Window Shade Having a Resistance Balancing Mechanism

Abstract

A window shade comprises first and second rails, and a shading structure and a suspension cord connected between the first and second rails. The second rail includes a resistance balancing unit and a cord winding unit to which the suspension cord respectively connects. The resistance balancing unit comprises a housing having an abuttal surface, a pulley pivotally connected with the housing, and a torsion spring. The pulley has a winding portion around which the suspension cord is wrapped, and a shaft portion extending coaxial to the winding portion from a side thereof. The torsion spring is tightly mounted around the shaft portion and has at least one end. The pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow rotation of the pulley relative to the torsion spring.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to Taiwan Patent Application No. 100127779 filed on Aug. 4, 2011.

BACKGROUND

1. Field of the Invention

The present invention relates to window shades.

2. Description of the Related Art

Many types of window shades are currently available on the market, such as Venetian blinds, roller shades and honeycomb shades. The shade when lowered can cover the area of the window frame, which can reduce the amount of light entering the room through the window and provided increased privacy. A typical window shade can include a top rail, a bottom rail, a shading panel and a drive mechanism. The bottom rail is usually connected with a lower end of the shading panel, whereas the drive mechanism is assembled in the top rail. The drive mechanism can include a winding drum, and an operating cord extending outside the top rail. A user can actuate the operating cord to drive rotation of the winding drum, which can raise or lower the shading panel.

While the use of the operating cord may be convenient for an adult, there is the risk that children strangle on the operating cords.

Therefore, there is a need for a window shade that is convenient to operate, safer in use and address at least the foregoing issues.

SUMMARY

The present application describes a window shade having a resistance balancing unit that can be adjusted by raising or lowering an elongated rail.

In one embodiment, the resistance balancing unit comprises a housing having an abuttal surface, a pulley pivotally assembled with the housing, and a torsion spring. The pulley has a winding portion around which a suspension cord is wrapped, and a shaft portion extending coaxial from a side of the winding portion. The torsion spring is tightly mounted around the shaft portion and has at least one end, wherein the pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow the pulley to rotate relative to the torsion spring.

In another embodiment, a window shade is described. The window shade comprises a first rail, a second rail, a shading structure disposed between the first rail and the second rail, and at least a suspension cord connected between the first and second rails. The second rail includes a resistance balancing unit and a cord winding unit, the suspension cord respectively connecting with the resistance balancing unit and the cord winding unit. The resistance balancing unit comprises a housing having an abuttal surface, a pulley pivotally connected with the housing, and a torsion spring. The pulley has a winding portion around which a suspension cord is wrapped, and a shaft portion extending coaxial from a side of the winding portion. The torsion spring is tightly mounted around the shaft portion and has at least one end, wherein the pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow the pulley to rotate relative to the torsion spring.

At least one advantage of the window shades described herein is the ability to conveniently adjust the shade by raising and lowering the lower rail. Moreover, the assembly of the resistance balancing unit in the window shade can allow to accurately hold the shading structure at any height.

The foregoing is a summary and shall not be construed to limit the scope of the claims. The operations and structures disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the invention, as defined solely by the claims, are described in the non-limiting detailed description set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an embodiment of a window shade in a downwardly deployed stage;

FIG. 2 is a schematic view illustrating the window shade in an upwardly retracting stage;

FIG. 3 is a perspective view of a resistance balancing unit assembled in the window shade shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along section C1 shown in FIG. 3;

FIG. 5 is a cross-sectional view taken along section C2 shown in FIG. 3;

FIG. 6 is a bottom view of the resistance balancing unit;

FIG. 7 is a front view illustrating a cord winding unit assembled in the window shade shown in FIG. 1;

FIG. 8 is a top view of the cord winding unit shown in FIG. 7;

FIG. 9 is a partial cross-sectional view of the cord winding unit;

FIG. 10 is a perspective view of the resistance balancing unit as the second rail is adjusted toward the first rail;

FIG. 11 is a cross-sectional view taken along section C1 shown in FIG. 10;

FIG. 12 is a cross-sectional view taken along section C2 shown in FIG. 10;

FIG. 13 is a schematic view illustrating another embodiment of a control module associating a resistance balancing unit with a cord winding unit;

FIG. 14 is a schematic view detailing the construction of the cord winding unit shown in FIG. 13;

FIG. 15 is a schematic view illustrating a window shade provided with the resistance balancing unit and the cord winding unit shown in FIG. 13;

FIG. 16 is a schematic view illustrating the window shade shown in FIG. 15 adjusted upward;

FIG. 17 is a cross-sectional view illustrating another embodiment of a resistance balancing unit;

FIG. 18 is a bottom view of the resistance balancing unit shown in FIG. 17; and

FIG. 19 is a schematic view illustrating another variant embodiment of a resistance balancing unit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 1 and 2 are schematic views illustrating one embodiment of a hand-pull type window shade 100. More particularly, FIG. 1 shows the window shade 100 in a downwardly deployed state, and FIG. 2 shows the window shade 100 in an upwardly retracting state. The window shade 100 can include a first rail 102, a second rail 104, a shading structure 106, suspension cords 108, resistance balancing units 110 and a cord winding unit 112. The shading structure 106 can have upper and lower ends respectively affixed with the first rail 102 and the second rail 104. The resistance balancing units 110 and the cord winding unit 112 can be respectively installed in the second rail 104. In one embodiment, two resistance balancing units 110 and one cord winding unit 112 can be provided to form a control module of the window shade 100, the cord winding unit 112 being installed between and spaced apart from the two resistance balancing units 110. Each of the suspension cords 108 can have a first end fixedly attached with the first rail 102, and an opposite second portion respectively passing through the resistance balancing units 110 and connected with the cord winding unit 112. The cord winding unit 112 can have a spring-driven mechanism that can be operable to wind the suspension cords 108 when the second rail 104 rises. Once the second rail 104 reaches and is released at a desired height, all of the applied forces including the spring force from the cord winding unit 112, the weights of the shading structure 106 and the second rail 104, and internal friction forces (including the resistive force generated by the resistance balancing unit 110), can be balanced to create an equilibrium condition. As a result, the second rail 104 can be held stationary at the desired height.

In one embodiment, the first rail 102 can be affixed with a top portion of a window opening frame, and the second rail 104 provided with the resistance balancing units 110 and the cord winding unit 112 can be suspended vertically from the first rail 102. In alternate embodiments, the positions of the first and second rails can also be interchanged: the second rail 104 provided with the resistance balancing units 110 and the cord winding unit 112 can be affixed with a top portion of a window opening frame, whereas the first rail 102 can be suspended vertically from the second rail 104.

Referring again to FIGS. 1 and 2, the shading structure 106 can be made of a fabric material, e.g., honeycomb structure formed from a fabric material. In alternate embodiments, the shading structure 106 can also have other types of constructions, e.g., slats, shading rows, etc.

FIG. 3 is a perspective view of the resistance balancing unit 110, FIG. 4 is a cross-sectional view taken along section C1 shown in FIG. 3, FIG. 5 is a cross-sectional view taken along section C2 shown in FIG. 3, and FIG. 6 is a bottom view of the resistance balancing unit 110. As shown in FIGS. 3-6, the resistance balancing unit 110 can include a housing 114, a pulley 116, a torsion spring 118 and a movable blade 120. The housing 114 can have a generally rectangular shape, including a first face 114A and a second face 114B. In the illustrated embodiment, the first face 114A and the second face 114B can be exemplary perpendicular to each other. The first face 114A can have a hole 122. The second face 114B can be formed with a slotted window 124 where the blade 120 is movably assembled, and a slit 126 can be defined between the blade 120 and a side edge 124A of the window 124 for passage of the suspension cord 108.

Moreover, an interior of the housing 114 can define a first receiving space 128A and a second receiving space 128B that are at least partially separated from each other by a sidewall 130. The first receiving space 128A can respectively communicate with the hole 122 and the slit 126.

The pulley 116 can include a winding portion 116A and a shaft extension 116B. The shaft extension 116B can project from a side of the winding portion 116A along a same axis of rotation. In one embodiment, the winding portion 116A and the shaft extension 116B can be formed integrally with the pulley 116. When the pulley 116 is pivotally assembled with the housing 114, the winding portion 116A can be placed in the first receiving space 128A, and the shaft extension 116B can pass through an opening of the sidewall 130 and be disposed in the second receiving space 128B. Accordingly, when the pulley 116 rotates relative to the housing 114, the winding portion 116A and the shaft extension 116B can rotate in unison about a same axis.

The torsion spring 118 can be tightly mounted on an outer peripheral surface of the shaft extension 116B. In one embodiment, the torsion spring 118 can be exemplary a bidirectional torsion spring. Two protruding ends 118A and 118B of the torsion spring 118 can be respectively disposed adjacent to two abuttal surfaces 132 of the housing 114 adjacent to the second receiving space 128B.

The suspension cord 108 can travel into the first receiving space 128A through the hole 122 of the first face 114A, wrap about one and half turn around the winding portion 116A, and extend outside the housing 114 via the slit 126 on the second face 114B. Accordingly, a first portion 108A of the suspension cord 108 outwardly adjacent to the first face 114A can be substantially perpendicular to a second portion 108B of the suspension cord 108 outwardly adjacent to the second face 114B. Moreover, owing to the pressure applied by the blade 120, the second portion 108B of the suspension cord 108 passing through the slit 126 can be kept in contact with the blade 120 and the side edge 124A of the window 124. It is worth noting that because the suspension cord 108 can be wrapped several turns around the pulley 116 (in particular at least one or more turn), the contact area between the suspension cord 108 and the pulley 116 can be increased, which can create suitable frictional resistance to balance other forces exerted on the second rail 104. As a result, the second rail 104 can be kept stationary at any height in a stable manner.

FIGS. 7 and 8 are respectively front and top views illustrating the cord winding unit 112, and FIG. 9 is a partial cross-sectional view of the cord winding unit 112. The cord winding unit 112 can include a casing 140, two winding drums 142, two coil springs 143 and two guide rollers 144. Two opposite sides of the casing 140 can respectively include openings 146 and 148 for the passage of the two suspension cords 108. The two guide rollers 144 can be movably assembled with two shaft portions 145 adjacent to the openings 146 and 148, respectively. Accordingly, each guide roller 144 can slide along the associated shaft portion 145.

Each of the winding drums 142 can be pivotally connected with the casing 140. An upper end of each winding drum 142 can be affixed with a gear 150. The pivot axes of the winding drums 142 can be parallel to the shaft portions 145, and substantially perpendicular to the pivot axis of the pulley 116. Moreover, the casing 140 can also be pivotally connected with a pivot shaft 152 disposed between the two winding drums 142. The pivot shaft 152 can be substantially parallel to the pivot axes of the winding drums 142, and can have an upper end affixed with a transmission gear 154. The transmission gear 154 can be respectively engaged with the gears 150 of the winding drums 142, whereby the winding drums 142 can rotate in unison to concurrently wind or unwind the suspension cords 108.

Pressing arms 156 can be respectively mounted adjacent to the winding drums 142, and can act to ensure that the suspension cords 108 are wound tightly around the winding drums 142. Each of the pressing arms 156 can have a first end pivotally connected with the casing 140, and a second end that presses the corresponding suspension cord 108 against the surface of the winding drum 142. As each suspension cord 108 progressively winds around the associated winding drum 142, the pressing arm 156 can pivotally displace for adjustment.

As shown in FIG. 9, the coiled springs 143 can be respectively assembled in the winding drums 142. Each of the coiled springs 143 can have a first end anchored with the casing 140, and a second end connected with the associated winding drum 142. The coiled springs 143 can respectively bias the winding drums 142 to rotate in directions for winding the suspension cords 108.

When the cord winding unit 112 is assembled, the two suspension cords 108 can respectively travel into the casing 140 via the openings 146 and 148, wrap around the two guide rollers 144, and then connect and wind on the two winding drums 142. Biased by the coiled springs 143, the winding drums 142 can rotate to wind the suspension cords 108. While the winding drums 142 are winding the suspension cords 108, the guide rollers 144 can respectively slide along the shaft portions 145 so that the suspension cords 108 can be respectively wound in turns uniformly distributed on the surfaces of the winding drums 142.

Exemplary operation of the window shade 100 is described hereafter with reference to FIGS. 1-11. First referring to FIGS. 1 and 3-9, the second rail 104 can be pulled downward in a direction F1 (i.e., in a direction that increases the distance between the first rail 102 and the second rail 104), which causes each suspension cord 108 to unwind from the associated winding drum 142 and drives the winding drum 142 in rotation. As it unwinds from the winding drum 142, the suspension cord 108 can drive the pulley 116 to rotate in a direction (e.g., in the anticlockwise direction shown in FIG. 5) to push the end 118A of the torsion spring 118 against the abuttal surface 132. As a result, the torsion spring 118 initially in a tightened state can loosen to permit rotation of the pulley 116 relative to the torsion spring 118. Accordingly, the length of the suspension cords 108 between the first and second rails 102 and 104 can progressively increase.

When the user stops pulling the second rail 104 downward (i.e., the first and second rails 102 and 104 are stationary), each torsion spring 118 can recover a tightened state on the associated pulley 116. As a result, the pulleys 116 no longer rotate, and a frictional resistance can be created owing to the wrapping of the suspension cords 108 around the pulleys 116. Accordingly, the spring forces exerted by the coiled springs 143 on the winding drums 142 can counterbalance the weight applied on the second rail 104, the resistance generated by the resistance balancing units 110, and other internal frictional forces to stop the winding drums 142. Owing to the balance of all the forces applied thereon, the second rail 104 can be kept stationary at the desired position in a stable manner.

As shown in FIG. 2, when the second rail 104 is moved upward in a direction F2 (i.e., in the direction that reduces the distance between the first and second rails 102 and 104), the portions of the suspension cords 108 between the first and second rails 102 and 104 can become loose (i.e., forming a slack). As a result, the winding drums 142 of the cord winding unit 112 can reversely rotate to wind the suspension cords 108.

In conjunction with FIG. 2, FIGS. 10-12 are schematic views illustrating intermediary stages of the resistance balancing unit 110 during an upward displacement of the second rail 104. More particularly, FIG. 10 is a perspective view of the resistance balancing unit 110, FIG. 11 is a cross-sectional view taken along section C1 shown in FIG. 10, and FIG. 12 is a cross-sectional view taken along section C2 shown in FIG. 10. As the winding drum 142 is winding the suspension cord 108, the pressure from the blade 120 can keep the portion of the suspension cord 108 that is located between the resistance balancing unit 110 and the cord winding unit 112 in a tensioned state. Accordingly, the suspension cord 108 can smoothly slip around the pulley 116, and be wound around the winding drum 142 without being interlaced. The length of the suspension cords 108 between the first and second rails 102 and 104 thus can progressively shorten.

When the user stops moving the second rail 104 upward, each torsion spring 118 can recover a tightened state on the associated pulley 116. As a result, each of the pulleys 116 is stopped, and a frictional resistance is created owing to an increased contact area between the suspension cord 108 and the pulley 116. Accordingly, the spring forces exerted by the coiled springs 143 on the winding drums 142 can counterbalance the weight applied on the second rail 104, the resistance generated by the resistance balancing units 110 and other internal frictional forces to stop the winding drums 142. Owing to the balance of all the forces applied thereon, the second rail 104 can be kept stationary at the desired position in a stable manner.

With the aforementioned construction, the second rail 104 can be held stationary at any position. Even if the second rail 104 is adjusted to reach a limit of the working range of the coiled springs 143, the resistance balancing units 110 can still create proper resistance that can balance the spring force of the cord winding unit 112 such that the operation of the window shade 100 can be facilitated, and the second rail 104 kept be stationary in an equilibrium condition at any heights. Aside the aforementioned embodiments, the resistance balancing unit can also be associated with other constructions of the cord winding unit.

FIG. 13 is a schematic view illustrating another embodiment associating a resistance balancing unit 210 with a cord winding unit 212, and FIG. 14 is a schematic view detailing the construction of the cord winding unit 212. As shown in FIG. 13, the resistance balancing unit 210 can be associated with the cord winding unit 212 to form a control module. The resistance balancing unit 210 can be similar in construction to the resistance balancing unit 110 of the previous embodiment, including a housing 214, a rotary pulley 216 and a torsion spring 218. The pulley 216 can be pivotally assembled with the housing 214, and can include a winding portion 216A and a shaft extension 216B. The shaft extension 216B can project from a side of the winding portion 216A along a same axis of rotation.

The torsion spring 218 can be tightly mounted on an outer peripheral surface of the shaft extension 216B. Two protruding ends 218A and 218B of the torsion spring 218 can be respectively disposed adjacent to two abuttal surfaces 232 of the housing 214.

The suspension cord 108 can enter the resistance balancing unit 210 from a first face thereof, wrap about one and half turn around the winding portion 216A, and extend outward from a second face of the resistance balancing unit 210. Accordingly, a first portion of the suspension cord 108 outwardly adjacent to the first face of the resistance balancing unit 210 can extend in a direction different from a second portion of the suspension cord 108 outwardly adjacent to the second face of the resistance balancing unit 210.

Referring to FIGS. 13 and 14, the cord winding unit 212 can include a casing 240. A side of the casing 240 can be provided with an extending plate 240A for affixing the resistance balancing unit 210. The suspension cord 108 can pass through the resistance balancing unit 210, and then travel into the casing 240 via a hole 242 to connect with one or more part inside the cord winding unit 212.

As shown in FIG. 14, the cord winding unit 212 can include a winding drum 244 and a coiled spring 246 mounted inside the casing 240. A side of the winding drum 244 can be connected with a hollow shaft portion 248. The winding drum 244 and the shaft portion 248 can be formed integral in a single body, or can be separate parts assembled together. The casing 240 can have an interior in which are defined a first receiving space 240B and a second receiving space 240C. The winding drum 244 can be disposed in the first receiving space 240B, and the shaft portion 248 can be disposed in the second receiving space 240C, such that the winding drum 244 and the shaft portion 248 can rotate about a same axis relative to the casing 240. Moreover, when the cord winding unit 212 is assembled with a window shade, a transmission axle 310 (shown with dotted lines) can pass through the winding drum 244 and the shaft portion 248, whereby multiple cord winding units can be driven concurrently via the transmission axle 310.

The coiled spring 246 can be installed around the shaft portion 248 in the second receiving space 240C. The coiled spring 246 can have a first end connected with the shaft portion 248, and a second end connected with the casing 240.

The suspension cord 108 can travel through the hole 242, and extend into the first receiving space 240B to connect with the winding drum 244. The winding drum 244 can be biased in rotation by the coiled spring 246 for winding the suspension cord 108.

In conjunction with FIGS. 13 and 14, FIG. 15 is a schematic view illustrating a window shade 300 provided with the resistance balancing unit 210 and the cord winding unit 212. The window shade 300 can include a first rail 302, a second rail 304 provided with the resistance balancing unit 210 and the cord winding unit 212, and a shading structure 306 connected between the first and second rails 302 and 304. The second rail 304 can be affixed with a top of a window frame, and the first rail 302 can be suspended vertically from the second rail 304.

The second rail 304 can include a transmission axle 310, and a plurality of resistance balancing units 210 and cord winding units 212. The transmission axle 310 can be assembled through the casing 240, the shaft portion 248 and the winding drum 244 of each cord winding unit 212, and thereby define a same axis of rotation about which the shaft portions 248 and the winding drums 244 of the cord winding units 212 can rotate in unison.

The suspension cords 108 (shown with dotted lines) can be respectively connected between the cord winding units 212 and the first rail 302. More specifically, each of the suspension cords 108 can have a first end connected with the winding drum 244 of one cord winding unit 212, and a second end securely affixed with the first rail 302.

Like the embodiments previously described, when the first rail 302 is lowered, each suspension cord 108 can unwind from the associated winding drum 244 which is driven in rotation. As it unwinds from the winding drum 244, the suspension cord 108 can drive the pulley 216 in rotation, which causes the end 218A of the torsion spring 218 to push against the abuttal surface 232. As a result, the torsion spring 218 previously in a tightened state can loosen, such that the pulley 216 can rotate relative to the torsion spring 218. When the user stops lowering the first rail 302, the torsion spring 218 can recover its tightened state on the pulley 216. As a result, the pulley 216 no longer rotates, and the increased contact area between the suspension cord 108 and the pulley 216 can create frictional resistance. Accordingly, the total spring force exerted by the coiled springs 246 on the winding drums 244 can counterbalance the weight applied on the first rail 302, the resistance created by the resistance balancing units 210, and frictional forces exerted by other internal parts. The winding drums 244 can thereby stop rotating, and the first rail 302 can be sustained at the desired height in equilibrium.

As shown in FIG. 16, when the first rail 302 is raised, the suspension cords 108 between the first rail 302 and the second rail 304 can become loose (i.e., form a slack). Accordingly, the winding drum 244 of each cord winding unit 212 can reversely rotate to wind the associated suspension cord 108. When the user stops raising the first rail 302, the torsion springs 218 can respectively tighten on the pulleys 216. As a result, each of the pulleys 216 can stop rotating, and the increased contact area between each suspension cord 108 and the associated pulley 216 can create frictional resistance. Accordingly, the total spring force exerted by the coiled springs 246 on the winding drums 244 can counterbalance the weight applied on the first rail 302, the resistance created by the resistance balancing units 210, and frictional forces exerted by other internal parts. The winding drums 244 can thereby stop rotating, and the first rail 302 can be sustained at the desired height in equilibrium.

The resistance balancing units described previously can also be implemented with other constructions. For example, while the resistance balancing unit has been described as using a bidirectional torsion spring, other embodiments of the resistance balancing unit can also use a unidirectional torsion spring. A variant embodiment of the resistance balancing unit is exemplary described hereafter with reference to FIGS. 17 and 18.

FIG. 17 is a cross-sectional view illustrating another construction of a resistance balancing unit 410, and FIG. 18 is a bottom view of the resistance balancing unit 410. The resistance balancing unit 410 can be similar to the previous embodiment in construction, including a housing 414, a pulley 416, a torsion spring 418 and a movable blade 420. The pulley 416 can be pivotally assembled with the housing 414, and can include a winding portion 416A and a shaft extension 416B. The shaft extension 416B can project from a side of the winding portion 416A along a same axis of rotation. The torsion spring 418 can be a unidirectional torsion spring having an end 418A. The torsion spring 418 can be tightly mounted on an outer peripheral surface of the shaft extension 416B, and the end 418A can be anchored with the housing 414. The suspension cord 108 can enter the resistance balancing unit 410 from a first face 414A, wrap about one and half turn around the winding portion 416A, travel past the blade 420, and extend outward from a second face 414B of the resistance balancing unit 410.

The operation of the resistance balancing unit 410 can be similar to the previous embodiments. When the second rail (i.e., the rail suspended from the first rail) is lowered, each stretched suspension cord 108 can drive rotation of the associated pulley 416, which causes the torsion spring 418 previously tightening on the pulley 416 to loosen. Accordingly, the pulleys 416 can respectively rotate relative to the torsion springs 418, and the suspension cords 108 extending between the first and second rails can lengthen. When the user stops lowering the second rail (i.e., the first and second rails become stationary), the torsion springs 418 can respectively tighten on the pulleys 416. As a result, the pulleys 416 stop rotating, and the wrap of the suspension cords 108 around the pulleys 416 can create frictional resistance, which can act to balance all of the forces exerted on the second rail. Accordingly, the second rail can be sustained at the desired position in equilibrium.

While the aforementioned embodiment has the resistance balancing unit arranged at a turn position of the suspension cord 108, it will be appreciated that the resistance balancing unit can also be used at other locations. For example, as shown in FIG. 19, the suspension cord 108 can turn around the a pulley 502, enter the resistance balancing unit 510 from a first face 514A thereof, wrap about one turn around the pulley 516, travel past the movable blade 520, exit the resistance balancing unit 510 via a second face 514B thereof, and then connect with the cord winding unit 112/212. Like previously described, the resistance balancing unit 510 can include a torsion spring tightly mounted around the pulley 516 (not shown). The second side 514B and the first side 514A can be substantially parallel to each other, such that the portions of the suspension cord 108 respectively entering and exiting the resistance balancing unit 510 can be parallel to a same direction.

The window shades described herein do not have any operating cords, and can be conveniently adjusted by raising and lowering the lower rail. Accordingly, the risk of children strangling on operating cords from the window shade can be prevented. Moreover, the assembly of the resistance balancing unit can allow to accurately hold the shading structure in equilibrium at any heights.

Realizations in accordance with the present invention therefore have been described only in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the invention as defined in the claims that follow.

Claims

1. A resistance balancing unit suitable for use with a window shade, comprising: a housing having an abuttal surface;a pulley pivotally assembled with the housing, the pulley having a winding portion around which a suspension cord is wrapped, and a shaft portion extending coaxial from a side of the winding portion; anda torsion spring tightly mounted around the shaft portion and having at least one end, wherein the pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow the pulley to rotate relative to the torsion spring.

2. The resistance balancing unit according to claim 1, wherein the housing has a first face and a second face, the suspension cord entering the housing from the first face, wrapping around the winding portion, and extending outside the housing from the second face.

3. The resistance balancing unit according to claim 2, wherein the first face and the second face are substantially perpendicular to each other.

4. The resistance balancing unit according to claim 2, wherein the first face and the second face are substantially parallel to each other.

5. The resistance balancing unit according to claim 2, wherein the housing includes a blade assembled at the second face, the blade and an edge of the housing defining a slit for passage of the suspension cord.

6. The resistance balancing unit according to claim 5, wherein the blade is movably assembled with the housing, and is operable to press against the suspension cord.

7. The resistance balancing unit according to claim 1, wherein the suspension cord wraps around the pulley about one or more turn.

8. A window shade comprising: a first rail;a second rail;a shading structure disposed between the first rail and the second rail; andat least a suspension cord connected between the first and second rails;wherein the second rail includes a resistance balancing unit and a cord winding unit, the suspension cord respectively connecting with the resistance balancing unit and the cord winding unit, the resistance balancing unit comprising: a housing having an abuttal surface;a pulley pivotally connected with the housing, the pulley having a winding portion around which a suspension cord is wrapped, and a shaft portion extending coaxial from a side of the winding portion; anda torsion spring tightly mounted around the shaft portion and having at least one end, wherein the pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow the pulley to rotate relative to the torsion spring.

9. The window shade according to claim 8, wherein the housing has a first face and a second face, the suspension cord enters the housing from the first face, wraps around the winding portion, and extends outside the housing via the second face.

10. The window shade according to claim 9, wherein the first face and the second face are substantially perpendicular to each other.

11. The window shade according to claim 9, wherein the first face and the second face are substantially parallel to each other.

12. The window shade according to claim 9, wherein the housing includes a blade assembled at the second face, the blade and an edge of the housing defining a slit for passage of the suspension cord.

13. The window shade according to claim 12, wherein the blade is movably assembled with the housing, and is operable to press against the suspension cord.

14. The window shade according to claim 8, wherein the suspension cord wraps around the pulley about one or more turn.

15. The window shade according to claim 8, wherein an adjustment that increases a distance between the first and second rails causes the suspension cord to unwind from the cord winding unit and drives the pulley in rotation, which results in the end of the torsion spring to push against the abuttal surface, whereby the torsion spring is loosened and the pulley is allowed to rotate relative to the torsion spring.

16. The window shade according to claim 8, wherein an adjustment that reduces a distance between the first and second rails causes the suspension cord between the first and second rails to become loose, which results in the cord winding unit to wind the suspension cord under a spring force.

17. The window shade according to claim 8, wherein the torsion spring recovers a tightened state on the pulley to stop the pulley when the first and second rails are stationary.

18. The window shade according to claim 8, wherein the resistance balancing unit is spaced apart from the cord winding unit.

19. The window shade according to claim 8, wherein the cord winding unit includes a casing, a winding drum, a coiled spring connected with the winding drum, and a guide roller movable along a shaft portion, the guide roller sliding along the shaft portion to facilitate uniform winding of the suspension cord on the winding drum during an adjustment that reduces a distance between the first and second rails.