Die Crux der niedrigen Drehzahl | Posts 32+

teileklaus wrote:

The area around the maximum torque is, for me, the ideal speed for saving

.

However, this doesn't apply generally. While it might still be somewhat relevant for turbocharged diesel engines, for many vehicles, the engine speed at which maximum torque is achieved is too high to actually save fuel.

The ideal engine speed for maximum torque is only achieved at full load. However, most diesel drivers operate their vehicles at partial load. In these conditions, the ideal engine speed quickly shifts to just above idle. This is evident in so-called 'torque curves,' and it's easy to understand and explain from a physical perspective.

For all gasoline engines (I don't know about Wankel engines), it's generally best to choose the lowest possible RPM when you only want to maintain a constant speed and not accelerate.

It's no longer as easy to determine the geometrically/structurally ideal engine speed at full load, even with turbocharged and electronically controlled engines, simply by looking at the rpm plateau. To do so, one would need to test the engine as a naturally aspirated engine on a dynamometer. This would likely be at the point where the maximum torque is achieved earliest.

But get ready for your first DPF cars. That's when you'll experience the problem of high exhaust backpressure, regardless of your driving style. After 40,000 km with a DPF, I'm really starting to dislike them...
The instantaneous power display can sometimes fluctuate by a full liter due to a faulty distance and speed calculation (unfortunately, not wind-compensated).
'But what's even worse is the actual feeling of 'stiffness' in the accelerator and the throttle. It feels like I'm always driving with somewhere between 175 and almost 200 horsepower, depending on how full the diaper is. Sometimes I think my tuning modification failed and the car is running in its stock configuration. Sometimes I think, wow, it's really kicking in, but it's happening in the 6-cylinder range. I've had 0-100 km/h times ranging from 4.2 to 5.4 seconds.'
While BMW, unlike the VAG group, has managed to produce mature DPF systems that never trigger a warning light or require a regeneration cycle, the perceived sluggishness towards the end of the week cannot be solely attributed to the weather.

Like an addicted Ironman or a Husky, I'm just waiting for that intense 'total workout' on the track! (Assuming it's free, of course).

The engine speed at which the maximum torque occurs is only and exclusively the ideal speed when operating at full load. However, most diesel drivers operate their vehicles under partial load conditions. In those situations, the ideal speed quickly becomes just above idle speed. This is evident from so-called 'torque curves,' and it is physically easy to understand and explain.

I suspect that 99% of drivers have never heard of a 'seashell diagram.' And how many of them would be able to interpret it if they saw one?

Therefore, automatic cars (or cars with automated manual transmissions) would likely be more suitable for a large portion of the population.

And those who actively want to implement the 'seashell diagram' would need 1-2 more gears. For example, I would need a gear that allows me to drive at 120 km/h at 2000 rpm, or 90 km/h at 1500 rpm (for constant speeds at low rolling resistance).

Best regards,

I don't think a fuel consumption gauge is actually necessary for driving in a resource-efficient way. I already drive according to the following principle, based on feel:

Always drive in the highest possible gear. I only shift down when the current gear isn't providing enough power.

That gets me very close to the shell diagram. In principle, the efficiency at partial load is highest at low speeds. Only at higher loads does the optimum shift towards approximately 2,000 rpm in the TDI engine.

@SeatArosa1.7SDI

The long sixth gear from the TDI range is translated exactly as you would like. You can also relax and cruise on the highway at 200 km/h with the cruise control activated at 3,300 rpm .

The automatic transmissions are actually counterproductive in this case, as they downshift under higher loads.

You all have more displacement, more torque - and not fewer problems...

My little car was also built with a rather long (5-speed) gearbox. This means that I can't use the 5th gear in the city. Even with a warm engine, the RPM is too low. Between 55 and 60 km/h, you're in 4th gear at 1600 to 1700 RPM. In 5th gear, you'd be around 1300-1400 RPM, and in 3rd gear, over 2200 RPM. However, the engine becomes noisy and shows its displeasure when it's below 1500 RPM. So, you should shift to 3rd gear when driving below 55 km/h. And when driving at 50 km/h, you're in 4th gear below the 1500 RPM threshold, which forces you to downshift.

So, you tend to rev the 1.4 HDI engine higher than you would with other diesel engines. However, thanks to the higher RPM, the engine runs with relatively little resistance and doesn't require much force to accelerate. This driving style allows me to achieve an average fuel consumption of 4-4.5 liters with a 50/50 mix of rural and city driving. Conversely, if you try to drive the engine at lower RPMs (i.e., staying in 4th gear as much as possible), you'll be penalized with an additional 0.5 to 1 liter of fuel consumption.

This uncomfortable gear ratio forces you to either speed (58-60 km/h in 4th gear is smooth and quiet) or drive noisily (in 3rd gear) within city limits. The gearing for the often-used 30 km/h is also problematic! In 3rd gear, you're below the aforementioned 1500 RPM, and in 2nd gear, you're around 2200 RPM. Driving at 30 km/h due to noise restrictions is not possible with my vehicle. Therefore, you either drive noisily at 30 km/h or quietly at 40 km/h. Because only above 40 km/h are you at a reasonable RPM in 3rd gear.

HI,

"Hmm... it seems that Renault's smaller diesel engine has a shorter gear ratio or is tuned differently. When I had the 1.5 dCI in the Twingo as a replacement car, I drove it similarly to my larger ASV. The gear ratio is slightly shorter (2300 RPM at 100 km/h in 5th gear according to the speedometer, while my ASV has about 2000 RPM at 100 km/h, also according to the speedometer), but city driving was easily done in 5th gear at around 1150-1200 RPM without it sounding rough. It only became rough when I used my strategy of driving in 30 km/h zones in 4th gear at idle – it didn't want to do that. The idle speed was exactly 30 km/h (while it's 35 km/h in my ASV), but it sounded terrible and didn't run smoothly. My ASV can do that without any problems... even going gently uphill in 4th gear at idle is possible, and I've even done it with a trailer. However, it should be noted that the dCI has a lower idle speed, and I increased mine to 945 RPM (originally it was about 21 RPM lower) so that the rest of the car doesn't rattle so much at idle."

Was das beim dCI fuer verbrauchstechnische Auswirkungen hat, weiss ich nicht, der ASV braucht laut MFA bei 55 (1100 U/min etwa) im 5. etwas weniger als im 4. oder 3. Okay.

Best regards,

Jan.