Control Aspects of ComplexHydromechanical Transmissions: with a Focus on Displacement Control

Abstract

This thesis deals with control aspects of complex hydromechanical transmissions. The overall purpose is to increase the knowledge of important aspects to consider during the development of hydromechanical transmissions to ensure transmission functionality. These include ways of evaluating control strategies in early design stages as well as dynamic properties and control aspects of displacement controllers, which are key components in these systems.Fuel prices and environmental concerns are factors that drive research on propulsion in heavy construction machinery. Hydromechanical transmissions are strong competitors to conventional torque-converter transmissions used in this application today. They offer high efficiency and wide speed/torque conversion ranges, and may easily be converted to hybrids that allow further fuel savings through energy recuperation. One challenge with hydromechanical transmissions is that they offer many different configurations, which in turn makes it important to enable evaluation of control aspects in early design stages. In this thesis, hardware-in-the-loop simulations, which blend hardware tests and standard software-based simulations, are considered to be a suitable method. A multiple-mode transmission applied to a mid-sized construction machine is modelled and evaluated in offline simulations as well as in hardware-in-the-loop simulations.Hydromechanical transmissions rely on efficient variable pumps/motors with fast, accurate displacement controllers. This thesis studies the dynamic behaviour of the displacement controller in swash-plate axial-piston pumps/motors. A novel control approach in which the displacement is measured with an external sensor is proposed. Performance and limitations of the approach are tested in simulations and in experiments. The experiments showed a significantly improved performance with a controller that is slightly more advanced than a standard proportional controller. The implementation of the controller allows simple tuning and good predictability of the displacement response.

Simulation-Based Optimization of a Series Hydraulic Hybrid Vehicle

“…Simulation models, however, provide by definition only a simplified representation of a physical system. Consequently, they are typically used in conjunction with real-life experiments for validation and verification (see the methodology described in [5]). While the thesis focuses on the use of simulation models without equivalent physical system representation (for validation), their applicability is nonetheless evaluated within an iterative process through analysis of the results obtained (verification) (see [6] for an overview of exact definitions).…”

Conceptual Design of Complex Hydromechanical Transmissions

“…The execution time is therefore also longer. With forward-facing simulation, critical control aspects can be investigated and used for concept scoring, such as mode shifting and pump/motor displacement control [73].…”