Shown in Figures 4A and 4B is a hand throttle linkage that
was part of a manual throttle system used by disabled drivers.
The linkage connected the accelerator pedal to a hand lever that
would operate the throttle. While the driver was operating the
vehicle, the throttle link failed, causing an accident. In Figure
4A, the arrow points to a fracture that occurred at a bend in the
linkage. The photo to the right shows the fracture surface of the
aluminum rod, which has evidence of metal fatigue.
Apparently, the installer of the system had bent the aluminum
rod in order to facilitate installation, causing a crack that initiated a progressive failure scenario. The bend occurred at a hole
provided for bolts used to attach the rod to the throttle system.
Metallurgical examination determined that metal fatigue had
reduced the rod cross section to the point of failure. This is an
installation-related defect with definite subrogation potential.
Electronic throttle control systems are being designed into
more recent vehicles and may become a more prevalent throttle
control system. Failure of electronic components may require
analysis of an event data recorder (EDR) on the vehicle, which
will often require that a manufacturer download the data, as the
software is usually proprietary. However, the mechanical parts of
the electronic throttle control system can exhibit failure modes
similar to those shown in the case studies.
Figure 5 displays information collected from a crash data recorder download where a malfunction of the accelerator was suspected. From 5 seconds to 1 second before impact, the throttle
percent was constant at approximately 72 percent (denoted by the
solid blue line). The brakes had been applied (lavender line) and
the vehicle was slowing from approximately 62 miles per hour (red
line), at 5 seconds before impact, to 50 miles per hour at 1 second
before impact. The engine was not at idle and varied from 3,200 to
3,600 revolutions per minute (green line). With the driver’s foot
on the brake, the percent throttle opening should decrease to near
zero, as indicated by the dashed blue line. The data shows that the
throttle stuck in a position of approximately 72 percent, which resulted in uncontrolled acceleration and an accident.
In cases where throttle control failure is claimed or suspected,
it would be prudent for the claims analyst to inspect the vehicle
to determine if evidence suggests a malfunction that could result in recovery from a party or even legal action. The evidence
should be preserved for future inspection by various experts, including those of the manufacturer. K