Environmental and economic factors are driving the development of more fuel efficient off-highway vehicles. The pathway to fuel savings of greater than 50% in an excavator application through utilisation of system architectures unlocked by Digital Displacement technology is presented. Pump flow distribution using digital valves instead of traditional proportional control valves is demonstrated experimentally. The “Workbus” power distribution scheme is demonstrated on a small scale backhoe arm on a laboratory test rig. These tests do not include hydraulic energy recovery. A backward-facing simulation of an 18 tonne excavator is described. The simulation uses input data collected from grading and lorry loading duty cycles. Applying the workbus system architecture to the excavator in simulation, fuel savings of 31% to 48% are realized. With the addition of energy recovery capability via Digital Displacement Pump-Motors, simulated fuel savings are 53% to 58% compared to the original excavator hydraulic system.

There is a long trend in off-highway vehicles toward higher energy efficiency and electro-hydraulic control. Digital pumps and motors are poised to become a significant enabling technology in this trend. This paper analyzes a 20-tonne tracked excavator that was equipped with digital displacement pumps and evaluated for efficiency and productivity. Previous research by Artemis Intelligent Power demonstrated improvements compared to a conventional, negative flow control excavator hydraulic system. With support from Artemis, the Danfoss Digital Displacement Excavator (DDE) is a step forward in terms of technology and commercial readiness. DDE is based on a CAT 320 next-generation excavator with completely electronic controls and advanced sensor and operator-assistance features. In before/after testing, DDE showed 15% higher productivity (in meters of trench per hour) and 13% higher efficiency (in meters per liter of fuel) for a trench digging cycle. Static pump efficiency is only part of the story; dynamic response and controllability contributed to the measured performance gains. Potential causes for variation in measurement were analyzed including operator variation, flow variation, and machine response.

In an aircraft turbofan engine, a fuel metering unit meters and supplies the required fuel to the engine according to the flight situation. When a centrifugal fuel pump (CFP) is used as the fuel pump, the ratio of hydraulic power per weight can be increased by raising the rated rotational speed, so the weight of the fuel pump can be decreased compared to when using a gear pump (GFP). There is an advantage that it can be reduced significantly. However, since the operating range of the fuel pump is wide, it is not effective to use CFP in an extremely low flow rate region because the fuel temperature rises due to its PQ characteristics and a large loss. Therefore, it is considered effective to combine CFP and GFP as pressure sources, and to use GFP in the low flow region and CFP in the high flow region. For that purpose, it is necessary to have a pump mode switching mechanism. The disadvantage in this case is that changing the pump mode causes a large pressure change of the fuel pressure source, which in turn causes fuel flow pulsations. There are three possible ways to solve this problem. The first method is to keep the differential pressure control valve (DPCV) unit response constant, which keeps the metering valve differential pressure constant in FMS. A second method is to remove high frequency components that the DPCV cannot follow pressure changes in the fuel control system. A third method is to keep the pressure difference between the two fuel sources small and to reduce the amplitude of the applied disturbance. In this paper, the first method, which makes DPCV response high response, is verified by modeling and simulation, and its effectiveness is confirmed.

As an effective approach to improving the fuel economy of heavy duty vehicles, hydraulic hybrid has shown great potentials in off-road applications. Although the fuel economy improvement is achieved through different hybrid architectures (parallel, series and power split), the energy management strategy is still the key to hydraulic hybrid powertrain. Different optimization methods provide powerful tools for energy management strategy of hybrid powertrain. In this paper a power optimization method based on equivalent consumption minimization strategy has been proposed for a series hydraulic hybrid wheel loader. To show the fuel saving potential of the proposed strategy, the fuel consumption of the hydraulic hybrid wheel loader with equivalent consumption minimization strategy was investigated and compared with the system with a rule-based strategy. The parameter study of the equivalent consumption minimization strategy has also been conducted.

Owing to its high power density, hydraulic hybrid is considered as an effective approach to reducing the fuel consumption of heavy duty vehicles. A gas-charged hydraulic accumulator serves as the power buffer, storing and releasing hydraulic power through gas. An accurate hydraulic accumulator model is crucial to predict its actual performance. There are two widely used accumulator models: isothermal and adiabatic models. Neither of these models are practical to reflect its real performance in the hydraulic hybrid system. Therefore, the influence of an accumulator model considering thermal hysteresis on a hydraulic hybrid wheel loader has been studied in this paper. The difference of three accumulator models (isothermal, adiabatic and energy balance) has been identified. A dynamic simulation model of the hydraulic hybrid wheel loader has been developed. The fuel consumptions of the hydraulic hybrid wheel loader with three accumulator models has been compared. The influence of heat transfer coefficient of the accumulator housing has also been studied.

In this paper, fuel consumption of a 5.7-ton municipal tractor in a wheel loader application is studied, and methods for improving the fuel efficiency are compared with each other. Experimental data from the baseline machine with load-sensing hydraulics has been gathered during a y-pattern cycle, and the data is inputted to an optimization function having realistic loss models for a hydraulic pump and diesel engine. Dynamic programming is used to analyze different system configurations in order to determine optimal control sequence for each system. Besides optimization of variable engine rotational speed on the baseline system during the working cycle (considering the point of operation), three hybrid supply systems are studied: 1) a hydraulic flywheel, 2) parallel supply pumps and 3) a throttled accumulator. These systems utilize a hydraulic accumulator as an energy source/sink alongside the diesel engine. The optimal sequence for charging and discharging of the accumulator is examined in order to minimize the fuel consumption of the machine. The idea is to use the lowest acceptable, constant engine rotational speed, to cut down the diesel losses. In addition, the study covers an analysis of adjusting the engine rotational speed for each point of operation also when the hybrid systems are considered. The results show that finding advantageous engine rotational speed for each loading condition can decrease the fuel consumption of the baseline machine around 14%, whereas hybridization of the supply system can further improve the result by a couple of percentage units. Hybrid systems also reduce engine’s maximum load by making it more uniform, which allegedly reduces emissions. The possibility of engine downsizing to further improve the fuel efficiency of hybrid systems is not considered, because the maximum engine power is usually determined by the hydrostatic transmission of a municipal tractor. However, the study assumes that actuators are controlled using traditional 4/3 proportional control valves; hence, there are still potential for greater fuel savings. For example, applying independent metering valves on the actuator control can further decrease the system losses.

One of the current and future trends in robotics is to reduce the weight of a robotic manipulator by using lightweight materials, such as ultra-high-strength steel or composites. The reduction in weight results in material and fuel savings, which are highly relevant for heavy-duty, off-highway manipulators found in excavators, truck-mounted cranes, and forestry machines. Due to the highly demanding working conditions of such manipulators, hydraulic actuation is mainly used. Automated and accurate control of these manipulators is very challenging due to the nonlinearities present in the system. Recent studies indicate that nonlinear model-based control (NMBC) methods can provide the most advanced control performance in the case of hydraulic robotic manipulators. An accurate model capturing the dynamics of the physical system is required for effective NMBC design. The present study proposes a hybrid rigid-flexible model for a flexible manipulator combined with a hydraulic actuator, implemented with the help of the floating frame of reference formulation (FFRF). The designed model is validated by comparing simulations with experimental reference data obtained from an OptiTrack motion-capture system and other sensors. The comparative results demonstrate that the model is able to capture the system’s dynamics accurately, which motivates further research on developing NMBC methods using the FFRF.

Environmental and economic factors are driving the development of lower emission and more fuel efficient off-highway vehicles. While a great deal of this development is focused on hybrid technology and novel system architectures, the simple application of a Digital Displacement ® Pump (DDP) in place of a conventional pump can deliver significant fuel savings and productivity benefits, whilst also acting as an enabler for more radical future development. This paper describes the ‘DEXTER’ project, in which a tandem 96cc/rev DDP was installed in a 16 tonne excavator. The energy losses in the unmodified excavator are calculated based on test data, confirming the scope for efficiency improvements. Next, the basic operating principle and efficiency of the DDP and its application to the excavator system are outlined, alongside simulation based fuel saving predictions. The model based design and ‘operator in the loop’ testing of the control system are then described. Side by side testing of the modified excavator and a standard excavator showed that when the modified excavator was operating in ‘efficiency mode’ a fuel saving of up to 21% and productivity improvement of 10% is possible. In ‘productivity’ mode, a 28% productivity improvement was recorded along with a 10% fuel saving. These results are validated with reference to the higher efficiency of the DDP and improved control system which allows the engine to run closer to its torque limit.

This paper is focused on the study of the sloshing in the fuel tank of vehicles. As well known, fluid dynamic in an automotive fuel tank have to be studied and optimized to allow the correct fuel suction in all driving conditions, prevent undesired slosh noise and limit its influence on fuel vapor formation and management. Experimentation to predict the sloshing with a good accuracy depends on the ability to replace real working parameters and conditions like accelerations, decelerations, slope variations and rotations. This paper shows results obtained studying the sloshing inside a reference tank with computational fluid-dynamic and experimental approaches. The test bench for automotive fuel tank, employed in this analysis, has been designed by Moog Inc. on specification from Fiat Chrysler Automobiles and it is aimed at covering the wider possible range of dynamic conditions. It basically consists of a hexapod, which uses six independent actuators arranged in three triangles and connecting a base and a top platform, thus allowing all six DOFs. Above the top platform is mounted a tilt table with two additional actuators, to extend pitch and roll envelope, thus the name of “8-DOF bench”. A dedicated CFD model has been built up using a CFD commercial code. The model has been integrated with the multiphase tool in order to correctly reply the real free surface. Results, numerical and experimental, have been post-processed with Matlab ® comparing percentage gaps of the free surfaces each other. The comparison has shown a good agreement. This research is the result of a scientific collaboration between the Industrial Engineering Department of University of Naples Federico II and FCA Fiat Chrysler Automobiles.

The cluster of excellence „Tailor-Made Fuels from Biomass“ at RWTH Aachen University develops and investigates new biofuel candidates, to reduce global emissions and create an alternative and sustainable diesel fuel. Biofuels pose a new challenge to existing common-rail injection pumps. Since fuels are used as lubricants for tribological contacts in these pumps, the deviating hydrodynamic properties in comparison to diesel can cause high leakage, wear, and a low overall-efficiency. In order to ensure a reliable pump performance, especially for low-viscosity fuels or fuels with worse lubricity than diesel, an optimization of the tribological contacts is necessary. The most critical contact is the piston-cylinder contact. One possibility to reduce the leakage in this contact is the use of a hollow piston design. This design can reduce the gap between piston and cylinder by minor pressure-dependent elastic deformations of the piston. In this paper, a first simulative look is taken at the compression behavior of the new piston design. The focus lies on the delayed pressure build-up due to the additional capacity caused by the shape of the piston. Based on the results, a new design approach is proposed subsequently in order to ensure a sufficient pressure build-up. The manufactured contour of the new design is investigated in order to ensure the geometric properties and first measurement results are discussed. For the measurement, a low-viscosity fluid is used to compare leakage rates of the standard and the new hollow piston design. Based on the results, a conclusion is made, deriving further usage of the hollow piston.

Reach stackers are heavy duty mobile machines mainly used for container handling on intermodal terminals or harbors. The increasingly restrictive legislation on pollutant emissions as well as the need to reduce fuel costs for operators motivate manufacturers to design more efficient machines. Previous studies highlighted three ways to improve the fuel consumption, namely: (i) improving the engine efficiency; (ii) recuperating the potential energy of elevated containers; (iii) recovering the kinetic energy of the vehicle during decelerations. The architecture proposed in this paper combines these three requirements while preserving most of the conventional components. It results in a moderately priced solution. Control strategies are also studied, especially focusing on the potential energy recovery system where an input-output linearization method is compared to a conventional linear controller. Simulation conducted on several duty cycles shows fuel savings of up to 18.4% and a good robustness to cycle variations.

This paper describes an application of direct drive volume control (DDVC) to ship speed control. The DDVC fuel injection device consists of an AC servo motor, a fixed-displacement oil-hydraulic pump, and an oil-hydraulic cylinder. The cylinder piston pushes a fuel pump to pressurize fuel and an injection valve opens to inject fuel into a combustion chamber. Timing and the quantity of fuel injection can be controlled by the electric signal added to the AC servo motor. In this paper, the DDVC fuel injection device is applied to engine speed control of marine diesel engine and ship speed control. A simulation model is made including a model of the DDVC fuel injection device, propeller model, and hull motion model. Firstly, engine speed control system is proposed. Stop injection angle is automatically adjusted according to engine speed error signal. Secondarily, ship speed control is proposed. Propeller pitch angle is used to control ship speed. Simulation study of these control systems are presented to show the capability of the DDVC fuel injection device for marine diesel engine.

The target application of this study is hydraulic excavators, which are one of the most common machines found at construction sites across the world. Road constructions and improvements, laying operation of cables or pipes and building can be seen in urban areas and digging and dumping operations of natural resource are done in country regions. For the construction site in urban areas, mini hydraulic excavators with operating weights up to 6 tons are often used and they make up more than 60% of the total hydraulic excavators market [1]. In recent years, a number of new system architectures for mobile hydraulic systems have been proposed. Examples of such improved architectures are displacement control, transformer systems and valve controlled systems with multiple pressure rails. For these systems, electronic controls are always used. Although these new methods are promising, they cannot be applied to mini-excavators, because today’s mini-hydraulic excavators do not use electronic controls as this would increase costs and make the system complex. Therefore, the goal of this study is to propose a fully hydro-mechanical valve controlled constant pressure system, which can be applied to mini-excavators in the future. This paper begins by introducing the details of this novel hydraulic system and shows its advantages. Using a simulation model of an 18 ton excavator, it is confirmed that the novel system functions well and the energy efficiency is compared to a conventional Load Sensing system. The simulation results show that the novel system can save 22% and 24% of fuel in leveling and 90° dig-dump cycles respectively.

Within the cluster of excellence “Tailor-made Fuels from Biomass” at RWTH Aachen University new biofuels are developed and investigated. Because common-rail injection pumps are generally lubricated by the fuel itself, the tribological characteristics of the fuel candidates is of interest. The lubricity and viscosity of the alternative fuels differ from diesel. Hence, a reliable function of the tribological contacts, which are designed for the operation with diesel, cannot be guaranteed. To achieve a reliable operation even for fuels with, for instance, a lower viscosity or worse lubricity an optimisation of the tribological contacts is necessary. The focus of the investigations presented in this paper lies on the piston-cylinder-contact. Prior to the simulative study the losses in a pump operating with various fuel candidates are quantified by means of efficiency measurements. By these measurements the great impact of the fuel’s rheology on the pump performance is clarified. Based on detailed EHD-simulations with various fuels under typical operating conditions, an optimisation of the piston-cylinder-contact is presented. The optimisation aims for the reduction of solid friction by changing the pressure field on the piston. The approaches can basically be separated into grooved and contoured pistons. The potential of the different approaches is discussed based on simulation results and effects, which occur in the lubricating film of the optimised contacts.

In the scope of the cluster of excellence “Tailor-Made Fuels from Biomass” new biofuels are developed. To ensure safe and reliable functioning of the injection system operating with the new fuels, the tribological characteristics of the fuel candidates have to be investigated. The biofuel candidates which have been studied so far tend to have a lower viscosity compared to diesel [1]. This has an enormous impact on the efficiency of common-rail piston pumps. For low viscosity fuels the volumetric losses become the dominant factor. These losses are influenced by the geometric parameters of the pump, the operating conditions and the rheological characteristics of the fuels. Regarding the geometric parameters, the gap height in the piston-cylinder-contact is the predominant factor. In modern common-rail pumps the nominal gap height is in the range of 2–3 μm [2]. A further reduction of the height is limited by tolerances of the manufacturing process and the risk of the piston getting stuck in the cylinder due to different temperature gradients and consequently different thermal expansions of piston and cylinder. Besides the nominal gap height, the high pressure in the lubricating film in operation leads to an expansion of the gap. If this expansion can be limited or even avoided, a significant reduction of the leakage losses will be possible. In the scope of this paper an approach to a gap compensation of the sealing and lubricating contact between piston and cylinder is presented. Based on a detailed study of the state of the art design, including efficiency measurements of pumps and EHD-simulation, a modified piston design is investigated and optimized. The results show a great potential for efficiency improvement of common-rail pumps, especially if operated with biofuels, which provide low viscosities.

Environmental and economic factors have driven the advancements in fluid power technologies over the last two decades. Gradual development has been made over time on the state-of-the-art fluid power technology; however, there has been no major advancement leading to radical improvement on systems’ efficiencies. Displacement-controlled (DC) actuation has been under investigation by the authors’ group since its conception in 1998 as a highly efficient alternative to its valve controlled counterpart, demonstrating fuel economy improvements of up to 40% and the possibility for engine downsizing of up to 50% for an excavator truck-loading cycle. Through the installation of a variable displacement hydraulic pump/motor per actuator, DC actuation entirely eliminates the losses due to resistive control and allows for the recuperation of energy from overriding loads. The one-pump-per-actuator requirement however represents the technology’s largest obstacle due to the increased machine production costs. For this reason the authors’ group proposed the idea of pump switching wherein a reduced number of hydraulic units is connected to the actuators in a multi-actuator machine through a distributing manifold. The idea relies on proper design of the distributing manifold and enabling controls to realize machine operability. Work by the authors’ group has demonstrated that the pump-switching idea is feasible on the actuator level, achieving seaming-less switching transitions while retaining the basic fuel savings demonstrated for DC actuation. This paper presents the first formal attempt to create a supervisory controller for a DC multi-actuator machine with pump switching. The controller is based on priority levels geared towards the maximization of the number of available actuator combinations. Implementation on a DC hydraulic hybrid excavator prototype show the feasibility of the control approach as well as the limitations and further improvements.

Due to a growing awareness of fuel prices and government regulations on emissions there has been an expanding interest in hybrid vehicle research. Though much of these efforts have been in electric hybrid vehicles, hydraulic hybrid vehicles show great potential due to their higher power density, higher efficiency in regenerative braking, and lower cost of materials. Many different hydraulic hybrid architectures have been proposed, one of the most common being the series hybrid. The series hybrid has many deficiencies due to the hydraulic units being connected directly to the high pressure accumulator. In many operating conditions the units operate inefficiently at low displacements and high pressures. Additionally the driver’s torque demand can exceed that available from the accumulator’s current pressure. As a result additional fluid must be pumped into the accumulator to raise the system pressure. This can result in a delay on the order of seconds in meeting the driver’s demand thereby yielding an undesirably sluggish response. To address these issues the authors’ research group previously introduced the blended hydraulic hybrid [1]. Using dynamic programming, an optimal control simulation tool, the blended hybrid showed improved efficiency and response when compared to the series hybrid [2]. This transmission achieves high efficiency and fast response partially through the inclusion of a hydrostatic transmission. In addition regenerative braking and blending of engine and accumulator power are realized through the use of actively and passively controlled valves. With these promising results, the Maha Fluid Power Research Center has begun designing and constructing a blended hydraulic hybrid SUV. In preparation for this the authors have developed a new sizing methodology to determine transmission sizing that meets both the efficiency and performance requirements of the designer. To explore the trends in blended hydraulic hybrid sizing a full factorial combination of hydraulic unit sizes, accumulator sizes and accumulator minimum pressures were optimally controlled for the Urban Dynamometer Driving Schedule (UDDS) using dynamic programming and maximum acceleration was simulated to obtain trends in performance.

A hydraulic propulsion system is a convenient choice for many earth-moving and construction machineries because of their large mass and low speed required during normal operations. Due to the increasing fuel cost occurred during the last decade, a growing attention in displacement-controlled architectures is taking place. The key factors that motivate this interest are the energy-saving actuation and the easy implementation of the regenerative braking. In this regard, solutions like hydrostatic transmissions and secondary controlled hydraulic motors were already investigated for generic applications. Nevertheless, in some machines it is necessary to have more axles driven while guaranteeing a precise control of the tractive/braking torque: this is the case of the railway machineries. Thus, this research paper is aimed at comparing the non-hybrid displacement-controlled architectures mentioned above applied to a railway track maintenance machine. Discussing the control algorithms and analyzing some virtual simulations performed with high-fidelity dynamic models are part of the work. Specifically, after confirming the proper system functioning, the final targets are gaining deeper insight into the system behaviors and determining the most convenient layout in terms of energy consumption.

A direct drive volume control (DDVC) is applied to fuel injection control for marine diesel engine. The DDVC consists of an AC servomotor, a fixed-displacement hydraulic pump, and a hydraulic cylinder. The hydraulic cylinder pushes a plunger pump and fuel is pressurized. When the fuel pressure becomes greater than injection pressure, fuel is injected to a combustion chamber. A brief introduction of the DDVC is described first in this paper referring to conventional fuel injection systems including a cam mechanism and a common rail system. A mathematical model of the DDVC for simulation is summarized. Experiments of fuel injection shows the control function of the DDVC fuel injection system. The topic of this paper is feedback control of the quantity of fuel injection (fuel mass per injection) of the DDVC. The feedback control system is simulated using the above mathematical model. Fuel injection is stopped by switching a drive signal of the AC servomotor and retracting a piston of the hydraulic cylinder. The timing to stop injection is adjusted based on crank angle. An algorithm of updating the crank angle to stop injection is proposed so that the quantity of fuel injection follows the target value. Simulation study shows that the update algorithm works successfully.

This paper is to study on a novel recovery and release hydraulic hybrid system for excavators (HHE). The HHE uses hydraulic accumulators to recover the potential energy of the boom, the kinetic energy of the swing motor and the overflow hydraulic energy of the excavator’s main relief. The recovered energy is then utilized through a variable hydraulic motor as assistant power of the engine. The key issue of the HHE is that the operation of the boom must be similar to the conventional one about the sensing of the driver and the system must achieve higher efficiency and save more energy when comparing with the conventional system. In order to improve the recovery efficiency and while controlling the boom velocity with the similar operation, one design concept named “microcut” is proposed. When the boom drops down fast, a proportional valve is used to control the boom. While the boom goes down slowly, the recovery system is cut off. Then, the multi-way valve of the original system works to ensure good handling. An experimental prototype is designed and built in a 21-tons excavator. A 16% fuel-saving effect is obtained by weighing engine’s fuel consumption with the same amount of work, under conditions of the similar operation and higher efficiency compared with the conventional excavator.