This article introduces the introduction of the Isuzu NKRUBS rear disc brake automatic adjustment device
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(1) General description When the parking brake lever is operated, the brake pads are mechanically pressed against the brake disc rotor.
This brake system is equipped with an automatic adjuster which maintains the clearance between the disc rotor and brake pad constant through the operation of the foot brake system. The automatic adjuster con-
sists of an adjusting screw, an adjusting nut, a wave washer, a drive ring, an adjuster spring, etc. as shown in the figure below.
(2) Component parts
(3) Operation Step 1
Due to the seal’s roll-back action, the thread face of the screw (8) is in contact with that of the nut (5). The nut is pressed in the axial direction by the force of the wave washer (7). The drive ring (4), under the twist-
ing torque of adjusting spring (6). is in a frictional contact with the grooved sleeve (2) at the conical surface
(K). The axial play of the screw (8) is caused only by the thread backlash (L).
Step 2
When the fluid pressure is applied, the piston (1) moves toward the disc. By this movement, the adjuster parts (screw (8). etc.) are moved as a whole forward along with the piston (1). by an amount equivalent to the thread backlash.
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Step 3
When the piston (1) strokes more than the backlash amount, the nut (5) separates from the piston due to deflection of the wave washer (7). Then, the grooved sleeve (2) and the drive ring (4) are forcibly moved for-
ward through the ring (3). The drive ring’s oblique slot overcomes the friction torque of the wave washer and turns the nut (5) in proportion to the piston stroke. At this point, the driving ring (4) does not rotatetogether with the grooved sleeve (2) due to the friction on the conical surface (K). Besides, the set load of the coil spring (6) is increased by the rotation of the nut (5).
Step 4
Release of fluid pressure Due to the seal’s roll-back action and by the force of the wave washer (7), the piston returns back by an amount equal to Rb from the disc. During this step, the friction torque at the conical surface (K) decreases.
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Step 5
The piston (1) is returned by the wave washer (7) until it comes into contact with the end surface of the nut(5). During this operation, the preloaded coil spring (6) turns the drive ring (4) by an amount equivalent to the friction (S).
The relative position of the nut (5) and the drive ring (4) is always set to the point at the beginning of the adjustment.
