Abstract:
The invention relates to a low-function vehicle tyre for driving training and to a method of producing a tyre. The tyke is characterized in that the contact surface of the tyre is a low-friction contact surface comprising grip-weakening material for enabling winter driving training.

Description:
FIELD 
       [0001]    The invention relates to a vehicle tyre and to a method of manufacturing a tyre. 
       BACKGROUND 
       [0002]    In the Finnish driving school system, the tuition includes compulsory winter driving training both in the first and in the second phase of driving school. Winter driving training is usually carried out on special driving tracks intended for training winter driving. During winter, the driving surface of the slippery driving training track consists of ice and condensed snow, enabling winter driving training, but at other times, the slippery driving surface has to be created artificially. The driving training track may be coated with plastic or sheet metal, which is spread with water or different oils to reduce friction. 
         [0003]    A disadvantage of the winter driving training based on lubricating the driving surface artificially is the high construction and maintenance costs. Furthermore, the plastic or sheet metal surface lubricated with oils or water may even be unreasonably slippery considering how realistic such winter driving training is. It is also to be noted that oils cause environmental damage and that after winter driving training, the vehicle tyres may still have oil on them, which not only affects the driving properties but also increases the risk of accident on the asphalt. 
         [0004]    U.S. Pat. No. 4,700,798 describes a four-wheel structure which is attached to the vehicle frame and which weakens the contact with the driving surface by lifting the vehicle from the driving surface. A disadvantage of the structure described in the above-mentioned publication is that the vehicle has to be provided with counterparts for attaching the structure to the vehicle. A further disadvantage of the structure is its unrealistic driving properties as the weight of the vehicle does not totally rest on its four wheels but also partly on the structure attached to the frame. 
         [0005]    U.S. Pat. No. 4,335,899 describes a pedal car whose rear tyres comprise rollers that rotate transversely to the tyre rotation direction, the purpose of the rollers being to weaken the grip of the rear tyres in a curve. This publication describes a complicated solution for reducing the grip of a tyre. Furthermore, the tyres according to the solution are intended to reduce the tyre grip only in curves due to the rotation direction of the rollers. Neither does the publication discuss the driving properties of the rollers functioning as a contact surface against the tyre driving surface when a vehicle moves straight ahead. The publication in question does not mention, for example, the material of the rollers, i.e. contact surface, or any other issue affecting grip. 
         [0006]    JP 10-81112 describes a vehicle tyre where the contact surface in contact with the driving surface is coated with a material that prevents mud from sticking to the tyre surface. Thus mud cannot block the tyre tread and reduce the grip. A tyre coated with such material improves the contact between the tyre and the driving surface and thus also the driving properties. 
         [0007]    GB 2351691 also describes a solution where material pre-venting mud from sticking to the grooves in the tread of a tyre or a shoe is added to the surface of a tyre, shoe or the like (to the bottom of a shoe). In the solution described in this publication, only the grooves of the tyre or shoe tread are coated with such material. A tyre or a shoe coated with this kind of material thus improves the contact between the tyre or shoe and the driving surface and consequently also the grip properties. 
       BRIEF DESCRIPTION 
       [0008]    The object of the present invention is to provide a driving training tyre designed for winter driving training to avoid the problems associated with prior art solutions. 
         [0009]    This object is achieved by a vehicle tyre according to the invention, which comprises a frame structure and a contact surface and which is characterized in that the contact surface is a low-friction contact surface comprising grip-weakening material for enabling winter driving training. 
         [0010]    An aspect of the invention relates to a method of producing a vehicle tyre, which is characterized by forming a low-friction contact surface on the tyre frame structure, the low-friction contact surface comprising frictionweakening material and enabling winter driving training. 
         [0011]    The driving training tyre according to the invention provides several advantages. The low-friction driving training tyre enables winter driving training in a technically simple manner on a conventional driving track coated with asphalt or concrete or on another suitable conventional substructure. Thus winter driving can be also trained in closed-off areas other than driving training tracks provided with lubricating apparatuses. Such areas include parking lots and infrequently used airfields. Winter driving can also be trained with different tyre grip properties using different tyre series that comprise different grip-weakening material compositions. This corresponds to winter driving training on different road surfaces, such as on an icy, wet or snowy road surface. Furthermore, winter driving training is economical because the driving conditions on slippery roads can be provided simply by changing the vehicle tyres. The driving training tyres according to the invention require no special features of the vehicle but the driving training tyres can be installed in the vehicle in the same way as conventional tyres intended for conventional driving. 
     
    
     
       LIST OF FIGURES 
         [0012]    In the following, the structure of a tyre according to prior art and a driving training tyre and a method of manufacturing a tyre according to the invention will be described in greater detail with reference to the accompanying figures, in which 
           [0013]      FIG. 1  illustrates a cross section of a prior art vehicle tyre, 
           [0014]      FIG. 2  illustrates a cross section of a low-friction vehicle tyre whose contact surface comprises grip-weakening material, and 
           [0015]      FIG. 3  illustrates a cross section of a low-friction vehicle tyre whose contact surface comprises grip-weakening material and is treaded. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]    In the following, the general structure of a motor vehicle tyre will be described with reference to  FIG. 1 . As a supporting structure, the tyre  100  comprises a frame  108 , which provides the tyre with its elastic properties and shape. The frame  108  may be made of a nylon braid reinforced with steel, for example. The uppermost layer of the frame  108  may be a belt structure  102  that surrounds the tyre  100 . The belt structure  102  may be made of nylon braid, for example. The belt structure is not, however, a necessary part of the tyre  100 . Furthermore, the tyre  100  comprises side surfaces  104 ,  106  on both sides of the frame  108 , which are usually made of a rubber composition and protect the tyre frame  108 . The tyre  100  further comprises a contact surface  112 , which affects the grip properties of the tyre  100 . The contact surface  112  is the part of the tyre  100  that is in contact with the driving surface, and thus the material and tread of the contact surface  112  have an essential effect on the vehicle&#39;s driving properties. Usually the contact surface  112  is made of a rubber composition. The contact surface  112  of the tyre  100  may be cast of the same material together with the side surfaces  104 ,  106  of the tyre or they all may be made of different materials. The tyre is typically installed around a disc wheel  110 . The disc wheel  110  is usually made of metal or a metal alloy. 
         [0017]    In the following, the structure of a low-friction driving training tyre will be described with reference to  FIGS. 2 and 3 . 
         [0018]    The friction coefficient between the contact surface of the tyre and the driving surface is decreased for winter driving training on an asphalt surface, for example. In a preferred embodiment of such a low-friction tyre, the contact surface  202  consists of a grip-weakening material which forms a friction coefficient between the contact surface  202  and the driving surface that is at most 50 percent of the friction coefficient of the rubber material of a high-friction vehicle tyre intended for road traffic use. The friction coefficient between the high-friction rubber material and the asphalt-coated driving surface is approximately 1, whereas the friction coefficient between the contact surface of a low-friction tyre and the asphalt-coated driving surface is below 0.5. The low-friction tyre can be used for simulating slippery driving conditions, such as driving properties in winter conditions, since in high-grip winter conditions, the friction coefficient may be approximately 0.35, whereas in very slippery winter conditions, the friction coefficient may be approximately 0.1. 
         [0019]    The grip-weakening material of the low-friction tyre may be polyurethane, for instance. Other feasible grip-weakening materials include polyethylene, polyamide, polytetrafluoroethylene (teflon), various silanes, epoxes, and rubber-based elastomers not suitable for use on roads due to their low friction. The grip-weakening material may also be a composition including, in addition to at least one of the above-mentioned materials, other components affecting the grip properties. Even though only a few examples of grip-weakening materials were described above for providing a tyre with a lower friction, it is clear that the tyre contact surface may also comprise other grip-weakening materials. Low-friction tyres with different grip properties can be obtained by using different grip-weakening material compositions on the tyre contact surface. This enables simulation of different driving conditions, such as high-grip or very slippery winter conditions, slippery conditions caused by water on the driving surface or other factors. 
         [0020]    As appears from  FIG. 2 , the low-friction tyre comprises a frame structure  208 , which may be similar to the frame structure of a prior art vehicle tyre. The contact surface  202  of the low-friction tyre  200  (“low-friction contact surface”) comprises grip-weakening material. The contact surface  202  may be completely made of grip-weakening material. The contact surface  202  may also be made of a mixture of a high-friction rubber composition and grip-weakening material, where the mixing ratio of the rubber composition and the grip-weakening material determine the grip properties of the low-friction tyre  200 . The grip-weakening material and the rubber composition may also be separate layers on the contact surface  202  of the low-friction tyre  200 . The grip-weakening material may also be a coating which is formed around the low-friction tyre  100  parallel with the tyre circumference and extends around the tyre, being substantially as wide as the contact surface  202  of the low-friction tyre  200 . 
         [0021]    In a preferred embodiment of the low-friction tyre  200 , the grip-weakening material also extends at least partly to either of the side surfaces  204 ,  206  of the tyre  200  or to both of them. The side surface or side surfaces  204 ,  206  may be completely made of grip-weakening material. The side surface or side surfaces  204 ,  206  may also be made of a mixture containing a high-friction rubber composition and grip-weakening material. The grip-weakening material and rubber composition may also be separate layers on the side surface or side surfaces  204 ,  206  of the tyre. 
         [0022]    The contact surface  202  of the low-friction tyre  200  according to  FIG. 2  is smooth. To affect the grip properties of the tyre  200 , the contact surface  202  may also be treaded. The contact surface may be treaded with longitudinal grooves to weaken the grip properties. The contact surface  302  of the low-friction tyre  300  according to  FIG. 3  comprises transverse grooves  304 , which, depending on the density of transverse grooves, make the tyre vibrate during driving (a vibrating tyre). Thus the tyre  300  makes a clearly audible sound during driving. When the tyres lock in connection with braking, the sound changes, which facilitates the noticing of the locking of the tyres. 
         [0023]    A low-friction tyre can be produced by tyre manufacturing methods known per se. In the production of a low-friction tyre, it is essential to form a low-friction contact surface comprising grip-weakening material so that it rests on the tyre frame structure. Either or both of the side surfaces of the low-friction tyre may be formed from grip-weakening material. A low-friction tyre may also be produced using an existing tyre which comprises at least a frame structure. A new contact surface containing grip-weakening material may be formed on an existing tyre contact surface. The original contact surface of an existing tyre may also be removed, in which case a new contact surface is formed. A low-friction tyre can also be produced by manufacturing a frame structure and forming a contact surface that rests on it and comprises grip-weakening material. 
         [0024]    To facilitate the noticing of the low-friction property of a tyre, a preferred embodiment of the low-friction tyre  200 ,  300  comprises a deviation indication area. The purpose of this is to reduce the risk of inadvertently using the low-friction tyre in road traffic. The deviation indication area may be included in the grip-weakening material of the low-friction tyre  200 ,  300 , for instance. The deviation indication area may comprise the tyre contact surface  202 , either or both of the tyre side structures  204 ,  206 , or several of the above-mentioned tyre components. The deviation indication area may also be a separate deviation indication means added to the tyre. Such a deviation indication means may be, for example, a sticker, stamp or paint highlighting. 
         [0025]    The deviation indication area may be implemented by, for example, colouring  306  so that it can be clearly noticed whether a tyre is a low-friction one. The deviation indication area may also be implemented by tread. If the deviation indication area is implemented by tread and the contact surface  302  is part of the deviation indication area, the contact surface  302  may be treaded such that the tyre makes a clearly audible sound during driving. The tread may be, for example, similar to the transverse grooves  304  in the tyre  300  as shown in  FIG. 3 . The tread may also be provided on the side surface  204 ,  206  of the tyre to indicate that the tyre is a low-friction one. 
         [0026]    Even though the invention was described above with reference to the examples according to the appended drawings, it is clear that the invention is not restricted to them but it may be varies on several ways within the inventive concept disclosed in the enclosed claims.