Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Patent
1996-05-01
1997-11-18
Nguyen, Hoang
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
60431, 60468, F16D 3102
Patent
active
056875673
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and to an hydraulic power unit of the kind defined in the respective preambles of the following independent method and apparatus claims.
The invention is concerned more particularly with a portable and "independent" type of hydraulic power unit intended to power a hydraulic tool which is connected to the power unit by means of a hose and handled and manipulated by an operator. The hydraulic tool may have the form of a crimping tool, crimping tongs, for instance.
2. Description of the Related Art
An arrangement of this kind is known from DE-A1-3835696.
Crimping tongs are tools by means of which an electrical end-contact can be pressed onto the end of an electric cable or the like. In industrial applications, such crimping tools may conveniently be hydraulically operated, using an hydraulic piston-cylinder device as the power means. The cylinder is conveniently connected hydraulically to an hydraulic power unit by means of a hydraulic hose, this power unit preferably being portable and also "independent", for many good reasons. By "independent" is meant that the unit will contain its own power source, for instance a rechargeable electric storage battery. The hydraulic power unit will also include an hydraulic circuit having an hydraulic pump which is driven by a motor that can be connected to the power source.
In the case of portable units it is necessary to take into account all significant points of view with regard to the operating functions of the unit. For instance, it is necessary for the pump to generate a relatively high pressure, for instance a pressure of 250 bars or more in order for the working cylinder to produce a required force of 15 kN for instance with the aid of an hydraulic cylinder of reasonable cross-sectional area, this cylinder also preferably forming the tool core or handle.
On the other hand, the pump must be relatively small and relatively light in weight in order for the hydraulic unit to be easily carried by hand, although this will result in a relatively long working cycle.
It is known, for instance, from U.S. Pat. No. 2,392,471, U.S. Pat. No. 2,641,106, U.S. Pat. No. 3,375,658, U.S. Pat. No. 4,096,727 to include in an hydraulic circuit an hydraulic accumulator which is charged by the pump and which provides a relatively large volume flow capable of quickly filling a working cylinder to a working state, as the accumulator is emptied. However, the accumulator pressure falls drastically, therewith resulting in a low accumulator pressure when the working cylinder is in its working state. Furthermore, from the aspect of weight among other things, it is unsuitable to give the accumulator a volume and pressure-durability which will enable the working cylinder to be pressurized from the accumulator at a desired pressure (for instance 250 bars).
It is actually unsuitable to construct the accumulator such as to pressurize the working cylinder with the desired tool working pressure as the accumulator is emptied.
Accordingly, one object oft he invention is to provide a power unit which can include an hydraulic accumulator of relatively low pressure and of relatively small volume, while, at the same time, giving the pump a relatively low flow capacity and low motor power, despite a high pump pressure and a high working pressure of the hydraulic cylinder of the tool. Another object of the invention is to provide a method of operation for one such unit.
These objects are achieved with a power unit having the characteristic features set forth in the independent apparatus claim below, while the inventive method is characterized by the steps set forth in the independent method claim.
Further embodiments of the invention are set forth in the dependent claims.
Fundamentally, the invention requires the hydraulic circuit to include an accumulator which is dimensioned for a pressure which is at most equal to and preferably slightly lower than the maximum pump-working pressure, and which may advantageously
REFERENCES:
patent: 2392471 (1946-01-01), Fox
patent: 2641106 (1953-06-01), Jelinek
patent: 3375658 (1968-04-01), Slover
patent: 4096727 (1978-06-01), Gargaillo
patent: 4969562 (1990-11-01), Saotome
patent: 5301505 (1994-04-01), Wright
patent: 5355676 (1994-10-01), Inokuchi
Hansson Mikael
Nilsson Mikael
Nguyen Hoang
Pressmaster Tool AB
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