There are many different
patents
related to various types of EDR features. Some EDRs continuously record
data, overwriting the previous few minutes until a crash stops them,
and others are activated by crash-like events (such as sudden changes in
velocity) and may continue to record until the accident is over, or
until the recording time is expired. EDRs may record a wide range of
data elements, potentially including whether the
brakes were applied, the speed at the time of impact, the steering angle, and whether
seat belt circuits were shown as "Buckled" or "Unbuckled" at the time of the crash. Current EDRs store the information internally on an
EEPROM until recovered from the module. Some vehicles have communications systems (such as
GM's
OnStar system) that may transmit some data, such as an alert that the airbags have been deployed, to a remote location.
Most EDRs in automobiles and light trucks are part of the restraint
system control module, which senses impact accelerations and determines
what restraints (airbags and/or seatbelt tensioners) to deploy.
[citation needed]
After the deployment (or non-deployment) decisions are made, and if
there is still power available, the data are written to memory. The data
downloaded from older EDRs usually contain 6 to 8 pages of information,
though many newer systems include many more data elements and require
more pages, depending on the make/model/year of the vehicle being
evaluated. Depending on the type of EDR, it may contain either a
deployment file or a non-deployment file or sometimes both, depending on
the circumstances of the collisions and the time interval between them,
among other things.
It is also possible that no data can be recovered from a data
recorder. One situation where this might occur is a catastrophic loss of
electrical power early in a collision event. In this situation, the
power reserve in the restraint system control module capacitors may be
completely spent by the deployment of the air bags, leaving insufficient
power to write data to the EEPROM. There are other circumstances where a
module may fail to record a data file as well.
Most EDRs in heavy trucks are part of the engine electronic control
module (ECM), which controls fuel injection timing and other functions
in modern heavy-duty diesel engines.
[citation needed]
The EDR functions are different for different engine manufacturers, but
most recognize engine events such as sudden stops, low oil pressure, or
coolant loss.
[citation needed] Detroit Diesel,
Caterpillar Inc.,
Mercedes-Benz,
Mack Trucks, and
Cummins
engines are among those that may contain this function. When a
fault-related event occurs, the data is written to memory. When an event
triggered by a reduction in wheel speed is sensed, the data that is
written to memory can include almost two minutes of data about vehicle
speed, brake application, clutch application, and cruise control status.
The data can be downloaded later using the computer software and cables
for the specific engine involved. These software tools often allow
monitoring of the driver
hours of service, fuel economy, idle time, average travel speeds, and other information related to the maintenance and operation of the vehicle.
Some EDRs only keep track of the car's speed along its length and not the speed going sideways.
[citation needed]
Analysts generally look at the momentum, energy, and crush damage, and
then compare
their speed estimates to the number coming out of the EDR
to create a complete view of the accident.
[
