In mobile working machines, there is a trend towards replacing combustion engines by electric machines to reduce their carbon footprint. This provides several advantages and challenges for the hydraulic system. The low efficiency of conventional hydraulic systems is no longer acceptable due to the volume and cost of batteries. Luckily, the advantages offered by electrification can be exploited for increased system efficiency. 

Electrified pump drives (electro-hydraulic energy converters) enable variable speed control, energy recuperation, power-on-demand, and new system architectures with more flexible control. Currently, electro-hydraulic energy converters are typically made by stacking off-the-shelf components. However, off-the-shelf hydraulic machines are not optimized to be combined with electric machines, and thus there is room for improvement. One of these potentials is the volume at the core of electric machines which does not contribute to torque creation. This volume can be used to tightly integrate a hydraulic machine. This tight integration leads to increased power density and the elimination of some parts (e.g., a pair of bearings). This thesis investigates and discusses the design of electro-hydraulic energy converters. 

Furthermore, this thesis discusses valve plate rotation for a double pump of floating piston type with two valve plates for the following reasons: Firstly, without the noise of the combustion engine, the noise of the hydraulic machine becomes more audible. Valve plate rotation provides variable pre- and de-compression, and is therefore investigated to reduce fluid-borne noise. Secondly, electric machines can be overloaded for some time. In order to protect them from overheating when maximum pressure is demanded continuously, the torque load can be reduced by reducing the hydraulic machine’s displacement. Conventional swash-plate tilting needs significant leakage to be stable, which reduces the efficiency. Valve plate rotation requires low control power and could therefore increase efficiency, and is thus investigated in this thesis. However, valve plate rotation remains challenging for the following reasons: For low displacement setting ratios, the axial speed of the pistons at commutation is increased, increasing the throttling effect. Also, the hydrostatic forces acting on the valve plate change when rotating the valve plate. 

In mobile working machines, there is a trend towards replacing combustion engines with electric machines to reduce their carbon footprint. This provides several advantages and challenges for their hydraulic systems. The low efficiency of conventional hydraulic systems is no longer acceptable because of the volume and cost of batteries. Fortunately, the advantages offered by electrification can be exploited for increased system efficiency.

Electrified pump drives enable variable speed control, energy recuperation, power-on-demand, and new system architectures with flexible control. However, legacy hydraulic machines (pump/motors) were not optimised to match the electric machines’ capabilities. This thesis has two main focus areas: the development of hydraulic machines that better match the abilities of electric drives, and the integration of a hydraulic machine with an electric machine.

The electric drive places new demands on the hydraulic machine to enable more sustainable hydraulic systems: higher efficiency, a broader speed range (lower and higher speeds), multi-quadrant capability, and reduced noise. Lubrication interfaces need to be redesigned for enhanced speed capabilities, and commutation requires attention due to its influence on the noise behaviour. Variable displacement can help downsize the electric machine, but control losses should be reduced compared with conventional displacement control. This thesis aims to support developments on the above-mentioned aspects.

Commercial electro-hydraulic energy converters usually combine hydraulic and electric units by axial stacking. Alternatively, research projects consider the radial integration of the hydraulic machine within the core of the electric machine or downsizing the electric machine using a gearbox. This thesis summarises analytical sizing methods for the active parts of each concept and examines trade-offs between volumes, aspect ratios, masses, and efficiencies.

Finally, noise is a challenge for electrified hydraulic systems. This thesis provides a starting point to investigate the combined noise of hydraulic and electric machines by describing the noise contributors and harmonic frequencies of both machines. Furthermore, the hydraulic noise from different electrically driven pump setups (e.g., speed control, displacement control, multi-pump) is assessed using audio files created from simulated flow pulsations.

Bland mobila arbetsmaskiner ersätts förbränningsmotorer av elmaskiner i allt större utsträckning. Syftet är i regel att minska maskinernas koldioxidavtryck. Elektrifieringen medför flera möjligheter och utmaningar för hydraulsystemet. Den låga verkningsgraden hos konventionella hydraulsystem är inte längre acceptabel på grund av storleken och kostnaden för batterierna som skulle krävas. Genom att nyttja elektriskt drivna pumpar (elektrohydrauliska energiomvandlare) möjliggörs varvtalsstyrning, energiåtervinning och nya systemarkitekturer med mer flexibel styrning. I dagsläget realiseras elektrohydrauliska energiomvandlare oftast genom att koppla samman konventionella hydraul- och elmaskiner som finns på marknaden. Konventionella hydraulmaskiner är dock inte optimerade för att kombineras med elmaskiner, och därför finns utrymme för förbättringar. Denna avhandling angriper två förbättringsområden: utveckling av hydraulmaskiner som bättre matchar egenskaperna hos elmaskiner, och integration av hydraulmaskiner med elmaskiner.

Elektrisk drivning ställer nya krav på hydraulmaskiner: högre verkningsgrad, ökat varvtalsområde (både till lägre och högre varvtal), minskade ljudemissioner, samt multikvadrantkapacitet för energiåtervinning och ökad system-flexibilitet. Variabelt deplacement kan också vara önskvärt då det kan minska storleksbehovet för elmaskinen, men förluster relaterade till deplacementstyrning bör minskas. Denna avhandling syftar till att stödja utvecklingen inom ovan nämnda punkter.

De elektrohydrauliska energiomvandlare som idag finns på marknaden kombinerar hydraul- och elmaskiner genom axiell stapling. Ett alternativ till detta är radiell integration av hydraulmaskinen i kärnan av elmaskinen. Ett annat alternativ är att nyttja en växellåda mellan hydraul- och elmaskinen, vilket möjliggör neddimensionering av elmaskinen. Denna avhandling sammanfattar analytiska dimensioneringsmetoder för de aktiva delarna i varje koncept och syftar till att ge insikter om avvägningarna mellan volymer, längd–diameterförhållande, massor och verkningsgrader.

Ytterligare en aspekt som behandlas i denna avhandling är det kombinerade ljudet från hydraul- och elmaskiner, ett område som ännu inte är väl undersökt. Denna avhandling syftar till att vara en utgångspunkt till detta genom att ge bakgrundsinformation om ljudkällor och harmoniska frekvenser för båda maskinerna. Vidare presenteras resultat från en enkät där det hydrauliska ljudet från olika elektriskt drivna pumpkonfigurationer (t.ex. hastighetsreglering, deplacementsreglering, multipump) har undersökts.