Abstract:
An actuator assembly includes a housing having a central axis, a motor compartment on one end defined about the central axis, a gear compartment on the other end. An electronic rotational position sensor is fixed relative to the housing proximate the motor compartment. A motor assembly is disposed in the motor compartment and has a hollow input shaft extending along the central axis into the gear compartment. An output shaft extends along the central axis and has a lower end extending out of the gear compartment and an upper end extending freely through the hollow input shaft to a point proximate to the electronic rotational position sensor. A gear assembly is supported within the gear compartment for translating rotation of the input shaft to the output shaft. A sensed object is disposed on the upper end of the output shaft opposed to the speed sensor.

Description:
TECHNICAL FIELD OF INVENTION 
       [0001]    The present invention relates to an actuator assembly; more particularly to an actuator assembly having an output shaft; and even more particularly to such an actuator with a rotational position sensor for determining the rotational position of the output shaft. 
       BACKGROUND OF INVENTION 
       [0002]    It is known for an actuator to have an output shaft that is connected to a member that is desired to be rotated based on input from a rotating machine, for example, an electric motor. It is also known for the electric motor to be attached to a gear assembly which is used to produce a given number of turns of the output shaft for a given number of turns of the electric motor. In a typical arrangement, the output shaft is distal from the electric motor such that the gear assembly is between the electric motor and the output shaft. In such an arrangement, electrical components, which may be included on a circuit board assembly, are disposed adjacent to the electric motor and distal from the gear assembly and output shaft. It may be desirable to monitor the rotational position of the output shaft. In order to monitor the rotational position of the output shaft, an electronic based sensing arrangement may be positioned proximal to the output shaft. Such a sensing arrangement will need to be remote from the circuit board assembly. However, it may be desirable to include at least a portion of the sensing arrangement with the circuit board assembly to simplify the electronic componentry of the actuator. 
         [0003]    What is needed is an actuator assembly which minimizes or eliminates one or more of the shortcomings as set forth above. 
       SUMMARY OF THE INVENTION 
       [0004]    Briefly described, an actuator assembly includes a housing having a central axis, a motor compartment on one end defined about the central axis and a gear compartment on the other end. An electronic rotational position sensor is fixed relative to the housing proximate the motor compartment. A motor assembly is disposed in the motor compartment and has a hollow substantially cylindrical input shaft extending along the central axis into the gear compartment. An output shaft extends along the central axis and has a lower end extending out of the gear compartment and an upper end extending freely through the hollow input shaft to a point proximate to the electronic rotational position sensor. A gear assembly is supported within the gear compartment defined about the central axis for translating rotation of the input shaft to the output shaft. A sensed object is disposed on the upper end of the output shaft opposed to the speed sensor. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    This invention will be further described with reference to the accompanying drawings in which: 
           [0006]      FIG. 1  is an exploded isometric view of an actuator in accordance with the present invention; 
           [0007]      FIG. 2  is an axial cross section of the actuator assembly of  FIG. 1 ; 
           [0008]      FIG. 3  is an elevation view of the actuator assembly of  FIG. 1 ; 
           [0009]      FIG. 4  is an isometric view of a gear assembly of the actuator assembly of  FIG. 1 ; 
           [0010]      FIG. 5  is an axial view of a portion of the gear assembly of  FIG. 4 ; 
           [0011]      FIG. 6  is an isometric view of a first side of a circuit board assembly of the actuator assembly of  FIG. 1 ; 
           [0012]      FIG. 7  is an isometric view of a second side of a circuit board assembly of the actuator assembly of  FIG. 1 ; and 
           [0013]      FIG. 8  is a top view of a magnet used to sense the rotational position of an output shaft of the actuator assembly of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0014]    Reference will be made to  FIGS. 1 and 2  in which  FIG. 1  is an exploded isometric view of an actuator assembly  10  and  FIG. 2  is an axial cross-section of actuator assembly  10 . Actuator assembly  10  generally includes a gear assembly  12 , a motor assembly  14 , and a circuit board assembly  16  all located within a housing  18 . Motor assembly  14  may generically be referred to as a rotating electric machine. Housing  18  extends along axis A and includes a gear compartment  20  for receiving gear assembly  12 , a motor compartment  22  for receiving motor assembly  14 , and a circuit board compartment  24  for receiving circuit board assembly  16 . Gear compartment  20  may be separated from motor compartment  22  by a bulkhead  26  having a bulkhead aperture  28  extending therethrough and centered about axis A. Bulkhead  26  generally defines a bottom wall of motor compartment  22 . Bulkhead  26  may contain features, for example, a plurality of grooves  30  that concentrically surround bulkhead aperture  28  on the side of bulkhead  26  that faces toward motor compartment  22 . Grooves  30  will be discussed in more detail later. Housing  18  may be made of a light weight metallic material, for example, aluminum. However, it should be understood that housing  18  may be made of any metallic or non-metallic material that has sufficient strength to withstand forces encountered by actuator assembly  10  and that is compatible with the operating environment of actuator assembly  10 . 
         [0015]    Motor assembly  14  will now be described with continued reference to  FIGS. 1 and 2 . Motor assembly  14  may be a brushless DC motor with a rotor assembly  32  and a stator assembly  34 , however it should be understood that motor assembly  14  may be a brushed motor rather than a brushless motor. Rotor assembly  32  passes through bulkhead aperture  28  and is supported within bulkhead aperture  28  by a first bearing  36  such that rotor assembly  32  is free to rotate about axis A within stator assembly  34 . First bearing  36  may be a conventional ball roller bearing which is press fit within bulkhead aperture  28  and which receives rotor assembly  32  in a press fit relationship. Rotor assembly  32  includes a rotor central bore  38  extending centrally through rotor assembly  32  and centered along axis A. Rotor central bore  38  will be discussed in more detail later. Rotor assembly  32  also includes a rotor bearing bore  40  in the end of rotor assembly  32  that is located within motor compartment  22  and distal from bulkhead  26 . Rotor bearing bore  40  is coaxial with rotor central bore  38  and receives a second bearing  42  therewithin for supporting rotor assembly  32  as will be described later. Second bearing  42  may be a conventional ball roller bearing that is press fit within rotor bearing bore  40 . Rotor assembly  32  also includes a multi-pole ring magnet  44  radially surrounding the perimeter thereof such that the poles are arranged in a polar array of alternating north and south poles. Multi-pole ring magnet  44  may, for example only, include five pole pairs where each pole is equal in angular length. 
         [0016]    Stator assembly  34  includes a stator  46  and a stator support frame  48  that is axially offset from said stator  46 . Stator  46  is fixed to stator support frame  48  with an over-molding material  50  to prevent relative rotation therebetween. In order to apply over-molding material  50  to stator  46  and stator support frame  48 , stator  46  and stator support frame  48  are placed in a mold (not shown) having a cavity corresponding to the outside surface of over-molding material  50 . Over-molding material  50  is then injected, in liquid form, into the cavity. After over-molding material  50  solidifies, the mold is removed and over-molding material  50  fixes stator  46  to stator support frame  48 . Over-molding material  50  may include a plurality of annular rings  52  that are concentric to axis A. Annular rings  52  will be discussed in greater detail later. Stator  46  includes a plurality of electric windings  54  spaced at equal angular intervals around stator  46 . While only two electric windings  54  are visible in  FIG. 2 , it should be understood that additional windings electric  54  may be included that are not visible in  FIG. 2 . For example, stator  46  may include a total of six electric windings  54  that are equiangularly spaced around stator  46 . 
         [0017]    Stator support frame  48  is coaxial with stator  46  and disposed at the end of stator assembly  34  that is distal from bulkhead  26 . Stator support frame  48  includes a central section  56  that is circular and centered about axis A. A hub  58  extends axially away from central section  56  toward bulkhead  26  such that hub  58  is centered about axis A. Hub  58  extends through second bearing  42  in a close fit nature, for example by press fit, in order to support second bearing  42  which in turn supports the end of rotor assembly  32  that is proximal to stator support frame  48 . Hub  58  includes a hub central bore  60  extending coaxially thereinto from the end of hub  58  that is proximal to bulkhead  26 . Hub central bore  60  will be discussed in more detail later. Stator support frame  48  also includes stator support frame rim  62  which radially surrounds central section  56  such that the length of stator support frame rim  62  in the direction of axis A is greater than the length of central section  56  in the direction of axis A. Stator support frame rim  62  may include one or more stator support frame apertures  64  that extend therethrough in the general direction of axis A. Stator assembly  34  is fixed within motor compartment  22 , for example, by press fit of stator support frame rim  62  with motor compartment  22  in order to prevent relative rotation between stator assembly  34  and housing  18 . The increased length of stator support frame rim  62  compared to central section  56  helps to prevent motor assembly  14  from tipping within housing  18 , thereby maintaining motor assembly  14  in a coaxial relationship with housing  18 . 
         [0018]    In order to dissipate heat generated by motor assembly  14 , a high thermal conductivity material  66  may be injected into the annular space formed radially between motor assembly  14  and motor compartment  22 , and more specifically radially between stator  46  and motor compartment  22 . High thermal conductivity material  66  is defined by a material that is more thermally conductive than air which has a thermal conductivity between 0.02 W/m·K (watts per meter kelvin) and 0.5 W/m·K over the range of operating temperatures of actuator assembly  10 . Preferably, high thermal conductivity material  66  has a thermal conductivity of at least 1.6 W/m·K (watts per meter kelvin). High thermal conductivity material  66  may be injected into this annular space in liquid form through stator support frame apertures  64 . After high thermal conductivity material  66  is injected, high thermal conductivity material  66  may be cured to form a solid material. High thermal conductivity material  66  may also possess adhesive properties which aid in fixing motor assembly  14 , and more specifically stator  46 , to housing  18 . In order to prevent high thermal conductivity material  66  from migrating to rotor assembly  32  and first bearing  36  during injection thereof, each annular ring  52  of over-molding material  50  may fit within one groove  30  in bulkhead  26 . The plurality of annular rings  52  together with grooves  30  form a tortuous path that prevent high thermal conductivity material  66  from migrating to rotor assembly  32  and first bearing  36 . In this way, high thermal conductivity material  66  is prevented from migrating radially inward of annular rings  52  and grooves  30 . While four annular rings  52  and four grooves  30  are shown, it should now be understood that a greater or lesser number of annular rings  52  and grooves  30  may be provided. While annular rings  52  and grooves  30  are shown as circular, it should now be understood that annular rings  52  and grooves  30  may take the form of other shapes. 
         [0019]    Reference will continue to be made to  FIGS. 1 and 2  and additional reference will be made to  FIG. 3  which is an elevation view of actuator assembly  10 . In order to further dissipate heat generated by motor assembly  14 , a cooling passage  68  may be provided through housing  18  at a location that preferably radially surrounds at least a portion of motor assembly  14 . Cooling passage  68  includes a cooling passage inlet  70  for receiving a liquid coolant at a relatively cool temperature from a coolant source (not shown). Cooling passage  68  also includes a cooling passage outlet  72  for discharging the liquid coolant from housing  18  at a temperature that is elevated compared to the temperature of the liquid coolant at cooling passage inlet  70 . Heat that is generated by motor assembly  14  is transferred through high thermal conductivity material  66  and housing  18  to the liquid coolant as the liquid coolant moves from the cooling passage inlet  70  to the cooling passage outlet  72 , thereby cooling actuator assembly  10 . 
         [0020]    Gear assembly  12  will now be described with continued reference to  FIGS. 1 and 2  and with additional reference to  FIG. 4  which is an isometric view of gear assembly  12  and  FIG. 5  which is an axial view of a portion of gear assembly  12 . Gear assembly  12  generally includes pinion gear  74 , input gear  76 , idler gears  78 , idler gear carrier  80 , output gear  82 , and output shaft  84 . 
         [0021]    Pinion gear  74  is fixed, for example by press fit, to the portion of rotor assembly  32  that extends into gear compartment  20  such that pinion gear  74  rotates with rotor assembly  32  in a one-to-one relationship. In this way, the portion of rotor assembly  32  that extends into gear compartment  20  acts as an input shaft to gear assembly  12 . Pinion gear  74  includes a plurality of pinion gear teeth  86  that extend radially outward therefrom and a pinion gear central bore  88  that extends axially through pinion gear  74  centered about axis A. Pinion gear  74  may be made, for example only, of a molded plastic material. 
         [0022]    Input gear  76  concentrically surrounds pinion gear  74  and includes a plurality of input gear teeth  90  that extend radially inward therefrom. Input gear  76  is larger in diameter than pinion gear  74  to define an annular space between input gear  76  and pinion gear  74 . Input gear  76  is fixed relative to housing  18 , as will be described later, in order to prevent relative rotation between input gear  76  and housing  18 . Input gear  76  may be made, for example only, of a molded plastic material. 
         [0023]    Each idler gear  78  is a stepped diameter gear with an idler gear input section  92  having a plurality of idler gear input section teeth  94  that extend radially outward therefrom. Idler gear input section  92  fits within the annular space between input gear  76  and pinion gear  74  such that idler gear input section teeth  94  mesh with pinion gear teeth  86  and input gear teeth  90 . Each idler gear  78  also includes an idler gear output section  96  having a plurality of idler gear output section teeth  98  that extend radially outward therefrom. Idler gear output section  96  is fixed to idler gear input section  92 , for example by molding idler gear output section  96  to idler gear input section  92  as a single piece of plastic, such that idler gear output section  96  rotates together with idler gear input section  92  in a one-to-one relationship. As shown, idler gear input section  92  is smaller in diameter than idler gear output section  96  and idler gear input section  92  has fewer idler gear input section teeth  94  than idler gear output section  96  has idler gear output section teeth  98 , however, it should be understood that this relationship may be reversed to achieve different gear ratios of gear assembly  12 . Each idler gear  78  also includes an idler gear bore  100  extending centrally therethrough in the same direction as axis A. 
         [0024]    Idler gear carrier  80  includes an idler gear carrier hub  102  with idler gear carrier hub bore  104  extending therethrough and centered about axis A. Idler gear carrier  80  also includes a plurality of regularly spaced idler gear carrier axles  106  radially offset from idler gear carrier hub  102 . The number of idler gear carrier axles  106  corresponds to the number of idler gears  78  such that each idler gear  78  is associated with one idler gear carrier axle  106 . Each idler gear carrier axle  106  extends into idler gear bore  100  of a respective idler gear  78 . Each idle gear carrier axle  106  is sized to be in a close fit relationship with idler gear bore  100  such that idler gear  78  is able to freely rotate about idler gear carrier axle  106  while supporting idler gear  78  to substantially prevent relative radial movement between idler gear  78  and idler gear carrier axle  106 . Idler gear carrier axles  106  are joined to idler gear carrier hub  102  with idler gear carrier bridge section  108 . Each idler gear  78  may be retained on its respective idler gear carrier axle  106  by enlarging a portion of each idler gear carrier axle  106  that protrudes beyond its respective idler gear  78  as shown in  FIG. 2 . It should now be understood that other methods of retaining idler gears  78  may be used, for example, by retention clips that fit within a groove on idler gear carrier axles  106  by retention clips that fit with idler gear carrier axles  106  in an interference relationship. Output shaft  84  passes through idler gear carrier hub bore  104  in a close fit relationship such that idler gear carrier  80  is able to freely rotate about output shaft  84  while output shaft  84  supports idler gear carrier  80  to substantially prevent relative radial movement between idler gear carrier  80  and output shaft  84 . In this way, a predetermined radial design clearance  109  is formed between idler gear output section  96  and output shaft  84  which may be most easily seen in  FIG. 5 . Idler gear carrier  80  may be retained on output shaft  84  with a retention clip  111  that may fit within a groove formed in output shaft  84  as shown in  FIG. 2 . 
         [0025]    Output gear  82  includes an outer output gear ring portion  112  with a plurality of output gear teeth  114  extending radially inward therefrom to mesh with idler gear output section teeth  98 . Output gear  82  also includes an output gear disk section  116  that extends radially inward from output gear ring portion  112  and terminates at an output gear bore  118  that extends through output gear disk section  116  in the same direction as axis A. Output shaft  84  passes through output gear bore  118  and is fixed thereto, for example by a press fit relationship between output shaft  84  and output gear bore  118 , in order to prevent relative rotation between output gear  82  and output shaft  84 . Output gear  82  defines a predetermined radial design clearance  119  with gear compartment  20 . Output gear  82  may be made, for example only, of a molded plastic material. 
         [0026]    Predetermined radial design clearances  109  and  119  allow a predetermined range of gear ratios for gear assembly  12  by providing sufficient room for different sized output gears  82  and idler gears  78  within gear compartment  20  of housing  18  having a fixed diameter. In this way, a common housing  18  may be used for the predetermined range of gear ratios, thereby a change in gear ratio of gear assembly  12  requires only a change of gear assembly components which are easily manufactured, for example by molded plastic. 
         [0027]    In addition to passing through output gear  82  and idler gear carrier  80 , output shaft  84  also passes through rotor assembly  32  by way of rotor central bore  38 . In this way, output shaft  84  extends into motor compartment  22 . Output shaft  84  extends into hub central bore  60  of stator support frame  48  where output shaft  84  is supported by a bushing  120  which is press fit within hub central bore  60 . Output shaft  84  interfaces with bushing  120  in a close fit relationship such that output shaft  84  is allowed to freely rotate with respect to bushing  120  and such that bushing  120  supports output shaft  84  to substantially prevent relative radial movement between output shaft  84  and bushing  120 . Bushing  120  may be made of a metallic material, for example only, brass or bronze. 
         [0028]    A gear compartment cover  122  is provided to support and enclose gear assembly  12  within gear compartment  20 . Gear compartment cover  122  is generally cup-shaped to provide a first gear compartment cover volume  124  and a second gear compartment cover volume  126  therewithin. A gear compartment cover shoulder  128  separates first gear compartment cover volume  124  and second gear compartment cover volume  126 . Pinion gear  74 , input gear  76 , idler gears  78 , idler gear carrier  80 , output gear  82 , and output shaft  84  are received within first gear compartment cover volume  124  such that input gear  76  is fixed to gear compartment cover  122 , for example by press fit within gear compartment cover  122 , to prevent relative rotation of input gear  76  with gear compartment cover  122 . Gear compartment cover  122  is fixed to housing  18 , for example by press fit within motor compartment  22 , in order to prevent relative rotation of gear compartment cover  122  with housing  18 , and consequently, relative rotation between input gear  76  and housing  18  is prevented. A gear compartment cover seal  130  may be provided to seal the interface between gear compartment seal cover  130  and gear compartment  20 . 
         [0029]    A return spring  132  may be provided within second gear compartment cover volume  126 . Return spring  132  may be a coiled torsional spring in which one end of return spring  132  may be grounded to gear compartment cover  122  while the other end of return spring  132  is attached to output gear  82 . If a failure of motor assembly  14  occurs during operation, return spring  132  may urge output gear  82 , and consequently output shaft  84 , to a predetermined default angular position. 
         [0030]    Second gear compartment cover volume  126  is terminated at an end distal from gear compartment cover shoulder  128  by gear compartment cover cap  134  which includes a gear compartment cover hub  136  having a gear compartment cover bore  138  extending therethrough in the same direction as axis A and centered about axis A. Gear compartment cover hub  136  may extend axially into second gear compartment cover volume  126 . Gear compartment cover bore  138  may include a gear compartment cover bore flange  140  that extends part way radially inward therefrom. In this way gear compartment cover bore flange  140  divides gear compartment cover bore  138  into a first gear compartment cover bore section  142  that faces toward first gear compartment cover volume  124  and a second gear compartment cover bore section  144  that faces away from first gear compartment cover volume  124 . First gear compartment cover bore section  142  may receive a third bearing  146 . Third bearing  146  may be a conventional ball roller bearing that is press fit within first gear compartment cover bore section  142  and which receives output shaft  84  in a press fit relationship such that output shaft  84  passes through third bearing  146  to the exterior of gear compartment cover  122 . Second gear compartment cover bore section  144  may receive an output shaft seal  148  in order to provide a seal between gear compartment cover bore  138  and output shaft  84 , thereby preventing contaminants such as dust or moisture from entering gear compartment  20 . 
         [0031]    Circuit board assembly  16  will now be described with reference to  FIGS. 1 ,  2 ,  6 , and  7  where  FIG. 6  is an isometric view of the side of circuit board assembly  16  which faces away from bulkhead  26  while  FIG. 7  is an isometric view of the side of circuit board assembly  16  which faces toward bulkhead  26 . Circuit board assembly  16  may be secured across motor compartment  22  within circuit board compartment  24  using circuit board fasteners  150 . In this way, circuit board assembly  16  separates motor compartment  22  from circuit board compartment  24 . 
         [0032]    Circuit board assembly  16  includes electrical circuits and electrical componentry generally indicated by reference numeral  152  which are connected to an external power source (not shown) through an electrical connector  154 . Electrical circuits and electrical componentry  152  are also connected with electrical windings  54  and are used to control the rotation of rotor assembly  32 . 
         [0033]    Reference will now be made to  FIGS. 1 ,  2 ,  7 , and  8 . In order to sense the rotational position of output shaft  84 , the end of output shaft  84  proximal to circuit board assembly  16  may include a sensed element which is illustrated as magnet  156  fixed to output shaft  84  to rotate with output shaft  84  in a one-to-one relationship. Magnet  156  is cylindrical and centered about axis A with a direction of magnetism that is through its diameter, i.e. a plane that is parallel and through axis A divides magnet  156  into its north and south poles represented by N and S respectively in  FIG. 8 . Magnet  156  produces a magnetic field as illustrated in  FIG. 8 . An electronic position sensor  158  is fixed to circuit board assembly  16  in close proximity to magnet  156  such that magnet  156  points toward position sensor  158 . When output shaft  84  is rotated in operation, the direction of the magnetic field produced by magnet  156  changes relative to position sensor  158  which is stationary. The change in direction of the magnetic field is sensed by position sensor  158  and consequently the rotational position of output shaft  84  is able to be determined. Alternatively, but not shown, magnet  156  may be offset relative to axis A and position sensor  158  may be a Hall Effect sensor. 
         [0034]    By allowing output shaft  84  with magnet  156  to pass through stator assembly  34 , the position of output shaft  84  can be sensed without the need for electronic componentry remote from circuit board assembly  16 . This allows all of the electronics for operation of actuator assembly  10 , i.e. operation of motor assembly  14  and sensing of output shaft  84 , to be included with circuit board assembly  16  which allows for ease of assembly of actuator assembly  10 . 
         [0035]    One or both of second bearing  42  and bushing  120  may act to shield position sensor  158  from magnetic flux generated by motor assembly  14 . The magnetic flux shielding properties of one or both of second bearing  42  and bushing  120  is the result of the metallic nature of the components of second bearing  42  (inner race, outer race, and ball bearings) and the metallic nature of bushing  120 . Shield  159  may also be provided to further protect position sensor  158  from magnetic flux generated by motor assembly  14 . Shield  159  may be ring shaped and made of a material, for example metal, that is able to shield magnetic flux. A shield  159  may be disposed at least partly within a shield bore  161  of stator support frame  48 . Shield bore  161  is formed in the face of stator support frame  48  that faces toward circuit board assembly  16  and is centered about axis A. Shield  159  may radially surround at least a portion of position sensor  158  as shown. In this way, second bearing  42 , bushing  120 , and shield  159  may reduce or eliminate magnetic flux generated by motor assembly  14  to allow position sensor  158  to operate in an environment that would otherwise be contaminated with magnetic flux from motor assembly  14  which could interfere with the operation of position sensor  158 . 
         [0036]    Circuit board assembly  16  is enclosed within circuit board compartment  24  with a circuit board compartment cover  160  which may be fastened to housing  18  with circuit board compartment cover fasteners  162 . Circuit board compartment cover seal  164  may be provided between circuit board compartment cover  160  and housing  18  to prevent intrusion of moisture and other foreign material that may have an undesirable effect on circuit board assembly  16 . Circuit board compartment cover seal  164  may be received within one or more grooves formed within circuit board compartment cover  160  and/or housing  18 . 
         [0037]    While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited.