Blade assembly
BACKGROUND OF THE INVENTION 
     The present invention relates to a blade assembly to be equipped on a motorized grader or the like. 
     A blade assembly illustrated in FIG. 1 is constructed in such manner than an auxiliary blade b is laterally extended from a main blade a by sliding the auxiliary blade b along the main blade a as a result of extension and contraction operations of a hydraulic cylinder c, thereby to vary the blade length. In the case where an edge portion d of the movable auxiliary blade b and an edge portion f of a cutting edge e of the main blade a are tapered in the same direction as shown in FIG. 1, although no problem arises in varying the blade length, the knife edges of the movable auxiliary blade b and the cutting edge e do not align on the same straight line but a step is formed therebetween. Hence, when the blade assembly is tilted (when the scraping angle is varied), a step is formed on a finished surface after the blade working operation, so that an adverse effect results. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the present invention to provide a novel blade assembly which is free from the above-mentioned disadvantges, and which can continuously vary the blade length while avoiding degradation of precision in finishing. 
     According to one feature of the present invention, there is provided a blade assembly for construction equipment or vehicles of the type wherein a blade length is made variable by sliding an auxiliary blade or blades along a main blade, in which cutting edge portions of the main blade and the auxiliary blade, respectively, are disposed in a back-to-back relation and the directions of the tapered surfaces of the respective edge portions are inclined away in opposite direction from the sliding surface between the main and auxiliary blades so that the knife edges of the respective edge portions are aligned substantially on the same straight line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and objects of the present invention will become more apparent by reference to the following description of a preferred embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a rear perspective view of a blade assembly according to the prior art; 
     FIG. 2 is a similar rear perspective view showing one preferred embodiment of the present invention; 
     FIG. 3 is a front perspective view of the same embodiment; 
     FIG. 4 is a side view of the same; and 
     FIG. 5 is a horizontal cross-sectional view taken along line V--V in FIG. 4. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIGS. 2-5 of the drawings, reference numeral 1 designates a curved movable auxiliary blade which can slide laterally along a curved main blade 5, numeral 2 designates a guide plate formed as projecting backwardly from the movable auxiliary blade 1, numeral 3 designates guide rods, and numeral 4 designates a hydraulic cylinder. Reference numerals 6 and 7 are guide brackets fixedly interposed between the main blade 5 and a blade support 9 for the main blade 5, and guide holes for slidably guiding the guide rods 3 are drilled in the guide brackets 6 and 7. First ends of the guide rods 3 are fixedly connected to the guide plate 2, and one end (on the rod side) of the hydraulic cylinder 4 is also pivotably connected to the guide plate 2. The other end of the hydraulic cylinder 4 is pivotably connected to the blade support 9, so that as a result of extension and contraction operations of the hydraulic cylinder 4, the movable auxiliary blade 1 is made to slide laterally along the front surface of the main blade 5 so as to extend sidewards from the main blade 5. The main and auxiliary blades and their complementary sliding surfaces are curved about a common axis extending generally parallel said same straight line. Reference numeral 8 designates a cutting edge mounted on the main blade 5, and numeral 10 designates a guide bracket for making the main blade slide laterally therealong. 
     Reference numeral 1a designates an edge portion of the movable auxiliary blade 1, numeral 8a designates a tapered knife surface (edge portion) of the cutting edge 8, and these edge portions 1a, 8a are disposed in a back-to-back relation with the directions of their tapered surfaces taken on the opposite sides of the curved complementary sliding surfaces between the main and auxiliary blades 5 and 1 so that the knife edges of the respective edge portions may be aligned substantially on the same straight line, as shown in the drawings (especially, refer to FIG. 4). 
     In the blade assembly according to the present invention which is constructed as described above, as a result of extension and contraction operations of the hydraulic cylinder 4 the movable auxiliary blade 1 slides laterally along the main blade 5. At this moment, since the edge portion 1a of the movable auxiliary blade 1 and the edge portion 8a of the cutting edge 8 have their tapered surfaces located in a back-to-back relation, it is possible to continuously vary the blade length while the knife edges of the respective edge portion are kept aligned on the same straight line over the entire blade length. Since the knife edges of the edge portions 1a and 8a always align on the same straight line even if the blade length is varied by the extension and contraction operations of the hydraulic cylinder as described above, variations of the blade length will not result in degradation of finishing precision in the blade working operation, and hence a clear finished earth surface can be obtained. 
     As described above, according to the present invention, in a blade assembly for construction equipment or vehicles, a blade length is made variable by sliding an auxiliary blade or blades along a main blade, with cutting edge portions of the main blade and the auxiliary blade being disposed in a back-to-back relation with the directions of the tapered surfaces of the respective edge portions extending from opposite sides of the curved sliding surfaces between the main and auxiliary blades. Thus the knife edges of the respective edge portions may be aligned substantially on the same straight line, even when the blade length is varied continuously. Therefore, degradation of finishing precision (uneven finished surface or finished surface having steps) will not occur, and the efficiency of working with the blade assembly will be enhanced. 
     Since many changes could be made to the above construction and many apparently widely different embodiments of this invention could be made without departing the scope thereof, it is intended that all matter contained in the above description or shown in the drawings shall be interpreted as illustrative and not as a limitation to the scope of the invention.