Study of grip and rolling resistance coefficients of automobile tires

Abstract

Determining the traction and traction indicators of cars, such as the coefficients of rolling resistance and traction, often uses a towing method. This method can be implemented with a simple device that includes a horizontally positioned dynamometer and a flexible towing belt. However, this approach is characterized by significant inaccuracies in measuring the average towing force. This inaccuracy arises from the variability in how the wheel drives interact with the supporting surface, which consequently affects the precision of determining both the grip coefficient and other traction-related indicators, including the rolling resistance coefficient.

The standard towing device used to evaluate the traction-coupling properties of mobile energy vehicles has a considerable elementary measurement interval (∆tdi). This interval is limited by the observer's ability to visually record the current readings from the dynamometer. The large elementary interval leads to low accuracy in determining the towing force, and consequently, the average values of force, rolling resistance coefficients, and grip. Rapid changes in the dynamometer readings, due to fluctuations in the road's micro-profile, further complicate accurate measurements. Therefore, relying on visual observation during these tests is highly imprecise.

To enhance the accuracy of determining the towing effort for mobile energy vehicles, a methodology and software complex have been developed. This improvement is achieved by reducing the elementary interval for recording measurement values. The proposed software module connects to the electronic dynamometer's power tension link. This module is designed as a microcircuit equipped with an analog-to-digital converter, which interfaces with a microcontroller and a bus for connecting external devices, along with a data output interface. This configuration ensures the efficient transfer of data to electronic storage media, such as a memory card or a personal computer.

The coefficients of rolling resistance and adhesion for Debica Passio 2 175/70 R13 82T wheels on the ZAZ Sens car were measured across various types of supporting surfaces. For an asphalt road, the grip coefficient (φi) ranged from 0.6914 to 0.7162, with an average value of 0.698. On a dirt road, φi values ranged from 0.5754 to 0.6144, averaging 0.595. For gravel surfaces, the values were between 0.3755 and 0.4451, averaging 0.408. The lowest φi values were observed on a wet dirt road, ranging from 0.3275 to 0.3767, with an average of 0.358.

For winter tires, the adhesion coefficient on an asphalt road (φi) ranged from 0.6138 to 0.6514, with an average value of 0.6280. On a dirt road, this coefficient was between 0.5799 and 0.6045, averaging 0.5919. For gravel surfaces, the values ranged from 0.3847 to 0.4041, with an average of 0.3945. Comparatively, with summer tires on a wet dirt road, the φi values were from 0.3761 to 0.3908, averaging 0.3825.