From this matrix, FEM model, as shown in Fig.4, is obtained per one cylinder (between cylinder centers) including crankcase, frame, and baseplate. Using this FEM model, influence from overall rigidity of engine structure can be taken into consideration.
Therefore, it may be expressed as
H = cr + (ex + αyZ) cosθ+(ey + αxZ) sinθ + Lp (2)
On the other hand, oil film strength F can be expressed as difference between integration of oil film pressure p obtained from Equation (1) and working load W, as shown below.
Where, Wx and Wy represent the fluctuating load on k step. Oil film pressure p and shaft eccentricity positions ex, and ey are obtained by solving equations (1) through (3) simultaneously. As each equation is non-linear, numeral analysis should be processed with formulation by Newton-Raphson method which enlarges them to multivariable non-linear equations. Fig.5 is the flowchart for the analysis.
Please note that bearing surface end has small meshes for further precise evaluation of influence from uneven contact. The values for working load on bearing and uneven contact are given as known from calculation by highly accurate bearing load evaluation method [2], which makes it possible to evaluate influence of bearing structural rigidity to bearing characteristics, especially to the peak value of oil film pressure.
3. OIL FILM PRESSURE MEASUREMENT UNDER FLUCTUATING LOAD BY THE TEST RIG.
3.1 Development of Oil Film Pressure Sensor
Oil film pressure in main bearing is generated in thin film of under 10μm. Oil film pressure sensors available on the market are diaphragm type which requires pressure leading hole whose low natural frequency causes insufficient pressure response for thin film. This is the reason for developing the sensor that makes it possible to measure oil film pressure of the order of 100MPa generated in thin film.
As seen from Fig.6, the experimental sensors and existing diaphragm type sensor are different in structure. As existing sensor is not capable of measuring the pressure because of its pressure leading hole with low natural frequency, any ooncavity on shaft surface has to be avoided. So the experimental sensors should have sensor heads which can be machined together with sliding surface.
To achieve this, sensor body is made of the same steel material as installing shaft. As the axial force of the sensor caused by oil film pressure can be detected by small strain gauge, this method is adopted as the main frame. The difference between the two experimental sensors is in their sealing method. The simpler is sensor ? in Fig.6 with an O-ring to seal shaft pressured part of φ5mm and embedded shaft hole. On the other hand, sensor ? adopts sealing by conical spring whose end support has sleeve.
In order to verify the two sensors, a preliminary test was performed. Fig.7 shows the cross section of specimen in testing equipment.
In this test, pressure sensor is installed in main shaft to measure pressure distribution on bearing surface continuously from rotating side by using slip ring to make strain gauge output available on static side.
Bearing is fit in bearing box situated above the hydraulic cylinder which gives static and dynamic loads.
Loads are measured by load cell inserted between hydraulic cylinder and bearing case.
Main shaft is rotated by AC motor whose speed is controlled by inverter via torque meter.
Fig. 6 Experimental and Existing Pressure Sensors
