The engine cooling water pump is the heart of the automobile engine cooling system. Its role is to increase the working pressure of the coolant in the circulating system, maintain the coolant circulation among the relevant engine components, and prevent the engine from running at too high temperature. According to the different matching requirements and working conditions, the engine cooling water pump has centrifugal pumps, vortex pumps, rotary volumetric pumps, etc. Due to the space size limitations, Generally, single-stage centrifugal pump composed of inlet chamber, impeller and outlet chamber is used. This structure has the characteristics of small size, light weight, large water supply, simple structure, etc., and is the most widely used structure. Typical centrifugal cooling circulating water pump is mainly composed of pump body, impeller, bearing, water seal and pulley.
There are many parts around the engine cooling water pump, and its structural design must comply with the overall layout requirements of the engine, so that the flow path direction of the water pump inlet and outlet, the shape and section of the worm chamber, the layout of the water pump inlet and outlet, the impeller inlet structure and the determination of the basic size are often difficult to meet the normal hydraulic design requirements, which directly affects the improvement of the operating performance, including efficiency. The inlet chamber structure of the engine cooling water pump is divided into straight cylinder type or spiral type, and the outlet chamber structure is spiral type and integrated with the engine casting. The structure and geometric parameters of the impeller have a decisive influence on the operation performance of the pump. The engine cooling water pump generally adopts a semi open impeller structure without a front cover plate.
The performance curve is used to express the conversion characteristics of water flow energy of the pump under different working conditions, and it is the external expression of the internal flow law of the pump. Like ordinary centrifugal pump, the constant speed characteristic curve of engine cooling water pump is the relationship curve between flow and head, flow and efficiency, and flow and power at a certain speed. It can visually describe the operating performance of the engine cooling water pump at a constant speed. However, because the speed of the engine cooling water pump is constantly changing when it is working, the variable speed characteristic curve of the pump must also be given. The variable speed characteristic curve of engine cooling water pump mainly maps out the flow, head and power curves corresponding to different speeds, reflecting the energy conversion characteristics under different speeds. In order to reflect the comprehensive performance of the engine cooling water pump more intuitively, it is sometimes necessary to draw the two performance curves on the same graph to represent each performance parameter.
Due to the particularity of the engine cooling water pump, such as high working water temperature (75~85 ℃), large speed variation range (2000~5000r/min), and overall limitation of structural dimensions, compared with ordinary water pumps, the complex design of the pump inlet and outlet water passages makes the flow direction of the inlet and outlet fluid and the shape of the fault surface change dramatically, increasing the hydraulic loss and reducing the efficiency. At the same time, under the working conditions of high temperature, high speed and large flow, the engine cooling water pump is more prone to cavitation. At the same time, the stream flow at the top clearance of the semi open impeller causes the extrusion of the main flow and the increase of the flow rate in the impeller passage, which worsens the cavitation characteristics of the impeller, seriously affects the normal operation of the cooling system, and greatly shortens the service life of the cooling water pump. The special working environment and matching conditions determine that the design of engine cooling water pump is different from that of ordinary centrifugal pump.
To sum up, the typical engine cooling water pump is a special application of single-stage centrifugal pump in automobiles, with simple type and complex structure. Because the space size of the engine cooling water pump is severely limited, and the operating environment is bad, resulting in its low efficiency and serious cavitation damage. Therefore, it is very important to deeply study the relationship between the efficiency and the structural parameters of the engine cooling water pump, and explore the key factors that restrict the development of the engine cooling water pump.
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