1 CEILING FAN This invention relates to a fan, more particularly to a ceiling fan. Referring to Fig. 1 and Fig. 2, a conventional ceiling 5 fan 10 disclosed in U.S. Patent No. 7,261,520 includes a shaft 11, a bracket 12 coupled to the shaft 11, a plurality of screws 13 tightened on the bracket 12, a canopy 14 mounted on the bracket 12, and a decorative rim cover 15 mounted on the canopy 14. The canopy 14 has a 10 top rim 141 formed with a plurality of L-shaped grooves 142 that receive respectively the screws 13, and a plurality of engaging grooves 143. The decorative rim cover 15 includes an outer body 151, a plurality of fingers 152 extending upwardly from an inner face of the outer 15 body 151 and cooperating with the outer body 151 to define a gap therebetween, and a plurality of protrusions 153 protruding inwardly and respectively from the fingers 152. During the assembling process of the conventional 20 ceiling fan 10, when the canopy 14 is fixed to the bracket 12, the decorative rim cover 15 is pushed upwardly to surround the canopy 14 with the fingers 152 being pushed outwardly to store elastic energy. When the protrusions 153 are aligned respectively with the engaging grooves 25 143, the fingers 152 are released resiliently to engage respectively the protrusions 153 with the engaging grooves 143. The decorative rim cover 15 is then fixed onto the canopy 14 and covers the screws 13. 5463380_1 (GHMatters) P97265.AU 6/06/14 2 Although the conventional ceiling fan 10 improves the aesthetic appeal thereof by preventing exposure of the bracket 12 and the screws 13, there are still practical problems to consider as set forth below: 5 1. The bracket 12 and the screws 13 have to be separately and respectively concealed by the canopy 14 and the decorative rim cover 15. Besides, a motor (not shown) of the conventional ceiling fan 10, which generally hangs from the shaft 11, 10 requires an additional motor cover for embellishing purposes. Therefore, the conventional ceiling fan 10 has a relatively complicated structure and a relatively time-consuming assembling process. 15 2. To properly secure the decorative rim cover 15 to the canopy 14 during the assembly of the conventional ceiling fan 10, the decorative rim cover 15 has to be rotated relative to the canopy 14 until the protrusions 153 are respectively 20 registered the engaging grooves 143 for engagement, which is relatively inconvenient. 3. The structures of the fingers 152 are fragile and may break easily from the bottom during assembly of the conventional ceiling fan 10. 25 Therefore, the object of the present invention is to provide a ceiling fan that can overcome at least one of the aforesaid drawbacks associated with the prior art. Accordingly, a ceiling fan of the present invention 5463380_1 (GHMatters) P97265.AU 6/06/14 3 comprises a suspension unit including a bracket, a motor, a blade hub, a plurality of blades, a shell and an engaging unit. The motor is mounted to the suspension unit, and includes a main body and a rotating shaft that is driven 5 rotatably by the main body and that extends downwardly. The blade hub is connected to the rotating shaft. The blades are connected to the blade hub. The shell covers the bracket and the main body of the motor, and has an inner surface. The engaging unit includes a plurality of 10 protrusions that protrudes resiliently and outwardly from the bracket, and an annular engaging groove that is formed in the inner surface of the shell. The protrusions engage the annular engaging groove so as to fix the shell to the bracket and the main body of the motor. 15 Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment of this invention, with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary exploded perspective view of 20 a conventional ceiling fan disclosed in U.S. Patent No. 7, 261, 520; Fig. 2 is a fragmentary partly-sectional view of the conventional ceiling fan disclosed in U.S. Patent No. 7, 261, 520; 25 Fig. 3 is a perspective view of a preferred embodiment of a ceiling fan according to the present invention; Fig. 4 is a fragmentary exploded perspective view of the preferred embodiment; and 5463380_1 (GHMatters) P97265.AU 6/06/14 4 Fig. 5 is a fragmentary sectional view of the preferred embodiment. Referring to Figs. 3 to 5, the preferred embodiment of a ceiling fan according to the present invention is 5 shown to include a suspension unit 20, a motor 30, a motor control unit 40, a blade hub 50, a plurality of blades 60, a shell 70 and an engaging unit 80. The suspension unit 20 is fixed onto a ceiling (not shown) and includes a bracket 21. The bracket 21 has a 10 base wall 211, an outer surrounding wall 212 that extends upwardly from a periphery of the base wall 211 and that is formed with a plurality of through holes 213, a plurality of abutment walls 214 extending from a lower portion of an inner surface of the outer surrounding wall 15 212, and a plurality of installation grooves 215. Each of the installation grooves 215 is formed between a respective one of the abutment walls 214 and the outer surrounding wall 212. In this embodiment, the number of the abutment walls 214 and that of the installation 20 grooves 215 are both four, and the number of the through holes 213 is eight. The motor 30 is mounted to the suspension unit 20, and includes a main body 31, a rotating shaft 32 that is driven rotatably by the main body 31 and that extends 25 downwardly, and a suspension plate 33 that is connected to a top end of the main body 31 and that is mounted to the bracket 21 of the suspension unit 20. The motor 30 in this embodiment is an external-rotor brushless direct 5463380_1 (GHMatters) P97265.AU 6/06/14 5 current (DC) motor. The motor control unit 40 is connected to the main body 31 of the motor 30 and is disposed under the suspension plate 33 to turn on or off and control operation 5 speed of the motor. The blade hub 50 is connected to the rotating shaft 32 and is driven rotatably by the motor 30. The blades 60 are connected to the blade hub 50. The shell 70 is fixed to and covers the bracket 21 10 and the main body 31 of the motor 30. The shell 70 includes a main wall having opposite inner and outer surfaces 71, 72, and a bottom ring wall 73 (see Fig. 5) that is connected to a bottom edge of the main wall for extension of the rotating shaft 32 therethrough. 15 The engaging unit 80 has a plurality of elastic plates 81, a plurality of protrusions 82 and an annular engaging groove 83. The number of the elastic plates 81 in this embodiment is four. The elastic plates 81 are received respectively in the installation grooves 215 of the 20 bracket 21 and are disposed fixedly on an inner side of the outer surrounding wall 212 by the abutment walls 214. The number of the protrusions 82 in this embodiment is eight. Each of the elastic plates 81 is formed with two of the protrusions 82. The protrusions 82 protrude 25 resiliently, outwardly, and respectively from the outer surrounding wall 212 of the bracket 21 through the through holes 213. The annular engaging groove 83 is formed in the inner surface 71 of the shell 70 close to, but spaced 5463380_1 (GHMatters) P97265.AU 6/06/14 6 apart, from a top edge of the inner surface 71. During assembly of the ceiling fan, the shell 70 is moved upwardly to cover the main body 31 of the motor 30 and the bracket 21. As the top edge of the inner surface 5 71 of the shell 70 reaches the protrusions 82, the inner surface 71 pushes the protrusions 82 inwardly to retract the protrusions 82 respectively from the through holes 213. The elastic plates 81 are thus elastically deformed with a middle segment thereof abutting against a 10 respective one of the abutment walls 214. When the shell 70 is further moved upwardly until the annular engaging groove 83 reaches the protrusions 82, the elastic plates 81 restore resiliently, and the protrusions 82 consequently return to being extended respectively 15 through the through holes 213 engaging the annular engaging groove 83. The shell 70 is then properly fixed to the bracket 21 and the main body 31 of the motor 30. According to the present invention, the ceiling fan has the following efficacy and advantages: 20 1. Only one shell 70 is needed to fix and cover the bracket 21 and the main body 31 of the motor 30, which simplifies the entire structure and makes the assembly of the ceiling fan more convenient. 2. During assembly, the annular engaging groove 83 25 facilitates engagement with the protrusions 82 without the need to rotate the shell 70. 3. The elasticplates 81 would not easily break during assembly of the ceiling fan. 5463380_1 (GHMatters) P97265.AU 6/06/14 7 For the purpose of this specification, it will be clearly understood that the word "comprising" means "including but not limited to," and that the word "comprises" has a corresponding meaning. 5 It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 10 5463380_1 (GHMatters) P97265.AU 6/06/14