Patent Publication Number: US-6669439-B2

Title: Variable flow impeller-type water pump with movable shroud

Description:
RELATED APPLICATIONS 
     This application claim all the benefits and priority to U.S. provisional application No. 60/289,960, filed on May 10, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates to a variable-capacity water pump with an impeller construction for use in automotive engines and the like. 
     2. Description of the Related Art 
     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  10  with the impeller  20  fastened to a rotating shaft  30  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 toward the inlet path  26 . When the pulley  40  rotates, the drive shaft  30  rotates, and the vanes  24  similarly rotate. Coolant enters the passageway  50  and is thrown outward by centrifugal force of the rotating impeller  20  to an outlet port (not shown) via the outlet path  28 . 
     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, which is up to an order of magnitude greater. This leads to poor cooling efficiencies and increased power losses. 
     An alternative arrangement uses an electric motor instead of the engine to drive the impeller. However, this adds weight and cost because extra components are required, and because the capacity of the battery and generator needs to be increased, to supply the extra power needed by the motor. 
     U.S. Pat. No. 4,094,613, assigned to Sundstrand Corporation, discloses a variable output centrifugal pump utilizing a volute type diffuser in addition to vane diffusers. The variable flow is produced by a telescoping sleeve that closes or opens a main volute diffuser. In this design, a second volute diffuser is always open, so the range of control does not extend to zero flow output. Furthermore, the vane diffusers do not lie in a common plane, which leads to an undesirable increase in the physical volume of the pump. 
     U.S. Pat. Nos. 4,752,183 and 4,828,455, both assigned to Aisin Seiki Kabushiki Kaisha, propose a variable capacity impeller-type water pump that uses an axially movable thrust shaft and an attached disk or shroud with recesses through which the vanes protrude. A thermostat responds to temperature changes to move the thrust shaft and attached shroud over the vanes to vary the exposed area and therefore the quantity of coolant that flows through the water pump. This design relies on the accuracy of the thermostat, which can be suspect. It also poorly controls flow into the volute, allowing coolant to pass beneath the impeller. Furthermore, it does not allow for varying the pump capacity with the engine rotational speed. 
     U.S. Pat. No. 5,169,286, also assigned to Aisin Seiki Kabushiki Kaisha, proposes a variable capacity impeller-type water pump that uses coil springs and an attached disk plate or shroud with over-sized recesses through which the impeller vanes protrude with wide clearances. The effective height of the vanes, and hence the cooling capacity of the pump, is determined by the balance of forces exerted by the coil springs and the opposing pressure in the pressurized chamber formed between the impeller flange and the surrounding shroud. Unfortunately, this arrangement has several disadvantages, including unstable flow, unpredictable spring return characteristics, and very small pressure differentials, all of which result in a shroud position that is difficult to determine or control accurately. 
     SUMMARY OF THE INVENTION 
     The present invention provides a water pump construction with its capacity variable in accordance with an axially movable shroud that exposes a variable amount of impeller vane surface. 
     According to the present invention, a variable capacity coolant pump includes a pump body having a passage for coolant, a rotatable shaft projecting into the passage, a pump impeller having a flange extending radially outward from the rotatable shaft and a plurality of vanes axially projecting from the flange and configured to cause the flow of coolant through the passage, and a shroud positioned so that it moves from a position whereby the entire vane surfaces of the impeller are surrounded by the shroud, to a position whereby only a portion of the vane surfaces are surrounded, the position determined by either a torsional spring or externally actuated control unit. The external control unit can be integrated with other vehicle management control systems and can operate independently of engine speed, coolant temperature or fluid resistance pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a cross-sectional view of a prior art water pump; 
     FIG. 2 is a cross-sectional view of a water pump according to the present invention, whereby the working height of the impeller vanes is maximized; 
     FIG. 3 is an exploded view of a water pump according to the present invention; 
     FIG. 4 is a perspective view of the invention showing the locking of the shroud via pins; 
     FIG. 5 is a cross-sectional view of a water pump according to the present invention, whereby the working height of the impeller vanes is minimized; and 
     FIG. 6 is a cross-sectional view of a water pump according to a second embodiment of the present invention, illustrating an external actuator for actively controlling the position of the shroud. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, FIGS. 2 and 3 show an embodiment of a water pump  100  according to one aspect of the invention comprising a housing  110  enclosing a disk-shaped impeller  120 . The impeller  120  includes a radial flange  122  having a plurality of integral vanes  124  projecting axially outward therefrom. The impeller  120  is fastened to a rotatable shaft  130  drivable by a pulley (not shown) bolted onto hub  135 , whereby the pulley is belt driven from the engine crankshaft in a well-known manner. 
     The impeller  120  is initially held in place against a hard stop by an actuation spring  140  that exerts a torsional force, which opposes the drag torque created by the rotational movement of the impeller vanes through the coolant medium in the housing  110 . The spring  140  is connected between a spring holder  150  and the impeller  120 . A seal  155  and complementary adapter  158  are located behind the spring holder  150  to prevent leakage of the coolant medium from the housing  110 . The adapter  158  may not be necessary, depending on the size of the seal  155 . 
     The axial movement of the impeller  120  is controlled by the spring holder  150  and the top part of spiral sleeve  160 . The impeller  120  is free to rotate over the spiral sleeve  160  in any direction within an angular range restricted by a hard stop located on the spring holder  150 . 
     Further, an axially movable shroud  170 , extending parallel to the axis of rotatable shaft  130 , is circumferentially disposed around the impeller vanes  124 . A plurality of grooves  172  is formed in the shroud  170 . When the shroud  170  is assembled in place, all of the impeller vanes  124  are respectively inserted into each of the grooves  172  to project or extend beyond the surface of the shroud  170 . The vanes  124  and grooves  172  are curved in the preferred embodiment to maximum the efficiency and force of the vanes, however, straight vanes and grooves are also within the scope of the invention. The shroud  170  also has an axially extending hollow portion  173  terminating in a cover or cup  174  wherein the hollow portion is designed to accommodate the spiral sleeve  160 . Like the impeller  120 , the shroud  170  slides axially over the spiral sleeve  160 , but its movement is controlled by locking pins  175  sliding along grooves  176  in the shroud insert  178  and complementary grooves  165  in the spiral sleeve  160 . The spring holder  150  is riveted or otherwise secured to the spiral sleeve  160 , and both parts are preferably press fitted or otherwise secured onto the bearing shaft assembly  180 . 
     In operation, after the engine is first started, the rotational engine speed is low and the drag torque needed to move the impeller through the coolant is therefore also low and is easily opposed by the torsional spring  140 . In this initial stage, the shroud  170  is held back in a retracted position as shown in FIG. 2, away from the inlet opening, by locking pins  175  located inside grooves  165  and  176  in the spiral sleeve  160  and shroud insert  178 , respectively, as shown clearly in FIG.  4 . This shroud position maximizes the exposed impeller vane surface and hence provides the maximum flow output at low engine speed. 
     As engine speed increases, the drag torque on the impeller vanes  124  also increases due the direct connection described earlier. At a certain point, which can be controlled by the torsional spring characteristics, for example, the drag torque overcomes the torque of the torsional spring  140 . When the impeller  120  and shroud  170  begin to change their relative angular position with the rotatable shaft  130 , the shroud  170  is pushed upward by the pins  175 , which follow the inside spiral grooves  165  of the spiral sleeve  160  to an extended position as shown in FIG.  5 . 
     As the exposed vane surface decreases, the drag torque experienced due to fluid resistance also decreases. Also, the relative turning of the impeller  120  on the bearing shaft  180  increases the torque produced by the torsional spring  140 , until it comes into equilibrium with the drag torque of the impeller  120  at the minimum flow configuration illustrated by FIG.  5 . 
     During pump operation, the impeller drag torque is proportional to the flow value, which is easily measurable and does not change if the coolant temperature rises. Therefore, the force applied to the impeller is stable, predictable and precise. By using calibrated spring parameters, the shroud movement is smooth and controllable. Each pump spring can be calibrated for a specific vehicle cooling system. 
     The control system can also be active instead of passive. With this type of design, illustrated in FIG. 6, an external electric, mechanical or other type of actuator  200  is introduced with an actuation arm  210  and push rod  220  connecting to the shroud of the variable flow pump. The push rod  220  rotates at the pump shaft speed and its axial movement is restrained by a locating pin  230  within a cutout slot in the bearing shaft assembly  180 . The pin  230  also controls the axial position of the shroud  170 . The push rod  220  and actuation arm  210  are connected via a bearing  240  to reduce friction. 
     The shroud is controlled by an actuator and push rod arrangement that responds to sensor measurements to supply a sufficient quantity of coolant tailored to the actual need of the engine and without unwanted power loss caused by excessive flow. Because the actuator works independently of the cooling system, water pump operation can always be controlled, regardless of coolant pressure, temperature or engine speed. This ability creates a large energy savings, especially during the engine warm-up phase, and prevents engine overheating. The active system can work in a closed loop and can be controlled by the vehicle&#39;s on-board electronic control unit. 
     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 shroud insert  178  and shroud  120  could be produced as one molded element together with the locking pins  175  by using an insert molding type of process.