Is there an engineering reason why auto boxes go from park to reverse?
Why not go to drive, particularly since on modern autos you can sideways or otherwise shift into tiptronic, sport or whatever?
Is there any reason why it couldn't be reverse on the other side of neutral?
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Off the top of my head, the only thing I can think of is to protect the parking lock. If park were next to drive, and the gear lever were inadvertantly moved while at speed, the gearbox would either lock, or break expensively. With Park being next to reverse and neutral, it's less likely to be engaged at speed.
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How would that work?
P N D 4 3 2 1 N R ?
You need N between D & R and ideally beween P and anything
Who would want to scroll through the ranges to change between R and D?
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You wouldn't have to. As I said, you could shift sideways from D into the ranges as auto boxes do now.
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It's down to US Government standards being applied everywhere for simplicty.
Before these standards were introduced P-N-D-L-R was common.
I think the logic of the change was something to with stopping worn selectors moving into R when L was intended.
The standards also cover how and when the engine may be turned off and on, how the starter interlock works, etc.
Federal Safety standard 571.102 if you want to look it up.
I guess it's possible some manufacturers who don't sell cars in the US and have no link to US companies might use a different pattern?
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Despite the car's many shortcomings, I found the 'J-gate' gearlever on the Jaguar XJ40 a model of ergonomics.
Alternatively known as the 'Randle Handle', I believe :-)
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Easy way to remember:
P = stop
R = backwards
N = wait
D = go
lol
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Its to make sure there is a safe haven between the set of 'drive' positions and the reverse position. And to allow a locking mechanism to make it less likely to accidentally select reverse.
There have been some very big crashes when people have accidentally gone into reverse whilst driving at speed (in automatics). I remember a coroner case 20 years ago where the following car saw the reversing lights some on, and it was found that the driver had a habit of selecting gears manually on his autobox, and also of pressing in the button on the selector - the coroner concluded he'd gone from drive, through neutral into reverse.
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Like oilrag says PNDLR was common until the late sixties at least.
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That's right. I can remember that on US cars in the early seventies and on cars here, I suppose. IIRC that's when autos were three speed and you could lock in first.
But doesn't that mean there's another N (even if not marked) between L and R?
Edited by Optimist on 20/11/2008 at 21:26
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>>But doesn't that mean there's another N (even if not marked) between L and R?
No, because all the selector* in an automatic actually moves is a hydraulic spool valve, and so by redesigning the spool and the connections, you can get any combination of gears adjacent to each other.
* The selector also allows the parking pawl to drop into slots on a disc on the output shaft when in P, and also moves the connections within the starter inhibitor & reversing lamp switch.
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So is the neutral actually necessary in engineering terms?
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To be clear, in this thread, I'm only going to talk about conventional torque convertor automatics - mainly because I know very little of the detail of DSG type gearboxes.
The only difference mechanically, electrically, and hydraulically between P and N is that in P, the parking pawl is engaged.
Unlike a manual gearbox, most automatics when the engine isn't running are effctively in neutral wherever the lever is, because there's no hydraulic pressure with which to engage a gear.
A very small number of automatics do have an output shaft driven secondary pump which allow them to be push started, and in these, there is a real use for the N position - typically, the car is got up to speed in N, and then, D is selected.
For example, early W124s do have the secondary pump, but, my later one doesn't. I can imagine MB saved quite a bit by deleting it, because there's not only the pump itself, but the extra valves within the valve block to isolate one pump from the other, and to route the fluid to be able to allow bump starting. The hydraulic diagram for the whole gearbox is way more complex than any automotive electrical wiring diagram I've ever seen!
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