Design of 5-speed powertrain for Ducati Supersport model motorcycle

Design of a Motorcycle Powertrain

Scope of the Project:

To design a 5-speed manual gearbox for a motorcycle with constant mesh gears, dog shifting mechanism for gears engagement and apply Geometric Dimensioning and Tolerancing to the various components.

Design Parameters:

The various components of the design assembly are:

• 5 Gear pairs producing 5 ratios
• 2 shafts-input and output
• Bearings-Cylindrical roller type to withstand radial and thrust load
• 3 shifting forks for the 3 dog gears
• Snaprings/retainers to hold gears in place
• Sprocket on the output shaft

Gear parameters:

Spur gears are designed with a module of 2 and a width of 8 times the module, and pressure angle of 20degrees.

The ratios for the gears are as follows:

• 1^st gear-2.467
• 2^nd gear-1.736
• 3^rd gear-1.476
• 4^th gear-1.167
• 5^th gear-0.850

Note: The calculations for the gear pairs are summarized in an excel sheet and attached with the mail

Shaft Parameters:

A nominal shaft diameter of 3/4^th an inch- 19mm~20mm(for bearing selection at 17mm dia) has been designed

The center to center distance is 52mm and the bearing to bearing span on the housing is 168mm.

Material Selection:

EN24T is chosen for the gears and shafts with a hardness of 250HB, with further nitriding.

Powertrain Parameters:

The above snip from an excel sheet indicates the gear teeth, gear ratios, centre to centre distance and the diameters of various gears.

the calculations are built into the excel sheet.

Follow the link to Calculations excel:-

Design of Free wheeling Gears,Shafts, Dog gears and shifting forks:

Freewheeling Gears:

The powertrain has 7 free wheeling gears that rotate about the shaft on a brass bushing with a frictionles surface finish.

The gear showin in the above figure is the 2nd gear of pair 1, that gives most torque(Gear 1). These gears have holes in them that can accomodate the mating dogs from the dog gears with adequant clearance around the perimeter of the dogs.

Dog Gears:

The above figure shows a 2 sided dog gear that has a groove for the shifter fork to slide the dog gear about splines on a shaft.

These gears have internal mating splines to help slide along external splines on the shaft.

Meshing gears(Gear Pairs):

The above image shows the 5th Gear pair of the powertrain that produces the least torque and maximum speed. The gears are meshed such that their PCDs are coincident and all the gear pairs have a centre to centre distance of 52mm.

Shafts:

Input shaft

Output Shaft

Both the input and output shafts have many steps for the gears and bearings and grooves for the external heavy duty snap rings.

The maximum step diameter is 22mm and minimum step diameter is 17mm.Thus a 25.4mm( 1 inch) standard diameter shaft is required to machine the shaft.

Shifter Forks:

The 5-speed powertrain has 3 shifter forks to engage 5 gears via 3 sliding dog gears.The shifter fork ends slide on a 10mm shaft that are simply supported at the ends by the gearbox casing. These forks move along the grooves on the shifter drum that is operated by the shifting lever, thus rotating the drum and enabling sliding motion of the forks.

Powertrain Assembly: