Introduction

This invention relates to a clutch for power door systems for use with truck and trailer bodies.

Background of the Invention

Current powered vertical lift doors on articulated trailer bodies and truck bodies are not usually operable in manual operation in the event of a failure of the powered drive. Often, where a powered door has failed the typical vertical lift door cannot be manually operated due to resistance of the drive system. Furthermore as most commercial doors are counterbalanced via wires coupled to a spring, if the door is manually operated the wires can drop off their pulleys and become tangled. Such doors are often made from several close- fitting interconnected panels that need to be, not only robust for security reasons, but also need to maintain temperature differentials when perishable goods are being transported. Such doors are heavy, in the order of 60kg.

Counterbalance springs are usually deployed to attempt to balance the effort to open or shut the door. The counterbalance spring will be located about a rotating shaft located above the door and bracketed to the trailer structure. The spring imparts a torgue to the shaft via a coupling, which in turn will provide tension onto two cables located close to the outer edge of the door and secured to the base of the lowest panel. The cables are fixed to the shaft via cable drums on either side of the shaft .

The door panels are contained in tracks at either side of the trailer to ensure smooth and constrained travel. The door is usually located horizontally under the ceiling of the trailer when in the open position. The powered drive is typically a geared electric motor coupled to the shaft to provide a rotational torque to the shaft which in turn operates the door action to raise and lower the door.

In the event of a loss of power or a mechanical breakdown of the drive system an operator will use a grab handle on the lowest panel and lift the door to its fully raised state to allow loading or unloading. When the door is to be closed the reverse occurs where the operator manually grabs the handle and pulls down on the door to shut the door. Notwithstanding the inclusion of a

counterbalance spring the ergonomic effort to start the door in either direction is very high due to the drive system resistance being added to door inertia. These problems together with the commercial need to get the door open, causes operators to sometimes deploy methods such as using the tynes of a lift truck to "force" the door open. Invariably this leads to further damage to the door and drive system.

It is these issues that have brought about the present invention. Summary of the Invention

According to one aspect of the present invention there is provided a clutch comprising an input shaft driving a cam positioned against a follower adapted to engage an output shaft, the follower being displaceable against biasing means by the cam to engage the output shaft, whereby rotation of the input shaft and cam in either direction causes the follower to transfer drive to the output shaft and when the input shaft is stationary the biasing means displaces the follower away from the output shaft to disconnect drive to the output shaft. Preferably, the follower comprises at least two arcuate segments located within a friction drive coupled to the output shaft, the arcuate segments being displaced against the biasing means by the cam to engage the

friction drive .

Description of the Drawings

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a perspective view of part of an electric powered door system at the rear of an articulated trailer,

Figure 2 is an exploded perspective view of an electric motor clutch and gearbox to power the door system illustrated in Figure 1,

Figure 3 is an exploded view showing detail of the clutch within the circle A on Figure 2,

Figure 4 is a side elevational view of the clutch showing input and output shafts,

Figure 5 is an end elevational view of the clutch from the input shaft,

Figure 6 is a cross sectional view of the clutch taken along the lines B-B of Figure 4,

Figure 7 is a cross sectional view of the clutch taken along the lines A-A of Figure 4,

Figure 8 is a perspective view showing the relationship between a cam follower and clutch housing,

Figure 9 is an end elevational view of the clutch housing,

Figure 10 is an enlarged view of the detail of the housing shown in the circle A of Figure 9,

Figure 11 is an exploded view of a clutch in accordance with the second embodiment,

Figure 12 is a side elevational view of the clutch of Figure 11, Figure 13a is a cross sectional view along the lines A-A of Figure 12 showing the clutch disengaged, and

Figure 13b is a cross sectional view along the lines A-A of Figure 12 showing the clutch engaged.

Description of the Preferred Embodiments

Figure 1 illustrates a typical electically powered door system of a trailer. The door is made up of several pivotally interlinked panels 14. An outboard hinge includes an axle and roller assembly 15. The axle and roller assembly 15 is engaged in a roller track 16 on each side of the door. The roller track 16 is fixed to the trailer internal body 17. The roller track 16 is arranged to extend from the floor at the rear of the trailer body 17 vertically and then through a radius at the top of the trailer to project along and below the roof of the trailer body 17. Thus by way of the axle and roller assemblies 15 the door panels 14 are constrained to move in a plane consistent with the roller track 16.

A balance shaft 10 is located internally at the rear of the trailer and above the door track 16. It is mounted via bearings 18 to the internal wall of the trailer 17. Cable drums 19 are mounted about the shaft 10 at each end and secured to the shaft 10 via screws (not shown) . A pair of cables (not shown) are wound about each cable drum 19 and extend to the outer lower edge of the bottom door panel 14. They are pivotally attached to the door panel 10 via a simple bracket (not shown) . The shaft 10 extends within a coil spring 20. The fixed end of the coilspring is secured via a bracket (not shown) to the trailer 17 structure. As the door is lowered the balance shaft 10 rotates due to the cable being extended and thus unwound from the drum 19 to in turn, impart a winding action on the coil spring 20 to resist the lowering of the door as it travels down the roller track 16 to a closed position. The coil spring 20 is provided with appropriate pre-tension to balance the weight of the door as the door panels 10 move from the horizontal portion of the roller track 16 to the vertical portion of the roller track 16. The door is activated typically by electric, via a switch 21 to either move up or down. A drive motor 12 rotates in the requested direction. The motor 12 is mechanically coupled to a gearbox 11 which in turn is mechanically coupled to the balance shaft 10. Thus as the motor 12 turns in either direction so does the balance shaft 10. This in turn, either raises or lowers the door as the case may be.

As shown in Figure 2 and 3 a clutch 25 is designed to be positioned between the motor 12 and gearbox 11 of the drive system shown in Figure 1. The output shaft 41 of the electric motor 12 extends into the clutch housing 30 via a bearing 4. The shaft 41 is keyed to a cam 1 that is positioned coaxially with a follower 2 which is inturn located within the housing 30. The drive shaft 41 of the electric motor terminates within the cam 1.

The clutch housing 30 has an enlarged end 34 with an internal throughway 35. The opposite end of the housing 30 defines a forwardly projecting spigot 36. The enlarged throughway 35 accommodates the end of the shaft 41 from the electric motor 12 that spins within ball bearings 37 positioned against the inner wall 38 of the housing 30. The shaft 41 drives the cam 1 which in turn drives the followers 26, 27, 28. At the entrance of the housing 30 the shaft supports a roller bearing 40 that is bound in an outer shaft 42 screwed to the housing 30 via three equally spaced screws 43. The inner race 44 of the roller bearing allows the shaft 41 to rotate relative to the housing 30. The forward spigot 36 houses an externally mounted bearing 48 which supports a forwardly extending pinion shaft 49, which is keyed to the spigot 36 of the housing 30 via a pin 50 (Figures 6 and 7) . Thus, rotation of the housing 30 imparts rotation to the pinion shaft 49. The forward end of the pinion shaft 49 is again supported by axial rotation about a bearing 51 located in the front face of the gearbox 11.

As shown in Figures 8 to 10 each follower 26, 27, 28 is of outer arcuate profile defining projecting teeth 60, 61 at either end. The extremities of the teeth 60, 61 have central groove 63 that accommodate a circular spring 6 holding the followers 2 in firm engagement against the cam 1. The teeth 60, 61 are adapted to engage the interior surface of the housing 30 that is formed with 26 flats 65 positioned around the periphery of the housing 30 interior. In a neutral position when the input shaft 41 is stationary the spring 6 holds the followers 2 against the cam 1 so that the teeth 60, 61 are within the housing 30 without engaging the 26 flats around the periphery of the housing interior. When the shaft 41 is spinning slowly the cam followers 26 to 28 continue to spin without engaging the housing 30. However, as the speed increases, the centrifugal forces on the followers 26 to 28 causes the followers to expand outwardly against the spring 6 causing the leading edge of each tooth 60, 61 to engage the adjacent flat 65 on the housing 30 interior. The tooth then locks into engagement with the flat 65 and imparts rotational force to the housing, and thus turns the output pinion shaft 49. As shown in particular detail in Figure 10 each tooth has a leading edge 66 that is adjacent the tooth of the adjacent follower. The leading edge 66 protects slightly outwardly from the trailing edge 67 to engage the flat 65 to impart drive. In this way the clutch 25 is

bidirectional and there is positive engagement with the flat 65 of the housing 30 whichever way the followers 26 to 28 are rotating. In the embodiment shown in Figures 11 to 13 the interior of the housing 30 does not have the drive surface defined by 26 flats 65. Instead a friction ring 5 of circular configuration is positioned outside the followers 26 to 28 and the followers have a substantially circular configuration when in the closed configuration as shown in Figure 4a. In this situation the clutch 25 is disengaged with the followers 26 to 28 being free to rotate within the friction ring 5. As the speed of the followers 26 to 28 increases and they expand outwardly against the spring 6 as shown in Figure 4b. The arcuate surface of the followers 26 to 28 engages the internal surface of the friction ring 5 to rotate the friction ring 5 which in turn rotates the housing 30. The friction ring 5 is a press fit within the housing 30.

Rotation of the cam 1 in either direction operates the clutch and thus the clutch has a simple bi- directional feature. Thus, in use, to open or close a door, the electric motor 12 drives the closing mechanism shown in Figure 1 through the clutch 25 by forcing the arcuate segments 26 to 28 outwards to operate the clutch. When the motor 12 stops, the spring 6 disengages the segments 26 to 28 thus disengaging the clutch and allowing the door to be manually opened or closed. Thus in the event of a breakdown in the electric motor or loss of power, the door can be opened and closed without having to act against the electric drive.

The above description illustrates a typical arrangement and is not limited as alternative methods may be employed to achieve the identical intended result. The mounting location of the clutch may be varied to achieve the same result. The invention is not limited to truck and trailer door drive mechanisms but can equally be employed on any similar equipment. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as

"comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.