Active Roll Over Protection System
Research and writing by Mechanical sub-system, ISA-Manipal student section.
It has been almost 200 years since first commercial vehicle has been in our world. We have been making progress ever since, improving speed, efficiency, quality of life and much more. Travel has become a necessary part of our life and many people’s lives are dependent on it. Be it heavy duty transportation by trucks or daily commute through city roads, more and more people are integrating travel in their lives and hence safety becomes an important metric of concern. According to WHO approximately 1.3 million people die due to accidents regarding travelling by any vehicle. It maybe speeding, distracted driving, unsafe roads, vehicles, etc. Speeding accounts for more than 60% of Accidents and hence is a major area of importance.
Over speeding has been a major problem recently as the world moves to more strict timing and deadlines, drivers try to compensate by speeding. Vehicle becomes very hard to control during uncertain situations. Active Roll over protection system helps drives to better control their vehicles by using various Sub-mechanisms.
How it works?
ARP for heavy commercial vehicles is basically an electronic control system built upon the following main sub-components — Anti lock Braking system, Yaw and Traction control. ARP can also detect forthcoming rollovers (rollovers is a type of crash in which vehicle is tripped over to its side or roof) during speeding over a sharp turn and can also prevent rollovers using suspension system to counteract the center of gravity of the vehicle.
Anti-Lock Braking System — This system prevents locking to brake plate-wheel which is necessary because when the wheel locks in and at high speeds the vehicle skids on the road making it harder to control and deceleration decreases.
This system works by actively checking to rotation speed of wheels and correcting the brake pressure in case of rotation of wheel doesn’t correspond to speed of vehicle.
It consists of electronic speed sensors for each wheel and at least two hydraulic valves within brake system. Speed sensors act as a control signal to hydraulic valves which can check rotation speed up to 15–30 times second in modern vehicles. After detecting mismatched conditions, it makes necessary changes. The ratio of changes is generally pre-defined based on vehicle use case after trying and testing on different roads, whether conditions, Tire material used, etc.
Modern stability control systems are complex systems based on the ABS. Here, a minimum of two or more sensors are added to help the system to be functional. A Gyroscopic sensory and Steering wheel angle sensor. During sharp turns gyroscopic sensors and steering wheel sensors should be in sync otherwise the vehicle wheel would lock itself and skid, hence when they are in a mismatch a software makes necessary adjustments to brake different wheels to produce the same effect as intentional turn made by the driver.
Traction Control System — This system prevents the wheel from slipping on acceleration or when driving on smooth and slippery surfaces. Traction control takes the input of the speed from each wheel using speed sensors. The onboard traction control system measures the difference in rotational speed of each tire and hence, determine which wheel has lost traction. If the system detects a wheel is slipping, the brake module applies pressure to the brakes of that wheel to reduce its speed. More advanced traction control systems can also reduce the engine power going to the wheel that is slipping and transfer it to a wheel that have more grip.
Yaw Control System — This system sustains longitudinal acceleration and improves lateral stability by controlling torque distribution between the driven wheels. It is generally used to maximize traction while cornering on sharp turns. The torque distribution is controlled by the ECU and is applied to the wheels through several mechanical components in the differential. In some cases, the clutch pressure is also varied to control the amount of torque going to the transmission system. If a vehicle begins to rotate in a manner inconsistent with the steering wheel position, torque from the outside wheel will be transferred to the inside wheel. As a result, the vehicle will rotate in the direction as inputted by the steering wheel.
Conclusion:
As said earlier, the ARP system works with the help of the Anti-Lock Braking System, Traction Control System and the Yaw Control System. When the driver turns suddenly, inputs are taken in from the steering angle, relative speed of the wheels from the speed sensors and tilt from the gyroscopic sensor. The traction control system prevents the wheels from slipping, thus, ensuring the vehicle stays on its path. The Yaw control system will take the input of steering angle and speed, then accordingly, distribute the torque between the wheels (more to the outer wheels compared to the inner wheels). And finally, if the driver is applying brakes while performing a sudden manoeuvre, the ABS module will apply brake pressure in pulses so that the wheels don’t lock up and causes the tires to slip. The gyroscope sensor keeps in check how much the vehicle is leaning while turning and accordingly apply brakes or limit the torque.
In this way, the ARP system works with its sub-systems to ensure that the driver can perform sharp and sudden manoeuvres without losing control of his vehicle and ensuring the safety of the passengers onboard.
References:
https://www.who.int/news-room/fact-sheets/detail/road-traffic-injuries
https://www.monash.edu/__data/assets/pdf_file/0020/218270/racv-abs-braking-system-effectiveness.pdf
https://www.nhtsa.gov/risky-driving/speeding
https://cecas.clemson.edu/cvel/auto/systems/yaw-control.html
https://auto.howstuffworks.com/28000-traction-control-explained.htm
