Electronic Stability Control - Review of Research and Regulations
Recent analysis of real world accidents in the USA, Japan and Europe suggests that Electronic Stability Control (ESC) can be remarkably effective at preventing loss-of-control accidents. Regulatory authorities and consumer test organisations around the world are therefore actively researching test methods that can be used to assess the performance of ESC. Researchers in the USA, Canada, Europe, Japan and Australia were contacted to establish the status of research and to obtain comments on ways in which ESC can be assessed and encouraged.
Methods of operation
There are potentially many ways that ESC could detect instability and intervene to maintain control. The simplest form detects when the vehicle is failing to follow the intended course, as indicated by the angle of the steering wheel, and applies a small amount of braking to an appropriate road wheel to provide a compensating moment that brings the vehicle back on course. The following diagrams are from a Insurance Institute for Highway Safety, IIHS Status Report.
An SAE paper by Van Zanten (2000) contains a detailed description of ESC components and functions. Van Zanten, from Robert Bosch GmbH (the major supplier of ESC) discusses the abnormal conditions for which ESC must be designed and tested: "Changes in the tire and car data such as resulting from usual wear and tear or even from small accidents must not reduce the ESP performance or at least must not result in adverse behaviour. Before the system is released, a catalog of special test manoeuvres must be checked. Flat tires and trailers should be included in the catalog. Also the “Moose Test” has become a part of the catalog. Particularly at low ambient temperatures where fast active braking is hampered by the increasing viscosity of the brake fluid the interventions must be checked to be fast enough to achieve the required yaw moment on the car in time. "
The SAE J2564 defines ESC as having the following functions:
Is computer controlled and the computer contains a closed-loop algorithm designed to limit understeer and oversteer of the vehicle.- Has a means to determine vehicle yaw velocity and side slip.
- Has a means to monitor driver steering input.
- Has a means of applying and adjusting the vehicle brakes to induce correcting yaw torques to the vehicle.
- Is operational over the full speed range of the vehicle (except below a low-speed threshold where loss of control is unlikely).
