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Development of look-ahead controller concepts for a wheel loader application: [Développement de concepts d’une commande prédictive, destinée à une application pour chargeur sur pneus]
Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska högskolan.
Volvo Construction Equipment, Eskilstuna, Sweden .
Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska högskolan.
2015 (Engelska)Ingår i: Oil & gas science and technology, ISSN 1294-4475, E-ISSN 1953-8189, Vol. 70, nr 1, s. 159-178Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper presents two conceptual methods, based on dynamic programming, for one-step look-ahead control of a Continuously Variable Transmission (CVT) in a wheel loader. The first method developed, designated Stochastic Dynamic Programming (SDP), uses a statistical load prediction and stochastic dynamic programming for minimizing fuel use. The second method developed, designated Free-Time Dynamic Programming (FTDP), has vehicle speed as a state and introduces a fixed 0.1 s delay in the bucket controls in a combined minimization of fuel and time. The methods are evaluated using a set of 34 measured loading cycles, used in a ‘leave one out’ manner.

The evaluation shows that the SDP method requires about 1/10th of the computational effort of FTDP and has a more transparent impact of differences in the cycle prediction. The FTDP method, on the other hand, shows a 10% lower fuel consumption, which is close to the actual optimum, at the same cycle times, and is able to complete a much larger part of the evaluation cycles.

Abstract [fr]

Ce document présente deux méthodes de conception, basées sur la programmation dynamique, pour la commande à un pas de prédiction d’une transmission continûment variable (Continuously Variable Transmission, CVT) d’un chargeur sur pneus. La première méthode développée, appelée programmation dynamique stochastique (Stochastic Dynamic Programming, SDP) utilise une prédiction statistique de la charge et la programmation dynamique stochastique pour minimiser l’utilisation de carburant. La seconde méthode développée, appelée programmation dynamique à temps libre (Free-Time Dynamic Programming, FTDP), établit la vitesse du véhicule en tant qu’état et introduit un retard de 0:1 s dans les commandes du godet pour minimiser à la fois l’utilisation de carburant et le temps nécessaire à l’opération.

Les méthodes sont évaluées en s’appuyant sur 34 cycles de chargement mesurés, utilisés selon la méthode de validation croisée « leave-one-out ».

L’évaluation montre que la méthode SDP requiert environ 1 dixième de l’effort de calcul de la méthode FTDP, et qu’elle a un impact plus transparent sur les écarts dans la prédiction du cycle. D’un autre côté, avec la méthode FTDP on obtient une réduction de 10% de la consommation de carburant, ce qui est proche de l’optimum réel, pour les mêmes durées de cycle, et elle permet de réaliser une plus grande partie des cycles d’évaluation.

Ort, förlag, år, upplaga, sidor
EDITIONS TECHNIP , 2015. Vol. 70, nr 1, s. 159-178
Nationell ämneskategori
Reglerteknik
Identifikatorer
URN: urn:nbn:se:liu:diva-112719DOI: 10.2516/ogst/2014022ISI: 000351444400011OAI: oai:DiVA.org:liu-112719DiVA, id: diva2:770140
Tillgänglig från: 2014-12-09 Skapad: 2014-12-09 Senast uppdaterad: 2017-12-05
Ingår i avhandling
1. Optimal Predictive Control of Wheel Loader Transmissions
Öppna denna publikation i ny flik eller fönster >>Optimal Predictive Control of Wheel Loader Transmissions
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The transmissions of present heavy wheel loaders are in general based on torque converters. The characteristics of this component suits these machines, especially in that it enables thrust from zero vehicle speed without risk of stalling the engine, without active control. Unfortunately, the component also causes losses which might become large compared to the transmitted power. One approach for mitigating these losses is to switch to a continuously variable transmission. Changing to such a system greatly increases the possibility, and the need, for actively selecting the engine speed, and here a conflict emerges. A low engine speed is desired for high efficiency but a high speed is required for high power.

Heavy wheel loaders often operate according to a common repeating pattern known as the short loading cycle. This cycle is extremely transient, which makes the choice of engine operating point both important and difficult. At the same time, the repeating pattern in the operation enables a rough prediction of the future operation. One way to use the uncertain prediction is to use optimization techniques for selecting the best control actions. This requires a method for detecting the operational pattern and producing a prediction from this, to formulate a manageable optimization problem, and for solving this, and finally to actually control the machine according to the optimization results. This problem is treated in the four papers that are included in this dissertation.

The first paper describes a method for automatically detecting when the machine is operating according to any of several predefined patterns. The detector uses events and automata descriptions of the cycles, which makes the method simple yet powerful. In the evaluations over 90% of the actual cycles are detected and correctly identified. The detector also enables a quick analysis of large datasets. In several of the following papers this is used to condense measured data sequences into statistical cycles for the control optimization.

In the second paper dynamic programming and Pontryagin’s maximum principle is applied to a simplified system consisting of a diesel engine and a generator. Methods are developed based on the maximum principle analysis, for finding the fuel optimal trajectories at output power steps, and the simplicity of the system enables a deeper analysis of these solutions. The methods are used to examine and visualize the mechanisms behind the solutions at power transients, and the models form the basis for the models in the following papers.

The third paper describes two different concepts for implementing dynamic programming based optimal control of a hydrostatic transmission. In this system one load component forms a stochastic state constraint, and the concepts present two different strategies for handling this constraint. The controller concepts are evaluated through simulations, in terms of implementability, robustness against uncertainties in the prediction and fuel savings.

The fourth paper describes the implementation and testing of a predictive controller, based on stochastic dynamic programming, for the engine and generator in a diesel electric powertrain. The controller is evaluated through both simulations and field tests, with several drivers, at a realistic work site, thus including all relevant disturbances and uncertainties. The evaluations indicate a ∼ 5% fuel benefit of utilizing a cycle prediction in the controller.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2015. s. 27
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1636
Nationell ämneskategori
Maskinteknik
Identifikatorer
urn:nbn:se:liu:diva-112722 (URN)10.3384/diss.diva-112722 (DOI)978-91-7519-171-3 (ISBN)
Disputation
2015-03-20, Visionen, Hus B, Campus Valla, Linköpings universitet, Linköpiong, 14:24 (Engelska)
Handledare
Tillgänglig från: 2015-01-12 Skapad: 2015-01-12 Senast uppdaterad: 2015-01-12Bibliografiskt granskad

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