(1) The center distance separability of a pair of involute spur cylindrical gears implies that a change in center distance does not affect the . `F4gal^ ^
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A. radii of the pitch circles B. transmission ratio C. working pressure angle ^~K[ bFbW
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(2) The main failure form of the closed gear drives with soft tooth surfaces is the . C5x* t Q|
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C. wear of tooth surfaces D. agglutination of tooth surfaces 0UOjk.~b
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(3) The tooth form factor in calculation of the bending fatigue strength of tooth root is independent of the . oxXCf%!
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D. helix angle of helical gear
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(4) The contact fatigue strength of tooth surfaces can be improved by way of . " r[Ob]/
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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.)
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A. equalize strengths of the two gears B. smooth the gear drive }56WAP}Z 4
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C. improve the contact strength of the smaller gear 3<HZ)w^B
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D. compensate possible mounting error and ensure the length of contact line %"^8$A?>,k
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(6) For a pair of involute spur cylindrical gears, if z1 < z2 , b1 > b2 , then . Z): Nd9
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(7) In a worm gear drive, the helix directions of the teeth of worm and worm gear are the same. G`RQl@W>)(
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(8) Because of , the general worm gear drives are not suitable for large power transmission.
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A. the larger transmission ratios B. the lower efficiency and the greater friction loss ~*x 2IPi H
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C. the lower strength of worm gear D. the slower rotating velocity of worm gear <Xw\:5
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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 . zd/ kr
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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 . U~USwUzgY
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C. out of the driving sheave D. out of the driven sheave )
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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°. f;AI4:#I
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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. r)#W`A1{A
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(13) In order to , the larger sprocket should normally have no more than 120 teeth. h3-^RE5\`S
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B. ensure the strength of the sprocket teeth C. limit the transmission ratio 6aOyI ;Ux
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D. reduce the possibility that the chain falls off from the sprockets due to wear out of the _GFh+eS}
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(14) In order to reduce velocity nonuniformity of a chain drive, we should take . ;mT}Q;F#
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C. the less z1 and the smaller p D. the more z1 and the smaller p df$.gP
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(Where z1 is the tooth number of the smaller sprocket, p is the chain pitch) fLqjBG]
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(15) In design of a chain drive, the pitch number of the chain should be . 3>^]r jFw
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2. (6 points) Shown in the figure is the simplified fatigue limit stress diagram of an element. *U,J Q
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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. ((+XzV>
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3. (9 points) Shown in the figure is the translating follower velocity curve of a plate cam mechanism. .FHk1~\%z^
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(1) Draw acceleration curve of the follower schematically. babL.Ua8o
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(2) Indicate the positions where the impulses exist, and determine the types of the impulses (rigid impulse or soft impulse). $uDgBZA\
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(3) For the position F, determine whether the inertia force exists on the follower and whether the impulse exists. TRm#H $
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4. (8 points) Shown in the figure is a pair of external spur involute gears. /yG7!k ]Eg
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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 , . +|LM"
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5. (10 points) For the elastic sliding and the slipping of belt drives, state briefly: L/ 7AGR|;C
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(1) the causes of producing the elastic sliding and the slipping. F LW VI4*
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(2) influence of the elastic sliding and the slipping on belt drives. >aA
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(3) Can the elastic sliding and the slipping be avoided? Why? @[g7\d
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6. (10 points) A transmission system is as shown in the figure. m8L *LB
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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. 66& uK|
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(1) Label the rotating direction of the worm 1. v7"VH90`!
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(2) Label the helix directions of the teeth of the helical gears 3, 4 and the worm gears 2, 6. @/:4beh
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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. "<=4]Z
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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. ~-k , $J?7
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(1) Label the action lines of the resultant forces of all the pairs for the position shown. 7<)H?;~;
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(2) Label the rotation angle d of the cam 1 during which the point C moves from its highest position to the position shown in the figure. Give the graphing steps and all the graphical lines. Ga 5s9wC
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8. (15 points) In the gear-linkage mechanism shown in the figure, the link 1 is a driver and rotates clockwise; the gear 4 is an output link. N~
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(1) Calculate the DOF of the mechanism and give the detailed calculating process. Pp } Z"
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(2) List the calculating expressions for finding the angular velocity ratios and for the position shown, using the method of instant centers. Determine the rotating directions of and . |aLK_]!
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(3) Replace the higher pair with lower pairs for the position shown. ; J|t-$Z
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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. eOb--@~8
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9. (15 points) An offset crank-slider mechanism is as shown in the figure. W5'6L =WG
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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. Il4]1d|
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(1) Find a, b, e (the offset). 6h5g!GQD
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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. nGWy4rY2S
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(3) Find the minimum transmission angle gmin of the mechanism, and indicate the corresponding position of the crank 1.
