The design of the Hüttlin Kugelmotor was in the same philosophy as the wankel engine, in that it harnesses combustion in a completely different manner than a conventional piston engine. It also has some weight and shape advantages built into the design.
The Kugelmotor is a round engine which uses guides to open and close pairs of piston-like chambers which compress and expand as the whole internal assembly rotates within the engine shell. In addition, the two sets of pistons are connected to the piston on the opposite end, so that while one section is open, the other one is closed. The design has much fewer parts than a traditional piston engine, but more than the wankel rotary engine.
The Kugelmotor converts combustion energy into torque by making the combustion expansion force push against the bearing/guide, which keeps the internal components spinning.
Some designs of this engine include a built-in alternator around the main sphere.
The design has a better power-to-weight ratio than the traditional piston engine, similar to the wankel engine. It has the potential to beat even the wankel after the guide friction is reduced.
There aren't any cars currently produced with a Hüttlin Kugelmotor, but the engine itself has proven to work, and may find itself in the vehicle of a car company willing to experiment with a new engine design in the future.