Abstract:
An automatic shoe clearance adjustment device for a drum brake device which improves the ease of assembly of the bimetal member and prevents misassembly of the device. The adjuster  11  has a screw mechanism which automatically extends in response to the excessive opening of the brake shoes  2, 3.  The bimetal member  15,  which suspends the extension of the adjuster  11  according to the brake temperature increase, is provided between the parts constituting the adjuster  11.  The bimetal member  15  is assembled together with and affixed to a non-rotating segment constituting the adjuster  11.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an automatic shoe clearance adjustment device for a drum brake device equipped with an over-adjustment preventive measure which suspends the adjustment operation when the brake temperature rises. 
     In traditional automatic shoe clearance adjustment devices for a drum brake device, an opening action of the two facing plates of a folded bimetal member provided at the strut restricts the over-adjustment operation in case the brake drum expands as the brake temperature rises. One example is shown in Japanese Patent Publication Number Showa 58-49739. 
     Yet, in the above-described device, simply, a tube of the strut fits over the screw rod with a gap therebetween. Hence, until the strut is actually placed between the brake shoe and the hand brake lever and until the return spring is fitted, the strut could freely come out in the direction of that axle and could freely rotate. 
     Then, a rib of the folded bimetal member is structurally apt to come out from a triangle-like concave portion of the tube. For this reason, assembling the strut, in which the concave portion of the rib is interlocked, is said to be difficult. 
     If the strut is assembled while the rib is dislocated off from the concave portion of the tube, due to a large thrust force on the strut while the hand brake lever is in operation, the rib is deformed and may adversely affect the automatic adjustment operation which requires a delicate adjustment operation. Also, the same type of adverse effect may occur if the folded bimetal member rotates to interfere with other parts such as the shoe return spring. In addition, even if the misassembled parts are fortunately found, a correction of the misassembled parts demands effort and time. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     This invention is designed to resolve the problems described above. To that end, an object of the invention is to provide a method to improve the ease of assembly of this bimetal member and to prevent misassembly, where a bimetal member is used as an over-adjustment preventive device which suspends the automatic adjustment operation of a clearance between the brake drum and the brake shoe when the brake temperature rises. 
     Another object of the invention is to provide an automatic shoe clearance adjustment device, wherein a bimetal member is movable in the direction of the adjuster axis with the stationary parts of the adjuster and is not relatively rotatable, thereby facilitating the assembling process and preventing misassembly. 
     Another object of the invention is to provide an automatic shoe clearance adjustment device, wherein the bimetal member is placed between the stationary parts of the adjuster, thereby improving the usability of the adjuster, increasing the ease of assembly, and preventing misassembly, if the worst should happen and the stationary parts are separated. 
     Another object of the invention is to provide an automatic shoe clearance adjustment device, wherein, from the above described advantages, the automatic shoe clearance adjustment operation between the brake drum and the brake shoe is accurately suspended when the brake temperature rises, thereby preventing over-adjustment. 
     In the first aspect of the invention, an automatic shoe clearance adjustment device for a drum brake device comprises an adjuster equipped with a screw mechanism for an automatic adjustment of the length of the adjuster in response to an excessive opening of brake shoes and a bimetal member provided between the parts constituting the adjuster. The bimetal member is provided to suspend the extension of the adjuster according to the brake temperature increase. In this invention, the bimetal member is connected together with an non-rotating segment which is a part of the adjuster. 
     In the second aspect of the invention, the bimetal member has a hook thereon and a cavity is formed in the non-rotating segment of the adjuster. The hook fits into the cavity. In this manner, the bimetal member is affixed to the non-rotating segment in the way that the bimetal member does not rotate about and does not come off from the longitudinal axis of the adjuster. 
     In the third aspect of the invention, the hook has a wider top portion and the cavity is specially shaped to receive the wider top portion. In this manner, the bimetal member is affixed to the non-rotating segment in the way that the bimetal member does not come off from the adjuster longitudinal axis. 
     In the fourth aspect of the invention, the bimetal member has an elastic hook, with the hook fitting locked with the non-rotating segment in a male-female contact. In this manner, the bimetal member is affixed to the non-rotating segment in the way that the bimetal member does not rotate about and does not come off from the adjuster longitudinal axis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and the attendant advantages of this invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a structural plan view of the entire drum brake device which includes the embodiments of this invention; 
     FIG. 2A is a lateral view and FIG. 2B is a partial cross-section plan view of the automatic adjuster in FIG. 1; 
     FIG. 3 is an analytical, exploded view of the automatic adjuster of FIG. 2; 
     FIG. 4A is a lateral view and 
     FIG. 4B is a partial cross-section view of another embodiment of the automatic adjuster; 
     FIG. 5 is an analytical, exploded view of the automatic adjuster of FIG. 4; and 
     FIG. 6 is a structural view of assembling the bimetal member of yet another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiment 1 
     A first embodiment of this invention is explained next with reference to the following figures. 
     A summary of the whole structure of the drum brake device is explained with reference to FIG.  1 . The back plate  1  is affixed to the stationary part of the vehicle. The brake shoes  2 ,  3  are movably and elastically supported on the back plate  1  by the shoe hold devices  4 ,  5 . The wheel cylinder  6  is an actuator, which operates upon activating the service brake, and is affixed on the back plate  1 . The pistons  6   a,    6   a  are positioned in the wheel cylinder  6  and respectively engage with the upper end of the brake shoes  2 ,  3 . The anchor  7  is affixed on the back plate  1  and supports the lower ends of the brake shoes  2 ,  3 . The brake lever  8  functions when the parking brake cable  9  is pulled. The pin  10  is placed on the upper part of the brake lever  8  so that the brake lever  8  is pivotally supported on the brake shoe  3  with the pin  10  as the fulcrum. The adjuster  11  is provided between the brake shoe  2  and the brake lever  8 . The adjustment lever  16  is pivotally supported at its potbellied hole  16   a  by the pin  17  mounted on the brake shoe  2 . The first to third arms  16   b,    16   c,    16   d  are formed at the adjustment lever  16 . The first arm  16   b  engages with the toothed adjustment ring  12   a;  the second arm  16   c  abuts against the stepped surface of the socket  14 . The adjustment spring  18  extends between the brake shoe  2  and the third arm  16   d  creating a counterclockwise force to the adjustment lever  16 . The shoe return springs  19 ,  20 , each extend between the brake shoe  2 ,  3 . 
     As shown in the FIGS. 2 and 3, the adjuster  11 , provided between the brake shoe  2  and the brake lever  8 , comprises a bolt  12 , a nut  13 , a socket  14 , and a bimetal member  15 . The bolt  12  is equipped with the toothed adjustment ring  12   a  in a middle portion, the threaded portion  12   b  at one side of the middle portion, and the stem  12   c  at the other side. The threaded portion  12   b  of the bolt  12  is screwed into the nut  13 . The notched groove at the left side of the nut  13  abuts against and engages with the brake lever  8 . The socket  14  is smoothly fitted over the stem  12   c  of the bolt  12  in a relatively rotatable condition. The notched groove at the right side of socket  14  abuts against and engages with the brake shoe  2 . 
     The bimetal member  15  is a folded plate having holes therethrough formed at the overlapped portion. The holes are sized to fit over the stem  12   c  with a gap. In this manner, the bimetal member  15  is positioned between the end surface of the toothed adjustment ring  12   a  and the end surface of the socket  14 . The bimetal member  15  has a hook  15   a  with a wider top portion. The hook  15   a  is formed by bending the bimetal member  15  at the socket  14  side of the bimetal member  15  and has a deformed or shaped portion. The hook  15   a  fits into a shaped cavity  14   a  formed on the socket  14 . The engagement of the hook  15   a  with the cavity  14   a  prevents the bimetal member  15  from rotating relative to the socket  14  and from moving axially of the adjuster  11 . Thus, the bimetal member  15  is held rotationally stationary and is stationary with respect to the adjuster longitudinal axis. 
     In use, when the wheel cylinder  6  is pressurized by the service brake, the pistons  6   a,    6   a  press the upper ends of the brake shoes  2 ,  3 . This causes the brake shoes  2 ,  3  spread open with the point of abutment against the anchor  7  as the fulcrum to frictionally engage with the brake drum, not shown in the diagram, thereby creating a braking effect. 
     When the parking brake cable  9  is pulled, the brake lever  8  rotates counterclockwise with the pin  10  as the fulcrum to press the adjuster  11 . This causes the brake shoe  2  spreads open with the point of abutment against the anchor  7  as the fulcrum to frictionally engage with the brake drum. Further, the brake lever  8  rotates with the point of abutment against the adjuster  11  to press the brake shoe  3  via pin  10 . Accordingly, the brake shoe  3  spreads open with the point of abutment against the anchor  7  as the fulcrum to frictionally engage with the brake drum. In this manner, a vehicle parking brake is set. 
     When the service brake is activated to pressurize the wheel cylinder  6 , the brake shoes  2 ,  3  spread open to abut against the brake drum. At this time, the adjustment lever  16  rotates counterclockwise by the force of the adjustment spring  18  with the pin  17  as the fulcrum, so that the adjuster  11  follows the brake shoe  3  and the brake lever  8 . In addition, the pin  17  and the pivoting portion of the adjustment lever  16  move together with the brake shoe  2 . 
     At this point, when the degree of opening of both brake shoes  2 ,  3  increases due to the wear of the lining of the brake shoes  2 ,  3 , the degree of rotation of the first arm  16   b  of the adjustment lever  16  exceeds the pitch between two teeth of the toothed adjustment ring  12   a  to rotate the bolt  12 . The threaded portion  12   b  of the bolt  12  screws out from the nut  13  to extend the effective length of the adjuster by a distance equal to only one tooth, thereby maintaining a constant clearance between the brake drum and the lining. At that time, the stem  12   c  of the bolt  12  rotates inside the socket  14 . 
     Repeating braking, the brake drum temperature begins to increase causing the brake drum to expand. In addition, the folded portion of the bimetal member  15  may start to open to form a V-shape to increase the effective length of the adjuster  11 , so that the automatic adjustment does not occur, thereby preventing overadjustment. 
     When releasing the brake, the adjuster  11  returns due to the spring force of the shoe return springs  19 ,  20 . Therefore, no adverse effect is created. 
     In addition, when the parking brake is in operation, the adjuster  11 , the adjustment lever  16 , etc., moves with the brake shoe  2  because of the large thrust force on the adjuster  11 . As a result, no automatic adjustment occurs. 
     A manufacturer may treat the adjuster  11  as an entire unit. For example, as shown in the FIGS. 2A,  2 B and  3 , the bimetal member  15  is actually structured together with the socket  14  unless the socket  14  comes off the bolt  12 , thereby eliminating the problems of the conventional devices described above. 
     Embodiment 2 
     A second embodiment of this invention is explained below with reference to the FIGS. 4A,  4 B and  5 . 
     In order to attain the same effect as the embodiment  1 , the convex portion of the hook  115   a  of the bimetal member  115  is inserted into a rectangular hole  114   a  of the socket  114 . The rectangular hole  114   a  could also be either a circular hole or a notched groove. 
     Embodiment 3 
     A third embodiment of this invention is explained below with reference to FIG.  6 . 
     The third embodiment is a modification of the second embodiment, where the bimetal member  215  is structured with the socket  114 . That is, the bimetal member  215  has a further deformed hook  215   b  formed by bending below as well as above the socket  114  in order to grasp or clamp the socket  114  between the two hooks  215   a  and  215   b.    
     It is readily apparent that the above-described has the advantage of wide commercial utility. It should be understood that the specific form of the invention hereinabove described is intended to be representative only, as certain modifications within the scope of these teachings will be apparent to those skilled in the art. This invention is also available and applicable to the conventional adjuster. On the other hand, the structure of the drum brake device is not limited to the above-described structure but also available to various type of drum brake devices. 
     Accordingly, reference should be made to the following claims in determining the full scope of the invention.