You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a movable sunshade base. 
     2. Description of the Related Art 
     A typical sunshade may provide a shield for people. The sunshade is bulky and heavy and thus requires a base to provide a stable support. The base has a considerable weight of tens of kilograms. As a result, it is difficult and inconvenient to move the sunshade to a desired position. The present invention is intended to provide a movable sunshade base to provide the sunshade with maneuverability. 
     SUMMARY OF THE INVENTION 
     A sunshade base in accordance with the present invention comprises a base adapted to engage with a support tube of a sunshade and two wheel assemblies each having a mounting plate and at least one wheel. The mounting plate is pivotally mounted to the base. The wheel is rotatably mounted to the mounting plate. The mounting plate is pivotable between a storage position in which the wheel does not contact the ground and an operative position in which said at least one wheel is located on the ground and thus raises the base above the ground. 
     The base includes two opposite first sides and two opposite second sides, each first side having an opening. The mounting plate of each wheel assembly covers an associated opening and is flush with an associated first side when the mounting plate is in the storage position. Each mounting plate includes a horizontal slot for grasp. 
     Each wheel assembly includes two said wheels and each mounting plate includes two arms to which the wheels are rotatably mounted, respectively. The base includes a bottom with a peripheral edge and each arm includes a hook for engaging with the peripheral edge of the base when the wheel assembly is in the operative position. The arms include aligned holes through which an axle extends. The axle also extends through the wheels and includes a first enlarged end and a threaded second end for engaging with a nut to preventing disengagement of the wheels. 
     Each second side of the base includes a horizontal slot for grasp while moving the base. Two brackets are provided for each mounting plate and each include a horizontal section fixed to an inner face of a top of the base. Each bracket further includes an inclined section fixed to an inner face of an associated first side. A pivotal section is formed between the horizontal section and the inclined section and includes a pivotal hole for pivotal engagement with the mounting plate. Each mounting plate includes an inclined portion and a bearing portion on an upper end of the inclined portion. The bearing portion includes two pivotal pins on both sides thereof for pivotal engagement with the pivot holes of the brackets, respectively. 
     A rod secured to the base for engaging with the support tube of the sunshade. In an embodiment of the invention, the base includes a central vertical hole and a seat is secured on top of the base. The seat has an outer diameter greater than an inner diameter of the central vertical hole and includes a flange on a side thereof. The flange is fittingly mounted in the central vertical hole and has an extension extending downward therefrom. A transverse hole is defined in the extension, a receptacle being defined in the seat and extending into the flange and the extension. The rod includes a lower end received in the receptacle. A pin extends through a transverse hole in the lower end of the rod and the transverse hole of the extension, and the support tube of the sunshade is engaged with an upper end of the rod. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a sunshade supported by a sunshade base in accordance with the present invention. 
     FIG. 2 is an enlarged side view of a lower portion of the sunshade and the sunshade base in accordance with the present invention. 
     FIG. 3 is an exploded perspective view of the sunshade base in accordance with the present invention. 
     FIG. 4 is a top view of the sunshade base in accordance with the present invention. 
     FIG. 5 is a bottom view of the sunshade base in accordance with the present invention. 
     FIG. 6 is a sectional view of the sunshade and sunshade base in FIG.  2 . 
     FIG. 7 is a sectional view similar to FIG. 6, illustrating adjustment of positions of two wheel assemblies of the sunshade base. 
     FIG. 8 is a side view illustrating movement of the sunshade base and the sunshade. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a sunshade base  2  in accordance with the present invention is provided to support a support tube  10  of a sunshade  1 . Referring to FIGS. 2 and 3, the sunshade base  2  comprises a base  20  having a top face  20   a  with a central vertical hole  21  around which a plurality of screw holes  211  are defined. A seat  40  has an outer diameter greater than an inner diameter of the central vertical hole  21  and includes a flange  44  on a side thereof, the flange  44  having an outer diameter the same as the inner diameter of the central vertical hole  21 . An extension  441  extends outward from an outer end face of the flange  44  and includes a transverse hole  442 . A receptacle  41  is defined in the seat  40  and extends into the flange  44  and the extension  441  and thus communicates with the transverse hole  442 . In assembly, as illustrated in FIGS. 3 and 6, the flange  441  of the seat  40  is fitted into the central vertical hole  21  of the base  20  and a lower end of a rod  30  is mounted into the receptacle  41  of the seat  40 . A pin  443  is extended through a transverse hole  31  in the lower end of the rod  30  and the transverse hole  442  of the extension  441 , thereby securing the rod  30  in place. Next, screws (not labeled) are extended through holes  43  in the seat  40  and then engage with the screw holes  211  of the base  20 , thereby securing the seat  40  to the base  20 . As illustrated in FIG. 6, a lower end of the support tube  10  of the sunshade  1  is mounted to the rod  30  and thus supported by the base  20 . 
     The base  20  further includes two inclined opposite sides  20   b  each having an opening  22 , and Each of the other two inclined opposite sides  20   c  of the base  20  includes a horizontal slot  23 . Each opening  22  includes an upper end extending into the top face  20   a  of the base  20 . 
     The sunshade base  2  further comprises two wheel assemblies  50  each including a mounting plate  51 , an axle  58 , and at least one wheel  57  (two in this embodiment). In this embodiment, the mounting plate  51  includes an inclined portion  51   a  with a horizontal slot  511  and a bearing portion  52  on an upper end of the inclined portion  51   a . Two pivotal pins  53  are formed on two sides of the bearing portion  52  and pivotally received in pivotal holes  61  of the base  20 . Two parallel arms  54  project outward from the bearing portion  52  and extend away from the inclined portion  51  a of the mounting plate  51  and each have a distal end with a hole  56  and a hook  55 . The axle  58  includes an enlarged end  581  and is extended through the holes  56  of the arms  54  and a longitudinal hole  571  of each wheel  583 , and a nut  583  is engaged with a threaded second end  582  of the axle  58 . 
     For each opening  22 , two brackets  60  are mounted to an inner face (not labeled) of an associated the base  20  and located on both sides of the opening  22 . Each bracket  60  includes a horizontal section  601  fixed to an inner surface of the top of the base  20  and an inclined section  602  fixed to the inner face of the associated side of the base  20 . The pivotal hole  61  is defined in a section  603  between the horizontal portion  601  and the inclined portion  602 . Each pivotal pin  53  of each mounting plate  51  is pivotally received in an associated pivotal hole  61  to thereby allowing pivotal movement of the mounting plate  51  and the wheels  57  relative to the base  20 . 
     FIG. 4 is a top view of the sunshade base  2  after assembly and FIG. 5 is a bottom view of the sunshade base  2  after assembly. FIG. 6 is a sectional view of the sunshade base  20 , wherein the wheels  57  are in their storage position with each mounting plate  51  covering the opening  22  and thus being flush with an associated inclined side of the base  20 . 
     When the user intends to move the sunshade base  2 , the user may insert his fingers into the slot  511  and grasp each mounting plate  51  and pivot the mounting plate  51  outward in a direction indicated by the arrow in FIG. 7 to a position shown by phantom lines in FIG.  7 . The bearing portion  52  of the mounting plate  51  and an upper edge of an associated opening  22  have a gap therebetween to thereby allow pivotal movement of the mounting plate  51 . The wheels  57  of each wheel assembly  50  are now moved to the ground and thus elevate raise the base  20  as well as the sunshade  1 . The arms  56  for mounting the wheels  57  are oriented to prevent folding of the mounting plate  51 . Namely, the arms  54  are exposed outside the base  20  when the associated mounting plate  51  is in the operative position and extend along a direction that is at an acute angle with respect to a vertical direction when the associated mounting plate  51  is in the operative position. It is noted that the hook  55  on each arm  56  of the mounting plate  51  is engaged with an inner edge  20   e  of a lower flange  20   d  of the base  2 . Thus, the user may insert his fingers of each hand into an associated slot  23  and grasp the base  20  to thereby move the sunshade base  2  as well as the whole sunshade  10 , best shown in FIG.  8 . It is noted that the wheels  57  will not be retracted into their storage position during movement of the base  20 , as the sunshade  1  and the sunshade base  2  have a considerable weight that will impose a downward force to the wheels  57  to prevent folding of the wheels  57 . 
     Although not specifically shown in the drawings, it is appreciated that means may be provided to releasably retain the wheels  57  in their operative position. When the sunshade  1  reaches a desired position, the user may pivot the mounting plates  51  downward to move the wheels  57  into their storage position shown in FIG.  6 . The wheels  57  may be replaced by casters to allow movement of the sunshade base  2  in any desired direction. 
     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.

Summary:
A sunshade base comprises a base adapted to engage with a support tube of a sunshade and two wheel assemblies each having a mounting plate and at least one wheel. The mounting plate is pivotally mounted to the base. The wheel is rotatably mounted to the mounting plate. The mounting plate is pivotable between a storage position in which the wheel does not contact the ground and an operative position in which the wheel is located on the ground and thus raises the base above the ground.