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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 . d54(6N%
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A. radii of the pitch circles B. transmission ratio C. working pressure angle xq1 =O
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(2) The main failure form of the closed gear drives with soft tooth surfaces is the . is_`UD
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A. pitting of tooth surfaces B. breaking of gear tooth ~L
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C. wear of tooth surfaces D. agglutination of tooth surfaces (5S(CYls
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(3) The tooth form factor in calculation of the bending fatigue strength of tooth root is independent of the . F<y $Q0Z}
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(4) The contact fatigue strength of tooth surfaces can be improved by way of . \9*wo9cV
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A. adding module with not changing the diameter of reference circle
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C. adding tooth number with not changing the diameter of reference circle `PK1z S r
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D. decreasing the diameter of reference circle _/0vmgQ&
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(5) In design of cylindrical gear drives, b1 = b2 +(5~10)mm is recommended on purpose to . (Where b1, b2 are the face widths of tooth of the smaller gear and the large gear respectively.)
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C. improve the contact strength of the smaller gear #M$Gj>E%4
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D. compensate possible mounting error and ensure the length of contact line pj ?wQ'
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(6) For a pair of involute spur cylindrical gears, if z1 < z2 , b1 > b2 , then . }nNZ p
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(7) In a worm gear drive, the helix directions of the teeth of worm and worm gear are the same. \d~sU, L;]
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(8) Because of , the general worm gear drives are not suitable for large power transmission. +R
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A. the larger transmission ratios B. the lower efficiency and the greater friction loss (3kz(6S
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C. the lower strength of worm gear D. the slower rotating velocity of worm gear {=n-S2 %
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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 . ~Y=v@] 2 /
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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 . nff
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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°. , l}mCY
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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. 5 \hJ&
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(13) In order to , the larger sprocket should normally have no more than 120 teeth. #Av6BGM|,
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(14) In order to reduce velocity nonuniformity of a chain drive, we should take . _oOE MQb
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(Where z1 is the tooth number of the smaller sprocket, p is the chain pitch) ,
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(15) In design of a chain drive, the pitch number of the chain should be . y^M ~zOe
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2. (6 points) Shown in the figure is the simplified fatigue limit stress diagram of an element. :?!kZD!
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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. <<xUh|zE
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3. (9 points) Shown in the figure is the translating follower velocity curve of a plate cam mechanism. *pu ,|
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(1) Draw acceleration curve of the follower schematically. mM6g-)cV
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(2) Indicate the positions where the impulses exist, and determine the types of the impulses (rigid impulse or soft impulse). #>I*c _-
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(3) For the position F, determine whether the inertia force exists on the follower and whether the impulse exists. $L~?!u&N
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4. (8 points) Shown in the figure is a pair of external spur involute gears. &#k eI.,
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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 , . { 8!\aYI
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5. (10 points) For the elastic sliding and the slipping of belt drives, state briefly: s)gU vS\
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(1) the causes of producing the elastic sliding and the slipping. vlygS(Y_ 7
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(2) influence of the elastic sliding and the slipping on belt drives. Tz PG(f
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(3) Can the elastic sliding and the slipping be avoided? Why? XL10W ^
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6. (10 points) A transmission system is as shown in the figure. |
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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. k O8W>
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(1) Label the rotating direction of the worm 1. gA/8Df\G:l
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(2) Label the helix directions of the teeth of the helical gears 3, 4 and the worm gears 2, 6. Xb'U
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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. NR@n% p
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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. y G{; kJ P
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(1) Label the action lines of the resultant forces of all the pairs for the position shown. B +w< 0No
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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. q, ->E<8
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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. JXa5snh{h
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(1) Calculate the DOF of the mechanism and give the detailed calculating process. [fjP.kw;J
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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 . ja_.{Zv
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(3) Replace the higher pair with lower pairs for the position shown. ?-HLP%C('
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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. -ghmLMS%t
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9. (15 points) An offset crank-slider mechanism is as shown in the figure. O'OVj
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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. |Zn |?#F
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(1) Find a, b, e (the offset). .sO.Y<- fl
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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. K_fQFuj +
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(3) Find the minimum transmission angle gmin of the mechanism, and indicate the corresponding position of the crank 1.
