VARJABLE SPEED FAN DRIVE

The invention relates to a fan drive for a cooling fan on a vehicle which drives a fan at a variable ratio with respect to an input drive

Vehicles which have an internal combustion engine, for example a tractor, typically require a fan which serves to cool the water in a radiator which, in turn, cools the engine. The demand for cooling can vary depending on the ambient temperature, the work rate of the engine and any auxiliary demands such as cab air conditioning requirements.

Known fan drives include those which have a fixed connection between the fan and an engine output delivering a fixed ratio The power consumption of the fan is proportional to the cubic speed of the rotation thereof. Therefore, the fan is often driven at an insufficient speed resulting in overheating, or at an excessive speed resulting in excessive power consumption. This presents a very inefficient system.

More recently, schemes to provide variable speed fan drives have been introduced. One route is to provide a vicostatic coupler between the engine output and the fan. The coupler delivers a percentage slippage which reduces the relative speed of the fan

In another arrangement, a Vistronic coupler is used which, again, delivers a percentage slippage but is dependent upon the temperature around the coupler. This can be controlled by electronics but the slippage approach still has a high degree of inefficiency

US-20O6/O070588 discloses a vanable speed fan drive which utilizes a hydraulic actuator to actuate a variable sheath assembly. The variable sheath assembly drives a sheath assembly by way of a V-belt. Therefore the driving to dπven ratio can be varied.

Although the variable pulley arrangement increases the efficiency of the fan drive, there is still a desire to provide extra functionality. For example, a radiator grille associated with a fan of a known type is particularly difficult to clean

Therefore, it is an object of the invention to provide an improved variable speed fan drive. It is a further object of the invention to provide a variable speed fan drive which facilitates easy cleaning of an associated radiator grille.

In accordance with the present invention there is provided a variable speed fan drive for a vehicle, comprising an input shaft driven by an engine, the input shaft arranged to drive a plurality of planetary gears which mesh with a sun gear in an epicychc gear arrangement, the sun gear being connected by a shaft to a fan, wherein the input shaft is also arranged to drive a further gear arrangement by a variable ratio, the further gear arrangement having an output which ts connected to a housing of the epicyclic gear arrangement, the housing being meshed with the planetary gears. By providing an epicychc gear arrangement in this manner the range of ratios at which the fan can be driven with respect to the engine output is greatly increased over known fan drives. This not only gives the system greater flexibility for optimising the fan speed to demand, but allows the fan to be driven in reverse.

Such reversing advantageously allows a simple method of removing dust and particulates from a radiator grille adjacent to the fan. This reduces the frequency at which an operator must wash the radiator with fluid such as water or compressed air from a hose, thereby saving time.

In one embodiment the further gear arrangement comprises a first pulley on the input shaft connected by a belt to a second pulley which drives a gear meshed with the epicyclic gear housing via an intermediate gear Preferably the belt is a V-belt and at least one of the first and second pulleys has a diameter which can be varied to change the ratio.

In a second embodiment the further gear arrangement comprises a hydrostatic transmission.

In a third embodiment the further gear arrangement comprises an input driven by the input shaft, and an output, wherein the ratio is varied by creating a slippage between the input and the output. ^v

The variable ratio may be within the range of 0 5 to 2 0 The ratio of fan speed to engine speed may vary in the range of -I to 2

Further advantages will become apparent from reading the following description of specific embodiments of the invention with reference to the drawings in which -

Figure 1 is a schematic diagram of a variable speed fan drive in accordance vv ith one embodiment of the invention,

Figure 2 is a schematic view of the meshed gears associated with the epicyclic gear arrangement of the fan drive of Figure 1 viewed from direction A, and,

Figure 3 is a plot showing a comparison of the fan speed in response to a varied ratio delivered by the further gear arrangement

Referring to Figures I and 2, a variable speed fan dπve 10 comprises an input shaft 1 1 driven by the output of an engine (not shown) The input shaft 1 1 is connected to a carrier 12 for three planetary gears 13 As can be seen in diagrammatic form in Fig 2, the carrier 12 maintains the fixed relationship between the planetary gears 13 as they rotate around a sun gear 14, with which they are meshed

An output shaft 15 is connected to a fan 16 The sun gear 34 is also disposed on the output shaft, and when driven by movement of the meshed epicyclic gears 13, causes the fan 16 to rotate at a driven speed

The epicyclic gear arrangement further comprises a housing 17 which surrounds, and meshes with, the planetary gears 13 This will be described in more detail later

A pulley 18 having a variable diameter is located on the input shaft 1 1 between the epicyclic gear arrangement and the engine A second pulley 19 is located on a further shaft 20 and is coupled to the variable diameter pulley 18 by a V-belt 21 The pulley 19 is driven by the

vaπabie diameter pulley 18 at a ratio which is dependent upon the diameter of the pulley 18 which is selected by the control system

The effective driving diameter of the pulley 18 can be varied using hydraulic or electrical actuation means to vary the dimension of an internal sheath upon which the V -belt acts For example, a hydraulic actuator, such as a 2-way ram, can be arranged to actuate a variable sheath assembly in a similar manner to that described in US-20O6/0O70588 Alternatively, an electric motor can be employed to actuate the vaπabie sheath

A gear 22 is located also on the further shaft 20 and therefore rotates at the same speed as the second pulley 19 An intermediate gear 23 is located on an intermediate shaft 24 and is meshed between gear 22 and an external gearing 25 on the epicyclic housing 17, thereby forming a gear train Therefore, the housing 17 is driven by means of the input shaft 1 1, first and second pulleys 18, 19 and gears 22, 23, 25

Operation of the vaπabie speed fan drive 10 will now be described with reference to Figures 1, 2 and 3 For the purpose of simple explanation, the input shaft is dπven at a steady speed of όOOrpm corresponding to an idling engine in this example

The output to input ratio of the variator pulley arrangement 18, 19, 21 can be vaπed, for example, within a range of 0 5 to 2 0 In a first case, when the ratio is set to 1 0 the epicyclic housing 17 is driven to rotate at the same rotational speed as the planetary carrier 12 From Figure 2, it can be seen that there is zero relative movement between the planetary gears 13, the housing 17, and the sun gear 14 Therefore, the rotational speed of the output shaft 15 (and the fan 16) is the same as the input shaft 1 1 , as represented by region 30 in Figure 3

In a second case, the ratio of the vaπator pulley arrangement 18,19,21 is reduced to 0 5 causing the rotational speed of the further shaft 20, and thus the epicyclic housing 17, to fall to 300rpm, as represented by region 4OA in Figure 3 This creates a relative movement between the planetary gears 13 and the housing 17 as the housing 17 is caused to rotate slower The planetary gears 13 orbit withm the housing 17 in a relative clockwise direction (Fig 2) resulting is an anti-clockwise motion of each planetary gear 13 on their respective

shafts. This has the effect of increasing the absolute (clockwise) rotational speed of the sun gear 14 and thus the output shaft 15. This is represented by region 4OB in Figure 3. The resulting output speed of the fan 16 is 1200rρm, twice that of the engine speed.

In a third case, the ratio of the variator 18, 19,21 is increased to 2.0 so that the rotational speed of the further shaft 20, and thus the epicyclic housing 17 is twice the speed of the engine. This is represented by region 5OA in Figure 3. The housing 17 rotates clockwise at the faster speed than the meshed planetary gears 13, This creates a relative anticlockwise orbiting motion of the planetary gears 13 within the housing 17 causing the clockwise speed of the sun gear 14 to be reduced to an extent that it has an absolute rotational movement in an anticlockwise direction. This results in a reverse action of the fan 16, represented by region 5OB in Figure 3.

Such reversal of the fan 16 serves to provide a cleaning mode which removes dust and particulates from a radiator grille (not shown) located next to the fan. The cleaning mode can be activated automatically or by selection by the operator. For example, automatic activation may occur when the temperature of the water in the radiator exceeds a predetermined threshold for a predetermined period of time, indicating a potential blockage in the radiator grille.

The invention also increases the range of engine speed to fan speed ratios available. For example, with reference to the embodiment described, without the epicyclic gear arrangement in place and a direct drive from pulley 19 to the fan 16, the available range of ratios would be 0.5 to 2.0. However, the incorporation of the epicyclic gear arrangement in accordance with the invention increases this range to -1 to 2.0. This is particularly advantageous when relatively low fan speeds are required.

The pulley arrangement 18,19,21 shown in Figure 1 provides an efficient mechanism to vary the drive ratio of the fan and delivers the advantages described in US-2006/0070588. However, it is envisaged that, instead, other mechanisms can be used to provide a variable ratio without deviating from the scope of the invention. For example, a hydrostatic transmission can be employed. In this case, a hydraulic pump is driven by the input shaft 1 1.

The output of the pump drives a motor which, in turn, drives the motion of the epicyclic housing 17 via a gear train for example.

It will be appreciated that a hydrostatic transmission is capable of delivering a wider range of ratios than the pulley-based vaπator, including a reverse ratio However, in order to maintain the advantages provided by the invention, a hydrostatic transmission should be employed in conjunction with the epicyclic gear arrangement

Further alternative arrangements that deliver a variable ratio include vicostatic and vistronic mechanisms which create a percentage slippage between the input shaft 1 1 and the epicyclic housing 17

In summary, there is provided a variable speed fan drive particularly suitable for a vehicle having an internal combustion engine. The fan drive comprises an input shaft driven by the output of an engine. The input dnves a earner for planetary gears which each orbit a sun gear in an epicychc gear arrangement. A fan is coupled to the sun gear A further gear arrangement, driven by the input shaft, delivers a variable output to input ratio, the output of which is coupled to a housing of the epicyclic gear arrangement which is meshed with the planetary gears The provision of the epicyclic gear arrangement in combination with the variable ratio allows the fan blade to operate in reverse. Advantageously, this can be exploited to provide a means to clean a radiator grille