TIRE

Stacked and standing car tires

The fundamental materials of modern tires are synthetic rubber, natural rubber, fabric and wire, along with other compound chemicals. They consist of a tread and a body. The tread provides traction while the body ensures support. Before rubber was invented, the first versions of tires were simply bands of metal that fitted around wooden wheels in order to prevent wear and tear. Today, the vast majority of tires are pneumatic inflatable structures, comprising a doughnut-shaped body of cords and wires encased in rubber and generally filled with compressed air to form an inflatable cushion. Pneumatic tires are used on many types of vehicles, such as bicycles, motorcycles, cars, trucks, earthmovers, and aircraft.

Tire Pressure Monitoring System

Tire pressure monitoring systems (TPMS) are electronic systems that monitor the tire pressures on individual wheels on a vehicle, and alert the driver when the pressure goes below a warning limit. There are several types of designs to monitor tire pressure. Some actually measure the air pressure, and some make indirect measurements, such as gauging when the relative size of the tire changes due to lower air pressure.

Inflation Pressure

Tires are specified by the vehicle manufacturer with a recommended inflation pressure, which permits safe operation within the specified load rating and vehicle loading. Most tires are stamped with a maximum pressure rating. For passenger vehicles and light trucks, the tires should be inflated to what the vehicle manufacturer recommends, which is usually located on a decal just inside the driver's door or in the vehicle owners handbook. Tires should not generally be inflated to the pressure on the sidewall; this is the maximum pressure, rather than the recommended pressure. High performance and dynamic drivers often increase the tire pressure to near the maximum pressure as printed on the sidewall. This is done to sacrifice comfort for performance and safety. It is definitely very dangerous to allow tire pressure to drop below the recommended placard vehicle pressure, although this is commonly done temporarily when driving on sand to reduce chance of bogging. The reason for this is that it increases the amount of tire wall movement as a result of cornering forces. Should a low pressure tire be forced to perform an evasive maneuver, the tire wall will be more pliable than had it been of a higher pressure, and thus it will "roll" under the wheel. This increases the entire roll movement of the car, and diminishes tire contact area on the negative side of the vector. Thus only half the tire is in contact with the road, and the tire may deform to such an extent that the side wall on the positive vector side becomes in contact with the road. The probability of failing in the emergency maneuver is thus increased.

Further, with low tire pressure—due to the side wall being more pliable—the tire will absorb more of the irregular forces from normal driving, and with this constant bending of the side wall as it absorbs the contours of the road, it heats up the tire wall to possibly dangerous temperatures, as well as degrades the steel wire reinforcement; this often leads to side wall blow-outs. In an extreme case of this phenomenon, the vehicle may drive into a pot-hole, or a hard elevation in the road. Due to the low tire pressure, the side wall at the contact area will temporarily collapse, thereby wedging the tire between the wheel and road, resulting in a tire laceration and blow-out, as well as a damaged wheel. High tire pressures are more inclined to keep its shape during any encounter, and will thus transmit the forces of the road to the suspension, rather than being damaged itself. This allows for an increased reaction speed, and "feel" the driver perceives of the road. Modern tire designs allow for minimal tire contact surface deformity during high pressures, and as a result the traditional wear on the center of the tire due to reasonably high pressures is only known to very old or poorly designed tires.

Feathering occurs on the junction between the tire tread and side wall, as a result of too low tire pressures. This is as a result of the inability of the tire to perform appropriately during cornering forces, leading to aberrant and shearing forces on the feathering area. This is due to the tire moving sideways underneath the wheel as the tire pressures are insufficient to transmit the forces to the wheel and suspension. It may be, that very high tire pressures have only two downsides: The sacrifice in comfort; and the increased chance of obtaining a puncture when driving over sharp objects, such as on a newly scraped gravel road. Many individuals have maintained their tire pressures at the maximum side wall printed value (inflated when cold) for the entire lifetime of the tire, with perfect wear until the end. This may be of negative economic value to the rubber and tire companies, as high tire pressures decrease wear, and minimize side wall blow outs.

Many pressure gauges available at fuel stations have been de-calibrated by manhandling and the effect of time, and it is for this reason that vehicle owners should keep a personal pressure gauge with them to validate the correct tire pressure.

During the early stages of tire engineering, and with current basic tires, the tire contact patch is readily reduced by both over-and-under inflation. Over-inflation may increase the wear on the center contact patch, and under-inflation will cause a concave tread, resulting in less center contact. Most modern tires will wear evenly at very high tire pressures, but will degrade prematurely due to low (or even standard) pressures. An increased tire pressure has many benefits, including decreased rolling resistance. It has been found, that an increased tire pressure almost exclusively results in shorter stopping distances, except in some circumstances that may be attributed to the low sample size. If tire pressure is too low, the tire contact patch is changed more than if it were over-inflated. This decreases rolling resistance, tire flexing, and friction between the road and tire. Under-inflation can lead to tire overheating, premature tread wear, and tread separation in severe cases.

Load Rating

Tires are specified by the manufacturer with a maximum load rating. Loads exceeding the rating can result in unsafe conditions that can lead to steering instability and even rupture. For a table of load ratings, see tire code.

Speed Rating

The speed rating denotes the maximum speed at which a tire is designed to be operated. For passenger vehicles these ratings range from 99 mph (159 km/h) to 186 mph (299 km/h). For a table of speed ratings, see tire code.

Replacing a tire on a vehicle with one with a lower speed rating than originally specified by the vehicle manufacturer may render the insurance invalid.

Service rating

Tires (especially in the U.S.) are often given service ratings, mainly used on bus and truck tires. Some ratings are for long haul, and some for stop-start multi-drop type work. Tires designed to run 500 miles (800 km) or more per day carrying heavy loads require special specifications.

Treadwear Rating

The treadwear rating or treadwear grade describes how long the tire manufacturers expects the tire to last. A Course Monitoring Tire (the standard tire that a test tire will be compared to) has a rating of "100". If a manufacturer assigns a treadwear rating of 200 to a new tire, they are indicating that they expect the new tire to have a useful lifespan that is 200% of the life of a Course Monitoring Tire. The "test tires" are all manufacturer-dependent. Brand A's rating of 500 is not necessarily going to give you the same mileage rating as Brand B's tire of the same rating. The testing is non-regulated and can vary greatly. Treadwear ratings are only useful for comparing Brand A's entire lineup against itself. Tread wear, also known as tire wear, is caused by friction between the tire and the road surface. Government legal standards prescribe the minimum allowable tread depth for safe operation.

Rotation

Tires may exhibit irregular wear patterns once installed on a vehicle and partially worn. Furthermore, front-wheel drive vehicles tend to wear the front tires at a greater rate compared to the rears. Tire rotation is the procedure of moving tires to different car positions, such as front-to-rear, in order to even out the wear, thereby extending the life of the tire.

Wheel alignment

When mounted on the vehicle, the wheel and tire may not be perfectly aligned to the direction of travel, and therefore may exhibit irregular wear. If the discrepancy in alignment is large, then the irregular wear will become quite substantial if left uncorrected.

Wheel alignment is the procedure for checking and correcting this condition through adjustment of camber, caster and toe angles. These settings also affect the handling characteristics of the vehicle.

Retread

Tires that are fully worn can be re-manufactured to replace the worn tread. This is known as retreading or recapping, a process of buffing away the worn tread and applying a new tread. Retreading is economical for truck tires because the cost of replacing the tread is less than the price of a new tire. Retreading passenger tires is less economical because the cost of retreading is high compared to the price of new cheap tires, but favorable compared to high-end brands.

Worn tires can be retreaded by two methods, the mold or hot cure method and the pre-cure or cold one. The mold cure method involves the application of raw rubber on the previously buffed and prepared casing, which is later cured in matrices. During the curing period, vulcanization takes place and the raw rubber bonds to the casing, taking the tread shape of the matrix. On the other hand, the pre-cure method involves the application of a ready-made tread band on the buffed and prepared casing, which later is cured in an autoclave so that vulcanization can occur.

During the retreading process, retread technicians must ensure the casing is in the best condition possible, in order to minimize the possibility of a casing failure. Casings with problems such as capped tread, tread separation, unrepairable cuts, corroded belts or sidewall damage, or any run-flat or skidded tires, will be rejected.

In most situations, retread tires can be driven under the same conditions and at the same speeds as new tires with no loss in safety or comfort. The percentage of retread failures should be about the same as for new tire failures, but many drivers, including truckers, are guilty of not maintaining proper air pressure on a regular basis, and, if a tire is abused (overloaded, underinflated, or mismatched to the other tire on a set of duals), then that tire (new or recapped) will fail.

Many commercial trucking companies put retreads only on trailers, using only new tires on their steering and drive wheels. This procedure increases the driver's chance of maintaining control in case of problems with a retreaded tire.

SPARK PLUG

Spark plug with single-ground electrode.

In 1860 Étienne Lenoir used an electric spark plug in his first internal combustion engine and is generally credited with the invention of the spark plug.

Early patents for spark plugs included those by Nikola Tesla (in U.S. Patent 609,250 for an ignition timing system, 1898), Frederick Richard Simms (GB 24859/1898, 1898) and Robert Bosch (GB 26907/1898). But only the invention of the first commercially viable high-voltage spark plug as part of a magneto-based ignition system by Robert Bosch's engineer Gottlob Honold in 1902 made possible the development of the internal combustion engine. Subsequent manufacturing improvements can also be credited to Albert Champion, the Lodge brothers, sons of Sir Oliver Joseph Lodge, who developed and manufactured their father's idea and also Kenelm Lee Guinness, of the Guinness brewing family, who developed the KLG brand.

A spark plug (very rarely in British English: a sparking plug) is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.

Spark plugs have an insulated central electrode which is connected by a heavily insulated wire to an ignition coilmagneto circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark gap inside the cylinder. or

Reciprocating internal combustion engines can be divided into spark-ignition engines, which require spark plugs to initiate combustion, and compression-ignition engines (diesel engines), which compress the air and then inject diesel fuel into the heated compressed air mixture where it autoignites.

Spark plugs may also be used in other applications such as furnaces where a combustible mixture should be ignited. In this case, they are sometimes referred to as flame igniters.

Components of a typical, four stroke cycle, DOHC piston engine.

(E) Exhaust camshaft, (I) Intake camshaft,

(S) Spark plug, (V) Valves, (P) Piston,

 (R) Connecting rod, (C) Crankshaft,

(W) Water jacket for coolant flow.

Operation

The plug is connected to the high voltage generated by an ignition coil or magneto. As the electrons flow from the coil, a voltage difference develops between the central electrode and side electrode. No current can flow because the fuel and air in the gap is an insulator, but as the voltage rises further, it begins to change the structure of the gases between the electrodes. Once the voltage exceeds the dielectric strength of the gases, the gases become ionized. The ionized gas becomes a conductor and allows electrons to flow across the gap. Spark plugs usually require voltage of 12,000–25,000 volts or more to 'fire' properly, although it can go up to 45,000 volts. They supply higher current during the discharge process resulting in a hotter and longer-duration spark.
As the current of electrons surges across the gap, it raises the temperature of the spark channel to 60,000 K. The intense heat in the spark channel causes the ionized gas to expand very quickly, like a small explosion. This is the "click" heard when observing a spark, similar to lightning and thunder.
The heat and pressure force the gases to react with each other, and at the end of the spark event there should be a small ball of fire in the spark gap as the gases burn on their own. The size of this fireball or kernel depends on the exact composition of the mixture between the electrodes and the level of combustion chamber turbulence at the time of the spark. A small kernel will make the engine run as though the ignition timing was retarded, and a large one as though the timing was advanced.

Parts of the Plug

Diagram of single-ground spark plug.

• Terminal : The top of the spark plug contains a terminal to connect to the ignition system.
• Insulator : Its major function is to provide mechanical support for the central electrode, while insulating  the high voltage.
• Ribs : to improve the electrical insulation and prevent electrical energy from leaking along the insulator surface from the terminal to the metal case.
• Insulator Tip : must resist high temperatures while retaining electrical insulation.
• Seals :  the seals ensure there is no leakage from the combustion chamber.
• Metal Case :  serves to remove heat from the insulator and pass it on to the cylinder head, and acts as the ground for the sparks passing through the central electrode to the side electrode.
• Central Electrode : The central electrode is usually the one designed to eject the electrons (the cathode) because it is the hottest (normally) part of the plug.
• Side Elektrode : Some designs have provided a copper core to this electrode, so as to increase heat conduction.

SPLIT-SINGLE

Post WWII arrangement,

carburettor to the front under the exhaust (neither visible).

Transfer port visible at back.

One connecting rod 'piggy-backed' on another.

 The split-single (Doppelkolbenmotor to its German and Austrian manufacturers), is a variant on the two-stroke engine with two cylinders sharing a single combustion chamber.

There have been "single" (ie twin-bore) and "twin" (ie four bore) models and several important internal developments, the last of them being obvious externally too, with the carburettor (uniquely amongst motorcycles) moving to the front of the engine under the exhaust.

The split-single system sends the intake fuel-air mixture up one bore to the combustion chamber, sweeping the exhaust gases down the other bore and out of the exposed exhaust port. The split-single two-stroke thus delivers better economy than the common forms of two-stroke and runs better at small throttle openings, at the cost of a heavier engine.

In the 60 year history of this arrangement there were two important variants, earlier versions have a single, Y-shaped or V-shaped connecting rod and these look much like a regular single cylinder two-stroke engine with a single exhaust, a single carburettor in the usual place behind the cylinders and a single sparkplug. Racing versions of this design can be mistaken for a regular twin-cylinder, since they had two exhausts or two carburettors but these are actually connected to a single bore in an engine with a single combustion chamber. Some models, including those in mass-production, used two spark-plugs igniting one combustion chamber.

After World War II, more sophisticated internal mechanisms improved mechanical reliability and led to the carburettor being placed in front of the barrel, tucked under and to the side of the exhaust. This is the arrangement seen in the United States and marketed by Sears as the Twingle.

For modern vehicle taxation purposes the split-single suffers no penalty and offers no advantage, as only the swept volume is considered, not the number of cylinders or spark plugs. This remains true even if the two pistons are not the same size and have different strokes (mechanically possible, if rarely used). This simple calculation was not always the case (see Tax horsepower, as used in the UK and some European countries in the 1920s and 1930s).
Lubrication weaknesses of the early "side-by-side" versions with the carburettor in the "normal" place behind the cylinder, were substantially the same as with all other two-strokes running on the same "petro-oil" mixture. However, they were greatly eased in the later ones, since the cool, lubricated mixture is delivered straight onto the hot (exhaust side) of the hotter, exhaust piston from the carburettor at the front of the engine under the exhaust.
Lubrication weaknesses of the early "side-by-side" versions with the carburettor in the "normal" place behind the cylinder, were substantially the same as with all other two-strokes running on the same "petro-oil" mixture. However, they were greatly eased in the later ones, since the cool, lubricated mixture is delivered straight onto the hot (exhaust side) of the hotter, exhaust piston from the carburettor at the front of the engine under the exhaust.

TWO-STROKE ENGINE

A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft (an up stroke and a down stroke of the piston, compared to twice that number for a four-stroke engine). This is accomplished by using the end of the combustion stroke and the beginning of the compression stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way, two-stroke engines often provide high specific power, at least in a narrow range of rotational speeds. The functions of some or all of the valves required by a four-stroke engine are usually served in a two-stroke engine by ports that are opened and closed by the motion of the piston(s), greatly reducing the number of moving parts. Gasoline (spark ignition) versions are particularly useful in lightweight (portable) applications, such as chainsaws, and the concept is also used in diesel compression ignition engines in large and weight insensitive applications, such as ships and locomotives.

Invention of the two-stroke cycle is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.

The two-stroke engine was very popular throughout the 20th century in motorcycles and small-engined devices, such as chainsaws and outboard motors, and was also used in some cars, a few tractors and many ships. Part of their appeal was their simple design (and resulting low cost) and often high power-to-weight ratio. Many designs use total-loss lubrication, with the oil being burned in the combustion chamber, causing "blue smoke" and other types of exhaust pollution. This is a major reason for two-stroke engines being replaced by four-stroke engines in many applications.

Two-stroke engines continue to be commonly used in high-power, handheld applications such as string trimmers and chainsaws. The light overall weight, and light-weight spinning parts give important operational and even safety advantages. For example, only a two-stroke engine that uses a gasoline-oil mixture can power a chainsaw operating in any position.

These engines are still used for small, portable, or specialized machine applications such as outboard motors, high-performance, small-capacity motorcycles, mopeds, underbones, scooters, tuk-tuks, snowmobiles, karts, ultralights, model airplanes (and other model vehicles) and lawnmowers. The two-stroke cycle is used in many diesel engines, most notably large industrial and marine engines, as well as some trucks and heavy machinery.

A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab and German manufacturers DKW and Auto-Union. The Japanese manufacturer Suzuki did the same in the 1970s. Production of two-stroke cars ended in the 1980s in the West, but Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Lotus of Norfolk, UK, has a prototype direct-injection two-stroke engine intended for alcohol fuels called the Omnivore which it is demonstrating in a version of the Exige.

two-stroke engine

 

The intake pathway is opened and closed by a rotating member. A familiar type sometimes seen on small motorcycles is a slotted disk attached to the crankshaft which covers and uncovers an opening in the end of the crankcase, allowing charge to enter during one portion of the cycle.
Another form of rotary inlet valve used on two-stroke engines employs two cylindrical members with suitable cutouts arranged to rotate one within the other - the inlet pipe having passage to the crankcase only when the two cutouts coincide. The crankshaft itself may form one of the members, as in most glow plug model engines. In another embodiment, the crank disc is arranged to be a close-clearance fit in the crankcase, and is provided with a cutout which lines up with an inlet passage in the crankcase wall at the appropriate time, as in the Vespa motor scooter.
The advantage of a rotary valve is it enables the two-stroke engine's intake timing to be asymmetrical, which is not possible with piston port type engines. The piston port type engine's intake timing opens and closes before and after top dead center at the same crank angle, making it symmetrical, whereas the rotary valve allows the opening to begin earlier and close earlier.
Rotary valve engines can be tailored to deliver power over a wider speed range or higher power over a narrower speed range than either piston port or reed valve engine. Where a portion of the rotary valve is a portion of the crankcase itself, it is particularly important that no wear is allowed to take place.

The Two-stroke cycle
1=TDC
2=BDC
 A: intake/scavenging 
 B: Exhaust 
 C: Compression 
 D: Expansion(power) 

 This method of scavenging uses carefully shaped and positioned transfer ports to direct the flow of fresh mixture toward the combustion chamber as it enters the cylinder. The fuel/air mixture strikes the cylinder head, then follows the curvature of the combustion chamber, and then is deflected downward. This not only prevents the fuel/air mixture from traveling directly out the exhaust port, but also creates a swirling turbulence which improves combustion efficiency, power and economy. Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme (above). Often referred to as "Schnuerle" (or "Schnürl") loop scavenging after the German inventor of an early form in the mid 1920s, it became widely adopted in that country during the 1930s and spread further afield after World War II. Loop scavenging is the most common type of fuel/air mixture transfer used on modern two-stroke engines. Suzuki was one of the first manufacturers outside of Europe to adopt loop-scavenged two-stroke engines. This operational feature was used in conjunction with the expansion chamber exhaust developed by German motorcycle manufacturer, MZ and Walter Kaaden. Loop scavenging, disc valves and expansion chambers worked in a highly coordinated way to significantly increase the power output of two-stroke engines, particularly from the Japanese manufacturers Suzuki, Yamaha and Kawasaki. Suzuki and Yamaha enjoyed success in grand Prix motorcycle racing in the 1960s due in no small way to the increased power afforded by loop scavenging. An additional benefit of loop scavenging was the piston could be made nearly flat or slightly dome shaped, which allowed the piston to be appreciably lighter and stronger, and consequently to tolerate higher engine speeds. The "flat top" piston also has better thermal properties and is less prone to uneven heating, expansion, piston seizures, dimensional changes and compression losses.
SAAB built 750 and 850 cc 3-cylinder engines based on a DKW design that proved reasonably successful employing loop charging. The original SAAB 92 had a two-cylinder engine of comparatively low efficiency. At cruising speed, reflected wave exhaust port blocking occurred at too low a frequency. Using the asymmetric three-port exhaust manifold employed in the identical DKW engine improved fuel economy. The 750 cc standard engine produced 36 to 42 hp, depending on the model year. The Monte Carlo Rally variant, 750 cc (with a filled crankshaft for higher base compression), generated 65 hp. An 850 cc version was available in the 1966 SAAB Sport (a standard trim model in comparison to the deluxe trim of the Monte Carlo). Base compression comprises a portion of the overall compression ratio of a two-stroke engine.

SIX-STROKE ENGINE

The six-stroke engine is a type of internal combustion engine based on the four-stroke engine, but with additional complexity intended to make it more efficient and reduce emissions. Two different types of six-stroke engine have been developed since the 1990s:

In the first approach, the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to power an additional power and exhaust stroke of the piston in the same cylinder. Designs use either steam or air as the working fluid for the additional power stroke. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel. There are two power strokes: one with fuel, the other with steam or air. The currently notable designs in this class are the Crower six-stroke engine, invented by Bruce Crower of the U.S. ; the Bajulaz engine by the Bajulaz S.A. company of Switzerland; and the Velozeta Six-stroke engine built by the College of Engineering, at Trivandrum in India.

The second approach to the six-stroke engine uses a second opposed piston in each cylinder that moves at half the cyclical rate of the main piston, thus giving six piston movements per cycle. Functionally, the second piston replaces the valve mechanism of a conventional engine but also increases the compression ratio. The currently notable designs in this class include two designs developed independently: the Beare Head engine, invented by Australian Malcolm Beare, and the German Charge pump, invented by Helmut Kottmann.

The M4+2 engine working cycle animation

The term "Six Stroke" was coined by the inventor of the Beare Head, Malcolm Beare. The technology combines a four stroke engine bottom end with an opposed piston in the cylinder head working at half the cyclical rate of the bottom piston. Functionally, the second piston replaces the valve mechanism of a conventional engine. first use of "sixstroke" 1994.

The M4+2 engines have much in common with the Beare Head engines, combining two opposed pistons in the same cylinder. One piston working at half the cyclical rate of the other. But while the main function of the second piston in a Beare Head engine is to replace the valve mechanism of a conventional four stroke engine, the M4+2 take the principle one step further.

The working principle of the engine is explained in the Two- and four-stroke engines article.