东大机械洋卷2

(1)       The center distance separability of a pair of involute spur cylindrical gears implies that a change in center distance does not affect the     . wE)] ah:  
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A. radii of the pitch circles     B. transmission ratio     C. working pressure angle  PE^eP}O1  
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(2)       The main failure form of the closed gear drives with soft tooth surfaces is the       . C+DG+_%V*S  
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A. pitting of tooth surfaces     B. breaking of gear tooth XC :;Rq'j  
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C. wear of tooth surfaces     D. agglutination of tooth surfaces "0!~g/X`rK  
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(3)       The tooth form factor in calculation of the bending fatigue strength of tooth root is independent of the       . )Uc$t${en  
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A. tooth number   B. modification coefficient   C. module ^- u [q- !  
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D. helix angle of helical gear #8P#^v]H  
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(4)       The contact fatigue strength of tooth surfaces can be improved by way of     . C3&17O6  
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A. adding module with not changing the diameter of reference circle +s#S{b  
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B. increasing the diameter of reference circle yg]suU<z]  
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C. adding tooth number with not changing the diameter of reference circle )->-~E}p9  
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D. decreasing the diameter of reference circle 2hj
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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.) QO
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A. equalize strengths of the two gears         B. smooth the gear drive > gA %MT  
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C. improve the contact strength of the smaller gear 8:3oH!n  

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D. compensate possible mounting error and ensure the length of contact line >Hd~Ca>  
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(6)       For a pair of involute spur cylindrical gears, if z1 < z2 , b1 > b2 , then     . )A>U<n$h  
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(7)       In a worm gear drive, the helix directions of the teeth of worm and worm gear are     the same. ($[r>)TG  
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A. certainly       B. not always       C. certainly not 9H !B)  
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(8)       Because of       , the general worm gear drives are not suitable for large power transmission. |p=.Gg=2  
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A. the larger transmission ratios   B. the lower efficiency and the greater friction loss

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C. the lower strength of worm gear   D. the slower rotating velocity of worm gear M<M#<kD  
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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       . eaYkYuS/  
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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     . mvL0F%\.\  
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A. into the driving sheave       B. into the driven sheave j-C42Pfr  
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C. out of the driving sheave       D. out of the driven sheave q.,p6D  
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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°. \0^rJ1*  
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A. greater than     B. equal to     C. less than     D. not less than Cr V2 V)|G  
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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. QE{;M  
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(13)   In order to     , the larger sprocket should normally have no more than 120 teeth. Z.Y;[Y  
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A. reduce moving nonuniformity of a chain drive l~Wk07r3  
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B. ensure the strength of the sprocket teeth     C. limit the transmission ratio 5S-o 2a  
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D. reduce the possibility that the chain falls off from the sprockets due to wear out of the [;V1y`/K1  
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(14)   In order to reduce velocity nonuniformity of a chain drive, we should take       . UN .[,
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A. the less z1 and the larger p     B. the more z1 and the larger p k.%W8C<Pa  
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C. the less z1 and the smaller p     D. the more z1 and the smaller p 3NxaOO`  
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(Where z1 is the tooth number of the smaller sprocket, p is the chain pitch) Sc"4%L  
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(15)   In design of a chain drive, the pitch number of the chain should be     . vhquHy.qi#  
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A. even number   B. odd number   C. prime number =*>4Gh i  
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D. integral multiple of the tooth number of the smaller sprocket ^(m6g&$(  
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2. (6 points) Shown in the figure is the simplified fatigue limit stress diagram of an element. F?,&y )ri  
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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. 't%%hw-m}  
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3. (9 points) Shown in the figure is the translating follower velocity curve of a plate cam mechanism. n ua8y(W  
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(1)   Draw acceleration curve of the follower schematically. '>mb@m  
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(2)   Indicate the positions where the impulses exist, and determine the types of the impulses (rigid impulse or soft impulse). XM@i|AK M0  
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(3)   For the position F, determine whether the inertia force exists on the follower and whether the impulse exists. DfzUGX
 
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4. (8 points) Shown in the figure is a pair of external spur involute gears. [%,=

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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 , . la|l9N^,  
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5. (10 points) For the elastic sliding and the slipping of belt drives, state briefly: .LcE^y[V
 
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(1)   the causes of producing the elastic sliding and the slipping. 9,>Y  
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(2)   influence of the elastic sliding and the slipping on belt drives. ~EkGG .  
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(3)   Can the elastic sliding and the slipping be avoided? Why? a(T4WDl^  
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6. (10 points) A transmission system is as shown in the figure. FQ^uX]<3j  
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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. M!@[lJ  
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(1)   Label the rotating direction of the worm 1. `rLMMYD=  
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(2)   Label the helix directions of the teeth of the helical gears 3, 4 and the worm gears 2, 6. I!~Omr@P  
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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. uqH;1T;s  
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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. p6*D^-  
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(1)   Label the action lines of the resultant forces of all the pairs for the position shown. hBw~l?G  
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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. 52,a5TVG  
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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. rX[R`,`>Z[  
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(1)   Calculate the DOF of the mechanism and give the detailed calculating process. \l~h#1|%;s  
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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 . _)Ms9RN  
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(3)   Replace the higher pair with lower pairs for the position shown. o0q{:An_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. mP-+];gg  
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9. (15 points) An offset crank-slider mechanism is as shown in the figure. <)M?qkjb  
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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. <Wl! Qog'  
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(1)   Find a, b, e (the offset). _yU e2Gd  
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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. ek.L(n,J|  
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(3)   Find the minimum transmission angle gmin of the mechanism, and indicate the corresponding position of the crank 1.