Abstract:
A fan drive assembly for a vehicle, which can provide reverse fan flow. The assembly has a fan, where separate forward and reverse clutches are coupled to the fan. The reverse clutch has a greater torque capacity than the forward clutch, such that when the reverse clutch is applied, the forward clutch is made to slip, allowing for the reverse rotation and flow of the fan.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0001]    The present invention relates to a fan drive assembly for a vehicle, in particular a reversible fan drive assembly. 
       Description of Related Art 
       [0002]    Modern vehicles are provided with engine fans used to draw a cooling airflow through a radiator or heat exchanger for the purposes of temperature regulation of a vehicle fluid, such as an engine coolant, a HVAC system, etc. 
         [0003]    During the lifetime of the vehicle, the blades of the fan, as well as any associated engine grilles, radiators, etc., may become covered with layers of dust or other debris. This may result in blockages to the airflow drawn by the fan, causing a loss in engine efficiency due to the reduced operational capacity of the cooling system. Such blockages can also result in an increased pressure drop across the system, which can lead to a corresponding increase in fan consumption. This effect can be particularly pronounced in the case of agricultural vehicles, such as tractors or combine harvesters, which are often operated in environments having high levels of environmental debris, e.g. dust, chaff, etc. 
         [0004]    It is known to provide engine fans having reversible fan blades, wherein the fan blades may be rotated about an axis on the hub of the fan, such that the direction of airflow generated by the fan is reversed. This reversed airflow can act to blow out any accumulated dust or debris from the flow path of the fan, thereby cleaning the system for future operation. 
         [0005]    However, engine fans having such reversible fan blades are a relatively complicated construction, involving a number of separate moving parts which must be accurately controlled and actuated to ensure optimal fan performance. Accordingly, engine fans having such reversible fan blades are relatively expensive components, requiring significant manufacturing time and cost, and which can present significant difficulties regarding repair and service in the event of a fault. 
         [0006]    Alternatively, hydraulic or electrical fans can be made to reverse fan direction. However, such fan constructions generally have poor efficiency, when compared with belt-driven fans. 
         [0007]    An example of a prior art fan construction having a slidable clutch can be seen in Japanese patent document JPH084528. However, the use of such a clutch arranged to slide between respective forward and reverse pulleys can present service problems, e.g. due to the use of moving parts having increased movement range. 
         [0008]    It is an object of the invention to provide an alternative engine fan which addresses the above issues. 
       OVERVIEW OF THE INVENTION 
       [0009]    Accordingly, there is provided a fan drive assembly for a vehicle comprising:
       a fan;   a forward clutch arranged to rotate the fan in a forward direction; and   a reverse clutch arranged to rotate the fan in a reverse direction.       
 
         [0013]    The ability to provide a vehicle fan assembly with a reverse drive allows for the fan to selectively reverse the airflow direction, for example to perform cleaning of the fan and any associated components, e.g. radiators, grilles, grids, etc., of accumulated dust and debris. 
         [0014]    The reverse clutch may be selected such that the torque capacity of the reverse clutch is greater than that of the forward clutch. 
         [0015]    As the reverse direction for the fan drive will most likely be used less often than the forward drive, the reverse clutch will only occasionally be engaged. In such situations, by providing the reverse clutch with a greater torque capacity than the forward clutch, a reverse fan rotation will be ensured when the reverse clutch can be engaged, whether or not the forward clutch is also engaged, as the reverse torque can exceed the forward torque. The torque capacity can be understood as the torque handling ability of a clutch, and can be dependent on any number of factors of the clutch construction, e.g. number and type of clutch plates, dimensions, diaphragm load rating, etc. 
         [0016]    In one aspect, the fan drive assembly is configured such that the forward clutch can be at least partly disengaged when the reverse clutch is engaged. By at least partly releasing the forward clutch, the torque capacity of the forward clutch may be reduced, ensuring that the fan rotates in the reverse direction due to the engagement of the reverse clutch. 
         [0017]    In a further additional or alternative aspect, the torque capacity of the forward clutch is adjustable, wherein the forward clutch is controlled such that, when the reverse clutch is engaged, the torque capacity of the forward clutch is less than the torque capacity of the reverse clutch. 
         [0018]    The torque capacity of the forward clutch may be adjustable, e.g. by controlling the level of engagement of the clutch. In this case, the torque capacity of the forward clutch may be reduced when it is desired to operate the fan in a reverse direction, so that the engagement of the reverse clutch, having a greater torque capacity than the minimum torque capacity level of the forward clutch, will cause the forward clutch to slip. 
         [0019]    Providing such a controllable clutch can result in a more efficient system construction, as in normal forward operation, a relatively large torque capacity forward clutch may be used, while a relatively small, more cost-efficient, clutch may be used for occasional reverse operation. 
         [0020]    Providing such a clutch system results in a reversible fan system which is of a relatively simple construction, and which allows for easier operation and service, when compared to prior art adjustable pitch fans. 
         [0021]    It will be understood that the forward and reverse clutches may be coupled with respective forward and reverse drive shafts. Alternatively, the fan may be provided on a fan shaft, wherein the fan shaft is selectably coupled with respective forward and reverse clutches. 
         [0022]    Preferably, the reverse clutch is an on/off clutch. 
         [0023]    By use of the term on/off clutch, it will be understood that the clutch is either in a substantially engaged or a substantially disengaged state with a reverse shaft. When the clutch is engaged, the full reverse force is applied to the shaft. When the clutch is disengaged, the shaft is free to rotate in the forward direction. 
         [0024]    Preferably, the forward clutch is a viscous clutch. 
         [0025]    Preferably, the reverse clutch is a dry clutch. The reverse clutch may comprise any suitable mechanical or electromechanical clutch. 
         [0026]    Preferably, the forward clutch is selectably coupled to a forward drive, preferably using a forward fan belt. 
         [0027]    Preferably, the reverse clutch is selectably coupled to a reverse drive, preferably using a reverse fan belt. 
         [0028]    Preferably, the forward drive and the reverse drive are provided as opposite output shafts from a bevel gearbox. 
         [0029]    A bevel gear box provides a compact mechanism which can output both forward and reverse driving motion. The bevel gear box may itself be driven by any suitable aspect of the greater vehicle engine. In a preferred aspect, the bevel gear box may be located below the fan and clutches, to minimise the space required for the fan drive assembly. It will be understood that any suitable driving mechanism may be used as an alternative to the bevel gear box, e.g. an epicyclical gear system. 
         [0030]    In one aspect, the forward and reverse clutches are located at opposite sides of the fan. 
         [0031]    Alternatively, the forward and reverse clutches can be located at the same side of the fan. 
         [0032]    There is further provided a vehicle, preferably an agricultural vehicle, comprising a fan drive assembly as described above. 
         [0033]    Preferably, the vehicle further comprises an Engine Control Unit (ECU), wherein the ECU is operable to control the reverse clutch of the fan drive assembly to perform a reverse fan flow of the fan drive assembly. 
         [0034]    Preferably, the ECU is arranged to receive a fan clean command from an operator, and responsive to said fan clean command, the ECU operates the fan drive assembly in a reverse direction to clean the fan or any associated components of debris. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0036]      FIG. 1  is an illustration of an agricultural tractor; 
           [0037]      FIG. 2  is an isometric perspective view of a fan drive assembly according to the invention; and 
           [0038]      FIG. 3  is a side plan view of the fan drive assembly of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    With reference to  FIG. 1 , an agricultural tractor is indicated at  10 . The tractor  10  comprises front wheels  12 , rear wheels  14 , an engine section  16  and a cab section  18 . An engine  20  is provided in the engine section  16 , wherein a cooling package  22  is provided adjacent the engine  20 , for the cooling of engine fluid, a HVAC system, transmission oil, etc. The engine section  16  is provided with an engine hood  24  to cover the contained components. It will be understood that the engine hood  24  may be provided with suitable grilles or vents, to allow for the flow of air to and from the cooling package  22 . 
         [0040]    The cooling package  22  comprises at least one radiator or heat exchanger (not shown), and an engine fan. Turning to  FIGS. 2 and 3 , a fan drive assembly for use in the cooling package  22  is indicated generally at  26 . 
         [0041]    In a first embodiment, the fan drive assembly  26  comprises a fan  28  having a plurality of fan blades  30  provided on a fan hub  32 . The fan  28  is provided on a rotating shaft  34 . The shaft  34  is coupled to a forward clutch  36  which is driven by a forward belt  38 , which can be provided on a pulley arranged on the forward clutch  36 . The forward belt  38  connects the forward clutch  36  to a forward drive shaft  40 . The forward drive shaft  40  is provided as an output from a bevel gear box  42 , which may be driven by a suitable connection (not shown) to the vehicle engine  20 . The forward clutch  36  is provided as a viscous clutch. 
         [0042]    In an alternative embodiment, the fan blades  30  may be provided on the forward clutch itself, the forward clutch effectively arranged as the fan hub  32 . The clutch may then be selectively coupled with fan shaft  34 , which is driven by pulley  36  coupled to forward fan belt  38 . 
         [0043]    The fan drive assembly  26  further comprises an electrical harness  44 , which provides a connection between the fan  28  and a suitable Engine Control Unit (ECU, not shown) of the vehicle. The ECU may be arranged to control the rotational speed of the fan  28 , to thereby control the cooling effect of the cooling package  22 . 
         [0044]    In normal operation modes, with regard to the numbering of the first embodiment, the viscous forward clutch  36  is engaged, such that the fan  28  rotates in a forward direction as driven by the connection to the forward drive shaft  40 . Accordingly, air is drawn through the fan  28  in a forward direction, as indicated by arrow A (shown in  FIGS. 1 and 3 ). The drawn air acts to cool the radiators and heat exchangers of the cooling package  22  during normal operation. 
         [0045]    The fan drive assembly  26  further comprises a reverse clutch  46 . In the embodiment shown in the figures, the reverse clutch  46  is located on the opposite side of the fan  28  to the forward clutch  36 , but it will be understood that the forward and reverse clutches  36 , 46  may alternatively be located at the same side of the fan  28 . 
         [0046]    The reverse clutch  46  is driven by a reverse belt  48  via a suitable pulley, which connects the reverse clutch  46  to a reverse drive shaft  50 . The reverse drive shaft  50  is provided as an opposed output from the bevel gear box  42  to the forward drive shaft  40 , but it will be understood that any suitable drive mechanism arranged to provide forward and reverse drives may be used, e.g. using an epicyclical gear system. The reverse clutch  46  is provided as a dry clutch, but any suitable clutch system may be used. The reverse clutch is preferably provided as an electromagnetic clutch, which can be controlled using a suitable control signal provided from the vehicle ECU via the electrical harness  44 , or using a further dedicated electrical harness (not shown). 
         [0047]    In one embodiment, the reverse clutch  46  may be selectively coupled to the fan shaft  34 . In an alternative embodiment, the reverse clutch  46  may be selectively coupled to a reverse fan shaft (not shown), to transfer reverse rotational force to the fan  28 . In a further alternative, the reverse clutch  46  may be mounted directly to the fan hub  32 , the reverse clutch  46  selectively engaging with the reverse drive provided by the reverse belt  48 . 
         [0048]    The reverse clutch  46  is preferably provided as an on/off clutch, wherein the clutch is either substantially fully engaged or disengaged. In one aspect, the reverse clutch  46  is selected such that the torque capacity of the reverse clutch  46  is greater than the torque capacity of the forward clutch  36 . 
         [0049]    When it is desired to provide for a reverse flow of air, e.g. in order to clear the cooling package  22  and any associated grilles or vents of accumulated dust and debris, the reverse clutch  46  is instructed to engaged with the fan shaft  34 . In one aspect, the forward clutch  36  may be fully disengaged from the fan shaft  34  when a reverse flow is desired. However, as the torque capacity of the reverse clutch  46  is greater than that of the forward clutch  36 , if the forward clutch  36  is partly or fully engaged, the greater clutch strength of the reverse clutch  46  will cause the forward clutch  36  to slip, and results in rotation of the fan shaft  34  and the fan  28  in the reverse direction. 
         [0050]    In an alternative aspect, the forward clutch  36  is controllable, to allow for adjustment of the torque capacity of the clutch. In this case, the torque capacity of the forward clutch  36  is reduced when it is desired to apply a reverse rotational flow, such that the instantaneous torque capacity of the forward clutch  36  is less than the torque capacity of the engaged reverse clutch  46 . 
         [0051]    This configuration allows for the use of a forward clutch having a relatively large maximum torque capacity, which has at least a minimum torque capacity less than the torque capacity of the engaged reverse clutch. As a result, the reverse clutch may be provided as a relatively small component having relatively low torque specifications, minimising the additional cost and space required for the system. 
         [0052]    As the fan blades  30  rotate in the reverse direction, airflow through the fan  28  is reversed, as indicated by arrow B ( FIG. 3 ). The reversed airflow acts to blow any dust or debris from the fan blades and the radiators and heat exchangers of the cooling package  22 , as well as from any vents or grilles provided in the vehicle. 
         [0053]    The reverse operation may be controlled by way of an automatically-generated signal from the vehicle ECU, and/or from a user-input signal, as to when a reverse flow cleaning of the vehicle components is required. 
         [0054]    As the fan drive assembly  26  is provided with a reversible fan drive, accordingly a relatively simple fan construction can be used, without the need for individually pitchable fan blades. As a result, the fan drive assembly  26  is of a relatively simple construction, which can be easily and efficiently manufactured and services, with minimal cost. 
         [0055]    The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.