At the 40th Tokyo Motor Show, which ran from October 27 to November 11, 2007, the Yamada Works was open to the public. Among the exhibits, Yamada Shokai Co., Ltd. showcased a unique oil pump design that integrates both internal and external Trochoid pumps into a single housing. This variable-capacity oil pump uses three sets of rotors with interlocking teeth to create a rotary lobe pump mechanism.
The innermost rotor, located at the center, has teeth on its outer surface, acting as the primary input shaft for rotational power. The two outer rotors are designed with teeth on their inner sides, while their outer surfaces remain smooth. These rotors rotate within the housing, creating a dynamic pumping action. A main pump is formed between the inner and middle rotors, while the space between the middle and outer rotors functions as a secondary, or sub-pump.
When the engine operates at low speeds, both the main and sub-pumps work in parallel, providing a higher flow rate. However, at high speeds, the flow can become excessive. To manage this, a slide valve redirects the excess oil from the sub-pump back to the oil pan. The trial model allows for a capacity ratio of 1:1, and the system can be adjusted to halve the output when needed. The ratio can be freely set based on operational requirements.
Recent engine designs have placed greater demands on oil pressure, especially with features like variable valve timing. At idle, the required oil pressure has increased, which poses a challenge. If a pump is designed solely to address low-speed oil pressure, it may result in excessive flow at higher RPMs due to the direct relationship between pump displacement and rotational speed.
Previously, engineers attempted to solve this by using two small pumps in parallel. However, this approach doubled the number of rotors, seals, and other components, leading to a more complex and inefficient system. The new design, by combining internal and external rotor mechanisms, maximizes efficiency by reusing components without waste. In larger pumps, dead zones often form at the center, but integrating a smaller diameter rotor helps improve space utilization and performance.
The trial model used a chain-driven system positioned lower than the crankshaft, eliminating the need for acceleration or deceleration demonstration. In reality, the pump could also be directly driven by the crankshaft, offering even more flexibility in design.
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