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A pusher axle suspension system having a single air spring includes a pair of frames having mounting brackets integrally formed at lower front portions of the pair of frames, respectively. A link arm includes a front end connected to each mounting bracket of the pair of frames by a mounting bush. Ax

A pusher axle suspension system having a single air spring includes a pair of frames having mounting brackets integrally formed at lower front portions of the pair of frames, respectively. A link arm includes a front end connected to each mounting bracket of the pair of frames by a mounting bush. Axle sheets are disposed at lower portions of the pair of frames, respectively, to support a pusher axle. The axle sheets are connected to a rear end of the link arm by a hinge. A composite air spring is provided between a rear end of the axle sheet and a bottom surface of the pair of frames. The composite air spring moves the axle sheet upward or downward to adjust a height of the pusher axle and to absorb vibration due to a road surface during traveling.

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1. A pusher axle suspension system having a single air spring comprising: a pair of frames having mounting brackets integrally formed at lower front portions of the pair of frames, respectively;a link arm, a front end of which is connected to each mounting bracket of the pair of frames by a mounting

1. A pusher axle suspension system having a single air spring comprising: a pair of frames having mounting brackets integrally formed at lower front portions of the pair of frames, respectively;a link arm, a front end of which is connected to each mounting bracket of the pair of frames by a mounting bush;axle sheets disposed at lower portions of the pair of frames, respectively, to support a pusher axle, the axle sheets connected to a rear end of the link arm by a hinge; anda composite air spring provided between a rear end of the axle sheets and a bottom surface of the pair of frames, the composite air spring configured to move the axle sheets upward or downward to adjust a height of the pusher axle and to absorb vibration due to a road surface during traveling,wherein the composite air spring comprises:a spring tube, a top side of which is coupled with a lower rear side of each frame by a mounting plate and having a first hollow air pressure chamber formed therein;an external piston connected to a lower portion of the spring tube so that a bottom side of the external piston is coupled with a rear side on the axle sheet, the external piston having a second hollow air pressure chamber formed therein in which the first and second hollow air pressure chambers are separated from air communication therebetween;an internal piston disposed inside the second air pressure chamber of the external piston; anda piston rod, a bottom end of which is connected to a center of the internal piston and a top end of which is connected to a linear bearing, which is attached to the mounting plate, inside the spring tube via a rotation joint. 2. The pusher axle suspension system of claim 1, wherein the top end of the piston rod is movably connected to the linear bearing in forward and backward directions and in a rotational direction so that the piston rod absorbs position variation of the internal piston. 3. The pusher axle suspension system of claim 1, wherein the linear bearing comprises: a linear rail fixed to the mounting plate at a top end of the spring tube; anda slider slidably moving along the linear rail and integrally connected to the rotating joint. 4. The pusher axle suspension system of claim 1, wherein the spring tube comprises a first air nozzle connected to a first air supply hose at an upper side of the spring tube to supply and exhaust air to and from the spring tube. 5. The pusher axle suspension system of claim 1, wherein the external piston comprises a second air nozzle connected to a second internal air supply hose, which is connected to a first internal air supply hose, at an upper side of the external piston inside the spring tube to supply and exhaust air to and from the external piston. 6. The pusher axle suspension system of claim 1, wherein when air supplied to the second air pressure chamber is exhausted after being compressed in the first air pressure chamber, the pusher axle moves upward, andwherein when the air supplied to the first air pressure chamber is exhausted after being compressed in the second air pressure chamber, the pusher axle moves downward. 7. The pusher axle suspension system of claim 2, wherein the linear bearing comprises: a linear rail fixed to the mounting plate at a top end of the spring tube; anda slider slidably moving along the linear rail and integrally connected to the rotating joint. 8. A pusher axle suspension system having a single air spring comprising: a pair of frames having mounting brackets integrally formed at lower front portions of the pair of frames, respectively;a link arm, a front end of which is connected to each mounting bracket of the pair of frames by a mounting bush;axle sheets disposed at lower portions of the pair of frames, respectively, to support a pusher axle, the axle sheets connected to a rear end of the link arm by a hinge; anda composite air spring provided between a rear end of the axle sheets and a bottom surface of the pair of frames, the composite air spring configured to move the axle sheets upward or downward to adjust a height of the pusher axle and to absorb vibration due to a road surface during traveling,wherein the composite air spring comprises:a spring tube, a top side of which is coupled with a lower rear side of the each frame by a mounting plate and having a first hollow air pressure chamber formed therein;an external piston connected to a lower portion of the spring tube so that a bottom side of the external piston is coupled with a rear side on the axle sheet, the external piston having a second hollow air pressure chamber formed therein;an internal piston disposed inside the second air pressure chamber of the external piston; anda piston rod, a bottom end of which is connected to a center of the internal piston and a top end of which is connected to a linear bearing, which is attached to the mounting plate, inside the spring tube via a rotation joint, andwherein the top end of the piston rod is movably connected to the linear bearing in forward and backward directions and in a rotational direction so that the piston rod absorbs position variation of the internal piston.