Abstract:
The present invention comprehends a gerotor or gear pump driven by a permanent magnet motor which exhibits cogging torque, i.e., resistance to rotation when de-energized caused by interaction between permanent magnets in the rotor and teeth on the stator. Such interaction causes the rotor to come to rest in one of many defined rotational positions and resist rotation when electrical power to the motor has been terminated. The permanent magnet motor is coupled, preferably directly, to a gerotor pump having meshing rotors or a gear pump having meshing gears. When the motor is de-energized, the pump rotors or gears come to rest and their rotation is resisted by the cogging torque of the motor. The invention finds particular application in automotive transmissions and systems with parallel pumps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/991,472, filed Nov. 30, 2007. The disclosure of the above application is incorporated herein by reference, 
    
    
     FIELD 
     The present disclosure relates to a motor and pump assembly and more particularly to a motor and pump assembly having improved sealing characteristics which reduce through flow when it is not operating. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Pumps for fluids encompass a broad range of mechanical configurations and flow characteristics. One frequent pump flow design requirement is constant or non-pulsating flow. This requirement generally eliminates piston pumps which typically have one or more reciprocating pistons producing a pulsating flow and pressure output. Centrifugal pumps provide a significantly smoother output flow but exhibit performance characteristics that vary widely with speed. 
     Gerotor and gear pumps represent a middle ground between the foregoing conflicting performance criteria. On the one hand, their construction, which includes two rotating and meshing members, provides a relatively smooth, i.e., non-pulsating, output. On the other, since the pump is essentially a positive displacement type, its speed versus flow and pressure characteristics are essentially proportional. Accordingly, gerotor and gear pumps find wide use in applications requiring a straightforward design, extended service life, minimal pulsation and predictable flow characteristics. 
     Occasionally, an issue arises with gerotor and gear pumps with regard to sealing between the meshing members and its influence on through flow. i.e., forward and especially reverse flow, when the pump is not operating. Aside from negligible flow between the side and end surfaces of the members and the stationary housing, the most significant flow occurs between the meshing or nearly meshing members. Depending upon the positions of the members and, more specifically, the extent to which any reverse (or forward) flow and pressure is capable of back driving the pump members, there may be an opportunity for relatively significant backward or forward flow through the non-operating pump. Such flow through a non-operating pump is generally undesirable especially in parallel pump installations or installations where air may be drawn through the non-operating pump into the suction side of the operating pump. 
     SUMMARY 
     The present invention provides a motor and pump assembly that provides reduced forward or reverse leakage through the pump when it is not operating. The present invention comprehends a gerotor or gear pump driven by a permanent magnet motor which exhibits cogging torque, i.e., resistance to rotation when de-energized caused by interaction between permanent magnets in the rotor and teeth on the stator. Such interaction causes the rotor to come to rest in one of many defined rotational positions and resist rotation when electrical power to the motor has been terminated. The permanent magnet motor is coupled, preferably directly, to a gerotor pump having meshing rotors or a gear pump having meshing gears. When the motor is de-energized, the pump rotors or gears come to rest and their rotation is resisted by the cogging torque of the motor. If the permanent magnet motor is a multiple phase design, additional rotation resisting torque may be generated by energizing one phase of the multiple phase motor. Internal friction within the pump caused by fluid pressure on the pump rotors or gears also inhibits their rotation. The invention finds particular application in automotive transmissions and systems with parallel pumps. It should be appreciated that in addition to gerotor and gear pumps, the present invention encompasses the combination of a permanent magnet motor with any type of positive displacement pump. 
     Thus it is an object of the present invention to provide a motor and positive displacement pump assembly which achieves minimum through flow when the motor is de-energized. 
     It is a further object of the present invention to provide a motor and gerotor or gear pump assembly having a permanent magnet motor which resists rotation of the rotors or gears when the motor is de-energized. 
     It is a still further object of the present invention to provide a motor and gear or gerotor pump assembly having a permanent magnet motor which resists rotation of the pump gears or rotors when one phase of a three phase motor is energized. 
     It is a still further object of the present invention to provide a motor and pump assembly having minimum through flow in a de-energized state which is especially suited for use in parallel pump installations. 
     It is a still further object of the present invention to provide a motor and gerotor pump assembly having gears which resist rotation when the motor is de-energized due to increased internal friction caused by fluid pressure acting on the stationary gears. 
     Further objects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples 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 illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic view of an automatic transmission having two hydraulic pumps disposed in parallel; 
         FIG. 2  is an exploded perspective view of a permanent magnet motor according to the present invention; 
         FIG. 3  is an exploded perspective view of a permanent magnet motor stator according to the present invention; 
         FIG. 4  is an exploded perspective view of a permanent magnet motor rotor according to the present invention; and 
         FIG. 5  is an end elevational view of a gerotor pump according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference now to  FIG. 1 , an automatic transmission incorporating the present invention is illustrated and generally designated by the reference number  10 . The automatic transmission  10  includes a metal housing  12  having a plurality of openings, bores, shoulders, flanges and other features which locate, support and secure various components such as, for example, an input shaft  14  and an output shaft  16 . The lowest portion of the housing  12  defines a sump  18  which collects hydraulic fluid from the various hydraulic components of the automatic transmission  10 . A filter  24  is submerged in the sump  18  and removes particulate matter from hydraulic fluid drawn into a bifurcated suction or inlet line  26  and provided to a first gear pump assembly  30  and a second gerotor or gear pump assembly  40 . The first gear pump assembly  30  includes a first gear pump driven by a component of the automatic transmission  10  and provides pressurized hydraulic fluid in a first output or supply line  34 . The second gerotor or gear pump assembly  40  includes a second gerotor pump  42  driven by a permanent magnet electric motor  44  and provides pressurized hydraulic fluid in a second output or supply line  46 . If desired, a check valve  48  may be disposed at the junction of the supply lines  34  and  46  to reduce back flow to and through the non-operating pump assembly  30  or  40 . The first and second supply lines  34  and  46  provide such hydraulic fluid to a transmission controller  50  which includes a plurality of control valves, spool valves and passageways that provide fluid outputs that control various torque transmitting devices such as clutches and brakes in the automatic transmission  10  to achieve operation. Typically, and as illustrated, the supply lines  34  and  46  will combine, either before or within the transmission controller  50 . 
     It will be appreciated that the first gear pump assembly  30  and the second gerotor or gear pump assembly  40  are both utilized in a single automatic transmission  10  to provide different pumping or flow characteristics. For example, since the first gear pump assembly  30  is driven by a component of the automatic transmission  10 , it will provide pressurized hydraulic fluid only when such component is rotating whereas the second gerotor pump assembly  40  may be activated or energized as desired or needed to provide pressurized hydraulic fluid. Alternatively, the first gear pump assembly  30  may have higher flow and lower pressure output than the second gerotor pump assembly  40  or vice versa or the second gerotor pump assembly  40  may have better cold temperature pumping characteristics than the first gear pump assembly  30 . In any event, it is envisioned that two pumps disposed on parallel will be utilized in the automatic transmission  10  to provide desirable and distinct hydraulic fluid pumping characteristics. 
     In such an installation, it is highly desirable to reduce or eliminate hydraulic fluid flow through the quiescent, i.e., at rest, gerotor pump assembly  40 . As explained above, the present invention is so directed. In this regard, it should be appreciated that while the present invention is especially suited for and described in conjunction with a parallel pump arrangement in an automatic transmission, the invention is equally suitable for use in other devices and in single, i.e., not parallel, or in multiple parallel installations where reduction in flow through the pump or pumps, especially reverse or back flow, when they are not operating, is either desirable or necessary. Moreover, it should be appreciated that while the second pump assembly  40  is described and referenced primarily as a gerotor pump, gear pumps and other positive displacement pumps are within the purview of the present invention. 
     Referring now to  FIGS. 2 ,  3  and  4 , the permanent magnet motor  44  of the second gerotor pump assembly  40  which drives the gerotor or gear pump  42  is illustrated. The electric motor  44  is disposed within and protected by a cylindrical housing  54  which supports a stator  56  of the electric motor  44 . As illustrated in  FIG. 3 , the stator  56  comprises a metal stator core  58  defining a plurality of axially extending T-shaped teeth  62 . In the current motor design, eighteen T-shaped teeth  62  are utilized in the stator core  58  but it should be understood that more or fewer teeth  62  may be utilized. A plurality of slot liners  64  are received between the teeth  62  and a like plurality of electrical windings  66  are disposed within the slot liners  64  between the teeth  62 . The electrical windings  66  may be arranged and connected in either a single or multiple, for example, three, phase configuration. A pair of insulating end caps or spiders  68  complete the stator  56  and protect the electrical windings  66 . 
     Rotatably disposed within the stator  56  is a rotor  72 . The rotor  72  includes a cylindrical rotor core  74  which contains a plurality of, for example, twelve, permanent magnets  76 . It will be appreciated that more or fewer permanent magnets  76  may be utilized in the rotor core  74 . The permanent magnets  76  are arranged with circumferentially alternating north and south poles around the rotor core  74 . A balance ring  78  is secured to each end face of the rotor core  74  and the rotor  72  is disposed upon and secured to a stepped drive shaft  82 , illustrated in  FIG. 2 . 
     Referring now to  FIGS. 1 ,  2  and  5 , the gerotor pump  42  is disposed at one end of and secured to the cylindrical housing  54  of the permanent magnet motor  44  by suitable means (not illustrated) and includes a cylindrical housing  90  which freely rotatably receives an outer rotor  92  surrounding and driven by an inner rotor  94  which is, in turn, driven by the stepped drive shaft  82  of the permanent magnet motor  44 . At one side of a pumping chamber  96  defined by the inner surface of the outer rotor  92  and the outer surface of the inner rotor  94  is an inlet or suction port  98 . On the opposite side of the pumping chamber  96  is an outlet or pressure port  102 . 
     The permanent magnet motor  44  also includes a plurality of ball bearing assemblies  104  associated with the stepped drive shaft  82  as well as fluid seals  106 , a bearing preload washer  108  and an end cap  110  secured to the cylindrical housing  54  by a plurality of threaded fasteners  112 . 
     Pumping operation of the second gerotor pump assembly  40  is essentially conventional. When, however, the flow of electrical power to the permanent magnet motor  44  is terminated, the magnetic force from the permanent magnets  76  will align the rotor  72  with the T-shaped teeth  62  of the stator  56  and thereby produce a rotation resisting torque, the cogging torque of the motor  44 . This cogging or rotation resisting (braking) torque is generally sufficient to prevent rotation of the pump rotors  92  and  94  and thus flow through the gerotor pump  42 , particularly reverse or backflow. This rotation resisting torque is augmented by friction or binding torque generated by the rotors  92  and  94  when stationary and subjected to reverse (or forward) fluid pressure. 
     It should be understood that if sufficient rotation resisting (braking) torque is not generated by the permanent magnet motor  44  in its deactivated or de-energized state, such that fluid pressure exerted on the outer rotor  92  and the inner rotor  94  of the gerotor pump  42  is sufficient to rotate the rotors  92  and  94  and cause undesirable flow through the gerotor pump  42 , one of the electrical windings  66  of a three phase permanent magnet motor  44  may be energized to increase braking torque to maintain the rotor  72  of the permanent magnet motor  44  and the rotors  92  and  94  of the gerotor pump  42  stationary. 
     It should also be understood that with the inner rotor  94  as well as the outer rotor  92  stationary due to the cogging torque of the permanent magnet motor  44 , fluid pressure in the outlet port  102  and the associated output or supply line  46  may be maintained at a low, positive value with a feed  113  from a pressurized circuit such as the output of the first gear pump assembly  30 . This low, positive pressure at the outlet port  102  eliminates the potential for air leakage into the common suction line  26  which is undesirable. 
     Finally, it should be understood that while the invention has been described primarily in connection with a gerotor pump, it is equally adapted to and will provide the same benefits when using a gear pump and, in fact, any positive displacement pump. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.