Bicycle frame, tires, pedals, brakes, chains and other 25 components, the basic components are indispensable. Among them, the frame is the skeleton of the bicycle, which bears the largest weight of people and goods. According to the working characteristics of each component, it can be roughly divided into guiding system, driving system and braking system.

1. 1 Steering system: It consists of handlebar, front fork, front axle, front wheel and other parts. The rider can change the driving direction and keep his body balanced by manipulating the handlebar.

1.2 drive (transmission or walking) system: it consists of pedal, central shaft, toothed plate, crank, chain, flywheel, rear axle and rear wheel. The pedaling force of people's feet is driven by pedals through crank, sprocket, chain, flywheel, rear axle and other parts, thus making the bicycle move forward continuously.

1.3 Brake system: It is composed of brake components, and the rider can control the brakes at any time to slow down and stop the running bicycle, thus ensuring the driving safety.

In addition, for safety and beauty, as well as from a practical point of view, it is also equipped with lights, brackets and other components.

Pedal parts: Pedal parts are assembled on the left and right cranks of the central shaft part, and are devices that convert translation force into rotation force. When a bicycle is riding, the pedal force is first transmitted to the pedal parts, and then the pedal shaft drives the crank, the middle shaft and the chain flywheel to rotate, so that the rear wheel rotates, thus making the bicycle move forward. Therefore, whether the structure and specifications of the pedal assembly are appropriate will directly affect whether the rider's foot position is appropriate and whether the bicycle can run smoothly.

Pedal: It can be divided into integral pedal and combined pedal. No matter what style of pedal, it must have a pedal surface, which is safe and reliable and has certain anti-skid performance.

The frame is generally composed of ordinary carbon and copper pipes welded together. In order to reduce the weight of steel pipes and improve the strength, low alloy steel pipes are used in high-grade bicycles. In order to reduce the resistance of fast driving, bicycles should adopt streamlined steel pipes.

Because the bicycle runs by the driving force and riding skills of the human body, the frame becomes an important structure to bear the impact load generated by the bicycle during running and whether it can carry the human body comfortably and safely. The manufacturing accuracy of frame components will directly affect the safety, stability and lightweight of vehicles.

Outer tire: there are two kinds of soft side tire and hard side tire. The cross section of the soft sidewall tire is wide, which can completely wrap the inner tube, and the landing area is relatively large, so it is suitable for driving on various roads. Hard-edged tires have the advantages of light weight, small landing area, small resistance and light driving.

Front fork assembly: The front fork assembly is located at the front of the bicycle structure, and its upper end is connected with the handlebar assembly, the frame assembly is matched with the front tube, and the lower end is matched with the front axle assembly to form the guiding system of the bicycle.

Turning the handlebar and the front fork can change the direction of the front wheel and play a guiding role in the bicycle. In addition, it can also play a role in controlling the operation of bicycles. The front fork is a cantilever beam, so the front fork should have enough strength and other properties.

Sprocket: It should be made of high-strength steel to ensure the required tension.

Working principle of flywheel: When the pedal is stepped forward, the chain drives the flywheel to rotate forward, and then the inner teeth and weights of the flywheel are contained. The rotating force of the flywheel is transmitted to the movement through the jack, and the movement drives the rear axle and the rear wheel to rotate, so that the bicycle moves forward. When the pedal stops, the chain and the jacket do not rotate, but the rear wheel still drives the movement and the jack to rotate forward under the inertia. At this time, the internal teeth of the flywheel slide relatively, so that the movement is pressed into the notch of the movement, and the jack compresses the jack spring. When the tooth top of the jack slides to the inner tooth top of the flywheel, the compression of the jack spring is maximum. If it slides forward a little, the jack spring bounces to the tooth root and makes a "click" sound. The movement rotates faster, and the jack slides quickly on the inner teeth of each flywheel, making a "click" sound. Pedal in the opposite direction, and the jacket rotates in the opposite direction, which will accelerate the sliding of the jack and make the "click" sound more urgent. Multi-stage flywheel is an important part of bicycle transmission.

On the basis of single-stage flywheel, multi-stage flywheel adds several flywheel blades, which are combined with the sprocket on the central shaft to form various transmission ratios, thus changing the speed of bicycle.

Chain: Chain, also called cart chain and roller chain, is installed on the coupling wheel and flywheel. Its function is to transfer pedal force from crank and sprocket to flywheel and rear wheel to drive the bicycle forward. The width of the chain should be reduced to make it closely contact with the gear, so as to reduce the probability of chain drop.

2. Mechanical knowledge of bicycles

2. 1 application of motion and force

2. 1. 1 Increase and decrease friction

When a bicycle is running, there is relative movement between parts that are in contact with each other, and there is friction in these places. Friction between hands and handlebars, between wheels and the ground, and between brake shoes and wheels are all beneficial frictions. The rubber sleeve on the handlebar is made of rubber with high friction coefficient, and the rubber sleeve is engraved with patterns to increase the friction between hands and handlebar; Carve patterns on the tire shell to increase the friction between the wheel and the ground; Increase the pressure to increase the friction between the brake shoe and the wheel. Friction between front axle, middle axle, rear axle, pedal, handlebar and frame is harmful friction. The way to reduce these harmful frictions is to install bearings on rotating parts and replace sliding friction with rolling friction; Lubricate these parts by adding butter (calcium base grease) or engine oil. Friction is related to two factors: pressure and roughness of contact surface. The greater the pressure, the greater the friction; The rougher the contact surface, the greater the friction. Bicycle tires have uneven patterns. By increasing the roughness between the bicycle and the ground, the friction is increased, and the purpose is to prevent the bicycle from slipping.

There are uneven patterns on the tire of bicycle, plastic cover of handlebar, pedal cover and brake handle cover to increase friction. When braking, firmly grasp the brake handle by hand to increase the pressure of the brake pad on the rim, so as to prevent the wheel from rolling. When braking, the wheels stop rolling and slide on the ground. After rolling becomes sliding, the friction is greatly increased, and the car can brake quickly.

The front axle, intermediate axle and rear axle of a car are all rolling to reduce friction. In order to further reduce friction, people often add lubricants to these parts. Many places are engraved with uneven patterns to increase friction.

When braking, the wheels stop rolling, but slide on the ground, so the friction is greatly increased and the car can stop quickly. At the same time of braking, hold the brake handle by hand to increase the pressure of the brake shoe on the steel ring, so that the wheel stops rolling.

Patterns on tires: increase friction.

Brake pads: increase pressure and friction.

Chain and gear: increase roughness and increase friction between them.

2. 1.2 damping effect of spring

There is a thick coil spring under the seat cushion of the car to absorb shock.

Damping effect of tires: Bicycle tires are filled with proper amount of compressed air, which has great pressure and can enhance elasticity. At the same time, a spring is installed on the saddle of the car to reduce the vibration of the car through the elastic deformation of the spring. These methods can make the bicycle ride smoothly and reduce limping.

2.2 Application of stress knowledge

2.2. 1 bicycle load

The bicycle tires are engraved with the load, which clearly tells people not to overload. If the vehicle load is too large, the tire stress area will remain unchanged, and the tire will be crushed if it is stressed too much. The inner tube of a bicycle should be full of air. When the volume and temperature of the gas are constant, the greater the mass of the gas, the greater the pressure.

2.2.2 Physics in car seats

The seat cushion is saddle-shaped, which can increase the contact area between the seat cushion and the human body, so as to reduce the pressure on the buttocks and make people feel more comfortable when riding.

2.3 the application of simple mechanical knowledge

Bicycle is a kind of machinery, which consists of many simple machines: the handlebar of the executive part, the brake handle of the control part, the front crank, the rear crank of the rear brake part and its bracket, the spring clip on the shelf, the button of the bell and other parts belong to the lever. The pedal in the transmission part and the big gear disc form power to act on the labor-saving axle of the wheel, and the flywheel and the rear wheel form power to act on the labor-saving axle of the axle; The handlebar of the executive part can also be regarded as an axle. All parts of the bicycle are connected and fastened by screws, and the spiral on the screw is around the inclined plane of the cylinder.

Brake handle and connecting rod in bicycle brake system are labor-saving levers, which can increase the tension of brake pads. In addition, sprocket tooth plate and pedal, rear wheel and flywheel, automobile faucet and rotating shaft are all wheel shafts, which can save labor. The handlebar of a bicycle is equivalent to an axle, the handlebar is equivalent to a wheel, and the front axle is an axle and a labor-saving lever. The pedal and the middle axle of a bicycle are equivalent to an axle, which is essentially a labor-saving lever. The flywheel of a bicycle is also equivalent to a labor-saving axle.

In addition, the brake handle: labor-saving lever, wheel and pedal: labor-saving shaft.

The brake on the handlebar is a labor-saving lever, so people can press the brake on the rim with little force, and the pressure is relatively high. Bicycle brakes use friction to slow down and stop bicycles. When we use the brake, the friction between the brake shoe and the wheel stops or slows down, and the friction between the wheel and the ground changes from rolling friction to sliding friction. Strong sliding friction makes the bicycle slow down quickly.

2.4 Knowledge application of energy

Conversion between kinetic energy and potential energy. Before riding a bicycle uphill, people often have to pedal several times to increase the speed (kinetic energy) and "kinetic energy rushing uphill". It is easier to reach the top of the slope by converting large kinetic energy into large potential energy. You don't have to pedal when riding downhill, and the speed is getting faster and faster. This is the conversion of potential energy into kinetic energy. The kinetic energy is increasing, so the speed of the car is also increasing.

2.5 Braking and inertia

When a bicycle is driving at a high speed, especially when going downhill, it is not allowed to use the front brake alone, otherwise a rollover accident will occur. The reason is that the front brakes and the front wheels are forced to stand still. The rear wheel frame and cyclist, as driving wheels, have to maintain the original high-speed movement trend due to inertia, and then turn forward with the contact between the front wheel and the ground as the fulcrum, causing rollover accidents.

When a person rides a bicycle forward, he encounters an emergency. Under normal circumstances, it is necessary to tighten the brakes first, then tighten the front brakes, or tighten them together before and after to prevent people from flying forward due to inertia.

2.6 Application of thermal expansion knowledge

In hot summer, don't inflate the air in the tire too much, and don't expose yourself to the scorching sun, because the air in the tire is heated rapidly.

2.7 Transformation of Mechanical Energy and Internal Energy

After a while, the tire is inflated with a pump, and the cylinder wall will heat up. This is because the gas in the cylinder is compressed, which overcomes the friction between the piston and the cylinder wall to do work, thus increasing the internal energy in the cylinder wall. The temperature rises, so the cylinder wall will get hot.

Springs under the cushion: reduce the cushioning effect.

3. Suggestions for improvement

(1) Some patterns are engraved on bicycle tires, handlebars, pedals and brake pads, which increase the roughness and friction of the contact surface.

(2) Bicycle pedals should be made of rubber, plastic or metal. The pedal must rotate flexibly, and the pedal must be flat to increase the stress area and reduce its pressure on the foot.

(3) Each shaft is equipped with balls, and sliding friction is changed into rolling friction, which reduces friction and facilitates rotation. Some lubricating oil is often coated on the axle to reduce the roughness of the contact surface and reduce friction.

(4) When braking, it is necessary to tighten the brake handle to increase the pressure between the brake pad and the rim, thus increasing the friction.

(5) The braking point of the common brake is on the inner side of the rim, that is, the inner surface of the rim where the brake rubs. It has great friction and good braking effect, but it will cause great wear and tear on the bicycle tire and brake pad, which will make the braking effect worse. If it is a roadside brake, it will also damage the electroplating layer of the rim.

(6) Frame: In order to reduce the pipe weight and improve the strength, high-grade bicycles use low-alloy steel pipes. In order to reduce the resistance of fast driving, some bicycles also use streamlined steel pipes. The frame shall be welded and assembled by ordinary carbon copper pipes. It should be made into variable diameter spokes with two big ends and a small middle, and the spokes should be made into flat streamline to reduce air resistance.

(7) Outer tire: The tread on the outer tire should be appropriately increased to increase the friction with the ground.

(8) Chain: The chain falls because it is too loose or the gap with the gear is too large, so the chain length can be shortened and tightened appropriately.

(9) Sprocket: made of high-strength steel to ensure the required tension.

(10) Foot: The saddle of the bicycle is made flat to increase the stress area and reduce the pressure on the body.