Question 1 Propose a functional design for a gear speed reducer, with a constant

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Question 1 Propose a functional design for a gear speed reducer, with a constant speed ratio and for which the input and output shafts are parallel but not necessarily collinear. The operating conditions are the following: speed ratio = 50, parallel input and output shafts . High input speed, the input shaft rotates in one direction . High torque High axial forces applied to the input and output shafts, two directions The gear is used in mining equipment: the rotation of the output shaft subject to very irregular resistance and can be stopped abruptly No special concern to the noise level, minimum cost desired a) Which type of gears did you choose? Justify their benefits. (5 points) b) How would you attach the gears to the shafts? Justify (3 points) c) Identify a different type of gear you could use. Why was this gear not your first choice? (3 points) d) Select the bearings required for your design, and justify. Note: make any assumption (s) in terms of load and identify these hypotheses. (5 points) e) Draw a diagram of your gearbox showing the positioning of gears, bearings and shafts, as well as the casing. (10 points)

Explanation / Answer

a. The operation requires high torque and input force with axial loading on shafts that are parallel to each other. Spur gear or helical gears are suitable. Also axial loading is present on shaft so some axial movement might occur. To avoid jamming of gears spur gears are selected. Noise level is not a concern so the choice is justified. Benefits of spur gears:

1. High transmission efficiency for precise gears ( 90+%)

2. Can be used for a long time if proper maintainance is done (greasing and cleaning)

3. Relatively cheaper to produce and design.

b. The gears would be attached using a spline shaft arrangement. Since the speed reduction us for mining purpose frequent shocks are expected which leave no room for using keys. Benefits of splined shaft gears is that they perform efficiently in high load high vibration and sudden shock applications. Also helical gears do not allow for any axial movement of shafts. Since significant load is present on the shafts in axial direction any misalignment will cause the gears to jam.

d. The bearing suitable for thus design are tapered roller bearings with taper in both directions. They are suitable for high speed application when both radial and axial load are present. Tapers are in both directions because the axial load is from both directions.

c. A different type of gear we can use is double helical gear. It offers quite operations and a realtively smoother load distribution on gear teeth. This was not our first choice because helical gears are costly to design and manufacture. Our aim is to keep cost minimum and no preference is given to noise while in operation.

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