Why designing an EV transmission is difficult

HostMost people think electric cars are simple because they have so many fewer moving parts, but making that one single gear work is actually a massive challenge. What makes it so much harder than a normal car gearbox?

GuestIt really comes down to how fast things are spinning. In a gas car, the engine might turn at maybe five or six thousand times a minute before it sounds like it's going to scream. An electric motor is a different beast. It can easily spin at twenty thousand times a minute. When things move that fast, the basic rules of how you build parts change. If you took a gear from a normal car and tried to spin it that fast, the heat and the stress would basically melt the metal or tear the part to pieces. It's not just about having one gear. It's about making a gear that can survive those speeds without turning into dust.

HostSo it's mostly a speed problem. But couldn't you just make the gear out of a tougher metal or make it thicker to handle the stress?

GuestYou could, but that leads to a much bigger problem that people don't expect, and that's the noise. In a gas car, the engine is making all these tiny explosions. It's loud. That noise covers up the sound of the gears touching each other. But an electric car is nearly silent. If those gear teeth aren't cut to a perfect shape, down to a tiny fraction of a human hair, they make this high-pitched whine. It sounds like a drill or a jet engine taking off right inside your car. Drivers hate it. So, you have to polish these gears to a level of smoothness that we never really needed before. It turns what used to be a basic metal part into a piece of high-end jewelry that has to be perfect every time.

HostWhy do we even bother with gears at all then? Why not just hook the motor straight to the wheels?

GuestWell, you need that leverage to get the car moving. Think about riding a bike. If you try to start from a dead stop in a really high gear, your legs have to work incredibly hard to get the wheels to turn. The motor is the same way. It's great at spinning fast, but to get a two-ton car moving from a stop sign, it needs the help of a gear to turn that speed into raw pushing power. If you didn't have that gear, the motor would've to be much bigger and heavier to get the car rolling, and all that extra weight would kill your battery range. One gear is the middle ground that keeps the car light but still gives it that punch when the light turns green.

HostBut isn't one gear a bit of a compromise? It seems like the car would eventually struggle once you're flying down the highway at high speeds.

GuestThat's exactly where the tension is. Most electric cars use one gear that has to do everything. It's low enough to get you moving fast, but high enough so the motor isn't spinning its brains out on the highway. But even then, once you hit seventy or eighty miles per hour, the motor starts to lose its edge. It gets less efficient. Some high-end sports cars are actually starting to use two gears now just to solve this, but then you're adding weight and more parts that can break. It kind of goes against the whole idea of a simple electric car.

HostIf we stick with one gear, does that mean the oil has to do more work too?

GuestThe oil is a huge part of the puzzle. In a normal car, the oil in the gearbox just kind of sits there and lets the gears dip into it. But at twenty thousand spins a minute, those gears act like a giant blender. They whip the oil into a foam. If the oil is full of air bubbles, it can't protect the metal or pull heat away from the teeth. Engineers are having to design ways to spray the oil exactly where it needs to go, while making sure the oil itself is thin enough to not slow the gears down but thick enough to keep them from grinding. It's this incredibly delicate balance that has to work in the freezing cold and the desert heat.

HostIt sounds like the simplicity is a bit of a lie, and we just traded a box of many gears for one gear that has to be a superhero.

GuestWe really did. That one gear has to be silent, it has to be strong enough to handle instant power without snapping, and it has to stay cool while spinning three times faster than we're used to. We're asking much more out of a smaller piece of metal. The way we treat the metal and the way we shape the teeth is becoming more important than the battery itself, because if the gearbox fails or makes too much noise, the whole quiet experience of the car just falls apart.

HostThe silent ride we love in these cars really comes down to whether those tiny metal teeth can keep their cool.