b'Industrial Machinery & Heavy Equipment | Engineer InnovationMobile machine equipment such asA hybrid hydraulic electric architecture excavators, backhoes, and skid steers(HHEA) is proposed in [2] to overcome are broadly referred to as off-highwaythe power density challenges of vehicles. They are an indispensable partelectrification. In the HHEA, the of several industries includingactuators are powered by hydraulic construction, agriculture, and mining,pressure rails, pressurized by a and represent a significant portion ofcombustion engine. Electric motors with global energy consumption andintegrated pumps replace hydraulic greenhouse gas emissions. Traditionally,throttles, to buck/boost the hydraulic off-highway vehicles are powered bypressure to each actuator. The electric diesel engines. The engine drives amotor power rating is minimized by hydraulic pump that distributes fluidhaving the combustion engine provide power to remote actuators which aremultiple hydraulic pressure rails to which responsible for everything from vehiclethe integrated motor-pumps intelligently propulsion to controlling theconnect to best meet the load implements. These hydraulic actuatorsrequirement. A system with more are controlled by throttling thepressure rails requires the motor-pump hydraulic fluid flow, leading to lowto provide less bucking/boosting, and system efficiency over a drive cycle. Atherefore less electric power. Thus, the recent study [1] shows that theHHEA can leverage efficient efficiency from the engine shaft tocontrollability that electric machines implement in an off-highway vehicle isoffer, while retaining most of the power approximately 20 percent. In addition,density of hydraulic components. For concerns over emissions are driving athis architecture to be successful, it is movement to downsize or completelycritical to maximize the power density of ban combustion engines in severalthe electric machine to utilize fewer countries. Electrification offers apressure rails and better support potential solution to both challenges. regeneration.Electric machines can efficiently controlIn this article, we present design actuators by operating fixedoptimization of an electric machine for displacement pumps at variable speed tointegration with a hydraulic pump to eliminate throttles. They can allow thehybridize an actuator in a 20-ton engine to operate at a nominal speed- excavator. The electric motor rating is torque point that reduces emissions.determined to be 20 kW at 15,000 RPM. Further, when paired with a battery,The hydraulic pump is a radial ball piston electrified off-highway vehicles have apump. More information is provided in tremendous potential for energy[3], which demonstrates the advantage recovery due to their highly transientof the axial flux PM machine (AFPM) for and repetitive drive cycles [2-3]. Whilethis application. Our project targets a electrifying these vehicles offers apower density over 5 kW/kg and compelling value proposition, theefficiency over 85 percent for the challenges involved are daunting.integrated hydraulic pump, electric Electric motors are not as power densemotor, and power electronics. This as combustion engines and hydraulictranslates to a power density of 9.5 kW/components. This issue is worsened bykg and efficiency of over 93 percent for the highly transient drive cycles requiringthe electric machine. This power density the motor to be significantly oversized.value resides near the upper limit of Further, the hostile operatingvalues reported in the electric machines environment (high temperature, dust,literature [4], making it quite and dirty air) introduces reliabilitychallenging.challenges for the electric machine and drive electronics. These factors togetherDesign optimization:pose a different set of challenges than isIn this study, we considered the found in electrifying passenger vehicles. following AFPM design variants (shown 43'