Disc brake for wheeled vehicle or the like
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a disc brake and more specifically to a disc brake in which the clearance between the pads and the disc may be effectively minimized. 
     2. Description of the Prior Art 
     In a prior art arrangement shown in FIG. 1 of the drawings, it has been proposed to mount friction pad supporting levers, 1, 2 individually on a bracket 3 via pins 4, 5. In this arrangement the upper ends of the levers 1, 2 are interconnected by a linkage arrangement 6 which, as shown, is operated in response to the movement of an inner cable 7 of a Bowden cable 8. 
     However, this arrangement has suffered from the drawback that in order to prevent one of the pads from annoyingly dragging on the disc 9 when the brake is not applied, it is necessary to provide a relatively large clearance between the pads and the faces of the disc. Accordingly, a relatively large amount of inner cable travel is required to move the pads from their rest position into contact with the faces of the disc. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a disc brake arrangement which enables the clearance between the pads and the disc to be minimized without an undesirable &#34;dragging&#34; phenomenon taking place. 
     More specifically, the present invention takes the form of a disc brake for a vehicle which comprises: a rotatable disc, a mounting bracket fixedly secured to a chassis of the vehicle, a first lever pivotally mounted on the mounting bracket in a manner to be pivotal about an axis, a second lever pivotally mounted on the mounting bracket so as to be pivotal about the same axis, the first and second levers having thereon first and second brake pads respectively, a linkage interconnecting the first and second levers for inducing in response to a manual command, the first and second levers to rotate in opposite rotational directions about the axis and in a manner to clamp the pads against the opposite faces of the disc, a first clearance adjustment device projecting from the first lever toward the second lever, the first clearance adjustment device being arranged to engage the second lever in a manner to limit the clearance which occurs between the first and second pads in the absence of the command signal, and a second clearance adjustment device projecting from the first lever toward the mounting bracket, the second clearance adjustment device being arranged to engage the mounting bracket in a manner to limit the clearance which occurs between the disc and the first pad in the absence of the command signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the arrangement of the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is an elevational view of the prior art disc brake arrangement discussed briefly in the opening paragraphs of the present invention; 
     FIG. 2 is a front elevational view of a first embodiment of the present invention; 
     FIG. 3 is a side elevation of the embodiment shown in FIG. 2; 
     FIG. 4 is a sectional view taken along section line IV--IV of FIG. 2; 
     FIG. 5 is a sectional view of a second embodiment of the present invention wherein the spring shown in FIG. 4 is replaced with an elastomeric member; 
     FIG. 6 is a partial front elevation of the arrangements shown in FIGS. 2 and 3 illustrating a feature via which excessive brake pad wear may be recognized; and 
     FIG. 7 is a front elevation of a simplified disc brake arrangement in which the brake wear indication feature is provided. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2 and 3 show in elevation a first embodiment of the present invention. In this arrangement, first and second levers 10, 12 are pivotally mounted on a bracket 14 fixedly connected to a chassis 16 (viz., of a vehicle or the like). As shown, the two levers 10, 12 are pivotally mounted on the same pin 18 so as to be pivotal about the same axis. Brake pads 20, 22 are detachably connected to the lower (as seen in the drawings) ends of the levers 10, 12 in a manner to be clamped against the opposite faces of a disc or brake rotor 24, upon rotation of the levers 10, 12 in opposite rotational directions about the afore-mention pin 18. 
     The upper ends of the levers 10, 12 are interconnected by a linkage arrangement generally denoted by the numeral 26. This linkage, as shown, takes the form of a link 28 pivotally connected at one end to the upper end of the first lever 10 by a pin 30 and a bell-crank lever 32 pivotally mounted on the top of the second lever 12, via pin 34. The link 28 and the bell crank lever 32 are pivotally connected by a pin 35. 
     The pins 30, 34 which serve to pivotally mount the link 28 and the lever 32 also serve in this arrangement as means for mounting a pair of springs 36, 38 between the tops of the levers 10, 12. These spring 36, 38 apply a bias to rotate the levers in a manner to hold the pads 20, 22 out of engagement with the faces of the disc 24. 
     A hydraulic cylinder or servo 40 is integrated with the bracket 14 in which the pivot pin 18 is disposed. This cylinder contains a piston (not shown) which is operatively connected with the pivot pin 34. The cylinder is fluidly connectable with a source of hydraulic fluid such as a foot operated master cylinder (by way of example only) via port 42. With this arrangement, upon the hydraulic fluid in the hydraulic cylinder being pressurized by the operation of the master cylinder, the piston is forced to drive the pivot pin 34 upwardly (as shown in the drawings) to induce the spreading of the upper ends of the levers 10, 12 and the consequent application of the friction pads 20, 22 against the faces of the disc 24. 
     The top of the bell-crank lever 32 is connected, as shown, with a cable or rod arrangement 44 operatively connected with a hand brake (or the like). With this arrangement application of the hand brake induces the bell crank lever 32 to rotate clockwise about the pin 34 and thus induce the spreading of the tops of the levers 10, 12 in a manner to apply the pads 20, 22 against the disc 24. 
     As best seen in FIG. 4 the first embodiment is provided with a first clearance adjustment device 50 which in this case takes the form of a bolt or screw 52 which threadedly mounted though the first lever 10 so as to project toward the second lever 12 in a manner to limit the degree by which the portions of the two levers located above the pivot pin 18 may approach each other and hence the degree by which the friction pads 20, 22 may separate (c.f. clearance S 1 ) from one and other. The bolt 52 is provided with a lock-nut 54. 
     A second clearance adjustment device 60 in the form of a second bolt or screw 62 is provided. In this case the bolt 62 is adapted to abut a portion of the bracket 14 in which the hydraulic cylinder 40 is formed in a manner to control the clearance S 2  between the pad 20 and the disc 24. This bolt has a lock-nut 64. 
     Interposed between the second lever 12 and the hydraulic cylinder 40 at a location essentially coaxial with the second adjustment bolt 62, is a spring 70. This spring resists the rotation of the first and second levers 10, 12 as a whole in a counter clockwise direction (as seen in FIG. 2) about the single axis and thus prevents pad 20 from undesirably dragging on the disc when the brake is not applied. That is to say, the spring 70 resiliently holds the arrangement against movement which is not prevented by the second adjustment bolt 62 abutting the hydraulic cylinder. 
     Accordingly, with the above disclosed arrangement, as the total clearance S 1  may be adjusted using the first clearance adjustment device 50 and the clearance between the brake pad 20 and the disc 24 may be controlled via the use of the second clearance adjustment device 60, it will be understood that the clearance between each of the pads and the disc can be adjusted. Viz., by firstly adjusting the clearance between the pad 10 and the disc 24 using the second clearance adjusting bolt 62, the clearance between the pad 22 and the disc 24 may be subsequently adjusted using the first clearance adjusting bolt 52. Further, as previously mentioned, as the bolt 62 and the spring 70 hold the levers and linkage arrangement in place and prevent any tendancy for the clearances between the pads 20, 22 and the disc 24 to vary due to one pad approaching the disc while the other moves away therefrom, (viz., the lever/linkage unit rotating as a whole) any dragging phenomenon is prevented while permitting small clearances between the pads 20, 22 and the disc. 
     FIG. 5 shows a second embodiment of the present invention wherein the spring 70 is replaced with a suitable elastomeric member 72 having the desired resilient properties. 
     A further feature possible with the present invention comes in the provision of means for indicating excessive brake pad wear. This arrangement takes the form of arranging the pivot pin 34 or a part of the linkage 26 in the path of the springs 20, 22 so that upon a predetermined amount of upward movement of the pin 36 being required to apply the brakes, the springs are engaged as shown in FIG. 6. With this arrangement upon the pin 34 engaging the springs, 34, 36 the resistance to further upward movement will be resisted by the distortion of the springs thus increasing the force which must be manually applied to the brake pedal of the vehicle. 
     FIG. 7 shows a simplified arrangement wherein the above mentioned feature is included. In this arrangement the hydraulic cylinder is omitted and the levers interconnected by a Bowden cable 90. With this arrangement upon the pin 92 interconnecting the bell crank lever 94 and the link 96 decending (as seen in the drawings) to the point of engaging the spring (or springs) 98, the force required for further brake application will notably increase.