The Motor Car Expalined

The Motor Car – The Mechanicals Explained

The following explanation of the motor car mechanicals is intended as a very rudimentary guide to understanding what is happening when the driver operates the various vehicle control gadgets found in the typical motorcar. It is aimed at those with no sensible understanding of the motorcar mechanicals.

First up, we all know that every car has an engine, often referred to as the motor – its power plant. The primary purpose of the motor is to generate sufficient usable mechanical energy. The motor is like a big powerful pump that sucks in a mixture of air and fuel where, under extreme pressure, it ignites and causes the internal components to move rapidly. The waste material from this explosion we call the ‘exhaust’. All these moving internal engine components are inter-connected in various ways. But there is a central, internal component to which all these mechanical moving parts are linked: the crankshaft. The crankshaft is located at the bottom of the motor and is what transmits the engine’s power to the gearbox.

The gearbox is a physical box made of steel. It has a series of connecting gears or cogs of different ratios. In a manual car, the driver selects which gear ratio he or she thinks best suits the situation. In an automatic, the selection is made by various components independent of the driver – hence the term ‘automatic’. So how do these gears work? One gear is the ‘driving’ gear – the one which transmits the power; the other is the ‘driven’ gear – the one having the power being transmitted to. The smaller the ‘driving’ gear (the ‘input’ gear) compared to the connected ‘driven’ gear (the ‘output’ gear) the more power from the motor can we transmit to the wheels. As always there’s a trade-off: in this case we sacrifice speed for power. As we ascend through the gears, say from 1st to 2^nd and then 3^rd and 4^th and even 5^th gears, we are changing the ratios at which, that particular set of gears operate. By changing the ratios, we inherently permit the car to go faster and faster (assuming no resistance elsewhere like hills, rough roads, weather conditions, etc). As we gain speed though, we once again come to realise that we don’t have the power to sustain the momentum like we had at the lower gears when resistance is introduced. We cannot have total speed and total power: no, it’s a balance between the two that we, the driver, determine (in a manual) as we see fit. The art of driving a manual car is, in part, the art of selecting the appropriate gearing by jockeying the gear lever properly.

For a manual car driver, there is another vital component we must come to understand: the clutch. We know that the power of the motor is transmitted to the gearbox through a central type shaft. When all is connected, motor and gearbox all want to turn and these in turn want to turn the car’s wheels! Sometimes we want to stop the car from moving, yet keep the motor running – say at traffic lights. How do we achieve this? We do so by the ingenious device we call the clutch. It is what connects and disconnects the transmission of power from motor to gearbox. There is in a manual car that extra pedal on the left. This is the pedal that operates the clutch: depress the pedal and you disengage the clutch (break the transmission of power between motor and gearbox). Release the clutch pedal (by raising your left foot) and once again the transmission of power is resumed, allowing the vehicle to progress. The easiest way to visualise the clutch is to imagine two large plates or discs mounted so as to face each other. One plate is connected to the motor, the other to the gearbox. With the motor running, the motor’s plate spins at speed. With the clutch pedal pushed down, the two plates are separated by a fine gap – no connection occurs: thus allowing motor to run, but not transmit power to the gearbox. Releasing the clutch moves these plates closer and closer to the point where they touch and friction occurs. The running motor slows as it begins to bear the weight of the car. The car starts to move forwards, albeit slowly and perhaps tentatively. Fully releasing the clutch pedal, forces the two plates together under extreme pressure: now connecting the path of power transmission completely. With the addition of the accelerator pedal, the car motors forwards.

In a conventional car (engine in front with rear wheels driving), power from the gearbox is transmitted through a drive shaft (commonly called a tail shaft or propeller shaft) – this is simply a strong piece of tubular piping whose sole purpose is to rotate at speed and transmit power to the remaining component in the power transmission path from engine to wheels: the differential (the ‘diff’). The purpose of the diff is to allow the two driving wheels to turn around a corner without damaging the other driveline components of the car. The fact that each driving wheel, when cornering, travels at a different speed due to the different arc or radius of the turn – the outer wheel travels further in the same amount of time, therefore faster. The diff accommodates this geometrical quirkiness! The driver has no control over the operation of the diff.

Steering. Typically the front wheels turn as you rotate the car’s steering wheel clockwise or anti-clockwise. Turn the steering wheel clockwise and the car’s front wheels will turn to the right … and obviously enough, the opposite when turned the other way. The steering wheel is connected to a long shaft which extends all the way down to the steering box, located at the bottom front of the car. A series of strategically placed steel rods which can move laterally enable the wheels themselves to be turned left or right.

It is one thing to go in a car, but equally important, arguably more important, is being able to stop at will! Your brakes do this job. In a manual car it is the centre pedal that operates the footbrakes – in an automatic, it is the left pedal. As you press the pedal down, essentially you are pushing special brake fluid under pressure through a network of pipes so as to activate the brakes themselves. There are four brakes on a car: one on each wheel. Brakes are of two types: ‘drum’ brakes (invariably found on older cars) and ‘disc’ brakes. Each works by expanding or contracting a movable surface onto another fixed surface where the friction is great enough to slow and eventually stop the car. The handbrake is simply a mechanical system of engaging the rear (usually) brakes for the purpose of stabilising the car once already stopped. Drum brakes consist of a drum in which two opposed ‘shoes’ – two semi-circled internal collars – that expand against the sides of the drum edge. Disc brakes have a clamp (‘callipers’) encasing a section of a rotating disc (‘rotor’) that when activated, tightly grip that part of the disc and let’s friction bring the car to a stop. Brakes can become extremely hot – beware!

This is all very well, but first we must get the car started! We place the key into the ignition (the ‘keyhole’). We turn the key. By doing so, we activate the battery which sends a charge of electricity to the starter motor: a powerful electric motor located at the back of the engine. The battery also charges up the fuel pumps. The starter motor turns the motor over quickly and, with the right air/fuel mixture will fire up the motor into mechanical life! It does this by sending a high voltage charge into the heart of the motor where this air/fuel mixture is. The mixture is ignited and through a chain of extra-ordinary events occurring internally, the motor breathes mechanical life to the car, enabling you to take control of that jalopy which will (hopefully) save you much shoe leather!

Look after your mechanicals. They need servicing, yes, your TLC. If you fail this, you will pay dearly!