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.

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.

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.

Cavitation erosion is a serious problem in the hydraulic system of construction machinery. In particular, the erosion which occurs even when cavitation bubbles only pass through oil passages, occurs at a connecting portion between the hydraulic components and piping, and the erosion causes oil leakage, which is a serious problem for hydraulic systems. However, it is difficult to predict the eroded area and to prevent the erosion because of a lack of research findings. The present study investigated erosion in the portion through which cavitation bubbles passes using a basic experimental apparatus that simulates an oil passage of hydraulic components, and by conducting a computational fluid dynamics simulation. The following results were obtained. Erosion occurs near the outlet of the oil passage, cavitation bubbles frequently disappear rapidly near the area of erosion, and the cause of bubble disappearance is the pressure distribution and amplification of the pressure wave of cavitation jets at the outlet of the oil passage. These results help explain the erosion generation mechanism and the characteristics of erosion in oil passages of hydraulic components, and can be used to design methods of reducing erosion.

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.

Oil is the main working fluid used in the hydraulics industry today — but water is nonflammable, environmentally friendly and cheap: it is the better choice of working fluid for hydraulic systems. However, there is one caveat. Water’s extremely low viscosity undermines its ability to carry load. In forest machinery, construction machinery, and aircraft systems, today’s hydraulic circuits have high operating pressures, with typical values between 300 and 420 bar. These high pressures create the need for high load-carrying abilities in the fluid films of the tribological interfaces of pumps and motors. The most challenging of these interfaces is the piston-cylinder interface of swashplate type piston machines, because the fluid must balance the entire piston side load created in this design. The low viscosity of the water turns preventing metal-to-metal contact into quite a challenge. Fortunately, an understanding of how pressure builds and shifts about in these piston-cylinder lubrication interfaces, coupled with some clever micro surface shaping, can allow engineers to drastically increase the load-carrying ability of water. As part of this research, numerous different micro surface shaping design ideas have been simulated using a highly advanced non-isothermal multi-physics model developed at the Maha Fluid Power Research Center. The model calculates leakage, power losses, film thickness and pressure buildup in the piston-cylinder interface over the course of one shaft revolution. The results allow for the comparison of different surface shapes, such as axial sine waves along the piston, or a barrel-shaped piston profile. This paper elucidates the effect of those surface profiles on pressure buildup, leakage, and torque loss in the piston-cylinder interface of an axial piston pump running at high pressure with water as the lubricant.

This research presents method for the online estimation and prediction of drive forces in heavy duty vehicles. The estimation is based on the measured velocity and longitudinal dynamics. The same method can be applied for the prediction but the reference velocity is given as the input of the system instead of actual velocity. The prediction and estimation of drive forces are essential when optimizing the fuel consumption or emission. Especially, the control of the diesel engine requires information about loading torque for the prevent stalling of engine and guarantee rapid reaction of the machine.