For a car with front and rear drive, the torque from the engine goes throughclutch、transmission case、a universal coupling, transmission shaftmain reducer、differential mechanismThe half axle is transmitted to the rear wheel, so the rear wheel is also calledDrive wheel。When the driving wheel gets the torque, it gives a backward force to the ground, and thus causes the ground to produce a forward reaction force against the driving wheel. This reaction force is the driving force of the car.Generally, the front wheel of a car has no direct power connection with the transmission system, so it is called the driven wheel.
The composition and layout of the transmission system vary with the type of engine, installation position, and vehicle use.For example, off-road vehicles often use4WD, the transfer case and other assemblies are added to its transmission system.For front drive vehicles, there is no transmission shaft in the transmission system.[1]
Layout type
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Mechanical drive trainThe common layout types are mainly related to the position of the engine and theDriving Type ofIt can be divided into:
This type of layout is often used on large buses, and a small number of mini and light cars also use this type.The rear engine makes the front axle not easy to overload, and can make full use of the trunk area. It can also effectively reduce the height of the body floor or make full use of the space under the floor in the middle of the car to place luggage, which is also conducive to reducing the impact of the high temperature and noise of the engine on the driver.The disadvantage is that the heat dissipation condition of the engine is poor, and some faults during driving are not easy to be detected by the driver.Remote control also makes the control mechanism complex and inconvenient to maintain and adjust.However, due to its outstanding advantages, it is applied more and more on large buses.
This type of control mechanism is simple and the engine has good heat dissipation conditions.But when going uphill, the carMass backwardThe adhesion mass of the front drive wheel is reduced, and the drive wheel is easy to slip;When braking downhill, because the vehicle mass moves forward, the front wheel load is too heavy, and it is easy to roll over at high speed.Today, most cars adopt this arrangement.
4. Drive train of off-road vehicle
The off-road vehicle is generally all wheel drive, with the front engine. A transfer case is installed behind the gearbox to transmit power to all wheels.Light off-road vehicles generally adopt 4 × 4 drive type, and medium off-road vehicles adopt 4 × 4 or 6 × 6 drive type;heavycross-countryThe vehicle generally adopts 6 × 6 or 8 × 8 drive type.[2]
working principle
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The structure of AT transmission system is quite different from that of manual gear in structure and use.The manual gear is mainly composed of gear and shaft, which can generate variable speed and torque through different gear combinations;The AT transmission system is composed of hydraulic torque converterplanet gearIt is composed of hydraulic control system, and can achieve variable speed and torque through hydraulic transmission and gear combination.amongHydraulic torque converterIt is the most characteristic part of AT transmission system, which is composed of pump wheel, turbine, guide wheel and other components. It directly inputs engine power and transmits torque, and has the function of clutch.The pump wheel and turbine are a pair of working combinations. They are like two fans placed opposite each other. The wind from one fan will drive the blades of the other fan to rotate, and the wind will become the medium of kinetic energy transmission. If liquid is used to replace air as the medium of kinetic energy transmission, the pump wheel will drive the turbine to rotate through the liquid, and then a guide wheel will be added between the pump wheel and the turbine,The speed difference between the pump wheel and the turbine can be achieved through the reaction force to achieve variable speed and torque conversion.Since the automatic transmission and torque conversion range of the hydraulic torque converter is not large enough, several rows of planetary gears are connected in series behind the turbine to improve efficiency. The hydraulic control system will automatically operate the planetary gears as the engine changes, thus realizing automatic transmission and torque conversion.The automatic shifting of the auxiliary mechanism can not meet various needs of driving, such as parking, reversing, etc., so there is also an intervention device, namely a manual paddle, marked with P (parking), R (rear position), N (vacant position), D (forward position). In addition, there are additional gears of "2" and "l" in the forward position for starting or climbing a slope.Because its speed change area is divided into several speed change ratio sections, and only within the specified speed change section is stepless, the AT transmission system is actually between stepless and steplessAutomatic transmission。[3]
Automatic hydraulic transmissionThere are usually two types: one is front and rear driven hydraulic automatic transmission;The other is front driven hydraulic automatic transmission.The electronic control of the hydraulic automatic transmission receives the electrical signal input from various sensors on the vehicle through the power transmission control module, and processes these information according to the operating conditions of the vehicle to determine the operating conditions of the hydraulic automatic transmission.According to these working conditions, the power transmission control module sends commands to the actuator, and realizes the following functions: up and down position of the transmission;Generally, a pair of electronic transposition solenoid valves are operated to switch between on/off states;The electronic pressure control solenoid valve is used to adjust the pipeline oil pressure;The torque converter clutch controls the apply and release time through the control solenoid valve, as well as the torque converter in some applicationsLock up clutchSense of engagement.
1. Manual transmission: generally referred to as "manual transmission".Shift manually.
2. Automatic transmission: generally referred to as "automatic transmission".Use the oil pressure to change the gear.
differential mechanism
When the vehicle is turning, the wheels on the left and right sides will have different rotational speeds, so the drive shafts on the left and right sides will also have different rotational speeds, so the differential is used to solve the problem of different rotational speeds on the left and right sides.
transmission shaft
Will pass throughVariable speed systemThe transmitted power is transmitted to the differential to generate a driving force channel.
After having the basic transmission system components, automotive engineers will design the transmission system as a two wheel drive (2WD) or four wheel drive (4WD) type according to the needs of the use purpose.
Engine configuration
The transmission system includes three important components: gearbox, differential and transmission shaft.The main task of the transmission system is to transmit the power of the engine to the wheels.Due to the different arrangement of the automobile engine on the body, the combination of the engine and the transmission system forms various changes.Most combinations are related to the use or performance requirements of the vehicle.Common combinations are front engine front wheel drive (FF), front engine rear wheel drive (FR), and mid engine rear wheel drive (MR).[2]
effect
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Deceleration and speed change
We know that only when theTractive forceOnly when the external resistance to the car is overcome can the car start and run normally.When the engine produces the maximum power of 99.3kWcrankshaftThe speed is 3000 rpm.If the engine is directly connected to the driving wheel, the vehicle speed corresponding to this crankshaft speed will reach 510km/h.Such a high speed is neither practical nor possible (because the corresponding traction force is too small, the car simply cannot start).
In order to solve these contradictions, the transmission system must have the function of deceleration and distance increase (referred to as deceleration), even if the speed of the drive wheel is reduced toengine speed And the torque obtained by driving the wheel is correspondingly increased to that of the engineTorqueSeveral times of.In order to keep the engine working within the favorable speed range, and the vehicle traction and speed can change within a large enough range, the transmission ratio of the transmission system (the so-called transmission ratio is the ratio of the torque of the driving wheel to the torque of the engine, and the ratio of the engine speed to the speed of the driving wheel) should change between the maximum and minimum values, that is, the transmission system should play a role in changing speed.
Realize reverse driving
In some cases, a car needs to run backward.However, the internal combustion engine cannot rotate in the opposite direction, so the transmission system working together with the internal combustion engine must ensure that the driving wheel can rotate in the opposite direction when the selected direction of the engine remains unchanged.The general structural measure is to add reverse gear (reduction gear pair with intermediate gear) in the transmission.[4]
Interrupt transmission
The internal combustion engine can only be started under no load, and the speed after starting must be kept at the lowest stable speed, otherwise it may stop. Therefore, before starting the car, the transmission line between the engine and the driving wheel must be cut off to start the engine.After the engine runs at normal idle speed, gradually restore the transmission capacity of the transmission system, that is, gradually load the engine crankshaft from zero, and at the same time increase theThrottle openingTo ensure that the engine will not go out and the car can start smoothly.A friend who has just learned to drive a car should have a deep understanding. If he forgets to step on the clutch or releases the clutch too fast when starting, he will "die".In addition, it is necessary to temporarily interrupt the power transmission before changing the transmission ratio gear (shifting) of the transmission system and braking the vehicle.For this reason, a mechanism clutch can be installed between the engine and the transmission, which is driven by friction, and its active and driven parts can be completely separated under the control of the driver, and then gently engaged.
At the same time, when the vehicle stops for a long time and the engine does not stop running, the transmission system should be able to interrupt the transmission status for a long time.For this reason, the transmission shall be set with neutral gear, that is, all gears at all gears can be automatically kept at the gear position away from the transmission position.
Differential action
When the car turns and runs, the left and right wheels roll over different distances at the same time. If the driving wheels on both sides are only driven by a rigid shaft, the angular speed of the two must be the same, so the wheel must slip relative to the ground when the car turns.This will make steering difficult, increase the power consumption of the car, and accelerate the wear of some parts and tires in the transmission system.So, we need toDevices in drive axleDifferential, a component with differential function, enables the left and right driving wheels to rotate at different angular speeds.
