Swash plate axial piston pump motor because of its structural characteristics, can achieve high efficiency and pressure resistance, can achieve a variety of variable functions, therefore, become the ace component in hydraulic technology. However, because it generally has at least four pairs of sliding friction pairs: oil distribution tray - cylinder block, cylinder block - plunger, plunger head - sliding ball and socket, sliding shoe - swash plate, the lubrication situation is complex, therefore, durability has become its key indicator, and it is also the biggest gap between domestic products and the world's advanced level. In order to cooperate with the strategy of industrial strengthening, this article is specially written, mainly referring to the literature review part and literature in Breuer's doctoral thesis (IFAS2007, Institute of Fluid Transmission Control, Aachen University, Germany). In order to facilitate the retrieval of references, the names in the text are kept in Latin letters.
1 Overview
Regarding the friction condition of ordinary plain bearings, the German Stribeck summarized the famous Stribeck curve in 1902 according to a large number of test results (see Figure 1). It can be seen that the friction coefficient is the smallest in the mixed friction region. Because in the liquid friction area, the material wear is the least, so the sliding bearing is ideal to work at the junction of mixed friction and liquid friction. The curve is very valuable for the design of plain bearings, so it is included in the German industry standard DIN50281:1977-10 "Friction in bearings: Concept, type, condition, physical quantity".
Compared with ordinary plain bearings, the relationship of load, pressure distribution, geometry and kinematics on the friction pair of axial piston pump is much more complicated. Due to the coupling of each slip point, the plunger has an uncertain degree of freedom in the ball-socket joint and the cylinder hole, which makes the calculation of frictional contact quite difficult. Take the plunger for example, although the plunger also has axial translation similar to the rotation of the shaft in the ordinary plain bearing, it is also subject to a lateral force outside the bearing area (cylinder) by the sliding shoe, making the friction loss caused by the plunger the main part of the power loss. Therefore, the experience accumulated on the basis of traditional plain bearing theory can only be applied in a limited way.
