What is Master Cylinder and How It Works?

Introduction

Great things are done by a series of small things brought together” very rightly said as when it comes to automobiles even a small components like sprockets, valves, piston rings etc. Have great impact on overall working of an automobile vehicle. We often talk about the components and forces that help the vehicle to speed up or to perform. But have you ever think about the amount of force required to stop the vehicle at such a high speed?.Now this question gives rise to many other questions like from where does this high force generated? , which component is responsible for this high stopping force? So let’s just discuss about the component responsible for generating this high brake force i.e. Master cylinder.

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 calliper for braking.

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.

Why We Need a Master Cylinder

As we all know now that a master cylinder in hydraulic braking system is an intermediate component that worked as an energy converter as well as force multiplier i.e. mechanical energy into hydraulic pressure so we need master cylinder in hydraulic braking system because-

• When we talk about today’s automobile vehicles due to their high speed, the brake force required (to stop or de-accelerate vehicle efficiently) is also high, which cannot be efficiently fulfilled by mechanical braking, so hydraulic braking with master cylinder is the new need of today’s vehicle as it generates higher brake force.
• As we all know that the brake force required in front wheels is higher than that of real wheels due to the shifting of mass from rear to front during braking, this distribution of brake force between rear and front wheels is a function of master cylinder.
• In hydraulic braking, the force applied by driver on brake pedal (in car) or brake lever (in bikes) during braking (50N-70N) is not enough to cause actual braking, so an intermediate component i.e. master cylinder is required that can multiply this force and further transfer this high force to the brake caliper which in turn generates high brake force and finally actual braking happens.
• In hydraulic braking the brake pedal or lever effort required for braking is drastically decreased due to the use of master cylinder as it acts as a converter that can convert the mechanical force applied by driver on brake pedal or lever into the high hydraulic pressure.
• The use of master cylinder decreases the chances of brake failure as it provides the constructional flexibility in which the braking in front and rear tyre can be made independent of each other.

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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

• It is the simple type of master cylinder just like a medical syringe, in this type of master cylinder single piston inside a cylinder is used to cause braking.
• 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

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

Single Circuit Master Cylinder

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.

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Tandem Master Cylinder

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 m c 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

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.

For better explanation watch the video given below:

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.