Porsche Works Out How To Improve Range When Towing With An Electric Car

It's a well-established fact that electric vehicles' driving range is drastically reduced when they are saddled with the task of towing, and Porsche has devised two new means of solving the problem. Both ideas are detailed in patents that CarBuzz discovered at the German Patent and Trade Mark Office, and both appear to be simple and cost-effective enough to find their way to production.

The first is somewhat simple in both concept and execution and concerns installing a switchable countershaft to enable a unique transmission ratio specifically for when the EV is towing, while the second discusses a means of enhancing energy recuperation by making the towed trailer less eager to brake itself.

Let's dig in.

The first patent includes a diagram that can be seen below. This graph shows an efficiency map for an electric motor. Along the x-axis at the bottom, we see the motor's revolutions per minute, while the y-axis to the left indicates the torque in Newton meters. The bar on the right represents a percentage value for efficiency.

The area marked by the number 11 shows the electric motor when the EV it is attached to is towing a trailer, and we see that it only operates at 89% efficiency. Basically, an EV with a single-speed transmission requires a lot of torque to tow the trailer at very low speeds, and that's because the transmission needs to be able to cater to a broad range of driving demands.

Systems already exist for detecting how much power an EV requires when towing and for altering shift behavior, but these fail to address the fundamental issue.

According to Porsche, the loss of driving range when towing "cannot be explained solely by the additional mass" or the additional wind resistance. It's also not down to the lack of energy recuperation from the trailer's wheels (but Porsche has a solution for that, too).

To solve this, Porsche suggests a variable gear ratio, noting that this may be achieved by installing a switchable countershaft atop the transmission. With this ratio optimized to compound torque for towing and only activating when the trailer is plugged into the EV, future products like the Macan EV may be able to get off the line with far less energy use. When the trailer is detached, the car automatically switches to its regular transmission ratio.

Best of all, Porsche says the idea is simple enough to be installed on a vehicle post-sale, meaning it won't be exclusive to buyers of new cars. Just ask your local dealer, and your Porsche EV of the future will become a more capable all-rounder.

The second idea concerns the trailer that the EV is towing. Most retail trailers include an overrun brake, a brake system connected to the wheels of the trailer that activates when the trailer pushes forward into the hitch of the towing vehicle ahead as the driver brakes.

The problem with traditional overrun brakes is that they activate almost immediately as soon as the towing EV hits the brakes, and while other patent documents suggest getting around this with an electric trailer that has a motor of its own, this is practically an add-on accessory that doesn't make the electric car or truck or SUV itself any more efficient. Other patent documents suggest installing an energy recovery device on the trailer itself, but that leaves us with the same problem. Finally, one could create an overrun system that only activates when the vehicle and trailer drop below a certain speed, but that has the same drawback as an electric trailer.

But all of these suggestions rob efficiency as they do not make the most of the inertia carried by the trailer. They're also bulky and complicated.

Porsche's solution is to fit the trailer with a small "controllable blocking device." This would communicate with the car to determine when it is recuperating kinetic energy as the vehicle decelerates and would include a means of detecting the stability of the EV and trailer train. This will combine with software that has protocols determining when the train has started rocking or otherwise become unstable. This will tell the overrun brake exactly when to activate and deactivate regardless of the speed of the train; the parameters will be solely on stability.

In a nutshell, as long as the trailer is not swaying or rocking, its brakes will not activate. Thus, the towing EV ahead can take full advantage of the momentum carried by the trailer for much longer, thereby maximizing efficiency and unlocking more driving range.

Combined with a bespoke transmission ratio, the Porsche EVs of the future should be able to tow more and go further without bigger batteries and motors, saving on costs and waste.

It's such a simple yet genius idea that we wouldn't be surprised to see it debut on the new electric Macan or its bigger Cayenne sibling later down the road.