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Definition
| have teeth inclined to the axis of rotation |
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Term
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Definition
| – have teeth formed on conical surfaces and are used mostly for transmitting motion between intersecting shafts. |
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Term
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Definition
| worm resembles a screw; the direction of rotation of the worm gear also called the worm wheel depends upon the direction of rotation of the worm and whether the worm teeth are cut right or left handed. |
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Definition
| theoretical circle upon which all calculations are usually based; pitch circles of a pair of mating gears are tangent to each other. |
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Term
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Definition
| diameter of the pitch circle |
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Term
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Definition
| smaller of two mating gears |
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Term
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Definition
| distance measured on the pitch circle from a point on one tooth to a |
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Term
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Definition
| ratio of pitch diameter and number of teeth |
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Term
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Definition
| ratio of number of teeth on gear to pitch diameter |
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Term
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Definition
| radial distance between the top land and the pitch circle. |
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Term
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Definition
| radial distance from bottom land to pitch circle |
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Term
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Definition
| sum of addendum and dedendum |
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Term
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Definition
| – circle that is tangent to addendum circle of the mating gear |
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Term
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Definition
| amount by which the dedendum in a given gear exceeds the addendum of its |
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Term
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Definition
| amount by which the width of a tooth space exceeds the thickness of the engaging tooth measured on the pitch circles |
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Term
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Definition
| designed so as to produce constant angular velocity ratio during meshing |
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Term
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Definition
| in universal use for gear teeth and is the only one which we should be concerned. |
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Term
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Definition
– represents the direction of action of forces normal to the contact.
• To transmit motion at a constant angular velocity ratio, the pitch point must remain fixed; that is, all the lines of action for every instantaneous point of contact must pass through the same point. |
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Term
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Definition
| – circle on which involute is generated |
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Term
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Definition
| – a number that indicates the average number of pairs of teeth in contact |
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Term
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Definition
| contact of portions of tooth profiles that are not conjugate. |
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Term
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Definition
| – when gear teeth are produced by a generation process, interference is automatically eliminated because the cutting tool removes the interfering portion of the flank |
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Term
| • Interference can also be reduced |
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Definition
| by using a large pressure angle. |
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Term
| • Ways of forming teeth of gears |
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Definition
o Sand casting
o Shell modling
o Investment casting
o Permanent mold casting
o Die casting
o Centrifugal casting
o Powder metallurgy process
o Extrusion |
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Term
| • Gears that carry large loads |
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Definition
| in comparison with their size are usually made of steel and are cut with either form cutters or generating cutters |
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Term
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Definition
| tooth space takes the exact form of cutter |
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Term
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Definition
| tool having a shape different from the tooth profile is moved relative to the gear blank so as to obtain the proper tooth shape. |
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Term
| • Gear teeth may be machined by: |
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Definition
o Milling – uses form milling cutter
o Shaping – uses either pinion cutter or rack cutter
o Hobbing – uses cutting tool called hob |
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Term
| • Gear teeth may be machined by: |
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Definition
o Shaving
o Burnishing
o Grinding
o Lapping |
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Term
| • Teeth may be finished by |
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Definition
o Shaving
o Burnishing – used with gears that have been cut but not heat treated; hardened gears with slightly oversize teeth are run in mesh with the gear until surfaces become smooth
o Grinding and lapping – used for hardened gear teeth after heat treatment. |
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Term
| shape of the tooth is an involute helicoids |
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Definition
| • For a helical gear, the |
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Term
| • The initial contact of helical gear teeth is a point that extends into a line as |
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Definition
| the teeth come into more engagement. |
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Term
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Definition
| a standard that specifies the relationship involving addendum, dedendum, working depth, tooth thickness, and pressure angle. |
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Term
| • Face width of helical gears should be at least __________ the axial pitch to obtain good ___________ ________action |
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Definition
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Term
| • Design of gear trains to accomplish a specific train value is straightforward: |
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Definition
o Number of teeth on gears must be integers, better to determine first
o Obtain pitch diameters
o Determine number of stages necessary to obtain overall ratio
o Divide overall ratio into portions to be accomplished in each stage
o To minimize package size, keep portions as evenly divided between the stage as possible. |
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Term
| • Compound reverted geartrain |
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Definition
| – Input shaft and the output shaft of two stage compound gear train is in line |
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Term
| • Planetary or epicyclic gear trains |
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Definition
permits some of the gear axes to rotate about others
o Have two degrees of freedom aka must have two inputs
o In most configurations, one element is fixed to the frame
o Elements include Sun gear, arm, and planet gears |
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Term
tangential or transmitted
midpoint |
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Definition
| • In determining shaft and bearing loads for bevel gear applications the usual practice is to use the _________ or ___________load that would occur if all the forces were concentrated at the _________ of the tooth. |
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Term
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Definition
| consists for cup keyed or splined to one of the shafts, a cone that must slide axially on splines or keys on the mating shaft, and a helical spring to hold the clutch in engagement. |
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Term
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Definition
| • Clutch is __________ by means of a fork that fits into shifting groove on friction cone |
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Term
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Definition
| • Kinetic energy is ____________ during slippage of either a clutch or a brake, and this energy appears as _____ |
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Term
o Characteristics of the material
o Ability of the clutch to dissipate heat |
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Definition
| • The capacity of a clutch is limited by two factos: |
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Term
| • A temperature-rise problem |
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Definition
| arises when heat is generated faster than it dissipates |
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Term
| • Clutch operation is completed |
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Definition
| at the instant in which the two angular velocities become equal. |
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Term
directly proportional
inversely proportional |
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Definition
| • Time required for the engagement operation is ______ _________to the velocity difference and _______ _____________to the torque. |
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Term
o High and reproducible coefficient of friction
o Imperviousness to environmental conditions such as moisture
o Good resiliency
o Flexibility |
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Definition
| • A brake or friction clutch should have the following lining material characteristics to a degree that is dependent on the severity of service: |
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Term
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Definition
| – produced as a fabric belt that is impregnated with resins and polymerized; used mostly in heavy machinery |
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Term
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Definition
| may contain metal particles; not quite flexible; widely used as brake material in heavy machinery |
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Term
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Definition
| contain asbestos fiber and friction modifiers; thermoset polymer used; used in drum brake |
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Term
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Definition
| similar to molded linings but have no flexibility; used for both clutches and brakes |
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Term
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Definition
| made of mixture of copper and/or iron particles with friction modifiers. |
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Term
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Definition
| similar to sintered metal pads and have substantial ceramic content |
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Term
| • Square jaw clutch characteristics (form of positive contact clutch) |
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Definition
o Do not slip
o No heat generated
o Cannot be engaged at high speeds
o Sometimes cannot be engaged when both shafts are at rest
o Engagement at any speed is accompanied by shock |
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Term
| • _________ used where synchronous operation is required (power presses or rolling mill screw downs |
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Definition
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Term
| • Overload release clutch |
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Definition
| spring loaded so as to release at predetermined torque. |
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Term
| • Failure by _________will occur when the significant tooth stress equals or exceeds either the yield strength or the bending endurance strength |
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Definition
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Term
| • A _______ ________ occurs when the significant contact stress equals or exceeds the surface endurance strength |
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Definition
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Term
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Definition
| American Gear Manufacturers Association |
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Term
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Definition
| introduced an equation for estimating the bending stress in gear teeth in which the tooth form entered into the formulation (1892) |
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Term
| • 4 things to look at when analyzing performance of clutches and breaks: |
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Definition
o Actuating force
o Torque transmitted
o Energy loss
o Temperature rise |
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Term
| • Various types of devices to be studied and may be classified as follows: |
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Definition
o Rim types with internal expanding shoes
o Rim types with external contracting shoes
o Band types
o Disk or axial types
o Cone types
o Misc types |
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Term
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Definition
| inertial energy storage device; absorbs mechanical energy by increasing its angular velocity and delivers energy by decreasing its velocity. |
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Term
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Definition
| frictions is reducing the necessary actuating force |
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Term
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Definition
| when critical value of coefficient of friction causes term (b-fa) to become zero; designer must insure this will not occur unless its specifically desired. |
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Term
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Definition
| the operating mechanism has been designed so that, if any element should fail to perform its function, no accidents will occur in the machine. |
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Term
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Definition
| from railway industry, refers to locomotive control mechanism which causes engine to come to a stop if operator should suffer a blackout or die at controls |
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Term
| • A break shoe is __________ _____________ if its moment sense helps set the brake, self deenergizing if the moment resists setting the brake. |
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Definition
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Term
| • Three elements of an internal shoe rim clutch: |
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Definition
o Mating frictional surface
o Means of transmitting torque to and from surfaces
o Actuating mechanism |
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Term
| • Classifications of clutches: |
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Definition
o Expanding ring
o Centrifugal (used mostly for automatic operation)
If no spring used, torque is proportional to square of speed
o Magnetic
Useful for automatic and remote control systems
o Hydraulic
Useful for complex loading cycles and in automatic machinery
o Pneumatic |
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Term
| • Hydraulic and pneumatic clutches are available as |
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Definition
o Disk
o Cone
o Multiple plate clutches |
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Term
| • Internal shoe or drum brake |
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Definition
| mostly used for automotive applications |
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Term
| • Pressure distribution has interesting and useful characteristics: |
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Definition
o Pressure distriubution is sinusoidal with respect to angle theta
o If shoe is short, large pressure on the shoe is p¬(a) occurring at end of shoe
o If shoe is long, largest pressure on shoe is p(a) occurring at 90 degrees |
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Term
| • Assumptions implied by analysis: |
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Definition
o Pressure at any point on shoe assumed to be proportional to distance from hinge pin, zero at the heel
o Effect of centrifugal force neglected; clutch design, this force must be considered in statics
o Shoe assumed to be rigid
o Analysis based on coefficient of friction |
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Term
| • Operating mechanisms can be classified as: |
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Definition
o Solenoids
o Levers, linkages, toggle devices
o Linkages with spring loading
o Hydraulic and pneumatic devices |
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Term
| • When external contracting designs are used as clutches, the effect of __________ ____________ is to decrease the normal force. Thus, as the speed __________ a larger values of the actuating force is required. |
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Definition
centrifugal force
increases, |
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Term
| • Flexible clutch and brake bands |
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Definition
| are used in power excavators and in hoisting other machinery |
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Term
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Definition
| mating frctional members are moved in a direction parallel to the shaft. |
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Term
| • Advantages of disk clutch: |
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Definition
o Freedom from centrifugal effects
o Large frictional area that can be installed in small space
o More effective heat dissipation surfaces
o Favorable pressure distribution |
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Term
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Definition
| caliper supports a single floating piston actuated by hydraulic pressure |
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