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Making your Automatic car dance to your tune October 27, 2007

Posted by Ragesh G R in Physics and Maths, Uncategorized.
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12 comments

The most common complaint and comment about an Automatic tranmission car, is that “You have less control over it, there is less involvement, compared to a manual transmission car”. Agreed, you can’t dictate the car to change to any gear that you please when you have an automatic transmission, but from my experience, I can tell you, if you know your know your car well enough, and if you are able to feel what it is doing, you can make even an automatic transmission car do whatever you please (well almost!).

First of all it’s possible due to the fact that most engine management system of today’s cars are intelligent and are based on a feedback system. The car does n’t just do pre-programmed actions irrespective of anything anymore, but on the contrary, listens to the driver input, tries to gauge the intention of the driver and tries to act accordingly, producing wonderful results almost always.

Next is your talent, how much you know your car and can undestand what it’s trying to tell you.

Downshifting in an Automatic car

Apart from the obvious manual change to”L” or “2”, the modern day cars downshift when you floor the throttle (full(open) throttle), provided the current revs of the engine can accomodate a higher rev as a result of a downshift. Imagine, you are cruising along at a rather relaxing speed of 70 km/hr in Overdrive(highest gear), when you need to pass a lorry in front of you, and an intersection is approaching, so it’s a case of now or never. But since you are in Overdrive, obviously you may not have enough acceleration to complete the overtaking manoeuvre before the intersection. No probs! You just floor the throttle, the car immediately shifts down to the previous(lower) gear, u get a jolt of acceleration, the next thing you know is you have passed the lorry at a speed of 90 km/hr. No more waiting for the speed to build up and no more nervous times during a pass

Warning: Do not ease the throttle(i.e., always keep it in full throttle) in the middle of the overtaking manoeuvre or else the car will upshift and lose acceleration and phew! you don’t want that to happen. So keep it floored till you have completed the overtaking.

Upshifting in an Automatic car

Now it’s not as straightforward as the downshift because here you have got to do all the work. The secret lies in judging if the rev (engine speed) is appropriate for an upshift and playing with the throttle. Generally, an automatic car upshifts to a higher gear in the start-middle of the rev band appropriate to the next higher gear. But sometimes we need power. So to prevent an upshift untill all the revs (max revs) at the current gear is utilised and you get maximum acceleration, floor the throttle and don’t ease it until it upshifts. But sometimes at higher speeds, not letting the car upshift will sometimes keep you in a low speed gear when you want speed and not torque. For that, just ease the throttle when you want an upshift. The engine management system(EMS) senses that since you are no longer in full throttle, you don’t the need the acceleration and torque and can upshift. Once it has shifted up, you can get back on the throttle (but not full throttle, else it might downshift again), and drive away. The beauty here is you can upshift almosy whenever you want to (i.e., at whatever rev you want to) by easing the throttle. But there is a limit to it. You can use this easing the throttle to upshift only when you are in the right rev band. If you ease the throttle too early (before the rev band of the next higher gear), the car will not upshift and you will just slow down, and if you don’t ease the throttle at all, it might not shift untill it hits the red line which might be unnecessary sometimes. It’s a delecate balance between speed and torque, and it’s a wonderful feeling when you get it just right.

When the driver sensitive EMS of the car, and your feel for the car work in tandom, you can make it dance to your tunes. It’s sometimes more challenging than a manual car because, there are no explicit levers to do anything, you are just overriding the car by thinking from it’s perspective.

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