Automatic Transmission & Transaxle
Work Example 7

WorkKey Level: 5
NATEF Automotive Tasks: background

You are changing the rear-axle ratio and replacing the automatic transmission on your car.The engine and transmission are coupled by a torque converter.The converter’s maximum torque multiplication is approximately 2.3:1.You know the final output torque for the entire drive train in a given gear is the product of the engine torque, maximum torque multiplication of the torque converter, gear ratio, and rear-axle ratio. The low-gear ratio n the transmission being replaced is 2.63:1.The low-gear ratio in the new transmission is 2.9:1.The rear-axle ratio is being changed from 2.89:1 to 3.84:1.

1.  What is the final output torque for the entire drive train in first gear before the changes when the engine is developing 250 pound-feet of torque?

2.  What is the final output torque for the entire drive train in first gear after the changes when the engine is developing 250 pound-feet of torque?

3.  What is the percent of increase in final output torque?

Solution:

1.  Final torque = 250 lb-ft x 2.3 x 2.63 x 2.89
     Final torque = 4370 lb-ft

2.  Final torque = 250 lb-ft x 2.3 x 2.9 x 3.84
     Final torque = 6403 lb = ft 

3.  Percent increase = (6403 – 4370)/4370> × 100
     Percent increase = 46.5%