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Discussion Starter #1
I am convinced that the CVT is more efficient than a traditional automatic on the freeway, especially if you are gentle with your right foot. I believe the 10% claim made by Nissan. The city, however, is another story.

Is the CVT transmission less efficient than a traditional automatic transmission in stop and go city driving? Are there any technical papers that discuss this? Is there a way to prove this one way or the other?
 

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I am not aware of a general discussion. In theory, the CVT should be better. Why? Because a typical engine operates at maximum efficiency over a fairly small RPM range. Things like variable cam timing and variable intake geometry extends the efiicient operating range, but it is still limited.

This is the key concept behind hybrid vehicles. Their engines are designed to be ultra-efficient at one specific RPM/load, and they only run at that RPM/load. The electrics function as a....... CVT. And, of course to store energy so when driving calls for more power than the engine can produce at that specific RPM, you draw on the batteries to help out.

The CVT should be able to keep the engine at an optimum RPM, more so than a normal AT, where engine RPM must follow road speed for a given gear ratio.

Now, as to how effectively Nissan executed this is debatable.

The Murano definitely rewards a light and steady right foot. My wife is primary driver. She needed a few months to adjust her driving. I risked marital strife by giving her feedback on this when I was riding shotgun. To her credit, she took the feedback well, and her city mileage went from 15.x to 19.x MPG. Some of this improvement was also due to the engine loosening up through break-in.

At this point, MY only complaint about Nissan's execution is at highway speeds, the CVT does not stay 'locked' in at it's lowest (numeric) ratio, so even minor speed adjustments (via the cruise control) result in (in my opinion) excessive RPM increase.
This said, I saw 22-23MPG at 70 MPH, and 20-21MPG at 80 MPH. 25 MPG might be realistic at 55 MPH, but I 'just can't drive 55'.
 

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Ok - I feel I have to weigh in here. I haven't seen a torque curve, but I think the reason for your CVT changing gears 'excessively' is that at the highest gear ratio, there just isn't enough torque available, at least not at speeds below 80 (and above 80 you're dealing with a heck of a lot of drag with 0.39 Cd and as wide and tall as the Murano is).

The reason I say this is that my '04 SE which has the 6 speed "manual" option is not very responsive if I leave it in 6th and hit a modest hill. Drop it into 5th however and I don't even have to press the accelerator any further to get the acceleration I want - I end up sometimes accelerating with my wrist rather than with my foot...
 

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Discussion Starter #4
I think the torque converter doesn't lock up until 18 mph in the MO. Doesn't this mean that there is a viscous coupling at speeds under 18 mph?

Doesn't the torque converter in a traditional automatic transmission lock up after each gear change? (I really don't know.) If it does, then isn't it locked up at a much lower speed than the MO? If the answer is yes, this would explain the bad stop and go mileage.

D.G.
 

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The torque converter in a traditional auto trans doesn't lock up until high gear or overdrive once the vehicle reaches a predetermined speed...in 60/70 kpm range(30/35 mph)....pressing on the accelerator unlocks the torque converter.
 

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senza said:
...pressing on the accelerator unlocks the torque converter.
Does anyone know if this is the case with WOT (open loop) and not WOT (closed loop) acceleration on the Murano?
 

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Tyler_Canada said:


Does anyone know if this is the case with WOT (open loop) and not WOT (closed loop) acceleration on the Murano?
I thought open loop referred the period when the ECU is running the engine rich during a cold startup. Once the coolant temp gets to 180 degrees or whatever the normal range is, the ECU triggers a closed loop mode which then starts using data from the oxygen sensors to control emissions.
 

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All ECU systems go open loop during WOT, throttle transitions, and at idle. Closed loop operation is only at 'cruise' conditions, but the ECU uses information from the O2 sensor to adjust fueling, which it then stores and applies as an offset during all other (open loop) conditions.
 

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turbodog said:
All ECU systems go open loop during WOT, throttle transitions, and at idle. Closed loop operation is only at 'cruise' conditions, but the ECU uses information from the O2 sensor to adjust fueling, which it then stores and applies as an offset during all other (open loop) conditions.
Right. There are numerous conditions that cause open loop operation. Closed loop only occurs under completely optimal conditions. Warm engine, probably warm tranny, constant throttle, all sensors functioning, etc.

The fuel offsets are stored in tables, known as fuel trim. Short term fuel trim is an instant measurement constantly changing, and if short term is either rich or lean for some number of measurements, the corresponding long term fuel trim value is updated.

I did not know that fuel trims were used during open loop. That's interesting.

I was just wondering if the torque converter unlocks during open loop acceleration, because you can’t really tell by feel. I'll find out soon enough, as this is one area I'm going to check out when I get my scantool built.
 
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