A poppet valve is a valve typically used to control the timing and quantity of gas or vapour flow into an engine. It consists of a hole, usually round or oval, the portion of the hole where the plug meets with it is referred to as the seat or valve seat. The shaft guides the plug portion by sliding through a valve guide, in exhaust applications a pressure differential helps to seal the valve and in intake valves a pressure differential helps open it. Poppet valves date from at least the 1770s, when James Watt used them on his steam engines, the word poppet shares etymology with puppet, it is from the Middle English popet, from Middle French poupette, which is a diminutive of poupée. The use of the poppet to describe a valve comes from the same word applied to marionettes. In the past, puppet valve was a synonym for poppet valve, the main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication. In most cases it is beneficial to have a balanced poppet in a direct-acting valve, less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces.
However, they are most well known for their use in combustion and steam engines. Presta and Schrader valves used on pneumatic tyres are examples of poppet valves, the Presta valve has no spring and relies on a pressure differential for opening and closing while being inflated. Poppet valves are employed extensively in the launching of torpedoes from submarines, poppet valves are used in most piston engines to open and close the intake and exhaust ports in the cylinder head. The valve is usually a disk of metal with a long rod known as the valve stem attached to one side. The stem is used to push down on the valve to open it, at high revolutions per minute, the inertia of the spring means it cannot respond quickly enough to return the valve to its seat between cycles, leading to valve float. The engine normally operates the valves by pushing on the stems with cams, the shape and position of the cam determines the valve lift and when and how quickly the valve is opened. The cams are normally placed on a camshaft which is geared to the crankshaft.
On high-performance engines, the camshaft is movable and the cams have a height so, by axially moving the camshaft in relation with the engine RPM. For certain applications the valve stem and disk are made of different steel alloys, or the stem may be hollow and filled with sodium to improve heat transport. Although a better conductor, an aluminium cylinder head requires steel valve seat inserts. Such a condition occurs when changing gear, five valve designs are in use
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part. An early cam was built into Hellenistic water-driven automata from the 3rd century BC, the camshaft was described in Turkey by Al-Jazari in 1206. He employed it as part of his automata, water-raising machines, the cam and camshaft appeared in European mechanisms from at least the 14th century, or possibly earlier. In internal combustion engines with pistons, the camshaft is used to operate poppet valves and it consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes protruding from it, one for each valve. The cam lobes force the valves open by pressing on the valve, or on some intermediate mechanism, Camshafts can be made out of several types of material. These include, Chilled iron castings, Commonly used in volume production. Other elements are added to the iron casting to make the material more suitable for its application. Billet Steel, When a high quality camshaft or low volume production is required, engine builders and this is a much more time consuming process, and is generally more expensive than other methods.
However, the product is far superior. CNC lathes, CNC milling machines, and CNC camshaft grinders will be used during production, different types of steel bar can be used, one example being EN40b. When manufacturing a camshaft from EN40b, the camshaft will be heat treated via gas nitriding and it gives a surface hardness of 55-60 HRC. These types of camshafts can be used in high-performance engines, the relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. Since the valves control the flow of the air/fuel mixture intake and exhaust gases, for this reason, the camshaft is connected to the crankshaft either directly, via a gear mechanism, or indirectly via a belt or chain called a timing belt or timing chain. Direct drive using gears is unusual because of the cost, the frequently reversing torque caused by the slope of the cams tends to cause gear rattle which for an all-metal gear train requires further expense of a cam damper. Rolls-Royce V8 used gear drive as, unlike chain, it could be made silent, where gears are used in cheaper cars, they tend to be made from resilient fibre rather than metal, except in racing engines that have a high maintenance routine.
Fibre gears have a life span and must be replaced regularly. In some designs the camshaft drives the distributor and the oil, some vehicles may have the power steering pump driven by the camshaft. With some early fuel injection systems, cams on the camshaft would operate the fuel injectors, honda redesigned the VF750 motorcycle from chain drive to the gear drive VFR750 due to insurmountable problems with the VF750 Hi-Vo inverted chain drive
The sleeve valve is a type of valve mechanism for piston engines, distinct from the usual poppet valve. Sleeve valve engines saw use in a number of pre-World War II luxury cars and in the United States in the Willys-Knight car, a sleeve valve takes the form of one or more machined sleeves. It fits between the piston and the wall in the cylinder of an internal combustion engine where it rotates and/or slides. Ports in the side of the sleeves come into alignment with the cylinders inlet, the first successful sleeve valve was patented by Charles Yale Knight, and used twin alternating sliding sleeves. It was used in luxury automobiles, notably Willys, Mercedes-Benz, Panhard, Peugeot. Mors adopted double sleeve-valve engines made by Minerva. The higher oil consumption was heavily outweighed by the quietness of running, early poppet-valve systems required decarbonization at very low mileages. A small number of used a cuff sleeve in the cylinder head instead of the cylinder proper. This design had the advantage of not having the piston within the sleeve, on the downside, this arrangement limited the size of the ports to that of the cylinder head, whereas in-cylinder sleeves could have much larger ports.
The main advantages of the engine are, High volumetric efficiency due to very large port openings. Sir Harry Ricardo demonstrated better mechanical and thermal efficiency, the size of the ports can be readily controlled. Good exhaust scavenging and controllable swirl of the inlet air/fuel mixture in single-sleeve designs, when the intake ports open, the air/fuel mixture can be made to enter tangentially to the cylinder. A problem with high-speed engines that use poppet valves is that as engine speed increases, the speed at which the valve moves has to increase. This in turn increases the loads involved due to the inertia of the valve, large poppet valves that allow good air-flow have considerable mass and require a strong spring to overcome their inertia when closing. At higher engine speeds, the spring may be unable to close the valve before the next opening event. This effect, called valve float can result in the valve being struck by the top of the rising piston. In addition, push-rods, and valve rockers can be eliminated in a sleeve valve design, in an aircraft engine, this provided desirable reductions in weight and complexity.
Longevity, as demonstrated in early applications of the Knight engine. Prior to the advent of leaded gasolines, poppet-valve engines typically required grinding of the valves, Sleeve valves did not suffer from the wear and recession caused by the repetitive impact of the poppet valve against its seat
A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels. In most petrol engines, the fuel and air are usually pre-mixed before compression, the process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed, and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites. The first practical petrol engine was built in 1876 in Germany by Nikolaus August Otto, although there had been attempts by Étienne Lenoir, Siegfried Marcus, Julius Hock. The first petrol engine was prototyped in 1882 in Italy by Enrico Bernardi. British engineer Edward Butler constructed the first petrol combustion engine. Butler invented the spark plug, ignition magneto, coil ignition and spray jet carburetor, with both air and fuel in a closed cylinder, compressing the mixture too much poses the danger of auto-ignition — or behaving like a diesel engine.
Spark plugs are typically set statically or at idle at a minimum of 10 degrees or so of crankshaft rotation before the piston reaches T. D, higher octane petrol burns slower, therefore it has a lower propensity to auto-ignite and its rate of expansion is lower. Thus, engines designed to run high-octane fuel exclusively can achieve higher compression ratios, Petrol engines run at higher rotation speeds than diesels, partially due to their lighter pistons, connecting rods and crankshaft and due to petrol burning more quickly than diesel. However the lower compression ratios of petrol engines give petrol engines lower efficiency than diesel engines, Bedford OB bus Bedford M series lorry GE 57-ton gas-electric boxcab locomotive Petrol engines may run on the four-stroke cycle or the two-stroke cycle. For details of working cycles see, Four-stroke cycle Two-stroke cycle Wankel engine Common cylinder arrangements are from 1 to 6 cylinders in-line or from 2 to 16 cylinders in V-formation. Flat engines – like a V design flattened out – are common in airplanes and motorcycles and were a hallmark of Volkswagen automobiles into the 1990s.
Flat 6s are still used in many modern Porsches, as well as Subarus, less common, but notable in vehicles designed for high speeds is the W formation, similar to having 2 V engines side by side. Alternatives include rotary and radial engines the latter typically have 7 or 9 cylinders in a single ring, Petrol engines may be air-cooled, with fins, or liquid-cooled, by a water jacket and radiator. The coolant was formerly water, but is now usually a mixture of water and either ethylene glycol or propylene glycol, the cooling system is usually slightly pressurized to further raise the boiling point of the coolant. Petrol engines use spark ignition and high current for the spark may be provided by a magneto or an ignition coil. In modern car engines the ignition timing is managed by an electronic Engine Control Unit, the most common way of engine rating is what is known as the brake power, measured at the flywheel, and given in kilowatts or horsepower. This is the mechanical power output of the engine in a usable
A crank is an arm attached at a right angle to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to convert circular motion into reciprocating motion, or vice versa, the arm may be a bent portion of the shaft, or a separate arm or disk attached to it. Attached to the end of the crank by a pivot is a rod, the end of the rod attached to the crank moves in a circular motion, while the other end is usually constrained to move in a linear sliding motion. The term often refers to a crank which is used to manually turn an axle, as in a bicycle crankset or a brace. In this case a persons arm or leg serves as the connecting rod, there is usually a bar perpendicular to the other end of the arm, often with a freely rotatable handle or pedal attached. Familiar examples include, Mechanical pencil sharpener Fishing reel and other reels for cables, ropes, manually operated car window The carpenters brace is a compound crank. The crank set that drives a handcycle through its handles, the crankset that drives a bicycle via the pedals.
Treadle sewing machine Almost all reciprocating engines use cranks to transform the motion of the pistons into rotary motion. The cranks are incorporated into a crankshaft, the displacement of the end of the connecting rod is approximately proportional to the cosine of the angle of rotation of the crank, when it is measured from top dead center. The mechanical advantage of a crank, the ratio between the force on the rod and the torque on the shaft, varies throughout the cranks cycle. The relationship between the two is approximately, τ = F r sin where τ is the torque and F is the force on the connecting rod. But in reality, the torque is maximum at crank angle of less than α = 90° from TDC for a force on the piston. One way to calculate this angle is to find out when the Connecting rod smallend speed becomes the fastest in downward direction given a steady crank rotational velocity. 17615° after TDC. Then, using the sine law, it is found that the crank to connecting rod angle is 88. 21738°.
When the crank is driven by the rod, a problem arises when the crank is at top dead centre or bottom dead centre. At these points in the cycle, a force on the connecting rod causes no torque on the crank. Therefore, if the crank is stationary and happens to be at one of two points, it cannot be started moving by the connecting rod. The eccentrically mounted handle of the rotary handmill which appeared in 5th century BC Celtiberian Spain, a Roman iron crank of yet unknown purpose dating to the 2nd century AD was excavated in Augusta Raurica, Switzerland
A crankshaft—related to crank—is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion, whereas in a reciprocating compressor, a Roman iron crank of yet unknown purpose dating to the 2nd century AD was excavated in Augusta Raurica, Switzerland. The 82.5 cm long piece has fitted to one end a 15 cm long bronze handle, the accompanying inscription is in Greek. The crank and connecting rod mechanisms of the other two archaeologically attested sawmills worked without a gear train, al-Jazari described a crank and connecting rod system in a rotating machine in two of his water-raising machines. His twin-cylinder pump incorporated a crankshaft, though the device was unnecessarily complex, the Italian physician Guido da Vigevano, planning for a new crusade, made illustrations for a paddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels.
In Renaissance Italy, the earliest evidence of a crank and connecting-rod is found in the sketch books of Taccola. A sound grasp of the motion involved is demonstrated a little by Pisanello. One of the drawings of the Anonymous of the Hussite Wars shows a boat with a pair of paddle-wheels at each end turned by men operating compound cranks. Crankshafts were described by Konrad Kyeser, Leonardo da Vinci and his wind-powered sawmill used a crankshaft to convert a windmills circular motion into a back-and-forward motion powering the saw. Corneliszoon was granted a patent for his crankshaft in 1597, large engines are usually multicylinder to reduce pulsations from individual firing strokes, with more than one piston attached to a complex crankshaft. Many small engines, such as found in mopeds or garden machinery, are single cylinder and use only a single piston. A crankshaft is subjected to stresses, potentially equivalent of several tonnes of force. The crankshaft is connected to the fly-wheel, the block, using bearings on the main journals.
An engine loses up to 75% of its energy in the form of friction and vibration in the crankcase. The remaining losses occur in the heat and blow by. The crankshaft has a linear axis about which it rotates, typically with several bearing journals riding on replaceable bearings held in the engine block. As the crankshaft undergoes a great deal of sideways load from each cylinder in an engine, it must be supported by several such bearings. This was a factor in the rise of V8 engines, with their shorter crankshafts, the long crankshafts of the latter suffered from an unacceptable amount of flex when engine designers began using higher compression ratios and higher rotational speeds
Hydrolock occurs when a volume of liquid greater than the volume of the cylinder at its minimum enters the cylinder. Since liquids are nearly incompressible the piston cannot complete its travel, if an engine hydrolocks while at speed, a mechanical failure is likely. Common damage modes include bent or broken connecting rods, a crank, a fractured head. Forces absorbed by other interconnected components may cause additional damage, physical damage to metal parts can manifest as a crashing or screeching sound and usually requires replacement of the engine or a substantial rebuild of its major components. If an internal combustion engine hydrolocks while idling or under low power conditions, in this case the engine can often be purged by unscrewing the spark plugs or injectors and spinning the engine to expel the liquid from the combustion chambers and restarted. If a cylinder fills with liquid while the engine is turned off, since the starter mechanisms torque is normally much lower than the engines operating torque and momentum this will usually not damage the engine but may burn out the starter.
The engine can be drained as above and restarted, if a corrosive substance such as water has been in the engine long enough to cause rusting, more extensive repairs will be required. Amounts of water significant enough to cause hydrolock tend to upset the air/fuel mixture in gasoline engines, if water is introduced slowly enough, this effect can cut power and speed in an engine to a point that when hydrolock actually occurs it does not cause catastrophic engine damage. Hydrolock most commonly occurs in automobiles when driving through floods, either where the water is above the level of the air intake or the speed is excessive. A vehicle fitted with an air intake mounted low on the vehicle will be especially vulnerable to hydrolocking when being driven through standing water or heavy precipitation. Engine coolant entering the cylinders through various means is another common cause, excessive fuel entering one or more cylinders in liquid form due to abnormal operating conditions can cause hydrolock.
Small boats with engines and PWCs tend to ingest water simply because they run in. During a rollover, or when a wave washes over the craft, its engine can hydrolock, though damage is rare due to the special air intakes. Inboard marine engines have a different vulnerability as these often have their cooling water mixed with the exhaust gases in the header to quiet the engine. Rusted out exhaust headers or lengthy periods of turning the starter can cause water to build up in the exhaust line to the point it back-flows through the exhaust manifold, diesel engines are more susceptible to hydrolock than gasoline engines. Due to their higher compression ratios, diesel engines have a smaller final combustion chamber volume. Diesel engines tend to have higher torque, rotating inertia, the result is that a diesel engine is more likely to suffer catastrophic damage. Hydrolock is common on radial and inverted engines when the engine sits for a long period, engine oil seeps down under gravity into the cylinder through various means and can fill a cylinder with enough oil to hydrolock it
The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine. This is achieved by sparking of the plugs in a gasoline engine in the correct order. In a gasoline engine, the firing order is obtained by the correct placement of the spark plug wires on the distributor. In a modern engine with a direct ignition and the Engine Control Unit or Engine Management system takes care of the firing sequence. Especially on cars with distributors, the order is usually cast on the engine somewhere, most often on the cylinder head. In these applications, the order is shown in a reverse order. For the most common configurations, this gives firing orders of 1-3-2, 1-2-4-3. In addition to the reconfiguration of the wires or injector tubes. When referring to cars, the side of the car is the side that corresponds with the drivers left. It can be thought of as the side that would be on the left if one was standing directly behind the car looking at it, the front of the engine may point towards the front, side or rear of the car.
In most rear-wheel drive cars, the engine is longitudinally mounted, in front-wheel drive cars with a transverse engine, the front of the engine usually points towards the right-hand side of the car. One notable exception is Honda, where many models have the front of the engine at the side of the car. One notable car with this layout is the Citroën Traction Avant, in a straight engine the spark plugs are numbered, starting with #1, usually from the front of the engine to the rear. In a radial engine the cylinders are numbered around the circle, in a V engine, cylinder numbering varies among manufacturers. To further complicate matters, manufacturers may not have used the system for all of their engines. It is important to check the system used before comparing firing orders. As an example, the Chevrolet Small-Block engine has cylinders 1-3-5-7 on the hand side of the car, and 2-4-6-8 on the other side. Note that the order alternates irregularly between the left and right banks, this is what causes the sound of this type of engine
Overhead valve engine
An overhead valve engine is an engine in which the valves are placed in the cylinder head. This was an improvement over the flathead engine, where the valves were placed in the block next to the piston. Overhead camshaft engines, while overhead valve by definition, are usually categorized apart from other OHV engines. Lifters or tappets are located in the block between the camshaft and pushrods. By contrast, overhead camshaft design avoids the use of pushrods by putting the camshaft directly above the valves in the cylinder head, in 1900, Marr was hired as chief engineer at the Buick Auto-Vim and Power Company in Detroit, where he worked until 1902. Marr said he got the idea of overhead valves when making the small tricycle engine, marrs engine employed pushrod-actuated rocker arms, which in turn pushed valves parallel to the pistons, and this is still in use today. This contrasts with previous designs which use of side valves. Marr left Buick briefly to start his own company in 1902, the Marr Auto-Car.
The OHV engine was patented in 1902 by Buicks second chief engineer Eugene Richard, at the Buick Manufacturing Company, precursor to the Buick Motor Company. The worlds first production overhead valve engine was put into the first production Buick automobile, the 1904 Model B, the engine was designed by Marr and David Buick. Eugene Richard of the Buick Manufacturing Company was awarded US Patent #771,095 in 1904 for the valve in head engine. Arthur Chevrolet was awarded US Patent #1,744,526 for an adapter that could be applied to an existing engine, in 1949, Oldsmobile introduced the Rocket V8. It was the first high-compression I-head design, and is the archetype for most modern pushrod engines, general Motors is the worlds largest pushrod engine producer, producing both I4, V6 and V8 pushrod engines. Nowadays, automotive use of side-valves has virtually disappeared, and valves are almost all overhead, most are now driven more directly by the overhead camshaft system. Few pushrod-type engines remain in production outside of the United States market and this is in part a result of some countries passing laws to tax engines based on displacement, because displacement is somewhat related to the emissions and fuel efficiency of an automobile.
This has given OHC engines a regulatory advantage in those countries, however, in 2002, Chrysler introduced a new pushrod engine, a 5. 7-litre Hemi engine. The new Chrysler Hemi engine presents advanced features such as variable displacement technology and has been an option with buyers. The Hemi was on the Wards 10 Best Engines list for 2003 through 2007, Chrysler produced the worlds first production variable-valve OHV engine with independent intake and exhaust phasing
In general mechanical terms, the word desmodromic is used to refer to mechanisms that have different controls for their actuation in different directions. A desmodromic valve is an engine valve that is positively closed by a cam and leverage system. The valves in a typical four-stroke engine allow the mixture into the cylinder at the beginning of the cycle. In a conventional four-stroke engine valves are opened by a cam, an engine using desmodromic valves has two cams and two actuators, each for positive opening and closing without a return spring. The word comes from the Greek words desmos and dromos and this denotes the major characteristic of the valves being continuously bound to the camshaft. The common valve spring system is satisfactory for traditional mass-produced engines that do not rev highly and are of a design that requires low maintenance, at the period of initial desmodromic development, valve springs were a major limitation on engine performance because they would break from metal fatigue.
Vacuum melt processes developed in the 1950s helped remove impurities in the used to make valve springs. The desmodromic system was devised to remedy this problem, fully controlled valve movement was conceived during the earliest days of engine development, but devising a system that worked reliably and was not overly complex took a long time. Desmodromic valve systems are first mentioned in patents in 1896 by Gustav Mees, the 1914 Grand Prix Delage and Nagant used a desmodromic valve system. The Mercedes-Benz W196 Formula One racing car of 1954-1955, and the Mercedes-Benz 300SLR sports racing car of 1955 both had desmodromic valve actuation. In 1956, Fabio Taglioni, a Ducati engineer, developed a desmodromic valve system for the Ducati 125 Grand Prix and he was quoted to say, The specific purpose of the desmodromic system is to force the valves to comply with the timing diagram as consistently as possible. In this way, any lost energy is negligible, the curves are more uniform. The engineers that came after him continued that development, and Ducati held a number of patents relating to desmodromics, Desmodromic valve actuation has been applied to top-of-the-range production Ducati motorcycles since 1968, with the introduction of the widecase Mark 3 single cylinders.
In 1959, the Maserati brothers introduced one of their final designs, in modern engines, valve spring failure at high RPM has been mostly remedied. The main benefit of the system is the prevention of valve float at high rpm. In traditional sprung-valve actuation, as speed increases, the momentum of the valve will eventually overcome the springs ability to close it completely before the piston reaches TDC. This can lead to several problems and most damaging, the piston collides with the valve and both are destroyed. Second, the valve does not completely return to its seat before combustion begins and this allows combustion gases to escape prematurely, leading to a reduction in cylinder pressure which causes a major decrease in engine performance
A solenoid is a coil wound into a tightly packed helix. The term was invented by French physicist André-Marie Ampère to designate a helical coil, a solenoid is a type of electromagnet when the purpose is to generate a controlled magnetic field. If the purpose of the solenoid is instead to changes in the electric current. Not all electromagnets and inductors are solenoids, for example, the first electromagnet, in engineering, the term may refer to a variety of transducer devices that convert energy into linear motion. Solenoid bolts, a type of locking mechanism, exist. An infinite solenoid is a solenoid with infinite length but finite diameter, in short, the magnetic field inside an infinitely long solenoid is homogeneous and its strength neither depends on the distance from the axis, nor on the solenoids cross-sectional area. This is a derivation of the flux density around a solenoid that is long enough so that fringe effects can be ignored. In Figure 1, we know that the flux density vector points in the positive z direction inside the solenoid.
We confirm this by applying the right hand rule for the field around a wire. If we wrap our right hand around a wire with the thumb pointing in the direction of the current, since we are dealing with a long solenoid, all of the components of the magnetic field not pointing upwards cancel out by symmetry. Outside, a similar cancellation occurs, and the field is pointing downwards. Now consider the imaginary loop c that is located inside the solenoid, by Ampères law, we know that the line integral of B around this loop is zero, since it encloses no electrical currents. We have shown above that the field is pointing upwards inside the solenoid, thus the integral of the up side 1 is equal to the integral of the down side 2. Note, that prohibits it from varying longitudinally. A similar argument can be applied to the loop a to conclude that the field outside the solenoid is radially uniform or constant, an intuitive argument can be used to show that the flux density outside the solenoid is actually zero.
Magnetic field lines only exist as loops, they diverge from or converge to a point like electric field lines can. The magnetic field lines follow the path of the solenoid inside. However, the volume outside the solenoid is much greater than the volume inside, now recall that the field outside is constant