It was once believed that the most economical overclocking is in pedal-to-floor mode! But are old recommendations good for modern cars? This is what we found out.
The overthrow of authority is a characteristic feature of our time.
For example, a growing number of adherents of the theory of a flat earth. It is not surprising that a similar thing happens in the automotive environment: statements are being made more often that it is necessary to accelerate the car as intensively as possible to save fuel, not to slow down the engine, turn on the “neutral” in the mechanical box, and also switch the selector of the machine to “neutral” when driving downhill. And it’s time to forget all the old-time covenants from the carburetor era.
It is useless to refer to textbooks here. Therefore, we decided to turn with questions to our automobile Olympus – US, as well as to the representations of automobile companies.
Sharp or smooth?
Why do I need to accelerate “gas to the floor”? The idea is this: the faster you go to the economy mode, the longer you will then move in this mode and, therefore, save more. There is another argument: since the efficiency of the motor grows with power, it is necessary to accelerate at maximum power, because efficiency and profitability are one field of the berry.
Both arguments seem strange to me. For example, the efficiency of the engine really grows with power, but after all, fuel consumption increases sharply.
Representatives of Audi, Nissan and Skoda unanimously answered: optimal acceleration is smooth. Subaru also recommended this type of acceleration: “When you press the accelerator pedal hard, the mixture is re-enriched by 10–20%, and the fuel consumption increases by the same amount. In vehicles with an automatic gearbox or variator, the fuel consumption during intensive acceleration is further increased due to the later locking of the torque converter. ”
Volkswagen representatives gave an interesting answer: “Fuel in a car is spent, ultimately, on heating. We warm air, tires, road surface, liquids in units. Everything else is in the pipe. The most economical mode of movement will be when the heat production is minimal. Abrupt acceleration requires the transfer of significant effort through the contact spots of the drive wheels. This leads to an increase in slippage, and together with the “economical” rolling friction, we get sliding friction, which is pure heat. The transmission of a significant moment increases the friction in the transmission – it is also warm. In general, smooth acceleration is preferable. “
How to slow down?
Engine braking once seemed to me a manifestation of basic driver training. And on long descents and slippery roads without such braking can become quite difficult. However, there are debaters who do not share this point of view.
All manufacturers unanimously speak out for engine braking. Moreover, a separate side of the issue is traffic safety.
In particular, the Kia instruction manual generally prohibits the movement of a car with a gear off, especially on slippery surfaces and downhills. Engine braking creates additional deceleration and helps to reduce braking distance.
And Volkswagen again gave the most “sincere” answer: “The less we touch the brake pedal, the more economical we drive. The brakes heat up – this is energy expelled. When engine braking, it will release the same amount of energy, but part of it can be used. In the simplest case, we use the energy of a moving car in order to pump oil and coolant in the engine and turn the generator. And modern preselective transmissions themselves decide whether it is possible and useful to open the transmission during braking. ”
Do not interfere with the machine!
Some drivers at a traffic light translate the automatic gearbox selector to “parking” – supposedly to extend the life of the unit. And they say that to save fuel, it turns out that when driving downhill, you must also use the “neutral” in the machine.
If such a method gives ghostly savings, it is definitely unsafe. Human life and health are hardly worth a few grams of gasoline. It seems that this is exactly what most automakers reasoned about. For example, the Subaru instruction manual clearly states: “Do not allow the vehicle to move when the selector lever is in position N”. The explanation is simple: when the transmission is open, engine braking becomes impossible, which increases the risk of emergency situations. Kia also talks about a possible loss of control. And Nissan adds that it’s bad for the box.
In general, everything is clear. The physical side of the process when disconnected from the engine of a classic machine was described in detail again by Volkswagen. Like, “neutral” will slightly reduce mechanical losses, but the main consumers, power steering, cooling system and oil pump will still be tied to the engine. At the same time, the included neutral transmission will deprive us of the opportunity to recover energy, or even make us press the brake, and this is already heating the atmosphere in its purest form. Another drawback is the wear of the parts of the selector box.
But is it possible to save fuel at least hypothetically? Skoda answers categorically: not. And he explains: “When coasting, when the selector is in position D or the gearbox is engaged, the fuel consumption is zero. When the selector is in position N, the on-board computer indicates that the engine is consuming fuel. ”
Thus, in all disputed positions, the opinion of machine manufacturers is unambiguous: they say, do not show off, guys … I can add that for the sake of experiment I went on a tank to Peter and back on a serial 170 ‑ horsepower machine with a gun (No. 9, 2008). To all the adherents of abrupt starts with twisting the motor, I suggest trying to repeat the same thing.
Instead of an epilogue
ABC truths can be trusted. And this is natural, because they are confirmed by experience. Well, new-fangled statements should be justified and proved, otherwise they remain theoretical assumptions.
WE RIDE ECONOMICALLY
Denis Zagarin, Head of NAMI Test Center
The most economical mode is to accelerate to the desired speed by pressing the accelerator pedal 2/3 of its stroke. Such acceleration conditions were incorporated into the standard city driving cycle, which is part of the NEDC driving cycle to evaluate the fuel economy of cars. Currently, a more dynamic WLTP driving cycle is being implemented with intensive accelerations, in which fuel consumption increases sharply in urban conditions. Hence the general wish: avoid sharp accelerations and braking.
The engine braking mode in comparison with the transition to the “neutral” gives an advantage in efficiency, as this stops the fuel supply to the engine. Do not forget about the safety rules – on cars with automatic gearbox it is forbidden to translate the selector to “neutral” not only on the slopes, but also in a straight line movement.
As for the economical driving of trucks, it is worth paying attention to the specific power of the engine. The larger it is, the more preferable it will be a smooth acceleration. However, with specific power less than 6.0 hp per ton it is more profitable to accelerate sharply, since it is difficult for the engine to realize acceleration during operation not at full power. It turns out that without load, smooth acceleration is more economical, and at full load it all depends on the specific power of the engine.
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