OT: automatic van hire - possible?

[dennis]

Be careful, using facts will upset a lot of people in this group.

[Steve Firth]

It's on later ZF boxes, the Jaguar XKR and XJR have it fitted, but I get a bit lost on Jag autoboxes, they used Mercedes for a time, but only on some of the range. I think they are back to exclusively ZF boxes now. AFAIR the first Jaguar to have a box with lateral-g sensors fitted was the S-type R in 2005.

Indeed, the Ford has no fancy jiggery-pokery in the autobox, I've never had it shift on a corner but OTOH I do left foot brake the Ford into fast bends to ensure that I'm at the right speed in the right gear.

To force a shift down in an autobox on a bend, one would have to have lead divers boots and to be pressing the accelerator at exactly the wrong time.

[The Natural Philosopher]

Look at te original context. He said they used gears to GET THE POWER mnxed OUT I said they dont use gears much at all teh torque converter handles everything until they are pretty much flying and then they may or may not change just one gear.

Because they have far too much power until they are doing at least 60mph to not slip the tyres. I,e, the whole thing is essentially a one geared or possibly two geared car with a torque converter to just smooth out the torque.

I have never heard a top fuel or funny dragster change gear in a run.

Listen here.

the bikes have about 6 gears and the changes are sequential and totally automatic, but no torque converters and it is instantaneous changes.

eg

some of the top fuel machines seem to run tirque converters and singles speed boxes.

[The Natural Philosopher]

I have never heard the really powerful acr stuff change gear down the strip.

I HAVE heard the bikes though.

The most time is gained really in comparable power setups by controlling wheelspin precisely: My assumption is the torque converter will do that slightly better than slipping a manual clutch. They have sufficient power in 'top gear' to slip the wheels right up to 60-70mph, and they hare always supercharged, so they have low down torque.

Rally cars and FI cars where power is at a premium, use fast acting auto boxes. But NO TIORQUE converters. I was at a presentation where an entrepreneur was trying to sell an infinitely variable gearbox to Dave Richards at Prodrive. Dave Richards said that the cost per millisecond was too high, and that he could get 5 ms/shift better merely by developing the automatic paddle boxes they had at less cost.. the auto infinitely variable was losing too much power and although there wasn't the gearchange time loss, the gearbox engineer said the overall stage improvement times would be negligible. So they didn't take it up.

Dave Richards is impressive. All the engineers present their development ideas in terms of seconds per hundred thousand pounds spent, per typical stage..and Dave picks out the lowest cost per unit gain ideas and gives them priority.

[The Natural Philosopher]

I suggest you do

I found one and there may be a single gearchange before the end, or it may be that the wheels stop slipping.

[The Natural Philosopher]

Thats only the bloody amateurs. With piddling amounts of power. If you only have a few hundred bhp its actually faster to shift a manual BUT keeping the car on the road and controlling wheelspin tends to need two hands.

The real funny cars and top fuellers are a lot more sophisticated.

[The Natural Philosopher]

They do. Initially they used locked down gears and stock torque converters: Now its hight tech one run clutches.

[The Natural Philosopher]

Not so. Typical situation..wet or greasy corner power being applied very softly, auto decides its time to change up a gear..and does so. instant loss of torque while it fiddles around, and if you are unlucky the tail steps out.

You assume the auto can change gear better than you can. It may be true in your case, but not in mine.

I probably know them better than you do.

Sigh. My pijnt is that it IS NOT a 'lock in gear' it indicates a preference that te auto may still override.

I have never ever broken an engine, but I for sure WOULD if throwing the engine into gear was the only way to slow down if the brakes failed completely, which HAS happened.

Fortunately the handbrake still worked and I didn't need to break the engine..

No, I am just a very sensitive driver. As one fiend put it 'the man who knows every single bump in the roads for 40 miles around cambridge. This was at that time largely true..

It was important when driving swing axles spitties, to know exactly where you were likely to get snap oversteer on a bump, and just let it run wide slightly.

[Dave Plowman (News)]

Power doesn't matter to a gearbox. Torque does.

Don't care. They all have gearboxes.

[Dave Plowman (News)]

As well as learning how to control your vehicle, it sounds like you need some decent tyres too.

[The Natural Philosopher]

Oh changing the game are we.

Yes, they all have differentials of some sort

And steering racks, That's a gearbox I suppose.

[The Natural Philosopher]

It sounds like you are turning into steve firth, and I am tempted to simply plonk you.

[Huge]

I suspect that the answer to this question is "it depends". I no longer care.

[Dave Plowman (News)]

No. You've tried and failed.

I'll take your word for it.

Gearbox as in the conventional sense, ie with more than one gear. which changes on the move.

[Dave Plowman (News)]

You seem to be basing all your auto comments on the behaviour of a Freelander. A vehicle which must be driven with care if fitted with off road tyres etc. And one which apparently thumps its gearchanges. I've had lots of auto cars - all with powerful engines - and not once had the problems you describe. But then I knew from the start not to use kickdown under stupid conditions in the same way as I knew not to floor a manual in a low gear too. An auto doesn't remove the need for the driver to drive the vehicle.

[The Medway Handyman]

bucksvehicle website, and found 2 interesting pages. The "Vans available page" contains 2 Renault automatic transmission vans, and their "extra's page" (dated May 2010) says -

have always been made with manual gearboxes only. This often causes problems for drivers who are only able (or willing) to drive automatic vehicles - whether due to licence entitlement, health and mobility restrictions or personal preference.

mean that vans can now have automated gearboxes and these are becoming increasingly widespread."

The Merc diesel ambulances used by LAS are all auto's, as were the LDV 'heaps of sh*t' they have (almost) replaced. They have 900 of them on the road.

[Grimly Curmudgeon]

You haven't been in any car showrooms recently, while dressed in leather jacket and yellow polo shirt?

[Steve Firth]

Sadly the truth, as usual, lies between the stuff spouted by both sides of the argument. It does also to an extent depend on what one means by "dragster".

In the 1960s and 70s when I took an interest in such things, dragsters tended to have a two speed gearbox with the 1:1 drive ratio being selected by bashing a big mushroom in front of the driver shortly after getting away from the Christmas Tree. Nowadays with engine outputs hitting 7000bhp for Top Fuel dragsters that gearbox has disappeared and the only gearing is the fixed 3.2:1 of the final drive.

Acceleration off the line is *not* "all done with the tyres" as TNP claims. If the rears were spinning as the car accelerated the driver would lose control, crash burn and die. Also the acceleration would be piss poor. Nor do Top Fuel dragsters use automatic gearboxes and torque converters as others have claimed.

The acceleration in a Top Fuel dragster is controlled by a multi-plate centrigually operated clutch pack with hyrdo-pneumatic timing optimised to the track conditions. That is why you see some guy pissing about with the clutch just prior to the burn out. The clutch mechanic will be making adjustments based on the track temperature and relative humidity at the last possible moment.

The clutch has five friction plates and four "floating" steel plates between them. Each friction plate has weighted "fingers" that fly out under centri(petal/fugal) force to lock up that plate. The weights on each finger can be adjusted to determine at what rpm the clutch locks up. There is also a hydropneumatic timing system that will sequence the clutch lock up.

As the dragster accelerates each clutch plate engages sequentially with the clutch slipping all the way to 1000ft at which time the final clutch locks up to give the final 1:1 drive. For each run the oldest clutch is removed and one one plate added so that the first four clutches are "seasoned" and the final clutch is brand new. Engine rebuilds are after every 10s of full power operation IIRC. So a new engine for every run.

Engines alone cost £60,000 so it's a sport for the wealthy.

And TNP continues to talk utter bollocks as always.

[Steve Firth]

No they bloody don't. A differential on a dragster would be absolutely bloody pointless. They don't turn corners so they don't need a diff. If they had a diff one tyre would light up and the car would go nowhere.

Do try to think before you start typing complete and utter crap.

[Steve Firth]

Hooray! You got one thing right, at last.

Had time to Google and discover you were talking s**te, eh?