Driving dynamics control
The term dynamics control ESC ( E lectronic S tability C ontrol), Electronic in German stability control, often in German-speaking countries with "ESP" for E lektronisches S tabilitäts P abbreviated rogram called an electronically controlled driver assistance system for motor vehicles , the individual by braking wheels counteracts the breakaway of the car. The current version of ESC is an extension and connection of the anti-lock braking system (ABS) with traction control (ASR) and electronic brake force distribution as well as with a brake assistant , in trucks with the electronic brake system .
Since 2014, all newly registered cars and trucks in the EU must be equipped with ESC.
The first Electronic Stability Control was mass-produced by Bosch in 1995 under the name Electronic Stability Program ( ESP ) for the Mercedes S-Class Coupé . The abbreviation ESP is a trademark of Daimler AG , which is why other vehicle manufacturers sometimes use different names. In 1995 BMW ( DSC Dynamic Stability Control in the 7 Series ) and Toyota ( VSC Vehicle Stability Control in the Japanese Crown , Lexus only in 1997 in the LS ) introduced their own driving dynamics controls.
Alfa Romeo calls its system VDC (Vehicle Dynamics Control), Ferrari CST (Controllo Stabilità e Trazione), General Motors Company (GMC) StabiliTrak, Honda VSA (Vehicle Stability Assist), Jaguar and Mazda DSC (Dynamic Stability Control), Maserati MSP ( Maserati Stability Program), Porsche PSM (Porsche Stability Management) and Volvo DSTC (Dynamic Stability and Traction Control).
The term ESC (Electronic Stability Control) or vehicle dynamics control is used for the system in vendor-neutral specialist groups.
Technology and functionality
This driver assistance system tries to prevent the vehicle from skidding in the limit area in bends, both when oversteering and when understeering , by means of targeted braking of individual wheels and thus secures control of the vehicle for the driver.
So that ESP can react to critical driving situations, the system continuously (up to 150 times per second) compares the driver's request with the driving situation. The steering angle sensor provides the driver's request with regard to the direction of travel. Engine management, the ABS speed sensors and the yaw rate sensor ( yaw rate , lateral acceleration ) provide the vehicle behavior data. Another acceleration sensor in newer systems also detects a rotation in the longitudinal axis of the car (rollover). If a significant deviation of the calculated driving state from the driver's request is detected, the system intervenes. Oversteering is corrected by braking the front wheel on the outside of the bend, and understeering is corrected by braking the rear wheel on the inside of the bend. The wheel position plays a double role: On the one hand, the braking force on the inside of the curve generates a yaw moment that supports turning, and vice versa. On the other hand, a braked wheel loses cornering ability, i. H. Braking force on the rear axle supports turning, and vice versa. Unilateral braking interventions on the front axle can be felt on the steering wheel. This effect can be interpreted as a reduction in comfort, which is why some manufacturers only allow the front axle to intervene if the correction on the rear axle proves to be insufficiently effective.
In addition, ESP can also throttle the engine output to reduce the vehicle speed and prevent the drive wheels from spinning. Right from the start, the ESP systems were also connected to traction control, which brakes a spinning drive wheel and thus shifts the drive torque to the other wheel. In addition to the additional sensors (see above), the ESP requires the separation of all wheel brake circuits so that each wheel can be braked individually.
There are only a few special cases in which ESP occasionally "interferes". This includes driving with snow chains , on steep, snow-covered inclines (because the required high slip is not permitted ), in banked turns (on racetracks), deliberate drifting in curves, rapid acceleration and generally deliberate driving in the limit area. Here the driver notices, for example, a throttling of the engine output. In addition, ESP is also suitable for correcting weaknesses in chassis design and tuning.
For these reasons, the activation threshold depends on the brand and product philosophy of the respective manufacturer, for example a somewhat later activation at Porsche. In addition, ESP can be switched off at many manufacturers. For some, however, it reactivates when the brake pedal is pushed to the limit. If that happens, the ESP regulates the vehicle until it is stable and then switches off again. This cannot be seen visually inside the vehicle, but it can be felt in the form of a "jerk". For others, the activation threshold can only be shifted from early / cautious to late / sporty via a switch. The mechanisms are partially undocumented.
- Example BMW
- Holding the DSC button for up to 2.5 seconds on the DSC in the DTC agile mode ( D se Dynamic T raction C ontrol ). If the button is pressed for more than 3 seconds, the DSC or ESP is completely deactivated. Pressing the DSC button again takes you back to normal DSC mode. If the button is pressed for more than 10 seconds, the DSC is set to normal mode for safety reasons until it is restarted.
- Example Ferrari
- The time of intervention and the degree of intervention of the CST (or ESP) can be set in several stages or switched off completely using the so-called Manettino (German: lever ), a small rotary knob on the steering wheel.
Since ESP and ABS functions work together both via the electronic control and mechanical subsystems, the system can no longer be deactivated by pulling a fuse without reducing the braking system to emergency functions.
Example of a driving situation
A car is turning to the right. If the rear end threatens to break out to the left due to a load change reaction , due to the vehicle rocking after a rapid change in the steering angle, due to a strong increase in power in rear-wheel drive vehicles (power oversteer), due to a technical defect (e.g. bursting a rear tire) or due to a change in the coefficient of friction in the curve the ESP brakes the front left wheel. This creates a yaw moment to the left which counteracts the oversteering of the vehicle. The front left wheel and thus the front axle also lose cornering force due to the braking (see Kamm circle ), which additionally weakens the turning moment and thus the oversteering of the vehicle.
History and Outlook
Even before the introduction of ESP, there were control systems that stabilized the vehicle in certain situations. With ABS vehicles were at full braking steerable, with the ABS ASR expansion was primarily in rear-wheel drive vehicles, a stability advantage.
In the meantime, there have also been further developments in which the vehicle is not only stabilized by automatic braking interventions, but also by automatic steering interventions ( ESP II ). With steering interventions, a vehicle can be stabilized very efficiently, especially when braking on inhomogeneous lanes (µ-split) or when oversteering. In order to be able to make active steering interventions, an actively controllable steering system must be installed in the vehicle. This can be, for example, a superimposed steering with which an additional steering angle independent of the driver can be "superimposed" on the steering angle preset by the driver on the front wheels. But also with electrical or freely controllable hydraulic power steering systems , additional stabilization of the vehicle through steering interventions is possible. In this case, however, the steering angle of the front wheels cannot be set independently of the driver's steering angle, as is the case with superimposed steering. Therefore, with an electric power steering, the driver is given a steering recommendation in the form of a steering wheel torque at an early stage, so that he can carry out the steering correction necessary for stabilization himself in good time and correctly. The steering recommendation is only so strong that the driver can effortlessly "override" it and thus always retain full control over the course guidance.
Integrated driving dynamics management
Integrated vehicle dynamics management is the second development stage in vehicle dynamics control. While a conventional electronic stability system ensures more stability in critical driving situations through targeted braking intervention on individual wheels, the integrated driving dynamics management goes one step further. Electronic brake force distribution, traction control and the power of the electric power steering are also taken into account, as are the adjustment options for the variable steering ratio or the active chassis . The introduction in Germany happened in 2005 in the Lexus GS (Vehicle Dynamics Integrated Management VDIM).
Additional functions of ESP
The following additional functions of the ESP are not available in all vehicles and depend on the version of the ESP:
- Electronic Brake Assist (EBA) or BAS: The speed at which the accelerator pedal to the brake pedal is changed is used to recognize that full braking is imminent and the brake system is pre-filled, which ensures that the brake pads are lightly on the discs, in order to shorten the response time of the brake. If the system detects emergency braking via the level of the brake pedal pressure, the brake pressure required to achieve the maximum deceleration is automatically built up.
- Roll Stability Control (RSC): Prevents the vehicle from rolling over by releasing the accelerator and braking individual wheels.
- Trailer Stability Assist (TSA): Stabilization when towing a trailer (e.g. with Audi, Mercedes, Honda and Opel, Subaru but also other manufacturers). The TSA prevents the trailer combination from rocking or skidding through targeted braking of individual wheels of the towing vehicle.
- Dry braking , Brake Disc Wiping (BDW), also brake disc wipers : When wet, the brake pads are lightly applied to the brake discs at regular intervals in order to minimize the film of moisture and thus to obtain an optimal response of the brake (wetness is detected by the operation of the windscreen wipers or an activated rain sensor).
- Hill start assist : From a certain angle of inclination of the vehicle, the brakes hold the vehicle for a short time despite "letting go" of the brake pedal in order to enable the vehicle to move off without rolling back.
- Fading compensation : Despite the extremely hot brake, the necessary pedal pressure does not increase.
- "Soft-Stop": Reduces the braking power shortly before the vehicle comes to a standstill, thus preventing the vehicle from jerking when it comes to a stop. Physically, this is achieved in that the jerk , i.e. H. the temporal change in vehicle deceleration is minimized.
- Engine drag torque control : prevents a too abrupt transition from pulling to pushing operation, so as not to provoke a loss of grip on the drive wheels on a slippery road surface.
- Superimposed steering: Prevents the car from pulling sideways by counter-steering on road surfaces with different grip. This function requires additional functions and intervention options in the vehicle's steering system.
- Tire pressure control: By comparing the speeds of the four tires and evaluating (longer lasting) deviations of one tire from the others, it is possible to determine a pressure drop in a tire and to warn the driver via a corresponding display.
- Electronic differential lock (EDS): At different speeds in different wheels, the power is better distributed according to the traction. Wheels with increased speed are braked in the process.
- Traction control through traction control : It ensures that the wheels do not spin when moving off on slippery or wet roads. This prevents the vehicle from breaking out to the side.
The challenge in the configuration is to also prevent the vehicle from not moving at all in unfavorable conditions (mirror-smooth road surface, deep snow) due to the ASR.
In 2004, the proportion of new vehicles equipped with ESP in Germany was 64% (as of February 16, 2005). On the other hand, of the total number of cars in Germany (as of March 2005) only approx. 23% ( ADAC estimate ) or 15 to 20% (Bosch estimate) are equipped with ESP, which is due to the fact that the average vehicle population in Germany is 8 years is old and only no longer appears in traffic after 13 years (as of mid-2007). 2009 had 72 per cent (2008: 67; 2007: 64; 2006: 58 percent) of the available in Germany car model series as standard ESP on board, 9 per cent (2008: 9; 2007: 14; 2006: 20 percent) of all new passenger car model series were not yet available with ESP as standard. According to a survey by the Federal Statistical Office, in 2015 70% of the existing cars were equipped with ESP, while the rate among new cars was 100%. This is also due to the fact that ESP has been mandatory for new vehicles since November 1, 2014.
Statistical data on dissemination:
- As of 2005, all newly registered vehicles in Germany: 72%.
- As of the first half of 2006 all newly registered vehicles in Germany: 75%, thereof
- Upper middle class and upper class: 100%
- Compact class: 96%
- Small car: 27%
- Microcar 30%
- In Western Europe 42% ( Bosch information )
As the statistics show, the equipment rate in the lower vehicle classes is lower than in the upper class due to cost reasons, although it is precisely these vehicles that can particularly benefit from ESP due to their low mass moment of inertia. In February 2006 the VDA issued a recommendation for all German automobile manufacturers to commit themselves to standard equipment of ESP in all vehicles, since the advantages of this system in normal everyday operation do not conflict with any disadvantages. According to Bosch, Germany takes the top position for ESP equipment within Europe. Competitors are Continental and for some time also TRW . In the case of buses, the equipping quota for new registrations (March 2005) is around 50%, whereas for trucks it is only 5%. This is mainly due to the greater complexity of the system in commercial vehicles and thus significantly higher costs.
Although it is difficult to evaluate the data on traffic accidents accordingly, the reduction in many serious traffic accidents ( active safety ) in recent years is also attributed to the introduction of ESP. ESP prevents vehicles from skidding, a major cause of accidents with seriously injured and fatalities. A study by Mercedes has shown that the accidents in their cars have decreased by 15% since they were fitted with ESP as standard. According to a study by Volkswagen, the number of vehicle occupants killed in road accidents could be reduced by around 25% if all vehicles were equipped with ESP. ESP is seen by accident researchers as being comparable to seat belts and airbags in terms of safety. The UDV investigations have shown that 25 percent of car accidents with personal injury and at least 35 percent of car accidents with fatalities could be positively influenced by ESP. If one relates these findings to the car / car and car single accidents of the official statistics for 2007, then in Germany - taking into account the fact that in 2007 already 36% of all cars were equipped with ESP - around 21,000 corresponding accidents with injuries and approx. 400 accidents with fatalities can be avoided or at least mitigated in their consequences by ESP.
According to a resolution by the European Parliament on March 10, 2009, since November 2011 all newly registered car and truck models in the EU must be equipped with ESP as standard. A transition period from already granted vehicle type approvals applied until the end of October 2014.
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- Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3
- German Patent and Trademark Office, register number 2912578
- http://www.toyota-global.com/company/history_of_toyota/75years/data/automotive_business/products_technology/technology_development/electronics_parts/index.html 75 Years of Toyota. Ever-better cars
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- S. Breuer, A. Rohrbach-Kerl: Vehicle dynamics: Mechanics of the moving vehicle. Springer 2015. p. 181 ISBN = 9783658094751
- Bosch graphics, status 2008 ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- European Parliament approves ESP obligation. Heise Online from March 17, 2009
- REGULATION (EC) No. 661/2009 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 13 July 2009 on the type approval of motor vehicles, motor vehicle trailers and of systems, components and independent technical units for these vehicles with regard to their general safety (PDF)