2.5 Position of oil-feed holes and number of oil-feed holes
As illustrated in Fig.4, the position of the upper oil-feed holes in the liner is set at 33mm (11% of the stroke) from the Top ring TDC, while the position of the lower oil-feed holes is set at 101mm position (34% of the stroke) from the Top ring TDC. The reference number of the oil-feed holes is set from the ratio of the number of the upper oil-feed holes to the number of the lower oil-feed holes ＝ 0/4 and the influence of the ratios of 4/4 and 0/8. Since the total number of the oil-feed holes is doubled in the case of the ratios of 4/4 and 0/8 with respect to 0/4, the oil-feed quantity of each oil-feed hole is set to 1/2.
The timing of the oil discharge is set to be immediately before every Top ring of the piston upward stroke passes through the lower oil-feed holes, and at the timing that the cylinder oil is scraped by the ring.
2.6 Engine speed
The test was carried out with the cylinder cover removed to observe the spreading condition of the cylinder oil, and thus, no in-cylinder pressure is applied, that is, no load by the in-cylinder pressure is applied to the ring and liner running surface. Thus, regarding the engine speed, the oil film parameter (as a target of the oil film forming condition is compared at the position of the lower oil-feed holes as illustrated in Table 3 so that the condition to form the oil film between the ring and liner is equivalent to that of the actual engine, and the reference engine speed of the tester was set to 70 rpm. The test was also carried out at 140 rpm in order to examine the influence of the change in speed.
3. Test results
Spreadability of the cylinder oil is evaluated from the condition completely free from the cylinder oil to the spreading condition of the discharged cylinder oil in each cycle on the liner running surface in terms of the ratio to the running area in the range of observation by the CCD camera, and also evaluated by the length L in the stroke direction and the length B in the circumferential direction as illustrated in Fig.2.
3.1 Influence of shape of liner running surface and oil-feed quantity
Figs.5-7 show the spreadability when the oil feed quantity is changed. The spreadability is considerably different by the oil feed quantity of 0.01 cc/ome feed, 0.02 cc/ome feed and 0.03 cc/ome feed, and the spreadability becomes faster as the oil feed quantity is larger. For example, the cycles until the cylinder oil is fully spread over the running surface with the wave cut is 170 cycles at 0.01 cc/ome feed, 109 cycles at 0.02 cc/ome feed, and 76 cycles at 0.03 cc/ome feed, respectively.
In comparison of the wave cut with the honing, the spreadability is more excellent with the wave cut in any oil feed quantity. On the other hand, with the wave cut together with the oil groove, the spreadability is started in the stroke direction from the valley parts after the oil groove are filled with the cylinder oil as illustrated in Fig.8, and thus, the time delay is generated by that time; however, after the cylinder oil is started to spread, the spreadability is substantially equal to that with the wave cut.
