this problem by using Hanns-Dieter Paschke's design and converting the DKM into what would later be known as the KKM (see figure 5.). The KKM proved to be a much more practical engine, as it has easily accessible spark plugs, a simpler cooling design, and a conventional power take-off shaft. Wankel disliked Froede's KKM engine because of its inner rotor's eccentric motion, which was not a pure circular motion, as Wankel had intended. He remarked that his "race horse" was turned into a "plough horse". Wankel also complained that more stresses would be placed on the KKM's apex seals due to the eccentric hula-hoop motion of the rotor. NSU could not afford to finance the development of both the DKM and the KKM, and eventually decided to drop the DKM in favor of the KKM, because the latter seemed to be the more practical design. Wankel obtained the US patent 2,988,065 on the KKM engine on 13 June 1961. Throughout the design phase of the KKM, Froede's engineering team had to solve problems such as repeated bearing seizures, the oil flow inside the engine, and the engine cooling. The first fully functioning KKM engine, the KKM 125, weighing in at only displaced 125 cm³ and produced at 11,000rpm. Its first run was on 1 July 1958. In 1963, NSU produced the first series-production Wankel engine for a car, the KKM 502 (see figure 6.). It was used in the NSU Spider sports car, of which about 2,000 were made. Despite its "teething troubles", the KKM 502 was a quite powerful engine with decent potential, smooth operation, and low noise emissions at high engine speeds. It was a single-rotor PP engine with a displacement of , a rated power of at 6,000rpm and a BMEP of . Operation and design The Wankel engine has a spinning eccentric power take-off shaft, with a rotary piston riding on eccentrics on the shaft in a hula-hoop fashion. The Wankel is a 2:3 type of rotary engine, i.e., two-thirds of its ideal total geometrical volume can be attributed to displacement. Thus, its housing's inner side resembles an oval-like epitrochoid, whereas its rotary piston has a trochoid (triangular) shape (similar to a Reuleaux triangle), and the Wankel engine's rotor always forms three moving working chambers. The Wankel engine's basic geometry is depicted in figure 7. Seals at the apices of the rotor seal against the periphery