Mobile machine electrification faces challenges as efficiency, cost, reliability, and performance lead to an increased focus on an integrated thermal management system (ITMS) and heat load reductions. Benefits such as waste heat recycling is considered a key feature of ITMSs but requires better understanding of thermal load distributions. This paper provides a thermal load analysis of a battery powered excavator-loader—often referred to as backhoe loader—during excavating and transportation in cold and hot ambient conditions. The analysis is based on measurements and data from an existing series-hybrid electric version. The results show that the working hydraulic system is the highest potential thermal load contributor corresponding to 71–75% of the total thermal load during excavating. The potential cooling demand reduction in cold ambient conditions by recycling waste heat during transportation is 38% compared to 10% during excavating.

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.

 The transition from internal combustion engines toalternative technologies—such as battery-electricpowertrains—in mobile machinery places increased demands onthermal management systems. Cooling requirements below theambient temperature during the summer, and intensiveheating requirements during the winter, lead to holistic but complex integrated solutions where energy efficiency isof high priority. Research into integrated system solutionsincluding heat pumps and waste-heat recovery has beencarried out mainly on passenger cars. In this study, mobilemachines are considered, and an articulatedexcavator-loader—also known as backhoe loader—is used as anexample. Apart from operating tasks, times, and conditions,the system architecture under the hood differs fromarchitectures usually found in passenger cars, includingworking hydraulic systems. During the early stages ofvehicle development, modeling and simulation of integratedthermal management systems are crucial forproof-of-concept, developing control strategies, andunderstanding subsystem interactions. These processes relyon data that would otherwise require testing on a completevehicle. This paper presents a model of a heat recoverysystem for cabin heating using the DLR Thermofluid StreamModelica library, together with input data from previousresearch based on experiments on a series-hybrid electricmachine. The study investigates the initial feasibility andperformance of a direct heat recovery system for thearchitecture of a battery-powered mobile machine. Theresults show that a simple system design can provide astrong foundation for cabin heating under many of thestudied excavating conditions, though it does not fullymatch the performance of the reference system, which issupplied with heat from an internal combustion engine.

Electrification of mobile machines requires focus on reducing unnecessary energy consumption, which is essential to avoid the need for oversized energy storage. Waste heat recovery of already existing heat flows in the vehicle, such as the working hydraulic system, is a promising way of reducing the energy consumption needed for keeping the cabin warm in the winter. This paper presents a model of a heat recovery concept from the working hydraulic system to the cabin, different from the ones typically seen in the literature. The model is created with the open-source tool OpenModelica together with the DLR Thermofluid Stream library. Focus of the model was to analyze how the dynamic characteristics of the working hydraulic system affects the cabin temperature, and to evaluate the waste heat performance. The results show that the cabin temperature fluctuates close to detectable variations without any interference of active temperature control, and also indicates promising cabin heating performance even under lower operation intensities.

The ongoing electrification of mobile machinery puts new demands on the hydraulic systems - they must become more efficient and quieter. One way to make them more efficient is to incorporate energy recovery. That often means that hydraulic pumps must also be able to work as motors. Efficient system solutions also need flow control for the pump. Traditionally, displacement control is used, but electrification makes speed control more relevant than ever before. All this increases the number of modes of operation for the hydraulic pump/motor, making commutation problematic. Commutation is crucial for both efficiency and noise. One feature sometimes used in pumps to facilitate commutation is the so-called ripple chambers. In this paper, the influence of such solutions is examined in simulation for different modes of operation. The results show that ripple chambers can be feasible for multi-mode operation.

 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.

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.

Displacement control of positive displacement machines has been a part of fluid power since the early days. Some of the early hydraulic presses already used two different displacement settings, though this was realised by using two different pumps rather than changing the displacement. Later, radial motors with variable stroke length appeared, followed by other designs of variable machines, such as swashplate machines, bent-axis machines, and variable vane machines. All these solutions control the displacement by varying the volume difference of the displacement element – but there are other ways of achieving this. Most have not passed the research state, but some are commercially available. In this paper, different ways of varying the displacement are presented and classified. The classification divides concepts into either control of displaced fluid or control of usage of displaced fluid. In turn, these concepts can be either on system level or displacement element level. This results in four main classes, which to some extent can describe the characteristics of the control.

Pump-controlled asymmetric cylinders need some kind ofcompensation for the difference between the in- and outlet flow.This can be done by using valves or additional pump/motors.An advantage with using valves is that only one pump/motor isrequired, but problems with mode-switch oscillations are morelikely to occur. On the other hand, cylinder areas should bewell matched with the pump/motor displacements for pump/motorcompensation if the pump/motors are fixed and connected to thesame shaft. However, this problem is avoided if the pump/motorsare individually controlled. Furthermore, with individually controlledpump/motors, it is possible to control the pressure in one ofthe cylinder chambers and the piston speed simultaneously. Thispaper is focusing on such architectures. There are several possibleconfigurations for architectures and control strategies for individuallycontrolled pump/motors, and some are compared here.Results show that one of the configurations is more efficient thanthe others, but that it is less efficient than valve-compensation (assuminglarge valves). A controller design where one pump/motoris used to control the speed and another to control the pressureis suggested. Results show that the controller should be adaptedbased on the mode of operation.