FIELD OF THE INVENTION:
[0001] This invention relates to an automatic brake shoe adjuster System for a motor vehicle, more particularly to drum brakes where drum and shoe clearance is adjusted automatically.
BACKGROUND OF THE INVENTION
[0002] For drum brakes to function correctly, the brake shoes must remain dose to the drum without touching it. If they get too far away from the drum (as the shoes wear down, for instance), the piston will require more fluid to travel that distance, and the brake pedal will sink closer to the floor when the brakes are applied. This type of brakes has cam adjusted brake shoes to compensate for wear whenever shoes get worn out; however, the shoe clearance is not maintained correctly since the adjustment is carried out manually resulting in Variation in adjustment from person to person.
[0003] As the liner wears down, more space will form between the shoe and the drum. Each time the vehicle stops while in reverse, the shoe is pulled tight against the drum. When the gap gets big enough, the adjusting lever rocks enough to advance the adjuster bolt by one tooth. The adjuster has broached teeth on it, like a bolt, so that it advances a little bit when it pulls, lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can advance again, so it always keeps the shoes dose to the drum.
[0004] Some cars have an adjuster that is achiated when the emergency brake is applied. This type of adjuster can come out of adjustment if the emergency brake is not used for long periods of time. So in this type of adjuster, one should apply the emergency brake at least once a week.
[0005] In the existing System brake shoes are adjusted manually for reducing gap between shoes and drum by rotating cam bolt. This will lead to inaccurate adjustment and the life of liner will be less and more pedal travel will occur when there is no proper adjustment of the cam.
SUMMARY OF THE INVENTION
[0006] This invention relates to internal shoe drum brakes which have a pair of brake shoes, which can be expanded and actuated by manual means to engage a brake drum for Service brake Operation and manually by an auxiliary actuator for parking. Automatic

adjusting is commonly provided to adjust the distance between the brake shoes to compensate for the wear of shoe friction linings. the adjusting means consist of an adjustable length strut acting between the brake shoes. The present invention however has an adjuster with broached bolt and diaphragm spring togelher, one of the parts comprising a broached bolt engage able by a diaphragm spring, which is movable when excess wear of the linings is sensed and adjust the length of the bolt. An internal shoe drum brake includes a pair of brake shoes which can be expanded, against the action of shoe by means of return spring. This is applicable to power actuated Service brakes as well as manually actuated auxiliary brakes, a strut of adjustable length which transmits the applied loads manually between the shoes, but load on the strut is relieved, when load acts upon actuation of the Service brake.
[0007] The present invention relates to brakes of this form, and provides such a brake, when applied the brake shoes moves apart against the return spring and is done by hydraulic vvheel cylinder. This invention also includes parking or secondary brake. With brakes in applied condition the brake shoes expand and pull both the shoes outward direction along with the broached bolt and strut which are engaged due to diaphragm spring which is riveted on strut. If it is parking brake, lever will pulls outward because of spring force acting between strut and broached
[0008] bolt. Strut consists of diaphragm spring riveted on it, having hole which can pass the broached both one way because of its tooth profile. When the brakes are released the shoes come closer because of return spring but the broached bolt will not allow to move further and will lock at specified position.
[0009] This invention will now be described in further detail by referring to the accompanying drawings which illustrate, by way of example, and not by way of limitation, one of possible embodiments of the brake adjuster System proposed herein. BRIEF DESCRIPTION OF THE DRAWINGST
[0010] Figure 1 shows a plan view of a drum brake in accordance with the present invention; [0011] Figure 2 shows a view of the adjuster used in the drum brake of figure 1 in the direction
of the arrow A of figure I; [0012] Figure 3 shows, on a larger Scale, the adjusting teeth of the broached bolt;

[0013] Figure 4 shows a view of diaphragm spring of the adjuster used in the brake of figure 1;
I DETAILED DESCRIPTION OF THE INVENTION
[0014] The drum brake illustrated in the accompanying drawings comprises a back plate 1, a pair of brake shoes 2 and 3, a fixed abutment 10 and a double ended brake sleeve cylinder 4 for applying the Service braking toad to the adjacent tips of the respective brake shoes. The drawings show back plate 1 having wheel cylinder 2 clamped by means of bolts and nuts as shown. Brake shoes 3r42 and 3 are assembled by means of locating pin 8 and shoe holder flat 7. These shoes are tightly packed on back plate 17 by means of top and bottom return spring 5, 6. An adjuster 9 is assembled at top spring location.
[0015] Auto adjusting mechanism consists of strut assembly in which diaphragm spring 12 is riveted to strut. Strut 9a is having a slot which can engage into shoe 3 Hb by means of strut return spring 13. Broached bolt 9b has similar slot which can assemble into shoe 4 Hb by means of broached bolt return spring 14.
[0016] Thus when the handbrake lever 11 is pivoted anticlockwise about the pin 15 as indicated by the arrow B in fig.2, the strut 9a forces the brake shoe 3 into contact with the associated brake drum via the contact "surface of strut 9a and the reaction of this shoe contact is transmitted via the adjuster 9, handbrake lever 113 and pin 15 to engage the other brake shoe 2 with the opposite side of the associated brake drum. Thus a handbrake function is provided in a conventional manner.
[b0191 In accordance with the present invention, an adjuster 9 is in two parts. A first part is strut 9a, which is held in contact with the brake shoe 3 by a coil-spring 13, which is hooked through an aperture 15 in the brake shoe 2 and into a cut out 16 in the strut part 9a. The second part broached bolt 9b is guided through a hole relative to the strut 9a via a diaphragm spring 12 which is riveted on strut 9a. Broached bolt 9b is provided with an array of teeth 17, which are engaged by an array of leaves on diaphragm spring 12. Broached bolt 9a-9b has similar slot which can assemble into shoe 4 rib by means of broached bolt return spring 14. As best seen in figure 1. the deflection of the diaphragm spring 12 which is defined by drum and shoe clearance. Thus at normal braking condition, there is initial deflection x between diaphragm spring 12 and broached bolt.

During normal hydraulic Operation of the brake the brake shoes 2 and 3 are applied against the associated drum by pressurizing the vvheel cylinder 4 and providing the distance which the brake shoes require to move to engage the drum does not exceed the initial deflection x between the diaphragm spring 12 and broached bolt_9b, there is no tendency of the brake shoes to attempt to move the two parts strut 9a and the broached bolt 9b of the cross-strut relative to each other.
[0020] If the movements required to apply these shoes against the drum exceeds this deflection x
then, since cross-strut part 9a is fixed to brake shoe 2 and the broached bolt is fixed to
shoe 3 by means return spring 14, there will be a tendency of the broached bolt 9b to be
i moved relative to the cross-strut part 9a in the direction of arrow A of figure 2. If this
tendency of movement exceeds the pitch of the inter engaging teeth on broached bolt 9b and then broached bolt 9b will be drawn away from cross-strut part 9a in direction A sufficiently to engage the next tooth formation and the effective length of an adjuster 9 is increased to take up the brake shoe clearance. Thus as the brake shoes wear down the effective length of an adjuster 9 progressively increases so that the retraction of the brake shoes under the action of spring 5 remain substantially constant.
[0021] In the tooth away configuration shown in figure 3 the teeth 17 extend in direction 'C and
the leaves on diaphragm spring 12 in direction 'D' both of these directions being generally
parallel to the direction A in which broached bolt 9b moves relative to part 9a. With such
i a configuration, when the brake has been lightly applied by the wheel cylinder 4 and the
teeth 17 and leaves 18 are only engaging each at their tips, if the handbrake lever 11 is then quickly applied the teeth may jump over each other which can lead to tooth damage and unintentional shortening of the effective length of strut 9.
[ )022] The problem can be overcome by inclining the directions of extension 'C and 'D' of the teeth 17 and leaves 18 at a slight angle 99 to the direction A in which the strut part 9b slides relative to the diaphragm spring as shown in figure 3. With the figure 3 arrangement there is an increased height 'h' of each tooth 17 available (see figure 3) to stop tooth slippage due to the angle of inclination 99. In a typical arrangement the inclination 99 is 15 to 20 degrees with a tooth depth_d of say 0.4 mm and a tooth pitch_P of say 0.8 mm. An adjuster can be used in a brake which does not have the brake lever 11 and which can only be applied by the wheel cylinder 4. In such an arrangement the

adjuster strut 9a slot is held onto the shoe 2 by strut return spring 13. broached bolt 9a having similar slot which can assemble into shoe 4 rib by means of broached bolt return spring 14. An adjuster strut 9 thus still functions to limit the retraction of the brake shoes when the brake is released and, as the effective length of the strut adjusts as the shoes wear, the retraction of the brake shoes remains substantially constant throughout the life of the brake.
" 3023] Figure 5 illustrates an exploded view of the automatic adjuster 9, which is in two parts. A first part is strut 9a, which is held in contact with the brake shoe 3 by a coil-spring 13. The second part, which is the broached bolt 9b is guided through a hole in the diaphragm spring 12 which is riveted on the strut 9a. The broached bolt 9b is provided with an array of teeth 17. which are engaged by an array of leaves on the diaphragm spring 12. The broached bolt 9b has similar slot 18 which can assemble into the brake shoe 4 rib by means of broached bolt return spring 14. Purine normal braking condition. there is initial deflection between the diaphragm spring leaves and the broached bolt 9b. Through which, the broached bolt 9b moves toward the brake shoe 4 pushing it closer to the drum. Further, due to angle of orientation of the teeth 17 in the broached bolt 9b. the broached bolt is not allowed to retain its previous Position and instead is locked in the pushed position and further retains the brake shoe 4 in the position further closer to the drum. Therefore, required gap is covered by the automatic adjuster between the brake shoes 3 and 4 and the drum.
")024] It will be appreciated that various other embodiments of this invention are possible
without departing from the scope and ambit thereof

We Claim:
I. An automatic brake shoe adiuster for a motor vehicle pertaining to internal shoe drum brakes. said automatic brake shoe adiuster compnsing:
a pair of brake shoes (3. 4) capable of expanding when actuated bv manual means to engage a brake drum for Service brake Operation; characterized in that,
an automatic adiuster in two parts. a flrst part consisting of a strut (9a) which is held in contact with the brake shoe bv a coil-spring (13), and a second part consisting of a broached bolt (9b) provided with an array of teeth (17) which are engaged bv an array of leaves on a diaphragm spring (12). wherein, the deflection of the diaphragm spring (12) being defined by drum and shoe clearance, said broached bolt (9b) being engageable bv a diaphram spring (12). which is movable when excess wear of the linings is sensed to adjust the length of the broached bolt (9b), such that when the brakes are in applied condition the brake shoes (3, 4) expand and pull both the brake shoes (3, 4) in the outward direction along with the broached bolt (9b) and the strut (9a) which are engaged due to diaphragm spring (12) and such that when the brakes are released the brake shoes (3. 4) come closer by reason of the return spring (14) but the broached bolt (9b) will not allow further movement and will lock at a specified position due to angle of inclination 9 degrees between each teeth (17). thus maintaining always the same clearance between drum and the brake shoe (3.4) irrespective of the brake shoe (3.4) wear.

We Claim:
I. 4-i-An automatic brake shoe adjuster system-for a motor vehicle pertaining to internal shoe drum brakes. said automatic brake shoe adjuster comprisingi
a pair of brake shoes (3. 4V-wkiek capable of expandjng when actuated by manual means to engage a brake drum for service brake Operation;
characterized in that.
an automatic adjuster in two parts, a first part consisting of a strut (9a) which is held in contact with the brake shoe by a coil-spring (131, and a second part consisting of a broached bolt_£9b) provided with an array of teeth (17) which are engaged by an array of leaves on a diaphragm spring (12), wherein, the deflection of the diaphragm spring (12) being defined by drum and shoe clearance, said broached bolt (9b) being engageable by a diaphragm spring (12), which is movable when excess wear of the linings ls-is_sensed to adjust the length of the broached bolt (9b), such that when the brakes are in applied condition the brake shoes (3, 4) expand and pull both the brake shoes (3, 4) in the outward direction along with the broached bolt (9b) and the strut (9a) which are engaged due to diaphragm spring (12) and such that when the brakes are released the brake shoes (3, 4) come closer by reason of the return spring (14) but the broached bolt (9b) will not allow further movement and will lock at a specified position^ thus maintaining always the same clearance between drum and the brake shoe (3,4) irrespective of the brake shoe (3,4) wear.

We Claim:
1. An automatic brake shoe adjuster for a motor vehicle pertaining to internal shoe drum brakes, said automatic brake shoe adjuster comprising:
a pair of brake shoes (3, 4) capable of expanding when actuated by manual means to engage a brake drum for Service brake Operation;
characterized in that,
an automatic adjuster in two parts, a first part consisting of a strut (9a) which is held in contact with the brake shoe by a coil-spring (13), and a second part consisting of a broached bolt (9b) provided with an array of teeth (17) which are engaged by an array of leaves on a diaphragm spring (12), wherein, the deflection of the diaphragm spring (12) being defined by drum and shoe clearance, said broached bolt (9b) being engageable by a diaphragm spring (12), which is movable when excess wear of the linings is sensed to adjust the length of the broached bolt (9b). such that when the brakes are in applied condition the brake shoes (3, 4) expand and pull both the brake shoes (3, 4) in the outward direction along with the broached bolt (9b) and the strut (9a) which are engaged due to diaphragm spring (12) and such that when the brakes are released the brake shoes (3, 4) come closer by reason of the return spring (14) but the broached bolt (9b) will not allow further movement and will lock at a specified position, thus maintaining always the same clearance between drum and the brake shoe (3,4) irrespective of the brake shoe (3,4) wear.