ABSTRACT

The term plotted ignition is applied to the case in the which an engine is equipped with a technology where the spark time is advanced with the speeds. In an engine the spark advance angle required increases with an increase in the speed. This technology actually advances the spark timing and gives a correct time so that the mixture gets enough time to burn to a near net completion.
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CHAPTER -I
INTRODUCTION

The purpose of the ignition system is to create a spark that will ignite the fuel-air mixture in the cylinder of an engine. It must do this at exactly the right instant and do it at the rate of up to several thousand times per minute for each cylinder in the engine. If the timing of that spark is off by a small fraction of a second, the engine will run poorly or not run at all.

The ordinary engines that we find have a fixed position of ignition in terms of crank angle the fuel while burning requires a particular time for full burning. The time available for the burning is from the start of the spark to the opening of the outlet valves, as the engine speed increases the time available is decreased. This contributes to lesser amount being burned and the rest going out unburned .This consistent loss contributes to losses resulting in the lesser mileage In normal vehicles the ignition starts at an angle before the TDC and this is kept fixed. This is altered when the plotted ignition is used. This method by which the crank angle at which the ignition starts is altered is called the plotted ignition

CHAPATER 2
GENERAL IDEA ADOUT TOPIC
PLOTTED IGNITION

Plotted ignition is the term used predominantly for the system that is installed on to a SI engine where by the efficiency and the power of the engine can be increased .this technology even though now popularly seen has immense advantages over the conventional ones

1. The need
The ordinary engines that we find have a fixed position of ignition in terms of crank angle the fuel while burning requires a particular time for full burning. The time available for the burning is from the start of the spark to the opening of the outlet valves, as the engine speed increases the time available is decreased. This contributes to lesser amount being burned and the rest going out unburned .This consistent loss contributes to losses resulting in the lesser mileage In normal vehicles the ignition starts at an angle before the TDC and this is kept fixed. This is altered when the plotted ignition is used. This method by which the crank angle at which the ignition starts is altered is called the plotted ignition
2. How it is achieved
The plotted ignition is achieved by first finding the correct angle at which the ignition must be given .this is done by first testing the engine at different crank angle of ignition at a particular speed and then finding the correct angle .this is done at different speeds. This data is transferred to a programmable chip, this chip controls the ignition timing.

3. The lay out

Fig :1The basic lay out is shown

Eg: AMI by hero Honda
D-FI LOGIC by Suzuki


Eg: cruise control by BAJAJ




4. V12 IGNITION SYSTEMS
One of the first fully electronic systems to become established was Lucas OPUS which was initially proven in racing at Formula One level and then entered production on the Jaguar V12 - an engine for which contact breakers would have been totally impractical. The name is derived from the method of operation, i.e. Oscillating Pick-Up System.
The amplifier contains an oscillator circuit with an output frequency of 600 kHz, this being transmitted through one winding of the pickup, which is actually a transformer with windings on an open ended E shaped ferrite core. The resistance of these windings should be nominally 2.5 Ohms (centre to red wire) and 0.9 Ohm (centre to black wire).
A molded nylon rotor is mounted on the distributor shaft and carries ferrite rods, spaced one per cylinder axially around the circumference so that they can periodically bridge the upper two legs of the core. As each rod passes the pickup the magnetic circuit of the upper part is completed, communicating the 600khz signal to the secondary pickup winding and back to the amplifier which turns off the current through the coil to generate an H.T. spark in the normal way. The constant 600 kHz signal to the pickup and the returning signal, with changes of amplitude as the ferrite rods pass the pickup; can be clearly observed with an oscilloscope. The ferrite rods only align across the upper half of the pickup E core, which is somewhat fragile and must be handled with care. An interesting effect is that if the ignition is turned on with the engine not running and one of the ferrite rods happens to be aligned with the pickup the oscillator signal will be transmitted continuously to the output transistor causing a weak HT spark train to be generated at the oscillator frequency. This phenomenon can be a fair, though not infallible, indication that the system is functioning properly. Whenever no ferrite rod is in proximity to the pickup the output transistor will be switched on and current will flow through the coil.
Because of this the circuit still requires a ballast resistor to limit current through the coil, which typically has a primary resistance of about 1 ohm, but the maximum spark rate capability is about double that of a contact breaker system. For the V12, as with most applications, the OPUS amplifier came inside a cast metal box with fins on top although it came built into the distributor for the early EFI 4.2 Jaguar, a configuration which proved troublesome.


There were a number of variations in the OPUS system as applied to the V12. A high energy (i.e. low resistance) coil was introduced during 1978 along with an up rated amplifier designed to handle the increased current. There were also variations in the ballast resistor arrangements and a long lead amplifier was introduced latterly to enable the amplifier to be remotely mounted because engine heat had been thought to be a cause of unreliability. There is nothing to prevent the leads being extended on the earlier amplifiers for the same purpose, despite uninformed claims to the contrary.
5. Timing Settings
All are with no vacuum applied. Static figure is target for initial setting up. Timing should then be set to higher speed figure approximating to the peak torque regime.
V12 E type (CD carbs) 9:1 compression.
750 r.p.m. (static) 12 degrees BTDC
3500 r.p.m. 31 degrees BTDC

Bosch Lucas EFI, 9:1 compression, 1975-80.
750 r.p.m. (static) 10 degrees BTDC
3000 r.p.m. 29 degrees BTDC

Lucas 6CU EFI, pre-HE 10:1 compression, 1980-81.
750 r.p.m. (static) 5 degrees BTDC
3000 r.p.m. 24 degrees BTDC
The slightly more advance applied to the V12 E type reflects the fuel rating of 98 RON (rather than 97 RON quoted for later 9:1 engines) and also the breathing limitations of the CD carburetor arrangement.
6. Lucas Constant Energy Ignition
In its original form the constant energy ignition system used a Fairchild SH 4240 control package which contained a high voltage Darlington power transistor and control circuitry based around a dedicated integrated circuit. Heat produced by the transistor was dissipated by mounting it on a substrate of beryllia (beryllium oxide), which is toxic so these units should never be broken open or crushed.
The trigger input used in all Jaguar applications is the simple inductive pick-up, essentially a magnetically sensitive coil which creates an output voltage when pole pieces move past, these being in the form of individual teeth for each cylinder disposed around a rotor. The winding resistance is likely to be about 3.3K Ohms, but is quoted as being from 2.2K to 4.8K, which seems a bit hazy really.
The waveform produced is a sort of distorted sine wave, rising to a peak positive value then abruptly swinging negative as the pole piece moves through the point of exact alignment (see diagram). Fortuitously this provides a very reliable switching point with which to trigger the ignition event. The drawback is that a sine wave type of signal spends the same amount of time in the negative phase, as in the positive, so even if the switching were to take place at the zero crossing point the maximum on time for the coil could never exceed half of a cycle. To complicate things further if, at low speeds, the coil were turned on for as long as half the cycle either the coil or the module would then have to dissipate a lot of heat. The clever thing about the constant energy module is that it deals with this conundrum rather well by biasing the trigger signal so that it lifts with rising speed. The switching-on point therefore can be quite late (in terms of rotation) at low speeds and then advances forward as speed increases. With the aid of an oscilloscope this can be seen as an upward distortion of the waveform (see diagram) with rising speed. A consequence of shifting the waveform in this way is that the firing point retards very slightly - barely 1 degree or so - with rising speed because of the downward signal slope at this point. This is of no concern because it amounts to less than the tolerance spread of a typical advance mechanism and can be allowed for in the timing setting.



1. An ignition spark timing control system for use with a spark ignition internal combustion engine and a sequence control arrangement comprising: a read only memory pre-programmed to produce an output binary signal representation of predetermined ignition spark timing angle based upon the instantaneous value of both of two selected engine operating parameters at each of a plurality of respective selected points within the range of values in response to respective input address signals whereby over the range of values of the two selected engine operating parameters the read only memory generates a three-dimensional surface of ignition spark timing angles based upon the two selected engine parameter values; means for producing input address signals for said read only memory in response to binary signal representations of instantaneous values of said selected two engine operating parameters; means for applying said input address signals to said read only memory whereby the binary signal representation of an ignition spark timing angle is produced by said read only memory in response to each of said input address signals; and means effective to vary the binary signal representations of the ignition spark timing angles as retrieved from said read only memory in accordance with engine manifold vacuum in substantial inverse proportion to atmospheric pressure whereby said three-dimensional surface generated by said read only memory is tilted about a selected engine parameter value as an axis in an amount substantially inversely proportional to actual atmospheric pressure.

2. An ignition spark timing control system for use with a spark ignition internal combustion engine and a sequence control arrangement comprising: a read only memory pre-programmed to produce an output binary signal representation of a predetermined ignition spark timing angle based upon the instantaneous value of both engine manifold vacuum and speed at each of a plurality of respective selected points within the range of values in response to respective input address signals whereby over the range of values of engine manifold vacuum and speed the read only memory generates ignition spark timing angles based upon engine manifold vacuum and speed in the form of a three-dimensional surface having engine speed, engine manifold vacuum and timing angles as respective axes; means for producing input address signals for said read only memory in response to binary signal representations of instantaneous values of engine manifold vacuum and speed; means for applying said input address signals to said read only memory whereby the binary signal representation of an ignition spark timing angle is produced by said read only memory in response to each of said input address signals; means for producing an output binary signal representation of a value derived from engine intake manifold vacuum values and atmospheric pressure values, said output binary signal representation value varying inversely with atmospheric pressure; and means for producing an output binary signal representation of the sum of said binary signal representation of an ignition spark timing angle retrieved from each read only memory and said output binary signal representation of said last named means whereby said three-dimensional surface generated by said read only memory is tilted about the engine speed axis thereof in an amount substantially inversely proportional to atmospheric pressure.

3. An ignition spark timing control system for use with a spark ignition internal combustion engine and a sequence control arrangement comprising: a read only memory pre-programmed to produce an output binary signal representation of a predetermined ignition spark timing angle based upon the instantaneous value of both of two selected engine operating parameters at each of a plurality of respective selected points within the range of values in response to respective input address signals whereby over the range of values of the two selected engine operating parameters the read only memory generates a three-dimensional surface of ignition spark timing angles based upon the two selected engine parameters values; means for producing input address signals for said read only memory in response to binary signal representations of instantaneous values of said selected two engine operating parameters; means for applying said input address signals to said read only memory whereby the binary signal representation of an ignition spark timing angle is produced by said read only memory in response to each of said input address signals; first means responsive to engine manifold vacuum for producing a binary signal representation of an ignition spark vacuum advance timing angle for each of various values of engine manifold vacuum; second means responsive to atmospheric pressure for producing a binary signal representation of a percentage of said binary signal representation of ignition spark advance angle produced by said first means as determined by atmospheric pressure, means responsive to said first and second means for producing the binary signal representation of the product of the said binary signal representations produced by said first and second means; and means responsive to said last means for adding the binary signal representation produced by said last means to the binary signal representation of ignition spark advance angle retrieved from said read only memory for producing a binary signal representation of total ignition spark advance angle.

4. An ignition spark timing control system for use with a spark ignition internal combustion engine and a sequence control arrangement comprising: a read only memory pre-programmed to produce an output binary signal representation of a predetermined ignition spark timing angle based upon the instantaneous value of both of two selected engine operating parameters at each of a plurality of respective selected points within the range of values in response to respect input address signals whereby over the range of values of the two selected engine operating parameters the read only memory generates a three-dimensional surface of ignition spark timing angles based upon the two selected engine parameters values; means for producing input address signals for said read only memory in response to binary signal representations of instantaneous values of said selected two engine operating parameters; means for applying said input address signals to said read only memory whereby the binary signal representation of an ignition spark timing angle is produced by said read only memory in response to each of said input address signals; first means responsive to engine manifold vacuum for producing a binary signal representation of an ignition spark vacuum advance timing angle for each value of engine manifold vacuum; second means responsive to atmospheric pressure for producing an output binary signal representation of a percent value which varies inversely from a maximum to a minimum value with increasing values of atmospheric pressure; means responsive to said binary signal representations produced by said first and second means for producing the binary signal representation of the product thereof; and means effective to produce the sum of said binary signal representation of an ignition spark timing angle retrieved from said read only memory and the binary signal representation of the product of the binary signal representations of said first and second means.

5. An ignition spark timing control system for use with a spark ignition combustion engine and a sequence control arrangement comprising: a read only memory pre-programmed to produce an output binary signal representation of a predetermined ignition spark timing angle based upon the instantaneous value of both of two selected engine operating parameters at each of a plurality of respective selected points within the range of values in response to respective input address signals whereby over the range of values of the two selected engine operating parameters the read only memory generates a three-dimensional surface of ignition spark timing angles based upon the two selected engine parameters values; means for producing input address signals for said read only memory in response to binary signal representations of instantaneous values of said selected two engine operating parameters; means for applying said input address signals to said read only memory whereby the binary signal representation of an ignition spark timing angle is produced by said read only memory in response to each of said input address signals; first means responsive to engine manifold vacuum for producing an output binary signal representation of an ignition spark vacuum advance timing angle for each value of engine manifold vacuum, second means responsive to atmospheric pressure for producing an output binary signal representation of a percent value which varies inversely from a maximum value at approximately two-thirds normal atmospheric pressure to zero at normal atmospheric pressure; means for producing an output binary signal representation of the product of the output binary signal representation of said first means multiplied by the output binary signal representation of said second means; and means for producing an output binary signal representation of the sum of said binary signal representation of an ignition spark timing angle retrieved from said read only memory and the output binary signal representation of said last means.

7. What is claimed is
1. An ignition timing control device for an engine having a spark plug, comprising:
ignition timing control means for controlling ignition timing, when the engine is warming up, to a warm-up reference ignition timing advanced relative to a warmed-up reference ignition timing when a representative value changing in accordance with atmospheric pressure is one of higher than a predetermined first reference value representing a high engine load and lower than a predetermined second reference value representing a low engine load, the ignition timing control means retarding the ignition timing relative to the warm-up reference ignition timing when the representative value is lower than the first reference value and higher than the second reference value; and
Reference value control means for lowering the first reference value while maintaining the second reference value unchanged when the atmospheric pressure falls below a normal atmospheric pressure.
2. An ignition timing control device for an engine as set forth in claim 1, wherein the representative value is a mass flow rate of intake air and the first reference value is a predetermined mass flow rate.
3. An ignition timing control device for an engine as set forth in claim 1, wherein the representative value is an absolute pressure and the first reference value is a predetermined absolute pressure.
4. An ignition timing control device for an engine as set forth in claim 1, further comprising means for deciding if the engine operating state is an idling operation, wherein, when the engine operating state is an idling operation, the ignition timing control means controls the ignition timing to the warm-up reference ignition timing.
5. An ignition timing control device for an engine as set forth in claim 1, wherein the ignition timing control means controls the amount of retard of the ignition timing in accordance with the representative value when the representative value is lower than the first reference value and higher than the second reference value.
6. An ignition timing control device for an engine as set forth in claim 5, wherein, when the representative value is lower than a third reference value lower than the first reference value and higher than the second reference value, the ignition timing control means makes an amount of ignition timing retard a predetermined maximum amount and reduces the amount of retard as the representative value increases above the third reference value.
7. An ignition timing control device for an engine as set forth in claim 6, wherein the representative value is a mass flow rate and of intake air and the third reference value is a predetermined mass flow rate.
8. An ignition timing control device for an engine as set forth in claim 7, wherein the predetermined mass flow rate is lowered the lower the atmospheric pressure is below the normal atmospheric pressure.
9. An ignition timing control device for an engine as set forth in claim 6, wherein the representative value is an absolute pressure value in an intake passage downstream of a throttle valve and the third reference value is a predetermined absolute pressure value.
10. An ignition timing control device for an engine as set forth in claim 1, further comprising means for detecting an engine cooling water temperature, wherein an amount by which the warm-up reference ignition timing is advanced relative to the warmed-up reference ignition timing is made larger as the engine cooling water temperature decreases and as the engine load increases and wherein the ignition timing control means retards the ignition timing relative to the warm-up reference ignition timing when the engine cooling water temperature is between a predetermined first temperature and a predetermined second temperature and the representative value is lower than the first reference value and higher than the second reference value, the second temperature being lower than the first temperature.
11. An ignition timing control device for an engine as set forth in claim 10, wherein the first temperature is the engine cooling water temperature at which the engine is deemed to be warmed up.


CHAPATER 3
IGNITION SYSTEMS
Currently, there are three distinct types of ignition systems; The Mechanical Ignition System was used prior to 1975. It was mechanical and electrical and used no electronics. By understanding these early systems, it will be easier to understand the new electronic and computer controlled ignition systems, so don't skip over it. The Electronic Ignition System started finding its way to production vehicles during the early '70s and became popular when better control and improved reliability became important with the advent of emission controls. Finally, the Distributor less Ignition System became available in the mid '80s. This system was always computer controlled and contained no moving parts, so reliability was greatly improved. Most of these systems required no maintenance except replacing the spark plugs at intervals from 60,000 to over 100,000 miles.
Let's take a detailed look at each system and see how they work.
3.1 The Mechanical Ignition System


3.1.1 The ignition switch.
There are two separate circuits that go from the ignition switch to the coil. One circuit runs through a resistor in order to step down the voltage about 15% in order to protect the points from premature wear. The other circuit sends full battery voltage to the coil. The only time this circuit is used is during cranking. Since the starter draws a considerable amount of current to crank the engine, additional voltage is needed to power the coil. So when the key is turned to the spring-loaded start position, full battery voltage is used. As soon as the engine is running, the driver releases the key to the run position which directs current through the primary resistor to the coil.
On some vehicles, the primary resistor is mounted on the firewall and is easy to replace if it fails. On other vehicles, most notably vehicles manufactured by GM, the primary resistor is a special resistor wire and is bundled in the wiring harness with other wires, making it more difficult to replace, but also more durable.
3.1.2The Distributor
When you remove the distributor cap from the top of the distributor, you will see the points and condenser. The condenser is a simple capacitor that can store a small amount of current. When the points begin to open, the current flowing through the points looks for an alternative path to ground. If the condenser were not there, it would try to jump across the gap of the points as they begin to open. If this were allowed to happen, the points would quickly burn up and you would hear heavy static on the car radio. To prevent this, the condenser acts like a path to ground. It really is not, but by the time the condenser is saturated, the points are too far apart for the small amount of voltage to jump across the wide point gap. Since the arcing across the opening points is eliminated, the points last longer and there is no static on the radio from point arcing.
The points require periodic adjustments in order to keep the engine running at peek efficiency. This is because there is a rubbing block on the points that is in contact with the cam and this rubbing block wears out over time changing the point gap. There are two ways that the points can be measured to see if they need an adjustment. One way is by measuring the gap between the open points when the rubbing block is on the high point of the cam. The other way is by measuring the dwell electrically. The dwell is the amount, in degrees of cam rotation, that the points stay closed.
On some vehicles, points are adjusted with the engine off and the distributor cap removed. A mechanic will loosen the fixed point and move it slightly, then retighten it in the correct position using a feeler gauge to measure the gap. On other vehicles, most notably GM cars, there is a window in the distributor where a mechanic can insert a tool and adjust the points using a dwell meter while the engine is running. Measuring dwell is much more accurate than setting the points with a feeler gauge.
Points have a life expectancy of about 10,000 miles at which time they have to be replaced. This is done during a routine major tune up. During the tune up, points, condenser, and the spark plugs are replaced, the timing is set and the carburetor is adjusted. In some cases, to keep the engine running efficiently, a minor tune up would be performed at 5,000 mile increments to adjust the points and reset the timing.
The coil secondary winding circuit contains 15,000 to 30,000 turns of fine copper wire, which also must be insulated from each other. The secondary windings sit inside the loops of the primary windings. To further increase the coils magnetic field the windings are wrapped around a soft iron core. To withstand the heat of the current flow, the coil is filled with oil which helps keep it cool.
The ignition coil is the heart of the ignition system. As current flows through the coil a strong magnetic field is built up. When the current is shut off, the collapse of this magnetic field to the secondary windings induces a high voltage which is released through the large center terminal. This voltage is then directed to the spark plugs through the distributor.
3.1.3 Ignition Timing
The timing is set by loosening a hold-down screw and rotating the body of the distributor. Since the spark is triggered at the exact instant that the points begin to open, rotating the distributor body (which the points are mounted on) will change the relationship between the position of the points and the position of the distributor cam, which is on the shaft that is geared to the engine rotation.
While setting the initial, or base timing is important, for an engine to run properly, the timing needs to change depending on the speed of the engine and the load that it is under. If we can move the plate that the points are mounted on, or we could change the position of the distributor cam in relation to the gear that drives it, we can alter the timing dynamically to suit the needs of the engine.
3.1.3.1 Why do we need the timing to advance when the engine runs faster?
When the spark plug fires in the combustion chamber, it ignites whatever fuel and air mixture is present at the tip of the spark plug. The fuel that surrounds the tip is ignited by the burning that was started by the spark plug, not by the spark itself. That flame front continues to expand outward at a specific speed that is always the same, regardless of engine speed. It does not begin to push the piston down until it fills the combustion chamber and has no where else to go. In order to maximize the amount of power generated, the spark plug must fire before the piston reaches the top of the cylinder so that the burning fuel is ready to push the piston down as soon as it is at the top of its travel. The faster the engine is spinning, the earlier we have to fire the plug to produce maximum power.
There are two mechanisms that allow the timing to change: Centrifugal Advance and Vacuum Advance.
3.1.3.2 Centrifugal Advance changes the timing in relation to the speed (RPM) of the engine. It uses a pair of weights that are connected to the spinning distributor shaft. These weights are hinged on one side to the lower part of the shaft and connected by a linkage to the upper shaft where the distributor cam is. The weights are held close to the shaft be a pair of springs. As the shaft spins faster, the weights are pulled out by centrifugal force against the spring pressure. The faster the shaft spins, the more they are pulled out. When the weights move out, it changes the alignment between the lower and upper shaft, causing the timing to advance.
Vacuum Advance works by changing the position of the points in relationship to the distributor body. An engine produces vacuum while it is running with the throttle closed. In other words, your foot is off the gas pedal. In this configuration, there is very little fuel and air in the combustion chamber.
Vacuum advance uses a vacuum diaphragm connected to a page link that can move the plate that the points are mounted on. By sending engine vacuum to the vacuum advance diaphragm, timing is advanced. On older cars, the vacuum that is used is port vacuum, which is just above the throttle plate. With this setup, there is no vacuum present at the vacuum advance diaphragm while the throttle is closed. When the throttle is cracked opened, vacuum is sent to the vacuum advance, advancing the timing.
On early emission controlled vehicles, manifold vacuum was used so that vacuum was present at the vacuum advance at idle in order to provide a longer burn time for the lean fuel mixtures on those engines. When the throttle was opened, vacuum was reduced causing the timing to retard slightly. This was necessary because as the throttle opened, more fuel was added to the mixture reducing the need for excessive advance. Many of these early emission controlled cars had a vacuum advance with electrical components built into the advance unit to modify the timing under certain conditions.
Both Vacuum and Centrifugal advance systems worked together to extract the maximum efficiency from the engine. If either system was not functioning properly, both performance and fuel economy would suffer. Once computer controls were able to directly control the engine's timing, vacuum and centrifugal advance mechanisms were no longer necessary and were eliminated.
3.2 The Electronic Ignition System
In the electronic ignition system, the points and condenser were replaced by electronics. On these systems, there were several methods used to replace the points and condenser in order to trigger the coil to fire. One method used a metal wheel with teeth, usually one for each cylinder. This is called an armature or reluctor. A magnetic pickup coil senses when a tooth passes and sends a signal to the control module to fire the coil.
Other systems used an electric eye with a shutter wheel to send a signal to the electronics that it was time to trigger the coil to fire. These systems still need to have the initial timing adjusted by rotating the distributor housing.
The advantage of this system, aside from the fact that it is maintenance free, is that the control module can handle much higher primary voltage than the mechanical points. Voltage can even be stepped up before sending it to the coil, so the coil can create a much hotter spark, on the order of 50,000 volts instead of 20,000 volts that is common with the mechanical systems. These systems only have a single wire from the ignition switch to the coil since a primary resistor is no longer needed.

3.3 The Distributorless Ignition system
Newer automobiles have evolved from a mechanical system (distributor) to a completely solid state electronic system with no moving parts. These systems are completely controlled by the on-board computer. In place of the distributor, there are multiple coils that each serve one or two spark plugs. A typical 6 cylinder engine has 3 coils that are mounted together in a coil "pack". A spark plug wire comes out of each side of the individual coil and goes to the appropriate spark plug. The coil fires both spark plugs at the same time. One spark plug fires on the compression stroke igniting the fuel-air mixture to produce power, while the other spark plug fires on the exhaust stroke and does nothing. On some vehicles, there is an individual coil for each cylinder mounted directly on top of the spark plug. This design completely eliminates the high tension spark plug wires for even better reliability. Most of these systems use spark plugs that are designed to last over 100,000 miles, which cuts down on maintenance costs.

REFERENCES

1. wekipedia.com
2. Automobile engineering Ganeshan
3. howstuffworks.com