GB2114245A - A pneumatic braking system for trailers - Google Patents

Abstract

The braking system for trailers (Figure 1) has pneumatic braking elements B and pneumomechanical elements B1-B2. The latter have chambers B which are pressurised to apply brakes and chambers B2 pressurised to hold off springbrakes and, are controlled by a valve device D having a shut off valve 31 operated by differential pressure between conduits 26 and 27 respectively upstream and downstream of service braking relay valve S. When, during service braking, the pressure in pneumatic chambers B1 of pneumomechanical elements B1-B2 reduces or disappears due to leakage, the valve 31 is operated to cut off the supply of pressure from parking valve C and discharge the spring chambers B2 of said elements B1-B2 to automatically provide for mechanical braking of the trailer. <IMAGE>

Description

SPECIFICATION Pneumatic braking system for trailers This invention relates to a pneumatic braking system for trailers or semitrailers of the type in which at least one braking section is fitted with pneumomechanical braking elements, that is elements of dual drive chamber, namely a pneumatic chamber and a spring chamber, both of which are normally under pressure.

In such systems, the pneumatic chambers are supplied during service braking on control of the foot distributor located on the towing vehicle (hereafter "tractor" for convenience), while the spring chambers are exhausted under control of a manual distributor located on the trailer for parking braking.

Therefore, by exhausting the spring chambers, said manual distributor will provide for parking braking, but not for emergency braking, or braking of running trailer, when for casual reasons the service breaking is inefficient due to lack or fall of pressure in the supply lines of the braking elements our failure in the servo-selfdistributor.

On the other hand, the spring chambers of the braking elements on the tractor are exhausted for emergency braking when service braking is inefficient and such braking is provided either by the driver's action through a manual cab distributor, or by automatic devices cutting off the driver's operation.

It is the object of the present invention to provide a pneumatic braking system for trailers or semitrailers in which provision is made for the latter to be automatically provided with emergency braking when service braking is inefficient.

According to the invention, a pneumatic braking system of the kind referred to is provided with a valving device with a changeover shut off valve controlling the supply to the spring chambers of the pneumatic braking elements, and the moving element of which is subjected to a differential pressure, for example as determined by the difference between the upstream and downstream pressures of the servo-selfdistributor, so that, during service braking, on reduction of the control pressure acting on the operating member of said changeover valve with respect to a predetermined value, shut off is automatically provided for the supply to the spring chambers of the pneumomechanical elements and discharge of said chambers, with resulting mechanical braking of the trailer.

According to a preferred embodiment of the valving device, said changeover shut off valve is inserted on the supply line to the spring chambers of the pneumomechanical braking elements and in series with the manual distributor for parking brak ing, and discharge of said spring chambers during emergency braking is carried out through said valving device.

The invention will now be explained with refer ence to the accompanying drawings which show by way of example a preferred embodiment of pneumatic braking system of this invention.

In the accompanying drawings: Figure 1 is a view schematically showing a pneumatic braking system for trailers provided with a shut off device according to the invention; and Figure 2 is a schematic axial sectional view of one type of shut off valving device useful herein.

In the schematic view of Figure 1, reference S designates the supply distributor during service braking for both the simple type of braking elements B and pneumomechanical type of braking elements B1-B2. Each of the latter comprise a pneumatic chamber B1, which is pressurized during such service braking, and a spring chamber B2, normally under pressure for holding the relative spring compressed.

Reference C indicates a manually operated distributor, which is normally open for supply to spring chambers B2. On the other hand, this distributor is brought to closed position for parking braking, which is obtained through discharge of spring chambers B2. so that the spring action is exerted on the brakes.

The system is integrated by coupling 5 connected pipings for automatic braking A and modulated braking M of the trailer with the corresponding pipings of the tractor, and a changeover shut off valve 6 connecting to servo-selfdistributor S or connection A through conduit 7, or manual distributor C through conduit 8. Two tanks 9 and 10, having a check valve 11 interposed therebetween, are connected to servo-selfdistributor S and manual distributor for supplying said pneumatic chambers 8, B1 and spring chambers B2, respectively.

Manual distributor C is actuated by the operator exclusively at stop condition of the vehicle, and such an actuation may occur with the trailer hitched to the tractor, or released therefrom.

Through conduit 12, such a distributor C is connected to tank 9 and when actuated, in addition to exhausting said spring chambers B2 of braking elements B1-B2, also allows supply for servo-selfdistributor S through valve 6, where the trailer is released from the tractor.

On the other hand, should the trailer be hitched to the tractor, valve 6 would shut off such a supply, since said servo-selfdistributor is already supplied through coupling 5.

Thus, when released from the tractor, such a trailer is automatically braked by the pneumatic brakes. Under such conditions, where said manual distributor C is actuated, pneumatic braking release is provided, since pneumatic chambers B and B1 are connected with exhaust, and at the same time parking braking is provided through the operation of springs of chambers B2.

Thus, said distributor C and changeover valve 6 also form a safety device inhibiting any simultaneous superposition of braking stresses.

Such conditions can be provided by known braking systems when the vehicle is in the stop condition. However, under conditions of normal running, exhaust of spring chambers B2 for the pneumomechanical elements cannot be carried out by such known systems, so that trailer braking is exclusively due to pressure action in pneumatic chambers of elements B and B1.

In order to provide for an automatic emergency braking of the trailer hitched to the tractor, at the step of service braking for the whole vehicle, when said trailer has failures in the conduits or in means controlling the supply for braking elements B and B1-B2, according to the invention the system is provided with a shut off valving device D. In the illustrated embodiment of the invention, such a device has four connectors 22, 23, 24 and 25.

Connectors 22 and 23 connect said device D to manual distributor C and chambers of elements B2, while connectors 24 and 25 connect said device respectively to supply conduits 26 upstream of servo-selfdistributor S and conduits 27 downstream of the latter.

Referring to Figure 2, device D comprises a changeover shut off valve 31 inserted between connectors 22 and 23 and a moving element 32 for controlling such a valve.

During service braking, said moving element 32 is subjected at one side to the pressure of a chamber D1 supplied by a reference pressure that in the example shown is the pressure of service braking upstream of the servo-selfdistributor, and at the other side to the pressure of a further chamber D2, supplied by a pressure to be controlled which, in the example shown, is the pressure of service braking downstream of the servo-selfdistributor.

In the presence of pressure in said chambers D1 and D2 and assuming that the pressure to be controlled in said chamber D2 corresponds to the predetermined normal value, as well as in the absence of pressures in said chambers, the above mentioned moving element 32 is at the position shown in Figure 2, and holds said changeover valve 31 at open position, so that connector 22 communicates with connector 23.

On the other hand, assuming that in chamber D2 the pressure has a value zero or anyhow lower than normal value, the pressure effect in chamber D1 is prevailing on the opposite pressure of chamber D2, so that said moving element 32 moves to the right, as seen in Figure 2, causing said changeover valve 31 to be closed, whereby shutting off the communication between connectors 22 and 23 and connecting the latter with the outside through outlet 35.

It will be appreciated from the foregoing that under efficient conditions for the system downstream of the servo-selfdistributor, said spring chambers B2 are maintained pressurized through connectors 22 and 23 and accordingly, during service braking, emergency braking cannot be carried out.

However, should such a portion of the braking system fail during service braking, owing to pressure fall in chamber D2 because of prevailing action of chamber D1, said moving element 32 will move with resulting discharge or exhaust of spring chamber B2 through connectors 23 and 35 and accordingly operation of emergency braking.

Hereinabove reference was made to shut off valving device D provided by a modulated servo switch. However, it will be apparent that such a device can be different in construction from that shown in the drawing, provided that its operation is based on a comparison between two pressures, namely a reference pressure and a pressure to be controlled or checked.

Moreover, the invention has been illustrated for the case where the pressure to be controlled or checked is the pressure referring to the portion of the braking system downstream of servo-selfdistributor S, but again it will be apparent that the pressure to be controlled or checked can be related to any other portion of the trailer braking system.

Thus, the actual constructional details of the braking system of this invention can be varied from those illustrated.

Claims (7)

1. A pneumatic braking system for trailers or semitrailers, provided with at least one braking section fitted with pneumomechanical braking elements, comprising pneumatic chambers and spring chambers, in which the pneumatic chambers are supplied by a servo-selfdistributor under the control of a distributor on the tractor, while the spring chambers are normally pressurized through a manual distributor on the trailer, characterized by a shut off valving device (D) having a changeover shut off valve (31) controlling the communication of the spring chambers (B2) of the pneumomechanical braking elements (B1-B2) either with the compressed air supply (9) or with the exhaust or outlet (35), and the moving element (32) of which is at one side (D1) subjected to a reference pressure, and at the other side (D2) to a pressure to be controlled or checked, so that during service braking, upon fall of the pressure to be controlled or checked (D2) relative to a predetermined value, supply shut off and exhaust of spring chambers (B2) of the pneumomechanical elements are automatically provided.

2. A pneumatic braking system according to Claim 1, characterized in that said reference pressure (D1) is the pressure upstream of the servo-selfdistributor (S), and the pressure to be controlled or checked (D2) is the pressure downstream of the servo-selfdistributor.

3. A pneumatic braking system according to Claim 2, characterized by means (26) for by-passing the reference pressure (D1) from the service pressure upstream of the servo-selfdistributor (S), and further means (27) for by-passing the pressure to be controlled or checked (D2) from the service pressure downstream of said servo-selfdistributor.

4. A pneumatic braking system according to any preceding claim, characterized in that a manual distributor (C) is connected in series to the changeover shut off valve (31) which is inserted in the supply line for the spring chambers (B2) of the pneumomechanical braking elements (B1-B2) and in that the exhaust of said chambers (B2) during emergency braking is carried out through the valving device (D).

5. A pneumatic braking system according to any preceding claim, characterized in that the moving element (32) of the changeover valve of the shut off valving device (D) is operatively connected with at least one piston, having the pressures by-passed upstream and downstream of the servo-selfdistributor (S) acting on the faces thereof.

6. A pneumatic braking system according to Claim 2, or any one of Claims 3-5 when appendant thereto, characterized in that said moving element (32) of the changeover valve comprises two tandem arranged spring pistons, of which one is integral with a perforated push rod of said changeover valve (31) and is under the action of the pressure upstream of the servo-selfdistributor (S), whereas the pressure downstream of said servo-selfdistributor is exerted on the opposite face of the second piston against the action of the relative springing means.

7. A pneumatic braking system substantially as hereinbefore described with reference to the accompanying drawings.