Transient analysis of geared neutral type half-toroidal CVT

An analytical model was developed to evaluate transient behavior of geared neutral (GN) type half-toroidal CVT. It combines a dynamic half-toroidal variator model with drivetrain, hydraulic system, engine and vehicle sub-models. Simulation results show good agreement with experimental data. The model was applied to analyze the GN state, launching characteristic and L/H mode change behavior.     

Performance optimization of CVT for two-wheeled vehicles

Continuously Variable Transmission (CVT) is one of the most promising automotive transmission technologies because of its continuously variable gear ratio and reduced shift shock. CVT is different from Manual Transmission and Automatic Transmission, and it is possible to operate the power source in its high efficiency region with CVT in the drive train. Several types of CVT exist that can be categorized based on the mechanism of power transmission, such as the belt pulley, traction drive, and hydrostatic types. This paper investigates the belt pulley CVT, which consists of a thrust actuator, driver pulley, belt, driven pulley, and preload spring of the output shaft. A complete CVT is constructed, and based on that a simulation program that analyzes the static performance of a CVT is implemented in Matlab/Simulink. From these simulation results, methods for improving the efficiency of the CVT are discussed. The coefficient of the torque capacity factor is proposed as affecting the matching between a power source and a CVT, and methods for improving the matching effect are also investigated.     

Speed ratio control of a parallel layout double cavity half-toroidal CVT for four-wheel drive

A double cavity half-toroidal CVT has two variators, which gives a hint of a new four-wheel drive without a center differential gear unit by applying each of them to drive front and rear drive shafts independently. Torque re-circulation at cornering or different tire radii between front and rear tire is avoided by compensating the speed ratio of variator. The controller adjusts the attitude angle of power roller of the front variator against the rear by measuring the steering angle at cornering. This paper describes the speed ratio control system of the 4WD-CVT with speed ratio range of 1 : 8.7 and test results of vehicle motion mounted on a 3.2L RV.     

Development of the Inner Spherical CVT for a motorcycle

An Inner Spherical CVT (ISCVT) transfers engine power by utilizing the traction force of the lubricant fluid film on the contact point between concave and convex spherical rolling bodies. Since the concave and the convex contact surfaces of the ISCVT are exactly spherical parts, they have a large circular (not elliptic) contact area, and the ISCVT mechanism has a larger torque capacity, less spin loss, and better stability than other traction drive mechanisms. The IVT (Infinitely Variable Transmission) performances also can easily be embodied in the ISCVT. In this work, we developed a prototype of the ISCVT for a motorcycle with a 125cc single cylinder engine having a maximum torque of 13.73 Nm at 8,000 rpm. The design parameters were determined, and the transmission performances were evaluated by optimal design procedure. The transmission efficiency, the life time, the maximum severe stresses on each part of the ISCVT, and the work needed for varying speed ratio were theoretically investigated, and the efficiency performances were experimentally measured. The manufactured prototype was installed in an actual motorcycle, which was fixed on the test-bench equipped with a dynamometer. The parasitic loss of the prototype and the cross-sectional road load performance were tested. The power efficiency of the simulated prototype was between 87∼92%, and the life span was more than 50,000 hours. The tested overall power efficiency was around 70∼92% under frequent driving conditions, which is an impressive performance in a motorcycle transmission despite the small difference from the simulation.     

Experimental investigation on the efficiency of the pulley-drive CVT

Because of their outstanding advantages over other transmissions, rubber V-belt pulley drive CVTs have been extensively used in low-power vehicles, such as scooters and snowmobiles. A rubber V-belt CVT installed on a snowmobile is used here to research transmission efficiency. The power loss of CVTs, including torque loss and speed loss, is studied based on an analysis of the transmission mechanism of CVTs. Experiments on CVT efficiency are conducted on a specific CVT test bench, on which the values of torque, speed, and displacement, etc., are measured. Results show that the variation trend of the efficiency is close to the operating conditions of CVTs and optimal structural parameters are given that can serve as a beneficial references for designing and tuning CVTs.     

Multi-objective geometrical optimization of full toroidal CVT

The objective of this research is geometrical and kinematical optimization of full-toroidal continuously variable transmission (CVT) in order to achieve high power transmission efficiency and low mass. At first, a dynamic analysis is performed for the system. A computer model is developed to simulate elastohydrodynamic (EHL) contact between disks and roller and consequently, calculate CVT efficiency. The validity of EHL model is investigated by comparing output of this model and experimental data. Geometrical parameters are obtained by means of Particle Swarm Optimization algorithm, while the optimization objective is to maximize CVT efficiency and minimize its mass. The algorithm is run for different values of selected input parameters that are oil temperature, roller tilting angle (speed ratio). Optimization results show that optimized geometrical parameters are approximately constant for various values of input parameters. Also, it is observed that, increasing values of oil temperature and roller tilting angle (in clockwise direction), will decrease power transmission efficiency. An average power transmission efficiency of 86.7% is achieved over a wide range of input parameters, using optimized geometry.     

Development of dry hybrid belt CVT

We have developed a continuously variable transmission (CVT) which has superior transfer efficiency, by thoroughly reducing transfer loss by means of using a dry hybrid belt, using no lubrication composition system around the belt, and using an electric control system of a DC motor.The fuel efficiency and driveability of the prototype vehicle equiped with the CVT were proven equivalent or even superior to a 5 speed manual transmission.     

新型剖分变径链式CVT虚拟样机

传统的无级变速器存在金属带式CVT直母线偏移的问题,而新型剖分变径链式CVT突破了传统的CVT结构方式。文章分析了新型剖分变径链式CVT的传动原理,在用CATIA建立的主传动部分三维模型的基础上,通过转换软件MSC.Simdesigner把其导入到ADAMS中,建立虚拟样机,进行动力学仿真分析,研究其传动特性,验证了该CVT传动方案的可行性。表明提出的剖分变径链式CVT设计方案,可以传递更大的转矩,消除了金属带式CVT直母线偏移的问题,为其物理样机的研制奠定了一定的理论基础。     

CVT ratio control with consideration of CVT system loss

A modified CVT ratio map is proposed to obtain the improved fuel economy for a metal belt CVT. Since the CVT system loss, which occupies most of the drivetrain loss, depends on the engine speed, input torque, primary and secondary actuator pressure, a modified CVT ratio map is produced to realize the highest engine-CVT overall efficiency through the consideration of CVT system loss. The modified CVT ratio map is constructed with respect to the demanded vehicle power and present vehicle speed based on the steady state CVT system loss. Using the modified CVT ratio map, performance simulations are carried out using the dynamic models of the CVT powertrain. The simulation results indicate that the modified CVT ratio control provides improved engine-CVT overall system efficiency, and improves the fuel economy of the federal urban driving schedule by 4.9 percent.     

金属带式无级变速器电—液控制系统的研究

本文分析了金属带式无级变速器的控制原理和控制方法，设计了用于研究无级变速器匹配规律的试验系统，通过对几种典型工况的性能试验测试的结果表明，所设计的电－液控制系统能够满足无级变速器的控制要求。     

金属带式无级变速传动系统动态特性的理论与试验分析

本文建立了无级变速传动系统的双质量模型，从理论和试验两方面研究了金属带式无级变速传动系统的动态特性。     

CVT轿车发动机建模及PID速比控制器设计

针对装备金属带式无级变速器轿车的发动机建立了其转矩模型和目标转速调节特性曲线。对无级变速器速比的取值范围进行了计算,并按照质量集中法简化了传动系的模型。设计了简单实用的PID速比控制器,并在simulink环境下对CVT整车模型起步、急加速和上坡工况进行了仿真分析。结果表明,实际速比对目标速比有很好的跟随效果。     

Development of a high torque capacity belt-drive CVT with a torque converter

A new belt-drive continuously variable transmission (CVT) has been developed and installed in a 2-liter class vehicle for the first time in the world. This paper describes the technical features of this high torque capacity transmission, the need for a torque converter, the importance of electronic control and the driving modes achieved. This new CVT provides better driving performance and fuel economy than current CVTs and 4-speed automatic transmissions.     

基于系统效率最优的CVT混合动力轿车转矩优化分配方法

无级变速器CVT消除了挡位概念,其速比在一定范围内连续可调。配备CVT的混合动力汽车能够实现动力源转矩和传动系统的优化匹配。针对此问题,提出了基于系统效率最优的CVT中度混合动力轿车动力源转矩优化分配方法:。该方法:综合考虑了各个关键部件的效率,以混合动力系统的总体效率为优化目标,以车速、车辆加速度、电池SOC为状态变量,优化分配了驱动工况下各动力源输出转矩,为整车能量管理策略的制定奠定了基础。     

Optimisation of full-toroidal continuously variable transmission in conjunction with fixed ratio mechanism using particle swarm optimisation

The aim of this research is the optimisation of full-toroidal continuously variable transmission (CVT) in conjunction with the fixed ratio (FR) mechanism, while the optimisation objective is to minimise fuel consumption (FC) of the vehicle in the new European driving cycle. After the dynamic analysis of the power train, a computer model is developed to simulate contact between CVT elements and consequently calculate its efficiency. Then an algorithm is presented to calculate FC of the vehicle in the driving cycle. Then, an optimisation using particle swarm optimisation on the CVT geometry and FR mechanism (which is embedded between CVT and final drive) is carried out to minimise FC. It is found that by utilisation of the optimised CVT; FC will be about 11% and 8% lower, compared with the application of a five-speed manual transmission and conventional CVT, respectively. Finally, effects of the roller tilt angle and oil temperature on the FC are investigated.     

Model-Based Integrated Control of Engine and CVT to Minimize Fuel Use

In this study, a model-based integrated control method for engines and continuous variable transmissions (CVTs) is developed. CVT refers to a type of transmission which allows an engine to be operated independently with respect to the vehicle speed, with the engine torque and CVT gear ratio controlled in an integrated manner. In the proposed integrated control scheme, engine operating points which minimize the rate of instantaneous fuel consumption are calculated, and the engine target torque and target gear ratio are determined in an integrated manner based on the results of the calculations. Unlike the previous map-based control method, the method introduced in this study does not require an engine torque map or a CVT ratio map for tuning, and the engine torque and CVT ratio are controlled to minimize the amount of fuel used while satisfying the level of acceleration demand from the driver. The control scheme is based on the powertrain model, and the CVT response lag and transmission loss are also considered in the integrated control processes. The algorithm is simulated with various driving cycles, with the simulation results showing that the fuel economy performance of the vehicle system is improved with the newly suggested engine-CVT integrated control algorithm.     

无级变速汽车自动驾驶系统模糊控制策略

为研究无级变速汽车自动驾驶系统的模糊控制策略，建立了简化的基于底盘测功机的无级变速汽车和自动驾驶系统模型。考虑到传动系统的高阶时变非线性特性、输入和输出之间的耦合效应以及汽车运行工况和复杂的外界环境因互的影响，提出了把参数自调整的模糊ＰＩ控制算法用于油门控制系统，混合型模糊ＰＩＤ控制算法用于发动机转速控制系统。仿真结构表明，文中给出的自动驾驶系统的模糊控制策略是可行和有效的，具有实用价值。     

基于CVT的混联式电动汽车动力切换平稳性研究

针对四轮驱动越野车提出了一种基于金属带式无级自动变速器(CVT)的混联式结构,其动力切换平稳性是这种混联式电动汽车必须解决的关键技术之一。通过发动机、电机、离合器和CVT的协调控制可以使系统在驾驶员发出加速命令时快速响应以及在模式切换时平稳,这将保证驾驶员在车辆切换过程中没有异常感觉。     

汽车无级变速器传动性能评价系统研究

根据无级变速器电子控制单元的控制算法,结合试验数据,建立了无级变速器(CVT)性能评价系统中的驾驶员模型、发动机模型、无级变速器模型与整车动力学模型。同时给出了各个模型在Simulink中具体的建模方法。最后,针对具体车型,建立了该车型的CVT传动性能的评价系统。     

金属带式CVT速比控制的仿真与试验研究

针对装备金属带式无级变速器(CVT)的整车,建立了无级变速传动系统数学模型.以无级变速汽车动力性和经济性相协调为目标,设计了Fuzzy-PI复合速比控制器.采用Fuzzy-PD控制策略和Fuzzy-PI复合控制策略对汽车起动工况进行了仿真分析,对装备金属带式CVT的某轿车进行了起动工况的模拟试验.结果表明,Fuzzy-PI复合控制策略优于Fuzzy-PD控制策略,速比的试验结果与理论数据一致,说明所建模型合理.