There is disclosed a bi-directional clutch, particularly useful in window shade applications. The bi-directional clutch includes a first or core member and an unwrap spring, that is, a spring having an inside diameter somewhat smaller than the diameter of the core, the spring being wound around the core. The unwrap spring has a number of helical turns and spring tangs which extend outwardly past the circumference of the spring and generally perpendicular to the axis of the spring. The spring is controlled by a second, control or driving member which, when rotated, applies force to one or the other of the spring tangs to unwrap or loosen the spring, thereby allowing the spring to rotate relative to the core. As the spring rotates, one of the spring tangs abuts a third or driven member. The third or driven member is rotated by the spring, allowing the third member to rotate relative to the first or core member. The third or driven member continues to rotate, relative to the first or core member, until the second, control or driving member stops rotating. However, when the driven member is rotated directly, the spring is locked onto the core member and further rotation of the driven member is prevented.

This invention relates to bi-directional clutches and, more particularly, 
to such clutches which offer improved reliability and ease of manufacture. 
There are numerous applications for bi-directional clutches. A typical 
bi-directional clutch includes a driving member and a driven member. When 
the clutch is engaged, a torque applied in either direction to the driving 
member causes it to turn, rotating the driven member along with it. But a 
torque applied directly to the driven member when the clutch is engaged, 
locks the driven member and does not result in either the driven or 
driving member turning. When the clutch is disengaged, a torque applied to 
the driving member will not cause the driven member to rotate and a torque 
applied to the driven member will not be transferred back to the driving 
member. 
A typical application for such a bi-directional clutch is for use with 
window shades. In this application, the clutch is always engaged and the 
driven element is locked in place when the driving element is stationary. 
Such bi-directional clutches are a decided improvement over the more 
conventional ratchet and pawl, spring-loaded mechanisms. In this latter 
case, the shade is often difficult to position accurately and, moreover, 
once the shade has been used for any length of time, the mechanism 
frequently becomes dirty resulting in difficulty in engagement between the 
ratchet and pawl. This often results in the shade rewinding itself, 
requiring re-rolling of the shade or even replacement. 
A bi-directional clutch has the advantage of overcoming the difficulty of 
ratchet and pawl, spring-loaded arrangements, such that there is no 
possibility of shade run-away. In a typical application for use with 
window shades, the bi-directional clutch may be used by attaching its 
driven member to a simple shade roller. The driving member may be provided 
with a cord loop for turning it in either direction. As the cord loop is 
pulled, torque is applied to the driving member, causing the driven member 
and shade roller to turn, and in this manner the shade can be raised or 
lowered. Once the shade position is adjusted, the weight of the shade 
tends to turn the driven roller directly. But the application of a direct 
torque to the driven member does not result in its turning, and the shade 
therefore remains in place. The only way to adjust the shade height is by 
applying a direct torque via the cord loop or chain to the driving member. 
The type of bi-directional clutch toward which the present invention is 
directed is exemplified by U.S. Pat. No. 3,135,369, which issued on June 
2, 1964. This patent discloses a bi-directional clutch having particular 
applicability to a window shade mechanism, and utilizes a spring to couple 
motion of the driving member to the driven member. This is accomplished by 
having one end of the spring pass through an arcuate slot in the driven 
member and by having the other spring end pass through a small opening in 
the driving member--the ends of the spring being in alignment with each 
other, being parallel to the spring axis and being within the 
circumference of the turns of the spring, that is, at the same radial 
distance from the spring axis as the turns of the spring. The driving 
member also has a projection or lug which fits into a second arcuate slot 
in the driven member. By moving the driving member, the spring is 
loosened, allowing ultimate movement of the driven member. 
Although the bi-directional clutch mechanism disclosed in U.S. Pat. No. 
3,135,369 operated satisfactorily in theory, it worked much less so in 
practice. To begin with, the bi-directional clutch mechanism utilized a 
relatively elaborate set of parts, requiring careful and precise 
positioning of slots, tabs and extra pieces. These parts were somewhat 
difficult to fabricate and also difficult to assemble, considerably 
increasing manufacturing costs. Furthermore, any deviation in tolerances 
was found to be critical to the operation of the device, poor tolerances 
adversely affecting the operation by preventing the mechanism from 
operating properly. 
In U.S. Pat. No. 3,920,106, which issued on Nov. 18, 1975, there is 
disclosed a single revolution clutch having an input element with a 
U-shaped channel and an actuating sleeve element with a rib. The clutch 
uses a coil spring having longitudinal terminals which are in alignment 
with each other, parallel to the spring axis and within the circumference 
of the spring turns. These spring ends fit into actuating rings. In 
operation, the actuating sleeve turns with the input element for a single 
revolution and, when movement of the input element is arrested, the spring 
is opened to prevent further movement of an output sleeve upon which the 
spring is wound. 
Once again, the clutch disclosed in U.S. Pat. No. 3,920,106 is somewhat 
difficult to fabricate, utilizes additional parts such as actuating rings 
and, as a single revolution clutch, has no applicability to window shade 
configurations. 
Accordingly, it is a broad object of the present invention to provide an 
improved bi-directional clutch. 
A more specific object of the present invention is to provide a 
bi-directional clutch particularly useful as part of a window shade 
mechanism used to raise or lower a window shade. 
Yet another object of the invention is to provide a bi-directional clutch 
having improved manufacturing advantages by having fewer, less complex 
parts and by having a lesser need for precise tolerances than 
bi-directional clutches according to the prior art. 
These and other objects of the present invention are obtained by providing 
a bi-directional clutch, particularly useful in a window shade mechanism, 
having a first core or spring-receiving member which, when the 
bi-directional clutch is used as part of a window shade, is held 
stationary by a bracket attached to a window frame. An unwrap spring, 
having end tangs extending outwardly past the circumference of the spring 
turns and being substantially perpendicular to the axis of the spring, is 
wrapped around the core member, such that the spring is normally held in 
place relative to the core. A second, control or driving member, which 
receives a shade cord or chain, acts as a spring-actuating element and has 
a tang-receiving surface adapted to abut one or the other of the spring 
tangs, depending on the rotation of the control or driving member, thereby 
loosening the spring and allowing it to move relative to the fixed core. 
The bi-directional clutch also includes, as part of its mechanism, a third 
or driven member which, when the device is used as part of a window shade 
configuration, has a window shade fixedly attached thereto. The third or 
driven member includes a tang-abutting surface, and as the spring is moved 
by the control or driving member relative to the stationary core, a tang 
of the spring hits the tang-abutting surface thereby moving the third or 
driven member. 
According to a first embodiment of the invention, the spring is a 
crossed-over spring, the tang-receiving surface of the second, control or 
driving member is a U-shaped channel which is adapted to contact one or 
the other outer surfaces of the spring tangs, and the tang-abutting 
surface of the third or driven member is an inside rib on the driven 
member which abuts the inner surface of one or the other of the spring 
tangs. 
In an alternative, second embodiment, the tangs of the spring are not 
crossed over, the tang-receiving surface of the second, control or driving 
member is a rib parallel to the axis of the spring and the tang-abutting 
surface of the third or driven member is a U-shaped channel. In this 
embodiment, the tang-receiving surface is located between the inner 
surfaces of the tangs and the tang-abutting surface is located between the 
outer surfaces of the tangs.

Referring now to the drawings and, more particularly, to FIGS. 1-6 thereof, 
a bi-directional clutch according to one embodiment of the invention is 
generally designated 10. Although the bi-directional clutch has wide use 
in other arrangements, it finds particular applicability when used as part 
of a window shade configuration. In this context, the clutch 10 is mounted 
by a mounting bracket 12 to a window frame 14. By way of example, bracket 
12 may be fastened to frame 14 by appropriate fastening elements, such as 
by mounting screws 16, which pass through openings 18 in the mounting 
bracket, thereby attaching the mounting bracket to the window frame 14. As 
shown in FIGS. 3-5, the bracket is attached to the underside of the window 
frame top. However, it is readily apparent that bracket 12 may be secured 
to the side of frame 14, if desired. 
The bi-directional clutch 10 functions in this environment to control 
raising and lowering of a window shade 20, which is wound around a shade 
roller 22, the latter formed of carboard or some other material as is well 
known. The shade roller 22 extends between the sides of the window frame 
14, and is mounted to the other side of the frame by another mounting 
bracket 24 of conventional design, having a series of openings 26 allowing 
the bracket to be attached by fastening elements, such as screws 28, 
either to the top of frame 14 or the side of frame 14, near the left hand 
corner of the window frame, as viewed in FIG. 1. The bracket 24 includes a 
slot 30 which receives and supports a pin 32 carried by the shade roller, 
thereby allowing the shade and shade roller to rotate relative to bracket 
24. 
The bi-directional clutch 10 includes a first or core member 34, one end of 
which has a bracket receiving slot 36 which receives a tab 38 of mounting 
bracket 12. In this manner, the bi-directional clutch is attached to the 
mounting bracket 12 and the core member 34 is held stationary to the 
bracket. By having tab 38 extend into the core member 34, the "gap" 
between the side of the shade and the window frame is kept to a minimum. 
This is especially so when a pulley mechanism is being used, since the tab 
and the pulley can occupy the same vertical space. 
The core member 34 is of a generally cylindrical configuration, having a 
first spring-receiving cylindrical surface 40 and a second narrower 
cylindrical surface 42. The core 34 has a central bore 44 extending along 
the longitudinal axis of the core. This bore is preferably threaded and is 
adapted to receive a fastening element 46, in the form of a threaded 
screw, which is threaded into bore 44 from the left hand end of core 34 
(see FIG. 4). Other techniques may be employed, however. For example, a 
drive screw could be used thereby eliminating the need to pre-thread the 
core. 
The cylindrical surface 40 of the fixed core receives an unwrap spring 48 
which has a series of helical turns 49 and which terminates in spring 
tangs 50 and 52. The tangs 50, 52 extend outwardly past the circumference 
of the spring turns and are generally perpendicular to the longitudinal 
axis of spring 48; that is, the tangs extend radially outward of the 
circumference of the helical turns. Each spring tang may have a respective 
tang extension 54 or 56 which is generally parallel to the axis of the 
spring. The tang extensions are provided, as will be explained, to provide 
extra surface area between each tang and the contacted surfaces of the 
driving and driven members of the bi-directional clutch assembly. This 
reduces distortion of the softer materials used in the fabrication of the 
driving and driven members. 
As noted, spring 48 is an unwrap spring, that is, the inside diameter of 
the spring is somewhat smaller than the outer diameter of cylindrical 
surface 40 of core 34. In this manner, the spring 48 normally "grips" the 
cylindrical surface 40 and the spring is held in place relative to the 
stationary core 34. However, as will be explained, force applied in the 
appropriate direction to either spring tang 50 or spring tang 52 tends to 
unwind the helical turns, thereby loosening or ungripping the helical 
turns of the spring from the spring-receiving cylindrical surface 40 and 
allowing the spring 48 to turn relative to core 34. 
In particular and referring generally to FIG. 2, a force applied to the 
outer or second surface 58 of tang 50 tends to cause the tang to move in 
the clockwise direction (when viewed from the left in FIG. 2) thereby 
expanding the helical turns 49 of spring 48 and allowing the spring to 
move relative to core 34. In a similar fashion, a force applied to the 
outer or second surface 60 of tang 52 causes this tang to move in the 
counterclockwise direction (when viewed from the left of FIG. 2), also 
causing the spring to unwind slightly by increasing the inner diameter of 
the helical turns and allowing the spring to move relative to the core. 
On the other hand, a force applied to the inner or first surface 62 of tang 
50 or to the inner or first surface 64 of tang 52 tends to cause the 
respective tangs to move in the opposite directions, tightening the spring 
around the cylindrical surface 40 of core 34 by applying a force which 
tends to cause the helical turns to grip or tighten about this 
spring-receiving surface. By controlling the force applied to spring tangs 
50 or 52, the spring is either loosened (thereby allowing turning of the 
spring relative to core 34) or tightened about core 34. In this manner, 
the bi-directional clutch 10 functions either to transmit motion from the 
driving to driven member to allow shade 20 to be raised or lowered, or to 
act as a lock for the shade. 
It should be noted that in this embodiment, unwrap spring 48 has tangs 
which are "crossed-over"; when viewed from the left hand side in FIG. 2, 
tang 50 is to the left of tang 52 (see also FIGS. 7-9). In other words, 
the distance from one spring tang to the other in helical turns is an 
integer plus less than one-half turn. This is to be contrasted to the 
second embodiment of the invention, wherein the tangs are not 
crossed-over. 
In order to move the appropriate tangs 50 or 52, the bi-directional clutch 
10 includes a second, control or driving member 66 which functions as a 
spring-actuating member. The control or driving member includes a hollow 
cylindrical sleeve portion 68 having an inner diameter of a size which 
allows the sleeve to fit over the helical turns of unwrap spring 48. In 
particular, the inner diameter of the cylindrical sleeve portion 68 should 
be large enough to allow some clearance 70 (see FIGS. 7 and 8) between the 
helical turns of the spring and the inner surface of the cylindrical 
sleeve portion, thereby allowing the spring to expand a sufficient amount 
to permit its movement relative to the core and so prevent the spring from 
hitting the inner wall of the sleeve. 
The cylindrical sleeve portion 68 also includes a cylindrical inner ring 72 
(see FIG. 2) which is located near the right hand end of sleeve 68. The 
inner ring 72 allows the control or driving member 66 to rotate about 
stationary core 34, the ring 72 rotatably engaging the cylindrical surface 
40 of the core, as best shown in FIG. 4. The core 34 advantageously 
includes a shoulder 74 which abuts one side of the inner ring 72 in order 
to prevent the control or driving member 66 from sliding off the 
stationary core member 34. 
The second, control or driving member 66 is rotated, when the 
bi-directional clutch is used to control a window shade, by the 
application of torque applied to this member by a cord or chain 76 
received within a cord channel 78, the latter extending outwardly from the 
cylindrical sleeve portion 68 of control or driving member 66. As 
illustrated particularly in FIG. 2 and FIG. 5, the cord channel is formed 
by a series of off-set radially extending projections 80, each of which 
advantageously includes an L-shaped rib 82 which extends inwardly from the 
channel projection into the path of cord 76 or, if a bead chain is used, 
between the heads of the chain. The spacing and size of the L-shaped ribs 
are chosen so that the chain fits within the perimeter of the pulley and 
there is clearance to allow for some variability of the spacing of the 
beads on the chain. The L-shaped rib on the channel projections 80 is 
provided to prevent slippage of the cord 76 within the cord channel 78, so 
that when the cord is pulled the force applied to the cord is translated 
into a torque which turns the control or driving member 66. 
When the bi-directional clutch is used as part of a window shade mechanism, 
a cord guide 84 is also provided. The cord guide is formed to include an 
aperture 86 which allows the cord guide to be placed on the cylindrical 
portion 115 of the third or driven member 98 described hereafter. Aperture 
86 is large enough to allow the cord guide to remain stationary in the 
orientation shown in FIG. 2, even though the driven member 98 is rotated. 
The bottom end of cord guide 84 provides a cord guideway 88, formed by 
bent flanges 90 through which cord 76 passes. The cord guideway 88 helps 
position cord 76 and keeps the cord within cord channel 78, thereby 
enabling the cord to be readily pulled by a user in order to raise or 
lower window shade 20. 
The cylindrical sleeve portion 68 of the second, control or driving member 
is formed to include a U-shaped channel 92 which defines two generally 
parallel tang-receiving surfaces 94, 96. As torque is applied to the 
control or driving member 66 by a user pulling on cord 76, the control or 
driving member is rotated and, depending on the direction of rotation, 
either tang-receiving surface 94 hits the outer surface 58 of tang 50 or 
tang-receiving surface 96 hits the outer surface 60 of tang 52, thereby 
loosening the unwrap spring 48 and allowing it to turn relative to the 
core 34. 
As spring 48 is turned relative to the stationary core 34, the spring 
transmits motion from the control or driving member 66 to a third or 
driven member, designated by the reference numeral 98. As illustrated 
particularly in FIG. 2 and FIG. 4, the third or driven member 98 includes 
a cylindrical sleeve 100 having a bore 102 which extends from the left 
hand end of the driven member. The bore 102 terminates in an inwardly 
extending ring 104 having a cylindrical surface 105 adapted to ride on the 
cylindrical surface 42 of stationary core 34 (see FIG. 4). This guides the 
driven member 98 as it turns about the stationary core 34. 
The third or driven member 98 also includes sleeve portion 106 having an 
inner diameter sized to enable this part of the third or driven member 98 
to slip over the cylindrical sleeve portion 68 of the control or driving 
member 66, as generally indicated in FIG. 4 and FIGS. 7-9. The sleeve 
portion 106 includes a rib 108, which extends inwardly from sleeve portion 
106, as also shown in FIGS. 4 and 7-9. The rib 108 extends inwardly from 
the sleeve portion 106 a distance sufficient for the rib to intercept the 
clockwise or counterclockwise rotation of the spring tangs 50, 52, but it 
does not interfere with the expansion of the helical turns 49 of the 
unwrap spring. Rib 108 is also sized to extend within the U-shaped channel 
98 of the second, control or driving member 66, the rib terminating before 
it hits the surface 110 which extends between the tang-receiving surfaces 
94 and 96 of the U-shaped channel. 
As illustrated in FIGS. 2 and 7-9, the rib 108 of the third or driven 
member 98 defines a first tang-abutting surface 112 and a second 
tang-abutting surface 114, which are provided to be abutted by the inner 
surface of the tangs 50 and 52. This enables the spring 48 to transfer 
motion from the second, control or driving member 66 to the third or 
driven member 98 when torque is applied to the driving member or, when 
torque is applied directly to the driven member 98, to lock to the driven 
member in place. 
Before describing the operation or interaction of the various component 
parts of the bi-directional clutch, the manner in which the bi-directional 
clutch is assembled will be described. 
In a typical assembly sequence, the second, control or driving member 66 is 
placed on the first or core member 34, with the control or driving member 
slipping over the cylindrical surface 40 of the core until the inner ring 
72 of the control or driving member hits the shoulder 74 of the core. 
The unwrap spring 48 is then placed about the cylindrical surface 40 of the 
core, the helical turns 49 of the spring having to be expanded slightly 
(by pinching the tangs 50, 52 toward each other), since the inner diameter 
of the helical turns 49 is smaller than the diameter of this cylindrical 
surface. The spring is positioned on cylindrical surface 40 with the tangs 
50 and 52 disposed within the U-shaped channel 92 of the control or 
driving member 66. Next, the cord guide 84 is positioned against the cord 
channel 78, as shown in FIG. 4. 
The third or driven member 98 is then slipped over the cylindrical sleeve 
portion 68 of the control or driving member, the rib 108 on the inside of 
the driven member being located between the tangs 50 and 52, and the cord 
guide 84 resting on the cylindrical portion 115 of the driven member. 
The various elements are kept in place by threaded screw 46 which is 
tightened within bore 44 sufficiently to hold the various members in 
place. The free relative rotations of the core 34, control or driving 
member 66, and third or driven member 98 are provided by making the length 
of cylindrical portion 42 of the core slightly longer than the width of 
cylindrical surface 105 of the driven member. 
The shade roller 22, carrying with it window shade 20, is then placed over 
the cylindrical sleeve 100 of the third or driven member, the shade roller 
being sized to provide a tight friction fit between the driven member and 
the roller, so that as the driven member turns it carries the shade roller 
22 and shade 20 with it. If desired, the shade roller 22 may be cemented 
or otherwise secured to the sleeve 100. Where rollers with larger inside 
diameters are used, molded or fiber bushings (not shown) of a cylindrical 
shape may be used to secure the clutch assembly to the shade roller. It 
should also be noted that the window shade 20 may desirably be somewhat 
longer than the shade roller 22, so that the shade extends to the cord 
guide 84 (see FIG. 4). This allows the shade 20 to extend substantially 
across the full extent of the window. 
The bi-directional clutch functions, when used in a window shade 
environment, such that torque applied to rotate the second, control or 
driving member 66 (the torque being applied by the user pulling on shade 
cord 76), either raises or lowers the window shade 20, by allowing the 
unwrap spring 48 to transmit the motion of the driving member to the third 
or driven member 98. On the other hand, torque applied directly to the 
third or driven member 98, for example, either by the user "tugging" on 
the window shade or by the weight of the shade itself, does not turn the 
driven member and the shade is therefore maintained in position. 
Thus, and as will be explained further by reference to the operation of the 
bi-directional clutch, the first or core member 34 functions as a 
spring-receiving member, the second or control or driving member 66 
functions as a spring-actuating member and the third or driven member 98 
functions as a spring-actuated member, the latter disposed for rotation 
with spring 48. If the spring rotates relative to the core member, the 
driven member also rotates relative to the core; but if the spring is 
locked in place relative to the core, so is the driven member. Since 
rotation of the spring relative to the core member is controlled by the 
spring-actuating driving member, this means that only driving 
member-controlled rotation of the spring transfers rotation to the driven 
member. 
The operation of the bi-directional clutch will be further apparent by 
particular reference to FIGS. 7-9. FIG. 7 illustrates the relative 
positions of cylindrical sleeve portion 68 of the second, control or 
driving member 66, the unwrap spring 48, and the sleeve portion 106 of the 
third or driven member 98 as a force is applied directly to the shade 20 
in the direction of the arrow. This force is applied either by a user 
pulling on the shade or, more probably, by the weight of the shade itself. 
In this situation, the force on the shade tends to rotate the sleeve 
portion 106 (and rib 108) of the driven member in a counterclockwise 
direction (when viewed in FIG. 7). The rib 108 and sleeve portion 106 move 
in this direction until the tang-abutting surface 112 of the rib 108 hits 
the inner or first surface 62 of tang 50. But a force applied to tang 50 
in this direction, i.e., a force applied to the inside surface of the 
tang, causes the helical turns 49 of spring 48 to tighten about stationary 
core 34. Accordingly, as rib 108 reaches tang 50, rotation of the driven 
member in the counterclockwise direction stops and the driven member is 
held in place by the spring--preventing movement of shade 20. (This is 
consistent with the aforesaid explanation that any torque applied directly 
to the third or driven member merely locks the member in place and does 
not allow relative rotation between the driven member and the driving 
member or between the driven member and core 34.) 
When it is desired to raise the shade 20, the shade cord 76 is pulled in a 
direction to cause cylindrical sleeve portion 68 of the control or driving 
member to rotate in a clockwise direction, indicated by the arrow in FIG. 
8. This movement causes the tang-receiving surface 94 of the U-shaped 
channel to hit the outer or second surface 58 of tang 50. But a force 
applied to the outside surface of this tang loosens the spring, allowing 
the spring 48 to rotate relative to core 34 in a clockwise direction (as 
viewed in FIG. 8). As the spring rotates in this direction, the inner 
surface 62 of tang 50 hits the tang-abutting surface 112 of rib 108, 
thereby turning the driven element 98 in the same clockwise direction to 
raise shade 20. The shade continues to be raised as long as the torque 
applied to the driving member 66 rotates it in the clockwise 
direction--driving member-controlled rotation of the spring tang 50 
functioning to transmit motion from the driving member 66 to the driven 
member 98. 
It will be appreciated that the distance between the tang-receiving 
surfaces 94 and 96 of the U-shaped channel 92 should be somewhat greater 
than the distance between tang surfaces 58 and 60 when the spring is 
tightly wound around surface 40 of core 34 to enable tang 50 to move 
toward tang 52, thereby loosening the spring around core 34, without 
surface 60 hitting surface 96, as the driving member is rotated. 
Furthermore, the width of rib 108, i.e., the distance between the 
tang-abutting surfaces 112 and 114, should be narrow enough such that as 
tang 50 moves the rib, the rib does not hit tang 52 (see FIG. 
8--tang-abutting surface 114 of rib 108 must not interfere with tang 52 as 
tang 50 moves the rib in the clockwise direction). 
If the third or driven member 98 did not support a load tending to rotate 
the driven member in a counterclockwise direction, then a torque applied 
to the control or driving member 66 in the counterclockwise direction 
would merely reverse the relative rotation of the tangs, driving and 
driven members. In other words and referring to FIG. 8, the tang-receiving 
surface 96 of the control or driving member would be caused to bear 
against the outer or second surface 60 of tang 52, causing this tang to 
move in a counterclockwise direction; the inner or first surface 64 of the 
tang would then hit the tang-abutting surface 114 of rib 108, causing the 
third or driven member 98 to also rotate in the counterclockwise 
direction; and the spring, driving and driven members would all be rotated 
counterclockwise. 
However, when the bi-directional clutch is used in a shade environment (or 
when a load is applied to the driven member tending to cause it to rotate 
counterclockwise), the weight of the shade must be taken into account as 
torque is applied to the control or driving member to lower the shade. 
This situation is illustrated in FIG. 9 which shows that a force has been 
applied to the control or driving member 66 causing the cylindrical sleeve 
portion 68 to move in the counterclockwise direction, as indicated by the 
arrow. Such rotation causes the tang-receiving surface 96 to move 
counterclockwise hitting the outside surface 60 of spring tang 52. This 
expands the helical turns 49 of the spring, allowing the spring to move 
relative to core 34 in the counterclockwise direction. However, and in 
contrast to the operation in raising the spring discussed as to FIG. 8, 
the weight of the shade (or other similar load applied to the driven 
member 98), causes the tang-abutting surface 112 of rib 108 to continue 
resting against the inner surface 62 of tang 50 since the shade weight is 
exerting a counterclockwise rotational force to the driven member 98. At 
constant angular velocity, tang 50 continues to exert a force on the rib 
108 producing a torque equal to the torque produced by the weight of the 
shade to be supported less any effects due to frictional forces, as spring 
48 rotates counterclockwise. There is therefore no need for the inner 
surface 64 of tang 52 to move rib 108 in the counterclockwise direction to 
rotate driven member 98. Rather, the weight of the shade itself will cause 
a counterclockwise rotation to allow the shade to be pulled down as the 
torque is applied to control or driving member 66 in the counterclockwise 
direction. The mechanism thereby allows controlled descent of shade 20, 
the tang 50 exerting a braking force on rotation of the driven member. Of 
course, if shade 20 is extremely light (or if it is rolled all the way 
onto shade roller 22), the weight of the shade is not a factor and the 
lowering of the shade is substantially the reverse of raising the shade, 
discussed with respect to FIG. 8. 
In order to assure smooth operation of the clutch when lowering the shade, 
it is important (referring to FIG. 9), that the outside surface 60 of tang 
52 remains in contact with the tang-receiving surface 96 of the control or 
driving member. If the weight of the shade can move the spring away from 
the tang-receiving surface, then the clutch will disengage and inhibit 
further motion of the shade until surface 96 again comes in contact with 
the tang and again releases the spring. This will cause a "jerky" motion 
of the shade which is undesirable. 
This separation and resulting jerky motion, can be prevented by insuring 
that the spring grips the core immediately upon the release of pressure 
from the control or driving member. Factors affecting this include: 
(1) the number of turns in the spring; 
(2) the stiffness of the spring wire; 
(3) the coefficient of friction between the spring and core material; and 
(4) the size interference between the inside diameter of the spring and the 
spring-receiving surface 34 of the core. 
Various combinations of the above factors will work satisfactorily, but in 
general, if the clutch is too free, it will jerk when being released under 
load, so a "trade off" must be made between load capacity and ease of 
operation. When the clutch is disengaged, that is, when the control or 
driven member is not in contact with either spring tang, the load is 
entirely supported by the spring tang which is in contact with the driven 
member. If this load is too great, the spring tang will deform or break 
off. An additional benefit can be obtained by adjusting the factors 
mentioned above so that the clutch will intentionally slip at a load 
smaller than that required to damage the spring tangs. 
It should be noted that dynamic loads encountered when the shade is raised 
do not hold the same danger for breaking or deformation of the spring 
tangs, since the tang is merely interposed between the spring receiving 
surface of the control or driving member, and the spring abutting surface 
of the driven member. 
The material used for the core is preferably a glass reinforced plastic 
which gives good wear and relatively consistent friction against the music 
wire spring. For longer wear, a powdered metal core material which is 
hardened and oil impregnated can be used, although the cost is greater 
than that of the reinforced plastic. 
An alternate, second embodiment of the invention is illustrated in FIGS. 10 
and 11. Once again, the clutch includes a first or spring-receiving core 
34 held stationary to a mounting bracket 12. The core 34 receives an 
unwrap spring 48 and a second spring actuating control or driving member 
66. When the bi-directional clutch is utilized in a window shade 
environment, the control or driving member 66 receives a cord 76 which 
travels within a cord channel 78 formed as part of the control or driving 
motor. A cord guide 84 is also provided to help direct the travel of the 
cord 76. Depending on the force applied to cord 76, a torque is applied to 
the control or driving member 66 to rotate third spring-actuated or driven 
member 98, thereby raising or lowering shade 20, the motion of the driving 
member being translated to the driven member by unwrap spring 48. A 
threaded screw 46 maintains the various parts of the bi-directional clutch 
assembly in place. 
The second embodiment differs from the embodiment of the invention shown in 
FIGS. 2, 4 and 7-9, in certain structural features of unwrap spring 48, 
control or driving member 66 and third or driven member 98. In particular, 
the unwrap spring 48 is an "uncrossed" spring having spring tangs 116, 118 
which extend radially outward past the cylindrical circumference of the 
helical spring turns. Tang 116 includes a tang extension 120 which extends 
parallel to the axis of the spring and tang 118 includes a tang extension 
122 which also extends parallel to the longitudinal spring axis. Tang 116 
and its extension define an inner or second tang surface 124 and an outer 
or first tang surface 126; tang 118 and its tang extension define an inner 
or second tang surface 128 and an outer or first tang surface 130. In this 
embodiment, the unwrap spring has tangs which are uncrossed; when viewed 
from the left in FIG. 10 and as indicated in FIG. 11, tang 116 is to the 
left of tang 118. In other words, the distance from one spring tang to the 
other in helical turns is an integer plus more than one-half turn. 
In contrast to the first embodiment, the control or driving member 66 now 
includes a rib element 132, which is adapted to fit between the two tangs 
116, 118, the rib defining tang-receiving surfaces 134 and 136. 
Tang-receiving surface 134 is adapted to hit the inner surface 124 of tang 
116 and tang-receiving surface 136 is adapted to hit the inner surface 128 
of tang 118. Furthermore, the third or driven member 98 now includes a 
U-shaped channel 138 located in the sleeve portion 106 of this member. The 
U-shaped channel has a tang-abutting surface 140 which is adapted to abut 
the outer surface 126 of tang 116 and a tang-abutting surface 142 which is 
adapted to hit the outer surface 130 of tang 118 (see FIG. 11). 
In operation, a torque applied to control element 66 rotates this member in 
either the clockwise or counterclockwise direction relative to stationary 
core 34. If the control or driving member is moved clockwise, rib 132 
eventually hits the inner surface of tang 118, causing the spring to 
unwrap and move clockwise. The outside surface 130 of this tang then hits 
the tang-abutting surface 142 of the driven member, and this causes the 
driven member to likewise move in the clockwise direction to raise the 
shade. When no rotational force is applied to the driving member, the 
weight of the shade tends to cause the driven member to rotate 
counterclockwise, as indicated by the arrow in FIG. 11, but no substantial 
movement of the shade occurs since tang-abutting surface 142 of the driven 
member hits the outer surface 130 of tang 118, thereby locking the spring 
in place and preventing further counterclockwise rotation of the driven 
member. 
In lowering the shade, the torque applied to the driving member 66 causes 
the rib 132 to move counterclockwise, the tang-receiving surface 134 of 
the rib hits the inner surface 124 of tang 116 and spring 48 is loosened 
and is rotated counterclockwise as the driving member continues to turn 
counterclockwise. The shade is lowered since the driven member also moves 
in the counterclockwise direction, but the shade moves in a controlled 
manner since the tang-abutting surface 142 rests against the outer surface 
of tang 118--this tang thereby providing a braking action which allows the 
shade to be lowered in a controlled or non-runaway manner. 
As with the first embodiment, rotation of the driving member in either 
direction loosens the spring and motion is transferred to the driven 
member; similarly, direct rotation of the driven member in either 
direction tightens the spring and locks the driven member. 
It will be appreciated that the present invention provides an improved 
bi-directional clutch which may be formed of a relativley few number of 
pieces and which has tolerances which can easily be achieved in the 
manufacturing process and maintained while the clutch is in use. By 
utilizing a rib and a U-shaped channel, either as part of the control or 
driving member or the driven member, and by utilizing an unwrap spring 
having tangs which extend outwardly past the circumference of the turns of 
the spring, problems with tolerances and increased manufacturing costs due 
to complicated parts are substantially reduced, if not eliminated. Thus by 
utilizing such an unwrap spring, problems in aligning the ends of the 
spring or in fitting the spring into slots or other apertures are 
eliminated. Moreover, by forming the spring tangs with tang-extensions, 
the surface area of the tangs is increased in the area where the tangs hit 
either the control or driving member or the driven member, and this 
reduces the pressure of the tangs on the tang-abutting and tang-receiving 
surfaces and enables the spring to efficiently transmit motion from the 
driving member to the driven member or to lock the driven member in place, 
as the case may be. 
It will also be appreciated that numerous modifications may be possible in 
light of the above teachings. For example, the core member could be 
disposed around the outside of the unwrap spring such that the spring 
normally grips the "core" (the tangs of the spring extending radially 
inward from the helical turns) and the control member could cause the 
spring to contract thereby allowing the spring to rotate relative to the 
core to transfer motion to the driven member. 
Accordingly, the above description is by way of example only, and 
modifications, changes and the like are contemplated within the scope of 
the invention which is set forth in the following claims.