At the 40th Tokyo Motor Show, which ran from October 27 to November 11, 2007, Yamada Shokai Co., Ltd. showcased its innovative Tamashoid Pump technology at the Yamada Works. This unique oil pump design integrates both internal and external trochoid pumps within a single housing, allowing for variable capacity operation. The system uses three sets of rotors with interlocking teeth to create a rotary lobe pump mechanism.
The innermost rotor, positioned at the center, features teeth on its outer surface, serving as the primary input shaft for rotational power. The two outer rotors also have teeth, but they are arranged so that their inner and outer surfaces interact during rotation. Meanwhile, the outer rotor has teeth on its inner side, while its outer side is circular, allowing it to rotate within the housing.
The space between the inner and middle rotors forms the main pump, while the area between the middle and outer rotors creates a secondary pump. At low engine speeds, both pumps operate in parallel, delivering a higher flow rate. However, when the engine speed increases and the flow becomes excessive, a slide valve redirects the oil from the secondary pump back to the oil pan. This allows the main and auxiliary pump capacities to be adjusted, with a ratio that can be freely set—such as 1:1 or even halved if needed.
Modern engines require higher oil pressure, especially for variable valve timing systems and idle performance. Designing a pump solely for idle conditions would lead to excessive flow at high speeds, since the displacement pump’s output increases proportionally with RPM. To address this, previous solutions used two small pumps in parallel, but this increased the number of components like rotors and seals, leading to a more complex and inefficient design.
The new design combines internal and external rotor functions, maximizing efficiency by using each rotor on both sides. This reduces waste and simplifies the structure. Additionally, in larger spinning pumps, a dead zone often forms at the center, but adding a smaller diameter pump in the same housing improves space utilization and overall performance.
The trial model used a chain drive system positioned lower than the crankshaft, avoiding any need for acceleration or deceleration mechanisms. However, direct drive from the crankshaft is also possible, offering flexibility in application.
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