GB2069645A

GB2069645A - Trailer emergency braking

Info

Publication number: GB2069645A
Application number: GB8104645A
Authority: GB
Original assignee: GL Rexroth GmbH
Current assignee: Bosch Rexroth AG
Priority date: 1980-02-15
Filing date: 1981-02-13
Publication date: 1981-08-26
Also published as: AT386163B; GB2069645B; FR2476007B1; DE3005703A1; DE3005703C2; ATA65881A; FR2476007A1

Abstract

A trailer emergency brake system, the brake lines (4) of which are normally subjected to service brake pressure from the hauling vehicle via a pressure line (3), comprises a hydraulic accumulator (7) which is charged from the pressure line (3) via a non-return valve (13) and which, separation of the trailer from the hauling vehicle is automatically and directly connected to the brake lines (4) via a pressure line (12) to activate the brakes while the pressure line (3) is cut off. On seperation a stop (8) is withdrawn by a cable (14) from a valve slide (16) permitting a spring (9) to displace the valve slide to its operative position. <IMAGE>

Description

SPECIFICATION Contact-breaking safety device for a trailer brake system The invention relates to a contact-breaking safety device for a trailer brake system, more particularly for a system having brake lines which can be subjected to pressure from the hauling vehicle via a pressure line.

There are known contact-breaking safety devices which operate the trailer brakes mechanically when a trailer breaks away from the hauling vehicle. Thus, for example, the energy of the falling trailer drawbar or hitch or the energy of a spring released by the trailer breaking away is used to transmit a force to brake traction cables which then operate the brakes.

The disadvantage of these mechanically operated contact-breaking safety devices is that, as a result of their relatively rare use, they may either fail completely or be only slightly effective in an actual dangerous situation since the operating mechanism is constantly exposed to the weather and therefore to corrosion, and any film of rust which may form on movable parts cannot always be removed.

An object underlying the invention is therefore to provide at least in preferred embodiments, a contact-breaking safety device which operates with constant reliability and with the minimum of maintenance.

The present invention provides a contactbreaking safety device for a trailer brake system, the brake lines of which can be subjected to pressure from the hauling vehicle via a pressure line, comprising a hydraulic accumulator which can be charged by the pressure line via a non-return valve and which, after separation of the trailer from the hauling vehicle, can be connected directly to the brake lines automatically while the pressure line is blocked.

The hydraulic accumulator, which is integrated in the trailer brake system and can be charged by the brake pressure, is absolutely maintenance-free and always supplies the necessary brake power. Additional braking facilities can be omitted as, when in use, the hydraulic accumulator subjects the normal brake lines to pressure.

The device preferably also comprises a directional control valve having a slide, which is retained in an inoperative position in opposition to the force of a spring, which can be released from the inoperative position by overcoming a predetermined contact-breaking resistance and which, under the influence of spring force, ca be pressed into an operative position in which the slide keeps the pressure line closed and the non-return valve of the hydraulic accumulator open in the direction of the brake line.

In a particularly advantageous embodiment, the slide is a piston which extends through a chamber of a housing of the control valve and the front end of which is in the form of a closing element for a pressure line connection which is coaxial with and leads into the chamber, the lateral or surface area of the said pressure line connection being in the form of a control surface for the radial operation of the non-return valve of the hydraulic accumulator leading radially into the housing chamber via a hydraulic accumulator connection, and the brake line leading freely into the housing chamber on the side lying opposite the hydraulic accumulator connection.

The mechanical valve displacing means is in this case situated in a closed housing chamber at a point which is constantly surrounded by hydraulic fluid so that signs of corrosion cannot occur and the reliability of the trailer brake system is thus increased considerably. This embodiment has the additional advantage that the individual control elements can be fitted in an extremely confined space thereby simplifying the design of the contact-breaking safety device and thus making it more reliable in operation.

Further developments emerge as a result of the subsidiary claims.

An embodiment of the invention is described in more detail below with the aid of diagrammatic drawings, in which: Figure 1 shows a circuit of a contact-breaking safety device according to the invention, and Figure 2 shows a section through an embodiment of the contact-breaking safety device.

Fig. 1 shows a trailer brake circuit 1 with a pressure line 3, which is connected via trailer coupling 2, and a brake line 4 which is connected to the brake cylinder 5 of the trailer. integrated between the pressure line 3 and the brake line 4 is a contact-breaking safety device 10 which consists of a directional control valve 6, a hydraulic accumulator 7 and a displacing means which has a stop 8 for the directional control valve 6, a slide 1 6 and a compression spring 9 which drives or actuates the slide 1 6.

The directional control valve 6 has two control positions. When in the first illustrated control position, it occupies an inoperative position A in which the pressure line 3 is connected to the brake line 4. Situated in the brake line 4 is a branch line 11, branching from which is a line 1 2 for charging the hydraulic accumulator 7. The charging line 12 leads via the sliding valve 6, the hydraulic accumulator 7 being charged via a non-return valve 1 3 when the sliding valve is in the inoperative position A. The sliding valve 6 is maintained in this inoperative position A while pretensioning the spring 9 and being in contact with the stop 8.

When the sliding valve 6 is in the second control position B, the connection between the pressure line 3 and the brake line 4 is broken, and the hydraulic accumulator 7 is connected directly to the brake line 4. The stop- 8 is connected to the hauling vehicle via a release cord 1 4 and can be removed when the trailer breaks away from the hauling vehicle. When the stop 8 is removed, the sliding valve 6 is displaced under the influence of the spring 9 into the second stop position or even into the operative position B in which the brake cylinders 5 are connected directly to the hydraulic accumulator 7 and the trailer executes an emergency braking action.

Fig. 2 shows an embodiment of the contactbreaking safety device according to Fig. 1. As can be seen from Fig. 1, the contact-breaking safety device 10 has a connection leading to the pressure line 3, the brake line 4 and the charging line 1 2. The contact-breaking safety device, which is integrated in a housing 20, comprises a housing chamber 21 with a housing bore 22 coaxial thereto, a connecting piece 23 with a pressure line connection 24 being fitted, preferably screwed, into a front section 21a of the housing chamber 21. Also leading into the said front section of the housing chamber 21 are a radial brake line connection 25 and a hydraulic accumulator connection 26, lying diametrically opposite the latter, for the non-return valve 1 3 which is also integrated in the housing 20.

The hydraulic accumulator connection 26 broadens via a valve seat 27 to form a nonreturn valve bore 28 in which a non-return valve spring 29 forces a non-return valve ball 31 against the valve seat 27 while being supported on the housing 20 on an axial locking ring 30.

Situated in the housing chamber 21, after the pressure connection 24, 25 and 26, is a slide 1 6 which is in the form of a T-shaped piston having a piston head 61 and a skirt 62 with which it extends, with a seal, through the bore 22 of the housing chamber 21. Between the rear side 68 of the piston head 61 and a shoulder 21c of the housing chamber 21 is a helical compression spring 9 which pretensions the piston 1 6 to the left as shown in Fig. 2. The piston 1 6 is maintained in the illustrated position by a detent pin 8 which protrudes through the skirt 62 and outside the housing 20, the said illustrated position corresponding to the inoperative position A of the sliding valve of Fig. 1.

The piston head 61 is in the form of a stepped cylinder which has a front cylindrical section 63, a rear cylindrical guide section 64 and a conical control section 65 which is formed between the said two sections. The front section 63 of the piston 1 6 is staggered radially inwards relative to the housing chamber 21, and a sealing cap 66 is formed on its front side. In the illustrated inoperative position A, the front section 63 comes to rest in the centre below the hydraulic accumulator connection 26, and the sealing cap 66 is situated at a certain axial distance D from the pressure line connection 24.

Situated in the hydraulic accumulator connection 26 is a control ball 67 which has a diameter smaller than that of the hydraulic accumulator connection 26. The control ball 67 is maintained in the hydraulic pressure connection 26 by the front section 63 of the piston head 61, a certain radial play remaining between the control ball 67 and the nonreturn valve ball 31.

When the contact-breaking safety device is in the illustrated inoperative position, the pressure line connection 24 is connected to the brake line connection 25 and the hydraulic accumulator connection 26 so that the hydraulic accumulator 7 can be charged by the pressure in the brake line 4.

The detent pin 8 is coupled to the hauling vehicle and it is removed from the piston skirt 62 when the trailer breaks away. As a result, while releasing the energy of the spring 9 to the left (in Fig. 2), the piston 1 6 is displaced by overcoming the axial distance D into an operative position B in which it is supported by the sealing cap 66 on a sealing seat 24a of the connecting piece 23 of the pressure line connection 24 and closes the latter. The spring is pretensioned so that it is still tensioned in the operative position B.During this movement the displaced control section 65 of the piston 1 6 creates, after overcoming the radial play between the control ball 67 and the non-return valve ball, a connection between the hydraulic accumulator 7 and the brake line 4 in which the non-return valve ball 31 is lifted from the valve seat 27 by the control ball 67. In this second position or operative position B there remains, between the front section 63 or the control section 65 of the piston head 61 and the wall of the housing chamber 21, an annular space through which hydraulic fluid can pass from the hydraulic accumulator 7 to the brake cylinders. Between the guide section 64 of the piston head 61 and the wall of the housing chamber 21 there is provided an axial groove 69 which makes it possible for the helical compression spring 9 to be always.

surrounded by hydraulic fluid. Moreover, the axial groove 69 ensures that a constant pressure compensation can take place between the front and rear sides of the piston head 61.

As a result, the helical compression spring 9 is not excessively pressure-loaded when the piston 1 6 is in the operative position B.

Due to the difference in area between the front and rear sides of the piston head 61, the piston 1 6 is forced back again under the influence of brake pressure into the inoperative position A, after the trailer is re-coupled to the hauling vehicle by operating the brake, and can be locked in this position by insertion of the detent pin 8. After the brake is re leased, the non-return valve ball 31 close the hydraulic accumulator off again and the system is ready for use.

Claims

1. A contact-breaking safety device for a trailer brake system, the brake lines of which can be subjected to pressure from the hauling vehicle via a pressure line, comprising a hydraulic accumulator which can be charged by the pressure line via a non-return valve and which, after separation of the trailer from the hauling vehicle, can be connected directly to the brake lines automatically while the pressure line is blocked.

2. A contact-breaking safety device according to Claim 1, further comprising a directional control valve having a slide, which is retained in an inoperative position in opposition to the force of a spring, which can be released from the inoperative position by overcoming a predetermined contact-breaking resistance and which, under the influence of spring force, can be pressed into an operative position in which the slide keeps the pressure line closed and the non-return valve of the hydraulic accumulator open in the direction of the brake line.

3. A contact-breaking safety device according to Claim 2, wherein the slide is a piston which extends through a chamber of a housing of the control valve and the front end of which is in the form of a closing element for a pressure line connection which is coaxial with the leads into the chamber, the lateral or surface area of the said pressure line connection being in the form of a control surface for the radial operation leading radially into the housing chamber via a hydraulic accumulator connection, and the brake line leading freely into the housing chamber on the side lying opposite the hydraulic accumulator connection.

4. A contact-breaking safety device according to Claim 3, wherein the piston is in the form of a T-shaped piston, the shaft of which extends with a seal through a bore in the housing coaxial with the housing chamber, and the piston head of which can be displaced with play in the housing chamber, the said piston head having the shape of a stepped cylindrical body which has a front cylindrical section, which forms the seat element, carries a sealing cap and is staggered radially inwards relative to the wall of the housing chamber, a rear cylindrical guide section, which extends through the housing chamber and is provided with an axial groove, and a control section which is formed be tween the said sections and forms the control surface of the piston.

5. A contact-breaking safety device according to Claim 4, wherein a helical compression spring, which surrounds the shaft and is subjected to pretensioning, is located between the rear side of the piston head and a shoulder of the housing chamber, the spring force being supported on the housing by way of a detent pin which protrudes through the shaft and outside the housing.

6. A contact-breaking safety device according to Claim 5 wherein the detent pin in the piston shaft can be drawn out by a release cord when the trailer breaks away.

7. Contact-breaking safety device according to any one of Claims 3 to 6 wherein in the hydraulic accumulator connection between the non-return valve and the head of the piston there is provided a control ball which, when the piston is in the inoperative position, rests on a front section of the piston head.

8. A contact-breaking safety device according to Claim 7 wherein when the piston is in the operative position, the control ball rests on a control surface of the piston head.

9. Contact-breaking safety device according to Claims 3 to 8, wherein a non-return valve ball closes the hydraulic accumulator connection, it being possible for the said ball to be pressed against a valve seat of the nonreturn valve bore by a non-return valve spring which is located in a non-return valve bore coaxial with the hydraulic accumulator connection and supported on the valve housing.

10. A contact-breaking safety device according to any one of Claims 3 to 9, wherein after the trailer is re-coupled to the hauling vehicle, the piston can be automatically reset by the brake line pressure exerted on the piston head, in opposition to the force of the spring, in the inoperative position in which the detent pin can be refitted into the shaft.