The motorcycle transmission, transmission principle, transmission form and clutch are described in detail.

In the previous mechanical unit, we discussed the power heart of motorcycle-engine. Next, we will lead you into the next stage of the power system, that is, the transmission and transmission system. With the transmission system, the power of the engine can be transmitted from the crankshaft to the rear wheels. Through the transmission system, the power of the engine can be exerted in different speed ranges at the right time. What is the principle of this variable speed system and what are the transmission modes of power? We enter the theme of this issue-"transmission and speed change".

Through the transmission system, the engine can output power to the rear wheels to accelerate the vehicle.

Why do you need transmission?

The transmission system is the medium to transmit the engine power. With the help of the transmission system, the torque output by the engine can be exerted from the tire, which really accelerates the vehicle. The text description is simple, but in fact, the transmission system is very important and intelligent. If there is no transmission system, the engine must be placed next to the rear wheel, directly connecting the crankshaft with the rear wheel for power output. In this way, the center of gravity of the vehicle will tilt backward, and the handling performance will be greatly reduced.

In order to give full play to the advantages of horizontal engine, BMW motorcycle had to put the engine straight.

Through the transmission system, the engine can be placed between the front and rear tires to keep the load ratio of the front and rear wheels close, and BMW can also design a horizontal engine on the motorcycle. When designing a horizontal engine, BMW engineers must straighten the engine, that is, the crankshaft will be parallel to the body, in order to give full play to the advantages of the engine. According to the general in-line four-cylinder engine configuration, the direction of the crankshaft is perpendicular to the direction of the car body, or the rotation direction of the crankshaft is the same as the rotation direction of the tire. But for the horizontal engine, the transmission system must turn the power output direction by a right angle, so that the tire will turn forward.

reduction ratio

In addition to transmitting power, the transmission system must also properly adjust the power output through the reduction ratio. If the power of engine rotation is directly transmitted to the rear wheel, then the engine rotates once and the rear wheel must also rotate once. After conversion, when the engine speed is 5000 rpm and the speed of 17 inch tire is the same, the linear speed is about 600 km/h ... This speed is obviously too fast, and it needs to be slowed down by gears and other similar mechanisms.

If the power of the engine is directly transmitted to the wheels, the vehicle will become difficult to control, so the transmission also plays a role in adjusting the power.

After the power slows down, although the speed slows down, the torque will be amplified, and there is a difference between crankshaft torque and wheel torque. What if the engine can run at 5000 rpm? Output torque of 2 Nm, and then decelerate to 2500 rpm? After that, the torque can be theoretically amplified to 4Nm. However, due to the power loss in the transmission process, such as friction loss, the actual measured data will be slightly lower, which is the problem of transmission efficiency.

Various transmissions

The transmission system usually uses the following common mechanical components for matching. The first is the chain and toothed disc system commonly used in imitation racing cars and street cars, the belt and toothed disc system for pedals, the toothed belt transmission system for American cruise vehicles, and the shaft transmission system for BMW multipurpose vehicles and station wagons. The transmission modes listed above have their own advantages and disadvantages, and are also applicable to different models. Next, a brief introduction.

As the multifunctional flagship of BMW, R 1250GS adopts horizontal and horizontal double cylinders with upper shaft transmission.

Chain and toothed disc

The transmission system composed of chain and toothed disc is the most common one at present, and this type of transmission parts are almost uniformly used to imitate racing cars. After passing through the engine and gearbox, the power is transmitted to the small toothed disc (front teeth) on the transmission shaft, and then to the passive large toothed disc (rear teeth) on the rear axle by means of the chain. The number of teeth of the small toothed disc and the number of teeth of the large toothed disc are converted into a reduction ratio, so after the chain and the gear are matched, a torque can amplify the power.

Power amplifies torque through the cooperation of front teeth and rear teeth.

The advantages of toothed disc and chain are high transmission efficiency and large torque. In a well-matched system, the efficiency can reach 95%? Above, it is a better design. Convenient maintenance is also the advantage of this transmission. There is no need to disassemble any parts, and the wear of the toothed disc and chain can be easily detected by naked eye observation. The chain and toothed disc are light in weight, especially the toothed disc can be made of aluminum alloy, which reduces the overall moment of inertia and will not increase the burden of vehicle acceleration.

Disadvantages: the contact between chain and toothed disc will not only wear each other, but also bring vibration and noise. In the case of starting or accelerating again, it will also bring annoying stiffness, and the driving comfort is not as good as other transmission systems. For this reason, leisure and cruise vehicles that mainly take long-distance rides will try to avoid the transmission system of chains and toothed discs.

Chain has a simple structure, but it can transmit high power, and it is the most common design at present.

Belt and traction wheel

Belt and disc are common transmission systems of pedals. Besides transmitting power, they can also be used as transmission systems. Is the belt referred to here a V? V-belt, V on both sides? Friction between the inclined plane and the dividing disk is used to transmit power. By adjusting the position of the belt according to the opening and closing situation of the valve disc, different reduction ratios can be made to realize the speed change function, so it can also be used as a speed change system.

CVT also has front and rear teeth, such as sprocket drive, to realize the function of speed change.

This type of system combination can not only increase the function of speed change, but also cooperate with centrifugal clutch, so that the driver can drive the vehicle only by operating the throttle. The whole system uses friction to transmit power, so there will be a conversion between dynamic friction and static friction, which makes the whole power transmission more flexible and increases comfort, but it also limits the efficiency of power transmission and the transmission of maximum torque. The transmission efficiency of power is about 80%? Between 90% and 90%, the transmission efficiency will be lower under the condition of variable speed.

Yamaha's YCC-AT changed the CVT with continuously variable speed into a segmented system that can move into and out of gear.

Straight drive

Shaft transmission system is widely used in automobiles, because it is easy to design a high-power transmission system as long as the diameter of the transmission shaft is increased. On motorcycles, only a few recreational vehicles choose axle transmission system, although the cost will be much higher than that of chain and toothed disc system, but the advantages are more flexible power transmission, no vibration of chain, long maintenance cycle and average life span, which are also indispensable advantages of axle transmission.

BMW is proud of its axle drive system.

Toothed belt and pulley

Finally, the design of toothed belt and pulley is mentioned, which is often used by Harley-American cruise locomotives. Here, the belt is not in contact with the pulley by friction, but is designed as a chain and a toothed disc, and the number of teeth on the belt is designed to be embedded with the dents on the pulley. Its advantages are soft power transmission, light weight, high quietness and long maintenance period; However, toothed belt transmission also has the disadvantages of high cost and difficult belt replacement. This type of system is also commonly used in the timing mechanism of engine valve system.

Besides American cruise cars, BMW is also in F800S? The tooth profile is used as a transmission element.

grasp

Both the pedal and the so-called shift car need clutch design, so that when the vehicle speed is zero, the tire can be separated from the engine and the engine will not be turned off when the vehicle stops. Generally, the pedal adopts centrifugal clutch, which is automatically controlled according to the engine speed without knight operation, which will be introduced in detail later. This paper mainly discusses the clutch mechanism that needs knight control on the shifting car.

The biggest function of the clutch is to cut off and combine the power output by the engine crankshaft. In general gearbox design, the power of crankshaft reaches the clutch after the first reduction ratio. After passing through the clutch, it is the variable speed gear set, and then it is output to the rear wheel by the transmission system. Therefore, when the clutch cuts off the power, there will be no power transmitted from the transmission gear to the rear wheel. On the other hand, when the clutch is cut off, the cyclist will turn down the throttle and increase the engine speed without affecting the vehicle speed. In addition, the clutch has an important function of starting the vehicle. When the vehicle stops, the rotation speed of the tire is zero. At this time, it is necessary to use the friction of the clutch to keep the minimum running speed of the engine with the power of the engine gradually increasing, so as to avoid flameout. This process is also called semi-clutch, or dynamic friction state. Simply put, the function of the clutch here is to reconcile the revolutions of the front end (engine) and the rear end (rear wheel) of the power output, and finally combine the two.

The clutch structure consists of clutch plate and friction plate.

In the structure of clutch, it can be divided into two parts, the first part is clutch plate, and the second part is friction plate. In the picture, the clutch plates and friction plates are crossed, and seven friction plates are placed between the eight clutch plates. The yellow friction plate is attached to the clutch plate, causing friction with the friction plate. When the yellow one is used up, the clutch will be insufficient and need to be replaced to maintain performance. From the shape, the clutch plate is a convex shape with teeth on the periphery, which just engages with the tooth groove of the clutch cover. On the other hand, the inner edge of the friction plate is designed with concave tooth grooves, which mesh with the convex grooves designed in the clutch inner hub.

As can be seen from the chart, the clutch cover is engaged with the clutch plate and connected with the crankshaft, belonging to the driving end. The clutch inner hub is engaged with the friction plate and connected with the gearbox, belonging to the passive end. When the clutch lever is loosened, another element called clutch pressure plate presses the clutch plate and friction plate together with a spring, so that the driving end and the driven end are engaged. When the clutch pull rod is pressed down, the pressure plate is released, the clutch plate and friction plate can move relatively freely, and the power is cut off.

Wet and dry

Knowing the basic working principle of clutch, readers will probably want to ask, what do you mean by wet clutch and dry clutch? The wet clutch mentioned here means that the whole clutch mechanism is immersed in lubricating oil (gear oil) to help the clutch plate and friction plate completely separate and rotate independently. Lubricating oil can also make them join smoothly when rubbing, and it also has the function of heat dissipation.

In the past, Ducati pursued the ultimate performance and used dry clutches in its high-end vehicles to improve performance. However, considering the problems of maintenance and noise, most of them now use wet clutches.

Dry clutch is the opposite design, and the whole clutch structure is not soaked in oil, or even directly exposed to the air, which is convenient for heat dissipation. Because of the lack of lubricating oil, dry clutch has strong engagement force and is often used in racing cars. When the vehicle starts, it needs high clutch operation skills, otherwise it will stall at the moment of engagement.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.