GB1588431A - Hydraulic master cylinder - Google Patents

Hydraulic master cylinder Download PDF

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Publication number
GB1588431A
GB1588431A GB2960977A GB2960977A GB1588431A GB 1588431 A GB1588431 A GB 1588431A GB 2960977 A GB2960977 A GB 2960977A GB 2960977 A GB2960977 A GB 2960977A GB 1588431 A GB1588431 A GB 1588431A
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GB
United Kingdom
Prior art keywords
piston
chamber
plunger
pressure
control chamber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2960977A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Automotive Products PLC
Original Assignee
Automotive Products PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Automotive Products PLC filed Critical Automotive Products PLC
Priority to GB2960977A priority Critical patent/GB1588431A/en
Priority to JP9681678U priority patent/JPS5921092Y2/en
Publication of GB1588431A publication Critical patent/GB1588431A/en
Expired legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T11/00—Transmitting braking action from initiating means to ultimate brake actuator without power assistance or drive or where such assistance or drive is irrelevant
    • B60T11/10—Transmitting braking action from initiating means to ultimate brake actuator without power assistance or drive or where such assistance or drive is irrelevant transmitting by fluid means, e.g. hydraulic
    • B60T11/16—Master control, e.g. master cylinders
    • B60T11/224—Master control, e.g. master cylinders with pressure-varying means, e.g. with two stage operation provided by use of different piston diameters including continuous variation from one diameter to another

Description

(54) HYDRAULIC MASTER CYLINDER (71) We, AUTOMOTIVE PRODUCTS LIM ITED, a British Company of Tachbrook Road, Leamington Spa, Warwickshire, CV3 1 3ER, 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 following statement:- The invention relates to hydraulic master cylinders, particularly, but not exclusively, for vehicle braking systems. In particular it relates to variable ratio master cylinders of the kind which utilises a stepped piston or piston assembly slidable in a stepped bore to provide a large piston area and a small piston area.Initial movement of the master cylinder piston, which takes up clearances in the brakes, utilises the large piston area, whereas a greater effort on the piston to apply the brake hard utilises the small piston area. A metering valve controls pressure in a control chamber to mask the transition from the hydraulic ratio obtained with the large piston area to that obtained with the small piston area.
According to the invention there is provided a hydraulic master cylinder for a hydraulic braking system comprising a stepped piston slidable in a stepped bore, a supply port for connection to a tank of hydraulic fluid, an outlet port for connection to a brake actuator, a pressurising chamber connected to the supply and outlet ports such that movement of the stepped piston in a brake-applying direction shuts off communication from the pressurising chamber to the supply port and reduces the volume of the pressurising chamber to create a brakeapplying pressure at the outlet port, a control chamber connected to the supply port such that movement of the stepped piston in a brake-applying direction shuts off communication from the control chamber to the supply port and increases the volume of the control chamber, first non-return valve means allowing communication from the control chamber to the pressurising chamber, second non-return valve means allowing communication from the supply port to the control chamber and a metering valve comprising a stepped plunger slidable in a bore in the stepped piston and biassed in one direction by the action of pressure in the pressurising chamber acting on a relatively large piston area of the plunger against the preloaded spring and the action of pressure in the control chamber acting on a relatively small piston area of the plunger biassing the plunger in the opposite direction, the metering valve plunger having an axial bore which is normally closed by a closure member but which is opened by restricting movement of the closure member with the plunger in said one direction to allow hydraulic fluid to pass from the pressurising chamber to the control chamber through said axial bore, the arrangement being such that pressure in the control chamber remains at supply port pressure by communication through the second non-return valve means up to a point when the metering valve becomes operative to allow controlled communication from the pressurising chamber to the control chamber whereupon the pressure in the control chamber increases with increasing pressure in the pressurising chamber and at a higher rate until becoming equal to the pressure in the pressurising chamber.
Other features of the invention will now be described with reference to the accompanying drawing which shows by way of example a cross-section of one embodiment of a hydraulic master cylinder according to the invention, the master cylinder being adapted for operation by a vacuum servo unit.
The master cylinder 11 shown in the drawing has a stepped bore in which is slidable a stepped primary piston assembly comprising an annular piston 12 and an inner piston assembly 20 slidable in an axial bore in the annular piston 12. The inner piston assembly 20 comprises an inner piston 13 and a stepped plunger 31.
The annular piston 12 has a stepped cylindrical surface, the smaller diameter portion of which is slidable in a first annular cup seal 14 and in a second annular cup seal 15.
The annular piston 12 is adapted to receive a thrust from the piston or diaphragm of a vacuum servo unit through a tubular plunger 16 whilst the inner piston assembly 20 can receive a thrust from a servo valve member through an extension of the servo valve member 17, the servo valve member being connected to the input pushrod of the servo.
The servo is of the kind described with respect to Fig. 1 of the Complete Specification of our co-pending British Patent Application No. 20569/76 cognate with No.
11753/77 (Serial No. 1,537,403).
A primary pressurising chamber 18 in the master cylinder II is formed between the primary piston assembly and a secondary piston 19 slidable in the master cylinder body. An annular control chamber 21 is formed between a third annular cup seal 22 which seals the larger diameter portion of the first piston 12, and the first annular cup seal 14. A recuperation port 23 connects the primary chamber 18 to the control chamber 21 when the annular piston 12 is retracted against a stop pin 24, port 23 opening into a counterbore which is closed by a plug 25 and which has a passage (not shown) connecting to the control chamber 21 which is in the same diametral plane as pin 24. Another recuperation port 26 connects the control chamber 21 to another annular chamber 27 via a port 28 and the axial bore of the annular piston 12 when the first piston is in the retracted position.Chamber 27 is open to a supply port 29 in the master cylinder body for connection to a tank of hydraulic brake fluid.
A metering valve assembly includes the stepped plunger 31 which has a larger diameter portion slidable in the axial bore of the annular piston 12 and a smaller diameter portion slidable in a blind axial bore in piston 13. A chamber 33 formed between the smaller diameter end of the plunger 31 and the blind end of the bore in piston 13 is vented to atmosphere.
The metering valve assembly also includes a valve closure member in the form of a ball 32 which is normally seated on an annular seat at the open end of an axial stepped bore in the plunger 31 by a light compression spring 30. A pin 34 is slidable in the bore of the plunger 31 so as to abut a diametral cross pin 35 carried by piston 13. A preloaded coil spring 36 urges the plunger 31 away from piston 13 to the limit allowed by the fit of the cross pin 35 in a diametral hole in the plunger 31 so that the cross pin 35 retains plunger 31 and piston 13 as an assembly.
Annular cup seal 22 acts as a first nonreturn valve to allow communication from the control chamber 21 to the primary chamber 18 when recuperation port 23 has been blocked or traversed by seal 22 when the annular piston 12 has been advanced in the brake-applying direction towards the secondary piston 19 and is supplemented in this function by the ball 32 which can drift away from its seat in plunger 31 when pressure in the control chamber 21 is greater than that in the primary chamber 18. Similarly seal 14 acts as a second non-return valve means to allow fluid from the tank to the control chamber 21.
An outlet port 37 in the master cylinder body is for connection to one set of brakes in a split braking system and another outlet port 38 is for connection to the other set of brakes. To apply the brakes the inner piston assembly 20 is pushed in the direction towards the secondary piston 19, followed immediately by the annular piston 12 so that seal 22 wipes over the recuperation port 23 to prevent communication from the primary chamber 18 to the control chamber 21. With a small further movement of the first piston 12, port 26 wipes over seal 14 to prevent communication from the control chamber 21 back to the tank via port 29. Thus a brakeapplying pressure is built up in the primary chamber 18, fluid being displaced out of the outlet port 37 to the brakes by a piston area equivalent to that defined by the outer diameter of seal 22.Seal 14 allows flow from the tank to the control chamber 21 as the volume of the control chamber 21 increases with brake-applying movement of the annular piston 12.
The rising pressure in the primary chamber 18 acts on the larger diameter of the metering valve plunger 31 to generate a force which tends to act against the preload of spring 36, this force being supplemented by a small force from spring 30. When an appreciable pressure in the primary chamber 18 has developed the metering valve plunger 31 moves against the load of spring 36 until the ball 32 rests on the pin 34. The force tending to move the metering valve plunger 31 against spring 36 is now that developed by pressure acting on the annular area of plunger 31 which is outside the seating diameter with ball 32, and is without the help of spring 30, the force of which is now reacted by pin 34. Hence the pressure in the primary chamber 18 continues to rise until sufficient to move the metering valve plunger 31 a further amount against the load of spring 36 and away from ball 32. This allows a quantity of fluid to flow out of the primary chamber 18 and into the control chamber 21.
The effective piston area operative to expel fluid from the first chamber 18 through port 37 to the brakes is now that of the inner diameter of seal 14, since the pressure in the control chamber 21 has increased by a marginal amount sufficient to prevent flow from the tank past seal 14.
The marginal increase in pressure in the control chamber 21 acts on the annular piston area defined by the shoulder between the larger and smaller diameter portions of the metering valve plunger 31 to assist spring 36 to reseat the ball 32. However, a further increase in pressure in the primary chamber 18 caused by brake-applying movement of the annular piston 12 causes the valve plunger 31 to move against spring 36 once more, allowing a further quantity of fluid into the control chamber 21 until the subsequent increase in pressure in the control chamber 21 assists spring 36 to reseat ball 32.
The ball 32 continues to unseat and seat as pressure in the primary chamber 18 increases, pressure in the control chamber 21 increasing at the same time and at a higher rate according to the ratios of the piston areas of the valve plunger 31 until the pressure in the control chamber 21 is equal to that in the primary chamber 18 and the ball 32 remains unseated.
Since the cross-sectional areas of the larger diameter portion of plunger 31 and piston 13 are the same thrust on the servo valve member 17 is at all times proportional to the braking pressure developed in the primary chamber 18.
In the event of a hydraulic line failure to the brake actuator served by port 37, a washer 39 contacts the secondary piston 19.
The secondary piston 19 serves to transmit pressure from the primary chamber 18 to a secondary chamber 41 to actuate the other brakes through port 38 in the usual manner of a tandem master cylinder. A rubber washer 42 acts as a reaction mechanism to apportion the driver effort applied through the inner piston assembly 20 and the servo effort applied through the annular piston 12 in this failure mode as described with reference to Fig. 1 of the Complete Specification of our British Patent Application No.
20569/76 cognate with No. 11753/77 (Serial No. 1,537,403), and referred to above.
WHAT WE CLAIM IS: 1. A hydraulic master cylinder for a hydraulic braking system comprising a stepped piston slidable in a stepped bore, a supply port for connection to a tank of hydraulic fluid, an outlet port for connection to a brake actuator, a pressurising chamber connected to the supply and outlet ports such that movement of the stepped piston in a brake-applying direction shuts off communication from the pressurising chamber to the supply port and reduces the volume of the pressurising chamber to create a brakeapplying pressure at the outlet port, a control chamber connected to the supply port such that movement of the stepped piston in a brake-applying direction shuts off communication from the control chamber to the supply port and increases the volume of the control chamber, first non-return valve means allowing communication from the control chamber to the pressurising chamber, second non-return valve means allowing communication from the supply port to the control chamber and a metering valve comprising a stepped plunger slidable in a bore in the stepped piston and biassed in one direction by the action of pressure in the pressurising chamber acting on a relatively large piston area of the plunger against the preloaded spring and the action of pressure in the control chamber acting on a relatively small piston area of the plunger biassing the plunger in the opposite direction, the metering valve plunger having an axial bore which is normally closed by a closure member but which is opened by restricting movement of the closure member with the plunger in said one direction to allow hydraulic fluid to pass from the pressurising chamber to the control chamber through said axial bore, the arrangement being such that pressure in the control chamber remains at supply port pressure by communication through the second non-return valve means up to a point when the metering valve becomes operative to allow controlled communication from the pressurising chamber to the control chamber whereupon the pressure in the control chamber increases with increasing pressure in the pressurising chamber and at a higher rate until becoming equal to the pressure in the pressurising chamber.
2. A master cylinder according to Claim 1, wherein movement of the closure member with the plunger in said one direction is restricted by a pin which is axially slidable in the plunger.
3. A master cylinder according to Claim 2, wherein the pin can abut a diametral cross pin carried by the stepped piston.
4. A master cylinder according to any preceding Claim, wherein the closure member is a ball.
5. A master cylinder according to any preceding Claim, wherein the stepped piston is an assembly comprising an annular piston having an axial bore in which is slidably an inner piston assembly including the metering valve plunger and an inner piston, the plunger and inner piston being retained together for limited relative axial movement and the preloaded spring acting between the plunger and inner piston, the annular piston being adapted to receive a thrust from a servo piston or diaphragm and the inner piston being adapted to receive a thrust from a servo valve member which is connected to the input pushrod of the servo.
6. A hydraulic master cylinder substantially as described herein with reference to the accompanying drawing.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

  1. **WARNING** start of CLMS field may overlap end of DESC **.
    36 to reseat the ball 32. However, a further increase in pressure in the primary chamber 18 caused by brake-applying movement of the annular piston 12 causes the valve plunger 31 to move against spring 36 once more, allowing a further quantity of fluid into the control chamber 21 until the subsequent increase in pressure in the control chamber 21 assists spring 36 to reseat ball 32.
    The ball 32 continues to unseat and seat as pressure in the primary chamber 18 increases, pressure in the control chamber 21 increasing at the same time and at a higher rate according to the ratios of the piston areas of the valve plunger 31 until the pressure in the control chamber 21 is equal to that in the primary chamber 18 and the ball 32 remains unseated.
    Since the cross-sectional areas of the larger diameter portion of plunger 31 and piston 13 are the same thrust on the servo valve member 17 is at all times proportional to the braking pressure developed in the primary chamber 18.
    In the event of a hydraulic line failure to the brake actuator served by port 37, a washer 39 contacts the secondary piston 19.
    The secondary piston 19 serves to transmit pressure from the primary chamber 18 to a secondary chamber 41 to actuate the other brakes through port 38 in the usual manner of a tandem master cylinder. A rubber washer 42 acts as a reaction mechanism to apportion the driver effort applied through the inner piston assembly 20 and the servo effort applied through the annular piston 12 in this failure mode as described with reference to Fig. 1 of the Complete Specification of our British Patent Application No.
    20569/76 cognate with No. 11753/77 (Serial No. 1,537,403), and referred to above.
    WHAT WE CLAIM IS: 1. A hydraulic master cylinder for a hydraulic braking system comprising a stepped piston slidable in a stepped bore, a supply port for connection to a tank of hydraulic fluid, an outlet port for connection to a brake actuator, a pressurising chamber connected to the supply and outlet ports such that movement of the stepped piston in a brake-applying direction shuts off communication from the pressurising chamber to the supply port and reduces the volume of the pressurising chamber to create a brakeapplying pressure at the outlet port, a control chamber connected to the supply port such that movement of the stepped piston in a brake-applying direction shuts off communication from the control chamber to the supply port and increases the volume of the control chamber, first non-return valve means allowing communication from the control chamber to the pressurising chamber, second non-return valve means allowing communication from the supply port to the control chamber and a metering valve comprising a stepped plunger slidable in a bore in the stepped piston and biassed in one direction by the action of pressure in the pressurising chamber acting on a relatively large piston area of the plunger against the preloaded spring and the action of pressure in the control chamber acting on a relatively small piston area of the plunger biassing the plunger in the opposite direction, the metering valve plunger having an axial bore which is normally closed by a closure member but which is opened by restricting movement of the closure member with the plunger in said one direction to allow hydraulic fluid to pass from the pressurising chamber to the control chamber through said axial bore, the arrangement being such that pressure in the control chamber remains at supply port pressure by communication through the second non-return valve means up to a point when the metering valve becomes operative to allow controlled communication from the pressurising chamber to the control chamber whereupon the pressure in the control chamber increases with increasing pressure in the pressurising chamber and at a higher rate until becoming equal to the pressure in the pressurising chamber.
  2. 2. A master cylinder according to Claim 1, wherein movement of the closure member with the plunger in said one direction is restricted by a pin which is axially slidable in the plunger.
  3. 3. A master cylinder according to Claim 2, wherein the pin can abut a diametral cross pin carried by the stepped piston.
  4. 4. A master cylinder according to any preceding Claim, wherein the closure member is a ball.
  5. 5. A master cylinder according to any preceding Claim, wherein the stepped piston is an assembly comprising an annular piston having an axial bore in which is slidably an inner piston assembly including the metering valve plunger and an inner piston, the plunger and inner piston being retained together for limited relative axial movement and the preloaded spring acting between the plunger and inner piston, the annular piston being adapted to receive a thrust from a servo piston or diaphragm and the inner piston being adapted to receive a thrust from a servo valve member which is connected to the input pushrod of the servo.
  6. 6. A hydraulic master cylinder substantially as described herein with reference to the accompanying drawing.
GB2960977A 1977-07-14 1978-05-17 Hydraulic master cylinder Expired GB1588431A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB2960977A GB1588431A (en) 1978-05-17 1978-05-17 Hydraulic master cylinder
JP9681678U JPS5921092Y2 (en) 1977-07-14 1978-07-13 hydraulic master cylinder

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2960977A GB1588431A (en) 1978-05-17 1978-05-17 Hydraulic master cylinder

Publications (1)

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GB1588431A true GB1588431A (en) 1981-04-23

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB2960977A Expired GB1588431A (en) 1977-07-14 1978-05-17 Hydraulic master cylinder

Country Status (2)

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JP (1) JPS5921092Y2 (en)
GB (1) GB1588431A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2148430A (en) * 1983-10-21 1985-05-30 Teves Gmbh Alfred Two-stage master cylinder pressurisation in a hydraulic brake system with wheel slip control

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2148430A (en) * 1983-10-21 1985-05-30 Teves Gmbh Alfred Two-stage master cylinder pressurisation in a hydraulic brake system with wheel slip control

Also Published As

Publication number Publication date
JPS5422686U (en) 1979-02-14
JPS5921092Y2 (en) 1984-06-20

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PS Patent sealed
PCNP Patent ceased through non-payment of renewal fee