Power Split Continuously Variable Transmission Research Articles

Shift quality of tractors fitted with hydrostatic power split CVT during starting

The matching of the control parameters of clutch hydraulic systems was studied in order to improve the shift quality of the tractors fitted with hydrostatic power split continuously variable transmission (CVT) during starting. Firstly, mathematical models of the clutch hydraulic system, CVT and tractor were constructed, and the models of the key components were tested and validated. Secondly, an evaluation indicator of the shift quality was determined, and 6 parameters which may affect shift quality were defined including instruction time and the instruction voltage for clutch pressure control. Thirdly, through single-factor simulation, the influence mechanism of parameters on tractor shift quality was determined. Finally, a solutions map was proposed, and a matching law of the control parameters was obtained accordingly. The results showed that the tractor shift quality improves with increasing of the initial instruction voltage at the first voltage rise and increasing instruction time consumed at the second voltage rise but decreases with the increasing of the terminal instruction voltage. If the interaction among various parameters is considered, the terminal instruction voltage should be taken as a low value, the pressure relief time of brake relative to shift start node should not be too long.

Optimization of multiple transmission layouts for minimal energy consumption of a battery electric vehicle

Battery electric vehicles (BEVs) are a promising solution for reducing the impacts of passenger vehicles on the environment. However, their driving range is restricted due to the limitations of battery technologies. This range can be extended by adoption of multiple-speed transmissions. Most of the comparisons in the related studies are based on non-optimal designs or limited to modal driving cycles. Furthermore, the impact of power-split continuously variable transmission (PS-CVT) layout with type III power flow on the power consumption of BEVs has never been examined. In this paper, single, two and three-speed transmissions along with PS-CVTs with type I and III power flows are optimized for a case study BEV. Furthermore, the effect of push belt and full-toroidal CVTs in construction of PS-CVT are compared. The results demonstrate that a PS-CVT with type I power flow equipped with the full-toroidal CVT has the best performance. However, it reduces the energy consumption by 0.36% compared to the optimal two-speed layout. In addition, its ratio range is more limited which can negatively impact the dynamic performance. Finally, simulation of the optimal designs along a different cycle proves that the obtained results are consistent, regardless of the driving cycle.

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.

Multi-objective Optimization of Hybrid Electric Vehicle Equipped with Power-split Continuously Variable Transmission

A B S T R A C T This paper aims to find the efficient state of hybrid electric vehicle (HEV) by simultaneous optimization of the control strategy and the power train. The power transmission employed in this vehicle is a power-split continuously variable transmission (CVT) which uses several fixed ratio mechanisms. After describing this transmission, the rules of electric assist control strategy are introduced. A modification on this strategy is proposed to decrease the start/stop frequency of the engine and electric motor. Afterwards, an optimization on the HEV’s power train size, power-split CVT and the control strategy is accomplished with the aim of minimizing the vehicle fuel consumption and emissions. The optimization results are some Pareto-optimal points which are tradeoff solutions between fuel consumption and emissions. Finally, in order to intuitively demonstrate the optimality of the optimization results, the Pareto points for the case of considering two objectives are shown.

Simulation study on the operating characteristics of a hybrid hydraulic passenger car with a power split transmission

In this paper, a hybrid hydraulic passenger car (HHPC) coupled with a power split continuously variable transmission (P-CVT) is proposed. This P-CVT is capable of splitting the power from the internal combustion engine into mechanical and hydraulic power flows. By adjusting the ratio of the mechanical power to hydraulic power, the P-CVT enables the transmission ratio to be changed continuously. Meanwhile, the P-CVT system can capture the braking energy and store it in the hydraulic accumulator for the next assistant driving. In order to quantitatively investigate the effect of applying P-CVT on improving the fuel economy and operating performance for the HHPC, a numerical simulation is conducted under typical city driving conditions. The simulation results demonstrate that, the P-CVT permits the engine to be run under a more efficient operating range. The total fuel consumption of the HHPC is reduced by 16.4% under the test conditions, compared with that of the original car.

Study on Dynamic Shifting of Power Split CVT (PSCVT)

In order to study the shift control of power split continuously variable transmission (PSCVT), the integrated shift dynamic models for the set of engine, magnetic powder clutch and transmission are established. The shift simulation shows that the magnetic powder clutch connecting condition can be adjusted and the shifting quality can be improved by means of controlling magnetic powders clutch field current, which at last result in the improvement of vehicle performance.

Performance Simulation Study of Power Split Continuously Variable Transmission (PSCVT)

This paper is concerned with the power and fuel economy performance simulation study of power splitcontinuously variable transmission(PSCVT). Firstly, mathematic model of PSCVT is established and the shifting rule is designed based on the introduction of PSCVT working principle; Secondly, the fuzzy-PID controller is designed according to the control requirements of electronic control system; Thirdly, the vehicle model with PSCVT and engine model are established to carry out the PSCVT power and fuel economy performance simulation. The simulation results indicate that the vehicle fuel consumption with PSCVT is reduced distinctly with the same power performance.

Control System Design on a Power-Split CVT for High-Power Agricultural Tractors

The problem considered in this paper is the design and tuning of the control system of a power-split continuously variable transmission (CVT) used in high-power tractors. Power-split CVTs are characterized by the combination of a traditional mechanical transmission and by a continuously-variable transmission. This guarantees, at the same time, smooth variations of the transmission-ratio and high efficiency of the overall transmission system. The control architecture of an hydrostatic power-split CVT is constituted by three main parts: 1) servo-controller on the current of the valve which drives the hydraulic transmission; 2) a servo-controller on the hydraulic transmission-ratio; and 3) a synchronizer which coordinates the hydraulic and the mechanical parts of the CVT. In this work, these three controllers are fully developed, including: design, implementation, and evaluation on an experimental system.

Continuously variable transmission design for optimum vehicle performance by analytical target cascading

The applicability of analytical target cascading (ATC) to the design of a continuously variable transmission (CVT) for optimum vehicle performance is studied. ATC is a powerful methodology for the optimisation of complex multilevel systems based on appropriate decomposition and coordination. Several time-dependent mathematical models of a mid-size truck's longitudinal dynamics, powertrain, and power-split CVT were developed and used to analyse the vehicle performance. A detailed geometric model of the CVT primary and secondary pulleys was also developed. These models were implemented in a three-level ATC formulation. In this paper, the decomposition and coordination procedure in the context of ATC is described. The development of system models and their level of detail are discussed with attention focused on tradeoffs between model complexity and computer execution speed. Practical aspects of the iterative process, the multi-criteria optimisation problems, and the selection of arbitrary parameters inherent to ATC are highlighted to offer insight to the practicing engineer. Numerical results of the study illustrate the applicability of ATC to simulation-based design of complex systems.

On the design and tuning of the controllers in a power-split continuously variable transmission for agricultural tractors

In this work, a power-split continuously variable transmission (CVT) used in high-power tractors is considered. Power-split CVTs are characterized by the combination of a traditional discontinuous mechanical transmission and a continuously variable transmission. This provides, at the same time, smooth variations of the transmission ratio and high efficiency of the overall transmission system. The CVT considered in this paper is a hydrostatic power-split unit conceived for top-power agricultural tractors. The goal of this paper is to present a case study on the design and tuning of the control system structure for this type of CVT. This structure consists of three main parts: a servo controller on the internal current of the valve of the hydraulic transmission; a servo controller on the hydraulic transmission ratio; a synchronizer which coordinates the hydraulic and the mechanical parts of the CVT. The design, tuning and testing of this set of automatic controllers is presented.

Nonlinear control of a continuously variable transmission (CVT)

Automotive engineers are continuously exploring various engine, transmission, and chassis technologies to increase overall vehicle performance, fuel economy, and safety. One promising powertrain concept is the continuously variable transmission (CVT), which offers a continuum of infinitely variable gear ratios between established minimum and maximum limits. This continuous gear ratio spectrum can increase the overall powertrain efficiency and eliminate the unwanted jerks associated with manual and automatic transmissions. Although basic CVT designs may have difficulty with high torque/low speed requirements, a power split continuously variable transmission configuration offers both fixed gearing and adjustable pulleys to satisfy driving demands. The effective control of the variable radius pulleys allows the designation of engine torque/speed to improve overall system performance for a given operating condition. In this paper, the fundamental components, configuration, and kinematics of a power split CVT will be briefly introduced. The problem of wheel speed (i.e., cruise) control of a CVT equipped vehicle will be considered. An innovative adaptive nonlinear controller will be designed to ensure asymptotic tracking of the desired wheel speed. Representative numerical results are presented and discussed to demonstrate the ability of the integrated CVT and engine controller in tracking the prescribed wheel speed.

Theoretical and experimental study of a power split continuously variable transmission system Part 2

In this work, theoretical and experimental results related to the power flow and efficiency of a power split continuously variable transmission (PS-CVT) system are reported. By means of two separate phases of operation, an original solution is studied that allows an increase in the transmission efficiency through the generation of a flow without recirculation of power. The experimental results related to the second phase of operation of the PS-CVT are reported. Such results are compared with those found through a theoretical model of the transmission. The advantages in terms of efficiency in comparison with a traditional CVT system are shown. A possible operational scheme for the PS-CVT is finally reported through which it is possible to increase the ratio range by means of a cyclical repetition of the operational phases.

Theoretical and experimental study of a power split continuously variable transmission system Part 1

Continuously variable transmissions (CVTs) have made notable progress, especially in the automotive industry, over the past years. In this paper the results of a theoretical and experimental study of an original power split CVT (PS-CVT) system are obtained. The main advantage of the proposed solution is to improve the efficiency of the CVTs by means of a power flow without recirculation using two separate phases of operation. The kinematic characteristics of the single-component devices are obtained. Using a special test rig, the power flows and the efficiency of the PS-CVT system are experimentally determined in the first operational phase. The results are compared with those obtained by a theoretical model. The advantages are therefore shown, in terms of power and efficiency, of the PS-CVT system proposed in this paper in comparison with the single CVT.

Power split continuously variable transmission systems with high efficiency

Continuously variable transmissions (CVTs) have developed notably in different applications over the past years. This is especially true in the automobile field because of advantages in terms of car handling and efficiency on urban roads. In this work an original functional solution of a power split CVT system is described. The proposed solution allows the generation of a power flow without recirculation. Kinetic characteristics of single-component devices are obtained and the power split CVT system's efficiency is determined by considering how the efficiency of the component devices changes as a function of operating conditions. The advantages for the power split CVT system are therefore shown in terms of power and efficiency in comparison with the single CVT.