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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.
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Encyclopedia
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.
History
Mercedes-Benz patented a device in 1959 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. In 1987, Toyota also introduced traction control system in the Toyota Crown. Traction control however only works under acceleration and is not designed to aid in steering.
In 1990, Mitsubishi released the Diamante (Sigma) in Japan. It featured a new electronically controlled active trace & traction control system (the first integration of these two systems in the world) that Mitsubishi developed. Simply named TCL in 1990, the system has since evolved into Mitsubishi's modern Active Skid and Traction Control (ASTC) system or ESC. Developed to help the driver maintain the intended line through a corner; an onboard computer monitored several vehicle operating parameters through various sensors. When too much throttle has been used when taking a curve, engine output and braking are automatically regulated to ensure the proper line through a curve and to provide the proper amount of traction under various road surface conditions. While conventional traction control systems at the time featured only a slip control function, Mitsubishi's newly developed TCL system had a preventive (active) safety function which improved the course tracing performance by automatically adjusting the traction force (called "trace control") thereby restraining the development of excessive lateral acceleration while turning. Although not a ‘proper’ modern stability control system, trace control monitors steering angle, throttle position and individual wheel speeds although there is no yaw input. The TCL system's standard wheel slip control function enables better traction on slippery surfaces or during cornering. In addition to the TCL system's individual effect, it also works together with Diamante's electronic controlled suspension and four-wheel steering that Mitsubishi had equipped to improve total handling and performance.
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). This was the first true stability control system, more advanced than Mitsubishi's TCL & TRACE system. 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.
Meanwhile, other manufactures were also developing their own electronic stability control systems which were released in 1995.
Introduction
Mercedes-Benz was the first to introduce ESC in 1995 on their W140 S-Class model. BMW and Volvo began offering ESC on some of their models later in the same year. In 1995, Toyota began offering ESC system called Vehicle Stability Control (VSC) on Toyota Crown Majesta, while Ford, General Motors, Volkswagen, and others investigated and developed their own ESC systems.
During a moose test (swerving to avoid an obstacle) which became famous in Germany as "the Elk test" a journalist during 1996 rolled a Mercedes-Benz A-Class (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 and the number of vehicles with ESC rose. Many high-end makes such as Cadillac, Mercedes-Benz, BMW, Volvo, Audi, Saab, and Lexus have made ESC standard on all vehicles, and the number of models with ESC continues to increase. Ford and Toyota have announced that all their North American vehicles will be equipped with ESC by the end of 2009. and General Motors has made a similar announcement for the end of 2010.
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. 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. 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. 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.
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.
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.
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. 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 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. including Nicole Nason, Administrator of the NHTSA, Jim Guest and David Champion of Consumers Union Max Mosley of the Fédération Internationale de l'Automobile (FIA), E-Safety Aware, Csaba Csere, editor of Car and Driver, and Bill Kozyra, CEO of Continental Automotive Systems The European New Car Assessment Program (EuroNCAP) "strongly recommends" that people buy cars fitted with stability control.
The IIHS and Consumer Reports are so impressed with ESC that vehicles cannot earn their Top Safety Pick ratings without ESC.
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.
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).
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 system, 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.
Availability and 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 $250 USD. However, ESC is rarely offered as a sole option, and is generally not available for aftermarket installation. Instead, it is frequently bundled it with other features or more expensive trims, so the cost of a package that includes ESC could be several thousand of dollars. Nonetheless, ESC is considered highly cost-effective and it might pay for itself in reduced insurance premiums.
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, 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 model years 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 that have traction control but not ESC. ESC is rare among subcompact cars as of 2008. The 2009 Toyota Corolla in the United States (but not Canada) has stability control as a $250 option on all trims outside the XRS which has it standard. In Canada, for the 2010 Mazda3, ESC is as an option on the midrange GS trim as part of the moonroof package, and is standard on the top-of-the-line GT version.
ESC is also available on some motor homes. Elaborate ESC and ESP systems (including Roll Stability Control (RSC)) are available for many commercial vehicles, including transport trucks, trailers, and buses from manufacturers such as Bendix Corporation, WABCO Daimler,, Scania AB, and Prevost
The Insurance Institute for Highway Safety (IIHS) website shows availability of ESC in individual US models and the National Highway Traffic Safety Administration (NHTSA website lists US models with ESC. The National Roads and Motorists' Association NRMA shows availability of ESC in Australian models. CHOOSE ESC! shows availability of ESC in European countries
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% 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) that works in the vertical plane much like ESC works in the horizontal plane. When RSC detects impending rollover (usually on transport trucks or SUVs), 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.
Laws
While Sweden used public awareness campaigns to promote ESC use, 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. 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. Canada 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. This prompted the Australian Federal Government to consider mandating ESC as early as 2009. The European Parliament has also called for the accelerated introduction of ESC. 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.
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
System manufacturers
ESC system manufacturers include:
External links
- a combined initiative from the European Commission, eSafetyAware, and Euro NCAP
- from eSafety Support
- (PDF)
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