FAQ: CVT Transmission - How does it Work ?

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DaveBerlin
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Location: Berlin, Germany
Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by DaveBerlin »

Obviously I along with others have been keeping track on the comments regarding the Nissan CVT Transmissions and there has been a load of Negative & Positive Comments on the problems. I for one did not fully understand how this Transmission worked. So I started looking and found some facts not all relative to the Nissan QQ but just a general overview which I thought might be of interest to some.
I am still no expert but have now a better understanding of the CVT Theory and working, I hope it is not too boring - Dave

These comments were put together from Nissan Technology :

Efficient and compact CVT technology for small vehiclesCVT (Continuously Variable Transmission) is a system with seamless, "Stepless" gear transmission. Early on Nissan understood the merits of CVT, low-fuel consumption and seamless acceleration, developing and adopting the technology for its vehicles.Extending the attributes of the efficient CVT even further, XTRONIC CVT now offers powerful acceleration performance that is also a pleasure to drive.
CVT (Continuously Variable Transmission) is a system with "stepless" gear transmission. It maintains optimum efficiency in engine rpm according to vehicle speed, resulting in improved vehicle fuel economy. At the same time CVT is also characterized by its smooth acceleration. Early on Nissan developed a new logic for controlling CVT and introduced it into its vehicles. By understanding the tendencies of the driver and then estimating the optimal engine rpm the system selects the most suitable transmission gear ratio, accelerating in line with the driver's intentions.As a result the system implements both a pleasurable and intuitive driving experience and low fuel consumption.Technology Functionality
CVT is a "Stepless" transmission system. As opposed to MT (Manual Transmission) or AT (Automatic Transmission), CVT can automatically select the most suitable transmission gear ratio without any steps. Vehicles with CVT can run on the most efficient (i.e. with the best fuel combustion) engine rotation for regular velocity. The technology realizes seamless performance without shift changes when accelerating and decelerating.It also expands the low-to-high gear ratio range, with transmission gear ratio control matching the way you drive, and delivering both excellent fuel economy and acceleration performance.
In order to attain a pleasurable driving experience the system expanded computer processing capacities. This allowed the system to select the optimal engine rpm from over 1,000 patterns according to adjustment of the accelerator and vehicle speed.Nissan calls this Linear Shift Control. Engine rpm naturally rises when accelerating, resulting in a smooth feeling of acceleration.Further, by adopting an auxiliary transmission it becomes compact enough to be included with small-size vehicles, while also expanding the low-to-high gear ratio range. Simultaneously, through transmission gear ratio control that matches the way you drive, it improves the response when starting off and moving at low speeds, and also delivering low engine rpm when traveling at high speeds.
Technology ConfigurationCVT adjusts the width of two pulleys and changes the arc radius of the steel belt running between them in order to control the transmission gear ratio.

The arc radius of the belt for the engine shaft pulley gets narrower. This is ideal for driving at slow speeds, when gears on MT or AT vehicles are lower (for example, first or second gear).On the other hand when in a high gear the belt on the drive pulley gets wider. This is suitable for high-speeds when the gear is high, such as in fifth or sixth.The steel belt is serving here to bridge the two pulleys and change the diameter.If the gear ratio at low gear is lowered even more, acceleration improves. This is the same as how starting in first gear has more power than starting in second. As well as when moving off vehicle response improves at lower speed.
Technology ConfigurationThe system sensitively perceives the current driving situation through always calculating the car's driving conditions, such as the gradient load or cornering load. It determines if the vehicle is driving in a city, cruising along a highway, or on a winding rural road.The system communicates the driving conditions and driving tendencies to the CVT Control Unit, so it can then select the transmission pattern most suitable for the current driving scenario. Through this process, the system achieves both improved fuel economy and a fun intuitive driving experience.In previous CVT systems it was necessary to increase the size of the pulleys to expand the range of the transmission gear ratio making it hard to implement in a small vehicle due to the layout limitations.The XTRONIC CVT with Auxiliary Transmission adds to the transmission function utilizing the pulley and belt, and by adopting an auxiliary two-speed transmission, the transmission range has been expanded while keeping the pulleys small in size.

If you are interested there are a lot more videos on youtube on this CVT subject.
https://www.youtube.com/watch?v=2OMqmpjOHWM

How Does a CVT Work ?
http://www.autoguide.com/auto-news/2014 ... -work.html


These are the comments on the attached video which might be easier to read up front :

"At this time most vehicle manufacturers are mass producing their own versions of a CVT Transmissions, which within the next decade will completely replace the regular Automatic Transmissions that use the old wet hydraulic clutches. The computer chooses to have the gasoline engine rotating at the optional speed, regardless of how fast the car is moving.
When cruising under low load conditions the engine will turn relatively slow while engine RPM will increase when accelerating or climbing a hill, providing improved fuel efficiency as compared to a typical Automatic Transmission. Because of the smooth transition in gear ratios provided by the CVT, it also gets constant, stepless acceleration from full stop all the way up to cruising speed, compared to the shift feeling provided by a normal Automatic.
The CVT Transmission provides less power loss than a typical Automatic Transmission, resulting in better efficiency and acceleration".
Exploded View Workings :
https://www.youtube.com/watch?v=DldUaOW ... e=youtu.be
11.19/1.3L/160PS/Tekna+/DCT/PrOPILOT/KAD Gun Metallic/Trunk Lower Finisher/Rear Glass Finisher/Ambient Lighting-LED’s Innen/Entry Guards Illuminated/Sport Pedals/Front Styling Plate/LED No.Plate/Chrome Door Handles/Rear Valance/Giacuzzo Alloys + Falken

Deleted User 759

Post by Deleted User 759 »

Thanks Dave, I will FAQ this shortly! I have been a fan of manual since I started driving many years ago now! I prefer the control I have. I have however driven an auto twice now. Once was when I hired a Jag XF, that was a normal AT gearbox with flappy paddles. This made the car so easy to drive and retained the control I love as I could pick and choose a gear I wanted to be in (with idiot mode so I didn't over/under rev the engine!). I could then leave it and It would sort itself out. In a word, best of both worlds and still felt 'normal' Then earlier this week I was loaned a Micra 1.2 CVT when my Micra DIG-S went in for service. I thought this should be fun, just a shame it wasn't a boosted engine! Anyway, jumped in, quickly remembered what I needed to do and off I went. What an odd experience the CVT box is! The seamless gearing is odd when you are so used to a fixed ratio box, you expect engine noise change as you accelerate and de-accelerate and from that you can roughly estimate your speed without having to look at the speedo. To loose this you almost forget what speed you are doing and have to look at the speedo all the time! Normal driving around town, great it just sorted itself out and was quite 'refined', it held the revs at around 2500rpm which was perfect for normal driving. However hard accelerating seems inefficient and laggy if you were already moving. Put your foot down and to me it looked as though the gearbox was tweaking itself before allowing the car to increase in speed. Put your foot right down past the first stop on the accelerator and the engine revs shoot up to ~5000rpm and you accelerate away quite quick, however unlike a normal gearbox, it held the revs at 5000rpm, only increasing once I hit 65/70ish to overcome drag. Hard acceleration from stop was not too bad as the engine had to get up to 5000rpm and an appropriate speed before the gearing needed to be tweaked. I did feel rather uneasy, having the engine screaming like that as you accelerate, people next to me must have thought I was simply abusing the bejesus out of the gearbox and engine rather than it being normal! It took some getting used to that's for sure. I understand that the QQ CTV box will be different to that of the Micra, and that it has been programmed differently however and it will behave more like a fixed ratio gearbox but will tune itself depending on how you drive, although I dare say the experience wont be that far off and would not be surprised if the CVT box has the "hard acceleration" option where engine revs are raised to peak torque/HP, held there and will just spool through the pulls just like the Micra did? If we ignore the current known faults with the boxes, would it be for me based on that one experience alone? I don't know, its a touch call to make. I think if I did more motorway miles or long trips I think I would, I can see the advantage of it, however I don't think my driving style suits a CVT and still prefer the old school way of a box of cogs and a clutch!
DaveBerlin
Posts: 8623
Joined: Wed Mar 19, 2014 12:39 pm
Location: Berlin, Germany
Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by DaveBerlin »

Steve, thanks for that I should I suppose have posted it there in FAQ in the first place.
Now did you get the Micra back to the Garage after your CVT Driving Experience in one piece or on the back of a RAC/AA Low loader ? - Dave
11.19/1.3L/160PS/Tekna+/DCT/PrOPILOT/KAD Gun Metallic/Trunk Lower Finisher/Rear Glass Finisher/Ambient Lighting-LED’s Innen/Entry Guards Illuminated/Sport Pedals/Front Styling Plate/LED No.Plate/Chrome Door Handles/Rear Valance/Giacuzzo Alloys + Falken
Deleted User 759

Post by Deleted User 759 »

Yep, returned it myself to their front door (almost through it mind!!) Was glad to be back in the DIG-S though!
Stevethegreatgolfer
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Post by Stevethegreatgolfer »

Manual or semi-automatics would always be my preference, except that when i spend so much time driving into and around London, crawling around the M25 and creeping along the M4 or M40, an automatic is the only sensible choice.
Storm White Tekna CVT - Collected on 23 August 2014.
Kentishman
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Post by Kentishman »

I've often wondered why Australia and USA where roads are long and straight and you change gear once an hour are predominately auto uses whereas in this country where we are constantly changing gear are mainly manual
Tekna 1.6 CVT Nightshade
PeterL
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Post by PeterL »

This is all good stuff and the essential difference I guess (IMHO) is what you expect of your car - is it a means to get from A-B with the minimum of fuss and intervention or do you really want to be in control of every aspect? CVT or indeed automatic is the minimum of fuss method and totally suited to the daily commute or even business trip whereas the total control offered by a manual shift is by far the more fun way to travel. Give me the 370 of similar and it's Manual Shift every time - a QQ really?
Tekna CVT 1.6 Magnetic Red - born 4/4/14 P/X 25/10/2015 for £19k with 12,000 on the clock - great car but time to change. No problems whatsoever in those 18 month's.
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