Many people do not understand motorcycles and cannot distinguish a sports bike from a motocross bike and decided to write a post so that people can distinguish enduro from cross, sport from classic, etc.
Types of motorcycles
Nowadays, there are a huge number of types of motorcycles. In each form, as a rule, there are many varieties. Some modern motorcycle models cannot be attributed to one specific type at all. Let's take a look at the main types of motorcycles to make it easier for you to choose the right one for you.
Classic
A classic motorcycle is a time-tested design and layout, a straight fit and low maintenance, reliability and ease of use. Outwardly, it may look a bit like a chopper, but not with such an imposing driver's position and tons of chrome, and a sports bike, only with quieter engine characteristics and long traction gears.
Sport bike
We say "sport bike" - we mean "power-to-weight ratio", the motto of the structures is maximum power with minimum weight. The rest is on the side. Why worry about dragging on the bottom, if the motor of a sportbike "loves to live" in a mode when the arrow is at the red line of the tachometer. This is a high-end technical thought of the motorcycle industry, they contain all the most modern developments. The best agility, acceleration dynamics and braking efficiency - all these are sportbikes - conveyor versions of the famous two-wheeled Grand Prix cars.
Enduro (Tourist, Urban)
Enduro motorcycles came to people from the rally-raid tracks. Having lost in the "swamp" and "desert" cross-country ability, they became more comfortable for driving on city streets and highways, allowing the driver to move off the asphalt and not be afraid of serious enough bumps, potholes, curbs, stairs and other surprises. Light weight, long suspension travel, minimum cladding and maintainability are the main advantages of these motorcycles. There are several directions of Enduro motorcycles: light enduro, hard enduro, urban, tourist.
Supermoto
Super Moto is an enduro motorcycle equipped with 17-inch wheel rims, road tires, more powerful brakes and suspensions tuned for asphalt driving. This class of motor vehicles is equally suited for driving on public roads, and for overcoming serious obstacles "urban off-road" (curbs, stairs, etc.).
Motocross
Cross-country motorcycles are designed for various kinds of cross-country sports. They are often equipped with two-stroke engines. Light weight, solid frame, reliable long-travel suspension plus a powerful engine - these are motocross bikes. Often they are not equipped with lighting devices, they are started by a kick-starter. Motorcycles of this class are also produced in miniature versions - especially for children and children's competitions.
Motocross with strollers (I'm standing in a stroller)
The crew is two people: a motorcycle pilot and a wheelchair user, whose task is to correctly distribute their weight to accelerate the motorcycle during turns and jumps.
Tourism and Sports Tourism
Tourist class is the limousine in the world of motorcycles. They are made for long trips on roads of excellent quality.
Most of the touring motorcycles are classified as sport-tourism, as they are sportbikes modified for a more comfortable fit for the driver and passenger. Only on them it is possible with great comfort and, if desired, to quickly overcome long distances. Often, these motorcycles are equipped with special wardrobe bags as standard, and have many additional functions such as ABS, radio, cruise control.
Minibike
A minibike is a small motorcycle. With its light weight and size, it accelerates quickly enough and handles well. The hardest part is learning how to keep your balance. Public roads are not very suitable for riding minibikes, but at the karting track you can have a great time.
Choppers (Custom and Cruiser)
Choppers are a comfortable upright fit and the ability to ride easily and imposingly, observing the surroundings and showing yourself. Only such motorcycles allow you to maximize your fantasies and turn an ordinary standard bike into a completely personal sparkling chrome wonder that can distinguish its owner from the crowd and surprise others. The motorcycle footboards are moved forward, a comfortable steering wheel, a two-level saddle. The smooth engine characteristics, thanks to the high engine torque, provide a calm and confident ride. Choppers are sometimes referred to as a Custom or Cruiser.
Trial
A trial motorcycle is a sports equipment designed exclusively for competition and training. It is devoid of all unnecessary, in this type of competition, structural elements. Minimum weight and high-torque engine allow you to perform incredible stunts on it.
Streetfighter
Streetfighters are usually redesigned sportbikes. As a result of an accident or simply at the request of the owner, the plastic is removed, sometimes the headlights, steering wheel, exhaust system and other elements change. The motorcycle becomes more comfortable in the city, but less comfortable at high speeds. Recently, motorcycle manufacturers themselves have begun releasing new streetfighter-style models.
Maxi scooters
Maxi scooters can be of interest to businessmen who do not want to waste time (and hence money) in traffic jams. The maxi-scooter will easily save you from these losses without reducing the comfort in movement and respectability in the image. These are the limousines in the scooter world. These scooters, like others, are equipped with an automatic transmission - a variator.
ATV (Utility & Sports)
The abbreviation ATV is translated from English as ALL Terrain Vechicle, which means "off-road vehicle" - these are ATVs or four-wheelers or ATVs. ATVs have exceptional cross-country ability that is not available on any car or motorcycle.
Utility ATVs are four-wheel drive, special tires and suspension design. All this provides amazing cross-country ability. They often have a downshift and the ability to install various attachments.
Sports ATVs are designed for intense off-road rides and sporting events. ATVs are equipped with powerful two and four-stroke engines, sporty durable suspensions and have only mechanical box gear.
Description of the main components of the motorcycle, the rules for their operation and recommendations for simple repair and maintenance. This material will be useful for novice motorists.
Motorcycle engine.
Motorcycle engines are 2-stroke and 4-stroke. A positive feature of 2-stroke engines is their large liter capacity. The negative side is the increased requirement for lubrication, and as a result, a low resource. The separate lubrication system consists of an oil tank and a pump combined with a metering mechanism. This device supplies oil in a ratio of 1 to 60, 1 to 100, so if you do not use a special 2-stroke oil, the engine will fail. The design of 4-stroke motorcycle engines is similar to automobile engines, but, as a rule, the engine is combined with a gearbox and has a single lubrication system.
Oil and oil filter it is recommended to change it after 5-10 thousand kilometers or once a season. Use a special 4-stroke oil, as the clutch on a motorcycle works in an oil bath, and some car oils contain additives that form surface films, which can lead to premature disc wear.
The gas distribution mechanism requires periodic adjustment. The most common method is a rocker or rocker screw with a locknut. There is an adjustment with washers, which are placed under the pusher glass, as on a VAZ 2108 car. Engines with hydraulic compensators do not require maintenance of this mechanism.
Valve clearances are usually set: for liquid-cooled engines, 0.08 -0.1 mm at the inlet and 0.1-0.15 at the outlet. For air-cooled engines, they are slightly larger: 0.1-0.15 at the inlet, 0.15-0.25 at the outlet. This is averaged data. Poor compression is often associated with a missing or incorrect valve clearance.
Cooling system for motorcycles.
In the water cooling system of 2-stroke and 4-stroke engines, a forced cooling fan is usually provided. It turns on when the temperature rises above 85 - 90 degrees. If the temperature rises above 100-105 degrees (red zone on the sensor), and the fan does not turn on, check the fuse. If it is intact, you need to check the fan switch, which is usually located at the bottom of the radiator. To check the inclusion, it is enough to connect the terminals removed from the sensor together, and if one wire is suitable, connect it to ground. In this case, the fan should start working. If it turns on, and when the motorcycle overheats, it does not rotate, then the sensor must be replaced. The fan may also not turn on due to poor coolant circulation or low coolant level.
For air cooling systems, an indispensable condition for the normal operation of the engine and its longevity is the state air filter... A dirty filter does not allow the engine to reach the required speed, power decreases, and fuel consumption increases. This filter should be changed. A filter made of foam rubber should be washed periodically. After drying, the filter must be impregnated special oil for the filter. If this is not done, it will lose its filtering properties.
One of the causes of engine malfunction is a fall. When, during a fall, the engine continues to operate in a mode close to the maximum, the exposed oil receiver does not allow oil to flow to the liners crankshaft and the distribution mechanism, which leads to their emergency wear.
Spark plug.
The most capricious part in a motorcycle engine is the candles. It is worth starting the engine several times in a row and not warming it up, as they immediately become covered with condensate, and further starting is difficult. Usually, it is enough to warm up the engine to operating temperature and the problem disappears - the plugs reach the self-cleaning temperature. Use only original candles specified in the catalog for installation on your motorcycle.
When starting after a long stay, for example, in winter, there may be a shortage of gasoline in the fuel mixture, despite the included enricher. You can correct the situation by blocking the air filter inlet with your hand or a rag. When starting a cold engine, it is also not recommended to turn the "throttle" knob with extended "suction".
Motorcycle carburetor.
"Either nothing or nothing" - that's what the mechanics say when the motorcycle engine won't start. If there is a spark and sufficient compression (9-12 kg / cm2), check the carburetor. Any water that has accidentally entered the carburetor can be removed without removing it from the motorcycle. For this, most models have a special screw in the bottom cover. It is enough to loosen the tapered needle of the valve with a screwdriver or hexagon and drain the sediment. The same screw can be used to test the check valve.
Freed from the cables and extracted from the bowels of the motorcycle, the carburetor conceals several pitfalls:
- rail of 2-4 carburetors, it is not recommended to disassemble. As a rule, all the main systems are available anyway, but if the rotary valve is backlash, you cannot do without disassembling the entire rack. It is important to remember the location of the springs that press one rod against the other. Do not touch the adjusting spring-loaded screws during disassembly;
- under the cover of the float chamber are: floats, a needle valve and nozzles. Usually, after a long period of inactivity, a large layer of plaque forms in the carburetor, which can fill the entire float chamber. It has to be removed mechanically. This must be done carefully and carefully. Never use steel wire to clean the jets, but rather use a strand of copper wiring. Plaque and debris must be removed not only from the jets, but also from the channels of the carburetor body. On some models, the starting enrichment jet is built into the float chamber cover and is often overlooked. If the needle valve seat is removable, check that the mesh underneath is clean;
- The throttle valve in modern constant vacuum carburetors is lifted by a rubber diaphragm. You need to be extremely careful with her. If the membrane is torn, then it is impossible to glue it, buying a new one will not be cheap. The throttle is pressed by a soft spring, which should be similar in elasticity to the springs of neighboring carburetors. Hence the conclusion - not to change it or stretch it;
- the mixture quality is adjusted at the factory, and during operation it does not need to be changed, since this requires special devices. If, when cleaning the carburetors, it is necessary to unscrew the adjusting screws, first check how many revolutions they have been unscrewed. After cleaning, put everything back in place.
Motorcycle front fork.
If the motorcycle has a leaking shock absorber front fork, and there are no traces of pitting corrosion or scratches on the working surface, you can just replace the oil seals. When the working surface has pits of corrosion, it is necessary to polish them, and it is better to solder the shells with tin. Only in this case, replacing the oil seals will give the desired result.
Front suspension knocking can be caused by clearance in the steering column bearings or bearing wear. front wheel... It is better to entrust this repair to a specialist.
Rear suspension of a motorcycle.
Knocks in it will appear with increased gaps of a progressive suspension with a monoshock. Knocking can also be caused by bearing wear. rear wheel... Rear suspension shock absorbers are difficult to repair, so if they are out of order, contact a specialist or buy new ones. If you have an enduro that is operated off-road, we recommend that you disassemble and lubricate the rear suspension arm system once a year.
Motorcycle chain.
A modern chain has rubber seals in each link and serves for a relatively long time (20-50 t.km.). To increase the service life, it is better to lubricate it periodically (500-2000 km). remember to do this after riding in the rain or on a muddy road. It is best to use a special lubricant in aerosol cans. Servicing the chain is best done after the ride. it takes time for the grease to cure. Pay attention to the correct tension of the chain - the slack of the lower branch should be within the range of three to five centimeters.
Motorcycle electrical equipment.
If you accidentally reversed the polarity of the battery connection, do not worry too much, the fuse installed for this case usually blows. If the electrical malfunction is more complex than a burned-out light bulb, contact a specialist. The main cause of failure of motorcycle electronic systems is overvoltage in on-board network, the cause of which is often simply poor contact of the battery terminals.
Motorcycle driven by an engine internal combustion, is a high-speed two-wheeled vehicle... According to the device, motorcycles are divided into single (Fig. 1) and with a sidecar (Fig. 2). Depending on the purpose, motorcycles are road, sports and special.
Rice. 1. Road bike "Sunrise"
There are two more mechanical means of transport intermediate between a motorcycle and a bicycle: motorbikes and mopeds.
Rice. 2. Road bike with a sidecar IZH "Jupiter"
Depending on the working volume of the engine cylinders, motorcycles are divided into: ultralight (50-100 cm 3), light (125-250 cm 3), medium (350-500 cm 3) and heavy (over 500 cm 3).
Below are the basic data of road bikes.
The motorcycle has the following mechanisms and systems: an engine with power supply, lubrication, cooling and ignition systems serving it, a power train, undercarriage, control mechanisms.
Engine converts thermal energy into mechanical energy, which, using a number of mechanisms, sets the motorcycle in motion.
Power transmission(Fig. 3) brings the force developed on the engine crankshaft to the drive wheel. This includes forward gear, clutch, gearbox and reverse gear.
There are three types of power transmission: chain, cardan and direct.
The chain drive (Fig. 4, a) transfers the rotational force or torque of the engine by means of the motor chain to the clutch, and through it to the gearbox, from where by the rear chain to the drive wheel of the motorcycle.
With a cardan drive (Fig. 4, b), the torque from the crankshaft is transmitted through the clutch directly to the gearbox, from where, using the cardan shaft and the main gear, to the driving wheel of the motorcycle.
The direct transmission consists of a gear transmission (motor), which, through the clutch mechanism and the gearbox, transmits the force to the shaft, which is at the same time the axle of the wheel.
Chassis ensures the movement of the motorcycle and serves as a skeleton for fastening its main mechanisms. It includes a frame, a front fork, wheels with tires, a saddle, a rack, footpegs, a stand, mud guards and a towed stroller.
Control mechanisms designed to control a motorcycle while driving, as well as to operate its units and devices. Control mechanisms include steering, brakes, and controls.
Hai, bikers, bikers, and just fans of two-, three-, four-wheeled vehicles! This portal is full of data, sometimes missing for many fans of the freedom of transport and restoration of moto. If you are directly looking for electrical or motor diagrams domestic motorcycles You need to follow this link. The same article contains information regarding general principles buildings iron horses... We will give confidence to those who have just started learning about bikes, and we will brighten the mood by describing unusual bikes for those who have already established themselves in the biker movement.
Bike circuit for a beginner
This section is intended to describe the scheme of moto technique for beginner lovers of two-wheeled horses. The following brief visual information will help you understand the simplest steel horses. This is what the bikes of the 1960s looked like. from the world's leading manufacturers of similar products. And this concerns the former motorcycle legends and modern brands of iron horses. From this picture, you can study the history of the structure of motorcycles.
The first number in the diagram shows the front shock absorber fork. At the same time, you will not see the springs themselves in the front of the motorcycle, since the latter are hidden under an iron casing called pants. Number 2 indicates light indication lamps dashboard... Older bikes were mounted directly on top of the headlight. The third number is the speedometer.
To collect such a miracle technique yourself, you need a lot of money and more free time. And the main thing that you need to stock up on is the desire to create something original in motorcycle mechanics. Finances, however, still play a decisive role in the motorcycle design process.
Be that as it may, the rest of the scheme of such a motorcycle remained practically unchanged. The same chain drive, the same pair of wheels. The X-shaped engine stands where other types of motors are installed - under the frame and between the two wheels. Perhaps only the fuel capacity and a normal seat are not visible on the bike diagram. Nevertheless, the designers left the place for both that, and another at your discretion and the possibilities of imagination.
Motorcycle electronics diagram
Well, the picture indicated at the bottom of this section describes in detail electronic system bike. It clearly indicates the main nodes that generate current and the main consumers of the latter. In addition, this picture shows in a clear perspective the connection between the above parts of the motorcycle.
As you know, internal combustion engines (ICE) are of three types, namely two-stroke, four-stroke and rotary. The latter are not very common, but some motorcycle manufacturers still use them (Triumf).
General structure and operation of the engine
Internal combustion engines (ICE) are installed on motorcycles, in the cylinders of which the thermal energy of the burning fuel is converted into mechanical work... The reciprocating motion of the piston, which receives the gas pressure, is converted into rotation of the crankshaft by means of a crank mechanism, which consists of a cylinder, a piston with rings, a piston pin, a connecting rod and a crankshaft. The extreme positions of the piston moving in the cylinder are called dead centers - top dead center (TDC) and bottom dead center (BDC). The distance from TDC to BDC is called the piston stroke, and the space formed is called the working volume of the cylinder (cm 3). The total internal volume of the cylinder consists of the working volume and the volume of the combustion chamber. The ratio of the total volume to the volume of the combustion chamber is called the compression ratio; the higher it is, the more efficient the engine's working process is. Modern engines have a compression ratio of 9-10 units (high values are found in sports models).
Reciprocating internal combustion engine
In two- and four-stroke internal combustion engines, the flow of the working process and the design of the parts are somewhat different.
Four-stroke engines
In four-stroke engines, the working cycle takes place in four piston strokes (stroke) and two crankshaft revolutions: inlet - the piston descends from TDC and sucks in the combustible mixture through the open inlet valve; compression - the piston rising from the BDC compresses the working mixture when the valves are closed; working stroke - the mixture burns out, ignited by an electric spark, and the resulting gases, expanding, move the piston down (this piston stroke is called working, since useful work is done during it); exhaust - an upward-moving piston pushes exhaust gases out through an open exhaust valve.
Working process of a four-stroke engine
Two-stroke engines
V two-stroke engines one working cycle occurs per one revolution of the crankshaft. Another feature is the absence of mechanically operated valves (intake and exhaust). Their role is played by the piston itself, opening and closing special windows and channels on the cylinder mirror, well, on some engines, a petal valve is installed at the intake. The crankcase volume under the piston is also used for gas exchange.
Working process of a two-stroke engine
When the piston moves upward from the BDC, the working mixture is injected into the sub-piston space, and in the over-piston space, the exhaust gases remaining from the previous cycle are first displaced, and later, when the windows are closed by the edge of the piston, compression. Around TDC, the mixture in the combustion chamber is ignited by an electric spark formed between the electrodes of the spark plug. The burning fuel-air mixture expands and pushes the piston downward - a working stroke occurs. Having dropped about 2/3 of its stroke, the upper edge of the piston opens the windows in the cylinder. Exhaust gases, which are under excessive pressure, exit through the outlet port into the exhaust pipe. Through other windows, a fresh charge from the crankcase cavity enters the cylinder, where the descending piston creates excess pressure. This overflow of the mixture is called blowdown, and the windows and channels are called blowdown.
Modern two-stroke internal combustion engines have a multichannel (3-7 channels) return-loop blowdown. In addition, a reverse plate (petal) valve is installed at the inlet to the cylinder, which is controlled by the vacuum in the crankcase. During admission to the crankcase (the piston moves from BDC to TDC), under the action of a vacuum in the sub-piston space, the valve plates open the passage of the combustible mixture from the carburetor. With the reverse movement of the piston (during purging), the excess pressure in the crankcase closes the valve plates, preventing the mixture from being thrown back from the crankcase into the carburetor. The petal valve improves cylinder filling, increases engine power and economy, especially at low and medium engine speeds. Many engines also have a special mechanism that changes the height of the exhaust port (and hence the duration of the exhaust) depending on the engine speed (the so-called "controlled exhaust"). Despite the measures taken to improve the gas exchange of two-stroke internal combustion engines, some of the mixture leaves with the exhaust gases, which reduces their efficiency compared to four-stroke ones.
The working process of both two- and four-stroke internal combustion engines takes place in the cylinder. The piston moves along the inner surface (mirror) of the cylinder or liner. In modern engines, instead of steel or cast iron liners, carbide nickel-silicon compositions ("nikasil") are used, sprayed directly onto the aluminum base of the cylinder. Depending on the type of cooling system adopted, the cylinder jackets have ribs ( air cooling) or internal cavities for the passage of coolant.
Piston perceives the gas pressure during the combustion of the working mixture. It consists of an upper and lower parts (head and skirt, respectively) and piston pin mounting bosses. The shape of the bottom is flat or convex; in four-stroke engines, recesses are often made in the bottom for valves. In the piston skirt of two-stroke engines, cutouts are made through which the combustible mixture passes, because in these engines the piston controls the gas distribution (intake, purge and exhaust).
Pistons of two-stroke (a) and four-stroke engines (b)
1 - piston head;
2 - sampling for valves;
3 - compression rings;
4 — oil scraper ring;
5 - piston pin fastening bosses;
6 - piston skirt;
7 - cutout for the blow-out window;
8 - oil catching cavity (refrigerator);
9 - cutout for an additional purge window
The piston head has thickened walls, in which 1-3 compression rings are placed, made of special cast iron or steel. These rings seal the gap between the piston and the cylinder bore, transfer heat to the cylinder walls. In four-stroke engines, in addition to compression rings, there is an oil scraper ring on the piston that removes excess oil from the cylinder bore.
The bosses support the piston pin and have retaining ring grooves and holes for oil mist lubrication. Often in the area of the bosses, on the outer surface of the piston, special recesses are made - refrigerators.
The skirt guides the movement of the piston. Due to the unequal thermal expansion of various parts of the piston, its outer surface is given a complex shape: barrel-shaped (conical) in height and oval in circumference. Pistons are made of high-quality aluminum alloys with a high silicon content, which can withstand high thermal and mechanical loads, and at the same time have a low coefficient of expansion.
Piston pin pivotally connects the piston to the connecting rod. Usually, a floating fit of the finger is used in the piston bosses and the upper head of the connecting rod - its fixation from axial movements is carried out by circlips in the bosses.
Connecting rod transfers the force from the piston to the crankshaft and consists of a rod (I-beam or elliptical section) and heads: upper and lower. Depending on the type of engine and the lubrication system used, the connecting rod heads are made with bearings sliding (with bushings or liners) or rolling (roller, needle). When a sliding bearing (insert) is used in the lower head, the head itself is split. In the case of using a needle bearing, the head is made one-piece and the lower journal of the shaft is pressed into the cheeks.
Connecting rods
a - with a split lower head ("Dnepr");
b - with one-piece bottom head ("Ural");
1 - connecting rod cover;
2 - connecting rod bolt;
3 - connecting rod;
4 - separator of the bearing of the lower head of the connecting rod and rollers;
5 - inserts
Crankshaft receives the force from the piston (through the connecting rod), converts it into rotary motion and then transmits the torque to the transmission. In addition, other systems and mechanisms are driven from the crankshaft: a gas distribution mechanism (timing), an oil pump (in four-stroke internal combustion engines), a generator, a cooling system pump, and balance shafts. Depending on the number of engine cylinders and the design, the crankshaft can have one or more knees, each of which is formed by two cheeks and a connecting rod journal. Main journals are located between the knees and along the edges of the shaft, supported by bearings.
Crankshafts are made integral, or non-separable (one-piece). The type of bearings for its bearings (main journals) depends on the lubrication system used. To increase the smooth operation of the engine (after all, only one piston stroke is working, and the rest - one for a two-stroke engine, and three for a four-stroke engine - require energy), the crankshafts have a remote flywheel, massive cheeks and counterweights. In addition, many modern engines have special balancing shafts driven by a gear train from the crankshaft.
Crankshaft of a two-cylinder engine
b - solid ("Dnieper");
1 - connecting rod with one-piece bottom head and roller bearing;
2 - counterweight;
3 D Motorcycle engine
Four-stroke internal combustion engine. How it works?
Dismantling the Honda CBR929RR engine (part 1).
The first part of a scary video of a Honda CBR929RR motorcycle engine disassembly.
Someone has settled in the engine and growls, rattles, knocks.
The daughters decided to find out who lives there and expel him.
To do this, they unscrewed everything attached: covers, generator, drives, etc.
The closer to "Alien" - the more terrible ...
Crankcase perform one-piece or with the plane of the part (longitudinal, transverse). In four-stroke engines, the crankcase (or sump) is usually a reservoir for oil draining from the lubricated parts. Many engines share a common crankcase with a clutch and gearbox. In two-stroke multi-cylinder engines, the volume of the crankcase of each cylinder must be separated from the others, this complicates the design of the crankcase when the number of cylinders is from two or more.
Gas distribution in four-stroke internal combustion engines controls the camshaft (or cam) shaft, which rotates twice as slow as the crankshaft. When rotating camshaft with its projections (cams) interacts with pushers, which directly or through a transmission link (rocker arm, rocker) open the valves (inlet and outlet); they are closed by the action of the valve springs. The periods of time when the intake and exhaust valves are open are called valve timing; they are matched to the piston strokes.
Valve timing diagram of a four-stroke engine
1 - opening of the inlet valve;
2 - closing the intake valve;
3 - closing the outlet valve;
4 - opening of the outlet valve;
angle "a" - valve overlap
To better fill the cylinder with a combustible mixture, the intake phase is started when the piston has not yet reached TDC. With the further stroke of the piston from TDC to BDC, it sucks in the combustible mixture through the open valve; the inlet is completed after passing the BDC, when part of the mixture enters the cylinder by inertia. Cleaning the cylinder from exhaust gases is also started at the end of the expansion stroke, when the piston has not yet reached BDC, but there is excess pressure in the cylinder. Then, during the piston stroke from BDC to TDC, the piston pushes the exhaust gases out. Close the exhaust valve after TDC to allow some of the exhaust gases to coast out of the cylinder. Thus, there is a period of time when both valves are open - this is called “valve overlap”. Each model of a four-stroke engine has its own optimal valve timing, which are preset at the factory by a cam profile camshaft... Some of the newest motorcycle engines have special devices that allow you to change the valve timing depending on the crankshaft speed.
On modern four-stroke internal combustion engines, several types are used Timing: OHV, OHC, DOHC.
Gas distribution schemes
|
a - OHV, |
7 - plate (thrust bearing); |
In the OHV scheme valves located in the cylinder head are driven from the "lower" camshaft by means of pushers, rods and rocker arms; the design does not provide a clear operation of the mechanism at high speeds of the crankshaft. Engines with timing belt type OHC have an "upper" camshaft acting on the valve lifters by means of levers (rockers); the shaft is driven by a chain or a toothed belt. In modern multi-valve heads with 4-5 valves per cylinder, two camshafts are used, each of which directly acts on the valve lifters with its cams (DOHC scheme). This design has a minimum of parts and because of this, the inertia of the valve drive is reduced, which makes it possible to increase the rotational speed of the engine crankshaft, and hence its power; Timing type DOHC are becoming more widespread.
Scheme of work OHV
Camshaft driven from the crankshaft by a gear, chain drive or by means of a toothed belt. In the latter two cases, the engines have chain (belt) tensioners and dampers.
For normal work valve train There must always be a thermal gap (0.05-0.15 mm) between the valve stem and its actuator. When there is no gap, the valves do not close tightly, as a result of which they burn out and fail. With an increased clearance, they do not open completely (power is lost) and, in addition, knock. Many engines of foreign motorcycles have a timing belt with hydraulic compensators (operating from the pressure in the lubrication system) that automatically maintain the required valve clearances. If such a system is not provided, the gap is adjusted at maintenance(THEN).
Four-stroke engines structurally more difficult two-stroke, since they additionally have Timing and a lubrication system. However, since the 70s of the twentieth century, they have been prevalent on motorcycles due to cleaner combustion and better economy. Currently, in developed countries, motorcycles with two-stroke engines are of limited use - these are old models, sport motorcycles and mopeds; for the foreseeable future, particularly in Europe, production of these engines is expected to cease entirely due to the extremely negative impact on the environment.
The cylinders of motorcycle engines are most often 1, 2 and 4, although there are 3-, 6- and even 10-cylinder. They have a variety of layouts: in-line (longitudinal and transverse), V- and L-shaped, horizontal opposed. The working volume of the engines of serial motorcycles usually does not exceed 1500 cm3, the power is 150-180 hp.
The arrangement of the cylinders of engines of modern motorcycles
|
a - single-cylinder two-stroke; |
e - four-stroke V-shaped with a transverse arrangement of the crankshaft; |
Engine lubrication and cooling systems
Lubrication of internal combustion engine parts is needed to reduce friction between them and remove heat. It is carried out with engine oils that are resistant to high temperatures in combination with a low viscosity at low temperatures (for confident engine start). Besides, engine oils should not form carbon deposits during combustion, should not be aggressive towards rubber seals and plastic parts. Used for lubrication mineral oils(obtained from petroleum by distillation), semi-synthetic and synthetic. Semi synthetic oils
represent a blend of high quality petroleum and synthetic base stocks. Have synthetic oils
the oil base is absent, due to effective antifriction additives it increases (in comparison with mineral oils) the service life of the engine, it is easier to start at low temperatures. Despite the higher price, semi-synthetic and synthetic oils are increasingly used. Special engine oils are produced, and they differ for engines that differ in stroke (two- and four-stroke) and in the degree of forcing. For Russian motorcycles with four-stroke engines, automotive oils of various viscosities are used, with two-stroke engines - MGD-14, or foreign analogues.
In four-stroke engines, there are three ways of supplying oil to rubbing surfaces: under pressure, spray and gravity. Most of the friction pairs are lubricated under pressure generated by an oil pump. Other friction pairs are lubricated with oil mist, which is formed when oil droplets are sprayed by the moving parts of the crank mechanism. And, finally, the third group of parts is lubricated with oil flowing down special channels and grooves. The crankcase (oil pan) is usually an oil reservoir (the so-called "wet" sump - fig. A).
Lubrication systems for a four-stroke engine
Some foreign motorcycles have dry sump system(Fig. b), from which oil is first pumped out by one of the pump sections into a separate oil tank, and by the other section under pressure is supplied to the friction surfaces. The tank can be located in different places: near the engine, at the rear wheel or in the front of the frame.
The oil level in all lubrication systems is monitored using a dipstick (with marks for minimum and maximum levels) or through a special inspection hole. Engine operation with a low oil level is not permitted.
The lubrication system contains an oil pump, an oil filter, valves (return and safety) and lines in the form of channels (pipes, drills in parts).
Oil pumps of four-stroke internal combustion engines there are plunger and gear types.
Types of oil pumps
a - plunger;
b - gear with external gearing of gears;
в - with internal gearing of gears
Gear pump, the most widespread, consists of a housing in which one or two pairs of gears with external or internal gearing are located; the gears are driven by the engine crankshaft or camshaft. Oil enters the inlet cavity of the housing, is captured by the gear teeth and is pumped to the outlet cavity.Of the filters, the most common are replaceable paper filters.
In two-stroke enginesrubbing pairs are lubricated with oil in the form of small droplets in fuel vapors. The oil is mixed with gasoline either preliminarily in the tank (in a ratio of 1: 25-1: 50), or directly in the inlet pipe, where it is supplied in the required amount by a special dosing pump. The last oil supply system is called "Separate lubrication system", it is predominantly used on foreign two-stroke engines. In such systems, the oil supply at low loads is brought to a ratio of 1: 200, which reduces the smoke of the exhaust, reduces the overall oil consumption and the formation of carbon deposits in the combustion chamber.
Two-stroke engine with separate lubrication system
1 - oil tank;
2 - carburetor;
3 - "gas" cable separator;
4 - throttle handle;
5 - oil supply control cable;
6 - plunger metering pump;
7 - hose supplying oil to the inlet pipe
In systems with separate lubrication, use plunger pumps driven by a crankshaft or motor transmission. The oil is stored in a special tank and flows to the pump by gravity. The design provides a signaling device low level oil in the tank. The amount of oil supplied to the inlet pipe depends on the engine speed; in some designs there is one more adjustment of its performance - from the position of the "throttle" handle, for which the pump is connected to it with a separate cable.
Cooling system
When fuel is burned in the internal combustion engine cylinder, heat is released, part of which (about 35%) goes to useful work, the rest is dissipated into the environment. If the heat dissipation is not efficient enough, the parts of the cylinder-piston group overheat, and due to their excessive expansion, as well as improper lubrication conditions, seizure and damage to parts can occur. To prevent overheating, all motorcycle engines, regardless of stroke, havecooling system - air or liquid.
Cooling systems for motorcycle internal combustion engines
