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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 . N1X;&qZDd
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A. radii of the pitch circles B. transmission ratio C. working pressure angle 1Ewg_/R
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(2) The main failure form of the closed gear drives with soft tooth surfaces is the . s7:w >,v/
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A. pitting of tooth surfaces B. breaking of gear tooth Fzn#>`qG
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C. wear of tooth surfaces D. agglutination of tooth surfaces M[KYt"v
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(3) The tooth form factor in calculation of the bending fatigue strength of tooth root is independent of the . l6HT}x7OiH
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A. tooth number B. modification coefficient C. module ;Yn_*M/*
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D. helix angle of helical gear l
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(4) The contact fatigue strength of tooth surfaces can be improved by way of . G>W:3y
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C. adding tooth number with not changing the diameter of reference circle Aq{7WA
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D. decreasing the diameter of reference circle W^dRA xVX
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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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C. improve the contact strength of the smaller gear ~
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D. compensate possible mounting error and ensure the length of contact line wvg>SfV,e
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(6) For a pair of involute spur cylindrical gears, if z1 < z2 , b1 > b2 , then . "Yf?33UNZ
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(7) In a worm gear drive, the helix directions of the teeth of worm and worm gear are the same. t&Z:G<;
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A. certainly B. not always C. certainly not _K| 513I
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(8) Because of , the general worm gear drives are not suitable for large power transmission. + Ek('KOF
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A. the larger transmission ratios B. the lower efficiency and the greater friction loss bLi>jE.%.
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C. the lower strength of worm gear D. the slower rotating velocity of worm gear mbRN W
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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 . G r?[s'Ze
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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 . x9!vtrM\Zr
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C. out of the driving sheave D. out of the driven sheave .5x+F Hu7
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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°. i@M^9|Gh
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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. ,@ Izx
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(13) In order to , the larger sprocket should normally have no more than 120 teeth. e/;chMCq
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B. ensure the strength of the sprocket teeth C. limit the transmission ratio Ppzd.=E
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(14) In order to reduce velocity nonuniformity of a chain drive, we should take . ,xew3 c'(W
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(Where z1 is the tooth number of the smaller sprocket, p is the chain pitch) Eg"DiI)7
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(15) In design of a chain drive, the pitch number of the chain should be . ^IxT.g
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2. (6 points) Shown in the figure is the simplified fatigue limit stress diagram of an element. fv !l {
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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. O~g _rcG
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3. (9 points) Shown in the figure is the translating follower velocity curve of a plate cam mechanism. cI4%z eR
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(1) Draw acceleration curve of the follower schematically. !Y-MUZ$f
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(2) Indicate the positions where the impulses exist, and determine the types of the impulses (rigid impulse or soft impulse). 5j`"@C5;O
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(3) For the position F, determine whether the inertia force exists on the follower and whether the impulse exists. {a9Z<P
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4. (8 points) Shown in the figure is a pair of external spur involute gears. ;=hl !CB
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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 , . e}f!zA
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5. (10 points) For the elastic sliding and the slipping of belt drives, state briefly: (SoV2[|
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(1) the causes of producing the elastic sliding and the slipping. H]"Z_n_
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(2) influence of the elastic sliding and the slipping on belt drives. [f.[C5f%"'
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(3) Can the elastic sliding and the slipping be avoided? Why? "f~S3 ?^!2
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6. (10 points) A transmission system is as shown in the figure. $iEM$
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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. B$ +YK%I
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(1) Label the rotating direction of the worm 1. YKJk)% ;+w
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(2) Label the helix directions of the teeth of the helical gears 3, 4 and the worm gears 2, 6. hvtg_w6 K
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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. /+1+6MqRn*
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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. 7Y&W^]UZ0t
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(1) Label the action lines of the resultant forces of all the pairs for the position shown. WogJ~N,d53
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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. E
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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. ;{[&&qMwU
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(1) Calculate the DOF of the mechanism and give the detailed calculating process. FloCR=^H
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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 . m X{_B!j^
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(3) Replace the higher pair with lower pairs for the position shown. u&z5)i U
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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. ~,3+]ts='\
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9. (15 points) An offset crank-slider mechanism is as shown in the figure. W<']Q_ s u
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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. ?
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(1) Find a, b, e (the offset). *Y"j 0Yob
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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. WB Oebv
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(3) Find the minimum transmission angle gmin of the mechanism, and indicate the corresponding position of the crank 1.
