Design
Throttle Limiting System (Saw-tooth Braking Mechanism)
Before conducting an actual test, a stress analysis simulation was run through the Inventor program to check for deformation of the braking mechanism.
To the right is a stress analysis done in Inventor that illustrates the displacement of the braking mechanism under a point load of 20 lbsf.
The free body diagram is used to solve for the force required for the ratcheting mechanism to be forced back. This is necessary to fulfill the dead man throttle requirement for the ASABE Quarter Scale Tractor Competition.
The saw-tooth section will be attached to a metal plate that also will create the cable pull. This saw-tooth and cable bracket will be attached to the pivot rod by a clamping collar.
The pawl and actuator will be attached to a metal plate inside of the casing that will allow for all of the saw-tooth braking mechanism parts to be aligned in a single plane. This removes any bending moments or torsion forces on the parts.
Throttle Handle
Clay models of potential handle designs were sculpted to serve multiple purposes. They were used to determine the comfort and feel of the handle designs. They were also used to aid in creating 3D models.
We decided to use the design from the model on the upper left. The existing dimensions from the model and the changes we wanted to make from it, helped us to create the CAD model to the left.
The handle was modified to fit a round lever arm as opposed to a rectangle, and the rocker switch we selected called for a round insert. The face was made deeper because the buttons set into the button face deeper than expected.
To print the handle with a 3D printer, and for assembly purposes, the part had to be split. It will be reassembled with screws demonstrated by the exploded view below.
Throttle Assembly
The image to the left shows the throttle assembly without the casing. In this picture, you can see the working parts of the assembly. The solenoid, linkage, and pawl assembly that seem to be floating in space will actually be attached to the casing itself. The rest of the assembly attaches to a rod to allow for rotation. The sawtooth wheel will rotate with the handle and cable plate when the brake system is not engaged. Once the brake is engaged, the solenoid will retract and the pawl will latch to the sawtooth, stopping forward rotation only. The cable plate will connect to the throttle of the engine and set engine speed.
The updated throttle assembly is shown to the right. This is the complete assembly that will be used to model the prototype.
Left:
The complete assembly without the casing allows to viewer to see how the parts are attached to the pivot rod.
Right:
The casing assembly had to be split into two parts because the case is too large for the printer deck. The case will be assembled with nuts and bolts.
General Information for Assembly
The cable travel is needed to know where to limit the throttle travel to keep from breaking the throttle cable or the the cable linkage.
To the right is a measurement at the engine for throttle cable pull. The cable pull is roughly an inch and quarter ( 1 1/4 in )
Using McMaster-Carr, we found a solenoid that meets our desired functions for rotation of the brake rack. The solenoid is part number 69905K113.
This spec sheet is for the seven position knob that will be placed in the throttle casing for the Transmission Group
The above image provides cutout dimensions for the
push buttons we bought to use on the handle face.
This retaining ring will keep the pawl from sliding off of its mount post.
This information is important to knowing how large the
facing holes should be for the rocker switch insert.