1. Field of the Invention
This invention relates to motive-powered vehicles and, more particularly, to vehicles such as fork lift trucks which operate in a hazardous environment and to cells and batteries serving as the motive power source for such trucks.
2. Description of the Prior Art
Lead-acid cells and batteries have been used in a variety of motive power applications in which an array of cells or batteries provides the motive power for vehicles ranging from Class 1 to Class 3 trucks, various automated guided vehicles, mining vehicles, and also railroad locomotives.
A variety of design circumstances for motive power applications serves to complicate the situation. In Class 1 and 2 trucks, i.e., electric rider trucks and electric narrow aisle trucks, respectively, the array of cells or batteries utilized have weight limits that must be met so as to provide the necessary counterbalance for the vehicle. Also, the physical space available for the motive power source in trucks is often limited.
The performance requirements for motive power vehicles are quite stringent. Motive power applications thus require relatively deep depths of discharge of the motive power source to be achieved on a continuing cycling basis over a period of time. Indeed, a common requirement for such trucks is that, in an 8-hour shift, the cell or battery assembly must be capable of delivering an 80% depth of discharge and that performance is required for about 300 cycles per year with a useful service life under these conditions of at least 4, and more typically 5, years.
Even further, many industries typically run three 8-hour shifts each day. The typical battery ratings are such that each battery is designed to be utilized for just one shift (typically being in service for about 6 hours or so). Because of the time involved in recharging lead-acid batteries, fork trucks which are used on a three-shift basis require three separate batteries. One battery is in service in the truck while two batteries are on charge.
The inventory burden involved becomes more significant for fork truck designed to work in a hazardous environment. Such environments require the use of a specially designed battery. Trucks and batteries operating in such hazardous environments have been termed xe2x80x9cEXxe2x80x9d trucks or batteries. To be suitable for such environments, EX batteries must comply with the appropriate safety standards, i.e., UL583. These standards require that the batteries have fully protected ventilation openings to limit access to the cell terminals from an outside source. Further, the current-carrying parts of the battery must be insulated or protected against possible contact with foreign objects when in use. Still further, the electrical connection in service (i.e., the running plug) must be interlocked with a switch so that the plugs can neither be inserted nor withdrawn while the receptacle contacts are live, or the plug must be locked in the receptacle to deter removal by unauthorized persons.
Accordingly, assembling EX batteries to meet such safety requirements involves providing the battery with an explosion-proof fuse box, switch, receptacle and a fully enclosed tray with a receptacle locking arm. These features require significant costs. These expenses become substantial when the service life of these specially designed batteries are compared with the typical 20-year service life of such electric trucks. Thus, over the 20-year service life of a fork truck, the user must purchase at least 12 specially-designed EX batteries. For service fleets having a relatively large number of trucks, the costs involved are multiplied, and even more substantial.
There is thus a need for a system which will satisfy the requirements for batteries used in hazardous environments in a reliable, yet more cost-effective, manner. It would accordingly be highly desirable to provide a system that would not require specially designed batteries.
It is accordingly a principal object of the present invention to provide a motive power system for trucks used in hazardous environments which allows the use of cells and batteries that do not have to be specially designed for such applications.
A further object of the present invention provides an explosion-proof enclosure designed for motive-powered trucks used in hazardous environments.
Yet another object of this invention is to provide a system for satisfying the safety requirements for motive-powered trucks working in a hazardous environment while utilizing cells and batteries of conventional configurations.
These objects and advantages of the present invention are apparent from the following description and drawings.
In its broadest aspects, the present invention provides an integrated system for providing the motive power for trucks working in a hazardous environment without requiring the use of expensive, specially designed batteries that individually satisfy the various safety requirements. The present invention thus provides an explosion-proof enclosure designed to accept a conventional battery as an interchangeable part. The enclosure has all of the required safety features and is configured to accept a standard battery.