sensor24that measures the boost pressure piof the air flowing into an engine28, and a temperature sensor26that measures the boost temperature Tiof the air flowing into the engine28.

The temperature Texand pressure pexof the exhaust gas from the engine28is measured by a temperature sensor30and a pressure sensor32, respectively. The exhaust gas flows to the turbine14with a flow rate Wexis estimated from the measured flow rate of air and injected fuel flow, and the outlet pressure ptoof the exhaust gas from the turbine14is measured by a sensor42. A waste gate40provides a path for a desired amount of the exhaust gas to bypass the turbine14. The path line for air flowing between the compressor16and the engine28and the path line exhaust gas flowing from the engine28to the compressor16are connected by a path line with an exhaust gas recirculation (EGR) cooler36and an EGR valve34that directs some of the exhaust gas from the exhaust path line to the air path line. This line also includes a path line38that allows some of the exhaust gas to bypass the EGR cooler36.

In a typical operation of the turbocharger system10, exhaust gas flows into the turbine14. As the turbine14spins with a speed of Nt, the turbine14drives the compressor16with the drive link or shaft18. As the compressor16spins, air is drawn into the compressor16with a flow rate Wc.

The dynamics of the air flow and exhaust flow through the turbocharger system10can be described by the following set of expressions:

where prcis the pressure ratio of piand pa, ƒ is a function of Wc, Ta, pa, and Nt, and where Ntis written as a function g of Wex, Tex, pa, and WG, which is the position of the wastegate40. Hence, the pressure ratio prccan be expressed as a function H, which is a function of x1(pa), x2(pa), x3as shown above.

Referring toFIG. 2, there is shown a comparison of the actual pressure ratio (pi/pa)actmeasured with the sensors20and24to the estimated pressure ratio (pi/pa)estobtained with the expressions shown in Eq.1described above for various ambient pressure at 100 kPa, 90 kPa; 80 kPa; and 70 kPa.

Referring toFIG. 3, there is shown a process100that implements the expressions Eq. 1 to estimate a compressor inlet pressure pa(k)estfor a step k in a recursive analysis. Specifically, the processes100employs a linear parameter varying (LPV) model that relates engine air and exhaust gas flow with the ambient pressure. The estimated ambient pressure or compressor inlet pressure can then be utilized to diagnose the operation of the sensor20that measures the actual ambient pressure. As such, the H function (114)

is provided as inputs102to the process100. Note that in Eq. 2, the barred values of paare moving averages of the estimated ambient pressure. That is the output110of the process100generates moving averages112that are incorporated into the H function114.

The inputs102are implemented into the process100as the recursive expressions

in a step104, where again k is the kth step of the recursive calculation. The step104calculates a boost pressure pi(k). Example calculations of the boost pressure piin kPa are shown inFIG. 4A. The process100proceeds to a step108, which is a Kalman filter. The Kalman filter108then provides an estimated ambient pressure or compressor inlet pressure pa(k)estas an output110. Example calculations of the output110are shown inFIG. 4B. More specifically,FIG. 4Bshows a comparison of the measured ambient pressure202to the estimated ambient pressure204.

Turning now toFIG. 5, there is shown that the output pa(k)estfrom the Kalman filter108and the measured ambient pressure paactcan be utilized to determine a residual R, which in turn can be employed for system diagnostics to isolate a fault detection. For example, as shown inFIG. 6, if the measured ambient pressure302diverges from the estimated ambient pressure304within a specified vehicle travel distance where the ambient pressure is not expected change much as indicated by its estimated value. then residual or difference between the estimated ambient pressure304and the measured ambient pressure302may indicated that the sensor20that measures the ambient pressure may have a fault or is defective.

As shown inFIG. 7, the system diagnostics can be utilized for other purposes as well. For example, the non-varying measured ambient pressure402indicates that the sensor20is working properly within a limited vehicle travel distance. The estimated ambient pressure404, however, shows a larger change in value, which may indicate that a variable geometry turbine (VGT) is stuck open, whereas the estimated ambient pressure406may indicate that the VGT is stuck closed. Further, the estimated ambient pressure408may indicate that the sensor24is not operating properly.