Continuously Variable Transmission Design Research Articles

Numerical Design Method for CVT Supported in Standard Variable Speed Rubber V-Belts

The design of a V-belt continuously variable transmission (CVT) system is a complex problem due to the multiple interactions between components during its operation. Literature on CVT system design methods is scarce, and the vast majority of works include implicit equations that hinder applications at a basic design level. This research aims to introduce a numerical CVT design method for electric vehicles (EV) and internal combustion engine (ICE) vehicles considering each one of their components and using mechanical centrifugal actuators and a rubber V-belt. This design method is based on user needs, for which there are three main requirements: road specifications, vehicle characteristics, and expected performance. This method is focused on a transmission for a vehicle traveling on the same route constantly, such as public transport vehicles. From three-wheelers to medium cargo vehicles, there is a greatly diverse range of potential applications for using this method for each type of standard rubber V-belt.

Integrated Plant and Control Design of a Continuously Variable Transmission

This paper presents an optimization framework to design the components and the controller of a Continuously Variable Transmission (CVT) in an integrated manner. Specifically, we aim at reducing the mass of the transmission and the leakage losses that occur in the system. To do so, we first formulate the joint plant and control design problem including the corresponding objectives and constraints. Thereafter, we propose a proportional integral structure for the design of the CVT ratio control. The combined plant and control design problem is formulated as a nonlinear multi-objective optimization problem, and is simultaneously solved using an interior point optimization method. We evaluate the obtained design on the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) as well as on more aggressive driving scenarios, and demonstrate that the optimized CVT design is always capable of realizing the required driving performance. Additionally, we study the impact of the plant design parameters on the control performance by analyzing the coupling strength between the subproblems. Thereby, the pulley radius is found to have the strongest influence in the resulting leakage losses that occur at the variator level. Finally, leveraging the presented design framework, we show that up to 13% and 18% reduction in the CVT variator mass and on leakage losses, respectively, can be achieved without compromising the desired ratio trajectory over a representative dynamic driving cycle.

Geometrical analysis of a continuously variable transmission system designed for human-robot interfaces

New robotic systems are placed out of their constrained workspaces in order to work alongside humans. Consequently, these applications call for robots monitoring and regulating physical human-robot interaction. These robots’ mechanical compliance should be varied when they are in physical contact with the human or their changing environments. This compliance variation can be achieved in a variety of ways. However, one common idea is the variation of joint stiffness mechanically, electromechanically or by control. The solution presented in this paper is an electromechanical way of varying the joint stiffness. Among the electromechanical methods for varying the joint stiffness, continuously variable transmission (CVT) systems can be used in human-robot interfaces if a set of design criteria are met. These criteria include backdrivability, independent output position and stiffness variation, shock absorbing and low mass/inertia. In this paper, a novel two-cone CVT design with a double spherical transmission element is introduced by taking into account the abovementioned criteria. Additionally, design parameters are identified via carrying out a geometrical analysis of this new CVT system.

Integrated design for a CVT: dynamical optimization of actuation and control

Abstract With increasing demands on more energy and fuel efficient vehicles, one can achieve the goal by improving the vehicle powertrain system. A continuously variable transmission (CVT) allows the engine or electric machine to operate on its optimal operation points. The optimal operation points are high efficiency points that lead to reduced energy consumption of the vehicle. However, this type of transmission may still have relatively high actuation losses (depending on the actuation type), which hinders the energy saving benefits. Classically, the plant (e.g., actuation system, variator) of the CVT was separately designed from the control design. In this paper, an integrated optimal CVT variator and actuation control design is presented. The aim of the new design is to minimize the CVT mass (pulley sheaves, belt), tracking error and control effort. To achieve this goal, a nested optimization framework is implemented to obtain an optimal transmission system design over a selected drive cycle. The results show that the optimized CVT design yields non-compromising tracking performance, however, with much smaller variator mass (-46%) and control effort (-62%).

Application of Numerical time Integration Schemes to Continuously Variable Transmission Dynamics Analysis

Numerical analysis of large-scale and multidisciplinary problems on high-performance computer (HPC) systems is one of the main computational challenges of the 21st century. Modelling the dynamics of a continuously variable transmission (CVT) is one of such problems. CVT has been used in the automotive industry for last decades. The complexity of physical interactions in CVT does not allow engineers to use any of the general purpose commercial software packages for CVT design. Our project aims to develop a mathematical model, computational algorithms and problem oriented in- house software for simulating CVT dynamics. One of the important steps in this project is the study of explicit and implicit time integration schemes for the stiff system of ordinary differential equations, as well as implementations of these schemes on HPC systems.

Principle and characteristics of original hydraulic traction drive CVT

A new CVT (continuously variable transmission) design which is a traction drive variator has been introduced. Analytical predictions and experimental results of the steady state which demonstrate higher efficiencies and power capacities of the new design are presented. The traction and power loss are then predicted by using models including evaluation of creep and spin in the contact patch. Analytical predictions of the transmission reach reasonable agreement with the experimental data, and the transmission efficiency of the system increases as the input torque increases while the input speed is certain. The research results can be further used in hydraulic traction drive CVT design and optimization.

Intelligent Multiobjective Slip and Speed Ratio Control of a Novel Dual-Belt Continuously Variable Transmission for Automobiles

Van Doorne’s continuously variable transmission (CVT) is the most popular CVT design for automotive transmission, but it is only applicable to low-power passenger cars because of its low torque capacity. To overcome this limitation of traditional single-belt CVT, a novel dual-belt Van Doorne’s CVT (DBVCVT) system, which is applicable to heavy-duty vehicles, has been previously proposed by the authors. This paper, based on the published analytical model and test rig of DBVCVT, further proposes an intelligent multiobjective fuzzy controller for slip and speed ratio control of DBVCVT. The controller aims to safely control the clamping forces of both the primary and the secondary pulleys in order to improve the transmission efficiency, achieve the accurate speed ratio, and avoid the belt slip under different engine loads and vehicle speeds. The slip, speed ratio, and transmission efficiency dynamics of DBVCVT are firstly analyzed and modeled in this paper. With the aid of a flexible objective function, the analytical model, and fuzzy logic, a Pareto rule base for fuzzy controller is developed for multiobjective DBVCVT control. Experimental results show that the proposed controller for slip and speed ratio regulation of DBVCVT is effective and performs well under different user-defined weights.

Causes of Microslip in a Continuously Variable Transmission

The continuously variable transmission (CVT) is a type of transmission that can adopt any arbitrary gear ratio. Whereas typical transmissions utilize toothed gears, the CVT employs a sphere in rolling contact with a set of rollers; loads applied to the CVT are supported across these rolling contacts, resulting in microslips of varying amounts at each contact area. In this paper, we describe the causes of microslips in the CVT and ways to lessen them through an alternative CVT design.

A Study on Metal Pushing V-Belt Type CVT. Characterization of Power Transmitting States of a CVT using Mean Coefficients of Friction as Parameters and their Application for CVT Design.

In order to characterize the power transmitting state of a continuously variable transmission (CVT) using metal V-belts, mean coefficients of friction between blocks and pulleys, and between the blocks and rings, are introduced. The present approach is primarily based on the classical Euler's equation for conventional V-belts. The existence of idle and active arcs is taken into consideration by adjusting the coefficients of friction, since the power is assumed to be transmitted through all the contact arcs of the belt in this study. The power transmitting mechanisms induced by the estimated mean coefficients of friction are highly consistent with the data measured by the sensors made by blocks. The mean coefficients of friction also have some universal trends with respect to transmitted power, torque ratio, speed ratio and so On. The mean coefficients of friction would be applicable not only for characterizing the power transmitting state, but also for designing a CVT using metal V-belts.