Engineering II Gears Getting Geared Up

What are they? GEARS Benefits Wheels with mating teeth cut in the rim or surface so that one can turn the other without slippage. The lever is basic to gearing. A pair of gears is essentially a set of spinning levers each with two equal arms acting in turn. Benefits Change the plane of rotation. Increase or decrease the speed of applied motion. Increase or decrease the applied force. Provide a drive without slippage.

Gears Driver Gears: are directly driven by a motor Drive Gear Driven Gear Driver Gears: are directly driven by a motor Driven Gears: mesh with the driver gear

Gear Ratios Mechanical Advantage: The PRODUCT of the number of teeth on the DRIVEN wheel (gear) DIVIDED BY the number of teeth on the DRIVER gear A "ratio" is a comparison. In the case of gears, it is the comparison of TURNS OF INPUT to TURNS OF OUTPUT. Example: A gear ratio of 5:1 ( an 8 toothed gear turning a 40 toothed gear), the input shaft must make five revolutions to produce one revolution of the output shaft. Output speed is five times slower, but the output torque is five times greater!

Gear Ratios Lets take a look…..Figure out the following gear ratio’s Hint: Output/Input 1. Drive 3. Drive 4. 2. Drive Drive

Gear Ratios How did you do? 3. 1. 4. 2. Drive Drive Drive Drive 20 to 18 18/20=.9:1 13 to 26 26/13=2:1 4. Drive Drive 2. 9 to 20 20/9=2.22:1 25 to 13 13/25=.52:1

Speed vs. Torque How do we achieve one or the other? Shapes Drive Gear: Large gear with more teeth attached to a smaller gear with less teeth will =more speed Drive Gear: Small gear with less teeth attached to larger gear with more teeth will = more torque Shapes Which are stronger? Drive Gear Drive Gear

Speed vs. Torque Real World Example Ford F150 has a 4.10 gear ratio Drive shaft will turn about 4x & the rear wheel will turn 1x Great for towing not on mpg’s Why do you think a 5-speed manual Ford Mustang is geared as followed? Gear 1, 3.35:1 Ratio Gear 2, 1.93:1 Ratio Gear 3, 1.29:1 Ratio Gear 4, 1.00:1 Ratio Gear 5, 0.68:1 Ratio (Overdrive)

Types of Gears Spur Gear Most common gear, straight teeth, mounted parallel Helical Gear Similar to the spur gear Teeth are cut at an angle for smother transition Bevel Gear Used when the direction of a shaft's rotation needs to be changed Usually mounted at 90 degrees apart

Types of Gears Worm Gear Used for large gear reductions (20:1, 100:1) Worm can turn the gear, gear can not turn worm Rack & Pinion Gear Used to convert rotation into linear motion.

Gear Review What is a gear? What is the MA of a drive gear with 10 teeth and a driven gear of 35 teeth? Would that set up produce more torque or speed? What is the difference between the drive gear and driven gear? What are some benefits of gears?

Gear Review 1. Wheels with mating teeth which turn each other without slipping. 2. 3.5:1- torque 3. Drive is attached to motor; driven gear is turned by drive 4. Increase speed, torque, change in output direction, provide a drive with no slipping

Gear Review How Gears Work Worksheet www.howstuffworks.com Complete the provided worksheet 30 pts. Each student must submit his or her own worksheet