Patent Application
20080236266
The field of this invention relates to diagnosing turbochargers for vehicular engines.
Internal combustion engines, particularly diesel engines are now commonly provided with turbochargers for enhancing the engine performance. When a engine feels sluggish and there is sub par performance, the turbocharger is often the first component suspected and it is often replaced without full diagnosis.
This quick replacement occurs more frequently, when the turbocharger is on a diesel engine of a motor vehicle that is at a remote service center. The turbocharger is often replaced under warranty and sent back to the manufacturer under warranty claims. When the turbocharger is tested after its return, it is often found that there was no problem with the turbocharger and the performance problems of the diesel engine were caused by other reasons and/or other components. Hence, needless expense, time and effort is wasted because there is no adequate in-field diagnosis for a turbocharger.
While it is known to diagnose a turbocharger while still mounted in place on the engine, the prior art diagnostic methods often require complicated electronic and computer equipment to make mathematical determinations and curves interpretations. Such equipment is often not available at all remote or distant service centers.
What is needed is an expeditious field test to determine if a turbocharger is performing according to acceptable parameters using expeditious readings of barometric pressure, ambient temperature, and turbine speed. What is also needed is a method of diagnosing the turbocharger while its housing is still mounted in place in a motor vehicle engine compartment by comparing performance results with a manufacturer's map of acceptable performance.
In accordance with one aspect of the invention, a method of testing a turbocharger to determine if its performance is within acceptable parameters includes the steps of running an engine with its intake manifold not taking air in from a compressor of the turbocharger; providing energy to drive a turbine of the turbocharger from exhaust gases of the engine; opening a compressor outlet of the turbocharger to ambient and providing a restriction within the compressor outlet to raise the pressure in the compressor outlet. One then measures outlet pressure at the compressor outlet upstream of the restriction; measures inlet pressure at the compressor inlet, measures the turbocharger rotational speed, calculates a compressor pressure ratio from the measured outlet pressure and inlet pressure and compares the ratio to map data of the turbocharger to determine if the turbocharger is operating within the acceptable parameters.
Preferably, the method also includes measuring the ambient air temperature and the barometric pressure and compensating the calculation of the compressor ratio to a comparable figure at standard temperature and pressure before comparing it to the map data at standard temperature and pressure. Desirably, the turbocharger has a variable geometry and one takes measurements at different geometries of the turbocharger.
According to another aspect of the invention, a method for field testing a turbocharger on an engine to determine if the turbocharger performance is within acceptable parameters includes the steps of: disconnecting a compressor outlet of the turbocharger so that the engine is naturally aspirated, providing energy to drive a turbine of the turbocharger from the exhaust gases of the engine and placing a restriction downstream in a compressor outlet of the turbocharger. One then measures outlet pressure and temperature at the compressor outlet upstream of the restriction, measures inlet pressure and temperature at an inlet of the turbocharger, measures the ambient barometric pressure, measuring the turbocharger rotational speed, calculates a compressor pressure ratio from the measured outlet pressure, inlet pressure, temperature and ambient barometric pressure and compares the ratio to map data for the turbocharger to determine if the turbocharger is operating within the acceptable parameters.
Reference now is made to the accompanying drawings in which:
Referring now to
The turbocharger 10 has it turbine 14 operably connected to the engine through an exhaust port 16 from exhaust manifold 17 to receive the exhaust gasses from the engine to drive the turbine 14. The turbine 14 is connected to the compressor 18 through the turbo shaft 20.
The compressor inlet 22 has a sensor 24 for measuring the inlet pressure and temperature. The ambient barometric pressure is also measured. The compressor outlet conduit 26 is operably disconnected from the engine intake manifold 19 such as from port 21 such that the engine becomes normally aspirated and draws in ambient air as it operates. The compressor outlet conduit 26 has a restriction 28 placed before its distal open end 30 to provide a pressure increase in the compressor outlet conduit 26 that can be measured. The restriction 28 may be included in a separate conduit member 31 attachable to the compressor outlet conduit 26. A sensor 32 is positioned upstream of the restriction 28 to measure the outlet pressure and the temperature. There is also a sensor 34 to measure the speed of the turbo shaft 20.
The test may be conducted at different speeds of the engine, such as at 1000 revolutions per minute (rpm), 1200 rpm, or 1600 rpm. Using the measured compressor inlet pressure, the measured compressor outlet pressure, the inlet temperature, and the barometric pressure, a compressor pressure ratio is conventionally calculated which then is converted to a flow rate measurement and then compared to the turbocharger manufacturer's compressor map data. The inlet temperature and barometric measurements are used to adjust the flow rate and to compensate against the manufacturer's compressor map data that is conventionally measured and recorded at a standard temperature and atmospheric pressure. In this way, a valid comparison is made between a map at standard temperature and pressure and in-field conditions which may have pressures and temperatures widely varying from standard temperatures and pressures.
The final flow rate is compared against the turbocharger manufacturer's minimum and maximum production flow rates to determine if the tested turbocharger is within specifications. If it is not within acceptable parameters, the turbocharger can then be replaced with the assurance that it is the cause of the diesel engine sub par performance.
If a variable geometry turbocharger is tested at the three illustrated speeds, there will be different compressor pressure ratios with different turbocharger speeds depending on the varied geometry of the turbocharger. The three curves for the three engine speeds 1,000 rpm, 1,200 rpm and 1,600 rpm are shown and may overlap as shown in
If a specific turbocharger that is being tested has no varied geometry, its test at the three engine speeds will produce, only three plotted points, i.e. a single plot point for each engine speed. So for example, with the engine at 1,000 rpm, 1,200 rpm and 1,600 rpm, only three points will show on the graph along the nominal curve. A minimum acceptable valve and a maximum acceptable valve for the compressor ratio is determined for each turbo speed.
If the tested compressor ratios are below the minimum acceptable values for the tested turbocharger speed or above the maximum acceptable value, the tested turbocharger is then considered not performing within acceptable parameters and needs to be replaced. If the compressor ratio however is within the band created between the minimum acceptable values and the maximum acceptable values, the turbocharger is diagnosed as acceptable and does not need to be replaced. Furthermore, the engine sub par performance can be then determined to be caused by another component or reason.
It should be understood that a single service tool may be constructed for use during the diagnosis. The tool may have a compressor inlet tube instrumented for temperature and pressure, with a compressor outlet tube instrumented for temperature and pressure, a barometric pressure sensor and turbo speed adaptor. The turbo speed adaptor is compatible for use on turbochargers that have turbocharger's speed measurement devices built-in or without any such device. If the turbocharger has a built-in speed measuring device, the signal from this device may be used. If there is no built-in speed measuring device, the turbo speed measurement needs to be measured by the service tool.
In this fashion, a turbocharger can be diagnosed and tested in the field to determine if it is working within acceptable parameters before it is replaced.
Variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.
