WO2012149125A2

WO2012149125A2 - Wrap spring device

Info

Publication number: WO2012149125A2
Application number: PCT/US2012/035151
Authority: WO
Inventors: Michael F. Leone
Original assignee: Thomson Industries, Inc.
Priority date: 2011-04-29
Filing date: 2012-04-26
Publication date: 2012-11-01
Also published as: WO2012149125A3

Abstract

A wrap spring device (40) including an improved interface between an output hub (60) and a load carrying helical spring (66). At least an end portion of the spring is disposed in a circumferential groove (70) formed in the output hub, and an end of the spring is formed into an axially extending tang (62) which is disposed in an axially extending tang slot (74) of the hub. In a relaxed state, the inside diameter of the end portion of the spring is smaller than an outside diameter of the circumferential groove in order to provide an interference fit there between. The tang slot has a profile configured to cooperatively engage an entire opposed surface of the axially extending tang.

Description

WRAP SPRING DEVICE

This application claims benefit of the 29 April 2011 filing date of United States provisional patent application number 61/480,741.

FIELD OF THE INVENTION

This invention relates generally to the field of wrap spring clutches and brakes.

BACKGROUND OF THE INVENTION

Wrap spring mechanisms are well known in the art for use as a clutch or brake for selective interconnection of a rotating input element with a rotatable output element (clutch) or for selective interconnection of the output element with a fixed element (brake). Such devices include those described in United States Patents 5,090,530 and 5,967,274. A variety of such clutches and brakes are sold under the trademark Deltran^® by Thomson Industries, Inc. FIG. 1 is an exploded view of the internal working components of one such device which is commercially identified as a Standard CB-6 Clutch/Brake.

The clutch/brake device 20 of FIG. 1 operates as a clutch to control the rotation of an output hub or assembly 6 relative to a rotating input hub 2 about an axis of rotation A, and it operates as a brake to control the rotation of the output assembly 6 relative to a brake hub 9. The input hub 2 may be attached by bolts to an input driver such as a pulley, sheave or sprocket (not shown) and the output assembly 6 may be journaled for rotation with a shaft of a driven device (not shown). The brake hub 9 is attached by fasteners 12 to a plate assembly 10, which in turn is affixed to an appropriate mounting structure (not shown).

The clutch function of the device 20 is accomplished by controlling the selective interconnection of the input hub 2 to the output assembly 6 through drive spring 4. When the device 20 is assembled, drive spring 4 has an output end 4_0Ut disposed around a central portion 18 of output assembly 6 with its radially inwardly extending tang (hidden from view in FIG. 1) extending into down tang hole 19 of output assembly 6, thereby causing drive spring 4 and output assembly 6 to rotate together. The drive 1

spring 4 also has an input end 4_in disposed around a hub end 21 of input hub 2. In its relaxed state, drive spring 4 has an inside diameter than is somewhat smaller than an outside diameter of both the input hub end 21 and the output assembly central portion 18 such that the drive spring 4 is normally contracted tightly around both of those components to transmit torque and rotational motion there between in a clutch engaged condition. The drive spring 4 also has a radially outwardly extending tang 22 which engages a notch 24 formed in an end of a control collar 3 which is disposed around the drive spring 4. Thus, in the clutch engaged condition with the drive spring 4 relaxed, the control collar 3 rotates together with the input hub 2 and the output assembly 6.

To disengage the clutch, rotation of the control collar 3 is stopped, such that the continued inertia-driven rotation of the output assembly 6 and any driven device connected thereto causes rotation of the output end 4_0Ut of the drive spring 4 relative to the input end 4_in, thereby unwrapping the spring and causing it to release one or both of the input hub 2 and output assembly 6 so that the input hub 2 may rotate independently of the output assembly 6. The rotation of the control collar 3 is stopped by the activation of a coil assembly 13, causing movement of pawl 26 into the path of a notch 28 formed on an exterior surface of the control collar 3.

The brake function of the device 20 is accomplished in a somewhat similar manner by selectively engaging output assembly 6 with brake hub 9 through brake spring 8. The brake spring 8 is disposed around the central portion 18 of output assembly 6. The brake spring 8 in its relaxed state has an inside diameter that is slightly larger than an outside diameter of the cooperating central portion 18 of output assembly 6; however, the brake spring 8 includes an inwardly extending tang 30 which extends into down tang hole 32 of the output assembly 6, thereby causing the brake spring 8 to rotate with the output assembly 6. The brake spring 8 is also disposed around the brake hub 9, and in its relaxed condition has an inside diameter that is somewhat larger than an outside diameter of the cooperating end 33 of the brake hub 9 so that it is free to rotate independently of the brake hub 9 in the clutch engaged condition. The brake spring 8 also includes an outwardly extending tang 34 which is engaged with a notch 36 formed in an end of control collar 3. Control collar 3 is disposed around brake spring 8 as well as the previously described drive spring 4. When the pawl 26 is activated by the coil assembly 13 to engage and stop the rotation of the control collar 3 to place the clutch into the disengaged condition, the continued inertia driven rotation of the output assembly 6 causes relative rotation between the two tangs 30, 34 of the brake spring 8, thereby causing the brake spring 8 to wrap down onto both the output assembly 6 and brake hub 9. Since the brake hub 9 is attached to the stationary plate assembly 10, the rotation of the output assembly 6 and any device attached thereto is stopped with the clutch in the disengaged condition.

Other elements and functions of the device 20 of FIG. 1 are known in the art and are not described further herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the drawings that show:

FIG. 1 is an exploded perspective illustration of the interior working component parts of a prior art wrap spring clutch/brake device.

FIG. 2 is an improved wrap spring clutch/brake.

FIG. 3A is a side view of a step wound helical spring including a radially outwardly extending control tang and an axially extending output hub tang.

FIG. 3B is an end view of the spring of FIG. 3A.

FIG. 4 is a perspective view of an output hub of a clutch/brake device showing axially extending output hub tangs of a drive spring and a brake spring.

DETAILED DESCRIPTION OF THE INVENTION

A Standard CB-6 clutch/brake as discussed above is rated for operation at 500 rpm. The present inventor desires to operate such a device at speeds of 750 rpm or more. To do so, larger component parts may be used with a similar design in order to carry the expected higher mechanical loads, but a larger size device may not be useful in many applications. Alternatively, stronger materials may be used, but higher strength materials tend to be more expensive, and cost is an important constraint for most wrap spring device applications. Not satisfied with these alternatives, the present inventor has innovatively developed a wrap spring device which is comparable in size and material selection to the prior art design, but which is capable of reliable operation at significantly higher speeds and mechanical loadings. This is accomplished by providing an interface between the wrap spring and a cooperating hub which is able to transmit torque loads with reduced component stress levels when compared to prior art devices. One embodiment of the present invention is shown in FIG. 2, which is a wrap spring clutch/brake device 40 that is similar to the clutch/brake device 20 of FIG. 1 , but that has an improved spring / output assembly combination. One will appreciate from the following description that the present invention may be embodied as a clutch, as a brake, or as a clutch/brake device.

FIGs. 3A and 3B illustrate side and end views respectively of a helical spring 50 which may be used as a drive spring (clutch embodiments) or brake spring (brake embodiments) in the wrap spring device 40. While spring 50 may be formed of the same type of wire used for the drive spring 4 or brake spring 8 of the prior art device 20 of FIG. 1 , spring 50 is step wound; i.e. it has two distinct inside diameter dimensions in its relaxed condition. In the illustrated embodiment, a smaller diameter portion 52 includes about 4 wraps and a larger diameter portion 54 includes about 11 wraps, with about a one wrap transition there between. The spring 50 also includes an outwardly extending control tang 56 and an axially extending output hub tang 58. The larger diameter portion 54 fits over the input hub (clutch embodiments) or the brake hub (brake embodiments) in a manner similar to the prior art device 20 of FIG. 1.

Furthermore, the control tang 56 engages a control collar similar to the control collar 3 of FIG. 1 to control disengagement of the clutch (clutch embodiments) or engagement of the brake (brake embodiments). In contrast to the prior art, the axially extending output hub tang 58 interfaces with a cooperating improved output assembly or hub, which is described more fully below, and the smaller diameter portion 52 of the spring 50 is sized to fit onto the output hub with an interference fit in its relaxed condition. In one embodiment, the interference may be .130" on the brake side of the output hub 6 and .180" on the drive side of the output hub 6. The interference fit grips the output hub and helps to reduce impact loads on the output hub tang 58 due to either re- engagement of the clutch (clutch embodiments) or engagement of the brake (brake embodiments).

For example, in the prior art device of FIG. 1, the brake spring 8 has an inside diameter in its relaxed state that is larger than an outside diameter of the central portion 18 of output assembly 6, and the inwardly extending tang 30 is exposed to a

considerable impact load when the clutch is disengaged and the brake is

simultaneously engaged. The brake side of such a device may experience loads that are twice those experienced by the clutch side due to the relatively faster response time of the brake engagement verses the clutch engagement. However, in the device of FIG. 2, the interference fit created by the smaller diameter portion 52 causes the spring 50 to grip its associated output hub in its relaxed condition, thereby absorbing some of the impact load when the brake is engaged.

FIG. 4 is a perspective view of an output hub 60 that may be used in the clutch/brake 40 of FIG. 2. This view illustrates the axially extending output hub tangs 62, 64 of both a brake spring 66 and a clutch spring 68. One will appreciate that in other embodiments only one of the springs may include an axially extending tang. For clarity of illustration, only a portion of a first wrap of each spring is shown for the smaller diameter portion of the respective step wound spring. At least the first wrap of each spring 66, 68 maintains an interference fit with the outer surface of the output hub 60 in its relaxed state. The springs are set into respective circumferential grooves 70, 72 which terminate in respective axially extending tang slots 74, 76. The springs 66, 68 engage against the sides of the circumferential grooves 70, 72 to resist axial movement of the springs 66, 68, and the tangs 62, 64 engage against the sides of the tang slots 74, 76 to resist rotation of the springs 66, 68 relative to the hub 60 about the axis of rotation A of the hub 60. Thus, the torque forces generated between the hub 60 and springs 66, 68 during clutch and brake engagement are distributed between both the friction created by the interference fit and by the interference between the respective tang and tang slot side.

The peak local stress in the respective tangs 62, 64 is further minimized by ensuring that the side profiles of the tang slots 74, 76 are configured to match the radius of curvature of the tangs 62, 64, thereby cooperatively engaging the entire opposed surface of the respective tangs to apply the mechanical loadings across the entire cooperating surface areas. One will appreciate that the circumferential grooves 70, 72 and tang slots 74, 76 may be formed in the hub 60 using a standard milling process to provide surfaces that fit flush against the flat sides of the rectangular or square shaped wire that is commonly used to manufacture such springs (e.g. music wire ASTM A228). In contrast, it may be appreciated that a prior art down tang hole 32 of FIG. 1 would normally be formed by a drilling process, which leaves a sharp edge to contact the bend radius of the down tang 30, thereby necessitating some type of edge rounding operation which tends to be imprecise and results in incomplete contact between the cooperating surface areas under load conditions.

An embodiment of the invention was tested by modifying a Standard CB-6 Clutch/Brake to include a step wound brake spring having an axially extending tang which interfaced with an interference fit into a circumferentially grooved output hub assembly. All materials of construction of the modified device were the same as those used in a Standard CB-6 Clutch/Brake. Whereas a Standard CB-6 Clutch/Brake might typically have an operating life of 1 - 2 million design basis stop cycles (5.55 lb-in²) before failure, the modified device underwent 11 ,850,000 design basis stop cycles without failure before the test was eventually terminated due to a time constraint. The design margin demonstrated by the modified device may be exploited as an improved lifetime under the standard operating conditions (i.e. 500 rpm), or it may be exploited as a higher operating speed (i.e. 750 rpm). This improved performance is achieved in embodiments of the invention without any increase in size or cost of the device.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims

The invention claimed is: 1. A wrap spring device comprising:

a first hub comprising a circumferential groove and an axially extending tang slot; a second hub;

a helical spring comprising an axially extending tang formed at a first end and a control tang formed at a second end opposed the first end;

the first end of the spring disposed about the first hub and a second end of the spring disposed about the second hub, with the axially extending tang being disposed within the tang slot and at least a first wrap of the spring proximate the first end being disposed within the circumferential groove; and

at least the first wrap of the spring formed to have an inside diameter in a relaxed state which is less than an outside diameter of the circumferential groove to provide an interference fit there between in the relaxed state;

wherein relative rotation between the control tang and the axially extending tang to move the spring between its relaxed state and a wound down state is effective to selectively engage the first and second hubs together.

2. The wrap spring device of claim 1 , wherein the first hub is an output hub and the second hub is an input hub of the device.

3. The wrap spring device of claim 1 , wherein the first hub is an output hub and the second hub is a brake hub of the device.

4. The wrap spring device of claim 1 , wherein the tang slot comprises a profile configured to cooperatively engage an entire opposed surface of the axially extending tang.

5. The wrap spring device of claim 1 , wherein the spring is step wound such that in the relaxed state the inside diameter of the at least the first wrap of the spring is less than an inside diameter of wraps of the spring proximate the second end of the spring.

6. The wrap spring device of claim 5, further comprising about four wraps of the spring proximate the first end having a first relatively smaller diameter in the relaxed state, about eleven wraps of the spring proximate the second end having a second relatively larger diameter, and about a one wrap transition there between.

7. A wrap spring device comprising:

an input hub;

an output assembly;

a brake hub;

a drive spring having a first end disposed about the output assembly and a second end disposed about the input hub, a first end wrap of the drive spring disposed in a first circumferential groove formed in the output assembly;

a brake spring having a first end disposed about the output assembly and a second end disposed about the brake hub, a first end wrap of the brake spring disposed in a second circumferential groove formed in the output assembly;

a tang extending axially at the first end of the drive spring and disposed in a first axially extending tang slot formed in the output assembly, the drive spring and output assembly thereby rotatable together;

a tang extending axially at the first end of the brake spring and disposed in a second axially extending tang slot formed in the output assembly, the brake spring and output assembly thereby rotatable together;

a control collar disposed about the drive spring and brake spring and connected to respective second ends of the drive spring and brake spring, the control collar thereby rotatable together with the drive spring, brake spring and output assembly; a pawl moveable for selective engagement of a notch on the control collar to selectively stop rotation of the control collar, thereby causing inertia driven relative rotation between the first and second ends of the respective drive and brake springs to selectively engage or disengage the output assembly with the input hub and the brake hub.

8. The wrap spring device of claim 7, wherein each of the drive spring and brake spring are step wound to have a relatively smaller inside diameter in a relaxed state proximate the respective first end and a relatively larger inside diameter in a relaxed state proximate the respective second end, thereby engaging the respective first and second circumferential grooves with an interference fit in the relaxed state.

9. The wrap spring device of claim 8, wherein each respective tang slot comprises a profile configured to cooperatively engage an entire opposed surface of the respective axially extending tang.

10. In a wrap spring device comprising an output hub selectively connected to a second hub with a wrap spring, the improvement comprising:

a circumferential groove and an adjoining axially extending tang slot formed in a surface of the wrap spring; and

an axially extending tang formed at an output end of the wrap spring such that at least a first wrap of the spring is disposed within the circumferential groove and the axially extending tang is disposed within the tang slot.

11. In the wrap spring device of claim 10, the improvement further comprising a profile of the tang slot configured to cooperatively engage an entire opposes surface of the wrap spring.

12. In the wrap spring device of claim 10, the improvement further comprising the wrap spring being step wound to have a relatively smaller inside diameter at the output end and a relatively larger inside diameter in a relaxed state at an opposed second hub end, thereby engaging the output hub with an interference fit in the relaxed state.