GB2457026A

GB2457026A - Centrifugal coupling for a cooling fan

Info

Publication number: GB2457026A
Application number: GB0801615A
Authority: GB
Inventors: Bernard Joseph Holmes
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-01-30
Filing date: 2008-01-30
Publication date: 2009-08-05
Also published as: GB201013827D0; WO2009095636A1; GB2470671A; GB0801615D0

Abstract

A coupling 10 for a cooling fan (for example in a vehicle) comprises first and second parts 12,14. A clutch plate 30 provided on the first part is biased into engagement with the second part by a spring 34, for transferring drive. On rotation of the first part, a plurality of radial weights 40 disposed around the spring generate a centrifugal force which is transferred to the clutch plate by link members 46. When the rotation reaches a threshold speed, a component of the force is sufficient to overcome the spring force and the clutch plate 30 is actuated from the engaged position to the disengaged position and drive ceases to be transferred to the second part 14.

Description

I

Coupling for a cooling fan The present invention relates to a coupling for a cooling fan and particularly but not exclusively to a coupling for a cooling fan for use in cooling an internal combustion engine of a vehicle.

Internal combustion engines in vehicles are often cooled by a pumping a coolant around the engine and into a radiator, which releases heat built up in the coolant to atmosphere. When the vehicle is moving at low speeds, for example below 32 kph (20 mph), airflow through the radiator is not sufficient to maintain the coolant and engine temperature at a low enough temperature. Therefore, it is usual to provide a cooling fan, which forces air through the radiator of the engine, thus ensuring that the coolant and engine temperature do not become too hot.

Commonly, the cooling fan is driven either directly from the engine by the same belt drive that drives the alternator and water pump, or by a separate electric motor.

Continuous operation of a cooling fan draws power from the engine and increases fuel consumption. Furthennore, as engine speed increases, the power used in driving the fan increases. For example, a typical fan draws 0.746 KW (1 HP) at 1000rpm, but may draw over 6.7 14 KW (9 HP) at 3000rpm. Therefore it is generally accepted that the drive to the fan should be disengaged when airflow through the radiator created by motion of the vehicle is sufficient to maintain the coolant and engine temperature at a

suitable level.

A fan driven from the engine is usually driven through a viscous coupling, for example, a clutch plate surrounded by silicon fluid. The viscous drag of the silicon fluid, caused by its resistance to shear, provides a drive that slips at an increasing rate as the engine speed increases. Viscous couplings are made to be either torque limiting, set by the viscosity of the fluid, or air temperature sensing, by controlling the amount of fluid in the coupling using a thermostatically controlled valve. An electrically driven fan is usually driven by an independent electric motor controlled by a thermostat.

Viscous fans generate heat in the engine compartment, which adds to the cooling problem and electrically driven fans often fail, usually due to failure of the thermostat, causing over-heating of the engine. Furthermore, electrically driven fans put an increased drain on the battery of the vehicle, resulting in increases in required battery size. Both systems are costly to manufacture, are bulky and require constant maintenance.

It is an object of the invention to provide a cooling fan coupling which reduces or substantially obviates the above mentioned problems.

According to the present invention there is provided a coupling for a cooling fan comprising a first part and a second part, respective engagement means provided on the first and second parts movable between an engaged position for transferring rotational drive from the first part to the second part and a disengaged position, in use, the engagement meams being actuated from the engaged position to the disengaged position by a force caused by the rotation of a mass of the first part when the first part is rotated above a pre-determined rotational speed.

The cooling fan coupling has the advantages that it does not rely on a thermostat, it does not generate heat and does not rely on the battery of the vehicle.

Preferably the first and second parts are mounted about an axial shaft.

Preferably the engagement means are first and second friction pads disposed on the first and second parts respectively, one of the first and second friction pads being biased towards the other friction pad in the engaged position.

Preferably a spring biases the first friction pad towards the second friction pad.

Preferably the spring is a coil spring and is disposed around the axial shaft.

Preferably a spring retainer is fastened to the axial shaft and supports one end of the spring.

Preferably a clutch plate is mounted for axial movement on the axial shaft, the first friction pad is attached to one side of the clutch plate and the spring bears against the other side of the clutch plate.

Preferably the mass comprises a plurality of weights disposed around the axial shaft and each connected to the spring retainer and the clutch plate.

Preferably each weight is connected to the spring retainer by a first link member and is connected to the clutch plate by a second link member.

Preferably each weight is pivotally connected to the first link member and the second link member, and the first and second link members are respectively pivotally connected to the spring retainer and the clutch plate.

Advantageously, when the speed of the axial shaft reaches a predetermined speed, the weights move radially outwards away from the axial shall, causing the clutch plate to move towards the spring retainer against the bias of the spring, and disengaging the engagement means.

Preferably there are four weights spaced substantially 90 degrees apart around the axial shaft. The weights are preferably identical and are balanced.

Preferably a fan coupling is attached to the second friction pad.

Preferably the fan coupling is mounted to the axial shaft about a bearing assembly allowing rotation of the fan coupling relative to the axial shaft.

Preferably a cooling fan is attached to the fan coupling.

Preferably a housing is disposed around the spring retainer, part of the axial shaft, the weights, the spring and the clutch plate.

A safety ring may be provided around the housing.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a schematic cross-sectional perspective view through the central axis of a coupling for a cooling fan of the invention; Figure 2 shows a schematic cross-sectional side view through the central axis of the coupling of Figure 1 with the engagement means in an engaged position; Figure 3 shows a schematic cross-sectional side view through the central axis of the coupling of Figure 1 with the engagement means in a disengaged position; Figure 4 shows a schematic perspective exploded view of the coupling of Figure 1; Figure 5 shows a side view of fan attached to engine of a car with the coupling of Figure 1;and Figure 6 shows a perspective view of the arrangement coupling shown in Figure 5.

Referring to Figure 1, a cooling fan coupling is indicated generally at 10. The coupling 10 includes first and second parts 12, 14 mounted about a central shall 16.

The shaft 16 has a first portion 18 of a first diameter and a second portion 20 of smaller diameter, which is splined. The first part 12 is disposed substantially around the first portion 18 of the shaft 16 and the second part 14 is mounted on the second portion 20 of the shaft 16, about a roller bearing assembly 22.

The first part 12 includes a spring retainer 24 comprising a circular plate 27 and a co-axial spigot 28 extending perpendicularly from one side of the plate. The spring retainer 24 has a central bore passing through the plate 27 and the spigot 28 which is located on the larger first portion 18 of the axial shaft 16. The spring retainer 24 is fastened to the shaft 16 by a grub screw 26, which is screwed into a threaded radial aperture in the spigot 28.

A circular clutch plate 30 is mounted on the splined portion of the axial shaft 16 and has a first friction pad 31 mounted on one side, facing away from the spring retainer.

A co-axial spigot 32 extends perpendicularly from the other side of the clutch plate towards the spigot 28 of the spring retainer 24. A coil spring 34 is disposed between the spring retainer 24 and the clutch plate 30 and is located on the respective spigots 28, 32. The spring is co-axial with the central axis of the shaft 16 and biases the clutch plate 30 away from the spring retainer 24.

Referring also to Figure 4, the clutch plate 30 has four pairs of formations 36 extending perpendicularly outwards from the plate, equi-spaced around the spigot 32.

Each pair of formations 36 defines a space for receiving the end of a link member.

The spring retainer 24 has four similar pairs of formations 38 extending perpendicularly outwards away from the plate 27 and equi-spaced around the spigot 28. The formations 36 of the clutch plate 30 are aligned with the formations 38 of the spring retainer 24.

Four indentical weights 40 are positioned around the axial shaft 16, each being radially aligned with and connected to a pair of formations 38 on the spring retainer 24 and a pair of formations 36 on the clutch plate 30 by respective first and second link members 46,48.

One end of each first link member 46 is pivotally mounted between a pair of formations 38 on the spring retainer 24 about a pivot pin 50. The pivot pin 50 passes through aligned apertures in the pair of formations 38 and the link member 46 and is retained in position by a circlip. The other end of the first link member 46 is pivotally mounted in a central slot 52 in one of the weights 40, about a pivot pin 54. The pivot pin 54 passes through aligned apertures in the weight and link member 46 and is retained in position by a circlip.

Similarly, one end of each corresponding second link member 48 is pivotally mounted between a pair of formations 36 on the clutch plate 30 about a pivot pin 55. The pivot pin 55 passes through aligned apertures in the in the pair of formations 36 and the link member 48 and is retained in position by a circlip. The other end of the first link member 46 is pivotally mounted in the central slot 52 in one of the weights 40, about a pivot pin 56. The pivot pin 56 passes through aligned apertures in the weight and link member 48 and is retained in position by a circlip.

The weights 40 are effectively suspended from the clutch plate 30 and spring retainer 24 around the axial shaft by a parallelogram linkage, which allows radial movement of the weights, as discussed below. A shroud or cover 42 fits over the assembly of the first part 12 and has a safety ring or coJlar 44 disposed around the cover 42 at the position of the weights to strengthen the cover.

A circular fan plate 58 is mounted about the roller bearing assembly 22 on the axial shaft 16 and has a second friction pad 60 attached to one side of the plate 58, facing the first friction pad 31. The other side of the fan plate 58 is attached to a fan 62, by bolts or cap screws 63. An end cap 64 fits onto the centre of the fan 62 and covers the roller bearing assembly to prevent unnecessary ingress of water and dirt. A circlip 65 retains the roller bearing assembly on the shaft 16.

In use, as seen in Figures 5 and 6, the shaft 16 of the coupling 10 is driven by a belt drive of a vehicle engine 66, in conventional manner. The coupling 10 is arranged with the fan 62 adjacent a major face of the vehicle's radiator 68. Referring also to Figure 2, when the coupling 10 is stationary or rotating at low speed, the spring 34 acts against the fixed spring retainer 24 and biases the first friction pad 31 of the clutch plate 30 against the second friction pad 60 of the fan plate 58. Friction between the pads 31,60 enables rotational drive to pass from the clutch plate of the first part 12 to the fan plate 58 of the second part 14 and the fan 62.

Referring also to Figure 3, as the engine speed increases, and the rotational speed of the coupling shaft 16 increases to a threshold speed, typically between 1500 to 1800 rpm, the centrifugal force acting on the spinning weights 40 causes the weights to move radially outwards. The arrangement of the link members 46,48 means that a component of the force is transmitted as an axial force acting on the clutch plate 30 and spring retainer 24, which overcomes the bias of the spring 34. The resultant effect is that the clutch plate 30 moves towards the spring retainer 24 against the bias of the spring 34, and the friction pads 31, 60 are moved apart. Drive is no longer transferred to the fan plate 58 and fan 62, which freewheel on the roller bearing assembly 22. When the speed of the axial shaft 16 is slowed below the threshold speed, then the spring force is greater than the axial force applied to the clutch plate through the link members and the friction pads 31,60 are forced back into engagement with one-another to transfer drive.

When the fan 62 is disengaged, the excess force produced by the action of the weights is transferred through the housing 42 to the safety ring 44. Also the movement of the clutch plate 30 along the shaft 16 is limited to around 2mm by a circumferential flange formed at the increase in diameter of the shaft 16.

The rotational speed at which the coupling 10 disengages is determined by the mass of the weights 40 and the strength of the spring 34. Ii is envisaged that a standard set of weights 40 can be used with any one of a number of different strength springs to suit a particular application. For example, a vehicle for use in a hot climate will require a stronger spring 34, ie with a higher spring constant, than a vehicle for use in a cool climate, so that the fan 62 disengages at a higher engine speed and hence higher road speed. This is because the temperature differential between the radiator and the ambient temperature is less in a warmer climate.

The coupling 10 is preferable to electrically driven fans, because no load is drawn from the vehicle battery, and no thermostat is required. It is preferable to viscous couplings, because the coupling 10 produces negligible heat. The coupling 10 is also highly reliable, because it utilises simple mechanical components. It is also cost effective to manufacture and easy to repair, should it become damaged. The coupling can also be used to drive an air-conditioning unit. Typically the coupling 10 is around 100mm diameter and 75mm long and can conveniently be fitted in an engine compartment.

Claims

1. A coupling for a cooling fan comprising a first part and a second part, respective engagement means provided on the first and second parts movable between an engaged position for transferring rotational drive from the first part to the second part and a disengaged position, in use, the engagement means being actuated from the engaged position to the disengaged position by a force caused by the rotation of a mass of the first part when the first part is rotated above a pre-determined rotational speed.

2. A coupling for a cooling fan as claimed in claim 1, in which the first and second parts are mounted about an axial shaft.

3. A coupling for a cooling fan as claimed in claim I or claim 2, in which the engagement means are first and second friction pads disposed on the first and second parts respectively, one of the first and second friction pads being biased towards the other friction pad in the engaged position.

4. A coupling for a cooling fan as claimed in claim 3, in which a spring biases the first friction pad towards the second friction pad.

5. A coupling for a cooling fan as claimed in claim 4, in which the spring is a coil spring and is disposed around the axial shaft.

6. A coupling for a cooling fan as claimed in claim 4 or claim 5, in which a spring retainer is fastened to the axial shaft and locates one end of the spring.

7. A coupling for a cooling fan as claimed in claim 6, in which a clutch plate is mounted for axial movement on the axial shaft, the first friction pad is attached to one side of the clutch plate and the spring bears against the other side of the clutch plate.

8. A coupling for cooling fan as claimed in claim 7, in which the mass comprises a plurality of weights disposed around the axial shaft and each connected to the spring retainer and the clutch plate.

9. A coupling for a cooling fan as claimed in claim 8, in which each weight is connected to the spring retainer by a first link member and is connected to the clutch plate by a second link member.

10. A coupling for a cooling fan as claimed in claim 9, in which each weight is pivotally connected to the first link member and the second link member, and the first and second link members are respectively pivotally connected to the spring retainer and the clutchplate.

11. A coupling for a cooling fan as claimed in any of claims 8 to 10, in which there are four weights spaced substantially 90 degrees apart around the axial shaft.

12. A coupling for a cooling fan as claimed in any one of claims 3 to 11, in which a fan coupling is attached to the second friction pad.

13. A coupling for a cooling fan as claimed in claim 12, in which the fan coupling is mounted to the axial shaft about a bearing assembly allowing rotation of the fan coupling relative to the axial shaft.

14. A coupling for a cooling fan as claimed in claim 12 or claim 13, in which a cooling fan is attached to the fan coupling.

15. A coupling for a cooling fan as claimed in any of claims 8 to 14, in which a housing is disposed around the spring retainer, part of the axial shaft, the weights, the spring and the clutch plate.

16. A coupling for a cooling fan substantially as claimed herein with reference to and as illustrated in Figures 1 to 6 of the accompanying drawings.