303a Flashcards
How is the gear tooth made up?
4 terms on one tooth*
Face
Flank
Heel
Toe
What is the pitch line on a gear tooth?
Pitch line is a line dividing the tooth width wise into two equal sides.
When 2 gears move along each other it is important to line both the pitch lines of each gear correctly for even wear and maximum efficiency
Explain what the face, flank, toe, and heel are on the gear tooth
The gear is divided lengthwise and the top half is FACE. The bottom half is FLANK. The narrow or smaller end is the TOE. The wider or larger side is the HEEL
What are the 4 other additional gear tooth terms are there? Courtesy Nissan Canada manufacturer them
-Coast (concave side)
-Drive (convex side)
-Root fillet (bottom, between two teeth)
-Tip (top of tooth)
What is pitch circle? How is it made up?
Pitch circle is made up of 3 lines that go around the teeth on the gear.
You have the ROOT which is the bottom of the gear.
You have the PITCH which is the line that divides the face and the flank.
Then you have the OUTSIDE which is just the outer circle of the teeth.
What is circular gear pitch?
The distance between the gear tooth centre line, on the pitch circle is the gear pitch.
When two gears are meshed with on another, the circular gear tooth pitch must be the same on each gear
What is clearance?
Clearance is when 2 gear teeth are in mesh a small gap exists between the tip and root of 2 gears. This helps them maintain a lubrication film between the teeth as they move.
What is back lash?
Back lash is the gap between where gear teeth mesh on the sides and engineers came up with this to ensure proper lubrication is there and gives enough room for gear tooth expansion.
What are timed gear seats?
Some manufacturers have gears that need to be timed with each other to ensure that they always operate in a specific relationship with one another.
What is a non hunting gear design?
-It is a gear the needs to be timed
-the number of pinion gear teeth will divide into the number of crown gear equally. Such as 10 and 30, or 13 and 39, (3:1)
-Writing the ratio is always Drivin divide by drive
Always a whole number
What are partial non hunting gear sets?
-this has to be timed
-The partial non hunting is when the crown gear must complete two or three revaluations before the number one pinion tooth returns to is original starting mesh point
-the number of pinion gear teeth will divide into the number of crown teeth unequally.
Example.
10 pinion teeth to 45 crown gear teeth 4.50:1
What are hunting gear sets?
A huntings gear is when each and every pinion tooth will come into mesh with each and every other crown gear tooth at some time during operation.
Number of teeth on both gears will divide unequally
Timing does not matter with hunting gear sets.
Example.
9 pinion teeth to 30 crown gear teeth (3.333:1)
Gears are the components in power transmission units that are used to create what?
3 of them
Direct drive-(1:1)
Reduction-(2:1)
Overdrive-(0.5:1)
Explain direct drive
-two gears identical in size are in mesh with one another
- there is no speed difference
- no torque change
-1:1 ratio
To calculate the gear ratio just use the number of teeth on each gear and write it as “driven gear teeth divide by drive gear teeth”
Example.
24 driven gear teeth
24 drive gear teeth
24/24=1:1
Explain reduction
Reduction is when a small diameter gear is used as a drive member and the driven member is a larger diameter gear
-this would have low speed and high torque
The output torque is multiplied by 2 which makes the ratio (2:1)
Example.
24 driven gear teeth
12 drive gear teeth
2:1 ratio
Explain overdrive
-In an overdrive condition the input drive gear has a larger diameter then the output driven gear
- overdrive gear is often set in highway vehicles.
- example
12 driven gear teeth
24 drive gear teeth
12/24=(0.5:1)
What do idlers do?
If an output gear has to turn the same direction as the input gear then an idler gear must be placed in between the gear. This does not after the overall speed or torque in the gear set.
What are straight cut spur gears?
5
Most basic gears
- straight cut teeth
-teeth push against each other
-low strength
-reasonably inexpensive
-can be noisy
What are external gears and internal gears?
External gears are where teeth are located on the outside of the perimeter of the gear
Internal gears are where teeth are located on the inner perimeter of the gear Internal gears
Due to their design, internal gears can be very strong. They are often used in planetary gear sets
Single helical gears
Single helical gears have teeth cut at an angle to the shaft, this provides great strength and less noice during operation.
Due to angle cuts of teeth, “axial thrust load” are created. This requires a washer or bearing to control thrust loads
-the gears will attempt to move out of mesh with one another because of axial thrust act in opposite directions
Double helical gear?
Also know as?
These are used during heavy torque loads must be handled, helical gears are also known as herringbone gears
Major advantage is the axial thrust loads are cancelled by each other
Disadvantage is the high cost to manufacture this gear
What is rack and pinion gears and what do they do?
They are used to change rotary motion to linear motion
What are angle drives?
Angle drives gear sets are used when it is necessary to make a directional change in the path of power
The angle can be quite small up to 90 degrees
Straight cut bevel gears
Bevel gear sets may use straight cut gear teeth because of the relative ease of production and low cost
Noisy and only can be used in 90 degree change in power
You have 3 main types of bevel gears used for different operation conditions.
What are they?
Spiral gears- in centre of bevel gear line. Even torque and speed
Hyoid angle gears- below the centre of bevel gear line. High torque applications, this has even more tooth contact during meshing
Amboid gears- above the centre of the bevel gear line. This allows a higher driveline position, which is useful for vehicles operating off-road where ground clearance is a problem
Worm and worm wheel
(Worm gear)
These gear sets are very strong, but also very expensive
-very useful in high torque loads must be handled
Example.
A winch drive and a basic worm and worm wheel
Three main components of a planetary gear set?
Sun gear, the middle gear that rides along the teeth of the planetary gears
Internal gear, outer gear where the planet gears ride along the teeth and along the teeth of the sun gear
Planet pinion gears, these gears are not allowed to move freely between the internal gear and sun gear
*in order for a planetary gear set to operate there must be a drive member, a driven member and a member that is held stationary. Sometimes the held member is referred as the “reactionary member”. A simple planetary gear set can be set to operate in a direct drive, reduction, reverse or overdrive arrangement.
