Hi am Pierre i would like to get details on scotch yoke mechanism calculations pdf

A Scotch-yoke mechanism is known to generate a pure harmonic motion. Kinematically, it is equivalent to the slider crank mechanism of conventional reci- procating compressors when the connecting rod is imagined to have an infinite length. Since pure harmonic motion is generated, shaking forces occur only at the fundamental running frequency of the compressor and perfect dynamic balance is possible. This feature plus a compact design are the major advantages of a Scotch-yoke mechanism in compressor design.
Until recently, Scotch-yoke mechanisms have been utilized only in compressors of relatively small capacity. For the application discussed herein, a Scotch-yoke mechanism has been employed in a line of four cylinder hermetic compressors ranging in capacity from 90,000 BTIJH to 145,000 BWH. With this design, two pair of opposed pistons are em- ployed perpendicular and in slightly offset planes. Figure 1 illustrates the general layout of one pair of these pistons and the corresponding Scotch-yoke mechanism.
As illustrated in Figure 1, an eccentric shaft (1)
drives block (2), which in turn drives the yoke and piston assembly with a pure harmonic motion. To achieve lightweight construction, aluminum was employed for these components and a Swedish steel bearing strip (6) was then used to minimize fric- tion and wear. To hold the bearing strip to the yoke, a steel rivet (7) was used. To complete the assembly, a retainer (5) was employed to guide the block in the yoke.
The design analysis of the above mechanism included consideration of three major components: the shaft, the slider block, and the yoke assembly. Of these, the determination of operating stress levels in the yoke assembly presented the most difficult and unique problem. Thus, in the following, several analysis techniques are described which employ both experimental and analytical means to determine operating stress levels for the yoke. With the first method, experimental cylinder pressure data is used in conjunction with a static load fixture to simulate operating loads on the yoke. Stress levels are then calculated at various yoke loca- tions using experimental strain data. With the second method, dynamic strains are measured on the operating yoke through the use of a special linkage which allows the transport of strain gage wires from the yoke to the compressor body. Yoke strains
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measured in this manner are then compared with the result obtained from the static strain analysis.
Both of the methods described above were utilized in the development of the yoke. Due to the straightforeward measurements of the static strain method, minor design changes in the yoke were evaluated by this method. The second method was then used to verify the general correctness of the more approximate first method and also, to evaluate the final yoke design. The tedious installation and short life (15 to 30 minutes) of the strain gage wiring used in the operating compressor pro- hibited the use of the second method as a practical development tool. As will be shown, the static strain measurements agreed well with those obtained from the operating compressor.