A pneumatic drive is an energy source that is used for braking and runs on compressed air. The device in question makes it possible to create significant braking force with minimal involvement 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, an uncoupling controller, and 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 outflow of air from the cylinders prevents the check valve. The pressure indicator is determined by the pressure gauge. After activating the brake pedal, air through the opening valve enters the brake compartments, resulting in compression of the pads. The reverse process occurs with the help of coupling springs.
The compressor structure includes a cylinder block, its head, crankcase, and lock caps. The crankshaft of the mechanism rotates in ball bearings, interacts with the pistons with the help of fingers and connecting rods. The front of the crankshaft is equipped with a V-belt, stuffing box and 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 discharge valve. The lower connecting rod heads are equipped with shims.
Lubrication and cooling
The pneumatic brake drive has a combined lubrication system. Oil is supplied from the main line through a pipe to the inside of the crankshaft. The connecting rod bearings are placed in an antifriction solution and are lubricated by force. The remaining elements receive oil by spraying. The mining from the crankcase is sent to the engine capacity through a special outlet.
The cooling system of the pneumatic drive compressor is a liquid type. It is connected to a similar unit of the power unit. When one of the pistons lowers to the lower position, a vacuum is created and air enters into it by means of a cleaner and an intake valve. After lifting the piston, the air mixture is compressed, then it enters through the valve into the cylinders and the main system. Then the whole process is repeated.
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 life of the unit. The design with the regulator is located under the valves, contains a pair of plungers and seals with pushers. The plunger beam is connected by a spring, the cavity under the inlet valves aggregates with the purifier pipe, and the plunger channel with a pressure controller.
Pneumatic brake drive device
Air cylinders are designed to store a chilled supply of liquefied air. Their design includes valves for condensate removal, as well as a safety valve. The cap nut protects the device from clogging.
The pressure regulator housing is closed by a casing, has a fitting with a valve stem. The spring mechanism, which is equipped with an adjusting cap, acts on the stem. An inlet and outlet valve is located in the center console of the housing. The channel is connected through the filter and the inlet to the cylinders, as well as the unloading device. There is a plug in the bottom of the case.
If the pressure in the line reaches an indicator below 560 kN / sq.m, the air mass enters the atmosphere. At the same time, the plungers release the inlet valves, the compressor begins to pump air into the system.
System management
The hydraulic pneumatic actuator is equipped with a crane for control. It allows you to adjust the supply of compressed air to the working chambers. Also, with its help, stable braking force and quick release are provided.
The body of this part is fixed on the frame. The diaphragm is made of rubberized fabric material, placed between the lid and the skeleton. In its center there is an exhaust valve seat resting on a glass of a control spring. The working cavity communicates with the atmosphere through the inlet window and valve. The return spring acts stably on the diaphragm and inlet valve. The saddle of the last element is clamped in the cover with a fitting. Due to the pressing of the valve, air from the cylinders does not enter the brake chambers.
Pneumatic drive operation
The two shoulders lever aggregates with the brake pedal, while resting on the glass. After depressing the pedal, the rod placed inside the corrugated protective cover turns the lever. The cup with the spring moves to the right, the diaphragm bends, after which the exhaust valve closes, and its inlet analog opens. The diaphragm with a spring mechanism and valves forms a follow-up unit. It has three positions.
In the first position, the brake pedal is released, both valves become 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 force is transformed on the lever, glass and diaphragm. The seat closes the valve, disconnecting the connection to the atmosphere. The opening of the valve is further 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. The diaphragm bends under the air, and the spring contracts. After balancing the acting forces, the diaphragm becomes in the second position, both valves are closed, providing constant braking force.
Features
Pneumatic brake drive receives an additional amount of air when pressing the pedal more. This leads to an increase in pressure in the working compartments. During disinhibition, the processes proceed in a proportional to the reverse order. The compressed air mixture exits through the valve. The idle mode is regulated by means of a special bolt.
To operate the pneumatic valve drive, a combined type crane is mounted on 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 is for the tractor. The right sections of the compartments are identical; a stem placed in a mechanism with a sleeve and a spring abuts against the seat of the exhaust valve. On the axis of the rod there is a lever aggregating with a small analogue.
pros
The use of the device in question is due to a number of advantages, namely:
- The pneumatic drive makes it possible to create significant downforce on the pads with little impact on the control pedals.
- Availability, safety and ease of use in ordinary air.
- The possibility of accumulating a significant amount of potential air energy in special tanks, which allows for long-term and effective braking even when the compressor fails.
- Minor air leaks are allowed, which are partially offset by a supply of compressed air.
- Simplicity and convenience of connecting and conductive parts.
- High efficiency.
- The possibility of using the design for the operation of various additional automotive equipment.
disadvantages
Now consider the cons of the device:
- Relatively slow response due to compressible air.
- Repair of a pneumatic actuator requires full or partial replacement of components.
- The complexity of the design and the high cost of multi-circuit modification.
- Large weight and dimensions compared to the hydraulic counterpart.
- Significant power consumption for a compressor drive.
- Possibility of unit breakdown during condensate freezing in winter.
The pneumatic brake actuator provides high force, while it contains a lot of elements. For example, at KamAZ this part includes about 25 devices, 6 receivers, about 70 meters of pipelines.
Finally
The design of a single-circuit pneumatic drive is simple. However, modern standards of traffic safety do not accept its operation due to low reliability. Multi-circuit analogs are installed on cars, which are equipped with several autonomous drives. The modern system provides two mandatory minimum circuits, as well as up to six circuits of other systems.
In addition, the design of the unit includes a mass 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, an integrated hydropneumatic brake drive is often used. In it, to give the necessary effort, compressed air is used, and transmission to the mechanism is carried out by means of a working fluid. Such a system increases the speed of operation of the structure, but significantly complicates it.