Auto parts manufacturer Aisin Seiki Co., Ltd., based in Kariya, Japan, has developed a compact, low-cost centrifugal electric cooling pump to replace traditional mechanical pumps that are much larger and whose flow rates are dependent on engine speed. Electric cooling pumps offer greater control over the water flow, allowing significant improvements in fuel economy according to Aisin Seiki. However, electric pumps are traditionally much larger than their mechanical counterparts, and it has typically been difficult to incorporate them into increasingly cluttered engine bays.
Among its other features, the new Aisin Seiki electric pump uses an impeller with a new profile to improve performance. In addition, the design positions the components so that both the motor’s efficiency and the centrifugal pump mutually benefit. The pump also uses fewer components, allowing it to occupy less space.
With the efficiency improvements, less heat is generated, according to Aisin Seiki. The pump design also incorporates an aluminum enclosure, which acts as a heat sink to further ease the heat resistance requirements. The cost of the electric pump was reduced by using an inexpensive printed circuit board possessing the necessary heat resistance.
Controlling the water flow in engine cooling systems has been identified as an effective approach to contributing to reduced fuel consumption. Following work to develop electric pumps for cooling inverters, Aisin Seiki has now focused on automobile cooling systems. Electric pumps run independently of engine speed, which allows greater control over the water flow and consequent reductions in fuel consumption.
From an engine design perspective, electric pumps should operate in the same part of the engine as mechanical ones. The main issue in substituting mechanical pumps with electric ones was size. Electric pumps tend to be much larger in order to achieve the same discharge flow rate.
Aisin Seiki tackled a number of factors that impinge on the efficiency and cost of electric pumps. The efficiency enhancements enabled the size of the new pump to be shrunk.
Optimizations to the shape of the impeller enabled more effective pumping operation. In addition, an operation point that mutually benefits the efficiency of the pump and motor was identified. The operation point for maximum efficiency of the motor differs from that for the pump, but a compromise was found.
Aisin Seiki also reduced the number of parts constituting the pump. A mechanical pump harnesses the engine’s power through a pump pulley connected to the engine crank. The rotation of the crank then drives the pump, which is connected to the pulley by a shaft. Mechanical seals on the shaft prevent leaks of the cooling water. On the contrary, the electric pump is driven directly by its motor so these seals can be eliminated. A plastic housing protects the electric motor parts from rust.
Cost issues were also addressed, primarily through the adoption of a lower-cost printed circuit board. Although the heat resistance of the less expensive board is lower, the optimized efficiency of the electric pump reduces the heat generated. And the pump’s heat-dissipating aluminum enclosure further reduced the level of heat resistance required of the printed circuit board.