Impeller in water pump

Abstract: An impeller (20) in a water pump for circulation of cooling medium in a cooling system of an engine. A shroud (24) has a boss shroud (23) to which the edges of the blade inlets (21) are attached and which is formed in the cylindrical configuration substantially parallel to the rotary shaft (15). Each of the edges (26a) of the blade inlets is shaped so that it is continuousley smooth from a boss shroud surface (24a) at the inlet side thereof and extends upstream in the axial direction, while each of the edges (26b) of the blade inlets at the side of a casing extends substantially perpendicularly to the rotary shaft (15), the edge (26a) of the blade inlet attached to the cylindrical boss (24a) shroud and the edge (26b) of the blade inlet at the casing side being connected therebetween by a smooth arc-like curve projecting convexly upstream. The inlet angle of said blade is set to substantially 0° at the inlet edge (26a) at the boss shroud and to an angle calculated substantially on the basis of the conventional design at the inlet edge (26b) at the casing side. The impeller (20) has the blades (25) each formed by connecting the blade inlet (26) of such configuration to an blade outlet (27) by a smooth curved surface.

Description: The present invention relates to an impeller in a water pump for circulation of a cooling medium in a cooling system of an engine according to the generic part of claim 1. A similar impeller, used in a turbo pump for a water jet propulsion machine, has been disclosed in EP-A-0,399,343. Figs 12 and 13 show a conventional water pump and an impeller thereof used in a cooling system of an engine, respectively. The water pump is mounted on a wall 2 at the side of an engine block having a suction opening 1. The water pump includes a pump housing 4 having a volute casing 3, and a rotary shaft 5 rotatably supported in a cylindrical projection of the pump housing 4. An impeller 10 made of steel plate having a boss 10a and blades 10b is firmly mounted on one end of the rotary shaft 5 within the pump housing 4, and a mechanical seal 8 is mounted between the pump housing 4 and the rotary shaft 5 adjacent to the impeller 10. A flange 9 for mounting a pulley (not shown) is firmly mounted on the other end of the rotary shaft 5, to which a torque is transmitted from a crank shaft of the engine through a pulley attached to the flange 9. In the conventional water pump as a centrifugal type pump, the impeller is designed on the basis of the conventional design. In recent years, the impellers made of steel plate as shown in Figs 12 and 13 or impellers made of plastic by injection moulding have been used with the view of reducing the manufacturing cost. Since each of these impellers has a thinner thickness of each of the blades and therefore a wider passage at each of the blade inlets, water pumps for use at higher temperatures and with faster revolutions and which incorporate those impellers are widely used because they are superior in the characteristic of anti-cavitation and have a longer service life as compared with the water pumps each having therein an impeller of cast iron designed faithfully on the basis of the conventional design of a centrifugal type impeller. However the water pumps in which those impellers are used have the disadvantages of greater noise, lower pump efficiency and the difficulty of further improving the characteristic of anti-cavitation due to an increase in circulation flow within the impeller. Recently, with an increase in the output power of the engine, the quantity of heat radiating from the engine to the cooling water has been bigger. In order to cope with this without effecting an increase in the cooling ability by increasing the size of the radiator or the cooling fan and so on, a demand for water pumps with a better characteristic of cavitation has come to be made. Furthermore, since it requirs to install many equipments in the engine room, it has been attempted to make the engine more compact, which, therefore, makes it necessary for the design to permit the water pump conventionally attached to the lower portion of an engine to be attached in any arbitrary position. This also requires a water pump with a better characteristic of anti-cavitation. In addition, since the improvement of fuel consumption has recently been required from the view of preventing air polution, the water pump which is smaller in size, lacking in weight and higher in the pump efficiency is also required. Even if it were attempted to fulfill these requirements by improving the impellers of the conventional water pumps, it would be impossible to effect the larger improvement because of the conventional design technique. The design point of the water pump lies in the pump specific speed of 300 to 400(m.rpm.m 3 /min), which is the design point at which the best pump characteristic is provided. This also makes the improvement of the impeller in the water pump difficult. SUMMARY OF THE INVENTION It is an object of the present invention to provide the design technique of the impeller which greatly improves the characteristic of anti-cavitation and pump efficiency, and to thereby sharply improve the characteristics of the engine cooling system. In order to achieve the above-mentioned object, there is provided an impeller in a water pump for use in an engine cooling system according to the features of claim 1. The above-mentioned object can also be achieved by forming the configurations of the blade inlets and the blades on a flat plate-like shroud as stated above. It is favorable from a reason to be stated later to form each of the blades, at the tip side thereof extending from the blade inlet to the blade outlet, in an arc-like configuration projecting convexly downstream. In the specification, the term "the tip side of the blade" means the edge of the blade at the side of the casing extending from the edge of the blade inlet at the casing side to the edge of the blade outlet. Now, the operation of the blades of the impeller in the water pump according to the present invention is explained as compared with the blades according to the conventional design. In the design of the blade inlets of the impeller in a conventional turbo pump, the inlet angle of the blade is set and the edge of the blade inlet is formed with a view to make the meridian velocity of flow uniform in the entire edge of the blade inlet on the basis of a velocity triangle at the blade inlet. Accordingly, the smaller the diameter of the blade inlet is, the greater the angle of the blade inlet is designed. That is, the inlet angle at the boss portion, to which the blades are attached, is usually larger than the inlet angle of the blade at the outer diameter portion of the inlet. In the conventional design, the design as stated above, is established as a technique for enhancing the pump efficiency and improving the characteristic of cavitation with the minimum loss at the inlet of the impeller. However, it is naturally told that with such a design technique, the meridian inflow at the blade inlet is not uniform, the work of the blade at the boss side becomes weak and only about 2/3 of the blade at the tip side works effectively. Nevertheless, since only the above-mentioned design technique has been established at present, the inlet angle of the blade is set widely on the basis of the velocity triangle. The impeller in a water pump according to the invention clears away the above-mentioned contradiction and provides a design technique of the impeller which works effectively in the entire region of the blade. The operation of the impeller according to the invention is explained with reference to Fig.11 in comparison with the conventional impeller and with the impeller according to EP-A-0 399 343. The inlet angle of the blade which is set according to the conventional design technique at the blade inlet with an outer diameter r io of the blade inlet and a diameter r ib of the boss, is described with the dotted line in Fig. 11, and the inlet angle of the blade becomes abruptly greater at the side of the boss diameter until it reaches 90° at the center of rotation. The inlet angle at the impeller according to EP-A-0 399 343 is uniform and substantially 0° through the entire length between the boss side and the casing side. Meanwhile, the inlet angle of the blade of the impeller according to the invention is set at a diameter r io of the blade inlet in the same way as the conventional design technique, but is set at the side of the boss diameter to substantially 0° as de-scribed by a full line, which has a slope completely opposite to that of the inlet angle of the blade according to the conventional design. In the theory of the conventional design based on the inlet triangle velocity, with the above-mentioned inlet angle of the blade according to the invention, the inflow of water into the blade is completely impossible in the vicinity of the boss at the blade inlet, which worsens the characteristics of the pump and the characteristic of cavitation. However, the truth is completely reverse. That is, when the blade inlet edge is shaped so that the blade inlet edge at the boss side extends upstream in the axial direction, while the inlet edge at the casing side is formed substantially perpendicular to the rotary shaft and then the edges of the blade inlets at the boss side and the casing side are connected therebetween by a smooth arc-like curve projecting conversely upstream, it is possible to ensure the wider area of flow passage at the blade inlet, and to cut off the flow at the blade inlet in the vicinity of the boss or the root of the shroud to thereby introduce it effectively into the blade, which results in the uniform flow at the blade inlet, so that the impeller which operates at the entire region of the blade (from the boss side to the chip side) can be provided,thereby improving the characteristic of cavitation and the pump characteristics. When the blade in the configuration of the inlet as stated above is combined with the shroud which form the concave arc-like surface of the revolution in the meridian section, the shroud permits a smooth change in the direction of the incoming water flow onto the shroud from the axial direction to the radial direction, so that the best characteristics of the pump can be obtained with a minimum loss within the impeller. In this case, for the arc forming the profile of the shroud, any curves may be used provided that they smoothly connect the boss and the shroud in the radial direction like a circle, an ellipse, a parabola and the like. The configuration of the blade inlet according to the invention as stated above, makes it possible to ensure the wider area of passage at the blade inlet and realize the uniform inflow of water into the blade inlet, so that the meridian velocity of flow at the blade inlet diameter r i o may be increased as compared with that in the conventional design. This makes it possible to design the blade inlet diameter r i o smaller than the diameter of the conventional blade inlet in order to obtain the characteristic of flow rate-head equal to that of the conventional impeller. This is because, as illustrated in the structural drawing of the water pump according to the invention in Fig. 1, the smaller clearance between the casing and the blade in the structure made as an open blade at the tip side functions as a seal line which prevents the fluid under higher pressure at the outer periphery of the impeller from being circulated into the lower pressure portion. Since the smaller blade inlet diameter may be constituted as stated above, the blade according to the invention which allows a longer seal line to be formed, makes it possible to increase the volume efficiency of the pump and allow a sufficient rise in pressure within the impeller, so that the pump efficiency may be largely enhanced. As for the characteristic of cavitation, in the conventional design it is worsened when the meridian velocity of flow at the blade inlet diameter r io is increased, but when the uniform inflow at the blade inlet has been realized according to the invention, the characteristic of cavitation can be largely enhanced by making the tip peripheral velocity at the blade inlet lower than the meridian velocity of flow at the blade inlet of the impeller. In the conventional impeller in the water pump, the blade inlet is only inclined slightly from the tip side of the blade to the shroud side as shown in Figs 12 and 13, and the diameters of the blade inlets at the tip side and the shroud side are not so varied therebetween. Judging from the specific speed in the above-mentioned pump design, that inclination is to be made larger, but such larger inclination requires that the inlet angle of the blade be set as described in Fig. 11. However, in practice, even if the inlet angle of the blade is set as stated above, it is impossible to realize an enhancement in the characteristic of cavitation and pump efficiency, and, taking into consideration the rise in cost to the effects, the configuration of the blade inlet in the present states is more advantageous than that with greater inclination, so the diameters of the blade inlet at the tip side and the shroud side are not made so different therebetween. This is an example which demonstrates the above-mentioned explanation. DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view of a water pump according to the invention; Fig. 2 is a front view of one embodiment of an impeller according to the invention incorporated in the water pump in Fig. 1; Fig. 3 is a longitudinal sectional view taken along the center axis of the impeller in Fig.2; Fig. 4 is a perspective view of the impeller illustrated in Figs 2 and 3; Fig. 5 is a meridian section of the blade taken along line B in Fig. 2; Fig. 6 is a meridian section of the blade taken along line C in Fig. 2; Fig. 7 is a meridian section of the blade taken along line D in Fig. 2; Fig. 8 is a front view of one embodiment of an impeller made by the stamping of steel plates; Fig. 9 is a longitudinal sectional view taken along the center axis of the impeller in Fig. 8; Fig. 10 is a graph illustrating the pump characteristics of both the water pump according to the invention shown in Fig. 1 and the conventional water pump in comparison; Fig. 11 is an explanation view showing the states of variation in the blade inlet angle from the blade inlet edge at the boss side to that at the casing side; Fig. 12 is a longitudinal view of a conventional water pump. Fig. 13 is a front view of the conventional impeller incorporated in the water pump in Fig. 12. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT An embodiment of an impeller in a water pump according to the invention is hereafter explained in detail with reference to the drawings attached thereto. Fig. 1 illustrates a longitudinal sectional view of a water pump according to the invention used in the cooling system of an engine. In the drawings, like reference characters plus 10 are affixed to the parts similar to those of the conventional water pump. The water pump of the invention is different from the conventional water pump in the provision of an impeller 20 and a front casing 22 provided on the wall of an engine block to guide the flow of water flowing into blade inlets 21 of the impeller 20. The impeller 20 in the water pump according to the invention is explained with reference to Figs 2 and 3. Fig. 4 is a perspective view of the impeller in Figs 2 and 3. Fig. 2 is a front view illustrating the form of the impeller as viewed in the direction of a rotary shaft, and Fig. 3 is a meridian section taken along the center of revolution of the impeller. Figs 5, 6 and 7 are sectional views of the impeller illustrating the configurations of the blade sections taken along the meridian B, C and D from the blade inlet to the blade outlet of the impeller. The configurations of the blade sections as viewed in the direction of the arrow marks A and E are shown with the full lines A and E in Fig. 3, respectively. In the impeller 20 according to the invention, the configuration of the meridian plane of the shroud 24 which stretches integrally with the boss 23 mounted on the rotary shaft 15 is formed as a concave arc-like surface of the revolution. The configuration of the inlet of each of the blades 25 is formed as stated below. Boss shroud 24a, to which the blade inlet edge 26 is attached, is formed in a cylindrical configuration substantially parallel to the axis L of revolution, and the blade inlet edge 26a at the side of the boss shroud is smoothly continuous to the surface 24a of the boss shroud at the inlet side, and extends upstream in the axial direction from the boss shroud towards a diameter r io of the blade inlet, while the blade inlet edge 26b at the side of the casing is made perpendicular to the axis of revolution. Furthermore, the blade inlet edge 26 is formed by a smooth arc-like curve projecting convexly upstream which connects the blade inlet edge 26a at the side of the boss and the blade inlet edge 26b at the side of the casing. The inlet angle of the blade inlet edge 26 is substantially 0 ° at the blade inlet edge 26a, which is attached to the boss shroud 24a, and is, at the casing side 26b, set to an angle calculated by the conventional design technique, the inlet angle between the boss side and the casing side being of a smoothly varied configuration. Each of the blades 25 is formed by connecting the configuration of the blade inlet 26 as stated above to a blade outlet end 27 with a smooth curve. In general impellers according to the conventional design having a plurality of blades, there is a tendency of not displaying the characteristic unless the blades are overlapped one above the other. However, in the impeller with the configuration of the blade according to the invention, the length of the blade (from the blade inlet to the blade outlet) is contained within an angle obtained by dividing the entire periphery by the number of blades, as shown in Fig. 2, and the overlapping of the blades is substantially removed, but the characteristic is not worsened. Accordingly, the shroud 24 (Fig. 3) having the above-mentioned arc-like surface of the revolution is the case, but if the blades with the configuration of the blade inlet according to the invention are formed on a simple disc-like shroud, it facilitates the production of the impeller by the stamping of steel plate, so that the cost of production can be reduced. Figs 8 and 9 are a front view of an embodiment of the construction of an impeller made of steel plate and a sectional view taken along the center axis, respectively. Like reference characters plus 100 are affixed to parts similar to those in Fig. 3. This impeller 120 comprises two parts, a part 128 having a boss to be mounted on a rotary shaft (not shown), and another part having blades 125 formed by stamping out the blades on the flat disc-like shroud 129 and raising up them. These parts are joined by suitable conventional means. Further, the profile at the tip side of the blades of the impeller according to the invention may be that of the straight line (PQ) connecting the blade inlet to the blade outlet as shown in Fig. 3, but it may be an arc-like profile projecting downstream as shown in a full line in Fig. 3. The impeller with such a profile at the side of the blades also provides the characteristic of flow rate-head equivalent to that of the impeller with the blades formed by the straight line (PQ). This naturally reduces the torque for rotating the impeller, so that the pump efficiency may be enhanced. Further, as explained above about Fig. 1, the curved profile (like a bell) of the blade tip side from the inlet to the outlet allows a longer seal line, which increases the volume efficiency of the pump and therefore the pump efficiency. Fig. 10 illustrates both the pump characteristics and the cavitation characteristics (NPSH characteristics) of the water pump shown in Fig. 1 having the impeller according to the invention and the conventional water pump shown in Fig. 12 having the impeller in Fig. 13, compairing only the pumps. Both impellers measure 60 mm in the outer diameter and 13 mm in the outlet width, but regarding the inlet diameter, the conventional impeller measures 50 mm and the impeller of the invention 40 mm. The number of revolution of both pumps were 6,000 r.p.m. As evident from Fig. 10, there is no great difference in the characteristics of flow rate-head between the two pumps, but there is a large difference in Req.NPSH in flow rates at the maximum efficiency, that is, 6.9 m in the conventional type and 2.9 m in the present invention. This illustrates that the cavitation characteristic of the water pump with the impeller according to the invention is greatly improved compared with that of the prior art. Fig. 10 further shows that the water pump according to the invention has increased the pump efficiency by approximately 20 %. This naturally illustrates that the water pump of the invention has remarkably less noise in the pump than that of the prior art. The test was carried out with the water pump of the invention and that of the prior art placed in a motor vehicle. The test result showed that since the water pump is driven through a pulley and belt transmission from an engine, the conventional water pump does not supply the flow rate of the pump proportional to the number of revolutions of the engine to the engine cooling system because of cavitation. In the actual running state of the conventional water pump, particularly in the state of low speed running at a low gear shift with higher revolution of the engine, which is caused when the motor vehicle runs on an upward slope which is one of the states of greater thermal load, the performance of the pump is remarkably worsened due to cavitation. On the contrary, in the water pump according to the invention, the worsening of the performance of the pump due to cavitation is not caused, and consequently when it is used in the engine cooling system, the design of the cooling system, taking into consideration the worsening of the pump performance due to cavitation, is not necessary. This permits a big improvement of the cooling system such as the smaller sized radiator. Further, since the pump efficiency of the invention is better, the output of the engine is increased to an extent, thereby permitting the fuel consumption to be reduced. In addition, less noise of the pump according to the invention makes it possible to facilitate the sound absorption within the engine room. The design conception of the configurations of the blade inlets of the impeller is also the conception which provides the configurations of the blade inlets of the impellers for all pieces of fluid machinery, including pumps for general industries, without being limitted to the impellers for the water pumps as stated above.

Claims: An impeller (20; 120) in a water pump for use in an engine cooling system, comprising a boss (23) mounted on a rotary shaft (15), said boss (23) having a shroud (24) which stretches integrally therewith and has a meridian configuration made as a concave arc-like surface of the revolution, and a plurality of blades (25; 125), each having a blade inlet and a blade outlet (27; 127), said shroud (24) having a boss shroud (24a) to which the edges (26; 126) of the blade inlets are attached and which is formed in the cylindrical configuration substantially parallel to the rotary shaft (15), each of the edges (26; 126) of the blade inlets being shaped so that it is continuous smoothly from the surface of said boss shroud (24a) at the inlet side thereof and extends upstream in the axial direction, while each of the edges (26b) of the blade inlets at the side of a casing extends substantially perpendicular to the rotary shaft (15), said edge of the blade inlet attached to the cylindrical boss shroud (24a) and said edge (26b) of the blade inlet at the casing side being connected therebetween by a smooth arc-like curve projecting convexly upstream to thereby form the edge of the blade inlet, characterized in that the inlet angle of said blade is set to substantially 0° at the blade inlet edge (26a) at the boss shroud (24a) and in that the inlet angle increases continuously from substantially 0° at the shroud end to an angle substantially greater than 0° and calculated substantially on the basis of the conventional design at the blade inlet edge (26b) at the casing side, said inlet angles of the blade being varied smoothly between the boss shroud side and the casing side to thereby form the blade inlet, and each of the said blade inlets with said configuration of each of the blades (25; 125) being connected to the end of the blade outlet (27; 127) by a smooth curved surface to thereby form the blade (25; 125). Impeller (120) in a water pump as set forth in claim 1, wherein said configurations of the blade inlets and the blades (125) as stated in claim 1 are formed on a flat plate-like shroud (129). Impeller (20; 120) in a water pump as set forth in claim 1, wherein each of said blades having said configurations of the blade inlets and the blades (25; 125) as stated in claim 1 is formed, at the tip side thereof extending from the blade inlet to the blade outlet, in an arc-like configuration projecting convexly downstream.

Inventors: FUKAZAWA TETSUO, IKUTA SHIRO, KAMATA KENKICHI, FUKAZAWA, TETSUO, IKUTA, SHIRO, KAMATA, KENKICHI, Fukazawa, Tetsuo, c/o Pacific Mach. &amp; Eng. C0. Ltd, Ikuta, Shiro, c/o Calsonic Corporation, Kamata, Kenkichi, c/o Pacific Mach. &amp; Eng. C0. Ltd
Applicants: PACIFIC MACH & ENG CO, PACIFIC MACHINERY & ENGINEERING CO., LTD.
Application year: 1992
Main classification: F04D29
IPC codes: F01P5, F04D29