Vehicle Mechanical Studies
A Vehicle Mechanical Study is necessary to determine the answers to two questions: 1) did a failure occur, and 2) did the alleged failure cause or contribute to an accident. The second question is as important as the first, as mechanical components are often damaged as a result of the accident.
Allegations of a vehicle defect or malfunction vary widely, and Donan Engineering has the knowledge and experience to thoroughly evaluate a vehicle to determine if an incident is related to a component failure.
Several typical studies include:
Brake Examinations
An allegation of brake failure requires a complete examination of the braking system, from the brake pedal to the tire contact patch. A study of the condition and tread depth of the tires is important, particularly if the roads were wet at the time of the accident. The prevalence of Antilock Braking Systems (ABS) requires an understanding of the function and operation of these additional components as well.
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| Photograph 1: Complete brake corner assembly. |
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| Photograph 2: Brake pad friction material is worn to approximately 1/16 of an inch. The brake pads were unable to dissipate heat generated during successive brake applications, resulting in brake fade and a subsequent collision. |
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| Photograph 3: Torn brake flex line at the strut bracket allowed brake fluid to leak, resulting in loss of braking ability and resulting in a vehicle accident. |
Steering and Suspension
An allegation of suspension failure often occurs after an accident when the driver observes a broken suspension component. Perhaps a tie rod is fractured, or a ball joint is separated. In some cases, the entire wheel, tire, and hub assembly may have separated from the vehicle. These cases can best be resolved by understanding the different types of failures which can occur: bending, torsion, impact, or fatigue. The presence or absence of corrosion on newly exposed surfaces may also indicate whether a component failed before or after an accident.
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| Photograph 4: Lower ball joint boot was deformed during installation by the manufacturer, allowing water intrusion into the ball joint. Corrosion and subsequent separation of the ball joint occurred, resulting in a loss of vehicle control. |
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| Photograph 5: Circumferential gouges and scrapes on the spindles, bearing races, and brake shoes indicate the wheel detached from the vehicle as it was rotating at speed – prior to an accident. |
Engine or Transmission Failures
A vehicle owner may allege that the engine or transmission in his or her vehicle is not operating properly after recent repairs or due to an act of vandalism. A claim may be made that a previous traffic accident resulted in engine or transmission damage. The level of disassembly required depends upon the situation. Removal of cylinder heads and oil pans may be required to determine the root cause of the failure. The possible failure modes can vary widely: thrown rods, broken timing chains, excessive oil consumption, spun bearings – the list of potential failures is extensive. With engine replacement costs running several thousand dollars or more, a complete engine tear-down may be cost-effective in determining the failure. If necessary, oil and transmission fluid samples can be analyzed in a laboratory to determine the condition of the engine and transmission.
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| Photograph 6: Our client needed to know the cause of damage on a Jaguar V8 engine. The left cylinder head is shown with its valve cover and exhaust camshaft removed. |
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| Photograph 7: The timing chain guide on the Jaguar V8 engine was fractured and embedded in the exhaust camshaft sprocket. This is a result of wear, and is clearly not due to accident damage or vandalism. |
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| Photograph 8: An Indian motorcycle engine with a circular hole punched through the piston. A 3/16 inch socket was discovered inside the engine. This damage was caused by vandalism. |
Unintended Acceleration
This phenomenon became widely publicized in the mid 1980s due to the perceived high rate of its occurrence in the Audi 5000. A thorough investigation by both NHTSA and Audi determined that the cause was driver error: the misapplication of the accelerator pedal when the driver intended to apply the brake pedal. Other failures may cause this condition as well: a vacuum leak, foreign debris in the throttle body, broken throttle return spring, rusted throttle cables. Resolution of this allegation requires an examination of the engine controls, intake system, and often the vehicle brakes.
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| Photograph 9: Rubber o-ring for the air intake tract was not properly seated after recent repairs, and was drawn into the throttle body. The o-ring prevented the throttle from closing, resulting in unintended acceleration of the vehicle and a subsequent accident. |
Supplemental Inflatable Restraints (Airbags)
Airbags may be the most misunderstood components on the modern vehicle, and with the proliferation of airbags, the confusion and misinformation is likely to continue. New vehicles today may be equipped with frontal airbags, side-impact airbags, head curtain restraints, knee bolster airbags, and more. Each airbag is designed to reduce the likelihood of injuries occurring in a specific set of circumstances.
For example, frontal airbags are designed to reduce serious injury from an occupant’s head or chest striking the windshield, dashboard, or steering wheel. Therefore, a side or rear impact is not likely to deploy the frontal airbags. A common misconception is that the speed of the vehicle at impact is the determining factor as to whether an airbag will deploy. In fact, actual vehicle speed is not used by the airbag computer to determine if a deployment is necessary. It is possible to have an accident at 100 mph with no airbag deployment; it is also possible to have a deployment while the vehicle speed is zero.
An examination of the vehicle crush and the determination of the delta-V by a proper Accident Reconstruction can be used to determine if an airbag should have deployed. This must be considered in light of the injuries sustained by the passengers. The airbag computer on some vehicles can be downloaded to provide additional insight as to whether the airbag system operated properly.
Black Box Downloads
Many vehicles today are manufactured with a downloadable airbag control module, or “Black Box,” which can provide information regarding the vehicle prior to an accident. This information may include vehicle speed, brake position, seat belt usage, throttle position, delta-V, and so forth. Some may also include seat position, which may be helpful in determining which occupant was driving at the time of an accident.
Current Black Box technology does not record vehicle speed at a user-selected point in time. Data is only recorded when an event triggers the device. The event may be as benign as striking a curb or as intense as an impact into a bridge abutment. It is important to remember that a sufficient deceleration must occur such that the airbag computer thinks it may be sensing the beginning stage (i.e. the first few milliseconds) of an accident.
Data may be recorded for download whether the airbags have deployed or not. Extreme care must be used in the downloading of this data to prevent overwriting the data for some types of event files.
Seat Belts
Without a doubt, the most effective safety device installed on the modern vehicle is the seat belt. Despite the well-documented safety benefits, and mandatory seat belt laws, many drivers still decide not to use seat belts. Sometimes it is necessary to determine if a seat belt was in use at the time of an accident. Physical evidence on the seat belt webbing, buckle, and D-ring may provide sufficient evidence to make a determination regarding usage.
There are several different types of seat belt mechanisms on vehicles today, each with different advantages. The type of mechanism will determine how the seat belt operates and under what type of circumstances it will be able to provide protection. A thorough seat belt examination must therefore begin with an understanding of what type of belt mechanisms are installed on the vehicle. In some cases, the front seat belt mechanisms may be of a different type than those in the rear.
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| Photograph 10: Material transfer from the plastic D-ring to the seat belt webbing indicates that the seat belt was in use at the time of an accident. |