The National Highway Traffic Safety Administration seeks public comment on a series of nine draft research test procedures developed by the agency to assess the performance of certain types of Advanced Driver Assistance Systems (ADAS). NHTSA is specifically requesting comment on whether these draft research test procedures adequately, objectively, and practically assess the system performance of the underlying ADAS in a test track environment. NHTSA intends to use these draft research test procedures to further its research goals by using the output from clearly defined test methods to help better understand system operation, performance, and potential limitations.
The following is an excerpt from a response to the NHTSA request for comments by Mark Thrasher, a former test engineer who worked at Robert Bosch LLC for 22 years and, in particular, in the chassis control division for the last 12 years:
Dear NHTSA and Driving Public:
As a former test engineer that worked at Robert Bosch LLC for 22 years and in particular in the chassis control division for the last 12 years, I would like to provide my feedback on these proposed test procedures.
Specifically, section 4.1.1 regarding the test temperature.
1 Outline of Concern
It seems that many new systems being developed for Pedestrian Automatic Emergency Braking (PAEB) are based on existing designs of Electronic Stability Control (ESC) devices. However, for PAEB applications, current ESC systems are not fast enough to autonomously brake a vehicle for the various incursion scenarios.
Because of this lack of dynamic response, it seems one option that is being attempted is to incorporate higher speed motors into current ESC designs so that they develop the needed flow rates to meet these new demands. However, a major flaw with this approach is that as temperature drops, brake fluid becomes more viscous and reduces the efficiency of these ESC units to the point where they may become ineffective below a certain temperature. A more detailed description of this claim will be discussed in section 3 below.
For ESC manufacturers that prescribe to this design philosophy, it would be of the utmost importance to request from regulatory agencies that the test temperatures are within the optimum performance of their ESC units. This seems to be what is happening as the lower temperature range of Euro NCAP pedestrian protection tests is set at 5C (41F) and in this latest proposal from NHTSA is even higher at 7C (45F). This despite the fact that winter low temperatures in the US are well below these test temperatures as shown in the Figure 1.
Application engineers in the industry might argue that the heat from the internal combustion engine will provide enough warmth to the brake components to optimum performance temperatures. I believe this is highly dependent on the brake system component locations as well as the heat-up time needed to achieve this temperature. In addition, this argument falls flat for completely electric vehicles. Thrasher’s entire letter and figures can be viewed by clicking on this sentence.