Ural vehicles have three independent brakes: a working brake with a hydropneumatic drive on all wheels, a parking brake with a mechanical drive acting on the transmission, and an auxiliary compression type installed on the pipelines of the gas exhaust system
Working brake system
A working brake system is designed to reduce the speed and stop the car, regardless of its speed, load and slopes of the roads for which it is intended.
Mixed (pneumatic-hydraulic) double-circuit brake drive, with separate braking of the wheels of the front and two rear axles.
The control is carried out by a pedal in the driver's cab, connected by levers and rods with a two-section brake valve.
The service brakes of vehicles have a hydropneumatic drive, consisting of the following main units: a brake valve compressor, a pressure regulator, two pneumatic boosters with main brake cylinders, an interballoon reducer of air cylinders, combined with pipelines, hoses and connecting fittings into a single system (Fig. .1).
A two-pointer pressure gauge and a fault signaling system are used to control the vehicle's service brake units.
The lower scale of the pressure gauge shows the air pressure in the area of the air cylinder - brake valve, the upper one - in the pneumatic boosters at the moment of braking.
The system for signaling malfunctions of service brakes consists of sensors installed in units (assemblies) of service brakes and red signal lamps located on the instrument panel.
The “Air” minimum air pressure warning light with the ignition on, gives a signal when the pressure in the air tank drops below 4 kgf/cm3.
Brake warning light “Brake” turns on when braking with a service brake that has a malfunction or in the mechanical part of the service brake (large gaps between the linings of the shoes and the brake drum, etc. . p.), or in the hydraulic brake system as a whole (liquid leakage, air entering the system, etc.).
Working drum-type brake mechanism with internal pads 4 (Fig. 2), interchangeable for all wheels.
Each brake mechanism has two hydraulic cylinders 7, made in one housing.
Brake pads are mounted on support axles 6.
The working brake mechanism is adjusted as the lining wears out by reducing the gap between the lining and the drum using eccentrics 2.
To adjust the brakes:
- - with a 22 mm key, turn the adjusting eccentrics of the pads to the stop, turning the right (on the side of the shield) eccentric clockwise, the left - counterclockwise;
- —release the eccentrics by a reverse rotation of approximately 30°, which corresponds to turning the head of the eccentric axis by half a face.
After doing the indicated operations with all wheels, check if the brake drums heat up when the car is moving.
When adjusting the brakes, do not violate the factory setting of the axles 6 of the brake pads.
Adjust the gaps between the brake shoe and the brake drum using the shoe axles only when replacing friction linings or shoe assemblies.
In this case, initially set the axles of the pads with marks at the ends to each other.
Through the hatch in the brake drum, insert a feeler gauge 0.2 mm thick and 200 mm ear between the drum and the shoe at a distance of 30 mm from the bottom edge of the lining.
By turning the axis 6 of the shoe, lightly clamp the probe. Remove the feeler gauge, turn the drum, and using another feeler gauge and adjusting eccentric 2, set a gap of 0.35 mm between the block and the drum at a distance of 30 mm from the top edge of the lining.
Fix the axles of the pads and recheck the gaps between the pad and the drum.
If the pads are worn down to the plane of the rivet head, replace them.
When oiling the brake linings, wash them with gasoline.
When the brake drum is worn, there are annular grooves with a depth of more than 2 mm, bore the working surface of the drum based on the outer rings of the hub bearings.
The runout of the working surface of the drum should not exceed 0.25 mm, and the diameter of the barabana - 424.38 mm.
On the front axles of heavy-duty vehicles, only pads of code 143-63 (gray) should be installed.
Combined (pneumatic-hydraulic) service brake drive
The car is equipped with a dual-circuit brake drive with a combined trailer drive and with additional brake devices.
The drive provides the possibility of connecting the brake systems of trailers with single-wire or dual-wire brake drives.
The circuit diagram of the brake actuator is shown in fig. 4.
Compressor 29 supplies compressed air through pressure regulator 4 to the safety valve block.
The block consists of triple 5 and single 7 safety valves that distribute and fill air tanks 3, 9 and 27 independent circuits:
- — front wheel brake drives;
- —drives of the brake mechanisms of the middle and rear wheels;
- —combined brake drive of the trailer wheels.
The first main circuit consists of an air cylinder 3, the upper section of the brake valve 28, a pneumatic booster 24 and wheel cylinders 23, and the second main circuit consists of an air bottle 27, the lower section of the brake valve 28, a brake force regulator 20, a pneumatic booster 24 , wheel cylinders 23.
The third circuit consists of an air cylinder 9, trailer brake control valves: 19 - with a single-wire drive and 15 - with a two-wire drive, a connecting head 18 type "A" for connecting trailers with a single-wire drive, automatic connecting heads 16, 17 for connecting trailers with two-wire brakes.
Air is taken from the air cylinders 3, 27 through the triple safety valve 5 to actuate the wipers, the air signal, the pneumatic clutch booster and other consumers.
If it is necessary to control the air pressure in each circuit, control outlet valves 25 are installed, to which a portable pressure gauge can be connected.
When driving a car with a trailer having a single-wire brake drive, the connection of the car with the trailer is carried out by the connecting head 18, the two-wire - by connecting heads 16, 17.
When you press the brake pedal, the first and second circuits of the brake drive of the car are activated, as well as the third circuit of the trailer brake drive.
If one of the circuits fails, the others remain operational.
To brake a car with a trailer in the parking lot, set the parking brake lever to the upper fixed position: in this case, the control valve 10 releases compressed air from outlet II of valve 15 (see Fig. 4) and actuates the brake mechanisms of the trailer
The car has a system for signaling and monitoring the condition of the brakes. The air cylinders are equipped with minimum air pressure sensors.
In the pneumatic boosters, sensors are installed to indicate a malfunction of the service brake system (leakage of brake fluid or large gaps between the pads and the drum).