This invention relates to a hydraulic cylinder and a method of forming a hydraulic cylinder.

Hydraulic cylinder assemblies are in common usage. The typical assembly includes a cylindrical main body member and a piston assembly disposed within the central bore of the cylindrical main body member. Pressurized hydraulic fluid is discharged from the cylindrical main body member in response to stroking reciprocal movement of the piston assembly within the bore of the cylindrical main body. Hydraulic cylinder assemblies were originally formed primarily of metallic materials but attempts have been made to form at least the cylindrical main body of the assembly out of a plastic material so as to facilitate the manufacturing process and reduce the cost of the assembly. Examples of such cylinders are shown in US-A-3 040 712. Forming the main body cylindrical member out of plastic, while reducing cost, has the disadvantage of creating sink marks along the bore of the cylinder adjacent the locations where appendages, such as mounting flanges and reservoirs, are provided exteriorally of the cylinder body. The sink marks interfere with effective sealing as between the elastomeric seals carried by the piston assembly and the bore of the cylinder and

further introduce a rocking or wobbling potential with respect to the piston assembly with resultant excessive wear of the piston assembly. In US-A-3 040 712 an appendage is provided in the form of a cap having a flattened tongue aranged to receive a clevis pin but it is necessary to mould both the cap and cylinder body separately and assemble them manually which is disadvantageous.

This invention is directed to the provision of an improved hydraulic cylinder assembly of the plastic type and a method of forming the same in which the creation of harmful sink marks along the bore of the cylindrical body is substantially eliminated or reduced and in which an appendage can be more readily provided.

According to one aspect of the invention the method applies to the formation of a hydraulic cylinder assembly of the type including a main body cylinder defining a central axial bore, a piston assembly mounted for reciprocal stroking axial movement in the bore, and an external appendage on the main body cylinder, the method comprising forming the main body cylinder and the appendage in a two step operation wherein one step comprises forming the main body cylinder with a cylindrical wall thickness t

while simultaneously forming an external wall on the exterior periphery of the cylinder body having an axial thickness not substantially exceeding t and the other step comprises forming an appendage having a portion sized to coact with the external walls on the cylinder body to form an external wall thickness at the juncture of the appendage with the cylinder body having a value substantially exceeding t, one of which forming steps interconnects the appendage and main body.

According to another aspect of the invention there is provided a method of forming a hydraulic cylinder including a main body defining a central axial bore for receiving a piston for axial movement in the bore, and an external appendage on said main body, said method comprising forming at least one of the main body and external appendage by a moulding step, said main body having a cylindrical wall thickness t and an external wall on the exterior periphery of said main body having an axial thickness not substantially exceeding t and causing by said moulding step said appendage and external wall to be interconnected to form an external axial wall thickness adjacent said main body having a value substantially exceeding t.

Such a forming operation has the effect of substantially eliminating any sink marks on the bore of the cylinder and the moulding operation effects the interconnection between the cylinder main body and appendage which is advantageous over US-A-3 040 712.

Preferably the external wall formed on the cylinder body comprises an external annular flange around the cylinder body having an axial thickness not substantially exceeding t and, in a further operation, the axial thickness of the external flange is effectively increased to a value substantially exceeding t so as to define a structurally adequate mounting appendage for the hydraulic cylinder assembly.

The cylinder main body preferably includes a moulded closure at one end which may define a passageway for hydraulic fluid.

Instead of taking the form of a mounting for the cylinder, the appendage may comprise an integral reservoir.

The main body forming step may be performed prior to the appendage forming step or vice versa.

The method may include forming the main body and appendage by moulding plastics material. The body and the appendage may be moulded from different materials. An annular member e.g. of metal, may extend around the cylinder main body adjacent to the external wall and the method may include introducing material around the annular metal member so as to define a mounting flange of substantial dimensions and further reinforced by the annular member, which may be formed from metal .

The method may include forming two axially spaced external walls on said main body with said annular member between said axial ly spaced walls. Each axial ly spaced wall may have an axial thickness not substantially exceeding t, and the annular member is preferably positioned between the axially spaced walls.

The method may include forming said external wall to provide an integral rim joined to the main body by an annular wall having said thickness not substantially exceeding t. The appendage is preferably formed as a reservoir which may have an annular mounting portion which coacts with said rim.

The rim is preferably an integral closed loop rim and the method may include moulding the reservoir around the closed loop rim on the cylinder main body to form said annular mounting portion mouldingly surrounding the rim on the main body and an annular main body portion positioned radially outwardly from the mounting portion and defining a main body of the reservoir. Alternatively the reservoir may be pre¬ formed and the main body moulded on to the reservoir.

According to a further aspect of the invention there is provided a method of forming a hydraulic cylinder assembly having a plastics cylinder body having a central axial bore and an integral reservoir communicating with said bore, said method comprising forming said plastics cylinder body with a cylindrical wall thickness t while simultaneously moulding an integral closed loop rim externally of said cylinder body and joined to the cylindrical wall of said cylinder body by an annular wall having an axial thickness not substantially exceeding t and forming a reservoir having an annular mounting portion sized to coact with said rim to form an axial wall thickness at the juncture of said reservoir with said cylinder main body substantially exceeding t, one of which forming steps interconnects the reservoir and main body.

The method may include forming the main body and/or the appendage by moulding plastic material.

According to yet another aspect of the invention there is provided method of forming a hydraulic cylinder assembly having a plastic cylinder body defining a central axial bore and an integral external annular mounting flange, said method comprising forming said plastics cylinder body with a cylindrical wall thickness t while simultaneously forming an external annular wall around said cylinder body having an axial thickness not substantially exceeding t and forming an annular mounting flange having a central annular portion sized to coact with said external wall on said cylinder body to form an external axial wall thickness at the juncture of said mounting flange with said cylinder body having a value substantially exceeding t, the forming of the cylinder body or forming of the annular mouting flange interconnecting the cylinder body and annular mounting flange.

In all the disclosed invention embodiments and features, the step of moulding the cylinder body may comprise the initial step in the invention process or, alternatively, the desired flange or reservoir

appendage may be formed in the initial step and thereafter utilized as a mould cavity insert around which the cylinder body is thereafter moulded.

The method may include providing an appendage in the form of a mounting flange and moulding material to mould a cylindrical mounting portion of the flange on to the main body so that moulded material forms an axially extending portion which overlies the cylindrical mounting portion.

According to a still further aspect of the invention there is provided a hydraulic cylinder including a main body defining a central axial bore for receiving a piston for axial movement in the bore and an external appendage on said main body, the main body having a cylindrical wall thickness t and having an external wall on the periphery of the cylinder body having an axial thickness not substantially exceeding t, at least one of the appendage and main body being moulded on to the other with the appendage coacting with said external wall to form an external axial wall thickness adjacent said cylindrical body having a value substantially exceeding t.

The appendage may take the form of a mounting flange which may include a cylindrical mounting portion

which lies beneath a moulded axially extending portion. The axial ly extended portion may be of annular form and may be radially spaced from the external wall of the main body. The cylindrical portion may be positioned between two axial ly spaced external walls one of which preferably carries the axially extending portion.

An annular member, e.g, of metal, may extend around the main body in juxtaposition to said external wall, the appendage being formed so as to extend around said annular member.

The annular member may be positioned between two axially spaced external walls on the main body. The annular member may have an annular body portion extending axially of said main body and a radial portion extending outwardly from the body portion, the appendage being formed around and radially outwardly of said radial portion. A plurality of said radial portions may be provided in axially spaced relation on said body portion of the annular member.

The external wall may include an integral rim joined to the main body by an annular wall having said thickness t. The appendage, preferably a reservoir,

may coact with said rim.

Preferably the external axial wall thickness is of a value substantially exceeding t at a juncture of said appendage with said cylindrical body.

Fig.1 is a cross-sectional view of a hydraulic master cylinder assembly according to the invention following a first moulding operation,

Fig.2 is a cross-sectional view of a hydraulic master cylinder assembly according to the invention following a second moulding operation,

Fig.3 is a cross-sectional view of a modified form of hydraulic master cylinder assembly according to the invention,

Fig.4 is a cross-sectional view of a further modified form of hydraulic master cylinder assembly according to the invention,

Figs.6 and 7 illustrate the invention as applied to the formation of a mounting flange on a hydraulic slave cylinder assembly, and

Figs.8 - 10 illustrate a still further modified form of hydraulic cylinder assembly according to the invention.

The hydraulic master cylinder assembly seen in Fig.1 includes a cylinder body 10 and a piston assembly 12. Cylinder body 10 is preferably formed of a plastic polymer material such, for example, as a polyamide. Specifically, cylinder 10 may be formed of Nylon 6-6 with glass fibre reinforcement. Body.10 includes a cylindrical main body portion 10a defining a cylindrical axial bore 10b, an end wall 10c closing the forward end of the cylinder and defining a central reservoir port 10d, a reservoir fitting 10e defining a central reservoir passage 10f communicating at its lower end with discharge port 10d, a discharge port 1Og defined by a discharge fitting 10h, and an external annular flange 10i generally adjacent the open end 10j of the cylinder body.

Piston assembly 12 includes a piston 14, a pushrod retainer 16, a valve stem 18, a valve stem retainer 20, a valving assembly 22, and a return spring 24. Piston 14 includes a nose portion 14a, a forward land portion 14b, a central spool portion 14c, and a rearward land portion 14d. Pushrod retainer 16 fits

into a blind bore 14e in the rearward end of piston 14 and includes spring finger portions 16a for trapping receipt of the head of a pushrod (not shown). Retainer 16 further includes an annular rearward flange portion 16b coacting with a snap ring 24 received in an annular retainer 26 to define the retracted position of the piston in the bore 10b. Valve stem retainer 20 is fitted over the forward end of piston nose portion 14a and coacts with piston land portion 14b to define an annular groove for receipt of an annular elastomeric seal 28. Retainer 20 includes a plurality of forwardly extending finger portions 20a snappingly receiving the head portion 18a of retainer 18 with head portion 18a being free to move relative to the piston in a blind bore 14f opening at the forward end of the piston. Valving assembly 22 includes a retainer member 30 positioned in concentric relation around reservoir port 10d and passing the forward end of stem 18, an elastomeric member 32 carried on the free forward end of stem 18 for sealing coaction with reservoir port 10d, and a spring 34 positioned within retainer 30.

It will be understood that the hydraulic master cylinder assembly illustrated in Fig.1 is of the centre feed type in which the piston, in its extreme retracted position, acts through the head 18a of

valve stem 18 to maintain elastomeric member 32 in a position clear of reservoir port 1Od so as to establish communication between the reservoir and the bore 10b and ensure that the bore 10b is totally filled with hydraulic fluid forwardly of the piston, and in which elastomeric member 32 moves into sealing engagement with reservoir port 1Od upon forward stroking movement of the piston so as to block communication between bore 10b and the reservoir and ensure the discharge of pressurized fluid through discharge port 10g to the user device ^' .

Cylinder body 10, as seen in Fig.1, is formed in a single moulding operation in which the reservoir fitting 10e, the discharge fitting 10h, and the external flange 10i are simultaneously formed. Cylinder body 10 has a cylindrical wall thickness t and flange 10i is formed with an axial wall thickness preferably equal to 1/4 to 1/2 t and, in any event, not substantially greater than t. It is critical that the axial thickness of flange 10i does not substantially exceed the thickness t of the cylinder wall since there is a high likelihood that sink marks will otherwise form along the internal periphery of bore 10b adjacent flange 10i. Flange 10i further includes several small triangular ribs 10j spaced circumferentially around the exterior of the

cylinder. The ribs 10j are spaced far enough apart and are of small enough volume so as not to create a danger of sink marks on the bore of the cylinder immediately adjacent the ribs.

Following the moulding and cooling of the cylinder body as shown in Fig.1, a further moulding operation is performed in which a large flange 10k is moulded around the small flange 10i. Specifically, as seen in Fig.2, flange 10k includes a radially inner annular hub portion 101 having an axial dimension substantially exceeding the axial dimension of flange 10i and substantially exceeding the cylindrical wall thickness t, and further incudes a radially outwardly extending annular portion 10m extending substantially radially outwardly from flange 10i and defining mounting holes 10n for receipt of suitable fasteners to secure the hydraulic cylinder assembly to a suitable mounting structure. Hub portion 101 mouldingly and tightly embraces and surrounds small flange 10i so as to form a composite, unitary, integral flange structure on the external periphery of the cylinder including the small flange 10i and the large flange 10k moulded thereto and therearound.

This two step moulding operation allows the formation of a structurally adequate mounting flange on a

plastic cylinder without creating any sink marks along the bore of the cylinder such as would interfere with the sealing action of seal 28 of such as would create wobble of the piston assembly 12 and ultimate wear of the piston assembly.

Whereas the invention has been illustrated and described in connection with Figs.1 and 2 as involving the formation of cylinder body 10 and small flange 10i prior to the addition of the large flange 10k, it will be apparent that the steps may be reversed. That is, the large flange 10k could be formed in a first moulding operation and used as an insert in the moulding body tool or mould cavity, and the cylindrical body 10 and small flange 10i could thereafter be formed by injection into the mould cavity with the large flange 10k positioned therein. It will also be understood that the invention can be carried out using a single tool or mould with twin injection heads wherein the cylinder body is formed utilising the first injection head and the large flange is formed utilising the second injection head, with the only requirement being that the plastic injected utilising the first head be allowed to set up (a matter of only a few seconds) prior to the utilisation of the second injection head to perform the second moulding operation.

It will further be understood that annular retainer 26 is mouldingly positioned within the open end 10j of the cylinder body during the moulding operation in which the cylinder body is formed, and that piston assembly 12 is positioned within bore 10d following the two step invention moulding operation to form the completed cylinder assembly.

A further form of the invention is illustrated by the hydraulic master cylinder assembly shown in Fig.3. The hydraulic master cylinder assembly shown in Fig.3 is identical to the hydraulic master cylinder assembly seen in Figs.1 and 2 with the exception that the external mounting flange is provided by moulding a pair of axially spaced external annular flanges 10p on the external periphery of the body 10 and mouldingly positioning a metallic annular insert member 36 axially between the flanges 10p. In practice, member 36 would be used as an insert in the mould cavity and the body 10, including flanges 10p, would be moulded around the insert to produce the configuration shown in Fig.3, whereafter large flange portion 10q would be moulded around flanges 10p and around insert 36 in a further moulding operation to provide an external mounting flange having the required structural integrity for use in mounting the

hydraulic cylinder assembly to an associated structure. Annular insert 36 may be formed of steel or a suitable powdered metal and includes an annular body portion 36a extending axially between flanges 10p and an external rib portion 36b extending radially outwardly from the main body portion 36a and totally encased by flange 10q in the final moulded configuration of the hydraulic cylinder assembly. Flanges 10p have an axial dimension less than the thickness t of the cylinder wall so as to minimize the possibility of sink marks being formed along the internal bore of the cylinder. The steel or powdered metal insert 36 has the effect of adding structural rigidity to the flange structure and further services to resist shrinkage of the composite structure.

The invention is seen in Fig.4 as applied to a hydraulic master cylinder assembly of the centre feed type in which a reservoir is moulded integrally with the cylinder body. Although the piston assembly is not shown in fig.4, it will be understood that the piston assembly of Fig.4 operates in the same manner and is constructed in the same manner as the piston assembly seen in Figs.1 and 2.

In the hydraulic cylinder assembly of Fig. , the cylinder body 10 is moulded to provide the main body

10a of the cylinder having a cylindrical wall thickness t and defining a bore 10b, and an integral external wall 1 Ow comprising a closed loop rim 10r, preferably of a circular configuration, is simultaneously formed integrally with the cylinder body 0 and including an annular lip portion 10s and an annular wall 10t defining an opening 10u therewithin which communicates with reservoir passage 10f. Annular wall 10t has an axial dimension or thickness that is less than the thickness t of the cylinder wall so as to minimize the danger of forming a sink along the internal bore 10b adjacent the annular wall 10t.

Following the formation of the cylinder body 10 including the integral closed loop rim 10r, a further moulding operation is performed in which a reservoir 38 is moulded onto the rim 10r. Reservoir 38 includes an annular mounting portion 38a surrounding cylinder body rim portion 10r and an annular main body portion 38b positioned radially outwardly from mounting portion 38a and defining the main body of the reservoir. it will be seen that cylinder mounting portion 38a mouldingly and lockingly engages cylinder main body rim portion 10r to form a reservoir that is integral with respect to the cylinder body 10.

The invention is seen in Fig.5 as applied to a hydraulic master cylinder assembly of the seal over port type in which, in the completed cylinder assembly, the forward annular seal 40 carried by the piston 42 coacts in known manner with a pair of reservoir ports 1 Ou and 10v in the wall of the cylinder body 10a to immediately seal the bore 10b of the cylinder body from the reservoir in response to forward stroking movement of the piston and to provide communication between the reservoir and the annular area behind the forward land portion of the piston in the fully retracted position of the piston.

In the invention as applied to the seal over port master cylinder assembly of Fig.5, an integral external wall 10w preferably of a circular configuration, is formed during the moulding operation in which the cylinder body 10a is formed. Wall 1 Ow is positioned on the exterior of cylinder body 10a in surrounding relation to ports 10u and 1 Ov and includes an annular closed loop rim 10x and an annular wall portion 1 Oy defining an opening 10z therewithin communicating with ports 1 Ou and 10v. The axial wall thickness of annular wall 1 Oy is less than the thickness t of the cylindrical walls of cylinder body 10a so as to minimise the possibility

of sink marks being formed along the internal bore 10b of the cylinder body in the area of annular wall 10y.

A pair of axially spaced external flanges 44 are also formed on the external periphery of cylinder body 10a during the initial moulding operation and an annular metallic member 46, positioned as an insert in the mould cavity prior to the injection moulding of the cylinder body, is moldingly positioned between flanges 44. Flanges 44 have an axial thickness less than the wall thickness t of the cylinder body so as to minimise the possibility of sink marks being formed on the internal bore 10b of the cylinder body adjacent the flanges 44. Metallic annular member 46 includes a series of axially spaced external ribs 46a.

Following the initial moulding operation to form the cylinder body 10a together with the integral reservoir rim 1 Ow and the flanges 44 moldingly surround the metal insert 46, the cylinder body is subjected to a further moulding operation in which a reservoir 48 is moulded to rim 10w and a mounting flange 50 is moulded to flanges 44 and metal insert 46. Reservoir 48 includes an annular mounting portion 48a moulded in surrounding relation to rim

10w and an annular main body portion 48b positioned radially outwardly from mounting portion 48a and defining the main body of the reservoir. Flange 50 is moulded in surround relation to flanges 44 and to metal insert 46 with the inner peripheral annular hub portion 50a of the flange 50 moldingly and interlockingly coacting with ribs 46a on insert 46 to firmly and integrally secure flange 50 to cylinder body 10a.

The invention is seen in Figs.6 and 7 as applied to a hydraulic master cylinder assembly of the slave type. The cylinder body 52 of the slave cylinder of Figs.6 and 7 includes a main body portion 52a defining a central bore 52b and defining cylindrical walls having a thickness t of the cylinder walls. During initial moulding of the cylinder body 52, an annular metal insert 53 is positioned in the mould cavity and the cylinder body 52 is moulded around the insert so as to position the insert moldingly between flanges 52e. Insert 53 includes a series of axially spaced external ribs 53a. Following the moulding of the cylinder body 52 to simul aneously form axially spaced flanges 52e moldingly embracing metal insert 53, the cylinder body is subjected to a further moulding operation in which a mounting flange 54 is moldingly secured to metal insert 53 with the hub

portion 54a of the flange moldingly and lockingly coacting with axial ribs 53a on metal insert 53 to integrally secure flange 54 to cylinder body 52.

The completed slave cylinder seen in Figs.6 and 7 further includes a piston assembly including a piston 55, a pushrod 56, a seal 58, and a return spring 60, all operating in known manner in response to entrance of pressurized hydraulic fluid through port 52d to move the piston assembly reciprocally within the bore 52b and actuate the associated control mechanism such, for example, as the clutch of a motor vehicle.

The invention is seen in Figs.8 - 10 as applied to a hydraulic cylinder assembly which may comprise a master cylinder assembly or a slave cylinder assembly. In the embodiment of Figs.8 - 10, a flange 70 is formed in a suitable stamping operation of a suitable metallic material that includes an axially extending cylindrical mounting hub portion 70a and a radially outwardly extending mounting portion 70b forming an L-snaped configuration in cross section with hub portion 70a. Following formation of metal flange 70, flange 70 is positioned as an insert in a suitable mould cavity, and a cylinder body 72 is thereafter injection moulded in the mould cavity around the flange 70 to moldingly encapsulate the

flange 70 and integrally secure the flange 70 to the cylinder body 72 so that the flange 70 forms a mounting flange for the cylinder body.

Specifically, in the final moulded configuration of the cylinder body and mounting flange, the cylinder body includes an external annular wall or flange 72a moldingly abutting one end of flange mounting portion 70a, a further annular wall or flange portion 72b moulded adjacent the free, other end 70c of flange mounting portion 70a, and an annular axially extending portion 72c formed integrally with wall portion 72b and moldingly overlying, surrounding and encapsulating the free end 70c of the flange hub portion. As with the other embodiments of the invention, the wall or flange portions 72a and 72b have an axial thickness that is not substantially greater than the axial thickness t of the wall of cylinder 72, and the combined axial extent of wall portions 72a, 72b and flange mounting portion 70a substantially exceeds the wall thickness t.

It will be understood that, in any of the disclosed invention embodiments, the appendage such as the flange or reservoir may be formed in the initial moulding operation and thereafter used as an insert in the mould cavity with the cylinder body thereafter

being moldingly formed around the appendage as an insert. It will further be understood that the material utilised in forming the appendage, whether it be a flange or a reservoir, may comprise the same plastic material as the material utilised to form the cylinder body, may comprise a dissimilar plastic material, or may, as seen in Figs.8 - 10, comprise a metallic material. Dissimilar plastic materials may be utilised, for example, in situations where the requirements of the cylinder body and the appendage differ significantly so as to justify or require a different plastic material. As one example, with reference to the embodiments involving the formation of a mounting flange as an appendage to the cylinder body, the cylinder body may be formed of Nylon 6 - 6 with 33 - 43% glass reinforced fibre and the mounting flange may be formed as Nylon 6 - 6 with 43 - 60% glass reinforced fibre. In any event, it will be understood that the invention allows dissimilar materials to be utilised, where desired, to address the dissimilar requirements of the different portions of the hydraulic assembly.

The invention will be seen to provide a method of forming a hydraulic cylinder assembly utilising the relatively inexpensive and readily formable plastic material without incurring the disadvantage of

forming sink marks in the areas of the cylinder body adjacent major appendages to the cylinder body such as the mounting flange and the reservoir.

Whereas preferred embodiments of the invention have been illustrated and described in detail, it will be apparent that various changes may be made in the disclosed embodiments without departing from the scope or spirit of the invention.