7G-Tronic & Tiptronic User Notes

[Paul/]

7G-Tronic & Tiptronic user notes

I had difficulty finding explanatory documentation on the subject (beyond what it says in the owner manual), so am sharing what I’ve learned in case it is of use or interest to others. My only experience is with an 09 CLS CD320cdi without Manual mode, so predates 7G-Tronic Plus.
For key points that I haven’t yet been able confirm, I’ve added <not confirmed>.

7G-Tronic

7 forward gears, of which the top 2 are overdriven, and 2 reverse gears.

“Features SOG (Shift Optimal Gear) software to achieve improved fuel economy. Upshifts and downshifts based on driving style and engine load. By analyzing speed versus throttle opening comparisons, the transmission knows whether the vehicle is going uphill, downhill, towing or coasting and will either delay upshifts or hasten downshifts accordingly.”

Despite some opinions to the contrary, it is OK to switch modes while moving.<though see comment at end>

Comfort (also known as Winter or Economy) mode

• Moves off in 2nd gear both forwards and reverse except moves off forwards in 1st gear if any of the following conditions apply:

à 1st gear is manually selected
à Accelerator depressed 75% or more from stationary
à Cold engine temp (pre catalytic warm up)
à Shifting to Drive from Park <not confirmed>
​

• Changes up at lower revs and down at higher revs than in Sport mode.

• Softer clutch operation than in Sport mode <feels plausible, hard to be sure>.

Sport mode

• Moves off in 1st gear both forwards and reverse.

• Changes up and down at the normal i.e. default shift points.

• Sharper clutch operation than in Comfort mode <feels plausible, hard to be sure>.

Technical documentation
http://www.scribd.com/doc/100685077/722-9-Mercedes-Benz-7-G-Tronic



Tiptronic

On 7gTronic, ranges can be limited to a maximum (not minimum) of any gear e.g. range 5 is gears 1-5. Full range, which is the default state, is displayed as “D” rather than 7.

"Tap-" shifts down 1 gear and limits range to that gear

"Hold-" limits range to current gear and then shifts down 1 or 2 gears <not confirmed>

"Tap+" shifts up 1 gear and, if currently limited to a lower range, extends range to the new gear

"Hold+" restores full range i.e. “D” (and shifts up if not in optimum gear for full range)

"Hold" by tipping and holding in place for 1 second.

Won’t select a gear which would put engine out of its normal rev range.

Regardless of range, shifts up at maximum engine speed.

Reset
There’s a “reset” procedure involving fully depressing the accelerator with engine off, but this appears to actually be a recalibration of throttle to accelerator, to ensure their corresponding ranges align correctly between min and max positions.

Shift Points
Can be changed from factory settings by driving with special menus temporarily activated via StarDiagnostics, so the car “learns” the appropriate shift points.


Thought so far on actual driving (<1000 mls)

Initial impression is that C mode shift points seem to better exploit the 320cdi torque profile- I’m still experimenting.

For urban driving, C mode is smoother and also a better match for normal conditions.

Using Tiptronic to change down also limits the gear range. This is helpful for gradients and towing, but if done to aid acceleration, the gear restriction will force the engine to change up at maximum revs, which is often not desirable, so would require additional stick work to restore optimal shift points.

“Hold-“ is better preparation than “Tip-“ for overtaking as is drops down to an optimum gear but first limits the range up to the current gear, so leaving more headroom for optimum shifts.
But it still requires another tip to restore full range.

Kickdown is the most convenient and effective option unless wanting to avoid the delayed response, or when anticipating a high likelihood of aborting e.g. if overtaking from shorter than ideal distance from vehicle in front.

My most common use of Tiptronic is when having reached cruising speed in S mode, want to change up for economy.

It’s probably safer to switch between C and S mode whilst at constant speed, to avoid small risk being caught out by a sudden change in transmission response.

 

[Paul/]

Pity I didn't find this, on the official US MB site, sooner. I'll incorporate it in to a single updated version of the original, but for now I've just copied it in its entireity as it reveals more sophistication- there are some interesting additional points (also, the 1st one being that the "Hold-" action can cause a downshift of up to 4 gears, not 2 as I previously stated)...


Unlike many transmissions, the seven-speed transmission will skip up to four gears if necessary when the driver downshifts, shifting directly from seventh to fifth, for example, or even sixth to second. This helps the transmission choose the right gear ratio for quick acceleration and ensure almost imperceptible shifts in the process.

Adaptive Electronic Wizardry
The heart of all Mercedes-Benz automatic transmissions is a high-performance micro-processor, which is designed so the transmission shifts as the driver expects and wishes it to react. Continuous electronic networking with the engine and chassis management systems allows the transmission computer to adapt to a wide variety of driving situations, and even to the driver’s style.
By comparing road speed changes and load, or throttle opening, the transmission computer can instantly discern uphill and downhill grades, and adjust shifting as a result. It delays upshifts on descents (for engine braking), as a driver is likely to do with a manual transmission. The micro-processor even considers cruise control and engine temperature in the shifting decision.
The computer also measures how fast the driver presses and releases the accelerator pedal. If the pedal is pressed relatively quickly, the transmission is more likely to downshift, for instance during sporty, more spirited driving, while upshifts are less likely when the pedal is released quickly. With normal pedal operation, shifts occur according to a basic program aimed at getting the best fuel mileage.
Smooth Shifts
The transmission computer is also networked to the ABS and traction control systems (and to yaw and steering sensors from the standard ESP stability control system) so that it can recognize cornering and low-traction conditions. Based on this data, the transmission may delay or hasten a gearshift to ensure that it creates no negative effect on vehicle stability or traction control. Not only does the transmission computer adjust shift feel according to engine speed and load (smooth shifts during leisurely driving, crisper shifting with more spirited driving), but it’s even able to reduce engine power for a split second (by retarding ignition timing) to ensure smooth gear changes.

 

[joecash]

very interesting

 

[Paul/]

15.09.12 updated version

OK, now combined the info from both posts, also attached as a .doc file. If anyone aware of errors or omissions, please advise (I've only used apparently definitive sources, but that doesn't guarantee that they're 100%).


7gTronic & Tiptronic user notes
Last updated 15.09.12

I had difficulty finding explanatory documentation on the subject (beyond what it says in the owner manual), so am sharing what I’ve learned in case it is of use or interest to others. My only experience is with an 09 CLS CD320cdi without Manual mode, so predates 7gTronic+.
For key points that I haven’t yet been able confirm, I’ve added <not confirmed>.

7gTronic

7 forward gears, of which the top 2 are overdriven, and 2 reverse gears.

Continuous electronic networking with the engine and chassis management systems allows the transmission system to adapt to a wide variety of driving situations and to the driver’s use of the accelerator pedal:

• If the accelerator pedal is pressed relatively quickly, the transmission is more likely to downshift, while upshifts are less likely when the pedal is released quickly.

• Shift feel is changed according to engine speed and engine load, to make smoother shifts during leisurely driving, and sharper shifts during more spirited driving. Smooth shifts are aided by retarding ignition timing to reduce power for a split second.

• The transmission system links with the ABS and traction control systems and yaw and steering sensors from the ESP stability control system, to enable it to recognize cornering and low-traction conditions, and where appropriate, delay or hasten a gearshift to ensure that it creates no negative effect on vehicle stability or traction control. <this might account for some reports of delayed response to Tiptronic inputs>

• Engine temperature and cruise control status are also taken in to account in the shifting decisions.

Kickdown (regardless of mode) shifts down by up to 4 gears and changes up at rev limit <not confirmed>

Comfort (also known as Winter or Economy) mode

• Moves off in 2nd gear both forwards and reverse except moves off forwards in 1st gear if any of the following conditions apply:

à 1st gear is manually selected

à Accelerator depressed 75% or more from stationary
à Cold engine temp (pre catalytic warm up)
à Shifting to Drive from Park <not confirmed>

​

• Changes up at lower revs and down at higher revs than in Sport mode.

• Softer clutch operation than in Sport mode <feels plausible, hard to be sure>.

Sport (also known as Standard) mode

• Moves off in 1st gear both forwards and reverse.

• Changes up and down at the normal i.e. default shift points.

• Sharper clutch operation than in Comfort mode <feels plausible, hard to be sure>.

Despite some opinions to the contrary, it appears OK to switch modes while moving.<though see comment at end>

Learning <not confirmed>
Lot of speculation on how this works, some say it’s just marketing hype, some others say that it learns from the driving style of all drivers since it was last reset. Clearly the system recognises and adapts to current conditions and driving style, but it’s quite possible that it doesn’t take account of (or remember) the non-current driving style any more than it would keep track and take account of non-current driving conditions.
There is however a definite learning process specific to configuring Shift Points (see below).

Reset
There’s a “reset” procedure involving fully depressing the accelerator with engine off, but this appears to actually be a recalibration of throttle to accelerator, to ensure their corresponding ranges align correctly between min and max positions.

Shift Points
Can be changed from factory settings by driving with special menus temporarily activated via StarDiagnostics, so the car “learns” the appropriate shift points. The primary purpose of this appears to be to configure the transmission to best match the characteristics of the engine and vehicle in which it is installed.

Technical documentation
http://www.scribd.com/doc/100685077/722-9-Mercedes-Benz-7-G-Tronic



Tiptronic

On 7gTronic, ranges can be limited to a maximum (not minimum) of any gear e.g. range 5 is gears 1-5. Full range, which is the default state, is displayed as “D” rather than 7.

‘Tap-‘ shifts down 1 gear and limits range to that gear

‘Hold-‘ limits range to current gear and then shifts down by up to 4 gears <not confirmed>

‘Tap+’ shifts up 1 gear and, if currently limited to a lower range, extends range to the new gear

‘Hold+’ restores full range i.e. “D” (and shifts up if not in optimum gear for full range)

‘Hold’ by tipping and holding in place for approx.1 second.

Won’t select a gear which would put engine out of its normal rev range.

If maximum engine speed is reached, will shift up regardless of range restrictions.




Thought so far on actual driving (<1000 mls)

Initial impression is that C mode shift points seem to better exploit the 320cdi torque profile- I’m still experimenting.

For urban driving, C mode is smoother and also a better match for normal conditions (at least with 320cdi).

Using Tiptronic to change down also limits the gear range. This is helpful for gradients and towing, but if done to aid acceleration, the gear restriction will force the engine to change up at maximum revs, which is often not desirable, so would require additional stick work to restore optimal shift points.

“Hold-“ is better preparation than “Tip-“ for overtaking as is drops down to an optimum gear but first limits the range up to the current gear, so leaving more headroom for optimum shifts.
But it still requires another tip to restore full range.

Kickdown seems the most convenient and effective option unless wanting to avoid the delayed response, or when anticipating a high likelihood of aborting e.g. if overtaking from shorter than ideal distance from vehicle in front.

My most common use of Tiptronic is when having reached cruising speed (at any speed) in S mode, want to change up for economy.

It’s probably safer to switch between C and S mode whilst at constant speed, to avoid slight risk of being caught out by a sudden change in transmission response.

 

[davidjpowell]

Confused.

D = Forwards.
R - Back.

C = lower change up S = Higher

Left or Right Nudge = Shift Down or up.
Left or Right Hold = optimum gear for acceleration or back to d.

When in D a right nudge will encourage an early gear change up.

 

[Paul/]

Confused.

D = Forwards.
R - Back.

C = lower change up S = Higher

Left or Right Nudge = Shift Down or up.
Left or Right Hold = optimum gear for acceleration or back to d.

When in D a right nudge will encourage an early gear change up.

Also confused, as my post started "I had difficulty finding explanatory documentation on the subject (beyond what it says in the owner manual), so am sharing what I’ve learned in case it is of use or interest to others. "

 

[Dash1]

Hi Paul/

Just an update for your current thread. I have supplied you to a direct link below for the Mercedes Benz 7 G-Tronic Technical Training site in the US. You will find quite a lot of information on the 722.9 transmissions here, which I am quite sure will suit exactly what I think you are looking for. It’s very informative and extremely detailed, some 79 pages or so. If it’s of no use, then please let me know and I will try and send you some further information/resources.

They are in pdf format so you won’t have a problem downloading it to your PC. Just click on the link and then click OK, it will automatically download.

Hope it is of some help. Let me know how you get on.

Regards,

Dash1

Link:- 286_722.9/286 HO 722.9 062504.pdf

 

[Paul/]

Hi Paul/
Just an update for your current thread. I have supplied you to a direct link below for the Mercedes Benz 7 G-Tronic Technical Training site in the US. You will find quite a lot of information on the 722.9 transmissions here, which I am quite sure will suit exactly what I think you are looking for. It’s very informative and extremely detailed, some 79 pages or so. If it’s of no use, then please let me know and I will try and send you some further information/resources.
Hope it is of some help. Let me know how you get on.
Regards,
Dash1/QUOTE]

Many thanks Dash1, it reveals many key pieces of info that were missing from the docs I'd found. These systems certainly are far more sophisticated than many people (including myself) would assume.

Could you clarify please the chart on p37, appears to be upshifts and downshifts plotted against speed and "pw(%)"- what is "pw(%)"- pulse width? related to hydraulic valve opening? or is it engine load e.g. % max rpm?

The only piece of detailed info that seems to be missing is SOG (Shift Optimal Gear)- the 722.9 docs refer to this as being the same as for the 722.6 system- but I can't find any 722.6 docs that explain it.

Cheers,

Paul

 

[Dash1]

Hi Paul/
Just an update for your current thread. I have supplied you to a direct link below for the Mercedes Benz 7 G-Tronic Technical Training site in the US. You will find quite a lot of information on the 722.9 transmissions here, which I am quite sure will suit exactly what I think you are looking for. It’s very informative and extremely detailed, some 79 pages or so. If it’s of no use, then please let me know and I will try and send you some further information/resources.
Hope it is of some help. Let me know how you get on.
Regards,
Dash1/QUOTE]

Many thanks Dash1, it reveals many key pieces of info that were missing from the docs I'd found. These systems certainly are far more sophisticated than many people (including myself) would assume.

Could you clarify please the chart on p37, appears to be upshifts and downshifts plotted against speed and "pw(%)"- what is "pw(%)"- pulse width? related to hydraulic valve opening? or is it engine load e.g. % max rpm?

The only piece of detailed info that seems to be missing is SOG (Shift Optimal Gear)- the 722.9 docs refer to this as being the same as for the 722.6 system- but I can't find any 722.6 docs that explain it.

Cheers,

Paul

Hi Paul/

I'm at work right now until 6.30pm this evening, I will come back on the site later tonight and explain everything in detail.

Regards,

Dash1

 

[Paul/]

Hi Paul/
I'm at work right now until 6.30pm this evening, I will come back on the site later tonight and explain everything in detail.
Regards,
Dash1

Thanks Dash1, I really appreciate that you are going to a lot of effort to help my understanding- I'd be happy to wait much longer to minimise the inconvenience to you!

Regards,
Paul

 

[Dash1]

Thanks Dash1, I really appreciate that you are going to a lot of effort to help my understanding- I'd be happy to wait much longer to minimise the inconvenience to you!

Regards,
Paul

Hi Paul/


NOTE. To all forum members, this post is specifically and only in relation to a request for information by Paul/ for the 7 G-Tronic thread. I could have sent it to him by email, but I thought I would post it in his thread as he has a great interest in the working principles in this particular area of his vehicle. It may be of interest to others who also possess such similar interests.

Sorry for the delay in posting Paul/. I don’t always seem to be able to get away from work these days on time, and when I do, I’m pretty much exhausted. To be honest, once you grasp the concept of it all here, it really will become much easier to understand and apply the concepts. This in turn will make it much easier to understand what “SOG” (Shift Optimal Gear Strategy) is and how that specific program works within the overall framework strategy of the TCM program. It’s a very very complex and certainly not easily understood computer program with many input devices being monitored within millisecond time frames of each other and equally given output commands at a similar pace. I’ll use the “PWM” terms in a simple equation later on so you can get a better understanding of why it’s employed within the system.

To be honest Paul, most people can’t even comprehend the time-frame speeds involved in the processing power of these systems, so ill keep this very brief and try and put this in to some form of perspective and context for you with this typically unrelated system analysis below. You will then later on as we go through it have a better appreciation as to what’s involved.

When a vehicle is involved in a frontal impact crash, several things happen immediately before the vehicle start to deform. Firstly, the “sensing” accelerometer, known to you as a “crash sensor”, located on the bonnet slam panel is automatically triggered, this in turn is sensed by the SRS modules “safing” sensors, which are located within the module and mounted on top of the transmission tunnel. When all the condition are met and verified by the SRS module that a crash is occurring, it triggers the drivers/passenger’s airbag, or even both, depending upon the severity of the impact. The driver’s airbag is actually fully deployed within a 30-millisecond time frame and is actually being deflated within 100 milliseconds. So, what does this actually mean, well, most people can blink the eye 4 times within a second, that represents 250 milliseconds per blink. If you now consider that the airbag was actually deployed in 30 milliseconds, then that represents the airbag being deployed 8 times quicker than a blink of an eye - fact.

On a side door collision impact, the thorax or side airbag in the side of the seat or door actually deploys within a 12 millisecond time frame, I don’t need to do the maths for that but that’s 20 times quicker that that single blink of the eye. So that’s the type of time frame comparisons we are referring to here when we talk about solenoid activation and gear changes within the transmission valve blocks, pretty quick I would say, wouldn’t you. If you notice the time frame periods of deployment of these airbags, then its understandable that the side airbag has to deploy that much quicker than that the drivers airbag because of the relatively short distance of some 6 inches from that of the door to the your body, compared to the 10-12 inches from the steering wheel to the chest and face. People don’t actually realise that when they hit the airbag in a crash, they do so when its actually being deflated, the other way round would be a cause for instant death because of the pressures involved in deploying it in the first instance. I won’t go into the physics here but gas expansion rates are pretty frightening to say the least. If you considered these at any level, you would be more frightened of the airbag than that of the crash.

If your even remotely interested, then the propellant used in steering wheel airbags is actually sodium azide, formerly known as rocket fuel, approx 2-3 grams used in steering wheels dependant upon how many litres of gas you require. The white stuff you see following such a deployed of the airbags is actually talcum powder or starch – it reduces the friction during deployment to prevent burns to the face and hands.

Lets now look at what you are actually asking first with regards, to the “pw%” terms. On P37, these are actually transmission analysis and statistical data graphs on” bench test” programs. It must be so as they are under the following heading -“Electrohydraulics”, which is clearly noted as a computer controlled activation sequence of events and tests. The graph, to me also represents that of gearshift output data patterns in relation to gear up/down change ratios, although it does not specify which mode the transmission is actually in at the time. Given the huge range on the kph scale on the vertical axis and the pw% on the horizontal axis, at any one point on the graph you can clearly see yourself that they do change up/down respectively, so your assumptions were in fact correct. Also, what I have noticed and is very odd from that graph, there is no indication whatsoever at what rpm change those gear patterns actually occurred in relation to the pulse width modulation on the respective solenoids in the transmission valve block, you could safely assume that they remain activated/increased at that level until instructed otherwise by the TCM module. I would love to have seen the hydraulic flow, pressure and temperature charts that would have accompanied that graph; there would have been one.

Alternatively, that graph could also have represented just the valve block under ”extreme” tests on its own, there are specific bench testing equipment for just that very reason, and the reason for that is during the quality control process individual valve blocks are selected and tested to monitor the manufacturing tolerances of those components inside, the results are as you see them, which is probably why you don’t see any other relevant or additional data on the graph, they already have it. They don’t always test every transmission for the simple reason it is an extremely expensive process. These tests, believe it or not, are actually run over an automated 24/7 period for many hundreds of hours to evaluate the “wear” characteristics and performance of the components.

Unfortunately, the graph does not even give any indication of the time-frame periods that was involved during those tests and any influencing factors/data such as loading effects etc., if it did, then I could have actually calculated the” on” time duty cycles for you. If you look at the horizontal axis, it clearly states that the pw% is a representation of 100%, but 100% of what? Is it 1 second, 1 minute, there is no data to actually calculate and work from. Given the graph, the only thing actually calculable is the conversion from kph to mph, with observations that the respective gears do change up/down, or the valves open and close.

The very same principle still applies to any graph for that matter though. The graph in general on P37 is not representative of any formal engineering terminology as in “PWM” (Pulse Width Modulation). But saying that, it is German data/information and one that I have never seen anyway, maybe it’s a genuine typographical error and the “m” was omitted from the end of “pw”, it would certainly have taken away any ambiguity. At the end of the day, it’s just an interpretation of statistical output data, its still the same principle. I always refer to it as “PWM”, anyway, so that’s what we will refer to it as here.

PWM - PULSE WIDTH MODULATION.

The term is always used when we employ some form of an application whereby the overall control of switching some form of power source and applying it to some form of electrical components or devices, in our case, the valve block pressure control solenoids or actuators which control gear shift operation, or, a type of mechanism that puts something into an automated action. So, what exactly does it do for us, well, lets break it down in to its respective terms and how its applied. Lets apply some basic voltage figures here in to the equation, not those of the actual solenoids, so we will have something to work with later on. We will use zero-volts as our baseline as the system is considered as switched “off” or “inactive” at this point and 12-volts as our maximum applied voltage as the system is switched “on” or “active” or “live” if you like.

The “average” numericalvalue of voltage and current that supply any particular load - valve block solenoids in this case, is solely controlled by turning the controller switch between the supply and the load “on” and “off” at an extremely rapid pace. In other words, the longer the switch is turned on in comparison to how long it is actually switched off. PWM switching frequencies invariably have to be so much faster and quicker than what would actually affect the applied load, which equally says the device thats consuming all of the power. The overall frequency measured of switching such a device has to be done in such a way that its actuated several hunred – thousandths or even millionths of times per second or minutes depending on whats actually being controlled. The frequency is actually measured in terms of Hertz. (Hz). PWM refers to the original concept of “rapidly pulsing” a digital signal of a wire or circuit board to stimulate a varying 0-volts –12-volts, or whatever on the wire or circuit board. This method in varying intensities is commonly used for driving electric motors, solenoids, lighting equipment and systems, pretty much anything nowadays in a modern car and the automotive industry.

The referance terms of a duty cycle actually refer and describes the proportion of electrical “on” time to the regular interval or a period of actual current time; whether it be seconds or even minutes, for example, a relatively low duty-cycle period corresponds to low power consumption, because the power is actually “off” for most of the time. Duty cycle is also expressed in percentage (%) terms, meaning that zero percent (0%) being off and (100%) being on permanantly. The main advantage of PWM is any power loss in the switching devices or circuits is considered to be very low or minimal. When a switch is turned off, there is practically no current flow whatsoever, and when it is switched on, there is almost no voltage drop across the switch, unless, there is some form of resistance to limit the current flow available – resulting in a volt-drop scenario. Any power lossses, which are measured in wattts, being the sole product of voltage times any current flow, is in both cases close to nothing. PWM works particularly well with all digitally and microprocessed controlled systems such as our TCM, which because of their on/off switching capability and nature, can easily set at a specific duty cycle for the individual component or actuators.

So, to sum up the above then, a few reference terms that are associated with PWM are “the time periods” - how long each complete pulse cycle actually takes -“the frequency - measured in hertz” - how often those specific pulses are actually being generated for. The respective values are typically specified and measured, which in our case is - cycles per second. The “duty cycle - measured in %” – always refers to the amount of time in that period that the pulse is “active” or “high” and the duty cycle is typically and almost always specified as a percentage of the complete period. At one point, some engineers used to use the “dwell” or “spout” period, but that was dropped because of the confusion in the industry. The modulation aspect to all of this is simply considered as the transmission of an electrical signal by using it to vary some carrier wave; changing the carrier's amplitude, frequency or phase cycle in the process.

Sorry if this really appears to be complex Paul, but look at this example here and it will become very easy once understood. If we have a system, and it really doesn’t matter what that system may be, we know its operating of between the ranges of 0-volts being no power and 12-volts being full power and the duty cycle is considered to be operating at 25% of its capacity, we would then say that there was actually an applied average voltage representing that of only 3-volts, therefore, the remaining 75% of that systems full power is not being utilised. Take it a step further and increase the duty cycle to 50%, this would now indicate the average output and you can see at 50% duty cycle equates to an output averages of 6-volts or 50% of full power. If it were operating at a duty cycle of its full 100%, then the full power or the full 12-volts would be applied all of the time.

SOG or Shift Optimal Gear Strategy

This system that you refer to is an adaptive intelligent system that is solely influenced not just by the driver, but also from outside influences that I mentioned in an earlier post. It has the ability to adapt to all conditions, diverse or otherwise. It has even been further advanced than that of the 722.6 series that I originally sent you the data on and referenced earlier. The addition information was that the 722.9 now has the ability of comfort shift and driving pleasure is further enhanced through the improvement of control of
individual gear changes, much shorter computer reaction time by 0.1 - (100 milliseconds), downshifts shortened by up to 0.2 - (200 milliseconds), coasting downshifts shortened by 0.4 (400 milliseconds up to – 2.5 seconds), an increase from 37 to 74 mph acceleration times shortened by 23 - 28% (depending on specific vehicle model). The fuel consumption, “allegedly” also reduced by up to 4% and even the noise levels reduced due to lower engine speed in 5th, 6th & 7th gear at constant vehicle speed and finally the overall flexible adaptation to vehicle and engine performances. Pretty impressive by anyone’s standards, refer back to the airbag scenario above and then put these values above in that context, you’ll appreciate much more the speeds involved in these applications and processes, don’t forget, the above published figures are actually MB’s own statistical data taken from their documentation, whether its right or not is another matter.

The only downside, if it can indeed be considered as a down side, is that I would have been concerned about the “hill hold” facility on the 722.9. Given what MB did with this transmission to incorporate the 6/7 gears, then it’s not surprising. To redesign a new transmission totally and then re-design the transmission tunnel to accommodate it would have been prohibitively expensive, as it would have meant and involved a new series of crash test analysis as the transmission tunnel is actually and forms part of the vehicles overall structure and stress/crumple zone areas. MB opted for the earlier use of the current 722.6 housing/casing and removed the sprag mechanisms, which was a much cheaper option. For those that do drive the 7-speed, you may have noticed that 722.9’s actually roll backwards with your foot off the brake. Some, I am led to believe believe have a hill holding feature where they use the brakes to hold briefly, although I have never personally driven one to confirm this,

The reason for the change is this, when the 722.9 transmission was commissioned, the design criteria was such that it had to fit into the same transmission casing as that of a 722.6, as it was already being fitted into vehicles already designed and in current production. If you change and/or modify the transmission tunnel as said above, then you have to repeat all the crash testing evaluations, as it is a crumple zone. Since the 722.6 has five gears and the 722.9 has 7 gears, the extra Ravigneaux gear sets that makes this possible has to fit into the same casing, necessitating and requiring something of non-critical components to be omitted. From the 722.6 designs, the two sprag clutches were removed. These units are essentially freewheeling elements that rotate in one direction but lock up in the another, without them, a transmission will not lock up when it rolls backward in 1st or 2nd gear on any form of gradient. If you have ever wondered why a 7-speed automatic doesn't hold on a gradient like the 5-speed automatic does, well, that’s the reason and it’s not a fault to be concerned with, so MB says anyway.

Paul, I do hope this information satisfies your curiosity, if not, then I really don’t know what else I can add to the above, it really is a very very clever and sophisticated piece of engineering, and at its best. The only other option that you could pursue, if you wish to do that, is to identify each and every single component with the framework of the overall transmission and evaluate the data of how they actually work within the system. I do have all the testing data, pin-outs and tolerances, but that is purely down to transmission diagnostics alone, and I am not sure that you would even want to go down that route. Most MB Technicians these days just plug it into their respective diagnostic machine in the hope that it gives them the relevant fault codes; even that equipment guides them through a process. To diagnose without it is pretty complex without understanding the system in the first place.

There are other alternative systems out there though that will in fact make this system look pretty dated by comparison. Maybe one day we will cover those, who knows. MB do have an 8 speed variant, I am not sure as to whether or not it is in current models, but I do know is was supposed to be in 2012/2013 MY vehicles. Maybe someone on here has one. Let us know what your views are if you have.

My apologies once again for not getting back to you last night, I did start to write this last night but after nearly 13 hours at work yesterday and another 11 today, I’m pretty much tired out. I have just managed to finish it so I hope this information is of further help in building a better picture.

Regards,

Dash1

 

[Paul/]

Hi Dash1,

Well what can I say, what a fantastic education you've given me (though to be honest it will take me several readings to properly grasp it all)- you should win the MBforum award for the most explained information in a single post! Really appreciate the effort you've gone to, I'm sure others do too. It certainly has helped me- and reassured me that the system is more than sophisticated enough for me to trust it to do the right thing without much intervention on my part. I'm just sorry it's taken up so much of your time when you are working such long hours! I'll copy everything to a local file just in case anything unthinkable happens to the forum servers.

Incidentally, your description of airbag mechanism makes me glad that I relegated my dog to travelling (harnessed) on the back seat when I discovered that my model CLS doesn't allow front passenger airbag to be disabled.

I can't buy you a drink to say thankyou, so I've attached a virtual pint below- wasn't sure what you prefer so there's a choice...

Thanks again & Regards,
Paul

 

[Dryce]

NOTE. To all forum members, this post is specifically and only in relation to a request for information by Paul/ for the 7 G-Tronic thread. I could have sent it to him by email, but I thought I would post it in his thread as he has a great interest in the working principles in this particular area of his vehicle. It may be of interest to others who also possess such similar interests.

What's your technical background?

 

[Dash1]

What's your technical background?

Hi Dryce,

Refer to one of my previous posts below.

General consensus ( 1 2)
Dash1

 

[Dryce]

Hi Dryce,

Refer to one of my previous posts below.

General consensus(1 2)
Dash1

So how on earth did you make the leap from pw% to a rather odd digression on PWM.

I'll lay my cards on the table. You've triggered my BS detector.

 

[Paul/]

So how on earth did you make the leap from pw% to a rather odd digression on PWM.

I'm obviously no expert, but a web search gave me this reason to believe that pw% was related to PWM, hence my original question to Dash1 about the chart...

"What is the difference between PWM and non-PWM torque converter clutches?
PWM stands for "pulse width modulation". In transmission control applications, PWM is a way of controlling a solenoid so that it applies varying amounts of hydraulic pressure according to computer control. PWM torque converter clutch systems use apply and release the clutch gradually to improve shift feel."

 

[Dash1]

So how on earth did you make the leap from pw% to a rather odd digression on PWM.

I'll lay my cards on the table. You've triggered my BS detector.

Hi Dryce,

Thanks very much for your question.

With the greatest respect Dryce, I value your opinions just as equally as any other forum members on here, but please, don’t dismiss my opinions as “BS”. I believe that comment was totally unfair in view of what you perceive pw% may of may not be. I can assure you that I have certainly not digressed and leapt from pw% to PWM. As I have indicated in my post to the OP, I myself am not familiar with just the term pw%, and assumed, rightly or wrongly, that the “m” had been omitted from the end of pw%, quite simply because I have never ever seen it on any form of graph or chart, you may very well have. I stopped at that point in the post because I had no more to say on that particular topic as I had covered what I perceived it to be and gave several interpretations and reasonable explanation to the OP what they may be in terms of statistical data representing either the gear ratio change with speed, and/or the solenoid frequency change with speed. Either way, it was one of those two. See my paragraph below

Quote.” The very same principle still applies to any graph for that matter though. The graph in general on P37 is not representative of any formal engineering terminology as in “PWM” (Pulse Width Modulation). But saying that, it is German data/information and one that I have never seen anyway, maybe it’s a genuine typographical error and the “m” was omitted from the end of “pw”, it would certainly have taken away any ambiguity. At the end of the day, it’s just an interpretation of statistical output data, its still the same principle. I always refer to it as “PWM”, anyway, so that’s what we will refer to it as here”.

I then based my comments purely and simply on several influential factors following the use of the manual and the question that was asked at the time from the OP himself. It was in fact the OP that actually first raised the question when he said, and I quote, “Could you clarify please the chart on p37, appears to be upshifts and downshifts plotted against speed and "pw(%)"- what is "pw(%)"- pulse width? related to hydraulic valve opening? or is it engine load e.g. % max rpm? .

Please read his post and you will see exactly what he was asking me. I naturally thought, again, rightly or wrongly, that he was seeking an explanation as to what PWM was and how it was employed within the system, and that’s exactly what I did, no digression whatsoever was ever thought on my part at that stage because I had already answered his question. I then proceeded to cover the area of PWM and its aspect and implications with the system. If you did happen to read the whole contents of that manual which I sent to the OP, which I have, then you would have seen that on page 40 that the heading clearly states “Electrohydraulic Control Module” and under that section is goes on to say the following:


Electrohydraulic Control Module

• Each valve body assembly is individually tested
• Hydraulic pressures and electrical currents are measured by sensors on a computerized test rig
• Test values are evaluated and corresponding algorithms are written to control modules permanent memory
• This process ensures that the control module is calibrated to mechanical and electrical solenoid valves of that valve body
• Once this process is complete, valve body assembly is installed in a transmission

Based upon the above criteria, this section of that manual covers from pages 37 to 52 with reference to the computer control of the solenoid valve activation/hydraulics, and by no coincidence, the graph on P37 which the OP was asking about, so happens to be on the front cover of this section, refer back to it and you will see exactly what I am saying. So, as I have said, if any of my comments have been conveyed in the incorrect manner or have been misinterpreted in the wrong way, then I apologise for that. But to be honest Dryce, I don’t see that what I have written is in any way misleading or incorrect, it is fact, and as I perceive it to be.

To be honest Dryce, I am somewhat disappointed that you feel that you have to write this “I'll lay my cards on the table. You've triggered my BS detector.” Why on earth would you want to say or even think that, let alone write it? My time on this forum is really to give advice to any member who may be in need of help or assistance, probably like that of yourself, I do so freely in the belief that I may be helping others, which is exactly what this forum is about and as I have just done so with the OP’s concerns. He has a general and genuine interest in learning what benefits he can use in understanding something that is quite complex area.
If you have not have understood anything that I have said, and I am certainly not being derogatory here, and in the way it was genuinely meant to be conveyed to the OP, then you should have asked me. With the greatest respect, as I have already said, I do value your opinions and input, but to use the tone that you have will only deter people like myself and others who genuinely want to help MB forum member. When people read comments such as you have written, then that in itself can trigger a chain reaction in a form of slanging match, that’s not what I am about.

Anyway, thanks once again for your question.

Regards,

Dash1

 

[Paul/]

03/10/2012 updated version

This is my final update, I don't expect to discover more on the subject unless I get an opportunity for rigorous roadtesting or get access to the Shift Optimal Gear software documentation. As previously, I've attached the file and copied the text below.

(Incidentally, I can confirm that Pulse Width Confirmation is indeed key to the operation of the G-Tronic torque converter- but I don't think further detail is relevant from a user perspective.)


7G-Tronic & Tiptronic user notes
Last updated 03.10.12

I had difficulty finding explanatory documentation on the subject (beyond what it says in the owner manual), so am sharing what I’ve learned in case it is of use or interest to others. My only experience is with an 09 CLS CD320cdi without Manual mode, so predates 7G-Tronic+.
For key points that I haven’t yet been able confirm, I’ve added <not confirmed>.

7G-Tronic

7 forward gears, of which the top 2 are overdriven, and 2 reverse gears.

Continuous electronic networking with the engine and chassis management systems allows the transmission system to adapt to a wide variety of driving situations and to the driver’s current style (ranging between smooth and sporty):

• If the accelerator pedal is pressed relatively quickly, the transmission is more likely to downshift, while upshifts are less likely when the pedal is released quickly.

• Shift feel is changed according to engine speed and engine load, to make smoother shifts during leisurely driving, and sharper shifts during more spirited driving. Smooth shifts are aided by retarding ignition timing to reduce power for a split second.

• The transmission system links with the ABS and traction control systems and yaw and steering sensors from the ESP stability control system, to enable it to recognize cornering and low-traction conditions, and where appropriate, delay or hasten a gearshift to ensure that it creates no negative effect on vehicle stability or traction control. <this might account for some reports of delayed response to Tiptronic inputs>

• Angle of gradient, road speed and engine load are used to assess whether the vehicle is coasting, or if downshifting is required, on descents to provide engine braking, or to negotiate climbs.

• Engine coolant and transmission fluid temperatures, and cruise control (or Distronic) status are also taken in to account in the shifting decisions.

Kickdown (regardless of mode) shifts down by up to 4 gears and changes up at rev limit <not confirmed>


Comfort (also known as Winter or Economy) mode

• Moves off in 2nd gear both forwards and reverse except moves off forwards in 1st gear if any of the following conditions apply:

à 1st gear is manually selected
à Accelerator depressed 75% or more from stationary
à Cold engine temp (pre catalytic warm up)
à Shifting to Drive from Park <not confirmed>

• Changes up at lower revs and down at higher revs than in Sport mode.

• Softer (slower) clutch operation than in Sport mode.

Sport (also known as Standard) mode

• Moves off in 1st gear both forwards and reverse.

• Changes up and down at the normal i.e. default shift points.

• Sharper (faster) clutch operation than in Comfort mode.

Despite some opinions to the contrary, it appears OK to switch modes while moving.<though see comment at end>

Limp mode
If transmission has a defective shift engagement or component, a limp-home mode will be activated ensuring that in almost all cases the vehicle can still be driven at reduced speed to
home or workshop.

Driving Style
There’s a Driver Status parameter which is used by the transmission to determine how to behave in response to the driver’s style. Its value ranges from 0 to 25, 25 is the most aggressively sporty style of driving, 0 the most relatively “normal” i.e. smooth.

The value defaults to 0 on removal of the ignition key, there is no memory of previous journeys.



Whilst driving, the system continuously monitors all of the following parameters and derives from them an updated driving style rating:

• Vehicle acceleration
• Vehicle deceleration
• Rate of change and position of accelerator pedal
• Lateral acceleration e.g. sideways forces during cornering
• Gear-change frequency

Reset
There’s a “reset” procedure involving fully depressing the accelerator with engine off (and key in ignition), but this only recalibrates the throttle to the accelerator, to ensure their corresponding ranges align correctly between their min and max positions.

Shift Point Learning
Shift Points can be changed from factory settings by driving with special menus temporarily activated via StarDiagnostics, so the car “learns” (& memorises) the appropriate shift points. The primary purpose of this is to configure the transmission to best match the characteristics of the engine and vehicle in which it is installed- it is not intended for drivers to customise the configuration to their own personal preferences, though it is possible.


Technical documentation
http://www.scribd.com/doc/100685077/722-9-Mercedes-Benz-7-G-Tronic
http://www.scribd.com/doc/84723749/25/Electronic-Transmission



Tiptronic

On 7G-Tronic, ranges can be limited to a maximum (not minimum) of any gear e.g. range 5 is gears 1-5. Full range, which is the default state, is displayed as “D” rather than 7.

‘Tap-‘ shifts down 1 gear and limits range to that gear

‘Hold-‘ limits range to current gear and then shifts down by up to 4 gears to gear that gives optimum acceleration and engine braking <not confirmed>

‘Tap+’ shifts up 1 gear and, if currently limited to a lower range, extends range to the new gear

‘Hold+’ restores full range i.e. “D” (and shifts up if not in optimum gear for full range)

‘Hold’ by tipping and holding in place for approx.1 second.

Won’t select a gear which would put engine out of its normal rev range.

If maximum engine speed is reached, will shift up regardless of range restrictions.




Thought so far on actual driving (<1000 mls)

Initial impression is that C mode shift points seem to better exploit the 320cdi torque profile- I’m still experimenting.

For urban driving, C mode is smoother and also a better match for normal conditions (at least with 320cdi).

Using Tiptronic to change down also limits the gear range. This is helpful for gradients and towing, but if done to aid acceleration, the gear restriction will force the engine to change up at maximum revs, which is often not desirable, so would require additional stick work to restore optimal shift points.

“Hold-“ is better preparation than “Tip-“ for overtaking as is drops down to an optimum gear but first limits the range up to the current gear, so leaving more headroom for optimum shifts.
But it still requires another tip to restore full range.

Kickdown seems the most convenient and effective option unless wanting to avoid the delayed response, or when anticipating a high likelihood of aborting e.g. if overtaking from shorter than ideal distance from vehicle in front.

My most common use of Tiptronic is when having reached cruising speed (at any speed) in S mode, I want to change up for economy.

It’s probably safer to switch between C and S mode whilst at constant speed, to avoid slight risk of being caught out by a sudden change in transmission response.

 

[Paul/]

oops- Pulse Width Modulation even

 

[Dryce]

Incidentally, I can confirm that Pulse Width Confirmation [modulation] is indeed key to the operation of the G-Tronic torque converter

How exactly can you confirm it?

PWM is only an ordinary industry method of encoding an analogue signal as series of digital pulses. No magic.

So to say it's 'key to the operation' in something today doesn't ring true. It's just a ubiquitous method of transmitting analogue information or power.