In this paper, a simulation study is carried out for the development of concepts to optimize the tribological contact of valve plate and cylinder block in an axial piston machine in swash plate design. The valve plate/cylinder block contact is one of the three essential tribological contacts in axial piston machines. In a research project at the Institute for Fluid Power Drives and Systems (ifas), this contact is investigated by a specifically designed simulation tool. In addition, a test rig exists for the experimental investigation. With the results of simulation and experiment, it was shown before that the cylinder block is tilting to the high pressure side. Due to this movement, the gap height is not constant. In the area of minimum gap height, not only the fluid friction, but also the danger of solid body friction increases. Because of the higher friction losses in the area of minimum gap height, the temperature increase reduces the lifetime of the leaded coatings. In this paper, the results of the measurements as well as the simulation model are briefly summarized. It is followed by a simulation study of different possibilities to raise the gap height. Based on this pre-study, a first concept for the optimization of the tribological contact valve plate/cylinder block is presented and its applicability is discussed.

This paper discusses an investigation on a novel hydraulic pump concept. The idea aims on a pump principle to be directly connected to high-speed electric motors to build compact high-pressure drives. The pump can theoretically work without solid contact and has no kinematic pulsation. The composition of the pump is basically similar to cylindrical journal bearings. In general, a journal bearing is used to support external loads on a rotating shaft. When the shaft rotates with the loads, hydrodynamic fluid force is generated in the fluid film, which compensates the external force and reduces an eccentricity of the shaft. The difference of the introduced pump concept from the bearing is that the eccentricity is fixed and it has an outlet port at the high pressure area, through which the fluid can be transferred. To examine the functionality of the pump, a test bench is constructed and experiments are performed to investigate the pressure build-up and discharging flow of the pump concept. The experimental results are numerically analyzed by using elasto-hydrodynamic lubrication (EHL) simulation, based on the 2D Reynold’s equation. From these results, the functionality of the pump concept is confirmed. Moreover, several variables that influence the characteristic curve of the pump are studied. Based on these results, geometric parameters of the test pump are redesigned to discharge sufficient flow rate for usage as commercial pumps.

The combination of hydrostatics and mechanical gearboxes cannot only improve system efficiency but also the usability of mobile machines. A possible solution could be a synchronized gearbox with two gears. Compared to the pure hydrostatic drivetrain, mobile machines with such a combination can have a larger drive torque with the first gear and higher efficiency at high speed. However, the calibration effort of this traditional drivetrain system is enormous; moreover, with a flow-based control, the degrees of freedom to achieve optimum shift performance in all conditions are limited. By adopting the primary torque control concept, we propose a novel hydrostatic-mechanical drivetrain control algorithm so that the holistic shift performance is better whilst the calibration effort is dramatically reduced by systematically adjusting only one hyper-parameter. Experienced engineers and machine operators validated the advantages mentioned here by a series of field experiments. Besides synchronized gearboxes, the controller proposed in this paper is also generalized to other kinds of mechanical transmissions.

This paper presents an active component damage reducing control approach for driving manoeuvres of a wheel loader. For this purpose, the front and rear axle loads will be manipulated by force pulses induced into the machine chassis via the lifting cylinders of the function drive. The associated control approach is based on the principles of Reinforcement Learning. The essential advantage of such methods against linear control approaches is that no descriptive system properties are required, but the algorithm automatically determines the system behaviour. Due to the high number of necessary training runs, the algorithm is designed and taught using a validated wheel loader simulation model. After over 850 training runs, an optimal strategy for damping the axle loads could not yet be determined. In spite of the unprecedented convergence, initial improvements of the damage values have already been achieved on tracks that deviate from the training track. Some of these results show a 4.9 % lower component damage compared to a machine setting with no damping system. The results and limits of this strategy are discussed due to a comparison with other scientific active vibration damping approaches. Currently, a linear control method (P-PI-controller) has a higher damage reduction potential, but it is expected that further training runs and another learning algorithm could make the reinforcement learning approach even more effective. Coupling the linear control method with the selflearning approach shows the highest potential for the axle damage reduction.

This article describes the Dana intelligent Twin Steering System designed for mobile vehicles with two steering axles (i.e. with four steering wheels). Current vehicles with four-wheel steering function are typically equipped with a hydraulic configuration where the two steering cylinders are connected in series. This type of connection highlights some limitations on available power, steering comfort and enabling advanced working functions. Dana evolved this type of hydraulic configuration introducing the possibility to disconnect the rear axle from the front one. In this way the rear axle, through the electronic control of its valve block, allows to improve the steering system performance and introduces advanced steering functions compared to the conventional steering systems.

Automation of mobile construction and agricultural equipment has gained wide acceptance based on increases in productivity, safety, and precision; while also helping upskill operators. On construction equipment, after-market automation of earthmoving crawler dozers and graders has driven a conversion of machines to electro-hydraulic (EH) implement control and integration into digital worksites. Unlike the aforementioned machines, conversion of the excavator into a semi or fully autonomous machine presents significant challenges due to kinematics, variable loads, non-linear multi-function of implements, safety, and robustness. The present work demonstrates the retrofit of a pilot-operated 21-ton excavator and development of automated controls to address these challenges. The operator pilot joysticks and existing hydraulic system were retained, while adding capability for autonomous functionality with integrated hardware, controls, and kinematic solvers within a production viable environment. Autonomous features for path planning, multi-function actuator velocity control, EH controls, and safety were developed to prove the value of precise and low latency control hardware for EH excavator operation.

In this paper, electrification of hydraulic systems is proposed using high-efficiency permanent magnet (PM) motors and wide bandgap power electronic drives. Direct driven hydraulics (DDH) is selected because of its higher efficiency compared to other conventional technologies such as valve-controlled systems. The DDH is directly driven by a servomotor. The ratings and design guidelines for a servomotor used in DDH applications are provided in this paper. Specifically, a surface permanent magnet synchronous machine (SPMSM) is designed. Finally, a state-of-the-art inverter using silicon carbide wide bandgap devices are designed for high performance operation.

There is a lot of gravitational potential energy waste when hydraulic excavators work, which seriously affects the efficiency of the whole machine and produces a large amount of emissions. In order to reduce the energy consumption and emissions of large hydraulic excavators which the boom is driven by two hydraulic cylinders, an integrated drive and potential energy recuperation principle is proposed. In the implementation, the original two-chamber hydraulic cylinders are replaced by three-chamber hydraulic cylinders with energy storage chambers, and the energy storage chambers are directly connected with the hydraulic accumulator. The dead weight of the working device is balanced by the initial hydraulic pressure of the hydraulic accumulator, and the gravitational potential energy is directly recuperated. A digital prototype is established for the simulation work to verify the energy-saving effect. Then a test prototype is constructed according to the simulation work. The standard 90° loading duty cycle tests show that compared with the standard hydraulic excavators of the same type, in the case of meeting the same digging force, the working efficiency of the excavator increases by 20.7% and the fuel consumption decreases by 17.1%. In terms of 8 hours of work per day, a single excavator can save fuel up to 47 L per day and reduce carbon dioxide emissions by 123.6 kg.

In contrast to constant operating states, particle and NOx emissions of internal combustion engines are significantly higher during transient operating states, which occur repeatedly at working cycles of mobile machines. This paper therefore deals with the conception, development and testing of hydraulic hybrid systems to reduce these emissions by phlegmatization of the engine. A wheel loader with its machine-typical working cycle serves as an example for the investigation of the benefits of such a system. Therefore, model based development techniques are used. In a holistic machine simulation, four different typical wheel loader cycles were carried out and the optimum size of the hydraulic accumulator for the hybrid system is identified by a parameter variation. The lowest emitted emissions and the smallest construction dimensions are the key elements for the accumulator selection. With an optimal hydraulic accumulator, a reduction in particle emissions of up to 29.4 % is achieved in one of the cycles investigated.

Pressure oscillation in hydrostatic drive trains can cause noise and damage to components. They impair function and reliability. The visualization of the oscillation mode helps to clarify the causal relationships in the hydrostatic drive train and is a basis for the development of remedial measures. Analysis of the pressure oscillation situation, however, can only be carried out in the complete system, since line branching and the impedance of the hydrostats have an influence on the resonance frequencies and the oscillation modes. If only the line length between the components is considered in the pressure oscillation analysis, neither the calculated frequencies nor the position of the pressure antinodes where possible remedial measures are to be placed are correct. This paper presents the metrological determination of the impedance of a hydrostat on a functional test bench (“mobile impedance measurement”) and the preparation of the measurement data for the subsequent simulative pressure oscillation analysis of a hydraulic drive train.