9.1. Features of a design
The Chery Amulet car is equipped with two independent brake systems: working and parking. The first system equipped with the hydraulic drive with the vacuum amplifier and anti-blocking system provides braking at the movement of the car, the second — slows down the car on the parking.
On the car use the 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 brake mechanisms, another — left forward and right back. At refusal of one of contours of the working brake system the second contour providing a car stop though with smaller efficiency is used. The hydraulic drive, besides a brake pedal, switched on the vacuum amplifier, the main brake cylinder, brake mechanisms of forward and back wheels together with working cylinders and pipelines.
The drive of the parking 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 1 with 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 the directing fingers 4 which are established in openings of the directing blocks. The directing plugs are greased with jellied lubricant 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 – the directing finger; 5 – brake shoes; 6 – the directing bracket of blocks; 7 – brake disk; 8 – a boot of the directing finger
In a cavity of the wheel cylinder the piston with a sealing ring is installed. Due to elasticity of this ring the optimum gap between blocks and a 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 reaction force the support moves on fingers and the external block nestles on a disk too, and force of pressing of blocks is identical. At a disinhibition the piston due to 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, 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 – lower coupling spring of blocks
The vacuum amplifier installed between the mechanism of a pedal of a brake and the main brake cylinder when braking due to depression in an engine receiver through a rod and the piston of the first camera of the main cylinder creates the additional effort proportional to effort from a pedal.
In the hose connecting the vacuum amplifier to a receiver the backpressure valve is installed. It holds in the amplifier depression at its falling in an inlet pipe and interferes with hit of fuel-air mix in the vacuum amplifier.
The main brake cylinder of the hydraulic drive of brakes consists of two separate cameras connected to independent hydraulic contours. One of cameras 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 cameras of the main cylinder.
By pressing a brake pedal pistons of the main cylinder begin to move, working edges of cuffs block compensation openings, cameras and a tank are separated and replacement of brake fluid begins.
The parking brake put in action mechanically consists of the lever installed on the basis of a body between front seats, drafts with the adjusting mechanism to which two back cables, and also the razzhimny levers installed 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 the sector and a doggie. Replace excessively worn-out details.
The anti-blocking system of brakes (ABS) consists of sensors of frequency of rotation of wheels, the hydraulic block, a control lamp and the sensor of acceleration. 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 regulation of pressure in brake mechanisms of all wheels when braking in difficult road conditions, preventing blocking of wheels, keeping the set trajectory of the direction of the movement and course stability.
During braking of the car the electronic control unit of ABS receives a signal from all sensors of speed of rotation of wheels and defines what wheel is on the verge of blocking at present. On the basis of the received signals the electronic block puts in action the corresponding electromagnetic valve in the hydraulic block for ensuring the required 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 brake application;
– reduction of a brake way at emergency brake application with preservation of course stability and controllability of the car, including in turn.
In case of malfunction of system functions of self-diagnostics and maintenance of work at system failures are provided.
The hydroelectronic control unit obtains information on the speed of the movement of the car, the direction of the movement and road conditions from sensors of frequency of rotation of wheels.
On the basis of this information the control unit defines the optimum mode of braking of wheels.
Distinguish the following operating modes of anti-blocking system:
– mode of normal braking. At normal braking the electromagnetic valve is cut off power, the entrance valve is open, the output valve is closed. When pressing a brake pedal brake fluid under pressure moves in the working cylinder via the electromagnetic valve and puts brake mechanisms of wheels in action. At a brake pedal otpuskaniye brake fluid comes back to the main brake cylinder via entrance and return valves;
– mode of emergency brake application. If at emergency brake application blocking of wheels begins, the hydroelectronic control unit issues the command for reduction of supply of brake fluid on the electronic valve, then tension moves on each electromagnetic valve. The entrance valve is closed, and supply of brake fluid from the main brake cylinder is blocked; the output valve opens, and brake fluid comes from the working cylinder in main, and then to a tank that causes pressure decrease;
– mode of maintenance of pressure. At the maximum pressure decrease in the working cylinder the hydroelectronic control unit issues the command for maintenance of pressure of brake fluid on the electromagnetic valve, tension moves on the entrance valve and does not move on the output valve. At the same time entrance and output valves are closed and brake fluid does not leave working cylinders;
– mode of increase in pressure. If the hydroelectronic control unit defines that the wheel is not blocked, then it cuts off power the electromagnetic valve. Tension does not move on electromagnetic valves, brake fluid comes via the entrance valve to working cylinders, pressure increases.
The hydraulic system of brakes is united in a whole by metal tubes and hoses. The system is filled with special brake fluid which needs to be replaced periodically. The replacement procedure of brake fluid is described in section 4 "Maintenance" (see. "Replacement of brake fluid in a hydraulic actuator of brakes"). Check of the brake system is described in the subsection "Procedural Maintenance".
Some drivers, seeking to wear out less a cable of the parking brake, try to use it less often. Such "economy" results in the return result: a cable, seldom moving in a cover, gradually loses mobility, gets jammed it, 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 has to be about 3-6 mm. Too low free wheeling demonstrates jamming of the working cylinder, causes the increased fuel consumption and the accelerated wear of brake shoes. Too big free wheeling — a sign of excess gaps in the mechanism of a pedal or violation of tightness of a hydraulic actuator of the 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 begins to increase, the system is untight.
If when braking the pedal of a brake begins to vibrate, most likely, brake disks are jarred on. Unfortunately, in their such situation it is only necessary to change, and at once both.
If when braking begins to pull the car aside, check working cylinders: perhaps, their repair or replacement will be required.
If in a forward suspension bracket there was a knock vanishing when braking check an inhaling of bolts of fastening of a support.
After replacement of brake shoes prior to the movement surely several times press a brake pedal — pistons in working cylinders have to rise into place.