during cornering. Tightly sprung cars, such as sports cars (think Mazda Miata), are less forgiving on bumpy roads, but they minimize body motion well, which means they can be driven aggressively, even around corners.
So, while springs by themselves seem like simple devices, designing and implementing them on a car to balance passenger comfort with handling is a complex task. And to make matters more complex, springs alone can't provide a perfectly smooth ride. Why? Because springs are great at absorbing energy, but not so good at dissipating it. Other structures, known as
СDAMPENING STRUCTURE
dampers, are required to do this.
иwill continue to bounce at its natural frequency until all of the energy originally put into it is used up. A suspension built on springs alone would
Unless a dampening structure is present, a car spring will extend and
spring motionбАthrough a process known as dampening. Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated through hydraulic fluid. To understand how this works, it's best to look inside a shock absorber to see its structure and function.
release the energy it absorbs from a bump at an uncontrolled rate. The spring
make for an extremely bouncy ride and, depending on the terrain, an uncontrollable car.
Enter the shock absorber, or snubber, a device that controls unwanted
wheel (i.e., the unsprung weight)Д. In a twin-tube design, one of the most common types of shock absorbers, the upper mount is connected to a piston
A shock absorber is basically an oil pump placed between the frame of
the car and the wheels. The upper mount of the shock connects to the frame
(i.e., the sprung weight), while the lower mount connects to the axle, near the
rod, which in turn is connected to a piston, which in turn sits in a tube filled with hydraulic fluid. The inner tube is known as the pressure tube, and the outer tube is known as the reserve tube. The reserve tube stores excess
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When the car wheel encounters a bump in the road and causes the |
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spring to coil and uncoil, the energy of the spring is transferred to the shock absorber through the upper mount, down through the piston rod and into the piston. Orifices perforate the piston and allow fluid to leak through as the piston moves up and down in the pressure tube. Because the orifices are relatively tiny, only a small amount of fluid, under great pressure, passes through. This slows down the piston, which in turn slows down the spring.
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Shock absorbers work in two cycles – the compression cycle and the extension cycle. The compression cycle occurs as the piston moves downward, compressing the hydraulic fluid in the chamber below the piston. The extension cycle occurs as the piston moves toward the top of the pressure tube, compressing the fluid in the chamber above the piston. A typical car or light truck will have more resistance during its extension cycle than its
Сcompression cycle. With that in mind, the compression cycle controls the motion of the vehicle's unsprang weight, while extension controls the heavier, sprung weight.
All modern shock absorbers are velocity-sensitive – the faster the suspension moves, the more resistance the shock absorber provides. This enables shocks to adjust to road conditions and to control all of the unwanted motions that can occur in a moving vehicle, including bounce, sway, brake
иstrut – basically a shock absorber mounted inside a coil spring. Struts perform two jobs: They provide a dampening function like shock absorbers,
dive and acceleration squat.
can allowбАexcessive vehicle-weight transfer from side to side and front to back. This reduces the tire's ability to grip the road, as well as handling and braking performance.
Common strut design. Another common dampening structure is the
and they provide structural support for the vehicle suspension. That means struts deliver a bit more than shock absorbers, which don't support vehicle weight – they only control the speed at which weight is transferred in a car, not the weight itself.
Because shocks and struts have so much to do with the handling of a
car, they can be considered critical safety features. Worn shocks and struts Д
Anti-sway Bars. Anti-sway bars (also known as anti-roll bars) are used
along with shock absorbers or struts to give a moving automobile additional stability. An anti-sway bar is a metal rod thatИspans the entire axle and effectively joins each side of the suspension together.
When the suspension at one wheel moves up and down, the anti-sway bar transfers movement to the other wheel. This creates a more level ride and reduces vehicle sway. In particular, it combats the roll of a car on its suspension as it corners. For this reason, almost all cars today are fitted with anti-sway bars as standard equipment, although if they're not, kits make it easy to install the bars at any time.
ENGINE
Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.
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You might want to know what's going on simply out of curiosity. Or |
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perhaps you are buying a new car, and you hear things like "3.0 liter V-6" |
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and "dual overhead cams" and "tuned port fuel injection." What does all of |
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that mean? |
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In this article, we'll discuss the basic idea behind an engine and then go |
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into detail about how all the pieces fit together, what can go wrong and how |
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to increase performance. |
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The purpose of a gasoline car engine is to convert gasoline into motion |
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so that your car can move. Currently the easiest way to create motion from |
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gasoline is to burn the gasoline inside an engine. Therefore, a car engine is an |
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internal combustion engine - combustion takes place internally. |
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Two things to note: |
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There are different kinds of internal combustion engines. Diesel |
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engines are one form and gas turbine engines are another. Each has its own |
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advantages and disadvantages. |
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There is such a thing as an external combustion engine. A steam |
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иengine in old-fashioned trains and steam boats is the best example of an |
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external combustion engine. The fuel (coal, wood, oil, whatever) in a steam |
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engine burns outside the engine to create steam, and the steam creates motion |
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inside the engine. Internal combustion is a lot more efficient (takes less fuel |
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per mile) than external combustion, plus an internal combustion engine is a |
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lot smaller than an equivalent external combustion engine. This explains why |
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we don't see any cars from Ford and GM using steam engines. |
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бАINTERNAL COMBUSTION |
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The principle behind any reciprocating internal combustion engine: If |
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you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed |
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space and ignite it, an incredible amount of energy is released in the form of |
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expanding gas. You can use that energy to propel a potato 500 feet. In this |
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case, the energy is translated into potato motion. You can also use it for more |
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interesting purposes. For example, if you can create a cycle that allows you to |
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set off explosions like this hundreds of times per minute, and if you can |
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harness that energy in a useful way, what you have is the of a car engine! |
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Almost all cars currently use what is called a four-stroke combustion |
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cycle to convert gasoline into motion. The four-stroke approach is also |
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known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. |
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The four strokes are illustrated in Figure 1. They are: |
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Intake stroke |
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Compression stroke |
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Combustion stroke |
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Exhaust stroke |
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You can see in the figure that a device called a piston replaces the potato in the potato cannon. The piston is connected to the crankshaft by a connecting rod. As the crankshaft revolves, it has the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle:
1. The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This Сis the intake stroke. Only the tiniest drop of gasoline needs to be mixed into
the air for this to work.
2. Then the piston moves back up to compress this fuel/air mixture.
Compression makes the explosion more powerful.
иNow the engine is ready for the next cycle, so it intakes another charge of air and gas.
3. When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes,
driving the piston down.
4. Once the piston hits the bottom of its stroke, the exhaust valve
starting withбАthe cylinders.
opens and the exhaust leaves the cylinder to go out the tailpipe.
Notice that the motion that comes out of an internal combustion engine
is rotational, while the motion produced by a potato cannon is linear (straight line). In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft. The rotational motion is nice because we plan to turn (rotate) the car's wheels with it anyway.
Now let's look at all the parts that work together to make this happen, Д
Basic Engine Parts
The core of the engine is the cylinder, with the piston moving up and
down inside the cylinder. The engine described above has one cylinder. That
is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). ИIn a multi-cylinder engine, the
cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed).
Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.
Let's look at some key engine parts in more detail.
Spark plug The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.
Valves The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.
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Piston A piston is a cylindrical piece of metal that moves up and down inside the cylinder.
Piston rings Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two
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They prevent the fuel/air mixture and exhaust in the combustion |
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chamber from leaking into the sump during compression and combustion. |
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They keep oil in the sump from leaking into the combustion area, |
where it would be burned and lost.
Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal
и moves andбАthe crankshaft rotates.
things properly.
Connecting rod The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston
Crankshaft The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.
Sump The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).
ENGINE PROBLEMS
So you go out one morning and your engine will turn over but it won't start... What could be wrong? Now that you know how an engine works, you can understand the basic things that can keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of compression or lack of spark. Beyond that, thousands of minor things can create problems, but these are the "big three." Based on the simple engine we have been
discussing, here is a quick rundown on how these problems affect your |
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Bad fuel mix - A bad fuel mix can occur in several ways:
You are out of gas, so the engine is getting air but no fuel.
The air intake might be clogged, so there is fuel but not enough air.
The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not burn.
Lack of compression - If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it should. Lack of compression might occur for these reasons:
Your piston rings are worn (allowing air/fuel to leak past the piston during compression). И
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