Efficiency optimization of the push-belt CVT by variator slip control

Continuously Variable Transmissions (CVT) are becoming increasingly popular in automotive applications. What makes them attractive is the ability to vary the transmission ratio in a stepless manner without interrupting the torque transfer. This increases comfort by eliminating the discrete shifting events and increases performance by choosing the most suitable transmission ratio for every driving situation. Using a CVT could potentially save more than 15% of fuel consumption compared to manually shifted vehicles. This figure however is never met, because of the internal losses in the CVTs in production today. If the losses in a CVT can be lowered, then the overall fuel economy of a CVT equipped vehicle will be improved with the same amount. With current CVTs ranging around 80% efficiency, an improvement of around 10% is possible compared to currently available CVTs if an optimal actuation and control system is used. This thesis is about the optimization of the control system of the CVT by using slip as the control variable. This is part of a larger project focussing on the entire actuation and control system. Also a CVT with Electro-Mechanically Pulley Actuation (EMPAct) is developed aiming to reduce the power consumption of the CVT actuation system. Combined, these two projects aim to improve the fuel economy of the CK2 transmission from Jatco with 10%. Models for the clamping forces and traction in the variator are compared. The continuous belt model is compared with a pushbelt model. A parameter study shows the influence of the model parameters on the outcome of the models. The output of the models are also compared to measured values. A nonlinear dynamic model for slip in the variator is derived. This model can be linearized in certain operating points. This model can be used for the design of a control system, simulation of slip in the variator or for analysis. Measurement of slip directly is not possible, therefore a good estimation method is needed. Several estimations of slip in the variator are compared. The position measurement of the pulley is used in the measurements shown in this thesis. Measurements on a beltbox testrig are given that clearly show a relation between slip and efficiency and slip and traction. This relation changes as a function of other parameters like speed, ratio, clamping force etc. Estimation of the efficiency potential of the pushbelt variator shows that a potential of between 5% for high torques and 20% for low torques exists. A slip control system is developed to show the possible efficiency improvement. First, a beltbox setup is used to test a simplified slip controlled variator. Ratio changing is not taken into account in this setup. After successful tests with this setup another setup is used that incorporates a Jatco CK2 transmission and an internal combustion engine. This test setup is more realistic, but therefore also more complicated to control. A gain scheduled approach is used to compensate for the slower actuation system. This system is then also applied to a testing vehicle

Slip controller design and implementation in a Continuously Variable Transmission

Continuously Variable Transmissions (CVT) can be used to operate a combustion engine in a more optimal working point. Unfortunately, due to the relatively low efficiency of modern production CVT’s the total efficiency of the driveline is not increased significantly. This low efficiency is mainly caused by losses in the hydraulic actuation system and the variator. Decreasing the clamping forces in the variator greatly improves the efficiency of the CVT. However, lower clamping forces increase the risk of excessive belt slip, which can damage the system. In this paper a method is presented to measure and control slip in a CVT in order to minimize the clamping forces while preventing destructive belt slip. To ensure robustness of the system against torque peaks, a controller is designed with optimal load disturbance response. A synthesis method for robust PI(D)-controller design is used to maximize the integral gain while making sure that the closed loop system remains stable. Experimental results prove the validity of the approach

The Empact CVT: modeling, simulation and experiments

This paper shows the implementation of a simulation model for newelectromechanically actuated metal V-belt type continuously variabletransmission (CVT), referred to as the Empact CVT. An analysis ofthe dynamics of the actuation system and of the driveline shows thatthe eigenfrequencies of the system depend on both the CVT ratio andthe slip in the variator. An accurate variator model is required to incorporateall characteristic dynamics. The implemented variator modelis an explicit formulation of a model which gives an estimation of thetension forces and compression forces in the pushbelt. The simulationmodel also includes slip, shifting losses based on transient variator modelsand friction. Simulations are compared to measurements, showinggood results

CVT ratio control strategy optimization

no abstract

Foraging Strategies Determine the Effect of Traffic Noise on Bats

© Museum and Institute of Zoology PAS. Anthropogenic noise is a concern in many ecological systems. One important source of noise pollution is traffic noise as it can dominate the soundscape in urban and peri-urban environments. Taxa that rely on acoustics for behavioural strategies are likely to be especially susceptible to noise, as noise can inhibit the perception of informational sounds. Bats use echolocation to hunt prey while foraging and are therefore prime candidates for adverse effects. Captive studies have shown that foraging efficiency can be significantly reduced in noisy environments for some bat species, and that these species actively avoid noisy areas. However, it remains unclear how this selective sensitivity manifests in urban environments. Given that mode of flying and use of echolocation is entwined with foraging strategies, we hypothesised that different foraging guilds (i.e. fast flyers versus slow flyers) may show different levels of sensitivity to noisy roads. We used transects running perpendicular to a major traffic route in Sydney, Australia, to record bat activity and traffic noise levels. Noise amplitude levels across each frequency band dropped by over 50% in the first 50 m, with high frequency components (> 10 kHz) being especially soft at this distance. Furthermore, all traffic noise above 5 kHz was lost within the first 150 m from the road. Fast flying bats flew close to the road, despite the traffic noise. In contrast, slow flying species appeared to fly more often away from the road. However, few calls of slow flyers were recorded, probably reflecting their difficulty in detecting them using acoustic surveys as well as their earlier decline in these peri-urban environments

Slip controller design and implementation in a Continuously Variable Transmission

Continuously Variable Transmissions (CVT) can be used to operate a combustion engine in a more optimal working point. Unfortunately, due to the relatively low efficiency of modern production CVT’s the total efficiency of the driveline is not increased significantly. This low efficiency is mainly caused by losses in the hydraulic actuation system and the variator. Decreasing the clamping forces in the variator greatly improves the efficiency of the CVT. However, lower clamping forces increase the risk of excessive belt slip, which can damage the system. In this paper a method is presented to measure and control slip in a CVT in order to minimize the clamping forces while preventing destructive belt slip. To ensure robustness of the system against torque peaks, a controller is designed with optimal load disturbance response. A synthesis method for robust PI(D)-controller design is used to maximize the integral gain while making sure that the closed loop system remains stable. Experimental results prove the validity of the approach

Solving Algebraic Riccati Equation Real Time for Integrated VehicleDynamics Control

In this paper we present a comparison study of different computational methods to implement State Dependent Riccati Equation (SDRE) based control in real time for a vehicle dynamics control application. Vehicles are mechatronic systems with nonlinear dynamics. One of the promising nonlinear control methods to control vehicle dynamics is based on SDRE. In this method, an Algebraic Riccati Equation (ARE) is solved at each sample to generate the control signal. However solving ARE is computationally complex. In this work, Extended Kalman Filter (EKF) iterative, Schur, Eigenvector, and Hamiltonian methods to solve ARE real time are implemented and studied for their timing, accuracy, and feasibility. Three methods, Schur, Eigenvector, and Hamiltonian are found to have an average calculation time of 3.9, 2.5, and 1.6 milliseconds on a dSPACE real time processor. This timing is acceptable as the controller sampling time is 10 milliseconds. In addition to the least processing time, the Hamiltonian based approach yields the lowest quadratic cost for SDRE based Integrated Vehicle Dynamics Control (IVDC)