tailieunhanh - Bearing Design in Machinery Episode 2 Part 4

Tham khảo tài liệu 'bearing design in machinery episode 2 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Similar to the hydrodynamic journal bearing the load of the hydrostatic journal bearing is also divided into two components Wx and Wy and the displacement of the bearing center e is divided into two components ex and ey. In Chapter 7 the two components of the journal bearing stiffness are defined Eq. 7-31 and the cross-stiffness components are defined in Eq. 7-32 . Crossstiffness components can result in bearing instability which was discussed in Chapter 9. APPLICATIONS An interesting application is the hydrostatic pad in machine tool screw drives Rumberger and Wertwijn 1968 . For high-precision applications it is important to prevent direct metal contact which results in stick-slip friction and limits the machining precision. Figure 10-7 shows a noncontact design that includes hydrostatic pads for complete separation of the sliding surfaces of screw drive. Another important application is in a friction testing machine which will be described in Chapter 14. HYDRAULIC PUMPS An example of a positive-displacement pump that is widely used for lubrication is the gear pump. The use of gear pumps is well known in the lubrication system of automotive engines. Gear pumps as well as piston pumps are positive-displacement pumps . the pumps deliver under ideal conditions a fixed quantity of liquid per cycle irrespective of the flow resistance head losses in the system . However it is possible to convert the discharge at a constant flow rate to discharge at a constant pressure by installing a pressure relief valve that maintains a constant pressure and returns the surplus flow. A cross section of a simple gear pump is shown in Fig. 10-8a. A gear pump consists of two spur gears or helix gears meshed inside a pump casing with one of the gears driven by a constant-speed electric motor. The liquid at the suction side is trapped between the gear teeth forcing the liquid around the casing and finally expelling it through the discharge. The quantity of liquid discharged