Rotary damper

Abstract: A rotary damper has a hollow cylinder (1) having upper (2a) and lower (2b) flanges to serve as a pivot. One arm (3) is tightly fitted on one of the upper and lower flanges and extends essentially in tangential direction of the associated flange. The other arm (4) is pivotal with rotation of the outer pivot and extends essentially in tangential direction of outer pivot. A coil spring (5) is wound around the outer periphery of the hollow cylinder. The ends of the coil spring are connected to the arms for exerting spring force in a direction opposite the pivoting direction of the arms.

Description: The present invention relates generally to a rotary damper which progressively or gradually reduces rotational torque to a rotating component of various devices. More specifically, the invention relates to a rotary damper which is easy in manufacture. One previously proposed rotary damper employing a coil spring has been disclosed in JP-U-62-81739 and JP-U-62-124343. In such prior proposed construction, a cylinder filled with viscous fluid prevents abrupt variation of the rotating torque by the viscous resistance of the fluid. To maintain the viscous fluid, the cylinder has to be formed with substantially high accuracy for establishing a liquid-tight seal. The requirement for high accuracy necessarily requires high production cost. US-A-1 585 797, on which the preamble of claim 1 is based, discloses a rotary damper comprising two cylindrical cups arranged coaxially with their open ends facing. A coil spring is arranged within the cups in frictional engagement with them. Relative rotation of the cups is retarded by frictional drag between each cup and the spring, which also causes the spring to contract or expand, decreasing or increasing, respectively, the frictional drag between the spring and the cups, so that substantial frictional drag is imposed in only one sense of relative rotation. It is an object of the present invention to provide a rotary damper which can reduce production cost. The invention provides a rotary damper comprising: a first cylindrical shaft; a second cylindrical shaft arranged in coaxial fashion with and for rotation relative to said first cylindrical shaft; a first arm connected to said first cylindrical shaft for a unitary rotational motion therewith; a second arm connected to said second cylindrical shaft for a unitary rotational motion therewith; and a coil spring operatively connected to said first and second arms; characterised by a friction mechanism including a set of frictionally and slidably engaged portions which are fixed to said first and second cylindrical shafts, respectively, said friction mechanism being so constructed and arranged such that, when said first and second arms are subject to a force in a rotational direction, said set of frictionally and slidably engaged portions slide to generate resistance to rotational motion of said first arm relative to said second arm and said first cylindrical shaft being made of a first plastics material, and said second cylindrical shaft being made of a second plastics material, said first and second plastics materials having different melting points and different thermal contractibilities; and in that the coil spring is disposed between the first and second arms for loading spring force for relative movement therebetween. The rotary damper preferably has a pivot assembly including coaxially arranged inner and outer pivots. The inner pivot has upper and lower flanges to serve as a pivot. One arm is tightly fitted on one of the upper and lower flanges and extends essentially in a tangential direction from the associated flange. The other arm is pivotal with rotation of the outer pivot and extends essentially in a tangential direction from the outer pivot. A coil spring is wound around the outer periphery of the outer pivot. The ends of the coil spring are connected to the arms for exerting spring force in a direction opposite the pivoting direction of the arms. The friction means may comprises tapered mating surfaces of the first and second shafts, which tapered mating surfaces establishing tight frictional engagement with each other. The second arm is preferably detachable from the second shaft. The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiment, but are for explanation and understanding only. In the drawings: Fig. 1 is a perspective view of the preferred embodiment of a rotary damper applied for a drawer type box housed in a casing as one example of application of the invention; Fig. 2 is a section taken along line A-A in Fig. 1; Fig. 3 is an enlarged perspective view of the rotary damper of the invention; Figs. 4 and 5 are sections respectively taken along lines B-B and C-C in Fig. 3; Fig. 6 is an exploded perspective view of a modified construction of the rotary damper according to the invention. Fig. 7 is an enlarged section of the modified embodiment of the rotary damper in Fig. 6; and Fig. 8 is an enlarged plan view of the modified embodiment of the rotary damper, in which is shown the rotary damper in an operating condition. Referring now to the drawings, particularly to Fig. 1, the preferred embodiment of a rotary damper, according to the present invention, will be discussed herebelow in terms of an application for a drawer type box assembly. Such a drawer type box assembly can be used in an automotive instrument panel as a coin pocket and so forth. The drawer type box assembly includes a sliding box 10 thrustingly housed within a hollow box shaped housing 11. The box 10 has a plurality of rollers 12 associated with guide rails 13. The box 10 also has guide projections 14 slidingly engaged with guide grooves 15 formed on the inner periphery of the housing 11. The box 10 is movable between a projected position projecting from the front mouth of the housing 11, and a retracted position to be placed within the housing. In the retracted position, the box 10 is latched or locked by means of a latching or locking means (not shown). Preferably, the locking means may be a toggle type lock which can be released by slightly depressing the box 10 in the retracting direction. A rotary damper assembly indicated generally by the reference number 20 is disposed in the housing 11 in the vicinity of the rear end of the internal space of the housing. The rotary damper assembly 20 is associated with the box 10 for exerting biasing force so that the box can be driven from the retracted position to the projected position in response to releasing of locking by the locking means. The rotary damper assembly 20 is designed for reducing the biasing force to be exerted on the box 10 according to travel of the box from the retracted position to the projected position. The rotary damper assembly 20 includes a hollow cylinder 1 which has tapered upper and lower (as shown in the drawings) ends 1a and 1b. A pivot shaft 2 is rotatably received within the interior space of the cylinder 1. The pivot shaft 2 has upper and lower flanges 2a and 2b extending from upper and lower ends of the cylinder 1. The upper and lower flanges 2a and 2b have tapered surfaces 2a' and 2b' mating with the tapered ends 1a and 1b. The taper angles of the tapered surfaces 2a' and 2b' are formed in conformance with those of the tapered ends 1a and 1b of the cylinder 1 for tight fitting. In production, the cylinder 1 is formed of a synthetic resin, such as ABS resin and so forth, by an injection process. Then, the cylinder 1 thus formed is inserted in a mold for forming the pivot shaft 2. The pivot shaft 2 is formed of a synthetic resin material having high thermal contractibility and lower melting point, such as polypropylene and so forth, than the material of the cylinder 1. With the molten material for the pivot shaft 2, injection molding is performed for forming the pivot shaft with the upper and lower flanges 2a and 2b. An upper arm 3 is integrally formed with the upper flange 2a for pivotal movement therewith. The upper arm 3 extends from the flange 2a in essentially tangential direction thereof. On the other hand, a lower arm 4 is formed integrally with the cylinder 1. The lower arm 4 is extended from the lower end 16 of the cylinder 1 to position the lower surface flush with the lower flange 2b. The lower arm 4 extends in essentially tangential direction. A coil spring 5 is wound around the cylinder 1. The upper end 5b of the coil spring 5 is connected to the upper arm 3. On the other hand, the lower end 5a of the coil spring 5 is connected to the lower arm 4. The coil spring 5 is designed for driving the arms 3 and 4 to pivotally move to increase the offset angle to each other. Namely, the spring force of the coil spring 5 is held accumulated when the arms 3 and 4 are oriented substantially in a parallel relationship to each other. On the other hand, the mating tapered surfaces 1a, 2a and 1b, 2b generate frictional force resisting relative angular displacement between the cylinder 1 and the pivot shaft 2. Therefore, when the arms 3 and 4 are driven to increase the offset angle, the friction force generated between the tapered surfaces 1a, 2a and 1b, 2b of the cylinder 1 and the pivot shaft 2 tends to reduce the speed of pivotal movement of the arms. In the shown embodiment, the lower arm 4 is connected to the housing 11 at the free end thereof 4b. Therefore, the free end of the arm section 4b serves as a stationary point of the rotary damper 20. On the other hand, the upper arm 3 is connected to the drawer type box 10 at a free end 3a thereof. When the lock of the locking means is released, the arms 3 and 4 become free from restriction and thus are driven by the spring force of the coil spring 5. In the shown embodiment, the rotational torque of the spring 5 causes counterclockwise (as seen from above in Fig. 1) pivotal movement of the upper arm 3 together with the pivot shaft 2. At the same time, a clockwise torque is then exerted on the lower arm 4. Since a free end 4b of the lower arm 4 is stationarily fixed on the housing 11, the reacting force is exerted on the lower arm. As a result, the pivot shaft 2 with the cylinder 1 and the coil spring 5 are driven forwards. By the forward movement of the pivot shaft 2 and by the counterclockwise pivotal movement of the upper arm 3, the drawer type box 10 is driven forwards to the projected position. As can be appreciated, the spring force accumulated in the coil spring 5 is gradually reduced according to the forward movement of the box 10. Simultaneously, during the foregoing movement, the friction between the mating surfaces 1a, 2a and 1b, 2b resists the rotational movement of the pivot shaft 2 relative to the cylinder 1. Therefore, the speed of extraction of the drawer type box 10 can be controlled so that extraction cannot occur at excessive speed. Figs. 6 through 8 show a modification of the foregoing embodiment of the present invention. In this embodiment, a cylinder 21 is formed integrally with a lower arm 23. A pivot shaft 22 extends through the interior space of the cylinder 21. The flanges 22a and 22b are formed in the same manner as that illustrated in the former embodiment. As can be seen from Fig. 6, the upper flange 22a includes a plurality of radial projections 25 which are designed to engage with radial groove sections 28a of a pivot section 28 of an upper arm 27. As shown, the upper arm 27 is secured to the pivot shaft 22 by a screw 29. With this embodiment, substantially the same operation as that discussed with respect to the former embodiment can be achieved. Furthermore, in the modified embodiment, since a spring 24 can be installed before the upper arm 27 is fitted to an upper end of the pivot shaft 22, assembly becomes easier.

Claims: A rotary damper comprising: a first cylindrical shaft (1, 21); a second cylindrical shaft (2, 22) arranged in coaxial fashion with and for rotation relative to said first cylindrical shaft (1, 21); a first arm (4, 23) connected to said first cylindrical shaft (1, 21) for a unitary rotational motion therewith; a second arm (3, 27) connected to said second cylindrical shaft (2, 22) for a unitary rotational motion therewith; and a coil spring (5, 24) operatively connected to said first and second arms (4, 3; 23, 27); characterised by a friction mechanism including a set of frictionally and slidably engaged portions (1a, 1b; 2a', 2b') which are fixed to said first and second cylindrical shafts (1, 21; 2, 22), respectively, said friction mechanism being so constructed and arranged such that, when said first and second arms (4, 23; 3, 27) are subject to a force in a rotational direction, said set of frictionally and slidably engaged portions slide to generate resistance to rotational motion of said first arm (4, 23) relative to said second arm (3, 24) and said first cylindrical shaft (1, 21) being made of a first plastics material, and said second cylindrical shaft (2, 22) being made of a second plastics material, said first and second plastics materials having different melting points and different thermal contractibilities; and in that the coil spring (5, 24) is disposed between the first and second arms (4, 23; 3, 37) for loading spring force for relative movement therebetween. A rotary damper as claimed in claim 1, characterised in that said first and second cylindrical shafts (1, 2; 21, 22) have tapered mating portions (1a, 1b; 2a', 2b'), mutually engaged with each other to serve as said set of frictionally and slidably engaged portions of said friction mechanism. A rotary damper as claimed in claim 1, characterised in that said second arm (27) is detachably connected to said second cylindrical shaft (22). A rotary damper as claimed in claim 1, characterised in that said second cylindrical shaft (22) includes projections (25), and said second arm (27) includes groove means (28a) for receiving said projections (25).

Inventors: OOSAWA TAKAFUSA C O NIHON PLAS, OOSAWA, TAKAFUSA, C/O NIHON PLAST CO., LTD.
Applicants: NIHON PLAST CO LTD, NIHON PLAST CO., LTD.
Application year: 1990
Main classification: F16F7
IPC codes: F16F3, F16F7, F16F13