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Dimensioning and Tolerancing Handbook Episode 2 Part 9

Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 2 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Minimum-Cost Tolerance Allocation 14-9 14.7 2-D Example One-way Clutch Assembly The application of tolerance allocation to a 2-D assembly will be demonstrated on the one-way clutch assembly shown in Fig. 14-6. The clutch consists of four different parts a hub a ring four rollers and four springs. Only a quarter section is shown because of symmetry. During operation the springs push the rollers into the wedge-shaped space between the ring and the hub. If the hub is turned counterclockwise the rollers bind causing the ring to turn with the hub. When the hub is turned clockwise the rollers slip so torque is not transmitted to the ring. A common application for the clutch is a lawn mower starter. Reference 5 Figure 14-6 Clutch assembly with vector loop The contact angle f between the roller and the ring is critical to the performance of the clutch. Variable b is the location of contact between the roller and the hub. Both the angle f and length b are dependent assembly variables. The magnitude of f and b will vary from one assembly to the next due to the variations of the component dimensions a c and e. Dimension a is the width of the hub c and e 2 are the radii ofthe roller and ring respectively. A complex assembly function determines how much each dimension contributes to the variation of angle f. The nominal contact angle when all of the independent variables are at their mean values is 7.0 degrees. For proper performance the angle must not vary more than 1.0 degree from nominal. These are the engineering design limits. The objective of variation analysis for the clutch assembly is to determine the variation of the contact angle relative to the design limits. Table 14-5 below shows the nominal value and tolerance for the three independent dimensions that contribute to tolerance stackup in the assembly. Each of the independent variables is assumed to be statistically independent not correlated with each other and a normally distributed random variable. The tolerances