Air mattress

An air mattress includes an upper sheet with a tufted top surface, a lower sheet, and front and rear sheets. The front sheet has upper, lower and lateral edges. The upper edge of the front sheet is sealed to a front edge of the upper sheet, is longer than the front edge of the upper sheet, and has excess portions on two sides of the front edge of the upper sheet. The rear sheet has upper edge, lower and lateral edges. The upper edge of the rear sheet is sealed to a rear edge of the upper sheet, is longer than the rear edge of the upper sheet, and has excess portions on two sides of the rear edge of the upper sheet. The lower sheet has a front edge sealed to the lower edge, the lateral edges, and the excess portions of the upper edge of the front sheet. The lower sheet has a rear edge sealed to the lower edge, the lateral edges, and the excess portions of the upper edge of the rear sheet. The lower sheet further has lateral edges sealed to lateral edges of the upper sheet. An air receiving space is confined by the upper, lower, front and rear sheets.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to an air mattress, more particularly to an air
 mattress which can be manufactured at a reduced cost.
 2. Description of the Related Art
 FIG. 1 illustrates a conventional air mattress 1 which includes an upper
 sheet 11, a lower sheet 13, and a surrounding sheet 12 interconnecting the
 upper and lower sheets 11, 13. An upper edge 121 of the surrounding sheet
 12 is sealed to four sides of the upper sheet 11. A lower edge 122 of the
 surrounding sheet 12 is sealed to four sides of the lower sheet 13. The
 upper sheet 11 has a top surface adapted to be in contact with the body of
 a user. To provide a comfortable feeling of touch, the top surface of the
 upper sheet 11 is pre-treated, such as by printing, by attaching with
 fabrics or by planting tufts thereon. However, a pre-treated plastic
 sheet, such as a tufted plastic sheet, has a significantly higher cost of
 material than a non-treated plastic sheet. In the conventional air
 mattress 1, the upper sheet 11 has a size generally identical to that of
 the lower sheet 13. The cost of material for manufacturing the air
 mattress 1 is relatively high.
 SUMMARY OF THE INVENTION
 Therefore, the main object of the present invention is to provide an air
 mattress which can be manufactured at a lower material cost.
 Accordingly, the air mattress of the present invention includes an
 inflatable main body which has an upper sheet, a lower sheet, and front
 and rear sheets. The upper sheet is made of a heat-sealable plastic
 material, and has front and rear edges and opposite lateral edges. The
 upper sheet further has a tufted top surface. The front sheet is made of a
 heat-sealable plastic material, and has an upper edge which is sealed to
 the front edge of the upper sheet, a lower edge, and opposite lateral
 edges interconnecting the upper and lower edges. The upper edge of the
 front sheet is longer than the front edge of the upper sheet, and has
 excess portions on two sides of the front edge of the upper sheet. The
 rear sheet is made of a heat-sealable plastic material, and has an upper
 edge which is sealed to the rear edge of the upper sheet, a lower edge and
 opposite lateral edges which interconnect the upper and lower edges of the
 rear sheet. The upper edge of the rear sheet is longer than the rear edge
 of the upper sheet, and has excess portions on two sides of the rear edge
 of the upper sheet. The lower sheet is made of a heat-sealable plastic
 material, and has a front edge, a rear edge and two opposite lateral edges
 interconnecting the front and rear edges of the lower sheet. The front
 edge of the lower sheet is sealed to the lower edge, the lateral edges,
 and the excess portions of the upper edge of the front sheet. The rear
 edge of the lower sheet is sealed to the lower edge, the lateral edges,
 and the excess portions of the upper edge of the rear sheet. The lateral
 edges of the lower sheet are sealed to the lateral edges of the upper
 sheet. An air receiving space is confined by the upper, lower, front and
 rear sheets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring to FIGS. 2 and 3, the preferred embodiment of the air mattress of
 the present invention is shown to include an inflatable main body 2 which
 is composed of an upper sheet 3, a lower sheet 4, and front and rear
 sheets 42, 43.
 The upper sheet 3 is made of a heat-sealable and flexible plastic material,
 and is rectangular in shape. The upper sheet 3 has a tufted top surface
 33, a front edge 34, a rear edge 35, and opposite lateral edges 31, 32
 interconnecting the front and rear edges 34, 35.
 The front sheet 42 is made of a heat-sealable and flexible plastic
 material, and has an upper edge 421, a lower edge 422, and opposite
 lateral edges 423 interconnecting the upper and lower edges 421, 422. The
 upper edge 421 of the front sheet 42 is sealed to the front edge 34 of the
 upper sheet 3. The upper edge 421 of the front sheet 42 is longer than the
 front edge 34 of the upper sheet 3, and has two excess portions 424 on two
 sides of the front edge 34 of the upper sheet 3.
 The rear sheet 43 is made of a heat-sealable and flexible plastic material,
 and has an upper edge 431, a lower edge 432, and opposite lateral edges
 433 interconnecting the upper and lower edges 431, 432. The upper edge 431
 of the rear sheet 43 is sealed to the rear edge 35 of the upper sheet 3.
 The upper edge 431 of the rear sheet 43 is longer than the rear edge 35 of
 the upper sheet 3, and has two excess portions 434 on two sides of the
 rear edge 35 of the upper sheet 3.
 The lower sheet 4 is also made of a heat-sealable plastic material, and is
 formed as a one-piece body. The lower sheet 4 has a front edge 44, a rear
 edge 45, and two opposite lateral edges 46, 47 interconnecting the front
 and rear edges 44, 45 thereof. The lower sheet 4 has a bottom portion 41
 disposed below the upper sheet 3, and two side portions 411, 412 which
 extend upwardly from the bottom portion 41 and which are formed with the
 lateral edges 46, 47, respectively. The front edge 44 of the lower sheet 4
 is sealed to the lower edge 422, the lateral edges 423 and the excess
 portions 424 of the upper edge 421 of the front sheet 42. The rear edge 45
 of the lower sheet 4 is sealed to the lower edge 432, the lateral edges
 433 and the excess portions 434 of the upper edge 431 of the rear sheet
 43. The lateral edges 46, 47 of the lower sheet 4 are sealed to the
 lateral edges 31, 32 of the upper sheet 3, respectively. An air receiving
 space is confined by the upper, lower, front and rear sheets 3, 4, 42, 43.
 Since the side portions 411, 412 of the lower sheet 4 extend to a top side
 of the main body 2 of the air mattress, the size of the upper sheet 3 is
 smaller than the area of the entire top surface of the main body 2 of the
 air mattress. The cost of material for the tufted upper sheet 3 is reduced
 accordingly, thereby lowering the manufacturing cost.
 Referring to FIG. 4, in a modified embodiment, each of the upper and lower
 sheets 3', 4' is trapezoid in shape. The front edge 34' of the upper sheet
 3' is slightly shorter than the rear edge 35' of the upper sheet 3'. The
 size of the upper sheet 3' can be further reduced to result in added cost
 savings.
 Referring to FIG. 5, to facilitate inflation of the air mattress of the
 present invention, a pumping unit 6 may be provided in the main body 2
 between the upper and lower sheets 3, 4. The pumping unit 6 includes an
 upper mounting seat 63 made of a rigid plastic and sealed to the upper
 sheet 3, a lower mounting seat 62 made of a rigid plastic and sealed to
 the lower sheet 4, a compression spring 64, such as a spiral spring,
 disposed between the upper and lower mounting seats 63, 62, and an annular
 surrounding wall 65 disposed around the compression spring 64 and the
 upper and lower mounting seats 63, 62. Each of the upper and lower
 mounting seats 63, 62 is formed with a retaining groove 631, 621 for
 retaining a respective one of upper and lower ends of the compression
 spring 64. The surrounding wall 65 is made of a heat-sealable plastic
 material, and has an upper edge 651 sealed to the upper sheet 3 of the
 main body 2, and a lower edge 652 sealed to the lower sheet 4 of the main
 body 2. The surrounding wall 65 cooperates with the upper and lower sheets
 3, 4 of the main body 2 to confine an airtight pumping chamber 70. The
 upper sheet 3 has an air inlet 34 which is communicated with the pumping
 chamber 70 and which is provided with a first uni-directional valve member
 67 and a plug 68 for closing the air inlet 34. The first uni-directional
 valve member 67 permits air to flow into the pumping chamber 70 via the
 air inlet 34, while preventing air to flow out of the pumping chamber 70
 via the air inlet 34. The surrounding wall 65 is formed with an air
 passage hole 653 which communicates the pumping chamber 70 with the air
 receiving space 5 of the main body 2 and which is provided with a second
 uni-directional valve member 66 that permits air to flow out of the
 pumping chamber 70 via the air passage hole 653 while preventing air to
 flow into the pumping chamber 70 via the air passage hole 653.
 The main body 2 of the air mattress can be inflated by stepping on the
 upper sheet 3 above the compression spring 64 to result in alternating
 compression and expansion of the compression spring 64 SO as to pump air
 into the air receiving space 5 via the air inlet 34, the pumping chamber
 70 and the air passage hole 653. A venting valve (not shown) may be
 provided in the main body 2 to permit release of air therefrom to
 facilitate storage and transport of the air mattress.
 While the present invention has been described in connection with what is
 considered the most practical and preferred embodiments, it is understood
 that this invention is not limited to the disclosed embodiments but is
 intended to cover various arrangements included within the spirit and
 scope of the broadest interpretation so as to encompass all such
 modifications and equivalent arrangements.