That was what I was thinking also. Mine regens less at lower rpm's. I ask my regional corporate Kubota tech but they seemed to not know a lot. The way the guy talked made me wonder if he even owned a tractor.
That system is very similar to the L01 series (3301, 3901, 4701). Has nothing to do with fuel consumption. If that were the case, it would never regen if a tractor was at idle speed.
Here's what's in it. Obviously from the exhaust manifold, there is a BIG metal can. Inside the can is the DOC and the DPF. No muffler to speak of; since they both do a good job of muffling the sound. DOC is diesel oxidizing catalyst. Basically a catalytic converter. Actually if you look closely at the can, you'll see 2 big marmon clamps holding the 3 sections together. DOC is the section closest to the exhaust manifold and the DPF is the 2nd section. The last is just part of the can that the tailpipe is connected to.
If you look at the can, you'll see several sensors. Two of them are EGT sensors. EGT is exhaust gas temperature. One is in the DOC and senses pre-DPF EGT. The other is in the DPF and senses EGT in the DPF itself. Basically pre and post DPF if you want to simplify things. Then there are two hoses at the top of the engine area that go to a sensor, the other end of the hoses go to the can/muffler. Those are differential pressure sensors. One is pre DPF and the other post DPF.
Exhaust gas passes through the manifold, through the DOC, then into the DPF, then out the tailpipe. DOC changes the content of the gases, removes most of the carbon monoxide, among other things. The DPF removes the soot from the exhaust by way of a fine mesh filter of sorts. That's why there's no black smoke when started or under a load. The EPA don't want no black smoke. Communist jack wagons! We like it...but anyway.
Now about the EGT sensors. The computer monitors them constantly. The reason for this is to tell the computer how hot the exhaust gas is. If it's too hot, it will defuel a little until it figures out why it's so hot. Also, during regen, they're used to keep from overheating the DPF and DOC, adjusting post injection quantity and injector pulsewidth accordingly. They're important.
The differential pressure sensor basically tells the computer how "full" the DPF is. That's why there's one before and one after the DPF. They're also important.
When the DPF gets dirty, the filter screen gets plugged, which causes a restriction in the exhaust. Think of stuffing a tater into the tailpipe. The dif pressure sensor notices this. When the pressure gets high, EGT will also climb. The computer has this programmed into it, and knows that a regen will need to be done; based on the programming and the sensor inputs. This is where we get into fail-safe's in the higher soot levels. At level 3, 4, 5 the engine power is derated. This is done because the EGT will already be high under a load with a dirty DPF; if derating (or defueling) was not done, the EGT will climb so high that the engine will eat itself. The DPF will melt the substrate. So when the light comes on, do a regen, just let it do it if possible. If not, hit the inhibit button and regen as soon as possible to get the junk out of the DPF. Or if you like to spend money, just leave it alone, let it beep until the engine will no longer physically start/run.
