How Automobiles Work?

In Brief:

The majority of western modern society holds a special place in their collective heart for the automobile, and regards them as indispensable to life itself. This of course is an over-glorification, but an understandable one when you think about the many benefits that they can bring to us on a daily basis.

And so, whenever they are criticized for pollution reasons, people from all walks of life leap to their defense with a gusto that few other topics could rouse.

Safety campaigners get a more sympathetic ear, as almost all owners and drivers worry about this as well (whether they admit it or not) but when it comes to criticizing that driving force of modern living - the internal combustion engine, then those daring to raise the possibility of ‘alternatives’ are often either insulted or ignored.

In time this may change as other technologies improve, but for now an assault on the automobile is seen as an assault on freedom, and anyway, pollution from cars is slowly being controlled.

So, dismissing this to the back of the mind is a common behavior, and the car is King.

As long as it works.

Mechanically Speaking

Then we find a paradox. Mechanics, who keep cars on the road when they need mending after all, are often viewed more as villains out to trick the honest owner, rather than heroes who come to the rescue.

They take too long to do anything, and overcharge for what they do. This seems to be the usual response from most citizens, and often borne by experience (or at least by perception anyways).

Some auto shops are indeed the dens of iniquity, but to tar all with the same brush is very unfair, as automobiles are complex things indeed. So let’s just have a simple overview of how things work, rather than try to wade through all the nuances and subsections that would be involved in a really close and detailed look at the workings of an automobile.

All about Strokes

The internal combustion engine itself is of course the main center of action, this is where all the power comes from needed to drive the wheels and allow for the mobile part of automobile.

There are different types of these engines, but since almost all cars have a piston engine design, then that is what we shall consider.

These pistons are forced up and down inside tubes known as cylinders in a cycle that is made up of four strokes (a stroke being a movement, either up or down, of a piston) and each piston has a connecting rod that leads to what is known as a crankshaft.

At the top of each cylinder (it is common to have four, six or eight, sometimes more). And how they are arranged can describe an engine type - either inline or straight, with the cylinders in a row: a flat, or horizontally opposed, or boxer where they are in opposite pairs: and v where they are configured in a v angle) are two valves known as the intake valve and the exhaust valve, as well as an opening for a spark plug (which provides the voltage to light things up) between them. The inlet valve is where the mixture of gasoline and air enters, and after combustion the exhaust valves allows the burnt fuel out again.

Suck

The intake stroke is first; this the where the piston starts off at TDC (Top Dead Center) and begins to descend, as it does this the intake valve is opened by the valve train. This is controlled by the camshaft and timed so that the valves and pistons move in unison. Nowadays this is simpler as the camshaft is sited above the valves (overhead cams) but the linkage used to time the valve openings on older engines is longer as the camshaft is positioned beneath near the sump (oil-pan).

When the intake valve is open the fuel enters; in old style carburetors the gasoline and air is mixed as they enter the cylinder. Fuel injection allows for better control and timing of this process, and there are two basic types; port fuel injection, where the mix is sent to above the intake valve; and direct fuel injection, where it is pressed directly through.

As the piston falls, more fuel enters, either sucked in by air pressure or injected, until the cylinder is full (how much will depend on its cubic capacity, or cc) and this is the end of the first of the four stroke cycle.

Squeeze

Now the intake valve will close, and the compression stroke begins as the piston starts to rise on its return to TDC, compressing the air/ fuel mix tightly into a small space just beneath the spark plug, from where a small surge of voltage ignites the mix and causes an explosive combustion.

Bang

This is the power stroke, where a sudden blast of heat and pressure pushes the piston down again with a mighty force, and as the piston reaches BDC (Bottom Dead Center) then the exhaust valve is opened by the camshaft.

Blow

The exhaust stroke is the fourth in order, and here the pressure is released and the burnt fuel sent off the to the exhaust system ( to where a catalytic converter can remove a lot of the pollutants) enabling the piston to rise once more to lower again in the next intake stroke, so completing the four stroke cycle.

Too Much of a Good Thing

All this generates considerable heat (which is essential of course) but too much of this causes problems, so engines must be cooled. The coolant usually consists of a blend of water and antifreeze, that is pumped around the engine by a camshaft or crankshaft powered pump to absorb the excess heat and remove it from the immediate vicinity.

It takes this thermal energy to the radiator, where the rush of through air disperses it to the outside environment, and cools the water so that it can return and collect more heat from the pistons.

Timing the Cycle

So with internal combustion engines (as with much else in life) timing is everything, things must work in harmony to maximize effectiveness, and listening to a healthily revving engine is music indeed to a mechanic’s ear.

Though it isn’t only the pistons and valves that need to be timed, the spark plugs follow a plan as well, and demand the voltage necessary for their sparking in only the correct strict operating order, which is controlled by the distributor.

Lighting the Spark

But where does all this energy come from to start things off if it’s a cycle? That’s where the electric starter system is so valuable. This power comes from the battery, which is needed for all electrical components in the car and draws the necessary voltage from the chemical reaction of its positive and negative plates, and the electrolyte solution (the mix of water and sulfuric acid that it contains).

This powers a starter solenoid which causes the engine just to give a few revolutions of its relevant parts so that the combustion cycle can begin. This takes quite a bit of energy, because as well as friction the starter has to overcome the pressure of any pistons which were in compression stroke when the engine was turned off, as well as the power to turn the camshaft and get those valves going.

All this saves having to use a hand crank for example; the rapid turning of these from a heavily breathing motorist was a common sight in the dawn of automobiles, so without electric power (which is seen now again as a deadly rival for gasoline) the whole caboodle would be a lot more troublesome.

Luckily though, the battery is recharged in a short time from the alternator once the engine has started, so nowadays should not get flat (unless you leave your lights on, the battery is used for more than just the starter remember).

Lubrication, Rings and Rods

So that’s the basic thing going, but an engine just can’t turn the wheels that easily; to allow for this, each piston has rings and a connecting rod that leads to the aforementioned crankshaft. Every rod is moveable at both ends and have shell bearings at the small-end (where they are attached to the piston, by way of a pin) and at the big-end (where they join the crankshaft) which are lubricated by pressurized oil that is forced between them and the moving parts they attach to for the reduction of wear through friction. This relative freedom of movement is to allow for the change of angle as the pistons move up and down, so that the energy can be transferred without interruption to the crankshaft, which is where engine torque is to be found.

Torque is a twisting force, and this is what the crankshaft is for; converting the energy delivered to it from the pistons into a rotating motion to get the wheels going. So this crankshaft is at the very heart of the whole system, and as such, needs to be well lubricated. For this purpose, the sump (oil-pan) is right at the bottom of the engine and surrounds the twisting crankshaft, and oil is also pumped around through oil lines to the crankshaft bearings and crankpins, and everywhere else that it is needed, like the camshaft and of course, the pistons themselves.

Flywheel Fly

So the crankshaft creates the rotary motion for movement, and to help it has an assistant called a flywheel which is a revolving weight. This is because the pistons send their energy (properly called reciprocating motion) in surges akin to a pulse in some ways, and so that this does not cause a lot of vibration at the crankshaft, the flywheel is utilized to provide an inertia of its own that counteracts these surges and leads to a more even transition of all that energy.

More Power

So the faster the crankshaft turns, the faster the car can go. And some like to have it go as fast as it can.

Lighter engines help of course, with new materials being just as strong without all the weight, but usually what it comes down to is displacement. This is a measure of how much air can be forced into a cylinder and ways to increase this involve the use of a turbocharger or supercharger.

The former boosts performance by pressurizing air to the cylinders by the use of a turbine which cleverly is powered by exhaust gases. This is simpler and more popular than a supercharger which is attached directly to the engine, more mechanically complicated, and often powered by a belt. Both of these increases the air flow to the cylinders and many cool this before it enters as well, so that its potential expansion rate is further increased.

Moving On

But whatever speed the automobile is traveling at, there now needs some fresh characters to be introduced upon the scene.

Next is the transmission, or gearing, and this quite literally, transmits the power onwards towards the wheels. In essence it allows for the wheels to turn at different speeds from the engine, which is of vital importance to actually getting anywhere (like uphill, just for starters).

Coming in two varieties, either automatic or manual, the energy is directed from the crankshaft to the clutch, through the transmission and on through the driveshaft and universal joints to the differential (which is important as it allows opposing wheels to turn at diverse speeds when cornering), then onto the axles which the wheels are mounted on.

High or Low Gear?

Automatic transmissions, which are more popular within North America than much of the rest of the world, have different ways of working. One way is called planetary gearing (or epicyclical gearing), and involves smaller toothed gear wheels (the planets) rotating around a larger toothed wheel (the sun), sometimes with other outer wheels which mesh with the planet gears. These planet gears are adaptable and can sometimes work on a holding arm which itself is movable. But whatever the configuration, they work through gear ratios (the relationship of the various sized gear wheels to one another) with one component either reducing or increasing the outgoing energy (to the driveshaft that turns the axles) that arrives from the crankshaft and flywheel in the engine.

The latest automatic torque-converter transmissions are getting more and more computerized, with hydraulic power from pressurized oil pumps, altering speeds of a device that connects with the driveshaft. This being better controlled to adapt faster to requirements than the older spring loaded system is for changing ratios by shifting the gear wheel patterns.

Controlling Power

So that’s basically it, apart from the brakes and steering!

The direction of the automobile is controlled by the steering wheel, which has a tube inside the steering column (on which the wheel sits). This goes down to where it meets a steering gear that guides the wheels and makes it possible to turn the car without the driver wrenching their arms, and hydraulic assisted or power steering makes thing easier still.

How Do I Stop?

An important question at any time was whether to make this so brakes come with discs or drums. Disc brakes have pads on a vise-like caliper which straddles and close on and grip a disc that is securely attached to the car wheels. While drum brakes involve curved shoes pressing hard against a metal drum that is similarly fixed to each wheel, and friction does the rest.

ABS (Antilock Braking System) is an electronic system that makes sudden braking safer by altering hydraulic pressure in brake lines that control such devices as above, to prevent wheels locking and the automobile spinning or skidding sideways.