Analysis of scooter belt drive and stepless speed change
There are many forms of mechanical transmission, and belt drive is the most widely used one. The belt drive can be used for transmission with a large distance between the two shafts, and also has the advantages of alleviating impact, absorbing vibration, low noise, low cost, and convenient maintenance. Because it is easy to slip and the transmission ratio is inaccurate, it is only used in the mechanism that has strict requirements on the transmission ratio. At the same time, it also has the disadvantages of poor heat resistance, poor overload resistance, and easy aging, so it is not used in mechanisms that need to transmit high power.
Belt drive generally has three types: flat belt drive, V-belt drive and synchronous toothed belt drive. The toothed V-belt drive is commonly used in motorcycles. Although its inner colloid also has a tooth shape, it is mostly for easy bending and not for synchronous transmission. In recent years, the toothed V-belt drive has been widely used in scooters, in order to use it to facilitate the realization of stepless speed change, and to make different transmission ratios for the engine and the wheels, so that users can drive a motorcycle more easily than a shift car. easy and convenient.
1. Common sense about light friction belt drive:
1. Advantages and disadvantages of belt drive:
Belt drive is available Because of the transmission with a large distance between the two axles, in the design of most motorcycles, it is mostly used to connect the engine to the transmission of the rear wheel gearbox. Because the belt drive has the advantages of alleviating impact, absorbing vibration, less noise, low cost, and more convenient maintenance and repair, it is beneficial to apply it to motorcycle transmission.
Because the V-belt can use the oblique edge to change the transmission diameter, it can also change the transmission ratio while acting as a deceleration transmission. The use of the automatic rationalizer and the automatic continuously variable transmission system makes the operation of controlling the speed of the motorcycle save the troublesome manual shifting. Driving is simplified to the point of using a “point-and-shoot camera”, so belt continuously variable transmission has become especially popular in urban motorcycles in recent years, which has been developed from the original simple light motorcycle to a medium-displacement scooter.
The shortcoming of belt drive is easy to slip and inaccurate transmission ratio is not a big problem in the driving transmission of motorcycle, so the belt drive can be widely used in civilian vehicles that are easy to operate.
Belts have shortcomings such as poor heat resistance, poor overload resistance, and easy aging. This can only be solved by improving the quality of the belt, so it is not often used in vehicles that need to transmit high power.
For light motorcycles, the biggest disadvantage of belt drive is the large transmission damping, especially when the car is cold. Because the belt consumes a part of the energy when transmitting power, the power performance of the belt car of the same displacement is not as good as that of the sprocket car. Its specific performance is in the taxiing and speed. The belt car is strenuous when it is pushed, and when it is taxiing, it seems to have a little brake, and the maximum speed is also greatly reduced. The fuel consumption of cruise control is often 30–50 more than that of a sprocket of the same level. %, it is also difficult to make fuel-saving tests.
Another disadvantage of belt drive is that the bearing is subjected to excessive lateral force, and most of the motorcycles are designed in the same direction as the work force. It is much more laborious to use on a sprocket, and it is easier to damage.
2. The center distance of the two pulleys and the length of the belt:
The center distance of the two pulleys refers to the distance between the front and rear two belt pulleys, although the belt can be used for two axles The advantage of the transmission with a large middle distance is that it should not be too large; if the middle distance is too large, the belt is too long and easy to shake. In addition to the mutual wear of the belt cover by the belt, it will also bring a great deal of lateral movement to the front and rear axles. It is easy to damage the parts and the belt itself.
Circumferential length of belt = center distance x 2 + 1/2 front belt diameter circumference + 1/2 rear belt diameter circumference. In the design of motorcycles, most of the transmission belts of BMX are not long. The longest belt for motorcycles is about the B-type belt of the old Jialing 50 car, about = 1014mm.
3. The diameter of the pulley and the linear speed of the belt:
The diameter of the pulley for vehicles should not be too small. Due to the influence of the thickness of the V-belt itself, the belt will not be bent too much. Small diameter, and the contact area of the belt with the belt pulley is small when the belt is driven at the smallest diameter, and the belt is easy to slip and heat up to burn. The diameter of the belt pulley is larger, the contact area between the belt and it is larger, the transmission efficiency is higher, and the lateral tension force can be smaller.
The transmission speed of the belt is easy to calculate; take the transmission diameter of the belt in the belt pulley x pi x the speed of the belt pulley/second = the linear speed of the belt/second. The linear speed of the belt for light motorcycles is generally not more than 25 m/s. If the belt is too large, it consumes too much energy and the belt is overheated. If the belt is too small, the transmission power is limited.
4. Transmission ratio of belt drive:
In belt drive, the ratio of the diameter of the driving wheel to the diameter of the driven wheel is called “transmission ratio”. The rotational speed of the driving wheel and the driven wheel is inversely proportional to the diameter of the two wheels. The formula is: transmission ratio = driving wheel speed / driving wheel speed = driving wheel diameter / driving wheel diameter. The static transmission ratio of most motorcycle belt pulleys is a deceleration state, between 1.5–2.5. In light motorcycles, the transmission ratio of the lowest speed can be measured statically: without starting the vehicle, just turn the front belt pulley by hand, and see how many turns it takes to make the rear pulley rotate once. It is inconvenient for amateurs to measure the dynamic rotation ratio, because the belt is subject to thermal deformation, elongation, sliding, and other changes during dynamic driving. It is estimated by witnessing the change in the diameter of the belt on the belt pulley. It is not too smart, and most of them are estimated by the change of the engine tachometer and the speed of the vehicle.
For example, the cj50 car: the static transmission ratio of the front and rear belt pulleys can be measured at about 1.5/1—-2/1; the dynamic transmission is estimated by the display of the engine tachometer and vehicle speed, about 1.5/1—-2/1. At 1/1—-1.5/1. It can be seen from this that the transmission ratio of the belt pulley of the original car does not change very much, and the change of the speed of the belt pulley increases by about 50% at most.
Second, common sense about belts for light motorcycles:
1. Types and specifications of V-belts:
General V-belts There are five grades of belts such as abcde, and most of the current light motorcycles are B-type. Take the bull brand belt for cj50 car as an example; its circumference is 1014mm, its outer width is 15mm, its inner width is 11mm, its thickness is 10mm, and its weight is about 75g. The belts used in other motorcycles are similar in section, but the lengths are different. Sometimes when it is necessary to emergency, find a type B belt, as long as the length is similar, it can be temporarily replaced.
2. The quality and price of the belt:
The quality and price of the belts of different brands vary greatly. The author has tried some a-type and b-type industrial V-belts and some brands The B-type V-belts have been recorded in detail. Write down the circumstances of trying them here, only for the reference of enthusiasts who are interested in studying motorcycle technology.
A-type industrial V-belt: 3 yuan a piece, the advantage is that it is easy to bend, the transmission damping is small, the belt is convenient, and the driving is brisk. It is the best choice for 24cc light mopeds. Be careful when using it on a 50cc light motorcycle. The A-type belt is too delicate to handle heavy loads. If you drive at high speed for a few kilometers, you can finish it. I even put a spare belt in the car, which is feasible in the city.
B-type industrial V-belt: 4–5 yuan a piece, it does not have the advantages of a-type industrial V-belt, it is thick and not easy to bend, and the upper belt is a little tight. Due to the large damping, the driving is stable, the belt can also have high speed after being heated, and the load and heat resistance are much stronger than that of the a-type belt. However, because the belt is too thick to withstand bending, it will not take less than 100 kilometers.
A kind of B-type motorcycle V-belt with the brand name of Southwest Jialing Company: the base price is about 7 yuan a piece, the appearance is decent, the hand feel is hard, the driving feeling is average, there are many motorcycle parts stores in the city Sales. The most obvious feature is that the endurance cable on the outer layer of the belt is an orange thick nylon thread. After 200 kilometers of use, the defect will start to appear. I have used several, but they are all broken at the value of driving 330km, and then I will not try it again.
Bull brand B-type motorcycle V-belt: 15 yuan per piece of yellow trademark, good appearance, good hand feel, and average driving feeling. “Ma Mobi” is available for sale. I ran nearly 5,000 kilometers on the first trial run. If I hadn’t climbed the mountain and made a fool of myself, I should have spent more time. The white label I bought later was ten yuan a piece, which was not as durable as the first one. The most obvious feature of the belt is that the endurance cable in the interlayer outside the belt is a light green multi-strand nylon thread, but the nylon thread is covered with a layer of black thin cotton thread. My feeling is that the endurance cable in the interlayer is best composed of soft thin threads. In this way, there will be no signs of damage caused by hard line defects.
3. The “critical point” and service life of belt wear:
After using more than a dozen belts, there is still no accurate measurement of the service life of various belts As a result, it was finally found that the wear of the belt generally has three conditions: surface wear, bending and fracture, and high temperature burnout. Among them, surface wear and bending fractures have an approximate service life, and only high temperature burning is unpredictable. I have tried driving wildly in the suburbs, and a belt can be burned in a quarter of an hour; while driving slowly, an old damaged belt can be dragged home for more than 100 kilometers.
When the belt truck is running at high speed, a lot of heat is generated by the friction between the belt and the belt disc. The heat generated by the friction is a troublesome thing that is difficult to accurately calculate. When the light motorcycle is running at a medium speed, the energy loss of the belt drive is about 20%. If the energy of these internal consumption is concentrated on the belt, it can heat up the belt by about one degree per second. If there is no way to dissipate heat, the belt will soon overheat and burn out.
The dissipation of internal heat is mainly by the rotating airflow passing the periphery of the metal belt pulley. There are fan blades on the belt pulley of the Dalmore yellow-brand car to dissipate the wind, while some belt pulleys in the light motorcycle have no fan blades. Because the greater the temperature difference with the air, the easier it is to dissipate heat, so although the frictional heat production of the belt pulley increases with the increase of the vehicle speed, the accumulated heat temperature difference will not be proportional to the vehicle speed, and the heat will stop at a certain level.
Vehicle belts, depending on the quality of their brands, have a “critical point” that can withstand high temperature work, and a good belt naturally has a higher “critical point”. In this way, there is such a situation, the life of the driving belt is very long, and there is no “high temperature burn” until “surface wear” or “bending and fracture” occurs. If you drive at high speed, the accumulated temperature of the belt pulley will rise rapidly. Once the “critical point” of the belt’s high temperature tolerance is exceeded, the belt will burn out quickly.
In the hands of ordinary amateur riders, there is no instrument that can measure the temperature of the belt pulley in rotation, only one thing to keep in mind: the belt of the ** brand is on this bike, and the long-distance ride can reach **km/ h speed, or you can ride the maximum speed in a short period of time.
I have an experience in riding a belt bike in my early years: whenever the driving is relaxed and the most enjoyable, it is when the belt is too hot and soft, approaching the “critical point”, and the belt drive has the least damping. I didn’t know it at first, but I broke a lot of belts for tuition, and I only counted them later. The best way is to add a self-made fan to the belt pulley to force air-cool the belt pulley and belt, which is quite effective.
4. Characteristics of belt-driven motorcycles:
Compared with sprockets, the most obvious feature is that the damping is large, even when the automatic clutch is already in a disengaged state, the It is still difficult, because even if the belt pulley and belt are idling, there is a lot of damping. This kind of car is not easy to slide, and it will slow down as soon as the accelerator is closed, which is convenient for urban traffic and downhill driving control; but it is very unfavorable for long-distance high-speed driving and fuel saving, and it also wears a lot of engine. , the engine is more difficult and easy to overheat at high speed or uphill.
After the stepless speed change of the belt drive is realized, there is no need to manually shift gears, and the driving operation is simple, which is conducive to maneuvering through the complex downtown environment. Compared with the gearless sprocket vehicle, the belt speed change vehicle has a larger starting torque, strong climbing ability, and a large range of speed change, which is conducive to forcing off-road on the difficult and dangerous ground in the mountains. The belt car is reliable in use, simple in structure, cheap in accessories, and much simpler in maintenance, which is an advantage for users to maintain and repair motorcycles by themselves under amateur conditions.
5. The rear belt pulley of the stepless speed change for light motorcycles: (take cj50 as an example.)
1. The rear belt that adjusts the belt tension and working diameter with its own spring pressure Disc: On a belt-driven CVT motorcycle, the rear belt disc is a relatively simple thing. It usually presses the movable side of the disk to the fixed side of the disk with its own spring pressure, and the trapezoidal belt is extruded on the outer circle of the disk, so that the belt can automatically maintain the maximum working diameter on the rear belt pulley at any time.
This kind of structure makes the speed ratio of the belt drive in the state of the maximum reduction ratio of the small front disc/large rear disc every time the belt car starts, so that the driver’s starting operation is very convenient. Moreover, when the engine speed drops below the variable disc value, the working diameter of the front disc becomes smaller, and the rear disc can automatically restore the maximum working diameter at any time.
When the engine speed is increased above the variable plate value, the two sides of the front speed change belt pulley are closed, and the belt is extruded into a larger working diameter. At this time, the rear belt pulley is pulled into a smaller working diameter by the belt, and the movable disk surface is pulled apart from the fixed disk surface by the belt. This is the smaller reduction gear state.
The structure of the general rear pulley is relatively simple. In recent years, there has been a movable pulley chute that can control the effect of the rear pulley by its own torque. The trend towards integrating the clutch on the rear pulley is also widespread, and the overall structure is a little more complicated, but the basic principles are the same. The advantage is that it improves the climbing performance and sliding effect of motorcycles, which is worth promoting.
2. The practical diameter and use of the rear belt pulley: (take cj50 as an example.)
The maximum diameter of the rear belt pulley is 104mm, and the minimum diameter is 52mm, but neither is the maximum and minimum working diameter of the belt on the rear disc. The maximum working diameter of the 10mm-thick trapezoidal belt on the rear disc should not exceed 92mm, that is to say, the outer edge of the belt should preferably not be larger than the maximum diameter of the rear disc, otherwise the belt will easily fall off at high speed.
The minimum working diameter of the trapezoidal belt on the rear disc will not be lower than 62mm, because this is the limit of the minimum diameter of the rear disc + the thickness of the belt. In this way, it can be calculated theoretically: the maximum reduction ratio of the belt drive transmission system of the cj50 is 1/2.3. (The minimum working diameter of the front disc is 40mm/the maximum working diameter of the rear disc is 92mm).
The quality and service life of the rear belt pulley of cj50 are very impermanent. I have used eight or nine rear pulleys in the past two years, and the fastest damaged one only took less than a week. Thousands of kilometers. Due to its original design flaws, other than adding viscous lubricating oil to the chute and enhancing heat dissipation, I couldn’t come up with a good solution for a while.
The simpler way is to change the variable value of the small front plate. Before the engine 65% of the standard speed, the front disc has to start to change the reduction gear ratio. (When the engine is at 4,000 rpm, the whole vehicle enters a high-speed driving state.) This is very effective for fuel-saving driving on flat ground, and the vibration of the engine is also reduced, but it will affect the acceleration at start and high-speed climbing.
3. The shortcomings of the belt pulley after cj50 and how to improve it:
There are three defects in the belt pulley after cj50, two of which are difficult for individuals to change: one is to give The size of the cylindrical part of the chute guided by the movable disc is too short, so that when the rear disc is at the maximum working diameter, the sliding surface pressure of the guide cylinder is very large, and the material of the guide cylinder is too poor, and it is inevitable to add lubricating oil frequently. Wear out quickly.
After the guide cylinder of the movable disk surface is worn out, the movable disk surface cannot be kept parallel to the fixed disk surface during operation, which will cause a special entrainment phenomenon. This special entrainment phenomenon is manifested in the fact that the engine is struggling to consume fuel when driving, the driving is difficult and the belt is overheating; and after the new rear disc is replaced, the whole vehicle runs fast with a new look.
The second defect is that when the belt enters the minimum working diameter of the rear disc, the minimum disc surface of the fixed disc surface is not a standard inclined surface, which has a great effect on the belt, which is not the case for the new belt car. For this reason, even when adjusting the working diameter range of the belt, you have to be careful to avoid this area, and the minimum working diameter is not used.
The third defect is that the rear disc will overheat when the belt is working. The belt drive has large damping and friction will naturally generate a lot of heat, but the heat resistance of the belt is limited. Burn a belt. This problem is still easy to solve. It is ok to cut a cooling fan with a thin iron sheet and sandwich it between the compression spring and the movable disk.
4. Measures to prolong the service life of motorcycle belt drive system:
There is one more thing to know about the belt drive of cj50: Due to the insufficient follow-up of the front disc, there is a reverse pulling force on the belt. Doing too much is also a factor of damage to the belt, but it seems a little more troublesome to rely on individuals to “solo” like a bicycle on the belt pulley.
The above-mentioned defects are only found on the cj50 car. The new style belt car mostly adopts the rear clutch type belt pulley, so naturally there is no longer these old troubles, so the content here is only for refer to. What an average person can do is: always add the most viscous type of lubricating oil to the movable guide part of the belt pulley to keep the sliding cylinder surface lubricated and reduce wear.
6. Adjustment and use effect of stepless speed change of belt for light motorcycle:
1. The speed change ratio of front and rear belt pulley and the effect of driving:
I have done many tests on the gear ratio of the front and rear belt pulleys. The maximum reduction ratio has been tried 2.5/1, and the 50 car climbs 20% of the slope without any problem. Later, it was found that the belt speed ratio of such old-style cars is limited by the original size of the front and rear belt pulleys. For the service life of the rear pulley and the belt, we can’t be too greedy.
Take the even jh50 car as an example, the best reduction ratio is between 1.8/1–2.2/1, and the 2/1 reduction ratio is equivalent to the low gear of the sprocket car 25km/h, such a low-speed torque can just climb a 20% slope. The deceleration ratio after changing the plate is about 1/1–1.2/1, the maximum speed is 50ma, and the highest has been 60ma.
Besides changing the minimum working diameter of the front disc, the reduction ratio range of the belt is mainly to adjust the front and rear position of the rear disc on the cantilever. The drive wheelbase can be adjusted for the old and new state of the belt, which is better than the new belt car. The maximum working diameter of the cold car adjustment belt on the rear disc is achieved by adjusting the front and rear positions of the rear disc on the cantilever.
Generally speaking, the performance of the belt car is better, and the larger the speed ratio of the belt continuously variable transmission, the better, which is the value of the maximum reduction ratio/minimum reduction ratio. , the speed change performance is almost equivalent to the fourth gear of the sprocket, and the original jh50 new car is only about 1.4, so the gap is too big.
One thing to note about the gear ratio of the belt car is that if the structure of the belt pulley is not good, the gear ratio should not be too large. First, the contact surface of the belt is small when the minimum working diameter of the front disc is small, which is easy to wear and burn. The second is that the damping of the belt drive is large, and it consumes a lot of power to overcome its own resistance at the minimum reduction ratio, and the total efficiency of useful work is low. In view of the large damping of the belt drive, the high fuel consumption rate, the low total transmission efficiency, the more serious wear than the chain, the changes in the working conditions are not as stable as the chain, and the speed ratio has certain limitations—-and so on. The application is also a “convenient” civilian, a typical “dumb machine” that only needs to turn the accelerator and brake.
If the user has no special requirements, a good 50 belt car is more suitable for urban traffic. In addition to being particularly simple and suitable for women, the general 30ma cruise can reach a fuel consumption rate of 70ma/l, the practical fuel consumption rate in the city is about 50km/l, and the maximum speed can reach 60ma. Especially in the alleys of the vegetable market or the difficult off-road areas in the hills, it is indeed the only one.
2. The “change plate” speed of the engine and the effect of driving:
The “change plate” speed of the engine has a great relationship with the effect of driving fuel consumption and starting acceleration . Because the choice of the general belt automatic transmission is not based on the driver, but on the speed of the engine. It is easy to use it in manoeuvring vehicles, but it is difficult to achieve the best gear ratio matching in long-distance cruising, so it is inevitable to consume more fuel.
General vehicle design will set the variable plate value of the front gear plate at about 80% of the standard engine speed. This speed is usually the area where the engine outputs the maximum torque. (Shifting) The force is larger, the load on the engine is smaller when changing the plate, and the speed of the vehicle is relatively stable. But the car I changed was different.
To put it simply, if the “change plate” value of the front gear plate is small, the engine will have a high speed at a low speed, which is equivalent to shifting gears at a low speed of the engine, which is of course a throttle. Oil, less engine vibration, and more durable belts. But without the conditions for the high engine speed to accelerate the motorcycle, the whole vehicle will start slower, and it will be slower going uphill.
For some engines that are fixed at a high-speed ignition angle, the torque is low at low speeds, resulting in weak acceleration or difficulty going uphill. In addition, for an engine without a low-speed ignition angle, if the throttle is abused at low speed, the loss of fuel and parts will be larger. For the above reasons, riders should think twice before changing their car.
If the “change plate” value of the front gear plate is larger in reverse, the engine can only have a high speed when the engine rotates at a high speed, which is equivalent to shifting gears when the engine rotates at a high speed. The usual medium speed also needs to use the larger throttle and high speed of the engine, which is of course not worth the cost of fuel. This is often the case with the throwing blocks of the front derailleur after wear and tear.
Usually the vehicle will start faster and go uphill faster. However, most of the engines run at high speeds, and wear and fuel consumption are inevitable. The vibration of the engine is larger, the cylinder block and the belt will be overheated, and the belt should be used carefully to prevent it from burning. Some riders will mistakenly think that the vehicle is “running in”. Here is one of the characteristic experiences of the belt car: when the vehicle performs best, it is about to break down.
3. Driving effects of cold and hot cars:
The driving effects of cold and hot cars usually refer to the effect of engine temperature on the effect of the carburetor. The response of the belt continuously variable transmission system. There are generally two situations: First, the lubricating oil in the rear gear reduction box is too viscous. After driving for a while, the lubricating oil is stirred and heated and becomes thinner. At this time, the driving will be easier, and the distance of flameout will be longer. .
The most important thing is that the belt will heat up and become soft after running, and the damping of the transmission will be much smaller, sometimes nearly doubled. The external performance of driving is that the vehicle runs more easily, the engine sound is small and not difficult, and it can run at a higher speed and lower fuel consumption. But if there is no effective heat dissipation measures, such a car condition is actually approaching the “critical point” where the belt is burned.
4. Measures to reduce belt drive damping and slippage:
The main disadvantage of belt trucks is transmission damping and slippage, which cannot be eliminated, but there are still some disadvantages to reducing them. way. The measures are as follows: a. Align the transmission axis of the front and rear belt pulleys to reduce the side sliding friction of the belt. b. Frequently check whether the guide sliding part of the belt pulley is worn or not, that is, whether there is excessive loose clearance on the movable disk surface.
c. Select the appropriate transmission reduction ratio and transmission speed ratio, and the variable plate value as low as possible. d. Check whether the lubricating oil in the rear gearbox is too thick and can be adjusted according to the season. e. Appropriately apply belt wax to the belt according to the vehicle condition. f. The cooling fan is essential, if you don’t have one, you can add one by yourself.
