GB2176554A - Master cylinder - Google Patents

Abstract

A master cylinder has a brake piping connecting part (15) including a through-bore (17) mounting a tube seat (22), having a metal insert (20) including a bore (21), and a tapered bore portion (19) for guiding the tube seat (22). The outer end portion of the through-bore (17) on the insert (20) side and the opening (21) of the insert (20) adjoining the end portion of the through-bore are increased in diameter as compared with the diameter of the other portion of the through-bore. The tapered portion (19) is formed adjacent the increased diameter end of the through-bore to compress an O-ring (25) seal as the tube seat is inserted. The master cylinder piston (33) (Fig. 2, not shown) has a diametral slot (36) through which extends a pin (42) for actuating a plunger (47) of an axial recuperation valve. <IMAGE>

Description

SPECIFICATION Master cylinder The present invention relates to a master cylinder made of synthetic resin for use in automobiles and the like, and more particularly to a structure of a piping connecting part of the master cylinder.

A piping connecting part of a master cylinder of this type is described in, for example, Japanese Laid-Open Utility Model Publication No. 49082/84.

Figure 6 of the accompanying drawings show a prior art piping connecting part of this type, wherein a master cylinder body 1 is formed of synthetic resin, and a bore 2 is formed in the cylinder body 1, into which bore a piston formed of a synthetic resin (not shown) is inserted from the open end of the bore. A hydraulic chamber A is formed between the piston and the closed end of the bore. A piping connecting part 3, formed integrally with the cylinder body and has a through-bore 5 opening toward the connecting bore 4 and communicates with the hydraulic chamber A. A metal insert 6 having a roughened outer peripheral surface, to prevent slip and at its inner surface, a female screw surface, the insert being fixed integrally with the piping connecting part 3 in the connecting bore 4.The metal insert 6 has a bore 6A provided in the interior thereof which has the same diameter as that of the through-bore 5.

A tube seat 7 whose stem 7A is fitted in the bore 6A and the through bore 5, has a head part 7B in contact with one end of piping (not shown). A sealing member 8 is mounted around the stem 7A.

The prior piping connecting part including, as described above, the metal insert 6 formed integrally therewith in forming the cylinder body 1 has a difference between the inner diameters of the insert 6 and the through-bore 5 of the piping connecting part 3 in cooling after the integral formation owing to a difference between thermal expansion coefficients of the metal and the synthetic resin. Accordingly, a level difference X may be produced as shown in Figure 7. With the level difference so produced, the sealing member 8 to be attached to the tube seat 7 strikes the level difference X in attaching the former to the latter, whereby corner a of the level difference part X damages the piping connecting part and causes the sealing property of the piping connecting part to be deteriorated.

In view of the drawbacks with the prior master cylinder, it is an object of the present invention to provide a master cylinder capable of mounting a tube seat on a piping connecting part with ease without damaging the sealing member provided on the tube seat and without reducing the sealing property of the piping connecting part even with the level different X being produced.

To achieve the above object, a master cylinder according to the present invention comprises a master cylinder comprising: (a) a cylinder body including a cylinder bore provided therein, a mounting flange extending outwardly from said cylinder body, and a hydraulic fluid reservoir communicating with said cylinder body, (b) a piston, (c) a hydraulic chamber formed between said piston and the interior of said cylinder body by slidably inserting said piston into the cylinder body, (d) a piping connecting part integrally formed with said cylinder body including a connecting bore, a through-bore, and a tapered portion, (e) a metal insert roughened on the outer surface thereof and mounted in said piping connecting part, (f) an opening of said through-bore being of increased diameter as compared with a bore in the other portion of said through-bore, (g) said through-bore extending to said hydraulic chamber adjacent said opening, and being partly increased in a diameter thereof, (h) a tube seat provided in close contact with a piping end part in a head thereof, including a stem and a sealing member fitted in a peripheral groove around said stem, (i) said sealing member being fitted into the interior of said through-bore beyond said tapered portion.

In the accompanying drawings: Figure 1 is a plan view of a master cylinder according to the present invention, Figure 2 is a longitudinal cross-sectional view of Figure 1.

Figure 3 is a cross-sectional view showing a piping connecting part of the embodiment shown in Figure 1, Figure 4 is an enlarged cross sectional view of a portion of Figure 3, Figure 5 is a plan view showing the piston of the embodiment shown in Figure 1, Figure 6 is a cross sectional view showing a piping connecting part of a prior master cylinder, and Figure 7 is a view, similar to Figure 4, showing a drawback of the prior master cylinder of Figure 6.

An embodiment of a master cylinder according to the present invention will now be described with reference to Figures 1 and 2.

A body 11 of the master cylinder formed by a synthetic resin, e.g., glass-filled nylon which has a closed-end cylinder bore 12 with an opening at the other end thereof (hereinfter referred to as a rear end). The body 11 also has an integral mounting flange 13 extending from an outer surface thereof on the rear end and a centrally disposed hydraulic fluid reservoir 14 spaced from the mounting flange 13.

The mounting flange 13 extends vertically from a cylindrical member 13B supported by a plurality of ribs 1 3A projecting radially from the cylinder body 11 . The hydraulic fluid reservoir 14 may be integrally formed with the body or formed as a separate part attached to the cylinder body 1.

A piping connecting part 5 is integrally formed with the cylinder body 11, as shown in Figure 3(a). The piping connecting part 15 has a hexagonal connecting hole therein as shown in Figure 3(b) as well as a throughbore 17 communicating at one end with a connecting bore 16 and at the other end with a hydraulic chamber A in the bore 12. The through-bore 17 is increased in its diameter at an end part 18 of the opening formed with the connecting bore 16. The piping connecting part 15 has a tapered portion 19 (tapered peripheral surface) formed adjacent the increased diameter portion 18, which tapered portion 19 has its diameter reduced more than the increased diameter portion 18. A hexagonal metal insert 20 having a roughened outer peripheral surface for preventing slip in the connecting hole 16.The metal insert 20 has a bore 21 in the interior thereof communicating with the through-bore 17, the opening 21 having an inner diameter not less than the increased diameter portion 18 of the throughbore 17 (the diameter of a mould core forming the increased diameter portion 18 is the same size as that of the opening 21).

A tube seat or nipple 22 having a head 23 connecting with piping (not shown), a stem 24, and a sealing member 25 is provided, the stem 24 being fitted into the through-bore 17 from the bore 21, and the sealing member 25 is positioned in a peripheral groove 24a formed in the stem 24 making contact with the inner peripheral surface of the throughbore 17 at a point between the tapered portion 19 and the hydraulic chamber A.

In addition, a portion of the increased diameter part 18 of the through-bore 17 after forming and cooling the cylinder body is more than the relaxed diameter of the sealing member 25 fitted in the tube seat 22 from the outer peripheral surface of the tube seat (relaxed diameter is the diameter before mounting the tube seat 22 in the piping connecting part 15).

A length of the tube seat 22 between the end surface of the stem 24 and the peripheral groove 24a is more than at least the increased diameter portion 18.

A piston 30 housed is slidably mounted in the cylinder bore 12, and the hydraulic chamber A is formed between the piston and the closed end of the bore 12. The piston 30 is formed of synthetic resin, for example, carbon-reinforced nylon and has, as shown in Figure 5, a large diameter body 31 and a reduced diameter projection 33 with a step 32 concentrically extending ahead of the body 31. The body 31 of the piston 30 has a front sliding part 34, a rear sliding part 35, and a plate-shaped slot 36 of predetermined width formed between the-sliding parts 34 and 35.

The rear sliding part 35 (Figure 2) includes a blind bore 35A adjacent, and connected to, the slot 36 formed around the axis of the piston, a concave push rod surface 35B on the rear end surface of the rear sliding part located on the piston axis described above, and a peripheral groove 35C, in which the sealing member is fitted, provided on the outer surface of the rear sliding part. The peripheral groove 35C is made relatively large and deep. The blind bore 35A is adapted to reduce the axial thickness of the rear sliding part 35 for preventing any void from being produced. The reduced diameter projection portion 33 of the piston 30 has an axial through-bore 37 formed therein which communicates with the slot 36.The piston 30 is urged toward the rear end of the cylinder body 1 by a return spring 39 located on a retainer 38 provided with apertures 38a mounted on the step 32 of the piston and engaging the forward end of the cylinder bore 12.

The piston, in the non-operational state shown in Figure 2, is adapted to make close contact, in the rear surface thereof, with a slip preventing metal insert 40 mounted on the end outer surface of the cylinder body 1, and is positioned as shown in which a throughbore (larger diameter part of a through-bore 41) 41a opens toward the front end of the slot 36. A restriction pin 42 for restricting the maximum axial movement of the piston 12 co-operates with the slot 26. The restriction pin having a thread on the head 43 is inserted, while turned down in the head side 43, from a pin 44 formed in the cylinder body 11 into the cylinder bore 12, and extends vertically into the slot 36 to reach the inside of the bore 41b (small diameter part of throughbore 41).The restriction pin 42 is threaded into a screw hole 44A which communicates with a pin bore 44 to open to the outer surface of the cylinder body 1 and having a larger diameter than the pin bore 44 and thereby assembled with the cylinder body 1. A sealing member 45 is positioned between the head 43 and body 11. In addition, to permit the formation of the bores 41, 44 the cylinder body is thickened to permit the opening end to be made concave by making use of a sinkmark effect of the bores on the cylinder bore 12 side.

A valve member 46 made of resilient material, is fitted to an end of a stem 47 having an axial bore 48 opening toward the other end thereof and a transverse bore 49 communicates with the bore 48. The stem 47 is slidably inserted into an axial through-bore in the reduced diameter projection 32 of the piston 30, and is urged toward the restriction pin 42 by a valve spring 50 interposed between the retainer 38 and the valve member 46 to permit the other end referred to above to be brought into close contact with the restriction pin 42. The valve member 46 forms an isolation valve M taking the reduced diameter projection 32 of the piston 30 as a valve seat 32A, and the transverse bore 49 is positioned to open toward a gap opposite the valve member 46 and the valve seat 32A in the non-operational state shown in the figure.A push rod 51, whose rear end is connected with a clutch pedal (not shown) and whose front end is inserted into the cylinder bore 12 and fitted in the push rod surface 35B of the piston 30.

A boot 52 for blocking the open end of the cylinder body 1, has an inwardly directed flange 52a which engages with the end of the slip preventing metal insert 40. The insert 40 has a pawl 40a and is fixed on the cylinder body 11 by engagement of the pawl 40a with a groove 53 formed in the outer surface of the cylinder body 11.

A cap member 54 having an engagement flange 54a is fitted on the mounting flange 13 by engagement of the flange 54a with a peripheral groove formed in the mounting flange 13 on the hydraulic fluid reservoir 14 side for blocking one end of the space S formed between the ribs 13a. A sealing member 55 is fitted in the peripheral groove 35C formed in the rear sliding part 35 of the piston 30 for sealing between the sliding part and the cylinder body 11 and a sealing member 56 is fitted to the reduced diameter 32 of the piston 30.

In the non-operational state of the master cylinder shown in Figure 2, the hydraulic fluid reservoir 14 and the hydraulic chamber A are connected with each other through the through-bore 41a, slot 56, stem 47, transverse bore 49, and isolation valve M. Depressing the clutch pedal (not shown) in this state, the push rod 51 is moved leftward in the figure, whereby the piston 30 is moved in the same direction against the resilient force of the return of spring 39. Accordingly, the valve member 46 seats on the valve seat 32A of the reduced diameter step 32 due to the movement of the piston 30 to close the isolation valve M and thereby the hydraulic chamber A and the hydraulic fluid reservoir 14 are shut off for producing a fluid pressure in the hydraulic chamber A.The produced fluid pressure is discharged from the through-bore 1 7 through the piping connecting part to the outside of the cylinder body 1, and supplied through the piping connected with the piping connecting part to a clutch operating cylinder (not shown).

The leading portion of the through-bore 17 on the insert 20 side is of greater diameter than the other portions thereof, and the increment of increased diameter of part 18 after forming and cooling the cylinder body is made greater than the relaxed diameter before mounting the tube seat 22 in the piping connecting part 15 of the sealing member 25 fitted around the tube seat 22. In addition, the tapered portion 19 serves to guide the tube seat 22 inserted through the opening 21 of the insert 20 axially into the through-bore 17 and thus the tube seat 22 is made insertable without allowing the sealing member 25 to strike a corner a of step X even with the step X produced after forming and cooling the cylinder body as described above between the insert 20 and the through-bore 17.

With the present embodiment, as described above, the inside opening of the metal insert integrally mounted on the piping connecting part and one part of the through bore in the piping connecting part, adjoining the opening described above, with the hydraulic chamber in the cylinder body are of increased diameter and the tapered portion is provided adjoining to the increased diameter portions described above. Thus, even if a step is produced by a difference between thermal expansion coefficients of the insert and the piping connecting part, the sealing member provided on the tube seat is prevented from striking the corner of the step when mounting the tube seat and thus from being damaged for markedly improving reliability of the master cylinder as compared with prior constructions.

Claims (5)

1. A master cylinder comprising: (a) a cylinder body including a cylinder bore provided therein, a mounting flange extending outwardly from said cylinder body, and a hydraulic fluid reservoir communicating with said cylinder body, (b) a piston, (c) a hydraulic chamber formed between said piston and the interior of said cylinder body by slidably inserting said piston into the cylinder body, (d) a piping connecting part integrally formed with said cylinder body including a connecting bore, a through-bore, and a tapered portion, (e) a metal insert roughened on the outer surface thereof and mounted in said piping connecting part, (f) an opening of said through-bore being of increased diameter as compared with a bore in the other portion of said through-bore, (g) said through-bore extending to said hydraulic chamber adjacent said opening, and being partly increased in a diameter thereof, (h) a tube seat provided in close contact with a piping end part in a head thereof, including a stem and a sealing member fitted in a peripheral groove around said stem, (i) said sealing member being fitted into the interior of said through-bore beyond said tapered portion.

2. A master cylinder according to claim 1, wherein said master cylinder body is formed of synthetic resin.

3. A master cylinder according to claim 1 or 2, wherein said piston is formed of synthetic resin.

4. A master cylinder according to any of claims 1 to 3, wherein a portion of said increased diameter of the through-bore after forming and cooling said cylinder body is more than the diameter of the relaxed diameter of said sealing member extending from the outer peripheral surface of said tube seat.

5. A master cylinder substantially as described with reference to, and as illustrated in, Figures 1 to 5 of the accompanying drawings.