Patent Publication Number: US-2017356141-A1

Title: Roller For Asphalt Compaction, In Particular A Rubber Tire Roller, And Method For Spraying A Rubber Tire Of A Roller For Asphalt Compaction

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 10 2016 007 166.4, filed Jun. 13, 2016, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a roller for asphalt compaction, in particular a rubber tire roller, with a rubber tire and a spray device for spraying a separating agent mixture onto the rubber tire, as well as a method for spraying the separating agent mixture onto a rubber tire of a roller for asphalt compaction, in particular a rubber tire roller. 
     BACKGROUND OF THE INVENTION 
     Generic rollers for asphalt compaction or asphalt rollers with at least one rubber tire, in particular rubber tire rollers, are sufficiently known from the prior art. Such self-propelled rollers usually include a machine frame, a chassis, at least one rubber tire, a water tank and an operating platform or driver&#39;s cabin, preferably with rollover protection. Furthermore, they include a main drive motor, which is usually a combustion engine, for example, a diesel engine. The rubber tire roller belongs to the group of static rollers and effects a compaction of a substrate or ground surface by means of its weight alone. The essential feature of a rubber tire roller are the rubber wheels, which are normally suspended individually and compact the ground by virtue of their compressing and kneading action. In addition to compaction, a closing of pores on the surface of the ground is realized. During operation, the rubber tire roller with the rubber tires is guided or rolled over the surface to be compacted. The rubber tires, driven by the main drive motor, are thus rotated about a rotational axis running horizontally and transversely to the working direction. The present invention thus generally relates to rollers for asphalt compaction comprising at least one rubber wheel used in the compaction process. In this respect, it is known to provide rollers for asphalt compaction with a metal drum and at least one rubber tire. Such rollers are also referred to as combined rollers. One example of such a roller is the Applicant&#39;s model BW 138 AC-5. A “pure” rubber tire roller is, for example, the model BW 27 RH of the Applicant, which exclusively comprises rubber tires for the asphalt compaction. Thus, as far as details regarding the construction of the roller are indicated below, these relate, in particular, to rubber tire rollers, in particular such that exclusively comprise rubber tires. 
     During the operation of the roller for asphalt compaction, it regularly occurs that the surface to be compacted, in particular asphalt, undesirably adheres to the rubber tires and is carried along. This tendency of the rubber tire to carry along surface material is decisively influenced by the temperature of the wheels and by the paving material/surface material to be compacted, in particular asphalt material. It has been found that adhesion is all the more probable the lower the temperature of the rubber tires. In order to counteract an adhesion of the surface material, in particular, to the rubber tires that have not yet warmed up at the onset of operation, it is thus common to spray the rubber tires with a so-called separation agent mixture. The separation agent mixture typically is an emulsion formed of a separation agent concentrate, often organic in nature, and water. A known separation agent concentrate is, for example, known under the name “BOMAG bitumen separation agent”, “BOMAG Separation Agent” or its trade name “BITU-TRENNKONZENT.GRÜN (BOMAG)”. Typically, the responsibility for the separation agent mixture lies with the roller operator, who fills the separation agent mixture into a tank fixed to the machine. In this case, the roller operator must observe the correct mixing ratio between water and separation agent concentrate, since this depends on the specific application for which the roller is currently being implemented, on the one hand, and, on the other hand, on the specific separation agent concentrate being used. As soon as a separation agent mixture of an unknown composition is present in the tank, it is more difficult to precisely adjust the desired mixing ratio of separation agent concentrate and water within the separation agent mixture so that it cannot be guaranteed that the prepared separation agent mixture meets the requirements for attaining the desired effect, namely the suppression of adherence of the surface material to the rubber tire, in accordance with the current application. 
     Moreover, it has repeatedly proven disadvantageous that the separation agent mixture has to be protected against frost. In practice, in cases where there is a risk of frost, this often results in the necessity that the separation agent mixture contained in the rubber tire roller, in a laborious procedure, first has to be drained after working operation, then collected, subsequently temporarily stored in an area protected against frost, and finally filled back into the tank or disposed of after collection. Segregation tendencies of the separation agent mixture also cause problems. For example, it may be necessary for the separation agent mixture to be manually re-mixed by the driver after prolonged downtimes of the roller, which is also deemed to be disadvantageous. 
     It is therefore an object of the present invention to provide a roller for asphalt compaction with at least one rubber tire, which permits a setting of the mixing ratio of separation agent concentrate and water that is as precise as possible, and the handling of which in case of the risk of frost is simplified in comparison with the prior art. Furthermore, a method for the operation of such a roller is indicated. 
     SUMMARY OF THE INVENTION 
     Specifically, the present invention proposes the separate provision of a first liquid, preferably water, in a first tank and a second liquid, preferably a separation agent concentrate, in a second tank on the roller for asphalt compaction, in particular the rubber tire roller. Specifically, the separating agent concentrate is typically a liquid comprising, for example, oil, particularly vegetable oils, and at least one additive, for example, an emulsifier. Separation agent concentrates per se are known. By means of the mixing device according to the present invention, the first liquid and the second liquid can be mixed on the roller, in particular the rubber tire roller, to form the separation agent mixture in accordance with the need at hand, even during operation, so that the separation agent mixture provided by the mixing device can essentially be used up by the spray device. Unlike methods to date, the separation agent mixture is thus mixed continuously from the first and the second liquid, throughout the operational process, on the roller on site. Accordingly, by means of the roller according to the present invention, it is avoided that a considerable remainder of separation agent mixture remains in the roller after operation. Consequently, in the case of a new operation of the roller, it is possible to prevent the disposal of the separation agent mixture still present in the roller as a result of not knowing the mixing ratio present. Moreover, the mixing ratio can be set precisely during the new operation independently of any knowledge regarding the previous applications of the roller. Furthermore, the use of a first tank and a second tank permits a more flexible handling since the first tank and second tank can be formed differently in terms of size. In particular, a volume capacity of the second tank is less than a volume capacity of the first tank, preferably less than half the volume capacity of the first tank, and especially less than a quarter of the volume capacity of the first tank. The volume capacity ratio of the first tank to the second tank is thus particularly preferably greater than 10:1 and especially greater than 15:1. Due to its smaller volume capacity, the second tank can be emptied more quickly and thus more flexibly and its contents can be exchanged faster than is the case with a tank provided for the separation agent mixture according to the prior art. This makes the handling of the roller according to the present invention more flexible, e.g., with respect to an exchange of the separation agent concentrate. Moreover, the premixing of the separation agent mixture, necessary up until now before a working operation, can be omitted. According to one aspect of the present invention, a first pump for conveying the first liquid from the first tank to the mixing device and/or a separate second pump for conveying the second liquid from the second tank to the mixing device is/are provided. In one embodiment, both liquids may be conveyed to the mixing device via their own respective pumps. 
     Preferably, the roller comprises a first supply line for delivering the first liquid, which connects the first tank to the mixing device, and/or a second supply line for delivering the second liquid, which connects the second tank to the mixing device. Preferably, the first supply line and/or the second supply line comprise a filter. By virtue of the filter, it is possible to remove impurities from the first or second liquid in an advantageous manner before they reach the mixing device or any pumps. This has a positive effect on the service life and functionality of the mixing device or any pump downstream of the filter. Downstream of the mixing device, viewed in the conveying direction from the tanks of the first and the second liquid, a connecting line to the spray device is also provided via which the produced separation agent mixture can be applied to the at least one wheel. Preferably, a filter is not present within this section of supply line. The first and second pumps are ideally both arranged between the first/second tank and the mixing device. 
     In the present invention, a mixing device denotes a functional whole of components, which enable a joining of the first liquid and the second liquid, a mixing of the first liquid and the second liquid to form the separation agent mixture and the delivery of the separation agent mixture at an outlet of the mixing device. To this end, the mixing device is connected to the first and the second tank, preferably via separate line connections. For the actual mixing, the mixing device ideally comprises a chamber, in particular a tubular chamber, in which the first liquid and the second liquid are mixed with one another. In order to further optimize this mixing process, it is also preferred if a mixing tool is provided, in particular inside the chamber, for example, a water jet pump or a static mixer with which the mixing of the two liquids is improved. The first liquid and the second liquid are preferably introduced into the chamber via a first opening and a second opening or a joint opening. Preferably, the chamber comprises, at its end, an outlet which forms the outlet of the mixing device and at which the separation agent mixture is provided for the spray device. The present invention also covers embodiments according to which the mixing device is part of the spray device or, together with the latter, constitutes a cohesive module. Alternatively, it can also be provided that the spray device is directly connected to the mixing device or that the mixing device is arranged in the engine compartment in the vicinity of the first tank and/or the second tank. In order to bridge a potential distance between spray device and mixing device, these are, in particular, connected to one another via a common supply line, via which the separation agent mixture is fed from the mixing device to the spray device. In principle, it is also possible for the roller to comprise a plurality of mixing devices, for example, for a spray device at the front and a spray device at the back, when viewed in the direction of travel. However, it is preferred that, if the roller comprises a plurality of spraying devices, for example, for different rubber tires, one mixing device supplies all spray devices with the separation agent mixture. It can thus be ensured in an advantageous manner that the mixing ratio is the same or identical for all spray devices and thus for all rubber tires. 
     Specifically, the spray device is preferably provided in the form of spraying bars, which, for example, extend along a wheel axis across one or more rubber tires. The spray bar preferably comprises one or more outlet openings, preferably outlet openings that are spaced out at a regular distance and are, in particular, equidistant from one another along the wheel axis. Preferably, the spray bar comprises one or more spray nozzles as the outlet openings, the spray nozzles being oriented in such a way that their respective spray cones hit at least, and preferably exactly, one or two rubber tires. Furthermore, according to a preferred embodiment, two spray bars are arranged across a front wheel axle in relation to the direction of travel (when the vehicle is travelling forward), while a single spray bar is arranged along a rear wheel axle in relation to the direction of travel (when the vehicle is travelling forward). 
     In principle, the separation agent mixture designates any liquid that is capable of reducing the probability of an adherence of the surface material to the rubber tire or of detaching the surface material from the rubber tire. The separation agent mixture here preferably forms an emulsion, preferably a macroemulsion (droplet diameter &gt;1 μm), miniemulsion (droplet diameter in the range of one μm) or a nanoemulsion (droplet diameter &lt;100 nm). For example, a separation agent concentrate available under the trade name “BITU-TRENNKONZENT.GR{acute over (α)}N (BOMAG)” is used for this purpose. 
     In accordance with one embodiment of the present invention, the attainable mixing ratio between the first and second liquids can be varied. To this end, the mixing device includes a regulating device for adjusting a mixing ratio of the first liquid and the second liquid in the separation agent mixture. By means of the regulating device, the roller operator change or adjust the mixing ratios of the first and second liquids in an uncomplicated manner. Specifically, the regulating device may, for example, comprise a mechanical, electrical and/or radio-controlled first actuating element, via which the roller driver can adjust and modify the mixing ratio set by the regulating device. Preferably, this first actuating element is arranged in the driver&#39;s cabin and/or in a lateral wall area that is accessible from outside the roller. Ideally, the regulating device can be controlled during the operation of the roller. As a result, the roller operator can change and optimize the composition of the separation agent mixture without interrupting the operation of the roller. In particular, the regulating device is actuated during operation in order to keep the mixing ratio in the separation agent mixture constant. Thus, the controllable regulating device can be used, for example, to counteract the circumstance that the respective viscosities of the first and the second liquid vary differently with increasing temperature and thus that temperature fluctuations during operation, especially in a period immediately after the roller has begun operation, or in the environment adversely influence the amount of first liquid and/or second liquid supplied. Furthermore, it is also possible that, by means of the regulating device, the supply of the first and/or second liquid during the operation of the roller is completely suppressed, in particular after expiry of a critical time frame following the initiation of the operation of the roller. Basically, the regulation device denotes any device with which a quantity of the first and/or second liquid delivered to the mixing device can be controlled so that the mixing ratio between the first liquid and the second liquid can be adjusted. For example, it may comprise one or more valves or one or more fine adjustment valves. Additionally, or alternatively, it is also possible to control the quantity of the first liquid and/or the quantity of the second liquid by means of a pump, in particular a variable displacement pump. 
     An element of the regulating device is a control device that controls the first and/or second pump. The control device may be part of a control circuit by means of which the quantity of the first or second liquid provided to the mixing device is adjusted automatically in order to be able to provide a separation agent mixture with a constant mixing ratio during operation. The control device is thus preferably a control arrangement with control electronics as opposed to a purely mechanical arrangement. For example, the control device can turn the first (preferred) and/or second pump on and off in intervals. A dosage of the conveyed volume thus occurs here by means of a modification of the intervals during which the pump is turned on or off. However, when the pump is on, it conveys an essentially constant volume during operation. The control device can, however, also control the first and/or second pump (preferred) in such a manner that their conveying volumes are varied during operation. This can occur, for example, by means of an adjustment of the angle of a swash plate. The pump can thus be operated continuously, while a modification of the conveyed volume can be simultaneously attained. The mixing ratio is thus attained in accordance with the invention by means of a corresponding control of both pumps by means of the control device. 
     According to one embodiment of the present invention, the control device for controlling the regulating device is connected to a first actuating element, in particular a first actuating element arranged in a driver&#39;s cabin of the roller, and/or to a second actuating element, in particular a second actuating element arranged in the driver&#39;s cabin of the roller, for setting an operating mode of the spray device. For example, the first and/or second actuating element is a switch, in particular a rotary or toggle switch, or a keypad. It is also conceivable for the first and/or second actuating elements to be integrated in a touch display. In addition to the operating modes in accordance with which the spray device is switched on or off, an interval mode is preferably provided as a further mode in the operation of the rubber roller, in accordance with which the rubber tire is sprayed with the separation agent mixture during a first time interval and spraying of the rubber tire is discontinued during a second time interval. This is adjusted, in particular, by means of the second actuating element, while the mixing ratio of both liquids is set via the first actuating element. Both actuating elements are connected to the control device. 
     Ideally, the roller comprises a control device that controls both the first pump for conveying the first liquid from the first tank to the mixing device and/or the second pump for conveying the second liquid from the second tank to the mixing device. The first pump and/or the second pump enable in an advantageous manner that the first liquid and/or the second liquid are respectively conveyed to the mixing device. It is also possible that both liquids are joined before they reach the mixing device or that they are not joined until they are in the mixing device. It is preferable that the first pump be configured to produce a first volume flow, for example, 3.8 L/min, and the second pump be configured to produce a second volume flow, for example, between 0.2 L/min to 0.95 L/min. Moreover, it is also conceivable that the first and/or the second pump are configured as a variable displacement pump, in particular one with a variable displacement volume, and in this way contribute to the adjustment of the mixing ratio. As described above, the first and/or second pump can also be configured as fixed displacement pumps so that a modification of the conveyed volume occurs by means of the intervals during which the pumps are turned on/off during interval operation. It is essential that both pumps are controlled by the control device, via which a modification of the conveyed volume per time unit and/or of the operation intervals, and thus a modification or the attainment of the predetermined mixing ratio of both liquids, is rendered possible. In particular, the first pump and/or the second pump are, for example, a hose pump, a gear pump or a diaphragm pump. The use of an economical hose pump also turns out to be advantageous inasmuch as it has little influence on viscosity and is comparatively robust, since the first liquid or the second liquid each only enter into contact with the hose. A gear pump advantageously generates a comparatively low pulsation, while a diaphragm pump is comparatively inexpensive. It is also conceivable that a pump of the same construction type is used as the first pump and as the second pump. It is particularly preferred if the first and/or second pump are connected to the electrical system on board the roller for their electrical energy supply. 
     In order to be able to store the second tank in a frost-protected way, if necessary, it is preferable that the second tank and the rest of the roller be detachably connected to one another via a coupling device. Such an attachable/detachable connection between the second tank and the roller also allows the second tank to be exchanged for a further second tank containing another liquid, for example, another separation agent concentrate or a second “filled” tank. Therefore, by simply exchanging the second tank in an uncomplicated manner, the separation agent concentrate can be changed or “replenished”. This can be accomplished using, in particular, a commercially available container, such as, e.g., a canister, so that special customized tanks are not necessary. In particular, for the purposes of removal, the connection can occur via an insert probe for suction, or the like. Alternatively, the lid of the commercially available container can also be accordingly configured for removal. A coupling device is understood, in particular, to be one with which a change between a connected state and a non-connected state can be effected repeatedly in the same manner and thus reversibly. For this purpose, the coupling device preferably comprises tank-side and roller-side coupling elements, which in the connected state, for example, interlock in a form-tight and/or frictional connection. It is also conceivable that a fastening element, such as a strap, a bracket or a bolt, ensures temporary coupling between the roller and the second tank. It is conceivable that a disengaging movement or rotational movement is effected for uncoupling the coupling elements, for example, a bayonet closure, by means of which the engagement between the coupling elements is released. It is ideal if the coupling device can be actuated without tools, i.e., purely manually, from a released position to a secured position, and vice versa. In order to ensure functionality after the mounting of a new second tank, the second tank preferably comprises a connection element which can be connected to an opening in the second supply line such that the second liquid can flow into the second supply line from the second tank. In an alternative embodiment, the roller has an outlet for draining the second liquid from the second tank. By removing the second liquid from the second tank, if necessary, it can be ensured that the second liquid does not freeze in the roller when the roller is not in use. 
     Furthermore, it is preferable that a spillage protection is provided in the outlet of the second tank. This spillage protection is characterized by the feature that it automatically closes the outlet of the second tank when the coupling device or the line to the supply system of the second tank is detached towards the mixing device and automatically opens when the second tank is connected to the coupling device. For this purpose, in particular quick couplings can be utilized, for example, the functional principle of which is, for example, illustrated in DE2653976A1. 
     In order to protect the second tank from external influences, it is also preferable to arrange the second tank within a casing, in particular an outer covering, of the roller. In particular, the tank is mounted on an inner face of the casing or the machine frame. By arranging the second tank so that at least one of its side walls lies flat against the inner surface of the casing, a stable arrangement is achieved in an advantageous manner. Additionally, or alternatively, it is also advantageous if the second tank is arranged in the engine compartment of the roller or in the region of the wheel housing. By arranging the second tank in the region of the wheel housing, an easy access—for example, for draining the second liquid—from outside the machine is advantageously possible. In a further alternative, the second tank is arranged outside the engine compartment, in particular below the driver&#39;s cabin. By means of such an arrangement, the influence of the engine&#39;s temperature on the second liquid and thus on the viscosity of the second liquid can be advantageously minimized. 
     In an alternative embodiment, the second tank is attached, for example, to an outer covering of the roller from the outside and is thus easily accessible from the outside. This advantageously allows direct access to the second tank. For example, the second tank is arranged on an engine hood of the roller, in particular next to the first tank or next to a water tank. Preferably, the second tank engages in a recess in the outer casing and is arranged in a slip-proof manner there due to a form-locking interaction with said recess. Furthermore, it is conceivable for the second tank attached to the outer casing to include a viewing window, with the help of which the roller operator obtains information regarding a fill level of the second tank directly. 
     Preferred mixing devices are water jet pumps or static mixers. However, it is in principle also possible to use moving or even driven mixing devices such as, for example, impellers, although the installation of such devices involves a greater effort. If a water jet pump is used, a pump in the second supply line can advantageously be omitted, since the second liquid is suctioned by the negative pressure present in the water jet pump. Moreover, when a water jet pump is used, there remain essentially no residues of separation agent mixture which would have to be removed from the mixing device after operation or before a new operation of the roller. A static mixer typically comprises a tube section and a flow-influencing mixing element arranged in this tube section. Conventional static mixers are known, for example, under the designations Kenics mixer and Sulzer SMV/SMX mixer. When a static mixer is used, the physical properties of the first and the second liquid may advantageously be taken into consideration. For example, a grid mixer facilitates the mixing of liquids with a comparatively high viscosity. A further advantage of the use of a static mixer is that the mixing process can be carried out in a manner that is as controlled as possible. In order to remove any residues of the separation agent mixture remaining in the static mixer, the static mixer is preferably connected to a drain for discharging the separation agent mixture from the static mixer. Furthermore, it is conceivable that the mixing device comprises a stirring tool to order to support the mixing process. 
     According to a preferred embodiment of the present invention, the roller includes a measuring device for determining at least one of the following properties:
         Viscosity of the second liquid, and/or   Temperature of the second liquid, and/or   Fill level of the first tank, the second tank and/or the static mixer, and/or   Temperature of the external environment, and/or   Temperature of one or more of the rubber tires or their surfaces, respectively, and/or—Temperature of the asphalt to be compacted,       

     wherein the measuring device is preferably connected to the control device. For the specific determination of the above-described parameters, the measuring device comprises suitable sensors, for example, a viscosity sensor, a temperature sensor or probe, a fill level sensor, etc. By detecting the viscosity or temperature of the second liquid, a control circuit can advantageously be established with the help of the control device, with the help of which the quantity of the second liquid is automatically corrected when the temperature or viscosity of the second liquid varies, in particular at the start of operation of the roller or due to fluctuations in the ambient temperature during operation, in order to maintain the mixing ratio. The control device comprises a corresponding correction function for this purpose. By means of the measuring devices for detecting the fill levels, the roller operator can advantageously be made aware of a possible need for the first or second liquid and/or can be informed about the travelling range still available. Additionally, or alternatively, the other aforementioned factors can also have an influence on the control. This relates, in particular, also to a control or regulation of the regulating device by means of the control device as a function of the tire temperature or its surface temperature, the asphalt temperature and/or the ambient temperature. Particularly, at low temperatures, the tendency of the asphalt to stick to the rubber tires increases. It is, in particular, in this situation that the application of the separation agent mixture to the rubber tires via the spray device is required. By means of suitable temperature sensors, one or more of the aforementioned temperatures can be determined and considered as a control variable by the control unit. Thus, the discharge of separation agent mixture can, in particular, be automatically interrupted as soon as a predetermined temperature threshold value is exceeded, since the asphalt then no longer adheres to the tires. In the same way, it is conversely possible to restart the discharge automatically if the temperature falls below a fixed temperature threshold value. This way, a particularly efficient use of the separation agent mixture is achieved. Additionally, or alternatively, it is also possible to vary the mixing ratio of the first and the second liquids in a temperature-dependent manner. This includes, in particular, a control according to which the proportion of the second liquid in the separation agent mixture is higher at low temperatures than at high temperatures, whether relating, for example, to the ambient temperature, tire temperature and/or asphalt temperature. Alternatively, however, a manual adjustment of the mixing ratio and/or sprinkling per se is also covered by the present invention. The use of the measuring device described above is, however, also advantageous for this purpose, while an indication of the detected measurement values to the driver then additionally occurs via a suitable display device. This can serve as an orientation for the operator for the manual adjustment of the mixing parameters and/or the starting of the spray device and the mixing device. 
     The measuring device in question can, in particular, be either directly integrated in an existing line section and/or supplied by a separate measurement line, e.g., in the form of a bypass line. 
     The object of the present invention is also realized with a method for spraying a rubber tire of a roller for asphalt compaction, in particular of a roller in accordance with the preceding embodiments. All features and advantages described for the roller according to the present invention can be analogously applied to the method according to the present invention, and vice versa. 
     Specifically, the method according to one embodiment of the present invention for spraying a rubber tire of the roller comprises a mixing of a first liquid and a second liquid to form a separation agent mixture in the mixing device, in particular according to need, and the subsequent spraying of the at least one rubber tire with said separation agent mixture provided by the mixing device. For this purpose, the first liquid is provided in a first tank and the second liquid is provided in a second tank, the first and the second tank being mounted or arranged on the roller during operation of the same. By mixing the first liquid with the second liquid, preferably immediately before spraying the separation agent mixture with the spray device, it is possible to react to alterations in the mixing ratio as quickly as possible and in an uncomplicated manner or to adapt the mixing ratio at short notice to a modified application of the roller. A mixing according to need is, in particular, a mixing in accordance with which the mixture of the first liquid and the second liquid occurs only during the operation of the roller and preferably directly before the spraying procedure, depending on the current need. In particular, the time that elapses between a mixing process in the mixing device and a spraying of the separation agent mixture by means of the spray device is less than 40 seconds, preferably less than 10 seconds and especially less than 5 seconds. 
     In order to adjust or change the mixing ratio between the first and the second liquid, an amount of the first or second liquid, which are respectively provided to the mixing device, is adjusted by means of a regulating device. In accordance with the present invention, the quantity of first and/or second liquid delivered to the mixing device is determined by means of a pump, in particular by means of a pump for each liquid, in particular a variable displacement pump, or in a manner described above. For this purpose, for example, an input voltage at the pump is varied in order to modify or vary the quantity of first and/or second liquid provided, a regular operating interval, the conveyed volume, etc. This occurs by means of a control device of a regulating device that controls the operation of both pumps during operation of the roller. Preferably, both the first and the second pump are controlled with the control device independently of one another in order to provide the desired mixing ratio of first and second liquid. 
     In order to counteract possible variations in the mixing ratio of the separation agent mixture during operation, in particular within a time frame at the beginning of the operation of the roller, the regulating device is, in particular, actuated during the operation of the roller, in particular as a function of a viscosity or temperature of the second liquid. By means of a constant mixing ratio, it can be ensured that the separation agent mixture does not lose its effect during operation due to a changed mixing ratio. It is also conceivable that the ambient temperature has changed between two operations of the roller and a resulting variation of the mixing ratio is counteracted by means of the regulating device. Additionally, or alternatively, the regulating device or the entire spray device may also be operated as a function of a temperature of at least one rubber tire or its surface and/or as a function of a temperature of the asphalt to be compacted and/or a temperature of the external environment. This relates, in particular, also to the automatic switching on and/or off of the spray device and/or the modification of the mixing ratio of the first and the second liquid in the separation agent mixture by means of the mixing device as a function of whether the temperature exceeds or falls below predetermined temperature threshold values. 
     In order to avoid a freezing of the second liquid when the roller is not in operation, the second liquid is preferably drained from the second tank after operation of the roller or the second tank is detached, in particular completely, from the roller. It is also conceivable that the second tank is detached from the roller and substituted by a further second tank containing a further second liquid. This way, an uncomplicated substitution of different separation agent concentrates can be achieved. The tank here is preferably a commercial container, for example, a conventional canister. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below by means of the illustrative embodiments indicated in the figures, which show schematically: 
         FIG. 1  is a side view of a roller for asphalt compaction, specifically a rubber tire roller; 
         FIG. 2  is a system for spraying a rubber tire of a roller for asphalt compaction according to a first illustrative embodiment of the present invention; 
         FIG. 3  is a system for spraying a rubber tire of a roller for asphalt compaction according to a second illustrative embodiment of the present invention; 
         FIG. 4  is a system for spraying a rubber tire of a roller for asphalt compaction according to a third illustrative embodiment of the present invention; 
         FIG. 5  is an arrangement of a second tank on a rubber tire roller; 
         FIG. 6  is an alternative arrangement of a second tank on a rubber tire roller; 
         FIG. 7  is a further alternative arrangement of a second tank for a rubber tire roller; and 
         FIG. 8  is a flowchart pertaining to a method for spraying a rubber tire. 
     
    
    
     Identical elements are indicated by the same reference numbers in all figures. Repetitive elements may not be separately designated in each figure. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a side view of generic roller  1 , specifically a rubber tire roller  1 , in particular a self-propelled rubber tire roller  1 , with a chassis  52 , an operating platform or driver&#39;s cabin  50 , rubber tires  2  and a motor  51 . The rubber tire rollers  1  depicted in  FIG. 1  and in the other figures are to be understood as representative for rollers  1  for asphalt compaction in general, in particular for so-called combined rollers. Of the said rubber tires  2 , only the wheels facing the viewer are discernable. Specifically, four rubber tires  2  are respectively arranged next to one another both in the front and in the rear, the front rubber tires being arranged relative to the rear rubber tires  2  in the gaps in the direction of travel in a manner known in the prior art. Such rubber tire rollers  1  are typically provided for compacting work in road construction, wherein they operate by travelling over a surface to be compacted. Here, a rolling and kneading effect emanating from the rubber tires  2  results in a homogeneous compaction and pore sealing on a surface layer of the surface material to be compacted. During operation, i.e., during the compaction of the surface material, it regularly occurs that the surface material to be compacted adheres to the rubber tires  2  and is thus carried along, this tendency of the rubber tire  2  to pick up material depending primarily on the temperature of the rubber tire  2 . An adhesion of the surface material occurs, in particular, at low temperatures of the rubber tires, which, for example, predominate immediately after the rubber tire roller  2  has been started up. In order to prevent this, a separation agent mixture  10  is used, which is sprayed onto the rubber tire  2  or all of the rubber tires  2  present by means of a spray device  70 . In particular, such a separation agent mixture  10  is composed of at least one first liquid  11 , preferably water, and at least one second liquid  12 , preferably a separation agent concentrate.  FIGS. 2 to 4  show embodiments of systems for mixing the two liquids and for spraying the rubber tires  2 . 
       FIG. 2  shows a system for spraying a rubber tire  2  for a rubber tire roller  1  in accordance with a first illustrative embodiment of the present invention. A first tank  21  for the first liquid  11 , a second tank  22  for the second liquid  12 , and a mixing device are provided. As a result, a common tank provided for the separation agent mixture  10  can advantageously be omitted and the separation agent mixture can be prepared from the two liquids on the machine during operation. By means of the mixing device, the first liquid  11  and the second liquid  12  are mixed in order to form the separation agent mixture  10  and then passed as the separation agent mixture to a spray device  70  via a common supply line. For example, the spray device  70  is a spraying bar  71  extending horizontally across the front or rear rubber tires and transversely to the working direction, on which spray nozzles  72 , preferably individually adjustable spray nozzles  72 , are arranged at regular intervals. These spray nozzles  72  are preferably pointed at the rubber tire  2  or are oriented in such a way that their spray cones hit the rubber tire  2 . However, other spraying devices  70 , e.g., those comprising simple outlet openings instead of spray nozzles  72 , are possible and within the scope of the present invention. 
     In the embodiment illustrated in  FIG. 2 , a water jet pump  5  is the mixing device, which enables the first liquid  11  and the second liquid  12  to be mixed with each other as needed. The first tank  21  containing the first liquid  11  is connected to the mixing device via a first supply line and the second tank  22  containing the second liquid  12  is connected to the mixing device via a second supply line. The water jet pump  5  here comprises, in particular, two inlets and one outlet. During operation of the water jet pump, a jet comprising the first liquid  11  is introduced at a first inlet from a nozzle into a tube with a larger diameter under the greatest possible line pressure. Via a second inlet, the second liquid  12  gains access to the tube with the larger diameter from the second supply line, in particular because of the negative pressure prevailing in the tube. Between the fast-flowing jet of the first liquid  11  and the medium comprising the second liquid  12 , turbulence is caused in the tube by friction so that a mixing of the first liquid  11  and the second liquid  12  occurs. An advantage of using a water jet pump  5  is that no residues from the composite separation agent mixture  5  remain in the system or mixing device. 
     Furthermore, the second supply line has a regulating device in the form of a valve  3  and a fine-regulating valve  4 . As a result, the quantity of the second liquid  12  supplied to the mixing device can be influenced in an advantageous manner, in particular in a situation-dependent manner. This proves particularly advantageous in that a change in the mixing ratio caused by changes in temperature after the start-up of the rubber tire roller or in the event of temperature variations in the environment of the rubber tire roller  1  can be counteracted. Such a change in the mixing ratio is to be expected, for example, when the first liquid  11  and the second liquid  12  have different temperature dependencies with regard to their viscosity and the quantity of the first liquid  11  and the second liquid  12  respectively delivered to the mixing device varies differently so that the mixing ratio is unintentionally modified. In addition, it is conceivable that the mixing ratio can be adjusted via the regulating device during operation of the rubber tire roller to the current need for the second liquid  12 , depending on the situation or particular application of the rubber tire roller  1 . 
     Furthermore, the first supply line, i.e., usually the water supply line, comprises a valve  3  as well as a filter  7  as part of a regulating device. By means of the filter  7 , the first liquid  11  supplied to the mixing device can advantageously be cleared of unwanted impurities. Furthermore, integrated in the first supply line is a first pump  13 ′, in particular a water pump, with which the pressure required for the water jet pump can be obtained in the first line. In the embodiment shown in  FIG. 2 , the filter  7  is arranged between the valve  3  and the water pump  5 . In order to be able to provide a desired target pressure at the spray device  70 , preferably between 1.5 and 2 bar, a pressure regulating device is also provided, which is realized in the illustrated embodiment by a bypass circumventing the pump  13 ′, the bypass comprising a check valve with a spring  6 ′. In this manner, the system pressure is regulated exclusively within the water circuit. Both the valves  3  as well as the pump  13 ′ are controlled by the control device  60  via suitable control lines. Via these lines, the control device  60  controls, e.g., the opened/closed position of the vales  3  and/or the operation of the pump  13 ′, e.g., with regard to the intervals during which it is turned on/off and/or with regard to the conveyed volume. The entirety of valves  3 , pump  13 ′, control device  60  and control lines constitutes the regulating device. This receives operational commands from the operator via corresponding actuating means, as illustrated, e.g., in  FIG. 4 . 
       FIG. 3  shows a system for spraying a rubber tire  2  for a rubber tire roller  1  according to a second illustrative embodiment of the present invention. In particular, the second tank  22  here is designed as a pressure tank  22 ′. The tank  22  can thus be overpressurized in relation to the external environment. According to the second illustrative embodiment, in order to transport the second liquid  12 , the second liquid  21  in the second tank  22  is pressurized by means of compressed air from a compressed air reservoir  31 , thus causing the transport of the second liquid  12  to the mixing device. A preferred pressure, for example, between 1.5 and 2 bar, can be set by means of a pressure-reducing valve  32  controlled by the control device  60 , said pressure-reducing valve  32  being inserted between the compressed air reservoir  31  and the pressure tank  22 ′. The second supply line, which connects the second tank  22  to the mixing device, furthermore preferably comprises, as part of the regulating device, a 2/2-way valve  8 , in particular an electrically actuable 2/2-way valve, and a fine-adjustment valve  3 , in order to set or adjust the mixing ratio of the first liquid  11  and the second liquid  12  in the separation agent mixture  10  depending on the situation and need. Furthermore, the second supply line between the 2/2-way valve  8  and the mixing device includes a check valve without a spring  6 ″ which, in a closed state, prevents the first liquid  11  from entering the second supply line. 
     As is known from the first embodiment, the first liquid  11 , driven by a first pump  13 ′, reaches the mixing device via a first supply line with a filter  7 . In order to be able to provide a desired target pressure at the spray device  70 , preferably between 1.5 and 2 bar, a bypass circumventing the pump  13 ′ is also connected as a pressure-regulating device to the first line, the bypass comprising a check valve with a spring  6 ″. 
     The adjustment of the aforementioned valves  3 ,  4  and/or  8  can be controlled manually or, in particular, also by means of a suitable control device which transmits corresponding control signals to the valves  3 ,  4  and/or  8 , for example, depending on determined parameters such as, e.g., temperature, viscosity, etc. 
     In the embodiment illustrated in  FIG. 3 , a static mixer  15  is provided as the mixing device. The person skilled in the art understands a static mixer  15  to be, in particular, a device for mixing fluids in which the flow movement of the fluids, in the present case the first and the second liquid, alone effects the mixing and which does not have any moving elements. The static mixer  15  preferably consists of flow-influencing elements arranged in a chamber or a mixing tube. These flow-influencing elements alternately divide the material stream and then bring it together again, whereby mixing is achieved. Flow-influencing elements are, for example, a helical mixer or a grid mixer. 
       FIG. 4  shows a system for spraying a rubber tire  2  for a rubber tire roller  1  according to a third illustrative embodiment of the present invention. The third embodiment, like the second embodiment, comprises a static mixer  15  as a mixing device. Moreover, as in the second embodiment, the first liquid  11  is led to the mixing device via a supply line with a first pump  13 ′, in particular a water pump, and a filter  7 . Furthermore, the first supply line comprises a valve  3  between the filter  7  and the first tank  21 . 
     In order to provide the second liquid  12 , the third embodiment provides, in particular, a second tank  22  comprising a drain  25 . This drain  25  advantageously allows the second liquid  12  to be discharged from the tank  22  after the operation of the rubber tire roller  1 . If the second liquid  12  has, in particular, a comparatively low freezing point temperature, the freezing of the second liquid  12  in the second tank  22  can thus be avoided. For the same purpose, the common supply line between the static mixer  15  and the spray device  70 , additionally, or alternatively, preferably comprises a drain  25  which allows the separation agent mixture  10  to be drained or removed from the common supply line and/or the static mixer  15 . In order to assist the draining of the second liquid, the bottom side of the second tank  22  preferably tapers in a funnel-shaped manner towards the drain  25  or the common supply line between the static mixer  15  and the spray device  70  preferably slopes, i.e., in the direction of a ground surface on which the rubber tire roller is standing. 
     Furthermore, the second liquid  12  is preferably conveyed to the static mixer  15  by means of a second pump  13 ″, in particular an adjustable variable displacement pump, controlled separately from the first pump  13 ′. For this purpose, a second pump  13 ″ is integrated in the second supply line. It is conceivable that the second pump  13 ″ is an electrically adjustable variable displacement pump with the aid of which the quantity of the second liquid  12  fed to the static mixer  15  per time unit is regulated by way of an electrical input voltage. In other words, the variable displacement pump controlled by the control device is preferably part of the regulating device. For its control, the variable displacement pump is connected to the control device  60 . Via a first actuating element  61 , which is preferably arranged in the driver&#39;s cabin  50  and connected to the control device  60 , a roller operator can preferably set and/or adjust the mixing ratio in the separation agent mixture  10  by adjusting, e.g., an input voltage at the variable displacement pump in such a way that the desired quantity of second liquid  12  is provided to the static mixer  15 . 
     Moreover, the first pump  13 ′ integrated in the first supply line is linked with a second actuating element  62  via the control device  60 . By means of the second actuating element  62 , an operating mode of the spray device  70  can preferably be set by the roller operator. For example, the spray device  70  can be turned off or on or operated in an interval mode, in particular during the operation of the rubber tire roller  1 , via the second actuating element  61 . For this purpose, the control device  60  preferably turns the first pump  13 ′ in the first supply line on and/or off again. Furthermore, a bypass line  57  is provided around the pump  13 ′ and a further check valve  6  is provided in the line portion downstream of the bypass line  57  in order to prevent an unintentional conveying of separation agent into the water path. 
     For the above variants, it is also possible that a corresponding arrangement is provided for the front and rear rubber tires, respectively. It is preferred, however, if the front and rear rubber tires are collectively sprinkled by a system for spraying the rubber tires with separation agent mixture. 
     Furthermore, a ventilation bypass  57 ′ is provided, which connects the line section downstream from the pump  13 ″ to the second tank  12  via a valve  3 ′ (a 2/2-way valve in the present case). Via this bypass, it is possible for the pump  13 ″ to convey in a first step, e.g., after the filling and/or installation of the second tank  12 , without pressure into the tank  12  for ventilation purposes. Once the pump  13 ″ has been ventilated, a blocking of the ventilation bypass  27 ′ occurs by means of the valve. 
     In the embodiment in accordance with  FIG. 4  with two pumps  13 ′ and  13 ″ controlled separately from one another and according to which the mixing ratio is thus adjusted by means of the control of both pumps  13 ′ and  13 ″, it is further provided that the tank is monitored with the help of the control device  60 . Specifically, the energy consumption of the pumps  13 ′ and  13 ″ is monitored. If the latter sinks suddenly, this is a sign that the tank  11  or  12  is empty. This information is relayed to the operator by means of a suitable display device. 
       FIGS. 5 to 7  show various arrangements of the second tank  22 . In this case, the second tank  12  is arranged in a recess  55  in the arrangement illustrated in  FIG. 4 , in particular in the region of the wheel housing  56 . For this purpose, the frame or outer covering is partly faded out in this figure. Such an arrangement proves advantageous inasmuch as it permits free access to the second tank  22 , for example, for draining the second liquid  12  via the clearance between the rubber tire  2  and the wheel housing  56 , while the second tank  22  is simultaneously protected against external environmental influences by the casing of the rubber tire roller  1 . In addition, the second tank  22  is arranged comparatively close to the spray device  70  so that installation space and costs for supply lines that would be necessary otherwise can be saved. 
     In contrast, the second tank  22  in the arrangement shown in  FIG. 6  is arranged on an outer side of the outer covering of the rubber tire roller  1  from the outside. In particular, the second tank  22  is arranged in a mounted state on or adjacent to a covering hood of the rubber tire roller  1 . In the mounted state, the second tank  22  preferably sits flush with at least one of its sides with the general profile of the outer covering. Furthermore, the second tank  22  is preferably temporarily mountable on the rubber tire roller via a coupling device. For example, the coupling device is a latching or tensioning device by means of which the coupling device is temporarily or reversibly mountable on the outer covering. This advantageously permits a removal and temporary storage of the second tank  22  when the rubber tire roller  1  is not being operated. Furthermore, it is conceivable that the second tank  22  comprises a viewing window, which advantageously directly conveys information about the fill level of the second tank  22  to the roller operator. 
     In the arrangement shown in  FIG. 7 , the second tank  22  is arranged in a recess near the wheel housing or below/adjacent to the water tank and/or near the water tank and the driver&#39;s cabin  50  or beneath the driver&#39;s cabin. In such an arrangement, the second tank  22  is protected from external environmental influences. 
       FIG. 8  schematically shows a method for spraying a rubber tire  2  in accordance with an illustrative embodiment of the present invention. With one of the rubber tire rollers  1  according to any one of the embodiments described above, for example, the following steps are performed:
         providing  41  a first liquid  11  in a first tank  21  and a second liquid  12  in a second tank  22 ,   delivering  42  the first liquid  11  with a first pump ( 13 ′) and/or the second liquid  12  with a second pump ( 13 ″) to a mixing device, wherein the mixing ratio of first liquid ( 11 ) to second liquid ( 12 ) in the mixed liquid is set, in particular during an operation of the roller ( 1 ), by means of a control device ( 60 ) of a regulating device, said control device ( 60 ) controlling the first pump ( 13 ′) and the second pump ( 13 ″),   mixing the first liquid  11  and the second liquid  12  in the mixing device during the operation of the rubber tire roller, and   spraying the rubber tire  2  with the separation agent mixture  10  provided by the mixing device. Furthermore, it is provided that the first tank  21  is filled with the first liquid  11  and the second tank  22  is filled with the second liquid  12  in order to provide the first liquid  11  and the second liquid  12 . It is particularly preferred that the operation of the spray device and/or of the mixing device occurs as a function of the detected temperature values, in particular the temperature of at least one of the rubber tires or the surface of a rubber tire, the outer environment and/or the asphalt to be compacted. In this context, the illustrated method can, in particular, be carried out in such a way that the illustrated steps are executed automatically by a control unit when the temperature falls below a predetermined temperature threshold value and stopped when the temperature exceeds a predetermined temperature threshold value. Furthermore, when supplying the first and second liquids, a further preferred embodiment lies in the modification of the mixing ratio of the first and the second liquid as a function of at least one of the temperature values described above. Specifically, an increase in the proportion of the second liquid in the separation agent mixture occurs at low or decreasing temperatures, and vice versa.       

     While the present invention has been illustrated by description of various embodiments and while those embodiments have been described in considerable detail, it is not the intention of Applicants to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will readily appear to those skilled in the art. The present invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicants&#39; invention.