1、 Function of transmission
The physical characteristics of the engine determine the existence of the transmission. First, any engine has its peak speed; Secondly, the maximum power and torque of the engine appear in a certain speed range. For example, the maximum engine power appears at 5500 rpm. The gearbox can produce different transmission ratios between the engine and the wheels during the driving of the vehicle. Shifting can make the engine work under its best dynamic performance. Ideally, the gearbox should have a flexible gear ratio. Continuously variable transmission (CVT) has this characteristic, which can give better play to the power performance of the engine.
Continuously variable transmission has continuous speed ratio. It has not been equipped with a large number of cars because of the relationship between price, size and reliability. Now, the improved design makes the use of CVT more common.
The transmission is connected to the engine through the clutch, so that the input shaft of the transmission can reach synchronous speed with the engine. A five speed transmission provides five different gear ratios, resulting in a speed difference between the input shaft and the output shaft.
3、 Simple gearbox
In order to better understand the working principle of the gearbox, let’s take a look at a simple model of a 2-speed gearbox and see how the parts cooperate:
The input shaft is connected to the engine through a clutch. The shaft and the gear on it are a component.
The shaft and gear are called intermediate shafts. They rotate together. Shaft rotation drives the rotation of the intermediate shaft through the meshed gear. At this time, the intermediate shaft can transmit the power of the engine.
The shaft is a spline shaft, which is directly connected with the drive shaft and drives the car through the differential. The wheel turns with the spline shaft.
The gear rotates freely on the splined shaft. When the engine stops but the vehicle is still in motion, the gear and intermediate shaft are stationary, while the spline shaft still rotates with the wheel.
The gear and spline shaft are connected by a sleeve. The sleeve can rotate with the spline shaft, and can also slide freely left and right on the spline shaft to mesh the gear.
4、 Real gearbox
Nowadays, 5-speed manual transmission is widely used.
There is a rotation point in the middle of the shift lever. When you shift into gear 1, you actually push the connecting rod and shift fork in the opposite direction. The so-called neutral taxiing means that the car is not engaged in any forward gear, but in the neutral position, uses inertia taxiing, and then puts on the high gear after the car speed decreases, so as to slowly refuel and improve the speed. Neutral taxiing is familiar to many old drivers, because it is very fuel-efficient.
First of all, the road traffic law expressly stipulates that no neutral taxiing and flameout taxiing are allowed downhill, and the deduction items listed in the road test for driver’s license also stipulate that neutral taxiing is more than 3 seconds, and the test is unqualified. So why should such a “fuel-saving” technical behavior be prohibited by law?
When the car is running at high speed, in case of emergency, it must quickly release the accelerator and step on the brake pedal to implement emergency braking. At this time, if the car is in normal operation, the wheels and all transmission systems are closely combined with the engine, and the engine speed slows down, which will produce a braking force for the car running by inertia, that is, what people usually call “engine braking”.
On the one hand, it can prevent the instantaneous brake pressure from killing the brake drum and reducing the braking effect; On the other hand, it can balance the braking effect of the left and right wheels and make the vehicle stop safely and slowly.
On the contrary, if you have already changed to neutral gear and stepped on the emergency brake, the chassis transmission system is not connected with the engine, and there is no help of the engine braking. In this way, not only the braking effect is poor (especially the overloaded vehicle), but also the vehicle will lose its balance and slide left and right, and finally the driver will cause an accident because he can’t control the vehicle. Moreover, the faster you brake, the stronger the braking force, the worse the braking force and the worse the sliding. It is worth reminding you that if you press the clutch when braking, the result is also bad. Especially when going downhill, you can’t neutral or step on the clutch brake, otherwise it’s easy to lose control and cause trouble.
From the working principle of the engine, the speed of carburetor engine increases gradually and the fuel consumption increases gradually with the increase of throttle opening. When sliding in neutral gear, the engine is in the state of idling and low fuel consumption, and the vehicle continues to drive, so fuel saving is realized. For EFI engine, its throttle sensor has three working states: idle speed, partial load and maximum load. In the partial load area, the throttle sensor can collect two signals of position and change rate, that is, the same throttle opening change, the slow acceleration of slowly stepping on the throttle and the rapid acceleration of suddenly stepping on the throttle are different, and the engine response is also different.