Master cylinder piston and device for mounting a check valve therein

A master cylinder piston for use in a motor vehicle having a flap (22) that is biased towards a position to shut off a pressure-fluid passage (24) by a return spring (28) resting on a cage (30). A flange (38) on a cage (30)for the Spring (28) is located in an annular groove (44) provided in the housing (20) for the flap (22) when the cage (30) bears axially on an inner shoulder (64) of the housing (20).

This invention relates to a master cylinder piston of a braking circuit, more particularly for a motor vehicle, as well as to a jig for the fitting of a flap into said piston.

BACKGROUND OF THE INVENTION

In a master cylinder, more particularly of the tandem type, each of the primary and secondary pistons is fitted with a moving shutter, or flap, for the opening and closing of a pressure-fluid passage provided in the piston, as a function of the strokes of the piston inside the master cylinder.

Such fluid passage opens axially into a housing formed at one end of the piston and accommodating the flap, which comprises a rod, guided within the fluid passage, and a head situated outside the passage and biased by a return spring towards the fluid passage outlet so as to close it in a tight manner.

Such return spring is a compression spring arranged between the flap head and bearing means, added to the piston.

It has already been suggested that these bearing means be constituted by a metal cage resiliently snapped in the flap housing. For this purpose, the cage comprises resiliently-deformable lugs, situated at its periphery, facing radially outwards and intended to enter and get latched in an annular groove provided in the cylindrical wall of the flap housing. In the course of the assembling process, such lugs are resiliently brought closer to the axis, as the cage is inserted in the flap housing and they rub against the cylindrical wall of the housing till the cage assumes an axial position inside the housing, in which the lugs engage the above-mentioned annular groove in a snapping manner.

The rubbing motions of the steel cage lugs against the cylindrical wall of the housing provided in the piston, made of aluminium or of a light alloy, are likely to scratch the cylindrical wall and tear away metal particles or chips, which may settle under the flap head or on the upper lip of a seal cup, or be the cause of scratches during the piston travel and consequently give rise to tightness failures in the master cylinder, actually a major drawback which it is essential to cure.

Besides, such cage should neither interfere with the brake-fluid flow nor restrict its flow rate.

SUMMARY OF THE INVENTION

Therefore, it is the main object of the present invention to provide a simple, efficient and inexpensive solution to the above-mentioned problem, in that any potential scratch or tightness failure of the master cylinder is prevented, which would result from the mounting of said cage on the piston of the master cylinder.

With this object in view, the present invention provides a master cylinder piston, more particularly for a motor vehicle, comprising at one end a substantially cylindrical housing accommodating a flap and a return spring arranged between the flap and a cage, added to the piston, characterised in that said cage is crimped inside said housing.

Crimping actually means a plastic deformation of part of the cage, which may be performed when the cage is in the desired axial position inside the housing, which precludes any risk of tearing away metal particles or chips, likely to give rise to scratches and tightness failures in the master cylinder.

In accordance with another feature of the invention, the crimping process is carried out using retaining, means, which are formed on the cage and accommodated, under a plastic deformation effect, in an annular groove provided in said housing.

According to a first embodiment of the present invention, the retaining means of the cage comprise a substantially cylindrical flange extending round the cage in the direction of the open end of the housing.

In another embodiment of this invention, such retaining means comprise lugs, extending substantially parallel to the axis of the cage around the latter in the direction of the open end of the housing.

Advantageously, such lugs are formed either by partial cuts or cutouts made in a substantially cylindrical or truncated-cone shaped wall of the cage.

Preferably, the retaining means are formed at one end of the cage and joined up with it by an annular flange extending radially inwards and comprising means for an applying to supporting means, formed inside the flap housing.

It results in that the cage may be set automatically in its crimping position inside the housing.

At its end facing away from said retaining means, the cage comprises another annular flange directed radially inwards and constituting bearing means for the return spring of the flap.

In an advantageous manner, the cage according to the invention is manufactured using a stamping process, in a simple and inexpensive way.

The invention also provides a jig for the fitting of a flap into a master cylinder piston, more particularly for a motor vehicle, such piston comprising, at one end, a substantially cylindrical housing accommodating a flap and a return spring arranged between the flap and a cages added to the piston and fastened using retaining means received within an annular groove made in the cylindrical wall of the housing, said device being characterised in that:in an initial free state, the cage has an outer diameter which is smaller than the inner diameter of the housing;the housing includes means for the axial support of the cage in a position in which its retaining means are radially in line with said annular groove;the jig comprises means for the support and application of the cage onto the supporting means of the housing, and means for a radially-outward deformation of said retaining means, so as to introduce them into the annular groove provided in the housing.

In an advantageous manner, the means for the support and application of the cage onto the supporting means of the housing comprise a central push rod, fitted inside a tubular member, a bevelled end of which constitutes said radial-deformation means.

Preferably, the central push rod is guided for an axial sliding motion within said tubular member, and biased by a return spring in a direction which corresponds to the applying of the cage onto the supporting means, formed in the housing.

According to this invention, one only has to proceed to the axial alignment of the jig with the master cylinder piston, and then move, in an axial translation motion, the jig towards the piston or vice versa, so as to insert the cage in the flap housing, position it axially inside said housing through its retaining means radially in line with the annular groove, provided in the housing for their accommodation, and move the jig farther on towards the piston for a plastic deformation of the retaining means of the cage and their radial introduction into the annular groove provided in the housing.

Afterwards, a reverse axial translation motion causes the piston to separate from the jig, whereas the cage is retained within the flap housing.

Other features, advantages and details of the present invention will be apparent from the following detailed description, by way of example and by no means as a limitation, when taken in conjunction with the accompanying drawings, in which:

DETAILED DESCRIPTION OF THE INVENTION

As a rule, in the drawings, the forward direction is indicated by arrow AV while arrow AR shows the rear direction.

FIG. 1is a schematic illustration of an embodiment of a secondary piston10of a tandem master cylinder of a braking circuit for a motor vehicle, the piston10comprising a body12, which is connected by means of an adjusting screw14to a spring stop16, biased by a spring18, arranged between the stop16and an end of the secondary piston body12, such spring stop16being intended for a cooperation with a primary piston (not shown) of the master cylinder.

At the end facing away from the spring stop16, the secondary piston exhibits a tubular axial end20, which defines a substantially cylindrical housing for the accommodation of a flap22, opening and closing an axial passage24, made in a transverse wall of the body12. The flap22includes an axial rod26, inserted in the passage24, and it is connected to a return spring28, arranged between the head of the flap22and a cage30, inserted inside the housing20.

In the position illustrated inFIG. 1, the head of the flap22is resiliently pushed by the return spring28to bear on the outlet of the passage24in the housing20, for a tight shut-off of said passage.

The cage30is a metal part, for instance a stamped steel one, and it comprises a truncated-cone shaped wall32widening rearwards, and the front end of which is connected to an annular flange34extending radially inwards, whereas the rear end of the truncated-cone shaped wall32is joined up with an annular flange36extending radially outwards, itself linked up with a cylindrical flange38which extends in the forward direction about the truncated-cone shaped wall32and spaced apart from it.

In the crimping position of the cage30, as shown inFIGS. 1 and 2, the front end40of the cylindrical flange38is deformed radially outwards and it extends slantwise so as to abut against the front edge42of an annular groove44, provided in the inner surface of the wall of the housing20, such groove having a rear edge46extending slantwise rearwards. The inner diameter of the cylindrical wall of the housing20is slightly greater than the outer diameter of the cylindrical flange38in the unstrained free condition. In said position, the cage30may be moved axially inside the housing20on a distance which corresponds to the axial play of the end40of the flange38within the groove44, with the result that openings48, made at regular intervals in the annular flange36, may be kept clear of the end part of the housing20, so as to facilitate the pressure-fluid flow through the passage24when the flap22is open, such pressure fluid also flowing through the central opening, defined by the annular flange34of the cage30.

FIG. 3shows an embodiment of a jig for the fitting of the cage30, in a schematic manner.

Such jig50comprises a central push rod52, slidably fitted inside a tubular member54, the rear end56of which is bevelled outwards and constitutes the means for the plastic deformation of the end40of the cylindrical flange38of the cage30.

A compression spring58is arranged inside the tubular member54, between the push rod52and a front stop60, the axial position of which can be adjusted when it is screwed in the tubular member54, and so the push rod52is permanently biased rearwards by the spring58in order to rest against an inner shoulder62of the tubular member54. The rear end of the push rod52comprises support means for the cage30.

The mode of operation of said jig is represented inFIG. 4, the lower part of which shows the cage30before it is crimped, while the upper part shows the cage30as it is being crimped.

Initially, the flap22is introduced by its rod26into the passage24and the spring28is fitted on the head of the flap22.

The jig according toFIG. 3is axially aligned with the secondary piston10in such a way that the cage30, carried by the end part of the push rod52, faces the open end of the housing20at the front end of the piston10. Then the device is subjected to an axial translation motion till it reaches the position shown in the lower part ofFIG. 4, in which the spring28is compressed between the head of the flap22and the annular flange34of the cage30, the latter resting at its annular flange36on an inner shoulder64of the housing20. For the time being, the front end of the cylindrical flange38of the cage30lies substantially at the level of the middle part of the annular groove44provided in the housing20.

Thereafter, the tubular member54of the jig is moved farther on rearwards so that its bevelled end56may enter the cylindrical flange38, with the result that it deforms the end40of such flange radially outwards within the annular groove44, and that it axially abuts against the annular flange36of the cage30, the latter flange abutting against the inner shoulder64of the housing20, as shown in the upper part of FIG.4.

In such a position, the outward deformation of the end40of the cylindrical flange38of the cage is a permanent set. In a preferred manner, such a process is carried out without the end40of the flange38bearing on the root of the groove44.

Next, the jig50is axially moved in the forward direction so as to be extracted from the housing20. Under the force exerted by the spring28, the cage30follows that translation motion till the end40of its cylindrical flange38comes to rest on the front edge of the annular groove44, in the position illustrated in FIG.2. This being so, the flap22is kept in a position in which the passage24is shut off in a leakproof manner, but a translation motion in the forward direction may be imparted to the flap, while the spring28is compressed, when the passage has to be opened.

The radial outward deformation of the end46of the flange38of the cage30implies no rubbing motion of part of said cage on the piston10, when the jig50is guided accurately in relation to the piston10, which is very simple to achieve. Moreover, an automated control of the jig is quite feasible.

As regards the variant illustrated inFIG. 5, the cage30comprises a cylindrical or truncated-cone shaped wall32, the rear end of which exhibits U-shaped lugs66, a first part68of which extends axially rearwards in the prolongation of the wall32, whereas an intermediate part70is bent radially outwards and serves the same purpose as the annular flange36according to the embodiment represented inFIG. 2, and the third part12of said lugs extending axially forwards and serving the same purpose as the cylindrical flange38according to the embodiment represented in FIG.2. At its front end, the wall32is connected to an annular flange34, in the same way as in the preceding embodiment.

FIG. 6shows another variant, in which the cage30comprises a wall32, in the shape of a truncated cone at least at its rear part while it may be cylindrical at its front part, and lugs74consisting of partial cuts in the rear part of the wall32, such lugs74extending forwards substantially parallel to the axis of the cage from the rear end of the latter, on a length corresponding to that of the cylindrical flange38according to the embodiment illustrated in FIG.2. At its front end, the cage comprises an annular flange34, which is directed radially inwards in the same way as in the preceding embodiments.

Another variant of the cage, as shown inFIGS. 7 and 8, corresponds fundamentally to the embodiment as perFIG. 2, and it comprises a truncated-cone shaped wall32, extending between a front annular flange34and a rear annular flange36, including openings48and united with a cylindrical flange38, the rear annular flange36further comprising protruding studs76, which extend axially rearwards and constitute the abutting means of the cage30against the inner shoulder64of the housing20.

As far as all these embodiments are concerned, the cage30is fastened inside the housing20in the above-described manner, in which there is no contact whatsoever either with the inner wall of the housing20or the edges and root of the annular groove44, thus precluding any removal of metal particles or chips.

It should also be noted that, in the embodiments shown inFIG. 5 through 8, the cage30does not have to be axially movable inside the housing in order to keep clear, of the end part of such housing, openings facilitating the pressure-fluid flow through the passage24.