Efficiency Evaluation of Continuously Variable Transmissions Including a Planetary Gear Train

With their advantages, continuously variable transmissions have gained more popularity in the last decade by their use in mechanical transmission systems. The present paper aims to analysis the efficiency of the transmission based on the mechanical efficiency of the planetary gear train integrated in such transmission. In this analysis, we consider the mechanical efficiency of the transmission has been determined considering how the efficiency of the CVT members changes as a function of the operating conditions. The efficiency of the planetary gear train as a function of the configuration, speeds in his three input/output shafts, and also with respect to the power flow type. Results are compared with those obtained from other methods performance evaluation of the transmission, available in the literature.

TORQUE CAPACITY AND CONTACT EFFICIENCY OF A HALF TOROIDAL CONTINUOUSLY VARIABLE TRANSMISSIONS

The automotive industry is seeking new concepts for a continuously variabletransmission (CVT) in the driveline. One possible solution for a CVT design is half toroidaltraction drive, providing a high torque capacity with quick ratio change. An analytical study on thecontact points of the half toroidal CVT has been detailed. The shapes of the contact areas amongthe input disk, power roller and output disk are considered ellipses. Mathematical equations forestimating the torque capacity, power loss due to spin action, and contact efficiency of theelliptical contacts of the half toroidal CVT are formulated and expressed in the form of integralswhich can be readily evaluated by numerical scheme. The contact efficiency calculations of the halftoroidal CVT have been developed for the proper spin point locations under the effect of systemparameters. Numerical results are presented hi graphical forms for considered parameters, which canhelp the designer to select the proper system parameters to minimize the undesirable spin effects.

An overview on research developments of toroidal continuously variable transmissions

As environmental protection agencies enact new regulations for automotive fuel economy and emission, the toroidal continuously variable transmissions (CVTs) keep on contribute to the advent of system technologies for better fuel consumption of automobiles with internal combustion engines (ICE). Toroidal CVTs use infinitely adjustable drive ratios instead of stepped gears to achieve optimal performance. Toroidal CVTs are one of the earliest patents to the automotive world but their torque capacities and reliability have limitations in the past. New developments and implementations in the control strategies, and several key technologies have led to development of more robust toroidal CVTs, which enables more extensive automotive application of toroidal CTVs. This paper concerns with the current development, upcoming and progress set in the context of the past development and the traditional problems associated with toroidal CVTs.

Design of Linear Functional Noncircular Gear with High Contact Ratio Used in Continuously Variable Transmission

Continuously variable transmission(CVT)of noncircular gear has the technical advantages of large bearing capacity and high transmission efficiency.The key technology of CVT with noncircular gear has been broken through some countries,and is in the stage of deep application research.Although the characteristics and design methods of noncircular gear pairs have been continuously studied in China,the noncircular gear CVT is still in the preliminary exploration and research stage.The linear functional noncircular gear pair,whose transmission ratio is a linear function in the working section,to realize continuously variable transmission was the research object in this paper.According to the required transmission ratio in the working section,the transmission ratio function in the non-working section was constructed by using a polynomial.And then the influence of pitch curve parameters in the working section on which in the non-working section was also analyzed to obtain the pitch curve suitable for transmission of this gear pair.In addition,for improving the stability and bearing capacity of gear transmission,the noncircular gear pair transmission with high contact ratio was designed.Furthermore,the accurate value of the contact tooth length was calculated based on the gear principle and the characteristics of the involute tooth profile,from this the contact tooth length error was calculated by comparing the accurate value with its actual value obtained by the rolling experiment.Finally,an indirect method to verify the contact ratio by detecting the contact length error of the tooth profile was proposed.

Rotational Swashplate Pulse Continuously Variable Transmission Based on Helical Gear Axial Meshing Transmission

The current research on pulse continuously variable transmission（CVT） is mainly focused on reducing the pulse degree and making pulse degrees a constant value. Current research mainly confined to find out new design parameters by using the method of optimization, and reduce the pulse degree of pulse CVT and its range of variation. But the fact is that the reduction of the pulse degree is not significant. This article presents a new structure of mechanical pulse CVT--the rotational swashplate pulse CVT with driven by helical gear axial meshing. This transmission is simple and compact in structure and low in pulsatile rate （it adopts 6 guide rods）, and the pulsatile degree is irrelevant to the transmission ratio. Theoretically, pulsatile rate could be reduced to zero if appropriate curved surface of the swashplate is used. Compared with the connecting rod pulse CVT, the present struc^tre uses helical gear mechanism as transmission part and it avoids unbalanced inertial force in the former model. This paper analyzes the principle of driving of this transmission, presents its mechanical structure, and discusses its motion characteristics. Experimental prototype of this type of CVT has been manufactured. Tests for the transmission efficiency（when the rotational speed of the output shaft is the maximum） and the angular velocity of the output shaft have been carried out, and data have been analyzed. The experimental results show that the speed of the output shaft for the experimental prototype is slightly lower than the theoretical value, and the transmission efficiency of the experimental prototype is about 70%. The pulse degree of the CVT discussed in this paper is less than the existing pulse CVT of other types, and it is irrelevant to the transmission ratio of the CVT. The research provides the new idea to the CVT study.

STUDY ON CONTROL STRATEGY OF CLUTCH STARTING FOR CAR WITH A METAL PUSHING BELT-PLANETARY GEAR CONTINUOUSLY VARIABLE TRANSMISSION SYSTEM

The automatic control of clutch starting in car with a metal pushingbelt-planetary gear continuously variable transmission (CVT) is a complex problem. A suited controlstrategy is required to realize quick and smooth start. A simulation state space equation isestablished on clutch staring control of a car with CVT by bond graph theory. According to the fuzzycontrol method with the expert system, a fuzzy control system of car starting process to weaken thejerk motion is introduced. The simulation results indicate that the jerk motion of clutch startingis below 10 m/s^3.

CONTROL STRATEGY OF A PARALLEL HYBRID CAR WITH A METAL BELT-PLANETARY GEAR CONTINUOUSLY VARIABLE TRANSMISSION SYSTEM

The most remarkable characteristic of a metal belt-planetary gearcontinuously variable transmission is a wider ratio range and a bigger torque capacity than aconventional metal pushing belt continuously variable transmission. A parallel hybrid car with thistransmission system not only can reduce fuel consumption and pollutant emission at a ECE city cycle,but also can keep the motor working in the most efficiency area and can be started by a lower powermotor by oneself. At the same time, the continuously variable transmission system can realize thesmooth switch between the motor and the engine.

POWER FLOW ANALYSIS AND APPLICATION SIMULATION OF ELECTROMAGNETIC CONTINUOUSLY VARIABLE TRANSMISSION

With the structure of two air gaps and two rotors, the electromagnetic continuously variable transmission（EMCVT） is a novel power-split continuously variable transmission（CVT）. There are two kinds of power flowing through the EMCVT, one is mechanical power and the other is electric power. In the mean time, there are three power ports in the EMCVT, one is the outer rotor named mechanical power port and the other two are the inner rotor and the stator named electric power ports. The mechanical power port is connected to the driving wheels through the final gear and the electric ports are connected to the batteries through the transducers. The two kinds of power are coupled on the outer rotor of the EMCVT. The EMCVT can be equipped on the conventional vehicle being regarded as the CVT and it also can be equipped on the hybrid electric vehicle（HEV） as the multi-energy sources assembly. The power flows of these two kinds of applications are analysed. The back electromotive force（EMF） equations are illatively studied and so the dynamic mathematic model is theorized. In order to certify the feasibility of the above theories, three simulations are carried out in allusion to the above two kinds of mentioned applications of the EMCVT and a five speed automatic transmission（AT） vehicle. The simulation results illustrate that the efficiency of the EMCVT vehicles is higher than that of the AT vehicle owed to the optimized operation area of the engine. Hence the fuel consumption of the EMCVT vehicles is knock-down.

Research and Design of Hydro-mechanical Continuously Variable Transmission for Tractors

A new type continuous variable transmission device, a hydro-mechanical continuously variable transmission （HMCVT） for agricultural tractors is developed, which is composed of a single planetary gear differential train, a hydraulic transmission system consisted of variable displacement pump and fixed displacement motor and a multi-gear fixed step radio transmission. Based on the analysis of types of hydrostatic mechanical transmission （HMT） and styles of hydraulic transmission, the general drive scheme for HMCVT is obtained. The method of selecting mechanical parameters and hydraulic units is explained, and the stepless speed regulation characteristic of HMCVT is analyzed. This paper also specializes the calculating method of transmission efficiency. It shows that tractors assembled with HMCVT can obtain a continuously variable speed and achieve high drive efficiency.

Optimization Transmission Efficiency with Driver Intention for Automotive Continuously Variable Transmission under Slip Mode

This study proposes and experimentally validates an optimal integrated system to control the automotive continuously variable transmission(CVT)by Model Predictive Control(MPC)to achieve its expected transmission efficiency range.The control system framework consists of top and bottom layers.In the top layer,a driving intention recognition system is designed on the basis of fuzzy control strategy to determine the relationship between the driver intention and CVT target ratio at the corresponding time.In the bottom layer,a new slip state dynamic equation is obtained considering slip characteristics and its related constraints,and a clamping force bench is established.Innovatively,a joint controller based on model predictive control(MPC)is designed taking internal combustion engine torque and slip between the metal belt and pulley as optimization dual targets.A cycle is attained by solving the optimization target to achieve optimum engine torque and the input slip in real-time.Moreover,the new controller provides good robustness.Finally,performance is tested by actual CVT vehicles.Results show that compared with traditional control,the proposed control improves vehicle transmission efficiency by approximately 9.12%-9.35%with high accuracy.

MODELING, VALIDATION AND OPTIMAL DESIGN OF THE CLAMPING FORCE CONTROL VALVE USED IN CONTINUOUSLY VARIABLE TRANSMISSION

Associated dynamic performance of the clamping force control valve used in continuously variable transmission （CVT） is optimized. Firstly, the structure and working principle of the valve are analyzed, and then a dynamic model is set up by means of mechanism analysis. For the purpose of checking the validity of the modeling method, a prototype workpiece of the valve is manufactured for comparison test, and its simulation result follows the experimental result quite well. An associated performance index is founded considering the response time, overshoot and saving energy, and five structural parameters are selected to adjust for deriving the optimal associated performance index. The optimization problem is solved by the genetic algorithm （GA） with necessary constraints. Finally, the properties of the optimized valve are compared with those of the prototype workpiece, and the results prove that the dynamic performance indexes of the optimized valve are much better than those of the prototype workpiece.

STUDY ON THE VIBRATION CHARACTERISTIC OF THE METAL PUSHING BELT CONTINUOUSLY VARIABLE TRANSMISSION

The solid and finite element model of metal pushing type continuously variable transmission are established at speed ratio of i =0 5 and i=2 0. In order to solve the problem of the complicated of structure,the node node rod discrete finite element model is put forward and the whole system is simplified and established.The natural frequency and mode shape of system are solved by iterative Lanczos reduce method for sensitivity analysis in finite element model.The new method and the result can be used to improve the smoothness of the variable transmission system and to propose the theory for reducing noise at operation.

Hydro-mechanical Transmit Performance Analysis for a Continuously Variable Transmission

Based on an exact CAD model of hydro-mechanical continuously variable transmission （HMCVT） gearbox which can transmit 180 horsepower, virtual prototype of the HMCVT was built. Revolution speed of shafts, gears and clutches of the HMCVT were calibrated by using results obtained by theoretical calculation and test methods. The needed power and torques of both mechanical power input shaft and hydropower input shaft were calculated by simulation. Hydraulic power distributing ratio and power flow of the system was also studied. The analysis results showed that cycle power was produced inevitably when the output shaft speed of HMCVT change smoothly during mechanical and hydraulic working state HM1 to HM4, and the instantaneous maximum cycle power was 39.5%. Then the overall transmission efficiency of HMCVT was studied, and the maximum overall efficiency of the system was about 87%. The results of the studies gave references to select suited engine and variable displacement pump for the HMCVT, and to develop rational speed control strategies for the HMCVT by changing displacement ratio of variable displacement pump.

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.

Counterformal contacts of full toroidal continuously variable transmission

The point and the line contacts of a toroidal continuously variable transmission (CVT) are studied. The contact shapes between the roller and input and output disks are formulated by using the classical Hertz contact theory. Based on the formulated equations, different system factors affecting the maximum Hertz stress in the elliptical and strip contacts of the full toroidal CVT are explored, which include the properties of the contacting material (Young’s modulus), operating condition (pushing load) and geometrical parameters (aspect cavity ratio, aspect roller ratio). The comparative results reveal the relations between the maximum Hertz stress and the speed ratio in the form of graphs. These graphs give useful information for designer to know the maximum Hertz stress during operation in such systems.

Control and Simulation of Continuously Variable Transmission for Electric Transmission System

According to the study of electric transmission, the concept of the fore and the aft power chain is presented. The control method of continuously variable transmission is established in the aft chain of electric transmission based on brushless DC motor. A fuzzy controller is designed with continuous fuzzy variables and the simulation module of the aft power chain is proved by test. The fuzzy controller controls the process of continuously variable transmission steadily and the acceleration of vehicle is quick according to simulation results. The elementary performance exhibited in the simulation is a foundation for the further study of the electric transmission track vehicle.

MODELING AND INTEGRATED CONTROL FOR A METAL PUSHING BELT CONTINUOUSLY VARIABLE TRANSMISSION SYSTEM

By the bond graph theory,a bond graph analysis model of continuously variable transmission is established On the basis of improving the ratio change response and reducing the engine torque response lag in normal control,a new synthetic control algorithm is developed By analyzing the engine driving torque characteristics and the transmission inertia torque while ratio is changed under transient condition,the compensation value for engine driving torque is presented The simulation result shows that by this compensation control algorithm the engine torque response lag can be reduced and the driving torque response can be improved effectively.

STRATEGIES FOR SOLVING KEY PROBLEMS IN RESEARCH AND DEVELOPMENT OF AUTOMOTIVE CONTINUOUSLY VARIABLE TRANSMISSION

Several key problems in the research and development of continuously variable transmission for automobile, such as those connected to the transmitting frictional pair and the related automatic tight pressing actuator, the transmission ratio control logic and the related automatic control system, are discussed. The strategies taken for solving these key problems are described.

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.

Combined-Type Continuous Variable Transmission with Quadric Crank Chains and One-Way Clutches

The conventional Continuously Variable Transmission （CVT） has been classified as belt-type or toroidal CVTs. Each CVT is fundamentally composed of several components to transmit the frictional force or torque generated by the driving force. Since the conventional CVTs use friction force, their energy （force or torque） transfer efficiency might be inferior due to slippage and pressure between the transmission components. Consequently, we propose a new type of structural CVT. The CVT we proposed in this paper means a combined-type transmission with quadric crank chains and one-way clutches.