Comparison of the Dynamic Behavior and Lubrication Characteristics of a Reciprocating Compressor Crankshaft in Both Finite and Short Bearing Models©

Figures & data

FIG. 1 Free body diagram of the reciprocating piston in the cylinder bore.

FIG. 2 Analytical model for the crankshaft-journal bearing system.

FIG. 3 The radial direction orbits at 4 locations of the piston showing the converged periodic solution.

FIG. 4 Comparison of the crankshaft orbits between finite bearing model and short bearing model.

TABLE 1 Design Parameters of the Reciprocating Compressor and Baseline Values Used in the Simulation

Mass of the piston (m p )	0.043 kg
Mass of the connecting rod (m c )	0.024 kg
Mass of the crankshaft and motor rotor (m e )	0.944 kg
Moment of inertia of the piston (I p )	3.93× 10^−6 N · m · s^2
Mass moment of inertia of the crankshaft and motor rotor about the axial gravity center.	I x = 0.82881× 10^−3 N · m · s^2 I y = 0.8313× 10^−3 N · m · s^2 I x = 0.3855× 10^−3 N · m · s^2
Radius of the piston (R p )	11.5 mm
Radius of crankshaft on bearings (R)	8 mm
Length of the piston	22 mm
Length of the connecting rod	41.2 mm
Length of the cylinder wall	28.85 mm
Radial clearance between the piston-pin and the cylinder wall (C p )	4 μ m
Journal clearance on bearings (C)	11 μ m
Lengths of the main bearing (l b1) and sub bearings (l b2)	13.09 mm, 9. 5 mm
Rotating radius between crankshaft center and crank-pin center	7.5 mm
Lubricant viscosity (λ)	5 mPa · s

FIG. 5 Comparison of the trajectories at 4 locations of the piston varying in radial clearance.

FIG. 6 Cycle-averaged power consumption and oil leakage of the piston as a function of radial clearance.

FIG. 7 Cycle-averaged power consumption and oil leakage of the piston as a function of lubricant viscosity.

FIG. 8 Comparison of the orbits with different bearing clearances.

FIG. 9 Cycle averaged power consumptions and oil leakages of the crankshaft as a function of clearance at main bearing.

FIG. 10 Cycle averaged power consumptions and oil leakages of the crankshaft as a function of clearance at sub bearing.

FIG. 11 Comparison of the crankshaft orbits varying in lubricant viscosity of the journal bearings.

TABLE 2 Comparison of the Friction Losses and Oil Leakages with Respect to the Bearing Analysis Model

		Finite Bearing				Short Bearing
		Main		Sub		Main		Sub
Condition	Classification	(W 1)avg (W)	Q z1 (cm^3/h)	(W 2)avg (W)	Q z 2 (cm^3/h)	(W 1)avg (W)	Q z1 (cm^3/h)	(W 2)avg (W)	Q z2 (cm^3/h)
Clearance	7 μm	5.05	362.43	3.46	279.32	4.02	414.20	3.33	278.76
(λ = 5 mPa · s)	11 μm	4.23	768.09	2.66	568.70	2.14	924.12	2.28	595.34
	13 μm	4.10	958.87	2.46	708.34	1.54	1191.96	1.98	759.82
Viscosity	4 mPa.s	3.67	798.63	2.26	590.55	1.54	982.76	1.83	631.61
(C = 11 μ m)	7 mPa.s	5.30	708.94	3.45	532.71	2.13	925.18	2.26	598.53
	12 mPa.s	7.77	577.50	5.31	443.73	6.12	660.87	5.08	444.75
Inertia of piston and connecting-rod (C = 11 μ m, λ = 5 mPa.s)	70%	4.23	768.14	2.67	548.88	2.17	918.04	2.36	585.05
	100%	4.23	768.09	2.66	568.70	2.14	924.12	2.28	595.34
	130%	4.23	767.60	2.66	589.02	2.11	928.80	2.21	607.86

FIG. 12 Comparison of the crankshaft orbits on main bearing and sub bearing variation in the mass and moment of inertia of crankshaft and connecting rod.