Ride quality and handling characteristics of an off-road vehicle with active anti-roll bar suspension

Abstract

A vehicle's suspension system isolates the car from road vibrations, resulting in a comfortable ride. In addition, it provides sufficient handling in the vehicle and helps the vehicle to drive stably and reliably. The anti-roll bar system contributes significantly to safety by reducing body roll during cornering. However, when used passively, this system negatively affects the vehicle's ride quality. Active anti-roll bar systems can adjust stiffness according to the driver's input or road conditions. Most current studies have focused on this feature to improve the stability and handling of the vehicle. However, ride quality is essential for many reasons in military vehicles. It is possible to observe effects such as loss of attention and discomfort and the emergence of health problems when the driver is exposed to poor road conditions. In this study, it is desired to examine the effect of the anti-roll bar on the system. According to the results, the goal is to develop a controller for a vehicle with better ride quality. In this context, analyses were made on roads with the same waviness and roughness values to compare each result clearly. In addition, analyses were made on roads with different phase angles to observe the vehicle's response to various conditions. It would need to be important to check essential parameters such as road holding and stability by increasing the ride quality while performing analyses on the off-road vehicle. As a result, analyses of these suspension systems, which are essential for vehicle dynamics such as cornering and lane change, should also be made. The aim is to create a system that will not adversely affect road holding and stability while contributing to the improvement of ride quality. Four different suspension systems were installed in the analyses to examine the ride quality with different anti-roll bar thicknesses. One of them is a thicker anti-roll bar. A front suspension produces higher torsional stiffness and load transfer in this case. The second is the anti-roll bar, which is actively used in the vehicle. The third one is a lower-thickness anti-roll bar. Thus, the results in the case where the effect of the anti-roll bar is reduced wanted to be examined. Finally, the anti-roll bar has been removed from the suspension system. The anti-roll bar model used does not have a complex structure. For this reason, the calculation method created by the SAE (Society of Automotive Engineers) was used while calculating the torsional stiffness. There are standards and methods such as ISO 2631, BS 6841, absorbed power, and VDI 2057 to evaluate ride quality. Within the scope of this study, the absorbed power method, frequency-weighted RMS, and vibration dose value (VDV) have been used to evaluate ride quality. The absorbed power is expressed in Watts to represent how much power the human body absorbs to measure the level of discomfort. In this method, which shows a number mathematically, high values indicate an increase in discomfort, while the limit value is determined as 6 Watts. In calculating the comfort level, getting data from the driver or passenger locations is more accurate. Therefore, acceleration data at the driver's location were taken for calculations. In order to extract acceleration values, first of all, analyses should be made in the multibody dynamics program. Then, with the acceleration values obtained from here, the absorbed power value can be transformed with the transfer functions specified by TARADCOM. Graphical programming and numeric computing environments were used simultaneously for this transformation, and the transfer functions provided are analyzed. Absorbed power values in all three global axes were obtained, and the results were transferred to tables and graphics. Another assessment criterion was ISO 2631. Examining the frequency-weighted RMS and vibration dose value (VDV) results, comments on ride quality were given. To determine these values, the signal processing application examined the acceleration data in all three axes. While analyzing the ride quality, the vehicle travels 300 meters to make the assessment correctly. In addition, the speed values between 12.87 km/h and 32.19 km/h were examined to observe different speed conditions. In order to examine different phase conditions, analyses were made on the paths at 0, 45, 90, and 180-degree phase angles, and their effects were examined. Anti-roll bars with different torsional stiffness values have been investigated for their impact on ride quality. According to the results obtained, the change in thickness did not have much effect on ride quality at a 0-degree phase angle due to the low effect of the anti-roll bar on the system. It also allows the vehicle to remain more stable at this phase angle. With the increase of the phase angle, significant increases were observed in the absorbed power values of the lateral axis. It has been determined that this difference widens even more, especially in the 180-degree phase angle. The presence of an anti-roll bar significantly increases the discomfort in the lateral axis. In addition, it was determined that the highest absorbed power values were on the vertical axis. It has been observed that the anti-roll bar has a negative effect on the vertical axis at the 180-degree phase angle. As a result, it has been deduced that the anti-roll bar has negatively affected ride quality, especially with the increase in the phase angle. According to the results, the lowest absorbed power values were achieved in the vehicle's longitudinal axis (x-axis). When frequency-weighted RMS and vibration dose value (VDV) values were also analyzed, it was found that similar results were obtained with the absorbed power method. In vehicle dynamics analyses such as cornering and double-lane change, it has been observed that vehicles with anti-roll bars in the front suspension have lower roll angle values. In addition, vehicles with and without an anti-roll bar were subjected to lane change analyses by the ISO 3888-2 standard. This analysis consists of an obstacle avoidance course and is based on double-lane change. According to ISO 3888-2 results, it has been observed that the vehicle with an anti-roll bar can complete the track at higher speeds. When the results of the model with active anti-roll bars operating according to the specified algorithm are analyzed, it is observed that the ride quality values of the vehicles have improved considerably, especially at high phase angles. In the analyses where the handling is evaluated, it is observed that the vehicles with the active anti-roll bar system produced similar results to the standard vehicle and performed better than the vehicles without an anti-roll bar. As a result, while the ride quality of the vehicle with the active system is better, there is no change in handling characteristics.