GB2160277A

GB2160277A - A motor vehicle hydraulic servo brake system

Info

Publication number: GB2160277A
Application number: GB08514141A
Authority: GB
Inventors: Hans-Dieter Reinartz; Helmut Steffes
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1984-06-14
Filing date: 1985-06-05
Publication date: 1985-12-18
Also published as: FR2565919B1; GB8514141D0; DE3422157A1; FR2565919A1; GB2160277B

Abstract

A motor vehicle hydraulic servo brake system comprises a brake pedal operated tandem master cylinder (11) with two outputs (12, 13) each connected to a respective front wheel brake cylinder (14, 15). A pump (18) supplies pressure to a brake force booster (16). A brake valve (19) controlled by brake pedal (20) controls the pressure supply to the first master cylinder piston and to the brake cylinders (21, 22) of the two rear wheels. Connected into the hydraulic brake conduit (23, 24) leading to each of the two rear wheel brake cylinders (21, 22) is a respective closure-valve (25) which via a hydraulic control conduit (26, 27) is connected to the master cylinder output (13 and 12, respectively) leading to the diagonally opposite front wheel brake cylinder (15 and 14, respectively). The closure valve (25), when the associated front wheel brake circuit is intact, is open and in the event of a pressure decrease in the associated front wheel brake circuit closes and preferably drains the line to the brake to a reservoir (17). <IMAGE>

Description

SPECIFICATION A motor vehicle hydraulic servo brake The present invention relates to a hydraulic servo brake for motor vehicles, comprising a brake pedal operated tandem master cylinder connected to each of the two outputs of which is a respective one of two front wheel brake cylinders, and comprising a brake force booster energised by a pump taking hydraulic pressure medium from a supply reservoir, and including a brake valve so controlled by the brake pedal that a controlled pressure generated by the pump is directly applied to a first master piston in the master cylinder, on the one hand, and to two wheel brake cylinders of the rear wheels, on the other hand.

In motor vehicle hydraulic servo brakes of the afore-described type it is of interest, for safety reasons, to eliminate in the event of a failure of a front wheel brake circuit, a braking operation through the rear wheel brake cylinder disposed in diagonal relationship thereto, in order to maintain a relative brake balance of the vehicle to thereby avoid slewing of the motor vehicle. Hence, in such a triple-circuit brake system it is of importance that the rear wheel brake cylinder disposed in diagonal relationship to a front wheel brake cylinder, be safely switched off in the event of a failure, e.g. due to leakage, of the brake circuit of the front wheel brake cylinder in question.

Conventionally (German Specification DE OS 31 50 218), a two-way valve has already been provided for this purpose; however, this has involved difficulties in connection with the pressure relief of the wheel cylinder.

It is, therefore, an object of the present invention, to provide a motor vehicle hydraulic servo brake of the afore-mentioned type in which, in the event of a failure of one of the two front wheel brake circuits, the associated diagonal rear wheel brake cylinder is safely switched off, with no problems being involved with the pressure relief of the wheel cylinder.

The operation of the motor vehicle servo brake is to be safe with an optimum separation between the dynamic brake circuit to which controlled pressure is applied, and the two static brake circuits to which pressure from the master cylinder is applied, being attained.

According to the present invention there is provided a motor vehicle hydraulic servo brake comprising a brake pedal operated tandem master cylinder connected to each of the two outputs of which is a respective one of two front wheel brake cylinders, and comprising a brake force booster energised by a pump taking hydraulic pressure medium from a supply reservoir and including a brake valve so controlled by the brake pedal that a controlled pressure generated by the pump is directly applied to a first master piston in the master cylinder on the one hand, and to two wheel brake cylinders of the rear wheels, on the other hand, characterised in that connected into two hydraulic brake conduits each of which lead to a respective one of the two rear brake cylinders is a respective way-valve comprising more than two ways and at least two positions, which valve, via a hydraulic control conduit is connected to the output of the master cylinder leading to the front wheel brake cylinder disposed respectively in diagonal relationship thereto and, with the associated front wheel brake circuit intact, is opened and, in the event of a pressure decrease in the associated front wheel brake circuit, is closed.

In accordance with the invention, therefore, a valve to which the brake pressure of the front wheel brake circuit disposed in diagonal relationship thereto, is connected into the brake conduit leading to each rear wheel brake cylinder. The valve, normally, is in the open position so as to safeguard an unimpeded application of pressure medium to the rear wheel brake cylinder. Only in the event of a pressure decrease in the associated diagonal front wheel brake circuit, e.g. due to leakage, will the way-valve close and prevent a further braking operation on the associated rear wheel brake cylinder.

According to a preferred embodiment, the way-valve comprises a sleeve valve preloaded by the pressure in the control conduit into one of its end positions, and a first valve in cooperation therewith and open in the respective end position of the sleeve valve, which first valve is connected between an input and an output for the controlled pressure. The path of displacement of the sleeve valve, feasibly, is such that volume is generated thereby in the branch leading to the rear wheel brake cylinder is such that the pressure medium contained in the rear wheel brake cylinder concerned can expand thus eliminating the brake force.

An advantageous structural form of embodiment is characterised in that the first valve is provided at the end face of the sleeve valve facing away from a control input thereby achieving a particularly compact and spacesaving construction.

Another form of embodiment is configured such that the first valve comprises a valve ball supported at the said end face end of the sleeve valve via a thin push rod, with the valve ball being disposed in a chamber in communication with the controlled pressure, and that a valve seat is disposed on the side of the valve ball facing away from the said chamber. This form of embodiment, equally, will safeguard a space-saving and nevertheless safe construction.

In the latter described form of embodiment, feasibly, the valve ball by a first spring, is slightly preloaded in the direction toward the valve seat.

In order that the sleeve valve, at the beginning of a braking operation, will occupy from the very-start the position required for applying pressure to the rear wheel brake cylinders, the sleeve valve, according to another form of embodiment, is slightly preloaded in the valve opening direction so that the sleeve valve, with the brake pedal non-applied, will occupy the valve opening position.

The rear wheel brake cylinder can be switched off with a particularly high degree of reliability if the way-valve includes a third position and a fourth way in which the associated rear wheel brake cylinder is connected to the supply reservoir and which it will occupy after the connection between the master cylinder and the associated rear wheel brake cylinder have been discontinued. Hence, in a first phase of the valve movement, the connection between the controlled pressure and the associated rear wheel brake cylinder will be discontinued and, subsequently, a connection between the rear wheel brake cylinder concerned and the supply reservoir will be opened so that the pressure medium can expand to eliminate the brake effect.

To realise the third position and the fourth way, a return valve, according to a preferred structural form of embodiment, is disposed at the sleeve valve next to or behind the first valve, which return valve will open after closing of the first valve and connect the output to a return output leading to the supply reservoir.

The construction can be such that the return valve has a respective valve ball normally forced by a respective push rod secured to the sleeve valve against an associated valve seat facing away from the sleeve valve.

An alternative form of embodiment is so configured that the return valve comprises a respective valve ball forced against an associated valve seat by a respective spring, said valve ball facing away from the control input and being disposed in a cavity of the sleeve valve, and removable from the associated valve seat by a respective push rod rigidly connected to the housing and from the control input side of protruding through an axial bore of the sleeve valve if the sleeve valve, after closure of the first valve, continues to move toward the control input.

Moreover, a complete de-braking operation of a rear wheel brake cylinder, in the event of a failure of the front wheel brake circuit in diagonal relationship thereto, can also be attained in that the way-valve includes a third position and a fourth way, in which the associated rear wheel brake cylinder is connected to a check valve, and which position it will occupy after the connection between the master cylinder and the associated rear wheel brake cylinder has been discontinued whereupon the check valve will open to balance the pressure between the rear wheel brake cylinder and the associated front wheel brake cylinder. Hence, here the rear wheel brake cylinder is not relieved toward the intake reservoir but rather to the defective front wheel brake circuit.The valves not only shut down but rather adjust the pressure on the rear wheel to that of the front wheel disposed in diagonal relationship thereto. While the check valve may be located externally of the way-valve as a separate component it is nevertheless preferred that the same be integrated into the way-valve.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure I shows a block diagram of a motor vehicle servo brake of the invention, comprising three brake circuits, Figure 2 shows an axial section through a first embodiment of way-valve of the invention, Figure 3 shows an axial section through a second embodiment of way-valve of the invention, Figure 4 shows an axial section through a third embodiment of way-valve of the invention, and Figure 5 shows an axial section through a fourth embodiment of way-valve of the invention.

According to Fig. 1, the brake pedal 20 of a motor vehicle, via a rod linkage 48, acts upon a brake valve 1 9 disposed in a brake force booster 1 6 and upon the primary master piston (not shown) of a tandem master cylinder 11 assembled with the brake force booster 1 6. The brake force booster 1 6 is energised by a pump 18 connected to a supply reservoir 1 7 and, in the usual manner, can also be connected in parallel to an accumulator (not shown).

Connected to the primary output 1 3 of the tandem master cylinder 11 is a brake circuit II acting upon the lefthand front wheel brake cylinder 15, while, connected to the secondary output 1 2 is a brake circuit I leading to the righthand front wheel brake cylinder 14.

Brake valve 1 9, for applying pressure to the primary master piston contained in the tan- dem master cylinder 11, will supply a controlled pressure GD derived from pump 18, which is also available at output 49 and guided, via a brake conduit 50, to the rear wheel brake circuit Ill.

Two brake conduits 23 and 24, respectively, branch from the rear wheel brake conduit 50 to lead to the rear wheel brake cylinders 21,22. In the practice of the present invention, way-valves 25 are connected to such brake conduits 23,24 which valves, respectively, comprise an input 30 for the controlled pressure GD, and an output 31 for passing on the controlled pressure to the rear wheel brake cylinders 21,22 with the wayvalves 25 opened.

Moreover, a control input 32 is provided on each way-valve 25, which, via hydraulic control conduits 26 and 27, respectively shown in dash-dotted lines, is connected to the brake conduit of the front wheel brake circuits II and I, respectively in diagonal relationship thereto, so that the brake pressure of the front wheel brake circuit in diagonal relationship to the way-valve 25 in question will be available on the control inputs 32.

If the brake system is furnished with a wheel slip brake control device (not shown), closure valves SO are connected into the feedin lines leading to the wheel brake cylinders 14,15,21 and 22, respectively, which closure valves SO, normally, are open and will be closed upon occurrence of a wheel slip, by the wheel slip brake control device. Moreover, opening valves SG will lead from the wheel brake cylinders 14,15,21,22, to the supply reservoir 1 7 in order to safeguard in the event of a wheel slip brake control a pressure medium discharge from the wheel brake cylinders 14,15,21,22.

It is essential that the way-valves 25 be connected into the brake conduits 23,24 in front of the wheel slip brake control closure valves SO.

The internal structure of a way-valve 25 so far described herein will now be explained with reference to Fig. 2; in that form of embodiment, the way-valve 25 comprises three ways (ports) and two positions, with not only the two end positions but depending on the pressures prevailing in the wheel brake cylinders of the front wheels in the event of a failure--also any intermediate position being suitably occupied for the pressure relief.

Provided within the way-valve 25, formed in a block, is a cylindrical bore 51 in which is accommodated, in axially slidable manner, a sleeve valve 28. Sealing cups 52 which seal pressure chambers 53 and 54, respectively, against one another, are provided at the opposite ends of the sleeve valve 28. An annular gap 55 between the two sealing cups 52, via a bore 56, is in communication with the atmosphere.

The sleeve valve 28, by a helical compression spring 38 supported on the bottom of the cylindrical bore 51, in Fig. 2, is preloaded to the left, in which it is in abutment with a closure stopper 57 containing a valve 29, for the cylindrical bore 51. Provided internally of the closure stopper 57 is a chamber 35 open to the sleeve valve 28, with a radial bore 58 branching off therefrom and leading to the input 30 of the way-valve 25.

Moreover, a helical coil compression spring 37 is accommodated in chamber 35 and urges a valve ball 33 towards the sleeve valve 28. A thin push rod 34 extending from the ball 33 to the sleeve valve 28 will keep the ball 33 in the normal position of Fig. 2, that is removed from its valve seat 36. Valve seat 36 is provided between ball 33 and the lefthand front side of the sleeve valve 28.

Annular recesses 28' at the end of the sleeve valve 28 which, in Fig. 2 is the lefthand end, will form there the pressure chamber 54 neighbouring the laterally provided output 31 of the way-valve 25.

Pressure chamber 53 provided at the opposite side of the sleeve valve 28 is connected to the control input 32 provided on the wayvalve 25.

The way of operation of the way-valve 25 according to Figs. 1 and 2 is as follows: Due to the function of the helical coil compression spring 38, the way-valve 25, normally, is in the open position as shown in Fig.

2 wherein the input 30, via the opened valve 29, is connected to the output 31. If a braking operation is performed in that the brake pedal 20 is pushed down, brake pressure, with intact brake circuits, will be simultaneously built up in all three brake circuits 1, II and Ill. Hence, substantially the same pressure will develop in the pressure chambers 53,54 of the way-valve 25 of Fig. 2, and the sleeve valve 28 will maintain the position as shown in Fig. 2. Minor usual pressure differences between the pressure chambers 53,54 can be allowed for by correspondingly dimensioning the helical coil compression springs 37,38 in a manner that the sleeve valve 28, with intact brake circuits, in any case will occupy the open position as shown in Fig. 2.

Let it now be assumed that leakage will occur in the lefthand front wheel brake circuit II causing the brake pressure originally prevailing therein, to disappear resulting in a pressure decrease in the pressure chamber 53 of the way-valve 25 so that the controlled pressure GD still effective from the opposite side over input 30, will displace the sleeve valve 28 in Fig. 2 to the right until the valve ball 33, under the action of spring 37, is closely seated on its valve seat 36 to close valve 29. Now, pressure medium can no longer flow to the associated rear wheel cylinder 21.

The path of displacement of the sleeve valve 28 will be so selected that during displacement to the right (in Fig. 2) so much volume will be generated on the pressure chamber 54 that the pressure medium in the rear wheel brake cylinder 21 will be expanded to a degree sufficient for de-braking. In other words, the pressure in the rear wheel brake cylinder 21 will displace the sleeve valve 28 upon closure of the valve 29 to the right until a relief and a de-braking will occur.

In the following examples of embodiment, identical reference numerals will designate corresponding parts referred to in Figs. 1 and 2. According to Fig. 3, in addition to the first valve 29, a return valve 39 is provided connecting the pressure chamber 54 to a return output 40 also illustrated in Fig. 1, which return output 40, via a conduit 59, shown in dashed lines in Fig. 1, leads to the supply reservoir. Valve 39 also comprises a valve ball 41 co-operating with a valve seat 42 provided on the side of ball 41 facing away from the sleeve valve 28. The valve ball 41, via a push rod 43, is connected to the sleeve valve 28.

The way of operation, here, in the first phase of a failure of a front wheel brake circuit I or II, corresponds to that of the embodiment of Fig. 2. However, upon closure of the first valve 29, sleeve valve 28, by removing the push rod 34 from the valve ball 33, can still move a distance toward the pressure chamber 53, whereby a stop 60 will engage at push rod 43 a corresponding counter-stop 61 of the sleeve valve 28 thereby removing, when further moving the sleeve valve 28 to the right (in Fig. 3), the valve ball 41 normally forced by spring 62 against its valve seat 42, from the said valve seat 42.

Now, a flow connection has been established between the pressure chamber 54 via a chamber 63 surrounding the push rod 43 and the ball 41 and also accommodating the helical coil compression spring 62, and via a hydraulic conduit 64 following the valve seat 42, and the return output 40 connected to the supply reservoir 1 7. The pressure medium contained in the rear wheel brake cylinder 21 or 22 in diagonal relationship to the defective brake circuit, hence, can expand into the supply reservoir 17.

The form of embodiment of Fig. 4 is distinguished from the one of Fig. 3 only in that the two valves 29,39 are no longer arranged in side-by-side relationship but rather in axial series relationship, with the return valve 39 being accommodated in an axial cavity 44 in the interior of the sleeve valve 28. A spring 45 accommodated in the said cavity 44 will force the valve ball 41 toward the pressure chamber 53 against its valve seat 42 provided therein.

A push rod 43 extends from the bottom of the way-valve 25 through an axial bore 47 of the sleeve valve 28 to a bore provided at the seat 42 of the valve ball 41.

The function is the same as the embodiment of Fig. 3, i.e. in the event of a pressure failure in the pressure chamber 53, first, the valve 29 will close and, subsequently, the return valve 39 will open due to the fact that push rod 43 of the valve will strike valve ball 41 thereby establishing a flow connection from the output 31 via the cavity 44 past the valve ball 41 through a radial bore 65 in the sleeve valve 28 to the return output 40.

According to Fig. 1, the return output 40, instead of being connected to the supply reservoir 17, via a check valve 46, can be connected to the associated hydraulic control conduit 26 and 27, respectively as shown in Fig. 1 by a dotted conduit 59'. In that case, during opening of the return valve 39, the pressure still contained in the associated rear wheel brake cylinder 21 or 22, is relieved, via check valve 46, toward the associated defective front wheel brake circuits II and I, respectively. The check valve 46, hence, will have to be so connected that, in the event of an excessive-pressure on the associated rear wheel brake cylinder 21 or 22, with the return valve 39 opened, it will open automatically.

Fig. 5 shows an embodiment analogous to that of Fig. 2 in which, however, the check valve 46 is integrated into the way-valve 25.

For this, a lateral bore 66 branches off from the axial bore 51 containing the sleeve valve 28, closely behind the pressure chamber 54, which bore will lead to the check valve 46 adjacent the control input 32.

The sleeve valve 28, in that form of embodiment, in addition, will perform the function of the return valve 39 according to the forms of embodiment of Figs. 3 and 4 in which, after closing of the first valve 29, it is displaceable to the right (Fig. 5) to such an extent that, virtually, the pressure chamber 54 will communicate with the lateral bore 66 whereupon the pressure of the associated rear wheel brake cylinder 21 or 22 as developed on output 31, via check valve 46, can relieve via the control connection 32 toward the diagonal front wheel brake circuits II and 1, respectively.

Due to the preloading of the sleeve valve 28 by helical spring 38, during the pressure relief from a rear wheel brake cylinder, the pressure prevailing there is always slightly in excess of the pressure in the associated diagonal front wheel brake circuit.

In the example of embodiment of Fig. 4 it will be essential for the two valves 29,39 to be mounted on one axis and for the return valve 39 to be accommodated completely in the interior of the sleeve valve 28 so that the accommodation thereof does not require any additional space.

All the way-valves described have in common that the controlled pressure supplied to the rear wheel brake cylinders 21 and 22, respectively, cannot be in excess of the static pressure on the outputs 1 2,1 3 of the tandem master cylinder, unless the helical coil compression spring 38 be of a correspondingly weak dimension. The way-valves 25, hence in addition to their safety function, will perform the function of a pressure reducing valve for the controlled pressure for adaptation to the static pressure of the front wheel brake cylinders 14,15. Hence, on account of the use of the way-valves of the invention, it will no longer be necessary to specifically adjust the brake force booster 1 6 relative to the dynamically controlled pressure.

Claims

1. A motor vehicle hydraulic servo brake comprising a brake pedal operated tandem master cylinder connected to each of the two outputs of which is a respective one of two front wheel brake cylinders, and comprising a brake force booster energised by a pump taking hydraulic pressure medium from a supply reservoir and including a brake valve so controlled by the brake pedal that a controlled pressure generated by the pump is directly applied to a first master piston in the master cylinder on the one hand, and to two wheel brake cylinders of the rear wheels, on the other hand, characterised in that connected into two hydraulic brake conduits (23,24) each of which lead to a respective one of the two rear brake cylinders (21,22) is a respective way-valve (25) comprising more than two ways and at least two positions which valve, via a hydraulic control conduit (26 and 27, respectively) is connected to the output (13 and 12, respectively) of the master cylinder (11) leading to the front wheel brake cylinder (15 and 14, respectively) disposed respectively in diagonal relationship thereto and, with the associated front wheel brake circuit (II and I, respectively) intact, is opened and, in the event of a pressure decrease in the associated front wheel brake circuit (II and I, respectively), is closed.

2. A motor vehicle brake according to claim 1, characterised in that at least one said way-valve (25) comprises a sleeve valve (28) preloaded by the pressure in the control conduit (26,27) into one of its end positions, and a first valve (29) co-operating with the sleeve valve (28) and opened in the respective end position of the sleeve valve (28), with the first valve (29) being connected between an input (30) and an output (31) for the controlled pressure.

3. A motor vehicle brake according to claim 2, characterised in that the first valve (29) is provided on the end face of the sleeve valve (28) facing away from a control input (32).

4. A motor vehicle brake according to claim 3, characterised in that the first valve (29) comprises a valve ball (33) supported at the said end face end of the sleeve valve (28) via a thin push rod (34), which valve ball (33) is disposed in a chamber (35) in communication with the controlled pressure, and that a valve seat (36) is located on the side of the valve ball (33) facing away from the chamber (35).

5. A motor vehicle brake according to claim 4, characterised in that the valve ball (33), by a first spring (37), is slightly preloaded toward the valve seat (36).

6. A motor vehicle brake according to any one of claims 2 to 5, characterised in that the sleeve valve (28), by a second spring (38), is slightly preloaded in the valve opening direction such that the sleeve valve (28) will occupy the valve opening position when the brake pedal (20) is not applied.

7. A motor vehicle brake according to any one of the preceding claims, characterised in that the at least one said way-valve (25) includes a third position and a fourth way in which the associated rear brake cylinder (21 and 22, respectively) is connected to the supply reservoir (17) and which it occupies after the connection between the master cylinder (11) and the associated rear wheel brake cylinder (21 and 22, respectively) have been discontinued.

8. A motor vehicle bake according to claim 7 as appendant to any one of claims 2 to 6, characterised in that a return valve (39) is provided at the sleeve valve (28) next to or behind the first valve (29), which return valve (39) will open after closing of the said first valve (29) and connect the output (31) to a return output (40) leading to the supply reservoir (17).

9. A motor vehicle brake according to claim 8, characterised in that the return valve (39) includes a respective valve ball (41) which, by a respective push rod (43) secured to the sleeve valve (28), normally, is forced against an associated valve seat (42) facing away from the sleeve valve (28).

10. A motor vehicle brake according to claim 8 as appendant to claim 3, characterised in that the return valve (39) comprises a respective valve ball (41), facing away from the control input (32) and located in a respective cavity (44) of the sleeve valve (28), which, by a respective spring (45) is forced against an associated valve seat (42) and, by a respective push rod (43) rigidly attached to a way-valve housing and protruding from the control input (32) side into an axial bore (47) of the sleeve valve (28), is removable from the respective valve seat (42) if the sleeve valve (28) upon closure of the first valve (29) continues to move toward the control input (32).

11. A motor vehicle brake according to any one of claims 1 to 6, characterised in that the way-valve (25) includes a third position and a fourth way in which the associated rear wheel brake cylinder (21 and 22, respectively) is connected to a check valve (46) and which it will occupy after the connection between the master cylinder (11) and the associated rear wheel brake cylinder (21 and 22, respectively) has been discontinued whereupon the check valve (46) will open for balancing the pressure between the rear wheel brake cylinder (21,22) and the associated front wheel brake cylinder (15 and 14, respectively).

12. A motor vehicle brake according to claim 11, characterised in that the check valve (46) is integrated into the way-valve (25).

1 3. A motor vehicle hydraulic servo brake substantially as herein described with reference to and as illustrated in Fig. 1 with reference to any one of Figs. 2 to 5 of the accompanying drawings.