GB2136521A - Two-circuit brake system - Google Patents

Abstract

A two-circuit brake system for motor vehicles, having a two-circuit driver's brake valve 24 and brake cylinders 34 to 37 which can be supplied from the said brake valve 24 by way of two brake circuits, and a common pressure control valve assembly 1 which is equipped with three pairs of valves 7, 8; 9, 10; 11, 12 and which is part of an anti-skid system which comprises wheel sensors, an electronic switching device and a solenoid pilot control valves eg 25 (Fig. 2) for each pair of valves is characterised in that the pressure-control valve assembly is of two-circuit design. Actuation of the pilot control valve 25 pressurises chamber 20 to separate further the diaphragm assemblies 15', 16' thereby lifting the valve elements 15, 16 from their adjacent seats which close the vent passages 43, 44 of Fig. 2 onto their remote seats to cut off the supply lines 40, 41. Pressurisation of the chambers 19 and 21 seat the valve elements 13, 14 and 17, 18 to retain the instant pressures in the actuators 35 to 37. <IMAGE>

Description

SPECIFICATION Two-circuit brake system The invention relates to a two-circuit brake system for motorvehicles, having a two-circuit brake valve and brake cylinders which can be supplied by the said brake valve by way of two brake circuits, and a pressure control valve which is equipped with main valves and which is part of an anti-skid system comprising wheel sensors, an electronic switching device and solenoid pilot control valves.

A brake system ofthis kind is known (German Offenlegungsschrift No. 26 25 502). In this known system, a pressure-control valve is used which is controllable by a brake valve through a single circuit (per axle). If it is desired to use a single-circuit pressure-control valve of this kind in brake systems which act upon one axle orwheel through two circuits, the cost ofthe anti-skid brake system is almost doubled.

Thus, for example,two pressure-control valves have to befitted to one vehicle wheel for the two brake circuits and are actuated in parallel bythe electronic switching device. In addition to doubling the cost of the valves, the elctronicswitching device also has to be specially constructed so that it can monitor the function of the pressure-control valves in parallel in addition to undertaking the parallel control thereof.

In contrast to this, a pressure-control valve of two-circuit design has the advantage that the cost of individual parts is substantially reduced. In addition to this it has been found that a special electronic switching device does not have to be used, and a normal standard electronic system can be used, such as is normally used in the case of single-circuit pressure-control valves.

In accordance with the invention there is provided a two-circuit brake system for motor vehicles, having a two-circuit brake valve and brake cylinders which can be supplied bythe said brake valve by way of two brake circuits, and a pressure control valve which is equipped with main valves and which is part of an anti-skid system which comprises wheel sensors, an electronic switching device and solenoid pilot control valves, characterised in that the pressure-control valve is oftwo-circuit design.

Preferably the two-circuit pressure control valve is single circuit controllable. The pairs of main valves in the pressure control valve preferably are disposed such thattheircontrol chambers form a common volume chamber.

Preferably a two-way valve is provided in the anti-skid system which is chargeable by both brake circuitsofthe brake system and which selects the pressureforthe solenoid pilot-control valves of the anti-skid system.

Preferably, the pressure control valve is of symmetrical construction about a central plane, an intermediate plate being disposed in the central plane, which plane incorporates passageforfeeding (Transmitting) the pressure made available bythe pilot-control valves.

Two two-port two-position valves are preferably disposed at the outlet of the pressure control valve, the control valve being oftwo-channel construction.

Alternatively, the pressure control valve may be of single-channel construction with one two-port, twoposition valve disposed at the outlet thereof.

Several embodiments ofthe invention are illustrated in the drawings and will be further explained in thefollowing description. In the drawings: Figure 1 shows a two-circuit, two-channel pressurecontrol valve, Figure 2 shows a two-circuit pilot control valve with pressure selection for single-circuit control, and Figure 3 shows a two-circuit, single-channel pressure-control valve.

A pressure-control valve 1 has a housing 2 which is constructed symmetrically at both sides of a central axis 3. Namely, two identical housing parts 5 and 6 are located one at each side of an intermediate plate 4 and each housing part has a three-port, two-position valve 7 or 8 respectively and two two-port, two-position valves 9, 11 and 10,12 respectively. The valves 7to 12 are main valves. They have valve seats secured relative to the housing and resilient members serving as closure elements whose control parts are di aphragms 13,14,15,16,17,18.

As a result of the symmetrical arrangement of the housing parts 5 and 6,the diaphragms 13 and 14,15 and 16, and 17 and 18 are located opposite one another and thereby form respective, common volume chambers 19,20,21. Each diaphragm 15 or 16 is a double element having a respective intermediate push rod member 15' or 16'.

The intermediate plate 4 serves on the one hand to centre the control diaphragms 13,14,15,16,17,18.

This is importantfor satisfactory transmission ofthe brake pressures predetermined by a two-circuit service brake valve 24. On the other hand, the intermediate plate 4 has the task of bringing up the control pressures which originate from a pilot control valve 25 illustrated in Figure 2. Three of these pilot control valves 25, that is to say, one for each pair of main valves 7/8,9/10, 11/12, are disposed in the housing 2 of the pressure-control valve 1. Two pairs of outlets 26, 27 and 28,29 respectively ofthe pressure-control valve 1 are connected by way of brake lines 30,31 and 32,33 respectively to wheel brake cylinders 34,35 and 36,37 respectively, a pair of the said wheel brake cylinders being disposed on a vehicle wheel 38 or39 respectively.Alternatively, however, each wheel brake cylinder can be a built-in unit in the form of a two-piston cylinder.

Two lines 40 and 41 leading from the two-circuit brake valve 24 are connected to the pilot control valve 25 where there is provided a two-way valve 42 by means of which the higher inlet pressure at any given time can be selected. Figure 2 also shows that each of the two three-port, two-position valves 7 and 8 control a respective atmospheric air passage 43 or44 which is connected to the atmospheric air by way of a relief valve 45. Only a single pilot control valve 25 is provided for each pair ofvalves 7/8, 9/1 0 and 11/12. A pilot control valve 25 of this kind has an armature 46 which carries closure members 47, 48fortwo valve seats 49,50 and which is reciprocable between the valve seats 49,50 against the force of a spring 52 by means of magnetic forces produced by a coil 51.

The two-circuit brake system which has been described operates in the following manner: During braking, the two lines 40 and 41 are charged bythetwo-circuit brake valve 24. The compressed air enters the brake lines 30,31,32,33 by way ofthe open main valves 7,8,9,10,11,12. The brakes are applied by two circuits, that is to say, by two brake cylinders 34, 35 and 36,37 on each wheel 38 or 39 respectively.

Wheel sensors respond when there is a risk of wheel-lock. The coil 51 ofthe central pilot control valve 25 is first energized by way of an electronic system, so thatthe pilot control valve 25 can switch to its other end position. The pressure which is higher at any given time enters the intermediate plate 4 byway of thetwo-wayvalve 42 and in thefirst instances urges the diaphragms 15,16 and their intermediate push rod members 15' and 16' into their other end positions.

The main valves 7 and 8 close. Hence, the inflow of compressed air is prevented. The pressure can then be held pulsed or, together with the pair of main valves 7 and 8, can be discharged by the other two pilot control valves 25 and the four main valves 9, 10,11,12.

Hence, itwill be seen thatthe brake pressuresflow through two entire circuits and are also two-circuit monitored in the case of anti-skid operation, although, owing to the common volume chambers 19,20, 21, only a single-circuit pilot control pressure is required.

Two-channel pressure regulation is then also possible with the combination of a respective three-port, two-position main valve 7 or 8 with a respective pair of two-port, two-position main valves 9 and 11 or 10 and 12, that is to say, each wheel 38 and 39 has individual regulation.

Hence, an essential prerequisiteforan inexpensive, compacttype of construction ofsuch a multi-function valve is realised. Since, moreover, the braking capac ity of a two-circuit wheel brake does not differ from a single-circuit wheel brake, that is to say, the volume of the two brake cylinders is substantially equal to the volume of the single-cylinder construction, the cross sections of the two-circuit pressure-control valve can also be correspondingly smaller than those of a single-circuit valve. Hence, this also provides the prerequisite for a compact type of construction.

However, the essential advantage results from the single-circuit pilot control valve 25 which renders it possibletocombinethe initially mentioned category of vehicles (having two-circuit wheel brakes) with a mass-produced standard electronic system designed for single-circuit wheel brakes. Thus it is only in this way that it is possible to realisean inexpensive unit-composed concept which can be applied, with identical structural elements or entire components, to the wide variety of types of commercial vehicles.

Itwill be appreciated thatthe safety and reliability of these components are also essential.

This safety and reliability of the proposed twocircuit pressure-control valve 1 resides in the fact that mass-produced individual elements are used, and the centring of the switching elements by way of the intermediate plate 4 also precludes the detrimental effect of differences caused by tolerances.

Even in the event offailure of a brake circuit, the regulating function of the intact circuit is maintained.

The simple, two-way valve 42 which is installed in the pilot control circuit, and which, as illustrated, can be, for example, a springless ball valve, ensuresthatthe pilot control pressure is taken from the intact brake circuit and that at the same time there is no pressure loss to the defective brake circuit.

In accordance with the construction already described, the type of construction which is illustrated in Figure 3, and which is also symmetrical, shows that it is also possible to construct a pressure-control valve 60 with only one channel (that isto say, to outlets 62 and 63for one wheel 61). However,thispressure- control valve 60 is also of two-circuit construction. The choice ofthe pilot control pressure made available by the two pilot-control valves 64 and 65 is effected by way of a two-wayvalve 66 in the same manner as in the type of construction shown in Figure 2.

Two pressure-control valves 60 of thins kind are required fortwo wheels of a vehicle axle. It will be seen that the cost of valves for one axle is correspondingly higher than that in the type of construction shown in Figures 1 and 2.

Claims (9)

1. Atwo-circuit brake system for motor vehicles, having a two-circuit brake valve and brake cylinders which can be supplied by the said brake valve byway of two brake circuits, and a pressure control valve which is equipped with main valves and which is part of an anti-skid system which comprises wheel sensors, an electronic switching device and solenoid pilot control valves, characterised in that the pressurecontrol valve is oftwo-circuit design.

2. Atwo-circuit brake system as claimed in claim 1, characterised in thatthe two-circuit pressure-control valve is single-circuit controllable.

3. Atwo-circuit brake system as claimed in claim 1 or 2, characterised in that the pressure-control valve has a plurality of main valves disposed in pairs such thatthe control chambers of each pair of main valves each form a common volume chamber.

4. Atwo-circuit brake system as claimed in any one of claims 1 to 3, characterised in that a two-way valve is provided which is chargeable by both brake circuits and which selectsthepressureforthe solenoid pilot control valves ofthe anti-skid system.

5. Atwo-circuit brake system as claimed in one of claims 1 to 4, characterised in that the pressurecontrol valve is of symmetrical construction about a central plane, and that there is disposed in the central plane an intermediate plate which incorporates pas sagesforfeeding the pressure made available bythe pilot-control valves.

6. Atwo-circuit brake system as claimed in one of the claims 1 to 5, characterised in that the pressurecontrol valve is oftwo-channel construction forthe purpose of supplying two different pressures, two two-port two-position valves being disposed atthe outlet thereof.

7. Atwo-circuit brake system as claimed in one of the claims 1 to 5, characterised in thatthe pressurecontrol valve is of single-channel construction, one two-port, two-position valve being disposed at the outlet thereof.

8. Atwo-circuit brake system as claimed in claim 1, substantially as hereinbefore described with referenceto and as illustrated in Figs. 1 and 2 ofthe accompanying drawings.

9. Atwo-circuit brake system as claimed in claim 1, substantially as hereinbefore described with reference to and as illustrated in Fig. 3 of the accompanying drawings.