automatic gears.pdf

automatic gears.pdf

• 1.
  Simple Epicyclic GearTrains Epicyclic gear trains have a number of new definitions not found in simple gear trains: Ring gear or annulus gear (R)
• 2.
  Kinematics of Epicyclic GearTrains Planet gear P can rotate freely on a pin attached to carrier C Carrier C rotates freely about the axis of sun gear S Only one planet gear P is needed to transmit motion Multiple planet gears can be added for balance, strength, and smooth operation Extra planet gears DO NOT change the speed ratios of epicyclic gear trains
• 3.
  Ring gears typicallyhave internal teeth Ring gears can have external teeth meshing with additional gears External gears are not part of the epicyclic gear train P S R C Simple Epicyclic Gear Trains
• 4.
  Advantage of epicyclicgear trains: P S R C Simple Epicyclic Gear Trains • Compact • Gears are constantly in mesh • Loads are shared between several gears
• 5.
  Advantage of epicyclicgear trains: P S R C Simple Epicyclic Gear Trains • Reverse can be achieved without the need for additional shaft
• 6.
  Advantage of epicyclicgear trains: P S R C Simple Epicyclic Gear Trains • Several gear (speed) ratios can be obtained • Three shafts available for selection of input and output shafts
• 7.
  Input/Output Shafts • Twoshafts can be selected for input and output (e.g. sun and carrier) and one shaft is locked (ring gear) • Sun gear or carrier can be locked and the remaining two components are used to determine the speed ratio
• 8.
  How many teethshould each gear have? Gear Teeth Number Relationships
• 9.
  Gear Teeth Number Relationships rR rS rS rR dP dP Wecan determine the required size of all the gear components visually. (1) P S R P s R P S R d 2 d d d 2 r 2 r 2 d r r      
• 10.
  10 rR rS dP
• 11.
  Module Recall that themodule is the length of pitch circle diameter per tooth 1 P n d m   To mesh, two gears must have the same module. To mesh, two gears must have the same module. Gear Teeth Number Relationships
• 12.
  Gear Teeth Number Relationships rR rS rS rR dP dP Usingthe equation for the module, we can write: (2) Module n m d n d m   Lecture Outline Compound gear train example Epicyclic gear trains Analysis of epicyclic gear trains Examples
• 13.
  (1) P S R P s R P S R d 2 d d d 2 r 2 r 2 d r r       (2) Module n m d n d m   (3) (2) and (1) From P s R P S R n 2 n n n m 2 n m n m     Gear Teeth Number Relationships rR rS rS rR dP dP Wenow have a relationship for the number of teeth of each gear.
• 14.
  Gear Teeth Number Relationships rDrE dB dC rA A compound epicyclic gear train is shown If we know how many teeth are on gears A, B, C & D, how many teeth are on gear E?
• 15.
  n n n n m m n m n m n m n m m m d d d d r r r r r r r r C B A E C B A E C B A E C B A E C B A E                 , If ly respective D, - B - A and C - E for trains modules the are and If 2 2 2 2 2 1 1 2 2 1 2 1 Gear TeethNumber Relationships rD rE dB dC rA
• 16.
  Schematics of EpicyclicGears Left: The epicyclic gear train Right: An example of an epicyclic gear sketch Teeth are indicated by “T” A B C E D F The gears and carrier are labelled
• 17.
  Another example... Schematics ofEpicyclic Gears
• 18.
  Analysing speed ratios Considerhere that the sun gear is held stationary What might the ratio of the ring gear shaft to the carrier shaft be…?