Advanced Analysis of Wheel Contact Forces in Dual-Unit Vehicles Using Kistler RoaDyn Sensors ^†

Abstract

The configuration under investigation consists of a car and a trailer connected by a coupling mechanism at a hinge point. Due to the dual-unit design, car–trailer combinations are prone to poor lateral stability at high speeds, often resulting in trailer sway, which is a significant factor in road accidents near the upper speed limit. This issue is exacerbated by the fact that drivers receive feedback primarily from the car, making it difficult to detect and respond to the trailer’s movements. To address this problem, vehicle manufacturers advocate for the use of active safety systems such as active trailer braking or steering. The comprehensive study of vehicle dynamics is essential for improving road safety, particularly in the context of car–trailer systems. This research aims to analyze the dynamic behavior of these systems using a specialized Kistler force and torque measurement instrument mounted on the vehicle’s wheels. By varying the position of the cargo mass forwards and backwards on the trailer, the effect of different load distributions on vehicle stability and handling will be evaluated. The findings of this study are expected to provide valuable insights into the role of mass distribution in dynamic performance, contributing to the development of more effective safety measures and enhanced vehicle performance.

1. Introduction

The study of vehicle dynamics, particularly in the context of car–trailer systems, is essential for improving road safety and enhancing the driving experience. These dual-unit systems, comprising a car and a trailer connected by a coupling mechanism, often exhibit poor lateral stability at high speeds, leading to potentially dangerous situations such as trailer sway. This phenomenon is a significant cause of road accidents, especially when the vehicle approaches the upper speed limit. Drivers typically receive feedback primarily from the car, making it challenging to detect the trailer’s movement and respond appropriately. To address this issue, vehicle manufacturers recommend the implementation of active safety systems, such as active trailer braking or steering, which can mitigate the adverse effects of trailer sway and improve overall stability. This research focuses on analyzing the forces at the wheel contact points in a car–trailer system during a double lane change maneuver, as specified in the international standard ISO 3888:1–2018 [1]. In their article, Stanojčić and co-authors examined the cornering behavior of vehicles under various conditions [2,3]. Roh et al. focused on controlling car–trailer systems using a driver assistance system, aiming to enhance stability and maneuverability through automated control strategies. Kutluay and Winner developed an assessment methodology for validating vehicle dynamics simulations using the double lane change maneuver, providing a structured approach to evaluate the accuracy of simulations in representing real-world vehicle behavior [4,5].

By examining the impact of different load distributions on vehicle stability and steering response, this study aims to provide insights that could inform the design and implementation of more effective safety systems. The results of this analysis are crucial for understanding the dynamic behavior of car–trailer combinations and enhancing their performance in real-world driving conditions.

2. Vehicle Dynamics Measurement Standards

Double Lane Change

Double lane change is described in the international standard ISO 3888:1–2018 [1], one of the tests used in the automotive industry. Specifically, this standard applies to the testing of strict lane change maneuvers in motor vehicles. The standard is designed to evaluate the performance and driving dynamics of vehicles in lane-changing situations that drivers may experience in real-world road conditions [6]. Double lane changing is an important vehicle dynamic test that is often used to evaluate the driving stability and steering of cars and other vehicles. The purpose of the test is to check the dynamic behavior of the vehicle, especially in situations where a sudden and intense lane change is required, such as during a dangerous overtaking maneuver or when avoiding an unexpected obstacle. In the measurements carried out, the passenger vehicle was equipped with a towing frame on which loads of different weights were placed [7]. In the double lane change test, the towing vehicle and its towed load are required to perform a rapid, consecutive lane change on a section of track defined and marked in the standard (Figure 1). During the test, the behavior of the vehicle is measured, such as speed change, steering response, and lateral displacement. The measurements focused on the rear axle of the vehicle, investigating the effect of different weight placements on the towing vehicle [8].

3. Measurement Methods and Environment

3.1. Instruments Used for Measurement

For the measurement, the instruments listed in

Table 1. Instruments used for measurement.

Equipment Name	Number of Items
Mercedes-Benz CLA250 (W117) produced in Hungary, 2013.	1
Kalydi-1 trailer	1
Kistler Roadyn S625 force transducers measure wheel	4
MOTEC I2 Pro software	1
EUR palette	1
water balloon 160 L	2
water balloon 20 L	4
water balloon 10 L	13

below were used.

3.2. Placement of Loads

The loads were made of water balloons of different volumes and numbers of pieces. The loads and their placement and the normal forces are symbolized in Figure 2 below. It is important to note that the optimal load distribution depends on the type, size, and design of the vehicle [9]. Vehicle manufacturers generally provide recommendations for the appropriate load distribution, and it is important to follow these recommendations for safe and stable driving. Maintaining load balance is key to maintaining vehicle stability and drivability [10].

4. Results and Comparison

For each load placement, three measurements were performed with the loads shown in Figure 2 above. After examining the measurements, the normal force functions on the right and left sides of the rear axle were established [11]. The results obtained on the track were compared between the most stable and the most unstable results. The most unstable is presented first, where a 530 kg load was placed on the rear of the trailer [12]. The left and right normal force variation functions for the rear wheels of the tow vehicle are shown in Figure 3 and Figure 4 below.

Each function is shown with the force corresponding to the rest position, which helps make the diagrams easier to understand. From the deviation from the resting state level, the movement of the vehicle about the X axis can be determined. The X axis is the median longitudinal line of the vehicle. In the next section, the load is placed on the front of the trailer. The normal force diagrams for the left and right wheels are shown in Figure 5 and Figure 6 below.

By comparing the figures, a para-movement is created when the trailer is rear-loaded. This movement is the result of an unpredictable movement when the towed mass “shocks” the towing vehicle. According to the time measured on the X-axis, in Figure 4 and Figure 6, after 42.5 s, several excursions can be observed in the function diagram, whereas for the front mass, in Figure 5 and Figure 7, after 44.5 s, the instantaneous normal forces approach the value corresponding to the rest condition [13,14,15].

Results

A comparative graph is essential to evaluate the measurement. As the measurements were taken manually, the distances covered by the vehicle between two steering movements varied over time. The graphs are averages of the data measured by the tests, correcting for time slips. The following comparison graphs show the normal force diagrams for the left and right rear wheels first. Figure 7 and Figure 8 show the front load values in blue and the rear load values in red, respectively, with critical para movements in green.

5. Conclusions

The objective of the study was to determine the effect of differently positioned weights on the controllability of the vehicle. The research aimed to analyze the vehicle’s stability and controllability during various maneuvers, as well as the factors influencing vehicle sliding or drifting. Based on the measured data, when the load was positioned behind the trailer axle (rear load), the driver experienced sliding despite the low initial speed. In the diagrams, the slip is represented by the instantaneous components of the normal direction forces crossing sinusoidally the constant vector corresponding to the rest position in both positive and negative directions. The results were used to assess the vehicle’s behavior during sudden lane changes and in response to varying wind strengths, contributing to safer vehicle design. Additionally, these results can be applied to evaluate the vehicle’s ability to maintain controllability during such maneuvers. These and similar tests are utilized by vehicle manufacturers to enhance the driving safety of their products. However, the limitations of the study include the fact that the conditions applied during the measurements may not fully represent real-world driving scenarios, such as extreme weather conditions or varying road surfaces. Moreover, the research focused primarily on a specific vehicle and its towed unit, which may limit the generalizability of the findings to other vehicle types or configurations. Further data may be required to validate simulations and enhance the accuracy of the models used. The dataset obtained from the measurements will be used to pursue further objectives, including the creation and validation of various simulations. Additionally, these data will be instrumental in building the measurement environment.