Patent Description:
The present invention relates to improved apparatus and method for performing non-destructive testing and inspection of railroad rails. More particularly, the present invention is directed to a roller search unit (sometimes referred to as an RSU) and method for inspecting for and identifying defects in underlying railroad rails using ultrasonic transducers mounted within a wheel assembly having a fluid-filled tire. The fluid within the tires is an ultrasonic coupling fluid that transmits ultrasonic beams between the transducers and the tire. The beams penetrate the tire and the underlying rail, and are reflected back to the transducers from defects in the rail for analysis. In order to maximize signal strength of the ultrasonic beams transmitted back and forth between the transducers and tire, the coupling fluid must fully occupy the interior of the tire under all operating conditions.

From time to time, and for various reasons, the rails of a railroad track may develop one or more detrimental flaws or defects. Such flaws may include transverse defects, vertical shear or split-head defects, horizontal shear or split-head defects or the like that may originate from manufacturing and construction processes, environmental factors or wear-and-tear from normal use. These flaws or defects are typically observed in the head of a rail, but may also be found within the web and foot of the rail, around the peripheries of the bolt holes, or any other portion of the cross-section of the rail. Due to the nature of railway travel, in which locomotives weighing tens of thousands of pounds regularly carry hundreds of tons of freight over rails while traveling at varying speeds, cracks within the rails may expand or propagate throughout the rail over time. Such flaws or defects that are left unattended or unaddressed can lead to a variety of problems, the most serious of which may include catastrophic rail failures or train derailments, and may pose serious financial, health and safety risks to goods and personnel, as well as the railway industry as a whole.

Rail failures may be predicted and avoided through routine non-destructive inspection, which may enable railway operators to identify and cure hidden or infinitesimal flaws or defects within rails before they develop into problems of much greater magnitude. To detect such flaws or defects, vehicles or rail car-mounted rail inspection carriages including ultrasonic rail inspection equipment have been built to travel along a railroad track, and continuously perform ultrasonic inspection of the underlying rails in situ by transmitting ultrasonic beams into the rails and analyzing any portions of the beams that may be reflected off flaws or defects in the rail. One such rail inspection carriage is disclosed in <CIT>.

One example of the ultrasonic rail inspection equipment for in situ rail inspection including a wheel assembly having a fluid-filled tire for maintaining rolling contact with the head of an underlying rail is disclosed in <CIT> to Havira. According to the teachings of Havira, the tire forms a contact patch with a head of an underlying rail and includes an ultrasonic transducer supported within the tire for projecting an ultrasonic beam along a beam axis through the fluid, the tire, a liquid couplant sprayed between the tire and rail, and into the head of the underlying rail. The couplant is normally a thin layer of a liquid, such as water or a mixture of water and other reagents, for improved contact between the tire and rail head. The ultrasonic beam propagates through the underlying rail and is reflected by any defects or flaws that may be present therein, which may cause some or all of the beam signals to be returned to the transducer or received by an ultrasonic detector. The reflected beam signals are then analyzed by one or more computer processors to determine the type, magnitude, and location of the flaw or defect from which the beam was reflected.

When an ultrasonic transducer is suspended within a fluid-filled tire, such as is disclosed in Havira, the tire and fluid provide the transmission medium between the ultrasonic transducer and the underlying rail. Due to the nature of sound propagation, the strength and quality of the ultrasonic waves that are both delivered and received by the transducer depend upon a continuous medium or mediums for transmission. Air pockets and other discontinuities in the mediums through which the ultrasonic beams are propagated destroy the beams and the signal information carried by the beams.

With slow speeds of travel during inspection operations, that is, less than <NUM> kph, the ultrasonic coupling fluid within the tire will generally maintain the necessary continuity of the medium with the tire for wave transmission. However, with higher speeds of travel sought in order to achieve shorter inspection times and less disruption to rail traffic, various problems develop.

<FIG> illustrates a rolling search unit <NUM> of the prior art having a wheel assembly with a tire <NUM> and components mounted within the tire, including ultrasonic transducers <NUM> and a heat exchanger <NUM> shown in phantom. As illustrated in <FIG>, the tire is filled with a coupling fluid <NUM>, such as a mixture of water and ethylene glycol, which serves as the medium for propagation of ultrasonic beams between the transducers <NUM> and the tire <NUM>. The function and purpose of the heat exchanger <NUM> is to maintain the coupling fluid <NUM> at a uniform temperature as described in greater detail in <CIT>.

When the unit <NUM> is placed with a light load on a railhead H of an underlying rail to perform an inspection operation, the tire <NUM> is flattened slightly and forms a contact patch P with the rail head H. The tire <NUM> is made from a coupling fluid generates centrifugal forces which are exerted against the inner surface of the tire and stretch the tire. The stretching simultaneously increases the interior volume of the tire by finite amounts, and with a fixed volume of coupling fluid, the static pressure of the fluid inflating the tire is reduced. In <FIG> the arrows A illustrate the centrifugal forces of the coupling fluid <NUM> pressing outwardly against the tire <NUM> when the unit <NUM> is rotated as indicated by the arrow R.

It has also been noted that a phenomenon referred to as "cupping" C, that is, a pucker or lifting of the tire membrane away from the rail head at the center of the contact patch P of the tire with the rail head, accompanies the reduction in static pressure as travel speed is increased. The cupping C is also illustrated in <FIG>. The cupping forms a pocket filled with a thicker layer of liquid couplant than desired and becomes a discontinuity of the medium in the path along which the ultrasonic beams B must pass between the transducers <NUM> and the rail head H. That discontinuity causes a distortion of the beam and reduction of the signal strength, and results in a loss of information sought by the inspection operation.

Another problem that arises with rolling inspection units of this type is the bouncing of ultrasonic beams within the tire <NUM> due to reflections from various surfaces within the tire. The bouncing beams can be picked up by a transducer the same as, or other than, the one from which the beam emanated, and can be misinterpreted as a defect where one does not exist. <CIT> discloses a rolling search unit for railroad rail inspection. The rolling search unit comprises an ultrasonic device and a heat exchanger within a fluid-filled tire.

Remedies for the problems discussed above are offered by the features of an improved rolling search unit and method for ultrasonically inspecting railroad rails as described below.

The problems discussed above are addressed by an improved rolling search unit (hereafter RSU) for ultrasonic railroad rail inspection. The improved RSU comprises a wheel assembly having a tire filled with an ultrasonic coupling fluid. The wheel assembly is mounted by means of hubs for rotation on an axle for rolling contact of the tire with the head of an underlying rail of the railroad as the wheel assembly is translated along the rail during an inspection operation. The tire is made of a flexible membrane material, and forms a contact patch when placed on the head of the underlying rail during the inspection operation.

An ultrasonic transducer is supported on the axle within the tire for propagating an ultrasonic beam through the coupling fluid and the tire into the head of the underlying rail, and for receiving ultrasonic beams reflected back from defects encountered in the underlying rail. The reflected beams revealing the defect can then be further analyzed to establish the criticality of the defect and to decide if any remedial steps need to be taken.

A baffle is mounted in stationary relationship on the axle in the coupling fluid within the tire to suppress rotation of the coupling fluid with the tire when the tire rotates on the axle. By suppressing the rotation of the fluid, the centrifugal forces that would otherwise be generated by the rotating fluid and be exerted outwardly against the tire are considerably reduced. Therefore, the flexible membrane material forming the tire is not significantly stretched at greater speeds, and the interior volume of the tire occupied by the fluid is not substantially expanded. As a consequence, the loss of static pressure within the tire is reduced or may be eliminated.

With the baffle mounted on the axle and projecting from the axle into the coupling fluid, the baffle also intercepts stray ultrasonic beam reflections within the wheel assembly. By eliminating the stray reflections, the opportunity for the ultrasonic transducers to pick up the reflections and produce erroneous defect signals is also minimized.

Dependent claims <NUM> to <NUM> describe advantageous embodiments of the rolling search unit.

An improved method for inspecting railroad rail ultrasonically is also provided by the invention, see claim <NUM> and dependent claims <NUM> to <NUM>.

Further features and advantages of an improved rolling search unit and the method of conducting ultrasonic inspections of railroad rails can be derived from the following description.

<FIG> and <FIG> illustrate a rolling search unit <NUM> of the prior art to illustrate the problems addressed by the improved rolling search unit as discussed above. <FIG> illustrate the improved rolling search unit <NUM> (RSU) which incorporates the features of the present invention. The RSU <NUM> has all of the features of the prior art unit <NUM>. The RSU <NUM> includes a wheel assembly <NUM> having a tire <NUM> filled with a coupling fluid <NUM> and a plurality of ultrasonic transducers <NUM> immersed in the fluid. The transducers generate ultrasonic beams B aimed in various downward directions to propagate through the fluid <NUM> and the tire <NUM> into the railhead H of an underlying rail in an inspection operation.

When the ultrasonic beams B encounter a defect in the railhead or deeper in the rail they are reflected back through the rail, the tire <NUM>, and the coupling fluid <NUM> to the transducers where the signal information carried by the reflected beams is captured and analyzed. The analyzed information can provide details regarding the type of defect, the size of the defect, and its location relative to the RSU.

The wheel assembly <NUM> as shown most clearly in <FIG> is supported in a frame <NUM> with a leg <NUM> at the gauge side and a leg <NUM> at the field side, so that the legs straddle the wheel assembly. A stub axle <NUM> is connected to the gauge side leg <NUM> of the frame <NUM> as shown in <FIG>. Another stub axle <NUM> is similarly connected to the field side leg <NUM> of the frame. The stub axles <NUM>, <NUM> are joined to each other at their inner ends by a bolt <NUM> shown in <FIG>. The stub axle <NUM> supports a number of components described hereafter within the tire <NUM> in stationary relationship with the frame <NUM>. A floating axle <NUM> shown in <FIG> is installed within the stub axle <NUM> and is connected through a cutaway section of the stub axle with a yoke <NUM> on which the transducers <NUM> are mounted. The floating axle projects out of the field side of the stub axle <NUM> and has a slotted flange <NUM> with a clamping screw <NUM> for trimming the mounting angle of the transducers by rotating the floating axle <NUM> within the stub axle <NUM> and then tightening the clamping screw <NUM> to fix the floating axle within the stub axle. With the floating axle clamped with the stub axle <NUM>, the stub axles <NUM>, <NUM> and the floating axle <NUM> are all fixed in stationary relationship to the frame <NUM>. The axles and yoke are non-rotating and serve as a stationary mount for all of the internal components of the wheel assembly <NUM> including the transducers <NUM> and the heat exchanger <NUM>.

An electrical plug <NUM> is connected to the field side end of the stub axle <NUM> and provides electrical connections for the transducers <NUM> within the wheel assembly <NUM>.

It will be understood that the frame <NUM> with the wheel assembly <NUM>, and typically multiple other similar wheel assemblies, are suspended from a rail inspection carriage such as disclosed in <CIT> during an inspection operation. The carriage is in turn suspended under a rail car or rail-mounted vehicle for traveling along the rails of a railroad and conducting an inspection of the rails in situ. The wheel assemblies are lowered into contact with the railheads H with a limited downward force that causes the tires of the wheel assemblies to flatten slightly, as shown most clearly in <FIG>, and forms the contact patch P of <FIG> and <FIG>. The contact patch is large enough to provide for favorable transmission of all the ultrasonic beams B penetrating the railhead from the tire.

As shown in <FIG>, the wheel assembly <NUM> includes a wheel hub <NUM> on which the tire <NUM> is mounted at the gauge side, and hub <NUM> on which the tire <NUM> is mounted on the field side. The tire <NUM> is a flexible membrane material, such as polyurethane, that has been molded into the toroidal configuration with beads <NUM>, <NUM> respectively at each circular edge. The hubs are provided with corresponding grooves for the beads. An annular clamping plate <NUM> with a groove matching the bead <NUM> clamps the bead against the wheel hub <NUM> in fluid-tight relationship by means of cap screws <NUM>. A similar clamping plate <NUM> with a groove matching the bead <NUM> clamps the bead against the wheel hub <NUM> in fluid-tight relationship by means of similar cap screws <NUM>. Together, the hubs <NUM>, <NUM>, beads <NUM>, <NUM>, and clamping plates <NUM>, <NUM> form a sealed connection between the tire <NUM> and hubs that prevents the coupling fluid <NUM> under pressure from escaping from the tire.

To fill the tire with coupling fluid a fill valve <NUM> is provided in the field side hub <NUM>. The fill valve is a self-closing valve such as a Schrader valve. To bleed air from the tire <NUM> when being filled with coupling fluid, the field side hub <NUM> has a bleed valve <NUM> and a bleed port <NUM> leading from the valve to the interior of the tire. The bleed valve is a manually operated valve to open and close the port for bleeding air from the tire.

As shown in <FIG>, to rotate the wheel assembly <NUM> in the frame <NUM> with the tire <NUM> against a railhead H during an inspection operation, the hub <NUM> is mounted on the stub axle <NUM> by means of roller bearing <NUM>, and the hub <NUM> is mounted on the stub axle <NUM> by means of roller bearing <NUM>. A shaft seal <NUM> is installed in the hub <NUM> to prevent coupling fluid from escaping through the bearing <NUM>. A similar shaft seal <NUM> is installed in the hub <NUM> to prevent coupling fluid from escaping through the bearing <NUM>. Other seals are provided at various joints between the bolts, valves, and axles to ensure that the coupling fluid <NUM> does not escape from the tire <NUM>.

As previously indicated in connection with <FIG>, shear forces between the tire and coupling fluid <NUM> when the tire <NUM> rotates cause the fluid to rotate with the tire. The forces create centrifugal forces against the tire and stretch the tire by finite amounts. With a fixed volume of fluid, the static pressure of the fluid within the tire, typically <NUM>-<NUM> psi, will drop and risk the cupping C phenomenon, cavitation, and foaming within the tire, all of which interfere with the transmission of the ultrasonic beams B.

To suppress the rotation of the coupling fluid with the tire and the associated centrifugal forces, an anti-rotation baffle <NUM> shown in <FIG> is supported in stationary relationship within the tire on the yoke <NUM> as seen most clearly in <FIG>. The baffle <NUM> projects radially outwardly from the axles toward the tire and has a shape that will generally obstruct the rotation of the coupling fluid with the tire. However, the baffle maintains a spaced relationship with the interior surface of the tire so that the baffle does not interfere with the rotation of the tire. By means of the baffle <NUM> and the obstruction of the coupling fluid, the centrifugal forces of the fluid on the tire are considerably reduced along with the associated loss of static pressure within the tire. Hence the cupping phenomenon is suppressed and a continuous medium for transmission of the ultrasonic beams between the transducers and the railhead is maintained.

The anti-rotation baffle <NUM> illustrated is flat, but curved and other shapes may also be employed to obtain the desired resistance to fluid rotation and maintain a spaced relationship with the interior of the tire <NUM>. The shape of the baffle may also accommodate other components within the tire. Additionally, more than one baffle may be employed at different locations within the tire to suppress the fluid rotation.

In addition to preventing coupling fluid rotation, the anti-rotation baffle <NUM> also serves the purpose of intercepting and dissipating unwanted ultrasonic beam reflections within the tire. The baffle or baffles may be strategically shaped, positioned, and provided with a surface texture to accomplish the beam intercepting and dissipating functions.

To further improve the continuity of the fluid medium through which the ultrasonic beams B pass between the transducers <NUM> and the tire <NUM>, the RSU <NUM> has a pressure regulator for controlling the pressure of the coupling fluid <NUM> in the wheel assembly during an inspection operation. The pressure regulator includes a component <NUM> within the tire <NUM> and a regulated pressure source <NUM> outside of the wheel assembly on the frame <NUM> or elsewhere. As illustrated in <FIG> the component <NUM> is a pressurizing bladder mounted on the stub axle <NUM> within the tire. As shown most clearly in <FIG>, the pressurizing bladder <NUM> has a housing <NUM> defining a pressure chamber <NUM> closed by a flexible diaphragm <NUM>. The pressurizing bladder is preferably an air bladder supplied with pressurized air from the regulated pressure source <NUM> outside of the tire. When pressurized air is delivered to the bladder <NUM>, the diaphragm <NUM> expands into the interior space of the tire occupied by the coupling fluid and pressurizes the fluid.

The regulated pressure source <NUM> in one embodiment is an air compressor that provides regulated air pressure. As shown most clearly in <FIG>, the pressurized air source <NUM> is connected to a fitting <NUM> on the gauge-side frame leg <NUM>, and supplies regulated air pressure from outside the wheel assembly <NUM> to the pressurizing bladder <NUM> within the wheel assembly through a drilled channel <NUM> in the frame leg <NUM>, and a manifold <NUM> formed in the stub axle <NUM>.

Fittings <NUM>, <NUM> are used to feed a heating/cooling fluid through the heat exchanger <NUM> by means of similar but separate channels and manifolds in the stub axle <NUM>. The heating or cooling is desirable to hold the temperature of the coupling fluid through which the ultrasonic beams B pass at a fixed level for standardized results since inspection of the rails is conducted in situ and may be performed in all seasons.

When the wheel assembly <NUM> is not in motion, the static pressure of the coupling fluid in the tire <NUM> is nominal, for example, <NUM>-<NUM> psi. The regulated pressure supplied from the pressure source <NUM> would be the same. However, when the wheel assembly is moving and centrifugal pressure of the rotating fluid causes the tire to stretch at higher inspection speeds, the pressure source <NUM> supplies increased air pressure to the pressurizing bladder <NUM> and expands the flexible diaphragm <NUM> against the fluid within the tire.

For this purpose the regulated pressure source <NUM> receives a speed signal from a speed sensor <NUM> shown in <FIG>, which signal regulates the air pressure supplied by the source as a function of speed. The speed sensor <NUM> may be responsive to either the rotational speed of the wheel assembly <NUM> or the translational speed of the wheel assembly along the rail being inspected. In general the speed signal increases the regulated air pressure delivered by the pressure source with increased speeds.

In this manner, the pressure regulator formed by the pressurizing bladder <NUM> and regulated pressure source <NUM> maintains or increases the pressure in the tire to compensate for the finite increase in volume of the stretched tire and the otherwise associated reduction of pressure in the tire. Correspondingly, the increased pressure at higher speeds presses the tire <NUM> against the rail head H and eliminates the cupping effect and the thicker layer of liquid couplant that would otherwise diminish the strength of the ultrasonic beams B and their reflections passing through the contact patch P.

While the present invention has been described in several embodiments, it will be understood that numerous modifications can be made without departing from the spirit of the invention. For example, although the anti-rotation baffle <NUM> is intended to prevent the coupling fluid from rotating with the tire <NUM>, some of the fluid will pass by the baffle in view of the spaced relationship of the baffle and tire and could produce centrifugal forces expanding the tire. Therefore, it is advantageous to use both the baffle <NUM> and the pressurizing bladder <NUM> in the wheel assembly together.

The internal component of the pressure regulator disclosed as the pressurizing bladder <NUM> and the regulated pressure source <NUM> can take various forms. The pressurizing component formed by the pressurizing baffle <NUM> may take the form of other expandable devices, such as a bellows, or a piston within or emerging from a cylinder for displacing or replacing fluid within the tire. The pressure source may also supply a pressurized liquid at a regulated pressure to activate the pressurizing component of the pressure regulator.

Claim 1:
A rolling search unit for ultrasonic railroad rail inspection comprising:
a wheel assembly (<NUM>) having a tire (<NUM>) filled with an ultrasonic coupling fluid and rotatably mounted on an axle (<NUM>, <NUM>) for rolling contact with a head (H) of an underlying rail of the railroad, the tire being made of a flexible membrane material, whereby the tire forms a contact patch (P) when placed on the head of the underlying rail during an inspection operation;
an ultrasonic transducer (<NUM>) supported on the axle (<NUM>, <NUM>) within the tire for propagating an ultrasonic beam (B) through the coupling fluid (<NUM>) and the tire into the head of the underlying rail, and for receiving ultrasonic beams reflected back from defects detected in the underlying rail; and characterized by
a baffle (<NUM>) mounted in stationary relationship on the axle in the coupling fluid (<NUM>) within the tire to suppress rotation of the coupling fluid with the tire when the tire rotates on the axle.