PRESSURE CYLINDER PIPE COUPLING

Abstract: A pressure cylinder, such as a master cylinder or wheel cylinder for an hydraulic vehicle braking system, has a plastic moulded body (1) within which a threaded insert (5) is engaged and restrained rotationally and axially. A seal (14) is positioned within the body between surfaces of the insert and body. The insert provides a seat (10) against which is clamped, in use, a corresponding seat on a flared end (11) of a pipe (7), the latter being retained within the body by a pipe nut (8) threadedly engaged with the insert. Long-term thread torque and clamping force are sustained by the insert rather than by the plastic body which can be subject to "creep".

Description: This invention relates to a pressure cylinder of plastics material, such as a master cylinder or wheel cylinder for use in a vehicle hydraulic braking system for example, and is particularly concerned with the connection of a pressure fluid supply pipe to a port of such a cylinder. Cylinders of plastics material are not capable of withstanding the stresses imposed by the conventional arrangement employed in metal pressure cylinders in which a pipe nut engaged in a threaded aperture formed in the cylinder body and tightened to clamp a flared portion of a supply pipe against a seat in the body. Attempts have been made to adapt this conventional arrangement for use with plastic pressure cylinders. In one such adaptation, a separate threaded component is inserted into a guide formation in the plastic cylinder body and receives a pipe nut which clamps a flared pipe end against a seat formed in the body. Although the inserted component sustains the torque arising at the threaded connection between the pipe nut and component, the cylinder body is still required to react the high clamp loading at the pipe flare seat. This can be unsatisfactory in practice because of the long term tendency of plastics materials to "creep" away from highly stressed areas, which can give rise to the pipe nut becoming loose with the consequent risk of fluid leakage. In another adaptation of the conventional pipe nut arrangement, a separate seat member is used in addition to a threaded component, the flared pipe end being clamped against the seat member by a pipe nut screwed into the threaded component, as before. This arrangement exhibits the disadvantage that the separate seat member may be lost in transit or inadvertently omitted during assembly, or when the pipe connection is made, and this can have potentially dangerous consequences in an hydraulic system used for vehicle brake actuation, for example. An object of the invention is to facilitate the connection of a hydraulic supply pipe to a pressure cylinder of plastics material whilst avoiding the disadvantages referred to above. A further object is to provide a method of making an hydraulic pressure cylinder of plastics material which is suitable for forming such a connection. According to one aspect of the invention, a method of making a pressure cylinder comprises moulding from plastics material a body having a cylindrical pressure-receiving chamber therein, a fluid port in communication with said chamber and a socket in communication with the port, placing within the socket an insert intended to form a connection with a pipe to be connected to the cylinder, the insert having an external locking formation for cooperation with the body, providing a sealing element between surfaces of the insert and body, and locking the insert axially and rotationally relative to the body by way of said locking formation, a method being characterised by use of a unitary insert having an integral seat for engagement by a corresponding seat on the pipe, and in that the insert is inserted within the socket by urging the body and insert together axially with the simultaneous application of sonic or ultra-sonic vibration in order to cause entry of the insert into the socket and deformation of body material into engagement with said locking formation in order to lock the insert axially and rotationally relative to the body. This arrangement enables both the long term torque in the screw threads and the clamping force at the seat to be sustained entirely by the insert without the use of additional components, the plastic body merely serving to provide the required axial and rotational restraint and being subjected only to short term forces such as those arising from tightening the pipe nut upon assembly, or hydraulic pressure force acting on the insert, in use. Preferably, the socket is of generally circular form. In one convenient arrangement, the insert provides a formation with an axially outwardly facing surface engaged by an opposed corresponding surface on the body to provide axial restraint of the insert. From another aspect of the invention, a pressure cylinder made by the method of the invention comprises a body moulded from plastics material, a unitary insert engaged within the formed body and restrained to preclude rotational and axial movement thereof, the insert serving to form a connection with a pipe to be connected to the cylinder and which is retained, in use, within the body by retention means cooperating with the insert, and a sealing element between surfaces of the insert and the body, the cylinder being characterised in that the insert is of unitary nature with the seat formed integrally therewith, and in that the rotational and axial restraint of the insert relative to the body is effected by cooperation of the material of the body within the socket with an external locking formation on the insert by deformation of the body material into engagement with said locking formation as a result of the application of sonic vibration during insertion of the insert into the body. In one convenient form of the method, said sealing element is assembled on and carried by the insert prior to insertion of the insert within the socket. The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a transverse cross-section through part of one form of the pressure cylinder of the invention, Figure 2 is a side view of a component of the cylinder of Figure 1, and Figure 3 is a cross-section along the line III-III of Figure 1; Referring to the drawings, the pressure cylinder partly illustrated therein has a body 1 formed of plastics material and containing a cylindrical pressure chamber 2 which, in use, receives a slidable piston (not shown) for pressurising fluid contained within the chamber, in conventional manner. The body is provided with a boss 3 within which is formed a generally cylindrical recess 4 containing an insert 5 of relatively tough material such as metal. The recess 4 communicates with the cylinder 2 via a passage 6 and the insert 5 serves for the connection to the body of a hydraulic fluid supply pipe 7 by means of a conventional pipe nut 8 screwed into a threaded bore 9 of the insert. The insert contains a conical seat 10 engaged, in use, by a conventionally flared pipe end 11, the latter being urged against the seat 10 by screwing the pipe nut 8 into the insert. The insert 5 has a concentric projecting hollow spigot 12 closely received within a relatively small diameter bore portion 13 of the body and a resilient sealing element 14, illustrated as an 0-ring, surrounds the spigot 12 within a peripheral groove 15 thereof and engages an adjacent wall of the recess 13. The seal 14 acts to prevent fluid leakage from the pressure cylinder 2 around the insert 5. Rotational restraint for the insert within the body is provided by a series of longitudinal flutes 16 on the insert, the sides of which flutes are engaged by the material of the body to effect rotational keying, as can be seen from Figure 3. The flutes 16 are divided longitudinally by a circumferential groove 17 in which an annular portion 18 of the body material engages to provide axial restraint of the insert within the body. Between the spigot 12 and flutes 16 is a cylindrical portion 19 which terminates, at its free end, in a larger diameter shoulder 20 and carries a projecting rib 2, the latter providing further axial keying of the insert within the body. The pressure cylinder of Figure 1 to 3 is made by moulding the pressure cylinder 1 from plastics material, as by an injection moulding technique for example. The moulded body is formed with the cylindrical recess 4 of which the diameter is slightly smaller than the maximum external diameter of the insert 5. The seal 14 is placed in the groove 15 and the insert placed against the mouth of the recess with the spigot extending within the recess. The insert and/or body is then subjected to a suitable conventional sonic or ultra-sonic vibration technique whilst the two components are urged together axially, the vibration causing displacement of the body material so as to permit entry of the insert and seal assembly into the recess and keying of the body material with the flutes 16 and groove 17 to lock the insert to the body both rotationally and axially. A portion 22 of the body material also lodges against an axially facing shoulder 23 formed near the outer end of the insert. The pipe 7 may subsequently be fitted using the pipe nut 8 in the manner described above. It is posible to use separate mechanical means to supplement the axial and/or rotational restraint between the insert and body. One example of such means is a pin 33, housed in facing half grooves formed respectively in the insert and body. In the embodiment described, after the initial tightening of the nut 8, both the long-term torque between the nut and insert and the clamping force applied to the seat 10 are sustained by the insert and the problems relating to conventional arrangements discussed herein are thereby overcome. The invention will be seen to provide a simple and effective means of forming a pipe coupling on a pressure cylinder. The assembly of the insert after moulding of the cylinder body has been completed simplifies the moulding procedures required and reduces the time required for moulding. This technique also enables the insert to be fitted in a controlled manner and tested during assembly and the presence and effectiveness of the seal 14 can also be checked at the assembly stage, following which there is no possibility of the seal being removed or displaced prior to installation of the cylinder in its location of use, as for example on a vehicle.

Claims: 1. A method of making a pressure cylinder, comprising moulding from plastics material a body (1) having a cylindrical pressure-receiving chamber (2) therein, a fluid port (6) in communication with said chamber (2) and a socket (4) in communication with the port (6), placing within the socket (4) an insert (5) intended to form a connection with a pipe (7) to be connected to the cylinder, the insert having an external locking formation for cooperation with the body, providing a sealing element (14) between surfaces of the insert and body, and locking the insert axially and rotationally relative to the body by way of said locking formation, the method being characterised by the use of a unitary insert (5) having an integral seat (10) for engagement by a corresponding seat (11) on the pipe (7), and in that the insert is inserted within the socket by urging the body and insert together axially with the simultaneous application of sonic or ultra-sonic vibration in order to cause entry of the insert into the socket and deformation of body material into engagement with said locking formation in order to lock the insert axially and rotationally relative to the body. 2. A method according to Claim 1, wherein the sealing element (14) is assembled on and carried by the insert (5) prior to insertion of the insert (5) within the socket (4). 3. A method according to Claim 1 or Claim 2, characterised in that the body (1) is heated to a temperature at which softening of the plastic occurs prior to insertion of the insert (5) in the socket. 4. A pressure cylinder made by the method of any one of Claims 1 to 3, and comprising a body (1) moulded from plastics material, a unitary insert (5) engaged within the formed body and restrained to preclude rotational and axial movement thereof, the insert serving to form a connection with a pipe (7) to be connected to the cylinder and which is retained, in use, within the body by retention means (8) cooperating with the insert, and a sealing element (14) between surfaces of the insert and the body the cylinder being characterised in that the insert is of a unitary nature with the seat (10) formed integrally therewith, and in that the rotational and axial restraint of the insert relative to the body is effected by cooperation of the material of the body within the socket with an external locking formation (16) on the insert by deformation of the body material into engagement with said locking formation as a result of the application of sonic vibration during insertion of the insert into the body. 5. A pressure cylinder according to Claim 4, characterised in that the seal (14) is carried by the insert and engages the body. 6. A pressure cylinder according to Claim 4 or Claim 5, characterised in that the socket (4) is of generally circular form to receive the insert (5). 7. A pressure cylinder according to any one of Claims 4 to 6, characterised in that the insert (5) provides a formation (17) with an axially outwardly facing surface engaged by an opposed corresponding surface on the body for axial restraint of the insert. 8. A pressure cylinder according to any one of Claims 4 to 7, characterised in that the rotationally restraining formation (16) on the insert comprises two groups of formations separated by a circumferentially extending groove (17) of which one of the side faces co-operates with material (18) of the body to provide axial restraint. 9. A pressure cylinder according to any one of Claims 4 to 8, characterised in that the insert (5) has a projecting relatively small diameter spigot (12) which is closely received with a corresponding bore portion (13) of the body, the spigot (12) being closely surrounded by said seal (14) which engages an internal wall of the body. 10. A pressure cylinder according to Claim 9, characterised in that said spigot (12) is hollow and serves to provide a passage between part of the insert receiving the pipe and a port (6) leading into a pressure cylinder (2) of the body (1). 11. A pressure cylinder according to Claim 9 or Claim 10, characterised in that said seal (14) is housed in an external groove (15) of the spigot. 12. A pressure cylinder according to any one of Claims 4 to 11, characterised in that said retention means is a pipe nut (8) co-operating with a threaded portion (9) of the insert (5).

Inventors: REYNOLDS, DESMOND HENRY JAMES
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1987
Main classification: F16L41
IPC codes: B60T11, F16L41