DE19855679A1 - Brake valve arrangement, e.g. for operating trailer braking systems, applies control pressure to regulating piston when defined braking pressure region is reached to reduce braking pressure - Google Patents

Abstract

The arrangement has a regulating piston (46) via which a brake connection (B) can be connected to a pump (P) or tank (T) connection and which is acted upon in the closing direction by a control spring (56) and in the opening direction by a regulating spring arrangement (60), whereby a pump (34) is driven depending on the braking pressure at the brake connection. A control arrangement applies a control pressure to the regulating piston when a defined braking pressure region is reached so that the braking pressure at the brake connection reduces to a level below the defined pressure region.

Description

The invention relates to a brake valve arrangement according to the preamble of claim 1.

Such brake valve assemblies are from the DE-PS 37 12 018 and DE-PS 37 37 579 are known and for example to control the braking system of trailers gladly used, which are attached to agricultural tractors.

A pressure on the brake circuit of the towing vehicle becomes common Usually used as a pilot print to brake the trailer control valve. In the well-known trailer brake valves The pilot pressure acts on a pilot piston that over Spring system on one end of a control piston of the Brake valve is supported. In the case of the aforementioned The disclosed brake valve assemblies is that Spring system preloaded in the valve housing.

DE 19 51 433 A1 describes an improvement of the described concept proposed, being instead of preloaded spring system (two single springs) one Spring without spring preload is used. Even through the Use of a single spring can remove the pressure medium from the pilot circuit at the maximum brake pressure (100 to 150 bar) can be kept to a minimum.

Fig. 1 shows in a very simplified form the Bremsan location of a trailer, which is controlled via the brake valve arrangements described above. Such brake systems are well known from the prior art, so that the following is limited to the description of the basic elements.

The brake system 2 shown in FIG. 1 of a trailer has a brake drum 4 , the brake shoes 6 of which can be brought into brake engagement by means of a lever mechanism 8 .

The lever mechanism 8 is actuated via a spring storage system 10 , via which three operating states can be realized, which are indicated in FIG. 1 by a) to c).

The brake valve arrangements described at the outset testify in the initial state, ie when the vehicle is not actuated and at idle speed of the hydraulic pump, a minimum pressure which is in the range between 8 to 18 bar, preferably 12 to 15 bar. This operating state is indicated in Fig. 1 with b).

If the trailer is suspended or if there is a fault in the hydraulic circuit, the brake pressure is below the specified range, ie 0 to 8 (12) bar. The na tional safety regulations require that the Anger engbremse engages when the brake pressure drops to the aforementioned level, so that the trailer is braked. This water operating state is shown in Fig. 1 with a).

When the brake of the towing vehicle is actuated, a brake pressure is built up via the brake valve arrangement, which is in the range between 18 bar and a maximum pressure, which can be, for example, 140 bar (c) in FIG. 1).

The spring storage system 10 thus has the task of controlling the brake drum in dependence on the aforementioned operating conditions. Such spring storage systems usually have a storage spring 12 which acts on a storage piston 14 which is in operative connection with the lever mechanism 8 . In the cup-shaped SpeI cherkolben 14 , a brake piston 16 is guided, which is biased via a control spring 18 (see Fig. 1b)) against the bottom of the SpeI cherkolbens 14 . The brake piston 16 acts directly or indirectly on the lever mechanism 8 , so that an axial movement of the storage piston 14 or the brake piston 16 can be converted into an actuating movement of the lever mechanism.

The accumulator piston 14 is guided in a spring accumulator housing 20 , on which an input connection 22 is formed, which is hydraulically connected to the output of the brake valve arrangement.

The spring rate of the accumulator spring 12 is such be considered that it is compressed in the pressure range between 8 and 18 bar on the accumulator piston 14, so that the accumulator piston 14 abuts an end stop. The brake shoes 6 are disengaged in this pressure range.

If the brake pressure falls below a minimum (in the range between 0 to 8 bar) at the input connection 22 , the storage piston 14 is moved to the left by the force of the storage spring 12 from the illustration according to FIG. 1b), so that the weak control spring 18 is compressed and the lever mechanism 8 is taken along and engage the brake shoes 6 of the brake drum 4 . That is, when the trailer is suspended from the towing vehicle or in the event of a fault in the system, the brake system 2 engages automatically due to the effect of the strong Speicherfe 12 .

When the brake of the towing vehicle is actuated, the brake pressure rises to the range between 18 to 140 bar (operating state c)), so that the accumulator piston 14 is brought into its end position. In this pressure range, the small brake piston 16 is moved against the force of the control spring 18 , so that it lifts off the bottom of the storage piston 14 and takes the lever mechanism 8 with it. The trailer is then braked depending on the applied brake pressure.

In the constructions described above, the parking brake function is realized in that a switching valve (not shown) is connected between the brake system 2 and the brake valve arrangement, which can be controlled via an electrical signal that is emitted when the parking brake is actuated or released. Ie when you press the parking brake or depend on the trailer, the Schaltven valve is switched so that the output of the Bremsventilanord voltage connected to a tank and the brake pressure at an input port 22 is reduced to the level shown in Fig. 1a) from.

When the parking brake intervention is released, the switching valve is returned to its basic position in which the output connection of the brake valve arrangement is connected to the input connection 22 of the brake system 2 .

A disadvantage of this construction is that the pressure medium has to flow through the switching valve switched between the brake valve arrangement and the brake system 2 , so that it must be designed with suitable flow cross sections in order to reduce the pressure losses to a minimum.

In contrast, the invention is based on the object to create a brake valve assembly with the minima all the safety radio equipment cations are achievable.

This task is accomplished with a brake valve assembly solved the features of claim 1.

The engagement of the brake system in the operating state shown in Fig. 1a) is made possible in that a control piston of the brake valve assembly is acted upon by actuating the parking brake with a control pressure which brings the control piston into a control position in which the brake pressure at the outlet of the brake valve assembly is reduced to the pressure level at which the braking system of the trailer engages automatically. Ie, this safety function is achieved according to the invention only by intervening in the control side of the brake valve arrangement, while in the aforementioned prior art an external switching valve had to be switched into the pressure medium circuit. The effort to implement the circuit can be significantly reduced by the measure according to the invention compared to the prior art.

The control piston is fiction, ge according to a control arrangement via which the control piston optionally with the tank pressure or the pressure in the range of one Pump connection of the brake valve assembly acted upon is.

A particularly simple control arrangement he stops if this is done with a 3-2-way valve is. This valve is preferably actuated via a control signal that occurs when the parking brake is applied is delivered.

The energy consumption of the entire brake system can be further reduced if, in the pressure range designated by c) in FIG. 1, the actual pressure at the brake device (8 to 18 bar) to the hydraulic pump is not reported, but a load pressure at a lower level, preferably a load pressure of 0 bar. This measure ensures that the stand-by pressure of the hydraulic pump is maintained. This means that the trailer brake pressure is only reported to the pump when the trailer is braked (in the pressure range between 18 and 140 bar).

This energy-saving function is made possible in a preferred embodiment of the invention by a way valve of the control arrangement, which connects the load pressure signal line to the hydraulic pump with the tank in a spring-loaded basic position. The control spring is designed such that the load pressure signaling line is only connected to the control line carrying the trailer brake pressure when the brake pressure reaches the level described in FIG. 1c).

The brake valve arrangement according to the invention is special simply constructed when the spring system is applied of the control piston the preload of 8 to 18 bar in the Ge achieved without additional components.

The operational security can be further increased if the brake valve assembly executed with two stops that limit axial movement of a spring plate, on which the spring system acts.

Other advantageous developments of the invention are the subject of further subclaims.

The invention will now be described more schematically Drawings explained in more detail. Show it:

Fig. 1 is a schematic diagram of the braking system of a trailer and

Fig. 2 is a circuit diagram of a brake valve assembly according to the invention for a trailer.

In Fig. 2, a longitudinal section of a Anhängerbremsven valve 30 is shown, the basic structure of which is already described in the aforementioned DE 195 14 733 A1 of the applicant. For the sake of simplicity, only the basic elements of the trailer brake valve 30 are explained below; for further details, reference is made to the disclosure of DE 195 14 733 A1, the disclosure of which is to be counted as that of the present application.

The trailer brake valve 30 has a valve housing 32 which is provided with a pump connection P, a tank connection T, a brake connection B and control connections W, X, Y and Z.

A pump, for example a constant pump with a downstream 3-way pressure compensator or a control pump 34, is connected to the pump connection P. The control pump 34 is associated with a control device 36 via which the pressure medium delivered by the control pump 34 can be supplied to a further consumer 38 or the trailer brake valve 30 . At the brake connection B, the brake system 2 described in Fig. 1 of a trailer, not shown, is closed.

The control pump 34 (or also a constant pump with pressure compensator) takes place in dependence on the load pressure at the consumer, ie in the present case on the brake pressure, which is tapped in the area of the brake connection B. In the circuit shown in FIG. 2, the load pressure is passed via a load pressure signaling line 40 to a pump controller 42 , via which the control pump 34 is controlled.

In the valve housing 32 of the trailer brake valve 30 egg ne valve bore 44 is formed, in which a control piston 46 is guided axially. The valve bore 44 has four axially spaced annular spaces 48 , 50 , 52 , 54 , the two annular spaces 48 and 54 being connectable to the tank T, while the two central annular spaces 50 , 52 are connected to the pump connection P and the brake connection B. .

In its position shown, the control piston 46 is acted upon by a control spring 56 and an intermediate booster piston 58 in the direction in which a control edge 60 of the control piston 46 opens the connection between the two annular spaces 52 and 54 , so that the brake connection B with the tank connection T connected is.

A control spring 60 acts on the control piston 36 in the opposite direction and acts on the control piston 46 via a spring plate 62 and is very rigid.

The control spring 60 is supported abge on a pilot piston 64 , on the back of which the pressure at the control port Y, ie the pressure in the pilot circuit acts.

In the embodiment shown in Fig. 2, the control spring 60 with a bias of about 8-18 bar, z. B. 16 bar in the valve housing, the ger geri than the control Δp of the pump 34 in the amount of z. B. is 20 bar. In the illustrated home position is the left end surface 66 of the pilot piston 64 at a distance from a radial shoulder 68 of the valve housing 32 is arranged so that the adjusting movement of the pilot piston is bounded 64 by emergence of the end face 66 to the radial shoulder 68th

The adjacent to the end face of the control piston 46 spring plate 62 is at a distance from a radial shoulder 70 of the spring chamber of the valve housing 32 angeord net. The movement of the spring plate 62 away from Ra dialschulter 70 is limited by a stop ring 72 which is inserted into a circumferential groove of the spring chamber.

The control connection Y is connected to the brake circuit of the towing vehicle, not shown, so that when a brake pedal 74 is actuated, a pilot pressure acts on the rear side of the pilot piston 64 .

The trailer brake valve 30 has to implement some safety and energy saving functions, the two control connections X and Z, via which the pressure in the annular space 50 or the pressure in the annular space 52 can be accessed as a control pressure.

The control connection X is connected via a parking control line 74 to the input connection of a parking valve 76 , which is designed as a 3-2-way valve. This is biased by a spring 79 into a switching position a, in which the parking control line 74 is connected to a control line 78 , which opens into the left-hand (view according to FIG. 2) annular space 48 via a control connection W.

When applying an electrical signal to a switching magnet 80 , the parking valve 76 is brought into the switching position b, in which the control line 78 is connected to a tank line 83 , so that the tank pressure prevails in the annular space 48 and thus the left end face of the control piston 46 is relieved .

The parking valve 76 assumes the switching position shown in FIG. 2 when the parking brake 82 is applied . The switching magnet 80 is de-energized. When the parking brake 82 is released, the solenoid is energized and the parking valve 76 is brought into the position designated b, in which the end face of the control piston 46 is acted upon by the tank pressure.

With regard to the effect of the parking valve 76 , reference is made to the following explanations.

The arrangement shown in Fig. 2 also has a directional control valve 84 , which is connected with its input port via egg ne brake pressure control line 86 to the port Z. In the basic position c shown, the input connection of the directional control valve 84 is blocked. The brake pressure control line 86 has a branch line 88 , via which the pressure at the control connection Z is guided to the end face of the directional control valve piston acting in the direction of the second switching position d of the directional control valve 84 . The Grundpo position c of the directional control valve 84 is determined by the action of a compression spring 90 , which only allows switching of the Wegeven valve piston 84 by pressure build-up in the branch line 88 when this switching pressure has exceeded the range indicated in FIG. 1. That is, the pressure force in the branch line 88 must, depending on the design, be greater than the pressure corresponding to the pretension of the control spring 60 . On the other hand, a force must be sufficient to switch over which corresponds to a switching pressure less than or at most equal to the control Δp of the pump 34 . With a 16 bar pre-tension of the control spring 60 and a pump Δp of 20 bar, the directional control valve 84 can thus be set to a switching pressure of 18 bar.

In the basic position c, the load pressure signaling line 40 is connected to a tank line 83 via a tank branch line 92 .

If the above-mentioned average pressure level is exceeded, the directional valve piston is brought into the switch position marked with d, in which a load pressure corresponding to the brake pressure is reported via the control connection Z, the brake pressure control line 86 and the load pressure signaling line 40 to the pump regulator 42 . That is, the stand-by pressure of the regulating pump 34 is only increased when the brake pressure has reached a level in which it can overcome the force of the compression spring.

It should be noted that the arrangement according to FIG. 2 can also be carried out alone with the parking valve 76 or with the directional valve 84 , ie the two valves 76 , 84 can be used independently of one another as a safety or energy-saving device.

For a better understanding of the aforementioned components be the function of the brake valve assembly in the following purifies.

When the trailer is coupled to the towing vehicle, the parking brake 82 is not actuated and the engine is running, the parking valve 76 is in its position designated b, while the directional control valve 84 is biased into the basic position c by the action of the compression spring 90 . The annular space 48 is connected to the tank via the control line 78 and the tank line 83 , so that no or a low control pressure acts on the left end face of the control piston 46 . In the load pressure reporting line 40 , the tank pressure is reported via the directional valve 84 , so that the control pump is operated with the stand-by pressure.

When the foot brake is not actuated, the trailer brake valve 30 generates a pressure which is in the middle pressure range according to FIG. 1. Ie the lever mechanism 8 of the trailer brake system 2 is in its basic position, the brake shoes 6 are not engaged.

If the parking brake 82 is now actuated, the switching magnet 80 is de-energized and the piston of the parking valve 76 is brought into the basic position shown by a by the action of the spring 79 , in which the parking control line 74 is connected to the control line 78 , so that the pressure at the pump connection P is guided into the annular space 48 . Then the control piston 46 together with the Regelfe the 60 is shifted to the right so that the connection between the pump connection P and the brake connection B controls and the connection from the brake connection B to the tank connection T is opened. The pressure at the Bremsan circuit B drops, so that the brake shoes 6 engage due to the action of the storage spring 12 and the trailer is braked. That is, the lower brake pressure is effected solely by engaging in the control of the control piston 46 , while in the prior art this was effected by actuating a downstream ex-directional valve through which the pressure medium flows. In the above-described operating state, the directional control valve 84 remains in its pretensioned basic position. The axial displacement of the control piston 46 is limited by the spring plate 62 running onto the stop 72 .

When the brake pedal 74 is actuated, the back of the pilot piston 64 is subjected to the pilot pressure, so that the control piston 46 is displaced to the left in the illustration according to FIG. 2 via the control spring 60 , the spring plate 62 and against the action of the control spring 56 . Since the spring rate of the control spring 60 is substantially greater than that of the control spring 56 , the control spring 60 is initially not compressed. This actuating movement of the control piston 46 controls the connection from B to T, while the connection from P to B is opened, so that the brake pressure at port B increases. This increased brake pressure is reported via the control connection Z and the branch line 88 to the directional control valve 84 , so that when the switching pressure of the directional control valve 84 is exceeded, the directional control valve piston is brought against the force of the compression spring 90 from its basic position c into the second switching position d. Ie when the brake pressure builds up at the brake connection B, this brake pressure is reported via the directional control valve 84 into the load pressure line 40 , so that the control pump 34 is controlled accordingly.

The brake pressure at the brake connection B is reported via a control line 94 in a spring chamber 96 of the control spring 56 , so that pressure builds up in this spring chamber 96 , which strikes the control piston 46 in the closed position. The position of the control piston 46 is then a function of the balance of forces between the one on the pilot piston 64 and the control spring 60 brought up pressure force and on the other hand the force of the Steuerfe the 56 and the control line 94 applied from the brake pressure resulting pressure force and Pressure in the annular space 78 . With increasing brake pressure, the control spring 60 is also compressed. When the brake valve 74 is actuated and the resulting increase in the brake pressure at port B, the directional control valve 84 remains in the switching position d, so that the control pump 34 is controlled as a function of the load pressure (brake pressure).

The arrangement according to the invention allows the trailer brake valve shown in FIG. 2 to be easily adapted to national regulations by optionally combining it with the parking valve 76 and / or the directional control valve 84 , so that a modular system is provided which can be used worldwide without major changes is.

Claims (10)

1. Brake valve arrangement with a control piston ( 46 ), via which a brake connection (B) can be connected to a pump connection (P) or a tank connection (T), and - based on the pump connection (P) - in the closing direction by a control spring ( 56 ) and in the opening direction can be acted upon by a control spring device ( 60 ), a pump ( 34 ) being controllable as a function of the brake pressure at the brake connection (B), characterized by a control arrangement ( 76 , 84 ) via which the pressure range when a predetermined brake is reached a control pressure can be applied to the control piston ( 46 ) such that the brake pressure at the brake connection (B) can be reduced to a level below the predetermined brake pressure range. 2. Brake valve arrangement according to claim 2, characterized in that the control arrangement has a parking valve ( 76 ) via which the control spring end face of the control piston ( 46 ) can be acted upon either with the tank pressure or the pressure in the region of the pump connection (P). 3. Brake valve arrangement according to one of the preceding Pa claims, characterized in that the parking valve is a 3-2-way valve ( 76 ) which is actuated electrically and / or elec tromechanically. 4. Brake valve arrangement according to claim 4, characterized in that an electrical signal of a parking brake ( 82 ) is used as a control signal for actuating the parking valve ( 76 ). 5. Brake valve arrangement according to claim 1, characterized in that a constant reference brake pressure to the pump arrangement is reported via the control arrangement ( 76 , 84 ) un below a predetermined braking limit pressure. 6. Brake valve assembly according to claim 5, characterized characterized in that the reference brake pressure is the tank pressure is. 7. Brake valve assembly according to claim 5 or 6, characterized in that the control arrangement has a Wegeven valve ( 84 ), the directional valve piston is biased by a pressure spring ( 90 ) into a basic position, and ent on its other end face with a brake pressure speaking control pressure is applied, the spring rate of the compression spring ( 90 ) is selected such that the directional valve piston can be brought from its basic position (c) to its second switching position (d) when the brake limit pressure is exceeded. 8. Brake valve arrangement according to claim 7, characterized in that the control pressure is tapped at the brake connection (B) and the directional valve piston in the basic position (c) a load signaling line ( 40 ) with the tank (T) and in the switching position (d) the load signaling line ( 40 ) with the brake connection (B). 9. Brake valve assembly according to one of the preceding Pa claims, characterized in that the control spring device ( 60 ) in its basic position with a bias of 8-18 bar in a valve housing ( 32 ) is taken up. 10. Brake valve arrangement according to claim 9, characterized in that the control spring device has a Regelfe ( 60 ) which is supported on a spring plate ( 62 ), the path of which is limited by two axially spaced stops ( 70 , 72 ).