There are many constraints to which the design idea must adhere. The following details pertain both to the basis of the design as well as physical limitations set by ARCCA.

• The mechanism must withstand 25,000 in-lbs of torque applied about the mechanism’s operating axis. (When used in a dual recliner system, it will withstand 50,000 in-lbs of torque.)

• Each angle adjuster shall include a minimum of 10 adjustment positions for every 20 degrees. The adjustment range can be between 20 and 40 degrees.

• When disengaged, the mechanism must not rotate freely.

• The overall thickness of the mechanism may not exceed 1 inch, excluding the spring and
release/handle mechanism.

• The total mechanism weight must not exceed 10 lbs.

• The mechanism does not have to be functional post test.

• The mechanism must include a least two separate mounting locations per rotating or adjusting aspects of the mechanism. These mounting locations shall consist of minimum 0.375 inch holes and will be used for validation testing.

Before fabrication of the prototype, parts of the seatback angle adjuster were analyzed using finite element software. Two software packages were used for this prototype, SolidWorks and ABAQUS. The finite element software allowed detailed stress analysis of the part to ensure the design would not fail. The finite element software indicated areas of high stress and allowed TRI Designs to modify the design for maximum strength. Hand calculations were also performed to verfiy the finite element models.

Figure 1 below is a screenshot from the finite element model for the seatbottom bracket. This was modeled by restraining the interior of the octagon cutout while applying a force to the two bolt holes. The model indicated that the areas of high stress were located at the bolt holes and portions around the cutout, however none of these were greater than the yeild strength of 1018 steel.

Figure 2 is a screenshot of the tooth analysis on the key. The solid portion of the key was restrained while a force was applied to the base of the tooth. The highest stress was found to be at the base of the tooth but was significantly less than the yeild strength of the steel.

• The seatback and seatbottom bracket were both cut at Skytop Machine and Tool using their waterjet machine. It was found to be more cost effective to let Skytop do this versus using the CNC machine.

• The key had to be done on the CNC machine because the waterjet maching could not cut to a specified depth.

• The parts were welded and assembled in the Learning Factory.
  

Waterjet seatback bracket

TRI Designs used ARCCA's testing facilities located in Penns Park, PA. A summary of the test setup is below.

• Seatback angle adjuster bolted test fixture.
• Force applied at 8.9 inches from the pivot point of the adjuster.
• Force sensor mounted inline with cable.
• Cable was mounted to middle beam to ensure a horizontal pull.
• Middle beam was then attached to winch.
• Extensometer and angle sensor were mounted to angle adjuster.
• All sensors were connected to computer with real-time readout.
• 3 cameras placed around angle adjuster and synchonized with data.

After carefully setup of the test, the winch pulled on the seatback bracket while the applied force was measured. While testing the middle beam, as well as the rest of the test fixture, started bending which forced the test operator to stop the winch.. After stopping the winch, the force was held for approximately 10 seconds and then released. The results show that the seatback angle adjuster withstood approximatly 30,000 in-lbs before the test fixture failed. This exceeded ARCCA's specification of 25,000 in-lbs by 5000 in-lbs. It was noted that there was no damage to the seatback angle adjuster and the adjuster was fully functional after the test. Figure 3 is a plot of torque versus time for the seatback angle adjuster before the test fixture failed. This indicates that we reached approximately 30,000 in-lbs.

 

Figure 3: Torque versus time before test fixture failure.

 

Pictures from the testing are shown below.

The prototype design is very strong. Finite element analysis indicates that the angle adjuster can withstand over 40,000 in-lbs before failing. This design has a secondary safetly feature which are the pins protruding from the key. These pins were designed to be able to carry the entire load if the teeth were to fail.

The following is a list of suggestions and comments for the seatback angle adjuster design.

• TRI Designs claims that the design would be more easily manufactured had we been allowed 3 degree adjustments instead of 2.

• CNCing the teeth on the key was painfully long and many end mills were broken. In practice, if the design were to make it into industry, we recommend a powder metal processes.

• For the seatbottom and seatback brackets, TRI Designs recommends using a forging or stamping process. Although waterjet provided results within our tolerances, it was relatively expensive.

We believe that this is a superior design to what is currently available in industry. The design is much stronger and, in many cases, simpler than most seatback angle adjusters on the market. We would like to see stronger seatback angle adjusters placed in all vehicles for passenger safety.