GB2148429A

GB2148429A - Quick fill master cylinder

Info

Publication number: GB2148429A
Application number: GB08425836A
Authority: GB
Inventors: Hans-Dieter Reinartz; Helmut Steffes
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1983-10-21
Filing date: 1984-10-12
Publication date: 1985-05-30
Also published as: GB2148429B; FR2553724B1; DE3338248C2; DE3338248A1; FR2553724A1; GB8425836D0

Abstract

A tandem master cylinder (1), particularly for the brake system of an automotive vehicle, has a first and a second pressure chamber (10 and 11) and a filling chamber (52). Upon operation of the tandem master cylinder (1), and movement of the input piston (6), piston (74) seats at one end on valve ball (56) and displaces fluid from the filling chamber (52) into the first pressure chamber (10) via bores 71 and 53 and an annular seal (67). Upon reaching of a certain pressure in the filling chamber (52), set by spring (62), the control valve (48) will open. Thus fluid from the filling chamber (52) will vent towards the chamber (31), exposed to atmospheric pressure, via the control valve (48). The pressure stage piston (25), together with the pressure chamber (10), form the first pressure stage required for the actual braking operation. The second pressure stage is formed by a second piston (9) and the second pressure chamber (11). Upon operation of the input piston (6), the second piston (9) will be operated by the compression spring (78) until there is a pressure build-up in the second pressure chamber (11). Thereupon, the second piston (9) will be displaced by the pressure of the first pressure chamber (10). The pressure stage is confined by the larger piston diameter (25) and the filling stage is confined by the smaller piston diameter (74). <IMAGE>

Description

SPECIFICATION Master cylinder This invention relates to a master cylinder with a variable transmission ratio, in particular for the brake system of an automotive vehicle of the kind which has a stepped bore provided in a housing for the reception of a stepped piston whose one piston diameter confines a pressure chamber and whose other piston diameter confines a filling chamber, the filling chamber and the pressure chamber communi cating in the stepped piston's release position with a supply reservoir via channels which may be closed by valves upon the operation of the stepped piston, the supply reservoir communicating with the filling chamber and the pressure chamber via a first non-return valve, and the filling chamber communicating with the pressure chamber via a second non return valve which opens towards the pressure chamber, and which has a control valve which upon actuation by the stepped piston may be closed by closure elements due to the force of a spring and may be opened by the hydraulic pressure against the force of a spring in order to establish communication between the sup ply reservoir and the filling chamber.

In a known master cylinder of this kind the larger portion of the stepped piston forms, together with the stepped bore, the filling stage. Also together with the stepped bore, the smaller portion of the stepped piston forms the pressure stage. The control valve in this construction is integrated into the stepped piston and simultaneously serves to function as the push rod of the pressure stage piston.

Thus, on the one hand, there results the disadvantage that the buckling length of the stepped piston is unusually long, so that the stepped piston has to be made relatively rigid.

On the other hand, there results the disadvan tage that the radial dimensions of the master cylinder are relatively large as the diameter of the filling stage always exceeds the diameter of the pressure stage. These characteristics result in an increased weight of the master cylinder. In order to allow the pressure stage in the release position of the master cylinder .to communicate with the supply reservoir via the valve designed as expansion bore, a bipar tite housing is required for the described mas ter cylinder. This results in increased costs of manufacture and renders assembly more diffi cult.

It is thus an object of this invention to reduce the dimensions and, simultaneously, the weight of a master cylinder of the kind referred to and at the same time to simplify its structure, so that the costs of manufacture are reduced.

According to the invention in its broadest aspect, a master cylinder of the kind referred to is characterised in that the larger piston diameter confines the pressure stage and the smaller piston diameter confines the filling stage. In this way, the largest diameter of the stepped bore is no longer determined by the filling stage, but rather by the pressure stage.

According to the invention, therefore, the radial dimensions of the housing can be reduced.

According to a feature of the invention, a reduction in the number of components and hence a reduction of costs and in weight are achieved in that the control valve divides the stepped piston into a filling stage piston and into a pressure stage piston, and in that a closure element of the control valve at the same time forms the filling stage piston. By means of the bipartite design of the stepped piston divided into a filling stage piston and a pressure stage piston the integration of the filling stage piston into the control valve will be achieved in a simple manner.

According to another feature of the invention, the closure elements of the control valve consist of a closure member and of a valve piston, the valve piston at the same time forming the filling stage piston, the closure elements of the control valve being guided within a central bore of the pressure stage piston, and the movement of the closure elements being limited in the closing direction by a stop provided at the pressure stage piston.

In addition to the pressure build-up, the pressure stage piston takes care of receiving and guiding the control valve and at the same time forms the stop of the filling stage piston after the completion of the filling operation.

A simple manufacture of the filling chamber which upon reaching of a certain pressure will abruptly open the control valve so as to establish a communication between the supply reservoir and the filling chamber for the purpose of a pressure reduction is achieved by the feature that the valve piston penetrates the pressure chamber, in that at the bottom of the housing a pocket bore is formed which, together with the end of the valve piston, forms the filling chamber, and in that the valve piston is penetrated by a channel.

In order to keep the control valve opened always after reaching of the predetermined pressure in the filling chamber, it is necessary to keep up a small residual pressure in the filling chamber. This residual pressure will slightly reduce the efficiency of the master cylinder but will, however, hardly have any bearing on the braking behaviour.

So as to ensure that during the filling operation the filling volume displaced in the filling chamber is supplied into the pressure chamber in as simple a manner as possible, the wheel brakes connected with the pressure chamber thus being applied as fast as possible, a further feature of the invention provides that on the surface area, at the opposite end of the filling chamber, on the valve piston two seals are fastened which are arranged at a small distance relative to each other and which are in sliding engagement with the central bore, in that between the two seals a bore extends from the channel to the surface area of the valve piston, the diameter of the surface area of the valve piston being slightly less than the diameter of the central bore and the seal at the valve piston which is closer to the filling chamber forming the second nonreturn valve which has the shape of a gasket.

The manufacture of this pressure medium connection provided for the filling operation may be realised in the valve piston in an especially simple way and will result in a simple, cheap, and reliably working guidance of the channel system from the filling chamber to the pressure chamber.

According to a further feature of this invention, the central bore is bipartite and is formed by the pressure stage piston, on the one side, and by a sleeve, on the other side, which sleeve is connected with the pressure stage piston in a pressure-sealed manner. This arrangement permits a particularly simple manufacture of the stop provided for the two closure elements and arranged between the sleeve and the pressure stage piston. This will especially facilitate assembly and manufacture of the control valve.

A further simplification of the control valve results from the feature that, radially outside the sealing seat at the closure member, axially extending passages are provided and the sealing seat at the closure member is formed by a ball fastened at the closure member. As the manufacture of the spherical sealing seat is particularly difficult, requiring a turning operation with high-degree surface precision, according to another feature of the invention a ball of the type used e.g. in ball bearings is caulked in the closure member. Thereby an especially good sealing effect will be achieved at the sealing seat of the control valve.

It is a particularly advantageous feature that the first non-return valve is a gasket fastened at the pressure stage piston, the gasket being bordered by the chamber communicating with the supply reservoir, on the one side, and by the pressure chamber, on the other side. Such a valve arrangement has proved reliable a million times in master cylinders and it allows a particularly low-cost manufacture.

So as to ensure that in the release position of the master cylinder the control valve will always urge the second piston into its initial position, on the one hand, and will reliably open, on the other hand, another feature of the invention provides that at the entrance of the filling chamber a stop is provided in the pocket bore, this stop limiting the direction of movement of the filling stage piston out of the filling chamber.

According to a further feature, the section of the stepped bore of a smaller diameter is provided within a second piston which is guided within a bore in the housing, the bore following the stepped bore of larger diameter, and forming a second pressure chamber.

Thus, it will be possible to realise this invention without any great changes in a tandem master cylinder of the kind having two pressure chambers.

An embodiment of the invention will now be described by way of example with reference to the single figure of the accompanying drawing.

The tandem master cylinder. 1 comprises a housing 2 and a bore 3 extending in the longitudinal direction of the housing 2. At its front end 4, the bore 3 is pressure-sealed by a sleeve 5 screwed into the bore 3 and by a stepped piston 6 penetrating the sleeve 5. At its rear end 7, the bore 3 is sealed by a cover 8 caulked with the bore 3 in a pressure-sealed manner. Between the stepped piston 6 and the rear end 7, a second piston 9 is provided in the bore 3, the piston 9 dividing the bore 3 into a first pressure chamber 10 and into a second pressure chamber 11. The two pressure chambers 10, 11 are each connected with a vehicular brake circuit, not shown in the drawing. The stepped piston 6 is guided in a section of larger diameter 12. The second piston 9 is guided in a section of smaller diameter 13.

The stepped piston 6 protrudes with its front end from the housing 2 of the tandem master cylinder 1. The front end is formed by a cylindrical shaft 14. By means of a retaining ring 1 5 a sheet metal plate 1 6 is fastened at the front end of the cylindrical shaft 14. A compression spring 1 7 is supported at the sheet metal plate 1 6. The other end of the compression spring 1 7 rests at the housing 2.

The compression spring 1 7 serves to move the stepped piston 6 and the second piston 9 into their initial positions, which are represented in the drawing, after the completion of the braking operation. The cylindrical shaft 14 has a recess 1 8 into which a brake-pedaloperable actuating tappet, not shown in the drawing, projects, resting at the spherical end 1 9 thereof. The actuating tappet e.g. may be part of a working piston of a brake booster or part of a brake pedal. At the housing 2, a flange 20 is provided which serves for attachment to e.g. a brake booster housing or to a splash wall of an automotive vehicle.

The seal 21 seals the sleeve 5 in respect of the housing 2, the seal 22 and the following gasket 23 sealing the sleeve 5 in respect of the cylindrical shaft 14. The seal 22 substantially performs the function of repelling the dirt whereas the seal 23 serves to repel the flow medium. The seals 21, 22, and 23 are stationarily fastened within the sleeve 5. Fastened on the portion of larger diameter 25 of the stepped piston 6, or rather on the pressure stage piston 25, is a first non-return valve which opens in the direction of a first pressure chamber 10 and which has the shape of a gasket 26. The gasket 26 fastened on the stepped piston 6 confines the first pressure chamber 10 towards the atmos phere.

Referring to the drawing, the larger dia- meter 12 of the bore 3 is followed to the right by an annular step 27 which is expanding and in which a first channel 28 ends. The first channel 28 extends into the chamber 29 which serves for the reception of a supply reservoir's outlet socket, not shown in the drawing. Towards the front end 4, the step 27 is followed by a bore section 30 forming the chamber 31, together with the surface area 24 of the cylindrical shaft 14. On the one side, the chamber 31 is confined by the step 27 and by the back wall 32 provided at the stepped piston 6 and, on the other side, it is confined by the front face 33 of the sleeve 5 and by the gasket 23. The gasket 23 is kept stationarily in its position by means of the ring 37.

Shortly ahead of the gasket 26 the channel 34 ends in the first pressure chamber 10. The channel 34 is also defined as an expansion bore. Together with the gasket 26, the channel 34 forms the first valve 43. The channel 34 extends radially out of the housing 2. At its outlet it is caulked in a pressure-sealed manner towards the atmosphere by means of a ball 35. Between the ball 35 and the opening of the channel 34 into the first pressure chamber 10, the channel 34 intersects the first channel 28 in the housing 2.

From the chamber 31, before the back wall 32, a channel 44 leads radially from the outside into the cylindrical shaft 14 of the stepped piston 6. The channel 44 ends in a pocket bore 45 extending concentrically to the longitudinal axis 39 of the stepped piston 6.

Referring to the drawing, the pocket bore 45 starts on the left behind the spherical end 1 9 and proceeds to the pressure-chamber-side end of the stepped piston 6. Following the pressure-chamber-side end of the stepped piston 6 is a hat-shaped sleeve 46 projecting into the pressure chamber 10. By means of its cramp 47, the sleeve 46 is caulked in a pressure-sealed manner at the pressure-chamber-side end of the stepped piston 6. The chamber formed by the pocket bore 45 and the sleeve 46 serves to receive the control valve 48 and the second valve 49.

The control valve 48 is formed by the closure member 50 consisting of a piston 51 with a ball 56 fastened at the front end of the piston 51 in a recess 55. Via the channel 44 and the chamber 31, the chamber 57 formed by the pocket bore 45 and the closure member 50 always communicates with the chamber 29 which is under atmospheric pressure.

Along the outside circumferential surface of the closure member 50 extend passages 58 which connect the sealing seat 59 with the chamber 57. In the illustrated release position of the tandem master cylinder 1, due to the valve spring 62, the front-side end of the closure member 50 abuts on the stop 60 designed as a disc. The cramp 47 and the caulking 61 keep the stop 60 stationarily in this position at the stepped piston 6. The valve spring 62 is provided in the chamber 57 and is supported at the closure member 50, on the one side, and on the bottom 38 of the pocket bore 45, on the other side.

Shortly before the sealing seat 59 of the ball 56 there is provided the annular surface 64 at the valve piston 65. This annular surface 64 cooperates with the sealing seat 59 of the ball 56. Via its radially outer surface area, the valve piston 65 is guided within the cylindrical bore 66 of the sleeve 46 and sealed towards the pressure chamber 10 by means of a gasket 67 while a seal 63 seals the valve piston 65 towards the chamber 57.

The valve piston 65 is biased in the direction of the front end 4 by means of a compression spring 68. The compression spring 68 is held between the end of the valve piston 65 and the cover-side end 69 of the sleeve 46. At the cover-side end 69 a central opening 70 is provided which is penetrated by a tappet 73 also penetrating the first pressure chamber 10. The tappet 73 has a central channel 71 which communicates with the control valve 48, on the one hand, and ends in the filling chamber 52, on the other hand.

Between the two seals 63 and 67 there extends a bore 53 from the central channel 71 to the surface area of the valve piston 65.

The diameter of the radially outside surface area of the valve piston 65 is slightly less than the diameter of the bore 66. The gasket 67 forms the second non-return valve. Thus, during the filling operation, the filling volume will be urged from the filling chamber 52 via the bore 53, beyond the gasket 67, and via the annular chamber 54 formed between the outside surface area of the valve piston 65 and the cylindrical bore 66, into the first pressure chamber 10. The filling chamber 52, on the one hand, is formed by a pocket bore 76 provided in the second piston 9 and, on the other hand, by the filling stage piston 74 guided in the pocket bore 76 in a pressuresealed manner by means of a seal 75. Via the tappet 73, the filling stage piston 74 is connected with the valve piston 65, forming one piece therewith.The filling stage piston 74 and the valve piston 65 have approximately the same diameter. Their diameter is larger than that of the tappet 73. The transition of the filling stage piston 74 towards the tappet 73 is formed by a step 36. Against the step 36 there rests the stop 77. The latter, in the form of a retaining ring, is fastened in the pocket bore 76. Thereby the direction of movement of the filling stage piston 74 out of the filling chamber 52 is limited and the catch device 72 formed by the filling stage piston 74, the tappet 73, and the valve piston 65 keeps the control valve 48 in its open position in the illustrated release position of the master cylinder 1.

In the pressure chamber 10, a compression spring 78 extends from the stepped piston 6 to the second piston 9. In this position, the compression spring 78 urges the two pistons 6 and 9 apart. The maximum distance between the pistons 6 and 9 will be achieved by the space resulting when the stepped piston 6 of larger diameter is urged so far to the right that the valve piston 65 compresses the compression spring 68 completely, at the same time, the filling stage piston 74 pressing the second piston 9 against the housing 2 via the stop 77. The stop may also be provided by a shoulder at the tappet 73. The catch device 72 thus couples the two pistons 6 and 9.

On the surface area of the second piston 9, respective gaskets 81, 82 rest in a pressuresealed manner, the gasket 81 confining the pressure chamber 10 and the gasket 82 confining the pressure chamber 11. Between the two gaskets 81 and 82, radially from the outside, a channel 83 extends via an annular groove 85 into the smaller diameter 13 of the bore 3. The channel 83 communicates with the chamber 84. The chamber 84 serves to receive a connecting socket of a supply reservoir, the socket not being illustrated in the drawing. As the smaller diameter 1 3 is slightly larger than the diameter of the second piston 9, a flow medium communication exists from the supply reservoir towards the two gaskets 81, 82. As the two gaskets 81 and 82 are designed as non-return valves, if required, flow medium may flow from the supply reservoir into the pressure chambers 10, 11.

The end of the second piston 9 facing the pressure chamber 11 terminates in an annular collar 86 which reaches behind the inner leg of a sleeve 87 having an essentially Z-shaped cross-section. The cylindrical portion of the sleeve 87 has a diameter slightly larger than the largest diameter of the second piston 9.

The cylindrical portion extends in the direction of the pressure chamber 11. At its end, an outwardly expanding annular collar 88 is provided which reaches behind the inwardly directed portion 89 of a valve disc 90 having a T-shaped cross-section and extending horizontally. The foot end of the T-shaped valve disc 90 projects into an axial annular groove 91 starting at a step 92 of the cover 8. This is to ensure the guidance of the valve disc 90. The annular portion 93 of the foot of the T-shaped valve disc is provided with respective seals 94 and 95. The seals 94, 95 are supported at the cross beam 96 of the valve disc 90 and are glued or vulcanised to the wall of the annular portion 93.A compression spring 97 resting against the housing 2 and at the valve disc 90 ensures that, upon the operation of the second piston 9, the operation of the valve disc 90, and hence of the valve arrange ment 98, will be exact and free from play.

Here, the step 92, together with the front ends of the seals 94 and 95, forms the sealing seat of the second valve arrangement 98.

The channel 99 communicating with the chamber 84 ends radially from the outside in the bottom of the axial annular groove 91. At the transition from the cover 8 towards the housing 2, seals 100, 101 each seal the channel 99 in respect of the atmosphere and in respect of the second pressure chamber 11. The ends of the channels 99 horizontally and vertically extending out of the housing 2 are pressure-sealed by means of a ball 102, 103.

The mode of operation of the tandem master cylinder in this embodiment will now be described in more detail.

In the release position shown of the tandem master cylinder 1, the first and sedond valves 43 and 49 as well as the valve arrangement 98 are open, a fluid communication existing from the chamber 29 to the first pressure chamber 10 and to the filling chamber 52 and from the chamber 84 to the second pressure chamber 11. Upon the initiation of a braking operation by the actuation of the stepped piston 6, the second piston 9 will be advanced by the compression spring 78 to the left in the drawing. In doing so, at first the first valve 43 or rather the expansion bore will be caused by the stepped piston 6 to adopt their closing positions and the second piston 9 will cause the valve arrangement 98 to adopt its closing position. Thus, there no longer exists any flow medium communication from the chamber 29 and from the chamber 84 to the first and second pressure chambers 10, 11.As in this phase of operation the stepped piston 6 and the second piston 9 are moved as a unit, the second valve 49 as well as the tappet 73 will remain in their initial or rather open positions.

Upon further operation, at first a small pressure will build up in the second pressure chamber 11. As a result thereof the second piston 9 now will be displaced more slowly than the stepped piston 6. Thereby it will be achieved that the tappet 73 as well as the valve piston 65 will move more slowly relative to the movement of the two pistons 6 and 9.

Thus the stepped piston 6 and the piston 51 of the control valve 48 will approach the valve piston 65 until the ball 56 comes to rest at the sealing seat 59 of the valve piston 65 in a pressure-sealed manner. The first pressure chamber 10 and the filling chamber 52 will be closed towards the chamber 31, and the filling operation will start.

Upon a further displacement of the stepped piston 6 to the left in the drawing, due to the filling stage piston 74, pressure medium will be supplied from the filling chamber 52 via the channel 71, the bore 53, beyond the gasket 67, into the first pressure chamber 10.

Thus there will be a fast application of the wheel brakes connected with the pressure chamber 10 and a very quick pressure buildup in the first brake circuit. The demand for volume resulting in the chamber 31 from the advancing movement of the stepped piston 6 will be supplied by the automatic feeding of the fluid from the chamber 29 via the first channel 28.

Upon a continued pressure build-up in the first pressure chamber 4 0, a pressure will also build up in the filling chamber 52. As soon as the pressure in the filling chamber 52 has reached a value corresponding to the force of the valve spring 62, the piston 51 will move to the right in the drawing. The valve piston 65, due to the stop 60, not being able to follow the movement of the piston 51, the control valve 48 will open and the pressure of the filling chamber 52 will decrease towards chamber 31. Upon a pressure drop below a certain value, now, due to the force of the valve spring 62, the piston 51 will be moved to the left and will again close the control valve 48. This operation will be repeated upon further operation of the stepped piston 6 until the required pressure has been established in the pressure chambers 10 and 11.

The filling chamber 52 will thus always remain below the limiting pressure of the control valve 48, the efficiency of the tandem master cylinder thus being slightly reduced.

However, the limiting pressure in the filling chamber 52 may be selected freely by the force of the valve spring 62.

If, after the completion of a braking operation the stepped piston 6 is moved back into its release position to the right in the drawing, the pistons 6 and 9 will again return into their initial positions. In doing so, the valve piston 65 will be retracted from the stop 60 while the piston 51 will move against the stop 60.

U.pon a further operation, now, there will be formed a slight partial vacuum in the filling chamber 52 which will act on the filling stage piston 74 so that the latter will lift off the ball 56, the control valve 48 opening and allowing flow medium to flow from the chamber 31 into the filling chamber 52. This operation will be repeated until the pistons 6 and 9 have regained their initial positions. Shortly before reaching the initial position, the first valve 43 and the valve arrangement 98 will be actuated so as to ensure that the pressure chambers 10 and 11 communicate with respectively the chambers 29 and 84 which are ih communication with the supply reservoirs.

Upon failure of a brake circuit, e.g. of the brake circuit connected with the first pressure chamber 10, the stepped piston 6 will operate the second piston 9 via the compression spring 78. As soon as there is a pressure build-up in the second pressure chamber 11, the second piston 9 will slow down its movement and the control valve 48 will be closed.

Upon a further operation of the stepped piston 6 a hydraulic pressure will build up in the filling chamber 52. As a result thereof, the control valve 48 will open against the force of the valve spring 62 and the pressure medium will be supplied from the filling chamber 52 into the defective first pressure chamber 10 which, upon failure, is always unpressurised.

This operation will be repeated until the stepped piston 6 abuts on the second piston 9. Upon a further operation of the tandem master cylinder 1, the stepped piston 6 will move the piston 9 further to the left, the pressure in the second pressure chamber 11 further increasing so that the brake circuit connected with the second pressure chamber 11 will effect an admittedly reduced, yet sufficient, slowing-down of a vehicle.

Upon failure of the brake circuit connected with the second pressure chamber 11, the two pistons 6 and 9 will move evenly to the left, maintaining the same distance relative to each other. The control valve 48 will not close until the second piston 9 rests on the bottom of the cover 8. At first, pressure medium will be supplied from the filling chamber 52 via the channel 71, the bore 53, beyond the gasket 67, into the first pressure chamber 10.

After the application of the wheel brakes connected with the first pressure chamber 10, the pressure in the pressure chamber 10 will also increase which will also lead to an increase in the pressure in the filling chamber 52. After the exceeding of a certain filling chamber pressure the control valve 48 will be opened against the force of the valve spring 62, the pressure medium of the filling chamber 52 flowing into the unpressurised chamber 31.

The filling operation will be completed. Upon a further operation of the tandem master cylinder 1 the wheel brakes connected with the first pressure chamber 10 will be pressurised and there will be a reduced slowing-down of the vehicle as but one pressure chamber 10 is operative.

Upon failure of the filling chamber 52 there will admittedly be an increase in the lost travel of the stepped piston 6 by the amount of the reduced filling volume, but the entire brake system will, however, remain intact.

Claims

1. A master cylinder with a variable transmission ratio, in particular for the brake system of an automotive vehicle, of the kind which has a stepped bore provided in a housing for the reception of a stepped piston whose one piston diameter confines a pressure chamber and whose other piston diameter confines a filling chamber, the filling chamber and the pressure chamber communicating in the stepped piston's release position with a supply reservoir via channels which may be closed by valves upon the operation of the stepped piston, the supply reservoir communicating with the filling chamber and the pressure chamber via a first non-return valve, and the filling chamber communicating with the pressure chamber via a second nonreturn valve which opens towards the pressure chamber; and which has a control valve which upon actuation by the stepped piston may be closed by closure elements due to the force of a spring and may be opened by the hydraulic pressure against the force of a spring in order to establish communication between the supply reservoir and the filling chamber, characterised in that the larger piston diameter (25) confines the pressure stage and the smaller piston diameter (74) confines the filling stage.

2. A master cylinder as claimed in claim 1, characterised in that the control valve (48) divides the stepped piston (6) into a filling stage piston (74) and into a pressure stage piston (25) and in that a closure element (65) of the control valve (48) at the same time forms the filling stage piston (74).

3. A master cylinder as claimed in claim 1 or 2, characterised in that the closure elements of the control valve consist of a closure member (51) and of a valve piston (65), the valve piston (65) at the same time forming the filling stage piston (74), the closure elements of the control valve being guided within a central bore (45 and 66) of the pressure stage piston (25), and the movement of the closure elements being limited in the closing direction by a stop (60) provided at the pressure stage piston (25).

4. A master cylinder as claimed in any one of the preceding claims, characterised in that the valve piston (65) penetrates the pressure chamber (10), in that at the bottom of the housing (2) a pocket bore (76) is formed which, together with the end of the valve piston (65), forms the filling chamber (52), and in that the valve piston (65) is penetrated by a channel (71).

5. A master cylinder as claimed in claim 4, characterised in that on the surface area, at the opposite end of the filling chamber (52), on the valve piston (65) two seals (63 and 67) are fastened which are arranged at a small distance relative to each other and which are in sliding engagement with the central bore (66), in that between the two seals (63 and 67) a bore (53) extends from the channel (71) to the surface area of the valve piston (65), the diameter of the surface area of the valve piston (65) being slightly less than the diameter of the central bore (66), and the seal (67) at the valve piston (65) which is closer to the filling chamber (52) forming the second non-return valve which has the shape of a gasket (67).

6. A master cylinder as claimed in any one of the preceding claims, characterised in that the central bore (66) is bipartite and is formed by the pressure stage piston (25), on the one side, and by a sleeve (46), on the other side, which sleeve (46) is connected with the pressure stage piston (25) in a pressure-sealed manner.

7. A master cylinder as claimed in any one of the preceding claims, characterised in that, radially outside the sealing seat (59) at the closure member (51), axially extending passages (58) are provided and the sealing seat (59) at the closure member (51) is formed by a ball (56) fastened at the closure member (51).

8. A master cylinder as claimed in any one of the preceding claims, characterised in that the first non-return valve is a gasket (26) fastened at the pressure stage piston (25), the gasket (26) being bordered by the chamber (31) communicating with the supply reservoir, on the one side, and by the pressure chamber (10), on the other side.

9. A master cylinder as claimed in any one of the preceding claims, characterised in that at the entrance of the filling chamber (52) a stop (77) is formed in the pocket bore (76), this stop limiting the direction of movement of the filling stage piston (74) out of the filling chamber (52).

10. A master cylinder as claimed in any one of the preceding claims, characterised in that the section of the stepped bore (3) of smaller diameter (76) is provided within a second piston (9) which is guided within a bore (13) in the housing (2), the bore (13) following the stepped bore (3) of larger diameter (12), and forming a second pressure chamber (11).

11. A master cylinder substantially as described with reference to the accompanying drawing.