Characteristics of Hydraulic and Electric Servo Motors

Until the 1970s, hydraulic actuators were widely used in many mechanical systems; however, recently, electric motors have become mainstream by virtue of their improved performance, and hydraulic motors have largely been replaced by electric motors in many applications. Although this trend is expected to continue into the future, it is important to comprehensively evaluate which motor is most suitable when designing mechanical systems. This paper presents the results of a survey of the performance of electric and hydraulic servo motors and aims to provide quantitative data that can be used as a reference for selecting appropriate motors. We surveyed AC, AC direct, brushless DC, and brushed DC electric motors and swash plate-type axial piston, bent axis-type axial piston, crank-type radial piston, and multistroke-type radial piston hydraulic motors. Performance data were collected from catalogs and nonpublic data. We compared and evaluated the characteristics of these diverse servo motors using indexes such as torque, rotating speed, output power, power density, and power rate.

Influence of Fluid Compressibility and Movements of the Swash Plate Axis of Rotation on the Volumetric Efficiency of Axial Piston Pumps

This paper describes the design of a swash plate axial piston pump and the theoretical models describing the bulk modulus of aerated and non-aerated fluids. The dead space volume is defined and the influence of this volume and the fluid compressibility on the volumetric efficiency of the pump is considered. A displacement of the swash plate rotation axis is proposed to reduce the dead space volume for small swash plate swing angles. A prototype design of a pump with a displaced axis of rotation of a swash plate with two directions of delivery is presented, in which the capacity is changed by means of a valve follow-up mechanism. Comparative results for a pump with a displaced and a non-displaced swash plate rotation axis are presented, which confirm that displacement of the swash plate rotation axis causes an increase in volumetric efficiency that is apparent for high pressure discharge and small swash plate angles. The determined characteristics were compared with a mathematical model taking into account the compressibility of the fluid in the dead space volume and a satisfactory consistency was obtained.

Failure analysis of excavator hydraulic pump

Hydraulic pump failures may be related to hardware or problem in oil. In this study, the excavator hydraulic pump failures were investigated by using visual observed and measuring the part component. The disassembled process of the pump was performed considering the manual part book of the excavator hydraulic pump. The abrasive wear on the pump slipper and swash plate was observed by comparing the guidelines for the reusable part. The value of more than 1.07 mm clearance within piston and cylinder bore was measured then the results over the allowable limit considering the manual part book. Properly analyzing of component failure can provide valuable information about what caused the failure and thus can be to avoiding future unscheduled downtime.

Investigating the Condition Monitoring Potential of Oil Conductivity for Wear Identification in Electro Hydrostatic Actuators

To meet future goals of more electric airplanes conventional hydraulic airplane control systems, consisting of redundant centralized pumps within the airplane’s fuselage, need to be substituted for compact electro-hydraulic actuators (EHA). The capsulated architecture of EHAs results in higher safety due to separate hydraulic circuits, simple practicability of redundancy, decreased maintenance because of simplified error location detection as well as an overall reduction in weight and complexity of the airplane control system. Currently, EHAs are only used as backup devices as the reliability does not achieve normative requirements for a frontline application. Thus, recent studies aim to increase the reliability. The axial piston pump of current EHA is the source of most failures. High dynamic requirements and challenging operation points and environments result in wear of contact pairs such as swash plate/piston shoes, pistons/cylinder block and cylinder block/valve plate. In the scope of the project MODULAR at ifas one goal is to increase the robustness of the contact surfaces. A second goal addresses the topic of developing a condition monitoring approach to constantly track the pumps’ health status. Next to signals such as pressures and temperatures, acceleration and oil status signals describing the actual particle contamination are needed. In this contribution different methods of oil status detection are explained and the method of electric conductivity analysis for condition monitoring is further investigated. Filtered HLP46 is used and impurities in form of metallic powders are added. Furthermore, degraded oil of a disc-on-disc Tribometer test bench is measured and compared.

Modelling of the Cross Angle and its Impact on Pump Performance

A secondary swash plate angle, also known as a cross angle, has been used in the past to reduce flow ripple with great success. However, for the past two decades, research in this field has been scarce. In this paper, a pressure controlled 9-piston pump is investigated to determine the effects of the cross angle on commutation, acting forces and torques, as well as volumetric flow rate pulsations. A detailed description of the piston kinematics, the simulation model used, and the subsequent simulation results are presented in this contribution.

A New Approach for Modeling Mixed Lubricated Piston-Cylinder Pairs of Variable Lengths in Swash-Plate Axial Piston Pumps

The swash-plate axial piston pump is one of the most widely used pumps due to its simplicity and compactness in structure. In such a pump, the piston-cylinder system plays a crucial role, with its lubrication characteristics greatly affecting the overall pumping performance. A new numerical approach is proposed in this study for modeling mixed lubricated piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps in the framework of multibody dynamics. The approach couples the hydrodynamic mixed lubrication model of the piston-cylinder interface with the multibody dynamics model of the piston pump. The lubrication model is established with a transient average Reynolds equation considering asperity contacts and is solved with the finite element method to derive the hydrodynamic forces of the lubricated pair, while the multibody dynamics model is established with Lagrangian formalism by considering hydrodynamic forces as external forces. Results for piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps are presented, and the impacts of cylinder length and the tilt angle of the swash plate on the tribological performances of the interface are discussed. The results indicate that increasing the cylinder length can improve the stability and wear resistance of the piston, but it can exacerbate the frictional power loss. Moreover, although enlarging the tilt angle of the swash plate can effectively increase pump displacement, it can easily lead to serious friction, wear, and leakage problems. Consequently, the tilt angle of the swash plate should be carefully selected in practical applications.

Evaluation of Muscle Activity and Human Standing Stability Index Using the Swash Plate in a Disturbance Application

Human standing stability was evaluated using a swash plate drop device in a disturbance application. Under different experimental conditions using the device, electromyogram (EMG) measurements showed that the left and right lower limb muscles were used differently. It also demonstrated that the dynamics also differed depending on the experimental conditions. In particular, the dynamics of standing stabilization in a tandem standing position and a normal standing position significantly differed, and the activities of related muscles were also significantly different; this indicates that standing stability may potentially depend on the subjects. These results indicate the need for the comprehensive consideration of the standing and disturbance conditions during the quantitative evaluation of human standing stability.

Calculation of the actuator system in swash plate axial piston machines by a coupled multibody and TEHL simulation

This paper presents a method for coupling a multibody simulation for the actuator system in axial piston machines in combination with a transient, three-dimensional, thermal elastohydrodynamic contact calculation. For the tribological investigation, the oscillating piston/cylinder contact is focused, whereby a simplified model of the actuator system simulates the loads. The developed method allows the integration of a complex tribological contact simulation under mixed friction conditions into a dynamic multibody simulation based on the Newton–Euler method. It is discussed how the accuracy of the results and the calculation time can be improved by the procedure.