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Sunday, May 8, 2011
Basic Engine Configuration
The term engine configuration refers to the way that cylinders of an engine are arranged. The basic arrangement as you know is in-line,but the engine is also configured in opposed or at an angle (V-type engines) but this time three main configurations will be discussed. there are number of variations made in the engines.
With in-line engines, the cylinders are arranged in a straight line, one behind other. Most in-line engines have their cylinders vertical, but some are slanted. that is, the engine is tilted at an angle to reduce the overall height. These engines are some times referred as slanted engines.
Some in-line engines have their cylinders horizontal, so the engine is more or less on its side.This reduces the overall height of the engine. This arrangement is used mainly in larger commercial vehicles with the engine mounted under part of the cabin.
The mechanical arrangement of a four-cylinder in-line engine for a passenger car, this has a single camshaft and sixteen valves operated by rocker arms. It has electronic fuel injection know as EFI.
The cut-way view enables to identify the parts easily
This has its cylinders arranged in two flat banks with the crankshaft between them. It has a short rigid crankshaft with five bearings. A horizontally opposed engine has even firing impulses and good balance. Movement of a piston in one direction is opposed by the movement of piston in opposite direction.
Horizontally opposed engines, with their flat design, give the engine a low height and also help to keep the center of gravity low. A low center of gravity gives the vehicle stability.
The center of gravity, stated simply, is the point which the mass of the vehicle can be considered to be concentrated
With v-type engines, the cylinders are arranged in two banks at an angle. This reduces the length of the engine and makes it more compact. This also reduces the length of the crankshaft, which can be designed to be more rigid than a long crankshaft.
A section view through a v-type engine with eight cylinders, with their cylinders at an angle need only four crank-pins the connecting rods of opposite cylinders are connected side-by-side to the same crank-pins.
the connecting rods of opposite cylinders are connected side-by-side to the same crank-pin. It has a camshaft in the V of the cylinder block and push rods to operate the valve mechanism on the cylinder head. The cylinders are at 90°.
A V-type engine with a different arrangement. This is a sectional view of a V-6 engine with two banks of three cylinders set at an angle of 60°.
It is a double overhead-camshaft (DOHC) engine, with two camshafts on each bank of cylinders. One camshaft on each bank operates the intake valves at one and the other operates the exhaust valves.
The intake camshafts on both banks are driven by a single timing belt from the crankshaft pulley. The exhaust camshafts are then driven by the gears from the intake shafts.
The crankshaft of this engine is supported in four main bearings as it has a separate crank pin for each connecting rod bearing.
The internal arrangement of this engine is shown in the lubrication
A number of different cylinder arrangements that are commonly used for in-line and V-type engines. The firing orders for the engines are also shown.
There are also other arrangements including: in-line engines with two cylinders, five cylinders and eight cylinders; v-type engines with two cylinders and twelve cylinders; and horizontally opposed engines with four and six cylinders.
With in-line engines, the cylinders are numbered in order from front to rear.
V-type engines are designed with one bank of cylinders a little in front of the other. This is necessary because the connecting rods are side by side on the crankshaft. The front cylinder is usually designated No.1. This can be the front cylinder on either the right or left bank, depending on the design of particular engine.
The front cylinder is on the right bank so this is No.1. The other cylinders are then numbered fro front or rear on each bank. In diagram (e) No.1 is on the left bank and the cylinders are numbered across the engine from bank to bank.
The diagram in figure 1.16 is an alternative arrangement for the cylinders of a V-6 engine No.1 cylinder is on the right bank because the cylinders on the right bank are set ahead of the cylinders of the left bank. Cylinder 1, 3 and 5 are on the right bank and 2, 4 and 6 are on the left bank.
The firing order is the order, or sequence, in which the cylinders of an engine fire or deliver their power strokes. The firing order is part of engine design and is determined by the design of both the crankshaft and the camshaft.
The arrangements of the cranks, or throws, of the crankshaft determines the movement of the pistons and the arrangement of the cams on the camshaft determines when the valves open and close. The crankshaft and camshaft are designed and timed so that the valves open correctly in relation to the piston strokes.
For petrol and gas engines, the ignition system is also timed so that it provides the spark at the right time and in the correct firing order. For a diesel, the injection pump is timed so that fuel is injected in the correct order.
Other firing orders
There are number of other firing orders. For example, a four cylinder engine can be 1-3-4-2 or 1-2-4-3.
A particular V-8 engine has firing order of 1-8-7-2-6-3-4-5. No.1 cylinder is the front cylinder on the left bank, with No.2 on the opposite bank, and so on. In all sequences, the firing order of the cylinder is staggered so that the power impulses are spaced as evenly as possible.
There are a couple of instances where engines fire in the sequence of the cylinder numbers. One is a three cylinder engine, where the cylinders must fire one after the other. Changing the firing order from 1-2-3 does not stagger the sequence because the cylinders will always fire consecutively.
The V-6 cylinders in fig.1.16 are another example of how cylinders can fire in sequence. The firing order here is 1-2-3-4-5-6. Again, the firing order depends on the design of the crankshaft, which controls piston movement and the design of the camshaft, wh9ich controls the opening and closing of the valves.
As well as knowing the firing order for the engine, the method of numbering the cylinders must also be known.