"sterben" moderne Dieselmotoren noch? | Posts 16+

SeatArosa1.7SDI wrote:

Positive example: The new five-cylinder engine in the T5 TDI-PD (solution: helical gears).

Do you know the defect statistics for that?
Apparently not, otherwise you wouldn't present it as a positive example.

Hi Bertil,

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However, the chain-driven system has a lot of problems, so it probably won't be around for very long.

My 1959 two-cylinder Eicher tractor has something like that. Awesome . It never breaks and never needs adjustment. By the way, 12 years ago, the gears still looked sharp (that's when new injectors and valves were installed in the engine).
However, the requirements are slightly different... By the way, the Eicher has a radial pump that is driven by the camshaft located at the bottom.

Best regards, Rainer.

Hello,

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The ZR drive has been available from FIAT since the early 1970s. No one has complained about it at FIAT. VW has used the ZR drive since the first Golf (1974).

Complaining back then didn't really achieve much. The interval for the timing belt on those Fiat 128 models with the 1100/1300 engines was 60,000 km. I had one of those engines fail due to a timing belt issue, and it was well under 100,000 km. The timing belts were quite narrow, and the other components like the rollers and guides weren't much better than they are today. Opel, for a while, used to advertise a 30,000 km interval for the timing belt on their 1.6-liter gasoline engines as a selling point. My neighbor's 1.6-liter Tigra then broke down with its second timing belt at 90,000 km.

Based on my experience, I claim that other components involved in the timing belt system (tensioner pulleys, tensioners, water pumps) are largely responsible for timing belt failures, in addition to assembly errors. It seems that while development might initially aim for high quality, the purchasing department often compromises the remaining reliability, leading to widespread failures for customers. The initial and relatively long-maintained 60,000 km service interval for VW PD engines speaks volumes. Fiat was able to achieve the same level of quality back in 1970.

I believe that timing belts are a viable drive technology, but only if they are designed to last for the entire lifespan of the engine.

Best regards,
Christian.

Hi Bertil, overall, you seem quite pessimistic regarding alternatives to the timing belt, especially for TDI-PD engines. Even if the timing belt is the best possible solution, one could still control the valves directly using pushrods or electrohydraulically. That way, at least you wouldn't have a complete engine failure if the darn timing belt breaks; that would already be a significant improvement.

The chain length adjustment in TDI-PD engines could, if desired, be compensated for electronically, perhaps through a servo motor that could rotate the camshaft wheel relative to the camshaft under load. This would also eliminate the need for the mechanical baseline adjustment during chain replacement, as the engine control unit would automatically handle it in the service menu. Furthermore, camshaft wear and other tolerances could be automatically adjusted in real-time. Whether such a design would be economically viable (considering the effort versus the benefit) is debatable. However, simply saying 'it's not possible' is too simplistic.

By the way, with motorcycles, a broken drive belt doesn't cause engine damage, and drive chains have completely different conditions (no lubrication, dirt and dust exposure due to open guides), so they are not very comparable to belt or chain drives in TDI engines.

200,000 km is not ideal for DC timing chains, I agree. However, given that mileage, it makes sense to combine it with a complete overhaul.

Why are you so skeptical about the wheel bearings in the T5? Are there already long-term experiences with them? Is there a specified lifespan or replacement interval for them?

Regards,
Holger.

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But it's easy to just say "it's not possible."

Okay, so let's say "doesn't work economically" ...
I hesitate to even consider the "improvement" in reliability achieved by adding an extra component that is, more or less, prone to failure. Especially since, in the case of raw PD power, that would require a very robust servo motor.

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By the way, with motorcycles, there is no engine damage in the event of a drive belt failure

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Well, let's hope that the limiter is fast enough .

Roger wrote:

Well, let's hope that the limiter is fast enough .

Believe me, the limiter is definitely fast enough, even under full load.

Best regards,
Uwe

But let's move beyond TDI-PD for a moment: Why did manufacturers move away from an overhead camshaft and pushrods? Surely, the inertia can be managed with modern materials like carbon fiber or Kevlar.

Okay, and now another argument against timing belts: How about engines in the medium to heavy-duty commercial vehicle sector, where reliability is a high priority?

chris11 wrote:

.... I believe that timing belts are a viable drive technology, but only if they are designed to last for the entire lifespan of the engine. ....

I tend to agree. There's a lot of potential in this technology. VW gasoline engines from the 1980s are still running today with their original spark plugs. Why shouldn't the same be possible with HD diesel engines in the future?

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Based on my experience, I would like to state that the other components involved in the timing belt (tensioner pulleys, tensioners, water pumps) are, in addition to assembly errors, responsible for a significant portion of timing belt failures.

Absolutely correct. Most e-scooters fail due to poor quality components. The same applies to chains, which is why the statistics look so bad. None of these systems offer a real advantage.

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Hi Bertil, overall, you seem to be quite pessimistic regarding alternatives to the timing belt, especially for TDI-PD engines.

Not only with PD (common rail) systems, but with all HD (heavy-duty) diesel engines. What do you think would be required in terms of force for CR systems to generate the injection pressures that PD systems already achieve today? CR systems even waste some of the generated pressure within the rail.

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Even if the timing belt represents the best possible solution, one could still control the valves directly using pushrods or an electro-hydraulic system. At the very least, this would prevent a total engine failure if the blasted timing belt breaks; that would be a significant improvement.

Well, your idea is fundamentally quite good, but it's clear that you haven't given enough thought to what it means to integrate a system into a car.
Decoupling the drive systems from the front axle (FWD) and rear axle (RWD) is the only way to avoid these problems. The F1 cars demonstrate this. Unfortunately, these systems are currently unable to operate under the conditions required by the automotive industry.

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If one were to compensate for chain elongation in a TDI-PD engine, it could theoretically be done electronically, perhaps using a servo motor that could rotate the camshaft wheel relative to the camshaft under load.

To create another vulnerability or point of failure.

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This could also eliminate the need for manual mechanical adjustments during chain replacement, as the control unit would automatically handle it in the service mode. Furthermore, valve wear and other tolerances would be automatically compensated for in real-time. Whether such a design would be economically viable (considering the effort versus the benefit) is debatable. But simply saying "it's not possible" is too simplistic.

I have never said "it's not possible" or "it can't be done."
These systems must function flawlessly in outdoor temperatures ranging from -40° to +85° Celsius. This is not possible with any of the current systems. In particular, hydraulic or pneumatic systems often have problems in these temperature ranges.

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By the way, with motorcycles, a broken drive belt doesn't cause engine damage, and drive chains have completely different conditions (no lubrication, dirt and dust exposure due to open guides), so they are not very comparable to belt or chain drive systems in TDI engines.

Both systems are exposed to the same environmental conditions. An engine failure in a scooter can be much worse than a timing chain rupture in a motorcycle engine.

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200,000 km is not ideal for DC timing chains, I agree. However, considering the mileage, it makes sense to combine this with a complete overhaul.

200,000 km and a complete overhaul?
I'd like to see your face when you have to pay for that.

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Why are you so skeptical about the idler pulleys in the T5?

Are there already long-term experiences with them? } Is there a specified lifespan or replacement interval for them? }
Vehicle lifespan (160,000 km with VW).
What makes me so skeptical?
I've seen several disassembled timing chain sets from this engine (no further comment).
Then consider the conditions under which this technology must function and the tolerances that arise at different temperatures. Add to that the (impact) loads caused by the HD diesel injection, and the tooth flanks will start to wear out. That's exactly what the gear sets looked like. A chain would be a better option.
Here's a quick question: Why do you think the new 4-cylinder 4-valve TDI engine from VW is once again a "827" type and even features a timing chain drive? The new 4-valve TDI was announced as an engine with a timing belt (and prototypes of that design existed). Furthermore, the engine was released significantly later than originally planned.

In my opinion, the spur gear technology is the best (F1 engines had it very early on), but the demands of modern high-pressure fuel injection systems require a certain degree of flexibility. Spur gear and chain technology can only offer this with vulnerable auxiliary components.
It cannot be the purpose of a system to eliminate one problem only to create a new one in its place.
Every system has its advantages and disadvantages. Currently, the ZR is the best compromise.

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But now, let's move beyond TDI-PD: Why did manufacturers move away from an under-mounted camshaft and pushrods?

Probably also for reasons of cost-effectiveness in mass production. The EA 827 engine has an overhead camshaft. As far as I know, there is only one other engine in the entire Volkswagen lineup that uses a pushrod design: a 1-liter 4-cylinder engine (AHT in the Lupo).

The mass would definitely not be a problem at 4,000 RPM, the only potential issue might be the PD drive system connected to the pistons.

The conditions in the commercial vehicle sector are difficult to compare with those in the passenger car sector due to the significantly lower engine speeds.

I believe that timing belts are a viable drive technology, but only if they are designed for the entire lifespan of the engine.
Please provide the text you would like me to translate from German to English.
I think so too. There is a lot of potential in this technology.

If the potential is exploited to the point where the intervals increase to what's called 'lifetime maintenance' (160,000 km), I promise, I'll stop complaining!

Here's another idea to prevent catastrophic failure: two parallel timing belts, both monitored for cracks. If one fails, the engine control unit immediately sets the power delivery elements (PDEs) to the lowest possible torque (hydraulic short circuit) within fractions of a second, and the engine is, of course, shut down. In vehicles with automatic/Tiptronic transmissions, the power transmission to the wheels is also interrupted to allow the engine to stop quickly. A prerequisite is that auxiliary components on the timing belt are not allowed.

Hello Bertil,

Why aren't CR pumps driven directly by the crankshaft? Is it a length issue? Or are there problems with uneven torque and torsional vibration on the side opposite the flywheel? Perhaps they could be integrated directly into the crankshaft, similar to the newer oil pumps. Unfortunately, with a PD (presumably referring to a specific engine type), the driving force is needed at the top of the cylinder head, so a drive system is unavoidable. A CR-like pressure accumulator could significantly reduce the load in this case.

Best regards,
Christian.

The conditions in the commercial vehicle sector are difficult to compare with those in the passenger car sector due to the significantly lower engine speed levels.

If you're already comparing systems of different sizes, you have to compare the piston speeds and the peripheral speeds, and those are certainly not lower in a truck.

By the way, I'm driving my AKU through Stuttgart at a lower speed than some 40-ton trucks.

SeatArosa1.7SDI wrote:

.... If the potential is exploited to the point where the intervals increase to what's called "lifetime maintenance" (160,000 km), I promise, I'll stop complaining!

Well, in that case, you'll unfortunately have to be much quieter.
For gasoline engines, we've already reached 150,000 km, and for the new PD TDIs, it's around 120,000 km .

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Condition: Auxiliary components for the timing belt are prohibited.

I agree. In a time-critical system, a non-time-critical process (like a water pump) has no place.

chris11 wrote:

Hello Bertil, Why aren't CR pumps driven directly by the crankshaft?

No idea.
The CR pump is not time-critical and does not need to be integrated into the main water circuit control system.
The cost factor likely plays a role here. One would have to create each power circuit twice.

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Problem with the size of the components? Uneven rotation and torsional vibration stress on the side opposite the flywheel? Perhaps integrate it directly into the crankshaft, similar to the newer oil pumps? Unfortunately, the PD (presumably referring to a specific engine type) requires the driving force at the top of the head, so a drive system is unavoidable. A pressure accumulator similar to a CR (presumably referring to a specific technology) would likely provide significant relief.

Furthermore, the fuel rail must be located close to the cylinder head, and the common rail pump must also be positioned near the fuel rail. This would likely prevent a direct crankshaft drive.

EDIT: And the higher the pressure, the more problematic the space issue becomes. PD is avoiding dealing with this.

For gasoline engines, we've already reached 150,000 km, and for the new PD TDIs, it's around 120,000 km.

120,000 km with the PD? Oops, I guess I wasn't up-to-date . How did they manage that? Wider belts? Ultra-modern material from aerospace? Hopefully, there will be some goodwill if the engine fails with the first belt replacement before 120,000 km, outside the warranty period, due to belt failure...

SeatArosa1.7SDI wrote:

.... 120,000 km with PD? Oops, I guess I wasn't up to date .

Ahhh, jetzt ist mir deine Ablehnung klar. Nicht auf der Höhe der Zeit und dann meckern ... Search function;
All PD TDI engines from model year 2004 onwards have a maintenance interval of 120,000 km.

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How did they manage that? Wider straps? Ultra-modern material from the aerospace industry?

Fiber optic cable and a 36mm wide strap. (Monster strap, see picture).
There, your VP "Riemchen" is a lonely boy against .