Chery A15. Manual — part 210

Chapter Three: Maintenance of Brake System

Section One: Structural Features of Brake System

A15 car is equipped with a diagonal dual-line vacuum assisted hydraulic brake system,

which consists of two brake devices: service brake and parking brake. Front wheels

adopt disk brake while rear wheel drum brake using self-regulated shoe plate

clearance. Servo system uses high-performance vacuum booster and dual-way

hydraulic braking master cylinder.

A15 also features an ABS system, which greatly improves the directional control

when braking and the braking performance as well. ABS also prevents wheels from

being locked up, and maximizes the longitudinal adhesion of tires. That is how ABS

ensures the steerability of front wheels and avoids skidding of rear wheels at the same

time, thus ensuring vehicle braking with the maximum road adhesion coefficient.

Parking brake control mechanism is located between the front seats, directly controls

the arm drags of rear wheel drum brakes through a jacketed guy wire with small

frictional resistance. Rear wheel brake also serves as parking brake; the simple and

functional structure helps achieve high efficiency.

I. Diagonal Dual-line Brake

Brake line of A15 car adopts diagonal dual-line brake system. Brake master cylinder

has two chambers: front one is connected to front left wheel brake and rear right brake,

and rear one is connected to front right brake and rear left brake. This simple structure

ensures 50% of normal value left in case of failure of any one of the two lines, that is,

no mater which line fails, the basic braking requirements are still met by the other

line.

A15 brake system is shown in the figure below.

Figure: Brake System of A15 Car

1-Brake master cylinder 2-Brake fluid tank 3-Vacuum booster 4-Brake pedal

5-Brake line 6-Rear wheel drum brake 7-Front wheel disk brake

II. Front Wheel Disk Brake

Front wheel disk brake has a one-cylinder floating caliper structure, in which the

brake calipers may skid in axial direction around brake disk. This structure is shown

in the figure below.

Front left brake

Figure: Front Wheel Disk Brake

1. Front wheel hub 2. Dust board 3. Internal brake friction shoe assembly 4. Dust cover
5. Guide rod 6. Venting screw 7. Bolt 8. Bolt 9. Left brake caliper shell 10. Piston
11. Piston packing ring 12. Piston dust cover 13. Piston shock damper 14. Bracket
15. Set screw 16. Brake disk 17. Bolt

1. Structure of Front Wheel Disk Brake

The rotating component of front brake is the brake disk, which is fixed on wheel hub

and rotates with the hub. Brake caliper bracket is a fixed component (integrated with

steering knuckle). When braking, the piston moves due to the hydraulic action, and

pushes friction shoe near it to brake disk. Since brake caliper shell is skidding on

guide rod of caliper bracket, the counterforce will push the caliper and friction shoe to

contact the other side of brake disk, until forces applied on both friction shoes are

equalized.

The piston packing ring installed in brake caliper shell will be elastically deformed

when braking, and will resume the original shape due to elastic restoring force when

the brake is released to return the piston. The brake clearance will exceed set value

due to friction shoe wear, in which case the piston will skid in regard to packing ring,

thus achieving self-regulation of clearance.

2. Features of Front Wheel Disk Brake

(1). Stable braking performance. Generally disk brakes are free of friction adding

effect, so the friction factor has a very limited impact on braking performance, and the

entire car braking stability is greatly improved.

(2). Good water stability, i.e., efficiency decrease is small after being soaked in water.

Brake shoes of disk brake have a high unit pressure, which is able to squeeze out

water easily. Due to centrifugal force, only one or two brakings are enough to resume

the normal braking condition after getting out of water, while for drum brakes, it

usually takes more than ten brakings to resume the normal condition.

(3). Lower possibility of forming hot crack or hotspot under high temperature than

brake drum, provided that the brake disk is not too thick.

(4). Smaller dimension and mass than drum brake with the same output brake torque.

(5). Very small thermal expansion of brake disk along the thickness direction, while

brake drums have a larger thermal expansion that may markedly increase the brake

clearance and enlarge the brake pedal travel.

(6). Easy self-regulation of clearance and easy servicing and maintenance.

III. Rear Wheel Drum Brake

A15 adopts non-balanced drum brake (leading trailing shoe brake) for rear wheels, as

shown in the figure below.