Drivers: Don’t Be Slow To React, Truck ESC Recall
A recent Recall by Daimler Trucks of 2006 to 2012 Freightliner Trucks highlights recent concern regarding inadvertent actuation of Electronic Stability Control (ESC) Systems. Potentially 47,000 units are recalled with Meritor Wabco ESC system manufactured since September of 2005. According to the recall summary, “Under certain road and driving conditions, vehicle body roll and road inclination characteristics may adversely affect the slip angle calculation of the Eectronic Stability Control (ESC) system. This might cause the ESC to perceive an over steering situation and therefore apply the outer wheel brake on the front axle until the vehicle is perceived to be stable.” The Meritor Wabco technologies include ESC, Roll Stability Control and trailer stability control. Some of these systems are described in the Meritor literature as being available since 2002.
Interesting that the vehicle based risk to motor vehicle safety (the recall) lists the defect’s consequence as, “If the driver is slow to react during this ESC intervention, the vehicle may deviate from the intended line of travel increasing the risk of a crash.” In other words, the manufacture is saying they are responsible for an unexpected and dangerous external disturbance to the vehicle – presumably a disturbance from no driver input – but the increased risk of a crash occurs if the driver is slow to react??
NHTSA Published Update of ESC Analysis
The August 10, 2011 Federal Register contained NHTSA’s updated statistical analysis on its existing Safety Standard 126, Electronic Stability Control Systems. The report’s title is: Crash Prevention Effectiveness in Light-Vehicle Electronic Stability Control: An Update of the 2007 NHTSA Evaluation. The Notice stated:
“Statistical analyses based on data for calendar years 1997 to 2009 from the Fatality Analysis Reporting System (FARS) and the General Estimates System (GES) of the National Automotive Sampling System (NASS) estimate the long-term effectiveness of electronic stability control (ESC) for passenger cars and LTVs (light trucks and vans). Safety Standard 126 establishes standards for electronic stability control systems manufactured for use in light vehicles. This report is an update of a previous NHTSA analysis of ESC effectiveness (72 FR 41582) published in 2007.”
“The principal findings are that ESC was associated with a six percent decrease in the likelihood that a vehicle would be involved in any police reported crash and an 18 percent reduction in the probability that a vehicle would be involved in a fatal crash. For passenger cars, the reductions are 5 percent and 23 percent, respectively; for LTVs, 7 percent and 20 percent. Each of these reductions is statistically significant except for the 5 percent overall effect in cars.”
Comments from the public are solicited and must be received by December 8, 2011.
Fire Suppression in Buses and Coaches
According to the brandposten (English edition) the number of fires in buses and coaches has more than doubled since the end of the 1990s. As a result many Buses and Coaches are now equipped with automatic fire suppression systems in the engine compartment. The brandposten goes on to describe a test method for evaluating fire suppression systems. There was an interesting recall on this topic in which a fire suppression system in certain Glaval Buses was incorrectly made with the discharge nozzles incorrectly placed in the driver’s area. The consequence was described: “In the event of a system discharge, a significant cloud of powder could be released into the driver’s compartment possibly obstructing the driver’s view. This situation could result in a vehicle crash.”
The Take Away on Rollover Drag Factors
Dolly rollover tests suggest that the appropriate drag factor range for use in rollover reconstruction, excluding special circumstance, is 0.38 to 0.50. The finding is from the calculated results of 81 dolly rollover crash tests statistically trimmed to exclude the upper and lower 15 percent.
Reevaluation of roll phase analysis of rollover tests on an actual highway found lowered average roll phase drag factors. The average roll phase drag factor as published in the papers was 0.53 g (min = 0.39, max = 0.74) and the average reevaluated drag factor was 0.45 g (min = 0.36, max = 0.52). Natural rollover tests suggest the appropriate drag factor range, excluding special circumstances, is 0.39 to 0.50. The finding is from the calculated results of 21 naturally occurring rollover crash tests statistically trimmed to exclude the upper and lower 15 percent.
Getting Rollover Drag Factors Right
A comparison was conducted of numerous historical studies by reexamination of the original works, analysis of their data, and centralized compilation and analysis of their results. In total 81 dolly rollover crash tests, 24 naturally occurring rollover crash tests, and 102 reconstructed rollovers were identified. Of the 24 naturally occurring tests 18 were steer induced rollover tests.
The range of drag factors for all examined dolly rollovers was 0.38 g to 0.50 g with the upper and lower 15 percent statistically trimmed. The average drag factor for dolly rollovers was 0.44 g (Standard Deviation = 0.064) with a reported minimum of 0.31 g and a reported maximum of 0.61 g. The range of drag factors for the set of naturally occurring rollovers was 0.39 g to 0.50 g with the upper and lower 15 percent statistically trimmed. The average drag factor for naturally occurring rollovers was 0.44 g (Standard Deviation = 0.063) with a reported minimum of 0.33 g and a reported maximum of 0.57 g.
Reevaluation of roll phase analysis published in two papers reporting results of rollover tests on an actual highway (Asay, 2009 and 2010) found lowered average roll phase drag factors as shown in table 1. The average roll phase drag factor published in the papers was 0.53 g (min = 0.39, max = 0.74) and the average reevaluated drag factor was 0.45 g (min = 0.36, max = 0.52). Reevaluation was performed from data published in the papers. A final analysis should be conducted using the actual test data.
Published results of reconstruction derived roll phase drag factors (Hight, 1972) between 0.40 g and 0.65 g was confirmed as the range representing the middle 60% of pre-1972 reconstructed rollover crashes on flat ground, figure 3. The reconstructed drag factors were in a range of 0.04 g to 1.20 g for all 102 plotted results, including downhill rollovers and rollovers with vertical drops. For rollovers on flat ground the reconstructed range was 0.21 g to 0.83 g.
Sudden Acceleration in Reverse
I ran across an interesting recall this morning. It is interesting because it points to potential for problems with software in the control modules of key safety systems. The recall summary is:
“Honda is recalling certain model year 2011 CR-Z passenger cars with manual transmissions, manufactured from January 8, 2010, through June 27, 2011. Should the engine stall while the brake pedal is not pressed, there is a possibility that the engine control unit (ECU) software may cause the electric motor of the hybrid system to move the vehicle unexpectedly in the opposite direction of the selected gear.”
Essentially this Honda recall identified a defect that results in sudden acceleration in the opposite direction of intended travel – sudden acceleration in reverse.
This is not the only recent recall on this issue: Buick Lacrosse’ were recalled because an improper diagnosis:
“may cause the ESC to falsely activate, resulting in sudden changes in vehicle handling and deceleration, particularly at higher speeds, which may cause the driver difficulty in maintaining the vehicle’s desired path of travel and desired vehicle speed, and could result in a crash without warning.”
Essentially the Lacrosse recall identified a defect that may result in brakes application on one side of a vehicle while it is traveling at highway speeds – sudden acceleration to the left (or right).
NTSB Reports Important Steer Axle Tire Failure Testing Results
After conducting testing of natural tire delamination and simulated tire blowout failures on the steer axle of a motorcoach, the US National Transportation Safety Board (NTSB) reported important results that questioned pervasive thought and conventional guidance to drivers regarding such events. Conclusions derived from the report include:
- Tire delaminations produced rotation and torque at the handwheel,
- Some tire failures trials produced lateral force impulse that presented considerable difficulty for maintaining control, while others were “no problem” and presented little challenge,
- Tire delaminations produced sudden, though different from event to event, turning of the vehicle,
- Detection of underinflated tires by visual inspection or “thumping” was not accurate and not advisable. A tire gauge must be used to evaluate tire pressure,
- Progressive loss of air pressure – even to less than 50% of manufactures recommended pressure – were imperceptible while driving and
- Braking, contrary to conventional wisdom and guidance, was shown to not degrade, but improved vehicle control.
The testing was commissioned in an effort to explain factors that may have contributed to a driver’s loss of control of a motorcoach. To this end the NTSB conducted a literature review and ultimately testing regarding effects of steering axle tire failures on handling characteristics and dynamics of a bus or motorcoach. The Board cited numerous studies it found instructive, but no published studies examining the dynamics of buses or motorcoaches in response to tire failure. For this reason, the NTSB undertook its tests to evaluate the effects of steering axle tire delamination or blowout failures on a driver’s ability to maintain control of a motorcoach. Although it was not part of the original plan, the effect of braking on vehicle control was also specifically evaluated.
The NTSB tests were supported by the parties to its investigation and with the active participation, advice and assistance of individuals associated with: Continental Tire, Federal Motor Carrier Safety Administration, Motor Coach Industries, Inc., Greyhound Lines, Inc., The Goodyear Tire & Rubber Company, SmarTire Systems, Inc., Continental AG, Detroit Diesel/Allison Transmission Distributor and TRW, Inc.
Test conditions and response were recorded via the Last Stop Record which provided a snapshot of vehicle data for the 104-second interval preceding engine shutdown, including the vehicle speed (mph), engine speed (rpm), engine load percentage, throttle percentage, and whether the brakes were applied at the time of the tire failure and/or in the intervening period until the vehicle was brought to a stop. Sensors to monitor tire pressure and temperature and steering wheel torque were used. Global Positioning System (GPS) data were recorded to track the location of the test vehicle on the track.
Problems with Tire Standard FMVSS 120
Filed under: Crash Reconstruction, News, Tread Separation
The US Federal Motor Vehicle Safety Standard (FMVSS) 120 covers tires and rims for motor vehicle other than passenger cars. The standard is applicable to multipurpose passenger vehicles, trucks, buses, trailers and motor cycles. The core of the standard attempts to assure that the tires and rims that are sold with a vehicle, and that the tires and rims that are specified on a tire label affixed to a vehicle, are capable of supporting the manufacturer’s specified gross axle load.
A manufacture can sell vehicles weighing more than 10,000 lbs with tires and rims different from its tire label specified tires, rims and inflation pressures. Such a vehicle must meet the requirements of FMVSS 120 with all sets of tires and rims listed on the label and mounted to the vehicle. The tires and rims on a vehicle are evaluated with information from the sidewall of the tire, including the maximum load at the sidewall inflation pressure. The tires and rims listed on a tire label are evaluated using a source like the Tire and Rim Association Yearbook to determine the load carrying capacity of each tire on the label at the recommended pressure. The evaluation process requires that the sum of load carrying capacity for all tires on an axle equal or exceed the manufacture’s front and rear Gross Axle Weight Rating (GAWR).
There are several problems that are presented by this standard including:
- There is no assurance that the tire inflation pressure listed on the tire label will be compatible with different tires in-use on a vehicle. In other words, the inflation pressure listed on a tire label may be too low for the in-use tire given the load and service provided.
- The requirement is that the combined tire carrying capacity of an axle must equal or exceed an axle’s weight rating, however in some vehicles large side to side weight differences exist rendering a tire or set of tires insufficient for the carrying load.
- The standard does not assure compatibility for the variety of tire to rim and mixed tire combinations that might occur given differences between the tire label and the tires sold with a vehicle. For example, the tires listed on a tire label may not properly fit a wider rim appropriate for larger tires sold with a vehicle.
Correcting the Record on NA Luxury Brand ESC Implementation
The North American (NA) implementation of Electronic Stability Control was detailed in the 2008 Society of Automotive Engineers (SAE) paper “Industry Implementation of Automotive Electronic Stability Control (ESC) Systems,” by Nicholas Durisek and Kevan Granat of Dynamic Analysis Group LLC. The Paper compares the luxury vehicle brands Mercedes, BMW and Lexus/Toyota and draws conclusions based upon this comparison. The problem is that Lexus/Toyota is two different brands owned by one manufacture and only Lexus is a luxury brand.
Automotive News Data records, in 2002 Toyota sold 1,756,127 vehicles in the United States; Lexus accounted for 234,109 sales. Also in 2002, the BMW division of the BMW group sold 232,032 vehicles and Mercedes sold 213,225 vehicles.
Comparing Mercedes, BMW and only Lexus passenger cars reveals a disturbing and diverging trend in ESC as standard equipment implementation rates beginning in 1998. Mercedes and BMW were essentially at zero implementation prior to 1998 and 100% implementation for 2000 and on, while Lexus using yearly sales recorded in Automotive News Data had ESC implemented as standard equipment in its passenger cars at the rate of 43% in 2000, 40% in 2001, 39% in 2002 and 37% in 2003. Mercedes and BMW saw the value of ESC and quickly implemented the technology in their entire North American fleet. Lexus missed the opportunity of ESC and delayed full standardized implementation by at least 8 years.
Comparing Mercedes, BMW and only Lexus, instead of Lexus and Toyota together, reflects a Toyota marketing strategy that left many Lexus owners with far inferior vehicles when it came to the benefits of ESC. ESC has been described as providing safety benefit second only to seatbelts. The underlying technology of using individual wheel brake application intervention when drivers lose control of their vehicles began development at Bosch in the late 1980s and was first commercialized in their home countries by Toyota and Mercedes in 1995.
According to Durisek and Granat, “Mercedes’ implementation included less than 2000 vehicles for each of the first three years an ESC system was offered, 1996 through 1998. Those units amounted to less than 2% of the total number of vehicles sold by Mercedes. By model year 2000, Mercedes equipped all models with an ESC system as standard equipment except the SLK. An ESC system was not available on the SLK until 2001…. Implementation by BMW similarly began with relatively low volumes in 1998 and was increased to 100% by model year 2001…. Toyota’s North American implementation of ESC systems as standard equipment began with its Lexus brand in 1998 and included over 50,000 units, more than any other manufacturer for that model year. In model year 2006, the number of Toyota vehicles with an ESC system as standard equipment was over 640,000 units, more than double the number of units sold by Mercedes or BMW.”
Durisek and Granat concluded, “The phase-in of ESC system technology by lower volume manufacturers (i.e. luxury brands) took five to six years before having 100% ESC system implementation into their vehicle lines.” However, according to the Durisek and Granat data, BMW’s North American implementation of ESC as standard equipment took four years with over 95% implementation in three years (by 2000). Mercedes’ implementation of ESC as standard equipment took six years with almost 95% implementation in five years (by 2000). Mercedes had less than 2% implementation in 1998, almost 95% standard equipment implementation in 2000 and in 2001 was at 100% implementation. Not to ignore the importance of full implementation, but Mercedes went from essentially zero to almost complete in two years. For both BMW and Mercedes the final standard implementation of ESC was on a single model with low production. Lexus began implementation in 1998, and completed implementation of ESC as standard equipment in 2007, a full ten years. The last Lexus model with ESC standard was its highest production volume ES line which in 2002, according to the Automotive News Data, accounted for 71,450 Lexus sales – almost half of all Lexus passenger cars sold in 2002.
NHTSA’s Research on Advanced Crash Avoidance Technologies
Ray Resendes, Chief of Intelligent Technologies Research, National Highway Traffic Safety Administration (NHTSA) provided an interesting overview of NHTSA’s efforts on Research on Advanced Crash Avoidance Technologies during his recent presentation at the special session on pre-crash technology during the Association for the Advancement of Automotive Medicine (AAAM) 53rd Annual Conference in Baltimore, Maryland, October 4th through October 7th, 2009.
Resendes described NHTSA’s current plans to include a New Car Assessment Program (NCAP) Advance Technologies Rating for Electronic Stability Control (ESC), Forward Collision Warning and Lane Departure Warning. The phase in period for ESC pursuant to Federal Motor Vehicle Safety Standard 126 (FMVSS126) is 55% in 2009, 75% in 2010, 95% in 2011 and 100% in 2012.
NHTSA’s approach groups intelligent technology interventions into Crash Prevention, Crash Severity Reduction, Injury Mitigation and Crash Notification. Examples of technologies in each area were provided. For example crash prevention technologies include: adaptive cruise control, ESC, rollover prevention, rear end collision avoidance, intersection collision avoidance and automatic alcohol detection interlock; and technologies in crash severity reduction include: Electronic Brake Assist and Brake Augmentation.
Interesting thoughts were presented on how sensing the state of various components of the automobile might be used in assisting drivers. For example intelligent sensing the windshield wipers to determine if a safe stopping distance under wet road conditions exists.
The substance of the presentation listed an array of state of the art technology including: Electronic Stability Control (ESC, first commercial use in 1995 and 100% phase-in pursuant to FMVSS126 by 2012), adaptive cruise control (first in Japan in 1998), forward collision warning, forward collision avoidance and mitigation (set for a 2011 rulemaking decision), blind spot detection, lane departure warning, lane departure prevention (set for a 2001 rulemaking decision), crossing path detection (a backup sensor), fatigue detection, night vision assistance (around for about 10-years), automatic alcohol detection, crash notification and vehicle to vehicle communication (set for rulemaking decision in 2013).
Mark W. Arndt
