Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
2000-03-08
2001-10-09
McCall, Eric S. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
C701S100000
Reexamination Certificate
active
06298718
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns turbocharger systems, such as systems for use with automotive engines. More particularly, the invention concerns a system for diagnosing abnormal compressor performance within the turbocharger.
Turbochargers for diesel and gasoline engines are well known. In a typical automotive turbocharger, radial inflow turbines are driven by engine exhaust gas. The turbine then drives a radial compressor that increases the pressure of intake air provided to the engine. It has been found that under certain operating conditions, the use of a turbocharger improves overall engine efficiency and provides increased power, particularly during vehicle acceleration.
The automotive turbocharger operates in the manner of a centrifugal compressor to provide intake air to the engine at pressures above atmospheric. The performance of the compressor element of a typical automotive turbocharger is usually represented by a pressure ratio versus volume flow graph, with compressor efficiency values superimposed. A performance map of a typical centrifugal compressor is depicted in FIG.
2
. The overall shape of the map, as defined by the constant speed and constant efficiency lines, is the product of years of empirical development to tailor the characteristics of the compressor to particular engine air requirements. The boundary of the compressor map is determined by the air requirements of the engine within a particular speed range, typically between the idle speed and the full rated load speed.
The left and right boundaries of the compressor map define a surge line and a choke line, respectively. Both of these lines define a limit of stable operation for the turbocharger or compressor. Referring to
FIG. 2
, reducing air flow to the compressor within the “surge region” to the left of the surge line, produces intermittent pulsation and interruption of steady air flow through the compressor. Increasing the inlet air flow to the right of the compressor map, namely within the “choke region”, causes the overall efficiency of the compressor to fall to very low values. In either case, namely with air flow falling within either the surge or choke regions, the output or performance of the compressor is not properly matched to the specific engine.
Turbocharger operation within either the surge or choke regions can result from various failures in the engine control and operation system, such as a leak in the air intake system. In addition, passage into these regions can occur during normal operation of the turbocharger and engine, but when subject to extreme environmental conditions. For instance, a turbocharger exhibits a well known “altitude-compensating” ability in which the turbocharger automatically speeds up and supplies an additional volume of less dense air to the engine as the vehicle is operated at increasing altitudes. However, the typical automotive turbocharger has a limit to its altitude-compensating characteristic. In a typical case, operation at altitudes above 12,000 feet can lead to compressor surge, which can interrupt the air supply to the engine, thereby causing loss of power, excessive exhaust smoke and high exhaust temperature.
Compressor surge or choke conditions can be overcome by modifying the engine operation. For example, a surge condition can be corrected by derating the engine fuel, or by increasing the engine speed to thereby increase the mass air flow through the turbocharger. At the other end of the spectrum, a compressor choke condition can be alleviated by derating engine speed. While altering the engine operation can overcome a surge or choke condition, it does so at a cost to engine performance and fuel economy. It is therefore important to accurately detect the existence of a compressor abnormal condition to avoid unnecessary modification of the engine operation.
The identification of a compressor abnormal operating condition is achieved using data from sensors throughout the power plant system. If the data is suspect, an abnormality may be misdiagnosed, or simply missed. It is therefore important to verify the information used to determine the existence of a compressor surge/choke condition. It is equally important to have a compressor diagnosis system and method that provides an accurate measure of the compressor performance. The need exists in the arena of turbocharger systems, particularly for automotive use, for such a diagnosis system and method.
SUMMARY OF THE INVENTION
In order to address this need for diagnosing abnormal turbocharger compressor operation, the present invention contemplates a system and method that first determines whether the sensor data used to gauge compressor performance is accurate. Thus, in one aspect of the invention, the data generated by a plurality of condition sensors is subject to a sequence of rationality tests. In these tests, data generated by particular one of the sensors is compared to a predetermined sensor rationality map. The map defines a region of normal operation bounded by upper and lower boundary lines. If the sensor data falls outside the boundary lines, the sensor fails the rationality test and an error signal is generated.
On the other hand, if one sensor passes its rationality test, a next successive sensor is then subject to its own rationality test. In accordance with the preferred embodiment of the invention, the rationality test for successive sensors will utilize data generated by a previously tested sensor. Thus, the integrity of the data of this previously tested sensor must be verified to ensure a proper rationality test for the successive sensor. In one specific embodiment of the invention, data form the following sensors is ultimately involved in determining whether the compressor is operating normally: boost pressure; ambient pressure; turbo speed, ambient temperature; and mass air flow. In this specific embodiment, the rationality testing begins with the boost pressure sensor, followed sequentially by the ambient pressure, turbo speed/ambient temperature, and mass air flow sensors.
The integrity of the boost pressure sensor is evaluated first because the boost pressure sensor data is used with the ambient pressure data to calculate a pressure ratio. This pressure ratio calculated from the sensor data can be compared with a predetermined threshold pressure ratio value to test the ambient pressure sensor. Similarly, the integrity tests of the boost pressure and ambient pressure sensors precedes the rationality test for the turbo speed/ambient temperature sensors. In the preferred embodiment, the rationality test for the turbo speed and temperature sensors utilizes the actual compressor pressure ratio data for comparison to a sensor rationality map. In this map, the turbo speed is plotted as a function of pressure ratio, with the upper and lower boundary lines defining the region of normal sensor operation. In one feature of the invention, these boundary lines are established by a second order polynomial relating turbo speed to pressure ratio. In one specific embodiment, the turbo speed is normalized to the ambient temperature, so the rationality test can be used to verify the accuracy of both the turbo speed sensor and the ambient temperature sensor.
A similar approach can be taken to test the rationality of the mass air flow sensor data. This rationality test relies upon a sensor map that relates turbo speed to mass air flow, hence the requirement that the turbo speed sensor data be acceptable. A similar second order polynomial can be used to define the upper and lower boundaries of the sensor rationality map. If the sensor passes this last rationality test, then the mass air flow data is determined to be sufficiently accurate to be used in assessing the compressor performance.
In one feature of the invention, a similar rationality analysis is conducted using a compressor performance map. The map is bounded by a surge boundary and a choke boundary line, both of which relate mass air flow to pressure ratio. The actual pressure ratio value is obtained from the
Barnes & Thornburg
Cummins Engine Company, Inc.
McCall Eric S.
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