Engine braking - autos ?

[Jonathan]

I'll tend to make use of the manual override quite a lot. I sometimes wonder if I'm doing it a bit too much, but after going out with several observers in my IAM group and a couple of others here I've yet to have anyone mention that, one or two saying they thought I made good use of the auto box so I can't be going too far wrong.

Certainly in my Rover 75 a high gear will be selected quite early and I'll usually hold 3rd in town and 30 limits to give myself some extra control and acceleration when I need it. With kickdown there's a short delay, and I still haven't quite mastered how far to push the pedal down to achieve the desired effect. Either nothing happens or I'm flung into next week!

Engine braking is minimal, but that can make judging subtle variations in speed through acceleration sense all the more interesting.

[Renny]

Interesting comments above. I agree with the description of DSG as an "automated manual" gearbox as it is mechanical in its transmission of drive or selection of ratios, involving no hydraulics as per a traditional auto'box. Modern "Automatics" are now very complex with electronic programmes controling the lock-up points of the torque converter and the gear selection for varying circumstances.

In my recent experience with a current Land Rover Discovery, fitted with the 6-speed auto, the electronics delay the converter lock-up when the engine is cold, also vary the gear change speed and point if different programmes are selected on the terrian response (Sand mode is very usefull if you need a quick getaway ). It also programmes the torque converter to remain locked longer on deceleration providing more engine breaking if "Sport" or "Command Shift" is selected.

If Rog is referring to "automatic" 'boxes in modern trucks, then I've been fortunate to drive some of them recently. Other than those fitted to specialist vehicles such as refuse trucks and sweepers which tend to be traditional autos designed for slow-speed work, the current generation are automated manual 'boxes. They are traditional manual gearboxes with automated control of gear selection and clutch operation, the most common seem to be ZF based.

One of the reasons these have been developed was that as the power and torque levels increased, the gearchange loads increased as the synchro's were beefed up accordingly. This resulted in the development of assisted gear selection such as Mercedes APS(?) which took the shift load away from the driver by removing the mecanical gear lever. Another issue was that the clutches were being subject to abuse and higher torque loadings so then control of that was automated. Combined, this gave us the modern automated manual box.

These 'boxes combine with the engine electronics to give optimal gearshift points, with matched revs giving quicker changes than most drivers could acheive. They will tend to default to a suitable low gear for starting off, then skip gears as appropriate if unladen. Engines operated in the best economy rev range, cannot be over rev'ed and the clutch does not get abused.

I like the new boxes but it does depend on the programming of the system and the torque characteristics of the engine. I drove an Iveco that I drove on manual selection as it constantly changed gear at the wrong point, either changing up too many at once, or hanging on until the governor kicked in before changing. I've also driven a DAF with the same 'box but programmed to give 12-speeds rather than the Iveco's 16 and it was so good that I just left it in auto leaving me free to concentrate on other things.
Hope this answered your Q Rog

[ROG]

It was about cars but the truck info was useful

Not knowing much, if anything, about how a car works - I wondered why some autos seemed to 'engine brake' and some did not.

On observed runs, I found that encouraging full use of the auto gearbox, if options were available, that the car seemed to slow better in a lower option whereas, if left in D, it would just 'keep going'.

Thanks for all the info so far folks

[TripleS]

I'm therefore interested to know why the Stressed one seems to (sort of) regard it as a manual gearbox.

No torque converter and the mechanics of the change are via synchromesh and constant mesh gears rather than epicyclic trains with brakes and clutches. While I accept that it's an automatic in that it can go from rest to Vmax without human intervention, underneath it's an automated manual gearbox.

OK, thanks for that, Dave.

Best wishes all,
Dave.