Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-11-24
2001-09-18
Walberg, Teresa (Department: 3742)
Pumps
Motor driven
Electric or magnetic motor
C060S475000, C091S031000
Reexamination Certificate
active
06290474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a machine having a hydraulic system and, more particularly, to an industrial truck having a hydraulic system with at least one reservoir for hydraulic fluid and at least one hydraulic pump.
2. Description of the Currently Available Technology
Machines are frequently equipped with a hydraulic system, by means of which, depending on the construction of the machine, various functions of the machine are driven. On industrial trucks, for example, such functions are generally the raising and tilting of a load, the steering of the industrial truck and possibly additional loadhandling functions.
The hydraulic system generally has a reservoir from which hydraulic fluid is sucked by a pump. Installed downstream of the pump is a priority valve which can supply a hydraulic steering device with hydraulic fluid. Hydraulic fluid is also made available to additional hydraulic users by distributor valves that can be actuated as desired. Most of the users in question are hydraulic cylinders, by means of which the forces required to raise, tilt or handle a load are generated. The steering device and the other hydraulic users are also connected to the reservoir by return lines. A descent braking valve to reduce the volume of the flow of hydraulic fluid or a pilot valve to maintain a specified pressure level can be located in corresponding return lines, as necessary.
In known machines, the above mentioned hydraulic components are generally fastened separately from one another to a frame of the machine, and are connected to one another by hoses or pipelines. The known art also discloses that different hydraulic components can be combined into modules and fastened jointly to the frame of the machine. In each case, the known hydraulic systems have a series of discontinuities and connections that are sealed with seals and gaskets of various types to prevent the escape of hydraulic fluid.
Preventing the escape of hydraulic fluid from the hydraulic system is necessary to meet the requirements of occupational health and safety regulations as well as environmental protection regulations. For this purpose, complex and expensive means are employed in the manufacture of the machine to help prevent such hydraulic fluid loss. Nevertheless, during the operation of such hydraulic machines, leaks in the hydraulic system occur repeatedly. These leaks have to be detected and eliminated in the course of service and maintenance operations.
As will be appreciated by one of ordinary skill in the industrial truck art, it would be advantageous to provide a machine of the general type described above in which the danger of the escape of hydraulic fluid can be reduced or eliminated, preferably using simple means.
SUMMARY OF THE INVENTION
The invention teaches that the above object can be accomplished by locating a hydraulic pump of the hydraulic system inside the hydraulic fluid reservoir. In the event of a leak in a casing of the hydraulic pump or in its hydraulic connections, the leaking hydraulic oil flows directly into the reservoir. Consequently, it is possible to reliably eliminate contamination of the machine and/or the environment. These leaks may thus only have to be repaired in the event of major damage to the seal elements, e.g., if the leaking hydraulic fluid leads to a reduction in the performance or power of the hydraulic system. Minor leaks can be repaired during normal maintenance activities because during the normal operation of the machine they do not pose a serious risk to the safety of operators or the environment. An additional advantage of locating the pump in the reservoir is that when leaks occur in a suction area of the pump, for example on a suction tube or a filter, the entry of air into the hydraulic pump and thus damage resulting from cavitation can be prevented.
It is further advantageous if an electric motor of the hydraulic pump is located inside the reservoir. Therefore, no mechanical openings need to be made through a wall of the reservoir. The hydraulic fluid in the reservoir can be used as coolant for the electrical drive motor. The installation of the electric drive motor inside the reservoir is particularly appropriate when a maintenance-free, three-phase motor is used.
If an electric drive motor of the hydraulic pump is located outside the reservoir, a secure seal is achieved if a shaft that connects the electric drive motor with the hydraulic pump is sealed with respect to the tank by a shaft seal. This system is particularly appropriate when a direct current motor is used, which should be accessible for maintenance work that is typically performed on a regular basis.
A further improvement regarding the escape of hydraulic fluid results if a priority valve is located inside the reservoir and in flow communication with the pump. The priority valve ensures that a steering device of the machine is supplied with sufficient hydraulic fluid at all times. Leaks in the vicinity of the priority valve, for example at the hydraulic connections, do not in this arrangement result in a contamination of the environment by hydraulic fluid. Instead, the escaping hydraulic fluid is retained in the reservoir.
If the priority valve is fastened by a flange connection to the hydraulic pump, no additional hydraulic lines between these components are necessary. The hydraulic pump and priority valve can be installed in the reservoir as pre-assembled modules.
It is also advantageous if there is at least one distributing valve located inside the reservoir and in flow communication with the pump. By means of the distributing valve(s), the delivery of hydraulic fluid to various hydraulic users is controlled as a function of a signal initiated by an operator. Leaks in the distributing valve(s), which are generally proportionally controlled but which can also be realized in the form of sliding valves, are recovered in the reservoir. With sliding valves, the complex and expensive tank return, required on known devices to catch oil leaks which are unavoidable on account of the design of the system, can be eliminated. It is even possible to do without the seals that are conventionally used to prevent contamination of the sliding valves since, on account of the location of the valve(s) in the reservoir, it is not exposed to any external influences. It is also possible to do without a seal of the individual slides of the distributing valve, as a result of which the distributing valve can be manufactured more economically.
When the distributing valve(s) is located in the reservoir, it is advantageous if the distributing valve(s) is realized so that it can be actuated electrically. The distributing valve(s) can thus be located spatially independently of the corresponding control levers.
There are appropriately a plurality of distributing valves which form a distributing valve block. The distributing valve block can be installed pre-assembled into the reservoir.
It is particularly advantageous if the priority valve is a component of the distributing valve block. Therefore, no hydraulic lines that connect the priority valve with the distributing valve block are necessary.
Advantages similar to those described above are achieved if a steering valve is located inside the reservoir and in flow communication with the pump. The steering valve can also be realized in the form of a component of the distributing valve block.
Additional advantages can be achieved if there are additional hydraulic components, such as one or more pilot valves and/or a descent braking valve, located inside the reservoir. The pilot valve and the descent braking valve are typically located in the return lines from hydraulic users. The invention teaches that these components can also be located inside the reservoir.
REFERENCES:
patent: 3754394 (1973-08-01), Morrison
patent: 3918683 (1975-11-01), Millar
patent: 3988089 (1976-10-01), Hehl
patent: 3988099 (1976-10-01), Hehl
patent: 4005636 (1977-02-01), Dunn
patent: 4169580 (1979-10-01), Hatlapa et al.
patent: 45519
Bavendiek Rainer
Jahns Claus-Peter
Fastovsky Leonid
Still GmbH
Walberg Teresa
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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