Letting up for gear change?

[4 Strings]

I'm still getting used to my new (to me) E240.

If you floor it, it seems that the power is automatically lifted for gear changes.

Is this the case? To save on the gearboxes clutches? Didn't do this on my old (lamented) C200k, the power kept on though the gear changes.

 

[John]

Assuming it is an auto - I've not heard of such a concept in any of the auto cars I've driven.

Sounds like it could be a problem with the transmission?

 

[kid-jensen]

Certainly, modern engine management systems talk to the Transmission ECU to reduce torque during gear changes. This is done to give a smoother change and reduce clutch wear.

Couldn't say for sure that this is a feature of your E240, but I suspect this is what you are feeling...

 

[4 Strings]

The wife has a Fiat with their 'Dualogic' system which is a manual box but with robotic actions for gear changes (inc clutch, the change itself and this lets up on the throttle for the changes).

When I floor the E240 Estate it definitely seems to let up for the gear changes but I'm surprised that an epicyclic type auto does this. So you don't get that surge as it changes but the car being such a big lump I'm happier if it reduces stress on the clutches etc.

(I suppose being an E240 you don't get that much of a surge anyway!)

 

[Bellow]

Petrol engined autos since the box was controlled by electronics have retarded the ignition timing on upshifts to ease the strain on the box and make the shifts smoother. In the beginning at least. Possibly they alter fuelling now (or throttle now there's FBW) but the aim is the same. Presumably diesels are programmed to do similarly.

 

[4 Strings]

Well, there you go, thought so and learned something. Presumably the extent of easing is in relation to the amount of throttle at the time as pootling about there is nothing noticeable.

This is a good thing to try and make things in the 'box last, hopefully not 'just something else to go wrong'!

 

[John]

News to me.

Every auto with a torque converter I've driven simply sounds like it drops revs as it uses the new gear as it would in a manual.

I've never experienced a "lift off" of power before the gear changes.

 

[Coruscator]

News to me.

Every auto with a torque converter I've driven simply sounds like it drops revs as it uses the new gear as it would in a manual.

I've never experienced a "lift off" of power before the gear changes.

Same experience for me too.

The engine revs match the gear selected automatically to suit the situation.

I'm not sure but don't all modern automatic mercs have torque converters and
not clutches?

Something else I've noticed too is that acceleration seems a bit more fierce
if I gradually depress the accelerator. Rather than just jamming it straight
to the floor. (unless I want to kick down)

It might be just a placebo effect but it seems to take off a bit quicker to me. :0)

 

[John]

Same experience for me too.

The engine revs match the gear selected automatically to suit the situation.

I'm not sure but don't all modern automatic mercs have torque converters and
not clutches?

Something else I've noticed too is that acceleration seems a bit more fierce
if I gradually depress the accelerator. Rather than just jamming it straight
to the floor. (unless I want to kick down)

It might be just a placebo effect but it seems to take off a bit quicker to me. :0)

Very modern Mercs have wet clutch automatics instead of a TC or a regular TC auto (but with more gears e.g. 7).

The OP is talking about an E240 which will have a TC (which do actually have clutches albeit not the sort you are referring to but don't worry about that!).

Certainly in my car, if I plant it too hard too quick, it kills the power for traction so fast progressive works best.

 

[Harridog]

My ducati has a "quick shifter" I don't have to lift of when accelerating and it auto blips on the way down.

 

[4 Strings]

Yep, auto and torque converter, it's the clutches/brake bands within the box rather than the dry plate on the flywheel type.

My experience with other autos (apart from the Fiat thing, which isn't the same sort of box) has been exactly the same as others hence the comment.

I'll give it another try tomorrow...

 

[John Jones Jr]

News to me.

Every auto with a torque converter I've driven simply sounds like it drops revs as it uses the new gear as it would in a manual.

I've never experienced a "lift off" of power before the gear changes.

I've never come across it either and not just on Merc's.

 

[Bellow]

News to me.

Every auto with a torque converter I've driven simply sounds like it drops revs as it uses the new gear as it would in a manual.

I've never experienced a "lift off" of power before the gear changes.

Same experience for me too.

The engine revs match the gear selected automatically to suit the situation.

It is torque that is reduced - not rpm.

 

[John]

It is torque that is reduced - not rpm.

I don't experience any discernible difference in forward force either until the gear is changed.

Perhaps it is subtle.

 

[Bellow]

I don't experience any discernible difference in forward force either until the gear is changed.

Perhaps it is subtle.

Well there has to be reduction in forward force between the gears because if you have a gearbox in two gears simultaneously the gearbox will either lock solid or explode.

BTW, I haven't seen electricity. Does it exist?

 

[John]

Well there has to be reduction in forward force between the gears because if you have a gearbox in two gears simultaneously the gearbox will either lock solid or explode.

My point is - if someone notices it, I'm not sure that sounds right to me given I've never noticed it.

BTW, I haven't seen electricity. Does it exist?

Lol!

Do you practice being condescending or does it come naturally?

 

[hotrodder]

I don't do properly modern cars but FWIW with traditional automatics (epicyclic gear train and a torque converter) messing with fuel and/or spark for gear changes has to be a solution to a problem that doesn't exist? With an epicyclic geartrain changing gear doesn't involve physically engaging gears as they're always engaged. Brake bands and clutches stop different components in the epicyclic geartrain from rotating which changes the output ratio

Throw a few one-way clutches (aka sprags although they're a specific type of one-way clutch rather than a different name for the same thing) into the mix and different components rotating at different speeds becomes irrelevant. Adding electronic control of this or that and lock up converters doesn't change things... usually less reliability, always better economy, sometimes more refinement and most of the time a 'box with 'quicker wits'

 

[Bellow]

Brakes and clutches only wear when they are slipping. To arrest or engage while transmitting a high torque will require a high clamping force while the brake or clutch is still slipping. If the torque is reduced the clamping pressure while slipping can be reduced and the wear also. Once locked, full torque can be reapplied with no wear penalty. There is good reason to feather the torque.
Initially (before FBW throttles) the method was to retard the spark a touch. Presumably nowadays there are more options open and the one that least hurts emissions gets the nod I'd guess.

 

[Coruscator]

Anyone fancy a game of transmission top trumps?

No?

Oh, you surprise me. :0)

 

[Bellow]

Anyone fancy a game of transmission top trumps?

No?

Oh, you surprise me. :0)

A truck driver or ex 1960s 50cc racer will come along and ruin your day. Eighteen speed gearbox - trump that.