With the electrification of mobile machinery comes the demand for new, efficient hydraulic systems. One system type of interest is the multi-pump architecture, which uses multiple pumps that can be connected to different actuators via on/off valves. This is a modular system that can perform efficiently, and the required installed power can be kept low compared to other similar approaches. It requires many valves, but offers many possible modes of operation. However, switching between modes is non-trivial and can cause disturbances and losses. In this paper, different controllers for a multi-pump system with two pumps and one actuator are investigated. Controllers that keep the pressure side of the pumps fixed are compared to controllers that allow varying pressure sides (meaning they can work in two or four quadrants, respectively). The ideal operating mode for each operating point was found using a genetic algorithm. The controllers were tested for different dynamics of the valves and pumps. It was found that the dynamics of the components have a similar impact regardless of the control strategy, assuming the dynamics are sufficiently fast. However, the controllers with fixed pressure sides generally performed marginally better.

Noise is a critical parameter for electrified mobile machinery. Both electric and hydraulic machines generate periodic forces that excite the surrounding structures and generate noise. This paper discusses harmonic orders and their origin in hydraulic pumps and permanent magnet synchronous motors (PMSMs). By combining the pump and motor, the harmonics of both machines interact, and the noise experience changes. This must be taken into account when designing electrically driven pumps. The effect of the combination of the design parameters; number of pistons, number of slots, and number of poles on the system harmonics is discussed. Traditionally, hydraulic pumps use odd piston numbers to reduce noise. However, if identical numbers of poles and pistons are chosen, the pump and motor harmonics coincide and can interact constructively or destructively. This paper shows, using torque ripple as an example, that selecting odd piston numbers is not straightforward when combining pumps with a PMSM.

Piston-type positive displacement machines are used across diverse applications and operating conditions, making it a critical design challenge to balance the minimization of solid-body contact while maintaining efficiency. This study investigates the potential of hydrostatic pockets between the cylinder block and valve plate to provide dynamically and passively controlled pressure forces, mitigating contact issues at low speeds without excessive losses at high speeds. Simulations of a baseline pump design revealed persistent solid-body contact under low-speed and high-pressure conditions, indicating the need for enhanced lubrication strategies. Retaining the baseline design, the study examined multiple hydrostatic pocket configurations through simulation, varying their location and quantity. Although the primary focus is on low-speed high-pressure and high-speed high-pressure scenarios, additional operating points at high-speed low-pressure and medium-speed medium-pressure were also considered. The effectiveness of each design was evaluated on the basis of film thickness, contact pressure, and viscous losses under key operating conditions. The experimental findings from previous studies were used to validate or challenge the conclusions from the simulation results. This paper seeks to deliver a better understanding of the hydrostatic pockets, offering design guidance for optimizing the lubrication management for future piston-type positive displacement machines and informing strategies for improved efficiency and longevity in demanding applications.

Noise is one of the major challenges for the electrification of hydraulic systems for mobile working machinery. Without the masking sounds of a combustion engine, the distinct noise of the hydraulic pump becomes more audible and thus needs to be reduced. Compressible pump flow pulsations caused by imperfect commutation are one of the main noise sources. Electric motor control offers the possibility to inject torque pulses at the pump's first harmonic frequency in order to reduce common noise. This paper uses lumped parameter simulation to drive a hydraulic pump with different shapes of drive torques, and in different operating conditions. The potential of injecting harmonics into the drive torque for the reduction of flow pulsations is explored. At the right phase and amplitudes, these pulses can basically eliminate flow pulsations at their frequency. Scaling laws for comparisons of different piston numbers are summarised, and the behaviour of a 9 and a 10 piston pump are compared, demonstrating that lower torque amplitudes are required when using smaller piston numbers. Required torque amplitudes are quantified, showing that torque amplitudes in the region multiples of the pump's ideal drive torque are required at medium or high speeds. Furthermore, these torque amplitudes significantly increase losses and increase the requirements for the inverter, making harmonic injection impractical at medium and high speeds. At low speeds, the first pump harmonic can be eliminated, but this is of limited benefit due to the low sensitivity of human hearing at these frequencies.

This paper explores the transition towards the electrification of hydraulic systems in material moving machines, highlighting both environmental benefits and the noise challenges posed by such technological change. With a focus on noise, the study examines the perceptual impact of replacing diesel engines with electric motors, which alters the noise profile of these machines. A survey assesses human responses to different hydraulic pump configurations in electrified setups, revealing significant variations in noise perception based on the specific design and the familiarity of the respondents with hydraulic sounds. The findings underscore the need for a nuanced approach to noise management in electric hydraulic systems, advocating for designs that consider both decibel levels and sound quality to enhance operator comfort and public acceptance.

 Hybrid and fully electric heavy machinery introduce new possibilities for hydraulic system design. Due to their lower energy density compared to conventional combustion engine systems, improving hydraulic efficiency is crucial. Electro-hydraulic actuators can achieve this but often require high installed power, as each actuator must be sized for maximum demand. The multi-pump system (MPS) in this paper addresses this by allowing all hydraulic machines to serve any actuator via a network of on/off valves, reducing losses and installed power. However, its multiple degrees of freedom make optimal operation non-trivial. This paper proposes a filtering strategy using a genetic algorithm to identify efficient operating points for the MPS. Although applicable for larger systems, the results here focus on an MPS with two pumps and one actuator as an example. A quasi-static system model is introduced, which the GA uses to determine steady-state control signals that minimise power consumption. The results highlight ideal operating conditions, significantly narrowing the range of viable valve combinations and pump/motor speeds. Finally, the paper discusses the limitations of the approach and its potential extension to more complex multi-pump systems for the development of dynamic control strategies.

Conventionally, variable hydraulic axial piston machines vary displacementby adjusting the length of the piston stroke. Another method to achieve variabledisplacement is to rotate the valve plate and thus adjust the effectiveuse of the piston stroke. This paper provides an analytical methodology tocalculate control torques for valve plate rotation. This methodology considerscompensation ratios in the contact between the valve plate and thepiston plate, and compensation ratios in the contact between the valve platein the housing. This paper adds the consideration of a spring force, pressuredependentviscosity, and a surrogate model for the compensation force fromthe area between high-pressure and low-pressure to the traditional calculationof the compensation ratio. The influence of the cylinder barrel’s rotation angleand the valve plate rotation angle is taken into account. The calculation resultsfor an exemplary pump of floating piston type reveal that the main shareof the required control torque originates from the contact between the valveplate and the housing. A hydrostatic compensation force in that interface canreduce this torque, but it is illustrated that a full compensation is not possible.For large valve plate rotation angles, the risk of valve plate tipping caused bythe axial ports in the housing is shown, which shows that valve plate rotationis not suitable for displacement control to small displacement levels whenusing axial ports.

In search of more efficient hydraulic systems, new system architectures are explored. These system architectures are often electrically driven and include energy recuperation. This requires hydraulic machines to function both as pumps, converting mechanical power into hydraulic power, and as motors, converting hydraulic power back into mechanical power. However, the availability of machines that can operate in all desired modes is limited. This indicates that operation in multiple modes comes with performance penalties. This paper highlights the challenges for multi-quadrant operation of hydraulic piston pump/motors, with a particular focus on commutation, i.e., the transition between high- and low-pressure level for each chamber. Various commutation strategies for piston machines are examined. Furthermore, other important aspects for pump/motor operation such as hydrostatic compensation ratios, design of inlet channels, low-speed capability, and flow control through speed or displacement control are discussed. The article shows that the design of multi-quadrant machines is challenging, and this has to be considered when choosing the system architecture.

An observable trend nowadays is the change in the prime movers of mobile heavy machinery to electric alternatives to achieve more eco-friendly equipment. These solutions often require large and heavy batteries with limited capacity, making the research of more efficient components and the development of different system architectures an important topic of study. Hydraulic actuation is still a relevant application for these vehicles because of its reliability, controllability, and high power density. The electrification and digitalization of mobile machinery allow for innovative designs and control strategies to be implemented that take advantage of electro-hydraulic systems and their characteristics. Similar research has shown that a higher number of degrees of freedom allow for the system to operate with higher total efficiency. This paper introduces a novel actuation architecture that combines multiple fixed displacement hydraulic pumps and on/off directional valves to control the position and force of two hydraulic actuators for the working functions of a mobile machine. Each pump is powered by a variable speed electric drive so that each one can be operated independently, and together with the set of directional valves, allows the selection of different combinations of pumps and flow sharing between the actuators’ chambers to achieve the desired flow and pressure on each cylinder. The multi-pump system favours the use of smaller pumps, and the possibility of combining their flows reduces the need to operate the components at lower efficiency points such as partial displacement. At the same time, controlling the pumps’ flow through the variable-speed electric motors means that throttling valves are not needed. The development of this architecture will allow for its use in mathematical models to analyse its behaviour and efficiency and to obtain insights regarding points of improvement in the system architecture.