Pneumatic drive is a power source that is used for braking and runs on compressed air. The device under consideration makes it possible to create a significant braking force with minimal participation of the driver or operator. A similar system is widely used in the arrangement of tractors, buses and trucks. The design consists of a compressor, air tanks, a crane, wheel compartments, a disconnecting regulator, a vessel for draining waste working fluids.
Compressor
This pneumatic drive element supplies compressed air to the system. It is processed in a purifier and then transported to tanks. The exit of the air mixture from the cylinders is prevented by a non-return valve. The pressure indicator is determined by the manometer. After the brake pedal is activated, air enters the brake compartments through the opened valve, as a result of which the compression of the pads is triggered. The reverse process occurs with the help of tie rods.springs.
The structure of the compressor includes a cylinder block, its head, crankcase, locking caps. The crankshaft of the mechanism rotates in ball-type bearings, interacts with the pistons with the help of fingers and connecting rods. The front part of the crankshaft is equipped with a V-belt, an oil seal and a key. A fan is provided as a cooler. In the cylinder head above each working element there is a plug with a spring and a pressure valve. The lower connecting rod heads are equipped with shims.
Lubrication and Cooling
Pneumatic brake actuator has a combined lubrication system. Oil is supplied from the main line through a pipe to the inside of the crankshaft. Connecting rod bearings are placed in an anti-friction solution and are forcibly lubricated. The rest of the elements receive oil by spraying. Mining from the crankcase is sent to the engine tank through a special outlet.
The air drive compressor cooling system is liquid type. It is connected to a similar unit of the power unit. When one of the pistons is lowered to the lower position, a vacuum is created and air enters it through the cleaner and intake valve. After the piston rises, the air mixture is compressed, then it enters through the valve into the cylinders and the main system. The whole process then repeats.
The air pressure indicator is limited by a special regulator, which reduces the cost of motor power to drive the compressor, which increases the working lifenode. The design with the regulator is located under the valves, contains a pair of plungers and seals with pushers. The plunger rocker is connected by a spring, the cavity under the inlet valves aggregates with the cleaner pipeline, and the plunger channel with the pressure controller.
Pneumatic drive brake system
Air cylinders are designed to store a cooled supply of liquefied air. Their design includes taps for removing condensate, as well as a safety valve. A cap-type nut protects the device from clogging.
The body of the pressure regulator is closed by a casing, has a fitting with a valve stem. The rod is acted upon by a spring mechanism, which is equipped with a regulating cap. The inlet and outlet valves are located in the center console of the body. The channel is connected through the filter and the inlet to the cylinders, as well as the unloading device. A plug is provided at the bottom of the case.
If the pressure in the line reaches a value below 560 kN/sq.m, the air mass escapes into the atmosphere. The plungers at the same time release the inlet valves, the compressor begins to pump air into the system.
System Management
The hydraulic pneumatic drive is equipped with a crane for control. It allows you to regulate the supply of compressed air to the working chambers. It also provides stable braking force and quick release.
The body of this part is fixed to the frame. The diaphragm is made of rubberfabric material, placed between the lid and the frame. In its center there is an exhaust valve seat, which rests on the glass of the control spring. The working cavity communicates with the atmosphere through an inlet port and a valve. The return type spring acts stably on the diaphragm and intake valve. The saddle of the last element is clamped in the cover with a fitting. By pressing the valve, the air from the cylinders does not enter the brake chambers.
Pneumatic actuator operation
Double shoulder lever aggregates with the brake pedal, while relying on the glass. After pressing the pedal, the rod placed inside the corrugated protective cover turns the lever. A glass with a spring moves to the right, the diaphragm flexes, after which the exhaust valve closes, and its inlet analogue opens. A diaphragm with a spring mechanism and valves forms a follower unit. It has three positions.
In the first position, the brake pedal is released, both valves are in the leftmost position. The intake valve is active, the brake compartments through it, as well as the working chambers are connected to the atmosphere.
The second position corresponds to pressing the pedal, the effort is transformed on the lever, glass and diaphragm. The seat closes the valve, separating the connection to the atmosphere. The opening of the valve is additionally prevented by air pressure and spring force.
In the third position, after additional pressing the pedal, the inlet valve opens, the compressed air mixture enters the brake chambers, and the braking process is carried out. Aperture underair flexes, and the spring is compressed. After balancing the acting forces, the diaphragm moves to the second position, both valves close, providing a constant braking force.
Features
Pneumatic brake drive receives additional air when pressing the pedal harder. This causes an increase in the pressure indicator in the working compartments. When disinhibiting, the processes proceed in a proportionally reverse order. The compressed air mixture exits through the valve. The idle speed is adjusted by means of a special bolt.
To operate the pneumatic actuator of the valves, a combined type crane is mounted on the trailers. It is an element with two sections, the upper of which is responsible for the operation of the towing device, and the lower part for the tractor. The right sections of the compartments are identical; a stem rests against the seat of the exhaust valve, placed in a mechanism with a bushing and a spring. On the rod axis there is a lever that aggregates with a small analogue.
Pros
The use of the device in question is due to a number of advantages, namely:
- Pneumatic drive allows you to create a significant downforce on the pads with little impact on the control pedals.
- Affordable, safe and easy to operate on conventional air.
- The ability to accumulate a significant amount of potential air energy in special reservoirs, which allows for long-term and effective braking even in case of failurecompressor.
- Minor air mixture leaks are allowed, which are partially compensated by the supply of compressed air.
- Simplicity and convenience of connecting and conductive parts.
- High efficiency.
- Ability to use the design for the operation of various additional automotive equipment.
Flaws
Now consider the cons of the device:
- Relatively slow response due to compressed air.
- Repair of a pneumatic actuator requires complete or partial replacement of elements.
- Design complexity and high cost of multi-loop modification.
- Large weight and dimensions compared to the hydraulic counterpart.
- Significant power consumption for the compressor drive.
- Possibility of unit failure when condensate freezes in winter.
The pneumatic brake actuator provides high force, while containing a lot of elements. For example, at KamAZ, this part includes about 25 devices, 6 receivers, about 70 meters of pipelines.
In conclusion
The design of single-circuit pneumatic actuator is simple. However, modern traffic safety standards do not accept its operation due to low reliability. Multi-circuit analogues are installed on cars, which are equipped with several autonomous drives. The modern system has two mandatory minimum circuits, as well as up to six circuits of other systems.
In addition, the design of the assembly includes a lot of devices designed to ensure the normal operation of the brake elements. They also monitor the condition of the drive on the tractor and trailer. The system under consideration is equipped with popular domestic trucks. This mechanism is especially relevant on road trains. On machines with an extended base, a complex hydropneumatic brake drive is often used. It uses compressed air to give the necessary force, and the transmission to the mechanism is carried out by means of a working fluid. Such a system increases the speed of the structure, but significantly complicates it.
