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(1) The center distance separability of a pair of involute spur cylindrical gears implies that a change in center distance does not affect the . A6;[r #C
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A. radii of the pitch circles B. transmission ratio C. working pressure angle tQMz1$
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(2) The main failure form of the closed gear drives with soft tooth surfaces is the . { v3@g[:|
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A. pitting of tooth surfaces B. breaking of gear tooth hg^k lQD
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C. wear of tooth surfaces D. agglutination of tooth surfaces +b dnTV6
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(3) The tooth form factor in calculation of the bending fatigue strength of tooth root is independent of the . AUU(fy#<
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A. tooth number B. modification coefficient C. module 57N<OQWf
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D. helix angle of helical gear rsK
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(4) The contact fatigue strength of tooth surfaces can be improved by way of . !NhVPb,
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A. adding module with not changing the diameter of reference circle %( 1y
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B. increasing the diameter of reference circle g+k
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C. adding tooth number with not changing the diameter of reference circle I \6^]pi,
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D. decreasing the diameter of reference circle s.!gsCQme
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(5) In design of cylindrical gear drives, b1 = b2 +(5~10)mm is recommended on purpose to . (Where b1, b2 are the face widths of tooth of the smaller gear and the large gear respectively.) T
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A. equalize strengths of the two gears B. smooth the gear drive \z=!It]f.
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C. improve the contact strength of the smaller gear OmECvL'Z
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D. compensate possible mounting error and ensure the length of contact line )!D,;,aQ
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(6) For a pair of involute spur cylindrical gears, if z1 < z2 , b1 > b2 , then . O ;B[ZMV
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(7) In a worm gear drive, the helix directions of the teeth of worm and worm gear are the same. NB)22 %
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(8) Because of , the general worm gear drives are not suitable for large power transmission. q!8aYw+c
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A. the larger transmission ratios B. the lower efficiency and the greater friction loss kR;Hb3hb
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C. the lower strength of worm gear D. the slower rotating velocity of worm gear rTtxmw0
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(9) In a belt drive, if v1, v2 are the pitch circle velocities of the driving pulley and the driven pulley respectively, v is the belt velocity, then . 7,Q>>%/0P
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(10) In a belt drive, if the smaller sheave is a driver, then the maximum stress of belt is located at the position of going . 4oRDvn7f&
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C. out of the driving sheave D. out of the driven sheave c^EU &q{4
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(11) In a V-belt drive, if the wedge angle of V-belt is 40°，then the groove angle of V-belt sheaves should be 40°. &`Ek-b!7
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(12) When the centerline of the two sheaves for a belt drive is horizontal, in order to increase the loading capacity, the preferred arrangement is with the on top. SK;c
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(13) In order to , the larger sprocket should normally have no more than 120 teeth. E8] kd
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A. reduce moving nonuniformity of a chain drive E]dmXH8A
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B. ensure the strength of the sprocket teeth C. limit the transmission ratio R-J^%4U`7
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D. reduce the possibility that the chain falls off from the sprockets due to wear out of the OV,t|
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(14) In order to reduce velocity nonuniformity of a chain drive, we should take . 6t
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(15) In design of a chain drive, the pitch number of the chain should be . zv0bE?W9
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2. (6 points) Shown in the figure is the simplified fatigue limit stress diagram of an element. E
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If the maximum working stress of the element is 180MPa, the minimum working stress is -80MPa. Find the angle q between the abscissa and the line connecting the working stress point to the origin. Z0%:j\W4c
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3. (9 points) Shown in the figure is the translating follower velocity curve of a plate cam mechanism. 10_# Z~aU
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(1) Draw acceleration curve of the follower schematically. Q[{RN ab
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(2) Indicate the positions where the impulses exist, and determine the types of the impulses (rigid impulse or soft impulse). eG7Yyz+t$
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(3) For the position F, determine whether the inertia force exists on the follower and whether the impulse exists. cj9C6Y!
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4. (8 points) Shown in the figure is a pair of external spur involute gears. NBHpM}1xtU
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The driving gear 1 rotates clockwise with angular velocity while the driven gear 2 rotates counterclockwise with angular velocity . , are the radii of the base circles. , are the radii of the addendum circles. , are the radii of the pitch circles. Label the theoretical line of action , the actual line of action , the working pressure angle and the pressure angles on the addendum circles , . ,J8n}7aI
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5. (10 points) For the elastic sliding and the slipping of belt drives, state briefly: 0EF~Ouef
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(1) the causes of producing the elastic sliding and the slipping. [q_+s
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(2) influence of the elastic sliding and the slipping on belt drives. X\/M(byn
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(3) Can the elastic sliding and the slipping be avoided? Why? Mx$&{.LFJ
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6. (10 points) A transmission system is as shown in the figure. - {QU>`2
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The links 1, 5 are worms. The links 2, 6 are worm gears. The links 3, 4 are helical gears. The links 7, 8 are bevel gears. The worm 1 is a driver. The rotation direction of the bevel gear 8 is as shown in the figure. The directions of the two axial forces acting on each middle axis are opposite. xc:E>-
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(1) Label the rotating direction of the worm 1. }}JMw T
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(2) Label the helix directions of the teeth of the helical gears 3, 4 and the worm gears 2, 6. G<;~nAo?f0
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7. (12 points) A planar cam-linkage mechanism is as shown in the figure with the working resistant force Q acting on the slider 4. z%;p lMj
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The magnitude of friction angle j (corresponding to the sliding pair and the higher pair) and the dashed friction circles (corresponding to all the revolute pairs) are as shown in the figure. The eccentric cam 1 is a driver and rotates clockwise. The masses of all the links are neglected. wV
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(1) Label the action lines of the resultant forces of all the pairs for the position shown. (#Y~z ',I
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(2) Label the rotation angle d of the cam 1 during which the point C moves from its highest position to the position shown in the figure. Give the graphing steps and all the graphical lines. _ 4ag-
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8. (15 points) In the gear-linkage mechanism shown in the figure, the link 1 is a driver and rotates clockwise; the gear 4 is an output link. OxlA)$.hpu
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(1) Calculate the DOF of the mechanism and give the detailed calculating process. N'Gq9A
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(2) List the calculating expressions for finding the angular velocity ratios and for the position shown, using the method of instant centers. Determine the rotating directions of and . NVyB EAoh
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(3) Replace the higher pair with lower pairs for the position shown. DiC z%'N
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(4) Disconnect the Assur groups from the mechanism and draw up their outlines. Determine the grade of each Assur group and the grade of the mechanism. MqyjTY::Xg
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9. (15 points) An offset crank-slider mechanism is as shown in the figure. ]'.qRTz'\t
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If the stroke of the slider 3 is H =500mm, the coefficient of travel speed variation is K =1.4, the ratio of the length of the crank AB to the length of the coupler BC is l = a/b =1/3. 'gwh:
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(1) Find a, b, e (the offset). P1#g{f
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(2) If the working stroke of the mechanism is the slower stroke during which the slider 3 moves from its left limiting position to its right limiting position, determine the rotation direction of the crank 1. l hUGo =
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(3) Find the minimum transmission angle gmin of the mechanism, and indicate the corresponding position of the crank 1.
