The oil pump must be able to supply a sufficient amount of oil at various engine speeds to maintain sufficient oil pressure and ensure engine lubrication. The fuel supply of the oil pump is related to its speed, and the speed of the oil pump is directly proportional to the engine speed. Therefore, when designing an oil pump, it is important to ensure sufficient fuel supply at low speeds. However, at high speeds, the fuel supply of the oil pump is significantly higher, and the oil pressure is also significantly higher. In addition, during engine cold start, the oil viscosity is high, the fluidity is poor, and the oil pressure will also increase significantly. To prevent excessive oil pressure, safety valves or pressure limiting valves are installed in the lubricating oil circuit. Generally, safety valves are installed on the main oil passage of the oil pump or engine body. When the safety valve is installed on the oil pump, if the oil pressure reaches the specified value, the safety valve opens and excess oil returns to the inlet of the oil pump. If the safety valve is installed on the main oil passage, when the oil pressure reaches the specified value, excess oil flows back to the oil pan through the safety valve.