Frame loads accuracy assessment of semianalytical multibody dynamic simulation methods of a recreational vehicle

Abstract

The design of a vehicle frame is largely dependent on the loads applied on the suspension and heavy parts mounting points. These loads can either be estimated through full analytical multibody dynamic simulations, or from semi-analytical simulations in which tire and road sub-models are not included and external vehicle loads, recorded during field testing, are used as inputs to the wheel hubs. Several semi-analytical methods exist, with various modeling architectures, yet, it is unclear how one method over another improves frame loads prediction accuracy. This study shows that a semi-analytical method that constrains the vehicle frame center of gravity movement along a recorded trajectory, using a control algorithm, leads to an accuracy within 1% for predicting frame loads, when compared to reference loads from a full analytical model. The control algorithm computes six degrees of freedom forces and moments applied at the vehicle center of gravity to closely follow the recorded vehicle trajectory. It is also shown that modeling the flexibility of the suspension arms and controlling wheel hub angular velocity both contribute in improving frame loads accuracy, while an acquisition frequency of 200 Hz appears to be sufficient to capture load dynamics for several maneuvers. Knowledge of these loads helps engineers perform appropriate dimensioning of vehicle structural components therefore ensuring their reliability under various driving conditions.

Dynamic input loads evaluation of a recreational vehicle frame using multibody dynamics hybrid modeling validated with experimental and full analytical modeling data

“…For instance, the Grounded Chassis method (GC) 11,12 uses a vehicle MBD model grounded at a fixed joint while WFTs recorded efforts are transmitted to the vehicle hubs. In the Controlled Chassis around Origin method (CCO), 12 the MBD model is free to move about a fixed point through a springdamper connection, while WFTs efforts are transmitted to the hubs. Other methods use both WFTs and IMU data.…”

“…Advantages and disadvantages of using semi analytical simulations over full analytical ones were well covered by Joubert et al 12 In a full analytical simulation, a road profile and a tire model are needed, along with the tire model commercial license. Obtaining road profiles and tire models are expensive and time-consuming tasks.…”

“…Other methods use both WFTs and IMU data. The Moved Chassis to a Recorded Position method (MCRP) 12,13 constrains the vehicle body to follow a recorded time varying trajectory while exerting the WFTs efforts to the wheel hubs. Finally, in the Controlled Chassis around a Recorded Position method (CCRP), 12,13 the MBD model is free to move about a recorded time varying trajectory through a spring-damper connection, while WTFs efforts are transmitted to the vehicle.…”

“…Joubert et al 12 previously showed that the CCRP method is the most accurate semi analytical method by simultaneously taking into account load transmission, vehicle orientation, and inertial effects with an acceptable level of non-causal corrective loads by the controller. Semi analytical simulations using the CCRP method connect the vehicle center of gravity (CoG) to a time-varying point trajectory through spring-damper connections along the six degrees of freedom (DoF).…”

“…These corrective forces can impact frame load evaluation if their amplitudes are significant. 12 Although the study conducted by Jouvert et al highlighted the importance of boundary conditions on semi analytical simulation results, simulations were performed using virtual input data previously computed from a full analytical MBD vehicle model simulation. Hence, the effectiveness of the method with experimental data is yet to be proven.…”