Pool Section 29 Regulation 3.2(2) AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Securing device for connecting bicycle rack to vehicle The following statement is a full description of this invention, including the best method of performing it known to us: 111ABAU/1 207 SECURING DEVICE FOR CONNECTING BICYCLE RACK TO VEHICLE FIELD OF THE INVENTION The present invention relates to a securing device for connecting a bicycle rack to a hitch ball at rear end of a vehicle. BACKGROUND OF THE INVENTION A conventional bicycle rack 8 is shown in Figs. 14A and 14B, and generally includes a securing device which is used to be connected with a hitch ball 71 fixed on a rear end of a vehicle which is not shown. The securing device includes a substantially C-shaped frame 82 including an open end and a slot 811 is defined in a bottom board 81 thereof. A U-shaped flange 812 extends from a top of the bottom bard 81 and encloses the slot 811. The hitch ball 71 is inserted from the open end and located within the slot 811 and is rested on the flange 812. A hole is defined through a top of the C-shaped frame 82 and a nut 821 is fixed to the top of the C-shaped frame 82, the hole communicates with the threaded hole in the nut 821. A threaded shank 83 threadedly extends through the nut 821 and the hole so as to press on the hitch ball 71. However, the threaded shank 83 is easily loosened by the shaking especially when the vehicle moves on bumpy roads and the threaded shank 83 tends to be deformed and the threads are easily damaged. Besides, there is no spring washer to secure the threaded shank 83 which can easily be loosened. Once the threaded shank 83 cannot position the hitch ball 71, the bicycle rack could be separated from the hitch ball 71. Besides, the threaded shank 83 is exposed without any protection and any one can 1 easily unscrew the threaded shank 83 to remove the bicycle rack together with the bicycles on the bicycle rack. The present invention intends to provide a securing device which includes two securing forces in two perpendicular directions to ensure that the securing device is secured and reliable so as to improve the drawbacks of the conventional securing device. SUMMARY OF THE INVENTION The present invention relates to a securing device for connecting a bicycle rack to a hitch ball, the securing device comprises a base having a hollow cup portion which has an open bottom and a top hole is defined through a top of the hollow cup portion. A latitude slot and a longitude slot are defined through a wall of the hollow cup portion, and the latitude slot communicates with the longitude slot. A later tube extends from the cup portion and is composed of two parts between which a longitudinal groove is defined. The longitude slot is located between the two parts. A clamping unit includes multiple clamping pieces received in the hollow cup portion and each clamping piece including a recess defined in an inside thereof. The recesses of the multiple clamping pieces define a space so as to receive the hitch ball. A main bolt has a head and a shank, the head of the main bolt is clamped between respective top ends of the clamping pieces and the shank extends from a top of a combination of the clamping pieces. A spring is mounted to the shank which extends into the hollow cp portion and through a top hole of the hollow cup portion. 2 A first securing unity includes a knob which is located on the top of the hollow cup portion and securely connected to the shank of the main bolt so as to pull the main bolt upward to allow the multiple clamping pieces to clamp the hitch ball. A second securing unit has a lever, a pull rod, and a push plate, wherein the lever has an end part and the pull rod has a head pivotably connected to the end part and a shank of the pull rod extends through and is securely connected to the two parts of the lateral tube. The push plate has an end pivotably connected to the end part and a protrusion extends from a side of the push plate. The protrusion pushes the fixed part to narrow the longitudinal slot when the lever is located at a locked position. The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view to show a bicycle rack is connected to the securing device of the present invention; Fig. 2 is an exploded view to show the securing device of the present invention; Fig. 3 is another exploded view to show the securing device of the present invention; 3 Fig. 4 is a cross sectional view to show that the hitch ball is clamped by the clamping pieces and the main bolt is connected with the knob; Fig. 5A is a cross sectional view to show that a cap is removed from the knob; Fig. 5B is a cross sectional view to show that the fixing bolt is unscrewed from the main bolt; Fig. 5C is a cross sectional view to show that the fixing bolt is removed from the main bolt; Fig. 5D is a cross sectional view to show that the knob is disengaged from the main bolt; Fig. 5E is a cross sectional view to show that the hollow cup portion is separated from the clamping pieces by the spring; Fig. 6A is a cross sectional view to show that the knob is completely separated from the main bolt; Fig. 6B is a cross sectional view to show that the hitch ball is separated from the hollow cup portion of the base; Fig. 7A shows that the lever is located at the unlocked position; Fig. 7B shows that the lever is located at the locked position; Fig. 8 is a perspective view to show that the lever is about to be pivoted from the locked position to the unlocked position; Fig. 9 shows that the restriction member restricts the pivotal movement of the bicycle rack; 4 Fig. 10 shows that the bicycle rack includes a foldable extension rack; Fig. 11 shows that the clamping pieces each have concavities to reduce their weight; Fig. 12 is a cross sectional view to show the securing device using the clamping pieces with concavities; Fig. 13 is a side view to show that the bicycle rack on the securing device of the present invention can be pivoted an angle; Fig. 14A is a perspective view to show a conventional securing device of a bicycle rack, and Fig. 14B is a partial cross sectional view to show the conventional securing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figs. 1 to 4, the securing device for connecting a bicycle rack 120 to a hitch ball 50on a vehicle 60 (Fig. 13) comprises a base 10 having a connection portion 12 on a first side thereof and a hollow cup portion 11 connected to a second side of the base 10. The connection portion 12 is connected to the bicycle rack 120 and the hollow cup portion 11 has an open bottom and a top hole 110 is defined through a top of the hollow cup portion 11. A latitude slot 111 and a longitude slot 112 are defined through a wall of the hollow cup portion 11, wherein the longitude slot 112 opens to the lower end of the hollow cup portion 11. The latitude slot 111 communicates with the longitude slot 112. A later tube 13 extends from the cup portion 11 and is composed of 5 two parts between which a longitudinal groove is defined, the longitude slot 112 is located between the two parts. A fixed part 130 is connected to an outside of one of the two parts of the lateral tube 13. A clamping unit 20 includes multiple clamping pieces 21 and each clamping piece 21 includes a recess 211 defined in an inside thereof. The recesses 211 of the multiple clamping pieces 21 define a space so as to receive the hitch ball 50 as shown in Fig. 4. The clamping pieces 21 are located within the hollow cup portion 11. Each of the clamping pieces 21 includes a notch 210 defined in the inside thereof and the notch 210 is located close to the top end of each clamping piece 21, A main bolt 22 has a head and a shank, the head of the main bolt 22 is accommodated within a space composed by the multiple notches 210 and the shank extends from a top of a combination of the clamping pieces 21. A spring 23 is mounted to the shank which extends into the hollow cp portion 11 and through a top hole 110 of the hollow cup portion 11. The shank of the main bolt 22 includes a threaded section 221 and a threaded hole 220 is defined in a top thereof. A first securing unity 30 includes a knob 31 which is located on the top of the hollow cup portion 11 and threadedly and securely connected to the threaded section 221 of the shank of the main bolt 22. A fixing bolt 32 extends through the knob 31 and is threadedly connected to the threaded hole 220 of the main bolt 22. The multiple clamping pieces 21 are pulled toward each other when the main bolt 22 is pulled upward by the knob 31. The spring 23 is biased between a protruding portion on the 6 combination of the clamping pieces 21 and an inner ceiling of the hollow cup portion 11. A second securing unit 40 has a lever 41, a pull rod 42, and a push plate 43, wherein the lever 41 has an end part 410 and the end part 410 of the lever 41 includes two sidewalls. Two through holes 411 are defined through the two sidewalls respectively. The pull rod 42 has a head pivotably connected between the two sidewalls of the end part 410 and a shank of the pull rod 42 extends through and is securely connected to the two parts of the lateral tube 13. The push plate 43 has an end pivotably connected to the end part 410 and a protrusion 430 extends from a side of the push plate 43. A pin 41 1A extends through the end of the push plate 43, the through holes 411 and the head of the pull rod 42. At least one of the two sidewalls of the end part 410 includes an elongate slot 412 and the protrusion 430 is movably engaged with the elongate slot 412. As shown in Fig. 7B, when the lever is in locked position where the lever 41 is pivoted about the pin 411A and oriented upward. The protrusion 430 on the push plate 43 pushes the fixed part 130 to push the left one of the two parts of the lateral tube 13 toward the right one of the two parts of the lateral tube 13, so as to narrow the longitude slot 112 to allow the hollow cup portion 11 to hold the clamping pieces 21. Therefore, the hitch ball 50 is securely clamped by the clamping pieces 21 which are controlled by the main bolt 22 and the knob 31 in vertical direction, and the clamping 7 pieces 21 are securely held by the hollow cup portion 11 by the lever 41 in horizontal direction. As shown in Figs. 7A and 8, When dismounting the bicycle rack 120 from the hitch ball 50, the lever 41 is pivoted to the unlocked position in horizontal position and the protrusion 430 is removed from the fixed part 130, so that the hollow cup portion 11 releases the holding of the clamping pieces 21. As shown in Figs. 5A to 5E, the cap (not numbered) in the knob 31 is first removed from the knob 31, and the fixing bolt 32 is unscrewed and removed from the threaded hole 220 of the main bolt 22 as shown in Fig. 5C. The knob 31 is then removed from the main bolt 22 and the spring 23 pushes the hollow cup portion 11 from the clamping pieces 21 as shown in Fig. 5E. As shown in Figs. 6A and 6B, the clamping pieces 21 can then be separated from the hitch ball 50 to dismount the bicycle rack 120 from the hitch ball 50. As shown in Figs. 9 and 13, a restriction member 14 is connected to the base 10 and located beside the connection portion 12, so that the restriction member 14 is used to restrict pivotal movement of the bicycle rack 120. This allows the hatchback door of the vehicle 60 to be opened while the bicycle rack 120 is connected to the hitch ball 50. Fig. 10 shows that the bicycle rack 120 may include an extension rack 121 which is designed to be foldable toward the upright post of the bicycle rack 120 to save space required. Figs. 11 and 12 show that the clamping pieces 21 each may have multiple concavities 212 defined in an outside thereof to reduce their weight. 8 The securing device provides two different directions of forces to ensure that the hitch ball 50 is securely clamped by the clamping pieces 21, so that the bicycle rack 120 does not separate from the hitch ball 50. Besides, the spring 23 separates the hollow cup portion 11 from the clamping pieces 21 when the two directions of forces are released, so that the user can easily dismount the bicycle rack 120 from the hitch ball 50. While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention. 9