Brake-Pressure Modulator Pilot Unit

Abstract

The invention relates to a valve control unit, made up of three valve units, preferably as a pilot unit (1) for two brake channels of an electropneumatic brake system, whereby each valve unit is embodied as a valve modulator device (7) for a braking pressure control circuit made up of an air inlet valve (22) with a primary solenoid (22a) and a bleed valve (23) with a secondary solenoid (23a), whereby each armature is provided with a common solenoid guide arrangement (10), controlled by the magnetic flux of a common magnetic coil (11). According to the invention, an independent operation of the armatures may be achieved, whereby, the flux through the secondary solenoid (23a) is weakened by a shunt (20) in the total magnetic flux circuit (3) which causes a switching delay for the secondary solenoid (23a) relative to the primary solenoid (22a) and, furthermore, the magnetic resistance of a non-magnetic disc (25) is effective for switch-off acceleration in the magnetic flux circuit (3) with energized secondary solenoid (23a), and weakens the field and causes the secondary solenoid (23a) to revert the spring-loaded base state thereof at a higher magnetic flux than the primary solenoid (22a).

Description

The invention relates to a valve pilot-control unit for a brake-pressure modulator.

From DE 100 09 116 A1 (hereinafter D1) there is known a valve device for the pilot-control unit of a brake-pressure modulator for an electronic air-brake system (EBS). As shown in FIG. 2 of that document, pneumatic circuit for the pilot-control unit of a brake-regulating loop of the brake-pressure modulator comprises a 3/2 solenoid valve (21) as a redundancy valve, a normally open 2/2 solenoid valve (22) as an air-admission valve and a normally open 2/2 solenoid valve (23) as a vent valve. As is known from the older DE 42 27 084 A1 (document D2, FIG. 2 therein), the redundancy valve in such circuit can also be used commonly for a second brake-regulating loop. According to this circuit layout, therefore, the pilot-control unit for two brake-regulating loops comprises one 3/2 redundancy valve for both loops and separate 2/2 vent valves and 2/2 air-admission valves for each individual loop. According to the prior art, a total of 5 solenoids is provided for actuating the respective armatures of these 5 solenoid valves. It is shown in FIG. 4 of D1 that the solenoid valves according to FIG. 2 can be constructed with only one sealing seat forming a hermetic seal, at which, while the solenoid is deenergized, an elastomeric insert (41) provided in the corresponding armature (39) is urged by the action of the solenoid restoring spring (40) against a first stroke limiter having a valve-sealing seat (31) (47 for valve 21 of 3/2 type, 43 for valve 23 of 2/2 type, no sealing seat corresponding to 45 for valve 22 of 2/2 type). Besides this sealing seat, the solenoid valves have a second position, in which the corresponding armature (39) is urged by the action of the magnetic force against a second stroke limiter (34), at which there is formed a detail metal valve seat (48 for valve 21 of 3/2 type, 46 for valve 22 of 2/2 type, no sealing seat corresponding to 44 for valve 21 of 2/2 type), which indeed does not seal the unavoidable leaks hermetically but because of the selected switching system has no significance for the operation of the brake-pressure modulator.

In DE-OS 24 03 770 (document D3) there are disclosed, for a hydraulic ABS solenoid valve, measures for influencing the magnetic forces, in order to obtain three stable and reproducible armature positions as a function of the magnet current, namely positions for the deenergized condition, the condition for an “exciter stage 1” and the condition for a “full exciter stage”. In the deenergized starting position of the solenoid valve, outlet valve (12/27) is closed and inlet valve (11/28) is open; thereby pressure source (3) is in communication with brake cylinder (2) and pressurization takes place in the brake cylinder. During energization corresponding to exciter stage 1, armature (13) travels a short distance and closes inlet valve (11/28), thus holding the pressure in brake cylinder (2). During energization corresponding to the full exciter stage, armature (13) is pushed up to spacer ring (16), outlet valve (12/27) opens and brake cylinder (2) is depressurized.

From WO 03/053758 (document D4) there is known a brake-pressure modulator for a trailer vehicle, wherein a pilot-control unit containing four valves in the form of one 3/2 “reservoir/venting” selection valve (110), one 3/2 redundancy valve (109) and two 2/2 modulator valves (106/107) is used for two different brake-regulating loops. In that document, therefore, the number of valves and thus also the number of valve magnets for two brake-regulating loops is reduced to four. However, the pilot-control circuit according to this document suffers from the disadvantage that it is not possible at any given instant to admit air via one of the two ducts while venting via the other. Instead, at all times it is only possible to admit air or vent via both ducts simultaneously. Consequently it is not possible to raise the pressure in one duct and simultaneously lower the pressure in the other duct, as would be highly advantageous for a flexible regulation strategy. A further disadvantage of this solution lies in the series connection of the valves, meaning that the achievable air flow is diminished and the effective nominal width of the pilot-control unit is reduced.

From DE 35 01 708 A1 (document 5) there is known an electromagnetically actuatable multi-way valve, in which two different valves, one of which is an inlet valve (9, 10) that can be actuated via a first armature (5) and the other is an outlet valve (23, 25) that can be actuated via a second armature (21), can be loaded by only one common coil (2). Armatures (5) and (21) are biased with restoring springs of different dimensions, one a weakly dimensioned restoring spring (13) for armature (5) and the other a strongly dimensioned restoring spring (17) for armature (21), so that they can be actuated independently of one another by controlling the current in coil (2). Basically, therefore, this valve can also be used as a combined air-admission/vent valve in a brake-pressure modulator. As explained in the following, however, the principle of different design of the restoring springs (13, 17) that underlies this valve for independent actuation leads to difficulties in valve design. The “weak” restoring spring must be able to overcome the gas force acting at inlet (9, 10) and it must therefore be strong enough that the restoring function for inlet valve (9, 10) is assured if the current fails. “Strong” restoring spring (17) must be strong enough that outlet valve (23, 25) is activated only at much higher magnet current than is the case for inlet valve (9, 10). The strong design of restoring spring (17) is therefore also limited by the force that the magnet can actually provide. To implement this principle, therefore, it is also necessary to provide a relatively large magnet with the necessary magnetic force. Besides causing higher manufacturing costs, such a magnet must be supplied with greater electrical power, which nevertheless does not lead to a satisfactorily short valve switching time, because of the increase of inertias related to structural size. In addition the choice of larger structural units works against the goal of producing compact devices.

The object of the invention is therefore to improve a valve control unit corresponding to the first-cited document with the goal of reduced manufacturing costs while maintaining a compact design, wherein two different brake-regulating ducts can be actuated independently of one another during application of the valve-control unit as a brake-regulating pilot-control unit.

This object is achieved by the invention specified in claim 1; improvements and advantageous practical examples of the invention are specified in the dependent claims.

The inventive valve control has the advantage of drawing low current, also resulting in the advantage of favorable heating behavior in the device. A further advantage of the invention is the reduced complexity of contacting and of electrical activation (number of needed end stages as well as associated components).

The invention will be explained in more detail hereinafter on the basis of a practical example, which is illustrated in the drawing, wherein:

FIG. 1 shows the pneumatic circuit of the inventive valve control device for two pressure-regulating loops, especially as a pilot-control unit for an electronic air-brake system (EBS);

FIGS. 2 to 8 show schematic diagrams of the respective switched conditions of the valves of the EBS pilot-control unit;

FIG. 2 shows the redundancy operation;

FIG. 3 shows air admission in EBS operation;

FIG. 4 shows pressure holding in EBS operation;

FIG. 5 shows venting in EBS operation;

FIG. 6 shows venting in anti-brake-lock operation (ABS operation);

FIG. 7 shows pressure holding in ABS operation;

FIG. 8 shows air admission in ABS operation;

FIG. 9 shows a combined sectional drawing of the constructional design of a valve-modulator device composed of one air-admission valve and one vent valve with one solenoid for both valves, and of a 3/2 redundancy valve;

FIG. 10 shows an individual sectional diagram of the valve-modulator device in its first embodiment according to FIG. 9;

FIG. 11 shows the explanation of a magnetic shunt in the valve-modulator device according to FIG. 10;

FIG. 12 shows a second embodiment of the valve-modulator device in the same type of diagram as FIG. 10;

FIG. 13 shows a third embodiment of the valve-modulator device in the same type of diagram as FIG. 10;

FIG. 14 shows a fourth embodiment of the valve-modulator device in the same type of diagram as FIG. 10;

FIG. 15 shows the circuit diagram of the magnetic loop for the valve-modulator device according to FIG. 10;

FIG. 16 shows the switching of the air-admission and vent valve of the valve-modulator device as a function of the magnet current flowing through the solenoid.

In all sectional diagrams of this drawing, the (non-ferromagnetic) parts that are not magnetically conductive are illustrated with cross hatching, so that they can be readily distinguished from the singly hatched magnetic parts.

To the extent technically appropriate, several reference numerals (1, 2, 4, 5, 6, 17, 18, 21, 22 and 23) are adopted from D4 for identification of devices having like effects.

FIG. 1 shows the inventive pneumatic valve control device, which in particular is used as a pilot-control unit (1) for an electronic air-brake system; it is capable of making a pilot-control pressure available for two different brake-pressure-regulating loops, designated as the first and second brake-pressure-regulating loops.

In this pilot-control unit, a 3/2 solenoid valve (21) with two inputs (4, 5) and one output (6) is used as the redundancy valve, while a first valve-modulator device (7) is used for the first brake-pressure-regulating loop and a second valve-modulator device (7′) is used for the second brake-pressure-regulating loop. In 3/2 solenoid valve (21) constructed as a redundancy valve, a supply pressure is applied at first input (4) and a redundancy pressure is applied at second input (5). As is standard in EBS systems, this redundancy pressure is generated with exclusively mechano-pneumatic means; if the pilot-control unit is used in a motor truck, the redundancy pressure is delivered by the operator-actuated motor-truck brake valve, while if the pilot-control unit is used in a trailer vehicle, the redundancy pressure generated in the motor truck is transmitted to the trailer via the yellow brake-pressure line (brake hose).

At least during application for EBS operation, one pneumatic output (8) of first valve-modulator device (7) is in communication with an input (17) of an air-flow-intensifying relay valve (2) for the first brake-pressure-regulating loop; in the same way, one pneumatic output (8′) of second valve-modulator device (7′) is in communication with an air-flow-intensifying relay valve (2′) for the second brake-pressure-regulating loop. The outputs (18, 18′) of relay valves (2, 2′) represent the fully developed brake pressures for the first and second brake-pressure-regulating loops respectively.

Because of the cost-effective construction of valve-modulator devices (7, 7′) explained hereinafter, pilot-control unit (1) can also be used advantageously for applications other than EBS regulation; for example, it can also be used in its basic design as an air-admission/venting device for the left and right air suspension springs of an electronically controlled air suspension system (ECAS). Hereinafter, therefore, the advantageous properties of pilot-control unit (1) will also be described as regards their general applicability.

According to FIG. 1, output (6) of 3/2 solenoid valve (21) is in pneumatic communication both with first valve-modulator device (7) for the first pressure-regulating loop and with second valve-modulator device (7′) for the second pressure-regulating loop. Second valve-modulator device (7′) is constructed identically to first valve-modulator device (7), and so it will be sufficient to explain its design hereinafter on the basis of first valve-modulator device (7), by means of the explanations for drawings 9 to 14.

Each valve-modulator device (7, 7′) is composed of a first normally open 2/2 solenoid valve (22, 22′) as an air-admission valve and of a second normally closed 2/2 solenoid valve (23, 23′) as a vent valve, these valves being in communication with one another via an internal connection (9, 9′).

As shown in FIG. 10, armatures disposed in a common armature-guide arrangement (10) for valve-modulator device (7) and loaded with respective springs (22f, 23f) are provided in the form of a first primary armature (22a) and a second secondary armature (23a) for first 2/2 solenoid valve (22) and second 2/2 solenoid valve (23) respectively, each armature being actuated by a common solenoid (11) provided for both solenoid valves, and at least secondary armature (23a) being equipped with an elastomeric insert (23e); in the embodiment according to FIG. 10, primary armature (22a) is also equipped with an elastomeric insert (22e). Primary armature (22a) is intended as a switching element for air-admission valve (22) and secondary armature (23a) is intended as a switching element for vent valve (23).

While solenoid (11) is de-energized, both primary armature (22a) of air-admission valve (22) and secondary armature (23a) of vent valve (23) are in their normal positions defined by spring loading (22f and 23f respectively).

If a magnet current I is injected into solenoid (11) by application of a voltage or current source, a magnetic force acts on both armatures as a function of the magnetic flux Φ flowing through the two armatures as a result of the magnetomotive force θ=w·I (where w is the number of turns). If the magnet current flowing through solenoid (11) reaches a first magnet current of defined magnitude I₁, primary armature (22a) of air-admission valve (22) is displaced into its switched position determined by the magnetic force, whereas secondary armature (23a) of vent valve (23) still remains in spring-loaded normal condition.

If the magnet current I flowing through solenoid (11) reaches a second magnet current of defined magnitude I₂, which is greater than the first magnet current I₁ by a defined amount, both primary armature (22a) of air-admission valve (22) and secondary armature (23a) of vent valve (23) are displaced into their switched positions determined by the magnetic force.

In the diagrams of FIG. 2 to FIG. 8, the switched conditions of the valves involved in the preferred application of the valve control unit as an EBS pilot-control unit are illustrated in highly schematic form, using the representation convention of FIG. 4 in D1; for clarity, only the functional elements for the first brake-pressure-regulating loop are illustrated, and the solenoids are omitted.

In the redundancy operation according to FIG. 2, 3/2 solenoid valve (21), first normally open 2/2 solenoid valve (22) and second normally closed 2/2 solenoid valve (23) are in their spring-loaded normal positions, and so the redundancy pressure present at first pneumatic input (5) of 3/2 solenoid valve (21) is transmitted to output (8) of valve-modulator device (7).

FIG. 3 shows air admission in EBS operation; during EBS operation, 3/2 valve (21) is in switched condition, so that the supply pressure present at second pneumatic input (4) is active. Second 2/2 solenoid valve (23) remains in its closed normal position, and first 2/2 solenoid valve (22) is opened; armature (22a) in its illustrated intermediate position indicates the usual “pulsing” during air-admission operation.

If a fully developed pressure is to be held in EBS operation, first 2/2 solenoid valve (22) moves from the switched position according to FIG. 3 to closed position(metal-to-metal sealing seat), as illustrated in FIG. 4, and so an effect of the pressure present at output (8) is no longer exerted via pilot-control unit (1).

For venting in EBS operation, 2/2 solenoid valve (23) is moved from the switched position according to FIG. 4 to open position, as illustrated in FIG. 5, usually also in pulsed manner.

For completeness, the valve positions for pure ABS operation are illustrated in FIG. 6 to FIG. 8; in ABS operation, the driver's intent, which is represented by the redundancy pressure, is active, and so 3/2 solenoid valve (21) remains in its spring-loaded normal condition: ABS venting according to FIG. 6 therefore corresponds to EBS venting according to FIG. 5 with switched 3/2 solenoid valve (21), ABS pressure holding according to FIG. 7 corresponds to EBS pressure holding according to FIG. 4 with switched 3/2 solenoid valve (21), and ABS air admission according to FIG. 8 corresponds to EBS pressure holding according to FIG. 3 with switched 3/2 solenoid valve (21).

In the further explanation hereinafter of the construction of valve-modulator device (7), reference will be made to FIG. 10, which shows a section B-B corresponding to the section direction illustrated in FIG. 9.

A solenoid holder (13) for common solenoid (11) is disposed on common armature-guide arrangement (10), and a U-shaped magnet yoke (14) is provided for generation of a strong magnetic field.

On common armature-guide arrangement (10) there is provided, in the region of primary armature (22a), a magnetic-field-concentrating yoke bush (15) of ferromagnetic material, which extends over a certain length region on an armature-guide tube (22r) provided for the primary armature (22a).

A magnetic-field-concentrating yoke bush (16) is also provided for secondary armature (23a), but this yoke bush (16), as shown in FIG. 10, extends over a greater length region on armature-guide tube (23r) provided for secondary armature (23a) than the length region of yoke bush (15) of primary armature (22a).

According to the invention, yoke bush (16) of secondary armature (23a), which is longer than yoke bush (15) of primary armature (22a), establishes a magnetic shunt connected in parallel with secondary armature (23a), as explained hereinafter.

To complete the magnetic loop, there is provided a magnet core (12), which is disposed immovably between air-admitting 2/2 solenoid valve (22) and venting 2/2 solenoid valve (23), and in which internal connection (9) has the form of a bore. A nonmagnetic disk (25) of nonmagnetic material is provided in magnet core (12), at the end thereof directed toward 2/2 solenoid valve (23).

In FIG. 10 there is also shown a plurality of O-rings, which will not be identified in further detail, and which are used for mutually sealing pressure spaces in valve-modulator device (7).

The construction of pilot-control unit (1) with 3/2 solenoid valve (21) and valve-modulator device (7) is illustrated in FIG. 9 as Section A-A, which corresponds to the section direction shown in FIG. 10. As illustrated in FIG. 9, armatures (21a, 22a, 23a) are identical, and this represents a preferred embodiment.

By analogy with DE 101 13 316 A1 (document D6), these identical armatures (21a, 22a, 23a) are advantageously constructed as small armatures with an approximate weight of only 6 g, wherein the metal body of the armature is completely coated with PTFE plastic and the elastomeric sealing element is indeed attached by simplified vulcanization without coupling agent, although this sealing element is joined interlockingly to the metal body of the armature by an undercut.

Similarly, it is also advantageous to construct common solenoid (11) of valve-modulator device (7) such that it is identical to solenoid (27) of 3/2 solenoid valve (21).

A comparison of the two valve units (21, 7) reveals the different configurations of the yoke bushes:

• • Yoke bush (28-1), disposed on armature-guide tube (21r) of 3/2 solenoid valve (21), is constructed such that it is equal in length to yoke bush (15) on armature-guide tube (22a). Yoke bush (28-2), as the counterpart at the lower end of U-shaped magnet yoke (29) of 3/2 solenoid valve (21), is identical in length to yoke bush (28-1). Compared with magnet yoke (28-2), however, as explained hereinabove, yoke bush (16) at the lower end of U-shaped magnet yoke (14) of valve-modulator device (7), as the counterpart for yoke bush (15) disposed on armature-guide tube (22r), is of considerably longer construction.

In implementing the magnetic shunt for secondary armature (23a) according to FIG. 10, armature-guide tube (23r) provided for this armature is made of nonmagnetic material such as non-rusting steel, as indeed are the other armature tubes (22r and 21r).

As illustrated in FIG. 11, a magnetic flux Φ₁ is generated in primary armature (22a) of valve-modulator device (7) by the above-explained magnetomotive force θ, which is generated on the basis of the current I flowing through solenoid (11); a component Φ_N of this flux is branched off by a magnetic shunt of secondary armature (23a), so that in this armature there is active a flux Φ₂ that is smaller than Φ₁ by shunt component Φ_N: Φ₂=Φ₁−Φ_N   (1)

For switching to occur, the magnetic-force-determining flux Φ₁ is controlling for primary armature (22a) and flux Φ₂ is controlling for secondary armature (23a); an armature (22a, 23a) changes over from its respective normal condition to its switched condition whenever the magnetic force acting on it exceeds the force of its restoring spring (22f, 23f).

For explanation of the magnetic shunt, the three-dimensional magnetic field in FIG. 11 is illustrated in simplified and schematic form as a magnetic-flux loop (3), comprising firstly a main path (19), namely the path for the flux Φ₂ that is active in secondary armature (23a), and secondly a shunt path (20), which forms the magnetic shunt and through which flux Φ_N passes.

In magnet core (12), the flux Φ₁ introduced by primary armature (22a) is split into fluxes Φ₂ and Φ_N at branch point (26), where a first common magnetic path with unattenuated flux Φ₁ is followed in magnet core (12) by a second magnetic path comprising part of the magnetic main path (19) and having attenuated flux Φ₂, while a third magnetic path comprising part of magnetic shunt path (20) and having shunt flux Φ_N is established in magnet core (12), in parallel with the second magnetic path.

The flux Φ_N that is active in shunt path (20) represents, according to the invention, the desired cause of the aforesaid switching threshold increase ΔI necessary for switching secondary armature (23a). To obtain a switching threshold increase ΔI, which is usually predetermined in the valve design of valve-modulator device (7), the shunt-path flux Φ_N together with the flux Φ₁ can therefore be established by primary armature (22a), by defining the magnetic resistances involved.

FIG. 15 a shows the equivalent circuit diagram of magnetic flux loop (3) with main and shunt paths (19, 20) according to FIG. 11, with the magnetic-flux-generating magnetomotive force θ, the magnetic fluxes Φ₁, Φ₂ and Φ_N, and what for the time being are generally assumed magnetic resistances R_A, R_B and R_C.

The explained fluxes can be determined by application of Kirchhoff's rules to the equivalent circuit diagram according to FIG. 15a; the unattenuated flux Φ₁ through primary armature (22a) is given by: $\begin{array}{cc}{\Phi }_1=\frac{\Theta }{R_A+\frac{R_B·R_C}{R_B+R_C}}& \left(2\right)\end{array}$

The attenuated flux Φ₂ through secondary armature (23a) is given by: $\begin{array}{cc}{\Phi }_2=\frac{\Theta }{\frac{R_A}{R_C}·\left(R_B+R_C\right)+R_B}& \left(3\right)\end{array}$

The shunt flux Φ_N is given by: $\begin{array}{cc}{\Phi }_N=\frac{\Theta }{\frac{R_A}{R_B}·\left(R_B+R_C\right)+R_C}& \left(4\right)\end{array}$

As shown in FIG. 15b, the magnetic resistances R_A, R_B, R_C represent series connections of magnetic resistances of individual mechanical devices according to FIG. 11, and by suitable dimensioning of these devices it is then possible, according to equations [2] and [3], to establish the magnetic fluxes Φ₁ and Φ_N necessary for the desired current I₁ for switching primary armature (22a) and for the switching threshold increase ΔI for switching secondary armature (23a).

According to FIG. 15b, the magnetic resistance R_A then represents the series connection of the magnetic resistances of the following mechanical devices according to FIG. 11 in the common magnetic path through which the flux Φ₁ is passing:

• • R₁ (R1) magnetic resistance of U-shaped magnet yoke (14);
  • R₂ (R2) magnetic resistance of yoke bush (15) provided for primary armature (22a);
  • R₃ (R3) magnetic resistance of nonmagnetic armature-guide tube (22r) for primary armature (22a) and of the air gap to primary armature (22a);
  • R₄ (R4) magnetic resistance of primary armature (22a);
  • R₅ (R5) magnetic resistance of the air gap between primary armature (22a) and its metal-to-metal sealing seat on magnet core (12);
  • R₆ (R6) magnetic resistance of the first common magnetic path in magnet core (12) without field attenuation by magnetic shunt path (20).

Furthermore, the magnetic resistance R_B represents the series connection of the magnetic resistances of the following mechanical devices in magnetic main path (19) according to FIG. 11:

• • R₇ (R7) magnetic resistance of the second magnetic path in magnet core (12), which resistance is attenuated by magnetic shunt path (20);
  • R₈ (R8) magnetic resistance of the air gap between secondary armature (23a) and its metal-to-metal sealing seat on magnet core (12);
  • R₉ (R9) magnetic resistance of secondary armature (23a);
  • R₁₀ (R10) magnetic resistance of the air gap to secondary armature (23a) and of nonmagnetic armature-guide tube (23r) for secondary armature (23a);
  • R₁₁ (R11) magnetic resistance of yoke bush (16) provided for secondary armature (23a) along the magnetic path of the bush in radial direction.

Finally, the magnetic resistance R_C represents the series connection of the magnetic resistances of the following mechanical devices in magnetic shunt path (20) according to FIG. 11:

• • R₁₂ (R12) magnetic resistance of the third magnetic path in magnet core (12) for field attenuation by magnetic shunt path (20);
  • R₁₃ (R13) magnetic resistance of yoke bush (16) provided for secondary armature (23a) along the magnetic path of the bush in axial direction, as part of magnetic shunt path (20).

Resistances R₁ to R₁₃ explained on the basis of FIG. 15 are valid for the condition illustrated in FIG. 11, in which primary armature (22a) and secondary armature (23a) are respectively in their normal positions determined by spring loading. When magnet current I increases from zero, the flux Φ₁ in primary armature (22a) increases in accordance with these resistances until it reaches current I₁, whereupon primary armature (22a) switches and bears with its end face directed toward magnet core (12) to form a metal-to-metal seal therewith.

At this instant (see FIG. 15c), the magnetic air-gap resistance (R5) drops practically to zero, and this is associated with a considerable increase of the flux Φ₁. To prevent secondary armature (23a) from also switching as soon as the magnet current I₁ is reached, a part Φ_N of this increased flux Φ₁ is branched off via magnetic shunt path (20), so that the flux Φ₂ remaining in main path (19) is not yet sufficient that it also switches secondary armature (23a). By means of magnetic shunt path (20), therefore, the magnetic properties of secondary armature (23a) are reduced compared with primary armature (22a) in a very specific manner defined by the division of magnetic flux between resistances R_B and R_C.

It is only when the magnet current I is increased above the first magnet current I₁by the value ΔI, so that it reaches the second magnet current with defined magnitude I₂, that the flux Φ₂ through secondary armature (23a) is increased to the point that secondary armature (23) also changes over to its switched condition (see FIG. 15d).

During switching of secondary armature (23a), the magnetic air-gap resistance (R8) drops practically to zero, and without further measures the flux Φ₂ in secondary armature (23a) would jump abruptly, with the consequence that, to switch secondary armature (23a) back to its normal condition, such a large decrease of the magnet current would be necessary that it would also cause primary armature (22a) to switch back, and thus independent actuation of primary and secondary armatures (22a, 23a) would no longer be assured.

Such a flux increase during switching of secondary armature (23a) is prevented by nonmagnetic disk (25) with its magnetic resistance R₁₄, which is disposed in series with the resistance R₆ (see FIG. 15d).

However, this resistance is active only when secondary armature (23a) is switched, since when secondary armature (23a) is not switched the lines of force in the air gap between secondary armature (23a) and magnet core (12) are concentrated at the ferromagnetic surfaces of these units, so that nonmagnetic disk (25) is affected only by a negligible stray flux. The magnetic resistance R₁₄ (R14) of nonmagnetic disk (25) is therefore negligibly small when secondary armature (23a) is not switched; for this case it will be set equal to zero and not considered further.

When the magnetic resistance R₈ of the air gap between secondary armature (23a) and magnet core (12) itself drops to zero during switching of secondary armature (23a), however, the conditions are changed: while secondary armature (23a) is bearing on magnet core (12), only one part of the secondary armature (23a) is in contact with magnet core (12) via direct iron-to-iron contact with good field transfer, whereas the other part of secondary armature (23a) is in contact with magnet core (12) indirectly via the end face of nonmagnetic disk (25). In the equivalent circuit diagram according to FIG. 15d, the magnetic resistance R₁₄ of nonmagnetic disk (25) is now active as a series resistance between resistances R6 and R7, whereupon the total resistance of magnetic-flux loop (3) is artificially increased, thus preventing a sudden increase of the flux Φ₂ through secondary armature (23a).

The switching of primary armature (22a) and secondary armature (23a) as a function of the magnet current I is illustrated in FIG. 16. As explained, primary armature (22a) switches when the magnet current I reaches at least the first magnet current I₁, and it changes over to its normal condition when the magnet current has dropped to at least a third magnet current I₃. In contrast, secondary armature (23a) switches at a magnet current of at least the second magnet current I₂ and it returns to its normal condition when the magnet current drops to at least a fourth magnet current I₄. As shown, the fourth magnet current I₄ is much larger than the third magnet current I₃, and so the switching ranges for primary and secondary armatures (22a, 23a) are substantially separate from one another. The sharpness of separation for actuation of the two armatures is achieved according to the invention by the explained two measures: The magnetic shunt path is controlling for the “retarded” forward switching of the secondary armature (I₂>I₁), and the nonmagnetic disk is controlling for the “advanced” backward switching of the secondary armature (I₄>I₃). It must be added that it is possible under certain circumstances to make the magnetic shunt flux so high that advanced backward switching of secondary armature (23a) is also achieved, in which case there is no need to incorporate nonmagnetic disk (25).

In the further embodiments of a magnetic shunt for secondary armature (22a) according to FIGS. 12 to 14, the shunt is generated not by changing yoke bush (16) for secondary armature (23a) but by changing armature-guide tube (23r) itself; in these configurations, therefore, yoke bush (16) for secondary armature (23a) is made such that it is identical to the “normal” construction (15 and 28-2).

In the embodiment according to FIG. 12, the armature-guide tube is made partly of ferromagnetic material in order to establish the magnetic shunt for secondary armature (23a); it is composed of a first ferromagnetic part (30) and a second nonmagnetic part (31), and the one-piece armature-guide tube (23r) is formed from the first and second parts.

In the embodiment according to FIG. 13, armature-guide tube (23r) for secondary armature (23a) is made completely of ferromagnetic material.

Finally, in the embodiment according to FIG. 14, the actual armature-guide tube (23r) for secondary armature (23a) is formed as a hollow-cylindrical extension of magnet armature (12) disposed immovably between primary armature (23) and secondary armature (23a); spring-holder attachment (32), which is made of nonmagnetic material and joined to armature-guide tube (23r), alternatively can also be made of magnetic material.

Claims

1. A pneumatic valve control device with the following features: a) a 3/2 solenoid valve (21) with two inputs (4, 5) and one output (6) is provided; b) the output (6) of the 3/2 solenoid valve (21) is in pneumatic communication with a first valve-modulator device (7) for a first pressure-regulating loop and with a second valve-modulator device (7′) of design identical to that of the first valve-modulator device (7) for a second pressure-regulating loop; c) each valve-modulator device (7, 7′) is composed of a first normally open 2/2 solenoid valve (22, 22′) as an air-admission valve and a second normally closed 2/2 solenoid valve (23, 23′) as a vent valve; d) armatures disposed in a common armature-guide arrangement (10) of the valve-modulator device (7) and loaded with a spring (22f, 23f) are provided in the form of a first primary armature (22a) and a second secondary armature (23a) for the first 2/2 solenoid valve (22) and the second 2/2 solenoid valve (23), each armature being actuated by a common solenoid (11) provided for both solenoid valves, and at least the secondary armature (23a) being equipped with an elastomeric insert (23e); e) the primary armature (22a) is intended as a switching element for the air-admission valve (22) and the secondary armature (23a) is intended as a switching element for the vent valve (23); f) when the solenoid (11) is de-energized, both the primary armature (22a) of the air-admission valve (22) and the secondary armature (23a) of the vent valve (23) are in their normal positions defined by the spring loading; g) by injecting a first magnet current of defined magnitude (I1) flowing through the solenoid (11), the primary armature (22a) of the air-admission valve (22) is displaced into its switched position determined by the magnetic force, while the secondary armature (23a) of the vent valve (23) remains in spring-loaded normal condition; h) by injecting a second magnet current of defined magnitude (I2) flowing through the solenoid (11), which current is greater by a defined amount (ΔI) than the first magnet current (I1), both the primary armature (22a) of the air-admission valve (22) and the secondary armature (23a) of the vent valve (23) are displaced into their switched positions determined by the magnetic force; i) the primary armature (22a) and the secondary armature (23a) are disposed in a common magnetic flux loop (3), in which the magnetic flux is generated by the magnet current (I) flowing through the solenoid (11) and in which the magnetic flux (Φ2) in the secondary armature (23a) is reduced compared with the magnetic flux (Φ1) in the primary armature (22a).

2. A valve control device according to claim 1, characterized in that, by lowering a magnet current flowing through the solenoid (11) from the magnitude of the second magnet current of the defined magnitude (I2) to a third magnet current with the defined magnitude (I3), the secondary armature (23a) of the vent valve (23) is displaced into its spring-loaded normal position, while the primary armature (22a) of the air-admission valve (22) remains in its switched position determined by the magnetic force.

3. A valve control device according to claim 1 or 2, characterized in that both the primary armature (22a) and the secondary armature (23a) are provided with an elastomeric insert (22e, 23e) and the two armatures are constructed such that they are identical to one another.

4. A valve control device according to at least one of claims 1 to 3, characterized in that it is intended as a pilot-control unit (1) for two brake-pressure-regulating loops, in the form of a first and a second brake-pressure-regulating loop of an electronic air-brake system, wherein the 3/2 solenoid valve (21) is constructed as a redundancy valve, and a supply pressure is applied at the first input (4) of the 3/2 solenoid valve (21) and a redundancy pressure is applied at the second input (5) of the 3/2 solenoid valve (21).

5. A valve control device according to one of claims 1 to 4, characterized in that the reduction of the magnetic flux (Φ2) in the secondary armature is achieved by a magnetic shunt (20) connected in parallel to the secondary armature (23a).

6. A valve control device according to one of claims 1 to 4, characterized by the following features: a) on the common armature-guide arrangement (10) of the valve-modulator device (7) there are provided, in the region of the primary armature (22a) and in the region of the secondary armature (23a), magnetic-field-concentrating yoke bushes (15, 16) of ferromagnetic material; b) to achieve the magnetic shunt, the yoke bush (16) provided for the secondary armature (23a) on an armature-guide tube (23r) for the secondary armature (23a) extends over a greater length region than the length region of the yoke bush (15) for the primary armature (22a) on an armature-guide tube (22r) for the primary armature (22a).

7. A valve control device according to one of claims 1 to 5, characterized in that, to achieve the magnetic shunt, the armature-guide tube (23r) provided for the secondary armature (23a) is composed at least partly of ferromagnetic material.

8. A valve control device according to one of claims 1 to 5, characterized in that, to achieve the magnetic shunt, the armature-guide tube (23r) provided for the secondary armature (23a) is constructed as a hollow-cylindrical extension of a magnet armature (12) disposed immovably in the common armature guide arrangement (10) between the primary and secondary armatures (22a, 23a).

9. A valve control device according to at least one of the preceding claims, characterized by the following features: a) in the common armature guide arrangement (10) of the valve-modulator device (7) there is provided, between the region of the primary armature (22a) and the region of the secondary armature (23a), the magnet core (12) of ferromagnetic material joined immovably to the armature guide arrangement (10); b) on the end of the magnet core (12) directed toward the secondary armature (23a), there is provided a nonmagnetic disk (25) of nonmagnetic material.