Useless 'creep' function. - Renault Z.E. Forum
 
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post #1 of 8 (permalink) Old 10-25-2013, 07:19 AM Thread Starter
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Useless 'creep' function.

On the topic of whether our cars work the same way .....

The 'creep' function on the Fluence is meant to work as a regular auto. Well, I don't consider mine does. The handbook also says it has a 'hill hold' functionality, and I don't see that either.

[I'll mention that my car has not yet had the replacement brake vacuum pump ECU. (To the new two owners - check this has been, or will be, replaced.) I don't know if this controls these functions, but in any case I'm not going to have the ECU swapped out until its next service as it's not a big enough issue in my current panorama of things I need to do in life!)

So this is the way my car works:

The mechanical brakes and the regeneration are completely independent. I presume that is standard. The handbrake is very conventional and is just a regular cable direct to the back, no electronic jiggery-pokery like the Leaf. I like this, and think it is an ideal to keep the braking system and the regen system of EVs entirely independent.

When the brake pedal is pressed, even very gently that the brakes are not actually on, it suppresses the creep function. To go forward you have to completely remove your foot from the pedal.

Now, here's the problem - if I'm on an uphill incline and I ease off the brake pedal, the car will roll back. If I am quick onto the accel pedal then it will only roll back a little, but it still rolls back. I'm used to autos with strong creep, so habit tends to cause me to ease off gently. This is a problem, because the car then rolls backwards and continues to roll backwards for so long as the brake pedal is being pressed a little.

The solution is that you have to drive it like a manual car - you have to engage the handbrake. With the handbrake engaged and the brake pedal released, the motor will push forward against the handbrake. The motor draws around 1kW while it is pushing against the handbrake. You can then simply apply accel and release handbrake and this prevents any roll back.

That's OK for inclines, as it goes, however the next problem comes in driving very accurately, slowly. Firstly, I can't see the front of the car. Seriously, I've been driving 100's of thousands of miles in every sort of car, and I flat out can't get used to judging where the front of this car is. Worse still is that if you are on a slight uphill incline you can't creep forward on the footbrake - you either roll backwards or accelerate!!! I nose up to my garage, which is a very slight incline, and I simply cannot do it accurately on the footbrake alone. I have to creep using the handbrake, which is not a skill I have ever previously needed to develop.

The other option is that you can left-foot brake and tickle the accel pedal. By doing this, it does begin to creep against the footbrake, but you can only do it for a couple of seconds because the motor starts getting confused and you can literally feel the rotor beginning to bounce around not quite knowing what it is supposed to be doing.

In all cases, you cannot allow the motor to apply torque while stationary or in very slow creep for more than a few seconds, as the motor coils might overheat. There is no warning of this, so maybe there is some inbuilt thermal protection. I don't know, I simply don't (and won't) push my car to find that out!! I guess it is OK to run a kW or two into it while stationary because when it is putting out 70kW then there will be at least a few kW of waste heat coming off it then. So the motor must be fit to tolerate that. (In any case, I would strongly advise against ever leaving the car with handbrake engaged and in drive, without the footbrake depressed.)

All the same, it is still a very awkward thing to do, to creep uphill on the foot or hand brake. A regular auto does this with ease, but with my Fluence I have still not perfected that skill.

In generally, I think the creep function is a liability. Not only is it rubbish, but it has the unfortunate safety defect that if you jump out of the car whilst it is in drive and 'go', then it'll drive off by itself!

If I was designing the system, I would design it so that below 3 mph the pedal is no longer a power-based algorithm (as it seems to be), but is tuned to work as a motor-speed algorithm instead, so you have a much more positive control over the motor moving forward and '0 mph' is enforced (rather than allowing a negative speed) on the motor when the pedal is released
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post #2 of 8 (permalink) Old 10-25-2013, 09:07 AM
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RE: Useless 'creep' function.

Quote:
Originally Posted by donald
Now, here's the problem - if I'm on an uphill incline and I ease off the brake pedal, the car will roll back. If I am quick onto the accel pedal then it will only roll back a little, but it still rolls back. [undefined=undefined]I'm used to autos with strong creep[/undefined], so habit tends to cause me to ease off gently. This is a problem, because the car then rolls backwards and continues to roll backwards for so long as the brake pedal is being pressed a little.
Sounds like you're used to autos with big American engines that will hold the car on a hill. I've driven all sorts of cars and the smaller autos under a 1.8 will usually start to roll back on an incline. Even some of the bigger cars will but less likely to or at least they'll roll back ever so slightly. The gf's little IQ auto is gutless and that will roll back if you're not quick off the brake and onto the gas.

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post #3 of 8 (permalink) Old 10-25-2013, 09:48 AM Thread Starter
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RE: Useless 'creep' function.

On a steep hill, maybe I'd give it that excuse. I'm talking about really gentle inclines. The Fluence will roll back without any resistance on anything but flat ground, just like a manual would if you put it in neutral and took all the brakes off.
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post #4 of 8 (permalink) Old 10-26-2013, 03:36 AM
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RE: Useless 'creep' function.

I have a different problem with the car's creep facility. I park my car nose downhill on my drive and have to play with brake and accelerator in order to move back, the car wanting to roll forward. Then once on the road (with a full charge of electricity) I drive off downhill to a tricky junction. I am forced to brake quite hard to stop the car accelerating away across the junction without my foot on the accelerator. Not nice. I say "with a full charge of electricity" because this only seems to happen under this circumstance. Explain that if you can!

On the subject of replacement ecu, obviously this job was done on my white car but I have no information about whether Renault's MD got the job done on my present car. That's something I need to check out.
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post #5 of 8 (permalink) Old 10-26-2013, 04:16 AM Thread Starter
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RE: Useless 'creep' function.

Quote:
Originally Posted by pauledg
I am forced to brake quite hard to stop the car accelerating away across the junction without my foot on the accelerator. Not nice. I say "with a full charge of electricity" because this only seems to happen under this circumstance. Explain that if you can!
If the battery charge is full then it will limit regeneration because it prevents you stuffing any more energy into the battery.

You have to leave a little 'space' in the battery to allow the regen energy to be put.

[hr]
Quote:
Originally Posted by pauledg
I park my car nose downhill on my drive and have to play with brake and accelerator in order to move back, the car wanting to roll forward.
This is the same problem as I described up hill. Because you are trying to move slowly, then you may be leaving your foot partially on the brake. That is tantamount to leaving it in neutral.

Pull on the handbrake just enough to prevent it rolling, then use the accel pedal against the handbrake. It'll begin rolling up the hill, then stamp on the brake pedal at the appropriate moment to stop the car.

You also should avoid setting the rear handbrake against the front transmission - pull the handbrake to fully engaged, select neutral, then release the footbrake before engaging the parking pawl. If you don't do this sequence then you will find the parking pawl is being loaded by the handbrake when you release the footbrake.

Feel free to ask if I didn't make myself clear in that last para!
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post #6 of 8 (permalink) Old 10-26-2013, 05:10 AM
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RE: Useless 'creep' function.

My parking sequence is
Stop
Engage P
Handbrake on
Release Footbrake
Smile
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post #7 of 8 (permalink) Old 10-26-2013, 05:37 AM Thread Starter
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RE: Useless 'creep' function.

Same effect; you may be setting the force of the handbrake against the parking pawl by releasing the footbrake last. There's no reason to think this would necessarily cause any damage, but it is just another of those things that, repetitively, may cause undue wear and tear. As I have no idea how this parking pawl works (clearly not on a flywheel!!), I'll be treating mine with kid gloves.
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post #8 of 8 (permalink) Old 10-26-2013, 06:01 AM
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RE: Useless 'creep' function.

Yeah, with traditional autos the pawl can jam making release difficult but there's no sign of that happening on the F.
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