Acceleration Explanation
 

Acceleration Explanation

I need some help understanding how the engine/transmission work together to create acceleration on the new G35 Sport, automatic. I have driven many cars over my life, but this is the first “modern computer” controlled automatic with autostick car I have driven for a long period of time (just over a week now).

Here are the scenarios, and maybe someone can tell me why this happens.

1) I am in autostick mode. I punch it, and the car takes off, hard and fast. At about 5000rpm, I feel a jolt in the car, like it just changed gears. But I did not tell it to, and the gear indicator still reads 1. Then I pull the paddle, and the car shifts to second, followed by another jolt. That is three serious, head moving jolts just to go from first to second in autostick when accelerating hard. Why does this happen? And yesterday, it also happened in second gear, which means when I floored it from a standstill, the car jolted 5 times just to get into 3rd. Shouldn’t it only jolt when I pull the paddle?

2) What determines when the computer shifts gears in automatic mode. For example, at a stoplight, I put my foot down to give the car a good amount of gas. Sometimes, the car shoots out like a bullet, and the car shifts very fast and I am speeding before I know it. Other times, I put my foot down to the exact same point, and the car sort of accelerates on its own and shifts when it feels like. Under the same conditions, I am doing 60 before I know it and other times I am barely doing 40. What is the computer doing to make this happen? Remember, I am not pushing my foot to the floor. This is just a normal amount of gas to give the car power to move.

3) In automatic mode, why is there such a huge delay between when I put my foot down on the gas and when the car chooses to accelerate when I am cruising down the street. Lets say I am doing about 30mph and I floor it to make a light. There is a good 2-3 second delay before the car picks up (I drove a stick before this car, and when I was in 3rd and punched it, the car had zero delay). Shouldn’t the time between stepping on it and the acceleration be much smaller on a modern engine, or is this the computer calculating whether or not I really meant to go fast?

4) In autostick mode, there is a delay between me pulling the paddle shifters and when the car actually shifts. What is the optimal RPMs I should be pulling the paddle in order to get the most out of the car?

Thanks in advance.
Herschel

OK.. for number 1.. What are the rpm's doing when you feel the kick in first gear. I think the active handling stability control is kicking in and you are feeling the control and then the release.
for number 2... this car is drive by wire (DBW). So the position of the throttle has different meanings depending on mph, engine speed, etc.
for question number 3.. when in automatic mode the tranny is going to creep up to 5th as soon as it can.. so when you are doing 30 and punch it, the tranny is going to drop down a few gears and then go.. thats the delay you are feeling.
This tranny is new to me too.. but I think it works fine with many performance options. Depending on the mode and how you drive... it will fit your needs fine once you get used to it.
I need more seat time with mine.. but on my test drive, it did everything well when pushed.. I like the way it keeps the shifts all the way to redline... good stuff!

I have not experienced anything strange with our tranny, I will say that the shift points are directly tied to throttle position....but this is really nothing new. When you apply full throttle in this car, it certainly shifts fast and hard close to redline. I imagine you are applying different levels of throttle (even though you think they are the same ) and the computer is shifting accordingly.

Thanks for the information. Everything you wrote makes sense. I guess I am still getting used to the feeling of an automatic. My previous car was an Acura 3.2 CL Type-S, 6 speed stick, so I had power in every gear and there was never any hesitation. I also believe that this car has the "learning" mode, which means it will eventually figure out my driving style and when to shift gears. I think part of the problem is that in the first week of driving, I have been in every driving condition, from wide open freeway to crawling traffic to winding mountains.

Our cars certainly have an abundance of power and I am having fun figuring out when and where that power will come. I have enjoyed every minute of driving this car. What I wrote in this post were just some of the things I was thinking about on the way to work today.

Thanks for all the input!

Herschel

Can you try and isolate exactly where it's happening, you have three spots. pedel/computer Drive by wire system (DBW), the tranny and the engine. Start by validating that the DBW system is doing what you are telling it to do, and that the engine is recieving those signals correctly and quickly. Put the car in park, and tap the gas, depress the gas at differnent levels, push it slow, push it fast, get a feel for how the engine reacts to the pedal... that's the first step.

Now get the car in motion, i.e. highway and while doing 65 mph, put the tranny in neutral and do a few taps on the gas, make sure it's reacting the same way as when the cars in park... again your trying to establish how the DBW feeds the engine, but your really training yourself. Also this is checking that the Speed sensor is not interfering with anything or adjusting the way the DBW tells the engine to pull.

Once your comfortable that there's nothing wrong with the DBW or engine responsiveness, and hopefully you've learned a little of how the pedal works, because it is such a light sensitive pedal, it will take some getting use to

Now put the tranny in DS mode and drive that for a while, that sport mode will try to make the most power available to you and go for sport shifting... don't bother with the paddles, just drive this for a bit and again get use to it and get a feel for how it's working

Then when you get comfortable, start driving 100% with paddle shifting, down shift to the traffic light, execute all your up shifts, downshift to pass... get a feel for this...

Lastly, put the tranny in auto (grandpa) and drive the same way you did while in DS and you will probably notice that the DBW system softens everything up so your more luxury, less sport, always pushign you to a higher gear.

I've gotten in the habbit of when I want to pass or shoot for a yellow light or close a gap, put the car in DS, step on the gas, put it back to auto. I get a little thrill out of it while telling the engine, wake up, I want to go and I'm serious.

I'd imagine the DBW system is also learning your driving style but I doubt you would notice it's learning behavior... right now it thinks you're a baboon "This guy cruises at 10% throttle, so I put it in 5th to save him some gas, and as soon as I put it in he guns it! I can't figure this guy out... where'd he get his license in Kentucky on a tractor!" J/K and My wife is from KY so I get a free pass on all the hick jokes

BTW for those that don't know, the 5AT WILL downshift for passing with the left paddle even while in auto mode.

Great info! I like that!!!!!!!! Learn something every day. now if I could just try that out.... doh!

yea thats a huge advantage! i love it!

I knew that it did this, but how long does it stay in that gear for if you don't change your throttle postion?

Yeah, I had a similar experience on the drive home last night. I was trying to change a lane to the left to get out of an "exit only" lane on the freeway, and was being paced off my left rear quarter as always seems to happen.

About 2-3 cars up ahead someone moved left out of my target lane, and the car that was behind it wasn't moving real fast. So I gave the accellerator a good push, and found myself roaring near redline, successfully changing lanes seconds later.

It was like it downshifted two gears, or something, when I hit it. I wasn't expecting that.

For me, I think it is just a very powerful car relative to the Maxima that I'm leaving, and I just haven't developed a good feel for the accellerator yet.

I noticed that too, that the paddle shifters work in D as well as DS.

In all my years of posting on boards about my cars, this was probably the most useful information I have recieved from one person. I did the tests as you suggested and the car reacts fine--I did not expect any malfunctions from the car. This is definitely a user error. I need to learn how to drive the car correctly. I need to know how much pressure to put on the gas and what results to expect. Wow, I thought learning to drive stick would be a challenge...who knew my automatic would be just as interesting!

But what I learned the most is what the DS stands for! Yes, yes, I should read the manual. But I work two jobs and have not had time to actual read it all the way through. But when you said that the DS is the "sport mode," it made much more sense why the car has been reacting the way it has been. I actually drove home in DS mode and could really feel a difference. In addition, I also learned why the car jolts more than once. Believe it or not, the roads around me are not smooth, and when I have that much power to the rear wheels, the car go over some of the bumps hard, which causes me to move my foot on the pedal. It happened when I left work...I floored it to and the rear dropped over a bump almost immediately and my foot moved on the pedal, causing the car to double jump because it thought I was asking for more power!

The D mode and DS mode remind me of the "drive" and "over-drive" found on American cars.

I also learned (from another member on this post) about using the paddle to down shift, even if you are in D. !!!!!! Fanastic advice, and now this car is even more fun to drive than I thought.

Thank to everyone who posted responses. They have been very helpful and I am enjoying learning this car. Now I just need a dragstrip with no cops...

Herschel

!!!!!! It is like discovering the pot of gold at the end of the rainbow !!!!!

Thank you for the advice. I did not know you could do that (I did hit the up-shift paddle, but I dont think anything happened)

I actually used this technique on the way home from work.

When I did this on the way home, it went into 3rd gear. Then I accelerated, and when I looked down, it said D again. So I think it changes when the car changes gear to the next highest gear. But I am not certain.

I don't think the display changes on the downdshift while in auto mode. But then again ... I usually don't look down to read the LCD when I nail it.:D

IMO, the auto does a very good job of downshifting even if you don't force it to downshift with the left paddle.

Alright, thank you.