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Engineering analysis of Tesla’s Cyber ​​Rodeo 4680 battery pack in section

There have been some significant changes to the Tesla structural package design since we analyzed the cutaway presented on the Giga Berlin factory tour. We’ve also uncovered some interesting new details about Cyber ​​Rodeo’s cutaway-based package.

Additionally, we referred to a video of the manufacturing process of the packages and displays that were unveiled at Giga Texas.

Summary

Here is the cross-section of the package we analyzed during the Giga Berlin factory tour:

Here’s the breakdown of the Texas Cyber ​​Rodeo package:

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The cutaway shown at the Giga Berlin was a mono plate. Cyber ​​Rodeo’s cutaway was split into four smaller cell arrays. It would be tempting to say they are modules, but make no mistake about the fact that this new package is still a structural package and is still cell to pack (CTP).

You can see this in the assembly process where a robot collects rows of cells and places them directly into the package. We think Tesla added reinforcement ribs (or corrugations) to the pack to increase the longitudinal strength, hence the spaces between the cell arrays.

The second thing we notice is that cooling snakes now run longitudinally in the pack instead of crosswise.

Third, it now appears that most of the backpack’s structural strength comes from the front and rear mega jets, the backpack’s belly cup, and the top lid. Cells are now playing a very small role. (More pictures of this are presented in the detailed discussion section.)

As we can see, Tesla has kept the Bandoliers concept used for the first time in the Model 3.

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These bandoliers are now larger to absorb the additional cooling flow from the larger 4680 cells. We renamed them “Megalier”.

Also, we know the number of cells (828 cells) so that we can calculate the energy in the package (74.1 kWh). We estimated the series-parallel arrangement of the cells (4 23S9P modules making up a 92S9P package). The volumetric energy density calculates an impressive 441 Wh / l. We also show the current new manifold and BMS board design. All of this is discussed in detail in the following section.

Detailed discussion

Figure 4 below shows the large longitudinal ribs in the mega cast that mate with the ribs in the bottom of the pack:

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Figure 5 shows how the cell case mates with mega casting:

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Figure 6 shows another view of the ribbed pack case extension:

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Figure 7 shows how both the top of the package (which doubles as the cockpit floor and seat supports) and the mega castings front and rear provide torsional rigidity:

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Bandoliers were an integral part of building the package in the Model 3. They were a big departure from all previous Tesla packages. They were also a big headache for Tesla during the early stages of Model 3 production, so we weren’t sure they would be eliminated in the new 4680 structural package. But sure enough, they’re still there, but they’re much larger than the 2170s. bandolier, so we renamed them “megalier”.

Here’s where we get our first chance to count cells. Referring to Figure 3 above, there are 35 cells on the left side of the megalier and 34 cells on the right side for a total of 69 cells per megalier and 12 megalier per pack, which gives us a total count of 828 cells. This provides a total usable energy of the package of 74.1 kWh based on the assumptions shown in Figure 8.

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We estimate this results in four 23S9P cell arrays as shown in Figure 9. This results in a 92S9P package:

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We know the Model 3 package dimensions. Jack Rickard EVTV measured the package and modules in a Model 3 teardown video. We used those dimensions for our package layout below. Also, we know the cell spacing from photos and cell count so you can arrange the package.

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4680 subpacks are roughly the same width as 2170 modules (11 inches) but are shorter. If you remember the 2170 package has two short and two long modules. In package 4680, we assume that all cell arrays are the same. We end up with a decent amount of space around the pack. We estimate 3.5 inches of clearance at each end of the package and 5 inches on each side. This leaves room for a longer or additional bandolier.

Tesla has integrated the package lid and the cockpit floor. This allowed them to fit a 10mm higher cell into the car. We also have a Munro teardown of the Plaid Model S showing the addition of what appears to be a flame retardant Mica layer to the top of the Plaid pack, and we can see this in the Cyber ​​Rodeo display under the pack’s cells (an orange mat). It is also mentioned in a Tesla patent.

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We now also have an image via a German publication showing the current new manifold design and the placement of the BMS board on the side of the package.

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The energy density comparisons of the pack are difficult because there are always all kinds of other things in and around the cells. For example, Tesla includes the electronics penthouse in the package. Therefore, we believe it is more appropriate to make comparisons at the module level. It gives you an idea of ​​how well the cells pack.

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These are some pretty impressive numbers. We are now seeing volumetric energy densities in the high range of 400 Wh / liter. The Bolt EV was only 334 Wh / l. The Tesla 2170 Model 3 package was 416 Wh / L. The new 4680 package comes in at 441 Wh / l. GM’s Ultium package looks like it could go even better than 441 Wh / l – next post.

Still so many unanswered questions

The first question is: why does this package only have an estimated 74.1 kWh? You can see from our layout in Figure 10 that there appears to be a lot of room in this package for more cells. The most obvious answer is that Tesla has a cell limit. We know this to be true as these cells come from the Kato Road pilot plant and Tesla is still working on speed and yield at that plant.

The second question is about the latest Model Y EPA range tests which only show a range of 279 miles. A few simple calculations can show that 74.1 kWh should give us more than 300 miles of range, not 279 miles.

Our guess is that these early packages have been cut back until Tesla runs out of time on the package. As they become more confident, they can take the package to its full potential. And when they get the Austin battery line up and have more cells, they can start putting more cells in the pack for more range.

Let us know what you think in the comments section.

George Bower BSME

Keith Ritter BSME, PE

Engineered compliance

Energy Analysis

engineeredcompliance@gmail.com

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