Driver Lumbar Comfort Research Based On Musculoskeletal Biomechanical Loadings

Drivers’ sitting comfort is one of the main characteristics of the vehicle. It has been generally considered that the cause of driver lumbar discomfort and low back pain is primarily biomechanical. An driver musculoskeletal biomechanical model was created to study drivers’ posture & vibration comfort via estimating corresponding lumbar biomechanical loadings like muscle forces and joint reaction force. The simulation research method established here lays a theoretical foundation for the quantitative evaluation and prediction of driving posture & vibration comfort, and helps the comfort design of vehicles.Based on Christophy(2012) lumbar spine model, a baseline driver musculoskeletal model was created and improved via adding intervertebral passive structures, transversus abdominis muscle and intra-abdominal pressure. After modeling intervertebral passive structures, millimeter-sized intervertebral translations were needed during inverse dynamics and static optimization simualtions, but their values are not easy to be economically and easily accessible in real-time. To solve this problem, an efficient iterative optimization method was created. Meanwhile, a stiffness modification method was provided here to solve the problem of mismatch between experimental measured stiffness in literatures and inputed kinematics. Consirdering the fundermental mechanicsm of generating intra-abdominal pressure(IAP) by contracting abdominal muscles, transversus abdominis muscles and a simulation estimation method based on staitic optimization were created. Comparing with experimental measured IAP values, high correlations of estimated IAP values were found.Contact reaction force and friction force were equivalent to be special “muscles” in driver musculoskeletal model and solved by inverse dynamics and static optimization. Interface pressure distribution experiment was done to validate its accuracy. A vechile prototyping and experimental platform for driver posture comfort research was created and reproduced in the OpenSim simulation platform. Based on this platform, effects of lumbar support prominence(LSP), main human body dimensions and torso postures on driver’s lumbar loadings were studied. Lower driver’s lumbar loadings was found to be the fundermental mechanism of driver lumbar comfort.Based on collected human erector spinae muscles’ Electromyography(EMG), effects of sinusoidal whole body vibration frequency on drivers’ muscle response was studied. Peak muscle response from both upper and low back occurred at reported frequencies of peak transmissiblility in vertical direction, which means human nervous system was actively controlling muscles according to the feedback of vibraitons. Two degrees of freedom(DOF) driver simplified model showed that both muscle system’s passive structures and actively muscle contraction affect human spine’s vibration characteristics. To better understand the effects of neural control on human spine’s vibration characteristics and fundamechanism of muscle responses to vibration, a PD control simulating nervous tendon reflex was created and integrated in the driver musculoskeletal model in OpenSim. While both stretch amplitude and stretch speed caused by vibration affects muscle reponses, peak stretch amplitude occurred at frequencies near driver-seat’s resonant frequency was found to be the main reason.