AND RESERVOIR ASSEMBLY

This invention relates to a hydraulic reservoir and master cylinder assembly in particular for hydraulic .systems on automobiles.

It is known from GB-A-1539879 to provide a hydraulic clutch control system comprising a master cylinder, a reservoir, and a slave cylinder which are assembled together with conduit, and then the entire system is fitted with hydraulic fluid prior to installation on a vehicle.

The present invention relates to a master cylinder and reservoir assembly which is particularly suitable for use in a pre-filled hydraulic clutch control system.

The present invention provides a compact, cheap master cylinder/reservoir assembly.

Accordingly there is provided a hydraulic master cylinder and reservoir assembly having a master cylinder body with a fluid reservoir, and a master cylinder bore with a piston assembly sealingly

reciprocal within the bore, the fluid reservoir having at least a portion thereof concentric with the master cylinder bore and being sealed from atmosphere by a rolling diaphragm, the inner periphery of which is sealed to the piston assembly, and the outer periphery of which is sealingly slidable relative to an internal surface of the reservoir allowing the volume of fluid within the reservoir to expand or contract.

It is an advantage of this construction that no sliding piston seal is in direct contact with the atmosphere.

The primary seal directly separates the pressure chamber from the reservoir chamber and the classic secondary seal is replaced by the deformable diaphragm which is substantially stationary during piston reciprocation and is airtight.

Also there is provided a hydraulic master cylinder and reservoir assembly comprising a master cylinder body including a cylindrical metal liner having a mouth at one end and an end wall at the other end, the liner being capable of limited axial movement in the body, and the end wall of the liner forming a recuperation valve controlling the flow of

hydraulic fluid between the master cylinder bore and the reservoir.

It is an advantage for the liner to be both rigid, of metal or other material, and of a material of low elasticity, and in this latter case, for the liner to be provided with a calculated functional play, and supported by the body after a slight expansion due to the effect of the pressure.

Yet another aspect of the invention is a hydraulic ^■ master cylinder/reservoir assembly in which the master cylinder has an outlet port which receives a conduit in form of a plastic flexible pipe, and the conduit is retained in position is the outlet port of the hydraulic master cylinder and reservoir, by chordal pins that are formed integrally with the master cylinder body.

Yet another aspect of the invention is a master cylinder/reservoir assembly having a master cylinder piston assembly comprising a push rod, a seal retainer which is a interference fit on the push rod, and a piston primary seal which is located co-axially between the push rod and the seal retainer.

Yet a further aspect of the invention is a master cylinder/reservoir assembly wherein the piston is sealed to the bore by a primary seal comprising a seal ring, preferably an elastomeric ring seated in a cup, preferably PTFE, which supports the radially- outer peripheral surface of the elastomer ring and its side adjacent the piston, the outer peripheral margin of the cup being supported by a backing ring, preferably a PTFE backing ring (PTFE = poly fluroethylene) .

This seal allows the piston assembly to tilt relative to the axis of the bore.

According to one execution of the invention, the coaxial outlet port of the master cylinder body is surrounded by an annular seal, which co-operates with a portion of the end wall of the liner to regulate the flow between the reservoir and the master cylinder bore.

The annular seal is kept in position by a coaxial ring clip at the outlet port, and this clip serves to limit the axial movement of the liner in the master cylinder body.

In another configuration of the invention, the

coaxial outlet port of the master cylinder body receives the conduit which is a force fit, the seal being secured by mini annular sealing flanges fitted into the coaxial outlet port. This arrangement cooperates with a portion of the liner end wall to regulate the flow between he reservoir and the master cylinder bore. The airtightness is reinforced by the presence of an annular band or mini sealing flange which is located on the shoulder of the body, and which also cooperates with the liner end wall.

Finally, in this configuration, the body of the master ^• cylinder is provided with lugs which are machined in the extension of the coaxial outlet port, and which come to engage with the coaxial opening of the end wall of the liner, in such a way as to limit the axial movement of this liner in the body of the master cylinder.

In a preferred arrangement of the invention, the reservoir is circled and enclosed in a housing which completely covers the part of the hydraulic master cylinder to be protected from the outside environment. In this design, the housing is made up of at least two cuplike shields., whose internal configuration conforms to the shape of the body in

order to exactly cap it in the area of the reservoir and its mouthpiece. The cuplike shields are kept in place by an outer casing. These assembled shields have an outer wall which has a cruciform section aperture which accommodates a cruciform section of the push rod in such a way as to ensure the direction of this rod.

Additionally in the invention, the predetermined friction, which exists between the sealing system of the piston and the inside of the master cylinder bore, is controlled in such a way that the piston assembly can have oscillations around a point related to the master cylinder axis.

According to the invention, this point is located approximately at the intersection of the sealed plane of said sealing system, which is found in the vicinity of the central area of the sealed periphery obtained. In this preferred execution of the invention, the end wall of the shields has a spherical outer face, and a spherical inner face which matches up with the spherical abutment face of the push rod of the piston assembly. These different spherical parts have as an approximate centre the previously defined point, in such a way that at one outer extent of movement of the push

rod, an annular spring clip comes to abut with the spherical outer face and that, at the other extent of movement, the spherical abutment face of the push rod comes into abutment with the spherical inner face. The preset play, according to the invention, between the cruciform opening of the outer wall and the crosspiece of the push rod give the possible oscillations of the piston assembly in relation to the body of the master cylinder.

Other characteristics and advantages of this invention arise from the following description, with reference to the attached drawings:

Figure 1 is a longitudinal cross section through an integrated and sealed master cylinder and reservoir assembly according to this invention, which shows above the centre line the master cylinder in operational condition, and below the centre line the master cylinder in the at-rest condition.

Figure 2 is a cross section following the II-II line of Figure 1 and Figure 2a is a partial view following 2a of Figure 2.

Figure 3 is a cross section through III-III of Figure 1.

Figure 4 is an enlargement of a part of Figure 1 and

Figure 5 is another means of showing area A in Figure 1.

With reference to Figures 1,2, and 3 there is shown a hydraulic master cylinder and reservoir assembly 10 comprising a master cylinder body 11 with coaxial reservoir tank 12 for fluid formed integrally therewith. The master cylinder body 11 and reservoir tank 12 are formed from a single moulding preferably of plastic material such as nylon 6 or nylon 66 and basically comprises a stepped through bore having different diameter co-axial portions 13-16.

The smallest diameter portion 13 provides the master cylinder outlet, the adjacent larger diameter portion 14 provides a seat for an annular seal 21, the adjacent still larger diameter portion 15 houses a metal cylindrical liner 22, and the largest diameter portion 16 forms the fluid reservoir tank.

The outlet port 13 receives a flexible conduit 23,

preferably nylon 12 tube, which axially extends into the adjacent larger diameter portion 14 of the bore. The axially inner end of the tube 23 has a resilient clip 24 thereon and the tube 23 is sealed in the outlet 13 by the seal 21. The seal 21 is retained in its larger diameter portion 14 of the bore by the clip 24 and the tube 23 is secured in the outlet 13 by a pair of chordal pins 25, best seen in Figs 2 and 2a.

The pins 25 are formed integrally with the master cylinder body 11 and are moulded in the position shown in Fig 2 being joined to the body by thin membranes. After the insertion of the tube 23, the pins 25 are pushed axially into co-operating holes 26 by means of a suitable clamping tool. The pins have flutes 27 thereon that cut into the outer surface of the plastics tube 23 thereby-securing it in position.

The shoulder 17 between the two different diameter portions 14,15 of the bore is in the form of frustoconical surface, and the outlet port seal 21 extends axially to intercept the plane of frustoconical shoulder 17. The ^' larger diameter portion 15 adjacent the reservoir tank 12 houses the cylindrical liner 22. The liner 22 is formed

from an aluminium pressing and is held spaced from the internal surface of the master cylinder body by circumferentially spaced axial ribs forming a fluid chamber 28 between the outer surface of the liner 22 and the master cylinder body 11.

Alternatively, the liner 22 is made of material of low elasticity, and is mounted with a functional play which is calibrated so that the liner 22 is supported by the body 11 after slight expansion due to hydraulic pressure.

The internal surface of the liner 22 constitutes the master cylinder bore 18 and the liner 22 extends axially into the reservoir tank 12 and has an open mouth 31 at the end adjacent the reservoir tank 12, and an end wall 32 at the other end adjacent the shoulder 17. The liner, end wall 32 has a frusto conical shape that matches the frusto conical shape of the shoulder 17, so that the end wall can seat against the seal 21 when the end wall 32 is in abutment with the shoulder 17 as shown in the upper portion of Figure 1. The end wall 32 has a coaxial hole 34 therein which receives the seal retaining clip 24. The clip 24 has three lugs 33 spaced equally and which extend radially outwards and limit the movement of the liner 22 away from

the seal 21 but allows the end wall 32 to separate from the seal 21 to allow fluid to flow therebetween. Thus there is provided a recuperation valve which opens and closes with the movement of the liner 22, temporarily linked to the piston assembly 35 by the friction existing between the airtight system of this piston assembly and the seal 18 of the liner 22. The movement of the liner 22 determines the amount of free travel of the push rod before the hydraulic system begins to operate.

A variation in the realisation of the invention is shown in Fig 5. In this configuration, the body 11 of the master cylinder has a coaxial outlet port 13, which receives a conduit 23 which is a force fit by its portion 50 into the annular deformations of mini-sealing ribs 49 which are fitted into the coaxial outlet port 13, and which cooperate with a portion of the end wall 32 of the liner 22 to regulate flow between the reservoir tank 12 and the master cylinder bore 18. In addition, the body 11 of the ^~ master cylinder possesses on its shoulder 17 an annular band or mini-sealing flange 30, which cooperates with the end wall 32 of the liner 22 in order to further improve the airtight system. The master cylinder body 11 is provided with three lugs 29, which are set at equal distances one from the

other inside the extension of the coaxial outlet port 13. The lugs 29 come to grip inside the coaxial opening 34 of the- end wall 32, in such a way as to limit the axial movement of the liner 22 in the master cylinder body 11.

The master cylinder body liner 22 houses the piston assembly 35 (best seen in Fig 3) which comprises a push rod 36, a piston body 37 and a primary seal 54. The push rod has a blind bore 45, the open end of which is directed towards the opening 34 in the end wall 32. The coaxial ring body 37 of the piston assembly 35 is mounted on the axially inner end of the push rod 36. The annular piston body 37 has a front face 38 which receives the primary seal 54, and a rear face 39 which abuts against the push rod 36.

The rear face 39 of the piston body 37 has a central recess 40 which receives the end portion of the push rod 36 and has outer rearwardly extending annular lip 41. The radially outer surface of the end portion of the push rod 36 is stepped to provide a shoulder 42. The front face 38 of the piston body 38 is stepped to provide a radially inner annular shoulder 43 and a radially outer annular shoulder 44 which is set axially behind the

shoulder 43 .

The piston body 37 has a central coaxial hole which aligns with the blind bore 45 in the push rod 36 and the piston body 37 is secured to the push rod 36 by a seal retainer 46 comprising a coaxial stem 47 which is an interference fit in the blind bore 45, and a radially outwardly projecting flange 48 thereon. The seal retainer 46 holds the primary seal 54 on the piston body 37, when it ^' is fully located in the blind bore 45 and is in abutment with the front face of the piston body 37.

The hydraulic master cylinder and hydraulic reservoir, according to the invention, thus comprise a hydraulic master cylinder and a reservoir tank 12 for a fluid which is integral with the master cylinder body 11. The master cylinder has an outlet port 13 made airtight with regard to the atmosphere. The master cylinder bore 18 houses the piston assembly 35 which can be moved by means of the push rod 36. The piston sealing system in relation to the bore 18 of the master cylinder is constituted by the primary seal 54. The seal 54 includes an annular elastic ring 51, generally in elastomer, retained in a PTFE (poly tetra fluro ethylene) cup 52 which seats on the

the shoulder 43 on the front face of the piston body 37. The cup 52 is supported at its radially outer margin by a PTFE backing ring 53 which seats on the shoulder 44 on the front face 38 of the piston body 37. The cup 52 contacts the inner surface of the liner 22 and the annular ring 51 seals against the retainer flange 48, and against the cup 52.

The radially outer surface of the piston body 37 tapers radially inwardly from the master cylinder bore. This allows the piston body 37 to tilt when the push rod 36 moves off centre due to sideways movement at its outer end.

The fluid chamber 28 around the liner 22 opens into the chamber 55 of the reservoir tank 16. The reservoir fluid chamber 55 is sealed from the atmosphere by a rolling diaphragm 56 which has a radially outer peripheral bead 57 and a radially inner peripheral bead 58. The annular space 59 between the liner 22, and the diaphragm 56 inter-connects with the reservoir fluid chamber 55 and is itself filled with fluid. The outer bead 57 is in form of a annular seal which is held against the internal the internal surface of the reservoir tank 16 by an internal ring 60. The outer bead 57

is sealingly slidable within the tank 16 so that the fluid chamber 55 can expand or contract. The inner bead 58 is sealed to the piston body 37 and is secured between the flange 41 on the piston body 37 and the shoulder 42 on the push rod 36. The diaphragm 56 acts as a secondary seal preventing air from entering the master cylinder bore.

The reservoir 12 is surrounded and enclosed in a housing 80 which completely covers the portion of the master cylinder to be protected from the outside environment. This housing 80 is principally, made up of cuplike parts 62-63 which are mounted on the body 11, which are kept in place by an outer casing 65. The cuplike parts of whatever number N are mounted on the body 11. In the method of execution shown in Fig 1 and 3 there are two cuplike parts or half cups 62 and 63, whose inside configuration has a forms matching that of the body 11, in such a way that it exactly caps it in the area of the reservoir tank 12 with its mouth 61. The cuplike parts 62 and 63 are kept in place by .the casing 65. Without departing from the scope of the invention, the cuplike parts 62 and 63 can be maintained by any method of fixing. The casing 65 and the cuplike parts 62 and 63 thus constitute a housing covering completely the portion of the

assembly to be protected from the external environment.

The cuplike parts 62 and 63 have an end wall 64 which includes a cruciform opening 66, which accommodates a cruciform section 67 of the push rod 36. The clearance between the cruciform opening 66 and the section 67 of the push rod 36 allows the oscillations of the push rod 36. These oscillations are principally effected in the section of Fig 1, e.g.these are strokes as one can see it on Fig 3. This end wall 64 has an outer spherical face 68, and an inner spherical face 69 which cooperates with a spherical abutment face on the push rod 36, which seats against the spherical inner face 69, when the push rod 36 is in the at-rest position. For that, the outer spherical face 68, the inner spherical face 69 and the spherical abutment face 70 of the push rod 36 have the same spherical centre C. This centre C is approximately in the seal plane of the primary seal 54, this seal plane located approximately in the central area of the periphery of the airtightness obtained.

The push rod 34 has two axially spaced grooves 71,72 therein which can accommodate an annular

spring clip 73.

Below the centre line of Fig 1, the master cylinder is shown in the at-rest condition. If the master cylinder forms part of a pre-assembled prefilled clutch actuation system, them during delivery and prior to use the spring clip 73 will be fitted ^' within the groove 72 immediately adjacent the end wall 64 of the cups 62 and 63. This will help prevent accidental operation of the master cylinder.

If the push rod 36 is moved more axially inwardly by an actuation load on the clutch pedal the spring clip 73 is forced out of the groove 72 and the push rod moves axially inwardly. The friction between the primary seal 54 and the liner 22 ensures that the liner remains stationary relative to the piston seal 54, but is moved axially inwardly with the push rod 36 until the end wall 32 abuts the shoulder 17 and seats against the seal 21.

Further inwards movement of the push rod causes the piston seal 41 to displace fluid through the outlet 13 for operation of the clutch slave cylinder. The radially inner bead 58 of the diaphragm 56 is moved axially into the liner 22 so that the diaphragm

becomes concentric with the liner 22.

Assuming a full pedal travel, the ring 73 will now be transferred into the groove 71. This is the position shown above the centre line in Figure 1.

On release of the clutch pedal the push rod will move out of the master cylinder under the bias of the clutch pedal return spring and the slave cylinder piston will be returned by the clutch spring and fluid will be displaced back into the master cylinder. The frictional engagement of the piston seal 41 on the line 22 will move the end wall 32 away from the seal 21 opening the hydraulic system to the fluid chamber 28 and reservoir chamber 55 allowing the system to recuperate. This is the position now shown in the lower half of Figure 1.

The hydraulic master cylinder according to the invention thus has an integrated reservoir which is sealed from the atmosphere. In addition the structure of this master cylinder assembly according to the invention allows for a recuperation valve which is controlled by the change in direction of the movement of the piston thanks to the friction of the liner 22 with the

primary seal 54, which is mounted on the piston 35, and this whatever the position of the piston. In addition, the recuperation valve remains closed as long as the difference in pressure is sufficient to overlay the valve on its seating, e.g. the force due to the difference in pressure is greater than the friction between the primary seal and the liner 22. Lastly, the cooperation existing between the sealing system of the piston assembly 35 and the inside of the bore is determined in such a way that the piston assembly 35 may have the oscillations around a point belonging to the axis of the master cylinder. The primary seal 54 thus serves as a joint to the push rod 36.

According to Fig 1 and 4, the parts being at rest, there exists between the liner 22 and valve, an opening so that the pressure chamber connects with the reservoir tank chamber 28. On starting, the piston assembly displaces the liner 22 by friction up to the contact with the valve. From that moment the pressure begins to grow, the liner 22 being pushed by the pressure on its inner differential face, which ensures the airtightness for as long as the sum of the forces of pressure and of friction keep that same direction. On the return, at the end of the movement, the friction of the primary

seal 54 of the piston assembly 35 on the liner 22 becomes preponderant in relation to the hydraulic pressure, and the liner 22 lifts from the recuperation valve. This corresponds to a relatively weak pressure. A very small displacement of the liquid towards the reservoir tank due to the wear on gaskets can then take place. The outer peripheral bead of the rolling diaphragm 56 is, then, displaced as it goes along in its housing throughout the life of the equipment.

It must be added according to the invention, that the variable volume reservoir within predetermined limits is adaptable in the two directions e.g. the increasing direction and the diminishing direction, and this thanks to its sliding seal controlled by the difference in pressure which is- relatively weak. The structure of this invention with mobile liner which constitutes the recuperation valve, determines the depression which can appear in the system at a very low level. The reopening of the recuperation valve always intervenes a little before the return to the initial position thanks to the friction of the piston and to the hysteresis in the system.