Why you can unscrew the bleed bolt on the cylinder after several steps of braking to remove the air from the brake system; why when the gap between the brake pad and the brake drum is too large, the first foot brake is soft and low, And the second leg will become hard and high?
When the brake pedal is released, the master cylinder piston returns to its position under the force of the return spring, the oil pressure in the working chamber drops, and the cylinder and pipeline return oil. But if you quickly release the brake pedal, the brake fluid at the rear of the piston will overturn the cup through the compensation hole on the piston and enter the working chamber in front of the piston. Then, when the brake is depressed again, the brake fluid in the working chamber is discharged to the oil circuit and the cylinder again. Such rapid and repeated braking and stepping on the brake, because the brake fluid at the rear of the piston is compensated into the working chamber, so that the working chamber has more oil and less oil return each time. This effect is called the compensation effect of the master cylinder.
In order to improve the safety of the car, the modern vehicle's service brake system uses a dual-circuit brake system. Dual circuit refers to the use of independent dual-chamber brake master cylinders to control the two-axle or three-axle wheel brakes through two independent pipelines. The characteristic is that if one of the pipelines fails and the other brake fails, the other The set of pipelines can still continue to play the role of braking, thereby improving the reliability and driving safety of automobile braking.
The two wheels in the diagonal direction of the front and rear axles share a set of pipelines. When any pipeline fails, the remaining total braking force can be maintained at 50% of the normal value, and the distribution ratio of the braking force of the front and rear axles remains unchanged. Helps to improve braking stability. This type of arrangement is mostly used for cars with engine front and front-wheel drive.
The two chambers of the master cylinder control the front axle and rear axle centrifugal brakes. This arrangement is the simplest and can be used in conjunction with single-wheel cylinder drum brakes. Its disadvantage is that when a set of pipelines fails, the front and rear axle braking forces The assigned ratio is destroyed. This kind of arrangement is mostly used for front-mounted engines and rear-wheel-drive vehicles.
Corresponding to the dual-circuit brake system, the brake master cylinder is commonly used in tandem dual-chamber system. At present, domestic cars and most foreign cars use equal-diameter brake master cylinders, that is, the cylinder bores of the front and rear chambers of the brake master cylinder are the same. The bores of the two chambers are not equal.
The first stage: the thrust from the first piston pushes the first and second piston assemblies forward, and the lips of the main cup close the two compensation holes.
The second stage: continue to push the piston. Because the resistance of the second return spring is less than that of the first return spring, it is compressed first and the second pressure chamber is built first. At this time, the brake fluid in the first pressure chamber is not compressed, so the first chamber has no hydraulic pressure.
The third stage: continue to push the piston, the reaction force generated by the hydraulic pressure from the second pressure chamber to the second piston plus the gradually increasing resistance of the second return spring is greater than the resistance of the first return spring, making the first Once the return spring is compressed, the first cavity also starts to build pressure.
If the brake line connected to the front cavity is damaged and oil is leaking, then when the brake pedal is depressed, hydraulic pressure can be established only in the rear cavity and there is no pressure in the front cavity. At this time, under the action of the hydraulic pressure difference, the front cavity piston quickly moves to the front end of the front cylinder piston and presses against the main cylinder block. After that, the hydraulic pressure in the working chamber of the rear chamber can be raised to the value required for braking.
If the brake line connected to the rear cavity is damaged and oil leaks, then when the brake pedal is depressed, at first, only the rear cavity (first) piston moves forward, and the front cavity (second) piston cannot be pushed, because the rear cylinder No hydraulic pressure can be established in the working chamber. But when the rear-cylinder piston directly touches the front-cylinder piston, the front-cylinder piston moves forward, so that the front-cylinder working chamber establishes the necessary hydraulic pressure and brakes.
When any circuit in the dual-circuit hydraulic brake system fails, the master cylinder can still work, but the required pedal stroke increases, which will cause the braking distance of the car to increase and the braking efficiency to decrease.