Abstract:
A compact variable pitch fan has a hydraulic pitch change mechanism. A pitch change piston is constrained to follow reciprocating motion under hydraulic control within a peripheral hub from which fan blades extend outward. An additional feature is the use of separated guiding and seal surfaces. A still further feature is the use of a pitch sensor, particularly on the hydraulic line leading to the variable pitch fan.

Description:
BACKGROUND 
       [0001]    Flexxaire Manufacturing Inc. of Edmonton, Canada, manufactures a hydraulically controlled fan, and a pneumatically controlled fan. The pneumatic fan uses a single acting spring return piston, and the hydraulic fan uses a double acting piston. Examples of these fans are shown in  FIGS. 1 and 2  of U.S. Pat. No. 7,229,250 issued Jun. 12, 2007. The pneumatic fan (AX) has a compact construction, which suits many applications where space is limited on the equipment on which it is used. However, the hydraulic fan (FX) also has advantages due to the use of hydraulic fluid as the drive force for the pitch change mechanism. A combination of compact fan with hydraulic drive would be desirable, but the design poses engineering challenges. 
       SUMMARY 
       [0002]    A compact variable pitch fan has a hydraulically driven pitch mechanism. An additional feature is the use of separated guiding and seal surfaces. A still further feature is the use of a pitch sensor, particularly on the hydraulic line leading to the variable pitch fan. These and other aspects of the device and method are set out in the claims, which are incorporated here by reference. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0003]    Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which: 
           [0004]      FIG. 1  is a section through a variable pitch fan showing a pitch change mechanism, with pitch change piston in a first operating position; 
           [0005]      FIG. 2  is a section through a variable pitch fan showing a pitch change mechanism, with pitch change piston in a second operating position; 
           [0006]      FIG. 3  is a section through another embodiment of a variable pitch fan; 
           [0007]      FIG. 4  is a section through a connecting block between pitch change piston and a fan blade; 
           [0008]      FIG. 5  is a section through a pitch sensor; 
           [0009]      FIG. 6  is a section through another embodiment of a pitch sensor; and 
           [0010]      FIG. 7  shows an exemplary hydraulic control system. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite article “a” before a claim feature does not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims. 
         [0012]    As shown in  FIG. 1 , a variable pitch fan  10  has a peripheral hub  12  in which blade shafts  13  of fan blades  14  are journalled and extend outward in conventional fashion. For each fan blade  14 , a bushing  16  and bearings  18  allow the fan blade  14  to rotate at least partially around a radially extending axis passing through the fan blade  14 . The fan blade  14  terminates radially inward in a fan blade connector piece  20 . The fan blade  14  will typically rotate between normal and reverse pitch, and pass through a continuous range of possible positions between normal and reverse, including a neutral position in which the fan blades  14  are parallel to the plane of rotation of the fan blades  14 . Attached to a back side  22  of the peripheral hub  12  by any suitable means is a back or mounting plate  24 . The mounting plate  24  permits the variable pitch fan  10  to be mounted directly on a rotating part of an engine (not shown), typically of a piece of heavy machinery, so that the entire variable pitch fan rotates together, apart from a rotary union  26 . 
         [0013]    A front plate  30  is secured by any suitable means to the front side of the peripheral hub  10 . One or more of the peripheral hub  12 , mounting plate  24  and front plate  30  together form a housing that defines a cylinder having an annular cylinder portion  32  (seen better in  FIG. 2 ). In the example shown, the peripheral hub  12 , mounting plate  24  and front plate  30  all cooperate to define the cylinder, but this is not necessary. An outer cylindrical wall  34  of the front plate  30  and inner cylindrical wall  36  together form walls of the annular cylinder portion  32 . A pitch change piston  40  is mounted within the cylinder. The pitch change piston  40  is closed at one end  42  and on its other end  44 , which is received within the annular cylinder portion  32 , there is an annular piston portion  46  formed between an outer piston wall  48  and an inner piston wall  50 . Various drive configurations may be used to drive the pitch change piston  40 . In the example shown, the pitch change piston  40  has a driven side  52  and a return side  54 . While the parts  12 ,  24  and  30  together form a housing in this embodiment, other configurations of housing are possible, such as including changes of shape, configuration, orientation or number of parts. 
         [0014]    The rotary union  26  is housed within the inner cylindrical wall  36 , and provides a hydraulic supply to the driven side  52  of the pitch change piston  40 . The rotary union  26  may be secured in place by any suitable means such as a spiral spring  53 . In use, a hydraulic line  56  is connected to the rotary union  26 . The hydraulic line  56  runs out to a hydraulic control system  100 . The control system  100  may be designed according to the principles described in U.S. Pat. No. 7,229,250 issued Jun. 12, 2007. The rotary union  26 , which is a commercially available part, such as a 6000 psi rotary union, is shown schematically, and will have conventional internal parts allowing the hydraulic line  56  to remain fixed, while the variable pitch fan  10  rotates. The annular piston portion  46  has an annular slot  58  on the return side  54  of the pitch change piston  40  in which lies a return spring  60 . The return spring  60  presses up against the return side  54  of the pitch change piston  40  deep within the slot  58  and against the mounting plate  24  to bias the pitch change piston  40  to the front side of the variable pitch fan  10 , as shown in  FIG. 1 , which may correspond to a normal blade position. Application of hydraulic fluid through the rotary union  26  into the space between the front plate  24  and the closed end  42  of the pitch change piston  40  urges the pitch change piston  40  against the force of the return spring  60  towards the position shown in  FIG. 2 , which may for example correspond to a reverse pitch position of the fan blades. A double acting piston could also be used as a return drive, but is not as simple to make as a return drive using a return spring  60 . 
         [0015]    The outer cylindrical wall  34  forms a guide surface or guiding wall for the pitch change piston  40 . That is, the dimensions of the outer piston wall  48  and the inner cylindrical wall  34  are chosen so that the outer piston wall  48  fits as closely as possible to the inner cylindrical wall  34  while allowing motion of the pitch change piston  40  within the cylinder. To avoid damage to a seal along the guide surface, hydraulic fluid injected between the front plate  30  and closed end  42  of the pitch change piston  40  is prevented from migrating out of the cylinder by an annular seal  62  the inner cylindrical wall  36  and the inner piston wall  50 . The annular seal  62  may for example be a U-seal. 
         [0016]    As shown in  FIG. 4 , the pitch change piston  40  interconnects with the fan blades  14  to control pitch of the fan blades  14  by any suitable means, such as a pin  64  extending from the fan blade connector piece  20  into a receiving socket  66  in a shifter block  68  that forms part of the pitch change piston  40  and is secured to the other parts of the pitch change piston  40  by for example cap screws  70  and spacers  72 . 
         [0017]    In operation, the variable pitch fan  10  is in its normal operating position shown in  FIG. 1  with the fan blades  14  in full normal pitch (corresponding to cooling). When a pitch change is desired, hydraulic fluid is pulsed through the rotary union  26  in an integral control scheme. Incrementally adding fluid in a series of pulses between the front plate  30  and closed end  42  of the pitch change piston  40  incrementally alters the pitch of the fan blades  14  towards full reverse thrust. Any desired operating position may be chosen depending on the amount of hydraulic fluid pulsed through the rotary union  26 . For example, each pulse may corresponding to a pitch change of one degree. Other methods of changing pitch with flow of hydraulic fluid may also be used. 
         [0018]    A further embodiment of a variable pitch fan is shown in  FIG. 3 . In this embodiment, reference characters shared in common with reference characters of  FIGS. 1 and 2  refer to the same parts, and the parts operate in the same manner in the two embodiments except as described in this paragraph. In the embodiment of  FIG. 3 , the front plate  30 A replaces front plate  30  of  FIGS. 1 and 2 , seal  62 A replaces the seal  62  of  FIGS. 1 and 2  and guiding wall  34 A replaces guiding wall  34  of  FIGS. 1 and 2 . Front plate  30 A differs from front plate  30  by including an annular groove in the guiding wall  34 A that holds seal  62 A. In this embodiment, therefore, the seal  62 A is in the exterior guiding wall  34 A. While this design risks damage to the seal  62 A, it has the added advantage of allowing for lower hydraulic pressure due to the larger diameter. There is a corresponding trade-off of increasing the amount of hydraulic fluid required, which may not be desired. 
         [0019]    During operation, it is sometimes useful to know the exact position of the fan blades  14 . For example, after a purge, when the fan blades  14  are driven by hydraulic fluid into full reverse position, it may be desirable to return the fan blades  14  to the position that the fan blades  14  were in prior to the purge. A pitch sensor may be used for this purpose. In one embodiment shown in  FIG. 5 , a pitch sensor  74  may be located on the hydraulic supply line  56 . The pitch sensor  74  generally comprises a sensor piston  76  coupled with the hydraulic supply  56  and having dimensions chosen to provide the sensor piston  76  with motion that is proportional to the movement of the pitch change piston  40 . A potentiometer  78  or other suitable motion detecting device, such as an accelerometer or a magnet arrangement, detects motion of the sensor piston  76  and converts it to an electric signal that is sent to the hydraulic control system  100  ( FIG. 7 ). 
         [0020]    The sensor piston  76  is a floating piston mounted for reciprocal movement within a housing  80  and sealed by seal  77 . A fluid inlet port  82  is provided on one end of the housing  80 , and a fluid outlet port  84  is provided in the other end of the housing  80 . The fluid inlet port  82  is formed in a plug  81  secured by a split ring  83  and sealed with seals  85 . The ports  82  and  84  connect the pitch sensor  74  within the hydraulic line  56 . A potentiometer  78  is fixed at one end of the housing  80  so that movement of the sensor piston  76  alters current flowing through the potentiometer and converts movement of the sensor piston  76  to an electric signal that can be sensed by the hydraulic control system  100 . Spring or wave washers (not shown) may be provided on each end of the sensor piston  76  to initiate return motion of the sensor piston  76  after end of stroke has been reached. 
         [0021]    Motion of the sensor piston  76  in one direction is induced by hydraulic fluid pulses from the hydraulic control system  100  and in the other direction by spring pressure from return spring  60 . As the sensor piston  76  moves under pressure from fluid pulses, a situation may occur in which it may bottom out before the fan blades  14  are in full reverse pitch. For this reason, a fluid bypass port  86  is provided that is opened when the sensor piston  76  is close to the end of its stroke under pulsed fluid pressure. A similar bypass port  88  is provided for the like situation on the return stroke induced by pressure from spring  60 . Various other methods may be used to provide the bypass function, as for example ports extending through the sensor piston  76 . 
         [0022]    As hydraulic fluid is pulsed into the pitch sensor  74 , or driven into the pitch sensor  74  by the return spring  60 , the potentiometer  78  or other displacement sensor converts the motion of the sensor piston  76  into an electrical signal that is sent to the hydraulic control system  100 . With a linear relation between displacement of sensor piston  76  and fan blade pitch, the absolute pitch of the fan blades can be tracked from full normal to full reverse. The operator may then use the hydraulic control system  100  to select a pitch position by providing a known number of fluid pulses. 
         [0023]    Another embodiment of a pitch sensor is shown in  FIG. 6 . Pitch sensor  74 A is formed of a body  80 A which is the same as the body  80  of the pitch sensor  74  except for the absence of by-pass ports  86  and  88 . Elements  77 ,  78 ,  81 ,  82 ,  83 ,  84  and  85  in  FIG. 6  are the same as the corresponding elements in  FIG. 5 . In  FIG. 6 , the piston  76 A is modified to include by-pass ports  86 A and  88 A. By-pass port  86 A includes a relief valve  87 A set to open for example at some suitable level such as  10  psi, and by-pass port  88 A includes a relief valve  89 A set to open for example at  10  psi. The pitch sensor  74 A works the same as pitch sensor  74  except as follows. In normal operation, since the piston  76 A is free floating, there is very little differential pressure across the piston  76 A. However, at end of stroke, as the piston  76 A hits one of the end walls of the body  80 A, the pressure on the driven side of the piston  76 A increases and a corresponding one of the relief valves  87 A or  89 A opens to allow by-pass of fluid through the piston  76 A. Thus, at end of stroke towards the right of  FIG. 6 , relief valve  87 A opens, while at end of stroke towards the left of  FIG. 6 , relief valve  89 A opens. 
         [0024]    Referring to  FIG. 7 , an exemplary hydraulic control system  100  includes an electronic controller  92  and a valve or set of valves  90  that control fluid delivered to hydraulic line  56 . The valves could be any of the configurations shown in  FIGS. 3-11  of U.S. Pat. No. 7,229,250 or other suitable valves to achieve control of fluid to the variable pitch fan. The valves  90  deliver fluid pulses through line  56  and pitch sensor  74  (if used). Sensor signals from the pitch sensor  74  are sent back to controller  92  on line  94 . The controller  92  can be a dedicated electronic device, or a virtual device: an existing programmable controller can be programmed to directly control the valves (i.e., the ECM-engine control module). There are a number of parameters that affect the cooling requirements of a machine, and therefore the required pitch of the fan. The types and numbers of parameters vary from machine to machine depending on which systems are cooled by the fan (i.e., Air conditioner condenser, hydraulic oil cooler, air to air after cooler, engine coolant etc.). Some machines have ECM&#39;s (electronic control modules) that already measure all of these parameters and this information can be tapped into. Some machines have fan speed outputs to control the speed of variable speed fans. This output takes into account all the appropriate parameters. Because of the variety, different types of control can be used. 
         [0025]    There are a variety of inputs that can be used for the controller  92 . These can be used individually, or in conjunction with each other, for example: A. The input may be an analog input such as temperature sensors (these are sensors that would be used exclusively by the fan control—i.e., they need to be installed with the control system) that could measure for example intake air temperature, coolant temperature, etc., pressure sensors (these are sensors that would be used exclusively by the fan control—i.e., they need to be installed with the control system), air pressure in fan control line or AC condenser core pressure. B. The input may be a control signal such as a PWM fan drive signal. Many engine manufacturers have programmed a PWM fan speed signal that is used on many hydraulic fan drives. This may be used to control the pitch by using an algorithm that converts this proportional signal to an integral signal—for example use a setpoint of 80% of fan speed. If you are below that, increase pitch, if you are above, decrease pitch. C. The input may be a digital input such as from temperature switches instead of temperature sensors, AC compressor input—a digital signal that indicates the AC compressor is running, a backup alarm input (to suppress purges), a fire suppression input, an operator input such as manual purge button, or ECM/Can bus inputs. ECM/Can bus inputs form a communication link. This allows data to be shared from other electronic devices eliminating the requirement for redundant sensors. For example, most ECM&#39;s monitor engine temperature. By connecting to the ECM, the control system would not need its own dedicated engine temperature sensor. Other digital inputs include a J1939 Can interface (or the diagnostic port) to capture sensor data, a direct ECM interface, other controllers existing on the equipment on which the fan is used, an IQAN hydraulic controller, or a transmission controller. 
         [0026]    The outputs of the controller  92  may include  2  or  3  digital solenoid driver outputs (depending on the valve configuration) and an optional digital output to indicate when the fan is purging (i.e., connect a dash light to the controller). The controller can either be a virtual device (a program running on an existing programmable controller) or a dedicated electronic device. It will determine the pitch requirements by looking at sensor data. The sensor data may be obtained directly by the controller  92 , or may be communicated to the controller by another electronic device, such as the pitch sensor  74  along one or more lines  94 . The controller will then adjust the pitch of the fan by pulsing the appropriate valves, by sending signals along conventional connectors  96 , as for example according to the principles of operation described in U.S. Pat. No. 7,229,250, but other methods could be used. Variations of the control system will be applicable to some machines where as other variations will be applicable to others: Large OEMS (for example Caterpillar) will use the virtual controller to save cost and complexity, where as smaller OEM&#39;s may not have the capability to reprogram an engine ECM, and will therefore require a separate device. 
         [0027]    Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.