Today, some netizens asked me, why is it equipped with the same displacement engine, the same type of transmission, the same size of the car, some cars save fuel, some fare fuel? In particular, compared with domestic cars and joint venture cars, they have obviously suffered losses in fuel consumption, why is this? Where are the key points of car fuel saving?
This problem is actually quite complicated, and there are many aspects involved. The following Lao Hou will use his own understanding to analyze where the key points of automobile fuel saving are.
1, engine thermal efficiency: the engine is essentially an energy conversion tool, gasoline engine is to convert the chemical energy contained in gasoline into mechanical energy for external output. But energy conversion cannot be 100%, and there must be energy loss. How much of the chemical energy in the fuel can be converted into mechanical energy is what we often call the thermal efficiency of the engine. The thermal efficiency of today's automobile engines is generally between 35 and 40%. Obviously, the higher the thermal efficiency of the engine, the more mechanical energy can be released with less fuel, and the car will naturally save fuel.
At this stage, the automobile engine is still a short board of domestic cars, whether in thermal efficiency or in reliability, power, there is still a gap with mainstream joint venture vehicles, which is an important reason for the high fuel consumption of domestic vehicles.
2, the mechanical efficiency of the transmission system: the engine sends out energy, to go through the clutch, gearbox, transmission shaft, drive axle, and finally can drive the wheel to run, in this process there are mechanical friction loss, hydraulic loss, parts deformation loss and other energy loss, and can not be 100% transmitted to the wheel, these energy losses will be dissipated in the form of heat. The ratio of the energy obtained on the final wheel to the energy emitted by the engine is what we call the mechanical efficiency of the driveline. Obviously, the more efficient the mechanical efficiency of the transmission system, the lower the fuel consumption of the car.
At present, the mechanical efficiency of the transmission system of the car is generally between 85 and 95%, which is directly related to the type of the gearbox. Among them, the manual transmission transmission efficiency is the highest, followed by the dual-clutch transmission, followed by the AT transmission, and the CVT transmission has the lowest transmission efficiency. In this regard, the gap between domestic cars and joint venture cars is not large, and the transmission efficiency of four-wheel drive vehicles is lower than that of two-wheel drive vehicles.
3, the powertrain tuning: the combination of engine and gearbox is collectively referred to as the automobile powertrain. The coordination and cooperation between the two is an important factor to ensure the normal operation of the car. The power emitted by the engine needs to be distributed by the gearbox, and this power distribution process is the so-called powertrain tuning. In particular, the automatic transmission, how to synchronize the engine load and speed with the gearbox gear and vehicle speed is a very complex knowledge. If the coordination is not good, a lot of power will be wasted, and the fuel consumption of the car will naturally be high.
The automatic transmission shift process, including power decoupling, gear switching, power combination and other steps, in this process there will be power loss, obviously, the faster the gear switching speed, the less power loss, the lower fuel consumption. The reason why the dual-clutch transmission is fuel-efficient is that the gear switching speed is fast and the power loss is small; and the CVT transmission has no obvious gear switching, the power transmission is almost uninterrupted, and the engine can always work in the optimal speed range, so the model equipped with the CVT gearbox, although the transmission efficiency is low, but the fuel consumption is not high. In addition, in the process of gear change, in order to coordinate with the transmission gear, speed, etc., the engine should be properly replenished or reduced, and the timing and quantity of this oil replenishment or oil reduction is a very big knowledge. In this regard, domestic cars are a short board, and there is a big gap with joint venture cars. This adjustment ability requires time and experience accumulation, and cannot be achieved overnight.
4, car driving resistance: the driving resistance of the car includes rolling resistance, air resistance, acceleration resistance and slope resistance. If the car is driving at a uniform speed on a straight road, there is only rolling resistance and air resistance. The biggest impact on rolling resistance is the tire, the car uses different tires, will have different fuel consumption. In addition, the preload of the wheel bearings and the retardant force of the brake system will also affect the rolling resistance. In this regard, the retardation force of the drum brake is smaller than the disc brake, and now a joint venture brand electric vehicle, the rear wheel uses the drum brake, many people say that this is to reduce the allocation, save costs, in fact, this is a means to reduce the rolling resistance. A simple way to measure the size of the car's rolling resistance is to glide distance in neutral gear, accelerate the car to a certain speed, and then hang into the neutral gear to coast, the longer the distance of taxiing, the smaller the rolling resistance.
The main factor affecting the size of air resistance is the air resistance coefficient of the car, that is, the wind resistance coefficient. At present, the wind resistance coefficient of the car is generally 0.24~0.28, and the wind resistance coefficient of the SUV is generally 0.28~0.32. The greater the wind resistance coefficient, the greater the air resistance encountered by the car, and the higher the fuel consumption. The main factors affecting the wind resistance coefficient are the shape of the car, as well as the flatness of the chassis and the flow of air on the body. Everyone looks at the SUV tall and powerful, but its wind resistance coefficient is high, and the fuel consumption is naturally not low. In terms of body design, there is also a certain gap between domestic cars and joint venture cars.
5, the weight of the car: the impact of car weight on the fuel consumption of the car is also larger. Generally speaking, every time the car increases the weight of 100kg, it will increase the fuel consumption by 5%, so now major car companies are doing lightweight design of automobiles. It should be noted that car lightweight is not a simple configuration or simple material saving, but on the basis of ensuring structural strength and driving safety, designing a more exquisite structure, or using lighter materials (such as aluminum, plastic, etc.). In this regard, there is also a certain gap between domestic cars and joint venture cars, to achieve the same body strength, domestic cars need to use more materials, which is also one of the reasons why many domestic cars are heavier.
The above are several important factors that affect the fuel consumption of automobiles, all from the perspective of automobile design and manufacturing, and there is no mention of use factors. In fact, the fuel consumption of a car is fixed at the moment the car leaves the factory, especially now that the car is more and more intelligent, the car driving is becoming more and more "foolish", and the impact of the later use factors is very small. If you want to save fuel for cars, you have to start from the main engine factory.