Experimental Investigation of a Hydrostatic Bearing Between Barrels and Port Plates in Floating Cup Axial Piston Pumps

Abstract

Hydrostatic machines often have multiple hydrodynamic bearing interfaces, which also serve as a sealing interface. In axial piston machines, the bearing and sealing interface between the barrel and the port plate is a well known example. At reasonably high operating speeds, hydrodynamic effects create an oil film between the barrel and the port plate. This oil film will then, to a certain extend, lift the barrel from the port plate, thereby avoiding metal-to-metal contact. The disadvantage of hydrodynamic bearings is, that they need a relatively high velocity of the sliding components, in order to reduce the friction. Below a certain speed, mixed lubrication and finally solid friction will occur. This results in strongly increased friction losses and wear. Low speed operation has always been of interest for hydrostatic motors, which are often operated at close to zero speed or at low rotational speeds. But low and near zero speed operation has also become of importance for pumps when being operated in electro-hydraulic actuators (EHAs). Many of the existing pump principles are not allowed to be operated below a certain minimum speed, due to excessive wear which results from coulomb friction conditions. Furthermore, the stick-slip-behaviour creates additional nonlinear behaviour of the EHA-operation, and makes it difficult to control EHAs. In order to overcome the disadvantages of hydrodynamic bearings, a new hydrostatic bearing has been developed [1]. In the new bearing, the sealing land of the barrel is divided into three concentric rings. In the middle ring, so called pockets are created. Each pocket has a direct connection with the corresponding port by means of a small groove. The new bearing not only lifts the barrel to a certain height, but also helps to counteract the tilting torque of the barrel. The size of the pocket grooves determines the height of the oil film, and therefore also the leakage and viscous friction of the bearing and sealing interface. In a recent research project, INNAS has performed a number of experiments to measure the influence of the groove size on the overall efficiency, as well as on the leakage and torque loss. Measurements have been performed on a 24 cc floating cup pump in a speed range between 500 and 4000 rpm and a pressure range between 100 and 400 bar. At the end of the project, the range has been extended to a speed range between 0.23 and 4400 rpm, and a pressure range between 50 and 450 bar. This paper describes some of the results of these experiments. The measured width of the pocket grooves is taken as a characteristic parameter for the size of the flow area and resistance of the pocket grooves.

Experimental Investigation of New Design Concepts for the Tribological Contact between the Valve Plate and the Cylinder Block in Axial Piston Machines

“…He develops an operating point dependent control and could prevent the tilting for all investigated operation points almost completely in this way. P. Achten investigates the effect of additional pressure pockets in the barrels of a floating cup axial piston [13]. They are connected with groves to the bores and build up a hydrostatic bearing in the contact between the barrel and the port plate.…”

“…But when they are at low pressure side, they have near no influence. In the concept of P. Achten [13], the surfaces are machined separated to the bores and then connected by groves to it. Another possibility, which is more easy to machine, is to integrate the pockets direct into the shape of the kidneys.…”

Research on Pump-Controlled AGC Micro-Displacement Position Control of Lithium Battery Pole Strip Mill Based on Friction Compensation Control Strategy of Imoroved LuGre Pattern

“…Combining the differential of the LuGre friction term is often used when devising the backstep to address the mismatched nonlinear friction of the hydraulic system. Combining the LuGre friction pattern with a hydraulic backstep device to enhance tracking capacity and robust performance with friction perturbations remains a research focus [6][7][8]. Electrohydraulic servo systems have many pattern uncertainties [9][10][11][12] that cannot be accurately patterned, including exterior interference, leakage and friction.…”