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1in10^9
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BMW is all over the place with valvetronic. E90 330i which was made only in 2006 for US market had valvetronic. Then N54 didn't have one. Then they put one in N55. Then they took it out of the brand new N63 (4.4L twin turbo V8) they again they put valvetronic in new F10 M5 S63 engine, which on paper has better gas mileage than N63. Crazy...

8/30/2011 8:18:06 PM

smc
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Quote :
"his is measuring how much heat is being absorbed in the engine. You can see that as the mixture enriches, the heat consumption shoots up which ultimately results in cooler exhaust temperatures. That's another reason why the mixture is enriched under heavy loads. High exhaust temperatures decrease component life, especially catalytic converters.
"


I've always been told that richer is cooler, but your statement confuses me. Do you mean more heat is actually absorbed by engine components? This seems backwards to the prevailing wisdom that lean mixtures melt pistons. Then on an air-cooled engine where getting rid of heat is difficult...would it be better to run lean?

8/30/2011 8:23:57 PM

sumfoo1
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More heat is converted to power or obsorbed during the phase change of the fuel

8/30/2011 9:12:23 PM

arghx
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What I mean is, as the mixture gets richer it absorbs more heat in the combustion chamber just as you thought. More heat is absorbed as you add more fuel. The brake-specific heat consumption is directly related to the mass consumption rate of the fuel:


Wu, "The influence of air–fuel ratio on engine performance and pollutant emission of an SI engine using ethanol–gasoline-blended fuels," 2004

Quote :
"BMW is all over the place with valvetronic. E90 330i which was made only in 2006 for US market had valvetronic. Then N54 didn't have one. Then they put one in N55. Then they took it out of the brand new N63 (4.4L twin turbo V8) they again they put valvetronic in new F10 M5 S63 engine, which on paper has better gas mileage than N63. Crazy..."


I think they are just balancing cost vs emissions benefit. BMW has done a lot of this type of internal study. Here's one from back around 2006:


Schwarz, "Potentials of the Spray-Guided BMW DI Combustion System," 2006

The benchmark is the "4 valve conventional" which would most likely be your run-of-the-mill BMW I6 engine with basic variable valve timing cam phasers (VANOS). So the direct injected twin turbo N54 would be "DI TC lambda = 1 without downsizing" and the non turbo port injected Valvetronic N52 from the 330 would be "Valvetronic" on that chart. At the time BMW must not have been far enough along on direct injected lambda = 1 + turbo + Valvetronic (like the N55) to include that in the study. If I had to guess, that configuration has specific fuel consumption similar to conventional throttle + lambda > 1 (meaning lean burn engine) but without the expensive emissions equipment.

The quality of the fuel, the price point of the car, and the operating rpm and load point of the engines, and the emissions standards all have a lot to do with these kinds of choices. In Europe they have better quality fuel but I am not sure if BMW is using any lean burn engines there right now like VW has done. No lean burn passenger car gas engines are being sold in the States to my knowledge due to the sulphur content of the fuel. I need to eventually talk more about direct injection configurations on here but it is a big topic and fuel injection timing and fuel quality are big issues.

One of the main things to understand about the downsizing trend is that it is usually more fuel efficient to run a smaller engine at higher loads (mostly through a turbo) than lug a larger displacement, greater # of cylinders naturally aspirated engine around.

[Edited on August 30, 2011 at 9:25 PM. Reason : .]

8/30/2011 9:19:22 PM

arghx
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Just ordered the Bosch Automotive Handbook, the new 8th edition. http://books.sae.org/book-bosch8 I think it was $58 shipped for the regular paperback version

DH Hill has the 6th edition and that's got some good stuff, but I wouldn't mind having the latest version since it just came out a couple months ago.

8/31/2011 11:14:31 PM

smoothcrim
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^^ Is that graph's X axis referring to percentage of volumetric efficiency?

9/1/2011 7:11:54 AM

arghx
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It doesn't really say how they are measuring it, but I imagine it is directly related to a pumping efficiency calculation, like the SAE J1979 "absolute load" calculation. http://obdcon.sourceforge.net/2010/06/about-pid-calculated-load-value/

[air mass (g)/intake stroke] / [maximum air mass (g)/intake stroke at WOT@STP at 100% volumetric efficiency]

where WOT = Wide open throttle and STP = standard temperature and pressure

I've seen enough "efficiency" formulas and calculations that I'm not 100% certain if there is standardized nomenclature.

9/1/2011 10:27:16 AM

arghx
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Found some interesting specs on brake fluid types. There are two main types of brake fluid: Polyglycol and Silicone. Polyglycol is the normal amberish stuff. It tends to attract moisture so you have to be careful about contamination. Silicone fluid is supposed to be purple. It is harder to bleed than polyglycol but it does not attract moisture.

DOT 3 - Polyglycol , minimum boiling point 401F dry 284F wet , blends w/ DOT 4

DOT 4 - Polyglycol , minimum boiling point 446F dry 311F wet , blends w/ DOT 3

DOT 5 - Silicone, minimum boiling point 500F dry 356F wet , compatible
but will not blend with other fluids

I get the sense that very few passenger cars run DOT5 and even most racing applications are using DOT 4.

9/1/2011 10:31:05 AM

zxappeal
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A couple things to note about brake fluid:

1. Glycol fluid is indeed hygroscopic, meaning that it has an affinity for water. The strength of affinity has to do with the grade of fluid. DOT 4 fluids have less affinity than DOT 3.

2. Silicone fluid (DOT 5) is NOT hygroscopic at all. I'd qualify its color as clear with a purple iridescent quality.

3. Glycol fluids are almost 100% incompressible, whereas silicone fluids exhibit a certain amount of compressibility. Your pedal feel with silicone fluid will be somewhat less firm than with glycol fluid.

In general, I feel that glycol based fluids are preferable to silicone fluids, as they do provide better pedal feel, and they will mix with water. This means that any condensation in the system can mix with the fluid instead of forming local pockets with greatly increased chances of local corrosion and subsequent damage/perforation. Of course, we all know that for this to truly be a benefit, the fluid must be flushed regularly, and if it isn't, corrosion WILL become a problem anyway.

9/1/2011 11:00:20 AM

arghx
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^ thanks for the input Dan. I think you're the only person I know who has used silicone based brake fluid on a car.

[Edited on September 1, 2011 at 12:25 PM. Reason : silicone damnit]

9/1/2011 12:20:56 PM

sumfoo1
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There was a thread you posted about the zr1 motor in, how different is the CTS-V motor... i know it has a smaller blower (1.9l) but thats about all i know right now.

lets add... no titanium rods and hypereutectic pistons instead of forged to the list of awesomeness it missed out on (still a cooler car *i like wagons* thats like 40k cheaper so... who really cares right?)

[Edited on September 1, 2011 at 3:20 PM. Reason : .]

9/1/2011 3:10:52 PM

arghx
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The technical discussions were originally buried on some GM website I found.

read here for LSA engine: https://docs.google.com/leaf?id=0BzoEDgrFUehAYTFmMTUwZmItNDI2Zi00ZmVkLTgzNmQtMDUzNDRlYTVhOWQy&hl=en_US

LS9: https://docs.google.com/leaf?id=0BzoEDgrFUehANmYzNWFlZGQtZWNmYS00ODlhLThkN2MtZmEyMDZlYzU3NzY1&hl=en_US

9/1/2011 6:59:21 PM

sumfoo1
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meeh so its block is the same but they cheapened up the rest a lot

9/2/2011 7:50:40 AM

arghx
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pretty much

9/2/2011 11:24:12 AM

sumfoo1
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i wonder how much a junk yard LS9 cost...

hmm dry sump forged pistons titanium rods and a bigger blower....

yummy

9/2/2011 11:58:43 AM

Air
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civic vx/hx/hybrid lean burn still works fine....
any documentation on how honda did it back in the 90's?

9/2/2011 1:08:07 PM

sumfoo1
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... built motors strong enough to withstand detonation when it occasionally happened.

9/2/2011 1:21:48 PM

Dr Pepper
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Quote :
"i wonder how much a junk yard LS9 cost...

hmm dry sump forged pistons titanium rods and a bigger blower....

yummy

"


you're not going to find one in a junkyard... salvage yard people would gank that thing before the car came off the roll-back

9/2/2011 1:37:57 PM

sumfoo1
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lol true...


ebay?

9/2/2011 1:41:53 PM

arghx
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Quote :
"civic vx/hx/hybrid lean burn still works fine....
any documentation on how honda did it back in the 90's?"


Masato, "Development of a Lean Burn Engine with a Variable Valve Timing Mechanism," 1996 http://papers.sae.org/960583 . It's on my wish-list right now since I can't find it floating around on the internet. It's too bad DH Hill has ZERO publications from SAE from the past few decades.

Abstract:

Quote :
"Most currently produced lean-burn engines can achieve good fuel economy, but must be further developed to gain better vehicle performance and driveability. Honda has developed a new lean-burn engine which incorporates 3-stage variable valve timing and lift mechanism, swirl promotion at low engine speed, and a new intake port configuration. This engine generates approximately 40% more power over our current lean burn engine and improves the dynamic performance of the vehicle. At the same time, it maintains a fuel consumption level equal to that of the current engine."


I can tell you right now that they had much less strict NOx emissions standards back then. Without having read that paper I can guess they used swirl, valve overlap, and maybe an EGR cooler like a diesel to keep NOx emissions within their targets. It might have had an NOx trap. Now all the direct injected lean burn engines have expensive NOx traps that need to be regenerated once they contaminate with sulphur. The problem is that regenerating a NOx trap requires you to enrich the mixture, offsetting the fuel economy gains. The more sulphur in the fuel, the more you have to regenerate the converter and the more it hurts your fuel economy. Here is some info on an NOx trap used in a VW direct injection application:

9/2/2011 3:39:01 PM

arghx
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Here's an interesting chart from a manual on 90s Toyota ABS systems showing braking force and cornering force vs tire slip.



With a moderate tire slip the brakes will work optimally (provided they aren't overheated etc). So this ABS system calculates the tire slip ratio based on wheel speed sensors and deceleration sensors. Then the ABS system controls brake fluid pressure to the wheels to bring the slip ratio into an acceptable tolerance.

9/2/2011 3:50:49 PM

arghx
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I had a request from Air for information on airflow sensors. I'll start with the basic background information. For even a very basic fuel injection system to work properly, the computer needs

1) engine speed signal
2) some way of determining how much air is entering the engine

In page 1 of this thread I gave a basic background on engine speed sensors. In most designs the sensors generate an AC voltage for the computer to determine engine speed at the very least. If the system is sophisticated enough it can figure out the position of the crankshaft and individual cylinders, while also determining which of the 4 strokes a cylinder may be on.

There are three main methods for figuring out how much air is entering the engine:

1) Measure the air pressure inside the intake manifold and use the ideal gas law to figure out air mass and volume

2) Directly measure the volume of air entering the engine

3) Directly measure the mass of air entering the engine

The first style, where air pressure is used to figure out how much air is in the engine, was popularized on the original Bosch D-Jetronic fuel injection system. D stands for "Druck" which is German for pressure. This system uses one or more pressure sensors in the air piping along with 1 or more air temperature sensors. The Porsche 914 had a Bosch D Jetronic system.



A pressure sensor uses a thin piezo-resistive silicon wafer. As force acts on it, its shape changes and so do its electrical resistance properties. On one side of the wafer is a perfect vacuum chamber, and the other side is connected to the manifold or whatever else you are trying to measure. The silicon chip is constantly flexing as pressure goes up and down. These sensors produce a linear 0 to 5 volt signal where a higher voltage indicates more manifold pressure. Manifold pressure is proportional to airflow so at a given engine speed more pressure (less engine vacuum) = more airflow.

9/5/2011 12:12:54 PM

arghx
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The original Bosch L Jetronic system measured airflow volume directly. The "L" stands for "Luft" in German, meaning air. There are four different styles of volume airflow meters that I've seen. Three use variable resistance (a potentiometer) to generate a signal: the 12 volt vane/flapper type, the 5 volt vane/flapper type, and the sliding type. A fourth kind of volume airflow sensor, the Karmen Vortex airflow meter, measures disturbances in intake air and then generates ON/OFF (binary square wave) pulses. A higher frequency of pulses (more hertz) corresponds to a higher volume of intake air.



The vane (flapper) type airflow meter was common up through the mid 80s. The sensor uses a revolving door which opens more as intake air volume increases. The movement of the door changes electrical resistance to generate a signal voltage. Earlier designs increased voltage as airflow increased. Later designs decreased voltage. This type of airflow meter also incorporated a signal for the fuel pump relay because a lot of old engines did not directly control the fuel pump from the ECU.



The sliding airflow meter is another type of volume airflow meter that uses a potentiometer. This was used mostly in the late 80s and early 90s. It has a less restrictive design than the flapper type. Its signal is like the 5 volt flapper type above. Notice that none of these airflow sensors have linear output like the pressure sensor does. The point of that is to have more precision at lower loads where the engine operates the most.



While the potentiometer-type airflow meter was fell out of favor in the 90s, the Karmen Vortex volume airflow meter was still being used until at least the mid 2000s. I know Toyota and Mitsubishi used this design, and Mitsubishi Lancer Evos had them until they switched to a mass air meter on the Evo X.



Compared to potentiometer-based volume airflow sensors the Karmen airflow meter causes negligible airflow restriction. Inside the meter is a vortex generator which causes disturbances in the air. A higher volume of airflow causes these disturbances to be created at a higher frequency (more Hz).



These disturbances make a small mirror oscillate inside. The oscillations cycle a transistor on and off, producing a square wave (binary ON/OFF signal) at the same frequency. The ECU figures out the frequency and uses it as part of its airflow and load calculations. A Karman airflow meter does not directly measure air mass, so the ECU must also rely on the barometric pressure sensor and intake air temperature sensor for an accurate calculation.



The bottom graph is the main airflow meter scaling table on an Evo IX. I am unsure what the airflow units really are. The other two graphs are compensation tables for barometric pressure and intake air temperature. Mitsubishi uses a pretty complicated algorithm to calculate the engine load value used to determine fuel and spark.

[Edited on September 5, 2011 at 12:25 PM. Reason : fixed graph]

9/5/2011 12:14:34 PM

arghx
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The mass airflow meter (MAF) is the most common type of airflow sensor in use today and can be found on Bosch Motronic engine management systems. Both the Hot-wire and Hot film type sensors use temperature differences to determine the actual mass of air entering the engine. The hot wire MAF sensor is probably the most common. It has two wires: a cold wire/thermistor to measure ambient temperature, and a hot wire that's constantly changing electrical resistance. There is also a completely separate air temperature sensor built into the MAF sensor unit.



The MAF sensor control system tries to maintain a constant temperature difference between the hot wire and the cold wire/thermistor. As airflow increases, more current is required to maintain this temperature difference due to the electrical properties of the hot wire. The MAF sensor outputs a voltage in proportion to the amount of current needed to maintain the temperature difference. As a side note, a wideband oxygen sensor actually uses a similar type of control system to measure oxygen concentration (by pumping current). Here is the main mass airflow sensor scaling table on a 2005 Subaru STi:



The other type of MAF sensor, the Hot Film type, outputs a frequency (like a Karman volume airflow meter) instead of a voltage like the hot wire type. Supposedly the hot film type is less prone to contamination than the hot wire sensor. The hot film sensor has a diaphragm with a small section that maintains a constant temperature above ambient.



On each end of the heated section is a sensor. The sensor on the left (T1) is the upstream sensor. This one is going to be cooler than the downstream sensor (T2). The temperature difference between the two is proportional to the mass airflow. The more air flowing through the sensor, the colder the upstream sensor (T1) will be in relation to the downstream sensor (T2). The hot film MAF sensor outputs a frequency signal. GM uses hot film MAF sensors a lot on their V8 engines. Here are the two MAF scaling graphs for a 2007 Corvette Z06. The scaling is divided into low airflow and high airflow calibrations.



This C6 Z06 MAF sensor can read a LOT of air. 500 grams/second is a LOT of flow. The 2005 STi hotwire MAF sensor reads around 300 grams/second.

9/5/2011 12:17:20 PM

arghx
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So just to review: for a fuel injection system to work, the computer needs engine speed and some way of figuring out how much air is entering the engine. The engine speed can come from a distributor or crankshaft position sensor. The engine air quantity can be determined from measuring the manifold pressure, directly measuring the intake airflow volume, or directly measuring the mass of the intake air. A manifold pressure sensor is cheap and produces a linear 0 to 5 volt signal that is directly related to the amount of pressure.

The volume airflow sensor is an older design that first started in the 1970s. These sensors produce an exponential/logarithmic voltage output in proportion to the volume of the intake airflow. The main types are flap/vane, sliding, and Karman vortex. These designs became progressively less restrictive to the incoming air.

The mass airflow sensor is the newest and probably most common way of measuring the actual mass of intake air. There are two types: the hot wire and hot film, with hot wire probably the most common. Both work by working to maintaining a temperature difference between two elements within the sensor, and then using that process to generate an output signal. The hot wire produces a voltage signal and the hot film produces a frequency signal.

9/5/2011 12:19:10 PM

arghx
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From Autoguide http://www.autoguide.com/auto-news/2011/09/volkswagen-brings-cylinder-deactivation-technology-to-the-4-cylinder-engine.html :

Quote :
"Cylinder shut off technology has been a staple in fuel-saving technology for many years now but until now it has yet to make its way into a four cylinder engine. At least not until now.

Volkswagen‘s 1.4 liter TSI engine will be the very first four cylinder to feature cylinder deactivation as two of its cylinders will shut off when operating at low to moderate rev ranges, resulting to a decrease in average consumption by 0.4 liters/100 km, or 2 mpg. In the illustration provided above, the left half shows all cylinders in operation, while in the right side, we see a diagram of cylinders 2 and 3 deactivated. Cylinder shut off is activated when engine revolutions are between 1400 to 4000 rpm while torque is between 25 to 75 Nm, or between 20 to 50 pound feet. Upon urgent acceleration, cylinders 2 and 3 will wake up from its nap to give the car its oomph.

If the 1.4 TSI is coupled with a start/stop system to prevent consumption during idling, fuel economy is expected to improve by another 0.6 liters/100 km, or 3 mpg.

Expect these engines to debut by the beginning of 2012."




It's interesting that VW is now adopting this technology for production cars, most likely due to the increasingly strict emissions regulations. Around 10 years ago VW did a study of different methods of improving fuel economy:



That was when they decided to be an early adopter of direct injection technology, which as many of you may know is still getting the bugs worked out by a lot manufacturers. You can see that they were concerned about the cost and complexity associated with balancing a 4 cylinder running on 2.

9/6/2011 10:41:49 AM

arghx
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Below is a diagram of a Bosch EV14 injector (for traditional multipoint port injection applications). EV14 is the current style of injector that Bosch makes for OEM and aftermarket applications. In the aftermarket the most common EV14 injector is sold by Injector Dynamics.



Here's a nice set of charts showing injector pulsewidth, solenoid current, injector valve lift, and fuel mass flow.



Notice in the bottom two graphs that there are four regions of injector behavior, based on the rate of change in valve lift. So first you have your ON command from the ECU, which commenses the t_on phase. After the injection command you first have the injection dead time phase which is where the internal ball valve has not yet begun to lift off its seat.

When the ball valve lifts off its seat you have a nonlinear mass flow rate. It seems logical to me that the fuel mass flow rate is directly related to the instantaneous rate of change for the valve position (1st derivative of the valve lift curve). After peak valve lift has been achieved, fuel mass flow proceeds at a linear rate until the injector is commanded to turn OFF. Once that occurs, the valve slowly closes and you have nonlinear fuel flow again.

I suspect that a fuel injector's nominal mass flow rating is based on the area under the fuel mass flow curve (integral of bottom chart). Some manufacturers use cc/min volume flow rates inside their ECU (I think Subaru does this) and others use mass flow rates. GM for example rates the injectors on the 2007 Corvette Z06 as 5.2588 grams/second under normal conditions, or at least that's what the ECU says.

9/7/2011 1:34:17 PM

arghx
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The original two main EPA tests are the FTP 75 (Federal Test Procedure) for city driving and a highway test. Those cycles have been around for a long time and were criticized for being unrealistic in terms of the speeds and driving style plus the fact that they don't use A/C. Over the past 10 years the EPA phased in two supplemental test cycles. One actually uses the A/C--that's the SC03 test. The other simulates speed fluctuations, considering that many/most drivers don't hold a constant speed. That one's called US06. Here are some charts



So if I'm certifying a new passenger vehicle for its individual emissions and fuel economy rating, I have to do all four tests. And then here's where the loopholes come in. The tests are weighted.

35% FTP 75 (the old test)
37% SC03 (the test with the A/C on)
28% US06 (the test with a more realistic driving style)

These weightings are used to calculate the emissions rating and the city fuel economy rating for the individual vehicle. For each of these three tests there is a cold start phase, a cruising phase, and a hot start phase (after engine shutdown). The highway test is separate and it is used for the highway rating.

Now here's a loophole... to calculate corporate average fuel economy (CAFE), the supplemental tests are not used. Only the older drive cycles (FTP 75 and Highway) are used, the ones without A/C, so that inflates the corporate rating some.

[Edited on September 9, 2011 at 2:20 PM. Reason : .]

9/9/2011 2:13:01 PM

arghx
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Here are some specs on oil viscosity:



notice that there is a significant difference even between the 20 weight (5w-20) and the 30 weight (5w-30)

9/14/2011 8:54:05 AM

arghx
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Here is a comparison chart of 3 basic types of limited slip differential as found on 2WD cars. As the saying goes, a limited slip differential's job is to transfer torque from "the wheel that slips to the wheel that grips."

The "bias" or "bias ratio" is rotational torque on high resistance side divided by low resistance (spinning) side.

The friction type on the right is the most common. It uses clutches to transfer torque and is generally considered best for drag racing. The torque-sensing "torsen" type and its variants use a system of gears inside; it's generally considered to be a good design for handling. The viscous type seems to have fallen out of favor for use as a differential on a 2WD car although various types of viscous couplings are used in AWD cars. Advanced AWD systems can be really complicated as they often use planetary gearsets and computer control to adjust the torque split to individual wheels.

9/19/2011 11:30:17 AM

sumfoo1
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the problem with torsen is when the low traction wheel goes to a no traction wheel.

torsen diffs no longer give power to the wheel that slips.

Clutch type limited slips stop working right around the time that the warranty goes by by (and most people don't notice)

And viscous diffs don't transfer torque fast enough to improve handling however still help some and they function in "0 traction" conditions.

9/19/2011 12:35:10 PM

arghx
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Quote :
"torsen diffs no longer give power to the wheel that slips."


That's the point though. During a turn on a front engine, RWD car you are reducing torque to the spinning inside wheel and increasing torque to the outside wheel. That should induce oversteer but that characteristic depends on whether you have a stability control system activated.

9/19/2011 1:08:19 PM

arghx
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I find the transition to plastic/composite intake manifolds to be interesting. GM was an early adopter on their V8 engines, and now even turbo 4 cylinders have it. Here is the new Ford Ecoboost 2.0:



and this is the intake manifold off a Subaru Legacy 2.5GT (turbo model)



The plastic manifolds reduce weight, can have smoother shapes inside, and do not heat up like aluminum does.

9/22/2011 3:37:24 PM

arghx
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Most cars up through the late 90s and early-mid 2000s used analog signals to relay information between a few control modules. The might be an engine control unit, an automatic transmission control unit, and maybe an anti-lock brake control unit and something related to chassis electrical systems. Modern cars use a serial network to connect control modules. The number of modules depends on the features the car has and the amount of responsibilities assigned to each module. GM was an early adopter of these serial networks.

Here is one example of a change: on a typical 90s car the instrument cluster would receive a signal directly from a vehicle speed sensor. The vehicle speed sensor would probably be in the transmission, and it would send pulses to the cluster that are proportional to the vehicle speed. On a new car a separate control module related to braking or traction control may receive one or more speed signals (either from the transmission or individual wheels). It would then calculate the vehicle speed and send a signal over a serial network to the instrument cluster and other control modules.

There are two main types of serial protocols: high speed protocol used for powertrain-related functions and low speed protocols used for chassis electrical stuff. Usually one control module has responsibility to direct traffic along the network and provide an interface between the different protocols used. Manufacturers have their own proprietary designs but as of a few years ago they are required to use a standardized network interface for emissions diagnostics (OBD II port).



Here is the architecture on a 2nd generation Prius. The CAN network is for powertrain management including traction control and braking. The body electrical network would handle things like power door locks. A third network handles audio.



Here is architecture for the main CAN system on an Evo X. There are a lot of control modules and abbreviations here. On the left side of the diagram are control modules for the engine, transmission, all wheel drive, and traction control systems. The middle part of the diagram shows control modules that relate to stuff the driver normally interacts with, like the instrument cluster and the entertainment system. The right part shows a separate network meant to comply with regulations on sending signals for emissions diagnostics.

For those of you familiar with principles of computer networking, here is a breakdown of OSI layers for a standardized SAE J1850 CAN network (high and low speed):

9/23/2011 2:18:01 PM

arghx
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So I read through most of the interesting stuff in the Bosch handbook that I mentioned in a previous post in this thread. I was a little disappointed on their sections about suspension and hybrid drive systems. It had a lot of definitions and drawings about vehicle dynamics but not enough explanation of how the different suspension geometries are used in various applications. The sections on gas and diesel engines were pretty sweet though. I learned a lot about fuel systems and cylinder head design for example.

So I'm thinking about picking up another book. This one is on special and it seems like an amazing deal considering how expensive SAE stuff is http://books.sae.org/book-pt-91.set It is a special boxed set with 90 different SAE papers on fuel and emissions systems for spark ignited [gasoline] engines. The cost is $50 plus shipping. I suspect 90% of the book will boring, esoteric, and useless. But the rest will probably be enlightening, and since a single SAE paper is normally about $22 dollars to download that's still a good deal.

[Edited on September 26, 2011 at 4:07 PM. Reason : .]

9/26/2011 4:06:26 PM

arghx
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just ordered that boxed set mentioned above ^

While I'm waiting for this to come in I've been reading more in-depth stuff about modern fully integrated stability control systems. Here are some definitions of what the various systems mean. Terminology can vary across manufacturers but this list from an Rx-8 training manual is pretty good.



ABS has been on production passenger vehicles for a long time. It adjusts fluid pressure for an axle or a specific wheel in order to reduce the tire slip ratio that I discussed in a previous post.

Traction control TCS came out next. It cuts power to the drive wheels when slip is detected in mostly straight line acceleration.

Dynamic Stability Control DSC and Electronic Brakeforce distribution EBD are newer and they integrate most aspects of powertrain control. The purpose is to reduce skidding and eliminate accidents. To a certain extent the car is pretty much doing the driving for you.

Vehicle Dynamics Variables

Three really important variables used in a stability control system are:

Nu_x : linear velocity of vehicle. This is the straight-line component of velocity, what most people would consider the road speed

Beta : Float angle --the angle between where the vehicle is intended to go and where it is actually going, or as the Bosch handbook calls it "the deviation in direction of travel from the vehicle longitudinal axis"

Psi : yaw velocity. This is rotation around an axis that goes through the center of the vehicle and is perpendicular to the ground.



This Bosch manual I have gives more detailed explanation of system architecture and what kind of calculations are used:



If this looks really complicated it's because it is in fact really complicated. In the Bosch architecture you have a high level control unit, the Transverse-dynamics controller, and a lower level controller.

The Transverse-dynamics controller calculates sort of idealized vehicle behavior according to model: all the complicated angles and moments and torques that should occur in response to driver commands and driving conditions. It uses this to make a bunch of calculations for what the various actuators and modules need to do to bring the observed vehicle behavior within an acceptable tolerance of the behavior according to the model.

The lower-level controller handles inputs from sensors and models other aspects of vehicle behavior that cannot be measured directly (the "observer" in the diagram). This control module also monitors driver commands from the accelerator, brake system, steering wheel, and transmission. The system issues commands to various actuators in order to respond to skidding and wheelspin. These modules might close the throttle, retard the ignition timing, or cut fuel. They might change the transmission behavior or adjust the amount of braking forces going to individual wheel. On a sophisticated AWD car it might distribute a separate torque value to each individual wheel to stop a skid.

Here is a diagram showing a Bosch stability system in action



You can see that it brakes the outside wheel and then the inside wheel to keep the float angle from exceeding acceptable tolerances. Here is a comparison of vehicle behavior with and without stability control:



Finally, here is a block diagram for an Rx-8 stability control etc system



[Edited on September 27, 2011 at 4:09 PM. Reason : more charts]

9/27/2011 4:01:35 PM

arghx
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Here is a manufacturer dyno sheet from Mazda's original 982cc 10A two-rotor Wankel engine. The torque curve is closer to what you might expect on a DOHC 4 or 6 cylinder today.

Notice the high specific fuel consumption in the idle rpm range. This is one of the biggest challenges on this style of rotary engine, and Mazda only "fixed" it with the Rx-8s Renesis engines which are capable of idling with a leaner mixture.

[Edited on September 29, 2011 at 12:31 PM. Reason : originally developed in 1967]

9/29/2011 12:30:51 PM

arghx
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Here are some comparisons between the starting behavior of a conventional port injected engine (PFI) and a gasoline direct injected (GDI) engine. The engine is a Mitsubishi inline-4 engine with a start/stop system that was used in the Japanese market. The main advantage of a GDI engine during cranking is its ability to fire the injector during the compression stroke, with all the valves closed. With the proper injection timing the engine can start quickly and consume less fuel than a comparable PFI engine.

10/3/2011 9:40:07 AM

dustm
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Quote :
"Yes I disagree with that article on the twin turbo moment of inertia aspect. Moment of inertia effects response more than it does boost threshold. I consider boost threshold to be the larger portion of spool. I think twins on an inline are a bad idea because they have the needless loss of pushing against eachother. On a v motor the increased pulse density of having a much shorter manifold is well worth the loss of compressor efficiency."



I don't understand why the turbos 'pushing against' one another makes a difference. Can someone explain? To me it seems that if the manifold pressure is x, then all the turbo has to push against is x, whether there is 1 turbo or 1,000 turbos.

What about the fact that 2 turbos are flowing y air through more surface area of two narrower passageways? Would one turbo not have better volumetric efficiency for that reason?

10/3/2011 12:43:21 PM

arghx
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Quote :
"I don't understand why the turbos 'pushing against' one another makes a difference. Can someone explain? To me it seems that if the manifold pressure is x, then all the turbo has to push against is x, whether there is 1 turbo or 1,000 turbos."


If you have two turbos and one throttlebody/intake manifold, the charge air has to collect somewhere. Typically there will be a Y pipe right before the throttlebody, a y pipe right after the turbo compressor outlets, or an intercooler with two inlets. When the charge air joins, it's going to be a bit like traffic merging on the highway... a little bit of a restriction/slowdown. I'm not sure if "pushing against each other" is the best way to describe it. So far I haven't seen any mention in the literature about this being a major issue. They always talk about the pulsation effects of the exhaust and the decreased inertia of two smaller units. I would think that you need to do significant computational fluid dynamics modeling to understand the complications/issues arising from joining two turbos' air streams.

Quote :
"What about the fact that 2 turbos are flowing y air through more surface area of two narrower passageways? Would one turbo not have better volumetric efficiency for that reason?"


Not entirely sure what you are specifically talking about here. There are a lot of ways to do plumbing for twin turbos.

[Edited on October 3, 2011 at 2:08 PM. Reason : .]

10/3/2011 2:05:26 PM

Dr Pepper
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^he's referring to the situation where you have dual inlet tubes versus a singular inlet tube, where the cross sectional area of the single tube is equivalent to that of both smaller tubes combined.... area vs. circumference - misinterpretation


ahhh, plumbing design.... sounds too 'theoretical' to me



as for parallel turbos merging into a single passage, as long as they are not firing directly at each other, I can't for the life of me see a real efficiency issue.



[Edited on October 3, 2011 at 2:22 PM. Reason : -]

10/3/2011 2:21:10 PM

arghx
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Quote :
"ahhh, plumbing design.... sounds too 'theoretical' to me"


yeah it's kind of hard to have a legit discussion about some of these things in the context of internet armchair engineering. There are so many dynamic effects involved with intake and exhaust systems, especially when you get turbochargers involved.

10/3/2011 2:36:54 PM

Dr Pepper
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yeah, but I spose my approach is geared toward 'the turbo(s)' going to mask minor inefficiencies'


carry on!



fwiw, there's a never ending discussion on compD regarding divided manifold with undivided versus divided turbine housing and spool time

[Edited on October 3, 2011 at 3:00 PM. Reason : -]

10/3/2011 2:58:41 PM

arghx
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Another somewhat "black art" to understand about engine design is charge motion. Charge motion is flow within the combustion chamber and it can be affected by many factors. Today I will briefly mention two of the most important types of flow, swirl flow and tumble flow.



Swirl flow goes around an imaginary Z axis in the combustion chamber. Think of it as a merry-go-round motion. Swirl flow can be heavily influenced by valve configuration, valve timing/lift/duration, and port/head design. Swirl flow can help produce a more homogenous mixture inside the combustion chamber, when the engine is in a homogenous operating mode.

If swirl flow is a merry-go-round, tumble flow is a ferris wheel about the imaginary x and y axes. I discussed in a previous post about the Ford Ecoboost engine that tumble flow can generate great combustion stability and improve knock resistance. In cold start scenarios tumble flow can be critical for helping keep fuel from sticking to the walls. Generating tumble flow typically involves imposing some kind of restriction in the flow path, either through the geometry of the port or by installing some kind of additional butterfly valve.


Charge motion is especially critical in gasoline direct injection (GDI) applications. I'm not going to go into great detail at this point, but there are three main types of GDI concepts:

1) Wall guided -- the injector is in the side of the combustion chamber and sprays into a specially shaped piston crown wall. This design relies on tumble flow and the shape of the piston crown to guide the mixture. VW/Audi applications use this concept.

2) Air guided -- the injector is in the side of the combustion chamber and relies on swirl and tumble flow to distribute the mixture. I can't think of a "pure" air guided production GDI engine off the top of my head, but the Ford Ecoboost and Hyundai Theta (2.0 Sonata) families do have a great emphasis on charge motion in their design concept. They are probably a blend of wall guided and air guided.

3) Spray guided -- the injector is located in the middle of the chamber near the spark plug and it uses a special conical pattern to distribute the mixture. This configuration has far less fuel sticking to parts of the combustion chamber, but there are major issues with cost and the injector coking up

10/4/2011 2:42:16 PM

arghx
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Here is a diagram of the spray pattern on a BMW central injection GDI engine (N54 here). This engine is designed to operate in homogenous mode, where the mixture is intended the be spread evenly throughout the combustion chamber. This is as opposed to a stratified charge, where the mixture is mostly concentrated near the spark plug and the overall air-fuel ratio is lean of stoichiometry (leaner than 14.7:1 air-fuel-ratio on 100% gasoline fuel) The green section is the acceptable tolerance in spray pattern deviation as the system ages.

10/4/2011 11:45:58 PM

arghx
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There has been increasing discussion about carbon deposit formation in engines, especially in gasoline direct injection engines where fuel is not directly sprayed on the back of the valves. These problems in GDI engines have been well known since at least the late 1990s. The three most important things affecting carbon deposit formation in an engine are

1) surface temperatures - There is a specific range of temperatures at which deposit formations tend to occur. If temperatures are low, the deposits won't adhere. If the surface temperatures are high enough, the deposits will burn off. An operating surface temperature range of 200-350C is most likely to promote deposit formation. Heatsoaking, especially when the surface reaches 80C for a sustain period of time, can also cause a buildup of carbon.

2) fuel and oil chemistry - the chemical makeup of the fuel and the oil has a major effect on their propensity to create deposits. However this does vary by application. Some "cleaners" can actually cause buildup in certain cases.

3) Contaminants introduced through emissions systems -- Exhaust Gas Recirculation (EGR), Positive Crankcase Ventilation (PCV), and fuel tank vapors can all be introduced into the engine for emissions purposes. Without careful overall system design they can lead to deleterious deposits.

This topics was discussed in a published meta-analysis by a Siemens engineer about 10 years ago:



10/6/2011 5:13:55 PM

arghx
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During the modern diesel combustion process the injector will fire and create a stream/spray pattern. The stream doesn't immediately combust--fuel from that stream begins to separate and mix with the air charge.



This time period of mixing prior to beginning of any combustion is called the ignition lag. Combustion then occurs in two phases: premixed phase, and the mixture-controlled phase.



The premixed phase burns this fuel that had started to blend with the charge air. This combustion occurs very quickly and can cause significant pressure spikes. Designers typically try to minimize the amount of combustion taking place in the premixed phase--a longer ignition lag corresponds with a longer premixed phase. Typically cold temperatures and low quality fuel will increase the ignition lag and extend the premixed phase. Multiple injection events and careful control of injection timing can help to minimize ignition lag and premixed combustion by raising in-cylinder temperatures.




The mixture-controlled phase is when the main stream of fuel spray begins to combust. Oxygen transfers into the combustion zone as this occurs. Boundary conditions (between the main spray and the surrounding air) are constantly changing in response to in-cylinder charge motion like swirl flows. High swirl while limiting high combustion temperatures are vital for minimizing soot and NOx emissions. EGR, exhaust gas recirculation, is especially important on a modern emissions-controlled diesel. EGR reduces that amount of oxygen in the combustion chamber and thus the reduces the kind of high temperature combustion that typically lead to significant NOx emissions.

10/9/2011 9:29:17 AM

arghx
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Any vehicle certified as a Partial Zero Emissions Vehicle (PZEV) in California must have the emissions equipment (especially the catalytic converter) last for 150k miles. The 2003+ Prius is surely the most well-known PZEV. The Prius has a pre-cat, located closer to the engine, and a main cat located under the floor.

In a published paper Toyota engineers explain that they did extensive testing to figure out the main causes of catalyst deterioration (which would result in warranty claims). Part of the improvements they made to older designs had to do with the internal arrangement of the materials inside the converters. The other main strategy was keeping temperatures down to minimize deterioration:



The chart above shows the effect of temperature on Prius catalyst conversion efficiency over time. You can see in the chart that the 700C catalyst temperature worked much more efficiently over time than at the higher temperatures, meaning that the converter was not breaking down nearly as quickly. Toyota engineers also came up with a system that disables the [presumably] deceleration fuel cut during high temperature operation because it was found to accelerate converter deterioration.

10/11/2011 10:42:31 AM

arghx
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Both the Evo and STi came with water sprayers from the factory. The STi has a top mount intercooler and a spray tank in the trunk. The sprayer is operated manually by a button. Pressing the button makes it spray for a couple seconds from the hood scoop on to the intercooler. If I remember correctly the sprayer cycles on its own timer: holding the button down doesn't make it spray longer. When I dyno an STi I hit the sprayer between pulls. Here's some crude diagrams showing the sprayer, which is directed at the top surface of the intercooler.



The Evo is more sophisticated. The tank is mounted under the hood and sprays on the stock front mount intercooler.



There is a manual mode and an automatic mode. The automatic mode cycles the sprayer on and off according to the interval set in the ECU. There are also a series of minimum conditions that all must be met: engine load (calculated from the rpm & airflow sensor reading), vehicle speed, engine speed, water temp, intake air temp, and throttle position. The intake air temp sensor is found in the airflow sensor on this car, which is located before the intercooler sprayer. Here are controller tables from an Evo 9:



The Dodge Neon SRT-4 also had an available intercooler sprayer offered by Mopar.

10/12/2011 12:19:06 PM

sumfoo1
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I wish someone would test the hood scoops on cars and give estimated airflows. There is rumor that on some cars at certain speeds the boundary layer is taller than the hood scoop and the scoop no longer functions properly.

10/12/2011 1:37:04 PM

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