Continuously Variable Transmission Efficiency Research Articles

Research on Designing the Continuously Variable Transmission Test Bench

The continuously variable transmission (CVT) is designed to enhance the performance of the powertrain system. It helps the vehicle have better acceleration as well as improves the fuel economy. Fuel consumption in a car is directly linked to transmission efficiency, primarily influenced by the vehicle's drivetrain system. Factors affecting the transmission efficiency of transmission including belt structure, hydraulic pressure, and control technique are factors that need to be studied and improved. This study was carried out to calculate and design the mechanical, hydraulic, and electrical control systems of a CVT test bench. With the initially designed test bench simulated, it is possible to evaluate the characteristic quantities controlling the transmission ratio of the gearbox such as the pressure acting on the pulleys, the force acting on the belt, the torque at axes corresponding to different load modes vary from 2kW to 6 kW. The results of this study will be the basis for manufacturing an experimental system for in-depth studies and evaluation of the CVT such as belt slip, as well as the factors affecting transmission efficiency of CVT.

Research on Clamping Force Control of CVT for Electric Vehicles Based on Slip Characteristics.

The low mechanical efficiency of metal belt’s continuously variable transmission (CVT) limits its application in new energy vehicles. To further improve CVT efficiency and reduce the energy consumption of electric vehicles (EVs) with CVT, this paper proposes a pure electric CVT configuration and a clamping force control strategy. The slip characteristics of CVT are obtained through a bench test, the dynamic model of CVT slip is established, and a clamping force fuzzy control strategy is designed. The strategy is studied by simulation under extreme conditions and standard driving cycles. The simulation results show that the proposed clamping force control strategy has good adaptability. Under extreme conditions, this strategy can ensure that CVT does not undergo macro slip, while reducing the clamping force by 12.86–21.65%. Energy consumption per 100 km is 14.90 kWh in NEDC, which is 6.67% lower compared with the traditional strategy. CVT average efficiency and average transmission efficiency increased by 3.71% and 6.40%. The research results demonstrate that adjusting the CVT clamping force through fuzzy control based on the slip rate can improve the CVT efficiency and energy economy of EVs, which provides a certain reference for CVT clamping force control strategy development and the application of CVT on EVs.

Analysis and optimization of a natural gas multi-stage expansion plant integrated with a gas engine-driven heat pump

Excessive preheating energy consumption is a persistent issue in natural gas expansion power plants. In this paper, a novel system is proposed to solve this problem by using multi-stage expansion and gas engine-driven heat pumps (GHP). A dynamic model based on phase equilibrium theory is established to predict hydrate formation. A control strategy with continuously variable transmission (CVT) for optimizing engine efficiency is investigated through simulation and experiment. Finally, the efficiency and economic performance are compared among GHP, electric heat pump (EHP), and cogeneration (CHP) in a case study. The results show that the engine efficiency of CVT is 4.89% higher than that for multi-level transmission. Compared to single-stage expansion, multi-stage design can reduce preheating temperature by 46%, preheating load by 4.41%, and improve the performance coefficient (COP) of GHP 1.4-fold. The COP of GHP is 33.38% higher than that of EHP, and the primary energy ratio (PER) is 1.81 times that of CHP accordingly. The annual average profit margin for GHP is 1.89 times that of CHP and 7.15 times that of EHP. Thus, the proposed system has significant energy savings and economic advantages.

Improving transmission efficiency and reducing energy consumption with automotive continuously variable transmission: A model prediction comprehensive optimization approach

This paper proposes an optimal comprehensive control framework to maximize the powertrain transmission efficiency and fuel economy meeting vehicle owners’ travel needs. The proposed control framework consists of vehicle layers and verification. In the vehicle layer, creatively, each set of automotive Continuously Variable Transmission (CVT) supply equipment is equipped with original comprehensive controller that estimates engine fuel consumption and CVT efficiency based on a newly dynamic equation of CVT, engine torque, clamping force, and upcoming trip information. The controller obtains the optimal input of engine torque and clamping force by repeatedly solving the optimization problem of each sampling point in real-time. In the verification layer, with the powertrain system model received from the comprehensive controller, the robustness was verified by bench and hardware-in-the-loop simulation platform. The proposed comprehensive optimization approach can enhance accuracy and solve the multi-objective control problems compared with traditional methods. It is also scalable to the expanding CVT fleet and robust to uncertainties future system condition and in further to meet the vehicle owner’s travel comfort and economy. The proposed method is studied using a prototypical driving platform developed at State Key Laboratory of Automotive Safety and Energy of Tsinghua University and detailed trip information extracted from 2019 BEIJING Transport Annual Report Survey. The main contribution of this study is to explore a novel way to optimize the comprehensive transmission efficiency of engine and CVT, compared with the Proportional Integral Derivative (PID) control, the comprehensive controller can improve the transmission efficiency by 8.92%, and reduce the fuel consumption by 4.9%, it also can save about 90 million liters of fuel and 70 million US dollar for CVT vehicles in Beijing.

Generation mechanism of friction anisotropy by surface texturing under boundary lubrication

Continuously variable transmission (CVT) is commonly used in automobile to reduce fuel consumption and emission. Apart from wider gear ratio, reduction of friction loss in a radial direction of the pulley surface is an effective method of improving CVT efficiency. On the other hand, to improve torque transmission efficiency, high frictional force on circumferential direction of the pulley is necessary. Therefore, required frictional characteristics differ depending on sliding directions. To create friction anisotropy on belt-pulley contacts, laser surface texturing was proposed to improve friction characteristic and generates friction anisotropy on the surface. In this study, the relationship between surface texture and friction anisotropy was investigated under boundary lubrication by cylinder-on-disk type sliding test. The sliding test was conducted in four different directions, parallel, thirty degrees, sixty degrees, and perpendicular to the direction of the surface texture. Analysis of real contact area was conducted repeatedly in the sliding directions to evaluate change in interaction of asperities in sliding directions over time. The experimental results were then compared with result of the continuous analysis of real contact area. When a groove-type texture was created by a processing laser, texture pattern changes the sliding distance on the plateaus of the texture, which affects the level of metal contact on the surface, generating friction anisotropy. This hypothesis was supplemented by the continuous analysis of the real contact area, which confirmed that the sliding distance on the plateaus of the texture decreased as the sliding angle increased. Furthermore, clear correlation between sliding distance and friction force was observed, which suggests the possibility that friction anisotropy by surface texturing under boundary lubrication will be predicted by a friction force function.

Car Fuel Economy Simulation Forecast Method Based on CVT Efficiencies Measured from Bench Test

Researchers face difficulties in studying the effects of driveline efficiency on car fuel economy via bench and road tests because of long working periods, high costs, and heavy workloads. To simplify the study process and shorten test cycles, a car fuel economy simulation forecast method for combining computer simulation forecasting with bench tests is proposed. Taking a continuously variable transmission (CVT) as the research object, a transmission efficiency model based on a bench test is constructed. An optimal economic variogram based on the original CVT variogram, the boundary conditions of vehicle performance, the road conditions and the driving behavior of the driver is generated in the Gear Shift Program (GSP)-Generation module in AVL Cruise. And on this basis a driveline simulation model that can calculate the fuel consumption based on the driveline data of a test car is built. The model is used to forecast fuel consumption and calculate real-time CVT efficiency under different conditions. Contrastive analyses on simulation results and real car drum test results are made. The largest error between simulation results and drum test results in driving cycles is 4.099%, which is 5.449% under constant velocity condition in driver control mode and 4.2% under constant velocity condition in automatic cruise mode. The results confirm the feasibility of the method and the good performance of the driveline simulation model in accurately forecasting fuel consumption. The method can efficiently investigate the effects of driveline efficiency on car fuel economy. Moreover, this research provides instruction for accurately forecasting fuel economy as well as references for studies on the effects of drivelines on car fuel economy.

Simulation and experimental study on the pump efficiency improvement of continuously variable transmission

To reduce the power loss of a pump in continuously variable transmission (CVT), a new hydraulic scheme is proposed. This new scheme adjusts the effective displacement of the pump by using lubrication pressure and controls the pressure of primary and secondary cylinders through the smart mode. The power matching model of the new hydraulic scheme is established. The models of hydraulic system, vehicle and transmission control unit are built. A closed loop is formed to place the software in loop simulation through Silver virtual integration platform. The simulation results show that the new hydraulic scheme can match the power demand well. In NEDC, the hydraulic efficiency of the new hydraulic scheme can increase by 24.7% and 23.6% compared with those in the quantitative and single pumps, respectively, the fuel consumption of the new hydraulic scheme can reduce 3% and 4.1% compared with those in the single and quantitative pumps. Finally, the new hydraulic scheme is verified through the bench test, which reveals that the variable pump of the new hydraulic scheme can considerably reduce the torque loss of the pump, the smart mode can improve the transmission efficiency of CVT by up to a maximum rate of 3.17%.

An Optimal Control Strategy for Parallel Hybrid Electric Vehicles

This paper proposes a new power management strategy (PMS) for parallel hybrid electric vehicles equipped with continuously variable transmission (CVT). The proposed PMS is established on the basis of electric assist control strategy (EACS) and equivalent consumption minimization strategy (ECMS). This control approach is based on maintaining the battery energy within a recommended range, considering the CVT efficiency in selecting the engine operating point, and finding the best power split between the engine and electric motor at certain moments of the driving. In order to evaluate the effectiveness of this scheme, it is compared with EACS, a modified version of EACS and ECMS. It is shown that, in all of the studied driving cycles, the proposed PMS is superior to the considered rival strategies in terms of the fuel consumption and also HC and CO emissions.

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.

Regenerative Braking Compensatory Control Strategy Considering CVT Power Loss for Hybrid Electric Vehicles

Hybrid electric vehicles (HEV) equipped with continuously variable transmission (CVT) adjust the motor operating point continuously to achieve the optimal motor operating efficiency during regenerative braking. Traditional control strategies consider the CVT efficiency as constant, while the CVT efficiency varies in different operating conditions. In order to reflect the transmission efficiency more accurately during regenerative braking, the CVT theoretical torque loss model is firstly established which then leads to the battery–front motor–CVT joint operating efficiency model. The joint operating efficiency model indicates that the system efficiency is influenced by input speed, input torque, CVT speed ratio, and battery SOC (state of charge). The compensatory strategy for the front motor barking force is proposed to make full use of its braking power and the CVT speed ratio control strategy is modified to maintain the optimal operating efficiency of the system. The simulations are performed under three typical braking conditions and UDDS, NYCC, US06 respectively, the results show that the modified control strategy increases the front motor braking power and improves the system operating efficiency.

Cyber-Physical Control for Energy-Saving Vehicle Following With Connectivity

This article aims to develop an optimal look-ahead control framework to maximize car-following fuel economy, while fulfilling requirements of intervehicle safety. Three original contributions make this work distinctive from the existing relevant literature. First, a model predictive fuel-optimal controller is constructed to optimize the vehicle speed and continuously variable transmission (CVT) gear ratio. The controller leverages state trajectories of the leading vehicle transmitted via Vehicle-to-Vehicle/Vehicle-to-Infrastructure (V2V/V2I) communication. How operating conditions affect the engine efficiency and CVT efficiency is explicitly taken into account. Second, the controller is sufficiently evaluated in a variety of traffic flows, such as cruising, urban, and highway-like driving, and is compared with a short-sighted alternative without V2V/V2I connectivity. Finally, we further demonstrate the advantages of the proposed scheme by a comparison with two existing benchmark controllers.

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.

Slip Enhancement in Continuously Variable Transmission by Using Adaptive Fuzzy Logic and LQR Controller

Enhancement of fuel consumption and transmission efficiency needs a continuous improved variator performance in continuously variable transmission (CVT). This paper focuses on the improvement of aslip controller for a hydraulically actuated metal push-belt continuously variable transmission (CVT), using model for variator dynamic in the CVT. The slip control purpose is to improve the performance of variator andto increase the efficiency of CVT by determination the line pressure which generates the clamping force. The selection of slip reference-point is taken at the transition region between the micro and macro slip region to guarantee the maximum variator efficiency. The adaptive fuzzy logic control (FLC) and Linear Quadratic Regulator (LQR) controllers are applied to control the clamping force. The proposed control systems are designed to ensure the existence of a slip values within the region, which has the traction coefficient maximum value, while the load disturbances caused by suddenly changed torques in the drive lines. These approaches have potential for the CVT efficiency improvement, as compared to PID controller. The adaptive fuzzy logic control technique uses a simple group of membership functions and rules to achieve the desired control requirements of slip in CVT. Simulation results show that satisfactory slip improvement is achieved together with good robustness against suddenly changed torques. It is further revealed that all adaptive fuzzy logic control and LQR controller have a valuable effect on minimizing the slip amount and maximize the variator efficiency.

Slip Enhancement in Continuously Variable Transmission (CVT) by Using Adaptive Fuzzy Logic and LQR Controller

Enhancement of fuel consumption and transmission efficiency needs a continuous improved variator performance in continuously variable transmission (CVT). This paper focuses on the improvement of a slip controller for a hydraulically actuated metal push-belt continuously variable transmission (CVT), using model for variator dynamic in the CVT. The slip control purpose is to improve the performance of variator and to increase the efficiency of CVT by determination the line pressure which generates the clamping force. The selection of slip reference-point is taken at the transition region between the micro and macro slip region to guarantee the maximum variator efficiency. The adaptive fuzzy logic control (FLC) and Linear Quadratic Regulator (LQR) controllers are applied to control the clamping force. The proposed control systems are designed to ensure the existence of a slip values within the region, which has the traction coefficient maximum value, while the load disturbances caused by suddenly changed torques in the drive lines. These approaches have potential for the CVT efficiency improvement, as compared to PID controller. The adaptive fuzzy logic control technique uses a simple group of membership functions and rules to achieve the desired control requirements of slip in CVT. Simulation results show that satisfactory slip improvement is achieved together with good robustness against suddenly changed torques. It is further revealed that all adaptive fuzzy logic control and LQR controller have a valuable effect on minimizing the slip amount and maximize the variator efficiency

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.

Study on the improvement in continuously variable transmission efficiency with a thermal management system

Recently, a thermal management system (TMS) was considered to improve fuel economy by reducing energy loss and parasitic energy. Furthermore, the TMS includes waste heat recovery (WHR), which warms up engine coolant or transmission oil and obtain electrical or mechanical energy. In particular, the TMS is necessary to resolve the drawback of hybrid electric vehicles (HEVs), as the transmission oil heats up more slowly compared to a conventional vehicle due to shorter engine operating time. In this report, a TMS with a WHR system was applied to supply heat source to the continuously variable transmission (CVT) oil of a HEV for a better operating region at the cold start condition. The research was performed using a simulation model, which consists of a thermal mass model, heat transfer model, friction model and waste heat recovery model with experimental data were used for validation. As a result, the simulation results showed that the CVT efficiency with the WHR model could be improved by as much as 2% with an oil temperature increase of 16 °C in the urban dynamometer driving schedule (UDDS) mode, and an additional 2–8% improvement in transmission efficiency could be achieved by expansion of the application area.

Geometrical optimization of half toroidal continuously variable transmission using particle swarm optimization

The objective of this research is geometrical optimization of half toroidal Continuously Variable Transmission (CVT) in order to achieve high power transmission efficiency. The dynamic analysis of CVT is implemented and contact between the disk and the roller is modeled viaelastohydrodynamic (EHL) lubrication principles. Computer model is created using geometrical, thermal and kinetic parameters to determine the efficiency of CVT. Results are compared by other models to confirm the model validity. Geometrical parameters are obtained by means of Particle Swarm Optimization (PSO) algorithm, while the optimization objective is to maximize the power transmission efficiency. Optimization was conducted over a wide range of selected input parameters that are EHL oil temperature, roller tilting angle and rotational velocity of input disk. Optimization results show that the power transmission efficiency alters with changes of input parameters, while the optimized geometrical parameters are approximately the same. Variations of power transmission efficiency over a wide range of input parameters were calculated for optimized geometry, while the highest value of power transmission efficiency occurs in low value of EHL oil temperatures and input disk rotational velocities. The optimized structure shows average power transmission efficiency equal to 93.4% over a wide range of input parameters.

Fuel Optimal Control of CVT Equipped Vehicles with Consideration of CVT Efficiency

Conventionally,continuously variable transmission(CVT) improves fuel economy by ensuring the engine works under a high efficiency condition.However,this method does not pay any attention to the CVT efficiency.The CVT efficiency changes from 70% to 95% with its work condition,which also has considerable influences on fuel consumption of the system.Based on the analysis of how CVT efficiency and engine efficiency influence the fuel consumption of the system,an optimal economy control method with consideration of both engine and CVT efficiency is proposed.An optimal algorithm is proposed to calculate the combinations between the engine torque and CVT ratio in order to achieve the highest overall efficiency of engine and transmission system.A simulation model is built to validate the optimal algorithm.Experiment under several static vehicle speeds are also carried out to validate the control method.Simulation and experiment results indicate that fuel consumption of the system is reduced by more than two percent after the optimization.

808 複合遊星歯車装置を基本型としたトラクタ用無段変速機の開発 : 車両搭載用変速機の設計製作と検証実験(OS11-2,オーガナイズドセッション:11 機械要素の高度化と精密機構の性能向上)

A new type of a tractor's continuously variable transmission (CVT), which consists of a 2 K-H type differential gear and a hydrostatic power transmission (HST) is devised. The hydrostatic power transmission (HST) consisted of a hydraulic pump and motor, which is a kind of CVT, has been applied to the smaller horsepower range of the tractor recently. One of concerns of the current HST system is lower efficiency on the power transmission. Then, further improvement for efficiency of the transmission is required more recently. The purpose of this development is to devise an adequate CVT providing with higher efficiency of the transmission in comparison with the current HST systems. Theoretical velocity ratio and efficiency of the CVT are investigated. And a prototype CVT is manufactured and incorporated into the tractor. The experimental results show that the efficiency of prototype CVT is several percent lower than theoretical value, but very nearly value. Then, the high efficient transmission for the tractor is offered. And the design method for the tractor's CVT that has high efficiency is built up.

Study of Transmission Performance of 2K-H Type CVT

The purpose of this study is to improve the transfer performance of 2K-H type CVT (Continuously Variable Transmission) by changing of an axial thrust generating unit and a shape of rolling element. An efficiency of CVT is obtained from relation between axial thrust and output torque by the experiment. In the experiment, compared with a compression spring, the use of the loading cam was useful for the axial thrust generating unit. When a contact area of CVT was changed by the shape of rolling element, the efficiency was influenced by aspect ratio of the contact area. As this result, a maximum efficiency of 2K-H type CVT was attained by an optimum loading cam and a minimum aspect ratio.