GB2226859A - Anti-skid braking system - Google Patents

Abstract

The system comprises a brake skid control circuit 15 and a vacuum brake force booster 14 disposed between the brake pedal 12 and a hydraulic master cylinder 53, wherein a pneumatic short-circuiting valve 18 arranged in the booster piston wall 11 opens in response to output signals from a control circuit on detection of brake-skid to equalise pressure in the booster chambers thus reducing the braking force, quick-closing valves 50 being provided in the feed-in lines to the pressure chamber and vacuum chamber. The quick<losing valves 50 each have a cup-shaped piston 35 with its open end facing the higher pressure and with a ring seal 43 at its closed end cooperable with an annular seat 42 surrounding an outlet 40. The piston 35 and/or a spring retainer ring 75 are made of magnetic material and the valve is controlled by an electromagnet 44. <IMAGE>

Description

1 r is BPAYING-SKID-CONTROLLED BRAKE SYSTEM This invention relates to a

brake system, for automotive vehicles, comprising a braking skid control and a vacuum brake force booster disposed between a brake pedal and an hydraulic master cylinder, wherein a auickacting pneumatic short-circuiting valve arranged to be actuated in response to outputsignals from a control circuit of the braking skid control, is provided in a piston wall of the brake force booster to cause, during a braking operation and upon occurrence of a braking skid, a pressure compensation between a pressure and a vacuum chamber reducing the braking skid.

A brake system for automotive vehicles of the aforedescribed type, comprising a short-circuiting valve provided in the piston wall of the vacuum brake force booster is known in the art (West German DE-OS 3428869). A special problem involved with short-circuiting valves of this type resides in that they fail to expose adeauately large flow crosssections and that the operation thereof requires substantial forces in particular in cases where they have to work against the pressure in the pressure chamber.

Before the short-circuiting valve, in the event of a braking skid control, is opened temporarily or in pulse- 2 is.

type manner, the atmospheric pressure and the vacuum are to be separated, by means of quick-closing valves, from the pressure chamber and the vacuum chamber of the vacuum brake force booster, respectively. It is, therefore, an object of the invention to provide a quick-acting valve closing which is particularly fast with the aid of the existing pressure forces.

The present invention therefore provides a brake system for automotive vehicles, comprising a brake skid control and a vacuum-brake force booster disposed between the brake pedal and a hydraulic master cylinder, wherein a fast-switching pneumatic short-circuiting valve arranged to be actuated in resDonse to output signals from a control circuit of the brake skid control is provided in the piston wall of the brake force booster, which short-circuiting valve, during applying the brake pedal, upon occurrence of a braking skid between pressure and vacuum chambers, causes a pressure equilibrium reducina the braking skid, with quick- acting valves being additionally provided in the feed-in lines of the atmospheric pressure and/or the vacuum to the pressure chamber and vacuum chamber, respectively.

In order to permit utilisation of the pressure difference prevailing on the fast-acting valve for quickly closing the fast-actina valve it is provided, in accordance with the present invention that the quickclosing valves comprise a cup-shaped piston the open side of which faces the higher pressure, is axially ( 1 1 3 is displaceable in a cylinder, that the cup-shaped piston, in the area of a bottom wall thereof, comprises circumferential passage ports terminating in an annular space provided between the cylinder and the cup-shaped piston, that an outlet opening is provided at a distance ahead of the bottom wall of the cup-shaped piston in the front wall of the cylinder and is surrounded by an annular sealing surface co-operating with an annular seal on the bottorr wall of the cup-shaped piston, and that a closing electromagnet is provided in the cylinder to act upon the cup- shaped piston.

The nresent invention will be better understood from the following description when read in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic block diacram of a brake system for automotive vehicles, comprising an hydraulic master cylinder and a vacuum brake force booster; Figure 2 shows, on an enlarged scale, a sectional view of one forir of short-circuiting valve which may be used in the system of Figure 1; Figure 3 shows an alternative form of short- circuitina valve which may be used in the systeir of Figure 1; Figure A shows a partial axial sectional view of a ouick-closina valve incorPorated in accordance with the invention in the brake systern of automotive vehicles according to Figure 1; and, Figure 5 shows a hydraulic switching systein of the 4 is quick-closing valve according to Figure 4, wherein the flow through the quick-closing valve is always from the side of the cup-shaped piston.

According to Figure 1, pressure is applied by a brake pedal 12 of an automotive vehicle through a standard vacuum valve 45 to a vacuum brake force booster control device 141 provided with a mechanical travelsimulator 46 and including a movable piston wall 111 separating a pressure chamber 161 from the vacuum chamber 1V. The mechanical simulator 46 comprises a spring which simulates the provision of a master cylinder by contracting the pedal actuation force applied to the brake pedal 12 when the pedal is depressed and the spring is compressed. In this way the travel simulator 46 provides a pedal travel/force characteristic similar to that which would be provided if the booster 141 were coupled to a master cylinder. The vacuum chamber 171, through a conduit 47, is in communication with an intermediate vacuuir tank 48 kelpt at a predetermined vacuum through a vacuum source 49. The vacuum source 49, feasibly, is the intake-tube of the internal combustion enaine of the automotive vehicle.

The pressure chamber 16', throuch the standard vacuum valve 45, in known manner, can be placed in communication with atmospheric pressure thereby displacing the piston wall ll' by the extent to which the brake pedal 12 is pressed down.

The pressure chamber 161 and the vacuum chamber 1V, 1 through respective quick-closing valves 50. are in communication with the pressure chamber 16 and the vacuum chamber 17 of a vacuum brake force booster 14 of larger diameter. The quick-closing valves 50 are actuated by closing electromagnets 44 which are connected to a control circuit 15 generating closing signals for the quick-closina valves 50 in the event that a braking slip control should be reauired.

Moreover, the electromagnet 21 of a short-circuiting valve 18 is applied to the control circuit 15 provided for the braking skid control, which short-circuiting valve 18 can establish a communication between the pressure chamber 16 and the vacuum chamber 17 of the vacuurp brake force booster 14. The short-circuiting valve 18 is - as individually disclosed in Figures 2 and 3 - in fact, located within the piston wall 11.

Figure 1 shows the position of the valves 50 and 18, respectively, in the event that no braking skid control takes place. Once the brake pedal 12 is pressed down, the pressure within the pressure chamber 16 and 161, respectively, increases and the piston walls 11 and 111 in Figure 1 move to the right, with the central plunger 51 of the piston wall 11 applying pressure to-the pistons 52 of a tandeir master cylinder 53 to develop the required hydraulic pressure in the hydraulic conduits 54,55 leadina to the brake conduits.

If, during a braking operation, a braking skid signal is provided to the control circuit 15 by a braking 6 skid sensors 551, which is generated upon commencement of a locking of one of the wheels, the control circuit 15, throuch the closing electromagnets 44, causes a quick closure of the fast-acting valves 50 and an opening of the short-circuiting valve 18. The opening of the shortcircuiting valve 18 is in a pulse-type manner, with a more or less substantial pressure equalisation occurring between the pressure chamber 16 and the vacuum chamber 17 until the braking skid on the wheel concerned is removed, whereafter the short-circuitina valve 18 will re- close and the quick-acting valves 50 re-open.

According to Figure 2, the short-circuiting valve 18 comprises a rotationally-symmetrical valve body 24 having a centre axis 83 standing upright on (perpendicular to) the piston wall 11. The valve body 24 is tightly secured in a circular opening 25 of the piston wall 11. In the area projecting into the pressure chamber 16, the valve body 24 comprises a large-area, circular connecting port 19 upon which is sealingly mounted froin. the pressure chamber 16 side a valve disc 20 radially extending across the connecting port 19, with the rim of the connecting port 19 forming a valve seat 84.

The valve disc 20, with a cylindrical projection 13 projecting away froir the pressure chamber 16, is slidably seated on a cylindrical guide surface 56 of the valve body 24. Provided circumferentially of the projection 13 is a broad flow passageway disposed circumferentially of the connecting channels 31 terminatina beyond the piston 7 wall 11 in the vacuum chamber 17.

Concentrically secured on the side of the valve body 24 facing the vacuum chamber 17 is an electromagnet 21 in the interior of which is located a sleeve-type magnetic armature 29 which is firmly disposed on the actuating plunger 22 of the valve disc 20.

The actuating plunger 22 is rigidly and centrally connected to the valve disc 20 and extends through a central port 57 of the valve body 24 and a central iport 58 of the electromagnet 21 and into the latter where the sleeve-type magnetic armature 29 is mounted thereon.

The actuating plunger 22 on the side facing away froir the pressure chamber 16, markedly, projects beyond the electromagnet 21 and the armature 29 to carry a conpensating piston 23. A restorina spring 34 extends between the electromaonet 21 and the compensating piston 23.

The actuating plunger 22 comprises a continuous central bore 26 interconnectina the pressure chamber 16 and a conpensating chamber 27 provided behind the compensating piston 23, which compensating chairber 27 is sealed by a solid wall 28. The compensating piston 23 is tightly secured by a radially outwardly gui0ed annular membrane 30 in relation to the circuTrference of the solid wall 28. The annular membrane permits the required axial movement of the coirpensating piston 23.

1 8 Circumferentially of the solid wall 28, a cap 59 including passage ports 60 toward-the vacuum chamber 17, extends to the circumference of the electromagnet 21 and is suitably attached thereto. The solid wall 22, hence, forms an integral component with the valve body 24.

The diameter of the compensating piston 23, the effective pressure surface of the annular membrane 30 included, corresponds to the diameter of the valve port 19.

Figure 2 shows the rest position of the short circuitina valve 18. Once the electromagnet 21 is energised, the armature 29 slightly projecting in the rest position toward the vacuum chamber 17 from the electromaanet 21, is drawn into the electromagnet 21 thereby moving the actuating plunger 22 in Figure 2 to the left and removing the valve disc 20 from the valve seat circumferentially of the valve port 19. Now, air can flow from the pressure chamber 16 around the valve disc 20 into the vacuum chamber 17 as long as the short circuitina valve 18 is open.

Once the electromagnet 21 is cut off, the restorina spring 34 restores the actuating plunger 22 and the valve disc 20 into the closing position as shown in Figure 2.

in the closing position of Fiaure 2, the pressure in the pressure chamber 16 acts upon the valve disc 20 in the direction of arrow F. However, thanks to the central bore 26,.n the actuating plunger 22, the said pressure 9 r, also acts in the compensating chamber 27 such that ecual pressure acts upon the compensating piston 23 from the direction opposite the direction of arrow F, thereby neutralisina the two pressure forces equal in opposite directions, on the actuating plunger 22, enabling the latter to operate independently of the pressure difference between the pressure chamber 16 and the vacuum chamber 17. However, this will require that the surface of the compensating piston 23 facing the electromagnet 21 as well as the back of the valve disc 20, be exposed to the vacuurp in the vacuum chamber 17, this is ensured by the ports 60 circumferentially located in the cap 59 and terminating in the vacuuir chamber 17.

In the short-circuiting valve construction according to Figure 3, identical numerals designate corresponding parts to those shown in Figure 2.

According to Figure 3, the actuating plunger 22 is disposed in parallel with the piston wall 11 which is provided with a depression 61 on the side facina the pressure chamber 16. The valve body 24 comprises a lateral passage port 32 adjacent the aperture 25 provided in the piston wall 11 and in registry therewith. From the passage port 32, a curved channel 33, slightly tapering, at an angle of 900, leads to the valve bore 19 including valve seat 84, which bore is externally closed by the valve disc 20. The actuating plunger 22 extends through a central bore 57 of the valve body 24 and through a port 62 provided in a partition 63 located 9 behind the channel 33 down to the compensating piston 23 which, in this embodiment, is in the form of a completely flexible membrane fixed radially inwardly to the actuating plunger 22 and radially outwardly to the circumference of a correspondingly large aperture 64 provided in the valve body 24.

Behind the membrane forming the compensating piston 23, a rounded mounting disc 65 is fixed to the actuating plunger 22 to support the ipembrane during gagging in a direction opposite the direction shown in Fioure 3.

The restorina spring 34 extends between the partition 63 and the membrane forning the coTnpensatina piston 23, with a spring abutment 66 covering the membrane being additionally provided between the membrane and the restoring spring 34.

The actuating plunger extends beyond the coinpensatina piston 23 through a central port 58 of the electromaanet 21 into the latter where the armature 29 is secured therein. Located between the compensating piston 23 and the electromagnet 21 is a compensating chamber 27 which, through a port 261, is in communication with the pressure chamber 16. The chamber containing the restoring spring 34, through the port 62, is in communication with the interior of the curved channel 33 such that the pressure of the vacuum chamber 17 prevails therein.

The operation of the embodiment according to Figure p c 11 is 3 corresponds to the embodiment according to Figure 2, with a pressure compensation equally taking place on the actuating plunger 22, provided that the face of the compensating piston 23 corresponds to the face of the valve bore 19.

Figure 4 shows a quick-closing valve 50 which is incorporated in accordance with the present invention in a brake system for automotive vehicles having features as shown in Figure 1.

According to Fig-ure 4, a cup-shaped stepped piston 35 is axially displaceable in a stepped cylinder 36. The bottom wall 37 of the cupshaped piston 35 is disposed opposite an outlet opening 40 at a distance defining the opening gap of the quick-closing valve 50, with the outlet opening 40 being centrally provided in the front wall 41 of the cylinder 36 which, in Figure 4, is the right-hand wall, and, on the side facing the cup-shamed piston 35, is surrounded by an annular sealing face 42. An annular seal 43 for co-operation with the annular sealing face 42 is provided axially opposite the annular sealinc face 42 at the bottom wall 37 of the cup-shaped piston 35 in concentric relationship to the outlet opening 40.

Provided in the circumferential area of the cumshaped piston 35 next to the bottom wall 37 are passage ports 32 obliquely extending circumferentially to the direction of flow (arrow f) and terminating in an annular chai-ber 39 formed by the inside diameter of the cylinder 12 is 36 at this point being markedly larger than the outer diameter of the cupshaped piston 35.

In the area behind the passage ports 38 the remainder of the cup-shaped cylinder 35 is disposed in a manner closely and axially displaceable within the cylinder 36.

Directly behind the passage ports 38, the cylinder 36 expands in a steptype manner radially outwardly, and provided behind the step 67 is a guiding ring 68 bridging the annular chamber 39 radially inwardly and externally, and being in sliding abutment with the cup-shaped piston 35.

At a distance 6.0 from the guide ring 68, the cupshaped piston 35 projects radially outwardly through an annular step 70 to reach, at that point, approximately the inside diameter of the front part of the cylinder 36.

The rear end of the cup-shaped piston 35 comprises a radially outwardly extending flange 71 which is in axial abutment with a ring-shaped projection 72 of the stepped cylinder 36.

Disposed circumferentially of the cup-shaped piston 35, in expansion 73 of the cylinder 36, is a closing electromacnet 44 which, upon energisation, acts, in the closing direction, on the cup piston 35 which may be of a maanetic material. Moreover, opposite the direction of flow f, an opening electromagnet 74 may be additionally provided behind the cup piston 35.

Disposed circumferentially of the flance 71, in 13 is abutting relationship, is a spring abutment ring 75, preferably of magnetic material, with a restoring spring 76 extending between the latter and the guide ring 68.

optionally, a weak auxiliary spring 78 serving to release the closing movement, may be additionally provided between an inner annular stop 77 disposed in the rear area of the cylinder 36, and the rear surface of the flange 71.

Figure 4 shows the open position of the quickclosing valve 50 which is defined by the restoring spring 76, wherein the flow fluid flows from the pressure side 79, in the direction of arrow f, through the passageways 38 to the outlet opening 40.

The flow cross-section is reduced from the valve inlet to increase the flow speed and to decrease the static pressure. In the accumulating space 80, ahead of the passage ports 38, thereby a static pressure will develop which acts in the closing direction of the quickclosina valve 50.

once the closing electromagnet 44 is energised, either the cup-shaped piston - when magnetically confiaured - or only the spring abutment 75 all of a sudden is displaced in the direction of the arrow f, with the cup-shape d piston either by itself or through the force of flow or, in addition, through the rragnetic the closina force, all of a sudden beina moved, in direction of Figure 4, to the right wherein the annular seal 43 is sealingly mounted onto the sealing face 42.

14 After de-energisation of the closing electromagnet 44, the restoring spring 76 restores the cup-shaped piston 35 through the spring abutment ring 75 back to the initial position. This restoring movement may be assisted by energising the opening electromagnet 74.

It should be noted that the magnetic circuit will not have to accelerate the m-ass of the whole of the valve body but will rather only have to move the spring abutment ring 75 against the relatively weak restoring spring 76. The opening process of the valve will solely have to be performed by the spring force for which reason corresponding anti- adhesive foils are provided in the macnetic circuit. Should this be inadequate, the opening electric magnet 74 assisting in opening would be additionally provided.

It is a prerequisite for the smooth operation of the quick-closina valve 50 accordina to Fiaure 4 that the flow therethrough is always in the direction of the arrow f. A switching action in a reversed flow direction is not readily insured. However, the hydraulic circuit 81 according to Figure 5 is capable of safeguarding that the flow through the valve 50 is always in the direction of arrow f. For that purpose, the quick-closina valve 50 is provided on a hydraulic ring system containing four check valves 82 switched in accordance with the illustration in Fiaure 5. Depending on the direction of flow (arrow in solid lines and arrow in dashed lines, respectively), the check valves P2 respectively open or close automatically such that the flow through the quick-closing valve 50 is always in the same direction f.

is k 16 1 R of which faceE

Claims (2)

CLAIMS;

1. A brake system. for automotive vehicles, comprising a brake skid control and a vacuum brake force booster disposed between the brake pedal and a hydraulic master cylinder, wherein a fast-switching pneumatic shortcircuiting valve arranged to be actuated in response to output signals from a control circuit of the brake skid control is provided in the piston wall of the brake force booster, quick-closing valves in feed-in lines of the atmospheric pressure and/or of the vacuum to the pressure chamber and the vacuum chamber, respectively, characterised in that the quick-closing valves comprise a cuip-shaped piston (35), the open side the higher pressure, is axially displaceable in a cylinder (36), in that the cup-shaped piston (35), in the area of a bottom (37) thereof, comprises circumferential passage ports (38) terminating in an annular chamber (39) provided between the cylinder (36) and the cup-shaped piston (35), in that an outlet opening (40) is provided at a distance ahead of the '25) in the bottom wall (37) of the cup-shaped piston (. front wall (41) of the cylinder (36) and surrounded by an annular sealing surface (42) in co-operation with an annular seal (43) on the bottom wall (37) of the cupshaped piston (35), and in that a closing electromagnet (44) acting upon the cup-shaped piston (35) is provided in the cylinder (36).

2. A brake system as claimed in claim 1, including 17 quick-closing valves substantially as herein described with reference to Figures 4 and 5, of the accompanying drawinqs.

Published 1990atThe patent Office. State House. 6671 Higb Holoorn. London WClR4TP.Further copies maybe obtained from The Patent Office. Wes Branch, St Mary Cray, Orpington. Kent BRS 3RD Printed by Itult-Ill", techniques Itd, St Mary Cray, Kent Con 1'87 DkLiub 'DI-L-4, W. --j