Toroidal CVT Research Articles

Fuel consumption and emission reduction by using a CVT in series with conventional multi-speed transmission

Fuel economy is a growing concern for both manufacturers within the automotive sector and consumers. Increasing government legislation is driving towards greener vehicles with reduced CO2 and NOx emissions and greater fuel economy, especially within urban environments. Manufacturers use new technologies in their powertrain systems to tackle these problems. This paper simulates and evaluates the performance of using a half toroidal CVT in series with a conventional multi-speed transmission, by analysing different shifting strategies to optimise fuel consumption and NOx emissions over the NEDC using this novel approach. The results show an 8.83% increase in fuel economy and up to an 11.34% reduction in NOx emissions is possible using this arrangement. The introduction of CVT adds a further 1.18% increase in fuel economy and 3.59% decrease in NOx emissions. The paper concludes that this novel arrangement should be considered by automotive manufacturers as a solution for improvements to powertrain technology.

Modeling, kinematics and traction performance of no-spin mechanism based on roller-disk type of traction drive continuously variable transmission

Modeling of no-spin mechanism based on roller-disk type of traction drive continuously variable transmission (t-CVT) is conducted by redesigning the working generatrix of the original disk to meet the no-spin condition, and a novel basic no-spin Conical CVT mechanism is acquired. According to the structural characteristics of Half Toroidal CVT(HT-CVT), the no-spin Swing Conical CVT(NSC-CVT) and no-spin Rolling Conical CVT(NRC-CVT) are developed by configuring the structural symmetry and speed changing motion form of the no-spin Conical CVT. Furthermore, the kinematics of NSC-CVT is studied and compared with HT-CVT. The result demonstrates that the actual spin ratio of the NSC-CVT are smaller than that of HT-CVT, and the half cone angle of NSC-CVT is recommended. At last, a computational method has been proposed to compute the efficiency of the NSC-CVT. Comparing with HT-CVT, the better efficiency is achieved by the NSC-CVT, whereas the advantage of no-spin characteristic is proved. But the torque capacity of NSC-CVT is not as good as that of HT-CVT, which will limit its use to high torque applications.

Performance Evaluation of Ball CVT and Comparison with Half Toroidal CVT

This study aims at finding an analytical model of ball continuously variable transmission (B-CVT) behavior and performance, based on the existing model of the half-toroidal traction drive. The geometrical and kinematical aspects of this model have been found. Then, force-moment equilibrium equations have been applied for a B-CVT. The contact behavior has been modeled using the isothermal elastohydrodynamic lubrication (EHL) theory, and spin and relative slip losses have been estimated for this CVT. Finally, the overall efficiencies of the B-CVT have been analyzed and compared with the halftoroidal traction drive. This study results have shown that B-CVT has higher torque efficiency and lower speed efficiency in comparison with half-toroidal CVT. Also, it has shown that the adjustment of axial forces in B-CVT leads to higher efficiency in lower input torques.

A comparison of the full and half toroidal continuously variable transmissions in terms of dynamics of ratio variation and efficiency

The full and half toroidal CVT have been the subject for many research papers. The efficiency and behavior in steady state of both topologies has already been discussed in detail but until now no special attention has been given to their behavior during ratio variation. Therefore, this paper discusses the comparison of the full and half toroidal CVT during periods of ratio variation focusing on the dynamic response and efficiency. The geometrical constraints for the comparison are as follows: equal output inertia, equal maximum output torque at a speed ratio of 1 and identical radial size. The results of the study are based on a model that describes the behavior of both topologies and an algorithm that determines the optimal ratio variation. The outcome of the study shows that the half toroidal outperforms the full toroidal CVT over the entire operating range in terms of dynamics and efficiency during ratio variation.

Half toroidal continuously variable transmission: Trade-off between dynamics of ratio variation and efficiency

This paper investigates the trade-off between efficiency and dynamics of CVT's. Energy efficiently varying the speed ratio of the CVT while maintaining the dynamic requirements is of primordial importance to fully utilize the advantages of the CVT in a drivetrain. Although the toroidal CVT is thoroughly discussed in literature, few articles describe its behavior during ratio variation. Therefore, in this paper a procedure is proposed to achieve optimal ratio variation in terms of settling time and efficiency with a half toroidal CVT. The key concept on which the procedure is based is the expression of the maximum output torque of the CVT. It turns out that the given method offers the fastest possible speed ratio variation for given constraints without excessive increase in slip and thus limited loss in efficiency. The most important constraint proves to be the clamping force which has a profound impact on the resulting dynamics and efficiency of the CVT. The paper indicates that higher clamping forces increase the dynamics of the CVT at a certain cost of loss in efficiency which implies that there is a trade-off between efficiency and dynamics.

3.トロイダルCVT復活に向けた取組み

3.トロイダルCVT復活に向けた取組み

2A1-Q10 広域無段変速装置搭載車両の研究 : 加減速制御アルゴリズム(【交通・物流部門】自動車分野におけるロボティクス)

Wide Range CVT(WRCVT) is a combination of half toroidal CVT and differential gear. The gear ratio of this transmission can be changed continuously from forward to reverse. This paper describes the acceleration and deceleration control algorithm of the vehicle which is driven by the WRCVT. Because the engine speed is kept by a regulator, the vehicle speed corresponds to the WRCVT reduction ratio. Acceleration or deceleration signal produced by an accelerator pedal is combined with the actual speed signal to be the reference signal to the controller. When breaking, brake activation signal cut off the accelerator signal, and the reference of reduction ratio controller follows the actual vehicle speed. This algorithm was verified successfully by an engine driven small cart.

Research of CVT efficiency:-Comparison of a Toroidal CVT and a Belt CVT-

Research of CVT efficiency:-Comparison of a Toroidal CVT and a Belt CVT-

High-pressure behavior of toroidal CVT fluid for automobile

Practical toroidal-type continuously variable transmission (t-CVT) is subjected to extremely severe operating conditions, viz., maximum contact pressure is very high at 4 GPa, rolling speed exceeds over 30 m/s and lubricant temperature goes up over 140 °C. Traction measurements were recently made at wide range of contact pressures, oil temperatures and rolling speeds by USCAR Group. The objective of this research is to investigate high-pressure rheology of the traction characteristics at extremely severe EHL contact conditions. The effects of contact pressure and temperature on maximum traction coefficient were evaluated using the phase diagram and the liquid/solid transition lubrication diagram.

A Study on the Contact Behaviors of Infinitely Variable Transmission System with Full Toroidal Shapes of Disks

The torque of the continuously variable transmission system with friction drive mechanism is transmitted by contacting roller with input and output disks. For the higher transmitted torque, it is necessary to apply large load in order to get higher friction force, which in turn generates severe high stress on the contact surfaces of roller and disks. The toroidal type CVT system has simple component arrays that have three contact points between roller and each input or output disk to get the torque transmitted. However, compact assembly design of the three sets of rollers contacting with input and output disks needs the roller to stay with unsymmetrical angled position with each other. Therefore, the contact shapes between roller and disk vary according to the transmission ratio and should be investigated to avoid the excessive contact stress over than ~1.8 GPa. In this study, the contact geometries of roller and disks in the toroidal type CVT system are computed during the gear ratios. The contact area of which the size depends on the material elasticity, curvatures of roller and disk, and applied load are all of elliptic shapes because of the convex and concave curvatures of roller and disk shapes, respectively. From the computed results considering the size of roller diameter, roller stroke and applied load, it is found that the shapes of contact area changes the sizes of major and minor elliptical diameters in the rolling direction during the gear ratios due to the unsymmetrical angled position of roller.

20907 トラクション機構設計(OS4 機構デバイスとトライボロジー)

The history of CVT can find into the patent. In this report, the mechanism and the design of CVT divide into three periods between the late 1800s and the present, and analyze the characteristic each period. Lastly Toroidal CVT is used as the example and surveys the change of the mechanism of it.

1P1-S-015 CVTと差動ギヤを用いた広域無段変速装置の小型車両への適用(車輪移動ロボット1,生活を支援するロボメカ技術のメガインテグレーション)

1P1-S-015 CVTと差動ギヤを用いた広域無段変速装置の小型車両への適用(車輪移動ロボット1,生活を支援するロボメカ技術のメガインテグレーション)

トロイダルCVTの幾何諸元と動力伝達効率の解析(O.S.10-2 CVT・TD(2))

トロイダルCVTの幾何諸元と動力伝達効率の解析(O.S.10-2 CVT・TD(2))

Ball toroidal CVT: a feasibility study based on topology, kinematics, statics and lubrication

In this paper, a feasibility study of a special kind of toroidal CVT is presented based on different standpoints. The mechanism is briefly described and its kinematic structure is analysed. Its corresponding graph, which turns out to be not planar, is detected by means of a new method for classifying the nonholonomic pairs. The degrees of freedom are so evaluated and the independent circuits are identified. The kinematic analysis leads to a symbolic expression of the global transmission ratio and a simple relation between the two control angles is found to be necessary to theoretically avoid sliding at the contact points. The static force analysis is also carried out in order to ascertain the best method for applying the static pre-load needed to operate the transmission by friction in automotive applications. Finally, the two spherical pairs, which are embodied in the system, are made subject to a feasibility check by analysing the hydrodynamic lubrication conditions and by obtaining through a numerical approach, the oil film thickness and the pressure field over all the spherical domain. Results are provided which show how the two pairs work better if a component of hydrostatic lubrication is adopted.

2512 自動車用トロイダル CVT のトラクション特性研究(第 3 報、実機トラクション特性)

It is essential to ascertain traction characteristics under actual operating conditions in order to apply a toroidal CVT incorporating a traction drive system to automobiles. This paper first describes the traction characteristics obtained quantitatively over a wide range of conditions by using an actual variator. The resulting characteristics showed the large influence of spin. Furthermore, an attempt was made to obtain the calculated prediction of an actual variator by using a viscoelastic-plastic model with a measured temperature of variator. A comparison was made between the calculated results and the actual variator test results. It was found that an accurate prediction of traction characteristics requires the surface temperature of variator.

605 トラクションドライブを応用したトロイダル CVT の開発

605 トラクションドライブを応用したトロイダル CVT の開発

3018 自動車用トロイダル CVT のトラクション特性研究 : 第 2 報粘弾性塑性モデル解析

Implementing a toroidal CVT, in which driving force is transmitted by traction drives, in a production vehicle requires knowledge of traction characteristics under actual operating conditions. A mathematical model was developed to calculate traction characteristics, taking into account spin and side slip and using the rheological parameters measured for the fluid in cylinder tests. The calculated results obtained with the model indicate that temperature has a significant effect on traction characteristics under actual usage conditions. A model that can simultaneously treat viscoelasticity and elastoplasticity is therefore needed to calculate the effects of temperature accurately.

Synchronization and Stability of Speed-Ratio Control Servomechanism of A Double Cavity Half Toroidal CVT.

A double cavity half toroidal contimlously variable power transmission transmits input torque through a pair of variable units and changes its speed ratio by controlling attitude angels of four power rollers. One power roller among them is controlled by a hydraulic servomechanism and the others are followed it under the control principle of equal force transmission. Synchronization of four power rollers is guaranteed by safety wires, however nonlinearities of friction force on the control pistons or pressure delay in hydraulic lines due to air mix or pipe length cause instability of the speed ratio servomechanism through the safety wires. This paper focuses the relation between the synchronization and stability of the CVT by making bond graph analyses and experiments, and shows design guidelines on the stabilization of the double cavity half toroidal CVT.

A geometrical study of toroidal CVT ? Comparison between half toroidal and full toroidal Takashi Imanishi, Hisashi Machida (NSK Ltd.), Hirohisa Tanaka (Yokohama National University)

A geometrical study of toroidal CVT ? Comparison between half toroidal and full toroidal Takashi Imanishi, Hisashi Machida (NSK Ltd.), Hirohisa Tanaka (Yokohama National University)

Torque - Distribution Control by a Double - Cavity Half - Toroidal CVT for Four Wheel Driveline

A double-cavity traction-drive CVT, continuously variable power transmission, for four-wheel-driveline has potential to provide a new type of four-wheel torque-distributing transmission without a center-differential gear unit. This paper describes its principle and bench-test result by making a CVT with speed-ratio-range from 0.345 to 2.9, input torque capacity of 250N'm and rotational speed of 5500rpm. The principle is to control the front and rear torque by controlling the front- and rear-speed-ratio of each CVT-unit. Their ratios are settled by measuring the front- and rear-axle torques. As to bench-test, dynamic characteristics of torque distribution at torque change is examined.