Technique for computing a measure on an ultrasonic signal having application to identify valve defects in operating engines

A measurement technique that generates a number value identifying the width of a noisy pulse in an analog signal that has particular application for determining whether a defect exists in a cylinder valve of a locomotive diesel engine. The algorithm samples the analog signal, and then the samples are bunched into successive groups where each group includes a predetermined number of samples. A root mean square is taken of the samples in each group to generate a representative amplitude value for that group. Successive amplitude values are multiplied together to generate product values. The product values are averaged over a predetermined number of product values to generate the number value that can be analyzed to determine if a defect in a valve exists.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a technique for measuring the width of a noisy pulse in an analog signal and, more particularly, to a technique for remotely determining whether a valve associated with a cylinder in a locomotive diesel engine is defective by measuring the width of ultrasonic pulses emitted therefrom.

2. Discussion of the Related Art

Locomotives employ diesel engines having sixteen or more cylinders. Each cylinder employs several valves, for example four valves, where some of the valves allow a fuel/air mixture to be emitted into the cylinder and other of the valves allow exhaust gas to be removed from the cylinder. It is important that the seal integrity of the valve relative to the valve seat around the opening in the cylinder is sufficient so that the engine operates properly and is not damaged. However, the rigors of the combustion process within the cylinder sometimes causes cracks and other defects in the valve or the valve seat which may affect seal integrity. Continued operation of the engine with a defective valve may cause valve failure. Further, valve failure in a locomotive engine can result in damage to the engine turbocharger which may cost $100,000.00 or more to replace or fix.

Heretofore, it was usually necessary for a technician to visually inspect the valve and valve seat to look for evidence of cracking or other damage during maintenance over hauls and the like. This is a costly process because the valve head needs to be removed and each valve inspected which includes significant labor and downtime. Further, the inspection process is highly subjective in that the technician determines whether a defect exists by his or her own visual assessment and experience.

To overcome these problems, it is known in the art to employ a detection system including an ultrasonic sensor probe that detects ultrasonic emissions from the engine while it is idling. Ultrasonic emissions are typically emitted from the engine during such times as fuel injection and exhaust emission when the valves are opened. The probe is placed in contact with suitable locations on the cylinder head and a measurement is taken for each cylinder. The detection system includes processing circuitry that provides heterodyning by mixing the ultrasonic signal for frequency down-conversion purposes, for example 40 kHz to 0-3 kHz, to make the sound energy audible. The detection system also includes a headset for listening to the down-converted signal.

Because a defect in the valve causes additional gases to leak during the compression stroke, additional ultrasonic energy is emitted if such a defect exists. Therefore, by knowing the “sounds” that the engine cylinder makes with no defect, a technician can listen for higher intensity signals indicating the presence of a valve defect. However, such a technique for determining valve defects still includes a subjective aspect where the technician must determine the defect by the sound perceived. It would be desirable to provide a more cost effective and objective technique for determining if a defect exists in a valve or valve seat associated with a cylinder of a locomotive engine.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a measurement technique is disclosed that generates a number value identifying the width of a noisy pulse in an analog signal. In one embodiment, the noisy pulse is part of a down-converted ultrasonic signal detected from sound transmissions from a cylinder in a locomotive diesel engine. A wider pulse, and thus a higher number value, provides an indication of whether a valve associated with the cylinder is defective, where the sealing integrity of the valve has been compromised.

The technique employs a mathematical algorithm that samples the down-converted signal at predetermined periods of time to provide an analog-to-digital conversion. The samples are then bunched into successive groups, where each group includes a predetermined number of samples. A root mean square is taken of the samples in each group to generate a representative amplitude value for that group. Successive amplitude values, such as three successive values, are then multiplied together to generate product values. The product values are averaged over a predetermined number of product values to generate the number value that can be analyzed to determine if a defect in the valve exists. If a noisy pulse in the signal generates a number value that is greater than a certain number valve, then the valve can be determined to have a defect. The number value can be ratioed against another product value of the amplitude values to compensate for gain differences in the signal.

Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion of the invention directed to a mathematical technique for determining whether a defect exists in a valve of a cylinder of an engine is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. Particularly, the discussion below concerns determining defects in a valve of a locomotive diesel engine. However, as will be appreciated by those skilled in the art, the algorithm of the present invention has a much wider application.

FIGS. 1-5are various graphs of an analog ultrasonic signal emitted from a cylinder of a locomotive engine that has been down-converted to audible frequencies. The known ultrasonic engine probe was used to generate the analog down-converted ultrasonic signals shown in these figures. Each of the graphs show time on the horizontal axis and signal intensity on the vertical axis, and cover a few cycles of the locomotive engine.FIG. 1shows the analog down-converted signal of a cylinder having valves with no defects, where fuel injection and exhaust valve opening are identified as noisy pulses on the graph.

The probe was used to sense the ultrasonic emissions from the engine cylinder where one of the valves of the cylinder had a known specific size defect. Particularly, the valve of the cylinder shown inFIG. 2had a {fraction (1/32)} by {fraction (1/32)} size defect; the valve of the cylinder shown inFIG. 3had a ⅓ by {fraction (1/16)} size defect; the valve of the cylinder shown inFIG. 4had a {fraction (1/32)} by {fraction (3/16)} size defect; and the valve of the cylinder shown inFIG. 5had a {fraction (1/32)} by ⅛ size defect. In these figures, reference numeral30shows a firing/injection pulse, reference numeral32shows an exhaust valve opening pulse, reference numeral34shows an increase in noise at high cylinder pressure after firing, reference numeral36shows an increase in noise as the cylinder pressurizes before firing, and reference numeral38shows significant noise before and after cylinder firing.

By comparing the signals outputs ofFIGS. 1-5, it becomes clear that the defect causes the noisy pulses to have a greater magnitude and a longer duration in time, where the duration and magnitude of the pulse is determined by the size of the defect. This is consistent with the understanding that valves with a notch or crack at the edge would fail to seal against compression and combustion pressures, resulting in gas leakage and higher ultrasonic energies.

According to the invention, a mathematical algorithm is disclosed that generates a number value indicative of the width of noisy pulses in the down-converted analog output from a engine cylinder. By comparing the generated number value against a number value from a cylinder having no valve defects, a substantially objective technique is provided for determining valve defects in a cylinder valve. In one embodiment, the algorithm employs an appropriate sample interval, and assumes that all noisy pulses in the signal are less than three sample intervals long. If the pulses were sufficiently spaced, then, in the binary case, the product of any four successive samples would be zero or near zero. In such a case, the local discreet-time function comprising the product of four adjacent samples would be highly discriminatory against pulses below two or so intervals in duration. In other words, the product of the samples would be less for those pulses having shorter durations and greater for those pulses having a longer duration. Therefore, the present invention proposes computing a product of adjacent time samples to determine the duration of the noisy pulse to determine the width of the pulse, and thus, whether a defect exists.

FIG. 6is a block diagram10showing the operation of an algorithm of this type. The down-converted ultrasonic analog signal is applied to a sample device12that generates a pulse at every predetermined time period, here at 5 kHz. This is a sufficient statistical sampling of the signal because the frequency will be between 0-3 kHz and noisy. The sample device12acts as an analog-to-digital converter that converts the analog signal to plus and minus digital signals at the sample rate to generate a 5 kHz data stream si. The sidata stream is applied to a buncher device14that creates bunches of successive samples. In this example, 25 samples are bunched in 5 msec groups. A root mean square (RMS) device16calculates the RMS of each 25 samples in each group. The RMS of each bunch gives a representative amplitude Vifor the pulses in that group. Thus, for every 5 msec, a new Viis generated providing a 200 Hz data stream corresponding to the RMS of each bunch.

The values Viare applied to a multiplying device18and a multiplying device20. The multiplying device18computes a product for every three consecutive Vi, or Vi, Vi−1, and Vi−2, and generates a product value fi. Thus, the longer the pulse of noise in the analog input signal, the greater the computed value. Therefore, if a particular pulse is more than a single bunch of 25 successive samples long, then the product will be greater than if the pulse width was less than the bunch sample time for collecting the bunch. The multiplying device20cubes each value Vifor normalization purposes and generates a product value gi. This normalization step is important to compensate for gain variations that may occur in the devices12,14and16and the ultrasonic pickup of the probe (not shown). Thus, by cubing each value Vi, variations in gain in the signal do not affect the overall output.

The product value fiis applied to an averaging device22and the product value giis applied to an averaging device24. The averaging devices22and24can generate an average, a means, a percentile, etc., on a moving basis or on a finite block of data. The averaging device22averages successive values fi, and the averaging device24averages successive values gi, preferably over each stroke of the engine. For example, each of the averaging devices22and24averages about 50 samples. The average values are applied to a ratio device26that generates a ratio of f/g. Thus, if the value computed in the multiplying device18is high because the pulse width is larger than normal as a result of a valve defect, then the ratio f/g will be higher than what is normally seen in a non-defective valve. Therefore, a number greater than a predetermined number value of a non-defective valve indicates a defective valve.

One of normal skill in the art would readily recognize what various circuits could be used for each of the devices12,14,16,18,20,22,24and26discussed above. Further, the various operations discussed herein could be performed by suitable software programs, also readily apparent to those skilled in the art.

Other embodiments of the invention can apply more sophisticated processing, including employing fourier transforms or other known mathematical algorithms, to multiply continuous samples together consistent with the discussion herein. However, the embodiment discussed above employs reduced processor memory and processing power to perform the same operation. Other approaches include exploiting wavelet analysis to map a function of one variable, time, into a function of two variables, time and duration. Wavelet analysis relies on the computation of convolution integrals at each point in time for a potentially large number of similarly-shaped functions of time-scale or duration. The resulting two-dimensional function, presented as a contour plot, can provide a visual indication of underlying processes characterized by different time scales, periods and phases, such as appear to be present in the data provided inFIGS. 2-5.