Basic composition of motorcycle

Motorcycle consists of five parts: engine, transmission system, running system, steering, braking system and electrical equipment. The overall structure of motorcycle and the names of its components. 1, characteristics of motorcycle engine

(1) The engine is a two-stroke or four-stroke gasoline engine.

(2) Adopt air cooling, including natural air cooling and forced air cooling. The general model adopts natural air cooling, relying on the air blowing through the cylinder head and the radiator on the cylinder liner to take away the heat. In order to ensure the cooling of high-power motorcycle engine at low speed and before driving, forced air cooling is adopted, equipped with a fan and an air guide cover, and the heat sink is cooled by forced air.

(3) The engine speed is high, generally above 5000 rpm. The rising power (the effective power per liter of engine displacement) is relatively large, generally around 60kw/ liter. This shows that the motorcycle engine has a high degree of reinforcement and a small overall size.

(4) The engine crankcase, clutch and gearbox are designed as a whole with compact structure.

2, the body

The engine block consists of three parts: cylinder head, cylinder block and crankcase. The cylinder head is made of aluminum alloy with fins. The new four-stroke motorcycle engines all adopt overhead valve, chain drive and overhead camshaft structure. The cylinder block adopts bimetal (aluminum fins cast outside the wear-resistant cast iron cylinder liner) to obtain better heat dissipation effect. Some motorcycles use wear-resistant cast iron cylinder blocks, such as Changjiang 750 and Jialing JH70. On some small mopeds, such as Yu He YH50Q small displacement (50 cubic centimeters) engine, the inner wall of aluminum alloy cylinder is plated with 0. 15 mm hard chromium layer. Crankcase is made of aluminum alloy by die casting, and consists of left and right boxes. Some motorcycles are equipped with buffer blocks between radiating parts to suppress the noise caused by vibration of radiating fins.

3. Crank connecting rod

The crankshaft of motorcycle engine is a combined type, which is formed by pressing a left crankshaft, a right crankshaft and a crank pin. Ball bearings are installed on the main journals of the left and right half shafts to support the crankshaft on the crankcase. Flywheel, magneto and clutch driving gear are installed at both ends of crankshaft respectively. The connecting rod has an integral structure, the big end is annular, and a needle bearing and a crank pin are installed inside to form a crank connecting rod group. When installing a piston ring on a two-stroke engine, it is necessary to align the opening of the piston ring with the locating pin in the piston ring groove to prevent the piston ring from rotating in the ring groove, causing air leakage and scratching the intake and exhaust ports on the cylinder liner.

4. Vaporizer

Carburetor is an important part of motorcycle fuel supply system, which is located between air filter and engine intake. Motorcycle engines generally adopt carburetor, plunger throttle valve and float chamber throttle valve with horizontal intake flow direction. The carburetor structure mainly consists of a float chamber and a mixing chamber. The float chamber is located below the carburetor, and the oil pipe is communicated with the oil tank through the throttle switch. The oil level in the float chamber is maintained at a certain height through the needle valve on the float, and the oil supply pressure is stable. The function of the mixing chamber is to evaporate and atomize gasoline and mix it with air, so that the engine can get the required mixture at various loads and speeds. It consists of throttle valve, injection needle, injection pipe, gas path and oil path.

By turning the throttle handle of motorcycle to drive the throttle steel wire to hang the rope, the throttle valve and the fuel injection needle are controlled to move up and down, and the cross section and fuel supply of the intake throat are changed to meet the needs of mixed gas at different speeds and loads. Idle speed adjusting screw is installed on one side of carburetor to adjust idle speed. Idle stop screw is used to prevent the throttle from rotating and adjust the minimum opening of the throttle. There is a return spring above the throttle to keep the throttle closed when the throttle handle is not turned.

On some two-stroke motorcycle engines, a one-way reed valve is installed between the carburetor and the cylinder block to control the air intake in order to avoid the phenomenon of back injection of the carburetor at low speed. The reed is thin spring steel, the valve seat is aluminum alloy, and there is an air inlet on it. In order to reduce the impact and vibration between the reed and the valve seat, a layer of oil glue is stuck on the contact part between the air inlet plane and the reed. When inhaling, a certain vacuum is formed in the crankcase. Under the action of pressure difference, the reed valve opens the mixed gas and enters the crankcase. When the piston descends and the vent has not been opened, the pressure in the crankcase rises and the reed valve closes, which prevents the mixture from flowing back and improves the power and economy of the engine at low speed.

5. Lubrication system

The four-stroke engine adopts splash lubrication and pressure lubrication. Two-stroke engines generally adopt a mixed lubrication method in which a certain proportion of QB gasoline engine oil is mixed into gasoline. However, no matter how the engine works, the mixed oil of this lubricating method is supplied with lubricating oil according to the set proportion, which increases the consumption of lubricating oil, causes incomplete combustion, more carbon deposition and exhaust pollution. The new generation of two-stroke engines all adopt separate lubrication mode, and are equipped with separate lubricating oil tank and oil pump. The oil pump generally adopts reciprocating plunger variable oil supply pump, which is driven by crankshaft gear through worm gear. The oil supply is linked with the carburetor throttle through the throttle handle and control cable, so that the oil supply changes with the change of engine speed. There is more oil supply at high speed and reasonable oil supply at low speed, which is more fuel-efficient than mixed lubrication. The engine oil is blown into tiny oil mist by high-speed mixed gas, which is supplied to the parts needing lubrication, so that the engine oil entering the combustion chamber is reduced, the mixed gas burns completely, and carbon deposition and exhaust pollution are reduced.

6. Start

The starting mode of motorcycle is mainly pedal starting. The starting mechanism has a sector gear starting mechanism represented by Happiness XF250 motorcycle. The pedal starting gear lever drives the sector gear, starting ratchet, clutch assembly sprocket, front chain and crankshaft sprocket to drive the crankshaft to rotate and start the engine. When the engine is started, the starting mechanism is restored to its original position through the one-way action of the starting ratchet and the action of the return spring. When the starting gear lever is set in neutral position and the pedal is depressed, the starting mechanism can be started.

The other is the starting pedal starting mechanism adopted by some imported models. Different from the former, the clutch handle must be pinched first to separate the clutch. The shift lever can be placed in any gear, not necessarily in neutral. After starting, loosen the clutch and step on the accelerator to start. When the starting pedal is depressed, the pawl on the shaft of the starting pedal meshes with the internal ratchet of the driving gear of the starting pedal, so that the driving gear rotates, and the crankshaft is driven to rotate through the idler gear, the driven gear, the clutch gear and the starting pinion, thereby starting the engine. After starting, the foot leaves the starting pedal rod, and the return spring makes the pedal rod rotate in the opposite direction, and the pawl disengages from the engagement with the internal ratchet and returns to its original position.

Motorcycles with large displacement, such as Changjiang brand 750D motorcycle, Yamaha two-cylinder motorcycle, Suzuki GT750 three-cylinder motorcycle and Honda CL 1000 four-cylinder motorcycle, are all started by starting the motor. The transmission system of a motorcycle consists of a primary reduction, a clutch, a gearbox and a secondary reduction.

1, main deceleration

The primary reduction is mainly composed of the driving sprocket (driving gear) installed at the crankshaft end, the sleeve roller chain and the driven sprocket (driven gear) on the clutch. As the primary reduction, it transfers the power of the engine to the clutch.

Step 2 grab it

Motorcycle clutches have the following structural types:

(1) The wet multi-disc friction clutch assembly is immersed in engine oil to work, which is divided into three parts: driving, driven and separating. The power of the engine is transmitted to the transmission cover through the sprocket. There are grooves around the cover, and friction plates (transmission plates) made of rubber and cork friction materials are embedded. The protrusions on the outer edge of the friction plates are put into the grooves of the transmission cover to rotate together as the transmission part of the clutch. Four steel driven plates are connected with the driven plate fixing basin through internal teeth to form a driven part. The driving disk and the driven disk are staggered, the fixed disk is connected with the main shaft of the gearbox through internal splines, and four clutch springs on the gland press the friction plate and the driven disk to transmit power to the gearbox. The clutch is usually engaged. When the clutch handle is gripped tightly, the screw sleeve rotates in the left cover through the steel cable, the adjusting screw in the screw sleeve moves to the right to push the push rod to separate from the gland, the spring pressure disappears, and the friction trace is separated from the driven plate.

(2) The automatic centrifugal clutch is used for Yamaha CY80, Suzuki FR50 and other mopeds, and the clutch is automatically controlled to be disengaged and engaged according to the engine speed. The clutch consists of driving, driven and disengaged engagement mechanisms. The driving part consists of clutch cover, thrust plate and clutch plate. The driven part consists of friction plate, center sleeve, etc. When the engine is running, the centrifugal force generated by the steel ball increases with the increase of the rotating speed, and its axial component overcomes the pulling force of the release spring and moves outward along the groove in the clutch housing, pressing the thrust plate against the clutch plate, so that the clutch is engaged due to friction and outputs power. When the engine speed decreases to idle speed or flameout, the centrifugal force of the steel ball decreases or does not decrease. The tension of the release spring overcomes the centrifugal force of the steel ball to make the steel ball return to its original position along the groove, and the clutch is separated.

(3) The structure of the shoe-type automatic clutch is used on some micro-motorcycles. The driving part is a fixed seat driven by crankshaft, and there are three shoe components on the seat, which are connected with the fixed seat through pins. The spring pulls the shoe toward the center of the crankshaft, thus maintaining a certain gap between the shoe of the shoe assembly and the clutch plate of the driven part. When the rotational speed increases, when the centrifugal force generated by the shoe is greater than the tensile force of the spring, it will be thrown out. When the centrifugal force reaches a certain value, it will mesh with the clutch disc to generate friction, which will drive the follower to rotate and transmit power.

3. Secondary deceleration and transmission

According to different motorcycle models, there are three transmission modes: belt transmission, chain transmission and universal joint shaft transmission. Miniature motorcycles often use belt drive as the rear transmission device, and the size of the driving and driven pulleys determines the secondary reduction ratio. Motorcycles generally use chain drive as rear drive. Chain drive, simple structure, few parts, convenient manufacture and maintenance. The output shaft of the gearbox is equipped with a rear drive driving sprocket, and the rear wheel is equipped with a driven sprocket, and the power is transmitted by the corresponding sleeve roller chain. In motorcycles equipped with high-power engines (such as Changjiang 750 motorcycle), the rear transmission mode is universal joint shaft transmission, and the rear wheel is equipped with a pair of spiral bevel gears for auxiliary deceleration. The function of the walking system is to support the weight of the whole vehicle and load, and ensure the stability of handling and the comfort of riding. The traveling system mainly includes frame, front fork, front shock absorber, rear shock absorber and wheels.

(1) Frame: It is the skeleton of the whole motorcycle, which is welded by steel pipes and steel plates. It connects the engine, gearbox, front fork and rear suspension with each other, and has high strength and rigidity. Most scooters use a spine-shaped frame made of stamped and tailor-welded steel plates. Motorcycles generally use welded steel frame, cradle frame or steel plate and steel tube combined frame. Some motorcycles with high-power engines adopt double-bracket cradle frames welded with steel pipes.

(2) Front fork: The front fork is the guiding mechanism of motorcycle, which organically connects the frame with the front wheel. The front fork consists of a front shock absorber, upper and lower connecting plates, and a steering column. The steering column is welded with the lower connecting plate and sleeved in the front sleeve of the frame. In order to make the steering column move flexibly, axial thrust ball bearings are installed at its upper and lower journals, and the left and right front shock absorbers are connected into a front fork through upper and lower connecting plates.

(3) Front and rear shock absorbers: The front shock absorber is used to attenuate the vibration caused by the front wheel impact load and keep the motorcycle running smoothly.

The rear shock absorber and the rear rocker arm of the frame constitute the rear suspension device of the motorcycle. The rear suspension device is an elastic connection device between the frame and the rear wheel, which bears the load of the motorcycle and reduces and absorbs the impact and vibration transmitted to the rear rotation due to uneven road surface.

(4) Wheels: The front wheels of motorcycles are guide wheels, and the rear wheels are driving wheels, both of which are spoke wheels. The wheel consists of tires (inner and outer tires), rims, spokes, wheels, brake rims, bearings and front and rear axles. The wheel rim (steel ring) is welded by rolled steel plate, the wheel hub is die-cast by aluminum alloy, and the brake steel ring is die-cast, with flanges at both ends for mounting spokes. Spokes are similar in shape to bicycle belts, and are used to connect rims and hubs. The wheel hub is equipped with a brake, the front wheel is also equipped with a worm wheel and worm of a speedometer, and the rear wheel is equipped with a driving mechanism. (1) Steering: The front wheels and handlebars cooperate to control the running direction of the motorcycle. The handlebar is installed on the upper connecting plate. When the handlebar rotates around the steering column, the upper and lower connecting plates rotate with it, and the front shock absorber drives the front wheel to rotate left and right. The right end of the handlebar is provided with an accelerator handle for controlling the throttle opening of the carburetor and a brake handle for controlling the front wheel braking; The left end is provided with a handle and a handle for controlling the clutch. The rearview mirror and various electrical switches are also installed at the left and right ends of the handlebar. The handlebar and brake handle control the front wheel brake, clutch and carburetor through steel cables. Wire ropes have different specifications, such as 1× 19 single-strand wire rope with an outside diameter of ∮ 2 ~ ∮ 2.5mm for brake and clutch, and ∮1.5 mm for carburetor.

(2) Braking: Generally, the front wheel braking is controlled by pinching the brake handle, and the rear wheel braking is completed by stepping on the brake pedal. Motorcycle braking devices include mechanical drum brakes and hydraulic disc brakes. Drum brakes are similar in structure to cars and tractors. The brake shoe is made of aluminum alloy by die casting, and the friction brake pad is stuck on it. The brake cam is rotated by the brake arm, and the brake shoe is pushed away to achieve the purpose of braking.

Brake consists of oil tank, plunger oil pump (all on handlebar), hydraulic oil pipe, brake caliper, brake disc, etc. The brake fork frame and the front fork guide rail are almost fixed together and are the fixed parts of the braking device. The brake disc is fixed with the wheel and rotates with the wheel. When braking, hold the brake handle tightly and the plunger valve acts to push the hydraulic oil into the two cylinders of the caliper along the hydraulic oil pipe. Under the action of pressure oil, the cylinder pushes the friction plate to clamp the brake disc from both sides, resulting in huge friction resistance and forcing the wheel to stop rotating. When the brake handle is released, the pressure in the hydraulic oil circuit drops rapidly, and the oil cylinder drives the friction plate to return to its original position to release the brake. Motorcycle trading needs inspection and adjustment.

1, motorcycle vehicle inspection

First, make a visual inspection. Vehicle parts should be in good condition and there are no missing parts. Paint layer, chromium plating layer and galvanized parts should be bright, without scratches and falling off. The vehicle shall have the product certificate and instruction manual, and the spare parts and tools on board shall be accepted according to the packing list. Then start the check. At room temperature, the cold car starts no more than three times, and the hot car starts successfully at one time. When the engine is running, there should be no abnormality and knocking sound, and the idling speed should be stable, and there should be no leakage of gasoline and engine oil.

2. Inspection and adjustment of components

(1) Front wheel braking. The front wheel brake is controlled by the right hand. Check its free travel first. The so-called free stroke refers to the stroke from the handle to the brake. If the stroke is too small, the front brake shoe and the front brake drum cannot be completely separated, which affects the driving speed; The stroke is too large, which affects the braking efficiency and cannot be braked in time.

(2) Rear wheel braking. The rear wheel brakes are controlled by pedals. First, check the free travel of the brake pedal.

(3) clutch. Generally speaking, the clutch is operated with the left hand. Check its free travel during adjustment.

(4) Rear shock absorber.

(5) Rear drive. The rear drive adjustment is mainly to check the tension of the drive chain (drive belt). Check that the parts are located in the middle position between the front and rear sprockets (pulleys). Pull the chain up and down with your fingers to see how far it moves up and down. Motorcycle distance 10 ~ 20mm, ordinary motorcycle distance 20 ~ 30mm. V-belt tension: press the belt [49 Newton (5 kg force)] by hand, and the belt will sag10 ~ 20 mm.

(6) The carburetor runs at idle speed. Idle speed is the lowest stable speed when the engine is empty. When the throttle handle is placed in the minimum position, the engine can keep running continuously. When adjusting, start the engine first, turn the throttle handle gradually, and check the free stroke of the throttle handle, which is generally set at 2 ~ 6 mm If the rotation is less than 2 mm, the engine speed will increase, indicating that the free stroke is too small; If the rotation stroke exceeds 6 mm and the engine speed does not increase, it means that the free stroke is too large. 1, arrangement of instruments and switches

Step 2 wire

The circuit of a motorcycle is basically similar to that of a car. The electrical circuit is divided into power supply, ignition, lighting, instrument and sound.

The power supply part is generally composed of alternator (or powered by magneto charging coil), rectifier and battery. For different motorcycle models, magneto for motorcycle has different structures. Generally, there are two forms: flywheel magneto and magnetic steel rotor magneto. Flywheel magneto is generally used for small displacement micromotors and mopeds. Four pieces of magnetic steel are evenly distributed inside the flywheel and rotate together with the crankshaft of the engine. The stator frame is fixed on the crankcase, and a magneto coil, an ignition coil and a circuit breaker assembly are fixed on the crankcase. When the flywheel rotates, the magnetic field lines alternately pass through each coil, so that the coils generate induced alternating current. In the magnetic steel rotor type magneto, the structure is opposite to the above. Six pieces of magnetic steel are evenly distributed on the circumference of the rotor. Magnetic steel and rotor are die-cast together with aluminum alloy, and rotor is connected with crankshaft through key. Six groups of coils with iron cores are distributed in the stator. When the rotor rotates in the stator, the magnetic field lines alternately pass through the stator coils to generate induced alternating current.

There are three ignition methods for motorcycles: battery ignition system, magneto ignition system and transistor ignition system. There are two types of ignition systems: contact capacitor discharge ignition and non-contact capacitor discharge ignition. Contactless capacitor discharge is abbreviated as C.D.I. In fact, C.D.I refers to the combined circuit composed of capacitor charging and discharging circuit and silicon controlled switch circuit, commonly known as electronic igniter.

Wires of various colors are distributed in motorcycle circuits. It is customary to use the red line as the power supply "+"line, the black line as the grounding line "-"line, the orange line as the line leading to the ignition coil, the output current of the magneto as the white line, the blue headlight and so on. This is just a general idiom for reference.