In Part 1 of the Superbike Braking project we came up with three brake caliper piston designs; a thicker aluminum piston, a steel piston using the original dimensions and a two-piece design using a slightly modified stock piston with a steel insert. The next step is to use SOLIDWORKS Simulation to create a Thermal Study to analyze the heat transfer of the three designs and compare them to the original piston.
Simulation Set-up: Know what you don’t know
When using Simulation software of any kind it’s imperative that we know what we’re trying to learn. That helps us understand what information we will need in order to generate a study that will give us accurate, and useful results.
In this case, I have four designs that I want to compare. So, my goal is not necessarily to gather temperature results but rather compare the thermal trends of my designs to learn which design best meets my primary goal of minimizing heat transfer from the brake pad to the brake fluid with the minimum increase of mass as a secondary goal.
Creating Thermal Studies
Inside of SOLIDWORKS Simulation I created a Transient (time-based) Thermal study. I set the initial temperature to 80°F and set the heat source from the brake pad to 1200°F. This temperature is based on researching documents released by Brembo, a performance brake system manufacturer.
To create the thermal profile I placed a sensor on the bottom face of the piston and used it to plot the average temperature of the face at each time step. Then I set the time study to run for 45 seconds with a 1 second step size.
Under no circumstances will the braking system ever see 45 seconds of uninterrupted braking force but my goal is not to recreate the exact circumstances that will be experienced on track. I want to gather information to create an accurate thermal profile for each design that can be directly compared. Because of this my initial temperature (80°F), heat source (1200°F) and duration (45s) will be constant for all thermal studies.
Comparison and Analysis
After running all four thermal studies I saved the Sensor Graphs and brought them into Microsoft Excel where I could easily overlay the data into a single graph for analysis.
Figure 1. Thermal Study Results.
Using the Excel graph we will analyze the results of each thermal study using “Original (Al)” as our baseline for comparison.
Thick Wall Aluminum Design: Wait… What??
At first glance the results from the thick wall design are perplexing. Why would the thicker aluminum piston transfer heat faster than the thin wall version? The answer: contact area. The thick wall design has a contact area between the piston and brake pad that is over twice as much as the thin wall design. Given that the thermal study assumes a constant heat input of 1200°F over the entire piston-pad interface it makes sense that the heat transfers to the bottom face faster.
We can safely rule this design out but we did learn that minimizing piston-pad contact area might be another design avenue that we could pursue in a later design cycle.
AISI 304 Stainless Steel Design: Too much of a good thing?
Judging from the chart the 304 (SS) piston is clearly the best performing design. It’s thermal profile suggests that even with 45 seconds of constant braking force the bottom face barely exceeds 400°F! Great results from a thermal properties perspective but, as we showed in part one of this story, the weight increase from switching materials was 0.7 pounds of unsprung mass to the front wheel. This increase makes the SS piston design less desirable from a vehicle dynamics viewpoint. Adding unsprung mass to the front of the motorcycle adversely affects suspension performance, and maneuverability; very significant factors in racing.
What’s the point of eliminating brake fade if lap times are slower right? This design won’t be entirely ruled out but rather, will be considered a last resort.
AISI 304 Stainless Steel Insert with Original Design: Goldilocks?
Let’s look at our final design; the SS insert in the shortened original piston. From the chart we see that this design is a considerable improvement over the original aluminum design. For example, at 10 seconds the insert design is at 600°F while the original design is over 950°F! Not as impressive as the full SS piston but as we saw in part one, the weight increase of the insert was only 0.15 pounds, a small enough mass increase that the difference in vehicle dynamics should be negligible.
With the added bonus that this design won’t need to be sent off for chemical treatment; it looks like we have our first prototype candidate.
Not too hot, not too heavy, looks like this one is juuuust right!
Manufacturing: Let’s build something!
From the SOLIDWORKS part files for the SS insert design it was basically no work at all to create the necessary 2D manufacturing drawings. Once we had our drawings and bought our material we were ready to get to work.
Because the overall design of the insert was fairly simple we decided against sending the work out and instead chose to manufacture it ourselves. Fortunately, my good friend Mike has a lathe in his garage which was more than enough for this project. Over the course of one (very long) evening, we were able to manufacture and assemble all eight pistons.
Figure 2. Stainless Steel Insert Assembly.
Figure 3. Jerry learning how to use the lathe.
Testing: The Crucible of Motorsport
With the AISI 304 Stainless Steel insert pistons installed in the brake calipers the brake system was bled (remove all air from the sealed hydraulic system) and we were ready to race.
And the fade fades away…
Despite our first test being in July at the high-desert racetrack of Utah Motorsports Campus with ambient air temperatures well into the triple-digits, Jerry suffered zero brake fade throughout the race weekend. He noted that his brakes worked so well, “they honestly never crossed my mind when I was on track. A complete non-issue now.”
Testing never ends
As with all Engineering projects, we will continue to monitor the brake system and we plan to disassemble and inspect the pistons after the last round of the season in October. At that time we will review the project and consider what, if any, changes need to be made to improve performance.
With the brake fade issue sorted we will continue working to go faster and when the next hurdle comes up we know that with SOLIDWORKS we have the tools we need to overcome them.
If you missed Superbike Braking: SOLIDWORKS at 190 MPH – Part 1, be sure to check it out.