DE2802852A1 - DUO COMPRESSED AIR CONTROL VALVE FOR VEHICLE BRAKING SYSTEMS - Google Patents

Description

15/5

HIDLAInID-ROSS CORPORATION, 55, Public Square,

Cleveland, Ohio 44113, USA

Duo compressed air control valve for vehicle braking systems

The invention relates to a dual air pressure control valve for vehicle brake systems. The usual trucks for the Long-distance transport can be in trucks for operation without a trailer and in trucks in the form of motor vehicle trains, consisting of the towing vehicle and the trailer, subdivided will.

Currently, both types of trucks use duo-brake systems, each of which has an independent compressed air supply to the front and rear axles. In trucks without a trailer, it is common to use pressure limiting devices such as converter valves, which limit the air output to the front axle brakes in the lower braking range with low braking force to 50 % of the size that is applied to the rear axle brakes, with higher braking forces such devices go into one Open position so that full pressure or the same pressure can be applied to both axes.

It is also generally known to add pressure relief valves for duo compressed air control foot valves to limit the brake pressure on the front axle of trucks, consisting of from towing wagons and trailers, but this is by no means satisfactory for all operating conditions of the towing wagon. The brake pressure air distribution on such trains is least critical if the tractor unit is equipped with a half

809851/0734

Midland-Ross Corp.

Trailer is connected because the essential, if not predominant braking force is in use of the trailer brakes occurs, although the total braking force is still in need of improvement here, too. But it will be one of those The towing wagon is then used without the semi-trailer, it is very desirable, but this has not yet been realized to limit the pressure on the rear axle brakes in the lower braking force range. A pulling car without a trailer drives is more heavily loaded on the front axle, especially with regard to the front position of the engine and the Driver's cab. As a result, greater pressure would be exerted on the brakes on the front axle of the towing vehicle without a trailer give more braking power and enable better braking than with a corresponding braking of the less heavily loaded brakes on the rear axle would be possible. With this starting point, limiting the Pressure on the rear axle brakes to prevent the axle from jumping and results in shorter braking distances. Such a one Braking would also be desirable in trucks that are subject to operating conditions with a heavily loaded rear axle such as trucks or truck-trailer trains with removable load-bearing boxes. Because it will now viewed as advantageous to have the greater braking force available on the front axle of the towing vehicle, when a heavily loaded trailer is hanging behind it, with a view to the torsional effect on the front axle, the is transferred from the trailer load through the fifth wheel.

Still unsatisfactory with the combinations known to date a duo compressed air control valve and a front axle converter valve is the low initial pressure that is normally developed on the rear axle by this combination, before pressure is applied to the front axle brakes.

809831

Midland-Ross Corp.

It is therefore desirable and considered advantageous to have a significantly higher initial pressure in the brakes the front axle, or if desired on the rear axle, to have a considerable pre-braking effect on the axle that has the higher initial pressure. Another disadvantage of the valve combinations known up to now is that the pressure in the limited system cannot reach that of the other to a point above the central one Input pressures of the entire system.

The present invention is based on the object of creating a dual compressed air control valve of the generic type, which fully meets the requirements set out in detail above.

The solution according to the invention results from the characterizing part of claim 1.

The dual compressed air control valve according to the invention is not only able to distribute compressed air separately to the front and rear axles of the vehicle, but can also ^{achieve a desired ratio between the levels from a low to a high level +} total braking force ⁺ that of the vehicle's braking system Generate pressures sent to the axles, and this ratio of pressures can be changed as the braking force increases.

Structurally, the normally foot operated valve includes a housing with five canons "A first pressure release chamber includes a piston that can be operated by the pedal. A second valve chamber contains a first valve member, which normally engages an annular seat between and from the first and second chambers The first piston can be lifted off by a third relay pressure chamber is connected to the first chamber via an eccentric passage. The fourth chamber is a pressure release chamber,

809831/0734

Midland-Ross Corp,

which has a cylinder wall in common with the third chamber, a second piston being provided here, which is supported by the Compressed air flowing from the first chamber to the third chamber through a connecting, eccentric passage. The fifth chamber is assigned a second valve member, which is normally on an annular seat between the third and fourth chambers.

The two pressure release chambers are connected to outlets, which are normally connected to the braking devices of the front and rear axles. The two valve chambers have inlets, which are normally connected to separate compressed air reservoirs.

If the first valve member in the second chamber is lifted from the seat, the first chamber can be pressurized, to deliver compressed air to the braking device of one axis. The pressure applied in the first chamber is transferred to the third Chamber transferred so that the second piston moves sufficiently to the second valve member in the fifth chamber from Lift off the seat, whereupon compressed air flows from the fifth chamber into the fourth chamber, which is used as a supply source for the Braking device of the other chamber is used. The so-called initial pressure of considerable magnitude obtained with the inventive Valve achievable is defined as the pressure that is generated in advance in the first chamber in order to reduce the frictional resistance, the springs supporting the second piston and the resistances which the second valve member moves away from Seat has to be overcome, as well as the resistance to the opening of this second valve member, which is results from the pressure in the fifth chamber.

An essential feature of the invention is based on the knowledge that this initial pressure and the manner of change the difference in the pressures in the two pressure release channels can be determined by the relation resulting from the size

8Q9831 / 07M "^: ' ^r - ^yL

Midland-Ross Corp.

area of the valve seat for the second valve member exists in the fifth chamber with the transverse axial area of the cross section on an outer surface of the second valve member which is in sliding sealed contact with a surrounding wall ^{r of} the fifth chamber. In principle, the size range of the valve seat can be enlarged beyond that of the aforementioned cross-sectional area in order to have a desired high initial pressure. It has also been found that other size ranges, which will be described in detail later, can also influence the equilibrium between the pressures on the front axle and the rear axle at high braking forces.

Another advantage of the subject matter of the invention is that the valve is used in a dual brake system in order to make other pressure-limiting devices unnecessary _{or the like}

An embodiment of the subject invention is shown below with reference to the accompanying drawing. Show it:

FIG _o 1 is a diagrammatic representation of a hitherto conventional brake system for a trailer Zuwagen system,

2 shows a diagrammatic representation of a brake system

with a compressed air control valve according to the invention,

3 shows a longitudinal axis section through a dual compressed air control valve according to the invention,

4 shows a representation of ratio curves, with the values of the pressures on the ordinate and the abscissa

plotted by the two sections of the Dua pneumatic control valve according to the invention be delivered.

SAD ORIGINAL

809831/0794

Midland-Roκö Corp.

Fig. 1 shows diagrammatically in a greatly simplified form a brake system of the previous type for a truck or a Towing vehicle trailer system in which a duo compressed air control valve 5, which is foot-operated, compressed air to the brake units 6 for braking the wheels 7 of a front axle through the lines and 9 and starting from a portion of the valve 5 by means of a memory 10, which with the valve via the Line 11 is connected. For the brake units 21 of the rear axle compressed air is from a second accumulator 12 via the line 15, a further section of the valve 5, the line 16, an anti-blocking device 17 and the lines 18, 19 are supplied.

In order to ensure that a lower braking force is effective on the wheels 5 than on the wheels 22 of the rear axle, the Lines 8 and 9 are connected to one another by a converter valve 24 which, in a conventional manner, controls the pressure that is applied to the Gears 7 wheels, limited to a size that is below the pressure level with which the brake units 21 of the rear Wheels are acted upon. The compressed air is fed to the overall system by a pump 26 which is connected to a main storage unit is connected, from which the compressed air then passes through check valves 28 to the accumulators 10 and 12.

As can be seen from Fig. 1, the portion 31 of the valve 5, which is closer to the pedal 32, directly from the pedal or any actuated other external agents to bring the compressed air to the brakes of the rear axle. Section 34 of the valve 5, which controls the flow of compressed air to the front axle brakes, is either in the usual way by foot valves operated by direct actuation, or operates in relay form, i.e. by means of compressed air flowing from the first section 31 into the second section 34 of valve 5 is blown. Usually there is a small delay in action and / or less Air pressure provided so that the braking force on the front axle is less than on the rear axle. The braking force reduction is to a significant extent from the converter

809831 / 073A

BATH

- 1ΰ -

Midland-Ross Corp.

valve 24 controlled, daö the pressure on the front brakes holds at a lower value than on the rear brakes come here, with the inclusion of heavy emergency braking actions on the vehicle.

In the brake system according to FIG. 2 , a structure similar to that of the system according to FIG. 1 is provided, but now the line from the memory 10 responsible for the front axle extends through that section 41 of a valve 40 which is closest to the pedal 42 and which is actuated directly by the mechanical action of the pedal, so that the air-IQ pressure can be transmitted to the front brake units without modification, ie without switching on a converter valve, as provided in FIG. 1. The compressed air which is transmitted to the brake units of the rear axle is modulated in the section 43 of the valve 12, as described in detail below.

The housing of the valve 40 includes two housing parts 46 and 47, defining an inner central passage extending through the two housing parts along an axis N-N, and from an end receiving the actuation pressure to an air outlet end. In general terms, this includes the housing part 46 the primary section of the valve and the housing part 47 the relay section of the valve. The inner passage is bounded by a series of coaxial, inner cylinder wall surfaces of varying diameter that delimit and partially define in order a first pressure discharge chamber 51, a second valve chamber 52, a third relay pressure chamber 53, a fourth pressure release chamber 54 and a fifth valve chamber 55 adjacent the air release end.

A first piston 56 is arranged in the first pressure delivery chamber, which is reciprocally sealed on a cylindrical side wall 57 of the chamber and on the inner cylindrical surface a wall 58, which acts as a spring holder, is performed.

0 9 8 31/0734

^BATH

I-iidland-Roö :. Corp.

- 11 -

Lie valve chamber ζ-2 contains a valve member 60 which is held resiliently pressed by a spring 52 against a valve seat 61 which is formed by a wall section at the connection between the first and second chambers. The chambers 53 and 54 have a common cylindrical wall 108 on which a second relay piston 64 is guided, which is under the pressure of a spring 97 which presses the piston in the direction of the chamber 52. The piston 64 has a central section which is partially designed as a tappet 65 which extends onto the piston 56 and is partially a hollow passage which extends in the fourth chamber 54 to the fifth chamber 55 and ends in an annular skirt 67 . The chamber 55 includes a valve member 70 which is held resiliently urged by a spring 10 against a valve seat 71 which faces the discharge end of the housing.

The first and fourth chambers, i.e. the pressure release chamber 51 and the pressure release chambers 54, respectively. Outlets 7 3 and 74. The second and fifth chambers, i.e. the valve chamber 5? and the Valve chambers 55, have inlets 75 and 76, respectively. The ends of the first and third chambers 51 and 53, which are connected to the Adjacent second chamber 52 are connected to one another by an eccentric passage 78.

As can be seen from Fig. 3, the piston 56 is pressed by a spring 81 against a retaining ring 82 which is in a Groove of the housing sits and acts as a stop. The piston 56 moves during actuation, for example through the Pedal 42 (FIG. 2) back and forth, with the pedal acting on the piston via a locking piece 83 that absorbs an impact force and a spring 84 acts which is arranged between the locking piece 83 and the bottom of a central recess in the piston. A retaining ring 85 in a groove in the inner wall of the piston prevents the closure piece from becoming detached from the piston.

809831/0734

Midland-Ross Corp.

- 12 -

This configuration enables the piston to relate to the internal valve forces while in actuation Pedal as a function of the pedal pressure, exerted via the locking piece 83, to be discontinued. The outer surface of the piston 56 has two cylindrical sections of different diameters on, which are complementary to the axially spaced apart housing walls 57 and 87, so that the Piston can reciprocate in a precise axial movement, as required for good valve function. A seal with respect to the atmosphere occurs through the O-ring 88, which seals against the wall 57. The piston 56 has one seen in the axial direction inner conical section 98, the outer circular lip of which is so large in diameter that continuous circular contact with the annular surface 81 of the valve member 60 is possible. As shown in Fig.

it can be seen that the first valve member 60 is held pressed against the seat 61 by a spring 92 in the non-actuated position, which under compression in the valve chamber 52 between an annular flange 93 of the valve body, which with a resilient Material is covered, and an annular body 94 is supported, which is fixed to the housing by a snap ring 95.

The piston 64 is pressed by means of a spring 97 in the direction of the valve chamber 52 against the frustoconical section 89 of the piston 56 as a stop , 6 mm, as the gap between the end lip of the frustoconical shoulder 89 and the surface 91 of the valve member 60. This ensures that the air pressure can enter the pressure delivery chamber 51, starting from the valve chamber 52, when the valve member 60 from its seat 61 has lifted before any lifting of the second valve member 70 from its seat occurs.

809831/0734 bad - ^ ,: _A

Midland-RoGi Corp.

The valve member 70 generally has the same structural design as the valve member GO, although eo in terms of dimensions deviates. It has a flange 101, which is covered by a resilient material, and a cylindrical section ICZ, its outer jacket on an annular holder 10 ". guided i» "L, which is laid in the drainage part of the housing.

The discharge end of the valve is designed so that the pressurized air is rapidly released from the pressure discharge chamber 51 and the relay pressure chamber 52 can flow out, through the central openings in the valve members 60 and 7u and the second piston 64.

In operation daa pedal is depressed 42 and e ^ L-'cöRt while the closure member 80 j in dö.z interior of the piston 56. The piston moves into the housing and lifts the valve member 60 from its seat 61, so that the Compressed air, which is held ready in the reservoir 10, for example at 7 atm, can flow from the valve chamber 5 2 into the pressure delivery chamber 51 and from there, as shown in FIG. 2, acts on the brake units 6 of the front brake. The compressed air flows from the pressure delivery chamber 51 via the passage 78 into that part of the relay chamber 53 which is adjacent to the valve chamber 52. The piston of the relay chamber 5 2 moves against the force of the spring 97 until the skirt 67 hits the valve member 70. Now comes an essential aspect of the invention int. Clearance, since pressure has been developed behind the piston 64 or in the portion of the chamber 53 which is adjacent to the chamber 52 in order to lift the valve member 70 from the seat. This pressure is referred to as the initial pressure. It occurs simultaneously in the chambers 51 and 53 and has a value which is sufficient to overcome the friction of the piston 64 and the valve 70 with the respective surrounding walls and the compression forces of the springs 97 and 105 and to apply the force required is to lift the valve member 70 against the supply pressure of the chamber 55 from the seat, which acts on a cross-section that is

809831/0734

Kidland-Ro ζ ζ Corp

au ο the opening defined by the 3itz T. minus the cross-section. '. the outer cylindrical surface 10 2 de .: Ventilglieder- τ is circumscribed. In the event of a lack. v; r duck im Prirrn rat - .; section of the valve 40 v / the Ξ Relairabn chiiitt of the valve is actuated mechanically by the pedal, whereby the piston. 5 € then old: Intermediate actuation song for the 3-loading of the ram: · CS de. ^c : Relair piston CA works.

In formal operation the function dec Kclben is wrong; 56 and the associated Spring 81 and S4 r-o designed that the piston :: i re

U relative to the locking piece S1 depressed by the pedal can move back when compressed air enters through the opened valve hole in order to ^{build up a pressure in H} he chamber 51 to achieve the desired braking force. If the equilibrium between the pedal force on the connector 8 "and the counter

IS set pressure force is reached on the piston 55 brings the spring 84 the piston in a position back, in which the valve member 60 can be placed on the valve seat Gl, vo that the pressure stabilized both in the pressure release chamber 51 as in the relay pressure chamber 53rd

Since the gap 39 is smaller than the gap 98, causes the opening of the primary valve area on the seat 61 by the normal Pedal actuation does not prevent the relay valve on the seat from opening In principle, the relay valve area is not actuated until an initial pressure Pl (initial) in the relay pressure chamber 53, the on the cross-sectional area A2 within the outer diameter of the piston 64 in chamber 53 minus the cross-sectional area Al within the outer diameter of that part of the passage 66, which extends through the housing wall or the ring 94 between the chambers 52 and 5 3, over a measure that is sufficient to apply the required piston force to firstly increase the compressive force (Sa and Sb) of the Springs 97 and 105, secondly the friction F of the piston 64 and the valve member 70 on the adjacent cylinder walls and thirdly, the force [jP5 (A3 - A4) ^] to be overcome by the

809831/0734

Midland-Ross Corp.

supply pressure P5 in the fifth chamber 55 to a cross-sectional area which is equal to the cross-sectional area A3 of the opening within the seat 71 minus the cross-sectional area A4 i.; T, which is equal to that within a trancaxial cross section of the cylindrical section 102 dec valve member 70 is. The relation described above can be expressed in the following equation:

Pl (initial; -)

A2 - Al

The well-known common duo compressed air control valves are designed in such a way that that A3 is roughly equal to A4. As a result, the supply pressure factor PS (A3 - A4) drops out of the equation and the initial pressure for actuating the relay valve mechanism only has to overcome the friction and spring forces corresponding to those of the spring and 105. Usual valves of this type are through low Initial pressures, lower than 0.35 at, marked, and the output pressures of the relay sections run along a curve, which is closely parallel to the straight line curve M of FIG. 4, which is representative of the hypothetical situation that the pressures for the front and rear axles are the same in all operating levels of the brake system. Such print parallelism is then usually modified by the use of converter valves, which are usually in the pressure lines to the front axle, such as shown in Figs. 3 and 2 of U.S. Patents 3,776,602 and 3,776,603. The brake actuation is characterized by a low initial pressure, which is only a very minor difference in the initial pressure Brake operation or the brake operation with low braking force on both axles results.

However, it is now considered beneficial, one worth mentioning greater braking force on one axis than on the other in areas of low braking force, starting with zero pressure, to raise. The braking force should be applied to an axis through a

809831/0734

Xi d 1 an d-Ro r ε Co rp.

Beg ar. 3: .pressure (_P (initial) J can be applied, whereby the initial pressure can be up to 1.4 at. The invention is based on a Girier valve construction, with which the desired high initial pressure can be developed, which enables braking on a V. Ach: -e enables, before an initial pressure is exceeded, that & itr from which the 2 j. ent sen begins on the other axis. According to the invention, a valve construction is also provided in which the initial pressure difference between the two axes is gradually reduced, if the total braking force of the vehicle

Iv ge.-, is increased. If the braking force increased, the pressure difference can be brought to zero, and can take a negative or inverse difference value at high braking forces, such as with the curves N and Q _o in Fig 4 is illustrated. Points along each straight line in Fig. 4 have an abscissa value representing the pedal-induced pressure P1 in the primary portion of the valve. The ordinate values correspond to the pressures P? in the relay section of the valve.

The curves N and Q present the behavior of two different valves according to the invention with P (initial) values of

? ⁿ 0.7 and 1.4 at. Curve P shows the effect which occurs when the values Sa, Sb, or Sa + Sb of springs 97 and 105 are increased in a conventional valve. A valve with a corresponding curve P does not work satisfactorily because the increase in the spring strength does not bring the initially different pressures on the front axle and rear axle to be equal at higher braking forces.

According to the invention and as shown by curves N and Q, the difference in brake actuation pressures is reduced of the two axes of a maximum corresponding to P (initial) at low pressures to the value zero with a pressurization of 5.6 at on both axes. The curves N and Q also show that the actuation pressure of that axle, the pressure of which is lower in the lower braking force range, over the

809831/0734 L _n ^

LD QR

Mi d 1 an d- Ro <c r Co r ρ.

those of the axle initially working with higher brake pressure, still rises if the braking still rises above 5.6 at becomes when one has a maximum Bren> 3 pressurization based on 7 at or even more.

The valve 40 works after the brake system according to FIG. 2 without a converter valve, such as a valve 24 in the brake system 1. However, instead of the T-piece 109 in the vicinity of the front axle of the system according to FIG. 2, a quick relief valve can be used (not shown) may be provided. For the reasons described above, the valve 40 effects the unlimited pressure supply from the primary section of the valve to the Front axle, with a modification of the pressure for the rear axle and that is in the case of motor vehicle trains from towing vehicles and Trailer as well as some types of trucks driving without a trailer are desirable.

The relationship between those shown in FIG. 3 is important Cross-sectional areas Al, A2, A3 and A4, and thus naturally the corresponding diameter Dl, D2. D3 and D4.

Based on a construction example of a duo compressed air control valve 40, which can work with a storage pressure of 7 at and an initial pressure of 1 at, the the following relations proved to be suitable:

A3 - 2.86 χ A4; Al = 0.244 χ A4; A2 = 14.2 χ A4. The respective diameters of the cross-sectional areas A1, A2, A3 and A4 are Dl = 9.4 mm; D2 = 71.1 mm; D3 = 32 mm; D4 = 17.8 mm. The affected cross-sectional areas Al, A2 and A3

1 {

2 2 2 then have a cross-section of 68.4 mm, 3968 mm, 800 mm and 279 mm

Such a valve works according to a straight curve (not shown), which lies approximately in the middle between the curves N and Q of FIG.

809831/0734 ^;; "^^, v-

[-.! αϊanc- he 'l Ccr;

Jk, c "de ::; AL / jabc ^ rucic P ^, äi ~ o dem Ao-jaLedruck de ^ uL .-. Ir ^ itte ^ -Je: / entile:;, of In the Kcin.mer ^r M ent v.'ifd, ru c; ri:; 5rlichcr, rich I; ei lift orcn. ^ kr'ifttn Cr _{1 to} align the back P ^, i ^ ie £ ".'ichuig that the ott, ic, uric, the Vcntiikurvo greeter aio 1 i ~ h. Lie Kurv ·: - i: in i'ic ,. 1 dcjiiicrii.hiiei ύ • üi .. «- · Vcr.til kui; / c iL.it.! Er LLvL young" 1 .

'Jr: Li.r four Ari', a:; i: i-. , cla ^ dia xvurv ^ ri i; urid Q Lypi ^ ciie Veriauxskurvcfi IHi: i / rnblie ytmäii of the invention £> irid, becomes the primary branch of the, V -'- nLilC; nit an initial pressure P ^ (initial) before, "at betäirijt, the air to define that pressure ict, dtii, fall-; it is exceeded, the 3et Operation de ^r Relai ^ - abrchnitteo de ^ Venclles auclö-; t. He, then set the pressure value at which the pressures of both sections are equal to each other when the braking force is high. For several practical reasons, this pressure value is assumed to be 5.6 at, f, 6 at:; the pressures Pl and P2 are the same.

The assumption sine ;: cpesifischen initial pressure Pl (initial) of the pressure equalization point creates two points on the curve which define the slope of the curve on which the design of the valve? based on / can be grounded. The slope of a curve with an initial pressure of lat and a compensation pressure point at 5, G at is 1.? 3 _O The applicable equation based only on the initial pressure is approximately as follows:

Slope = - 1.23

The determining relation for the determination of the initial printing s pl (initial) is expressed by:

Sa + Sb + F + P5 (A3 - A4)

Pl (initial) =

A2 - Al

809831/0734 ^AL

Midland-Rorc Corp.

Invention ^ -according to i ': t A3 always bigger air A4. The values of (A3 - AA) can easily be calculated using these equations by choosing the quantity A? b2w _o D? can be found, such as fourth for D2 between 50 and 76 mm, var leads to a valve, wac corresponds to the practical spatial requirements within a truck, in which case D1 is kept sufficiently large, for example at values between G and 12 mm, in order to ensure a sufficiently unimpeded air flow through the diameter Dl o If the dimensions of A2 and Al have thus been determined, it is clear that the relationship between A3 and A4 is of decisive importance and can be increased or decreased by one, if desired greater or greater value for P1 (initial) to be obtained In order to increase the value P1 (initial), either the value of A3 can be increased or the value of A4 reduced, or both.

The importance of the foregoing is that two main factors are at work on the subject of the registration, firstly the amount of the initial pressure Pl (initial) and secondly

A2 - A1

the influence of the variable on determining a behavior curve for the valve, which curve has a slope greater than 1 Has.

The valve described above creates a dual air pressure control valve for vehicle braking systems, which is a desired

2 S can create patterns of pressure differences and pressure ratios in the low braking force range, without the use of a converter valve or other pressure reducing device. This also creates a brake system in which all pressure modulations between the front and rear axles are achieved with a single valve, namely the duo compressed air control valve in question.

_BATH ö

809831/0734

Blank

Claims (8)

Patent attorneys Dr. O. Loesenbeck Dipl.-Ing. Stracke ku, .md-pr, ^; Corp. Dipl.-Ing. Loesenbeck 4S Bielefeld, Herford * Strasse 17 P a t e η t a. η "> ρ i" ü c h 1. Duo compressed air control valve, characterized in that d = iß in the valve housing (46,47) in succession five coaxial chambers, - starting from the end of actuation to Compressed air discharge end of the valve are arranged, and κν / ar a first pressure release chamber (51) including an externally movable first piston (56), a second valve chamber (52), which includes a first valve member (60) which is normally resilient against a coaxial annular Valve seat (61) is pressed between the first and second chamber, this valve member (60) in the unactuated Position with a small gap distance (99) from the first piston (56) and can be moved away from the seat by this piston, and further a third relay pressure chamber (53) and a fourth pressure release chamber (54), the third and fourth chambers are partially defined by an inner cylinder wall (108) on which a second piston (64) reciprocally guided separating the third and fourth chambers with the piston (64) in the inoperative position toward is pressed onto the second chamber (52), and finally a fifth chamber (55) which has a second valve member (70) . takes, which is usually resilient against a coaxial annular Valve seat (71) is printed between the fourth and fifth chambers, the valve members and he second > The pistons are open in the middle of the air outlet end of the valve and a separate passage (78) connects those ends of the first and third chambers (51,53) which the ·· '"are adjacent to the second chamber (52) in such a way that the second piston (64) can be moved to and fro by variations in air pressure which are transmitted from the first chamber to the third chamber, further characterized in that the two pressure delivery- QRIGSNAL INSPECTED. ■. ■ 809831/0714 Midland-Ross Corp. chambers (51,54) each have an outlet (73,74) and the two valve chambers (52,55) have an inlet (75,76) and the second piston (64) has an axially central, open passage in its interior which is in open communication with the interior of the two valve members (60,70) is, which passage has an end surface in enclosing contact with a is to bring annular surface of the second valve member (70), but in the non-actuated position in one Gap distance (98) to it, the second valve member (70) being sealed with an outer cylindrical surface (107) a wall section (103) of the valve housing (47) is guided, which encloses the fifth chamber (55) and furthermore the second valve seat (71) has a larger diameter than the outer cylindrical surface (102), so that in operation a considerable initial pressure in the first and third chamber (51,53) can be generated before the pressure in the fourth Chamber (54) developed. 2. Valve according to claim 1, characterized in that the five chambers (51 to 55) through a central passage in the valve housing (46,47) are defined, the a number of cylindrical, mutually coaxial inner wall sections of different Having diameters defining the chambers in their named order. 3. Valve according to claim 2, characterized in that the first piston (56) in the first chamber (51) and reciprocating is guided in a sealed manner on the cylindrical wall (57) of the first chamber and resiliently by means of a spring (81) against a Stop (85) is held down, which is located near the actuating end of the housing (46). 4. Valve according to claim 1, characterized in that the end face of the central, axially open passage is annular. 809831/073 * Midland-Ross Corp. 5. Valve according to claim 1 or 4, characterized by a cross-sectional area Al, defined as the diametrical cross-section of the passage on its outer surface, which is slidably sealed on a wall of the housing between the second and the third chamber is guided through a further cross-sectional area A2, defined as the cross-section of the second Piston (64), a further cross-sectional area A3, defined as the cross-sectional area of the second valve seat (71), as well as a further cross-sectional area A4, defined as the diametrical cross-sectional area of the outer Cylinder surface (102) of the second valve member (70), A2 - Al where the size ■ is greater than 1 or an equivalent Incline unit. 6. Valve according to claim 5, characterized in that to create an initial pressure Pl (initial) from an AT in the first and third chambers A1 approximately equal to 0.244 A4, A2 approximately equal to 14.2 A4, A3 is approximately equal to 2.86 A4. 7. Valve according to claim 5, characterized in that the cross-sectional areas Al, A2, A3 and A4 in that order are 68.4, 3968, 800, and 279 in millimeter squares. 8. Valve according to claim 1, characterized in that the outlet (73) of the first pressure delivery chamber (51) in the primary section of the valve with the braking devices (6) of the front axle of the vehicle and the outlet (74) of the pressure delivery chamber (54) of the relay section of the valve is connected to the braking devices (21) on the rear axle of the vehicle. 809831/0714