Cavitation erosion produced by impingement of a cavitating jet was experimented using aluminum alloy specimens in tap water and petroleum-based hydraulic fluid.In this report, the effects of the configuration of nozzles, outlets of nozzles, and specimens are clarified. We use three types of nozzles, three types of configuration of outlets of nozzles and nine types specimens (oblique, convex, and concave). The results are as follows : 1) The larger the diameter of the nozzle, the larger the erosion-mass losses, the eroded regions, and the stand-off distance. In the case of larger diameter nozzles, we observe the cavitating jet in the downstream region by transmitted light-photographs. 2) The configuration of outlets of nozzles is not an essential erosion factor but it influences the mass losses.3) For both cases of tap water and petroleum-based hydraulic fluid, the peak erosion rate and the stand-off distance are correlated but independent of the configuration of outlets of nozzles. 4) On the experiment of the oblique specimens, in the case that the jet impinges perpendicularly to the surface of the specimens, the mass losses become the largest. 5) On the experiment involving conical convex and concave specimens, the mass losses become the largest in the case of slightly convex specimens, and they become the smallest in the case of the concave specimens. 6) These variation of mass losses can be explained by the degree of approach of bubbles to the specimen-surfaces due to centrifugal effect.

抄録全体を表示

It is strongly desired to clarify performances of hydrostatic bearings under mixed lubrication conditions because seldom there is information available on them. Therefore, in a previous paper, we calculated the performances of friction, leakage flow rate and power losses under conditions ranging from mixed to fluid film lubrication and clarified numerically the effects of surface roughness, the eccentric loads (moment loads), the supply pressure and the speed of rotation. In this paper, by the use of an apparatus featuring circular hydrostatic thrust bearings acting on concentric loads, we measure the frictional force and leakage flow rate under a lubrication range from mixed to fluid film. The surface roughness, the supply pressure, the loads, the speed of rotation and the restrictors are selected as main experimental parameters. We evaluate the coefficient of friction, the leakage flow rate and power losses for the bearing-modulus and the ratios of hydrostatic balance. Furthermore, these experimental results are compared with the theoretical ones. The conclusions are as follows : 1) the minimum power losses are given by the ratio of hydrostatic balance being close to unity independent of the surface roughness, the loads, and the speed of rotation; 2) the coefficient of friction of hydrostatic bearings can be clarified generally versus a bearing-modulus by use of the load carrying capacity due to asperities; 3) a larger surface roughness, causes a larger leakage flow rate in mixed lubrication; 4) the larger the supply pressure, the larger the power losses in fluid film and under mixed lubrication; 5) the larger the speed of rotation, the larger are the proportional power losses under mixed lubrication; 6) the size of restrictors seldom have any effects under mixed lubrication conditions.

抄録全体を表示

Switching valves are used in the pulse flow control systems of automotive power transmissions and construction machines. These systems require rapid switching speed for improving precision in control. A combination of overexcitation and demagnetization of the solenoid shortens the switching lag time, while it increases the eddy current in the magnetic circuit. This paper clarifies the nonlinear transient characteristics of magnetic flux flow and electric current by both FEM magnetic analysis and measurement of the solenoid. Newly developed magnetic stainless steel material with a quarter of the electrical conductivity of usual low carbon steel reduces the eddy current and shortens the lag time of magnetic flux flow. The valve switches the flow rate of 7L/min at 14 MPa within 0.8ms.

抄録全体を表示