Patent Application
20080190529
None
Wheeled transportation has existed for a long time. A common problem in wheeled transportation is caused by bumps in the pathway of vehicles. For example, when patients in a medical facility are transport on carts, those carts typically have solid wheels that absorb little or none of the impact cause as the cart travels over transitions in the floor such as might occur at an elevator for example. Patients who may be critically ill, suffer as their bodies must absorb the jolt of the impact as a wheel travels over a transition. Solid wheels provided in the prior art are noisy because they do not absorb shock. Small hand carts typically do not have any shock absorbing capability so as a hand cart with prior art solid wheel rolls down a hall even very small objects and irregularities will cause the hand cart to rattle and jar creating noise, vibrating loads and setting up potential ergonomic problems for workers who frequently move hand carts.
U.S. Pat. No. 4,782,875 provides one solution to attempt to smooth the ride of a wheeled vehicle on a surface. A suspension arrangement is built in to a spoked wheel hub. The arrangement mounts each spoke on a leaf spring that allows the wheel to deflect as the wheel moves over an obstacle. The hub and wheel provides a potential solution but the complexity of this arrangement is not likely to be cost effective and may not work for small diameter wheels such as might be found inside a hospital or on various hand operated carts. Further, the design includes specialty leaf springs that would also be costly.
U.S. Pat. No. 1,890,442 discloses a spring wheel having telescoping spokes. The patent does allow for some radial and tangential motion of the wheel relative to the hub but the telescoping spokes are allowed to move relative to the hub requiring that the spokes be provided in pairs and that the spokes are not coplanar requiring a very deep wheel because the spokes must be staked. The patent also allows the wheel to ‘bottom out’ on the springs which will make an uncomfortable ride and quickly lead to spring failure. It is also felt that the wheel made according to this patent would produce a sudden ‘clunk’ each time the spoke passed through the upright position, this is caused because the spoke pairs will suddenly shift from a trailing position on the guide ‘F’ to a lead position as shown in
As can be seen there is a need for a simple and inexpensive shock absorbing wheel.
According to the invention, a wheel assembly is provided, including a rim and a central hub assembly, having a plurality of spokes threaded to the central hub. A plurality of tangential slots are provided on the rim and the spoke can move radially and tangentially within the slot. An resilient member such as a spring is provided for each spoke, with a first end of the spring engaging the wheel rim or wheel and a second end of the spring engaging the central hub. When the wheel assembly is rolling and encounters a bump and the rim deflects radially relative to the hub assembly, the spokes can move radially and tangentially along the slots while the springs absorb the impact caused by the bump.
In another aspect of the invention a wheel assembly is provided that uses internal springs to absorb shock.
These and other advantages of the present invention will become apparent from the detailed description of the invention.
As shown, the wheel 100 includes 5 spoke assemblies 106, each spoke assembly 106 includes a solid radially extending one piece member such as central spoke 120 and an elastomeric or resilient member such as spring 122 surrounding the spoke 120. The wheel 100 is designed so that if the wheel 100 encounters an obstacle such as a threshold in a building, that some of the spoke assemblies 106 will compress to absorb a portion of the impact caused by the obstacle (See
To assemble the wheel 100, a spring 122 is placed over a spoke 120 and that spoke 120 is threaded into the hub 108. After the five spokes 120 are threaded to the hub 108, the hub 108 with spokes 120 attached is placed into the outer rim 105 with the washers 140 resting on the inner diameter of the outer rim 105. Then the inner rim 104 is aligned and bolted to the outer rim 105 using bolts 164. Each spoke 120 includes a slotted head portion 170 that can move tangentially and radially within the wheel 100 within the slot 148 created by raised portions 172 on the inner rim 104 and raised portions 174 on the outer rim 105. The hub 108 floats on the springs 122 and is normally centered in the wheel assembly 100 until a load is applied to the axle 110. The length L of the slot 148 determines the maximum travel of the spoke 120 that is traveling in the slot 148. A spoke 120 will normally float and not contact the end 146 of slot 148 but under loading in excess of a design limit amount the spoke 120 will come in contact with a padded end 146 located at either end of the slot 148 and separated by the distance L. The padded end 146 can be an elastomeric material such as phenolic or rubber and will cushion the impact as the spoke 120 comes in contact with the slot 148 wall. The travel of the spoke 120 under load is thus limited in the tangential direction and the spoke 120 will not ‘bottom out’ in the radial direction against the rim. There continues to be a gap (at number 148 in
As can also be seen in
Spring rate of the springs 122 will be determined by design and the application. The springs 122 can be a constant rate spring or the springs 122 can be proportional springs having a variable rate of compression. The springs 122 will typically have a preload.
Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
