Measuring and testing – Vibration – Sensing apparatus
Patent
1995-07-20
1997-06-03
Williams, Hezron E.
Measuring and testing
Vibration
Sensing apparatus
364565, 73488, G01N 2904, G01H 100, G01H 1100
Patent
active
056356463
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Engine turbochargers normally operate at extremely high speeds of the order of 120,000 revolutions per minute. To obtain maximum power from the engine, it is essential that the speed of the turbocharger unit be as high as possible; the higher the speed, the greater the quantity of air supplied to the engine. However, the speed is subject to a highly critical threshold which must not be exceeded. If this occurs, bearing life will be drastically reduced by breakup of the lubricating oil film.
In predelivery testing of engines, it is desirable to measure the speed of the turbo at full load and to adjust the value by means of a bypass valve to ensure that the threshold is not exceeded. Since the turbocharger is an integral part of both the engine exhaust and intake systems, access for measurement by conventional methods is difficult.
In the method used until now, a magnetised nut is mounted on the turbo shaft and the speed of the magnetic field generated as the nut rotates is measured. This method is both time-consuming and unreliable since it is difficult to measure the speed of the field with the desired accuracy; the measuring device or probe, which consists essentially of a pickup, cannot be located sufficiently close to the shaft due to the size of the turbo.
SUMMARY OF THE INVENTION
The method of the invention is for measuring the rotational speed of an engine turbocharger. The method includes the steps of: picking up sound generated by rotation of the turbocharger with a microphone and supplying a microphone signal containing signal components; filtering out low-frequency signal components from the microphone signal generated by engine operation including noise from valves, fans and gas flows; tuning an electronic bandpass filter to the remaining signal component having the highest amplitude in the filtered microphone signal; determining the frequency of the remaining signal component having the highest amplitude; and, with a knowledge of the turbocharger geometry, converting the value of the frequency of the remaining signal component having the highest amplitude to the rotational speed of the turbocharger.
The purpose of the present invention is to measure the turbo speed with the aid of a microphone. In tests with a microphone, it has been found that the rotating turbocharger generates a tone whose frequency and amplitude are a function of the speed. The microphone used in the test picks up all sound generated by both the turbo and engine. Low-frequency sound generated by the engine valves, fans, gas flows etc. is removed as far as possible by filtering and the remaining signal contains a turbocharger tone which can be separated by means of a bandpass filter. Since this tone contains too much interference for direct measurement, an electronic tuning fork is instead tuned to the same frequency and that value of frequency is measured. The speed of the turbo may then be determined when the number of turbine blades has been established.
Thus, and according to another feature of the invention, the method can include the following additional steps: tuning an electronic tuning fork to the remaining signal component having the highest amplitude; determining the frequency of the tuning fork; and, with a knowledge of the turbocharger geometry, converting the value of tuning fork frequency to the rotational speed of the turbocharger.
This method of sound measurement enables the speed of the unit to be determined quickly and simply without physical intervention in the turbo.
The method in accordance with the invention also provides a simple means of checking whether the turbo is running at the correct speed in the course of service work. Under normal circumstances, the speed of the unit falls as the turbine driving the compressor becomes fouled, with an adverse effect on engine efficiency. The speed of the turbo can be measured quickly and simply by the proposed method.
BRIEF DESCRIPTION OF THE DRAWING
The single figure of the drawing shows a block circuit diagram of the device
REFERENCES:
patent: 3815426 (1974-06-01), Rohner
patent: 4452079 (1984-06-01), Tiller
patent: 4988979 (1991-01-01), Sasaki et al.
patent: 5115671 (1992-05-01), Hicho
patent: 5365787 (1994-11-01), Hernandez et al.
patent: 5477730 (1995-12-01), Carter
F. Wennstrom System AB
Miller Rose M.
Ottesen Walter
Williams Hezron E.
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