03-08-2013, 01:07 PM
Design And Fabrication Of Wrist Pin & Crank Pin Journal Bearing
Design And Fabrication.pptx (Size: 1.38 MB / Downloads: 44)
Abstract:
The objective of this project was to design the wrist pin bearing and crank pin bearing for a piston, connecting rod, and crankshaft system. The specifications for the system are a piston with a 2.375” diameter weighing 0.379 lbs. and a connecting rod of length 3.125” weighing 0.124 lbs. From the crank pin end the connecting rod has a mass eccentricity of 0.4” and the crank shaft has a length of 0.875”. A constant angular velocity of 3000 RPM for the rotating crank was assumed. Using the provided engine data a rounded indicator diagram was created. In order to design the wrist pin and crank pin bearings it was important to first calculate the dynamic forces as a function of the crank angle to find the maximum force caused by the reciprocating load. Calculations were based on SAE50W oil at a constant 200ᵒF. The necessary dimensions for the piston pin bearing were a length of 0.6875” and a diameter of 0.4375” and the crank pin bearings length and diameter were 1.125” and 1.25”, respectively.
Calculations
To solve the problem of bearing design, the force loads on the bearings must be found.
This is obtained from the values of the cylinder pressure throughout the cycle range.
To calculate the pressure values in the cylinder, one must start with the basic engine geometry and parameters.
The known given information along with the calculated data for the engine in question is listed below
Dynamic Forces
It is important to understand the dynamic forces change throughout the cycle of operation while acting against the bearings of a piston, connecting rod, and crankshaft system.
It is necessary to understand these dynamic forces so that the engineer may design the bearings properly.
Due to the reciprocating loads on the bearings, a detailed analysis of the system is necessary to determine these dynamic forces acting on the piston pin (wrist pin) and crank pin as a function of the crank angle for720˚of crank rotation.
The cycle was analyzed for 720 ˚ to account for a complete four-stroke cycle, which require two complete rotations per power cycle.
Conclusions and Recommendations
The wrist pin bearings and crank pin bearings selected, for the purpose of this design, meet the defined criteria. The proposed design can be recommended based on the calculations and analysis performed in this report. The final dimensions of the wrist pin were a length of 0.6875in and a diameter of 0.4375in. The crank pin bearing dimensions were determined to be a length of 1.125in and a diameter of 1.25in. All calculations were based on the assumption that the engine operates at a constant speed of 3000RPM. This consideration however provides an overestimate as long as engine speed does not exceed the design criteria for extended periods.