Abstract:
A thin flexible metal tube comprising two flexible bendable portions having low corrugations and a straight flexible portion having higher corrugations easy to absorb vibrations and disposed between both the bendable portions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a thin flexible metal tube used, for example, at a radiator, and required to be bent in use, subjected to large vibrations under conditions of high temperature and high pressure, and required to have reliable durability. 
     2Description of the Prior Art 
     As a conventional technique of such field, for example, a tube connecting an engine 11 and a radiator 12 includes a flexible rubber tube 13 having large flexibility to abosrb great vibrations generated by the engine and transmitted, as shown in FIG. 6. 
     However, the tube is so thick to satisfy the required pressure tightness, and, therefore, weighty. It must usually be bent in use, so that it is low in productivity and expensive. In addition, since it is made of rubber, it has low heat and weather resistances, so that it is likely to be deteriorated and cracked due to vibrations applied for a long time. Namely, it has the problem of durability. 
     It is therefore an object of this invention to provide a flexible tube which solves the problems of low productivity, durability and reliability with the conventional flexible tube. 
     In order to achieve the object, this invention provides a thin flexible metal tube made, for example, of stainless steel, and including a low-corrugation bendable portion and a higher-corrugation straight portion, preferably, having a successive-U- or -Ω(omega)-like cross section. Provision of the low-corrugation bendable portion in the tube serves to facilitate the bending of the tube with a small force and to increase the rigidity of the bendable portion and to transmit vibrations applied externally to the straight portion. On the other hand, provision of higher-corrugation straight portion of an successive-U- or -Ω-like cross section serves to absorb vibration transmitted externally via the bendable portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a thin flexible metal tube according to this invention. 
     FIG. 2 is a partially cutaway cross-sectional view of a radiator tube provided in a vehicle; 
     FIG. 3 is an enlarged cross-sectional view taken along the line III--III of FIG. 1; 
     FIG. 4 is an enlarged cross-sectional view taken along the line IV--IV of FIG. 1; 
     FIG. 5 is a view, similar to FIG. 4, of another embodiment; 
     FIG. 6 is a side view of a conventional flexible rubber tube. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the drawings, reference numerals 1, 2 and 3 denot an engine, a radiator and a thin flexible metal tube according to this invention, respectively. The tube 3 is made, for example, of thin stainless steel of a material SUS 304, and has an outer diameter 40 mm and a thickness of 0.3 mm. For bending purposes, the stainless steel tube has two bendable flexible corrugated portions 3a, one near each of the engine 1 and radiator 2, each having a successive-U-like cross section in which the top-top diameter is 45 mm, the bottom-bottom diameter is 40 mm and the pitch is 9 mm (FIG. 3). The tube has an intermediate straight flexible corrugated portion 3b between the bendable portions 3a for absorbing vibrations. The straight portion has a successive-Ω-cross section in which the top-top diameter is 52 mm, the bottom-bottom diameter is 40 mm and the pitch is 6 mm (FIG. 4). Reference numeral 4 denotes a spool which accommodates an O-seal ring 5; 6, a slip off-preventive U-like band; 7, a draw-preventive pawl; 8, an annular groove provided on a connection branch tube of the radiator 2 for engaging the pawl 7. 
     By such arrangement, it is possible to bend the bendable portions 3a in a short time using an inexpensive manual bender so that the radius of curvature of the bendable portion is 40 mm (from the center of curvature to the center of the bendable portion) when the tube is disposed so as to connect the engine 1 and the radiator 2. It is unnecessary to use a power bender or the like which would be required to bend a tube without flexible portions. The bending process results in an increased tube rigidity compared to the unbent original tube, so that there is little deformation due to vibrations in the bendable portions 3a, thereby reducing stresses generated. The straight portion 3b, which has flexible higher-corrugation successive-Ω-cross section, collectively absorbs vibrations transmitted through the bendable portions 3a. The higher-corrugation successive-Ω-cross-sectional corrugation results in the scatter of stresses, thereby reducing the stresses generated, absorbing vibrations and providing highly reliable duarability. 
     FIG. 5 shows another embodiment of this invention in which the flexible vibration absorbing portion 3b has a higher-corrugation successive-U-like cross section to provide an effect equal to that provided by the tube having the cross-section of FIG. 4. 
     The thin flexible metal tube according to this invention and a conventional flexible rubber tube were compared. The flexible rubber tube had an outer diameter of 45 mm, a thickness of 4 mm, an extended length of about 360 mm and a weight of about 250 grams while the embodiment of this invention had a weight of about 190 grams which was about 25% lighter than the conventional tube, had no cracks such as those which would be generated due to low heat and weather resistances in the conventional rubber tube and did not require large heat energy consumption and a long bending time which would be required for bending the conventional rubber tube (including the steps of winding a sheet of cloth around a bent core bar many times, and vulcanizing and shaping the resulting product). 
     As described above, a flexible tube provided by this invention has flexibility equal to, or higher than, the conventional rubber flexible tube, is free from fragility and hence cracks and leakage such as would be generated due to low heat and weather resistances with the conventional rubber tube, and improves its heat resistance, durability and reliability. This invention does not require any so-called rubber hose bending process which includes winding a rubber sheet and optionally a cord around a bent core bar repeatedly, applying a pressure to the resulting semi-finished product using a metal mold, keeping the semi-finished product at a high temperature for a long time, vulcanizing it, cooling it to lift the semi-finished product off the core bar (subsequently the process may require a secondary vulcanizing process depending on the kind of rubber used). Therefore, the number of processes is greatly reduced, the processing time and energy are saved, and the tube is manufactured inexpensively. 
     In addition, according to this invention, the bendable portion includes a corrugated flexible portion although the corrugations are low, so that bending can be performed by a small bending force with the aid of a simple manual bender.