Abstract:
A variable-capacity water pump includes a housing having an impeller mounted on a rotatable shaft. The impeller includes a plurality of vanes pivotally coupled between upper and lower shroud and operatively coupled to a pitch plate. As the pump speed increases in response to increasing engine speed, the pitch plate controls the rotation of the impeller vanes about a fixed rivet from a maximum pitch position, toward a minimum pitch position, thereby lowering pump output according to engine cooling requirements.

Description:
FIELD OF THE INVENTION  
         [0001]    The subject invention relates to a variable capacity water pump with an impeller for use in automotive engines and the like.  
         DESCRIPTION OF RELATED ART  
         [0002]    The cooling mechanism for an internal combustion engine used in an automobile normally comprises a coolant pump, commonly referred to as a water pump, of a centrifugal-type. The most common arrangement utilizes the engine rotation to drive a shaft via a belt connection between a driving pulley (connected to the crankshaft) and a driven pulley. The example shown in FIG. 1 shows a typical water pump P with an impeller  20  fastened to a rotating shaft  30  and drivable by the pulley  40 , which is attached to the engine crankshaft (not shown). The impeller  20  includes a flange  22  having several integral blades or vanes  24  projecting axially therefrom toward the inlet path  26 . When the pulley  40  rotates, the drive shaft  30  rotates, and thus, the vanes  24  similarly rotate with the impeller  20 . Coolant enters the passageway  50  and is thrown outward by centrifugal force to an outlet port (not shown) via the outlet path  28 .  
           [0003]    Although this system is simple, it has the disadvantage of supplying a fixed capacity of coolant that is often unnecessarily large. This over-capacity arises because the pump output is sized to deliver a minimum flow amount of coolant at low engine speeds. At higher engine speeds, such as those experienced under normal highway driving conditions, the flow amount becomes excessive because it is directly proportional to engine speed. This leads to poor cooling efficiencies and increased power losses.  
           [0004]    An alternative arrangement uses an electric motor instead of the engine to drive the impeller. For instance, U.S. Pat. No. 3,840,309 discloses a variable capacity centrifugal pump with vanes that move via a pivoting linkage mechanism between a threaded nut and a cross-mount that is attached to a propeller shaft rotated by an electric motor. However, this type of design adds weight and cost because extra components are required. Also, the capacity of the battery and generator needs to be increased in order to supply the extra power needed by the motor.  
           [0005]    Still further, U.S. Pat. Nos. 4,752,183 and 5,169,286 disclose two similar variations of a variable output centrifugal pump utilizing a shroud with recesses through which the vanes protrude. The shroud is axially moved over the vanes to vary the exposed area and, therefore, the quantity of coolant that flows through the water pump. This design fails to properly control fluid flow into the volute and allows coolant to pass beneath the impeller. Furthermore, it does not allow for varying the pump capacity with the engine rotational speed.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a water pump having variable capacity in accordance with a relatively simple mechanical means that obviates the need for expensive electric motors or shrouds that can cause turbulent flow.  
           [0007]    According to the present invention, a variable capacity coolant pump includes a pump body for directing the flow of fluid through the pump between an inlet and an outlet and a shaft rotatably connected to the pump body. An impeller is coupled to the pump body for pumping fluid through the pump body from the inlet to the outlet. The impeller includes a shroud and at least one vane pivotally coupled to the shroud for pivotal movement between a plurality of pitch angles relative to the shaft. A pitch plate is operatively coupled to the vane for controlling the pitch angle of the vane. A spring is coupled to the pitch plate for biasing the vane to a maximum pitch angle wherein the vane varies in pitch in response to a force of fluid pressure from the inlet and automatically reduces the pitch angle of the vane upon an increase in the fluid pressure from the inlet to reduce the flow of fluid to the-outlet. In an alternative embodiment, the pitch angle is also controlled externally via an actuator. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0009]    [0009]FIG. 1 is a cross-sectional view of a prior art water pump;  
         [0010]    [0010]FIG. 2 is a cross-sectional view of a water pump of one embodiment according to the present invention;  
         [0011]    [0011]FIG. 3 is a top view of a pitch plate of the water pump according to FIG. 2;  
         [0012]    [0012]FIG. 4 is a perspective view of an impeller vane and pitch control tab of the water pump according to FIG. 2;  
         [0013]    [0013]FIG. 5 a  is a partial section view of a water pump according to FIG. 2 showing the location of the vanes in the highest pitch position;  
         [0014]    [0014]FIG. 5 b  is a partial section view of a water pump according to FIG. 2 showing the location of the vanes in the lowest pitch position;  
         [0015]    [0015]FIG. 6 is a cross-sectional view of a water pump of a second embodiment according to the present invention;  
         [0016]    [0016]FIG. 7 is a top view of the pitch plate of the water pump according to FIG. 6;  
         [0017]    [0017]FIG. 8 is a perspective view of the impeller vane and pitch control tab of the water pump according to FIG. 6;  
         [0018]    [0018]FIG. 9 a  is a partial section view of a water pump according to FIG. 6 showing the location of the vanes in the highest pitch position;  
         [0019]    [0019]FIG. 9 b  is a partial section view of a water pump according to FIG. 6, and showing the location of the vanes in the lowest pitch position;  
         [0020]    [0020]FIG. 10 is a partial cross-sectional view of a water pump of a third embodiment according to the present invention;  
         [0021]    [0021]FIG. 11 is a cross sectional view of a water pump of a fourth embodiment according to the present invention;  
         [0022]    [0022]FIG. 12 is a partial section of the water pump according to FIG. 11, showing details of the internal moving parts; and  
         [0023]    [0023]FIG. 13 is a perspective view of the pitch plate of FIG. 11. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, FIG. 2 shows a first preferred embodiment of a variable capacity coolant pump, or water pump P comprised of a housing  4  including an impeller I. The impeller I is fastened to a rotatable shaft  10  drivable by a pulley (not shown) that is belt driven from the engine crankshaft in a well-known manner.  
         [0025]    The impeller I includes a lower flange or shroud  5  having a plurality of pivotal vanes  2  projecting axially toward the inlet path of the pump. Each vane  2  is connected to an upper flange or shroud  1  via rivets  11  and guided within arcuate shaped slots  3   a ,  3   b  between the shrouds  1 ,  5 . Directly underneath the lower shroud  5 , and rigidly connected to the rotatable shaft  10 , is a pitch plate  6  having slots  13  to accommodate the pitch control tabs  12  projecting from the bottom of each of the plurality of vanes  2 , as best shown in FIGS. 3 and 4.  
         [0026]    Further, a torsional pitch spring  7  is disposed around the rotatable shaft  10 , and extends to the edge of the lower shroud  5 , such that the torsional spring  7  normally biases the impeller I to its most forward position, where the vanes  2  are held in their highest pitch position. The slots  13  in the pitch plate  6  restrict the movement of the vanes so that they are set to an optimal position, or pitch, for low pump rotational speeds.  
         [0027]    In operation, when the engine is first started, the torsional pitch spring  7  holds the impeller in its most forward position. The vanes  2  rotate about their rivets  11  and are held in their highest pitch position, as shown in FIG. 5 a . The highest pitch position may be further defined by the vanes  2  extending generally transverse or approaching perpendicular to the center axis of the shroud  1 . As the pump speed increases, the drag torque on the impeller I increases, causing the impeller I to rotate in a reverse direction relative to the pitch plate  6 . This movement of the impeller I relative to the pitch plate  6  causes the vanes  2  to rotate about their rivets  11  to a lower pitch position, as shown in FIG. 5 b . The lower pitch position may be further defined by the vanes arranged generally parallel with the circumferential outer edge of the shroud  1 . A force balance is realized between the torsional pitch spring  7 , which biases the impeller I to its forward most position (and vanes  2  in the highest pitch position), and the fluid drag torque, which biases the impeller I to its rearward position (and vanes  2  in the lowest pitch position).  
         [0028]    Therefore, as the pump speed increases in response to increasing engine speed, the vanes  2  rotate about their rivets  11  from their highest pitch position, illustrated in FIG. 5 a,  toward their lowest pitch position, illustrated in FIG. 5 b . The guiding slots  13  that are cut into the pitch plate  6  limit the maximum position, or range of movement, of the vanes  2  to a predetermined limit, dependent on engine cooling requirements.  
         [0029]    Referring now to FIGS.  6 - 9 , another embodiment of the impeller arrangement is illustrated. The essential elements are arranged in a similar fashion as before, except that the pitch plate  106  is axially fixed to the rotational shaft  10 , but is rotationally free thereon and is affected by the torsion pitch spring  107 , which no longer contacts the lower shroud  105 . Further, the pitch control tabs  112  are now located on the outer edges of the vanes  102 , and the rivets  111  are located on the opposite edge, as shown in FIGS. 6 and 8.  
         [0030]    At low rotational speeds, the torsion pitch spring  107  holds the vanes  102  in their outer most, or highest pitch, position, shown in FIG. 9 a.  The torsional pitch spring  107  reacts against the rotational shaft  110  and rotates the pitch plate  106  against the pitch control tabs  112  on the bottom of the vanes  102 . As the pump rotational speed increases, the fluid pressure on the vanes  102  causes the vanes  102  to rotate about their rivets  111  against the pressure being applied to the pitch control tabs  112  by the pitch plate  106 . A balance of forces is once again achieved, where the force exerted by the torsional pitch spring  107  onto the vanes  102  is opposed by the back pressure of the fluid flowing across the forward face of the vanes  102 . At high rotational speeds, the vanes  102  are rotated to their lowest pitch positions, illustrated in FIG. 9 b.    
         [0031]    [0031]FIG. 10 discloses an alternate embodiment whereby the torsional pitch spring is replaced by a compression pitch spring  113 , a sliding shell  114 , a helically motivated rotating shell  115  and a C-clip  116 . The sliding shell  114  is rotationally fixed onto the main rotational shaft  110  by the spline  117 , and the rotating shell  115  is axially fixed by the C-clip  116 . Tabs  119  on the sliding shell  114  consequently impart a rotating torque onto the rotating shell  115  by applying an axial force to a helical slot  120  in the rotating shell  115 . The combination of compression pitch spring  113 , sliding shell  114 , rotating shell  115  and the straight spline  117  applies the same outward force to the vanes  102  by imparting a rotating force onto the pitch plate  106 . This applies an outward force to the pitch control tab  112  located on the bottom of the vane  102 . The rotating force is generated when the compression pitch spring  113  axially pushes the sliding shell  114  against the rotating shell  115 . The outward force on the vanes  102 , derived from the compression spring  113 , is again balanced by the fluid pressure acting on the vanes.  
         [0032]    Finally, FIGS.  11 - 13  illustrate yet another alternate embodiment of the invention whereby the vane pitch is controlled by an external actuator  256 . In operation, the actuator  256  moves the rod  255  axially. An arm  254  connects the rod  255  to a bearing  253 . The subsequent motion of the rod  255  and arm  254  combination causes the bearing  253  to move axially. The bearing  253  then drives the control rod  259  axially. The internal shaft is rigidly attached to pin  260 , which acts on the helical grooves  262  in the rotation shell  252 , illustrated more clearly in FIG. 13, to cause it to rotate. The direction of rotation, clockwise or counterclockwise, depends on the direction that the control rod  259  moves in. The rotation shell  252  acts on or otherwise engages the lower shroud  205 , and, indirectly, the entire impeller sub-assembly, causing the sub-assembly to rotate. The pitch plate  206 , which is rigidly attached to the rotating shaft  210 , acts on the pitch control tabs  212  of the vanes  202  to change the pitch of the vanes  202 . In operation, an external electronic controller can be used to determine the vane  202  pitch angle for a given pump speed and engine temperature.  
         [0033]    Having now fully described the invention, any changes can be made by one of ordinary skill in the art without departing from the scope of the invention as set forth herein. For example, the pitch plate or vanes can also be driven by an electronic or hydraulic actuator. Further, the pitch plate could be replaced by a set of linkages.  
         [0034]    The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.