What is the pressure in the brake system of the car?
What is the pressure in the hydraulic brakes of passenger cars?
Initially, it makes sense to understand such concepts as the pressure in the hydraulic system and the pressure exerted by calipers or cylinder rods directly on the brake pads.
The pressure in the hydraulic system of the car itself in all its sections is approximately the same and at its peak in the most modern cars is about 180 bar (if you count in atmospheres, then this is approximately 177 atm). In sports or civilian charged cars, this pressure can reach up to 200 bar.
Of course, it is impossible to directly create such pressure only by the effort of the muscular strength of a person. Therefore, there are two reinforcing factors in the braking system of a car.
- Pedal lever. Due to the lever, which is provided by the design of the pedal assembly, the pressure on the pedal initially applied by the driver increases by 4-8 times, depending on the brand of car.
- vacuum booster. This assembly also increases the pressure on the brake master cylinder by approximately 2 times. Although different designs of this unit provide for a rather large difference in additional force in the system.
In fact, the working pressure in the brake system during normal operation of a car rarely exceeds 100 atmospheres. And only during emergency braking, a well-developed person is able to press the foot on the pedal to create pressure in the system above 100 atmospheres, but this happens only in exceptional cases.
The pressure of the caliper piston or working cylinders on the pads is different from the hydraulic pressure in the brake system. Here the principle is similar to the principle of operation of a manual hydraulic press, where a small section pump cylinder pumps liquid into a cylinder of a much larger section. The force increase is calculated as the ratio of the cylinder diameters. If you pay attention to the brake caliper piston of a passenger car, it will be several times larger in diameter than the piston of the brake master cylinder. Therefore, the pressure on the pads themselves will increase due to the difference in cylinder diameters.
Air brake pressure
The principle of operation of the pneumatic system is somewhat different from the hydraulic system. First, the pressure on the pads is created by air pressure, not fluid pressure. Secondly, the driver does not create pressure with the muscular strength of the leg. The air in the receiver is pumped by the compressor, which receives energy from the engine. And the driver, by pressing the brake pedal, only opens the valve, which distributes air flows along the highways.
The distribution valve in the pneumatic system controls the pressure that is sent to the brake chambers. Due to this, the pressing force of the pads to the drums is regulated.
The maximum pressure in the lines of the pneumatic system usually does not exceed 10-12 atmospheres. This is the pressure for which the receiver is designed. However, the pressing force of the pads to the drums is much higher. Strengthening occurs in membrane (less often - piston) pneumatic chambers, which put pressure on the pads.
The pneumatic brake system on a passenger car is rare. Pneumatics are beginning to appear en masse on utility vehicles or small trucks. Sometimes pneumatic brakes duplicate hydraulic ones, that is, the system has two separate circuits, which complicates the design, but increases the reliability of the brakes.
