EP0406262A1

EP0406262A1 - Hydraulic master cylinder

Info

Publication number: EP0406262A1
Application number: EP89903189A
Authority: EP
Inventors: David Curtis Barker; Keith Vernon Leigh-Monstevens
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1988-02-17
Filing date: 1989-02-08
Publication date: 1991-01-09
Also published as: GB2231930A; JPH03502790A; GB2231930B; AU4031889A; KR900700799A; GB9013899D0; WO1989007541A1

Abstract

Le maître-cylindre hydraulique comporte un cylindre (10) renfermant un piston (12) destiné à décharger du fluide hydraulique d'une chambre de pression (10c) dans le cylindre, et un réservoir (16) pourvu d'une membrane tubulaire souple (20). Cette membrane divise le réservoir en une partie chambre de liquide (16b) d'un côté de ladite membrane, destinée à communiquer avec ladite chambre de pression (10c), et en une partie chambre de gaz (16c) de l'autre côté de ladite membrane, destinée à communiquer avec l'atmosphère. La membrane (20) possède une partie principale (20b) pourvue, transversalement à son axe (26), d'une pluralité de bras (20g) s'étendant radialement et agencés autour dudit axe. Chaque bras comporte une paire de parois latérales (20j, 20k) définissant entre elles une partie du volume de ladite chambre de gaz. La membrane est mobile entre une position déployée et une position aplatie dans laquelle chacune desdites paires de membranes latérales (20j, 20k) desdits bras (20g) est aplatie par rapport à l'autre afin de réduire le volume de ladite chambre de gaz (16c).The hydraulic master cylinder comprises a cylinder (10) enclosing a piston (12) intended to discharge hydraulic fluid from a pressure chamber (10c) in the cylinder, and a reservoir (16) provided with a flexible tubular membrane ( 20). This membrane divides the reservoir into a liquid chamber part (16b) on one side of said membrane, intended to communicate with said pressure chamber (10c), and into a gas chamber part (16c) on the other side of said membrane, intended to communicate with the atmosphere. The membrane (20) has a main part (20b) provided, transversely to its axis (26), with a plurality of arms (20g) extending radially and arranged around said axis. Each arm has a pair of side walls (20j, 20k) defining between them a part of the volume of said gas chamber. The membrane is movable between a deployed position and a flattened position in which each of said pairs of lateral membranes (20j, 20k) of said arms (20g) is flattened relative to the other in order to reduce the volume of said gas chamber (16c ).

Description

HYDRAULIC MASTER CYLINDER

This invention relates to a hydraulic master cylinder which includes a reservoir having a diaphragm therein.

More specifically, the present invention is concerned with a master cylinder assembly of the type including a housing containing a piston for discharging hydraulic fluid from a pressure chamber in the housing, and a reservoir having a flexible tubular diaphragm therein and dividing said reservoir into a liquid chamber portion on one side of said diaphragm arranged to communicate with said pressure chamber and gas chamber portion on the other side of said diaphragm arranged to communicate with atmosphere.

The diaphragm forms an impervious barrier within the reservoir to keep liquid in the system and air out of the system, prevents moisture from entering the liquid, allows for expansion and contraction of the liquid under temperature variations, allows for variations in atmospheric conditions, and acts as a flexible medium to compensate for liquid flow into and out of the reservoir during actuation of the associated master cylinder and to compensate for changes in the volume of the liquid in the system due to wear in the system or system leakage. Several forms of diaphragms have been used in the prior art.

One form of diaphragm in common usage has a generally top hat cross-sectional configuration as in US-A-4 590 765. Whereas this diaphragm is satisfactory in some applications, it is capable of only a minor expansion relative to its total volume so that it is limited in its ability to compensate for under filling of the system, wear in the system, or leakage in the system.

Another form of diaphragm in common usage employs a pleated or bellows configuration as shown in US-A-3 357 181. Whereas this type of diaphragm has a larger expansion capacity, it is possible in some instances to trap air between the pleats of the diaphragm as the diaphragm moves axially to a collapsed or contracted condition. This air can ultimately find its way into the master cylinder system. The pleated diaphragms are also subject to fatigue cracking at the crease points of the pleats.

Another form of diaphragm in popular usage includes a general top hat cross-sectional configuration with a rolled portion adjacent the upper end of the top hat. Whereas the rolled portion increases the capacity of the diaphragm as compared to the simple, top hat type diaphragm, the rolls tend to eventually fatigue at the crease points with consequent failure of the diaphragm.

The present invention is directed to the provision of a master cylinder assembly having a diaphragm of a master cylinder assembly having a diaphragm of improved performance characteristics.

According to the invention there is provided a hydraulic master cylinder including a housing containing a piston for discharging hydraulic fluid from a pressure chamber in the housing, and a reservoir having a flexible tubular diaphragm therein and dividing said reservoir into a liquid chamber portion on one side of said diaphragm arranged to communicate with said pressure chamber and gas chamber portion on the other side of said diaphragm arranged to communicate with atmosphere, said diaphragm having a main body portion formed transverse to its axis with a plurality of radially extending arms arranged about said axis each of which arms includes a pair of side walls defining therebetween a portion of the volume of said gas chamber said diaphragm being movable between an expanded condition and a collapsed condition in which each of said pair of side walls of said arms are collapsed with respect to each other to reduce the volume of said gas chamber.

In the expanded condition the diaphragm preferably assumes a substantially circular configuration.

Preferably the main body includes a series of axially extending circumferentially spaced flutes and said arms comprise axially extending circumferentially spaced rounded ridges between the flutes. The rounded ridges are less prone to fatigue than the creased bellows types of diaphragm of the prior art. Fatigue and tendency to crack may further be reduced by forming the side walls of the arms so that they blend smoothly into the flutes. The walls of the arms are preferably formed in part from concavely curved portions of the flutes resulting in a diaphragm of curved and wave-like cross-sectional configuration. Each arm is preferably of pear-shaped cross-section with the bulbous portion of the pear shape preferably lying remote from the longitudinal axis of the tubular diaphragm.

Although three arms may be provided a four arm cross- like configuration is preferred. The arms are preferably arranged symmetrically about the axis.

Preferably, the diaphragm has an open end by means of which it is secured to a housing defining the reservoir.

The diaphragm may conveniently be provided with an annular mounting pportion at its upper end which can be secured between a portion, preferably an upper rim, of the reservoir housing and a reservoir closure member such as a screw-on or snap-on cap.

In one embodiment the master cylinder may be a dual- type with separate pistons and respective pressure chambers. In such a case the pressure chambers may be arranged to communicate with respective liquid chambers of a reservoir housing, each liquid chamber being separated from its associated gas chamber by diaphragm main body portions. The diaphragm, in such a case, may comprise a single unit having two said main body portions. Preferably the single unit diaphragm has a mounting portion at an open end thereof enabling it to be mounted between a surface of the housing and a closure member for the housing. Part of the mounting portion between the two main body portions may include a sealing section which sealingly engages the closure member. Said part of the mounting portion may sealingly locate on a portion or divider between the liquid chambers of the reservoir.

Such diaphragms are inexpensive and readily mouldable, are extremely durable, and provide a large co-efficient of expansion so as to provide excellent compensating capacity with respect to changes in the volume of the liquid in the system.

Master cylinders in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: -

Fig.1 is a cross-sectional view of one form of master cylinder assembly according to the invention,

Fig.2 is a perspective view of a diaphragm employed in the master cylinder assembly of Fig.1,

Fig.3 is a side view of the diaphragm in Fig.2,

Fig.4 is a cross-sectional view of the diaphragm taken on line 4-4 of Fig.3,

Fig.5 is an interior view of the diaphragm looking in the direction of the arrow 5 in Fig.3, Fig.6 is a cross-sectional view of the diaphragm taken on line 6-6 of Fig.3,

Fig.7 is a cross-sectional view of the diaphragm showing the diaphragm in its extreme expanded condition,

Fig.8 is a cross-sectional view of the invention diaphragm showing the diaphragm in its extreme collapsed condition, and

Fig.9 is a cross-sectional view of a dual master cylinder assembly in accordance with the invention.

The master cylinder assembly seen in Fig.1 includes a cylinder 10 defining an internal bore 10a and a discharge port 10b at the forward end of the cylinder, a ^'piston 12 mounted for reciprocal movement within the bore 10a and including a nose 12a, a flange 12b, a forward land 12c, a central reduced diameter spool portion 12d, a rearward land 12e, a piston rod 14, and a reservoir 16 formed integrally with cylinder 10. Reservoir 16 includes a reservoir body 16a closed at its lower end by cylinder 10 and open at its upper end, a screw-on cap 18 threadably engageable with the upper end of body 16a and including a central bleed port 18a, and a diaphragm 20.

Diaphragm 20 is positioned within reservoir body 16a and divides reservoir body 16a into a lower liquid chamber 16b, defined outside of the diaphragm, and an upper gas chamber 16c, defined with the diaphragm.

Upper gas chamber 16c is in communication with atmosphere through bleed port 18a and lower liquid chamber 16b is in communication with the pressure chamber 10c defined forwardly of piston 12 through an orifice or port 10d and through a second orifice or port 10e. Orifice 1 Od is disposed immediately forwardly of an annular seal 22 disposed in the seal groove defined between piston flange 12b and piston land portion 12c so that the pressure chamber 10c is in fluid communication with liquid chamber 16b of the reservoir with the piston in the extreme retracted position as seen in Fig.1 and so that the port 1 Od is immediately closed upon forward movement of the piston in response to actuation of the master cylinder to block communication between the pressure chamber and the reservoir as the piston moves through its forward working stroke. As the piston is thereafter retracted to its position of Fig.1, port 1 Od is again opened to provide communication between liquid chamber 16b and pressure chamber 1 Oc so as to allow compensating flow, if necessary, into the chamber 10c. Port 10e maintains constant communication between liquid chamber 16b and they are behind piston land portion 12c such that the annular chamber 24 defined around the piston spool portion 12d is always filled with hydraulic fluid as is well- known in the art.

Diaphragm 20 is generally tubular and includes an open upper end and a blind or closed lower end. The diaphragm includes an annular mounting or collar portion 20a defining the open upper end of the diaphragm and a main body portion 20b extending downwardly from collar portion 20a to define the closed lower end 20c of the diaphragm. Collar portion 20a includes a lip 20d, an annular shoulder portion 20e, and a conical portion 20f. The diaphragm is mounted within reservoir 16 by clamping lip 20d between the upper annular edge of reservoir body 16a and reservoir cap 18 with the main body of the diaphragm extending downwardly into the reservoir.

Main body portion 20b, in transverse cross section as seen in Fig.6, includes a plurality of radially extending arms 20g arrayed symmetrically about the central axis 26 of the diaphragm. As disclosed, there are four arms 20g arranged symmetrically about the central axis of the diaphragm so as to define a cross or cruciform configuration. The arms are defined by a series of circumferentially spaced axially extending flutes 20h extending along the main body portion from conical portion 20f of the collar portion to the closed end 20c of the diaphragm and a series of rounded ridges 20i generally co-extensive with the flutes and interconnecting the flutes to form the final cruciform configuration. Ridges 20i and flutes 2Oh each have an arcuate configuration and the centres and radii of the arcs are chosen such that the resulting arm has a generally pear-shaped, re-entrant configuration with the larger, bulbous portion of the arm remote from the central diaphragm axis. The adjacent flutes and ridges will also be seen to coact to define pairs of side walls 20j and 20k,^' each defining arm 20g with each side wall defined in part by a portion of a rounded ridge 20i and in part by a portion of an adjacent flute 20h. The diaphragm is, therefore, curved and wave-like in cross section.

As best seen in Figs.7 and 8, the diaphragm may expand substantially from its relaxed or normal position of Fig.6 and may contract substantially from its relaxed or normal configuration of Fig.6.

Specifically, as seen in Fig.7, the main body portion of the diaphragm, in its extreme expanded condition, may assume a circular configuration with the radius of the circle significantly exceeding the radius of the arms 20g with the diaphragm in its relaxed condition. In its extreme expanded condition, the diaphragm assumes a circular configuration at section 6-6 having a diameter substantially approximating the diameter of shoulder portion 20e of collar portion 20a.

Conversely, in its extreme collapsed condition as seen in fig.8, the side walls 20j and 20k, defining each arm, collapse totally upon each other to substantially eliminate the gas chamber defined within the diaphragm. Whereas neither of these extreme conditions are typically ever achieved or utilized in the normal operation of the associated master cylinder assembly, the expanded and collapsed configurations as seen in Figs.7 and 8 illustrate the extreme variation in capacity provided by the invention diaphragm.

The diaphragm may be formed of any suitable impervious elastomeric material. An ethylene propylene rubber material has been found to be particularly suitable for use in forming the invention diaphragm.

It will be understood that, in use, the diaphragm expands and contracts to selectively maintain a totally filled condition on the liquid side of the diaphragm. For example, the diaphragm is ordinarily utilized in a master and slave cylinder assembly in which the pressure fluid discharged from discharge port 10b is delivered by a conduit 25 to a slave cylinder 126 for use, for example, in actuating a clutch release member 27 of a motor vehicle. The master cylinder, conduit, slave cylinder, and reservoir are prefilled with hydraulic fluid prior to delivery to the motor vehicle manufacturer. If the prefill is somewhat less than the specified prefill amount, the diaphragm automatically expands to provide^' a totally filled configuration on the liquid side of the diaphragm and, conversely, if the prefill amount is in excess of the specified amount, the diaphragm automatically contracts to allow the overfill while maintaining a totally filled condition on the liquid side of the diaphragm. Similarly, as wear occurs in the system over an extended period of usage, the diaphragm selectively contracts to maintain the totally filled condition of the liquid system and as leakage occurs in the system, the diaphragm similarly expands to maintain a totally filled liquid condition in the system. Further, as . liquid flows into the out of the reservoir during the actuation of the associated master cylinder, the diaphragm selectively expands and contracts to maintain a completely liquid-filled condition on the liquid side of the diaphragm. Therefore the diaphragm maintains a static system of balance as between the liquid chamber portion 16b and the gas chamber 16c.

The diaphragm will be seen to provide many important advantages as compared to prior art diaphragms. Specifically, the diaphragm provides a high ratio as between the fully expanded and fully contracted volumes of the diaphragm so as to easily maintain a totally liquid-filled condition on the liquid side of the diaphragm in any operating condition encountered in the associated master cylinder assembly. Further, the diaphragm is of simple construction and can therefore be readily and inexpensively manufactured. Further, the diaphragm has a totally rounded configuration so as to avoid creasing and ultimate fatigue cracking at the crease points. Further, the diaphragm, by virtue of the manner in which it moves between its fully collapsed and fully expanded conditions, totally avoids the problem of certain prior art diaphragms with respect to trapping air between portions of the diaphragm as the diaphragm moves to its collapsed condition.

Another embodiment of hydraulic master cylinder is seen in Fig.9. The cylinder assembly of Fig.9 discharge ports (not shown) is of a dual kind and includes a pair of pistons 28 and 30 positioned in tandem fashion and in known manner within the dual cylinder 32. A reservoir 34 is mounted on cylinder 32 and includes a central partition 34a dividing the reservoir chamber into a first chamber 34b for coaction with piston 30 through ports 32a and 32b with a second chamber 34c for coaction with piston 28 through ports 32c and 32d; and a diaphragm 36 according to the invention formed as a single unit adapted for coaction with reservoir chambers 34b and 34c.

Specifically, diaphragm 36 has a construction generally conforming to the construction described with reference to Figs.1 - 8 but replicated so that a first main body portion 36a is positioned within chamber 34b and a second main body portion 36b is positioned within chamber 34c to, in each case, divide the reservoir chamber into a liσuid chamber portion and a gas chamber portion. The diaphragm 36 includes a lip portion 36c clamped to the upper peripheral edge or rim of the reservoir body by a reservoir cap 38, including bleed holes 38a and 38b for respective communication between atmosphere and the interiors of main body portions 36a and 36b. Diaphragm 36 further includes a central mounting portion 36c interconnecting the two main body portions 36a and 36b and including a groove 36d for frictional receipt of the upper edge of partition 34a and a ridge 36e for sealing coaction with the adjacent underface of reservoir cap 38.

The compound diaphragm of Fig.9 acts in conjunction with the illustrated dual master cylinder assembly to provide a large expansion and contraction capacity with respect to each of the reservoir chambers 34b and 34c in the manner previously described with respect to the diaphragm illustrated in Figs.1 - 8. Specifically, the compound diaphragm seen in Fig.9 acts to maintain a totally liquid-filled condition in each of the dual systems of the dual master cylinder assembly irrespective of wear in the system, leakage in the system, temperature variations, pressure variations, or overfill or underfill conditions. 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.

Claims

1. A hydraulic master cylinder including housing containing a piston for discharging hydraulic fluid from a pressure chamber in the housing, and a reservoir having a flexible tubular diaphragm therein and dividing said reservoir into a liquid chamber portion on one side of said diaphragm arranged to communicate with said pressure chamber and a gas chamber portion on the other side of said diaphragm arranged to communicate with atmosphere, said diaphragm having a main body portion formed transverse to its axis with a plurality of radially extending arms arranged about said axis each of which includes a pair of side walls defining therebetween a portion of the volume of said gas chamber, said diaphragm being movable between an expanded condition and a collapsed condition, in which collapsed condition each of said pairs of side walls of said arms are collapsed with respect to each other to reduce the volume of said gas chamber.

2. A hydraulic master cylinder according to Claim 1 in which the main body includes a series of axially extending circumferential ly spaced flutes and said arms comprise axially extending circumferential ly spaced rounded ridges between the f lutes .

3. A hydraulic master cylinder according to Claim 2 in which the side walls of the arms blend smoothly into the adjacent flutes.

4. A hydraulic master cylinder according to Claim 1, 2 or 3 in which each arm is substantially pear shaped in cross-section.

5. A hydraulic master cylinder according to Claim 4 in which a larger bulbous portion of the pear shape lies remote from the axis of the diaphragm.

6. A hydraulic master cylinder according to any preceding Claim in which at least three arms are provided.

7. A hydraulic master cylinder according to Claim 6 in which four arms are provided to define a cross-like configuration.

8. A hydraulic master cylinder according to any preceding Claim in which the arms are arranged symmetrically about said axis.

9. A hydraulic master cylinder according to any preceding Claim in which the diaphragm has an open end by means of which it is secured to a housing defining the reservoir.

10. A hydraulic master cylinder according to Claim 9 in which said open end is formed with an annular mounting portion.

11. A hydraulic master cylinder according to Claim 10 in which the annular mounting portion is secured between a portion of the reservoir housing and a reservoir closure member.

12. A hydraulic master cylinder according to any preceding Claim in which the master cylinder is a dual master cylinder assembly with separate pistons and a reservoir housing having respective liquid chambers, each liquid chamber being separated from its associated gas chamber by a diaphragm main body portion.

13. A master cylinder according to Claim 12 in which said diaphragm comprises a single unit having two main body portions.

14. A master cylinder according to Claim 13 in which the single unit diaphragm has a mounting portion at an open end thereof enabling it to be mounted between a surface of the housing and a closure member for the housing.

15. A master cylinder according to Claim 14 in which part of the mounting portion between the two main body portions includes a sealing section which sealingly engages the closure member.

16. A master cylinder according to Claim 14 or 15 in which said part of the mounting portion sealingly locates on a portion or divider between the liquid chambers of the reservoir.