The rotational speed differences of the vehicle wheels equipped and non-equipped with ABS system

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1 TRANSCOM 2015, June 2015 University of Žilina, Žilina, Slovak Republic The rotational speed differences of the vehicle wheels equipped and non-equipped with ABS system * Diana Młodzińska, * Rafał S. Jurecki, * Emilia Szumska * Kielce University of Technology, Faculty of Mechatronics and Mechanical Engineering, Department of Automotive Vehicles and Transportation, Tysiąclecia Państwa Polskiego 7, Kielce, Poland, dmlodzinska@tu.kielce.pl, rjurecki@tu.kielce.pl, eszumska@tu.kielce.pl Abstract. There is a lot of vehicles equipped with ABS system currently. The system has been obligatory for all new models of the passenger cars since May 1 st, 2004 in the EU countries. The device prevents wheel from lock during brake process and helps driver to acquire brake stability in emergency situations. The goal of paper is to present the results of the investigations of the rotational speed differences of the wheels ABSequipped and non-abs during braking process in winter conditions. Additionally the vehicle was fitted with summer and winter tires. Keywords: ABS, winter tires, summer tires, 1. Introduction Electronic active safety systems of modern passenger cars are intended to reduce or avoid the risk of a road accident. Nowadays, the majority of vehicles are equipped with ABS - an electronic device preventing the vehicle wheel from locking during brake process, ensuring the shortest possible brake distance and brake stability. As a result of the ABS action it is possible to avoid a collision with an obstacle. The driver has ability to control the vehicle in emergency situations. The ABS constantly monitors the rotational speed of each wheel. If it detects a wheel rotating significantly slower than the others, a condition indicating impending wheel lock, by reducing hydraulic pressure to the brake at the affected wheel it is possible to reduce the braking force on that wheel. The wheel then turns faster. Conversely, if the system detects a wheel turning significantly faster than the others, brake hydraulic pressure is increased, the braking force is applied, slowing down the wheel. In modern ABS systems pressure changes can occur up to 100 times per second [1,2,3,4]. During braking, the wheel peripheral speed is lower than the speed of the car motion. When the rotational speed of the wheels equals zero and the car is still in motion the maximum slip is observed. Braking efficiency is dependent on the type of road surface and weather conditions. The wheel slips most frequently on a slippery surface, such as a road which is wet, icy or covered with snow. Braking performances is also influenced by the tire condition. The vehicle tires must provide the best possible adhesion to the road surface [5]. Before the winter season some drivers are considering if it is reasonable to use snow tires in our climate zone or is it better to use the all-season tires. Winter tires are designed to provide enhanced traction on mud or slush road surfaces when the temperature drops below 0 o C. Many European countries have obliged the car owners to use winter tires at a specified time of the year or on prevailing traffic conditions. Polish law has not establish such a requirement but a lot of Polish drivers change the tires before winter. The aim of this contribution is to present some investigation results of the differences in rotational speed of the wheels for ABS-equipped and non-abs equipped vehicles fitted with summer and winter tires during braking process on snow-covered asphalt.

2 2. Test procedure Experiment was carried out on track section of the Kielce University of Technology located in Dąbrowa. Brake tests were conducted on asphalt covered by snow homogeneously. The ambient temperature was -4 o C. The test procedure consisted of accelerating the car to specified speed and then rapid braking initiated by rapid pressing of the brake pedal. The initial velocity was sequentially 10, 15 and 20 km/h. The experiment was conducted with use of two types of tires: summer tires Kleber Dynaxer HP3 185/65/R15 (read wear indicator = 0,1 mm), winter tires Fulda Kristall Montero 2 185/65/R15 (read wear indicator = 0,7 mm). The vehicle tire pressures were set in accordance to the manufacturer s recommendations. Fig. 1. The test track and test vehicle The test vehicle (Opel Astra G) was equipped with - ABS system, - data acquisition station μeep-12 - Corrsys - Datron (Kistler) with ARMS software and a control tablet, which enabled the collection, visualization and pre-processing of the results non-contact - optoelectronic sensor S-350 Corrsys - Datron which can measure the longitudinal and transverse speed of the vehicle and a vehicle drift angle, - directional linear acceleration sensor of measuring range +/- 2g necessary to determine the longitudinal and lateral acceleration of a car body block, - WPT - wheel pulse transducer for acquisition data delivered from vehicle wheel rotation. 3. Results and verification Wheel speed sensors were used to detect any sudden changes of the rotational speed of the wheel. It enabled collecting data of the wheels work and calculation of wheel speeds as well as the changes of the speed at the time, ie. the acceleration and deceleration. Fig. 2 presents a comparison of the rotational speed wheel changes of the ABS-equipped and ABS-unequipped vehicle during braking process. The initial speed was 20km/h. The summer tires were used for this experiment. The rotational speed of the wheels of the ABS unequipped vehicle decreased rapidly (within approx s) to zero, but the car was completely stopped after 5.5 seconds. In the same conditions with the ABS system working and with the wheels initially blocked, their rotation without slipping was restored after about s.

3 a) b) Fig. 2. The rotational speed of the wheels during braking a) ABS unequipped and b) ABS-equipped vehicle fwith the summer tires Fig. 3 presents a comparison of the rotational speed of the wheels of the ABS-equipped and unequipped vehicle fitted with the winter tires during braking process. The initial speed was 20 km/h. The rotational speed of the wheels of the ABS unequipped car fallen to zero after approx. 0.2 s. The car stopped after 6.3 seconds. The ABS-equipped car wheels were blocked initially, but after about s they restored to rotate. The wheels fitted with winter tires rolled longer without slipping than summer tires. The car stopped after 4 seconds. a)

4 Wfeel RPM [1/min] b) Fig. 3. The rotational speed of the wheels during braking a) ABS unequipped and b) ABS-equipped vehicle fitted with the winter tires Fig. 4 shows a comparison of the rotational speeds characteristics for the ABS-equipped vehicle fitted with winter and summer tires respectively during braking process. The intensity of the reduction of the rotational speed lines were traced. An average deceleration of a vehicle equipped with winter tires was 1,26m/s 2, whereas the average deceleration of a vehicle fitted with wheels with summer tires, was 0,75m/s a vg =0,77m/s/s left wheel, summer tires right wheel, summer tires a vg=1,32m/s/s left wheel, winter tires right wheel, winter tires time [s] Fig. 4. The rotational speed of the wheels during braking ABS-equipped vehicle Fig. 5 presents the impact of an initial speed on average deceleration during braking process. The initials speed were small and amounted sequentially 10, 15 and 20 km/h. Differences in the average deceleration were not significant and the influence of the initial speed on average deceleration was negligible.

5 Wheel RPM [1/min] Wheel RPM [1/min] a) avg=0,77m/s/s avg=0,73m/s/s avg=0,73m/s/s left wheel, summer tires 10km/h right wheel, summer tires 10km/h left wheel, summer tires 15km/h right wheel, summer tires 15km/h left wheel, summer tires 20km/h right wheel, summer tires 20km/h time [s] b) avg=1,32m/s/s avg=1,33m/s/s avg=1,32m/s/s left wheel, winter tires 10km/h right wheel, winter tires 10km/h left wheel, winter tires 15km/h right wheel, winter tires 15km/h left wheel, winter tires 20km/h 80 right wheel, winter tires 20km/h time, s Fig. 5. The rotational speed of the wheels during braking ABS-equipped vehicle fitted with a) summer tires, b) winter tires. 4. Conclusions The test results indicated that during braking on snow-covered road: 1. Reduction of the intensity of the wheel rotation speed was dependent on the value of deceleration. 2. The initial braking speed value does not significantly affect on the value of the deceleration. 3. The braking process lasted longer for vehicle fitted with summer tires and ABS system. 4. The shortest braking time was observed for the car equipped with ABS system and winter tires. 5. The experiment showed that the usage of the winter tires on the snow-covered road is fully reasonable and recommended. The ABS system allows to keep control of the vehicle and enables the wheel to rotate without slipping in emergency situations. Acknowledgement This paper has been based on subsidy from LABIN Wsparcie Aparaturowe Innowacyjnych Laboratoriów Naukowo Badawczych Politechniki Świętokrzyskiej w Kielcach projekt nr POPW /09, Ruchome laboratorium badań bezpieczeństwa i komfortu w transporcie zbiorowym WND- RPSW /11, Ruchome laboratorium badań bezpieczeństwa i własności dynamicznych pojazdów samochodowych WND-RPSW /11 and Modernizacja i rozwój infrastruktury dydaktyczno - badawczej dla innowacyjnego kształcenia na kierunku Transport nr WND-RPSW /11.

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