Selectable Locking Differential

Team Members

Scott Leach

Dillon Voegeli

Xingyu Xu

Weeriya Meesook

Jihwan Kim

Project Goal To create a selectable locking differential that can be installed by

the average consumer without removing the carrier and ring gear,

drastically reducing installation complexity and saving the consumer

money on professional installation.

A model of the design and how it installs within the carrier

Background Most vehicles have open differentials, which allow the wheels to

turn at different rates when turning. This makes everyday driving

easy, but can make off-roading quite difficult. A locked differential

forces the wheels to turn together, resulting in much easier travers-

ing of rough terrain but making turning extremely difficult.

A selectable locking differential allows the operator to lock or un-

lock the wheels at will, however current market offerings are expen-

sive, require the purchase of additional hardware such as an air

compressor and tank, and require removing the whole differential

carrier and ring gear assembly to install. Reinstalling these compo-

nents requires the skills of a professional mechanic, as the ring

gear’s helical teeth must mesh perfectly with the teeth of the helical

bevel gear attached to the drive shaft.

This product installs within the original carrier, called a

“lunchbox” locker within the industry, and as such gives the func-

tionality of a selectable locking differential without the added cost

of purchasing additional equipment and without needing to pay a

mechanic to properly reinstall the ring gear.

Design This design uses three sets of spur gears to move the differential

action desirable when cornering outside of the center of the carrier,

freeing up this area to be used for the locking mechanism. The side

gear carriers are held in place by the pin that comes with the stock

differential. The locking shoe has two levers that can be moved to

engage its teeth with those of the axle gear. This uses these teeth

and the aforementioned pin to lock the two axles together.

Analysis Analysis of this design was performed in two parts. The first was

to approximate portions of the design as simpler systems for easy

analysis, such as approximating gears as shafts whose diameter is

equal to the pitch diameter of the gear. These calculations were used

to approximate the forces at work on the design for initial material

selection based on desired safety factor to yield strength.

Simplified model of torsional shaft loading

The second part was to perform FEA analysis using Siemens NX

and CAD models of the design. These analyses were compared

against the simplified calculations and compared against the me-

chanical performance of a variety of potential materials to maximize

safety factor per unit cost.

FEA Analysis of the two Axle Gears

Manufacturing The large axle gears were manufactured using an EDM. A special

copper head was created using a 3-axis mill and used to create the

recessed locking teeth. The side gears were created from 16-tooth

bar stock sold by McMaster-Carr turned on a Collet lathe and with

holes bored using a 3-axis mill. Finally, the side gear carriers and lock-

ing shoe were created using a 3-axis mill and CNC mill, respectively.

Bill of Materials

Item Quantity

Axle Gear, 36-Tooth 1

Axle Gear, 36 Tooth with recessed Locking Teeth 1

Side Gears, 16-tooth 6

Side Gear Carrier 2

Locking Shoe 1

Gears turned on the collet lathe Gear being cut with the EDM

Boring holes with the mill Recessed teeth created with the EDM

Axle Gears and Locking Shoe