GB2043188A

GB2043188A - Hydraulic trailer brake systems

Info

Publication number: GB2043188A
Application number: GB7943077A
Authority: GB
Original assignee: Fritzmeier AG
Current assignee: Fritzmeier AG
Priority date: 1978-12-13
Filing date: 1979-12-13
Publication date: 1980-10-01
Also published as: FR2443953A1; DE2853804C2; DE2853804A1; FR2443953B3; IT1127727B; IT7928069A0

Abstract

A trailer brake line 9 is pressurized through a control valve 5 operated by pressure in a line 10 connected to the tractor brake circuit. The trailer brake line can also be pressurised by means of a lever 18, which operates a valve 11 to by-pass the valve 5, by connecting supply line 12 to the brake line 6. Alternatively, the lever 18 may be connected to the spool of the valve 5, so as to open it when the control line 10 is unpressurized. <IMAGE>

Description

SPECIFICATION Hydraulic trailer brake system for commercial vehicles This invention relates to a hydraulic trailer brake system for commercial vehicles of the kind comprising a constant pressure circuit which is operated by an accumulator and which is adapted to be connected to the trailer brake cylinder via a brake valve actuated hydraulically by the towing vehicle footbrake.

Atrailer brake system of this kind is known (German Auslegeschrift 27 34 315) which can be actuated solely by the towing vehicle foot brake. For safety reasons, however, such hydraulic trailer brake systems should have a facility by means of which the trailer brake system can be actuated by means of the towing vehicle hand brake as well.

The object of the invention, therefore, is so to develop a hydraulic trailer brake system of the kind referred to hereinabove as to enable the system to be actuated by the towing vehicle hand brake as well.

According to the present invention there is provided a hydraulic trailer brake system for commercial vehicles, comprising a constant pressure circuit which is operated by an accumulator and which is adapted to be connected to the trailer brake cylinder via a brake valve actuated hydraulically by the towing vehicle foot brake, characterised in that a selector is connected in parallel with the brake valve and enables the brake cylinder to be connected to the accumulator or to the return of the constant pressure circuit and the hand brake lever of the towing vehicle enables the selector to be set to the accumulator by way of a spring against a stop, and to the return by means of the stop in opposition to the spring. In this construction, the trailer brakes are actuated when the hand brake is applied.If the trailer is to be uncoupled with the hand brake applied after leaving the towing vehicle, the pressure must first be released from the trailer brakes, and this is effected by means of the stop which, without influencing the position of the hand brake, enables the system to be set to the return against spring force and, after release, jumps back into the initial position by the action of the same spring, so that the "handbrake applied" condition is restored at the towing vehicle, while the trailer brakes are released and the trailer can be uncoupled after the brake system has been rendered pressureless.

The invention will be explained in detail hereinafter with reference to diagrammatic drawings of two exemplified embodiments.

Figures 1 and 2 are similar diagrams of two embodiments of a hydraulic trailer brake installation according to the invention.

Figures 1 and 2 show a detail of a brake installation for a trailer, the installation being independent of the brake system of the towing vehicle. A trailer brake system of this kind enables the trailer to be reliably braked even if the towing vehicle engine breaks down, for example.

The brake system comprises an accumulator 1 for pressure fluid and a constant pressure pump 2, which may be driven in any desired manner and which feeds the accumulator 1 and a supply line 4 with pressure fluid from a return flow reservoir 3.

The supply line 4 is also connected to the accumulator, so that pressure fluid at a constant pressure is always available on the supply line 4. The discharge of the pressure fluid is controlled by a directional valve 5, which has three positions A, B and C. The supply line 4 is shut off in the position A and a discharge line 6 of the directional valve is connected to a return line 7 leading to the reservoir 3. When valve 5 is in position B, the supply line 4, discharge line 6 and return line 7 are shut off. In position C of the valve 5 the return line 7 is shut off, while the supply line 4 and the discharge line 6 are interconnected. The discharge line 6 leads to a hydraulic coupling 8 between the towing vehicle and the trailer, to which a line 9 leading to at least one brake cylinder of the trailer is connected on the trailer side.

The directional valve 5 is actuated by a pressure transmitter, which is actuated by means of brake pedal (not shown) and which is connected via a control line 10 to the valve 5 which assumes one of its three positions A, B or C depending on the pressure head on the control line 10. To this extent the two embodiments shown in Figures 1 and 2 are identical.

In the case of Figure 1, the discharge line 6 contains a two-way valve 11 connected to the accumulator 1 via a bypass line 12. By means of a lever 13 the two-way valve 11 can-be brought into a position in which the discharge line 6 is directly connected to the bypass line 12, and into a position in which the bypass line 12 is closed and the discharge line 6 is connected to the reservoir 3 via the directional valve 5 in position A. The lever can be pulled into the solid-line position shown in Figure 1 via a cable 14, and a spring 15, using a hand brake (not shown) provided on the towing vehicle. In the solid line position shown in Figure 1 the bypass line 12 is short-circuited with the discharge line 6 and is under pressure.To allow the lever 13 to be brought into the broken-line position independently of the hand brake, so that the line 6 is connected to the reservoir 3, another cable 16 is provided and its end 17 acts as a stop for the position of the lever 13 when the hand brake is actuated and cable 16 can be pulled to the right in Figure 1 by means of a lever 18, in which case it pivots the lever against the spring 15 and into the broken-line position shown in Figure 1, in which the valve 11 opens to the reservoir 3. The cable 14 remains in the position illustrated in these conditions, while the lever moves to the right relatively thereto, the spring 15 being compressed. If the hand lever 18 is released, the lever 13 snaps back to the solid-line position shown.If the hand brake is not actuated, the lever 13 remains in the broken-line position by the action of a return spring 19.

In Figure 2, the selector for use of the hand brake is a mechanical element 20 by means of which the directional valve 5 can be mechanically moved, against the resistance of a return spring 21, out of the position A illustrated and into position C, in which the accumulator 1 is connected to the dis charge 6 via the supply. The mechanical element, which may be a push rod, is actuated by means of a lever 22, which is mounted pivotally at 24 in a housing 23 upstream of the directional valve 5, and which in its solid-line position illustrates the position with the hand brake released while the broken-line illustration shows the position with the hand brake applied. When it is pivoted out of the solid-line position into the other position, the return spring 21 is compressed against the housing 23. This lever 22 is again actuated by a cable system identical to that shown in Figure 1,so that like references have been used for like parts. If, in this case, the hand lever 18 is pivoted out of the solid-line position shown, into the broken-line position, the lever 22 is pivoted in the clockwise direction, so that the directional valve 5 assumes position A and the line 6 to the reservoir 3 is open.

The lever 18 is advantageously situated immediately next to the hydraulic coupling 8 to the trailer.

To release the coupling, the lever is simply pulled up, the coupling is released and then the lever is released and returns into the position imparted by the actuated hand brake.

Claims

1. A hydraulic trailer brake system for commercial vehicles, comprising a constant pressure circuit which is operated by an accumulator and which is adapted to be connected to the trailer brake cylinder via a brake valve actuated hydraulically by the towing vehicle foot brake, characterised in that a selector is connected in parallel with the brake valve and enables the brake cylinder to be connected to the accumulator ortho the return of the constant pressure circuit and the hand brake lever of the towing vehicle enables the selector to be set to the accumulator by way of a spring against a stop, and to the return by means of the stop in opposition to the spring.

2. A system according to claim 1, characterised in that the selector is a two-way valve which is disposed in the discharge line leading from the brake valve to the brake cylinder and which is connected directly to the accumulator via a bypass line.

3. A system according to claim 1, characterised in that the selector is a mechanical element which actuates the brake valve in opposition to the force of a spring.

4. A system according to claim 2 or 3, characterised in that the selector is adapted to be actuated by means of a lever which bears by a spring against a cable connected to the hand brake, the stop being formed by a co-acting cable connected to a lever.

5. A hydraulic trailer brake system for commercial vehicles substantially as hereinbefore described with reference to either Figure 1 or Figure 2.