Function Of Transmission Device

The basic function of the automotive powertrain is to transmit the power generated by the engine to the driving wheels. Its primary task is to work in conjunction with the automotive engine to ensure that the vehicle can operate normally under different conditions and exhibit good power performance and fuel economy. To this end, the automotive powertrain possesses the following functions:
Deceleration and speed change
We know that a car can only start and run normally when the traction force acting on the driving wheels is sufficient to overcome the external resistance to the car. Experiments have shown that even when a car is driving at a low and constant speed on a flat asphalt road, it needs to overcome rolling resistance equivalent to approximately 1.5% of the total weight of the car. Taking the Dongfeng EQ1090E car as an example, its full-load total mass is 9290kg (total weight is 91135N), and its minimum rolling resistance is about 1367N. If the fully loaded car is required to drive uphill at a constant speed on a road with a 30% gradient, the uphill resistance to be overcome will reach 2734N. The maximum torque that the 6100Q-1 engine of the Dongfeng EQ1090E car can generate is 353Nm (1200-1400rpm). Assuming that this torque is directly transmitted to the driving wheels as it is, the traction force that the driving wheels may receive is only 784N. Obviously, in this situation, the car cannot only climb the slope, but also cannot drive at a constant speed even on a flat and good road.
On the other hand, the crankshaft speed of the 6100Q-1 engine when delivering its maximum power of 99.3 kW is 3000 rpm. If the engine were directly connected to the drive wheels, the vehicle speed corresponding to this crankshaft speed would reach 510 km/h. Such a high vehicle speed is neither practical nor achievable (because the corresponding traction force is too small, and the vehicle would simply not be able to start).
Deceleration effect
To resolve these contradictions, it is necessary to equip the transmission system with a function of reducing speed and increasing torque (referred to as the "reducing speed function"). This means that the rotational speed of the drive wheel is reduced to a fraction of the engine speed, and correspondingly, the torque obtained by the drive wheel is increased to several times the engine torque.
The operating conditions of a vehicle, such as its actual load, road slope, road surface condition, as well as the speed allowed by road width, curvature, and traffic conditions, vary widely. This requires a considerable range of variation in vehicle traction and speed. For piston internal combustion engines, the torque variation range is not large throughout their entire speed range, while the power and fuel consumption rates vary greatly. Therefore, the range of crankshaft speeds that ensures high engine power and low fuel consumption, known as the favorable speed range, is very narrow. In order to enable the engine to operate within the favorable speed range of the translation company while allowing the vehicle traction and speed to vary within a sufficiently large range, the transmission ratio of the driveline (the ratio of the torque of the driving wheel to the torque of the engine, and the ratio of the engine speed to the driving wheel speed) should be able to vary between its maximum and minimum values, that is, the driveline should function as a variable speed device.