Electronic stability control

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Electronic stability control (ESC) is a computerized technology that improves the safety of a vehicle's handling by detecting and preventing skids. When ESC detects loss of steering control, ESC automatically applies individual brakes to help "steer" the vehicle where the driver wants to go. Braking is automatically applied to individual wheels, such as the outer front wheel to counter oversteer, or the inner rear wheel to counter understeer. Some ESC systems also reduce engine power until control is regained.[1]

Contents

[edit] Operation

During normal driving, ESC works in the background, continuously monitoring steering and vehicle direction. ESC compares the driver's intended direction (by measuring steering angle) to the vehicle's actual direction (by measuring lateral acceleration, vehicle rotation (yaw), and individual road wheel speeds).

ESC only intervenes when it detects loss of steering control, i.e. when the vehicle is not going where the driver is steering.[2] This may happen, for example, when skidding during emergency evasive swerves, understeer or oversteer during poorly judged turns on slippery roads, or hydroplaning. ESC measures the direction of the skid, and then applies the brakes to individual wheels asymmetrically in order to create torque about the vehicle's vertical axis, opposing the skid and bringing the vehicle back in line with the driver's commanded direction. Additionally, the system may reduce engine power or operate the transmission to slow the vehicle down.

ESC can work on any surface, from dry pavement to frozen lakes.[3][4] It reacts to and corrects skidding much faster and more effectively than the typical human driver, often before the driver is even aware of any imminent loss of control.[5] In fact, this led to some concern that ESC could allow drivers to become overconfident in their vehicle's handling and/or their own driving skills. For this reason, ESC systems typically inform the driver when they intervene, so that the driver knows that the vehicle's handling limits have been approached. Most activate a dashboard indicator light and/or alert tone; some intentionally allow the vehicle's corrected course to deviate very slightly from the driver-commanded direction, even if it is possible to more precisely match it.[6]

Indeed, all ESC manufacturers emphasize that the system is not a performance enhancement nor a replacement for safe driving practices, but rather a safety technology to assist the driver in recovering from dangerous situations. ESC does not increase traction, so it does not enable faster cornering (although it can facilitate better-controlled cornering). More generally, ESC works within inherent limits of the vehicle's handling and available traction between the tires and road. A reckless maneuver can still exceed these limits, resulting in loss of control. For example, in a severe hydroplaning scenario, the wheel(s) that ESC would use to correct a skid may not even initially be in contact with the road, reducing its effectiveness.

[edit] Components and design

ESC incorporates yaw rate control into the anti-lock braking system (ABS). Yaw is rotation around the vertical axis; i.e. spinning left or right. Anti-lock brakes enable ESC to brake individual wheels. Many ESC systems also incorporate a traction control system (TCS or ASR), which senses drive-wheel slip under acceleration and individually brakes the slipping wheel or wheels and/or reduces excess engine power until control is regained. However, ESC achieves a different purpose than ABS or Traction Control.[4]

The ESC system uses several sensors to determine what the driver wants (input). Other sensors indicate the actual state of the vehicle (response). The control algorithm compares driver input to vehicle response (25 times per second) and decides, when necessary, to apply brakes and/or reduce throttle by the amounts calculated through the state space (set of equations used to model the dynamics of vehicle).[7]

The sensors used for ESC have to send data at all times in order to detect possible defects as soon as possible. They have to be resistant to possible forms of interference (rain, holes in the road, etc.). The most important sensors are:

  • Steering wheel angle sensor: determines the driver's intended rotation; i.e. where the driver wants to steer. This kind of sensor is often based on AMR-elements.
  • Yaw rate sensor : measures the rotation rate of the car; i.e. how much the car is actually turning. The data from the yaw sensor is compared with the data from the steering wheel angle sensor to determine regulating action.
  • Lateral acceleration sensor: often based on the Hall effect. Measures the lateral acceleration of the vehicle.
  • Wheel speed sensor : measures the wheel speed.

ESC uses a hydraulic modulator to assure that each wheel receives the correct brake force. A similar modulator is used in ABS. ABS needs to reduce pressure during braking, only. ESC additionally needs to increase pressure in certain situations.

The heart of the ESC system is the Electronic Control Unit (ECU). The various control techniques are embedded in it. Often, the same ECU is used for diverse systems at the same time (ABS, Traction control, climate control, etc.). The input signals are sent through the input-circuit to the digital controller. The desired vehicle state is determined based upon the steering wheel angle, its gradient and the wheel speed. Simultaneously, the yaw sensor measures the actual state. The controller computes the needed brake or acceleration force for each wheel and directs via the driver circuits the valves of the hydraulic modulator. Via a CAN interface the ECU is connected with other systems (ABS, etc.) in order to avoid giving contradictory commands.

Many ESC systems have an "off" override switch so the driver can disable ESC, which may be desirable when badly stuck in mud or snow, or driving on a beach, or if using a smaller-sized spare tire which would interfere with the sensors. However, ESC defaults to "On" when the ignition is re-started. Some ESC systems that lack an "off switch", such as on many recent Toyota and Lexus vehicles, can be temporarily disabled through an undocumented series of brake pedal and handbrake operations.[8]

[edit] Effectiveness

Numerous studies around the world confirm that ESC is highly effective in helping the driver maintain control of the car and saving lives and reducing the severity of crashes.[9] In the fall of 2004 in the U.S., the National Highway and Traffic Safety Administration confirmed the international studies, releasing results of a field study in the U.S. of ESC effectiveness. NHTSA concluded that ESC reduces crashes by 35%. Additionally, Sport utility vehicles (SUVs) with stability control are involved in 67% fewer accidents than SUVs without the system. The Insurance Institute for Highway Safety (IIHS) issued its own study in June 2006 showing that up to 10,000 fatal US crashes could be avoided annually if all vehicles were equipped with ESC[10] The IIHS study concluded that ESC reduces the likelihood of all fatal crashes by 43%, fatal single-vehicle crashes by 56%, and fatal single-vehicle rollovers by 77-80%.

ESC is described as the most important advance in auto safety since the seat belt by many experts.[11] including Nicole Nason,[12] Administrator of the NHTSA,[13] Jim Guest and David Champion[14] of Consumers Union[15] Max Mosley of the Fédération Internationale de l'Automobile (FIA), E-Safety Aware,[16] Csaba Csere, editor of Car and Driver,[17] and Bill Kozyra, CEO of Continental Automotive Systems[13] The European New Car Assessment Program (EuroNCAP) "strongly recommends" that people buy cars fitted with stability control.[18]

The IIHS and Consumer Reports are so impressed with ESC that vehicles cannot earn their Top Safety Pick ratings without ESC.[19][20]

[edit] Cost

ESC is built on top of an anti-lock brake (ABS) system, and all ESC-equipped vehicles are fitted with traction control. The ESC components include a yaw rate sensor, a lateral acceleration sensor, a steering wheel sensor, and an upgraded integrated control unit. According to National Highway Traffic Safety Administration research, ABS costs an estimated US$368 (in 2005) and ESC costs an additional US$111. The retail price of ESC varies; as a stand-alone option it retails for as little as US$450, however, ESC itself is often not available as an individual. Instead, many manufactures bundle ESC with other features or more expensive levels of luxury, so the cost of a package that includes ESC could be several thousand of dollars.

ESC is highly cost-effective[21] and it might pay for itself in reduced insurance premiums.[22]

[edit] Availability

ESC is not generally available for aftermarket installation, so consumers have to purchase a vehicle equipped by the manufacturer with standard or optional ESC. ESC is rarely offered as a sole option, so it is frequently bundled it with other features or more expensive trims.

Availability of ESC in passenger vehicles varies between manufacturers and countries. In 2007, ESC was available in roughly 50% of new North American models, whereas that figure is about 75% in Sweden. However, consumer awareness affects buying patterns so that roughly 45% of vehicles sold in North America and the UK are purchased with ESC,[23] contrasting with 78-96% in other European countries such as Germany, Denmark, and Sweden. While few vehicles had ESC prior to 2004, increased awareness will increase the number of vehicles with ESC on the used car market.

ESC is available on cars, SUV's, and pickup trucks from all major auto makers. Luxury cars, sports cars, SUVs, and crossovers are usually equipped with ESC. Midsize cars are also gradually catching on, though the 2008 models of the Toyota Camry, Nissan Altima and Ford Fusion only offered ESC on their V6 engine-equipped cars. While ESC includes traction control, there are vehicles such as the 2008 Chevrolet Malibu LS and 2008 Mazda6 GS that have traction control but not ESC. ESC is rare among compact and subcompact cars as of 2008.

ESC is also available on some motor homes. Elaborate ESC and ESP systems (including Roll Stability Control (RSC)[24]) are available for many commercial vehicles,[25] including transport trucks, trailers, and buses from manufacturers such as Bendix Corporation,[26] WABCO [27] Daimler,[28], Scania AB,[29] and Prevost[30]

The Insurance Institute for Highway Safety (IIHS) website[31] shows availability of ESC in individual US models and the National Highway Traffic Safety Administration (NHTSA website[32] lists US models with ESC. The National Roads and Motorists' Association NRMA shows availability of ESC in Australian models.[33] CHOOSE ESC! shows availability of ESC in European countries[34]

[edit] Laws

While Sweden used public awareness campaigns to promote ESC use,[35] others implemented or proposed legislation. Quebec was the first jurisidiction to implement an ESC law, making it mandatory for carriers of dangerous goods (without data recorders) in 2005.[36] The United States was next, mandating ESC for all passenger vehicles under 10,000 pounds (4536 kg), phasing in the regulation starting with 55% of 2009 models (effective September 1, 2008), 75% of 2010 models, 95% of 2011 models, and 100% of 2012 models.[32] Canada[37][38] will likely require 100% of passenger vehicles to have ESC on September 1, 2011. The United Nations Economic Commission for Europe has passed a Global Technical Regulation to harmonize ESC standards.[39] This prompted the Australian Federal Government to consider mandating ESC as early as 2009.[40] The European Parliament has also called for the accelerated introduction of ESC.[41] The European Commission has confirmed a proposal for the mandatory introduction of ESC on all new cars and commercial vehicles sold in the EU from 2012, with all new cars being equipped by 2014.[42]

[edit] History

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In 1959, Mercedes-Benz patented a device that prevents drive wheels from spinning by intervening at the engine, transmission, or brakes. In 1987, Mercedes-Benz applied its patent by introducing a Traction control system that worked under both braking and acceleration. Around the same time, BMW developed a Traction control system.

Worlds first Electronic Stability Control(ESC) was debuted in Mitsubishi Sigma in 1990, Mitsubishi`s system called TCL & TRACE[43][citation needed][44]

From 1987 to 1992, Mercedes-Benz and Robert Bosch GmbH co-developed a system called Elektronisches Stabilitätsprogramm (Ger. "electronic stability programme" trademarked as ESP) a lateral slippage control system, the electronic stability control (ESC). Meanwhile, BMW, working with Robert Bosch GmbH and Continental Automotive Systems, developed a system to reduce engine torque to prevent loss of control and applied it to the entire BMW model line for 1992.

In 1995 Mercedes-Benz, BMW and Volvo began offering ESC on some of their models while Ford, General Motors, Volkswagen, and others investigated and developed ESC systems. In 1995 Toyota began offering ESC system called Vehicle Stability Control (VSC) on Toyota Crown Majesta.

In 1996, during a moose test (swerving to avoid an obstacle) which became famous in Germany as "the Elk test" a journalist rolled a Mercedes-Benz A-Class people-carrier (without ESC) at 37 km/h. Because Mercedes-Benz promotes its reputation for safety, they recalled and retrofitted 130,000 A-Class cars with ESC. This produced a significant reduction in crashes[45] and the number of vehicles with ESC rose. Many high-end makes such as Cadillac, Mercedes-Benz, BMW, Volvo, Audi, and Lexus have made ESC standard on all vehicles, and the number of models with ESC continues to increase.[32] Ford and Toyota have announced that all their North American vehicles will be equipped with ESC by the end of 2009.[46][47] and General Motors has made a similar announcement for the end of 2010.[48]

[edit] Future

The market for ESC is growing at a very robust rate, especially in European countries such as Sweden, Denmark, and Germany. For example, in Sweden, in 2003, the purchase rate on new cars with ESC was 15%. The Swedish road safety administration issued a strong ESC recommendation and in September 2004, 16 months later, the purchase rate was 58%. A stronger ESC recommendation was then given and in December 2004, the purchase rate on new cars had reached 69%[49] and by 2008 it had grown to 96%. ESC advocates around the world are promoting increased ESC use through legislation and public awareness campaigns and by 2012, most new vehicles should be equipped with ESC.

Just as ESC is founded on the Anti-lock braking system (ABS), ESC is the foundation for new advances such as roll stability control (RSC) [50] that works in the vertical plane much like ESC works in the horizontal plane. When RSC detects impending rollover (usually on transport trucks[27] or SUVs[51]), RSC applies brakes, reduces throttle, induces understeer, and/or slows down the vehicle.

The computing power of ESC facilitates the networking of active and passive safety systems, addressing other causes of crashes. For example, sensors may detect when a vehicle is following too closely and slow down the vehicle, straighten up seat backs, and tighten seat belts, avoiding and/or preparing for a crash.

[edit] Active Front Steering

Active Front Steering (AFS) System will superimpose an angle on driver’s steering input via an electromechanical actuator between the steering wheel and steering gear. The motor controlled angle is based on the vehicle’s dynamic state. At all times, the mechanical link between the steering wheel and road wheels are maintained. The superimposed steering angle is not limited mechanically. It has as much authority necessary to achieve the desired vehicle dynamics. With this type of system, many benefits can be added to the functionality of the steering system; including continuously variable steering ratio and enhanced vehicle stability control. The system also provides the driver with tactile feedback of the external forces reacting against the front tires.[52]

[edit] Product names

Electronic stability control (ESC) is the generic term recognized by the Society of Automotive Engineers and other authorities. However, vehicle manufacturers use a variety of different trade names for ESC:

  • Acura: Vehicle Stability Assist (VSA)
  • Alfa Romeo: Vehicle Dynamic Control (VDC)
  • Audi: ESP - Electronic Stability Programme
  • Bentley: ESP - Electronic Stability Programme
  • Bugatti: ESP - Electronic Stability Programme
  • Buick: StabiliTrak
  • BMW: Dynamic Stability Control (DSC) (including Dynamic Traction Control)
  • Cadillac: StabiliTrak & Active Front Steering (AFS)
  • Chery Automobile: Electronic Stability Programme
  • Chevrolet: StabiliTrak; Active Handling (Corvette only)
  • Chrysler: Electronic Stability Programme (ESP)
  • Citroën: Electronic Stability Programme (ESP)
  • Dodge: Electronic Stability Programme (ESP)
  • Daimler: Electronic Stability Programme (ESP)
  • Fiat: Electronic Stability Programme (ESP) and Vehicle Dynamic Control (VDC)
  • Ferrari: Controllo Stabilità (CST)
  • Ford: AdvanceTrac with Roll Stability Control (RSC) and Interactive Vehicle Dynamics (IVD) and Electronic Stability Programme (ESP); Dynamic Stability Control (DSC) (Australia only)
  • General Motors: StabiliTrak
  • Honda: Electronic Stability Control (ESC) and Vehicle Stability Assist (VSA) and Electronic Stability Programme (ESP)
  • Holden: Electronic Stability Programme (ESP)
  • Hyundai: Electronic Stability Programme (ESP), Electronic Stability Control (ESC), and Vehicle Stability Assist (VSA)
  • Infiniti: Vehicle Dynamic Control (VDC)
  • Jaguar: Dynamic Stability Control (DSC)
  • Jeep: Electronic Stability Program (ESP)
  • Kia: Electronic Stability Programme (ESP)
  • Lamborghini: ESP - Electronic Stability Programme
  • Land Rover: Dynamic Stability Control (DSC)
  • Lexus: Vehicle Dynamics Integrated Management (VDIM) with Vehicle Stability Control (VSC) and Traction Control (TRAC) systems
  • Lincoln: AdvanceTrac
  • Maserati: Maserati Stability Programme (MSP)
  • Mazda: Dynamic Stability Control (DSC) (Including Dynamic Traction Control)
  • Mercedes-Benz (co-inventor): Electronic Stability Programme (ESP)
  • Mercury: AdvanceTrac
  • MINI: Dynamic Stability Control
  • Mitsubishi: Active Skid and Traction Control MULTIMODE and Active Stability Control (ASC)
  • Nissan: Vehicle Dynamic Control (VDC)
  • Oldsmobile: Precision Control System (PCS)
  • Opel: Electronic Stability Programme (ESP)
  • Peugeot: Electronic Stability Programme (ESP)
  • Pontiac: StabiliTrak
  • Porsche: Porsche Stability Management (PSM)
  • Renault: Electronic Stability Programme (ESP)
  • Rover Group: Dynamic Stability Control (DSC)
  • Saab: Electronic Stability Programme
  • Saturn: StabiliTrak
  • SEAT: ESP - Electronic Stability Programme
  • Škoda: ESP - Electronic Stability Programme
  • Smart: Electronic Stability Programme (ESP)
  • Subaru: Vehicle Dynamics Control Systems (VDCS)
  • Suzuki: Electronic Stability Programme (ESP)
  • Toyota: Vehicle Dynamics Integrated Management (VDIM) with Vehicle Stability Control (VSC)
  • Vauxhall: Electronic Stability Programme (ESP)
  • Volvo: Dynamic Stability and Traction Control (DSTC)
  • Volkswagen: ESP - Electronic Stability Programme

[edit] System manufacturers

ESC system manufacturers include:

[edit] See also

[edit] References

  1. ^ http://www.chooseesc.eu/download/press/ESC%20Background%20Paper.pdf
  2. ^ Q&As: Electronic Stability Control
  3. ^ YouTube - Truck ESP System
  4. ^ a b YouTube - How Effective is Stability Control
  5. ^ Toyota Glossary
  6. ^ Welcome to IEEE Xplore 2.0: The development of vehicle stability control at Ford
  7. ^ "Bosch Esp Systems: 5 Years of Experience". SAE.
  8. ^ "How to switch off VSC on a Lexus GS430". Automobile Magazine.
  9. ^ The Effectiveness of Electronic Stability Control in Reducing Real-World Crashes: A Literature Review - Traffic Injury Prevention
  10. ^ IIHS news release
  11. ^ EU Commission, FIA, And Euro NCAP Recommend — 'No Car Without ESP', http://www.carpages.co.uk/news/esp-09-05-07.asp, retrieved on 28 December 2007 
  12. ^ U.S. to Require Anti-Rollover Technology on New Cars by 2012, http://www.insurancejournal.com/news/national/2006/09/15/72448.htm, retrieved on 28 December 2007 
  13. ^ a b U.S. set to mandate Anti-Rollover Technology vehicles, http://www.cbc.ca/news/story/2006/09/13/auto-stability.html, retrieved on 28 December 2007 
  14. ^ Stability system called the best thing since seat belts, http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/06/13/MNG7UJD1451.DTL, retrieved on 28 December 2007 
  15. ^ Consumer Reports 2007 Annual Report, http://www.consumerreports.org/cro/resources/streaming/PDFs/2007annualreport.pdf, retrieved on 28 December 2007 
  16. ^ http://www.esafetyaware.eu/download/related_documents/esafetyaware_flyer.pdf
  17. ^ The Greatest Advance in Safety Since Seatbelts, http://www.caranddriver.com/columns/9036/the-greatest-advance-in-safety-since-seatbelts.html?al=128, retrieved on 28 December 2007 
  18. ^ http://www.euroncap.com/content/safety_ratings/recommendation.php
  19. ^ IIHS news release
  20. ^ ConsumerReports.org - Top Picks 2008
  21. ^ http://www.chooseesc.eu/download/press/University%20of%20Cologne_ESC_cost_benefit.pdf
  22. ^ "Farmers Insurance Introduces Auto Insurance Electronic Stability Control (ESC) Discount In Wisconsin". WisBusiness. WisPolitics (2008-01-29). Retrieved on 2008-10-23.
  23. ^ Electronic Stability Control
  24. ^ http://www.esafetysupport.org/en/learn_about_esafety_systems/esafety_systems/roll_stability_control_system_rsc.htm
  25. ^ http://www.bendix.com/Lists/Bendix%20News/Attachments/122/Bendix_ESP_update.pdf
  26. ^ http://www.bendix.com/en-us/products/abs/Pages/ABS6.aspx
  27. ^ a b Meritor WABCO - Products - System Saver Air Dryers
  28. ^ Daimler Increases Safety In Buses Through Electronic Stability
  29. ^ Electronic Stability Program
  30. ^ Prevost – Passenger coaches and bus shells manufacturer
  31. ^ Vehicles equipped with ESC
  32. ^ a b c Electronic Stability Control (ESC) | National Highway Traffic Safety Administration(NHTSA) | U.S. Department of Transportation
  33. ^ Electronic Stability Control in Australia - NRMA Insurance
  34. ^ ChooseESC! Availability of ESC
  35. ^ The Effectiveness of ESC (Electronic Stability Control) in Reducing Real Life Crashes and Injuries
  36. ^ http://www.mtq.gouv.qc.ca/portal/page/portal/entreprises_en/camionnage/matieres_dangereuses/reglement/reglement_modifiant_reglement_transport_matiere_dangeureuses
  37. ^ Electronic Stability Control
  38. ^ Prince George Citizen - MP’s car safety bill reaches Parliament
  39. ^ Press Release: Continental: United Nations Group Action on Electronic Stability Control Helps Advance Auto Safety Worldwide
  40. ^ Australia joins global initiative to mandate electronic stability control | Safety | Carcentral.com.au
  41. ^ eSafetySupport.org European Parliament adopts Intelligent Car Report
  42. ^ EU: Electronic Stability Control to be Standard on all Vehicles from 2014 - Carscoop
  43. ^ http://www.mitsubishi-motors.co.za/featuresites/mm_history/TCL.asp
  44. ^ http://www.desperateseller.co.uk/reviews/Mitsubishi/Mitsubishi-Sigma-used-car-review.asp?models=MitsubishiI%20Sigma%20(1991-1996)].
  45. ^ http://www.whnet.com/4x4/pix/esp_stat.jpg
  46. ^ Ford Motor Company - Press Release - FORD TO MAKE ELECTRONIC STABILITY CONTROL STANDARD ON ALL CARS AND TRUCKS BY END OF 2009
  47. ^ Imports sweep safety list in U.S
  48. ^ Electronic Stability Control, GM
  49. ^ ESC Effectiveness
  50. ^ ROLL RATE BASED STABILITY CONTROL - THE ROLL STABILITY CONTROL ™ SYSTEM
  51. ^ CanadianDriver: Auto Tech - Volvo's Roll Stability Control
  52. ^ http://gsi.xw.gm.com/si/showDoc.do?docSyskey=2084515&pubCellSyskey=169103&pubObjSyskey=2084515&from=sm&laborOpCode=&cellId=169103
  53. ^ ADVICS ESC Modulator

[edit] External links


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