Power Split Transmission Research Articles

Powertrain control and evaluation of Hybrid Powersplit Systems

This paper focuses on a method to control an hybrid power-split transmission. The main issue is the multivariable aspect of these systems. From a practical point of view, the control needs to track simultaneously a wheel torque, an engine speed and an electric power target. The approach proposed here is based on a two level control strategy. The first one is a so-called energy management which aims at calculating an optimal set of targets minimizing fuel consumption and deciding to stop or start the engine with a sub-optimal but reasonable method. Given these targets, the second control level aims at controlling the transmission, taking into account inertia in a multivariable way in order to achieve some good tracking and decoupling objectives. Each driving mode has to be considered and corresponds to a specific control requirement. To give more realism to previous papers on this topic, we focus here on the fuel cut-off and start modes which are described in details. To this purpose, an observer based state feedback in described. In the last section, we present simulations results for two power-split transmissions on two different driving cycles. The achieved fuel consumption and the control behavior are presented.

Optimal control of one hybrid electric vehicle with four-shaft planetary power-split transmission

A new electromechanical power-split full-hybrid transmission with three shifting elements for various driving modes named four-shaft planetary power-split transmission (FSPPST) has been developed and introduced in this paper. This FSPPST HEV is a kind of single-mode compound power-split system. This paper analyses the differences among the FSPPST HEV, THS single-mode HEV and GM dual-mode HEV. The development of this transmission has been aimed to combine all advantages of the internal combustion engine (ICE) and two electric motors in an optimal way as to improve the power performance and fuel economy. In this study, the transmission characteristics and the working states are analysed, and the acceleration performance was evaluated, and the control strategy on the NEDC was validated. The simulation results indicated that the acceleration time is 10.9 s from 0 to 100 km/h and the control strategy works properly.

Efficiency evaluation of gearboxes for parallel hybrid vehicles: Theory and applications

In this investigation is presented a systematic approach for the modelling and analysis of power split transmissions which include an epicyclic gear train, in various configurations, as they are used in hybrid vehicles. Emphasis is placed on the efficiency of the epicyclic gear trains and the associated power-flow in the transmission. The approach is based on the graph based representation of the kinematic chains and numerical examples are provided to further illustrate the applicability to hybrid vehicle transmissions with epicyclic gear trains and CVT elements. The graph-theory approach is shown to be a practical way to discern all possible configurations and their associated efficiencies.

Modeling and Simulation of a Vehicle Equipped with Power Split Automatic Transmission

his paper is concerned with the fuel economy of a mini car with power split automatic transmission (PSAT) by means of simulation. Firstly, a PSAT prototype is developed featured with high efficiency by power split. Secondly, mathematic models of PSAT, based on the PSAT scheme and experiment on the prototype, is established and embedded into the simulation software NREL’s Advanced Vehicle Simulator (ADVISOR) to carry out the whole vehicle fuel economy simulation. Thirdly, fuel economy comparison between vehicle with PSAT and traditional mechanical transmission is present, after fuel economy simulation under different driving cycle. Finally, approach to the energy save scheme of PSAT and matching between PSAT and the whole vehicle is discussed which builds up a good foundation for future optimization on control strategy of PSAT.

Optimization of hydro-mechanical power split transmissions

The increasing attention to comfort, automation and drivability is pushing the driveline technology to ever complex solutions, such as power-shift or continuously variable transmissions. Between these, the hydro-mechanical solution seems promising for heavy duty vehicle, due to the reliability and the capability of transferring high power. However, the double energy conversion occurring in the hydraulic branch of the transmission could lower excessively the total efficiency, highlighting the needs for a careful design of the whole system. In this work, the design of a hydro-mechanical transmission is defined as an optimization problem in which the objective function is the average efficiency of transmission, while the design variables are the displacements of the two hydraulic machines and gear ratios of ordinary and planetary gears. The optimization problem is solved by a “direct search” algorithm based on the swarm method, which showed a good speed convergence and the ability to overcome local minima. The optimization design method will be applied to study the transmission of two vehicles: a 62 kW compact loader and a high power agricultural tractor.

Reversibility of Power-Split Transmissions

Recent applications of continuously variable transmissions with large ratio spread, such as mechanical Kinetic Energy Recovery Systems or recent hybrid architectures, need the transmission to be perfectly reversible. This short paper deals with the mechanical efficiency of power-split continuously variable transmissions with particular emphasis on the switching from forward to reverse power flow. Forward and reverse transmission efficiency are calculated and compared, and the conditions which make it impossible to switch to reverse mode are studied. In particular, it is suggested that, although less efficient at high transmission ratios, a forward power circulation should be preferred because it has almost the same efficiency in forward and reverse operation.

An Instantaneous Optimization Based Power Management Strategy to Reduce Fuel Consumption in Hydraulic Hybrids

An instantaneous optimization based power management strategy for output-coupled power-split based hydraulic hybrids has been described in this work. Design considerations for a hydraulic accumulator based regenerative system for hybrids have been outlined. Optimal operation of the non-hybrid version of the power-split transmission provides useful insight into the system optimization and its result has been utilized later. Instantaneous optimization based control combines the efficient system operation with the braking energy regeneration to achieve fuel savings with the hydraulic hybrids in this work. Fuel mileage for a hybrid passenger car has been simulated for standard drive cycles under the instantaneous optimization based control. An output-coupled power-split transmission prototype built on the Hardware-In-the-Loop (HIL) principle has been described briefly. Proposed instantaneous optimization based control has been implemented on the test-rig. The proposed management strategy is compared through measurements and simulations to validate its effectiveness in improving fuel economy.

Design of power split transmission: Design of dual mode power split transmission

The power split type hybrid system transmits engine power by dividing it into the electrical unit and the mechanical unit. Its power transmission efficiency is highest at the mechanical point (MP), where the full power is transmitted to the mechanical unit. In this study, the equation for the MP was derived for the gear ratios of a general 4-node lever model. The MP characteristics for the transmission ratio (TR) of the input split and compound split structures were examined using the equation derived. Using the examined input split and compound split structures, a systematic design method for the dual mode power split transmission was proposed. In the dual mode power split transmission, the MP could be positioned at the desired TR, and the input split and compound split modes could be selectively used according to the clutch combination, which leads to the operation of the vehicle within a high system efficiency range.

Design parameters for continuously variable power-split transmissions using planetaries with 3 active shafts

Since 1996, when the first agricultural tractor with CVT transmission was shown, the presence of this type of transmissions has been increasing. All companies offer them in their products range. Nevertheless, there is little technical documentation that explains the basics of its operation. This report shows all types of CVT transmissions: non-power-split type and power-split ones, as well as the three types used in agricultural tractors, hydro-mechanical power-split transmissions (3 active shafts, input coupled planetary; 3 active shafts, output coupled planetary and 4 active shafts). The report also describes the design parameters of a type of CVT transmission, which use a power-split system with 3 active shafts as well as the fundamental relations among them.

Operation Mode Analysis and Parameters Design of a Novel Power Split Hybrid Transmission System

A new type of power split hybrid transmission system based on metal belt-type continuously variable transmission(CVT) and planetary gear is provided.Different operation modes of the new type of hybrid transmission system are analyzed.The parameters related to power source and powertrain are designed.The vehicle performance simulation model is built under the Matlab/Simulink environment,the acceleration performance under motor driving and engine-motor combined driving as well as fuel economy under UDDS and 10～15 cycle are simulated.The simulation results show that the acceleration time is only 9.65 s from 0 to 100 km/h,and fuel consumption is 4.32 and 3.74 L under UDDS and 10～15 cyclic condition respectively.

Control of Dual Mode Power Split Transmission for a Hybrid Electric Vehicle

Motor control algorithm for a dual power split system is proposed for hybrid electric vehicles (HEV). The dual mode power split system consists of an electric variator, MG1 and MG2, and three planetary gear sets. In order to develop the control algorithm for the best fuel economy, the dual mode PST is analyzed by network analysis. From the network analysis results, it is found that the dual mode PST efficiency decreases in the speed ratios where the power circulation occurs, and it is required that the ICE needs to be operated on the speed ratio region where the powertrain efficiency is relatively high. Using the dynamic models of the HEV powertrain, a motor control algorithm to obtain the high system efficiency is designed by inversion-based control. In order to evaluate performance of the control algorithm, HEV simulator is developed using Cruise and MATLAB Simulink. It is found from the simulation results that the motor control algorithm proposed in this study provides improved fuel economy since the motor control is able to provide the ICE operation on the speed ratio range, which gives relatively high powertrain system efficiency.

POWER MANAGEMENT AND CONTROL STRATEGIES FOR A HYBRID VEHICLE WITH A DUAL MODE POWER SPLIT TRANSMISSION

The design of hybrid vehicles inevitably involves two, or sometimes more, power sources. Although successful designs have required a whole range of technological developments, two particular aspects are highlighted here (a) the power splitting or power combining transmission often based on a combination of mechanical and electrical components and (b) the supervisory control strategy for managing the power flows to obtain both high efficiency and good driveability.First, power splitting transmissions (PST) have been reviewed and the performance properties of single and dual mode systems have been analysed and compared. Second, the control system problem has been analysed, focusing on the high level, supervisory controller. Various control approaches are described and comparisons made about the relative merits of competing strategies.It is concluded that a Dynamic Programming approach to this complex multivariable optimization problem offers significant advantages in understanding the problem and in setting a benchmark target for the optimum performance of the hybrid vehicle operation.

Control Analysis of the Wind Turbine with Transmission to Split Power

In this article, a wind turbine with power splitting transmission, which is realized through a three-shaft planetary gearbox, is presented. The input shaft of the transmission is driven by the rotor of the wind turbine, the output shaft is connected to the grid via the main generator (asynchronous generator), and the third shaft is driven by a control motor with variable speed. The dynamic models of the subsystems of this wind turbine, e.g. the rotor aerodynamics, the drive train dynamics, and the power generation unit dynamics, were given and linearized at an operating point. These submodels were integrated in a multi-disciplinary dynamic model, which is suitable for control syntheses to optimize the utilization of wind energy and to reduce the excessive dynamic loads. The important dynamic behaviours were investigated and the suggestions to design a suitable control system were given.

Local sparse coding control of CVPSTs

This paper discusses simulations of a control scheme based on locally sparse coded networks (CMACs) for a novel previously proposed continuously variable transmission (CVT), a hybrid continuously variable power split transmission (CVPST) (Osdemir and Schueller, 2002). Automotive transmissions match the speed and the torque of the power source to the speed and torque requirements of the load. Properly designed CVTs have shown potential to improve efficiency and performance. The main advantage of CMACs is fast computation because of their simple operational principles. Simulation results have shown that memory contents either reach a stable limit cycle or an attractor based on the selection of network parameters and the training method. Both online and offline training are possible.

Potentials for the development of continuously variable transmissions

In co-operation with LuK as the developing partner and supplier of the Continuously Variable Transmission (CVT) components, Audi has succeeded in defining the benchmark for the CVT sector with its Multitronic transmission. This is also impressively documented by the constantly increasing demand for this transmission and the positive resonance it has achieved with the end users. This article describes the further possibilities for the development of the individual components — the pulley sets, the hydraulic system and the chain — based on mass-production applications with an engine torque of more than 300 Nm and a ratio spread of 6 and going up to 550 Nm with an overall ratio spread of 7 in power-split transmission structures.

A new hybrid CVT design: CVPSTs

Automotive transmissions match the speed and the torque of the power source to the speed and torque requirements of the load. Properly designed continuously variable transmissions (CVTs) have shown promise to improve efficiency and performance. This work discusses some existing CVTs and proposes a new hybrid continuously variable power split transmission (CVPST). The speed relationships are analysed in power split and power recirculation mechanisms, the problem of geared neutral phenomenon with recirculating transmissions are identified and these two separate issues are left out as a topic for another paper. A new "all-in-one" CVPST transmission incorporating power split and power recirculation is proposed.

Design of continuously variable power split transmission systems for automotive applications

The continuously variable power split transmission (CVPST) concept is presented in the context of an automotive application. The system consists of a variable pulley set (variator) coupling two of the three rotating elements of a planetary gear train, namely the sun and the ring gears. The arrangement is such that a ‘power split’ feature is attained in which the input shaft delivers power to the sun gear as well as to the driving pulley, which in turn drives the ring gear of the planetary through the variator. Because the input shaft delivers the input power at two locations (at the sun gear and at the driving pulley), the variator carries only a fraction of the total power flowing through the input shaft. The third rotating element of the planetary gear set (the planet carrier) collects the power flows from the ring and the sun gears, delivering the total power output to the vehicle. This feature allows an increased engine power envelope for potential automotive applications. This feature also reduces the power losses associated with power transmission, especially at the low speed-high torque modes, while providing continuously variable transmission ratio capability. A term dubbed the ‘cross-over coefficient’ is established which can be used to prescribe both the fraction of total power flowing through the variable element and the velocity ratio span for the transmission. An extension of this can be obtained by means of an external gearbox, allowing a stepless span in the optimum range of both engine and transmission. Design procedures are presented for an automotive application in which a stepless extension (synchronized variator) of the useful transmission ratio span is achieved by means of an external step-up gearbox. The two-stage system allows operation in the optimum range of both engine and transmission.

Hydrostatic Power Splitting Transmissions Design and Application Examples

After recalling the inventive methods used in the design analysis procedure of hydrostatic power splitting transmissions, theoretical and experimental application examples are presented. More particulars are detailed: (1) determining elements and tests results of a 230-Kw experimental transmission that can be applied to road and off-road propulsion. (2) design analysis procedure and prediction of a large ratio coverage transmission appropriate to light vehicles such as automotive cars. Conclusions are drawn as regards the future prospects of these transmissions.

Optimal Control of Flywheel Hybrid Transmissions

Selection of variable transmission ratio in a vehicle with a flywheel energy storage element to maximize the kinetic energy transfer for specified vehicle accelerations is formulated as an optimal control problem. Models for single and parallel power-flow path configurations are presented as generic hybrid propulsion system types. For both systems variation of the ratio of the continuously variable transmission results in inherently nonlinear control, with velocity trajectories found by the solution of two-point boundary value problems. For the single power-flow path system a closed loop controller is synthesized which tracks acceleration command. For the parallel path system, which is representative of conventional power split transmissions, the open loop control yields useful information, indicating tradeoffs between system energy recovery efficiency and component design parameters. Maximum energy recovery during regenerative braking is achieved by minimizing power losses to vehicle drag and transmission elements. Planetary gear geometry is shown to have the strongest influence on efficiency, maximum transmission component loading, and CVT ratio range.