GB2142397A

GB2142397A - Hydraulic overrun brake arrangement in wheeled trailer

Info

Publication number: GB2142397A
Application number: GB08415220A
Authority: GB
Inventors: Josef Buchmuller
Original assignee: Eisenwerk Grumer & Co KG GmbH
Current assignee: Eisenwerk Grumer & Co KG GmbH
Priority date: 1983-06-15
Filing date: 1984-06-14
Publication date: 1985-01-16
Also published as: DE3321511C2; DE3321511A1; FR2548120A1; GB8415220D0; FR2548120B3; GB2142397B

Abstract

A wheeled trailer has a drawbar (7) slidable in a hollow shaft (5). When the trailer overruns the drawbar, an operating piston (21) pressurises a hydraulic master cylinder (20) and brakes a trailer wheel via a supply duct (15) and a selector valve (49) responsive to direction of rotation of the braked wheel. The valve (49) responds to reverse motion of the trailer to connect the brake actuator to a pressure release duct (16) and thence to a further cylinder (27) instead of to the hydraulic master cylinder (20); when the drawbar is pulling, e.g. with the trailer tending to roll back down an incline, pressure in the further cylinder (27) brakes the trailer, but when the drawbar overrides the trailer (7), e.g. during reversing, the further cylinder (27) is vented to a chamber (11), releasing the brake. <IMAGE>

Description

SPECIFICATION Trailer with overriding brake arrangement The invention relates to a hydraulic overriding brake arrangement in single or multi-axle trailers, that is, an arrangement whereby a trailer drawbar is movably disposed in a shaft and an hydraulic system responds to the drawbar position to brake the trailer. This occurs when the drawbar is forced into the trailer shaft, the trailer assuming an "overriding" position.

Such a hydraulic overriding brake arrangement is known, e.g. from DE-PS 876 216.

The hydraulic system here includes a transmitting cylinder with an operating piston, and compression and pressure-release ducts to a brake cylinder disposed in each wheel brake having a brake piston for actuating the brake-shoe. This known overriding brake arrangement, however, suffers from the drawback that for backing the vehicle a special backing locking device is necessary, in order to put the overriding brake out of operation so that no braking torque is created.

From DE-AS 21 61 559 a mechanical overriding brake arrangement for an internal shoe brake is known in which the supporting device in each wheel brake is so constructed that on forward running the full braking torque can be achieved, and on reversing there is practically no braking. For this purpose the two brake shoes of each wheel brake are supported on a swivelling cam eccentrically mounted on a guiding element, said cam, when the brakes are applied when reversing, being able to be pivoted under the greater force of the secondary shoe, thus making possible a reduction of the distance between the support ends of the primary and secondary shoe. This mechanical overriding brake arrangement does indeed incorporate a socalled "reversing automatic device", but suffers from the complexity of the mechanical arrangement.

The object of the invention is to provide a simply constructed hydraulic overriding brake arrangement with which, on moving forward, the full braking torque can be achieved and, on reversing, braking does not take place, without the need for a special reversing locking device.

The invention consists in a single- or multiaxle wheeled trailer comprising: a drawbar arranged in a shaft connected to the trailer, and moveable therein between pulling and overriding positions, being respectively its foremost and rearmost positions relative to the trailer; a transmitting cylinder and operating piston arrangement connected between the drawbar and the shaft for generating overriding braking pressure; an hydraulically-operated brake adjacent a trailer wheel, having a brake cylinder connected via a servo piston and a compression duct to the transmitting cylinder; and a pressure-release duct connected to the brake cylinder via the servo piston; the servo piston responding to forward and reverse rotation of the wheel to connect the brake cylinder respectively to the compression duct and the pressure-release duct, whereby overriding braking is precluded in reverse.

A further disadvantage with both of the known devices described above is that they cannot prevent the trailer rolling back down an incline, under its own weight. In a preferred embodiment, therefore, a trailer comprises a further piston-and-cylinder arrangement, connected between the drawbar and the moveable part of said transmitting cylinder and operating piston arrangement to generate an hydraulic pressure when the drawbar moves towards the pulling position, the further cylinder connected to the pressure-release duct, whereby the brake operates to prevent reverse motion in the pulling position.

In one preferred form, the transmitting cylinder and further cylinder are connected to the drawbar, the operating piston drives the further piston, and each piston is resiliently biased away from its respective cylinder. Advantageously, the trailer comprises a pressure medium compensating chamber within the shaft, into which the transmitting cylinder vents with the drawbar pulling, and the further cylinder vents with the drawbar overriding.

In a preferred example, if the direction of rotation of the wheel is reversed by about 2" from the forward motion to reverse direction, the servo-brake closes the connection of the compression duct and opens the connection of the pressure-release duct to the brake cylinders. The brake pressure resulting from overriding in reverse direction is then completely annulled.

In this same example, the further pistonand-cylinder generates a braking pressure proportioned to the trailer load, so that after a stop on a slope, as soon as the trailer rolls back, the braking torque is then proportional to the towed load.

In the preferred embodiment, the further cylinder-andpiston arrangement is disposed around a stem of the operating piston, and the further piston comprises two parts, referred to as push and pull pistons, defining between them an annular cylinder. The transmitting cylinder is disposed in the drawbar itself and is widened in stepped fashion, there being connected to an operating cylinder for the operating piston a throttling channel for connection with the pressure medium compensating container, an abutment for the pull piston and finally the annular space to constitute the further cylinder.In this arrangement, provision is made for an oscillating channel between the abutment and the connection to the pressure medium compen sating container, and the operating piston has a head with a compensating channel between the throttling channel and a valve seat for the pull piston as well as, behind the head, a constriction on which the pull and push pistons are arranged.

The pressure medium compensating container may consist appropriately in an endless ring, U-shaped in crosssection, fixed on the drawbar.

For the detection of the direction of rotation of the wheel and for moving the servo-piston a sliding shoe is proposed, applying on the wheel hub, which is in operative connection via a twin-armed shift lever and a bending spring with the servo-piston.

In order that the invention may be better understood, two embodiments of the invention will now be described with reference to the drawings, wherein: Fig. 1 is a single-axle trailer with a hydraulic overriding brake arrangement according to a first embodiment, in its basic position in top view; Fig. 2 is a magnified section from Fig. 1 with the hydraulic overriding brake arrangement in its basic position in cross-sectional view; Fig. 3 is an inner shoe brake, being part of the first embodiment as shown in Figure 1, seen from the inside with the brake cylinder in its basic position seen in cross-section; Fig. 4 is the overriding brake arrangement of Figure 2 in its operative position on forward running or braking on an incline, in cross-section;; Fig. 5 is the overriding brake arrangement of Figures 2 and 4 in its operative position on overriding braking on forward running or in reverse, in crosssection; Fig. 6 is the inner shoe brake of Figure 3 in its operative position on overriding braking when moving forward, in cross-section; Fig. 7 is the inner Shoe brake of Figures 3 and 6, in its operative position when the reversing automatic device becomes operative or on braking on an incline, in cross-section; Fig. 8 shows the second embodiment of the overriding brake arrangement in its full completely overridden operative position, in crosssection.

Referring to Figure 1, a drawbar 7 with a pulling loop 8 is movably mounted on a shaft 1 with longitudinal bars 2, a supporting stay 3, a cross-stay 4 and a central bar 5 in a drawbar bearing 6. A pulling abutment 9 is fixed on the drawbar 7, while the rearward end of the pulling loop 8 forms a brake abutment 10.

A pressure medium compensating container 11 is fixed on the drawbar 7 in the central bar 5. The rearward ends of the longitudinal bars 2 are in the single-axle trailer represented rigidly connected with an axle body 1 2 (dashed lines in Fig. 1), but in the case of a multi-axle trailer they may also be joined by means of articulations 1 3 with the forward axle body 1 2 which is then guidable. Hydraulic inner shoe brakes 14 are arranged on the axle body 1 2 and they are actuated via a compression duct 1 5 and a pressure release duct 16.

Additionally, joined with the two inner shoe brakes 14, is a mechanical parking brake with hand brake lever and a tear-off rope 1 8 which, via a rope pull 1 9 acts upon a mechanical spreader device-not represented in the inner shoe brakes 1 4.

A transmitting cylinder 20 (Figure 2) for an operating piston 21 is disposed in the drawbar 7. The transmitting cylinder 20 is widened in stepped fashion and forms a working cylinder 22, a throttling channel 23 which is joined with the pressure medium compensating container 11 via a connection channel 24, an abutment 25 for a pull piston 26 and an annular space 27 for a push piston 28.

Between the abutment 25 and the connection channel 24 an oscillating channel 29 is disposed. The pull piston 26 and the push piston 28 are compressed by means of a compression spring 30 into their starting poSitions.

The pull piston 26 has a control ring channel 31 which connects the abutment 25 with the annular space 27.

The operating piston 21 has a head 32 which operates in the operating cylinder 22 and a compensating channel 33 which connects the throttle channel 23 with the abutment 25. Behind its head 32 the operating piston 21 has a control bead 34 closing the throttling channel 23 and behind it a valve seat 35 which cooperates with the pull piston 26. Behind, the operating piston 21 has a stem 36 on which the pull piston 26 and the push piston 28 are arranged. At its outer end the operating piston 21 has a foot 37 widened in stepped fashion on the heels 38 and 39 of which the push piston 28 and a compression spring 40 are supported; the central bar 5 applies against the other end of the operating piston. The compression spring 40 determines the level of pressure in the annular space 27.

In the outer end of the operating piston 21 an opening 41 is provided which is connected inside with the annular space 27 and outside with the pressure release duct 1 6. The pressure duct 1 5 is connected via a hole 42 with the transmitting cylinder 20.

Each inner shoe brake 14 (Figure 3) consists in a brake drum 43 with brake shoes 44 disposed in it which are supported on a bearing 46 fixed on the brake plate 45 and which can be expanded with a brake cylinder 47 also fixed to the brake cylinder 47.

A sliding shoe 54 applies against a wheel hub 53; this shoe detects the direction of rotation of the wheel hub 53 and is in operative connection with the servo-piston 49 via a rotatably mounted bending spring 55 and a pivotably-mounted twin-armed switch lever 56. The bending spring 55 engages with one arm into the sliding shoe 54 and with its other arm rests against the shoe brake 44 adjoining it. The switch lever 56 on which the bending spring 55 is fixed engages by means of a pin 57 into the servo-piston 49.

In the embodiment shown inFig. 8, between the outer end of the operating piston 21 and the supporting stay 3, an additional compression spring 58 is mounted in order to maintain and limit the brake pressure in the transmitting cylinder 20 also on complete overriding of the drawbar 7. For this purpose a guide cup 59 is slidably mounted on the supporting stay 3; this cup takes up the outer end of the operating piston 21 and the compression spring 40 rests on it also. The operating piston 21 has inside the guide cup 59 a flange 60 against which the compression spring 58 applies.

The hydraulic overriding brake arrangement represented in the drawings and described hereinabove operates as follows in the various operating positions: 1 Working Brake on Forward Motion When the drawbar 7 on forward motion according to Fig. 4 is pulled out, the transmitting cylinder 20 is still connected, via the operating cylinder 22, the throttling channel 23 and the connection channel 24, with the pressure medium compensating container 11, because a relative movement between the drawbar 7 and the operating piston 21 has not taken place. As a consequence of this a braking pressure cannot build up to actuate the brake piston 48 in the brake cylinders 47.

As compared with the starting position represented in Fig. 2 only the compression spring 40 is tensioned until the pulling abutment 9 applies on the drawbar bearing 6.

In the event of the overriding of the trailer on an application of brakes in forward motion, the drawbar 7 assumes the position represented in Fig. 5. In so doing the operating piston 21 moves in the operating cylinder 22 and closes the return path to the pressure medium compensating container 11. As a result a braking pressure can build up in the transmitting cylinder which is transmitted to the brake cylinder 47 via the pressure duct 1 5 and the servo-piston 49 which, on forward motion, in in the starting position represented in Fig. 3. In this situation the two brake pistons 48 are then pressed into the braking position represented in Fig. 6.As soon as the overriding braking is ended, the drawbar 7 again moves into the position represented in Fig. 4, so that a discharge of the brake cylinder 47 can take place via the pressure duct 1 5 into the transmitting cylinder 20 or the pressure medium compensating container 11.

2 Reversing Automatic Device If the trailer is pushed back or parked by reversing, the drawbar 7 moves out of the starting position represented in Fig. 2 or out of the pulling position represented in Fig. 4 into the position shown in Fig. 5 on an overriding braking, so that per se a braking pressure is again built up in the brake cylinders 47 via the pressure duct 1 5. As a result of the reverse rotation of the wheel hub 53 in the direction of the arrow R, however, the servo-piston 49 is moved into the position shown in Fig. 7, so that the brake pressure prevailing in the brake cylinders 47 is discharged via the connection channel 52, the control ring channel 51 and the discharge duct 16.

The reversing of the servo-piston 49 takes place in this operation via the sliding shoe 44, the bending spring 55, the switch lever 56 and the pin 57.

The discharge of the brake cylinder 47 via the discharge duct 1 6 is effected via the hole 41 in the operating cylinder 21, the annular space 27, the control ring channel 31 and the connection channel 24 into the pressure medium compensating container 11.

As soon as the trailer is again moved in the forward direction a reversal takes place anew of the servopiston 49 as a result of the movement of the wheel hub 53 in the direction of the arrow V. Then the starting position represented in Figs. 2 to 4 is resumed.

3. Braking on an Incline If the trailer has been braked on an incline, the drawbar 7, as a result of the action of the towed load, is in the pulling position represented in Fig. 4. The pressure medium in the annular space 27 is tensioned, because the pull piston 26 and the push piston 28 are pushed together against the action of the compression spring 40 proportionally to the magnitude of the towed load. As soon as the trailer moves backwards, the servo-piston 49 is reversed into the position represented in Fig. 7, so that a transmission of the dynamic pressure out of the annular space 27 via the pressure release duct 1 6 into the brake cylinder 47 can take place. The trailer is then braked proportionally to the towed load. As soon as the trailer is again pulled in the forward direction there again takes place a reversal of the servo-piston 49 into the position shown in Fig. 6, so that a discharge of the brake cylinder 47 via the pressure duct 1 5 can take place into the transmitter cylinder 20.

The hydraulic overriding brake arrangement has been represented and described using an inner shoe brake as an example. Naturally, the subject of this invention can also be used with a hydraulic disc brake or any other hydraulically-operable brake.

Claims

1. A single- or multi-axle wheeled trailer comprising: a drawbar arranged in a shaft connected to the trailer, and moveable therein between pulling and overriding positions, being respectively its foremost and rearmost positions relative to the trailer; a transmitting cylinder and operating piston arrangement connected between the drawbar and the shaft for generating overriding braking pressure; an hydraulically-operated brake adjacent a trailer wheel, having a brake cylinder connected via a servo piston and a compression duct to the transmitting cylinder,; and a pressure-release duct connected to the brake cylinder via the servo piston; the servo piston responding to forward and reverse rotation of the wheel to connect the brake cylinder respectively to the compression duct and the pressure-release duct, whereby overriding braking is precluded in reverse.

2. A trailer in accordance with claim 1, comprising a further piston-and-cylinder arrangement, connected between the drawbar and the moveable part of said transmitting cylinder and operating piston arrangement to generate an hydraulic pressure when the drawbar moves towards the pulling position, the further cylinder connected to the pressurerelease duct, whereby the brake operates to prevent reverse motion in the pulling position.

3. A trailer in accordance with claim 2, wherein the transmitting cylinder and further cylinder are connected to the drawbar, the operating piston drives the further piston, and each piston is resiliently biased away from its respective cylinder.

4. A trailer in accordance with claim 3, comprising a pressure medium compensating chamber within the shaft, into which the transmitting cylinder vents with the drawbar pulling, and the further cylinder vents with the drawbar overriding.

5. A trailer according to claim 1, wherein the transmitting cylinder is connected with the drawbar and the operating piston movable in it is supported in the pulling direction with the interposition of a compression spring and in the overriding position is supported on the trailer; wherein, in an annular space between the transmitting cylinder and the operating piston, a pull piston and a push piston are disposed, between which a compression spring lies; and wherein the pressure-release duct is connected to the said annular space.

6. A trailer according to claim 5, characterised in that the transmitting cylinder is disposed in the drawbar and is widened in stepped fashion to provide: a throttling channel for connection with a pressure medium compensating container, an abutment for the pull piston and finally the annular space which is connected to an operating cylinder for the operating piston.

7. A trailer according to claim 6, characterised in that an oscillating channel is provided between the abutment and the connection to the pressure medium compensating container.

8. A trailer according to claim 6 or 7 characterised in that the operating piston has a head with a compensating channel between the throttling channel and a valve seat for the pull piston, and behind the head a stem on which the pull and push pistons are disposed

9. A trailer according to claim 8 characterised in that a control ring channel connecting the valve seat with the annular space is disposed in the pull piston.

10. A trailer according to claim 5, 6, 7 or 9, characterised in that the operating piston has a foot widened in stepped fashion, on the heels of which the push piston and the compression spring are supported.

11. A trailer according to claim 4 or 6 or any claim appendant to claim 6. characterised in that the pressure medium compensating container comprises an endless ring fixed on the drawbar and U-shaped in cross-section.

1 2. A trailer according to any preceding claim, characterised in that each servo-piston cooperates with a sliding shoe applying on the wheel hub.

1 3. A trailer according to claim 12, characterised in that between the servo-piston and the sliding shoe a twin-arm switch lever is disposed which, on the one hand, engages with a pin into a hole of the servopiston, and on the other hand, has. disposed on it, a bending spring which is supported in the sliding shoe and on a shoe brake.

14. A trailer according to any preceding claim, characterised in that the drawbar is mounted on a drawbar bearing fixed on the shaft, which bearing cooperates in the pulling direction with a pulling abutment fixed on the drawbar and in the overriding direction with a brake abutment provided on a pulling loop.

1 5. A trailer according to claim 14, characterised in that between the outer end of the operating piston and the shaft a compression spring is disposed which, when the drawbar has overriden as far as the brake abutment, maintains the pressure in the operating cylinder and limits it.

1 6. A trailer according to claim 15, characterised in that the compression spring is disp6sed in an annular space between the end of the operating piston and a guide cup supported on the shaft.

1 7. An hydraulic overriding brake arrangement comprising a drawbar and shaft, and an hydraulic brake, substantially as described herein with reference to the accompanying drawings.

1 8. A single- or multi-axle wheeled trailer substantially as described herein with reference to the accompanying drawings.