A METHOD AND APPARATUS FOR PATTERN CUTTING OF TYRES

Abstract: A worn vehicle tyre (10) is placed in a tread pattern cutting apparatus (20) for renewal of the pattern of the tread by a deepening thereof. The tread pattern cutting apparatus is provided with an endless chain (22) which encompasses at least two mutually spaced-apart carrier rollers (23, 24). Therebetween, the chain is in the form of a bight in which the tyre rests during the pattern cutting operation. By drive means (not shown on the drawing), the endless chain (22) is moved in its path, a tyre (10) resting in the chain being thereby rotated. By detector means (36), the distance of the tread to the cords of the tyre is sensed throughout the entire circumference of the tyre and these distances are registered so as, on the bases of the thereby registered smallest distance on renewal of the pattern of the tread, to adjust the cutting head (33) in a cutter (30) to a cutting depth which entails that the tread pattern depth will be substantially uniform throughout the entire circumference of the tyre.

Description: A METHOD AND APPARATUS FOR PATTERN CUTTING OF TYRES The present invention relates to a method and an apparatus for re¬ newing the pattern of the tread of a worn vehicle tyre, according to the preambles of the independent method claim and the independent apparatus claim. Vehicle tyres are subject to a number of requirements, such as a high degree of mechanical strength and a certain rigidity, long working life, a good gripping power whatever the road surface, and an econom¬ ical price. The properties of the tyre are determined, apart from by the rigidity of the tyre body, also by the rubber composition and pattern which are employed. The pattern is adapted to serve different purposes, and adaptation which, however, may entail undesirable draw¬ backs concerning, for example, the abrasion and wear resistance of the tyre. In general, it applies that a coarse and deep pattern makes for good vehicular road adhesion and traction, but entails a high de- gree of tyre wear, while a completely smooth tyre has, in most cases, poor gripping power but very long service life. Tyre manufacturers strive to strike the happy medium between these properties according to the contemplated use of the tyre, for example if the tyre s to serve a driving or simply rolling purpose. Concerning the wear of a standard tyre, a rule of thumb is that when approximately 2/3 of the tread depth is worn off, there remains approximately 50 % of the tyre ' s working life, which is as a result of the fact that a tyre with great tread pattern depth wears more quickly. Consequently, in order to meet requirements of economy, the tyres - and in particular heavy-duty tyres such as lorry and truck tyres - are not only provided with a certain pattern, but are also provided with a relatively thick layer of solid rubber which has no pattern and is disposed between the tread pattern and the body of the tyre. The intention with this provision is to be able, when the tyres are worn to an unacceptable pattern depth, to deepen the pattern by so-called pattern cutting. On a normal lorry tyre, the layer of solid rubber is of a thickness of approximately 7 mm, which provides for the possibility of a deep¬ ening of a worn pattern tread by approximately 4 mm, whereby the work¬ ing l fe of the tyre will be further extended by between 15-20%, over and above the working l fe provided by the original pattern tread depth. It is previously known in the Art to pattern cut worn vehicle tyres, the cutting operation being effected at a constant distance from the tyre cords, which entails that the tyre, after the cutting operation, has-a-varying pattern depth. That such is the case is because tyres always wear unevenly and because the worn tyre, prior to renewal of the tread pattern has, in certain cases, a slight pattern depth and in other areas a greater pattern depth. This varying pattern depth makes for a vary ng degree of wear which is, among other things, as a result of the fact that wear is more rapid in cases of greater pat¬ tern depth. As a consequence of this, the remaining working l fe of the tyre is shortened. The present invention relates to a method and an apparatus in which tyres may be pattern cut so as to employ the above-disclosed layer of solid rubber for deepening a worn pattern, and in which the drawbacks inherent in prior Art methods and apparatuses are obviated. In the characterising clauses of the -independent claims appended hereto re¬ lating to the method and the apparatus, respectively, the method and the apparatus according to the present invention are described for realising the contemplated effect. Preferred, advantageous embodi¬ ments of the present invention are disclosed in the subordinate claims appended hereto. The nature of the present invention and its aspects will be more readily understood from the following brief description of the accompanying drawings, and discussion relating thereto. In the accompanying drawings: Fig. 1 is a partial section through a tyre; Fig. 2 is a schematic perspective view of one apparatus according to the present invention; and Fig. 3 is a schematic perspective view of a detector device together with registration means. Referring to the drawings, Fig. 1 shows a tyre 10 with a body in which are included a number of cord layers 12a-d. The tread with its pattern is disposed outside the cord layers. The pattern is formed by grooves 11 whose bottom 15 is separated from the cord layers by a rubber layer 14. The outer defining surface of the tread layer which constitutes the tread surface of the tyre is designated 13 in the drawing figure. Fig. 2 illustrates an apparatus 20 for pattern cutting according to one embodiment of the invention, in which the apparatus includes a frame 21 in which there are journalled two mutually spaced-apart upper carrier rollers 23 and 24. In a region below the upper carrier rollers, there are at least two lower tensioning rollers 25a and 25b. An endless chain 22 forms an upper chain part 22a and a lower chain part 22b, and encompasses both the upper carrier rollers and the lower tensioning rollers. The upper chain part forms a bight between the carrier rollers. The width of the chain is, in the illustrated embodiment, at least substantially of the same order of magnitude as the width of the tread of the tyre. The upper carrier rollers 23 and 24 are disposed for movement rela¬ tive to one another and are locked in the set position, whereby the distance between the carrier rollers s adapted to the diameter of the tyre which is intended to be placed in the bight of the upper chain part. Furthermore, the carrier rollers are, as a rule, rota- tably journalled. At least one of the lower tensioning rollers 24a,25b shown in the illustrated embodiment is adjustable to posi¬ tions in which it may be locked. The length of the bight of the upper chain part is, thus, determined on the one hand by the distance between the upper carrier rollers, and, on the other hand, by the position of the lower tensioning roller. At least one of the tensioning or carrier rollers is disposed as a drive means for movement of the chain 22. In certain embodiments, at least one of the upper carrier rollers 23,24 is provided with a sub¬ stantially smooth cylindrical surface so as to allow the chain 22 to slide in relation thereto. As a rule, the tensioning or carrier rol¬ ler or rollers provided as drive means are fitted with gearing or sprocketing (not shown on the drawings) for cooperation with corre¬ sponding members for driving the chain. As s shown in the drawing figure, in one embodiment, that carrier roller 23 where the chain, on its movement, goes about to form the lower chain part, is located on a higher level than the other carrier roller 24. The figure also shows a preferred embodiment in which the upperjnost-located carrier roller 23 is placed substantially in dia¬ metric relationship to a cutter 30. Fig. 2 also shows support means 26a,26b for the lateral positioning of the tyre when the tyre rests in the bight of the upper chain part. Corresponding support members are provided on the opposing side of the tyre. Alternatively, the apparatus includes, for example, at least one substantially vertical wall which constitutes a part of the frame of the apparatus and, moreover, forms support means for the tyre. The embodiment of the cutter 30 illustrated in the drawing figure is provided with a journal 32 preferable designed as a knuckle. At its one end region, the cutter is provided with a cutting head 33 shown in the figure as a cutting knife, and at its other end region is pro¬ vided with a handle 35. The journal 32 is connected to a shaft 34 along which the journal may be moved substantially at right angles to the direction of movement of the chain 22. A drawbar 31 or a chain with an anchorage 46 to, for example, the frame of the apparatus and movable in parallel with the journal 32 connects the cutter (for ex¬ ample by the intermediary of a lever) to the frame for accommodating friction forces between the cutter and the rubber of the tyre. The position or length of the drawbar (or chain) is locked by means of locking members 39, for example a clamp, pin or the like. The loca¬ tion of the cutter is, thereby adjustable in a position determined on each pattern cutting occasion, this, in turn, being determinative of the pattern tread depth. The combination of locking members 39 and drawbar (chain) constitutes a non-restrictive example of positioning members for adjustment of the cutting depth. It will be obvious to the skilled reader of this specification that such positioning de- vices with alternative embodiments are available within the Art. Such embodiments as, for example, are adjusted by direct mechanical effect by, or signal transmittance from, a detector device 36 as dis¬ closed below also fall within the inventive concept of the present invention. A detector device 36,41,42 (cf. also Fig. 3) is shown on the drawings in one embodiment in which the sensor 36 of the detector device is, by means of suspension arms 37a,37b mounted in journals 38a,38b, piv- otally connected with the frame of the apparatus. The sensor is dis¬ posed so as, for example, to slidingly abut against the outer defin- ing surface 13 of the tyre, whereby the exact distance between the defining surface and the cord layers of the tyre will be determined. In certain embodiments, the sensor is split into subunits 40 which are distributed about the width direction (axial di ection) of the tyre in order, on sensing of obliquely worn tyres, to detect the shortest distance to the cords in one such obliquely worn region. Fig. 3 shows one embodiment in which the exact position of the sensor 36, and, in particular, the subunits 40, in relation to the frame 21 and thereby in relation to the centre of rotation of the wheel, is determined by means of a transmitter 41 included in the detector de- vice, whose radiation 47, for example parallel light beam radiation, is detected by the receiver 42. A register device 43 and calculator 45 are connected to the receiver and register the cord distance and/or the distance of the tread to the centre of rotation of the tyre for each portion of the tyre and, for example by the interme- diary of a digital device 44, indicate the value at which the cut- ting depth is to be set when this portion is to be pattern cut. In certain physical applications, this value is displayed to the ope¬ rator, while in other physical applications, this information is transmitted to positioning devices, for example via mechanical means or via electric signals to servo-members for adjustment of the cut¬ ting depth of the cutter 30. To facili ate placing of the tyre in the bight of the upper chain part, a roll-on ramp 29 is provided in the apparatus. On employment of an apparatus according to the present invention, a tyre is rolled up on the roll-on ramp 29 to a position in the bight of the upper chain part 22a, whereupon the support means 26a,26b are brought into abutment against the side walls of the tyre, and the endless chain 22 is set in motion by the drive means 23-25 employed. The motors, or corresponding devices, acting on the drive means 23-25 may consist of any appropriate devices whatsoever and, for purposes of simplicity, have been omitted from the drawings. On movement of the chain, the tyre 10 is set in rotation. Initially, the rotation of the tyre is employed for inspection purposes, for example for deter¬ mining possible damage, for removing stones and other objects which have fastened in the tyre and for determining the smallest distance between the outer defining surface of the tyre and the cord layers of the tyre. This latter determination is effected by means of the de¬ tector device 36,41,42. Moreover, an operation is, as a rule, employ¬ ed to determine and register the distance, throughout the entire cir- cu ference of the tyre, between the outer defining surface and the cord layers of the tyre and/or the distance from the outer defining surface to the axis about which the tyre rotates. By means of the cutter 30, the desired pattern is cut out in the tyre, the depth of the grooves thus formed being generally the same throughout the entire circumference of the tyre. On determination of the size of the depth of the grooves, the point of departure is the smallest distance between the outer defining surface of the tyre and the cord layers of the tyre. This ensures that the cords remain in¬ tact, at the same time as the tyre, on continued use, will retain the form it assumed during its earlier wear. This procedure reduces to a minimum the coming wear to which the newly pattern-cut tyre will be exposed in subsequent use. It will be obvious to the skilled reader of this specification that the movement of the drive means and, thereby, the chain 22, may be controlled by, for example, a foot pedal, which entails that the operator quite simply directs the rotation of the tyre, at the same time as both of the operator ' s hands are free to be employed in con¬ junction with the pattern cutting operation. As a rule, the apparatus is disposed to be able to move the chain 22 and thereby the tyre in any optional direction of rotation depending upon the needs which arise during the pattern cutting work. It is further obvious that the bight of the upper chain part forms a large abutment surface against the tyre, whereby pointwise severe loadings on the tyre are avoided and the risk of deformation of the tyre is reduced. As a result of the high coefficient of friction of the tyre material, a reliable driving of the tyre will be ensured despite the low surface pressure. The forces which strive to deform the tyre are, .thus, slight, and ft has proved, in purely practical terms, to be possible to pattern-cut tyres which are neither inflated nor mounted on rims. For the operator, an apparatus according to the present invention entails a reduction in stress and strain, since at least the cutting forces in the circumferential di ection of the tyre are obtained as a result of the driving of the tyre by the chain. Reaction forces directed in the circumferential direction of the tyre are taken up by the force-absorbing member 31 which connects the cutter with the frame of the apparatus. It will also be apparent from the body of this specification that the tyre placed in the apparatus is surrounded on its both sides by sup- port means. As a result, the tyre is mechanically stabilised in sub¬ stantially horizontal pattern cutting, i.e. pattern cutting directed fundamentally in the axial direction of the tyre, whereby the pattern cutting may be executed using any optional cutting head or device which is apt to this purpose. Suitably, such pattern cutting is ef- fected in a region which is located on the tyre between the support members. In certain embodiments, the cutter 30 is provided with cut¬ ting heads 33 suitable for and/or adjustable for the pattern cutting described in th s paragraph. In certain embodiments, the cutter is also provided with drive means which move the cutting heads in the above-mentioned pattern cutting operation. The above detailed description has referred only to a limited number of embodiments of the present invention, but the skilled reader of this specification will readily perceive that a great number of em¬ bodiments of the present invention are conceivable without departing from the spirit and scope of the appended claims.

Claims: CLAIMS 1. A method of renewing, in a worn vehicle tyre (10), the tread pat¬ tern by removal of material portions from the tyre for forming pattern-creating grooves in the tread (11), one or more cord layers (12) embedded in the tyre being used as reference level on setting of maximum depth of the grooves which are formed on re¬ newal of the pattern of the tread, characterised in, that the distance between said cord layers (12) and the outer defining surface (13) (the wear surface of the tyre tread) of the worn tyre is determined throughout the entire circumference of the tyre; that the smallest measured value for the d stance governs the adjustment of cutting means (32) to a cutting depth substan¬ tially in agreement in relation to the extant tread; and that the set cutting depth is applied about the entire tyre on renewal of the pattern of the tread. 2. The method as claimed in claim 1, characterised in, that the smallest measured distance between the wearing surface of the tread and the cord layers (12) is registered in a registration device (43). 3. The method as claimed in claim 2, characterised in, that the distances between the cord layers (12) and the outer defining surface (13) throughout the entire ci cumference of the tyre are registered in the registration device (43). 4. The method as claimed in claim 2, characterised in, that the distances between the outer defining surface (13) and that axis about which the tyre rotates are, throughout the entire circum¬ ference of the tyre, registered in the registration device (43). 5. The method as claimed in anyone of claims 2-4, characterised in, that the values of the registration device (43) for the measured distances are transmitted to calculator means (45); and that said calculator means, during the cutting-out of the pattern for each position of the tyre in relation to the cutter (30), calculates and displays the closest position of the cutter in relation to the cord layers (12). 6. The method as claimed in claim 5, characterised in, that the position of the cutter (30) is visually displayed. 7. The method as claimed in claim 5, characterised in, that the position of the cutter head (33) is transmitted to positioning means connected to the cutter head. 8. An apparatus for renewing, in a worn vehicle tyre (10) the pat¬ tern of the tyre read by removal of mater al portions from the tyre for formation of pattern-creating grooves in the tread (11), one or more cord layers (12) embedded in the tyre being used as reference level on adjustment of maximum depth of the grooves which are formed on renewal of the pattern of the tyre tread, the apparatus including at least one cutting head (33) for removal of said material portions, an endless chain (22) forming a path which passes and encompasses two mutually spaced-apart carrier rollers (23,24), whereby the chain has an upper chain part (22a) and a lower chain part (22b), of which the upper chain part forms a bight in which the tyre rests during the pattern cutting opera¬ tion, and the apparatus further including drive means (23-25) for rotation of the tyre during the pattern cutting, characterised in, that a detector device (36,41,42) is disposed for sensing of the distance between the tread (13) and the cord layer (12); that registration means (43) are provided for receiving and registra¬ tion of information relating, to sensed distance; and that calcu¬ lating means (45) are provided for indicating, on the basis of in- formation received from the registration means, a substantially corresponding cutting depth relative to the extant tread in each portion thereof about the circumference of the tyre tread. 9. The apparatus as claimed in claim 8, characterised in, that the detector device (36,41,42) includes sensing means (36) movably journalled in the apparatus and disposed to abut against the tread (13) of the tyre during rotation of the tyre. 10. The apparatus as claimed in claim 9, characterised in that the detector means (36,41,42) includes means (41,42) for sensing of the position of the sensor (36) in relation to the axis about which the tyre rotates.

Inventors: TROLLE STEN, TROLLE, STEN
Applicants: TROLLE STEN, TROLLE, STEN
Application year: 1985
Main classification: B29D30
IPC codes: B29D30