GB1593939A

GB1593939A - Fans for cooling vehicle engines

Info

Publication number: GB1593939A
Application number: GB1682078A
Authority: GB
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1977-05-03
Filing date: 1978-04-27
Publication date: 1981-07-22
Also published as: AU519704B2; AU3519578A; DE2815680A1; DE7810818U1; JPS53136712A

Description

(54) FANS FOR COOLING VEHICLE ENGINES (71) We, AISIN SEIKI KABUSHIKI KAISHA, a corporation organised and existing under the laws of Japan, of 1, Asahi-Machi 2-chome, Kariya city, Aichi Pref., Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to fans for cooling vehicle engines.

The engine cooling fan of a vehicle is generally coupled direct with the engine, so the speed of rotation of the fan increases with increase of engine speed. At high running speeds an increased quantity of air is sucked through the radiator grill by the fan, and thus the engine may be overcooled. On the other hand, noise develops at high fan speeds, and power consumption is increased.

The invention provides a fan for cooling a vehicle engine comprising a hub formed in one piece with a number of blades of plastics material having elasticity, each blade being formed with a notch extending inwards from the trailing edge between the hub and a tangent to the hub at the leading edge of the blade. The notch moderates the increase of air flow on increase of engine speed, and so improves the overall engine performance.

The invention is illustrated by way of example in the drawings of which: Figure 1 is a front view of part of a fan according to the invention; Figure 2 is a vector diagram showing the speed of air flow at the inner and outer circumferential portions of the fan; Figure 3 is a view similar to Figure 1 showing the flexing obtained by centrifugal force at a part of the fan in Figure 1; Figure 4 is a section through the fan blade showing the moment produced by centrifugal force at the line A-A in Figure 3; Figure 5 is similar to Figure 4 showing the flexing due to the differences of the air pressure between the upper and lower surfaces of the fan blade at the line A-A in Figure 3; Figure 6 is a graph showing the stress distribution on a fan blade; Figure 7 is a view of part of a fan showing the positions of distortion gauges attached to measure the stress distortion in Figure 6; and Figure 8 is a graph showing the rotational speed and the flow quantity of air comparing a fan according to the invention with a conventional fan blade.

With particular reference to Figure 1 a hub 10 of a fan is formed in one piece with a number of radial blades 11 of plastics material having elasticity. The blades 11 are formed with a notch 12 extending inwards from the trailing edge between the hub and a tangent to the hub at the leading edge of the blade. The fan is rotated in the direction of the arrow B.

The speed of the air flow in the radial direction which is produced by the centrifugal force and the pressure difference on the air mass on both faces of the blade 11 is almost the same at the inner and outer circumferential portions of the blade 11. The circumferential speed varies in proportion to the radius of the blade 11: the speed in the circumferential direction at the outer portion is faster than that at the inner portion. This is demonstrated in Figure 2.

The radius and the speed of the flow in the radial direction at the inner and outer circumferential portions are fixed. Accordingly, supposing that the vector of the speed of the flow in the radial direction is v1, and the circumferential speeds of the inner and outer portions are V2, V3 (V2 < V3), the resultants of v1 and v2, v1 and V3 are V2 and V1, respectively, the inflow angles being H2 and 1, V1 > V2, 2 < 02. The direction of the flow at the outer circumference is A in Figure 1, and that at the inner circumference is C.The flow C does not contribute significantly to the cooling of an engine (not shown) as can be seen from the stress distribution curve A' in Figure 1.

The effect of centrifugal force on the flexible portion of the blade 11 is explained in Figure 3: the position of the centre with respect to the centrifugal force on the flexible portion . ....... ....... ....... ............... P the weight of the flexible portion ................ .. . M the centrifugal force acting on M on rotation of the fan . . .

the component of force in the circumferential direction of F . . . .. ....... ....... ................. Fx (These factors directly influence the flexibility of the fan).

the component of the force in the radial direction . ....... ....... Fy (This does not directly influence the flexibility of the fan.) The centrifugal force F on the centre of force P of the blade 11 has components Fx and Fy. The component Fx has a component F1 perpendicular to a chord of the blade 11 and a component F2 parallel to the said chord as viewed in Figure 4. If the line of flexing of the blade 11 is S, the moment Ms about the line S is Ms=LF1, obtained by dropping a perpendicular from P to S, and is one of the primary factors in the flexibility of the fan (the distance between S and P is L).

Supposing that the inclination of the blade 11, the angle of entry of the air flow to the blade 11, is a and its indication to the plane of the fan is ss (Figure 5), the pressure distribution of the air pressure over the lower and upper faces of the blade 11, namely, the pressure distribution over the lower and upper faces of the blade 11 on the section line A A in Figure 3, is shown by arrows in Figure 5. The lower face of the blade 11 provides a positive pressure and the upper face a negative pressure (on the principle of a pump). The centre of this pressure distribution is Ml, and is located more to the rear in relation to the rotation of the blade 11 than the flexure line S.The distance between the centre of pressure M, and the flexure line S is L1 (Figure 5) so the moment TM about the line S is: TM = LIA (Pl - P2) P: positive pressure on the blade 11 P2 : negative pressure on the blade 11 A : the surface area of the blade 11.

Accordingly, TM is another primary factor in the flexibility of the blade 11. That is to say, the sum of the moments (M5 + TM) about the line S determines the flexibility of the blade 11. The line S of a conventional fan blade having no recess (Figure 7) is relatively to the rear, so the distaces L1, L from the line S to the point P (Figure 4) and from the line S to the point M, (Figure 5) are small. Consequently the sum of the moments (M5 + TM) about the line S is low and flexbility is not expected in the conventionl fan blade. The distortion of the inner circumferential portion of the conventional blade in Figure 7 is shown in Figure 6.

Distortion gauges 1,2,3,4,5 are attached along the width L3 of the inner circumferential portion of the blade at the equal intervals and the fan is rotated at 1000 rpm, 2000 rpm, 3000 rpm and 4000 rpm (revolutions per minute). Most of the distortion is produced at position 2 in Figure 7. The stress distribution determines the size and position of the notch 12 (A' in Figure 1).

The capacity of the engine determines the amount of heat produced, the necessary cooling or the speed of the fan rotation. The outer diameter of the fan, the inclination angle of the blade and the width of the fan blade are calculated from the amount of ventilation, and so the specification of the fan is finally determined. The strength of the fan is worked out taking into account the speed of rotation, nature of the material, temperature, etc.

If the necessary strength at 6000 rpm is fixed at 80 C taking into account the safety factor for a vehicle type H, and that the maximum value is 8000 rpm for a blade without recess, the thickness of the blade being constant, the difference becomes: 8000 rpm - 6000 rpm = 2000 rpm The notch 12 in the blade 11 can be designed accordingly. The position of the notch and the width of the blade are not fixed solely by such design considerations. The notch is on the hub side following the line C as in Figures 1 (the line C being tangential to the hub at the leading edge of the blade) to make the blade 11 flexible without decreasing its ability particularly in the low speed area.

The distortion is greatest at 2 in Figures 6 and 7 in a conventional fan, so strength is most necessary at the leading edge of the blade.

When the maximum rotational speed for a fan having no notch is 8000 rpm and the speed used is 6000 rpm, the strength of the blade is calculated from the weight of the blade, centrifugal force and various elements like the rotational radius. The maximum strength P for a maximum rotational speed N= 8000 rpm can be expressed as follows: P=Km.r fpN2 g 60 where K: safety factor g: the acceleration of gravity m: the weight of the blade r: the rotational radius in the position of centre of gravity of the blade The necessary strength at the above rotational speed N=6000 rpm is: P = Km .r (2on)2 g 60 The necessary strength P in relation to the maximum strength P is as follows: a'--~ (=0.6) p Generally speaking, it is possible for the notch to be about 40% of the cross-sectional area of the blade. The basic shape (without recess) in the cross-sectional area of the root portion of the blade is A and the cross-sectional area of the root portion of the blade with notch is A such that ss'=A is equal to a', and the width of the notch is fixed. A A fan blade having the notch as abovementioned has maximum flexibility with strength.Once the cross-sectional area of the root portion of the blade is decided, the width of the notch is fixed according to the cross-sectional shape of the blade.

In Figure 8 the straight line 0 D shows the characteristics of a rigid blade, the curve 0 E the characteristics of a flexible blade of the invention, and the zone r surrounded by the straight line 0 D and the curved line 0 E is where the quantity of the air flow is decreased according to the speed of rotation by the recess 12. The curve 0 F shows the characteristics of the necessary quantity of air flow against the rotational speed.

WHAT WE CLAIM IS: 1. A fan for cooling a vehicle engine comprising a hub formed in one piece with a number of blades of plastics material having elasticity, each blade being formed with a notch extending inwards from the trailing edge between the hub and a tangent to the hub at the leading edge of the blade.

2. A fan for cooling a vehicle engine as herein described with reference to Figures 1 to 5 of the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

8000 rpm - 6000 rpm = 2000 rpm The notch 12 in the blade 11 can be designed accordingly. The position of the notch and the width of the blade are not fixed solely by such design considerations. The notch is on the hub side following the line C as in Figures 1 (the line C being tangential to the hub at the leading edge of the blade) to make the blade 11 flexible without decreasing its ability particularly in the low speed area.

The distortion is greatest at 2 in Figures 6 and 7 in a conventional fan, so strength is most necessary at the leading edge of the blade.

When the maximum rotational speed for a fan having no notch is 8000 rpm and the speed used is 6000 rpm, the strength of the blade is calculated from the weight of the blade, centrifugal force and various elements like the rotational radius. The maximum strength P for a maximum rotational speed N= 8000 rpm can be expressed as follows: P=Km.r fpN2 g 60 where K: safety factor g: the acceleration of gravity m: the weight of the blade r: the rotational radius in the position of centre of gravity of the blade The necessary strength at the above rotational speed N=6000 rpm is: P = Km .r (2on)2 g 60 The necessary strength P in relation to the maximum strength P is as follows: a'--~ (=0.6) p Generally speaking, it is possible for the notch to be about 40% of the cross-sectional area of the blade. The basic shape (without recess) in the cross-sectional area of the root portion of the blade is A and the cross-sectional area of the root portion of the blade with notch is A such that ss'=A is equal to a', and the width of the notch is fixed. A A fan blade having the notch as abovementioned has maximum flexibility with strength.Once the cross-sectional area of the root portion of the blade is decided, the width of the notch is fixed according to the cross-sectional shape of the blade.

In Figure 8 the straight line 0 D shows the characteristics of a rigid blade, the curve 0 E the characteristics of a flexible blade of the invention, and the zone r surrounded by the straight line 0 D and the curved line 0 E is where the quantity of the air flow is decreased according to the speed of rotation by the recess 12. The curve 0 F shows the characteristics of the necessary quantity of air flow against the rotational speed.

WHAT WE CLAIM IS: 1. A fan for cooling a vehicle engine comprising a hub formed in one piece with a number of blades of plastics material having elasticity, each blade being formed with a notch extending inwards from the trailing edge between the hub and a tangent to the hub at the leading edge of the blade.
2. A fan for cooling a vehicle engine as herein described with reference to Figures 1 to 5 of the drawings.