Brake pressure control device.

The invention relates to a device for controlling the brake pressure for a by a tractor drawn trailer vehicle according to the preamble of claim 1.

Such a device is previously known from DE-OS 33 38 690th With the known device it is achieved that during a braking operation which is triggered by an actuation of the brake valve of the towing vehicle, in the braking device of the trailer brake pressure develops which leads the brake pressure of the towing vehicle in time. Characterized the tractor vehicle and the trailer vehicle is kept in stretched condition during a braking operation.

The prior art device employs a valve means with two series-connected control piston and with two acting on a control piston acting surfaces that are offset in time by a respective control circuit with its own source of pressure medium and controlled independently of each other. The leading control circuit which initiates a time-leading braking of the trailer before towing vehicle is powered by a source of pressurized fluid to a predetermined and constant pressure as possible so that repetitive braking operations with consistent action can be initiated.

An adaptation to the different movement rate of the mechanical actuators of the braking device of the trailer as well as a universal use of the known valve device in various trailers and brands, each with different mechanical force for initiating a braking operation may with the prior art device only by using expensive means such. B . a controllable pressure relief valve in the control circuit leading be achieved downstream of the prior art valve means.

The invention is therefore based on the object to improve a device of the aforementioned type so that the be introduced braking force in its height, in particular to the respective to be overcome mechanical resistances as well as restoring forces of the braking elements of the trailer can be adapted by the leading control circuit in the trailer braking device ,

This object is achieved by the described in claim 1 invention. Further developments and advantageous embodiments are indicated in the dependent claims.

The invention has the advantage that the effective in the braking device of the trailer leading braking force according to the individual braking of the train set in a simple manner is nachregulierbar while driving.

The invention will be explained in more detail using an exemplary embodiment which is illustrated in the drawing.

The drawing shows a dual-circuit means for controlling the brake pressure for a by a tractor drawn trailer vehicle.

Serving as a trailer control valve valve device (1) comprising a housing (2) is connected via a pressure medium connection (3) and a pressure medium line (4) to a brake valve (5). A with a pressure medium line (6) connected to the pressure medium source is connectable via the brake valve (5) to the line (4) and via a line (7) to the braking device of the towing vehicle.

A pressure medium connection (8) of the valve device (1) is connected via a pressure medium line (9) with a directional control valve (10), via which the pressure medium connection (8) either via a pressure medium line (11) with a pressure medium source or to an outlet (12) for atmosphere is connectable. The directional control valve (10) is electrically switchable. A switching device (13) which is connected via an electrical line (14) with an electrical control input (15) of the directional valve (10) is switchable in dependence on the position of an actuating element (16) of the valve device (1).

The pressure medium connection (8) opens into a pressure medium chamber (17), which is delimited by an annular effective surface (18) of a control piston (19). Under the action of a pressure medium in the pressure medium chamber (17) of the control piston (19) is ä- against the force of a restoring spring (20) up to a stop (21) of the housing (2) slidably.

The pressure medium connection (3) opens into a pressure medium chamber (22), which is delimited by the active surface (23) of a control piston (24). The control pistons (24 and 19) are arranged telescopically and relative to one another. A spring (25) supported on one side on a broken piston surface (26) of the control piston (19) and via a spring plate (29) and a set screw (28) on the control piston (24) from. The control piston (24) rests by the force of the spring (25) having a portion of its action face (30) on a stop (31) of the control piston (19). The control piston (19) and (24) are biased against each other by the spring (25). The power of this tension can be adjusted by the adjusting screw (28).

The control piston (24) has an extension (32) which is longitudinally displaceable with a sealing surface (33) of in the housing (2) the valve body (34) forms an outlet valve (32, 33), over a chamber (37) via a AuslaÅ (41) is connectable with the atmosphere. The sealing surface (33) forms with a Ventilstiz (35) an inlet valve (33, 35) which in the rest position by the housing (2) on the one hand and on the valve body (34) on the other hand, supporting spring (36) is held in the closed position. Below the control piston (19) and (24) is the chamber (37) which is connected via a housing-outlet (38) with the braking system of the trailer. The chamber (37) is 20 through the inlet valve (33, 35) connectable to a chamber (39) via a housing-fixed inlet (40) is connected to a pressure medium source, which serves as a pressure medium supply for the braking device of the trailer vehicle.

The pressure medium chamber (22) with the first control piston (24) in communication with said brake valve (5) comprises a first control circuit, with which the braking force of the trailer vehicle can be controlled. The pressure medium chamber (17) with the second control piston (19) in connection with the directional control valve (10) a second control circuit with which, leading in front of the first control circuit, the braking device of the trailer vehicle at a predetermined pressure of the pressure medium is acted upon.

The pressure medium chambers (17, 22 and 37) are permanently sealed against each other, so that in the various possible working positions of the valve device (1) there is no exchange of pressure medium between these chambers.

The operation of this device is as follows:

The operation of the brake valve (5) triggers a braking operation in the interconnected brake systems of the tractor and of the trailer vehicle by the to the pressure medium line (6) connected to the pressure medium source via the pressure medium line (7) to the braking device of the towing vehicle and via the pressure medium conduit (4) and the valve device (1) is connected to the braking device of the trailer. The position of the actuating element (16) of the brake valve (5) takes place in accordance to brake the towing vehicle and the trailer vehicle more or less.

To achieve the towing time leading braking of the trailer, the braking system of the trailer is supplied with a time voreilendes pressure medium predetermined pressure. This causes also the mechanical part of the braking device of the trailer to the towing vehicle, leading activated, ie, that the friction linings of the brakes of the trailer vehicle in touch with the brake drums or rotors contact, but without the driving characteristics of the car train, particularly at the beginning of weak braking, is adversely affected inadvertently and undesirably.

At the start of a braking operation (16) a switching current is supplied through an initial stroke of the actuator, the switching device (13) is actuated and thus the electric Steueereingang (15) via the electrical line (14). In this way, the directional control valve (10) is switched from the basic position into the working position, whereby the pressure medium line (11) connected to the pressure medium source via the pressure medium line (9) and the fluid port (8) to the pressure medium chamber (17) is connected.

The application of the active surface (18) with pressure causes a displacement of the control piston (19) against the force of the return spring (20) toward the stop (21), until the control piston (19) on the stop (21) comes to rest. Still during the displacement of the control piston (19) of the extension (32) contacts the valve body (34), whereby in a further, joint displacement of the control piston (19) and the valve body (34) the inlet valve (32, 35) opens. In the chamber (39) pressure prevailing agent then enters via the opened inlet valve (32, 35) in the chamber (37) and via the outlet (38) of the braking device of the trailer is supplied. When the pressure medium entering the chamber (37), the said chamber (37) facing the effective surface (30) of the control piston (24) and which, however, negligible effective surface (31) of the control piston (19) as a stop for the piston (24 ) is acted upon with the prevailing in the chamber (37) pressure.

This results in a displacement of the control piston (24) within the control piston (19) in the closing direction of the inlet valve (32, 35) against the force of the spring (25) and in the direction of the force of the spring (36) until a state of equilibrium between the pressure of chamber (37) plus the force of the spring (36) on the one hand and the pressure of the pressure medium chamber (22) is made plus the force of the spring (25).

The above-defined equilibrium state causes the control piston (24) is lifted against the force of the spring (25) and the stop (31) in a position relative to the control piston (19) brought, in which the inlet valve (32, 35) the braking device of the trailer delivers a leading, predetermined brake pressure.

The height of the leading brake pressure can be regulated by the control piston between the first (24) and the second control piston (19) acting force of the spring (25) by the screw (28) is adjustable. Depending on the degree of bias of the spring (25) of the braking device of the trailer vehicle is through the inlet valve (32, 35), a pressure of predetermined amount is supplied in the so-called pilot phase.

Instead of only one screw (28) and a plurality of axially to the turns of the spring (25) acting adjusting screws can be used. Hereby, a, z. B. offset by manufacturing tolerances induced deviation of the spring force direction of the axis of symmetry of the spring (25) and thereby the responsiveness of the valve device (1) to be refined.

According to the constructive design of the valve means (1), the screw (28) or screws can also be arranged on the second control piston (19) with the effective direction of the first control piston (24).

The adjustment of the adjusting screw (28) is effected with a tool which can be passed through the outlet (41).

After passing through the switch (13) triggered activation of the braking device of the trailer vehicle is brought in a further stroke of the actuating element (16), the brake valve (5) in the open position. In this way, with the conduit (6) is connected to the pressure medium source via the pressure medium line (7) to the braking device of the towing vehicle and via the pressure medium conduit (4) and the valve device (1) connected to the braking device of the trailer vehicle. Depending on the position of the actuating element (16) the braking means of the towing vehicle and the trailer vehicle is supplied with a more or less strong braking pressure.

The via the pressure medium conduit (4) of the pressure medium chamber (22) pressure medium supplied causes a displacement of the control piston (24) towards the inlet valve (33, 35) so that the braking device of the trailer vehicle via the existing leading braking pressure addition, a continuously variable braking pressure is supplied.

Upon completion of the braking operation of the tractor and the trailer, the actuating member (16) moves back into the starting position. The to the pressure medium line (6) connected pressure fluid source is shut off relative to the pressure medium lines (4 and 7). The pressure medium lines (4 and 7) to be vented via the brake valve (5) into the atmosphere.

The pressure drop in the pressure medium chamber (22) of the control piston (24) acting pressure of the chamber (37) into a position in which the inlet valve (33, 35) travels through the to the active surface (30) is closed and the outlet valve (32, 33) is open. In the chamber (37) existing pressure medium is discharged through the outlet (41) into the atmosphere.

In the initial position of the actuating element (16) the current supply to the electrical control input (15) of the directional valve (10) is interrupted. The directional control valve (10) has assumed the initial position, in which the pressure medium chamber (17) is connected via the outlet (12) with the atmosphere. By the force of the return spring (20) of the control piston (19) has returned to the initial position. Thus also the braking process of the trailer vehicle is stopped.

Instead of the electrical switching device (13) can also be a pneumatic switching means are used, a pneumatic control input of the directional valve (10), a pressure medium, z. B. enclosed by the to the pressure medium line (11) pressure medium source, respectively.