Continuously Variable Transmission Ratio Research Articles

Electronic system of rubber belt electro-mechanical continuously variable transmission for motorcycle applications

This paper deals with the design of electronic system for changing the transmission ratio of a rubber belt electro-mechanical continuously variable transmission (CVT) for motorcycle applications. In this CVT, the rubber belt is used as a medium to transfer both the speed and torque from the input pulley to the output pulley based on contact friction force existed between the belt and both pulley surfaces. Each pulley set consists of one fixed and one sliding pulley sheaves. The axial position of the input sliding pulley sheave is detected using a two channel incremental rotary encoder and controlled by an electro-mechanical shifter system utilizing DC motor, actuator gear set and cam mechanism. The sliding sheave of the output pulley is axially pushed by contra spring to provide sufficient belt compression for preventing belt slip. The CVT ratio is changed by varying the input and output belt-pulley contact radii. It can be done by controlling the axial position of sliding input pulley sheave, the angular speeds of input and output pulleys are sensed using one channel incremental rotary encoders. By knowing these two speed values, the CVT ratio can be computed. The microcontroller system of Arduino is programmed to detect and control the axial position of the input sliding pulley sheave to regulate the CVT ratio. The experimental results show that the electronic system can perform the CVT ratio changes adequately.

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.

Current usage by a DC motor to vary ratio in an electro-mechanical continuously variable transmission

In a typical continuously variable transmission (CVT) for automotive, engine torque is transmitted from the primary pulley (connected to the vehicle’s engine) to the secondary pulley (connected to the wheels) through a metal pushing V-belt. The CVT ratio (rCVT ) is defined as the pitch radius of the belt on the secondary pulley divided by the pitch radius on the primary pulley. Conventionally, rCVT is varied using hydraulic pressure generated by an oil pump which is powered by the engine. A continuous hydraulic pressure is required to maintain high clamping force applied on the belt so that sufficient traction between the belt and the pulleys can always be provided. This requirement, unfortunately, causes significant power losses in the CVT and to address this, the idea of electro-mechanical CVT (EM CVT) is proposed. In an EM CVT, rCVT is varied using a power screw mechanism and a DC motor while the desired ratio and the belt’s clamping force is maintained using the thread of the power screw mechanism, consequently eliminating the aforementioned issue. This paper describes the process of measuring the current used by a DC motor to vary rCVT in an EM CVT. The results show that the current usage is higher during upshifting from rCVT of 1.95 to 1.43 (about 45 A) as compared to downshifting from 1.43 to 1.95 (about 23 A). This is due to the application of disc springs in the secondary pulley that reduces the required motor torque for downshifting. The results also prove that no current is consumed by the motor during a constant rCVT . In conclusion, the motor’s current usage has been successfully measured and the results can be used for a future development of the EM CVT’s battery system.

Research on the novel discretized ratio control strategies and hardware-in-the-loop test for continuous variable transmission system

Based on traditional continuous control strategy for Continuously Variable Transmission (CVT) ratio, according to the principles of shift control strategy for stepped automatic transmission, the influences of throttle opening and external resistance or vehicle speed on CVT ratio control are analyzed on bumpy road. Under the same variation of external resistance condition, the differences between optimal economic control strategy and optimal dynamic control strategy are discussed. Then, the traditional continuous optimal dynamic and economic control lines are divided into multi-step upshift points. Meanwhile, the corresponding downshift points are set to avoid the interference near shift points. After that, the novel discretized ratio control methods for CVT system are proposed. By respectively discretizing throttle opening and vehicle speed, the discretized ratio control strategy for throttle opening, and the integrated discretized ratio control strategy for throttle opening and vehicle speed are further proposed and simulated. Furthermore, the hardware-in-the-loop (HIL) test system is built to further verify the feasibility and accuracy of discretized ratio control strategies. Both simulation and HIL test results show that the sensitivity of throttle opening and vehicle speed to ratio control is reduced dramatically, the fluctuation of ratio is decreased considerably, the transmission efficiency is increased significantly, and the jerk is declined moderately.

Forward parameter optimization design for actuator of electromechanical continuously variable transmission

An electromechanical continuously variable transmission (EMCVT) with an actuator containing two direct current (DC) motors is proposed to improve the transmission efficiency of a continuously variable transmission (CVT) by reducing the power consumed by the CVT actuator. To enhance the EMCVT efficiency, the ratio and driven pulley clamping force are adjusted using an electromechanical actuator. It is required that the adjustable range of the driven pulley clamping force of the EMCVT is maximized and the operating power of the DC motors in the actuator is minimized. However, this adjustable range is limited when the actuator is designed for the maximum required driven pulley clamping force. To ameliorate this issue, the electromechanical actuator is optimized in this paper. The structure and operating principles of the EMCVT are illustrated, and the main actuator part models are built. Accordingly, the design principle of the main actuator parts is determined. The required clamping force for four standard driving cycles is considered, and the structural parameters of Belleville springs in the actuator are optimized using a genetic algorithm. Two DC motors are suitably selected, and the mechanical transmission system of the actuator is determined. The optimization results show that the adjustable range of the driven pulley clamping force is increased by over 80% for a high CVT ratio and that the energy consumed by the actuator is reduced for ECE and EUDC driving cycles by ~ 56% and ~ 28%, respectively, as compared to the energy consumed by the actuator before optimization.

Modeling and matching performance of a hybrid-power gas engine heat pump system with continuously variable transmission

Based on the steady-state efficiency of the engine and the motor and characteristic curve of Lithium iron phosphate (LiFePO4) battery, an energy management strategy is proposed for a coaxial parallel hybrid-power gas engine heat pump (HPGHP) with V-belt continuously variable transmission (CVT) by using logic threshold approach to control the dynamical transitions between the various operation modes. The torque distribution between engine and motor, and CVT ratio are regulated through predetermined optimal operation lines of hybrid powertrain system in different operations. The results demonstrate that the energy management strategy can satisfy heat pump demand performance and reduce gas consumption effectively, as well as keep battery state of charge (SOC) in reasonable range. The average thermal efficiency of driving system in three main operating modes is 3.8%, 1.9% and 2.5% higher than that of multi-stage transmission system respectively, indicating that the system has better energy saving performance.

A fuel-optimal driving strategy for a single vehicle with CVT

The efficiency of the continuously variable transmission (CVT) is within 70∼95%, so the effects on the fuel consumption cannot be ignored. In this paper, we first analyze the quantitative relationship between the running states of inertial combustion engine with CVT and the fuel consumption, and then propose a fuel-optimal driving strategy for a vehicle with CVT. In the strategy, the vehicle speed and acceleration, the engine torque and speed, and the CVT ratio in the processes of acceleration, uniform motion and deceleration are calculated. The numerical results show that when the driving distance is less than a critical value, this vehicle experiences an acceleration–deceleration process, otherwise this vehicle experiences an acceleration–constant–deceleration process. The results can provide a fuel-optimal strategy for a vehicle under different driving distance, which can be used to the human driving guidance, the driving assistance system and the autonomous vehicles.

Research on regenerative braking control strategy of plug-in hybrid electric vehicle considering CVT ratio rate of change

At present, the regenerative braking control strategies for hybrid electric vehicles equipped with continuously variable transmission (CVT) mainly focus on improving the regenerative braking efficiency. But the influence of dynamic change of the CVT ratio is not considered with regard to the intended braking effect. For a CVT ratio control strategy based on steady-state optimal efficiency, the performance of motor-only braking and engine/motor combined braking modes are analyzed. The analysis of these modes shows that actual braking strength deviates from that required during the dynamic braking process. After analyzing the dynamic characteristics of a transmission system, a CVT ratio control strategy based on the limitations of the ratio rate of change is proposed, with the use of a discrete exhaustive optimization method. The simulation results show that, under a variety of braking conditions, the proposed regenerative braking control strategy can make the actual braking strength follow the requirements and recover more braking energy.

Optimisation and comparison of different powertrain layouts for parallel hybrid electric vehicles equipped with continuous transmission

The development of an efficient hybrid electric vehicle (HEV) platform needs an optimal design of its powertrain layout. This study is concerned with parallel HEVs (PHEVs) equipped with continuous transmission. First, different types of continuous transmissions, including continuously variable transmission (CVT), power-split CVT (PS-CVT) and multi-fixed ratio PS-CVT (MF-CVT), are discussed and their simulation models are presented. Also, various combinations of these continuous transmissions with PHEV configurations (namely, pre-transmission and post-transmission configurations) are introduced. Then, for a given PHEV model, several powertrain layouts resulting from combining the considered continuous transmissions and PHEV configurations are optimised over a standard drive cycle. The optimised powertrain layouts are compared from different perspectives, for instance the vehicle fuel consumption, emissions and some dynamic performance measures. In particular, the sensitivity of the PHEV performance characteristics to the driving cycle pattern, when it is equipped with each optimised layout, is investigated.

Transmission ratio calibration for electro-mechanically actuated continuously variable transmission

Continuously variable transmission (CVT) with a metal pushing V-belt is widely used by car manufacturers for its advantages particularly in fuel economy. Nevertheless, this CVT currently applies a hydraulic-based actuation system to change and to maintain the desired CVT ratio which leads to reduction of CVT's efficiency due to engine's continuous power consumption. To address this issue, a prototype of electro-mechanically actuated CVT is introduced in this paper. Here, the prototype's working principle is explained and the process to evaluate its workability is described. This evaluation process is necessary to provide reference data for future development of the prototype especially in the areas of ratio control and belt's clamping force control. The evaluation's results suggest that the prototype has a ratio range from 2.93 to 0.67 with using only one DC motor to vary the ratio instead of typically two DC motors used by previous designs of electro-mechanically actuated CVT.

DESIGN OF ELECTRO-MECHANICAL DUAL-ACTING PULLEY CONTINUOUSLY VARIABLE TRANSMISSION

Pulley-based continuously variable transmission (CVT) with a metal pushing V-belt is fast becoming the preferred choice for global carmakers due to its potential particularly in terms of fuel efficiency thanks to its continuous and wide ratio range. Nevertheless, the existing CVTs still face the issues of high power consumption from the engine because of the application of an electro-hydro-mechanical (EHM) actuation system for its ratio changing process and clamping force mechanism. To address this issue, researchers from Universiti Teknologi Malaysia have successfully developed the prototype of an electro-mechanical dual-acting pulley continuously variable transmission (EMDAP CVT) for automotive applications. The prototype of EMDAP CVT is developed for a maximum input torque of 160 Nm with the application of a metal pushing V-belt. The results from the testing prove that the prototype can vary its ratio from 2.8 to 0.6 and no continuous power is required to maintain a constant CVT ratio. These results suggest that the prototype is workable and future testing in a real car is possible.

Development of Performance Simulator for a HEV with CVT and Validation with Dynamometer Test Data

In this paper, control analysis was performed for a hybrid electric vehicle (HEV) equipped with a continuously variable transmission (CVT) under various driving conditions. First, a dynamic CVT model was developed by considering hydraulic and mechanical losses. The hydraulic loss accounts for the majority of the total losses at low vehicle speeds, whereas the mechanical loss accounts for the majority at high speeds. In addition, CVT ratio control and clamping force control strategies were developed, including manipulation of the CVT shift dynamics. On the basis of the dynamic model of the CVT, an HEV performance simulator was developed using Argonne National Laboratory (ANL)’s model-based simulation program, Autonomie. Second, by analysing the test results from ANL, an engine optimal operating line was constructed on the basis of the engine brake-specific fuel consumption. Third, the battery state-of-charge range and the battery characteristics of the maximum charging and discharging power were investigated. Using the analysis results, vehicle operation control strategies were developed for the acceleration, cruising, deceleration and idling modes. Also, control algorithms were developed for each vehicle operation mode. Finally, the control algorithms were verified by comparing the simulation results with the test results.

Design of Single Acting Pulley Actuator (SAPA) Continuously Variable Transmission (CVT)

The design of Single Acting Pulley Actuator (SAPA) Continuously Variable Transmission (CVT) utilizes combinations of DC motor system, gear reducers and power cam mechanisms to actuate primary movable pulley sheaves on the transmission shaft. The secondary pulley supported by spring provides a belt clamping force to prevent slips, while the secondary controls the rubber v-belt from slipping. Since the methods of controlling these are similar, this paper only discusses the primary part. The servomotor regulates the axial movement of primary movable pulley sheaves to shift the rubber v-belt placed between the sheaves, and change the belt-pulley contact radius. Changing this contact radius means changing the CVT ratio. Computer simulation results are presented to demonstrate the effectiveness of the proposed PD controller. The research outcome gives a significant result to complete 75.08° rotation of the CAM from lower gear ratio to top gear ratio is less than 6.79 sec, with minimum error and less overshoot with a manual PD tuning contribution to the field of DC motor based electro-mechanical CVT control system.

Experimental Study of Electro-Mechanical Dual Acting Pulley Continuously Variable Transmission Ratio Calibration

This paper presents an experimental study of Electro-mechanical Dual Acting Pulley (EMDAP) Continuously Variable Transmission (CVT) ratio calibration. When there is no slip between belt and pulley sheaves, the CVT ratio will be the same as the geometrical ratio of secondary to primary pulley radii as well as the primary to secondary speed ratio. In EMDAP CVT system, both primary and secondary DC motors are used to control the primary and secondary axial pulley positions to vary the primary and secondary pulley radii. In this case, the pulley radii can be measured indirectly using axial pulley position sensors. Calibration process is carried out by manually adjusting the geometrical ratio of secondary to primary radii based on measurements of primary and secondary pulley positions and validated with the primary to secondary speed ratio determined from primary (input) and secondary (output) shaft speed measurements for the CVT ratio range of 0.7 to 2.0. The calibration results are recorded and used as reference data for future EMDAP CVT calibration and ratio control developments.

Pulleys' Axial Movement Mechanism for Electro-Mechanical Continuously Variable Transmission

Pulley-based continuously variable transmission (CVT) with Metal Pushing V-belt (V-belt) is a type of automotive transmission that is widely applied currently by many car manufacturers worldwide. Unlike the conventional automotive transmissions, in a pulley-based CVT with V-belt, the transmission ratio (CVT ratio) is changed continuously without the use of discrete gears. Instead, the CVT ratio is varied through the simultaneous axial movement of the primary pulley and the secondary pulley. By axially moving both pulleys simultaneously, the radius of the V-belt on both pulleys will be changed accordingly, resulting in the change of the CVT ratio. The existing pulley-based CVTs in the market use electro-hydro-mechanical (EHM) actuation system to change and to maintain the desired CVT ratio through the hydraulic pressure. However, the application of EHM actuation system leads to some disadvantages, particularly in term of the high power consumption from the engine needed to maintain the desired CVT ratio. This reduces the efficiency of the powertrain system, which eventually increases the fuel consumption of the vehicles. In addition to that, the existing pulley-based CVTs also use single acting pulley mechanism to axially move the pulleys for changing the CVT ratio. Therefore, the issue of V-belt's misalignment, which shortens the lifespan of the V-belt, is inevitable here. In this paper, the pulleys' axial movement mechanism that uses electro-mechanical (EM) actuation system is proposed. Consequently, the working principle of the proposal is described and its potential benefits are discussed.

Adaptive neuro-fuzzy maximal power extraction of wind turbine with continuously variable transmission

In recent years the use of renewable energy including wind energy has risen dramatically. Because of the increasing development of wind power production, improvement of the control of wind turbines using classical or intelligent methods is necessary. To optimize the power produced in a wind turbine, the speed of the turbine should vary with the wind speed. Variable-speed operation of wind turbines presents certain advantages over constant-speed operation. In this paper, in order to maintain the maximal output power of wind turbine, a novel intelligent controller based on the adaptive neuro-fuzzy inference system (ANFIS) is designed. To improve the wind energy available in an erratic wind speed regime, a wind generator equipped with continuously variable transmission (CVT) was proposed. In this model the ANFIS regulator adjusts the system speed, i.e. CVT ratio, for operating at the highest efficiency point. The performance of proposed controller is confirmed by simulation results. Some outstanding properties of this new controller are online implementation capability, structural simplicity and its robustness against any changes in wind speed and system parameter variations. Based on the simulation results, the effectiveness of the proposed controllers was verified.

Microcontroller Based Proportional Derivative Plus Conditional Integral Controller for Electro-Mechanical Dual Acting Pulley Continuously Variable Transmission Ratio Control

Electro-Mechanical Dual Acting Pulley (EMDAP) Continuously Variable Transmission (CVT) is a transmission utilized by electro-mechanical actuated system. It has a potential to reduce energy consumption because it only needs power during changing CVT ratio and no power is needed to maintain CVT ratio due to self lock mechanism design. This paper proposed simple proportional derivative plus conditional integral (PDCI) controller to control EMDAP CVT ratio which can be simply implemented on a microcontroller. This proposed controller used Astrom-Hagglund method and Ziegler-Nichols formula to tune PDCI gain. The Proportional Derivative controller is directly activated from the start but Integral controller is only activated when the error value reaches error value setting point. Simulation using Matlab/Simulink software was conducted to evaluate PDCI system performance. The simulation results showed PDCI controller has ability to perform maximum overshoot 0.1%, 0.001 steady state error and 0.5s settling time. For clamping condition, settling time is about 11.46s during changing ratio from 2.0 to 0.7, while for release condition, settling time is about 8.33s during changing ratio from 0.7 to 2.0.

Integrated control strategy for CVT powertrains with consideration of vehicle drivability

During shift, power flow is not interrupted in powertrains equipped with continuously variable transmission (CVT). When hard acceleration is commanded, engine speed will flare and corresponding torque will be consumed, which leads to a drop in vehicle drive torque and also the vehicle acceleration. This is the reason why CVT vehicles have poor drivability during hard acceleration maneuver. Conventional method such as torque compensation doesn’t always work due to the limited backup torque of engine. According to this, means to evaluate the drivability of CVT vehicles are studied, affect factors of drivability are analyzed in detail. Hard acceleration process of CVT vehicle is studied by theoretical analysis, based on which engine torque and ratio change rate of CVT are identified as two key control parameters that decide the drivability of CVT vehicles during hard acceleration maneuver. Therefore, a control strategy based on restricting the change rate of CVT ratio together with torque compensation is proposed, and two different algorithms to establish the limitation of ratio change rate are proposed. These two algorithms are simulated and compared with each other, results indicate that drop of vehicle acceleration is eliminated evidently by limit the change rate of CVT ratio, but small ratio change rate also results in a longer time to finish the accelerate process, an algorithm to decide a proper ratio change rate is needed in order to tune these different characteristics. In order to get better control effects, a new fuzzy logic based algorithm is proposed to decide a proper ratio change rate during kick down conditions, simulation and experiment results indicate that, the amount of vehicle acceleration decrease is reduced from about 1 m/s2 to almost 0, in the mean time the accelerate process only delayed for about 0.3 s. The proposed control strategy and algorithm can effectively tune the characteristics of CVT equipped vehicle during kick down conditions.

Modelling the performance of a continuously variable supercharger drive system

This paper details a simulation-based investigation into a novel forced-induction boosting system with a centrifugal-type supercharger driven from the engine crankshaft via a continuously variable transmission (CVT). This system acts as a pre-boost to a traditional fixed-geometry turbocharger and has been identified as a possible solution to improving the low-speed engine torque and transient response of future downsized and existing turbocharged engines. The concept was modelled around an existing baseline high-speed direct-injection diesel engine model featuring a variable-geometry turbocharger. Conclusions are drawn comparing the potential of the proposed system with the baseline engine in terms of the brake specific fuel consumption, and both the steady state and the transient performance. A design-of-experiments approach is applied to investigate the effects of the supercharger compressor size, the turbocharger compressor and turbine size, the CVT ratio, and the engine compression ratio on the system performance. Optimization techniques are then applied to identify the best settings for these parameters in the proposed system. Transient simulation was undertaken in a MATLAB/Simulink Ricardo WAVE co-simulation environment to develop the required control strategies for the CVT supercharger. The proposed system demonstrates a significant improvement in the low-speed engine torque and transient response of the boosting system during tip-in pedal events, which it is proposed will result in a significant improvement in the vehicle performance and driveability.

The Empact CVT: modelling, simulation and experiments

This paper shows the implementation of a simulation model for new electromechanically actuated metal V-belt type Continuously Variable Transmission (CVT), referred to as the Empact CVT. An analysis of the dynamics of the actuation system and of the driveline shows that the eigenfrequencies of the system depend on both the CVT ratio and the slip in the variator. An accurate variator model is required to incorporate all characteristic dynamics. The implemented variator model is an explicit formulation of a model which gives an estimation of the tension forces and compression forces in the pushbelt. The simulation model also includes slip, shifting losses based on transient variator models and friction. Simulations are compared to measurements, showing good results.