Maximum oil film pressure MOFP MPa

Oil leakage OLK ml/s

the orthogonal experiment including one component (oil hole loca- tion) with 2 levels and 9 variables with 4 levels。 L(2 × 49) the design is described as a 32 design of resolution。 This means that an overall of n = 10 factors are studied only needing more than 32 h。 How- ever, the variables interaction is neglected in the experiment。 In the future work, we will also design the experiment with variables interaction。

2。8。Regression model

y can be a particular response (e。g。, friction loss, oil leakage, MOFP, MOFT) to the ten input variables x1, x2, 。 。 。, x10, the response variable y related with the input variable is called a regression model which can be written as:

y = f (x1, x2, x3, 。 。 。, x9, x10) (18)

If the regression model neglects the variable interaction, the linear regression model can be written as:

y = ˇ0 + ˇ1x1 + ˇ2x2 + ˇ3x3 + ˇ4x4 + ˇ5x5 + ˇ6x6 + ˇ7x7

+ ˇ8x8 + ˇ9x9 + ˇ10x10 (19)

Crank angle/°CA

MOFT and MOFP of the case 64

The linear regression model can simplify the calculation model, and eliminate the correlation between the regression coefficient and interaction, so it is widely used in all kinds of fields。 However, some realistic problem needs to consider interaction between two variables or even high orders, sometimes, using quadric regression design to establish regression equation can satisfy the common nonlinear problem。 In the future work, we will establish the non- linear regression model。

3。Results and discussion

3。1。Basic lubrication characteristics analysis

Some lubrication characteristics are used to verify the bearing performances, such as the MOFP, MOFT, Qaverage, the friction mean effective pressure (FMEP) and so on。 Qaverage and FMEP are always the most important indexes to evaluate the bearing performances, they can be written  as:

¸ 720 Q d&

0 0

0 90 180 270 360 450 540 630 720

Crank angle/°CA

Friction  loss of the case 33 and case 64

Fig。 6。 Lubrication characteristics of the connecting rod。 (a) MOFT and MOFP of the case 64。 (b) Friction loss of the case 33 and case 64。

In this paper, the wear condition = 2 when the wear occurs, if the wear condition = 1 when the wear does not occur。

Fig。 6 presents some lubrication characteristics of the connect- ing rod calculated with the case 64。 Fig。 6(a) is the MOFT and MOFP

changing with the crank angle, the results show that the MOFT in one cycle is 1。422 µm which appears at 22 ◦CA, the maximum oil film pressure in one cycle is 126 MPa which appears at 13 ◦CA。 The

MOFT and MOFP in one cycle appear at different crank angles。 Com- pared with the maximum of the in-cylinder pressure, the relative lagging time of the maximum oil film pressure is 3 ◦CA。

Fig。 6(b) presents the friction loss of different cases。 The results

show that the asperity contact friction loss appears in case 64,

the asperity contact happens at the crank angle 0–90 ◦CA and 300 ◦CA–420 ◦CA, when the oil viscosity is lower, its load capac- ity is also lower, which will lead asperity contact to happen easily。