GB2126295A

GB2126295A - Dual master cylinders for hydraulic brake systems

Info

Publication number: GB2126295A
Application number: GB08224780A
Authority: GB
Inventors: Michel Vermoesen
Original assignee: General Motors France SA
Current assignee: General Motors France SA
Priority date: 1982-08-28
Filing date: 1982-08-28
Publication date: 1984-03-21
Also published as: ES8406955A1; GB2126295B; IT8348877A0; FR2532262A1; FR2532262B1; IT1170449B; ES525178A0; DE3326410C2; DE3326410A1; IT8348877A1

Abstract

In a dual circuit hydraulic brake master cylinder, for a motor vehicle, having primary and secondary pressurizing pistons 12 and 14, a primary piston return spring 74 acting between the respective pistons is retained with a design amount of preload by a caging arrangement 98 in which an externally flanged tubular spring retainer cage 100 of heat- protected elastic plastics material has an internally projecting annular detent portion in the form of internal detent projections 114 disposed at the free ends of respective resilient cantilever segments that are formed by longitudinally extending slits 112 in an end region 110 of the cage, permitting the plastics cage to be snap-fitted in an axial direction on to a head portion 68 of a piston stop rod 62 that projects in the axial direction from the rear end of the secondary pressurizing piston. Alternatively a spring steel retainer cage 130 with a single longitudinal slit may be used. <IMAGE>

Description

SPECIFICATION Dual master cylinders for hydraulic brake systems This invention relates two dual master cylinders suitable for use in motor vehicle hydraulic brake systems.

The invention is primarily concerned with the caging of a preloaded compression spring acting between primary and secondary pressurizing pistons ofa dual master cylinder.

By the invention there is provided a dual master cylinderfora hydraulic brake system, in which a primary pressurizing piston is slidably mounted in a bore in a master cylinder housing, between a closed end ofthe bore and an open end of the bore provided with a piston stop, a secondary pressurizing piston is slidably mounted in the bore between the primary pressurizing piston and the closed end ofthe bore, a return spring forthe primary piston is disposed in a first pressurizing chamberformed between the primary and secondary pistons, a return spring for the secondary piston is disposed in a second pressurizing chamberformed between the secondary piston and the closed end ofthe bore, the primary and secondary pressurizing chambers are provided with respective supply and pressure discharge ports, and a caging arrangementforthe primary piston return spring comprises a spring seatfortransmitting force between one end of the primary piston return spring and one ofthe pistons, a piston stop rod which extends axially from the said one piston into the first pressurizing chamber and comprises a shank portion separated by an annular shoulder from a head portion having a terminal stop surface disposed for selective abutment with a terminal stop surface on the other of the pistons, and a spring retainercagewhich extends axially in the first pressurizing chamber for abutment with an abutment surface of the said other piston and comprises a generally cylindrical body portion having a hollow interiorfor slidably accommodating the head portion of the stop rod, and having at one end region an externally projecting portion forming a spring seat for the other end ofthe primary piston return spring and also having at an opposite end region ofthe body portion an internally projecting annular detent portion adapted during assembly to pass in the axial direction overthe head portion ofthe piston stop rod and thereupon engagethe annular shoulder ofthe piston stop rod, to form a caged assembly retaining the primary piston return spring in a preloaded condition.

In this way it is possible to achieve a caged assembly for the primary piston return spring which is relatively simple, easy to manufacture, and easy to assemble.

Thus the caged assembly may comprise only to ree elements, namely the primary piston return spring itself, a cast secondary piston having the piston stop rod formed integral with the piston, and the spring retainer cage, which can for example be formed as a moulding of elastic plastics material. Inasmuch as the piston rod and cage can be respectively cast and moulded theirfinal dimensions, no machining is necessaryforthe caged assembly.To assemble the parts, the spring is located relative to the piston, and the cage is introduced intothefree end portion ofthe spring and then moved in an axial direction towards the piston, with progressive compression of the spring until the cage snaps overthe shoulder ofthe piston stop rod, so completing the caged assembly retaining the primary piston return spring with a design amount of preload.

In the drawings: Figure lisa fragmentary longitudinal section, with parts shown in elevation or schematically, of one embodimentofa dual master cylinder in accordance with the present invention, for use in a hydraulic brake system of a motor vehicle; Figure2 isan elevation of a first form of spring retainer cage forming part of a caging assemblyfor a primary piston pressurizing spring of the dual master cylinder shown in Figure 1; Figure 3 is an end view of the spring retainer cage, on the line 3-3 of Figure 2, in the direction of the arrows; Figure 4 is a view of the other end ofthe spring retainer cage, on the line 4-4 of Figure 2, in the direction ofthe arrows;; Figure 5 is an end view of a second form of spring retainer cage suitable for use as part of a caging assembly in a dual master cylinder otherwise as shown in Figure 1; and Figures 6 and 7 are longitudinal sectional views on the lines Vl - VI and VII -VII respectively of Figure 5, in the direction of the arrows.

As is shown in Figure 1 ofthe drawings, a dual mastercylinder 10 in accordance with the present invention,foruseina hydraulic brake system of a motor vehicle, includes a primary pressurizing piston 12 and a secondary pressurizing piston 14which are both slidably mounted in a common bore 16 in a generally conventional master cylinder housing 18 that is made of cast iron, or aluminium machined to form the bore 16.The bore 16 has a closed front end 20 (the left-hand end as viewed in Figure 1) and an open rear end 22, adjacent its open rear end the bore is provided with a circumferential groove 24 having a frustoconical forward wall and a radially extending rearward wall. Aspring ring 26 is retained within the circumferential groove 24, in abutment with the radially extending rearward wall of the groove, and forms a piston stop limiting rearward movement of the primary piston 12.

The primary pressurizing piston 12, which is made of aluminium, has an axially spaced pairof lands constituted by a front land 28 connected by means of a waisted portion of the piston to a rear land 30, and the piston 12 also has a forward extension 32 which projectsforwardlyfromthefront land 28 and terminates in a radially extending forward stop surface 34. A forwardlyfacing elastomeric cup seal 36 is mounted on the forward extension 32 of the primary piston 12, between the front land 28 and an external flange portion 38 of the forward extension, to provide a sliding fluid seal againstthewall ofthe housing bore 16. An elastomeric O-ring seal 40 is mounted in a circumferential groove in the rear land 30, and likewise provides a sliding fluid seal against the wall of the housing bore.

Instead of O-ring seal 40, a cup seal similarto cup seal 36 could be used, with corresponding modifica tion ofthe shape ofthe rear land 30.

The secondary pressurizing piston 14 is slidably mounted in the bore 16 between the primary piston 12 and the closed end 20 of the bore, and in this embodiment is made of a magnesium-zinc alloy, although it could alternatively be made of aluminium, another metal oralloy, orforsome applications might possibly be made of a plastics material.The secondary piston 14 has an axially spaced pairof lands constituted by a front land 42 connected by means of a waisted portion provided with longitudinally extending ribs to a rear land 44, and the secondary piston also has a forward extension 46 which projects forwardly from the front land 42 and terminates in a radially extending stop surface 48. Theforward extension 46 is of stepped configuration, forming a shoulder50which serves to retain an annularspring seat and seal retainer member 52.A forwardly facing elastomeric cup seal 54 is mounted on the forward extension 46 ofthe secondary piston 14, adjacent the frontland42: this cup seal 54 is retained by the annularspring seat and seal retainer member 52, and provides a sliding fluid seal against the wall ofthe housing bore 16.

Thesecondarypressurizing piston 14 also incl udes a rearward extension 56 which projects rearwardly from the rear land 44 and includes an external flange 58 which forms a spring seat portion, in conjunction with an adjacent spring guide portion 60 of the rearward extension, as will be further described later.

A rearwardlyfacing elastomeric cup seal 61 is retained on the rearward extension 56 between the rear land 44 of the secondary piston and the external flange 58, and provides a sliding fluid seal againstthe wall of the housing bore 16.

The rearward extension 56 of the secondary pressurizing piston 14 also includes an axially extending piston stop rod 62 which projects in a rearward direction from the spring guide portion 60 and comprises a shank portion 64 that is separated bya radially extending annular shoulder 66 from a head portion 68 of generally right cylindrical shape. The head portion 68 of the piston stop rod 62 terminates in a radially extending rear stop surface 70.

The piston stop rod 62 thus forms part of the rearward extension 56 ofthe secondary pressurizing piston 14. Both the forward extension 46 and the rearward extension 56 including the piston stop rod are castintegrallywith the landed central portion of thesecondarypiston 14. In otherwords,thesecondary piston 14 is one-piece construction.

Alternatively, the piston stop rod could be formed as a separate part, which would then be permanently connected to the secondary pressurizing piston.

The part ofthe housing bore 16 between the primary pressurizing piston 12 and the secondary pressurizing piston 14 constitutes a primary pressurizing chamber 72, and this primary pressurizing chambercontainsa helical compression spring 74 which acts as a return spring forthe primary piston and will be further described later.Correspondingly, the part of the housing bore 16 between the secondary pressurizing piston 14 and the closed end 20 of the bore constitutes a secondary pressurizing chamber 76, and this secondary pressurizing chamber contains a helical compression spring 78 that has its forward end seated on the closed end 20 of the housing bore, which is shaped to act as a spring guide, and its rearward end seated on the annularspring seat and seal retainer member 52 of the secondary piston, whereby the spring 78 acts as a return spring forthe secondary piston 14.

The primary and secondary pressurizing chambers 72 and 76 are provided with generally conventional respective supply and pressure discharge ports.

Specifically, the master cylinder housing 18 is provided with first and second recesses 80 and 82 for the reception of respective plug-in ports of a brake fluid reservoir (not shown, and of conventional construction), and of these the first recess 80 has a supply port 84 which in the position of the primary pressurizing piston 12 shown in Figure 1 is in fluid communication with the primary pressurizing chamber 72. The first recess also has a pressure relief port 86 which is in fluid communication with the annular area between the valve lands 28 and 30 ofthe primary pressurizing piston 12, and correspondingly the second recess has a supply port 88 which in the position ofthe secondary pressurizing piston 14shown in Figure 1 is in fluid communication with the secondary pressurizing chamber 76.The second recess also has a pressure relief port 90 which is in fluid communication with the annular area between the valve lands 42 and 44 of the secondary pressurizing piston 14. The master cylinder housing 18 is additionally formed with a first pressure discharge port92which is in fluid communication withtheforward end region of the primary pressurizing chamber 72 and provides a fluid connection externally ofthe master cylinder housing to a first hydraulic brake circuit of the vehicle, and a second pressure discharge port94which is in fluid communication with the forward end region of the secondary pressurizing chamber 76 and provides a fluid connection externally of the master cylinder housing to a second hydraulic brake circuit of the vehicle.

The first and second recesses 80 and 82, instead of providing for plug-in connection of a pairofseparate brake fluid reservoir ports, could alternatively comprise parts of respective brake fluid reservoirs that are formed integrally with the master cylinder housing.

As hasalready been mentioned,thehelicalcom- pression spring 74 constituting the primary piston return spring is contained within the primary pressurizing chamber 72, and the piston stop rod 62 is likewise contained within the primary pressurizing chamber. The forward end of the primary piston return spring 74 is seated on the external flange 58 of the rearward extension 56 ofthe secondary pressurizing piston 14, and maintained centred relativetothe longitudinal axis 96 of the master cylinder by means of the spring guide portion 60. The piston stop rod 62 and the spring seat constituted by the external flange 58 form part of a caging arrangement 98forthe primary piston return spring 74, and act in conjunction with a spring retainer cage 100 which will now be described in some detail.

The spring retainer cage 100 is shown in Figure 1 of the drawing in an assembled, operative condition, in which the spring retainer cage extends in an axial direction within the primary pressurizing chamber 72.

Details of the spring retainer cage 100 as such are shown in Figure 2,3 and 4 of the drawing, these Figures showing the spring retainer cage itself in elevation.

The spring retainer cage 100 is formed as a tubular one-piece moulding of elastic plastics material, of a general configuration not dissimilar to a hollow rivet having a partially slit shank portion. Specifically, the spring retainer cage 100 comprises a generally cylindrical body portion 102 having a hollow interior in the form of a longitudinally extending passage 104 sized for slidably accomodating the head portion 68 of the piston stop rod 62. Atthe end region which is to the rear in the installed position (to the right as viewed in Figures 1 and 2) the spring retainer cage 100 has a head-like externally projecting flange portion 106 sized to act as a spring seatforthe primary piston return spring 74. The flange portion 104 is formed with fluid-flow notches 108 round its outer periphery.The opposite end region 110 ofthespring retainer cage 100 is of slightly smaller diameter than the part ofthe body portion 102 adjacenttheflange portion 106, and is subdivided circumferentially by means ofthree symmetrically arranged axially extending slits 112 which extend from the free end ofthe spring retainer cageforthe major part ofthe length ofthe end region 110. Thereby, the end region 110 ofthe spring retainer cage 100 is subdivided circumferential iy to form three circumferentially spaced cantilever segments, making upthemajorpartoftheendregion 110.

These cantilever segments 110 are provided at their free end region (namely the left-hand end region as viewed in Figures 1 and 2) with respective inwardly directed detent projections 114 that are each separated by a radially inwardly extending shoulder portion 116 from the full-diameter passage 104that extends through the body portion of the cage.

The three detent projections 1 l4togetherform in effect an internal interrupted annular detent member having a radially inwardly extending interrupted annular shoulder (constituted by the three shoulder portions 116) that is of essentiallythe same dimensions as the annular shoulder66 of the head portion 68 ofthe piston stop rod 62. The three detent projections 114 also have respective convexly curved lead-in surfaces 118togetherforming an interrupted annular lead-in surface facing towards the free end ofthe end region 110 ofthe spring retainer cage 100.

Instead of being convexly curved, the lead-in surfaces could alternatively comprise chamfered sur- faces.

Atthe opposite end ofthe spring retainer cage 100, namely the right-hand end as viewed in Figures 1 and 2, the part of the annularflange 106 surrounding the through passage 104 is provided with a shallow annular recess 120 sized to accommodate the external flange portion 38 ofthe forward extension 32 ofthe primary piston 12.

With the construction as described, the spring retainer cage 100 can provide a snap-on connection with the head portion 68 ofthe piston stop rod 64.

Specifically, assembly ofthe caging arrangement 98 forthe primary piston return spring 74 involves simply passing the spring 74 in the direction along the piston stop rod 62 into a position of seating engagement with the external flange 58, introducing the body portion 102 of the spring retainer cage 100 in an axial direction into the interior of the coils of the spring 74, and then applying sufficient force in an axial direction to the flange portion 106 of the spring retainer cage to cause the head portion 68 of the piston stop rod 62 to exert a camming action on the lead-in surfaces 118 ofthe spring retainer cage to move the free end portions of the cantilever segments of the cage end region 110 in a radially outward direction sufficiently to allowthe detent projections 1 14to pass over the head portion of the piston stop rod and thereupon engage the annular shoulder 66 of the piston stop rod with a snap-in action, so forming a caged assembly retaining the primary piston return spring 74 in a preloaded condition. The effective axial length ofthe spring retainer cage 100 is such as to provide the desired amount of preload forthe primary piston return spring in the complete caged assembly.

The resulting secondary piston subassembly can then be introduced into the bore 16 ofthe master cylinder housing 18,followed by introduction of the primary pressurizing piston 12 into the bore and location ofthe piston stop ring 26 in its circumferential groove 24 adjacentthe open rear end of the bore.

When the dual master cylinder 10 is installed in a motor vehicle with the first and second pressure discharge ports 92 and 94 connected to respective brake circuits and a push rod (not shown) of a conventional brake booster co-operating with a recess 122 in the rear end portion of the primary pressurizing piston 12, apply movement ofthe booster push rod in a forward direction causes the primary and secondary pressurizing pistons 12 and 14to move forwardly to supply hydraulic fluid (replenished from the brake fluid reservoirs) from the primary and secondary pressurizing chambers 72 and 76to the respective brake circuits.Piston apply force is transmitted from the primary piston to the secondary piston by way of the caging arrangement 98 and primary piston return spring 74, with the minimum distance between the primary and secondary pressurizing pistons being established by abutment of the respective stop surfaces34and70.

If disassembly of the caging arrangement is required, the spring retainer cage 100 is angled slightly from the axial direction and simultaneously pulled in a direction away from the piston stop rod, to cause the head portion 68 of the piston stop rod to exert a wedging action moving the cantilever segments of the cage end region 110 apartsufficientlyforthe detent projections 114to be moved free of the head portion.

Forsubsequentassemblyofthe caging arrangement, a new spring retainer cage would be utilised.

The spring retainer cage may be moulded from polyamide plastics material such as polyamide 6/6 heat protected, orthe unfilled polyamide sold under the trade name "Zytel", or an acetal resin such as that sold under the trade name "Delrin", or any other elastic material providing sufficient elasticity to permit assembly. The elastic characteristics of these materials are to be such that the spring retainer cage can be snap-fitted in an axial direction on the head portion of the piston stop rod, but cannot be removed from the piston stop rod by an axially directed force of the same order of magnitude as theforce exerted bythe primary piston return spring.

The end region 110 of the spring retainer cage 100 could alternatively have only two slits, so forming an opposed pair of cantilever segments, or even no slits at all if the selected material is elastic enough. If required, one or more through apertures forfluid flow may be provided in the unslit part ofthe cage body portion 102, or possibly in the end region 110.

In the construction described, the primary piston return spring 74 is concentric with the piston stop rod 62 extending in a rearward direction from the secondary pressurizing piston 14, and is emprisoned between the piston flange and the plastics cage. A separate spring seat for the spring 74 could be provided atthesecondary pressurizing piston if desired.

An alternative possibility isforthe piston stop rod to be incorporated into the primary piston, although for most applications the described arrangement, with the piston stop rod incorporated into the secondary piston will be found more convenient.

In Figures 5to 7 ofthe drawingsthere isshown a spring retainer cage 130 that is formed as a split cage from spring steel, and is usable instead of the spring retainer cage shown in Figure 2 to 4 in a dual master cylinder 10 otherwise as shown in Figure 1 of the drawings.

The spring retainer cage 130 has a tubular body portion 132 of hollow-cylindrical form sized for slidably accommodating the head portion 68 ofthe piston stop rod 62 shown in Figure 1. At its right-hand end as viewed in Figures 6 and 7 the spring retainer cage 130 has an external flange portion 134that is sized to act as a spring seatforthe primary piston return spring 74 shown in Figure 1, and is formed with a shallow annular recess 136 sized to accommodate the primary piston flange portion 38. Fluid-flow notches 138 are formed round the outer periphery of the flange portion 134.The left-hand end region of the spring retainer cage 130 is formed with a depressed annular groove-like portion 140 having an outwardly flared free end wall portion 142 to form a lead-in surface forthe head portion 68 of the piston stop rod 62, and a radially extending wall portion 144 providing an annularshoulder 146forengaging the annular shoulder 66 ofthe piston stop rod in the assembled condition of the spring retainer cage.

A single axially extending slit 148 extends the entire length ofthe spring retainer cage 130, to provide the required amount of elasticity for snap-in engagement overthe head portion 68 ofthe piston stop rod 62 during assembly in the axial direction. Additionally, several opposed elongate flow apertures 150 extend through the body portion 132 at a location in the vicinity of the annular shoulder 146.

The spring caging arrangements which have been descirbed, for use in a dual master cylinder in accordance with the present invention, are effective and yet of relatively simple construction, consisting as they do of only three parts; they are also easyto assemble.

Claims

1. Adual mastercylinderfora hydraulic brake system, in which a primary pressurizing piston is slidably mounted in a bore in a master cylinder housing, between a closed end ofthe bore and an open end ofthe bore provided with a piston stop, a secondary pressurizing piston is slidably mounted in the bore between the primary pressurizing piston and the closed end of the bore, a return spring forthe primary piston is disposed in a first pressurizing chamberformed between the primary and secondary pistons, a return spring for the secondary piston is disposed in a second pressurizing chamber formed between the secondary piston and the closed end of the bore, the primary and secondary pressurizing chambers are provided with respective supply and pressure discharge ports, and a caging arrangement forthe primary piston return spring comprises a spring seatfortransmitting force between one end of the primary piston return spring and one of the pistons, a piston stop rod which extends axiallyfrom the said one piston into thefirst pressurizing chamber and comprises a shank portion separated by an annularshoulderfrom a head portion having a terminal stop surface disposed for selective abutment with a terminal stop surface on the other ofthe pistons, and a spring retainer cage which extends axially in the first pressurizing chamber for abutment with an abutment surface of the said other piston and comprises a generally cylindrical body portion having a hollow interiorfor slidably accommodating the head portion of the stop rod, and having at one end region an externally projecting portion forming a spring seat forthe other end ofthe primary piston return spring and also having at an opposite end region of the body portion an internally projecting annular detent portion adapted during assembly to pass in the axial direction overthe head portion of the piston stop rod and thereupon engage the annular shoulder ofthe piston stop rod, to form a caged assembly retaining the primary piston return spring in a preloaded condition.

2. A dual master cylinder according to claim 1, in which the spring seatfortransmitting force between one end of the primary piston return spring and one of the pistons comprises a flange portion ofthe said one piston.

3. A dual master cylinder according to claim 2, in which the said one piston includes a spring guide portion disposed adjacenttheflange portion of the piston.

4. Adual mastercylinder according to any one of claims 1 to 3, in which the primary and secondary pressurizing pistons have resilient fluid seals mounted at respective ends thereof, and at least the fluid seals in the first pressurizing chamber are formed as cup-type seals.

5. A dual master cylinder according to any one of claims 1 to 4, in which the piston stop rod is formed integrally with, or permanently connected to, the said one piston.

6. A dual master cylinder according to any one of claims 1 to 5, in which the piston stop rod extends into the first pressurizing chamber from the secondary pressurizing piston.

7. A dual master cylinder according to any one of claims 1 to 6, in which the abutment surface on the said other piston comprises an external flange portion in the region ofthe stop surface on the piston.

8. A dual master cylinder according to any one of claims 1 to 7, in which the externally projecting spring seat portion ofthe spring retainer cage comprises a terminal flange portion provided with fluid-flow apertures.

9. A dual mastercylinder according to any one of claims 1 to 8, in which the annularshoulderofthe piston stop rod extends radially outwardlyfrom the shank portion.

10. A dual master cylinder according to claim 9, in which the head portion ofthe piston stop rod is of right cylindrical shape.

11. A dual master cylinder according to claim 9 or 10, in which the internally projecting annular detent portion of the spring retainer cage includes a convexly curved or chamfered lead-in surfaceforfacilitating passage ofthe detent portion in the axial direction overthe head portion ofthe piston stop rod during assembly, and a radially extending annular shoulder for subsequent engagement with the annular shoulder ofthe piston stop rod.

12. A dual master cylinder according to any one of claims 1 to 11, in which the said opposite end region of the body portion of the spring retainer cage is subdivided circumferentially by means of axially extending slits to form circumferentially spaced resilient cantileversegments, and the individual cantilev er segments are provided attheirfree end region with respective inwardly directed detent projections that together constitutethe said internally projecting annular detent portion.

13. A dual master cylinder according to claim 12, in which the said opposite end region of the body portion ofthe spring retainer cage is subdivided circumferentially by means ofthree equally circumferentially spaced axially extending slits, forming three circumferentially spaced resilient cantilever segments.

14. A dual master cylinder according to claim 12, in which the said opposite end region ofthe body portion of the spring retainer cage is subdivided circumferentially by means of two diametrically opposed axially extending slits, forming two opposed like resilient cantilever segments.

15. A dual master cylinder according to any one of claims 1 to 11, in which the spring retainer cage is made of elastic material, and the internally projecting annular detent portion of the said opposite end region ofthe body portion ofthe cage forms a ring-like annularshoulderforengagementwith the annular shoulder of the piston stop rod.

15. A dual master cylinder according to any one of claims 1 to 11, in which the spring retainer cage is made of elastic material, and the internally projecting annular detent portion of the said opposite end region ofthe body portion ofthe cage forms a continuous annular shoulderfor engagement with the annular shoulder ofthe piston stop rod.

16. Adual master cylinder according to claim 15, in which the body portion ofthe spring retainer cage is circumferentially continuous.

17. A dual master cylinder according to any one of claims 1 to 16, in which the body portion of the spring retainer cage includes a hollow cylindrical portion disposed between the externally projecting spring seat portion and the said opposite end region ofthe body portion, and the said opposite end region ofthe body portion has a smaller external diameterthan the hollow cylindrical portion.

18. Adual mastercylinderaccording to anyone of claims 1 to 17, in which at least onethrough aperture forfluid flow isformed in the body portion ofthe spring retainer cage.

19. A dual master cylinder according to any one of claims 1 to 18, in which the spring retainer cage is made of elastic plastics material.

20. A dual master cylinder according to any one of claims 1 to 18, in which the spring retainer cage is made of metal.

21. Adual mastercylinderfora hydraulic brake system, substantially as hereinbefore particularly described and as shown in Figures 1 to 4 ofthe accompanying drawings.

22. A dual master cylinder for a hydraulic brake system, substantially as hereinbefore particularly described and as shown in Figures 1 to 4, as modified by Figures 5 to 7, of the accompanying drawings.

New claims or amendments to claims filed on 17 June 83 Superseded claim 15 New or amended claim