Fy  = −Fn(˛) cos ˛ − Fı (˛) sin ˛ (17)

The initial force of the piston system is written as:

The studied engine is a typical diesel engine, with a peak power at 2500 rpm and peak torque at 2200 rpm。 The applied load to the

Fj = −

。

mpiston +

。 mrodlb 。。 Rw2(cos ˛

l

+ ˛ cos 2˛) (11)

big-end bearing is shown in Fig。  5。

Frc =

(l − lb)mrodrw2 l

2。7。Design of experiments

F (Fg + Fj ) (13)

=  cos ˇ

Fı  = F  sin(˛ + ˇ) (14)

Fn = F cos(˛ + ˇ) − Frc (15)

The bearing load along x, y direction is written as:

Fx  = −Fn(˛) sin ˛ + Fı (˛) cos ˛ (16)

Table 1

Engine specifications。

Parameters Unit

Young’s modulus, connecting rod GPa 210

Young’s modulus, crankshaft GPa 210

Poisson’s ratio – 0。3

Connecting rod structure density kg/m3 7800

Piston mass kg 1。943

Piston pin mass kg 1。272

Connecting rod mass kg 2。093

DOE is important as a formal way of maximizing information gained while minimizing required resources, especially for the orthogonal experiment。 It has more to offer than “one change at a time” experimental methods because it allows a judgment on the significance to the output of input variables acting alone。 It is useful to quantify the main effects of the input variables on global responses when optimizing a connecting rod big-end bearing。 In this paper, 10 input variables with 4 different levels (as shown in Table 2), some outputs are selected to evaluate the lubrication per- formances, such as friction power loss, oil leakage, MOFT and MOFP (as shown in Table 3)。

10 input parameters, with 4 levels for each of them, imply a set of 410 runs for the whole experiment with one change at a time。 Every experiment to do the simulation needs at least 1 h, so 410 h are needed to achieve our goal, to overcome this problem, we introduce

Table 3

Bearing response。

Global responses Abbreviation Unit

Connecting rod length mm 219

Center of mass mm 63

Stroke mm 130

Bore diameter mm 126

Crank-pin diameter mm 82

Friction loss FMEP kPa

Minimum oil film thickness MOFT