Emissions Tuning Fundamentals: Emissions Drive Cycles

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Emissions Drive Cycles

08.08

00:00	Whether you're preparing for certification testing or not, the common emissions drive cycles can be useful in development.
00:06	In this module we'll focus on the common drive cycles used in the United States.
00:10	Depending on your own location, there will almost certainly be some differences but the general concepts are still worth understanding.
00:17	Drive cycles are designed to reflect common driving conditions.
00:21	They're also sometimes called driving schedules because they tell you how fast to go and when to do it.
00:26	A number of the tests involve stop and go driving typical of the streets and traffic in Los Angeles where CARB focuses many of their efforts to reduce smoke.
00:35	Also included is highway cruising, merging onto the highway and various other transient conditions.
00:42	You should avoid making a tune that only runs clean during specific drive cycles but they're a great place to start.
00:49	Because the driving behaviour varies a lot, it'll likely include things outside of your normal driving habits.
00:55	This can help you to test and tune areas of operation which you might not encounter naturally.
01:01	We'll review the 6 most common used drive cycles in the United States.
01:05	We'll also provide a link to files which include the full datasets as well as graphical representations in the course resources.
01:12	First up, the FTP cycle which is also referred to as the EPA75 or sometimes the FTP75 test.
01:20	FTP is actually a combination of two other tests, the UDDS which stands for Urban Dynamometer Driving Schedule and the 505.
01:30	The first 500.5 seconds of the UDDS is what's known as the 505.
01:37	Since the FTP test starts with the vehicle at ambient temperature, the first 505 is called the cold 505.
01:44	Then the rest of the UDDS and then another 505 completes the FTP cycle.
01:49	The second pass through the 505 is called the hot 505 since the vehicle is already warmed up to operating temperature this time around.
01:58	The full FTP test is around 11 miles long with about 31 minutes of driving and also includes a 10 minute hot soak after completion of the UDDS, making the total test take around 41 minutes.
02:11	Preparation for this involves a cold soak, meaning the vehicle is turned off so the engine, fluids etc cool to ambient temperature over a period of time.
02:20	The soak time and temperature depend on the requirements of the specific test but in the aftermarket, generally we aren't required to perform a cold weather FTP test.
02:30	The UDDS is said to be derived from someone's actual commute in Los Angeles and it's meant to reflect typical city driving.
02:37	Based on all of the stopping, it seems that they got it about right.
02:41	Peak speed is about 56 mph and the average speed is about 21.
02:46	Most of the driving involves coming to a stop then speeding up to 25 to 35 mph then slowing back down to a stop again.
02:53	Most of the accelerations aren't particularly aggressive and the top speed is quite low.
02:58	While that sounds mundane, this test can still catch you out if your transient tuning isn't well dialled in.
03:04	On the plus side, most vehicles don't have to get into high load areas to drive for this particular cycle.
03:10	Because it incorporates a cold start and warm up which can cause a vehicle to fail a test in the first few seconds alone, that's another area to make sure that you get right.
03:19	Later in the test I mentioned there's a 10 minute hot soak.
03:22	This is when the vehicle comes to a stop, gets turned off and the dyno fan is off during the hot soak.
03:28	The vehicle essentially bakes on the dyno and it's brutal.
03:32	After 10 minutes you start the engine back up and drive the hot 505.
03:36	For this reason, making sure the vehicle cleanly hot restarts after being severely heat soaked should be on your preparation checklist.
03:44	Next up is the US06 which tests aggressive driving and is also referred to as the supplemental FTP driving schedule.
03:53	It includes the most aggressive acceleration events and the highest top speed so this is where you really need to have your mid to high load areas of your tune dialled in.
04:02	The test is so aggressive that relatively low horsepower vehicles at full throttle actually can't keep up with the drive trace and exceptions have to be made.
04:12	To put things in perspective, many 4 cylinder turbo cars are at or near full boost during parts of this test.
04:18	If you're preparing for certification testing, you should also be warned that they limit fan airflow during this test to only 15000 CFM.
04:26	When performed as part of a lab test, the test starts with the vehicle already hot from driving a US06 cycle that isn't emissions monitored.
04:34	After completing the first cycle, the US06 cycle is repeated, this time while recording emissions.
04:41	With that in mind, if you're testing outside of a lab, make sure you get the vehicle and catalyst hot prior to this test to achieve useful results.
04:50	US06 is about 8 miles long and only takes around 10 minutes due to the higher average speed.
04:55	It still includes several stop and goes but it has a maximum speed of 18 mph and the vehicle is over 60 mph for over half of the test.
05:04	What's often most challenging is how aggressively the vehicle has to accelerate to stay on the drive trace.
05:10	If the vehicle is manually shifted, this also means shifts have to be completed quickly and cleanly to avoid going off the trace or disrupting engine operation.
05:19	If a shift is slow enough, you'll likely have to floor the accelerator to catch up to the trace and that may cause a spike in emissions that causes failure so driving this trace takes practice.
05:30	If you've made it through the FTP and US06 with passing results, you're probably going to be OK on the next two but we'll cover them briefly.
05:38	Next we have the SC03 which is a supplemental test related to running the air conditioning.
05:44	The dyno room is heated to 95°F and the air conditioning is set to max or the in car climate control is set to 72°F if the vehicle is fitted with automated climate control.
05:56	That'll generally get the air conditioning system blasting and that's what they're after here.
06:01	So in your own testing, test with the AC on and off to see if it presents any issues.
06:07	SC03 is under 4 miles long and still takes about 10 minutes so it's a much lower speed than the US06 and less aggressive in terms of acceleration requirements.
06:17	The last common test we'll mention is the highway fuel economy test or HWFET for short.
06:25	Usually it's simply called the highway test and it's designed to test, you guessed it, highway fuel economy.
06:31	Lasting about 12.5 minutes and spanning about 10 miles, the highway test is actually a bit slower than you'd assume.
06:38	The first section is mostly in the 40-50 mph range and the second portion is mostly between 50 -60 mph with 60 being the maximum speed in this test.
06:48	There are various speed changes so like all of the tests, it does require proper transient tuning although the transient in this test are very mild.
06:57	It's highly unlikely you'd pass all of the other tests and then fail emissions on this one.
07:03	Fuel economy is also generally not considered as part of aftermarket regulatory evaluation.
07:08	We do of course suggest trying to maintain the fuel economy the factory vehicle had since if that suffers heavily, it may raise an eyebrow.
07:16	A loss of fuel economy often comes from less efficient, less clean tuning which would also show up in the emissions results.
07:23	Keep the tune clean and optimised and fuel economy will follow.
07:28	So those are the main emissions drive cycles used in the US regulations.
07:31	FTP is the test that includes a cold start, the urban driving dynamometer schedule, hot soak and then a hot 505.
07:39	US06 has the highest top speed and the most aggressive accelerations.
07:44	SC03 is tested in a heated room with the AC on.
07:47	The highway fuel economy test is the easiest but you have to pass all the applicable testing to achieve an EO or SEMA certification.
07:55	Transient behaviours will be tested over and over during these tests so make sure that portion of your tune is dialled in and we'll cover that more in an upcoming module.