WO1995016094A1

WO1995016094A1 - Friction hinge with selectively tightening bands

Info

Publication number: WO1995016094A1
Application number: PCT/US1994/012475
Authority: WO
Inventors: Edward T. Rude; David A. Carpenter
Original assignee: General Clutch Corporation
Priority date: 1993-12-10
Filing date: 1994-10-27
Publication date: 1995-06-15
Also published as: AU1084995A

Abstract

An inventive friction hinge is disclosed that uses two or more bands (3, 13) each operating in their loosening mode of operation. The loosening mode is used to take advantage of the more reliable frictional characteristics that it provides. Each band wraps nearly around the hinge pin (7). Any number of bands can be used in each direction to obtain the desired torque characteristics. The novel friction hinge exhibits no lost motion and very slight spring-back.

Description

FRICTION HINGE WITH SELECTIVELY TIGHTENING BANDS

This invention relates to hinges and, more particular¬ ly, to friction hinges of the type that are used in laptop and notebook computers as well as the still smaller ones such as palmtops and personal data assistants. Friction hinges also find applications in cabinet doors, luggage, and other instances wherein it is desired to add a controlled amount of friction to the pivotal movement of one element about another. Friction hinges of the prior art have been criticized for being too large, too expensive, for wearing out too quickly, and for having excessive lost motion and spring- back. Lost motion is the name for movement of one side of the hinge with respect to the other than does not require overcoming the frictional torque that the hinge is intended to provide. That is to say, lost motion is free play in the hinge and is usually expressed in degrees. Spring-back is a different effect, also expressed in degrees. There is always some springiness in a friction hinge. Some springi- ness is inherent in any friction hinge, and there will always be some more due to compliance in the surfaces to which it is mounted. For our purposes, spring-back refers to springiness in the friction hinge itself. It is the maximum arcuate distance through which one side of the friction hinge can be moved with respect to the other side such that, upon release, the hinge will return to the same position it had initially. Lost motion and spring-back are each disadvantageous, and every manufacturer of friction hinges seeks to minimize them. As the electronic devices in which they are used become smaller, manufacturers of fric¬ tion hinges are being asked to provide smaller hinges at lower prices, yet with superior operating characteristics that will remain constant over the expected life of the device. GENERAL DESCRIPTION OF THE TECHNOLOGY AND THE PRIOR ART

Prior art friction hinges have been made using various technologies to achieve a controlled amount of frictional torque. One technology that has seen common usage is that of a spring wrapped tightly around a metal pin. If the pin is slightly larger than the free diameter of the spring, then friction between the spring and the pin will resist relative movement between them. A force, applied at one end of the spring so as to cause movement of the spring about the pin, will have to be larger if it acts so as to tighten the spring about the pin than if it acts in the opposite direction which tends to loosen the spring about the pin. Prior art friction hinges have been made using a single wrap spring operating in the loosening mode for both directions of rotation. During rotation, forces are selectively ap¬ plied at an end of the spring in the direction that tends to loosen the grip of the spring on the pin.

Operation in the loosening mode has the disadvantage that the torque provided by that spring and pin is low compared the torque that can be achieved on a pin of the same diameter by a considerably lighter spring operating in the tightening mode. However, operation in the loosening mode has the advantage that the torque is much less sensi¬ tive to the coefficient of friction between the spring and the pin than is operation in the tightening mode. Since the coefficient of friction is a very difficult parameter to control in manufacturing, the loosening mode of operation is often used to minimize its effect on the torque.

BRIEF DESCRIPTION OF OUR INVENTION

The hinge of our invention employs two bands, each slightly less than one turn, wrapped about a pin in such a way that they both operate in the loosening mode. When the hinge is opened, one of the bands slips on the pin while the other, being tightened in that rotational direction, does not. Therefore, the pin moves with the band being tighten¬ ed. When the hinge is closed, the band that previously slipped is now tightened, moving the pin with it as it rotates; and the band that was tight when the hinge was opening, now becomes loose, allowing the pin to slip within it. An important characteristic of the inventive hinge is that, as the hinge is opened and closed, the pin rotates in a hitching motion. The hinge is, in that sense, equivalent to a rotational hitch-feed. This rotational motion has two desirable characteristics, (1) that wear takes place evenly about the cylindrical surface of the pin, and (2) that lubricant is continuously redistributed around the cylindri- cal surface as the pin rotates. In some embodiments, the bands are split into segments to achieve desirable mounting characteristics.

Producing frictional torque by using a multiturn spring in the loosening mode has the disadvantage that a certain, substantial amount of spring-back must be tolerated. The reason for this is that when a force acts on one end of the spring to cause it to slip in the loosening direction, sufficient moment must be applied to the spring to increase its radius of curvature until it is essentially equal to the radius of the pin. And a multiturn spring, with its greater length of wire, must be deflected further to achieve this. Additionally, a spring with substantially one turn.can be far less flexible than a multiturn spring that produces the same frictional torque, further reducing the spring-back. The friction hinge of our invention has less than one turn acting in each direction which provides a significant bene¬ fit.

Most applications for friction hinges require the same torque for both directions of rotation, and that can be done using one spring in a bi-directional, loosening mode of operation. However, in doing so, one of two problems must be dealt with. Either there will be lost motion or the hinge elements must be in simultaneous contact with both ends of the spring. Obviously, lost motion is undesirable. But, simultaneous contact with both ends of the spring makes it very difficult to control the frictional torque that the spring will provide. Even a microscopic amount of wear in either the spring or the pin can result in a significant change in torque, creating problems with the perceived durability of the hinge in use. Our inventive hinge mini- mizes spring-back by employing springs of less than one turn in length, and it eliminates lost motion by firmly attaching one end of each of the springs to one of the hinged ele¬ ments.

It is an objective of our invention to provide a fric- tion hinge with torque characteristics that remain constant over a large number of cycles of operation.

It is a further objective of our invention to provide a friction hinge having no lost motion.

It is a still further objective of our invention to provide a friction hinge having minimal spring-back.

Other objects and advantages of our invention will become apparent from the descriptions that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Further understanding of our invention will become apparent upon consideration of the following detailed de¬ scription in conjunction with the drawings, in which:

FIG. 1 is a perspective view of the hinge of our inven¬ tion configured as a butt hinge.

FIG. 2 is a partially exploded, perspective view of a second embodiment of the friction hinge of our invention. FIG. 3 shows the hinge of FIG. 2 after assembly. FIG. 4 shows a partially exploded view of an enclosed version of the hinge of our invention.

FIG. 5 shows the hinge of FIG. 4 fully assembled. DETAILED DESCRIPTION OF THE DRAWINGS

Our inventive friction hinge can be produced in most of the standard hinge configurations. The butt hinge configu¬ ration shown in FIG. 1 has only three component parts; the hinge pin, or pin, and the two sides of the hinge itself, which, herein, will be called elements. Element 1 is com¬ prised of flange 3 and a portion formed into band 5, which wraps around pin 7. Element 9 has flange 11 and two band portions 13 and 15. Bands 13 and 15 are each wrapped about pin 7 in the same direction as is band 5. Elements 1 and 3 must be made of a spring material . They are formed into a shape that is as nearly circular as possible, with an inside diameter somewhat smaller than the outside diameter of pin 7. The delivered torque is proportional to the interfer- ence, this difference in diameter. As the hinge is closed, band portion 5 of element 1 tightens about pin 7 causing pin 7 to rotate along with it. This motion tends to loosen the grip of bands 13 and 15 about pin 7 so that slippage takes place between bands 13 and 15 and the pin. The torque at which this slippage occurs will depend upon the angle of wrap; the coefficient of friction between the band and shaft, including the effects of any lubricants used; the elastic modulus; thickness and width of the material from which element 9 is fabricated; the interference; and the diameter.

As the hinge is opened, band portions 13 and 15 tighten about pin 7 while band portion 5 loosens, permitting slip¬ page between band portion 5 and pin 7. The same factors, this time with respect to element 1, determine the torque required to produce slippage.

The embodiment shown in FIG. 3 functions in the same manner as the embodiment of FIG. 1 but, in this case, the two hinge elements have the same general configuration, and can, in fact, be identical parts if the torque is to be the same in both directions. Element 17 has flange 19 and band portion 21. Element 23 is similar to element 17. Pin 25 is a simple cylindrical pin which, in this embodiment has been shown with snap ring 25 in a centrally located groove. In FIG. 3, the hinge has been assembled by forcing band por¬ tions 21 and 29 over the ends of pin 25. Snap ring 27 assists in centering the pin inside the bands. The use of a snap ring is entirely optional. It is included to keep the pin from drifting axially during repeated operation. The operation of the hinge of FIG. 2 is identical in principal to that of the hinge of FIG. 1, pin 25 moving alternately with one element and then the other as the hinge is opened and closed.

FIGS. 4 and 5 show an embodiment in which the bands are enclosed within housings. The housings serve to grip the ends of the springs and to connect them to the external parts being hinged. The housing also serve to prevent dirt from entering the frictional interface between the bands and the pin, and to retain lubricants within the hinge. One of the advantages to the use of housings is that standard pins and bands can be used while the connection between the bands and the external parts being hinged can be customized to the requirements of a particular application.

FIG. 4 shows the hinge with bands 31 and 33 already assembled onto pin 35. Bands 31 and 33 are similar to the band portions of the earlier embodiments. In this case, however, there is no large mounting flange attached thereto. Rather, each band has a short tail, 37 and 39 respectively, which is firmly gripped by the housing. Housing 41 fits over band 31 and housing 43 fits over band 33. Housings for this embodiment of the invention have been made from injec- tion molded plastic and from die-cast zinc. In either case, it is essential for the prevention of lost motion that the tails of the springs be held firmly in their respective housings. Each housing has a slot for receiving the tail of its band. In FIG. 4, slot 45 in housing 43 is visible. During assembly, tail 39 of band 33 is inserted into slot

45. Likewise, housing 41, which is an identical part, has a slot for receiving tail 37 of band 31. For plastic parts, the tails must be a press fit within the slots to prevent lost motion. Where zinc parts are used, the slots can be somewhat larger. Then, after the housings are installed over the bands, the zinc can be staked to eliminate any gap between the slot and its respective tail. Pin 35 has shoul¬ der 47, which is hat shaped in cross-section, provides radial bearing support and a thrust bearing for both hous¬ ings. In use, the fully assembled hinge, as shown in FIG. 5, is inserted into closely fitting nests or cavities in the parts that are to be connected by this friction hinge. Each housing has keys to prevent rotation with respect to the hinge mounting. In this case there are two keys, although any other number of keys could be used if properly sized and matched to the mating hardware. Housing 41 has keys 49 and 51, and housing 43 has key 53, all visible in FIG. 5. Housing 43 also has key 55 which is visible only in FIG. 4. Obviously, there must be no free play between the keys and the mating hardware which permits lost motion. One tech¬ nique that has been successfully used to prevent lost motion in the mounting joints is to form the housings and the mating hardware each with a slight taper. Then providing a means for forcing the tapered parts together will prevent lost motion.

Those skilled in the art of wrap spring and wrap band devices will recognize that any number of bands can be used in parallel to tailor the torque provided to a particular requirement. It will thus be seen that the objects set forth above among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the construction of the inventive spring clutch without departing from the spirit and scope of the inven- tion, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific fea¬ tures of the invention herein described and all statements of the scope of the invention which, as a matter of lan¬ guage, might be said to fall therebetween.

Claims

1. A friction hinge assembly comprising: a rotatable pin; a first hinge element having at least one band and wound at least partially about said pin in one of a clock¬ wise and counterclockwise direction; a second hinge element having at least one band wound at least partially about said pin in the same direction as said band of said first hinge element; wherein each of said bands is wound sufficiently tight¬ ly about said pin such that said pin rotates with said at least one band of said first hinge element when said hinge elements close and said pin rotates with said at least one band of said second hinge element when said hinge elements open.

2. The friction hinge of claim 1, wherein each of said first and second hinge elements is made of spring material.

3. The friction hinge assembly of claim 1, wherein said at least one element comprises a pair of bands.

4. The friction hinge of claim 3, wherein said at least one band of said second hinged element is wound about said pin at a location along said pin between where each of said bands of said first hinge element is wound about said pin.

5. The friction hinge assembly of claim 1, further including a first housing in engagement with said first hinge element and a second housing in engagement with said second hinge element.

6. The friction hinge assembly of claim 5, wherein the engagements of said housings to said hinge elements prevents lost motion.

7. The friction hinge assembly of claim 5, wherein each of said at least one bands of said hinge elements includes a tail.

8. The friction hinge assembly of claim 7, wherein each of said housings includes a slot for receiving respec¬ tively the tails of said at least one bands.