Damper device

A damper device includes a casing, a rotor partly housed in the casing, a viscous fluid filled in the casing around the rotor, and a torque generator for generating a torque during a rotating stroke of the rotor. The torque generator includes a fluid torque adjuster for producing a relatively large torque in at least a terminal range of the rotating strokes in normal and reverse directions of the rotor.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a damper device for use on the door of a
 container to apply damping forces to the angular movement of the door in
 terminal ranges of opening and closing movements of the door, or for use
 on an electrically powered tool such as an electrically powered saw or
 plane to reduce shocks in terminal ranges of reciprocating movements
 thereof.
 2. Description of the Related Art
 Heretofore, some containers are equipped with a damper device mounted on
 the door for preventing the door from banging against the door frame when
 the door is closed. Since the damper device operates only when the door is
 closed, however, the damper device is not active when the door is quickly
 opened. When the door is quickly opened, therefore, the door tends to hit
 a stop, producing undesirable noise or causing damage to itself or the
 stop. For producing a damping action in a terminal range of the opening
 movement of the door, the door needs to incorporate another separate
 damper device separately from the existing damper device which operates
 only when the door is closed.
 There has not been known any example in which the above damper device is
 applied to a reciprocally movable electrically powered tool. Heretofore,
 it has been customary for the user of a reciprocally movable electrically
 powered tool to empirically control forces produced by the tool in
 terminal regions of its reciprocating actions to avoid unwanted impacts or
 damage to the tool. However, controlling forces produced by the tool in
 terminal regions of its reciprocating actions needs a skilled experience
 on the part of the user, and is physically fatiguing to the user.
 Installing two damper devices on one door is highly costly. In addition, it
 is a complex task to install two damper devices on one door and also to
 perform maintenance on the two damper devices mounted on the door. There
 has been a demand for a single damper device which is capable of producing
 a damping force in both terminal ranges of opening and closing movements
 of a door on which the damper device is installed.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to provide a damper
 device which is capable of generating a damping force in both terminal
 ranges of opening and closing movements or reciprocating movements of an
 apparatus on which the damper device is installed.
 To achieve the above object, there is provided a damper device comprising a
 cylindrical casing, a rotor partly housed in the casing, a viscous fluid
 filled in the cylindrical casing around the rotor, and torque generating
 means for generating a torque during a rotating stroke of the rotor, the
 torque generating means including fluid torque adjusting means for
 producing a relatively large torque in a terminal range of each of the
 rotating strokes in normal and reverse directions of the rotor and a
 relatively small torque in other range of each of the rotating strokes.
 Therefore, if the damper device is installed on a door, then the damper
 device can produce a damping force in terminal periods of opening and
 closing movements of the door, thereby preventing the door from banging
 against a stopper or a door frame when the door is fully closed or opened.
 Furthermore, since the damper device generates a relatively small torque
 in the rotating strokes in the normal and reverse directions, it is
 possible not to apply a damping force in a period other than the terminal
 periods of opening and closing movements of the door. As a result, the
 door can be opened and closed with a small force.
 The torque generating means may have a first ridge extending axially on an
 outer surface of the rotor and having a radially outer surface held in
 sliding contact with an inner surface of the casing, and the fluid torque
 adjusting means may comprise a first land extending axially on the inner
 surface of the casing, a pair of first axial grooves defined axially in a
 radially inner end of the first land and spaced circumferentially from
 each other, a pair of first needle valves loosely fitted in the first
 axial grooves, respectively, for movement in the width direction of the
 first axial grooves, and a first circumferential groove defined
 circumferentially on the outer surface of the rotor, the first
 circumferential groove being positioned out of facing relation to at least
 one of the first needle valves in the terminal range of each of the
 rotating strokes. When the at least one of the needle valves is held
 against the outer surface of the rotor in the terminal range, the one of
 the first needle valves and the first ridge jointly divide an interior
 space of the casing into two chambers, for effectively preventing the
 viscous fluid from moving between the chambers to produce the relatively
 large torque. The fluid torque adjusting means of the above structure can
 easily be incorporated in the damper device, and can reliably generate a
 relatively large torque in the terminal range of each of the rotating
 strokes.
 Alternatively, the torque generating means may have a second land extending
 axially on an inner surface of the casing and having a radially inner
 surface held in sliding contact with an outer surface of the rotor, and
 the fluid torque adjusting means may comprise a third land extending
 axially on the outer surface of the rotor, a pair of second axial grooves
 defined axially on a radially outer end of the third land on the rotor and
 spaced circumferentially from each other, a pair of second needle valves
 loosely fitted in the second axial grooves, respectively, for movement in
 the width direction of the second axial grooves, and a second
 circumferential groove defined circumferentially in the inner surface of
 the casing, the second cylindrical groove being positioned out of facing
 relation to at least one of the second needle valves in the terminal range
 of each of the rotating strokes. When the at least one of the second
 needle valves is held against the inner surface of the casing in the
 terminal range, the one of the second needle valves and the second land of
 the casing jointly divide an interior space of the casing into two
 chambers for effectively preventing the viscous fluid from moving between
 the chambers to produce the relatively large torque. The fluid torque
 adjusting means of the above structure can easily be incorporated in the
 damper device, and can reliably generate a relatively large torque in the
 terminal range of each of the rotating strokes.
 Further alternatively, the torque generating means may have a fourth land
 extending axially on an inner surface of the casing and having a radially
 inner surface held in sliding contact with a outer surface of the rotor,
 and the fluid torque adjusting means may comprise a pair of second ridges
 extending axially on the outer surface of the rotor, a pair of valve
 bodies loosely mounted on the second ridges, respectively, and a third
 circumferential groove defined circumferentially in the inner surface of
 the casing, the third cylindrical groove being positioned out of facing
 relation to at least one of the needle valves in the terminal range of
 each of the rotating strokes. When the at least one of the valve bodies is
 held against the inner surface of the casing in the terminal range, the
 one of the valve bodies and the second ridges jointly divide an interior
 space of the casing into two chambers for effectively preventing the
 viscous fluid from moving between the chambers to produce the relatively
 large torque. The fluid torque adjusting means of the above structure can
 easily be incorporated in the damper device, and can reliably generate a
 relatively large torque in the terminal range of each of the rotating
 strokes.
 The above and other objects, features, and advantages of the present
 invention will become apparent from the following description when taken
 in conjunction with the accompanying drawings which illustrate preferred
 embodiments of the present invention by way of example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Like or corresponding parts are denoted by like or corresponding reference
 characters throughout views.
 FIG. 1 through FIGS. 4A-4I show a damper device according to a first
 embodiment of the present invention.
 As shown in FIG. 1, the damper device, generally denoted by the reference
 numeral 1, comprises a cylindrical casing 2, a rotor 3 having a portion
 rotatably mounted in the 2, and a viscous fluid 5 such as silicone oil
 filled in the casing 2 around the rotor 3. The casing 2 has a closed end 7
 and an opposite open end fitted with an annular cap 6 having an opening 61
 through which an axial protrusion 32 of the rotor 3 projects out of the
 casing 2. A sealing member 10 such as an O-ring is mounted between the
 rotor 3 and the cap 6 for preventing the viscous fluid 3 from leaking out
 of the casing 2 along the outer surface of the rotor 3. The casing 2
 includes flanges 21 projecting radially outwardly from the open end
 thereof.
 As shown in FIG. 2, the rotor 3 has an axial ridge 31 projecting radially
 outwardly from an outer surface thereof and fitted between
 circumferentially spaced radial walls 41, 41' of a spacer 4 which is of a
 substantially U-shaped cross section. The spacer 4 is placed on the
 radially outer end of the ridge 31 with substantially no play in
 circumferential and radial directions between the spacer 4 and the ridge
 31. Substantially no play between the spacer 4 and the ridge 31 means that
 the spacer 4 is snugly mounted on the ridge 31 so that the spacer 4 will
 not wobble on the ridge 31, but the spacer 4 and the ridge 31 are not
 required to be dimensionally accurate as with precision parts.
 When the rotor 3 rotates, the spacer 4 rotates in unison with the ridge 31
 with a very small clearance present between the outer circumferential
 surface of the spacer 4 and the inner surface of the casing 2.
 The spacer 4 may be integrally formed with the ridge 31 of the rotor 3.
 As shown in FIG. 2, the rotor 3 has a first groove 33 defined in the outer
 surface thereof at an axially intermediate position, the first groove 33
 having a constant width and depth and extending from a starting end S to a
 terminal end E. The starting end S is spaced circumferentially a given
 distance from the ridge 31. The groove 33 extends circumferentially from
 the starting end S away from the ridge 31 to the terminal end E at a
 position that is diametrically opposite to the starting end S and which is
 spaced a given distance from the ridge 31. The groove 33 angularly extends
 about 190.degree. around the central axis O (FIG. 1) of the rotor 3. The
 width and depth of the groove 33 may be varied circumferentially and/or
 axially to obtain a desired torque from the damper device 1.
 As shown in FIG. 3, the cylindrical casing 2 has an axial land 8 projecting
 radially inwardly from the inner surface thereof and angularly extends
 about 130.degree. around the central axis O (FIG. 1) of the casing 2 which
 is aligned with the central axis O of the rotor 3. When the rotor 3
 rotates, the spacer 4 also rotates until it abuts against one of
 circumferentially opposite ends 81, 81' of the land 8, whereupon the rotor
 3 is stopped against rotation.
 It is more preferable to stop the rotation of the rotor 3 with stoppers
 positioned outside of the damper device 1 before the spacer 4 abuts
 against one of circumferentially opposite ends 81, 81' because use of such
 stoppers is effective in increasing the durability of the spacer 4 and the
 land 8.
 The land 8 has a pair of axial grooves 82, 82', and needle valves 9, 9'
 having smaller diameters than the widths of the axial grooves 82, 82' are
 loosely fitted in the axial grooves 82, 82', respectively. The groove 82
 has a depth progressively greater circumferentially toward the end 81, and
 the groove 82' has a depth progressively greater circumferentially toward
 the end 81'. The needle valves 9, 9' are movable between shallowest groove
 portions 82a, 82a' of the grooves 82, 82' and deepest groove portions 82b,
 82b' of the grooves 82, 82'.
 As shown in FIGS. 4B through 4E, when the rotor 3 rotates counterclockwise
 with respect to the casing 2, the needle valve 9 is positioned in the
 deepest groove portion 82b, and the needle valve 9' is positioned in the
 shallowest groove portion 82a'. As shown in FIGS. 4F through 4I, when the
 rotor 3 rotates clockwise with respect to the casing 2, the needle valve 9
 is positioned in the shallowest groove portion 82a, and the needle valve
 9' is positioned in the deepest groove portion 82b'.
 While the needle valve 9 or 9' is being positioned in the shallowest groove
 portion 82a or 82a', when the needle valve 9 or 9' face the groove 33 in
 the rotor 3, a clearance which is as deep as the groove 33 is present
 between the needle valve 9 or 9' and the rotor 3, and when the needle
 valve 9 or 9' does not face the groove 33, the needle valve 9 or 9'
 contact the outer surface of the rotor 3.
 While the needle valve 9 or 9' is being positioned in the deepest groove
 portion 82b or 82b', when the needle valve 9 or 9' face the groove 33 in
 the rotor 3, a clearance which is deeper than the groove 33 is present
 between the needle valve 9 or 9' and the rotor 3.
 The damper device 1 is installed on a container or the like as follows: The
 flanges 21 of the casing 2 are fastened to a container body such as a
 frame for the door of the container. The door is pivotally supported on
 the container body by a hollow shaft or the like. The protrusion 32 of the
 rotor 3 is fitted in the hollow shaft and lockingly secured to the hollow
 shaft, so that the rotor 3 is coupled to the door by the hollow shaft.
 Conversely, the flanges 21 may be fastened to the door of the container,
 and protrusion 32 of the rotor 3 may be fitted in a hollow shaft mounted
 on a container body such as a frame for the door of the container, and
 lockingly secured to the hollow shaft, so that the rotor 3 is coupled to
 the door by the hollow shaft.
 According to the first embodiment as described above, a fluid torque
 adjuster comprises the needle valves 9, 9' disposed axially on the inner
 surface of the casing 2, and the first groove 33 defined circumferentially
 in the outer surface of the rotor 3.
 Operation of the fluid torque adjuster according to the first embodiment
 will be described below with reference to FIGS. 4A through 4I. First, an
 action of the fluid torque adjuster when the door of the container is
 closed from a fully open, still position will be described below.
 When the door of the container with the dapper device 1 mounted thereon is
 fully open, the parts of the dapper device 1 are in the position shown in
 FIG. 4A. The wall 41 of the spacer 4 mounted on the ridge 31 is held
 against the end 81 of the land 8. Since the viscous fluid does not flow at
 this stage, the needle valves 9, 9' are in a free state in the respective
 grooves 82, 82'.
 When the rotor 3 slightly rotates counterclockwise from the position shown
 in FIG. 4A, the needle valve 9 moves counterclockwise into the deepest
 groove portion 82b and the needle valve 9' moves counterclockwise into the
 shallowest groove portion 82a' as shown in FIG. 4B.
 As the rotor 3 rotates from the position shown in FIG. 4B to the position
 shown in FIG. 4C, the needle valve 9 is positioned in the deepest groove
 portion 82b though it does not face the groove 33. Therefore, a passage
 for the viscous fluid 5 is provided between opposite sides of the needle
 valve 9. Inasmuch as the needle valve 9' faces the groove 33, a passage
 for the viscous fluid 5 is also provided between opposite sides of the
 needle valve 9'. Since passages for the viscous fluid 5 are thus provided
 between opposite sides of the needle valves 9, 9', the fluid torque
 adjuster generates a relatively small torque.
 When the rotor 3 rotates from the position shown in FIG. 4C to the position
 shown in FIG. 4D, the needle valve 9' positioned in the shallowest groove
 82a' passes the terminal end E of the groove 33 and contact the surface of
 the rotor 3. Therefore, as the passages for the viscous fluid 5 between
 opposite sides of the needle valve 9' is interrupted, the fluid torque
 adjuster generates a relatively large torque.
 When the rotor 3 further rotates counterclockwise from the position shown
 in FIG. 4D, the other wall 41' of the spacer 4 abuts against the other end
 81' of the land 8 as shown in FIG. 4E, whereupon the rotor 3 is stopped
 against rotation. While the rotor 3 is rotating from the position shown in
 FIG. 4D to the position shown in FIG. 4E, the needle valve 9' does not
 face the groove 33 and is positioned in the shallowest groove portion
 82a', and hence is in contact with the outer surface of the rotor 3. Since
 no passage for the viscous fluid 5 is provided between opposite sides of
 the needle valve 9', the fluid torque adjuster generates a relatively
 large torque.
 Consequently, when the door of the container is closed from the fully open
 position, the fluid torque adjuster generates a relatively large torque in
 a terminal range of the rotating stroke of the rotor 3, and generates a
 relatively low torque from a starting range of the rotating stroke of the
 rotor 3 prior to the terminal range of the rotating stroke thereof.
 Now, an action of the fluid torque adjuster when the door of the container
 is opened from a fully closed position will be described below.
 When the door of the container with the damper device 1 mounted thereon is
 fully closed, the parts of the damper device 1 are in the position shown
 in FIG. 4E.
 When the rotor 3 slightly rotates clockwise from the position shown in FIG.
 4E, the needle valve 9 moves clockwise from the deepest groove portion 82b
 into the shallowest groove portion 82a and the needle valve 9' moves
 clockwise from the shallowest groove portion 82a' into the deepest groove
 portion 82b' as shown in FIG. 4F.
 As the rotor 3 rotates from the position shown in FIG. 4F to the position
 shown in FIG. 4G, the needle valve 9' is still positioned in the deepest
 groove portion 82b' while not facing the groove 33, and the needle valve 9
 faces the groove 33. Therefore, the passages for the viscous fluid 5 are
 thus kept between opposite sides of the needle valves 9, 9', and the fluid
 torque adjuster generates a relatively small torque.
 When the rotor 3 rotates from the position shown in FIG. 4G to the position
 shown in FIG. 4H, the needle valve 9 positioned in the shallowest groove
 82a passes the starting end S of the groove 33 and contact the
 circumferential surface of the rotor 3, while the needle valve 9' faces
 the groove 33. Therefore, as the passages for the viscous fluid 5 between
 opposite sides of the needle valves 9 is thus interrupted, the fluid
 torque adjuster generates a relatively large torque.
 As the rotor 3 further rotates from the position shown in FIG. 4H, when the
 wall 41 of the spacer 4 abuts against the end 81 of the land 8 as shown in
 FIG. 4I, whereupon the rotor 3 is stopped against rotation.
 As the rotor 3 rotates from the position shown in FIG. 4H up to the
 position shown in FIG. 4I, the needle valve 9' is positioned in the
 deepest groove portion 82b' while facing the groove 33. Therefore, the
 clearance is still kept between the needle valve 9' and the rotor 3.
 However, the needle valve 9 is no longer facing the groove 33 and contacts
 the outer surface of the rotor 3. Since no passage for the viscous fluid 5
 is produced between opposite sides of the needle valve 9, the fluid torque
 adjuster generates a relatively large torque.
 Consequently, when the door of the container is opened from the fully
 closed position, the fluid torque adjuster generates a relatively large
 torque in a terminal range of the rotating stroke of the rotor 3, and
 generates a relatively low torque from a starting range prior to the
 terminal range of the rotating stroke thereof, as when the door of the
 container is closed from the fully open position.
 A damper device according to a second embodiment of the present invention
 will be described below with reference to FIGS. 5 through 8A-8I.
 As shown in FIG. 5, the damper device, generally denoted by the reference
 numeral 101, comprises a cylindrical casing 102, a rotor 103 having a
 portion rotatably mounted in the casing 102, and a viscous fluid 105
 filled in the casing 102 around the rotor 103. An axial protrusion 132 of
 the rotor 103 projects out of an opening 161 in an annular cap 106 in the
 open end of the casing 102. A sealing member 110 prevents the viscous
 fluid 103 from leaking out of the casing 102.
 As shown in FIG. 6, the casing 102 has a first land 122 projecting radially
 inwardly from an inner surface thereof. When the rotor 103 rotates, the
 outer surface of the rotor 103 slides against a radially inner surface of
 the land 122. When a second land 135 (described later on) of the rotor 103
 abuts against one of circumferentially opposite ends 122a, 122a' of the
 land 122, the rotor 103 is stopped against rotation.
 As shown in FIG. 6, the casing 102 has a second groove 134 defined in the
 inner surface thereof, the second groove 134 having a constant width and
 depth and extending from a starting end S to a terminal end E. The second
 groove 134 extends diametrically opposite to the land 122. Specifically,
 the distance between the starting end S and the end 122a is equal to the
 distance between the terminal end E and the other end 122a'.
 Alternatively, the distance between the starting end S and the end 122a
 may be different from the distance between the terminal end E and the
 other end 122a'. The groove 134 angularly extends about 140.degree. around
 the central axis O (FIG. 5) of the casing 102. The width and depth of the
 groove 134 may be varied circumferentially and/or axially to obtain a
 desired torque from the damper device 101.
 As shown in FIG. 7, the rotor 103 has a second land 135 extending axially
 on the outer surface thereof. The land 135 has a pair of axial grooves
 136, 136' defined in an outer surface thereof, and also has a pair of
 circumferentially opposite ends 137, 137'. The land 135 angularly extends
 about 80.degree. around the central axis O (FIG. 5) of the rotor 103.
 Needle valves 109, 109' having smaller diameters than the widths of the
 axial grooves 136, 136' are loosely fitted in the axial grooves 136, 136',
 respectively. The groove 136 has a depth progressively greater
 circumferentially toward the end 137, and the groove 136' has a depth
 progressively greater circumferentially toward the end 137'. The needle
 valves 109, 109' are movable between shallowest groove portions 136a,
 136a' and deepest groove portions 136b, 136b' of the grooves 136, 136'.
 As shown in FIGS. 8B through 8E, when the rotor 103 rotates
 counterclockwise with respect to the casing 102, the needle valve 109 is
 positioned in the deepest groove portion 136b, and the needle valve 109'
 is positioned in the shallowest groove portion 136a'. As shown in FIGS. 8F
 through 8I, when the rotor 103 rotates clockwise with respect to the
 casing 102, the needle valve 109 is positioned in the shallowest groove
 portion 136a, and the needle valve 109' is positioned in the deepest
 groove portion 136b'.
 While the needle valve 109 or 109' is being positioned in the shallowest
 groove portion 136a or 136a', when the needle valve 109 or 109' face the
 groove 134 in the casing 102, a clearance which is as deep as the groove
 134 is created between the needle valve 109 or 109' and the casing 102,
 and when the needle valve 109 or 109' does not face the groove 134, the
 needle valves 109 or 109' contact the inner surface of the casing 102.
 While the needle valve 109 or 109' is being positioned in the deepest
 groove portion 136b or 136b', when the needle valve 109 or 109' faces the
 groove 134 in the casing 102, a clearance which is deeper than the groove
 134 is created between the needle valve 109 or 109' and the casing 102.
 According to the second embodiment as described above, a fluid torque
 adjuster comprises the grooves 136, 136' defined axially in the land 135
 on the outer surface of the rotor 103, and the second groove 134 defined
 circumferentially in the inner surface of the casing 102.
 The damper device 101 according to the second embodiment is connected to
 the door of a container or the like as with the damper device according to
 the first embodiment.
 Operation of the fluid torque adjuster according to the second embodiment
 will be described below with reference to FIGS. 8A through 8I. First, an
 action of the fluid torque adjuster when the door of the container is
 closed from a fully open position will be described below.
 When the door of the container with the damper device 101 mounted thereon
 is fully open, the parts of the damper device 101 are in the position
 shown in FIG. 8A. The end 137 of the land 135 is held against the end 122a
 of the land 122. Since the viscous fluid does not flow at this stage, the
 needle valves 109, 109' are in a free state in the respective grooves 136,
 136'.
 When the rotor 103 slightly rotates counterclockwise from the position
 shown in FIG. 8A to the position shown in FIG. 8B, the needle valve 109
 moves clockwise into the deepest groove portion 136b and the needle valve
 109' moves clockwise into the shallowest groove portion 136a'.
 As the rotor 103 rotates from the position shown in FIG. 8B to the position
 shown in FIG. 8C, the needle valve 109 is positioned in the deepest groove
 portion 136b though it does not face the groove 134. Therefore, a passage
 for the viscous fluid 105 is provided between opposite sides of the needle
 valve 109. Inasmuch as the needle valve 109' faces the groove 134 a
 passage for the viscous fluid 105 is also provided between opposite sides
 of the needle valve 109', and as a result, the fluid torque adjuster
 generates a relatively small torque.
 When the rotor 103 rotates from the position shown in FIG. 8C to the
 position shown in FIG. 8D, the needle valve 109' positioned in the
 shallowest groove 136a' comes to the terminal end E of the groove 134 and
 contacts the inner surface of the casing 102 while the needle valve 109
 faces the groove 134. Therefore, since the passages for the viscous fluid
 105 between opposite sides of the needle valve 109' is thus interrupted,
 the fluid torque adjuster generates a relatively large torque.
 When the rotor 103 further rotates counterclockwise from the position shown
 in FIG. 8D, the other end 137' of the land 135 abuts against the other end
 122a' of the land 122 as shown in FIG. 8E, whereupon the rotor 103 is stop
 against rotation. While the rotor 103 is rotating from the position shown
 in FIG. 8D to the position shown in FIG. 8E, the needle valve 109' does no
 longer face the groove 134 and is positioned in the shallowest groove
 portion 136a', and hence is in contact with the inner surface of the
 casing 102. Since no passage for the viscous fluid 105 is provided between
 opposite sides of the needle valve 109', the fluid torque adjuster
 generates a relatively large torque.
 Consequently, when the door of the container is closed from the fully open
 position, the fluid torque adjuster generates a relatively large torque in
 a terminal range of the rotating stroke of the rotor 103, and generates a
 relatively low torque from a starting range of the rotating stroke of the
 rotor 103 prior to the terminal range of the rotating stroke thereof.
 Now, an action of the fluid torque adjuster when the door of the container
 is opened from a fully closed position will be described below.
 When the door of the container with the damper device 101 mounted thereon
 is fully closed, the parts of the dapper device 101 are in the position
 shown in FIG. 8E.
 When the rotor 103 slightly rotates clockwise from the position shown in
 FIG. 8E, the needle valve 109 moves counterclockwise from the deepest
 groove portion 136b into the shallowest groove portion 136a and the needle
 valve 109' moves counterclockwise from the shallowest groove portion 136a'
 into the deepest groove portion 136b' as shown in FIG. 8F.
 As the rotor 103 rotates from the position shown in FIG. 8F to the position
 shown in FIG. 8G, the needle valve 109' is still positioned in the deepest
 groove portion 136b' while not facing the groove 134, and the needle valve
 109 faces the groove 134. Therefore, the passages for the viscous fluid
 105 are thus kept between opposite sides of the needle valves 109, 109',
 the fluid torque adjuster generates a relatively small torque.
 When the rotor 103 rotates from the position shown in FIG. 8G to the
 position shown in FIG. 8H, the needle valve 109 positioned in the
 shallowest groove 136a comes to the starting end S of the groove 134 and
 contacts the inner surface of the casing 102 while the needle valve 109'
 faces the groove 134. Therefore, as the passages for the viscous fluid 105
 between opposite sides of the needle valve 109 is thus interrupted, the
 fluid torque adjuster generates a relatively large torque.
 As the rotor 103 further rotates from the position shown in FIG. 8H, when
 the end 137 of the land 135 abuts against the end 122a of the land 122 as
 shown in FIG. 8I, whereupon the rotor 103 is stopped against rotation. In
 the position shown in FIG. 8I, the needle valves 109, 109' are in the
 initial free state as shown in FIG. 8A.
 As the rotor 103 rotates from the position shown in FIG. 8H up to the
 position shown in FIG. 8I, the needle valve 109' is positioned in the
 deepest groove portion 136b' while facing the groove 134. Therefore, the
 clearance is still kept between the needle valve 109' and the casing 102.
 However, the needle valve 109 positioned in the shallowest groove portion
 136a is no longer facing the groove 134 and contacts the inner surface of
 the casing 102. Since no passage for the viscous fluid 105 is provided
 between opposite sides of the needle valve 109, the fluid torque adjuster
 continues to generate a relatively large torque.
 Consequently, according to the second embodiment, as with the first
 embodiment, when the door of the container is opened from the fully closed
 position, the fluid torque adjuster generates a relatively large torque in
 a terminal range of the rotating stroke of the rotor 103, and generates a
 relatively low torque from a starting range prior to the terminal range of
 the rotating stroke thereof, as when the door of the container is closed
 from the fully open position.
 A damper device according to a third embodiment of the present invention
 will be described below with reference to FIG. 9 through 12A-12I.
 As shown in FIG. 9, the dapper device, generally denoted by the reference
 numeral 201, comprises a cylindrical casing 202, a rotor 203 having a
 portion rotatably mounted in the casing 202, and a viscous fluid 205
 filled in the casing 202 around the rotor 203. An axial protrusion 232 of
 the rotor 203 projects out of an opening 261 in an annular cap 206 in the
 open end of the casing 202. A sealing member 210 prevents the viscous
 fluid 203 from leaking out of the casing 202.
 As shown in FIG. 10, the casing 202 has a land 222 projecting radially
 inwardly from an inner surface thereof. When the rotor 203 rotates, the
 outer surface of the rotor 203 slides against a radially inner surface of
 the land 222. When the rotor 203 rotates clockwise in FIGS. 12F-12H, an
 end 241a of a valve body 204a abuts against an end 222a of the land 222,
 whereupon the rotor 203 is stopped against rotation. When the rotor 203
 rotates counterclockwise in FIGS. 12B-12D, an end 241b of a valve body
 204b abuts against an opposite end 222a' of the land 222, whereupon the
 rotor 203 is stopped against rotation.
 As shown in FIG. 10, the casing 202 has a third groove 234 defined in the
 inner surface thereof, the third groove 234 having a constant width and
 depth and extending from a starting end S to a terminal end E. The third
 groove 234 extends diametrically opposite to the land 222. Specifically,
 the distance between the starting end S and the end 222a is equal to the
 distance between the terminal end E and the other end 222a'.
 Alternatively, the distance between the starting end S and the end 222a
 may be different from the distance between the terminal end E and the
 other end 222a'. The groove 234 angularly extends about 190.degree. around
 the central axis O of the casing 202. The width and depth of the groove
 234 may be varied circumferentially and/or axially to obtain a desired
 torque from the damper device 201.
 As shown in FIG. 11, the rotor 203 has a pair of circumferentially spaced
 axial ridges 235a, 235b projecting radially outwardly from an outer
 surface thereof and having respective recesses p, q defined axially
 centrally in radially outer ends thereof. The ridges 235a, 235b extend
 respectively along planes angularly spaced about 50.degree. from each
 other about the central axis O of the rotor 203.
 Valve bodies 204a, 204b, each of a substantially U-shaped cross section,
 are loosely fitted over the respective ridges 235a, 235b for rotation with
 the ridges 235a, 235b upon rotation of the rotor 203. The valve body 204a
 has a pair of circumferentially spaced radial walls 241a, 242a, and the
 valve body 204b has a pair of circumferentially spaced radial walls 241b,
 242b. The circumferential distance between the walls 241a, 242a and the
 circumferential distance between the walls 241b, 242b are greater than the
 circumferential widths of the ridges 235a, 235b. Therefore, the ridges
 235a, 235b can move between the walls 241a, 242a and between the walls
 241b, 242b.
 The walls 242a, 242b which are positioned adjacent to each other have
 respective recesses r, s defined axially centrally therein. The walls
 241a, 241b have no such recesses.
 As shown in FIGS. 12B through 12E, when the rotor 203 rotates
 counterclockwise with respect to the casing 202, the ridge 235a rotates
 with its forward face held against the wall 242a of the valve body 204a,
 and the ridge 235b rotates with its forward face held against the wall
 241b of the valve body 204b. As shown in FIGS. 12F through 12I, when the
 rotor 203 rotates clockwise with respect to the casing 202, the ridge 235a
 rotates with its forward face held against the wall 241a of the valve body
 204a, and the ridge 235b rotates with its forward face held against the
 wall 242b of the valve body 204b.
 According to the third embodiment, a fluid torque adjuster comprises the
 valve bodies 204a, 204b loosely fitted over the respective ridges 235a,
 235b, and the third groove 234 defined circumferentially in the inner
 surface of the casing 202. The valve bodies 204a, 204b include the radial
 walls 242a, 242b, respectively, each having a recess and the radial walls
 241a, 241b, respectively, each having no recess.
 The damper device 201 according to the third embodiment is connected to the
 door of a container or the like as with the damper devices according to
 the first and second embodiments.
 Operation of the fluid torque adjuster according to the third embodiment
 will be described below with reference to FIGS. 12A through 12I. First, an
 action of the fluid torque adjuster when the door of the container is
 closed from a fully open position will be described below.
 When the door of the container with the damper device 201 mounted thereon
 is fully open, the parts of the damper device 201 are in the position
 shown in FIG. 12A. The wall 241a of the valve body 204a has an inner
 surface held against the lower surface, as shown in FIG. 12A, of the ridge
 235a, and an outer surface held against the end 222a of the land 222. The
 radially outer surface of the valve body 204a is held against the inner
 surface of the casing 202. The wall 242b of the valve body 204b has an
 inner surface held against the lower surface, as shown in FIG. 12A, of the
 ridge 235b. The radially outer surface of the valve body 204b faces the
 groove 234. A clearance which is as deep as the groove 234 is present
 between the radially outer surface of the valve body 204b and the inner
 surface of the casing 202.
 When the rotor 203 slightly rotates counterclockwise from the position
 shown in FIG. 12A to the position shown in FIG. 12B, the valve bodies
 204a, 204b do not rotate until the inner surface of the wall 242a of the
 valve body 204a is brought into contact with the upper surface, as shown
 in FIG. 12B, of the ridge 235a, and the inner surface of the wall 241b of
 the valve body 204b is brought into contact with the upper surface, as
 shown in FIG. 12B, of the ridge 235b.
 In the position shown in FIG. 12B, as with the position shown in FIG. 12A,
 the radially outer surface of the valve body 204a is held against the
 inner surface of the casing 202, and the radially outer surface of the
 valve body 204b in its entirety faces the groove 234 while the wall 242b
 having the recess r being held against the forward face of the ridge 235a.
 Therefore, a passage for the viscous fluid is provided between the
 radially outer surface of the valve body 204b and the inner surface of the
 casing 202, and through the recesses r, p of the wall 242a and the ridge
 235a, respectively.
 As the rotor 203 rotates from the position shown in FIG. 12B to the
 position shown in FIG. 12C, a passage for the viscous fluid 205 extends
 from the groove 234 which faces the valve body 204b, through the recess r
 in the wall 242a and through the recess p in the ridge 235a, to a space
 between the inner surface of the wall 241a and one side surface of the
 ridge 235a. As a result, the fluid torque adjuster produces a relatively
 small torque.
 When the rotor 203 rotates from the position shown in FIG. 12C to the
 position shown in FIG. 12D, the wall 241b of the valve body 204b comes to
 the terminal end E of the groove 234 and a front end of the radially outer
 surface of the valve body 204b contacts the inner surface of the casing
 202 which has no groove. As a result, a fluid communication through the
 groove 234 is interrupted at the terminal end E of the groove 234. Since
 no recess is defined in the wall 241b of the valve body 204b, no fluid
 communication is established between the wall 241a of the valve body 204a
 and the wall 241b of the valve body 204b. Therefore, the fluid torque
 adjuster now produces a relatively large torque.
 When the rotor 203 further rotates from the position shown in FIG. 12D, the
 outer surface of the wall 241b of the valve body 204b abuts against the
 other end 222a' of the land 222, as shown in FIG. 12E, whereupon the rotor
 203 is stopped against rotation. During the rotation of the rotor 203 from
 the position shown in FIG. 12D to the position shown in FIG. 12E, as the
 radially outer surface of the valve body 204b is held against the inner
 surface of the casing 202, the fluid torque adjuster continues to produce
 a relatively large torque.
 Consequently, according to the third embodiment, as with the first
 embodiment, when the door of the container is closed from the fully open
 position, the fluid torque adjuster generates a relatively large torque in
 a terminal range of the rotating stroke of the rotor 203, and generates a
 relatively low torque from a starting range of the rotating stroke of the
 rotor 203 prior to the terminal range of the rotating stroke thereof.
 Now, an action of the fluid torque adjuster when the door of the container
 is opened from a fully closed position will be described below.
 When the door of the container with the damper device 201 mounted thereon
 is fully closed, the parts of the damper device 201 are in the position
 shown in FIG. 12E. The wall 241b of the valve body 204b has an inner
 surface held against the lower surface, as shown in FIG. 12E, of the ridge
 235b, and an outer surface held against the end 222a' of the land 222. The
 radially outer surface of the valve body 204b is held against the inner
 surface of the casing 202. The wall 242a of the valve body 204a has an
 inner surface held against the lower surface, as shown in FIG. 12E, of the
 ridge 235a. The radially outer surface of the valve body 204a faces the
 groove 234.
 When the rotor 203 slightly rotates clockwise from the position shown in
 FIG. 12E to the position shown in FIG. 12F, the valve bodies 204a, 204b do
 not rotate until the inner surface of the wall 242b of the valve body 204b
 is brought into contact with the upper surface, as shown in FIG. 12F, of
 the ridge 235b, and the inner surface of the wall 241a of the valve body
 204a is brought into contact with the upper surface, as shown in FIG. 12F,
 of the ridge 235a.
 In the position shown in FIG. 12F, as with the position shown in FIG. 12E,
 the radially outer surface of the valve body 204b is held against the
 inner surface of the casing 202, and the radially outer surface of the
 valve body 204a faces the groove 234. Therefore, a clearance which is as
 deep as the groove 234 is provided between the radially outer surface of
 the valve body 204a and the inner surface of the casing 202.
 As the rotor 203 rotates from the position shown in FIG. 12F to the
 position shown in FIG. 12G, a passage for the viscous fluid 205 extends
 from the groove 234 which faces the valve body 204a, through the recess s
 in the wall 242b and through the recess q in the ridge 235b, to a space
 between the inner surface of the wall 241b and one side surface of the
 ridge 235b. As a result, the fluid torque adjuster produces a relatively
 small torque.
 When the rotor 203 rotates from the position shown in FIG. 12G to the
 position shown in FIG. 12H, the wall 241a of the valve body 204a reaches
 the starting end S of the groove 234, and a front end of the radially
 outer surface of the valve body 204a contacts the inner surface of the
 casing 202 which has no groove. As a result, a fluid communication through
 the groove 234 is interrupted at the starting end S of the groove 234.
 Since no recess is defined in the wall 241a of the valve body 204a, no
 fluid communication is established between the wall 241a of the valve body
 204a and the wall 241b of the valve body 204b. Therefore, the fluid torque
 adjuster now produces a relatively large torque.
 When the rotor 203 further rotates from the position shown in FIG. 12H, the
 outer surface of the wall 241a of the valve body 204a abuts against the
 end 222a of the land 222, as shown in FIG. 12I, whereupon the rotor 203 is
 stopped against rotation. During the rotation of the rotor 203 from the
 position shown in FIG. 12H to the position shown in FIG. 12I, as the
 radially outer surface of the valve body 204a is held against the inner
 surface of the casing 202, the fluid torque adjuster continues to produce
 a relatively large torque.
 Consequently, according to the third embodiment, as with the first and
 second embodiments, when the door of the container is closed from the
 fully open position, the fluid torque adjuster generates a relatively
 large torque in a terminal range of the rotating stroke of the rotor 203,
 and generates a relatively low torque from a starting range of the
 rotating stroke of the rotor 203 prior to the terminal range of the
 rotating stroke thereof.
 FIGS. 13 and 14 show how a torque is generated in the rotating strokes of
 the rotor 3 (103, 203), in normal and reverse directions. FIG. 13 shows a
 generated torque when the rotor 3 (103, 203) rotates in a counterclockwise
 stroke in FIGS. 4A-4E, 8A-8E, and 12A-12E, and FIG. 14 shows a generated
 torque when the rotor 3 (103, 203) rotates in a clockwise stroke in FIGS.
 4E-4I, 8E-8I, and 12E-12I. It can be seen from FIGS. 13 and 14 that a
 higher torque is generated in the terminal range of each of the
 counterclockwise and clockwise strokes of the rotor 3 (103, 203).
 Various modifications of the first through third embodiments will be
 described below.
 FIGS. 15A and 15B show a modification of the first embodiment. As shown in
 FIGS. 15A and 15B, two spacers 304 are mounted respectively on
 diametrically opposite ridges 331 on the rotor 303, and two diametrically
 opposite pairs of needle valves 309, 309' are disposed axially on the
 inner surface of the cylindrical casing 302. Two first grooves 333 are
 defined in diametrically opposite relation in the outer surface of the
 rotor 303. Therefore, the various parts are provided in two sets.
 FIGS. 16A and 16B show a modification of the second embodiment. As shown in
 FIGS. 16A and 16B, two diametrically opposite axial lands 422 project
 radially inwardly from the inner surface of the cylindrical casing 402,
 and two diametrically opposite pairs of needle valves 409, 409' are
 loosely fitted in respective grooves defined in lands 435 of the rotor
 403. Two grooves 434 are defined in diametrically opposite relation in the
 inner surface of the casing 402. Therefore, the various parts are provided
 in two sets.
 FIGS. 17A and 17B show a modification of the third embodiment. As shown in
 FIGS. 17A and 17B, two diametrically opposite axial lands 522 project
 radially inwardly from the inner surface of the cylindrical casing 502,
 and two diametrically opposite pairs of valve bodies 404a, 404b are
 circumferentially loosely fitted over respective ridges 435a, 435b of the
 rotor 403. Two grooves 434 are defined in diametrically opposite relation
 in the inner surface of the casing 402. Therefore, the various parts are
 provided in two sets.
 FIGS. 15A, 16A, and 17A show the positions of the parts when the rotors
 303, 403, 503 rotate counterclockwise, and FIGS. 15B, 16B, and 17B show
 the positions of the parts when the rotors 303, 403, 503 rotate clockwise.
 Fluid torque adjusters according to these modifications operate in the same
 manner as with the fluid torque adjusters where the parts are provided in
 one set. The parts of the modified fluid torque adjusters may be
 dimensioned and positioned differently from those illustrated. While the
 parts are provided in two sets according to the modifications shown in
 FIGS. 15A, 15B, 16A, 16B, and 17A, 17B, the parts may be provided in three
 or more sets.
 Other modifications of the first through third embodiments will be
 described below.
 FIGS. 18A and 18B show another modification of the first embodiment. As
 shown in FIGS. 18A and 18B, a pair of diametrically opposite axial lands
 608, 608' is disposed on the inner surface of the cylindrical casing 602,
 and radially movable needle valves 609, 609' are loosely fitted in
 respective grooves 682, 682' defined axially in the lands 608, 608'. A
 pair of diametrically opposite ridges 631, 631' is disposed on the outer
 surface of the rotor 603, and spacers 604, 604' are mounted on the
 respective ridges 631, 631'. Two grooves 633, 633' are defined in
 diametrically opposite relation in the outer surface of the rotor 603. In
 the modification shown in FIGS. 18A and 18B, the various parts are
 provided in two sets. However, the grooves 682, 682' and the needle valves
 609, 609' loosely fitted therein are provided one in each set.
 FIGS. 19A and 19B show another modification of the second embodiment. As
 shown in FIGS. 19A and 19B, a pair of diametrically opposite first axial
 lands 722, 722' is disposed on the inner surface of the cylindrical casing
 702, and a pair of diametrically opposite second axial lands 735, 735' is
 disposed on the outer surface of the rotor 703. Radially movable needle
 valves 709, 709' are loosely fitted in respective grooves 736, 736'
 defined axially in the second lands 735, 735'. Two grooves 734, 734' are
 defined in diametrically opposite relation in the inner surface of the
 casing 702. In the modification shown in FIGS. 19A and 19B, the various
 parts are provided in two sets. However, the grooves 736, 736' and the
 needle valves 709, 709' loosely fitted therein are provided one in each
 set.
 FIGS. 20A and 20B show another modification of the third embodiment. As
 shown in FIGS. 20A and 20B, a pair of diametrically opposite first axial
 lands 822, 822' is disposed on the inner surface of the cylindrical casing
 802, and a pair of diametrically opposite axial ridges 835a, 835b is
 disposed on the outer surface of the rotor 803. Valve bodies 804, 804' are
 loosely mounted on the respective ridges 835a, 835b, and two grooves 834,
 834' are defined in diametrically opposite relation in the inner surface
 of the casing 802. In the modification shown in FIGS. 20A and 20B, the
 various parts are provided in two sets. However, the ridges 835a, 835b and
 the valve bodies 804a, 804b mounted thereon are provided one in each set.
 FIGS. 18A, 19A, and 20A show the positions of the parts when the rotors
 603, 703, 803 rotate counterclockwise, and FIGS. 18B, 18B, and 20B show
 the positions of the parts when the rotors 603, 703, 803 rotate clockwise.
 Fluid torque adjusters according to these modifications operate in the same
 manner as with the fluid torque adjusters where the parts are provided in
 one set. The parts of the modified fluid torque adjusters may be
 dimensioned and positioned differently from those illustrated. While the
 parts are provided in two sets according to the modifications shown in
 FIGS. 18A, 18B, 19A, 19B, and 20A, 20B, the parts may be provided in three
 or more sets.
 The damper device according to the present invention has been described as
 being applied to the door of a container for damping the door in terminal
 ranges of opening and closing movements of the door. However, the damper
 device may be used in other applications. For example, the damper device
 may be used in combination with reciprocally movable devices for applying
 damping forces to back-and-forth movements thereof in terminal ranges.
 One of the other applications is as an electrically powered saw.
 Specifically, when the electrically powered saw is pushed to cut a piece
 of wood, the damper device applies damping forces to the saw in a terminal
 range of its stroke before the saw hits a rear stop, and when the
 electrically powered saw is pulled, the damper device also applies damping
 forces to the saw in a terminal range of its stroke before the saw hits a
 front stop.
 In each of the above embodiments and modifications, the casing is fixed in
 position and the rotor is rotatable. However, the rotor may be fixed in
 position and the casing may be rotatable.
 Although certain preferred embodiments of the present invention have been
 shown and described in detail, it should be understood that various
 changes and modifications may be made therein without departing from the
 scope of the appended claims.