Motor cut-out on steep hill climb

[phevnev]

I'd seen in a couple Youtube videos that the electric drive cuts out once the load got to high for the motor's.

I wanted to know myself the actual limits around this and get a feel for how it presents itself, etc so took my 2020 Outlander up a fire-track (basically an rough unsealed vehicle track, lots of which go straight up the side of a hill). I found a steep one near where I was and took 2 other adults with me (so lets say ~300kg total payload inc petrol, jack, etc).

Sorry I should have taken a photo of the track to help give more of an idea too.

I captured the data using PHEV Watchdog and have charted the relevant metrics below, enjoy...

View attachment Fire trail (motor cut-out).png

It was a short climb, I got about 30m along before reaching a steeper 3rd wash-out at the 7:43:40 mark (you can kind of make out me slowing right down over the first two, no scrapes but I was really picking my lines and taking it slow).

When I reached that steepest part I feel the power reducing even though I was increasing throttle until forward motion came to a stop (note the car is facing up a hill). I then at 7:43:54 enabled "Charge" mode to fire up the ICE for more KWs, and then pressed "SPORT" at 7:44:02 but that just took it out of "Charge" and stopped the ICE.

As you can see with the flat RPM lines that none of this did anything. I've since noticed that at low RPM you get max motor torque (140Nm front, 200Nm rear) without a lot of KW, at least within the peak 70KW electric only I've seen PHEV Watchdog report at normal driving speeds. This seems a little strange to me as I would have expected a direct relationship between torque (Nm) and power (KW), perhaps someone here has some elec motor knowledge and can explain?

An interesting thing it was doing though is it was happy to hold the car on the slope, with me only just depressing the accelerator pedal, without rolling back, but wouldn't move forward. It really felt like a software thing, perhaps even a gradient sensor reporting too steep?

One thing I didn't try which I wish I had at the time was turning off the stability control, see if I could have at least got some wheel spin on the loose dirt and rock.

 

[greendwarf]

Remember this only has an electric drive train with no mechanical coupling and no momentum to keep the wheels turning once stopped. This is the same phenomenon demonstrated here years ago which prevents it climbing over a brick without a "run-up".

 

[nkane]

Interesting! this seems consistent with the guy who couldn't tow his boat out of the water in Sweden. It seems like the car has little ability to provide torque from stopped when there's too much resistance.

My question is whether this is true of all electric cars, or is it just an Outland PHEV thing? Anyone seen similar testing on a RAV4 Prime or Tesla or similar AWD electric?

 

[ThudnBlundr]

You can see this by driving (or reversing) up to a kerb and stopping when you're touching it. I was parked like this and then someone parked blocking me in a bit, so I needed to reverse up the kerb to get out. The car would not climb the kerb from a standstill whatever combination of buttons I pressed. Moving forward a couple of inches meant I could get a "run-up" and it went up fine.

This was just a normal kerb a few inches high, like you find at the edge of a road with a footpath in town

 

[greendwarf]

AFAIK it is a basic feature of electric motors - they rely on switching on & off of the current, each of which provides a small kick to move to the next contact and so on. In a traditional motor you have a heavy armature to provide the momentum to keep it going from one burst to the next which would also provide energy to drive the wheels.

Electric cars use electronic control to switch the current on and off in sequence as the motor turns but there is no mass producing a momentum to jerk the vehicle forward.

With an ICE the explosive force of ignition provides enough mechanical energy to overcome resistance but an electric motor if jammed just turns the electricity into heat burning out the motor - unless it has a cut out.

 

[khayyam]

It's not just an electric motor thing. Our tesla model 3 is in total control - stop, start, restart, whatever - on a very steep grade that the outlander struggles with slightly. Admittedly it has about 2x more power-to-weight than the outlander, but my suspicion is that this is exacerbated by the PHEV's reluctance to engage series hybrid mode at low speed, meaning that actually there's only about 60kw power available and so the ratio is more like 4x.

 

[greendwarf]

It could also be to do with the hill start feature. :idea:

 

[ThudnBlundr]

You could have 1,000,0000hp electric motors (and a comparable ICE), but that's meaningless if the torque isn't enough to get things moving. Power is meaningless without torque. And there's no point adding more current from the ICE/generator if the existing motors aren't able to handle the existing current from the battery when stationary - unless you want to burn out the motors, of course.