In axial piston pumps and motors, the interface between the cylinder block and the port plate is one of the most complicated design details. This interface is a combination of a thrust bearing and a face sealing. The gap height, i.e. the thickness of the oil film, is only allowed to be a few micrometers. A smaller gap height results in high friction losses and possibly in metal-to-metal contact, causing wear and particle generation. On the other hand, a large gap height causes high leakage. In most cases, the barrel or cylinder block will be tipping instead of lifting, thereby causing a variable gap height and combining both high friction losses (where the gap height is small) and high volumetric losses (where the gap height is large). This paper investigates the factors that determine the barrel force and torque balance. Two axial piston pump principles are investigated and compared: a swash plate, slipper type machine and a floating cup pump/motor.
Keywords: Axial piston pump, barrel tipping