US 4,629,258 A · Hydraulic dual circuit brake system for road vehicles

Abstract

A hydraulically power-assisted dual circuit brake system for road vehicles combined with an anti-locking brake system has a stepped tandem master cylinder and a primary piston. The primary piston includes a ring piston which is displaceable in a larger cylinder step and a plunger which is displaceable in said ring piston. A pre-pressure acting on the control area of the plunger of the primary piston is built up by pedal actuation of a further plunger. This pre-pressure operates as a reference pressure and is also coupled into a proportional control valve. The proportional control valve provides a control output pressure which is taken from the auxiliary pressure source and is higher. The control output pressure is used to impinge the ring piston and thereby move the plunger of the primary piston. With use of the ABS control, at least a secondary brake circuit, in a special design a primary brake circuit as well, is switched over from static to dynamic operation. In dynamic operation, the output pressure of the proportional control valve is used to operate the selected brake circuit. A stroke sensor monitoring the displacement stroke of the ring piston generates an output signal independently of the ABS control, which signal triggers the changeover of both brake circuits to dynamic operation when a threshold value of the ring piston stroke is reached.

In a combination hydraulic dual circuit brake system and anti-locking brake system that is of the type having a tandem master cylinder for controlling two vehicle brake circuits and including a plurality of output pressure chambers and a primary piston mounted for movement in the cylinder to produce a brake pressure buildup in at least one of the output pressure chambers and to define a working area, an auxiliary pressure source for providing an auxiliary output pressure at a predetermined level, and a proportional control valve means for supplying a control output pressure proportional to a force applied to a vehicle brake pedal, the proportional control valve means including a supply pressure input in fluid communication with the auxiliary pressure source and formed to include a pressure output, the control output pressure being usable to impinge the working area of the primary piston, wherein the improvement comprises

the tandem master cylinder includes a cylinder casing and is formed to include, in serial order, a secondary pressure bore stage, a primary pressure bore stage, a pre-pressure chamber, an auxiliary pressure bore stage, the primary piston includes a ring piston formed to include a central bore and a plunger mounted for movement in said central bore, the ring piston and the primary pressure bore stage cooperating to define a primary pressure output chamber, the ring piston including a first ring flange arranged in a pressure-tight displaceable manner in the primary pressure bore stage, a second ring flange axially spaced in relation to the first ring flange, and arranged in a pressure-tight displaceable manner in the auxiliary pressure bore stage, and a sleeve-shaped adaptor extending therebetween for joining the first and second ring flanges, the plunger including a driving flange in communication with the primary pressure chamber and biased against the first ring flange of the ring,
the cylinder casing includes a partition between the auxiliary pressure bore stage and the pre-pressure chamber, the partition, second ring flange, and cylinder casing cooperating to define an annular control pressure chamber, the partition being formed to include a bore through which the plunger is displaceable in a pressure-tight manner,
plunger means, responsive to actuation of the brake pedal, for generating a pressure in pre-pressure chamber for use as a reference pressure by the proportional control valve means,
means for coupling the control output pressure of the proportional control valve means to the annular control pressure chamber, and
means for activating the pressure control valve means of the anti-locking system to introduce the control pressure into the control pressure chamber to cause the control pressure to impinge the working surface of the primary piston, whereby a secondary brake circuit is changed over to dynamic pressure admission from static pressure admission by the control output pressure and a brake line for fluidly coupling the secondary pressure bore stage of the tandem master cylinder and the wheel brakes of the secondary brake circuit is blocked to disable static operation of said wheel brakes during operation of said anti-locking system.

2 more elements

Facts

Application

06/686,477Filed 26 Dec 1984

Priority

DE 334761830 Dec 1983

Granted

16 Dec 1986

Term ends

Not estimatedThe source records don’t support an estimate.

Classification5 codes

B60T 8/445
Co-operating with a power-assist booster means associated with a master cylinder for controlling the release and reapplication of brake pressure…:…
B60T 8/885
With failure responsive means, i.e. means for detecting and indicating faulty operation of the speed responsive control means: using electrical…
B60T 13/145
Systems with master cylinder: master cylinder integrated or hydraulically coupled with booster
B60T 17/225
Devices for monitoring or checking brake systems; Signal devices: brake fluid level indicators

Hydraulic dual circuit brake system for road vehicles

Life of this patent

Hydraulic dual circuit brake system for road vehicles

Life of this patent

Abstract

Claims22