Patent Publication Number: US-10760577-B2

Title: Spring regulated variable flow electric water pump

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 15/079,123 filed Mar. 24, 2016 which claims the benefit of U.S. Provisional Application No. 62/140,854 filed Mar. 31, 2015. The entire disclosure of each of the above applications is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates generally to water pumps for motor vehicles. More specifically, the present disclosure relates to a variable flow electric water pump equipped with an axially-moveable rotor/impeller assembly. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     As is well known, water pumps are typically used in motor vehicles as part of a thermal management system for pumping a liquid coolant to facilitate heat transfer between the coolant and the internal combustion engine during vehicle warm-up and operation. Most commonly, a centrifugal water pump having a rotary pump member, such as an impeller, is configured to draw the coolant into an axial inlet and discharge the coolant through a radial discharge outlet. In many vehicular arrangements, the impeller is fixed to an impeller shaft that is rotatably driven (via an accessory drive system) by the crankshaft of the engine. Thus, the impeller speed is directly proportional to the engine speed. To provide a variable flow feature to such shaft-driven water pumps, it is known to permit limited axial displacement of the impeller within the pump chamber. For example, U.S. Pat. No. 7,789,049 discloses a water pump having an axially-moveable impeller that is spline mounted to the engine-driven shaft, and an electromagnetic actuator operable to control axial movement of the impeller between extended and retracted positions along the shaft so as to variably regulate the fluid flow characteristic between the fluid inlet and the discharge outlet. Similarly, U.S. Pat. No. 5,800,120 discloses a water pump having a shaft-driven impeller equipped with axially-moveable blades, the position of which is controlled via a hydraulic actuator. 
     It is also well known to install an auxiliary water pump, such as an electric water pump, in the engine coolant system to provide augmented control over the fluid flow. Generally, electric water pumps include an electric motor having a stationary stator and a rotor that is drivingly coupled to the impeller. Examples of electric water pumps are disclosed in commonly-owned U.S. Publication No. US2013/0259720 titled “Electric Water Pump With Stator Cooling” and U.S. Publication No. US2014/0017073 titled “Submerged Rotor Electric Water Pump with Structural Wetsleeve”, the entire disclosures of which are incorporated herein by reference. One drawback associated with many conventional electric water pumps is the need to provide a rotor encoder or another type of speed sensor within the electric motor to assist in accurate low speed (i.e. less than 600 RPM) pump control via a closed loop motor control system. Additionally, a need exists to provide variable flow at such low speeds that is not directly proportional to motor speed in an effort to meet customer expectations. 
     In view of the above, a need exists in the art to design and develop simplified and low-cost electric water pumps capable of providing variable flow characteristics and which can be easily substituted for otherwise conventional electric water pumps in motor vehicle applications. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not intended to act as a comprehensive and exhaustive disclosure of its full scope or all of its features, advantages, objectives and aspects. 
     It is an objective of the present disclosure to provide an electric water pump that meets the above-identified needs and provides a technological advancement over conventional electric water pumps. 
     It is another objective of the present disclosure to provide an electric water pump equipped with an electric motor having a stationary stator assembly and an axially-moveable rotor unit adapted to cause concurrent axial movement of a rotary pump member within a pump chamber for variably regulating fluid flow between an inlet and an outlet communicating with the pump chamber. 
     It is similar objective of the present disclosure to provide an electric water pump having a rotor/impeller assembly that is axially moveable relative to a stationary stator assembly for varying the size of a clearance gap between a volute in the pump chamber and the impeller. 
     It is a related objective of the present disclosure to control movement of the rotor/impeller assembly so as to provide a low flow output at low rotor speeds and a high flow output at high rotor speeds. In this regard, the rotor/impeller assembly is located in a low flow position relative to the stator assembly when rotated at low rotor speeds and in a high flow position relative to the stator assembly when rotated at high rotor speeds. 
     In accordance with a first embodiment of an electric water pump constructed and functional in accordance with the objectives of the present disclosure, the rotor/impeller assembly is normally biased toward its low flow position by a mechanical biasing arrangement disposed between the rotor unit and a stationary member within a pump housing. Movement of the rotor/impeller assembly from its low flow position toward its high flow position is a result of a pressure differential (ΔP) generated between upper (i.e. outer) and lower (i.e. inner) portions of the impeller and which is a function of the rotary speed of the rotor/impeller assembly. 
     In accordance with a second embodiment of an electric water pump constructed and functional in accordance with the objectives of the present disclosure, the rotor/impeller assembly is normally located in its low flow position by a magnetic biasing arrangement provided by an axially-offset magnetic field between the stator assembly and the rotor unit that is established by rotor magnets having an increased length in the direction of the impeller so as to provide a centering relationship with the stator assembly during low speed operation. 
     The present disclosure is directed to a variable flow electric water pump for use in an engine coolant system of a motor vehicle comprising: a pump housing defining a fluid chamber and a motor chamber, the fluid chamber including a fluid inlet and a discharge outlet for providing a flow of a coolant through the fluid chamber; an electric motor disposed in the motor chamber and including a stationary stator assembly and a rotor unit having a rotor shaft supported for rotation about a longitudinal axis and at least partially extending into the fluid chamber; an impeller fixed for rotation with the rotor shaft and disposed within the fluid chamber and being operable to pump the coolant from the fluid inlet to the discharge outlet; and a biasing arrangement operable for normally locating the rotor unit in a first position axially offset relative to the stator assembly for locating the impeller in a retracted position within the fluid chamber so as to provide a low flow characteristic between the fluid inlet and the discharge outlet when the impeller is rotatable driven by the rotor shaft at a low impeller speed. 
     The variable flow electric water pump of the present disclosure is further operable when the impeller is rotatably driven at a higher impeller speed to forcibly move the impeller to an extended position within the fluid chamber, in opposition to the preload exerted by biasing arrangement, for causing the rotor unit to be located in a second position axially aligned with the stator assembly. 
     The variable flow electric water pump of the present disclosure can be equipped with a mechanical biasing arrangement configured to normally exert a biasing force on the rotor unit selected to bias the rotor unit toward its first position. The mechanical biasing arrangement can include a mechanical biasing member, such as one or more spring members, disposed between an upper portion of the rotor unit and a stationary member or portion of the pump housing. 
     The variable flow electric water pump of the present disclosure can optionally be equipped with a magnetic biasing arrangement configured to normally locate the rotor unit in its first position. 
     The variable flow electric water pump of the present disclosure can further include an interface formed in the pump housing between the fluid inlet and the discharge outlet defining a flange surface. The impeller can be configured to include an outer rim surfaced aligned with the flange surface such that a first larger clearance gap is established therebetween when the impeller is located in its retracted position. The first larger clearance gap functions to establish a low flow characteristic when the impeller is driven at the low impeller speeds by the electric motor. In contrast, a second smaller clearance gap is established when the impeller is located in its extended position so as to create a high flow characteristic when the impeller is driven by the electric motor at the high impeller speeds. 
     Further areas of applicability will become apparent from the detailed description provided herein. As noted, the description of the objectives, aspects, features and specific embodiments disclosed in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and, as such, are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a sectional view of a variable flow electric water pump constructed in accordance with a first embodiment of the present disclosure to include a mechanically-biased rotor/impeller assembly which is shown located in a first or low flow position relative to a stationary stator assembly; 
         FIG. 2  is another sectional view of the variable flow electric water pump shown in  FIG. 1  now illustrating the spring-biased rotor/impeller assembly located in a second or high flow position relative to the stator assembly; 
         FIG. 3  is a graph illustrating the low-speed flow characteristics provided by the variable flow electric water pump shown in  FIGS. 1 and 2  in comparison to a conventional fixed flow electric water pump; 
         FIG. 4  is a sectional view of a variable flow electric water pump constructed in accordance with a second embodiment of the present disclosure to include a magnetically-biased rotor/impeller assembly which is shown located in a first or low flow position relative to the stationary stator assembly; 
         FIG. 5  is another sectional view of the variable flow electric water pump shown in  FIG. 4  now illustrating the rotor/impeller assembly located in a second or high flow position relative to the stator assembly; and 
         FIGS. 6A and 6B  are a partial sectional view of a slightly modified version of the variable flow electric water pump of  FIGS. 1 and 2 . 
     
    
    
     Corresponding reference numerals indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be more fully describe with reference to the accompanying drawings. However, the following description is merely exemplary in nature and is not intended to limit the present disclosure, its subject matter, applications or uses. To this end, example embodiments of an electric water pump are provided so that this disclosure will be thorough and will fully convey the scope to those skilled in this art. Numerous specific details are set forth, such as examples of specific components, devices and methods to provide a thorough understanding of the embodiments in many different forms, and such should not be construed to limit the intended scope of protection afforded by this disclosure. As is understood, some well-known processes, structures and technologies are not described in detail herein in view of the understanding afforded thereto by those skilled in this art. 
     In general, the present disclosure relates to an electric pump and, more particularly, to an electric water pump of the type applicable and well-suited for use and installation in motor vehicles for pumping a liquid coolant through an engine cooling system. However, the teachings provided herein are considered to be adaptable to any other electric pump required to move a medium (i.e. air, water, coolant, oil, etc.) within a pumping system requiring a variable flow capability. 
     With particular reference to  FIGS. 1 and 2  of the drawings, an electric water pump  10  constructed and functional in accordance with a first example embodiment of the present disclosure will now be described in greater detail. Pump  10  generally includes a pump housing  12 , an electric motor  14 , and a pump unit  16 . Pump housing  12  is shown in this non-limiting example to include a cylindrical outer housing  18 , a first or bottom cap  20 , and a second or top cap  22 . Outer housing  18  is generally cup-shaped and includes an open end section  24  to which bottom cap  20  is secured, and an end plate section  26  to which top cap  22  is secured. End plate section  26  of outer housing  18  is formed to define a raised annular rim  28  extending from a planar mounting surface  30 . A central pump pocket  32  is formed in rim  28  and is aligned on the longitudinal axis “A” of pump  10 . A pair of internal annular bosses  34  and  36  also extend from end plate section  26  of outer housing  18  and are aligned with the longitudinal axis. A thorough bore  38  extends between pump pocket  32  and a bearing pocket  40  associated with annular boss  34 . 
     Bottom cap  20  is configured, in this non-limiting example, to include an annular rim  44  extending from a planar mounting surface  46 , and an elongated cylindrical hub  48 , both of which are concentric with the longitudinal axis. End section  24  of outer housing  18  includes an inner diameter wall surface  50  configured to be pressed against an outer diameter surface  52  of annular rim  44 . End section  24  also includes a planar end surface  54  configured to engage mounting surface  46  on bottom cap  20 . While not specifically shown, a suitable fastening arrangement is provided to secure bottom cap  20  to outer housing  18  so as to define an internal motor chamber  56 . A blind bore  58  is formed in hub  48  and further defines a bearing pocket  60 . 
     Top cap  22  is shown, in this non-limiting example, configured to include an axially-extending tubular section  64  defining a fluid inlet  66 , a radially-extending tubular section  68  defining a fluid discharge outlet  70 , and a volute section  72  defining an impeller cavity  74  in fluid communication with fluid inlet  66  and discharge outlet  70 . An interface  76  is formed in top cap  22  between fluid inlet  66  and impeller cavity  74  and includes a first flange surface  78  and a second flange surface  80 . Top cap  22  includes a stepped flange section  82  configured to enclose a portion of raised rim  28  on end plate section  26  of outer housing  18 . Top cap  22  also includes a planar inner mounting surface  84  configured to engage outer mounting surface  30  on outer housing  18 . Suitable fasteners, such as a plurality of bolts  86 , are provided for securely connecting top cap  22  to outer housing  18 . 
     With continued reference to  FIGS. 1 and 2 , electric motor  14  is generally shown, in this non-limiting example, to include a stator assembly  90 , a rotor unit  92 , and a sleeve  94 . Sleeve  94  has a first end section  96  engaging end plate section  26  of outer housing  18 , a second end section  98  surrounding a portion of hub  48  on bottom cap  20 , and an elongated intermediate sleeve section  100  therebetween. An O-ring seal  102  is provided between annular rim  36  of end plate section  26  and first end section  96  of sleeve  94 . Sleeve  94  is configured to delineate motor chamber  56  into a toroidal stator cavity  56 A and a cylindrical rotor cavity  56 B. Stator assembly  90  is located within stator cavity  56 A and is configured to be non-moveable (i.e. stationary) therein. Rotor unit  92  is located within rotor cavity  56 B and is configured to be both rotatable and axially moveable therein, as will be detailed hereinafter with greater specificity. 
     Stator assembly  90  includes, in this non-limiting example, a coil winding  106  and a plurality or stack of plates  108  retained on a stator cage  110 . Stator cage  110  in non-moveably mounted to outer housing  18  and/or sleeve  94  within stator cavity  56 A. 
     Rotor unit  92  is shown, in this non-limiting example, to include a rotor shaft  114  and a plurality of circumferentially-aligned permanent magnets  116  retained by or encapsulated in a rotor shell  118 . An annular magnetic air gap  120  is established between intermediate sleeve segment  100  of sleeve  94  and rotor unit  92 . The components of rotor unit  92  are fixed to rotor shaft  114  for common rotation about the longitudinal axis. A first or lower end portion  114 A of rotor shaft  114  is disposed in blind bore  58  formed in bottom cap  20  and is supported for rotary and axial movement therein by a first or lower guide bushing  122  retained in bearing pocket  60 . Likewise, a second or upper end portion  114 B of rotor shaft  114  extends through throughbore  38  and into impeller cavity  74 . End portion  114 B of rotor shaft  114  is supported for rotary and axial movement by a second or upper guide bushing  124  retained in bearing pocket  40  formed in annular boss  34 . 
     Pump unit  16  is shown, in this non-limiting example, to include a rotary pump member, such as an impeller  126 , that is rigidly fixed to second end portion  114 B of rotor shaft  114  for rotation within pump pocket  32 . Impeller  126  is configured to include a central hub segment  128 , a first or lower rim segment  130  extending radially from hub segment  128 , a second or upper rim segment  132 , and a plurality of contoured impeller blades  134  extending between lower rim segment  130  and upper rim segment  132 . The actual number of impeller blades  134  and their particular contoured configuration (i.e. profile, shape, thickness, etc.) can be selected to provide the desired flow characteristic for a specific pump application. Upper rim segment  132  is configured to define a first rim surface  136  that is generally aligned with first flange surface  78  of volute interface  76 , and define a second rim surface  138  that is generally aligned with second flange surface  80 . 
     In accordance with the present disclosure, a rotor/impeller assembly  150  (comprised of rotor unit  92 , rotor shaft  114  and impeller  126 ) is moveable axially with respect to stator assembly  90  and inlet/volute interface  76  to provide a means for varying the flow characteristics of pump  10 . In this regard,  FIGS. 1 and 2  further illustrate pump  10  to include a mechanical biasing arrangement  152  acting between rotor unit  92  and a stationary component or portion of pump housing  12 . In particular, mechanical biasing arrangement  152  is shown, in the non-limiting example, to include a thrust washer  154  fixed to annular boss  34  (or abutting guide bushing  124 ) and a biasing member  156  acting between thrust washer  154  and an upper portion of rotor unit  92 . In the non-limiting example shown, biasing member  156  is a helical coil spring surrounding rotor shaft  114  and configured to apply a predefined spring load (i.e. “preload”) on rotor unit  92  for normally biasing rotor unit  92  toward a first position within rotor cavity  56 B, as shown in  FIG. 1 . In this first position, rotor unit  92  is axially offset relative to stator assembly  90 . Since impeller  126  is fixed via rotor shaft  114  to rotor unit  92 , impeller  126  is located in a “retracted” position when rotor unit  92  is located in its first position. As such, rotor/impeller assembly  150  is defined to be located in a “low flow” position within pump  10 . 
     As seen in  FIG. 1 , with rotor/impellor assembly  150  located in its low flow position, a small clearance “X 1 ”, is established between a lower surface  140  of impeller hub  128  and a bottom surface  142  of impeller pocket  32 . In contrast, a large clearance “Y 1 ” is established between corresponding interface surfaces  78 ,  80  and impeller rim surfaces  136 ,  138 . The preload provided by biasing member  156  is selected to establish this offset relationship shown in  FIG. 1  between stator assembly  90  and rotor unit  92  when the rotor shaft speeds are low so as to increase the clearance gap “Y” between impeller  126  and volute interface  76  to intentionally provide decreased pump efficiency and reduced flow. 
     In contrast to the arrangement shown in  FIG. 1 ,  FIG. 2  illustrates pump  10  when rotor shaft  114  is driven at a higher rotary speed. Specifically, when impeller  126  is rotated at higher speeds, a fluid pressure differential across impellor  126  acts to compress biasing member  156  which permits axial movement of rotor/impeller assembly  150  to a “high-flow” position ( FIG. 2 ). With rotor/impeller assembly  150  located in its high flow position, rotor unit  92  is located in a second position relative to stator assembly  90  and impeller  126  is located in an “extended” position relative to volute interface  76 . In its second position, rotor unit  92  is axially aligned with stator assembly  90  such that a large clearance “X 2 ” is established between lower surface  140  of impeller hub  128  and bottom surface  142  of impeller pocket  32  while, concomitantly, a small clearance “Y 2 ” is established between corresponding interface surfaces  78 ,  80  and impeller rim surfaces  136 ,  138 . The counterforce generated to oppose and overcome the preload of biasing member  156  is a result of the pressure differential (ΔP) generated when impeller  126  is rotated at higher speed. 
     In one non-limiting example, the clearance gap “Y 1 ” is in the range of 3 to 5 mm at low impellor rotary speeds in the range of 400 to 600 RPM. In contrast, the clearance gap “Y 2 ” is in the range of 0.3 to 0.6 mm at higher impellor rotary speeds.  FIG. 3  provides a graphical illustration of the flow vs speed characteristics for a conventional electric water pump with a fixed rotor/impeller assembly (see line  160 ) in comparison to pump  10  of the present disclosure (see line  162 ). What is evident is that the reduced efficiency provided by spring-biasing rotary/impeller assembly  150  to its low flow position ( FIG. 1 ) results in reduced flow rates (LPM) at lower pump speeds. The illustration further illustrates that upon movement of rotor/impeller assembly  150  to its high flow position ( FIG. 2 ), the flow vs. speed characteristics of pump  10  tend to align with those of the conventional pump, identified in this non-limiting example as point “P”. 
     Based on the above, the present disclosure provides a unique and non-obvious variant of an electric water pump  10  that is configured to generate lower flow at low rotor speeds as well as generate high flow at higher rotor speeds. It is contemplated that the preload applied by biasing member  156  to rotor unit  92  can be calibrated based on pump speed so as to maintain rotor/impeller assembly  150  in its low flow position until increased pumping efficiency is required. 
     Referring now to  FIGS. 4 and 5 , a second embodiment of an electric water pump  10 ′ constructed and functional in accordance with the present disclosure will be disclosed. Based on the similarity of a majority of the components associated with water pumps  10 ,  10 ′, common reference numbers are used with the exception that primed reference numerals identified slightly modified components. In general, pump  10 ′ does not rely on spring-biasing arrangement  152  to provide axial movement of rotor/impeller assembly  150 ′, but rather utilizes a magnetic biasing arrangement  152 ′ provided by an axially-offset magnetic field arrangement between rotor unit  92 ′ and stator assembly  90 . In particular, rotor unit  92 ′ is shown equipped with a plurality of elongated magnets  116 ′ having extended end segments  116 A extending axially outwardly from the top portion of rotor unit  92 ′. Under normal circumstances, the center of magnets  116 ′ will naturally align with stator assembly  90 , as shown in  FIG. 4 , so as to locate rotor/impeller assembly  150 ′ in the low flow position establishing clearance X 1 , and Y 1 , similar to those clearances associated with pump  10  of  FIG. 1 . As noted previously, rotor unit  92 ′ is located in its first position relative to stator assembly  90  and impeller  126  is located in its retracted position relative to volute interface  76  when rotor/impeller assembly  150  is in its low flow position. This “self-centering” action at low rotor speeds is caused by the centering behavior of the magnetic flux associated with the generated magnetic field. 
     In contract to  FIG. 4 ,  FIG. 5  illustrates pump  10 ′ when rotor unit  92 ′ is driven at a higher speed which causes the pressure differential (ΔP) across impeller  126  to forcibly move rotor/impeller assembly  150 ′ in an upward direction to its second or extended position, thereby establishing clearances X 2 , Y 2  similar to pump  10  of  FIG. 2 . Again, rotor unit  92 ′ is located in its second position relative to stator assembly  90  while impeller  126  is located in its extended position relative to volute interface  76 . Thus, pump  10 ′ provides a magnetic biasing arrangement as an option to the mechanical biasing arrangement associated with pump  10 . Line “B” in  FIG. 5  identifies the stator&#39;s center magnetic field aligned with the rotor&#39;s center magnetic field. The clearance “D” in  FIG. 4  identifies an example amount of magnetic offset between the rotor&#39;s center magnetic field and the stator&#39;s center magnetic field. 
     While pump  10  was illustrated to include a helical coil spring as biasing member  156  those skilled in the art recognize that other types and/or combinations of biasing devices configured to normally bias rotor/impeller assembly  150  to its low flow position during low speed/low flow operation can be employed. In addition, a combination of the spring-biased arrangement  152  of  FIGS. 1 and 2  can be integrated with the magnetic field arrangement  152 ′ of  FIGS. 4 and 5  to provide a hybrid variant of yet another embodiment of an electric water pump that is within the anticipated scope of this disclosure. 
     While not expressly shown, those skilled in the art will recognize that electric pumps  10 ,  10 ′ would be equipped with a controller device which functions to control operation of electric motor  12  and the rotational speed of impeller  126 . The controller device may include an electronic circuit board (ECB) electrically connected to stator assembly  90  and which can be mounted within pump housing  18 . 
     Referring to  FIGS. 6A and 6B , another alternative embodiment of an electric water pump  10 ″ is shown which is generally similar to electric water pump  10  of  FIGS. 1 and 2  with the exception that impeller  126 ″ now includes a molded-in sleeve  170  within which end portion  114 B of rotor shaft  114  is pressed into. In addition, mechanical biasing arrangement  152 ″ now includes a plurality of stacked wave or spring washers  172 , such as Belleville washers, surrounding rotor shaft  114  and being disposed between a top portion of rotor unit  92  and thrust washer  154 . Otherwise, the structure and function of water pump  10 ″ is generally similar to that of water pump  10 . While specific aspects, features and arrangements have been described in the specification and illustrated in the drawings, it will be understood that various changes can be made and equivalent elements be substituted therein without departing from the scope of the teachings associated with the present disclosure. Furthermore, the mixing and matching of features, elements and/or functions between various aspects of the inventive electric water pumps is expressly contemplated. Accordingly, such variations are not to be regarded as departures from the disclosure and all reasonable modifications are intended to be within the anticipated scope of the disclosure.