In December, we brought you thefirst of three tightly focused arti-cles about what were the most

important issues facing the automatictransmission service sector. We contact-ed key people at the engineering levelwith a number of automakers in thehopes of getting an idea of the roadsoon to be taken with even more com-plex automatic transmission designs.The manufacturers that responded rec-ognize that opening a dialogue with therepair community makes good businesssense.

Our three-part technology seriestakes a look at the major markets: USA,Europe and Asia. A set of six questionsis asked of each participant and thismonth we present the European per-spective. Our report required sortingout trans-continental communicationsand translations by a host of public rela-tions people and generous engineeringexecutives who put some seriousthought into their answers.

Speaking for the European market,we have:

BMWGordon B. Keil,BMW Product Information Specialist

Mercedes-BenzNoah Yanowitz,Mercedes-Benz USA, Senior StaffEngineer/Transmissions

ZFTony Price, ZF Transmissions Manager,Passenger Car Transmissions

1. What type of training are youemphasizing in today’s vehi-cles? BMW: Of our 16 training programscurrently running, the majority of themare for vehicle electronics and diagnos-tics of those electronic systems. Manyof our mechanical systems now containelectronic enhancements or controls, soeven mechanical training has a largeelectronic element (for example, brakesnow contain ABS and are also used bytraction control systems and electroni-cally actuated parking brakes).

Mercedes Benz: There is no doubt thatelectronic transmission controls areplaying an increasingly important rolein today’s vehicles. As the complexityand capabilities of these controls havegrown, so has the need to stress theirimportance in training, and we doemphasize this. That being said, we stillspend a good deal of time on the com-plete disassembly and assembly of allour transmissions, including geartrainand valve bodies. Students are requiredto do a complete disassembly andassembly on each transmission series,ensuring that all measurements arecompleted and are within specificationsalong the way. We also focus on properelectronic adaptation of the transmis-sion after any repairs are complete,

which is essential to a smooth shiftingtransmission.

ZF: As transmissions become morecomplex and more reliant on othervehicle functions, diagnosis is the keyin repairing transmission problems.Transmissions today are able to shiftdifferently under more different engineand vehicle operating conditions than in

30 GEARS April 2002

TECHNOLOGY SERIES by “Landspeed” Louise Ann Noeth

Gordon B. Keil,BMW Product Information

Specialist

Noah Yanowitz,Mercedes-Benz USA, Senior

Staff Engineer/Transmissions

years before to improve shift quality,reduce emissions, increase fuel econo-my or any combination of these. Anyfailure of these other vehicle controlsystems can result in poor transmissionperformance and of course, any prob-lem with the transmission can manifestitself as poor performance of someother vehicle system.

Of course, most of these systemsare electronic and a strong backgroundin electronic systems will aid anyonetrying to troubleshoot transmissionproblems today and in the future. Manysystems on today’s cars have beenredesigned to eliminate mechanicalsystems in favor of electronic systems.This has gone a long way in improvingreliability and reducing size and weight.Knowing when these electrical systemshave failed is not as easy as looking fora broken throttle cable or a vacuumleak, but it is just as important to under-stand these electronic systems today asit is was to understand those mechani-cal systems 20 years ago.

2. What type of technology areyou using to shift today’s transmissions in comparison tothe technology from the past?

BMW: Five- speed ZF transmissionsare currently using On/Off solenoids inconjunction with PWM pressure regu-lators. six-speed ZF transmissions usePWM pressure regulators exclusively.All ZF transmissions use a PWM sole-noid for the torque converterclutch. Our GM-sourced transmis-

sions use On/Off solenoids in conjunc-tion with variable bleed solenoids(VBS) to control the main pressure. Thetorque converter clutch uses a PWMsolenoid.

Mercedes Benz: We are currently usingboth On/Off and pulse-width modula-tion solenoids to control various trans-mission functions. For example, we usepulse-width modulation for actuation ofthe torque converter lock-up clutches(which by the way, never actually locksup 100% but rather is a controlled slipof the torque converter reaching 98%efficiency in the coupling range).

The actual shift initiation is donethrough the use of On/Off solenoids,but pressure regulating is accomplishedthrough the use of two regulating sole-noids, which control the transmission’sadaptive qualities.

ZF: On/Off solenoids are still usedwhere a simple binary signal isrequired. These were an improvementover the spring and valve systems theyreplaced. They didn’t stick, the springsdidn’t fatigue, and you could makethem switch whenever you wanted bycontrolling them with the transmissioncontrol unit. For filling clutches, how-ever, they still needed to be connectedto an accumulator, because shift qualitywould be terrible if you applied theclutch with a simple On/Off signal.

Pulse width modulated solenoidsare an improvement, but they usuallycan’t handle the flow to be connecteddirectly to a clutch and are more expen-sive than On/Off solenoids. They are

most often used to pilot a more com-mon spring and valve system, some-times with an accumulator. Efforts havebeen made to improve the reliabilityand reduce complexity of accumulatorsystems, but they really haven’t beeneliminated yet.

Some of the more recent improve-ments in the clutch/solenoid systeminvolve the adaptive abilities of currentengine and transmission controllers.The controllers now have the ability to“learn” the particular current vs. pres-sure or frequency vs. pressure charac-teristic and adjust for variations fromsolenoid to solenoid. This reduces theneed for a carefully calibrated solenoid,and can offer improved shifting charac-teristics.

3. What is the average time todesign a transmission and whatcomes first, the vehicle or thepowertrain?BMW: A rough number would be fouryears. Transmissions are developedsimultaneously by the transmissionsupplier, for example ZF or GM, inconjunction with the requirements ofthe automobile manufacturer.Generally, the manufacturer will supplythe requirements for the transmission,but in some cases, e.g., CVT transmis-sions or other new technology, the sup-plier will be able to offer new technolo-gy to the manufacturer, and the processwill be reversed.

Tony Price,ZF Transmissions Manager,

Passenger Car Transmissions

GEARS April 2002 31

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Mercedes Benz: Not including thedecisions about which technologies touse, the actual design/developmentprocess takes about 40 months. Thevehicle is designed independently of itspowertrain, because transmissions usu-ally have a longer life cycle than thevehicle platform, and transmissionswill fit multiple platforms.

ZF: We have developed ideas for trans-missions that didn’t initially have anapplication, and have designed trans-missions from scratch for customersthat come to us with special needs.Sometimes an existing product can bemodified to satisfy the requirements,and the development time can be veryshort, maybe two years from idea toproduction. For a completely new con-cept it takes longer. For example, thenew six-speed transmission introducedin the latest BMW 7 series went frominitial concept to production in justunder four years.

The transmission is only an appara-tus to convey power from the crankshaftof the motor to the wheels in a mannerthat will propel the vehicle. The trans-mission must bridge the gap betweenwhat the engine produces and what thevehicle needs to be propelled. The bestexamples of well matched engine andtransmission combinations are always aresult of the engine and transmissiondesigners working closely together. Aproperly calibrated transmission pro-gram can make the difference betweena car that shifts acceptably and one thatperforms outstandingly.

Very few people buy a car becauseit has a particular transmission. Theybuy it because it’s stylish, powerful,efficient, comfortable and so on. Thetransmission can contribute to thesethings, but transmission selection is atbest a secondary factor in most vehiclepurchases. As a result, the transmissionis almost invariably designed to com-plement a particular vehicle.Sometimes it is fitted as an improve-ment to an existing vehicle or is devel-oped to handle the requirements ofsome new one, but rarely, if ever, doesthe transmission dictate the design ofthe rest of the car.

4. Why the change in fluids inthe past ten years? Example:Type F, Dexron II, III, Mercon IV, Vand Synthetics. BMW: Synthetics are used primarilyfor our slip-controlled lock-up clutch,an extra benefit gained is longer servicelife. We are currently on a “lifetime”maintenance schedule for the transmis-sion fluid. Another benefit is reducedcost of ownership and reduced impacton the environment due to less fluidbeing exchanged. This also answersquestion number five.

Mercedes Benz: We made a changefrom Dexron to synthetic for the fol-lowing reasons:a. It was necessary to switch to synthet-

ics for us to achieve our current filled-for-life philosophy, since conventionaloil must be changed more frequently.The filled-for-life approach is also

more environmentally friendly.b. Synthetic oils also maintain a more

consistent viscosity over a wider tem-perature range, which gives a moreconsistent flow through the pulsewidth modulation solenoids. Thismeans more consistent transmissionfunction over a wider range of condi-tions.

c. In addition, it is important to have thesuperior qualities of synthetic oil forproper function of the clutches in thelocking portion of the torque convert-er to prevent “chatter” in the couplingmode.

ZF: Fluid requirements have changeddramatically over the past 10 years.Transmissions were expected to operateat temperatures under 250 degrees andhave the fluid changed every 30,000miles or so. The old Type F and Dexronwere adequate in these situations, butwhen cooling systems were downsizedto save weight leaving less capacity tocool, transmission problems developed.Airflow under the car was minimized toimprove aerodynamics and fuel econo-my, reducing the convective coolingeffect of the air.

As cars got smaller and engine out-put increased, more heat was introducedinto the transmission, as the converterhad to absorb more torque and theengine compartment got hotter.Continuous slip torque converterclutches were designed to improve fueleconomy and reduce the annoyingbumps usually associated with them.This slipping produces extremely hightemperatures between the friction mate-rial and the corresponding steel platethat can quickly destroy normal oils.Today, changing the oil every 30,000miles is no longer acceptable for somecarmakers as they start to consider thelong-term environmental impact oftheir products.

Synthetic oils were the obvious solu-tion as they usually exhibit stable per-formance over a wider temperature rangeand therefore can last much longer. Thefriction modifiers that are added to thoseoils are now more customized than everbefore as shift quality has become of crit-ical importance. This has lead to anexplosion in the number of different oilsthat car manufacturers recommend fortheir particular transmissions.

34 GEARS April 2002

Part 2 – The European Perspective

5. Did the change in fluids pre-empt the change of clutch-es? Example: Fluid or clutchesfirst? Mercedes Benz: The fluid change isbecause of the filled-for-life philoso-phy, so fluid first.

ZF: Taking a step back, the perform-ance of the transmission is what is real-ly important. As stated above, fluidshave changed to address several issuesover the years. Clutch material haschanged as well. New materials that cangive better friction characteristics overa wider temperature range over a longerperiod of time are being chosen over theold standard materials. The resultantchanges in fluids have been necessaryto best utilize the benefits of theimproved material.

Fluids are currently a necessaryevil in transmissions. ATF performsmany functions in an automatic trans-mission very well. It aids in powertransmission in the torque converter, itlubricates clutches and bearings, itremoves heat from the transmission,and it is used as the hydraulic mediumfor the clutches and valve body.However, if a transmission could bemade that doesn’t use a fluid, it wouldbe a great step forward. Fluid is a main-tenance problem. As a vehicle getsolder it likes to leak out. It adds cost toproducing a vehicle as well as owner-ship. But before fluids can be eliminat-ed from the transmission, all of thefunctions of the fluid must be per-formed by something else or the needfor those functions has to be eliminated.This will not be easy to do, and maynever happen.

In short, neither element is sacredin the transmission. If engineers coulddesign a transmission that eliminatedthe complexity of the clutch system ortransmission fluid, and performed aswell as current transmissions, we wouldbe driving those transmissions today.

6. What is the trend for tomor-row’s transmissions? BMW: More gears will be used. Forexample, the debut of our six-speedelectronic automatic transmissions in

the 2002 745i, 745Li and 760Li. Thistrend will continue with our other mod-els. More fully electronic controls willbe used, with the control units eventual-ly being contained within the transmis-sion housing. Transmissions arebecoming lighter weight due to moreusage of lightweight materials. Also, wewill debut the new Mini Cooperusing CVT technology this year as well.

Mercedes Benz: I will speak of tomor-row in the context of our next genera-tion of vehicles, since anything furtherinto the future is too speculative.a . For front wheel drive platforms

with a maximum input torque of upto 300Nm (214 ft. lbs.), the choicewill be a CVT.

b . More powerful vehicles will makeuse of a planetary type transmis-sion with more than five forwardgears and a locking torque convert-er as well. That’s about all thedetail we can currently provide.

ZF: What transmission producers arecontinuously looking for is improvedperformance (fuel economy, shift quali-ty, reliability, lower weight, etc.), andlower cost. The result will be some

revolutionary ideas, as well as someevolutionary ideas being used by allcarmakers. We see this already withsome manufacturers remaining loyal tothe stepped transmission but improvingits design in an evolutionary fashion,while other car makers are using moreunconventional transmissions, likeCVT’s.

A combination of all types of trans-missions will likely be in store for thefuture. In the search for increased per-formance, fuel economy, comfort andreduced emissions, carmakers will bemore creative in the future than everbefore. Today’s car buyers are moredemanding, and the government is push-ing carmakers to be more environmen-tally responsible. The result will be someinteresting and exciting technology.

GEARS April 2002 35