Master cylinder
The main brake cylinder is referred to in the hydraulic brake system of the pressurizing cylinder. He is, for example, in a car from the brake pedal via a plunger. Inside the car, a so-called tandem master cylinder is installed. This is due to its two pressure chambers, the separation of two independent brake circuits forth, as it is required by law.
Construction
The master cylinder consists of the following components:
Pressure piston
The pressure piston is moved by the piston rod in the cylinder. Thereon the primary and secondary cup attached. In addition, he has behind the primary seal over caster holes.
Primary cup
It is the build up pressure cuff. It also allows the additional -flow of fluid in so-called pumping brake.
Secondary cup
It usually is a cup seal, which has the task to seal the piston chamber to the outside.
Refill
It ensures the supply of brake fluid. He sits on top of the cylinder. The container threads always have a ventilation hole. This hole must always be open. To prevent dirt from entering the brake system, this hole is kept small. The settling on the Behälterverschraubung layer of dirt must be removed during inspection or during refilling brake fluid by cleaning with alcohol. The vent hole must be closed when washing the engine.
Compensation and supply bore
You make the connection between refill and cylinder interior. The smaller balance hole used to compensate for temperature-induced volume changes in the brake lines and the rapid degradation of the brake pressure. The far greater supply bore allows tracking with the so-called brake fluid pumps.
Filling disk
The filling disk sits between primary cup and filling holes in the pressure piston. It prevents the sleeve is urged by the braking pressure by the filling holes. This would lead to brake failure, since no pressure can be built.
Bottom valve
The bottom valve was previously the task of a low residual pressure to keep (about 0.4 to 1.7 bar) in the brake line to mechanical games, especially on the drum brake, balance and cavitation ( gas formation by rapid pressure reduction, which leads to corrosion) prevent. It was attached to the brake master cylinder and installed in vehicles with wheel brake cylinder cup seals on the drum brake. Nowadays form valves are used instead of bottom valves. They are bolted to the main brake cylinder in the brake circuit for the drum brake. The form also serves to provide a better seal of the cuffs in the wheel used. There are also drum brakes that have no form, there take on so-called " lip spreader " the seal.
The special base valve is fitted with disc brakes, so the brake fluid pressure bar with a time delay degrades at a residual pressure of about 2, which prevents cavitation. However, the full pressure reduction is possible and meaningful through the throttle bore in the valve, as the brake lining otherwise bear unnecessary and would lead to high wear.
Function
The brake pedal operated by the driver, the push rod transmitting the pedal force on the pressure piston. This is shifted toward brake line. The primary cup runs over the compensating hole. Characterized the pressure chamber is closed and there may be a brake pressure can be generated. The brake pedal is released, pushes the brake pressure - supported by a spring - the pressure piston in its initial position. The primary cuff folds forwards and allows the brake fluid coast to a halt over the filling holes of the pressure piston. If, immediately the brake pedal is depressed ( the brake pump ), a larger amount of liquid is present that can be moved. A higher brake pressure so it is generated.
In tandem master brake cylinder two individual pressure piston mounted in tandem. The primary piston is actuated by the plunger. By the pressure generated by it, the secondary piston or floating piston is actuated, and also creates a pressure in the second brake circuit. In case of failure of one of the two brake circuits is still the other brake circuit function, makes the failure of a circle by an extended pedal travel mechanically noticeable.
The use of the tandem master cylinders also makes it possible to create different pressures in the two brake circuits. This is done by varying the diameter of the two pistons. This master cylinder is then called a graded or stepped master cylinder.
Special for vehicles with anti -lock braking system
Vehicles with ABS have special requirements to the master brake cylinder. Since the pressure in the brake line at an ABS braking can vary greatly, the plunger is brought into vibration, which makes on the brake pedal by strong pulsation felt. However, this leads to that the primary cup is often moved on the vent hole. The resulting vibrations this a greatly increased load is suspended and is under risk to leak early. Therefore, in vehicles with ABS, a so-called central valve is installed. This replaces the balance hole, filling disk and filling holes completely. In this case, a movable pin in the center of the pressure piston is mounted, which closes, upon actuation of the piston and is pushed until it reaches its end position by a mechanical stop again.