Noah D. Manring

Modeling and Designing a Variable-Displacement Open-Loop Pump

This study develops closed-form equations that may be used to guide the up-front design of a variable-displacement pump. In particular, the initial design of the control actuation system and the controller flow-gain is considered. A dynamic model of the pumping system is also presented and the dynamic effect of parameter variations such as actuator volume, discharge-hose volume, controller flow-gain and system leakage is discussed.

The Discharge Flow Ripple of an Axial-Piston Swash-Plate Type Hydrostatic Pump

This research examines the idealized and actual flow-ripple of an axial-piston swash-plate type hydrostatic pump. For the idealized case, a perfect pump is examined in which the leakage is considered to be zero and the fluid is considered to be incompressible. Based upon these assumptions, closed-form expressions which describe the characteristics of the idealized flow-ripple are derived. Both the ripple height and the pulse frequency of the ripple are described for a pump with an even and an odd number of pistons. Next, the actual flow-ripple of the pump is examined by considering the pump leakage and the fluid compressibility and for computing these results a numerical program is used. For both the idealized case and the actual case-a comparison is made between a nine-piston, an eight-piston, and a seven-piston pump. From the idealized analysis it is quantitatively shown that the eight-piston design is less attractive than the nine or seven-piston design; however, the analysis of the actual pump flow reveals that the qualitative difference between all three designs may not be too significant. From a flow ripple point of view, the numerical results of this research show that a pump designed with an even number of pistons may be as feasible as one that is designed with an odd number of pistons. This is an unexpected conclusion.

Valve-Plate Design for an Axial Piston Pump Operating at Low Displacements

The objectives of this research are to investigate the principal advantages of using various valve-plate slot geometries within an axial piston pump. In particular, three types of geometries are considered: a constant area slot geometry, a linearly varying slot geometry, and a quadratically varying slot geometry. By analyzing the pressure transients that are associated with each design at low pump displacements, it is shown that the magnitude of the pressure transition itself and the maximum pressure time rate-of-change may be specified for each design. In conclusion, it is shown that the constant area slot design exhibits the principal advantage of minimizing the required discharge area of the slot, the linearly varying slot design exhibits the principal advantage of utilizing the shortest slot length, while the quadratically varying slot design exhibits no principal advantage over either of the other two designs. The results of this research suggest that the use of quadratically varying slot geometry is not justified since it offers no obvious performance improvement.

The control and containment forces on the swash plate of an axial-piston pump

In this research, the control and containment forces and moments acting on the swash plate of an axial-piston pump are examined. From a practical standpoint, swash plate control and containment devices take on many different designs; however, they must all resist the same essential moments and forces that attempt to dislocate the swash plate from its proper position. By considering the basic machine design without its control and containment mechanisms, this work generally derives the needed forces and moments for insuring proper swash-plate motion and thereby gives the designer of these machines a useful tool for designing control and containment devices of any type. The success of the actual control and containment devices will be measured by how well they exert the proper forces and moments on the swash plate which are presented here.

The Control Torque on the Swash Plate of an Axial-Piston Pump Utilizing Piston-Bore Springs

This research begins by presenting a nontraditional pump design which utilizes a pistonbore spring. The piston-bore spring is included in this design for the purpose of holding the cylinder block against the valve plate and for forcing the pistons in the negative x-direction. By forcing the pistons in this direction, the piston-bore spring also assists in holding the slippers against the swash plate during the normal operation of the pump. Though these advantages of the design may be readily seen by inspection, it is not obvious how the control torque on the swash plate is effected by the piston-bore spring nor is it obvious how one would go about designing the spring to produce a favorable result. To clarify the benefit of this design, a mechanical analysis is conducted to describe the effect of the spring on the control torque itself. As a result of this analysis, a general equation which describes the swash-plate motion is presented. Within this equation, it may be seen that the spring force provides a restoring force on the swash plate which tends to stabilize the design. The piston-bore spring is also shown to be capable of eliminating the crossover from a stroke increasing swash-plate torque to a stroke decreasing swash-plate torque. By eliminating this cross over, the backlash in the pump control (which is commonly observed in practice) can be prevented. @DOI: 10.1115/1.1386654#

Tipping the Cylinder Block of an Axial-Piston Swash-Plate Type Hydrostatic Machine

Tipping the cylinder block within an axial-piston swash-plate type hydrostatic machine is a phenomenon that results in a momentary and sometimes permanent failure of the machine since the fluid communication between the cylinder block and the valve plate is instantaneously lost. The efforts of this research are to identify the physical contributors of this phenomenon and to specify certain design guidelines that may be used to prevent the failure of cylinder block tipping. This research begins with the mechanical analysis of the machine and presents a tipping criterion based upon the centroidal location of the force reaction between the cylinder block and the valve plate. This analysis is followed by the derivation of the effective pressurized area within a single piston bore and the cylinder block balance is defined based upon this result. Using standard control volume analysis, the pressure within a single piston bore is examined and it is shown that an approximate pressure profile may be used in place of the more complex representation for this same quantity. Based upon the approximate pressure profile a design criterion is presented which ensures that the pressures within the system never cause the cylinder block to tip. Furthermore, if this criterion is satisfied, it is shown that the worst tipping conditions exist when the system pressures are zero and therefore a criterion governing the design of the cylinder block spring is presented based upon the inertial forces that contribute to the tipping failure.

The Effective Fluid Bulk-Modulus Within a Hydrostatic Transmission

In this study, the fluid bulk-modulus within a hydrostatic transmission is examined. Specifically, a method for measuring the effective fluid bulk-modulus is proposed based upon the definition of the fluid bulk-modulus and the conservation of mass within the system. Using the measured parameters of flow and pressure, a numerical solution for the effective fluid bulk-modulus is carried out and a closed-form approximation to this solution is presented. Furthermore, the accuracy expectations of this method are discussed and compared with traditional methods of estimating the fluid bulk-modulus and it is shown that significant improvements can be made when the method of this research is employed.

Experimental Studies on the Performance of Slipper Bearings Within Axial-Piston Pumps

The objectives of this study are to experimentally investigate the performance characteristics of similar slipper bearings using different socket geometries. In this study, the lubrication equations for the bearing are derived based upon an assumption that the bearing deformations are small and that they may be modeled linearly. This study is based upon the hypothesis that variations in the socket geometry will impact the deformation characteristics of the bearing and thereby have an effect on the overall performance of the design. To test this hypothesis, bearings with different socket geometries are designed and tested and compared to the original bearing design with standard socket geometry. The experimental results are then used with the analytical results to numerically infer the minimum fluid-film thickness and the magnitude of deformation for the bearing. Conclusions are drawn from these results which indicate that socket geometry has a significant impact on the bearing performance and that both leakage and load-carrying capacity may be altered by adjusting the location of the contact point within the ball-and-socket joint relative to the center of the ball. @DOI: 10.1115/1.1698936#

Translating circular thrust bearings

Thrust bearings have been the object of a considerable amount of research for many years. The attention that these bearings have received is primarily due to the important role they play in the design and operation of heavy equipment. The objectives of this work are to examine the effect of translation and bearing geometry, such as recess depth and width, on the performance of circular thrust bearings. A closed-form solution is obtained for laminar viscous flow that extends prior results which generally focus on stationary or hydrostatic bearings. Earlier studies have examined specific aspects of translation, such as recirculation in the recess, but the current study is a comprehensive analysis in the case of laminar flow. The analysis reveals a single dimensionless parameter that describes the influence of the bearing speed. Expressions that predict the load-carrying capacity of the bearing, the tilting moment exerted on the bearing, the volumetric leakage of the bearing, and power due to lubricant injection and translation are obtained. Streamline patterns under the bearing show conditions at higher speeds when the injected lubricant does not penetrate underneath the entire bearing surface.

The impact of linear deformations on stationary hydrostatic thrust bearings

In this work, the operating sensitivity of the hydrostatic thrust bearing with respect to pressure-induced deformations will be studied in a stationary setting. Using the classical lubrication equations for low Reynolds number flow, closed-form expressions are generated for describing the pressure distribution, the flow rate, and the load carrying capacity of the bearing. These expressions are developed to consider deformations of the bearing that result in either concave or convex shapes relative to a flat thrust surface. The impact of both shapes is compared, and the sensitivity of the flow rate and the load carrying capacity of the bearing with respect to the magnitude of the deformation is discussed. In , it is shown that all deformations increase the flow rate of the bearing and that concave deformations increase the load carrying capacity while convex deformations decrease this same quantity relative to a non-deformed bearing condition.