Porsche offers two hybrid systems right now, depending on which of its performance vehicles you’re interested in. But that’s clearly not enough. Or at least not good enough. CarBuzz discovered the company has just obtained a patent for yet another system. One that’s designed to work with engines mounted behind the driver without making the vehicle appreciably longer.
The patent, titled “Hybrid drive system of a motor vehicle with axial flow machine” focuses on putting an axial flux electric motor inline with the engine and transmission. It’s a significant advancement on the layout currently used in the PHEVs offered by most automakers.
In just about every rear-drive PHEV, including Porsche’s Cayenne and Panamera e-Hybrid models, the same system from supplier ZF is used. It puts a small radial flux electric motor inside the casing of an eight-speed automatic. It is effective, but the motor is only capable of around 215 horsepower and most applications make significantly less.
The motor and eight-speed automatic are long. That’s why you’ll find them in big SUVs and sedans, though Porsche does use a similar layout in the T-Hybrid system on the latest GTS (with a PDK box). Porsche wants one that will work better and with more power in sports cars with the engine behind the driver. This innovation would help it do that.
An axial flux motor is much smaller in thickness than a radial flux motor. Mercedes-AMG supplier Yasa’s latest prototype makes 1,005 horsepower, weighs just 28 pounds, and is about three-inches thick.
Porsche’s patent idea is to put a motor like that one in between the engine and transmission. So small, it could fit between the two sections of a dual-mass flywheel. To support the high-torque and high-power motor, it would get its own bell housing section, and be bolted to the engine and/or the transmission.
The patent suggests using the axial flux motor with a dual-clutch transmission. A DCT, Porsche says, works better because it has a longer input shaft. It’s also much more in-keeping with Porsche’s plans to use it in the back of a sports car than a conventional automatic would be. As far as a manual, it should be possible but it’s not mentioned. Or likely.
It seems like the kind of system that would be perfect as a PHEV, but it doesn’t seem that the system would be set up that way. Porsche describes the output shaft of the engine and the input shaft of the transmission both as being coupled to the rotor of the motor. If one spins, they all spin. The engine could shut off fuel for motor-only running, but that would be a high-friction way to do it.
Because of the simple layout, adding cooling is also simple. Another cooling circuit is added, with both the motor and transmission sharing an oil-water heat exchanger. The water, in that case, is shared with the engine’s cooling system and goes through the conventional radiators.
This is a relatively simple way to pack massive extra horsepower into the back of a Porsche 911 or 718 model. While the T-Hybrid system of the GTS uses smaller electric motors to spin the turbochargers more quickly, this would work just fine on a car without any turbos. Using electric assistance to move something like the GT3 and letting it rev even more aggressively than it can now, with more total horsepower and, crucially, without softening that car with a turbocharger.
It’s an interesting idea, with a great deal of promise. The question comes down to the cost of an axial flux motor and its extra power versus the cost and limitations of the system used now. We know which one we’re rooting for.
Patent filings do not guarantee the use of such technology in future vehicles and are often used exclusively as a means of protecting intellectual property. Such a filing cannot be construed as confirmation of production intent.
Source: EUIPO
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