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Master Cylinder | Types , Working Principles and Applications

“Great things are done by a series of small things brought together”

Master cylinder in an automobile braking system is a hydraulic device in which cylinder and one or two pistons are arranged in such a manner that the mechanical force applied by the driver of a vehicle either by brake pedal (in cars) or by brake lever (in bikes) is converted into hydraulic pressure which in turn transferred to the brake caliper for braking.

Hydraulic systems are comprised of three basic parts: a master cylinder (piston) that pushes fluid through the lines, the lines that carry the fluid and a slave cylinder that moves when fluid pressure pushes upon it. Modern “tandem” master cylinders utilize a pair of pistons in the same tube that control two different fluid circuits for redundancy that no single-piston design can offer.

In hydraulic braking system, master cylinder is a device that provides required amount of pressure or braking force to the final braking components after multiplication of the mechanical force applied by the driver through brake pedal or brake lever.

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TYPES OF MASTER CYLINDER

On the basis of its construction and application brake master cylinders are of 2 types that are-

1. SINGLE CIRCUIT MASTER CYLINDER

The brake pedal lever pushes the plunger (piston) inside the cylinder, which shoves fluid through the lines and into the slave cylinders. When the brake pedal is released, a spring inside of the cylinder pushes the plunger back to its original position. Negative pressure pulls the brake fluid into the cylinder from the lines and from the brake fluid reservoir.

Single circuit m c (master cylinder) distributes equal force in all the wheels due to the use of single cylinder single piston or circuit.

This type of master cylinder is commonly used in many 2 wheelers and some light weight 4 wheelers

Construction

It consist of 5 parts :-

1. Reservoir

It is the storage tank used for storing the brake fluid in hydraulic type of braking system, usually it is made up of plastic.

2. Cylinder

It is the air tight housing inside which the piston moves with the moment of brake pedal which in turn causes conversion and multiplication of force. Cylinder is usually made up of cast iron or aluminium.

It is connected with the reservoir through inlet valve and also with brake lines through outlet valve.
In single circuit m c there is only 1 compression chamber.

3. Piston

It is the reciprocating part of the master cylinder that reciprocates inside the cylinder due to the movement of brake pedal, the piston causes compression of brake fluid inside the cylinder which in turn generates high hydraulic pressure.
In single circuit only 1 piston is used.

4. Returning Spring

It is the simple coil type of spring used inside the cylinder which helps the piston and brake pedal to retain its original position after brake pedal is released.

5. Valve

In single circuit m c it is the outlet valve through which the brake line is attached, the compressed brake fluid is further transferred to the caliper through this valve.

2. TANDEM MASTER CYLINDER OR DUAL CIRCUIT MASTER CYLINDER

It is the modified type of m c in which dual cylinder-dual piston or single cylinder dual piston along with dual circuit is used for independent braking between front and rear wheels.
This type of master cylinder is used in almost all cars as it is more efficient than single circuit m c.
It provides the independency between front and rear wheels braking or diagonal type of braking which is the important safety feature for a vehicle.

Construction

1. Reservoir

In tandem master cylinder instead of single reservoir 2 or dual chamber reservoir is used as a storage tank for brake fluid.

2. Cylinder

Same cylinder as in single circuit type is used with the little modification i.e. it is the housing of 2 pistons and also there are 2 outlet and 2 inlet valves.
In tandem master cylinder there are 2 compression chamber inside the cylinder.

3. Piston

Instead of one piston, 2 pistons that are primary piston and secondary piston are used in tandem m c, the actuation of secondary piston occurs after completion of the primary piston movement.
Primary piston is connected to the brake pedal and secondary piston is placed just behind the returning spring of primary piston.

4. Returning Spring

In tandem m c 2 returning springs are used one with the primary piston and second with the secondary piston.

5. Valves

In tandem master cylinder as it is the dual circuit m c , 2 inlet and 2 outlet valves are used .

WORKING PRINCIPLES

Single Circuit Master Cylinder

In single circuit master cylinder when brake pedal is not pressed i.e. non actuation position the piston remains at its original position which in turn closes the inlet valve of the reservoir due to which there is no incoming of brake fluid takes place between reservoir to compression chamber.
When brake pedal is pressed i.e. actuated position, the piston which is connected to the brake pedal through connecting rod moves which in turn opens the inlet valve due to which incoming of brake fluid from reservoir to compression chamber takes place.
This brake fluid inside the compression chamber is compressed due to the movement of piston inside the cylinder just like the medical syringe.
After compression up to a certain pressure the outlet valve opens and this highly compressed brake fluid is further transferred to the brake lines for further brake actuation.

Tandem Master Cylinder

The working of tandem master cylinder is 70% same as the single circuit m c but in this type 2 independent circuits of braking is used let see how its work-
When brake pedal is not actuated, the piston remains at their original place, closing the inlet valve of both the compression chambers, which in turn cuts the incoming of brake fluid between both the reservoir or both the reservoir chambers.
When the brake pedal is actuated, at first the primary piston moves due to which opening of primary inlet valve takes place.
Initially due to the movement of primary piston compression of the brake fluid inside primary chamber takes place.
After completion of the compression in primary chamber primary outlet valve opens up and this compressed brake fluid is further sent to brake callipers through brake lines and actuation of the primary circuit brakes take place.
After the completion of the primary piston movement i.e. at its extreme end, the secondary piston starts moving because of the force applied by the primary piston’s spring which in turn opens the secondary valve and incoming of brake fluid from secondary reservoir to secondary compression chamber takes place.
This brake fluid is then compressed and after complete compression secondary outlet opens up and this highly compressed fluid is sent to the brake callipers through brake lines and actuation of the secondary circuit brakes take place.

APPLICATION

Single Circuit Master Cylinder

It is mainly used in 2 wheelers like Bajaj pulsar, TVS apache etc.
Many light weight vehicles like e-rikshaws are also using this type of master cylinder.

Tandem Master Cylinder

It is widely used in almost all the cars equipped with hydraulic braking system.
Using tandem master c in vehicle equipped with hydraulic braking system is made compulsory by governments of many countries because of its safety to brake failure.

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