Conventional Continuously Variable Transmission Research Articles

CVT for a Small Electric Vehicle Using Centrifugal Belt Pulley

In a conventional continuously variable transmission (CVT), the belt slides up and down along the slope of the pulley to shift gears. Efficiency is reduced because of slippage from the shifting of the belt. In this study, the centrifugal belt pulley for CVT were investigated. Instead of applying the belt slip method, a rail groove was machined on the side of the pulley, and a push piece pushed the belt up by centrifugal force along the rail groove. The CVT was designed and manufactured using this mechanism. A CVT tester was manufactured to validate the performance of the proposed transmission. The suitability of the CVT was verified through structural analysis.

Active-Type Continuously Variable Transmission System Based on a Twisted String Actuator

This letter presents an active-type twisted string actuator (TSA)-based continuously variable transmission (CVT). The proposed mechanism improves the advantage of the intrinsic CVT nature of TSA by compensating its nonlinear transmission ratio (TR) with the active and continuous conversion of the TR during contraction at a constant load as well as variable load. To change the TR, the proposed CVT adjusts the ratio of rotation between individual twists and overlap twists, which are two different types of string-twisting patterns. The performance of the TSA-based active CVT was experimentally assessed with the fabricated prototype and compared with a mathematical model. This adjustment in the rotation ratio between individual and overlap twists is realized using a planetary gear. By adjusting the rotating speed ratio between the sun and ring gear, the ratio of rotation between individual and overlap twists can be adjusted. Unlike the conventional TSA-based CVT, the proposed CVT can actively and continuously change the TR independent of the external load, even during operation. Consequently, it allows an increase in the operating range of the TSA while maintaining a high contraction speed.

Implementation of automatic manual transmission for a two wheeler

The concept of Automatic Manual Transmission (AMT) is picking up speed in India after the launch of the Maruti Suzuki Celerio. But very few of the two-wheeler manufacturers in the world have tried to implement the AMT concept in a motorcycle. There are gearless motorcycles available which use a Continuously Variable Transmission (CVT) and a Centrifugal clutch, but this setup is very inefficient compared to a positive gear drivetrain. Thus these gearless motorcycles get low mileage and are also more expensive to manufacture. Geared motorcycles, on the other hand, have better starting torque, greater mileage and a higher span of gear ratios. They are also cheaper, but the average buyer is discouraged by the complexity of the operation. Even those familiar with riding a motorcycle do not shift optimally to obtain the best mileage/performance. The aim of this paper is to present an innovative AMT system developed and implemented on a manual geared motorcycle having a sequential constant-mesh gearbox with a multi-plate clutch. This was carried out by interfacing the manual gear shifting motorcycle with a microcontroller and using an electronic actuation mechanism to make it an automatic gear shifting motorcycle. The significant steps of this project would involve the sensor readouts of the parameters necessary, the actuation of the controls and, most importantly, the algorithm for the optimal shift points for a given motorcycle. These would be obtained experimentally and using the manufacturer data, if available. This AMT setup has been successfully developed and implemented. This setup can then be applied to any geared motorcycle with minimal structural changes without any modification to its existing gearbox. This converts the manual geared motorcycle into the automatic gear shifting motorcycle having better fuel economy and lower maintenance costs as compared to the conventional CVT motorcycles.

Analysis of a Continuously Variable Transmission in which Four-Bar Linkages Are Arranged in Parallel

This paper describes a development of a new structural type of continuously variable transmission (CVT). We here propose a CVT with linkages and irreversible mechanisms which does not positively depend upon frictional conduction force between conduction components. In the proposed CVT, four lever-crank units are connected in parallel mechanically with the cranks at an input shaft, and the output shaft is also connected mechanically via an irreversible mechanism installed at the fulcrum of the lever. In the experiment, we confirm that the continuous control of gear ratios in real time by realizing high-precision control for expansion and contraction of the links using electric linear actuators. As a merit of the developed linkage type of CVT, it reduces power consumption, compared to other conventional CVTs.

Review of latest technological advancement in electro-mechanical continuously variable transmission

Continuously variable transmission (CVT) is a type of automotive transmission commonly used to achieve minimum fuel consumption. Nevertheless, a conventional CVT applies a hydraulic actuation system, which is powered by the vehicle's engine, to vary its ratio and to clamp the metal pushing V-belt accordingly. As a result, a significant portion of the engine power is diverted for the CVT's operation, making the powertrain system significantly less efficient. To address this challenge, many researchers have proposed the idea of electro-mechanical CVT (EM CVT). This paper provides a review of the latest designs of EM CVT, followed by highlights on the relevant research areas that should be pursued so that the advances made in EM CVT can be brought closer to commercialisation. These areas are: 1) efficiency validation of an EM CVT vs. a conventional CVT; 2) durability of the screw-thread system and the thrust bearing; 3) ratio and belt slip controls; 4) packaging of the actuation system.

Review of latest technological advancement in electro-mechanical continuously variable transmission

Continuously variable transmission (CVT) is a type of automotive transmission commonly used to achieve minimum fuel consumption. Nevertheless, a conventional CVT applies a hydraulic actuation system, which is powered by the vehicle's engine, to vary its ratio and to clamp the metal pushing V-belt accordingly. As a result, a significant portion of the engine power is diverted for the CVT's operation, making the powertrain system significantly less efficient. To address this challenge, many researchers have proposed the idea of electro-mechanical CVT (EM CVT). This paper provides a review of the latest designs of EM CVT, followed by highlights on the relevant research areas that should be pursued so that the advances made in EM CVT can be brought closer to commercialisation. These areas are: 1) efficiency validation of an EM CVT vs. a conventional CVT; 2) durability of the screw-thread system and the thrust bearing; 3) ratio and belt slip controls; 4) packaging of the actuation system.

Application of envelope theorem to determine the shapes of contact components in toroidal continuously variable transmission

The efficiency of toroidal continuously variable transmission (CVT) is limited by the spin loss caused by different speed distributions of the contact areas between discs and rollers. Although two types of zero-spin CVTs are offered, a demerit in the form of difficult speed ratio variation is observed simultaneously. The core idea of this study is the realisation of a method based on the envelope theorem to optimise the shapes of discs and rollers. After the envelopes are calculated, two zero-spin CVTs (i.e. inner cone and outer cone CVTs) are proposed. The calculation of the spin ratio shows that the two proposed CVTs can both transmit power without the spin motion. The total efficiency of the proposed CVTs can therefore be improved, as evidenced by a widely accepted computational model. A comparison of the proposed CVTs and the conventional CVTs is conducted, and the results show that the durability properties of the proposed CVTs are both improved. Although it is hard to manufacture, the inner cone CVT surpassed the demerit of the control difficulty which remains observable in conventional zero-spin CVTs and the outer cone CVT.

Influence of a CVT on the fuel consumption of a parallel medium-duty electric hybrid truck

Hybrid electric vehicles are being developed to reduce the pollutant emissions and the fossil-fuel consumption of transportation. Innovative technologies are inserted to improve the performance of hybrid vehicles, including trucks and buses. Thereby, trends towards gear shifting automation motivate the research on replacing a discrete conventional Automated Manual Transmission (AMT) with a Continuously Variable Transmission (CVT). Theoretically, such a transmission enables better operation points of the thermal engine, and therefore a reduction of its fuel consumption and emissions. However, the conventional (hydraulic actuated) CVT efficiency during quasi-stationary operation is typically lower than the efficiency of a classical discrete gearbox, which leads to higher fuel consumption. This paper is focused on the study of the interests of a CVT for a medium-duty Hybrid Electric Truck (HET). The complete model and control of CVT-based and AMT-based HET are described in a unified way using Energetic Macroscopic Representation (EMR). These models are transformed to backward-models to be computed by the Dynamic Programming Method (DPM). Such a method leads to define the (off-line) optimal energy management strategies for a fair comparison of both hybrid trucks. For the studied driving cycle, the hybridization allows a fuel saving of 10% with an AMT and 3% with a CVT. The fuel consumption is higher for the CVT-based HET in comparison with the AMT-based HET due to the lowest efficiency of the CVT (85%) compared to the AMT (around 92%). However, future (on-demand) CVTs with an increased efficiency could be a solution of interest to reduce the fuel consumption of such applications. The developed method can be used to test these new CVTs, other vehicles or other driving cycles.

Continuously Variable Transmissions - outline

Paper concerned the Continuously Variable Transmission (CVT). The comparison of the engine’s work conditions with conventional manual transmission and CVT’s is presented. Also, a short historical track is included. Furthermore, a production data with the forecast is presented for different parts of the World. Various current solutions of continuous ratio change are mentioned with the more detailed description of the most popular design used in passenger cars. Technological challenges and possibilities of further transmission improvement are included.

Parameter design and performance analysis of zero inertia continuously variable transmission system

In order to solve the problem of weak power performance of vehicle equipped with continuously variable transmission (CVT) system working under transient operating conditions, a new CVT equipped with planetary gear mechanism and flywheel was researched, a design method of transmission parameter optimization was proposed, and the comprehensive matching control strategy was established for the new transmission system. Fuzzy controllers for throttle opening and CVT speed ratio were designed, and power performance and fuel economy of both vehicles respectively equipped with conventional CVT system and new transmission system wrere compared and analyzed by simulation. The results show that power performance and fuel economy of the vehicle equipped with new transmission system are better than that equipped with conventional CVT, thus the rationality of the parameter design method and control algorithm are verified.

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.

Continuously variable transmission using quadric crank chains and ratchets

This paper describes the CVT (continuously variable transmission). Generally, CVTs are classified as belt-type or toroidal CVTs, and each CVT is basically composed of two parts such as the V-belt and pulley, or friction wheels. In the belt-type CVT, the pulley is driven by a belt placed between two (left and right) circle boards, while in the toroidal CVT, two rollers rotate under the condition being pushed by strong compression power. Since these conventional CVTs use friction force, their energy transfer efficiency might be inferior. Furthermore, although these CVTs require precise structures and processing, they make noise, and are not durable. Consequently, we propose a new structural CVT in this paper.

1P1-Q08 Linkage-Type Continuously Variable Transmission Using a Plate Cam(Dynamics & Design of Robot System)

In this paper, we consider the continuously variable transmission (CVT). The conventional CVTs are classified as belt-type CVTs or toroidal CVTs, and each CVT is basically composed of several friction parts or wheels. Since these conventional CVTs use friction force, their energy transfer efficiency might be inferior. Although these CVTs require precise processing, they make noise, and are not durable. Consequently, we propose a new structural CVT in this paper. The proposed CVT mainly consists of a couple of quadric crank chains, ratchets (or one-way clutches), and a plate cam.

103 四節リンク,ワンウェイクラッチ,およびカムを用いた無断変速機の開発

In this paper, we consider the continuously variable transmission (CVT). The conventional CVTs are classified into belt type CVT and toroidal CVT, and each CVT was basically composed of two friction wheels. Fcr the belt type CVT, the pulley is driven by the belt placed between the middle of two circle-boards in the pulley. For the toroidal CVT, two rollers are being pushed by strong compression power. Since these conventional CVTs are transmission utilizing friction force, their energy transfer efficiency might be inferior. Also these CVTs require a precise processing, the noise was caused, and they did not have durability. Consequently, we propose a new structural CVT in this paper. In the proposed CVT, two identical quadric crank chains are placed symmetrically. Since the proposed method is not based on friction conduction, it provides a mechanism that creates no noise, is durable, and offers high transmission efficiency.

2P1-A21 四節リンク機構を用いた無段変速機の検討(エコ・ロボティクス・メカトロニクス)

As for rotation power generated by engine power in the vehicle, the transmission is a mechanism to adjust power/torque transmitted to the wheel, and the rotation speed of the wheel. The transmission can be categorized as manual (MT), automatic (AT), and continuously variable transmission (CVT). In this paper, we consider the continuously variable transmission (CVT). CVT is basically composed of the friction wheels; each wheel squarely combines two conic boards. CVTs include belt type CVT and toroidal CVT. For the belt type CVT, the pulley is driven by the belt placed between the middle of two circle-boards in the pulley. For the toroidal CVT, two rollers are being pushed by strong compression power. Since these conventional CVTs are transmission utilizing friction force, their efficiency are inferior. Also these CVTs require a precise processing, the noise was caused, and they did not have durability. Consequently, we propose a new structural CVT in this paper.

Regenerative braking algorithm for a hybrid electric vehicle with CVT ratio control

A regenerative braking algorithm is proposed for a hybrid electric vehicle with a continuously variable transmission (CVT) to make the maximum use of the regenerative braking energy. In the regenerative braking algorithm, the regenerative torque is determined by considering the motor capacity, battery state of charge (SOC), and vehicle velocity. The regenerative braking force is calculated from the brake control unit by comparing the demanded brake torque and the motor torque available. The wheel pressure is reduced by the amount of the regenerative braking force and is supplied from the hydraulic brake module. In addition, the CVT speed ratio control algorithm is suggested during braking for optimal motor operation. The optimal operation line is proposed to operate the motor in the most efficient region while keeping the motor speed as low as possible by considering engine noise and friction. It is found from the experiments that the regenerative braking algorithm with CVT ratio control offers an improved battery SOC, which provides increased recuperation energy by 8 per cent for the federal urban driving schedule compared with that of the conventional CVT ratio control.

Improvement in fuel economy for a parallel hybrid electric vehicle by continuously variable transmission ratio control

A continuously variable transmission (CVT) ratio control algorithm is proposed to achieve the improved fuel economy of the parallel hybrid electric vehicle (HEV) by considering the HEV powertrain response lag. In this algorithm, the target CVT ratio is modified by the vehicle velocity that is estimated after the powertrain response lag. To estimate the vehicle velocity after the response lag, an acceleration map is suggested. The CVT ratio control algorithm is validated by the HEV bench tester. From experimental results, it is found that the engine operation trajectory by the modified ratio control algorithm is shifted to a more efficient region compared with those by the conventional CVT ratio control for the mild acceleration mode, which gives better fuel economy. In addition, performance simulations for the federal urban driving schedule are carried out to evaluate the effect of the response lag on the HEV fuel economy using the HEV powertrain model. The simulation results show that a better fuel economy can be achieved as the response lag used in the modified CVT ratio increases. However, in actual applications, a compromise between the fuel economy and the acceleration performance would be required.

Power flows and efficiency in infinitely variable transmissions

An infinitely variable transmission (IVT) is a continuously variable transmission with an infinite ratio range, which means that the transmission ratio may achieve zero. This paper compares the efficiency of possible IVT configurations consisting of a conventional CVT (continuously variable transmission) coupled to a planetary gear train and a fixed ratio mechanism. A kinematic analysis has been performed to determine the transmission ratio of the IVT components for two types of power flow. The efficiency of the IVT has been determined considering how the efficiency of the IVT members changes as a function of the operating conditions. The power and efficiency curves for the different functional solutions have been compared.