A recent post on EV pulse revealed that Dodge’s Charger Daytona SRT concept car has a transmission and that future Dodge EVs will have a “more than two-speed” transmission. I know Tesla fans will immediately jump on this and point out that Tesla vehicles (especially the Plaid variants) are very fast and don’t have transmissions. So in this post, I want to explain (again) why transmissions actually make sense for EVs.
Before I get into the engineering behind transmissions and why they are necessary, I want to point out that Stellantis (Dodge’s parent company) already sells at least one EV with a transmission. When I tested the 2021 Jeep Wrangler 4xe, I quickly realized that it was using the transmission in EV mode, even when there was no gas power of any kind.
If you’ve driven electric cars at all, you know that they have a lot of low-end torque, but that torque tends to decrease as the vehicle picks up speed. At some point, the power really tapers off and might even hit a wall (or a speed limiter or the engine’s physical limits). Either way, reduced acceleration power in EVs at higher speeds is usually noticeable, and especially noticeable in cheaper models.
In EV mode, the 4xe did the same. I heard the familiar EV hum, felt the torque and felt it start to drop. But then something very interesting happened: the vehicle went into second gear and the EV engine got a second wind. the familiar vortex rose again, starting at a low step and ascending as before. The vehicle did this two more times after shifting under EV power.
While it’s hard to gauge this in a Jeep, it was pretty clear that the vehicle got a better range doing it. Instead of sitting down to whatever rpm the engine needed to be at when cruising, the 4xe can select a gear for maximum range. Of course, the small battery pack and inefficiency of the off-road optimized Jeep Wrangler won’t give it a fantastic range, but it certainly did better than it would have with a single gear.
Why EVs with transmissions can have better performance and range
Unlike gas engines, electric engines can run over a much wider range of speed (RPM). To prevent the electric motor from over-revving and breaking down, as with a gas engine, EVs only need one gear that covers all of its speeds. This means that the vehicles do not strictly require multiple gear ratios or a transmission.
Although an EV doesn’t need multiple gear ratios, Tesla has found a way to make the driving experience even better. At lower speeds, more power is sent to the rear wheels for launch purposes. At higher cruising speeds (highway driving), power is sent primarily to the front engine, which has a higher gear ratio and thus acts as second gear. In addition, because the front engine in the performance models is smaller and better suited for the job, it gets more power.
So while it would not be technically correct to say that twin-engine Teslas have one transmission, it is correct to say that they have multiple gear ratios. So even the staunchest Tesla Stan has to admit that’s a good thing.
Porsche took things a step further by offering a two-speed gearbox in the rear unit. Both the front and rear drive units have an 8.5:1 gear ratio at highway speeds, but the rear drive can go up to 15:1, allowing for greater torque multiplication during initial launch before shift into a gear that’s taller than the Tesla’s for highway cruising.
The Taycan’s stellar showing in Edmunds testing is largely due to this, as well as other elements. In its most efficient drive mode (which the EPA doesn’t use), it had significantly more real-world highway range than expected, while the Tesla fell short of the EPA’s expectations. However, what happens when we go beyond 2 speeds? Would an electric car benefit from 3, 4, or even 5 gears? The correct answer to this is “Yes”.
By having lower gears for more torque at low speeds and higher gears for lower engine RPMs at high speeds, both performance and range should see a big bump with a transmission.
But does this work in the real world?
For this, I will have to refer readers to the field of EV conversions. People in garages for decades before mass-produced EVs became available have been converting their ICE (internal combustion engine) vehicles into electric cars. They most often just put an electric motor into the ICE car’s transmission since they didn’t have access to a gear reducer. We don’t have to wonder if this would help because it has already been demonstrated to provide all the theoretical advantages.
Want an extreme example? A Ferrari 308 that was converted to run on batteries after it was almost destroyed by fire. To make this car electric, they added three motors that work together to power a Porsche 4-speed manual transmission. (CleanTechnica reviewed this electric Ferrari.) Reviewers have called the car “terrible” because it had such a ridiculous amount of low-end torque. But when you’re on the highway, the vehicle gets adequate range for what it is simply shifting into a high gear.
Plus, you don’t have to worry about the motor stalling because electric motors don’t stall. If you are coming to a stop, just roll into a stop. There is no need to depress the clutch pedal except when shifting gears.
Automatic transmission technology can also be useful here. The cool thing about using a manual gearbox is that you don’t run into the problems that Tesla had with its failed two-speed project: you can cut the power during shifts to prevent damage to the gears. The driver does this in a manual, but if you want to build your own electric automatic, a torque converter can just as easily soften the blow (although it would require a TCC system to keep that converter locked between shifts so that to do does not lose the glide radius).
In the testing of the ZF transmission firm, this has been proven the benefits are just as real for mass-produced EVs as they are for conversions. Not only did they increase the cars range by 5%, they also improved the acceleration figures against a single speed vehicle. This enables a vehicle to bypass the trade-off between efficiency and performance, allowing for both. The ZF unit shifts gears at 70 km/h (just under 45 MPH). They also allow the car’s computer to control the drive unit and optimize the displacement to better suit the manufacturer’s objectives (performance, efficiency, traction, etc.).
In the end, it all comes back to cost. For a less expensive car that will use most of it in the city, one gear is enough. However, for a performance car or a car that will be driven regularly at high speeds, it would make more sense to find ways to get another gear ratio – and that’s exactly what Tesla did.
Eventually, the time of “city-only” electric vehicles will end, because people want cars that can be driven in many places. Also, customers will continue to put pressure on companies to produce the types of vehicles they want. Manufacturers will use multi-speed gearboxes to deliver the performance customers want. And you’ll be so glad when they do!
With all that in mind, I’d say for sure that Dodge is making the right calls when they say they’re putting the transmission in their upcoming performance EVs.
Featured image provided by Dodge.
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