GB2139721A - Actuating apparatus for the wheel brakes of a hydraulic braking system - Google Patents

Abstract

The invention is based on an actuating apparatus for the wheel brakes (10, 11, 17, 18) of a hydraulic braking system for automotive vehicles with a master cylinder stepped bore (3, 2) which bounds both a pressure chamber (8, 15) associated with at least one wheel brake and a filling stage or quick-take-up chamber (22). Through a master cylinder sealing cup, hydraulic fluid is displaceable from the filling stage chamber (22) to the pressure chamber (15). The filling stage chamber (22), has a filling valve (24) which limits the maximum pressure in the filling stage chamber (22). In order to realise an assistance of the actuating force with the aid of servo hydraulic pressure, it is proposed that the stepped filling stage piston (7, 21) has a larger diameter part facing away from the pressure chamber (8, 15) and which bounds the servo pressure chamber (25) of a hydraulic power booster. Servo pressure is adjustable in the servo pressure chamber (25) independence on the actuating force exerted on the brake pedal (28). <IMAGE>

Description

SPECIFICATION Actuating apparatus for the wheel brakes of a hydraulic braking system The invention relates two an actuating apparatus for the wheel brakes of a hydraulic brakes of a hydraulic braking system for automotive vehicles. Such apparatus may have a step-bore mastercylinderwhich bounds a powerchamberwhich is connected to at least one wheel brake, a filling stage chamber in which hydraulic fluid is displaceable toward the power chamberthrough a master cylinder cup and a filling valve connected with the filling stage chamberto limit the pressure within the filling stage chamberto a maximum value.

An apparatus with the forementioned features is known from the German printed and published patent application No. 2430 167. In the known brake actuating apparatus, in a casing, a step-bore is provided with two master cylinder pistons axially slidable arranged in a bore section having a smaller diameter. Two powerchambersare bounded bythe casing and the master cylinder piston, and a brake circu it with two wheel brakes is associated with each ofthe power chambers.

At the master cylinder piston nearest to the pedal, an extension is provided which extends right through a filling stage chamber and has a rigid connection with a filling stage piston guided in the larger diameter bore section and which is axially slidable under the action of a brake pedal. Between the master cylinder piston nearest to the pedal and the filling stage piston, a filling stage chamber isformed which has a hydraulic connection to a pressureless supplytankvia a non-return valve.

When an actuating force is exerted on the brake pedal,thefilling stage piston slides atfirst in the direction of application ofthe brakes, whereby hyd raulicfluid is displaced from the filling stage chamber into that powerchamber ofthe actuating apparatus which is nearesttothe brake pedal through inlet ducts at the master cylinder piston nearesttothe pedal and through the sealing cup relatedtothatmastercylinder piston, so that a corresponding pressure rise results in the powerchambernearesttothe pedal andatthe wheel brakes associated with that power chamber.

The pressure surge is limited bythe action of a non-return valve which is in hydraulic connection with the filling stage chamber and which opens at a predetermined pressure in the filling stage chamber and discharges excess hydraulisfluid to the pressureless supplytank. On increasing the actuating effort on the brake pedal,the mastercylinderpiston nearestto the brake pedal is then shifted in the direction of brake application, whilethe master cylinder piston further away from the pedal is aiso shifted under the effect of the pressure cushion in the power chamber next to the pedal so that also that power chamber of the brake actuating apparatus which is distant from the brake pedal is pressurised and a pressure increase is brought about in the brake circuit associated with the powerchamberfurther away from the brake pedal.

ltisevidentfromtheforementioned description that the brake actuating apparatus described in the Ger man printed and published patent application 2430 167 exclusively provides for a brake application by direct action of an actuating force on the brake pedal, an assistance of the braking action by an extraneous pressure not being envisaged.

The present invention seeks to provide a simple design apparatus of the kind previously mentioned in which the generation of pressure in the brake circuits is assisted by an auxiliary hydraulic force.

According to the invention, there is provided an actuating apparatus for the wheel brakes of a hydraulic braking system with a step-bore master cylinder which bounds both a power chamber associated with at least one wheel brake and a filling stage chamber, hydraulicfluidbeing displaceablefromthefilling stage chamberto the powerchamberthrough a master cylinder cup and a filling valve being connected with the filling stage chamber which filling valve limits the pressure in the filling stage chamber to a maximum value, characterised in that the filling stage piston has a larger diameter part facing away from the power chamber which bounds a pressure chamber of a hydraulic power booster in which an auxiliary pressure is adjustable dependent on the actuating force.

Advantageously, a configuration as defined results in the filling stage piston constituting at the same time the booster piston of a hydraulic power booster. The brake actuating apparatus is operable with only a single filling valve.

In a refinement ofthe invention the filling stage piston is oftwo part design and the larger piston part forms a booster piston which is connected to the smaller piston part by means of a push rod. Savings in manufacturing and assembly costs resultfrom the two-part design of the filling stage piston. Nevertheless, the two piston stages are virtually rigidly connected to each other, since the movement ofthe larger piston stage is limitable by casing stops in the release direction of the brakes and since spring forces act on the minor piston partforadjustmentofthe brakes' release position. In principle, the push rod can be formed as part ofthe larger piston part or the piston part with the smaller diameter.The push rod may be advantageously configured as an integral component ofthe smaller piston part so that, ideally, the push rod has the same diameter as the smaller piston stage so that a simplification of manufacture results.

Avarietyofdifferent brake application valves may be employed for the adjustment of the auxiliary hydraulic pressure in the pressure chamber ofthe hydraulic power booster. However, slide valves as such already known are particularly reliable in operation.

The brake actuating apparatus maycomprisea return chamber connected to the pressure chamber in the release position of the brakes which is separated hydraulically from the filling stage chamber. The slide valve may be arranged substantially parallel to the filling stage piston and may be actuated by a lever mechanism.

Advantageously, the present invention may enable one entire braking system, as a result of which changes oftheviscosity due to mixing of different brake fluids are avoided and mistakes in filling ofthe braking system are less likely. In a refinement ofthe invention a further master cylinder piston is arranged coaxiallyrelativetothefilling stage piston and is slidable into a second power chamber underthe effect ofthe pressure in the power chamber located next to the brake pedal. In this manner, a brake actuating apparatusfurnished with two power chambers, that is a dual-circuit braking system is formed.In that configuration, two wheel brakes may be associated with each power chamber of the actuating apparatus, said heel brakes being either arranged diagonally opposite to each other or else both located at one vehicle axle. With use ofthe principles of the invention atriple-circuit braking system can be provided if a third dynamic brake circuit is connected to the pressure chamber ofthe hydraulic power booster which third circuit preferably serves wheel brakes at the rear axe of an automotive vehicle, whereas with each power chamber ofthe brake actuating apparatus a wheel brake is associated which is preferably arranged atthefront axle ofthe automotive vehicle.

In orderthatthe invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, byway of example only with reference to a sectional illustration shown in the drawing.

In the illustration, reference numeral 1 denotes a casing of a brake actuating apparatus constructed in accordance with the present invention. In the casing 1 a cylinder bore 2 with three bore sections 3,4,5 is arranged. Relative to the bore section 3 of the cylinder bore 2, the bore section 5 has a large diameter, while the bore section 4 is the largest diameter section ofthe cylinder bore 2.

In the bore section 3 with thesmallest diameter, two master cylinder pistons 6,7 are arranged axially slidably,the master cylinder piston 6 together with the casing 1 bounding a power chamber8which through a casing connection 9 and relevant pressure lines has a hydrauliclinktowheel brakes 10,11 which arefor example located at the front axle of an automotive vehicle.

The master cylinder piston 6 is provided with a central valve 12which interrupts a connection between the power chamber8 and an annular chamber 13 in the event of a predetermined slight axial slide of the master cylinder piston 6 in the direction of brake application. As soon as the central valve 12 is closed, a connection between an unpressurised supplytank 14 and the power chamber 8 is interrupted so thatthe brake circuit linked to the power chamber 8 constitutes a closed hydraulic system.

The master cylinder piston 7 is arranged coaxially relative to the master cylinder piston 6 and together with the piston 6 and casing 1 bounds a power chamber 1 5from which a hydraulic connection to wheel brakes 17,18 is established through a casing connection 16. The master cylinder piston 7 is also provided with a central valve 19 corresponding to the central valve 12 in the master cylinder piston 6 and featuring an identical mode of operation. Beyond the controlvalvetowardsthe brake pedal end a push rod 20 is provided on the master cylinder piston 7, which push rod 20 protrudes right th rough the bore section 4 ofthe cylinder bore 2 and with its end nea rest to the pedal engages a booster piston 21.Between the master cylinder piston 7 and the booster piston 21, an annular chamber 22 is formed which constitutes the filling stage chamber. From the filling stage chamber 22, a hydraulicfluid duct 23 leads to a filling valve 24 which limits the hydraulic pressure in the filling stage chamber22 to a presetable maximum value and through which superfluous hydraulicfluid is dis charged to the pressureless supplytank 14.

The end ofthe booster piston 21 facing awayfrom thefillingstagechamber22 bounds a pressure chamber 25 ofthe hydraulic power booster in which an auxiliary pressure is adjustable depending on the intensity of brake actuation. The booster piston 21 is in connection with an actuating piston 26 which is, in its turn, coupled mechanicallyto a brake pedal 28 by means of a pedal rod 27. Afurther component ofthe hydraulic power booster is constituted by a brake application valve 29 having a control slide valve 30 which dependent on the position ofthe brake pedal 28 assumes a certain position relative to a valve body 31 surrounds the control slide valve 30.On the left ofthe control slide valve 30 as viewing the drawing, a booster return chamber 32 is formed which is connected to the pressu reless supplytank 14through a casing connection 33.

A lever-type actuating means comprises two levers 34,35 arranged parallel to each otherwhich actuating means is coupled with the control slide valve 30 of the brake application valve 29. In this configuration, the lever35 is provided with a ball-shaped head 36 which is firmly coupled with the casing. The other end of the lever 35 engages in a recess of the actuating piston 36.

The upper end ofthe lever 34 as viewed in the drawing abuts the control slide valve 30 ofthe brake application valve 29. The lower end ofthe lever 34 as viewed in the drawing acts againstthe booster piston 21. The levers34, 35 are linkedto each other by means of a pivot joint37.

The described braking system operates as follows: In the release position of the brakes, all moving parts are positioned as seen in the drawing. When an actuating force is exerted on the pedal 28, the actuating piston 26 slides to the left as viewed in the drawing, thereby adjusting an auxiliary hydraulic pressure dependent on the position of the brake pedal 28 and by the action ofthe brakeapplication valve 29 which is connected with an accumulator 38. At a predetermined pressure level in the presssure chamber 25 ofthe hydraulic power booster, the forces counteracting a sliding movement of the booster piston 21 are overcome so that the booster piston 21 starts to move in the direction of brake application and pressurisesthefilling stage chamber 22. The filling valve 24 remains closed initially so that the hydraulic fluiddisplacedfromthefilling stage chamber 22 passes to the power chamber 1 Sthrough openings 39 in the master cyclinder piston 7. By the pressure adjusted in this manner in the power chamber 15 pressure is applied to the wheel brakes 17, 18 atthe rear axle of the vehicle. In addition to that, the hydraulic pressure in the power chamber 15 causes the master cylinder piston 6to move in the direction of brake application sothata hydrauliopressureis generated in the power chamber 8, which pressure is supplied to the wheel brakes 10,11 through the casing connection Sand relevant pressure lines.

As soon as a predetermined hydraulic pressure has been reached in the filling stage chamber 22, the filling valve 24 opens. The hydraulicfluid which is now displaced from the filling stage chamber 22 as a result of the reduction in size of the filling stage chamber 22 is then conveyed to the pressureless supply tank 14 through thefilling valve 24. Everytime the actuating force on the brake pedal 28 is increased, the pressure in the pressure chamber 25 ofthe hydraulic power booster and in the wheel brakes 10,11, 17,18 rises.

When the actuating force exerted on the brake pedal 28 is reduced to such an extentthatthe booster piston 21 moves to the right as viewed in the drawing, hydraulic fluid is aspirated from the pressureless supplytank 14 into the filling stage chamber 22 through the filling valve 24 due to the increase in size ofthefilling stage chamber 22. In this direction of flow ofthehydraulicfluid,thefillingvalve24does not obstruct the flow of the brake fluid. Theforementioned procedure continues until the described brake actuating apparatus is restored to the position shown in the drawing, that is until the release condition of the brakes has been reached.

Claims (10)

1. An actuating apparatusforthewheel brakes of a hydraulic braking system with a step-bore master cylinder which bounds both a powerchamberassoci- ated with at least one wheel brake and a filling stage chamber, hydraulicfluid being displaceablefromthe filling stage chamber to the powerchamberthrough a master cylinder cup and afilling valve being connected with the filling stage chamberwhich filling valve limits the pressure in thefilling stage chamber to a maximum value, characterised in thatthe filling stage piston (7,21) has a larger diameter partfacing awayfromthe powerchamber(8, 15) which bounds a pressure chamber (25) of a hydraulic power booster in which an auxiliary pressure is adjustable dependent on the actuating force.

2. An actuating apparatus as claimed in claim 1, characterised in thatthe filling stage piston (7,21) is of two-part design and the larger piston part (21) constitutes a booster piston which is connected to the smaller piston part p) by means of a push rod (20).

3. An actuating apparatus as claimed in claim 2, characterised inthatthe push rod (20) keeps the piston parts (7, 21 ) at a defined distance from each other.

4. An actuating apparatus as claimed in claim 2 or 3, characterised inthatthe push rod (20) is an integral portion ofthe smaller piston part (7).

5. An actuating apparatus as claimed in any one of the preceding claims, characterised in that the hydraulic pressure is adjustable in the pressure chamber (25) ofthe hydraulic power booster by means of a slide valvet29lactuable by the brake pedal.

6. An actuating apparatus as claimed in any one of the preceding claims, characterised in that a return chamber (32) connected to the pressure chamber (25) in the release position ofthe brakes is separated hydraulicallyfrom the filling stage chamber (22).

7. An actuating apparatus as claimed in claim 6, characterised inthattheslidevalve (29) is arranged substantially parallel to the filling stage piston (7,21) and is actuatable by means of a lever mechanism (34, 35).

8. An actuating apparatus as claimed in anyone of the preceding claims, characterised in that solely one single brake fluid is employed in the entire braking system.

9. An actuating apparatus as claimed in any one of the preceding claims, characterised in that a master cylinder piston (6) is arranged coaxially relative to the filling stage piston (7,21)which master cylinder piston (6) is slidable into a power chamber (8) awayfrom the brake pedal underthe effect of the pressure in the power chamber (15) located next to the pedal.

10. An actuating apparatusforthewheel brakes of a hydraulic braking system substantially as described herein with reference to the drawing.