|Publication number||US2116185 A|
|Publication date||May 3, 1938|
|Filing date||Aug 7, 1935|
|Priority date||Aug 7, 1935|
|Publication number||US 2116185 A, US 2116185A, US-A-2116185, US2116185 A, US2116185A|
|Inventors||Bernhard Benjamin S|
|Original Assignee||Bernhard Benjamin S|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (11), Classifications (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
B. s. BERNHARD DOOR CLOSER AND CHECK May 3, 1938.
Filed Aug. '7, 1935 2 Sheets-Sheet l ZZZ? W I '/j M y 3, 1938. B. s. BERNHARD 2,116,185
DOOR CLOSER AND CHECK Filed Aug. 7, 1955 2 Sheets-Sheet 2 M /4Zf s j,j
f4 1/ fW/ZW r Am.
(large! Patented May 3, 1938 UNITED STATES nane FATENT OFFIE 21 Claims.
This invention relates to door closing and checking devices of the concealed type which are adapted to be set into either the lintel or the threshold of a door frame or doorway and to be 5 suitably connected with a swinging door so as to close the door after it has been opened and released. My objects have been to increase the power and efliciency of closers of this type; to provide means by which a new and better regu- 1 laticn of the closing movement of the door may be effected, to facilitate assemblage and adjustment of the connections by which force is transmitted between the door and the closing springs, and to furnish other improvements, the nature 15 and character of which appear from the following description.
I have shown in'the drawings provided herewith the operating parts, and to some extent suitable details of construction, of the presently preferred embodiment of the invention, together with illustrative modes of app-lying it to door frames and swinging doors; but without intending thereby to imply limitation of the protection herein claimed to the details thus illustrated.
25 In the drawings,-- 7
Figs. 1, 2 and 3 illustrate the application of the present door closer to the lintel of a door frame and an operating connection between the same and the upper member of a door; Fig. 1 being a 30 fragmentary elevation, partly broken away, of
the door frame and door; Fig. 2 being a horizontal section on line 2-2 of Fig. 1; and Fig. 3 being a vertical section on line 33 of Fig. 1;
Figs. 4 and 5 show a mode of setting the same 35 closer in the threshold of a doorway, and another mode of connecting it with a door; Fig. 4 being a partial elevation and section of the necessary parts, and Fig. 5 a horizontal section on line 55 of Fig. 4;
40 Figs. 6-13 inclusive show the details of the closer; and of these Fig. 6 is a vertical longitudinal section of the device, Figs. '7 and 8 hori zontal sections on lines l'l and 8-8 respectively of Fig. 6, Fig. 9 a cross section on line 9-9 of Fig.
45 6, Figs. 10, 11 and 12 fragmentary sectional views illustrating the action of the closing check and speed regulating adjustment, and Fig. 13 a perspective View of the closer check piston.
Like reference characters designate the same 50 parts wherever they occur in all the figures.
I will first describe the construction of the door closer here illustrated, and then explain its mode of action and some of the ways in which it may be connected with a door. A base I I is provided 55 with separated shaft supports 1 2 and I3 in which are rotatably mounted shafts l4 and I5 respectively. The support I2 is of suitable internal formation to provide seats for bearings it and I! for the shaft !4, and space for apinion l8 and sprocket H] on said shaft; and correspondingly 5 the support I 3 is appropriately formed to hold bearings 20 and 2| for shaft l5 and leave space for a sprocket 22 on said shaft. The supports may be otherwise of any design and construction preferred by the designer, whether integral with the base, or in one or more parts otherwise connected together and to the base. In this illustration both supports and thebase are made as an integral casting, shaped and finished as clearly shown by the drawings.
An intermediate frame or block 23 is secured to the base between the shaft supports, screws for connecting it detachably being indicated at M in Fig. 6. This intermediate structure contains a check cylinder 25, with auxiliary fluid chambers 26 and 2?, and spaces for the reception of four helical compression springs. Two of such springs are shown at 29 and 3!! in Fig. '7, located with their axes in the same horizontal plane as the sprockets l9 and 22, this plane being below the axis of the check cylinder. Two other and like springs are contained in the intermediate frame directly above the springs 29 and 30 respectively with their axes in a plane above the check cylinder and in the same plane with upper 30 sprockets 3| and 32 on the shafts l4 and i5 respectively. Conveniently the intermediate frame may be made as a casting, cored out to form the cylinder and other spaces described and yet to be described. Each of the springs is preferably confined in a tubular spring housing 33 of suitable internal diameter to prevent buckling of the spring when compressed, while at the same time permitting it to expand and contract freely. These tubes are placed in the spaces provided for 4.0 them and are secured by sleeves or thimbles 34 and 35, screwed into the ends of the spaces and abutting against the ends of the tubes as shown in Fig. 7. The use of separate tubes for housing the springs simplifies the task and expense of 4.5 properly housing springs of diiferent diameters provided for different duties, for suitable housings can be cut from tubing of appropriate diam eters and secured as described in a frame of standard dimensions designed to accommodate a considerable range of springs. That is, a casting such as the block 23 here shown need not be made with the spring chambers of the exact diameter necessary to fit the springs, nor need different blocks be provided especially for all the different '55 sizes of springs which may be required to meet commercial demands; and the intermediate frame may be made otherwise than in one piece or as a block casting.
Spring 29 reacts against a shoulderin thimble and presses against a flange 38 carried by one member 3'! of a two part adjustable rod 38. Spring 30 acts in the same manner, but in the opposite direction, on a flange 39 carried by an adjustable rod 40. Rods 38 and 4B are connected to one another at one end by a chain 4| which surrounds and meshes with sprocket l9; and are connected to one another at the opposite end' by a chain 42 surrounding and in mesh with sprocket 22. The two springs in the upper level act and react in the same manner upon rodsthe duplicates of 38 and which are connected to one another and to the upper sprockets 3i and 32 by chains 43 and 44. Sprockets l9 and at are keyed to shaft l4. Hence all of the springs act in conjunction with one another to exert torque in one direction on shaft I9 and resist its rotation in the opposite direction. For convenience of definition in the claims, the two part rods 38 and 40 are considered as links ina closed-circuit or endless chain, of which the chain sections 4i and 42, made of conventional links, constitute'theremaining parts. Similarly, the duplicate rods above described form with the chain sections '43 and 44 a second closed-circuit chain. Both chains so defined surround both shafts.
Pinion l8 integral with or fixed on shaft l4 meshes with a rack 45 suitably guided in the support l2, and connected by a piston-rod 46 with a piston 41 fitted to slide in the cylinder 25. A head 48 closes the end of the cylinder next to the rack and contains a packing 49 surrounding piston rod 46, the head and packing being both substantially leakage tight. The opposite head of the cylinder may be an integral wall of the block 23 as shown, or a plug fitted leakage tight into the block if the cylinder is originally made open at both ends. A passageway 50 is formed throughout the length of the piston, large enough to permit free flowof the checkingliquid with which the cylinder is filled, when the piston is moved by rotation of the shaft I4 against the resistance of the springs. A ball Valve 5! cooperates with a seat in this passage, in the well known manner, to prevent flow of the liquid through it when the piston is moved in the opposite direction. The piston rod enters one end of this passage, which is there enlarged to permit free flow of the liquid around the rod, and is connected to the piston by a pin 52.
The fluid is by-passed around the piston under control of valves 53 and 54 for checking effect. The channels for such by-passage of the fluid comprise a passage in the cylinder wall opening into the cylinder through ports 56, 51 and 58, and grooves 59and Ell in the side of the piston adjacent 'to these ports. The ports and grooves are all in the same radial plane of the cylinder. Groove 59 extends from the end of the piston nearer to the rack, which for the purpose of this specification may be called the outer or tail end. It is large enough to permit flow of the liquid with little impedance. Groove 68 extends from the opposite inner or head end of the piston and is of tapered form, diminishing gradually from maximum width and depth at the end of the piston to zero dimensions at a point short of the termination of groove 59. The land 6| between the adjacent ends of grooves 59 and 6G is of suitable width and suitably positioned to close port 58 when the piston is at the inner end of its stroke, or at least the land substantially cuts ofi port 58 from groove 59, although the small end of groove may slightly overlap the port 58 when the piston is in the position stated.
The valves 53 and 54 are of the needle valve type, being plugs which may be adjusted by virtue of their screw threaded connection with bushings set into the side of the block 23. They are so located as to be accessible for adjustment when the apparatus is installed for use, and the oypassage channels are located to correspond.
.Valve 53 may be set to close the passage 55 between ports 53 and 51 to a greater or less extent, and. valve 54 to close more or less the communication between this passage and port 58. Port 56 is always open to the cylinder at the tail end of the piston.
The checking effect takes place only during the travel of the piston from the outer to the inner s end of its stroke, that is, from left to right with respect to these drawings. Throughout most of this travel the liquid from in front of the piston enters passage 55 through port 51, which is wide open, and also through port 58 to the extent permitted by the position of valve 54. When the piston approaches its innermost position its land 6| crosses the port 51, closing such port to the inner, and opening it to the outer, end of the cylinder. Valve 53 controls the speed of piston movement until port 5'! has been obstructed by the piston, which does not occur until the dooris nearly closed. The final step of closing is controlled by valve 54 and groove 30. If this latter valve is nearly enough closed to obstruct the flow considerably, the door reaches closed position with a gradual slow motion, which is further and increasingly retarded after the overlapping area of groove 60 over port 58 becomes less than the opening of Valve 54, so that the door closes with out shock. It is sometimes desirable to let the door close slowly throughout the major part of its movement, and then give it a quick movement just before it is fully closed, in order to preclude arrest of the door by striking of the projecting latch on the edge of the jamb. This is accomplished by largely closing valve 53 and Widely opening valve 54, as shown by Fig. 12. After the piston land passes and uncovers port 57, there is then a wide passage opened from port 53 to the front side of the piston, which allows the springs to give the door a quick motion, developing enough momentum to overcome the resistance of even a stubborn latch when striking the door jamb. But thereafter the contraction of the groove 60 throttles the flow so rapidly that the door is checked and comes to the stop quietly and without shock.
The presence of the piston rod makes the capacity of the cylinder less when the piston is at the inner or head end of the cylinder than when at the outer or tail end. To compensate for this difference of volume I have provided the auxiliary chamber 26 which is connected with the cylinder by a port 62 and contains a reserve supply of liquid and a quantity of air, the reserve displaced by liquid above the port when the piston rod is withdrawn being at least as great as the volume of the piston rod when fully advanced into the cylinder. The air space of this chamber may be open to the outer air, through one or more openings equipped with inlet and outlet valves 63 and 64, if desired to maintain approximately atmospheric pressure at all times. I have found that such external communication is usually not necessary in practice, for the body of air, even when hermetically confined, offers too little compressive and expansive resistance to affect the operation of the closer appreciably. Hence the valves 63 and 64 may be replaced by air tight plugs, which need be opened only for initial introduction, or replenishment, of the liquid.
This door closer is designed to be used either in the upright position shown in Fig. 6, or in an inverted position. When inverted, the chamber 21 beneath the cylinder, and connected with it by port '65, is uppermost and functions in the same manner as the foregoing description of chamber 26. The air is then displaced by gravity into the top of inverted chamber 21. When inverted, the openings controlled by valves 63 and 64 must be closed. This may be done either by substituting plugs, as previously described, or by screwing down the screws 61 and 68 far enough to close the external ports 69 of these valves.
The entire assemblage above described is enclosed in a box or housing It, the edges of which meet the base H and are secured in any suitable way, Extensions H and 72 of the base beyond the ends of the housing provide means by which the closer may be secured in position.
The closer may be mounted either in the lintel of a door frame or in the threshold or floor beneath the door; and in either position it may be coupled to the door directly or through the medium of an arm. Figs. 1, 2 and 3 show its application in a lintel 13, and its connection with a hinged door 14 by an arm 15. One end of arm 15 has a hole which fits the non-circular end Ma of shaft M, while its opposite end carries a stud running in a trackway 16 in the upper edge of the door. The extension lugs H and 12 of the closer base are shown as fastened by screws to parts l! and 18 of the lintel structure. This drawing represents a metal door frame but typifies any structure.
Figs. 4 and 5 show the closer inverted and set into a threshold, or a'floor structure 19 beneath a door 80. The door here shown is one of the type which is held by pivots or trunnions instead of being hung by hinges. The shaft [4 of the closer serves as the lower pivot, and its projecting non-circular end is fitted to a socket 81 in one end of a bar 82 which is secured to the bottom edge of the door. The cooperating pivot is attached to the top of the door in vertical alinement with shaft I l and occupies rotatably a bearing in the lintel.
Notwithstanding the foregoing specific showing, it is to be understood that the connecting arm shown with the overhead position of the closer may equally well be used when the closer is set into the floor; and that the direct connection shown in Figs. 4 and 5 may alternatively be used with the overhead position of the closer. It is also to be understood that these illustrated connections between the closer and door are not exhaustive and are not to be construed as limiting the uses or environment of the closer.
In the closer when ready for mounting, the parts are in equilibrium with'the piston against the inner or head end of the cylinder, which limits the thrust action of the springs. When put to use, however, the piston is slightly withdrawn when the door is closed, whereby the force of the springs is available to bring the door to fully closed position. This is accomplished by giving the side faces of the non-circular shaft extension Ma and of its complemental socket in the door or door-operating arm, the proper angularity with respect to the closed position of the door. The organization of springs and check as here described provides ample power for closing even the heaviest of doors, and any door against considerable wind resistance; while the rate and character of its closing movement can be regulated exactly as desired. With all this, the combination of parts enables them to be assembled, and adjusted when necessary, readily and exactly. In order to couple the springs under compression 7 with the shafts, the intermediate frame or block 23, detached from the base but containing the springs and adjustable rods, is placed in a press and pressure is applied externally to the flanges 36 and 39 of the respective rods, in turn, in the direction to compress their respective springs. The rods are thus displaced until the end of each projects from the spring abutment thimble 35 far enough to expose a'groove 83. Temporary locking means are interlocked with the grooves of the respective rods and, by abutting against the contiguous ends of the frame 23 hold the rod ends protruding with freedom to be rotated. Such rotation by screwing the threaded end of the rod into or out of the companion socket piece 37 shortens or lengthens the combined rod. By so adjusting the rods, when the intermediate frame has been applied to the base, they are adapted to the lengths of the chain sections 4| and 42, 23 and 44, respectively which, having previously been connected each to the flanged end of one rod, are now passed around the sprockets I9, 22 and Hi, 32, and are coupled to the pro-truding ends of the other rods. The temporary locks are removed after the chains have been connectcd. Further adjustments may be made in the same way to take up looseness resulting from wear of the chains.
It will be clear to those skilled in the art that various omissions, changes and additions may be made within the scope of the invention as defined in the claims; for example, two or even one closing spring may be employed in certain cases.
What I claim and desire to secure by Letters Patent is:
1. A door closer and check comprising separated parallel shafts, one of which is adapted to be connected for transmission of force to and from a door, sprockets on said shafts, links connected together in a closed circuit embracing both sprockets, and springs applied to both stretches of such connected series of links so as to exert force tending to rotate both shafts in one and the same direction.
2. A door closer and check comprising separated parallel shafts, one of which is adapted to be connected for transmission of force to and from a door, compression springs located on respectively opposite sides of the line of centers of said shafts and between the shafts, said springs being supported to exert force in lines parallel to said line of centers and in directions opposite to one another, sprockets on said shafts, and a chain embracing said sprockets, opposite stretches of said chains being connected to receive thrust from the respective springs.
A door check and closer comprising separated supports, shafts rotatably mounted in said supports in parallel with each other, one of the shafts being adapted for force-transmitting connection with a swinging door, sprockets on the shafts, a chain embracing and meshing with said sprockets and having spring thrust receiving flanges on its opposite stretches, helical springs each sturounding one of the stretches of the chain and abutting at one end against the flange on such stretch, and stationary abutments against which the opposite ends of the springs respectively bear, said spring thrust abutment and flanges being relatively opposite to each other on the two stretches of the chain, whereby both springs cooperate to exert torque in. the same direction on said force transmission shaft.
4. A door check and closer comprising a base, separated supports on said base, parallel shafts rotatably mounted in said supports, an intermediate frame structure having a cylinder, a
piston operating in said cylinder, 2. piston rod connected to the piston and protruding from the cylinder toward one of said shafts, a rack connected to the piston rod, a pinion on the last named shaft in mesh with said rack, sprocket chains in driving and driven connection with both shafts, springs applied to opposite stretches of said chains to exert force thereon tending to turn the shafts in one direction, checking liquid in the cylinder, and means permitting controlled flow of liquid from. one side of the piston to the other during movement of the piston in the direction caused by the spring induced rotation of said shaft.
5. A door closer and check comprising in combination with a shaft adapted to be connected with the door, spring means coupled with said shaft for resisting its rotation in one direction and causing it to rotate in the opposite direction, a cylinder containing checking liquid, a piston fittedto reciprocate in said cylinder, a stuffing box for said cylinder, a rod connected to said piston and protruding from the cylinder 7 substantially leakage tight through said stufling box, connections between said rod and the shaft through which the piston is reciprocated by oscillation of the shaft, by-pass means for conduction of liquid from one end of the cylinder to the other past the piston, and means for causing different rates of by-pass flow of the liquid during respectively different parts of the piston travel.
6. A door closer comprising a shaft adapted to be coupled with a door, a fluid check coupled with said shaft for resisting movement thereof in one direction, a second shaft parallel to the first named shaft and located at the opposite side of said check therefrom, two sprockets on each shaft, two chains embracing both shafts and engaged operatively with said sprockets, and four springs coupled one with each stretch of each chain, and organized to exert force cooperatively on said chains in resistance to rotation of the first named shaft in one direction and tending to rotate said shaft in the direction against the resistance of said check.
7. A door closer comprising a base having separated shaft supports, shafts mounted in parallel on said supports, one of said shafts being adapted for force transmitting connection with a door, and an intermediate frame between said supports having a fluid cylinder and spring abutment, a piston mounted in said cylinder and coupled with one of said shafts to be reciprocated by turning movement of the shaft in opposite directions, said cylinder adapted to contain checking fluid and having means for permitting impeded flow of the fluid from one side to the other of the piston, a sprocket chain in meshed connection with both shafts, and springs abutting on the intermediate frame and applied respectively to the opposite stretches of said chain in a manner to exert force in respectively opposite directions on said stretches to exert torque on the shafts in one direction of rotation.
8. A door closer comprising a supporting structure, shafts rotatably mounted in parallel on said supporting structure and separated from one another, one of said shafts being adapted for force transmitting connection with a door, and an intermediate frame secured to the supporting structure between said shafts, a fluid checking device in said intermediate frame coupled with one of said shafts, helical springs supported by and abutting against said intermediate frame, and sprocket chains in meshed connection with both shafts having stretches passing through said intermediate frame in force receiving engagement with said springs, all of the springs being organized to exert force on the chains tending to turn. the shafts in one direction.
9. In a door closer the combination with two shafts supported rotatably in parallel and at a distance from one another, one of which is adapted to rotate and be rotated by a swinging door, sprockets mounted on said shafts in one plane, an intermediate frame between the shafts, a chain embracing said sprockets in mesh therewith, including rods in its opposite stretches, spring housings mounted in the intermediate frame enclosing said rods, helical springs in the spring housings surrounding the respective rods, each reacting at one end against an abutment in the housing and pressing at the other end against an abutment on the contiguous rod, and a fluid check in the intermediate frame coupled to one of said shafts.
10. In a device of the character indicated, a pair of spaced shafts one of which is adapted to be connected for transmission of force to and from a door, sprockets on said shafts, link means embracing both said sprockets, and a compression spring operable upon a stretch of said link means to exert force thereon tending to rotate both shafts.
11. In a device of the character indicated, a pair of spaced shafts one of which is adapted to be connected for transmission of force to and from a door, sprockets on said shafts, link means embracing said sprockets for connecting said shafts, and a coil spring surrounding said link means and operable to urge said link means in one direction to rotate at least one of said shafts.
12. In a device of the character indicated, a pair of spaced shafts one of which is adapted to be connected for transmission of force-to and from a door, sprockets on said shafts, link means embracing said sprockets and connecting said shafts, check mechanism coacting with one of said shafts for checking rotation thereof in one direction, and a compression spring coacting with said link means for rotating said one of said shafts in said one direction, for the purpose described.
13. In a device of the character indicated, a shaft adapted to be connected for transmission of force to and from a door, check means, means connecting said check means and said shaft for checking movement thereof in one direction, a compression spring, means including a flexible power transmitting means connecting said compression spring and shaft for urging said shaft in said one direction by the compressive force of said spring.
14. In a device of the character indicated, a shaft adapted to be connected for transmission of force to and from a door, check mechanism,
a rack connected thereto and coacting with said shaft for checking movement thereof in one direction, a compression spring, and means including a flexible power transmitting means connectingsaid compression spring and shaft for urging the same in said one direction by the compressive force of said spring.
15. In a device of the character indicated, a
shaft adapted to be connected for transmission of force to and from a door, a compression spring, and a flexible power transmitting means coacting With said spring and shaft for causing said compression spring to urge said shaft in one direction by thecompressive force of said spring, a fluid check, and means coacting with said fluid check and shaft for resisting movement of the latter in said one direction.
16. In a device of the character indicated, a shaft adapted to be connected for transmission of force to and from a door, two separate means acting on said shaft, one of said means comprising a fluid check and connection from said shaft to said check, the other of said means comprising a compression spring and means of connec tion between said shaft and compression spring including a flexible power transmitting means, said means being arranged whereby said compression spring urges said shaft in one direction by the compressive force of said spring and said fluid check resists movement of said shaft in said one direction.
17. In a door check, a cylinder, a piston there in, a cylinder head having a passage for a piston rod, a piston rod connected to said piston and passing through said passage, means for urging said piston in door checking direction, checking means to resist free movement of said piston in said direction, and a fluid reservoir in communication with said cylinder and having a volume at least as great as the volume of fluid displaced by said piston rod when moving from its extreme tail end position to extreme head end position.
18. In a device of the character indicated, a pair of spaced shafts one of which is adapted to be connected for transmission of force to and from a door, flexible means connecting said shafts to cause same to rotate together, a coil spring coacting with a part of said flexible means and with an abutment to urge said shafts in door closing direction, said flexible means including a pair of relatively adjustable members, for the purpose described.
19. In a door check, a cylinder, a piston therein, valve means for permitting a flow of fluid in said cylinder from one side of said piston to the other when moving in door openingdirection and preventing a reverse flow, said cylinder having a port, means for adjusting the size of said port, said cylinder and piston having a variable fluid passage therebetween in communication with said port near the end of the stroke of said piston, for the purpose described.
20. In a door check, a cylinder, a piston therein, Valve means for permitting a flow of fluid in said cylinder from one side of said piston to the other when moving in door opening direction and preventing a reverse flow, a plurality of ports in said cylinder, controlling means for varying said ports, said piston and cylinder having a variable flow fluid passage in communication with one of said ports near the end of the checking stroke of said piston, said variable flow passage including a tapered V-shaped groove in the face of said piston and extending over said last mentioned port for the purpose described.
21. In a door check, a cylinder, a piston therein, means for permitting a flow of fluid in said cylinder from one side of said piston to the other when moving in door opening direction and preventing a reverse flow, means for urging said piston in checking direction, means for restricting the flow of checking fluid so as to permit but a relatively slow movement of said piston, means for thereafter permitting a greater flow of fluid to permit a greater speed of said piston, and means for again checking the flow of fluid to again permit but a slow speed of said piston near the extreme end of its checking stroke.
BENJAMIN S. BERNHARD.
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US2528904 *||May 23, 1946||Nov 7, 1950||Gunge Norballe Svend||Closing device for doors|
|US2701383 *||Apr 24, 1950||Feb 8, 1955||Billeter Ernst||Door closer|
|US2769195 *||Mar 25, 1953||Nov 6, 1956||Ellison Bronze Company Inc||Door check with fluid bumper|
|US2774987 *||Feb 11, 1953||Dec 25, 1956||Ferguson Arlington A||Door closing mechanism|
|US2994906 *||Jan 8, 1958||Aug 8, 1961||Yale & Towne Mfg Co||Door closer with expansion chamber|
|US3025558 *||Jul 24, 1958||Mar 20, 1962||Hawks Otis J||Hydraulic door control device|
|US3040372 *||Dec 19, 1958||Jun 26, 1962||Oscar C Rixson Co||Door closer mechanism|
|US3042957 *||Nov 2, 1959||Jul 10, 1962||Kawneer Co||Door closer|
|US3142095 *||Nov 15, 1961||Jul 28, 1964||Triad Plastics Products Inc||Door construction and closure means therefor|
|US8225458||Jul 24, 2012||Hoffberg Steven M||Intelligent door restraint|
|DE4024121A1 *||Jul 30, 1990||Oct 24, 1991||Dorma Gmbh & Co Kg||Door shutting drive - has pressure relief valve connected to outside of hydraulic damper housing|
|U.S. Classification||16/62, 16/55|
|International Classification||E05F3/00, E05F3/10|