Wheel impacts are serious problems for rolling stock and
can lead to axle box failures. Early detection of wheel defects, such
as skids (i.e. wheel flats), cracks and wheels that are out of shape,
prevents major damage and reduces the cost of repairs. Wheel Impact
Load Detector (WILD) is designed for the early detection of faulty
wheels and to encourage rail operators to properly maintain their
wagons. The maintenance crew will use the information from WILD to plan
and perform wheel replacements before the wheels become so damaged that
they cause service interruptions. This should reduce operational costs
Basic System Equipment
The basic component of a WILD system is the track
mounted sensor array (Figure 1). There are two basic types of sensors,
the original sensors are based on strain gauges and measure force and
the new type is based on accelerometers and measures rail motion. The
sensors are installed at strategic places along the track to monitor
passing trains to investigate specific safety related symptoms.
Figure 1 Wheel sensors (Left circle) and the
accelerometers installed on track.
The modern WILD system is usually equipped with on-site
signal processor, a control PC, modems, Automatic Equipment
Identification (AEI) and computers for local or remote diagnosis and
monitoring. Together with other equipment, such as Weighbridge (Figure
2) and Hot Box Wheel & Bearing Detector, they form a comprehensive
Wheel Condition Monitoring (WCM) System.
Figure 2 Weighbridge for axle balancing or
to check the weight of wagons.
New type of weighbridge has weighbridge load cell in place the
Using rail mounted strain gauges as the wheel sensors,
it can weigh each wheel of a train as it passes over, and detect skid
flats in the wheels. A wheel with flat spots can create impact loads
many times higher than the fully loaded weight of the car it carries
and cause serious damage to the railroad.
New WILD systems use an array of accelerometers (Figure
3) to measure the change in motion. Air bags in cars are released when
an accelerometer senses sudden extreme changes. When the wheel goes
over them, they read positive and as the wheel rolls past, they read
negative. Any irregularities in the wheel cause the signals to go both
positive and negative as the wheel rolls over them.
Figure 3 Typical WILD site - Left circle:
Accelerometers determine the impact of the wheel defect,
Right circle: Automatic Equipment Identifier (AEI) Readers are used to
Figure 4 Another typical site for WILD system
The array of sensors is mounted on track, together with
an Automatic Equipment Identification (AEI) tag reader (Figure 5) which
determines the Car ID when a train passes, identify and trace every
wheel in the fleet for as long as that wheel is in service.
Figure 5 AEI tag reader to read the car
The data gathered for each axle is automatically
recorded on a database by the signal processor and the control PC. It
is then transmitted to the railway control centre or depot maintenance
centre for remote monitoring and diagnosis.
When a wheel generates a force that causes too high an
impact such as it reaches a predetermined impact level compared to the
historical value (e.g. a freight car wheel exerts a peak impact load of
90 kips (Note 1) or above, is considered "out of round" and is on the
path to failure.
Figure 6 A wheel experiences a 106 kip peak
The train might be requested to slow down and come to a
stop at the nearest sidings or yard to uncouple the car whose wheel is
damaged. This minimizes the chance of damage to the tracks and bridges.
However, reductions in the speed of the trains and the obligation to
stop for repair introduce lots of delays in the delivery of goods and
reduce the throughput of the railway network.
WILD allows early detection of many types of wheel
defects. It can be used as a predictive and proactive maintenance
system that detects and reports potential safety problems and poorly
performing equipment before they result in accidents or undue rail
damage. It enables the maintainer to track data on a single wheel as
far back in time as data is retained. The defective wheels can be
quarantined for immediate repair. They can pro-actively apply trim
blocks to tread-braked rolling stock with mild to moderate wheel flats,
too. The use of WILD system enhances safety, decreases disruptions of
service, improves operating efficiency and reduces overall system
costs. It reduces noise along with reduced incidence of audible wheel
flats across the network, too.
The railway industry has undergone a remarkable
technological upheaval during the past years. A wide range of Wayside
Detection Systems such as the Hot Box Wheel & Bearing Detector
(HBWD), Dragging Equipment Detector (DED) and the Wheel Impact Load
Detector (WILD) have been developed. They are permanently placed at
strategic locations along railroad tracks to monitor passing trains to
investigate specific safety related symptoms. A comprehensive Wheel
Conditioning Monitoring (WCM) system completed with the widespread
implementation of AEI tag optimizes the productivity and minimizes the
costs of operation with accurate and reliable condition monitoring
Note 1: kip - it is a unit of
force equal to 1,000 pounds