1. Field of the Invention
The present invention relates, generally, to a jack stand apparatus and more particularly to a jack stand with a spring triggered safety engagement.
2. Description of the Prior Art
The demand for inexpensive jack stands has arisen over the years due to a consumer need to perform a wide range of automobile maintenance and repair functions at home. Jacking type devices have proven to have certain safety drawbacks when used to maintain the automobile in a vertically suspended position. By utilizing inexpensive jack stands, a single more expensive jacking device may be used to meet all of the consumer's jacking needs. In its basic application, the jack stand provides a wide base and a sturdy support structure for maintaining a vehicle suspended in a raised position to enable maintenance and repair type functions to be performed on the vehicle. A variety of jack stands have been utilized to meet the diverse and changing needs of a society dependent on the automobile.
Jack stands, in general, have developed from a basic design which is made up of a sturdy wide base structure and a telescoping vertical support member or stem. The vertical support member can be adjusted to increase or decrease the overall height at which the jack stand will support a vehicle. Once a particular height has been selected, movement of the vertical member relative to the base is locked, in some manner, thereby providing a secure sturdy means of supporting the vehicle.
Devices of this type can fall generally into two categories. A first design category requires the insertion of an engaging pin to secure the vertical member at selected positions for various different heights relative to the base structure. While the pin type device provides a sturdy work structure, the limited number of holes allowed by the limits on structural integrity can substantially increase the distance between the jack stand and the height of an elevated vehicle. Designs of this type are shown in U.S. Pat. Nos. 1,416,896 by Simmons, 2,439,854 by Lipski, and 4,042,202 by Molinari. While satisfactory for some applications, in other applications jack stands of this type suffer shortcomings in positioning caused by large gaps between the jack stand and the elevated vehicle. These positioning errors may cause the jack stand to slide out of position or to support the automobile in an undesirable manner resulting in damage to other automobile components having insufficient structural integrity to support the weight of the vehicle. In order to avoid this problem the user may need to adjust the height of the stand while under the vehicle. This condition may expose the user to the dangers associated with a vehicle supported by a jacking device of the type which may not possess the structural integrity of a jack stand.
A second design category incorporates a set of interlocking teeth disposed on a vertical edge of the vertical support member. A pawl positioned on the base support structure by a pivot pin engages with the teeth providing a variety of support positions for the jack stand device. Typically such teeth are of a general saw tooth shape for free and rapid ratcheting upwardly of the stand relative to the pawl. A jack stand of this type is more convenient to position at a height closely nesting under the axle of the vehicle to be supported by a jacking device. By reducing the distance the vehicle will travel when the jacking device is released, the problems that may arise from a sudden change in the vertical position of the vehicle has been reduced.
The pawl is usually mounted on the base support structure by a pivot pin. When the vehicle is to be removed from the jack stand, the jacking device resumes the load of the vehicle and a handle located on the pivot pin may be grasped to release the pawl from engagement with the teeth of the vertical support member to free it for lowering. The handle provides a quick release allowing the vertical member to telescopically decline to its lowest position for quick retrieval from the underside of the vehicle. A device of this type is shown in U.S. Pat. No. 1,320,613 by Gilcrease.
While these ratchet type devices provide an advantage over the pin type jack stands, there still remains some disadvantages. The pawl engagement with the vertical support stem sustains the position of the vertical support member only against retraction into the base. This typically leaves the support stem free to be drawn or to fall free of the base and become disassociated therefrom.
This can create an unsafe situation for the automobile mechanics or do-it-yourselfer employing the stand. The general tendency is for the workman to, when transporting the stand from place to place, grasp it by either the stem or the base to carry it in an inverted orientation.
This can create a serious problem in that the vertical support stem is free to slide past the pawl free of the base to impact the workman's foot or toe. This condition can also result in a substantial hazard to the work area caused by the heavy vertical support member falling out of the base support and damaging other delicate tools or automobile components. Further, the unwanted disassociation of the vertical support from the base is an inconvenient and irritating problem for the workman seeking to repeatedly transport the stand from one location to another.
While some ratchet type designs provide a stop to restrict the vertical support member from coming completely free from the base structure, the vertical member may still slide freely out to a fully extended position. By creating such a sudden change in its center of gravity or impact upon engagement with the stop, the sudden load change may still cause the person carrying the device to drop the jack stand or allow the free falling stem to strike the workman or nearby object causing injury or damage.
Some ratchet type designs recommend a spring loaded pin to engage the vertical support member at its lowest vertical position within the base. This type of safety device locks the position of the vertical member within the base structure. The major drawback of this safety feature is that to be effective, the user must manually engage by pin each time the device is used. This manual engagement, which should be initiated during cleanup, may often be overlooked in the press of time often surrounding the completion of a major automotive repair project.
In instances where it is necessary to employ two to four jack stands for a particular task, the setting of a fixed equal height on all the jacks may be critical in providing a safe working environment. The procedure of moving the vertical support stem to the safety position may result in losing the specific height necessary for work on a continuing project. While the safety pin design provides a manually engaged safety device and a quick release to lower the device's height, there remains a safety hazard for those instances that would require that the jack stand be maintained in a pre-positioned height for continued work on a particular project.
Other ratchet type jack stands provide for a pin to be biased into normal engagement with the teeth of the vertical support member. Disengagement of the pin can then only be accomplished by manually holding the pin in its disengaged position. This task can be difficult from certain positions under the car, especially if the mechanics hands are greasy, thus creating a safety hazard which hampers the effectiveness of the ratchet device to quickly adjust to various heights.
Consequently, there exists a need for a jack stand which can be quickly adjusted to permit convenient positioning and retrieval while securing the vertical support member from movement automatically when the device is being transported in an inverted position.