The present invention relates to a gripper ring for a tube coupling, said coupling comprising a one piece or divisible nipple and a sealing ring, preferably an O-ring, said gripper ring being adapted to be situated axially outside of the sealing ring and having an external conical surface adapted to cooperate with a complementary conical surface inside the nipple or inside an attached element of the nipple, in order to cause compression of the gripper ring.

A tube coupling of this kind is known from US-PS 3.815.940. The gripper ring is split, and cooperates with a conical surface inside the nipple, which is not divisible. There¬ fore, the gripper ring must be able to be substantially deformed in order to be placed inside the nipple. Another possibility, which is near at hand, is to use a separate element, for instance some kind of nut which is attached after the gripper ring has been brought into place.

Said known gripper ring has an axially innermost edge which is bevelled externally, in order to permit the O-ring to be pressed into the thereby defined annular groove when the pressure inside the coupling is extremely high.

Said type of couplings is adapted to be used in such a manner that a tube or hose is introduced into the coupling after the O-ring and the gripper ring have been brought into place inside the nipple, possibly inside an attached element of the nipple. The locking of the tube or hose is achieved by means of the gripper ring, which clamps suffi¬ ciently around the tube or hose to effect that the gripper ring will follow the axial movements of the tube or hose. Thus, when the coupling and the tube are pressurized for the first time after the mounting of the tube, or the coup¬ ling and the tube are exposed to an axial, mechanical force

tending to bring those parts apart, the tube and the gripper ring will move slightly axially outwardly relative¬ ly to the nipple, and the gripper ring will be further compressed around the tube when the gripper ring enters the conical surface in the nipple or in the attached element thereof. By some applications of such couplings it is of vital importance that the tube is clamped and held safely in place by means of the gripper ring and that a proper sealing is achieved by means of the O-ring (or a sealing ring having another cross sectional shape) , and as far as the mounting of the tube in the nipple is concerned it is desirable that the resistance against the mounting is as small as possible, because in some applications it may be a very small working space, and moreover the tubes may bend during the attempt of mounting. An example of an applica¬ tion where the clamping, the sealing and the small resis¬ tance against the mounting of tubes or hoses are very impor¬ tant is brake systems for larger vehicles, such as trucks and buses, in which the number of couplings may be more than 100 per vehicle. The nipples, having their O-ring and gripper ring properly situated, and having their possible attached element properly fastened, said element being for instance a nut having an inner conical surface, are fastened at the proper locations on the vehicle, whereafter tubes or hoses of proper lengths, and possible bent to the desired shape, are mounted by being forced into the nipples, until their ends abut shoulders in the bores of the nipples or until a mark on the tubes or hoses is no longer visible, in order to ensure that the tubes or hoses have been moved sufficiently into the nipples. Such a procedure of mounting the tubes is very simple and time-saving compared with the tightening of each nut after the tubes or hoses have been moved into the nipples, and moreover it is avoided a tightening more or less at random with respect to the torque applied, or a time-consuming tightening with the use of a torque wrench, because the tightening, by use of said type of couplings, is carried out in connection with the manu-

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facture of the coupling parts.

Said type of couplings has, however, caused certain prob¬ lems, and in particular when being used together with plastic tubes. Even when the tubes are reinforced they have a tendency to sag during long-lasting strain. In couplings of said type the tube is exposed to an external pressure from the sealing ring. The pressure is necessary to ensure sealing, and must in some applications be rather high. In order to achieve this, the sealing ring must have an opening which in not expanded condition is relatively much smaller than the outer dimension of the tube, thus causing the sealing ring to contract as the diameter of the tube is gradually reduced because of the sag. The relative¬ ly small diameter of the opening in the ring, however, acts more or less to prevent the mounting of the tube. One possibility to avoid this is to taper the end of the tube, but it is desirable to avoid the encreased costs involved therein.

Also the gripper ring causes resistance against the mounting of the tube. Although it is usual that the gripper ring is tapered on its axially outermost end, as shown in said US Patent, this is not sufficient to achieve that the mounting can be carried out with as small resistance as desired, and particularly not when the gripper ring is adapted to give a relatively high pressure against the tube.

A further problem is related to the manufacture of the gripper rings, in cases when it is necessary to provide a surface layer in order to encrease the resistance against corrosion. The most attractive method of surface treat¬ ment, seen from the view point of corrosion resistance and economy, is the use of electric current, and by the use of such a method it has been found necessary to tumble the gripper rings, i.e. to place the rings in a rotatable con¬ tainer, in order to ensure that the surface treatment takes

place on the entire surface. During the tumbling the rings will scrub against each other, and it is of great impor¬ tance to avoid that the sharp edge intended to be forced into the tube wall is not blunted. The present invention leads to a solution of this problem.

The main object of the present invention is, however, to achieve reduced resistance against the mounting of the tube. From the above example of application in the brake system of a vehicle it will be apparent that an improvement is highly desirable. Said application and several other applications necessitate a high degree of safety against leakages and loosening of the tubes from the couplings, and moreover a simplified mounting of the tubes will have great economic consequences.

In accordance with the present, invention the above object is achieved by means of a gripper ring as disclosed intro- ductorily and which is characterized in that the inner sur¬ face of the gripper ring is conical substantially in its entire length, and that the axially innermost end of the gripper ring is tapered in such a manner that the sealing ring is caused to expand when the gripper ring is pressed axially against the sealing ring.

In accordance with an embodiment the gripper ring has only a single gripper edge, positioned substantially axially innermost on the conical inner surface, the edge being preferably situated in a slight distance from said inner¬ most end of the gripper ring. Thereby, the edge is protec¬ ted against being blunted prior to being placed in a nipple, as for instance during said tumbling or by handling, storing and transportation.

Due to the fact that the gripper ring is conical along at least the major part of its length the conus angle may be small, and consequently the axial force necessary to move

a tube through the opening in the gripper ring will be small, also in case the smallest diameter of the gripper ring opening, i.e. the diameter of the gripper edge, is relatively much smaller than the outer diameter of the tube when the gripper ring is not expanded.

When a tube is being mounted, the gripper ring will be pressed axially against the sealing ring, and the tapered, axially innermost end of the gripper ring will act to expand the sealing ring sufficiently to facilitate the mounting of the tube.

It is preferred that the gripper ring has only a single gripper edge. Thereby, the conical inner surface will have a maximum length (with a given total length of the ring) , and easy mounting is ensured by providing that the outer¬ most, largest opening of the ring has a diameter which is sufficiently larger than the tube diameter, because the conus angle will be relatively small by a given difference between the largest and smallest diameter of said opening.

The invention will hereinafter be described morein detail, by means of two embodiments shown in the accompanying drawing.

Fig. 1 shows a gripper ring in accordance with the present invention placed within a coupling which comprises a nipple having an attached element and a sealing ring.

Fig. 2 shows another embodiment of the gripper ring, placed within a somewhat different tube coupling.

The tube coupling shown in Fig. 1 comprises a nipple 1 having an attached element 4 in the form of a nut, and further an O-ring 2 and a gripper ring 3. Also shown is the end of a tube 5 mounted in the nipple 1.

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The gripper ring 3 has a conical inner surface, the largest inner diameter of the ring facing outwardly of the nipple 1 , and the gripper ring is tapered towards the O-ring 2, the conus angle of the tapered end being substantially larger than that of said inner surface, whereby a sharp edge is defined between the conical inner surface and the tapered end. Moreover, the gripper ring has a third coni¬ cal, outer surface, adapted to cooperate with a complemen¬ tary conical surface in the attached element 4 of the nipple.

When the attached element 4 has been screwed into the main part of the nipple 1 and tightened, there is still a space to permit a certain axial movement of the gripper ring 3. The gripper ring 3 is split, and the conical inner surface thereof will permit entering of the tube 5. When the tube is moved inwardly the gripper ring will be pressed axially towards and against the O-ring 2, and the tapered surface facing the O-ring will cause expansion of the O-ring, which in its relaxed condition has a somewhat smaller inner diameter than the outer diameter of the tube. The inner conical surface of the gripper ring has a small conus angle and causes a very small resistance against the movement of the tube.

After the tube has been mounted any small axial movement of the tube outwardly will cause the gripper edge of the gripper ring 3 to clamp the tube, because the gripper ring will be compressed when being moved axially outwardly relatively to the attached element 4. Simultaneously the expansion of the O-ring caused by the gripper ring will cease, and the O-ring will press against the tube with its full sealing force.

Fig. 2 shows an embodiment of the gripper ring 3 where the gripper edge 6 is situated at a slight distance from the axially innermost end of the ring. Thereby, the edge is

protected against damage and blunting, as for instance during said tumbling of the surface treatment.

Moreover, the coupling shown in Fig. 2 is somewhat different from that of Fig. 1 , in that the attached element 4 is screwed on external threads on the main part of the nipple 1 , said element having an inner groove which receives the O-ring 2. Further, the nipple 1 comprises a sleeve-like part 7, which upon the mounting of the tube is situated in¬ side the tube and prevents radial compression of the tube. By this embodiment the gripper ring 3 is placed in the attached element 4, whereupon the O-ring 2 is placed in its groove. Thereby, the gripper ring is prevented in falling out of the element 4 before the element 4 is screwed on the nipple part 1. In the embodiment shown the groove for the O-ring is shallow, and when the nipple part 1 and the element 4 have been screwed together a shoulder inside the nipple part 1 forms the major part of the abutment for the O-ring.

It will be appreciated that a gripper ring according to the present invention may be applied in different kinds of couplings as far as different combinations of a nipple main part and an attached element thereof are concerned. The only necessary features in this respect are that the nipple, possibly comprising an attached element, defines a space for. the gripper ring and a sealing ring, and that there exists an inner conical surface adapted to cooperate with an outer conical surface of the gripper ring.

It will also be appreciated that the conus angles may be different from what is shown. In the illustrated embodi¬ ments the inner conus angle of the gripper ring is rather small, and it may be desirable to use an encreased conus angle in order to ensure that the gripper edge is forced sufficiently into the tube wall. It will still be ensured a small resistance against mounting of the tube compared

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with the use of prior art gripper rings, said prior art rings usually having a tapering for the entering of the tube of about 45 , i.e. a conus angle of about 90°. A suitable inner conus angle of a gripper ring in accordance with the present invention may for instance be about 30 .

Moreover, it will be appreciated that the nipple may be constructed mainly as shown in the above mentioned US Paten 3.815.940, i.e. having a conical element formed integrally with the main part of the nipple.