Hydro-gas suspension system for a tracked vehicle: Modeling and analysis

Tracked vehicles fitted with torsion bar suspensions are limited in their ability to achieve high mobility. This limitation is due to the linear characteristics and the consequent poorer ride performance. Hydro-gas suspensions due to their inherent non-linear behavior can provide higher mobility and better ride comfort performance. The hydro-gas suspension model has usually been developed from experimental force-displacement characteristics, which requires availability of suspension hardware.In this paper, a hydro-gas suspension system is modeled using polytropic gas compression model to represent the spring characteristics, while the damper orifices are modeled using hydraulic conductance. The analytical model is then validated with experiments individually for spring and damper flow characteristics and then as a suspension-wheel assembly in a test rig. The validated suspension model is incorporated in an in-plane model. Using this model, simulation is carried out for sinusoidal inputs of different wavelengths, amplitudes and vehicle speeds. The simulation model is validated with data measured on a vehicle traversing an APG course. The proposed model agrees very well with the measured data. Based on the validated model, studies on the influence of suspension parameters on the ride comfort of a tracked vehicle are carried out.     

Analytical track models for ride dynamic simulation of tracked vehicles

This paper presents various modelling strategies to account for track in the ride dynamic simulation of high mobility tracked vehicles negotiating rough off-road terrains. Four analytical track representations of varying complexities are formulated in conjuction with an in-plane ride dynamic model of a typical tracked vehicle. These track models are conceived in view of the tracked vehicle kinematics while ignoring the track belt vibrations. The ride dynamic response of a conventional armoured personnel carrier is evaluated in conjunction with different track methods, and validated against field-measured ride data. The relative performances of these track models are thus assessed based on the accuracy of response predictions, and associated computational time.     

Semi-active hydro-gas suspension system for a tracked vehicle

A semi-active hydro-gas suspension is proposed for a tracked vehicle to improve ride comfort performance, without compromising the road holding and load carrying capabilities of the passive suspension. This is achieved through an active damper used in parallel with a gas spring. The suspension damper parameters are varied by a control mechanism based on sky-hook damping theory, which alters the flow characteristics. A damper prototype has been developed, tested for its flow characteristics, after which it has been integrated into an existing hydro-gas suspension system. An analytical model has been proposed from first principles rather than developing a phenomenological model based on experimental characteristics. This model is validated with experiments carried out on a suspension test rig. In order to compare the performance with the original passive system, an in-plane vehicle model is developed and the simulations clearly show that the semi-active system performance is superior to the passive system.     

Design and testing of lateral seat suspension for off-road vehicles

Operators of off-road vehicles such as construction, forestry, agricultural vehicles and mining vehicles are exposed to excessively high levels of vertical and lateral vibrations which can pose health risks to the drivers. Ride improvement through seat suspensions has been successful in the vertical mode, however, seat suspensions have been virtually ineffective in the lateral mode. Computer simulation studies have shown that a seat suspension with a dynamic absorber can significantly improve lateral ride. In this investigation, the lateral ride performance of an off-road vehicle with a seat suspension having a dynamic vibration absorber is studied. Based on parametric sensitivity and optimization analyses in establishing optimal parameters, a prototype suspension is designed and fabricated, and then tested in the laboratory as well as on the field. Analytical results are compared to those derived from the test data in order to illustrate the validity of the computer model. The investigations through laboratory and field testing of the lateral seat suspension system have demonstrated potential in improving ride.     

Assessment of tracked vehicle suspension system using a validated computer simulation model

A non-linear, in-plane computer simulation model of a typical high-mobility tracked vehicle is developed for suspension dynamic analysis and ride quality assessment. The Langrangian model formulation of the tracked vehicle is derived considering an arbitrary rigid terrain profile and constant vehicle speed. The model incorporates detailed representations of a trailing arm suspension system and dynamic wheel-track-terrain interactions. The computer model predictions are validated against field measurements, which were gathered from tests of an armoured personnel carrier traversing a discrete half-round bump and a random course. A parametric sensitivity analysis was carried out using the validated computer model in order to assess the influence of conventional suspension parameters on the ride performance of the test vehicle. In addition, the ride performance potentials of an alternate hydrogas suspension configuration were investigated.     

Optimal vehicle suspension characteristics for increased structural fatigue life

Heavy off-road vehicle suspension systems face unique challenges. The ride comfort versus handling compromise in these vehicles has been frequently investigated using mathematical optimisation. Further challenges exist due to the large variations in vehicle sprung mass. A passive suspension system can only provide optimal isolation at a single payload. The designer of such a suspension system must therefore make a compromise between designing for a fully-laden or unladen payload state. This work deals with suspension optimisation for vehicle structural life. The paper mainly addresses two questions: (1) What are the suspension characteristics required to ensure optimal isolation of the vehicle structure from road loads? and (2) If such optimal suspension characteristics can be found, how sensitive are they to changes in vehicle payload? The study aims to answer these questions by examining a Land Rover Defender 110 as test vehicle. An experimentally validated non-linear seven degree-of-freedom mathematical model of the test vehicle is constructed for the use in sensitivity studies. Mathematical optimisation is performed using the model in order to find the suspension characteristics for optimal structural life for the vehicle under consideration. Sensitivity studies are conducted to determine the robustness of the optimal characteristics and their sensitivity to vehicle payload variation. Recommendations are made for suspension characteristic selection for optimal structural life.     

Effectiveness evaluation of hydro-pneumatic and semi-active cab suspension for the improvement of ride comfort of agricultural tractors

Advances have been made to agricultural tractors to improve their ride comfort. However, the ride comfort of tractors is relatively low compared to that of passenger vehicles. Many researchers have developed various types of suspension for tractors. While most studies have focused on the geometry of the suspension, few studies have been carried out on the development of a control algorithm for tractor suspension.In this paper, to improve the ride comfort of an agricultural tractor, a hydro-pneumatic suspension model with a semi-active suspension control is developed with computer simulation, and the effectiveness of the suspension is evaluated before the vehicle is equipped with the suspension and placed into production.An optimal control algorithm for the semi-active suspension of the tractor is developed using a linear quadratic Gaussian. In the simulation, a hydro-pneumatic suspension system model is developed using SimulationX and is applied to a full vehicle model using MATLAB/Simulink. The suspension is assessed by experiments and simulations. The ride comfort using the ride comfort index according to ISO 2631 is evaluated by comparing a vehicle with a passive cab suspension to that with a hydro-pneumatic suspension applied with the semi-active control.     

A roll stability performance measure for off-road vehicles

The roll stability is significant for both road and off-road commercial vehicles, while the majority of reported studies focus on road vehicles neglecting the contributions of uneven off-road terrains. The limited studies on roll stability of off-road vehicles have assessed the stability limits using performance measures derived for road vehicles. This study proposes an alternative performance measure for assessing roll stability limits of off-road vehicles. The roll dynamics of an off-road mining vehicle operating on random rough terrains are investigated, where the two terrain-track profiles are synthesized considering coherency between them. It is shown that a measure based on steady-turning root-mean-square lateral acceleration corresponding to the sustained period of unity lateral-load-transfer-ratio prior to the absolute-rollover, could serve as a reliable measure of roll stability of the vehicle operating on random rough terrains. The robustness of proposed performance measure is demonstrated considering sprung mass center height variations and different terrain excitations. The simulation results revealed adverse effects of terrain elevation magnitude on the roll stability, while a relatively higher coherency resulted in lower terrain roll-excitation and thereby enhanced vehicle roll stability. Terrains with relatively higher waviness increased the magnitude of lower spatial frequency components, which resulted in reduced roll stability limits.     

An optimization method designed to improve 3-D vehicle comfort and road holding capability through the use of active and semi-active suspensions

The primary purpose of this paper is to analyze the effects of vibrations on the comfort and road holding capability of road vehicles as observed in the variation of different parameters such as suspension coefficients, road disturbances, and the seat position. This study required the development of a mathematical model to simulate the dynamic behavior of a 3-D vehicle. With this model, various types of non-linear suspensions such as active and semi-active suspensions may be investigated. The results obtained from the simulation of the 3-D vehicle demonstrate that the use of active and semi-active suspension models on road vehicles prove to be beneficial for comfort without unduly compromising road holding capability.     

Computer-aided methods for the optimization of the mobility of single-unit and two-unit articulated tracked vehicles

In the past decade, a series of computer-aided methods (computer-simulation models) have been developed for design and performance evaluation of tracked vehicles, particularly those with short track pitch designed for high speed operations. The latest version, known as NTVPM-86, developed under the auspices of Vehicle Systems Development Corporation, Nepean, Ontario, Canada, takes into account all major vehicle design parameters and terrain characteristics. The basic features of the model have been validated by field tests over a variety of terrains, including mineral, organic and snow-covered terrains. It has been gaining increasingly wide acceptance by industry and governmental agencies in the development and procurement of new vehicles in North America, Europe and Asia. In this paper, the effects of suspension characteristics, initial track tension, track width and ground clearance on the mobility of single unit and two-unit articulated track vehicles over deep snow are systematically evaluated using the computer simulation model NTVPM-86. It is found that these parameters have noticeable effects on vehicle mobility over marginal terrain. The approach to the optimization of tracked vehicle design from the mobility point of view is also examined. It is shown that the simulation model can play a significant role in assisting the procurement manager to select the appropriate vehicle candidates and the design engineer to optimize vehicle design for a given mission and environment.     

基于分数阶磁流变液阻尼器模型的车辆悬架组合控制

磁流变液阻尼器的分数阶Bingham模型结构形式简单, 而且可以更好地描述系统的滞回特性. 建立了含有分数阶Bingham模型的单自由度1/4车辆悬架系统模型, 利用磁流变液阻尼器对在路面简谐激励下的非线性车辆悬架系统进行振动控制. 研究了含有分数阶Bingham模型的悬架系统在天棚阻尼半主动控制下的主共振响应, 利用平均法得到了系统的近似解析解. 求解了系统定常解的幅频响应方程, 并根据李雅普诺夫稳定性理论得到了悬架系统的稳定性条件. 通过绘制数值解和解析解的幅频响应曲线对比图, 验证了近似解析解的正确性. 利用簧载质量垂直方向的加速度均方根值分析了半主动控制对车辆乘坐舒适性的影响, 发现天棚阻尼半主动控制策略在低频激励区域反而会降低车辆的乘坐舒适性. 因此提出了一种被动控制与半主动控制相结合的组合控制策略, 并分析了半主动控制参数对振动控制效果的影响. 分析结果表明, 该组合控制策略不但能够提高车辆的乘坐舒适性, 而且能有效抑制悬架系统的主共振振动幅值.      

A study of the hydraulically interconnected inerter-spring-damper suspension system

A new hydraulically interconnected inerter-spring-damper suspension (HIISDS) is developed to compensate for traditional passive suspension limitations, such as the imbalance of ride performance and handling stability. In this article, the structure and mechanism of the HIISDS system is briefly introduced at first, and compiled with hydraulically interconnected suspension (HIS) mode and hydraulic inerter-spring-damper (ISD) suspension mode. A vehicle dynamic model of HIISDS system is then derived through these two suspension modes by using Matlab/Simulink. Two different road excitations are used to validate the adaption of the two suspension modes. The effectiveness of HIISDS has been verified by simulation results, in which vehicle ride comfort and handling stability are effectively coordinated through the HIISDS model switch. Finally, an HIISDS suspension prototype is designed based on Simulink results, and test results reconfirm the partial performances of HIISDS modes effectively.     

A spatial motion analysis model of tracked vehicles with torsion bar type suspension

A spatial motion analysis model for high-mobility tracked vehicles was constructed for evaluation of ride performance, steerability, and stability on rough terrain. Ordinary high-mobility tracked vehicles are equipped with independent torsion bar type suspension system, which consists of road arms and road wheels. The road arm rotates about the axis of torsion bar, and rigidity of the torsion bar and cohesion of damper absorb sudden force change exerted by interaction with the ground. The motion of the road arms should be considered for the evaluation of off-road vehicle performance in numerical analysis model. In order to obtain equations of motion for the tracked vehicles, the equations of motion for the vehicle body and for the assembly of a road wheel and a road arm were constructed separately at first. Two sets of equations were reduced with the constraint equations, which the road arms are mechanically connected to the vehicle body. The equations of motion for the vehicle have been expressed with minimal set of variables of the same number as the degrees of freedom for the vehicle motion. We also included the effect of track tension in the equations without constructing equations of motion for the tracks. Numerical simulation based on the vehicle model and experiment of a scale model passing over a trapezoidal speed bump were performed in order to examine the numerical model. It was found that the numerical results reasonably predict the vehicle motion.     

Suspension settings for optimal ride comfort of off-road vehicles travelling on roads with different roughness and speeds

This paper reports on an investigation to determine the spring and damper settings that will ensure optimal ride comfort of an off-road vehicle, on different road profiles and at different speeds. These settings are required for the design of a four stage semi-active hydro-pneumatic spring damper suspension system (4S₄). Spring and damper settings in the 4S₄ can be set either to the ride mode or the handling mode and therefore a compromise ride-handling suspension is avoided. The extent to which the ride comfort optimal suspension settings vary for roads of different roughness and varying speeds and the levels of ride comfort that can be achieved, are addressed. The issues of the best objective function to be used when optimising and if a single road profile and speed can be used as representative conditions for ride comfort optimisation of semi-active suspensions, are dealt with. Optimisation is performed with the Dynamic-Q algorithm on a Land Rover Defender 110 modelled in MSC.ADAMS software for speeds ranging from 10 to 50 km/h. It is found that optimising for a combined driver plus rear passenger seat weighted root mean square vertical acceleration rather than using driver or passenger values only, returns the best results. Results indicate that optimisation of suspension settings using one road and speed will improve ride comfort on the same road at different speeds. These settings will also improve ride comfort for other roads at the optimisation speed and other speeds, although not as much as when optimisation has been done for the particular road. For improved ride comfort damping generally has to be lower than the standard (compromised) setting, the rear spring as soft as possible and the front spring ranging from as soft as possible to stiffer depending on road and speed conditions. Ride comfort is most sensitive to a change in rear spring stiffness.     

Dynamical investigation of railway vehicles on a curved track

The main objective of this article is an examination of railway vehicle dynamics during motion along a curved track. Two main aspects are presented in the paper. First, two different methods used while investigating multi-rigid body systems such as railway vehicles are discussed, i.e. the quasi-statical (or kineto-statical) and dynamical approaches. Second, two practical problems dealing with vehicle motion along a curved track are investigated. The problems under consideration refer to vibrations as well as stability, examined via finding obtained with the author's software as a result of numerical simulation. The work has both a practical and a cognitive character. The aim of the investigations is firstly to indicate the limitations of quasi-statical (and kineto-statical) methods and secondly to study the problems which cannot be treated by these methods. Two specific problems of the type investigated using a dynamical approach are the influence of track geometrical irregularities on the evaluation of vehicle ride properties and limit cycle occurrence during vehicle curve negotiation. Due to the renewed interest in the rapid passenger railway, the investigations take into consideration curves of large radii introduced along railway routes for increased velocities. Furthermore, it is shown under which conditions the obtained results may have an important practical application. This concerns the influence of vehicle suspension parameters as well as conditions of motion (speed, superelevation, curve radius, transition curve existence) on limit cycle occurrence. The limited value of conclusions dealing with vehicle ride properties obtained while using quasi-statical (kineto-statical) methods is proved through quantitative analysis. The problem of the influence of geometrical irregularities on wheel-rail pair wear is also pointed out.     

Development of high-mobility tracked vehicles for over snow operations

This paper describes a detailed investigation into the effects of some of the major design features on the mobility of tracked vehicles over snow. The investigation was carried out using the latest version of an advanced computer simulation model, known as NTVPM, developed under the auspices of Vehicle Systems Development Corporation (VSDC), Ottawa, Ontario, Canada. Results show that the road wheel system configuration, initial track tension (i.e., the tension in the track system when the vehicle is stationary on a level, hard ground) and track width have significant effects on vehicle mobility over snow. On deep snow where the vehicle belly (hull) contacts the snow surface, the location of the centre of gravity (C.G.) of the sprung weight in the longitudinal direction has a noticeable effect on vehicle mobility, as it affects the attitude of the belly and the belly–snow interaction. Based on the investigation, a conceptual high-mobility tracked vehicle for over snow operations is discussed. Results of this study will provide the vehicle designer with guiding principles for the development of high-mobility tracked vehicles. It also demonstrates that NTVPM is a useful and effective tool for design and performance evaluation of tracked vehicles from a traction perspective.     

Evolutionary algorithm-based PID controller tuning for nonlinear quarter-car electrohydraulic vehicle suspensions

The basic challenge associated with the design of vehicle suspension system is the attainment of an optimal trade-off between the various design objectives. This study presents the design of proportional-integral-derivative (PID) controller for a quarter-car active vehicle suspension system (AVSS) using evolutionary algorithms (EA) such as the particle swarm optimization (PSO), genetic algorithm (GA) and differential evolution (DE). Each of the EA-based PID controllers showed overall improvement in suspension travel, ride comfort, settling time and road holding from the manually tuned controller and the passive vehicle suspension system. These improvements were, however, achieved at the cost of increased actuator force, power consumption and spool-valve displacement. DE-optimized PID control resulted in the best minimized suspension performance, followed by the GA and PSO, respectively. Frequency-domain analysis showed that all the signals were attenuated within the whole body vibration frequency range and the EA-optimized controllers had RMS frequency weighted body acceleration of the vehicle within allowable limits for vibration exposure. Robustness analysis of the DE-optimized PID-controlled AVSS to model uncertainties is carried out in the form of variation in vehicle sprung mass loading, tyre stiffness and speed.     

Ride quality analysis of a tracked vehicle suspension with a preview control

The feasibility of a preview control is examined for tracked vehicle’s suspension systems to improve the performance of tracked vehicle systems. Numerical results are compared with LQ, robust H_∞, reference model tracking and hybrid preview control methods. The ride quality analysis is performed based on the vertical acceleration at the driver’s position. On the simulations, it is proven that the hybrid preview controller is the most efficient and practical method.     

基于智能驾驶电动汽车的多车?桥梁耦合系统动力学特性研究

迫于能源和环保问题的压力, 电动汽车及智能驾驶受到了各国高度重视. 轮毂电机驱动电动汽车车轮振动剧烈, 与桥梁路面动力学相互作用更加突出, 现有研究主要针对传统汽车, 关于电动车轮与公路桥梁接触动力学相互作用及智能驾驶车队的多车?桥梁耦合作用研究尚不多见. 本文以轮毂电机驱动电动汽车为研究对象, 考虑车轮和桥面多点接触关系, 研究了两个智能驾驶汽车过桥时的车桥耦合动力学特性. 分析了电机质量、电机激励、轮胎悬架刚度非线性、车距、车速对系统振动特性的影响, 以及桥面不平顺激励、三重耦合激励对电动汽车平顺性的影响. 研究表明: 车距和车速是影响车?桥系统振动特性的重要因素, 在车?桥耦合动态设计中, 车距和车速的影响应重点关注; 桥面越平坦, 电机激励及桥面二次激励对车辆平顺性和道路友好性影响越加显著, 当汽车行驶在平坦桥面时两种激励对轮毂电机驱动电动汽车的影响不容忽视. 所建模型有望为智能驾驶电动汽车与桥梁的耦合作用研究提供理论参考.