Transmissions and Gearing

1
Transmissions and Gearing
2
Engine to Axle Torque
naxle ne/Gpt
Gpt GtGDGFD
Taxle TeeptGpt
Ept eteDeFD
ne/Gt/GD/GFD
TeetGteDGDeFDGFD
GFD eFD
ne/Gt/GD
TeetGteDGD
ne/Gt
GD eD
Gt et
TeetGt
3
Torque, Power, and the Transmission

• What is the ideal relationship between torque and
  speed at the axle?
• Remember our torque speed curve for the engine?
• Not very similar

4
Gear Modified Torque Curves

• Gear reductions provide a variety of Torque-speed
  curves at the axle that help to approximate the
  ideal
• More gears allows a closer appoximation of full
  power at any speed of the axle

• Overlap allows more than one engine speed option
  for a given axle speed

5
Types of Transmissions

• Sliding Gear Gears must synchronize. No
  automatic mechanism to synchronize
• Synchromesh- Gears are always in mesh, but are
  connected to shaft when needed
• Power shift uses clutches brakes and usually a
  planetary drive
• CVT continuously variable transmission
• Hydrokinetic much like your car uses

6
Gear Design

• Mostly we will leave this to D.O.M.E.
• A few basics we need to know
• Diametral Pitch, PD N/pitch diameter(inches)
• Pitch diameter is imaginary circle where gears
  appear to roll together
• N number of teeth

7
Gear Relationships

• In most cases gears that mesh must have the same
  diametral pitch or module
• Metric gear terminology
• Instead of diametral pitch we have
• Module Pitch diameter (mm)/N

8
Gear Relationships

• Gm Gear reduction from a single mesh
• Gm Nin/Nout nout/nin
• N numbers of teeth input and output
• n Speeds in and out
• For meshing gears operating on stationary
  centers Ninnin Noutnout
• Torqueout/Torquein emGm

9
Manual Sliding Gear Transmission
10
A Synchromesh Transmission
Hmmm. Now thats hard to follow!
11
Sliding (Splined)
42T Solid
36T
28T
22T
14 T Solid
Input
Output
Countershaft
41T keyed
47T
55T Free
61T Free
45T Free
Sliding Couplings
12
1st Gear
Power Flow
Sliding (Splined)
42T Solid
36T
28T
22T
14 T Solid
Input
41T keyed
47T
55T Free
61T Free
45T Free
Sliding Couplings
13
6th Gear
Power Flow
Sliding (Splined)
42T Solid
36T
28T
22T
14 T Solid
Input
41T keyed
47T
55T Free
61T Free
45T Free
Sliding Couplings
14
8th Gear
Power Flow
Sliding (Splined)
42T Solid
36T
28T
22T
14 T Solid
Input
41T keyed
47T
55T Free
61T Free
45T Free
Sliding Couplings
15
Slider - Synchronizers
16
Power Shift Approaches
Annular Cylinder
Direct Drive
17
Power Shift Approaches
Annular Cylinder
UnderDrive
18
Planetary Gear Sets
19
Additional Planetary Set Considerations(Courtesy
of Roman Cisek Senior Engineer Gear Design,
John Deere)

• Assembly condition
• teethsun teethring
• Divided by planets
• integer

20
Additional Planetary Set Considerations(Courtesy
of Roman Cisek Senior Engineer Gear Design,
John Deere)

• Clearance condition
• Must be positive clearance between neighboring
  planet pinions. Important for high reduction
  gear sets where planet pinions are large
• Tooth Mesh condition - see next slide

21
Tooth Mesh Condition in Planetary Sets(Courtesy
of Roman Cisek Senior Engineer Gear Design,
John Deere)

• For a given center distance, a proper mesh
  condition must be created for the sun-planet and
  planet-ring meshes. This is usually a non
  standard design, with planet pinion working on a
  different operating pitch diameters with the sun
  gear and the ring gear.
• This can be explained by analyzing spread or
  compressed center distance gear designs to
  balance strength and durability of a gear set

22
Calculating Planetary Ratios

• Nr teeth on the Ring
• Np teeth on the planets
• Ns teeth on the sun gear
• Now specify which is input
• Specify which is fixed
• Many times the Planet Carrier is the output member

23
Planetary Table Procedure Example
SUN
PLANETS
CARRIER
RING
1
1
1
1
-1
-Nr/Np
Nr/Np x Np/Ns Nr/Ns
0
1- Nr/Np
0
1
1Nr/Ns

• ID the input, output, and the grounded members
• Row 1 Give all components 1 turn
• Put a 0 in row two under the carrier (hold it
  fixed)
• Rotate the grounded member backward 1 turn to get
  it back to grounded
• Calculate the rotation of the other members
• Add Rows 1 2 into row 3 and calculate IO ratio

24
Another way to look at planetary ratios
D

• Drive sun, fix the ring, output at Planet Carrier
• VBrB?s
• VD 0
• ?p VB/rDB
• Vc ?prDC
• Vc rcarrier?carrier
• ?carrier VC/rAC
• Substitute to get ?carrier as f(?s)

C
B
A
25
Another way to look at planetary ratios
D

• Drive sun, fix the ring, output at Planet Carrier
• After substitutions
• ?c rB?s/rDB x rDC/rAC
• Now note that rDB is the planet pitch diameter
• And rB is the sun pitch diameter/2
• And rAC is the sum of the sun and planet pitch
  radii

C
B
A
26
A High-Low Planetary Power Shift
Planets rotate on fixed centers as a
standard gear reduction
Case 1 Ground the Planet Carrier
Now Drive the first Sun
Power Flow
27
A High-Low Planetary Power Shift
Case 2 Connect Input to the case
Now Drive the first Sun
Power Flow
Now planet centers rotate At same rate as sun.
No Relative motion. Direct Drive
28
Full Power Shift Transmission

• By connecting several sections of planetary sets
  in series we can make a transmission with a
  number of gearing options with power shift
  capability between all possible ratios
• Lets look at a full power shift planetary
  transmission in sections

29
Full Power Shift Schematic
30
Power Shift Xmission Section I

• Two input clutches, C1 and C2
• Activate C1 and we get direct drive on the inner
  shaft

31
Power Shift Xmission Section I

• Activate C2 and we rotate this member
• Activate CLO and we get direct drive of the outer
  shaft
• This occurs because the PC and the sun rotate at
  the same speed so there is no relative rotation
  of the Planets
• Power flow

32
Power Shift Xmission Section I

• Again we activate C2 and we rotate this member
• But now we activate brake BHI to Ground the Sun
• Now the Large planet rotates on the sun while the
  small one drives the Ring as the output. A gear
  reduction (increase) results
• Power flow

33
Input Section Compound Planetary Ratio
SUN
PLarge
CARRIER
RING
PSmall
1
1
1
1
1
-1
(Ns/NpL)(NPS/NR)
0
Ns/NpL
Ns/NpL
0
1
1(Ns/NpL)(NPS/NR)

• Now for 1 turn of the input (carrier) we get
• 1(33/42)(18/93)
• Ratio is 1 turn of input for 1.152 turns of
  output

34
Section One Results

• We can drive the inner shaft at engine speed or
  disengage it and let it spin freely
• We can drive the outer shaft at engine speed
• We can drive the outer shaft at a gear reduction
  (or increase)
• What gear reduction? Lets see

35
Power Shift Xmission Sections II and III
36
Power Shift Xmission Section II

• Use one clutch and one brake (C1C2 special case)
• Lets activate C2 and B1
• S1 is driven
• R1 is grounded
• Planets react and drive Carrier as OUTPUT
• S2, and R2 are free to spin
• This is a simple planetary as analyzed earlier

37
Simple planetary Ratios

• Use the table as before
• 1 turn of the carrier (output) for each 1Nr/Ns
  turns of the input sun
• N refers to number of teeth on respective gear

38
Power Shift Xmission Section II

• Lets activate C2 and B2
• S1 is driven as before
• But R2 is grounded
• Planets react and drive Carrier as OUTPUT
• P1 is driven at S1 while P2 rolls on the inside
  of R2
• R1 and s2 are free to spin
• This is a Compound planetary
• Look at it from the end.

R2
P2
P1
S1
39
Compound Planetary Ratios

• S1 drives P1
• P1 coincides with P2 (solid)
• P2 rolls inside grounded R2
• Carrier is driven by planet stubs
• Re-run the table to determine the ratio of input
  to output

R2
P2
P1
S1
40
Power Shift Xmission Sections II and III