Transmission is a mechanism used to change the speed and torque from the engine. It can change the transmission ratio of output shaft and input shaft in fixed or divided gears, also known as transmission. Transmission is composed of transmission and control mechanism, and some vehicles also have power output mechanism. Most of the transmission mechanism is driven by common gears, and some are driven by planetary gears. The common gear transmission transmission mechanism generally uses sliding gear and synchronizer.
Basic terms for transmission:
(1) Driving gear, driven gear. The input shaft is connected with the clutch and rotates under the engine drive. The gear fixed on the input shaft rotates synchronously. The gear is called the driving gear, and then the gear connected with the output shaft is forced to rotate, so the gear is called the driven gear.
(2) Transmission ratio I. The ratio of the number of teeth of the driven gear to the number of teeth of the driving gear is defined as the transmission ratio.
When the relationship between the number of teeth of the driven gear and the number of teeth of the driving gear changes, the change of the transmission ratio I will affect the change of the output shaft speed, that is, the change of the wheel speed. A pair of meshing gears, the number of teeth will not change in use, so its transmission ratio is fixed. If a number of gears with different number of teeth are installed on the input shaft to mesh with the gears with different number of teeth on the output shaft, a group of step transmissions with different transmission ratio I can be obtained. Automobile transmission is to shift gears according to this basic principle.
(3) Forward gear, a gear that enables the car to move forward. Reverse gear is a gear that can reverse the car. In neutral, all gears in the transmission are not in the working position. At this time, the engine power input to the input shaft is no longer transmitted to the output shaft.
(4) Direct transmission. The engine power is not transmitted by any gear in the transmission, but is directly output through the transmission input shaft and the output shaft which is directly connected with it. The direct gear ratio is1.
(5) Overdrive. That is, the speed of the output shaft is higher than that of the input shaft.
(6) Number of files. It refers to the number of gears in a step gear transmission. Commonly used gear transmissions have four to five gears, while three gear transmissions are rare. The more the number of gears, the better the adaptability of the car to driving conditions and the lower the fuel consumption. However, the more complex the transmission mechanism and control mechanism are, the more difficult the operation is and the higher the cost is.
(7) Low grade and high grade. In the transmission gear, the gear with small number is called low gear. The smaller the number is, the greater the transmission ratio, the greater the traction, and the lower the speed is. For example, the transmission ratio of the first gear is the largest in the forward gear, the speed is the lowest, and the traction force is the largest. The higher the number, the smaller the transmission ratio and the traction, but the higher the speed.
(8) Shift gears. The transmission completes the transmission ratio transformation process, which is called shift. Gearshift of shift sleeve is realized by meshing (or separating) the engagement ring gear and the engagement sleeve on the tooth side, which are integrated with the gear. It is called gearshift of shift sleeve. Synchronizer shift, using synchronizer shift. There is not only no impact and noise on the engagement teeth, but also short shift time.
(9) Jump gear. Due to the wear and vibration of the engagement gear, the engagement sleeve and the engagement ring gear are separated, and the transmission is in neutral.
The class transmission is the most widely used one. It adopts gear transmission, and has several fixed transmission ratios. According to the different types of gear trains used, there are two types of fixed transmission (common transmission) and axial rotary transmission (planetary transmission). The transmission ratio of car and light and medium-sized freight car transmission usually has 3-5 forward gears and one reverse gear, and there are more gears in the combined transmission for heavy trucks. The so-called transmission gear number refers to the number of forward gears.
CVT is a variable speed system which can continuously obtain any transmission ratio in the range of transmission. The best matching between the transmission system and the engine can be obtained by stepless transmission. The common CVT includes hydraulic mechanical CVT and metal belt CVT.
The comprehensive transmission is a kind of hydraulic mechanical transmission composed of hydraulic torque converter and gear type progressive transmission. Its transmission ratio can be changed steplessly in the range of several discontinuities between the maximum value and the minimum value. It is widely used at present.
The transmission is composed of transmission mechanism and transmission control mechanism. The main function of the variable speed transmission mechanism is to change the value and direction of torque and speed; The main function of the control mechanism is to control the transmission mechanism and realize the transmission ratio transformation, that is, to realize the shift, so as to achieve the variable speed torque.
The simple transmission has the advantages of high efficiency and simple construction and convenient use. However, the number of gears is small, and the range of I change is small (traction force and speed range is small), and it is only suitable for some drivers with few gears. If the range of I is increased, the transmission size will be increased and the shaft span will be increased. In order to increase the number of gears and not make the shaft span too large, the component transmission can be adopted. The so-called constituent transmission is usually composed of two simple transmission, among which the main transmission with more gears is called the main transmission, and the less is called the secondary transmission.
Mechanical gearbox mainly uses the principle of gear speed reduction. In short, there are many groups of gear pairs with different transmission ratios in the gearbox, and the shifting behavior of a car is to make different gear pairs in the gearbox work through the operating mechanism. For example, at low speed, let the gear pair with large transmission ratio work, while at high speed, let the gear pair with small transmission ratio work.
Transmission gears are often in changing speed and work under load. The gear tooth surface is also impacted by impact load, which causes damage to gears (especially tooth surface). Common damage includes:
(1) Gear wear transmission gear under normal working conditions, the tooth surface shows uniform wear, requiring that the wear along the direction of the tooth length should not exceed 30% of the original tooth length; The tooth thickness shall not exceed 0.40; The meshing area of gear shall not be less than 2/3 of the tooth surface; The meshing clearance of running gear shall be generally 0.15-0.26mm, and the limit of use is 0.80mm; The engagement clearance of the joint gear shall be 0.10-0.15mm, and the limit of use is 0.60mm. It can be measured by dial gauge or soft metal rolling method. If the clearance is exceeded, it shall be replaced in pairs
(2) The gear teeth are broken, mainly due to the gear meshing clearance is not in conformity with the requirements, the meshing part of the gear teeth is improper or the work is subject to a large impact load. If there is small crushing not more than 2mm on the edge of the gear teeth, it can be used after the grinding with oil stone; If there are more than 3 small pieces beyond this range, they should be replaced in pairs
Transmission working principle
(3) The end face of the regular engagement gear is worn and the inclined tooth face with constant engagement shall have an axial clearance of 10-0.30mm to ensure the gear to work well. If the tooth end is worn and started, it can be ground and repaired, but the grinding amount shall not exceed.50mm
(4) The mating clearance between the bore of the gear seat and the needle roller bearing and the journal shall be 0.01-0.08mm after the wear of the Journal of the normally engaged gear, the needle bearing and the seat hole. Otherwise, it should be replaced