NISSAN T302 Manual Transmissions & Transaxle

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Section 1

Torque Chart
Usable torque is produced beginning at about 1200 rpm and then increases proportionally with engine rpm to a certain point where it peaks around 2500 to 3000 rpm.

Torque The transmission converts engine speed into the needed torque output Multiplication required for different driving conditions.
High torque is needed to start off from a stop and engine torque must be greatly multiplied at low engine RPM. High torque for climbing hills is provided by increased engine RPM and torque multiplication. Less torque is required to keep the vehicle moving at intermediate or high speeds, allowing engine speed to be reduced.

Changing Speed Several devices, such as, gears, chains and sprockets can be used to or Torque change the speed or torque of a rotating output shaft. Gears with
different teeth counts can be used to change the speed of a rotating shaft. Reducing the speed increases the torque proportionately; likewise, Increasing the speed reduces the torque. The driven gear (output) always rotates in a direction opposite to the drive gear (input). If the drive gear and driven gear need to rotate in the same direction, the power can be routed through two gears sets, or through a combination of internal and external gears.

Changing the Speed or Torque of a Rotating Shaft
Gears with different teeth counts can be used to change the speed of a rotating shaft.

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Introduction to Manual Transmissions & Transaxles

Gear Ratios Gear ratio is the ratio of the size of two or more gears acting on each
other. Gear teeth are cut in proportion to their diameter; if you have a drive gear that has 9 teeth and a driven gear that is twice as large as the drive gear, the driven gear will have 18 teeth. (see figure 1-7) When the drive gear rotates one revolution, the driven gear will rotate 1/2 revolution­9 teeth of each gear will come into contact for each revolution of the drive gear. Determining Gear Gear ratios are determined by dividing the number of teeth on the Rations driven gear by the number of teeth on the drive gear. In the example in figure 1-7, 18 9 = 2, therefore the ratio is 2:1.

Gear Ratio
When two gears with a gear ratio of 2:1 rotate together, the smaller drive gear will rotate one revolution to produce one-half revolution of the larger driven gear.

In this example, two revolutions of the drive gear will produce one revolution of the driven gear. This is called reduction­a reduction in speed, but an increase in torque. The higher the number of rotations on the drive gear, the lower the ratio. If the drive gear has 9 teeth and the driven gear 6, there will be an increase in speed and a reduction in torque. This is referred to as overdrive. The ratio is determined as follows: 6 - 9 = 0.6 (6/9 = 0.6); so the ratio is 0.6:1. In this case, the drive gear turns 0.6 or three-fifths revolution for each turn of the driven gear. A gear ratio is always written so that the number 1 is to the right of the colon. This represents one turn of the output gear, while the number to the left represents the revolutions of the input.

Manual Transmissions & Transaxles - Course 302

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Section 1

Determining Gear Ratios
Most gear ratios are determined by dividing the number of teeth on the driven gear by the number of teeth on the drive gear.

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