Double pipe

A double pipe has an outer pipe and an inner pipe that is formed in a spiral or wavy configuration and is held by an inner circumferential face of the outer pipe.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2003-038626 filed on Feb. 17, 2003 and No. 2003-282402 filed on Jul. 30, 2003; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a double pipe and a method of manufacturing the same.

2. Description of Related Art

Piping for circulating, for example, coolant employs, among others, a double pipe composed of an outer pipe and an inner pipe arranged in the outer pipe to form dual passages.

Employing the double pipe makes a piping layout simpler and more compact, and therefore, is advantageous for a piping layout with many restrictions. In particular, a double pipe is highly advantageous for a vehicle air conditioner where a piping layout is greatly limited due to vehicle structure. Employing the double pipe is also advantageous in simplifying air-conditioner assembling work and reducing manufacturing cost.

A conventional double pipe is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2001-341027 that arranges connecting ribs between an outer pipe and an inner pipe of the double pipe. The double pipe with the connecting ribs is usually produced by extruding or drawing an aluminum material through dies.

The extruding or drawing process to form the double pipe having the connecting ribs requires complicated metal dies. In addition, the double pipe with the connecting ribs involves a cutting process of the connecting ribs when terminating ends of the double pipe. These necessities increase the manufacturing cost of the double pipe.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a low-cost double pipe.

In order to accomplish the object, an aspect of the present invention provides a double pipe including an outer pipe and an inner pipe that is spirally formed and is held by an inner circumferential face of the outer pipe.

In order to accomplish the object, another aspect of the present invention provides a double pipe including an outer pipe and a wavy inner pipe that is held by an inner circumferential face of the outer pipe.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be explained with reference to the accompanying drawings.

FIGS. 1A and 1Bshow a double pipe and a method of manufacturing the same according to the first embodiment of the present invention. The double pipe10comprises an outer pipe1and an inner pipe2that are independent of each other. The outer pipe1passes a first fluid therethrough and the inner pipe2passes a second fluid therethrough. The inner pipe2is spirally formed and is held in the outer pipe1. There are no connecting ribs to keep a constant gap between the outer pipe1and the inner pipe2.

A method of manufacturing the double pipe10will be explained. InFIG. 1A, the independent inner pipe2having a small diameter is spirally formed. At this time, the outer diameter of the spiral of the inner pipe2is set to be equal to or slightly smaller than the inner diameter of the outer pipe1. Then, the spiral inner pipe2is inserted into the larger outer pipe1that is independent of the inner pipe2. Then, the outer pipe1is curved into a predetermined shape according to a piping layout as shown inFIG. 1B, so that each curved part of the outer pipe1may press the inner pipe2against an inner wall of the outer pipe1. This results in joining the inner pipe2with the outer pipe1.

As shown inFIGS. 2A and 2B, even at a gently curved part of the outer pipe1, the outer pipe1is flattened or reduced so as to strongly hold or grip the inner pipe2.

Effects of this embodiment will be explained.

The double pipe10is a combination of the outer pipe1and inner pipe2that are independent of each other. Accordingly, unlike the conventional double pipe employing connecting ribs, the double pipe10needs no complicated extrusion dies. Without the connecting ribs, the double pipe10involves a simple termination process, to thereby reduce manufacturing cost.

The first embodiment inserts the spiral inner pipe2into the outer pipe1and bends the outer pipe1according to a piping layout to strongly press and hold the outer pipe1and inner pipe2against each other. This simplifies the manufacturing of the double pipe10.

When inserting the spiral inner pipe2into the outer pipe1, there is a gap between the outer pipe1and the inner pipe2, and therefore, no excessive force is needed for the insertion of the inner pipe.

According to the embodiment, the outer pipe1and inner pipe2press against each other even at locations where the outer pipe1is gently curved, and therefore, the inner pipe2is firmly secured by the outer pipe1even when the double pipe10is installed in a vibrating body, such as a vehicle.

Compared with a straight inner pipe, the spiral inner pipe2has higher rigidity, and therefore, does not easily vibrate and is suitable for vehicle mounting applications.

The outer pipe1and spiral inner pipe2may be pressed against each other in other ways.FIGS. 3 to 6show alterations to locally or wholly deform the outer pipe1toward the inner pipe2, to join the outer pipe1and inner pipe2together.

InFIG. 3, a part of the wall of the outer pipe1is crushed to form a flattened cross-section, to fix the outer pipe1and inner pipe2to each other. Reference numeral5indicates the crushed part.

InFIG. 4, the outer pipe1is ironed to form a reduced diameter so that the outer pipe1may strongly press against the inner pipe2at the reduced part. More precisely, the outer pipe1is drawn through an ironing tool21in the direction of the arrow to reduce the diameter of the outer pipe1so that the outer pipe1and inner pipe2are fixed to each other at the reduced part.

InFIG. 5, the outer pipe1is drawn to reduce the diameter thereof, so that the outer pipe1and inner pipe2are pressed against each other at the reduced part. More precisely, the outer pipe1is drawn with rollers22.

InFIG. 6, the wall of the outer pipe1is crushed by a tool at a plurality of circumferential locations, to join the outer pipe1and inner pipe2together at a plurality of inwardly protruding regions. A reference numeral5indicates the crushed regions or parts. There are a plurality of crushed parts5in the circumferential direction of the outer pipe1. Such crushing may easily be carried out with the use of crushing or rolling tools.

Fixing the outer pipe1to the inner pipe2by locally or wholly deforming the outer pipe1toward the inner pipe2as shown inFIGS. 3 to 6secures the outer pipe1and inner pipe2to each other irrespective of whether or not the double pipe10is curved later. Namely, the outer pipe1and inner pipe2are strongly held together along the entire length thereof including straight parts where no bending is conducted. The spiral inner pipe2is inserted into the outer pipe1with a gap between the two pipes, so that no excessive force is required for the insertion procedure. This makes the manufacturing of the double pipe10easier. A method of manufacturing a double pipe according to the second embodiment of the present invention utilizes a force when inserting an inner pipe into an outer pipe.

The method of manufacturing a double pipe according to the second embodiment will be explained.

FIG. 7shows the double pipe manufacturing method according to the second embodiment. When processing an inner pipe2into a spiral shape, the second embodiment makes an outer diameter D1of the spiral of the inner pipe2greater than an inner diameter D2of an outer pipe1, unlike the first embodiment. After forming the spiral inner pipe2, the second embodiment inserts the inner pipe2into the outer pipe1so that the inner pipe2is pressed against the inner wall of the outer pipe1. When inserting the inner pipe2into the outer pipe1, the resiliency of the spiral inner pipe2is used to reduce the diameter of the spiral. After the insertion, the reaction force of the resilient spiral of the inner pipe2strongly presses the inner pipe2against the outer pipe1. Namely, the difference between the diameters D1and D2works as a fitting margin to fix the outer pipe1and inner pipe2to each other.

Irrespective of whether or not the outer pipe1is curved later, the outer pipe1and inner pipe2are strongly pressed against each other. Namely, the outer pipe1and inner pipe2are strongly joined together along the entire length thereof including straight parts where no bending is applied. Like the first embodiment, the second embodiment involves no connecting ribs between the outer pipe1and the inner pipe2, to reduce manufacturing cost.

Examples of methods of forming an inner pipe2into a spiral shape will be explained with reference toFIGS. 8to10.

The method ofFIGS. 8A to 8Cwill be explained. InFIG. 8A, two inner pipes2are prepared and are spirally wound around each other. InFIG. 8B, the two wound pipes2are released from each other, to provide spiral pipes2. InFIG. 8C, the spiral pipe2is inserted into an outer pipe1, and the outer pipe1and inner pipe2are fixed to each other as discussed above.

The method ofFIGS. 9A to 9Cwill be explained. InFIG. 9A, an inner pipe2and a columnar core31are prepared. InFIG. 9B, the inner pipe2is spirally wound around the core31, and then, the wound inner pipe2is released from the core31to provide a spiral inner pipe2. InFIG. 9C, the spiral inner pipe2is inserted into an outer pipe1, and the outer pipe1and inner pipe2are fixed to each other as discussed above.

The method ofFIGS. 10A to 10Dwill be explained. InFIG. 10A, an inner pipe2and a core32are prepared. The core32is selected so as to make a spiral of the inner pipe2have an outer diameter D0that is greater than a required spiral diameter D1. InFIG. 10B, the inner pipe2is spirally wound around the core32at a narrow pitch. The inner pipe2is released from the core32to provide a spiral inner pipe2. InFIG. 10C, the spiral inner pipe2is extended in an axial direction so that the inner pipe2may have the required outer spiral diameter D1. InFIG. 10D, the spiral inner pipe2is inserted into the outer pipe1, and the outer pipe1and inner pipe2are fixed to each other as mentioned above.

The method ofFIGS. 10A to 10Dprovides the inner pipe2with an outer spiral diameter that is greater than the required outer spiral diameter D1and elongates the spiral inner pipe2to the pitch of extend spiral and reduce the outer spiral diameter to the required outer spiral diameter D1. After the inner pipe2is inserted into the outer pipe1, the inner pipe2is tightly pressed against the outer pipe1due to the springback of the spiral inner pipe2.

The methods shown inFIGS. 8 to 10can form the spiral inner pipe2at low cost without the special metal dies shown inFIGS. 11 to 13.

According to other embodiments of the present invention, an inner pipe2is provided with a spiral shape by extruding or drawing the straight inner pipe2through an extrusion die23as shown inFIG. 11, or through a hot forming die24as shown inFIG. 12, or through a monocoque bender25as shown inFIG. 13.

A method of manufacturing a double pipe according to the third embodiment of the present invention will be explained with reference toFIGS. 14A to 14C.

InFIGS. 14A and 14B, a wavy inner pipe2is formed with a press die41. InFIG. 14C, the inner pipe2is inserted into an outer pipe1, and the inner pipe2is pressed against an inner wall of the outer pipe1. Pressing the inner pipe2against the outer pipe1is achieved by setting an amplitude (wave height) H of the wavy inner pipe2in the manner of any one of the first and second embodiments. For example, the amplitude H of the inner pipe2may be equal to or smaller than an inner diameter D2of the outer pipe1like the first embodiment. Alternatively, the amplitude H of the inner pipe2may be greater than the inner diameter D2of the outer pipe1, like the second embodiment. The details of the first and second embodiments have already been explained, and therefore, are not repeated. Providing the inner pipe2with a wavy shape may be achieved in any manner other than the pressing ofFIGS. 14A and 14B.

The third embodiment provides the same effects as the first and second embodiments.

As explained above, any one of the embodiments of the present invention manufactures a double pipe by inserting a spiral or wavy inner pipe into an outer pipe and pressing the inner pipe and outer pipe against each other without arranging connecting ribs between the inner pipe and the outer pipe. Accordingly, any one of the embodiments needs no complicated extrusion dies when manufacturing the double pipe and simplifies a termination of the double pipe, to thereby reduce the manufacturing cost of the double pipe.

The double pipe according to any one of the embodiments has another advantage.

As a comparison example, a technique is considered that simply inserts an inner pipe into an outer pipe and fixes ends of the inner pipe to the ends of the outer pipe to form a double pipe. This comparison example involves a possibility that one of the outer and inner pipes strongly vibrates due to the vibration of a vehicle in which the double pipe is installed and intermittently comes into contact with the other pipe to produce a chattering noise.

If the double pipe of the comparison example is bent along a given piping layout as shown inFIG. 15, the outer pipe1and inner pipe2will form contacts A, B, C, and D. In particular, the loose contacts C and D may produce a chattering noise due to the vibration of the vehicle. In addition, the inner pipe2may produce a slack E in the outer pipe1. The slack E will produce a large chattering noise at the contact C. To avoid the problem, there may be an idea to enlarge the curvature of each bend so that the inner pipe2may be strongly pressed against an inner wall of the outer pipe1. However, such an arrangement restricts the shape of each bend of the double pipe. On the other hand, any one of the embodiments firmly fixes the outer and inner pipes of a double pipe to each other to suppress a chattering noise without restricting the shape of each bend of the double pipe.

In each of the above embodiments, the inner pipe is arranged in a spiral or wavy configuration along the entire length of the pipe. The present invention also allows other arrangements in which the inner pipe is arranged in a spiral or wavy configuration and has partially straight parts.

Although the present invention has been explained in connection with the embodiments, it will be appreciated by those skilled in the art that the present invention is not limited by the embodiments. Without departing from the scope and spirit of the present invention defined in the claims, the present invention may allow many modifications or alterations. Accordingly, the descriptions in this application are only for explanatory purposes and are not intended to limit the present invention.