The invention relates to a safety device for vehicles with a trailer which is coupled to the vehicle's coupling device by means of a trail bar.

When driving with a trailer it is not advisable to turn so sharply that the vehicle and the trailer touch each other which would cause damage to both the vehicle and the trailer. Consequently, some experience and routine is required before one can drive with a trailer without causing damage when tur¬ ning. Especially backing manoeuvres require considerable skill and care in order to avoid that the trailer reaches an angle exceeding a certain maximum in relation to the longitudinal axis of the vehicle.

It is the object of the invention to describe a safety device for vehicles which device in order to prevent damage when tur¬ ning gives a signal before the driver reaches the trailer's maximum turning angle in relation to the longitudinal axis of the vehicle.

This is achieved with a safety device according to the inven¬ tion and as disclosed and characterized in the preamble to claim 1. When the trail bar reaches a certain angle in rela¬ tion to the vehicle's longitudinal axis, the safety device signals to the driver who is hereby made aware of the risk of the trailer and the vehicle touching each other, if the ma¬ noeuvre (the backing manoeuvre) is continued. The actual sig¬ nalling can be made in any known manner, that is with a pilot lamp or with an acoustic signal or the like.

In practice the safety device can be placed on the vehicle's coupling device and could, moreover, be designed as disclosed and characterized in claims 2-6. Hereby an efficient and re¬ liable device is achieved which will not be in the way for the

coupling of the trailer and the vehicle and which does not re¬ quire electric connection from the vehicle to the trailer.

The safety device according to the invention could also be de- signed as disclosed in the preamble to claim 7, since in this manner wiring on the trail bar is avoided, as is actually wi¬ ring to the trailer. If the detectors are placed in suitable spots on the vehicle's rear, the application of position indi¬ cators on the trailer is rendered unnecessary, since parts of the trailer itself, e.g. the bumper, can be used as position indicator, depending on the trailer design.

The safety device according to the invention is preferably de¬ signed as disclosed and characterized in claims 8-10. Hereby a simple and reliable circuit is achieved which can be adapted to any vehicle with any kind of trailer and which signals to the driver in a suitable manner when the trail bar reaches a certain angle in relation to the longitudinal axis of the ve¬ hicle.

In the following the invention will be described in more de¬ tail with reference to two embodiments of the invention, in that

fig. 1 shows the coupling of a vehicle and a trailer with a safety device according to a first embodiment of the invention,

fig. 2 shows the same as fig. 1, but from above, and

fig. 3 shows the principle of the safety device according to a second embodiment.

The reference 1 in figs. 1 and 2 is a trail bar secured to a motor vehicle, e.g. an ordinary passenger car. The trail bar is ended by a coupling knob 2 and constitutes perfectly ordi¬ nary trail gear. A draw bar 3 is coupled to the vehicle's

trail gear, the trail bar comprising a protrusive portion 5, a gripper, which by employing the manoeuvring handle 4, can lock the draw bar 3 on to the knob 2 in the usual manner. This design is very often applied for the coupling of trailers to passenger cars.

Furthermore, a detector 6 is provided on the trail gear which is screwed adjustably on to the trail bar 1 by means of a fit¬ ting 9. On the trail bar 3 of the trailer two position indica- tors 7 are provided in the form of a plate, e.g. a metal or a plastic plate having outwards projecting fins.

The vehicle's ordinary power supply also supplies the detector 6 with power and a signal cable 10 from the detector leads to a signalling device 8, e.g. an optical or an acoustic signal indicator placed in the driver's cab, or the vehicle's ordi¬ nary horn.

When the trail bar 3, see fig. 2 in particular, has been tur- ned to a certain angle in relation to the trail bar 1 which is positioned in the longitudinal axis of the vehicle, one of the position indicators 7 will reach across the detector 6 which will immediately detect this and activate the signalling de¬ vice 8 and the driver is now aware that he has reached the trailer's maximum turning angle.

Fig. 3 shows a draft of a second embodiment of the invention where a vehicle 11 trails a trailer 12 by means of a trail bar 3 which is coupled to the trail gear 1 of the vehicle, exactly as shown in figs. 1 and 2. Instead of- placing the detector on the trail bar, two detectors 6 have been applied here, placed at or in the vicinity of the outer edges of the vehicle's 11 rear. The detectors 6 are arranged so as to signal, e.g. via a signalling device as explained in connection with figs. 1 and 2, when the trailer 12 has been turned so much in relation to the longitudinal axis of the vehicle 11 that one of the detec¬ tors 6 almost touches the trailer 12 or any position indica-

tors placed on the trailer.

By the embodiment shown in fig. 2 the fins 7 can be designed so that parts hereof can be cut or broken off for the position indicator to be adapted to any trailer, that is depending on the length of the trail bar and the width of the trailer and the vehicle.

The detector 6 can be any known kind of detectors, e.g. elec- trie or electronic proximity detectors based on inductive or magnetic detection; however, detectors based on light, sound or other kinds of oscillations are naturally applicable as well.