GB2411444A

GB2411444A - Releasing the brakes of an uncoupled trailer

Info

Publication number: GB2411444A
Application number: GB0404034A
Authority: GB
Inventors: Antoon Germain Vermeulen; Christiaan Andre Camie Lippens
Original assignee: CNH Belgium NV
Current assignee: CNH Industrial Belgium NV
Priority date: 2004-02-24
Filing date: 2004-02-24
Publication date: 2005-08-31
Also published as: GB0404034D0

Abstract

A braking mechanism for a wheel of a trailer, comprises an actuating lever 32 for operating a brake 36 of the wheel, and a hydraulic slave cylinder 22 for displacing the actuating lever 32 to operate the brake when hydraulic fluid is supplied to it by a hydraulic circuit of the trailer connectible (through line 14) to receive fluid from a tractor vehicle. In the invention, a manually controlled brake release mechanism 48 is provided for releasing the brake 36, when the hydraulic circuit is not connected to a tractor vehicle without discharging fluid from the hydraulic circuit.

Description

241 1 444 - 1

TRAILER BRAKING SYSTEM

Field of the invention

The present invention relates to a braking mechanism for a wheel of a trailer, comprising an actuating lever for operating a brake of the wheel, and a hydraulic slave cylinder for displacing the actuating lever to operate the brake when hydraulic fluid is supplied thereto by a lO hydraulic circuit of the trailer connectible to receive fluid from a tractor vehicle. The invention also relates to a trailer having a braking system incorporating such wheel braking mechanisms.

Background of the invention

Trailers towed by an agricultural tractor, including such agricultural implements as bailers, need to be braked when the tractor vehicle is being braked either by operation of a foot pedal or by application of a hand (or emergency) brake. When braking is effected by the foot pedal (or by two foot pedals operated in unison in the case of a tractor that can be steered by its brakes), hydraulic fluid is supplied from the tractor vehicle to a hydraulic circuit in the trailer which operates the braking mechanism. When the hand brake is applied, an electrical switch operated by the hand brake operates a solenoid valve in the trailer which supplies fluid to the brake slave cylinders from a pressurized accumulator in the trailer.

A problem that is currently encountered is that the trailer can only be moved by a tractor vehicle having the appropriate connections for the hydraulic circuit of the trailer. If one wishes to move a parked trailer using, for example, a fork lift truck that does not have the necessary connections, releasing the brake that is applied automatically when the trailer is parked can only be 2 - effected by bleeding fluid from the hydraulic circuit to reduce the braking pressure in the slave cylinders. It is not uncommon for a farmer to allow the discharged fluid to spill on the ground, which is clearly not environmentally

acceptable.

Summary of the invention

_

With a view to mitigating the foregoing problem, the lo present invention provides in accordance with a first aspect, a braking mechanism for a wheel of a trailer, comprising an actuating lever for operating a brake of the wheel, and a hydraulic slave cylinder for displacing the actuating lever to operate the brake when hydraulic fluid is supplied thereto by a hydraulic circuit of the trailer connectable to receive fluid from a tractor vehicle, wherein a manually controlled brake release mechanism is provided for releasing the brake when the hydraulic circuit is not connected to a tractor vehicle without discharging fluid from the hydraulic circuit.

It is a legal requirement in some countries for the braking mechanism of each trailer wheel to comprise a locking mechanism for preventing movement of the actuating lever and unintentional release of the brake in the event of loss of pressure in the hydraulic circuit while the trailer is parked.

In a preferred embodiment of the invention, the manually controlled brake release mechanisms may comprise a lost motion coupling having a first abutment surface for contacting the actuating lever to apply the brake when the lost motion coupling is in one end position and a second abutment surface for contacting the opposite side of the actuating lever to release the brake, against the action of the slave cylinder, when the lost motion coupling is in a second end position. - 3 -

The two abutment surfaces may simply be arranged a fixed distance apart to permit the brake to be applied and released hydraulically without interference from the manually controlled brake release mechanism when the latter is an inoperative intermediate position.

It is however preferred for the second abutment surface to be formed by a pin retractably mounted on the lost motion coupling to couple the lost motion coupling selectively to lo the actuating lever when the brake is to be released. This reduces the amount of jack movement required to move the actuating lever from a locked to a released position.

Manually releasing the brakes is preferably done by a mechanical jack that is used to move the lost motion coupling between a first position for contacting the first abutment surface with the actuating lever, and a second position for contacting the second abutment surface with the actuating lever.

The jack may conveniently be a manually operable screw jack, but it alternatively be operated by a pawl and ratchet mechanism. There is indeed no reason why the jack may not be powered electrically, hydraulically or pneumatically.

As an alternative to applying a force to move the actuating lever of the brake mechanism, it is possible to have a manually controlled brake release mechanism to isolate the slave cylinder from the hydraulic circuit of the trailer and to provide an auxiliary piston/cylinder unit having a working chamber connected to draw and store hydraulic fluid from the slave cylinder, so as to relieve the pressure in the slave cylinder and thereby release the brake. 4 -

In a further aspect, the invention provides a trailer having a plurality of wheels each provided with a braking mechanism as described above.

The trailer may suitably comprise further a hydraulic circuit for supplying hydraulic fluid to the slave cylinders of the wheel brake mechanisms which hydraulic circuit has an input line connectable to a tractor vehicle to allow the braking pressure to be controlled by the tractor vehicle lo when the trailer is being towed and a hydraulic reservoir for supplying hydraulic fluid to the slave cylinders when the trailer is parked and the input line is not connected to a tractor vehicle.

The hydraulic circuit may conveniently further comprise a two position three-way valve for connecting the slave cylinders to the input line when the trailer is being towed and for automatically connecting the slave cylinders to the hydraulic reservoir when the trailer is uncoupled from a tractor vehicle. The latter valve may be solenoid operated to connect the slave cylinders to the hydraulic reservoir when an electrical signal is received from the tractor vehicle to indicate that a hand brake has been applied. The valve may also for additional safety have a valve spool that is mechanically moved to connect the slave cylinders to the hydraulic reservoir when the trailer is separated from a tractor vehicle.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure l is a schematic diagram of the a conventional trailer wheel braking mechanism connected to a hydraulic circuit of the trailer, and Figures 2 and 3 are two similar diagrams showing two different embodiments of the present invention.

Detailed description of the drawings

In Figure 1, everything to the right of the dotted line is mounted on board a trailer and the lines 12, 14 and 16 drawn to the left of the dotted line 10 represent respectively mechanical, hydraulic and electrical lo connections to the tractor vehicle to ensure normal operation of the trailer braking system.

The line 14 represents a hydraulic control line which is pressurised when the brakes of the tractor vehicle are applied in unison, or applied separately in the case of a tractor vehicle having separate braking of the left and right wheels to enable it to be steered by the use of separate left and right brake pedals.

The line 16 is an electric conductor which carries an electrical signal to indicate that the hand brake of the tractor vehicle has been applied. Typically, this line is connected to a switch operated by the hand brake lever.

The line 12 represents a chain or a mechanical linkage which, as described below, acts to apply the trailer brakes automatically when it is not connected to a tractor vehicle.

The function of line 12 can be integrated into line 16.

In case of an emergency situation such as disconnecting the trailer from the tractor, the electrical signal will be disrupted and the valve 18 will move as described below.

The hydraulic circuit of tractor comprises a two position three way valve 18 which is maintained in the illustrated position by the electrical signal from line 16 when connected to a tractor vehicle. In this position, the - 6 valve 18 allows hydraulic fluid from the tractor line 14 to flow through a line 20 to the slave cylinders 22 of the different wheels so that the trailer wheels are braked at the same time as the tractor wheels. Because of clarity, only one brake system for one wheel of a trailer is shown in the drawings. Fluid from the line 14 can also flow at all times, in one direction only, through a non-return valve 24 to an accumulator 26, the pressure in which is indicated by a meter 28. This ensures that the accumulator 26 is lo pressurized at all times.

If the electrical line 16 is disconnected, the valve 18 moves into its second position. The spool of the valve 18 is also connected by a mechanical linkage 30 to the line 12 ib so that it is moved into the second position as soon as the trailer is mechanical separated from the tractor vehicle. In the second position, slave cylinders 22 are isolated from the line 20 and are instead connected to the accumulator 26 so that all the brakes are applied automatically.

The piston of each slave cylinder 22 acts on an actuating lever 32 connected to rotate a cam 34 which in turn forces brake shoes 36 into contact with a brake drum. A return spring 33 biases the actuating lever 32 in a direction to release the brake.

As above described, the trailer is hydraulically braked automatically as soon as it is disconnected from the tractor vehicle or whenever the hand brake of the tractor brake is operated, the latter acting both as a parking brake and as an emergency braking. However, there is a danger if the trailer is left parked for some time that the hydraulic pressure may drop, for example if the hydraulic system develops a leak, and for this reason certain legislations also require a mechanical operation of the trailer brakes.

In Figure 1, the mechanical backup is provided by a screw jack 38 which urges the actuating lever in the direction to > - 7 - the apply the brakes and preventing movement of any actuating lever that would release the brake.

It can be seen that when the vehicle is parked, even if the jack 38 is released and the valve 18 is forced into its first position by manual operation of the linkage 30, the brakes will remain applied because fluid will remain in the slave cylinders 22. The only way to release the brakes to allow the trailer to be moved by a fork lift truck that does lo not have a control line 14 or a matching connector 40 is to bleed the slave cylinders 22 after they have been isolated from the accumulator 26.

Figures 2 and 3 show different embodiments of the invention which avoid this problem. Many of the components of both Figure 2 and Figure 3 have already been described with reference to Figure 1 and to avoid repetition they have been allocated the same reference numerals. The essential difference in the case of the embodiment of Figure 2 is that the screw jack 38 is connected to the actuating lever 32 by means of a manually controlled brake release mechanism 48 comprising at least a lost motion coupling 50. Instead of being able to move the actuating lever 32 in only one direction, the coupling 50 allows the screw jack 38 to pull the actuating lever 32 to apply the brake and to push the actuating lever 32 to release the brake. The purpose of the lost motion is to allow the position of the actuating lever 32 to be set by the pressure in the hydraulic control line 14 when the trailer is in normal use.

If one now wishes to release the brake, after the trailer has been coupled to a fork lift truck, for example, the jack 38 is turned manually while the valve 18 is still in its second position. After the lost motion in the coupling has been taken up, the jack will force the actuating lever 32 back towards the position to release the brake at the same time pumping hydraulic fluid back from the - 8 - slave cylinder 22 into the accumulator 26. When the trailer reaches its new position, the jack 38 must again be operated to allow the actuating lever to apply the brake.

To reduce the amount of movement required of the jack 38 it is possible to provide a retractable pin 52 that either directly couples the jack 38 to the actuating lever 32 or reduces the amount of lost motion in the coupling 50 before the jack 38 is turned to move the actuating lever 32 lo into the brake release position.

In the embodiment of Figure 3, the releasing of the brake is effected by means of a manually controlled brake release mechanism 58 comprising at least an auxiliary piston/cylinder unit 60 having a working chamber connected to the working chamber of the slave cylinder 22, the piston 62 of the piston/cylinder unit 60 being movable manually by means of screw 64.

In this case, releasing of the brake is effected by first ensuring that the screw 64 is fully wound in, while the slave cylinder 22 remains connected to the accumulator 26, any fluid in the piston/cylinder unit 60 being pumped into the accumulator 26. Next the valve 18 is moved into its first position (by means of the linkage 30) to isolate the slave unit 22 from the accumulator 26 and the screw jack 38 is retracted. When the screw 64 is now unwound, the piston 62 moves in a direction to increase the volume of its working chamber and the fluid drawn from the slave cylinder 22 results in the brake being released. Though a separate screw jack 38 is required for each braked wheel of the trailer it is possible to use a single piston/cylinder unit to release all the brakes at the same time. 9 -

Claims

CLAIMS 1. A braking mechanism for a wheel of a trailer, comprising an actuating lever (32) for operating a brake of the wheel, and a hydraulic slave cylinder (22) for displacing the actuating lever (32) to operate the brake when hydraulic fluid is supplied thereto by a hydraulic circuit of the trailer connectible to receive fluid from a tractor vehicle, characterized in that a manually controlled lo brake release mechanism (48,58) is provided for releasing the brake when the hydraulic circuit is not connected to a tractor vehicle without discharging fluid from the hydraulic circuit.

1

2. A braking mechanism as claimed in claim 1, further comprising a locking mechanism (38) for preventing movement of the actuating lever (32) and unintentional release of the brake in the event of loss of pressure in the hydraulic circuit while the trailer is parked.

3. A braking mechanism as claimed in claim 2, wherein the manually controlled brake release mechanism (48) comprises a lost motion coupling (50) having a first abutment surface for contacting the actuating lever (32) to apply the brake when the lost motion coupling (50) is in one end position and a second abutment surface for contacting the opposite side of the actuating lever (32) to release the brake, against the action of the slave cylinder (22), when the lost motion coupling (50) is in a second end position.

4. A braking mechanism as claimed in claim 3, wherein the two abutment surfaces are arranged a fixed distance apart, thereby permitting the brake to be applied and released hydraulically without interference from the manually controlled brake release mechanism (48) when the latter is an inoperative intermediate position. t -

5. A braking mechanism as claimed in claims 3 or 4, wherein the second abutment surface is provided by a pin (52) retractably mounted on the lost motion coupling (50) to couple the lost motion coupling (50) selectively to the actuating lever (32) when the brake is to be released.

6. A braking mechanism as claimed in any of claims 3 to 5, wherein a mechanical jack (38) is used to move said lost motion coupling (50) between a first position for lo contacting the first abutment surface with the actuating lever (32), and a second position for contacting the second abutment surface with the actuating lever (32).

7. A braking mechanism as claimed in claim 6, wherein the mechanical jack is a manually operable screw jack (38).

8. A braking mechanism as claimed in claim 1 or 2, wherein the manually controlled brake release mechanism (58) comprises a valve (18) for isolating the slave cylinder (22) from the hydraulic circuit of the trailer and an auxiliary piston/cylinder unit (60) having a working chamber connected to draw and store hydraulic fluid from the slave cylinder (22) so as to relieve the pressure in the slave cylinder (22) and thereby release the brake.

9. A trailer having a plurality of wheels each provided with a braking mechanism as claimed in any preceding claim.

10. A trailer as claimed in claim 9, wherein the trailer further comprises a hydraulic circuit for supplying hydraulic fluid to the slave cylinders (22) of the wheel brake mechanisms having an input line (20) connectable to a tractor vehicle to allow the braking pressure to be controlled by the tractor vehicle when the trailer is being towed and a hydraulic reservoir (26) for supplying hydraulic fluid to the slave cylinders (22) when the trailer is parked - 11 and the input line (20) is not connected to a tractor vehicle.

11. A trailer as claimed in claim 10, wherein the hydraulic circuit further comprises a two position three-way valve (18) for connecting the slave cylinders (22) to the input line (20) when the trailer is being towed and for automatically connecting the slave cylinders (22) to the hydraulic reservoir (26) when the trailer is uncoupled from lo a tractor vehicle.

12. A trailer as claimed in claim 11, wherein the valve (18) is solenoid operated and connects the slave cylinders (22) to the hydraulic reservoir (26) when an electrical signal is received from the tractor vehicle to indicate that a hand brake has been applied.

13. A trailer as claimed in claim 11 or 12, wherein the valve (18) has a valve spool that is mechanically moved to connect the slave cylinders (22) to the hydraulic reservoir (26) when the trailer is separated from a tractor vehicle.

14. A trailer as claimed in any of claims 10 to 13, wherein the hydraulic reservoir is an accumulator (26).

15. Method for releasing the braking mechanism for a wheel of a trailer characterized in that it comprises the step of releasing the brake of the wheel when the hydraulic circuit is not connected to a tractor without discharging fluid from the hydraulic circuit.