A novel intelligent experimental research environment (LUTERGO laboratory) for developing the usability of off-road machines was created at LUT University. The environment combines a real-time simulator and an experimental system for measuring human body responses when driving the virtual prototypes of machines. Based on the quantities measured from the operator, such as heart rate, electrodermal, muscular, and brain activity, the stress level of the operator can be evaluated. It is assumed that by combining simulated machine data and biosignals, the usability of every virtual prototype of a new machine can be assessed during the R&D process. This is an alternative to a traditional approach when usability is studied with physical prototypes after conceptual R&D phases using qualitative data from questionnaires. The paper describes the structure and capabilities of the LUTERGO laboratory. Results of the initial tests are presented, which studied the influence of hydraulic valve dynamics on excavator vibration and operator biosignals. The results show that the biosignal parameters used as stress indicators change following the variation of time constant for directional valves controlling the main boom cylinders of the excavator. The paper concludes with future research directions using the novel environment.

Typically, off-road construction machines are not equipped with suspensions at the wheel axles. This has led to alternative concepts that uses the working implement to mitigate the vibration transmitted to the cabin. The most common solutions are based on passive ride control (PRC) methods. A PRC usually requires a hydraulic accumulator and dissipating valves properly connected to the working hydraulics. In this way, the PRC is able to dissipate the fluid energy and damp the oscillations of the pressure inside the hydraulic actuators, with clear benefits on the machine vibration. This paper focuses instead on an active ride control (ARC) methodology, which controls the working hydraulic motion to counter-reach the machine vibrations, avoiding the use of an accumulator. The paper addresses the main challenge of designing the controller for the ARC for the reference case of a wheel loader. A high pass pressure filter control with pressure feedback is proposed for this application. The controller is first studied in a simulation model and then validated through experiments on a stock machine. The bandwidth limitation of the standard hydraulic system does not permit to achieve the same performance of a state-of-art PRC system considered as baseline. Notwithstanding, the experimental results on the proposed ARC shows significant improvements with respect to a case where no controller is used. Moreover, the proposed method could be applied with more effectiveness in hydraulic systems with higher dynamic response.

Traditionally, off-road mobile machines such as excavators and wheel loaders are primarily powered by hydraulics and throttling valves are used to control their work circuits. In recent years, two general trends are towards more energy efficient systems and electrification. With electrification, both efficiency and control performance can be improved by the elimination of throttling losses and the use of high-bandwidth inverter control. Electrification is generally accomplished with Electro-hydraulic actuators (EHA) but they are limited to lower powered systems due to the high cost of electric machines capable of high power or high torque. This paper presents preliminary results of a new system architecture for off-road vehicles to improve efficiency and control performance. The architecture combines hydraulic power and electric power in such a way that the majority of power is provided hydraulically while electric drives are used to modulate this power. The hybrid hydraulic-electric architecture (HHEA) and its rationale are described. In addition, a case study is presented to illustrate its operation, its potential for energy saving, and its benefits of component downsizing. The case study indicates that compared to a baseline load sensing system, the HHEA has the potential to reduce energy consumption by more than 50%. Furthermore, the torque capability of the electrical components need only be ∼ 28% of what is required for the direct application of EHA.

ISO 4409 is the most important international standard for measuring the efficiency of hydraulic pumps and motors, the latest edition being 4409:2007. The standard describes methods for determining the steady-state performance in terms of overall efficiency. It also defines equations for calculating the volumetric efficiency of pumps and motors. The hydro-mechanical efficiency is only defined for motors, not for pumps. This paper analyses the efficiency and losses of pumps and motors in an alternative way. The preference is on loss analysis instead of efficiencies. Especially the effects of the bulk modulus are considered in a different and more inclusive manner. The new methodology results in a higher total loss for motor and a lower total loss for pumps than the current ISO 4409 standard. Furthermore, it results in significant changes of the hydro-mechanical and volumetric losses. The differences between the new methodology and ISO 4409 become larger for high load pressures. The new methodology demands knowledge about the minimum volume of the displacement chamber. The ratio between this volume and the full displacement of a single displacement chamber strongly influences the hydro-mechanical and volumetric losses of the pump or motor. The new methodology is valid for all positive displacement hydrostatic pumps and motors. The volumetric efficiency, as defined in ISO 4409, can still be used as a flow rate factor, but should not be regarded as an energy conversion efficiency. The importance of adopting the proposed methodology is further demonstrated by analyzing and comparing the measurement data about a fixed displacement pump and motor, showing the differences in the loss analysis by means of ISO 4409 and the new equations. The methodology, observations and validation results presented in this paper are significant and can pave the road for improving the current ISO 4409:2007 standard, which would ultimately benefit the industry.

This paper deals with the hydraulic oil consumption of mobile working machines. Different mobile working machines are going to be investigated by setting out their hydraulic oil consumption per hour. The substitutable amount of mineral by bio-based hydraulic oil is examined by an exemplary calculation for a construction project. The observations are intended to establish the working medium bio-based hydraulic oil on the lubricants market and to increase its use quantities, especially for mobile machines, with regard to environmental protection. Environmentally friendly lubricants and process materials are used in a wide variety of technical applications. In mobile machines in particular, efforts are being made to further establish bio-based lubricants. Due to unforeseeable accidents and leaks, a considerable amount of lubricants is released into the environment every year. This results in contamination of the affected environment. For this reason, contaminated ground, for example, has to be excavated refurbished after contact with hydraulic oil in order to return them to their original natural state. Bio-based hydraulic oils minimize this risk through their biodegradability and antitoxicity. Despite the proven performance of environmentally friendly hydraulic oil, the market share of biolubricants is stagnating at a constant and very low level. The majority of mobile machines use mineral oil, as working fluid in their hydraulic systems. To evaluate the substitution potential of mineral oil by bio-based oil in construction projects, various mobile machines are considered. In addition to widely used mobile machines like, for example excavators or wheel loaders, road construction equipment is also considered, due to a high hydraulic oil consumption resulting through heavy heat loads.

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.

This paper deals with design optimisation of hydraulic hybrid drivelines during early concept design phases. To set the design parameters of a hybrid driveline such as gear ratios, pump/motor displacements and size of energy storage, the energy management of the hybrid machine needs to be considered as well. This is problematic since a nested design and control optimisation normally requires substantial computer power and is time-consuming. Few previous studies have treated combined design and control optimisation of hydraulic hybrid vehicles using detailed, non-linear component driveline models. Furthermore, previously proposed design optimisation methods for on-road vehicles are not suitable for heavy off-road machines operating in short repetitive cycles with high transient power output. The paper demonstrates and compares different optimisation approaches for design and control optimisation combining deterministic dynamic programming and non-gradient based numerical optimisation. The results show that a simple rule-based energy management strategy can be sufficient to find the optimal hardware design even though non-optimal control laws are used.

As an effective approach to improving the fuel economy of modern heavy-duty vehicles, hydraulic hybrids have shown great advantages in off-road vehicles. Wheel loader is one of the representative vehicles in off-road applications as they are usually designed for single and repetitive task such as loading material. In a typical short loading cycle, there are many accelerations and decelerations, showing great hybridization potentials. Therefore in this paper a series hydraulic hybrid powertrain has been proposed for compact wheel loader since its hydrostatic powertrain can be easily transformed to a series hydraulic hybrid with an additional hydraulic accumulator. The modeling and system design of the series hydraulic hybrid wheel loader have been presented. Three controllers have been designed for vehicle speed control, engine torque control and engine speed control respectively. A dynamic simulation model has been developed in MATLAB/Simulink. A rule-based energy management strategy (EMS) has been proposed for the series hydraulic hybrid wheel loader. Two different EMS schemes were investigated and compared through simulation studies.

The development of a suitable traction control system for off-road heavy machinery is complicated by several different factors, which differentiate these machines from typical on-road systems. One such difficulty arises from the fact that they are often operated on ground conditions which can vary widely and rapidly. Due to this, traction control systems designed for these vehicles must be robust to a large array of surface types, and they must be capable of reacting quickly to significant changes in those types. In order to accomplish this, this paper proposes an online parameter optimization technique suitable for tuning the setpoint of a control system to maximize the tractive potential of a construction vehicle in real time. The traction control principle itself is based on selectively braking wheels which are slipping. It also attempts to account for the interactions of the transmission systems that deliver power from the engine to the wheels. This research uses a wheel loader as a reference machine for assessing controller performance. Drawing on previous work in simulation and controller design, a system model was developed which incorporates the vehicle dynamics of the machine as well as the behavior of the electrohydraulic brakes. This system model was leveraged to understand the effect of different optimization schemes on the performance of the traction control. The self-tuning algorithm is based on a compound optimization method utilizing both a system identification component and a parameter tuning component. The first part optimizes the model parameters to fit it as well as possible to measured slip-friction data. Based on the results of this, the second part draws from theories of wheel traction to maximize a balance of pushing force and traction effectiveness. The result is a method which can achieve the proper setpoint based on real-time data describing the ground condition. This system was run first in simulation and then on a modified vehicle system. In both cases, the algorithm allows the controller to find better setpoints to improve the traction control performance online.

Hydraulic hybrid powertrains, which can be applied to many types of vehicles including cars, have several important advantages over electric hybrids, such as lower costs, higher power density, and more regenerative energy available from braking. There have been various investigations for hydraulic hybrid architectures and there always exists room for improvement in terms of performance and efficiency. In order to achieve improved performance and efficiency, a novel hydraulic hybrid transmission architecture has recently been suggested in Maha Fluid Power Research Center, which is implemented in the platform of 1999 Range Rover. Previous studies of the Maha hydraulic hybrid vehicle (HHV) mainly focused on the optimization of system components and controller. In order to further study and optimize hydraulic hybrid architectures, the thermal behavior has to be considered as well. A few existing thermal studies on other hydraulic systems have mostly focused on steady state characteristics due to the difficulty of simulating the unsteady state conditions. In this paper, a novel approach to thermal modeling of HHV for a novel HHV architecture is presented. The results have been validated with the measured data collected while driving the vehicle. The thermal model utilizes the flow rate and pressure obtained from the hydraulic system model and calculates the system temperature at different locations. In order to capture the rapid transition of the hydraulic system in HHV, a novel simulation scheme considering the flow direction for the control volume inputs is applied in the presented study. In addition, the presented model considers compressible flow in order to improve the accuracy of the model.

Government regulations incentivize investigation of the potential for hybridization of non-road mobile machinery (NRMM). Many approaches to energy saving in hydraulic systems have been established. One of the methods first introduced in the aerospace industry is “decentralized” or “zonal” hydraulics. The decentralized system is realized with pump-controlled actuators, which are distributed throughout the system. In this research, decentralized hydraulics are realized with a direct-driven hydraulics (DDH) drive and implemented on a 1-ton class JCB micro excavator. The original valve-controlled system for boom, stick, and bucket is replaced with three DDH units. In a DDH unit, a double fixed displacement pump/motors with a speed-controlled electric servomotor directly controls the amount of hydraulic oil pumped into and out of the system. The hydraulic pump/motors create flows dependant on the rotating speed of the servomotor. A hydraulic accumulator is used as a conventional tank replacement. The aim of this paper is to investigate the efficiency improvement of the excavator with decentralized hydraulics compared to an electrified conventional load sensing system, from an energy consumption point of view under a typical digging cycle. In order to acquire the energy consumption distributions of the DDH and load sensing (LS) system, a model of the micro excavator which comprises mechanics, hydraulics, electronics, and control systems is developed in Matlab/Simulink. Simulation results demonstrate that the total efficiency of the excavator with LS control is 18.3%, and with DDH (decentralized hydraulics) is 71.3 % for a selected typical working cycle.

In this paper, the operational conditions of a new hydraulic/pneumatic system conception for medium and heavy-duty vehicles are evaluated. The design comprises a hydraulic system, coupled to a pneumatic system, with ability to recover braking energy in driving cycles characterized by frequent stop-and-go, and also on highways with small inclinations. In order to evaluate the potential of the hybrid system, the vehicle is subjected to a driving cycle, whose route is comprised in part by a road in the horizontal plane, and in part by a road with slope. A heuristic control strategy is presented, whose approach is based on a mathematical model built in platform-MATLAB/SIMULINK and supported by maps of performance and efficiency and physical parameters of the components. The control strategy provides five operating modes for the vehicle in order to meet the different traffic conditions, in accordance with the driving cycle analyzed. As the trip occurs, is required the hybrid system supply the pneumatic auxiliaries of the vehicle employing the regenerated energy stored in the accumulators preferably, or the power generated from internal combustion engine when the accumulators are empty. The simulating results prove the effectiveness of the control strategy to command the hybrid system properly, as well as the ability of the vehicle to achieve the requirements of performance and maintaining a high overall efficiency of the engine.

Remote operation of hydraulic non-road mobile machinery (NRMM) is becoming more and more common. The remote operation has plenty of advantages in many applications. However, a significant drawback of remote operation is that the level of sensory feedback for operator is weaker compared to onboard operation. The lack of the sense of touch is decreasing the working efficiency and can lead to premature wear out of machine components. This can also lower the safety of the operation. In this work a haptic joystick controller for controlling NRMM is introduced. The haptic joystick is able to feedback constant forces and wide range of vibrations for operators. The haptic feedback force is calculated based on the sensor signals from the working machine. This paper introduces a setup for remote operation of a wheel loader. The control of the lift and tilt cylinders of the bucket is taking advantage of haptic feedback. The experimental study is carried out in a virtual environment. A multibody dynamic model of the wheel loader is run in real-time to study the effects of haptic feedback for the remote operation. Results of the remote operation with and without haptic feedback are compared. The comparison shows that the haptic feedback clearly affects on the force levels and the loads of the boom structure of the remote operated wheel loader. Taking advantage of haptic feedback in controllers of remote operated NRMM increases the operator’s understanding about the dynamic behavior of the machinery significantly. The results encourages to carry out further studies on improving the human-machine-interfaces (HMI) of remote operated hydraulic NRMM using haptic feedback.

Several types of off-road machinery, such as industrial trucks, forklifts, excavators, mobile cranes, and wheel loaders, are set to be operated in environments which can differ considerably from each other. This sets certain limits for both the drive transmissions and working hydraulics of these machines. The ambient temperature must be taken into account when selecting the hydraulic fluid since the viscosity and density of the fluid are changing at different operating temperatures. In addition to the temperature, energy efficiency can also be a problem in off-road machinery. In most off-road machines, diesel engines are employed to produce mechanical energy. However, there are energy losses during the working process, which causes inefficiency in produced energy. For better energy efficiency, hybridization in off-road machinery is an effective method to decrease fuel consumption and increase energy savings. One of the possible methods to save energy with hybrids is energy regeneration. However, it means that the basic hydraulic system inside off-road machinery needs to be modified. One solution for this is to utilize zonal or decentralized approach by means of direct driven hydraulic (DDH) system. This paper aims to investigate a DDH system for off-road machinery by means of modelling and analyzing the effect of the temperature. In the direct-driven hydraulic system, the actuator is controlled directly by the hydraulic pump which is operated by the electric motor. Specifically, it is a valveless closed-loop hydraulic system. Thus, there will be no energy losses caused by the valves, and the total efficiency is assumed to be significantly higher. In order to examine the DDH system, a thermo-hydraulic model was created. Additionally, a thermal camera was utilized in order to illustrate the temperature changes in the components of the DDH system. To reproduce the action of the system in different circumstances DDH system was run at different ambient temperatures, and the component temperatures in the system were measured and saved for the analysis. The thermo hydraulic model was proven capable to follow the general trend of heating up.

The focus of this paper is the biphasic phenomena that occurs in a lubrication system of a CVT gearbox transmission of an agricultural tractor, in particular a Method of Analysis is outlined with the aim of mapping and assessing the behavior of the lubrication circuit. The study of the lubrication in gearboxes is an important issue in the design of off-road machines because their reliability depends mostly on the lubrication performance, as well as the machine’s lifetime and overall energy efficiency of the transmission is strongly dependent on the lubrication system behavior. In fact the role of the lubrication system is twofold: firstly to remove the heat generated in the highly loaded rolling bearings and the gears found in the power and accessory gearboxes via heat exchangers; secondly to lubricate these parts. The trend in the development of gearbox transmissions has been towards lower consumption and higher power transmitted, consequently it is necessary to conceive more effective and efficient lubrication systems. Nonetheless the lubrication problem often relies on a trial and error approach and most available scientific literature is based on lumped element model dynamic simulation or one phase thermo-fluid dynamic simulations, overlooking the effects linked to cavitation and air inclusion. One important phenomenon in lubrication systems is that of air suction. This can be seen in particular at high rotational speeds of shafts when the centrifugal force causes a positive pressure drop between inner lubrication pipes and outer radial conduits. In this case the air occupies part of the lubrication conduits, and since the domain is shared by the outflowing liquid phase and the air included, the monophase CFD simulation fails to predict the correct lubrication flow. If this effect is not carefully considered it could cause a lubrication unbalance among the various parts of the gearbox, creating a risk of transmission damage. In this paper the methodology will be presented step by step until in final a complete map of operation condition is created. A preliminary analysis of the circuitry is an essential phase of the project since the tractor’s transmission is an extremely complex assembly composed by hundreds of components therefore the lubrication circuit appears as a large net of moving hydraulic connections and consumers. From this analysis a computational domain is obtained and appropriately meshed. After the pivotal choice of the proper turbulence model and boundary conditions, various runs at different rotating speeds corresponding to the different operating ranges will be performed. The result will be contextualized by commenting on the fluid dynamics phenomena involved and the influence parameters on flow rate distribution, finally evaluating the performances of the lubrication circuit, and in particular highlighting the most critical conditions in terms of speed condition and locating the most critical gearbox parts.

The reliable and repeatable experimental testing of automotive components is a challenge, especially when human occupants are involved. In most circumstances full vehicle testing over a range of road conditions is used even though this is expensive, difficult and time-consuming. In this work an experimental platform that compensates for the vehicle motion using the principle of hardware-in-the-loop (HIL) simulation is developed using a multi-axis simulation table (MAST) available in the Center for Power Transmission and Motion Control (PTMC) laboratory at the University of Bath. The MAST was tested in both the time and frequency domains with a range of road profiles including a random and single bump in the low frequency range (0.5–25 Hz). Also, uncertainties in the vehicle suspension characteristics such as the damping coefficient, the stiffness rate and the vehicle mass are examined. The experimental results in the frequency and time domain show that the MAST can be used to reproduce the dynamic characteristics of a quarter vehicle model with an excellent degree of agreement with the simulated response.

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.

The improvement of the energy efficiency is an important topic for non-road mobile machinery developers and manufacturers. These machines normally use fluid power transmission in drivelines and working actuators. New energy efficient technologies, e.g. a hybrid power transmission with an energy recovery feature, have been introduced. Currently most of the manufacturers are still using conventional technologies in their product development process. Human operators have an effect on the overall efficiency of the machines. Taking into account the human effects is difficult and expensive using the conventional design processes and tools. The objective of this study is to provide international machine manufacturers instrumental, yet novel, community and simulation-based (ICT-enabled) tools/methods for the strategic and cost effective development of their product practices and design processes. The development of models and methods will allow for rapid real-time virtual prototyping of complex machines and machine fleets that operate within a number of worksites or geographical conditions. The introduction of this state-of-the art (and going beyond) advancement in real-time virtual technology, simulation, internet based design technologies and software, cyber-physical and big data processing systems, will present a holistic approach to improve the entire product life. Targeted user groups are manufacturers of non-road mobile machinery (i.e. excavators, wheel loaders, etc.). These machines and production systems share the following key features: 1) They are complex mechatronic systems with several interconnections between hydraulic drives; mechanics, electronics, software and 2) they include autonomous, semiautonomous and human driven operated systems. Methods developed will enable machine manufacturers’ access to technologies that will lead to a more cost effective consumer ordinated, life cycle optimization process. This paper will introduce the method of developing customized products in a fast, agile and networked way that will lead to significantly reduced life-cycle costs.

In the past few years, direct-driven hydraulic drive (DDH) has synthesized the advantages of compact high power of the hydraulic system and flexible control of the electric motor. This paper investigates the direct-driven hydraulic setup for the non-road mobile machinery (NRMM) application. In the proposed setup, the speed and position control of a double-acting cylinder is implemented directly with a Synchronous Torque Motor drive in a close-loop system without conventional control valves and oil tank. In relation to this, hydraulic accumulator is employed as a replacement of the conventional oil tank. For position and speed control of this closed-loop system, only single feedback is applied from motor’s rotor encoder. As a result, excellent control capabilities of a modern electric drive brings along safety functions and monitoring capabilities of the motor and controller to benefit the hydraulic system. Functionalities of motor controllers offer opportunities to duplicate conventional sensors based on either safety or reliability demands. The system is investigated by means of measurements and also simulation models.

Hydraulic hybrid transmissions have demonstrated considerable potential in improving the fuel economy of on-road and off-highway vehicles. The authors have previously proposed a novel hydraulic hybrid transmission architecture termed the Blended Hybrid with benefits in efficiency and performance over existing systems. Recently an optimally controlled simulation study found that a blended hybrid power split transmission consumed 16% less energy than an equivalent series hybrid power split transmission over the US standard Urban Dynamometer Driving Schedule. To further explore this novel architecture the authors constructed a hardware-in-the-loop transmission test rig. In this paper the authors detail the construction, control, and measurements results of the blended hybrid on this test rig.