Abstract:
A cooling unit for an agricultural vehicle has a grid for allowing air to enter the unit while limiting debris and a heat exchanger for transferring heat from a coolant to air passing across the heat exchanger. The cooling unit further has a duct with motor driven fan, and a controller to monitor fan current and operate the fan in alternating directions. The controller generates a heat exchanger blockage warning when desirable fan current thresholds are not achieved.

Description:
BACKGROUND OF THE INVENTION 
     Field of Invention 
     The present invention relates to cooling systems for commercial agricultural vehicles and in particular, but not exclusively, to a cooling unit for a tractor and method of controlling the same. 
     Description of Related Art 
     Commercial agricultural vehicles, such as tractors, frequently operate in off-highway environments in which a substantial volume of debris lies on the ground. For example, during crop harvesting, a large volume of waste product is generated by the harvester. This waste falls to the ground behind the harvester. When tractor wheels subsequently pass over the debris it can be thrown into the air and drawn into the tractor&#39;s cooling system. This can cause the cooling system to become blocked which can limit the efficiency of the heat exchanger and potentially damage the engine. 
     The cooling system typically comprises a heat exchanger for removing heat from the engine coolant, a fan for blowing air across the heat exchanger to increase the rate of heat exchange, and a grid positioned upstream of the fan to prevent larger debris from entering the cooling system. 
     Blockage can occur upstream of the fan at the grid, or downstream of the fan at the heat exchanger. 
     It is known to monitor the fan motor&#39;s current and to reverse the direction of the fan in the event that the current drawn by the motor increases in response to a blocking of the cooling system. However, reversing the fan is only effective at removing debris from the over-pressure side of the cooling package, that is to say, from the grid. 
     It is an objective of the present invention to at least mitigate one or more of the above problems. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided a cooling unit for an agricultural vehicle, the cooling unit including:
         a grid for allowing air to enter the unit whilst limiting the ingress of debris into the unit,   a heat exchanger for transferring heat from a coolant carried within the heat exchanger to air passing across the heat exchanger,   a duct situated between the grid and the heat exchanger,   a fan situated in the duct, the fan driven by a motor to move air along the duct and across the heat exchanger,   a controller in communication with the motor to monitor the current drawn by the motor,   wherein the fan is operable by the controller in a first direction to draw air through the grid and across the heat exchanger and in a second direction for a predetermined period of time upon the current drawn by the motor rising above a first predetermined value, and   wherein the controller generates a heat exchanger blockage warning in the event that the motor current fails to drop below a second predetermined value upon the subsequent rotation of the fan in the first direction.       

     Advantageously, the monitoring of the fan motor current once the fan has been returned to the first direction of rotation following a period of time of reversal of the direction of the fan in an attempt to clear the blockage allows the controller to determine whether the blockage has been cleared. In the event that the blockage has been cleared (in all likelihood a grid blockage), no further action is taken, but in the event that the blockage has not been cleared (likely to be a heat exchanger blockage) a warning message is generated. This allows the vehicle user to manually clear the blockage.
         Preferably, the second predetermined value is less than or equal to the first predetermined value.       

     According to a second aspect of the invention there is provided a method of detecting and/or removing debris from the cooling unit of an agricultural vehicle, the cooling unit including:
         a grid for allowing air to enter the unit whilst limiting the ingress of debris into the unit,   a heat exchanger for transferring heat from a coolant carried within the heat exchanger to air passing over the heat exchanger,   an air duct between the grid and the heat exchanger,   a fan situated in the air duct, the fan driven by a motor to move air along the air duct,   a controller in communication with the motor,   the method including the steps of:   operating the fan in a first direction to draw air through the grid and across the heat exchanger,   monitoring the current drawn by the motor,   operating the fan in a second direction for a predetermined period of time when the current drawn by the motor rises above a first predetermined value,   operating the fan once more in the first direction,   generating a heat exchanger blockage warning if the motor current does not drop below a second predetermined value.   Preferably, the second predetermined value is less than or equal to the first predetermined value.       

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will now be described, by way of example only, and with reference to the following drawings, in which: 
         FIG. 1  is a schematic representation of the cooling unit according to the present invention, shown in an unblocked state; 
         FIG. 2  is a schematic representation of the cooling unit of  FIG. 1 , shown in a first blocked state; 
         FIG. 3  is a plot of the motor current of the cooling unit of  FIG. 1  against time; and 
         FIG. 4  is schematic representation of the cooling unit of  FIG. 1  shown in a second blocked state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a cooling unit indicated generally at  10 . The unit is typically situated under the hood of an agricultural vehicle (not shown for clarity). The purpose of the unit  10  is to receive heated coolant fluid from the vehicle engine or oil cooler and transfer heat from the coolant fluid to the ambient air. 
     Accordingly, the unit  10  is provided with a heat exchanger  12  which has a coolant fluid inlet  14  and outlet  16  (shown only in  FIG. 1  for clarity). The heat exchanger  12  is located within a duct  18  defined by an outer wall indicated generally at  20 . The entrance  22  to the duct  18  is protected by a grid  24  which prevents larger debris from being drawn into the duct  18 . Positioned within the duct  18  is a fan  26  driven by a motor  28  (shown in  FIG. 1  only) which is operated by a controller  30  (also shown in  FIG. 1  only), as will be described in further detail shortly. 
     In use the controller  30  operates the motor  28  to drive the fan  26  in a first direction to draw air through the grid  24  and into the duct  18  via the duct entrance  22 . This entrained air is blown across the heat exchanger  12  allowing a transfer of heat from the coolant fluid to the entrained air. Thus, heated air leaves the unit  10  via a duct exit  32  and cooled coolant fluid exits the unit  10  via the heat exchanger outlet  16 . 
     As described above it is not uncommon for debris to cause the unit  10  to become blocked, particularly when the vehicle is used in off-highway locations. There are two principal locations within the unit  10  which can become blocked. The first of these is described with reference to  FIG. 2 . 
     In  FIG. 2  the grid  24  has become at least partially blocked by larger debris indicated generally at  34 . This is problematic as the flow rate of the air through the grid  34  and thereby across the heat exchanger  12  is reduced which in turn limits the efficiency of the heat exchanger. This can lead to the engine overheating, potentially causing internal damage to the engine. 
     As a result of the grid blockage, the pressure P 1  in the duct  18  between the grid  24  and the fan  26  decreases as does the pressure P 2  in the duct  18  between the fan  26  and the heat exchanger  12 . This causes an increase in the load on the fan motor  28 . Since the supply voltage to the motor  28  is constant, the current drawn by the motor  28  increases. 
     Referring now to  FIG. 3 , a plot of motor current against time is shown. At time T 0  a blockage in the grid  24  occurs. As a result the motor current increases from the normal operation level C 1  to an elevated predetermined level C 2 . As soon as the controller  30  detects that the motor current has reached the predetermined level C 2 , the controller  30  reverses the direction of the motor  28 . This causes the fan  26  to blow in a reversed, second direction causing the direction of flow of the air within the duct  18  to reverse for a predetermined period of time (T 2 -T 1 ). This blows the debris  34  from the grid  24 . At T 2 , the controller  30  once again switches the direction of the motor  28  to drive the fan in its original, first direction. The motor current then drops from C 2  to its normal operation level C 1  along plot line A as the unit resumes normal operation. 
     The second mode of blocking is shown in  FIG. 4 . The heat exchanger  12  (rather than the grid  24  as in  FIG. 2 ) has become at least partially blocked by debris indicated generally at  36 . This is problematic for the same reasons as set out above in respect of the grid blockage. 
     As a result of the heat exchanger blockage, there is an increase in the pressure P 2  in the duct  18  between the fan  26  and the heat exchanger  12 . This causes an increase in the load on the motor  28  and a corresponding increase in the current drawn by the motor  28 . 
     Referring again to  FIG. 3 , at time T 0  a blockage in the heat exchanger occurs. As a result the motor current increases from the normal operation level C 1  to a predetermined level C 2 , just as it did in the event of a grid blockage as described above. As soon as the controller  30  detects that the motor current has reached the predetermined level C 2 , the controller  30  reverses the direction of the motor  28 . This changes the direction of the fan  26  to its reversed second direction causing the direction of flow of the air within the duct  18  to reverse. However, this is unlikely to dislodge the debris  36  from the heat exchanger  12  as the flow rate during reversal is unlikely to be sufficient to entrain the debris  36 . 
     Referring again to  FIG. 3 , at T 1  the predetermined motor current C 2  is reached and the motor changes direction for a predetermined period of time (T 2 -T 1 ). At T2, the controller  30  switches the motor  28  to drive the fan in its original first direction. However, since the debris  34  has not been successfully cleared from the heat exchanger  12 , the motor current will remain at or near C 2  along plot line B. 
     In the event that the controller  30  detects that the motor current does not fall significantly below the predetermined level C 2 , the controller generates a warning to the vehicle driver that the heat exchanger  12  is blocked. 
     It will be appreciated that it is conceivable that both the grid  24  and heat exchanger  12  could become blocked. In such an eventuality, the controller would still detect that the motor current had not dropped after fan reversal and generate a warning that the heat exchanger  12  is blocked. 
     The cooling unit of the present invention therefore achieves significant advantages over the prior art in that it warns the driver of a blockage in the event that the blockage is not cleared by the reversal of the fan, and furthermore indicates to the driver the location of the blockage.