Design Optimisation Strategies for a Hydraulic Hybrid Wheel Loader

Abstract

This paper deals with design optimisation of hydraulic hybrid drivelines during early concept design phases. To set the design parameters of a hybrid driveline such as gear ratios, pump/motor displacements and size of energy storage, the energy management of the hybrid machine needs to be considered as well. This is problematic since a nested design and control optimisation normally requires substantial computer power and is time-consuming. Few previous studies have treated combined design and control optimisation of hydraulic hybrid vehicles using detailed, non-linear component driveline models. Furthermore, previously proposed design optimisation methods for on-road vehicles are not suitable for heavy off-road machines operating in short repetitive cycles with high transient power output. The paper demonstrates and compares different optimisation approaches for design and control optimisation combining deterministic dynamic programming and non-gradient based numerical optimisation. The results show that a simple rule-based energy management strategy can be sufficient to find the optimal hardware design even though non-optimal control laws are used.

Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines

“…In addition to the driveline, wheel loaders also have work functions, thereby resulting in multiple substantial power consumers. These aspects have a strong influence on both the design [7] and high-level control [5] of hybrid wheel loaders and should consequently also be taken into account in the low-level control. In addition, the unique conditions and complex nature of wheel loaders make the operator play a key role in maximizing their performance [17].…”

“…In this context, a commonly-addressed challenge concerns the optimal use of the added power source; continuously during vehicle operation, a proper decision is required whether the accumulator should be charged or discharged [2]. The maker of this decision is commonly referred to as a high-level control strategy and has been investigated for both on-road vehicles [3,4] and mobile working machines in the past [5][6][7].…”

Control of Hybrid Hydromechanical Transmissions

“…In a telehandler application, 13 % fuel savings were predicted for a similar cycle when compared to a hydrostatic transmission [16]. The presence of multiple power consumers is often stressed, both in terms of management of the accumulator state-of-charge [17] and the transmission design [18,19]. Furthermore, some authors stress the benefits of complex power-split transmissions for this application.…”

“…A parallel hybrid is realised by adding a pump/motor and an accumulator to a conventional driveline. Parallel hybrids are out of the scope of this thesis but have, for instance, been investigated for wheel loaders in [36,19].…”

“…In addition, the strong influence of the energy management strategy on fuel consumption motivates simultaneous optimisation of energy management and system component sizing. The performance of a simple rule-based controller may then be comparable to that of a more sophisticated approach [19].…”