GB1583391A

GB1583391A - Master cylinders

Info

Publication number: GB1583391A
Application number: GB2143177A
Authority: GB
Original assignee: Nissan Motor Co Ltd; Tokico Ltd
Current assignee: Nissan Motor Co Ltd; Tokico Ltd
Priority date: 1976-05-20
Filing date: 1977-05-20
Publication date: 1981-01-28
Also published as: AU511703B2; AU2526677A; DE2722609A1

Description

(54) IMPROVEMENTS IN MASTER CYLINDERS (71) We, NISSAN MOTOR CO., LTD., a Japanese body corporate, of 2, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa-ken, Japan and TOKICO LTD. a Japanese body corporate, of 6-3, Fujimi 1-chome, Kawasaki-ku, Kawasaki-shi, Kanagawa-ken, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the followin statement: This invention relates to master cylinders for use in hydraulic systems, such as hydraulic braking systems or hydraulic clutch actuating systems in automobiles.

In a hydraulic system utilizing hydraulic fluid, such as oil, as actuating fluid it is necessary to remove or expel air completely from the system including various components and pipe lines to operate the system satisfactorily. Usually, a bleed valve is provided in one or more components of the system for expelling air which has remained in the system in filling hydraulic fluid into the system, but the air-bleeding operation is tlme-consuming and troublesome.

A method has been proposed for filling hydraulic fluid quickly and completely into a hydraulic system or into a hydraulic component, such as a master cylinder, in which, firstly, the system or the component is connected to a source of high vacuum pressure (for example, 10 or less than lOmmHg absolute) so as to extract or remove air from the interior of the system or the component substantially, and secondly, hydraulic fluid is supplied into the system or the component by, for example, changing-over a three way valve which is connected to the source of vacuum pressure, a hydraulic fluid supplying tank, and a suitable fitting formed or connected to the system or the component. The method is particularly adapted in filling hydraulic fluid into a newly assembled hydraulic system or into a newly manufactured hydraulic component quickly and easily.

While master cylinders used in hydraulic braking systems or hydraulic clutch actuating systems in automobiles have been usually formed such that a cup-shaped seal member fitted in a peripheral groove in a piston working in a cylinder acts to prevent oil leakage from the inside of the cylinder to the outside of master cylinder. But the cupshaped seal cannot effectively prevent intrusion of atmospheric air into the cylinder when a high vacuum pressure is applied in the interior of the master cylinder in performing aforementioned oil filling method.

Therefore, a desired high vacuum pressure cannot be attained in the master cylinder and a considerable amount of residual air will remain in the system or in the master cylinder when the space under vacuum pressure has been filled with oil.

The present invention in a first aspect provides a master cylinder for use in a vehicle hydraulic braking system and including a piston slidably fitted in a bore of a cylinder body of the master cylinder, a spring disposed in the bore of the cylinder body for urging the piston rearwardly, a stop in the rear end of the bore of the cylinder body to define a non-actuated position of the piston, and a seal member disposed on the stop so as to air-tightly seal the gap between the rear end of the bore of the cylinder body and the rear end of the piston when the piston is in said non-actuated position and so that the piston separates from the seal member when the piston is displaced from said non-actuated position.

The invention provides in a second aspect a master cylinder for use in a vehicle hydraulic braking system and including a piston slidably fitted in a bore of a cylinder portion of the master cylinder, a spring disposed in the bore of the cylinder portion for urging the piston rearwardly, a stop ring retained in the bore of the cylinder body to define a non-actuated position of the piston, and a seal member attached to the stop ring so as to air-tightly seal the inner periphery of the bore of the cylinder body, the seal member having a resilient lip. portion which sealingly engages with the rear end portion of the piston when the piston is in the non-actuated position.

The present invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section of a master cylinder according to the present invention; Figure 2 is a larger scale fragmentary sectional view showing portion A in Figure 1; Figure 3 is a detail cross-sectional view of a seal member and a stop ring of a modified form; Figure 4 is a view similar to Figure 3 but showing a further modified form; and Figure 5 is a view similar to Figure 2 and showing another modified form.

A tandem type master cylinder 1 shown in Figure 1 comprises a cylinder body 2 defining a bore 2a therein to receive a primary piston 3 and a secondary piston 4 fitted slidably therein. Defined in the bore 2a are, a first pressure chamber 5 between a bottom wall 2b of the bore 2a and the primary piston 3, a first supply chamber 6 formed of an annular space around a reduced diameter portion 3b of the primary piston 3 and between a primary cup seal 9 and a secondary cup seal 10, a second pressure chamber 7 between the primary piston 3 and the secondary piston 4, and a second supply chamber 8 formed of an annular space around a reduced diameter portion 4b of the secondary piston 4 and between a primary cup seal 12 and a secondary cup seal 13, respectively.

Secondary cup seals 10 and 11 partition the first supply chamber 6 and the second pressure chamber 7 fluid-tightly, and the secondary cup seal 13 partitions the second supply chamber 8 from the outside fluidtightly. The primary cup seal 9 prevents oil passing across the cup seal 9 from the first pressure chamber 5 to the first supply chamber 6, and similarly, the primary cup seal 12 prevents oil from flowing from the second pressure chamber 7 to the second supply chamber 8. But oil can pass across the primary cup seals 9 and 12 respectively from the supply chambers 6 and 8 to the pressure chambers 5 and 7 through openings 3a and 4a formed respectively in the pistons 3 and 4 upon respective retracting movements (rightward in Figure 1) of the pistons 3 and 4.

Reservoirs 14 and 15 are integrally formed on the upper side of the cylinder body 2 and are connected permanently with supply chambers 6 and 8 respectively through communicating passages 17 and 19 respectively. Further, in the non-actuated condition shown in the drawing, the reservoirs 14 and 15 are communicated respectively with pressure chambers 5 and 7 through relief openings 16 and 18 respectively. When the master cylinder 1 is incorporated in a hydraulic system such as a vehicle braking system, the first pressure chamber 5 is connected to a first braking circuit (not shown) through a passage 20, and the second pressure chamber 7 to a second braking circuit (not shown) through a passage 21.

A spring 22 is disposed between the primary piston 3 and the bottom wall 2b to urge the piston in the rightward direction in the drawing, and a stop bolt 23 threadingly engaged in the cylinder body 2 defines the non-actuated position of the primary piston 3. A spring 24 whose spring force is weaker than that of the spring 22 is disposed between the primary piston 3 and the secondary piston 4 to urge the secondary piston in the rightward direction in the drawing. The non-actuated position or the most retracted position of the secondary piston 4 is defined ya stop ring 25 fitted and retained in the open end portion of the bore 2a of the cylinder body 2. The stop ring 24 is retained in its position by a retaining ring 27 which preferably is snap-fitted in an annular groove 26 formed in the open end portion 2c of the cylinder body 2.A push rod 28 engages with the secondary piston 4 to actuate the master cylinder.

Referring particularly to Figure 2 illustrating an enlarged view of portion A in Figure 1, an elastic seal member 29 (which is not shown in Fig. 1 because of the small scale of that figure) is attached to the stop ring 25 and engages air-tightly with the inner periphery of the end portion 2c of the cylinder body 2. When the piston 4 is in its most retracted position or the non-actuated position shown in the drawing, a resilient inwardly extending radially inner end portion 29c of the seal member 29 engages airtightly with the rear end portion 4c of the secondary piston 4.Preferably the seal member 29 is integrally attached to the stop ring 25 by baking, bonding or the like, and comprises a portion 29a covering the radially outer periphery of the stop ring 25, a portion 29b covering the axially forward side (left-hand side in the drawing) of the stop ring 25, and the radially inner end portion 29c extending inwardly and forwardly from the portion 29b to contact with the rear end (right-hand side end in the drawing) portion 4c of the secondary piston 4 when the piston 4 is in its illustrated nonactuated position, When the piston 4 is displaced from its non-actuated position, it separates from the lip portion 29c of the seal member 29. The portions 29a and 29b are adapted to engage air-tightly with the inner periphery of the cylinder body 2 when the stop ring with the seal member 29 is mounted in the open end portion 2c of the cylinder body 2.

Figure 3 illustrates a modified form of the seal member 29, in which the seal member comprises a radially outer peripheral portion 29a covering the outer periphery of the stop ring 29, an intermediate portion 29d covering the rear surface of the stop ring 25, and a resilient radially inner end portion 29c extending forwardly and inwardly from the intermediate portion 29d to engage with the rear end portion 4c of the secondary piston 4. The seal member 29 is secured to the stop ring 25 by bonding or the like.

Figure 4 shows a further modified form of stop ring and seal member, in which seal member 29 is formed of two separate seal portions 29e and 29c. The seal portion 29e engages air-tightly with a shoulder defined between the bore 2a and a counterbore formed in the open end portion 2c of the cylinder body 2 to receive the stop ring 25.

The seal portion 29c acts similarly to the seal portion 29c of Figure 2 or Figure 3.

The seals 29 illustrated in Figures 2, 3 and 4 are generally moulded to the required shapes and attached to the ring as explained before.

Further modification of the seal is illustrated in Figure 5 wherein a suitable fused elastic material is applied at the open end portion of the cylinder body 2 after installing the primary and secondary pistons, stop ring and retaining ring thereinto.

The application of the material is performed so as to cover the end portion 2c of the cylinder body 2 and the rear end surface of the portion 4c.

The material used for this coating Process is selected from liquid material (usually having high viscosity) which is cured and hardened during a suitable period after the coating. If the viscosity of the material is very high, a material of non-curing type may be used. Examples of suitable materials are rubber material including latex-neoprene rubber, and liquid rubber, self-curable resin, such as epoxy resin.

By this coating, any size of master cylinder is effectively sealed without preparing different size seals 29. Also, several coating processes such as dipping, spraying or brush coating may be easily employed.

The master cylinder according to the present invention having the construction as heretofore described enables atmospheric air to be prevented from being sucked through the cup-shaped seal 13 when a high vacuum pressure is applied in the interior of the cylinder body 2 in performing the aforesaid oil filling method, since a portion between the inner periphery of the bore 2a of the cylinder body 2 and the stop ring 25 and a portion between the rear end of the secondary piston 4 and the stop ring 25 are sealed air-tightly by the seal member 29.It will be noted that the force of the springs 22 and 24 is sufficiently large to position the secondary piston 4 at the non-actuated position against a differential pressure generated across the piston 4 according to the vacuum pressure, and the seal portion 29c of the seal member 29 is tightly pressed against the rear surface of the secondary piston 4 according to a differential pressure generated across the seal portion 29c.

The master cylinder shown in the drawings is of a tandem type, but the present invention may be applied to a single piston type master cylinder in which a single piston works in a cylinder, and also be applied to a dual type master cylinder in which two pistons of different diameters work in respective cylinders.

Advantages of the present invention as described by way of example above can be summarized as follows: a) It is possible to obtain a master cylinder preventing atmospheric air being sucked therein without providing any major additional part thus reducing manufacturing cost.

b) Operational characteristics of the master cylinder will not be impaired as compared with usual master cylinders.

c) The present invention can be applied to master cylinders of any types and sizes.

d) Impact noise occurring in the end of retracting movement of piston in usual master cylinders can be prevented.

e) The present invention can be applied to any of usual master cylinders by simply exchanging the stop ring fitted in the open end portion of the cylinder body or by coating viscous material at the open end portion of the cylinder body and such operation can be performed easily at a maintenance shop.

WHAT WE CLAIM IS: 1. A master cylinder for use in a vehicle hydraulic braking system and including a piston slidably fitted in a bore of a cylinder body of the master cylinder, a spring disposed in the bore of the cylinder body for urging the piston rearwardly, a stop in the rear end of the bore of the cylinder body to define a non-actuated position of the piston, and a seal member disposed on the stop so as to air-tightly seal the gap between the rear end of the bore of the cylinder body and the rear end of the piston when the piston is in said non-actuated position and so that the piston separates from the seal member when the piston is displaced from said non-actuated position.

2. A master cylinder for use in a vehicle hydraulic braking system and including a piston slidably fitted in a bore of a cylinder portion of the master cylinder, a spring disposed in the bore of the cylinder portion for urging the piston rearwardly, a stop ring retained in the bore of the cylinder body to define a non-actuated position of the piston, and a seal member attached to the stop ring so as to air-tightly seal the inner periphery

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

comprises a radially outer peripheral portion 29a covering the outer periphery of the stop ring 29, an intermediate portion 29d covering the rear surface of the stop ring 25, and a resilient radially inner end portion 29c extending forwardly and inwardly from the intermediate portion 29d to engage with the rear end portion 4c of the secondary piston 4. The seal member 29 is secured to the stop ring 25 by bonding or the like.

Figure 4 shows a further modified form of stop ring and seal member, in which seal member 29 is formed of two separate seal portions 29e and 29c. The seal portion 29e engages air-tightly with a shoulder defined between the bore 2a and a counterbore formed in the open end portion 2c of the cylinder body 2 to receive the stop ring 25.

The seal portion 29c acts similarly to the seal portion 29c of Figure 2 or Figure 3.

The seals 29 illustrated in Figures 2, 3 and 4 are generally moulded to the required shapes and attached to the ring as explained before.

Further modification of the seal is illustrated in Figure 5 wherein a suitable fused elastic material is applied at the open end portion of the cylinder body 2 after installing the primary and secondary pistons, stop ring and retaining ring thereinto.

The application of the material is performed so as to cover the end portion 2c of the cylinder body 2 and the rear end surface of the portion 4c.

The material used for this coating Process is selected from liquid material (usually having high viscosity) which is cured and hardened during a suitable period after the coating. If the viscosity of the material is very high, a material of non-curing type may be used. Examples of suitable materials are rubber material including latex-neoprene rubber, and liquid rubber, self-curable resin, such as epoxy resin.

By this coating, any size of master cylinder is effectively sealed without preparing different size seals 29. Also, several coating processes such as dipping, spraying or brush coating may be easily employed.

The master cylinder according to the present invention having the construction as heretofore described enables atmospheric air to be prevented from being sucked through the cup-shaped seal 13 when a high vacuum pressure is applied in the interior of the cylinder body 2 in performing the aforesaid oil filling method, since a portion between the inner periphery of the bore 2a of the cylinder body 2 and the stop ring 25 and a portion between the rear end of the secondary piston 4 and the stop ring 25 are sealed air-tightly by the seal member 29.It will be noted that the force of the springs 22 and 24 is sufficiently large to position the secondary piston 4 at the non-actuated position against a differential pressure generated across the piston 4 according to the vacuum pressure, and the seal portion 29c of the seal member 29 is tightly pressed against the rear surface of the secondary piston 4 according to a differential pressure generated across the seal portion 29c.

The master cylinder shown in the drawings is of a tandem type, but the present invention may be applied to a single piston type master cylinder in which a single piston works in a cylinder, and also be applied to a dual type master cylinder in which two pistons of different diameters work in respective cylinders.

Advantages of the present invention as described by way of example above can be summarized as follows: a) It is possible to obtain a master cylinder preventing atmospheric air being sucked therein without providing any major additional part thus reducing manufacturing cost.

b) Operational characteristics of the master cylinder will not be impaired as compared with usual master cylinders.

c) The present invention can be applied to master cylinders of any types and sizes.

d) Impact noise occurring in the end of retracting movement of piston in usual master cylinders can be prevented.

e) The present invention can be applied to any of usual master cylinders by simply exchanging the stop ring fitted in the open end portion of the cylinder body or by coating viscous material at the open end portion of the cylinder body and such operation can be performed easily at a maintenance shop.

WHAT WE CLAIM IS: 1. A master cylinder for use in a vehicle hydraulic braking system and including a piston slidably fitted in a bore of a cylinder body of the master cylinder, a spring disposed in the bore of the cylinder body for urging the piston rearwardly, a stop in the rear end of the bore of the cylinder body to define a non-actuated position of the piston, and a seal member disposed on the stop so as to air-tightly seal the gap between the rear end of the bore of the cylinder body and the rear end of the piston when the piston is in said non-actuated position and so that the piston separates from the seal member when the piston is displaced from said non-actuated position.
2. A master cylinder for use in a vehicle hydraulic braking system and including a piston slidably fitted in a bore of a cylinder portion of the master cylinder, a spring disposed in the bore of the cylinder portion for urging the piston rearwardly, a stop ring retained in the bore of the cylinder body to define a non-actuated position of the piston, and a seal member attached to the stop ring so as to air-tightly seal the inner periphery

of the bore of the cylinder body, the seal member having a resilient lip portion which sealingly engages with the rear end portion of the piston when the piston is in the non- actuated position.
3. A master cylinder according to claim 2, wherein the seal member includes an outer circumferential portion covering the outer circumference of the stop ring and an intermediate portion covering the forward surface of the stop ring, and wherein the lip portion extends inwardly and forwardly from the intermediate portion.
4. A master cylinder according to claim 3, wherein the seal member is permanently secured to the stop ruing.
5. A master cylinder according to claim 2, wherein the seal member includes a first annular seal portion engaging air-tightly with a shoulder at a step formed between said bore and a counterbore formed in the open end portion of the cylinder body, and the lip portion is a second annular seal portion whose radially outer end is secured to the radially inner periphery of the stop ring, said second seal portion extending inwardly and forwardly for engaging with the rear end portion of the piston when the piston is in the non-actuated position.
6. A master cylinder according to claim 2, wherein the seal member includes an outer circumferential portion covering the outer circumference of the stop ring and an intermediate portion covering the rear surface of the stop ring, and wherein the lip portion extends inwardly and forwardly from the intermediate portion.
7. A master cylinder according to claim 1 wherein said seal member is formed by coating a viscous material on to the rear ends of the cylinder body and the piston and on to the stop.
8. A master cylinder as claimed in any preceding claim in which the piston is sealed to its cylinder bore by a cup type seal.
9. A master cylinder as claimed in any preceding claim in which the spring force applied to said piston is sufficient to hold the piston against the stop against a pressure difference of one atmosphere across the piston.
10. A master cylinder as claimed in any preceding claim which is a tandem master cylinder having two axially aligned pistons which are spring biassed apart and of which one is spring biassed towards the other which is thereby biassed against said stop.
11. A master cylinder constructed substantially as herein described with reference to and as illustrated in Figs. 1 to 4 of the accompanying drawings.
12. A master cylinder constructed substantially as herein described with reference to and as illustrated in Fig. 5 of the accompanying drawings.