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Examples of Cam and Follower Systems in Use

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The purpose of this section is to try and shine some light on where cam and follower systems are used.  It also tries to show how dynamic, complex and exciting these uses are.  To do this we will examine what is probably the most frequently used cam and follower system which is the cam and follower system in an engine, known to us as the cams and camshaft of an engine.  This section concentrates mainly on cam and follower systems in relation to how they are used in engines.

The section is laid out in the following parts:

  1. firstly we will discuss the function of cam and follower systems in an internal combustion engines
  2. then we will consider the mechanisms that the cam and follower system interact with inside the internal combustion engine and
  3. finally we will try to look at the how the cam and follower system interact with these other mechanisms.

 

The function of Cam and follower Systems in Engines

Part 1

 

Camshaft of an Engine

The use of cam and follower systems are vital in engines, where they are used to open and close the inlet valve and the exhaust valve to the cylinder head.  The diagram shown opposite shows us a typical camshaft that could be found in a lawnmower engine.  The cam and follower system is a plate cam and flat follower system, and of course the function of the system is to open and close the valves at the correct time during the four stroke cycle of the engine (this will be dealt with in more depth later).  If you examine the image close you will see that the peaks of the cams are offset by approximately 120 degrees. These ensures that the both valves aren't fully open at the same time.

Camshaft with Plate Cams imparting on a Flat Followers and Valves

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Another variation of a cam and follower system that could be used to open and close the inlet and exhaust valves in an engine

Camshaft of an Engine incorporating a Rocker Arm

The diagram shown below is another typical cam and follower system that could be used in an engine.  This system incorporates a rocker arm (shown in blue in the image).  In this case the motion the cam imparts on the follower is translated to the valve through a push rod amd the rocker arm.

Camshaft with Plate Cam imparting on a Flat Follower, a Push Rod, a Rocker arm and the Valve.

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Animation of the cam and follower
Animation of the cam and follower from the mechanism shown above

 

What mechanism does the cam and follower system of an engine interaect with inside the engine

Part 2

 

The other mechanism that the cam and follower system interact with in an engine is the actual mechanism that produces the power, i.e. the crankshaft, connection rod and piston mechanism.  The cam and follower system in an engine is an integral part of the production of power by the engine

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How the cam and follower system interacts with this mechanism

Part 3

In doing this we will

  1. take a brief look at what the history of the combustion engine and the four stroke cycle.
  2. examine what the cam and follower system is required to do.
  3. look at an example of a cam and follower system at work within an internal combustion engine.  

 

History of the Combustion Engine and the Four Stroke Cycle

The First Commercial Internal Combustion Engine:

A person by the name of Etienne Lenoir, in 1860, was the first person to make a successful comercial internal combustion engine.  This engine ran on coal gas.   However it worked on a cycle that didn't involve compression of the gas before ignition and therefore lacked any great efficiency. 

 

The Four Stroke Engine

The four strokes of the four stroke cycle are:

The Induction Stroke

       Starting with the induction stroke and the piston at top dead centre, t.d.c., as the crankshaft rotates the piston travels down the cylinder.  The camshaft has at this stage opened the inlet valve so as the piston travels down the cylinder, the cylinder fills with a mixture of petrol vapour and air.

 The Compression Stroke

       As the crankshaft rotates the piston passes bottom dead centre, b.d.c., and starts to travel up the cylinder, beginning the compression stroke.   The rotation of the cam shaft will have closed the inlet valve at this stage so that as the piston moves up the cylinder the gaseous mixture that filled the cylinder during the induction stroke will be compressed.

Top Dead Centre and Bottom Dead Centre

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The Power Stroke 

        At the end of the compression stroke the compressed gaseous mixtrue is ignited by a timed spark that jumps across a gap on a spark plug.  This ignites the gaseous mixture and thus increasing the temperature and pressure above the piston head.  As a result the piston is driven down the cylinder.   This is known as the power stroke

The Exhaust Stroke

   The final stroke is the exhaust stroke as as the name suggests this is the stroke where the burnt gases are expelled.  Again the camshaft will have timed the opening of the exhaust stroke for this stage and as the piston moves up the cylinder once again the burnt gases are expelled through the open exhaust valve.   Then the exhaust valve closes and the cycle begins again.

 

What is required of the Cam and Follower System in the Internal Combustion Engine

In the internal combustion system the cam and follower system are required to control the opening and the closing of the inlet and exhaust valve.  This implies that that the followers must open the valves they are connected to once in the four stroke cycle.  For instance the follower in contact with the inlet valve opens the inlet valve for the induction stroke and closes it for the other three strokes.  The follower for the exhaust valve must open the exhaust valve for the exhaust stroke and close it for the other three strokes. 

 

Example of a Cam and Follower System at work within an Internal Combustion Engine

How the cam and follower system in an internal combustion engine work is shown in the animation of the four stroke cycle below.

Animation of the Four Stroke Cycle

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Another Common Use of a Cam and Follower System

Another common use of a Cam and Follower system is within a pump, such as an oil pump.  In such pumps the cam and follower system is used to suck oil in through one non-return valve and push it out through on other non-return valve.  The suck action is achieved by the system because the follower is cylindrically shaped and moves within a tight fitting cylinder so oil is sucked in and pushed out as the follower moves up and down.  This is similar to the gaseous mixtures being sucked into and forced out of  the engine cylinder as the piston moved up and down in the previous example.

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