[andrew]

I'm just posting this for the sake of documenting it.
Not sure if anyone else has had this issue.

I was exiting a parking lot in the mountains going downhill and held the car in first gear via the manual selection just so I didn't have to ride my brakes to keep my speed low.

At about 15-20MPH it felt like the car threw the transmission into park for a split second.
There was a giant thump, the whole car shuddered, and I got thrown forward in my seat harder than an emergency brake stop.

In essence something caused the drivetrain to try and stop for a split second.
This was in EV mode, so also maybe it tried to engage the gas engine when it wasn't running.
That's about the only other thing I can think off.


After that I just put it back into normal drive, drove home, and things are working fine.
I didn't get any warning lights when this happened.

 

[StevetheTech]

That is a very interesting scenario you put that car into.

The only thing I can tell you about what happened there is there is zero chance the car went into park. P<R<N<D require a physical valve to divert pressurized fluid from one path to another.

You were overriding normal control functions by manually shifting, in an extreme load situation. With an ICE it would not be an issue as the overrun clutch would usually apply force against the engine to allow you to slowly coast down the mountain. In the hybrid the AC motor was probably doing all of the energy recapturing it could. The function of the overrun clutch that usually controls engine braking functions very differently on your car so it is highly likely what you experienced was a switch within the transmission of either one of the hybrid clutches, hydraulic clutches or something similar. Under the type of extreme load you experienced this at I would not be surprised if the car was trying to save itself from extreme pressures, temperatures, or overwhelming load.

From your description of this incident I would strongly recommend using the brakes in that situation while leaving the car in D or Sport mode. This will allow the hybrid powertrain to make the best determination of what it needs to be doing to function correctly given the inputs at that moment. Unlike conventional vehicles the friction brakes will not be used much to slow the car in the situation you were under, it would actually probably have benefited the hybrid system.

 

[InfinitiPlusOne]

I think 1st gear is for going up steep slope, not for braking down hill. It's better to use actual brake for going downhill.

 

[avanti5010]

I think SteveTheTech nailed it.

 

[cvipgo]

Seems the classic situation of person behind the machine error.

 

[StevetheTech]

I think 1st gear is for going up steep slope, not for braking down hill. It's better to use actual brake for going downhill.

I remember when I was being taught to drive stick my father insisted on teaching me the benefits of downshifting to "save" the brake pads. In doing so he saved the relatively cheap brake pads while increasing load,strain, and stress on the drive line.

I think this case is a bit different but a great example of unintended consequences of applying traditional practices to a vehicle that is anything but traditional.

 

[andrew]

FTR, the car started moving in first. I never downshifted it.

I backed out of my parking spot, put it in drive, then manual mode, and just started moving in first.
This worked fine every time in my G35.
[edit] I know the Q will shift out of gear in manual mode which the G35 wouldn't do. So I guess it's possible it threw it into 2nd and back into 1st as well? I wasn't looking at the console gauges when this happened. I was looking at the road.

Anyhow, I'll use the brakes from now on.

I grew up driving on stick shift, so I'm stuck on the age old habbit of holding gears on hills to help with holding the speed constant (vs. using the brakes).


BTW, car drove fine to work today to, so what ever it was doesn't seem to have caused any immidiate damaging problems.

 

[hunter81]

That is a very interesting scenario you put that car into.

The only thing I can tell you about what happened there is there is zero chance the car went into park. P<R<N<D require a physical valve to divert pressurized fluid from one path to another.

You were overriding normal control functions by manually shifting, in an extreme load situation. With an ICE it would not be an issue as the overrun clutch would usually apply force against the engine to allow you to slowly coast down the mountain. In the hybrid the AC motor was probably doing all of the energy recapturing it could. The function of the overrun clutch that usually controls engine braking functions very differently on your car so it is highly likely what you experienced was a switch within the transmission of either one of the hybrid clutches, hydraulic clutches or something similar. Under the type of extreme load you experienced this at I would not be surprised if the car was trying to save itself from extreme pressures, temperatures, or overwhelming load.

From your description of this incident I would strongly recommend using the brakes in that situation while leaving the car in D or Sport mode. This will allow the hybrid powertrain to make the best determination of what it needs to be doing to function correctly given the inputs at that moment. Unlike conventional vehicles the friction brakes will not be used much to slow the car in the situation you were under, it would actually probably have benefited the hybrid system.

Steve, do you know enough about the braking system to know if the car can come to a complete stop without using friction brakes at all? I know when I'm braking the charge meter going to the left is an indication of regenerative braking. If I can keep that meter over there does the car completely stop without using friction brakes at all? It would be awesome if it does. Brakes sure would last a lot longer.

 

[druhoops]

This article plus another in the same area states the regen brake functions down to 3 km/hr (or almost 0).
EDIB (Electric Driven Intelligent Brake) | NISSAN | TECHNOLOGICAL DEVELOPMENT ACTIVITIES

I'm a little surprised its "not ok" to drive downhill in 1st manual. Why should the car care as long as the redline is not reached? I can think of several situations where i'd like to never touch the brake on a downhill run, using engine braking and regen braking to keep speeds in check.

 

[hunter81]

This article plus another in the same area states the regen brake functions down to 3 km/hr (or almost 0).
EDIB (Electric Driven Intelligent Brake) | NISSAN | TECHNOLOGICAL DEVELOPMENT ACTIVITIES

I'm a little surprised its "not ok" to drive downhill in 1st manual. Why should the car care as long as the redline is not reached? I can think of several situations where i'd like to never touch the brake on a downhill run, using engine braking and regen braking to keep speeds in check.

Awesome explanatory website! Thanks!

 

[lKoRTy]

Not sure if same issue, but I have noticed on several occasions when the car is switching form gas to ev on low speeds, I hear a thump/jerk. Will try to pay more attention as to which conditions it happens in.

 

[selzini]

Not sure if same issue, but I have noticed on several occasions when the car is switching form gas to ev on low speeds, I hear a thump/jerk. Will try to pay more attention as to which conditions it happens in.

Yes, at very low speeds, you can feel the transition from EV to engine - it's the nature of the beast. At speeds above 10 mph, I never hear or feel the change-over.