Patent Application
20060236610
The present invention relates to industrial castings and more particularly to spring-assisted lift hatches.
Castings with lift assist hatches are well-known in the industry. These castings typically include a frame that is mounted in a support structure to cover an opening and a cover that is hingedly secured to the frame. In use, the cover can be opened to gain access to the opening. In some applications, the cover must be capable of bearing high loads. For example, these types of castings may be used at airports, parking lot and along streets where they may be required to bear the weight of heavy vehicles. In these types of applications, the hatch is manufactured from relatively heavy cast components. The weight of the cast cover can make it difficult to open and close the hatch.
To address this problem, it is known to provide the casting with lift assist springs that provide a mechanical assist in lifting the cover. In some case, the lift assist springs are torsion springs that are mounted to the frame with one free end engaging the cover and the other free end engaging the structure in which the casting is mounted, for example, a concrete box. In many applications, the lift assist mechanism includes two torsion springs that cooperate in providing assistance. In use, the free ends of the torsion springs typically move with respect to the cover as the cover is opened and closed. Direct sliding engagement between the free end of the torsion springs and the cover can result in damage to the casting and make it difficult to operate the hatch. To provide an improved interface between the torsion springs and the cover, a slide block is typically mounted to the free ends of the torsion springs to engage the cover. These slide blocks ride along surfaces of the cover, for example, within a channel cast into the cover. Also, to distribute the force of the other free end of the torsion springs against the support structure, pressure blocks have been mounted to the free ends of the torsion springs that engage the support structure.
Although lift assist springs make it easier to operate the hatch, conventional lift assist springs suffer disadvantages resulting from the mechanism used to secure the pressure and slide blocks to the torsion springs. Typically, the slide and pressure blocks are secured to the torsion springs by set screws. More specifically, the blocks are fitted over the ends of the torsions springs and then secured in place by a set screw that is tightened through the blocks against the outside surface of the torsion spring. Over time, the blocks have a tendency to become loose and may ultimately fall off of the torsion springs. Once off, the slide blocks may fall into the opening covered by the casting and become lost. Once lost, the lift hatch is typically operated without the block. This can lead to damage to the casting, such as the lift hatch, the frame or the hinge joining the two components. Although it may be possible to reduce the likelihood of this problem by periodically checking and tightening the set screws, this type of maintenance typically does not occur and, even if it were to occur, it would have an undesirable associated cost.
The aforementioned problems are overcome by the present invention wherein a hatch is provided with a lift assist mechanism having at least one torsion spring with a threaded free end and a block that is threadedly secured to the threaded free end. The attachment structure of the present invention can be incorporated into slide blocks and pressure blocks by including threads on one or both free ends of the torsion spring.
In one embodiment, the block is fitted over the threaded free end of the torsion spring and secured in place by nuts or other threaded fasteners threaded directly onto the threaded segments of the spring. For example, the block may be sandwiched between a pair of nuts or other threaded fasteners. In an alternative embodiment, the block may define a bore having internal threads so that the block can be threaded directly onto the torsion spring without the need for separate threaded fasteners, such as nuts.
In another embodiment, the lift assist mechanism may include two torsion springs that cooperate in assisting the lifting of the cover. The ends of the two springs that interact with the cover may both be threaded and mounted to a single slide block. Also, the ends of the two springs that interact with the support structure may be threaded and mounted to separate pressure blocks.
In yet another embodiment, the block may include a plurality of flat engagement surfaces and define an eccentric internal bore that is fitted over the free end of the torsion spring. The plurality of engagement surfaces and the eccentric internal bore permit the block to be rotated into different positions to vary the distance between the free end and the bearing surface (such as the lift hatch or the frame), which in turn varies the amount of lift assist provided by the spring. By increasing this distance, the tension in the spring and consequently the amount of assist can be increased. By decreasing this distance, the tension in the spring and consequently the amount of assist can be decreased.
The present invention provides a simple and effective mechanism for securing slide and pressure blocks to the torsion springs. The threaded connection between the blocks and the torsion springs is easy to operate, secure and is far less likely to become loose over time than the set screw attachment of conventional systems The threaded connection does not require a high torque attachment, thereby facilitating installation. Further, the position of the blocks on the ends of the torsion springs can be easily adjusted to vary the tension in the spring and consequently the amount of assist simply by adjusting the location of the threaded fastener(s). In applications where the block includes an eccentric bore, the tension in a spring can be easily adjusted simply by rotating the block about the free end of the spring.
These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings.
A lift hatch casting in accordance with an embodiment of the present invention is shown in
As noted above, the hatch 10 includes a frame 12 intended to be mounted to a support structure over an underlying hole, such as a manhole. The frame 12 is a generally conventional lift assist hatch frame. Referring to
The cover 14 is a generally conventional hatch cover. The cover 14 is configured to be operatively interfitted with the frame 12. In this embodiment, the cover 14 is generally square and is designed to be fitted into the space defined by should 30 (See
The lift assist mechanism 16 generally includes a mounting pipe 52, a pair of torsion springs 54a-b, a slide block 22 and a pair of pressure blocks 24a-b. The mounting pipe 52 provides a mounting structure for the lift assist mechanism 16. As perhaps best shown in
As noted above, the lift assist mechanism 16 also includes slide block 22 that provides an interface between the cover and the springs 54a-b. In this embodiment, the slide block 22 includes a main body 70 and a finger 72 (See
As discussed above, the structure end 60b of each spring 54a-b is intended to engage the support structure in which the hatch 10 is mounted. This may be a concrete box or other similar structure. A pressure block 24a-b may be mounted to each structure end 60b to provide an interface between the springs 54a-b and the support structure. In the illustrated embodiment, a separate pressure block 24a-b is mounted to each structure end 60b. The pressure blocks 24a-b are generally identical and therefore only one will be described. Referring now to
As can be seen, the threading of the spring ends 60a-b allows the slide block 22 and pressure blocks 24a-b to be securely and easily secured to the springs 54a-b. Although the illustrated embodiment discloses the use of jam nuts for securing the blocks 22 and 24a-b onto the threaded sections of the springs 54a-b, other threaded fastening configurations can be used. For example, if desired, the bores in the slide block and/or pressure blocks may be threaded so that the block can themselves be threaded onto the spring ends 60a-b. In this embodiment, a single jam nut may be used to lock the threaded block in the desired position.
The hatch 10 may also include a generally conventional safety bar 90 that can be manually swung up to secure the cover 14 in the open position and manually swung down to permit the cover 14 to be closed again. The safety bar 90 and its attachment structure are generally conventional and therefore will not be described in detail in this application.
The above description is that of a preferred embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.
