GB1565542A

GB1565542A - Security device for a semi-trailer leg

Info

Publication number: GB1565542A
Application number: GB1800076A
Authority: GB
Original assignee: BLAKELOCK R
Current assignee: BLAKELOCK R
Priority date: 1977-05-02
Filing date: 1977-05-02
Publication date: 1980-04-23

Description

(54) SECURITY DEVICE FOR A SEMI-TRAILER LEG (71) I, RONALD THOMAS BLAKELOCK of 11, Kidbrooke Way, London, S.E.3, a British Subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a leg for a semitrailer including a security device for locking the leg in a predetermined position.

A semi-trailer is a trailer adapted to be towed by a road vehicle and typically has an axle or axles towards the rear for supporting the rear of the trailer and adjacent its front end a coupling known as a fifth wheel by which the rtailer is connected to and supported on a towing vehicle or tractor.

In order to support the front end of the trailer at a height at which the tractor can engage or disconnect from the coupling a pair of telescopic legs are located towards the front of the trailer, one on each side. These legs are extensible between a retracted po sition to enable the trailer to be towed and an extended position in which they support the front end of the trailer so that it can be parked independently of the tractor. Typically, the telescopic mechanism by which the legs are extended and contracted includes a manually operable gearing system.

It is an object of the present invention to provide a security device to prevent unauthorised operation of the telescopic mechanism.

Thus, when a semi-trailer incorporating the security device of the present invention is parked with the legs in the extended position the or each leg is/are locked in this position and this prevents the semi-trailer from being coupled to a tractor and driven away.

According to the present invention there is provided a leg for a semi-trailer including a security device for locking the leg in a predetermined position, the leg including a telescoping mechanism including a gear train, for extending and retracting the leg, the security device including means adapted to be engageable with a gear element in the gear train to prevent movement of said gear element to thereby prevent extension and retraction of the leg, and a lock for locking said means in the gear element engaging position.

Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figures la and ib show respectively plan and side views of part of a supporting leg of a semi-trailer, Figures 2a, 2b and 2c show respectively side, top and end elevations of the main body of a security device, Figures 3a and 3b show two views of a locking bar of the security device engageable with a gear in the leg, Figure 4 shows an embodiment of a cam of a modified security device, and Figures 5a and 5b show respectively plan and side views of the main body of the modified security device showing the locking bar and a latch bar, Figure 6 shows a schematic part sectional isometric view of the modified security device.

Referring now to Figures la and ib there is shown part of a leg for supporting the front of a semi-trailer when the semi-trailer is not mounted on a tractive vehicle, one leg being provided on each side of the semi-trailer. The leg has a main body 1 in the shape of a square tube which is rigidly secured to the frame of the semi-trailer. The leg has a second lower member of slightly smaller size in crosssection, than the body member 1 which lower member is telescopically movable longitudinally within the body member 1 by means of a gear system to enable the overall length of the leg to be varied. Thus, the leg is retracted to enable the semi-trailer to be towed along and is extended to support the trailer when the trailer is parked, without being supported by a tractor.

The gear system includes a bevel gear wheel 2 mounted in the body 1 of the leg so as to be rotatable about the longitudinal axis of the body 1 but fixed in the longitudinal direction by means of a mounting-plate 3 secured to the body 1. The bevel gear 2 is secured to a threaded shaft 4 for rotation therewith, a nut (not shown) mounted on the threaded shaft being secured to the lower leg (not shown) so that rotation of the bevel gear 2 causes the nut to move longitudinally on the shaft 4 and hence causes the lower leg mem ber of the leg to move longitudinally relative to the body 1 thus causing the leg to extend or contract in dependence upon the direction of rotation of the bevel gear 2.

The bevel gear is rotated by a manually operable crank handle which is selectively attachable to one of two input shafts 5 or 6 of the gear train. Rotation of either of the input shafts 5 or 6 causes rotation of a pinion shaft 7 located within the body 1 and which carries secured thereto a bevel pinion 8 meshed with the bevel gear 2. The input shaft 6 is connected directly to the pinion shaft 7 but the input shaft 5 is connected through a gear train 9 to the shaft 7 to provide a low gear ratio.

In order to prevent unauthorised retraction of the legs when the semi-trailer is parked a security device 10 is located within the body 1 of each leg.

The security device consists essentially of a main block 11, illustrated in Figures la, 2b and 2c, a locking bar 12 illustrated in Figures 3a and 3b and a key operated lock shown schematically in Figure lb as reference 13. The main block 11 is formed of steel and is welded to the inner wall of the body 1 immediately above the bevel gear 2. The block 11 has a stepped bore 14 for accommodating the lock 13, the body of the lock lying within the bore so that it cannot be sawn off, and a blind bore 15 for accommodating the locking bar 12.

The locking bar 12 is slidable longitudinally in the bore 15 between a retracted position and an extended, locking position in which it is engageable with a gear of the gear train. As shown in Figure la the bar 12 engages the pinion 8 but an alternative is shown in Figure 6 in which the bar 12 engages the bevel gear 2. The blind bore 15 has an elongate slot 16 in one wall through which a pin 17 secured in the locking bar 12 projects to engage with a fork-shaped element 18 on the lock 13. The lock may be adapted to positively hold the locking bar in the retracted position when the lock is in the inoperative position.

In the case where the lock is of the type which does not positively hold the locking bar 12 in the retracted position it is necessary to provide some additional means for doing this.

As shown schematically in Figures 3a and 3b in one form this additional means takes the form of a leaf spring 19 located in a slot in the bar 12 so as to bear against the wall of the bore 15 thus providing a frictional force which retains the bar in a position set by the lock 13. Alternatively, a light tension spring (not shown) may be provided to extend between the main block 11 and the pin 18 secured to the locking bar 12 to bias the locking bar 12 to a retracted position within the blind bore 15. It will be appreciated however that any form of retaining means, latch or return spring would perform this function. The locking bar 12 is formed of phosphor bronze, manganese bronze or stainless or high tensile steel.

In operation, when it is desired to lock the gear train in the leg to prevent the leg being extended or retracted the lock 13 is operated through a key to rotate the forked arm 18 thus moving the pin 17 down the elongate slot 16, the pin 17 carrying the locking bar 12 until the locking bar engages in one of the teeth of the bevel gear 2. In this position the lock 13 is fully engaged in the locked position and the key can be withdrawn. The mechanical advantage provided by the gear train is such that it is virtually impossible to apply sufficient force to a crank handle to break the locking bar, but to prevent excessive force being applied to the gears and the locking bar a load limiting arrangement is provided either on the shafts 5 or 6 or in the connection piece, through which the handle can be attached to the selected input shaft. This limiting arrangement may take the form of a pin designed to shear when greater than a predetermined toque is applied to the handle or specially weakened regions may be provided on the input shafts so that in the event of excessive load being applied thereto the shafts shear off more or less flush with the leg body or housing of the gear train 9.

To release the locking device the key is inserted in the lock 13 and the lock turned to the unlocking position, this action causing the forked arm 18 to move anti-clockwise to move the locking bar out of engagement with the bevel gear 2.

When the lock 13 is in the fully unlocked position the pin 17 is adjacent the upper end of the elongate slot 16 and the key can be withdrawn from the lock 13.

In a modified embodiment, as shown in Figures 5a and 5b, the main block 11 of a security device has therein the bore 15 within which the locking bar is longitudinally slidable and also a further bore 23 entering the bore 15 at right-angles thereto, the bore 23 being adapted to accommodate a latch bar 24 slidable longitudinally therein. The latch bar 24 has a pin 25 therein projecting through a slot 26 in the wall of the main body in a similar manner to the pin 17 secured to the locking bar 12.

The lock carries a cam 27 (shown in Fig. 4 and in dotted lines in Fig. 5b) secured to the lock mechanism so as to pivot about the axis la when the lock is moved between the unlocked and locked positions. The cam carries two projections 28 and 29 which are adapted to entrain the pins 25 and 17. The spacing of the projections about the cam 27 are such that when the key is operated to move the locking bar to its locked position the cam 27 rotates clockwise as viewed in Figs. 4 and 5, the projection 28 engages the pin 17 to move the locking bar to the locking position. A light spring 30 (shown in Fig. 6) biasses the latch bar 24 into the bore 15 to a latching position to prevent the locking bar 12 from being inadvertently retracted. The latch bar and the locking bar are shown in this position in out line in Figure 5b.

When the security device is unlocked the cam 27 is rotated anticlockwise and the projection 28 first engages the pin 25 to move the latch bar to the retracted position to enable the locking bar 12 to be retracted by the projection 29 engaging the pin 17. Although shown as solid projections, it will be appreciated that the projections 28 and 29 could well be forkshaped elements to positively move the latch bar and locking bar respectively between their retracted and operative positions.

WHAT I CLAIM IS: 1. A leg for a semi-trailer including a security device for locking the leg in a predetermined position, the leg including a telescoping mechanism including a gear train, for extending and retracting the leg, the security device including means adapted to be engageable with a gear element in the gear train to prevent movement of said gear element to thereby prevent extension and retraction of the leg, and a lock for locking said means in the gear element engaging position.

2. A leg as claimed in claim 1 wherein the means engageable with the gear element comprises a locking bar movable to the gear engaging position.

3. A leg as claimed in claim 2 wherein the lock includes a rotatable lock member cooperable with said locking bar, rotation of the lock member from an inoperative to a locking position causing the locking bar to be moved to the gear engaging position.

4. A leg as claimed in claim 3 wherein the lock member comprises cam means for moving said locking bar.

5. A leg as claimed in claim 3 wherein said lock includes an element having a notch adapted to engage said locking bar so that movement of the lock member to said locking position rotates said element to thereby move the locking bar.

6. A leg as claimed in any one of claims 2 to 5, further including a latch bar movable by resilient means to a latch position, when the locking bar is in the gear engaging position to prevent withdrawal of the locking bar.

7. A leg as claimed in claim 6 wherein the lock includes a cam carrying two projections adapted to entrain the locking bar and the latch bar, so that upon separation of the lock the locking bar is moved to the gear engaging position by a first one of said projections and, to return the bar to the inoperative position said first projection entrains the latch to move the latch to an inoperative position prior to the second projection entraining the bar to move the bar to the inoperative position.

8. A leg as claimed in any one of claims 2 to 7 wherein the lock is adapted to positively hold the locking bar in the retracted position when the lock is in the inoperative position and to positively hold the locking bar in the locking position when the lock is moved into the lock position.

9. A leg as claimed in claim 8 wherein resilient means is arranged to urge the locking bar against a surface of the lock to provide a frictional force which force retains the bar in the position set by the locking device.

10. A leg as claimed in claim 7, 8 or 9 wherein resilient means serves to bias the locking bar to a retracted position.

11. A leg as claimed in any one of claims 2 to 10 wherein the locking bar is formed of phosphor bronze, manganese bronze or stainless or high tensile steel.

12. A leg as claimed in any one of the preceding claims wherein the telescoping mechanism is manually operable, load limiting means being provided in said mechanism, to prevent greater than a predetermined load being applied to said gear train.

13. A leg of a semi-trailer substantially as described herein with reference to and as illustrated in Figures la, lh, 2a-2c, 3a, 3b of the accompanying drawings.

14. A leg of a semi-trailer, substantially as described herein with reference to and as illustrated in Figures 4, 5a, 5b and 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. bar 24 into the bore 15 to a latching position to prevent the locking bar 12 from being inadvertently retracted. The latch bar and the locking bar are shown in this position in out line in Figure 5b. When the security device is unlocked the cam 27 is rotated anticlockwise and the projection 28 first engages the pin 25 to move the latch bar to the retracted position to enable the locking bar 12 to be retracted by the projection 29 engaging the pin 17. Although shown as solid projections, it will be appreciated that the projections 28 and 29 could well be forkshaped elements to positively move the latch bar and locking bar respectively between their retracted and operative positions. WHAT I CLAIM IS:

1. A leg for a semi-trailer including a security device for locking the leg in a predetermined position, the leg including a telescoping mechanism including a gear train, for extending and retracting the leg, the security device including means adapted to be engageable with a gear element in the gear train to prevent movement of said gear element to thereby prevent extension and retraction of the leg, and a lock for locking said means in the gear element engaging position.