How to make old cars more fuel efficient?

Simply speaking, fuel economy, carburetor car neutral certainly fuel economy, EFI car is not necessarily.

The structure of carburetor truck is different from that of EFI truck. In a carburetor car, air is sucked in by the vacuum generated by the downward movement of the piston. When flowing through the carburetor, part of the engine oil atomized by the carburetor is mixed with the intake air, and the other part is mixed with the air in the intake manifold and enters the combustion chamber. That is to say, gasoline is sucked in the carburetor car instead of actively injected. Although the carburetor has an accelerator pump to spray a little oil every time you step on the accelerator, it is only used as a thickening of the mixture. Therefore, the greater the air intake of the engine, the more oil it absorbs, the lower the speed and the lower the fuel consumption. At the same time, the carburetor has no fuel cut-off function (in some later European cars, the carburetor also has the ability to cut off fuel by dragging), so the idle speed of the carburetor car is the lowest in all working conditions, and neutral taxi is equivalent to engine idle speed, which will of course save fuel than gear taxi.

EFI vehicle is different from carburetor vehicle. The computer judges the load according to the crankshaft speed and throttle opening, determines the target fuel injection quantity according to the pre-stored working curve, and then obtains the final fuel injection pulse width after numerical correction according to the air intake, water temperature sensor and oxygen sensor, and the pulse width determines the fuel injection quantity. Gasoline is not mixed in the intake manifold, and the diameter of the engine oil sprayed from the nozzle is below 150 micron, so it is not necessary to atomize it separately, but directly sucked into the combustion chamber together with the intake air. Therefore, the nozzles of the EFI engine are basically installed near the intake valve, and the fuel is actively injected in a controlled state. Therefore, the fuel injection quantity of EFI engine is mainly controlled not by the engine speed, but by the working condition, which is one of the reasons why EFI engine replaces carburetor engine: it can control the fuel injection quantity more accurately to achieve the ideal mixing ratio under various working conditions.

EFI engines are basically divided into eight working conditions: starting, after starting, warming-up, idling, partial load, full load, transition and starting. All kinds of working conditions are completely monitored by computer. Idling in neutral, throttle closed, crankshaft speed low. Sliding with gears is the supporting condition. When the accelerator pedal is completely released in the engine-driven state, the computer knows from the idle switch that the vehicle is in the idle state and the crankshaft speed is still high, so it knows that the vehicle is in the engine-driven state. At this time, the computer will delay the ignition time to reduce the engine power consumption, and then stop fuel injection according to the speed. ECU generally has three speed points: fuel cut-off, recovery and emergency recovery. When the rotational speed is higher than the fuel cut-off point and the throttle valve is closed for a period of time, fuel injection will stop and the rotational speed will drop to the recovery point to resume fuel injection. If the speed drops sharply (such as emergency braking), fuel injection will start at the emergency recovery point higher than the recovery point. This process can be clearly observed in some cars with driving computers (such as Bora and Golf).

There is a question that many people have asked in other forums: If you don't inject fuel into the engine, isn't it a car? Not exactly. Although there is no fuel injection, the spark plug has been working. From this perspective, it is not exactly the same as stopping the car. In fact, it doesn't matter if the car is killed. The key point is that we always think that the engine drives the car. If the engine doesn't work, the car can't move, but at this time the car is moving. It is a process that the engine does work to obtain potential energy, and the engine keeps doing work to maintain potential energy. If the engine is not engaged or disengaged, the maintained potential energy (inertia) in turn drives the engine to rotate, and the exchange of potential energy itself is a reversible process. The reason why the sliding distance with gear is shorter than that with neutral is that potential energy is converted into heat through friction in gear meshing, compressed air through piston, heat through wind resistance and so on.

Another problem is that some people may think that driving conditions have damaged the car, which is wrong. The engine load in the supporting state is less than that in the working state. Without mixed gas, the heat will be reduced and the amount of lubricating oil will be reduced, because the oil pump is driven by crankshaft. Crankshaft speed is high, oil circulation speed is fast, and the more lubricating oil per unit time, the better. Although the engine is driven by tires, there is no reverse operation inside the engine. For gearbox, half axle, ball cage and other parts, the load in driving state is smaller than that in driving. How can it damage the car?

It's really hard to say whether the EFI car can save fuel by sliding with gears, because the fuel cut-off is limited by many conditions. First, short driving time will not save fuel. Generally, ECU knows that the fuel will be cut off for 3 ~ 5 seconds after driving. Before, it only delayed the ignition time to reduce energy consumption, even if it saved fuel, it could not be seen. Secondly, the engine speed is too low, even if it is delayed, it will not cut off the oil, so it is not fuel-efficient; Thirdly, when the air conditioner is turned on on the vehicle with fixed displacement compressor, the oil supply is not stopped, so as to prevent the vehicle from stalling due to insufficient power during refueling operation, and the suction of the compressor is contracted (the vehicle with variable displacement compressor is basically powered off). Therefore, in theory, it can only be said that if there is a large enough downhill slope to keep the sliding resistance of the EFI vehicle above the fuel cut-off speed, then the EFI vehicle will hardly burn oil. In real life, with such a 20% discount, the EFI car can't save a few oil when it is towed.

I personally support sliding with gears, not because of the safety of fuel consumption. Underpinning improves driving safety. This improvement in safety is manifested in the auxiliary braking of the engine, which is very important and often mentioned. In fact, if you try it yourself, you can obviously find that the sliding distance of the gear is shorter than that of the neutral gear, but it is not obvious on a small-displacement vehicle, because each piston diameter of the small-displacement vehicle is very small, so it does not need too much force to drive the engine to compress once, and the reduction ratio of the gearbox is also small. It is more obvious in medium and large displacement vehicles, because such vehicles have large piston diameter and high compression ratio, and the energy consumption of driving the piston to compress once is much higher, and the reduction ratio of the gearbox is large. Significant auxiliary braking is definitely a good way to enhance the braking effect. A friend said that when you slide in neutral, you feel the braking spirit, which is just a feeling. Because the neutral inertia potential energy loss is slow, the vehicle slows down slowly, and the feeling is quite different from that of the brake deceleration person, so you feel refreshed. The engine with resistance is already helping to slow down. The deceleration is large, and the deceleration after braking is not so obvious. If the braking distance is measured, the resistance is still shorter than the neutral position.

One more thing: at present, many sleeping cars are front transverse engines. The purpose of this layout is to reduce the space occupied by the engine. However, due to structural restrictions, the gearbox cannot be placed on the center line of the car body, so the lengths of the half shafts on both sides are different, that is to say, the power output acting on the two tires is different, and the brakes are the same. Although the brake cylinder force is the same, the braking force acting on the tire is different because of the different length of the semi-axle. If the neutral car tends to lean to one side, and the engine's, when replacing the brake pads, it can be noted that the wear residual thickness of the brake pads on both sides of the same side is different.

From these two points of view, the gear is very helpful to improve safety. In some automatic cars, there is indeed a design that the throttle gearbox is disengaged, but the connection will be automatically restored when the brake is pressed, and this connection will start to work before the brake system works. To put it bluntly, the engine will assist the braking before the braking system works, but the manual operation is often not so accurate and smooth. This design is rarely adopted by vehicles, because the requirements for transmission oil circulating pump are too high. Automatic gearbox is not allowed to slide in neutral. When coasting in neutral, the engine speed is low and the gearbox speed is high. The circulating pump is driven by the engine. The function of gearbox oil is to transmit power and reduce temperature, and lubrication is the second. If the transmission oil circulation is not enough to dissipate heat, it will be very poor, resulting in the burning of the internal grinding plates of the transmission. The circulating pump of the isolatable autotransformer is driven by the output shaft and also pumped by the engine (the output shaft does not rotate at idle speed), so the whole system is complicated, difficult to maintain and high in production cost.

Even for cars with ABS system, the danger of sliding in neutral is still greater than towing. Or the deceleration problem mentioned above. In neutral, the inertia of the vehicle is completely offset by the braking system without the help of the engine. The friction coefficient between the tire and the ground is relatively fixed. The higher the vehicle speed, the easier it is for the tire to lock, so ABS will start earlier and the braking distance will be longer than when it is in gear. The main function of ABS is not to shorten the braking distance, but to maintain the ability to control the direction when braking. Under some road conditions, vehicles with ABS system will brake longer than those without ABS, so the master cylinder used in all ABS systems is larger than those without ABS. In VW cars and vehicles equipped with C54 system, the master cylinder with a diameter of 22mm is used for vehicles without ABS, and the master cylinder with a diameter of 23.8mm is used for vehicles with ABS. Once the tire is locked, the lateral force provided is almost zero. No matter how it hits after the tire is locked, the direction of the car is not controlled by the tire direction. In fact, the ABS system mainly provides the driver with the ability to avoid at the same time in emergency braking.

Whether in gear or neutral, it doesn't matter how you drive a good car. It is mainly a problem of driving habits, which has little to do with fuel economy. Stop two cars every 100 km, although it is not a small number according to 10 years. The money saved can't be saved every time you refuel, and it can't be spent. /kloc-do not add oil once every 0/0 years. But good driving habits often play a big role at critical moments. Sliding in neutral may not cause an accident, but the risk factor of sliding in neutral is higher than that of dragging. Just as people with heart disease don't necessarily walk in front of patients without heart disease, on the whole, their lives are more dangerous and they are more likely to fall down, although we don't usually feel it. Whether you can slide in neutral does not mean the level of driving skills. Whether you can slide in the gap is not a measure of driving skills, but luck.

Driving fuel-saving skills

Magic weapon one: soft start and low gear

Start, step on the accelerator slowly, and accelerate slowly. When the car reaches a certain gear speed, learn to listen to the sound of the engine to gradually change from low gear to high gear. This can reduce the heating time of the engine and improve the utilization rate of fuel. If you burst the throttle to accelerate at the beginning, it will not only hurt the car, but also greatly increase fuel consumption.

Magic weapon 2: use economic speed

The economic speed of an ordinary car is between 60 km/h and 80 km/h, and it is the most fuel-efficient to drive at the economic speed. Too high or too low a speed is not conducive to fuel-saving. When the vehicle speed is low, the movement speed of the piston is low and the combustion is incomplete. When the vehicle speed is high, the increase of intake speed leads to the increase of intake resistance and fuel consumption.

Magic weapon three: gently lift the throttle

Lightly lifting the throttle can save fuel.

If the throttle is suddenly raised, the engine speed will suddenly decrease to play a drag role, offset part of the driving inertia, and make the car "vibrate", thus increasing fuel consumption.

Magic weapon 4: shift gears in time

Shift gears quickly and timely, especially when driving on slopes. The shorter the shift time, the better the dynamic performance of the car, which can save more fuel. If the shift is not timely and the hands and feet are not well matched, the fuel consumption will increase greatly.

Magic weapon five: reduce the use of brakes

Braking is essentially a process of energy conversion, and braking means energy consumption. Therefore, when crossing the intersection and going downhill, you should increase the throttle in advance. If the car has good performance, you can also put neutral to let the car slow down naturally, so as to achieve the purpose of "replacing the brake with slip".

Magic weapon six: keep your distance from the car

If the road is congested, the front car often brakes, and it is necessary to keep enough distance from the front car, so as to slow down calmly, reduce the number of brakes and achieve the purpose of saving fuel.

Magic weapon seven: high gear driving saves fuel

Generally speaking, try to use high-speed gear and less mid-range.

Of course, don't drive high. Learn to listen to the sound of the engine to shift gears and understand the situation of your car. When the engine is going to "tremble", it is necessary to downshift, let the speed go up and change back to high gear.