ASPHALT UNIFORMLY PAVING EQUIPMENT

Abstract

 In an asphalt paver in which on a base paver provided with a base conveyor for conveying and supplying paving materials onto an applied surface, either an attachment for laying a single layer or that for laying multiple layers is selectively mounted, a hopper for upper layer constituting the attachment for multiple layers is provided with a pair of left and right buckets, each having a substantially trapezoidal cross-section, the buckets being openably and closably supported by a support shaft extending in a longitudinal direction of a vehicle body and having an upper portion, respectively, permitted for being folded. Thus, the capacity of the buckets can be increased by extending the upper portions from the folded position thereof. When the buckets are opened and when the upper portions are folded, the overall height of the asphalt paver can be lowered to thereby reduce such an anxiety that the paver might interfere with any lower face of a structure such as a bridge during the conveyance of the paver.

Description

TECHNICAL FIELD

[0001] The present invention relates to a paver for laying asphalt mixture on an applied surface and more particularly, relates to a technique for improving the efficiency of conveyance of the paver and that of laying operation for paving materials performed by the paver.

BACKGROUND ART

[0002] In an asphalt paving, a method of laying a plurality of paving materials in layers has been employed for improving drainage and noise-reduction properties as well as for reducing a cost spent for the materials. In such paving operation, when a thin layer is laid to form an upper layer, aggregate projecting from or coming out of the surface of the upper layer might be drawn by a screed to result in forming damages and scratches on the surface of the upper layer, and therefore in order to prevent such formation of damages, it is necessary to lay the upper layer on the lower layer in unhardened state at a high temperature. Also, when the upper layer is laid by a thin layer, the temperature is quickly lowered so as to make it difficult to obtain an appropriate density of the layer after application of rolling to the layer. Thus, in order to lay the upper layer immediately after application of laying work to the lower layer, a paver capable of simultaneously completing pavement of multiple layers (it will be hereinafter referred to as a multi-layer paver) has been utilized.

[0003] Nevertheless, frequency in use of the multi-layer paver is ordinarily less than the paver for laying a single layer and accordingly, there occurs a problem such that it is very difficult to collect investment required for installation of the multi-layer paver. Therefore, as described in the publication of Japanese translation version of Intemational Application for Patent No. 2002-504636, a proposal for technique for cost reduction by simply detachable attachment for laying multiple layers on the conventional asphalt paver (it will be hereinafter referred to as a base paver) for laying the single layer has been made.

[0004] While when such asphalt multi-layer paver is to be conveyed to a construction site, the attachment should desirably be conveyed without being dismounted from the base paver by taking into consideration the conveying efficiency of the base paver and the attachment. Nevertheless, in the state where the attachment is mounted on the base paver, the overall height of the paver becomes large, and as a result, the top end of the asphalt paver might come into interference with a lower face of a structure such as a bridge during conveying of the paver. For this reason, even if the conveying efficiency of the asphalt paver might be decreased, it has been necessary for the base paver and the attachment to be individually conveyed.

[0005] Further, it is desired that the asphalt paver be provided with a hopper having a large capacity thereof capable of receiving therein the asphalt mixture in order to improve the laying efficiency. However, when the efficiency of conveyance of the asphalt paver is taken into consideration, more increases in the capacity of the hopper must have been avoided.

[0006] Therefore, taking the foregoing problems encountered by the conventional art into consideration, an object of the present invention is to provide an asphalt paver including a hopper mounted on the top end of the asphalt paver and arranged to be closably openable and be foldable so that the hopper may increase the capacity thereof and may permit the overall height of the paver to be lowered to thereby make it possible to improve the efficiency of conveyance of the paver as well as that of the laying operation applied to paving materials.

DISCLOSURE OF THE INVENTION

[0007] To this end, an asphalt paver according to the present invention is constructed so that an attachment either for laying a single layer or for laying multiple layers is selectively and removably attached to a base paver provided with a base conveyor for conveying paving materials and supplying the materials onto an applied surface. The attachment for laying a single layer is constructed to include a base hopper unit for storing therein the paving materials and for supplying the materials to the base conveyor, and a base screed unit for laying the paving materials supplied by the base conveyor onto the applied surface.

[0008] On the other hand, the attachment for laying multiple layers is constructed to include a hopper unit for lower layer, which stores therein paving materials for the lower layer and supplies the materials to the base conveyor, a screed unit for lower layer for laying the paving materials for the lower layer conveyed and supplied onto the applied surface by the base conveyor, a hopper-conveyor unit for upper layer which is provided with a hopper for upper layer storing therein paving materials for the upper layer and a conveyor for upper layer conveying and supplying, onto the laid paving materials for the lower layer, the paving materials for the upper layer stored in the hopper for upper layer, and a screed unit for upper layer for laying the paving materials for the upper layer, which are conveyed and supplied onto the paving materials for the lower layer. Also; the upper layer hopper is constructed to have a pair of left and right buckets, each having a substantially trapezoidal cross-section, which are supported to be closably openable by a support shaft extending in a longitudinal direction of a vehicle body, each of the pair of buckets being constructed to have an upper end capable of being collapsible.

[0009] Due to the above-described construction, a single-layer paver or a multi-layer paver may be alternatively constructed by selectively attaching an attachment for either a single layer or multiple layers to the base paver. Thus, the asphalt paver can be a wide-use apparatus enabling it to achieve cost reduction and to improve working efficiency of the asphalt paver. Also, when a base paver is possessed, installation of only attachments enables it to achieve simultaneous laying of multiple layers and accordingly, facility investment can be suppressed to the minimum limit of requirement.

[0010] Further, in the case of laying multiple layers, an upper layer is laid immediately after the laying of a lower layer. Thus, the upper layer will be always laid above the lower layer kept in an unhardened state at a high temperature and therefore, engagement of aggregate can be improved to result in a good bonding of both layers compared with the case where multiple single-layer pavers are employed for individually laying respective one of multiple layers. In addition, during the laying of an upper layer by compacting, the lower layer can be re-compacted and hardened to exhibit a good degree of compaction and as a result, surface roughness is improved.

[0011] Further, in the case where the paving materials for an upper layer is laid in thin layer, aggregate in the upper layer is pressed into the lower layer during compacting of the upper layer, and accordingly, the aggregate is neither exposed to nor projected from the upper layer. Thus, generation of rough texture of the laid surface due to dragging of aggregate can be prevented, so that the surface of pavement of high quality may be formed.

[0012] When an asphalt paver having a base paver to which an attachment for multiple layers is attached is conveyed, buckets for upper layer are opened and the upper ends thereof are collapsed. Thus, the overall height of the asphalt paver can be lowered and accordingly, occurrence of any interference of the top end of the asphalt paver with lower faces of a structure such as a bridge or the like during conveyance of the asphalt paver could be diminished. Therefore, when the asphalt paver is to be conveyed, it is not necessary to separately convey the base paver and the attachment, and thus the efficiency of conveyance of the asphalt paver can be improved.

[0013] On the other hand, when a work for asphalt paving is performed, the capacity of a hopper for upper layer can be increased by extending upper portions of buckets of the hopper for upper layer. Thus, when the amount of paving materials stored in the buckets is reduced, the bottom faces of the buckets can be inclined by closing the buckets so that any residue of paving materials left in the bucket bottom faces might be delivered into delivery channels. By doing this, supply of the paving materials can be smoothly carried out, and the efficiency of laying can be improved.

[0014] At this stage, it is desired that the upper portion of the rear wall of the hopper for upper layer might be extended upward to a position higher than the other side walls and be collapsible. Due to adoption of such construction, when the paving materials for an upper layer are fed from the front of the asphalt paver while extending the rear wall, the rear wall might be used as a kind of indicator for controlling the work while permitting an operator to perceive a feeling of distance. Therefore, the feeding work of the paving materials can be easy. On the other hand, when the asphalt paver is conveyed, collapsing or folding of the rear wall of the hopper for upper layer will result in lowering of the overall height of the asphalt paver and accordingly, a risk of interference of the rear wall with any lower face of a structure such as a bridge can be diminished.

[0015] Also, the screed unit for lower layer should preferably be constructed to integrally include a spreader for lower layer for spreading paving materials conveyed and supplied onto an applied surface over the entire paving width, a screed for lower layer for laying the paving materials for the lower layer by applying thereto a compaction, and a spreader for upper layer for spreading paving materials conveyed and supplied onto the paving materials for the laid lower layer over the entire paving width. By this construction, the entire length of the asphalt paver could be reduced so as to improve the weight balance of the paver in the longitudinal direction thereof and to spread respective paving materials for the lower and upper layers over the entire paving width. Therefore, it is possible to control the final thickness of the pavement at a high accuracy. In addition, the integral provision of the spreader for lower layer, the screed for lower layer, and the spreader for upper layer facilitates mounting and dismounting of the attachment for the laying of multiple layers.

[0016] Further, the above-mentioned screed unit for lower layer should preferably be constructed in a manner such that the screed for lower layer for laying the paving materials for the lower layer is suspended by a hydraulic jack. By this construction, the entire width and the entire length of the asphalt paver can be lessened and accordingly, the conveyance of the paver can be rendered easier.

[0017] Furthermore, a difference between the height of the laid surface achieved by the screed unit for upper layer and that by the screed unit for lower layer should preferably be detected, and the laid height of the paving materials for the lower layer should desirably be adjusted so that the above-mentioned detected value becomes a predetermined value. By this construction, the lift thickness of the upper layer can be highly accurately controlled so that an amount of use of the expensive paving materials for the upper layer can be limited to the minimum requirement. Owing to this, the quality of pavement can be kept high with a reduced cost spent for the construction of pavement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 

Fig. 1 is a constructional view of an asphalt paver according to the present invention;

Fig. 2 illustrate in detail, a hopper-conveyor unit for upper layer in which (A) is an explanatory view of a bucket upon being opened, and (B) is an explanatory view of the bucket upon being closed;

Fig. 3 illustrates an upper foldable or collapsible construction of a hopper for upper layer in which (A) is an explanatory view of a bucket, and (B) is an explanatory view of a rear wall of the bucket;

Fig. 4 is a detailed view of a unit including therein a screed for lower layer and a spreader for lower and upper layers;

Fig. 5 illustrates an asphalt paver used when an construction of pavement is performed, in which (A) is a constructional view of the paver upon conducting the laying of a single layer, and (B) is a constructional view of the paver upon conducting the laying of multiple layers;

Fig. 6 is an explanatory view illustrating a method of laying multiple layers;

Fig. 7 is an explanatory view illustrating conveyance of the asphalt paver,

Fig. 8 is a schematic view illustrating a first embodiment for controlling the lift thickness of an upper layer;

Fig. 9 is explanatory view illustrating a height detecting sensor; and,

Fig. 10 is a schematic view illustrating a second embodiment for controlling the lift thickness of an upper layer.

BEST MODE OF CARRYING OUT THE INVENTION

[0019] The present invention will hereinafter be described in detail with reference to the accompanying drawings.

[0020] As shown in Fig. 1, an asphalt paver (it will be hereinafter referred to as "a paver") according to the present invention is constructed to include a base paver 10, and an attachment for either a single layer or multiple layers, which is selectively mounted and dismounted.

[0021] The base paver 10 is constructed to have a vehicle body 10A, which is mounted thereon a drive-power unit such as a diesel engine and is provided with crawlers 10B as a running unit, a master console 10C, and a seat 10D. Also, on the left and right sides as well as on the rear side of the vehicle body 10A, hydraulic cylinders 10E and 10F are swingably mounted respectively for adjusting the height of a screed as against an applied surface A. The hydraulic cylinders 10E mounted on the left and right sides of the vehicle body 10A have an operating rod, respectively, which is provided with an extreme end portion rotatably connected to an end portion of a lever 10G pivotably attached, at its substantially middle portion, to the vehicle body 10A. Further, a bottom portion of the vehicle body 10A, which is arranged to be laterally sandwiched by the crawlers 10B is provided with a base conveyor 10H such as a bar-feeder, for conveying paving materials from the front side of the vehicle body 10A to the rear side thereof and supplying the conveyed paving materials onto the applied surface.

[0022] The attachment for laying a single layer is constructed to include a base hopper unit 20, a base spreader unit 30, and a base screed unit 40.

[0023] The base hopper unit 20 stores therein paving materials such as asphalt mixture, and is constructed to supply the paving materials from a delivery port opening at the bottom of the unit 20 to the base conveyor 10H. The base spreader unit 30 includes a screw 30A having a main axis extending in a direction corresponding to the direction from the left to right and vice versa of the vehicle body 10A, and spreading the paving materials supplied onto the applied surface A over the entire width of an area to be paved, and the base spreader unit 30 per se is mounted on the rear portion of the vehicle body 10A via a mounting bracket 30B. It should, however, be noted that when either the base hopper unit 20 or the base conveyor 10H is constructed to supply the paving materials onto the entire width of the area to be paved, the above-mentioned base spreader unit 30 is not necessarily needed. The base screed unit 40 is constructed to include a pair of left and right leveling arms 40A extending in a direction corresponding to the longitudinal direction of the vehicle body 10A, and screeds 40B secured to the ends of the leveling arms 40A. The leveling arms 40A are rotatably connected, at their basic ends, to the other end of the afore-mentioned lever 10G, and at their portions adjacent to the extreme ends thereof, to the extreme end of the operating rod of the hydraulic cylinder 10F positioned at the rear end of the vehicle body 10A. The screeds 40B operate so as to apply a compaction by its own weight to the paving materials and to lay the paving materials on the applied surface.

[0024] An attachment for multiple layers is constructed to include a hopper unit 50 for lower layer, a hopper-conveyor unit 60 for upper layer, a unit 70 incorporating therein a screed for lower layer and spreaders for upper and lower layers (it will be merely referred to as "a screed unit for lower layer" throughout the specification and the accompanying claims), and a screed unit 80 for upper layer.

[0025] Like the base hopper unit 20, the hopper unit 50 for lower layer is constructed to store therein paving materials for a lower layer, which are to be laid on a lower layer, and to supply the paving materials to the base conveyor 10H from a delivery port opening in the bottom portion of the unit 50. At this stage, it should be noted that the width and height of the hopper unit 50 for lower layer are desirably formed to have the possible maximum dimensions permitting the unit to be conveyed by a conveyance vehicle in the state where it is mounted on the base paver 10, in order to increase the capacity of the unit 50 to a possible largest extent thereby improving the efficiency of laying operation. Also, the bottom face of the hopper unit 50 for lower layer should preferably be formed to have an inclination permitting the paving materials for the lower layer to be slid down there toward the delivery port.

[0026] The hopper-conveyor unit 60 for upper layer is mounted on an upper face of the vehicle body 10A at a position behind the hopper unit 50 for lower layer. The hopper-conveyor unit 60 for upper layer is constructed to include a hopper 62 for upper layer for storing therein paving materials for an upper layer, which is to be laid on an upper layer, and a conveyor 64 for upper layer, such as a screw feeder, which conveys paving materials for an upper layer from the front to the rear side of the vehicle body 10A and supplies the conveyed materials onto the lower layer. The upper layer hopper 62 is formed to have the shape of a box having an opening on respective front and upper faces thereof. As shown in Fig. 2, the bottom face of the hopper 62 for upper layer is formed with two delivery channels 62A having a substantially semi-circular section and extending in a direction corresponding to the longitudinal direction of the vehicle body 10A. The conveyor 64 for upper layer has a part thereof fitted in the above-mentioned two semi-circular delivery channels. Further, a pair of left and right buckets 62B having a substantially trapezoidal cross-section thereof are axially supported to be openable and closable at the sides of the delivery channels 62A which correspond to the left and right outward positions of the vehicle body 10A. The buckets 62B are opened toward a position shown in Fig. 2 (A) to lower the entire height of the paver during the conveying thereof.

[0027] On the other hand, the buckets 62B are closed to a state as shown in (B) of Fig. 2, when the paving materials are left as residual materials in the bottom of the buckets 62B during construction of the asphalt pavement, so as to bring each bucket bottom to a state inclining against the delivery channel 62A. Further, respective upper portions of the buckets 62B are formed to be foldable or collapsible to occupy two positions i.e., a conveyance position and a working position as shown in (A) of Fig. 3, in order to avoid interference with any lower face of a structure such as a bridge during the conveyance of the paver as well as to increase the storing capacity of the paving materials for an upper layer during construction of laying work. In this case, the width of folding of the upper portion of each bucket 62B is desirably set so that when the paver is mounted on a conveyance vehicle for the conveying purpose, the top end portion of the paver is located below a predetermined maximum height legally determined by a specific regulation such as the vehicle control regulations.

[0028] The hopper 62 for upper layer is provided with a rear wall 62C, which is provided to extend more upward than the other sidewalls of the hopper, so that when the paving materials are fed from the front of the paver, the rear wall becomes a kind of indicator for an operator conducting the feeding operation. Thus, during the conveyance of the paver, the top end of the rear wall 62C might come into interference with the lower face of a structure such as a bridge. Therefore, similar to the upper portion of the above-mentioned buckets, the rear wall of the hopper 62 for upper layer is made foldable or collapsible so as to come either one of the two positions, i.e., a conveyance position and a working position, as shown in (B) of Fig. 3. The front wall of the hopper 62 for upper layer is formed by the rear wall of the hopper unit 50 for lower layer.

[0029] As shown in Fig. 4, the screed unit 70 for lower layer is mounted on the rear portion of the vehicle unit 10A via a mounting bracket 70A. The screed unit 70 for lower layer is constructed to include a spreader 72 for lower layer, a screed 74 for lower layer, and a spreader 76 for upper layer, which are in turn mounted on frame 70B extending rearward from the rear portion of the vehicle body 70A. The spreader 72 for lower layer and the spreader 76 for upper layer spread the paving materials for a lower layer and the paving materials for an upper layer, which are supplied onto the applied surface A in the left and right directions of the vehicle body 10A by using a screws 72A and 76A, respectively, having a length corresponding to a width to be paved. Also, the screws 72A and 76A can be adjusted in their respective heights at the positions where they are mounted on the frame 70B, in compliance with the lift thickness of each of the lower layer and the upper layer to be laid.

[0030] The screed 74 for lower layer is provided for compacting and laying the paving materials for a lower layer, which are spread by the spreader 72 for lower layer, by applying compaction and vibrating effects to the paving materials due to its gravity and a tamper thereof. The screed 74 for lower layer might be provided with extensions for permitting it to adjustably change the lengths thereof on both the left and right sides of the vehicle body 10A in compliance with the width of pavement.

[0031] Further, a system described below is provided for adjusting the thickness of pavement as required. Namely, the frame 70B is mounted to be capable of moving up and down along a slide guide 70C of the mounting bracket 70A, and is suspended from the bracket 70A by a hydraulic cylinder 70D. The screed 74 for lower layer is suspended from the frame 70B by a hydraulic jack 70E, and is connected to the front portion of the frame 70B via every two tie-rods 70F arranged on the left and right sides, respective two tie-rods 70F being arranged to be vertically spaced apart but in parallel with one another. Here, the tie-rods 70F form a mechanism of a parallel links, so that even when the screed 74 for lower layer is moved up and down by the hydraulic jack 70E, the bottom end of the screed 74 for lower layer is always guaranteed to be in substantially parallel with the applied surface A. Further, by adjusting the length of each of the tie-rods 70F, it is possible to selectively change the laying angle of the screed 74 for lower layer in compliance with the sort and thickness of the paving materials used for laying operation. Moreover, the arrangement in which the screed 74 for lower layer is suspended by hydraulic jack 70E makes it possible to reduce the entire length and width of the paver, and therefore the conveyance of the paver can be made easier.

[0032] Like the base screed unit 40, the screed unit 80 for upper layer is constructed by including a pair of left and right leveling arms 80A extending in a longitudinal direction of the vehicle body 10A, and screeds 80B attached to the extreme end portions of the arms 80A. The leveling arms 80A are rotatably connected, at their respective base portions, to the other end of the lever 10G, and are rotatably connected, at positions adjacent to the front ends thereof, to the end of the operating rod of the hydraulic cylinder 10F. Further, the screed 80B is provided for laying the paving materials for an upper layer, which are spread over the paving materials for a lower layer by the spreader 76 for upper layer, by applying compaction and vibrating effects to the paving materials by the use of its gravity and a tamper thereof. At this stage, the entire length of the leveling arms 80A of the screed unit 80 for upper layer is selected to be longer than that of the leveling arms 40A of the base screed unit 40 by taking into consideration the fact that the screed unit 70 for lower layer is interposed and positioned between the vehicle body 10A and the screed 80B.

[0033] There will now be provided hereinbelow a description of asphalt laying method by the use of the above-described paver.

[0034] When a single layer of asphalt mixture is laid on an applied surface A, the base hopper unit 20, the base spreader unit 30 and base screed unit 40 are mounted on the base paver 10, as shown in (A) of Fig. 5. Subsequently, paving materials are fed into the base hopper unit 20.

[0035] When the paver is started for operation, the paving materials are supplied from the base hopper unit 20 into the base conveyor 10H. The paving materials supplied into the base conveyor 10H are conveyed toward the rear portion of the vehicle body 10A, and are in turn supplied onto the applied surface A from the rear end portion of the vehicle body 10A. The paving materials supplied onto the applied surface A are spread by the base spreader unit 30 over the whole area of the paving width. Then, the spread paving materials are compacted by the screed 40B of the base screed unit 40 to have a predetermined thickness of pavement after being laid.

[0036] On the other hand, when two layers of asphalt mixture are laid on an applied surface A, the hopper unit 50 for lower layer, the hopper-conveyor unit 60 for upper layer, the screed unit 70 for lower layer, and the screed unit 80 for upper layer are mounted on the base paver 10, as shown in (B) of Fig. 5. Subsequently, paving materials for a lower layer are fed into the hopper unit 50 for lower layer and paving materials for an upper layer are fed into the hopper 62 for upper layer of the hopper-conveyor unit 60 for upper layer. At this time, the buckets 62B of the hopper 62 for upper layer are opened to come to the position shown in (A) of Fig. 2, and also the buckets 62B and the upper portion of the rear wall 62C are extended to come to the respective working positions shown in Fig. 3.

[0037] When the paver is started for operation, the paving materials B for a lower layer are supplied from the hopper unit 50 for lower layer into the base conveyor 10H. Thus, the paving materials B for a lower layer supplied into the base conveyer 10H are conveyed toward the rear portion of the vehicle body 10A, and are then supplied onto the applied surface A from the rear end of the vehicle body 10A, as shown in Fig. 6.The paving materials B for the lower layer supplied onto the applied surface A are spread by the spreader 72 for lower layer over the entire area of the paving width. The spread paving materials B for the lower layer are then compacted by the screed 74 for lower layer to have a predetermined pavement thickness. Thus, the lower layer of the pavement is completed by the described laying operation.

[0038] Paving materials C for an upper layer supplied from the hopper 62 for upper layer to the conveyor 64 for upper layer of the hopper-conveyor unit 60 for upper layer are then supplied onto a lower layer from the rear end portion of the conveyor 64 through a delivery chute 66. The paving materials C for an upper layer supplied onto the lower layer are spread by the spreader 76 for upper layer over the entire area of the paving width. The spread paving materials C for the upper layer are compacted and laid by the screed 80B of the screed unit 80 for upper layer so as to have a predetermined pavement thickness. Thus, the process for paving the upper layer of the pavement is completed. Then, the laid paving materials are rolled by a suitable road roller to harden the paving materials and as a result, the asphalt pavement is completed.

[0039] As described above, when either an attachment for laying a single layer or an attachment for laying multiple layers is selectively mounted on the base paver 10, a single-layer paver or a multi-layer paver is constructed. Therefore, the paver can be of general purpose to thereby allow a cost reduction as well as an improvement of the working efficiency of the paver. More specifically, when the base paver is possessed, installation of only attachments makes it possible to conduct simultaneous laying of multiple layers, and as a result, the facility investment can be suppressed to the possible minimum limit.

[0040] Also, when multiple layers are simultaneously laid, the attachment for laying multiple layers, mounted on the base paver 10 lays an upper layer immediately after the laying of a lower layer. Therefore, the upper layer is laid over the lower layer in the unhardened state and at a high temperature and accordingly, bonding of both layers can be improved compared with the case where multiple layers are laid by employing a plurality of pavers for a single layer. Furthermore, when the upper layer is compacted during the laying process, compaction is additionally applied to the lower layer so as to re-compact the lower layer to thereby obtain a good degree of compaction of the lower layer.

[0041] Furthermore, when aggregate is contained in the paving materials for an upper layer, the aggregate will be pressed into the lower layer by the screed unit 80 for upper layer, and is neither exposed to nor projected from the surface of the upper layer. Thus, the pavement surface of high quality can be obtained. Particularly, when pavement of a thin layer should be performed, diverse drawbacks might have been encountered by the conventional art. For example, dragging of aggregate as well as cracking might have occurred during paving of the thin layer, resulting in damages to the surface of the pavement and further, quick and large temperature lowering of the paving materials have often caused a poor bonding of both layers. In addition, sufficient density of the paving materials couldn't have been obtained even if a compaction by a road roller was applied. Nevertheless, these drawbacks can be overcome by the above-described simultaneous laying of multiple layers.

[0042] In the described embodiment, the paving materials for an upper layer and those for a lower layer may consist of the same kind of asphalt mixture. In this paving, when a thick layer of pavement approximately from 10 through 30 centimeters thick should be performed, components in the upper portion of the layer and those in the lower potion of the layer might vary from one another, and the degree of compaction in the lower portion of the thick layer might be insufficient and weak. These are obvious drawbacks of the conventional art. Nevertheless, according to the described embodiment, it is possible to eliminate these drawbacks by separating the single thick layer into multiple layers to be simultaneously laid by the paver of the present invention.

[0043] When the paver formed by mounting an attachment for laying multiple layers on the base paver 10 is conveyed, the hopper 62 for upper layer of the hopper-conveyor unit 60 for upper layer is pivotally rotated and folded to the position for conveyance position. Namely, the buckets 62B are brought to the open position thereof, as shown in (A) of Fig. 2, and the upper portion of the respective buckets 62B and the upper portion of the rear wall 62C are folded to the conveyance positions as shown in Fig. 3. When these processes are completed, the overall height of the paver can be lowered from the height H1 shown in Fig. 6 to that H2 shown in Fig. 7, and therefore the top end of the paver can be lessened to reduce occurrence of any interference with a lower face of a structure such as a bridge. Thus, when the paver is conveyed, it is not necessary to separately convey the base paver 10 and the attachments and therefore, the efficiency of the conveyance of the paver can be improved.

[0044] On the other hand, when the asphalt mixture is to be applied, the upper portion of the buckets 62B and the upper portion of the rear wall 62C are extended, so that the capacity of the hopper 62 for upper layer can be increased. When an amount of paving materials stored in the buckets 62B are reduced, the residue of paving materials left in the bottom of the buckets 62B can be delivered toward the delivery channels 62A by closing the buckets 62B. Thus, supply of the paving materials can be smoothly carried out, and as a result the efficiency of the laying operation is improved with certainty.

[0045] At this stage, when the asphalt pavement of multiple layers is applied, rather expensive paving materials are often employed for an upper layer or layers. Therefore, when highly accurate controlling of the lift thickness of the upper layer is conducted, it is possible to reduce expense for the construction of such asphalt pavement while maintaining the high quality in pavement. Accordingly, in the present embodiment, a mechanism described below is provided for highly accurately controlling the lift thickness of the upper layer.

[0046] Namely, in order to detect any difference in the height of the laid surface performed by the screed unit 80 for upper layer and the screed unit 70 for lower layer, the screed 80B (it will be hereinafter referred to as a screed for upper layer) of the screed unit 80 for upper layer has an upper face to which a bracket 90 curved in a substantially L-letter shape toward the front portion of the vehicle body 10A is secured as shown in Fig. 8. The extreme end portion of the bracket 90 is formed in the shape of a substantial cylinder. On such extreme end portion of the bracket 90, a substantially columnar support 92 extending vertically is mounted so as to be able to adjust the height thereof. The lower end of the support 92 is provided with a height detection sensor 94 (a detection apparatus) arranged to be in constant contact with the upper face of the screed 74 for lower layer to thereby detect the height thereof. As shown in Fig. 9, the height detection sensor 94 has an arm 94B of which the base end portion is secured to the rotating shaft 94A extending in the left and right direction of the vehicle body 10A, and also has a follower plate 94C rotatably secured to the extreme end portion of the arm 94B and arranged to be in constant contact with the upper face of the screed 74 for lower layer. Thus, when the screed 74 for lower layer is moved up and down with respect to the screed 80B for upper layer, the arm 94B is rotated, and an angle of rotation can be detected by a built-in potentiometer. The angle of rotation of the arm 94B is input in a control unit containing therein an electronic computer. In the control unit, on the basis of the angle of rotation of the arm 94B detected by the height detection sensor 94, a difference between the heights of the laid surfaces, which have been laid by the screed 80B for upper layer and the screed 74 for lower layer, respectively, is calculated. Then, the hydraulic jack 70E of the screed unit 70 for lower layer is controlled so that the calculated difference between the heights of the laid surfaces becomes a predetermined value, and the height of the screed 74 for lower layer as against the applied surface A is adjusted. Here, the height adjustment apparatus is brought into practice by the control unit in the manner of controlling software. Although the described method is achieved by the employment of a contact type sensor, the present invention is not limited to this method, and non-contact type sensor using, for example, infrared and supersonic waves might be employed.

[0047] At this stage, the construction and arrangement for detecting the difference in the heights between the surfaces laid by the screed 80B for upper layer and the screed 74 for lower layer is not limited to the described one, and as shown in Fig. 10, the height detection sensor 94 may be supported and secured on the upper surface of the screed 74 for lower layer, via brackets 90 and support 92.

INDUSTRIAL APPLICABILITY

[0048] From the foregoing description, it will be understood that since the asphalt paver according to the present invention is provided with a construction such that the hoppers mounted and positioned on the top end portion of the asphalt paver are closably openable and foldable or collapsible, the capacity of the hoppers can be increased while reducing the overall height of these hoppers. As a result, the efficiency of conveyance of the paver and the efficiency of laying operation for paving materials are improved and therefore, the asphalt paver can be greatly useful.

Claims

1. An asphalt paver in which an attachment either for laying a single layer or for laying multiple layers is selectively and removably attached to a base paver provided with a base conveyor for conveying paving materials and supplying the materials onto an applied surface,
   wherein said attachment for laying a single layer comprises a base hopper unit for storing therein paving materials and for supplying said materials to said base conveyor, and a base screed unit for laying the paving materials conveyed and supplied to said applied surface by said base conveyer,
   wherein said attachment for laying multiple layers comprises a hopper unit for lower layer for storing therein paving materials for a lower layer and supplying the paving materials to said base conveyor, a screed unit for lower layer for laying the paving materials for the lower layer which are conveyed and supplied onto said applied surface by said base conveyor, a hopper-conveyor unit for upper layer provided with a hopper for upper layer for storing therein paving materials for an upper layer and a conveyor for upper layer for conveying and supplying the paving materials for the upper layer stored in said hopper for upper layer onto the paving materials for the lower layer laid by said screed unit for lower layer, and a screed unit for upper layer for laying the paving materials for the upper layer conveyed and supplied onto the paving materials for the lower layer by said conveyor for upper layer, and
   wherein said hopper for upper layer comprises a pair of left and right buckets, each having a substantially trapezoidal cross-section thereof, said buckets being pivotally supported to be openable and closable by a support shaft extending in a direction corresponding to a longitudinal direction of a vehicle body, said buckets having an upper portion capable of being folded, respectively.

2. An asphalt paver according to claim 1, wherein said hopper for upper layer has a rear wall provided with an upper portion thereof which is extended upward to a position higher than those of the other side walls while being allowed to be folded.

3. An asphalt paver according to claim 1, wherein said screed unit for lower layer is integrally provided with a spreader for lower layer for spreading the paving material for the lower layer conveyed and supplied onto said applied surface by said base conveyor over the paving width, a screed for lower layer for laying the spread paving materials for the lower layer by compacting, and a spreader for upper layer for spreading the paving materials for the upper layer conveyed and supplied onto the paving materials for the lower layer by said conveyor for upper layer over the paving width.

4. An asphalt paver according to claim 1, wherein said screed unit for lower layer comprises an arrangement in which a screed for lower layer for laying the paving materials for the lower layer is suspended by a hydraulic jack.

5. An asphalt paver according to claim 1, further comprising:

a detection apparatus for detecting a difference in height between laid surfaces leveled by said screed unit for upper layer and by said screed unit for lower layer; and

a height adjustment apparatus for adjusting the laying height of the paving materials for the lower layer leveled by said screed unit for lower layer in such a manner that the difference in height between the laid surfaces detected by said detection apparatus comes to a predetermined value.

Drawing