Floating caliper with eccentric shaft and lever

(Fig. 11.54(a)) With this type of heavy duty commercial vehicle disc brake a floating caliper is used in conjunction with an eccentric and lever to clamp the pads against the friction faces of the disc. The eccentric part of the eccentric shaft is surrounded

Fig. 11.52 (a-d) Rear brake circuit pressure regulator and cut-off device

by needle rollers positioned inside a bored hole in the bridge block and is connected to the inside pad via two threaded adjustment barrels and a load plate. On either side of the eccentric are stub shafts which are mounted via needle rollers in the caliper.

When the brakes are released the lever arm takes up a position in which the lobe side of the eccentric leans slightly to the right hand side of the vertical (Fig. 11.54(c)). As the brake is applied (Fig. 11.54(b)) the lever arm and eccentric swivels so that the lobe moves to the vertical position or just beyond, hence the bridge block will have moved to the right hand side (towards the disc face) by x = x2 — x1 where x equals pad take-up clearance. Thus when the brakes are applied compressed air is released into the actuator chamber; this pushes the diaphragm and push rod to the left hand side, causing the lever arm to rotate anticlockwise. As a result the eccentric lobe forces

Fig. 11.53(a and b) Pneumatic operated disc brake - floating caliper with integral half eccentric lever arm

(b) Brake applied

(c) Brake released

Force

Needle rollers

Eccentric shaft

(b) Brake applied

(c) Brake released

Force

Needle rollers

Eccentric shaft

Threaded adjustment barrel

Bevel gear

Vented disc Load plate Slide pin

Gear plate segment

Fig. 11.54(a-c) Pneumatic operated disc brake - eccentric shaft and lever with gear driven automatic adjustment mechanism

Adjuster gear train cassette

Override clutch

Threaded adjustment barrel

Bevel gear

Vented disc Load plate Slide pin

Gear plate segment

Fig. 11.54(a-c) Pneumatic operated disc brake - eccentric shaft and lever with gear driven automatic adjustment mechanism

(b) Brake applied

(c) Brake released

Sleeve fork & barrel rotated while brake is applied

Sleeve fork & barrel rotated while brake is applied

Needle rollers

Half eccentric

Override clutch

Drive spindle

Sleeve fork

Fork prongs

Ventilated disc Caliper carrier

Fig. 11.55 (a-c) Pneumatic operated disc brake - half eccentric shaft and lever with gear driven automatic adjustment mechanism

Needle rollers

Half eccentric

Override clutch

Drive spindle

Sleeve fork

Chain sprocket wheel

Fork prongs

Strike pins

Adjuster chain

Bearing pin

Pull-off spring Needle rollers

Sprocket wheel & spindle

Half eccentric and lever arm

Threaded adjustment barrel

Bridge block

Slide pin & sleeve Load plate Pads

Ventilated disc Caliper carrier

Fig. 11.55 (a-c) Pneumatic operated disc brake - half eccentric shaft and lever with gear driven automatic adjustment mechanism the bridge block and consequently the inner pad towards the right hand face of the disc. Conversely a reaction force acting though the eccentric stub shaft and caliper pulls the whole caliper, and subsequently the outer pad, towards the left hand face of the disc until the desired amount of friction force is generated between the pads and disc to either slow down or park the vehicle.

Automatic pad clearance gear-driven type adjuster mechanism (Fig. 11.54(a, b and c)) A constant running clearance between the pad and disc is maintained with this mechanism; this device operates by the to and fro movement of the lever arm about the eccentric stub shafts every time the brakes are applied and released (Fig. 11.54(a)). Drawing together of the brake pads is achieved by partial rotation of the eccentric lobe within the bridge block, thus movement is transmitted to the pads via the two threaded adjustment barrels which are screwed either side of the eccentric onto the threaded adjuster posts which are rigidly attached to the inner brake pad load plate.

A gear-plate segment is attached to one side of the eccentric via a slot and tongue. The segment teeth mesh with a bevel gear which houses the override clutch (one-way clutch operating between balls rolling up and down inclined plains), see Fig. 11.54(a). Any partial rotation of the eccentric is transferred to the threaded adjustment barrels via the override clutch and the train of gears.

Thus every time the brake lever arm moves from the released to the applied position, the threaded adjustment barrels are partially screwed out from the threaded adjustment posts, thereby causing the load plate and pad to move further towards the inside face of the disc. Conversely each time the lever arm moves from the applied to the released position, the override one-way clutch disengages, so preventing the threaded adjustment barrels being screwed in again. Eventually after many braking applications, the threaded adjustment barrels will have screwed out the threaded adjustment posts sufficiently to cause the inner pad to touch the inner face of the disc.

Eventually after many braking applications, the threaded adjustment barrels will have screwed the threaded adjustment posts sufficiently out to cause the inner pad to touch the inner face of the disc. At this point, the slight tightening between the male and female threads generates sufficient friction in the screw threads and underneath the flange head of the threaded adjustment barrels to cause the override clutch to slip, hence further rotation of the threaded adjustment barrels ceases. As pad and disc wear occurs, the threaded adjustment barrels once again commence to turn; a constant running clearance is thus maintained during service.

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