cp1 - gear
Post on 02-Jun-2018
248 Views
Preview:
TRANSCRIPT
-
8/10/2019 CP1 - GEAR
1/58
1
MACHINE ELEMENTS INMECHANICAL DESIGN
Chapter 1:
Kinematics of Gears
-
8/10/2019 CP1 - GEAR
2/58
2
http://en.wikipedia.org/wiki/Image:Gears_animation.gif -
8/10/2019 CP1 - GEAR
3/58
3
Objectives
Recognize and describe the main features of spur gears,
helical gears, bevel gearsand worm/wormgear sets.
Describe the important operating characteristics of these
various types of gears with regards to the similarities and
differences among them and their general advantages and
disadvantages.
Describe the involute-toothform and discuss its relationshipto the law of gearing.
-
8/10/2019 CP1 - GEAR
4/58
4
Define velocity ratio as it pertains to two gears operatingtogether.
Specify appropriate numbers of teeth for a mating pair ofgears to produce a given velocity ratio
Define train valueas it is pertains to the overall speed ratiobetween the input and output shafts of a gear-type speed
reducer (or speed increaser) that uses more than two gears.
Objectives (Concluded)
-
8/10/2019 CP1 - GEAR
5/58
5
INTRODUCTION
A gear is a component within a transmission device that transmits rotational force toanother gear or device.
A gear is different from a pulley in that a gear is a round wheel which has linkages("teeth" or "cogs") that mesh with other gear teeth, allowing force to be fully
transferred without slippage.
Depending on their construction and arrangement, geared devices can transmitforces at different speeds, torques, or in a different direction, from the power source.ears are a very useful simple machine.
ears are used to reverse rotational direction, increase or decrease speed of rotation,transfer rotation to a different a!is, or to synchronie rotation across two or more a!isin a machine or engine
#he smaller gear in a pair is often called thepinion$ the larger, either the gear, or thewheel.
-
8/10/2019 CP1 - GEAR
6/58
6
INTRODUCTION
Gears may be classified according to the relative
position of the axes of revolution. The axes may be parallel,
intersecting,
neither parallel nor intersecting.
-
8/10/2019 CP1 - GEAR
7/58
7
Gears for connecting parallel
shafts:
Spur gear
pair of gears makes ete!n"l
cont"ctpair of gears makes inte!n"l
cont"ct
#
-
8/10/2019 CP1 - GEAR
8/58
8
arallel helical gears$
-
8/10/2019 CP1 - GEAR
9/58
9
!ac" and pinion%
Rack and pinion gears are usedto conert rotation into linear
motion!
"#ample: $
-
8/10/2019 CP1 - GEAR
10/58
1%
Ge"!s &o! connectin'
inte!sectin' s"&ts
Straight bevel gears
&'piral (eel gears
#
$
-
8/10/2019 CP1 - GEAR
11/58
11
Neite! "!"llel no!
inte!sectin' s"&ts
Crossed#helical gears
&&)orm and *orm gear$
#
-
8/10/2019 CP1 - GEAR
12/58
*+ Use Ge"!s,,
!educe speed
$ncrease tor%ue
&ove po'er from one point to another Change direction of po'er
Generally this functionality is accomplished by many
gears mounted in a gear box
12
-
8/10/2019 CP1 - GEAR
13/58
13
#- Su! 'e"!s
Gears that have teeth that are straight and arranged
parallel to the axis of the shaft that carries the gear.
Spur gears are the most common type of gears. They
have straight teeth, and are mounted on parallel shafts!
-
8/10/2019 CP1 - GEAR
14/58
14
(bove: the involute
tooth form (bove: diagram
illustrating the la' of
gearing.
+eeth hae inolutes cures to maintain a constant angular elocit, ratio
*hen t*o *orking gears mate!
-ngular elocit, can (e achieed *hen a line dra*n perpendicular to the
surfaces of t*o rotating (odies at their point of contact al*a,s crosses
the center.line (et*een the t*o (odies at the same place!+he a(oe statement is also kno*n as the law of gearing!
-
8/10/2019 CP1 - GEAR
15/58
15
Te!.inolo'+ &o! Su! Ge"!s
-
8/10/2019 CP1 - GEAR
16/58
16
Spur gear teeth features: Circular pitch:
)iametral itch
*teeth+in:
&odule *mm:
where N - number of teeth and the
D -pitch diameters of the gears.
-
8/10/2019 CP1 - GEAR
17/58
Ge"! Toot /e"tu!es
17
Pitch surface: The surface of the imaginary rolling cylinder *cone, etc. that the toothed gearmay be considered to replace.
Pitch circle: ( right section of the pitch surface. Addendum circle: ( circle bounding the ends of the teeth, in a right section of the gear. Root (or dedendum) circle: The circle bounding the spaces bet'een the teeth, in a right section
of the gear. Addendum: The radial distance bet'een the pitch circle and the addendum circle. Dedendum: The radial distance bet'een the pitch circle and the root circle.
Clearance: The difference bet'een the dedendum of one gear and the addendum of the matinggear. Face of a tooth: That part of the tooth surface lying outside the pitch surface. Flank of a tooth: The part of the tooth surface lying inside the pitch surface. Circular thickness*also called the tooth thickness : The thic"ness of the tooth measured on the
pitch circle. $t is the length of an arc and not the length of a straight line. Tooth space: The distance bet'een ad-acent teeth measured on the pitch circle.
Backlash: The difference bet'een the circle thic"ness of one gear and the tooth space of themating gear. Circular pitchp: The 'idth of a tooth and a space, measured on the pitch circle. Diametral pitch: The number of teeth of a gear per inch of its pitch diameter. ( toothed gear
must have an integral number of teeth. Thecircular pitch, therefore, e%uals the pitchcircumference divided by the number of teeth. Thediametral pitchis, by definition, the numberof teeth divided by thepitch diameter.
-
8/10/2019 CP1 - GEAR
18/58
18
Modulem: itch diameter divided by number of teeth. The pitch diameter isusually specified in inches or millimeters in the former case the module is the
inverse of diametral pitch. Fillet : The small radius that connects the profile of a tooth to the root circle. Pinion: The smaller of any pair of mating gears. The larger of the pair is called
simply the gear. Velocity ratio: The ratio of the number of revolutions of the driving *or input gear
to the number of revolutions of the driven *or output gear, in a unit of time.
Pitch point: The point of tangency of the pitch circles of a pair of mating gears. Common tanent: The line tangent to the pitch circle at the pitch point. !ine of action: ( line normal to a pair of mating tooth profiles at their point of
contact. Pressure anle : The angle bet'een the common normal at the point of tooth
contact and the common tangent to the pitch circles. $t is also the angle bet'een theline of action and the common tangent.
Base circle:(n imaginary circle used in involute gearing to generate the involutesthat form the tooth profiles.
-
8/10/2019 CP1 - GEAR
19/58
19
-
8/10/2019 CP1 - GEAR
20/58
2%
-
8/10/2019 CP1 - GEAR
21/58
21
-
8/10/2019 CP1 - GEAR
22/58
22
-
8/10/2019 CP1 - GEAR
23/58
23
-
8/10/2019 CP1 - GEAR
24/58
24
-
8/10/2019 CP1 - GEAR
25/58
25
-
8/10/2019 CP1 - GEAR
26/58
26
-
8/10/2019 CP1 - GEAR
27/58
27
-
8/10/2019 CP1 - GEAR
28/58
28
-
8/10/2019 CP1 - GEAR
29/58
29
-
8/10/2019 CP1 - GEAR
30/58
3%
-
8/10/2019 CP1 - GEAR
31/58
31
-
8/10/2019 CP1 - GEAR
32/58
32
-
8/10/2019 CP1 - GEAR
33/58
33
-
8/10/2019 CP1 - GEAR
34/58
34
ressure angle The pressure angle is the angle bet'een the tangent to the
pitch circles and the line dra'n normal to the surfaces of the
gear tooth.
cosDDb =
-
8/10/2019 CP1 - GEAR
35/58
35
Su.."!+ o& Ge"! No.encl"tu!e0
/0 0itch diameter of pinion
/G 0itch diameter of gear
0 o! teeth t for pinion
G o! teeth t or gear
0d diametral pitch / constant for meshing gears
p circular pitch / constant for meshing gears
n0 speed of pinion rpm
nG speed of gear rpm
R elocit, ratio n0nG G00o*er constant across mating gears or series s,stem:
0in 0out0o*er in (ranched s,stem is consered:
0in 0- 0 !!
+orue *ill change;;rpm
hpinlbTorque
=
///,0* 0 +elix angle *? typically range from 1
-
8/10/2019 CP1 - GEAR
44/58
44
%- 1evel Ge"!s
Gear teeth arranged in a cone shape manner.
Types:
Straight bevel gears
Spiral bevel gears >ypoid gears
-
8/10/2019 CP1 - GEAR
45/58
45
1evel Ge"!s
Gear axis at @/;, based on
rolling cones
(dvantages
!ight angle drives )isadvantages
Get axial loading 'hich
complicates bearings and
housings
G i l f f i h b l
-
8/10/2019 CP1 - GEAR
46/58
46
Geometrical features of straight bevel gears
-
8/10/2019 CP1 - GEAR
47/58
47
2- *o!. Ge"!s
Ased to transmit motion and po'er bet'een t'o
nonintersecting shafts, usually @/; to each other.
>ave threads rather than teeth as li"e most gears.
Can achieve higher speed reduction, but lo'er mechanicalefficiency.
Worms and Worm gears
-
8/10/2019 CP1 - GEAR
48/58
48
*o!. Ge"!s $ears that are -./ to each other Ad0antaes
Buiet + smooth drive
Can transmit tor%ue at right angles
2o bac" driving Good for positioning systems
Disad0antae
&ost inefficient due to excessive
friction *sliding 2eeds maintenance
Slo'er speed applications
*orm
*orm gear
-
8/10/2019 CP1 - GEAR
49/58
49
3- Ge"! T!"ins
$ear trainsconsist of t'o or more gears for the purpose of
transmitting motion from one axis to another. 1rdinary ear trains
have axes, relative to the frame, for all gears comprising the train.
5elocity ratio:
)efined as the ratio of the rotational speed of the input gear to thatof the output gear for a single pair of gears.
P
G
G
P
P
G
P
G
P
G
G
P
G
P
size
size
speed
speed
N
N
D
D
R
R
n
nVR =======
where subscripts P and G represents the pinion and
the driven gear respectively
-
8/10/2019 CP1 - GEAR
50/58
5%
Ge"! t!"insare a group of gears that *ork together toproduce large gear ratios
- 'e"! t!"inis a set or s,stem of gears arranged totransfer rotational torue from one part of a
mechanical s,stem to another
-
8/10/2019 CP1 - GEAR
51/58
51
Gear trains consists of:
Dri0in ears# attached to the input shaft
Dri0en ears# attached to the output shaft
2dler ears# interposed bet'een the driving anddriven gear in order to maintain the direction of theoutput shaft the same as the input shaft or to increasethe distance bet'een the drive and driven gears. (
compound gear train refers to t'o or more gears usedto transmit motion.
-
8/10/2019 CP1 - GEAR
52/58
52
34amples of $ear Trains
Types of gear trains
1. Simple gear train4. Compound gear train
. picyclic gear train
9. !everted gear train
-
8/10/2019 CP1 - GEAR
53/58
53
Gear Train !ule 7 itch of t'o gears in mesh must be
identical
G(!
P2"21"D$
"$#P
DP
"P#
-
8/10/2019 CP1 - GEAR
54/58
54
Train value:
!efers to the ratio of the input speed *for the first
gear in the train to the output speed *for the last gearin the train.
$t is the product of the values of 5! of each gear pair
in the train.
gear teethdrivingofproduct
gear teethdrivenofproduct=TV
ninnout
#TV
-
8/10/2019 CP1 - GEAR
55/58
55
4- Te AGMA
The (merican Gear &anufacturers (ssociation
*(G&( Standardi=es terms and symbols use, gear design and
applications. &ore information can be obtained from their 'ebsite:
http!""wwwagmaorg
-
8/10/2019 CP1 - GEAR
56/58
56
5UI6 /OR TODA7
)>-+ +?0" @A +>B' G"-R$
http://en.wikipedia.org/wiki/Image:Gears_animation.gifhttp://en.wikipedia.org/wiki/Image:Rack_and_pinion_animation.gif -
8/10/2019 CP1 - GEAR
57/58
57
-/ A@R +>B' +@@
http://en.wikipedia.org/wiki/Image:Rack_and_pinion_animation.gif -
8/10/2019 CP1 - GEAR
58/58
58
TUTORIAL HOME*OR8
D$CECF G(! !(T$ 7 F($2 >H $T
H!KI
>H 2)AFA& CFCKS H!KI
>H C(! &(2A(F T!(2S&$SS$2S H!KI
FIND OUT THE INFO !O"EONE NEED! TO
E#$%&IN. 'OOD %U().
top related