DEVICE FOR PROTECTING THE RADIATOR OF A MOTOR VEHICLE AGAINST PROJECTED PARTICLES The invention relates to a radiator in a motor vehicle in accordance with the concept of claim 1. The radiators of motor vehicles contain, in general terms, several cooling conduits. which are placed in parallel, at intervals, as a pipe with ribs, joined together by corrugated heat deflection blades. As cooling pipes that carry a medium, round pipes or flat pipes are used. Such radiators are used, for example, as heat exchangers in the engine cooling circuit or as condensers in an air conditioning installation in a vehicle. In order to obtain an effective cooling performance, such radiators are usually located in the front of the vehicle in a well ventilated area by the air of vehicle displacement. Such a cooling air stream may contain particles such as, for example, small particles of gravel, especially when one vehicle exceeds another, in the case of traffic in the opposite direction and columns of vehicles in streets with an insufficiently consolidated road. To reduce the weight of the radiator and to obtain a good exchange of heat between the cooling air and the cooling medium, the thinnest cooling tube walls are used, such that these particles can mechanically damage the pipes with ribs where the cooling medium is found. Surface damage can be created, and leaking pipes with thin-walled ribs can also be created. This causes a loss of cooling of the engine and can cause damage to the vehicle with the consequent expense of composing. To reduce the problem of soiling or percussion by particles, several techniques were proposed of which the following are examples of only some of them. In the heat exchanger of the vehicle radiator according to EP 0 060 393 A2, the dust of the cooling air is removed through a changeable trap placed on the air intake side by means of easily detachable fasteners. Lateral guide shapes welded onto the rib tubes for a slidably constructed trap. Said fasteners increase the manufacturing cost and complicate the subsequent maintenance of the protection against particles in the form of a trap, since welding is required. If, as stated in EP 0 076 928 Al, the trap has a grid structure that corresponds to the grid structure of the heat exchanger, also of the pipeline arrangement of ribs, this trap solution has the advantage that the Current resistance for cooling air is almost not increased, and may not increase until the grid ribs of the trap in front of the rib pipes according to EP 0 076 928 A1 are slightly larger than the width of the rib pipe. The aforementioned advantage of the resistance limited to the current does not have other constructions in which the protection against particles covers the whole width of the cooling air current and does not take into account that in the spaces between the pipes with ribs are surfaces that are relatively insensitive to particles. Thus, US Pat. No. 3,385,355 discloses a cooler with an air inlet side plate with slits and cutouts, which form channels for air at right angles to deflect the particles. The object of the present invention is to provide a radiator with a protection against incoming particles, which while having a good protection function does not affect the cooling air stream or only the influence slightly and can therefore be manufactured and installed in an arrangement light and that requires little space and economic price. This object is achieved by means of a radiator with the characteristics of the main claim, with preferred embodiments described in the subclaims. The invention also employs facing strips or grid ribs that are preferably arranged spaced apart from the walls of rib tubes that must be covered in a grid assembly. The covering bands or the grid part can be fastened directly on the rib tubes or in the intermediate spaces. The necessary fasteners can be formed directly in the covering strips or the grid part or they can be introduced as separate fasteners. The coating strips or the grid part and the fastening elements can be made of sheet or preferably of plastic as plastic injection parts. The coating bands used here may have a width slightly larger than the area of the rib tube wall to be covered. Since the area of rib tube wall to be covered, especially in the case of flat tubes compared to the total radiator surface represents only a limited extent, an extension of the width of the coating band by 20% to 30% in comparison with the width of the rib tube walls with the possibility of damage, it only influences in an insignificant way the passage of the air current. By using the particle guard according to the present invention, essentially all assembly parts, installations and equipment can be used as in the case of a corresponding radiator without protection. Depending on the special construction of a vehicle and the radiator arrangement, there may be an area in the front of the radiator that is more or less threatened by the impact of the particles. The expense that corresponds to the protection against the particles can therefore be reduced to the extent that only areas of radiator or areas of ribs pipes are strongly covered at risk of damage. In relation to a perspective drawing an exemplary embodiment of the present invention is presented. The figure shows an area of a radiator 1 for a car with tubes with ribs in parallel, horizontal
2, 3, 4, 5 and 6, joined together by corrugated heat deflection blades 7, 8, 9 and 10. The rib tubes are in the form of flat tubes with an elongated, narrow, rectangular cross section, each with two opposite narrow sides 11, 12 and two large sides 13, 14. In the tubes with ribs 2 to 6 are found as a union between the corresponding wide sides 13, 14 parallel ribs 15 constructed to carry a cooling medium (arrow 20) through longitudinal chambers 16, in our case six longitudinal chambers 16. The external ribs 17, 18 that laterally limit the pipes with ribs 2 to 6 form the narrow sides 11, 12. During the operation of the radiator 1 in installed condition said radiator is arranged in the front of a vehicle in such a way that a stream of cooling air flows in the direction of the outer ribs 18 and through the corrugations of the diverting blades heat 7 to 10, as indicated by arrow 19. With the cooling air stream (arrow 19), there are also small particles such as, for example, small stones, sand, etc. The grid part 22 consisting of horizontal and parallel covering strips 23, joined by vertical ribs 25 and which in the assembled state cover the narrow sides 11 of the pipes with ribs 2 to 6 or their external ribs 18 prevent the arrival of these particles on the narrow sides 11 of the pipes with ribs 2 to 6. The grid part 22 is fixed on the pipes with ribs 2 to 6 or in their intermediate spaces by integrated fasteners 24 or with separate fasteners 26 (FIG. shows alternately in dotted lines). The covering bands 23 can also be fixed individually without grid structure on the tubes with ribs 2 to 6. The grid part 22 is made of injected plastic. A grid part 22 fastened on a radiator 1 represents an effective protection against damage caused by the impact of particles and especially prevents perforations of the tubes with ribs 2 to 6. The protective effect can be increased to the extent that the width of the covering of the coating strips 23 is 20% to 30% greater than the width of the corresponding narrow sides 11 of the tubes with ribs 2 to 6. It may also eventually be sufficient to protect a radiator only in the places particularly affected by the flow of particles.