D-Drive Infinitely Variable Geared Transmission

Posted: August 3, 2010 in Automotive Technology, BMW, Hyundai, Kia, Mazda

Here’s an interesting power-train concept that I’ve come across recently. What it essentially is, is a geared transmission with the ability to infinitely vary gear ratios right through from reverse, neutral and top gear through controlling the relative speeds of two drive shafts within the transmission. These two shafts however, need an input source separate from the main input source which turns the wheels. At the moment, the mode of input used in the model is a small electric motor.

So what are implications of this Aussie invention? Well unlike conventional automatic transmissions, there is no torque converter, nor fixed gears. It does not have any friction components either, like clutches in manual transmissions. Although it uses toothed gears, there are no fixed ratio gears like in conventional transmissions. Therefore you would expect energy losses to be minimal, and thus the transmission would be in theory far more efficient than conventional forms of transmissions. Also since the D-Drive transmission uses toothed gears, it can handle large amounts of torque, which is the primary short coming of conventional CVT transmissions that rely on friction and belts.

However, there is the issue of the energy required to control the relative speed of the two drive shafts. Although the energy requirement of the drive shafts won’t be too great since the shafts are really opposing any other force. In reality, if the relative speeds of the two shafts are powered by electric motors, you would have in effect a hybrid power-train. I’m not quite sure if it can really be called a ‘hybrid’ in the sense that used in this way, the electric motors don’t provide any sort of torque to the wheels. The inventor of the D-Drive does mention that there can be other ways of controlling the relative speeds of the drive shafts, such as stored kinetic energy, for example from a fly wheel.

I’m not of an engineering background but I do start questioning the need for all these extra components. Not so much because they add weight, (since a lot of modern transmissions nowadays are largely complex, with numerous parts which contribute to weight, and in comparison, the D-Drive uses relatively fewer parts), but because of size. In the automotive world, right now its all about efficiency and packaging. Additional components to the D-Drive would overshadow its merits if it is to the detriment of the compactness of the transmission. The other thing that I might mention is that when the transmission is in Neutral, the drive shafts and other components are still spinning which would be a waste of energy. If somehow they could channel this unused energy to perhaps a motor generator and then store the kinetic energy as electricity in battery packs, this would increase the efficiency of the product. Or another alternative would be to incorporate engine start-stop technology into the drivetrain. This would probably be the most feasible option at this point as a lot of manufacturers already have this feature on their newer engine lineup. BMW, Mazda, Hyundai/Kia come to mind.

For the D-Drive to be successful, it needs to be compact enough to be used in a multitude of products yet it also needs to offer efficiency in excess of its competitors. For the moment though, although the idea of the D-Drive transmission is very intriguing, there is still a lot of development work to be done. For efficiency, compactness and performance though, I will still say that Toyota (whether its rightfully their technology or not) still has every other transmission beat with its PowerSplitDevice (PSD) used in its HybridSynergyDrive. It works in a similar way to the D-Drive transmission, however instead of drive shafts and infinitely variable gearing, it uses a planetary gearset with a single fixed ratio, equivalent to driving at top gear all the time. One key element though, it has the ability to capture otherwise wasted energy while at a standstill, and the internal combustion engine only comes into play at higher speeds when the electric motor is out of its torque range.

I will add one last thing – I really do think that the D-Drive transmission would work brilliantly with the Mazda rotary engine, perhaps with a mild hybrid system like the Honda Integrated Motor Assist to help boost low rpm torque.

  1. Found out your webblog via msn the other day and absolutely liked it so much. Carry on the fantastic work.

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