GB2291388A - Safety towing bracket - Google Patents

Abstract

A towing bracket/coupling 1 for a towing/towed vehicle combination is provided with a secondary towing bracket/coupling assembly 10, 12 that can act as a primary coupling in the event of the main coupling 4, 5. A plurality of secondary couplings may be fitted, and they may be connected to the vehicle drawbar through damping means 14. <IMAGE>

Description

A FAIL-SAFE TOWING BRACKET The invention relates to a fail-safe double towing bracket. The towing of trailer by a car, truck, train or other vehicle requires a towing bracket, of which several types exist. If the towing bracket breaks, or becomes loose, for any reason, this can lead to serious accident, such as: (i) the trailer ramming the tractor (or towing vehicle), e.g. in a descent; (ii) the trailer falling behind and hitting other traffic, e.g. in a climb; (ii) the trailer going off the road, and causing injury to passers - by or residents, and/or damage to houses or other construction, e.g. in a bend.

The principle of the present invention, is to have, in addition to the normal towing bracket (henceforth designated 'main' or 'primary' towing bracket), a second towing bracket henceforth designated 'safety' or 'secondary' towing bracket), such that: (i) in normal operation, the 'main' towing bracket carries all the load, and the 'secondary' towing bracket does not interfere with the relative motion of the trailer and tractor; (ii) in an 'emergency' situation, i.e. if the main towing bracket, for any reason, is broken or becomes disengaged, the 'secondary' bracket takes over, and prevents the trailer from beloming loose or ramming the tractor.

The usual precaution to prevent a trailer, whose towing bracket has disengaged, from becoming loose, is to use safety chains. The latter allow considerable relative motion of the trailer and towing vehicle, e.g. the latter may ram the former. Several devices have been patented, to improve upon the safety chain, but they also suffer from lesser limitations, namely: (I) they limit, to some extent, the full range of relative motion which the trailer and tractor can have, when compared with the towing bracket alone, without the safety device; (II) if the towing bracket breaks or becomes disengaged, the safety device acts as a second-rate towing bracket, i.e. is not as good as the original towing bracket, e.g. lacks damping or allows the build-up of forces and moments which could de-stabilize the ensemble.

In order to explain these two deficiences of existing patented safety towing brackets, and how they can be overcome, we must consider first the possible relative motions of a trailer and a tractor. They consist of a combination of three degrees-offreedom, which are best visualized (Figure 0) taking one reference plane, formed by the wheel axis and towing bar, for each of the trailer and tractor:: - in yaw, i.e. trailer to the right or left, of the tractor, viz. the trailer and tractor stay in the same horizontal plane, with the axis of the trailer making an angle to the axis of the tractor, for example, when driving along a bend on a road (sketch A); - in pitch, i.e. trailer higher or lower than tractor, viz. the trailer and tractor lie on different planes, intersecting normal to the towing axis, for example when driving over a large hole or hump (sketch B): - in roll, i.e. trailer banked relative to the tractor, viz. the trailer and tractor lie on different planes intersecting obliquely to the towing axis, e.g. when driving over uneven surfaces (sketch C).

A normal ball coupling allows at least 90" of yaw, and up to about 30 of pitch and roll. Most of the safety brackets so far patented limit the relative motion of trailer and towing vehicle to less than this on at least one axis. For example: - GB patent 1 241 504, for a towing safety hitch, limits roll; - US patent 4 428 596, for a towing safety hitch, limits roll and pitch; - US patent 4 211 428, for a trailer safety hitch, limits roll and pitch; - US patent 3 782 759, for safety arms for trailer hitch, also limits roll and pitch.

The problem with safety brackets that limit pitch and/or roll is that, when the limit is bumped on, there are respectively forces and moments, that can destabilize the trailer and tractor, e.g. the latter may cause the former to overturn.

Besides, reducing the range of possible relative motion of the trailer and tractor limits mobility over bumpy or uneven ground, e.g. cross-country.

When the main towing bracket becomes disengaged, most safety hitches do a less good job in preventing potentialy dangerous relative motions, or are less practical than the original towing bracket. For example: - GB 448 724, for a triple drawbar for coupling road vehicles, leads to asymmetric forces if one side bar breaks: the trailer will be towed with a non-zero pitch angle, i.e. partly sideways; - US 3 917 315 for a safety hitch shows no compatibility with the widely used ball coupling.

None of the patented devices makes explicit provision for damping some of the oscillations, whose build-up causes so many accidents with trailers.

We present two embodiments of a safety towing bracket which overcomes these limitations: First embodiment This is illustrated in three drawings: - Figure 1 shows, in perspective, the double tow-bracket, in the towing mode - Figure 2 shows, in perspective, the double tow-bracket, as it is engaged or disengaged - Figure 3 shows some of the possible improvements to the 'secondary' tow bracket.

Refering to the Figure 1, the basic constitution of the double tow-bracket is described next. Here the 'main' tow-bracket is the upper, consisting of a ball (4) attached by a bar (3) to the tractor (1), and fitting into an hemispherical housing (5), with a handle (6), attached by a bar (7), to the trailer (2); this is one of the several existing types of tow bracket, and it is of no consequence to what follows if it were of another type. The essence of the invention lies on the 'safety' tow-bracket, below the 'primary' tow-bracket, in the Figure 1 (it is possible to conceive operation with reversed positions of the 'main' and 'safety' brackets or with other positions, e.g.

horizontal side-by-side). The 'safety' bracket consists of a catch (10), with a closing hinged lever (11), attached by a bar (9) to the same towing vehcicle (1). Around the catch (10) is free to move a ring (12), attached to a bar (13), which has a detent (15), but otherwises slides freely in a sleeve (14), attached (16) to the same trailer (2).

In normal operation all the towing load is carried by the 'main bracket'; in the case of the Figure the ball-bracket at the top, although other types of 'main' towing bracket are possible, above or below the 'safety' bracket. The 'safety' bracket carries no force since if the ring (12) touches the catch (10), it slides along the sleeve (14). By choosing the length of the rod (13) and the position of the detent (15) it is possible to make sure that the ring (12) is loose around the catch (10), for any relative position of the trailer (2) and towing vehicle (1), with 'main' bracket engaged. Thus the 'secondary' bracket does not limit the relative motion of trailer and tractor which is determined solely by the 'main' bracket.

Imagine now that, for any reason, the main bracket breaks or becomes loose, e.g. the sphere (4) separates from the bar (3), or the sphere (4) motes out of the hemisperical housing (5). This situation, or any other, in which the 'main' towing bracket becomes inoperative, is the the emergency case, when the 'safety' bracket takes over. The trailer still remains connected to the tractor through the 'safety' bracket, and: (i) the trailer cannot ram the tractor, because its most forward position is limited by the ring (12) hitting the catch (10) at the front, and the sleeve (14) at the rear; (ii) the trailer cannot separate from the tractor, because its rearmost position correponds to the detent (15) hitting the sleeve (14).The two preceding cases (i) and (ii) set the limits of the motion of the trailer relative to the towing vehicle, in the emergency mode, when the 'main' bracket is inoperative.

The way in which the double tow bracket can be engaged, is illustrated in Figure 2. Disengagement is by the reverse sequence. The following is the sequence for engagement: (i) the hemispherical housing (5) and ring (12) on the trailer side are put at higher level than respetively the ball (4) and catch (10), and behind; (ii) they are moved horizontally forward, in the direction of the arrow (A), until the hemispherical housing (5) lies above the ball (4); (iii) the rod (13) is made to slide along the sleeve (14), so that the hole in the ring (12) lies above the free end of the catch (10); (iv) the trailer is lowered verticaly, in direction of the arrow (B), until the hemispherical housing (5) catches the sphere (4), and the 'main' bracket at the top is engaged; (v) then the ring (12) is around the catch (10), and the lever (11) can turn to horizontal position, in the direction of arrow (C), to 'close' the safety bracket. The inverse sequence applies to disengage. The details will differ if the 'main' bracket is of another type, e.g. also of ring and catch type, like the 'safety' bracket, but the sequence is the same.

Figure 3 shows some improvements to the 'emergency' tow bracket. In the form shown in Figure 1, in the emergency mode, with 'main' bracket inoperative, the 'safety' bracket may slide between two 'bump' stops: (a) ring (12) hitting the sleeve (14); (b) detent (15) hitting the sleeve (14). To make this motion smoother, a damper (16) may be inserted between the ring (12) and the sleeve (14). The damper could alternatively, or aditionaly, be put at (17) between the detent (15) and the sleeve (14).

The 'safety' bracket with damping allows the trailer to be towed-on, even with the main bracket inoperative; in this case, however, there is no further fail-safe protection. A fail-safe protection against N breakages or disengagements would require a total of N+1 towing brackets, viz. 1 'main' and N 'safety' operating on the same principles.

Second embodiment The second embodiment (Figure 4) is entirely similar to the first on the trailer side, but on the side of the tractor uses one ball and one pin coupling, leading to a slighty different engagement or disengagement sequence (Figure 5), but generally similar operation (Figure 6).

Ve need not describe again the trailer side in Figure A, which is the same as in Figure 1. On the side of the tractor (2), the upper towing bracket (39 is of ball type (4), but the lower towing bracket (9), is of a ring (11) and pin (10) type. The pin (10) can be removed (Figure 5) by unscrewing from the base (3) and pulling through the ring (11). When in towing use (Figure 6), accidental unscrewing of then pin (10), can be prevented by using a stop (16), consisting of a smaller pin sciding into a hole, above the ring (11).

In normal operation (Figure 6), all forces are carried by the ball (4) and hemispherical (5) coupling. The ring (12) around the pin (10) carries no force, because the bar (13) slides in the sleeve (14), up to the limit set by the detent (15) and ring (12).

If the ball (4) breaks or becomes disengaged, then the pin (10) and ring (12) act as a new towing bracket. They limit the relative motion as follows: (i) the stop (15) hitting the rear of the sleeve (14), prevents the trailer from receding too far behind the tractor; (ii) the ring (12) hitting the front of the sleeve (14), prevents the trailer from ramming the tractor.

To connect the double towing bracket the following sequence is used. The small pin (16) is removed (Figure 4), allowing the larger pin (10) to be unscrewed, from the ring (3), and pulled out through ring (11), as shown in Figure 5. The ball (4) may then be engaged in the hemispherical housing (5). The bar (13) is slid along the sleeve (14), so that the ring (12) is alligned with ring (11). The large pin (10) is then slid through the two rings ((11) and (12)), and screwed into the base (3), as shown on Figure 6. The small pin (16) is inserted, to prevent the large pin (10) from unscrewing, and becoming loose.

To disconnect the double towing bracket, the same sequence is followed in reverse.

The addition of damper to the second towing bracket is similar to the first embodiment, as well as the extension to any number of towing brackets.

Claims (1)

1. CLKIM1- A double-fail-safe towing bracket, which will: (i) operate like a single

   normal towing bracket, as long as the latter does not break or become disengaged, (ii) in the latter case a second 'safety' towing bracket takes over, and prevents the trailer from becoming detached from, or ramming, the tractor. Furthermore, it combines the following four features: - the relative motion of the trailer and towing vehicle in all three axis of yaw, pitch and roll, is the same as for a single towing bracket alone, i.e. the second does not limit the motion, or cause additional forces or moments; - if the first towing bracket breaks or becomes disengaged, the second towing bracket is equally effective to the first, apart from allowing a sliding motion; - both towing systems use some standard items available on the market, which simple modifications to allow engagement, disengagement and simultaneous use; ; - the possibility of having damping not just on the first, but also on the second towing bracket.

   CLAIM 2- An extension to any number of secondary towing brackets, with the same features as in Claim 1.