Piezo-electric unit injectors from Volkswagen

[wxman]

http://www.dieselnet.com/news/0412vw.html

Volkswagen Mechatronic—a Volkswagen-Siemens joint venture—has launched the industry’s first unit injector with piezo actuators. The new piezo-electric unit injection system is characterized by a more precise and flexible multi-point fuel injection control, enabled by replacing the conventional solenoid valves by a piezo actuator, said Volkswagen Mechatronic.

Piezo-electric crystals provide motion when given a pulse of electrical energy. Piezo-electric crystals are arranged in wafer form, and when several wafers are stacked and energized, they are capable of producing displacements of a few hundredths of a millimeter that are sufficient for precise valve needle opening and closing in high-pressure injection systems. Piezo actuators have response times on the order of just a few tenths of a millisecond.

The piezo-electric technology was commercialized in common rail injection systems by Siemens in September 2000. But unit injectors—a technology featured in several Volkswagen engines since 1998—still relied on solenoid-actuated valves. Unit injectors, due to the absence of long, high pressure fuel lines, allow for higher pressures (up to 2,000 bar) than other types of injection systems, including the common rail.

 

[golftdibrad]

VW needs to cut to the chase with their tech and join the 21st century. The halex oil pressure based (like in the newer ford powerstrokes) system is the only way to fly. Untill then they are just making improvments on old tech. Which is great-old is proven and time tested. I just think if they are going to make things complicated and high tech they should do it to today or tomorows technology, not yesteryears.

BTW, who wants 4 piezo buzzers in their engine? I thought they were tring to make them queiter!

 

[TDIMeister]

While arguably elegant in design, the Powerstroke's intensifier-based HEUI injection system is far, FAR from being problem-free in practise. I'd rather take the PD system or common-rail any day.

And if one thinks VW is picky about oil requirements on the PD, just read the Powerstroke boards about the numerous issues and outright failures of the injection system due to oil-related factors. Thankfully, there has so far not been a single registered PD or TDI engine failure that can be directly attributable to the oil under normal circumstances (engine not modified) and the proper oil was used.

 

[saabguru]

It's the industry's first. What makes it old tech?

 

[VelvetFoot]

So does this mean that VW is going to stick with PD for the small engines and not go to common rail?

 

[golftdibrad]

While arguably elegant in design, the Powerstroke's intensifier-based HEUI injection system is far, FAR from being problem-free in practise. I'd rather take the PD system or common-rail any day.

And if one thinks VW is picky about oil requirements on the PD, just read the Powerstroke boards about the numerous issues and outright failures of the injection system due to oil-related factors. Thankfully, there has so far not been a single registered PD or TDI engine failure that can be directly attributable to the oil under normal circumstances (engine not modified) and the proper oil was used.

Agree 100%. My dad has one of those in his truck and puts 30 to 40k miles a year on his truck. We both use mobil delo 1300 and have had no problems thus far.

I'm just saying that while i think vw is doing a great job with their diesles, they should move on technology wise. Their PD system is similar in basic design and theroy to what detroit and cat were doing over 20 years ago. While halex (this is what dad says CAT calles it) has its issues, it has its advantages. No limits on injection timing is a big one. As far as the powerstroke boards having reports of failuers due to oil, If you listen to these boards too much one may think VW has alot of belt and turbo failures and think its a problem plagued engine, when its not in reality. Stuff breaks, thats life. I'll bet the failure rate for turbos and tming belts is well under 0.1% of vehicles on the road.

I'm rambling, sorry. Point, this sounds like cool technology, but VW needs to comeup with the 'next big thing' instead of improving on old ideas. I do think that this is a good step towards that.

-Brad

 

[Arthur]

My dad also drives a ford powerstroke. While the engine in his truck does seem to be running strong it is plagued with some strange glitches which I would not blame on the engine entirely, rather on Ford for poor installation.

And as for the HEUI design working well, well it works, but it (the engine) *feels* far far more ancient than the engine in my 04 tdi. Its very loud, very rough, and VERY powerful.

While we're drawing comparisons I will be fair to the powerstroke and make a note. You know how the oil goes black very quickly in the TDI's because its a diesel yada yada yada. Well can someone explain why the engine oil in his 6.0L diesel hardly gets dark, as compared to my tdi, where it goes jet black.

 

[2004_Passat]

While arguably elegant in design, the Powerstroke's intensifier-based HEUI injection system is far, FAR from being problem-free in practise. I'd rather take the PD system or common-rail any day.

I agree completely. HEUI systems are at a big disadvantage in cold starts due to the oil viscosity problems. Add to that the oil-actuated VNT in the PowerStroke, and you've got a cold-start nightmare. The injection-to-injection delivery variability inherent in the HEUI system is a big problem for 4 cylinder engines as well. HEUI's had its day, but I'd much rather have a common rail or mechanically-driven unit injector system.

 

[GoFaster]

I'm just saying that while i think vw is doing a great job with their diesles, they should move on technology wise. Their PD system is similar in basic design and theroy to what detroit and cat were doing over 20 years ago.

Electronically-controlled unit injectors may have been in use 20 years ago but I don't think they were commonplace ... and certainly not at the injection pressures we are seeing now, and DEFINITELY not with the piezo-controlled arrangement!

Besides, just because something is an old idea doesn't automatically make it a bad idea. Practically everything in use on any internal combustion engine today, gasoline or diesel or whatever, had its roots in ideas the better part of a century ago!

While halex (this is what dad says CAT calles it) has its issues, it has its advantages. No limits on injection timing is a big one.

Common-rail and HEUI are indeed capable of injecting fuel at any time during the 4-stroke cycle. P-D is capable of injecting fuel at any *practical* time during the compression and early expansion stages. The capability of injecting fuel outside of that time doesn't serve any useful purpose except *maybe* post-injection for raising exhaust temperature, and there are ways of making a P-D system do that if you had to. The more useful capability of common-rail injection is to do the injection cycle in multiple stages. There is no reason that this cannot be done with the P-D piezo injectors just as well as it can be done with common-rail. The piezo valve can open and close several times during the plunger stroke - there's nothing stopping that from happening.

The P-D system reduces power losses that have been inherent in common-rail systems because it only pressurizes the fuel that's actually going into the cylinder. (Common-rail systems pressurize the maximum fuel delivery rate all the time and spill what isn't used - this uses more power.) The P-D system is not subject to the headaches associated with using the engine oil to pressurize the fuel. The one thing that a P-D system cannot do is independently control injection pressure from engine speed, but it's questionable whether there's any benefit from that anyway given that P-D systems are capable of operating at higher pressures than common-rail systems throughout the useful speed range ...

I'm rambling, sorry. Point, this sounds like cool technology, but VW needs to comeup with the 'next big thing' instead of improving on old ideas. I do think that this is a good step towards that.

Don't dismiss the advantages of the P-D system too quickly ...

 

[Figster]

The P-D system reduces power losses that have been inherent in common-rail systems because it only pressurizes the fuel that's actually going into the cylinder. (Common-rail systems pressurize the maximum fuel delivery rate all the time and spill what isn't used - this uses more power.) The P-D system is not subject to the headaches associated with using the engine oil to pressurize the fuel. The one thing that a P-D system cannot do is independently control injection pressure from engine speed, but it's questionable whether there's any benefit from that anyway given that P-D systems are capable of operating at higher pressures than common-rail systems throughout the useful speed range ...

The spill setup is true for the older common rail setups. The newer versions use a variable displacement pump to pressurize the rail, using a rail pressure sensor as feedback and a controller to vary the displacement of the pump to achieve a constant rail pressure. This results in less energy absorbed by the pump.

We tested engines with both types of pumps. I know that at least John Deere uses the variable displacement common rail pump - it was made by nippondenso. We used one on a project that we were doing at work.

Figster

 

[TDIMeister]

Even so, by the simple equation (uh oh, here I go again

), the work required to raise a given volume of fluid in a steady-flow system by a pressure differential is equal to the integral of VdP, where V is the volume and P is pressure (grossly simplified, of course). A relatively large volume of fuel to pressurize (in a fuel rail for example) will require more work than a small volume to the same pressure (like inside a unit injector plunger, for example).

Can you disclose where you work, Figster? I'm not aware of any Diesel development work in VA, but I do know that Siemens Diesel Systems recently relocated from Auburn Hills, MI to Columbia, SC.

 

[Tin Man]

My dad also drives a ford powerstroke. While the engine in his truck does seem to be running strong it is plagued with some strange glitches which I would not blame on the engine entirely, rather on Ford for poor installation.

And as for the HEUI design working well, well it works, but it (the engine) *feels* far far more ancient than the engine in my 04 tdi. Its very loud, very rough, and VERY powerful.

While we're drawing comparisons I will be fair to the powerstroke and make a note. You know how the oil goes black very quickly in the TDI's because its a diesel yada yada yada. Well can someone explain why the engine oil in his 6.0L diesel hardly gets dark, as compared to my tdi, where it goes jet black.

My 7.2 Powerstroke oil got black immediately. I once heard that there will be more soot in the engine oil with newer pollution control regs. Perhaps the engines have a different amount of blow-by of diesel exhaust or fuel past the rings designed in???

 

[2004_Passat]

The spill setup is true for the older common rail setups. The newer versions use a variable displacement pump to pressurize the rail, using a rail pressure sensor as feedback and a controller to vary the displacement of the pump to achieve a constant rail pressure. This results in less energy absorbed by the pump.

We tested engines with both types of pumps. I know that at least John Deere uses the variable displacement common rail pump - it was made by nippondenso. We used one on a project that we were doing at work.

Cat has also used variable displacement pumps (oil pumps in this case) for their HEUI-equipped 3400-series engines since the mid 90's.

 

[HIDTDI]

The heui injectors used in the new 6.0 and 7.3 powerstroke imo is some of the most long term reliability problems I've seen. The 7.3 injectors will fail on the electrical side while the 6.0 injectors leak fuel into the crank case. High pressure oil pumps on 7.3 leak. injector control pressure sensors that fail causing erratic starts and performance problems.

VW injector pumps are cheap compared to repairs on this
system.
IDM 1100
injectors 300 - 500 per injector
high pressure oil pump 550
6 - 10 hour labor times for repairs to system

Both 7.3 and 6.0 injectors have no tolerance for water or
contaminated fuel. Farm fuel is also another big no no due to the low quality control of the fuel. I have seen severe cases of contamination ruin all 8 injectors at once.

Both systems are also plauged with electrical harness issues on engine and under valve covers.

I see all this working at the dealer and I am not saying they are bad trucks, but are very expensive to repair compaired to the older mechanical injection systems.

Benefits though are way reduced emissions and high amounts of horsepower and torque while getting better mpg

 

[wxman]

More info on piezo injection technology (Siemens VDO specifically):


http://www.dieselforum.org/factsheet/commonrail-piezo.html

 

[Pat Dolan]

There is one more thing to consider in the common rail vs. unit injector debate: ALL fuel contains dissolved air, and when it is pumped (or even run accross a sharp edge) it is removed from solution, but can take hundreds of ATU press to reach the miscibility point and re-dissolve. All of that takes time and space, which is one of the reasons why old-style diesels were a bear to make clean and accurate for timing (you couldn't tell when it would actually inject, because the amount of free air was not that predictable. The only truly elegant solution was the VW/Bosch answer of putting a needle lift sensor on one injector to get a proper reference signal.

The Ford Powerjoke....er, Navistar thing with Cat HEUIs suffers from all kinds of really serious trouble because it has not only air troubles on the fuel side, but I suspect some on the oil drive side as well. The electronics only ASSUME that it will fire when the computer says go bang. Take a look in a 7.3 PSD, the injector in the #8 hole is DIFFERENT from the rest (longer mechanical lead ground into the pilot shot). I have seen cylinder pressure curves that show the first phase of combustion happening more or less on time with a nice rise, and coming in way EARLY and spiking high (missed pilot shot due to too much air in injector) on the same engine at the same time, (called cackle if it happens at 1500-2000 rpm and idle knock at idle). Why would anyone WANT to compromise their injection strategies with this basically flawed reasoning? Using piezo switching will NOT avoid this basic fact of the laws of physics.

So, for obvious reasons, I am a common rail fan (fuel is already at high enough pressure to ensure air remains in solution, so you can be absolutely accurate in timing). BTW, just have a listen to the current common rail Cummins 5.9...sorry, you can't, they are that quiet.

Pat

 

[fastvicar]

My business owns a Powerstroke 7.3L and a Cat 3116. Both are hard-starting engines, I blame the injections systems. On cold mornings that Powerstroke has to crank awhile to build up pressure through the 2 oil pumps, filter, fuel pump & injectors. The HEUI design works relatively well for over-the-road trucks that are running continuously, but seem a poor choice for start-stop applications like pickup trucks & UPS delivery vehicles.

I had read an article in Diesel Progress magazine about the Siemens injectors in the new 6.0L Powerstroke engine. Siemens was pulling their hair out because of the tight tolerances in the injector design (5 microns, IIRC) and the sheer quantities needed to meet demand. They had to bring production to a halt for some time until they could get it under control. Think about trying to meet those tolerances on roughly a million units/year. It is mind-boggling to me that they could even attempt it.

I'm all for common-rail & piezos, but I am worried about technology exceeding practical application. At what point is good-enough actually good-enough?

 

[TDIMeister]

I'm all for common-rail & piezos, but I am worried about technology exceeding practical application. At what point is good-enough actually good-enough?

In a world of an every-tightening noose on emissions regulations, and the competitive pressure for technological progress giving us more economical, powerful and quieter engines, NEVER!

 

[wxman]

One thing this technology's achieving is that the power density of light-duty diesels is now approaching that of the best gassers:

"...With 60kW/litre already in production we believe that the latest developments in diesel technology will ultimately enable peak ratings of 80-100kW/litre. This is likely to lead to a rapid growth in the sports diesel market which is currently in its infancy...."

Source: http://www.ricardo.com/mediaCentre/newsArticle.asp?id=201&sector=1

 

[nortones2]

According to Autocar (UK mag) yesterday, VW will market 168bhp/258lb ft version of the 2-litre 16 valve equipped with piezo injectors, in a so-called GTTDI. Should be available in UK before end of 2005. Still a bit down on 80kw/litre, but not bad

 

[Pat Dolan]

My business owns a Powerstroke 7.3L and a Cat 3116. Both are hard-starting engines, I blame the injections systems. On cold mornings that Powerstroke has to crank awhile to build up pressure through the 2 oil pumps, filter, fuel pump & injectors. The HEUI design works relatively well for over-the-road trucks that are running continuously, but seem a poor choice for start-stop applications like pickup trucks & UPS delivery vehicles.

Actually, just the opposite it true. At startup, the timing of events isn't that critical. I can't speak for the 3116, but you must watch the glow plug relay in the 7.3s like a hawk. I put an LED on the load side to know for sure they are recieving power. The 7.3 should only turn over three or four revolutions before having sufficient ICP for the computer to recognize it and begin opening HP oil solenoids. If it takes a lot longer and the glow plug circuit is right, you may have leaking injector o-rings allowing bleed-down of pressure. Adequate battery voltage is also super-critical (for cranking speed). If you need to crank cold, you should also run a full synth such as Delvac 1.

I have a Y2K 7.3 Ford, and one thing I can say FOR it, is that it is a very good cold starting engine (to about -30 without aux heating of any kind - when unavoidable).

Pat