Leilei Zhao

Hybrid modelling and damping collaborative optimisation of Five-suspensions for coupling driver-seat-cab system

ABSTRACT For the complex structure and vibration characteristics of coupling driver-seat-cab system of trucks, there is no damping optimisation theory for its suspensions at present, which seriously restricts the improvement of vehicle ride comfort. Thus, in this paper, the seat suspension was regarded as ‘the fifth suspension’ of cab, the ‘Five-suspensions’ for this system was proposed. Based on this, using the mechanism modelling method, a 4 degree-of-freedom coupling driver-seat-cab system model was presented; then, by the tested cab suspensions excitation and seat acceleration response, its parameters identification mathematical model was established. Based on this, taking optimal ride comfort as target, its damping collaborative optimisation mathematical model was built. Combining the tested signals and a simulation model with the mathematical models of parameters identification and damping collaborative optimisation, a complete flow of hybrid modelling and damping collaborative optimisation of Five-suspensions was presented. With a practical example of seat and cab system, the damping parameters were optimised and validated by simulation and bench test. The results show that the model and method proposed are correct and reliable, providing a valuable reference for the design of seat suspension and cab suspensions.

Hybrid modelling of driver seat-cushion coupled system for metropolitan bus

For the complex structure of driver seat-cushion coupled system for metropolitan buses, there are still lack of convenient and reliable modelling methods for the system at present. To improve ride comfort, the coupled dynamic model is urgently needed to give insight into the dynamic properties of the coupled system. In this paper, for a standard commercially available seat fitted into metropolitan buses, the coupling between the seat and cushion, the nonlinear damping characteristics of the seat damper, and the elastic properties of the damper mounting bushings have been accounted for in a three degree-of-freedom driver seat-cushion coupled system model. Combing field measurements of the seat suspension excitation and cushion acceleration response, a specific flow of hybrid modelling of driver seat-cushion coupled system without the requirement of further bench tests was presented. The analogy between acceleration responses in the frequency domain and the time courses proves that the model can predict the dynamic characteristics of the coupled system with good accuracy for stationary random excitation. The model parameters were also validated by the corresponding bench test. The results show that the accuracy of the model parameters is sufficient and the hybrid modelling method is reliable, which provide a foundation for the optimal design of seat suspension and/or cushion to further improve ride comfort.

An analytical formula of driver RMS acceleration response for quarter-car considering cushion effects

ABSTRACT In this paper, a 3-DOF (degree-of-freedom) model of quarter-car coupled with driver and cushion is used to derive an analytical formula, which can describe the driver RMS (root-mean-square) acceleration response with cars under random excitation generated by road irregularities. The study starts with the 3-DOF model. Based on the vehicle random vibration theory, using the residue theorem, the analytical formula of driver RMS acceleration considering cushion effects is obtained. Then, the driver RMS acceleration values calculated from the measured data and from the analytical formulae of the 3-DOF and the classical 2-DOF model are compared. The results show the analytical formula for the 3-DOF model provides a more reasonable approximation of the real response of the test car. Having obtained the analytical formula, the effects of vehicle parameters on driver RMS acceleration are studied. Finally, to provide critical foundations for the selection of the cushion damping, the optimal damping ratio of driver-cushion system is deciphered from the analytical formula. To uncover how each dynamic parameter effects the optimal damping ratio, the analysis of influencing factors is performed and some important conclusions are obtained. The derived analytical formula can be also conveniently used either during preliminary design or for other special purposes.

Damping Collaborative Optimization of Five-suspensions for Driver-seat-cab Coupled System

Both the seat and cab system of truck play a vital role in ride comfort. The damping matching methods of the two systems are studied separately at present. However, the driver, seat, and cab system are one inseparable whole. In order to further improve ride comfort, the seat suspension is regarded as the fifth suspension of the cab, a new idea of “Five-suspensions” is proposed. Based on this idea, a 4 degree-of-freedom driver-seat-cab coupled system model is presented. Using the tested cab suspensions excitations as inputs and seat acceleration response as compared output, the simulation model is built. Taking optimal ride comfort as target, a new method of damping collaborative optimization for Five-suspensions is proposed. With a practical example of seat and cab system, the damping parameters are optimized and validated by simulation and bench test. The results show the seat vertical frequency-weighted RMS acceleration values tested for the un-optimized and optimized Five-suspensions are 0.50 m/s2 and 0.39 m/s2, respectively, with a decrease by 22.0%, which proves the model and method proposed are correct and reliable. The idea of “Five-suspensions” and the method proposed provide a reference for achieving global optimal damping matching of seat suspension and cab suspensions.

A method to evaluate stiffness and damping parameters of cabin suspension system for heavy truck

Both stiffness and damping parameters of cabin suspension have important influences on the dynamic performance of cabin system for heavy truck. To theoretically study ride comfort of cabin system, the stiffness and damping parameter values of cabin suspension are often required. At present, there is no convenient method unless by bench test to accurately obtain all the stiffness and damping parameters; however, the cost of bench test is relatively high and inconvenient. In this article, according to the real cabin system of a heavy truck, a 3 degree-of-freedom cabin system linear model was presented and its vibration equations were built. By the tested cabin suspension excitations and seat acceleration response, based on curve fitting method, a stiffness and damping parameter identification mathematical model was established. With a practical example of cabin system, the stiffness and damping parameters were identified and validated by bench test. The results show that the built model and the proposed method are workable and lay a good foundation for the theoretical analysis and/or optimal design of cabin suspension to improve ride comfort.

Vibration Characteristics Analysis of Convalescent-Wheelchair Robots Equipped with Dynamic Absorbers

To provide a theoretical guidance for the vibration isolation design, the vibration responses characteristics for the convalescent-wheelchair robot with DA (dynamic absorber) undergoing the random road were revealed. Firstly, the vibration model of the convalescent-wheelchair system with DA was created. The frequency response functions of the road excitation velocity to the convalescent acceleration, the wheelchair body acceleration, and the tire dynamic deflection were deduced. Then, the numerical calculation method of the PSD (power spectral density) and the RMS (root mean square) responses were proposed. Thirdly, the vibration isolation performances of the wheelchair robot with DA and without DA were compared. Finally, the sensitivity analysis of the vibration responses to the mass ratios, the damping ratios, and the natural frequencies was carried out to reveal the effects of the parameters on the vibration responses. The results show that the DA can partly suppress the vibration of the convalescent and the wheelchair body, especially in the resonance area of the wheelchair body. However, the DA cannot successfully improve the tire contact behavior.

Kinetodynamic Model and Simplified Model of X-Type Seat System with an Integrated Spring Damper

A simplified analytical model with transformation coefficients of X-type seat system with an integrated spring damper for control strategies development is proposed on the basis of a kinetodynamic model. Firstly, based on a commercial seat of trucks, the relationship between the suspension support force and the spring force was created by using virtual work principle. The analytical formulae of the equivalent stiffness and the stiffness transformation coefficient were deduced. Based on the principle of conservation of energy, the analytical formulae of the equivalent damping coefficient and the damping transformation coefficient were deduced. Then, the motion equation of the simplified model was created. Secondly, the nonlinear dynamic equation of a complex seat model including the kinematic characteristics was established. Thirdly, the road test was conducted using a heavy truck to collect the seat vibration signals. Finally, the simplified model was validated by the tested data and compared with the complex model. The results show that the accuracy of the simplified model is acceptable. Moreover, the influence laws of kinematic parameters on and were revealed. The proposed simplified model provides an accurate and efficient tool for designing controllable seat suspension system that minimizes a necessary tuning process.

Modelling and validation of a seat suspension with rubber spring for off-road vehicles:

To improve seat performance of low-frequency vibration isolation, this paper investigates a new type of seat suspension with a hollow composite rubber spring. To better describe the real system, a nonlinear suspension model was built. Then, the model parameters were identified and validated, the results show that the model is workable and the identified parameters are acceptable. The acceleration transmissibility of the new suspension was also analyzed by test and simulation. The resonant frequencies measured are close to the simulated under different excitation amplitudes, and all the relative deviations of the resonant frequency are less than 2.0%. Finally, in order to make clear how much the new suspension is better than the traditional suspension with the coil spring, the comparison of ride comfort was conducted under different working conditions. The results show that the new suspension can more effectively attenuate the low frequency from the uneven ground, meanwhile, it can provide a more stable support so that the driver can control the vehicle effectively. The model proposed can be used to predict the performance of the new seat suspension. The new suspension and the model provide a valuable reference for broadening the type of the seat suspension and exploring the optimal performance.

Simulation of vertical characteristics and in-wheel motor vibration of electric vehicles with asymmetric suspension damper under road impact

Abstract For wheel-drive electric vehicles (WDEVs), it has become an urgent problem how to eliminate the adverse effects of the in-wheel motor on ride comfort and to reduce the road impact on the motor. The aim of this paper is to explore the effect rule of the suspension damper damping on the vertical characteristics and the motor vibration of WDEVs under road impact, so as to provide theoretical guidance for the design of WDEVs. Firstly, by considering the nonlinear damping characteristics of the damper, the nonlinear dynamic model of WDEVs is established. Secondly, according to the national standard GB/T 4970-2009, the triangular bump model is created and the evaluation indexes are introduced for WDEVs under road impact. Thirdly, through a case study, the evaluation indexes of a WDEV with different damper damping characteristics are numerically simulated and analyzed. Finally, the evaluation indexes are normalized and the comprehensive performance evaluation is carried out using a radar chart. The results show that under the triangular bump impact, the WDEV with the damper rebound damping less than the compression damping behaves better in terms of comprehensive performance, which is more favorable to avoid the motor damage.

Test verification of a seat-cabin system vertical dynamic model for high-grade fork lift trucks

The seat-cabin system of fork lift trucks has a great influence on ride comfort. On the basis of the structure and characteristics of the seat-cabin system for a high-grade fork lift truck, a seat-cabin system vertical dynamic model was created. The vertical dynamic responses of the model under the random irregularities excitation were calculated. The calculated responses including the seat dynamic response and the cabin dynamic responses at the four corners are very close to the field measurement data and the relative deviations of the (root mean square) RMS acceleration responses are all less than 6.0%. The results show that the vertical dynamic model is acceptable and can truly describe the basic mechanical behavior of the seat-cabin system. The model provides a good basis for investigating the relations between the dynamic parameters and the vibration attenuation characteristics of the seat-cabin system to further improve ride comfort.