9.1. Features of a design
The Chery Amulet car is equipped with two independent brake systems: working and lay. The first system equipped with a hydraulic drive with the vacuum amplifier and anti-blocking system, provides braking at the car movement, the second — затормаживает the car on parking.
On the car apply working brake system with diagonal division of contours that considerably increases safety of driving of the car. One contour ensures functioning right forward and left back of brake mechanisms, another — left forward and right back. At refusal of one of contours of working brake system the second contour providing a stop of the car, though with smaller efficiency is used. In a hydraulic drive, besides a brake pedal, the vacuum amplifier, the main brake cylinder, brake mechanisms of lobbies and back wheels together with working cylinders and pipelines are switched on.
The drive of lay brake system is carried out on brake mechanisms of back wheels.
Brake mechanisms of forward wheels
disk, with automatic adjustment of a gap between brake shoes 5 (fig. 9.1)
and a disk 7, with a floating bracket. The mobile bracket is formed by a support of 1 c the one-piston working cylinder. The directing bracket of 6 blocks is attached by bolts to a rotary fist of a forward suspension bracket. The mobile bracket is attached by bolts to directing fingers 4 which are established in openings of directing blocks. Directing plugs are greased with konsistentny greasing and protected by rubber boots 8.
|Fig. 9.1. Brake mechanism of a forward wheel: 1–support of the brake mechanism; 2–brake hose; 3–Perepuskny valve; 4–a directing finger; 5–brake shoes; 6–a directing bracket of blocks; 7–brake disk; 8–a boot of a directing finger
In a cavity of the wheel cylinder the piston with a sealing ring is established. At the expense of elasticity of this ring the optimum gap between blocks and the brake disk which surface is protected by a brake board is supported. When braking the piston under the influence of pressure of liquid presses an internal block to a disk, as a result of force of reaction the support moves on fingers and the external block too nestles on a disk, and force of pressing of blocks appears identical. At a rastormazhivaniye the piston at the expense of elasticity of a sealing ring is taken away from a block, between blocks and a disk the small gap is formed.
Brake mechanisms of back wheels
drum-type, with automatic adjustment of a gap between blocks and a drum. Brake shoes 1 and 5 (fig. 9.2)
are put in action by one hydraulic working cylinder 2 with two pistons.
|Fig. 9.2. Brake mechanism of a back wheel: 1, 5 – brake shoes; 2–brake cylinder; 3–top coupling spring of blocks; 4, 8 – basic racks of blocks; 6–guard; 7–bottom coupling spring of blocks
The vacuum amplifier established between the mechanism of a pedal of a brake and the main brake cylinder, when braking at the expense of depression in an engine receiver through a rod and the piston of the first chamber of the main cylinder creates the additional effort proportional to effort from a pedal.
In a hose, connecting the vacuum amplifier with a receiver, is established the return valve. It holds in the amplifier depression at its falling in an inlet pipe and interferes with hit of a toplivovozdushny mix in the vacuum amplifier.
The main brake cylinder of a hydraulic drive of brakes consists of two separate chambers connected to independent hydraulic contours. One of chambers is connected with right forward and left back brake mechanisms, another — with left forward and right back.
The main cylinder is supplied with a tank which internal cavity is divided by a partition into two compartments. Each compartment feeds one of chambers of the main cylinder.
By pressing a brake pedal pistons of the main cylinder start to move, working edges of cuffs block compensatory openings, chambers and a tank are separated and replacement of brake liquid begins.
The parking brake put in action mechanically, consists of the lever established on the basis of a body between forward seats, draft with the adjusting mechanism to which two back cables, and also the razzhimny levers established in brake mechanisms of back wheels are attached.
The parking brake does not demand special leaving. At maintenance check degree of wear of its details, be convinced of serviceability of teeths of sector and a doggie. Excessively worn-out details replace.
The anti-blocking system of brakes (ABS) consists of sensors of frequency of rotation of wheels, the hydraulic block, a control lamp and the acceleration sensor. Besides, the anti-blocking system is equipped with system of the self-diagnostics revealing malfunctions of components.
The electronic control unit and the hydraulic ABS block, united in the uniform module, are established in a motor compartment under the vacuum amplifier of brakes and fixed on the right mudguard.
ABS serves for pressure regulation in brake mechanisms of all wheels when braking in difficult road conditions, preventing blocking of wheels, keeping the set trajectory of the direction of movement and course stability.
During car braking the electronic ABS control unit receives a signal from all sensors of speed of rotation of wheels and defines, what wheel is at present on the verge of blocking. On the basis of the received signals the electronic block puts in action the corresponding electromagnetic valve in the hydraulic block for ensuring demanded pressure in the pipeline of the corresponding wheel.
The anti-blocking system provides the following advantages:
– a detour of obstacles with higher degree of safety, including at emergency braking;
– reduction of a brake way at emergency braking with preservation of course stability and controllability of the car, including in turn.
In case of malfunction of system functions of self-diagnostics and work maintenance at system refusals are provided.
The hydroelectronic control unit receives information on speed of movement of the car, the direction of movement and road conditions from sensors of frequency of rotation of wheels.
On the basis of this information the control unit defines an optimum mode of braking of wheels.
Distinguish the following working hours of anti-blocking system:
– mode of normal braking. At normal braking the electromagnetic valve is disconnected, the entrance valve is open, the target valve is closed. By pressing a brake pedal brake liquid under pressure moves in the working cylinder via the electromagnetic valve and puts in action brake mechanisms of wheels. At an otpuskaniye of a pedal of a brake brake liquid comes back to the main brake cylinder via entrance and return valves;
– mode of emergency braking. If at emergency braking blocking of wheels begins, the hydroelectronic control unit gives out command for reduction of supply of brake liquid on the electronic valve, then tension moves on each electromagnetic valve. The entrance valve is closed, and supply of brake liquid from the main brake cylinder is blocked; the target valve opens, and brake liquid arrives from the working cylinder in main, and then in a tank that causes pressure decrease;
– mode of maintenance of pressure. At the maximum pressure decrease in the working cylinder the hydroelectronic control unit gives out command for maintenance of pressure of brake liquid on the electromagnetic valve, tension moves on the entrance valve and does not move on the target valve. Thus entrance and target valves are closed and brake liquid does not leave working cylinders;
– mode of increase of pressure. If the hydroelectronic control unit defines that the wheel is not blocked, it disconnects the electromagnetic valve. Tension does not move on electromagnetic valves, brake liquid arrives via the entrance valve in working cylinders, pressure increases.
Some drivers, aspiring to wear out less a cable of the parking brake, try to use it less often. Such "economy" leads to return result: a cable, seldom moving in a cover, gradually loses mobility, it gets jammed, as a result the cable breaks. Therefore use the parking brake in all cases, when necessary.
The free wheeling of a pedal of a brake at the idle engine should be about 3-6 mm. Too low free wheeling testifies to jamming of the working cylinder, causes the increased fuel consumption and the accelerated wear of brake shoes. Too big free wheeling — a sign of gaps above permitted standard in the mechanism of a pedal or violation of tightness of a hydraulic actuator of brake system. If the free wheeling decreases by numerous pressing a pedal, i.e. it becomes more rigid", – in system air. If the full speed of a pedal starts to increase, the system is not tight.
If when braking the pedal of a brake starts to vibrate, most likely, brake disks are jarred on. Unfortunately, in their such situation it is necessary to change only, and at once both.
If when braking the car starts to pull aside, check working cylinders: probably, their repair or replacement is required.
If in a forward suspension bracket there was a knock vanishing at braking, check an inhaling of bolts of fastening of a support.
After replacement of brake shoes prior to the beginning of movement surely several times press a brake pedal — pistons in working cylinders should rise into place.