Shock absorber

1. Technical Field

The present disclosure generally relates to shock absorbers for damping vibration transmitted to a vehicle according to a road state and, more particularly, to a shock absorber capable of changing a damping force according to a displacement of a piston rod.

2. Description of the Related Art

Generally, a vehicle is provided with a suspension system for enhancing driving comfort by buffering impact or vibration transmitted to an axle from a road during driving. One component constituting the suspension system is a shock absorber. The shock absorber is disposed between the axle and a vehicle body. The shock absorber includes a cylinder and a piston rod reciprocating within the cylinder. The cylinder is filled with an operating fluid, such as gas or oil, such that the operating fluid is moved by a piston valve secured to one end of the piston rod to generate a damping force.

A conventional shock absorber has a restriction in that it exhibits constant damping force characteristics with respect to variation of a road state or a driving posture of the vehicle. Therefore, a low damping force characteristic can improve driving comfort but does not ensure stability of the vehicle, whereas a high damping force characteristic can maintain the stable posture of the vehicle but entails deterioration of driving comfort. As such, the conventional shock absorber is incapable of controlling damping force characteristics in response to variation of the road state or the posture of the vehicle.

Accordingly, in order to solve the problem of such a conventional shock absorber, a shock absorber capable of providing variable damping force characteristics according to a displacement of the piston rod has been developed.

FIG. 1 is a cross-sectional view of a portion of a conventional shock absorber.

Referring to FIG. 1, the shock absorber 10 includes a piston rod 14 connected to a vehicle body, and a cylinder 12 secured to an axle connected to wheels. The piston rod 14 reciprocates within the cylinder 12.

The piston rod 14 includes a piston valve 16 disposed at a lower end of the piston rod 14 to divide the interior of the cylinder 12 into a tensile chamber RC and a compression chamber CC. The piston valve 16 is formed with tensile orifices 16a and compression orifices 16b through which the tensile chamber RC and the compression chamber CC communicate with each other. The shock absorber 10 further includes disc valves 18a and 18b disposed on upper and lower sides of the tensile orifices 16a and the compression orifices 16b to elastically deform and generate a damping force according to movement of an operating fluid.

The piston rod 14 has a hollow chamber 20 formed therein. The hollow chamber 20 is provided with a floating piston 22 that can move up and down and divides the hollow chamber 20 into an upper chamber 20a and a lower chamber 20b. The hollow chamber 20 has a first orifice that is defined by a through-hole 24 through which an upper portion of the upper chamber 20a communicates with the tensile chamber RC, and a second orifice that is defined by a shaft hole 26 through which a lower portion of the lower chamber 20b communicates with the compression chamber CC.

As the piston rod 14 is slightly displaced, the floating piston 22 is lifted or lowered, and the operating fluid flows into or from the first or second orifice through the through-hole 24 or the shaft hole 26. As a result, the damping force of the shock absorber 10 is lowered.

The conventional shock absorber 10 reduces the damping force at a low displacement and low speed. However, the hollow chamber 20 has a restricted size so that a range of motion of the floating piston 22 is limited, thereby providing a low effect in reduction of the damping force. Further, when increasing the size of the hollow chamber 20 to improve the effect of reducing the damping force, there are problems of a manufacturing cost increase and a durability deterioration of the piston rod 14. Additionally, the conventional shock absorber undergoes friction between the outer surface of the floating piston and the inner surface of the hollow chamber while the floating piston moves up and down within the hollow chamber to cause an inefficient initial movement and a stick slip phenomenon between the floating piston and the hollow chamber, thereby lowering driving comfort. Furthermore, when the floating piston contacts the upper end or the lower end of the upper chamber or the lower chamber, the conventional shock absorber generates noise, thereby deteriorating quality satisfaction.

According to one aspect a shock absorber is provided that includes a floating piston disposed within a hollow chamber of a piston rod to reduce a damping force and can significantly reduce the damping force in a section where the piston rod moves repetitiously.

Another aspect of the present invention is to provide a shock absorber that can gradually reduce the damping force according to a displacement of the piston rod.

A further aspect of the present invention is to provide a shock absorber that can prevent a stick slip phenomenon.

According to one embodiment, a shock absorber includes a cylinder, and a piston valve connected to a piston rod within the cylinder to divide the cylinder into a first chamber and a second chamber. The shock absorber further includes a hollow chamber formed within the piston rod; first and second orifices formed in upper and lower ends of the hollow chamber and connected to the first and second chambers, respectively; a floating piston disposed within the hollow chamber to move up and down and to divide the hollow chamber into upper and lower chambers; and a moving mechanism formed in the hollow chamber to move an operating fluid above and below the floating piston.

In accordance with one aspect, the moving mechanism disposed within the hollow chamber may be a bypass passage formed longitudinally in the hollow chamber to allow the upper chamber and the lower chamber to communicate with each other through the bypass passage. The shock absorber may further include an upper spring and a lower spring provided to the upper chamber and the lower chamber to elastically support upper and lower surfaces of the floating piston, respectively. The upper and lower springs may be coil springs. The upper and lower springs may be conical coil springs, each having a gradually decreasing radius toward the floating piston. The upper and lower surfaces of the floating piston may be formed with mounting protrusions into which the upper and lower springs are fitted, respectively. The bypass passage may be a groove formed to have a predetermined length in the hollow chamber. The bypass passage may be an internal passage formed to have a predetermined length in the piston rod to connect the upper chamber and the lower chamber within the hollow chamber.

In accordance with another aspect of the invention, the moving mechanism disposed within the hollow chamber may be a flexible moving plate disposed within the floating piston to be deformed toward the upper or lower chamber. The floating piston may include a ring, the ring having an inner surface, on which an outer circumference of the flexible moving plate is disposed, and an outer surface contacting an inner surface of the hollow chamber, and the flexible moving plate comprises a bent part having an outer circumference disposed on the inner surface of the ring, the bent part being symmetrically formed with respect to a center of the bent part and alternately bent up and down. The bent part may be thin near the ring and thick at the center of the bent part.

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Piston-cylinder unit with piston rod protector
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