Reduction Gear Oil Change - Benefits for Range

[knightmb]

Fantastic research. Thank you

I will check the temp on my next highway journey.

I am keen to try the ULV if hitting the 140F barrier.

Yeah, to summarize a little bit the data in this topic, I know it is a lot of pages, data, and photos to read through.

The ULV tends to run 20F cooler than the Nissan Matic S (factory default), even when it's 100 F (37 C) outside. This is only 1.5 quarts of liquid I'm referring to, but that heat will migrate into the motor, electronics stack eventually. Constant driving under 55 MPH is where one gear oil operates above the 140F mark and the ULV operates under the 140F mark, so the energy savings is more noticeable on longer trips than short trips. If the weather is under 90F, even driving at 70 MPH, the ULV is just cool enough to keep a few degrees under the 140F mark, the Nissan Matic S tends to operate a lot hotter at this speed no matter the outside temperature, often 160F or hotter as the outsider temperature increases.

The ULV is no magic bullet to energy savings, but it's enough to make it worth the energy savings for longer trips, especially at higher speeds. It doesn't mean the default Nisan Matic S is garbage, just that if you are willing to spend the money and time to change it out, the range benefit is basically permanent, at least in warm to hot weather. No data yet on what cold weather driving does.

As others have pointed out in this topic, it doesn't *have* to be ULV type gear oil, some others that are good at keeping the gears cooler also would get the same benefit, even if they are thicker by definition but chemically different in another way for the benefit.

 

[denwood]

Just a few data points after looking at motor/pack temps via LeafSpy on my 2018 LEAF SL during longer highway runs. I'm running the Amsoil D6 ATF which I believe is not ULV.

I've been running the LEAF out to our cottage which is about 130 kms (80 miles) and running at pretty conservative speeds 95km/h (60mph) for about 90 minutes. Ambient temps did not rise above 27C (80 F). Overall elevation change going out is an increase of about 300 meters (around 1000 feet) with some short but steeper climbs along the way.

Motor and pack temps stayed surprising close to ambient, reaching about 12F over ambient (max of around 93-97F on the motor). This is not even close to the 140F cooling limit so I'm guessing would be typical for temperate climates like ours.

Range given the 10% battery degradation (it's at 90% SOH) was tracking pretty much spot on the 230km mark (all highway) which is about exactly what you'd expect from a 40kwh pack and 10% degradation. The car has about 62K kms, and is running fairly new Ecopias at 40psi.

 

[DougWantsALeaf]

Ok, now that we have our S+ back I tried a run in both cars at local, 55, and ~70mph.

Car local / 55mph / ~70 mph

S+ 101F / 112F / 122F
SV+ 99F / 109F / 118F

Ambient was 73-75F and fairly humid

I did floor the S+ a couple times up I to the 80s (that was fun), and that pushed its temp up to 127F

In both cars the temps dropped as I slowed before exiting the highway relatively quickly, so pretty sure I was at steady stste temps.

On the circuit the S+ ended with 4.7 miles/kWh and the SV+ 4.4. The S+ was being beaten a bit harder, hence why the numbers were so close.

I was expecting that the SV+ would have run hotter, but it was the opposite, though pretty close. Very curious that the SV+ was consistently a couple degrees cooler.

So I could see if ambient was 90F and you were pushing 70, you could trip the 140F barrier and the cooling.

I was curious to see if that maybe this was why the S+ is so much more efficient that the SV+, but no such luck.

 

[LeftieBiker]

I'm guessing that the plumbing for the heat pump on the SV+ somehow manages to cool the oil a little. Or the plumbing for the A/C unit on the S+ heats it more.

 

[DougWantsALeaf]

As a follow up point, no AC was run for either car.

 

[Stanton]

So I could see if ambient was 90F and you were pushing 70, you could trip the 140F barrier and the cooling.

Good stuff...but I would like to see this: 90F is pretty normal in Texas (and other places in the South) in the summer months.

 

[SageBrush]

I will patiently wait for winter results,
Although I am not sure how the test mavens will go about their craft. In the winter it will not be a question of keeping cooling equipment off, but whether a lower viscosity translates to lower drivetrain losses worth another visit under the car.

Does part of the gearbox spin in neutral when the go pedal is pressed ?

 

[bobkart]

Does part of the gearbox spin in neutral when the go pedal is pressed?

My understanding is that neutral is just an electrical power disconnect rather than a mechanical power disconnect. Actuating the throttle does nothing when in neutral.

 

[GerryAZ]

Electric motor is directly connected--nothing turns unless vehicle is moving. Motor rotates one direction going forward, opposite direction in reverse. Neutral provides a low impedance path for induced motor current to flow instead of regenerative braking.

I am now waiting until I replace tires again before changing the gear oil. I will use new Matic S fluid so I should be able to compare efficiency of old vs new fluid directly in my 2019 SL Plus. I planned to make this comparison when I changed the fluid in my 2015, but a flat tire shortly after the fluid change ended the comparison because the new tires had higher rolling resistance.

 

[DougWantsALeaf]

So would the ULV oil potentially improve the Leafs neutral rolling ability?

 

[bobkart]

So would the ULV oil potentially improve the Leafs neutral rolling ability?

That's a YES from me. But not as much as when the gears are transmitting power.

 

[GerryAZ]

So would the ULV oil potentially improve the Leafs neutral rolling ability?

That's a YES from me. But not as much as when the gears are transmitting power.

Since there is no load on the gear teeth, the coasting improvement would probably be minimal (but should be at least a slight improvement).

 

[bobkart]

Since there is no load on the gear teeth, the coasting improvement would probably be minimal (but should be at least a slight improvement).

Agree; it would be mostly viscous drag of moving the gears through the lubricant. Just a TINY amount of load would be involved, as even the best bearings have friction (in the motor). How this drag compares to other sources of rolling resistance (tires, aero, wheel bearings, ...) is a good question. Probably negligible (<1%), especially as speed increases.

Neutral provides a low impedance path for induced motor current to flow instead of regenerative braking

I do wonder about this though . . . is it low impedance or high impedance (such as an open circuit). I think effectively opening the circuit between inverter and motor is best the way neutral could be achieved. Neither give it energy in (acceleration) nor take energy out (deceleration). But I'm no expert.

 

[goldbrick]

Low impedance. The am is to let any induced motor current pass through without generating heat or flowing backwards through the motor windings since that would cause a braking effect.

 

[knightmb]

Winter will be interesting for two reasons to me.

A Leaf with a heat-pump means running the "heat" is extracting the energy from the passing air and blowing it against the motor block. That means the air hitting it is colder than the outside air. So I would imagine in the winter time, the motor is going to stay very cold, maybe? Not a bad thing for a motor. Maybe not a great thing for the gear oil.

Second reason, the gear oil, if the first reason holds out, is going to be operating in a much lower temperature. During the summer, it's easy to warm up the gear oil and keep it flowing smoothly as the higher the temperature, the lower the viscosity. In the winter, the gear oil is going to be thicker and that of course will create more friction. Kind of a feed-back loop, the friction will need to warm it up to keep if flowing, but how much energy will that take and what temperature will it "settle" on during normal, cold weather driving is anyone's guess?

I guess a third thing I just thought about, if the gear oil has an "optimal" temperature it needs to run at, will it have to be constantly fed energy to keep it warm to defeat the cold air blowing against it? So many variables. :shock:

 

[nlspace]

When the motor is mechanically back-driven, then an AC voltage is created and present at the ends of the phase windings.

The amount of braking or drag torque is proportional to any current flow in the windings which would generate a counter magnetic field in the pole pieces to oppose the direction of shaft rotation.

To coast in Neutral the ends of the windings must be held isolated and open circuit from each other.

Shorting the windings together is the worst case condition which creates a locked rotor that is nearly impossible to back drive.

 

[bobkart]

When the motor is mechanically back-driven, then an AC voltage is created and present at the ends of the phase windings.

The amount of braking or drag torque is proportional to any current flow in the windings which would generate a counter magnetic field in the pole pieces to oppose the direction of shaft rotation.

To coast in Neutral the ends of the windings must be held isolated and open circuit from each other.

Shorting the windings together is the worst case condition which creates a locked rotor that is nearly impossible to back drive.

That's more like what I thought. Low impedance would be like applying high braking.

Thanks for clarifying.

 

[lorenfb]

When the motor is mechanically back-driven, then an AC voltage is created and present at the ends of the phase windings.

The amount of braking or drag torque is proportional to any current flow in the windings which would generate a counter magnetic field in the pole pieces to oppose the direction of shaft rotation.

To coast in Neutral the ends of the windings must be held isolated and open circuit from each other.

Shorting the windings together is the worst case condition which creates a locked rotor that is nearly impossible to back drive.

It's the output driver semiconductors', e.g. IGBTs, functions in the motor controller.

 

[goldbrick]

IMO, the impedance question depends on where the current is routed. There is such a thing as a 'dynamic brake' which uses the induced current to generate a reverse current to slow the motor as described above. There are other ways to route that current though that would not create this effect.

I don't even know how many phases the Leaf motor uses or how it is wired but I would imagine the induced voltage spikes of a open motor coil would be enormous and hard to handle to prevent damage to the drive circuitry. I'd think it would be much easier to provide a low impedance path for that current to circulate in a way that would not retard the motor. I guess it's time to do some research, since inquiring minds want to know...

 

[lorenfb]

IMO, the impedance question depends on where the current is routed. There is such a thing as a 'dynamic brake' which uses the induced current to generate a reverse current to slow the motor as described above. There are other ways to route that current though that would not create this effect.

I don't even know how many phases the Leaf motor uses or how it is wired but I would imagine the induced voltage spikes of a open motor coil would be enormous and hard to handle to prevent damage to the drive circuitry. I'd think it would be much easier to provide a low impedance path for that current to circulate in a way that would not retard the motor. I guess it's time to do some research, since inquiring minds want to know...

Start here; https://training.ti.com/field-oriented-control-permanent-magnet-motors

and then here; https://www.ti.com/lit/an/sprabz0a/sprabz0a.pdf?ts=1628009501220&ref_url=https%253A%252F%252Fwww.google.com%252F